title:
Quasi-isotropic solution of the Einstein equations near a cosmological
  singularity for a two-fluid cosmological model

abstract:
  The quasi-isotropic inhomogeneous solution of the Einstein equations near a
cosmological singularity in the form of a series expansion in the synchronous
system of reference, first found by Lifshitz and Khalatnikov in 1960, is
generalized to the case of a two-fluid cosmological model. This solution
describes non-decreasing modes of adiabatic and isocurvature scalar
perturbations and gravitational waves in the regime when deviations of a
space-time metric from the homogeneous isotropic Friedmann-Robertson-Walker
(FRW) background are large while locally measurable quantities like Riemann
tensor components are still close to their FRW values. The general structure of
the perturbation series is presented and the first coefficients of the series
expansion for the metric tensor and the fluid energy densities and velocities
are calculated explicitly.


title: Dynamical Gauge Conditions for the Einstein Evolution Equations

abstract:
  The Einstein evolution equations have been written in a number of symmetric
hyperbolic forms when the gauge fields--the densitized lapse and the shift--are
taken to be fixed functions of the coordinates. Extended systems of evolution
equations are constructed here by adding the gauge degrees of freedom to the
set of dynamical fields, thus forming symmetric hyperbolic systems for the
combined evolution of the gravitational and the gauge fields. The associated
characteristic speeds can be made causal (i.e. less than or equal to the speed
of light) by adjusting 14 free parameters in these new systems. And 21
additional free parameters are available, for example to optimize the stability
of numerical evolutions. The gauge evolution equations in these systems are
generalizations of the ``K-driver'' and ``Gamma-driver'' conditions that have
been used with some success in numerical black hole evolutions.


title: Quantum Evolution of the Dilaton-Inflaton Model

abstract:
  The quantum evolution of a model of the universe with account of two scalar
fields ({\it dilaton} and {\it inflaton}) is considered. For this case, the
closed and flat models has been examined. It is shown that in both cases the
realization of conditions necessary for inflation is strongly depends on
coupling constant for dilaton and inflaton fields.


title: Kerr black hole quasinormal frequencies

abstract:
  Black-hole quasinormal modes (QNM) have been the subject of much recent
attention, with the hope that these oscillation frequencies may shed some light
on the elusive theory of quantum gravity. We compare numerical results for the
QNM spectrum of the (rotating) Kerr black hole with an {\it exact} formula
Re$\omega \to T_{BH}\ln 3+\Omega m$, which is based on Bohr's correspondence
principle. We find a close agreement between the two. Possible implications of
this result to the area spectrum of quantum black holes are discussed.


title: Canonical Phase Space Formulation of Quasilocal General Relativity

abstract:
  We construct a Hamiltonian formulation of quasilocal general relativity using
an extended phase space that includes boundary coordinates as configuration
variables. This allows us to use Hamiltonian methods to derive an expression
for the energy of a non-isolated region of space-time that interacts with its
neighbourhood. This expression is found to be very similar to the Brown-York
quasilocal energy that was originally derived by Hamilton-Jacobi methods. We
examine the connection between the two formalisms and find that when the
boundary conditions for the two are harmonized, the resulting quasilocal
energies are identical.


title: Kantowski-Sachs Brane Cosmology

abstract:
  We consider brane Kantowski-Sachs Universe when bulk space is
five-dimensional Anti-deSitter space. The corresponding cosmological equations
with perfect fluid are written. For several specific choices of relation
between energy and pressure it is found the behavior of scale factors at early
time. In particulary, for $\gamma=3/2$ Kantowski-Sachs brane cosmology is
modified to become the isotropic one, while for $\gamma=1$ it remains the
anisotropic cosmology in the process of evolution.


title: Non-linear Gravity on Branes and Effective Action

abstract:
  We develop the general formalism to study the low energy regime of the brane
world. We apply our formalism to the single brane model where the AdS/CFT
correspondence will take an important role. We also consider the two-brane
system and show the system is described by the quasi-scalar tensor gravity. Our
result provides a basis for predicting CMB fluctuations in the braneworld
models.


title: Born-Again Braneworld

abstract:
  We propose a cosmological braneworld scenario in which two branes collide and
emerge as reborn branes with signs of tensions opposite to the original
tensions of respective branes. In this scenario, the branes are assumed to be
inflating. However, the whole dynamics is different from the usual inflation
due to the non-trivial dynamics of the radion field. Transforming the conformal
frame to the Einstein frame, this born-again scenario resembles the
pre-big-bang scenario. Thus our scenario has features of both inflation and
pre-big-bang scenarios. In particular, the gravitational waves produced from
vacuum fluctuations will have a very blue spectrum, while the inflaton field
will give rise to a standard scale-invariant spectrum.


title:
Axisymmetric core collapse simulations using characteristic numerical
  relativity

abstract:
  We present results from axisymmetric stellar core collapse simulations in
general relativity. Our hydrodynamics code has proved robust and accurate
enough to allow for a detailed analysis of the global dynamics of the collapse.
Contrary to traditional approaches based on the 3+1 formulation of the
gravitational field equations, our framework uses a foliation based on a family
of outgoing light cones, emanating from a regular center, and terminating at
future null infinity. Such a coordinate system is well adapted to the study of
interesting dynamical spacetimes in relativistic astrophysics such as stellar
core collapse and neutron star formation. Perhaps most importantly this
procedure allows for the unambiguous extraction of gravitational waves at
future null infinity without any approximation, along with the commonly used
quadrupole formalism for the gravitational wave extraction. Our results
concerning the gravitational wave signals show noticeable disagreement when
those are extracted by computing the Bondi news at future null infinity on the
one hand and by using the quadrupole formula on the other hand. We have strong
indication that for our setup the quadrupole formula on the null cone does not
lead to physical gravitational wave signals. The Bondi gravitational wave
signals extracted at infinity show typical oscillation frequencies of about 0.5
kHz.


title: Black Hole Entropy from Spin One Punctures

abstract:
  Recent suggestion, that the emission of a quantum of energy corresponding to
the asymptotic value of quasinormal modes of a Schwarzschild black hole should
be associated with the loss of spin one punctures from the black hole horizon,
fixes the Immirzi parameter to a definite value. We show that saturating the
horizon with spin one punctures reproduces the earlier formula for the black
hole entropy, including the $ln (area)$ correction with definite coefficient (-
3/2) for large area.


title: Black hole mass and angular momentum in 2+1 gravity

abstract:
  We propose a new definition for the mass and angular momentum of neutral or
electrically charged black holes in 2+1 gravity with two Killing vectors. These
finite conserved quantities, associated with the SL(2,R) invariance of the
reduced mechanical system, are shown to be identical to the quasilocal
conserved quantities for an improved gravitational action corresponding to
mixed boundary conditions. They obey a general Smarr-like formula and, in all
cases investigated, are consistent with the first law of black hole
thermodynamics. Our framework is applied to the computation of the mass and
angular momentum of black hole solutions to several field-theoretical models.


title: Area Quantization in Quasi-Extreme Black Holes

abstract:
  We consider quasi-extreme Kerr and quasi-extreme Schwarzschild-de Sitter
black holes. From the known analytical expressions obtained for their
quasi-normal modes frequencies, we suggest an area quantization prescription
for those objects.


title:
The conformal metric associated with the U(1) gauge of the Stueckelberg-
  Schr\"odinger equation

abstract:
  We review the classical and quantum mechanics of Stueckelberg, and introduce
the compensation fields necessary for the gauge covariance of the Stueckelberg-
Schr\"odinger equation. To achieve this, one must introduce a fifth, Lorentz
scalar, compensation field, in addition to the four vector fields which
compensate the action of the space-time derivatives. A generalized Lorentz
force can be derived from the classical Hamilton equations associated with this
evolution function. We show that the fifth (scalar) field can be eliminated
through the introduction of a conformal metric on the spacetime manifold. The
geodesic equation associated with this metric coincides with the Lorentz force,
and is therefore dynamically equivalent. Since the generalized Maxwell
equations for the five dimensional fields provide an equation relating the
fifth field with the spacetime density of events, one can derive the spacetime
event density associated with the Friedmann-Robertson-Walker solution of the
Einstein equations. The resulting density, in the conformal coordinate space,
is isotropic and homogeneous, decreasing as the square of the Robertson-Walker
scale factor. Using the Einstein equations, one sees that both for the static
and matter dominated models, the conformal time slice in which the events which
generate the world lines are contained becomes progressively thinner as the
inverse square of the scale factor, establishing a simple correspondence
between the configurations predicted by the underlying
Friedmann-Robertson-Walker dynamical model and the configurations in the
conformal coordinates.


title: A numerical analysis for G(t) in a scalar tensor theory

abstract:
  We calculated the evolution of the Newton gravitational in a scalar tensor
theory, using parameters that holds for the present Universe. We analised the
evolution from one billion of years ago.


title: Adaptive Mesh Refinement for Characteristic Codes

abstract:
  The use of adaptive mesh refinement (AMR) techniques is crucial for accurate
and efficient simulation of higher dimensional spacetimes. In this work we
develop an adaptive algorithm tailored to the integration of finite difference
discretizations of wave-like equations using characteristic coordinates. We
demonstrate the algorithm by constructing a code implementing the
Einstein-Klein-Gordon system of equations in spherical symmetry. We discuss how
the algorithm can trivially be generalized to higher dimensional systems, and
suggest a method that can be used to parallelize a characteristic code.


title:
Self-Similar Solutions, Critical Behavior and Convergence to Attractor
  in Gravitational Collapse

abstract:
  General relativity as well as Newtonian gravity admits self-similar solutions
due to its scale-invariance. This is a review on these self-similar solutions
and their relevance to gravitational collapse. In particular, our attention is
mainly paid on the crucial role of self-similar solutions in the critical
behavior and attraction in gravitational collapse.


title: Properties of Solutions in 2+1 Dimensions

abstract:
  We solve the Einstein equations for the 2+1 dimensions with and without
scalar fields. We calculate the entropy, Hawking temperature and the emission
probabilities for these cases. We also compute the Newman-Penrose coefficients
for different solutions and compare them.


title:
Time variation of the gravitational and fine structure constants in
  models with extra dimensions

abstract:
  We derive formulae for the time variation of the gravitational ``constant''
and of the fine structure ``constant'' in various models with extra dimensions
and analyze their consistency with the observational data.


title: The Space-time Transformations Between Accelerated Systems

abstract:
  We determine transformations between coordinate systems which are mutually in
linear accelerated motion. In case of the symmetrical linear mutual
acceleration, we immediately get the maximal acceleration limit which was
derived by Caianiello from quantum mechanics. The derived results can play
crucial role in modern particle physics.


title:
On the active gravitational mass of a non-spherical source leaving
  hydrostatic equilibrium

abstract:
  We obtain an expression for the active gravitational mass (Tolman) of a
source of the $\gamma$ metric, just after its departure from hydrostatic
equilibrium, on a time scale of the order of (or smaller than) the hydrostatic
time scale. It is shown that for very compact sources, even arbitrarily small
departures from sphericity, produce significant decreasing (increasing) in the
values of active gravitational mass of collapsing (expanding) spheres, with
respect to its value in equilibrium, enhancing thereby the stability of the
system.


title: Black Hole Entropy as Causal Links

abstract:
  We model a black hole spacetime as a causal set and count, with a certain
definition, the number of causal links crossing the horizon in proximity to a
spacelike or null hypersurface $\Sigma$. We find that this number is
proportional to the horizon's area on $\Sigma $, thus supporting the
interpretation of the links as the ``horizon atoms'' that account for its
entropy. The cases studied include not only equilibrium black holes but ones
far from equilibrium.


title: Self-Dual Cosmic Strings and Gravitating Vortices in Gauged Sigma Models

abstract:
  Cosmic strings are considered in two types of gauged sigma models, which
generalize the gravitating Abelian Higgs model. The two models differ by
whether the U(1) kinetic term is of the Maxwell or Chern-Simons form. We obtain
the self-duality conditions for a general two-dimensional target space defined
in terms of field dependent "dielectric functions". In particular, we analyze
analytically and numerically the equations for the case of O(3) models
(two-sphere as target space), and find cosmic string solutions of several kinds
as well as gravitating vortices. We classify the solutions by their flux and
topological charge. We note an interesting connection between the Maxwell and
Chern-Simons type models, which is responsible for simple relations between the
self-dual solutions of both types. There is however a significant difference
between the two systems, in that only the Chern-Simons type sigma model gives
rise to spinning cosmic vortices.


title: Scalar Field Solutions in Colliding Einstein-Maxwell Waves

abstract:
  A simple method is presented which enables us to construct scalar field
solutions from any given Einstein-Maxwell solution in colliding plane waves. As
an application we give scalar field extensions of the solution found by Hogan,
Barrabes and Bressange.


title:
Selective readout and back-action reduction for wideband acoustic
  gravitational wave detectors

abstract:
  We present the concept of selective readout for broadband resonant mass
gravitational wave detectors. This detection scheme is capable of specifically
selecting the signal from the contributions of the vibrational modes sensitive
to the gravitational waves, and efficiently rejecting the contribution from non
gravitationally sensitive modes. Moreover this readout, applied to a dual
detector, is capable to give an effective reduction of the back-action noise
within the frequency band of interest. The overall effect is a significant
enhancement in the predicted sensitivity, evaluated at the standard quantum
limit for a dual torus detector. A molybdenum detector, 1 m in diameter and
equipped with a wide area selective readout, would reach spectral strain
sensitivities 2x10^{-23}/sqrt{Hz} between 2-6 kHz.


title: Resolving signals in the LISA data

abstract:
  We estimate the upper frequency cutoff of the galactic white dwarf binaries
gravitational wave background that will be observable by the LISA detector.
This is done by including the modulation of the gravitational wave signal due
the motion of the detector around the Sun. We find this frequency cutoff to be
equal to $10^{-3.0}$Hz, a factor of 2 smaller than the values previously
derived. This implies an increase in the number of resolvable signals in the
LISA band by a factor of about 4. Our theoretical derivation is complemented by
a numerical simulation, which shows that by using the maximum likelihood
estimation technique it is possible to accurately estimate the parameters of
the resolvable signals and then remove them from the LISA data.


title: On Effective Constraints for the Riemann-Lanczos System of Equations

abstract:
  There have been conflicting points of view concerning the Riemann--Lanczos
problem in 3 and 4 dimensions. Using direct differentiation on the defining
partial differential equations, Massa and Pagani (in 4 dimensions) and Edgar
(in dimensions n > 2) have argued that there are effective constraints so that
not all Riemann tensors can have Lanczos potentials; using Cartan's criteria of
integrability of ideals of differential forms Bampi and Caviglia have argued
that there are no such constraints in dimensions n < 5, and that, in these
dimensions, all Riemann tensors can have Lanczos potentials. In this paper we
give a simple direct derivation of a constraint equation, confirm explicitly
that known exact solutions of the Riemann-Lanczos problem satisfy it, and argue
that the Bampi and Caviglia conclusion must therefore be flawed. In support of
this, we refer to the recent work of Dolan and Gerber on the three dimensional
problem; by a method closely related to that of Bampi and Caviglia, they have
found an 'internal identity' which we demonstrate is precisely the three
dimensional version of the effective constraint originally found by Massa and
Pagani, and Edgar.


title:
Application of the Campbell-Magaard theorem to higher-dimensional
  physics

abstract:
  Stated succinctly, the original version of the Campbell-Magaard theorem says
that it is always possible to locally embed any solution of 4-dimensional
general relativity in a 5-dimensional Ricci-flat manifold. We discuss the proof
of this theorem (and its variants) in n dimensions, and its application to
current theories that postulate that our universe is a 4-dimensional
hypersurface Sigma_0 within a 5-dimensional manifold, such as Space-Time-Matter
(STM) theory and the Randall & Sundrum (RS) braneworld scenario. In particular,
we determine whether or not arbitrary spacetimes may be embedded in such
theories, and demonstrate how these seemingly disparate models are
interconnected. Special attention is given to the motion of test observers in 5
dimensions, and the circumstances under which they are confined to Sigma_0. For
each 5-dimensional scenario considered, the requirement that observers be
confined to the embedded spacetime places restrictions on the 4-geometry. For
example, we find that observers in the thin braneworld scenario can be
localized around the brane if its total stress-energy tensor obeys the
5-dimensional strong energy condition. As a concrete example of some of our
technical results, we discuss a Z_2 symmetric embedding of the standard
radiation-dominated cosmology in a 5-dimensional vacuum.


title: Projective connections associated with second order ODEs

abstract:
  We show that every 2nd order ODE defines a 4-parameter family of projective
connections on its 2-dimensional solution space. In a special case of ODEs, for
which a certain point transformation invariant vanishes, we find that this
family of connections always has a preferred representative. This preferred
representative turns out to be identical to the projective connection described
in Cartan's classic paper "Sur les Varietes a Connection Projective".


title: Gravitational Collapse of Null Radiation and a String fluid

abstract:
  We consider the end state of collapsing null radiation with a string fluid.
It is shown that, if diffusive transport is assumed for the string, that a
naked singularity can form (at least locally). The model has the advantage of
not being asymptotically flat. We also analyse the case of a radiation-string
two-fluid and show that a locally naked singularity can result in the collapse
of such matter. We contrast this model with that of strange quark matter.


title: Causality in spin foam models for quantum gravity

abstract:
  We describe how the Barrett-Crane spin foam model defines transition
amplitudes for quantum gravity states and how causality can be consistently
implemented in it.


title:
Evolving Maximally Symmetric Spacetime Bubbles from Spontaneous
  Z_2-Violation at Electroweak Symmetry Breaking Scale

abstract:
  The Einstein-Gordon equations for Friedmann-Robertson-Walker (FRW) geometries
in feedback reaction with the quartically self-interacting physical field,
arisen from the "inner parity" spontaneous breaking, are explicitly formulated.
The Hamiltonian density non-positive extrema would classically forbid both
spatially closed and flat homogeneous and isotropic worlds if these were to
allow the physical field to (repeatedly) go through and to (finally) settle
down in a ground state. In this respect, the fixed point exact solutions of the
spontaneous Z_2-symmetry breaking Einstein-Gordon equations (mandatory)
describe (k=-1)-FRW manifolds which actually are either Milne or anti-de Sitter
Universes. Setting the Z_2-invariance breaking scale at the one of the
electroweak symmetry, we speculate on the cosmological implications of the
Higgs-anti-de Sitter bubbles and derive a set of particular closed-form
solutions to the S_2-cobordism with a spatially flat FRW Universe.


title: The Energy of a Dynamical Wave-Emitting System in General Relativity

abstract:
  The problem of energy and its localization in general relativity is
critically re-examined. The Tolman energy integral for the Eddington spinning
rod is analyzed in detail and evaluated apart from a single term. It is shown
that a higher order iteration is required to find its value. Details of
techniques to solve mathematically challenging problems of motion with powerful
computing resources are provided. The next phase of following a system from
static to dynamic to final quasi-static state is described.


title: Non linear stability of einsteinian spacetimes with U(1) isometry group

abstract:
  We prove global completeness in the expanding direction of spacetimes
satisfying the vacuum Einstein equations on a manifold of the form $\Sigma
\times S^{1}\times R$ where $\Sigma $ is a compact surface of genus $G>1.$ The
Cauchy data are supposed to be invariant with respect to the group $S^{1}$ and
sufficiently small, but we do not impose a restrictive hypothesis made in gr-qc
0112049 on the lowest eigenvalue of a relevant Laplacian. The total energy
decay still holds, but its rate depends of the asymptotic value of this
eigenvalue.


title: On a generalized gravitational Aharonov-Bohm effect

abstract:
  A massless spinor particle is considered in the background gravitational
field due to a rotating body. In the weak field approximation it is shown that
the solution of the Weyl equations depend on the angular momentum of the
rotating body, which does not affect the curvature in this approximation. This
result may be looked upon as a generalization of the gravitational
Aharonov-Bohm effect.


title: Remarks on some quantum effects in the spacetime of a cosmic string

abstract:
  We study the behaviour of a non-relativistic quantum particle interacting
with different potentials, in the background spacetime generated by a cosmic
string. We find the energy spectra for the quantum systems under consideration
and discuss how they differ from their flat Minkowski spacetime values.


title:
Electronic Enhancements in the Detection of Gravitational Waves by
  Metallic Antennae

abstract:
  For mechanical Weber gravitational wave antennae, it is thought that gravity
waves are weakly converted into acoustic vibrations. Acoustic vibrations in
metals (such as Aluminum) are experimentally known to be attenuated by the
creation of electron-hole pairs described via the electronic viscosity. These
final state electronic excitations give rise to gravitational wave absorption
cross sections which are considerably larger (by four orders of magnitude) than
those in previous theories which have not explicitly considered electronic
excitations.


title: Gravitational Waves from Perturbed Black Holes and Relativistic Stars

abstract:
  These lectures aim at providing an introduction to the properties of
gravitational waves and in particular to those gravitational waves that are
expected as a consequence of perturbations of black holes and neutron stars.
Imprinted in the gravitational radiation emitted by these objects is, in fact,
a wealth of physical information. In the case of black holes, a detailed
knowledge of the gravitational radiation emitted as a response to perturbations
will reveal us important details about their mass and spin, but also about the
fundamental properties of the event horizon. In the case of neutron stars, on
the other hand, this information can provide a detailed map of their internal
structure and tell us about the equation of state of matter at very high
density, thus filling-in a gap in energies and densities that cannot be
investigated by experiments in terrestrial laboratories.


title:
Resolving the Degeneracy: Experimental tests of the New Self Creation
  Cosmology and a heterodox prediction for Gravity Probe B

abstract:
  The new theory of Self Creation Cosmology has been shown to yield a
concordant cosmological solution that does not require inflation, exotic
non-baryonic Dark matter or Dark Energy to fit observational constraints. In
vacuo there is a conformal equivalence between this theory and canonical
General Relativity and as a consequence an experimental degeneracy exists as
the two theories predict identical results in the standard tests. However,
there are three definitive experiments that are able to resolve this degeneracy
and distinguish between the two theories. Here these standard tests and
definitive experiments are described. One of the definitive predictions, that
of the geodetic precession of a gyroscope, has just been measured on the
Gravity Probe B satellite, which is at the present time of writing in the data
processing stage. This is the first opportunity to falsify Self Creation
Cosmology. The theory predicts a 'frame-dragging' result equal to GR but a
geodetic precession of only 2/3 the GR value. When applied to the Gravity Probe
B satellite, Self Creation Cosmology predicts an E-W
gravitomagnetic/frame-dragging precession, equal to that of GR, of 40.9
milliarcsec/yr but a -S gyroscope (geodetic + Thomas) precession of just 4.4096
arcsec/yr.


title: Rotation in string cosmology

abstract:
  We describe exact cosmological solutions with rotation and expansion in the
low-energy effective string theory. These models are spatially homogeneous
(closed Bianchi type IX) and they belong to the family of shear-free metrics
which are causal (no closed timelike curves are allowed), admit no parallax
effects and do not disturb the isotropy of the background radiation. The
dilaton and the axion fields are nontrivial, in general, and we consider both
cases with and without the central charge (effective cosmological constant).


title: Emergent Relativity

abstract:
  A possible resolution of the incompatibility of quantum mechanics and general
relativity is that the relativity principle is emergent. I show that the
central paradox of black holes also occurs at a liquid-vapor critical surface
of a bose condensate but is resolved there by the phenomenon of quantum
criticality. I propose that real black holes are actually phase boundaries of
the vacuum analogous to this, and that the Einstein field equations simply fail
at the event horizon the way quantum hydrodynamics fails at a critical surface.
This can occur without violating classical general relativity anywhere
experimentally accessible to external observers. Since the low-energy effects
that occur at critical points are universal, it is possible to make concrete
experimental predictions about such surfaces without knowing much, if anything
about the true underlying equations. Many of these predictions are different
from accepted views about black holes - in particular the absence of Hawking
radiation and the possible transparency of cosmological black hole surfaces.
[To appear in the C. N Yang Festschrift (World Sci., Singapore, 2003).]


title: Nonsingular vacuum cosmologies with a variable cosmological term

abstract:
  We present nonsingular cosmological models with a variable cosmological term
described by the second-rank symmetric tensor $\Lambda_{mn}$ evolving from
$\Lambda g_{mn}$ to $\lambda g_{mn}$ with $\lambda < \Lambda$. All
$\Lambda_{mn}$ dominated cosmologies belong to Lemaitre type models for an
anisotropic perfect fluid. The expansion starts from a nonsingular
nonsimultaneous de Sitter bang, with $\Lambda$ on the scale responsible for the
earliest accelerated expansion, which is followed by an anisotropic Kasner type
stage. For a certain class of observers these models can be also identified as
Kantowski-Sachs models with regular R regions. For Kantowski-Sachs observers
the cosmological evolution starts from horizons with a highly anisotropic
``null bang'' where the volume of the spatial section vanishes. We study in
detail the spherically symmetric case and consider the general features of
cosmologies with planar and pseudospherical symmetries. Nonsingular
$\Lambda_{mn}$ dominated cosmologies are Bianchi type I in the planar case and
hyperbolic analogs of the Kantowski-Sachs models in the pseudospherical case.
At late times all models approach a de Sitter asymptotic with small $\lambda$.


title: The Inflaton and Time in the Matter-Gravity System

abstract:
  The emergence of time in the matter-gravity system is addressed within the
context of the inflationary paradigm. A quantum minisuperspace-homogeneous
minimally coupled inflaton system is studied with suitable initial conditions
leading to inflation and the system is approximately solved in the limit for
large scale factor. Subsequently normal matter (either non homogeneous inflaton
modes or lighter matter) is introduced as a perturbation and it is seen that
its presence requires the coarse averaging of a gravitational wave function
(which oscillates at trans-Planckian frequencies) having suitable initial
conditions. Such a wave function, which is common for all types of normal
matter, is associated with a ``time density'' in the sense that its modulus is
related to the amount of time spent in a given interval (or the rate of flow of
time). One is then finally led to an effective evolution equation (Schroedinger
Schwinger-Tomonaga) for ``normal'' matter. An analogy with the emergence of a
temperature in statistical mechanics is also pointed out.


title: Propagation of perturbations in non-linear spin-2 theories

abstract:
  In this communication I analyze the problem of complete exceptionality of
wave propagation in a class of spin 2 field theories. I show that, under the
imposition of the good weak-field limit, only two Lagrangians are completely
exceptional. These are the linear Fierz Lagrangian, and a Born-Infeld-like
Lagrangian. As a byproduct, I reobtain the result that in a nonlinear theory,
spin 2 particles follow an effective metric that depends on the nonlinearities
of the Lagrangian.


title:
Boundary conditions for hyperbolic formulations of the Einstein
  equations

abstract:
  In regards to the initial-boundary value problem of the Einstein equations,
we argue that the projection of the Einstein equations along the normal to the
boundary yields necessary and appropriate boundary conditions for a wide class
of equivalent formulations. We explicitly show that this is so for the
Einstein-Christoffel formulation of the Einstein equations in the case of
spherical symmetry.


title: On the roots of the Poincare structure of asymptotically flat spacetimes

abstract:
  The analysis of vacuum general relativity by R. Beig and N. O Murchadha (Ann.
Phys. vol 174, 463 (1987)) is extended in numerous ways. The weakest possible
power-type fall-off conditions for the energy-momentum tensor, the metric, the
extrinsic curvature, the lapse and the shift are determined, which, together
with the parity conditions, are preserved by the energy-momentum conservation
and the evolution equations. The algebra of the asymptotic Killing vectors,
defined with respect to a foliation of the spacetime, is shown to be the
Lorentz Lie algebra for slow fall-off of the metric, but it is the Poincare
algebra for 1/r or faster fall-off. It is shown that the applicability of the
symplectic formalism already requires the 1/r (or faster) fall-off of the
metric. The connection between the Poisson algebra of the Beig-O Murchadha
Hamiltonians and the asymptotic Killing vectors is clarified. The value H[K^a]
of their Hamiltonian is shown to be conserved in time if K^a is an asymptotic
Killing vector defined with respect to the constant time slices. The angular
momentum and centre-of-mass, defined by the value of H[K^a] for asymptotic
rotation-boost Killing vectors K^a, are shown to be finite only for 1/r or
faster fall-off of the metric. Our center-of-mass expression is the difference
of that of Beig and O Murchadha and the spatial momentum times the coordinate
time. The spatial angular momentum and this centre-of-mass form a Lorentz
tensor, which transforms in the correct way under Poincare transformations.


title: Rotating Stars in Relativity

abstract:
  Rotating relativistic stars have been studied extensively in recent years,
both theoretically and observationally, because of the information one could
obtain about the equation of state of matter at extremely high densities and
because they are considered to be promising sources of gravitational waves. The
latest theoretical understanding of rotating stars in relativity is reviewed in
this updated article. The sections on the equilibrium properties and on the
nonaxisymmetric instabilities in f-modes and r-modes have been updated and
several new sections have been added on analytic solutions for the exterior
spacetime, rotating stars in LMXBs, rotating strange stars, and on rotating
stars in numerical relativity.


title: Variations on the Seventh Route to Relativity

abstract:
  As motivated in the full abstract, this paper further investigates Barbour,
Foster and O Murchadha (BFO)'s 3-space formulation of GR. This is based on
best-matched lapse-eliminated actions and gives rise to several theories
including GR and a conformal gravity theory. We study the simplicity postulates
assumed in BFO's work and how to weaken them, so as to permit the inclusion of
the full set of matter fields known to occur in nature.
  We study the configuration spaces of gravity-matter systems upon which BFO's
formulation leans. In further developments the lapse-eliminated actions used by
BFO become impractical and require generalization. We circumvent many of these
problems by the equivalent use of lapse-uneliminated actions, which furthermore
permit us to interpret BFO's formulation within Kuchar's generally covariant
hypersurface framework. This viewpoint provides alternative reasons to BFO's as
to why the inclusion of bosonic fields in the 3-space approach gives rise to
minimally-coupled scalar fields, electromagnetism and Yang--Mills theory. This
viewpoint also permits us to quickly exhibit further GR-matter theories
admitted by the 3-space formulation. In particular, we show that the spin-1/2
fermions of the theories of Dirac, Maxwell--Dirac and Yang--Mills--Dirac, all
coupled to GR, are admitted by the generalized 3-space formulation we present.
Thus all the known fundamental matter fields can be accommodated. This
corresponds to being able to pick actions for all these theories which have
less kinematics than suggested by the generally covariant hypersurface
framework. For all these theories, Wheeler's thin sandwich conjecture may be
posed, rendering them timeless in Barbour's sense.


title: Trace anomaly and black holes evaporation

abstract:
  A model is proposed to describe a transition from a Schwarzschild black hole
of mass $M_{0}$ to a Schwarzschild black hole of mass $M_{1}$ $\leq M_{0}$. The
basic equations are derived from the non-vacuum Einstein field equations taking
a source representing a null scalar field with a nonvanishing trace anomaly. It
is shown that the nonvanishing trace anomaly of the scalar field prevents a
complete evaporation.


title: Nucleation of $^{(4)}R$ Brane Universes

abstract:
  The creation of brane universes induced by a totally antisymmetric tensor
living in a fixed background spacetime is presented, where a term involving the
intrinsic curvature of the brane is considered. A canonical quantum mechanical
approach employing Wheeler-DeWitt equation is done. The probability nucleation
for the brane is calculated taking into account both an instanton method and a
WKB approximation. Some cosmological implications arose from the model are
presented.


title: Thermodynamics for radiating shells in anti-de Sitter space-time

abstract:
  A thermodynamical description for the quasi-static collapse of radiating,
self-gravitating spherical shells of matter in anti-de Sitter space-time is
obtained. It is shown that the specific heat at constant area and other
thermodynamical quantities may diverge before a black hole has eventually
formed. This suggests the possibility of a phase transition occurring along the
collapse process. The differences with respect to the asymptotically flat case
are also highlighted.


title:
Resonant interaction between gravitational waves, electromagnetic waves
  and plasma flows

abstract:
  In magnetized plasmas gravitational and electromagnetic waves may interact
coherently and exchange energy between themselves and with plasma flows. We
derive the wave interaction equations for these processes in the case of waves
propagating perpendicular or parallel to the plasma background magnetic field.
In the latter case, the electromagnetic waves are taken to be circularly
polarized waves of arbitrary amplitude. We allow for a background drift flow of
the plasma components which increases the number of possible evolution
scenarios. The interaction equations are solved analytically and the
characteristic time scales for conversion between gravitational and
electromagnetic waves are found. In particular, it is shown that in the
presence of a drift flow there are explosive instabilities resulting in the
generation of gravitational and electromagnetic waves. Conversely, we show that
energetic waves can interact to accelerate particles and thereby \emph{produce}
a drift flow. The relevance of these results for astrophysical and cosmological
plasmas is discussed.


title: Three lectures on Poincare gauge theory

abstract:
  In these lectures we review the basic structure of Poincare gauge theory of
gravity, with emphasis on its fundamental principles and geometric
interpretation. A specific limit of this theory, defined by the teleparallel
geometry of spacetime, is discussed as a viable alternative for the description
of macroscopic gravitational phenomena.


title:
Quantum noise in laser-interferometer gravitational-wave detectors with
  a heterodyne readout scheme

abstract:
  We analyze and discuss the quantum noise in signal-recycled laser
interferometer gravitational-wave detectors, such as Advanced LIGO, using a
heterodyne readout scheme and taking into account the optomechanical dynamics.
Contrary to homodyne detection, a heterodyne readout scheme can simultaneously
measure more than one quadrature of the output field, providing an additional
way of optimizing the interferometer sensitivity, but at the price of
additional noise. Our analysis provides the framework needed to evaluate
whether a homodyne or heterodyne readout scheme is more optimal for second
generation interferometers from an astrophysical point of view. As a more
theoretical outcome of our analysis, we show that as a consequence of the
Heisenberg uncertainty principle the heterodyne scheme cannot convert
conventional interferometers into (broadband) quantum non-demolition
interferometers.


title:
Analytical solution of the neutrino wave equation in Kerr geometry with
  Vaidya-Patel coordinates

abstract:
  Analytical solution of Weyl neutrino wave equation in Kerr geometry is
presented by making use of the two-spinor component spin-coefficient
Newman-Penrose (NP) calculus. So far only asymptotic or approximate solutions
have been found for the Weyl equation in this background. It is shown that
neutrino current asymmetry is also present in this solution.


title: Time Variation of Photons' Velocity in a "Dark" Universe

abstract: See hep-ph/0304045


title: Constraints in Quantum Geometrodynamics

abstract:
  We compare different treatments of the constraints in canonical quantum
gravity. The standard approach on the superspace of 3--geometries treats the
constraints as the sole carriers of the dynamic content of the theory, thus
rendering the traditional dynamical equations obsolete. Quantization of the
constraints in both the Dirac and ADM square root Hamiltonian approaches leads
to the well known problems of time evolution. These problems of time are of
both an interpretational and technical nature. In contrast, the geometrodynamic
quantization procedure on the superspace of the true dynamical variables
separates the issues of quantization from the enforcement of the constraints.
The resulting theory takes into account states that are off-shell with respect
to the constraints, and thus avoids the problems of time. We develop, for the
first time, the geometrodynamic quantization formalism in a general setting and
show that it retains all essential features previously illustrated in the
context of homogeneous cosmologies.


title:
Coupling of Linearized Gravity to Nonrelativistic Test Particles:
  Dynamics in the General Laboratory Frame

abstract:
  The coupling of gravity to matter is explored in the linearized gravity
limit. The usual derivation of gravity-matter couplings within the
quantum-field-theoretic framework is reviewed. A number of inconsistencies
between this derivation of the couplings, and the known results of tidal
effects on test particles according to classical general relativity are pointed
out. As a step towards resolving these inconsistencies, a General Laboratory
Frame fixed on the worldline of an observer is constructed. In this frame, the
dynamics of nonrelativistic test particles in the linearized gravity limit is
studied, and their Hamiltonian dynamics is derived. It is shown that for
stationary metrics this Hamiltonian reduces to the usual Hamiltonian for
nonrelativistic particles undergoing geodesic motion. For nonstationary metrics
with long-wavelength gravitational waves (GWs) present, it reduces to the
Hamiltonian for a nonrelativistic particle undergoing geodesic
\textit{deviation} motion. Arbitrary-wavelength GWs couple to the test particle
through a vector-potential-like field $N_a$, the net result of the tidal forces
that the GW induces in the system, namely, a local velocity field on the system
induced by tidal effects as seen by an observer in the general laboratory
frame. Effective electric and magnetic fields, which are related to the
electric and magnetic parts of the Weyl tensor, are constructed from $N_a$ that
obey equations of the same form as Maxwell's equations . A gedankin
gravitational Aharonov-Bohm-type experiment using $N_a$ to measure the
interference of quantum test particles is presented.


title:
Robertson-Walker fluid sources endowed with rotation characterised by
  quadratic terms in angular velocity parameter

abstract:
  Einstein's equations for a Robertson-Walker fluid source endowed with
rotation Einstein's equations for a Robertson-Walker fluid source endowed with
rotation are presented upto and including quadratic terms in angular velocity
parameter. A family of analytic solutions are obtained for the case in which
the source angular velocity is purely time-dependent. A subclass of solutions
is presented which merge smoothly to homogeneous rotating and non-rotating
central sources. The particular solution for dust endowed with rotation is
presented. In all cases explicit expressions, depending sinusoidally on polar
angle, are given for the density and internal supporting pressure of the
rotating source. In addition to the non-zero axial velocity of the fluid
particles it is shown that there is also a radial component of velocity which
vanishes only at the poles. The velocity four-vector has a zero component
between poles.


title: Energy Distribution of a Black Hole Solution in Heterotic String Theory

abstract:
  We calculate the energy distribution of a charged black hole solution in
heterotic string theory in the M{\o}ller prescription.


title: Test of inverse square law through precession of orbits

abstract:
  Using precession of orbits due to non-Newtonian interaction between two
celestial bodies and modern tracking data of satellites, planets and a pulsar
we obtain new more precise limits on possible Yukawa-type deviations from the
Newton law in planets (satellites)radii ranges.


title: Morris-Thorne wormholes with a cosmological constant

abstract:
  First, the ideas introduced in the wormhole research field since the work of
Morris and Thorne are briefly reviewed, namely, the issues of energy
conditions, wormhole construction, stability, time machines and astrophysical
signatures. Then, spherically symmetric and static traversable Morris-Thorne
wormholes in the presence of a generic cosmological constant are analyzed. A
matching of an interior solution to the unique exterior vacuum solution is done
using directly the Einstein equations. The structure as well as several
physical properties and characteristics of traversable wormholes due to the
effects of the cosmological term are studied. Interesting equations appear in
the process of matching. For instance, one finds that for asymptotically flat
and anti-de Sitter spacetimes the surface tangential pressure of the
thin-shell, at the boundary of the interior and exterior solutions, is always
strictly positive, whereas for de Sitter spacetime it can take either sign as
one could expect, being negative (tension) for relatively high cosmological
constant and high wormhole radius, positive for relatively high mass and small
wormhole radius, and zero in-between. Finally, some specific solutions with
generic cosmological constant, based on the Morris-Thorne solutions, are
provided.


title: Detectability of Gravitational Waves from SN 1987A

abstract:
  We discuss the potential for detection of gravitational waves from a rapidly
spinning neutron star produced by supernova 1987A taking the parameters claimed
by Middleditch et al. (2000) at face value. Asssuming that the dominant
mechanism for spin down is gravitational waves emitted by a freely precessing
neutron star, it is possible to constrain the wobble angle, the effective
moment of inertai of the precessing crust and the crust cracking stress limit.
Our analysis, suggests that, if the interpretation of the Middleditch data is
correct, the compact remnant of SN 1987A may well provide a reliable and
predictable source of gravitational waves well within the capability of LIGO
II.


title: The Issue of Time in Quantum Geometrodynamics

abstract:
  Standard techniques of canonical gravity quantization on the superspace of
3--metrics are known to cause insurmountable difficulties in the description of
time evolution. We forward a new quantization procedure on the superspace of
true dynamic variables -- geometrodynamic quantization. This procedure takes
into account the states that are ``off-shell'' with respect to the constraints
and thus circumvents the notorious problems of time. In this approach quantum
geometrodynamics, general covariance, and the interpretation of time emerge
together as parts of the solution to the total problem of geometrodynamic
evolution.


title: Effective Geometry

abstract:
  We introduce the concept of effective geometry by studying several systems in
which it arises naturally. As an example of the power and conciseness of the
method, it is shown that a flowing dielectric medium with a linear response to
an external electric field can be used to generate an analog geometry that has
many of the formal properties of a \Sch black hole for light rays, in spite of
birefringence. The surface gravity of this analog black hole has a contribution
that depends only on the dielectric properties of the fluid (in addition to the
usual term dependent on the acceleration). This term may be give a hint to a
new mechanism to increase the temperature of Hawking radiation.


title: Spin Flavor Conversion of Neutrinos in Loop Quantum Gravity

abstract:
  Loop quantum gravity theory incorporates a new scale length ${\cal L}$ which
induces a Lorentz invariance breakdown. This scale can be either an universal
constant or can be fixed by the momentum of particles (${\cal L}\sim p^{-1}$).
Effects of the scale parameter ${\cal L}$ and helicity terms occurring in the
dispersion relation of fermions are reviewed in the framework of spin-flip
conversion of neutrino flavors.


title: Braneworld inflation driven by dynamics of a bulk scalar field

abstract:
  We review a viable alternative scenario of the inflationary universe in the
context of the Randall-Sundrum (RS) braneworld. In this scenario, the dynamics
of a 5-dimensional scalar field, which we call a bulk scalar field, plays the
central role. Focusing on the second (single-brane) RS model, we discuss
braneworld inflation driven by a bulk scalar field without introducing an
inflaton on the brane. As a toy model, for the bulk scalar field, we consider a
minimally coupled massive scalar field in the 5-dimensional spacetime, and look
for a perturbative solution of the field equation in the anti-de Sitter
background with an inflating brane. For a suitable range of the model
parameters, we find a solution that realizes slow-roll inflation on the brane.
When the Hubble parameter on the brane and the mass of a bulk scalar field are
much smaller than a typical 5-dimensional mass scale, it is found that this
proposed inflation scenario reproduces the standard inflation scenario in the
4-dimensional theory.


title: Gravitational and magnetosonic waves in gamma-ray bursts

abstract:
  One of the possible sources of gamma-ray bursts are merging, compact
neutronstar binaries. More than 90% of the binding energy of such a binary is
released in the form of gravitational waves (GWs) in the last few seconds of
the spiral-in phase before the formation of a black hole. In this article we
investigate whether a fraction of this GW-energy is transferred to
magnetohydrodynamic waves in the magnetized plasma wind around the binary.
Using the 3+1 orthonormal tedrad formalism, we study the propagation of a
monochromatic, plane fronted, linearly polarized GW perpendicular to the
ambient magnetic field in an ultra-relativistic wind, first in the comoving and
then in the observer frame. A closed set of general relativistic
magnetohydrodynamic equations is derived in the form of conservation laws for
electric charge, matter energy, momentum and magnetic energy densities. We
linearize these equations under the action of a monochromatic GW, which acts as
a driver and find that fast magneto-acoustic waves grow, with amplitudes
proportional to the GW amplitude and frequency and the strength of the
background magnetic field.


title: Concepts for a Theory of the Electromagnetic Field

abstract:
  The object of this contribution is twofold. On one hand, it rises some
general questions concerning the definition of the electromagnetic field and
its intrinsic properties, and it proposes concepts and ways to answer them. On
the other hand, and as an illustration of this analysis, a set of quadratic
equations for the electromagnetic field is presented, richer in pure radiation
solutions than the usual Maxwell equations, and showing a striking property
relating geometrical optics to all the other Maxwell solutions.


title:
Comparison of the oscillatory behaviors of a gravitating Nambu-Goto
  string with a test string

abstract:
  Comparison of the oscillatory behavior of a gravitating infinite Nambu-Goto
string and a test string is investigated using the general relativistic gauge
invariant perturbation technique with two infinitesimal parameters on a flat
spacetime background. Due to the existence of the pp-wave exact solution, we
see that the conclusion that the dynamical degree of freedom of an infinite
Nambu-Goto string is completely determined by that of gravitational waves,
which was reached in our previous works [K. Nakamura, A. Ishibashi and H.
Ishihara, Phys. Rev. D{\bf 62} (2002), 101502(R); K. Nakamura and H. Ishihara,
Phys. Rev. D{\bf 63} (2001), 127501.], do not contradict to the dynamics of a
test string. We also briefly discuss the implication of this result.


title: Hoop Conjecture and Black Holes on a Brane

abstract:
  The initial data of gravity for a cylindrical matter distribution confined to
a brane are studied in the framework of the single-brane Randall-Sundrum
scenario. In this scenario, the 5-dimensional nature of gravity appears in the
short-range gravitational interaction. We find that a sufficiently thin
configuration of matter leads to the formation of a marginal surface, even if
the configuration is infinitely long. This implies that the hoop conjecture
proposed by Thorne does not hold on the brane: Even if a mass $M$ does not
become compacted into a region whose circumference ${\cal C}$ in every
direction satisfies ${\cal C}> 4\pi GM$, black holes with horizons can form in
the Randall-Sundrum scenario.


title:
Diffeomorphism covariant representations of the holonomy-flux
  star-algebra

abstract:
  Recently, Sahlmann proposed a new, algebraic point of view on the loop
quantization. He brought up the issue of a star-algebra underlying that
framework, studied the algebra consisting of the fluxes and holonomies and
characterized its representations. We define the diffeomorphism covariance of a
representation of the Sahlmann algebra and study the diffeomorphism covariant
representations. We prove they are all given by Sahlmann's decomposition into
the cyclic representations of the sub-algebra of the holonomies by using a
single state only. The state corresponds to the natural measure defined on the
space of the generalized connections. This result is a generalization of
Sahlmann's result concerning the U(1) case.


title:
General relativistic gravitational field of a rigidly rotating disk of
  dust: Solution in terms of ultraelliptic functions

abstract:
  In a recent paper we presented analytic expressions for the axis potential,
the disk metric, and the surface mass density of the global solution to
Einstein's field equations describing a rigidly rotating disk of dust. Here we
add the complete solution in terms of ultraelliptic functions and quadratures.


title: Note on ingoing coordinates for binary black holes

abstract:
  In a previous paper, a binary black hole four-metric was presented in a
post-Newtonian corotating coordinate system valid only up to the holes'
apparent horizons. In this paper, I define an ingoing coordinate transformation
that extends this corotating coordinate system through the holes' horizons and
into their interiors. The motivation for using ingoing coordinates is that
numerical simulations of black holes require the computational grid to extend
inside the horizons. The coordinate transformation presented here makes the
binary black hole four-metric suitable as a source of initial data for
numerical simulations.


title:
Solutions of Einstein's field equations related to Jacobi's inversion
  problem

abstract:
  A new class of exact solutions to the axisymmetric and stationary vacuum
Einstein equations containing n arbitrary complex parameters and one arbitrary
real solution of the axisymmetric three-dimensional Laplace equation is
presented. The solutions are related to Jacobi's inversion problem for
hyperelliptic Abelian integrals.


title:
Counter-example where cosmic time keeps its original role in quantum
  cosmology

abstract:
  In the minisuperspace models of quantum cosmology, the absence of time in the
Wheeler-DeWitt (constraint) equation, is the main point leading to the
generally accepted conclusion that in the quantum cosmology there is no
possibility to describe the evolution of the universe procceding in the cosmic
time (the time usually used in classical cosmology). We show that in spite of
the constraint, under the specific circumstances, the averaging of some of the
Heisenberg equations can give nontrivial additional information about explicit
time dependence of the expectation values of certain dynamical variables in
quantum cosmology. This idea is realized explicitly in a higher dimensional
model with a negative cosmological constant and dust as the sources of gravity.
When there is an anisotropy in the evolution of the universe, the above
phenomenon (i.e. explicit cosmic time dependence of certain expectation values)
appears and we find the new quantum effect which consists in "quantum
inflationary phase" for some dimensions and simultaneous "quantum deflationary
contraction" for the remaining dimensions. The expectation value of the
"volume" of the universe remains constant during this quantum
"inflation-deflation" process.


title: Consistent discrete gravity solution of the problem of time: a model

abstract:
  The recently introduced consistent discrete lattice formulation of canonical
general relativity produces a discrete theory that is constraint-free. This
immediately allows to overcome several of the traditional obstacles posed by
the ``problem of time'' in totally constrained systems and quantum gravity and
cosmology. In particular, one can implement the Page--Wootters relational
quantization. This brief paper discusses this idea in the context of a simple
model system --the parameterized particle-- that is usually considered one of
the crucial tests for any proposal for solution to the problem of time in
quantum gravity.


title: Geodesics and geodesic deviation in a two-dimensional black hole

abstract:
  We introduce an exactly solvable example of timelike geodesic motion and
geodesic deviation in the background geometry of a well-known two-dimensional
black hole spacetime. The effective potential for geodesic motion turns out to
be either a harmonic oscillator or an inverted harmonic oscillator or a linear
function of the spatial variable, corresponding to the three different domains
of a constant of the motion. The geodesic deviation equation also is exactly
solvable. The corresponding deviation vector is obtained and the nature of the
deviation is briefly discussed by highlighting a specific case.


title: Black Hole Thermodynamics without a Black Hole?

abstract:
  In the present paper we consider, using our earlier results, the process of
quantum gravitational collapse and argue that there exists the final quantum
state when the collapse stops. This state, which can be called the ``no-memory
state'', reminds the final ``no-hair state'' of the classical gravitational
collapse. Translating the ``no-memory state'' into classical language we
construct the classical analogue of quantum black hole and show that such a
model has a topological temperature which equals exactly the Hawking's
temperature. Assuming for the entropy the Bekenstein-Hawking value we develop
the local thermodynamics for our model and show that the entropy is naturally
quantized with the equidistant spectrum S + gamma_0*N. Our model allows, in
principle, to calculate the value of gamma_0. In the simplest case, considered
here, we obtain gamma_0 = ln(2).


title: Galactic Potentials

abstract:
  The information contained in galactic rotation curves is examined under a
minimal set of assumptions. If emission occurs from stable circular geodesic
orbits of a static spherically symmetric field, with information propagated to
us along null geodesics, observed rotation curves determine galactic potentials
without specific reference to any metric theory of gravity. Given the
potential, the gravitational mass can be obtained by way of an anisotropy
function of this field. The gravitational mass and anisotropy function can be
solved for simultaneously in a Newtonian limit without specifying any specific
source. This procedure, based on a minimal set of assumptions, puts very strong
constraints on any model of the "dark matter".


title:
Inhomogeneous cosmologies, the Copernican principle and the cosmic
  microwave background: More on the EGS theorem

abstract:
  We discuss inhomogeneous cosmological models which satisfy the Copernican
principle. We construct some inhomogeneous cosmological models starting from
the ansatz that the all the observers in the models view an isotropic cosmic
microwave background. We discuss multi-fluid models, and illustrate how more
general inhomogeneous models may be derived, both in General Relativity and in
scalar-tensor theories of gravity. Thus we illustrate that the cosmological
principle, the assumption that the Universe we live in is spatially
homogeneous, does not necessarily follow from the Copernican principle and the
high isotropy of the cosmic microwave background.


title: Evolution of cosmological constant in effective gravity

abstract:
  In contrast to the phenomenon of nullification of the cosmological constant
in the equilibrium vacuum, which is the general property of any quantum vacuum,
there are many options in modifying the Einstein equation to allow the
cosmological constant to evolve in a non-equilibrium vacuum. An attempt is made
to extend the Einstein equation in the direction suggested by the
condensed-matter analogy of the quantum vacuum. Different scenarios are found
depending on the behavior of and the relation between the relaxation parameters
involved, some of these scenarios having been discussed in the literature. One
of them reproduces the scenario in which the effective cosmological constant
emerges as a constant of integration. The second one describes the situation,
when after the cosmological phase transition the cosmological constant drops
from zero to the negative value; this scenario describes the relaxation from
this big negative value back to zero and then to a small positive value. In the
third example the relaxation time is not a constant but depends on matter; this
scenario demonstrates that the vacuum energy (or its fraction) can play the
role of the cold dark matter.


title: Gravitational Effects Associated With Gravitomagnetic Fields

abstract:
  Several relativistic quantum gravitational effects such as spin-rotation
coupling, gravitomagnetic charge and gravitational Meissner effect are
investigated in the present letter. The field equation of gravitomagnetic
matter is suggested and a static spherically symmetric solution of this
equation is offered. With foreseeable improvements in detecting and measuring
technology, it is possible for us to investigate quantum mechanics in
weak-gravitational fields. The potential implications of these gravitational
effects (or phenomena) to some problems are briefly discussed.


title: Einstein boundary conditions for the 3+1 Einstein equations

abstract:
  In the 3+1 framework of the Einstein equations for the case of vanishing
shift vector and arbitrary lapse, we calculate explicitly the four boundary
equations arising from the vanishing of the projection of the Einstein tensor
along the normal to the boundary surface of the initial-boundary value problem.
Such conditions take the form of evolution equations along (as opposed to
across) the boundary for certain components of the extrinsic curvature and for
certain space-derivatives of the intrinsic metric. We argue that, in general,
such boundary conditions do not follow necessarily from the evolution equations
and the initial data, but need to be imposed on the boundary values of the
fundamental variables. Using the Einstein-Christoffel formulation, which is
strongly hyperbolic, we show how three of the boundary equations should be used
to prescribe the values of some incoming characteristic fields. Additionally,
we show that the fourth one imposes conditions on some outgoing fields.


title:
Novel finite-differencing techniques for numerical relativity:
  application to black hole excision

abstract:
  We use rigorous techniques from numerical analysis of hyperbolic equations in
bounded domains to construct stable finite-difference schemes for Numerical
Relativity, in particular for their use in black hole excision. As an
application, we present 3D simulations of a scalar field propagating in a
Schwarzschild black hole background.


title: Black Hole Thermodynamics and Riemann Surfaces

abstract:
  We use the analytic continuation procedure proposed in our earlier works to
study the thermodynamics of black holes in 2+1 dimensions. A general black hole
in 2+1 dimensions has g handles hidden behind h horizons. The result of the
analytic continuation is a hyperbolic 3-manifold having the topology of a
handlebody. The boundary of this handlebody is a compact Riemann surface of
genus G=2g+h-1. Conformal moduli of this surface encode in a simple way the
physical characteristics of the black hole. The moduli space of black holes of
a given type (g,h) is then the Schottky space at genus G. The (logarithm of
the) thermodynamic partition function of the hole is the Kaehler potential for
the Weil-Peterson metric on the Schottky space. Bekenstein bound on the black
hole entropy leads us to conjecture a new strong bound on this Kaehler
potential.


title: Polytropic stars in three-dimensional spacetime

abstract:
  We investigate three-dimensional perfect fluid stars with polytropic equation
of state, matched to the exterior three-dimensional black hole geometry of
Banados, Teitelboim and Zanelli. A new class of exact solutions for a generic
polytropic index is found and analysed.


title:
Perturbative Approach to an orbital evolution around a Supermassive
  black hole

abstract:
  A charge-free, point particle of infinitesimal mass orbiting a Kerr black
hole is known to move along a geodesic. When the particle has a finite mass or
charge, it emits radiation which carries away orbital energy and angular
momentum, and the orbit deviates from a geodesic.
  In this paper we assume that the deviation is small and show that the
half-advanced minus half-retarded field surprisingly provides the correct
radiation reaction force, in a time-averaged sense, and determines the orbit of
the particle.


title: Indefinite Information Processing in Ever-expanding Universes

abstract:
  We show that generic anisotropic universes arbitrarily close to the open
Friedmann universe allow information processing to continue into the infinite
future if there is no cosmological constant or stable gravitationally repulsive
stress, and the spatial topology is non-compact. An infinite amount of
information can be processed by ``civilisations'' who harness the temperature
gradients created by gravitational tidal energy. These gradients are driven by
the gravitational waves that sustain the expansion shear and three-curvature
anisotropy.


title:
Self-similar collapse of a scalar field in dilaton gravity and critical
  behaviour

abstract:
  We present new analytical self-similar solutions describing a collapse of a
massless scalar field in scalar-tensor theories. The solutions exhibit a type
of critical behavior. The black hole mass for the near critical evolution is
analytically obtained for several scalar-tensor theories and the critical
exponent is calculated. Within the framework of the analytical models we
consider it is found that the black hole mass law for some scalar-tensor
theories is of the form $M_{BH}=f(p-p_{cr})(p-p_{cr})^\gamma$ which is slightly
different from the general relativistic law $M_{BH}=const (p-p_{cr})^\gamma$.


title: The square of the Weyl tensor can be negative

abstract:
  We show that the square of the Weyl tensor can be negative by giving an
example.


title: Thermodynamics of black holes in finite boxes

abstract:
  We analyze the thermodynamical behavior of black holes in closed finite
boxes. First the black hole mass evolution is analyzed in an initially empty
box. Using the conservation of the energy and the Hawking evaporation flux, we
deduce a minimal volume above which one black hole can loss all of its mass to
the box, a result which agrees with the previous analysis made by Page. We then
obtain analogous results using a box initially containing radiation, allowed to
be absorbed by the black hole. The equilibrium times and masses are evaluated
and their behavior discussed to highlight some interesting features arising.
These results are generalized to $N$ black holes + thermal radiation. Using
physically simple arguments, we prove that these black holes achieve the same
equilibrium masses (even that the initial masses were different). The entropy
of the system is used to obtain the dependence of the equilibrium mass on the
box volume, number of black holes and the initial radiation. The equilibrium
mass is shown to be proportional to a {\it positive} power law of the effective
volume (contrary to naive expectations), a result explained in terms of the
detailed features of the system. The effect of the reflection of the radiation
on the box walls which comes back into the black hole is explicitly considered.
All these results (some of them counter-intuitive) may be useful to formulate
alternative problems in thermodynamic courses for graduate and advanced
undergraduate students. A handful of them are suggested in the Appendix.


title: Conformal Einstein equations and Cartan conformal connection

abstract:
  Necessary and sufficient conditions for a space-time to be conformal to an
Einstein space-time are interpreted in terms of curvature restrictions for the
corresponding Cartan conformal connection.


title: Five-dimensional metrics of Petrov type 22

abstract:
  We classify all five-dimensional Einstein manifolds that are static, have an
SO(3) isometry group and have Petrov type 22. We use this classification to
show that the localized black hole in the Randall-Sundrum scenario necessarily
has Petrov type 4.


title:
Path integral for minisuperspaces and its relation with non equivalent
  canonical quantizations

abstract:
  The relation between a recently proposed path integral for minisuperspaces
and different canonical quantizations is established. The step of the procedure
where a choice between non equivalent theories is made is identified.
Coordinates avoiding such a choice are found for a class of homogeneous
cosmologies.


title: General-covariant evolution formalism for Numerical Relativity

abstract:
  A general covariant extension of Einstein\'{}s field equations is considered
with a view to Numerical Relativity applications. The basic variables are taken
to be the metric tensor and an additional four-vector $Z_\mu$. Einstein's
solutions are recovered when the additional four-vector vanishes, so that the
energy and momentum constraints amount to the covariant algebraic condition
$Z_\mu=0$. The extended field equations can be supplemented by suitable
coordinate conditions in order to provide symmetric hyperbolic evolution
systems: this is actually the case for either harmonic coordinates or normal
coordinates with harmonic slicing.


title:
Hamiltonian linearization of the rest-frame instant form of tetrad
  gravity in a completely fixed 3-orthogonal gauge: a radiation gauge for
  background-independent gravitational waves in a post-Minkowskian Einstein
  spacetime

abstract:
  In the framework of the rest-frame instant form of tetrad gravity, where the
Hamiltonian is the weak ADM energy ${\hat E}_{ADM}$, we define a special
completely fixed 3-orthogonal Hamiltonian gauge, corresponding to a choice of
{\it non-harmonic} 4-coordinates, in which the independent degrees of freedom
of the gravitational field are described by two pairs of canonically conjugate
Dirac observables (DO) $r_{\bar a}(\tau ,\vec \sigma)$, $\pi_{\bar a}(\tau
,\vec \sigma)$, $\bar a = 1,2$. We define a Hamiltonian linearization of the
theory, i.e. gravitational waves, {\it without introducing any background
4-metric}, by retaining only the linear terms in the DO's in the
super-hamiltonian constraint (the Lichnerowicz equation for the conformal
factor of the 3-metric) and the quadratic terms in the DO's in ${\hat
E}_{ADM}$. {\it We solve all the constraints} of the linearized theory: this
amounts to work in a well defined post-Minkowskian Christodoulou-Klainermann
space-time. The Hamilton equations imply the wave equation for the DO's
$r_{\bar a}(\tau ,\vec \sigma)$, which replace the two polarizations of the TT
harmonic gauge, and that {\it linearized Einstein's equations are satisfied} .
Finally we study the geodesic equation, both for time-like and null geodesics,
and the geodesic deviation equation.


title: Background-Independent Gravitational Waves

abstract:
  A Hamiltonian linearization of the rest-frame instant form of tetrad gravity
(gr-qc/0302084), where the Hamiltonian is the weak ADM energy ${\hat E}_{ADM}$,
in a completely fixed (non harmonic) 3-orthogonal Hamiltonian gauge is defined.
For the first time this allows to find an explicit solution of all the
Hamiltonian constraints and an associated linearized solution of Einstein's
equations. It corresponds to background-independent gravitational waves in a
well defined post-Minkowskian Christodoulou-Klainermann space-time.


title: Remarks on experimental bounds on quantum gravity effects on fermions

abstract:
  Effects of space time geometry fluctuations on fermionic fields have recently
been looked for in nuclear physics experiments, and were found to be much lower
than predicted, at a phenomenological level, by loop quantum gravity. We show
that possible corrections to the canonical structure in the semi classical
regime may introduce important changes in the outcome of the theory, and may
explain the observed mismatch with experiments.


title: Invariants of the Kerr Vacuum

abstract:
  The Kerr vacuum has two independent invariants derivable from the Riemann
tensor without differentiation. Both of these invariants must be examined in
order to avoid an erroneous conclusion that the ring singularity of this
spacetime is "directional".


title:
The derivation of the coupling constant in the new Self Creation
  Cosmology

abstract:
  It has been shown that the new Self Creation Cosmology theory predicts a
universe with a total density parameter of one third yet spatially flat, which
would appear to accelerate in its expansion. Although requiring a moderate
amount of 'cold dark matter' the theory does not have to invoke the hypotheses
of inflation, 'dark energy', 'quintessence' or a cosmological constant
(dynamical or otherwise) to explain observed cosmological features. The theory
also offers an explanation for the observed anomalous Pioneer spacecraft
acceleration, an observed spin-up of the Earth and an problematic variation of
G observed from analysis of the evolution of planetary longitudes. It predicts
identical results as General Relativity in standard experimental tests but
three definitive experiments do exist to falsify the theory. In order to match
the predictions of General Relativity, and observations in the standard tests,
the new theory requires the Brans Dicke omega parameter that couples the scalar
field to matter to be -3/2 . Here it is shown how this value for the coupling
parameter is determined by the theory's basic assumptions and therefore it is
an inherent property of the principles upon which the theory is based.


title: From Einstein's Hole Argument to Dirac and Bergmann Observables

abstract:
  The individuation of point-events and the Hamiltonian way of distinguishing
gravitational from inertial effects in general relativity are discussed.


title:
On the superselection theory of the Weyl algebra for diffeomorphism
  invariant quantum gauge theories

abstract:
  Much of the work in loop quantum gravity and quantum geometry rests on a
mathematically rigorous integration theory on spaces of distributional
connections. Most notably, a diffeomorphism invariant representation of the
algebra of basic observables of the theory, the Ashtekar-Lewandowski
representation, has been constructed. This representation is singled out by its
mathematical elegance, and up to now, no other diffeomorphism invariant
representation has been constructed. This raises the question whether it is
unique in a precise sense.
  In the present article we take steps towards answering this question. Our
main result is that upon imposing relatively mild additional assumptions, the
AL-representation is indeed unique.
  As an important tool which is also interesting in its own right, we introduce
a C*-algebra which is very similar to the Weyl algebra used in the canonical
quantization of free quantum field theories.


title: A field theory approach to cosmological density perturbations

abstract:
  Adiabatic perturbations propagate in the expanding universe like scalar
massless fields in some effective Robertson-Walker space-time.


title: The Equivalence Principle as a Symmetry

abstract:
  It is shown that the extra coordinate of 5D induced-matter and membrane
theory is related in certain gauges to the inertial rest mass of a test
particle. This implies that the Weak Equivalence Principle is a geometric
symmetry, valid only in the limit in which the test mass is negligible compared
to the source mass. Exact solutions illustrate this, and show the way to
possible resolutions of the cosmological-constant and hierarchy problems.


title: Mechanical Loss in Tantala/Silica Dielectric Mirror Coatings

abstract:
  Current interferometric gravitational wave detectors use test masses with
mirror coatings formed from multiple layers of dielectric materials, most
commonly alternating layers of SiO2 (silica) and Ta2O5 (tantala). However,
mechanical loss in the Ta2O5/SiO2 coatings may limit the design sensitivity for
advanced detectors. We have investigated sources of mechanical loss in the
Ta2O5/SiO2 coatings, including loss associated with the coating-substrate
interface, with the coating-layer interfaces, and with the bulk material. Our
results indicate that the loss is associated with the bulk coating materials
and that the loss of Ta2O5 is substantially larger than that of SiO2.


title: On the Stability of the Einstein Static Universe

abstract:
  We show using covariant techniques that the Einstein static universe
containing a perfect fluid is always neutrally stable against small
inhomogeneous vector and tensor perturbations and neutrally stable against
adiabatic scalar density inhomogeneities so long as c_{s}^2>1/5, and unstable
otherwise. We also show that the stability is not significantly changed by the
presence of a self-interacting scalar field source, but we find that spatially
homogeneous Bianchi type IX modes destabilise an Einstein static universe. The
implications of these results for the initial state of the universe and its
pre-inflationary evolution are also discussed.


title:
Second Order Scalar Invariants of the Riemann Tensor: Applications to
  Black Hole Spacetimes

abstract:
  We discuss the Kretschmann, Chern-Pontryagin and Euler invariants among the
second order scalar invariants of the Riemann tensor in any spacetime in the
Newman-Penrose formalism and in the framework of gravitoelectromagnetism, using
the Kerr-Newman geometry as an example. An analogy with electromagnetic
invariants leads to the definition of regions of gravitoelectric or
gravitomagnetic dominance.


title:
Time Evolution of a Quantum Particle and a Generalized Uncertainty
  Principle

abstract:
  Some of the possible consequences of a generalized uncertainty principle
(which emerges in the context of string theory and quantum gravity models as a
consequence of fluctuations of the background metric) are analyzed considering
the case of a quantum particle immersed in a homogeneous gravitational field.
It will be shown that the expectation value of the momentum operator depends in
a novel way on the mass of the involved particle. This kind of physical
characteristics could be, in principle, detected. In other words, one way of
confronting against the experiment some of the models around quantum gravity is
given by the detection of the dependence upon the mass parameter of the
expectation value of the momentum operator.


title:
Exact vacuum solution of a (1+2)-dimensional Poincare gauge theory: BTZ
  solution with torsion

abstract:
  In (1+2)-dimensional Poincar\'e gauge gravity, we start from a Lagrangian
depending on torsion and curvature which includes additionally {\em
translational} and {\em Lorentzian} Chern-Simons terms. Limiting ourselves to
to a specific subcase, the Mielke-Baekler (MB) model, we derive the
corresponding field equations (of Einstein-Cartan-Chern-Simons type) and find
the general vacuum solution. We determine the properties of this solution, in
particular its mass and its angular momentum. For vanishing torsion, we recover
the BTZ-solution. We also derive the general conformally flat vacuum solution
with torsion. In this framework, we discuss {\em Cartan's} (3-dimensional) {\em
spiral staircase} and find that it is not only a special case of our new vacuum
solution, but can alternatively be understood as a solution of the
3-dimensional Einstein-Cartan theory with matter of constant pressure and
constant torque.


title: General properties of cosmological models with an Isotropic Singularity

abstract:
  Much of the published work regarding the Isotropic Singularity is performed
under the assumption that the matter source for the cosmological model is a
barotropic perfect fluid, or even a perfect fluid with a $\gamma$-law equation
of state. There are, however, some general properties of cosmological models
which admit an Isotropic Singularity, irrespective of the matter source. In
particular, we show that the Isotropic Singularity is a point-like singularity
and that vacuum space-times cannot admit an Isotropic Singularity. The
relationships between the Isotropic Singularity, and the energy conditions, and
the Hubble parameter is explored. A review of work by the authors, regarding
the Isotropic Singularity, is presented.


title: Horizon Entropy

abstract:
  Although the laws of thermodynamics are well established for black hole
horizons, much less has been said in the literature to support the extension of
these laws to more general settings such as an asymptotic de Sitter horizon or
a Rindler horizon (the event horizon of an asymptotic uniformly accelerated
observer). In the present paper we review the results that have been previously
established and argue that the laws of black hole thermodynamics, as well as
their underlying statistical mechanical content, extend quite generally to what
we call here "causal horizons". The root of this generalization is the local
notion of horizon entropy density.


title: Attractor Solution of Phantom Field

abstract:
  In light of recent study on the dark energy models that manifest an equation
of state $w<-1$, we investigate the cosmological evolution of phantom field in
a specific potential, exponential potential in this paper. The phase plane
analysis show that the there is a late time attractor solution in this model,
which address the similar issues as that of fine tuning problems in
conventional quintessence models. The equation of state $w$ is determined by
the attractor solution which is dependent on the $\lambda$ parameter in the
potential. We also show that this model is stable for our present observable
universe.


title: Conserved superenergy currents

abstract:
  We exploit once again the analogy between the energy-momentum tensor and the
so-called ``superenergy'' tensors in order to build conserved currents in the
presence of Killing vectors. First of all, we derive the divergence-free
property of the gravitational superenergy currents under very general
circumstances, even if the superenergy tensor is not divergence-free itself.
The associated conserved quantities are explicitly computed for the
Reissner-Nordstrom and Schwarzschild solutions. The remaining cases, when the
above currents are not conserved, lead to the possibility of an interchange of
some superenergy quantities between the gravitational and other physical fields
in such a manner that the total, mixed, current may be conserved. Actually,
this possibility has been recently proved to hold for the Einstein-Klein-Gordon
system of field equations. By using an adequate family of known exact
solutions, we present explicit and completely non-obvious examples of such
mixed conserved currents.


title: Mach's Principle and Model for a Broken Symmetric Theory of Gravity

abstract:
  We investigate spontaneous symmetry breaking in a conformally invariant
gravitational model. In particular, we use a conformally invariant scalar
tensor theory as the vacuum sector of a gravitational model to examine the idea
that gravitational coupling may be the result of a spontaneous symmetry
breaking. In this model matter is taken to be coupled with a metric which is
different but conformally related to the metric appearing explicitly in the
vacuum sector. We show that after the spontaneous symmetry breaking the
resulting theory is consistent with Mach's principle in the sense that inertial
masses of particles have variable configurations in a cosmological context.
Moreover, our analysis allows to construct a mechanism in which the resulting
large vacuum energy density relaxes during evolution of the universe.


title: A survey of spinning test particle orbits in Kerr spacetime

abstract:
  We investigate the dynamics of the Papapetrou equations in Kerr spacetime.
These equations provide a model for the motion of a relativistic spinning test
particle orbiting a rotating (Kerr) black hole. We perform a thorough parameter
space search for signs of chaotic dynamics by calculating the Lyapunov
exponents for a large variety of initial conditions. We find that the
Papapetrou equations admit many chaotic solutions, with the strongest chaos
occurring in the case of eccentric orbits with pericenters close to the limit
of stability against plunge into a maximally spinning Kerr black hole. Despite
the presence of these chaotic solutions, we show that physically realistic
solutions to the Papapetrou equations are not chaotic; in all cases, the
chaotic solutions either do not correspond to realistic astrophysical systems,
or involve a breakdown of the test-particle approximation leading to the
Papapetrou equations (or both). As a result, the gravitational radiation from
bodies spiraling into much more massive black holes (as detectable, for
example, by LISA, the Laser Interferometer Space Antenna) should not exhibit
any signs of chaos.


title: Anisotropic relativistic stellar models

abstract:
  We present a class of exact solutions of Einstein's gravitational field
equations describing spherically symmetric and static anisotropic stellar type
configurations. The solutions are obtained by assuming a particular form of the
anisotropy factor. The energy density and both radial and tangential pressures
are finite and positive inside the anisotropic star. Numerical results show
that the basic physical parameters (mass and radius) of the model can describe
realistic astrophysical objects like neutron stars.


title:
To the problem on the Universe evolution and the condensed description
  in the field theory

abstract:
  On the basis of hypotheses, that a density of weakly interacting particles in
the Universe has an order of nuclear matter density or more the Lagrangian is
offered, through which one can be obtained a propagator of a vector boson with
a non-zero rest-mass. The dependence of vector bosons masses on the time allows
to explain the availability of the hot stage of the Universe evolution, not
using to the hypothesis of the Universe expansion.


title:
Grad-Shafranov equation in noncircular stationary axisymmetric
  spacetimes

abstract:
  A formulation is developed for general relativistic ideal
magnetohydrodynamics in stationary axisymmetric spacetimes. We reduce basic
equations to a single second-order partial differential equation, the so-called
Grad-Shafranov (GS) equation. Our formulation is most general in the sense that
it is applicable even when a stationary axisymmetric spacetime is noncircular,
that is, even when it is impossible to foliate a spacetime with two orthogonal
families of two-surfaces. The GS equation for noncircular spacetimes is crucial
for the study of relativistic stars with a toroidal magnetic field or
meridional flow, such as magnetars, since the existence of a toroidal field or
meridional flow violates the circularity of a spacetime. We also derive the
wind equation in noncircular spacetimes, and discuss various limits of the GS
equation.


title: The wormhole hazard

abstract:
  To predict the outcome of (almost) any experiment we have to assume that our
spacetime is globally hyperbolic. The wormholes, if they exist, cast doubt on
the validity of this assumption. At the same time, no evidence has been found
so far (either observational, or theoretical) that the possibility of their
existence can be safely neglected.


title:
Graviton and Dark Matter in a Hot Homogenous Isotropic Brane Universe: A
  Relativistic Theory of Gravitation Approach

abstract: See hep-ph/0304045


title: A new phenomenological approach to the Universe expansion

abstract: See hep-ph/0304045


title:
N=2 Gauged Supergravity with Stable dS Vacuum and Masses of Ultra-Light
  Scalars in Einstein Field Equations

abstract: See hep-ph/0304045


title: Close encounters of black holes

abstract:
  This is an introduction into the problem of how to set up black hole
initial-data for the matter-free field equations of General Relativity. The
approach is semi-pedagogical and addresses a more general audience of
astrophysicists and students with no specialized training in General Relativity
beyond that of an introductory lecture.


title:
The accelerated expansion of the Universe as a quantum cosmological
  effect

abstract:
  We study the quantized Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) model
minimally coupled to a free massless scalar field. In a previous paper,
\cite{fab2}, solutions of this model were constructed as gaussian
superpositions of negative and positive modes solutions of the Wheeler-DeWitt
equation, and quantum bohmian trajectories were obtained in the framework of
the Bohm-de Broglie (BdB) interpretation of quantum cosmology. In the present
work, we analyze the quantum bohmian trajectories of a different class of
gaussian packets. We are able to show that this new class generates bohmian
trajectories which begin classical (with decelerated expansion), undergo an
accelerated expansion in the middle of its evolution due to the presence of
quantum cosmological effects in this period, and return to its classical
decelerated expansion in the far future. We also show that the relation between
luminosity distance and redshift in the quantum cosmological model can be made
close to the corresponding relation coming from the classical model suplemented
by a cosmological constant, for $z<1$. These results suggest the posibility of
interpreting the present observations of high redshift supernovae as the
manifestation of a quantum cosmological effect.


title: Quantum Scattering in Two Black Hole Moduli Space

abstract:
  We discuss the quantum scattering process in the moduli space consisting of
two maximally charged dilaton black holes. The black hole moduli space geometry
has different structures for arbitrary dimensions and various values of dilaton
coupling. We study the quantum effects of the different moduli space geometries
with scattering process. Then, it is found that there is a resonance state on
certain moduli spaces.


title:
Asymptotically flat solutions to the Ernst equation with reflection
  symmetry

abstract:
  It is shown that the class of asymptotically flat solutions to the
axisymmetric and stationary vacuum Einstein equations with reflection symmetry
of the metric is uniquely characterized by a simple relation for the Ernst
potential on the upper part of the symmetry axis. This result generalizes a
well-known fact from potential theory.


title: Differential rotation of nonlinear r-modes

abstract:
  Differential rotation of r-modes is investigated within the nonlinear theory
up to second order in the mode amplitude in the case of a slowly-rotating,
Newtonian, barotropic, perfect-fluid star. We find a nonlinear extension of the
linear r-mode, which represents differential rotation that produces large scale
drifts of fluid elements along stellar latitudes. This solution includes a
piece induced by first-order quantities and another one which is a pure
second-order effect. Since the latter is stratified on cylinders, it cannot
cancel differential rotation induced by first-order quantities, which is not
stratified on cylinders. It is shown that, unlikely the situation in the
linearized theory, r-modes do not preserve vorticity of fluid elements at
second-order. It is also shown that the physical angular momentum and energy of
the perturbation are, in general, different from the corresponding canonical
quantities.


title: Causality and Superluminal Light

abstract:
  The causal properties of curved spacetime, which underpin our sense of time
in gravitational theories, are defined by the null cones of the spacetime
metric. In classical general relativity, it is assumed that these coincide with
the light cones determined by the physical propagation of light rays. However,
the quantum vacuum acts as a dispersive medium for the propagation of light,
since vacuum polarisation in QED induces interactions which effectively violate
the strong equivalence principle (SEP). For low frequencies the phenomenon of
gravitational birefringence occurs and indeed, for some metrics and
polarisations, photons may acquire {\it superluminal} phase velocities. In this
article, we review some of the remarkable features of SEP violating
superluminal propagation in curved spacetime and discuss recent progress on the
issue of dispersion, explaining why it is the high-frequency limit of the phase
velocity that determines the characteristics of the effective wave equation and
thus the physical causal structure.


title: Entropy bounds for charged and rotating systems

abstract:
  It was shown in a previous work that, for systems in which the entropy is an
extensive function of the energy and volume, the Bekenstein and the holographic
entropy bounds predict new results. In this paper, we go further and derive
improved upper bounds to the entropy of {\it extensive} charged and rotating
systems. Furthermore, it is shown that for charged and rotating systems
(including non-extensive ones), the total energy that appear in both the
Bekenstein entropy bound (BEB) and the causal entropy bound (CEB) can be
replaced by the {\it internal} energy of the system. In addition, we propose
possible corrections to the BEB and the CEB.


title: Computation of Lyapunov Exponents in General Relativity

abstract:
  Lyapunov exponents (LEs) are key indicators of chaos in dynamical systems. In
general relativity the classical definition of LE meets difficulty because it
is not coordinate invariant and spacetime coordinates lose their physical
meaning as in Newtonian dynamics. We propose a new definition of relativistic
LE and give its algorithm in any coordinate system, which represents the
observed changing law of the space separation between two neighboring particles
(an 'observer' and a 'neighbor'), and is truly coordinate invariant in a curved
spacetime.


title: Quantum Mechanics of the Early Universe and its Limiting Transition

abstract:
  In this paper Quantum Mechanics with Fundamental Length is chosen as the
theory for describing the early Universe. This is possible due to the presence
in the theory of General Uncertainty Relations from which unavoidable it
follows that in nature a fundamental length exits. Here Quantum
  Mechanics with Fundamental Length is obtained as a deformation of Quantum
Mechanics. The distinguishing feature of the proposed in this paper approach in
comparison with previous ones, lies on the fact that here density matrix
subjects to deformation as well as so far commutators had been deformed. The
deformed density matrix mentioned above, is named throughout this paper density
pro-matrix. Within our approach two main features of Quantum Mechanics are
conserved: the probabilistic interpretation of the theory and exact predefined
measuring procedure corresponding to that interpretation. The proposed here
approach allows to describe dynamics. In particular, the explicit form of
deformed Liouville's equation and the deformed Shr\"odinger's picture are
given. Some implications of obtained results are discussed. In particular, the
problem of singularity, the hypothesis of cosmic censorship, a possible
improvement of the statistical entropy definition and the problem of
information loss in black holes are considered.


title: On 3+1 Dimensional Friedman-Robertson-Walker Universes with Matter

abstract:
  We examine the dynamical behavior of matter coupled to gravity in the context
of a linear Klein-Gordon equation coupled to a Friedman-Robertson-Walker
metric. The resulting ordinary differential equations can be decoupled, the
effect of gravity being traced in rendering the equation for the scalar field
nonlinear. We obtain regular (in the massless case) and asymptotic (in the
massive case) solutions for the resulting matter field and discuss their
ensuing finite time blowup in the light of earlier findings. Finally, some
potentially interesting connections of these blowups with features of focusing
in the theory of nonlinear partial differential equations are outlined,
suggesting the potential relevance of a nonlinear theory of quantum cosmology.


title: Quantizing the line element field

abstract:
  A metric with signature (-+++) can be constructed from a metric with
signature (++++) and a double-sided vector field called the line element field.
Some of the classical and quantum properties of this vector field are studied.