title:
Lorentz invariance and quantum gravity: an additional fine-tuning
  problem?

abstract:
  Trying to combine standard quantum field theories with gravity leads to a
breakdown of the usual structure of space-time at around the Planck length,
1.6*10^{-35} m, with possible violations of Lorentz invariance. Calculations of
preferred-frame effects in quantum gravity have further motivated high
precision searches for Lorentz violation. Here, we explain that combining known
elementary particle interactions with a Planck-scale preferred frame gives rise
to Lorentz violation at the percent level, some 20 orders of magnitude higher
than earlier estimates, unless the bare parameters of the theory are
unnaturally strongly fine-tuned. Therefore an important task is not just the
improvement of the precision of searches for violations of Lorentz invariance,
but also the search for theoretical mechanisms for automatically preserving
Lorentz invariance.


title: Interaction of higher-dimensional rotating black holes with branes

abstract:
  We study interaction of rotating higher dimensional black holes with a brane
in space-times with large extra dimensions. We demonstrate that in a general
case a rotating black hole attached to a brane can loose bulk components of its
angular momenta. A stationary black hole can have only those components of the
angular momenta which are connected with Killing vectors generating
transformations preserving a position of the brane. In a final stationary state
the null Killing vector generating the black hole horizon is tangent to the
brane. We discuss first the interaction of a cosmic string and a domain wall
with the 4D Kerr black hole. We then prove the general result for slowly
rotating higher dimensional black holes interacting with branes. The
characteristic time when a rotating black hole with the gravitational radius
$r_0$ reaches this final stationary state is $T\sim r_0^{p-1}/(G\sigma)$, where
$G$ is the higher dimensional gravitational coupling constant, $\sigma$ is the
brane tension, and $p$ is the number of extra dimensions.


title: World-line deviation and spinning particles

abstract:
  A set of world-line deviation equations is derived in the framework of
Mathisson-Papapetrou-Dixon description of pseudo-classical spinning particles.
They generalize the geodesic deviation equations. We examine the resulting
equations for particles moving in the space-time of a plane gravitational wave.


title:
General Relativity and Quantum Jumps: The Existence of Nondiffeomorphic
  Solutions to the Cauchy Problem in Nonempty Spacetime and Quantum Jumps as a
  Provider of a Canonical Spacetime Structure

abstract:
  It is shown that in spite of a generally accepted concept, there exist
nondiffeomorphic solutions to the Cauchy problem in nonempty spacetime, which
implies the necessity for canonical complementary conditions. It is nonlocal
quantum jumps that provide a canonical global structure of spacetime manifold
and, by the same token, the canonical complementary conditions.


title: Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers

abstract:
  Spacetime foam, also known as quantum foam, has its origin in quantum
fluctuations of spacetime. Arguably it is the source of the holographic
principle, which severely limits how densely information can be packed in
space. Its physics is also intimately linked to that of black holes and
computation. In particular, the same underlying physics is shown to govern the
computational power of black hole quantum computers.


title: Bowen-York Tensors

abstract:
  There is derived, for a conformally flat three-space, a family of linear
second-order partial differential operators which send vectors into tracefree,
symmetric two-tensors. These maps, which are parametrized by conformal Killing
vectors on the three-space, are such that the divergence of the resulting
tensor field depends only on the divergence of the original vector field. In
particular these maps send source-free electric fields into TT-tensors.
Moreover, if the original vector field is the Coulomb field on
$\mathbb{R}^3\backslash \lbrace0\rbrace$, the resulting tensor fields on
$\mathbb{R}^3\backslash \lbrace0\rbrace$ are nothing but the family of
TT-tensors originally written down by Bowen and York.


title: Friedmann universe with dust and scalar field

abstract:
  We study a spatially flat Friedmann model containing a pressureless perfect
fluid (dust) and a scalar field with an unbounded from below potential of the
form $V(\fii)=W_0 - V_0\sinh(\sqrt{3/2}\kappa\fii)$, where the parameters $W_0$
and $V_0$ are arbitrary and $\kappa=\sqrt{8\pi G_N}=M_p^{-1}$. The model is
integrable and all exact solutions describe the recollapsing universe. The
behavior of the model near both initial and final points of evolution is
analyzed. The model is consistent with the observational parameters. We single
out the exact solution with the present-day values of acceleration parameter
$q_0=0.5$ and dark matter density parameter $\Omega_{\rho 0}=0.3$ describing
the evolution within the time approximately equal to $2H_0^{-1}$.


title:
Model-Dependence of Shapiro Time Delay and the "Speed of Gravity/Speed
  of Light" Controversy

abstract:
  Fomalont and Kopeikin have recently succeeded in measuring the
velocity-dependent component of the Shapiro time delay of light from a quasar
passing behind Jupiter. While there is general agreement that this observation
tests the gravitomagnetic properties of the gravitational field, a controversy
has emerged over the question of whether the results depend on the speed of
light, $c$, or the speed of gravity, $c_g$. By analyzing the Shapiro time delay
in a set of ``preferred frame'' models, I demonstrate that this question is
ill-posed: the distinction can only be made in the context of a class of
theories in which $c\ne c_g$, and the answer then depends on the specific class
of theories one chooses. It remains true, however, that for a large class of
theories ``close enough'' to general relativity, the leading contribution to
the time delay depends on $c$ and not $c_g$; within this class, observations
are thus not yet accurate enough to measure the speed of gravity.


title:
Solution of Dirac equation in the near horizon geometry of an extreme
  Kerr black hole

abstract:
  Dirac equation is solved in the near horizon limit geometry of an extreme
Kerr black hole. We decouple equations first as usual, into an axial and
angular part. The axial equation turns out to be independent of the mass and is
solved exactly. The angular equation reduces, in the massless case, to a
confluent Heun equation. In general for nonzero mass, the angular equation is
expressible at best, as a set of coupled first order differential equations apt
for numerical investigation. The axial potentials corresponding to the
associated Schrodinger-type equations and their conserved currents are found.
Finally, based on our solution, we verify in a similar way the absence of
superradiance for Dirac particles in the near horizon, a result which is
well-known within the context of general Kerr background.


title: The Chaplygin gas as a model for dark energy

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


title: The conformal frame freedom in theories of gravitation

abstract:
  It has frequently been claimed in the literature that the classical physical
predictions of scalar tensor theories of gravity depend on the conformal frame
in which the theory is formulated. We argue that this claim is false, and that
all classical physical predictions are conformal-frame invariants. We also
respond to criticisms by Vollick [gr-qc/0312041], in which this issue arises,
of our recent analysis of the Palatini form of 1/R gravity.


title: Quantum Horizons

abstract:
  Treating macro-black hole as quantum states, and using Brown-York quaselocal
gravitational energy definition and Heisenberg uncertainty principle, we find
out the classical horizon with singularity spreads into a quantum horizon in
which the space-time is non-commutative and the spread range is determined
dynamically. A Quantum Field Theory (QFT) model in curved space with quantum
horizon is constructed. By using it, the black hole entropy and the Hawking
temperature are calculated successfully. The $\phi-$field mode number is
predicted and our quantum horizon model favors to support the Minimal
Super-symmetric Standard Model.


title: Solvegeometry gravitational waves

abstract:
  In this paper we construct negatively curved Einstein spaces describing
gravitational waves having a solvegeometry wave-front (i.e., the wave-fronts
are solvable Lie groups equipped with a left-invariant metric). Using the
Einstein solvmanifolds (i.e., solvable Lie groups considered as manifolds)
constructed in a previous paper as a starting point, we show that there also
exist solvegeometry gravitational waves. Some geometric aspects are discussed
and examples of spacetimes having additional symmetries are given, for example,
spacetimes generalising the Kaigorodov solution. The solvegeometry
gravitational waves are also examples of spacetimes which are indistinguishable
by considering the scalar curvature invariants alone.


title: Initial data engineering

abstract:
  We present a local gluing construction for general relativistic initial data
sets. The method applies to generic initial data, in a sense which is made
precise. In particular the trace of the extrinsic curvature is not assumed to
be constant near the gluing points, which was the case for previous such
constructions. No global conditions on the initial data sets such as
compactness, completeness, or asymptotic conditions are imposed. As an
application, we prove existence of spatially compact, maximal globally
hyperbolic, vacuum space-times without any closed constant mean curvature
spacelike hypersurface.


title:
Deformation of the Planetary Orbits Caused by the Time Dependent
  Gravitational Potential in the Universe

abstract:
  In the paper are studied the deformations of the planetary orbits caused by
the time dependent gravitational potential in the universe. It is shown that
the orbits are not axially symmetric and the time dependent potential does not
cause perihelion precession. It is found a simple formula for the change of the
orbit period caused by the time dependent gravitational potential and it is
tested for two binary pulsars.


title:
Parametrized Post-Newtonian Theory of Reference Frames, Multipolar
  Expansions and Equations of Motion in the N-body Problem

abstract:
  We discuss a covariant generalization of the parametrized post-Newtonian
(PPN) formalism in a class of scalar-tensor theories of gravity. It includes an
exact construction of a set of global and local (Fermi-like) references frames
for an isolated N-body astronomical system as well as PPN multipolar
decomposition of gravitational field in these frames. We derive PPN equations
of translational and rotational motion of extended bodies taking into account
all gravitational multipoles and analyze the body finite-size effects in
relativistic dynamics that can be important at the latest stages of orbital
evolution of coalescing binary systems. We also reconcile the IAU 2000
resolutions on the general relativistic reference frames in the solar system
with the PPN equations of motion of the solar system bodies used in JPL
ephemerides.


title: An Improved Search Method for Gravitational Ringing of Black Holes

abstract:
  A black hole has characteristic quasi-normal modes that will be excited when
it is formed or when the geometry is perturbed. The state of a black hole when
the quasi-normal modes are excited is called the gravitational ringing, and
detections of it will be a direct confirmation of the existence of black holes.
To detect it, a method based on matched filtering needs to be developed.
Generically, matched filtering requires a large number of templates, because
one has to ensure a proper match of a real gravitational wave with one of
template waveforms to keep the detection efficiency as high as possible. On the
other hand, the number of templates must be kept as small as possible under
limited computational costs. In our previous paper, assuming that the
gravitational ringing is dominated by the least-damped (fundamental) mode with
the least imaginary part of frequency, we constructed an efficient method for
tiling the template space. However, the dependence of the template space metric
on the initial phase of a wave was not taken into account. This dependence
arises because of an unavoidable mismatch between the parameters of a signal
waveform and those given discretely in the template space. In this paper, we
properly take this dependence into account and present an improved, efficient
search method for gravitational ringing of black holes.


title:
Accelerated cosmological expansion due to a scalar field whose potential
  has a positive lower bound

abstract:
  In many cases a nonlinear scalar field with potential $V$ can lead to
accelerated expansion in cosmological models. This paper contains mathematical
results on this subject for homogeneous spacetimes. It is shown that, under the
assumption that $V$ has a strictly positive minimum, Wald's theorem on
spacetimes with positive cosmological constant can be generalized to a wide
class of potentials. In some cases detailed information on late-time
asymptotics is obtained. Results on the behaviour in the past time direction
are also presented.


title: Light deflection in Weyl gravity: critical distances for photon paths

abstract:
  The Weyl gravity appears to be a very peculiar theory. The contribution of
the Weyl linear parameter to the effective geodesic potential is opposite for
massive and nonmassive geodesics. However, photon geodesics do not depend on
the unknown conformal factor, unlike massive geodesics. Hence light deflection
offers an interesting test of the Weyl theory.
  In order to investigate light deflection in the setting of Weyl gravity, we
first distinguish between a weak field and a strong field approximation.
Indeed, the Weyl gravity does not turn off asymptotically and becomes even
stronger at larger distances.
  We then take full advantage of the conformal invariance of the photon
effective potential to provide the key radial distances in Weyl gravity.
According to those, we analyze the weak and strong field regime for light
deflection. We further show some amazing features of the Weyl theory in the
strong regime.


title: Simplicial and asymptotical aspects of the holographic principle

abstract:
  In this thesis, we study some aspects of a possible holographic
correspondence in two different systems: three dimensional Chern-Simons theory
and asymptotically flat space-times. In the former we use simplicial techniques
to study CS/WZW correspondence and in particular we construct the discretized
WZW partition function for SU(2) group at level 1. In the latter we outline the
main characteristics of a field theory living at null infinity invariant under
the action of the asymptotic symmetry group: the BMS group. In particular,
using fibre bundle techniques, we derive the covariant wave equations for
fields carrying BMS representations in order to investigate the nature of
boundary degrees of freedom.


title: Nonrelativistic and Relativistic Continuum Mechanics

abstract:
  There is described a spacetime formulation of both nonrelativistic and
relativistic elasticity. Specific attention is devoted to the causal structure
of the theories and the availability of local existence theorems for the
initial-value problem. Much of the presented material is based on joint work of
B.G.Schmidt and the author (in Class.Quantum Grav.\textbf{20} (2003), 889-904).


title: Torsion and Gravitation: A new view

abstract:
  According to the teleparallel equivalent of general relativity, curvature and
torsion are two equivalent ways of describing the same gravitational field.
Despite equivalent, however, they act differently: whereas curvature yields a
geometric description, in which the concept of gravitational force is absent,
torsion acts as a true gravitational force, quite similar to the Lorentz force
of electrodynamics. As a consequence, the right-hand side of a
spinless-particle equation of motion (which would represent a gravitational
force) is always zero in the geometric description, but not in the teleparallel
case. This means essentially that the gravitational coupling prescription can
be minimal only in the geometric case. Relying on this property, a new
gravitational coupling prescription in the presence of curvature and torsion is
proposed. It is constructed in such a way to preserve the equivalence between
curvature and torsion, and its basic property is to be equivalent with the
usual coupling prescription of general relativity. According to this view, no
new physics is connected with torsion, which appears as a mere alternative to
curvature in the description of gravitation. An application of this formulation
to the equations of motion of both a spinless and a spinning particle is made


title: A singularity-free space-time

abstract:
  We show that the solution published in Ref.1 is geodesically complete and
singularity-free. We also prove that the solution satisfies the stronger energy
and causality conditions, such as global hyperbolicity, causal symmetry and
causal stability. A detailed discussion about which assumptions in the
singularity theorems are not fulfilled is performed, and we show explicitly
that the solution is in accordance with those theorems. A brief discussion of
the results is given.


title: The Nonlinear Sigma Model With Distributed Adaptive Mesh Refinement

abstract:
  An adaptive mesh refinement (AMR) scheme is implemented in a distributed
environment using Message Passing Interface (MPI) to find solutions to the
nonlinear sigma model. Previous work studied behavior similar to black hole
critical phenomena at the threshold for singularity formation in this flat
space model. This work is a follow-up describing extensions to distribute the
grid hierarchy and presenting tests showing the correctness of the model.


title:
Accretion-driven gravitational radiation from nonrotating compact
  objects. Infalling quadrupolar shells

abstract:
  This paper reports results from numerical simulations of the gravitational
radiation emitted from non--rotating compact objects(both neutron stars and
Schwarzschild black holes) as a result of the accretion of matter. A hybrid
procedure is adopted: we evolve, in axisymmetry, the linearized equations
describing metric and fluid perturbations, coupled with a nonlinear
hydrodynamics code that calculates the motion of the accreting matter. The
initial matter distribution is shaped in the form of extended quadrupolar
shells of dust or perfect fluid. Self--gravity and radiation reaction effects
of the accreting fluid are neglected. This idealized setup is used to
understand the qualitative features appearing in the energy spectrum of the
gravitational wave emission from compact stars or black holes, subject to
accretion processes involving extended objects. A comparison for the case of
point--like particles falling radially onto black holes is also provided. Our
results show that, when the central object is a black hole, the spectrum is far
from having only one clear, monochromatic peak at the frequency of the
fundamental quasi-normal mode, but it shows a complex pattern, with
interference fringes produced by the interaction between the infalling matter
and the underlying perturbed spacetime: most of the energy is emitted at
frequencies lower than that of the fundamental mode of the black hole. Similar
results are obtained for extended shells accreting onto neutron stars, but in
this case the stellar fundamental mode is clearly excited. Our analysis shows
that the gravitational wave signal driven by accretion is influenced more by
the details and dynamics of the process, than by the quasi--normal mode
structure of the central object.


title: Numerical simulation of a possible counterexample to cosmic censorship

abstract:
  A numerical simulation is presented here of the evolution of initial data of
the kind that was conjectured by Hertog, Horowitz and Maeda to be a violation
of cosmic censorship. That initial data is essentially a thick domain wall
connecting two regions of anti-deSitter space. The initial data has a free
parameter that is the initial size of the wall. The simulation shows no
violation of cosmic censorship, but rather the formation of a small black hole.
The simulation described here is for a moderate wall size and leaves open the
possibility that cosmic censorship might be violated for larger walls.


title:
Topology change in (2+1)-dimensional gravity with non-Abelian Higgs
  field

abstract:
  We study topology change in (2+1)D gravity coupling with non-Abelian SO(2,1)
Higgs field from the point of view of Morse theory. It is shown that the Higgs
potential can be identified as a Morse function. The critical points of the
latter (i.e. loci of change of the spacetime topology) coincide with zeros of
the Higgs field. In these critical points two-dimensional metric becomes
degenerate, but the curvature remains bounded.


title:
Ultra-stable performance of an underground-based laser interferometer
  observatory for gravitational waves

abstract:
  In order to detect the rare astrophysical events that generate gravitational
wave (GW) radiation, sufficient stability is required for GW antennas to allow
long-term observation. In practice, seismic excitation is one of the most
common disturbances effecting stable operation of suspended-mirror laser
interferometers. A straightforward means to allow more stable operation is
therefore to locate the antenna, the ``observatory'', at a ``quiet'' site. A
laser interferometer gravitational wave antenna with a baseline length of 20m
(LISM) was developed at a site 1000m underground, near Kamioka, Japan. This
project was a unique demonstration of a prototype laser interferometer for
gravitational wave observation located underground. The extremely stable
environment is the prime motivation for going underground. In this paper, the
demonstrated ultra-stable operation of the interferometer and a well-maintained
antenna sensitivity are reported.


title:
The Physical Role of Gravitational and Gauge Degrees of Freedom in
  General Relativity - I: Dynamical Synchronization and Generalized Inertial
  Effects

abstract:
  This is the first of a couple of papers in which, by exploiting the
capabilities of the Hamiltonian approach to general relativity, we get a number
of technical achievements that are instrumental both for a disclosure of
\emph{new} results concerning specific issues, and for new insights about
\emph{old} foundational problems of the theory. The first paper includes: 1) a
critical analysis of the various concepts of symmetry related to the
Einstein-Hilbert Lagrangian viewpoint on the one hand, and to the Hamiltonian
viewpoint, on the other. This analysis leads, in particular, to a
re-interpretation of {\it active} diffeomorphisms as {\it passive and
metric-dependent} dynamical symmetries of Einstein's equations, a
re-interpretation which enables to disclose the (nearly unknown) connection of
a subgroup of them to Hamiltonian gauge transformations {\it on-shell}; 2) a
re-visitation of the canonical reduction of the ADM formulation of general
relativity, with particular emphasis on the geometro-dynamical effects of the
gauge-fixing procedure, which amounts to the definition of a \emph{global
(non-inertial) space-time laboratory}. This analysis discloses the peculiar
\emph{dynamical nature} that the traditional definition of distant simultaneity
and clock-synchronization assume in general relativity, as well as the {\it
gauge relatedness} of the "conventions" which generalize the classical
Einstein's convention.


title: The Gravitational Red-Shift

abstract:
  Attention is drawn to the fact that the well-known expression for the
red-shift of spectral lines due to a gravitational field may be derived with no
recourse to the theory of general relativity. This raises grave doubts over the
inclusion of the measurement of this gravitational red-shift in the list of
crucial tests of the theory of general relativity.


title: Global properties of higher-dimensional cosmological spacetimes

abstract:
  We study global existence problems and asymptotic behavior of
higher-dimensional inhomogeneous spacetimes with a compact Cauchy surface in
the Einstein-Maxwell-dilaton (EMD) system. Spacelike $T^{D-2}$-symmetry is
assumed, where $D\geq 4$ is spacetime dimension. The system of the evolution
equations of the EMD equations in the areal time coordinate is reduced to a
wave map system, and a global existence theorem for the system is shown. As a
corollary of this theorem, a global existence theorem in the constant mean
curvature time coordinate is obtained. Finally, for vacuum Einstein gravity in
arbitrary dimension, we show existence theorems of asymptotically
velocity-terms dominated singularities in the both cases which free functions
are analytic and smooth.


title: Sudden Future Singularities

abstract:
  We show that a singularity can occur at a finite future time in an expanding
Friedmann universe even when the density is positive and the density plus the
sum of the principal pressures is positive. Explicit examples are constructed
and a simple condition is given which can be used to eliminate behaviour of
this sort if it is judged to be unphysical.


title: The Random Walk in Generalized Quantum Theory

abstract:
  One can view quantum mechanics as a generalization of classical probability
theory that provides for pairwise interference among alternatives. Adopting
this perspective, we ``quantize'' the classical random walk by finding, subject
to a certain condition of ``strong positivity'', the most general Markovian,
translationally invariant ``decoherence functional'' with nearest neighbor
transitions.


title: Casimir Effect in Compact Universes

abstract:
  The Casimir effect in compact hyperbolic Universes was numerically obtained
in previous publications. In this talk, I expose these results.


title: Gravitational-wave astronomy: the high-frequency window

abstract:
  This contribution is divided in two parts. The first part provides a
text-book level introduction to gravitational radiation. The key concepts
required for a discussion of gravitational-wave physics are introduced. In
particular, the quadrupole formula is applied to the anticipated
``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300:
inspiralling compact binaries. The second part provides a brief review of high
frequency gravitational waves. In the frequency range above (say) 100Hz,
gravitational collapse, rotational instabilities and oscillations of the
remnant compact objects are potentially important sources of gravitational
waves. Significant and unique information concerning the various stages of
collapse, the evolution of protoneutron stars and the details of the
supranuclear equation of state of such objects can be drawn from careful study
of the gravitational-wave signal. As the amount of exciting physics one may be
able to study via the detections of gravitational waves from these sources is
truly inspiring, there is strong motivation for the development of future
generations of ground based detectors sensitive in the range from hundreds of
Hz to several kHz.


title:
Coincidence analysis to search for inspiraling compact binaries using
  TAMA300 and LISM data

abstract:
  Japanese laser interferometric gravitational wave detectors, TAMA300 and
LISM, performed a coincident observation during 2001. We perform a coincidence
analysis to search for inspiraling compact binaries. The length of data used
for the coincidence analysis is 275 hours when both TAMA300 and LISM detectors
are operated simultaneously. TAMA300 and LISM data are analyzed by matched
filtering, and candidates for gravitational wave events are obtained. If there
is a true gravitational wave signal, it should appear in both data of detectors
with consistent waveforms characterized by masses of stars, amplitude of the
signal, the coalescence time and so on. We introduce a set of coincidence
conditions of the parameters, and search for coincident events. This procedure
reduces the number of fake events considerably, by a factor $\sim 10^{-4}$
compared with the number of fake events in single detector analysis. We find
that the number of events after imposing the coincidence conditions is
consistent with the number of accidental coincidences produced purely by noise.
We thus find no evidence of gravitational wave signals. We obtain an upper
limit of 0.046 /hours (CL $= 90 %$) to the Galactic event rate within 1kpc from
the Earth. The method used in this paper can be applied straightforwardly to
the case of coincidence observations with more than two detectors with
arbitrary arm directions.


title: A snapping cosmic string in a de Sitter or anti-de Sitter universe

abstract:
  We present and describe an exact solution of Einstein's equations which
represents a snapping cosmic string in a vacuum background with a cosmological
constant $\Lambda$. The snapping of the string generates an impulsive spherical
gravitational wave which is a particular member of a known family of such
waves. The global solution for all values of $\Lambda$ is presented in various
metric forms and interpreted geometrically. It is shown to represent the limit
of a family of sandwich type N Robinson-Trautman waves. It is also derived as a
limit of the C-metric with $\Lambda$, in which the acceleration of the pair of
black holes becomes unbounded while their masses are scaled to zero.


title: Chaotic Inflation on the Brane with Induced Gravity

abstract:
  We study the slow-roll inflationary dynamics in a self-gravitating induced
gravity braneworld model with bulk cosmological constant. For E \gg
M_{5}^{3}/M^{2}_{2} we find important corrections to the four-dimensional
Friedmann equation which bring the standard chaotic inflationary scenario in
closer agreement with recent observations. For \lambda/M^{3}_{5} \ll E \ll
M^{3}_{5}/M^{2}_{4} we find five-dimensional corrections to the Friedmann
equation, which give the known Randall-Sundrum results of the inflationary
parameters.


title: Gravitational Wave Emission from a Bounded Source: the Nonlinear Regime

abstract:
  We study the dynamics of a bounded gravitational collapsing configuration
emitting gravitational waves, where the exterior spacetime is described by
Robinson-Trautman geometries. The full nonlinear regime is examined by using
the Galerkin method that allows us to reduce the equations governing the
dynamics to a finite-dimensional dynamical system, after a proper truncation
procedure. Amongst the obtained results of the nonlinear evolution, one of the
most impressive is the fact that the distribution of the mass fraction
extracted by gravitational wave emission satisfies the distribution law of
nonextensive statistics and this result is independent of the initial
configurations considered.


title: Nonlinear Gravity Theories in the Metric and Palatini Formalisms

abstract:
  We study nonlinear gravity theories in both the metric and the Palatini
(metric-affine) formalisms. The nonlinear character of the gravity lagrangian
in the metric formalism causes the appearance of a scalar source of matter in
Einstein's equations that can be interpreted as a quintessence field. However,
in the Palatini case no new energy sources appear, though the equations of
motion get modified in such a way that usual matter can lead to repulsive
gravity at very low densities. Thus, the Palatini formalism could provide a
mechanism to explain the recent acceleration of the universe without the
necessity of dark energy sources. We also show that in contrast to the metric
formalism where only the Einstein frame should be considered as physical, the
Palatini formalism allows both the Einstein and the Jordan frames to be
physically acceptable.


title:
Optimal combination of signals from co-located gravitational wave
  interferometers for use in searches for a stochastic background

abstract:
  This article derives an optimal (i.e., unbiased, minimum variance) estimator
for the pseudo-detector strain for a pair of co-located gravitational wave
interferometers (such as the pair of LIGO interferometers at its Hanford
Observatory), allowing for possible instrumental correlations between the two
detectors. The technique is robust and does not involve any assumptions or
approximations regarding the relative strength of gravitational wave signals in
the detector pair with respect to other sources of correlated instrumental or
environmental noise. An expression is given for the effective power spectral
density of the combined noise in the pseudo-detector. This can then be
introduced into the standard optimal Wiener filter used to cross-correlate
detector data streams in order to obtain an optimal estimate of the stochastic
gravitational wave background. In addition, a dual to the optimal estimate of
strain is derived. This dual is constructed to contain no gravitational wave
signature and can thus be used as on "off-source" measurement to test
algorithms used in the "on-source" observation.


title: World function and time transfer: general post-Minkowskian expansions

abstract:
  In suitably chosen domains of space-time, the world function may be a
powerful tool for modelling the deflection of light and the time/frequency
transfer. In this paper we work out a recursive procedure for expanding the
world function into a perturbative series of ascending powers of the Newtonian
gravitational constant G. We show rigorously that each perturbation term is
given by a line integral taken along the unperturbed geodesic between two
points. Once the world function is known, it becomes possible to determine the
time transfer functions giving the propagation time of a photon between its
emission and its reception. We establish that the direction of a light ray as
measured in the 3-space relative to a given observer can be derived from these
time transfer functions, even if the metric is not stationary. We show how to
deduce these functions up to any given order in G from the perturbative
expansion of the world function. To illustrate the method, we carry out the
calculation of the world function and of the time transfer function outside a
static, spherically symmetric body up to the order G^2, the metric containing
three arbitrary parameters.


title:
The Density Matrix Deformation in Physics of the Early Universe and Some
  of its Implications

abstract:
  In this paper a new approach to investigation of Quantum and Statistical
Mechanics of the Early Universe (Planck scale) - density matrix deformation -
is proposed. The deformation is understood as an extension of a particular
theory by inclusion of one or several additional parameters in such a way that
the initial theory appears in the limiting transition...


title:
Reply to the Comment ``On the thermodynamics of inhomogeneous perfect
  fluid mixtures''

abstract:
  We show that the analysis presented in a recent comment by Coll and Ferrando
\cite{comment} (qr-qc/0312058) is based on the erroneous assumption that the
chemical potential and fractional concentration of a {\it mixture} of perfect
fluids are unknown variables.


title:
Energy and momentum associated with a Static Axially Symmetric Vacuum
  Space-Time

abstract:
  We use the Einstein and Papapetrou energy-momentum complexes to calculate the
energy and momentum densities of Weyl metric as well as Curzon metric. We show
that these two different definitions of energy-momentum complexes do not
provide the same energy density for Weyl metric, although they give the same
momentum density. We show that, in the case of Curzon metric, these two
definitions give the same energy only when $R \to \infty$. Furthermore, we
compare these results with those obtained using Landau and Lifshitz, Bergmann
and M{\o}ller.


title: Rotating metrics admitting non-perfect fluids in General Relativity

abstract:
  In this paper, by applying Newman-Janis algorithm in spherical symmetric
metrics, a class of embedded rotating solutions of field equations is
presented. These solutions admit non-perfect fluids


title: A Singular Conformal Spacetime

abstract:
  The infinite cosmological "constant" limit of the de Sitter solutions to
Einstein's equation is studied. The corresponding spacetime is a singular,
four-dimensional cone-space, transitive under proper conformal transformations,
which constitutes a new example of maximally-symmetric spacetime. Grounded on
its geometric and thermodynamic properties, some speculations are made in
connection with the primordial universe.


title: Testing Alternative Theories of Gravity using LISA

abstract:
  We investigate the possible bounds which could be placed on alternative
theories of gravity using gravitational wave detection from inspiralling
compact binaries with the proposed LISA space interferometer. Specifically, we
estimate lower bounds on the coupling parameter \omega of scalar-tensor
theories of the Brans-Dicke type and on the Compton wavelength of the graviton
\lambda_g in hypothetical massive graviton theories. In these theories,
modifications of the gravitational radiation damping formulae or of the
propagation of the waves translate into a change in the phase evolution of the
observed gravitational waveform. We obtain the bounds through the technique of
matched filtering, employing the LISA Sensitivity Curve Generator (SCG),
available online. For a neutron star inspiralling into a 10^3 M_sun black hole
in the Virgo Cluster, in a two-year integration, we find a lower bound \omega >
3 * 10^5. For lower-mass black holes, the bound could be as large as 2 * 10^6.
The bound is independent of LISA arm length, but is inversely proportional to
the LISA position noise error. Lower bounds on the graviton Compton wavelength
ranging from 10^15 km to 5 * 10^16 km can be obtained from one-year
observations of massive binary black hole inspirals at cosmological distances
(3 Gpc), for masses ranging from 10^4 to 10^7 M_sun. For the highest-mass
systems (10^7 M_sun), the bound is proportional to (LISA arm length)^{1/2} and
to (LISA acceleration noise)^{-1/2}. For the others, the bound is independent
of these parameters because of the dominance of white-dwarf confusion noise in
the relevant part of the frequency spectrum. These bounds improve and extend
earlier work which used analytic formulae for the noise curves.


title: Quasilocal Center-of-Mass for Teleparallel Gravity

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


title: Angular Momentum Surface Density of the Kerr Metric

abstract:
  A method for interpreting discontinuities of the twist potential of vacuum
stationary axisymmetric solutions of Einstein's equations is introduced.
Surface densities for the angular momentum of the source can be constructed
after solving a linear partial differential equation with boundary conditions
at infinity. This formalism is applied to the Kerr metric, obtaining a
regularized version of the density calculated with other formalisms. The main
result is that the integral defining the total angular momentum is finite for
the Kerr metric.


title: Quasilocal Center-of-Mass

abstract:
  Gravitating systems have no well-defined local energy-momentum density.
Various quasilocal proposals have been made, however the center-of-mass moment
(COM) has generally been overlooked. Asymptotically flat graviating systems
have 10 total conserved quantities associated with the Poincar{\'e} symmetry at
infinity. In addition to energy-momentum and angular momentum (associated with
translations and rotations) there is the boost quantity: the COM. A complete
quasilocal formulation should include this quantity. Getting good values for
the COM is a fairly strict requirement, imposing the most restrictive fall off
conditions on the variables. We take a covariant Hamiltonian approach,
associating Hamiltonian boundary terms with quasilocal quantities and boundary
conditions. Unlike several others, our {\it covariant symplectic} quasilocal
expressions do have the proper asymptotic form for all 10 quantities.


title: Solutions without singularities in gauge theory of gravitation

abstract:
  A de-Sitter gauge theory of the gravitational field is developed using a
spherical symmetric Minkowski space-time as base manifold. The gravitational
field is described by gauge potentials and the mathematical structure of the
underlying space-time is not affected by physical events. The field equations
are written and their solutions without singularities are obtained by imposing
some constraints on the invariants of the model. An example of such a solution
is given and its dependence on the cosmological constant is studied. A
comparison with results obtained in General Relativity theory is also
presented.
  Keywords: gauge theory, gravitation, singularity, computer algebra


title: Very high quality factor measured in annealed fused silica

abstract:
  We present the results of quality factor measurements for rod samples made of
fused silica. To decrease the dissipation we annealed our samples. The highest
quality factor that we observed was $Q=(2.03\pm0.01)\times10^8$ for a mode at
384 Hz. This is the highest published value of $Q$ in fused silica measured to
date.


title:
Inflationary Cosmology and Quantization Ambiguities in Semi-Classical
  Loop Quantum Gravity

abstract:
  In loop quantum gravity, modifications to the geometrical density cause a
self-interacting scalar field to accelerate away from a minimum of its
potential. In principle, this mechanism can generate the conditions that
subsequently lead to slow-roll inflation. The consequences for this mechanism
of various quantization ambiguities arising within loop quantum cosmology are
considered. For the case of a quadratic potential, it is found that some
quantization procedures are more likely to generate a phase of slow--roll
inflation. In general, however, loop quantum cosmology is robust to ambiguities
in the quantization and extends the range of initial conditions for inflation.


title: On the Energy Problem in General Relativity

abstract:
  The Energy Problem (EP) in General Relativity (GR) is analyzed in the context
of GR's axiomatic inconsistencies. EP is classified according to its local and
global aspects. The local aspects of the EP include noncovariance of the
energy-momentum pseudotensor (EMPT) of the gravitational field, non-uniqueness
of the EMPT, asymmetry of EMPT, and vanishing metric energy-momentum tensor.
The global aspect of the EP relates to the lack of integral conservation laws
due to the general difficulties in defining invariant integrals of tensors in
non-Euclidean space. These difficulties are related to the lack of precise
definition of a reference frame in the GR. A reference frame is defined here as
a differential manifold with an affine connection. The resulting unique
decomposition of the Levi-Civita connection into its affine and nonmetric parts
allows for a covariant definition of the gravitational energy-momentum tensor.
It is pointed out that the invariance of the Lagrangian (or action functional)
is a necessary but not sufficient condition to secure the covariance of the
Lagrange-Euler field theory. A rigorous definition of the Lagrange Field
Structure (LFS) on differential manifolds is proposed. A covariant
generalization of the first Noether theorem for LFS is obtained. Different
approaches to the EP are discussed.


title: Primordial and asymptotic inflation in Brans-Dicke cosmology

abstract:
  The basic motivation of this work is to attempt to explain the rapid
primordial inflation and the observed slow late-time inflation by using the
Brans-Dicke theory of gravity. We show that the ratio of these two inflation
parameters is proportional to the square root of the Brans-Dicke parameter $%
\omega$ $(\omega\gg1) $. We also calculate the Hubble parameter $% H$ and the
time variation of the time dependent Newtonian gravitational constant $G$ for
both regimes. The variation of the Hubble parameter predicted by Brans-Dicke
cosmology is shown to be consistent with recent measurements: The value of $H$
in the late-time future is predicted as 0.86 times the present value of $H$.


title:
Extremal limit of the regular charged black holes in nonlinear
  electrodynamics

abstract:
  The near horizon limit of the extreme nonlinear black hole is investigated.
It is shown that resulting geometry belongs to the AdS2xS2 class with different
modules of curvatures of subspaces and could be described in terms of the
Lambert functions. It is demonstrated that the considered class of Lagrangians
does not admit solutions of the Bertotti-Robinson type.


title: Proposal for an Interpretation of the Hermitian Theory of Relativity

abstract:
  The equilibrium conditions for charges and currents, apparent in exact
solutions of the field equations, lead one to regard the Hermitian theory of
relativity as the theory of a field endowed with two sources: electromagnetic
and colour four-currents.


title:
Sagnac effect, twin paradox and space-time topology - Time and length in
  rotating systems and closed Minkowski space-times

abstract:
  We discuss the Sagnac effect in standard Minkowski coordinates and with an
alternative synchronization convention. We find that both approaches lead to
the same result without any contradictions. When applying standard coordinates
to the complete rim of the rotating disk, a time-lag has to be taken into
account which accounts for the global anisotropy. We propose a closed Minkowski
space-time as an exact equivalent to the rim of a disk, both in the rotating
and non-rotating case. In this way the Sagnac effect can be explained as being
purely topological, neglecting the radial acceleration altogether. This proves
that the rim of the disk can be treated as an inertial system. In the same
context we discuss the twin paradox and find that the standard scenario is
equivalent to an unaccelerated version in a closed space-time. The closed
topology leads to preferred frame effects which can be detected only globally.
The relation of synchronization conventions to the measurement of lengths is
discussed in the context of Ehrenfest's paradox. This leads to a confirmation
of the classical arguments by Ehrenfest and Einstein.


title: Short-Distance Cutoffs in Curved Space

abstract:
  It is shown that space-time may possess the differentiability properties of
manifolds as well as the ultraviolet finiteness properties of lattices. Namely,
if a field's amplitudes are given on any sufficiently dense set of discrete
points this could already determine the field's amplitudes at all other points
of the manifold. The criterion for when samples are sufficiently densely spaced
could be that they are apart on average not more than at a Planck distance. The
underlying mathematics is that of classes of functions that can be
reconstructed completely from discrete samples. The discipline is called
sampling theory and is at the heart of information theory. Sampling theory
establishes the link between continuous and discrete forms of information and
is used in ubiquitous applications from scientific data taking to digital
audio.


title: Moment Density of Zipoy's Dipole Solution

abstract:
  Zipoy used spheroidal coordinates to construct a family of static
axisymmetric gravitational fields included in Weyl's class. We calculate the
mass moment source for the dipole solution using techniques previously
developed for magnetic and angular momentum densities and compare it with the
Newtonian analog studied by Bonnor and Sackfield.


title: Vetoes for Inspiral Triggers in LIGO Data

abstract:
  Presented is a summary of studies by the LIGO Scientific Collaboration's
Inspiral Analysis Group on the development of possible vetoes to be used in
evaluation of data from the first two LIGO science data runs. Numerous
environmental monitor signals and interferometer control channels have been
analyzed in order to characterize the interferometers' performance. The results
of studies on selected data segments are provided in this paper. The vetoes
used in the compact binary inspiral analyses of LIGO's S1 and S2 science data
runs are presented and discussed.


title:
Arnowitt-Deser-Misner gravity with variable G and Lambda and fixed point
  cosmologies from the renormalization group

abstract:
  Models of gravity with variable G and Lambda have acquired greater relevance
after the recent evidence in favour of the Einstein theory being
nonperturbatively renormalizable in the Weinberg sense. The present paper
applies the Arnowitt-Deser-Misner (ADM) formalism to such a class of
gravitational models. Are modified action functional is then built which
reduces to the Einstein-Hilbert action when G is constant, and leads to a
power-law growth of the scale factor for pure gravity and for a massless Phi**4
theory in a Universe with Robertson-Walker symmetry, in agreement with the
recently developed fixed-point cosmology. Interestingly, the
renormalization-group flow at the fixed point is found to be compatible with a
Lagrangian description of the running quantities G and Lambda.


title:
Covariant approach to the conformal dynamical equivalence in
  astrophysics

abstract:
  We use covariant techniques to examine the implications of the dynamical
equivalence between geodesic motions and adiabatic hydrodynamic flows. Assuming
that the metrics of a geodesically and a non-geodesically moving fluid are
conformally related, we calculate and compare their mass densities. The density
difference is then expressed in terms of the fundamental physical quantities of
the fluid, such as its energy and isotropic pressure. Both the relativistic and
the non-relativistic case are examined and their differences identified. Our
analysis suggests that observational determinations of astrophysical masses
based on purely Keplerian motions could underestimate the available amount of
matter.


title: The Determination of the Metric by the Weyl and Energy-Momentum Tensors

abstract:
  This brief paper investigates the consequences for the metric tensor of
space-time when the Weyl tensor (in its conformally invariant form) and the
energy-momentum tensor is specified. It is shown that, unless rather special
conditions hold, the metric is uniquely determined up to a constant conformal
factor.


title:
Differential Form Approach for Stationary Axisymmetric Maxwell Fields in
  General Relativity

abstract:
  A formulation for stationary axisymmetric electromagnetic fields in general
relativity is derived by casting them into the form of an anisotropic fluid.
Several simplifications of the formalism are carried out in order to analyze
different features of the fields, such as the derivation of electromagnetic
sources for the Maxwell field in the form of thin layers, construction of new
solutions, and generation techniques.


title: Accelerating cosmology in modified gravity with scalar field

abstract:
  The modified gravity with 1/R term (R being scalar curvature) and the
Einstein-Hilbert term is studied by incorporating the phantom scalar field. A
number of cosmological solutions are derived in the presence of the phantom
field in the perfect fluid background. It is shown the current inflation
obtained in the modified gravity is affected by the existence the phantom
field.


title: Lagrangian and Hamiltonian for the Bondi-Sachs metrics

abstract:
  We calculate the Hilbert action for the Bondi-Sachs metrics. It yields the
Einstein vacuum equations in a closed form. Following the Dirac approach to
constrained systems we investigate the related Hamiltonian formulation.


title: Causal paradoxes: a conflict between relativity and the arrow of time

abstract:
  It is often argued that superluminal velocities and nontrivial spacetime
topologies, allowed by the theory of relativity, may lead to causal paradoxes.
By emphasizing that the notion of causality assumes the existence of a time
arrow (TA) that points from the past to the future, the apparent paradoxes
appear to be an artefact of the wrong tacit assumption that the relativistic
coordinate TA coincides with the physical TA. The latter should be identified
with the thermodynamic TA, which, by being absolute and irrotational, does not
lead to paradoxes.


title:
Equations of motion of compact binaries at the third post-Newtonian
  order

abstract:
  The equations of motion of two point masses in harmonic coordinates are
derived through the third post-Newtonian (3PN) approximation. The problem of
self-field regularization (necessary for removing the divergent self-field of
point particles) is dealt with in two separate steps. In a first step the
extended Hadamard regularization is applied, resulting in equations of motion
which are complete at the 3PN order, except for the occurence of one and only
one unknown parameter. In a second step the dimensional regularization (in d
dimensions) is used as a powerful argument for fixing the value of this
parameter, thereby completing the 3-dimensional Hadamard-regularization result.
The complete equations of motion and associated energy at the 3PN order are
given in the case of circular orbits.


title: Energy and Momentum in General Relativity

abstract:
  The energy and momentum for different cosmological models using various
prescriptions are evaluated. In particular, we have focused our attention on
the energy and momentum for gravitational waves and discuss the results. It is
concluded that there are methods which can provide physically acceptable
results.


title: Centre of mass in spaces with torsion free flat linear connection

abstract:
  The concept "centre of mass" is analyzed in spaces with torsion free flat
linear connection. It is shown that under sufficiently general conditions it is
almost uniquely defined, the corresponding arbitrariness in its definition
being explicitly described.


title:
Time and "angular" dependent backgrounds from stationary axisymmetric
  solutions

abstract:
  Backgrounds depending on time and on "angular" variable, namely polarized and
unpolarized $S^1 \times S^2$ Gowdy models, are generated as the sector inside
the horizons of the manifold corresponding to axisymmetric solutions. As is
known, an analytical continuation of ordinary $D$-branes, $iD$-branes allows
one to find $S$-brane solutions. Simple models have been constructed by means
of analytic continuation of the Schwarzchild and the Kerr metrics. The
possibility of studying the $i$-Gowdy models obtained here is outlined with an
eye toward seeing if they could represent some kind of generalized $S$-branes
depending not only on time but also on an ``angular'' variable.


title: Semiclassical States in Quantum Cosmology: Bianchi I Coherent States

abstract:
  We study coherent states for Bianchi type I cosmological models, as examples
of semiclassical states for time-reparametrization invariant systems. This
simple model allows us to study explicitly the relationship between exact
semiclassical states in the kinematical Hilbert space and corresponding ones in
the physical Hilbert space, which we construct here using the group averaging
technique. We find that it is possible to construct good semiclassical physical
states by such a procedure in this model; we also discuss the sense in which
the original kinematical states may be a good approximation to the physical
ones, and the situations in which this is the case. In addition, these models
can be deparametrized in a natural way, and we study the effect of time
evolution on an "intrinsic" coherent state in the reduced phase space, in order
to estimate the time for this state to spread significantly.


title:
Weight Measurements of High-Temperature Superconductors during Phase
  Transition in Stationary, Non-Stationary Condition and under ELF Radiation

abstract:
  There have been a number of claims in the literature about gravity shielding
effects of superconductors and more recently on the weight reduction of
superconductors passing through their critical temperature. We report several
experiments to test the weight of superconductors under various conditions.
First, we report tests on the weight of YBCO and BSCCO high temperature
superconductors passing through their critical temperature. No anomaly was
found within the equipment accuracy ruling out claimed anomalies by Rounds and
Reiss. Our experiments extend the accuracy of previous measurements by two
orders of magnitude. In addition, for the first time, the weight of a rotating
YBCO superconductor was measured. Also in this case, no weight anomaly could be
seen within the accuracy of the equipment used. In addition, also weight
measurements of a BSCCO superconductor subjected to extremely-low-frequency
(ELF) radiation have been done to test a claim of weight reduction under these
conditions by De Aquino, and again, no unusual behavior was found. These
measurements put new important boundaries on any inertial effect connected with
superconductivity - and consequently on possible space related applications.


title:
Classification of surface charges for a spin 2 field on a curved
  background solution

abstract:
  We give an explicit proof of the result that non trivial conserved n-2 forms
for a spin 2 field on a background corresponding to a solution to Einstein's
equation (with or without cosmological constant) are characterized uniquely by
the Killing vector fields of the background.


title: The Einstein-Vlasov system with a scalar field

abstract:
  We study the Einstein-Vlasov system coupled to a nonlinear scalar field with
a nonnegative potential in locally spatially homogeneous spacetime, as an
expanding cosmological model. It is shown that solutions of this system exist
globally in time. When the potential of the scalar field is of an exponential
form, the cosmological model corresponds to accelerated expansion. The
Einstein-Vlasov system coupled to a nonlinear scalar field whose potential is
of an exponential form shows the causal geodesic completeness of the spacetime
towards the future. The asymptotic behaviour of solutions of this system in the
future time is analysed in various aspects, which shows power-law expansion.


title: Magnetic Surfaces in Stationary Axisymmetric General Relativity

abstract:
  In this paper a new method is derived for constructing electromagnetic
surface sources for stationary axisymmetric electrovac spacetimes endowed with
non-smooth or even discontinuous
  Ernst potentials. This can be viewed as a generalization of some classical
potential theory results, since lack of continuity of the potential is related
to dipole density and lack of smoothness, to monopole density. In particular
this approach is useful for constructing the dipole source for the magnetic
field. This formalism involves solving a linear elliptic differential equation
with boundary conditions at infinity. As an example, two different models of
surface densities for the Kerr-Newman electrovac spacetime are derived.


title:
Near-extremal and extremal quantum-corrected two-dimensional charged
  black holes

abstract:
  We consider charged black holes within dilaton gravity with
exponential-linear dependence of action coefficients on dilaton and minimal
coupling to quantum scalar fields. This includes, in particular, CGHS and RST
black holes in the uncharged limit. For non-extremal configuration quantum
correction to the total mass, Hawking temperature, electric potential and
metric are found explicitly and shown to obey the first generalized law. We
also demonstrate that quantum-corrected extremal black holes in these theories
do exist and correspond to the classically forbidden region of parameters in
the sense that the total mass $M_{tot}<Q$ ($Q$ is a charge). We show that in
the limit $T_{H}\to 0$ (where $T_{H}$ is the Hawking temperature) the mass and
geometry of non-extremal configuration go smoothly to those of the extremal
one, except from the narrow near-horizon region. In the vicinity of the horizon
the quantum-corrected geometry (however small quantum the coupling parameter
$\kappa $ would be) of a non-extremal configuration tends to not the
quantum-corrected extremal one but to the special branch of solutions with the
constant dilaton (2D analog of the Bertotti-Robinson metric) instead.
Meanwhile, if $\kappa =0$ exactly, the near-extremal configuration tends to the
extremal one. We also consider the dilaton theory which corresponds classically
to the spherically-symmetrical reduction from 4D case and show that for the
quantum-corrected extremal black hole $M_{tot}>Q$.


title:
Acceleration field of a Universe modeled as a mixture of scalar and
  matter fields

abstract:
  A model of the Universe as a mixture of a scalar (inflaton or rolling tachyon
from the string theory) and a matter field (classical particles) is analyzed.
The particles are created at the expense of the gravitational energy through an
irreversible process whereas the scalar field is supposed to interact only with
itself and to be minimally coupled with the gravitational field. The
irreversible processes of particle creation are related to the non-equilibrium
pressure within the framework of the extended (causal or second-order)
thermodynamic theory. The scalar field (inflaton or tachyon) is described by an
exponential potential density added by a parameter which represents its
asymptotic value and can be interpreted as the vacuum energy. This model can
simulate three phases of the acceleration field of the Universe, namely,(a) an
inflationary epoch with a positive acceleration followed by a decrease of the
acceleration field towards zero, (b) a past decelerated period where the
acceleration field decreases to a maximum negative value followed by an
increase towards zero, and (c) a present accelerated epoch. For the energy
densities there exist also three distinct epochs which begin with a scalar
field dominated period followed by a matter field dominated epoch and coming
back to a scalar field dominated phase.


title:
Irreversible processes and the accelerated-decelerated phases of the
  Universe

abstract:
  A model for the Universe is proposed where it is considered as a mixture of
scalar and matter fields. The particle production is due to an irreversible
transfer of energy from the gravitational field to the matter field and
represented by a non-equilibrium pressure. This model can simulate three
distinct periods of the Universe: (a) an accelerated epoch where the energy
density of the scalar field prevails over the matter field, (b) a past
decelerated period where the energy density of the matter field becomes more
predominant than the scalar energy density, and (c) a present acceleration
phase where the scalar energy density overcomes the energy density of the
matter field.


title: Oscillatons formed by non linear gravity

abstract:
  Oscillatons are solutions of the coupled Einstein-Klein-Gordon (EKG)
equations that are globally regular and asymptotically flat. By means of a
Legendre transformation we are able to visualize the behaviour of the
corresponding objects in non-linear gravity where the scalar field has been
absorbed by means of the conformal mapping.


title: On static solutions in 2D dilaton gravity with scalar matter

abstract:
  Within the first order formalism static solutions of generic dilaton gravity
in 2D with self-interacting (scalar) matter can be discussed with ease. The
question of (non)existence of Killing horizons is addressed and the interplay
with asymptotic conditions is investigated. Naturally, such an analysis has to
be a global one. A central element in the discussion is the rank of the Jacobi
matrix of the underlying dynamical system. With some (pathological) exceptions
Killing horizons exist only if it equals to 3. For certain self-interactions
asymptotically flat black holes with scalar hair do exist. An example relevant
to general relativity is provided. Finally, generalizations are addressed
including 2D type 0A string theory as a particular example. Additionally, in a
pedagogical appendix the mass definition in dilaton gravity is briefly reviewed
and a unique prescription to fix scaling and shift ambiguity is presented.


title:
Evolution of the Schr\"odinger--Newton system for a self--gravitating
  scalar field

abstract:
  Using numerical techniques, we study the collapse of a scalar field
configuration in the Newtonian limit of the spherically symmetric
Einstein--Klein--Gordon (EKG) system, which results in the so called
Schr\"odinger--Newton (SN) set of equations. We present the numerical code
developed to evolve the SN system and topics related, like equilibrium
configurations and boundary conditions. Also, we analyze the evolution of
different initial configurations and the physical quantities associated to
them. In particular, we readdress the issue of the gravitational cooling
mechanism for Newtonian systems and find that all systems settle down onto a
0--node equilibrium configuration.


title: Small Black Holes on Branes: Is the horizon regular or singular ?

abstract:
  We investigate the following question: Consider a small mass, with $\epsilon$
(the ratio of the Schwarzschild radius and the bulk curvature length) much
smaller than 1, that is confined to the TeV brane in the Randall-Sundrum I
scenario. Does it form a black hole with a regular horizon, or a naked
singularity? The metric is expanded in $\epsilon$ and the asymptotic form of
the metric is given by the weak field approximation (linear in the mass). In
first order of $\epsilon$ we show that the iteration of the weak field
solution, which includes only integer powers of the mass, leads to a solution
that has a singular horizon. We find a solution with a regular horizon but its
asymptotic expansion in the mass also contains half integer powers.


title: Stability of Cauchy Horizon under perturbations

abstract:
  We use perturbations in order to study the stability of the Cauchy Horizon in
a Reissner-Nordstr\"om space-time. The perturbations are either scalar or
gravitational, and indicate some strong instabilities.


title: Singularity-Free Cylindrical Cosmological Model

abstract:
  A cylindrically symmetric perfect fluid spacetime with no curvature
singularity is shown. The equation of state for the perfect fluid is that of a
stiff fluid. The metric is diagonal and non-separable in comoving coordinates
for the fluid. It is proven that the spacetime is geodesically complete and
globally hyperbolic.


title: Background Independent Quantum Gravity: A Status Report

abstract:
  The goal of this article is to present an introduction to loop quantum
gravity -a background independent, non-perturbative approach to the problem of
unification of general relativity and quantum physics, based on a quantum
theory of geometry. Our presentation is pedagogical. Thus, in addition to
providing a bird's eye view of the present status of the subject, the article
should also serve as a vehicle to enter the field and explore it in detail. To
aid non-experts, very little is assumed beyond elements of general relativity,
gauge theories and quantum field theory. While the article is essentially
self-contained, the emphasis is on communicating the underlying ideas and the
significance of results rather than on presenting systematic derivations and
detailed proofs. (These can be found in the listed references.) The subject can
be approached in different ways. We have chosen one which is deeply rooted in
well established physics and also has sufficient mathematical precision to
ensure that there are no hidden infinities. In order to keep the article to a
reasonable size, and to avoid overwhelming non-experts, we have had to leave
out several interesting topics, results and viewpoints; this is meant to be an
introduction to the subject rather than an exhaustive review of it.


title: Comparison of Two Stationary Spherical Accretion Models

abstract:
  The general relativistic accretion onto a black hole is investigated in which
the motion is steady and spherically symmetrical, the gas being at rest at
infinity. Two models with different equations of state are compared. Numerical
calculations show that the predictions of the models are similar in most
aspects. In the ultrarelativistic regime the allowed band of the asymptotic
speed of sound and the mass accretion rate can be markedly different.


title: Numerical computation of Maass waveforms and an application to cosmology

abstract:
  We compute numerically eigenvalues and eigenfunctions of the Laplacian in a
three-dimensional hyperbolic space. Applying the results to cosmology, we
demonstrate that the methods learned in quantum chaos can be used in other
fields of research.


title: Flat Spacetime Vacuum in Loop Quantum Gravity

abstract:
  We construct a state in the loop quantum gravity theory with zero
cosmological constant, which should correspond to the flat spacetime vacuum
solution. This is done by defining the loop transform coefficients of a flat
connection wavefunction in the holomorphic representation which satisfies all
the constraints of quantum General Relativity and it is peaked around the flat
space triads. The loop transform coefficients are defined as spin foam state
sum invariants of the spin networks embedded in the spatial manifold for the
SU(2) quantum group. We also obtain an expression for the vacuum wavefunction
in the triad represntation, by defining the corresponding spin networks
functional integrals as SU(2) quantum group state sums.


title: Simulation of gravitational objects in Bose-Einstein condensates

abstract:
  In this diplom-arbeit I consider a specific class of "analogue models" of
curved spacetime that are specifically based on the use of Bose-Einstein
condensates.
  As is usual in "analogue models", we are primarily interested in the
kinematics of fields and quanta immersed in a curved-space background. We are
not directly concerned with the Einstein equations of general relativity. Over
the last few years numerous papers concerning "analogue models" have been
published, the key result being that in many dynamical systems the
perturbations have equations of motion that are governed by an "effective
metric" that can often be interpreted in terms of an equivalent gravitational
field.
  After a brief introduction concerning Bose-Einstein condensates and general
relativity, I explain the connection between these two fields. Several specific
examples are then explored in a little more detail:
  1) Sinks and acoustic black holes [dumb holes].
  2) Ring-shaped Laval nozzles and acoustic horizons.
  3) the de Sitter universe.
  In particular, the de Sitter universe is modelled by a freely expanding
condensate obtained by suddenly switching off the trap that normally holds the
condensate in place.


title:
Kranc: a Mathematica application to generate numerical codes for
  tensorial evolution equations

abstract:
  We present a suite of Mathematica-based computer-algebra packages, termed
"Kranc", which comprise a toolbox to convert (tensorial) systems of partial
differential evolution equations to parallelized C or Fortran code. Kranc can
be used as a "rapid prototyping" system for physicists or mathematicians
handling very complicated systems of partial differential equations, but
through integration into the Cactus computational toolkit we can also produce
efficient parallelized production codes. Our work is motivated by the field of
numerical relativity, where Kranc is used as a research tool by the authors. In
this paper we describe the design and implementation of both the Mathematica
packages and the resulting code, we discuss some example applications, and
provide results on the performance of an example numerical code for the
Einstein equations.


title: Path integral quantization of parametrised field theory

abstract:
  Free scalar field theory on a flat spacetime can be cast into a generally
covariant form known as parametrised field theory in which the action is a
functional of the scalar field as well as the embedding variables which
describe arbitrary, in general curved, foliations of the flat spacetime.
  We construct the path integral quantization of parametrised field theory in
order to analyse issues at the interface of quantum field theory and general
covariance in a path integral context. We show that the measure in the
Lorentzian path integral is non-trivial and is the analog of the Fradkin-
Vilkovisky measure for quantum gravity. We construct Euclidean functional
integrals in the generally covariant setting of parametrised field theory using
key ideas of Schleich and show that our constructions imply the existence of
non-standard `Wick rotations' of the standard free scalar field 2 point
function. We develop a framework to study the problem of time through
computations of scalar field 2 point functions. We illustrate our ideas through
explicit computation for a time independent 1+1 dimensional foliation. Although
the problem of time seems to be absent in this simple example, the general case
is still open. We discuss our results in the contexts of the path integral
formulation of quantum gravity and the canonical quantization of parametrised
field theory.


title:
Detecting gravitational radiation from neutron stars using a
  six-parameter adaptive MCMC method

abstract:
  We present a Markov chain Monte Carlo technique for detecting gravitational
radiation from a neutron star in laser interferometer data. The algorithm can
estimate up to six unknown parameters of the target, including the rotation
frequency and frequency derivative, using reparametrization, delayed rejection
and simulated annealing. We highlight how a simple extension of the method,
distributed over multiple computer processors, will allow for a search over a
narrow frequency band. The ultimate goal of this research is to search for
sources at a known locations, but uncertain spin parameters, such as may be
found in SN1987A.


title:
Cosmology and Gravitation: Summary talk at the XXIV Brazilian Meeting on
  Particles and Fields

abstract:
  This is a brief summary with comments on selected contributions to the
Cosmology and Gravitation section at the $24^{th}$ Brazilian Meeting on
Particle and Fields (ENFPC XXIV), held at Caxambu, from September 30 to October
4, 2003.


title:
Systematic measurement of the intrinsic losses in various kinds of bulk
  fused silica

abstract:
  We systematically measured and compared the mechanical losses of various
kinds of bulk fused silica. Their quality factors ranged widely from 7x10^5 to
4x10^7, the latter being one of the highest reported among bulk fused silica.
We observed frequency-dependent losses and a decrease in the losses upon
annealing.


title: An excuse for revising a theory of time-varying "constants"

abstract:
  In this paper we compare the dimensional method with the Lie groups tactic in
order to show the limitations and advantages of each technique. For this
purpose we study in detail a perfect fluid cosmological model with time-varying
"constants" by using dimensional analysis and the symmetry method. We revise
our previous conclusion about the variation of the fine structure constant
finding for example that in the radiation predominance era if $\alpha$ varies
is only due to the variation of $e^{2}\epsilon_{0}^{-1}$ since $c\hbar=const$
in this era.


title:
IIR Adaptive Filters for Detection of Gravitational Waves from
  Coalescing Binaries

abstract:
  In this paper we propose a new strategy for gravitational waves detection
from coalescing binaries, using IIR Adaptive Line Enhancer (ALE) filters. This
strategy is a classical hierarchical strategy in which the ALE filters have the
role of triggers, used to select data chunks which may contain gravitational
events, to be further analyzed with more refined optimal techniques, like the
the classical Matched Filter Technique. After a direct comparison of the
performances of ALE filters with the Wiener-Komolgoroff optimum filters
(matched filters), necessary to discuss their performance and to evaluate the
statistical limitation in their use as triggers, we performed a series of
tests, demonstrating that these filters are quite promising both for the
relatively small computational power needed and for the robustness of the
algorithms used. The performed tests have shown a weak point of ALE filters,
that we fixed by introducing a further strategy, based on a dynamic bank of ALE
filters, running simultaneously, but started after fixed delay times. The
results of this global trigger strategy seems to be very promising, and can be
already used in the present interferometers, since it has the great advantage
of requiring a quite small computational power and can easily run in real-time,
in parallel with other data analysis algorithms.


title:
A Scenario for the Dimensional Compactification in Eleven-Dimensional
  Space-Time

abstract:
  We discuss the inhomogeneous multidimensional mixmaster model in view of
appearing, near the cosmological singularity, a scenario for the dimensional
compactification in correspondence to an 11-dimensional space-time. Our
analysis candidates such a collapsing picture toward the singularity to
describe the actual expanding 3-dimensional Universe and an associated
collapsed 7-dimensional space. To this end, a conformal factor is determined in
front of the 4-dimensional metric to remove the 4-curvature divergences and the
resulting Universe expands with a power-law.inflation. Thus we provide an
additional peculiarity of the eleven space-time dimensions in view of
implementing a geometrical theory of unification.


title:
Inhomogeneous de Sitter Solution with Scalar Field and Perturbations
  Spectrum

abstract:
  We provide an inhomogeneous solution concerning the dynamics of a real self
interacting scalar field minimally coupled to gravity in a region of the
configuration space where it performs a slow rolling on a plateau of its
potential. During the inhomogeneous de Sitter phase the scalar field dominant
term is a function of the spatial coordinates only. This solution specialized
nearby the FLRW model allows a classical origin for the inhomogeneous
perturbations spectrum.


title: Sagnac Effect of Goedel's Universe

abstract:
  We present exact expressions for the Sagnac effect of Goedel's Universe. For
this purpose we first derive a formula for the Sagnac time delay along a
circular path in the presence of an arbitrary stationary metric in cylindrical
coordinates. We then apply this result to Goedel's metric for two different
experimental situations: First, the light source and the detector are at rest
relative to the matter generating the gravitational field. In this case we find
an expression that is formally equivalent to the familiar nonrelativistic
Sagnac time delay. Second, the light source and the detector are rotating
relative to the matter. Here we show that for a special rotation rate of the
detector the Sagnac time delay vanishes. Finally we propose a formulation of
the Sagnac time delay in terms of invariant physical quantities. We show that
this result is very close to the analogous formula of the Sagnac time delay of
a rotating coordinate system in Minkowski spacetime.


title: Approximately self-similar critical collapse in 2+1 dimensions

abstract:
  Critical collapse of a self-gravitating scalar field in a (2+1)-dimensional
spacetime with negative cosmological constant seems to be dominated by a
continuously self-similar solution of the field equations without cosmological
constant. However, previous studies of linear perturbations in this background
were inconclusive. We extend the continuously self-similar solutions to
solutions of the field equations with negative cosmological constant, and
analyse their linear perturbations. The extended solutions are characterized by
a continuous parameter. A suitable choice of this parameter seems to improve
the agreement with the numerical results. We also study the dynamics of the
apparent horizon in the extended background.


title: Does Quantum Cosmology Predict a Constant Dilatonic Field?

abstract:
  Quantum cosmology may permit to determine the initial conditions of the
Universe. In particular, it may select a specific model between many possible
classical models. In this work, we study a quantum cosmological model based on
the string effective action coupled to matter. The Schutz's formalism is
employed in the description of the fluid. A radiation fluid is considered. In
this way, a time coordinate may be identified and the Wheeler-DeWitt equation
reduces in the minisuperspace to a Schr\"odinger-like equation. It is shown
that, under some quite natural assumptions, the expectation values indicate a
null axionic field and a constant dilatonic field. At the same time the scale
factor exhibits a bounce revealing a singularity-free cosmological model. In
some cases, the mininum value of the scale factor can be related to the value
of gravitational coupling.


title: Stationary strings near a higher-dimensional rotating black hole

abstract:
  We study stationary string configurations in a space-time of a
higher-dimensional rotating black hole. We demonstrate that the Nambu-Goto
equations for a stationary string in the 5D Myers-Perry metric allow a
separation of variables. We present these equations in the first-order form and
study their properties. We prove that the only stationary string configuration
which crosses the infinite red-shift surface and remains regular there is a
principal Killing string. A worldsheet of such a string is generated by a
principal null geodesic and a timelike at infinity Killing vector field. We
obtain principal Killing string solutions in the Myers-Perry metrics with an
arbitrary number of dimensions. It is shown that due to the interaction of a
string with a rotating black hole there is an angular momentum transfer from
the black hole to the string. We calculate the rate of this transfer in a
spacetime with an arbitrary number of dimensions. This effect slows down the
rotation of the black hole. We discuss possible final stationary configurations
of a rotating black hole interacting with a string.


title: A remedy for constraint growth in Numerical Relativity

abstract:
  Rapid growth of constraints is often observed in free evolutions of highly
gravitating systems. To alleviate this problem we investigate the effect of
adding spatial derivatives of the constraints to the right hand side of the
evolution equations, and we look at how this affects the character of the
system and the treatment of boundaries. We apply this technique to two
formulations of Maxwell's equations, the so-called fat Maxwell and the
Knapp-Walker-Baumgarte systems, and obtain mixed hyperbolic-parabolic problems
in which high frequency constraint violations are damped. Constraint-preserving
boundary conditions amount to imposing Dirichlet boundary conditions on
constraint variables, which translate into Neumann-like boundary conditions for
the main variables. The success of the numerical tests presented in this work
suggests that this remedy may bring benefits to fully nonlinear simulations of
General Relativity.


title: Cosmological evolution of a ghost scalar field

abstract:
  We consider a scalar field with a negative kinetic term minimally coupled to
gravity. We obtain an exact non-static spherically symmetric solution which
describes a wormhole in cosmological setting. The wormhole is shown to connect
two homogeneous spatially flat universes expanding with acceleration. Depending
on the wormhole's mass parameter $m$ the acceleration can be constant (the de
Sitter case) or infinitely growing.


title:
Can One Understand Black Hole Entropy without Knowing Much about Quantum
  Gravity?

abstract:
  It is a common belief now that the explanation of the microscopic origin of
the Bekenstein-Hawking entropy of black holes should be available in quantum
gravity theory, whatever this theory will finally look like. Calculations of
the entropy of certain black holes in string theory do support this point of
view. In the last few years there also appeared a hope that an understanding of
black hole entropy may be possible even without knowing the details of quantum
gravity. The thermodynamics of black holes is a low energy phenomenon, so only
a few general features of the fundamental theory may be really important. The
aim of this review is to describe some of the proposals in this direction and
the results obtained.


title: The Bianchi IX model in Loop Quantum Cosmology

abstract:
  The Bianchi IX model has been used often to investigate the structure close
to singularities of general relativity. Its classical chaos is expected to
have, via the BKL scenario, implications even for the approach to general
inhomogeneous singularities. Thus, it is a popular model to test consequences
of modifications to general relativity suggested by quantum theories of
gravity. This paper presents a detailed proof that modifications coming from
loop quantum gravity lead to a non-chaotic effective behavior. The way this is
realized, independently of quantization ambiguities, suggests a new look at
initial and final singularities.


title: Could the Gravitons Have Rest Masses?

abstract:
  If the cosmological constant $\Lambda $ can not be neglected, we will show in
this short report, that graviton should have a rest mass $m_g=\sqrt{2\Lambda
}=\sqrt{2\Lambda}\hbar c^{-1}$ different from zero.


title: Hamiltonian Analysis of Plebanski Theory

abstract:
  We study the Hamiltonian formulation of Plebanski theory in both the
Euclidean and Lorentzian cases. A careful analysis of the constraints shows
that the system is non regular, i.e. the rank of the Dirac matrix is
non-constant on the non-reduced phase space. We identify the gravitational and
topological sectors which are regular sub-spaces of the non-reduced phase
space. The theory can be restricted to the regular subspace which contains the
gravitational sector. We explicitly identify first and second class constraints
in this case. We compute the determinant of the Dirac matrix and the natural
measure for the path integral of the Plebanski theory (restricted to the
gravitational sector). This measure is the analogue of the
Leutwyler-Fradkin-Vilkovisky measure of quantum gravity.


title: Vector field and rotational curves in dark galactic halos

abstract:
  We study equations of a non-gauge vector field in a spherically symmetric
static metric. The constant vector field with a scale arrangement of
components: the time component about the Planck mass m_{Pl} and the radial
component about M suppressed with respect to the Planck mass, serves as a
source of metric reproducing flat rotation curves in dark halos of spiral
galaxies, so that the velocity of rotation v_0 is determined by the hierarchy
of scales: \sqrt{2} v_0^2= M/m_{Pl}, and M\sim 10^{12} GeV. A natural estimate
of Milgrom's acceleration about the Hubble rate is obtained.


title:
Cosmological Models with Variable Constants.Their Solution Through
  Similarity Methods

abstract:
  In this work we compile a few differential equations (ODEs) that arise from
the relativistic equations in cosmological models that consider the
``constants'' as scalars functions dependent on time and they are described as
perfect as well as viscous fluids. The general idea of the paper is to show how
to solve the equations of the models through dimensional techniques
(self-similarity). The results are compared with those obtained by other
authors and new solutions are introduced.


title: A Theory of time-varying Constants

abstract:
  We present a flat (K=0) cosmological model, described by a perfect fluid with
the ``constants'' $G,c$ and $\Lambda$ varying with cosmological time $t$. We
introduce Planck\'s ``constant'' $\hbar$ in the field equations through the
equation of state for the energy density of radiation. We then determine the
behaviour of the ``constants'' by using the zero divergence of the second
member of the modified Einstein\'s field equations i.e.
$div(\frac{G}{c^{4}}T_{i}^{j}+\delta_{i}^{j}\Lambda)=0,$ together with the
equation of state and the Einstein cosmological equations. Assuming realistic
physical and mathematical conditions we obtain a consistent result with $\hbar
c=constant$. In this way we obtain gauge invariance for the Schr\"{o}dinger
equation and the behaviour of the remaining ``constants''


title: Full Causal Bulk Viscous Cosmologies with time-varying Constants

abstract:
  We study the evolution of a flat Friedmann-Robertson-Walker Universe, filled
with a bulk viscous cosmological fluid, in the presence of time varying
``constants''. The dimensional analysis of the model suggests a proportionality
between the bulk viscous pressure of the dissipative fluid and the energy
density. On using this assumption and with the choice of the standard equations
of state for the bulk viscosity coefficient, temperature and relaxation time,
the general solution of the field equations can be obtained, with all physical
parameters having a power-law time dependence. The symmetry analysis of this
model, performed by using Lie group techniques, confirms the unicity of the
solution for this functional form of the bulk viscous pressure. In order to
find another possible solution we relax the hypotheses assuming a concrete
functional dependence for the ``constants''.


title: Perfect Fluid Cosmological Models with time-varying Constants

abstract:
  In this paper, we study in detail a perfect fluid cosmological model with
time-varying "constants" using dimensional analysis and the symmetry method. We
examine the case of variable "constants" in detail without considering the
perfect fluid model as a limiting case of a model with a causal bulk viscous
fluid as discussed in a recent paper. We obtain some new solutions through the
Lie method and show that when matter creation is considered, these solutions
are physically relevant.


title: About Brill Initial Data Sets and HPC

abstract:
  The goal of this paper is to present the physics behind Brill initial data
sets as an excellent tool for numerical experiments of axisymmetric spacetimes,
data sets which are practical applications of HPC for numerical solutions of
Einstein's vacuum equations.


title:
Stabilization of a Fabry-Perot interferometer using a suspension-point
  interferometer

abstract:
  A suspension-point interferometer (SPI) is an auxiliary interferometer for
active vibration isolation, implemented at the suspension points of the mirrors
of an interferometric gravitational wave detector. We constructed a prototype
Fabry-Perot interferometer equipped with an SPI and observed vibration
isolation in both the spectrum and transfer function. The noise spectrum of the
main interferometer was reduced by 40 dB below 1 Hz. Transfer function
measurements showed that the SPI also produced good vibration suppression above
1 Hz. These results indicate that SPI can improve both the sensitivity and the
stability of the interferometer.


title:
Gravitational Waves and GRBs from Tidal Disruption of Stars in the
  Center of Galaxies

abstract:
  Recent measurements of the Chandra satellite have shown that a supermassive
black hole of $M = 2.6 \times 10^{6} M_{\odot}$ is located in the Galactic
Center; it seems probable that, from other observations, this fact is common in
the majority of galaxies. On the other hand, GRB explosions are typical
phenomenon linked to the galactic dynamics. In the present paper we discuss the
possibility that GRBs are tidal disruption of stars by supermassive black holes
located in the center of galaxies. This conjecture can be tested by a
gravitational wave detector of the class of AURIGA.


title: Cylindrical thin-shell wormholes

abstract:
  A general formalism for the dynamics of non rotating cylindrical thin-shell
wormholes is developed. The time evolution of the throat is explicitly obtained
for thin-shell wormholes whose metric has the form associated to local cosmic
strings. It is found that the throat collapses to zero radius, remains static
or expands forever, depending only on the sign of its initial velocity.


title:
Quantum modes around a scalar-tensor black hole: breakdown of the
  normalization conditions

abstract:
  Black holes arising in the context of scalar-tensor gravity theories, where
the scalar field is non-minimally coupled to the curvature term, have zero
surface gravity. Hence, it is generally stated that their Hawking temperature
is zero, irrespectivelly of their gravitational and scalar charges. The proper
analysis of the Hawking temperature requires to study the propagation of
quantum fields in the space-time determined by these objects. We study scalar
fields in the vicinity of the horizon of these black holes. It is shown that
the scalar modes do not form an orthonormal set. Hence, the Hilbert space is
ill-definite in this case, and no notion of temperature can be extracted for
such objects.


title: Consistent and mimetic discretizations in general relativity

abstract:
  A discretization of a continuum theory with constraints or conserved
quantities is called mimetic if it mirrors the conserved laws or constraints of
the continuum theory at the discrete level. Such discretizations have been
found useful in continuum mechanics and in electromagnetism. We have recently
introduced a new technique for discretizing constrained theories. The technique
yields discretizations that are consistent, in the sense that the constraints
and evolution equations can be solved simultaneously, but it cannot be
considered mimetic since it achieves consistency by determining the Lagrange
multipliers. In this paper we would like to show that when applied to general
relativity linearized around a Minkowski background the technique yields a
discretization that is mimetic in the traditional sense of the word. We show
this using the traditional metric variables and also the Ashtekar new
variables, but in the latter case we restrict ourselves to the Euclidean case.
We also argue that there appear to exist conceptual difficulties to the
construction of a mimetic formulation of the full Einstein equations, and
suggest that the new discretization scheme can provide an alternative that is
nevertheless close in spirit to the traditional mimetic formulations.


title: Gravitational waves in the generalized Chaplygin gas model

abstract:
  The consequences of taking the generalized Chaplygin gas as the dark energy
constituent of the Universe on the gravitational waves are studied and the
spectrum obtained from this model, for the flat case, is analyzed. Besides its
importance for the study of the primordial Universe, the gravitational waves
represent an additional perspective (besides the CMB temperature and
polarization anisotropies) to evaluate the consistence of the different dark
energy models and establish better constraints to their parameters. The
analysis presented here takes this fact into consideration to open one more
perspective of verification of the generalized Chapligin gas model
applicability. Nine particular cases are compared: one where no dark energy is
present; two that simulate the $\Lambda$-CDM model; two where the gas acts like
the traditional Chaplygin gas; and four where the dark energy is the
generalized Chaplygin gas. The different spectra permit to distinguish the
$\Lambda$-CDM and the Chaplygin gas scenarios.


title: Relational Physics and Quantum Space

abstract:
  In a purely relational theory there exists a tension between the relational
character of the theory and the existence of quantities like distance and
duration. We review this issue in the context of the Leibniz-Clarke
correspondence. We then address this conflict by showing that a purely
relational definition of length and time can be given, provided the dynamics of
the theory is known. We further show that in such a setting it is natural to
expect Lorentz transformations to describe the mapping between different
observers. We then comment on how these insights can be used to make progress
in the search for a theory of quantum gravity.


title: Ln(3) and Black Hole Entropy

abstract:
  We review an idea that uses details of the quasinormal mode spectrum of a
black hole to obtain the Bekenstein-Hawking entropy of $A/4$ in Loop Quantum
Gravity. We further comment on a recent proposal concerning the quasinormal
mode spectrum of rotating black holes. We conclude by remarking on a recent
proposal to include supersymmetry.


title: A single-domain spectral method for black hole puncture data

abstract:
  We calculate puncture initial data corresponding to both single and binary
black hole solutions of the constraint equations by means of a pseudo-spectral
method applied in a single spatial domain. Introducing appropriate coordinates,
these methods exhibit rapid convergence of the conformal factor and lead to
highly accurate solutions. As an application we investigate small mass ratios
of binary black holes and compare these with the corresponding test mass limit
that we obtain through a semi-analytical limiting procedure. In particular, we
compare the binding energy of puncture data in this limit with that of a test
particle in the Schwarzschild spacetime and find that it deviates by 50% from
the Schwarzschild result at the innermost stable circular orbit of
Schwarzschild, if the ADM mass at each puncture is used to define the local
black hole masses.