title:
Some Bianchi Type I Viscous Fluid Cosmological Models with a Variable
  Cosmological Constant

abstract:
  Some Bianchi type I viscous fluid cosmological models with a variable
cosmological constant are investigated in which the expansion is considered
only in two direction i.e. one of the Hubble parameter $(H_{1} =
\frac{A_{4}}{A})$ is zero. The viscosity coefficient of bulk viscous fluid is
assumed to be a power function of mass density whereas the coefficient of shear
viscosity is considered as constant in first case whereas in other case it is
taken as proportional to scale of expansion in the model. The cosmological
constant $\Lambda$ is found to be positive and is a decreasing function of time
which is supported by results from recent supernovae Ia observations. Some
physical and geometric properties of the models are also discussed.


title:
Probing the Microscopic Origin of Gravity via Precision Polarization and
  Spin Experiments

abstract:
  As in other parts of physics, we advocate the interaction approach:
experiments <--> phenomenology <--> low-energy effective (field) theory <-->
microscopic theory to probe the microscopic origin of gravity. Using chi-g
phenomenological framework, we discuss the tests of equivalence principles. The
only experimentally unconstrained degree of freedom is the axion freedom. It
has effects on the long-range astrophysical/cosmological propagation of
electromagnetic waves and can be tested/measured using future generation of
polarization measurement of cosmic background radiation. The verification or
refutal of this axionic effect will be a crucial step for constructing
effective theory and probing the microscopic origin of gravity. The interaction
of spin with gravity is another important clue for probing microscopic origin
of gravity. The interplay of experiments, phenomenology and effective theory is
expounded. An ideal way to reveal the microscopic origin of gravity is to
measure the gyrogravitational ratio of particles. Three potential experimental
methods are considered.


title:
Inflationary Quantum Cosmology: General Framework and Exact Bianchi I
  Solution

abstract:
  Using the methods of loop quantum gravity, we derive a framework for
describing an inflationary, homogeneous universe in a purely quantum theory.
The classical model is formulated in terms of the Ashtekar-Sen connection
variables for a general subclass of Bianchi class A spacetimes. This
formulation then provides a means to develop a corresponding quantum theory. An
exact solution is derived for the classical Bianchi type I model and the
corresponding semi-classical quantum state is found to also be an exact
solution to the quantum theory. The development of a normalizable quantum state
from this exact solution is presented and the implications for the
normalizability of the Kodama state discussed. We briefly consider some
consequences of such a quantum cosmological framework and show that the quantum
scale factor of the universe has a continuous spectrum in this model. This
result may suggest further modifications that are required to build a more
accurate theory. We close this study by suggesting a variety of directions in
which to take the results presented.


title: Propagation of Dirac Wave Functions in Accelerated Frames of Reference

abstract:
  The first-order gravity effects of Dirac wave functions are found from the
inertial effects in the accelerated frames of reference. Derivations and
discussions about Lense-Thirring effect and the gyrogravitational ratio for
intrinsic spin are presented. We use coordinate transformations among reference
frames to study and understand the Lense-Thirring effect of a scalar particle.
For a Dirac particle, the wave-function transformation operator from an
inertial frame to a moving accelerated frame is obtained. From this, the Dirac
wave function is solved and its change of polarization gives the
gyrogravitational ratio 1 for the first-order gravitational effects. The
eikonal approach to this problem is presented in the end for ready extension to
investigations involving curvature terms.


title: Gravitomagnetic Effects

abstract:
  The paper summarizes the most important effects in Einsteinian
gravitomagnetic fields related to propagating light rays, moving clocks and
atoms, orbiting objects, and precessing spins. Emphasis is put onto the
gravitational interaction of spinning objects. The gravitomagnetic field lines
of a rotating or spinning object are given in analytic form.


title:
A geometrically-induced varying speed of light (VSL) and the
  accelerating universe

abstract:
  We tackle the problem of the accelerating universe by reconsidering the most
general form of the metric when the speed of light is allowed to evolve with
time in a homogeneous and isotropic universe. A new varying speed of light
(VSL) model naturally emerges. We find it unconvenient to perform a general
coordinate transformation to obtain the usual constant $g_{tt}$ as such an
operation would mask the relation existing between the evolution of the scale
factor and the frequency shifts. In the model proposed the expansion rate and
the acceleration of the universe turn out to be apparent effects induced by the
evolution of the speed of light. The model is beneficial in that no sort of
exotic (and so far unobserved) fluids, not even a cosmological constant, are
needed for our solutions to be compatible with observations. Only dust and
radiation are put into the energy-momentum tensor and these are found to be
sufficient to reach the critical density for the model and therefore to obtain
a spatially-flat universe. The field equations for the model are derived and
solved. Among others, one fashinating possibility is that of an eternally
bouncing universe. The relation with the varying-$\alpha_\textsc{em}$ results
is discussed.


title:
Gravitomagnetic Fields in Rotating Superconductors due to Fractal
  Space-Time

abstract:
  This paper has been withdrawn by the authors due to the inconsistency of the
computations used for extra dimensions and the fractal dimensional approach of
the paper.
  An updated version of the paper will be published under a different title.


title: De Sitter Breaking in Field Theory

abstract:
  I argue against the widespread notion that manifest de Sitter invariance on
the full de Sitter manifold is either useful or even attainable in gauge
theories. Green's functions and propagators computed in a de Sitter invariant
gauge are generally more complicated than in some noninvariant gauges. What is
worse, solving the gauge-fixed field equations in a de Sitter invariant gauge
generally leads to violations of the original, gauge invariant field equations.
The most interesting free quantum field theories possess no normalizable, de
Sitter invariant states. This precludes the existence of de Sitter invariant
propagators. Even had such propagators existed, infrared divergent processes
would still break de Sitter invariance.


title: Hyperbolicity and Constrained Evolution in Linearized Gravity

abstract:
  Solving the 4-d Einstein equations as evolution in time requires solving
equations of two types: the four elliptic initial data (constraint) equations,
followed by the six second order evolution equations. Analytically the
constraint equations remain solved under the action of the evolution, and one
approach is to simply monitor them ({\it unconstrained} evolution). Since
computational solution of differential equations introduces almost inevitable
errors, it is clearly "more correct" to introduce a scheme which actively
maintains the constraints by solution ({\it constrained} evolution). This has
shown promise in computational settings, but the analysis of the resulting
mixed elliptic hyperbolic method has not been completely carried out. We
present such an analysis for one method of constrained evolution, applied to a
simple vacuum system, linearized gravitational waves.
  We begin with a study of the hyperbolicity of the unconstrained Einstein
equations. (Because the study of hyperbolicity deals only with the highest
derivative order in the equations, linearization loses no essential details.)
We then give explicit analytical construction of the effect of initial data
setting and constrained evolution for linearized gravitational waves. While
this is clearly a toy model with regard to constrained evolution, certain
interesting features are found which have relevance to the full nonlinear
Einstein equations.


title:
Classical and quantum dynamics of confined test particles in brane
  gravity

abstract:
  A model is constructed for the confinement of test particles moving on a
brane. Within the classical framework of this theory, confining a test particle
to the brane eliminates the effects of extra dimensions, rendering them
undetectable. However, in the quantized version of the theory, the effects of
the gauge fields and extrinsic curvature are pronounced and this might provide
a hint for detecting them. As a consequence of confinement the mass of the test
particle is shown to be quantized. The condition of stability against small
perturbations along extra dimensions is also studied and its relation to dark
matter is discussed.


title: The purely gravitational generalization of spin-rotation couplings

abstract:
  The nature of Mashhoon's spin-rotation coupling is the interaction between a
particle spin (gravitomagnetic moment) and a gravitomagnetic field. Here we
will consider the coupling of graviton spin to the weak gravitomagnetic fields
by analyzing the Lagrangian density of weak gravitational field, and hence
study the purely gravitational generalization of Mashhoon's spin-rotation
couplings.


title: Regge calculus: a unique tool for numerical relativity

abstract:
  The application of Regge calculus, a lattice formulation of general
relativity, is reviewed in the context of numerical relativity. Particular
emphasis is placed on problems of current computational interest, and the
strengths and weaknesses of the lattice approach are highlighted. Several new
and illustrative applications are presented, including initial data for the
head on collision of two black holes, and the time evolution of vacuum
axisymmetric Brill waves.


title: Differential Invariants for Higher-Rank Tensors. A Progress Report

abstract:
  We outline the construction of differential invariants for higher--rank
tensors.


title: Energy and entropy conservation for dynamical black holes

abstract:
  The Ashtekar-Krishnan energy-balance law for dynamical horizons, expressing
the increase in mass-energy of a general black hole in terms of the infalling
matter and gravitational radiation, is expressed in terms of trapping horizons,
allowing the inclusion of null (isolated) horizons as well as spatial
(dynamical) horizons. This first law of black-hole dynamics is given in
differential and integral forms, regular in the null limit. An effective
gravitational-radiation energy tensor is obtained, providing measures of both
ingoing and outgoing, transverse and longitudinal gravitational radiation on
and near a black hole. Corresponding energy-tensor forms of the first law
involve a preferred time vector which plays the role for dynamical black holes
which the stationary Killing vector plays for stationary black holes.
Identifying an energy flux, vanishing if and only if the horizon is null,
allows a division into energy-supply and work terms, as in the first law of
thermodynamics. The energy supply can be expressed in terms of area increase
and a newly defined surface gravity, yielding a Gibbs-like equation, with a
similar form to the so-called first law for stationary black holes. A
Clausius-like relation suggests a definition of geometric entropy flux. Taking
entropy as area/4 for dynamical black holes, it is shown that geometric entropy
is conserved: the entropy of the black hole equals the geometric entropy
supplied by the infalling matter and gravitational radiation. The area or
entropy of a dynamical horizon increases by the so-called second law, not
because entropy is produced, but because black holes classically are perfect
absorbers.


title: On the Universality of the Hawking Effect

abstract:
  Addressing the question of whether the Hawking effect depends on degrees of
freedom at ultra-high (e.g., Planckian) energies/momenta, we propose three
rather general conditions on these degrees of freedom under which the Hawking
effect is reproduced to lowest order. As a generalization of Corley's results,
we present a rather general model based on non-linear dispersion relations
satisfying these conditions together with a derivation of the Hawking effect
for that model. However, we also demonstrate counter-examples, which do not
appear to be unphysical or artificial, displaying strong deviations from
Hawking's result. Therefore, whether real black holes emit Hawking radiation
remains an open question and could give non-trivial information about Planckian
physics.
  PACS: 04.70.Dy, 04.62.+v, 04.60.-m, 04.20.Cv.


title: On the interaction of mesoscopic quantum systems with gravity

abstract:
  We review the different aspects of the interaction of mesoscopic quantum
systems with gravitational fields. We first discuss briefly the foundations of
general relativity and quantum mechanics. Then, we consider the
non-relativistic expansions of the Klein-Gordon and Dirac equations in the
post-Newtonian approximation. After a short overview of classical gravitational
waves, we discuss two proposed interaction mechanisms: (i) the use of quantum
fluids as generator and/or detector of gravitational waves in the laboratory,
and (ii) the inclusion of gravitomagnetic fields in the study of the properties
of rotating superconductors. The foundations of the proposed experiments are
explained and evaluated.


title:
On the initial value problem for second order scalar fluctuations in
  Einstein static

abstract:
  We consider fluctuations in a perfect irrotational fluid coupled to gravity
in an Einstein static universe background. We show that the homogeneous linear
perturbations of the scalar and metric fluctuations in the Einstein static
universe must be present if the second order constraint equations are to be
integrable. I.e., the 'linearization stability' constraint forces the presence
of these homogeneous modes. Since these linear homogeneous scalar modes are
well known to be exponentially unstable, the tactic of neglecting these modes
to create a long-lived, almost Einstein universe does not work, even if all
higher order (L $>$ 1) modes are dynamically stable.


title: Study of the Coleman - de Luccia instanton of the second order

abstract:
  We study the second order Coleman - de Luccia instanton which appears as the
curvature of the effective potential reaches a sufficiently large value. We
show how one can find the approximative formula for this instanton by
perturbative expansion in the case when the second derivative of the effective
potential divided by the Hubble parameter squared is close to -10, and we
perform a numerical study of this instanton in the case of quasi-exponential
potential.


title:
Tunneling into black hole, escape from black hole, reflection from
  horizon and pair creation

abstract:
  Within classical general relativity, a particle cannot reach the horizon of a
black hole during a finite time, in the reference frame of an external
observer; a particle inside cannot escape from a black hole; and the horizon
does not produce any reflection. We argue that these processes may possibly be
allowed in the quantum world. It is known that quantum mechanics allows pair
creation at the horizon (one particle inside, another particle outside) and
Hawking radiation. One can extend this idea to propose other processes.
Tunneling of an external particle inside black hole may be produced by the
creation of a pair at the horizon, followed by the annihilation of one created
particle with the initial particle outside, with the other created particle
appearing inside. Escape of a particle from a black hole may result from the
creation of a pair, followed by the annihilation of one created particle with
the particle inside, with the other created particle appearing outside. The
escape may allow the transfer of information to the outside.Finally, the
reflection of an external particle from the horizon may be modelled by a
combination of the two processes presented above. The relationship between
these "pair creation-annihilation'' mechanisms and the "horizon tunneling"
calculations [1-5] is discussed.


title: Brane-world Cosmologies with non-local bulk effects

abstract:
  It is very common to ignore the non-local bulk effects in the study of
brane-world cosmologies using the brane-world approach. However, we shall
illustrate through the use of three different scenarios, that the non-local
bulk-effect ${\cal P}_{\mu\nu}$ does indeed have significant impact on both the
initial and future behaviour of brane-world cosmologies.


title:
Space-Time geometry and thermodynamic properties of a self-gravitating
  ball of fluid in phase transition

abstract:
  A numerical solution of Einstein field equations for a spherical symmetric
and stationary system of identical and auto-gravitating particles in phase
transition is presented. The fluid possess a perfect fluid energy momentum
tensor, and the internal interactions of the system are represented by a van
der Walls like equation of state able to describe a first order phase
transition of the type gas-liquid. We find that the space-time curvature, the
radial component of the metric, and the pressure and density show
discontinuities in their radial derivatives in the phase coexistence region.
This region is found to be a spherical surface concentric with the star and the
system can be thought as a foliation of acronal, concentric and isobaric
surfaces in which the coexistence of phases occurs in only one of these
surfaces. This kind of system can be used to represent a star with a high
energy density core and low energy density mantle in hydrodynamic equilibrium.


title: The geodesic structure of the Schwarzschild Anti-de Sitter black hole

abstract:
  In the present work we found the geodesic structure of an AdS black hole. By
means of a detailed analyze of the corresponding effective potentials for
particles and photon, we found all the possible motions which are allowed by
the energy levels. Radial and non radial trajectories were exactly evaluated
for both geodesics. The founded orbits were plotted in order to have a direct
visualization of the allowed motions. We show that the geodesic structure of
this black hole presents new type of motions not allowed by the Schwarzschild
spacetime.


title: Schwarzschild and Synge once again

abstract:
  We complete the historical overview about the geometry of a Schwarzschild
black hole at its horizon by emphasizing the contribution made by J. L. Synge
in 1950 to its clarification.


title: The fine structure of Gowdy spacetimes

abstract:
  The approach to the singularity in Gowdy spacetimes consists of velocity term
dominated behavior, except at a set of isolated points. At and near these
points, spiky features grow. This paper reviews what is known about these
spikes.


abstract:
  The nature of gravitational singularities, long mysterious, has now become
clear through a combination of mathematical and numerical analysis. As the
singularity is approached, the time derivative terms in the field equations
dominate, and the singularity behaves locally like a homogeneous oscillatory
spacetime.


title:
Comparison of two field theoretical forms of gravitational wave
  equations

abstract:
  In the lowest nonlinear approximation I compare two gravitational wave
equations,- those of Weinberg and Papapetrou. The first one is simply a form of
Einstein equation and the second is claimed to be yet another field theoretical
form in which the energy-momentum tensor is obtained by Belinfante or Rosenfeld
method. I show that for interacting gravitational field these methods lead to
different energy-momentum tensors. Both these tensors need to be complemented
"by hand" with some interaction energy-momentum tensors in order that the
conservation laws of the total energy-momentum tensor give equation of motion
for particles in agreement with general relativity. In approximation considered
by Thirring, the Papapetrou wave equation must coincide with that of Thirring.
But they differ because Thirring inserted the necessary interaction term. I
show that Thirring wave equation is equivalent to Weinberg's one. Hence the
Papapetrou equation is not yet another form of Einstein equation.


title:
Leading order corrections to the cosmological evolution of tensor
  perturbations in braneworld

abstract:
  Tensor type perturbations in the expanding brane world of the Randall Sundrum
type are investigated. We consider a model composed of slow-roll inflation
phase and the succeeding radiation phase. The effect of the presence of an
extra dimension through the transition to the radiation phase is studied,
giving an analytic formula for leading order corrections.


title: Causal structure of acoustic spacetimes

abstract:
  The so-called ``analogue models of general relativity'' provide a number of
specific physical systems, well outside the traditional realm of general
relativity, that nevertheless are well-described by the differential geometry
of curved spacetime. Specifically, the propagation of acoustic disturbances in
moving fluids are described by ``effective metrics'' that carry with them
notions of ``causal structure'' as determined by an exchange of sound signals.
These acoustic causal structures serve as specific examples of what can be done
in the presence of a Lorentzian metric without having recourse to the Einstein
equations of general relativity. (After all, the underlying fluid mechanics is
governed by the equations of traditional hydrodynamics, not by the Einstein
equations.) In this article we take a careful look at what can be said about
the causal structure of acoustic spacetimes, focusing on those containing sonic
points or horizons, both with a view to seeing what is different from standard
general relativity, and to seeing what the similarities might be.


title:
A review of conventional explanations of anomalous observations during
  solar eclipses

abstract:
  Conventional explanations for observations of anomalous behaviour of
mechanical systems during solar eclipses are critically reviewed. These
observations include the work of Allais with paraconical pendula, those of Saxl
and Allen with a torsion pendulum and measurements with gravimeters. Attempts
of replications of these experiments and recent gravimeter results are
discussed and unpublished data by Latham and by Saxl et al. is presented. Some
of the data are summarized and re-analyzed. Especially, attention is paid to
observations of tilt of the vertical, which seems to play an important role in
this matter and recommendations for future research are given. It is concluded
that all the proposed conventional explanations either qualitatively or
quantitatively fail to explain the observations.


title: Light deflection in Weyl gravity: constraints on the linear parameter

abstract:
  Light deflection offers an unbiased test of Weyl's gravity since no
assumption on the conformal factor needs to be made. In this second paper of
our series ``Light deflection in Weyl gravity'', we analyze the constraints
imposed by light deflection experiments on the linear parameter of Weyl's
theory. Regarding solar system experiments, the recent CASSINI Doppler
measurements are used to infer an upper bound, $\sim 10^{-19} $m$^{-1}$, on the
absolute value of the above Weyl parameter. In non-solar system experiments, a
condition for unbound orbits together with gravitational mirage observations
enable us to further constrain the allowed negative range of the Weyl parameter
to $\sim -10^{-31} $m$^{-1}$. We show that the characteristics of the light
curve in microlensing or gravitational mirages, deduced from the lens equation,
cannot be recast into the General Relativistic predictions by a simple
rescaling of the deflector mass or of the ring radius. However, the corrective
factor, which depends on the Weyl parameter value and on the lensing
configuration, is small, even perhaps negligible, owing to the upper bound
inferred on the absolute value of a negative Weyl parameter. A statistical
study on observed lensing systems is required to settle the question.
  Our Weyl parameter range is more reliable than the single value derived by
Mannheim and Kazanas from fits to galactic rotation curves, $\sim +10^{-26}\
$m$^{-1}$. Indeed, the latter, although consistent with our bounds, is biased
by the choice of a specific conformal factor.


title: Consistent discretizations and quantum gravity

abstract:
  We review a recent proposal for the construction of a quantum theory of the
gravitational field. The proposal is based on approximating the continuum
theory by a discrete theory that has several attractive properties, among them,
the fact that in its canonical formulation it is free of constraints. This
allows to bypass many of the hard conceptual problems of traditional canonical
quantum gravity. In particular the resulting theory implies a fundamental
mechanism for decoherence and bypasses the black hole information paradox.


title: Dark energy, dark matter and fermion families in the two measures theory

abstract:
  A field theory is proposed where the regular fermionic matter and the dark
fermionic matter are different states of the same "primordial" fermion fields.
In regime of the fermion densities typical for normal particle physics, each of
the primordial fermions splits into three generations identified with regular
fermions. In a simple model, this fermion families birth effect is accompanied
with the right lepton numbers conservation laws. It is possible to fit the muon
to electron mass ratio without fine tuning of the Yukawa coupling constants.
When fermion energy density becomes comparable with dark energy density, the
theory allows new type of states - Cosmo-Low Energy Physics (CLEP) states.
Neutrinos in CLEP state can be both a good candidate for dark matter and
responsible for a new type of dark energy. In the latter case the total energy
density of the universe is less than it would be in the universe free of
fermionic matter at all. The (quintessence) scalar field is coupled to dark
matter but its coupling to regular fermionic matter appears to be extremely
suppressed.


title: The Hamilton-Jacobi Approach to Teleparallelism

abstract:
  We intend to analyse the constraint structure of Teleparallelism employing
the Hamilton-Jacobi formalism for singular systems. This study is conducted
without using an ADM 3+1 decomposition and without fixing time gauge condition.
It can be verified that the field equations constitute an integrable system.


title: A relativistic toy model for back-reaction

abstract:
  We consider a quantized massless and minimally coupled scalar field on a
circular closed string with a time-dependent radius $R(t)$, whose undisturbed
dynamics is governed by the Nambu-Goto action. Within the semi-classical
treatment, the back-reaction of the quantum field onto the string dynamics is
taken into account in terms of the renormalized expectation value of the
energy-momentum tensor including the trace anomaly. The results indicate that
the back-reaction could prevent the collapse of the circle $R\downarrow0$ --
however, the semi-classical picture fails to describe the string dynamics at
the turning point (i.e., possible bounce) at finite values of $R$ and $\dot R$.
The fate of the closed string after that point (e.g., oscillation or eternal
acceleration) cannot be determined within the semi-classical picture and thus
probably requires the full quantum treatment. PACS: 04.62.+v, 03.70.+k,
11.15.Kc, 04.60.-m.


title: A New Class of Path Equations in AP-Geometry

abstract:
  In the present work, it is shown that, the application of the Bazanski
approach to Lagrangians, written in AP-geometry and including the basic vector
of the space, gives rise to a new class of path equations. The general equation
representing this class contains four extra terms, whose vanishing reduces this
equation to the geodesic one. If the basic vector of the
  AP-geometry is considered as playing the role of the electromagnetic
potential, as done in a previous work, then the second term
  (of the extra terms) will represent Lorentz force while the fourth term gives
a direct effect of the electromagnetic potential on the motion of the charged
particle. This last term may give rise to an effect similar to the
Aharanov-Bohm effect. It is to be considered that all extra terms will vanish
if the space-time used is torsion-less.


title:
Cosmology and Static Spherically Symmetric solutions in D-dimensional
  Scalar Tensor Theories: Some Novel Features

abstract:
  We consider scalar tensor theories in D-dimensional spacetime, D \ge 4. They
consist of metric and a non minimally coupled scalar field, with its non
minimal coupling characterised by a function. The probes couple minimally to
the metric only. We obtain vacuum solutions - both cosmological and static
spherically symmetric ones - and study their properties. We find that, as seen
by the probes, there is no singularity in the cosmological solutions for a
class of functions which obey certain constraints. It turns out that for the
same class of functions, there are static spherically symmetric solutions which
exhibit novel properties: {\em e.g.} near the ``horizon'', the gravitational
force as seen by the probe becomes repulsive.


title:
Towards a few-percent measurement of the Lense-Thirring effect with the
  LAGEOS and LAGEOS II satellites?

abstract:
  Up to now attempts to measure the general relativistic Lense-Thirring effect
in the gravitational field of Earth have been performed by analyzing a suitable
J_2-J_4-free combination of the nodes Omega of LAGEOS and LAGEOS II and the
perigee omega of LAGEOS II with the Satellite Laser Ranging technique. The
claimed total accuracy is of the order of 20-30%, but, according to some
scientists, it could be an optimistic estimate. The main sources of systematic
errors are the mismodelling in the even zonal harmonic coefficients J_l of the
multipolar expansion of the gravitational potential of Earth and the
non-gravitational perturbations which plague especially the perigee of LAGEOS
II and whose impact on the proposed measurement is difficult to be reliably
assessed. Here we present some evaluations of the accuracy which could be
reached with a different J_2-free observable built up with the nodes of LAGEOS
and LAGEOS II in view of the new preliminary 2nd-generation Earth gravity
models from the GRACE mission. According to the GRACE-only based EIGEN-GRACE02S
solution, a 1-sigma upper bound of 4% for the systematic error due to the even
zonal harmonics can be obtained. In the near future it could be possible to
perform a reliable measurement of the Lense-Thirring effect by means of the
existing LAGEOS satellites with an accuracy of a few percent by adopting a time
span of a few years. The choice of a not too long observational temporal
interval would be helpful in reducing the impact of the secular variations of
the uncancelled even zonal harmonics dot J_4 and dot J_6 whose impact is
difficult to be reliably evaluated.


title:
Detecting extra dimensions with gravity wave spectroscopy: the black
  string brane-world

abstract:
  Using the black string between two branes as a model of a brane-world black
hole, we compute the gravity wave perturbations and identify the features
arising from the additional polarizations of the graviton. The standard
four-dimensional gravitational wave signal acquires late-time oscillations due
to massive modes of the graviton. The Fourier transform of these oscillations
shows a series of spikes associated with the masses of the Kaluza-Klein modes,
providing in principle a spectroscopic signature of extra dimensions.


title: On the counting of black hole states in loop quantum gravity

abstract:
  We argue that counting black hole states in loop quantum gravity one should
take into account only states with the minimal spin at the horizon.


title:
Initial state of matter fields and trans-Planckian physics: Can CMB
  observations disentangle the two?

abstract:
  The standard, scale-invariant, inflationary perturbation spectrum will be
modified if the effects of trans-Planckian physics are incorporated into the
dynamics of the matter field in a phenomenological manner, say, by the
modification of the dispersion relation. The spectrum also changes if we retain
the standard dynamics but modify the initial quantum state of the matter field.
We show that, given {\it any} spectrum of perturbations, it is possible to
choose a class of initial quantum states which can exactly reproduce this
spectrum with the standard dynamics. We provide an explicit construction of the
quantum state which will produce the given spectrum. We find that the various
modified spectra that have been recently obtained from `trans-Planckian
considerations' can be constructed from suitable squeezed states above the
Bunch-Davies vacuum in the standard theory. Hence, the CMB observations can, at
most, be useful in determining the initial state of the matter field in the
standard theory, but it can {\it not} help us to discriminate between the
various Planck scale models of matter fields. We study the problem in the
Schrodinger picture, clarify various conceptual issues and determine the
criterion for negligible back reaction due to modified initial conditions.


title:
Well-posed first-order reduction of the characteristic problem of the
  linearized Einstein equations

abstract:
  A choice of first-order variables for the characteristic problem of the
linearized Einstein equations is found which casts the system into manifestly
well-posed form. The concept of well-posedness for characteristic problems
invoked is that there exists an \textit{a priori} estimate of the solution of
the characteristic problem in terms of the data. The notion of manifest
well-posedness consists of an algebraic criterion sufficient for the existence
of the estimates, and is to characteristic problems as symmetric hyperbolicity
is to Cauchy problems. Both notions have been made precise elsewere.


title: Quantum Singularities

abstract:
  The definitions of classical and quantum singularities in general relativity
are reviewed. The occurence of quantum mechanical singularities in certain
spherically symmetric and cylindrically symmetric (including infinite line
mass)spacetimes is considered. A strong repulsive ``potential'' near the
classical singularity is shown to turn a classically singular spacetime into a
quantum mechanically nonsingular spacetime.


title:
Classical and Quantum Causality in Quantum Field Theory. Or, "The
  Quantum Universe"

abstract:
  Based on a number of experimentally verified physical observations, it is
argued that the standard principles of quantum mechanics should be applied to
the Universe as a whole. Thus, a paradigm is proposed in which the entire
Universe is represented by a pure state wavefunction contained in a
factorisable Hilbert space of enormous dimension, and where this statevector is
developed by successive applications of operators that correspond to unitary
rotations and Hermitian tests. Moreover, because by definition the Universe
contains everything, it is argued that these operators must be chosen
self-referentially; the overall dynamics of the system is envisaged to be
analogous to a gigantic, self-governing, quantum computation. The issue of how
the Universe could choose these operators without requiring or referring to a
fictitious external observer is addressed.
  The processes by which conventional physics might be recovered from this
fundamental, mathematical and global description of reality are particularly
investigated. Specifically, it is demonstrated that by considering the changing
properties, separabilities and factorisations of both the state and the
operators as the Universe proceeds though a sequence of discrete computations,
familiar notions such as classical distinguishability, particle physics, space,
time, special relativity and endo-physical experiments can all begin to emerge
from the proposed picture. A pregeometric vision of cosmology is therefore
discussed, with all of physics ultimately arising from the relationships
occurring between the elements of the underlying mathematical structure.


title: Back-reaction effect in power-law inflation

abstract:
  I consider a power-law inflationary model taking into account back-reaction
effects. The interesting result is that the spectrum for the scalar field
fluctuations does not depends on the expansion rate of the universe $p$ and
that it result to be scale invariant for cosmological scales. However, the
amplitude for these fluctuations depends on $p$.


title: General Slow-Roll Spectrum for Gravitational Waves

abstract:
  We derive the power spectrum P_\psi(k) of the gravitational waves produced
during general classes of inflation with second order corrections. Using this
result, we also derive the spectrum and the spectral index in the standard
slow-roll approximation with new higher order corrections.


title:
The Speciality Index as invariant indicator in the BKL Mixmaster
  Dynamics

abstract:
  The speciality index, which has been mainly used in Numerical Relativity for
studying gravitational waves phenomena as an indicator of the special or
non-special Petrov type character of a spacetime, is applied here in the
context of Mixmaster cosmology, using the Belinski-Khalatnikov-Lifshitz map.
Possible applications for the associated chaotic dynamics are discussed.


title: Fluid accretion onto relativistic stars and gravitational radiation

abstract:
  This article reports results from numerical simulations of the gravitational
radiation emitted from nonrotating relativistic stars as a result of the
axisymmetric accretion of layers of perfect fluid matter, shaped in the form of
quadrupolar shells. We adopt a {\em hybrid} procedure where we evolve
numerically the polar nonspherical perturbations equations of the star coupled
to a fully nonlinear hydrodynamics code that calculates the motion of the
accreting matter. Self-gravity of the accreting fluid as well as radiation
reaction effects are neglected.


title:
Quasinormal modes for single horizon black holes in generic 2-d dilaton
  gravity

abstract:
  There has been some recent speculation that a connection may exist between
the quasinormal-mode spectra of highly damped black holes and the fundamental
theory of quantum gravity. This notion follows from a conjecture by Hod that
the real part of the highly damped mode frequencies can be used to calibrate
the semi-classical level spacing in the black hole quantum area spectrum.
However, even if the level spacing can be fixed in this manner, it still
remains unclear whether this implies a physically significant "duality" or
merely a numerical coincidence. This tapestry of ideas serves as the motivation
for the current paper. We utilize the "monodromy approach" to calculate the
quasinormal-mode spectra for a generic class of black holes in two-dimensional
dilatonic gravity. Our results agree with the prior literature whenever a
direct comparison is possible and provide the analysis of a much more diverse
class of black hole models than previously considered.


title:
Tilted Bianchi Type V Bulk Viscous Cosmological Models with Varying
  $\Lambda$-Term

abstract:
  Conformally flat tilted Bianchi type V cosmological models in presence of a
bulk viscous fluid and heat flow are investigated. The coefficient of bulk
viscosity is assumed to be a power function of mass density. The cosmological
constant is found to be a decreasing function of time, which is supported by
results from recent type Ia supernovae observations. Some physical and
geometric aspects of the models are also discussed.


title: The Jang equation, apparent horizons, and the Penrose inequality

abstract:
  The Jang equation in the spherically symmetric case reduces to a first order
equation. This permits an easy analysis of the role apparent horizons play in
the (non)existence of solutions. We demonstrate that the proposed derivation of
the Penrose inequality based on the Jang equation cannot work in the
spherically symmetric case. Thus it is fruitless to apply this method, as it
stands, to the general case. We show also that those analytic criteria for the
formation of horizons that are based on the use of the Jang equation are of
limited validity for the proof of the trapped surface conjecture.


title: Finitary-Algebraic `Resolution' of the Inner Schwarzschild Singularity

abstract:
  A `resolution' of the interior singularity of the spherically symmetric
Schwarzschild solution of the Einstein equations for the gravitational field of
a point-particle is carried out entirely and solely by finitistic and algebraic
means. To this end, the background differential spacetime manifold and
Calculus-free purely algebraic (:sheaf-theoretic) conceptual and technical
machinery of Abstract Differential Geometry (ADG) is employed via Sorkin's
finitary (:locally finite) poset substitutes of continuous manifolds in their
Gel'fand-dual picture in terms of discrete differential incidence algebras and
the finitary spacetime sheaves thereof. It is shown that the Einstein equations
hold not only at the finitary poset level of `discrete events', but also at a
suitable `classical continuum limit' of the said finitary sheaves and the
associated differential triads that they define ADG-theoretically. We infer
that the law of gravity does not break down in any (differential geometric)
sense in the vicinity of the locus of the point-mass as the usual manifold
based analysis of spacetime singularities in General Relativity has hitherto
maintained. Various possible implications that such a total evasion of smooth
gravitational singularities, as well as some anticipations of the wider
significance that the general ADG-framework, may have for certain current `hot'
issues in both classical and quantum gravity research are briefly discussed at
the end.


title:
Classical and thermodynamical aspects of black holes with conformally
  coupled scalar field hair

abstract:
  We discuss the existence, stability and classical thermodynamics of
four-dimensional, spherically symmetric black hole solutions of the Einstein
equations with a conformally coupled scalar field. We review the solutions
existing in the literature with zero, positive and negative cosmological
constant. We also outline new results on the thermodynamics of these black
holes when the cosmological constant is non-zero.


title: Symmetric Hyperbolic System in the Self-dual Teleparallel Gravity

abstract:
  In order to discuss the well-posed initial value formulation of the
teleparallel gravity and apply it to numerical relativity a symmetric
hyperbolic system in the self-dual teleparallel gravity which is equivalent to
the Ashtekar formulation is posed. This system is different from the ones in
other works by that the reality condition of the spatial metric is included in
the symmetric hyperbolicity and then is no longer an independent condition. In
addition the constraint equations of this system are rather simpler than the
ones in other works.


title: Self-dual teleparallel gravity and the positive energy theorem

abstract:
  A self-dual and anti-self-dual decomposition of the teleparallel gravity is
carried out and the self-dual Lagrangian of the teleparallel gravity which is
equivalent to the Ashtekar Lagrangian in vacuum is obtained. Its Hamiltonian
formulation and the constraint analysis are developed. Starting from Witten's
equation Nester's gauge condition is derived directly and a new expression of
the boundary term is obtained. Using this expression and Witten's identity the
proof of the positive energy theorem by Nester et al is extended to a case
including momentum.


title: Weyl metrics and the generating conjecture

abstract:
  By means of Ernst complex potential formalism it is shown, that previously
studied static axisymmetric Einstein-Maxwell fields obtained though the
application of the Horsky-Mitskievitch generating conjecture represent a
combination of Kinnersley's transformations [W. Kinnersley: J. Math. Phys. 14
(1973) 651]. New theoretical background for the conjecture is suggested and
commented.


title:
Fundamental decoherence from relational time in discrete quantum
  gravity: Galilean covariance

abstract:
  We have recently argued that if one introduces a relational time in quantum
mechanics and quantum gravity, the resulting quantum theory is such that pure
states evolve into mixed states. The rate at which states decohere depends on
the energy of the states. There is therefore the question of how this can be
reconciled with Galilean invariance. More generally, since the relational
description is based on objects that are not Dirac observables, the issue of
covariance is of importance in the formalism as a whole. In this note we work
out an explicit example of a totally constrained, generally covariant system of
non-relativistic particles that shows that the formula for the relational
conditional probability is a Galilean scalar and therefore the decoherence rate
is invariant.


title:
Gravity as elasticity of spacetime: a paradigm to understand horizon
  thermodynamics and cosmological constant

abstract:
  It is very likely that the quantum description of spacetime is quite
different from what we perceive at large scales, $l\gg (G\hbar/c^3)^{1/2}$. The
long wave length description of spacetime, based on Einstein's equations, is
similar to the description of a continuum solid made of a large number of
microscopic degrees of freedom. This paradigm provides a novel interpretation
of coordinate transformations as deformations of "spacetime solid" and allows
one to obtain Einstein's equations as a consistency condition in the long
wavelength limit. The entropy contributed by the microscopic degrees of freedom
reduces to a pure surface contribution when Einstein's equations are satisfied.
The horizons arises as "defects" in the "spacetime solid" (in the sense of well
defined singular points) and contributes an entropy which is one quarter of the
horizon area. Finally, the response of the microstructure to vacuum energy
leads to a near cancellation of the cosmological constant, leaving behind a
tiny fluctuation which matches with the observed value.


title:
Static spherically symmetric constant density relativistic and Newtonian
  stars in the Lobachevskyan geometry

abstract:
  The present paper has the purpose to illustrate the importance of the ideas
and constructions of the Non-Euclidean (Lobachevsky) Geometry, which can be
applied even today for solving some conceptually important problems. We study
the static and spherically symmetric solutions to the Einstein field equations
under the assumption that the space-time may possess an arbitrary number of
spatial dimensions. A new exact solution of a perfect fluid sphere of constant
(homogeneous) energy-density which agrees with interior Lobachevsky geometry
for 3D and 4D spaces are found. We discuss the property of temporal scalar
field arise in lower-dimensional theories as the reduction of extra dimension.


title:
Mathematical properties of cosmological models with accelerated
  expansion

abstract:
  An introduction to solutions of the Einstein equations defining cosmological
models with accelerated expansion is given. Connections between mathematical
and physical issues are explored. Theorems which have been proved for solutions
with positive cosmological constant or nonlinear scalar fields are reviewed.
Some remarks are made on more exotic models such as the Chaplygin gas, tachyons
and $k$-essence.


title:
Extra force and extra mass from noncompact Kaluza-Klein theory in a
  cosmological model

abstract:
  Using the Hamilton-Jacobi formalism, we study extra force and extra mass in a
recently introduced noncompact Kaluza-Klein cosmological model. We examine the
inertial 4D mass $m_0$ of the inflaton field on a 4D FRW bulk in two examples.
We find that $m_0$ has a geometrical origin and antigravitational effects on a
non inertial 4D bulk should be a consequence of the motion of the fifth
coordinate with respect to the 4D bulk.


title: Simulations of laser locking to a LISA arm

abstract:
  We present detailed numerical simulations of a laser phase stabilization
scheme for LISA, where both lasers emitting along one arm are locked to each
other. Including the standard secondary noises and spacecraft motions that
approximately mimic LISA's orbit, we verify that very stable laser phases can
be obtained, and that time delay interferometry can be used to remove the laser
phase noise from measurements of gravitational wave strains. Most importantly,
we show that this locking scheme can provide significant simplifications over
LISA's baseline design in the implementation of time delay interferometry.


title: On 3+1 Dimensional Scalar Field Cosmologies

abstract:
  In this communication, we analyze the case of 3+1 dimensional scalar field
cosmologies in the presence, as well as in the absence of spatial curvature, in
isotropic, as well as in anisotropic settings. Our results extend those of
Hawkins and Lidsey [Phys. Rev. D {\bf 66}, 023523 (2002)], by including the
non-flat case. The Ermakov-Pinney methodology is developed in a general form,
allowing through the converse results presented herein to use it as a tool for
constructing new solutions to the original equations. As an example of this
type a special blowup solution recently obtained in Christodoulakis {\it et
al.} [gr-qc/0302120] is retrieved. Additional solutions of the 3+1 dimensional
gravity coupled with the scalar field are also obtained. To illustrate the
generality of the approach, we extend it to the anisotropic case of Bianchi
types I and V and present some related open problems.


title: Nonsingular Spherical Models with a Variable Cosmological term

abstract:
  Exact solutions of the Einstein's field equations describing a spherically
symmetric cosmological model without a big bang or any other kind of
singularity recently obtained by Dadhich and Patel (2000) are revisited. The
matter content of the model is a shear-free perfect fluid with isotropic
pressure and a radial heat flux. Three different exact solutions are obtained
for both perfect fluid and fluid with bulk viscosity. It turns out that the
cosmological rerm $\Lambda(t)$ is a decreasing function of time, which is
consistent with recent observations of type Ia supernovae.


title:
A Note on Energy-Momentum Conservation in Palatini Formulation of L(R)
  Gravity

abstract:
  By establishing that Palatini formulation of $L(R)$ gravity is equivalent to
$\omega=-3/2$ Brans-Dicke theory, we show that energy-momentum tensor is
covariantly conserved in this type of modified gravity theory.


title:
Numerical computation of constant mean curvature surfaces using finite
  elements

abstract:
  This paper presents a method for computing two-dimensional constant mean
curvature surfaces. The method in question uses the variational aspect of the
problem to implement an efficient algorithm. In principle it is a flow like
method in that it is linked to the gradient flow for the area functional, which
gives reliable convergence properties. In the background a preconditioned
conjugate gradient method works, that gives the speed of a direct elliptic
multigrid method.


title:
Unstable even-parity eigenmodes of the regular static SU(2)
  Yang-Mills-dilaton solutions

abstract:
  In this paper we obtain unstable even-parity eigenmodes to the static regular
spherically symmetric solutions of the SU(2) Yang-Mills-dilaton coupled system
of equations in 3+1 Minkowski space-time. The corresponding matrix
Sturm-Liouville problem is solved numerically by means of the continuous
analogue of Newton's method. The method, being the powerful tool for solving
both boundary-value and Sturm-Liouville problems, is described in details.


title:
Knot points of double--covariant system of elliptic equations and
  preferred frames in general relativity

abstract:
  The elliptic system of equations, which is general-covariant and locally
SU(2)-covariant, is investigated. The new condition of the Dirichlet problem
solvability and the condition of zeros absence for solutions are obtained for
this system, which contains in particular case the Sen-Witten equation. On this
basis it is proved the existence of the wide class of hypersurfaces, in all
points of which there exists a correspondence between the Sen-Witten spinor
field and three-frame, which generalizes the Nester orthoframe. The Nester
special orthoframe also exists on a certain subclass containing not only the
maximal hypersurfaces.


title:
Time asymmetric spacetimes near null and spatial infinity. I. Expansions
  of developments of conformally flat data

abstract:
  The Conformal Einstein equations and the representation of spatial infinity
as a cylinder introduced by Friedrich are used to analyse the behaviour of the
gravitational field near null and spatial infinity for the development of data
which are asymptotically Euclidean, conformally flat and time asymmetric. Our
analysis allows for initial data whose second fundamental form is more general
than the one given by the standard Bowen-York Ansatz. The Conformal Einstein
equations imply upon evaluation on the cylinder at spatial infinity a hierarchy
of transport equations which can be used to calculate in a recursive way
asymptotic expansions for the gravitational field. It is found that the the
solutions to these transport equations develop logarithmic divergences at
certain critical sets where null infinity meets spatial infinity. Associated to
these, there is a series of quantities expressible in terms of the initial data
(obstructions), which if zero, preclude the appearance of some of the
logarithmic divergences. The obstructions are, in general, time asymmetric.
That is, the obstructions at the intersection of future null infinity with
spatial infinity are different, and do not generically imply those obtained at
the intersection of past null infinity with spatial infinity. The latter allows
for the possibility of having spacetimes where future and past null infinity
have different degrees of smoothness. Finally, it is shown that if both sets of
obstructions vanish up to a certain order, then the initial data has to be
asymptotically Schwarzschildean to some degree.


title:
Sen-Witten orthonormal three-frame and gravitational energy
  quasilocalization

abstract:
  Expression for the Witten-Nester 4-spinor 3-form of the Hamiltonian density
of gravitational field in the asymptotically flat space-time in terms of the
Sommers-Sen spinors, direct with a certain orthonormal three-frame connect, is
obtained. A direct connection between the one and the ADM Hamiltonian density
in the Sen-Witten frame is established on this basis.


title: Gravitational collapse in anti de Sitter space

abstract:
  A numerical and analytic treatment is presented here of the evolution of
initial data of the kind that was conjectured by Hertog, Horowitz and Maeda to
lead to a violation of cosmic censorship. That initial data is essentially a
thick domain wall connecting two regions of anti de Sitter space. The evolution
results in no violation of cosmic censorship, but rather the formation of a
small black hole.


title: Entropy of gravitationally collapsing matter in FRW universe models

abstract:
  We look at a gas of dust and investigate how its entropy evolves with time
under a spherically symmetric gravitational collapse. We treat the problem
perturbatively and find that the classical thermodynamic entropy does actually
increase to first order when one allows for gravitational potential energy to
be transferred to thermal energy during the collapse. Thus, in this situation
there is no need to resort to the introduction of an intrinsic gravitational
entropy in order to satisfy the second law of thermodynamics.


title: The Penrose inequality and apparent horizons

abstract:
  A spherically symmetric spacetime is presented with an initial data set that
is asymptotically flat, satisfies the dominant energy condition, and such that
on this initial data $M<\sqrt{A/16\pi}$, where M is the total (ADM) mass and A
is the area of the apparent horizon. This provides a counterexample to a
commonly stated version of the Penrose inequality, though it does not
contradict the ``true'' Penrose inequality.


title: Schwarzschild and Birkhoff a la Weyl

abstract:
  We provide a simple derivation of the Schwarzschild solution in General
Relativity, generalizing an early approach by Weyl, to include Birkhoff's
theorem: constancy of the mass; its deeper, Hamiltonian, basis is also given.
Our procedure is illustrated by a parallel derivation of the Coulomb field and
constancy of electric charge, in electrodynamics.


title: Compactness of the space of causal curves

abstract:
  We prove that the space of causal curves between compact subsets of a
separable globally hyperbolic poset is itself compact in the Vietoris topology.
Although this result implies the usual result in general relativity, its proof
does not require the use of geometry or differentiable structure.


title: Newtonian limit of the singular f(R) gravity in the Palatini formalism

abstract:
  Recently D. Vollick [Phys. Rev. D68, 063510 (2003)] has shown that the
inclusion of the 1/R curvature terms in the gravitational action and the use of
the Palatini formalism offer an alternative explanation for cosmological
acceleration. In this work we show not only that this model of Vollick does not
have a good Newtonian limit, but also that any f(R) theory with a pole of order
n in R=0 and its second derivative respect to R evaluated at Ro is not zero,
where Ro is the scalar curvature of background, does not have a good Newtonian
limit.


title:
Generation of Bianchi type V cosmological models with varying
  $\Lambda$-term

abstract:
  Bianchi type V perfect fluid cosmological models are investigated with
cosmological term $\Lambda$ varying with time. Using a generation technique
(Camci {\it et al.}, 2001), it is shown that the Einstein's field equations are
solvable for any arbitrary cosmic scale function. Solutions for particular
forms of cosmic scale functions are also obtained. The cosmological constant is
found to be decreasing function of time, which is supported by results from
recent type Ia supernovae observations. Some physical aspects of the models are
also discussed.


title: A local potential for the Weyl tensor in all dimensions

abstract:
  In all dimensions and arbitrary signature, we demonstrate the existence of a
new local potential -- a double (2,3)-form -- for the Weyl curvature tensor,
and more generally for all tensors with the symmetry properties of the Weyl
curvature tensor. The classical four-dimensional Lanczos potential for a Weyl
tensor -- a double (2,1)-form -- is proven to be a particular case of the new
potential: its double dual.


title:
Existence and stability of even dimensional asymptotically de Sitter
  spaces

abstract:
  A new proof of Friedrich's theorem on the existence and stability of
asymptotically de Sitter spaces in 3+1 dimensions is given, which extends to
all even dimensions. In addition, we characterize the possible limits of spaces
which are globally asymptotically de Sitter, to the past and future.


title: Negative energy and stability in scalar-tensor gravity

abstract:
  Linearized gravitational waves in Brans-Dicke and scalar-tensor theories
carry negative energy. A gauge-invariant analysis shows that the background
Minkowski space is stable at the classical level with respect to linear scalar
and tensor inhomogeneous perturbations.


title:
Difficulties with Recollapsing models in Closed Isotropic Loop Quantum
  Cosmology

abstract:
  The use of techniques from loop quantum gravity for cosmological models may
solve some difficult problems in quantum cosmology. The solutions under a
number of circumstances have been well studied. We will analyse the behaviour
of solutions in the closed model, focusing on the behaviour of a universe
containing a massless scalar field. The asymptotic behaviour of the solutions
is examined, and is used to determine requirements of the initial conditions.


title: Finite temperature effects in brane cosmology

abstract:
  Finite temperature effects in brane world cosmology are studied by
considering the interaction between scalar field and bulk gravity. One-loop
correction to zero-temperature potential is computed by taking into account,
interaction of scalar field and bulk gravity. Phase transitions and high
temperature symmetry restoration are examined. Critical temperature of phase
transitions depends on the interaction constant of the scalar field and bulk
gravity, and these constant is an order parameter. Present study can account
for second order phase transition in early universe, in brane world
cosmological scenario.


title: On the laser frequency stabilization by locking to a LISA arm

abstract:
  LISA is an array of three spacecraft flying in an approximately equilateral
triangle configuration, which will be used as a low-frequency detector of
gravitational waves. Recently a technique has been proposed for suppressing the
phase noise of the onboard lasers by locking them to the LISA arms. In this
paper we show that the delay-induced effects substantially modify the
performance of this technique, making it different from the conventional
locking of lasers to optical resonators. We analyze these delay-induced effects
in both transient and steady-state regimes and discuss their implications for
the implementation of this technique on LISA.


title:
Late time tails from momentarily stationary, compact initial data in
  Schwarzschild spacetimes

abstract:
  An L-pole perturbation in Schwarzschild spacetime generally falls off at late
times t as t^{-2L-3}. It has recently been pointed out by Karkowski,
Swierczynski and Malec, that for initial data that is of compact support, and
is initially momentarily static, the late-time behavior is different, going as
t^{-2L-4}. By considering the Laplace transforms of the fields, we show here
why the momentarily stationary case is exceptional. We also explain, using a
time-domain description, the special features of the time development in this
exceptional case.


title: Exact Solutions of Lovelock-Born-Infeld Black Holes

abstract:
  The exact five-dimensional charged black hole solution in Lovelock gravity
coupled to Born-Infeld electrodynamics is presented. This solution interpolates
between the Hoffmann black hole for the Einstein-Born-Infeld theory and other
solutions in the Lovelock theory previously studied in the literature. The
conical singularity of the metric around the origin can be removed by a proper
choice of the black hole parameters. The thermodynamic properties of the
solution are also analyzed and, in particular, it is shown that the behaviour
of the specific heat indicates the existence of a stability transition point in
the vacuum solutions. We discuss the similarities existing between this
five-dimensional geometry and the three-dimensional black hole. Like BTZ black
hole, the Lovelock black hole has an infinite lifetime.


title: Background independence in a nutshell

abstract:
  We study how physical information can be extracted from a background
independent quantum system. We use an extremely simple `minimalist' system that
models a finite region of 3d euclidean quantum spacetime with a single
equilateral tetrahedron. We show that the physical information can be expressed
as a boundary amplitude. We illustrate how the notions of "evolution" in a
boundary proper-time and "vacuum" can be extracted from the background
independent dynamics.


title: Two Loop Scalar Self-Mass during Inflation

abstract:
  We work in the locally de Sitter background of an inflating universe and
consider a massless, minimally coupled scalar with a quartic self-interaction.
We use dimensional regularization to compute the fully renormalized scalar
self-mass-squared at one and two loop order for a state which is released in
Bunch-Davies vacuum at t=0. Although the field strength and coupling constant
renormalizations are identical to those of lfat space, the geometry induces a
non-zero mass renormalization. The finite part also shows a sort of growing
mass that competes with the classical force in eventually turning off this
system's super-acceleration.


title: Analogue Hawking Radiation from Astrophysical Black Hole Accretion

abstract:
  We show that spherical accretion onto astrophysical black holes can be
considered as a natural example of analogue system. We provide, for the first
time, an exact analytical scheme for calculating the analogue Hawking
temperature and surface gravity for general relativistic accretion onto
astrophysical black holes. Our calculation may bridge the gap between the
theory of transonic astrophysical accretion and the theory of analogue Hawking
radiation. We show that the domination of the analogue Hawking temperature over
the actual Hawking temperature may be a real astrophysical phenomena. We also
discuss the possibilities of the emergence of analogue white holes around
astrophysical black holes. Our calculation is general enough to accommodate
accreting black holes with any mass.


title: Quantum Holonomies in (2+1)-Dimensional Gravity

abstract:
  We describe an approach to the quantization of (2+1)--dimensional gravity
with topology R x T^2 and negative cosmological constant, which uses two
quantum holonomy matrices satisfying a q--commutation relation. Solutions of
diagonal and upper--triangular form are constructed, which in the latter case
exhibit additional, non--trivial internal relations for each holonomy matrix.
This leads to the notion of quantum matrix pairs. These are pairs of matrices
with non-commuting entries, which have the same pattern of internal relations,
q-commute with each other under matrix multiplication, and are such that
products of powers of the matrices obey the same pattern of internal relations
as the original pair. This has implications for the classical moduli space,
described by ordered pairs of commuting SL(2,R) matrices modulo simultaneous
conjugation by SL(2,R) matrices.


title: Some Applications of the ADM Formalism

abstract:
  The ADM Formalism is discussed in the context of 2+1--dimensional gravity,
uniting two areas of relativity theory in which Stanley Deser has been
particularly active. For spacetimes with topology R x T^2 the partially reduced
and fully reduced ADM formalism are related and quantized, and the role of
"large diffeomorphisms" (the modular group) in the quantum theory is
illustrated.


title: Asymmetric radiating brane-world

abstract:
  At high energies on a cosmological brane of Randall-Sundrum type, particle
interactions can produce gravitons that are emitted into the bulk and that can
feed a bulk black hole. We generalize previous investigations of such radiating
brane-worlds by allowing for a breaking of Z_2-symmetry, via different bulk
cosmological constants and different initial black hole masses on either side
of the brane. One of the notable features of asymmetry is a suppression of the
asymptotic level of dark radiation, which means that nucleosynthesis
constraints are easier to satisfy. There are also models where the radiation
escapes to infinity on one or both sides, rather than falling into a black
hole, but these models can have negative energy density on the brane.


title: Newtonian limits of warp drive spacetimes

abstract:
  We find a class of warp drive spacetimes possessing Newtonian limits, which
we then determine. The same method is used to compute Newtonian limits of the
Schwarzschild solution and spatially flat Friedmann-Robertson-Walker
cosmological models.


title: Energy-Momentum of a regular MMaS-class black hole

abstract:
  We compute the energy and momentum of a regular black hole of type defined by
Mars, Martin-Prats, and Senovilla using the Einstein and Papapetrou definitions
for energy-momentum density. Some other definitions of energy-momentum density
are shown to give mutually contradictory and less reasonable results. Results
support the Cooperstock hypothesis.


title:
Anomalous Polarization-Curvature Interaction in a Gravitational-Wave
  Field

abstract:
  An exact solution to the dynamic equations for a massive boson traveling in a
pp-wave gravitational background under the influence of the force induced by
curvature, is presented. We focus on the effect of anomalous
polarization-curvature interaction and consider models in which the coupling
constant of such an interaction is treated to be either a deterministic
quantity or a random variable.


title: Effective Action and Hawking Flux from Covariant Perturbation Theory

abstract:
  The computation of the radiation flux related to the Hawking temperature of a
Schwarzschild Black Hole or another geometric background is still well-known to
be fraught with a number of delicate problems. In spherical reduction, as shown
by one of the present authors (W. K.) with D.V. Vassilevich, the correct black
body radiation follows when two ``basic components'' (conformal anomaly and a
``dilaton'' anomaly) are used as input in the integrated energy-momentum
conservation equation. The main new element in the present work is the use of a
quite different method, the covariant perturbation theory of Barvinsky and
Vilkovisky, to establish directly the full effective action which determines
these basic components. In the derivation of W. K. and D.V. Vassilevich the
computation of the dilaton anomaly implied one potentially doubtful
intermediate step which can be avoided here. Moreover, the present approach
also is sensitive to IR (renormalisation) effects. We realize that the
effective action naturally leads to expectation values in the Boulware vacuum
which, making use of the conservation equation, suffice for the computation of
the Hawking flux in other quantum states, in particular for the relevant Unruh
state. Thus, a rather comprehensive discussion of the effects of (UV and IR)
renormalisation upon radiation flux and energy density is possible.


title: Distorted Black Hole Initial Data Using the Puncture Method

abstract:
  We solve for single distorted black hole initial data using the puncture
method, where the Hamiltonian constraint is written as an elliptic equation in
R^3 for the nonsingular part of the metric conformal factor. With this approach
we can generate isometric and non--isometric black hole data. For the isometric
case, our data are directly comparable to those obtained by Bernstein et al.,
who impose isometry boundary conditions at the black hole throat. Our numerical
simulations are performed using a parallel multigrid elliptic equation solver
with adaptive mesh refinement. Mesh refinement allows us to use high resolution
around the black hole while keeping the grid boundaries far away in the
asymptotic region.


title:
Late-time evolution of charged massive Dirac fields in the
  Reissner-Nordstr\"om black-hole background

abstract:
  The late-time evolution of the charged massive Dirac fields in the background
of a Reissner-Norstr\"om (RN) black hole is studied. It is found that the
intermediate late-time behavior is dominated by an inverse power-law decaying
tail without any oscillation in which the dumping exponent depends not only on
the multiple number of the wave mode but also on the field parameters. It is
also found that, at very late times, the oscillatory tail has the decay rate of
$t^{-5/6}$ and the oscillation of the tail has the period $2\pi/\mu$ which is
modulated by two types of long-term phase shifts.


title: Geophysical studies with laser-beam detectors of gravitational waves

abstract:
  The existing high technology laser-beam detectors of gravitational waves may
find very useful applications in an unexpected area - geophysics. To make
possible the detection of weak gravitational waves in the region of high
frequencies of astrophysical interest, ~ 30 - 10^3 Hz, control systems of laser
interferometers must permanently monitor, record and compensate much larger
external interventions that take place in the region of low frequencies of
geophysical interest, ~ 10^{-5} - 3 X 10^{-3} Hz. Such phenomena as tidal
perturbations of land and gravity, normal mode oscillations of Earth,
oscillations of the inner core of Earth, etc. will inevitably affect the
performance of the interferometers and, therefore, the information about them
will be stored in the data of control systems. We specifically identify the
low-frequency information contained in distances between the interferometer
mirrors (deformation of Earth) and angles between the mirrors' suspensions
(deviations of local gravity vectors and plumb lines). We show that the access
to the angular information may require some modest amendments to the optical
scheme of the interferometers, and we suggest the ways of doing that. The
detailed evaluation of environmental and instrumental noises indicates that
they will not prevent, even if only marginally, the detection of interesting
geophysical phenomena. Gravitational-wave instruments seem to be capable of
reaching, as a by-product of their continuous operation, very ambitious
geophysical goals, such as observation of the Earth's inner core oscillations.


title: Chi-square test on candidate events from CW signal coherent searches

abstract:
  In a blind search for continuous gravitational wave signals scanning a wide
frequency band one looks for candidate events with significantly large values
of the detection statistic. Unfortunately, a noise line in the data may also
produce a moderately large detection statistic.
  In this paper, we describe how we can distinguish between noise line events
and actual continuous wave (CW) signals, based on the shape of the detection
statistic as a function of the signal's frequency. We will analyze the case of
a particular detection statistic, the F statistic, proposed by Jaranowski,
Krolak, and Schutz.
  We will show that for a broad-band 10 hour search, with a false dismissal
rate smaller than 1e-6, our method rejects about 70 % of the large candidate
events found in a typical data set from the second science run of the Hanford
LIGO interferometer.


title: Braneworld cosmological solutions and their stability

abstract:
  We consider cosmological solutions and their stability with respect to
homogeneous and isotropic perturbations in the braneworld model with the
scalar-curvature term in the action for the brane. Part of the results are
similar to those obtained by Campos and Sopuerta for the Randall-Sundrum
braneworld model. Specifically, the expanding de Sitter solution is an
attractor, while the expanding Friedmann solution is a repeller. In the
braneworld theory with the scalar-curvature term in the action for the brane,
static solutions with matter satisfying the strong energy condition exist not
only with closed spatial geometry but also with open and flat ones even in the
case where the dark-radiation contribution is absent. In a certain range of
parameters, static solutions are stable with respect to homogeneous and
isotropic perturbations.


title: Coordinate time dependence in Quantum Gravity

abstract:
  The intuitive classical space-time picture breaks down in quantum gravity,
which makes a comparison and the development of semiclassical techniques quite
complicated. Using ingredients of the group averaging method to solve
constraints one can nevertheless introduce a classical coordinate time into the
quantum theory, and use it to investigate the way a semiclassical continuous
description emerges from discrete quantum evolution. Applying this technique to
test effective classical equations of loop cosmology and their implications for
inflation and bounces, we show that the effective semiclassical theory is in
good agreement with the quantum description even at short scales.


title:
Slice Energy in Higher Order Gravity Theories and Conformal
  Transformations

abstract:
  We study the generic transport of slice energy between the scalar field
generated by the conformal transformation of higher-order gravity theories and
the matter component. We give precise relations for this exchange in the cases
of dust and perfect fluids. We show that, unless we are in a stationary
spacetime where slice energy is always conserved, in non-stationary situations
contributions to the total slice energy depend on whether or not test matter
follows geodesics in both frame representations of the dynamics, that is on
whether or not the two conformally related frames are physically
indistinguishable.


title: Torsion and the Gravitational Interaction

abstract:
  By using a nonholonomous-frame formulation of the general covariance
principle, seen as an active version of the strong equivalence principle, an
analysis of the gravitational coupling prescription in the presence of
curvature and torsion is made. The coupling prescription implied by this
principle is found to be always equivalent with that of general relativity, a
result that reinforces the completeness of this theory, as well as the
teleparallel point of view according to which torsion does not represent
additional degrees of freedom for gravity, but simply an alternative way of
representing the gravitational field.


title: Backreaction in the Lemaitre-Tolman-Bondi model

abstract:
  We study backreaction analytically using the parabolic Lemaitre-Tolman-Bondi
universe as a toy model. We calculate the average expansion rate and energy
density on two different hypersurfaces and compare the results. We also
consider the Hubble law and find that backreaction slows down the expansion if
measured with proper time, but speeds it up if measured with energy density.


title: Exact uncertainty approach in quantum mechanics and quantum gravity

abstract:
  The assumption that an ensemble of classical particles is subject to
nonclassical momentum fluctuations, with the fluctuation uncertainty fully
determined by the position uncertainty, has been shown to lead from the
classical equations of motion to the Schroedinger equation. This 'exact
uncertainty' approach may be generalised to ensembles of gravitational fields,
where nonclassical fluctuations are added to the field momentum densities, of a
magnitude determined by the uncertainty in the metric tensor components. In
this way one obtains the Wheeler-DeWitt equation of quantum gravity, with the
added bonus of a uniquely specified operator ordering. No a priori assumptions
are required concerning the existence of wavefunctions, Hilbert spaces,
Planck's constant, linear operators, etc. Thus this approach has greater
transparency than the usual canonical approach, particularly in regard to the
connections between quantum and classical ensembles. Conceptual foundations and
advantages are emphasised.


title: Quasinormal modes and classical wave propagation in analogue black holes

abstract:
  Many properties of black holes can be studied using acoustic analogues in the
laboratory through the propagation of sound waves. We investigate in detail
sound wave propagation in a rotating acoustic (2+1)-dimensional black hole,
which corresponds to the ``draining bathtub'' fluid flow. We compute the
quasinormal mode frequencies of this system and discuss late-time power-law
tails. Due to the presence of an ergoregion, waves in a rotating acoustic black
hole can be superradiantly amplified. We compute superradiant reflection
coefficients and instability timescales for the acoustic black hole bomb, the
equivalent of the Press-Teukolsky black hole bomb. Finally we discuss
quasinormal modes and late-time tails in a non-rotating canonical acoustic
black hole, corresponding to an incompressible, spherically symmetric
(3+1)-dimensional fluid flow.

categories: gr-qc astro-ph hep-ph hep-th physics.flu-dyn


title: Noncommutative Quantum Cosmology

abstract:
  We consider noncommutative quantum cosmology in the case of the low-energy
string effective theory. Exacts solutions are found and compared with the
commutative case.The Noncommutative quantum cosmology is considered in the case
of the low-energy string effective theory. Exacts solutions are found and
compared with the commutative case.


title: Duality in linearized gravity

abstract:
  We show that duality transformations of linearized gravity in four
dimensions, i.e., rotations of the linearized Riemann tensor and its dual into
each other, can be extended to the dynamical fields of the theory so as to be
symmetries of the action and not just symmetries of the equations of motion.
Our approach relies on the introduction of two "superpotentials", one for the
spatial components of the spin-2 field and the other for their canonically
conjugate momenta. These superpotentials are two-index, symmetric tensors. They
can be taken to be the basic dynamical fields and appear locally in the action.
They are simply rotated into each other under duality. In terms of the
superpotentials, the canonical generator of duality rotations is found to have
a Chern-Simons like structure, as in the Maxwell case.


title: Euclidean action for vacuum decay in a de Sitter universe

abstract:
  The behavior of the action of the instantons describing vacuum decay in a de
Sitter is investigated. For a near-to-limit instanton (a Coleman-de Luccia
instanton close to some Hawking-Moss instanton) we find approximate formulas
for the Euclidean action by expanding the scalar field and the metric of the
instanton in the powers of the scalar field amplitude. The order of the
magnitude of the correction to the Hawking-Moss action depends on the order of
the instanton (the number of crossings of the barrier by the scalar field): for
instantons of odd and even orders the correction is of the fourth and third
order in the scalar field amplitude, respectively. If a near-to-limit instanton
of the first order exists in a potential with the curvature at the top of the
barrier greater than 4 $\times$ (Hubble constant)$^2$, which is the case if the
fourth derivative of the potential at the top of the barrier is greater than
some negative limit value, the action of the instanton is less than the
Hawking-Moss action and, consequently, the instanton determines the outcome of
the vacuum decay if no other Coleman-de Luccia instanton is admitted by the
potential. A numerical study shows that for the quartic potential the physical
mode of the vacuum decay is given by the Coleman-de Luccia instanton of the
first order also in the region of parameters in which the potential admits two
instantons of the second order.


title:
Gravitational wave detectors based on matter wave interferometers (MIGO)
  are no better than laser interferometers (LIGO)

abstract:
  We show that a recent claim that matter wave interferometers have a much
higher sensitivity than laser interferometers for a comparable physical setup
is unfounded. We point out where the mistake in the earlier analysis is made.
We also disprove the claim that only a description based on the geodesic
deviation equation can produce the correct physical result. The equations for
the quantum dynamics of non-relativistic massive particles in a linearly
perturbed spacetime derived here are useful for treating a wider class of
related physical problems. A general discussion on the use of atom
interferometers for the detection of gravitational waves is also provided.


title: Decay Rate and Low-Energy Near-Horizon Dynamics of Acoustic Black Holes

abstract:
  We study the low-energy dynamics of an acoustic black hole near the sonic
horizon. For the experimental test of black hole evaporation in the laboratory,
the decay rate (greybody factor) of the acoustic black hole (sonic hole) can be
calculated by the usual low-energy perturbation method. As a consequence, we
obtain the decay rate of the sonic horizon from the absorption and the
reflection coefficients. Moreover, we show that the thermal emission from the
sonic horizon is only proportional to a control parameter which describes the
velocity of the fluid.


title: On astrophysical bounds of the cosmological constant

abstract:
  Astrophysical bounds on the cosmological constant are examined for
spherically symmetric bodies. Similar limits emerge from hydrostatical and
gravitational equilibrium and the validity of the Newtonian limit. It is argued
that the bound coming from the analysis of exact solutions is not a feature of
the relativistic theory since it also emerges from the Newtonian theory.
  The methods in use seem to be disjoint from the basic principles, however
they have the same implication regarding the upper bounds. Therefore we will
compare different inequalities and comment on the possible relationship between
them.


title:
Gravitational instability of Einstein-Gauss-Bonnet black holes under
  tensor mode perturbations

abstract:
  We analyze the tensor mode perturbations of static, spherically symmetric
solutions of the Einstein equations with a quadratic Gauss-Bonnet term in
dimension $D > 4$. We show that the evolution equations for this type of
perturbations can be cast in a Regge-Wheeler-Zerilli form, and obtain the exact
potential for the corresponding Schr\"odinger-like stability equation. As an
immediate application we prove that for $D \neq 6$ and $\alpha >0$, the sign
choice for the Gauss-Bonnet coefficient suggested by string theory, all
positive mass black holes of this type are stable. In the exceptional case $D
=6$, we find a range of parameters where positive mass asymptotically flat
black holes, with regular horizon, are unstable. This feature is found also in
general for $\alpha < 0$.


title:
Semiclassical Quantum Gravity: Statistics of Combinatorial Riemannian
  Geometries

abstract:
  This paper is a contribution to the development of a framework, to be used in
the context of semiclassical canonical quantum gravity, in which to frame
questions about the correspondence between discrete spacetime structures at
"quantum scales" and continuum, classical geometries at large scales. Such a
correspondence can be meaningfully established when one has a "semiclassical"
state in the underlying quantum gravity theory, and the uncertainties in the
correspondence arise both from quantum fluctuations in this state and from the
kinematical procedure of matching a smooth geometry to a discrete one. We focus
on the latter type of uncertainty, and suggest the use of statistical geometry
as a way to quantify it. With a cell complex as an example of discrete
structure, we discuss how to construct quantities that define a smooth
geometry, and how to estimate the associated uncertainties. We also comment
briefly on how to combine our results with uncertainties in the underlying
quantum state, and on their use when considering phenomenological aspects of
quantum gravity.


title: Counter example to a quantum inequality

abstract:
  A `quantum inequality' (a conjectured relation between the energy density of
a free quantum field and the time during which this density is observed) has
recently been used to rule out some of the macroscopic wormholes and warp
drives. I discuss the possibility of generalizing that result to other similar
spacetimes and first show that the problem amounts to verification of a
slightly different inequality. This new inequality \emph{can} replace the
original one, if an additional assumption (concerning homogeneity of the
`exotic matter' distribution) is made, and \emph{must} replace it if the
assumption is relaxed. Then by an explicit example I show that the `new'
inequality breaks down even in a simplest case (a free field in a simply
connected two dimensional space). Which suggests that there is no grounds today
to consider such spacetimes `unphysical'.


title:
Obtaining a class of Type N pure radiation metrics using invariant
  operators

abstract:
  We develop further the integration procedure in the generalised invariant
formalism, and demonstrate its efficiency by obtaining a class of Petrov type N
pure radiation metrics without any explicit integration, and with comparatively
little detailed calculations. The method is similar to the one exploited by
Edgar and Vickers when deriving the general conformally flat pure radiation
metric. A major addition to the technique is the introduction of non-intrinsic
elements in generalised invariant formalism, which can be exploited to keep
calculations manageable.


title:
Renormalization and dimensional regularization for a scalar field with
  Gauss-Bonnet-type coupling to curvature

abstract:
  We consider a scalar field with a Gauss-Bonnet-type coupling to the curvature
in a curved space-time. For such a quadratic coupling to the curvature, the
metric energy-momentum tensor does not contain derivatives of the metric of
orders greater than two. We obtain the metric energy-momentum tensor and find
the geometric structure of the first three counterterms to the vacuum averages
of the energy-momentum tensor for an arbitrary background metric of an
N-dimensional space-time. In a homogeneous isotropic space, we obtain the first
three counterterms of the n-wave procedure, which allow calculating the
renormalized values of the vacuum averages of the energy-momentum tensors in
the dimensions N=4,5. Using dimensional regularization, we establish that the
geometric structures of the counterterms in the $n$-wave procedure coincide
with those in the effective action method.


title: Confusion Noise from LISA Capture Sources

abstract:
  Captures of compact objects (COs) by massive black holes (MBHs) in galactic
nuclei will be an important source for LISA, the space-based gravitational-wave
(GW) detector. However, a large fraction of captures will not be individually
resolvable--either because they are too distant, have unfavorable orientation,
or have too many years to go before final plunge--and so will constitute a
source of ``confusion noise,'' obscuring other types of sources. Here we
estimate the shape and overall magnitude of the spectrum of confusion noise
from CO captures. The overall magnitude depends on the capture rates, which are
rather uncertain, so we present results for a plausible range of rates. We show
that the impact of capture confusion noise on the total LISA noise curve ranges
from insignificant to modest, depending on these rates. Capture rates at the
high end of estimated ranges would raise LISA's overall (effective) noise level
by at most a factor \sim 2. While this slightly elevated noise level would
somewhat decrease LISA's sensitivity to other classes of sources, overall, this
would be a pleasant problem for LISA to have: It would also imply that
detection rates for CO captures were at nearly their maximum possible levels
(given LISA's baseline design). This paper includes several other results that
should be useful in further studies of LISA capture sources, including (i) a
calculation of the total GW energy output from generic inspirals into Kerr
MBHs, and (ii) an approximate GW energy spectrum for a typical capture.


title: Cotton Blend Gravity $pp$ Waves

abstract:
  We study conformal gravity in d=2+1, where the Cotton tensor is equated to
a--necessarily traceless--matter stress tensor, for us that of the improved
scalar field. We first solve this system exactly in the $pp$ wave regime, then
show it to be equivalent to topologically massive gravity.


title: High Frequency Asymptotics for the Spin-Weighted Spheroidal Equation

abstract:
  We fully determine a uniformly valid asymptotic behaviour for large $a
\omega$ and fixed $m$ of the angular solutions and eigenvalues of the
spin-weighted spheroidal differential equation. We fully complement the
analytic work with a numerical study.


title:
Asymptotic quasinormal modes of a coupled scalar field in the
  Garfinkle-Horowitz-Strominger dilaton spacetime

abstract:
  The analytic forms of the asymptotic quasinormal frequencies of a coupled
scalar field in the Garfinkle-Horowitz-Strominger dilaton spacetime is
investigated by using the monodromy technique proposed by Motl and Neitzke. It
is found that the asymptotic quasinormal frequencies depend not only on the
structure parameters of the background spacetime, but also on the coupling
between the scalar fields and gravitational field. Moreover, our results show
that only in the minimal couple case, i.e., $\xi$ tends zero, the real parts of
the asymptotic quasinormal frequencies agrees with the Hod's conjecture,
$T_H\ln{3}$.


title: Vortex geometry for the equatorial slice of the Kerr black hole

abstract:
  The spacetime geometry on the equatorial slice through a Kerr black hole is
formally equivalent to the geometry felt by phonons entrained in a rotating
fluid vortex. We analyse this situation in some detail: First, we find the most
general ``acoustic geometry'' compatible with the fluid dynamic equations in a
collapsing/expanding perfect-fluid line vortex. Second, we demonstrate that
there is a suitable choice of coordinates on the equatorial slice through a
Kerr black hole that puts it into this vortex form; though it is not possible
to put the entire Kerr spacetime into perfect-fluid ``acoustic'' form. Finally,
we briefly discuss the implications of this formal equivalence; both with
respect to gaining insight into the Kerr spacetime and with respect to possible
vortex-inspired experiments.


title: How Spacetime Foam modifies the brick wall

abstract:
  We re-examine the brick-wall model in the context of spacetime foam. In
particular we consider a foam composed by wormholes of different sizes filling
the black hole horizon. The contribution of such wormholes is computed via a
scale invariant distribution. We obtain that the brick wall divergence appears
to be logarithmic when the cutoff is sent to zero.


title: Casimir Energy and the Cosmological Constant

abstract:
  We regard the Wheeler-De Witt equation as a Sturm-Liouville problem with the
cosmological constant considered as the associated eigenvalue. The used method
to study such a problem is a variational approach with Gaussian trial wave
functionals. We approximate the equation to one loop in a Schwarzschild
background. A zeta function regularization is involved to handle with
divergences. The regularization is closely related to the subtraction procedure
appearing in the computation of Casimir energy in a curved background. A
renormalization procedure is introduced to remove the infinities together with
a renormalization group equation.


title:
Ultrarelativistic Motion: Inertial and Tidal Effects in Fermi
  Coordinates

abstract:
  Fermi coordinates are the natural generalization of inertial Cartesian
coordinates to accelerated systems and gravitational fields. We study the
motion of ultrarelativistic particles and light rays in Fermi coordinates and
investigate inertial and tidal effects beyond the critical speed c/sqrt(2). In
particular, we discuss the black-hole tidal acceleration mechanism for
ultrarelativistic particles in connection with a possible origin for
high-energy cosmic rays.


title: Surface stresses on a thin shell surrounding a traversable wormhole

abstract:
  We match an interior solution of a spherically symmetric traversable wormhole
to a unique exterior vacuum solution, with a generic cosmological constant, at
a junction interface, and the surface stresses on the thin shell are deduced.
In the spirit of minimizing the usage of exotic matter we determine regions in
which the weak and null energy conditions are satisfied on the junction
surface. The characteristics and several physical properties of the surface
stresses are explored, namely, regions where the sign of the tangential surface
pressure is positive and negative (surface tension) are determined. This is
done by expressing the tangential surface pressure as a function of several
parameters, namely, that of the matching radius, the redshift parameter, the
surface energy density and of the generic cosmological constant. An equation
governing the behavior of the radial pressure across the junction surface is
also deduced.


title:
Exhaustive Ghost Solutions to Einstein-Weyl Equations for Two
  Dimensional Spacetimes

abstract:
  Exhaustive ghost solutions to Einstein-Weyl equations for two dimensional
spacetimes are obtained, where the ghost neutrinos propagate in the background
spacetime, but do not influence the background spacetime due to the vanishing
stress-energy-momentum tensor for the ghost neutrinos. Especially, those
non-trivial ghost solutions provide a counterexample to the traditional claim
that the Einstein-Hilbert action has no meaningful two dimensional analogue.


title: Causal Loop Quantum Gravity and Cosmological Solutions

abstract:
  We shall present here the causal interpretation of canonical quantum gravity
in terms of new variables. Then we shall apply it to the minisuperspace of
cosmology. A vacuum solution of quantum cosmology is obtained and the Bohmian
trajectory is investigated. At the end a coherent state with matter is
considered in the cosmological model.


title: Weak field reduction in teleparallel coframe gravity. Vacuum case

abstract:
  The teleparallel coframe gravity may be viewed as a generalization of the
standard GR. A coframe (a field of four independent 1-forms) is considered, in
this approach, to be a basic dynamical variable. The metric tensor is treated
as a secondary structure. The general Lagrangian, quadratic in the first order
derivatives of the coframe field is not unique. It involves three dimensionless
free parameters. We consider a weak field approximation of the general coframe
teleparallel model. In the linear approximation, the field variable, the
coframe, is covariantly reduced to the superposition of the symmetric and
antisymmetric field. We require this reduction to be preserved on the levels of
the Lagrangian, of the field equations and of the conserved currents. This
occurs if and only if the pure Yang - Mills type term is removed from the
Lagrangian. The absence of this term is known to be necessary and sufficient
for the existence of the viable (Schwarzschild) spherical-symmetric solution.
Moreover, the same condition guarantees the absence of ghosts and tachyons in
particle content of the theory. The condition above is shown recently to be
necessary for a well defined Hamiltonian formulation of the model. Here we
derive the same condition in the Lagrangian formulation by means of the weak
field reduction.