The Thirteenth Marcel Grossmann Meeting

The following sections are included:

• THE MARCEL GROSSMANN MEETINGS
• SPONSORS
• ORGANIZING COMMITTEES AND ACKNOWLEDGEMENTS
• DEDICATION
• MARCEL GROSSMANN AWARDS
• PREFACE
• CONTENTS

The long story of the oscillatory approach to the initial cosmological singularity and its more recent incarnation in multidimensional universe models is told.

This paper is written in occasion of the Marcel Grossmann Award I received at the 13th Marcel Grossmann Meeting held in Stockholm in 2012 July 2–7. I review the story of the BeppoSAX discovery of the Gamma Ray Burst afterglow and cosmological distance determination, starting from the first GRB detection with Vela satellites and from the efforts done before BeppoSAX. An extended review of this story has also been given,1 on the occasion of the award of the Fermi Prize 2010.

As a preparation for the generation of a new set of core collapse progenitor models, a new investigation of the physics of such stars has begun. Supercomputers allow the simulation of three dimensional highly turbulent flow. Treating these numerical “experiments” as valid representations of the behavior of high energy density (HED) plasma, a view supported by laboratory experiments with inertial confinement fusion (ICF) devices, we are beginning to develop a theory of this behavior appropriate to stellar interiors. Unlike conventional astrophysical convection theory, the Richardson-Kolmogorov turbulent cascade and the Lorenz strange attractor make an appearance, as well as a rich set of boundary-region physics. The process of developing physical insight from numerical simulations will be illustrated, and implications for stellar evolution, from the Sun to gamma-ray bursts and supernovae, will be discussed.

Recent developments concerning oscillatory spacelike singularities in general relativity are taking place on two fronts. The first treats generic singularities in spatially homogeneous cosmology, most notably Bianchi types VIII and IX. The second deals with generic oscillatory singularities in inhomogeneous cosmologies, especially those with two commuting spacelike Killing vectors. This paper describes recent progress in these two areas: in the spatially homogeneous case focus is on mathematically rigorous results, while analytical and numerical results concerning generic behavior and so-called recurring spike formation are the main topic in the inhomogeneous case. Unifying themes are connections between asymptotic behavior, hierarchical structures, and solution generating techniques, which provide hints for a link between the nature of generic singularities and a hierarchy of hidden asymptotic symmetries.

In this contribution we aim to provide a very brief introduction to some of the work that has been done over the last 50 years on the problem of trying to understand the dynamics of space-time close to a cosmological singularity. Starting with the pioneering work of BKL, we move on to outline how their early work has more recently led to surprising connections with the theory of Kac-Moody algebras. We will discuss the stimulus these developments have had for the problem of quantising gravity.

The current state of the vacuum evolution problem in general relativity is reviewed from a perspective of rigorous mathematical results.

This article reviews black hole solutions of higher-dimensional General Relativity. The focus is on stationary vacuum solutions and recent work on instabilities of such solutions.

Causal Dynamical Triangulations provide a non-perturbative regularization of a theory of quantum gravity. We describe how it connects to the asymptotic safety program and to the Hořava-Lifshitz gravity theory and present the most recent results from computer simulations.

We discuss the conceptual ideas underlying the Asymptotic Safety approach to the nonperturbative renormalization of gravity. By now numerous functional renormalization group studies predict the existence of a suitable nontrivial ultraviolet fixed point. We use an analogy to elementary magnetic systems to uncover the physical mechanism behind the emergence of this fixed point. It is seen to result from the dominance of certain paramagnetic-type interactions over diamagnetic ones. Furthermore, the spacetimes of Quantum Einstein Gravity behave like a polarizable medium with a “paramagnetic” response to external perturbations. Similarities with the vacuum state of Yang-Mills theory are pointed out.

The talk will review recent developments showing that in a precise sense gravity scattering amplitudes are double copies of corresponding gauge theory ones used to describe the strong subnuclear interactions. Underlying this is a correspondence between the color charges and kinematic numerators appearing in gauge theory scattering amplitudes. An application of these ideas will be given, demonstrating that within perturbation theory standard supergravity theories are much tamer in the ultraviolet than had been believed possible.

Type Ia supernovae (SNe Ia) have been used with remarkable success to map the expansion history of the Universe. These measurements dramatically changed our description of nature as they revealed cosmic acceleration, indicating the presence of new physics, dark energy, counteracting the effect of gravity at the largest scales. Understanding the source of the acceleration ranks among the most pressing undertakings in fundamental physics. Current and future surveys are challenged to accurately measure the equation state of dark energy, the parameter used to explore its nature. Distances measurements using SNe Ia remain among the most powerful techniques in observational cosmologists. The recent history of the field is reviewed, as well as current limitations and opportunities for the future.

he history of cosmic expansion can be accurately traced using Type Ia supernovae (SN Ia) as standard candles. Over the past 40 years, this effort has improved its precision and extended its reach in redshift. Recently, the distances to SN Ia have been measured to a precision of ~5% using luminosity information that is encoded in the shape of the supernova's rest frame optical light curve. By combining observations of supernova distances as measured from their light curves and redshifts measured from spectra, we can detect changes in the cosmic expansion rate. This empirical approach was successfully exploited by the High-Z Supernova Team and by the Supernova Cosmology Project to detect cosmic expansion and to infer the presence of dark energy. The 2011 Nobel Prize in Physics was awarded to Perlmutter, Schmidt and Riess for this discovery. The world's sample of well-observed SN Ia light curves at high redshift and low, approaching 1000 objects, is now large enough to make statistical errors due to sample size a thing of the past. Systematic errors are now the challenge. To learn the properties of dark energy and determine, for example, whether it has an equation-of-state that is different from the cosmological constant demands higher precision and better accuracy. The largest systematic uncertainties come from light curve fitters, photometric calibration errors, and from uncertain knowledge of the scattering properties of dust along the line of sight. Efforts to use SN Ia spectra as luminosity indicators have had some success, but have not yet produced a big step forward. Fortunately, observations of SN Ia in the near infrared (NIR), from 1 to 2 microns, offer a very promising path to better knowledge of the Hubble constant and to improved constraints on dark energy. In the NIR, SN Ia are better standard candles and the effects of dust absorption are smaller. We have begun an HST program dubbed RAISIN (SN IA in the IR) to tighten our grip on dark energy properties

The traditional Tolman-Oppenheimer-Volkoff (TOV) equations of NSs assume local charge neutrality and electromagnetic structure is not accounted for. We show that such an assumption is inconsistent when all known interactions in NS equilibrium equations are present, including electromagnetism. We present the new Einstein-Maxwell-Thomas-Fermi (EMTF) set of equations, which must be solved under the constraint of global, but not local, charge neutrality. We discuss new gravito-electrodynamic effects and present their implications on the mass-radius relation and observational properties of neutron stars.

The past decade has witnessed the successful operation of the first generation of large scale ground-based gravitational-wave interferometers — LIGO, Virgo, and GEO600 — each demonstrating remarkably sensitive, robust performance over a series of observing runs beginning in 2002 and continuing through 2011. Although gravitational waves have not yet been directly detected, searches by these detectors have established noteworthy limits on the possible emission of gravitational waves from astrophysical sources. Second generation instruments currently under construction such as Advanced LIGO, Advanced Virgo, and KAGRA will begin observing in the second half of this decade with sensitivities that are predicted to lead to direct detections of binary neutron star mergers and possibly other sources of gravitational waves.

The origin of gamma-ray burst (GRB) prompt emission, bursts of γ-rays lasting from shorter than one second to thousands of seconds, remains not fully understood after more than 40 years of observations. The uncertainties lie in several open questions in the GRB physics, including jet composition, energy dissipation mechanism, particle acceleration mechanism, and radiation mechanism. Recent broad-band observations of prompt emission with Fermi sharpen the debates in these areas, which stimulated intense theoretical investigations invoking very different ideas. I will review these debates, and argue that the current data suggest the following picture: A quasi-thermal spectral component originating from the photosphere of the relativistic ejecta has been detected in some GRBs. Even though in some cases (e.g. GRB 090902B) this component dominates the spectrum, in most GRBs, this component either forms a sub-dominant “shoulder” spectral component in the low energy spectral regime of the more dominant “Band” component, or is not detectable at all. The main “Band” spectral component likely originates from the optically thin region due to synchrotron radiation. The diverse magnetization in the GRB central engine is likely the origin of the observed diverse prompt emission properties among bursts.

I review some recent progress in understanding the nature of Gamma Ray Bursts (GRBs) and in particular, of the relationship between short GRBs and binary neutron stars, as well as long GRBs and Supernovae (SNe). The coincidental occurrence of a GRB with a SN is explained within the Induced Gravitational Collapse (IGC) paradigm in a prototypical case. The following sequence is shown to occur: 1) an initial binary system consists of a compact Carbon-Oxygen (CO) core star and a Neutron Star (NS); 2) the CO core explodes as a SN, part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a Black Hole (BH) giving rise to a GRB; 3) a new NS is generated by the SN as a remnant; 4) after ~ 13 days in the GRB cosmological rest frame the supernova is observed. The observational consequences of this scenario are outlined and the first example of a genuine short GRB is described.

In the quest of understanding gravity, binary pulsars provide indispensable laboratories for precision tests of gravity. Effects that can be studied in great detail include the emission of gravitational waves, Shapiro delay, orbital precession and more. But also fundamental differences between general relativity and alternative theories of gravity can be probed, such as possible violations of the strong equivalence principle, preferred frame effects or the existence of gravitational dipole radiation or scalar fields. Also the effects of spin precession in strongly self-gravitating bodies can be studied by observing effects of geodetic precession.

We provide a description of the latest status and performance of the Planck satellite, focusing on the final predicted sensitivity of Planck. The optimization of the observational strategy for the additional surveys following the nominal fifteen months of integration (about two surveys) originally allocated and the limitation represented by astrophysical foreground emissions are presented. An outline of early and intermediate astrophysical results from the Planck Collaboration is provided. A concise view of some fundamental cosmological results that will be achieved by exploiting Planck's full set of temperature and polarization data is presented. Finally, the perspectives opened by Planck in answering some key questions in fundamental physics, with particular attention to Parity symmetry analyses, are described.

The discovery of a new particle while searching for the standard model Higgs boson in the Compact Muon Solenoid experiment at the LHC is presented. The data samples analysed correspond to integrated luminosities of up to 5.1 fb⁻¹ at and 5.3 fb⁻¹ at . The search is performed in five decay modes: . An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, γγ and ZZ; a fit to these signals gives to the new boson a mass of 125.3 ± 0.4 (stat.) ± 0.5 (syst.) GeV.

Spectral features in the CMB energy spectrum contain a wealth of information about the physical processes in the early Universe, z ≲ 2 × 10⁶. The CMB spectral distortions are complementary to all other probes of cosmology. In fact, most of the information contained in the CMB spectrum is inaccessible by any other means. This review outlines the main physics behind the spectral features in the CMB throughout the history of the Universe, concentrating on the distortions which are inevitable and must be present at a level observable by the next generation of proposed CMB experiments. The spectral distortions considered here include spectral features from cosmological recombination, resonant scattering of CMB by metals during reionization which allows us to measure their abundances, y-type distortions during and after reionization and μ-type and i-type (intermediate between μ and y) distortions created at redshifts z ≳ 1.5 × 10⁴.

This document presents a brief overview of some of the experimental techniques employed by the ATLAS experiment at the CERN Large Hadron Collider in the search for the Higgs boson predicted by the standard model of particle physics. The data and the statistical analyses which allowed in July 2012, only few days before this presentation at the Marcel Grossman Meeting, to firmly establish the observation of a new particle, are described. The additional studies needed to check the consistency between the newly discovered particle and the Higgs boson are also discussed.

Some personal reflections on the life of Fang Lizhi, my friend and scientific twin…

This article reviews the biography of the Swiss mathematician Marcel Grossmann (1878–1936) and his contributions to the emergence of the general theory of relativity. The first part is his biography, while the second part reviews his collaboration with Einstein in Zurich which resulted in the Einstein-Grossmann theory of 1913. This theory is a precursor version of the final theory of general relativity with all the ingredients of that theory except for the correct gravitational field equations. Their collaboration is analyzed in some detail with a focus on the question of exactly what role Grossmann played in it.

The investigation of Dark Matter (DM) particles has its foundation in many astrophysical observations and theoretical developments dating back nearly a century, and efforts to study the presence of Dark Matter at galactic scales are compelling and have been in progress already for decades. Some aspects of the present state of this topic are recalled here together with a discussion of some interesting ways to address it in the future.

We present an overview of recent developments in numerical relativity studies of higher dimensional spacetimes with a focus on time evolutions of black-hole systems. After a brief review of the numerical techniques employed for these studies, we summarize results grouped into the following three areas: (i) Numerical studies of fundamental properties of black holes, (ii) Applications of black-hole collisions to the modeling of Trans-Planckian scattering, (iii) Numerical studies of asymptotically anti-de Sitter spacetimes in the context of the gauge-gravity duality.

We review cosmological solutions and their stability in nonlinear massive gravity. After constructing homogeneous and isotropic solutions, we show that they suffer from ghost instability. We then find new attractor solutions, in which the physical metric is of FRW type but anisotropy in the fiducial metric leads to statistical anisotropy of perturbations.

The main focus of this session was the presentation of new higher-dimensional black hole solutions, including black rings, black strings, and multi black holes, and the study of their properties. Besides new asymptotically flat and locally asymptotically flat black objects also new black holes with anti-de Sitter asymptotics were reported. The studies of their properties included the investigation of their stability, their thermodynamics, their analyticity and their existence. Furthermore, the geodesics in such higher-dimensional space-times were investigated.

This contribution is a review of some talks presented at the session ‘Magneto-Plasma Processes in Relativistic Astrophysics’ of the Thirteenth Marcel Grossmann Meeting MG13. We discuss the modern developments of relativistic astrophysics, connected with presence of plasma and magnetic fields. The influence of magneto-plasma processes on the structure of the compact objects and accretion processes is considered. We also discuss a crucial role of magnetic field for the mechanism of core-collapse supernova explosions. Gravitational lensing in plasma is also considered.

From the quasinormal modes of black holes, we obtain the quantizations of the entropy and horizon area of black holes via Bohr-Sommerfeld quantization, based on Bohr's correspondence principle. For this, we identify the appropriate action variable of the classical system corresponding to a black hole. By considering the BTZ black holes in topologically massive gravity as well as Einstein gravity, it is found that the spectra of not the horizon areas but the entropies of black holes are equally spaced. We also propose that other characteristic modes of black holes, which are non-quasinormal modes or holographic quasinormal modes, can be used in quantization of entropy spectra just like quasinormal modes. From these modes, it is found that only the entropy spectrum of the warped AdS₃ black hole is equally spaced as well. Furthermore, by considering a scattering problem in a black hole, we propose that the total transmission modes and total reflection modes of black holes can be regarded as characteristic modes of black holes and result in the equally spaced entropy of the Kerr and Reissner-Nordström black holes. Finally, we conclude that there is a universal behavior that the entropy spectra of various black holes are equally spaced.

In this article we focus on the astrophysical results and the related cosmological implications derived from recent microwave surveys, with emphasis to those coming from the Planck mission. We critically discuss the impact of systematics effects and the role of methods to separate the cosmic microwave background signal from the astrophysical emissions and each different astrophysical component from the others. We then review of the state of the art in diffuse emissions, extragalactic sources, cosmic infrared background, and galaxy clusters, addressing the information they provide to our global view of the cosmic structure evolution and for some crucial physical parameters, as the neutrino mass. Finally, we present three different kinds of scientific perspectives for fundamental physics and cosmology offered by the analysis of on-going and future cosmic microwave background projects at different angular scales dedicated to anisotropies in total intensity and polarization and to absolute temperature.

We review recent developments on possible effects of a heavy scalar field on the power spectrum for the primordial fluctuations. Though the heavy scalar field is usually assumed to be stuck to its potential minimum, it can be excited when the background trajectory is curved. The excitation could leave various signatures on the power spectrum. In this paper, we introduce two example: a feature induced by mixing between the light and heavy modes and enhancement of the fluctuations through the resonance with the excited oscillation. Though no strong evidence is found at present, if they are detected, they will improve our understanding the physics behind inflation.

Dark energy models account for the present accelerated expansion of the universe. Many models were suggested and investigated, based on very different physical principles. We will review some representative models emphasizing similarities and differences between these various approaches.

This report comprises two parts. On the one hand, I will, based on the talks at the CM4 parallel session which I chaired, point to interesting recent developments in quantum cosmology. On the other hand, some of the basics of supersymmetric quantum cosmology are briefly reviewed, pointing to promising lines of research to explore. I will start with the latter, finishing the report with the former.

Cosmological models that invoke warm or cold dark matter can not explain observed regularities in the properties of dwarf galaxies, their highly anisotropic spatial distributions, nor the correlation between observed mass discrepancies and acceleration. These problems with the standard model of cosmology have deep implications, in particular in combination with the observation that the data are excellently described by Modified Newtonian Dynamics (MOND). MOND is a classical dynamics theory which explains the mass discrepancies in galactic systems, and in the universe at large, without invoking ‘dark’ entities. MOND introduces a new universal constant of nature with the dimensions of acceleration, a₀, such that the pre-MONDian dynamics is valid for accelerations a ≫ a₀, and the deep MONDian regime is obtained for a ≪ a₀, where space-time scale invariance is invoked. Remaining challenges for MOND are (i) explaining fully the observed mass discrepancies in galaxy clusters, and (ii) the development of a relativistic theory of MOND that will satisfactorily account for cosmology. The universal constant a₀ turns out to have an intriguing connection with cosmology: . This may point to a deep connection between cosmology and internal dynamics of local systems.

Recent observations, especially by the Fermi satellite, point out the importance of the thermal component in GRB spectra. This fact revives strong interest in photospheric emission from relativistic outflows. Early studies already suggested that the observed spectrum of photospheric emission from relativistically moving objects differs in shape from the Planck spectrum. However, this component appears to be subdominant in many GRBs and the origin of the dominant component is still unclear. One of the popular ideas is that energy dissipation near the photosphere may produce a non-thermal spectrum and account for such emission. Before considering such models, though, one has to determine precise spectral and timing characteristics of the photospheric emission in the simplest possible case. Hence this paper focuses on various physical effects which make the photospheric emission spectrum different from the black body spectrum and quantifies them.

We discuss recent developments related to certain blow up methods suitable for the analysis of cosmological singularities and asymptotics. We review results obtained in a variety of currently popular themes and describe ongoing research about universes with various kinds of extreme states, higher order gravity, and certain models of braneworlds.

Future gravitational wave observatories will be realized underground in order to reduce external disturbances, such as seismic, Newtonian and environmental noises. The Japanese gravitational wave telescope KAGRA is under construction at the Kamioka site and the Einstein Telescope gravitational wave observatory is under study in Europe; the common aspects, the differences and the expected performances of these innovative machines are investigated.

Gamma–Ray Bursts (GRB) emit in a few dozen of seconds up to ~10⁵⁴ erg, in terms of isotropic equivalent radiated energy E_iso, therefore they can be observed up to z ~ 10 and appear very promising tools to describe the expansion rate history of the Universe. In this paper we review the use of the E_p,i–E_iso correlation of Gamma–Ray Bursts to measure Ω_M. We show that the present data set of GRBs, coupled with the assumption that we live in a flat universe, can provide indipendent evidence, from other probes, that Ω_M~0.3. We show that current (e.g., Swift, Fermi/GBM, Konus–WIND) and next GRB experiments (e.g., CALET/GBM, SVOM, Lomonosov/UFFO, LOFT/WFM) will allow us, within a few years, to constrain Ω_M and the evolution of dark energy with time, with an accuracy comparable to that currently exhibited by SNe–Ia.

The following sections are included:

• Prologue
• Introduction
• The readiness for spectroscopic surveys
• The early spectroscopic work
• Hunting the mass
• Toward a new era
• What Next?
• Conclusions
• Acknowledgments
• APPENDIX I
• APPENDIX II
• APPENDIX III
• References

I offer a perspective on opportunities for quantum-gravity phenomenology involving GRB neutrinos and macroscopic bodies. Among the neutrinos observed by the IceCube neutrino telescope some are expected to be GRB neutrinos and if that is confirmed an important opportunity for quantum-gravity phenomenology will arise. A few recent studies concerned opportunities for quantum-gravity phenomenology involving macroscopic bodies, but several related issues still need to be investigated.

A SL(5, ℝ) gauge-invariant topological field theory of gravity and possible gauge unifications are considered in four-dimensions. The problem of quantization is evaluated in the asymptotic safety scenario. ‘Minimal’ BF type models for the high energy limit are physically not quite realistic, a tiny symmetry breaking is needed to recover standard Einsteinian gravity for the macroscopic metrical background with induced cosmological constant.

It is now widely accepted that soft gamma repeaters and anomalous X-ray pulsars are the observational manifestations of magnetars, i.e. sources powered by their own magnetic energy. This view was supported by the fact that these ‘magnetar candidates’ exhibited, without exception, a surface dipole magnetic field (as inferred from the spin-down rate) in excess of the electron critical field (≃4.4 × 10¹³ G). The recent discovery of fullyqualified magnetars, SGR 0418+5729 and Swift J1822.3−1606, with dipole magnetic field well in the range of ordinary radio pulsars posed a challenge to the standard picture, showing that a very strong field is not necessary for the onset of magnetar activity (chiefly bursts and outbursts). Here we summarise the observational status of the low-magneticfield magnetars and discuss their properties in the context of the mainstream magnetar model and its main alternatives.

The origin of cosmic rays remains a mystery, even over 100 years since their discovery. Neutron stars (NSs) are considered textbook cases of particle acceleration sites in our Galaxy, but many unresolved numerical problems remain. Searches for new acceleration sites are crucial for astrophysics. The magnetized white dwarfs (MWDs) have the same kind of rotating magnetosphere as NSs, and may be the source of up to 10% of galactic cosmic ray electrons. In the parallel session of the “white dwarf pulsars and rotating white dwarf theory”, we focus on the current observational results on white dwarf pulsars, related theories of the radiation process both in white dwarfs and neutron stars, and the origin and rule of white dwarf pulsars, as well as surveying on the current theories of the internal structure and the equation of state of white dwarfs.

We present the last developments of the LAUE project, whose main goal is to build a Laue lens for soft gamma–ray astronomy (80–600 keV) and to set an advanced technology for assembling high focal length focusing optics. With such a lens we expect to increase the sensitivity of the current non-focusing instruments by 2 orders of magnitude in the energy range above mentioned.

We describe the GRB and All-sky Monitor Experiment (GAME) mission submitted by a large international collaboration (Italy, Germany, Czech Repubblic, Slovenia, Brazil) in response to the 2012 ESA call for a small mission opportunity for a launch in 2017 and presently under further investigation for subsequent opportunities. The general scientific objective is to perform measurements of key importance for GRB science and to provide the wide astrophysical community of an advanced X-ray all-sky monitoring system. The proposed payload was based on silicon drift detectors (~1–50 keV), CdZnTe (CZT) detectors (~15–200 keV) and crystal scintillators in phoswich (NaI/CsI) configuration (~20 keV–20 MeV), three well established technologies, for a total weight of ~250 kg and a required power of ~240 W. Such instrumentation allows a unique, unprecedented and very powerful combination of large field of view (3–4 sr), a broad energy energy band extending from ˜1 keV up to ˜20 MeV, an energy resolution as good as ~250 eV in the 1–30 keV energy range, a source location accuracy of ~1 arcmin. The mission profile included a launch (e.g., by Vega) into a low Earth orbit, a baseline sky scanning mode plus pointed observations of regions of particular interest, data transmission to ground via X-band (4.8 Gb/orbit, Alcantara and Malindi ground stations), and prompt transmission of GRB / transient triggers.

Holographic modeling of strongly correlated many-body systems motivates the study of novel spacetime geometries where the scaling behavior of quantum critical systems is encoded into spacetime symmetries. Einstein-Dilaton-Maxwell theory has planar black brane solutions that exhibit Lifshitz scaling and in some cases hyperscaling violation. Entanglement entropy and Wilson loops in the dual field theory are studied by inserting simple geometric probes involving minimal surfaces into the black brane geometry. Coupling to background matter fields leads to interesting low-energy behavior in holographic models, such as U(1) symmetry breaking and emergent Lifshitz scaling.

After introducing the Szekeres and Lemaître–Tolman cosmological models, the real-time cosmology program is briefly mentioned. Then, a few widespread misconceptions about the cosmological models are pointed out and corrected. Investigation of null geodesic equations in the Szekeres models shows that observers in favourable positions would see galaxies drift across the sky at a rate of up to 10^-6 arc seconds per year. Such a drift would be possible to measure using devices that are under construction; the required time of monitoring would be ≈ 10 years. This effect is zero in the FLRW models, so it provides a measure of inhomogeneity of the Universe. In the Szekeres models, the condition for zero drift is zero shear. But in the shearfree normal models, the condition for zero drift is that, in the comoving coordinates, the time dependence of the metric completely factors out.

The periastron shift, the Lense-Thirring effect, and the conicity of bound orbital motion in a general six-parameter axially symmetric black hole space-time are considered. We analyze the influence of the different space-time parameters on the these observables and characterize Kerr, Taub-NUT, Schwarzschild-de Sitter, and other space-times.

We reexamine the post-Newtonian effects on Lagrange's equilateral triangular solution for the three-body problem. For three finite masses, it is found that a triangular configuration satisfies the post-Newtonian equation of motion in general relativity, if and only if it has the relativistic corrections to each side length. For the same masses and angular velocity, the post-Newtonian triangular configuration is always smaller than the Newtonian one.

In order to arrive at a full analytical solution to the leading post-Newtonian (pN) order spin-squared dynamics of a compact binary system we investigate the geodesic solutions of a test mass moving in a Kerr spacetime field produced by a rotating black hole. As the Kerr field incorporates arbitrary powers of the spin parameter ‘a’ when expanded in a post-Newtonian manner we truncate the expansion at second order in ‘a’ and at leading pN order and show how to solve the resulting geodesic equations analytically exact in elliptic functions.

Recently we derived the next-to-next-to-leading order post-Newtonian Hamiltonians at spin-orbit and spin(1)-spin(2) level for a binary system of compact objects. In this talk the derivation of them will be shortly outlined at an introductory level. We will also discuss some checks of our (complicated and long) results in the first part of the talk. In the second part we will show how to apply our results to the calculation of the last stable circular orbit of such a binary system of black holes or neutron stars.

We use the post-Newtonian-Affine model to assess the validity of the adiabatic approximation in modeling tidal effects in the phase evolution of compact binary systems. We compute the dynamical evolution of the tidal tensor, which we estimate at the 2PN order, and of the quadrupole tensor, finding that their ratio, i.e. the tidal deformability, increases in the last phases of the inspiral. We derive the gravitational wave phase corrections due to this phenomenon and quantify how they affect gravitational wave detectability.

An outline of a proof of the decomposition of the linear metric perturbation into gaugeinvariant and gauge-variant parts on an arbitrary background spacetime is discussed through an exlicit construction of gauge-invariant and gauge-variant parts. Although this outline is incomplete, yet, due to our assumptions, we propose a conjecture which states that the linear metric perturbation is always decomposed into its gauge-invariant and gageu-variant parts. If this conjecture is true, we can develop the higher-order gaugeinvariant perturbation theory on an arbitrary background spacetime.

Gravitational waveforms generated by unequal mass black hole binaries are expected to be common sources for future gravitational wave detectors. We derived the waveforms emitted by such systems during the last part of the inspiral, when the larger spin dominates over the orbital angular momentum and the smaller spin is negligible. These Spin-Dominated Waveforms (SDW) arise as a double expansion in the post-Newtonian parameter and another parameter proportional to the ratio of the orbital angular momentum and the dominant spin. The time spent by the gravitational wave as an SDW in the sensitivity range of the KAGRA detector is presented for the first time.

Using the pseudo-Newtonian (PN) potential, we estimate the influence of the repulsive cosmological constant Ʌ ~ 1.3×10^–56 cm^–2 implied by recent cosmological tests onto the motion of both Small and Large Magellanic Clouds (SMC and LMC) in the gravitational field of the Milky Way. The role of the cosmological constant is most conspicuous when binding mass is estimated for the satellite galaxies. We have found a strong influence of cosmic repulsion on the total binding mass for both galaxies. We have found that in some cases, the effect of the cosmic repulsion can be even comparable to the effects of the dynamical friction and the Andromeda galaxy.

We estimate virial masses of galaxy clusters using the parametrized post-Newtonian (PPN) virial theorem. Also, we show explicitly that post-Newtonian corrections can not address the mass discrepancy in the galaxy clusters.

We derive gravitational waveforms needed to compute the 18th post-Newtonian (18PN) order energy flux, i.e. v³⁶ beyond the Newtonian approximation, where υ is the orbital velocity of a test particle, in a circular orbit around a Schwarzschild black hole. Comparing our 18PN formula for the energy flux with high precision numerical results, we find that the relative error of the 18PN flux at the innermost stable circular orbit is about 10⁻⁵. Finally, we derive the 8PN expression of the energy flux for circular and equatorial orbits around a Kerr black hole and examine the applicability of our 18PN expressions to the case of the Kerr black hole by combining our 8PN formula for the Kerr black hole.

We present results from calculations of the orbital evolution in eccentric binaries of nonrotating black holes with extreme mass-ratios. Our inspiral model is based on the method of osculating geodesics, and is the first to incorporate the full gravitational self-force (GSF) effect, including conservative corrections. The GSF information is encapsulated in an analytic interpolation formula based on numerical GSF data for over a thousand sample geodesic orbits. We assess the importance of including conservative GSF corrections in waveform models for gravitational-wave searches.

In order to extract physical parameters from the waveform of an extreme-mass-ratio binary, one requires a second-order–accurate description of the motion of the smaller of the two objects in the binary. Using a method of matched asymptotic expansions, I derive the second-order equation of motion of a small, nearly spherical and non-rotating compact object in an arbitrary vacuum spacetime. I find that the motion is geodesic in a certain locally defined effective metric satisfying the vacuum Einstein equation through second order, and I outline a method of numerically determining this effective metric.

We present some recent results on the motion of test bodies with internal structure in General Relativity. On the basis of a multipolar approximation scheme, we study the motion of extended test bodies endowed with an explicit model for the quadrupole. The model is inspired by effective actions recently proposed in the context of the post-Newtonian approximation, including spin-squared and tidal contributions. In the equatorial plane of the Kerr geometry, the motion can be characterized by an effective potential of the binding energy. We compare our findings to recent results for the conservative part of the self-force in astrophysically realistic situations.

We report on numerical simulations of charged-black-hole collisions.We focus on head-on collisions of non-spinning black holes, starting from rest and with the same charge to mass ratio. The addition of charge to black holes introduces a new interesting channel of radiation and dynamics. The amount of gravitational-wave energy generated throughout the collision decreases by about three orders of magnitude as the charge-to-mass ratio is increased from 0 to 0.98. This is a consequence of the smaller accelerations present for larger values of the charge.

Within numerical relativity, the most accurate method available to transport gravitational radiation from a finite worldtube to I⁺ is characteristic extraction. In this method, the coordinates are based on radially compactified outgoing null cones, the metric is written in Bondi-Sachs form and is evolved into the future using the vacuum Einstein equations. Existing characteristic codes are only second order accurate. Further, because of numerical stability issues, they use a special “parallelogram” algorithm for evolution which cannot be extended to higher order. We develop a new approach that uses the method of lines in both the radial and time directions with angular dependence handled pseudo spectrally. The method can, in principle, be applied to any desired order of convergence, and we have implemented and tested the method for stability and convergence at fourth order.

We present new numerical techniques we developed for launching the first parameter study of magnetized black hole–neutron star (BHNS) mergers, varying the magnetic fields seeded in the initial neutron star. We found that magnetic fields have a negligible impact on the gravitational waveforms and bulk dynamics of the system during merger, regardless of magnetic field strength or BH spin. In a recent simulation, we seeded the remnant disk from an unmagnetized BHNS merger simulation with large-scale, purely poloidal magnetic fields, which are otherwise absent in the full simulation. The outcome appears to be a viable sGRB central engine.

The addition of nuclear and neutrino physics to general relativistic fluid codes allows for a more realistic description of hot nuclear matter in neutron star and black hole systems. This additional microphysics requires that each processor have access to large tables of data, such as equations of state. Modern many-tasking execution models contain special semantic constructs designed to simplify distributed access to such tables and to reduce the negative impact in distributed large table access through network latency hiding measures such as local control objects. We present evolutions of a neutron star obtained using a message driven multi-threaded execution model known as ParalleX.

Direct detection experiments are reporting intriguing indications of a possible dark matter signal, the most noticeable case being the annual modulation effect observed by the DAMA experiments. A relevant interpretation of these results is in terms of light neutralino dark matter, arising in supersymmetric models where gaugino universality is broken. These supersymmetric models possess specific features that differentiate them from more typical supersymmetric scenarios and that can be tested at the LHC.

The DAMA/LIBRA experiment, running at the Gran Sasso National Laboratory of the INFN, has a sensitive mass of about 250 kg highly radiopure NaI(Tl). It is mainly devoted to the investigation of Dark Matter (DM) particles in the Galactic halo by exploiting the model independent DM annual modulation signature. The present DAMA/LIBRA experiment and the former DAMA/NaI one (the first generation experiment having an exposed mass of about 100 kg) have released so far results corresponding to a total exposure of 1.17 ton × yr over 13 annual cycles. They provide a model independent evidence of the presence of DM particles in the galactic halo at 8.9 σ C.L..

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is a direct Dark Matter detection experiment located in the Gran Sasso underground laboratory. In 2011, the CRESST–II Dark Matter search completed 730 kgd of data taking operating scintillating CaWO4 crystals at mK temperatures. The simultaneous detection of the deposited energy by the phonon signal and the scintillation light allows the discrimination of the interacting particles on an event-by-event basis. In the acceptance region of the detectors, 67 events where observed in total. A maximum-likelihood analysis shows that an additional signal on top of the known backgrounds of α–, β–, γ–radiation and neutrons is required to explain the observed distribution both in energy and light–yield. The excess signal however is compatible with the signal expected from a WIMP (Weakly Interacting Massive Particle) with a mass in the range of 10–30 GeV/c².

Recently enlarged, the Canfranc Underground laboratory hosts a multidisciplinary scientific program, with a focus on rare event physics. Up to now, seven experiments have been approved and are being installed at the new facilities. We present the main research activity that our group is developing in the underground facilities: ANAIS, an experiment that will look for dark matter annual modulation with 250 kg of NaI(Tl) scintillators.

We have recently proposed a new scenario where blazars are classified as flat-spectrum radio quasars or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted radiation from the jet, emission from the accretion disk, the broad line region, and light from the host galaxy. This mix of different components leads to strong selection effects, which are properly taken into account in our scheme. We describe here the main features of our approach, which solves many long-standing issues of blazar research, give the most important results, and discuss its implications and testable predictions.

It is believed that jets emerging from blazars (flat spectrum radio quasars (FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually exhibit lower luminosity and harder power law spectra at gamma-ray energies than FSRQs. It was argued previously that the difference in accretion rates is mainly responsible for the large observed luminosity mismatch between them. However, when intrinsic luminosities are derived by correcting for beaming effects, this mismatch is significantly reduced. We show that spin plays an important role to reveal the dichotomy of luminosity distributions between BL Lacs and FSRQs, suggesting BL Lacs to be low luminous and slow rotators compared to FSRQs.

We report about recent progress in the first numerical implementations of spectral energy distribution (SED) fits to estimate synchrotron-self Compton (SSC) model parameters. Using two well observed objects, Markarian 421 and Markarian 501, we will highlight the strength of the method, as well as plans for future improvements.

The Milagro experiment was a TeV gamma-ray observatory designed to continuously monitor the overhead sky in the 0.1-100 TeV energy range. It operated from 2000 and 2008 and was characterized by a large field of view (∼ 2 sr) and a high duty cycle (≥ 90%). Here we report on the long-term monitoring of the blazar Mrk 421 with Milagro over the period from September 21, 2005 to March 15, 2008. We present a study of the TeV variability of the source and provide upper limits for the measured flux for different time scales, ranging from one week up to one year.

We summarize recent results based on an analysis of Fermi-LAT data for the lobes of the nearby radio galaxy Centaurus A (Cen A). The high-energy gamma-ray emission extends up to 6 GeV, with a significance of more than 10 and 20 σ for the north and the south lobe, respectively. We provide a short discussion of the lobe's spectral energy distribution (SED) in the context of hadronic and time-dependent leptonic scenarios.

This paper reports on recent results from measurements of energy spectrum and nuclear composition of galactic cosmic rays performed with the IceCube Observatory at the South Pole in the energy range between about 300 TeV and 1 EeV.

A basic quantity in the characterization of relativistic particles is the proton-to-electron (p/e) energy density ratio. We derive a simple approximate expression suitable to estimate this quantity, U_p/U_e = (m_p/m_e)^(3−q)/2, valid when a nonthermal ‘gas’ of these particles is electrically neutral and the particles' power-law spectral indices are equal — e.g., at injection. This relation partners the well-known p/e number density ratio at 1GeV, N_p/N_e = (m_p/m_e)^(q−1)/2.

The Pierre Auger Observatory has been designed to investigate the origin and the nature of Ultra High Energy Cosmic Rays (UHECRs). Selected results concerning the measurements of the energy spectrum and the mass composition are presented.

The Telescope Array is a hybrid detector using fluorescence telescopes and an array of particle counters to observe extensive air showers generated by ultra-high cosmic rays. The recent results from the experiment, including the energy spectrum, primary mass composition, and a search for anisotropy in arrival directions are reviewed.

We discuss recent developments in gravitational fields with sources, regular black holes, quasiblack holes, and analogue black holes, related to the talks presented at the corresponding Parallel Session AT3 of the 13th Marcel Grossmann Meeting.

We discuss new classes of degenerate horizon geometries in Einstein gravity in all dimensions greater than five. Cross-sections of the horizon are inhomogeneous metrics on 2-sphere and Lens space bundles over any Fano Kähler-Einstein manifold. The horizons are consistent with the known restrictions on the topology and symmetry for black holes.

We consider the radiation emitted in a collision of shock waves, in D-dimensional General Relativity (GR), and describe a remarkably simple pattern, hinting at a more fundamental structure, unveiled by the introduction of the parameter D.

Higher dimensional Ricci-flat black branes suffer from the Gregory-Laflamme instability. In this talk I will present a very simple and efficient long-wavelength approximation to this instability. This hydrodynamic approximation exhibits a conformal symmetry much like in AdS/CFT, where gravitational modes in AdS encode CFT quantities. This fact links to recent developments suggesting that conformal symmetry plays a role in all kinds of black holes, including Ricci-flat ones.

We discuss the peeling bahaviour of the Weyl tensor near null infinity for an asymptotivally flat higher dimensional spacetime and describe how these results can be used to write the Bondi energy flux in terms of “Newman-Penrose” Weyl components.

Main results on a generalization of the Goldberg-Sachs theorem to five-dimensional Einstein spacetimes are briefly overviewed. In particular, we focus on necessary conditions on the optical matrix of a multiple WAND. We point out that there are three canonical classes of 3 × 3 optical matrices, each involving just two parameters. We refer to explicit examples of spacetimes corresponding to each of these forms.

We study exact vacuum solutions to Einstein gravity and quadratic gravity (QG) of the Weyl types N and III. We show that in an arbitrary dimension all Einstein spacetimes of the Weyl type N and a subclass of Einstein type III spacetimes are exact solutions to QG and we refer to explicitly known metrics within these classes. We also study a wider class of spacetimes admitting a pure radiation term in the Ricci tensor. In contrast to the Einstein case, the field equations of generic QG determine optical properties of the geometry and restrict such exact solutions to the Kundt class.

Critical Gravity in D dimensions is discussed from the point of view of its exact solutions. A non-linear realization of the logarithmic modes of linearized Critical Gravity is seen to emerge as a peculiarity of the sector of anti-de Sitter wave solutions.

We consider a class of higher dimensional theories consisting of D-dimensional gravity coupled to a scalar dilaton and a form field propagating over a warped higher dimensional spacetime. In the simplest set-up, the models are characterized by two moduli: one related to the volume of the internal space, the other to the modulus of the warp factor. While the volume-modulus can be fixed by appropriately tuning the gauge field strength, curvature of the internal space, and cosmological constant, the same mechanism cannot work for the warp modulus. Here, we will present a stabilizing mechanism for the warp modulus and its mass in terms of quantum fluctuations from both moduli. We will show that, while quantum effects from the modulus associated to the warp modulus can only provide a stabilization mechanism of the mass scale in a restricted region of the parameter space, quantum effects from the volume modulus offer an efficient mechanism of stabilization.

We present a higher order generalisation of the perturbative method to find the metric after the collision of two Aichelburg-Sexl gravitational shock waves in D-dimensions. A central challenge is to extract a higher order estimate for the inelasticity. We present an adaptation of the Bondi mass loss formula in D-dimensions, which allows us to obtain an expression valid non-perturbatively, for axially symmetric asymptotically flat spaces.

We present a U(1) gauge cosmic string solution on a warped 5-dimensional space time, where we solved the effective 4-dimensional equations modified by the projection of the Weyl tensor on the brane together with the junction and boundary conditions. Where the mass per unit length of the string in the bulk can be of order of the Planck scale, in the brane it will be warped down to unobservable GUT scale. It turns out that the induced 4-dimensional space time does not show asymptotic conical behavior as in the 4D counterpart model. So there is no angle deficit and the space time seems to be unphysical at finite distance from the core of the string. This could explain the absence of observational evidence of the lensing effect cosmic strings would produce and could have consequences for the (2+1)-dimensional related models.

Five-dimensional(5D) black-hole and black-ring formation are investigated numerically. We express the matter with collisionless particles, and prepare these distribution in homogeneous spheroidal and toroidal configurations under the momentarily static assumption. Evolutions are followed by using ADM formalism (4 + 1 decomposition) and solving the geodesic equation. For spheroidal configurations, we repeat the 4D simulations performed by Shapiro and Teukolsky (1991) that announced an appearance of a naked singularity, and discuss the differences in the 5D version. For toroidal configurations, we consider the rotating collisionless particles which consist of equal numbers co-rotating and counterrotating under a certain rotational law. We show topology change of apparent horizon from ring-shaped to spherical shape during its evolution.

We present the vacuum polarisation of a massless, conformally coupled scalar field on the brane for a Schwarzschild–Tangherlini black hole in a bulk of zero to seven additional dimensions.

By computing coordinate time Lyapunov exponent, we prove that for more than four spacetime dimensions (N ≥ 3), there are no Innermost Stable Circular Orbit (ISCO) in charged Myers Perry blackhole spacetime.Using it, we show that the instability of equatorial circular geodesics, both massive and massless particles for such types of blackhole space-times.

Several issues coming from Cosmology, Astrophysics and Quantum Field Theory suggest to extend the General Relativity in order to overcome several shortcomings emerging at conceptual and experimental level. From one hand, standard Einstein theory fails as soon as one wants to achieve a full quantum description of space-time. In fact, the lack of a final self-consistent Quantum Gravity Theory can be considered one of the starting points for alternative theories of gravity. Specifically, the approach based on corrections and enlargements of the Einstein scheme, have become a sort of paradigm in the study of gravitational interaction. On the other hand, such theories have acquired great interest in cosmology since they “naturally” exhibit inflationary behaviours which can overcome the shortcomings of standard cosmology. From an astrophysical point of view, Extended Theories of Gravity do not require to find candidates for dark energy and dark matter at fundamental level; the approach starts from taking into account only the “observed” ingredients (i.e., gravity, radiation and baryonic matter); it is in full agreement with the early spirit of General Relativity but one has to relax the strong hypothesis that gravity acts at same way at all scales. Several scalar-tensor and f(R)-models agree with observed cosmology, extragalactic and galactic observations and Solar System tests, and give rise to new effects capable of explaining the observed acceleration of cosmic fluid and the missing matter effect of self-gravitating structures. Despite these preliminary results, no final model addressing all the open issues is available at the moment, however the paradigm seems promising in order to achieve a complete and self-consistent theory working coherently at all interaction scales.

We construct self/anti-self charge conjugate (Majorana-like) states in the (1/2, 0) ⊕ (0, 1/2) representation of the Lorentz group, and their analogs for higher spins within the quantum field theory. The problem of the basis rotations and that of the selection of phases in the Dirac-like and Majorana-like field operators are considered. The discrete symmetries properties (P, C, T) are studied. The corresponding dynamical equations are presented. In the (1/2, 0) ⊕ (0, 1/2) representation they obey the Dirac-like equation with eight components, which has been first introduced by Markov. Thus, the Fock space for corresponding quantum fields is doubled (as shown by Ziino). The particular attention has been paid to the questions of chirality and helicity (two concepts which are frequently confused in the literature) for Dirac and Majorana states. We further review several experimental consequences which follow from the previous works of M.Kirchbach et al. on neutrinoless double beta decay, and G.J.Ni et al. on meson lifetimes.

We present our Finsler spacetime formalism which extends the standard formulation of Finsler geometry to be applicable in physics. Finsler spacetimes are viable non-metric geometric backgrounds for physics; they guarantee well defined causality, the propagation of light on a non-trivial null structure, a clear notion of physical observers and the existence of physical field theories determining the geometry of space-time dynamically in terms of an extended gravitational field equation. Here we give the precise definition of Finsler spacetimes, the notion of well-defined observers, their measurements and extended Lorentz transformations between them. Moreover we show how to formulate action based field theories.

Stationary, asymptotically flat black holes in scalar-tensor theories of gravity are studied. It is shown that such black holes have no scalar hair and are the same as in General Relativity.

We consider super-inflating solutions in modified gravity for several popular families of f(R) functions. Using scalar field reformulation of f(R)-gravity we describe how the form of effective scalar field potential can be used for explaining existence of stable superinflation solutions in the theory under consideration. Several new solutions of this type have been found analytically…

In this paper we show how in the most natural extension of gravity with torsion, fermion fields are endowed with running coupling in spinorial interaction that are eventually shown to reproduce the strength and structure of the leptonic weak forces.

We review a class of higher derivative theories of gravity consistent at quantum level. This class is marked by a non-polynomal entire function (form factor), which averts extra degrees of freedom (including ghosts) and improves the high energy behaviour of the loop amplitudes. By power counting arguments, it is proved that the theory is superrenormalizable, i.e. only one-loop divergences survive. At classical level, black holes and cosmological solutions are singularity free.

Horava-Lifshitz gravity has covariance only under the foliation-preserving diffeomorphism. This implies that the quantities on the constant-time hypersurfaces should be regular. In the original theory, the projectability condition which strongly restricts the lapse function is proposed. We assume that a star is filled with a perfect fluid, that it has the reflection symmetry about the equatorial plane. As a result, we find a no-go theorem for stationary axisymmetric star solutions in projectable Horava-Lifshitz gravity under the physically reasonable assumptions on the matter sector.

Thermodynamics of extended gravity static spherically symmetric black hole solutions is investigated. The energy issue is discussed making use of the derivation of Clausius relation from equations of motion, evaluating the black hole entropy by the Wald method and computing the related Hawking temperature.

The importance of Astrometry as a powerful technique for accurate tests of gravity theories has constantly grown during the last years. Usually these tests are formulated in the framework of the PPN formalism. We provide a short review of the forthcoming experimental scenario, and suggest how its results can be reformulated and interpreted in the context of the Extended Theories of Gravity.

The chameleon mechanism appearing in massive tensor-scalar theory of gravity can effectively reduce the nonminimal coupling between the scalar field and matter. This mechanism is invoked to reconcile cosmological data requiring introduction of Dark Energy with small-scale stringent constraints on General Relativity. In this communication, we present constraints on this mechanism obtained by a cosmological analysis (based on Supernovae Ia data) and by a Solar System analysis (based on PPN formalism).

Two Measures Field Theory (TMT) uses both the Riemannian volume element and a new one Φd⁴x, this new measure of integration Φ can be build of four scalar fields or a totally antisymmetric three index field. Here we summarize the basic idea of the theory, present some arguments in favour, and present applications of TMT to cosmology and particle physics.

This article presents an extended model of gravity obtained by gauging the AdS-Mawell algebra. It involves additional fields that shift the spin connection, leading effectively to theory of two independent connections. Extension of algebraic structure by another tetrad gives rise to the model described by a pair of Einstein equations.

We present a new model of gravity which explicitly breaks Lorentz-invariance by the introduction of a unit time-like vector field, thereby giving rise to an extra (scalar) degree of freedom. We discuss its cosmology, exact solutions and the dynamics of the scalar mode. We show that it predicts inflation without an inflaton and admits the black hole solutions of General Relativity (GR). We argue that the scalar mode is well behaved and contains none of the pathologies previously found in similar models.

We present an extension of general relativity in which an f(R) term á la Palatini is added to the usual metric Einstein-Hilbert Lagrangian. Expressing the theory in a dynamically equivalent scalar-tensor form, we show that it can pass the Solar System observational tests even if the scalar field is very light or massless. Applications to cosmology and astrophysics, and some exact solutions are discussed.

In this paper we consider a tomographic representation of quantum cosmology, in which tomograms (i.e. a standard positive probability distribution function) describe the quantum state of universe in place of the the wave function or density matrices. Extending this representation to classical cosmology we define a classical tomogram in order to reconstruct the initial conditions of the universe.

A metric approach through mass-length acceleration scales is built in regions where usually dark matter and dark energy are introduced. The approach is based on pure observations of dynamical motion of stars and of bending of light through gravitational lensing. A first cosmological calibration is done using the SNIa magnitude-redshift relation and turns out to be equivalent with the approach made at galactic and extragalactic scales.

Significative developments on the primordial black hole quantization seem to indicate that the structure formation in the universe behaves under a unified scheme. This leads to the existence of scaling relations, whose validity could offer insights on the process of unification between quantum mechanics and gravity. Encouraging results have been obtained in order to recover the observed magnitudes of angular momenta, peculiar radii and virialized times for large and small structures. In the cosmological regime, we show that it seems possible to infer the magnitude of the cosmological constant in terms of the matter density, in agreement with the observed values.

We consider a maximal extension of the Hilbert-Einstein action and analyze several interesting features of the theory. More specifically, the motion is non-geodesic and takes place in the presence of an extra force. These models could lead to some major differences, as compared to the predictions of General Relativity or other modified theories of gravity, in several problems of current interest, such as cosmology, gravitational collapse or the generation of gravitational waves. Thus, the study of these phenomena may also provide some specific signatures and effects, which could distinguish and discriminate between the various gravitational models.

Recently, a unified model of the primordial inflation and the present cosmic acceleration has been proposed in the context of f(R) gravity. In this model, the reheating dynamics after the inflation is significantly altered. We investigated the reheating dynamics and found that typical parameter range of the model has already been excluded by the observations of cosmic microwave background and gravitational waves…

In f(R) extensions of General Relativity the Palatini approach provides ghost-free theories with second-order field equations and allows to obtain charged black hole solutions which depart from the standard Reissner-Nordström solution.

We consider a static cylindrically symmetric spacetime with elastic matter and show that the Einstein field equations can be reduced to a system of two nonlinear ordinary differential equations. We present analytical and numerical solutions satisfying the dominant energy conditions. The solutions are matched at a finite radius to suitable exteriors given by the Linet-Tian spacetime.

We consider static conformally flat cylindrically symmetric spacetimes with a cosmological constant and study the matching problem with the exterior Linet-Tian spacetime. We show that the matching is impossible if Λ < 0.

We investigate static inhomogeneous charged planar black hole solutions of the Einstein- Maxwell system in an asymptotically anti-de Sitter spacetime. Within the framework of linear perturbations, the inhomogeneous solutions predict that the Cauchy horizon always disappears for any wavelength perturbation. For extremal black holes, we analytically show that an observer freely falling into the black hole feels infinite tidal force at the horizon for any long wavelength perturbation, even though the Kretschmann scalar curvature invariant remains small.

We discuss a method to study linear perturbations of generic rotating spacetimes in the slow-rotation limit. The framework is valid for any perturbation field and it is particularly advantageous when the field equations are not separable. Using this approach, we show that massive vector perturbations in the Kerr metric exibit strong superradiant instabilities, which put competitive constraints on the mass of the photon: m_γ ≲ 10⁻²⁰ eV.

Continuous sequences of asymptotically flat solutions to the Einstein-Maxwell equations describing regular equilibrium configurations of ordinary matter can reach a black hole limit. For a distant observer, the spacetime becomes more and more indistinguishable from the metric of an extreme Kerr-Newman black hole outside the horizon when approaching the limit. From an internal perspective, a still regular but non-asymptotically flat spacetime with the extreme Kerr-Newman near-horizon geometry at spatial infinity forms at the limit. Interesting special cases are sequences of Papapetrou-Majumdar distributions of electrically counterpoised dust leading to extreme Reissner-Nordström black holes and sequences of rotating uncharged fluid bodies leading to extreme Kerr black holes.

We present results concerning the existence of static electrically charged spheres made by a charged perfect fluid with polytropic equation of state that are arbitrarily close to a quasiblack hole configuration. The study is performed by solving the Tolman-Oppenheimer- Volkoff equation, by assuming that the charge distribution is proportional to the energy density. We search for compact equilibrium configurations and verify that the extremal limit for charged polytropic spheres, i.e., the quasiblack hole limit, is approached when considering high polytropic indexes and large charge densities.

Quadratic gravity is a general class of quantum-gravity-inspired theories, where the Einstein–Hilbert action is extended through the addition of all terms quadratic in the curvature tensor coupled to a scalar field. In this article, we focus on the scalar Gauss– Bonnet (sGB) theory and consider the black hole binary inspiral in this theory. By applying the post-Newtonian (PN) formalism, we found that there is a scalar dipole radiation which leads to -1PN correction in the energy flux relative to gravitational radiation in general relativity. From the orbital decay rate of a low-mass X-ray binary A0600-20, we obtain the bound that is six orders of magnitude stronger than the current solar system bound. Furthermore, we show that the excess in the orbital decay rate of XTE J1118+480 can be explained by the scalar radiation in sGB theory.

We give a summary of quasiblack hole properties with special emphasis on the drawing of the corresponding Carter-Penrose diagrams.

We discuss a general procedure to generate a class of (everywhere regular) solutions of Einstein equations that can have an (a-priori fixed) arbitrary number of horizons. We then report on work currently in progress i) to find a suitable classification scheme for the maximal extension of these solutions and ii) to interpret the source term in Einstein equations as an effective contribution arising from higher dimensional and/or modified gravity.

Black brane solutions with scalar hair and with non-AdS asymptotics have several features that make them very interesting for holographic applications: (1) They allow to circumvent usual no-hair theorems; (2) They may have a non singular extremal limit in the form of a scalar soliton that interpolates between AdS and non-AdS vacua; (3) They allow for phase transitions between the Schwarzschild-AdS (SADS) and scalar dressed black branes; (4) They give an holographic realization of hyperscaling violation in critical systems. In this note I illustrate these features using an exact integrable Einstein-scalar gravity model.

We study a gauge field subsystem which is of a special non-linear form containing a square-root of the Maxwell term and which previously has been shown to produce a QCD-like confining gauge field dynamics in flat space-time. The condition of finite energy of the system or asymptotic flatness on one side of the horned particle implies that the charged object sitting at the throat expels all the flux it produces into the other side of the horned particle, which turns out to be of a “tube-like” nature. An outside observer in the asymptotically flat universe detects, therefore, apparently neutral object. The hiding of the electric flux behind the tube-like region of a horned particle is the only possible way that a truly charged particle can still be of finite energy, in a theory that in flat space describes confinement…

We construct a regular black hole model which is constituted of a de Sitter core, a massive shell and Reissner-Nordstrüm spacetime. We obtain some stationary solutions and the parameters of the solutions range in limited region. And the stable solutions have positive mass of the shell.

Gravitational vacuum condensate stars or gravastars have been proposed as the final state of complete gravitational collapse, consistent with all quantum and statistical principles. In this brief contribution the main features of gravastars are summarized and the prospects for observationally distinguishing them from black holes are discussed.

We consider the possibility that wormhole geometries are sustained by their own quantum fluctuations, in the context of noncommutative geometry and Gravity's Rainbow models. More specifically, the energy density of the graviton one-loop contribution to a classical energy in a wormhole background is considered as a self-consistent source for wormholes. In this semi-classical context, we consider the effects of a smeared particle-like source in noncommutative geometry and of the Rainbow's functions in sustaining wormhole geometries…

We present an investigation of the quasinormal modes of the draining bathtub using three different methods, namely: finite difference, continued fraction and geodesic expansion. We compare the results obtained with these different approaches.

A fundamental property in wormhole physics is the flaring-out condition of the throat, which through the Einstein field equation entails the violation of the null energy condition. In the context of modified theories of gravity, it has also been shown that the normal matter can be imposed to satisfy the energy conditions, and it is the higher order curvature terms, interpreted as a gravitational fluid, that sustain these non-standard wormhole geometries, fundamentally different from their counterparts in general relativity. We review recent work in wormhole physics in the context of modified theories of gravity.

A classical analogue to the Aharonov-Bohm (AB) effect occurs in a (idealized) draining bathtub (DBT) vortex system. The DBT vortex presents a sonic horizon, at which the flow rate exceeds the speed of sound. The sonic horizon is the analogue of a black hole event horizon. The DBT vortex also presents an ergoregion, similar to a rotating black hole. Because of the sonic event horizon, the AB effect is modified and has two tuning coefficients proportional to the flow draining and circulation couplings with the perturbation frequency.

In this article a discussion of Analogue Gravity is presented in relation with its recently discovered relation, valid at any perturbative order, with the nonlinear Von Mises wave equation of fluid dynamics. A discussion of the role of the acoustic metric at nonlinear level is presented.

We discuss some consequences of changing the matter to gravity coupling without affecting the gravitational dynamics. The Einstein tensor is usually assumed to be proportional to the stress tensor due to the divergence free property of both object. This is not the only consistent way to couple matter to gravity; we explore some aspect of consistent modification to the matter/gravity coupling using the recently proposed Eddington inspired Born Infeld extension of gravity.

In this work we present an analytical solution of a slowly rotating black hole in a modified theory of gravity in four dimensions, described by the Einstein-Hilbert action plus all quadratic, algebraic curvature invariants, generically coupled to a single scalar field. We explicitly show the frequencies of the innermost stable circular orbits and the light ring in this modified theory of gravity, to first order in the spin parameter.

We discuss static, spherically symmetric solutions with an electric field in a quadratic extension of general relativity formulated in the Palatini approach (assuming that metric and connection are independent fields). Unlike the usual metric formulation of this theory, the field equations are second-order and ghost-free. It is found that the resulting black holes present a central core whose area is proportional to the Planck area times the number of charges. Some of these solutions are nonsingular. In this case, the charge-to-mass ratio implies that the core matter density is independent of the specific amounts of charge and mass and of order the Planck density.

We analyze the apparent horizon dynamics in the inhomogeneous Clifton-Mota-Barrow solution of Brans-Dicke theory. This solution models a central matter configuration embedded in a cosmological background. In certain regions of the parameter space we find solutions exhibiting dynamical creation or merging of two horizons.

I review the theoretical aspects and phenomenology of a class of gravitational theories incorporating violation of the Lorentz invariance. The observational constraints on the parameters of these theories following from the tests of general relativity, as well as the consequences of the Lorentz violation in the dark energy and dark matter sectors are discussed.

We use a dynamical systems analysis to investigate the future behaviour of Einstein-aether cosmological models. In particular, we study the inflationary scenario.

Recently, there has been a lot of progress in the area of non-linear massive gravity. A theory free from the Boulware-Deser ghost has been proposed by de Rham, Gabadadze, Tolley (dRGT). We clarify some of its existing formulations, and provide a new and elegant alternative approach to the counting of the number of degrees of freedom of dRGT theory.

The recent discovery of a ghost-free, non-linear extension of the Fierz—Pauli theory of massive gravity, and its bigravity formulation, introduced new possibilities of interpreting cosmological observations, in particular, the apparent late-time accelerated expansion of the Universe. Here we discuss such possibilities by studying the background cosmology of the model and comparing its predictions to different cosmological measurements. We place constraints on the model parameters through an extensive statistical analysis of the model, and compare its viability to that of the standard model of cosmology. We demonstrate that the model can yield perfect fits to the data and is capable of explaining the cosmic acceleration in the absence of an explicit cosmological constant or dark energy, but there are a few caveats that must be taken into account when interpreting the results.

A brief summary of some of the main consequences of spontaneous Lorentz violation in gravity is presented, including evasion of a no-go theorem, concomitant spontaneous diffeomorphism breaking, the appearance of massless Nambu-Goldstone modes and massive Higgs modes, and the possibility of a Higgs mechanism in gravity.

As a first step toward understanding a lanscape of vacua in a theory of non-linear massive gravity, we consider a landscape of a single scalar field and study tunneling between a pair of adjacent vacua. We study the Hawking-Moss (HM) instanton that sits at a local maximum of the potential, and evaluate the dependence of the tunneling rate on the parameters of the theory. It is found that provided with the same physical HM Hubble parameter H_{H M}, depending on the values of parameters α₃ and α₄ in the action, the corresponding tunneling rate can be either enhanced or suppressed when compared to the one in the context of General Relativity (GR). Furthermore, we find the constraint on the ratio of the physical Hubble parameter to the fiducial one, which constrains the form of potential. This result is in sharp contrast to GR where there is no bound on the minimum value of the potential.

We summarise some results of work in progress in collaboration with Giovanni Amelino-Camelia about momentum dependent (Rainbow) metrics in a Relative Locality framework and we show that this formalism is equivalent to the Hamiltonian formalization of Relative Locality obtained in arXiv:1102.4637.

Massive Gravity or Massive General Relativity (MGR) is a modification of GR originated from the very natural question: what is the way to give the graviton a mass? This question was partially answered back in the 1930's by Fierz and Pauli who wrote down a theory of a massive spin 2 field in Minkowski background. However, the generalization to the full self-gravitating case was proved to be notoriously difficult due hurdles like the van Dam–Veltman–Zakharov (vDVZ) discontinuity and the discovery of the Boulware–Deser (BD) ghost…

The purpose of this contribution is to elucidate some of the properties of Shape Dynamics (SD) and is largely based on the longer article. We shall point out some of the key differences between SD and related theoretical constructions, illustrate the central mechanism of symmetry trading in electromagnetism and finally point out some new quantization strategies inspired by SD. We refrain from describing mathematical detail and from citing literature. For both we refer to¹.

Massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure can lead to an interesting interplay between the “background” and “foreground” metrics in a cosmological context. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit. Thus, solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true…

We study a theory of dilaton gravity in a 5D brane scenario, with the dilaton nonminimally coupled to the matter content of the universe localized on the brane. We investigate whether the observed large-scale structure of the universe can exist on the brane in the effective 4D dilaton gravity model with an exact anti de Sitter bulk. The corresponding constraint on the spatial derivative of the matter energy density is derived, and subsequently quantified using the current limits resulting from searches for variation of Newton's constant. By confronting it with the observational data from galaxy surveys, we show that the derived bound does not allow for the existence of the large-scale structure as is observed today. Thus, such a dilaton gravity brane scenario is ruled out.

We show how generic off—diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive gravity using the anholonomic frame deformation method. Such metrics describe the late time acceleration due to effective cosmological terms induced by nonlinear off—diagonal interactions and graviton mass and include matter, graviton mass and other effective sources modelling nonlinear gravitational and matter fields interactions with polarization of physical constants and deformations of metrics, which may explain certain dark energy and dark matter effects.

Rotation curves of spiral galaxies are fundamental tools in the study of dark matter. Here we test the Bose-Einstein condensate (BEC) dark matter model against rotation curve data of High and Low Surface Brightness (HSB and LSB) galaxies, respectively. When the rotational velocities increase over the whole observed range, the fit of the BEC model is similar to the one of the Navarro-Frenk-White (NFW) dark matter model. When however the rotation curves exhibit long flat regions, the NFW profiles provide a slightly better fit.

The importance of choosing suitable tetrads for the study of exact solutions in f(T) gravity is discussed. For any given metric, we define the concept of good tetrads as the tetrads satisfying the field equations without constrainig the function f(T). Employing local Lorentz transformations, good tetrads in the context of spherical symmetry are found for Schwarzschild-de Sitter solutions.

We investigate the Weyl space-time extension of general relativity. We have derived the equations of evolution for expansion, shear and rotation. We have performed the study of the FLRW cosmology through focusing and defocusing of the geodesic congruences in the Weyl space-time. In particular, the Einstein-Palatini formalism turns out to reduce to a subclass of this spacetime, the Weyl integrable space-time (WIST). In this particular case we have considered the Starobinsky modification, f(R) = R + βR² − 2Λ, of gravity in order to study the formation of the caustics. In this model, it is possible to have a Big Bang singularity free cyclic Universe but unfortunately the periodicity turns out to be extremely short.

We test the consistency of the cosmic growth of structure predicted by General Relativity (GR) and the cosmic expansion history predicted by the cosmological constant plus cold dark matter paradigm (ΛCDM) by combining galaxy cluster data from ROSAT and Chandra, cosmic microwave background (CMB) data from WMAP, and galaxy clustering data from WiggleZ, 6dFGS and SDSS-III BOSS. The combination of these three independent, well studied measurements of the evolution of the mean energy density and its fluctuations is able to break strong degeneracies between growth parameters. To further tighten the constraints on the expansion parameters, we also include supernova, Cepheid variable and baryon acoustic oscillation data. For a spatially flat geometry, accounting for systematic uncertainties, and allowing for convenient departures from the expansion and growth histories of GR+ΛCDM, we obtain results that are in excellent agreement with this model and represent the tightest and most robust simultaneous constraint on cosmic growth and expansion to date.

We consider Jordan frame scalar-tensor gravity with arbitrary potential and coupling functions in flat Friedmann-Lemaître-Robertson-Walker cosmological spacetimes, in the dust matter and potential dominated epochs. We develop and apply an approximation scheme in the regime close to the so-called limit of general relativity and solve the ensuing nonlinear equations for the scalar field and Hubble parameter analytically in cosmological time. This allows us to recognize the theories with solutions that asymptotically converge to general relativity and draw some implications about the cosmological dynamics near this limit. Further, we also apply these methods and get some results in the generalized case with multiple scalar fields.

We study linear perturbations around static, spherically-symmetric spacetimes in f(R, C) theory, the nondynamical and dynamical Chern-Simons theory, and the most general scalar-tensor theory with second-order field equations. By explicitly constructing the second order action, we have derived the no-ghost condition and the no-tachyon condition, and the propagation speed for each mode.

A simplification of the full teleparallel theory of gravity is considered. The theory, resembling electrodynamics, admits a full hamiltonian treatment and yields the standard algebra of the scalar and vector constraints. The structure of the scalar constraint is very similar to the one obtained in the case of the full theory.

This paper shows how a quasi-Newton's law of gravitation, relying on an erfc potential, can be derived when a statistical pattern recognition paradigm based on the Bayes' law and the Central Limit Theorem is applied to the Einstein's field equation. This method incorporates a probabilistic factor that takes into account the probability of presence of a given energy-momentum density in its corresponding 4D curved spacetime manifold. The resulting symmetric and axisymmetric metrics and their corresponding geometries are briefly investigated.

In second-order scalar-tensor theories we study how the Vainshtein mechanism works in a spherically symmetric background with a matter source. In the presence of the field coupling with the Ricci scalar we generally derive the Vainshtein radius within which the General Relativistic behavior is recovered even for the coupling constant of the order of unity. Our analysis covers the models such as the extended Galileon and Brans-Dicke theories with a dilatonic field self-interaction. We show that, if these models are responsible for the cosmic acceleration today, the corrections to gravitational potentials are generally small enough to be compatible with local gravity constraints.

The effect of a universal scalar/matter coupling are investigated in Scalar-Tensor theories where the scalar potential is null. It is shown that the metric can be put in its standard post-Newtonian form. However, considering an effective Lagrangian for the matter field, it is pointed out that 1 − γ could be either positive, null or negative for finite value of ω, depending on the coupling function; while Scalar-Tensor theories without coupling always predict γ < 1 for finite value of ω.

In this work an extension to Eddington's gravitational action is analyzed. We consider the tensor perturbations of a FLRW space-time in the Eddington regime in where the tensor mode is linearly unstable deep and the resulting modifications to Einstein regime are quite strong.

The Noether symmetries with gauge term are studied for the f(R) cosmological model. By utilization of the Noether Symmetry approach, we obtain a time-varying invariant for the Lagrangian despite the fact that it does not depends on time explicitly.

We examine a flat (N + 1)-dimensional universe filled with a homogeneous magnetic field in Gauss-Bonnet gravity and take an interest in the behavior of cosmological solutions near the singularity.

We present numerical evidence for the existence of balanced black ring solutions in d ≥ 6 spacetime dimensions. They approach asymptotically the Minkowski background and have a regular event horizon with S¹ × S^d−3 topology, the case d = 6 being studied in a systematic way. The black ring solutions are found within a nonperturbative approach, by directly solving the Einstein field equations with suitable boundary conditions.

Various higher-dimensional black holes have been shown to be unstable by studying linearized gravitational perturbations. A simpler method for demonstrating instability is to find initial data that describes a small perturbation of the black hole and violates a Penrose inequality. We use the method to confirm the existence of the “ultraspinning” instability of Myers-Perry black holes. We also study black rings and show that “fat” black rings are unstable. We find no evidence of any rotationally symmetric instability of “thin” black rings.

The dimensional reduction of (the bosonic sector of) five-dimensional minimal supergravity to four dimensions leads to a theory with a massless axion and a dilaton coupled to gravity and two U(1) gauge fields (one of which has Chern-Simons coupling), whose field equations have SL(2, R) invariance. Utilizing this SL(2, R)-duality in the dimensionally reduced spacetime, we provide a new formalism for solution generation. Using the SL(2, R)-duality, we construct general Kaluza-Klein black hole solutions which carry six independent charges, its mass, angular momentum along four dimensions, electric and magnetic charges of the Maxwell fields in addition to Kaluza-Klein electric and magnetic monopole charges.

We construct a new exact solution describing a charged black hole on the Taub-Bolt instanton within the five-dimensional Einstein-Maxwell-dilaton gravity. Some general relations regarding the properties of the 5D black holes on asymptotically locally flat gravitational instantons are derived and demonstrated on the constructed solution, including a Smarr-like relation.

We present a new solution in 5D Einstein-Maxwell-dilaton gravity describing an equilibrium configuration of extremal rotating black holes with lens space horizon topologies. The basic properties of the solution are investigated and the physical quantities are calculated. It is shown that the black hole horizons are superconducting in the sense that they expel the magnetic flux lines.

In this talk I review some basic results on rotating black rings on Taub-NUT, which are generalisations of the Emparan–Reall and Pomeransky–Sen'kov black rings to a Taub-NUT background space. The talk is based on the authors' published work in Ref. 1.

We show that there exist chaotic bound orbits of a particle around a singly rotating black ring in five-dimensions by using Poincaré map.

we show the existence of the regular thermodynamic black di-ring system, in which the temperatures and angular velocities of the inner black ring and the outer black ring in the system are the same so that the system may be considered globally thermal equilibrium states. We also comment on some peculiar properties of the thermodynamic black di-ring system.

We consider equilibrium configurations of strongly magnetized neutron stars. Within full general relativity and assuming axisymmetry, we construct rotating stars with both poloidal and toroidal fields. Using a self-consistent field approach, we investigate the relative contributions from both magnetic components.

Spin-down rates of 6 X-ray pulsars inferred from observations of their spin-down trends are presented. We note that these pulsars brake harder than it is expected in the conventional accretion scenarios. The observed rapid spin-down favors the magnetic accretion scenario in which the neutron star is accreting material from a magnetized wind. The observed spin-down rate in this case can be explained provided the neutron star accretes from a non-Keplerian magnetic slab and the interchange instabilities of its magnetospheric boundary are suppressed.

The coefficients that determine the electron heat transfer and diffusion in the crust of neutron stars are calculated on the basis of a solution of the Boltzmann equation with allowance for degeneracy.

We study non-thermal processes produced by the injection of relativistic particles in a strongly magnetized corona around an accreting black hole. The spectral energy distribution produced in this component of X-ray binaries can be strongly affected by different interactions between locally injected relativistic particles and the different fields of the source. We compute in a self-consistent way the effects of relativistic Bremsstrahlung, inverse Compton scattering, synchrotron radiation, and pair-production/annihilation of leptons, as well as of hadronic interactions. Our goal is to determine the non-thermal broadband radiative output of the corona. The set of coupled kinetic equations for electrons, positrons, protons and photons are solved and the resulting particle distributions are computed self-consistently. We apply our model to Cygnus X-1 obtaining a good fit of the observational data.

In this contribution we discuss the dynamics of a twisted fully relativistic accretion disc around a slowly rotating black hole. At first, we outline the derivation of basic equations assuming that geometrical thickness of disc, inclination angle of its rings with respect to the black hole equatorial plane and rotation parameter of the black hole are small. Then, we analyse the shapes of the stationary twisted configurations for a particular case of the Novikov-Thorne model of the disc.

The conditional symmetries of the reduced Einstein–Hilbert action emerging from a static, spherically symmetric geometry are used as supplementary conditions on the wave function. Based on their integrability conditions, only one of the three existing symmetries can be consistently imposed, while the unique Casimir invariant, being the product of the remaining two symmetries, is calculated as the only possible second condition on the wave function. This quadratic integral of motion is identified with the reparametrization generator, as an implication of the uniqueness of the dynamical evolution, by fixing a suitable parametrization of the r-lapse function. In this parametrization, the determinant of the supermetric plays the role of the measure. The combined Wheeler–DeWitt and linear conditional symmetry equations are analytically solved. The solutions obtained depend on the product of the two “scale factors”.

We study orbits and accretion disks around Kerr black holes in f(R) gravity with constant curvature and compare the results of the emitted spectra with what is expected in General Relativity.

We investigate possible signatures of a Kerr naked singularity (superspinar) in the profiled spectral lines of radiation emitted by monochromatically and isotropically radiating point sources forming a Keplerian ring or disc around such compact object. We have found out that the profiled spectral line of the radiating Keplerian ring can be splitted into two parts due to the fact that there is no event horizon in the naked singularity spacetimes.

We obtain the absorption cross section of Reissner-Nordström black holes when the incident wave is purely gravitational. We verify the equality between Gravitational and Electromagnetic Absorption Cross Sections of Extreme Reissner-Nordström Black Holes.

We compute the proper time principal Lyapunov exponent(LE) for extremal Reissner Nordstrøm(RN) space-time which is precisely zero for the geodesics r₀ = r_c = M.

Kerr naked singularities (superspinars) have to be efficiently converted to a black hole due to accretion from Keplerian discs. In the final stages of the conversion process the near-extreme Kerr naked singularities (superspinars) provide a variety of extraordinary physical phenomena. Such superspinning Kerr geometries can serve as an efficient accelerator for extremely high-energy collisions enabling direct and clear demonstration of the outcomes of the collision processes. We shall discuss the efficiency and visibility of the ultra-high energy collisions in the deepest parts of the gravitational well of superspinning near-extreme Kerr geometries for the whole variety of particles freely falling from infinity. We demonstrate that the ultra high-energy processes can be obtained with no fine tuning of the motion constants and the products of the collision can escape to infinity with efficiency higher than in the case of the near-extreme black holes.

We study the scalar sector of the quasinormal modes of charged general relativistic, static and spherically symmetric black holes coupled to nonlinear electrodynamics and embedded in a class of scalar-tensor theories. It turns out that for certain values of the parameters unstable modes are present. This implies the existence of scalar-tensor black holes with primary hair that bifurcate from the embedded general relativistic black-hole solutions at critical values of the parameters corresponding to the static zero-modes. We prove that such scalar-tensor black holes really exist by solving the full system of scalartensor field equations for the static, spherically symmetric case. The obtained branches of hairy black holes are in one to one correspondence with the bounded states of the potential governing the linear perturbations of the scalar field. The stability of the new hairy black holes is also examined.

The following sections are included:

• Introduction
• Black holes, naked singularities, or what?
• Acknowledgments
• References

Bañados, Silk and West have indicated that Kerr black holes act as particle accelerators to arbitrarily high energy. In this context, we discuss the relevance of an ISCO particle around a nearly maximally rotating black hole. This implies that high-velocity collisions of compact objects are naturally expected around a rapidly rotating supermassive black hole. We also discuss that the particle acceleration would not be so sensitive to gravitational radiation reaction if the mass ratio of the inspiraling particle to the black hole is sufficiently small.

The extreme limit of the Kerr solution has recently attracted much attention, see and references therein. We have investigated hypersurfaces called velocity-of-light surfaces for extreme and near extreme Kerr.

We present an expression for the center-of-mass (CM) energy of two colliding general geodesic massive and massless particles around a Kerr black hole. We show that the CM energy can be arbitrarily high only in the limit to the horizon and then derive a formula for the CM energy of two general geodesic particles colliding near the horizon. To have an arbitrarily high CM energy, the angular momentum of either of the two particles must be fine-tuned to the critical value. We show that, in the direct collision scenario, the collision with an arbitrarily high CM energy can occur near the horizon of maximally rotating black holes not only at the equator but also on a belt centered at the equator. This belt lies between latitudes .

We analyze several approaches at obtaining a fluid interpretation for a fully dynamical solution of Einstein's equations describing an accreting (or evaporating) black hole in an expanding universe, using the generalized McVittie solution as a starting point. We show that a description in terms of multiple perfect fluids is severely constrained by consistency checks of the field equations. Extending the analysis to consider imperfect fluids alleviates some of these difficulties.

The entropy of the Schwarzschild-anti de Sitter black hole in the recently proposed four-dimensional critical gravity is trivial in the Euclidean action formulation, while it can be expressed by the area law in terms of the brick wall method given by 't Hooft. To resolve this discrepancy, we relate the Euclidean action formulation to the brick wall method semiclassically, and show that the entropy of the black hole can be expressed by the area law even at the critical point.

Previously we investigated classical motion of a string in (3+1)-dimensional spherically symmetric neutral and charged black holes. As an extension the solutions in (3+1)-dimensional axially symmetric rotating black hole are investigated. The solutions for the wiggly string exhibit open strings lying in the radial direction in the equatorial plane outside the horizon.

In this work we study linear fields on Kerr's spacetime, both in the region behind the Cauchy horizon of a black hole, and in the a² > M² naked singularity. The main result is the proof of existence of a family of axially symmetric unstable (i.e exponentially growing in time) modes satisfying appropriate spatial boundary conditions for all relevant linear fields: gravitational perturbations, electromagnetic fields, Weyl spinors and massless scalar fields. We then argue that these spacetimes are lineary unstable, and use this as an argument that favours the cosmic censorship hypotesis. We also give details related to the field reconstruction for the case of the electromagnetic perturbation, and study the behaviour of the unstable fields near the ring singularity.

Four decades after its first postulation by Bekenstein, black hole entropy remains mysterious. It has long been suggested that the entanglement entropy of quantum fields on the black hole gravitational background should represent at least an important contribution to the total Bekenstein-Hawking entropy, and that the divergences in the entanglement entropy should be absorbed in the renormalization of the gravitational couplings. In this talk, we describe how an improved understanding of black hole entropy is obtained by combining these notions with the renormalization group. By introducing an RG flow scale, we investigate whether the total entropy of the black hole can be partitioned in a “gravitational” part related to the flowing gravitational action, and a “quantum” part related to the unintegrated degrees of freedom. We describe the realization of this idea for free fields, and the complications and qualifications arising for interacting fields.

We review the Seiberg-Witten instability of topological black holes in Anti-de Sitter space due to nucleation of brane-anti-brane pairs. We start with black holes in general relativity, and then proceed to discuss the peculiar property of topological black holes in Hořava-Lifshitz gravity – they have instabilities that occur at only finite range of distance away from the horizon. This behavior is not unique to black holes in Hořava-Lifshitz theory, as it is also found in the relatively simple systems of charged black hole with dilaton hair that arise in low energy limit of string theory.

We investigate the four dimensional gravitational theories which admit homogeneous but anisotropic black brane solutions in asymptotically AdS spacetime. The gravitational theories we consider are 1) Einstein-Maxwell-dilaton theory, and 2) Einstein-Maxwelldilaton- axion theory with SL(2, Z) symmetry. We obtain the solutions both analytically and numerically. Our solutions approach singular behavior at the horizon in the extremal limit but in non-extremal case, they are smooth everywhere. We also discuss how the third law of thermodynamics holds in our set-up.

In the Einstein-dilaton theory, we find a Schwarzschild-type black hole solution, whose asymptotic geometry is described by the warped geometry and which is thermodynamically stable in some parameter range. Applying the gauge/gravity duality, we find that the dual theory corresponds to a relativistic non-conformal theory with the equation of state depending on the non-conformality.

We study a class of holographic superconductors dual to Einstein-Gauss-Bonnet AdS gravity coupled to nonlinear matter fields. We find an exact formula for the free energy of this system in any dimension and an approximate formula in terms of the thermodynamic quantities. We provide a simple method to select the couplings that admit charged black hole solutions in the bulk and have phase transitions on the boundary.

We consider a discrete model of a stretched horizon of the Schwarzschild black hole. Using our model it is possible to obtain an explicit, analytic expression for the partition function of the hole. Among other things, our partition function implies the Bekenstein-Hawking entropy law and provides a microscopic explanation to the Hawking effect.

We give a detailed treatment of the back-reaction effects on the Hawking spectrum in the semiclassical approach to the Hawking radiation. We solve the exact system of non linear equations giving the action of the system, by a rigorously convergent iterative procedure. The first two terms of such an expansion give the O(ω/M) correction to the Hawking spectrum.

We observe the past and present of the universe, but can we predict the far future? Observations suggest that in thousands of billions of years from now most matter and radiation will be absorbed by the cosmological horizon. As it absorbs the contents of the universe, the cosmological horizon is pushed further and further away. In time, the universe asymptotes towards an equilibrium state of the gravitational field. Flat Minkowski space is the limit of this process. It is indistinguishable from a space with an extremely small cosmological constant (Λ → 0) and thus has divergent entropy.

These are promising times for the study of cosmic microwave background and foregrounds. While, at the date of this meeting, WMAP is close to release its final maps and products, Planck early and intermediate results have been presented with the first release of the compact source catalog, and the presentation of the first cosmological products is approaching. This parallel session is focussed on the astrophysical sky as seen by Planck and other observatories, and on their scientific exploitation, regarding diffuse emissions, sources, galaxy clusters, cosmic infrared background, as well as on critical issues coming from systematic effects and data analysis, in the view of fundamental physics and cosmology perspectives. At the same time, a new generation of CMB anisotropy and polarization experiments is currently operated using large arrays of detectors, boosting the sensitivity and resolution of the surveys to unprecedented levels. Mainstream projects are observations of the polarization of the CMB, looking for the inflationary B-modes at large and intermediate angular scales, fine-scale measurements of the Sunyaev-Zel'dovich effect in clusters of galaxies, and the precise measure of CMB spectrum.

This contribution reviews the most difficult observational aspect of Zodiacal Light Emission (ZLE) in CMB missions below 1 THz: its separability from the background. We compare the background subtraction based on the use of priors and on differential methods exploiting signal time dependence. We illustrate the impact of systematics such as the straylight. Finally, we address the problem of differences in the ZLE geometrical properties possibly relevant at these frequencies.

Planck is the most sensitive space mission to date dedicated to accurate measurements of the Cosmic Microwave Background. Its μK sensitivity calls for a comparable level of control of systematic effects, that represents the primary challenge to fully extract the wealth of scientific information encoded in the data. Planck has been designed and built to ensure, as much as possible, “in-hardware” rejection to spurious signals. Residual effects, however, need to be detected in the data and removed during data processing. In this talk we present a review of the main systematic effects in Planck, and of the design solutions adopted in the satellite and instruments to keep them under control. We then discuss the impact of the residual effects after data processing on the main scientific products.

In this review we discuss some of the most relevant results obtained by recent surveys of extragalactic sources at millimeter and sub–mm wavelengths emphasizing some of the main results achieved by the Planck satellite during the first 1.6 full-sky surveys. Bright extragalactic point sources (EPS) – i.e., nearby or distant galaxies – observed in this frequency range can be classified into two main source classes: a) radio sources, i.e., sources with emission dominated by non-thermal synchrotron radiation, at intermediate to high–redshift; b) far–infrared sources, i.e. nearby dusty galaxies with a spectrum dominated by thermal dust emission, typically at very low redshift. Planck's number counts of EPS at LFI frequencies are found in agreement with Wilkinson Microwave Anisotropy Probe (WMAP) counts. However, a clear steepening of the mean spectral index of bright radio sources is observed above 70 GHz, that has recently been interpreted in terms of a “break” frequency in the spectra of sources, in agreement with standard models of synchrotron emission in jets of compact radio sources. For nearby dusty galaxies, current observations find evidence of colder dust, with T < 20 K, than has previously been found. Moreover, the number counts and the local luminosity function (l.l.f.) of bright local dusty galaxies have been measured, for the first time, at sub–millimetre wavelengths by exploiting the new and unique data published in the Planck Early Release Compact Source Catalogue (ERCSC).

The expected sensitivity of cluster SZ number counts to neutrino mass in the sub-eV range is assessed. We find that from the ongoing Planck/SZ measurements the (total) neutrino mass can be determined at a (1σ) precision of 0.06 eV, if the mass is in the range 0.1 – 0.3 eV, and the survey detection limit is set at the 5σ significance level. The mass uncertainty is predicted to be lower by a factor ˜ 2/3, if a similar survey is conducted by a cosmic-variance-limited experiment, a level comparable to that projected if CMB lensing extraction is accomplished with the same experiment. At present, the main uncertainty in modeling cluster statistical measures reflects the difficulty in determining the mass function at the high-mass end.

Silk damping in the early Universe, before and during recombination, erases anisotropies in the cosmic microwave background (CMB) on small scales. This power, which disappears from anisotropies, appears in the monopole as y-type, i-type and μ-type distortions. The observation of the CMB spectral distortions will thus make available to us the information about the primordial power spectrum on scales corresponding to the comoving wavenumbers 8 ≲ k ≲ 10⁴ Mpc⁻¹ increasing our total view of inflation, when combined with CMB anisotropies, to span 17 e-folds. These distortions can be understood simply as mixing of blackbodies of different temperatures and the subsequent comptonization of the resulting distortions.