The Tenth Marcel Grossmann Meeting

PUBLICATIONS IN THIS SERIES AND SPONSORS.

ORGANIZING COMMITTEES.

MARCEL GROSSMANN AWARDS.

PREFACE.

INAUGURAL ADDRESS.

The initial value problem is introduced after a thorough review of the essential geometry. The initial value equations are put into elliptic form using both conformal transformations and a treatment of the extrinsic curvature introduced recently. This use of the metric and the extrinsic curvature is manifestly equivalent to the author’s conformal thin sandwich formulation. Therefore, the reformulation of the constraints as an elliptic system by use of conformal techniques is complete.

No abstract received.

We show that the cosmological constant may be reduced by thermal production of membranes by the cosmological horizon, analogous to a particle going over the top of the potential barrier, rather than tunneling through it. The membranes are endowed with charge associated with the gauge invariance of an antisymmetric gauge potential. In this new process, the membrane collapses into a black hole, thus the net effect is to produce black holes out of the vacuum energy associated with the cosmological constant. We study here the corresponding Euclidean configurations (thermalons), and calculate the probability for the process in the leading semiclassical approximation.

We investigate quasi-spherical Szekeres models, including the anisotropic generalisation of the Lemaitre-Tolman wormhole topology. We: (a) derive the conditions for physically reasonable models, including a regular origin, maxima and minima, and the absence of shell-crossings; (b) obtain the relations between the local mass dipole, apparent horizon, light propagation rate, and shell crossings; (c) show non-zero dipole requires non-zero density, and cannot compensate for the effects of non-vacuum in any direction, so communication through the neck is still worse than the vacuum case; (d) show that a handle topology cannot be created by identifying hypersurfaces on either side of a wormhole, unless a surface layer is allowed. This impossibility includes the vacuum (Schwarzschild-Kruskal-Szekeres) case.

Galactic dark matter is modelled by a scalar field in order to effectively modify Kepler’s law without changing standard Newtonian gravity. In particular, a solvable toy model with a self-interaction U(Φ) borrowed from non-topological solitons produces already qualitatively correct rotation curves and scaling relations. Although relativistic effects in the halo are very small, we indicate corrections arising from the general relativistic formulation. Thereby, we can also probe the weak gravitational lensing of our soliton type halo. For cold scalar fields, it corresponds to a gravitationally confined Boson-Einstein condensate, but of galactic dimensions.

The Geroch, Hansen and Simon multipole moments for stationary gravitational fields are reviewed and their relationship with the gravitational potentials discussed. Algorithms for computing these moments from the gravitational potential of axially symmetric space-times are presented. The question is considered to what extent the causal behavior of asymptotically flat space-times can be characterized in terms of moments.

The electromagnetic structure of the stationary axisymmetric force-free magnetosphere around a black hole is characterized by the stream function Ψ, the current potential I, and the angular velocity of the magnetic field lines Ω_F. These functions are governed by the ‘stream equation’. Possible solutions of the ‘stream equation’ are studied in this work. Starting from some solutions known in the limit of vanishing Ω_F and I, we investigate modifications of these solutions which can lead to solutions in the general case of nonzero Ω_F and I. Assuming small values of Ω_F and I, we solve the ‘stream equation’ perturbatively to obtain asymptotic forms of such solutions in the large-r region in one case and in the region near the event horizon in another.

The evolution equations of the Lemaître-Tolman (LT) model are reformulated in such a way that the distributions of matter density ρ_i or matter velocity υ_i at two different times t_i, i = 1, 2 are the input data (any two of the four quantities uniquely determine an LT model). This formulation is better suited to observational practice in cosmology. Then, numerical examples of the LT models are constructed that evolve between a certain density or velocity distribution at t₁ = last scattering epoch and a model of a modern structure at t₂ = the present time. The amplitude of the inhomogeneity at t₁ is kept within the limits implied by observations, and the final modern structures are galaxy clusters, voids or galaxies with a central black hole. Among other things, it is shown that the initial velocity distribution plays an essential role in the formation of structures, the density distribution alone does not even determine whether the final structure will be a void or a condensation.

I describe different approaches in which string theory attempts to reproduce the structure of the Standard Model of Particle Physics, with an emphasis on recent constructions of brane world models (where the gauge sector is localized on a subspace of spacetime, while gravity propagates over all of spacetime) using D-branes.

We discuss recent developments and insights concerning open string theory tachyons and unstable D-branes. We begin with a brief introduction where we explain what tachyons are and how they are studied in string field theory. We discuss stable and unstable D-branes, and then turn to the Sen conjectures in tachyon condensation. Finally we discuss rolling tachyons and the endpoint of the dynamical process of tachyon condensation.

No abstract received.

After reviewing the Green-Schwarz superstring, the superstring is covariantly quantized by constructing a BRST operator from the fermionic constraints and a bosonic pure spinor ghost variable. Physical massless vertex operators are constructed and, for the first time, N-point tree amplitudes are computed in a manifestly ten-dimensional super-Poincaré covariant manner.

In this paper we calculate the emission of gravity waves by the binary pulsar in the framework of five dimensional braneworlds. We consider only braneworlds with one compact extra-dimension. We show that the presence of additional degrees of freedom, especially the ‘gravi-scalar’ leads to a modification of Einstein’s quadrupole formula. We compute the induced change for the binary pulsar PSR 1913+16 in the simple example of a 5d Minkowski background. It amounts to about 20% which is by far excluded by present experimental data.

Vector perturbations induced on the brane by gravitational waves propagating in the bulk are studied in a cosmological framework. Cosmic expansion arises from the brane motion in a non-compact Z₂ symmetric five-dimensional anti-de Sitter space-time. By solving the vector perturbation equations in the bulk, for generic initial conditions, we find that they give rise to growing modes on the brane in the Friedmann-Lemaître era. Among these modes, we exhibit a class of normalizable perturbations, which are exponentially growing with respect to conformal time on the brane. The presence of these modes is strongly constrained by the homogeneity and isotropy of the observable Universe.

I give a brief overview of some Quantum-Gravity-Phenomenology research lines, focusing on studies of cosmic rays and gamma-ray bursts that concern the fate of Lorentz symmetry in quantum spacetime. I also stress that the most valuable phenomenological analyses should not mix too many conjectured new features of quantum spacetime, and from this perspective it appears that it should be difficult to obtain reliable guidance on the quantum-gravity problem from the analysis of synchrotron radiation from the Crab nebula and from the analysis of phase coherence of light from extragalactic sources. Forthcoming observatories of ultra-high-energy neutrinos should provide several opportunities for clean tests of some simple hypothesis for the short-distance structure of spacetime. In particular, these neutrino studies, and some related cosmic-ray studies, should provide access to the regime .

Affine quantum gravity is based on a 3+1 split of spacetime in Einstein’s theory, and gets its name from its use of affine commutation relations. Unlike canonical commutation relations, affine commutation relations involve self-adjoint kinematical field operators that preserve strict positivity of the 3 × 3 metric tensor. Gravitational physics enters through constraints, and because the quantum version of gravitational constraints are partially second class, we use the projection operator method to enforce them since this method treats all kinds of constraints on an equal basis. Enforcing the constraints fully requires fine tuning of the basic operator representation along with a proper choice of any counterterms. When perturbatively nonrenormalizable theories are understood as due to hard-core interactions, it is recognized that traditional counterterms are generally incorrect and are to be replaced by alternative counterterms. To assist in this program, functional methods such as coherent states and functional integrals with continuous-time regularization provide an especially useful framework for analysis.

From a functional integral viewpoint, it is characteristic of nonrenormalizable quantum theories that the nonlinear interaction is sufficiently singular that it forbids certain field histories that would otherwise be allowed by the noninteracting theory alone. Since such forbidden field histories are projected out of the functional integral no matter how small the coupling constant – exactly like a hard-core potential would behave – the interacting theory is not even continuously connected to the noninteracting theory as the coupling constant vanishes. Although, regularization and expansion of the interaction in a perturbation series is invariably inappropriate, alternative procedures have been difficult to formulate. Recent schemes for dealing with quartically coupled scalar fields in spacetime dimensions greater than four are presented, and arguments are even given to indicate that they may also be used to overcome triviality in four spacetime dimensions. Possible implications for quantum gravity are also mentioned.

Research on the very early Universe has gradually been benefiting from an attractive line of investigation: Supersymmetric Quantum Cosmology. The essential feature is that supersymmetry is explicitly present. In this review we will analyse some of the consequences of explicitly including supersymmetry in a quantum cosmological scenario.

The software tool GRworkbench is an ongoing project in visual, numerical General Relativity at The Australian National University. Recently, GRworkbench has been significantly extended to facilitate numerical experimentation in analytically-defined space-times. The numerical differential geometric engine has been rewritten using functional programming techniques, enabling objects which are normally defined as functions in the formalism of differential geometry and General Relativity to be directly represented as function variables in the C++ code of GRworkbench. The new functional differential geometric engine allows for more accurate and efficient visualisation of objects in space-times and makes new, efficient computational techniques available. Motivated by the desire to investigate a recent scientific claim using GRworkbench, new tools for numerical experimentation have been implemented, allowing for the simulation of complex physical situations.

The prospect of variations in the constants of nature is re-examined. We first review the constraints from terrestrial, astrophysical and cosmological observations and experiments on variations in the electromagnetic fine-structure constant, α, and the gravitational constant, G. The relevant constraints from tests of the weak equivalence principle and related quantities such as the electron-proton mass ratio are also listed. Finally we briefly review theoretical motivations for α variations from fundamental and phenomenological models.

The effort to detect gravitational waves has increased steadily in recent years. More than 20 major projects in gravitational wave detection are underway around the world. They span the spectrum from below 10^-16 Hz to above 10⁴ Hz. Detectors can be divided into two categories: those that use resonant masses and those that use electromagnetic beams. For electromagnetic beams the approaches vary according to the frequency band. In the microhertz band the timing of pulsar signals offers the possibility of detecting the coalescence of massive black holes during galactic mergers. In the millihertz band numerous galactic binary star sources plus extragalactic mergers should be detectable using space laser interferometry. Smaller scale space laser techniques could also be used in the band around 1Hz. In the audiofrequency band terrestrial laser interferometers should detect signals associated with stellar mass compact objects, particularly neutron star births and coalescences. Resonant mass detectors in the form of bars and spheres offer high sensitivity in the 1-10kHz range. This article presents an overview of the field emphasising the present experimental efforts and the future projects which will make gravitational wave astronomy a reality.

Coincident events were searched for between the gravitational wave (g.w.) detectors EXPLORER and NAUTILUS during the years 1998 and 2001. Excess coincidences were found when the detectors were favorably oriented with respect to the Galactic Disk.

The LIGO interferometers are operating as gravitational wave observatories, with a noise level near an order of magnitude of the goal and the first scientific data recently taken. This data has been analyzed for four different categories of gravitational wave sources; millisecond bursts, inspiralling binary neutron stars, periodic waves from a known pulsar, and stochastic background. Research and development is also underway for the next generation LIGO detector, Advanced LIGO.

An introduction into the fundamental quests addressed in space missions is given. These quests are the exploration of the relativistic gravitational field, the Universality of Free Fall, the Universality of the Gravitational Redshift, Local Lorentz Invariance, the validity of Einstein’s field equations, etc. In each case, the corresponding missions take advantage of the space conditions which are essential for the improvement of the accuracy of the experiments as compared to experiments on ground. A list and a short description of past, current and planned projects is given. Also the key technologies employed in space missions are described.

Our knowledge of Gamma-Ray Burst (GRB) progenitors is based on three cases at relatively low redshift (between 0.01 and 0.2) in which the association with a supernova (SN) has been firmly established. In a number of higher redshift GRBs the presence of a SN has been suggested, although the properties of the SN could not be precisely determined. However, the study of several tens of multiwavelength afterglows has now provided evidence that GRBs are associated with star formation. The observational results which point to this connection are reviewed, and the high energy properties of afterglows and SNe are compared.

We outline the confluence of three novel theoretical fields in our modeling of Gamma-Ray Bursts (GRBs): 1) the ultrarelativistic regime of a shock front expanding with a Lorentz gamma factor ~ 300; 2) the quantum vacuum polarization process leading to an electron-positron plasma originating the shock front; and 3) the general relativistic process of energy extraction from a black hole originating the vacuum polarization process. There are two different classes of GRBs: the long GRBs and the short GRBs. We here address the issue of the long GRBs. The theoretical understanding of the long GRBs has led to the detailed description of their luminosities in fixed energy bands, of their spectral features and made also possible to probe the astrophysical scenario in which they originate. We are specially interested, in this report, to a subclass of long GRBs which appear to be accompanied by a supernova explosion. We are considering two specific examples: GRB980425/SN1998bw and GRB030329/SN2003dh. While these supernovae appear to have a standard energetics of 10⁴⁹ ergs, the GRBs are highly variable and can have energetics 10⁴ − 10⁵ times larger than the ones of the supernovae. Moreover, many long GRBs occurs without the presence of a supernova. It is concluded that in no way a GRB can originate from a supernova. The precise theoretical understanding of the GRB luminosity we present evidence, in both these systems, the existence of an independent component in the X-ray emission, usually interpreted in the current literature as part of the GRB afterglow. This component has been observed by Chandra and XMM to have a strong decay on scale of months. We have named here these two sources respectively URCA-1 and URCA-2, in honor of the work that George Gamow and Mario Shoenberg did in 1939 in this town of Urca identifying the basic mechanism, the Urca processes, leading to the process of gravitational collapse and the formation of a neutron star and a supernova. The further hypothesis is considered to relate this X-ray source to a neutron star, newly born in the Supernova. This hypothesis should be submitted to further theoretical and observational investigation. Some theoretical developments to clarify the astrophysical origin of this new scenario are outlined.

The cosmic reionization era, which includes formation of the first stars, galaxies, and AGN, is now one of the most active frontiers of cosmological research. We review briefly our current understanding of the early structure formation, and use the ideas about a joint formation of massive black holes (which power the early QSOs) and their host galaxies to employ high-redshift QSOs as probes of the early galaxy formation and primordial large-scale structure. There is a growing evidence for a strong biasing in the formation of the first luminous sources, which would lead to a clumpy reionization. Absorption spectroscopy of QSOs at z ≥ 6 indicates the end of the reionization era at z ~ 6; yet measurements from the WMAP satellite suggest and early reionization at z ~ 10 − 20. The first generation of massive stars, perhaps aided by the early mini-quasars, may have reionized the universe at such high redshifts, but their feedback may have disrupted the subsequent star and galaxy formation, leading to an extended and perhaps multimodal reionization history ending by z ~ 6. Observations of γ-ray bursts from the death events of these putative Population III stars may provide essential insight into the primordial structure formation, reionization, early chemical enrichment, and formation of seed black holes which may grow to become central engines of luminous quasars.

Absorption and reprocessing of Gamma-ray burst radiation in the environment of cosmological GRBs can be used as a powerful probe of the elusive nature of their progenitors. Although it is widely accepted that long-duration GRBs are associated with the deaths of massive stars, at least two fundamentally different scenarios concerning the final collapse are currently being considered. Delayed reddened excesses in the optical afterglows of several GRBs indicate that a supernova, possibly of Type Ic, takes place within a few days of a GRB. This supports the collapsar model, where the core of a massive star collapses promptly to a black hole. Variable X-ray features observed in the prompt and afterglow spectra of several GRBs, suggest that a highly metal enriched and dense shell of material surrounds the sources of GRBs. In some cases, evidence for expansion of these shells with velocities of a substantial fraction of the speed of light has been claimed. These observations have been interpreted as support for the supranova model, where a massive star collapses first to a supramassive neutron star, which later collapses to a black hole following loss of rotational support. In this review paper, I will present a brief overview of the current status of the observational evidence for X-ray spectral features in GRBs, and discuss their implications for both the collapsar and the supranova model.

This rapporteur review summarizes results presented in Parallel Session GBT2 (Gamma Ray Burst Theory 2) on the Collapsar and Supranova Models held 25 July 2003 at the 10th Marcel Grossmann Meeting on General Relativity, Rio de Janeiro, Brazil. A central issue in GRB studies is the process whereby energy is released from the GRB engine. One scenario is the collapsar model, where the evolved stellar core promptly collapses to a black hole surrounded by a massive, intermittently-accreting torus of nuclear density material. A second scenario is the supranova model, where the first step of a two-step collapse process leaves behind a rapidly rotating neutron star stabilized by rotation, which later collapses to a black hole while making the GRB. In the supranova model, a powerful pulsar wind lasting days to weeks after the supernova makes distinctive signatures from the heating of the supernova remnant (SNR) shell, which should be discovered with Swift. This model also predicts nonstandard reddened excesses from the cooling SNR due to the range of delays between the two collapse events, contrary to observations of SN emissions from low redshift GRBs which favor the collapsar model. The observational basis for both models is critically reviewed. Problems of the collapsar/internal shock scenario powered by the Blandford-Znajek process, and a two-collapse supranova scenario powered by the B-Z process or the Penrose mechanism, or even Ruffini’s pair electromagnetic pulse, are briefly discussed. In view of the standard γ-ray energy upper limit, an external shock model involving jetted relativistic ejecta powered by an explosive event provides the most consistent explanation for GRB observations. An outline of a GRB model is proposed where the second collapse takes place within minutes to hours after the primary SN event, during which time loss of centrifugal support along the rotation axis of the neutron star provides a relatively baryon-clean polar environment along which a newly formed, rapidly spinning black hole drives collimated baryon-dilute outflows.

Recent studies have shown that strong correlations are observed between the low frequencies (1–10 Hz) of quasiperiodic oscillations (QPOs) and the spectral power law index of several Black Hole (BH) candidate sources, in low hard state, steep power-law (soft) state and in transition between these states. The observations indicate that the X-ray spectrum of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission indicated the probable presence of a jet. Strong QPOs (> 20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant (i.e. 60–90%). This evidence contradicts the dominant long standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model, that identifies and explains the origin of the QPOs and how they are imprinted on the properties of power-law flux component. We argue the existence of a bounded compact coronal region which is a natural consequence of the adjustment of Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) hard state, in which the TL is optically thin and very hot (kT ≳ 50 keV) producing photon upscattering via thermal Componization; the photon spectrum index Γ ~ 1.7 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius; (2) a soft state which is optically thick and relatively cold (kT ≲ 5 keV); the index for this state, Γ ~ 2.8 is determined by soft-photon upscattering and photon trapping in converging flow into BH. In the TL model for corona the QPO frequency ν_high is related to the gravitational (close to Keplerian) frequency ν_K at the outer (adjustment) radius and ν_low is related to the TL’s normal mode (magnetoacoustic) oscillation frequency ν_MA. The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

I review the current knowledge of high-energy emission from extragalctic jets. First I discuss γ-ray emission from blazars, which provides us numerous precious information on the innermost portions of the relativistic jets. I describe the constraints on the dynamics of the jet from the subpc to the pc scale provided by recent VLBI studies of TeV sources, together with the modelling of the emission from the blazar jet. Finally I discuss high energy emission from large scale jets as seen by Chandra and I report on the expected gamma-ray emission from large-scale regions of jets.

Evidence is mounting that some Ultra-luminous X-ray sources (ULXs) may contain accreting intermediate-mass black holes (IMBHs). We review the current observational evidence for IMBH-ULXs. While low-luminosity ULXs with L_X ≲ 10^39.5 erg s^-1 (assuming isotropic emission) are consistent with mildly X-ray beamed high-mass X-ray binaries, there are a considerable number of ULXs with larger X-ray luminosities that are not easily explained by these models. Recent high-S/N XMM X-ray spectra are showing an increasing number of ULXs with “cool disks” – accretion disks with multicolor blackbody inner disk temperatures kT_in ~ 0.1–0.2 keV, consistent with accreting IMBHs. Optical emission-line studies of ULX nebulae provide useful measurements of X-ray energetics, and can thus determine if the X-rays are emitted isotropically. Analysis of an optical spectrum of the Ho II ULX nebulae implies an X-ray energy source with ~10⁴⁰ erg s^-1 is present, suggesting an isotropically-emitting IMBH. The spatial coincidence of ULXs with dense star clusters (young clusters and globular clusters) suggests that IMBHS formed in these clusters could be the compact objects in the associated ULXs. Quasi-periodic oscillations and frequency breaks in XMM power-density spectra of ULXs also suggest that the black hole masses are more consistent with IMBHs than stellar-mass black holes. Since all of these ULXs with evidence for IMBHs are high-luminosity ULXs, i.e., L_X ≳ 10⁴⁰ erg s^-1, we suggest that this class of ULXs is generally powered by accreting IMBHs.

We show that the rapid formation of super-massive black holes in quasars can indeed be understood in terms of major galaxy mergers followed by disk accretion. The necessary short disk evolution time can be achieved provided the disk viscosity is sufficiently large, which, for instance, is the case for hydrodynamic turbulence, unlimited by shock dissipation. We present numerical calculations for a representative case. This general picture can account for (a) the presence of highly luminous quasars at redshifts z > 6; (b) for the peak in quasar activity at z ~ 2; and (c) for a subsequent rapid disappearance of quasars at later epochs.

We discuss how disk models may limit the scope of identifying astrophysical black holes. We show that the standard Keplerian thin disk model, the thick disk model, slim disks, ADAFs etc. are fundamentally limited. We present the most complete solution to date called the advective accretion disk and discuss how it has the scope to address every observational aspects of a black hole. Though the magnetic field is not fully self-consistently taken care of yet, the details with which the present model can handle various issues successfully are astounding. We present some of the examples.

We generate the 2-dimensional high-resolution density field of galaxies of the Early Data Release of the Sloan Digital Sky Survey and the Las Campanas Redshift Survey with a smoothing length 0.8 h^-1 Mpc to extract clusters and groups of galaxies, and a low-resolution field with a smoothing length 10 h^-1 Mpc to extract superclusters of galaxies. We investigate properties of density field clusters and superclusters and compare the properties of these clusters and superclusters with those of Abell clusters, and superclusters found on the basis of Abell clusters. We found that clusters in a high-density environment have a luminosity a factor of 5 – 10 higher than in a low-density environment. Clusters and superclusters in the Northern slice of SDSS are much richer than those in the Southern slice.

The evidences in favor of neutrino oscillations are reviewed and shown to be explained by the most simple and natural scheme of mixing of three massive neutrinos. The connections with tritium β-decay experiments, cosmological measurements of neutrino masses and neutrinoless double-β decay are discussed.

I review the progress made in the physics and astrophysics of black hole jet systems of all masses. The observations of stellar black hole jet sources (microquasars) provide clues to gain insight into Special Relativity effects in the jets, and strong field General Relativity phenomena, such as the quasi-periodic oscillations in the radiated power, and the redshifted iron lines produced close the horizon. Besides, microquasars provide clues on Astrophysical issues such as the accretion-jet connection, collapsars and black hole formation, the black hole spin, and a diversity of high energy astrophysical phenomena.

In the past, they were recognized as the most destructive force in nature. Now, following a cascade of astonishing discoveries, supermassive black holes have undergone a dramatic shift in paradigm—these objects may have been critical to the formation of structure in the early universe, spawning bursts of star formation and planets. As many as 300 million of them may now be lurking through the vast expanses of the observable cosmos. The most accessible among them appears to be lurking at the center of our own Galaxy. In this review, we will examine the evidence that has brought us to this point, and we will see why the astrophysical community is now looking with great anticipation to the imminent breakthroughs that will permit us to see the shadow of a black hole within this decade.

This talk reviews the constraints imposed by binary-pulsar data on gravity theories, focusing on “tensor-scalar” ones which are the best motivated alternatives to general relativity. We recall that binary-pulsar tests are qualitatively different from solar-system experiments, because of nonperturbative strong-field effects which can occur in compact objects like neutron stars, and because one can observe the effect of gravitational radiation damping. Some theories which are strictly indistinguishable from general relativity in the solar system are ruled out by binary-pulsar observations. During the last months, several impressive new experimental data have been published. Today, the most constraining binary pulsar is no longer the celebrated (Hulse-Taylor) PSR B1913+16, but the neutron star-white dwarf system PSR J1141−6545. In particular, in a region of the “theory space”, solar-system tests were known to give the tightest constraints; PSR J1141−6545 is now almost as powerful. We also comment on the possible scalar-field effects for the detection of gravitational waves with future interferometers. The presence of a scalar partner to the graviton might be detectable with the LISA space experiment, but we already know that it would have a negligible effect for LIGO and VIRGO, so that the general relativistic wave templates can be used securely for these ground interferometers.

The nature and the location of the lenses discovered in the microlensing surveys done so far towards the LMC remain unclear. Motivated by these questions we computed the optical depth for the different intervening populations and the number of expected events for self-lensing, using a recently drawn coherent picture of the geometrical structure and dynamics of the LMC. By comparing the theoretical quantities with the values of the observed events it is possible to put some constraints on the location and the nature of the MACHOs. Clearly, given the large uncertainties and the few events at disposal it is not yet possible to draw sharp conclusions, nevertheless we find that up to 3-4 MACHO events might be due to lenses in LMC, which are most probably low mass stars, but that hardly all events can be due to self-lensing. The most plausible solution is that the events observed so far are due to lenses belonging to different intervening populations: low mass stars in the LMC, in the thick disk, in the spheroid and some true MACHOs in the halo of the Milky Way and the LMC itself. We report also on recent results of the SLOTT-AGAPE and POINT-AGAPE collaborations on a search for microlensing events in direction of the Andromeda galaxy, by using the pixel method. The detection of 4 microlensing events, some likely to be due to self-lensing, is discussed. One microlensing light curve is shown to be compatible with a binary lens. The present analysis still does not allow us to draw conclusions on the MACHO content of the M31 galaxy.

The EROS-II microlensing survey has been operated for 7 years from the ESO La Silla Observatory (Chile). Observations ended on 2003, February 28th. Its main purpose was the search for gravitational microlensing amplification of magellanic stars induced by baryonic compact objects (MACHOs). Other topics were however covered, such as microlensing searches toward the galactic center and plane, nearby high proper motion halo dwarf stars, supernovæ and variable stars. In this review we will present a summary of the microlensing results achieved up to now, and propects for the completion of these analysis.

This rapporteur review covers selected results presented in the Parallel Session HEA2 (High Energy Astrophysics 2) of the 10th Marcel Grossmann Meeting on General Relativity, held in Rio de Janeiro, Brazil, July 2003. The subtopics are: ultra high energy cosmic ray anisotropies, the possible connection of these energetic particles with powerful gamma ray bursts, and new exciting scenarios with a strong neutrino-nucleon interaction in the atmosphere.

The present status of anisotropy studies for the highest energy cosmic rays is presented including the first full sky survey. Directions and prospects for the future are also discussed in light of new statistical methods and the last quantities of data expected in the near future from the Pierre Auger Observatory.

After a short review of the ultrahigh energy cosmic ray puzzle – the apparent observation of cosmic rays originating from cosmological distances with energies above the expected Greisen-Zatsepin-Kuzmin cutoff 4 × 10¹⁹ eV – we consider strongly interacting neutrino scenarios as an especially interesting solution. We show that all features of the ultrahigh energy cosmic ray spectrum from 10¹⁷ eV to 10²¹ eV can be described to originate from a simple power-like injection spectrum of protons, under the assumption that the neutrino-nucleon cross-section is significantly enhanced at center of mass energies above ≈ 100 TeV. In such a scenario, the cosmogenic neutrinos produced during the propagation of protons through the cosmic microwave background initiate air showers in the atmosphere, just as the protons. The total air shower spectrum induced by protons and neutrinos shows excellent agreement with the observations. We shortly discuss TeV-scale extensions of the Standard Model which may lead to a realization of a strongly interacting neutrino scenario. We emphasize, however, that such a scenario may even be realized within the standard electroweak model: electroweak instanton/sphaleron induced processes may get strong at ultrahigh energies. Possible tests of strongly interacting neutrino scenarios range from observations at cosmic ray facilities and neutrino telescopes to searches at lepton nucleon scattering experiments.

We use Clebsch potentials and an action principle to derive a complete closed system of gauge invariant equations for sound superposed on a general background flow ¹. Our system reduces to the Unruh (1981) and Pierce (1990) wave equations when the flow is irrotational, or slowly varying.

We investigate the stability of a spatially homogeneous and isotropic non-singular cosmological model. We show that the complete set of independent perturbations (the electric part of the perturbed Weyl tensor and the perturbed shear) are regular and well behaved functions which have no divergences, contrary to previous claims in the literature.

In the past few years, there has been an increasing interest on bouncing cosmological models. In this contribution, I first describe the conditions for the occurrence of bounces in the far past of the Standard Cosmological Model. I enumerate the matter models and theories containing General Relativity in which these conditions can be fulfilled. Then, I describe the evolution of cosmological perturbations in such bouncing models, I discuss how a scale invariant spectrum of perturbations can be obtained in this framework, and whether it is possible to verify observationally if our Universe has ever experienced a bounce. Finally, I make a critical comparison between bouncing and usual inflationary models.

In the late eighties the European Southern observatory embarked on the VLT project. Four eight-metre class telescopes to be built in the Chilean Atacama desert and to be operated both as stand-alone instruments and in combined interferometric mode. The selected site was Cerro Paranal. Construction in earnest started in the early nineties and the first 8.2-m telescope had first light in May of 1998. Since the middle of 2001 all four telescopes have been operating with high efficiency and impressive scientific output. The interferometric mode is also operational and additional auxiliary telescopes that improve the UV-plane coverage are arriving at the observatory. In this article the capabilities of the observatory are described and some of the more exciting scientific results reviewed. The next generation extremely large telescope project is presented.

We report on preliminary results of IBIS/ISGRI observations of Compact Galactic Sources in the Cygnus Region during the INTEGRAL Performance and Verification (PV) phase in November and December 2002. The main target of the PV phase was the Black Hole binary Cyg X-1 and the total observing time was ~ two million of seconds but other well known hard X-ray sources were in the instrument field of view. We will focus on the 3 brightest sources: Cyg X-1, the microquasar Cyg X-3 and the transient X-ray pulsar EXO 2030+375. During the observing period Cyg X-1 was in its characteristic low/hard state, in which a few flares and dips were observed. No state changes were observed, but spectral variations associated with flares were clearly detected. During staring observations of Cyg X-1, the peculiar microquasar Cyg X-3 was at a ~ 9° distance from the pointing direction. From these observations we obtained two light curve in the 20-40 keV and 40-100 keV energy band which exhibits the characteristic 4.8-hour modulation with a shape consistent with a standard template. The two light curves' phase zero have no measurable offset and their values are consistent with historical ephemeris. Finally from 9 to 21 December 2002 IBIS/ISGRI detected one periodic outburst of the transient X-ray pulsar EXO 2030+375. The outburst light curve and spectral shape are consistent with already published results. The IBIS/ISGRI results demonstrate that the INTEGRAL observatory offers a unique capability for studying temporal and spectral behavior of several bright sources in the FOV.

We review the essential features of the Chaplygin gas cosmological models and provide some examples of appearance of the Chaplygin gas equation of state in modern physics. A possible theoretical basis for the Chaplygin gas in cosmology is discussed. The relation with scalar field and tachyon cosmological models is also considered.

The discovery of a supernova emerging at late times in the afterglow of GRB 030329 has apparently settled the issue on the nature of the progenitor of gamma-ray bursts. We now know that at least a fraction of cosmological GRBs are associated with the death of massive stars, and that the two explosions are most likely simultaneous. Even though the association was already suggested for GRB 980425, the peculiarity of that burst did not allow to extend the association to all GRBs. The issue is now to understand whether GRB 030329 is a “standard burst” or not. I will discuss some peculiarities of GRB 030329 and its afterglow lightcurve showing how, rather than a classical cosmological GRB, it looks more like a transition object linking weak events like GRB 980425 to the classical long duration GRBs. I will also discuss the problems faced by the Hypernova scenario to account for the X-ray features detected in several GRBs and their afterglows.

Multidimensional cosmological models with factorizable geometry and their dimensional reduction to effective four-dimensional theories are analyzed on sensitivity to different scalings. It is shown that a non-correct gauging of the effective four-dimensional gravitational constant within the dimensional reduction results in a non-correct rescaling of the cosmological constant and the gravexciton/radion masses. The relationship between the effective gravitational constants of theories with different dimensions is discussed for setups where the lower dimensional theory results via dimensional reduction from the higher dimensional one and where the compactified space components vary dynamically.

The rapporteur summary is presented by reviewing the contributions at the APT5 parallel session on radiative transfer in relativistic astrophysics.

We report on results obtained for a class of N = 1 supergravity inflationary models in which the evolution of the inflaton dynamics is controlled by a single power (quadratic or cubic in the inflaton field) at the point where the observed density fluctuations are produced. We find that the so-called η-problem encountered in such models can be naturally solved in the context of braneworld scenario for some range of α, the ratio of the dominant term in the inflationary potential and the brane tension, and the value of the inflaton field at the end of inflation, ϕ_F. We have also shown that successful tachyonic inflation can be achieved in the context of a five-dimensional ADS braneworld scenario. We argue that the bosonic String Field Theory action around the top of the tachyon potential does allow a sufficiently long period of inflation provided the string remains very weakly coupled and the string energy density τ₃ is sufficiently below the Planck scale to render the low-energy four-dimensional gravity theory description reliable.

We study the cosmology of the Randall-Sundrum brane-world where the Einstein-Hilbert action is modified by curvature correction terms: a four-dimensional scalar curvature from induced gravity on the brane, and a five-dimensional Gauss-Bonnet curvature term. The combined effect of these curvature corrections to the action removes the infinite-density big bang singularity, although the curvature can still diverge for some parameter values. A radiation brane undergoes accelerated expansion near the minimal scale factor, for a range of parameters. This acceleration is driven by the geometric effects, without an inflaton field or negative pressures. At late times, conventional cosmology is recovered.

Silicon double paddle oscillators are well suited for the detection of weak forces because of their high Q factor (about 10⁵ at room temperature). We describe an experiment aimed at the detection of gravitational forces between masses at sub-mm distance using such an oscillator. Gravitational excitation is produced by a rotating aluminium disk with platinum segments. The force sensitivity of this apparatus is about 10 fN at room temperature for 1000 s averaging time at room temperature. The current limitations to detection of the gravitational force are mentioned.

The annihilation of neutralino dark matter may result in observable signals in different wavelength. In the present paper we will discuss the effect of neutralino annihilation in the halo of our Galaxy and in its center. According to high resolution cold dark matter simulations, large virialized halos are formed through the constant merging of smaller halos appeared at previous times. At each epoch, dark matter halos have then a clumpy component which is made of these merging subhalos. The annihilation of dark matter in these clumps, always present in the halo of our Galaxy, may be responsible for appreciable fluxes of γ-rays, potentially detectable. We find that, depending on the fundamental parameters of the clump density profile and on the distribution of clumps in the Galactic halo, the contribution to the diffuse γ-ray background from clumps could be used to obtain constraints on the neutralino properties such as mass and annihilation cross section. On the other hand the annihilation of neutralino dark matter in the galactic center may result in radio signals. At the galactic center, infact, the accretion flow onto the central black hole sustains strong magnetic fields that can induce synchrotron emission, in the radio wavelength, by electrons and positrons generated in neutralino annihilations during advection onto the black hole. We find that the observed emission from the galactic center is consistent with neutralinos following a Navarro Frenk and White density profile at the galactic center while it is inconsistent with the presence of a spike density profile, supposed to be generated by the formation history of the central black hole.

Evidence is mounting for the existence of intermediate mass black holes, which occupy the mass spectrum somewhere between the stellar-mass variety (a few to tens of solar masses) and the supermassive variety (millions to billions of solar masses). Theoretical stellar and black hole evolutionary models predict intermediate mass black holes, but until recently, there have been few observational signs of them. A new class of x-ray sources with apparent luminosities that are tens to thousands of times the Eddington limit for a neutron star is offering hope of finding intermediate mass black holes. However, the nature of these x-ray sources is still controversial. I will review observations of ultraluminous x-ray sources and the arguments for and against intermediate mass black holes. I suggest that, instead of just concentrating on ultraluminous x-ray sources as a class, the chance of finding genuine intermediate mass black holes might improve if we concentrate on places where we most expect to find them from an evolutionary standpoint.

According to hierarchical galaxy merger models, binary black holes should form frequently, and should be common in the cores of galaxies. The presence of massive black hole binaries has been invoked to explain a number of class properties of different types of galaxies, and in triggering various forms of activity. Coalescing massive black hole binaries are powerful emitters of gravitational waves. The search for such binary black holes is therefore of great interest for key topics in astrophysics ranging from galaxy formation to activity in galaxies. This review concentrates on the observational evidence for the presence of supermassive binary black holes in galaxies, and briefly summarizes scenarios for their formation and evolution.

Theodor Kaluza (1885–1954) attracted the attention of the physical community in 1921 with his unified field theory of gravitation and electromagnetism in five dimensions. Despite Einstein's great interest in Kaluza's theory, 50 years elapsed before it contributed toward a paradigm shift in modern theoretical physics. The biography of this unknown scientist is briefly presented along with an outline of his four physical theories. There follows a short discussion of Kaluza's five-dimensional unified field theory and the impression it made on Einstein.

Progress and plans are reported for a program of gravitational physics experiments using cryogenic torsion pendula undergoing large amplitude torsional oscillation. The program includes a UC Irvine project to measure the gravitational constant G and joint UC Irvine–U. Washington projects to test the gravitational inverse square law at a range of about 10 cm and to test the weak equivalence principle.

We examine how the new forthcoming Earth gravity models from the CHAMP and, especially, GRACE missions could improve the measurement of the general relativistic Lense–Thirring effect according to the various kinds of observables which could be adopted. In a very preliminary way, we use the recently released EIGEN2 CHAMP–only and GRACE01S GRACE–only Earth gravity models in order to assess the impact of the mismodelling in the even zonal harmonic coefficients of geopotential which represents one of the major sources of systematic errors in this kind of measurement.

Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been investigated by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that most of the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dimension D not equal to an even integer the corresponding Casimir energy arising from massless fields interior and exterior to a hyperspherical shell is finite. It has also long been recognized that the Casimir energy for massive fields is divergent for curved boundaries. These conclusions are reinforced by a calculation of the relevant leading Feynman diagram in D dimensions. Divergences do occur in third order, as has been recognized for many years, but this logarithmic divergence is of questionable relevance to real shells.

A new solution for the final state of gravitational collapse is proposed. A simple model with a purely vacuum energy de Sitter interior with p_v = −ρ_v, and Schwarzschild exterior of arbitrary total mass M is outlined. These are separated by a thin shell with a small but finite proper thickness ℓ of fluid with eq. of state p = +ρ. This boundary layer is a quantum transition region which replaces the event horizons of the classical de Sitter and Schwarzschild solutions, through which the vacuum energy changes. The new solution has no singularities, no event horizons, and a global time. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of order k_BℓMc/ħ, instead of the Bekenstein-Hawking entropy formula, S_BH = 4πk_BGM²/ħc. Unlike black holes, the new solution is thermodynamically stable and has no information paradox.

We discuss type IIB orientifolds with D-branes, and NSNS and RR field strength fluxes, with D-brane sectors leading to open string spectra with non-abelian gauge symmetry and charged chiral fermions. The closed string field strengths generate a scalar potential stabilizing most moduli. Hence the models combine the advantages of leading to phenomenologically interesting (and even semirealistic) chiral open string spectra, and of stabilizing the dilaton and most geometric moduli. We describe the explicit construction of two classes of non-supersymmetric models on T⁶ and orbifolds/orientifolds thereof, with chiral gauge sector arising from configurations of D3-branes at singularities, and from D9-branes with non-trivial world-volume magnetic fields. The latter examples yield the chiral spectrum of just the Standard Model.

The study of the universe at energies above 100 GeV is a relatively new and exciting field. The current generation of pointed instruments have detected TeV gamma rays from at least 10 sources and the next generation of detectors promises a large increase in sensitivity. We have also seen the development of a new type of all-sky monitor in this energy regime based on water Cherenkov technology (Milagro). To fully understand the universe at these extreme energies requires a highly sensitive detector capable of continuously monitoring the entire overhead sky. Such an instrument could observe prompt emission from gamma-ray bursts and probe the limits of Lorentz invariance at high energies. With sufficient sensitivity it could detect short transients (~15 minutes) from active galaxies and study the time structure of flares at energies unattainable to space-based instruments. Unlike pointed instruments a wide-field instrument can make an unbiased study of all active galaxies and enable many multi-wavelength campaigns to study these objects. This paper describes the design and performance of a next generation water Cherenkov detector. To attain a low energy threshold and have high sensitivity the detector should be located at high altitude (> 4km) and have a large area (~40,000 m²). Such an instrument could detect gamma ray bursts out to a redshift of 1, observe flares from active galaxies as short as 15 minutes in duration, and survey the overhead sky at a level of 50 mCrab in one year.

For many years, the most active area of quantum cosmology has been the issue of choosing boundary conditions for the wave function of a universe. Recently, loop quantum cosmology, which is obtained from loop quantum gravity, has shed new light on this question. In this case, boundary conditions are not chosen by hand with some particular physical intuition in mind, but they are part of the dynamical law. It is then natural to ask if there are any relations between these boundary conditions and the ones provided before. After discussing the technical foundation of loop quantum cosmology which leads to crucial differences to the Wheeler–DeWitt quantization, we compare the dynamical initial conditions of loop quantum cosmology with the tunneling and the no-boundary proposal and explain why they are closer to the no-boundary condition. We end with a discussion of recent developments and several open problems of loop quantum cosmology.

A brief update on some key topics on cosmic microwave background radiation anisotropies and polarization is given with special emphasis on the latest results for cosmological parameter estimation.

We address the issue of the possible detection of non-trivial topologies in the context of a dark-energy and dark-matter unification. In this so-called quartessence model, a single fluid is responsible for both the recent accelerated expansion and structure formation. We focus on the particular case of a universe dominated by a generalized Chaplygin gas (GCG), and investigate how sensitive to the model parameters the detectability of cosmic topology is. We discuss which manifolds could have potentially detecatable topologies within current observational bounds. Finally, we examine constraints on the parameter of the GCG equation of state, which arises from a possible detection of the cosmic topology. Our analysis shows that alternatives to the ΛCDM model lead to changes on the detectability of the cosmic topology, motivating further investigations into other models, such as in scalar field quintessence.

The general solution for a stationary circularly symmetric metric ds² = −N(r)²dt² + dr²/F(r)² + r² (dϕ + W(r)dt)², coupled to a differentially rotating perfect fluid and a cosmological constant, is determined through arbitrarily given functions N(r), and W(r), which allow the evaluation of the structural function F(r), the energy density, and the isotropic pressure.

The latest results of the measurements on the vibration isolation system of MiniGRAIL at room temperature as well as an overview of the results of the ultra-cryogenic tests with the dilution refrigerator are presented. Two types of capacitive transducers have been developed and tested separately in a cryogenic set-up. The rosette-design transducers have been mounted on the sphere and tested at low temperature. We also report the progress in developing a two-mode inductive transducer with an Al5056 resonator as a second resonating mass and a Nb film coil as superconducting pick-up loop. Furthermore, we developed and tested two double-SQUID systems based on two types of dc SQUIDs as sensors and a DROS as the preamplifier stage.

I review the conceptual, algebraical, and geometrical structure of Doubly Special Relativity. I also speculate about the possible relevance of DSR for quantum gravity phenomenology.

We review constraints on the short-range non-Newtonian gravity obtained recently from the Casimir force measurements between metals and from gravitational experiments of Eötvos- and Cavendish-type. Corrections to the Newton's law of gravitation at small distances are predicted by the multi-dimensional theories with large extra dimensions. They are generated also by the exchange of light and massless elementary particles predicted in many extensions to the Standard Model. It is shown that the Casimir force measurements are of profound importance as a test for predictions of fundamental physical theories.

The AdS/CFT correspondence is an exact duality between string theory in anti-de Sitter space and conformal field theories on its boundary. Inspired in this correspondence some relations between strings and non conformal field theories have been found. Exact dualities in the non conformal case are intricate but approximations can reproduce important physical results. A simple approximation consists in taking just a slice of the AdS space with a size related to an energy scale. Here we will discuss how this approach can be used to reproduce the scaling of high energy QCD scattering amplitudes. Also we show that very simple estimates for glueball mass ratios can emerge from such an approximation.

A family of generalized S-brane solutions with orthogonal intersection rules and n Ricciflat factor spaces in the theory with several scalar fields, antisymmetric forms and multiple scalar potential is considered. Two subclasses of solutions with power-law and exponential behaviour of scale factors are singled out. These subclasses contain sub-families of solutions with accelerated expansion of certain factor spaces. The solutions depend on charge densities of branes, their dimensions and intersections, dilatonic couplings and the number of dilatonic fields. Certain examples of solutions with exponential dependence of one scale factor and constant scale factors of "internal" spaces (e.g. "Freund-Rubin" type solutions) are also considered.

The possible relevance of the decay of accelerated protons in the context of high energy astrophysics is discussed.

Current phenomenological and cosmological constraints on supersymmetric dark matter will be reviewed. Particular attention will be given to the effect of the WMAP results on the CDM density.

Propagation of fermions in curved space-time generates a gravitational interaction due to the coupling between spin of the fermion and space-time curvature. This gravitational interaction, which is an axial-vector appears as the CPT violating term in the Lagrangian, can generate the neutrino asymmetry in Universe. If the back-ground metric is spherically asymmetric, say, of rotating black hole, the axisymmetric space-time of an expanding Universe, this interaction as well as the neutrino asymmetry is non-zero.

A new method to study the effects of neutrino masses on a supernova neutrino signal is proposed. The method relies exclusively on the analysis of the full statistics of neutrino events, it is independent of astrophysical assumptions, and does not require the observation of any additional phenomenon to trace possible delays in the neutrino arrival times. A statistics of several thousands of events as could be collected by SuperKamiokande, would allow to explore a neutrino mass range somewhat below 1 eV.

We introduce decoherence phenomena to Neutrino flavor oscillation in the most general way. With the results we adjust the KamLAND data and obtain a good fit.

Recent constraints on neutrino mass and chemical potential are discussed with application to large scale structure formation. Power spectra in cosmological model with hot and cold dark matter, baryons and cosmological term are calculated in newtonian approximation using linear perturbation theory. All components are considered to be ideal fluids. Dissipative processes are taken into account by initial spectrum of perturbations so the problem is reduced to a simple system of equations. Our results are in good agreement with those obtained before using more complicated treatments.

In this short contribution, a possible strategy to determine some of the yet unknown neutrino oscillation parameters by combining information from two long-baseline oscillation experiments of JHF and NuMI projects is discussed.

A model based on SUSY SO(10) combined with SU(2) family symmetry is constructed. In contrast with the commonly used effective operator approach, 126-dim Higgs fields are utilized to construct the Yukawa sector. The symmetric mass textures arising from the left-right symmetry breaking chain of SO(10) give rise to very good predictions for quark and lepton masses and mixings and three angles of the unitarity triangle. In the neutrino sector, our predictions are in good agreement with results from atmospheric neutrino experiments. Our model gives rise to the LMA solution to the solar neutrino anomaly. The prediction for the |U_eν3| element in the MNS matrix is close to the sensitivity of current experiments; thus the validity of our model can be tested in the near future. We also investigate the correlation between the |U_eν3| element and tan²θ_⊙ in a general two-zero neutrino mass texture.

The recent analysis of the cosmic microwave background data carried out by the WMAP team seems to show that the sum of the neutrino masses is < 0.7 eV. However, this result is not model-independent, depending on precise assumptions on the cosmological model. We study how this result is modified when the assumption of perfect lepton symmetry is dropped out.

Present status of spin flavor precession (SFP) in the Sun is reviewed. Using the recent solar neutrino data it is shown that this mechanism is disfavored as a leading solution to the solar neutrino problem. The case of SFP as a sub-leading solution is also discussed. In this case, it is shown that the recent KamLAND constraint on solar anti-neutrino flux provides a stringent constraint on the neutrino magnetic moment down to μν ≤ few × 10⁻¹².

I review the results obtained with recent XMM-Newton and INTEGRAL observations of the Center of our Galaxy, and concerning Sgr A*, the radiative counterpart of the massive black hole at the galactic nucleus. The X-ray observations performed in 2001 and 2002 have led to the discovery of bright X-ray flares from Sgr A* in the range 2-10 keV confirming previous Chandra detection and opening new perspectives to understand the processes at work in this object. The INTEGRAL observations of spring 2003 have provided evidence for an excess in the energy range 20-100 keV in the central 10′ of the Galaxy. With a measured flux of ~ 3 mCrabs the excess is compatible with a point source located at the Sgr A* position and a contribution to the measured flux from the massive black hole cannot be excluded. I will mention the implications of these results on the proposed models of Sgr A* and the future observational perspectives.

We present the results we have obtained on the non-thermal hard X-ray emission from IC443, a supernova remnant interacting with molecular cloud (MC), from the initial discovery with BeppoSAX/PDS to the most recent results with XMM/Newton. This remnant has been detected up to EGRET bandwidth, and we have resolved part of the hard emission as 1) a plerion nebula with a compact central object, 2) a set of isolated point sources in the MC interaction regions, and 3) a diffuse extended component. We introduce the models we have invoked to explain all these components and the problems still open.

X-ray observations of black hole X-ray transients in their quiescent phase show that transient systems containing neutron stars are significantly dimmer than those containing black holes, as expected since black holes have no solid surface, in agreement with the predictions of the Advection Dominated Accretion Flow (ADAF) models.

Analysis of observations with XMM-Newton have made a significant contribution to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area, bandpass and resolution of the EPIC instrument permit the study of a wide variety of spectral features. In particular, strong, time-dependent, soft X-ray emission lines have been discovered in some bursts. The emission mechanism and energy source for these lines pose major problems for the current generation of GRB models. Further XMM-Newton observations of GRBs discovered by the Swift satellite should help unlock the origin of the GRB phenomenon over the next few years.

We summarize the results of our monitoring observations of the X-ray remnant of supernova (SN) 1987A with the Chandra X-Ray Observatory. As of 2002 December, we have performed a total of seven observations of SN 1987A. The images from the latest data reveal the development of X-ray-bright spots in the northwestern and the southwestern portions, as well as in the eastern side, of the remnant. The latest 0.5–2 keV band flux (L_X ~ 6 × 10⁻¹³ ergs s⁻¹ cm⁻²) is four times brighter than three years ago. The overall X-ray emission is primarily from the blast wave shock with kT ~ 2.4 keV. As the blast wave approaches the dense circumstellar material, the contribution from the decelerated shock (kT ~ 0.22 keV) to the observed X-ray emission is becoming significant. Based on the best-fit two-shock component model, we derive the densities of the X-ray-emitting regions (n_e ~ 235 cm⁻³ for the fast shock and n_e ~ 7500 cm⁻³ for the slow shock). An upper limit on the X-ray luminosity of any embedded point source is L_X ≤ 1.5 × 10³⁴ ergs s⁻¹ in the 2−10 keV band.

We present the results of a series of XMM-Newton observations of Her X-1, spread over a wide range of the 35 d precession period. The strong fluorescence emission line at ~6.4 keV is detected in all observations (apart from one taken in the middle of eclipse), with higher line energy, width and normalisation during the main-on state. Spin resolved spectroscopy just after the rise to the main-on state shows that the variation of the Fe Kα at 6.4 keV is correlated with the soft X-ray emission. This confirms our past finding based on the XMM-Newton observations made further into the main-on state, and indicates the common origin for the thermal component and the Fe Kα line detected at these phases. We also find that, during the low state, the normalisation of the 6.4keV line is correlated with the binary orbital phase, having a broad maximum centered near ϕ_orbit ~ 0.5. In addition, we detect a second line near 7 keV in 10 of the 15 observations taken during the low-intensity states of the system. The RGS spectrum taken during the low state shows a series of broad absorption lines and two radiative recombination continuum features. Taken together, these facts strengthen the interpretation of the low state emission in term of an extended source that we identify with a photoionized accretion disk atmosphere and corona.

Recent Chandra and XMM-Newton surveys have confirmed that the cosmic X-ray background is mostly due to accretion onto super-massive black holes, integrated over cosmic time. Here we review the results obtained from the photometric and spectroscopic follow-up observations of the 122 X-ray sources detected by the HELLAS2XMM 1dF Survey down to a 2−10 keV flux of ≈ 10⁻¹⁴ erg cm⁻² s⁻¹. In particular, we focus on the multi-wavelength properties of a few intriguing classes of X-ray sources: high X-ray-to-optical flux ratio sources, Type 2 quasars, and XBONGs.

Recent observations with Chandra and XMM-Newton, aided by broad-band spectral coverage from RXTE, have revealed skewed relativistic iron emission lines in stellarmass Galactic black hole systems. Such systems are excellent laboratories for testing General relativity, and relativistic iron lines provide an important tool for making such tests. In this contribution to the Proceedings of the 10th Annual Marcel Grossmann Meeting on General Relativity, we briefly review recent developments and present initial results from fits to archival ASCA observations of Galactic black holes. It stands to reason that relativistic effects, if real, should be revealed in many systems (rather than just one or two); the results of our archival work have borne-out this expectation. The ASCA spectra reveal skewed, relativistic lines in XTE J1550−564, GRO J1655−40, GRS 1915+105, and Cygnus X-1.

We present the results of XMM-Newton and Chandra observations of two FRI radio galaxies, NGC 4261 and NGC 6251, harboring supermassive black holes of known mass. The unprecedented photon statistics of XMM-Newton combined with the high spatial resolution of Chandra allows detailed spectral, temporal, and spatial analyses of the core region. We investigate the origin of the X-ray emission from the nuclear regions of these two FRI radio galaxies and the nature of the accretion process.

We model the spectral energy distribution of the ultrasoft broad-line AGN RE J2248-511 with Comptonised accretion disc models. These are able to reproduce the steep optical and ultrasoft X-ray slopes, and the derived black hole mass is consistent with independent mass estimates. This AGN displays properties of both broad and narrow line Seyfert 1 galaxies, but we conclude that it is intrinsically a 'normal' Seyfert 1 viewed at high inclination angle.

I discuss the stability of accretion disks when the black hole is considered to be rotating. I show, how the fluid properties get changed for different choices of angular momentum of black holes. I treat the problem in pseudo-Newtonian approach with a suitable potential from Kerr geometry. When the angular momentum of a black hole is considered to be significant, the valid disk parameter region affects and a disk may become unstable. Also the possibility of shock in an accretion disk around rotating black holes is checked. When the black hole is chosen to be rotating, the sonic locations of the accretion disk get shifted or disappear, making the disk unstable by means of loosing entropy. To bring the disk in a stable situation, the angular momentum of the accreting matter has to be reduced/enhanced (for co/counter-rotating disk) by means of some physical process.

During last few years, a substantial (although circumstantial) evidence for the presence of the event horizons around some black hole candidates (BHCs) was accumulated. (1)X-ray Novae containing BHCs as compact components never produce Type I bursts. The most recent extensive observations failed to find even a single burst. At the same time, X-ray Novae containing neutron stars (NSs) produce frequently Type I bursts (as expected). (2) Quiescent (between the outbursts) luminosities of the systems containing BHCs are by about two and a half orders of magnitude dimmer than the systems containing NSs. As Chandra detects more and more sources in quiescence, this conclusion becomes stronger. BHCs are "blacker" because they have no solid surfaces on which part of the accretion energy could be released. (3) Systems containing BHCs and those containing NSs occupy different regions in the X-ray color-color diagrams. The difference might be naturally attributed to the fact, that the NS sources have solid surfaces and develop boundary layers in the process of accretion. (4) The inner part of the disc in some systems (GRS 1915+105) occasionally suddenly disappears. This implies that the matter is dumped on the compact object. However, we do not see the accompanying flash which should be produced if this matter hit the solid surface.

No abstract received.

We report the photometric evidence of bullet like features in SS433 in X-rays, Infra-red and Radio bands through a multi-wavelength campaign.

Microquasars, enigmatic X-ray binaries with relativistic high-energy jets, occasionally eject massive jet blobs, which are far more energetic than the continuous jet flow seen in the usual state. Because those massive jet-ejection events are rare (a few per year) and difficult to predict, they have been hardly observed with X-ray detectors. We have successfully observed a massive jet-ejection event from the microquasar SS 433 with RXTE. The source undergoing the ejection shows a variety of new phenomena including fast time variability (on time scales of 10 seconds), a QPO-like feature at 0.1 Hz, and bursting activities, none of which had been detected from this system.

No abstract received.

Very large baseline interferometry has revealed the existence of relativistic jets emanating from the core of several active galactic nuclei. A substantial fraction of them shows discrete features, which are moving apparently with superluminal velocities. Superluminal motions are thought being caused by a geometrical effect due to the small angle between the relativistic jet and the line of sight. In some cases, jet components are observed being ejected in distinct directions with different apparent proper motions. In this work, we select some objects that exhibit these characteristics and interpret them as due to jet precession. The parameters of precession model for such objects are constrained using their high-resolution radio maps and their optical variability. With the precession parameters and assuming that precession is induced by a secondary supermassive black hole in a non-coplanar orbit in relation to the accretion disc, we estimate some physical parameters of the binary system, such as the separation between the black holes and limits for their masses.

We briefly review some of the basic properties of the Chandra Deep Field (CDF) X-ray sources, explore the CDF X-ray number counts for both AGN and galaxies and how they contribute to the X-ray background, and highlight a few recent results regarding the host-galaxy morphologies of the CDF AGN using HST ACS data. We also discuss how these AGN relate to the evolution and feeding of super-massive black holes in the Universe.

Black holes have historically been thought to come in two flavors: between a few and tens of solar masses, formed in supernovae; and millions to billions of solar masses, grown in the centers of galaxies. However, several recent lines of evidence point to intermediate-mass black holes that exist in a number of dense stellar clusters. These black holes are expected to be found in binaries. As a result, three and four body interactions are common, in a realm including both Newtonian effects and general relativistic effects such as precession of the pericenter and orbital evolution due to gravitational radiation. These objects may therefore be a new source of gravitational waves with unique properties. We discuss the possibility of detecting this gravitational radiation with future instruments such as LISA and Advanced LIGO.

We consider possibilities for obtaining information about the equation of state for quark matter by using future direct observational data on gravitational waves. We study the nonradial oscillations of the fluid modes of pure quark stars. If we observe the f modes from quark stars, by using the simultaneously obtained radiation radius we can constrain the bag constant B with reasonable accuracy, independently of the s quark mass.

No abstract received.

We present a new numerical scheme for solving the initial value problem for quasiequilibrium binary neutron stars allowing for arbitrary spins. We construct sequences of circular-orbit binaries of varying separation, keeping the rest mass and circulation constant along each sequence. The spin angular frequency of the stars is shown to vary along the sequence, a result that can be derived analytically in the PPN limit. This spin effect, in addition to leaving an imprint on the gravitational waveform emitted during binary inspiral, is measurable in the electromagnetic signal if one of the stars is a pulsar visible from Earth.

We review here the classical argument used to justify the electrical neutrality of stars and show that if the pressure and density of the matter and gravitational field inside the star are large, then a charge and a strong electric field can be present. For a neutron star with high pressure (~ 10³³ to 10³⁵ dynes /cm²) and strong gravitational field (~ 10¹⁴ cm/s²), these conditions are satisfied. The hydrostatic equation which arises from general relativity, is modified considerably to meet the requirements of the inclusion of the charge. In order to see any appreciable effect on the phenomenology of the neutron stars, the charge and the electrical fields have to be huge (~ 10²¹ Volts/cm). These stars are not however stable from the viewpoint that each charged particle is unbound to the uncharged particles, and thus the system collapses one step further to a charged black hole.

We derive a third post-Newtonian equation of motion for two self-gravitating point masses in a harmonic coordinate using surface integral approach and strong field point particle limit. Our equation of motion is unambiguous, Lorentz invariant (in the post-Newtonian perturbative sense), and conservative (modulo the radiation reaction effect). Namely, we determine the ambiguous parameter found by the other works.

We describe kHz QPOs from the hydrodynamical model of accretion disks for LMXB systems. Out of the pair, the higher frequency originates due to the viscous effects of an accretion disk involving the formation of shock, while the lower one is due to the Keplerian motion of accreting matter. Comparing our results with observations for two fast rotating compact stellar candidates, namely, 4U 1636–53 and KS 1731–260, we find that they match to a very good approximation.

Binary star systems containing stellar mass black holes and normal stars as companions have been detected in our Galaxy over the last decade. Ejecting collimated bipolar radio jets with apparent superluminal velocities, these objects have been named microquasars thanks to their similarity with the distant extragalactic quasars [1]. We here propose that the large scale superluminal ejections observed in these microquasars (e.g., GRS 1915+105 source) during radio flare events are produced by violent magnetic reconnection episodes in the corona just above the inner regions of the magnetized accretion disk (with B ≃ 10⁷ G) that surrounds the central 10-solar mass black hole.

We present results of several numerical simulations of two dimensional advective flows which include cooling processes. We show that the computed light curve is similar to the χ state in GRS 1915+105. The power density spectrum (PDS) also shows presence of QPOs near the break frequency.

The effects of bulk motion comptonization on the spectral formation in a converging flow onto a black hole are discussed and new results are presented. The problem has been tackled by means of both a fully relativistic, angle-dependent trasfer code and a semi-analytical, diffusion-approximation method.

We find that a power-law high-energy tail is a ubiquitous feature in converging flows and that the two approaches produce consistent results at large enough accretion rates, when photon diffusion holds. The photon index in the tail is found to be largely independent on the spatial distribution of soft seed photons when the accretion rate is either quite low (< 5 in Eddington units) or sufficiently high (> 10). Our analysis confirms that a hard tail with photon index Γ < 3 is produced by the up-scattering of primary photons onto infalling electrons if the central object is a black hole.

A derivation of the γγ → e⁺ e⁻ optical depth for γ rays produced in a comoving spherical emitting region is presented. Employing a simplified expression for the γγ absorption cross section, analytic expressions for the minimum Doppler factor implied by the requirement of γ-ray transparency are derived for a broken power-law spectrum of target photons which are isotropically distributed in the comoving frame. Application to specific systems is illustrated.

Accurate accounting of particle number and 4-momentum in radiative transfer may be facilitated by the use of transport equations that allow transparent conversion between volume and surface integrals in both spacetime and momentum space. Such conservative formulations of general relativistic radiative transfer in multiple spatial dimensions are presented, and their relevance to core-collapse supernova simulations described.

We use a curvilinear coordinate system, which is natural to the dipolar magnetic field of accreting white dwarfs and solve the hydrodynamic equations governing the filed channelled accretion flow in magnetic cataclysmic variables. This take into account the effects due to curvature of the accretion stream under the gravity of the accretor. Our calculations show that the temperature and density profiles in the accretion stream are significantly different to those obtained from models assuming simple spherical or planar flows.

We calculate the atmospheric structure of an accretion disk around a Kerr black hole and obtain its X-ray spectrum, which exhibits prominent atomic transitions under certain circumstances. The gravitational and Doppler (red)shifts of the C V, C VI, O VII, O VIII, and Fe I–XXVI emission lines are observable in active galaxies. We quantify the line emissivities as a function of radius, to identify the effects of atmospheric structure, and to determine the usefulness of these lines for probing the disk energetics. The line emissivities do not always scale linearly with the incident radiative energy, as in the case of Fe XXV and Fe XXVI. Our model incorporates photoionization and thermal balance for the plasma, the hydrostatic approximation perpendicular to the plane of the disk, and general relativistic tidal forces. We include radiative recombination rates, fluorescence yields, Compton scattering, and photoelectric opacities for the most abundant elements.

No abstract received.

I review the basic features of a time-dependent radiative transfer code recently developed by Perna & Lazzati (2002). The code combines self-consistently metal evolution and dust destruction under an intense X-ray UV radiation field. The evolution of dust grains is computed with the inclusion of the processes of sublimation and ion field emission (IFE). The relative importance of IFE with respect to X-ray and UV sublimation as a function of grain size, intensity and hardness of the incident spectrum is discussed. The code also follows the evolution of the ionization states of the metals and their relative radiative transitions. It treats, self-consistently, the gradual recycling of metals into gas as dust is sublimated away; it allows for any initial dust grain distribution and follows its evolution in space and time. An application of this code to Gamma-Ray Bursts is discussed, and it is shown how the time variability of the low-energy and high-energy opacities can yield powerful clues on the characteristics of the medium in which the bursts occur.

Low angular momentum accretion flows very often have centrifugal pressure supported standing shock waves which can accelerate flow particles. The accelerated particles in turn emit synchrotron radiation in presence of magnetic fields. Efficient cooling of the electrons reduces its temperature in comparison to the protons. In this paper, we assume two temperature flows to explore this property of shocks and present an example of the emitted radiation spectrum.

We show that with the wind/jet activity, the spectral index of hard X-ray is changed in galactic microquasars. When mass loss takes place, the spectrum becomes softer and when mass gain takes place, the spectrum becomes harder. We present examples of such changes in GRS1915+105.

We formulate and solve the diffusion problem of line photon propagation in a bulk outflow from a compact object (black hole or neutron star) using a generic assumption regarding the distribution of line photons within the outflow. Thomson scattering of the line photons within the expanding flow leads to a decrease of their energy which is of first order in υ/c, where υ the outflow velocity and c is the speed of light. We demonstrate that the emergent line profile is closely related to the time distribution of photons diffusing through the flow (the light curve) and consists of a broad redshifted feature. We analyzed the line profiles for the general case of outflow density distribution. We emphasize that the redshifted lines are intrinsic properties of the powerful outflow that are supposed to be in many compact objects.

No abstract received.

A higher-dimensional gravity invariant both under local Lorentz rotations and under local anti-de Sitter boosts is constructed. It is shown that such a construction is possible both when odd dimensions and when even dimensions are considered. It is also proved that such actions have the same coefficients as those obtained by Troncoso and Zanelli [Class. Quantum Grav. 17 (2000) 4451]. Journal-Ref.: Phys. Lett. B574, 283 (2003).

The authors generalization of general relativity on the manifold of the de Sitter group manifests in its mathematical structure the following features which are required by observational results:.

(i) A cosmological member.

(ii) The existence of inner and outer dynamical variables (as spin and orbital angular momenta).

(iii) The existence of dark energy resulting from a generalization of the gravitational law.

These features follow from the mathematical structure without that any constant (not even the gravitational constant) has to be inserted.

All vacuum solutions of general relativity with cosmological member are also solutions of the present theory but other solutions (Riemannian and with contortion) exist and give rise to the possibility of sources of the first set of field equations (which are a generalization of the equations of C.N. Yang). Such sources may be identified with spin or angular momentum fulfilling.

(iv) Machs principle. The vacuum solutions of general relativity may be excluded as unphysical because they collapse to a singularity. Einsteins equations with a geometric dark energy term form the second set of equations. The discussed features result from the structure and little attempt is made to find new solutions before the role of each part is clarified. Special cases of the theory can in ten dimensions be given a teleparallelistic form.

It is shown that screening the background of super-strong interacting gravitons ensures the Newtonian attraction, if a part of single gravitons is pairing and graviton pairs are destructed by collisions with a body. If the considered quantum mechanism of classical gravity is realized in the nature, than an existence of black holes contradicts to the equivalence principle. In such the model, Newton's constant is proportional to H²/T⁴, where H is the Hubble constant, T is an equivalent temperature of the graviton background. The estimate of the Hubble constant is obtained for the Newtonian limit: H = 3.026 · 10⁻¹⁸ s⁻¹ (or 94.576 km · s⁻¹ · Mpc⁻¹).

No abstract received.

Recently, it has been shown that Absolute Parallelism (AP) geometry admits paths that are naturally quantized. These paths have been used to describe the motion of spinning particles in a background gravitational field. In case of a weak static gravitational field limits, the paths are applied successfully to interpret the discrepancy in the motion of thermal neutrons in the Earth's gravitational field (COW-experiment). The aim of the present work is to explore the properties of the deviation equations corresponding to these paths. In the present work the deviation equations are derived and compared to the geodesic deviation equation of the Riemannian geometry.

Within a Lorentz invariance violating extension of the Maxwell sector of the Standard Model, modifications of light propagation lead to changes in the resonance frequency of light in electromagnetic cavities. The effect can be tested in Michelson–Morley experiments. Due to the covariant structure of the modified Maxwell equations, the equation determining the Coulomb potential is also modified. For resonators made of ionic crystals or other solids, this changes the resonator length and leads to an additional modification of the resonance frequency. Here we consider Michelson–Morley experiments taking into account both effects. The new effects can be neglected for present experiments but may play some role in future ones.

It is shown that if the source in General Relativity is taken to be a string, then the equation of motion may still be derived from the Bianchi identities. Although the result is wildly different to the geodesic, on a time average it reduces to the expected result.

Recent studies of spacetime anisotropy in the context of local Lorentz invariance (LLI) based on classical Michelson–Morley experiments, as well Kennedy–Thorndyke tests, pointed out the existence of terms first order in υ/c and of angular signatures independent of υ. This contribution replaces the Lorentz symmetry by a velocity gauge transformation following an argument centred on observability. Results show even and odd order terms and indicate that motion is always underestimated in the spatiotemporal platform. Though LLI is not recovered in exact special relativistic terms, the alternative looks compatible with the relational aspects of general relativity (GR). This raises the hypothesis that Einstein equivalence principle, and consequently LLI, is a cornerstone of GR, but not necessarily a fundamental one of SR.

We discuss the possibility to obtain, from a five-dimensional free spinor Lagrangian, the Quantum Electro-Dynamics (QED) coupling via a Kaluza-Klein reduction of the theory. This result is achieved taking a phase dependence of the spinor field on the extra-coordinate and modifying the corresponding connection. The five-dimensional spinor theory is covariant under the admissible coordinates transformations and its four-dimensional reduction provides the QED coupling term.

We discuss the dynamics of particles moving in a five-dimensional space-time and the anomalous acceleration caused by the extra dimension in the framework of the induced-matter theory of gravity.

A relativistic 3-brane can be given a conformally invariant, gauge-type, formulation provided the embedding space is six-dimensional. The implementation of conformal invariance requires the use of a modified measure, independent of the metric in the action. A brane-world scenario without the need of a cosmological constant in 6D can be constructed. Thus, no "old" cosmological constant problem appears at this level.

It is shown that in d = 11 supergravity, under a very reasonable ansatz, the nearly flat spacetime in which we are living must be 4-dimensional without appealing to the Anthropic Principle.

Analyzing the geometry of a non-Abelian Teleparallel Theory and the one of an Extended Gauge Theory and comparing one to the other, we find some similar structures that may help us to understand the gravitational model emerging from each theory.

At high energy densities the geometry of the Universe could deviate from Riemaniann, and correct description of the Universe evolution can be given within framework of gauge theories of gravity. One of the most important cosmological implications of such theories is a possibility to avoid cosmological singularity of general relativity. From the other hand, it is a wide spread opinion that at the early Universe the scalar field could give dominant contribution to the energy density. Solutions of cosmological equations of gauge theories of gravity for the Universe filled by scalar field are discussed. Special attention is devoted to initial conditions for inflation and conditions leading to nonsingular solutions.

Asymptotically flat gravitating systems have 10 conserved quantities, which lack proper local densities. It has been hoped that the teleparallel equivalent of Einstein's GR (TEGR, aka GR_∥) could solve this gravitational energy-momentum localization problem. Meanwhile a new idea: quasilocal quantities, has come into favor. The earlier quasilocal investigations focused on energy-momentum. Recently we considered quasilocal angular momentum for the teleparallel theory and found that the popular expression (unlike our "covariant-symplectic" one) gives the correct result only in a certain frame. We now report that the center-of-mass moment, which has largely been neglected, gives an even stronger requirement. We found (independent of the frame gauge) that our "covariant symplectic" Hamiltonian-boundary-term quasilocal expression succeeds for all the quasilocal quantities, while the usual expression cannot give the desired center-of-mass moment. We also conclude, contrary to hopes, that the teleparallel formulation appears to have no advantage over GR with regard to localization.

We explore a way to obtain the metric from an action principle that does not refer to it a priori. We study local theories that start with Schrödinger's purely affine theory, then we couple it to matter fields. We show that the propagation of shock waves does not define a lightcone and avoids the explicit use of the Ricci tensor in realizing the weak equivalence principle. When the Ricci tensor is substituted for the metric, the equations seem to have only a very limited set of solutions. This backs the conviction that viable purely affine theories have to be non–local.

Alternatives to the usual general relativity (GR) Riemannian framework include Riemann-Cartan and teleparallel geometry. The "teleparallel equivalent of GR" (TEGR, aka GR_∥) has certain virtues, however there have been allegations of serious source coupling limitations. Now it is quite straightforward to show that the coupled dynamical field equations of Einstein's GR with any source can be accurately represented in terms of any other connection, in particular teleparallel geometry. Using an argument similar to one used long ago to show the "effective equivalence" between GR and the Einstein-Cartan theory, we construct the teleparallel action which is equivalent to a given Riemanian one; thereby finding the "effectively equivalent" coupling principle for all sources, including spinors. No auxiliary field is required. Can one decide which is the real "physical" geometry? Invoking the minimal coupling principle may give a unique answer.

By exploring the similarity of teleparallel gravity with electromagnetism, a global formulation for gravitation is developed, which is based on the gauge invariant action of a nonintegrable phase-factor. As an application, the phase shifts of both the Colella-Overhauser-Werner and the gravitational Aharonov-Bohm effects are obtained.

In Einstein's general relativity, geometry replaces the concept of force in the description of the gravitation interaction. Such an approach rests on the universality of free-fall—the weak equivalence principle—and would break down without it. On the other hand, the teleparallel version of general relativity, a gauge theory for the translation group, describes the gravitational interaction by a force similar to the Lorentz force of electromagnetism, a non-universal interaction. It is shown that, similarly to the Maxwell's description of electromagnetism, the teleparallel gauge approach provides a consistent theory for gravitation even in the absence of the weak equivalence principle.

In models with large extra dimensions particle collisions with centre-of-mass energy larger than the fundamental gravitational scale can generate non-perturbative gravitational objects such as black holes and branes. They might be created in the next generation particle colliders or by neutrino induced air showers in the Earth's atmosphere. The decay of these non-perturbative gravitational objects is significantly different from other standard model processes. We present a comprehensive study of how to differentiate extensive air showers generated by TeV gravity effects from those generated by standard model interactions.

We numerically investigate the formation of black holes in high-energy particle collision with an impact parameter in D-dimensional spacetimes and evaluate the total cross section of the black hole production. We find that the formation of the apparent horizon occurs when the distance between the colliding particles is less than 1.5 times the effective gravitational radius of each particle. Our numerical result indicates that the characteristic (D − 3)-dimensional volume of the system provides a condition to approximately estimate the maximal impact parameter for the apparent horizon formation.

The hierarchy between the electroweak and Planck scales can be reduced when the extra dimensions are compactified with large volume or with warped geometry, resulting in the fundamental scale of the order of TeV. In such a scenario, one can experimentally study the physics above the Planck scale. We discuss black hole/ring production at future colliders.

If TeV-scale gravity is realized in nature, microscopic black holes (BHs) should be produced in atmospheric cosmic ray collisions. Their decays, largely via the Hawking process, would trigger extensive air showers that could be detected at facilities coming on line later this decade. In this talk we describe the main characteristics of these BH-mediated showers and show how earth-skimming neutrinos may act as a powerful discriminator of BH events.

The master equation describing massless fields of different spin in the Kerr-Taub-NUT spacetime representing a source with a mass plus gravitomagnetic monopole and dipole moments is studied. This equation can be separated into its radial and angular parts. The behaviour of the radial functions at infinity and near the horizon can be used to examine the influence of the NUT parameter on the phenomenon of superradiance. Moreover, we discuss the coupling between the spin of the perturbing field and the gravitomagnetic monopole moment.

We discuss the relation between bulk de Sitter three-dimensional spacetime and the corresponding conformal field theory at the boundary, in the framework of the exact quasinormal mode spectrum. We show that the quasinormal mode spectrum corresponds exactly to the spectrum of thermal excitations of Conformal Field Theory at the past boundary I⁻, together with the spectrum of a Conformal Field Theory at the future boundary I⁺.

The properties of principal null directions of a perturbed black hole are investigated. It is shown that principal null directions are directly observable quantities characterizing the space-time. A definition of a perturbed space-time, generalizing that given by Stewart and Walker is proposed. This more general framework allows one to include descriptions of a given space-time other than by a pair (M, g) where M is a four-dimensional differential manifold and g a Lorentz metric. Examples of alternative characterizations are the curvature representation of Karlhede and others, the Newman-Penrose representation or observable quantities involving principal null directions. The conditions are studied under which the various alternative choices of observables provide equivalent descriptions of the space-time.

The phenomenon of slow light (electromagnetically induced transparency), which would seem an ideal candidate for constructing a black hole analogue, cannot be used to simulate Hawking radiation. Even though an appropriately designed slow-light set-up may model classical features of black holes – such as horizon, mode mixing, “Bogoliubov” coefficients, etc. – it does not reproduce the related quantum effects.

No abstract received.

No abstract received.

The surface gravity for the extreme Reissner–Nordström black hole is zero suggesting that it has a zero temperature. However, the direct evaluation of the Bogolubov's coefficients, using the standard semi-classical analysis, indicates that the temperature of the extreme black hole is ill definite: the Bogolubov's coefficients obtained by performing the usual analysis of a collapsing model of a thin shell, and employing the geometrical optical approximation, do not obey the normalization conditions. We argue that the failure of the employement of semi-classical analysis for the extreme black hole is due to the absence of orthonormal quantum modes in the vicinity of the event horizon in this particular case.

From the Entanglement Thermodynamics, in the context of the Thermofield Dynamics, the Unruh Effect in curved spacetime is examined.

The conservation of energy implies that an isolated radiating black hole cannot have an emission spectrum that is precisely thermal.

Moreover, the no-hair theorem is only approximately applicable. We consider the implications for the black hole information puzzle.

We present a new method of recovering the power spectrum of initial perturbations to an unprecedently small scale of ~ 10h⁻¹ kpc. We apply this method to a sample of 4500 Ly-α absorbers and recover the cold dark matter (CDM) like power spectrum at scales ≥ 300h⁻¹kpc with a precision of ~ 10%. However at scales ~ 10 − 300h⁻¹kpc the measured and ΛCDM-like spectra are noticeably different.

Archeops is a balloon borne CMB experiment.¹ It was built by an international collaboration, led by A. Benoit (CRTBT, CNRS, Grenoble, France), with several groups from France, Italy, the UK, USA and Russia. Its goals were twofold. On the physics point of view, it was aimed at the measurement of large scale (ℓ ~ 20 − 200) CMB temperature anisotropies in a region were the pre-WMAP data exhibited a gap. The study of the polarisation of the galactic emission was another important target, since it may constitute an important foreground for the measurement of the CMB polarisation anisotropies precision measurements that are being planned. In parallel with these physics objectives, Archeops was also set up as a test bench for concepts and detectors for the Planck HFI instrument. In this proceeding, I give a brief summary of the CMB power spectrum analysis and of the galactic emission polarisation measurement by Archeops.

It has been argued that by removing a pressure gradient term in the continuity equation, it is possible to obtain, with a semiclassical formulation, the same expression for the density contrast growing mode, as obtained in a full relativistic treatment. In this context, we reinvestigate the evolution of perturbations in an expanding Newtonian universe with pressure, but we consider a general scenario in which the equation of state parameter is time dependent and the perturbations are not necessarily adiabatic. We verify that, in this case, the suggested modification of the continuity equation do not provide equivalence between the relativistic and Newtonian descriptions.

The present speculation shows that a standard FRW world-model with positive curvature is both suggested by observations and by theoretical arguments. With this characteristic in mind, it turns out that the Horizon and Flatness problems have straightforward issues.

We present preliminar results and tests of a new general relativistic code to simulate the hydrodynamic collapse of a 21 solar masses star. We have assumed spherical symmetry and used the formalism of Misner and Sharp to construct a finite-difference scheme to solve the Einstein’s equations, energy-momentum conservation equations and baryonic conservation equation. The code is similar to the one originally developed by May and White (1967). Here we discuss the capabilities of the code that make it well suited for numerical relativity on a personal computer and some caveats based on the experiments we have made with it.

In order to further our understanding of the instabilities which develop in numerical relativity codes, I study vacuum solutions of the cosmological type (T³ topology). This involves testing the numerical code using the following non-trivial periodic solutions; Kasner, Gowdy, Bondi and non-linear gauge waves. I look for constraint violating and gauge mode instabilities and study numerical convergence. I will discuss techniques developed to investigate the stability properties of the numerical code.

The conformal approach to the description of isolated systems in General Relativity based on the notion of asymptotic simplicity usually assumes that the conformal boundary —null infinity— is a smooth submanifold. Some work on the so-called polyhomogeneous spacetimes has shown that much of the standard formalism holds on much weaker assumptions on the smoothness of null infinity. Furthermore, some recent work has shown that developments of Misner and Brill-Lindquist data have a non-smooth boundary. The latter raises the questions regarding the suitability of smooth null infinity to model “realistic” systems as different assumptions of the smoothness of the conformal boundary would yield slightly different physical predictions. This is an issue that is not only of relevance not for numerical simulations based on the conformal approach but in general for any code simulating asymptotically flat systems as some sort of asymptotic behaviour must at any rate be prescribed in order to model the “isolatedness” of the system. This prescribed asymptotic behaviour will contain implicit and explicit assumptions regarding the smoothness of null infinity. The relation between hyperboloidal initial data and Cauchy initial data is discussed within this context.

We investigate the gravitational collapse of rapidly rotating relativistic supermassive stars by means of a 3+1 hydrodynamical simulations in conformally flat spacetime of general relativity. We study the evolution of differentially rotating supermassive stars of q ≡ J/M² ~ 1 (J is the angular momentum and M is the gravitational mass of the star) from R/M ~ 65 (R is the circumferential radius of the star) to the point where the conformally flat approximation breaks down. We find that the collapse of the star of q ≳ 1, a radially unstable differentially rotating star form a black hole of q ≲ 1. The main reason to prevent the formation of a black hole of q ≳ 1 is that quite a large amount of the angular momentum stays at the surface. We also find that the collapse is coherent and that it likely leads to the formation of a supermassive black hole with no appreciable disk nor bar. In the absence of nonaxisymmetric deformation, the collapse of differentially rotating supermassive stars are the promising sources of burst and quasinormal ringing waves in the Laser Interferometer Space Antenna.