title: Macroscopic Effects of the Quantum Trace Anomaly

abstract:
  The low energy effective action of gravity in any even dimension generally
acquires non-local terms associated with the trace anomaly, generated by the
quantum fluctuations of massless fields. The local auxiliary field description
of this effective action in four dimensions requires two additional scalar
fields, not contained in classical general relativity, which remain relevant at
macroscopic distance scales. The auxiliary scalar fields depend upon boundary
conditions for their complete specification, and therefore carry global
information about the geometry and macroscopic quantum state of the
gravitational field. The scalar potentials also provide coordinate invariant
order parameters describing the conformal behavior and divergences of the
stress tensor on event horizons. We compute the stress tensor due to the
anomaly in terms of its auxiliary scalar potentials in a number of concrete
examples, including the Rindler wedge, the Schwarzschild geometry, and de
Sitter spacetime. In all of these cases, a small number of classical order
parameters completely determine the divergent behaviors allowed on the horizon,
and yield qualitatively correct global approximations to the renormalized
expectation value of the quantum stress tensor.


title: Is the physics within the Solar system really understood?

abstract:
  A collection is made of presently unexplained phenomena within our Solar
system and in the universe. These phenomena are (i) the Pioneer anomaly, (ii)
the flyby anomaly, (iii) the increase of the Astronomical Unit, (iv) the
quadrupole and octupole anomaly, and (v) Dark Energy and (vi) Dark Matter. A
new data analysis of the complete set of Pioneer data is announced in order to
search for systematic effects or to confirm the unexplained acceleration. We
also review the mysterious flyby anomaly where the velocities of spacecraft
after Earth swing--bys are larger than expected. We emphasize the scientific
aspects of this anomaly and propose systematic and continuous observations and
studies at the occasion of future flybys. Further anomalies within the Solar
system are the increase of the Astronomical Unit and the quadrupole and
octupole anomaly. We briefly mention Dark Matter and Dark Energy since in some
cases a relation between them and the Solar system anomalies have been
speculated.


title: Violation of Strong Energy Condition in Effective Loop Quantum Cosmology

abstract:
  In loop quantum cosmology nonperturbative modification to a scalar matter
field at short scales implies inflation which also means a violation of the
strong energy condition. In the framework of effective Hamiltonian we discuss
the issue of violation of the strong energy condition in the presence of
quantum geometry potential. It shows that the appearance of quantum geometry
potential strengthens the violation of the strong energy condition in small
volume regions. In the small volume regions superinflation can easily happen.
Furthermore, when the evolution of the universe approaches the bounce scale,
this trend of violating the strong energy condition can be greatly amplified.


title: Universal properties from local geometric structure of Killing horizon

abstract:
  We consider universal properties that arise from a local geometric structure
of a Killing horizon. We first introduce a non-perturbative definition of such
a local geometric structure, which we call an asymptotic Killing horizon. It is
shown that infinitely many asymptotic Killing horizons reside on a common null
hypersurface, once there exists one asymptotic Killing horizon. The
acceleration of the orbits of the vector that generates an asymptotic Killing
horizon is then considered. We show that there exists the $\textit{diff}(S^1)$
or $\textit{diff}(R^1)$ sub-algebra on an asymptotic Killing horizon
universally, which is picked out naturally based on the behavior of the
acceleration. We also argue that the discrepancy between string theory and the
Euclidean approach in the entropy of an extreme black hole may be resolved, if
the microscopic states responsible for black hole thermodynamics are connected
with asymptotic Killing horizons.


title: Cold Black Holes in the Einstein-Scalar Field System

abstract:
  We study Einstein gravity coupled to a massless scalar field in a static
spherically symmetric space-time in four dimensions. Black hole solutions exist
when the kinetic energy of the scalar field is negative, that is, for a phantom
field. These ``scalar black holes'' have an infinite horizon area and zero
temperature. They are related through a conformal transformation with similar
objects in the Jordan frames of scalar-tensor theories of gravity. The
thermodynamical properties of these solutions are discussed. It is proved that
any \ssph \bhs with an infinite horizon area have zero Hawking temperature.


title:
Stability of general relativistic static thick disks: the isotropic
  Schwarzschild thick disk

abstract:
  We study the stability of general relativistic static thick disks, as an
application we consider the thick disk generated by applying the ``displace,
cut, fill and reflect" method, usually known as the image method, to the
Schwarzschild metric in isotropic coordinates. The isotropic Schwarzschild
thick disk obtained from this method is the simplest model to describe, in the
context of General Relativity, real thick galaxies. The stability under a
general first order perturbation of the disk is investigated. The first order
perturbation, when applying to the conservation equations, leads to a set of
differential equations that are, in general, not self-consistent. This opens
the possibility of performing various kinds of perturbations to transform the
resulting system of equations into a self-consistent system. We perform a
complete classification of the perturbations as well as the stability analysis
for all the relevant physical perturbations. We found that, in general, the
isotropic Schwarzschild thick disk is stable under these kinds of
perturbations.


title: LXCDM: a cosmon model solution to the cosmological coincidence problem?

abstract:
  We consider the possibility that the total dark energy (DE) of the Universe
is made out of two dynamical components of different nature: a variable
cosmological term, Lambda, and a dynamical ``cosmon'', X, possibly interacting
with Lambda but not with matter -- which remains conserved. We call this
scenario the LXCDM model. One possibility for X would be a scalar field, but it
is not the only one. The overall equation of state (EOS) of the LXCDM model can
effectively appear as quintessence or phantom energy depending on the mixture
of the two components. Both the dynamics of Lambda and of X could be linked to
high energy effects near the Planck scale. In the case of Lambda it may be
related to the running of this parameter under quantum effects, whereas X might
be identified with some fundamental field (say, a dilaton) left over as a
low-energy ``relic'' by e.g. string theory. We find that the dynamics of the
LXCDM model can trigger a future stopping of the Universe expansion and can
keep the ratio rho_D/rho_m (DE density to matter-radiation density) bounded and
of order 1. Therefore, the model could explain the so-called ``cosmological
coincidence problem''. This is in part related to the possibility that the
present value of the cosmological term can be Lambda<0 in this framework (the
current total DE density nevertheless being positive). However, a cosmic halt
could occur even if Lambda>0 because of the peculiar behavior of X as ``Phantom
Matter''. We describe various cosmological scenarios made possible by the
composite and dynamical nature of LXCDM, and discuss in detail their impact on
the cosmological coincidence problem.


title: Quasi-particle creation by analogue black holes

abstract:
  We discuss the issue of quasi-particle production by ``analogue black holes''
with particular attention to the possibility of reproducing Hawking radiation
in a laboratory. By constructing simple geometric acoustic models, we obtain a
somewhat unexpected result: We show that in order to obtain a stationary and
Planckian emission of quasi-particles, it is not necessary to create an
ergoregion in the acoustic spacetime (corresponding to a supersonic regime in
the flow). It is sufficient to set up a dynamically changing flow either
eventually generating an arbitrarily small sonic region v=c, but without any
ergoregion, or even just asymptotically, in laboratory time, approaching a
sonic regime with sufficient rapidity.


title: Static cylindrically symmetric spacetimes

abstract:
  We prove existence of static solutions to the cylindrically symmetric
Einstein-Vlasov system, and we show that the matter cylinder has finite
extension. The same results are also proved for a quite general class of
equations of state for perfect fluids coupled to the Einstein equations,
extending the class of equations of state considered in \cite{BL}. We also
obtain this result for the Vlasov-Poisson system.


title:
Gravimagnetic effect of the barycentric motion of the Sun and
  determination of the post-Newtonian parameter gamma in the Cassini experiment

abstract:
  The most precise test of the post-Newtonian gamma parameter in the solar
system has been achieved in measurement of the frequency shift of radio waves
to and from the Cassini spacecraft as they passed near the Sun. The test relies
upon the JPL model of radiowave propagation that includes, but does not
explicitly parametrize, the impact of the non-stationary component of the
gravitational field of the Sun, generated by its barycentric orbital motion, on
the Shapiro delay. This non-stationary gravitational field of the Sun is
associated with the Lorentz transformation of the metric tensor and the affine
connection from the heliocentric to the barycentric frame of the solar system
and can be treated as gravimagnetic field.
  The gravimagnetic field perturbs the propagation of a radio wave and
contributes to its frequency shift at the level up to 4 10^{-13} that may
affect the precise measurement of the parameter gamma in the Cassini experiment
to about one part in 10,000. Our analysis suggests that the translational
gravimagnetic field of the Sun can be extracted from the Cassini data, and its
effect is separable from the space curvature characterized by the parameter
gamma.


title: Torsion as a dynamic degree of freedom of quantum gravity

abstract:
  The gauge approach to gravity based on the local Lorentz group with a general
independent affine connection A_{\mu cd} is developed. We consider SO(1,3)
gauge theory with a Lagrangian quadratic in curvature as a simple model of
quantum gravity. The torsion is proposed to represent a dynamic degree of
freedom of quantum gravity at scales above the Planckian energy. The
Einstein-Hilbert theory is induced as an effective theory due to quantum
corrections of torsion via generating a stable gravito-magnetic condensate. We
conjecture that torsion possesses an intrinsic quantum nature and can be
confined. A minimal Abelian projection for the Lorentz gauge model has been
constructed, and an effective theory of the cosmic knot at the Planckian scale
is proposed.


title: Vacuum Energy: Myths and Reality

abstract:
  We discuss the main myths related to the vacuum energy and cosmological
constant, such as: ``unbearable lightness of space-time''; the dominating
contribution of zero point energy of quantum fields to the vacuum energy;
non-zero vacuum energy of the false vacuum; dependence of the vacuum energy on
the overall shift of energy; the absolute value of energy only has significance
for gravity; the vacuum energy depends on the vacuum content; cosmological
constant changes after the phase transition; zero-point energy of the vacuum
between the plates in Casimir effect must gravitate, that is why the zero-point
energy in the vacuum outside the plates must also gravitate; etc. All these and
some other conjectures appear to be wrong when one considers the thermodynamics
of the ground state of the quantum many-body system, which mimics macroscopic
thermodynamics of quantum vacuum. In particular, in spite of the ultraviolet
divergence of the zero-point energy, the natural value of the vacuum energy is
comparable with the observed dark energy. That is why the vacuum energy is the
plausible candidate for the dark energy.

categories: gr-qc astro-ph cond-mat.stat-mech hep-ph


title: Cosmologies with Energy Exchange

abstract:
  We provide a simple mathematical description of the exchange of energy
between two fluids in an expanding Friedmann universe with zero spatial
curvature. The evolution can be reduced to a single non-linear differential
equation which we solve in physically relevant cases and provide an analysis of
all the possible evolutions. Particular power-law solutions exist for the
expansion scale factor and are attractors at late times under particular
conditions. We show how a number of problems studied in the literature, such as
cosmological vacuum energy decay, particle annihilation, and the evolution of a
population of evaporating black holes, correspond to simple particular cases of
our model. In all cases we can determine the effects of the energy transfer on
the expansion scale factor. We also consider the situation in the presence of
anti-decaying fluids and so called phantom fluids which violate the dominant
energy conditions.


title:
Half century of black-hole theory: from physicists' purgatory to
  mathematicians' paradise

abstract:
  Although implicit in the discovery of the Schwarzschild solution 40 years
earlier, the issues raised by the theory of what are now known as black holes
were so unsettling to physicists of Einstein's generation that the subject
remained in a state of semiclandestine gestation until his demise. That turning
point -- just half a century after Einstein's original foundation of relativity
theory, and just half a century ago today -- can be considered to mark the
birth of black hole theory as a subject of systematic development by physicists
of a new and less inhibited generation, whose enthusastic investigations have
revealed structures of unforeseen mathematical beauty, even though questions
about the physical significance of the concomitant singularities remain
controversial.


title: Entropy of 2+1 de Sitter space with the GUP

abstract:
  By introducing the generalized uncertainty principle (GUP) on the quantum
state density, we calculate the statistical entropy of a scalar field on the
background of (2+1)-dimensional de Sitter space without artificial cutoff. The
desired entropy proportional to the horizon perimeter is obtained.


title: Mathematical Analyses of an accelerating (Griffiths-Podolsky) Black Hole

abstract:
  An exact solution of Einsteins equations which represents a pair of
accelerating and rotating black holes was presented by J. B. Griffiths and J.
Podolsky [2]. In the paper [2] they have shown the explicit form of a spinning
C-metric starting from the Plebanski-Demianski metric, and transformed it using
NUT and angular velocity parameters in addition to the usual parameters and
thus gave a generalized form of such solutions. In the forthcoming discussion,
an attempt has been made to realize the Riemann components of the proposed
metric. Furthermore, certain optical characteristics of the metric have been
analyzed using the Newman-Penrose formalism.


title:
Probing the non-linear structure of general relativity with black hole
  binaries

abstract:
  Observations of the inspiral of massive binary black holes (BBH) in the Laser
Interferometer Space Antenna (LISA) and stellar mass binary black holes in the
European Gravitational-Wave Observatory (EGO) offer an unique opportunity to
test the non-linear structure of general relativity. For a binary composed of
two non-spinning black holes, the non-linear general relativistic effects
depend only on the masses of the constituents. In a recent letter, we explored
the possibility of a test to determine all the post-Newtonian coefficients in
the gravitational wave-phasing.
  However, mutual covariances dilute the effectiveness of such a test. In this
paper, we propose a more powerful test in which the various post-Newtonian
coefficients in the gravitational wave phasing are systematically measured by
treating three of them as independent parameters and demanding their mutual
consistency. LISA (EGO) will observe BBH inspirals with a signal-to-noise ratio
of more than 1000 (100) and thereby test the self-consistency of each of the
nine post-Newtonian coefficients that have so-far been computed, by measuring
the lower order coefficients to a relative accuracy of $\sim 10^{-5}$
(respectively, $\sim 10^{-4}$) and the higher order coefficients to a relative
accuracy in the range $10^{-4}$-0.1 (respectively, $10^{-3}$-1).


title: On the Pioneer Anomaly

abstract:
  In this paper an explanation of the Pioneer anomaly is given, using the
hypothesis of the time dependent gravitational potential. The implications of
this hypothesis on the planetary orbits and orbital periods are given in
section 2. In sections 3 and 4 we give a detailed explanation of the Pioneer
anomaly, which corresponds to the observed phenomena.


title: Review on possible gravitational anomalies

abstract:
  This is an updated introductory review of 2 possible gravitational anomalies
that has attracted part of the Scientific community: the Allais effect that
occur during solar eclipses, and the Pioneer 10 spacecraft anomaly,
experimented also by Pioneer 11 and Ulysses spacecrafts. It seems that, to
date, no satisfactory conventional explanation exist to these phenomena, and
this suggests that possible new physics will be needed to account for them. The
main purpose of this review is to announce 3 other new measurements that will
be carried on during the 2005 solar eclipses in Panama and Colombia (Apr. 8)
and in Portugal (Oct.15).


title: On the cosmological constant in quantum cosmology

abstract:
  Quantization of a dust-like closed isotropic cosmological model with a
cosmological constant is realized by the method of B. DeWitt \cite{1}. It is
shown that such quantization leads to interesting results, in particular, to a
finite lifetime of the system, and appearance of the Universe in our world as
penetration via the barrier. These purely quantum effects appear when
$\Lambda>0$.


title: Weaker Gravity at Submillimetre Scales in Braneworld Models

abstract:
  Braneworld models typically predict gravity to grow stronger at short
distances. In this paper, we consider braneworlds with two types of additional
curvature couplings, a Gauss-Bonnet term in the bulk, and an Einstein-Hilbert
(EH) term on the brane. In the regime where these terms are dominant over the
bulk EH term, linearized gravity becomes weaker at short distances on the
brane. In both models, the weakening of gravity is tied to the presence of
ghosts in the graviton mass spectrum. We find that the ordinary coupling of
matter to gravity is recovered at low energies/long wavelengths on the brane.
We give some implications for cosmology and show its compatibility with
observations. We also discuss the stability of compact stars.


title:
Information-preserving black holes still do not preserve baryon number
  and other effective global quantum numbers

abstract:
  It has been claimed recently that the black hole information-loss paradox has
been resolved: the evolution of quantum states in the presence of a black hole
is unitary and information preserving. We point out that, contrary to some
claims in literature, information-preserving black holes still violate baryon
number and any other quantum number which follows from an effective (and thus
approximate) or anomalous symmetry.


title:
The Highly Damped Quasinormal Modes of $d$-dimensional
  Reissner-Nordstrom Black Holes in the Small Charge Limit

abstract:
  We analyze in detail the highly damped quasinormal modes of $d$-dimensional
Reissner-Nordstr$\ddot{\rm{o}}$m black holes with small charge, paying
particular attention to the large but finite damping limit in which the
Schwarzschild results should be valid. In the infinite damping limit, we
confirm using different methods the results obtained previously in the
literature for higher dimensional Reissner-Nordstr$\ddot{\rm{o}}$m black holes.
Using a combination of analytic and numerical techniques we also calculate the
transition of the real part of the quasinormal mode frequency from the
Reissner-Nordstr$\ddot{\rm{o}}$m value for very large damping to the
Schwarzschild value of $\ln(3) T_{bh}$ for intermediate damping. The real
frequency does not interpolate smoothly between the two values. Instead there
is a critical value of the damping at which the topology of the
Stokes/anti-Stokes lines change, and the real part of the quasinormal mode
frequency dips to zero.


title: The quantum black hole in 2+1 dimensions

abstract:
  In this paper we investigate the quantum nature of a 2+1 dimensional black
hole using the method [arXiv: gr-qc/0504030] which earlier revealed the quantum
nature of a black hole in 3+1 dimensions.


title: Emergent General Relativity

abstract:
  We review different approaches to quantum gravity in which spacetime is
emerging. We discuss in some detail the proposals by G. Volovik and S. Lloyd
and show how they differ in the way they treat time. We further propose an
approach to quantum gravity in which the Einstein equations are derived rather
then used. We call this approach Internal Relativity.


title: 'Antigravity' Propulsion and Relativistic Hyperdrive

abstract:
  Exact payload trajectories in the strong gravitational fields of compact
masses moving with constant relativistic velocities are calculated. The strong
field of a suitable driver mass at relativistic speeds can quickly propel a
heavy payload from rest to a speed significantly faster than the driver, a
condition called hyperdrive. Hyperdrive thresholds and maxima are calculated as
functions of driver mass and velocity.


title: Spin Zero Perturbation in the Kerr-Randall-Sundrum Space-Time

abstract:
  This dissertation aims at studying the braneworld models in the context
proposed by Randall and Sundrum. The focus is on the spin-0 perturbations in
the Kerr space-time as a 4-dimensional braneworld.
  The work deals the main aspects of Einstein General Relativity as well as
perturbations of black holes metrics. We also review the Randall-Sundrum models
and their motivations and attempts to describe braneworld black holes. In the
end the Kerr-Randall-Sundrum black string scalar perturbation and superradiance
are obtained.


title:
Measurement of Optical Response of a Detuned Resonant Sideband
  Extraction Interferometer

abstract:
  We report on the optical response of a suspended-mass detuned resonant
sideband extraction (RSE) interferometer with power recycling. The purpose of
the detuned RSE configuration is to manipulate and optimize the optical
response of the interferometer to differential displacements (induced by
gravitational waves) as a function of frequency, independently of other
parameters of the interferometer. The design of our interferometer results in
an optical gain with two peaks: an RSE optical resonance at around 4 kHz and a
radiation pressure induced optical spring at around 41 Hz. We have developed a
reliable procedure for acquiring lock and establishing the desired optical
configuration. In this configuration, we have measured the optical response to
differential displacement and found good agreement with predictions at both
resonances and all other relevant frequencies. These results build confidence
in both the theory and practical implementation of the more complex optical
configuration being planned for Advanced LIGO.


title: Accelerating Universe as Window for Extra Dimensions

abstract:
  Homogeneous cosmological solutions are obtained in five dimensional space
time assuming equations of state $ p = k\rho $ and $ p_{5}= \gamma\rho$ where p
is the isotropic 3 - pressure and $p_{5}$, that for the fifth dimension. Using
different values for the constants k and $\gamma$ many known solutions are
rediscovered. Further the current acceleration of the universe has led us to
investigate higher dimensional gravity theory, which is able to explain
acceleration from a theoretical view point without the need of introducing dark
energy by hand. We argue that the terms containing higher dimensional metric
coefficients produce an extra negative pressure that apparently drives an
acceleration of the 3D space, tempting us to suggest that the accelerating
universe seems to act as a window to the existence of extra spatial dimensions.
Interestingly the 5D matter field remains regular while the \emph{effective}
negative pressure is responsible for the inflation. Relaxing the assumptions of
two equations of state we also present a class of solutions which provide early
deceleration followed by a late acceleration in a unified manner. Interesting
to point out that in this case our cosmology apparently mimics the well known
quintessence scenario fuelled by a generalised Chaplygin-type of fluid where a
smooth transition from a dust dominated model to a de Sitter like one takes
place.


title:
Performing a theoretically robust Ryan test using intermediate-mass
  black holes

abstract:
  We investigate the possibility of using binary IMBH inspirals to perform the
Ryan test of general relativity in a theoretically robust manner using data
from early in the detectable part of the inspiral. We find this to be feasible
and compute the masses of the most favourable systems.


title: Second Order Gauge-Invariant Perturbations during Inflation

abstract:
  The evolution of gauge invariant second-order scalar perturbations in a
general single field inflationary scenario are presented. Different second
order gauge invariant expressions for the curvature are considered. We evaluate
perturbatively one of these second order curvature fluctuations and a second
order gauge invariant scalar field fluctuation during the slow-roll stage of a
massive chaotic inflationary scenario, taking into account the deviation from a
pure de Sitter evolution and considering only the contribution of super-Hubble
perturbations in mode-mode coupling. The spectra resulting from their
contribution to the second order quantum correlation function are nearly
scale-invariant, with additional logarithmic corrections to the first order
spectrum. For all scales of interest the amplitude of these spectra depend on
the total number of e-folds. We find, on comparing first and second order
perturbation results, an upper limit to the total number of e-folds beyond
which the two orders are comparable.


title: Friedmann Equation for Brans Dicke Cosmology

abstract:
  In the context of Brans-Dicke scalar tensor theory of gravitation, the
cosmological Friedmann equation which relates the expansion rate $H$ of the
universe to the various fractions of energy density is analyzed rigorously. It
is shown that Brans-Dicke scalar tensor theory of gravitation brings a
negligible correction to the matter density component of Friedmann equation.
Besides, in addition to $\Omega_{\Lambda}$ and $\Omega_{M}$ in standard
Einstein cosmology, another density parameter, $\Omega_{_{\Delta}}$, is
expected by the theory. This implies that if $\Omega_{_{\Delta}}$ is found to
be nonzero, data will favor this model instead of the standard Einstein
cosmological model with cosmological constant and will enable more accurate
predictions for the rate of change of Newtonian gravitational constant in the
future.


title: Black Holes in Brans-Dicke Theory with a Cosmological Constant

abstract:
  Since the Brans-Dicke theory is conformal related to the dilaton gravity
theory, by applying a conformal transformation to the dilaton gravity theory,
we derived the cosmological constant term in the Brans-Dicke theory and the
physical solution of black holes with the cosmological constant. It is found
that, in four dimensions, the solution is just the Kerr-Newman-de Sitter
solution with a constant scalar field. However, in $n>4$ dimensions, the
solution is not yet the $n$ dimensional Kerr-Newman-de Sitter solution and the
scalar field is not a constant in general. In Brans-Dicke-Ni theory, the
resulting solution is also not yet the Kerr-Newman-de Sitter one even in four
dimensions. The higher dimensional origin of the Brans-Dicke scalar field is
briefly discussed.


title:
Hamiltonian analysis of the double null 2+2 decomposition of General
  Relativity expressed in terms of self-dual bivectors

abstract:
  In this paper we obtain a 2+2 double null Hamiltonian description of General
Relativity using only the (complex) SO(3) connection and the components of the
complex densitised self-dual bivectors. We carry out the general canonical
analysis of this system and obtain the first class constraint algebra entirely
in terms of the self-dual variables. The first class algebra forms a Lie
algebra and all the first class constraints have a simple geometrical
interpretation.


title: Weak Values and Relational Generalisations

abstract:
  We justify generalisations of weak values from a tentatively relational
perspective by deriving them from a generalisation of Bayes' rule. We also
argue that these generalisations have implications of quantum nonlocality and
may form a novel approach to quantum gravity and cosmology.


title:
The York map as a Shanmugadhasan canonical transformation in tetrad
  gravity and the role of non-inertial frames in the geometrical view of the
  gravitational field

abstract:
  A new parametrization of the 3-metric allows to find explicitly a York map in
canonical ADM tetrad gravity, the two pairs of physical tidal degrees of
freedom and 14 gauge variables. These gauge quantities (generalized inertial
effects) are all configurational except the trace ${}^3K(\tau ,\vec \sigma)$ of
the extrinsic curvature of the instantaneous 3-spaces $\Sigma_{\tau}$ (clock
synchronization convention) of a non-inertial frame. The Dirac hamiltonian is
the sum of the weak ADM energy $E_{ADM} = \int d^3\sigma {\cal E}_{ADM}(\tau
,\vec \sigma)$ (whose density is coordinate-dependent due to the inertial
potentials) and of the first-class constraints. Then: i) The explicit form of
the Hamilton equations for the two tidal degrees of freedom in an arbitrary
gauge: a deterministic evolution can be defined only in a completely fixed
gauge, i.e. in a non-inertial frame with its pattern of inertial forces. ii) A
general solution of the super-momentum constraints, which shows the existence
of a generalized Gribov ambiguity associated to the 3-diffeomorphism gauge
group. It influences: a) the explicit form of the weak ADM energy and of the
super-momentum constraint; b) the determination of the shift functions and then
of the lapse one. iii) The dependence of the Hamilton equations for the two
pairs of dynamical gravitational degrees of freedom (the generalized tidal
effects) and for the matter, written in a completely fixed 3-orthogonal
Schwinger time gauge, upon the gauge variable ${}^3K(\tau ,\vec \sigma)$,
determining the convention of clock synchronization. Therefore it should be
possible (for instance in the weak field limit but with relativistic motion) to
try to check whether in Einstein's theory the {\it dark matter} is a gauge
relativistic inertial effect induced by ${}^3K(\tau ,\vec \sigma)$.


title:
Explaining Leibniz-equivalence as difference of non-inertial
  appearances: dis-solution of the Hole Argument and physical individuation of
  point-events

abstract:
  "The last remnant of physical objectivity of space-time" is disclosed in the
case of a continuous family of spatially non-compact models of general
relativity (GR). The {\it physical individuation} of point-events is furnished
by the intrinsic degrees of freedom of the gravitational field, (viz, the {\it
Dirac observables}) that represent - as it were - the {\it ontic} part of the
metric field. The physical role of the {\it epistemic} part (viz. the {\it
gauge} variables) is likewise clarified as emboding the unavoidable
non-inertial aspects of GR. At the end the philosophical import of the {\it
Hole Argument} is substantially weakened and in fact the Argument itself
dis-solved, while a specific four-dimensional {\it holistic and structuralist}
view of space-time, (called {\it point-structuralism}), emerges, including
elements common to the tradition of both {\it substantivalism} and {\it
relationism}. The observables of our models undergo real {\it temporal change}:
this gives new evidence to the fact that statements like the {\it frozen-time}
character of evolution, as other ontological claims about GR, are {\it model
dependent}. \medskip Forthcoming in Studies in History and Philosophy of Modern
Physics


title: Black Holes in Einstein-Aether Theory

abstract:
  We study black hole solutions in general relativity coupled to a unit
timelike vector field dubbed the "aether". To be causally isolated a black hole
interior must trap matter fields as well as all aether and metric modes. The
theory possesses spin-0, spin-1, and spin-2 modes whose speeds depend on four
coupling coefficients. We find that the full three-parameter family of local
spherically symmetric static solutions is always regular at a metric horizon,
but only a two-parameter subset is regular at a spin-0 horizon. Asymptotic
flatness imposes another condition, leaving a one-parameter family of regular
black holes. These solutions are compared to the Schwarzschild solution using
numerical integration for a special class of coupling coefficients. They are
very close to Schwarzschild outside the horizon for a wide range of couplings,
and have a spacelike singularity inside, but differ inside quantitatively. Some
quantities constructed from the metric and aether oscillate in the interior as
the singularity is approached. The aether is at rest at spatial infinity and
flows into the black hole, but differs significantly from the the 4-velocity of
freely-falling geodesics.


title: Quasi-spherical collapse with cosmological constant

abstract:
  The junction conditions between static and non-static space-times are studied
for analyzing gravitational collapse in the presence of a cosmological
constant. We have discussed about the apparent horizon and their physical
significance. We also show the effect of cosmological constant in the collapse
and it has been shown that cosmological constant slows down the collapse of
matter.


title:
The effect of Pressure in Higher Dimensional Quasi-Spherical
  Gravitational Collapse

abstract:
  We study gravitational collapse in higher dimensional quasi-spherical
Szekeres space-time for matter with anisotropic pressure. Both local and global
visibility of central curvature singularity has been studied and it is found
that with proper choice of initial data it is possible to show the validity of
CCC for six and higher dimensions. Also the role of pressure in the collapsing
process has been discussed.


title:
Poynting vector in stationary axisymmetric electrovacuum spacetimes
  reexamined

abstract:
  A simple formula, invariant under the duality rotation \Phi -> exp(i\alpha)
\Phi, is obtained for the Poynting vector within the framework of the Ernst
formalism, and its application to the known exact solutions for a charged
massive magnetic dipole is considered.


title:
General Relativistic Galaxy Rotation Curves: Implications for Dark
  Matter Distribution

abstract:
  It has recently been suggested that observed galaxy rotation curves can be
accounted for by general relativity without recourse to dark-matter halos. Good
fits have been produced to observed galatic rotation curves using this model.
We show that the implied total mass is infinite, adding to the evidence
opposing the hypothesis.


title:
Kerr black hole lensing for generic observers in the strong deflection
  limit

abstract:
  We generalize our previous work on gravitational lensing by a Kerr black hole
in the strong deflection limit, removing the restriction to observers on the
equatorial plane. Starting from the Schwarzschild solution and adding
corrections up to the second order in the black hole spin, we perform a
complete analytical study of the lens equation for relativistic images created
by photons passing very close to a Kerr black hole. We find out that, to the
lowest order, all observables (including shape and shift of the black hole
shadow, caustic drift and size, images position and magnification) depend on
the projection of the spin on a plane orthogonal to the line of sight. In order
to break the degeneracy between the black hole spin and its inclination
relative to the observer, it is necessary to push the expansion to higher
orders. In terms of future VLBI observations, this implies that very accurate
measures are needed to determine these two parameters separately.


title: Instabilities in the nonsymmetric theory of gravitation

abstract:
  We consider the linearized nonsymmetric theory of gravitation (NGT) within
the background of an expanding universe and near a Schwarzschild metric. We
show that the theory always develops instabilities unless the linearized
nonsymmetric lagrangian reduces to a particular simple form. This theory
contains a gauge invariant kinetic term, a mass term for the antisymmetric
metric-field and a coupling with the Ricci curvature scalar. This form cannot
be obtained within NGT. Next we discuss NGT beyond linearized level and
conjecture that the instabilities are not a relic of the linearization, but are
a general feature of the full theory. Finally we show that one cannot add
ad-hoc constraints to remove the instabilities as is possible with the
instabilities found in NGT by Clayton.


title: Traversable wormholes coupled to nonlinear electrodynamics

abstract:
  In this work we explore the possible existence of static, spherically
symmetric and stationary, axisymmetric traversable wormholes coupled to
nonlinear electrodynamics. Considering static and spherically symmetric (2+1)
and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event
horizon and the non-violation of the null energy condition at the throat. For
the former spacetime, the principle of finiteness is imposed, in order to
obtain regular physical fields at the throat. Next, we analyze the
(2+1)-dimensional stationary and axisymmetric wormhole, and also verify the
presence of an event horizon, rendering the geometry non-traversable.
Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole
geometry, we find that the field equations impose specific conditions that are
incompatible with the properties of wormholes. Thus, we prove the non-existence
of the general class of traversable wormhole solutions, outlined above, within
the context of nonlinear electrodynamics.


title: Polynomial Hamiltonian form of General Relativity

abstract:
  Phase space of General Relativity is extended to a Poisson manifold by
inclusion of the determinant of the metric and conjugate momentum as additional
independent variables. As a result, the action and the constraints take a
polynomial form. New expression for the generating functional for the Green
functions is proposed. We show that the Dirac bracket defines degenerate
Poisson structure on a manifold, and a second class constraints are the Casimir
functions with respect to this structure. As an application of the new
variables, we consider the Friedmann universe.


title: Extrinsically flat static spacetimes

abstract:
  We consider static spacetimes whose spatial part admits foliations with the
extrinsic curvature tensor K_{ab}=0. There are two complementary cases when the
gradient of the lapse function points 1) to the direction of foliation or 2)
orthogonally to it. Case 1) gives generalization of metrics like
Bertotti-Robinson or Nariai. In case 2) the matter source violates the null
energy condition at least on the part of the manifold, having in this sense
phantom nature. We also demonstrate that for the manifolds under discussion the
horizon can be naked in the sense that certain Weyl components diverge in the
free-falling frame although the Kretschmann scalar is finite. The Petrov type
is D or O. Explicit solutions for (i) the linear anisotropic equation of state,
(ii) Chaplygin gas and (iii) uniform energy density are found.


title: A class of space-times of non-rigidly rotating dust

abstract:
  We find a class of exact solutions of differentially rotating dust in the
framework of General Relativity. There exist asymptotically flat space-times of
the flow with positive mass function that for radii sufficiently large is
monotonic and tends to zero at infinity. Some of the space-times may have
non-vanishing total angular momentum. The flow is essentially different from
another exactly solvable flow described by van Stockum line element.


title: The Hyperfine Einstein-Infeld-Hoffmann Potential

abstract:
  We use recently developed effective field theory techniques to calculate the
third order post-Newtonian correction to the spin-spin potential between two
spinning objects. This correction represents the first contribution to the
spin-spin interaction due to the non-linear nature of general relativity and
will play an important role in forthcoming gravity wave experiments.


title: Spin Dependence in Computational Black Hole Data

abstract:
  We have implemented a parallel multigrid solver, to solve the initial data
problem for 3+1 General Relativity. This involves solution of elliptic
equations derived from the Hamiltonian and the momentum constraints. We use the
conformal transverse-traceless method of York and collaborators which consists
of a conformal decomposition with a scalar $\phi$ that adjusts the metric, and
a vector potential $w^i$ that adjusts the longitudinal components of the
extrinsic curvature. The constraint equations are then solved for these
quantities $\phi$, $w^i$ such that the complete solution fully satisfies the
constraints. We apply this technique to compare with theoretical expectations
for the spin-orientation- and separation-dependence in the case of spinning
interacting (but not orbiting) black holes. We write out a formula for the
effect of the spin-spin interaction which includes a result of Wald as well as
additional effect due to the rotation of the mass quadrupole moment of a
spinning black hole. A subset of these spin-spin effects are confirmed via our
numerical calculations, however due to computer time limitations the full
parameter space has not yet been surveyed and confirmed. In particular, at the
relatively small s eparations ($d \leq 18m$) we are able to consider, we are
unable to confirm the expected asymptotic fall-off of $d^{-3}$ for these
effects.


title: Stability of naked singularities and algebraically special modes

abstract:
  We show that algebraically special modes lead to the instability of naked
singularity spacetimes with negative mass. Four-dimensional negative-mass
Schwarzschild and Schwarzschild-de Sitter spacetimes are unstable. Stability of
the Schwarzschild-anti-de Sitter spacetime depends on boundary conditions. We
briefly discuss the generalization of these results to charged and rotating
singularities.


title: Einstein equations: exact solutions

abstract:
  In Einstein's general relativity, with its nonlinear field equations, the
discoveries and analyzes of various specific explicit solutions made a great
impact on understanding many of the unforeseen features of the theory. Some
solutions found fundamental applications in astrophysics, cosmology and, more
recently, in the developments inspired by string theory. In this short article
we survey the invariant characterization and classification of the solutions
and describe the properties and role of the most relevant classes: Minkowski,
(anti-)de Sitter spacetimes, spherical Schwarzschild and Reissner-Nordstroem
metrics, stationary axisymmetric solutions, radiative metrics describing plane
and cylindrical waves, radiative fields of uniformly accelerated sources and
Robinson-Trautman solutions. Metrics representing regions of spacetimes filled
with matter are also discussed and cosmological models are very briefly
mentioned. Some parts of the text are based on a detailed survey which appeared
in gr-qc/0004016 (see Ref. 2).


title:
Obtaining a class of Type O pure radiation metrics with a cosmological
  constant, using invariant operators

abstract:
  Using the generalised invariant formalism we derive a class of conformally
flat spacetimes whose Ricci tensor has a pure radiation and a Ricci scalar
component. The method used is a development of the methods used earlier for
pure radiation spacetimes of Petrov types O and N respectively. In this paper
we demonstrate how to handle, in the generalised invariant formalism,
spacetimes with isotropy freedom and rich Killing vector structure. Once the
spacetimes have been constructed, it is straightforward to deduce their
Karlhede classification: the Karlhede algorithm terminates at the fourth
derivative order, and the spacetimes all have one degree of null isotropy and
three, four or five Killing vectors.


title: Ultrarelativistic sources in nonlinear electrodynamics

abstract:
  The fields of rapidly moving sources are studied within nonlinear
electrodynamics by boosting the fields of sources at rest. As a consequence of
the ultrarelativistic limit the delta-like electromagnetic shock waves are
found. The character of the field within the shock depends on the theory of
nonlinear electrodynamics considered. In particular, we obtain the field of an
ultrarelativistic charge in the Born-Infeld theory.


title: Singularities in Isotropic Non-Minimal Scalar Field Models

abstract:
  Non-minimally coupling a scalar field to gravity introduces an additional
curvature term into the action which can change the general behavior in strong
curvature regimes, in particular close to classical singularities. While one
can conformally transform any non-minimal model to a minimally coupled one,
that transformation can itself become singular. It is thus not guaranteed that
all qualitative properties are shared by minimal and non-minimal models. This
paper addresses the classical singularity issue in isotropic models and extends
singularity removal in quantum gravity to non-minimal models.


title:
An explicit quantum weak energy inequality for Dirac fields in curved
  spacetimes

abstract:
  The quantized Dirac field is known, by a result of Fewster and Verch, to
satisfy a Quantum Weak Energy Inequality (QWEI) on its averaged energy density
along time-like curves in arbitrary four-dimensional globally hyperbolic
spacetimes. However, this result does not provide an explicit form for the
bound. By adapting ideas from the earlier work, we give a simplified derivation
of a QWEI for the Dirac field leading to an explicit bound. The bound
simplifies further in the case of static curves in static spacetimes, and, in
particular, coincides with a result of Fewster and Mistry in four-dimensional
Minkowski spacetime. We also show that our QWEI is compatible with local
covariance and derive a simple consequence.


title:
A Lorentz-Poincar\'e type interpretation of the Weak Equivalence
  Principle

abstract:
  The validity of the Weak Equivalence Principle relative to a local inertial
frame is detailed in a scalar-vector gravitation model with Lorentz-Poincar\'e
type interpretation. Given the previously established first Post-Newtonian
concordance of dynamics with General Relativity, the principle is to this order
compatible with GRT. The gravitationally modified Lorentz transformations, on
which the observations in physical coordinates depend, are shown to provide a
physical interpretation of \emph{parallel transport}. A development of
``geodesic'' deviation in terms of the present model is given as well.


title:
Neutral perfect fluids and charged thin shells with electromagnetic mass
  in general relativity

abstract:
  We build extended sources for the Reissner-Nordstr\"{o}m metric. Our models
describe a neutral perfect fluid core bounded by a charged thin shell, and
feature everywhere positive rest mass density and everywhere non-negative
active gravitational mass, as well as classical electron radius and
electromagnetic total mass. We contrast our results with previously discussed
models featuring similar properties at the expense of including anisotropic
pressures within the fluid. Our charged thin shells are restricted by the 2D
texture equation of state which causes the continuity of the active
gravitational mass, in spite of the singularity of the energy-momentum tensor.
We mention possible extensions of this study suggested by modified active mass
formulae proposed in the literature.


title:
Perturbative photon flux generated by high-frequency relic gravitational
  waves and utilization of them for their detection

abstract:
  There exist corresponding metric perturbations of the relic gravitational
waves (GWs) in the region of approximately h~10^(-30)-10^(-32)in the GHz band.
A detector for these GWs is described in which we measure the perturbative
photon flux (PPF) or signal generated by such high-frequency relic GWs (HFRGWs)
via a coupling system of fractal membranes and a Gaussian beam (GB) passing
through a static magnetic field. It is found that under the synchro-resonance
condition in which the frequency of the GB is set equal to the frequency of the
expected HFRGWs (h~2.00*10^(-31), v_g=10^10Hz in the quintessential
inflationary models (QIM) and h~6.32*10^(-31), v_g=10^10Hz in the pre-big bang
scenario (PBBS) may produce the PPFs of ~4.04*10^2/s and ~1.27*10^3/s in a
surface of 100cm^2 area at the waist of the GB, respectively. The relatively
weak first-order PPF, directed at right angles to the expected HFRGWs, is
reflected by fractal membrane and the resulting reflected PPF (signal) exhibits
a very small decay in transit to the detector (tunable microwave receiver)
compared with the much stronger background photon flux, which allows for
detection of the reflected PPF with signal to background noise ratios greater
than one at the distance of the detector. We also discuss the selection
capability of system and directional sensitivity for the resonance components
from the stochastic relic GW background. The resolution of tiny difference
between the PPFs generated by the relic GWs in the QIM and in the PBBS may be
established and will be of cosmological significance. PACS numbers: 04.30.Nk,
04.30.Db, and 98.80.Cq.


title: Boson stars from a gauge condensate

abstract:
  The boson star filled with two interacting scalar fields is investigated. The
scalar fields can be considered as a gauge condensate formed by SU(3) gauge
field quantized in a non-perturbative manner. The corresponding solution is
regular everywhere, has a finite energy and can be considered as a quantum
SU(3) version of the Bartnik - McKinnon particle-like solution.


title:
Linear Connections and Curvature Tensors in the Geometry of
  Parallelizable Manifolds

abstract:
  In this paper we discuss curvature tensors in the context of Absolute
Parallelism geometry. Different curvature tensors are expressed in a compact
form in terms of the torsion tensor of the canonical connection. Using the
Bianchi identities some other identities are derived from the expressions
obtained. These identities, in turn, are used to reveal some of the properties
satisfied by an intriguing fourth order tensor which we refer to as Wanas
tensor. A further condition on the canonical connection is imposed, assuming it
is semi-symmetric. The formulae thus obtained, together with other formulae
(Ricci tensors and scalar curvatures of the different connections admitted by
the space) are calculated under this additional assumption. Considering a
specific form of the semi-symmetric connection causes all nonvanishing
curvature tensors to coincide, up to a constant, with the Wanas tensor.
Physical aspects of some of the geometric objects considered are mentioned.


title: Background independent quantizations: the scalar field II

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. Assumed in our paper homeomorphism
invariance allows to derive the complete class of the states. They are
determined by the homeomorphism invariant states defined on the CW-complex
*-algebra. The corresponding GNS representations of the polymer *-algebra and
their self-adjoint extensions are derived, the equivalence classes are found
and invariant subspaces characterized. In the preceding letter (the part I) we
outlined those results. Here, we present the technical details.


title: A Toy Model for Black Hole in Noncommutative Spaces

abstract:
  We present a new point of view on the problem of the Schwarzschild black hole
in the noncommutative spaces, proposed recently by F. Nasseri. We apply our
treatment also to the case of the 2+1 dimensional Ba\~ nados-Teitelboim-Zanelli
black hole.


title:
Merger Transitions in Brane--Black-Hole Systems: Criticality, Scaling,
  and Self-Similarity

abstract:
  We propose a toy model for study merger transitions in a curved spaceime with
an arbitrary number of dimensions. This model includes a bulk N-dimensional
static spherically symmetric black hole and a test D-dimensional brane
interacting with the black hole. The brane is asymptotically flat and allows
O(D-1) group of symmetry. Such a brane--black-hole (BBH) system has two
different phases. The first one is formed by solutions describing a brane
crossing the horizon of the bulk black hole. In this case the internal induced
geometry of the brane describes D-dimensional black hole. The other phase
consists of solutions for branes which do not intersect the horizon and the
induced geometry does not have a horizon. We study a critical solution at the
threshold of the brane-black-hole formation, and the solutions which are close
to it. In particular, we demonstrate, that there exists a striking similarity
of the merger transition, during which the phase of the BBH-system is changed,
both with the Choptuik critical collapse and with the merger transitions in the
higher dimensional caged black-hole--black-string system.


title: Strategies for observing extreme mass ratio inspirals

abstract:
  I review the status of research, conducted by a variety of independent
groups, aimed at the eventual observation of Extreme Mass Ratio Inspirals
(EMRIs) with gravitational wave detectors. EMRIs are binary systems in which
one of the objects is much more massive than the other, and which are in a
state of dynamical evolution that is dominated by the effects of gravitational
radiation. Although these systems are highly relativistic, with the smaller
object moving relative to the larger at nearly light-speed, they are well
described by perturbative calculations which exploit the mass ratio as a
natural small parameter. I review the use of such approximations to generate
waveforms needed by data analysis algorithms for observation. I also briefly
review the status of developing the data analysis algorithms themselves.
Although this article is almost entirely a review of previous work, it includes
(as an appendix) a new analytical estimate for the time over which the
influence of radiation on the binary itself is observationally negligible.


title:
Spontaneous excitation of an accelerated hydrogen atom coupled with
  electromagnetic vacuum fluctuations

abstract:
  We consider a multilevel hydrogen atom in interaction with the quantum
electromagnetic field and separately calculate the contributions of the vacuum
fluctuation and radiation reaction to the rate of change of the mean atomic
energy of the atom for uniform acceleration. It is found that the acceleration
disturbs the vacuum fluctuations in such a way that the delicate balance
between the contributions of vacuum fluctuation and radiation reaction that
exists for inertial atoms is broken, so that the transitions to higher-lying
states from ground state are possible even in vacuum. In contrast to the case
of an atom interacting with a scalar field, the contributions of both
electromagnetic vacuum fluctuations and radiation reaction to the spontaneous
emission rate are affected by the acceleration, and furthermore the
contribution of the vacuum fluctuations contains a non-thermal
acceleration-dependent correction, which is possibly observable.


title:
Can universe exit from phantom inflation due to gravitational back
  reaction?

abstract:
  The effects of the gravitational back reaction of cosmological perturbations
are investigated in a phantom inflation model. The effective energy-momentum
tensor of the gravitational back reaction of cosmological perturbations whose
wavelengths are larger than the Hubble radius is calculated. Our results show
that the effects of gravitational back reaction will counteract that of the
phantom energy. It is demonstrated in a chaotic phantom inflation model that if
the phantom field at the end of inflation is larger than a critical value
determined by the necessary e-folds, the phantom inflation phase might be
terminated by the gravitational back reaction.


title: Relativistic Rotation: A Comparison of Theories

abstract:
  Alternative theories of relativistic rotation considered viable as of 2004
are compared in the light of experiments reported in 2005. En route, the
contentious issue of simultaneity choice in rotation is resolved by showing
that only one simultaneity choice, the one possessing continuous time, gives
rise, via the general relativistic equation of motion, to the correct Newtonian
limit Coriolis acceleration. In addition, the widely dispersed argument
purporting Lorentz contraction in rotation and the concomitant curved surface
of a rotating disk is analyzed and argued to be lacking for more than one
reason. It is posited that not by theoretical arguments, but only via
experiment can we know whether such effect exists in rotation or not.
  The Coriolis/simultaneity correlation, and the results of the 2005
experiments, support the Selleri theory as being closest to the truth, though
it is incomplete in a more general applicability sense, because it does not
provide a global metric. Two alternatives, a modified Klauber approach and a
Selleri-Klauber hybrid, are presented which are consistent with recent
experiment and have a global metric, thereby making them applicable to rotation
problems of all types.


title: Space Noncommutativity Corrections to the Cardy-Verlinde Formula

abstract:
  In this letter we compute the corrections to the Cardy-Verlinde formula of
Schwarzschild black holes. These corrections stem from the space
noncommutativity. Because the Schwarzschild black holes are non rotating, to
the first order of perturbative calculations, there is no any effect on the
properties of black hole due to the noncommutativity of space.


title:
The Chrono-geometrical Structure of Special and General Relativity: a
  Re-Visitation of Canonical Geometrodynamics

abstract:
  A modern re-visitation of the consequences of the lack of an intrinsic notion
of instantaneous 3-space in relativistic theories leads to a reformulation of
their kinematical basis emphasizing the role of non-inertial frames centered on
an arbitrary accelerated observer. In special relativity the exigence of
predictability implies the adoption of the 3+1 point of view, which leads to a
well posed initial value problem for field equations in a framework where the
change of the convention of synchronization of distant clocks is realized by
means of a gauge transformation. This point of view is also at the heart of the
canonical approach to metric and tetrad gravity in globally hyperbolic
asymptotically flat space-times, where the use of Shanmugadhasan canonical
transformations allows the separation of the physical degrees of freedom of the
gravitational field (the tidal effects) from the arbitrary gauge variables.
Since a global vision of the equivalence principle implies that only global
non-inertial frames can exist in general relativity, the gauge variables are
naturally interpreted as generalized relativistic inertial effects, which have
to be fixed to get a deterministic evolution in a given non-inertial frame. As
a consequence, in each Einstein's space-time in this class the whole
chrono-geometrical structure, including also the clock synchronization
convention, is dynamically determined and a new approach to the Hole Argument
leads to the conclusion that "gravitational field" and "space-time" are two
faces of the same entity. This view allows to get a classical scenario for the
unification of the four interactions in a scheme suited to the description of
the solar system or our galaxy with a deperametrization to special relativity
and the subsequent possibility to take the non-relativistic limit.


title: Note on aligned Petrov type D purely magnetic perfect fluids

abstract:
  We recently showed (Class. Quantum Grav.\ 23, 3353; gr-qc/0602091) that
aligned Petrov type D purely magnetic perfect fluids are necessarily locally
rotationally symmetric (LRS) and hence are all explicitly known. We provide
here a more transparent proof.


title: On leading order gravitational backreactions in de Sitter spacetime

abstract:
  Backreactions are considered in a de Sitter spacetime whose cosmological
constant is generated by the potential of scalar field. The leading order
gravitational effect of nonlinear matter fluctuations is analyzed and it is
found that the initial value problem for the perturbed Einstein equations
possesses linearization instabilities. We show that these linearization
instabilities can be avoided by assuming strict de Sitter invariance of the
quantum states of the linearized fluctuations. We furthermore show that quantum
anomalies do not block the invariance requirement. This invariance constraint
applies to the entire spectrum of states, from the vacuum to the excited states
(should they exist), and is in that sense much stronger than the usual Poincare
invariance requirement of the Minkowski vacuum alone. Thus to leading order in
their effect on the gravitational field, the quantum states of the matter and
metric fluctuations must be de Sitter invariant.


title:
Gravitational radiation from nonaxisymmetric spherical Couette flow in a
  neutron star

abstract:
  The gravitational wave signal generated by global, nonaxisymmetric shear
flows in a neutron star is calculated numerically by integrating the
incompressible Navier--Stokes equation in a spherical, differentially rotating
shell. At Reynolds numbers $\Rey \gsim 3 \times 10^{3}$, the laminar Stokes
flow is unstable and helical, oscillating Taylor--G\"ortler vortices develop.
The gravitational wave strain generated by the resulting kinetic-energy
fluctuations is computed in both $+$ and $\times$ polarizations as a function
of time. It is found that the signal-to-noise ratio for a coherent,
$10^{8}$-{\rm s} integration with LIGO II scales as $ 6.5 (\Omega_*/10^{4} {\rm
rad} {\rm s}^{-1})^{7/2}$ for a star at 1 {\rm kpc} with angular velocity
$\Omega_*$. This should be regarded as a lower limit: it excludes pressure
fluctuations, herringbone flows, Stuart vortices, and fully developed
turbulence (for $\Rey \gsim 10^{6}$).


title: On Recovering Continuum Topology from a Causal Set

abstract:
  An important question that discrete approaches to quantum gravity must
address is how continuum features of spacetime can be recovered from the
discrete substructure. Here, we examine this question within the causal set
approach to quantum gravity, where the substructure replacing the spacetime
continuum is a locally finite partial order. A new topology on causal sets
using ``thickened antichains'' is constructed. This topology is then used to
recover the homology of a globally hyperbolic spacetime from a causal set which
faithfully embeds into it at sufficiently high sprinkling density. This implies
a discrete-continuum correspondence which lends support to the fundamental
conjecture or ``Hauptvermutung'' of causal set theory.


title: Gauge invariance and massive torsionic scalar field

abstract:
  The Hojman-Rosenbaum-Ryan-Shepley dynamical theory of torsion preserves local
gauge invariance of electrodynamics and makes minimal coupling compatible with
torsion. It also allows propagation of torsion in vacuum. It is known that
implications of this model disagree with the Eotvos-Dicke-Braginsky solar tests
of the principle of equivalence. We modify this theory and make it consistent
with experiment by introducing a massive component of the torsionic potential.


title: Complex Lagrangians and phantom cosmology

abstract:
  Motivated by the generalization of quantum theory for the case of
non-Hermitian Hamiltonians with PT symmetry, we show how a classical
cosmological model describes a smooth transition from ordinary dark energy to
the phantom one. The model is based on a classical complex Lagrangian of a
scalar field. Specific symmetry properties analogous to PT in non-Hermitian
quantum mechanics lead to purely real equation of motion.


title: Numerical Bianchi I solutions in semi-classical gravitation

abstract:
  It is believed that soon after the Planck era, spacetime should have a
semi-classical nature. In this context we consider quantum fields propagating
in a classical gravitational field and study the backreaction of these fields,
using the expected value of the energy-momentum tensor as source of the
gravitational field. According to this theory, the escape from General
Relativity theory is unavoidable. Two geometric counter-term are needed to
regularize the divergences which come from the expected value. There is a
parameter associated to each counter-term and in this work we found numerical
solutions of this theory to particular initial conditions, for general Bianchi
Type I spaces. We show that even though there are spurious solutions some of
them can be considered physical. These physical solutions include de Sitter and
Minkowski that are obtained asymptotically.


title: Chaplygin gas with non-adiabatic perturbations

abstract:
  Perturbations in a Chaplygin gas, characterized by an equation of state $p =
-A/\rho$, may acquire non-adiabatic contributions if spatial variations of the
parameter $A$ are admitted. This feature is shown to be related to a specific
internal structure of the Chaplygin gas. We investigate how perturbations of
this type modify the adiabatic sound speed. A reduction of the effective sound
speed compared with the adiabatic value is expected to suppress oscillations in
the matter power spectrum. This text is an abridged version of the following
reference: W. Zimdahl and J.C. Fabris, Classical and Quantum Gravity, {\bf 22},
4311(2005).


title:
Coherent network analysis technique for discriminating
  gravitational-wave bursts from instrumental noise

abstract:
  Existing coherent network analysis techniques for detecting
gravitational-wave bursts simultaneously test data from multiple observatories
for consistency with the expected properties of the signals. These techniques
assume the output of the detector network to be the sum of a stationary
Gaussian noise process and a gravitational-wave signal, and they may fail in
the presence of transient non-stationarities, which are common in real
detectors. In order to address this problem we introduce a consistency test
that is robust against noise non-stationarities and allows one to distinguish
between gravitational-wave bursts and noise transients. This technique does not
require any a priori knowledge of the putative burst waveform.


title: Entanglement Entropy on Fuzzy Spaces

abstract:
  We study the entanglement entropy of a scalar filed in 2+1 spacetime where
space is modeled by a fuzzy sphere and a fuzzy disc. In both models we evaluate
numerically the resulting entropies and find that they are proportional to the
number of boundary degrees of freedom. In the Moyal plan limit of the fuzzy
disc the entanglement entropy per unit area (length) diverges if the ignored
region is of infinite size. The divergence is (interpreted) of IR-UV mixing
origin. In general we expect the entanglement entropy per unit area to be
finite on a non-commutative space if the ignored region is of finite size.


title:
Principles of wide bandwidth acoustic detectors and the single-mass DUAL
  detector

abstract:
  We apply the standard theory of the elastic body to obtain a set of equations
describing the behavior of an acoustic Gravitational Wave detector, fully
taking into account the 3-dimensional properties of the mass, the readout and
the signal. We show that the advantages given by a Dual detector made by two
nested oscillators can also be obtained by monitoring two different acoustic
modes of the same oscillator, thus easing the detector realization. We apply
these concepts and by means of an optimization process we derive the main
figures of such a single-mass Dual detector designed specifically for the
frequency interval 2-5kHz. Finally we calculate the SQL sensitivity of this
detector.


title:
ZM theory III: Classical oscillators and semi-classical Bohr-Sommerfeld
  quantization

abstract:
  We consider the description of classical oscillatory motion in ZM theory, and
explore the relationship of ZM theory to semi-classical Bohr-Sommerfeld
quantization. The treatment illustrates some features of ZM theory, especially
the inadequacies of classical and semi-classical treatments due to
non-analyticity of the mapping of classical trajectories onto the ZM clock
field. While the more complete ZM formalism is not developed here, the
non-analyticities in the classical treatment resemble issues in the comparison
of classical and quantum formalisms. We also show that semi-classical
quantization is valid for a periodic manifold in ZM theory, though the quantum
number $n=0$ is allowed, as it would be in quantum mechanics for a periodic
manifold. Still, this suggests a connection to the first-order success of Bohr
theory in describing the phenomenology of atomic quantum states. The
approximate nature of the semi-classical treatment of three dimensional atomic
orbits is, however, also apparent in relation to ZM theory. These observations
are preliminary to a discussion of ZM theory in relation to quantum mechanics
and quantum field theory in subsequent papers.


title: Discreteness without symmetry breaking: a theorem

abstract:
  This paper concerns sprinklings into Minkowski space (Poisson processes). It
proves that there exists no equivariant measurable map from sprinklings to
spacetime directions (even locally). Therefore, if a discrete structure is
associated to a sprinkling in an intrinsic manner, then the structure will not
pick out a preferred frame, locally or globally. This implies that the
discreteness of a sprinkled causal set will not give rise to ``Lorentz
breaking'' effects like modified dispersion relations. Another consequence is
that there is no way to associate a finite-valency graph to a sprinkling
consistently with Lorentz invariance.


title: An Introduction of Multiple Scales in a Dynamical Cosmology

abstract:
  The discovery of scale acceleration evidenced from supernovae luminosities
and spatial flatness of feature evolution in the cosmic microwave background
presents a challenge to the understanding of the evolution of cosmological
vacuum energy. Although some scenarios prefer a fixed cosmological constant
with dynamics governed in a Friedman-Robertson-Walker (FRW) geometry, an early
inflationary epoch remains a popular model for cosmology. It is therefore
advantageous to develop a metric framework that allows a transition from an
early inflationary period to a late stage dominated by dark energy. Such a
metric is here developed, and some properties of this metric are explored.


title:
Deviation equations and weak equivalence principle in spaces with affine
  connection

abstract:
  Some connections between the deviation equations and weak equivalence
principle are investigated.


title: Quantum gravitational optics: Effective Raychaudhuri equation

abstract:
  Vacuum polarization in QED in a background gravitational field induces
interactions which {\it effectively} modify the classical picture of light
rays, as the null geodesics of spacetime. These interactions violate the strong
equivalence principle and affect the propagation of light leading to
superluminal photon velocities. Taking into account the QED vacuum
polarization, we study the propagation of a bundle of rays in a background
gravitational field. To do so we consider the perturbative deformation of
Raychaudhuri equation through the influence of vacuum polarization on photon
propagation. We analyze the contribution of the above interactions to the
optical scalars namely, shear, vorticity and expansion using the Newman-Penrose
formalism.


title: Relativistic Fluid Dynamics: Physics for Many Different Scales

abstract:
  The relativistic fluid is a highly successful model used to describe the
dynamics of many-particle, relativistic systems. It takes as input basic
physics from microscopic scales and yields as output predictions of bulk,
macroscopic motion. By inverting the process, an understanding of bulk features
can lead to insight into physics on the microscopic scale. Relativistic fluids
have been used to model systems as ``small'' as heavy ions in collisions, and
as large as the universe itself, with ``intermediate'' sized objects like
neutron stars being considered along the way. The purpose of this review is to
discuss the mathematical and theoretical physics underpinnings of the
relativistic (multiple) fluid model. We focus on the variational principle
approach championed by Brandon Carter and his collaborators, in which a crucial
element is to distinguish the momenta that are conjugate to the particle number
density currents. This approach differs from the ``standard'' text-book
derivation of the equations of motion from the divergence of the stress-energy
tensor, in that one explicitly obtains the relativistic Euler equation as an
``integrability'' condition on the relativistic vorticity. We discuss the
conservation laws and the equations of motion in detail, and provide a number
of (in our opinion) interesting and relevant applications of the general
theory.


title: Gravity, Geometry and the Quantum

abstract:
  After a brief introduction, basic ideas of the quantum Riemannian geometry
underlying loop quantum gravity are summarized. To illustrate physical
ramifications of quantum geometry, the framework is then applied to homogeneous
isotropic cosmology. Quantum geometry effects are shown to replace the big bang
by a big bounce. Thus, quantum physics does not stop at the big-bang
singularity. Rather there is a pre-big-bang branch joined to the current
post-big-bang branch by a `quantum bridge'. Furthermore, thanks to the
background independence of loop quantum gravity, evolution is deterministic
across the bridge.


title: Dimensionality and the Cosmological Constant

abstract:
  In the Kaluza-Klein model with a cosmological constant and a flux, the
external spacetime and its dimension of the created universe from a $S^s \times
S^{n-s}$ seed instanton can be identified in quantum cosmology. One can also
show that in the internal space the effective cosmological constant is most
probably zero.


title:
Stability and quasinormal modes of the massive scalar field around Kerr
  black holes

abstract:
  We find quasinormal spectrum of the massive scalar field in the background of
the Kerr black holes. We show that all found modes are damped under the
quasinormal modes boundary conditions when $\mu M$ is not large, thereby
implying stability of the massive scalar field. This complements the region of
stability determined by the Beyer inequality for large masses of the field. We
show that, similar to the case of a non-rotating black holes, the massive term
of the scalar field does not contribute in the regime of high damping. Thereby,
the high damping asymptotic should be the same as for the massless scalar
field.


title: Quantum geometry and microscopic black hole entropy

abstract:
  Quantum black holes within the loop quantum gravity (LQG) framework are
considered. The number of microscopic states that are consistent with a black
hole of a given horizon area $A_0$ are counted and the statistical entropy, as
a function of the area, is obtained for $A_0$ up to $550 l^2_{\rm Pl}$. The
results are consistent with an asymptotic linear relation and a logarithmic
correction with a coefficient equal to -1/2. The Barbero-Immirzi parameter that
yields the asymptotic linear relation compatible with the Bekenstein-Hawking
entropy is shown to coincide with a value close to $\gamma=0.274$, which has
been previously obtained analytically. However, a new and oscillatory
functional form for the entropy is found for small, Planck size, black holes
that calls for a physical interpretation.


title:
Compactification and signature transition in Kaluza-Klein spinor
  cosmology

abstract:
  We study the classical and quantum cosmology of a 4+1-dimensional space-time
with a non-zero cosmological constant coupled to a self interacting massive
spinor field. We consider a spatially flat Robertson-Walker universe with the
usual scale factor $R(t)$ and an internal scale factor $a(t)$ associated with
the extra dimension. For a free spinor field the resulting equations admit
exact solutions, whereas for a self interacting spinor field one should resort
to a numerical method for exhibiting their behavior. These solutions give rise
to a degenerate metric and exhibit signature transition from a Euclidean to a
Lorentzian domain. Such transitions suggest a compactification mechanism for
the internal and external scale factors such that $a\sim R^{-1}$ in the
Lorentzian region. The corresponding quantum cosmology and the ensuing
Wheeler-DeWitt equation have exact solutions in the mini-superspace when the
spinor field is free, leading to wavepackets undergoing signature change. The
question of stabilization of the extra dimension is also discussed.


title: Gravitons in Kaluza-Klein Theory

abstract:
  This is a pedagogical introduction to original Kaluza-Klein theory and its
salient features. Most of the technical calculations are given in detail and
the nature of gravitons is discussed.


title: Geometric obstruction of black holes

abstract:
  We study the global structure of Lorentzian manifolds with partial sectional
curvature bounds. In particular, we prove completeness theorems for homogeneous
and isotropic cosmologies as well as static spherically symmetric spacetimes.
The latter result is used to rigorously prove the absence of static spherically
symmetric black holes in more than three dimensions. The proofs of these new
results are preceded by a detailed exposition of the local aspects of sectional
curvature bounds for Lorentzian manifolds, which extends and strengthens
previous constructions.


title:
Hydro-without-Hydro Framework for Simulations of Black Hole-Neutron Star
  Binaries

abstract:
  We introduce a computational framework which avoids solving explicitly
hydrodynamic equations and is suitable to study the pre-merger evolution of
black hole-neutron star binary systems. The essence of the method consists of
constructing a neutron star model with a black hole companion and freezing the
internal degrees of freedom of the neutron star during the course of the
evolution of the space-time geometry. We present the main ingredients of the
framework, from the formulation of the problem to the appropriate computational
techniques to study these binary systems. In addition, we present numerical
results of the construction of initial data sets and evolutions that
demonstrate the feasibility of this approach.


title: Isolated and dynamical horizons from a common perspective

abstract:
  A framework is developed in which one can write down the constraint equations
on a three--dimensional hypersurface of arbitrary signature. It is then applied
to isolated and dynamical horizons. The derived equations can be used to
extract physicaly relevant quantities describing the horizon irrespective to
whether it is isolated (null) or dynamical at a given instant of time.
Furthermore, small perturbation of isolated horizons are considered, and
finally a family of axially--symmetric exact solution of the constraint
equations on a dynamical horizon is presented.


title: Waves in the Griffiths-Podolsky Metric

abstract:
  Perturbations form an important section of black hole analyses. This paper
deals with the effect of perturbations as in the delineation of waves that
occur. It makes use of the spin coefficients from [3] to represent the general
equations of waves in an accelerating black hole proposed in [2].


title:
Parameter estimation of coalescing supermassive black hole binaries with
  LISA

abstract:
  Laser Interferometer Space Antenna (LISA) will routinely observe coalescences
of supermassive black hole (BH) binaries up to very high redshifts. LISA can
measure mass parameters of such coalescences to a relative accuracy of
$10^{-4}-10^{-6}$, for sources at a distance of 3 Gpc. The problem of parameter
estimation of massive nonspinning binary black holes using post-Newtonian (PN)
phasing formula is studied in the context of LISA. Specifically, the
performance of the 3.5PN templates is contrasted against its 2PN counterpart
using a waveform which is averaged over the LISA pattern functions. The
improvement due to the higher order corrections to the phasing formula is
examined by calculating the errors in the estimation of mass parameters at each
order. The estimation of the mass parameters ${\cal M}$ and $\eta$ are
significantly enhanced by using the 3.5PN waveform instead of the 2PN one. For
an equal mass binary of $2\times10^6M_\odot$ at a luminosity distance of 3 Gpc,
the improvement in chirp mass is $\sim 11%$ and that of $\eta$ is $\sim 39%$.
Estimation of coalescence time $t_c$ worsens by 43%. The improvement is larger
for the unequal mass binary mergers. These results are compared to the ones
obtained using a non-pattern averaged waveform. The errors depend very much on
the location and orientation of the source and general conclusions cannot be
drawn without performing Monte Carlo simulations. Finally the effect of the
choice of the lower frequency cut-off for LISA on the parameter estimation is
studied.


title:
Absorption and quasinormal modes of classical fields propagating on 3D
  and 4D de Sitter spacetime

abstract:
  We extensively study the exact solutions of the massless Dirac equation in 3D
de Sitter spacetime that we published recently. Using the Newman-Penrose
formalism, we find exact solutions of the equations of motion for the massless
classical fields of spin s=1/2,1,2 and to the massive Dirac equation in 4D de
Sitter metric. Employing these solutions, we analyze the absorption by the
cosmological horizon and de Sitter quasinormal modes. We also comment on the
results given by other authors.


title: On Quantization of the Electrical Charge--Mass

abstract:
  Suggested a non-linear, non-gauge invariant model of Maxwell equations, based
on the Kaluza-Klein theory. The spectrum of elementary charges and masses is
obtained.


title:
Relativistic mechanics of neutron superfluid in (magneto) elastic star
  crust

abstract:
  At densities below the neutron drip threshold, a purely elastic solid model
(including, if necessary, a frozen-in magnetic field) can provide an adequate
description of a neutron star crust, but at higher densities it will be
necessary to allow for the penetration of the solid lattice by an independently
moving current of superfluid neutrons. In order to do this, the previously
available category of relativistic elasticity models is combined here with a
separately developed category of relativistic superfluidity models in a unified
treatment based on the use of an appropriate Lagrangian master function. As
well as models of the purely variational kind, in which the vortices flow
freely with the fluid, such a master function also provides a corresponding
category of non-dissipative models in which the vortices are pinned to the
solid structure.


title: Relativistic elastodynamics

abstract:
  There are many different formulations of relativistic elasticity. Most of
them are only concerned with formal questions rather than questions regarding
the PDE point of view. The aim of this thesis is to obtain various local
existence results for dynamical scenarios involving elastic matter. Following
Beig and Schmidt we treat relativistic elasticity as a Lagrangian field theory.
The basic unknowns are mappings between spacetime and an abstract material
manifold. The equations of motion will be the Euler-Lagrange equations arising
from the action principle. Under certain (physically reasonable) restrictions
on the elastic properties of the material the resulting system is hyperbolic
and local existence results can be derived. This way we can show well-posedness
for the equations describing elastic matter on a fixed gravitational
background, self-gravitating elastic matter and a finite elastic body on a
fixed background. The thesis also contains some results on energy conservation
and on linearized elasticity.


title: Symmetric non-expanding horizons

abstract:
  Symmetric non-expanding horizons are studied in arbitrary dimension. The
global properties -as the zeros of infinitesimal symmetries- are analyzed
particularly carefully. For the class of NEH geometries admitting helical
symmetry a quasi-local analog of Hawking's rigidity theorem is formulated and
proved: the presence of helical symmetry implies the presence of two
symmetries: null, and cyclic.
  The results valid for arbitrary-dimensional horizons are next applied in a
complete classification of symmetric NEHs in 4-dimensional space-times (the
existence of a 2-sphere crossection is assumed). That classification divides
possible NEH geometries into classes labeled by two numbers - the dimensions
of, respectively, the group of isometries induced in the horizon base space and
the group of null symmetries of the horizon.


title: Quasinormal modes of D-dimensional de Sitter spacetime

abstract:
  We calculate the exact values of the quasinormal frequencies for an
electromagnetic field and a gravitational perturbation moving in
$D$-dimensional de Sitter spacetime ($D \geq 4$). We also study the quasinormal
modes of a real massive scalar field and we compare our results with those of
other references.


title:
Coherent searches for periodic gravitational waves from unknown isolated
  sources and Scorpius X-1: results from the second LIGO science run

abstract:
  We carry out two searches for periodic gravitational waves using the most
sensitive few hours of data from the second LIGO science run. The first search
is targeted at isolated, previously unknown neutron stars and covers the entire
sky in the frequency band 160-728.8 Hz. The second search targets the accreting
neutron star in the low-mass X-ray binary Scorpius X-1, covers the frequency
bands 464-484 Hz and 604-624 Hz, and two binary orbit parameters. Both searches
look for coincidences between the Livingston and Hanford 4-km interferometers.
  For isolated neutron stars our 95% confidence upper limits on the
gravitational wave strain amplitude range from 6.6E-23 to 1E-21 across the
frequency band; For Scorpius X-1 they range from 1.7E-22 to 1.3E-21 across the
two 20-Hz frequency bands. The upper limits presented in this paper are the
first broad-band wide parameter space upper limits on periodic gravitational
waves using coherent search techniques. The methods developed here lay the
foundations for upcoming hierarchical searches of more sensitive data which may
detect astrophysical signals.


title: On existence of matter outside a static black hole

abstract:
  It is expected that matter composed of a perfect fluid cannot be at rest
outside of a black hole if the spacetime is asymptotically flat and static
(non-rotating). However, there has not been a rigorous proof for this
expectation without assuming spheical symmetry. In this paper, we provide a
proof of non-existence of matter composed of a perfect fluid in static black
hole spacetimes under certain conditions, which can be interpreted as a
relation between the stellar mass and the black hole mass.


title:
How to move a black hole without excision: gauge conditions for the
  numerical evolution of a moving puncture

abstract:
  Recent demonstrations of unexcised black holes traversing across
computational grids represent a significant advance in numerical relativity.
Stable and accurate simulations of multiple orbits, and their radiated waves,
result. This capability is critically undergirded by a careful choice of gauge.
Here we present analytic considerations which suggest certain gauge choices,
and numerically demonstrate their efficacy in evolving a single moving puncture
black hole.


title: Fermion scattering by a Schwarzschild black hole

abstract:
  We study the scattering of massive spin-half waves by a Schwarzschild black
hole using analytical and numerical methods. We begin by extending a recent
perturbation theory calculation to next order to obtain Born series for the
differential cross section and Mott polarization, valid at small couplings. We
continue by deriving an approximation for glory scattering of massive spinor
particles by considering classical timelike geodesics and spin precession.
Next, we formulate the Dirac equation on a black hole background, and outline a
simple numerical method for finding partial wave series solutions. Finally, we
present our numerical calculations of absorption and scattering cross sections
and polarization, and compare with theoretical expectations.


title: Analysis of spherically symmetric black holes in Braneworld models

abstract:
  Research on black holes and their physical proprieties has been active on
last 90 years. With the appearance of the String Theory and the Braneworld
models as alternative descriptions of our Universe, the interest on black
holes, in these context, increased. In this work we studied black holes in
Braneworld models. A class of spherically symmetric black holes is investigaded
as well its stability under general perturbations. Thermodynamic proprieties
and quasi-normal modes are discussed. The black holes studied are the SM (zero
mass) and CFM solutions, obtained by Casadio {\it et al.} and Bronnikov {\it et
al.}. The geometry of bulk is unknown. However the Campbell-Magaard Theorem
guarantees the existence of a 5-dimensional solution in the bulk whose
projection on the brane is the class of black holes considered. They are stable
under scalar perturbations. Quasi-normal modes were observed in both models.
The tail behavior of the perturbations is the same. The entropy upper bound of
a body absorved by the black holes studied was calculated. This limit turned
out to be independent of the black hole parameters.


title: Geodesic deviation and gravitational waves

abstract:
  The detection of gravitational waves based on the geodesic deviation equation
is discussed. In particular, it is shown that the only non-vanishing components
of the wave field in the conventional traceless-transverse gauge in linearized
general relativity do not enter the geodesic deviation equation, and therefore,
apparently, no effect is predicted by that equation in that specific gauge. The
reason is traced back to the fact that the geodesic deviation equation is
written in terms of a coordinate distance, which is not a directly measurable
quantity. On the other hand, in the proper Lorentz frame of the detector, the
conventional result described in standard textbooks holds.


title: Electromagnetic quasinormal modes of D-dimensional black holes

abstract:
  Using the monodromy method we calculate the asymptotic quasinormal (QN)
frequencies of an electromagnetic field moving in D-dimensional Schwarzschild
and Schwarzschild de Sitter (SdS) black holes ($D\geq 4$). For the
D-dimensional Schwarzschild anti-de Sitter (SadS) black hole we also compute
these frequencies with a similar method. Moreover, we calculate the
electromagnetic normal modes of the D-dimensional anti-de Sitter (AdS)
spacetime.


title: Models of helically symmetric binary systems

abstract:
  Results from helically symmetric scalar field models and first results from a
convergent helically symmetric binary neutron star code are reported here;
these are models stationary in the rotating frame of a source with constant
angular velocity omega. In the scalar field models and the neutron star code,
helical symmetry leads to a system of mixed elliptic-hyperbolic character. The
scalar field models involve nonlinear terms that mimic nonlinear terms of the
Einstein equation. Convergence is strikingly different for different signs of
each nonlinear term; it is typically insensitive to the iterative method used;
and it improves with an outer boundary in the near zone. In the neutron star
code, one has no control on the sign of the source, and convergence has been
achieved only for an outer boundary less than approximately 1 wavelength from
the source or for a code that imposes helical symmetry only inside a near zone
of that size. The inaccuracy of helically symmetric solutions with appropriate
boundary conditions should be comparable to the inaccuracy of a waveless
formalism that neglects gravitational waves; and the (near zone) solutions we
obtain for waveless and helically symmetric BNS codes with the same boundary
conditions nearly coincide.


title: Path Deviation Equations in AP-Geometry

abstract:
  Recently, it has been shown that Absolute Parallelism (AP) geometry admits
paths that are naturally quantized. These paths have been used to describe the
motion of spinning particles in a background gravitational field. In case of a
weak static gravitational field limits, the paths are applied successfully to
interpret the discrepancy in the motion of thermal neutrons in the Earth's
gravitational field (COW-experiment). The aim of the present work is to explore
the properties of the deviation equations corresponding to these paths. In the
present work the deviation equations are derived and compared to the geodesic
deviation equation of the Riemannian geometry.


title: Doppler Effects from Bending of Light Rays in Curved Space-Times

abstract:
  We study Doppler effects in curved space-time, i.e. the frequency shifts
induced on electromagnetic signals propagating in the gravitational field. In
particular, we focus on the frequency shift due to the bending of light rays in
weak gravitational fields. We consider, using the PPN formalism, the
gravitational field of an axially symmetric distribution of mass. The zeroth
order, i.e. the sphere, is studied then passing to the contribution of the
quadrupole moment, and finally to the case of a rotating source. We give
numerical estimates for situations of physical interest, and by a very
preliminary analysis, we argue that analyzing the Doppler effect could lead, in
principle, in the foreseeable future, to the measurement of the quadrupole
moment of the giant planets of the Solar System.


title:
Lorentz violation in brane cosmology, accelerated expansion and
  fundamental constants

abstract:
  The notion of Lorentz violation in four dimensions is extended to a
5-dimensional brane-world scenario by utilizing a dynamical vector field
assumed to point in the bulk direction, with Lorentz invariance holding on the
brane. The cosmological consequences of this theory consisting of the time
variation in the gravitational coupling $G$ and cosmological term $\Lambda_4$
are explored. The brane evolution is addressed by studying the generalized
Friedmann and Raychaudhuri equations. The behavior of the expansion scale
factor is then considered for different possible scenarios where the bulk
cosmological constant is zero, positive or negative.


title: Inflating Brane inside hyper-spherically symmetric defects

abstract:
  Static and inflating brane world models are considered in $4+n$-dimensions
with a non zero bulk cosmological constant and with a hyper-spherically
symmetric topological defect residing in the $n$ extra dimensions. Several
vacuum solutions can be constructed explicitely when the bulk and inflating
constants are non zero. We study how these solutions are deformed by the
presence of a global monopole for generic values of $n$ and a local monopole
for $n=3$. New types of solutions, regular and periodic in the radial variable
relative to the extra dimensions, are constructed.


title: Non-abelian black strings and cosmological constant

abstract:
  We study the classical solutions of the Einstein-Yang-Mills model in five
dimensions in the presence of a cosmological constant $\Lambda$. Using a
spherically symmetric ansatz and assuming that the fields do not depend on the
extra dimension, we transform the equations into a set of differential
equations that we solve numerically. We construct new types of regular (resp.
black holes) solutions which, close to the origin (resp. the event horizon)
resemble the 4-dimensional gravitating monopole (resp. non abelian black hole)
and study their global properties.


title: Thermal Evolution of a Dual Scale Cosmology

abstract:
  Previous work developed a space-time metric with two cosmological scales; one
that conveniently describes the classical evolution of the dynamics, and the
other describing a scale associated with macroscopic quantum aspects like
vacuum energy. The present work expands upon the dynamics of these scales to
demonstrate the usefulness of these coordinates for describing early and late
time behaviors of our universe. A convenient parameter, the fraction of
classical energy density, is introduced as a means to parameterize the various
early time models for the microscopic input.


title: Thin Domain Walls in Lyra Geometry

abstract:
  This paper studies thin domain walls within the frame work of Lyra Geometry.
We have considered two models. First one is the thin domain wall with
negligible pressures perpendicular and transverse direction to the wall and
secondly, we take a particular type of thin domain wall where the pressure in
the perpendicular direction is negligible but transverse pressures are existed.
It is shown that the thin domain walls have no particle horizon and the
gravitational force due to them is attractive.