title: Quantum Black Holes: Entropy and Entanglement on the Horizon

abstract:
  We are interested in black holes in Loop Quantum Gravity (LQG). We study the
simple model of static black holes: the horizon is made of a given number of
identical elementary surfaces and these small surfaces all behaves as a spin-s
system accordingly to LQG. The chosen spin-s defines the area unit or area
resolution, which the observer uses to probe the space(time) geometry. For
s=1/2, we are actually dealing with the qubit model, where the horizon is made
of a certain number of qubits. In this context, we compute the black hole
entropy and show that the factor in front of the logarithmic correction to the
entropy formula is independent of the unit s. We also compute the entanglement
between parts of the horizon. We show that these correlations between parts of
the horizon are directly responsible for the asymptotic logarithmic
corrections. This leads us to speculate on a relation between the evaporation
process and the entanglement between a pair of qubits and the rest of the
horizon. Finally, we introduce a concept of renormalisation of areas in LQG.


title:
Quantization of Friedmann-Robertson-Walker spacetimes in the presence of
  a negative cosmological constant and radiation

abstract:
  We quantize three Friedmann-Robertson-Walker models in the presence of a
negative cosmological constant and radiation. The models differ from each other
by the constant curvature of the spatial sections, which may be positive,
negative or zero. They give rise to Wheeler-DeWitt equations for the scale
factor which have the form of the Schroedinger equation for the quartic
anharmonic oscillator. We find their eigenvalues and eigenfunctions by using a
method first developed by Chhajlany and Malnev, and use the eigenfunctions in
order to construct wave packets for each case and evaluate the time-dependent
expected value of the scale factors. We find for all of them that the expected
values of the scale factors oscillate between maximum and minimum values. Since
the expectation values of the scale factors never vanish, we conclude that
these models do not have singularities.


title: Plane symmetric inhomogeneous bulk viscous domain wall in Lyra geometry

abstract:
  Some bulk viscous general solutions are found for domain walls in Lyra
geometry in the plane symmetric inhomogeneous spacetime. Expressions for the
energy density and pressure of domain walls are derived in both cases of
uniform and time varying displacement field $\beta$. The viscosity coefficient
of bulk viscous fluid is assumed to be a power function of mass density. Some
physical consequences of the models are also given. Finally, the geodesic
equations and acceleration of the test particle are discussed.


title: Finiteness and Dual Variables for Lorentzian Spin Foam Models

abstract:
  We describe here some new results concerning the Lorentzian Barrett-Crane
model, a well-known spin foam formulation of quantum gravity. Generalizing an
existing finiteness result, we provide a concise proof of finiteness of the
partition function associated to all non-degenerate triangulations of
4-manifolds and for a class of degenerate triangulations not previously shown.
This is accomplished by a suitable re-factoring and re-ordering of integration,
through which a large set of variables can be eliminated. The resulting
formulation can be interpreted as a ``dual variables'' model that uses
hyperboloid variables associated to spin foam edges in place of representation
variables associated to faces. We outline how this method may also be useful
for numerical computations, which have so far proven to be very challenging for
Lorentzian spin foam models.


title:
Kaluza-Klein Type Robertson Walker Cosmological Model With Dynamical
  Cosmological Term $\Lambda$

abstract:
  In this paper we have analyzed the Kaluza-Klein type Robertson Walker (RW)
cosmological models by considering three different forms of variable $\Lambda$:
$\Lambda\sim(\frac{\dot{a}}{a})^2$,$\Lambda\sim(\frac{\ddot{a}} {a})$ and
$\Lambda \sim \rho$. It is found that, the connecting free parameters of the
models with cosmic matter and vacuum energy density parameters are equivalent,
in the context of higher dimensional space time. The expression for the look
back time, luminosity distance and angular diameter distance are also derived.
This work has thus generalized to higher dimensions the well-known results in
four dimensional space time. It is found that there may be significant
difference in principle at least, from the analogous situation in four
dimensional space time.


title: Bianchi-I classical and quantum spinor cosmology with signature change

abstract:
  We study the classical and quantum evolution of a universe in which the
matter source is a massive Dirac spinor field and the universe is described by
a Bianchi type I metric. We focus attention on those classical solutions that
admit a degenerate metric in which the scale factors have smooth behavior in
transition from a Euclidean to a Lorentzian domain and show that this
transition happens when the cosmological constant, $\Lambda$, is negative. The
resulting quantum cosmology and the corresponding Wheeler-DeWitt equation are
also studied and closed form expressions for the wave functions of the universe
is presented. We have shown that there is a close relationship between the
quantum states and signature changing classical solutions, suggesting a
mechanism for creation of a Lorentzian universe from a Euclidean region by a
continuous change of signature. The quantum solutions also represent a
quantization rule for the mass of the spinor field.


title: Background independent quantizations: the scalar field I

abstract:
  We are concerned with the issue of quantization of a scalar field in a
diffeomorphism invariant manner. We apply the method used in Loop Quantum
Gravity. It relies on the specific choice of scalar field variables referred to
as the polymer variables. The quantization, in our formulation, amounts to
introducing the `quantum' polymer *-star algebra and looking for positive
linear functionals, called states. The assumed in our paper homeomorphism
invariance allows to determine a complete class of the states. Except one, all
of them are new. In this letter we outline the main steps and conclusions, and
present the results: the GNS representations, characterization of those states
which lead to essentially self adjoint momentum operators (unbounded),
identification of the equivalence classes of the representations as well as of
the irreducible ones. The algebra and topology of the problem, the derivation,
all the technical details and more are contained in the paper-part II.


title:
Petrov type I silent universes with G3 isometry group: the uniqueness
  result recovered

abstract:
  The \emph{silent universe conjecture} (Sopuerta 1997, van Elst et al. 1997)
states that the only algebraically general silent universes are the
orthogonally spatially homogeneous Bianchi I models. In the same paper by
Sopuerta this was confirmed for the subcase where the spacetime also admits a
group G3 of isometries. However the proof contains a conceptual mistake. We
recover the result in a different way.


title: Dynamics and instability of false vacuum bubbles

abstract:
  This paper examines the classical dynamics of false vacuum regions embedded
in surrounding regions of true vacuum, in the thin-wall limit. The dynamics of
all generally relativistically allowed solutions -- most but not all of which
have been previously studied -- are derived, enumerated, and interpreted. We
comment on the relation of these solutions to possible mechanisms whereby
inflating regions may be spawned from non-inflating ones. We then calculate the
dynamics of first order deviations from spherical symmetry, finding that many
solutions are unstable to such aspherical perturbations. The parameter space in
which the perturbations on bound solutions inevitably become nonlinear is
mapped. This instability has consequences for the Farhi-Guth-Guven mechanism
for baby universe production via quantum tunneling.


title: Quantized Intrinsic Redshift in Cosmological General Relativity

abstract:
  There are now several analyses reporting quantized differences in the
redshifts between pairs of galaxies. In the simplest cases, these differential
redshifts are found to be harmonics of fundamental periods of approximately 72
km/s and 37.5 km/s. In this paper a wave equation is derived based on
cosmological general relativity, which is a space-velocity theory of the
expanding Universe. The wave equation is approximated to first order and
comparisons are made between the quantized solutions and the reported
observations.


title: Radiation of the Inner Horizon of the Reissner-Nordstr\"om Black Hole

abstract:
  Despite of over thirty years of research of the black hole thermodynamics our
understanding of the possible role played by the inner horizons of
Reissner-Nordstr\"om and Kerr-Newman black holes in black hole thermodynamics
is still somewhat incomplete: There are derivations which imply that the
temperature of the inner horizon is negative and it is not quite clear what
this means. Motivated by this problem we perform a detailed analysis of the
radiation emitted by the inner horizon of the Reissner-Nordstr\"om black hole.
As a result we find that in a maximally extended Reissner-Nordstr\"om spacetime
virtual particle-antiparticle pairs are created at the inner horizon of the
Reissner-Nordstr\"om black hole such that real particles with positive energy
and temperature are emitted towards the singularity from the inner horizon and,
as a consequence, antiparticles with negative energy are radiated away from the
singularity through the inner horizon. We show that these antiparticles will
come out from the white hole horizon in the maximally extended
Reissner-Nordstr\"om spacetime, at least when the hole is near extremality. The
energy spectrum of the antiparticles leads to a positive temperature for the
white hole horizon. In other words, our analysis predicts that in addition to
the radiation effects of black hole horizons, also the white hole horizon
radiates. The black hole radiation is caused by the quantum effects at the
outer horizon, whereas the white hole radiation is caused by the quantum
effects at the inner horizon of the Reissner-Nordstr\"om black hole.


title: Bayesian estimation of pulsar parameters from gravitational wave data

abstract:
  We present a method of searching for, and parameterizing, signals from known
radio pulsars in data from interferometric gravitational wave detectors. This
method has been applied to data from the LIGO and GEO 600 detectors to set
upper limits on the gravitational wave emission from several radio pulsars.
Here we discuss the nature of the signal and the performance of the technique
on simulated data. We show how to perform a coherent multiple detector analysis
and give some insight in the covariance between the signal parameters.


title: Characteristic Evolution and Matching

abstract:
  I review the development of numerical evolution codes for general relativity
based upon the characteristic initial value problem. Progress is traced from
the early stage of 1D feasibility studies to 2D axisymmetric codes that
accurately simulate the oscillations and gravitational collapse of relativistic
stars and to current 3D codes that provide pieces of a binary black spacetime.
A prime application of characteristic evolution is to compute waveforms via
Cauchy-characteristic matching, which is also reviewed.


title: Developments in GRworkbench

abstract:
  The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. Recently, GRworkbench
has been significantly extended to facilitate numerical experimentation in
analytically-defined space-times. The numerical differential geometric engine
has been rewritten using functional programming techniques, enabling objects
which are normally defined as functions in the formalism of differential
geometry and General Relativity to be directly represented as function
variables in the C++ code of GRworkbench. The new functional differential
geometric engine allows for more accurate and efficient visualisation of
objects in space-times and makes new, efficient computational techniques
available. Motivated by the desire to investigate a recent scientific claim
using GRworkbench, new tools for numerical experimentation have been
implemented, allowing for the simulation of complex physical situations.


title: Cosmological Models in Lyra Geometry: Kinematics Tests

abstract:
  In this paper the observational consequence of the cosmological models and
the expression for the neoclassical tests, luminosity distance, angular
diameter distance and look back time are analyzed in the framework of Lyra
geometry. It is interesting to note that the space time of the universe is not
only free of Big Bang singularity but also exhibits acceleration during its
evolution.


title: On the quantum origin of the seeds of cosmic structure

abstract:
  The current understanding of the quantum origin of cosmic structure is
discussed critically. We point out that in the existing treatments a transition
from a symmetric quantum state to an (essentially classical) non-symmetric
state is implicitly assumed, but not specified or analyzed in any detail. In
facing the issue we are led to conclude that new physics is required to explain
the apparent predictive power of the usual schemes. Furthermore we show that
the novel way of looking at the relevant issues opens new windows from where
relevant information might be extracted regarding cosmological issues and
perhaps even clues about aspects of quantum gravity.


title: The double-Kerr equilibrium configurations involving one extreme object

abstract:
  We demonstrate the existence of equilibrium states in the limiting cases of
the double-Kerr solution when one of the constituents is an extreme object. In
the `extreme-subextreme' case the negative mass of one of the constituents is
required for the balance, whereas in the `extreme-superextreme' equilibrium
configurations both Kerr particles may have positive masses. We also show that
the well-known relation |J|=M^2 between the mass and angular momentum in the
extreme single Kerr solution ceases to be a characteristic property of the
extreme Kerr particle in a binary system.


title:
Frequency-Dependent Squeeze Amplitude Attenuation and Squeeze Angle
  Rotation by Electromagnetically Induced Transparency for Gravitational Wave
  Interferometers

abstract:
  We study the effects of frequency-dependent squeeze amplitude attenuation and
squeeze angle rotation by electromagnetically induced transparency (EIT) on
gravitational wave (GW) interferometers. We propose the use of low-pass,
band-pass, and high-pass EIT filters, an S-shaped EIT filter, and an
intra-cavity EIT filter to generate frequency-dependent squeezing for injection
into the antisymmetric port of GW interferometers. We find that the EIT filters
have several advantages over the previous filter designs with regard to optical
losses, compactness, and the tunability of the filter linewidth.


title: Energy-momentum for Randall-Sundrum models

abstract:
  We investigate the conservation law of energy-momentum for Randall-Sundrum
models by the general displacement transform. The energy-momentum current has a
superpotential and are therefore identically conserved. It is shown that for
Randall-Sundrum solution, the momentum vanishes and most of the bulk energy is
localized near the Planck brane. The energy density is $\epsilon = \epsilon_0
e^{-3k \mid y \mid}$.


title:
Towards a fully consistent relativistic quantum mechanics and a change
  of perspective on quantum gravity

abstract:
  This paper can be seen as an exercise in how to adapt quantum mechanics from
a strict relativistic perspective while being respectful and critical towards
the experimental achievements of the contemporary theory. The result is a fully
observer independent relativistic quantum mechanics for N particle systems
without tachyonic solutions. A remaining worry for the moment is Bell's
theorem.


title: Liouville Cosmology at Zero and Finite Temperatures

abstract:
  We discuss cosmology in the context of Liouville strings, characterized by a
central-charge deficit Q^2, in which target time is identified with (the
world-sheet zero mode of the) Liouville field: Q-Cosmology. We use a specific
example of colliding brane worlds to illustrate the phase diagram of this
cosmological framework. The collision provides the necessary initial
cosmological instability, expressed as a departure from conformal invariance in
the underlying string model. The brane motion provides a way of breaking
target-space supersymmetry, and leads to various phases of the brane and bulk
Universes. Specifically, we find a hot metastable phase for the bulk string
Universe soon after the brane collision in which supersymmetry is broken, which
we describe by means of a subcritical world-sheet sigma model dressed by a
space-like Liouville field, representing finite temperature (Euclidean time).
This phase is followed by an inflationary phase for the brane Universe, in
which the bulk string excitations are cold. This is described by a
super-critical Liouville string with a time-like Liouville mode, whose zero
mode is identified with the Minkowski target time. Finally, we speculate on
possible ways of exiting the inflationary phase, either by means of subsequent
collisions or by deceleration of the brane Universe due to closed-string
radiation from the brane to the bulk. While phase transitions from hot to cold
configurations occur in the bulk string universe, stringy excitations attached
to the brane world remain thermalized throughout, at a temperature which can be
relatively high. The late-time behaviour of the model results in
dilaton-dominated dark energy and present-day acceleration of the expansion of
the Universe, asymptoting eventually to zero.


title:
On the perturbative expansion of a quantum field theory around a
  topological sector

abstract:
  The idea of treating general relativistic theories in a perturbative
expansion around a topological theory has been recently put forward in the
quantum gravity literature. Here we investigate the viability of this idea, by
applying it to conventional Yang--Mills theory on flat spacetime. We find that
the expansion around the topological theory coincides with the usual expansion
around the abelian theory, though the equivalence is non-trivial. In this
context, the technique appears therefore to be viable, but not to bring
particularly new insights. Some implications for gravity are discussed.


title: Black hole boundaries

abstract:
  Classical black holes and event horizons are highly non-local objects,
defined in relation to the causal past of future null infinity. Alternative,
quasilocal characterizations of black holes are often used in mathematical,
quantum, and numerical relativity. These include apparent, killing, trapping,
isolated, dynamical, and slowly evolving horizons. All of these are closely
associated with two-surfaces of zero outward null expansion. This paper reviews
the traditional definition of black holes and provides an overview of some of
the more recent work on alternative horizons.


title: The Information Geometry of Space and Time

abstract:
  Is the geometry of space a macroscopic manifestation of an underlying
microscopic statistical structure? Is geometrodynamics - the theory of gravity
- derivable from general principles of inductive inference? Tentative answers
are suggested by a model of geometrodynamics based on the statistical concepts
of entropy, information geometry, and entropic dynamics. The model shows
remarkable similarities with the 3+1 formulation of general relativity. For
example, the dynamical degrees of freedom are those that specify the conformal
geometry of space; there is a gauge symmetry under 3d diffeomorphisms; there is
no reference to an external time; and the theory is time reversible. There is,
in adition, a gauge symmetry under scale transformations. I conjecture that
under a suitable choice of gauge one can recover the usual notion of a
relativistic space-time.


title: Causal sets and the deep structure of spacetime

abstract:
  The causal set approach to quantum gravity embodies the concepts of causality
and discreteness. This article explores some foundational and conceptual issues
within causal set theory.


title: Adaptive Mesh Refinement for Coupled Elliptic-Hyperbolic Systems

abstract:
  We present a modification to the Berger and Oliger adaptive mesh refinement
algorithm designed to solve systems of coupled, non-linear, hyperbolic and
elliptic partial differential equations. Such systems typically arise during
constrained evolution of the field equations of general relativity. The novel
aspect of this algorithm is a technique of "extrapolation and delayed solution"
used to deal with the non-local nature of the solution of the elliptic
equations, driven by dynamical sources, within the usual Berger and Oliger
time-stepping framework. We show empirical results demonstrating the
effectiveness of this technique in axisymmetric gravitational collapse
simulations. We also describe several other details of the code, including
truncation error estimation using a self-shadow hierarchy, and the
refinement-boundary interpolation operators that are used to help suppress
spurious high-frequency solution components ("noise").


title:
Schwarzschild Tests of the Wahlquist-Estabrook-Buchman-Bardeen Tetrad
  Formulation for Numerical Relativity

abstract:
  A first order symmetric hyperbolic tetrad formulation of the Einstein
equations developed by Estabrook and Wahlquist and put into a form suitable for
numerical relativity by Buchman and Bardeen (the WEBB formulation) is adapted
to explicit spherical symmetry and tested for accuracy and stability in the
evolution of spherically symmetric black holes (the Schwarzschild geometry).
The lapse and shift which specify the evolution of the coordinates relative to
the tetrad congruence are reset at frequent time intervals to keep the
constant-time hypersurfaces nearly orthogonal to the tetrad congruence and the
spatial coordinate satisfying a kind of minimal rate of strain condition. By
arranging through initial conditions that the constant-time hypersurfaces are
asymptotically hyperbolic, we simplify the boundary value problem and improve
stability of the evolution. Results are obtained for both tetrad gauges
(``Nester'' and ``Lorentz'') of the WEBB formalism using finite difference
numerical methods. We are able to obtain stable unconstrained evolution with
the Nester gauge for certain initial conditions, but not with the Lorentz
gauge.


title:
The Lense-Thirring effect in the Jovian system of the Galilean
  satellites and its measurability

abstract:
  In this paper we investigate the possibility of measuring the post-Newtonian
general relativistic gravitomagnetic Lense-Thirring effect in the Jovian system
of its Galilean satellites Io, Europa, Ganymede and Callisto in view of recent
developments in processing and modelling their optical observations spanning a
large time interval (125 years). The present day best observations have an
accuracy between several kilometers to few tens of kilometers, which is just
the order of magnitude of the Lense-Thirring shifts of the orbits of the
Galilean satellites over almost a century. From a comparison between analytical
development and numerical integration it turns out that, unfortunately, most of
the secular component of the gravitomagnetic signature is removed in the
process of fitting the initial conditions. Indeed, an estimation of the
magnitude of the Lense-Thirring effect in the ephemerides residuals is given;
the resulting residuals have a maximum magnitude of 20 meters only (over 125
years).


title: Angular Momentum Conservation Law for Randall-Sundrum Models

abstract:
  In Randall-Sundrum models, by the use of general Noether theorem, the
covariant angular momentum conservation law is obtained with the respect to the
local Lorentz transformations. The angular momentum current has also
superpotential and is therefore identically conserved. The space-like
components $J_{ij}$ of the angular momentum for Randall-Sundrum models are
zero. But the component $J_{04}$ is infinite.


title: Gravitational radiation reaction

abstract:
  We give a short personally-biased review on the recent progress in our
understanding of gravitational radiation reaction acting on a point particle
orbiting a black hole. The main motivation of this study is to obtain
sufficiently precise gravitational waveforms from inspiraling binary compact
stars with a large mass ratio. For this purpose, various new concepts and
techniques have been developed to compute the orbital evolution taking into
account the gravitational self-force. Combining these ideas with a few
supplementary new ideas, we try to outline a path to our goal here.


title: Stable dark energy stars

abstract:
  The gravastar picture is an alternative model to the concept of a black hole,
where there is an effective phase transition at or near where the event horizon
is expected to form, and the interior is replaced by a de Sitter condensate. In
this work, a generalization of the gravastar picture is explored, by
considering a matching of an interior solution governed by the dark energy
equation of state, $\omega\equiv p/ \rho<-1/3$, to an exterior Schwarzschild
vacuum solution at a junction interface. The motivation for implementing this
generalization arises from the fact that recent observations have confirmed an
accelerated cosmic expansion, for which dark energy is a possible candidate.
Several relativistic dark energy stellar configurations are analyzed by
imposing specific choices for the mass function. The first case considered is
that of a constant energy density, and the second choice, that of a monotonic
decreasing energy density in the star's interior. The dynamical stability of
the transition layer of these dark energy stars to linearized spherically
symmetric radial perturbations about static equilibrium solutions is also
explored. It is found that large stability regions exist that are sufficiently
close to where the event horizon is expected to form, so that it would be
difficult to distinguish the exterior geometry of the dark energy stars,
analyzed in this work, from an astrophysical black hole.


title:
A late-accelerating universe with no dark energy - and a
  finite-temperature big bang

abstract:
  Brane-world models offer the possibility of explaining the late acceleration
of the universe via infra-red modifications to General Relativity, rather than
a dark energy field. However, one also expects ultra-violet modifications to
General Relativity, when high-energy stringy effects in the early universe
begin to grow. We generalize the DGP brane-world model via an ultra-violet
modification, in the form of a Gauss-Bonnet term in the bulk action. The
combination of infra-red and ultra-violet modifications produces an intriguing
cosmology. The DGP feature of late-time acceleration without dark energy is
preserved, but there is an entirely new feature - there is no hot big bang in
the early universe. The universe starts with finite density and pressure, from
a "sudden" curvature singularity.


title: Rotating Scalar Field Wormhole

abstract:
  We derive an exact solution to the Einstein's equations with a stress-energy
tensor corresponding to an opposite-sign scalar field, and show that such a
solution describes the internal region of a rotating wormhole. We also derive
an static wormhole asymptotically flat solution and match them on both regions,
thus obtaining an analytic solution for the complete space-time. We explore
some of the features of these solutions.


title:
Degenerate Configurations, Singularities and the Non-Abelian Nature of
  Loop Quantum Gravity

abstract:
  Degenerate geometrical configurations in quantum gravity are important to
understand if the fate of classical singularities is to be revealed. However,
not all degenerate configurations arise on an equal footing, and one must take
into account dynamical aspects when interpreting results: While there are many
degenerate spatial metrics, not all of them are approached along the dynamical
evolution of general relativity or a candidate theory for quantum gravity. For
loop quantum gravity, relevant properties and steps in an analysis are
summarized and evaluated critically with the currently available information,
also elucidating the role of degrees of freedom captured in the sector provided
by loop quantum cosmology. This allows an outlook on how singularity removal
might be analyzed in a general setting and also in the full theory. The general
mechanism of loop quantum cosmology will be shown to be insensitive to recently
observed unbounded behavior of inverse volume in the full theory. Moreover,
significant features of this unboundedness are not a consequence of
inhomogeneities but of non-Abelian effects which can also be included in
homogeneous models.


title: Non-integrability of density perturbations in the FRW universe

abstract:
  We investigate the evolution equation of linear density perturbations in the
Friedmann-Robertson-Walker universe with matter, radiation and the cosmological
constant. The concept of solvability by quadratures is defined and used to
prove that there are no "closed form" solutions except for the known Chernin,
Heath, Meszaros and simple degenerate ones. The analysis is performed applying
Kovacic's algorithm. The possibility of the existence of other, more general
solutions involving special functions is also investigated.


title: Quantum Gravity: General Introduction and Recent Developments

abstract:
  I briefly review the current status of quantum gravity. After giving some
general motivations for the need of such a theory, I discuss the main
approaches in quantizing general relativity: Covariant approaches (perturbation
theory, effective theory, and path integrals) and canonical approaches (quantum
geometrodynamics, loop quantum gravity). I then address quantum gravitational
aspects of string theory. This is followed by a discussion of black holes and
quantum cosmology. I end with some remarks on the observational status of
quantum gravity.


title: Probing spacetime foam with extragalactic sources

abstract:
  Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.


title: Spacetime symmetries and varying scalars

abstract:
  This talk discusses the relation between spacetime-dependent scalars, such as
couplings or fields, and the violation of Lorentz symmetry. A specific
cosmological supergravity model demonstrates how scalar fields can acquire
time-dependent expectation values. Within this cosmological background,
excitations of these scalars are governed by a Lorentz-breaking dispersion
relation. The model also contains couplings of the scalars to the
electrodynamics sector leading to the time dependence of both the
fine-structure parameter alpha and the theta angle. Through these couplings,
the variation of the scalars is also associated with Lorentz- and CPT-violating
effects in electromagnetism.


title: Self-forces on extended bodies in electrodynamics

abstract:
  In this paper, we study the bulk motion of a classical extended charge in
flat spacetime. A formalism developed by W. G. Dixon is used to determine how
the details of such a particle's internal structure influence its equations of
motion. We place essentially no restrictions (other than boundedness) on the
shape of the charge, and allow for inhomogeneity, internal currents,
elasticity, and spin. Even if the angular momentum remains small, many such
systems are found to be affected by large self-interaction effects beyond the
standard Lorentz-Dirac force. These are particularly significant if the
particle's charge density fails to be much greater than its 3-current density
(or vice versa) in the center-of-mass frame. Additional terms also arise in the
equations of motion if the dipole moment is too large, and when the
`center-of-electromagnetic mass' is far from the `center-of-bare mass' (roughly
speaking). These conditions are often quite restrictive. General equations of
motion were also derived under the assumption that the particle can only
interact with the radiative component of its self-field. These are much simpler
than the equations derived using the full retarded self-field; as are the
conditions required to recover the Lorentz-Dirac equation.


title: Graviton propagator from background-independent quantum gravity

abstract:
  We study the graviton propagator in euclidean loop quantum gravity, using the
spinfoam formalism. We use boundary-amplitude and group-field-theory
techniques, and compute one component of the propagator to first order, under a
number of approximations, obtaining the correct spacetime dependence. In the
large distance limit, the only term of the vertex amplitude that contributes is
the exponential of the Regge action: the other terms, that have raised doubts
on the physical viability of the model, are suppressed by the phase of the
vacuum state, which is determined by the extrinsic geometry of the boundary.


title: Redshifts and Killing Vectors

abstract:
  Courses in introductory special and general relativity have increasingly
become part of the curriculum for upper-level undergraduate physics majors and
master's degree candidates. One of the topics rarely discussed is symmetry,
particularly in the theory of general relativity. The principal tool for its
study is the Killing vector. We provide an elementary introduction to the
concept of a Killing vector field, its properties, and as an example of its
utility apply these ideas to the rigorous determination of gravitational and
cosmological redshifts.


title: Gauge theories as a geometrical issue of a Kaluza-Klein framework

abstract:
  We present a geometrical unification theory in a Kaluza-Klein approach that
achieve the geometrization of a generic gauge theory bosonic component.
  We show how it is possible to derive the gauge charge conservation from the
invariance of the model under extra-dimensional translations and to geometrize
gauge connections for spinors, thus we can introduce the matter just by free
spinorial fields. Then, we present the applications to i)a pentadimensional
manifold $V^{4}\otimes S^{1}$, so reproducing the original Kaluza-Klein theory,
unless some extensions related to the rule of the scalar field contained in the
metric and the introduction of matter by spinors with a phase dependence from
the fifth coordinate, ii)a seven-dimensional manifold $V^{4}\otimes
S^{1}\otimes S^{2}$, in which we geometrize the electro-weak model by
introducing two spinors for any leptonic family and quark generation and a
scalar field with two components with opposite hypercharge, responsible of
spontaneous symmetry breaking.


title: The Cauchy problem of scalar-tensor theories of gravity

abstract:
  The 3+1 formulation of scalar-tensor theories of gravity (STT) is obtained in
the physical (Jordan) frame departing from the 4+0 covariant field equations.
Contrary to the common belief (folklore), the new system of ADM-like equations
shows that the Cauchy problem of STT is well formulated (in the sense that the
whole system of evolution equations is of first order in the time-derivative).
This is the first step towards a full first order (in time and space)
formulation from which a subsequent hyperbolicity analysis (a well-posedness
determination) can be performed. Several gauge (lapse and shift) conditions are
considered and implemented for STT. In particular, a generalization of the
harmonic gauge for STT allows us to prove the well posedness of the STT using a
second order analysis which is very similar to the one used in general
relativity. Some spacetimes of astrophysical and cosmological interest are
considered as specific applications. Several appendices complement the ideas of
the main part of the paper.


title: Space Time Matter inflation

abstract:
  We study a model of power-law inflationary inflation using the
Space-Time-Matter (STM) theory of gravity for a five dimensional (5D) canonical
metric that describes an apparent vacuum. In this approach the expansion is
governed by a single scalar (neutral) quantum field. In particular, we study
the case where the power of expansion of the universe is $p \gg 1$. This kind
of model is more successful than others in accounting for galaxy formation.


title: Primeval symmetries

abstract:
  A detailed examination of the Killing equations in Robertson-Walker
coordinates shows how the addition of matter and/or radiation to a de Sitter
Universe breaks the symmetry generated by four of its Killing fields. The
product U = (a^2)(dH/dt) of the squared scale parameter by the time-derivative
of the Hubble function encapsulates the relationship between the two cases: the
symmetry is maximal when U is a constant, and reduces to the six-parameter
symmetry of a generic Friedmann-Robertson-Walker model when it is not. As the
fields physical interpretation is not clear in these coordinates, comparison is
made with the Killing fields in static coordinates, whose interpretation is
made clearer by their direct relationship to the Poincare group generators via
Wigner-Inonu contractions.


title: A new relativistic kinematics of accelerated systems

abstract:
  We consider transformations between uniformly accelerated systems, assuming
that the Clock Hypothesis is false. We use the proper velocity-time description
of events rather than the usual space-time description in order to obtain
linear transformations. Based on the generalized principle of relativity and
the ensuing symmetry, we obtain transformations of Lorentz-type. We predict the
existence of a maximal acceleration and time dilation due to acceleration. We
also predict a Doppler shift due to acceleration of the source in addition to
the shift due to the source's velocity. Based on our results, we explain the W.
K\"{u}ndig experiment, as reanalyzed by Kholmetski \textit{et al}, and obtain
an estimate of the maximal acceleration.


title:
Sensitivity of high precision Michelson-Morley experiments to tilting of
  their setups

abstract:
  We describe the effects to be expected of unwanted or voluntary deviations
from the vertical of the axis of the active rotation of modern high precision
experiments of the Michelson-Morley type. The theoretical description that we
use is a particular implementation of the Principle of free mobility.


title: Quantum Gravity as Theory of "Superfluidity"

abstract:
  A version of the cosmological perturbation theory in general relativity (GR)
is developed, where the cosmological scale factor is identified with spatial
averaging of the metric determinant logarithm and the cosmic evolution acquires
the pattern of a superfluid motion: the absence of "friction-type" interaction,
the London-type wave function, and the Bogoliubov condensation of quantum
universes. This identification keeps the number of variables of GR and leads to
a new type of potential perturbations. A set of arguments is given in favor of
that this "superfluid" version of GR is in agreement with the observational
data.


title: Radial fall of a test particle onto an evaporating black hole

abstract:
  A test particle falling into a classical black hole crosses the event horizon
and ends up in the singularity within finite eigentime. In the `more realistic'
case of a `classical' evaporating black hole, an observer falling onto a black
hole observes a sudden evaporation of the hole. This illustrates the fact that
the discussion of the classical process commonly found in the literature may
become obsolete when the black hole has a finite lifetime. The situation is
basically the same for more complex cases, e.g. where a particle collides with
two merging black holes. It should be pointed out that the model used in this
paper is mainly of academic interest, since the description of the physics near
a black hole horizon still presents a difficult problem which is not yet fully
understood, but our model provides a valuable possibility for students to enter
the interesting field of black hole physics and to perform numerical
calculations of their own which are not very involved from the computational
point of view.


title: Modified gravity and the stability of de Sitter space

abstract:
  Within the context of modified gravity and dark energy scenarios of the
accelerating universe, we study the stability of de Sitter space with respect
to inhomogeneous perturbations using a gauge-independent formalism. In modified
gravity the stability condition is exactly the same that one obtains from a
homogeneous perturbation analysis, while the stability condition in
scalar-tensor gravity is more restrictive.


title: Nonanalytic metric in the presence of gravitomagnetic monopoles

abstract:
  The nonanalytic property of metric resulting from the presence of
gravitomagnetic monopoles is considered. The curvature tensors, dual curvature
tensors, dual Einstein tensor (and hence the gravitational field equation of
gravitomagnetic matter) expressed in terms of nonanalytic metric are analyzed.
It is shown that the spinor gravitomagnetic monopole may be one of the
potential origins of the cosmological constant. An alternative approach to the
cosmological constant problem is thus proposed based on the concept of
gravitomagnetic monopole.


title: Nonmetricity and torsion induced by dilaton gravity in two dimension

abstract:
  We develop a theory in which there are couplings amongst Dirac spinor,
dilaton and non-Riemannian gravity and explore the nature of connection-induced
dilaton couplings to gravity and Dirac spinor when the theory is reformulated
in terms of the Levi-Civita connection. After presenting some exact solutions
without spinors, we investigate the minimal spinor couplings to the model and
in conclusion we can not find any nontrivial dilaton couplings to spinor.


title: On Some Accelerating Cosmological Kaluza-Klein Models

abstract:
  We consider (4+D)-dimensional Kaluza-Klein cosmological model with two
scaling factors, as real, p-adic and adelic quantum mechanical one. One of the
scaling factors corresponds to the D-dimensional internal space, and second one
to the 4-dimensional universe. In standard quantum cosmology, i.e. over the
field of real numbers R, it leads to dynamical compactification of additional
dimensions and to the accelerating evolution of 4-dimensional universe. We
construct corresponding $p$-adic quantum model and explore existence of its
p-adic ground state. In addition, we explore evolution of this model and a
possibility for its adelic generalization. It is necessary for the further
investigation of space-time discreteness at very short distances, i.e. in a
very early universe


title:
Parametric derivation of the observable relativistic periastron advance
  for binary pulsars

abstract:
  We compute the dimensionless relativistic periastron advance parameter $k$,
which is measurable from the timing of relativistic binary pulsars. We employ
for the computation the recently derived Keplerian-type parametric solution to
the post-Newtonian (PN) accurate conservative dynamics of spinning compact
binaries moving in eccentric orbits. The parametric solution and hence the
parameter $k$ are applicable for the cases of \emph{simple precession}, namely,
case (i), the binary consists of equal mass compact objects, having two
arbitrary spins, and case (ii), the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. Our
expression, for the cases considered, is in agreement with a more general
formula for the 2PN accurate $k$, relevant for the relativistic double pulsar
PSR J0737--3039, derived by Damour and Sch\"afer many years ago, using a
different procedure.


title:
Invariant Class Operators in the Decoherent Histories Analysis of
  Timeless Quantum Theories

abstract:
  The decoherent histories approach to quantum theory is applied to a class of
reparametrization invariant models, which includes systems described by the
Klein-Gordon equation, and by a minisuperspace Wheeler-DeWitt equation. A key
step in this approach is the construction of class operators characterizing the
questions of physical interest, such as the probability of the system entering
a given region of configuration space without regard to time. In
non-relativistic quantum mechanics these class operators are given by
time-ordered products of projection operators. But in reparametrization
invariant models, where there is no time, the construction of the class
operators is more complicated, the main difficulty being to find operators
which commute with the Hamiltonian constraint (and so respect the invariance of
the theory). Here, inspired by classical considerations, we put forward a
proposal for the construction of such class operators for a class of
reparametrization-invariant systems. They consist of continuous infinite
temporal products of Heisenberg picture projection operators. We investigate
the consequences of this proposal in a number of simple models and also compare
with the evolving constants method.


title:
Analytic solutions to Riemann-squared gravity with background isotropic
  torsion

abstract:
  Motivated by conventional gauge theories, we consider a theory of gravity in
which the Einstein-Hilbert action is replaced by a term that is quadratic in
the Riemann tensor. We focus on cosmological solutions to the field equations
in flat, open and closed universes. The gravitational action is scale
invariant, so the only matter source considered is radiation. The theory can
also accommodate isotropic torsion and this generically removes singularities
from the evolution equations. For general initial conditions the Hubble
parameter H(t) is driven in a seemingly chaotic fashion by torsion to produce
irregularly occuring inflationary regions. In the absence of torsion, the
theory reproduces the standard cosmological solutions of a simple big bang
model. A satisfying feature is that a cosmological constant arises naturally as
a constant of integration, and does not have to be put into the Lagrangian by
hand.


title: Almost-stationary motions and gauge conditions in General Relativity

abstract:
  An almost-stationary gauge condition is proposed with a view to Numerical
Relativity applications. The time lines are defined as the integral curves of
the timelike solutions of the harmonic almost-Killing equation. This vector
equation is derived by a variational principle, by minimizing the deviations
from isometry. The corresponding almost-stationary gauge condition allows one
to put the field equations in hyperbolic form, both in the free-evolution ADM
and in the Z4 formalisms.


title:
Thermodynamics of (1+1) dilatonic black holes in global flat embedding
  scheme

abstract:
  We study thermodynamics of (1+1) dimensional dilatonic black holes in global
embedding Minkowski space scheme. Exploiting geometrical entropy correction we
construct consistent entropy for the charged dilatonic black hole. Moreover,
(1+1) dilatonic black holes with higher order terms are shown to possess (3+2)
global flat embedding structures regardless of the details of the lapse
function, and to yield a generic entropy.


title:
On the Possibility to Explain "The Pioneer Anomaly" within the Framework
  of Conformal Geometrodynamics

abstract:
  Einstein-Infeld-Hoffmann method is used to solve the problem of motion of two
bodies when the equations of general relativity are of the generalized form:
they have been reduced to a form invariant under conformal transformations. It
is proved that not only metric degrees of freedom, but also derivatives of
vector $A_{\alpha}$ appearing in the generalized equations can exert influence
on the motion of bodies in a certain space-time domain. This influence can
account for the recently observed anomalous acceleration of spacecrafts Pioneer
10, Pioneer 11. The impact of vector $A_{\alpha}$ on the motion of bodies is
interpreted as a consequence of viscosity in geometrodynamic continuum.


title: Targeted searches for gravitational waves from radio pulsars

abstract:
  An overview of the searches for gravitational waves from radio pulsars with
LIGO and GEO is given. We give a brief description of the algorithm used in
these targeted searches and provide end-to-end validation of the technique
through hardware injections. We report on some aspects of the recent S3/S4 LIGO
and GEO search for signals from several pulsars. The gaussianity of narrow
frequency bands of S3/S4 LIGO data, where pulsar signals are expected, is
assessed with Kolmogorov-Smirnov tests. Preliminary results from the S3 run
with a network of four detectors are given for pulsar J1939+2134.


title: Potential Capabilities of Lunar Laser Ranging for Geodesy and Relativity

abstract:
  Lunar Laser Ranging (LLR), which has been carried out for more than 35 years,
is used to determine many parameters within the Earth-Moon system. This
includes coordinates of terrestrial ranging stations and that of lunar
retro-reflectors, as well as lunar orbit, gravity field, and its tidal
acceleration. LLR data analysis also performs a number of gravitational physics
experiments such as test of the equivalence principle, search for time
variation of the gravitational constant, and determines value of several metric
gravity parameters. These gravitational physics parameters cause both secular
and periodic effects on the lunar orbit that are detectable with LLR.
Furthermore, LLR contributes to the determination of Earth orientation
parameters (EOP) such as nutation, precession (including relativistic
precession), polar motion, and UT1. The corresponding LLR EOP series is three
decades long. LLR can be used for the realization of both the terrestrial and
selenocentric reference frames. The realization of a dynamically defined
inertial reference frame, in contrast to the kinematically realized frame of
VLBI, offers new possibilities for mutual cross-checking and confirmation.
Finally, LLR also investigates the processes related to the Moon's interior
dynamics. Here, we review the LLR technique focusing on its impact on Geodesy
and Relativity. We discuss the modern observational accuracy and the level of
existing LLR modeling. We present the near-term objectives and emphasize
improvements needed to fully utilize the scientific potential of LLR.


title: A locally anisotropic geometrical model of space-time based on CMBR

abstract:
  We study a locally anisotropic model of General Relativity in the framework
of a more general geometrical structure than the Riemannian one. In this model
the observable anisotropy of the CMBR (WMAP) is represented by a tensor of
anisotropy and it is included in the metric structure of space-time. As well,
some interesting special cases of spaces are considered.


title: Pioneer anomaly: What can we learn from LISA?

abstract:
  The Doppler tracking data from two deep-space spacecraft, Pioneer 10 and 11,
show an anomalous blueshift, which has been dubbed the "Pioneer anomaly". The
effect is most commonly interpreted as a real deceleration of the spacecraft -
an interpretation that faces serious challenges from planetary ephemerides. The
Pioneer anomaly could as well indicate an unknown effect on the radio signal
itself. Several authors have made suggestions how such a blueshift could be
related to cosmology. We consider this interpretation of the Pioneer anomaly
and study the impact of an anomalous blueshift on the Laser Interferometer
Space Antenna (LISA), a planned joint ESA-NASA mission aiming at the detection
of gravitational waves. The relative frequency shift (proportional to the light
travel time) for the LISA arm length is estimated to 10E-16, which is much
bigger than the expected amplitude of gravitational waves. The anomalous
blueshift enters the LISA signal in two ways, as a small term folded with the
gravitational wave signal, and as larger term at low frequencies. A detail
analysis shows that both contributions remain undetectable and do not impair
the gravitational-wave detection. This suggests that the Pioneer anomaly will
have to be tested in the outer Solar system regardless if the effect is caused
by an anomalous blueshift or by a real force.


title: Energy-Momentum of a Stationary Beam of Light in Teleparallel Gravity

abstract:
  This paper has been removed by arXiv administrators because it overlaps
gr-qc/0303034.
  This paper also has excessive overlap with the following paper also written
by the authors or their collaborators: gr-qc/0606022, and others.


title:
Different Approaches to the Einstein Energy Associated with the de
  Sitter C-Space-time

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0404108, gr-qc/0306101, hep-th/0301046, and gr-qc/0303034.


title: Extreme Mass Ratio Inspirals: LISA's unique probe of black hole gravity

abstract:
  In this review article I attempt to summarise past and present-ongoing-work
on the problem of the inspiral of a small body in the gravitational field of a
much more massive Kerr black hole. Such extreme mass ratio systems, expected to
occur in galactic nuclei, will constitute prime sources of gravitational
radiation for the future LISA gravitational radiation detector. The article's
main goal is to provide a survey of basic celestial mechanics in Kerr spacetime
and calculations of gravitational waveforms and backreaction on the small
body's orbital motion, based on the traditional `flux-balance' method and the
Teukolsky black hole perturbation formalism.


title: A Note on Frame Dragging

abstract:
  The measurement of spin effects in general relativity has recently taken
centre stage with the successfully launched Gravity Probe B experiment coming
toward an end, coupled with recently reported measurements using laser ranging.
Many accounts of these experiments have been in terms of frame-dragging. We
point out that this terminology has given rise to much confusion and that a
better description is in terms of spin-orbit and spin-spin effects. In
particular, we point out that the de Sitter precession (which has been mesured
to a high accuracy) is also a frame-dragging effect and provides an accurate
benchmark measurement of spin-orbit effects which GPB needs to emulate.


title:
Massive vector field perturbations in the Schwarzschild background:
  stability and quasinormal spectrum

abstract:
  We consider the perturbations of the massive vector field around
Schwarzschild black hole, (generally, with non-vanishing $\Lambda$ - term). The
monopole massive vector perturbation equations can be reduced to a single
wave-like equation. We have proved the stability against these perturbations
and investigated the quasinormal spectrum. The quasinormal behaviour for
Schwarzschild black hole is quite unexpected: the fundamental mode and all
higher overtones shows totally different dependence on the mass of the field
$m$: as $m$ is increasing, the damping rate of the fundamental mode is
decreasing, what results in appearing of the infinitely long living modes,
while, on contrary, damping rate of all higher overtones are increasing, and
their real oscillation frequencies gradually go to tiny values. Thereby, for
all higher overtones, almost non-oscillatory, damping modes can exist. In the
limit of asymptotically high damping, $Re \omega$ goes to $ln3/(8 \pi M)$,
while imaginary part shows equidistant behaviour with spacing $Im \omega_{n+1}-
Im \omega_{n}=i/4M$. In addition, we have found quasinormal spectrum of massive
vector field for Schwarzschild-anti-de Sitter black hole.


title: Hawking radiation in moving plasmas

abstract:
  Bi-metricity and Hawking radiation are exhibit in non-relativistic moving
magnetohydrodynamics (MHD) plasma medium generating two Riemannian effective
spacetimes. The first metric is a flat metric although the speed of "light" is
given by a time dependent signal where no Hawking radiation or effective black
holes are displayed. This metric comes from a wave equation which the scalar
function comes from the scalar potential of the background velocity of the
fluid and depends on the perturbation of the magnetic background field. The
second metric is an effective spacetime metric which comes from the
perturbation of the background MHD fluid. This Riemann metric exhibits a
horizon and Hawking radiation which can be expressed in terms of the background
constant magnetic field. The effective velocity is given Alfven wave velocity
of plasma physics. The effective black hole found here is analogous to the
optical black hole in moving dielectrics found by De Lorenci et al [Phys. Rev.
D (2003)] where bi-metricity and Hawking radiation in terms of the electric
field are found.


title: Origin of the Immirzi Parameter

abstract:
  Using quadratic spinor techniques we demonstrate that the Immirzi parameter
can be expressed as ratio between scalar and pseudo-scalar contributions in the
theory and can be interpreted as a measure of how Einstein gravity differs from
a generally constructed covariant theory for gravity. This interpretation is
independent of how gravity is quantized. One of the important advantage of
deriving the Immirzi parameter using the quadratic spinor techniques is to
allow the introduction of renormalization scale associated with the Immirzi
parameter through the expectation value of the spinor field upon quantization.


title:
Unification of inflation and cosmic acceleration in the Palatini
  formalism

abstract:
  A modified model of gravity with additional positive and negative powers of
the scalar curvature, $R$, in the gravitational action is studied. This is done
using the Palatini variational principle. It is demonstrated that using such a
model might prove useful to explain both the early time inflation and the late
time cosmic acceleration without the need for any form of dark energy.


abstract:
  Reconsideration of the Regge-Wheeler equation is processed by using the
Painlev\'{e} coordinate and "good" timelier to define the initial time. We find
that: the Regge-Wheeler equation could has positive imaginary frequency.
Because the Regge-Wheeler equation is the odd (angular) perturbation to the
Schwarzschild black hole, the conclusion is that the Schwarzschild black hole
is unstable with respect to the rotating perturbation.


title:
Global Existence of Solutions for the Einstein-Boltzmann System in a
  Bianchi Type I Space-Time

abstract:
  We prove a global in time existence theorem, for the initial value problem
for the Einstein-Boltzmann system, with arbitrarily large initial data, in the
homogeneous case, in a Bianchi type I space-time


title: The Futures of Bianchi type VII0 cosmologies with vorticity

abstract:
  We use expansion-normalised variables to investigate the Bianchi type VII$_0$
model with a tilted $\gamma$-law perfect fluid. We emphasize the late-time
asymptotic dynamical behaviour of the models and determine their asymptotic
states. Unlike the other Bianchi models of solvable type, the type VII$_0$
state space is unbounded. Consequently we show that, for a general
non-inflationary perfect fluid, one of the curvature variables diverges at late
times, which implies that the type VII$_0$ model is not asymptotically
self-similar to the future. Regarding the tilt velocity, we show that for
fluids with $\gamma<4/3$ (which includes the important case of dust,
$\gamma=1$) the tilt velocity tends to zero at late times, while for a
radiation fluid, $\gamma=4/3$, the fluid is tilted and its vorticity is
dynamically significant at late times. For fluids stiffer than radiation
($\gamma>4/3$), the future asymptotic state is an extremely tilted spacetime
with vorticity.


title:
Quantum geometry and black hole entropy: inclusion of distortion and
  rotation

abstract:
  Equilibrium states of black holes can be modelled by isolated horizons. If
the intrinsic geometry is spherical, they are called type I while if it is
axi-symmetric, they are called type II. The detailed theory of geometry of
quantum type I horizons and the calculation of their entropy can be generalized
to type II, thereby including arbitrary distortions and rotations. The leading
term in entropy of large horizons is again given by 1/4th of the horizon area
for the same value of the Barbero-Immirzi parameter as in the type I case.
Ideas and constructions underlying this extension are summarized.


title: Analogue non-Riemannian black holes in vortical moving plasmas

abstract:
  Analogue black holes in non-Riemannian effective spacetime of moving vortical
plasmas described by moving magnetohydrodynamic (MHD) flows. This example is an
extension of acoustic torsion recently introduced in the literature (Garcia de
Andrade,PRD(2004),7,64004), where now the presence of artificial black holes in
moving plasmas is obtained by the presence of an horizon in the non-Riemannian
spacetime. Hawking radiation is computed in terms of the background magnetic
field and the magnetic permeability. The metric is singular although Cartan
analogue torsion is not necessarily singular. The effective Lorentz invariance
is shown to be broken due to the presence of effective torsion in strong
analogy with the Riemann-Cartan gravitational case presented recently by
Kostelecky (PRD 69,2004,105009).


title: Weyl Invariant Dynamics in 3 Dimensions

abstract:
  We analyze a variety of Weyl invariant dynamical problems in three
dimensions.


title: Statefinder parameters for quintom dark energy model

abstract:
  We perform in this paper a statefinder diagnostic to a dark energy model with
two scalar fields, called "quintom", where one of the scalar fields has a
canonical kinetic energy term and the other has a negative one. Several kinds
of potentials are discussed. Our results show that the statefinder diagnostic
can differentiate quintom model with other dark energy models.


title: Space-times produced by a time-dependent scalar field

abstract:
  Models of Lorentz/diffeomorphism violation frequently make use of a
time-dependent scalar field. We investigate space-times produced by such a
field.


title: Quantum spectrum of black holes

abstract:
  The black hole as the thermodynamical system in equilibrium possesses the
periodicity of motion in imaginary time, that allows us to formulate the
quasi-classical rule of quantization. The rule yields the equidistant spectrum
for the entropy of non-rotating black holes as well as for the appropriately
scaled entropy in the case of rotation. We clarify and discuss a role of
quasi-normal modes.


title:
Bibliography of Publications related to Classical Self-dual variables
  and Loop Quantum Gravity

abstract:
  This bibliography attempts to give a comprehensive overview of all the
literature related to what is known as the Ashtekar-Sen connection and the
Rovelli-Smolin loop variables, from which the program currently known as Loop
Quantum Gravity emerged. The original version was compiled by Peter Huebner in
1989, and it has been subsequently updated by Gabriela Gonzalez, Bernd
Bruegmann, Monica Pierri, Troy Schilling, Christopher Beetle, Alejandro Corichi
and Alberto Hauser. The criteria for inclusion in this list are the following:
A paper in the classical theory is included if it deals with connection
variables for gravity. If the paper is in the quantum domain, it is included
when it is related directly with gravity using connection/loop variables, with
mathematical aspects of connections, or when it introduces techniques that
might be useful for the construction of the (loop) quantum theory of gravity.
Information about additional literature, new preprints, and especially
corrections are always welcome.


title: Equation of state for an interacting holographic dark energy model

abstract:
  We investigate a model of the interacting holographic dark energy with cold
dark matter (CDM). If the holographic energy density decays into CDM, we find
two types of the effective equation of state. In this case we have to use the
effective equations of state ($\omega^{\rm eff}_{\rm \Lambda}$) instead of the
equation of state ($\omega_{\rm \Lambda})$. For a fixed ratio of two energy
densities, their effective equations of state are given by the same negative
constant. Actually, the cosmic anti-friction arisen from the vacuum decay
process may induce the acceleration with $\omega^{\rm eff}_{\rm \Lambda}<-1/3$.
For a variable ratio, their effective equations of state are slightly
different, but they approach the same negative constant in the far future.
Consequently, we show that such an interacting holographic energy model cannot
accommodate a transition from the dark energy with $\omega^{\rm eff}_{\rm
\Lambda}\ge-1$ to the phantom regime with $\omega^{\rm eff}_{\rm \Lambda}<-1$.


title:
Benefits of joint LIGO -- Virgo coincidence searches for burst and
  inspiral signals

abstract:
  We examine the benefits of performing a joint LIGO--Virgo search for
transient signals. We do this by adding burst and inspiral signals to 24 hours
of simulated detector data. We find significant advantages to performing a
joint coincidence analysis, above either a LIGO only or Virgo only search.
These include an increased detection efficiency, at a fixed false alarm rate,
to both burst and inspiral events and an ability to reconstruct the sky
location of a signal.


title: The Closed Cosmological Model with Variable Lambda-term

abstract:
  We have studied the closed universe model with the variable cosmological
term, which is presented as a sum of two terms: Lambda=Lambda_0 -k R. First
term Lambda_0 is a constant and it is describing a sum of quantum field's zero
oscillations. In the geometrical sense it determines an own constant curvature
of the space-time. The second term is variable, it is proportional to curvature
of the space-time and can be interpretable as response of vacuum to curvature
of the space-time. In the framework of such model we have investigated the time
dynamic of Lambda-term and try to explain a mechanism which to give rise to a
large value of Lambda hence leading to the "cosmological constant problem". It
was studied models for different dark matter equation of state: p=0 and
p=varepsilon. It was shown that the presence of a variable Lambda-term alters
the evolution of the scale factor a in the very early epoch. In the context of
this model, a severe decrease of the module of vacuum energy density at the
primitive stage of Universe's development is explained. The numerical results
for the value of the Lambda-term agree with theoretical predictions for the
early epoch and with recent observation data.


title: T-spheres as a limit of Lemaitre-Tolman-Bondi solutions

abstract:
  In the Tolman model there exist two quite different branches of solutions -
generic Lemaitre-Tolman-Bondi (LTB) ones and T-spheres as a special case. We
show that, nonetheless, T-spheres can be obtained as a limit of the class of
LTB solutions having no origin and extending to infinity with the areal radius
approaching constant. It is shown that all singularities of T-models are
inherited from those of corresponding LBT solutions. In doing so, the disc type
singularity of a T-sphere is the analog of shell-crossing.


title: Inflationary and dark energy regimes in 2+1 dimensions

abstract:
  In this work we investigate the behavior of three-dimensional (3D)
cosmological models. The simulation of inflationary and dark-energy-dominated
eras are among the possible results in these 3D formulations; taking as
starting point the results obtained by Cornish and Frankel.
  Motivated by those results, we investigate, first, the inflationary case
where we consider a two-constituent cosmological fluid: the scalar field
represents the hypothetical inflaton which is in gravitational interaction with
a matter/radiation contribution. For the description of an old universe, it is
possible to simulate its evolution starting with a matter dominated universe
that faces a decelerated/accelerated transition due to the presence of the
additional constituent (simulated by the scalar field or ruled by an exotic
equation of state) that plays the role of dark energy. We obtain, through
numerical analysis, the evolution in time of the scale factor, the
acceleration, the energy densities, and the hydrostatic pressure of the
constituents. The alternative scalar cosmology proposed by Cornish and Frankel
is also under investigation in this work. In this case an inflationary model
can be constructed when another non-polytropic equation of state (the van der
Waals equation) is used to simulate the behavior of an early 3D universe.


title: Towards a self-consistent model of analogue gravity

abstract:
  A nonlinear scalar field theory from which an effective metric can be deduced
is considered. This metric is shown to be compatible with requirements of
general relativity. It is demonstrated that there is a class of solutions which
fulfill both the nonlinear field equation as the Einstein equations for this
metric.


title: The Dynamics of a Classical Spinning Particle in Vaidya Space-Time

abstract:
  Based on the Mathisson-Papapetrou-Dixon (MPD) equations and the Vaidya
metric, the motion of a spinning point particle orbiting a non-rotating star
while undergoing radiation-induced gravitational collapse is studied in detail.
A comprehensive analysis of the orbital dynamics is performed assuming distinct
central mass functions which satisfy the weak energy condition, in order to
determine a correspondence between the choice of mass function and the spinning
particle's orbital response, as reflected in the gravitational waves emitted by
the particle. The analysis presented here is likely most beneficial for the
observation of rotating solar mass black holes or neutron stars in orbit around
intermediate-sized Schwarzschild black holes undergoing radiation collapse. The
possibility of detecting the effects of realistic mass accretion based on this
approach is considered. While it seems unlikely to observe such effects based
on present technology, they may perhaps become observable with the advent of
future detectors.


title: Gravitational Energy-Momentum Density in Bianchi Type-II Space-times

abstract:
  This paper has been removed by arXiv administrators because of overlap with
gr-qc/0303034.
  This paper also has excessive overlap with the following papers also written
by the authors or their collaborators: gr-qc/0601133, gr-qc/0602012,
gr-qc/0601070, gr-qc/0606028, and others.


title: Dynamical horizon of evaporating black hole in Vaidya spacetime

abstract:
  We consider how the mass of the black hole decreases by the Hawking radiation
in the Vaidya spacetime, using the concept of dynamical horizon equation,
proposed by Ashtekar and Krishnan. Using the formula for the change of the
dynamical horizon, we derive an equation for the mass incorporating the Hawking
radiation. It is shown that final state is the Minkowski spacetime in our
particular model.


title: Eigenvalues of the volume operator in loop quantum gravity

abstract:
  We present a simple method to calculate certain sums of the eigenvalues of
the volume operator in loop quantum gravity. We derive the asymptotic
distribution of the eigenvalues in the classical limit of very large spins
which turns out to be of a very simple form. The results can be useful for
example in the statistical approach to quantum gravity.


title:
Space Dynamics in Global Time as an Effective Alternative to General
  Relativity

abstract:
  The fundamental physical object of the Global Time Theory is a
three-dimensional curved space dynamically developing in global time. The
equations of its dynamics are derived from the Lagrangian, and the Hamiltonian
of ravitation turns out to be nonzero. The General Relativity solutions are
shown to be a subset of the GTT solutions with zero energy density. In Global
time Theory, the quantum theory of gravitation can be built on the basis of the
Schredinger equation, as for other fields. The quantum model of the Big Bang is
presented in some detailes.


title: Gravity and the Quantum: Are they Reconcilable?

abstract:
  General relativity and quantum mechanics are conflicting theories. The seeds
of discord are the fundamental principles on which these theories are grounded.
General relativity, on one hand, is based on the equivalence principle, whose
strong version establishes the local equivalence between gravitation and
inertia. Quantum mechanics, on the other hand, is fundamentally based on the
uncertainty principle, which is essentially nonlocal in the sense that a
particle does not follow one trajectory, but infinitely many trajectories, each
one with a different probability. This difference precludes the existence of a
quantum version of the strong equivalence principle, and consequently of a
quantum version of general relativity. Furthermore, there are compelling
experimental evidences that a quantum object in the presence of a gravitational
field violates the weak equivalence principle. Now it so happens that, in
addition to general relativity, gravitation has an alternative, though
equivalent description, given by teleparallel gravity, a gauge theory for the
translation group. In this theory torsion, instead of curvature, is assumed to
represent the gravitational field. These two descriptions lead to the same
classical results, but are conceptually different. In general relativity,
curvature geometrizes the interaction, while torsion in teleparallel gravity
acts as a force, similar to the Lorentz force of electrodynamics. Because of
this peculiar property, teleparallel gravity describes the gravitational
interaction without requiring any of the equivalence principles. The
replacement of general relativity by teleparallel gravity may, in consequence,
lead to a conceptual reconciliation of gravitation with quantum mechanics.


title: Gravitational wave holography

abstract:
  We represent and discuss a theory of gravitational holography in which all
the involved waves; subject, reference and illuminator are gravitational waves
(GW). Although these waves are so weak that no terrestrial experimental
set-ups, even the large LIGO, VIRGO, GEO and TAMA facilities, were able up to
now to directly detect them they are, nevertheless, known under certain
conditions (such as very small wavelengths) to be almost indistinguishable (see
P. 962 in Ref. \cite{mtw}) from their analogue electromagnetic waves (EMW). We,
therefore theoretically, show, using the known methods of optical holography
and taking into account the very peculiar nature of GW, that it is also
possible to reconstruct subject gravitational waves.


title:
Spontaneous excitation of an accelerated atom in a spacetime with a
  reflecting plane boundary

abstract:
  We study a two-level atom in interaction with a real massless scalar quantum
field in a spacetime with a reflecting boundary. The presence of the boundary
modifies the quantum fluctuations of the scalar field, which in turn modifies
the radiative properties of atoms. We calculate the rate of change of the mean
atomic energy of the atom for both inertial motion and uniform acceleration. It
is found that the modifications induced by the presence of a boundary make the
spontaneous radiation rate of an excited inertial atom to oscillate near the
boundary and this oscillatory behavior may offer a possible opportunity for
experimental tests for geometrical (boundary) effects in flat spacetime. While
for accelerated atoms, the transitions from ground states to excited states are
found to be possible even in vacuum due to changes in the vacuum fluctuations
induced by both the presence of the boundary and the acceleration of atoms, and
this can be regarded as an actual physical process underlying the Unruh effect.


title:
Relational particle models as toy models for quantum gravity and quantum
  cosmology

abstract:
  It is argued that substantial portions of both Newtonian particle mechanics
and general relativity can be viewed as relational (rather than absolute)
theories. I furthermore use the relational particle models as toy models to
investigate the problem of time in closed-universe canonical quantum general
relativity. I consider thus in particular the internal time, semiclassical and
records tentative resolutions of the problem of time.


title:
Geodesics, the Equivalence Principle and Singularities in
  Higher-dimensional General Relativity and Braneworlds

abstract:
  The geodesics of a spacetime seldom coincide with those of an embedded
submanifold of codimension one. We investigate this issue for
higher-dimensional general relativity-like models, firstly in the simpler case
without branes to isolate which features are already present, and then in the
more complicated case with branes. The framework in which we consider branes is
general enough to include asymmetric braneworlds but not thick branes. We apply
our results on geodesics to study both the equivalence principle and
cosmological singularities. Among the models we study these considerations
favour $Z_2$ symmetric braneworlds with a negative bulk cosmological constant.


title:
On the Internal Solution of the Schwarzschild Type in the Field Theory
  of Gravitation

abstract:
  It is shown that the internal solution of the Schwarzschild type in the
Relativistic Theory of Gravitation does not lead to an {infinite pressure}
inside a body as it holds in the General Theory of Relativity. This happens due
to the graviton rest mass, because of the stopping of the time slowing down.


title: Acoustic horizons in axially symmetric relativistic accretion

abstract:
  Transonic accretion onto astrophysical objects is a unique example of
analogue black hole realized in nature. In the framework of acoustic geometry
we study axially symmetric accretion and wind of a rotating astrophysical black
hole or of a neutron star assuming isentropic flow of a fluid described by a
polytropic equation of state. In particular we analyze the causal structure of
multitransonic configurations with two sonic points and a shock. Retarded and
advanced null curves clearly demonstrate the presence of the acoustic black
hole at regular sonic points and of the white hole at the shock. We calculate
the analogue surface gravity and the Hawking temperature for the inner and the
outer acoustic horizons.


title: Notes about Noise in Gravitational Wave Antennas Created by Cosmic Rays

abstract:
  Thermodynamical fluctuations of temperature in mirrors may produce surface
fluctuations not only through thermal expansion in mirror body but also through
thermal expansion in mirror coating. We analyze the last "surface" effect which
can be larger than the first "volume" one due to larger thermal expansion
coefficient of coating material and smaller effective volume. In particular,
these fluctuations may be important in laser interferometric gravitational
antennae.


title: The Power of General Relativity

abstract:
  We study the cosmological and weak-field properties of theories of gravity
derived by extending general relativity by means of a Lagrangian proportional
to $R^{1+\delta}$. This scale-free extension reduces to general relativity when
$\delta \to 0$. In order to constrain generalisations of general relativity of
this power class we analyse the behaviour of the perfect-fluid Friedmann
universes and isolate the physically relevant models of zero curvature. A
stable matter-dominated period of evolution requires $\delta >0$ or $\delta
<-1/4$. The stable attractors of the evolution are found. By considering the
synthesis of light elements (helium-4, deuterium and lithium-7) we obtain the
bound $-0.017<\delta <0.0012.$ We evaluate the effect on the power spectrum of
clustering via the shift in the epoch of matter-radiation equality. The horizon
size at matter--radiation equality will be shifted by $\sim 1%$ for a value of
$\delta \sim 0.0005.$ We study the stable extensions of the Schwarzschild
solution in these theories and calculate the timelike and null geodesics. No
significant bounds arise from null geodesic effects but the perihelion
precession observations lead to the strong bound $\delta =2.7\pm 4.5\times
10^{-19}$ assuming that Mercury follows a timelike geodesic. The combination of
these observational constraints leads to the overall bound $0\leq \delta
<7.2\times 10^{-19}$ on theories of this type.


title:
On the instabilities of the static, spherically symmetric SU(2)
  Einstein-Yang-Mills-Dilaton solitons and black holes

abstract:
  We prove that the number of odd parity instabilities of the n-th SU(2)
Einstein-Yang-Mills-Dilaton soliton and black hole equals n.


title:
The Momentum 4-Vector of Static Bianchi-type Space-times in
  Tele-parallel Gravity

abstract:
  This paper has excessive overlap with the following paper also written by the
authors or their collaborators: gr-qc/0511095.


title:
Electrically charged and neutral wormhole instability in scalar-tensor
  gravity

abstract:
  We study the stability of static, spherically symmetric, traversable
wormholes with or without an electric charge, existing due to conformal
continuations in a class of scalar-tensor theories with zero scalar field
potential (so that Penney's or Fisher's well-known solutions hold in the
Einstein conformal frame). Specific examples of such wormholes are those with
nonminimally (e.g., conformally) coupled scalar fields. All boundary conditions
for scalar and metric perturbations are taken into account. All such wormholes
with zero or small electric charge are shown to be unstable under spherically
symmetric perturbations. The instability is proved analytically with the aid of
the theory of self-adjoint operators in Hilbert space and is confirmed by
numerical computations.


title: Horizon Mass Theorem

abstract:
  A new theorem for black holes is found. It is called the horizon mass
theorem. The horizon mass is the mass which cannot escape from the horizon of a
black hole. For all black holes: neutral, charged or rotating, the horizon mass
is always twice the irreducible mass observed at infinity. Previous theorems on
black holes are: 1. the singularity theorem, 2. the area theorem, 3. the
uniqueness theorem, 4. the positive energy theorem. The horizon mass theorem is
possibly the last general theorem for classical black holes. It is crucial for
understanding Hawking radiation and for investigating processes occurring near
the horizon.


title: Fundamental Structure of Loop Quantum Gravity

abstract:
  In this review, the fundamental structure of loop quantum gravity is
presented pedagogically. Our main aim is to help non-experts to understand the
motivations, basic structures, as well as general results. It may also be
beneficial to practitioners to gain insights from different perspectives on the
theory. We will focus on the theoretical framework itself, rather than its
applications, and do our best to write it in modern and precise langauge while
keeping the presentation accessible for beginners. After reviewing the
classical connection dynamical formalism of general relativity, as a
foundation, the construction of kinematical Ashtekar-Isham-Lewandowski
representation is introduced in the content of quantum kinematics. The
algebraic structure of quantum kinematics is also discussed. In the content of
quantum dynamics, we mainly introduce the construction of a Hamiltonian
constraint operator and the master constraint project. At last, some
applications and recent advances are outlined. It should be noted that this
strategy of quantizing gravity can also be extended to obtain other background
independent quantum gauge theories. There is no divergence within this
background independent and diffeomorphism invariant quantization programme of
matter coupled to gravity.


title:
On avoiding cosmological oscillating behavior for S-brane solutions with
  diagonal metrics

abstract:
  In certain string inspired higher dimensional cosmological models it has been
conjectured that there is generic, chaotic oscillating behavior near the
initial singularity -- the Kasner parameters which characterize the asymptotic
form of the metric "jump" between different, locally constant values and
exhibit a never-ending oscillation as one approaches the singularity. In this
paper we investigate a class of cosmological solutions with form fields and
diagonal metrics which have a "maximal" number of composite electric S-branes.
We look at two explicit examples in D=4 and D=5 dimensions that do not have
chaotic oscillating behavior near the singularity. When the composite branes
are replaced by non-composite branes chaotic oscillating


title: Evidence for an anisotropy of the speed of light

abstract:
  By comparing with the most recent experimental results, we point out the
model dependence of the present bounds on the anisotropy of the speed of light.
In fact, by replacing the CMB with a class of preferred frames that can better
account for the experimental data, one obtains values of the RMS anisotropy
parameter (1/2 -beta + delta) that are one order of magnitude larger than the
presently quoted ones. The resulting non-zero anisotropy can be understood
starting from the observation that the speed of light in the Earth's
gravitational field is not the basic parameter c=1 entering Lorentz
transformations. In this sense, light can propagate isotropically only in one
`preferred' frame.


title:
On the compatibility of Lorentz-metrics with linear connections on
  4-dimensional manifolds

abstract:
  This paper considers 4-dimensional manifolds upon which there is a Lorentz
metric, h, and a symmetric connection and which are originally assumed
unrelated. It then derives sufficient conditions on the metric and connection
(expressed through the curvature tensor) for the connection to be the
Levi-Civita connection of some (local) Lorentz metric, g, and calculates the
relationship between g and h. Some examples are provided which help to assess
the strength of the sufficient conditions derived.


title: Properties of homogeneous cosmologies in scalar tensor theories

abstract:
  We study the isotropisation of the homogeneous but anisotropic Bianchi class
A models in presence of a minimally coupled and massive scalar field with or
without a perfect fluid. To this end, we use the Hamiltonian formalism of
Arnowitt, Deser and Misner(ADM) and the dynamical systems analysis methods. Our
results allow to define three kinds of isotropisation called class 1, 2 and 3.
We have specifically studied the class 1 and obtained some general constraints
on scalar-tensor theories which are necessary conditions for isotropisation.
The asymptotical behaviors of the metric functions and potential in the
neighborhood of isotropy have also been determined when the isotropic state is
reached sufficiently quickly. We show that the scalar field responsible for
isotropisation may be quintessent and that the presence of curvature favor a
late times acceleration and quintessence. Some applications are made with the
well known exponential law potential by using our theoretical results but also
by help of numerical analysis. The isotropisation process with a power law
potential is also explored. We think this work represents a framework able to
guide some future researches on the isotropisation of homogeneous models in
scalar-tensor theories and we argue by discussing briefly about some recent
results we have obtained in presence of a non minimally coupled scalar field or
several scalar fields.


title: Homogeneous cosmology dynamics revealed by Hamiltonian ADM formalism

abstract:
  We study the homogeneous but anisotropic cosmological models of Bianchi in
presence of a massive scalar field using the ADM Hamiltonian formalism. We
begin to describe the main steps to find the ADM Hamiltonian of the General
Relativity with a massive scalar field and then we study the dynamics of the
flat Bianchi type $I$ anisotropic Universe according to initial and final
values of this Hamiltonian and sign of the potential. After a brief recall of
the conditions necessary to isotropise an anisotropic Bianchi class A model
with such a field, we extend them to a non minimally coupled scalar field by
using a conformal transformation of the metric which casts the General
Relativity with a scalar field into a scalar-tensor theory. The new line
element then corresponds to the so-called Brans-Dicke frame, the former one
being the Einstein frame. Then, we study the isotropisation process of the
Bianchi class A model when we consider the low energy form of the string theory
without its antisymmetric tensor and the Brans-Dicke theory with some
exponential or power laws of the scalar field for the potential. Finally,
assuming an isotropic Universe such as all the metric functions behave as some
power or exponential laws of the proper time, we find the conditions such that
the gravitation function and the potential of the scalar field are bounded as
it is observed today, and compare them with the necessary conditions for
isotropy.


title:
Isotropisation of flat homogeneous Bianchi type I model with a non
  minimally coupled and massive scalar field

abstract:
  In previous works, we studied the isotropisation of Bianchi class A models
with a minimally coupled scalar field. In this paper, we extend these results
to the case of a non minimally coupled one. We first make the calculations in
the Einstein frame where the scalar field is minimally coupled to the curvature
but non minimally coupled to the perfect fluid. Then, we use a conformal
transformation to generalise our results to a scalar field non minimally
coupled to the curvature. Universe isotropisation for the Brans-Dicke and low
energy string theories are studied.


title:
Bianchi type IX asymptotical behaviours with a massive scalar field:
  chaos strikes back

abstract:
  We use numerical integrations to study the asymptotical behaviour of a
homogeneous but anisotropic Bianchi type IX model in General Relativity with a
massive scalar field. As it is well known, for a Brans-Dicke theory, the
asymptotical behaviour of the metric functions is ruled only by the Brans-Dicke
coupling constant with respect to the value -3/2. In this paper we examine if
such a condition still exists with a massive scalar field. We also show that,
contrary to what occurs for a massless scalar field, the singularity
oscillatory approach may exist in presence of a massive scalar field having a
positive energy density.


title: Black hole pair creation and the stability of flat space

abstract:
  We extend the Gross-Perry-Yaffe approach of hot flat space instability to
Minkowski space. This is done by a saddle point approximation of the partition
function in a Schwarzschild wormhole background which is coincident with an
eternal black hole. The appearance of an instability in the whole manifold is
here interpreted as a black hole pair creation.


title:
Higher Dimensional Dust Cosmological Implications of a Decay Law for
  $\Lambda$ Term : Expressions for Some Observable Quantities

abstract:
  In this paper we have considered the multidimensional cosmological
implications of a decay law for $\Lambda$ term that is proportional to $\beta
\frac{\ddot {a}}{a}$, where $\beta$ is a constant and $a$ is the scale factor
of RW-space time. We discuss the cosmological consequences of a model for the
vanishing pressure for the case $k=0$. It has been observed that such models
are compatible with the result of recent observations and cosmological term
$\Lambda$ gradually reduces as the universe expands. In this model $\Lambda$
varies as the inverse square of time, which matches its natural units. The
proper distance, the luminosity distance-redshift, the angular diameter
distance-redshift, and look back time-redshift for the model are presented in
the frame work of higher dimensional space time. The model of the Freese {\it
et al.} ({\it Nucl. Phys. B} {\bf 287}, 797 (1987)) for $n=2$ is retrieved for
the particular choice of $A_{0}$ and also Einstein-de Sitter model is obtained
for $A_{0} = {2/3}$. This work has thus generalized to higher dimensions the
well-know result in four dimensional space time. It is found that there may be
significant difference in principle at least, from the analogous situation in
four dimensional space time.


title: Quantum geometry and the Schwarzschild singularity

abstract:
  In homogeneous cosmologies, quantum geometry effects lead to a resolution of
the classical singularity without having to invoke special boundary conditions
at the singularity or introduce ad-hoc elements such as unphysical matter. The
same effects are shown to lead to a resolution of the Schwarzschild
singularity. The resulting quantum extension of space-time is likely to have
significant implications to the black hole evaporation process. Similarities
and differences with the situation in quantum geometrodynamics are pointed out.


title: Anti-de Sitter space, squashed and stretched

abstract:
  We study the Lorentzian analogues of the squashed 3-sphere, namely 2+1
dimensional anti-de Sitter space, squashed or stretched along fibres that are
either spacelike or timelike. The causal structure, and the property of being
an Einstein--Weyl space, depend critically on whether we squash or stretch. We
argue that squashing, and stretching, completely destroys the conformal
boundary of the unsquashed spacetime. As a physical application we observe that
the near horizon geometry of the extremal Kerr black hole, at constant
Boyer--Lindquist latitude, is anti-de Sitter space squashed along compactified
spacelike fibres.


title: The Volume of 2D Black Holes

abstract:
  It is shown that the definition for the volume of stationary black holes
advocated in hep-th/0508108 readily generalizes to the case of dilaton gravity
in D=2. The dilaton field is included as part of the measure. A feature
observed in D=3 and 4 has been the impossibility to obtain infinite volume
while retaining finite area without encountering some kind of pathology. It is
demonstrated that this also holds in D=2. Consistency with spherically reduced
gravity is shown. For the Witten black hole it is found that the area is
proportional to the volume.


title: Loop quantum black hole

abstract:
  In this paper we consider the Kantowski-Sachs space-time in Ashtekar
variables and the quantization of this space-time starting from the complete
loop quantum gravity theory. The Kanthowski-Sachs space-time coincides with the
Schwarzschild black hole solution inside the horizon. By studying this model we
can obtain information about the black hole singularity and about the dynamics
across the point r=0. We studied this space-time in ADM variables in two
previous papers where we showed that the classical black hole singularity
disappears in quantum theory. In this work we study the same model in Ashtekar
variables and we obtain a regular space-time inside the horizon region and that
the dynamics can be extend further the classical singularity.


title:
Universality and backreaction in a general-relativistic accretion of
  steady fluids

abstract:
  The spherically symmetric steady accretion of polytropic perfect fluids onto
a black hole is the simplest flow model that can demonstrate the effects of
backreaction. The analytic and numerical investigation reveals that
backreaction keeps intact most of the characteristics of the sonic point. For
any such system, with the only free parameter being the relative abundance of
the fluid, the mass accretion rate achieves maximal value when the mass of the
fluid is universally 1/3 of the total mass.


title: Positivity in Lorentzian Barrett-Crane Models of Quantum Gravity

abstract:
  The Barrett-Crane models of Lorentzian quantum gravity are a family of spin
foam models based on the Lorentz group. We show that for various choices of
edge and face amplitudes, including the Perez-Rovelli normalization, the
amplitude for every triangulated closed 4-manifold is a non-negative real
number. Roughly speaking, this means that if one sums over triangulations,
there is no interference between the different triangulations. We prove
non-negativity by transforming the model into a ``dual variables'' formulation
in which the amplitude for a given triangulation is expressed as an integral
over three copies of hyperbolic space for each tetrahedron. Then we prove that,
expressed in this way, the integrand is non-negative. In addition to implying
that the amplitude is non-negative, the non-negativity of the integrand is
highly significant from the point of view of numerical computations, as it
allows statistical methods such as the Metropolis algorithm to be used for
efficient computation of expectation values of observables.


title: Approximate pre-classical solutions in loop quantum cosmology

abstract:
  In this paper we introduce a numerical approximation technique to obtain
pre-classical solutions to models of loop quantum gravity. In particular, we
apply the technique to vacuum Bianchi I cosmological models and recover known
solutions. We also present a pre-classical solution to the Bianchi I LRS model
with cosmological constant, which has not appeared elsewhere.


title:
Gravitationally-Induced Quantum Superpopsition Reduction with Large
  Extra Dimensions

abstract:
  A gravity-driven mechanism (``objective reduction'') proposed to explain
quantum state reduction is analyzed in light of the possible existence of large
extra dimensions in the ADD scenario. By calculating order-of-magnitude
estimates for nucleon superpositions, it is shown that if the mechanism at
question is correct, constraints may be placed on the number and size of extra
dimensions. Hence, measurement of superposition collapse times ({\it e.g.}
through diffraction or reflection experiments) could represent a new probe of
extra dimensions. The influence of a time-dependent gravitational constant on
the gravity-driven collapse scheme with and without the presence of extra
dimensions is also discussed.