title: Semiclassical approximation to supersymmetric quantum gravity

abstract:
  We develop a semiclassical approximation scheme for the constraint equations
of supersymmetric canonical quantum gravity. This is achieved by a
Born-Oppenheimer type of expansion, in analogy to the case of the usual
Wheeler-DeWitt equation. The formalism is only consistent if the states at each
order depend on the gravitino field. We recover at consecutive orders the
Hamilton-Jacobi equation, the functional Schrodinger equation, and quantum
gravitational correction terms to this Schrodinger equation. In particular, the
following consequences are found:
  (i) the Hamilton-Jacobi equation and therefore the background spacetime must
involve the gravitino, (ii) a (many fingered) local time parameter has to be
present on $SuperRiem \Sigma$ (the space of all possible tetrad and gravitino
fields), (iii) quantum supersymmetric gravitational corrections affect the
evolution of the very early universe. The physical meaning of these equations
and results, in particular the similarities to and differences from the pure
bosonic case, are discussed.


title: Type III Einstein-Yang-Mills solutions

abstract:
  We construct two distinct classes of exact type III solutions of the D=4
Einstein-Yang-Mills system. The solutions are embeddings of the non-abelian
plane waves in spacetimes in Kundt's class. Reduction of the solutions to type
N leads to generalized $pp$ and Kundt waves. The geodesic equations are briefly
discussed.


title: Self-Similar Evaporation of a Rigidly-Rotating Cosmic String Loop

abstract:
  The gravitational back-reaction on a certain type of rigidly-rotating cosmic
string loop, first discovered by Allen, Casper and Ottewill, is studied at the
level of the weak-field approximation. The near-field metric perturbations are
calculated and used to construct the self-acceleration vector of the loop.
Although the acceleration vector is divergent at the two kink points on the
loop, its net effect on the trajectory over a single oscillation period turns
out to be finite. The net back-reaction on the loop over a single period is
calculated using a method due to Quashnock and Spergel, and is shown to induce
a uniform shrinkage of the loop while preserving its original shape. The loop
therefore evolves by self-similar evaporation.


title:
Quasinormal modes of Rarita-Schwinger field in Reissner-Nordstr\"{o}m
  black hole spacetimes

abstract:
  The Newman-Penrose formalism is used to deal with the quasinormal
modes(QNM's) of Rarita-Schwinger perturbations outside a Reissner-Nordstr\"{o}m
black hole. We obtain four kinds of possible expressions of effective
potentials, which are proved to be of the same spectra of quasinormal mode
frequencies. The quasinormal mode frequencies evaluated by the WKB potential
approximation show that, similar to those for Dirac perturbations, the real
parts of the frequencies increase with the charge $Q$ and decrease with the
mode number $n$, while the dampings almost keep unchanged as the charge
increases.


title:
Motion of a Vector Particle in a Curved Spacetime. II First Order
  Correction to a Geodesic in a Schwarzschild Background

abstract:
  The influence of spin on a photon's motion in a Schwarzschild and FRW
spacetimes is studied. The first order correction to the geodesic motion is
found. It is shown that unlike the world-lines of spinless particles, the
photons world-lines do not lie in a plane.


title: Energy Flow in Acoustic Black Holes

abstract:
  We present the results of an analysis of superradiant energy flow due to
scalar fields incident on an acoustic black hole. In addition to providing
independent confirmation of the recent results in [5], we determine in detail
the profile of energy flow everywhere outside the horizon. We confirm
explicitly that in a suitable frame the energy flow is inward at the horizon
and outward at infinity, as expected on physical grounds.


title: Stability of phantom wormholes

abstract:
  It has recently been shown that traversable wormholes may be supported by
phantom energy. In this work phantom wormhole geometries are modelled by
matching an interior traversable wormhole solution, governed by the equation of
state $p=\omega \rho$ with $\omega<-1$, to an exterior vacuum spacetime at a
finite junction interface. The stability analysis of these phantom wormholes to
linearized spherically symmetric perturbations about static equilibrium
solutions is carried out. A master equation dictating the stability regions is
deduced, and by separating the cases of a positive and a negative surface
energy density, it is found that the respective stable equilibrium
configurations may be increased by strategically varying the wormhole throat
radius. The first model considered, in the absence of a thin shell, is that of
an asymptotically flat phantom wormhole spacetime. The second model constructed
is that of an isotropic pressure phantom wormhole, which is of particular
interest, as the notion of phantom energy is that of a spatially homogeneous
cosmic fluid, although it may be extended to inhomogeneous spherically
symmetric spacetimes.


title: From the self-force problem to the Radiation reaction formula

abstract:
  We review a recent theoretical progress in the so-called self-force problem
of a general relativistic two-body system. Although a two-body system in
Newtonian gravity is a very simple problem, some fundamental issues are
involved in relativistic gravity. Besides, because of recent projects for
gravitational wave detection, it comes to be possible to see those phenomena
directly via gravitational waves, and the self-force problem becomes one of
urgent and highly-motivated problems in general relativity. Roughly speaking,
there are two approaches to investigate this problem; the so-called
post-Newtonian approximation, and a black hole perturbation.
  In this paper, we review a theoretical progress in the self-force problem
using a black hole perturbation. Although the self-force problem seems to be
just a problem to calculate a self-force, we discuss that the real problem is
to define a gauge invariant concept of a motion in a gauge dependent metric
perturbation.


title:
Self-Force in the Radiation Reaction Formula -- Adiabatic Approximation
  of a Metric Perturbation and an Orbit --

abstract:
  We propose a new metric perturbation scheme under a possible constraint of
the gauge conditions in which we obtain a physically expected prediction of the
orbital evolution caused by the MiSaTaQuWa self-force. In this new scheme of a
metric perturbation, an adiabatic approximation is applied to both the metric
perturbation and the orbit. As a result, we are able to predict the
gravitational evolution of the system in the so-called radiation reaction time
scale, which is longer than the dephasing time scale. However, for
gravitational wave detection by LISA, this may still be insufficient. We
further consider a gauge transformation in this new metric perturbation scheme,
and find a special gauge condition with which we can calculate the
gravitational waveform of a time scale long enough for gravitational wave
detection by LISA.


title: Conformally Flat Noncircular Spacetimes

abstract:
  The general metric for conformally flat stationary cyclic symmetric
noncircular spacetimes is explicitly given. In spite of the complexity
introduced by the inclusion of noncircular contributions, the related metric is
derived via the full integration of the conformal flatness constraints. It is
also shown that the conditions for the existence of a rotation axis
(axisymmetry) are the same ones which restrict the above class of spacetimes to
be static. As a consequence, a known theorem by Collinson is just part of a
more general result: any conformally flat stationary cyclic symmetric
spacetime, even a noncircular one, is additionally axisymmetric if and only if
it is also static. Since recent astrophysical motivations point in the
direction of considering noncircular configurations to describe magnetized
neutron stars, the above results seem to be relevant in this context.


title:
Some aspects of the three dimensional gravity theories with temporal
  scalar field

abstract:
  The present paper proposes a new explanation for the 3-dimensional Einstein
general theory of relativity which is free of contradictions and consistent
with usual 4-dimensional physics. We discuss the property of the new gravity
theory with temporal scalar field arise in lower-dimensional theories as the
reduction of timelike extra dimension. These ideas we continued by using the
3-dimensional analog of Jordan, Brans-Dicke theory with temporal scalar field
where space and time are treated in different ways.


title: Quantum black hole and Hawking radiation at microscopic magnifying

abstract:
  We establish a state of stopping the Hawking radiation by quantum
Schwarzschild black hole in the framework of quasi-classical thermal
quantization for particles behind the horizon. The mechanism of absorption and
radiation by the black hole is presented.


title: A New Interpretation about the Evolution of the Cosmos

abstract:
  Based on Lorentz and Levi-Civita's conservation laws, it can be shown that
the energy of the matter field in the universe might originate from the
gravitational field as a result of the latter field's energy decrease and the
total entropy increase followed by cosmic expansion. By exploring this
possibility and by using some new evidences discovered from recent astronomical
observations, we establish an alternative theory of cosmology, which gives a
new interpretation about the evolution of the cosmos and a number of new
explanations regarding dark energy and dark matter.


title: Extreme Mass Ratio Binary: Radiation reaction and gravitational waveform

abstract:
  For a successful detection of gravitational waves by LISA, it is essential to
construct theoretical waveforms in a reliable manner. We discuss gravitational
waves from an extreme mass ratio binary system which is expected to be a
promising target of the LISA project.
  The extreme mass ratio binary is a binary system of a supermassive black hole
and a stellar mass compact object. As the supermassive black hole dominates the
gravitational field of the system, we suppose that the system might be well
approximated by a metric perturbation of a Kerr black hole. We discuss a recent
theoretical progress in calculating the waveforms from such a system.


title: Influence Of Collapsing Matter On The Enveloping Expanding Universe

abstract:
  Using a collapsing matter model at the center of an expanding universe as
described by Weinberg we assume a special type of generated pressure. This
pressure transmits into the surrounding expanding universe. Under certain
restriction the ensuing hubble parameter is positive. The deacceleration
parameter fluctuates with time, indicating that the universe accelerates for
certain time and decelerates for other time intervals.


title: Kink Stability of Self-Similar Solutions of Scalar Field in 2+1 Gravity

abstract:
  The kink stability of self-similar solutions of a massless scalar field with
circular symmetry in 2+1 gravity is studied, and found that such solutions are
unstable against the kink perturbations along the sonic line (self-similar
horizon). However, when perturbations outside the sonic line are considered,
and taking the ones along the sonic line as their boundary conditions, we find
that non-trivial perturbations do not exist. In other words, the consideration
of perturbations outside the sonic line limits the unstable mode of the
perturbations found along the sonic line. As a result, the critical solution
for the scalar collapse remains critical even after the kink perturbations are
taken into account.


title: Quantum geons

abstract:
  We describe solutions of the Klein-Gordon equation which are spherically
symmetric and localized, and may be regarded as massive particles without
charge or spin. The proposed model, which is based on the action for a complex
scalar field minimally coupled to the electromagnetic and gravitational fields,
contains no adjustable parameters and predicts five particle species with
masses of the order of the Planck mass. These particles appear to be candidates
for dark matter.


title: Acceleration disturbances and requirements for ASTROD I

abstract:
  ASTRODynamical Space Test of Relativity using Optical Devices I (ASTROD I)
mainly aims at testing relativistic gravity and measuring the solar-system
parameters with high precision, by carrying out laser ranging between a
spacecraft in a solar orbit and ground stations. In order to achieve these
goals, the magnitude of the total acceleration disturbance of the proof mass
has to be less than 10−13 m s−2 Hz−1/2 at 0.1 m Hz. In this
paper, we give a preliminary overview of the sources and magnitude of
acceleration disturbances that could arise in the ASTROD I proof mass. Based on
the estimates of the acceleration disturbances and by assuming a simple
controlloop model, we infer requirements for ASTROD I. Our estimates show that
most of the requirements for ASTROD I can be relaxed in comparison with Laser
Interferometer Space Antenna (LISA).


title: Local existence of dynamical and trapping horizons

abstract:
  Given a spacelike foliation of a spacetime and a marginally outer trapped
surface S on some initial leaf, we prove that under a suitable stability
condition S is contained in a ``horizon'', i.e. a smooth 3-surface foliated by
marginally outer trapped slices which lie in the leaves of the given foliation.
We also show that under rather weak energy conditions this horizon must be
either achronal or spacelike everywhere. Furthermore, we discuss the relation
between ``bounding'' and ``stability'' properties of marginally outer trapped
surfaces.


title: Birkhoff for Lovelock Redux

abstract:
  We show succinctly that all metric theories with second order field equations
obey Birkhoff's theorem: their spherically symmetric solutions are static.


title: Beyond LISA: Exploring Future Gravitational Wave Missions

abstract:
  The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer
(BBO) have been proposed as follow on missions to the Laser Interferometer
Space Antenna (LISA). Here we study the capabilities of these observatories,
and how they relate to the science goals of the missions. We find that the
Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension
to the ALIA mission, will go considerably further toward meeting ALIA's main
scientific goal of studying intermediate mass black holes. We also compare the
capabilities of LISA to a related extension of the LISA mission, the Laser
Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the
initial deployment phase of the BBO would be sufficient to address the BBO's
key scientific goal of detecting the Gravitational Wave Background, while still
providing detailed information about foreground sources.


title: Radiative spacetimes approaching the Vaidya metric

abstract:
  We analyze a class of exact type II solutions of the Robinson-Trautman family
which contain pure radiation and (possibly) a cosmological constant. It is
shown that these spacetimes exist for any sufficiently smooth initial data, and
that they approach the spherically symmetric Vaidya-(anti-)de Sitter metric. We
also investigate extensions of the metric, and we demonstrate that their order
of smoothness is in general only finite. Some applications of the results are
outlined.


title: Spin precession in the Schwarzschild spacetime: circular orbits

abstract:
  We study the behavior of nonzero rest mass spinning test particles moving
along circular orbits in the Schwarzschild spacetime in the case in which the
components of the spin tensor are allowed to vary along the orbit, generalizing
some previous work.


title: Classification of Cohomogeneity One Strings

abstract:
  We define the cohomogeneity one string, string with continuous symmetries, as
its world surface is tangent to a Killing vector field of a target space. We
classify the Killing vector fields by an equivalence relation using isometries
of the target space. We find that the equivalence classes of Killing vectors in
Minkowski spacetime are partitioned into seven families. It is clarified that
there exist seven types of strings with spacelike symmetries and four types of
strings with timelike symmetries, stationary strings.


title: The world problem: on the computability of the topology of 4-manifolds

abstract:
  Topological classification of the 4-manifolds bridges computation theory and
physics. A proof of the undecidability of the homeomorphy problem for
4-manifolds is outlined here in a clarifying way. It is shown that an arbitrary
Turing machine with an arbitrary input can be encoded into the topology of a
4-manifold, such that the 4-manifold is homeomorphic to a certain other
4-manifold if and only if the corresponding Turing machine halts on the
associated input. Physical implications are briefly discussed.


title: Beyond the Horizon

abstract:
  Cosmic horizons arise in general relativity in the context of black holes and
in certain cosmologies. Classically, regions beyond a horizon are inaccessible
to causal observers. However, quantum mechanical correlations may exist across
horizons that may influence local observations. For the case of de Sitter
space, we show how a single particle excitation behind the horizon changes the
density matrix governing local observables. As compared to the vacuum state, we
calculate the change in the average energy and entropy per unit volume. This
illustrates what may be a generic property allowing some features of spacetime
beyond a horizon to be inferred.


title: Scalar-Tensor-Vector Gravity Theory

abstract:
  A covariant scalar-tensor-vector gravity theory is developed which allows the
gravitational constant $G$, a vector field coupling $\omega$ and the vector
field mass $\mu$ to vary with space and time. The equations of motion for a
test particle lead to a modified gravitational acceleration law that can fit
galaxy rotation curves and cluster data without non-baryonic dark matter. The
theory is consistent with solar system observational tests. The linear
evolutions of the metric, vector field and scalar field perturbations and their
consequences for the observations of the cosmic microwave background are
investigated.


title:
Generating functional for the gravitational field: implementation of an
  evolutionary quantum dynamics

abstract:
  We provide a generating functional for the gravitational field, associated to
the relaxation of the primary constraints as extended to the quantum sector.
This requirement of the theory, relies on the assumption that a suitable time
variable exist, when taking the T-products of the dynamical variables. More
precisely, we start from the gravitational field equations written in the
Hamiltonian formalism and expressed via Misner-like variables; hence we
construct the equation to which the T-products of the dynamical variables obey
and transform this paradigm in terms of the generating functional, as taken on
the theory phase-space. We show how the relaxation of the primary constraints
(which correspond to break down the invariance of the quantum theory under the
4-diffeomorphisms) is summarized by a free functional taken on the Lagrangian
multipliers, accounting for such constraints in the classical theory. The issue
of our analysis is equivalent to a Gupta-Bleuler approach on the quantum
implementation of all the gravitational constraints; in fact, in the limit of
small $\hbar$, the quantum dynamics is described by a Schr\"odinger equation,
as soon as the mean values of the momenta, associated to the lapse function and
the shift vector, are not vanishing. Finally we show how, in the classical
limit, the evolutionary quantum gravity reduces to General Relativity in the
presence of an Eckart fluid, which corresponds to the classical counterpart of
the physical clock, introduced in the quantum theory.


title: Scalar Field Entropy in Brane World Black Holes

abstract:
  A semiclassical calculation of entropy of a scalar field in the background of
a class of brane world black holes (BWBH) is carried out in the presence of a
brick wall cutoff when the 5D-bulk induced \textquotedblleft tidal charge" has
generic or extreme values.


title: Separable sequences in Bianchi I loop quantum cosmology

abstract:
  In this paper, we discuss the properties of one-parameter sequences that
arise when solving the Hamiltonian constraint in Bianchi I loop quantum
cosmology using a separation of variables method. In particular, we focus on
finding an expression for the sequence for all real values of the parameter,
and discuss the pre-classicality of this function. We find that the behavior of
these preclassical sequences imply time asymmetry on either side of the
classical singularity in Bianchi I cosmology.


title:
A Data Analysis Technique for the LIGO-ALLEGRO Stochastic Background
  Search

abstract:
  We describe the cross-correlation measurements being carried out on data from
the LIGO Livingston Observatory and the ALLEGRO resonant bar detector. The LIGO
data are sampled at 16384 Hz while the ALLEGRO data are base-banded, i.e.,
heterodyned at 899 Hz and then sampled at 250 Hz. We handle these different
sampling parameters by working in the Fourier domain, and demonstrate the
approximate equivalence of this measurement to a hypothetical time-domain
method in which both data streams are upsampled.


title: Minkowski Vacuum Stress Tensor Fluctuations

abstract:
  We study the fluctuations of the stress tensor for a massless scalar field in
two and four-dimensional Minkowski spacetime in the vacuum state. Covariant
expressions for the stress tensor correlation function are obtained as sums of
derivatives of a scalar function. These expressions allow one to express
spacetime averages of the correlation function as finite integrals. We also
study the correlation between measurements of the energy density along a
worldline. We find that these measurements may be either positively correlated
or anticorrelated. The anticorrelated measurements can be interpreted as
telling us that if one measurement yields one sign for the averaged energy
density, a successive measurement with a suitable time delay is likely to yield
a result with the opposite sign.


title: False vacuum decay in a brane world cosmological model

abstract:
  The false vacuum decay in a brane world model is studied in this work. We
investigate the vacuum decay via the Coleman-de Luccia instanton, derive
explicit approximative expressions for the Coleman-de Luccia instanton which is
close to a Hawking-Moss instanton and compare the results with those already
obtained within Einstein's theory of relativity.


title: Massive Klein--Gordon equation from a BEC-based analogue spacetime

abstract:
  We extend the "analogue spacetime" programme by investigating a
condensed-matter system that is in principle capable of simulating the massive
Klein--Gordon equation in curved spacetime. Since many elementary particles
have mass, this is an essential step in building realistic analogue models, and
a first step towards simulating quantum gravity phenomenology. Specifically, we
consider the class of two-component BECs subject to laser-induced transitions
between the components. This system exhibits a complicated spectrum of normal
mode excitations, which can be viewed as two interacting phonon modes that
exhibit the phenomenon of "refringence". We study the conditions required to
make these two phonon modes decouple. Once decoupled, the two distinct phonons
generically couple to distinct effective spacetimes, representing a bi-metric
model, with one of the modes acquiring a mass. In the eikonal limit the massive
mode exhibits the dispersion relation of a massive relativistic particle: omega
= sqrt[omega_0^2 + c^2 k^2], plus curved-space modifications. Furthermore, it
is possible to tune the system so that both modes can be arranged to travel at
the same speed, in which case the two phonon excitations couple to the same
effective metric. From the analogue spacetime perspective this situation
corresponds to the Einstein equivalence principle being satisfied.


title:
Electrostatic self-energy and Bekenstein entropy bound in the massive
  Schwinger model

abstract:
  We obtain the electrostatic energy of two opposite charges near the horizon
of stationary black-holes in the massive Schwinger model. Besides the confining
aspects of the model, we discuss the Bekenstein entropy upper bound of a
charged object using the generalized second law. We show that despite the
massless case, in the massive Schwinger model the entropy of the black hole and
consequently the Bekenstein bound are altered by the vacuum polarization.


title: Gravitational Billiards, Dualities and Hidden Symmetries

abstract:
  The purpose of this article is to highlight the fascinating, but only very
incompletely understood relation between Einstein's theory and its
generalizations on the one hand, and the theory of indefinite, and in
particular hyperbolic, Kac Moody algebras on the other. The elucidation of this
link could lead to yet another revolution in our understanding of Einstein's
theory and attempts to quantize it.


title: Intrinsic definitions of "relative velocity" in general relativity

abstract:
  Given two observers, we define the "relative velocity" of one observer with
respect to the other in four different ways. All four definitions are given
intrinsically, i.e. independently of any coordinate system. Two of them are
given in the framework of spacelike simultaneity and, analogously, the other
two are given in the framework of observed (lightlike) simultaneity. Properties
and physical interpretations are discussed. Finally, we study relations between
them in special relativity, and we give some examples in Schwarzschild and
Robertson-Walker spacetimes.


title: On inflation and torsion in cosmology

abstract:
  In a recent letter by H. Davoudiasl, R. Kitano, T. Li and H. Murayama ``The
new Minimal Standard Model'' (NMSM) was constructed that incorporates new
physics beyond the Minimal Standard Model (MSM) of particle physics. The
authors follow the principle of minimal particle content and therefore adopt
the viewpoint of particle physicists. It is shown that a generalisation of the
geometric structure of spacetime can also be used to explain physics beyond the
MSM. It is explicitly shown that for example inflation, i.e. an exponentially
expanding universe, can easily be explained within the framework of
Einstein-Cartan theory.


title: Gravitational contribution to fermion masses

abstract:
  In the context of a nonlinear gauge theory of the Poincar\'e group, we show
that covariant derivatives of Dirac fields include a coupling to the
translational connections, manifesting itself in the matter action as a
universal background mass contribution to fermions.


title: Counting a black hole in Lorentzian product triangulations

abstract:
  We take a step toward a nonperturbative gravitational path integral for
black-hole geometries by deriving an expression for the expansion rate of null
geodesic congruences in the approach of causal dynamical triangulations. We
propose to use the integrated expansion rate in building a quantum horizon
finder in the sum over spacetime geometries. It takes the form of a counting
formula for various types of discrete building blocks which differ in how they
focus and defocus light rays. In the course of the derivation, we introduce the
concept of a Lorentzian dynamical triangulation of product type, whose
applicability goes beyond that of describing black-hole configurations.


title: A spacetime realization of kappa-Poincare algebra

abstract:
  We study a Hamiltonian realization of the phase space of kappa-Poincare
algebra that yields a definition of velocity consistent with the deformed
Lorentz symmetry. We are also able to determine the laws of transformation of
spacetime coordinates and to define an invariant spacetime metric, and discuss
some possible experimental consequences.


title: Hyperbolicity of second-order in space systems of evolution equations

abstract:
  A possible definition of strong/symmetric hyperbolicity for a second-order
system of evolution equations is that it admits a reduction to first order
which is strongly/symmetric hyperbolic. We investigate the general system that
admits a reduction to first order and give necessary and sufficient criteria
for strong/symmetric hyperbolicity of the reduction in terms of the principal
part of the original second-order system. An alternative definition of strong
hyperbolicity is based on the existence of a complete set of characteristic
variables, and an alternative definition of symmetric hyperbolicity is based on
the existence of a conserved (up to lower order terms) energy. Both these
definitions are made without any explicit reduction. Finally, strong
hyperbolicity can be defined through a pseudo-differential reduction to first
order. We prove that both definitions of symmetric hyperbolicity are equivalent
and that all three definitions of strong hyperbolicity are equivalent (in three
space dimensions). We show how to impose maximally dissipative boundary
conditions on any symmetric hyperbolic second order system. We prove that if
the second-order system is strongly hyperbolic, any closed constraint evolution
system associated with it is also strongly hyperbolic, and that the
characteristic variables of the constraint system are derivatives of a subset
of the characteristic variables of the main system, with the same speeds.


title: On the local Lorentz invariance in N=1 supergravity

abstract:
  We discuss the local Lorentz invariance in the context of N=1 supergravity
and show that a previous attempt to find explicit solutions to the Lorentz
constraint in terms of $\gamma-$matrices is not correct. We improve that
solution by using a different representation of the Lorentz operators in terms
of the generators of the rotation group, and show its compatibility with the
matrix representation of the fermionic field. We find the most general wave
functional that satisfies the Lorentz constraint in this representation.


title:
The robustness of a many-body decoherence formula of Kay under changes
  in graininess and shape of the bodies

abstract:
  In ``Decoherence of macroscopic closed systems within Newtonian quantum
gravity'' (Kay B S 1998 Class. Quantum Grav. 15 L89-L98) it was argued that,
given a many-body Schroedinger wave function \psi(x_1,...,x_N) for the
centre-of-mass degrees of freedom of a closed system of N identical
uniform-mass balls of mass M and radius R, taking account of quantum
gravitational effects and then tracing over the gravitational field amounts to
multiplying the position-space density matrix \rho(x_1,...,x_N; x_1',...,x_N')=
\psi(x_1,...,x_N)\psi*(x_1',...,x_N') by a multiplicative factor, which, if the
positions {x_1,...,x_N; x_1',...,x_N'} are all much further away from one
another than R, is well-approximated by the product from 1 to N over I, J, K
(I<J) of ((|x_K-x_K'|/R)(|x_I'-x_J||x_I-x_J'|/|x_I-x_J||x_I'-x_J'|))^{-24M^2}.
Here we show that if each uniform-mass ball is replaced by a grainy ball or
more general-shaped lump of similar size consisting of a number, n, of
well-spaced small balls of mass m and radius r and, in the above formula, R is
replaced by r, M by m and the products are taken over all Nn positions of all
the small balls, then the result is well-approximated by replacing R in the
original formula by a new value R_eff. This suggests that the original formula
will apply in general to physically realistic lumps -- be they macroscopic
lumps of ordinary matter with the grains atomic nuclei etc. or be they atomic
nuclei themselves with their own (quantum) grainy substructure -- provided R is
chosen suitably. In the case of a cubical lump consisting of n=(2L+1)^3 small
balls (L > 0) of radius r with centres at the vertices of a cubic lattice of
spacing a (assumed to be very much bigger than 2r) and side 2La we establish
the bound e^{-1/3}(r/a)^{1/n}La < R_eff < 2\sqrt 3(r/a)^{1/n} La.


title: Regular two-component bouncing cosmologies and perturbations therein

abstract:
  We present a full investigation of scalar perturbations in a rather generic
model for a regular bouncing universe, where the bounce is triggered by an
effective perfect fluid with negative energy density. Long before and after the
bounce the universe is dominated by a source with positive energy density,
which may be a perfect fluid, a scalar field, or any other source with an
intrinsic isocurvature perturbation. Within this framework, we present an
analytical method to accurately estimate the spectrum of large-scale scalar
perturbations until their reentry, long after the bounce. We also propose a
simple way to identify non-singular gauge-invariant variables through the
bounce and present the results of extensive numerical tests in several possible
realizations of the scenario. In no case do we find that the spectrum of the
pre-bounce growing mode of the Bardeen potential can be transferred to a
post-bounce constant mode.


title: Scalar potentials out of canonical quantum cosmology

abstract:
  Using canonical quantization of a flat FRW cosmological model containing a
real scalar field $\phi$ endowed with a scalar potential $V(\phi)$, we are able
to obtain exact and semiclassical solutions of the so called Wheeler-DeWitt
equation for a particular family of scalar potentials. Some features of the
solutions and their classical limit are discussed.


title: On the theory of the skewon field: From electrodynamics to gravity

abstract:
  The Maxwell equations expressed in terms of the excitation $\H=({\cal H},
{\cal D})$ and the field strength $F=(E,B)$ are metric-free and require an
additional constitutive law in order to represent a complete set of field
equations. In vacuum, we call this law the ``spacetime relation''. We assume it
to be local and linear. Then $\H=\H(F)$ encompasses 36
permittivity/permeability functions characterizing the electromagnetic
properties of the vacuum. These 36 functions can be grouped into 20+15+1
functions. Thereof, 20 functions finally yield the dilaton field and the metric
of spacetime, 1 function represents the axion field, and 15 functions the
(traceless) skewon field $\notS_i{}^j$ (S slash), with $i,j=0,1,2,3$. The
hypothesis of the existence of $\notS_i{}^j$ was proposed by three of us in
2002. In this paper we discuss some of the properties of the skewon field, like
its electromagnetic energy density, its possible coupling to Einstein-Cartan
gravity, and its corresponding gravitational energy.


title: Higher Order Slow-Roll Predictions for Inflation

abstract:
  We study the WKB approximation beyond leading order for cosmological
perturbations during inflation. To first order in the slow-roll parameters, we
show that an improved WKB approximation leads to analytical results agreeing to
within 0.1% with the standard slow-roll results. Moreover, the leading WKB
approximation to second order in the slow-roll parameters leads to analytical
predictions in qualitative agreement with those obtained by the Green's
function method.


title: Bulk Viscosity Effects on the Early Universe Stability

abstract:
  We present a discussion of the effects induced by the bulk viscosity on the
very early Universe stability. The matter filling the cosmological (isotropic
and homogeneous) background is described by a viscous fluid having an
ultrarelativistic equation of state and whose viscosity coefficient is related
to the energy density via a power-law of the form $\zeta=\zeta_0 \rho^\nu$. The
analytic expression of the density contrast (obtained for $\nu=1/2$) shows
that, for small values of the constant $\zeta_0$, its behavior is not
significantly different from the non-viscous one derived by E.M. Lifshitz. But
as soon as $\zeta_0$ overcomes a critical value, the growth of the density
contrast is suppressed forward in time by the viscosity and the stability of
the Universe is favored in the expanding picture. On the other hand, in such a
regime, the asymptotic approach to the initial singularity (taken at $t=0$) is
deeply modified by the apparency of significant viscosity in the primordial
thermal bath i.e. the isotropic and homogeneous Universe admits an unstable
collapsing picture. In our model this feature regards also scalar perturbations
while in the non-viscous case it appears only for tensor modes.


title: Comment on "What does the Letelier-Gal'tsov metric describe?"

abstract:
  We show that the Letelier-Gal'tsov (LG) metric describing multiple crossed
strings in relative motion does solve the Einstein equations, in spite of the
discontinuity uncovered recently by Krasnikov [gr-qc/0502090] provided the
strings are straight and moving with constant velocities.


title:
Twisting Null Geodesic Congruences, Scri, H-Space and Spin-Angular
  Momentum

abstract:
  The purpose of this work is to return, with a new observation and rather
unconventional point of view, to the study of asymptotically flat solutions of
Einstein equations. The essential observation is that from a given
asymptotically flat space-time with a given Bondi shear, one can find (by
integrating a partial differential equation) a class of asymptotically
shear-free (but, in general, twistiing) null geodesic congruences. The class is
uniquely given up to the arbitrary choice of a complex analytic world-line in a
four-parameter complex space. Surprisingly this parameter space turns out to be
the H-space that is associated with the real physical space-time under
consideration. The main development in this work is the demonstration of how
this complex world-line can be made both unique and also given a physical
meaning. More specifically by forcing or requiring a certain term in the
asymptotic Weyl tensor to vanish, the world-line is uniquely determined and
becomes (by several arguments) identified as the `complex center-of-mass'.
Roughly, its imaginary part becomes identified with the intrinsic spin-angular
momentum while the real part yields the orbital angular momentum.


title: Resonant growth of stellar oscillations by incident gravitational waves

abstract:
  Stellar oscillation under the combined influences of incident gravitational
wave and radiation loss is studied in a simple toy model. The star is
approximated as a uniform density ellipsoid in the Newtonian gravity including
radiation damping through quadrupole formula. The time evolution of the
oscillation is significantly controlled by the incident wave amplitude $h$,
frequency $\nu$ and damping time $\tau$. If a combination $ h \nu \tau $
exceeds a threshold value, which depends on the resonance mode, the resonant
growth is realized.


title: Role of Pressure in Quasi-Spherical Gravitational Collapse

abstract:
  We study quasi-spherical Szekeres space-time (which possess no killing
vectors) for perfect fluid, matter with tangential stress only and matter with
anisotropic pressure respectively. In the first two cases cosmological
solutions have been obtained and their asymptotic behaviour have been examined
while for anisotropic pressure, gravitational collapse has been studied and the
role of the pressure has been discussed.


title: Symmetries of Locally Rotationally Symmetric Models

abstract:
  Matter collineations of locally rotationally symmetric spacetimes are
considered. These are investigated when the energy-momentum tensor is
degenerate. We know that the degenerate case provides infinite dimensional
matter collineations in most of the cases. However, an interesting case arises
where we obtain proper matter collineations. We also solve the constraint
equations for a particular case to obtain some cosmological models.


title: Effects of nonzero neutrino masses on black hole evaporation

abstract:
  We study the consequences of nonzero neutrino masses for black holes
evaporating by the emission of Hawking radiation. We find that the evolution of
small, hot, black holes may be unaffected (if neutrinos are Majorana
particles), or may show an increase in neutrino luminosity and a decrease in
lifetime by up to a factor of 1.85 (if neutrinos are Dirac particles). However,
for sufficiently large (e.g., stellar mass) black holes, neutrino emission is
largely or entirely suppressed, resulting in a decrease in emitted power and an
increase in lifetime by up to a factor of 7.5.


title:
Decoherence during Inflation: the generation of classical
  inhomogeneities

abstract:
  We show how the quantum to classical transition of the cosmological
fluctuations produced during inflation can be described by means of the
influence functional and the master equation. We split the inflaton field into
the system-field (long-wavelength modes), and the environment, represented by
its own short-wavelength modes. We compute the decoherence times for the
system-field modes and compare them with the other time scales of the model. We
present the renormalized stochastic Langevin equation for an homogeneous
system-field and then we analyze the influence of the environment on the power
spectrum for some modes in the system.


title:
Global spectral representations of black hole spacetimes in the complex
  plane

abstract:
  Binary black hole coalescence produces a finite burst of gravitational
radiation which propagates towards quiescent infinity. These spacetimes are
analytic about infinity and contain a dimensionless coupling constant $M/s$,
where $M$ denotes the total mass-energy and $s$ an imaginary distance. This
introduces globally convergent Fourier series on a complex radial coordinate,
allowing spectral representation of black hole spacetimes in all three
dimensions. We illustrate this representation theory on a Fourier-Legendre
expansion of Boyer-Lindquist initial data and a scalar wave equation with
signal recovery by Cauchy's integral formula.


title:
Entropy of BTZ black hole and its spectrum by quantum radial geodesics
  behind horizons

abstract:
  In the framework of thermal quantization of radial geodesics completely
confined behind the horizons we calculate the entropy of BTZ black hole in
agreement with the Bekenstein--Hawking relation. Particles in the BTZ black
hole occupy the only quantum ground level. The quantization allow us to find a
linear dependence of black hole mass versus its orbital momentum.


title:
A Question About Standard Cosmology and Extremely Dense Stars'
  Collapsing

abstract:
  We ask if the conventional variable separation techniques in the studying of
standard cosmology and the collapsing of extremely dense stars introduce
Newton's absolute space-time concepts. If this is the case, then a completely
relative cosmology is needed. We build the basic frame-works for such a
cosmology and illustrate that, the observed luminosity-distance v.s. red-shift
relations of supernovaes can be explained naturally even without any conception
of dark energies.


title: Bayesian modeling of source confusion in LISA data

abstract:
  One of the greatest data analysis challenges for the Laser Interferometer
Space Antenna (LISA) is the need to account for a large number of gravitational
wave signals from compact binary systems expected to be present in the data. We
introduce the basis of a Bayesian method that we believe can address this
challenge, and demonstrate its effectiveness on a simplified problem involving
one hundred synthetic sinusoidal signals in noise. We use a reversible jump
Markov chain Monte Carlo technique to infer simultaneously the number of
signals present, the parameters of each identified signal, and the noise level.
Our approach therefore tackles the detection and parameter estimation problems
simultaneously, without the need to evaluate formal model selection criteria,
such as the Akaike Information Criterion or explicit Bayes factors. The method
does not require a stopping criterion to determine the number of signals, and
produces results which compare very favorably with classical spectral
techniques.


title: Dimensionally Regulated Graviton 1-Point Function in de Sitter

abstract:
  We use dimensional regularization to compute the 1PI 1-point function of
quantum gravity at one loop order in a locally de Sitter background. As with
other computations, the result is a finite constant at this order. It
corresponds to a small positive renormalization of the cosmological constant.


title: Conserved Charges of Higher D Kerr-AdS Spacetimes

abstract:
  We compute the energy and angular momenta of recent D-dimensional Kerr-AdS
solutions to cosmological Einstein gravity, as well as of the BTZ metric, using
our invariant charge definitions.


title:
Expected Coalescence Rate of Double Neutron Stars for Ground Based
  Interferometers

abstract:
  In this paper we present new estimates of the coalescence rate of neutron
star binaries in the local universe and we discuss its consequences for the
first generations of ground based interferometers. Our approach based on both
evolutionary and statistical methods gives a galactic merging rate of 1.7
10$^{-5}$ yr$^{-1}$, in the range of previous estimates 10$^{-6}$ - 10$^{-4}$
yr$^{-1}$. The local rate which includes the contribution of elliptical
galaxies is two times higher, in the order of 3.4 10$^{-5}$ yr$^{-1}$. We
predict one detection every 148 and 125 years with initial VIRGO and LIGO, and
up to 6 events per year with their advanced configuration. Our recent detection
rate estimates from investigations on VIRGO future improvements are quoted.


title: LISA Data Analysis using MCMC methods

abstract:
  The Laser Interferometer Space Antenna (LISA) is expected to simultaneously
detect many thousands of low frequency gravitational wave signals. This
presents a data analysis challenge that is very different to the one
encountered in ground based gravitational wave astronomy. LISA data analysis
requires the identification of individual signals from a data stream containing
an unknown number of overlapping signals. Because of the signal overlaps, a
global fit to all the signals has to be performed in order to avoid biasing the
solution. However, performing such a global fit requires the exploration of an
enormous parameter space with a dimension upwards of 50,000. Markov Chain Monte
Carlo (MCMC) methods offer a very promising solution to the LISA data analysis
problem. MCMC algorithms are able to efficiently explore large parameter
spaces, simultaneously providing parameter estimates, error analyses and even
model selection. Here we present the first application of MCMC methods to
simulated LISA data and demonstrate the great potential of the MCMC approach.
Our implementation uses a generalized F-statistic to evaluate the likelihoods,
and simulated annealing to speed convergence of the Markov chains. As a final
step we super-cool the chains to extract maximum likelihood estimates, and
estimates of the Bayes factors for competing models. We find that the MCMC
approach is able to correctly identify the number of signals present, extract
the source parameters, and return error estimates consistent with Fisher
information matrix predictions.


title: Stellar Oscillations in Scalar-Tensor Theory of Gravity

abstract:
  We derive the perturbation equations for relativistic stars in scalar-tensor
theories of gravity and study the corresponding oscillation spectrum. We show
that the frequency of the emitted gravitational waves is shifted proportionally
to the scalar field strength. Scalar waves which might be produced from such
oscillations can be a unique probe for the theory, but their detectability is
questionable if the radiated energy is small. However we show that there is no
need for a direct observation of scalar waves: the shift in the gravitational
wave spectrum could unambiguously signal the presence of a scalar field.


title: Energy and Momentum Associated with Kasner-type Universes

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0011027, "Viscous cosmologies in scalar-tensor theories for Kasner type
metrics," by M. Cataldo, S. del Campo and P. Salgado; and gr-qc/0404108,
"Energy and Momentum Densities Associated with Solutions Exhibiting Directional
Type Singularities," by Ragab M. Gad.


title: Exact Solutions of the Photon Equation in Anisotropic Spacetimes

abstract:
  This paper has inappropriate amounts of overlap with the following papers
also written by the authors or their collaborators: gr-qc/0506135,
gr-qc/0207026, gr-qc/0502059, gr-qc/0502061, gr-qc/0510037, and others.


title: The roots of scalar-tensor theory: an approximate history

abstract:
  Why are there no fundamental scalar fields actually observed in physics
today? Scalars are the simplest fields, but once we go beyond
Galilean-Newtonian physics they appear only in speculations, as possible
determinants of the gravitational constants in the so-called Scalar-Tensor
theories in non-quantum physics, and as Higgs particles, dilatons, etc., in
quantum physics. Actually, scalar fields have had a long and controversial life
in gravity theories, with a history of deaths and resurrections. This paper
presents a brief overview of this history.


title: Ultrarelativistic boost of spinning black rings

abstract:
  We study the D=5 Emparan-Reall spinning black ring under an ultrarelativistic
boost along an arbitrary direction. We analytically determine the resulting
shock pp-wave, in particular for boosts along axes orthogonal and parallel to
the plane of rotation. The solution becomes physically more interesting and
simpler if one enforces equilibrium between the forces on the ring. We also
comment on the ultrarelativistic limit of recently found supersymmetric black
rings with two independent angular momenta. Essential distinct features with
respect to the boosted Myers-Perry black holes are pointed out.


title: Classical General Relativity

abstract:
  This survey paper is divided into two parts. In the first (section 2), I give
a brief account of the structure of classical relativity theory. In the second
(section 3), I discuss three special topics: (i) the status of the relative
simultaneity relation in the context of Minkowski spacetime; (ii) the
"geometrized" version of Newtonian gravitation theory (also known as
Newton-Cartan theory); and (iii) the possibility of recovering the global
geometric structure of spacetime from its "causal structure".


title: Half polarized U(1) symmetric vacuum spacetimes with AVTD behavior

abstract:
  In a previous work, we used a polarization condition to show that there is a
family of U(1) symmetric solutions of the vacuum Einstein equations such that
each exhibits AVTD (Asymptotic Velocity Term Dominated) behavior in the
neighborhood of its singularity. Here we consider the general case of U(1)
bundles and determine a condition, called the half polarization condition,
necessary and sufficient in our context, for AVTD behavior near the
singularity.


title: A group field theory for 3d quantum gravity coupled to a scalar field

abstract:
  We present a new group field theory model, generalising the Boulatov model,
which incorporates both 3-dimensional gravity and matter coupled to gravity. We
show that the Feynman diagram amplitudes of this model are given by Riemannian
quantum gravity spin foam amplitudes coupled to a scalar matter field. We
briefly discuss the features of this model and its possible generalisations.


title: Is empty spacetime a physical thing?

abstract:
  This article deals with empty spacetime and the question of its physical
reality. By "empty spacetime" we mean a collection of bare spacetime points,
the remains of ridding spacetime of all matter and fields. We ask whether these
geometric objects--themselves intrinsic to the concept of field--might be
observable through some physical test. By taking quantum-mechanical notions
into account, we challenge the negative conclusion drawn from the
diffeomorphism invariance postulate of general relativity, and we propose new
foundational ideas regarding the possible observation--as well as conceptual
overthrow--of this geometric ether.


title: Rigorous steps towards holography in asymptotically flat spacetimes

abstract:
  Scalar QFT on the boundary $\Im^+$ at null infinity of a general
asymptotically flat 4D spacetime is constructed using the algebraic approach
based on Weyl algebra associated to a BMS-invariant symplectic form. The
constructed theory is invariant under a suitable unitary representation of the
BMS group with manifest meaning when the fields are interpreted as suitable
extensions to $\Im^+$ of massless minimally coupled fields propagating in the
bulk. The analysis of the found unitary BMS representation proves that such a
field on $\Im^+$ coincides with the natural wave function constructed out of
the unitary BMS irreducible representation induced from the little group
$\Delta$, the semidirect product between SO(2) and the two dimensional
translational group. The result proposes a natural criterion to solve the long
standing problem of the topology of BMS group. Indeed the found natural
correspondence of quantum field theories holds only if the BMS group is
equipped with the nuclear topology rejecting instead the Hilbert one.
Eventually some theorems towards a holographic description on $\Im^+$ of QFT in
the bulk are established at level of $C^*$ algebras of fields for strongly
asymptotically predictable spacetimes. It is proved that preservation of a
certain symplectic form implies the existence of an injective $*$-homomorphism
from the Weyl algebra of fields of the bulk into that associated with the
boundary $\Im^+$. Those results are, in particular, applied to 4D Minkowski
spacetime where a nice interplay between Poincar\'e invariance in the bulk and
BMS invariance on the boundary at $\Im^+$ is established at level of QFT. It
arises that the $*$-homomorphism admits unitary implementation and Minkowski
vacuum is mapped into the BMS invariant vacuum on $\Im^+$.


title:
Gravitational waves from oscillating accretion tori: Comparison between
  different approaches

abstract:
  Quasi-periodic oscillations of high density thick accretion disks orbiting a
Schwarzschild black hole have been recently addressed as interesting sources of
gravitational waves. The aim of this paper is to compare the gravitational
waveforms emitted from these sources when computed using (variations of) the
standard quadrupole formula and gauge-invariant metric perturbation theory. To
this goal we evolve representative disk models using an existing general
relativistic hydrodynamics code which has been previously employed in
investigations of such astrophysical systems. Two are the main results of this
work: First, for stable and marginally stable disks, no excitation of the black
hole quasi-normal modes is found. Secondly, we provide a simple, relativistic
modification of the Newtonian quadrupole formula which, in certain regimes,
yields excellent agreement with the perturbative approach. This holds true as
long as back-scattering of GWs is negligible. Otherwise, any functional form of
the quadrupole formula yields systematic errors of the order of 10%.


title: Discrete quantum gravity in the framework of Regge calculus formalism

abstract:
  An approach to the discrete quantum gravity based on the Regge calculus is
discussed which was developed in a number of our papers. Regge calculus is
general relativity for the subclass of general Riemannian manifolds called
piecewise flat ones. Regge calculus deals with the discrete set of variables,
triangulation lengths, and contains continuous general relativity as a
particular limiting case when the lengths tend to zero. In our approach the
quantum length expectations are nonzero and of the order of Plank scale
$10^{-33}cm$. This means the discrete spacetime structure on these scales.


title:
On the area expectation values in area tensor Regge calculus in the
  Lorentzian domain

abstract:
  Wick rotation in area tensor Regge calculus is considered. The heuristical
expectation is confirmed that the Lorentzian quantum measure on a spacelike
area should coincide with the Euclidean measure at the same argument. The
consequence is validity of probabilistic interpretation of the Lorentzian
measure as well (on the real, i.e. spacelike areas).


title: Charged black holes in compactified spacetimes

abstract:
  We construct and investigate a compactified version of the four-dimensional
Reissner-Nordstrom-NUT solution, generalizing the compactified Schwarzschild
black hole that has been previously studied by several workers. Our approach to
compactification is based on dimensional reduction with respect to the
stationary Killing vector, resulting in three-dimensional gravity coupled to a
nonlinear sigma model. Using that the original non-compactified solution
corresponds to a target space geodesic, the problem can be linearized much in
the same way as in the case of no electric nor NUT charge. An interesting
feature of the solution family is that for nonzero electric charge but
vanishing NUT charge, the solution has a curvature singularity on a torus that
surrounds the event horizon, but this singularity is removed when the NUT
charge is switched on. We also treat the Schwarzschild case in a more complete
way than has been done previously. In particular, the asymptotic solution (the
Levi-Civita solution with the height coordinate made periodic) has to our
knowledge only been calculated up to a determination of the mass parameter. The
periodic Levi-Civita solution contains three essential parameters, however, and
the remaining two are explicitly calculated here.


title: Critical behavior in vacuum gravitational collapse in 4+1 dimensions

abstract:
  We show that the 4+1 dimensional vacuum Einstein equations admit
gravitational waves with radial symmetry. The dynamical degrees of freedom
correspond to deformations of the three-sphere orthogonal to the $(t,r)$ plane.
Gravitational collapse of such waves is studied numerically and shown to
exhibit discretely self-similar Type II critical behavior at the threshold of
black hole formation.


title: General Relativity in the Undergraduate Physics Curriculum

abstract:
  Einstein's general relativity is increasingly important in contemporary
physics on the frontiers of both the very largest distance scales (astrophysics
and cosmology) and the very smallest(elementary particle physics). This paper
makes the case for a `physics first' approach to introducing general relativity
to undergraduate physics majors.


title: Q-stars in scalar-tensor gravitational theories

abstract:
  We study q-stars in Brans-Dicke gravitational theory. We find that when the
Brans-Dicke constant, $\omega_{\textrm{BD}}$, tends to infinity, the results of
General Relativity are reproduced. For other values of $\omega_{\textrm{BD}}$,
the particle number, mass and radius of the star and the absolute value of the
matter field are a few percent larger than in the case of General Relativity.
We also investigate the general scalar-tensor gravitational theory and find
that the star parameters are a few percent larger than in the case of General
Relativity.


title: Numerical validation of the Kerr metric in Bondi-Sachs form

abstract:
  A metric representing the Kerr geometry has been obtained by Pretorius and
Israel. We make a coordinate transformation on this metric, thereby bringing it
into Bondi-Sachs form. In order to validate the metric, we evaluate it
numerically on a regular grid of the new coordinates. The Ricci tensor is then
computed, for different discretizations, and found to be convergent to zero. We
also investigate the behaviour of the metric near the axis of symmetry and
confirm regularity. Finally we investigate a Bondi-Sachs representation of the
Kerr geometry reported by Fletcher and Lun; we confirm numerically that their
metric is Ricci flat, but find that it has an irregular behaviour at the pole.


title: Black Holes in Astrophysics

abstract:
  This article reviews the current status of black hole astrophysics, focusing
on topics of interest to a physics audience. Astronomers have discovered dozens
of compact objects with masses greater than 3 solar masses, the likely maximum
mass of a neutron star. These objects are identified as black hole candidates.
Some of the candidates have masses of 5 to 20 solar masses and are found in
X-ray binaries, while the rest have masses from a million to a billion solar
masses and are found in galactic nuclei. A variety of methods are being tried
to estimate the spin parameters of the candidate black holes. There is strong
circumstantial evidence that many of the objects have event horizons. Recent
MHD simulations of magnetized plasma accreting on rotating black holes seem to
hint that relativistic jets may be produced by a magnetic analog of the Penrose
process.


title: The Cosmic Time in Terms of the Redshift

abstract:
  In cosmology one labels the time t since the Big Bang in terms of the
redshift of light emitted at t, as we see it now. In this Note we derive a
formula that relates t to z which is valid for all redshifts. One can go back
in time as far as one wishes, but not to the Big Bang at which the redshift
tends to infinity.


title: Second order formalism in Poincare gauge theory

abstract:
  Changing the set of independent variables of Poincare gauge theory and
considering, in a manner similar to the second order formalism of general
relativity, the Riemannian part of the Lorentz connection as function of the
tetrad field, we construct theories that do not contain second or higher order
derivatives in the field variables, possess a full general relativity limit in
the absence of spinning matter fields, and allow for propagating torsion fields
in the general case. A concrete model is discussed and the field equations are
reduced by means of a Yasskin type ansatz to a conventional Einstein-Proca
system. Approximate solutions describing the exterior of a spin polarized
neutron star are prsented and the possibility of an experimental detection of
the torsion fields is briefly discussed.


title: Quantum Roots in Geometry: I

abstract:
  In the present work, it is shown that the geometerization philosophy has not
been exhausted. Some quantum roots are already built in non-symmetric
geometries. Path equations in such geometries give rise to spin-gravity
interaction. Some experimental evidences (the results of the COW-experiment)
indicate the existence of this interaction. It is shown that the new quantum
path equations could account for the results of the COW-experiment. Large scale
applications, of the new path equations, admitted by such geometries, give rise
to tests for the existence of this interaction on the astrophysical and
cosmological scales. As a byproduct, it is shown that the quantum roots
appeared explicitly, in the path equations, can be diffused in the whole
geometry using a parameterization scheme.


title: Quantized Black Holes, Their Spectrum and Radiation

abstract:
  Under quite natural general assumptions, the following results are obtained.
The maximum entropy of a quantized surface is demonstrated to be proportional
to the surface area in the classical limit. The general structure of the
horizon spectrum is found. The discrete spectrum of thermal radiation of a
black hole Under quite natural general assumptions, the following results are
obtained. The maximum entropy of a quantized surface is demonstrated to be
proportional to the surface area in the classical limit. The general structure
of the horizon spectrum is found. The discrete spectrum of thermal radiation of
a black hole fits the Wien profile. The natural widths of the lines are much
smaller than the distances between them. The total intensity of the thermal
radiation is estimated.
  In the special case of loop quantum gravity, the value of the Barbero --
Immirzi parameter is found. Different values for this parameter, obtained under
additional assumption that the horizon is described by a U(1) Chern -- Simons
theory, are demonstrated to be in conflict with the firmly established
holographic bound.


title: Gravitational Waves from Compact Sources

abstract:
  We review sources of high-frequency gravitational waves, summarizing our
current understanding of emission mechanisms, expected amplitudes and event
rates. The most promising sources are gravitational collapse (formation of
black holes or neutron stars) and subsequent ringing of the compact star,
secular or dynamical rotational instabilities and high-mass compact objects
formed through the merger of binary neutron stars. Significant and unique
information for the various stages of the collapse, the structure of
protoneutron stars and the high density equation of state of compact objects
can be drawn from careful study of gravitational wave signals.


title: Doubly Special Relativity as a Limit of Gravity

abstract:
  Doubly Special Relativity (DSR) is a theory with two observer-independent
scales, of velocity and mass, which is expected to replace Special Relativity
at ultra-high energies. In these notes we first discuss the postulates of DSR,
and then turn to presenting arguments supporting the hypothesis that DSR can be
regarded as a flat space, semiclassical limit of gravity. The notes are based
on the talk presented at the conference ``Special Relativity -- Will it Survive
the Next 100 Years?''


title:
Rough Solutions of the Einstein Constraint Equations on Compact
  Manifolds

abstract:
  We construct low regularity solutions of the vacuum Einstein constraint
equations on compact manifolds. On 3-manifolds we obtain solutions with metrics
in $H^s$ where $s>3/2$. The constant mean curvature (CMC) conformal method
leads to a construction of all CMC initial data with this level of regularity.
These results extend a construction from Ma04 that treated the asymptotically
Euclidean case.


title: Explicit multipole moments of stationary axisymmetric spacetimes

abstract:
  In this article we study multipole moments of axisymmetric stationary
asymptotically flat spacetimes. We show how the tensorial recursion of Geroch
and Hansen can be reduced to a recursion of scalar functions. We also
demonstrate how a careful choice of conformal factor collects all moments into
one complex valued function on R, where the moments appear as the derivatives
at 0. As an application, we calculate the moments of the Kerr solution. We also
discuss the freedom in choosing the potential for the moments.


title: Accelerating Observers, Area and Entropy

abstract:
  We consider an explicit example of a process, where the entropy carried by
radiation through an accelerating two-plane is proportional to the decrease in
the area of that two-plane even when the two-plane is not a part of any horizon
of spacetime. Our results seem to support the view that entropy proportional to
area is possessed not only by horizons but by all spacelike two-surfaces of
spacetime.


title:
Spacetime topology from the tomographic histories approach I:
  Non-relativistic Case

abstract:
  The tomographic histories approach is presented. As an inverse problem, we
recover in an operational way the effective topology of the extended
configuration space of a system. This means that from a series of experiments
we get a set of points corresponding to events. The difference between
effective and actual topology is drawn. We deduce the topology of the extended
configuration space of a non-relativistic system, using certain concepts from
the consistent histories approach to Quantum Mechanics, such as the notion of a
record. A few remarks about the case of a relativistic system, preparing the
ground for a forthcoming paper sequel to this, are made in the end.


title: A Measure of Cosmological Acceleration

abstract:
  We propose quantifying the quantum gravitational back-reaction on inflation
with an invariant measure of the local acceleration rather than the expansion
rate. Our observable is suitable for models in which there is no scalar
inflaton to provide a preferred velocity field with which to define the
expansion. As an example, we use stochastic techniques to evaluate the local
acceleration at one loop order for Lambda-driven inflation in pure quantum
gravity.


title:
Form invariant transformations between n-- and m-- dimensional flat
  Friedmann--Robertson--Walker cosmologies

abstract:
  We illustrate how the group of symmetry transformations, which preserve the
form of the n--dimensional flat Friedmann--Robertson--Walker cosmologies
satisfying Einstein equations, acts in any dimension. This group relates the
energy density and the isotropic pressure of the cosmic fluid to the expansion
rate. The freedom associated with the dimension of the space time yields
assisted inflation even when the energy density of the fluid is a dimensional
invariant and enriches the set of duality transformations leading to phantom
cosmologies.


title: Born-Infeld-Einstein theory with matter

abstract:
  The field equations associated with the Born-Infeld-Einstein action including
matter are derived using a Palatini variational principle. Scalar,
electromagnetic, and Dirac fields are considered. It is shown that an action
can be chosen for the scalar field that produces field equations identical to
the usual Einstein field equations minimally coupled to a scalar field. In the
electromagnetic and Dirac cases the field equations reproduce the standard
equations only to lowest order. The spherically symmetric electrovac equations
are studied in detail. It is shown that the resulting Einstein equations
correspond to gravity coupled to a modified Born-Infeld theory. It is also
shown that point charges are not allowed. All particles must have a finite
size. Mass terms for the fields are also considered.


title: Adiabatic radiation reaction to the orbits in Kerr Spacetime

abstract:
  Geodesic motion of a point particle in Kerr geometry has three constants of
motion, energy $E$, azimuthal angular momentum $L$, and Carter constant $Q$.
Under the adiabatic approximation, radiation reaction effect is characterized
by the time evolution of these constants. In this letter we show that the
scheme to evaluate them can be dramatically simplified.


title:
Exact Quantization of Einstein-Rosen Waves Coupled to Massless Scalar
  Matter

abstract:
  We show in this letter that gravity coupled to a massless scalar field with
full cylindrical symmetry can be exactly quantized by an extension of the
techniques used in the quantization of Einstein-Rosen waves. This system
provides a useful testbed to discuss a number of issues in quantum general
relativity such as the emergence of the classical metric, microcausality, and
large quantum gravity effects. It may also provide an appropriate framework to
study gravitational critical phenomena from a quantum point of view, issues
related to black hole evaporation, and the consistent definition of test fields
and particles in quantum gravity.


title: Brane World Cosmology In Jordan-Brans-Dicke Theory

abstract:
  We consider the embedding of 3+1 dimensional cosmology in 4+1 dimensional
Jordan-Brans-Dicke theory. We show that exponentially growing and power law
scale factors are implied. Whereas the 4+1 dimensional scalar field is
approximately constant for each, the effective 3+1 dimensional scalar field is
constant for exponentially growing scale factor and time dependent for power
law scale factor.


title: Phantom cosmology with general potentials

abstract:
  We present a unified treatment of the phase space of a spatially flat
homogeneous and isotropic universe dominated by a phantom field. Results on the
dynamics and the late time attractors (Big Rip, de Sitter, etc.) are derived
without specifying the form of the phantom potential, using only general
assumptions on its shape. Many results found in the literature are quickly
recovered and predictions are made for new scenarios.


title: On the Newtonian limit of Generalized Modified Gravity Models

abstract:
  We consider the Newtonian limit of modified theories of gravity that include
inverse powers of the curvature in the action in order to explain the cosmic
acceleration. It has been shown that the simplest models of this kind are in
conflict with observations at the solar system level. In this letter we point
out that when one adds to the action inverse powers of curvature invariants
that do not vanish for the Schwarzschild geometry one generically recovers an
acceptable Newtonian limit at small distances. Gravity is however modified at
large distances. We compute the first correction to the Newtonian potential in
a quite general class of models. The characteristic distance entering in these
modifications is of the order of 10pc for the Sun and of the order of 10^2 kpc
for a galaxy.


title:
Asymptotic analysis of spatially inhomogeneous stiff and ultra-stiff
  cosmologies

abstract:
  We calculate analytically the past asymptotic decay rates close to an initial
singularity in general G_0 spatially inhomogeneous perfect fluid models with an
effective equation of state which is stiff or ultra-stiff (i.e., $\gamma \ge
2$). These results are then supported by numerical simulations in a special
class of G_2 cosmological models. Our analysis confirms and extends the BKL
conjectures and lends support to recent isotropization results in cosmological
models of current interest (with $\gamma > 2$).


title: Dirac Quasinormal frequencies of the Kerr-Newman black hole

abstract:
  The Dirac quasinormal modes (QNMs) of the Kerr-Newman black hole are
investigated using continued fraction approach. It is shown that the
quasinormal frequencies in the complex $\omega$ plane move counterclockwise as
the charge or angular momentum per unit mass of the black hole increases. They
get a spiral-like shape, moving out of their Schwarzschild or
Reissner-Nordstr\"om values and "looping in" towards some limiting frequencies
as the charge and angular momentum per unit mass tend to their extremal values.
The number of the spirals increases as the overtone number increases but
decreases as the angular quantum number increases. It is also found that both
the real and imaginary parts are oscillatory functions of the angular momentum
per unit mass, and the oscillation becomes faster as the overtone number
increases but slower as the angular quantum number increases.


title: N=1 de Sitter Supersymmetry Algebra

abstract:
  Recalling the universal covering group of de Sitter, the transformation
properties of the spinor fields $\psi(x)$ and ${\bar\psi}(x)$, in the ambient
space notation, are presented in this paper. The charge conjugation symmetry of
the de Sitter spinor field is then discussed in the above notation. Using this
spinor field and charge conjugation, de Sitter supersymmetry algebra in the
ambient space notation has been established. It is shown that a novel
dS-superalgebra can be attained by the use of spinor field and charge
conjugation in the ambient space notation.


title: Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions

abstract:
  We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.


title:
The Einstein-scalar field constraints on asymptotically Euclidean
  manifolds

abstract:
  We use the conformal method to obtain solutions of the Einstein-scalar field
gravitational constraint equations. Handling scalar fields is a bit more
challenging than handling matter fields such as fluids, Maxwell fields or
Yang-Mills fields, because the scalar field introduces three extra terms into
the Lichnerowicz equation, rather than just one. Our proofs are constructive
and allow for arbitrary dimension (>2) as well as low regularity initial data.


title:
Absolute Objects and Counterexamples: Jones-Geroch Dust, Torretti
  Constant Curvature, Tetrad-Spinor, and Scalar Density

abstract:
  James L. Anderson analyzed the novelty of Einstein's theory of gravity as its
lack of "absolute objects." Michael Friedman's related work has been criticized
by Roger Jones and Robert Geroch for implausibly admitting as absolute the
timelike 4-velocity field of dust in cosmological models in Einstein's theory.
Using the Rosen-Sorkin Lagrange multiplier trick, I complete Anna Maidens's
argument that the problem is not solved by prohibiting variation of absolute
objects in an action principle. Recalling Anderson's proscription of
"irrelevant" variables, I generalize that proscription to locally irrelevant
variables that do no work in some places in some models. This move vindicates
Friedman's intuitions and removes the Jones-Geroch counterexample: some regions
of some models of gravity with dust are dust-free and so naturally lack a
timelike 4-velocity, so diffeomorphic equivalence to (1,0,0,0) is spoiled.
Torretti's example involving constant curvature spaces is shown to have an
absolute object on Anderson's analysis, viz., the conformal spatial metric
density. The previously neglected threat of an absolute object from an
orthonormal tetrad used for coupling spinors to gravity appears resolvable by
eliminating irrelevant fields. However, given Anderson's definition, GTR itself
has an absolute object (as Robert Geroch has observed recently): a change of
variables to a conformal metric density and a scalar density shows that the
latter is absolute.


title:
Thermodynamics and Stability of Higher Dimensional Rotating (Kerr) AdS
  Black Holes

abstract:
  We study the thermodynamic and gravitational stability of Kerr anti-de Sitter
black holes in five and higher dimensions. We show, in the case of equal
rotation parameters, $a_i=a$, that the Kerr-AdS background metrics become
stable, both thermodynamically and gravitationally, when the rotation
parameters $a_i$ take values comparable to the AdS curvature radius. In turn, a
Kerr-AdS black hole can be in thermal equilibrium with the thermal radiation
around it only when the rotation parameters become not significantly smaller
than the AdS curvature radius. We also find with equal rotation parameters that
a Kerr-AdS black hole is thermodynamically favored against the existence of a
thermal AdS space, while the opposite behavior is observed in the case of a
single non-zero rotation parameter. The five dimensional case is however
different and also special in that there is no high temperature thermal AdS
phase regardless of the choice of rotation parameters. We also verify that at
fixed entropy, the temperature of a rotating black hole is always bounded above
by that of a non-rotating black hole, in four and five dimensions, but not in
six and more dimensions (especially, when the entropy approaches zero or the
minimum of entropy does not correspond to the minimum of temperature). In this
last context, the six dimensional case is marginal.


title: Fundamental Physics with the Laser Astrometric Test Of Relativity

abstract:
  The Laser Astrometric Test Of Relativity (LATOR) is a joint European-U.S.
Michelson-Morley-type experiment designed to test the pure tensor metric nature
of gravitation - a fundamental postulate of Einstein's theory of general
relativity. By using a combination of independent time-series of highly
accurate gravitational deflection of light in the immediate proximity to the
Sun, along with measurements of the Shapiro time delay on interplanetary scales
(to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will
significantly improve our knowledge of relativistic gravity. The primary
mission objective is to i) measure the key post-Newtonian Eddington parameter
\gamma with accuracy of a part in 10^9. (1-\gamma) is a direct measure for
presence of a new interaction in gravitational theory, and, in its search,
LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test.
The mission will also provide: ii) first measurement of gravity's non-linear
effects on light to ~0.01% accuracy; including both the Eddington \beta
parameter and also the spatial metric's 2nd order potential contribution (never
measured before); iii) direct measurement of the solar quadrupole moment J2
(currently unavailable) to accuracy of a part in 200 of its expected size; iv)
direct measurement of the "frame-dragging" effect on light by the Sun's
gravitomagnetic field, to 1% accuracy. LATOR's primary measurement pushes to
unprecedented accuracy the search for cosmologically relevant scalar-tensor
theories of gravity by looking for a remnant scalar field in today's solar
system. We discuss the mission design of this proposed experiment.


title: Uniformly Rotating Rings in General Relativity

abstract:
  In this paper, we discuss general relativistic, self-gravitating and
uniformly rotating perfect fluid bodies with a toroidal topology (without
central object). For the equations of state describing the fluid matter we
consider polytropic as well as completely degenerate, perfect Fermi gas models.
We find that the corresponding configurations possess similar properties to the
homogeneous relativistic Dyson rings. On the one hand, there exists no limit to
the mass for a given maximal mass-density inside the body. On the other hand,
each model permits a quasistationary transition to the extreme Kerr black hole.


title: The universe seen at different scales

abstract:
  A large-scale smoothed-out model of the universe ignores small-scale
inhomogeneities, but the averaged effects of those inhomogeneities may alter
both observational and dynamical relations at the larger scale. This article
discusses these effects, and comments briefly on the relation to gravitational
entropy.


title: Numerical simulations of stiff fluid gravitational singularities

abstract:
  Numerical simulations of the approach to the singularity in spacetimes with
stiff fluid matter are presented here. The spacetimes examined have no
symmetries and can be regarded as representing the general behavior of
singularities in the presence of such matter. It is found that the singularity
is spacelike and that as it is approached, the spacetime dynamics becomes local
and non-oscillatory.


title: Dark energy from quantum wave function collapse of dark matter

abstract:
  Dynamical wave function collapse models entail the continuous liberation of a
specified rate of energy arising from the interaction of a fluctuating scalar
field with the matter wave function. We consider the wave function collapse
process for the constituents of dark matter in our universe. Beginning from a
particular early era of the universe chosen from physical considerations, the
rate of the associated energy liberation is integrated to yield the requisite
magnitude of dark energy around the era of galaxy formation. Further, the
equation of state for the liberated energy approaches $w \to -1$
asymptotically, providing a mechanism to generate the present acceleration of
the universe.


title: Wide parameter search for isolated pulsars using the Hough transform

abstract:
  We use the Hough transform to analyze data from the second science run of the
LIGO interferometers, to look for gravitational waves from isolated pulsars. We
search over the whole sky and over a large range of frequencies and spin-down
parameters. Our search method is based on the Hough transform, which is a
semi-coherent, computationally efficient, and robust pattern recognition
technique. We also present a validation of the search pipeline using hardware
signal injections.


title:
Black-hole thermodynamics with modified dispersion relations and
  generalized uncertainty principles

abstract:
  In several approaches to the quantum-gravity problem evidence has emerged of
the validity of a "GUP" (a Generalized position-momentum Uncertainty Principle)
and/or a "MDR" (a modification of the energy-momentum dispersion relation), but
very little is known about the implications of GUPs and MDRs for black-hole
thermodynamics, another key topic for quantum-gravity research. We investigate
an apparent link, already suggested in an earlier exploratory study involving
two of us, between the possibility of a GUP and/or a MDR and the possibility of
a log term in the area-entropy black-hole formula. We then obtain, from that
same perspective, a modified relation between the mass of a black hole and its
temperature, and we examine the validity of the "Generalized Second Law of
black-hole thermodynamics" in theories with a GUP and/or a MDR. After an
analysis of GUP- and MDR-modifications of the black-body radiation spectrum, we
conclude the study with a description of the black-hole evaporation process.


title:
A non-singular black hole model as a possible end-product of
  gravitational collapse

abstract:
  In this paper we present a non-singular black hole model as a possible
end-product of gravitational collapse. The depicted spacetime which is type
[II,(II)], by Petrov classification, is an exact solution of the Einstein
equations and contains two horizons. The equation of state in the radial
direction, is a well-behaved function of the density and smoothly reproduces
vacuum-like behavior near r=0 while tending to a polytrope at larger r, low
density, values. The final equilibrium configuration comprises of a de
Sitter-like inner core surrounded by a family of 2-surfaces of matter fields
with variable equation of state. The fields are all concentrated in the
vicinity of the radial center r=0. The solution depicts a spacetime that is
asymptotically Schwarzschild at large r, while it becomes de Sitter-like for
vanishing r. Possible physical interpretations of the macro-state of the black
hole interior in the model are offered. We find that the possible state admits
two equally viable interpretations, namely either a quintessential intermediary
region or a phase transition in which a two-fluid system is in both dynamic and
thermodynamic equilibrium. We estimate the ratio of pure matter present to the
total energy and in both (interpretations) cases find it to be virtually the
same, being 0.83. Finally, the well-behaved dependence of the density and
pressure on the radial coordinate provides some insight on dealing with the
information loss paradox.


title:
Higher Dimensional Cosmological Implications Of A Decay Law For
  $\Lambda$ Term : Expressions For Some Observable Quantities

abstract:
  Implications of cosmological model with a cosmological term of the form
$\Lambda = \beta \frac{\ddot {a}}{a}$, where $\beta$ is a constant, are
analyzed in multidimensional space time. The proper distance, the luminosity
distance-redshift, the angular diameter distance-redshift, and look back
time-redshift for the model are presented. It has been shown that such models
are found to be compatible with the recent observations. This work has thus
generalized to higher dimensions the well-know result in four dimensional space
time. It is found that there may be significant difference in principle at
least,from the analogous situation in four dimensional space time.


title:
Plane-symmetric inhomogeneous magnetized viscous fluid universe with a
  variable $\Lambda$

abstract:
  The behavior of magnetic field in plane symmetric inhomogeneous cosmological
models for bulk viscous distribution is investigated. The coefficient of bulk
viscosity is assumed to be a power function of mass density $(\xi
=\xi_{0}\rho^{n})$. The values of cosmological constant for these models are
found to be small and positive which are supported by the results from recent
supernovae Ia observations. Some physical and geometric aspects of the models
are also discussed.


title:
A geometric description of the intermediate behaviour for spatially
  homogeneous models

abstract:
  A new approach is suggested for the study of geometric symmetries in general
relativity, leading to an invariant characterization of the evolutionary
behaviour for a class of Spatially Homogeneous (SH) vacuum and orthogonal
$\gamma -$law perfect fluid models. Exploiting the 1+3 orthonormal frame
formalism, we express the kinematical quantities of a generic symmetry using
expansion-normalized variables. In this way, a specific symmetry assumption
lead to geometric constraints that are combined with the associated
integrability conditions, coming from the existence of the symmetry and the
induced expansion-normalized form of the Einstein's Field Equations (EFE), to
give a close set of compatibility equations. By specializing to the case of a
\emph{Kinematic Conformal Symmetry} (KCS), which is regarded as the direct
generalization of the concept of self-similarity, we give the complete set of
consistency equations for the whole SH dynamical state space. An interesting
aspect of the analysis of the consistency equations is that, \emph{at least}
for class A models which are Locally Rotationally Symmetric or lying within the
invariant subset satisfying $N_{\alpha}^{\alpha}=0 $, a proper KCS \emph{always
exists} and reduces to a self-similarity of the first or second kind at the
asymptotic regimes, providing a way for the ``geometrization'' of the
intermediate epoch of SH models.


title: Does Standard Cosmology Express Cosmological Principle Faithfully?

abstract:
  In 1+1 dimensional case, Einstein equation cannot give us any information on
the evolution of the universe because the Einstein tensor of the system is
identically zero. We study such a 1+1 dimensional cosmology and find the metric
of it according to cosmological principle and special relativity, but the
results contradict the usual expression of cosmological principle of standard
cosmology. So we doubt in 1+3 dimensional case, cosmological principle is
expressed faithfully by standard cosmology.


title:
Detecting extreme mass ratio inspirals with LISA using time-frequency
  methods II: search characterization

abstract:
  The inspirals of stellar-mass compact objects into supermassive black holes
constitute some of the most important sources for LISA. Detection of these
sources using fully coherent matched filtering is computationally intractable,
so alternative approaches are required. In a previous paper (Wen and Gair 2005,
gr-qc/0502100), we outlined a detection method based on looking for excess
power in a time-frequency spectrogram of the LISA data. The performance of the
algorithm was assessed using a single `typical' trial waveform and
approximations to the noise statistics. In this paper we present results of
Monte Carlo simulations of the search noise statistics and examine its
performance in detecting a wider range of trial waveforms. We show that typical
extreme mass ratio inspirals (EMRIs) can be detected at distances of up to 1--3
Gpc, depending on the source parameters. We also discuss some remaining issues
with the technique and possible ways in which the algorithm can be improved.


title:
Building a case for a Planck-scale-deformed boost action: the
  Planck-scale particle-localization limit

abstract:
  "Doubly-special relativity" (DSR), the idea of a Planck-scale Minkowski limit
that is still a relativistic theory, but with both the Planck scale and the
speed-of-light scale as nontrivial relativistic invariants, was proposed
(gr-qc/0012051) as a physics intuition for several scenarios which may arise in
the study of the quantum-gravity problem, but most DSR studies focused
exclusively on the search of formalisms for the description of a specific
example of such a Minkowski limit. A novel contribution to the DSR physics
intuition came from a recent paper by Smolin (hep-th/0501091) suggesting that
the emergence of the Planck scale as a second nontrivial relativistic invariant
might be inevitable in quantum gravity, relying only on some rather robust
expectations concerning the semiclassical approximation of quantum gravity. I
here attempt to strengthen Smolin's argument by observing that an analysis of
some independently-proposed Planck-scale particle-localization limits, such as
the "Generalized Uncertainty Principle" often attributed to string theory in
the literature, also suggests that the emergence of a DSR Minkowski limit might
be inevitable. I discuss a possible link between this observation and recent
results on logarithmic corrections to the entropy-area black-hole formula, and
I observe that both the analysis here reported and Smolin's analysis appear to
suggest that the examples of DSR Minkowski limits for which a formalism has
been sought in the literature might not be sufficiently general. I also stress
that, as we now contemplate the hypothesis of a DSR Minkowski limit, there is
an additional challenge for those in the quantum-gravity community attributing
to the Planck length the role of "fundamental length scale".


title: The Bianchi identity and weak gravitational lensing

abstract:
  We consider the Bianchi identity as a field equation for the distortion of
the shapes of images produced by weak gravitational lensing. Using the spin
coefficient formalism of Newman and Penrose [1962], we show that certain
complex components of the Weyl and Ricci curvature tensors are directly related
to fundamental observables in weak gravitational lensing. In the case of weak
gravitational fields, we then show that the Bianchi identity provides a field
equation for the Ricci tensor assuming a known Weyl tensor. From the Bianchi
identity, we derive the integral equation for weak lensing presented by
Miralda-Escude [1996], thus making the Bianchi identity a first principles
equation of weak gravitational lensing. This equation is integrated in the
important case of an axially symmetric lens and explicitly demonstrated in the
case of a point lens and a SIS model.


title: Marginally trapped tubes and dynamical horizons

abstract:
  We investigate the generic behaviour of marginally trapped tubes (roughly
time-evolved apparent horizons) using simple, spherically symmetric examples of
dust and scalar field collapse/accretion onto pre-existing black holes. We find
that given appropriate physical conditions the evolution of the marginally
trapped tube may be either null, timelike, or spacelike and further that the
marginally trapped two-sphere cross-sections may either expand or contract in
area. Spacelike expansions occur when the matter falling into a black hole
satisfies $\rho - P \leq 1/A$, where $A$ is the area of the horizon while
$\rho$ and $P$ are respectively the density and pressure of the matter.
Timelike evolutions occur when $(\rho - P)$ is greater than this cut-off and so
would be expected to be more common for large black holes. Physically they
correspond to horizon "jumps" as extreme conditions force the formation of new
horizons outside of the old.


title: Distortion of Schwarzschild-anti-de Sitter black holes to black strings

abstract:
  Motivated by the existence of black holes with various topologies in
four-dimensional spacetimes with a negative cosmological constant, we study
axisymmetric static solutions describing any large distortions of
Schwarzschild-anti-de Sitter black holes parametrized by the mass $m$. Under
the approximation such that $m$ is much larger than the anti-de Sitter radius,
it is found that a cylindrically symmetric black string is obtained as a
special limit of distorted spherical black holes. Such a prolonged distortion
of the event horizon connecting a Schwarzschild-anti-de Sitter black hole to a
black string is allowed without violating both the usual black hole
thermodynamics and the hoop conjecture for the horizon circumference.


title: Einsteins Arbeiten in Bezug auf die moderne Kosmologie

abstract:
  We comment on the paper [1] by Albert Einstein from 1918 to Willem De
Sitter's solution [2] of the Einstein field equation from today's point of
view. To this end, we start by describing the geometry of the De Sitter
space-time and present its importance for the inflationary cosmological model.


title: Density fluctuations in $\kappa$-deformed inflationary universe

abstract:
  We study the spectrum of metric fluctuation in $\kappa$-deformed inflationary
universe. We write the theory of scalar metric fluctuations in the
$\kappa-$deformed Robertson-Walker space, which is represented as a non-local
theory in the conventional Robertson-Walker space. One important consequence of
the deformation is that the mode generation time is naturally determined by the
structure of the $\kappa-$deformation.
  We expand the non-local action in $H^2/\kappa^2$, with $H$ being the Hubble
parameter and $\kappa$ the deformation parameter, and then compute the power
spectra of scalar metric fluctuations both for the cases of exponential and
power law inflations up to the first order in $H^2/\kappa^2$. We show that the
power spectra of the metric fluctuation have non-trivial corrections on the
time dependence and on the momentum dependence compared to the commutative
space results. Especially for the power law inflation case, the power spectrum
for UV modes is weakly blue shifted early in the inflation and its strength
decreases in time. The power spectrum of far-IR modes has cutoff proportional
to $k^3$ which may explain the low CMB quadrupole moment.


title: Post-Newtonian Parameters from Alternative Theories of Gravity

abstract:
  Alternative theories of gravity have been recently studied in connection with
their cosmological applications, both in the Palatini and in the metric
formalism. The aim of this paper is to propose a theoretical framework (in the
Palatini formalism) to test these theories at the solar system level and
possibly at the galactic scales. We exactly solve field equations in vacuum and
find the corresponding corrections to the standard general relativistic
gravitational field. On the other hand, approximate solutions are found in
matter cases starting from a Lagrangian which depends on a phenomenological
parameter. Both in the vacuum case and in the matter case the deviations from
General Relativity are controlled by parameters that provide the Post-Newtonian
corrections which prove to be in good agreement with solar system experiments.