title: Energy Norms and the Stability of the Einstein Evolution Equations

abstract:
  The Einstein evolution equations may be written in a variety of equivalent
analytical forms, but numerical solutions of these different formulations
display a wide range of growth rates for constraint violations. For symmetric
hyperbolic formulations of the equations, an exact expression for the growth
rate is derived using an energy norm. This expression agrees with the growth
rate determined by numerical solution of the equations. An approximate method
for estimating the growth rate is also derived. This estimate can be evaluated
algebraically from the initial data, and is shown to exhibit qualitatively the
same dependence as the numerically-determined rate on the parameters that
specify the formulation of the equations. This simple rate estimate therefore
provides a useful tool for finding the most well-behaved forms of the evolution
equations.


title: Time-Dependent Solution for a Star Immersed in a Background Radiation

abstract:
  We study a time-dependent and spherically-symmetric solution with a star-like
source. We show that this solution can be interpreted as an exterior solution
of a contracting star which has a decreasing temperature and is immersed in a
homogenous and isotropic background radiation. Distribution of the temperature
in the fields and close-to Schwarzschild approximation of the solution are
studied. By identifying the radiation with the cosmic background one, we find
that the close-to-Schwarzschild approximate solution is valid in a wide range
in our solar system. Possible experimental tests of the solution are discussed
briefly.


title: Complexifier Coherent States for Quantum General Relativity

abstract:
  Recently, substantial amount of activity in Quantum General Relativity (QGR)
has focussed on the semiclassical analysis of the theory. In this paper we want
to comment on two such developments: 1) Polymer-like states for Maxwell theory
and linearized gravity constructed by Varadarajan which use much of the Hilbert
space machinery that has proved useful in QGR and 2) coherent states for QGR,
based on the general complexifier method, with built-in semiclassical
properties. We show the following: A) Varadarajan's states {\it are}
complexifier coherent states. This unifies all states constructed so far under
the general complexifier principle. B) Ashtekar and Lewandowski suggested a
non-Abelean generalization of Varadarajan's states to QGR which, however, are
no longer of the complexifier type. We construct a new class of non-Abelean
complexifiers which come close to the one underlying Varadarajan's
construction. C) Non-Abelean complexifiers close to Varadarajan's induce new
types of Hilbert spaces which do not support the operator algebra of QGR. The
analysis suggests that if one sticks to the present kinematical framework of
QGR and if kinematical coherent states are at all useful, then normalizable,
graph dependent states must be used which are produced by the complexifier
method as well. D) Present proposals for states with mildened graph dependence,
obtained by performing a graph average, do not approximate well coordinate
dependent observables. However, graph dependent states, whether averaged or
not, seem to be well suited for the semiclassical analysis of QGR with respect
to coordinate independent operators.


title:
Fake signals caused by heavy mass motions near a sensitive spherical
  gravitational wave antenna

abstract:
  This paper analyses in quantitative detail the effect caused by a moving mass
on a spherical gravitational wave detector. This applies to situations where
heavy traffic or similar disturbances happen near the GW antenna. Such
disturbances result in quadrupole tidal stresses in the antenna mass, and they
therefore precisely fake a real gravitational signal. The study shows that
there always are characteristic frequencies, depending on the motion of the
external masses, at which the fake signals are most intense. It however appears
that, even at those frequencies, fake signals should be orders of magnitude
below the sensitivity curve of an optimised detector, in likely realistic
situations.


title:
Four-dimensional anti-de Sitter black holes from a three-dimensional
  perspective: Full complexity

abstract:
  The dimensional reduction of black hole solutions in four-dimensional (4D)
general relativity is performed and new 3D black hole solutions are obtained.
Considering a 4D spacetime with one spacelike Killing vector, it is possible to
split the Einstein-Hilbert-Maxwell action with a cosmological term in terms of
3D quantities. Definitions of quasilocal mass and charges in 3D spacetimes are
reviewed. The analysis is then particularized to the toroidal charged rotating
anti-de Sitter black hole. The reinterpretation of the fields and charges in
terms of a three-dimensional point of view is given in each case, and the
causal structure analyzed.


title: Quantum field theory in curved space-time and the early Universe

abstract:
  New results on finite density of particle creation for nonconformal massive
scalar particles in Friedmann Universe as well as new counterterms in
dimensions higher than 5 are presented. Possible role of creation of superheavy
particles for explaining observable density of visible and dark matter is
discussed.


title: Gravitational Waves from Gravitational Collapse

abstract:
  Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.


title: Role of initial data in spherical collapse

abstract:
  We bring out here the role of initial data in causing the black hole and
naked singularity phases as the final end state of a continual gravitational
collapse. The collapse of a type I general matter field is considered, which
includes most of the known physical forms of matter. It is shown that given the
distribution of the density and pressure profiles at the initial surface from
which the collapse evolves, there is a freedom in choosing rest of the free
functions, such as the velocities of the collapsing shells, so that the end
state could be either a black hole or a naked singularity depending on this
choice. It is thus seen that it is the initial data that determines the end
state of spherical collapse in terms of these outcomes, and we get a good
picture of how these phases come about.


title:
Flashing Dark Matter-- Gamma-Ray Bursts from Relativistic Detonations of
  Electro-Dilaton Stars

abstract:
  We speculate that the universe is filled with stars composed of
electromagnetic and dilaton fields which are the sources of the powerful
gamma-ray bursts impinging upon us from all directions of the universe. We
calculate soliton-like solutions of these fields and show that their energy can
be converted into a relativistic plasma in an explosive way. As in classical
detonation theory the conversion proceeds by a relativistic self-similar
solution for a spherical detonation wave which extracts the energy from the
scalar field via a plasma in the wave front.


title:
Linear second-order differential equations for barotropic FRW
  cosmologies

abstract:
  Simple linear second-order differential equations have been written down for
FRW cosmologies with barotropic fluids by Faraoni. His results have been
extended by Rosu, who employed techniques belonging to nonrelativistic
supersymmetry to obtain time-dependent adiabatic indices. Further extensions
are presented here using the known connection between the linear second-order
differential equations and Dirac-like equations in the same supersymmetric
context. These extensions are equivalent to adding an imaginary part to the
adiabatic index which is proportional to the mass parameter of the Dirac
spinor. The natural physical interpretation of the imaginary part is related to
the particular dissipation and instabilities of the barotropic FRW
hydrodynamics that are introduced by means of this supersymmetric scheme


title:
Killing-Yano symmetry for a class of spacetimes admitting parallel null
  1-planes

abstract:
  A possible generalization of plane fronted waves with parallel rays
(gpp-wave) fall into a more general class of metrics admitting parallel null
1-planes. For gpp-wave metric, the zero-curvature condition is given, the
Killing-Yano tensors of order two and three are found and the corresponding
Killing tensors are constructed. Henceforth, the compatibility between
geometric duality and non-generic symmetries is presented.


title: Polar Perturbations of Self-gravitating Supermassive Global Monopoles

abstract:
  Spontaneous global symmetry breaking of O(3) scalar field gives rise to
point-like topological defects, global monopoles. By taking into account
self-gravity,the qualitative feature of the global monopole solutions depends
on the vacuum expectation value v of the scalar field. When v < sqrt{1 / 8 pi},
there are global monopole solutions which have a deficit solid angle defined at
infinity. When sqrt{1 / 8 pi} <= v < sqrt{3 / 8 pi}, there are global monopole
solutions with the cosmological horizon, which we call the supermassive global
monopole. When v >= sqrt{3 / 8 pi}, there is no nontrivial solution. It was
shown that all of these solutions are stable against the spherical
perturbations. In addition to the global monopole solutions, the de Sitter
solutions exist for any value of v. They are stable against the spherical
perturbations when v <= sqrt{3 / 8 pi}, while unstable for v > sqrt{3 / 8 pi}.
We study polar perturbations of these solutions and find that all
self-gravitating global monopoles are stable even against polar perturbations,
independently of the existence of the cosmological horizon, while the de Sitter
solutions are always unstable.


title:
A test of Einstein's theory of gravitation: Velocity distribution of
  low-energy particles in a spherically symmetric gravitational field

abstract:
  We propose a new test of Einstein's theory of gravitation. It concerns the
velocity distribution of low-energy particles in a spherically symmetric
gravitational field.


title: Odd statistics in odd dimensions for odd couplings

abstract:
  We consider the response of a uniformly accelerated monopole detector that is
coupled non-linearly to the nth power of a quantum scalar field in
(D+1)-dimensional flat spacetime. We show that, when (D+1) is even, the
response of the detector in the Minkowski vacuum is characterized by a
Bose-Einstein factor for all n. Whereas, when (D+1) is odd, we find that a
Fermi-Dirac factor appears in the detector response when n is odd, but a
Bose-Einstein factor arises when n is even. We emphasize the point that, since,
along the accelerated trajectory, the Wightman function and, as a result, the
(2n)-point function satisfy the Kubo-Martin-Schwinger condition (as required
for a scalar field) in all dimensions, the appearance of a Fermi-Dirac factor
(instead of the expected Bose-Einstein distribution) for odd (D+1) and n
reflects a peculiar feature of the detector rather than imply a fundamental
change in field theory.


title:
Conical Singular Solutions in (2+1)-Dimensional Gravity Employing the
  ADM Canonical Formalism

abstract:
  Topological solutions in the (2+1)-dimensional Einstein theory of gravity are
studied within the ADM canonical formalism. It is found that a conical
singularity appears in the closed de Sitter universe solution as a topological
defect in the case of the Einstein theory with a cosmological constant. Quantum
effects on the conical singularity are studied using the de Broglie-Bohm
interpretation. Finite quantum tunneling effects are obtained for the closed de
Sitter universe, while no quantum effects are obtained for an open universe.


title:
Early radiative properties of the developments of time symmetric,
  conformally flat initial data

abstract:
  Using a representation of spatial infinity based in the properties of
conformal geodesics, the first terms of an expansion for the Bondi mass for the
development of time symmetric, conformally flat initial data are calculated. As
it is to be expected, the Bondi mass agrees with the ADM at the sets where null
infinity ``touches'' spatial infinity. The second term in the expansion is
proportional to the sum of the squared norms of the Newman-Penrose constants of
the spacetime. In base of this result it is argued that these constants may
provide a measure of the incoming radiation contained in the spacetime. This is
illustrated by means of the Misner and Brill-Lindquist data sets.


title: Gravitational Waves from Neutron Stars with Large Toroidal B-fields

abstract:
  We show that NS's with large toroidal B-fields tend naturally to evolve into
potent gravitational-wave (gw) emitters. The toroidal field B_t tends to
distort the NS into a prolate shape, and this magnetic distortion can easily
dominate over the oblateness ``frozen into'' the NS crust. An elastic NS with
frozen-in B-field of this magnitude is clearly secularly unstable: the wobble
angle between the NS's angular momentum J^i and the star's magnetic axis n_B^i
grow on a dissipation timescale until J^i and n_B^i are orthogonal. This final
orientation is clearly the optimal one for gravitational-wave (gw) emission.
The basic cause of the instability is quite general, so we conjecture that the
same final state is reached for a realistic NS. Assuming this, we show that for
LMXB's with B_t of order 10^{13}G, the spindown from gw's is sufficient to
balance the accretion torque--supporting a suggestion by Bildsten. The spindown
rates of most millisecond pulsars can also be attributed to gw emission sourced
by toroidal B-fields, and both these sources could be observed by LIGO II.
While the first-year spindown of a newborn NS is most likely dominated by em
processes, reasonable values of B_t and the (external) dipolar field B_d can
lead to detectable levels of gw emission, for a newborn NS in our own galaxy.


title:
You Can't Get Through Szekeres Wormholes - or - Regularity, Topology and
  Causality in Quasi-Spherical Szekeres Models

abstract:
  The spherically symmetric dust model of Lemaitre-Tolman can describe
wormholes, but the causal communication between the two asymptotic regions
through the neck is even less than in the vacuum
(Schwarzschild-Kruskal-Szekeres) case. We investigate the anisotropic
generalisation of the wormhole topology in the Szekeres model. The function
E(r, p, q) describes the deviation from spherical symmetry if \partial_r E \neq
0, but this requires the mass to be increasing with radius, \partial_r M > 0,
i.e. non-zero density. We investigate the geometrical relations between the
mass dipole and the locii of apparent horizon and of shell-crossings. We
present the various conditions that ensure physically reasonable
quasi-spherical models, including a regular origin, regular maxima and minima
in the spatial sections, and the absence of shell-crossings. We show that
physically reasonable values of \partial_r E \neq 0 cannot compensate for the
effects of \partial_r M > 0 in any direction, so that communication through the
neck is still worse than the vacuum.
  We also show that a handle topology cannot be created by identifying
hypersufaces in the two asymptotic regions on either side of a wormhole, unless
a surface layer is allowed at the junction. This impossibility includes the
Schwarzschild-Kruskal-Szekeres case.


title: Quantization Ambiguities in Isotropic Quantum Geometry

abstract:
  Some typical quantization ambiguities of quantum geometry are studied within
isotropic models. Since this allows explicit computations of operators and
their spectra, one can investigate the effects of ambiguities in a quantitative
manner. It is shown that those ambiguities do not affect the fate of the
classical singularity, demonstrating that the absence of a singularity in loop
quantum cosmology is a robust implication of the general quantization scheme.
The calculations also allow conclusions about modified operators in the full
theory. In particular, using holonomies in a non-fundamental representation of
SU(2) to quantize connection components turns out to lead to significant
corrections to classical behavior at macroscopic volume for large values of the
spin of the chosen representation.


title: Inflation from Quantum Geometry

abstract:
  Quantum geometry predicts that a universe evolves through an inflationary
phase at small volume before exiting gracefully into a standard Friedmann
phase. This does not require the introduction of additional matter fields with
ad hoc potentials; rather, it occurs because of a quantum gravity modification
of the kinetic part of ordinary matter Hamiltonians. An application of the same
mechanism can explain why the present-day cosmological acceleration is so tiny.


title: Canonical quantization of general relativity in discrete space-times

abstract:
  It has long been recognized that lattice gauge theory formulations, when
applied to general relativity, conflict with the invariance of the theory under
diffeomorphisms. Additionally, the traditional lattice field theory approach
consists in fixing the gauge in a Euclidean action, which does not appear
appropriate for general relativity. We analyze discrete lattice general
relativity and develop a canonical formalism that allows to treat constrained
theories in Lorentzian signature space-times. The presence of the lattice
introduces a ``dynamical gauge'' fixing that makes the quantization of the
theories conceptually clear, albeit computationally involved. Among other
issues the problem of a consistent algebra of constraints is automatically
solved in our approach. The approach works successfully in other field theories
as well, including topological theories like BF theory. We discuss a simple
cosmological application that exhibits the quantum elimination of the
singularity at the big bang.


title:
Quantum phase shift and neutrino oscillations in a stationary, weak
  gravitational field

abstract:
  A new method based on Synge's world function is developed for determining
within the WKB approximation the gravitationally induced quantum phase shift of
a particle propagating in a stationary spacetime. This method avoids any
calculation of geodesics. A detailed treatment is given for relativistic
particles within the weak field, linear approximation of any metric theory. The
method is applied to the calculation of the oscillation terms governing the
interference of neutrinos considered as a superposition of two eigenstates
having different masses. It is shown that the neutrino oscillations are not
sensitive to the gravitomagnetic components of the metric as long as the spin
contributions can be ignored. Explicit calculations are performed when the
source of the field is a spherical, homogeneous body. A comparison is made with
previous results obtained in Schwarzschild spacetime.


title: Geometrization of perfect fluid in 5-D Kaluza-Klein theory

abstract:
  General formulation of geometrization matter problem by scalar field $\phi
=\sqrt{-G_{55}}$ with the help of possibilities of classical 5-D Kaluza-Klein
theory is given. Mathematical integrability conditions for such geometrization
for the case of perfect fluid are derived.


title:
Time at the origin of the Universe: fluctuations between two
  possibilities

abstract:
  A variation of Hawking's idea about Euclidean origin of a nonsingular birth
of the Universe is considered. It is assumed that near to zero moment $t = 0$
fluctuations of a metric signature are possible.


title: Gravitational Radiation Damping and the Three-Body Problem

abstract:
  A model of three-body motion is developed which includes the effects of
gravitational radiation reaction. The radiation reaction due to the emission of
gravitational waves is the only post-Newtonian effect that is included here.
For simplicity, all of the motion is taken to be planar. Two of the masses are
viewed as a binary system and the third mass, whose motion will be a fixed
orbit around the center-of-mass of the binary system, is viewed as a
perturbation. This model aims to describe the motion of a relativistic binary
pulsar that is perturbed by a third mass. Numerical integration of this
simplified model reveals that given the right initial conditions and parameters
one can see resonances. These (m,n) resonances are defined by the resonance
condition, $m\omega=2n\Omega$, where $m$ and $n$ are relatively prime integers
and $\omega$ and $\Omega$ are the angular frequencies of the binary orbit and
third mass orbit, respectively. The resonance condition consequently fixes a
value for the semimajor axis of the binary orbit for the duration of the
resonance; therefore, the binary energy remains constant on the average while
its angular momentum changes during the resonance.


title:
Resonance Behavior and Partial Averaging in a Three-Body System with
  Gravitational Radiation Damping

abstract:
  In a previous investigation, a model of three-body motion was developed which
included the effects of gravitational radiation reaction. The aim was to
describe the motion of a relativistic binary pulsar that is perturbed by a
third mass and look for resonances between the binary and third mass orbits.
Numerical integration of an equation of relative motion that approximates the
binary gives evidence of such resonances. These $(m:n)$ resonances are defined
for the present purposes by the resonance condition, $m\omega=2n\Omega$, where
$m$ and $n$ are relatively prime integers and $\omega$ and $\Omega$ are the
angular frequencies of the binary orbit and third mass orbit, respectively. The
resonance condition consequently fixes a value for the semimajor axis $a$ of
the binary orbit for the duration of the resonance because of the Kepler
relationship $\omega=a^{-3/2}$. This paper outlines a method of averaging
developed by Chicone, Mashhoon, and Retzloff which renders a nonlinear system
that undergoes resonance capture into a mathematically amenable form. This
method is applied to the present system and one arrives at an analytical
solution that describes the average motion during resonance. Furthermore,
prominent features of the full nonlinear system, such as the frequency of
oscillation and antidamping, accord with their analytically derived formulae.


title: The Weyl tensor in Spatially Homogeneous Cosmological Models

abstract:
  We study the evolution of the Weyl curvature invariant in all spatially
homogeneous universe models containing a non-tilted gamma-law perfect fluid. We
investigate all the Bianchi and Thurston type universe models and calculate the
asymptotic evolution of Weyl curvature invariant for generic solutions to the
Einstein field equations. The influence of compact topology on Bianchi types
with hyperbolic space sections is also considered. Special emphasis is placed
on the late-time behaviour where several interesting properties of the Weyl
curvature invariant occur. The late-time behaviour is classified into five
distinctive categories. It is found that for a large class of models, the
generic late-time behaviour the Weyl curvature invariant is to dominate the
Ricci invariant at late times. This behaviour occurs in universe models which
have future attractors that are plane-wave spacetimes, for which all scalar
curvature invariants vanish. The overall behaviour of the Weyl curvature
invariant is discussed in relation to the proposal that some function of the
Weyl tensor or its invariants should play the role of a gravitational 'entropy'
for cosmological evolution. In particular, it is found that for all
ever-expanding models the measure of gravitational entropy proposed by Gron and
Hervik increases at late times.


title: Stochastic backgrounds of gravitational waves and spherical detectors

abstract:
  The analysis of how a stochastic background of gravitational radiation
interacts with a spherical detector is given in detail, which leads to explicit
expressions for the system response functions, as well as for the
cross-correlation matrix of different readout channels. It is shown that
distinctive features of GW induced random detector excitations, relative to
locally generated noise, are in practice insufficient to separate the signal
from the noise by means of a single sphere, if prior knowledge on the GW
spectral density is nil. The situation significantly improves when such
previous knowledge is available, due to the omnidirectionality and multimode
capacities of a spherical GW antenna.


title: Epicyclic orbital oscillations in Newton's and Einstein's dynamics

abstract:
  We apply Feynman's principle, ``The same equations have the same solutions'',
to Kepler's problem and show that Newton's dynamics in a properly curved 3-D
space is identical with that described by Einstein's theory in the 3-D optical
geometry of Schwarzschild's spacetime. For this reason, rather unexpectedly,
Newton's formulae for Kepler's problem, in the case of nearly circular motion
in a static, spherically spherical gravitational potential accurately describe
strong field general relativistic effects, in particular vanishing of the
radial epicyclic frequency at the marginally stable orbit.


title: Holography and the Cosmic Coincidence

abstract:
  Based on an analysis of the entropy associated to the vacuum quantum
fluctuations, we show that the holographic principle, applied to the cosmic
scale, constitutes a possible explanation for the observed value of the
cosmological constant, theoretically justifying a relation proposed 35 years
ago by Zel'dovich. Furthermore, extending to the total energy density the
conjecture by Chen and Wu, concerning the dependence of the cosmological
constant on the scale factor, we show that the holographic principle may also
lie at the root of the coincidence between the matter density in the universe
and the vacuum energy density.


title: Quantum stabilization of dilatonic Anti-de Sitter Universe

abstract:
  The possibility of quantum creation of a dilatonic AdS Universe is
discussed.Without dilaton it is known that quantum effects lead to the
annihilation of AdS Universe. We consider the role of the form for the
dilatonic potential in the quantum creation of a dilatonic AdS Universe. Using
the conformal anomaly for dilaton coupled scalar, the anomaly induced action
and the equations of motion are obtained. The anomaly induced action is added
to classical dilaton gravity action. The solutions of the full theory which
correspond to quantum-corrected AdS Universe are given for number of dilatonic
potentials.


title: Quantum interest in two dimensions

abstract:
  The quantum interest conjecture of Ford and Roman asserts that any
negative-energy pulse must necessarily be followed by an over-compensating
positive-energy one within a certain maximum time delay. Furthermore, the
minimum amount of over-compensation increases with the separation between the
pulses. In this paper, we first study the case of a negative-energy square
pulse followed by a positive-energy one for a minimally coupled, massless
scalar field in two-dimensional Minkowski space. We obtain explicit expressions
for the maximum time delay and the amount of over-compensation needed, using a
previously developed eigenvalue approach. These results are then used to give a
proof of the quantum interest conjecture for massless scalar fields in two
dimensions, valid for general energy distributions.


title: Area Regge calculus and continuum limit

abstract:
  Encountered in the literature generalisations of general relativity to
independent area variables are considered, the discrete (generalised Regge
calculus) and continuum ones. The generalised Regge calculus can be either with
purely area variables or, as we suggest, with area tensor-connection variables.
Just for the latter, in particular, we prove that in analogy with corresponding
statement in ordinary Regge calculus (by Feinberg, Friedberg, Lee and Ren),
passing to the (appropriately defined) continuum limit yields the generalised
continuum area tensor-connection general relativity.


title: Large Universe as the initial condition for a Collapsing Universe

abstract:
  Using the extension of the standard Hawking-Hartle prescription for defining
a wave function for the universe, we show that it is possible, given a suitable
form for the scalar field potential, to have the universe begin at its largest
size and thereafter contract, with the growth of perturbations proceeding from
small, at the largest size, to largest when the universe is small. This
solution would dominate the wave function by an exponentially large amount if
one chooses the Hartle Hawking prescription for the wave-function, but is
exponentially sub-dominant for the Linde-Vilenkin prescription.


title: The Einstein-Vlasov sytem/Kinetic theory

abstract:
  The main purpose of this article is to guide the reader to theorems on global
properties of solutions to the Einstein-Vlasov system. This system couples
Einstein's equations to a kinetic matter model. Kinetic theory has been an
important field of research during several decades where the main focus has
been on nonrelativistic- and special relativistic physics, e.g. to model the
dynamics of neutral gases, plasmas and Newtonian self-gravitating systems. In
1990 Rendall and Rein initiated a mathematical study of the Einstein-Vlasov
system. Since then many theorems on global properties of solutions to this
system have been established. The Vlasov equation describes matter
phenomenologically and it should be stressed that most of the theorems
presented in this article are not presently known for other such matter models
(e.g. fluid models). The first part of this paper gives an introduction to
kinetic theory in non-curved spacetimes and then the Einstein-Vlasov system is
introduced. We believe that a good understanding of kinetic theory in
non-curved spacetimes is fundamental in order to get a good comprehension of
kinetic theory in general relativity.


title: Three Dimensional Distorted Black Holes

abstract:
  We present three-dimensional, {\it non-axisymmetric} distorted black hole
initial data which generalizes the axisymmetric, distorted, non-rotating
[Bernstein93a] and rotating [Brandt94a] single black hole data developed by
Bernstein, Brandt, and Seidel. These initial data should be useful for studying
the dynamics of fully 3D, distorted black holes, such as those created by the
spiraling coalescence of two black holes. We describe the mathematical
construction of several families of such data sets, and show how to construct
numerical solutions. We survey quantities associated with the numerically
constructed solutions, such as ADM masses, apparent horizons, measurements of
the horizon distortion, and the maximum possible radiation loss ($MRL$).


title: Perturbative Quantum Gravity and its Relation to Gauge Theory

abstract:
  In this review we describe a non-trivial relationship between perturbative
gauge theory and gravity scattering amplitudes. At the semi-classical or tree
level, the scattering amplitudes of gravity theories in flat space can be
expressed as a sum of products of well defined pieces of gauge theory
amplitudes. These relationships were first discovered by Kawai, Lewellen and
Tye in the context of string theory, but hold more generally. In particular,
they hold for standard Einstein gravity. A method based on D-dimensional
unitarity can then be used to systematically construct all quantum loop
corrections order-by-order in perturbation theory using as input the gravity
tree amplitudes expressed in terms of gauge theory ones. More generally, the
unitarity method provides a means for perturbatively quantizing massless
gravity theories without the usual formal apparatus associated with the
quantization of constrained systems. As one application, this method was used
to demonstrate that maximally supersymmetric gravity is less divergent in the
ultraviolet than previously thought.


title:
Gauge conditions for long-term numerical black hole evolutions without
  excision

abstract:
  Numerical relativity has faced the problem that standard 3+1 simulations of
black hole spacetimes without singularity excision and with singularity
avoiding lapse and vanishing shift fail after an evolution time of around
30-40M due to the so-called slice stretching. We discuss lapse and shift
conditions for the non-excision case that effectively cure slice stretching and
allow run times of 1000M and more.


title:
A new proposal for measuring the Lense-Thirring effect with a pair of
  supplementary satellites in the gravitational field of the Earth

abstract:
  In this letter we further analyze the concept of the use of a pair of
identical geodetic satellites placed in identical orbits except for the
inclinations which should be supplementary for measuring the Lense-Thirring
effect in the terrestrial gravitational field. It turns out that not only the
sum of the nodes, as already proposed for the LAGEOS-LARES mission, but also
the difference of the perigees could be fruitfully adopted.


title:
On a new observable for measuring the Lense-Thirring effect with
  Satellite Laser Ranging

abstract:
  In this paper we present a rather extensive error budget for the difference
of the perigees of a pair of supplementary SLR satellites aimed to the
detection of the Lense-Thirring effect.


title:
The characteristic initial value problem for colliding plane waves: The
  linear case

abstract:
  The physical situation of the collision and subsequent interaction of plane
gravitational waves in a Minkowski background gives rise to a well-posed
characteristic initial value problem in which initial data are specified on the
two null characteristics that define the wavefronts. In this paper, we analyse
how the Abel transform method can be used in practice to solve this problem for
the linear case in which the polarization of the two gravitational waves is
constant and aligned. We show how the method works for some known solutions,
where problems arise in other cases, and how the problem can always be solved
in terms of an infinite series if the spectral functions for the initial data
can be evaluated explicitly.


title:
Spherically symmetric models for charged radiating stars and voids:
  Theoretical approach

abstract:
  We study the matching of a general spherically symmetric spacetime with a
Vaidya-Reissner-Nordstrom solution. To that end, we study the properties of
spherically symmetric electromagnetic fields and develop the proper
gravitational and electromagnetic junction conditions. We prove that generic
spacetimes can be matched to a Vaidya-Reissner-Nordstrom solution or one of its
specializations, and that these matchings have clear physical interpretations.
Furthermore, the non-spacelike nature of the matching hypersurface is proved
under very general hypotheses. We obtain the fundamental result that any
spherically symmetric body, be it in evolution or not, has un upper limit for
the total net electric charge that carries.


title: The modular geometry of Random Regge Triangulations

abstract:
  We show that the introduction of triangulations with variable connectivity
and fluctuating egde-lengths (Random Regge Triangulations) allows for a
relatively simple and direct analyisis of the modular properties of 2
dimensional simplicial quantum gravity. In particular, we discuss in detail an
explicit bijection between the space of possible random Regge triangulations
(of given genus g and with N vertices) and a suitable decorated version of the
(compactified) moduli space of genus g Riemann surfaces with N punctures. Such
an analysis allows us to associate a Weil-Petersson metric with the set of
random Regge triangulations and prove that the corresponding volume provides
the dynamical triangulation partition function for pure gravity.


title: Time, Closed Timelike Curves and Causality

abstract:
  General Relativity is contaminated with non-trivial geometries which generate
closed timelike curves. These apparently violate causality, producing
time-travel paradoxes. We shall briefly discuss these geometries and analyze
some of their physical aspects.


title:
Effect of cosmic rays on the resonant gravitational wave detector
  NAUTILUS at temperature T=1.5 K

abstract:
  The interaction between cosmic rays and the gravitational wave bar detector
NAUTILUS is experimentally studied with the aluminum bar at temperature of
T=1.5 K. The results are compared with those obtained in the previous runs when
the bar was at T=0.14 K. The results of the run at T = 1.5 K are in agreement
with the thermo-acoustic model; no large signals at unexpected rate are
noticed, unlike the data taken in the run at T = 0.14 K. The observations
suggest a larger efficiency in the mechanism of conversion of the particle
energy into vibrational mode energy when the aluminum bar is in the
superconductive status.


title: Shear-free rotating inflation

abstract:
  We demonstrate the existence of shear-free cosmological models with rotation
and expansion which support the inflationary scenarios. The corresponding
metrics belong to the family of spatially homogeneous models with the geometry
of the closed universe (Bianchi type IX). We show that the global vorticity
does not prevent the inflation and even can accelerate it.


title: Unequal arm space-borne gravitational wave detectors

abstract:
  Unlike ground-based interferometric gravitational wave detectors, large
space-based systems will not be rigid structures. When the end-stations of the
laser interferometer are freely flying spacecraft, the armlengths will change
due to variations in the spacecraft positions along their orbital trajectories,
so the precise equality of the arms that is required in a laboratory
interferometer to cancel laser phase noise is not possible. However, using a
method discovered by Tinto and Armstrong, a signal can be constructed in which
laser phase noise exactly cancels out, even in an unequal arm interferometer.
We examine the case where the ratio of the armlengths is a variable parameter,
and compute the averaged gravitational wave transfer function as a function of
that parameter. Example sensitivity curve calculations are presented for the
expected design parameters of the proposed LISA interferometer, comparing it to
a similar instrument with one arm shortened by a factor of 100, showing how the
ratio of the armlengths will affect the overall sensitivity of the instrument.


title: Length measurement in accelerated systems

abstract:
  We investigate the limitations of length measurements by accelerated
observers in Minkowski spacetime brought about via the hypothesis of locality,
namely, the assumption that an accelerated observer at each instant is
equivalent to an otherwise identical momentarily comoving inertial observer. We
find that consistency can be achieved only in a rather limited neighborhood
around the observer with linear dimensions that are negligibly small compared
to the characteristic acceleration length of the observer.


title: Quantum Dynamics of the Polarized Gowdy Model

abstract:
  The polarized Gowdy ${\bf T}^3$ vacuum spacetimes are characterized, modulo
gauge, by a ``point particle'' degree of freedom and a function $\phi$ that
satisfies a linear field equation and a non-linear constraint. The quantum
Gowdy model has been defined by using a representation for $\phi$ on a Fock
space $\cal F$. Using this quantum model, it has recently been shown that the
dynamical evolution determined by the linear field equation for $\phi$ is not
unitarily implemented on $\cal F$. In this paper: (1) We derive the classical
and quantum model using the ``covariant phase space'' formalism. (2) We show
that time evolution is not unitarily implemented even on the physical Hilbert
space of states ${\cal H} \subset {\cal F}$ defined by the quantum constraint.
(3) We show that the spatially smeared canonical coordinates and momenta as
well as the time-dependent Hamiltonian for $\phi$ are well-defined,
self-adjoint operators for all time, admitting the usual probability
interpretation despite the lack of unitary dynamics.


title:
Coincidence of large numbers, exact value of cosmological parameters and
  their analytical representation

abstract:
  A new approach to the phenomenon of large numbers coincidence leads to
unexpected results. No matter how strange it might sound, the exact value of
cosmological parameters and their analytical expression through fundamental
constants have been founded. The basis for obtaining these unusual results is
the equality of the fundamental Large Number to the exponent of the inverse
value of the fine structure constant.


title: Cosmology with positive and negative exponential potentials

abstract:
  We present a phase-plane analysis of cosmologies containing a scalar field
$\phi$ with an exponential potential $V \propto \exp(-\lambda \kappa \phi)$
where $\kappa^2 = 8\pi G$ and $V$ may be positive or negative. We show that
power-law kinetic-potential scaling solutions only exist for sufficiently flat
($\lambda^2<6$) positive potentials or steep ($\lambda^2>6$) negative
potentials. The latter correspond to a class of ever-expanding cosmologies with
negative potential. However we show that these expanding solutions with a
negative potential are to unstable in the presence of ordinary matter, spatial
curvature or anisotropic shear, and generic solutions always recollapse to a
singularity. Power-law kinetic-potential scaling solutions are the late-time
attractor in a collapsing universe for steep negative potentials (the ekpyrotic
scenario) and stable against matter, curvature or shear perturbations.
Otherwise kinetic-dominated solutions are the attractor during collapse (the
pre big bang scenario) and are only marginally stable with respect to
anisotropic shear.


title:
What role pressures play to determine the final end-state of
  gravitational collapse?

abstract:
  We examine here in what way the pressures affect the final fate of a
continual gravitational collapse. It is shown that the presence of a
non-vanishing pressure gradient in the collapsing cloud determines directly the
epoch of formation of trapped surfaces and the apparent horizon, thus changing
the causal structure in the vicinity of singularity.


title: Cosmic Censorship: A Current Perspective

abstract:
  End state of gravitational collapse and the related cosmic censorship
conjecture continue to be amongst the most important open problems in
gravitation physics today. My purpose here is to bring out several aspects
related to gravitational collapse and censorship, which may help towards a
better understanding of the issues involved. Possible physical constraints on
gravitational collapse scenarios are considered. It is concluded that the best
hope for censorship lies in analyzing the genericity and stability properties
of the currently known classes of collapse models which lead to the formation
of naked singularities, rather than black holes, as the final state of collapse
and which develop from a regular initial data.


title:
Fundamental equations for the gravitational and electromagnetic
  perturbations of a charged black hole

abstract:
  A pair of wave equations is presented for the gravitational and
electromagnetic perturbations of a charged black hole. One of the equations is
uncoupled and determines the propagation of the electromagnetic perturbation.
The other is for the propagation of the shear of a principal null direction and
has a source term given by the solution of the first equation. This result is
expected to have important applications in astrophysical models.


title:
Variation of G, $\Lambda_{(4)}$ and Vacuum Energy From Brane-World
  Models

abstract:
  In brane-world theory in five dimensions, the bulk metric is usually written
in gaussian coordinates, where $g_{4\mu} = 0$ and $g_{44} = - 1$. However, the
choice $g_{44} = - 1$ is an external condition, not a requirement of the field
equations. In this paper we study the consequences of having $g_{44} = \epsilon
\Phi^2$, where $\epsilon = \pm 1$ and $\Phi$ is a scalar function varying with
time, $\dot{\Phi} \neq 0$. This varying field entails the possibility of
variable fundamental physical "constants". These variations are different from
those predicted in scalar-tensor and multidimensional theories. We solve the
five-dimensional equations for a {\em fixed} brane and use the brane-world
paradigm to determine the fundamental parameters in the theory, which are the
vacuum energy $\sigma$, the gravitational coupling $G$ and the cosmological
term $\Lambda_{(4)}$. We present specific models where these physical
quantities are variable functions of time. Different scenarios are possible but
we discuss with some detail a model for which $\dot{G}/G \sim H$ and
$\Lambda_{(4)} \sim H^2$, which seems to be favored by observations. Our
results are not in contradiction to previous ones in the literature. In
particular, to those where the brane is described as a domain wall moving in a
static $Sch-AdS$ bulk. Indeed these latter models in RS scenarios describe the
same spacetime as other solutions (with fixed brane) in gaussian coordinates
with $\dot{\Phi} = 0 $. We conclude that the introduction of a time-varying
$\Phi$ in brane-world theory yields a number of models that show variation in
the fundamental physical "constants" and exhibit reasonable physical
properties.


title:
Bianchi - Euler system for relativistice fluids and Bel - Robinson type
  energy

abstract:
  We write a first order symmetric hyperbolic system coupling the Riemann with
the dynamical acceleration of a relativistic fluid. W determine the associated,
coupled, Bel - Robinson energy, and the integral equality that it satisfies.


title:
Dirac spinors for Doubly Special Relativity and $\kappa$-Minkowski
  noncommutative spacetime

abstract:
  We construct a Dirac equation that is consistent with one of the
recently-proposed schemes for a "doubly-special relativity", a relativity with
both an observer-independent velocity scale (still naturally identified with
the speed-of-light constant) and an observer-independent length/momentum scale
(possibly given by the Planck length/momentum). We find that the introduction
of the second observer-independent scale only induces a mild deformation of the
structure of Dirac spinors. We also show that our modified Dirac equation
naturally arises in constructing a Dirac equation in the kappa-Minkowski
noncommutative spacetime. Previous, more heuristic, studies had already argued
for a possible role of doubly-special relativity in kappa-Minkowski, but
remained vague on the nature of the consistency requirements that should be
implemented in order to assure the observer-independence of the two scales. We
find that a key role is played by the choice of a differential calculus in
kappa-Minkowski. A much-studied choice of the differential calculus does lead
to our doubly-special relativity Dirac equation, but a different scenario is
encountered for another popular choice of differential calculus.


title:
Fermions, bosons, and locality in special relativity with two invariant
  scales

abstract:
  We present a Master equation for description of fermions and bosons for
special relativities with two invariant scales (c and lambda_P). We introduce
canonically-conjugate variables (chi^0, chi) to (epsilon, pi) of Judes-Visser.
Together, they bring in a formal element of linearity and locality in an
otherwise non-linear and non-local theory. Special relativities with two
invariant scales provide all corrections, say, to the standard model of the
high energy physics, in terms of one fundamental constant, lambda_P. It is
emphasized that spacetime of special relativities with two invariant scales
carries an intrinsic quantum-gravitational character.


title: On some gravitomagnetic spin-spin effects for astronomical bodies

abstract:
  In this paper we look at the gravitational spin--spin interaction between
macroscopic astronomical bodies. In particular, we calculate their
post--Newtonian orbital effects of order $\mathcal{O}(c^{-2})$ on the
trajectory of a spinning particle with proper angular momentum ${\bf s}$ moving
in the external gravitomagnetic field generated by a central spinning mass with
proper angular momentum ${\bf J}$. It turns out that, at order $\mathcal{O}(e)$
in the orbiter's eccentricity, the eccentricity the pericenter and the mean
anomaly rates of the moving particle are affected by long--term harmonic
effects. If, on one hand, they are undetectable in the Solar System, on the
other, maybe that in an astrophysical context like that of the binary
millisecond pulsars there will be some hopes of measuring them in the future.


title:
Screening the graviton background, graviton pairing, and Newtonian
  gravity

abstract:
  It is shown that screening the background of super-strong interacting
gravitons creates for any pair of bodies as an attraction force as well an
repulsion force due to pressure of gravitons. For single gravitons, these
forces are approximately balanced, but each of them is much bigger than a force
of Newtonian attraction. If single gravitons are pairing, a body attraction
force due to pressure of such graviton pairs is twice exceeding a corresponding
repulsion force under the condition that graviton pairs are destructed by
collisions with a body. If the considered quantum mechanism of classical
gravity is realized in the nature, then an existence of black holes contradicts
to Einstein's equivalence principle. In such the model, Newton's constant is
proportional to $H^{2}/T^{4},$ where $H$ is the Hubble constant, $T$ is an
equivalent temperature of the graviton background. The estimate of the Hubble
constant is obtained $H=2.14 \cdot 10^{-18} s^{-1}$ (or $66.875 km \cdot s^{-1}
\cdot Mpc^{-1}$).


title:
Stueckelberg Redux: How Classical Gravity Can Induce Changes in Particle
  Lifetimes

abstract:
  ECG Stueckelberg (1905-1984) often published important theories years before
those who would receive the Nobel Prize for their discoery. Perhpas other
jewels may remain the work of this prescient genius. In a short paper in
1957--coming shortly on the heels of the suggestion and experimental
confirmation of parity non-conservation by the weak force--Stueckelberg noted
that sine there exist completely antisymmetric four-tensors (e) with covariant
derivative zero, non-parity conserving forces can readily be accomodated by
general relativity as the product of such a tensor and the non-parity
conserving terms. Stueckelberg also pointed out that in classical general
relativity the covariant derivative, D, of e is De=(-g)^1/2*d[e(-g)^-1/2]=0,
where g is the determinant of the metric tensor, and d is an ordinary
derivative. Since g is non-zero, if g is constant, e is a constant and mean
proper particle lifetimes are the same in all Lorenz frames. I point out that
Stueckelberg's paper has three further deep and important implications. (1) We
see how gravity-- matter--can influence particle lifetimes by forcing the e
tensor to be non-constant to have to "adjust" so that d[e(-g)^-1/2] is zero,
and we can get some quantitative feel for the magnitude of this effect. (2) If
any difference in the lifetimes of particles and antiparticles are to occur, in
the absence of Lorenz invariance violation, it would be in regions where dg is
non-zero. (3) If indeed, differences in particle and antiparticle lifetimes are
found, before they can be ascibed to effects of quantum gravity, supersymmetry,
or string theory, the effects of classical gravity need to be accounted for.


title: Bulk Fermion Stars with New Dimensions

abstract:
  Many efforts have been devoted to the studies of the phenomenology in
particle physics with extra dimensions. We propose degenerate fermion stars
with extra dimensions and study what features characterized by the size of
extra dimensions should appear in its structure. We find that Kaluza-Klein
excited modes arise for the larger scale of extra dimensions and examine the
conditions on which different layers should be caused in the inside of the
stars. We expound how the extra dimensions affect on physical quantities.


title:
The radial infall of a highly relativistic point particle into a Kerr
  black hole along the symmetry axis

abstract:
  In this Letter we consider the radial infall along the symmetry axis of an
ultra-relativistic point particle into a rotating Kerr black hole. We use the
Sasaki-Nakamura formalism to compute the waveform, energy spectra and total
energy radiated during this process. We discuss possible connections between
these results and the black hole-black hole collision at the speed of light
process.


title: The fields of uniformly accelerated charges in de Sitter spacetime

abstract:
  The scalar and electromagnetic fields of charges uniformly accelerated in de
Sitter spacetime are constructed. They represent the generalization of the Born
solutions describing fields of two particles with hyperbolic motion in flat
spacetime. In the limit Lambda -> 0, the Born solutions are retrieved. Since in
the de Sitter universe the infinities I^+- are spacelike, the radiative
properties of the fields depend on the way in which a given point of I^+- is
approached. The fields must involve both retarded and advanced effects: Purely
retarded fields do not satisfy the constraints at the past infinity I^-.


title:
Binary black hole initial data for numerical general relativity based on
  post-Newtonian data

abstract:
  With the goal of taking a step toward the construction of astrophysically
realistic initial data for numerical simulations of black holes, we for the
first time derive a family of fully general relativistic initial data based on
post-2-Newtonian expansions of the 3-metric and extrinsic curvature without
spin. It is expected that such initial data provide a direct connection with
the early inspiral phase of the binary system. We discuss a straightforward
numerical implementation, which is based on a generalized puncture method.
Furthermore, we suggest a method to address some of the inherent ambiguity in
mapping post-Newtonian data onto a solution of the general relativistic
constraints.


title: Qualitative Analysis of Universes with Varying Alpha

abstract:
  Assuming a Friedmann universe which evolves with a power-law scale factor,
$a=t^{n}$, we analyse the phase space of the system of equations that describes
a time-varying fine structure 'constant', $\alpha$, in the
Bekenstein-Sandvik-Barrow-Magueijo generalisation of general relativity. We
have classified all the possible behaviours of $\alpha (t)$ in ever-expanding
universes with different $n$ and find new exact solutions for $\alpha (t)$. We
find the attractors points in the phase space for all $n$. In general, $\alpha
$ will be a non-decreasing function of time that increases logarithmically in
time during a period when the expansion is dust dominated ($n=2/3$), but
becomes constant when $n>2/3$. This includes the case of negative-curvature
domination ($n=1$). $\alpha $ also tends rapidly to a constant when the
expansion scale factor increases exponentially. A general set of conditions is
established for $\alpha $ to become asymptotically constant at late times in an
expanding universe.


title: Rigidly rotating cylinders of charged dust

abstract:
  The gravitational field of a rigidly rotating cylinder of charged dust is
found analytically. The general and all regular solutions are divided into
three classes. The acceleration and the vorticity of the dust are given, as
well as the conditions for the appearance of closed timelike curves.


title: Removal of Closed Timelike Curves in Kerr-Newman Spacetime

abstract:
  A simple yet systematic new algorithm to investigate the global structure of
Kerr-Newman spacetime is suggested. Namely, the global structure of
\theta=const. timelike submanifolds of Kerr-Newman metric are studied by
introducing a new time coordinate slightly different from the usual
Boyer-Lindquist time coordinate. In addition, it is demonstrated that the
possible causality violation thus far regarded to occur near the ring
singularity via the development of closed timelike curves there is not really
an unavoidable pathology which has plagued the Kerr-Newman solution but simply
a gauge (coordinate) artifact as it disappears upon transforming from
Boyer-Lindquist to the new time coordinate. This last point appears to lend
support to the fact that, indeed, the Kerr-Newman spacetime is a legitimate
solution to represent the interior as well as the exterior regions of a
rotating, charged black hole spacetime.


title:
The CWKB approach to non-reflecting potential and cosmological
  implications

abstract:
  We discuss the method of calculating the reflection coefficient using complex
trajectory WKB (CWKB) approximation. This enables us to give an interpretation
of non-reflecting nature of the potential under certain conditions and clarify
some points, reported incorrectly elsewhere [vs:ejp] for the potential
$U(x)=-U_0cosh^2(x/a)$. We show that the repeated reflectios between the
turning points are essential, which most authors overlooked, in obtaining the
non-reflecting c ondition. We find that the considered repeated reflection
paths are in conformity with Bogolubov transformation technique. We discuss the
implications of the results when applied to the particle production scenario,
considering $x$ as a time variable and also stress the cosmological
implications of the result with reference to radiation domonated and de Sitter
spacetime.


title: Gravitational Waves from Spinning Compact Binaries

abstract:
  Binary systems of rapidly spinning compact objects, such as black holes or
neutron stars, are prime targets for gravitational wave astronomers. The
dynamics of these systems can be very complicated due to spin-orbit and
spin-spin couplings. Contradictory results have been presented as to the nature
of the dynamics. Here we confirm that the dynamics - as described by the second
post-Newtonian approximation to general relativity - is chaotic, despite claims
to the contrary. When dissipation due to higher order radiation reaction terms
are included, the chaos is dampened. However, the inspiral-to-plunge transition
that occurs toward the end of the orbital evolution does retain an imprint of
the chaotic behaviour.


title: A model of gravitation with global U(1)-symmetry

abstract:
  It is shown that an embedding of the general relativity $4-$space into a flat
$12-$space gives a model of gravitation with the global $U(1)-$symmetry and the
discrete $D_{1}-$one. The last one may be transformed into the $SU(2)-$symmetry
of the unified model, and the demand of independence of $U(1)-$ and
$SU(2)-$transformations leads to the estimate $\sin^{2}\theta_{min}=0,20$ where
$\theta_{min}$ is an analog of the Weinberg angle of the standard model.


title: Convergence and stability in numerical relativity

abstract:
  It is often the case in numerical relativity that schemes that are known to
be convergent for well posed systems are used in evolutions of weakly
hyperbolic (WH) formulations of Einstein's equations. Here we explicitly show
that with several of the discretizations that have been used through out the
years, this procedure leads to non-convergent schemes. That is, arbitrarily
small initial errors are amplified without bound when resolution is increased,
independently of the amount of numerical dissipation introduced. The lack of
convergence introduced by this instability can be particularly subtle, in the
sense that it can be missed by several convergence tests, especially in 3+1
dimensional codes. We propose tests and methods to analyze convergence that may
help detect these situations.


title:
Long-wavelength Cosmological Perturbation in the Universe with Multiple
  Perfect Fluids

abstract:
  We investigate the large scale cosmological perturbation in the Universe with
multiple perfect fluids. Using the long-wavelength approximation with
Hamilton-Jacobi method, we derive the formula for the gauge invariant comoving
curvature perturbation. As an application of our approach, we examine the large
scale perturbation in a brane cosmology.


title: Comment on "Ruling out chaos in compact binary systems"

abstract:
  In a recent Letter, Schnittman and Rasio argue that they have ruled out chaos
in compact binary systems since they find no positive Lyapunov exponents. In
stark constrast, we find that the chaos discovered in the original paper under
discussion, J.Levin, PRL, 84 3515 (2000), is confirmed by the presence of
positive Lyapunov exponents.


title:
A comparison of search templates for gravitational waves from binary
  inspiral - 3.5PN update

abstract:
  Phasing formulas in a recent paper of ours' (Phys. Rev. D 63, 044023-1 (2001)
are updated taking into account the recent 3.5PN results. Some misprints in the
published version of the recent paper are also corrected.


title:
Global behavior of solutions to the static spherically symmetric EYM
  equations

abstract:
  The set of all possible spherically symmetric magnetic static
Einstein-Yang-Mills field equations for an arbitrary compact semi-simple gauge
group $G$ was classified in two previous papers. Local analytic solutions near
the center and a black hole horizon as well as those that are analytic and
bounded near infinity were shown to exist. Some globally bounded solutions are
also known to exist because they can be obtained by embedding solutions for the
$G=SU(2)$ case which is well understood. Here we derive some asymptotic
properties of an arbitrary global solution, namely one that exists locally near
a radial value $r_{0}$, has positive mass $m(r)$ at $r_{0}$ and develops no
horizon for all $r>r_{0}$. The set of asymptotic values of the Yang-Mills
potential (in a suitable well defined gauge) is shown to be finite in the
so-called regular case, but may form a more complicated real variety for models
obtained from irregular rotation group actions.


title:
Bulk Viscous Solutions to the Field Equations and the Deceleration
  Parameter-Revisited

abstract:
  We utilise a form for the Hubble parameter to generate a number of solutions
to the Einstein field equations with variable cosmological constant and
variable gravitational constant in the presence of a bulk viscous fluid. The
Hubble law utilised yields a constant value for the deceleration parameter. A
new class of solutions is presented in the Robertson-Walker spacetimes. The
coefficient of bulk viscosity is assumed to be a power function of the mass
density. For a class of solutions, the deceleration parameter is negative which
is consistent with the supernovae Ia observations.


title: Plane Symmetric Domain Wall in Lyra Geometry

abstract:
  In this paper general solutions are found for domain walls in Lyra geometry
in the plane symmetric spacetime metric given by Taub. Expressions for the
energy density and pressure of domain walls are derived in both cases of
uniform and time varying displacement field $\beta$. It is also shown that the
results obtained by Rahaman et al [IJMPD, {\bf 10}, 735 (2001)] are particular
case of our solutions. Finally, the geodesic equations and acceleration of the
test particle are discussed.


title: Nonlinear Spinor Field in Anisotropic Universes

abstract:
  Evolution of an anisotropic universe described by a Bianchi type I (BI) model
in presence of nonlinear spinor field has been studied by us recently in a
series of papers. On offer the Bianchi models, those are both inhomogeneous and
anisotropic. Within the scope of Bianchi type VI (BVI) model the
self-consistent system of nonlinear spinor and gravitational fields are
considered. The role of inhomogeneity in the evolution of spinor and
gravitational field is studied.


title:
The Massless DKP Equation and Maxwell Equations in Bianchi Type III
  Spacetimes

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
P.K. Jena, P.C. Naik and T. Pradhan, "Photon As The Zero Mass Limit Of Dkp
Field," J. Phys. A {\bf 13}, 2975 (1980) [not cited within submission]. In
addition, the following submissions by the authors and their collaborators all
contain a great deal of overlap: gr-qc/0502059, gr-qc/0502061, gr-qc/0207026,
hep-th/0110228, and hep-th/0207088.


title: Bulk Viscous Cosmological Models in Barber's Second Self Creation Theory

abstract:
  Barber's second self creation theory with bulk viscous fluid source for an
LRS Bianchi type-I metric is considered by using deceleration parameter to be
constant where the metric potentials are taken as function of $x$ and $t$. The
coefficient of bulk viscosity is assumed to be a power function of the mass
density. Some physical and geometrical features of the models are discussed


title:
Decay of charged scalar field around a black hole: quasinormal modes of
  R-N, R-N-AdS and dilaton black holes

abstract:
  It is well known that the charged scalar perturbations of the
Reissner-Nordstrom metric will decay slower at very late times than the neutral
ones, thereby dominating in the late time signal. We show that at the stage of
quasinormal ringing, on the contrary, the neutral perturbations will decay
slower for RN, RNAdS and dilaton black holes. The QN frequencies of the nearly
extreme RN black hole have the same imaginary parts (damping times) for charged
and neutral perturbations. An explanation of this fact is not clear but,
possibly, is connected with the Choptuik scaling.


title:
Late-time particle creation from gravitational collapse to an extremal
  Reissner-Nordstrom black hole

abstract:
  We investigate the late time behavior of particle creation from an extremal
Reissner-Nordstrom (RN) black hole formed by gravitational collapse. We
calculate explicitly the particle flux associated with a massless scalar field
at late times after the collapse. Our result shows that the expected number of
particles in any wave packet spontaneously created from the ``in'' vacuum state
approaches zero faster than any inverse power of time. This result confirms the
traditional belief that extremal black holes do not emit particles. We also
calculate the expectation value of the stress energy tensor in a 1+1 RN black
hole and show that it also drops to zero at late times. Some comments on
previous work by other authors are provided.


title: Towards the QFT on Curved Spacetime Limit of QGR. I: A General Scheme

abstract:
  In this article and a companion paper we address the question of how one
might obtain the semiclassical limit of ordinary matter quantum fields (QFT)
propagating on curved spacetimes (CST) from full fledged Quantum General
Relativity (QGR), starting from first principles. We stress that we do not
claim to have a satisfactory answer to this question, rather our intention is
to ignite a discussion by displaying the problems that have to be solved when
carrying out such a program. In the present paper we propose a scheme that one
might follow in order to arrive at such a limit. We discuss the technical and
conceptual problems that arise in doing so and how they can be solved in
principle. As to be expected, completely new issues arise due to the fact that
QGR is a background independent theory. For instance, fundamentally the notion
of a photon involves not only the Maxwell quantum field but also the metric
operator - in a sense, there is no photon vacuum state but a "photon vacuum
operator"! While in this first paper we focus on conceptual and abstract
aspects, for instance the definition of (fundamental) n-particle states (e.g.
photons), in the second paper we perform detailed calculations including, among
other things, coherent state expectation values and propagation on random
lattices. These calculations serve as an illustration of how far one can get
with present mathematical techniques. Although they result in detailed
predictions for the size of first quantum corrections such as the gamma-ray
burst effect, these predictions should not be taken too seriously because a)
the calculations are carried out at the kinematical level only and b) while we
can classify the amount of freedom in our constructions, the analysis of the
physical significance of possible choices has just begun.


title:
Towards the QFT on Curved Spacetime Limit of QGR. II: A Concrete
  Implementation

abstract:
  The present paper is the companion of [1] in which we proposed a scheme that
tries to derive the Quantum Field Theory (QFT) on Curved Spacetimes (CST) limit
from background independent Quantum General Relativity (QGR). The constructions
of [1] make heavy use of the notion of semiclassical states for QGR. In the
present paper, we employ the complexifier coherent states for QGR recently
proposed by Thiemann and Winkler as semiclassical states, and thus fill the
general formulas obtained in [1] with life. We demonstrate how one can, under
some simplifying assumptions, explicitely compute expectation values of the
operators relevant for the gravity-matter Hamiltonians of [1] in the
complexifier coherent states. These expectation values give rise to effective
matter Hamiltonians on the background on which the gravitational coherent state
is peaked and thus induce approximate notions of n-particle states and matter
propagation on fluctuating spacetimes. We display the details for the scalar
and the electromagnetic field. The effective theories exhibit two types of
corrections as compared to the the ordinary QFT on CST. The first is due to the
quantum fluctuations of the gravitational field, the second arises from the
fact that background independence forces both geometry and matter to propagate
on a spacetime that is the product of the real line and a (random) graph.
Finally we obtain explicit numerical predictions for non-standard dispersion
relations for the scalar and the electromagnetic field. They should, however,
not be taken too seriously, due to the many ambiguities in our scheme, the
analysis of the physical significance of which has only begun. We show however,
that one can classify these ambiguities at least in broad terms.


title:
Interacting Bosons at Finite Temperature: How Bogolubov Visited a Black
  Hole and Came Home Again

abstract:
  The structure of the thermal equilibrium state of a weakly interacting Bose
gas is of current interest. We calculate the density matrix of that state in
two ways. The most effective method, in terms of yielding a simple, explicit
answer, is to construct a generating function within the traditional framework
of quantum statistical mechanics. The alternative method, arguably more
interesting, is to construct the thermal state as a vector state in an
artificial system with twice as many degrees of freedom. It is well known that
this construction has an actual physical realization in the quantum
thermodynamics of black holes, where the added degrees of freedom correspond to
the second sheet of the Kruskal manifold and the thermal vector state is a
state of the Unruh or the Hartle-Hawking type. What is unusual about the
present work is that the Bogolubov transformation used to construct the thermal
state combines in a rather symmetrical way with Bogolubov's original
transformation of the same form, used to implement the interaction of the
nonideal gas in linear approximation. In addition to providing a density
matrix, the method makes it possible to calculate efficiently certain
expectation values directly in terms of the thermal vector state of the doubled
system.


title:
The criteria for a solution of the field equations to be a classical
  limit of a quantum cosmology

abstract:
  If the gravitational field is quantized, then a solution of Einstein's field
equations is a valid cosmological model only if it corresponds to a classical
limit of a quantum cosmology. To determine which solutions are valid requires
looking at quantum cosmology in a particular way. Because we infer the geometry
by measurements on matter, we can represent the amplitude for any measurement
in terms of the amplitude for the matter fields, allowing us to integrate out
the gravitational degrees of freedom. Combining that result with a
path-integral representation for quantum cosmology leads to an integration over
4-geometries. Even when a semiclassical approximation for the propagator is
valid, the amplitude for any measurement includes an integral over the
gravitational degrees of freedom. The conditions for a solution of the field
equations to be a classical limit of a quantum cosmology are: (1) The effect of
the classical action dominates the integration, (2) the action is stationary
with respect to variation of the gravitational degrees of freedom, and (3) only
one saddlepoint contributes significantly to each integration.


title:
Energy spectra of spinning particles around spinning strings in
  Einstein-Cartan gravity

abstract:
  Riemannian Killing conserved currents are used to find the energy spectra of
classical spinning particles moving around a spinning string in Einstein-Cartan
(EC) theory of gravity. It is shown that a continuos spectrum is obtained for
planar open orbits the energy shift between the upper and lower bounds obtained
for circular planar orbits. A spin-spin effect between the spin of the test
particle and the spin of the spinning string contributes to the energy spectrum
splitting.


title: Asymptotic Behavior of a Class of Expanding Gowdy Spacetimes

abstract:
  A systematic asymptotic expansion is developed for the gravitational wave
degrees of freedom of a class of expanding, vacuum Gowdy cosmological
spacetimes. In the wave map description of these models, the evolution of the
gravitational wave amplitudes defines an orbit in the target space. The
circumference of this orbit decays to zero indicating that the asymptotic
spacetime is spatially homogeneous. A prescription is given to identify the
asymptotic cosmological model for the gravitational wave degrees of freedom
using the asymptotic point in the target space. The remaining metric function
of the asymptotic cosmological model, found by solving the constraints, is
determined by an effective energy of the gravitational waves rather than from
the asymptotic point in the target space.


title: Gravitational deflection of light and helicity asymmetry

abstract:
  The helicity modification of light polarization which is induced by the
gravitational deflection from a classical heavy rotating body, like a star or a
planet, is considered. The expression of the helicity asymmetry is derived;
this asymmetry signals the gravitationally induced spin transfer from the
rotating body to the scattered photons.


title: On the accuracy of the post-Newtonian approximation

abstract:
  We apply standard post-Newtonian methods in general relativity to locate the
innermost circular orbit (ICO) of irrotational and corotational binary
black-hole systems. We find that the post-Newtonian series converges well when
the two masses are comparable. We argue that the result for the ICO which is
predicted by the third post-Newtonian (3PN) approximation is likely to be very
close to the ``exact'' solution, within 1% of fractional accuracy or better.
The 3PN result is also in remarkable agreement with a numerical calculation of
the ICO in the case of two corotating black holes moving on exactly circular
orbits. The behaviour of the post-Newtonian series suggests that the
gravitational dynamics of two bodies of comparable masses does not resemble
that of a test particle on a Schwarzschild background. This leads us to
question the validity of some post-Newtonian resummation techniques that are
based on the idea that the field generated by two black holes is a deformation
of the Schwarzschild space-time.


title: Isotropic Loop Quantum Cosmology with Matter

abstract:
  A free massless scalar field is coupled to homogeneous and isotropic loop
quantum cosmology. The coupled model is investigated in the vicinity of the
classical singularity, where discreteness is essential and where the quantum
model is non-singular, as well as in the regime of large volumes, where it
displays the expected semiclassical features. The particular matter content
(massless, free scalar) is chosen to illustrate how the discrete structure
regulates pathological behavior caused by kinetic terms of matter Hamiltonians
(which in standard quantum cosmology lead to wave functions with an infinite
number of oscillations near the classical singularity). Due to this
modification of the small volume behavior the dynamical initial conditions of
loop quantum cosmology are seen to provide a meaningful generalization of
DeWitt's initial condition.


title:
Properties of the static, spherically symmetric solutions in the Jordan,
  Brans-Dicke theory

abstract:
  We have studied the properties of the static, spherically symmetric solution
of Jordan, Brans-Dicke theory. An exact interior solution for standard
space-time line element in the Schwarzschild form is obtained.


title: Anisotropic geodesic fluid spheres in general relativity

abstract:
  It is shown that unlike the perfect fluid case, anisotropic fluids (principal
stresses unequal) may be geodesic, without this implying the vanishing of
(spatial) pressure gradients. Then the condition of vanishing four acceleration
is integrated in non-comoving coordinates. The resulting models are necessarily
dynamic, and the mass function is expressed in terms of the fluid velocity as
measured by a locally Minkowskian observer. An explicit example is worked out.


title: A spin foam model for pure gauge theory coupled to quantum gravity

abstract:
  We propose a spin foam model for pure gauge fields coupled to Riemannian
quantum gravity in four dimensions. The model is formulated for the
triangulation of a four-manifold which is given merely combinatorially. The
Riemannian Barrett--Crane model provides the gravity sector of our model and
dynamically assigns geometric data to the given combinatorial triangulation.
The gauge theory sector is a lattice gauge theory living on the same
triangulation and obtains from the gravity sector the geometric information
which is required to calculate the Yang--Mills action. The model is designed so
that one obtains a continuum approximation of the gauge theory sector at an
effective level, similarly to the continuum limit of lattice gauge theory, when
the typical length scale of gravity is much smaller than the Yang--Mills scale.


title: Rotating Einstein-Yang-Mills Black Holes

abstract:
  We construct rotating hairy black holes in SU(2) Einstein-Yang-Mills theory.
These stationary axially symmetric black holes are asymptotically flat. They
possess non-trivial non-Abelian gauge fields outside their regular event
horizon, and they carry non-Abelian electric charge. In the limit of vanishing
angular momentum, they emerge from the neutral static spherically symmetric
Einstein-Yang-Mills black holes, labelled by the node number of the gauge field
function. With increasing angular momentum and mass, the non-Abelian electric
charge of the solutions increases, but remains finite. The asymptotic expansion
for these black hole solutions includes non-integer powers of the radial
variable.


title:
Covariant hamiltonian formalism for field theory: Hamilton-Jacobi
  equation on the space G

abstract:
  Hamiltonian mechanics of field theory can be formulated in a generally
covariant and background independent manner over a finite dimensional extended
configuration space. The physical symplectic structure of the theory can then
be defined over a space G of three-dimensional surfaces without boundary, in
the extended configuration space. These surfaces provide a preferred
over-coordinatization of phase space. I consider the covariant form of the
Hamilton-Jacobi equation on G, and a canonical function S on G which is a
preferred solution of the Hamilton-Jacobi equation. The application of this
formalism to general relativity is equivalent to the ADM formalism, but fully
covariant. In the quantum domain, it yields directly the
Ashtekar-Wheeler-DeWitt equation. Finally, I apply this formalism to discuss
the partial observables of a covariant field theory and the role of the spin
networks --basic objects in quantum gravity-- in the classical theory.


title: Spacetime algebraic skeleton

abstract:
  The cosmological constant Lambda, which has seemingly dominated the primaeval
Universe evolution and to which recent data attribute a significant
present-time value, is shown to have an algebraic content: it is essentially an
eigenvalue of a Casimir invariant of the Lorentz group which acts on every
tangent space. This is found in the context of de Sitter spacetimes but, as
every spacetime is a 4-manifold with Minkowski tangent spaces, the result
suggests the existence of a "skeleton" algebraic structure underlying the
geometry of general physical spacetimes. Different spacetimes come from the
"fleshening" of that structure by different tetrad fields. Tetrad fields, which
provide the interface between spacetime proper and its tangent spaces, exhibit
to the most the fundamental role of the Lorentz group in Riemannian spacetimes,
a role which is obscured in the more usual metric formalism.


title:
Reconstruction of inhomogeneous metric perturbations and electromagnetic
  four-potential in Kerr spacetime

abstract:
  We present a procedure that allows the construction of the metric
perturbations and electromagnetic four-potential, for gravitational and
electromagnetic perturbations produced by sources in Kerr spacetime. This may
include, for example, the perturbations produced by a point particle or an
extended object moving in orbit around a Kerr black hole. The construction is
carried out in the frequency domain. Previously, Chrzanowski derived the vacuum
metric perturbations and electromagnetic four-potential by applying a
differential operator to a certain potential $\Psi $. Here we construct $\Psi $
for inhomogeneous perturbations, thereby allowing the application of
Chrzanowski's method. We address this problem in two stages: First, for vacuum
perturbations (i.e. pure gravitational or electromagnetic waves), we construct
the potential from the modes of the Weyl scalars $\psi_{0}$ or $\phi_{0}$.
Second, for perturbations produced by sources, we express $\Psi $ in terms of
the mode functions of the source, i.e. the energy-momentum tensor $T_{\alpha
\beta}$ or the electromagnetic current vector $J_{\alpha}$.


title:
Radar Time and a State-Space Based Approach To Quantum Field Theory In
  Gravitational and Electromagnetic Backgrounds

abstract:
  In a recent paper (hep-th/0103228) a new initial value formulation of
fermionic QFT was presented that is applicable to an arbitrary observer in any
electromagnetic background. This approach suggests a consistent particle
interpretation at all times, with the concept of `radar time' used to
generalise this interpretation to an arbitrarily moving observer. In the
present paper we extend this formalism to allow for gravitational backgrounds.
The observer-dependent particle interpretation generalises Gibbons' definition
to non-stationary spacetimes. This allows any observer to be considered,
providing a particle interpretation that depends {\it only} on the observer's
motion and the background, not on any choice of coordinates or gauge, or on
details of their particle detector. Consistency with known results is
demonstrated for the cases of Rindler space and deSitter space. Radar time is
also considered for an arbitrarily moving observer in an arbitrary 1+1
dimensional spacetime, and for a comoving observer in a 3+1 dimensional FRW
universe with arbitrary scale factor $a(t)$. Finite volume measurements and
their fluctuations are also discussed, allowing one to say with definable
precision where and when the particles are observed.


title: Gravitation and cosmology in a brane-universe

abstract:
  Recent theoretical developments have generated a strong interest in the
``brane-world'' picture, which assumes that ordinary matter is trapped in a
three-dimensional submanifold, usually called brane, embedded in a higher
dimensional space. The purpose of this review is to introduce some basic
results concerning gravity in these models and then to present various aspects
of the cosmology in a brane-universe.


title:
Second Order Perturbations of Flat Dust FLRW Universes with a
  Cosmological Constant

abstract:
  We summarize recent results concerning the evolution of second order
perturbations in flat dust irrotational FLRW models with $\Lambda\ne 0$. We
show that asymptotically these perturbations tend to constants in time, in
agreement with the cosmic no-hair conjecture. We solve numerically the second
order scalar perturbation equation, and very briefly discuss its all time
behaviour and some possible implications for the structure formation.


title: Doubly Special Relativity

abstract:
  I give a short non-technical review of the results obtained in recent work on
"Doubly Special Relativity", the relativistic theories in which the
rotation/boost transformations between inertial observers are characterized by
two observer-independent scales (the familiar velocity scale, $c$, and a new
observer-independent length/momentum scale, naturally identified with the
Planck length/momentum). I emphasize the aspects relevant for the search of a
solution to the cosmic-ray paradox.


title:
Hydrostatic Equilibrium of a Perfect Fluid Sphere with Exterior
  Higher-Dimensional Schwarzschild Spacetime

abstract:
  We discuss the question of how the number of dimensions of space and time can
influence the equilibrium configurations of stars. We find that dimensionality
does increase the effect of mass but not the contribution of the pressure,
which is the same in any dimension. In the presence of a (positive)
cosmological constant the condition of hydrostatic equilibrium imposes a lower
limit on mass and matter density. We show how this limit depends on the number
of dimensions and suggest that $\Lambda > 0$ is more effective in 4D than in
higher dimensions. We obtain a general limit for the degree of compactification
(gravitational potential on the boundary) of perfect fluid stars in
$D$-dimensions. We argue that the effects of gravity are stronger in 4D than in
any other number of dimensions. The generality of the results is also
discussed.


title: Inflationary Lambda-Universe with Time Varying Fundamental Constants

abstract:
  Barrow, and Barrow and collaborators, have put forward theoretical models
with variable fundamental constants including JBD theories. The experimental
evidence for an accelerating Universe points out to a deceleration parameter
approximately equal to -- 1. On the other hand, there is evidence for a time
varying fine structure constant alpha . We have included the above results in a
JBD cosmological model modified by J.D. Barrow by including a time varying
speed of light, thus, finding an exponential inflationary phase with variables
G, alpha and c . This means that the primordial value of alpha was
exponentially larger than its present value. Planck`s time may not be then
approximately 10 to the power - 43 s ; the same may happen to other Planck`s
quantities. We found an exponentially time-decaying Cosmological term.


title: On the frequency shift of gravitational waves

abstract:
  Considering plane gravitational waves propagating through flat spacetime, it
is shown that curvatures experienced both in the starting point and during
their arrival at the earth can cause a considerable shift in the frequencies as
measured by earth and space-based detectors. Particularly for the case of
resonant bar detectors this shift can cause noise-filters to smother the
signal.


title:
Nonunitary HD gravity classically equivalent to Einstein gravity and its
  Newtonian limit

abstract:
  Runaway solutions can be avoided in fourth order gravity by a doubling of the
matter operator algebra with a symmetry constraint with respect to the exchange
of observable and hidden degrees of freedom together with the change in sign of
the ghost and the dilaton fields. The theory is classically equivalent to
Einstein gravity, while its non-unitary Newtonian limit is shown to lead to a
sharp transition, around $10^{11}$ proton masses, from the wavelike properties
of microscopic particles to the classical behavior of macroscopic bodies, as
well as to a trans-Planckian regularization of collapse singularities. A
unified reading of ordinary and black hole entropy emerges as entanglement
entropy with hidden degrees of freedom. The emergent picture gives a
substantial agreement with B-H entropy and Hawking temperature.


title: Naked Singularity and Thunderbolt

abstract:
  We consider quantum theoretical effects of the sudden change of the boundary
conditions which mimics the occurrence of naked singularities. For a simple
demonstration, we study a massless scalar field in $(1 + 1)$-dimensional
Minkowski spacetime with finite spatial interval. We calculate the vacuum
expectation value of the energy-momentum tensor and explicitly show that
singular wave or {\em thunderbolt} appears along the Cauchy horizon. The
thunderbolt possibly destroys the Cauchy horizon if its backreaction on the
geometry is taken into account, leading to quantum restoration of the global
hyperbolicity. The result of the present work may also apply to the situation
that a closed string freely oscillating is traveling to a brane and changes
itself to an open string pinned-down by the ends satisfying the Dirichlet
boundary conditions on the brane.


title: A geometrical origin for the covariant entropy bound

abstract:
  Causal diamond-shaped subsets of space-time are naturally associated with
operator algebras in quantum field theory, and they are also related to the
Bousso covariant entropy bound. In this work we argue that the net of these
causal sets to which are assigned the local operator algebras of quantum
theories should be taken to be non orthomodular if there is some lowest scale
for the description of space-time as a manifold. This geometry can be related
to a reduction in the degrees of freedom of the holographic type under certain
natural conditions for the local algebras. A non orthomodular net of causal
sets that implements the cutoff in a covariant manner is constructed. It gives
an explanation, in a simple example, of the non positive expansion condition
for light-sheet selection in the covariant entropy bound. It also suggests a
different covariant formulation of entropy bound.


title: The Mixmaster Universe in Five Dimensions

abstract:
  We consider a five dimensional vacuum cosmology with Bianchi type-IX spatial
geometry and an extra non-compact coordinate. Finding a new class of solutions,
we examine and rule out the possibility of deterministic chaos. We interpret
this result within the context of induced matter theory.


title: The quantum inequalities do not forbid spacetime shortcuts

abstract:
  A class of spacetimes (comprising the Alcubierre bubble, Krasnikov tube, and
a certain type of wormholes) is considered that admits `superluminal travel' in
a strictly defined sense. Such spacetimes (they are called `shortcuts' in this
paper) were suspected to be impossible because calculations based on `quantum
inequalities' suggest that their existence would involve Planck-scale energy
densities and hence unphysically large values of the `total amount of negative
energy' E_tot. I argue that the spacetimes of this type may not be unphysical
at all. By explicit examples I prove that: 1) the relevant quantum inequality
does not (always) imply large energy densities; 2) large densities may not lead
to large values of E_tot; 3) large E_tot, being physically meaningless in some
relevant situations, does not necessarily exclude shortcuts.


title:
The CWKB particle production and classical condensate in de Sitter
  spacetime

abstract:
  The complex time WKB approximation is an effective tool in studying particle
production in curved spacetime. We use it in this work to understand the
formation of classical condensate in expanding de Sitter spacetime. The CWKB
leads to the emergence of thermal spectrum that depends crucially on horizons
(as in de Sitter spacetime) or observer dependent horizons (as in Rindler
spacetime). A connection is sought between the horizon and the formation of
classical condensate. We concentrate on de Sitter spacetime and study the
cosmological perturbation of $k=0$ mode with various values of $m/H_0$. We find
that for a minimally coupled free scalar field for $m^2/H_0^2<2$, the one-mode
occupation number grows more than unity soon after the physical wavelength of
the mode crosses the Hubble radius and soon after diverges as $N(t)\sim
O(1)[\lambda_{phys}(t)/{H_0^{-1}}]^{2\sqrt{\nu^2-1/4}}$, where $\nu\equiv (9/4
-m^2/{H_0^2})^{1/2}$. The results substantiates the previous works in this
direction. We also find the correct oscillation and behaviour of $N(z)$ at
small $z$ from a single expression using CWKB approximation for various values
of $m/H_0$. We also discuss decoherence in relation to the formation of
classical condensate. We also find that the squeezed state formalism and CWKB
method give identical results.


title: Nonunitary Classically Stable HD Gravity

abstract:
  Classical instability in fourth order gravity is cured at the expense of
unitarity. The appearance of hidden degrees of freedom replicating those of
ordinary matter allows for ordinary thermodynamic entropy and black hole
entropy to be identified with von Neumann entropy. The emergent picture gives a
substantial agreement with B-H entropy and Hawking temperature.


title:
Flows and particles with shear-free and expansion-free velocities in
  (L^-_n,g)- and Weyl's spaces

abstract:
  Conditions for the existence of flows with non-null shear-free and
expansion-free velocities in spaces with affine connections and metrics are
found. On their basis, generalized Weyl's spaces with shear-free and
expansion-free conformal Killing vectors as velocity's vectors of spinless test
particles moving in a Weyl's space are considered. The necessary and sufficient
conditions are found under which a free spinless test particle could move in
spaces with affine connections and metrics on a curve described by means of an
auto-parallel equation. In Weyl's spaces with Weyl's covector, constructed by
the use of a dilaton field, the dilaton field appears as a scaling factor for
the rest mass density of the test particle. PACS numbers: 02.40.Ky, 04.20.Cv,
04.50.+h, 04.90.+e


title: Geodetic Brane Gravity

abstract:
  Within the framework of geodetic brane gravity, the Universe is described as
a 4-dimensional extended object evolving geodetically in a higher dimensional
flat background. In this paper, by introducing a new pair of canonical fields
{lambda, P_{lambda}}, we derive the quadratic Hamiltonian for such a brane
Universe; the inclusion of matter then resembles minimal coupling. Second class
constraints enter the game, invoking the Dirac bracket formalism. The algebra
of the first class constraints is calculated, and the BRST generator of the
brane Universe turns out to be rank-1. At the quantum level, the road is open
for canonical and/or functional integral quantization. The main advantages of
geodetic brane gravity are: (i) It introduces an intrinsic, geometrically
originated, 'dark matter' component, (ii) It offers, owing to the Lorentzian
bulk time coordinate, a novel solution to the 'problem of time', and (iii) It
enables calculation of meaningful probabilities within quantum cosmology
without any auxiliary scalar field. Intriguingly, the general relativity limit
is associated with lambda being a vanishing (degenerate) eigenvalue.


title:
Searching for Gravitational Waves from the Inspiral of Precessing Binary
  Systems: Problems with Current Waveforms

abstract:
  We consider the problem of searching for gravitational waves emitted during
the inspiral phase of binary systems when the orbital plane precesses due to
relativistic spin-orbit coupling. Such effect takes place when the spins of the
binary members are misaligned with respect to the orbital angular momentum. As
a first step we assess the importance of precession specifically for the
first-generation of LIGO detectors. We investigate the extent of the
signal-to-noise ratio reduction and, hence, detection rate that occurs when
precession effects are not accounted for in the template waveforms. We restrict
our analysis to binary systems that undergo the so-called simple precession and
have a total mass close to 10 solar mass. We find that for binary systems with
rather high mass ratios (e.g., a 1.4 solar mass neutron star and a 10 solar
mass black hole) the detection rate can decrease by almost an order of
magnitude. Current astrophysical estimates of the rate of binary inspiral
events suggest that LIGO could detect at most a few events per year, and
therefore the reduction of the detection rate even by a factor of a few is
critical. In the second part of our analysis, we examine whether the effect of
precession could be included in the templates by capturing the main features of
the phase modulation through a small number of extra parameters. Specifically
we examine and tested for the first time the 3-parameter family suggested by
Apostolatos. We find that, even though these ``mimic'' templates improve the
detection rate, they are still inadequate in recovering the signal-to-noise
ratio at the desired level. We conclude that a more complex template family is
needed in the near future, still maintaining the number of additional
parameters as small as possible in order to reduce the computational costs.


title: Nonunitary Newtonian Gravity

abstract:
  It is shown that the Newtonian limit of a stable realization of HD gravity
leads to a sharp transition, around 10^{11} proton masses, from the wavelike
properties of microscopic particles to the classical behaviour of macroscopic
bodies. Besides, due to nonunitarity, a pure state is expected to evolve into a
microcanonical ensamble leading to thermal equilibrium even for truly closed
systems.


title: String Cosmology in the Jackiw-Telteiboim Model with Quantum Corrections

abstract:
  This note deals with the possibility of non-trivial cosmological solutions
given by quantum corrections in the framework of the Jackiw-Telteiboim model to
the bidimensional gravity. The resulting model shows that the quantum
corrections transform, in some cases, the classical solution into a more
interesting one with initial singularity.