The Twelfth Marcel Grossmann Meeting

The following sections are included:

• THE MARCEL GROSSMANN MEETINGS

• SPONSORS

• ORGANIZING BODIES OF THE TWELFTH MARCEL GROSSMANN MEETING:

• MARCEL GROSSMANN AWARDS

• PREFACE

• CONTENTS

We develop the spectral point of view on geometry based on the formalism of quantum physics. We start from the simple physical question of specifying our position in space and explain how the spectral geometric point of view provides a new paradigm to model space-time whose fine structure can be encoded by a finite geometry. The classification of the irreducible finite geometries of KO-dimension 6 singles out a “symplectic-unitary” candidate F, which when used as the fine texture of space-time delivers from pure gravity on M × F the Standard Model coupled to gravity and, once extrapolated to unification scale, gives testable predictions.

In 1965 Penrose¹ introduced the fundamental concept of a trapped surface, on the basis of which he proved a theorem which asserts that a spacetime containing such a surface must come to an end. The presence of a trapped surface implies, moreover, that there is a region of spacetime, the black hole, which is inaccessible to observation from infinity. A major challenge since that time has been to find out how trapped surfaces actually form, by analyzing the dynamics of gravitational collapse. I recently published a monograph² which achieves this aim by establishing the formation of trapped surfaces in pure general relativity through the focusing of gravitational waves. The theorems proved in the monograph constitute the first foray into the long-time dynamics of general relativity in the large, that is, when the initial data are no longer confined to a suitable neighborhood of trivial data. The main new method, the short pulse method, applies to general systems of Euler-Lagrange equations of hyperbolic type, and provides the means to tackle problems which have hitherto seemed unapproachable.

We present an exact electrovacuum solution of Einstein-Maxwell equations with infinite sets of multipole moments which can be used to describe the exterior gravitational field of a rotating charged mass distribution. We show that in the special case of a slowly rotating and slightly deformed body, the exterior solution can be matched to an interior solution belonging to the Hartle-Thorne family of approximate solutions. To search for exact interior solutions, we propose to use the derivatives of the curvature eigenvalues to formulate a C³–matching condition from which the minimum radius can be derived at which the matching of interior and exterior spacetimes can be carried out. We prove the validity of the C³–matching in the particular case of a static mass with a quadrupole moment. The corresponding interior solution is obtained numerically and the matching with the exterior solution gives as a result the minimum radius of the mass configuration.

We describe how black hole solutions are being used to gain information about physical systems that arise in various areas of physics.

We survey recent results on the exact dyon spectrum in a class of N = 4 supersymmetric string theories, and discuss how the results can be understood from the macroscopic viewpoint using AdS₂/CFT₁ correspondence. The comparison between the microscopic and the macroscopic results includes power suppressed corrections to the entropy, the sign of the index, logarithmic corrections and also the twisted index measuring the distribution of discrete quantum numbers among the microstates.

(Based on lectures given by A.S. at the 12th Marcel Grossmann Meeting On General Relativity, 12-18 Jul 2009, Paris, France; CERN Winter School on Supergravity, Strings, and Gauge Theory, 25-29 January 2010; String Theory: Formal Developments And Applications, 21 Jun - 3 Jul 2010, Cargese, France, and notes taken by I.M. at the Cargese school.)

I will review recent progress on transplanckian scattering in string theory and, in particular, the issue of determining the parameter-space region where quantum phenomena associated with classical gravitational collapse are expected to occur.

I review the field-theoretic renomalization group approach to quantum gravity, built around the existence of a non-trivial ultraviolet fixed point in four dimensions. I discuss the implications of such a fixed point, found in three largely unrelated non-perturbative approaches, and how it relates to the vacuum state of quantum gravity, and specifically to the running of G. One distinctive feature of the new fixed point is the emergence of a second genuinely non-perturbative scale, analogous to the scaling violation parameter in non-abelian gauge theories. I argue that it is natural to identify such a scale with the small observed cosmological constant, which in quantum gravity can arise as a non-perturbative vacuum condensate. I then show how the lattice cutoff theory of gravity can in principle provide quantitative predictions on the running of G, which can then be used to construct manifestly covariant effective field equations, and from there estimate the size of non-local quantum corrections to the standard GR framework.

We review our recent work on linear stability for scalar perturbations of Kerr spacetimes, that is to say, boundedness and decay properties for solutions of the scalar wave equation □_gψ = 0 on Kerr exterior backgrounds (M, g_a,M). We begin with the very slowly rotating case |a| ≪ M, where first boundedness and then decay has been shown in rapid developments over the last two years, following earlier progress in the Schwarzschild case a = 0. We then turn to the general subextremal range |a| < M, where we give here for the first time the essential elements of a proof of definitive decay bounds for solutions ψ. These developments give hope that the problem of the non-linear stability of the Kerr family of black holes might soon be addressed.

Over the past decade, gravitational wave detectors have undergone dramatic transitions in both sensitivity and scale — from laboratory-sized resonant bar detectors to kilometer-length-scale laser interferometers. The construction and operation of large-scale laser-interferometric gravitational wave detectors such as the Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo interferometer as well as others have enabled searches for extra-galactic gravitational waves with unprecedented range and sensitivity. Here, we review the present state of the global laser-interferometric gravitational wave detector network, highlight the results of recent science runs, and provide a preview of the state of the network in the coming decade and beyond.

The successful detection and analysis of gravitational wave (GW) signals from coalescing binary black holes necessitates the accurate prior knowledge of the form of the GW signals. This knowledge can be acquired through a synergy between Analytical Relativity (AR) methods and Numerical Relativity (NR) ones. We describe here the most promising AR formalism for describing the motion and radiation of coalescing binary black holes, the Effective One Body (EOB) method, and discuss its comparison with NR simulations.

Pulsars are very stable clocks in space which have many applications to problems in physics and astrophysics. Observations of double-neutron-star binary systems have given the first observational evidence for the existence of gravitational waves (GWs) and shown that Einstein’s general theory of relativity is an accurate description of gravitational interactions in the regime of strong gravity. Observations of a large sample of pulsars spread across the celestial sphere forming a “Pulsar Timing Array” (PTA), can in principle enable a positive detection of the GW background in the Galaxy. The Parkes Pulsar Timing Array (PPTA) is making precise timing measurements of 20 millisecond pulsars at three radio frequencies and is approaching the level of timing precision and data spans which are needed for GW detection. These observations will also allow us to establish a “Pulsar Timescale” and to detect or limit errors in the Solar System ephemerides used in pulsar timing analyses. Combination of PPTA data with that of other groups to form an International Pulsar Timing Array (IPTA) will enhance the sensitivity to GWs and facilitate reaching other PTA goals. The principal source of GWs at the nanoHertz frequencies to which PTAs are sensitive is believed to be super-massive binary black holes in the cores of distant galaxies. Current results do not signficantly limit models for formation of such black-hole binary systems, but in a few years we expect that PTAs will either detect GWs or seriously constrain current ideas about black-hole formation and galaxy mergers. Future instruments such as the Square Kilometre Array (SKA) should not only detect GWs from astrophysical sources but also enable detailed studies of the sources and the gravitational theories used to account for the GW emission.

After the first prediction to expect geodetic precession in binary pulsars in 1974, made immediately after the discovery of a pulsar with a companion, the effects of relativistic spin precession have now been detected in all binary systems where the magnitude of the precession rate is expected to be sufficiently high. Moreover, the first quantitative test leads to the only available constraints for spin-orbit coupling of a strongly self-gravitating body for general relativity (GR) and alternative theories of gravity. The current results are consistent with the predictions of GR, proving the effacement principle of spinning bodies. Beyond tests of theories of gravity, relativistic spin precession has also become a useful tool to perform beam tomography of the pulsar emission beam, allowing to infer the unknown beam structure, and to probe the physics of the core collapse of massive stars.

In this paper I shall review the observational status of the supernova (SN) and gamma-ray burst (GRB) connection. With a publishing rate of about 1 referred paper per day in the last decade, the study of gamma-ray bursts is one of the most prolific topics of the modern astrophysics.

Gamma-Ray Bursts are among the most relativistic objects known. They involve a relativistic motion with large bulk Lorentz factors (⌈ > 100 or even higher). They arise, most likely, when black holes form. Their expected progenitors: Collapsars and in particular neutron star binary mergers are the classical candidates for sources of Gravitational Radiation. Moreover, the acceleration process of their jets also leads to gravitational radiation emission that might be detectable. Finally, the high energy photons and possibly neutrinos emitted in GRBs provide the best tools to explore and set limits on Lorentz Invariance Violations.

Gamma-ray bursts (GRBs) and supernovae (SNe) bring new perspectives to the study of neutron stars and white dwarfs, as well as opening new branches of theoretical physics and astrophysics.

The status of very high energy gamma-ray astronomy is described with an emphasis on the astrophysical implications of recent discoveries of galactic sources of gamma-rays in the TeV energy regime. The scientific rationale and potential of the field is briefly discussed in the context of future generation of ground-based detectors.

Observations suggest that AGN activity regulates the thermal state of the gas by injecting energy into the intra-cluster medium in the cores of relaxed clusters, where radiative cooling time is often as short as few 10⁸ years. Bubbles of relativistic plasma are inflated by a supermassive black hole and rise buoyantly through the gaseous atmosphere, leading to a number of spectacular phenomena like expanding shocks, X-ray dim and radio bright cavities, X-ray dim and radio dim “ghost” cavities (aged version of “normal” cavities), filaments in the wakes of the rising bubbles formed by the entrained low entropy gas, etc.

Simple estimates of the energetics involved (based on the estimates of the energy content of bubbles/cavities and their life-time) suggest that amount of mechanical energy supplied by AGNs is sufficient to offset gas cooling losses in objects vastly different in size and luminosity. This hints on some form of self-regulation controlling the AGN power as the gas cools or gets heated. One can build a toy model where accretion rate (and therefore the amount of energy provided by the AGN) is sensitive to the gas properties, in particular to its entropy, thus closing the feedback loop.

How the mechanical energy, provided by the AGN, is dissipated depends on the ICM microphysics (e.g. magnetic fields, viscosity, conduction etc). However it is easy to imagine the situation when close to 100% of mechanical energy is eventually dissipated in the cluster core, regardless of the particular physical process involved. Comparison of the gravitational potential profiles of the elliptical galaxies derived from X-ray and optical data suggests that the combined contribution of cosmic rays, magnetic fields and micro-turbulence to the gas pressure is of order 10-30%. This in turn suggests that the dissipation time scale of the energy deposited by the AGN is a similar 10-30% fraction of the gas cooling time.

The same process of AGN-ICM interaction, operating in nearby clusters, could be important at z = 2 – 3 when present day massive ellipticals were forming. The importance of this process depends critically on the physics of accretion. An analogy with the Galactic stellar mass black holes suggests that a black hole can switch from the radiation dominated mode to the mechanically dominated mode when the accretion rate drops below the fraction 10^-2 – 10⁻¹ of the Eddington value. Given that the coupling constant of these two forms of energy output with the ICM can differ by a factor of 10⁴ – 10⁵ this change in the accretion mode may explain the switch of a SMBH (and its parent galaxy) from the QSO-type behavior and an intense star formation to the radiatively inefficient AGN and essentially passive evolution of the parent galaxy.

When galaxy clusters collide, they generate shock fronts in the hot intracluster medium. Observations of these shocks can provide valuable information on the merger dynamics and physical conditions in the cluster plasma, and even help constrain the nature of dark matter. To study shock fronts, one needs an X-ray telescope with high angular resolution (such as Chandra), and be lucky to see the merger from the right angle and at the right moment. As of this writing, only a handful of merger shock fronts have been discovered and confirmed using both X-ray imaging and gas temperature data — those in 1E 0657–56, A520, A754, and two fronts in A2146. A few more are probable shocks awaiting temperature profile confirmation — those in A521, RXJ 1314–25, A3667, A2744, and Coma. The highest Mach number is 3 in 1E 0657–56, while the rest has M ⋍ 1.6 – 2. Interestingly, all these relatively weak X-ray shocks coincide with sharp edges in their host cluster’s synchrotron radio halos (except in A3667, where it coincides with the distinct radio relic, and A2146, which does not have radio data yet). This is contrary to the common wisdom that weak shocks are inefficient particle accelerators, and may shed light on the mechanisms of relativistic electron production in astrophysical plasmas.

This paper reviews the studies of Dark Energy using observations of galaxy clusters. There are two broad classes of observable effects of dark energy: evolution of the expansion rate of the Universe, and slow-down in the rate of growth of cosmic structures. X-ray observations of galaxy clusters has detected and characterized both of these effects. Combination of the X-ray cluster results with other cosmological datasets leads to 5% constraints on the dark energy equation-of-state parameter, and limits possible deviations of gravity on large scales from General Relativity.

In this paper, we present results from recent infrared, high–spatial–resolution studies on the Galactic center that have demonstrated the existence of a central supermassive black hole and revealed several unexpected properties of the stars in the central nuclear star cluster. These results provide the best evidence to date that supermassive black holes exist at the center of normal galaxies, that star formation does proceed in its vicinity despite the strong tidal fields, and that the giant star population does not have the predicted cusp distribution. Future observations of stellar orbits have the potential for detecting post-Newtonian effects in the short-period stars and should probe the distribution of orbital parameters at larger radii, which is key to understanding star and cusp formation around a central supermassive black hole.

Below scales of about 100/h Mpc our universe displays a complex inhomogeneous structure dominated by voids, with clusters of galaxies in sheets and filaments. The coincidence that cosmic expansion appears to start accelerating at the epoch when such structures form has prompted a number of researchers to question whether dark energy is a signature of a failure of the standard cosmology to properly account, on average, for the distribution of matter we observe. Here I discuss the timescape scenario, in which cosmic acceleration is understood as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. This affects the calibration of local geometry to the solutions of the volume–average evolution equations corrected by backreaction. I further discuss recent work on defining observational tests for average geometric quantities which can distinguish the timescape model from a cosmological constant or other models of dark energy.

An overview is provided for 200 years of galactic studies at the Tartu Observatory. Galactic studies have been one of the main topics of studies in Tartu over the whole period of the history of the Observatory, starting from F.G.W. Struve and J.H. Mädler, followed by Ernst Öpik and Grigori Kuzmin, and continuing with the present generation of astronomers. Our goal was to understand better the structure, origin and evolution of stars, galaxies and the Universe.

Clusters of galaxies are the most massive gravitationally collapsed systems in the Universe, with total masses as large as ~ 10¹⁵M_⊙. The dominant form of mass in clusters is dark matter. Most of the “visible” matter is in the form of a hot (10⁷ to 10⁸K) diffuse gas, which comprises ~ 85% of the baryonic mass in clusters, with the remainder primarily being the stars in galaxies. Since the hot X-ray emitting gas traces the cluster gravitational potential, it provides an excellent means for mapping cluster structure and determining the total mass and its distribution.

Einstein and ROSAT surveys of several hundred low redshift clusters detected significant substructures in ~50% of the systems, showing conclusively that most clusters were still growing through subcluster mergers. With the high angular resolution of Chandra and XMM-Newton, coupled with multiwavelength observations, cluster mergers are being studied in great detail. Cluster mergers often exhibit “cold fronts”, contact discontinuities seen at the interface between the merging, less massive and thus cooler gas subcluster and the hotter cluster gas. Measurements of the gas temperature and density across the fronts allow the total velocity of the merging subcluster to be determined. Cold fronts also provide excellent sites for measuring the microscopic properties of the gas, in particular the degree to which thermal conduction must be reduced from the Spitzer rate and the suppression of transport processes. Although the infall velocities of most subclusters are found to be near the sound speed, the rare examples of supersonic mergers and their associated shock fronts allow both additional constraints on the microphysics of the gas, as well as the possibility of observing the spacial separation of the baryonic gas from the dark matter.

Prior to the launch of Chandra and XMM-Newton, the clusters not undergoing mergers, particularly the set of clusters generally referred to as “cooling flow” clusters, were still believed to be relaxed, at least in their cores. But, instead of the expected uniform intracluster medium (ICM) in these clusters, high resolution X-ray images show that cluster cores are often perturbed, either by outbursts from supermassive black holes residing in the nuclei of the central dominant cluster galaxy or by the “sloshing” of the core gas due to the “flyby” of a perturbing subcluster. Jets, driven by the AGN (active galactic nuclei) outbursts, can produce cavities in the hot ICM and associated shocks that may be detected through jumps in the gas density and temperature. From measurements of cavity positions and the gas mass they displaced and from the shock strength, the outburst history of the supermassive black hole can be determined. Observations show that outbursts are common and often recurrent and that the kinetic energies of the AGN are much greater than their radiative energies.

This paper reviews recent results on cluster mergers and on the effects of the outbursts from supermassive black holes on the surrounding hot atmospheres. The X-ray images, as well as the understanding of how these processes occur and effect the growth of both clusters and galaxies have been spectacular.

The supermassive black holes harboured in active galactic nuclei are at the origin of powerful jets which can emit copious amounts of γ-rays. The exact interplay between the infalling matter, the black hole and the relativistic outflow is still poorly known, and this parallel session of the 12^th Marcel Grossman meeting intended to offer the most up to date status of observational results with the latest generation of ground and space-based instruments, as well as the theoretical developments relevant for the field.

In the context of string theory and with the advent of brane-world theories higher dimensional black holes received much interest in recent years. This session on black holes in higher dimensions features predominantly contributions on new higher dimensional black hole solutions, including black rings, black strings, and multi black objects, and studies of their properties. Further topics are geodesics in such higher dimensional space-times, gravitational collapse, etc.

Recently our understanding of black holes in D-spacetime dimensions, as solutions of the Einstein equation, has advanced greatly. Besides the well established spherical black hole we have now explicitly found other species of topologies of the event horizons. Whether in asymptotically flat, AntideSitter or deSitter spaces, the different species are really non-unique when D ≥ 5. An example of this are the black rings. Another issue in higher dimensions that is not fully understood is the struggle for existence of regular black hole solutions. However, we managed to observe a selection rule for regular solutions of thin black rings: they have to be balanced i.e. in vacuum, a neutral asymptotically flat black ring incorporates a balance between the centrifugal repulsion and the tension. The equilibrium condition seems to be equivalent to the condition to guarantee regularity on the geometry of the black ring solution. We will review the tree of species of black holes and present new results on exotic black holes with charges.

This contribution is a review of talks by G.S.Bisnovatyi-Kogan ‘MHD of a large scale magnetic field in the advective accretion disks’, H.C.Spruit ‘Physics of the magnetized accretion disks’ and S.G.Moiseenko ‘Magnetorotational supernovae’ given a the section Black Holes and Magneto-Hydrodynamics (BHT3).

G.S.Bisnovatyi-Kogan’s talk was devoted to the problem of the formation of a largescale magnetic field in the accretion disks around black holes with account of the nonuniform vertical structure of the disk. The high electrical conductivity of the outer layers of the disk prevents the outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole. Global solution of advective accretion disk structure around a black hole is constructed numerically. The presence of the effectively optically thin regions in the innermost part of accretion disks results in a significant increase of the plasma temperature in those regions and this increase can be discriminated in observations in the form of the observed hard radiation tails.

In the talk of H.C.Spruit the problems of existence of strong, highly ordered and dynamically important magnetic fields in the central regions of accretion disks form observations and circumstantial theoretical arguments were discussed. The magnetic fields power the jets seen from accreting objects ranging from protostars to black holes. The observational evidence and the processes that may be responsible for the origin and maintenance of these fields are reviewed.

S.G.Moiseenko spoke about results of simulations of magnetorotational core collapse supernovae. It was shown in the simulations that amplification of the magnetic field due to the differential rotation leads to the angular momentum transfer and formation of the MHD shock wave. This shock wave produce supernova explosion. The supernova explosion energy in our simulations can be up to 2.6·10⁵¹erg. The shape of the supernova explosion depends on the initial configuration of the magnetic field.

This work summarises some of the attempts to explain the phenomenon of dark energy as an effective description of complex gravitational physics and the proper interpretation of observations. Cosmological backreaction has been shown to be relevant for observational (precision) cosmology, nevertheless no convincing explanation of dark energy by means of backreaction has been given so far.

The construction of an averaged theory of gravity based on Einstein’s General Relativity is very difficult due to the non-linear nature of the gravitational field equations. This problem is further exacerbated by the difficulty in defining a mathematically precise covariant averaging procedure for tensor fields over differentiable manifolds. Together, these two ideas have been called the averaging problem for General Relativity. In the first part of the talk, an attempt to review some the various approaches to this problem will be given, highlighting strengths, weaknesses, and commonalities between them. In the second part of the talk, an argument will be made, that if one wishes to develop a well-defined averaging procedure, one may choose to parallel transport along geodesics with respect to the Levi-Cevita connection or, use the Weitzenböck connection and ensure the transportation is independent of path. The talk concludes with some open questions to generate further discussion.

Quantum cosmology from the late sixties into the early XXI^st century is reviewed and appraised in the form of a debate, set up by two presentations on mainly the Wheeler–DeWitt quantization and on loop quantum cosmology, respectively. (Open) questions, encouragement and guiding lines shared with the audience are provided here.

Special Relativity is absolutely basic for our understanding of physical phenomena. It has been invented to overcome the incompatibility of Newtonian mechanics and electrodynamics. The foundations as well as the predictions of Special Relativity have been tested in many respects and with very high accuracy. Here we shortly review the foundations of Special Relativity and report on various attempts to model theoretically violations of Special Relativity. We describe experiments testing the foundations and the predictions of Special Relativity and also discuss ongoing projects to improve the accuracy of these tests even more.

Second generation gravitational wave detectors are in the process of being researched, designed, and constructed. They include Advanced LIGO in the United States, Advanced Virgo in Italy, the Large Cryogenic Gravitational-wave Telescope in Japan, GEO High Frequency in Germany, and the Australian International Gravitational Observatory in Australia. It is expected that these second generation detectors will have the sensitivity needed to regularly detect gravitational waves and usher in the era of gravitational astronomy. To achieve this sensitivity, new technology to reduce seismic, thermal, quantum and other noise sources is being developed and implemented. Advanced LIGO, Advanced Virgo, and GEO HF have already been funded and are building and buying new hardware, while LCGT is awaiting a funding decision, and AIGO is preparing to submit a funding proposal.

More than thirty years passed since the first discoveries of various aspects of integrability of the symmetry reduced vacuum Einstein equations and electrovacuum Einstein - Maxwell equations were made and gave rise to constructions of powerful solution generating methods for these equations. In the subsequent papers, the inverse scattering approach and soliton generating techniques, Bäcklund and symmetry transformations, formulations of auxiliary Riemann-Hilbert or homogeneous Hilbert problems and various linear integral equation methods have been developed in detail and found different interesting applications. Recently many efforts of different authors were aimed at finding of generalizations of these solution generating methods to various (symmetry reduced) gravity, string gravity and supergravity models in four and higher dimensions. However, in some cases it occurred that even after the integrability of a system was evidenced, some difficulties arise which do not allow the authors to develop some effective methods for constructing of solutions. The present survey includes some remarks concerning the history of discoveries of some of the well known solution generating methods, brief descriptions of various approaches and their scopes as well as some comments concerning the possible difficulties of generalizations of various approaches to more complicate (symmetry reduced) gravity models and possible ways for avoiding these difficulties.

This is a summary of presentations delivered at the OC1 parallel session “Primordial Gravitational Waves and the CMB” of the 12^th Marcel Grossmann meeting in Paris, July 2009. The reports and discussions demonstrated significant progress that was achieved in theory and observations. It appears that the existing data provide some indications of the presence of gravitational wave contribution to the CMB anisotropies, while ongoing and planned observational efforts are likely to convert these indications into more confident statements about the actual detection.

Toward the end of the 1990s it was fashionable to argue that within 10 or even 5 years there would have been a fully satisfactory solution of the quantum-gravity problem, but it is still not in sight. I here take as working assumption that the path to Quantum Gravity will not consist of a single huge conceptual step, but it will rather be a path analogous to the one that took us to Quantum Mechanics only after a long and disorienting multi-step process, the first three decades of the 20th century which we now label as the phase of the “Old Quantum Theory”. In order for us to gain access to such a phase of “Old Quantum-Gravity Theory” phenomenology should necessarily take the lead, and I here comment on a few quantum-gravity-phenomenology research programs that at least should be viewed as illustrative examples of what we can realistically try. And I stress that, in addition to the better known phenomenology inspired by “ultraviolet aspects” of the quantum-gravity problem, the possibility of “ultraviolet/infrared mixing” should invite us to also consider the opportunities provided by the fundamental-physics “infrared” studies performed at some particle decelerators.

In due time (1968) we had been put forward a gravimagnetism hypothesis. Its essence consists in the statement that a gravitational field varying in time creates a magnetic field. The Hypothesis of gravimagnetism allows to substantiate known Wilson and Blackett hypotheses concerning magnetism of massive bodies and Einstein’s remark: ”it is similar to as though magnetic fields arise at a rotary motion of neutral mass more likely. Similar generation of fields cannot predict neither the theory of Maxwell in an original form, nor the theory of Maxwell generalized in sense of the General Relativity. Here the nature specifies us, apparently, fundamental, for the present the law not united by the theory”. In the offered work the question is discussed: how it will be transformed a gravimagnetic field at transition from one harmonic system of coordinates to another.

In the framework of general relativity, we discuss choreographic solutions for the three-body problem, where a solution is called choreographic if every massive particles move periodically in a single closed orbit. In general relativity, the periastron shift prohibits a binary system from orbiting in a single closed curve. Remarkably, a “figure-eight” solution is shown to be choreographic even at the PN approximation by carefully examining initial conditions. Next, gravitational waves for two- and three-body gravitating systems are discussed as an inverse problem. It is shown that quadrupole waveforms cannot distinguish these sources at particular configurations, especially through extending the definition of the chirp mass to such a three-body system. Finally, we present a conjecture on N particles for classification of sources with multipolar waveforms.

We use surface adapted ellipsoidal coordinates to obtain a first order post-Newtonian (PN) approximation to Dedekind ellipsoids with the intention of proceeding to higher orders.

The Hamiltonian for a system of relativistic bodies interacting by their gravitational field is found in the post-Minkowskian approximation, including all terms linear in the gravitational constant. It is given in a surprisingly simple closed form as a function of canonical variables describing the bodies only. The field is eliminated by solving inhomogeneous wave equations, applying transverse-traceless projections, and using the Routh functional. By including all special relativistic effects our Hamiltonian extends the results described in classical textbooks of theoretical physics. As an application, the scattering of relativistic objects is considered.

An increasing number of forthcoming spatial experiments will require a description of the solar system gravitational field including all the second order terms in the PN (Post-Newtonian) metric. This will be the case for missions planned or in project, like TIPO, ASTROD, LATOR. However, the solar system metric recommended by the IAU resolution B1.3, during its 24th general assembly in 2000, allows light propagation calculations until order 1.5 only. Hence, it is necessary to generalize this framework to include relevant contributing terms, which indeed are required for a great number of near-future interplanetary space missions. The present paper proposes such an extension for both General Relativity and Scalar-Tensor theories.

We study the gravitational dynamics in the early inspiral phase of coalescing compact binaries using Non-Relativistic General Relativity (NRGR) - an effective field theory formalism based on the post-Newtonian expansion, but which provides a consistent lagrangian framework and a systematic way in which to study binary dynamics and gravitational wave emission. We calculate in this framework the spin-orbit correction to the newtonian potential at 2.5 PN.

Recently, different methods succeeded in calculating the spin dynamics at higher orders in the post-Newtonian (PN) approximation. This is an essential step toward the determination of more accurate templates for gravitational waves, to be used in future gravitational wave astronomy. We focus on the extension of the ADM canonical formalism to spinning binary black holes. Using the global Poincarée invariance of asymptotically flat spacetimes as the most important guiding consistency condition, this extension can be constructed order by order in the PN approximation. We were able to reach a high order both in the spin power and the PN counting.

Gravitational waves are described by the Einstein equations linearized around the Minkowski metric η_μν. Writing the space-time metric in the form g_μν = η_μν + h_μν, introducing the trace-reversed perturbation and choosing the harmonic gauge □_gx^μ = 0 we get from the Einstein equations

Recently, a new class of restricted gravitational wave search templates, termed the TaylorEt template was proposed for the search of inspiralling compact binaries. The TaylorEt approximant is different from the usual time-domain post-Newtonian approximants in that it employs the orbital binding energy rather than the orbital frequency or the closely related parameter “x”. We perform detailed studies to probe the fitting factors of TaylorEt at 3.5pN for nonspinning comparable mass compact binaries vis-a-vis the TaylorT1, TaylorT4, and TaylorF2 at 3.5pN approximants in LIGO, Advanced LIGO and Virgo interferometers.

The hyperbolic encounter of compact objects results burst like gravitational wave signal. We analyze the motion of spinning binary systems with the construction of a general parametrization of the radial motion which is valid for all types of the orbits. With the time dependence of the parameter the gravitational waveforms can be constructed.

The properties of neutron star matter above nuclear density are not precisely known. Gravitational waves emitted from binary neutron stars during their late stages of inspiral and merger contain imprints of the neutron-star equation of state. Measuring departures from the point-particle limit of the late inspiral waveform allows one to measure properties of the equation of state via gravitational wave observations. This and a companion talk by J. S. Read reports a comparison of numerical waveforms from simulations of inspiraling neutron-star binaries, computed for equations of state with varying stiffness. We calculate the signal strength of the difference between waveforms for various commissioned and proposed interferometric gravitational wave detectors and show that observations at frequencies around 1 kHz will be able to measure a compactness parameter and constrain the possible neutron-star equations of state.

Notions like energy and angular momentum and the associated conservation laws play an invaluable role in Newtonian dynamics. In General Relativity, however, the estimate of angular momentum and other physical observables is complicated by a number of factors, such as their non-localizability and the ambiguities in defining a reference frame in which to measure them. Most of these issues seriously affect numerical simulations, where only portions of a spacetime are usually accessible, and one has very little control over the coordinates used and their evolution. We will discuss how surfaces of constant expansion show the potential to alleviate these problems.

The Gowdy waves metric is proposed as a strong-field test-bed for constraint-preserving boundary conditions in Numerical Relativity. The 3-torus space topology allows periodic boundary conditions, so that one can test the constraint-related degrees of freedom by themselves, without requiring any further ansatz for the remaining modes. Also, the planar symmetry of the solution allows testing separately the longitudinal and transverse modes, by applying the boundary conditions selectively to one or another face.

In this talk, we investigate the cosmic no-hair conjecture for perturbed Nariai solutions within the class of Gowdy symmetric solutions of Einstein’s field equations in vacuum with a positive cosmological constant. In particular, we are interested whether these perturbations allow to construct new cosmological black hole solutions.

The Einstein equations are a special in two ways: (1) they are geometric equations in the sense that they express conditions on the underlying geometry and are therefore invariant under arbitrary coordinate transformations and they are (2) derivable from a variational principle, which implies that there is an underlying symplectic structure. Both aspects could be used in numerical simulations.

We present a numerical code based on the Galerkin method to integrate numerically the field equations for massless and massive scalar fields in spherically symmetric spacetimes.

Two examples of black hole binary configurations are studied examining the question under what condition overlapping marginally outer trapped surfaces exist. A series of time- and axisymmetric black hole binary initial data and simulations of inspiraling black holes were analyzed. In both cases no overlap was found. Using embedding diagrams an explanation is given why these results need not be contradictory to results obtained in different contexts. Differences in the gauge are likely to explain the disagreements.

Among the most important systems of partial differential equations (PDEs) in numerical relativity are those of the first-order in time and mixed first and second-order in space. Namely, impressive results were obtained by several groups using so-called BSSN system belonging to this category. While the analysis of the first-order in space systems had provided a method of construction of boundary conditions compatible with PDEs, no such recipe is available for second-order in space systems unless it is symmetric hyperbolic. We show, that introducing potentials for evolution variables of a linearized BSSN system, one can find an associated symmetric-hyperbolic system of PDEs which provides boundary conditions for the original BSSN system.

Constrained formulations of Einstein equations can exhibit some uniqueness problems within their elliptic part, for instance when calculating the numerical spacetime of very compact stars or black holes. The same holds for the approximation of the conformal atness condition (CFC). We present here a reformulation of the elliptic sector of such formulations that solves this uniqueness problems. The correct behavior of our new formulation is confirmed in CFC with numerical tests.

Using a constrained formalism for Einstein equations in Dirac gauge, we propose to compute excised quasistationary initial data for black hole spacetimes in full general relativity. Vacuum spacetime settings are numerically constructed by using the isolated horizon formalism; we especially tackle the conformal metric part of our equations, assuming global stationarity. We show that a no-boundary treatment can be used on the horizon for the equation related to the conformal metric. We relate this finding to previous suggestions in the literature, and use our results to assess the widely used conformally flat approximation for computing black hole initial data.

We study the dynamics of a mini-collapse induced by a phase transition in the core of an isolated rotating neutron star by means of performing, with the use of general relativistic hydrodynamical code CoCoNuT, a series of numerical simulations. The immediate cause of the collapse is the back bending instability that can be reached via the angular momentum loss. We study a resonant nonlinear coupling of axisymmetric modes of pulsation, their damping and resonant effects, as well as the emission of gravitational waves for configurations composed of a microphysical equation of state with kaon-condensed core and for an analytic equation of state, approximating the mixed-phase transition to quark matter.

Alfvén oscillations of magnetars are a possible explanation for at least some of the observed quasi- periodic oscillations (QPOs) in soft gamma repeaters. We present results of axisymmetric simulations of Alfvén torsional oscillations in magnetars, modeled as relativistic stars with a dipolar magnetic field. We use a general relativistic magnetohydrodynamics code in the anelastic approximation, which allows for an effective suppression of fluid modes and an accurate description of the Alfvén waves. We present also a new method to compute the QPOs frequencies and compare it to the numerical results.

We study torsional Alfvén oscillations of magnetars, i.e., neutron stars with a strong magnetic field. We consider the poloidal and toroidal components of the magnetic field and a wide range of equilibrium stellar models. Our results can explain both the lower and the higher observed frequencies in SGR 1806-20 and SGR 1900+14.

We present some new results for g-modes of fast rotating stratified neutron stars in the general relativistic Cowling approximation. This is the first study of its kind in a general relativistic framework. In a recent paper [A. Passamonti, B. Haskell, N. Andersson, D. I. Jones, and I. Hawke, Mon. Not. R. Astron. Soc. 394, 730 (2009)], a similar study was performed within the Newtonian framework, where the authors presented results about the onset of CFS-unstable g-modes and the close connection between inertial and gravity modes. In our relativistic treatment of the problem, we find an excellent qualitative agreement with respect to the Newtonian results.

Using a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions, the dynamics of magnetized, rigidly rotating neutron stars are studied. Beginning with fully consistent initial data constructed with Magstar, part of the Lorene project, we study the dynamics and stability of rotating, magnetized polytropic stars as models of neutron stars. Evolutions suggest that some of these rotating, magnetized stars may be minimally unstable occurring at the threshold of black hole formation.

We investigate the collapse of differentially rotating supermassive stars by means of 3+1 hydrodynamic simulations in general relativity. We particularly focus on the formation of a rapidly rotating dynamic black hole, and find the following two features. Firstly, quasi-periodic gravitational waves continue to be emitted after the quasi-normal mode frequency has decayed. Secondly, when the newly formed black hole is almost extreme Kerr, the amplitude of the quasi-periodic oscillation is enhanced during the late stages of the evolution. Geometrical features, shock waves, and instabilities of the fluid are suggested as a cause of this amplification behaviour. This alternative scenario for the collapse of differentially rotating supermassive stars might be observable by LISA.

We study polar Alfvén oscillations of relativistic stars endowed with a strong global poloidal dipole magnetic field. Here we focus only on the axisymmetric oscillations which are studied by evolving numerically the two-dimensional perturbation equations. Our study shows that the spectrum of the polar Alfvén oscillations is discrete in contrast to the spectrum of axial Alfvén oscillations which is continuous. We also show that the typical fluid modes, such as the f and p modes, are not significantly affected by the presence of the strong magnetic field.

The computation of frequencies of nonaxisymmetric f-modes in rapidly rotating stars in full general relativity is a long-standing problem that has not been solved, to date, without resorting to some approximation, such as the slow-rotation approximation or the Cowling approximation. We present the first computation of such frequencies in full general relativity and rapid rotation, without any such approximation. We achieve this by using long-term simulations of oscillating polytropic models with a nonlinear numerical code, where spacetime is evolved in the harmonic formulation. We compare our results to previous results for zero-frequency (neutral modes) that were obtained with a perturbative method, and comment on the relevance of our work to the gravitational-radiation-driven (CFS) secular instability of nonaxisymmetric f-modes.

We examine the radiative transfer of energy and momentum by gravitational radiation emission in the head-on collision of two Schwarzschild black holes. This problem is examined in the scenario of Robinson-Trautman (RT) spacetimes, when a global apparent horizon has already formed. We construct characteristic initial data for the problem to be evolved by RT equation, which is numerically integrated using a combination of the Galerkin and collocation methods. The initial data depend on two parameters, the namely, α₁ associated with the ratio of the rest mass of the two black holes, and γ associated with the infalling velocity of the initial black holes. We obtain that the final configuration (when gravitational radiation is considered to have ceased) is a black hole with recoil velocity smaller than the initial infalling velocity and rest mass larger than the sum of the rest masses of the colliding black holes considered individually. For α₁ = 1 the recoil velocity is zero. The total energy E_W carried out by gravitational waves (GW’s) is evaluated through the Bondi mass formula, increasing monotonically (but not exponentially) with α₁. We also discuss the linear momentum distribution of the remnant black hole that exibits a maximum at α₁ = α_m ≃ 0:667, for any initial infalling velocity. Two distinct regimes of gravitational wave emission can be distinguished according to (i) α₁ < α_m: bursts of gravitational Bremsstrahlung and (ii) α_m < α₁ < 1: quiescent longtime emission of GW’s. This picture is also sustained by the analysis of the time behavior of the power emitted P_W = dE_W/du.

The following sections are included:

• Introductory Remarks

• Cauchy Evolution

• Characteristic Extraction

• Binary Black Hole Evolution

• Acknowledgments

• References

We study gravitational wave emission, zoom-whirl behavior and the resulting spin of the remnant black hole in highly boosted collisions of equal-mass, non spinning black-hole binaries with generic impact parameter.

Supermassive black hole binary inspirals are among the most important sources for the future LISA gravitational wave observatory. The scattering of stars and/or the effects of an ambient gaseous accretion disk can lead to a significant initial eccentricity. Taking into account the eccentricity in the waveform improves the parameter estimation accuracy for these sources, as shown using a Fisher matrix analysis.

This article focuses on the scaling performance of the evolution portion of openGR, a code for Numerical Relativity. As expected, openGR scales considerably better for unigrid domains than it does for domains using Fixed Mesh Refinement (FMR).

The evolution of black holes in “confining boxes” is interesting for a number of reasons, particularly because it mimics some aspects of anti-de Sitter space-times. We are here interested in the potential role that boundary conditions play in the evolution of such systems. Therefore, we imprison and study a black hole binary in a box, at which boundary we set mirror-like boundary conditions.

We establish the jump conditions for the wavefunction and its derivatives through the formal solutions of the wave equation. These conditions respond to the requirement of continuity of the perturbations at the position of the particle and they are given for any mode at first order. Using these jump conditions, we then propose a new method for computing the radiated waveform without direct integration of the source term. We consider this approach potentially applicable to generic orbits.

In a recent work, we presented the first application of the Poisson-Wiseman-Anderson method of “matched expansions” to compute the self-force acting on a point particle moving in a curved spacetime. The method employs two expansions for the Green function which are respectively valid in the “quasilocal” and “distant past” regimes, and which may be matched together within the normal neighbourhood. In this article, we introduce the method of matched expansions and discuss transport equation methods for the calculation of the Green function in the quasilocal region. These methods allow the Green function to be evaluated throughout the normal neighborhood and are also relevant to a broad range of problems from radiation reaction to quantum field theory in curved spacetime and quantum gravity.

We introduce a new time-domain method for computing the self-force acting on a scalar particle in a Schwarzschild geometry. The principal feature of our method consists in the division of the spatial domain into several subdomains and locating the particle at the interface betweem two them. In this way, we avoid the need of resolving a small length scale associated with the presence of a particle in the computational domain and, at the same time, we avoid numerical problems due to the low differentiability of solutions of equations with point-like singular behaviour.

We present the first successful application of the method of Matched Expansions for the calculation of the self-force on a point particle in a curved spacetime. We investigate the case of a scalar charge in the Nariai spacetime, which serves as a toy model for a point mass moving in the Schwarzschild black hole background. We discuss the singularity structure of the Green function beyond the normal neighbourhood and the interesting effect of caustics on null wave propagation.

A formalism is described that greatly simplifies the derivation of scalar, electromagnetic, and gravitational self-forces and self-torques acting on extended bodies in curved spacetimes. Commonly-studied aspects of these effects are normally dominated by the so-called “regular” component of a body’s self-field. The only consequence of the remaining (much larger) portion of the self-field turns out to be very simple. It exerts forces and torques that effectively renormalize all multipole moments of the body’s stress-energy tensor in its laws of motion.

We study the self-interaction of a massive scalar field with a point-like particle in a Kerr resp. Schwarzschild background black hole space-times. We find that in addition to regularization of the self-field a finite renormalization of the particle mass is also necessary to obtain a unique equation of motion. We expand the renormalized equation of motion for large scalar masses and apply this approximation for the neutral pion radiation by protons in the strong electromagnetic field of a magnetar. Our results show that taking into account general relativistic effects to leading order has a significant influence on the proton energy and the intensity of neutral pion radiation.

In this talk I summarize briefly recent results of joint work with P. Bizoń, T. Chmaj and S. Zając, on the nonlinear origin of the power-law tails in the long-time evolution of self-gravitating massless fields. We focus on a spherically symmetric massless scalar field and wave map matter coupled to gravity. Using a third-order perturbation method we derive explicit expressions for the tail (the decay rate and the amplitude) for solutions starting from small initial data and we verify this prediction via numerical integration of the full system of Einstein field equations. Our results show that the nonlinear effects can dominate the late time asymptotics.

We have studied thermalization of optically thick pair plasma with baryon loading by particle collisions and followed the evolution of distribution functions starting far from equilibrium configuration. With this goal we solved numerically relativistic Boltzmann equations with collisional integrals given by QED matrix elements for the corresponding processes. We computed the relevant timescales of reaching kinetic and thermal equilibria as functions of plasma total energy density and baryon loading parameter.

Beam-plasma instabilities represent a key issue for the physics of relativistic collisionless shocks. They play a role in the very shock formation when triggered by the collision of two plasma shells. Once the shock is formed, Fermi accelerated particles at the shock front interact with the upstream medium. In this phase, the beam-plasma instabilities can amplify the upstream magnetic field and generate small scale turbulence. Both kind of effects are believed to play a major role in the generation of High Energy Cosmic Rays and Gamma Ray Bursts.

Anomalous excesses in the flux of high-energy cosmic e^± have been observed by several experiments. These may be explained in terms of solar neighbourhood WIMP annihilations primarily to leptons for a few TeV mass WIMP with a Sommerfeld-corrected boost ~ 10⁴ − 10⁵; provided that a small component of the dark matter is in cold subhalo substructure.

Directional detection of galactic Dark Matter is a promising search strategy for discriminating genuine WIMP events from background ones. We present technical progress on gaseous detectors as well as recent phenomenological studies, allowing the design and construction of competitive experiments.

The lensing data of the galaxy cluster Abell 1689 can be explained by an isothermal fermion model with a mass of 1-2 eV. The best candidate is the 1.5 eV neutrino; its mass will be searched down to 0.2 eV in KATRIN 2015. If its righthanded (sterile) modes were created too, there is 20% neutrino hot dark matter. Their condensation on clusters explains the reionization of the intercluster gas without Pop. III stars. Baryonic structure formation is achieved by gravitional hydrodynamics alone, without dark matter trigger.

EURECA (European Underground Rare Event Calorimeter Array) is a one-tonne cryogenic dark matter experiment, aiming to search for WIMP interactions with a scattering cross-section down to 10⁻¹⁰pb. It will use cryogenic detector technology developed by the CRESST and EDELWEISS groups, and a selection of different target materials.

The EDELWEISS II experiment is devoted to the search for the Weakly Interactive Massive Particles (WIMP) that would constitute the Dark Matter halo of our Galaxy. For this purpose, the experiment uses cryogenic germanium detector, cooled down at 20 mK, in which the collision of a WIMP with an atom produces characteristic signals in terms of ionization and elevation of temperature. We will present the preliminary results of the first operation of the detectors installed in the underground laboratory of the Frejus Tunnel (LSM), attesting to the very low radioactive background conditions achieved so far. Novel detectors, with a special electrode design for active rejection of surface events, have been shown to be suited for searches of WIMPs with scattering cross-sections on nucleon well below 10⁻⁸ pb. Preliminary results of WIMP search performed with a first set of these detectors will be shown as well.

ZEPLIN-III is a 12 kg two-phase xenon time projection chamber searching for weakly interacting massive particles (WIMPs) accounting for dark matter in our Galaxy. Scintillation and ionisation in the liquid differentiate between nuclear and electron recoils above ∼10 keVnr. 847 kg·days data acquired between Feb 27th and May 20th 2008 has excluded a coherent WIMP-nucleon scattering cross-section above 8:1 × 10⁻⁸ pb at 60 GeVc⁻²

Gravitational waves can be produced in the early Universe by many different mechanisms. Here we briefly discuss how their propagation is affected by the interaction with matter, with particular regard to the role of the anisotropic stress of the cosmological neutrinos.

We describe a new mechanism for the production of ultra high-energy neutrinos based upon meson synchrotron emission. The acceleration of ultra-relativistic protons and nuclei in the presence of strong magnetic fields (H ~ 10¹⁵ G) in such environments as Magnetars, or GRB central engines could be a viable site for strong meson synchrotron emission. We show that charged scalar mesons like π^± (along with π⁰’s), vector mesons like ρ, and even heavier mesons like D_S, J/Ψ and ϒ, could be emitted with high intensity (~ 10³ times the photon intensity) through strong couplings to ultra-relativistic nucleons. We estimate the flux of energetic neutrinos originating from the decay of ultra-high-energy neutrons produced in a SGR magnetar environment by proton synchrotron emission of p → π⁺ + n. We deduce the event rate in energetic neutrino detectors and show that a nearby strong SGR burst might be detectable. We also analyze the possibility that the synchrotron emission of massive mesons like the ϒ might produce a burst of three avors of ultra high-energy cosmic neutrinos with Eν ≥ 10¹² eV and evaluate the spectra of νe, νμ and ντ from this process.

This work aims to present results from a numerical time dependent cosmic ray modulation model. These calculations are compared to a selected data set of the Ulysses spacecraft at a certain rigidity to show compatibility. Model calculations at other rigidities are also presented to show the 11 year solar and 22 year magnetic cycle present in these. Results from such a model can be used in future to compare to e.g. PAMELA spacecraft observations.

We review the main results on propagation models of galactic cosmic rays and discuss their compatibility with recent data on nuclei and leptons. We also focus on the production of antimatter in space, in particular on antiprotons and positrons. The discussion addresses the impact that new data have on the theoretical study of primary and secondary standard cosmic rays as well as of possible exotic contributions in the halo of the Milky Way.

PAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature in a wide energy range (protons: 80 MeV-700 GeV, electrons 50 MeV-400 GeV). Main objective is the study of the antimatter component: antiprotons (80 MeV-190 GeV), positrons (50 MeV-270 GeV) and search for antinuclei with a precision of the order of 10⁻⁸). In this work we present the measurements of the December 13^th 2006 Solar Particle Event.

Dark Matter constitutes more that 80% of the total amount of matter in the Universe, yet almost nothing is known about its nature. A powerful investigation technique is that of searching for the products of annihilations of Dark Matter particles in the galactic halo, on top of the ordinary cosmic rays. Recent data from the PAMELA and FERMI satellites and a number of balloon experiment have reported unexpected excesses in the measured uxes of cosmic rays. Are these the first direct evidences for Dark Matter? If yes, which DM models and candidates can explain these anomalies (in terms of annihilations) and what do they imply for future searches? What are the constraints from gamma rays measurements and cosmology? [Saclay T-09/222, CERN-PH-TH/2009-252]

The instrument PAMELA, in orbit since June 15th, 2006 on board the Russian satellite Resurs DK1, is delivering to ground 16 Gigabytes of data per day. The apparatus is designed to study charged particles in the cosmic radiation, with a particular focus on antiparticles; the combination of a magnetic spectrometer and different detectors - indeed - allows antiparticles to be reliably identified from a large background of other charged particles. New results on the antiproton-to-proton and positron-to-all-electron ratios over a wide energy range (1 – 100 GeV) have been recently released by the PAMELA collaboration, and will be summarized in this paper.

The rarefied components of the cosmic-ray flux impinging upon the Earth have been a fertile ground to search for particle physics signatures for the ubiquitous dark matter. Thus, in the last two decades, a number of balloon and satellite experiments have undertaken the extremely challenging task of measuring the cosmic positron, antiproton, electron and gamma-ray fluxes. Any dark matterinduced enhancements of these signals are likely to be subtle effects requiring a detailed understanding of instrumental response as well as more mundane astrophysical sources and galactic propagation effects. We review the status of recent, ongoing and future efforts at teasing out a dark matter signal from the antimatter and electromagnetic cosmic fluxes.

A new method, based on the absorption of very high-energy gamma-rays by the cosmic infrared background, is proposed to constrain the value of the Hubble constant. As this value is both fundamental for cosmology and still not very well measured, it is worth developing such alternative methods. Our lower limit at the 68% confidence level is H₀ > 74km/s/Mpc, leading, when combined with the HST results, to H₀ ≈ 76km/s/Mpc. Interestingly, this value, which is significantly higher than the usually considered one, is in exact agreement with other independent approaches based on baryonic acoustic oscillations and X-ray measurements. Forthcoming data from the experiments HESS-2 and CTA should help improving those results. Finally, we briefly mention a plausible correlation between absorption by the extragalactic background light and the absence of observation of gamma-ray bursts (GRBs) at very high energies.

One of the proeminent features of active galactic nuclei (AGN) is their strong luminosity variability from radio wavelengths up to the most energetic γ-rays. The progress in the characterization and the understanding of γ-ray variability in AGN observations by space- and ground-based telescopes is shortly reviewed, as well as the relationship between the two spectral continua they define.

We present observations of the extended optical counterpart of the bright, elongated ULX in the interacting galaxy pair NGC 5953/54 using the FLAMES-ARGUS integral field spectrograph on the VLT. We describe spectroscopic and spatial information of the ionized surroundings of this ULX in order to distinguish between two possible scenarios: a stellar-mass black hole binary or an intermediate-mass (~ 50 solar masses) black hole.

Tidal effects on clumps of material during random non-stationary accretion onto a black hole produce phenomena with distinct temporal characteristics in observed light-curves. During such non-stationary accretion events, the shape of the accreting object evolves in time, and observable quasi-periodic phenomena with variable quasi-periods are produced. A number of characteristic light-curves, obtained with numerical simulations, will be shown. Their relevance to observed phenomena will be briefly discussed.

We summarize influence of the tidal charge parameter of the braneworld models onto some optical phenomena in rotating black hole spacetimes. The shape of an equatorial thin accretion disk and profiled spectral lines of thin keplerian rings around the black holes are given and classified in terms of the black hole rotational and tidal parameters. It is shown that rising of negatively-valued tidal parameter, with rotational parameter fixed, generally strengthens the relativistic effects and suppresses the rotation induced asymmetries in the optical phenomena.

Humpy profile of the LNRF-related orbital velocity was found for accretion discs orbiting rapidly rotating Kerr black holes with a spin a > 0.9953 (Keplerian discs) and a > 0.99979 (marginally stable thick discs). Maximal positive rate of change of the orbital velocity in terms of the proper radial distance is used to define a local frequency characterising possible physical processes in the disc connected with the velocity hump. Comparing the “humpy frequency” related to distant observers with epicyclic frequencies of perturbed orbital motion, it was shown that in Keplerian discs orbiting near-extreme Kerr black holes (a > 0.998) the the ratio of radial epicyclic frequency and humpy frequency (both evaluated at the same radius) is in terms of small integers asymptotically going to the ratio ~ 3:2 for a → 1. The Extended Orbital Resonance Model with non-linear hump-induced oscillations was applied to two X-ray variable sources GRS 1915+105 and XTE J1650-500. In the case of GRS 1915+105, the model is able to address the whole set of reported QPOs, giving the mass and spin of the central black hole: a = 0.9998; M = 14:8M_⊙. For XTE J1650-500, similar ideas give values a = 0.9982; M = 5:1M_⊙.

Using known frequencies of the twin peak quasiperiodic oscillations (QPOs) and the known mass of the central black hole, the black hole dimensionless spin a can be determined, assuming a concrete version of the orbital resonance model. However, because of large range of observationally limited values of the black hole mass, its spin can be estimated with a low precision only. Higher precision of the black hole dimensionless spin measurement is possible in the framework of multi-resonance model of QPOs inspired by complex high-frequency QPO patterns observed in some black hole and neutron star systems.

The following sections are included:

• Estimating BH Masses

• Beyond Crude Estimates

• FWHM(MgII) as a Virial Estimator for Higher z Quasars?

• References

We investigate the possibility that stellar mass black holes, with masses in the range of 3:8M_⊙ and 6M_⊙, respectively, could be in fact quark stars in the Color-Flavor-Locked (CFL) phase. Depending on the value of the gap parameter, rapidly rotating CFL quark stars can achieve much higher masses than standard neutron stars, thus making them possible stellar mass black hole candidates. Moreover, quark stars have a very low luminosity and a completely absorbing surface - the infalling matter on the surface of the quark star is converted into quark matter. A possibility of distinguishing CFL quark stars from stellar mass black holes could be through the study of thin accretion disks around rapidly rotating quark stars and Kerr type black holes, respectively. Strange stars exhibit a low luminosity, but high temperature bremsstrahlung spectrum, which, in combination with the emission properties of the accretion disk, may be the key signature to differentiate massive strange stars from black hole.

We investigate the composition and equation of state of dense matter in neutron star interior using axial w-modes. We obtain complex frequencies of first axial w-modes for equations of state involving hyperons as well as Bose-Einstein condensates of antikaons. The presence of condensates in neutron stars may lead to the appearance of a new stable branch called the third family of superdense stars beyond the neutron star branch. The compact stars with same mass in both branches known as neutron star twins may exist. Further we discuss first axial w-mode frequencies of superdense stars in the third family and those of the corresponding twins in the neutron star branch.

We investigate the role of the tidal charge in orbital models of high-frequency quasiperiodic oscillations (QPOs) observed in neutron star binary systems. We show how the standard relativistic precession (RP) model modified by the tidal charge fits the observational data, giving estimates of the allowed values of the tidal charge and the brane tension based on the processes going in the vicinity of neutron stars. We compare our strong field regime restrictions with those given in the weak field limit of solar system experiments.

We present estimates on the efficiency of neutrino trapping in brany extremely compact stars, using the simplest model with uniform distribution of energy density, assuming massless neutrinos and uniform distribution of neutrino emissivity. Computation have been done for two different uniform-density stellar solution in the Randall–Sundrum II type braneworld, namely with the Reissner-Nordström-type of geometry and the second one, derived by Germani and Maartens.¹

The photospheric absorption lines in the XMM-Newton spectra of the X-ray bursting neutron star EXO0748-676 were found by Cottam et al. (2002)¹ and identified as the n = 2 − 3 transitions in hydrogen and helium like ions of iron, gravitationally redshifted with z = 0.35. We check these conclusions using model atmosphere calculations. The extended set of the NLTE model atmospheres with effective temperature from 1 to 20 MK and various iron abundance, from solar up to practically pure iron atmospheres was calculated. Results of these computations were checked by LTE calculations for investigations of Compton scattering and chemical compositions influence. Results are in the good qualitative agreement. Main our conclusion is the following. The n = 2 − 3 lines of FeXXV are very weak and can not be observed, even if the atmosphere has 99% of iron. But the lines of previous state of ionization, lithium like iron, Fe XXIV, are more intensive, but they correspond to gravitational redshift z = 0.24. Iron XXIV lines are more prominent in comparison to iron XXV lines in this energy band for all effective temperatures. It is necessary to remark that the equivalent widths of iron XXIV also too weak in comparison to the observed absorption features.

We present equation of state of dense nuclear matter based on relativistic Brueckner—Hartree—Fock theory. The models of static neutron stars are calculated. The results are compared with neutron star models based on Skyrme equations of state and with models of strange stars following MIT bag model.

We give a brief review on the neutron star spin frequency and its relation to the kHz QPOs. A simple power law relation can be applicable for the Atoll and Z sources with the slightly different power index, e.g. ν1 ~ 700(Hz)(ν2/1000)^1.8; However, for the two accretion induced millisecond X-ray pulsars, Sax J 1808.4-3658 and XTE 1807-294, their low values of twin kHz QPO separations make them different from the other QPO sources. In addition, there are not found the clear relation between a spin frequency and the twin kHz QPO separation, which seems to hint that the beat model for kHz QPOs confronts the difficulty. The kHz QPO separations are not constant, varied up and down with accretion rate, so the models that follow this tendency are the relativistic precession model by Stella & Vietri and the Alfvën wave oscillation model by Zhang. Averagely, the ratio of upper kHz QPO frequency to the lower one is very close to 1.5, then for Cir X-1 this ratio (~ 3) is unusual higher than those of the other sources.

The galactic black hole GRS 1915+105 exhibits at least 13 types of X-ray variability classes. Transitions from one class to another take place in a matter of hours. Within each class, the spectral state transitions take place in a matter of few seconds, hinting at the fact that it is the free-falling, and not the Keplerian disk that is involved. In the present paper, we establish that one of the reasons of the class transitions is the variation of the Comptonizing efficiency (CE), i.e., the ratio of the power-law photons and the black body photons in the average spectrum of each class. Around a mean CE, there is a scatter in time scales of a few to a few tens of seconds which can be achieved by variation of the cooling effects of the outflow through Comptonization. Thus, we pinpoint two major causes of the variability of the enigmatic black hole candidate GRS 1915+105.

Massive black holes (BH) are now believed to power active galactic nuclei (e.g. quasars and Seyfert galaxies). BH detected in the centers of many nearby galaxies are linearly correlated with the luminosity of the host bulge (spheroid), the black hole mass being about 0.1% of the stellar mass. In active galaxies, the BH mass measured by reverberation mapping follows the same relation with the luminosity of the host galaxy as in ordinary (inactive) galaxies, with the exception of narrow line AGN which apparently have significantly lower BH/host mass/luminosity ratios. Then we review the empirical L-R (“Kaspi”) relation between the luminosity and the size of the Broad-Line Region in AGN and derive a toy-model explanation. We also present a new method of estimating BH masses from the uctuations in their X-ray spectrum, which suggests a common mechanism for the X-ray radiation from accretion onto stellar and super massive BHs, over 8 orders of magnitude in BH mass.

We model two temperature viscous accretion flows in the sub-Keplerian, optically thin, regime around rotating black holes including important radiation effects self-consistently. The model successfully explains observed luminosities from ultra-luminous to under-luminous sources and predicts the spin parameter of black holes.

Matter falling onto a black hole is trans-relativistic, transonic, and close to the horizon it is sub-Keplerian. Such a flow shows the existence of multiple critical point, shocks etc. Employing relativistic equation of state and realistic composition, it has been shown that the solution strongly depend on the composition of the uid. Electron-positron fluid is the least relativistic, to the extent that multiple critical points, shocks etc do not form. The most relativistic fluid is the one whose ratio of proton to electron number density is ~ 0.2. Since the solution strongly depend on composition, the emitted radiation should strongly depend on the composition too.

A black hole accretion may have both the Keplerian and the sub-Keplerian components. In the so-called Chakrabarti-Titarchuk scenario, the Keplerian component supplies low energy (soft) photons while the sub-Keplerian component supplies hot electrons which exchange their energy with the soft photons through Comptonization or inverse Comptonization processes. In the sub-Keplerian component, a shock is generally produced due to the centrifugal force. The post-shock region is known as the CENtrifugal pressure-supported BOundary Layer (CENBOL). In this paper, we compute the effects of the thermal and the bulk motion Comptonization on the soft photons and study the emerging spectrum when the converging inflow and the diverging outflow (generated from the CENBOL) are simultaneously present. From the strength of the shock, we calculate the percentage of matter being carried away by the outflow and determine how the emerging spectrum depends on the outflow rate. The interplay between the up-scattering and down-scattering effects determines the effective shape of the emerging spectrum.

Relativistic jets have been observed in radio and/or in X-rays in some X-ray binaries. In the case of Cygnus X-1, the signatures of interaction between these relativistic outflows and the surrounding interstellar medium have been also observed. This data provides evidence of very efficient acceleration of particles to multi-TeV energies in these systems.

Motivated by detections of hypervelocity stars that may originate from the Galactic Center, we revist the problem of a binary disruption by a passage near a much more massive point mass. The six order of magnitude mass ratio between the Galactic Center black hole and the binary stars allows us to formulate the problem in the restricted parabolic three-body approximation. In this framework, results can be simply rescaled in terms of binary masses, its initial separation and binary-to-black hole mass ratio. Consequently, an advantage over the full three-body calculation is that a much smaller set of simulations is needed to explore the relevant parameter space. Contrary to previous claims, we show that, upon binary disruption, the lighter star does not remain preferentially bound to the black hole. In fact, it is ejected exactly in 50% of the cases. Nonetheless, lighter objects have higher ejection velocities, since the energy distribution is independent of mass. Focusing on the planar case, we provide the probability distributions for disruption of circular binaries and for the ejection energy. We show that even binaries that penetrate deeply into the tidal sphere of the black hole are not doomed to disruption, but survive in 20% of the cases. Nor do these deep encounters produce the highest ejection energies, which are instead obtained for binaries arriving to 0:1 – 0:5 of the tidal radius in a prograde orbit. Interestingly, such deep-reaching binaries separate widely after penetrating the tidal radius, but always approach each other again on their way out from the black hole. Finally, our analytic method allows us to account for a finite size of the stars and recast the ejection energy in terms of a minimal possible separation. We find that, for a given minimal separation, the ejection energy is relatively insensitive to the initial binary separation (see Sari, Kobayashi and Rossi 2010, ApJ 708, 605 for the full discussion).

The 1-30 GHz light curves of the microquasars GRS1915+105, Cyg X-3, and SS433 were measured in the intensive daily monitoring programs with the RATAN-600 (SAO RAS) radio telescope during 2002-2009. A lot of the powerful flaring events were detected, being alerts of the VLBI or e-VLBI mapping. We detected clear correlations between radio emission (RATAN), soft (ASM XTE) and hard (ASM Swift/BAT) X-ray emission for Cyg X-3 and GRS 1915+105. The repeatedly similar pre-flaring evolution of the radio and X-ray emission of Cyg X-3 allow us to predict the strong flares (> 3 Jy) as in the case of the flare in December 2008. We used it in the high-energy emission (MAGIC, AGILE) search of the X-ray binary. The super-critical black hole accretor SS433 was mapping with the European e-VLBI during its unusual radio activity in November 2008. Possible microquasar, X-ray binary and luminous star LSI+61d303 was monitored during May-October 2009 and six periodically flaring events were detected. But we found that the most accurate ephemerids (Gregory, 2002) of radio flares according to super-orbital period (P2= 1664days) were not coincident with the mean (for six flares) light curves. That could be explained by or slightly the shorter P2, near 1600 days, or the variability of this super-orbital period on timescale of 10 years.

The Large Area Telescope on the Fermi γ-ray Space Telescope provides unprecedented sensitivity for all-sky monitoring of γ-ray activity. It has detected a few Galactic sources, including 2 γ-ray binaries and a microquasar. In addition, it is an adequate telescope to detect other transient sources. The observatory scans the entire sky every three hours and allows a general search for flaring activity on daily timescales. This search is conducted automatically as part of the ground processing of the data and allows a fast response to transient events, typically less than a day. Most of the outbursts detected are spatially associated with known blazars, but in several cases during the first years of observations, γ-ray flares occurring near the Galactic plane did not reveal any initially compelling counterparts. This prompted follow-up observations in X-ray, optical, and radio to attempt to identify the origin of the emission and probe the possible existence of a class of transient γ-ray sources in the Galaxy. Here we report on these LAT events and the results of the multiwavelength counterpart searches.

The very high energy gamma-ray telescope HESS has surveyed most of the galactic volume revealing over 50 new TeV sources, the majority of which are extended^1,2. Of the small fraction of point-like sources, only two show variable emission; PSR B1259+63 and LS 5039. Both of these objects are associated with X-ray and radio emitting binary stellar systems. The unidentified point-like source HESS J0632+057 has been suggested as a new member of this rare class of objects.

The “dyadotorus” is defined as the region where e⁻ − e⁺ pair creation can occur in a Kerr-Newman spacetime via vacuum polarization. The geometry of this very peculiar region as well as its energetics are mathematically and physically discussed.

We study the motion of neutral test particles along circular orbits in the Reissner-Nordström spacetime. We use the method of the effective potential with the constants of motion associated to the underlying Killing symmetries. A comparison between the black hole and naked singularity cases is performed. In particular we find that in the naked singularity case for r < Q²/M no circular orbits can exist, this radius plays a fundamental role in the physics of the naked singularity. For r > Q²/M and there are two stability regions together with a region where all the circular orbits are instable and a zone in which all trajectory are possible but not circular orbits, for one stability region and a region where all circular orbits are instable appear, finally for there are all stable circular orbits for r > Q²/M.

Recent observations of the time modulation of two-body weak decays of heavy ions reveal the mass content of the electron neutrinos via interference patterns in the recoilingion wave function. From the modulation period we derive the difference of the square masses △m² ≈ 22.5 × 10⁻⁵ eV², which is about 2.8 times larger than that derived from a combined analysis of KamLAND and solar neutrino oscillation experiments. It is, however, compatible with a data regime to which the KamLAND analysis attributes a smaller probability.

We generalize Killing equations to a test particle system which is subjected to external force. We relax the conservation condition by virtue of reparametrization invariance of a particle orbit. As a result, we obtain generalized Killing equations which have hierarchical structure on the top of which a conformal Killing equation exists.

A remarkable property of naked singularities in general relativity is their repulsive nature. The effects generated by repulsive gravity are usually investigated by analyzing the trajectories of test particles which move in the effective potential of a naked singularity. This method is, however, coordinate and observer dependent. We propose to use the properties of the Riemann tensor in order to establish in an invariant manner the regions where repulsive gravity plays a dominant role. In particular, we show that in the case of the Kerr-Newman singularity and its special subcases the method delivers plausible results.

Gravitational hydrodynamics acknowledges that hydrodynamics is essentially nonlinear and viscous. In the plasma, at z = 5100, the viscous length enters the horizon and causes fragmentation into plasma clumps surrounded by voids. The latter have expanded to 38 Mpc now, explaining the cosmic void scale 30/h = 42 Mpc. After the decoupling the Jeans mechanism fragments all matter in clumps of ca 40,000 solar masses. Each of them fragments due to viscosity in millibrown dwarfs of earth weight, so each Jeans cluster contains billions of them. The Jeans clusters act as ideal gas particles in the isothermal model, explaining the flattening of rotation curves. The first stars in old globular clusters are formed by aggregation of milli brown dwarfs, without dark period. Star formation also happens when Jean clusters come close to each other and agitate and heat up the cooled milli brown dwarfs, which then expand and coalesce to form new stars. This explains the Tully-Fischer and Jackson-Faber relations, and the formation of young globular clusters in galaxy mergers. Thousand of milli brown dwarfs have been observed in quasar microlensing and some 40,000 in the Helix planetary nebula.

While the milli brown dwarfs, i.e., dark baryons, constitute the galactic dark matter, cluster dark matter consists probably of 1.5 eV neutrinos, free streaming at the decoupling. These two types of dark matter explain a wealth of observations.

Using the relativistic Thomas-Fermi equation we consider the two limiting cases of compressed atoms and compressed massive nuclear density cores. Each configuration is confined by a Wigner-Seitz cell and is characterized by a positive electron Fermi energy. In both cases there exists a limiting configuration with a maximum value of the electron Fermi energy reached when the Wigner—Seitz cell radius equals the radius of the core while the configuration with , reached when the Wigner-Seitz cell radius tends to infinity corresponds to the ground state of the system.

We formulate the set of self-consistent ground-state equilibrium equations of a system of degenerate neutrons, protons and electrons in beta equilibrium taking into account quantum statistics and electro-weak interactions within the framework of general relativity. We point out the existence of globally neutral neutron star configurations in contrast with the traditional locally neutral ones. We discuss new gravito-electrodynamic effects present in such globally neutral neutron star equilibrium configurations.

Suppose that neutron star core be composed by degenerate neutrons, protons and electrons above nuclear density. Applying theWeizsacker mass formula for the nuclear potential energy of neutron star cores, we integrate Einstein-Maxwell equation with electro and β- equilibrium to obtain the radial distributions of baryon and electron densities in the global neutrality condition. It is shown that at nuclear density baryon densities sharply go to zero in a few fermi, while the electron density well extends to a few hundred Compton lengths, as results a strong electric field is developed in the core surface-shell of thickness of a few fermi.

We present numerical evidence for the existence of new black hole solutions in d ≥ 6 spacetime dimensions. These asymptotically flat static solutions have an event horizon topology S² × S^{d − 4} and share the basic properties of the static black rings in five dimensions.

With a new method based on the theory of hyperelliptic functions we solve geodesic equations in higher dimensional spherically symmetric space-times: Schwarzschild (9,11), Schwarzschild-de Sitter (9,11), Reissner-Nordström (7) and Reissner-Nordström-de Sitter (4,7). The equations of motion in the considered space-times contain the underlying polynomial of degree 5 or 6, corresponding to a genus 2 curve.

The dynamics of the gravitational collapse is examined in the realm of braneworld theory that encompasses General Relativity as a low energy limit. A complete analytical solution is given to the spherically symmetric collapse of a pure dust star, including its matching with a corrected Schwarzschild exterior spacetime. The collapse forms a black hole (an exterior event horizon) enclosing not a singularity but perpetually bouncing matter. The maximal analytical extension has the structure analogous to that of the Reissner-Nordstrom solution, except that no timelike singularities are present inside the collapsed matter.

We summarize recent results about the study of higher dimensional gravitational collapse to topological black holes. In particular, we considered models with interiors given by classes of 5-dimensional collapsing solutions built on Riemannian Bianchi IX spatial metrics and we proved local existence and uniqueness of radiating exteriors given by the Bizon-Chmaj-Schmidt metric.

We show some characteristics of the solutions of five-dimensional black dirings, especially the relation of the two different solution-sets of the black di-rings; the one was generated by the authors with the solitonic method similar to the Backlund transformation and the other was by Evslin and Krishnan with the inverse scattering method that is modified by Pomeransky. First by reconstructing the former by the use of the inverse scattering method we clarify that the difference between these representations comes from the difference of the corresponding seeds, and give the moduli-parameters and physical quantities to the solution-sets respectively. Then we discuss the equivalence of these two solution-sets with the aid of the facts established by Hollands and Yazadjiev, which concern the uniqueness of higher-dimensional black holes.

We obtain the dilaton solution in the background of a spherically symmetric black hole with curvature-squared corrections in arbitrary d spacetime dimensions and a spherically symmetric black hole solution with dilatonic charge and curvature-squared corrections in heterotic string theory compactified on a torus. For this black hole we obtain its entropy, temperature, specific heat and mass.

Effective potential for a class of static solutions of Kaluza-Klein equations with threedimensional spherical symmetry is studied. Test particles motion is analyzed. In attempts to read the obtained results with the experimental data, particular attention is devoted to the Schwarzschild’s limit of the four dimensional counterpart of these electromagnetic free solutions. Massive particles stable circular orbits in particular are studied, and a comparison between the well known results if the Schwarzschild’s case and those found for the static higher dimensional case is performed. A modification of the circular stable orbits is investigated in agreement with the experimental constraints.

Mass thresholds and lifetimes for micro black holes close to their late Schwarzschild phase are computed using two different generalized uncertainty principles, in the framework of models with extra spatial dimensions. Emission of both photons and gravitons (in the bulk) are taken into account. Results are discussed and compared.

Rotating black holes in the brany universe of the Randall—Sundrum type with infinite additional dimension are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b < 0 rotating black holes with dimensionless spin a > 1 are allowed. We investigate the role of the tidal charge in the orbital resonance model of quasiperiodic oscillations (QPOs) in black hole systems.

We derive the higher dimensional generalization of Penrose—Tod equation describing past horizon in Robinson–Trautman spacetimes with a cosmological constant and pure radiation. Results for D = 4 dimensions are summarized. Existence of its solutions in D > 4 dimensions is proved using tools for nonlinear elliptic partial differential equations.

We present recent results on the phases of AdS higher dimensional black strings. The AdS uniform black string is known to suffer from a Gregory-Laflamme instability, the uniform phase is connected to a non uniform string phase. We present the first steps in the phase diagram by constructing perturbatively and non perturbatively the non uniform black string.

We classify all spacetimes with a rank-2 closed conformal Killing-Yano tensor. They give a generalization of Kerr-NUT-de Sitter spacetime. The Einstein condition is explicitly solved. The Kerr-NUT-de Sitter spacetime is obtained as a spacetime with a non-degenerate CKY tensor.

We construct new exact solutions of 5D Einstein-Maxwell equations describing sequences of Kaluza-Klein bubbles and dipole black rings. The solutions are generated by 2-soliton Bäcklund transformations from vacuum black ring - bubble sequences. The physical properties of the solutions are investigated and the Smarr-like relations are presented exhibiting a novel feature - contribution of the magnetic flux

We discuss basic features of steady accretion disk morphology around magnetized compact astrophysical objects. A comparison between the standard model of accretion based on visco-resistive MHD and the plasma instabilities, like ballooning modes, triggered by very low value of resistivity, is proposed.

We consider the stationary problem of accretion on a nonrotating black hole. Advection is taken into account and used bridging formula for radiative loses at high and low effective optical depths. Investigate the global solutions for the accretion disc, describing the continuous transition between optically thick outer and optically thin inner regions. The existence of maximum temperature of the disk for model with the viscosity parameter α = 0:5. For model with α = 0:01 is shown the absence of optically thin regions for any values of the of accretion rate.

Results of Monte-Carlo simulation of X-ray continuum of the galactic superaccreting microquasar SS433 are presented. We use observations of INTEGRAL in 2003 and INTEGRAL/RXTE in 2004. A model of the object, based on the observational data, was created, and Monte-Carlo simulation was used to obtain the model spectrum. Comparison with the experiment allowed us to infer physical parameters of SS433.

In this work we describe the results of our numerical study on the possibility of magnetic origin of relativistic jets of long duration gamma ray bursts within the collapsar scenario which is expansion of works Barkov & Komissarov.¹⁻³ We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state of stellar matter, takes into account the cooling associated with emission of neutrinos, and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe the solutions for several models where the progenitor star has magnetic field from B = 3 × 10¹⁰G to B = 3 × 10⁹G, for different envelop accretion rates, black hole rotation parameter a and specific angular momentum of the stellar envelop. The some solution exhibits strong explosion driven by the Poynting-dominated jets whose power exceeds up to 12 × 10⁵¹ erg s⁻¹. The criterion for explosion were derived. The jets originate mainly from the black hole and they are powered via the Blandford-Znajek mechanism.

We investigate numerically the spinning-down of magnetars rotating at the propeller stage and propagating supersonically through the interstellar medium. Fast moving magnetars lose angular momentum due to direct interaction of the rotating magnetospheres with the non-rotating interstellar medium. Simulations have shown that magnetars spin-down very fast due to such interaction, much faster compared to non-moving ones.

It is known that the Meissner effect of black holes is seen in the vacuum solutions of blackhole magnetosphere: no non-monopole component of magnetic flux penetrates the event horizon if the black hole is extreme. In this article, in order to see the effects of charge currents, we study the force-free magnetic field on the extreme Reissner-Nordström background. In this case, we should solve one elliptic differential equation called the Grad-Shafranov equation which has singular points called light surfaces. In order to see the Meissner effect, we consider the region near the event horizon and try to solve the equation by Taylor expansion about the event horizon. Moreover, we assume that the small rotational velocity of the magnetic field, and then, we construct a perturbative method to solve the Grad-Shafranov equation considering the efftect of the inner light surface and study the behavior of the magnetic field near the event horizon.

We develop a model of gravitational lensing in plasma. Our approach allows us consider two effects simultaneously: the difference of the gravitational deflection in plasma from the vacuum case and the non-relativistic effect (refraction) connected with the plasma inhomogeneity.

A disturbing point in the derivation of black hole radiance is the seemingly fundamental role of frequencies above (or distances below) the Planck scale. In this talk we argue that this is not necessarily the case if the question is presented in a covariant way. We show that Hawking radiation can be derived differently and in such a way that an invariant cutoff can be introduced to remove the trans-Planckian contributions in the calculations, which results in the well-known thermal spectrum plus small corrections.

Using the exactness criteria of entropy from the first law of black hole thermodynamics, we study quantum corrections for axially symmetric black holes.

We discuss the use of information geometry in black hole physics and present the outcomes. We utilize thermodynamic (Ruppeiner) geometry defined on the state space of a given thermodynamic system in equilibrium. Stability and critical phenomena in black hole physics are captured by the Ruppeiner geometry with results agreeing with the Poincaré stability analysis for black holes and black rings. In general the Ruppeiner metric encodes thermodynamic properties such as the sign of the specific heat, but also the presence or not of extremal limits of a black hole family. We discuss general results in brief, in particular the ultraspinning instability of Myers-Perry black holes obtained by this method.

We describe a black hole slice by a density matrix and evolve the slice in semiclassical time to search for the origin of Hawking radiation.

We revisit the asymptotically Anti de Sitter spacetimes in three dimensions. Using the conformal-completion technique, we formulate the boundary conditions in a covariant fashion and construct the global charges associated with the asymptotic symmetries. The charges so constructed are conserved for the asymptotic Killing vectors fields but are not conserved for the asymptotic conformal Killing vector fields. The quantity integrated to obtain the global charge is interpreted as the Brown-York boundary stress-energy tensor and it is found not to be traceless. The trace is interpreted as the Trace Anomaly and it turns out to be the same as the Brown-Henneaux central charge.

In this talk, we focus on the corrections to Bekenstein-Hawking entropy by associating it with the entanglement between degrees of freedom inside and outside the horizon. Using numerical techniques, we show that the corrections proportional to fractional power of area result when the field is in a superposition of ground and excited states. We explain this result by identifying that the degrees of freedom contributing to such corrections are different from those contributing to Bekenstein-Hawking entropy.

In the past years, the Hamilton-Jacobi method of tunnelling has proved to be a reliable tool to compute surface gravities and Hawking temperatures for a large number of black hole horizons, both static and dynamic ones,^1–5 but much less is known about the class of horizons of cosmological interest. The present discussion is devoted to fill the gap and provide evidence of thermodynamic properties associated with these horizons.

An exact computational counting of quantum states of a black hole in the framework of Loop Quantum Gravity shows an effective discretization of the entropy of the black hole as a function of the horizon area.

We analyze the effects of the back reaction due to a conformal field theory (CFT) on a black hole spacetime with negative cosmological constant. We study the geometry numerically obtained by taking into account the energy momentum tensor of CFT approximated by a radiation fluid. We find a sequence of configurations without a horizon in thermal equilibrium (CFT stars), followed by a sequence of configurations with a horizon. We discuss the thermodynamic properties of the system and how back reaction effects alter the space-time structure. We also provide an interpretation of the above sequence of solutions in terms of the AdS/CFT correspondence. The dual five-dimensional description is given by the Karch-Randall model, in which a sequence of five-dimensional floating black holes followed by a sequence of brane localized black holes correspond to the above solutions.

A dynamical theory of traversable wormholes is detailed in spherical symmetry. Generically a wormhole consists of a tunnel of trapped surfaces between two mouths, defined as temporal outer trapping horizons with opposite senses, in mutual causal contact. In static cases, the mouths coincide as the throat of a Morris-Thorne wormhole, with surface gravity providing an invariant measure of the radial curvature or “aring-out”. The null energy condition must be violated at a wormhole mouth. Zeroth, first and second laws have been derived for the mouths, as for black holes. Dynamic processes involving wormholes are reviewed, including enlargement or reduction, and interconversion with black holes. A barely explored new area of wormhole thermodynamics is suggested.

Several authors have claimed that the observable Hawking emission from a microscopic black hole is significantly modified by the formation of a photosphere or chromosphere around the black hole due to QED or QCD interactions between the emitted particles. Analyzing these models we identify a number of physical and geometrical effects which invalidate them. In all cases, we find that the observational signatures of a cosmic or Galactic background of black holes or an individual black hole remain essentially those of the standard Hawking model, with little change to the detection probability.

In this contribution we show that Lorentzian dynamic wormholes emit thermal phantomlike radiation. Analogously to as it occurs for black holes, the consideration of such a radiation process allows the formulation of a wormhole thermodynamics which might help in the understanding of these space-time construct.

We give a review of Taub-NUT/bolt solutions in Einstein Gauss-Bonnet gravity in six dimensions. Although the spacetime with base space S² × S² has a curvature singularity at r = N, which does not admit NUT solutions, we may proceed with the same computations as in the ℂℙ² case. The investigation of thermodynamics of NUT/bolt solutions in six dimensions is carried out. We compute the finite action, mass, entropy, and temperature of the black hole in counterterm method. Then the validity of the first law of thermodynamics is demonstrated. Stability analysis is done by investigating the heat capacity and entropy in the allowed range. For NUT solution, there exists a stable phase at a narrow range and in bolt solutions, the metric is completely stable for S² × S² and is completely unstable for the ℂℙ² case.

The fields equations of f(R) gravity have been studied at the event horizon of spherically symmetric black hole spacetimes. It is shown that the field equations can be interpreted as a first law containing an extra entropy production term. particular solutions for f(R)-gravity are obtained by taking entropy production term to be zero for which the equilibrium set up is obtained.

Previous work on dynamical black hole instability is further elucidated within the Hamilton-Jacobi method for horizon tunneling and the reconstruction of the classical action by means of the null-expansion method and making use of a coordinate invariance approach.

I derive the Hawking flux from black holes of constant negative curvature and from a black hole of constant negative curvature conformally coupled to a scalar field, using the covariant gravitational anomalies method.

The string-black hole correspondence principle can be investigated in the non-BPS scenario by studying the string configuration and entropy when the string coupling is slowly increased. Through a rigorous analysis, it is shown how an ensemble of string states at fixed mass and Neveu-Schwarz charges gets dominated in any dimension by compact states for which the one-loop corrections are important (possibly signaling the transition to a black hole regime/description) and with a size (spread) within the horizon radius of the expected correspondent black holes.

Using the recently introduced ACV reduced-action approach to transplanckian scattering of light particles, we show that the S-matrix in the region of classical gravitational collapse is related to a tunneling amplitude in an effective field space. The resulting model exhibits some non-unitary S-matrix eigenvalues for parameters b < b_c, a critical value of the order of the gravitational radius , thus showing that some (inelastic)unitarity defect is generally present, and can be studied quantitatively.

Regular space-times were given which describe the formation of a (locally defined) black hole from an initial vacuum region, its quiescence as a static region, and its subsequent evaporation to a vacuum region. The static region is Bardeen-like, supported by finite density and pressures, vanishing rapidly at large radius and behaving as a cosmological constant at small radius. The dynamic regions are Vaidya-like, with ingoing radiation of positive energy flux during collapse and negative energy flux during evaporation, the latter balanced by outgoing radiation of positive energy flux and a surface pressure at a pair creation surface. The black hole consists of a compact space-time region of trapped surfaces, with inner and outer boundaries which join circularly as a single smooth trapping horizon.

We study the internal structure of a two-dimensional dilatonic evaporating black hole, based on the CGHS model. At the semiclassical level, a (weak) spacelike singularity was previously found to develop inside the black hole. We employ here a simplified quantum formulation of spacetime dynamics in the neighborhood of this singularity, using a minisuperspace-like approach. Quantum evolution is found to be regular and well-defined at the semiclassical singularity. A well-localized initial wave-packet propagating towards the singularity bounces off the latter and retains its well-localized form. Our simplified quantum treatment thus suggests that spacetime may extend semiclassically beyond the singularity, and also signifies the specific extension.

In the framework of acoustic geometry, we investigate the transonic accretion onto gravitating astrophysical objects to establish that such a configuration is a unique example of an classical analogue system realized naturally in the Universe. Only for an accreting astrophysical black hole, on which we mainly concentrate in our work, both kind of horizons, gravitational as well as acoustic (generated due to transonicity of accreting fluid) are simultaneously present in the same system, which indicates that accreting astrophysical black holes are the most ideal candidate to study theoretically and to compare the properties of these two different kind of horizons. Such a system is also unique in the aspect that accretion onto the black holes represents the only classical analogue system found in the nature so far, where the analogue Hawking temperature may exceed the actual Hawking temperature.

Excessive formation of topological defects (monopoles, vortices, and domain walls) between the subregions separated by cosmological horizons is a long-standing problem in treatment of the phase transitions in the early Universe. An important hint at its resolution was given in the last decade by the multi-Josephson-junction loop (MJJL) experiment and the experiments with ultracold atoms in optical potentials, which revealed the specific thermal correlations between the phases of order parameter in the spatial subregions disconnected in the course of the phase transition. It is shown in the present report that inclusion of such correlations into the simplest FRW cosmological model considerably reduces the number of the defects formed and, thereby, shows a promising way to resolve the long-standing cosmological puzzle.

The analog models of gravity presented in this session are unable to account for the full geometric structure of spacetime. The purpose of this lecture is to point out that a perfect analog can be achieved by imagining the world to be a crystal at the Planckian length scale (world crystal). The defects in this crystal have precisely the degrees of freedom of a Riemann-Cartan geometry. Disclinations characterize the curvature content, dislocations the torsion content of the spacetime. The memory of the crystal structure is lost by quantum uctuations of the Kostelitz-Thouless type. In the region of high curvature, the defects are so dense that the crystal melts and spacetime aquires completely novel properties. On the world lattice, quantum mechanics become classical at Planck scales modifying significantly the properties of mini-black holes.

The following sections are included:

• Introduction

• Optical Vortex Metric and Superradiance

• Experimental Proposal and Numerical Results

• References

Phenomena in gravitational fields are usually interpreted in terms of a fundamentally curved space-time. However, as proposed by several authors, one could adopt a different perspective: an effective curvature might also emerge, in some hydrodynamic limit, from distortions of the same physical, flat-space vacuum viewed as a form of quantum ether. To explore this idea, one could start by representing the physical vacuum as a Bose condensate of elementary quanta and look for vacuum excitations that, on a coarse grained scale, resemble the Newtonian potential U_N. By a rescaling of the basic spacetime units, it is then relatively easy to match the weak-field limit of classical General Relativity or of some of its possible variants. Here, I consider the possibility that U_N might originate from the far-infrared region of the physical, standard model vacuum.

This article provides a brief overview of some fundamental effects of quantum fields under extreme conditions. For the Schwinger mechanism, Hawking radiation, and the Unruh effect, analogies to quantum optics are discussed, which might help to approach to these phenomena from an experimental point of view.

In this article, I consider the evolution of quantum fluctuations in trapped time-dependent Bose—Einstein condensates. Their potential utilization for simulating scalar field modes in expanding space-times, e.g., during cosmic inflation, is discussed.

We point out that if quantum field renormalization is taken into account the predictions of slow-roll inflation for both the scalar and tensorial power spectra change significantly for wavelengths that today are at observable scales.

We shortly review a recent classical model which suggests the idea that child universe formation could be an effective process to regulate ultraviolet divergences in quantum theories of gravity. We discuss undergoing generalizations which show evidence that the essential properties of this classical model do survive semiclassical quantization.

We propose a novel class of F-term hybrid inflation models in supergravity (SUGRA) where the η-problem is resolved using either a Heisenberg symmetry or a shift symmetry of the Kähler potential. In addition to the inflaton and the waterfall field, this class (referred to as tribrid inflation) contains a third “driving” field which contributes the large vacuum energy during inflation by its F-term. In contrast to the “standard” hybrid scenario, it has several attractive features due to the property of vanishing inflationary superpotential (W_inf = 0) during inflation. Quantum corrections induced by symmetry breaking terms in the superpotential generate a slope of the potential and lead to a spectral tilt consistent with recent WMAP observations.

We show that higher-order actions for cosmological perturbations in the multi-field DBI-inflation model are obtained by a Lorentz boost from the rest frame of the brane to the frame where the brane is moving. We confirm that this simple method provides the same third- and fourth- order actions at leading order in slow-roll and in the small sound speed limit as those obtained by the usual ADM formalism. As an application, we compute the leading order connected four-point function of the primordial curvature perturbation coming from the intrinsic fourth-order contact interaction in the multi-field DBI-inflation model. At third order, the interaction Hamiltonian arises purely by the boost from the second-order action in the rest frame of the brane. The boost acts on the adiabatic and entropy modes in the same way thus there exists a symmetry between the adiabatic and entropy modes. But at fourth order this symmetry is broken due to the intrinsic fourth-order action in the rest frame and the difference between the Lagrangian and the interaction Hamiltonian. Therefore, contrary to the three-point function, the momentum dependence of the purely adiabatic component and the components including the entropic contributions are different in the four-point function. This suggests that the trispectrum can distinguish the multi-field DBI-inflation model from the single field DBI-inflation model.

We explain the motivation and main idea of our work in Ref. 1. We present a simple model of multifield Dirac-Born-Infeld inflation whose bispectrum exhibits a linear combination of the equilateral and local shapes, which are usually considered as separate possibilities. We also point out the presence of a particularly interesting component of the primordial trispectrum.

Inflation is considered to be the best paradigm for describing the early universe. However, it is still unclear what is the nature of the field which drives inflation. In this talk, we discuss the possibility of spinor field driving inflation. Spinflaton — a scalar condensate of the dark spinor field — has a single scalar degree of freedom and leads to the identical acceleration equation as the scalar field. We also discuss the advantages of this model compared to the scalar field driven inflation and discuss its observational relevance.

We propose a version of chaotic inflation, in which a fundamental scale M, well below the Planck scale M_P, fixes the initial value of the effective potential. If this scale happens to be the scale of grand unified theories, there are just enough e-foldings of inflation. An initial epoch of fast-roll breaks scale-invariance at the largest observable scales.

It is shown that the Higgs boson can also serve as an inflaton in the early Universe if one assumes its strong non-minimal coupling to gravity and takes quantum corrections from Standard Model particles to the tree action into account. This builds a bridge between modern cosmology and particle physics without introducing any new particles. We predict the range for allowed values of the Higgs mass in this scenario which can be tested at LHC. This contribution is based on the recent work.¹

Inflation is studied in the context of induced gravity (IG) γσ²R, where R is the Ricci scalar, σ a scalar field and γ a dimensionless constant. We study in detail cosmological perturbations in IG and examine both a Landau-Ginzburg (LG) and a Coleman-Weinberg (CW) potential toy models for small field and large field (chaotic) inflation and find that small field inflationary models in IG are constrained to γ ≲ 3 × 10⁻³ by WMAP5+BAO+SN Ia data. Finally we describe the regime of coherent oscillations in induced gravity by an analytic approximation, showing how the homogeneous inflaton can decay in its short-scale fluctuations when it oscillates around a non-zero value σ₀.

We consider some models of dark energy based on perfect fluids, tachyons and phantom scalar fields. It is shown that the cosmological perturbations in the generalized Chaplygin gas model, where the pressure is inversely proportional to the power of the energy density which is greater than 3 are compatible with observations. The tachyon model, implying as a possible outcome of the cosmological evolution en encounter with the big brake cosmological singularity is compared with supernovae data and some characteristics of such evolutions are numerically estimated. Finally we consider a cosmological model with two scalar fields (one of which is effectively phantom), based on PT symmetry.

We present a new mechanism that allows to unify inflation and dark energy. We use a scalar field ϕ with a potential ν(ϕ) that has two at regions at high and low energies that are associated with inflation and dark energy respectively. After inflation ϕ decays completely and reheat the universe. Eventually ϕ is regenerated at late times close to present via a quantum process and the dark energy epoch begins. The ϕ particles production starts at low energies and this explains the cosmological coincidence problem.

The following sections are included:

• Introduction

• The Dirac-Milne Universe

• Primordial Nucleosynthesis

• Type Ia Supernovæ

• Position of the First Acoustic Peak of the CMB

• Conclusion

• References

In the framework of Kaluza-Klein theory, we investigate a (4 + 1)-dimensional universe consisting of a (4 + 1) dimensional Robertson-Walker type metric subject to a (4 + 1) dimensional energy-momentum tensor.

In this talk, we consider Brans-Dicke type non minimally coupled scalar field as a candidate for dark energy. In the conformally transformed frame, our model is similar to coupled quintessence model. We consider potentials for the scalar field which satisfy the slow-roll conditions and show that the equation of state for the scalar field can be described by a universal behaviour provided the slow-roll conditions are satisfied.

We study the strong gravity regime in viable models of so-called f(R) gravity that account for the observed cosmic acceleration. Using a relaxation algorithm, we construct numerically static relativistic stars for a polytropic equation of state. We can reach a gravitational potential up to Φ ~ 0.3 at the surface of the star, even in f(R) theories with an “unprotected” curvature singularity. However, we find static configurations only if the pressure does not exceed one third of the energy density, except possibly in a limited region of the star (otherwise, one expects tachyonic instabilities to develop). This constraint is satisfied by realistic equations of state for neutron stars.

We consider the linear growth of matter perturbations on low redshifts in a specific f(R) dark energy (DE) model. We introduce a new parameterization for the growth factor γ(z) and show that for chosen parameters, this factor is clearly distinct from the one in ΛCDM and from results in other DE models. This may be an observational signature for f(R) models.

We show that there exists a T-duality symmetry between two-dimensional warp drives and two dimensional Tolman-Hawking and Gidding-Strominger baby universes respectively correlated in pairs, so that the creation of warp drives is also equivalent to space-time squeezing. It has been also seen that the nucleation of warp drives entails a violation of the Bell’s inequalities. These results are generalized to the case of any dynamically accelerating universe whose creation is also physically equivalent to spacetime squeezing and to the violation of the Bell’s inequalities, so that the universe we are living in should be governed by essential sharp quantum theory laws and must be a quantum entangled system.

An approach to the consistency test of dark energy models with observations is presented. To test a dark energy model, we suggest introducing a characteristic Q(z) that in general varies with the redshift z but in that model plays the role of a constant distinct parameter. Then, by reconstructing dQ(z)/dz from observational data and comparing it with zero we can assess the consistency between data and the model under consideration. The general principle of our approach is not limited to dark energy. It may also be applied to the testing of various cosmological models and even the models in other fields beyond the scope of cosmology.

We study analytical models of dark energy accretion on late time small mass black holes. We first consider a stationary test fluid embedded on a Schwarzschild metric, analyzing the combined effect of radiation and phantom energy accretion and Hawking evaporation. Next we move to the accretion of an evolving dark fluid, coupling the Friedmann equations to the system. It is found that, for late and future epochs, accretion in a ΛCDM scenario tends to a model with an asymptotically constant black hole mass. We also consider the accretion of a simplified Chaplygin gas, and find that both the effects of phantom energy and quintessence can be obtained.

A solution of cosmological constant problem based on discrete space-time at electroweak scale is presented and the theoretically calculated cosmological constant agrees excellently with the cosmological observations. The GEO600 gravitational waves detection experiment may also provide important experimental evidence that supports such proposed solution.

In the coming years, the next generation wide field surveys will lead to the discovery of large numbers of galaxy clusters, both from optical identifications and through the Sunyev-Zel’dovich effect, providing extensive databases to study these objects. The abundance of clusters above a given mass threshold as a function of redshift is sensitive to the Dark Energy (DE) equation of state (eos) and, therefore, this observable can be used to constrain its parameters. In this work we assume the simple eos p = wρ and study the impact of the mass threshold and the width of the redshift bin on the determination w. We use a Monte Carlo approach generating many realizations of the cluster distribution with a fiducial value of the eos parameter and obtaining the best fitting value of w and its uncertainty. We use two methods to recover w: the standard X² for the number of clusters in each bin and a product of Poisson distributions for each bin. Our results show that the uncertainty in w is independent of the redshift bin width and strongly dependent on the mass threshold. For both methods, the correct values of w are recovered when the mass threshold is smaller than ~ 10¹⁵h⁻¹ M_⊙. However, for higher masses, the X² method introduces a significant bias in w.

We propose a new infrared cut-off for the holographic dark-energy, which avoids the problems of causality and the coincidence. Using the holographic-scalar field corresponence, the scalar potential and dynamics for some scalar field models of DE are reconstructed.

The present closure contributions in dark energy and dark matter are nearly equal suggesting that they could be different aspects of the same physical phenomenon. We review constraints three postulates as to how such a unification might have been achieved. These include the possibility that: 1) the dark matter decays producing a bulk viscosity in the cosmic fluid; 2) the modification of the expansion rate by the inflow of dark matter from a bulk dimension in brane-world cosmology; and 3) relativistic corrections to the Friedmann equation from the presence of local inhomogeneities. Constraints on and observational tests of each of these cosmologies are described.

We here investigate the model of interacting dark energy in the context of five dimensional brane cosmology. The effective equations of state of dark energy are evaluated for various choices of the variable time dependent cosmological constant. It is shown that interacting dark energy in this generalized model also resolves the cosmic coincidence problem.

Cold dark matter and dark energy may interact weakly with one another via some coupling term, Q. Taking this into account, we constrain the parameter space of the equation of state w of dark energy fields assuming that the variation of the field since last scattering does not exceed Planck’s mass. We consider three w parametrizations and two expressions for Q. This work extends previous ones.

Mimicking the cosmological constant by a scalar field with potential wells, we show that decoherence due to additional degrees of freedom can localize the field in one of the wells and modify the tunneling rate to other wells. This could justify the observation of a small positive cosmological constant.

By using exclusively the Sunyaev-Zel’dovich effect and X-ray surface brightness data from 25 galaxy clusters in the redshift range 0:023 ≤ z ≤ 0:784 we access cosmic acceleration employing a kinematic description. Such result is fully independent on the validity of any metric gravity theory, the possible matter-energy contents filling the Universe, as well as on the SNe Ia Hubble diagram.

The free parameters of a flat accelerating model without dark energy are constrained by using Supernovae type Ia and observational H(z) data. Instead of the vacuum dominance, the present accelerating stage in this modified Einstein-de Sitter cosmology is a consequence of the gravitationally-induced particle production of cold dark matter. The model present a transition from a decelerating to an accelerating regime at low redshifts, and is also able to harmonize a cold dark matter picture with the latest measurements of the Hubble constant H₀, the Supernovae observations (Constitution sample), and the H(z) data.