title: Asymptotic silence of generic cosmological singularities

abstract:
  In this letter we investigate the nature of generic cosmological
singularities using the framework developed by Uggla et al. We do so by
studying the past asymptotic dynamics of general vacuum G2 cosmologies, models
that are expected to capture the singular behavior of generic cosmologies with
no symmetries at all. In particular, our results indicate that asymptotic
silence holds, i.e., that particle horizons along all timelines shrink to zero
for generic solutions. Moreover, we provide evidence that spatial derivatives
become dynamically insignificant along generic timelines, and that the
evolution into the past along such timelines is governed by an asymptotic
dynamical system which is associated with an invariant set -- the silent
boundary. We also identify an attracting subset on the silent boundary that
organizes the oscillatory dynamics of generic timelines in the singular regime.
In addition, we discuss the dynamics associated with recurring spike formation.


title:
Geodesics in a quasispherical spacetime: A case of gravitational
  repulsion

abstract:
  Geodesics are studied in one of the Weyl metrics, referred to as the M--Q
solution. First, arguments are provided, supporting our belief that this
space--time is the more suitable (among the known solutions of the Weyl family)
for discussing the properties of strong quasi--spherical gravitational fields.
Then, the behaviour of geodesics is compared with the spherically symmetric
situation, bringing out the sensitivity of the trajectories to deviations from
spherical symmetry. Particular attention deserves the change of sign in proper
radial acceleration of test particles moving radially along symmetry axis,
close to the $r=2M$ surface, and related to the quadrupole moment of the
source.


title: Loop Quantum Cosmology: Recent Progress

abstract:
  Aspects of the full theory of loop quantum gravity can be studied in a
simpler context by reducing to symmetric models like cosmological ones. This
leads to several applications where loop effects play a significant role when
one is sensitive to the quantum regime. As a consequence, the structure of and
the approach to classical singularities are very different from general
relativity: The quantum theory is free of singularities, and there are new
phenomenological scenarios for the evolution of the very early universe
including inflation. We give an overview of the main effects, focussing on
recent results obtained by several different groups.


title: Time Asymmetry and Chaos in General Relativity

abstract:
  In this work the late-time evolution of Bianchi type $VIII$ models is
discussed. These cosmological models exhibit a chaotic behaviour towards the
initial singularity and our investigations show that towards the future, far
from the initial singularity, these models have a non-chaotic evolution, even
in the case of vacuum and without inflation. These space-time solutions turn
out to exhibit a particular time asymmetry. On the other hand, investigations
of the late-time behaviour of type $VIII$ models by another author have the
result that chaos continues for ever in the far future and that these solutions
have a time symmetric behaviour: this result was obtained using the
approximation methods of Belinski, Khalatnikov and Lifshitz ($BKL$) and we try
to find out a possible reason explaining why the different approaches lead to
distinct outcomes. It will be shown that, at a heuristic level, the $BKL$
method gives a valid approximation of the late-time evolution of type $VIII$
models, agreeing with the result of our investigations.


title: Solar constraints on new couplings between electromagnetism and gravity

abstract:
  The unification of quantum field theory and general relativity is a
fundamental goal of modern physics. In many cases, theoretical efforts to
achieve this goal introduce auxiliary gravitational fields, ones in addition to
the familiar symmetric second-rank tensor potential of general relativity, and
lead to nonmetric theories because of direct couplings between these auxiliary
fields and matter. Here, we consider an example of a metric-affine gauge theory
of gravity in which torsion couples nonminimally to the electromagnetic field.
This coupling causes a phase difference to accumulate between different
polarization states of light as they propagate through the metric-affine
gravitational field. Solar spectropolarimetric observations are reported and
used to set strong constraints on the relevant coupling constant k: k^2 < (2.5
km)^2.


title: Maxwell Fields and Shear-Free Null Geodesic Congruences

abstract:
  We study and report on the class of vacuum Maxwell fields in Minkowski space
that possess a non-degenerate, diverging, principle null vector field (null
eigenvector field of the Maxwell tensor) that is tangent to a shear-free null
geodesics congruence. These congruences can be either surface forming (the
tangent vectors proportional to gradients) or not, i.e., the twisting
congruences. In the non-twisting case, the associated Maxwell fields are
precisely the Lienard-Wiechert fields, i.e., those Maxwell fields arising from
an electric monopole moving on an arbitrary worldline. The null geodesic
congruence is given by the generators of the light-cones with apex on the
world-line. The twisting case is much richer, more interesting and far more
complicated. In a twisting subcase, where our main interests lie, it can be
given the following strange interpretation. If we allow the real Minkowski
space to be complexified so that the real Minkowski coordinates x^a take
complex values, i.e., x^a => z^a=x^a+iy^a with complex metric g=eta_abdz^adz^b,
the real vacuum Maxwell equations can be extended into the complex and
rewritten as curlW =iWdot, divW with W =E+iB. This subcase of Maxwell fields
can then be extended into the complex so as to have as source, a complex
analytic world-line, i.e., to now become complex Lienard-Wiechart fields. When
viewed as real fields on the real Minkowski space, z^a=x^a, they possess a real
principle null vector that is shear-free but twisting and diverging. The twist
is a measure of how far the complex world-line is from the real 'slice'. Most
Maxwell fields in this subcase are asymptotically flat with a time-varying set
of electric and magnetic moments, all depending on the complex displacements
and the complex velocities.


title:
Mean curvature flow and quasilocal mass for two-surfaces in Hamiltonian
  General Relativity

abstract:
  A family of quasilocal mass definitions that includes as special cases the
Hawking mass and the Brown-York ``rest mass'' energy is derived for spacelike
2-surfaces in spacetime. The definitions involve an integral of powers of the
norm of the spacetime mean curvature vector of the 2-surface, whose properties
are connected with apparent horizons. In particular, for any spacelike
2-surface, the direction of mean curvature is orthogonal (dual in the normal
space) to a unique normal direction in which the 2-surface has vanishing
expansion in spacetime. The quasilocal mass definitions are obtained by an
analysis of boundary terms arising in the gravitational ADM Hamiltonian on
hypersurfaces with a spacelike 2-surface boundary, using a geometric time-flow
chosen proportional to the dualized mean curvature vector field at the boundary
surface. A similar analysis is made choosing a geometric rotational flow given
in terms of the twist covector of the dual pair of mean curvature vector
fields, which leads to a family of quasilocal angular momentum definitions
involving the squared norm of the twist. The large sphere limit of these
definitions is shown to yield the ADM mass and angular momentum in
asymptotically flat spacetimes, while at apparent horizons a quasilocal version
of the Gibbons-Penrose inequality is derived. Finally, some results concerning
positivity are proved for the quasilocal masses, motivated by consideration of
spacelike mean curvature flow of 2-surfaces in spacetime.


title:
Harmonic Analysis of Linear Fields on the Nilgeometric Cosmological
  Model

abstract:
  To analyze linear field equations on a locally homogeneous spacetime by means
of separation of variables, it is necessary to set up appropriate harmonics
according to its symmetry group. In this paper, the harmonics are presented for
a spatially compactified Bianchi II cosmological model -- the nilgeometric
model. Based on the group structure of the Bianchi II group (also known as the
Heisenberg group) and the compactified spatial topology, the irreducible
differential regular representations and the multiplicity of each irreducible
representation, as well as the explicit form of the harmonics are all
completely determined. They are also extended to vector harmonics. It is
demonstrated that the Klein-Gordon and Maxwell equations actually reduce to
systems of ODEs, with an asymptotic solution for a special case.


title: Cosmology with exponential potentials

abstract:
  We examine in the context of general relativity the dynamics of a spatially
flat Robertson-Walker universe filled with a classical minimally coupled scalar
field \phi of exponential potential ~ e^{-\mu\phi} plus pressureless baryonic
matter. This system is reduced to a first-order ordinary differential equation,
providing direct evidence on the acceleration/deceleration properties of the
system. As a consequence, for positive potentials, passage into acceleration
not at late times is generically a feature of the system, even when the
late-times attractors are decelerating. Furthermore, the structure formation
bound, together with the constraints on the present values of \Omega_{m},
w_{\phi} provide, independently of initial conditions and other parameters,
necessary conditions on \mu. Special solutions are found to possess intervals
of acceleration. For the almost cosmological constant case w_{\phi} ~ -1, as
well as, for the generic late-times evolution, the general relation
\Omega_{\phi}(w_{\phi}) is obtained.


title: A note on the structural stability of tachyonic inflation

abstract:
  We study the structural stability of tachyonic inflation against changes in
the shape of the potential. Following Lidsey (Gen. Rel. Grav. 25 (1993) 399),
the concepts of rigidity and fragility are defined through a condition on the
functional form of the Hubble factor. We find that the models are rigid in the
sense that the attractor solutions never change as long as the conditions for
inflation are met.


title: Universal canonical entropy for gravitating systems

abstract:
  The thermodynamics of general relativistic systems with boundary, obeying a
Hamiltonian constraint in the bulk, is argued to be determined solely by the
boundary quantum dynamics, and hence by the area spectrum. Assuming, for large
area of the boundary, (a) an area spectrum as determined by Non-perturbative
Canonical Quantum General Relativity (NCQGR), (b) an energy spectrum that bears
a power law relation to the area spectrum, (c) an area law for the leading
order microcanonicai entropy, leading thermal fluctuation corrections to the
canonical entropy are shown to be logarithmic in area with a universal
coefficient. Since the microcanonical entropy also has univeral logarithmic
corrections to the area law (from quantum spacetime fluctuations, as found
earlier) the canonical entropy then has a universal form including logarithmic
corrections to the area law. This form is shown to be independent of the index
appearing in assumption (b). The index, however, is crucial in ascertaining the
domain of validity of our approach based on thermal equilibrium.


title: Canonical quantum gravity and consistent discretizations

abstract:
  This is a summary of the talk presented by JP at ICGC2004. It covered some
developments in canonical quantum gravity occurred since ICGC2000, emphasizing
the recently introduced consistent discretizations of general relativity.


title:
Towards a formalism for mapping the spacetimes of massive compact
  objects: Bumpy black holes and their orbits

abstract:
  Observations have established that extremely compact, massive objects are
common in the universe. It is generally accepted that these objects are black
holes. As observations improve, it becomes possible to test this hypothesis in
ever greater detail. In particular, it is or will be possible to measure the
properties of orbits deep in the strong field of a black hole candidate (using
x-ray timing or with gravitational-waves) and to test whether they have the
characteristics of black hole orbits in general relativity. Such measurements
can be used to map the spacetime of a massive compact object, testing whether
the object's multipoles satisfy the strict constraints of the black hole
hypothesis. Such a test requires that we compare against objects with the
``wrong'' multipole structure. In this paper, we present tools for constructing
bumpy black holes: objects that are almost black holes, but that have some
multipoles with the wrong value. The spacetimes which we present are good deep
into the strong field of the object -- we do not use a large r expansion,
except to make contact with weak field intuition. Also, our spacetimes reduce
to the black hole spacetimes of general relativity when the ``bumpiness'' is
set to zero. We propose bumpy black holes as the foundation for a null
experiment: if black hole candidates are the black holes of general relativity,
their bumpiness should be zero. By comparing orbits in a bumpy spacetime with
those of an astrophysical source, observations should be able to test this
hypothesis, stringently testing whether they are the black holes of general
relativity. (Abridged)


title: Comments on area spectra in Loop Quantum Gravity

abstract:
  We examine and compare different area spectra that have been recently
considered in Loop Quantum Gravity (LQG). In particular we focus our attention
on a Equally Spaced (ES) spectrum operator introduced by Alekseev et. al. that
has gained recent attention. We show that such operator is not well defined
within the LQG framework, and comment on the issue regarding area spectra and
QNM frequencies.


title: Gravitational Wave Spectrum in Inflation with Nonclassical States

abstract:
  The initial quantum state during inflation may evolve to a highly squeezed
quantum state due to the amplification of the time-dependent parameter,
$\omega_{phys}(k/a)$, which may be the modified dispersion relation in
trans-Planckian physics. This squeezed quantum state is a nonclassical state
that has no counterpart in the classical theory. We have considered the
nonclassical states such as squeezed, squeezed coherent, and squeezed thermal
states, and calculated the power spectrum of the gravitational wave
perturbation when the mode leaves the horizon.


title:
Effects of a cosmological constant on the X-ray fluorescence spectra of
  black hole accretion disks

abstract:
  We investigate the effects of cosmological constant on the characteristic
peaks in the iron line profile in the black hole accretion disk X-ray spectrum.
Our results show that for a fixed mass black hole, the peaks become less
pronounced and closer together with increasing cosmological constant. This
effect is mainly due to the slower rotational velocity of Keplerian orbits at
large radii in the Schwarzschild-de Sitter spacetime as compared to those for
the Schwarzschild spacetime. This change of the iron line profile is similar to
that obtained from increasing the outer radius of the accretion disk size or
reducing the emission intensity power law exponent in the accretion disk
emissivity models.


title: Wormholes in the Braneworld

abstract:
  We discuss brane wormhole solution when classical brane action contains 4d
curvature. The equations of motion for the cases with R=0 and $R\ne 0$ are
obtained. Their numerical solutions corresponding to wormhole are found for
specific boundary conditions.


title: AdS/CFT correspondence in a Friedmann-Lemaitre-Robertson-Walker brane

abstract:
  According to the AdS/CFT correspondence conjecture, the Randall-Sundrum
infinite braneworld is equivalent to four dimensional Einstein gravity with
${\cal N}=4$ super Yang-Mills fields at low energies. Here we derive a four
dimensional effective equation of motion for tensor-type perturbations in two
different pictures, and demonstrate their equivalence.


title: Dirty black holes: Spacetime geometry and near-horizon symmetries

abstract:
  We consider the spacetime geometry of a static but otherwise generic black
hole (that is, the horizon geometry and topology are not necessarily
spherically symmetric). It is demonstrated, by purely geometrical techniques,
that the curvature tensors, and the Einstein tensor in particular, exhibit a
very high degree of symmetry as the horizon is approached. Consequently, the
stress-energy tensor will be highly constrained near any static Killing
horizon. More specifically, it is shown that -- at the horizon -- the
stress-energy tensor block-diagonalizes into ``transverse'' and ``parallel''
blocks, the transverse components of this tensor are proportional to the
transverse metric, and these properties remain invariant under static conformal
deformations. Moreover, we speculate that this geometric symmetry underlies
Carlip's notion of an asymptotic near-horizon conformal symmetry controlling
the entropy of a black hole.


title: Phase space for the Einstein equations

abstract:
  A Hilbert manifold structure is described for the ADM phase space of
asymptotically flat initial data $(g,\pi)$ with local $H^2\times H^1$ Sobolev
regularity. Solutions of the constraint equations form a Hilbert submanifold. A
regularized RT Hamiltonian is defined and smooth on the full phase space and
generates the Einstein evolution for any lapse-shift asymptotic to a (time)
translation at infinity. Critical points for the total (ADM) mass, considered
as a function on the Hilbert manifold of constraint solutions, arise precisely
at initial data generating stationary vacuum spacetimes.


title: Pre-inflationary perturbations spectrum

abstract:
  In the framework of a flat FLRW model we derive an inflationary regime in
which the scalar field, laying on the plateau of its potential, admits a linear
time dependence and remains close to a constant value. The behaviour of
inhomogeneous perturbations is determined on the background metric in agreement
to the "slow-rolling" approximation. We show that the inhomogeneous scales
which before inflation were not much greater then the physical horizon,
conserve their spectrum (almost) unaltered after the de Sitter phase.


title: Mixmaster Chaos via the Invariant Measure

abstract:
  The chaoticity of the Mixmaster is discussed in the framework of Statistical
Mechanics by using Misner--Chitre-like variables and an ADM reduction of its
dynamics. We show that such a system is well described by a microcanonical
ensemble whose invariant measure is induced by the corresponding Liouville one
and is uniform. The covariance with respect to the choice of the temporal gauge
of the obtained invariant measure is outlined.


title: QED Coupling from a 5-D Kaluza-Klein Theory

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


title: Hawking Radiation in Trace Anomaly Free Frames

abstract:
  We have used the results of renormalization of a two-dimensional quantum
stress tensor to develop a conformally invariant dynamical model. The model
requires the consideration of those conformal frames in which there exists a
correspondence between the trace anomaly and a cosmological constant. We apply
this model to a two dimensional-Schwarzschild (-de Sitter) spacetime to show
that in these conformal frames one may achieve Hawking radiation without
recourse to the trace anomaly .


title:
Dust and Radiation Quantum Perfect Fluid Cosmology : Selection of Time
  Variable

abstract:
  We studied the expectation value of the scale factor in radiation and dust
quantum perfect fluid cosmology. We used Schutz variational formalism to
describe perfect fluid and selected the conjugate coordinate of perfect fluid
be dynamical variable. After quantization and solving the Wheeler-DeWitt
equation can obtain the exact solution. By superposition of the exact solution,
we obtained one wave packets and used it to compute the expectation value of
the scale factor. We found that if one select different dynamical variable be
the time variable in each of these two systems, the expectation value of the
scale factor of these two systems can fit in with the prediction of General
Relativity. Therefore we thought that the selection of reference time can be
different for different quantum perfect fluid systems.


title: Information Entropy in Cosmology

abstract:
  The effective evolution of an inhomogeneous cosmological model may be
described in terms of spatially averaged variables. We point out that in this
context, quite naturally, a measure arises which is identical to a fluid model
of the `Kullback-Leibler Relative Information Entropy', expressing the
distinguishability of the local inhomogeneous mass density field from its
spatial average on arbitrary compact domains. We discuss the time-evolution of
`effective information' and explore some implications. We conjecture that the
information content of the Universe -- measured by Relative Information Entropy
of a cosmological model containing dust matter -- is increasing.


title: On the Singularities of Reissner-Nordstr\"{o}m Space-Time

abstract:
  It is shown that if two Reissner-Nordstr\"{o}m space-times, both with the
same mass m and charge e, glued together in the singularities, then the light
ray in black hole of the first space-time can go continuously through the
singularity into black hole of the second. The behavior of tidal forces near
the Reissner-Nordstr\"{o}m space-time singularity is examined by considering
what happens between two particles falling freely towards the singularity.


title:
Particle Production of Coherently Oscillating Nonclassical Inflaton in
  FRW Universe

abstract:
  We study particle production of coherently oscillating inflaton in the
semiclassical theory of gravity by representing inflaton in coherent and
squeezed state formalisms. A comparative study of the inflaton in classical
gravity with coherent state inflaton in semiclassical gravity is also
presented.


title:
Symmetric hyperbolic form of systems of second-order evolution equations
  subject to constraints

abstract:
  Motivated by the initial-boundary value problem for the Einstein equations,
we propose a definition of symmetric hyperbolicity for systems of evolution
equations that are first order in time but second order in space. This can be
used to impose constraint-preserving boundary conditions. The general methods
are illustrated in detail in the toy model of electromagnetism.


title:
Boundary Conditions, Energies and Gravitational Heat in General
  Relativity (a Classical Analysis)

abstract:
  The variation of the energy for a gravitational system is directly defined
from the Hamiltonian field equations of General Relativity. When the variation
of the energy is written in a covariant form it splits into two (covariant)
contributions: one of them is the Komar energy, while the other is the
so-called covariant ADM correction term. When specific boundary conditions are
analyzed one sees that the Komar energy is related to the gravitational heat
while the ADM correction term plays the role of the Helmholtz free energy.
These properties allow to establish, inside a classical geometric framework, a
formal analogy between gravitation and the laws governing the evolution of a
thermodynamic system. The analogy applies to stationary spacetimes admitting
multiple causal horizons as well as to AdS Taub-bolt solutions.


title:
Geometric Inequalities and Trapped Surfaces in Higher Dimensional
  Spacetimes

abstract:
  Geometric inequalities of classical differential geometry are used to extend
to higher dimensional spacetimes the Penrose-Gibbons isoperimetric inequalities
and the hoop conjecture of general reltivity.


title:
Static black holes with a negative cosmological constant: Deformed
  horizon and anti-de Sitter boundaries

abstract:
  Using perturbative techniques, we investigate the existence and properties of
a new static solution for the Einstein equation with a negative cosmological
constant, which we call the deformed black hole. We derive a solution for a
static and axisymmetric perturbation of the Schwarzschild-anti-de Sitter black
hole that is regular in the range from the horizon to spacelike infinity. The
key result is that this perturbation simultaneously deforms the two boundary
surfaces--i.e., both the horizon and spacelike two-surface at infinity. Then we
discuss the Abbott-Deser mass and the Ashtekar-Magnon one for the deformed
black hole, and according to the Ashtekar-Magnon definition, we construct the
thermodynamic first law of the deformed black hole. The first law has a
correction term which can be interpreted as the work term that is necessary for
the deformation of the boundary surfaces. Because the work term is negative,
the horizon area of the deformed black hole becomes larger than that of the
Schwarzschild-anti-de Sitter black hole, if compared under the same mass,
indicating that the quasistatic deformation of the Schwarzschild-anti-de Sitter
black hole may be compatible with the thermodynamic second law (i.e., the area
theorem).


title: LISA Response Function and Parameter Estimation

abstract:
  We investigate the response function of LISA and consider the adequacy of its
commonly used approximation in the high-frequency range of the observational
band. We concentrate on monochromatic binary systems, such as white dwarf
binaries. We find that above a few mHz the approxmation starts becoming
increasingly inaccurate. The transfer function introduces additional amplitude
and phase modulations in the measured signal that influence parameter estmation
and, if not properly accounted for, lead to losses of signal-to-noise ratio.


title:
Motion of a test body in the presence of an external scalar field which
  respects the weak equivalence principle

abstract:
  It is shown that the main contribution to the rotational curve of a spiral
galaxy may be due essentially to the interaction, in the general relativistic
spacetime, of the galactic matter with a very light long range scalar field
which respects the weak equivalence principle. The comparison of the
theoretical results with 23 spiral galaxy rotation curves shows a good
agreement between our proposal and observations.


title:
Properties of four numerical schemes applied to a scalar nonlinear
  scalar wave equation with a GR-type nonlinearity

abstract:
  We study stability, dispersion and dissipation properties of four numerical
schemes (Iterative Crank-Nicolson, 3'rd and 4'th order Runge-Kutta and
Courant-Fredrichs-Levy Non-linear). By use of a Von Neumann analysis we study
the schemes applied to a scalar linear wave equation as well as a scalar
non-linear wave equation with a type of non-linearity present in GR-equations.
Numerical testing is done to verify analytic results. We find that the method
of lines (MOL) schemes are the most dispersive and dissipative schemes. The
Courant-Fredrichs-Levy Non-linear (CFLN) scheme is most accurate and least
dispersive and dissipative, but the absence of dissipation at Nyquist
frequency, if fact, puts it at a disadvantage in numerical simulation. Overall,
the 4'th order Runge-Kutta scheme, which has the least amount of dissipation
among the MOL schemes, seems to be the most suitable compromise between the
overall accuracy and damping at short wavelengths.


title:
On the construction of global models describing isolated rotating
  charged bodies; uniqueness of the exterior gravitational field

abstract:
  A relatively recent study by Mars and Senovilla provided us with a uniqueness
result for the exterior vacuum gravitational field of global models describing
finite isolated rotating bodies in equilibrium in General Relativity (GR). The
generalisation to exterior electrovacuum gravitational fields, to include
charged rotating objects, is presented here.


title: On analyticity of static vacuum metrics at non-degenerate horizons

abstract:
  We show that static metrics solving vacuum Einstein equations (possibly with
a cosmological constant) are one-sided analytic at non-degenerate Killing
horizons. We further prove analyticity in a two-sided neighborhood of
"bifurcate horizons".
  It is a pleasure to dedicate this work to Prof. Staruszkiewicz, on the
occasion of his 65th birthday.


title: A scalar field modelling of the rotational curves of spiral galaxies

abstract:
  In a previous work \cite{mbeleka}, we have modelled the rotation curves (RC)
of spiral galaxies by including in the equation of motion dynamical terms from
an external real self-interacting scalar field, $\phi$, minimally coupled to
gravity and which respects the equivalence principle in the absence of
electromagnetic fields. This model appears to have three free parameters : the
turnover radius, $r_{0}$, the maximum rotational velocity, $v_{max} =
v(r_{0})$, plus a strictly positive integer, $n$. Here, the coupling of the
$\phi$-field to other kinds of matter is emphasized at the expense of its
self-interaction. This reformulation presents the very advantageous possibility
that the same potential may be used now for all galaxies. New correlations are
established.


title: Black hole mass decreasing due to phantom energy accretion

abstract:
  Solution for a stationary spherically symmetric accretion of the relativistic
perfect fluid with an equation of state $p(\rho)$ onto the Schwarzschild black
hole is presented. This solution is a generalization of Michel solution and
applicable to the problem of dark energy accretion. It is shown that accretion
of phantom energy is accompanied with the gradual decrease of the black hole
mass. Masses of all black holes tend to zero in the phantom energy universe
approaching to the Big Rip.


title: Perturbations in the Einstein theory of gravity: Conserved currents

abstract:
  General relativity in the form where gravitational perturbations together
with other physical fields propagate on an auxiliary background is considered.
With using the Katz-Bi{\v{c}}\'ak-Lynden-Bell technique new conserved currents,
divergences of antisymmetric tensor densities(superpotentials), in an arbitrary
curved spacetime are constructed.


title:
The Pauli Exclusion Principle, Spin, and Statistics in Loop Quantum
  Gravity: SU(2) versus SO(3)

abstract:
  Recent attempts to resolve the ambiguity in the loop quantum gravity
description of the quantization of area has led to the idea that j=1 edges of
spin-networks dominate in their contribution to black hole areas as opposed to
j=1/2 which would naively be expected. This suggests that the true gauge group
involved might be SO(3) rather than SU(2). We argue that the idea that a
version of the Pauli principle is present in loop quantum gravity allows one to
maintain SU(2) as the gauge group while still naturally achieving the desired
suppression of spin-1/2 punctures. Such an idea can be motivated by arguments
from geometric quantization even though the SU(2) under consideration does not
have the geometrical interpretation of rotations in 3-dimensional space, and
its representation labels do not correspond to physical angular momenta. In
this picture, it is natural that macroscopic areas come almost entirely from
j=1 punctures rather than j=1/2 punctures, and this is for much the same reason
that photons lead to macroscopic classically observable fields while electrons
do not.


title:
Some encouraging and some cautionary remarks on Doubly Special
  Relativity in Quantum Gravity

abstract:
  The idea of a role for DSR (doubly-special relativity) in quantum gravity
finds some encouragement in a few scenarios, but in order to explore some key
conceptual issues it is necessary to find a well-understood toy-quantum-gravity
model that is fully compatible with the DSR principles. Perhaps the most
significant source of encouragement comes from the recent proposal of a path
for the emergence of DSR in Loop Quantum Gravity, which however relies on a few
assumptions on the results of some computations that we are still unable to
perform. Indications in favor of the possibility of using some elements of
$\kappa$-Poincar\'e Hopf algebras (and of the related $\kappa$-Minkowski
noncommutative spacetime) for the construction of a DSR theory have been
discussed extensively, but a few stubborn open issues must still be resolved,
especially in the two-particle sector. It has been recently observed that
certain structures encountered in a formulation of 2+1-dimensional
classical-gravity models would fit naturally in a DSR framework, but some key
elements of these 2+1-dimensional models, including the description of
observers, might be incompatible with the DSR principles.


title: On the Closed Form Solution for the Geodesics in SdS Space

abstract:
  The closed form solution for the geodesics of classical particles in SdS
space are obtained in terms of hyperelliptic modular functions and multiple
hypergeometric functions. The closed form solution for the five roots of the
fifth degree polynomial are found giving the branch places on the genus two
Riemann surface. The `Inversion Problem', for the genus two hyperelliptic
integral is solved in a closed form. Thus a couple of mathematical problems
that have been around for a couple of centuries are solved. The solution is
important in astrophysical applications of measuring the cosmological constant.


title: Bonnor-type Black Dihole Solution in Brans-Dicke-Maxwell Theory

abstract:
  It was originally thought that Bonnor's solution in Einstein-Maxwell theory
describes a singular point-like magnetic dipole. Lately, however, it has been
demonstrated that indeed it may describe a black {\it dihole}, i.e., a pair of
static, oppositely-charged extremal black holes with regular horizons.
Motivated particularly by this new interpretation, in the present work, the
construction and extensive analysis of a solution in the context of the
Brans-Dicke-Maxwell theory representing a black dihole are attempted. It has
been known for some time that the solution-generating algorithm of Singh and
Rai produces stationary, axisymmetric, charged solutions in Brans-Dicke-Maxwell
theory from the known such solutions in Einstein-Maxwell theory. Thus this
algorithm of Singh and Rai's is employed in order to construct a Bonnor-type
magnetic black dihole solution in Brans-Dicke-Maxwell theory from the known
Bonnor solution in Einstein-Maxwell theory. The peculiar feature of the new
solution including internal infinity nature of the symmetry axis and its
stability issue have been discussed in full detail.


title: Vector field as a quintessence partner

abstract:
  We derive generic equations for a vector field driving the evolution of flat
homogeneous isotropic universe and give a comparison with a scalar filed
dynamics in the cosmology. Two exact solutions are shown as examples, which can
serve to describe an inflation and a slow falling down of dynamical
``cosmological constant'' like it is given by the scalar quintessence. An
attractive feature of vector field description is a generation of ``induced
mass'' proportional to a Hubble constant, which results in a dynamical
suppression of actual cosmological constant during the evolution.


title: Quantum Cylindrical Waves and Sigma Models

abstract:
  We analyze cylindrical gravitational waves in vacuo with general polarization
and develop a viewpoint complementary to that presented recently by Niedermaier
showing that the auxiliary sigma model associated with this family of waves is
not renormalizable in the standard perturbative sense.


title:
Electronic Detection of Gravitational Disturbances and Collective
  Coulomb Interactions

abstract:
  The cross section for a gravitational wave antenna to absorb a graviton may
be directly expressed in terms of the non-local viscous response function of
the metallic crystal. Crystal viscosity is dominated by electronic processes
which then also dominate the graviton absorption rate. To compute this rate
from a microscopic Hamiltonian, one must include the full Coulomb interaction
in the Maxwell electric field pressure and also allow for strongly
non-adiabatic transitions in the electronic kinetic pressure. The view that the
electrons and phonons constitute ideal gases with a weak electron phonon
interaction is not sufficiently accurate for estimating the full strength of
the electronic interaction with a gravitational wave.


title: Charged black holes in quadratic gravity

abstract:
  Iterative solutions to fourth-order gravity describing static and
electrically charged black holes are constructed. Obtained solutions are
parametrized by two integration constants which are related to the electric
charge and the exact location of the event horizon. Special emphasis is put on
the extremal black holes. It is explicitly demonstrated that in the extremal
limit, the exact location of the (degenerate) event horizon is given by $\rp =
|e|.$ Similarly to the classical Reissner-Nordstr\"om solution, the
near-horizon geometry of the charged black holes in quadratic gravity, when
expanded into the whole manifold, is simply that of Bertotti and Robinson.
Similar considerations have been carried out for the boundary conditions of
second type which employ the electric charge and the mass of the system as seen
by a distant observer. The relations between results obtained within the
framework of each method are briefly discussed.


title: Plane symmetric traversable wormholes in an anti-de Sitter background

abstract:
  We construct solutions of plane symmetric wormholes in the presence of a
negative cosmological constant by matching an interior spacetime to the
exterior anti-de Sitter vacuum solution. The spatial topology of this plane
symmetric wormhole can be planar, cylindrical and toroidal. As usual the null
energy condition is necessarily violated at the throat. At the junction
surface, the surface stresses are determined. By expressing the tangential
surface pressure as a function of several parameters, namely, that of the
matching radius, the radial derivative of the redshift function and of the
surface energy density, the sign of the tangential surface pressure is
analyzed. We then study four specific equations of state at the junction: zero
surface energy density, constant redshift function, domain wall equation of
state, and traceless surface stress-energy tensor. The equation governing the
behavior of the radial pressure, in terms of the surface stresses and the
extrinsic curvatures, is also displayed. Finally, we construct a model of a
plane symmetric traversable wormhole which minimizes the usage of the exotic
matter at the throat, i.e., the null energy condition is made arbitrarily small
at the wormhole throat, while the surface stresses on the junction surface
satisfy the weak energy condition, and consequently the null energy condition.
The construction of these wormholes does not alter the topology of the
background spacetime (i.e., spacetime is not multiply-connected), so that these
solutions can instead be considered domain walls. Thus, in general, these
wormhole solutions do not allow time travel.


title: Conformally Invariant Brane-universe and the Cosmological Constant

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


title: Constraint propagation in N+1-dimensional space-time

abstract:
  Higher dimensional space-time models provide us an alternative interpretation
of nature, and give us different dynamical aspects than the traditional
four-dimensional space-time models. Motivated by such recent interests,
especially for future numerical research of higher-dimensional space-time, we
study the dimensional dependence of constraint propagation behavior. The $N+1$
Arnowitt-Deser-Misner evolution equation has matter terms which depend on $N$,
but the constraints and constraint propagation equations remain the same. This
indicates that there would be problems with accuracy and stability when we
directly apply the $N+1$ ADM formulation to numerical simulations as we have
experienced in four-dimensional cases. However, we also conclude that previous
efforts in re-formulating the Einstein equations can be applied if they are
based on constraint propagation analysis.


title: Equilibrium Configurations of Homogeneous Fluids in General Relativity

abstract:
  By means of a highly accurate, multi-domain, pseudo-spectral method, we
investigate the solution space of uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies. It turns out that this space can be
divided up into classes of solutions. In this paper, we present two new classes
including relativistic core-ring and two-ring solutions. Combining our
knowledge of the first four classes with post-Newtonian results and the
Newtonian portion of the first ten classes, we present the qualitative
behaviour of the entire relativistic solution space. The Newtonian disc limit
can only be reached by going through infinitely many of the aforementioned
classes. Only once this limiting process has been consummated, can one proceed
again into the relativistic regime and arrive at the analytically known
relativistic disc of dust.


title: Scalar fields properties for flat galactic rotation curves

abstract:
  The whole class of minimally coupled and massive scalar fields which may be
responsible for flattening of galactic rotation curves is found. An interesting
relation with a class of scalar-tensor theories able to isotropise anisotropic
models of Universe is shown. The resulting metric is found and its stability
and scalar field properties are tested with respect to the presence of a second
scalar field or a small perturbation of the rotation velocity at galactic outer
radii.


title:
Isotropisation of Bianchi class A models with a minimally coupled scalar
  field and a perfect fluid

abstract:
  We look for the necessary conditions allowing the Universe isotropisation in
presence of a minimally coupled and massive scalar field with a perfect fluid.
We conclude that it arises only when the Universe is scalar field dominated,
leading to flat spacelike sections and accelerated expansion, and examine the
case of a SUGRA theory.


title: Cosmology, cohomology, and compactification

abstract:
  Ashtekar and Samuel have shown that Bianchi cosmological models with compact
spatial sections must be of Bianchi class A. Motivated by general results on
the symmetry reduction of variational principles, we show how to extend the
Ashtekar-Samuel results to the setting of weakly locally homogeneous spaces as
defined, e.g., by Singer and Thurston. In particular, it is shown that any
m-dimensional homogeneous space G/K admitting a G-invariant volume form will
allow a compact discrete quotient only if the Lie algebra cohomology of G
relative to K is non-vanishing at degree m.


title: A poor man's positive energy theorem

abstract:
  We show that positivity of energy for stationary, asymptotically flat,
non-singular domains of outer communications is a simple corollary of the
Lorentzian splitting theorem.


title: A Note on Stress-Tensors, Conservation and Equations of Motion

abstract:
  Some unusual relations between stress tensors, conservation and equations of
motion are briefly reviewed.


title:
Origin of FRW cosmology in slow-roll inflation from noncompact
  Kaluza-Klein theory

abstract:
  Using a recently introduced formalism we discuss slow-roll inflaton from
Kaluza-Klein theory without the cylinder condition. In particular, some
examples corresponding to polynomic and hyperbolic $\phi$-potentials are
studied. We find that the evolution of the fifth coordinate should be
determinant for both, the evolution of the early inflationary universe and the
quantum fluctuations.


title: Gravitational Waves on Conductors

abstract:
  We consider a gravitational wave of arbitrary frequency incident on a normal
or a super-conductor. The gravitationally induced fields inside the conductor
are derived. The outward propagating EM waves are calculated for a low
frequency wave on a small sphere and for a high frequency wave incident on a
large disk. We estimate for both targets the GW to EM conversion efficiencies
and also the magnitude of the superconductor's phase perturbation.


title:
Three dimensional loop quantum gravity: physical scalar product and spin
  foam models

abstract:
  In this paper, we address the problem of the dynamics in three dimensional
loop quantum gravity with zero cosmological constant. We construct a rigorous
definition of Rovelli's generalized projection operator from the kinematical
Hilbert space--corresponding to the quantization of the infinite dimensional
kinematical configuration space of the theory--to the physical Hilbert space.
In particular, we provide the definition of the physical scalar product which
can be represented in terms of a sum over (finite) spin-foam amplitudes.
Therefore, we establish a clear-cut connection between the canonical
quantization of three dimensional gravity and spin-foam models. We emphasize
two main properties of the result: first that no cut-off in the kinematical
degrees of freedom of the theory is introduced (in contrast to standard
`lattice' methods), and second that no ill-defined sum over spins (`bubble'
divergences) are present in the spin foam representation.


title: Three dimensional loop quantum gravity: coupling to point particles

abstract:
  We consider the coupling between three dimensional gravity with zero
cosmological constant and massive spinning point particles. First, we study the
classical canonical analysis of the coupled system. Then, we go to the
Hamiltonian quantization generalizing loop quantum gravity techniques. We give
a complete description of the kinematical Hilbert space of the coupled system.
Finally, we define the physical Hilbert space of the system of self-gravitating
massive spinning point particles using Rovelli's generalized projection
operator which can be represented as a sum over spin foam amplitudes. In
addition we provide an explicit expression of the (physical) distance operator
between two particles which is defined as a Dirac observable.


title:
Dynamics of loop quantum gravity and spin foam models in three
  dimensions

abstract:
  We present a rigorous regularization of Rovellis's generalized projection
operator in canonical 2+1 gravity. This work establishes a clear-cut connection
between loop quantum gravity and the spin foam approach in this simplified
setting. The point of view adopted here provides a new perspective to tackle
the problem of dynamics in the physically relevant
  3+1 case.


title: Observability and Geometry in Three dimensional quantum gravity

abstract:
  We consider the coupling between massive and spinning particles and three
dimensional gravity. This allows us to construct geometric operators (distances
between particles) as Dirac observables. We quantize the system a la loop
quantum gravity: we give a description of the kinematical Hilbert space and
construct the associated spin-foam model. We construct the physical disctance
operator and consider its quantization.


title: A spherically symmetric dust-space-time with a NUT-like rotation

abstract:
  A deduction of a solution of the Einstein's equations, employing the
Mitskievich's field theoretic description of perfect fluids, is presented. This
solution describes a dust-space-time with a spherical-like symmetry and a
NUT-like rotation. This solution is of Petrov type D, and has an isometry group
G4. It also admits closed timelike geodesics. It has Minkowski space-time as a
limit, when both dust and rotation disappear.


title: The effects of curvature correction terms on brane cosmology

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


title: Newton-Cartan connections with torsion

abstract:
  We re-formulate the notion of a Newton-Cartan manifold and clarify the
compatibility conditions of a connection with torsion with the Newton-Cartan
structure.


title: Troubles with quantum anisotropic cosmological models: loss of unitarity

abstract:
  The anisotropic Bianchi I cosmological model coupled with perfect fluid is
quantized in the minisuperspace. The perfect fluid is described by using the
Schutz formalism which allows to attribute dynamical degrees of freedom to
matter. It is shown that the resulting model is non-unitary. This breaks the
equivalence between the many-worlds and dBB interpretations of quantum
mechanics.


title:
A relational solution to the problem of time in quantum mechanics and
  quantum gravity induces a fundamental mechanism for quantum decoherence

abstract:
  The use of a relational time in quantum mechanics is a framework in which one
promotes to quantum operators all variables in a system, and later chooses one
of the variables to operate like a ``clock''. Conditional probabilities are
computed for variables of the system to take certain values when the ``clock''
specifies a certain time. This framework is attractive in contexts where the
assumption of usual quantum mechanics of the existence of an external,
perfectly classical clock, appears unnatural, as in quantum cosmology. Until
recently, there were problems with such constructions in ordinary quantum
mechanics with additional difficulties in the context of constrained theories
like general relativity. A scheme we recently introduced to consistently
discretize general relativity removed such obstacles. Since the clock is now an
object subject to quantum fluctuations, the resulting evolution in the time is
not exactly unitary and pure states decohere into mixed states. Here we work
out in detail the type of decoherence generated, and we find it to be of
Lindblad type. This is attractive since it implies that one can have loss of
coherence without violating the conservation of energy. We apply the framework
to a simple cosmological model to illustrate how a quantitative estimate of the
effect could be computed. For most quantum systems it appears to be too small
to be observed, although certain macroscopic quantum systems could in the
future provide a testing ground for experimental observation.


title: A wide family of singularity-free cosmological models

abstract:
  In this paper a family of non-singular cylindrical perfect fluid cosmologies
is derived. The equation of state corresponds to a stiff fluid. The family
depends on two independent functions under very simple conditions. A sufficient
condition for geodesic completeness is provided.


title:
Pioneer acceleration and variation of light speed: experimental
  situation

abstract:
  The situation with respect to the experiments is presented of a recently
proposed model that gives an explanation of the Pioneer anomalous acceleration
$a_{\rm P}$. The model is based on an idea already discovered by Einstein in
1907: the light speed depends on the gravitational potential $\Phi$, so that it
is larger the higher if $\Phi$. The potential due to all the mass and energy in
the universe increases in time because of its expansion, which has the
consequence that light must be slowly accelerating. Moreover it turns out that
the observational effects of a universal adiabatic acceleration of light
$a_\ell =a_{\rm P}$ and of an extra acceleration towards the
  Sun $a_{\rm P}$ of a spaceship would be the same: a blue shift increasing
linearly in time, precisely what was observed. The phenomenon would be due to a
cosmological acceleration of the proper time of bodies with respect to the
coordinate time. It is shown that it agrees with the experimental tests of
special relativity and the weak equivalence principle if the cosmological
variation of the fine structure constant is zero or very small, as it seems
now.


title: The role of Topology in the classical geometric theories of gravitation

abstract:
  I withdraw the previous version of the paper since it contains conceptual and
mathematical mistakes. I will soon replace it with a radically revised version.


title:
General Relativity in Space and Sensitive Tests of the Equivalence
  Principle

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


title: Strongly hyperbolic second order Einstein's evolution equations

abstract:
  BSSN-type evolution equations are discussed. The name refers to the
Baumgarte, Shapiro, Shibata, and Nakamura version of the Einstein evolution
equations, without introducing the conformal-traceless decomposition but
keeping the three connection functions and including a densitized lapse. It is
proved that a pseudo-differential first order reduction of these equations is
strongly hyperbolic. In the same way, densitized Arnowitt-Deser-Misner
evolution equations are found to be weakly hyperbolic. In both cases, the
positive densitized lapse function and the spacelike shift vector are arbitrary
given fields. This first order pseudodifferential reduction adds no extra
equations to the system and so no extra constraints.


title: Non-singular radiation cosmological models

abstract:
  In this paper we analyse the possibility of constructing singularity-free
inhomogeneous cosmological models with a pure radiation field as matter
content. It is shown that the conditions for regularity are very easy to
implement and therefore there is a huge number of such spacetimes.


title: Silent universes with a cosmological constant

abstract:
  We study non-degenerate (Petrov type I) silent universes in the presence of a
non-vanishing cosmological constant L. In contrast to the L=0 case, for which
the orthogonally spatially homogeneous Bianchi type I metrics most likely are
the only admissible metrics, solutions are shown to exist when L is positive.
The general solution is presented for the case where one of the eigenvalues of
the expansion tensor is 0.


title:
The violation of the weak energy condition, Is it generic of spontaneous
  scalarization ?

abstract:
  It was recently shown by Whinnett & Torres \cite{WT} that the phenomenon of
spontaneous scalarization (SC) in compact objects (polytropes) was accompanied
also by a {\it spontaneous violation of the weak energy condition} (WEC).
Notably, by the encounter of negative-energy densities at several star places
as measured by a static observer. Here we argue that the negativeness of such
densities is not generic of scalar tensor theories of gravity (STT). We support
this conclusion by numerical results within a class of STT and by using three
realistic models of dense matter. However, we show that the ``angular parts''
of the additional conditions for the WEC to hold $\rho_{\rm eff} + T^{i ({\rm
eff})}_{i} \geq 0$ tend to be ``slightly violated'' at the outskirts of the
star.


title: The Physics of 'Now'

abstract:
  The world is four-dimensional according to fundamental physics, governed by
basic laws that operate in a spacetime that has no unique division into space
and time. Yet our subjective experience is divided into present, past, and
future. This paper discusses the origin of this division in terms of simple
models of information gathering and utilizing systems (IGUSes). Past, present,
and future are not properties of four-dimensional spacetime but notions
describing how individual IGUSes process information. Their origin is to be
found in how these IGUSes evolved or were constructed. The past, present, and
future of an IGUS is consistent with the four-dimensional laws of physics and
can be described in four-dimensional terms. The present, for instance, is not a
moment of time in the sense of a spacelike surface in spacetime. Rather there
is a localized notion of present at each point along an IGUS' world line. The
common present of many localized IGUSes is an approximate notion appropriate
when they are sufficiently close to each other and have relative velocities
much less than that of light. But modes of organization that are different from
present, past and future can be imagined that are consistent with the physical
laws. We speculate why the present, past, and future organization might be
favored by evolution and therefore a cognitive universal.


title: Rotating black holes in brane worlds

abstract:
  We study interaction of rotating higher dimensional black holes with a brane
in space-times with large extra dimensions. We demonstrate that a rotating
black hole attached to a brane can be stationary only if the null Killing
vector generating the black hole horizon is tangent to the brane world-sheet.
The characteristic time when a rotating black hole with the gravitational
radius $r_0$ reaches this final stationary state is $T\sim
r_0^{p-1}/(G\sigma)$, where $G$ is the higher dimensional gravitational
coupling constant, $\sigma$ is the brane tension, and $p$ is the number of
extra dimensions.


title: Cartan's Torsion: Necessity and Observational Evidence

abstract:
  This article starts with the mathematical definition, concrete description,
and physical meaning of Cartan's torsion. I proceed with the argumentation that
torsion is required for the description of intrinsic spin. Moreover I argue
that the duality between curvature and torsion is analogous to the duality
between electricity and magnetism. I conclude this article by pointing out that
the aligned rotation axes of the galaxies of the Perseus-Pisces supercluster
may be interpreted as a topological defect generated by torsion.


title: Generalizing Optical Geometry

abstract:
  We show that by employing the standard projected curvature as a measure of
spatial curvature, we can make a certain generalization of optical geometry
(Abramowicz and Lasota 1997, Class. Quantum Grav. 14 (1997) A23). This
generalization applies to any spacetime that admits a hypersurface orthogonal
shearfree congruence of worldlines. This is a somewhat larger class of
spacetimes than the conformally static spacetimes assumed in standard optical
geometry. In the generalized optical geometry, which in the generic case is
time dependent, photons move with unit speed along spatial geodesics and the
sideways force experienced by a particle following a spatially straight line is
independent of the velocity. Also gyroscopes moving along spatial geodesics do
not precess (relative to the forward direction). Gyroscopes that follow a
curved spatial trajectory precess according to a very simple law of
three-rotation. We also present an inertial force formalism in coordinate
representation for this generalization. Furthermore, we show that by employing
a new sense of spatial curvature (Jonsson, Class. Quantum Grav. 23 (2006) 1)
closely connected to Fermat's principle, we can make a more extensive
generalization of optical geometry that applies to arbitrary spacetimes. In
general this optical geometry will be time dependent, but still geodesic
photons move with unit speed and follow lines that are spatially straight in
the new sense. Also, the sideways experienced (comoving) force on a test
particle following a line that is straight in the new sense will be independent
of the velocity.


title: Magnetic Black Holes Are Also Unstable

abstract:
  Most black holes are known to be unstable to emitting Hawking radiation (in
asymptotically flat spacetime). If the black holes are non-extreme, they have
positive temperature and emit thermally. If they are extremal rotating black
holes, they still spontaneously emit particles like gravitons and photons. If
they are extremal electrically charged black holes, they are unstable to
emitting electrons or positrons. The only exception would be extreme
magnetically charged black holes if there do not exist any magnetic monopoles
for them to emit. However, here we show that even in this case, vacuum
polarization causes all magnetic black holes to be unstable to emitting smaller
magnetic black holes.


title: Spherically symmetric dissipative anisotropic fluids: A general study

abstract:
  The full set of equations governing the evolution of self--gravitating
spherically symmetric dissipative fluids with anisotropic stresses is deployed
and used to carry out a general study on the behaviour of such systems, in the
context of general relativity. Emphasis is given to the link between the Weyl
tensor, the shear tensor, the anisotropy of the pressure and the density
inhomogeneity. In particular we provide the general, necessary and sufficient,
condition for the vanishing of the spatial gradients of energy density, which
in turn suggests a possible definition of a gravitational arrow of time. Some
solutions are also exhibited to illustrate the discussion.


title: Strongly hyperbolic systems in General Relativity

abstract:
  We discuss several topics related to the notion of strong hyperbolicity which
are of interest in general relativity. After introducing the concept and
showing its relevance we provide some covariant definitions of strong
hyperbolicity. We then prove that is a system is strongly hyperbolic with
respect to a given hypersurface, then it is also strongly hyperbolic with
respect to any near by one.
  We then study for how much these hypersurfaces can be deformed and discuss
then causality, namely what is the maximal propagation speed in any given
direction.
  To show that the concept is needed in the area of general relativity we
discuss two results for which the theory of symmetric hyperbolic systems shows
to be insufficient. The first deals with the hyperbolicity analysis of systems
which are second order in space derivatives, they include certain versions of
the ADM and the BSSN families of equations.
  The second result deals with systems having constraints. The question posed
is which hyperbolicity properties, if any, are inherited from the original
evolution system by the subsidiary system satisfied by the constraint
quantities. The answer is that, subject to some condition on the constraints,
if the evolution system is strongly hyperbolic then the subsidiary system is
also strongly hyperbolic and the causality properties of both are identical.


title:
The n-wave procedure and dimensional regularization for the scalar field
  in a homogeneous isotropic space

abstract:
  We obtain expressions for the vacuum expectations of the energy-momentum
tensor of the scalar field with an arbitrary coupling to the curvature in an
N-dimensional homogeneous isotropic space for the vacuum determined by
diagonalization of the Hamiltonian. We generalize the n-wave procedure to
N-dimensional homogeneous isotropic space-time. Using the dimensional
regularization, we investigate the geometric structure of the terms subtracted
from the vacuum energy-momentum tensor in accordance with the n-wave procedure.
We show that the geometric structures of the first three subtractions in the
n-wave procedure and in the effective action method coincide. We show that all
the subtractions in the n-wave procedure in a four- and five-dimensional
homogeneous isotropic spaces correspond to a renormalization of the coupling
constants of the bare gravitational Lagrangian.


title: On angular momentum of gravitational radiation

abstract:
  The quasigroup approach to the conservation laws (Phys. Rev. D56, R7498
(1997)) is completed by imposing new gauge conditions for asymptotic
symmetries. Noether charge associated with an arbitrary element of the
Poincar\'e quasialgebra is free from the supertranslational ambiquity and
identically vanishes in a flat spacetime


title: How to lasso a plane gravitational wave

abstract:
  Beginning with the stress-energy tensor of an elastic string this paper
derives a relativistic string and its form in a parallel transported Fermi
frame including its reduction in the Newtonian limit to a Cosserat string. In a
Fermi frame gravitational curvature is seen to induce three dominant relative
acceleration terms dependent on: position, velocity and position, strain and
position, respectively. An example of a string arranged in an axially flowing
ring (a lasso) is shown to have a set of natural frequencies that can be
parametrically excited by a monochromatic plane gravitational wave. The lasso
also exhibits, in common with spinning particles, oscillation about geodesic
motion in proportion to spin magnitude and wave amplitude when the spin axis
lies in the gravitational wave front. Coordinate free notation is used
throughout including the development of the properties of the Fermi frame.


title: Hawking radiation for Dirac spinors on the RP^3 geon

abstract:
  We analyse the Hawking(-Unruh) effect for a massive Dirac spinor on the Z_2
quotient of Kruskal spacetime known as the RP^3 geon. There are two distinct
Hartle-Hawking-like vacua, depending on the choice of the spin structure, and
suitable measurements in the static region (which on its own has only one spin
structure) distinguish these two vacua. However, both vacua appear thermal in
the usual Hawking temperature to certain types of restricted operators,
including operators with support in the asymptotic future (or past). Similar
results hold in a family of topologically analogous flat spacetimes, where we
show the two vacua to be distinguished also by the shear stresses in the
zero-mass limit. As a by-product, we display the explicit Bogolubov
transformation between the Rindler-basis and the Minkowski-basis for massive
Dirac fermions in four-dimensional Minkowski spacetime.


title: Static fluid cylinders and their fields: global solutions

abstract:
  The global properties of static perfect-fluid cylinders and their external
Levi-Civita fields are studied both analytically and numerically. The existence
and uniqueness of global solutions is demonstrated for a fairly general
equation of state of the fluid. In the case of a fluid admitting a
non-vanishing density for zero pressure, it is shown that the cylinder's radius
has to be finite. For incompressible fluid, the field equations are solved
analytically for nearly Newtonian cylinders and numerically in fully
relativistic situations. Various physical quantities such as proper and
circumferential radii, external conicity parameter and masses per unit
proper/coordinate length are exhibited graphically.


title: The Pioneer anomaly as an effect of the dynamics of time

abstract:
  A model is presented in which the Pioneer anomaly is not related to the
motion of the spaceship, but is a consequence of the acceleration of the
cosmological proper time $\tau$ with respect to the coordinate parametric time
$t$, what is an effect of the background gravitational potential of the entire
universe. The light speed, while being constant if defined with respect to
$\tau$ ({\it i. e.} as ${\rm d}\ell /{\rm d} \tau$), would suffer an adiabatic
secular acceleration, $a_\ell={\rm d}c/{\rm d}t >0$, if defined in terms of $t$
({\it i. e.} as ${\rm d}\ell /{\rm d} t$). Such an adiabatic acceleration of
light, and a small acceleration of the Pioneer towards the Sun $a_{\rm P}$
could be mistaken the one for the other, because they do have the same
fingerprint: a blue shift. However, this shift would be quite unrelated to any
anomalous motion of the Pioneer, being just an observational effect of the
acceleration of light with respect to time $t$. The Pioneer anomaly turns out
then to be an interesting case of the dynamics of time, its explanation
involving the interplay between the two times $\tau$ and $t$.


title:
Annual modulation of the Galactic binary confusion noise bakground and
  LISA data analysis

abstract:
  We study the anisotropies of the Galactic confusion noise background and its
effects on LISA data analysis. LISA has two data streams of the gravitational
waves signals relevant for low frequency regime. Due to the anisotropies of the
background, the matrix for their confusion noises has off-diagonal components
and depends strongly on the orientation of the detector plane. We find that the
sky-averaged confusion noise level $\sqrt {S(f)}$ could change by a factor of 2
in three months, and would be minimum when the orbital position of LISA is
either around the spring or autumn equinox.


title: Quantum Cosmology for Tunneling Universes

abstract:
  In a quantum cosmological model consisting of a Euclidean region and a
Lorentzian region, Hartle-Hawking's no-bounary wave function, and Linde's wave
function and Vilenkin's tunneling wave function are briefly described and
compared with each other. We put a particular emphasis on semiclassical gravity
from quantum cosmology and compare it with the conventional quantum field
theory in curved spacetimes. Finally, we discuss the recent debate on
catastrophic particle production in the tunneling universe between Rubakov and
Vilenkin within the semiclassical gravity.


title:
Spinor couplings to dilaton gravity induced by the dimensional reduction
  of topologically massive gravity

abstract:
  A Dirac spinor is coupled to topologically massive gravity and the D=3
dimensional action is reduced to D=2 dimensions with a metric that includes
both the electromagnetic potential 1-form A and a dilaton scalar \phi. The
dimensionnaly reduced spinor is made a mass eigenstate with a (local) chiral
rotation. The non-trivial interactions thus induced are discussed.


title: Some Cosmological Applications of Two Measures Theory

abstract:
  Scale invariance is considered in the context of a gravitational theory where
the action, in the first order formalism, is of the form S = \int L_{1} \Phi
d^4x + \int L_{2}\sqrt{-g}d^4x where \Phi is a density built out of degrees of
freedom independent of the metric. For global scale invariance, a "dilaton"
\phi has to be introduced, with non-trivial potentials
V(\phi)=f_{1}e^{\alpha\phi} in L_1 and U(\phi) = f_{2}e^{2\alpha\phi} in L_2.
In the effective Einstein frame, this leads to a non-trivial \phi potential (of
the Morse type) which has a flat region with energy density f_{1}^{2}/4f_{2} as
\phi\to\infty. The addition of an R^{2} term produces an effective potential
with two connected flat regions: one of the Planck scale, that can be
responsible for early inflation, and another for the description of the present
universe.


title:
Universality of massive scalar field late-time tails in black-hole
  spacetimes

abstract:
  The late-time tails of a massive scalar field in the spacetime of black holes
are studied numerically. Previous analytical results for a Schwarzschild black
hole are confirmed: The late-time behavior of the field as recorded by a static
observer is given by $\psi(t)\sim t^{-5/6}\sin [\omega (t)\times t]$, where
$\omega(t)$ depends weakly on time. This result is carried over to the case of
a Kerr black hole. In particular, it is found that the power-law index of -5/6
depends on neither the multipole mode $\ell$ nor on the spin rate of the black
hole $a/M$. In all black hole spacetimes, massive scalar fields have the same
late-time behavior irrespective of their initial data (i.e., angular
distribution). Their late-time behavior is universal.


title:
Symmetric hyperbolicity and consistent boundary conditions for
  second-order Einstein equations

abstract:
  We present two families of first-order in time and second-order in space
formulations of the Einstein equations (variants of the Arnowitt-Deser-Misner
formulation) that admit a complete set of characteristic variables and a
conserved energy that can be expressed in terms of the characteristic
variables. The associated constraint system is also symmetric hyperbolic in
this sense, and all characteristic speeds are physical. We propose a family of
constraint-preserving boundary conditions that is applicable if the boundary is
smooth with tangential shift. We conjecture that the resulting initial-boundary
value problem is well-posed.


title: Singularities in scalar-tensor gravity

abstract:
  The analysis of certain singularities in scalar-tensor gravity contained in a
recent paper is completed, and situations are pointed out in which these
singularities cannot occur.


title:
Laboratory Tests of Gravitational Physics Using a Cryogenic Torsion
  Pendulum

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


title: The Simon and Simon-Mars Tensors for Stationary Einstein-Maxwell Fields

abstract:
  Modulo conventional scale factors, the Simon and Simon-Mars tensors are
defined for stationary vacuum spacetimes so that their equality follows from
the Bianchi identities of the second kind. In the nonvacuum case one can absorb
additional source terms into a redefinition of the Simon tensor so that this
equality is maintained. Among the electrovacuum class of solutions of the
Einstein-Maxwell equations, the expression for the Simon tensor in the
Kerr-Newman-Taub-NUT spacetime in terms of the Ernst potential is formally the
same as in the vacuum case (modulo a scale factor), and its vanishing
guarantees the simultaneous alignment of the principal null directions of the
Weyl tensor, the Papapetrou field associated with the timelike Killing vector
field, the electromagnetic field of the spacetime and even the Killing-Yano
tensor.


title: LISA Science Results in the Presence of Data Disturbances

abstract:
  Each spacecraft in the Laser Interferometer Space Antenna houses a proof mass
which follows a geodesic through spacetime. Disturbances which change the proof
mass position, momentum, and/or acceleration will appear in the LISA data
stream as additive quadratic functions. These data disturbances inhibit signal
extraction and must be removed. In this paper we discuss the identification and
fitting of monochromatic signals in the data set in the presence of data
disturbances. We also present a preliminary analysis of the extent of science
result limitations with respect to the frequency of data disturbances.


title: Unique characterization of the Bel-Robinson tensor

abstract:
  We prove that a completely symmetric and trace-free rank-4 tensor is, up to
sign, a Bel-Robinson type tensor, i.e., the superenergy tensor of a tensor with
the same algebraic symmetries as the Weyl tensor, if and only if it satisfies a
certain quadratic identity. This may be seen as the first Rainich theory result
for rank-4 tensors.


title:
Determination of the velocity of an emitter in spaces with affine
  connections and metrics

abstract:
  Doppler effect and Hubble effect in different models of space-time related to
the space-time velocity of an observer are considered. The Doppler effect and
Doppler shift frequency parameter are connected with the kinematic
characteristics of the relative velocity and the relative acceleration of the
emitter with respect to the observer (detector). The Hubble effect and Hubble
shift frequency parameter are considered in analogous way. It is shown that by
the use of the variation of the shift frequency parameter during a time period,
considered locally in the proper frame of reference of an observer, one can
directly determine the radial (centrifugal, centripetal) relative velocity and
acceleration as well as the tangential (Coriolis) relative velocity and
acceleration of an astronomical object moving relatively to the observer. All
results are obtained on purely kinematic basis without taking into account the
dynamic reasons for the considered effect. PACS numbers: 98.80.Jk; 98.62.Py;
04.90.+e; 04.80.Cc


title: Dirty black holes: Symmetries at stationary non-static horizons

abstract:
  We establish that the Einstein tensor takes on a highly symmetric form near
the Killing horizon of any stationary but non-static (and non-extremal) black
hole spacetime. [This follows up on a recent article by the current authors,
gr-qc/0402069, which considered static black holes.] Specifically, at any such
Killing horizon -- irrespective of the horizon geometry -- the Einstein tensor
block-diagonalizes into ``transverse'' and ``parallel'' blocks, and its
transverse components are proportional to the transverse metric. Our findings
are supported by two independent procedures; one based on the regularity of the
on-horizon geometry and another that directly utilizes the elegant nature of a
bifurcate Killing horizon. It is then argued that geometrical symmetries will
severely constrain the matter near any Killing horizon. We also speculate on
how this may be relevant to certain calculations of the black hole entropy.


title: Comments on photonic shells

abstract:
  We investigate in detail the special case of an infinitely thin static
cylindrical shell composed of counter-rotating photons on circular geodetical
paths separating two distinct parts of Minkowski spacetimes--one inside and the
other outside the shell--and compare it to a static disk shell formed by null
particles counter-rotating on circular geodesics within the shell located
between two sections of flat spacetime. One might ask whether the two cases are
not, in fact, merely one.


title: Optical cavities as amplitude filters for squeezed fields

abstract:
  We explore the use of Fabry-P\'erot cavities as high-pass filters for
squeezed light, and show that they can increase the sensitivity of
interferometric gravitational-wave detectors without the need for long
(kilometer scale) filter cavities. We derive the parameters for the filters,
and analyze the performance of several possible cavity configurations in the
context of a future gravitational-wave interferometer with squeezed light
(vacuum) injected into the output port.


title:
Three-dimensional relativistic simulations of rotating neutron-star
  collapse to a Kerr black hole

abstract:
  We present a new three-dimensional fully general-relativistic hydrodynamics
code using high-resolution shock-capturing techniques and a conformal traceless
formulation of the Einstein equations. Besides presenting a thorough set of
tests which the code passes with very high accuracy, we discuss its application
to the study of the gravitational collapse of uniformly rotating neutron stars
to Kerr black holes. The initial stellar models are modelled as relativistic
polytropes which are either secularly or dynamically unstable and with angular
velocities which range from slow rotation to the mass-shedding limit. We
investigate the gravitational collapse by carefully studying not only the
dynamics of the matter, but also that of the trapped surfaces, i.e. of both the
apparent and event horizons formed during the collapse. The use of these
surfaces, together with the dynamical horizon framework, allows for a precise
measurement of the black-hole mass and spin. The ability to successfully
perform these simulations for sufficiently long times relies on excising a
region of the computational domain which includes the singularity and is within
the apparent horizon. The dynamics of the collapsing matter is strongly
influenced by the initial amount of angular momentum in the progenitor star
and, for initial models with sufficiently high angular velocities, the collapse
can lead to the formation of an unstable disc in differential rotation. All the
simulations performed with uniformly rotating initial data and a polytropic or
ideal-fluid equation of state show no evidence of shocks or of the presence of
matter on stable orbits outside the black hole.


title: Dirac quasinormal frequencies in Schwarzschild-AdS space-time

abstract:
  We investigate the quasinormal mode frequencies for the massless Dirac field
in static four dimensional $AdS$ space-time. The separation of the Dirac
equation is achieved for the first time in $AdS$ space. Besides the relevance
that this calculation can have in the framework of the $AdS/CFT$ correspondence
between M-theory on $AdS_4\times S^7$ and SU(N) super Yang-Mills theory on
$M_3$, it also serves to fill in a gap in the literature, which has only been
concerned with particles of integral spin $0,1,2$.


title: Calculating Symmetries in Newman-Tamburino metrics

abstract:
  In this paper I show that the Newman-Tamburino spherical metrics always admit
a Killing vector, correcting a claim by Collinson and French, (1967 J. Math.
Phys. 8 701) and also admit a homothety. A similar calculation is given for the
limit of the Newman-Tamburino cylindrical metric.


title: Spherically symmetric spacetimes with a trapped surface

abstract:
  This paper investigates the global properties of a class of spherically
symmetric spacetimes. The class contains the maximal development of
asymptotically flat spherically symmetric initial data for a wide variety of
coupled Einstein-matter systems. For this class, it is proven here that the
existence of a single trapped surface or marginally trapped surface implies the
completeness of future null infinity and the formation of an event horizon
whose area radius is bounded by twice the final Bondi mass.


title: On naked singularities and the collapse of self-gravitating Higgs fields

abstract:
  We consider the problem of collapse of a self-gravitating Higgs field, with
potential bounded below by a (possibly negative) constant. The behaviour at
infinity may be either asymptotically flat or asymptotically AdS. This problem
has received much attention as a source for possible violations of weak cosmic
censorship in string theory. In this paper, we prove under spherical symmetry
that ``first singularities'' arising in the non-trapped region must necessarily
emanate from the centre. In particular, this excludes the formation of a
certain type of naked singularity which was recently conjectured to occur.


title: A note on boundary value problems for black hole evolutions

abstract:
  In recent work of Allen at. al., heuristic and numerical arguments were put
forth to suggest that boundary value problems for black hole evolution, where
an appropriate Sommerfeld radiation condition is imposed, would fail to produce
Price law tails. The interest in this issue lies in its possible implications
for numerical relativity, where black hole evolution is typically studied in
terms of such boundary formulations. In this note, it is shown rigorously that
indeed, Price law tails do not arise in this case, i.e. that Sommerfeld (and
more general) radiation conditions lead to decay faster than any polynomial
power. Our setting is the collapse of a spherically symmetric self-gravitating
scalar field. We allow an additional gravitationally coupled Maxwell field. The
proof also applies to the easier problem of a spherically symmetric solution of
the wave equation on a Schwarzschild or Reissner-Nordstrom background. The
method relies on previous work of the authors.


title: Dynamical evolution of unstable self-gravitating scalar solitons

abstract:
  Recently, static and spherically symmetric configurations of globally regular
self-gravitating scalar solitons were found. These configurations are unstable
with respect to radial linear perturbations. In this paper we study the
dynamical evolution of such configurations and show that, depending on the sign
of the initial perturbation, the solitons either collapse to a Schwarzschild
black hole or else ``explode'' into an outward moving domain wall.


title:
New criterion for direct black hole formation in rapidly rotating
  stellar collapse

abstract:
  We study gravitational collapse of rapidly rotating relativistic polytropes
of the adiabatic index $\Gamma = 1.5$ and 2, in which the spin parameter $q
\equiv J/M^{2} > 1$ where $J$ and $M$ are total angular momentum and
gravitational mass, in full general relativity.
  First, analyzing initial distributions of the mass and the spin parameter
inside stars, we predict the final outcome after the collapse. Then, we perform
fully general relativistic simulations on assumption of axial and equatorial
symmetries and confirm our predictions. As a result of simulations, we find
that in contrast with the previous belief, even for stars with $q > 1$, the
collapse proceeds to form a seed black hole at central region, and the seed
black hole subsequently grows as the ambient fluids accrete onto it. We also
find that growth of angular momentum and mass of the seed black hole can be
approximately determined from the initial profiles of the density and the
specific angular momentum. We define an effective spin parameter at the central
region of the stars, $q_{c}$, and propose a new criterion for black hole
formation as $q_{c} \alt 1$. Plausible reasons for the discrepancy between our
and previous results are clarified.


title: Geometric phase shift for detection of gravitational radiation

abstract:
  An effect of geometrical phase shift is predicted for a light beam
propagating in the field of a gravitational wave. Gravitational radiation
detection experiments are proposed using this new effect, the corresponding
estimates being given.


title: Hamiltonian formalism and spacetime symmetries in generic DSR models

abstract:
  We study the structure of the phase space of generic models of deformed
special relativity that gives rise to a definition of velocity consistent with
the deformed Lorentz symmetry. As a byproduct we also determine the laws of
transformation of spacetime coordinates.


title:
M{\o}ller Energy-Momentum Complex of a Static Axially Symmetric Vacuum
  Space-Time

abstract:
  The energy and momentum densities associated with the Weyl metric are
calculated using M{\o}ller's energy-momentum complex. These results are
compared with the results obtained by using the energy-momentum complexes of
Einstein, Landau and Lifshitz, Papapetrou and Bergmann. We show that the
aforementioned different prescriptions and that of M{\o}ller do not give the
same energy density, while give the same momentum density.


title: The Asymptotic Behaviour of Tilted Bianchi type VI$_0$ Universes

abstract:
  We study the asymptotic behaviour of the Bianchi type VI$_0$ universes with a
tilted $\gamma$-law perfect fluid. The late-time attractors are found for the
full 7-dimensional state space and for several interesting invariant subspaces.
In particular, it is found that for the particular value of the equation of
state parameter, $\gamma=6/5$, there exists a bifurcation line which signals a
transition of stability between a non-tilted equilibrium point to an extremely
tilted equilibrium point. The initial singular regime is also discussed and we
argue that the initial behaviour is chaotic for $\gamma<2$.


title:
Mathematical Clarification of General Relativistic Variational
  Principles

abstract:
  In this paper a mathematically precise global (i.e. not the usual local)
approach is presented to the variational principles of general relativistic
classical field theories.
  Problems of the classic (usual) approaches are also discussed in comparison.
  The aim of developing a global approach is to provide a possible tool for
future efforts on proving global existence theorems of field theoretical
solutions.


title: KIDs are non-generic

abstract:
  We prove that generic solutions of the vacuum constraint Einstein equations
do not possess any global or local space-time Killing vectors, on an
asymptotically flat Cauchy surface, or on a compact Cauchy surface with mean
curvature close to a constant, or for CMC asymptotically hyperbolic initial
data sets. More generally, we show that non-existence of global symmetries
implies, generically, non-existence of local ones. As part of the argument, we
prove that generic metrics do not possess any local or global conformal Killing
vectors.


title:
Photon deflection and precession of the periastron in terms of spatial
  gravitational fields

abstract:
  We show that a Maxwell-like system of equations for spatial gravitational
fields $\bf g$ and $\bf B$ (latter being the analogy of a magnetic field),
modified to include an extra term for the $\bf B$ field in the expression for
force, leads to the correct values for the photon deflection angle and for the
precession of the periastron.


title:
Quasigroups, Asymptotic Symmetries and Conservation Laws in General
  Relativity

abstract:
  A new quasigroup approach to conservation laws in general relativity is
applied to study asymptotically flat at future null infinity spacetime. The
infinite-parametric Newman-Unti group of asymptotic symmetries is reduced to
the Poincar\'e quasigroup and the Noether charge associated with any element of
the Poincar\'e quasialgebra is defined. The integral conserved quantities of
energy-momentum and angular momentum are linear on generators of Poincar\'e
quasigroup, free of the supertranslation ambiguity, posess the flux and
identically equal to zero in Minkowski spacetime.


title: Barotropic FRW cosmologies with a Dirac-like parameter

abstract:
  Using the known connection between Schroedinger-like equations and Dirac-like
equations in the supersymmetric context, we discuss an extension of FRW
barotropic cosmologies in which a Dirac mass-like parameter is introduced. New
Hubble cosmological parameters H_K(eta) depending on the Dirac-like parameter
are plotted and compared with the standard Hubble case H_0(eta). The new
H_K(eta) are complex quantities. The imaginary part is a supersymmetric way of
introducing dissipation and instabilities in the barotropic FRW hydrodynamics


title: Long term study of the seismic environment at LIGO

abstract:
  The LIGO experiment aims to detect and study gravitational waves using ground
based laser interferometry. A critical factor to the performance of the
interferometers, and a major consideration in the design of possible future
upgrades, is isolation of the interferometer optics from seismic noise. We
present the results of a detailed program of measurements of the seismic
environment surrounding the LIGO interferometers. We describe the experimental
configuration used to collect the data, which was acquired over a 613 day
period. The measurements focused on the frequency range 0.1-10 Hz, in which the
secondary microseismic peak and noise due to human activity in the vicinity of
the detectors was found to be particularly critical to interferometer
performance. We compare the statistical distribution of the data sets from the
two interferometer sites, construct amplitude spectral densities of seismic
noise amplitude fluctuations with periods of up to 3 months, and analyze the
data for any long term trends in the amplitude of seismic noise in this
critical frequency range.


title: Separable Hilbert space in Loop Quantum Gravity

abstract:
  We study the separability of the state space of loop quantum gravity. In the
standard construction, the kinematical Hilbert space of the
diffeomorphism-invariant states is nonseparable. This is a consequence of the
fact that the knot-space of the equivalence classes of graphs under
diffeomorphisms is noncountable. However, the continuous moduli labeling these
classes do not appear to affect the physics of the theory. We investigate the
possibility that these moduli could be only the consequence of a poor choice in
the fine-tuning of the mathematical setting. We show that by simply choosing a
minor extension of the functional class of the classical fields and
coordinates, the moduli disappear, the knot classes become countable, and the
kinematical Hilbert space of loop quantum gravity becomes separable.


title: Evolving a puncture black hole with fixed mesh refinement

abstract:
  We present an algorithm for treating mesh refinement interfaces in numerical
relativity. We detail the behavior of the solution near such interfaces located
in the strong field regions of dynamical black hole spacetimes, with particular
attention to the convergence properties of the simulations. In our applications
of this technique to the evolution of puncture initial data with vanishing
shift, we demonstrate that it is possible to simultaneously maintain second
order convergence near the puncture and extend the outer boundary beyond 100M,
thereby approaching the asymptotically flat region in which boundary condition
problems are less difficult and wave extraction is meaningful.


title: Comparison of QG-Induced Dispersion with Standard Physics Effects

abstract:
  One of the predictions of quantum gravity phenomenology is that, in
situations where Planck-scale physics and the notion of a quantum spacetime are
relevant, field propagation will be described by a modified set of laws.
Descriptions of the underlying mechanism differ from model to model, but a
general feature is that electromagnetic waves will have non-trivial dispersion
relations. A physical phenomenon that offers the possibility of experimentally
testing these ideas in the foreseeable future is the propagation of high-energy
gamma rays from GRB's at cosmological distances. With the observation of
non-standard dispersion relations within experimental reach, it is thus
important to find out whether there are competing effects that could either
mask or be mistaken for this one. In this letter, we consider possible effects
from standard physics, due to electromagnetic interactions, classical as well
as quantum, and coupling to classical geometry. Our results indicate that, for
currently observed gamma-ray energies and estimates of cosmological parameter
values, those effects are much smaller than the quantum gravity one if the
latter is first-order in the energy; some corrections are comparable in
magnitude with the second-order quantum gravity ones, but they have a very
different energy dependence.


title: Towards a Covariant Theory of Gravitation

abstract:
  A covariant reformulation of General Relativity is briefly considered from
three points of view: geometrodynamics, Lagrange-Euler field theory, and gauge
field theory. From a geometrodynamics perspective, a definition of the
reference frame as a differential manifold with an affine connection results in
separation of the respective contributions of inertial and gravitational fields
represented by the affine connection and the tensor of nonmetricity within the
Levi-Civita connection of GR. Resulting decomposition of the Einstein curvature
tensor into affine and nonmetric parts allows to recast Einstein's field
equations in a form invariant with respect to the choice of a reference frame
wherein the gravity is described by nonmetricity of space-time . A covariant
Lagrangian is proposed leading to the same field equation. All three approaches
ultimately lead to the same fully covariant theory of gravitation with a
covariant tensor of energy-momentum of the gravitational field and differential
and integral conservation laws. The role of the frames of reference, as
distinguished from coordinate systems, is discussed.


title:
Matters of Gravity, the newsletter of the APS Topical Group in
  Gravitation

abstract:
  GGR News:
  We hear that... by Jorge Pullin
  * Research Briefs:
  Too many coincidences?, by Laura Mersini
  The Quest for a Realistic Cosmology in String Theory, by Andrew Chamblin
  SFB/TR 7, by A. Gopakumar and D. Petroff
  The mock LISA data archive, by John Baker
  * Conference reports:
  Second Gravitational Wave Phenomenology Workshop, by Neil Cornish
  Apples with apples II, by Miguel Alcubierre
  3 Conferences for 30 years of Gravity at UNAM, by Alejandro Corichi
  Building bridges, by Mario Diaz
  Strings Meet Loops, by Martin Bojowald
  ICGC -- 2004, by Ghanashyam Date
  27th Spanish Relativity Meeting (ERE-2003), by J Miralles, J Font, J Pons
  Mathematical Relativity: New Ideas and Developments, by Simonetta Frittelli


title: Einstein-Schrodinger theory using Newman-Penrose tetrad formalism

abstract:
  The Einstein-Schrodinger theory is modified to include a large cosmological
constant caused by zero-point fluctuations. This ``extrinsic'' cosmological
constant which multiplies the symmetric metric is assumed to be nearly
cancelled by Schrodinger's ``bare'' cosmological constant which multiplies the
nonsymmetric fundamental tensor, such that the total cosmological constant is
consistent with measurement. This modified Einstein-Schrodinger theory is
expressed in Newman-Penrose form, and tetrad methods are used to confirm that
it closely approximates ordinary general relativity and electromagnetism. A
solution for the connections in terms of the fundamental tensor is derived in
the tetrad frame. The tetrad form of an exact electric monopole solution is
shown to approximate the Reissner-Nordstrom solution and to be of Petrov
type-D.