title:
A physical template family for gravitational waves from precessing
  binaries of spinning compact objects: Application to single-spin binaries

abstract:
  The detection of the gravitational waves (GWs) emitted by precessing binaries
of spinning compact objects is complicated by the large number of parameters
(such as the magnitudes and initial directions of the spins, and the position
and orientation of the binary with respect to the detector) that are required
to model accurately the precession-induced modulations of the GW signal. In
this paper we describe a fast matched-filtering search scheme for precessing
binaries, and we adopt the physical template family proposed by Buonanno, Chen,
and Vallisneri [Phys.Rev.D 67, 104025 (2003)] for ground-based interferometers.
This family provides essentially exact waveforms, written directly in terms of
the physical parameters, for binaries with a single significant spin, and for
which the observed GW signal is emitted during the phase of adiabatic inspiral
(for LIGO-I and VIRGO, this corresponds to a total mass M < 15Msun). We show
how the detection statistic can be maximized automatically over all the
parameters (including the position and orientation of the binary with respect
to the detector), except four (the two masses, the magnitude of the single
spin, and the opening angle between the spin and the orbital angular momentum),
so the template bank used in the search is only four-dimensional; this
technique is relevant also to the searches for GW from extreme--mass-ratio
inspirals and supermassive blackhole inspirals to be performed using the
space-borne detector LISA. Using the LIGO-I design sensitivity, we compute the
detection threshold (~10) required for a false-alarm probability of
10^(-3)/year, and the number of templates (~76,000) required for a minimum
match of 0.97, for the mass range (m1,m2)=[7,12]Msun*[1,3]Msun.


title: A Covariant Information-Density Cutoff in Curved Space-Time

abstract:
  In information theory, the link between continuous information and discrete
information is established through well-known sampling theorems. Sampling
theory explains, for example, how frequency-filtered music signals are
reconstructible perfectly from discrete samples. In this Letter, sampling
theory is generalized to pseudo-Riemannian manifolds. This provides a new set
of mathematical tools for the study of space-time at the Planck scale: theories
formulated on a differentiable space-time manifold can be completely equivalent
to lattice theories. There is a close connection to generalized uncertainty
relations which have appeared in string theory and other studies of quantum
gravity.


title: The ST7 Interferometer

abstract:
  Two homodyne Michelson interferferometers aboard the LISA Pathfinder
spacecraft will measure the the positions of two free-floating test masses, as
part of the NASA ST7 mission. The interferometer is required to measure the
separation between the test masses with sensitivity of 30 pm/sqrt(Hz) at 10
mHz. The readout scheme is described, error sources are analyzed, and
experimental results are presented.


title:
Comment about the "Newtonian limit of String-Dilaton Gravity" paper
  [Int. J. Mod. Phys. D12 (2003) 843-852]

abstract:
  In this comment we point out some problems with the approach used in the
paper "Newtonian limit of String-Dilaton Gravity" in the attempt to explain the
properties of a weak field approximation for gravity theories.


title: Periodic self-similar wave maps coupled to gravity

abstract:
  We continue our studies of spherically symmetric self-similar solutions in
the SU(2) sigma model coupled to gravity. Using mixed numerical and analytical
methods we show existence of an unstable periodic solution lying at the
boundary between the basins of two generic attractors.


title: The conformal geometry of Random Regge Triangulations

abstract:
  We review some of our recent work on the conformal geometry corresponding to
the triangulated surfaces used in 2-dimensional simplicial quantum gravity. In
particular, we discuss the regularized Liouville action associated with random
Regge triangulations and its connection with Hodge-Deligne theory.


title: Black hole formation from a complete regular past

abstract:
  An open problem in general relativity has been to construct an asymptotically
flat solution to a reasonable Einstein-matter system containing a black hole in
the future and yet past-causally geodesically complete, in particular,
containing no white holes. We give such an example in this paper--in fact, a
family of such examples, stable in a suitable sense--for the case of a
self-gravitating scalar field.


title: A minimal no-radiation approximation to Einstein's field equations

abstract:
  An approximation to Einstein's field equations in Arnowitt-Deser-Misner (ADM)
canonical formalism is presented which corresponds to the magneto-hydrodynamics
(MHD) approximation in electrodynamics. It results in coupled elliptic
equations which represent the maximum of elliptic-type structure of Einstein's
theory and naturally generalizes previous conformal-flat truncations of the
theory. The Hamiltonian, in this approximation, is identical with the
non-dissipative part of the Einsteinian one through the third post-Newtonian
order. The proposed scheme, where stationary spacetimes are exactly reproduced,
should be useful to construct {\em realistic} initial data for general
relativistic simulations as well as to model astrophysical scenarios, where
gravitational radiation reaction can be neglected.


title: Evolutions in 3D numerical relativity using fixed mesh refinement

abstract:
  We present results of 3D numerical simulations using a finite difference code
featuring fixed mesh refinement (FMR), in which a subset of the computational
domain is refined in space and time. We apply this code to a series of test
cases including a robust stability test, a nonlinear gauge wave and an excised
Schwarzschild black hole in an evolving gauge. We find that the mesh refinement
results are comparable in accuracy, stability and convergence to unigrid
simulations with the same effective resolution. At the same time, the use of
FMR reduces the computational resources needed to obtain a given accuracy.
Particular care must be taken at the interfaces between coarse and fine grids
to avoid a loss of convergence at higher resolutions, and we introduce the use
of "buffer zones" as one resolution of this issue. We also introduce a new
method for initial data generation, which enables higher-order interpolation in
time even from the initial time slice. This FMR system, "Carpet", is a driver
module in the freely available Cactus computational infrastructure, and is able
to endow generic existing Cactus simulation modules ("thorns") with FMR with
little or no extra effort.


title:
On spherically symmetric solutions with horizon in model with
  multicomponent anisotropic fluid

abstract:
  A family of spherically symmetric solutions in the model with m-component
anisotropic fluid is considered. The metric of the solution depends on
parameters q_s, s = 1,...,m, relating radial pressures and the densities and
contains (n -1)m parameters corresponding to Ricci-flat "internal space"
metrics and obeying certain m(m-1)/2 ("orthogonality") relations. For q_s = 1
(for all s) and certian equations of state (p_i^s = \pm \rho^s) the metric
coincides with the metric of intersecting black brane solution in the model
with antisymmetric forms. A family of solutions with (regular) horizon
corresponding to natural numbers q_s = 1,2,... is singled out. Certain examples
of "generalized simulation" of intersecting M-branes in D=11 supergravity are
considered. The post-Newtonian parameters \beta and \gamma corresponding to the
4-dimensional section of the metric are calculated.


title:
Static post-Newtonian equivalence of GR and gravity with a dynamical
  preferred frame

abstract:
  A generally covariant extension of general relativity (GR) in which a
dynamical unit timelike vector field is coupled to the metric is studied in the
asymptotic weak field limit of spherically symmetric static solutions. The two
post-Newtonian parameters known as the Eddington-Robertson-Schiff parameters
are found to be identical to those in the case of pure GR, except for some
non-generic values of the coefficients in the Lagrangian.


title: Dynamics of thick discs around Schwarzschild-de Sitter black holes

abstract:
  We consider the effects of a cosmological constant on the dynamics of
constant angular momentum discs orbiting Schwarzschild-de Sitter black holes.
The motivation behind this study is to investigate whether the presence of a
radial force contrasting the black hole's gravitational attraction can
influence the occurrence of the runaway instability, a robust feature of the
dynamics of constant angular momentum tori in Schwarzschild and Kerr
spacetimes. In addition to the inner cusp near the black hole horizon through
which matter can accrete onto the black hole, in fact, a positive cosmological
constant introduces also an outer cusp through which matter can leave the torus
without accreting onto the black hole. To assess the impact of this outflow on
the development of the instability we have performed time-dependent and
axisymmetric hydrodynamical simulations of equilibrium initial configurations
in a sequence of background spacetimes of Schwarzschild-de Sitter black holes
with increasing masses. The simulations have been performed with an unrealistic
value for the cosmological constant which, however, yields sufficiently small
discs to be resolved accurately on numerical grids and thus provides a first
qualitative picture of the dynamics. The calculations, carried out for a wide
range of initial conditions, show that the mass-loss from the outer cusp can
have a considerable impact on the instability, with the latter being rapidly
suppressed if the outflow is large enough.


title: SO(3,2)/Sp(2) symmetries in BTZ black holes

abstract:
  We study global flat embeddings, three accelerations and Hawking temperatures
of the BTZ black holes in the framework of two-time physics scheme associated
with Sp(2) local symmetry, to construct their corresponding SO(3,2) global
symmetry invariant Lagrangians both inside and outside event horizons.
Moreover, the Sp(2) local symmetry is discussed in terms of the metric
time-independence.


title: Chiral gravity in higher dimensions

abstract:
  We construct a chiral theory of gravity in 7 and 8 dimensions, which are
equivalent to Einstein-Cartan theory using less variables. In these dimensions,
we can construct such higher dimensional chiral gravity because of the
existence of gravitational instanton. The octonionic-valued variables in the
theory represent the deviation from the gravitational instanton, and from their
non-associativity, prevents the theory to be SO(n) gauge invariant. Still the
chiral gravity holds G_2 (7-D), and Spin(7) (8-D) gauge symmetry.


title:
On the nonexistence of conformally flat slices in the Kerr and other
  stationary spacetimes

abstract:
  It is proved that a stationary solutions to the vacuum Einstein field
equations with non-vanishing angular momentum have no Cauchy slice that is
maximal, conformally flat, and non-boosted. The proof is based on results
coming from a certain type of asymptotic expansions near null and spatial
infinity --which also show that the developments of Bowen-York type of data
cannot have a development admitting a smooth null infinity--, and from the fact
that stationary solutions do admit a smooth null infinity.


title: Binary Neutron Star Inspiral Search in LIGO S1

abstract:
  We describe the search for gravitational waves from inspiraling neutron star
binary systems, using data from the first Scientific Run of the LIGO Science
Collaboration.


title: Chaotic self-similar wave maps coupled to gravity

abstract:
  We continue our studies of spherically symmetric self-similar solutions in
the SU(2) sigma model coupled to gravity. For some values of the coupling
constant we present numerical evidence for the chaotic solution and the fractal
threshold behavior. We explain this phenomenon in terms of horseshoe-like
dynamics and heteroclinic intersections.


title: Reflection, radiation and interference for black holes

abstract:
  Black holes are capable of reflection: there is a finite probability for any
particle that approaches the event horizon to bounce back. The albedo of the
black hole depends on its temperature and the energy of the incoming particle.
The reflection shares its physical origins with the Hawking process of
radiation, both of them arise as consequences of the mixing of the incoming and
outgoing waves that takes place on the event horizon.


title: Isocurvature Perturbations in Quintessence Cosmologies

abstract:
  We present a systematic treatment of the initial conditions and evolution of
cosmological perturbations in a universe containing photons, baryons,
neutrinos, cold dark matter, and a scalar quintessence field. By formulating
the evolution in terms of a differential equation involving a matrix acting on
a vector comprised of the perturbation variables, we can use the familiar
language of eigenvalues and eigenvectors. As the largest eigenvalue of the
evolution matrix is fourfold degenerate, it follows that there are four
dominant modes with non-diverging gravitational potential at early times,
corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature
and neutrino isocurvature perturbations. We conclude that quintessence does not
lead to an additional independent mode.


title: Scalar Field for Breaking Lorentz and Diffeomorphism Invariance

abstract:
  A scalar field can be inserted in Maxwell and/or Einstein theory to effect
symmetry breaking. Consequences of such a modification are discussed. Possible
dynamics for the scalar field are presented.


title: Circular stationary cyclic symmetric spacetimes; conformal flatness

abstract:
  A subclassification of stationary spacetimes, endowed with one timelike and
one spacelike Killing vectors, i.e., Petrov $G{_2}I$ on $T_2$ spaces, is
proposed. Special attention deserves the Collison's theorem [1] and the branch
of metrics circularly cyclicly (axially) symmetric possessing additionally the
conformal flatness property reported by Garcia and Campuzano [2].


title: Induced Gravity from Theory Space

abstract:
  The mass spectrum of a model constructed in a theory space is expressed by
eigenvalues of the Laplacian on the graph structure of the theory space. The
nature of the one-loop UV divergence in the vacuum energy is then controlled
only by the degree matrix of the graph. Using these facts, we can construct
models of induced gravity which do not suffer from divergences at the one-loop
level.


title:
Dynamics of super-horizon photons during inflation with vacuum
  polarization

abstract:
  We study asymptotic dynamics of photons propagating in the polarized vacuum
of a locally de Sitter Universe. The origin of the vacuum polarization is
fluctuations of a massless, minimally coupled, scalar, which we model by the
one-loop vacuum polarization tensor of scalar electrodynamics. We show that
late time dynamics of the electric field on superhorizon scales approaches that
of an Airy oscillator. The magentic field amplitude, on the other hand,
asymptotically approaches a nonvanishing constant (plus an exponentially small
oscillatory component), which is suppressed with respect to the initial
(vacuum) amplitude. This implies that the asymptotic photon dynamics is more
intricate than that of a massive photon obeying the local Proca equation.


title: Cosmology with primordial black holes

abstract: Some aspects of Cosmology with primordial black holes are briefly reviewed


title:
The Einstein static universe with torsion and the sign problem of the
  cosmological constant

abstract:
  In the field equations of Einstein-Cartan theory with cosmological constant a
static spherically symmetric perfect fluid with spin density satisfying the
Weyssenhoff restriction is considered. This serves as a rough model of space
filled with (fermionic) dark matter. From this the Einstein static universe
with constant torsion is constructed, generalising the Einstein Cosmos to
Einstein-Cartan theory.
  The interplay between torsion and the cosmological constant is discussed. A
possible way out of the cosmological constant's sign problem is suggested.


title:
The Speed of Gravity in General Relativity and Theoretical
  Interpretation of the Jovian Deflection Experiment

abstract:
  Recent measurements of the propagation of the quasar's radio signal past
Jupiter are directly sensitive to the time-dependent effect from the geometric
sector of general relativity which is proportional to the speed of propagation
of gravity but not the speed of light. It provides a first confirmative
measurement of the fundamental speed of the Einstein general principle of
relativity for gravitational field.

categories: gr-qc astro-ph hep-ph hep-th physics.class-ph


title: Scalar fields superdense gravitating systems

abstract:
  Solutions for scalar fields superdense gravitating systems of flat, open and
closed type obtained in the frame of gauge theories of gravitation are
discussed. Properties of these systems in dependence on parameter $\beta$ and
initial conditions are analyzed.


title:
Approximate Matching of Analytic and Numerical Solutions for Rapidly
  Rotating Neutron Stars

abstract:
  We investigate the properties of a closed-form analytic solution recently
found by Manko et al. (2000) for the exterior spacetime of rapidly rotating
neutron stars. For selected equations of state we numerically solve the full
Einstein equations to determine the neutron star spacetime along constant rest
mass sequences. The analytic solution is then matched to the numerical
solutions by imposing the condition that the quadrupole moment of the numerical
and analytic spacetimes be the same. For the analytic solution we consider,
such a matching condition can be satisfied only for very rapidly rotating
stars. When solutions to the matching condition exist, they belong to one of
two branches. For one branch the current octupole moment of the analytic
solution is very close to the current octupole moment of the numerical
spacetime; the other branch is more similar to the Kerr solution. We present an
extensive comparison of the radii of innermost stable circular orbits (ISCOs)
obtained with a) the analytic solution, b) the Kerr metric, c) an analytic
series expansion derived by Shibata and Sasaki (1998) and d) a highly accurate
numerical code. In most cases where a corotating ISCO exists, the analytic
solution has an accuracy consistently better than the Shibata-Sasaki expansion.
The numerical code is used for tabulating the mass-quadrupole and
current-octupole moments for several sequences of constant rest mass.


title:
Gravitational effects on light rays and binary pulsar energy loss in a
  scalar theory of gravity

abstract:
  A scalar bimetric theory of gravity with a preferred reference frame is
summarized. Dynamics is governed by an extension of Newton's second law. In the
static case, geodesic motion is recovered together with Newton's attraction
field. In the static spherical case, Schwarzschild's metric is found.
Asymptotic schemes of post-Newtonian (PN) and post-Minkowskian (PM)
approximation are built, each based on associating a conceptual family of
systems with the given system. At the 1PN approximation, there is no
preferred-frame effect for photons, hence the standard predictions of GR for
photons are got. At the 0PM approximation, an isolated system loses energy by
quadrupole radiation, without any monopole or dipole term. Inserting this loss
into the Newtonian 2-body problem gives the Peters-Mathews coefficients of the
theory.


title: Weak field limit of Reissner-Nordstrom black hole lensing

abstract:
  We study gravitational lensing by a Reissner-Nordstrom (RN) black hole in the
weak field limit. We obtain the basic equations for the deflection angle and
time delay and find analytical expressions for the positions and amplifications
of the primary and secondary images. Due to a net positive charge, the
separation between images increases, but no change in the total magnification
occurs.


title:
Einstein boundary conditions in relation to constraint propagation for
  the initial-boundary value problem of the Einstein equations

abstract:
  We show how the use of the normal projection of the Einstein tensor as a set
of boundary conditions relates to the propagation of the constraints, for two
representations of the Einstein equations with vanishing shift vector: the ADM
formulation, which is ill posed, and the Einstein-Christoffel formulation,
which is symmetric hyperbolic. Essentially, the components of the normal
projection of the Einstein tensor that act as non-trivial boundary conditions
are linear combinations of the evolution equations with the constraints that
are not preserved at the boundary, in both cases. In the process, the
relationship of the normal projection of the Einstein tensor to the recently
introduced ``constraint-preserving'' boundary conditions becomes apparent.


title:
On the Speed of Gravity and Relativistic v/c Corrections to the Shapiro
  Time Delay

abstract:
  Recent papers by Samuel declared that the linearized post-Newtonian v/c
effects are too small to have been measured in the recent experiment involving
Jupiter and quasar J0842+1845 that was used to measure the ultimate speed of
gravity defined as a fundamental constant entering in front of each time
derivative of the metric tensor in the Einstein gravity field equations. We
describe our Lorentz-invariant formulation of the Jovian deflection experiment
and confirm that v/c effects are do observed, as contrasted to the erroneous
claim by Samuel, and that they vanish if and only if the speed of gravity is
infinite.


title:
The wave equation on the Schwarzschild metric II: Local decay for the
  spin 2 Regge Wheeler equation

abstract:
  Odd-type spin 2 perturbations of Einstein's equation can be reduced to the
scalar Regge-Wheeler equation. We show that the weighted norms of solutions are
in L^2 of time and space. This result uses commutator methods and applies
uniformly to all relevant spherical harmonics.


title: The Big Bang as a Phase Transition

abstract:
  We study a five-dimensional cosmological model, which suggests that the
universe bagan as a discontinuity in a (Higgs-type) scalar field, or
alternatively as a conventional four-dimensional phase transition.


title:
How to approach Quantum Gravity - Background independence in 1+1
  dimensions

abstract:
  The application of quantum theory to gravity is beset with many technical and
conceptual problems. After a short tour d'horizon of recent attempts to master
those problems by the introduction of new approaches, we show that the aim, a
background independent quantum theory of gravity, can be reached in a
particular area, 2d dilaton quantum gravity, without any assumptions beyond
standard quantum field theory.


title: New solutions in 3D gravity

abstract:
  We study gravitational theory in 1+2 spacetime dimensions which is determined
by the Lagrangian constructed as a sum of the Einstein-Hilbert term plus the
two (translational and rotational) gravitational Chern-Simons terms. When the
corresponding coupling constants vanish, we are left with the purely Einstein
theory of gravity. We obtain new exact solutions for the gravitational field
equations with the nontrivial material sources. Special attention is paid to
plane-fronted gravitational waves (in case of the Maxwell field source) and to
the circularly symmetric as well as the anisotropic cosmological solutions
which arise for the ideal fluid matter source.


title:
Type I vacuum solutions with aligned Papapetrou fields: an intrinsic
  characterization

abstract:
  We show that Petrov type I vacuum solutions admitting a Killing vector whose
Papapetrou field is aligned with a principal bivector of the Weyl tensor are
the Kasner and Taub metrics, their counterpart with timelike orbits and their
associated windmill-like solutions, as well as the Petrov homogeneous vacuum
solution. We recover all these metrics by using an integration method based on
an invariant classification which allows us to characterize every solution. In
this way we obtain an intrinsic and explicit algorithm to identify them.


title:
Discrete Group Actions on Spacetimes: Causality Conditions and the
  Causal Boundary

abstract:
  Suppose a spacetime $M$ is a quotient of a spacetime $V$ by a discrete group
of isometries. It is shown how causality conditions in the two spacetimes are
related, and how can one learn about the future causal boundary on $M$ by
studying structures in $V$. The relations between the two are particularly
simple (the boundary of the quotient is the quotient of the boundary) if both
$V$ and $M$ have spacelike future boundaries and if it is known that the
quotient of the future completion of $V$ is past-distinguishing. (That last
assumption is automatic in the case of $M$ being multi-warped.)


title:
On the problem of uniqueness of energy-momentum tensor of gravitational
  field

abstract:
  For an island-like distribution of matter the gravitational energy-momentum
tensor is defined according to Weinberg as a source of metric. If this source
is formed by self-interactions of gravitons, so that nonphysical degrees of
freedom are excluded, then this source is a reasonable candidate for the
energy-momentum tensor of gravitational field. The disastrous influence of the
nonphysical degrees of freedom is demonstrated by comparing the gravitational
energy-momentum tensors in the harmonic, isotropic and standard frames for the
Schwarzschild solution. The harmonic frame is clearly preferable for defining
the gravitational energy-momentum tensor.


title:
Conformal-thin-sandwich initial data for a single boosted or spinning
  black hole puncture

abstract:
  Sequences of initial-data sets representing binary black holes in
quasi-circular orbits have been used to calculate what may be interpreted as
the innermost stable circular orbit. These sequences have been computed with
two approaches. One method is based on the traditional
conformal-transverse-traceless decomposition and locates quasi-circular orbits
from the turning points in an effective potential. The second method uses a
conformal-thin-sandwich decomposition and determines quasi-circular orbits by
requiring the existence of an approximate helical Killing vector. Although the
parameters defining the innermost stable circular orbit obtained from these two
methods differ significantly, both approaches yield approximately the same
initial data, as the separation of the binary system increases. To help
understanding this agreement between data sets, we consider the case of initial
data representing a single boosted or spinning black hole puncture of the
Bowen-York type and show that the conformal-transverse-traceless and
conformal-thin-sandwich methods yield identical data, both satisfying the
conditions for the existence of an approximate Killing vector.


title: On the Theory of Killing Orbits in Space-Time

abstract:
  This paper gives a theoretical discussion of the orbits and isotropies which
arise in a space-time which admits a Lie algebra of Killing vector fields. The
submanifold structure of the orbits is explored together with their induced
Killing vector structure. A general decomposition of a space-time in terms of
the nature and dimension of its orbits is given and the concept of stability
and instability for orbits introduced. A general relation is shown linking the
dimensions of the Killing algebra, the orbits and the isotropies. The
well-behaved nature of "stable" orbits and the possible miss-behaviour of the
"unstable" ones is pointed out and, in particular, the fact that independent
Killing vector fields in space-time may not induce independent such vector
fields on unstable orbits. Several examples are presented to exhibit these
features. Finally, an appendix is given which revisits and attempts to clarify
the well-known theorem of Fubini on the dimension of Killing orbits.


title: Boundaries on Spacetimes: An Outline

abstract:
  The causal boundary construction of Geroch, Kronheimer, and Penrose has some
universal properties of importance for general studies of spacetimes,
particularly when equipped with a topology derived from the causal structure.
Properties of the causal boundary are detailed for spacetimes with spacelike
boundaries, for multi-warped spacetimes, for static spacetimes, and for
spacetimes with group actions.


title: Holonomy groups and spacetimes

abstract:
  A study is made of the possible holonomy group types of a space-time for
which the energy-momentum tensor corresponds to a null or non-null
electromagnetic field, a perfect fluid or a massive scalar field. The case of
an Einstein space is also included. The techniques developed are also applied
to vacuum and conformally flat space-times and contrasted with already known
results in these two cases. Examples are given.


title: Revised Canonical Quantum Gravity via the Frame Fixing

abstract:
  We present a new reformulation of the canonical quantum geometrodynamics,
which allows to overcome the fundamental problem of the frozen formalism and,
therefore, to construct an appropriate Hilbert space associate to the solution
of the restated dynamics. More precisely, to remove the ambiguity contained in
the Wheeler-DeWitt approach, with respect to the possibility of a (3 +
1)-splitting when the space-time is in a quantum regime, we fix the reference
frame (i.e. the lapse function and the shift vector) by introducing the
so-called kinematical action; as a consequence the new super-Hamiltonian
constraint becomes a parabolic one and we arrive to a Schroedinger-like
approach for the quantum dynamics. In the semiclassical limit our theory
provides General Relativity in the presence of an additional energy-momentum
density contribution coming from no longer zero eigenvalues of the Hamiltonian
constraints; the interpretation of these new contributions comes out in natural
way as soon as it is recognized that the kinematical action can be recasted in
such a way it describes a pressureless, but, in general, non geodesic perfect
fluid.


title:
Extra force from an extra dimension. Comparison between brane theory,
  STM and other approaches

abstract:
  We investigate the question of how an observer in 4D perceives the
five-dimensional geodesic motion. We consider the interpretation of null and
non-null bulk geodesics in the context of brane theory, space-time-matter
theory (STM) and other non-compact approaches. We develop a "frame-invariant"
formalism that allows the computation of the rest mass and its variation as
observed in 4D. We find the appropriate expression for the four-acceleration
and thus obtain the extra force observed in 4D. Our formulae extend and
generalize all previous results in the literature. An important result here is
that the extra force in brane-world models with ${\bf Z}_{2}$-symmetry is
continuous and well defined across the brane. This is because the momentum
component along the extra dimension is discontinuous across the brane, which
effectively compensates the discontinuity of the extrinsic curvature. We show
that brane theory and STM produce identical interpretation of the bulk geodesic
motion. This holds for null and non-null bulk geodesics. Thus, experiments with
test particles are unable to distinguish whether our universe is described by
the brane world scenario or by STM. However, they do discriminate between the
brane/STM scenario and other non-compact approaches. Among them the canonical
and embedding approaches, which we examine in detail here.


title: Restricting quark matter models by gravitational wave observation

abstract:
  We consider the 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 both fluid and
spacetime modes of pure quark stars. If we observe the $f$ and the lowest
$w_{\rm II}$ 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.


title: Non-adiabatic collapse of a quasi-spherical radiating star

abstract:
  A model is proposed of a collapsing quasi-spherical radiating star with
matter content as shear-free isotropic fluid undergoing radial heat-flow with
outgoing radiation. To describe the radiation of the system, we have considered
both plane symmetric and spherical Vaidya solutions. Physical conditions and
thermodynamical relations are studied using local conservation of momentum and
surface red-shift. We have found that for existence of radiation on the
boundary, pressure on the boundary is not necessary.


title:
Screening and absorption of gravitation in pre-relativistic and
  relativistic theories

abstract:
  After commenting on the early search for a mechanism explaining the Newtonian
action-at-a-distance gravitational law we review non-Newtonian effects
occurring in certain ansatzes for shielding, screening and absorption effects
in pre-relativistic theories of gravity. Mainly under the aspect of absorption
and suppression (or amplification), we then consider some implications of these
ansatzes for relativistic theories of gravity and discuss successes and
problems in establishing a general framework for a comparison of alternative
relativistic theories of gravity. We examine relativistic representatives of
theories with absorption and suppression (or amplification) effects, such as
fourth-order theories, tetrad theories and the Einstein-Cartan-Kibble-Sciama
theory.


title: Are there Thermodynamical Degrees of Freedom of Gravitation?

abstract:
  In discussing fundamentals of general-relativistic irreversible continuum
thermodynamics, this theory is shown to be characterized by the feature that no
thermodynamical degrees of freedom are ascribed to gravitation. However,
accepting that black hole thermodynamics seems to oppose this harmlessness of
gravitation one is called on consider other approaches. Therefore, in brief
some gravitational and thermodynamical alternatives are reviewed.


title: Generalised Kundt waves and their physical interpretation

abstract:
  We present the complete family of space-times with a non-expanding,
shear-free, twist-free, geodesic principal null congruence (Kundt waves) that
are of algebraic type III and for which the cosmological constant ($\Lambda_c$)
is non-zero. The possible presence of an aligned pure radiation field is also
assumed. These space-times generalise the known vacuum solutions of type N with
arbitrary $\Lambda_c$ and type III with $\Lambda_c=0$. It is shown that there
are two, one and three distinct classes of solutions when $\Lambda_c$ is
respectively zero, positive and negative. The wave surfaces are plane,
spherical or hyperboloidal in Minkowski, de Sitter or anti-de Sitter
backgrounds respectively, and the structure of the family of wave surfaces in
the background space-time is described. The weak singularities which occur in
these space-times are interpreted in terms of envelopes of the wave surfaces.


title:
Some high-frequency gravitational waves related to exact radiative
  spacetimes

abstract:
  A formalism is introduced which may describe both standard linearized waves
and gravitational waves in Isaacson's high-frequency limit. After emphasizing
main differences between the two approximation techniques we generalize the
Isaacson method to non-vacuum spacetimes. Then we present three large explicit
classes of solutions for high-frequency gravitational waves in particular
backgrounds. These involve non-expanding (plane, spherical or hyperboloidal),
cylindrical, and expanding (spherical) waves propagating in various universes
which may contain a cosmological constant and electromagnetic field. Relations
of high-frequency gravitational perturbations of these types to corresponding
exact radiative spacetimes are described.


title: Cosmic magnetic fields from velocity perturbations in the early Universe

abstract:
  We show, using a covariant and gauge-invariant charged multifluid
perturbation scheme, that velocity perturbations of the matter-dominated dust
Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of
cosmic magnetic fields. Moreover, using cosmic microwave background (CMB)
constraints, it is argued that these fields can reach strengths of between
10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them
plausible seed field candidates.


title: Energy-Momentum Tensor of Cosmological Fluctuations during Inflation

abstract:
  We study the renormalized energy-momentum tensor (EMT) of cosmological scalar
fluctuations during the slow-rollover regime for chaotic inflation with a
quadratic potential and find that it is characterized by a negative energy
density which grows during slow-rollover. We also approach the back-reaction
problem as a second-order calculation in perturbation theory finding no
evidence that the back-reaction of cosmological fluctuations is a gauge
artifact. In agreement with the results on the EMT, the average expansion rate
is decreased by the back-reaction of cosmological fluctuations.


title: Thermodynamic scheme of inhomogeneous perfect fluid mixtures

abstract:
  We analyze the compatibility between the geometrodynamics and thermodynamics
of a binary mixture of perfect fluids which describe inhomogeneous cosmological
models. We generalize the thermodynamic scheme of general relativity to include
the chemical potential of the fluid mixture with non-vanishing entropy
production. This formalism is then applied to the case of Szekeres and Stephani
families of cosmological models. The compatibility conditions turn out to
impose symmetry conditions on the cosmological models in such a way that only
the limiting case of the Friedmann-Robertson-Walker model remains compatible.
This result is an additional indication of the incompatibility between
thermodynamics and relativity.


title:
Can conventional forces really explain the anomalous acceleration of
  Pioneer 10/11 ?

abstract:
  A conventional explanation of the correlation between the Pioneer 10/11
anomalous acceleration and spin-rate change is given. First, the rotational
Doppler shift analysis is improved. Finally, a relation between the radio beam
reaction force and the spin-rate change is established. Computations are found
in good agreement with observational data. The relevance of our result to the
main Pioneer 10/11 anomalous acceleration is emphasized. Our analysis leads us
to conclude that the latter may not be merely artificial.


title:
Gravitational and electromagnetic fields near an anti-de Sitter-like
  infinity

abstract:
  We analyze asymptotic structure of general gravitational and electromagnetic
fields near an anti-de Sitter-like conformal infinity. Dependence of the
radiative component of the fields on a null direction along which the infinity
is approached is obtained. The directional pattern of outgoing and ingoing
radiation, which supplements standard peeling property, is determined by the
algebraic (Petrov) type of the fields and also by orientation of principal null
directions with respect to the timelike infinity. The dependence on the
orientation is a new feature if compared to spacelike infinity.


title:
Boulware state and semiclassical thermodynamics of black holes in a
  cavity

abstract:
  A black hole, surrounded by a reflecting shell, acts as an effective
star-like object with respect to the outer region that leads to vacuum
polarization outside, where the quantum fields are in the Boulware state. We
find the quantum correction to the Hawking temperature, taking into account
this circumstance. It is proportional to the integral of the trace of the total
quantum stress-energy tensor over the whole space from the horizon to infinity.
For the shell, sufficiently close to the horizon, the leading term comes from
the boundary contribution of the Boulware state.


title:
Semilinear wave equations on the Schwarzschild manifold I: Local decay
  estimates

abstract:
  The semilinear wave equation on the (outer) Schwarzschild manifold is
studied. We prove local decay estimates for general (non-radial) data, deriving
a-priori Morawetz type estimates.


title: Killing-Yano tensors and surface terms

abstract:
  New geometries were obtained by adding a suitable surface term involving the
components of the angular momentum to the corresponding free Lagrangians.
Killing vectors, Killing-Yano and Killing tensors of the obtained manifolds
were investigated.


title: Surface terms,angular momentum and Hamilton-Jacobi formalism

abstract:
  Quadratic Lagrangians are introduced adding surface terms to a free particle
Lagrangian. Geodesic equations are used in the context of the Hamilton-Jacobi
formulation of constrained sysytem. Manifold structure induced by the quadratic
Lagrangian is investigated.


title: Hamilton-Jacobi formalism of the massive Yang-Mills theory revisited

abstract:
  Using Hamilton-Jacobi formalism we investigated the massive Yang-Mills theory
on both extended and reduced phase-space. The integrability conditions were
discussed and the actions were calculated.


title: Gauge Fixing and Observables in General Relativity

abstract:
  The conventional group of four-dimensional diffeomorphisms is not realizeable
as a canonical transformation group in phase space. Yet there is a larger
field-dependent symmetry transformation group which does faithfully reproduce
4-D diffeomorphism symmetries. Some properties of this group were first
explored by Bergmann and Komar. More recently the group has been analyzed from
the perspective of projectability under the Legendre map. Time translation is
not a realizeable symmetry, and is therefore distinct from
diffeomorphism-induced symmetries. This issue is explored further in this
paper. It is shown that time is not "frozen". Indeed, time-like diffeomorphism
invariants must be time-dependent. Intrinsic coordinates of the type proposed
by Bergmann and Komar are used to construct invariants. Lapse and shift
variables are retained as canonical variables in this approach, and therefore
will be subject to quantum fluctuations in an eventual quantum theory. Concepts
and constructions are illustrated using the relativistic classical and quantum
free particle. In this example concrete time-dependent invariants are displayed
and fluctuation in proper time is manifest.


title: Almost product manifolds as the low energy geometry of Dirichlet branes

abstract:
  Any candidate theory of quantum gravity must address the breakdown of the
classical smooth manifold picture of space-time at distances comparable to the
Planck length. String theory, in contrast, is formulated on conventional
space-time. However, we show that in the low energy limit, the dynamics of
generally curved Dirichlet p-branes possess an extended local isometry group,
which can be absorbed into the brane geometry as an almost product structure.
The induced kinematics encode two invariant scales, namely a minimal length and
a maximal speed, without breaking general covariance. Quantum gravity effects
on D-branes at low energy are then seen to manifest themselves by the
kinematical effects of a maximal acceleration. Experimental and theoretical
implications of such new kinematics are easily derived. We comment on
consequences for brane world phenomenology.


title: Dirty black holes: Quasinormal modes for "squeezed" horizons

abstract:
  We consider the quasinormal modes for a class of black hole spacetimes that,
informally speaking, contain a closely ``squeezed'' pair of horizons. (This
scenario, where the relevant observer is presumed to be ``trapped'' between the
horizons, is operationally distinct from near-extremal black holes with an
external observer.) It is shown, by analytical means, that the spacing of the
quasinormal frequencies equals the surface gravity at the squeezed horizons.
Moreover, we can calculate the real part of these frequencies provided that the
horizons are sufficiently close together (but not necessarily degenerate or
even ``nearly degenerate''). The novelty of our analysis (which extends a
model-specific treatment by Cardoso and Lemos) is that we consider ``dirty''
black holes; that is, the observable portion of the (static and spherically
symmetric) spacetime is allowed to contain an arbitrary distribution of matter.


title: Conserved Charges in Einstein Gauss-Bonnet theory

abstract:
  Using Noether's identities, we define a superpotential with respect to a
background for the Einstein Gauss-Bonnet theory of gravity. As an example, we
show that its associated conserved charge yields the mass-energy of a
D-dimensional Gauss-Bonnet black hole in an anti-de Sitter spacetime.


title:
Black hole solutions coupled to Born-Infeld electrodynamics with
  derivative corrections

abstract:
  We investigate black hole solutions in the Einstein-Born-Infeld system. We
clarify the role played by derivative corrections to the Born-Infeld (BI)
action. The qulitative differences from the case without derivative corrections
are: (i) there is no particlelike solution. (ii) the existence of the inner
horizon is restricted to the near extreme solutions. (iii) contribution of the
BI parameter $b$ to the gravitational mass and the Hawking temperature works in
the opposite direction.


title:
Numerical stability of the AA evolution system compared to the ADM and
  BSSN systems

abstract:
  We explore the numerical stability properties of an evolution system
suggested by Alekseenko and Arnold. We examine its behavior on a set of
standardized testbeds, and we evolve a single black hole with different gauges.
Based on a comparison with two other evolution systems with well-known
properties, we discuss some of the strengths and limitations of such simple
tests in predicting numerical stability in general.


title: The Pioneer anomaly in the context of the braneworld scenario

abstract:
  We examine the Pioneer anomaly - a reported anomalous acceleration affecting
the Pioneer 10/11, Galileo and Ulysses spacecrafts - in the context of a
braneworld scenario. We show that effects due to the radion field cannot
account for the anomaly, but that a scalar field with an appropriate potential
is able to explain the phenomena. Implications and features of our solution are
analyzed.


title: Unimodular relativity and cosmological constant : Comments

abstract:
  We show that the conclusion that matter stress-energy tensor satisfies the
usual covariant continuity law, and the cosmological constant is still a
constant of integration arrived at by Finkelstein et al (42, 340, 2001) is not
valid.


title: Two-Brane Randall-Sundrum Model in AdS_5 and dS_5

abstract:
  Two flat Randall - Sundrum three-branes are analyzed, at fixed mutual
distance, in the case where each brane contains an ideal isotropic fluid. Both
fluids are to begin with assumed to obey the equation of state p=(\gamma
-1)\rho, where \gamma is a constant. Thereafter, we impose the condition that
there is zero energy flux from the branes into the bulk, and assume that the
tension on either brane is zero. It then follows that constant values of the
fluid energies at the branes are obtained only if the value of \gamma is equal
to zero (i.e., a `vacuum' fluid). The fluids on the branes are related: if one
brane is a dS_4 brane (the effective four-dimensional constant being positive),
then the other brane is dS_4 also, and if the fluid energy density on one brane
is positive, the energy density on the other brane is larger in magnitude but
negative. This is a non-acceptable result, which sheds some light on how far it
is possible to give a physical interpretation of the two-brane scenario. Also,
we discuss the graviton localization problem in the two-brane setting,
generalizing prior works.


title:
Global existence problem in $T^3$-Gowdy symmetric IIB superstring
  cosmology

abstract:
  We show global existence theorems for Gowdy symmetric spacetimes with type
IIB stringy matter. The areal and constant mean curvature time coordinates are
used. Before coming to that, it is shown that a wave map describes the
evolution of this system.


title: Sound Wave in Vortex with Sink

abstract:
  Using Komar's definition, we give expressions for the mass and angular
momentum of a rotating acoustic black hole. We show that the mass and angular
momentum so defined, obey the equilibrium version of the first law of Black
Hole thermodynamics. We also show that when a phonon passes by a vortex with a
sink, its trajectory is bent. The angle of bending of the sound wave to leading
order is quadratic in $A/cb$ and $B/cb$, where $b$ is the impact parameter and
$A$ and $B$ are the parameters in the velocity of the fluid flow. The time
delay in the propagation of sound wave which to first order depends only on
$B/c^2$ and is independent of $A$.


title:
Stability of Naked Singularity arising in gravitational collapse of Type
  I matter fields

abstract:
  Considering gravitational collapse of Type I matter fields, we prove that,
given an arbitrary $C^{2}$- mass function $\textit{M}(r,v)$ and a $C^{1}$-
function $h(r,v)$ (through the corresponding $C^{1}$- metric function
$\nu(t,r)$), there exist infinitely many choices of energy distribution
function $b(r)$ such that the `true' initial data ($\textit{M},h(r,v)$) leads
the collapse to the formation of naked singularity. We further prove that the
occurrence of such a naked singularity is stable with respect to small changes
in the initial data. We remark that though the initial data leading to both
black hole and naked singularity form a "big" subset of the true initial data
set, their occurrence is not generic. The terms `stability' and `genericity'
are appropriately defined following the theory of dynamical systems. The
particular case of radial pressure $p_{r}(r)$ has been illustrated in details
to get clear picture of how naked singularity is formed and how, it is stable
with respect to initial data.


title: Stable gravastars - an alternative to black holes?

abstract:
  The "gravastar" picture developed by Mazur and Mottola is one of a very small
number of serious challenges to our usual conception of a "black hole". In the
gravastar picture there is effectively a phase transition at/ near where the
event horizon would have been expected to form, and the interior of what would
have been the black hole is replaced by a segment of de Sitter space. While
Mazur and Mottola were able to argue for the thermodynamic stability of their
configuration, the question of dynamic stability against spherically symmetric
perturbations of the matter or gravity fields remains somewhat obscure. In this
article we construct a model that shares the key features of the Mazur-Mottola
scenario, and which is sufficiently simple for a full dynamical analysis. We
find that there are some physically reasonable equations of state for the
transition layer that lead to stability.


title:
Mathematical Equivalency of the Ether Based Gavitation Theory of Janossy
  and General Relativity

abstract:
  "There are several interpretations and approaches to relativity. All of them
are characterized by the fact that none of them is accepted by physicists
without doubts, even the Einsteinian General Relativity! Only those theories
can get into the spotlight that predicts something that is different from
predictions of other concurrent theories. From this point of view the theory of
Janossy [1] is not an excellent idea, as he tried to show that his
materialistic approach also corresponds to the general principles and equations
of relativity. As his program was basically successful there was not any
additional result, except the philosophical part."
  Since the death of Janossy, his work has almost been forgotten. Both what he
achieved and what he was not succeeded in. He was one of the founders of KFKI
(Central Physics Research Institute of the Hungarian Scientific Academy) but
his effort has not been carried over even there, however his collegues are
still remember his name and his work. Luckily his books are still available in
the Hungarian libraries. Additionally the most informed etherists in the world
who are lucky enough to know his work are consider his work as a No1 reference.
  This paper is designated to refresh the idea of the ether based gravitation
theory of Janossy and introduce a well founded way to adjust it to be
equivalent with the experiences and General Relativity.


title:
Scale-invariance in gravity and implications for the cosmological
  constant

abstract:
  Recently a scale invariant theory of gravity was constructed by imposing a
conformal symmetry on general relativity. The imposition of this symmetry
changed the configuration space from superspace - the space of all Riemannian
3-metrics modulo diffeomorphisms - to conformal superspace - the space of all
Riemannian 3-metrics modulo diffeomorphisms and conformal transformations.
However, despite numerous attractive features, the theory suffers from at least
one major problem: the volume of the universe is no longer a dynamical
variable. In attempting to resolve this problem a new theory is found which has
several surprising and atractive features from both quantisation and
cosmological perspectives. Furthermore, it is an extremely restrictive theory
and thus may provide testable predictions quickly and easily. One particularly
interesting feature of the theory is the resolution of the cosmological
constant problem.


title: Gravitation: Global Formulation and Quantum Effects

abstract:
  A nonintegrable phase-factor global approach to gravitation is developed by
using the similarity of teleparallel gravity with electromagnetism. The phase
shifts of both the COW and the gravitational Aharonov-Bohm effects are
obtained. It is then shown, by considering a simple slit experiment, that in
the classical limit the global approach yields the same result as the
gravitational Lorentz force equation of teleparallel gravity. It represents,
therefore, the quantum mechanical version of the classical description provided
by the gravitational Lorentz force equation. As teleparallel gravity can be
formulated independently of the equivalence principle, it will consequently
require no generalization of this principle at the quantum level.


title: General Relativity as a SO(3) Gauge-Theory

abstract:
  The Einsteinian Theory of Gravitation ("General Theory of Relativity") is
founded essentially; on the reception that the geometrical properties of the
4-dimensional space-time continuum are defined from the matter in it. Contrary
to this, in the Newtonian Mechanics space and time obey a absolute,
matter-independent meaning. This thesis offers a compromise between the two
conceptions: The spontaneous splitting of space-time in a "universal time" and
a "absolute space" in the sense of Newton is accepted, but this (1+3)-splitting
will receive the status of a dynamical object in the sense of Einstein. Herein,
the (large scale) dynamics of the (1+3) splitting is coupled only weakly to the
(local) fluctuation of the matter density with the help of the Einsteinian
equations, so that these will keep their validity, regarding the gravitational
phenomena, in a bounded domain of space (planets, stars, galaxies). However, at
a cosmic scale, the properties of the universe as whole will be determined
essentially from the selfdynamics of the space-time splitting. The geometry of
the (1+3)-splitting and the expansion of the empty universe will be examined in
detail. Contrary to the Einsteinian theory, the resulting new theory of
gravitation contains a new degree of freedom, that comes into question as a
carrier for the energy-momentum tensor of the the gravitational interaction.
The "ground state" of the empty universe (-> maximal symmetry)is described by
means of a deSitter-geometry, where only the expanding universe renders stable.


title: Conformal frames and D-dimensional gravity

abstract:
  We review some results concerning the properties of static, spherically
symmetric solutions of multidimensional theories of gravity: various
scalar-tensor theories and a generalized string-motivated model with multiple
scalar fields and fields of antisymmetric forms associated with p-branes. A
Kaluza-Klein type framework is used: there is no dependence on internal
coordinates but multiple internal factor spaces are admitted. We discuss the
causal structure and the existence of black holes, wormholes and particle-like
configurations in the case of scalar vacuum with arbitrary potentials as well
as some observational predictions for exactly solvable systems with p-branes:
post-Newtonian coefficients, Coulomb law violation and black hole temperatures.
Particular attention is paid to conformal frames in which the theory is
initially formulated and which are used for its comparison with observations;
it is stressed that, in general, these two kinds of frames do not coincide.


title:
Restrictions on possible forms of classical matter fields carrying no
  energy

abstract:
  It is postulated in general relativity that the matter energy-momentum tensor
(named the stress tensor) vanishes if and only if all the matter fields vanish.
In classical lagrangian field theory the stres tensor is the variational
(symmetric) one and a priori it might occur that for some systems the tensor is
identically zero for all field configurations whereas evolution of the system
is subject to deterministic equations of motion. Such a system would not
generate its own gravitational field. To check if suchsystems may exist we find
a relationship between the stress tensor and the Euler operator. We prove that
if a system of n interacting scalar fields (n cannot exceed the spacetime
dimension d) or a single vector field (if d is even) has the stress tensor such
that its divergence is identically zero ("on and off shell"), then the Lagrange
equations of motion hold identically too. These systems are unphysical as
having no propagation equations at all. Thus nontrivial field equations imply
the nontrivial stress tensor. The theorem breaks down if the of the field
components n is greater than d. We show that for n>d matter systems without
energy and their own gravity (and yet detectable) are in principle admissible.
Their equations of motion are degenerate. We also show for which matter systems
their stress tensors cannot vanish for all solutions of the field equations.


title: On exact solutions in multidimensional gravity with antisymmetric forms

abstract:
  This short review deals with a multidimensional gravitational model
containing dilatonic scalar fields and antisymmetric forms. The manifold is
chosen in the product form. The sigma-model approach and exact solutions are
reviewed.


title:
4-Dimensional Einstein Theory Extended by a 3-Dimensional Chern-Simons
  Term

abstract:
  When 4-dimensional general relativity is extended by a 3-dimensional
gravitational Chern-Simons term an apparent violation of diffeormorphism
invariance is extinguished by the dynamical equations of motion for the
modified theory. The physical predictions of this recently proposed model show
little evidence of symmetry breaking, but require the vanishing of the
Pontryagin density.


title: A Numerical Study of Relativistic Fluid Collapse

abstract:
  We investigate the dynamics of self-gravitating, spherically-symmetric
distributions of fluid through numerical means. In particular, systems
involving neutron star models driven far from equilibrium in the strong-field
regime of general relativity are studied. Hydrostatic solutions of Einstein's
equations using a stiff, polytropic equation of state are used for the stellar
models. Many of the scenarios we examine involve highly-relativistic flows that
require improvements upon previously published numerical methods to simulate.
Here our particular focus is on the physical behavior of the coupled
fluid-gravitational system at the threshold of black hole formation--so-called
black hole critical phenomena. To investigate such phenomena starting from
conditions representing stable stars, we must drive the star far from its
initial stable configuration. We use one of two different mechanisms to do
this: setting the initial velocity profile of the star to be in-going, or
collapsing a shell of massless scalar field onto the star. Both of these
approaches give rise to a large range of dynamical scenarios that the star may
follow. These scenarios have been extensively surveyed by using different
initial star solutions, and by varying either the magnitude of the velocity
profile or the amplitude of the scalar field pulse. In addition to illuminating
the critical phenomena associated with the fluid collapse, the resulting phase
diagram of possible outcomes provides an approximate picture of the stability
of neutron stars to large, external perturbations that may occur in nature.


title: Electromagnetic mass-models in general relativity reexamined

abstract:
  The problem of constructing a model of an extended charged particle within
the context of general relativity has a long and distinguished history. The
distinctive feature of these models is that, in some way or another, they
require the presence of negative mass in order to maintain stability against
Coulomb's repulsion. Typically, the particle contains a core of $negative$ mass
surrounded by a positive-mass outer layer, which emerges from the
Reissner-Nordstr\"{o}m field.
  In this work we show how the Einstein-Maxwell field equations can be used to
construct an extended model where the mass is positive everywhere. This
requires the principal pressures to be unequal inside the particle. The model
is obtained by setting the "effective" matter density, rather than the rest
matter density, equal to zero. The Schwarzschild mass of the particle arises
from the electrical and gravitational field (Weyl tensor) energy. The model
satisfies the energy conditions of Hawking and Ellis. A particular solution
that illustrates the results is presented.


title:
Complete higher dimensional global embedding structures of various black
  holes

abstract:
  We study global flat embeddings inside and outside of event horizons of black
holes such as Schwarzschild and Reissner-Nordstr\"{o}m black holes, and of de
Sitter space. On these overall patches of the curved manifolds we investigate
four accelerations and Hawking temperatures by introducing relevant Killing
vectors.


title: Upper limits on stray force noise for LISA

abstract:
  We have developed a torsion pendulum facility for LISA gravitational
reference sensor ground testing that allows us to put significant upper limits
on residual stray forces exerted by LISA-like position sensors on a
representative test mass and to characterize specific sources of disturbances
for LISA. We present here the details of the facility, the experimental
procedures used to maximize its sensitivity, and the techniques used to
characterize the pendulum itself that allowed us to reach a torque sensitivity
below 20 fNm /sqrt{Hz} from 0.3 to 10 mHz. We also discuss the implications of
the obtained results for LISA.


title: Highly structured tensor identities for (2,2)-forms in four dimensions

abstract:
  In an n dimensional vector space, any tensor which is antisymmetric in k>n
arguments must vanish; this is a trivial consequence of the limited number of
dimensions. However, when other possible properties of tensors, for example
trace-freeness, are taken into account, such identities may be heavily
disguised. Tensor identities of this kind were first considered by Lovelock,
and later by Edgar and Hoeglund.
  In this paper we continue their work. We obtain dimensionally dependent
identities for highly structured expressions of products of (2,2)-forms. For
tensors possessing more symmetries, such as block symmetry W_{abcd} = W_{cdab},
or the first Bianchi identity W_{a[bcd]} = 0, we derive identities for less
structured expressions.
  These identities are important tools when studying super-energy tensors, and,
in turn, deriving identities for them. As an application we are able to show
that the Bel-Robinson tensor, the super-energy tensor for the Weyl tensor,
satisfies the equation T_{abcy}T^{abcx} = 1/4g^{x}_{y}T_{abcd}T^{abcd} in four
dimensions, irrespective of the signature of the space.


title: Generalized plane-fronted gravitational waves in any dimension

abstract:
  We study the gravitational waves in spacetimes of arbitrary dimension. They
generalize the pp-waves and the Kundt waves, obtained earlier in four
dimensions. Explicit solutions of the Einstein and Einstein-Maxwell equations
are derived for an arbitrary cosmological constant.


title: Black hole formation in perfect fluid collapse

abstract:
  We construct here a special class of perfect fluid collapse models which
generalizes the homogeneous dust collapse solution in order to include non-zero
pressures and inhomogeneities into evolution. It is shown that a black hole is
necessarily generated as end product of continued gravitational collapse,
rather than a naked singularity. We examine the nature of the central
singularity forming as a result of endless collapse and it is shown that no
non-spacelike trajectories can escape from the central singularity. Our results
provide some insights into how the dynamical collapse works, and into the
possible formulations of the cosmic censorship hypothesis, which is as yet a
major unsolved problem in black hole physics.


title: Spin Foam Models of Gravity and BF Theory as evolution of Spin Networks

abstract: This article has been replaced by gr-qc/0412011


title: Einstein-Schrodinger theory in the presence of zero-point fluctuations

abstract:
  The Einstein-Schrodinger theory is modified by adding a cosmological constant
contribution caused by zero-point fluctuations. This cosmological constant
which multiplies the symmetric metric is assumed to be nearly cancelled by
Schrodinger's ``bare'' cosmological constant which multiplies the nonsymmetric
fundamental tensor, such that the total ``physical'' cosmological constant
matches measurement. We first derive the field equations of the theory from a
Lagrangian density. We show that the divergence of the Einstein equations
vanishes using the Christoffel connection formed from the symmetric metric,
allowing additional fields to be included in the same manner as with ordinary
general relativity. We show that the field equations match the ordinary
electro-vac Einstein and Maxwell equations except for additional terms which
are $<10^{-16}$ of the usual terms for worst-case field strengths and
rates-of-change accessible to measurement. We also show that the theory avoids
ghosts in an unusual way. We show that the Einstein-Infeld-Hoffmann (EIH)
equations of motion for this theory match the equations of motion for
Einstein-Maxwell theory to Newtonian/Coulombian order, which proves the
existence of a Lorentz force. We derive an exact electric monopole solution,
and show that it matches the Reissner-Nordstrom solution except for additional
terms which are $\sim10^{-66}$ of the usual terms for worst-case radii
accessible to measurement. Finally, we show that the theory becomes exactly
electro-vac Einstein-Maxwell theory in the limit as the cosmological constant
from zero-point fluctuations goes to infinity.


title:
LISA Capture Sources: Approximate Waveforms, Signal-to-Noise Ratios, and
  Parameter Estimation Accuracy

abstract:
  Captures of stellar-mass compact objects (COs) by massive ($\sim 10^6
M_\odot$) black holes (MBHs) are potentially an important source for LISA, the
proposed space-based gravitational-wave (GW) detector. The orbits of the
inspiraling COs are highly complicated; they can remain rather eccentric up
until the final plunge, and display extreme versions of relativistic perihelion
precession and Lense-Thirring precession of the orbital plane. The strongest
capture signals will be ~10 times weaker than LISA's instrumental noise, but in
principle (with sufficient computing power) they can be disentangled from the
noise by matched filtering. The associated template waveforms are not yet in
hand, but theorists will very likely be able to provide them before LISA
launches. Here we introduce a family of approximate (post-Newtonian) capture
waveforms, given in (nearly) analytic form, for use in advancing LISA studies
until more accurate versions are available. Our model waveforms include most of
the key qualitative features of true waveforms, and cover the full space of
capture-event parameters (including orbital eccentricity and the MBH's spin).
Here we use our approximate waveforms to (i) estimate the relative
contributions of different harmonics (of the orbital frequency) to the total
signal-to-noise ratio, and (ii) estimate the accuracy with which LISA will be
able to extract the physical parameters of the capture event from the measured
waveform. For a typical source (a $10 M_\odot$ CO captured by a $10^6 M_\odot$
MBH at a signal-to-noise ratio of 30), we find that LISA can determine the MBH
and CO masses to within a fractional error of $\sim 10^{-4}$, measure $S/M^2$
(where $S$ and $M$ are the MBH's mass and spin) to within $\sim 10^{-4}$, and
determine the sky location of the source to within $\sim 10^{-3}$ stradians.


title: Self-gravitating global monopole and nonsingular cosmology

abstract:
  We review some recent results concerning the properties of a spherically
symmetric global monopole in $(D=d+2)$-dimensional general relativity. Some
common features of monopole solutions are found independently of the choice of
the symmetry-breaking potential. Thus, the solutions show six types of
qualitative behavior and can contain at most one simple horizon. For the
standard Mexican hat potential, we analytically find the $D$-dependent range of
$\gamma$ (the gravitational field strength parameter) in which there exist
globally regular solutions with a monotonically growing Higgs field, containing
a horizon and a Kantowski-Sachs (KS) cosmology outside it, where the topology
of spatial sections is $\R\times \S^d$. Their cosmological properties favor the
idea that the standard Big Bang might be replaced with a nonsingular static
core and a horizon appearing as a result of some symmetry-breaking phase
transition on the Planck energy scale. We have also found families of new
solutions with an oscillating Higgs field, parametrized by the number of its
knots. All such solutions describe space-times of finite size, possessing a
regular center, a horizon and a singularity beyond it.


title: Gowdy phenomenology in scale-invariant variables

abstract:
  The dynamics of Gowdy vacuum spacetimes is considered in terms of
Hubble-normalized scale-invariant variables, using the timelike area temporal
gauge. The resulting state space formulation provides for a simple mechanism
for the formation of ``false'' and ``true spikes'' in the approach to the
singularity, and a geometrical formulation for the local attractor.


title: Phantom and quantum matter in an Anti-de Sitter Universe

abstract:
  We consider an Anti-de Sitter Universe filled by quantum CFT with classical
phantom matter and perfect fluid. The model represents the combination of a
trace-anomaly annihilated and a phantom driven Anti-de Sitter Universes. The
influence exerted by the quantum effects and phantom matter on the AdS space is
discussed. Different energy conditions in this type of Universe are
investigated and compared with those for the corresponding model in a de Sitter
Universe.


title:
An action principle for the quantization of parametric theories and
  nonlinear quantum cosmology

abstract:
  By parametrizing the action integral for the standard Schrodinger equation we
present a derivation of the recently proposed method for quantizing a
parametrized theory. The reformulation suggests a natural extension from
conventional to nonlinear quantum mechanics. This generalization enables a
unitary description of the quantum evolution for a broad class of constrained
Hamiltonian systems with a nonlinear kinematic structure. In particular, the
new theory is applicable to the quantization of cosmological models where a
chosen gravitational degree of freedom acts as geometric time. This is
demonstrated explicitly using three cosmological models: the Friedmann universe
with a massless scalar field and Bianchi type I and IX models. Based on these
investigations, the prospect of further developing the proposed quantization
scheme in the context of quantum gravity is discussed.


title: Single field inflationary models with non-compact Kaluza-Klein theory

abstract:
  We discuss a semiclassical treatment to inflationary models from Kaluza-Klein
theory without the cylinder condition. We conclude that the evolution of the
early universe could be described by a geodesic trayectory of a cosmological 5D
metric here proposed, so that the effective 4D FRW background metric should be
a hypersurface on a constant fifth dimension.


title: Gravitomagnetic effect and spin-torsion coupling

abstract:
  We study the gravitomagnetic effect in the context of absolute parallelism
with the use of a modified geodesic equation via a free parameter b. We
calculate the time difference in two atomic clocks orbiting the Earth in
opposite directions and find a small correction due to the coupling between the
torsion of the spacetime and the internal structure of atomic clocks measured
by the free parameter.


title: Generating Static Black Holes in Higher Dimensional Space-Times

abstract:
  In this article we extend to higher dimensional space-times a recent theorem
proved by Salgado which characterizes a three-parameter family of static and
spherically symmetric solutions to the Einstein Field Equations. As it happens
in four dimensions, it is shown that the Schwarzschild, Reissner-Nordstrom and
global monopole solutions in higher dimensions are particular cases from this
family.


title:
Relativistic anisotropic charged fluid spheres with varying cosmological
  constant

abstract:
  Static spherically symmetric anisotropic source has been studied for the
Einstein-Maxwell field equations assuming the erstwhile cosmological constant $
\Lambda $ to be a space-variable scalar, viz., $ \Lambda = \Lambda(r) $. Two
cases have been examined out of which one reduces to isotropic sphere. The
solutions thus obtained are shown to be electromagnetic in origin as a
particular case. It is also shown that the generally used pure charge
condition, viz., $ \rho + p_r = 0 $ is not always required for constructing
electromagnetic mass models.


title: Reflection from black holes and space-time topology

abstract:
  The quantum corrections make the black hole capable of reflection: any
particle that approaches the event horizon can bounce back in the outside
world. The albedo of the black hole depends on its temperature. The reflection
shares physical origins with the phenomenon of Hawking radiation; both effects
are explained as consequences of the singular nature that the event horizon
exhibits on the quantum level.


title: Rotating Boson Stars in 2+1 Dimensions

abstract:
  We consider rotating boson star solutions in a three-dimensional anti-de
Sitter spacetime and investigate the influence of the rotation on their
properties. The mass and angular momentum of these configurations are computed
by using the counterterm method. No regular solution is found in the limit of
vanishing cosmological constant.


title:
Non commutative quantum spacetime with topological vortex states, and
  dark matter in the universe

abstract:
  Non commutative geometry is creating new possibilities for physics. Quantum
spacetime geometry and post inflationary models of the universe with matter
creation have an enormous range of scales of time, distance and energy in
between. There is a variety of physics possible till the nucleosynthesis epoch
is reached. The use of topology and non commutative geometry in cosmology is a
recent approach. This paper considers the possibility of topological solutions
of a vortex kind given by non commutative structures. These are interpreted as
dark matter, with the grand unified Yang-Mills field theory energy scale used
to describe its properties. The relation of the model with other existing
theories is discussed.


title:
The double role of Einstein's equations: as equations of motion and as
  vanishing energy-momentum tensor

abstract:
  Diffeomorphism covariant theories with dynamical background metric, like
gravity coupled to matter fields in the way expressed by Einstein-Hilbert's
action or relativistic strings described by Polyakov's action, have `on-shell'
vanishing energy-momentum tensor $t_{\mu\nu}$ because $t_{\mu\nu}$ is,
essentially, the Eulerian derivative associated with the dynamical background
metric and thus $t_{\mu\nu}$ vanishes `on-shell.' Therefore, the equations of
motion for the dynamical background metric play a double role: as equations of
motion themselves and as a reflection of the fact that $t_{\mu\nu}=0$.
Alternatively, the vanishing property of $t_{\mu\nu}$ can be seen as a
reflection of the so-called `problem of time' present in diffeomorphism
covariant theories in the sense that $t_{\mu\nu}$ are written as linear
combinations of first class constraints only.


title:
Linearized stability analysis of thin-shell wormholes with a
  cosmological constant

abstract:
  Spherically symmetric thin-shell wormholes in the presence of a cosmological
constant are constructed applying the cut-and-paste technique implemented by
Visser. Using the Darmois-Israel formalism the surface stresses, which are
concentrated at the wormhole throat, are determined. This construction allows
one to apply a dynamical analysis to the throat, considering linearized radial
perturbations around static solutions. For a large positive cosmological
constant, i.e., for the Schwarzschild-de Sitter solution, the region of
stability is significantly increased, relatively to the null cosmological
constant case, analyzed by Poisson and Visser. With a negative cosmological
constant, i.e., the Schwarzschild-anti de Sitter solution, the region of
stability is decreased. In particular, considering static solutions with a
generic cosmological constant, the weak and dominant energy conditions are
violated, while for $a_0 \leq 3M$ the null and strong energy conditions are
satisfied. The surface pressure of the static solution is strictly positive for
the Schwarzschild and Schwarzschild-anti de Sitter spacetimes, but takes
negative values, assuming a surface tension in the Schwarzschild-de Sitter
solution, for high values of the cosmological constant and the wormhole throat
radius.


title:
Quantum suppression of the generic chaotic behavior close to
  cosmological singularities

abstract:
  In classical general relativity, the generic approach to the initial
singularity is very complicated as exemplified by the chaos of the Bianchi IX
model which displays the generic local evolution close to a singularity.
Quantum gravity effects can potentially change the behavior and lead to a
simpler initial state. This is verified here in the context of loop quantum
gravity, using methods of loop quantum cosmology: the chaotic behavior stops
once quantum effects become important. This is consistent with the discrete
structure of space predicted by loop quantum gravity.


title: Homogeneous Loop Quantum Cosmology: The Role of the Spin Connection

abstract:
  Homogeneous cosmological models with non-vanishing intrinsic curvature
require a special treatment when they are quantized with loop quantum
cosmological methods. Guidance from the full theory which is lost in this
context can be replaced by two criteria for an acceptable quantization,
admissibility of a continuum approximation and local stability. A quantization
of the corresponding Hamiltonian constraints is presented and shown to lead to
a locally stable, non-singular evolution compatible with almost classical
behavior at large volume. As an application, the Bianchi IX model and its
modified behavior close to its classical singularity is explored.


title: Novel results on trapped surfaces

abstract:
  A unifying definition of trapped submanifold for arbitrary codimension by
means of its mean curvature vector is presented. Then, the interplay between
(generalized) symmetries and trapped submanifolds is studied, proving in
particular that (i) stationary spacetimes cannot contain closed trapped nor
marginally trapped submanifolds S of any codimension; (ii) S can be within the
subset where there is a null Killing vector only if it is marginally trapped
with mean curvature vector parallel to the null Killing; (iii) any submanifold
orthogonal to a timelike or null Killing vector has a mean curvature vector
orthogonal to it. All results are purely geometric, hold in arbitrary
dimension, and can be appropriately generalized to many non-Killing vector
fields, such as conformal Killing vectors and the like. A simple criterion to
ascertain the trapping or not of a family of codimension-2 submanifolds is
given. A path allowing to generalize the singularity theorems is conjectured as
feasible and discussed.


title: A comment on Liu and Yau's positive quasi-local mass

abstract:
  With the aid of a simple family of examples, we show that the quasi-local
mass defined by Kijowski and Liu and Yau, and shown by Liu and Yau to be
positive, may be strictly positive for space-like, topologically spherical
2-surfaces in flat space-time.


title: Geometric Algebra Techniques for General Relativity

abstract:
  Geometric (Clifford) algebra provides an efficient mathematical language for
describing physical problems. We formulate general relativity in this language.
The resulting formalism combines the efficiency of differential forms with the
straightforwardness of coordinate methods. We focus our attention on
orthonormal frames and the associated connection bivector, using them to find
the Schwarzschild and Kerr solutions, along with a detailed exposition of the
Petrov types for the Weyl tensor.


title:
Some comments on a recently derived approximated solution of the
  Einstein equations for a spinning body with negligible mass

abstract:
  Recently, an approximated solution of the Einstein equations for a rotating
body whose mass effects are negligible with respect to the rotational ones has
been derived by Tartaglia. At first sight, it seems to be interesting because
both external and internal metric tensors have been consistently found,
together an appropriate source tensor; moreover, it may suggest possible
experimental checks since the conditions of validity of the considered metric
are well satisfied at Earth laboratory scales. However, it should be pointed
out that reasonable doubts exist if it is physically meaningful because it is
not clear if the source tensor related to the adopted metric can be realized by
any real extended body. Here we derive the geodesic equations of the metric and
analyze the allowed motions in order to disclose possible unphysical features
which may help in shedding further light on the real nature of such
approximated solution of the Einstein equations.


title: Position space of Doubly Special Relativity

abstract:
  We consider three possible approaches to formulating coordinate
transformations on position space associated with non-linear Lorentz
transformations on momentum space. The first approach uses the definition of
velocity and gives the standard Lorentz transformation. In the second method,
we translate the behavior in momentum space into position space by means of
Fourier transform. Under certain conditions, it also gives the standard Lorentz
transformation on position space. The third approach investigates the
covariance of the modified Klein-Gordon equation obtained from the dispersion
relation.


title: Deflection of Highly Relativistic Particles in a Gravitational Field

abstract:
  A novel approach to the calculation of the deflection of highly relativistic
test particles in gravitational fields is described. We make use of the
light-like boosts of the gravitational fields of the sources. Examples are
given of the deflection of highly relativistic particles in the Schwarzschild
and Kerr gravitational fields, in the field of a static, axially symmetric,
multipole source and in the field of a cosmic string. The deflection of
spinning particles is also discussed.


title: Deformations of the Schwarzschild Black Hole

abstract:
  Due to its large number of symmetries the Schwarzschild Black Hole can be
described by a specific two-dimensional dilaton gravity model. After reviewing
classical, semi-classical and quantum properties and a brief discussion of
virtual black holes deformations are studied: the first part is devoted to
deformations of the Lorentz-symmetry, the second part to dynamical deformations
and its role for the long time evaporation of the Schwarzschild Black Hole.


title: Planck Scale Physics, Pregeometry and the Notion of Time

abstract:
  Recent progress in quantum gravity and string theory has raised interest
among scientists to whether or not nature behaves discretely at the Planck
scale. There are two attitudes twoards this discretenes i.e. top-down and
bottom-up approach. We have followed up the bottom-up approach. Here we have
tried to describe how macroscopic space-time or its underlying mesoscopic
substratum emerges from a more fundamental concept. The very concept of
space-time, causality may not be valid beyond Planck scale. We have introduced
the concept of generalised time within the framework of Sheaf Cohomology where
the physical time emrges around and above Planck scale. The possible physical
amd metaphysical implications are discussed.


title: Strong field limit analysis of gravitational retro-lensing

abstract:
  We present a complete treatment in the strong field limit of gravitational
retro-lensing by a static spherically symmetric compact object having a photon
sphere. The results are compared with those corresponding to ordinary lensing
in similar strong field situations. As examples of application of the
formalism, a supermassive black hole at the galactic center and a stellar mass
black hole in the galactic halo are studied as retro-lenses, in both cases
using the Schwarzschild and Reissner-Nordstrom geometries.


title:
Stability criterion for self-similar solutions with a scalar field and
  those with a stiff fluid in general relativity

abstract:
  A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state $P=\rho$. A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.


title: 5-Dimensional Kaluza-Klein Theory with a Source

abstract:
  A free test particle in 5-dimensional Kaluza-Klein spacetime will show its
electricity in the reduced 4-dimensional spacetime when it moves along the
fifth dimension. In the light of this observation, we study the coupling of a
5-dimensional dust field with the Kaluza-Klein gravity. It turns out that the
dust field can curve the 5-dimensional spacetime in such a way that it provides
exactly the source of the electromagnetic field in the 4-dimensional spacetime
after the dimensional reduction.


title: Spin-Torsion, Braneworlds and Changing Symmetry in the Universe

abstract:
  In this thesis, we explore three phenomenological alternatives to the current
paradigm of the standard inflationary big bang scenario. The three alternative
themes are spin torsion (or Einstein-Cartan-Kibble-Sciama) theories, extra
dimensions (braneworld cosmology) and changing global symmetry. In the spin
torsion theories, we found new cosmological solutions with a cosmological
constant as alternative to the standard scalar field driven inflationary
scenario and we conclude that these toy models do not exhibit an inflationary
phase. In the theme of extra dimensions, we discuss the dynamics of linearized
scalar and tensor perturbations in an almost Friedmann-Robertson-Walker
braneworld cosmology of Randall-Sundrum type II using the 1+3 covariant
approach. We derive a complete set of frame-independent equations for the total
matter variables, and a partial set of equations for the non-local variables,
which arise from the projection of the Weyl tensor in the bulk. The latter
equations are incomplete since there is no propagation equation for the
non-local anisotropic stress. In the simplest approximation, we show the
braneworld imprint as a correction to the power spectra for standard
temperature and polarization anisotropies and similarly show that the tensor
anisotropies are also insensitive to the high energy effects. Finally in the
theme of changing global symmetry, we constructed a bounded isothermal solution
embedded in an expanding Einstein de Sitter universe and showed that there is a
possible phase transition in the far future.


title:
Gravitational waveforms from a point particle orbiting a Schwarzschild
  black hole

abstract:
  We numerically solve the inhomogeneous Zerilli-Moncrief and Regge-Wheeler
equations in the time domain. We obtain the gravitational waveforms produced by
a point-particle of mass $\mu$ traveling around a Schwarzschild black hole of
mass M on arbitrary bound and unbound orbits. Fluxes of energy and angular
momentum at infinity and the event horizon are also calculated. Results for
circular orbits, selected cases of eccentric orbits, and parabolic orbits are
presented. The numerical results from the time-domain code indicate that, for
all three types of orbital motion, black hole absorption contributes less than
1% of the total flux, so long as the orbital radius r_p(t) satisfies r_p(t)> 5M
at all times.


title:
A skeleton approximate solution of the Einstein field equations for
  multiple black-hole systems

abstract:
  An approximate analytical and non-linear solution of the Einstein field
equations is derived for a system of multiple non-rotating black holes. The
associated space-time has the same asymptotic structure as the Brill-Lindquist
initial data solution for multiple black holes. The system admits an
Arnowitt-Deser-Misner (ADM) Hamiltonian that can particularly evolve the
Brill-Lindquist solution over finite time intervals. The gravitational field of
this model may properly be referred to as a skeleton approximate solution of
the Einstein field equations. The approximation is based on a conformally flat
truncation, which excludes gravitational radiation, as well as a removal of
some additional gravitational field energy. After these two simplifications,
only source terms proportional to Dirac delta distributions remain in the
constraint equations. The skeleton Hamiltonian is exact in the test-body limit,
it leads to the Einsteinian dynamics up to the first post-Newtonian
approximation, and in the time-symmetric limit it gives the energy of the
Brill-Lindquist solution exactly. The skeleton model for binary systems may be
regarded as a kind of analytical counterpart to the numerical treatment of
orbiting Misner-Lindquist binary black holes proposed by Gourgoulhon,
Grandclement, and Bonazzola, even if they actually treat the corotating case.
Along circular orbits, the two-black-hole skeleton solution is quasi-stationary
and it fulfills the important property of equality of Komar and ADM masses.
Explicit calculations for the determination of the last stable circular orbit
of the binary system are performed up to the tenth post-Newtonian order within
the skeleton model.


title: Gravitational potential in Palatini formulation of modified gravity

abstract:
  General Relativity has so far passed almost all the ground-based and
solar-system experiments. Any reasonable extended gravity models should
consistently reduce to it at least in the weak field approximation. In this
work we derive the gravitational potential for the Palatini formulation of the
modified gravity of the L(R) type which admits a de Sitter vacuum solution. We
conclude that the Newtonian limit is always obtained in those class of models
and the deviations from General Relativity is very small for a slowly moving
source.


title: The Laser Astrometric Test of Relativity (LATOR) Mission

abstract:
  This paper discusses new fundamental physics experiment that will test
relativistic gravity at the accuracy better than the effects of the second
order in the gravitational field strength, $\propto G^2$. The Laser Astrometric
Test Of Relativity (LATOR) mission uses laser interferometry between two
micro-spacecraft whose lines of sight pass close by the Sun to accurately
measure deflection of light in the solar gravity. The key element of the
experimental design is a redundant geometry optical truss provided by a
long-baseline (100 m) multi-channel stellar optical interferometer placed on
the International Space Station (ISS). The spatial interferometer is used for
measuring the angles between the two spacecraft and for orbit determination
purposes. The geometric redundancy enables LATOR to measure the departure from
Euclidean geometry caused by the solar gravity field to a very high accuracy.
LATOR will not only improve the value of the parameterized post-Newtonian (PPN)
$\gamma$ to unprecedented levels of accuracy of 1 part in 10$^{8}$, it will
also reach ability to measure effects of the next post-Newtonian order
($c^{-4}$) of light deflection resulting from gravity's intrinsic
non-linearity. The solar quadrupole moment parameter, $J_2$, will be measured
with high precision, as well as a variety of other relativistic effects
including Lense-Thirring precession. LATOR will lead to very robust advances in
the tests of Fundamental physics: this mission could discover a violation or
extension of general relativity, or reveal the presence of an additional long
range interaction in the physical law. There are no analogs to the LATOR
experiment; it is unique and is a natural culmination of solar system gravity
experiments.


title: Improving LLR Tests of Gravitational Theory

abstract:
  Accurate analysis of precision ranges to the Moon has provided several tests
of gravitational theory including the Equivalence Principle, geodetic
precession, parameterized post-Newtonian (PPN) parameters $\gamma$ and $\beta$,
and the constancy of the gravitational constant {\it G}. Since the beginning of
the experiment in 1969, the uncertainties of these tests have decreased
considerably as data accuracies have improved and data time span has
lengthened. We are exploring the modeling improvements necessary to proceed
from cm to mm range accuracies enabled by the new Apache Point Observatory
Lunar Laser-ranging Operation (APOLLO) currently under development in New
Mexico. This facility will be able to make a significant contribution to the
solar system tests of fundamental and gravitational physics. In particular, the
Weak and Strong Equivalence Principle tests would have a sensitivity
approaching 10$^{-14}$, yielding sensitivity for the SEP violation parameter
$\eta$ of $\sim 3\times 10^{-5}$, $v^2/c^2$ general relativistic effects would
be tested to better than 0.1%, and measurements of the relative change in the
gravitational constant, $\dot{G}/G$, would be $\sim0.1$% the inverse age of the
universe. Having this expected accuracy in mind, we discusses the current
techniques, methods and existing physical models used to process the LLR data.
We also identify the challenges for modeling and data analysis that the LLR
community faces today in order to take full advantage of the new APOLLO ranging
station.


title: Is there paradox with infinite space?

abstract:
  We argue that whether the universe is infinite or finite is less crucial than
usually supposed. Paradoxes of repeating behaviour in the infinite, or eternal
inflationary, universe can be alleviated by a realistic definition of differing
lives. We also critically question the notion that our universe could simply be
a simulation in somebody else's computer.


title:
Upper limits on the strength of periodic gravitational waves from PSR
  J1939+2134

abstract:
  The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times $10^{-22}$.


title: Gravito-electromagnetism versus electromagnetism

abstract:
  The paper contains a discussion of the properties of the gravito-magnetic
interaction in non stationary conditions. A direct deduction of the equivalent
of Faraday-Henry law is given. A comparison is made between the
gravito-magnetic and the electro-magnetic induction, and it is shown that there
is no Meissner-like effect for superfluids in the field of massive spinning
bodies. The impossibility of stationary motions in directions not along the
lines of the gravito-magnetic field is found. Finally the results are discussed
in relation with the behavior of superconductors.


title:
Essential Constants for Spatially Homogeneous Ricci-flat manifolds of
  dimension 4+1

abstract:
  The present work considers (4+1)-dimensional spatially homogeneous vacuum
cosmological models. Exact solutions -- some already existing in the
literature, and others believed to be new -- are exhibited. Some of them are
the most general for the corresponding Lie group with which each homogeneous
slice is endowed, and some others are quite general. The characterization
``general'' is given based on the counting of the essential constants, the
line-element of each model must contain; indeed, this is the basic contribution
of the work. We give two different ways of calculating the number of essential
constants for the simply transitive spatially homogeneous (4+1)-dimensional
models. The first uses the initial value theorem; the second uses, through
Peano's theorem, the so-called time-dependent automorphism inducing
diffeomorphisms