title:
Comments on ``Improved limit on quantum-spacetime modifications of
  Lorentz symmetry from observations of gamma-ray blazars"

abstract:
  We address several criticisms by Amelino-Camelia of our recent analyses of
two observational constraints on Lorentz violation at order E/M_{Planck}. In
particular, we emphasize the role of effective field theory in our analysis of
synchrotron radiation, and we strengthen the justification for the constraint
coming from photon annihilation.


title: Equivalence principle in classical electrodynamics

abstract:
  The principle of equivalence in gravitational physics and its mathematical
base are reviewed. It is demonstrated how this principle can be realized in
classical electrodynamis. In general, it is valid at any given single point or
along a path without selfintersections unless the field considered satisfies
some conditions.


title: Brane-world Singularities

abstract:
  We study the behavior of spatially homogeneous brane-worlds close to the
initial singularity in the presence of both local and nonlocal stresses. It is
found that the singularity in these brane-worlds can be locally either
isotropic or anisotropic. We then investigate the Weyl curvature conjecture,
according to which some measure of the Weyl curvature is related to a
gravitational entropy. In particular, we study the Weyl curvature conjecture on
the brane with respect to the dimensionless ratio of the Weyl invariant and the
Ricci square and the measure proposed by Gr{\o}n and Hervik. We also argue that
the Weyl curvature conjecture should be formulated on brane
  (i.e., in the four-dimensional context).


title: Density Perturbations in the Early Universe

abstract:
  We propose a way to construct manifestly gauge independent quantities out of
the gauge dependent quantities occurring in the linearized Einstein equations.
Thereupon, we show that these gauge-invariant combinations can be identified
with measurable perturbations to the particle and energy densities.
  In the radiation-dominated era we find, for small-scale perturbations,
acoustic waves with an increasing amplitude, while standard treatments predict
acoustic waves with a decaying amplitude. For large-scale perturbations we find
exactly the same growth rates as in the standard literature.
  When considering the non-relativistic limit of the linearized Einstein
equations we find the Poisson equation.
  It is shown, using the linearized Einstein equations, that the usual
Newtonian treatment of density perturbations does not describe the evolution of
density perturbations.


title: Uniqueness of the electrostatic solution in Schwarzschild space

abstract:
  In this Brief Report we give the proof that the solution of any static test
charge distribution in Schwarzschild space is unique. In order to give the
proof we derive the first Green's identity written with p-forms on (pseudo)
Riemannian manifolds. Moreover, the proof of uniqueness can be shown for either
any purely electric or purely magnetic field configuration. The spacetime
geometry is not crucial for the proof.


title: Remarks on 't Hooft's Brick Wall Model

abstract:
  A semi-classical reasoning leads to the non-commutativity of the space and
time coordinates near the horizon of Schwarzschild black hole. This
non-commutativity in turn provides a mechanism to interpret the brick wall
thickness hypothesis in 't Hooft's brick wall model as well as the boundary
condition imposed for the field considered. For concreteness, we consider a
noncommutative scalar field model near the horizon and derive the effective
metric via the equation of motion of noncommutative scalar field. This metric
displays a new horizon in addition to the original one associated with the
Schwarzschild black hole. The infinite red-shifting of the scalar field on the
new horizon determines the range of the noncommutativ space and explains the
relevant boundary condition for the field. This range enables us to calculate
the entropy of black hole as proportional to the area of its original horizon
along the same line as in 't Hooft's model, and the thickness of the brick wall
is found to be proportional to the thermal average of the noncommutative
space-time range. The Hawking temperature has been derived in this formalism.
The study here represents an attempt to reveal some physics beyond the brick
wall model.


title:
The Ghost (Phantom) Universe: A Model in which the Universe is Flat,
  Quantum Ghost Matter and Vacuum Dominated and Accelerating

abstract: See hep-ph/0304045


title: Eppur, si muove !

abstract:
  Simple ideas that shed new light on the physics of rotation as it concerns
two famous experiments: The Wilson and Wilson, and the Michelson and Morley
experiments.


title: Energy Distribution in 2d Stringy Black Hole Backgrounds

abstract:
  We utilize Moller's and Einstein's energy-momentum complexes in order to
explicitly evaluate the energy distributions associated with the
two-dimensional "Schwarzschild" and "Reissner-Nordstrom" black hole
backgrounds. While Moller's prescription provides meaningful physical results,
Einstein's prescription fails to do so in the aforementioned gravitational
backgrounds. These results hold for all two-dimensional static black hole
geometries. The results obtained within this context are exploited in order
Seifert's hypothesis to be investigated.


title: Symmetries leading to inflation

abstract:
  We present here the general transformation that leaves unchanged the form of
the field equations for perfect fluid Friedmann--Robertson--Walker and Bianchi
V cosmologies. The symmetries found can be used as algorithms for generating
new cosmological models from existing ones. A particular case of the general
transformation is used to illustrate the crucial role played by the number of
scalar fields in the occurrence of inflation. Related to this, we also study
the existence and stability of Bianchi V power law solutions.


title:
Quasinormal modes of Kerr black holes: The determination of the
  quasinormal frequencies with a new technique

abstract:
  We compute the quasinormal frequencies of rotating black holes using the
continued fraction method first proposed by Leaver. The main difference with
former works, is that our results are obtained by a new numerical technique
which avoids the use of two dimensional root-finding routines. The technique is
applied to evaluate the angular eigenvalues of Teukolsky's angular equation.
This method allow us to calculate both the slowly and the rapidly damped
quasinormal frequencies with excellent accuracy.


title: Reflection coefficient for superresonant scattering

abstract:
  We investigate superresonant scattering of acoustic disturbances from a
rotating acoustic black hole in the low frequency range. We derive an
expression for the reflection coefficient, exhibiting its frequency dependence
in this regime.


title: Implementation of Time-Delay Interferometry for LISA

abstract:
  We discuss the baseline optical configuration for the Laser Interferometer
Space Antenna (LISA) mission, in which the lasers are not free-running, but
rather one of them is used as the main frequency reference generator (the {\it
master}) and the remaining five as {\it slaves}, these being phase-locked to
the master (the {\it master-slave configuration}). Under the condition that the
frequency fluctuations due to the optical transponders can be made negligible
with respect to the secondary LISA noise sources (mainly proof-mass and shot
noises), we show that the entire space of interferometric combinations LISA can
generate when operated with six independent lasers (the {\it one-way method})
can also be constructed with the {\it master-slave} system design. The
corresponding hardware trade-off analysis for these two optical designs is
presented, which indicates that the two sets of systems needed for implementing
the {\it one-way method}, and the {\it master-slave configuration}, are
essentially identical. Either operational mode could therefore be implemented
without major implications on the hardware configuration. We then.......


title: Scalar-field cosmologies with an arbitrary potential

abstract:
  We study the late time evolution of flat and negatively curved FRW models
with a perfect fluid matter source and a scalar field having an arbitrary
non-negative potential function $V(\phi) .$ We prove using a dynamical systems
approach four general results for a large class of non-negative potentials
which show that almost always the universe ever expands. In particular, for
potentials having a local zero minimum, flat and negatively curved FRW models
are ever expanding and the energy density asymptotically approaches zero. We
investigate the conditions under which the scalar field asymptotically
approaches the minimum of the potential. We discuss the question of whether a
closed FRW with ordinary matter can avoid recollapse due to the presence of a
scalar field with a non-negative potential.


title: Lagrangian theory for perfect fluids

abstract:
  The theory of perfect fluids is reconsidered from the point of view of a
covariant Lagrangian theory. It has been shown that the Euler-Lagrange
equations for a perfect fluid could be found in spaces with affine connections
and metrics from an unconstrained variational principle by the use of the
method of Lagrangians with covariant derivatives (MLCD) and additional
conditions for reparametrizations of the proper time of the mass elements
(particles) of the perfect fluid. The last conditions are not related to the
variational principle and are not considered as constraints used in the process
of variations. The application of the whole structure of a Lagrangian theory
with an appropriate choice of Lagrangian invariant as the pressure of the fluid
shows that the Euler-Lagrange equations with their corresponding
energy-momentum tensors lead to Navier-Stokes' equation identical with the
Euler equation for a perfect fluid in a space with one affine connection and
metrics. The Navier-Stokes equations appear as higher order equations with
respect to the Euler-Lagrange equations.


title: More examples of structure formation in the Lemaitre-Tolman model

abstract:
  In continuing our earlier research, we find the formulae needed to determine
the arbitrary functions in the Lemaitre-Tolman model when the evolution
proceeds from a given initial velocity distribution to a final state that is
determined either by a density distribution or by a velocity distribution. In
each case the initial and final distributions uniquely determine the L-T model
that evolves between them, and the sign of the energy-function is determined by
a simple inequality. We also show how the final density profile can be more
accurately fitted to observational data than was done in our previous paper. We
work out new numerical examples of the evolution: the creation of a galaxy
cluster out of different velocity distributions, reflecting the current data on
temperature anisotropies of CMB, the creation of the same out of different
density distributions, and the creation of a void. The void in its present
state is surrounded by a nonsingular wall of high density.


title: High velocity spikes in Gowdy spacetimes

abstract:
  We study the behavior of spiky features in Gowdy spacetimes. Spikes with
velocity initially high are, generally, driven to low velocity. Let n be any
integer greater than or equal to 1. If the initial velocity of an upward
pointing spike is between 4n-3 and 4n-1 the spike persists with final velocity
between 1 and 2, while if the initial velocity is between 4n-1 and 4n+1, the
spiky feature eventually disappears. For downward pointing spikes the analogous
rule is that spikes with initial velocity between 4n-4 and 4n-2 persist with
final velocity between 0 and 1, while spikes with initial velocity between 4n-2
and 4n eventually disappear.


title: Hydrodynamic Stability of Cosmological Quark-Hadron Phase Transitions

abstract:
  Recent results from linear perturbation theory suggest that first-order
cosmological quark-hadron phase transitions occurring as deflagrations may be
``borderline'' unstable, and those occurring as detonations may give rise to
growing modes behind the interface boundary. However, since nonlinear effects
can play important roles in the development of perturbations, unstable behavior
cannot be asserted entirely by linear analysis, and the uncertainty of these
recent studies is compounded further by nonlinearities in the hydrodynamics and
self-interaction fields. In this paper we investigate the growth of
perturbations and the stability of quark-hadron phase transitions in the early
Universe by solving numerically the fully nonlinear relativistic hydrodynamics
equations coupled to a scalar field with a quartic self-interaction potential
regulating the transitions. We consider single, perturbed, phase transitions
propagating either by detonation or deflagration, as well as multiple phase and
shock front interactions in 1+2 dimensional spacetimes.


title: Positivity of Quasilocal Mass

abstract:
  Motivated by the important work of Brown adn York on quasilocal energy, we
propose definitions of quasilocal energy and momentum surface energy of a
spacelike 2-surface with positive intrinsic curvature in a spacetime. We show
that the quasilocal energy of the boundary of a compact spacelike hypersurface
which satisfies the local energy condition is strictly positive unless the
spacetime is flat along the spacelike hypersurface.


title: Causal symmetries

abstract:
  Based on the recent work \cite{PII} we put forward a new type of
transformation for Lorentzian manifolds characterized by mapping every causal
future-directed vector onto a causal future-directed vector. The set of all
such transformations, which we call causal symmetries, has the structure of a
submonoid which contains as its maximal subgroup the set of conformal
transformations. We find the necessary and sufficient conditions for a vector
field $\xiv$ to be the infinitesimal generator of a one-parameter submonoid of
pure causal symmetries. We speculate about possible applications to gravitation
theory by means of some relevant examples.


title: New approach to calculating the News

abstract:
  We consider the problem of finding the gravitational radiation output, or
news, within the context of a numerical simulation of a spacetime by means of
the null-cone, or characteristic, approach to numerical relativity. We develop
a method for computing the news that uses an explicit coordinate transformation
to a coordinate system that satisfies the Bondi conditions. The method has been
implemented computationally. We present results of applying the method to
certain test problems, demonstrating second order convergence of the news to
the analytic value.


title: Problem of cosmological singularity and inflationary cosmology

abstract:
  Problem of cosmological singularity of general relativity theory is
discussed. The possible resolution of this problem in the framework of
inflationary cosmology is proposed. Physical conditions leading to bouncing
inflationary solutions in the frame of general relativity theory and gauge
theories of gravitation are compared. It is shown that gauge theories of
gravitation allow to build regular inflationary cosmological models of closed,
open and flat type with dominating ultrarelativistic matter at a bounce.


title: The Holographic Entropy Bound and Local Quantum Field Theory

abstract:
  The maximum entropy that can be stored in a bounded region of space is in
dispute: it goes as volume, implies (non-gravitational) microphysics; it goes
as the surface area, asserts the "holographic principle." Here I show how the
holographic bound can be derived from elementary flat-spacetime quantum field
theory when the total energy of Fock states is constrained gravitationally.
This energy constraint makes the Fock space dimension (whose logarithm is the
maximum entropy) finite for both Bosons and Fermions. Despite the elementary
nature of my analysis, it results in an upper limit on entropy in remarkable
agreement with the holographic bound.


title: Extended open inflationary universes

abstract:
  In this paper we study a type of one-field model for open inflationary
universe models in the context of the Jordan-Brans-Dicke theory. In the
scenario of a one-bubble universe model we determine and characterize the
existence of the Coleman-De Lucia instanton, together with the period of
inflation after tunnelling has occurred. Our results are analogous to those
found in the Einstein General Relativity models.


title: A new recipe for causal completions

abstract:
  We discuss the asymptotic structure of spacetimes, presenting a new
construction of ideal points at infinity and introducing useful topologies on
the completed space. Our construction is based on structures introduced by
Geroch, Kronheimer, and Penrose and has much in common with the modifications
introduced by Budic and Sachs as well as those introduced by Szabados. However,
these earlier constructions defined ideal points as equivalence classes of
certain past and future sets, effectively defining the completed space as a
quotient. Our approach is fundamentally different as it identifies ideal points
directly as appropriate pairs consisting of a (perhaps empty) future set and a
(perhaps empty) past set. These future and past sets are just the future and
past of the ideal point within the original spacetime. This provides our
construction with useful causal properties and leads to more satisfactory
results in a number of examples. We are also able to endow the completion with
a topology. In fact, we introduce two topologies, which illustrate different
features of the causal approach. In both topologies, the completion is the
original spacetime together with endpoints for all timelike curves. We explore
this procedure in several examples, and in particular for plane wave solutions,
with satisfactory results.


title: Spin Foam Quantization and Anomalies

abstract:
  The most common spin foam models of gravity are widely believed to be
discrete path integral quantizations of the Plebanski action. However, their
derivation in present formulations is incomplete and lower dimensional simplex
amplitudes are left open to choice. Since their large-spin behavior determines
the convergence properties of the state-sum, this gap has to be closed before
any reliable conclusion about finiteness can be reached. It is shown that these
amplitudes are directly related to the path integral measure and can in
principle be derived from it, requiring detailed knowledge of the constraint
algebra and gauge fixing. In a related manner, minimal requirements of
background independence provide non trivial restrictions on the form of an
anomaly free measure. Many models in the literature do not satisfy these
requirements. A simple model satisfying the above consistency requirements is
presented which can be thought of as a spin foam quantization of the
Husain--Kuchar model.


title:
Matters of Gravity, the newsletter of the APS Topical Group on
  Gravitation, Spring 2003

abstract:
  Contents:
  * Community news:
  GGR activities, by Richard Price
  We hear that..., by Jorge Pullin
  Institute of Physics Gravitational Physics Group, by Elizabeth Winstanley
  Center for gravitational wave astronomy, by Mario Diaz
  * Research briefs:
  LIGO's first preliminary science run, by Gary Sanders
  Quantization of area: the plot thickens, by John Baez
  Convergence of G measurements -Mysteries remain, by Riley Newman
  * Conference reports:
  Brane world gravity, by Elizabeth Winstanley
  Massive black holes focus session, by Steinn Sigurdsson
  GWDAW 2002, by Peter Saulson
  Source simulation focus session, by Pablo Laguna
  RRI workshop on loop quantum gravity, by Fernando Barbero
  Lazarus/Kudu Meeting, by Warren G. Anderson


title: On Slow Light as a Black Hole Analogue

abstract:
  Although slow light (electromagnetically induced transparency) would seem an
ideal medium in which to institute a ``dumb hole'' (black hole analog), it
suffers from a number of problems. We show that the high phase velocity in the
slow light regime ensures that the system cannot be used as an analog
displaying Hawking radiation. Even though an appropriately designed slow-light
set-up may simulate classical features of black holes -- such as horizon, mode
mixing, Bogoliubov coefficients, etc. -- it does not reproduce the related
quantum effects. PACS: 04.70.Dy, 04.80.-y, 42.50.Gy, 04.60.-m.


title: The Hypothesis of Locality and its Limitations

abstract:
  The hypothesis of locality, its origin and consequences are discussed. This
supposition is necessary for establishing the local spacetime frame of
accelerated observers; in this connection, the measurement of length in a
rotating system is considered in detail. Various limitations of the hypothesis
of locality are examined.


title: Black hole entropy: quantum vs thermal fluctuations

abstract:
  The relation between logarithmic corrections to the area law for black hole
entropy, due to thermal fluctuations around an equilibrium canonical ensemble,
and those originating from quantum spacetime fluctuations within a
microcanonical framework, is explored for three and four dimensional
asymptotically anti-de Sitter black holes. For the BTZ black hole, the two
logarithmic corrections are seen to precisely cancel each other, while for four
dimensional adS-Schwarzschild black holes a partial cancellation is obtained.
We discuss the possibility of extending the analysis to asymptotically flat
black holes.


title:
Quintessential solution of dark matter rotation curves and its
  simulation by extra dimensions

abstract:
  On the base of an exact solution for the static spherically symmetric
Einstein equations with the quintessential dark matter, we explain the
asymptotic behavior of rotation curves in spiral galaxies. The parameter of the
quintessence state, i.e. the ratio of its pressure to the density is tending to
-1/3. We present an opportunity to imitate the relevant quintessence by
appropriate scalar fields in the space-time with extra 2 dimensions.


title:
Plane-symmetric inhomogeneous Brans-Dicke cosmology with an equation of
  state $p=\gamma \rho$

abstract:
  We present a new exact solution in Brans-Dicke theory. The solution describes
inhomogeneous plane-symmetric perfect fluid cosmological model with an equation
of state $p=\gamma \rho$. Some main properties of the solution are discussed.


title: On multi-graviton and multi-gravitino gauge theories

abstract:
  This paper studies nonlinear deformations of the linear gauge theory of any
number of spin-2 and spin-3/2 fields with general formal multiplication rules
in place of standard Grassmann rules for manipulating the fields, in four
spacetime dimensions. General possibilities for multiplication rules and
coupling constants are simultaneously accommodated by regarding the set of
fields equivalently as a single algebra-valued spin-2 field and single
algebra-valued spin-3/2 field, where the underlying algebra is factorized into
a field-coupling part and an internal multiplication part. The condition that
there exist a gauge invariant Lagrangian (to within a divergence) for these
algebra-valued fields is used to derive determining equations whose solutions
give all allowed deformation terms, yielding nonlinear field equations and
nonabelian gauge symmetries, together with all allowed formal multiplication
rules as needed in the Lagrangian for demonstration of invariance under the
gauge symmetries and for derivation of the field equations. In the case of
spin-2 fields alone, the main result of this analysis is that all deformations
(without any higher derivatives than appear in the linear theory) are
equivalent to an algebra-valued Einstein gravity theory. By a systematic
examination of factorizations of the algebra, a novel type of nonlinear gauge
theory of two or more spin-2 fields is found, where the coupling for the fields
is based on structure constants of an anticommutative, anti-associative
algebra, and with formal multiplication rules that make the fields
anticommuting (while products obey anti-associativity). Supersymmetric
extensions of these results are obtained in the more general case when spin-3/2
fields are included.


title: The energy of the universe in teleparallel gravity

abstract:
  The teleparallel versions of the Einstein and the Landau-Lifshitz
energy-momentum complexes of the gravitational field are obtained. By using
these complexes, the total energy of the universe, which includes the energy of
both the matter and the gravitational fields, is then obtained. It is shown
that the total energy vanishes independently of both the curvature parameter
and the three dimensionless coupling constants of teleparallel gravity.


title: Trans-Planckian footprints in inflationary cosmology

abstract:
  We consider a minimum uncertainty vacuum choice at a fixed energy scale
Lambda as an effective description of trans-Planckian physics, and discuss its
implications for the linear perturbations of a massless scalar field in
power-law inflationary models. We find possible effects with a magnitude of
order H/\Lambda in the power spectrum, in analogy with previous results for
de-Sitter space-time.


title: New electromagnetic conservation laws

abstract:
  The Chevreton superenergy tensor was introduced in 1964 as a counterpart, for
electromagnetic fields, of the well-known Bel-Robinson tensor of the
gravitational field. We here prove the unnoticed facts that, in the absence of
electromagnetic currents, Chevreton's tensor (i) is completely symmetric, and
(ii) has a trace-free divergence if Einstein-Maxwell equations hold. It follows
that the trace of the Chevreton tensor is a rank-2, symmetric, trace-free, {\em
conserved} tensor, which is different from the energy-momentum tensor, and
nonetheless can be constructed for any test Maxwell field, or any
Einstein-Maxwell spacetime.


title: Quantum field theory as eigenvalue problem

abstract:
  A mathematically well-defined, manifestly covariant theory of classical and
quantum field is given, based on Euclidean Poisson algebras and a
generalization of the Ehrenfest equation, which implies the stationary action
principle. The theory opens a constructive spectral approach to finding
physical states both in relativistic quantum field theories and for flexible
phenomenological few-particle approximations.
  In particular, we obtain a Lorentz-covariant phenomenological multiparticle
quantum dynamics for electromagnetic and gravitational interaction which
provides a representation of the Poincare group without negative energy states.
The dynamics reduces in the nonrelativistic limit to the traditional
Hamiltonian multiparticle description with standard Newton and Coulomb forces.
  The key that allows us to overcome the traditional problems in canonical
quantization is the fact that we use the algebra of linear operators on a space
of wave functions slightly bigger than traditional Fock spaces.


title:
T-Duality and Penrose limits of spatially homogeneous and inhomogeneous
  cosmologies

abstract:
  Penrose limits of inhomogeneous cosmologies admitting two abelian Killing
vectors and their abelian T-duals are found in general. The wave profiles of
the resulting plane waves are given for particular solutions. Abelian and
non-abelian T-duality are used as solution generating techniques. Furthermore,
it is found that unlike in the case of abelian T-duality, non-abelian T-duality
and taking the Penrose limit are not commutative procedures.


title: Effective Gravitational Equations on Brane World with Induced Gravity

abstract:
  We present the effective equations to describe the four-dimensional gravity
of a brane world, assuming that a five-dimensional bulk spacetime satisfies the
Einstein equations and gravity is confined on the $Z_2$ symmetric brane.
Applying this formalism, we study the induced-gravity brane model first
proposed by Dvali, Gabadadze and Porrati. In a generalization of their model,
we show that an effective cosmological constant on the brane can be extremely
reduced in contrast to the case of the Randall-Sundrum model even if a bulk
cosmological constant and a brane tension are not fine-tuned.


title: Detecting ill posed boundary conditions in General Relativity

abstract:
  A persistent challenge in numerical relativity is the correct specification
of boundary conditions. In this work we consider a many parameter family of
symmetric hyperbolic initial-boundary value formulations for the linearized
Einstein equations and analyze its well posedness using the Laplace-Fourier
technique. By using this technique ill posed modes can be detected and thus a
necessary condition for well posedness is provided. We focus on the following
types of boundary conditions: i) Boundary conditions that have been shown to
preserve the constraints, ii) boundary conditions that result from setting the
ingoing constraint characteristic fields to zero and iii) boundary conditions
that result from considering the projection of Einstein's equations along the
normal to the boundary surface. While we show that in case i) there are no ill
posed modes, our analysis reveals that, unless the parameters in the
formulation are chosen with care, there exist ill posed constraint violating
modes in the remaining cases.


title: First-Order Transitions in Charged Boson Nebulae

abstract:
  Using the first-order approximating solutions to the
Einstein-Maxwell-Klein-Gordon system of equations for a complex scalar field
minimally coupled to a spherically symmetric spacetime, we study the feedback
of gravity and electric field on the charged scalar source. Within a
perturbative approach, we compute, in the radiation zone, the transition
amplitudes and the coherent source-field regeneration rate.


title: The black holes of topologically massive gravity

abstract:
  We show that an analytical continuation of the Vuorio solution to
three-dimensional topologically massive gravity leads to a two-parameter family
of black hole solutions, which are geodesically complete and causally regular
within a certain parameter range. No observers can remain static in these
spacetimes. We discuss their global structure, and evaluate their mass, angular
momentum, and entropy, which satisfy a slightly modified form of the first law
of thermodynamics.


title: Gravitational collapse of barotropic spherical fluids

abstract:
  The gravitational collapse of spherical, barotropic perfect fluids is
analyzed here. For the first time, the final state of these systems is studied
without resorting to simplifying assumptions - such as self-similarity - using
a new approach based on non-linear o.d.e. techniques, and formation of naked
singularities is shown to occur for solutions such that the mass function is
analytic in a neighborhood of the spacetime singularity.


title:
Fifth force from fifth dimension: a comparison between two different
  approaches

abstract:
  We investigate the dynamics of particles moving in a spacetime augmented by
one extra dimension in the context of the induced matter theory of gravity. We
examine the appearance of a fifth force as an effect caused by the extra
dimension and discuss two different approaches to the fifth force formalism. We
then give two examples of application of both approaches by considering the
case of a Ricci-flat warped-product manifold and a generalized Randall-Sundrum
space.


title: Future complete vacuum spacetimes

abstract:
  In this paper we prove a global existence theorem, in the direction of
cosmological expansion, for sufficiently small perturbations of a family of
spatially compact variants of the $k=-1$ Friedmann--Robertson--Walker vacuum
spacetime. We use a special gauge defined by constant mean curvature slicing
and a spatial harmonic coordinate condition, and develop energy estimates
through the use of the Bel-Robinson energy and its higher order
generalizations. In addition to the smallness condition on the data, we need a
topological constraint on the spatial manifold to exclude the possibility of a
non--trivial moduli space of flat spacetime perturbations, since the latter
could not be controlled by curvature--based energies such as those of
Bel--Robinson type. Our results also demonstrate causal geodesic completeness
of the perturbed spacetimes (in the expanding direction) and establish precise
rates of decay towards the background solution which serves as an attractor
asymptotically.


title: Cosmological Quantum Jump Dynamics II. The Retrodictive Universe

abstract:
  This paper is a continuation of the paper gr-qc/0203045 and is devoted to the
problem of the arrow of time. A deterministic past-directed dynamics is
constructed, which results in the retrodictive universe. A future-directed
dynamics of the latter is indeterministic and reproduces standard probabilistic
quantum dynamics. The arrow of time is inherent in the retrodictive universe as
well as a future-directed increase of informational entropy.


title: Gravitational fields and dark matter

abstract:
  In this paper a hypothesis is considered, in which neutrinos and other weakly
interacting particles play a fundamental role in Universe. In addition the
Newton gravitational constant $G_N$ and the Hubble constant $H$ are interpreted
as parameters, characterizing the neutrinos background of Universe.


title: Conformally Invariant Braneworld and the Cosmological Constant

abstract:
  A six dimensional braneworld scenario based on a model describing the
interaction of gravity, gauge fields and 3+1 branes in a conformally invariant
way is described. The action of the model is defined using a measure of
integration built of degrees of freedom independent of the metric. There is no
need to fine tune any bulk cosmological constant or the tension of the two (in
the scenario described here) parallel branes to obtain zero cosmological
constant, the only solutions are those with zero 4-D cosmological constant. The
two extra dimensions are compactified in a "football" fashion and the branes
lie on the two opposite poles of the compact "football-shaped" sphere.


title: Gravito-magnetic vacuum spacetimes: kinematic restrictions

abstract:
  We show that there are no vacuum solutions with a purely magnetic Weyl tensor
with respect to an observer submitted to kinematic restrictions involving first
order differential scalars. This result generalizes previous ones for the
vorticity-free and shear-free cases. We use a covariant approach which makes
evident that only the Bianchi identities are used and, consequently, the
results are also valid for non vacuum solutions with vanishing Cotton tensor.


title:
Nematic Structure of Space-Time and its Topological Defects in 5D
  Kaluza-Klein Theory

abstract:
  We show, that classical Kaluza-Klein theory possesses hidden nematic
dynamics. It appears as a consequence of 1+4-decomposition procedure, involving
4D observers 1-form \lambda. After extracting of boundary terms the, so called,
"effective matter" part of 5D geometrical action becomes proportional to square
of anholonomicity 3-form \lambda\wedge d\lambda. It can be interpreted as twist
nematic elastic energy, responsible for elastic reaction of 5D space-time on
presence of anholonomic 4D submanifold, defined by \lambda. We derive both 5D
covariant and 1+4 forms of 5D nematic equilibrium equations, consider simple
examples and discuss some 4D physical aspects of generic 5D nematic topological
defects.


title: Asymptotic expansions close to the singularity in Gowdy spacetimes

abstract:
  We consider Gowdy spacetimes under the assumption that the spatial
hypersurfaces are diffeomorphic to the torus. The relevant equations are then
wave map equations with the hyperbolic space as a target. In an article by
Grubisic and Moncrief, a formal expansion of solutions in the direction toward
the singularity was proposed. Later, Kichenassamy and Rendall constructed a
family of real analytic solutions with the maximum number of free functions and
the desired asymptotics at the singularity. The condition of real analyticity
was subsequently removed by Rendall. In an article by the author, it was shown
that one can put a condition on initial data that leads to asymptotic
expansions. In this article, we show the following. By fixing a point in
hyperbolic space, we can consider the hyperbolic distance from this point to
the solution at a given spacetime point. If we fix a spatial point for the
solution, it is enough to put conditions on the rate at which the hyperbolic
distance tends to infinity as time tends to the singularity in order to
conclude that there are smooth expansions in a neighbourhood of the given
spatial point.


title:
Quasinormal behavior of the D-dimensional Schwarzshild black hole and
  higher order WKB approach

abstract:
  We study characteristic (quasinormal) modes of a $D$-dimensional Schwarzshild
black hole. It proves out that the real parts of the complex quasinormal modes,
representing the real oscillation frequencies, are proportional to the product
of the number of dimensions and inverse horizon radius $\sim D r_{0}^{-1}$. The
asymptotic formula for large multipole number $l$ and arbitrary $D$ is derived.
In addition the WKB formula for computing QN modes, developed to the 3rd order
beyond the eikonal approximation, is extended to the 6th order here. This gives
us an accurate and economic way to compute quasinormal frequencies.


title: Neutrino-Antineutrino Asymmetry around Rotating Black Holes

abstract:
  Propagation of fermion in curved space-time generates gravitational
interaction due to the coupling between spin of the fermion and space-time
curvature. This gravitational interaction, which is an axial-vector appears as
CPT violating term in the Lagrangian. It is seen that this space-time
interaction can generate neutrino asymmetry in Universe. If the back-ground
metric is spherically asymmetric, say, of a rotating black hole, this
interaction is non-zero, thus the net difference to the number density of the
neutrino and anti-neutrino is nonzero.


title:
Perturbative evolution of particle orbits around Kerr black holes: time
  domain calculation

abstract:
  Treating the Teukolsky perturbation equation numerically as a 2+1 PDE and
smearing the singularities in the particle source term by the use of narrow
Gaussian distributions, we have been able to reproduce earlier results for
equatorial circular orbits that were computed using the frequency domain
formalism. A time domain prescription for a more general evolution of nearly
geodesic orbits under the effects of radiation reaction is presented. This
approach can be useful when tackling the more realistic problem of a
stellar-mass black hole moving on a generic orbit around a supermassive black
hole under the influence of radiation reaction forces.


title: Light-Like Boost of the Kerr Gravitational Field

abstract:
  We describe light-like boosts of the Kerr gravitational field transverse and
parallel to the symmetry axis. In the transverse case the boosted field is that
of an impulsive gravitational wave having a line singularity displaced relative
to its position if the rotation of the source were removed. The parallel boost
is insensitive to the rotation of the source. The literature contains a number
of diverse results for light-like boosts of the Kerr gravitational field. Our
conclusions confirm the correctness of the limits calculated by Balasin and
Nachbagauer [Class.and Quantum Grav.13(1996),731]. To avoid any ambiguity our
approach is centered on evaluating the light-like boost of the Riemann tensor
for the Kerr space-time with the metric playing a secondary role.


title: Tidal effects cannot be absent in a vacuum

abstract:
  It is shown that there are no vacuum space-times (with or without
cosmological constant) for which the Weyl-tensor is purely gravito-magnetic
with respect to a congruence of freely falling observers.


title: Linear and Nonlinear Dynamics of Relativistic Tori

abstract:
  I present results of two-dimensional general relativistic hydrodynamical
simulations of constant specific angular momentum tori orbiting around a
Schwarzschild black hole. After introducing axisymmetric perturbations, these
objects either become unstable to the runaway instability or respond with
regular oscillations. The latter, in particular, are responsible for
quasi-periodic bursts of accretion onto the black hole as well as for the
emission of intense gravitational radiation, with signal-to-noise ratios at the
detector which are comparable or even larger than the typical ones expected in
stellar-core collapse.


title:
Gravitational Waves from Sub-lunar Mass Primordial Black Hole Binaries -
  A New Probe of Extradimensions

abstract:
  In many braneworld models, gravity is largely modified at the electro-weak
scale ~ 1TeV. In such models, primordial black holes (PBHs) with lunar mass M ~
10^{-7}M_sun might have been produced when the temperature of the universe was
at ~ 1TeV. If a significant fraction of the dark halo of our galaxy consists of
these lunar mass PBHs, a huge number of BH binaries will exist in our
neighborhood. Third generation detectors such as EURO can detect gravitational
waves from these binaries, and can also determine their chirp mass. With a new
detector designed to be sensitive at high frequency bands greater than 1 kHz,
the existence of extradimensions could be confirmed.


title: Can wormholes have negative temperatures?

abstract:
  We study (3+1) Morris-Thorne wormhole to investigate its higher dimensional
embedding structures and thermodynamic properties. It is shown that the
wormhole is embedded in (5+2) global embedding Minkowski space. This embedding
enables us to construct the wormhole entropy and Hawking temperature by
exploiting Unruh effects. We also propose a possibility of negative temperature
originated from exotic matter distribution of the wormhole.


title:
A New Approach to Quantising Space-Time: I. Quantising on a General
  Category

abstract:
  A new approach is suggested to the problem of quantising causal sets, or
topologies, or other such models for space-time (or space). The starting point
is the observation that entities of this type can be regarded as objects in a
category whose arrows are structure-preserving maps. This motivates
investigating the general problem of quantising a system whose `configuration
space' (or history-theory analogue) can be regarded as the set of objects in a
category. In this first of a series of papers, we study this question in
general and develop a scheme based on constructing an analogue of the group
that is used in the canonical quantisation of a system whose configuration
space is a manifold $Q\simeq G/H$ where G and H are Lie groups. In particular,
we choose as the analogue of G the monoid of `arrow fields' on the category.
Physically, this means that an arrow between two objects in the category is
viewed as some sort of analogue of momentum. After finding the `category
quantisation monoid', we show how suitable representations can be constructed
using a bundle of Hilbert spaces over the set of objects.


title: Generalized Uncertainty Principle and Quantum Electrodynamics

abstract:
  In the present work the role that a generalized uncertainty principle could
play in the quantization of the electromagnetic field is analyzed. It will be
shown that we may speak of a Fock space, a result that implies that the concept
of photon is properly defined. Nevertheless, in this new context the creation
and annihilation operators become a function of the new term that modifies the
Heisenberg algebra, and hence the Hamiltonian is not anymore diagonal in the
occupation number representation. Additionally, we show the changes that the
energy expectation value suffers as result of the presence of an extra term in
the uncertainty principle. The existence of a deformed dispersion relation is
also proved.


title: On a wave map equation arising in general relativity

abstract:
  This paper has been withdrawn by the author. The paper has been accepted for
publication in Communications on Pure and Applied Mathematics.


title: A scalar hyperbolic equation with GR-type non-linearity

abstract:
  We study a scalar hyperbolic partial differential equation with non-linear
terms similar to those of the equations of general relativity. The equation has
a number of non-trivial analytical solutions whose existence rely on a delicate
balance between linear and non-linear terms. We formulate two classes of
second-order accurate central-difference schemes, CFLN and MOL, for numerical
integration of this equation. Solutions produced by the schemes converge to
exact solutions at any fixed time $t$ when numerical resolution is increased.
However, in certain cases integration becomes asymptotically unstable when $t$
is increased and resolution is kept fixed. This behavior is caused by subtle
changes in the balance between linear and non-linear terms when the equation is
discretized. Changes in the balance occur without violating second-order
accuracy of discretization. We thus demonstrate that a second-order accuracy
and convergence at finite $t$ do not guarantee a correct asymptotic behavior
and long-term numerical stability.
  Accuracy and stability of integration are greatly improved by an exponential
transformation of the unknown variable.


title:
Existence of initial data satisfying the constraints for the spherically
  symmetric Einstein-Vlasov-Maxwell system

abstract:
  Using ODE techniques we prove the existence of large classes of initial data
satisfying the constraints for the spherically symmetric
Einstein-Vlasov-Maxwell system. These include data for which the ratio of total
charge to total mass is arbitrarily large.


title: Exponential stretch-rotation (ESR) formulation of general relativity

abstract:
  We study a tensorial exponential transformation of a three-dimensional metric
of space-like hypersurfaces embedded in a four-dimensional space-time,
$\gamma_{ij} = e^{\epsilon_{ikm}\theta_m} e^{\phi_k}
e^{-\epsilon_{jkn}\theta_n}$, where $\phi_k$ are logarithms of the eigenvalues
of $\gamma_{ij}$, $\theta_k$ are rotation angles, and $\epsilon_{ijk}$ is a
fully anti-symmetric symbol. Evolution part of Einstein's equations, formulated
in terms of $\phi_k$ and $\theta_k$, describes time evolution of the metric at
every point of a hyper-surface as a continuous stretch and rotation of a local
coordinate system in a tangential space. The exponential stretch-rotation (ESR)
transformation generalizes particular exponential transformations used
previously in cases of spatial symmetry. The ESR 3+1 formulation of Einstein's
equations may have certain advantages for long-term stable integration of these
equations.


title:
Squeezed-input, optical-spring, signal-recycled gravitational-wave
  detectors

abstract:
  We theoretically analyze the quantum noise of signal-recycled laser
interferometric gravitational-wave detectors with additional input and output
optics, namely frequency-dependent squeezing of the vacuum entering the dark
port and frequency-dependent homodyne detection. We combine the work of
Buonanno and Chen on the quantum noise of signal-recycled interferometers with
ordinary input-output optics, and the work of Kimble el al. on
frequency-dependent input-output optics with conventional interferometers.
Analytical formulas for the optimal input and output frequency dependencies are
obtained. It is shown that injecting squeezed light with the optimal
frequency-dependent squeezing angle into the dark port yields an improvement on
the noise spectral density by a factor of exp(-2r) (in power) over the entire
squeezing bandwidth, where r is the squeezing parameter. It is further shown
that frequency-dependent (variational) homodyne read-out leads to an additional
increase in sensitivity which is significant in the wings of the doubly
resonant structure. The optimal variational input squeezing in case of an
ordinary output homodyne detection is shown to be realizable by applying two
optical filters on a frequency-independent squeezed vacuum. Throughout this
paper, we take as example the signal-recycled topology currently being
completed at the GEO600 site. However, theoretical results obtained here are
also applicable to the proposed topology of Advanced LIGO.


title: Non-Linear Relativity in Position Space

abstract:
  We propose two methods for obtaining the dual of non-linear relativity as
previously formulated in momentum space. In the first we allow for the (dual)
position space to acquire a non-linear representation of the Lorentz group
independently of the chosen representation in momentum space. This requires a
non-linear definition for the invariant contraction between momentum and
position spaces. The second approach, instead, respects the linearity of the
invariant contraction. This fully fixes the dual of momentum space and dictates
a set of energy-dependent space-time Lorentz transformations. We discuss a
variety of physical implications that would distinguish these two strategies.
We also show how they point to two rather distinct formulations of theories of
gravity with an invariant energy and/or length scale.


title: Brief comments on Jackiw-Teitelboim gravity coupled to Liouville theory

abstract:
  Jackiw-Teitelboim gravity with non-vanishing cosmological constant coupled to
Liouville theory is considered as a non-critical string on $d$ dimensional flat
spacetime. It is discussed how the presence of cosmological constant yields
additional constraints on the parameter space of the theory, even when the
conformal anomaly is independent of the cosmological constant. Such constraints
agree with the necessary conditions for the tachyon field to be a primary
--prelogarithmic-- operator of the worldsheet conformal field theory. Thus, the
linearized tachyon field equation allows to impose the diagonal condition for
the interaction term. We analyze the neutralization of the Liouville mode
induced by the coupling to the Jackiw-Teitelboim Lagrangian. The free field
prescription leads to obtain explicit expressions for three-point correlation
functions for the case of vanishing cosmological constant in terms of a product
of Shapiro-Virasoro integrals. This is a consequence of the mentioned
neutralization effect.


title:
A hyperbolic slicing condition adapted to Killing fields and densitized
  lapses

abstract:
  We study the properties of a modified version of the Bona-Masso family of
hyperbolic slicing conditions. This modified slicing condition has two very
important features: In the first place, it guarantees that if a spacetime is
static or stationary, and one starts the evolution in a coordinate system in
which the metric coefficients are already time independent, then they will
remain time independent during the subsequent evolution, {\em i.e.} the lapse
will not evolve and will therefore not drive the time lines away from the
Killing direction. Second, the modified condition is naturally adapted to the
use of a densitized lapse as a fundamental variable, which in turn makes it a
good candidate for a dynamic slicing condition that can be used in conjunction
with some recently proposed hyperbolic reformulations of the Einstein evolution
equations.


title: Conflict between anthropic reasoning and observation

abstract:
  Anthropic reasoning often begins with the premise that we should expect to
find ourselves typical among all intelligent observers. However, in the
infinite universe predicted by inflation, there are some civilizations which
have spread across their galaxies and contain huge numbers of individuals.
Unless the proportion of such large civilizations is unreasonably tiny, most
observers belong to them. Thus anthropic reasoning predicts that we should find
ourselves in such a large civilization, while in fact we do not. There must be
an important flaw in our understanding of the structure of the universe and the
range of development of civilizations, or in the process of anthropic
reasoning.


title: Fuchsian methods and spacetime singularities

abstract:
  Fuchsian methods and their applications to the study of the structure of
spacetime singularities are surveyed. The existence question for spacetimes
with compact Cauchy horizons is discussed. After some basic facts concerning
Fuchsian equations have been recalled, various ways in which these equations
have been applied in general relativity are described. Possible future
applications are indicated.


title: Loop Quantum Cosmology, Boundary Proposals, and Inflation

abstract:
  Loop quantum cosmology of the closed isotropic model is studied with a
special emphasis on a comparison with traditional results obtained in the
Wheeler-DeWitt approach. This includes the relation of the dynamical initial
conditions with boundary conditions such as the no-boundary or the tunneling
proposal and a discussion of inflation from quantum cosmology.


title: Homogeneous Loop Quantum Cosmology

abstract:
  Loop quantum cosmological methods are extended to homogeneous models in
diagonalized form. It is shown that the diagonalization leads to a
simplification of the volume operator such that its spectrum can be determined
explicitly. This allows the calculation of composite operators, most
importantly the Hamiltonian constraint. As an application the dynamics of the
Bianchi I model is studied and it is shown that its loop quantization is free
of singularities.


title: Irreducibility of the Ashtekar-Isham-Lewandowski representation

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-Isham-Lewandowski
representation, has been constructed. Recently, several uniqueness results for
this representation have been worked out. In the present article, we contribute
to these efforts by showing that the AIL-representation is irreducible,
provided it is viewed as the representation of a certain C*-algebra which is
very similar to the Weyl algebra used in the canonical quantization of free
quantum field theories.


title:
Massive complex scalar field in the Kerr-Sen geometry: Exact solution of
  wave equation and Hawking radiation

abstract:
  The separated radial part of a massive complex scalar wave equation in the
Kerr- Sen geometry is shown to satisfy the generalized spheroidal wave equation
which is, in fact, a confluent Heun equation up to a multiplier. The Hawking
evaporation of scalar particles in the Kerr-Sen black hole background is
investigated by the Damour-Ruffini-Sannan method. It is shown that quantum
thermal effect of the Kerr-Sen black hole has the same character as that of the
Kerr-Newman black hole.


title: Entropy of a Kerr-de Sitter black hole due to arbitrary spin fields

abstract:
  The Newman-Penrose formalism is used to derive the Teukolsky master equations
controlling massless scalar, neutrino, electromagnetic, gravitino, and
gravitational field perturbations of the Kerr-de Sitter spacetime. Then the
quantum entropy of a non-extreme Kerr-de Sitter black hole due to arbitrary
spin fields is calculated by the improved thin-layer brick wall model. It is
shown that the subleading order contribution to the entropy is dependent on the
square of the spins of particles and that of the specific angular momentum of
black holes as well as the cosmological constant. The logarithmic correction of
the spins of particles to the entropy relies on the rotation of the black hole
and the effect of the cosmological constant.


title: Anisotropic Stars II : Stability

abstract:
  We investigate the stability of self-gravitating spherically symmetric
anisotropic spheres under radial perturbations. We consider both the Newtonian
and the full general-relativistic perturbation treatment. In the
general-relativistic case, we extend the variational formalism for spheres with
isotropic pressure developed by Chandrasekhar. We find that, in general, when
the tangential pressure is greater than the radial pressure, the stability of
the anisotropic sphere is enhanced when compared to isotropic configurations.
In particular, anisotropic spheres are found to be stable for smaller values of
the adiabatic index $\gamma$.


title: Dirac Quasi-Normal Modes in Schwarzschild Black Hole Spacetimes

abstract:
  We evaluate both the massless and the massive Dirac quasi-normal mode
frequencies in the Schwarzschild black hole spacetime using the WKB
approximation. For the massless case, we find that, similar to those for the
integral spin fields, the real parts of the frequencies increase with the
angular momentum number $\kappa$, while the imaginary parts or the dampings
increase with the mode number $n$ for fixed $\kappa$. For the massive case, the
oscillation frequencies increase with the mass $m$ of the field, while the
dampings decrease. Fields with higher masses will therefore decay more slowly.


title: Open static Chaplygin universe

abstract: This paper is withdrawn by the authors


title: Possible effects of spacetime non-metricity on neutrino oscillations

abstract:
  The contribution of gravitational neutrino oscillations to the solar neutrino
problem is studied by constructing the Dirac Hamiltonian and calculating the
corresponding dynamical phase in the vicinity of the Sun in a non-Riemann
background Kerr space-time with torsion and non-metricity. We show that certain
components of non-metricity and the axial as well as non-axial components of
torsion may contribute to neutrino oscillations. We also note that the rotation
of the Sun may cause a suppression of transitions among neutrinos. However, the
observed solar neutrino deficit could not be explained by any of these effects
because they are of the order of Planck scales.


title:
Variation of the speed of light due to non-minimal coupling between
  electromagnetism and gravity

abstract:
  We consider an Einstein-Maxwell action modified by the addition of three
terms coupling the electromagnetic strength to the curvature tensor. The
corresponding generalized Maxwell equations imply a variation of the speed of
light in a vacuum. We determine this variation in Friedmann-Robertson-Walker
spacetimes. We show that light propagates at a speed greater than $c$ when a
simple condition is satisfied.


title: Surface terms and the Gauss-Bonnet Hamiltonian

abstract:
  We derive the gravitational Hamiltonian starting from the Gauss-Bonnet
action, keeping track of all surface terms. This is done using the language of
orthonormal frames and forms to keep things as tidy as possible. The surface
terms in the Hamiltonian give a remarkably simple expression for the total
energy of a spacetime. This expression is consistent with energy expressions
found in hep-th/0212292. However, we can apply our results whatever the choice
of background and whatever the symmetries of the spacetime.


title:
Epicyclic orbital oscillations in Newton's and Einstein's gravity from
  the geodesic deviation equation

abstract:
  In a recent paper Abramowicz and Klu{\'z}niak have discussed the problem of
epicyclic oscillations in Newton's and Einstein's dynamics and have shown that
Newton's dynamics in a properly curved three-dimensional space is identical to
test-body dynamics in the three-dimensional optical geometry of Schwarzschild
space-time. One of the main results of this paper was the proof that different
behaviour of radial epicyclic frequency and Keplerian frequency in Newtonian
and General Relativistic regimes had purely geometric origin contrary to claims
that nonlinearity of Einstein's theory was responsible for this effect.
  In this paper we obtain the same result from another perspective: by
representing these two distinct problems (Newtonian and Einstein's test body
motion in central gravitational field) in a uniform way -- as a geodesic
motion. The solution of geodesic deviation equation reproduces the well known
results concerning epicyclic frequencies and clearly demonstrates geometric
origin of the difference between Newtonian and Einstein's problems.


title: Relic gravitational waves from colliding bubbles and cosmic turbulence

abstract:
  A stochastic background of gravitational waves can be generated during a
cosmological first order phase transition, at least by two distinct mechanisms:
collisions of true vacuum bubbles and turbulence in the cosmic fluid. I compare
these two contributions, analyzing their relative importance for a generic
phase transition. In particular, a first order electroweak phase transition is
expected to generate a gravitational wave signal peaked at a frequency which
today falls just within the band of the planned space interferometer LISA. For
this transition, I find constraints for the relevant parameters in order to
produce a signal within the reach of the sensitivity of LISA. The result is
that the transition must be strongly first order, alpha > 0.2. In this regime
the signal coming from turbulence dominates over that from colliding bubbles.


title: TASI Lectures on Gravitational Waves from the Early Universe

abstract:
  These lectures discuss how the direct detection of gravitational waves can be
used to probe the very early Universe. We review the main cosmological
mechanisms which could have produced relic gravitational waves, and compare
theoretical predictions with capabilities and time scales of current and
upcoming experiments.


title:
Hyperbolicity of the Kidder-Scheel-Teukolsky formulation of Einstein's
  equations coupled to a modified Bona-Masso slicing condition

abstract:
  We show that the Kidder-Scheel-Teukolsky family of hyperbolic formulations of
the 3+1 evolution equations of general relativity remains hyperbolic when
coupled to a recently proposed modified version of the Bona-Masso slicing
condition.


title: The Teleparallel Lagrangian and Hamilton-Jacobi Formalism

abstract:
  We analyze the Teleparallel Equivalent of General Relativity (TEGR) from the
point of view of Hamilton-Jacobi approach for singular systems


title: On the Lorentz Invariant Gravitation Field Theory

abstract:
  The theory of gravitation field within the special theory of relativity is
analyzed.


title:
Time and Matter in the Interaction between Gravity and Quantum Fluids:
  Are there Macroscopic Quantum Transducers between Gravitational and
  Electromagnetic waves?

abstract:
  Measurements of the tunneling time are briefly reviewed. Next, time and
matter in general relativity and quantum mechanics is examined. In particular,
the question arises: How does gravitational radiation interact with a coherent
quantum many-body system (a ``quantum fluid'')? A minimal coupling rule for the
coupling of the electron spin to curved spacetime in general relativity implies
the possibility of a coupling between electromagnetic (EM) and gravitational
(GR) radiation mediated by a quantum Hall fluid. This suggests that quantum
transducers between these two kinds of radiation fields might exist. We report
here on a first attempt at a Hertz-type experiment, in which a high-$\rm{T_c}$
superconductor (YBCO) was the material used as a quantum transducer to convert
EM into GR microwaves, and a second piece of YBCO in a separate apparatus was
used to back-convert GR into EM microwaves. An upper limit on the conversion
efficiency of YBCO was measured to be $1.6\times10^{-5}$.


title: Gauge Invariant Variables in Two-Parameter Nonlinear Perturbations

abstract:
  The procedure to find gauge invariant variables for two-parameter nonlinear
perturbations in general relativity is considered. For each order metric
perturbation, we define the variable which is defined by the appropriate
combination with lower order metric perturbations. Under the gauge
transformation, this variable is transformed in the manner similar to the gauge
transformation of the linear order metric perturbation. We confirm this up to
third order. This implies that gauge invariant variables for higher order
metric perturbations can be found by using a procedure similar to that for
linear order metric perturbations. We also derive gauge invariant combinations
for the perturbation of an arbitrary physical variable, other than the
spacetime metric, up to third order.

categories: gr-qc astro-ph hep-ph hep-th math-ph math.MP


title: Radiative fields in spacetimes with Minkowski and de Sitter asymptotics

abstract:
  The classical Bondi-Penrose approach to the gravitational radiation theory in
asymptotically flat spacetimes is recalled and recent advances in the proofs of
the existence of such spacetimes are briefly reviewed. We then mention the
unique role of the boost-rotation symmetric spacetimes, representing uniformly
accelerated objects, as the only explicit radiative solutions known which are
asymptotically flat; they are used as test beds in numerical relativity and
approximation methods.
  The main part of the review is devoted to the examples of radiative fields in
the vacuum spacetimes with positive cosmological constant. Type N solutions are
analyzed by using the equation of geodesic deviation. Both these and
Robinson-Trautman solutions of type II are shown to approach de Sitter universe
asymptotically. Recent work on the the radiative fields due to uniformly
accelerated charges in de Sitter spacetime ("cosmological Born's solutions") is
reviewed and the properties of these fields are discussed with a perspective to
characterize general features of radiative fields near a de Sitter-like
infinity.


title:
Effect of a non null pressure on the evolution of perturbations in the
  matter dominated epoch

abstract:
  We analyze the effect of pressure on the evolution of perturbations of an
Einstein-de Sitter Universe in the matter dominated epoch assuming an ideal gas
equation of state. For the sake of simplicity the temperature is considered
uniform. The goal of the paper is to examine the validity of the linear
approximation. With this purpose the evolution equations are developed
including quadratic terms in the derivatives of the metric perturbations and
using coordinate conditions that, in the linear case, reduce to the
longitudinal gauge. We obtain the general solution, in the coordinate space, of
the evolution equation for the scalar mode, and, in the case of spherical
symmetry, we express this solution in terms of unidimensional integrals of the
initial conditions: the initial values of the Newtonian potential and its first
time derivative. We find that the contribution of the initial first time
derivative, which has been systematically forgotten, allows to form
inhomogeneities similar to a cluster of galaxies starting with very small
density contrast. Finally, we obtain the first non linear correction to the
linearized solution due to the quadratic terms in the evolution equations. Here
we find that a non null pressure plays a crucial role in constraining the non
linear corrections. It is shown, by means of examples, that reasonable thermal
velocities at the present epoch (non bigger than $10^{-6}$) make the ratio
between the first non linear correction and the linear solution of the order of
$10^{-2}$ for a galaxy cluster inhomogeneity.


title: Linearized stability of charged thin-shell wormholes

abstract:
  The linearized stability of charged thin shell wormholes under spherically
symmetric perturbations is analized. It is shown that the presence of a large
value of charge provides stabilization to the system, in the sense that the
constrains onto the equation of state are less severe than for non-charged
wormholes.


title: An Investigation of the Tomimatsu-Sato Spacetime

abstract:
  We investigate the structure of the $\delta=2$ Tomimatsu-Sato spacetime. We
show that this spacetime has degenerate horizons with two components, in
contrast to the general belief that the Tomimatsu-Sato solutions with even
$\delta$ do not have horizons.


title: WKB analysis of the Regge-Wheeler equation down in the frequency plane

abstract:
  The Regge-Wheeler equation for black-hole gravitational waves is analyzed for
large negative imaginary frequencies, leading to a calculation of the cut
strength for waves outgoing to infinity. In the--limited--region of overlap,
the results agree well with numerical findings [Class. Quantum Grav._20_, L217
(2003)]. Requiring these waves to be outgoing into the horizon as well
subsequently yields an analytic formula for the highly damped Schwarzschild
quasinormal modes,_including_ the leading correction. Just as in the WKB
quantization of, e.g., the harmonic oscillator, solutions in different regions
of space have to be joined through a connection formula, valid near the
boundary between them where WKB breaks down. For the oscillator, this boundary
is given by the classical turning points; fascinatingly, the connection here
involves an expansion around the black-hole singularity r=0.


title: Anisotropy and inflation in Bianchi I brane worlds

abstract:
  After a more general assumption on the influence of the bulk on the brane, we
extend some conclusions by Maartens et al. and Santos et al. on the asymptotic
behavior of Bianchi I brane worlds. As a consequence of the nonlocal
anisotropic stresses induced by the bulk, in most of our models, the brane does
not isotropize and the nonlocal energy does not vanish in the limit in which
the mean radius goes to infinity. We have also found the intriguing possibility
that the inflation due to the cosmological constant might be prevented by the
interaction with the bulk. We show that the problem for the mean radius can be
completely solved in our models, which include as particular cases those in the
references above.


title: Oskar Klein, the sixth dimension and the strength of a magnetic pole

abstract:
  This work extends to six dimensions the idea first proposed by Klein
regarding a closed space in the context of a fifth dimension and its link to
quantum theory. The main result is a formula that expresses the value of the
characteristic length of the sixth dimension in terms of the strength of a
magnetic monopole $g$. It is shown that in the case of Dirac's monopole, the
ratio of the characteristic lengths of the fifth and sixth dimension
corresponds to twice the fine structure constant $\alpha$. Possible
consequences of the idea are discussed.


title:
On irreducible partials of Ricci tensor traceless part in finite
  space-time region in GR

abstract:
  Riemann tensor irreducible part $E_{iklm} = {1/2} (g_{il}S_{km} +
g_{km}S_{il} - g_{im}S_{kl} - g_{kl}S_{im})$ constructed from metric tensor
$g_{ik}$ and traceless part of Ricci tensor $S_{ik} = R_{ik} - {1/4} g_{ik} R$
is expanded into bilinear combinations of bivectorial fields being
eigenfunctions of $E$. Field equations for the bivectors induced by Bianchi
identities are studied and it is shown that in general case it will be
3-parametric local symmetry group Yang-Mills field.


title: Tracking Black Holes in Numerical Relativity

abstract:
  This work addresses and solves the problem of generically tracking black hole
event horizons in computational simulation of black hole interactions.
Solutions of the hyperbolic eikonal equation, solved on a curved spacetime
manifold containing black hole sources, are employed in development of a robust
tracking method capable of continuously monitoring arbitrary changes of
topology in the event horizon, as well as arbitrary numbers of gravitational
sources. The method makes use of continuous families of level set viscosity
solutions of the eikonal equation with identification of the black hole event
horizon obtained by the signature feature of discontinuity formation in the
eikonal's solution. The method is employed in the analysis of the event horizon
for the asymmetric merger in a binary black hole system. In this first such
three dimensional analysis, we establish both qualitative and quantitative
physics for the asymmetric collision; including: 1. Bounds on the topology of
the throat connecting the holes following merger, 2. Time of merger, and 3.
Continuous accounting for the surface of section areas of the black hole
sources.


title:
Conceptual tensions between quantum mechanics and general relativity:
  Are there experimental consequences?

abstract:
  One of the conceptual tensions between quantum mechanics (QM) and general
relativity (GR) arises from the clash between the spatial nonseparability of
entangled states in QM, and the complete spatial separability of all physical
systems in GR, i.e., between the nonlocality implied by the superposition
principle, and the locality implied by the equivalence principle. Possible
experimental consequences of this conceptual tension will be discussed for
macroscopically entangled, coherent quantum fluids, such as superconductors,
superfluids, atomic Bose-Einstein condensates, and quantum Hall fluids,
interacting with tidal and gravitational radiation fields. A minimal-coupling
rule, which arises from the electron spin coupled to curved spacetime, leads to
an interaction between electromagnetic (EM) and gravitational (GR) radiation
fields mediated by a quantum Hall fluid. This suggests the possibility of a
quantum transducer action, in which EM waves are convertible to GR waves, and
vice versa.


title: Comments on tails in Schwarzschild spacetimes

abstract:
  We performed a careful numerical analysis of the late tail behaviour of waves
propagating in the Schwarzschild spacetime. Specifically the scalar monopole,
the electromagnetic dipole and the gravitational axial quadrupole waves have
been investigated. The obtained results agree with a falloff $1/t^{2l+3}$ for
the general initial data and $1/t^{2l+4}$ for the initially static data.


title:
Collision of Electromagnetic Shock Waves Coupled with Axion Waves: An
  Example

abstract:
  We present an exact solution that describes collision of electromagnetic
shock waves coupled with axion plane waves. The axion has a rather special
coupling to the cross polarization term of the metric. The initial data on the
null surfaces is well-defined and collision results in a singularity free
interaction region. Our solution is a generalization of the Bell-Szekeres
solution in the presence of an axion field.


title:
Irreversible Processes in a Universe modelled as a mixture of a
  Chaplygin gas and radiation

abstract:
  The evolution of a Universe modelled as a mixture of a Chaplygin gas and
radiation is determined by taking into account irreversible processes. This
mixture could interpolate periods of a radiation dominated, a matter dominated
and a cosmological constant dominated Universe. The results of a Universe
modelled by this mixture are compared with the results of a mixture whose
constituents are radiation and quintessence. Among other results it is shown
that: (a) for both models there exists a period of a past deceleration with a
present acceleration; (b) the slope of the acceleration of the Universe
modelled as a mixture of a Chaplygin gas with radiation is more pronounced than
that modelled as a mixture of quintessence and radiation; (c) the energy
density of the Chaplygin gas tends to a constant value at earlier times than
the energy density of quintessence does; (d) the energy density of radiation
for both mixtures coincide and decay more rapidly than the energy densities of
the Chaplygin gas and of quintessence.


title:
First-order quasilinear canonical representation of the characteristic
  formulation of the Einstein equations

abstract:
  We prescribe a choice of 18 variables in all that casts the equations of the
fully nonlinear characteristic formulation of general relativity in
first--order quasi-linear canonical form. At the analytical level, a
formulation of this type allows us to make concrete statements about existence
of solutions. In addition, it offers concrete advantages for numerical
applications as it now becomes possible to incorporate advanced numerical
techniques for first order systems, which had thus far not been applicable to
the characteristic problem of the Einstein equations, as well as in providing a
framework for a unified treatment of the vacuum and matter problems. This is of
relevance to the accurate simulation of gravitational waves emitted in
astrophysical scenarios such as stellar core collapse.


title:
A gravitational shock wave generated by a beam of null matter in
  quadratic gravity

abstract:
  In the present work we approximate an ultrarelativistic jet by a homogeneous
beam of null matter with finite width. Then, we study the influence of this
beam over the space-time metric in the framework of higher-derivative gravity.
We find an exact shock wave solution of the quadratic gravity field equations
and compare it with the solution to Einstein's gravity. We show that the effect
of higher-curvature gravity becomes negligible at large distances from the beam
axis. We also observe that only the Ricci-squared term contribute to modify the
Einstein's gravity prediction. Furthermore, we note that this higher-curvature
term contribute to regularize the discontinuities associated to the solution to
Einstein's general relativity.


title: A Quantum Weak Energy Inequality for Spin-One Fields in Curved Spacetime

abstract:
  Quantum weak energy inequalities (QWEI) provide state-independent lower
bounds on averages of the renormalised energy density of a quantum field. We
derive QWEIs for the electromagnetic and massive spin-one fields in globally
hyperbolic spacetimes whose Cauchy surfaces are compact and have trivial first
homology group. These inequalities provide lower bounds on weighted averages of
the renormalized energy density as ``measured'' along an arbitrary timelike
trajectory, and are valid for arbitrary Hadamard states of the spin-one fields.
The QWEI bound takes a particularly simple form for averaging along static
trajectories in ultrastatic spacetimes; as specific examples we consider
Minkowski space [in which case the topological restrictions may be dispensed
with] and the static Einstein universe.
  A significant part of the paper is devoted to the definition and properties
of Hadamard states of spin-one fields in curved spacetimes, particularly with
regard to their microlocal behaviour.


title: Classical Electrodynamics in Quasi-Metric Space-Time

abstract:
  The quasi-metric manifold $\cal N$ is equipped with two one-parameter
families of metric tensors ${\bf {\bar g}}_t$ and ${\bf g}_t$, each
parametrized by the global time function $t$. Moreover, in $({\cal N},{\bf
{\bar g}}_t)$ one must define two different electromagnetic field tensor
families corresponding to the active electromagnetic field tensor family ${\bf
{\tilde F}}_t$ and the passive electromagnetic field tensor family ${\bf {\bar
F}}_t$, respectively. The active electromagnetic field tensor family ${\bf
{\tilde F}}_t$ couples to gravity. By construction, the norm of the passive
electromagnetic field tensor family ${\bf {\bar F}}_t$ experiences a secular
decrease, defining a global cosmic attenuation (not noticeable locally) of the
electromagnetic field. Local conservation laws for passive electromagnetism
imply that ${\bf {\bar {\nabla}}}{\cdot} {\bf {\bar F}}_t=0$ in electro-vacuum,
ensuring that photons move on null geodesics of $({\cal N},{\bf {\bar g}}_t)$.
From ${\bf {\bar F}}_t$, one may construct the passive electromagnetic field
tensor family ${\bf F}_t$ in $({\cal N},{\bf g}_t)$ in the same way as ${\bf
g}_t$ is constructed from ${\bf {\bar g}}_t$. This ensures that photons move on
null geodesics of $({\cal N},{\bf g}_t)$ as well. As a simple example, the
(exact) quasi-metric counterpart to the Reissner-Nordstr\"{o}m solution in
General Relativity is calculated. Besides, it is found that a classical charged
test particle electromagnetically bound to a central charge will participate in
the cosmic expansion. But since quantum-mechanical states should be unaffected
by the expansion, this classic calculation is hardly relevant for
quantum-mechanical systems such as atoms, so there is no reason to think that
the cosmic expansion should apply to them. Finally, it is shown that the main
results of geometric optics hold in quasi-metric space-time.


title: Geometry and cosmological perturbations in the bulk inflaton model

abstract:
  We consider a braneworld inflation model driven by the dynamics of a scalar
field living in the 5-dimensional bulk, the so-called ``bulk inflaton model'',
and investigate the geometry in the bulk and large scale cosmological
perturbations on the brane. The bulk gravitational effects on the brane are
described by a projection of the 5-dimensional Weyl tensor, which we denote by
$E_{\mu\nu}$. Focusing on a tachionic potential model, we take a perturbative
approach in the anti-de Sitter (AdS$_5$) background with a single de Sitter
brane. We first formulate the evolution equations for $E_{\mu\nu}$ in the bulk.
Next, applying them to the case of a spatially homogeneous brane, we obtain two
different integral expressions for $E_{\mu\nu}$. One of them reduces to the
expression obtained previously when evaluated on the brane. The other is a new
expression that may be useful for analyzing the bulk geometry. Then we consider
superhorizon scale cosmological perturbations and evaluate the bulk effects
onto the brane. In the limit $H^2\ell^2\ll1$, where $H$ is the Hubble parameter
on the brane and $\ell$ is the bulk curvature radius, we find that the
effective theory on the brane is identical to the 4-dimensional Einstein-scalar
theory with a simple rescaling of the potential even under the presence of
inhomogeneities. % atleast on super-Hubble horizon scales. In particular, it is
found that the anticipated non-trivial bulk effect due to the spatially
anisotropic part of $E_{\mu\nu}$ may appear only at %second order in the low
energy expansion, i.e., at $O(H^4\ell^4)$.


title:
Adaptive Event Horizon Tracking and Critical Phenomena in Binary Black
  Hole Coalescence

abstract:
  This work establishes critical phenomena in the topological transition of
black hole coalescence. We describe and validate a computational front tracking
event horizon solver, developed for generic studies of the black hole
coalescence problem. We then apply this to the Kastor - Traschen axisymmetric
analytic solution of the extremal Maxwell - Einstein black hole merger with
cosmological constant. The surprising result of this computational analysis is
a power law scaling of the minimal throat proportional to time. The minimal
throat connecting the two holes obeys this power law during a short time
immediately at the beginning of merger. We also confirm the behavior
analytically. Thus, at least in one axisymmetric situation a critical
phenomenon exists. We give arguments for a broader universality class than the
restricted requirements of the Kastor - Traschen solution.


title: A Spacetime in Toroidal Coordinates

abstract:
  We present an exact solution of Einstein's field equations in toroidal
coordinates. The solution has three regions: an interior with a string equation
of state; an Israel boundary layer; an exterior with constant isotropic
pressure and constant density, locally isometric to anti-de Sitter spacetime.
The exterior can be a cosmological vacuum with negative cosmological constant.
The size and mass of the toroidal loop depend on the size of the cosmological
constant.


title: On the existence of maximizing curves for the charged-particle action

abstract:
  The classical Avez-Seifert theorem is generalized to the case of the Lorentz
force equation for charged test particles with fixed charge-to-mass ratio.
Given two events x_{0} and x_{1}, with x_{1} in the chronological future of
x_{0}, and a ratio q/m, it is proved that a timelike connecting solution of the
Lorentz force equation exists provided there is no null connecting geodesic and
the spacetime is globally hyperbolic. As a result, the theorem answers
affirmatively to the existence of timelike connecting solutions for the
particular case of Minkowski spacetime. Moreover, it is proved that there is at
least one C^{1} connecting curve that maximizes the functional
I[\gamma]=\int_{\gamma} ds+q/(mc^2) \omega over the set of C^{1}
future-directed non-spacelike connecting curves.


title:
Exploring Large-scale Gravitational Quantization without h-bar in
  Planetary Systems, Galaxies, and the Universe

abstract:
  We explore a theory of large-scale gravitational quantization, using the
general relativistic Hamilton-Jacobi equation to create quantization conditions
via a new scalar wave equation dependent upon the total mass and the total
vector angular momentum only. Instead of h-bar, a local invariant quantity
proportional to the total angular momentum dictates the quantization
conditions. In the Schwarzschild metric the theory predicts eigenstates with
quantized energy per mass and angular momentum per mass. We find excellent
agreement to the orbital spacings of the satellites of the Jovian planets and
to the planet spacings in the Solar System. For galaxies we derive the baryonic
Tully-Fisher relation and the MOND acceleration, so galaxy velocity curves are
explained without requiring 'dark matter'. For the universe, we derive a new
Hubble relation that accounts for the accelerated expansion with a matter
density at about 5% of the critical matter/energy density, with the remainder
being large-scale quantization zero-point energy. A possible laboratory test is
proposed.


title: Path integral measure for first order and metric gravities

abstract:
  The equivalence between the path integrals for first order gravity and the
standard torsion-free, metric gravity in 3+1 dimensions is analyzed. Starting
with the path integral for first order gravity, the correct measure for the
path integral of the metric theory is obtained.


title:
Quasinormal modes for the SdS black hole : an analytical approximation
  scheme

abstract:
  Quasinormal modes for scalar field perturbations of a Schwarzschild-de Sitter
(SdS) black hole are investigated. An analytical approximation is proposed for
the problem. The quasinormal modes are evaluated for this approximate model in
the limit when black hole mass is much smaller than the radius of curvature of
the spacetime. The model mirrors some striking features observed in numerical
studies of time behaviour of scalar perturbations of the SdS black hole. In
particular, it shows the presence of two sets of modes relevant at two
different time scales, proportional to the surface gravities of the black hole
and cosmological horizons respectively. These quasinormal modes are not
complete - another feature observed in numerical studies. Refinements of this
model to yield more accurate quantitative agreement with numerical studies are
discussed. Further investigations of this model are outlined, which would
provide a valuable insight into time behaviour of perturbations in the SdS
spacetime.


title: Brane classical and quantum cosmology from an effective action

abstract:
  Motivated by the Randall-Sundrum brane-world scenario, we discuss the
classical and quantum dynamics of a (d+1)-dimensional boundary wall between a
pair of (d+2)-dimensional topological Schwarzschild-AdS black holes. We assume
there are quite general -- but not completely arbitrary -- matter fields living
on the boundary ``brane universe'' and its geometry is that of an
Friedmann-Lemaitre-Robertson-Walker (FLRW) model. The effective action
governing the model in the mini-superspace approximation is derived. We find
that the presence of black hole horizons in the bulk gives rise to a complex
action for certain classically allowed brane configurations, but that the
imaginary contribution plays no role in the equations of motion. Classical and
instanton brane trajectories are examined in general and for special cases, and
we find a subset of configuration space that is not allowed at the classical or
semi-classical level; these correspond to spacelike branes carrying tachyonic
matter. The Hamiltonization and Dirac quantization of the model is then
performed for the general case; the latter involves the manipulation of the
Hamiltonian constraint before it is transformed into an operator that
annihilates physical state vectors. The ensuing covariant Wheeler-DeWitt
equation is examined at the semi-classical level, and we consider the possible
localization of the brane universe's wavefunction away from the cosmological
singularity. This is easier to achieve for branes with low density and/or
spherical spatial sections.


title: Space--time torsion contribution to quantum interference phases

abstract:
  From the latest experimental readouts in this context an intriguing
discrepancy has been elicited. Indeed, theory and experiment dissent by one per
cent, and though this fact could be a consequence of the mounting of the
experimental device, it might also embody a difference between the way in which
gravity behaves in classical and quantum mechanics. In this work the effects,
upon the interference pattern, of space--time torsion will be analyzed heeding
its coupling with the spin of the neutron beam. It will be proved that, even
with this contribution, there is enough leeway for a further discussion of the
validity of the equivalence principle in nonrelativistic quantum mechanics.


title: Gravitational Wave Detectors: A report from LIGO-land

abstract:
  At the time of this conference, in June 2002, The LIGO Science Collaboration
was getting ready to perform its first Science Run, where data will be taken
with all three LIGO detectors. We describe here the status of the LIGO
detectors as of February 2003, their performance during the ``Engineering Run''
E7 (Dec 28'01-Jan 14'02) and subsequent Science Runs in 2002/3. We also
describe ongoing efforts on data analysis for setting upper limits of different
gravitational wave sources.


title: Classical solutions from quantum regime for barotropic FRW model

abstract:
  The quantization of gravity coupled to barotropic perfect fluid as matter
field and cosmological constant is made and the wave function can be determined
for any $\kappa$ in the FRW minisuperspace model. The meaning of the existence
of the classical solution is discussed in the WKB semiclassical approximation


title: The past attractor in inhomogeneous cosmology

abstract:
  We present a general framework for analyzing spatially inhomogeneous
cosmological dynamics. It employs Hubble-normalized scale-invariant variables
which are defined within the orthonormal frame formalism, and leads to the
formulation of Einstein's field equations with a perfect fluid matter source as
an autonomous system of evolution equations and constraints. This framework
incorporates spatially homogeneous dynamics in a natural way as a special case,
thereby placing earlier work on spatially homogeneous cosmology in a broader
context, and allows us to draw on experience gained in that field using
dynamical systems methods. One of our goals is to provide a precise formulation
of the approach to the spacelike initial singularity in cosmological models,
described heuristically by Belinski\v{\i}, Khalatnikov and Lifshitz.
Specifically, we construct an invariant set which we conjecture forms the local
past attractor for the evolution equations. We anticipate that this new
formulation will provide the basis for proving rigorous theorems concerning the
asymptotic behavior of spatially inhomogeneous cosmological models.


title: Smoothness at null infinity and the structure of initial data

abstract:
  We describe our present understanding of the relations between the behaviour
of asymptotically flat Cauchy data for Einstein's vacuum field equations near
space-like infinity and the asymptotic behaviour of their evolution in time at
null infinity.


title:
Comments on the 2001 run of the EXPLORER/NAUTILUS gravitational wave
  experiment

abstract:
  The recently published analysis of the coincidences between the EXPLORER and
NAUTILUS gravitational wave detectors in the year 2001 (Astone et al. 2002) has
drawn some criticism (Finn 2003). We do not hold with these objections, even if
we agree that no claim can be made with our data. The paper we published
reports data of unprecedented quality and sets a new procedure for the
coincidence search, which can be repeated again by us and by other groups in
order to search for signature of possible signals. About the reported
coincidence excess, we remark that it is not destined to remain an intriguing
observation for long: it will be confirmed or denied soon by interferometers
and bars operating at their expected sensitivity.


title:
Dirac spinor fields in the teleparallel gravity: comment on
  "Metric-affine approach to teleparallel gravity"

abstract:
  We show that the coupling of a Dirac spinor field with the gravitational
field in the teleparallel equivalent of general relativity is consistent. For
an arbitrary SO(3,1) connection there are two possibilities for the coupling of
the spinor field with the gravitational field. The problems of consistency
raised by Y. N. Obukhov and J. G. Pereira in the paper {\it Metric-affine
approach to teleparallel gravity} [gr-qc/0212080] take place only in the
framework of one particular coupling. By adopting an alternative coupling the
consistency problem disappears.


title: Regge calculus from discontinuous metrics

abstract:
  Regge calculus is considered as a particular case of the more general system
where the linklengths of any two neighbouring 4-tetrahedra do not necessarily
coincide on their common face. This system is treated as that one described by
metric discontinuous on the faces. In the superspace of all discontinuous
metrics the Regge calculus metrics form some hypersurface. Quantum theory of
the discontinuous metric system is assumed to be fixed somehow in the form of
quantum measure on (the space of functionals on) the superspace. The problem of
reducing this measure to the Regge hypersurface is addressed. The quantum Regge
calculus measure is defined from a discontinuous metric measure by inserting
the $\delta$-function-like phase factor. The requirement that this reduction
would respect natural physical properties (positivity, well-defined continuum
limit, absence of lattice artefacts) put rather severe restrictions and allows
to define practically uniquely this phase factor.


title: Critical Phenomena in the Einstein-Massless-Dirac System

abstract:
  We investigate the general relativistic collapse of spherically symmetric,
massless spin-1/2 fields at the threshold of black hole formation. A
spherically symmetric system is constructed from two spin-1/2 fields by forming
a spin singlet with no net spin-angular momentum. We study the system
numerically and find strong evidence for a Type II critical solution at the
threshold between dispersal and black hole formation, with an associated mass
scaling exponent $\gamma ~ 0.26$. Although the critical solution is
characterized by a continuously self-similar (CSS) geometry, the matter fields
exhibit discrete self-similarity with an echoing exponent $\Delta ~ 1.34$. We
then adopt a CSS ansatz and reduce the equations of motion to a set of ODEs. We
find a solution of the ODEs that is analytic throughout the solution domain,
and show that it corresponds to the critical solution found via dynamical
evolutions.


title: Perturbed Einstein field equations using Maple

abstract:
  We obtain the perturbed components of affine connection and Ricci tensor
using algebraic computation. Naturally, the perturbed Einstein field equations
for the vacuum can be written. The method can be used to obtain perturbed
equations of the superior order.


title: The Real Scalar Field in Schwarzschild-de Sitter Spacetime

abstract:
  In this paper, the real scalar field equation in Schwarzschild-de Sitter
spacetime is solved numerically with high precision. A method called polynomial
approximation is introduced to derive the relation between the tortoise
coordinate x and the radius r. This method is diﬀerent from the tangent
approximation [1] and leads to more accurate result. The Nariai black hole is
then discussed in details. We find that the wave function is harmonic only near
the horizons as I. Brevik and B. Simonsen [1] found. Howerver the wave function
is not harmonic in the region of the potential peak, with amplitude increasing
instead. Furthermore, we also find that, when cosmological constant decreases,
the potential peak increases, and the maximum wave amplitude increases.


title: A simple theorem to generate exact black hole solutions

abstract:
  Under certain conditions imposed on the energy-momentum tensor, a theorem
that characterizes a two-parameter family of static and spherically symmetric
solutions to Einstein's field equations (black holes), is proved. A discussion
on the asymptotics, regularity, and the energy conditions is provided. Examples
that include the best known exact solutions within these symmetries are
considered. A trivial extension of the theorem includes the cosmological
constant {\it ab-initio}, providing then a three-parameter family of solutions.


title:
The impact of the new Earth gravity models on the measurement of the
  Lense-Thirring effect

abstract:
  In this paper we use, in a preliminary way, the recently released EIGEN2
Earth gravity model, which is based on six months of data of CHAMP only, in
order to reassess the systematic error due to the mismodelling in the even
zonal harmonics of geopotential in the LAGEOS-LAGEOS II Lense-Thirring
experiment involving the nodes of both the LAGEOS satellites and the perigee of
LAGEOS II. The first results from the GGM01C Earth gravity model including the
first GRACE data are very promising.

categories: gr-qc astro-ph physics.geo-ph physics.space-ph


title: Spherically symmetric relativistic stellar structures

abstract:
  We investigate relativistic spherically symmetric static perfect fluid models
in the framework of the theory of dynamical systems. The field equations are
recast into a regular dynamical system on a 3-dimensional compact state space,
thereby avoiding the non-regularity problems associated with the
Tolman-Oppenheimer-Volkoff equation. The global picture of the solution space
thus obtained is used to derive qualitative features and to prove theorems
about mass-radius properties. The perfect fluids we discuss are described by
barotropic equations of state that are asymptotically polytropic at low
pressures and, for certain applications, asymptotically linear at high
pressures. We employ dimensionless variables that are asymptotically homology
invariant in the low pressure regime, and thus we generalize standard work on
Newtonian polytropes to a relativistic setting and to a much larger class of
equations of state. Our dynamical systems framework is particularly suited for
numerical computations, as illustrated by several numerical examples, e.g., the
ideal neutron gas and examples that involve phase transitions.