title: Hollow sphere, a flexible multimode Gravitational Wave antenna

abstract:
  Hollow spheres have the same theoretical capabilities as the usual solid
ones, since they share identical symmetries. The hollow sphere is however more
flexible, as thickness is an additional parameter one can vary to approach
given specifications. I will briefly discuss the more relevant properties of
the hollow sphere as a GW detector (frequencies, cross sections), and suggest
some scenarios where it can generate significant astrophysical information.


title:
The spectrum of endstates of gravitational collapse with tangential
  stresses

abstract:
  The final state--black hole or naked singularity--of the gravitational
collapse of a marginally bound matter configuration in the presence of
tangential stresses is classified, in full generality, in terms of the initial
data and equation of state. If the tangential pressure is sufficiently strong,
configurations that would otherwise evolve to a spacelike singularity, result
in a locally naked singularity, both in the homogeneous and in the general,
inhomogeneous density case.


title: Moving Mirrors, Black Holes, Hawking Radiation and All That

abstract:
  In this talk I show how to canonically quantize a massless scalar field in
the background of a Schwarzschild black hole in Lema\^itre coordinates and then
present a simplified derivation of Hawking radiation based upon this procedure.
The key result of quantization procedure is that the Hamiltonian of the system
is explicitly time dependent and so problem is intrinsically non-static. From
this it follows that, although a unitary time-development operator exists, it
is not useful to talk about vacuum states; rather, one should focus attention
on steady state phenomena such as the Hawking radiation. In order to clarify
the approximations used to study this problem I begin by discussing the related
problem of the massless scalar field theory calculated in the presence of a
moving mirror.


title:
Circular Holonomy and Clock Effects in Stationary Axisymmetric
  Spacetimes

abstract:
  Stationary axisymmetric spacetimes containing a pair of oppositely-rotating
periodically-intersecting circular geodesics allow the study of various
so-called `clock effects' by comparing either observer or geodesic proper time
periods of orbital circuits defined by the observer or the geodesic crossing
points. This can be extended from a comparison of clocks to a comparison of
parallel transported vectors, leading to the study of special elements of the
spacetime holonomy group. The band of holonomy invariance found for a dense
subset of special geodesic orbits outside a certain radius in the static case
does not exist in the nonstatic case. In the Kerr spacetime the dimensionless
frequencies associated with parallel transport rotations can be expressed as
ratios of the proper and average coordinate periods of the circular geodesics.


title: A general-covariant concept of particles in curved background

abstract:
  A local current of particle density for scalar fields in curved background is
constructed. The current depends on the choice of a two-point function. There
is a choice that leads to local non-conservation of the current in a
time-dependent gravitational background, which describes local particle
production consistent with the usual global description based on the Bogoliubov
transformation. Another choice, which might be the most natural one, leads to
the local conservation of the current.


title: "Peeling property" for linearized gravity in null coordinates

abstract:
  A complete description of the linearized gravitational field on a flat
background is given in terms of gauge-independent quasilocal quantities. This
is an extension of the results from gr-qc/9801068. Asymptotic spherical
quasilocal parameterization of the Weyl field and its relation with Einstein
equations is presented. The field equations are equivalent to the wave
equation. A generalization for Schwarzschild background is developed and the
axial part of gravitational field is fully analyzed. In the case of axial
degree of freedom for linearized gravitational field the corresponding
generalization of the d'Alembert operator is a Regge-Wheeler equation. Finally,
the asymptotics at null infinity is investigated and strong peeling property
for axial waves is proved.


title: Are the String and Einstein Frames Equivalent

abstract:
  The low energy physics as predicted by strings can be expressed in two
(conformally related) different variables, usually called {\em frames}. The
problem is raised as to whether it is physically possible in some situations to
tell one from the other.


title: Testing angular momentum effects on the space time

abstract:
  The paper contains a proposed experiment for testing the angular momentum
effect on the propagation of light around a rotating mass. The idea is to use a
rotating spherical laboratory-scale shell, around which two mutually orthogonal
light guides are wound acting as the arms of an interferometer. Numerical
estimates show that time of flight differences between the equatorial and polar
guides could be in the order of $\sim 10^{-20}$ s per loop. Using a few
thousands loops the time difference is brought in the range of feasible
interference measurements.


title: (1+3) Covariant Dynamics of Scalar Perturbations in Braneworlds

abstract:
  We discuss the dynamics of linear, scalar perturbations in an almost
Friedmann-Robertson-Walker braneworld cosmology of Randall-Sundrum type II
using the 1+3 covariant approach. We derive a complete set of frame-independent
equations for the total matter variables, and a partial set of equations for
the non-local variables which arise from the projection of the Weyl tensor in
the bulk. The latter equations are incomplete since there is no propagation
equation for the non-local anisotropic stress. We supplement the equations for
the total matter variables with equations for the independent constituents in a
cold dark matter cosmology, and provide solutions in the high and low-energy
radiation-dominated phase under the assumption that the non-local anisotropic
stress vanishes. These solutions reveal the existence of new modes arising from
the two additional non-local degrees of freedom. Our solutions should prove
useful in setting up initial conditions for numerical codes aimed at exploring
the effect of braneworld corrections on the cosmic microwave background (CMB)
power spectrum. As a first step in this direction, we derive the covariant form
of the line of sight solution for the CMB temperature anisotropies in
braneworld cosmologies, and discuss possible mechanisms by which braneworld
effects may remain in the low-energy universe.


title: Holography and the large number hypothesis

abstract:
  Dirac's large number hypothesis is motivated by certain scaling
transformations that relate the parameters of macro and microphysics. We show
that these relations can actually be explained in terms of the holographic $N$
bound conjectured by Bousso and a series of purely cosmological observations,
namely, that our universe is spatially homogeneous, isotropic, and flat to a
high degree of approximation and that the cosmological constant dominates the
energy density at present.


title:
Energy-Momentum Tensor of Field Fluctuations in Massive Chaotic
  Inflation

abstract:
  We study the renormalized energy-momentum tensor (EMT) of the inflaton
fluctuations in rigid space-times during the slow-rollover regime for chaotic
inflation with a mass term. We use dimensional regularization with adiabatic
subtraction and introduce a novel analytic approximation for the inflaton
fluctuations which is valid during the slow-rollover regime. Using this
approximation we find a scale invariant spectrum for the inflaton fluctuations
in a rigid space-time, and we confirm this result by numerical methods. The
resulting renormalized EMT is covariantly conserved and agrees with the
Allen-Folacci result in the de Sitter limit, when the expansion is exactly
linearly exponential in time. We analytically show that the EMT tensor of the
inflaton fluctuations grows initially in time, but saturates to the value H^2
H(0)^2, where H is the Hubble parameter and H(0) is its value when inflation
has started. This result also implies that the quantum production of light
scalar fields (with mass smaller or equal to the inflaton mass) in this model
of chaotic inflation depends on the duration of inflation and is larger than
the usual result extrapolated from the de Sitter result.


title: Energy-momentum current for coframe gravity

abstract:
  The obstruction for the existence of an energy momentum tensor for the
gravitational field is connected with differential-geometric features of the
Riemannian manifold. It has not to be valid for alternative geometrical
structures. A teleparallel manifold is defined as a parallelizable
differentiable 4D-manifold endowed with a class of smooth coframe fields
related by global Lorentz, i.e., SO(1,3) transformations. In this article a
general free parametric class of teleparallel models is considered. It includes
a 1-parameter subclass of viable models with the Schwarzschild coframe
solution. A new form of the coframe field equation is derived from the general
teleparallel Lagrangian by introducing the notion of a 3-parameter conjugate
field strength $\F^a$. The field equation turns out to have a form completely
similar to the Maxwell field equation $d*\F^a=\T^a$. By applying the Noether
procedure, the source 3-form $\T^a$ is shown to be connected with the
diffeomorphism invariance of the Lagrangian. Thus the source $\T^a$ of the
coframe field is interpreted as the total conserved energy-momentum current.
The energy-momentum tensor for coframe is defined. The total energy-momentum
current of a system of a coframe and a material fields is conserved. Thus a
redistribution of the energy-momentum current between a material and a coframe
(gravity) fields is possible in principle, unlike as in the standard GR. For
special values of parameters, when the GR is reinstated, the energy-momentum
tensor gives up the invariant sense, i.e., becomes a pseudo-tensor. Thus even a
small-parametric change of GR turns it into a well defined Lagrangian theory.


title:
A note on the foundation of relativistic mechanics. I: Relativistic
  observables and relativistic states

abstract:
  Is there a version of the notions of "state" and "observable" wide enough to
apply naturally and in a covariant manner to relativistic systems? I discuss
here a tentative answer.


title:
Gravitational Perturbations of the Kerr black hole due to arbitrary
  sources

abstract:
  We describe the Kerr black hole in the ingoing and outgoing Kerr-Schild
horizon penetrating coordinates. Starting from the null vector naturally
defined in these coordinates, we construct the null tetrad for each case, as
well as the corresponding geometrical quantities allowing us to explicitly
derive the field equations for the ${\Psi_0}^{(1)}$ and ${\Psi_4}^{(1)}$
perturbed scalar projections of the Weyl tensor, including arbitrary source
terms. This perturbative description, including arbitrary sources, described in
horizon penetrating coordinates is desirable in several lines of research on
black holes, and contributes to the implementation of a formalism aimed to
study the evolution of the space time in the region where two black holes are
close.


title:
On the linear stability of solitons and hairy black holes with a
  negative cosmological constant: the even-parity sector

abstract:
  Using a recently developed perturbation formalism based on curvature
quantities, we complete our investigation of the linear stability of black
holes and solitons with Yang-Mills hair and a negative cosmological constant.
We show that those solutions which have no linear instabilities under odd- and
even-parity spherically symmetric perturbations remain stable under
even-parity, linear, non-spherically symmetric perturbations. Together with the
result from a previous work, we have therefore established the existence of
stable hairy black holes and solitons with anti-de Sitter asymptotic.


title: (Conformal) Killing vectors in the Newman-Penrose formalism

abstract:
  This paper presents an efficient technique for finding Killing, homothetic,
or even proper conformal Killing vectors in the Newman-Penrose (NP) formalism.
Leaning on, and extending, results previously derived in the GHP formalism we
show that the (conformal) Killing equations can be replaced by a set of
equations involving the commutators of the Lie derivative with the four NP
differential operators applied to the four coordinates.
  It is crucial that these operators refer to a preferred tetrad relative to
the (conformal) Killing vectors, a notion to be defined. The equations can then
be readily solved for the Lie derivative of the coordinates, i.e. for the
components of the (conformal) Killing vectors. Some of these equations become
trivial if some coordinates are chosen intrinsically (where possible), i.e. if
they are somehow tied to the Riemann tensor and its covariant derivatives.
  If part of the tetrad, i.e. part of null directions and gauge, can be defined
intrinsically then that part is generally preferred relative to any Killing
vector. This is also true relative to a homothetic vector or a proper conformal
Killing vector provided we make a further restriction on that intrinsic part of
the tetrad. If because of null isotropy or gauge isotropy, where part of the
tetrad cannot even in principle be defined intrinsically, the tetrad is defined
only up to (usually) one null rotation parameter and/or a gauge factor, then
the NP-Lie equations become slightly more involved and must be solved for the
Lie derivative of the null rotation parameter and/or of the gauge factor as
well. However, the general method remains the same and is still much more
efficient than conventional methods.
  Several explicit examples are given to illustrate the method.


title: Rindler Particles and Classical Radiation

abstract:
  We describe the quantum and classical radiation by a uniformly accelerating
point source in terms of the elementary processes of absorption and emission of
Rindler scalar photons of the Fulling-Davies-Unruh bath observed by a
co-accelerating observer.To this end we compute the emission rate by a DeWitt
detector of a Minkowski scalar particle with defined transverse momentum per
unit of proper time of the source and we show that it corresponds to the
induced absorption or spontaneous and induced emission of Rindler photons from
the thermal bath. We then take what could be called the inert limit of the
DeWitt detector by considering the limit of zero gap energy. As suggested by
DeWitt, we identify in this limit the detector with a classical point source
and verify the consistency of our computation with the classical result.
Finally, we study the behavior of the emission rate in D space-time dimensions
in connection with the so called apparent statistics inversion.


title: An analysis of a QND speed-meter interferometer

abstract:
  In the quest to develop viable designs for third-generation optical
interferometric gravitational-wave detectors (e.g. LIGO-III and EURO), one
strategy is to monitor the relative momentum or speed of the test-mass mirrors,
rather than monitoring their relative position. This paper describes and
analyzes the most straightforward design for a {\it speed meter interferometer}
that accomplishes this -- a design (due to Braginsky, Gorodetsky, Khalili and
Thorne) that is analogous to a microwave-cavity speed meter conceived by
Braginsky and Khalili. A mathematical mapping between the microwave speed meter
and the optical interferometric speed meter is developed and is used to show
(in accord with the speed being a Quantum Nondemolition [QND] observable) that
{\it in principle} the interferometric speed meter can beat the
gravitational-wave standard quantum limit (SQL) by an arbitrarily large amount,
over an arbitrarily wide range of frequencies, and can do so without the use of
squeezed vacuum or any auxiliary filter cavities at the interferometer's input
or output. However, {\it in practice}, to reach or beat the SQL, this specific
speed meter requires exorbitantly high input light power. The physical reason
for this is explored, along with other issues such as constraints on
performance due to optical dissipation. This analysis forms a foundation for
ongoing attempts to develop a more practical variant of an interferometric
speed meter and to combine the speed meter concept with other ideas to yield a
promising LIGO-III/EURO interferometer design that entails low laser power.


title: Exploring the Conformal Constraint Equations

abstract:
  One method of studying the asymptotic structure of spacetime is to apply
Penrose's conformal rescaling technique. In this setting, the Einstein
equations for the metric and the conformal factor in the unphysical spacetime
degenerate where the conformal factor vanishes, namely at the boundary
representing null infinity. This problem can be avoided by means of a technique
of H. Friedrich, which replaces the Einstein equations in the unphysical
spacetime by an equivalent system of equations which is regular at the
boundary. The initial value problem for these equations produces a system of
constraint equations known as the conformal constraint equations. This work
describes some of the properties of the conformal constraint equations and
develops a perturbative method of generating solutions near flat space under
certain simplifying assumptions.


title:
Hawking Radiation of a Non-stationary Kerr-Newman Black Hole:
  Spin-Rotation Coupling Effect

abstract:
  Hawking evaporation of Klein-Gordon and Dirac particles in a non-stationary
Kerr-Newman space-time is investigated by using a method of generalized
tortoise coordinate transformation. The location and the temperature of the
event horizon of a non-stationary Kerr-Newman black hole are derived. It is
shown that the temperature and the shape of the event horizon depend not only
on the time but also on the angle. However, the Fermionic spectrum of Dirac
particles displays a new spin-rotation coupling effect which is absent from
that of Bosonic distribution of scalar particles. The character of this effect
is its obvious dependence on different helicity states of particles spin-1/2.
  PACS numbers: 04.70.Dy, 97.60.Lf


title: Hawking Radiation of Photons in a Vaidya-de Sitter Black Hole

abstract:
  Hawking evaporation of photons in a Vaidya-de Sitter black hole is
investigated by using the method of generalized tortoise coordinate
transformation. Both the location and the temperature of the event horizon
depend on the time. It is shown that Hawking radiation of photons exists only
for the complex Maxwell scalar $\phi_0$ in the advanced Eddington-Finkelstein
coordinate system. This asymmetry of Hawking radiation for different components
of Maxwell fields probably arises from the asymmetry of spacetime in the
advanced Eddington-Finkelstein coordinate system. It is shown that the black
body radiant spectrum of photons resembles that of Klein-Gordon particles.
  PACS numbers: 04.70.Dy, 97.60.Lf


title: On rotating regular nonabelian solutions

abstract:
  A general relation for the total angular momentum of a regular solution of
the Einstein-Yang-Mills-Higgs equations is derived. Two different physical
configurations, rotating dyons and rotating magnetic dipoles are discussed as
particular cases. The issue of rotating pure Einstein-Yang-Mills regular
solutions is addressed as well. Based on the results, we conjecture the absence
of rotating regular solitons with a net magnetic charge.


title: Quintessence with Coupled Scalar Fields

abstract:
  We discuss the dynamics of a quintessence model involving two coupled scalar
fields. The model presents two types of solutions, namely solutions that
correspond to eternal and transient acceleration of the universe. In both
cases, we obtain values for the cosmological parameters that satisfy current
observational bounds as well as the nucleosynthesis constraint on the
quintessence energy density.


title: The eternal fractal in the universe

abstract:
  Models of eternal inflation predict a stochastic self-similar geometry of the
universe at very large scales and allow existence of points that never
thermalize. I explore the fractal geometry of the resulting spacetime, using
coordinate-independent quantities. The formalism of stochastic inflation can be
used to obtain the fractal dimension of the set of eternally inflating points
(the ``eternal fractal''). I also derive a nonlinear branching diffusion
equation describing global properties of the eternal set and the probability to
realize eternal inflation. I show gauge invariance of the condition for
presence of eternal inflation. Finally, I consider the question of whether all
thermalized regions merge into one connected domain. Fractal dimension of the
eternal set provides a (weak) sufficient condition for merging.


title: Analytic Continuation for Asymptotically AdS 3D Gravity

abstract:
  We have previously proposed that asymptotically AdS 3D wormholes and black
holes can be analytically continued to the Euclidean signature. The analytic
continuation procedure was described for non-rotating spacetimes, for which a
plane t=0 of time symmetry exists. The resulting Euclidean manifolds turned out
to be handlebodies whose boundary is the Schottky double of the geometry of the
t=0 plane. In the present paper we generalize this analytic continuation map to
the case of rotating wormholes. The Euclidean manifolds we obtain are quotients
of the hyperbolic space by a certain quasi-Fuchsian group. The group is the
Fenchel-Nielsen deformation of the group of the non-rotating spacetime. The
angular velocity of an asymptotic region is shown to be related to the
Fenchel-Nielsen twist. This solves the problem of classification of rotating
black holes and wormholes in 2+1 dimensions: the spacetimes are parametrized by
the moduli of the boundary of the corresponding Euclidean spaces. We also
comment on the thermodynamics of the wormhole spacetimes.


title: Data analysis of continuous gravitational wave: Fourier transform-I

abstract:
  We present the Fourier Transform of a continuous gravitational wave. We have
analysed the data set for one day observation time and our analysis is
applicable for arbitrary location of detector and source. We have taken into
account the effects arising due to rotational as well as orbital motions of the
earth.


title: On the Quantum Origin of the Mixmaster Chaos Covariance

abstract:
  Our analysis shows how the covariant chaotic behavior characterizing the
evolution of the Mixmaster cosmology near the initial singularity can be taken
as the semiclassical limit in the canonical quantization performed by the
corresponding Hamiltonian representation.


title:
Gravity and Antigravity with Discrete Interactions: Alternatives I and
  II

abstract:
  Questioning the experimental basis of continuous descriptions of fundamental
interactions we discuss classical gravity as an effective continuous
first-order approximation of a discrete interaction. The sub-dominant
contributions produce a residual interaction that may be repulsive and whose
physical meaning is of a correction of the excess contained in the continuous
approximation. These residual interactions become important (or even dominate)
at asymptotical conditions of very large distances from where there are data
(rotation curves of galaxies, inflation, accelerated expansion, etc) and
cosmological theoretical motivations that suggest new physics (new forms of
interactions) or new forms (dark) of matter and energy. We show that a discrete
picture of the world (of matter and of its interactions) produce, as an
approximation, the standard continuous picture and more. The flat rotation
curve of galaxies, for example, may have a simple and natural explanation.

categories: gr-qc astro-ph hep-ph hep-th math-ph math.MP


title: Appearance of the central singularity in spherical collapse

abstract:
  We analyze here the structure of non-radial nonspacelike geodesics
terminating in the past at a naked singularity formed as the end state of
inhomogeneous dust collapse. The spectrum of outgoing nonspacelike null
geodesics is examined analytically. The local and global visibility of the
singularity is also examined by integrating numerically the null geodesics
equations. The possible implications of existence of such families towards the
appearance of the star in late stages of gravitational collapse are considered.
It is seen that the outgoing non-radial geodesics give an appearance to the
naked central singularity as that of an expanding ball whose radius reaches a
maximum before the star goes within its apparent horizon. The radiated energy
(along the null geodesics) is shown to decay very sharply in the neighbourhood
of the singularity. Thus the total energy escaping via non-radial null
geodesics from the naked central singularity vanishes in the scenario
considered here.


title: No time machines in classical general relativity

abstract:
  Irrespective of local conditions imposed on the metric, any extendible
spacetime U has a maximal extension containing no closed causal curves outside
the chronological past of U. We prove this fact and interpret it as
impossibility (in classical general relativity) of the time machines, insofar
as the latter are defined to be causality-violating regions created by human
beings (as opposed to those appearing spontaneously).


title: Fermionic microstates within Painlev\'e-Gullstrand black hole

abstract:
  We consider the quantum vacuum of fermionic field in the presence of a
black-hole background as a possible candidate for the stabilized black hole.
The stable vacuum state (as well as thermal equilibrium states with arbitrary
temperature) can exist if we use the Painlev\'e-Gullstrand description of the
black hole, and the superluminal dispersion of the particle spectrum at high
energy, which is introduced in the free-falling frame. Such choice is inspired
by the analogy between the quantum vacuum and the ground state of quantum
liquid, in which the event horizon for the low-energy fermionic quasiparticles
also can arise. The quantum vacuum is characterized by the Fermi surface, which
appears behind the event horizon. We do not consider the back reaction, and
thus there is no guarantee that the stable black hole exists. But if it does
exist, the Fermi surface behind the horizon would be the necessary attribute of
its vacuum state. We also consider exact discrete spectrum of fermions inside
the horizon which allows us to discuss the problem of fermion zero modes.


title:
Have we already detected astrophysical symptoms of space-time
  noncommutativity ?

abstract:
  We discuss astrophysical implications of $\kappa$-Minkowski space-time, in
which there appears space-time noncommutativity. We first derive a velocity
formula for particles based on the motion of a wave packet. The result is that
a massless particle moves at a constant speed as in the usual Minkowski
space-time, which implies that an arrival time analysis by $\gamma$-rays from
Markarian (Mk) 421 does not exclude space-time noncommutativity. Based on this
observation, we analyze reaction processes in $\kappa$-Minkowski space-time
which are related to the puzzling detections of extremely high-energy cosmic
rays above the Greisen-Zatsepin-Kuzmin cutoff and of high-energy ($\sim$20 TeV)
$\gamma$-rays from Mk 501.


title: GRworkbench: A Computational System Based on Differential Geometry

abstract:
  We have developed a new tool for numerical work in General Relativity:
GRworkbench. While past tools have been ad hoc, GRworkbench closely follows the
framework of Differential Geometry to provide a robust and general way of
computing on analytically defined space-times. We discuss the relationship
between Differential Geometry and C++ classes in GRworkbench, and demonstrate
their utility.


title:
The embedding of the spacetime in five-dimensional spaces with arbitrary
  non-degenerate Ricci tensor

abstract:
  We discuss and prove a theorem which asserts that any n-dimensional
semi-Riemannian manifold can be locally embedded in a (n+1)-dimensional space
with a non-degenerate Ricci tensor which is equal, up to a local analytic
diffeomorphism, to the Ricci tensor of an arbitrary specified space. This may
be regarded as a further extension of the Campbell-Magaard theorem. We
highlight the significance of embedding theorems of increasing degrees of
generality in the context of higher dimensional spacetimes theories and
illustrate the new theorem by establishing the embedding of a general class of
Ricci-flat spacetimes.


title: Refringence, field theory, and normal modes

abstract:
  In a previous paper [gr-qc/0104001; Class. Quant. Grav. 18 (2001) 3595-3610]
we have shown that the occurrence of curved spacetime ``effective Lorentzian
geometries'' is a generic result of linearizing an arbitrary classical field
theory around some non-trivial background configuration. This observation
explains the ubiquitous nature of the ``analog models'' for general relativity
that have recently been developed based on condensed matter physics. In the
simple (single scalar field) situation analyzed in our previous paper, there is
a single unique effective metric; more complicated situations can lead to
bi-metric and multi-metric theories. In the present paper we will investigate
the conditions required to keep the situation under control and compatible with
experiment -- either by enforcing a unique effective metric (as would be
required to be strictly compatible with the Einstein Equivalence Principle), or
at the worst by arranging things so that there are multiple metrics that are
all ``close'' to each other (in order to be compatible with the {\Eotvos}
experiment). The algebraically most general situation leads to a physical model
whose mathematical description requires an extension of the usual notion of
Finsler geometry to a Lorentzian-signature pseudo-Finsler geometry; while this
is possibly of some interest in its own right, this particular case does not
seem to be immediately relevant for either particle physics or gravitation. The
key result is that wide classes of theories lend themselves to an effective
metric description. This observation provides further evidence that the notion
of ``analog gravity'' is rather generic.


title: Evolution of the discrepancy between a universe and its model

abstract:
  We study a fundamental issue in cosmology: Whether we can rely on a
cosmological model to understand the real history of the Universe. This
fundamental, still unresolved issue is often called the ``model-fitting problem
(or averaging problem) in cosmology''. Here we analyze this issue with the help
of the spectral scheme prepared in the preceding studies.
  Choosing two specific spatial geometries that are very close to each other,
we investigate explicitly the time evolution of the spectral distance between
them; as two spatial geometries, we choose a flat 3-torus and a perturbed
geometry around it, mimicking the relation of a ``model universe'' and the
``real Universe''. Then we estimate the spectral distance between them and
investigate its time evolution explicitly. This analysis is done efficiently by
making use of the basic results of the standard linear structure-formation
theory.
  We observe that, as far as the linear perturbation of geometry is valid, the
spectral distance does not increase with time prominently,rather it shows the
tendency to decrease. This result is compatible with the general belief in the
reliability of describing the Universe by means of a model, and calls for more
detailed studies along the same line including the investigation of wider class
of spacetimes and the analysis beyond the linear regime.


title: Time and Cosmic Clock

abstract:
  The nature of time vis-a-vis relativity is critically examined. Based on the
author's space-time interaction hypothesis of late 1970's, cosmological model
with time-varying velocity of light is discussed.


title:
Quantum Effects of an Extra Compact Dimension on the Wave Function of
  the Universe

abstract:
  We extend the direct quantum approach of the standard FRW cosmology from 4D
to 5D and obtain a Hamiltonian formulation for a wave-like 5D FRW cosmology.
Using a late-time approximation we isolate out a y-part from the full wave
function of the 5D Universe. Then we find that the compactness of the fifth
dimension y yields a quantized spectrum for the momentum $P_{5}$ along the
fifth dimension, and we show that the whole space-part of the wave function of
the 5D Universe satisfies a two-dimensional Schr\"odinger equation.


title:
Path integral measure in Regge calculus from the functional Fourier
  transform

abstract:
  The problem of fixing measure in the path integral for the Regge-discretised
gravity is considered from the viewpoint of it's "best approximation" to the
already known formal continuum general relativity (GR) measure. A rigorous
formulation may consist in comparing functional Fourier transforms of the
measures, i.e. characteristic or generating functionals, and requiring these to
coincide on some dense set in the functional space. The possibility for such
set to exist is due to the Regge manifold being a particular case of general
Riemannian one (Regge calculus is a minisuperspace theory). The two versions of
the measure are obtained depending on what metric tensor, covariant or
contravariant one, is taken as fundamental field variable. The closed
expressions for the measure are obtained in the two simple cases of Regge
manifold. These turn out to be quite reasonable one of them indicating that
appropriately defined continuum limit of the Regge measure would reproduce the
original continuum GR measure.


title:
On the observational determination of squeezing in relic gravitational
  waves and primordial density perturbations

abstract:
  We develop a theory in which relic gravitational waves and primordial density
perturbations are generated by strong variable gravitational field of the early
Universe. The generating mechanism is the superadiabatic (parametric)
amplification of the zero-point quantum oscillations. The generated fields have
specific statistical properties of squeezed vacuum quantum states.
Macroscopically, squeezing manifests itself in a non-stationary character of
variances and correlation functions of the fields, the periodic structures of
the metric power spectra, and, as a consequence, in oscillatory behavior of the
higher order multipoles C_l of the cosmic microwave background anisotropy. We
start with the gravitational wave background and then apply the theory to
primordial density perturbations. We derive an analytical formula for the
positions of peaks and dips in the angular power spectrum l(l+1)C_l as a
function of l. This formula shows that the values of l at the peak positions
are ordered in the proportion 1:3:5:..., whereas at the dips they are ordered
as 1:2:3:.... We compare the derived positions with the actually observed
features, and find them to be in reasonably good agreement. It appears that the
observed structure is better described by our analytical formula based on the
(squeezed) metric perturbations associated with the primordial density
perturbations, rather than by the acoustic peaks reflecting the existence of
plasma sound waves at the last scattering surface. We formulate a forecast for
other features in the angular power spectrum, that may be detected by the
advanced observational missions, such as MAP and PLANCK. We tentatively
conclude that the observed structure is a macroscopic manifestation of
squeezing in the primordial metric perturbations.


title: Stars on branes: the view from the brane

abstract:
  We consider spherically symmetric matter configurations on a four dimensional
"brane" embedded in a five dimensional $Z_2$-symmetric "bulk". We write the
junction conditions between the interior and exterior of these "stars", treat a
couple of static examples in order to point out the differences with ordinary
four dimensional Einstein gravity, consider briefly a collapse situation and
conclude with the importance of a global view including asymptotic and
regularity conditions in the bulk.


title: Axial perturbations of general spherically symmetric spacetimes

abstract:
  The aim of this paper is to present a governing equation for first order
axial metric perturbations of general, not necessarily static, spherically
symmetric spacetimes. Under the non-restrictive assumption of axisymmetric
perturbations, the governing equation is shown to be a two-dimensional wave
equation where the wave function serves as a twist potential for the
axisymmetry generating Killing vector. This wave equation can be written in a
form which is formally a very simple generalization of the Regge-Wheeler
equation governing the axial perturbations of a Schwarzschild black hole, but
in general the equation is accompanied by a source term related to matter
perturbations. The case of a viscous fluid is studied in particular detail.


title: Geometry of Generic Isolated Horizons

abstract:
  Geometrical structures intrinsic to non-expanding, weakly isolated and
isolated horizons are analyzed and compared with structures which arise in
other contexts within general relativity, e.g., at null infinity. In
particular, we address in detail the issue of singling out the preferred
normals to these horizons required in various applications. This work provides
powerful tools to extract invariant, physical information from numerical
simulations of the near horizon, strong field geometry. While it complements
the previous analysis of laws governing the mechanics of weakly isolated
horizons, prior knowledge of those results is not assumed.


title: Entropy from the foam II

abstract:
  A simple model of spacetime foam, made by two different types of wormholes in
a semiclassical approximation, is taken under examination: one type is a
collection of $N_{w}$ Schwarzschild wormholes, while the other one is made by
Schwarzschild-Anti-de Sitter wormholes. The area quantization related to the
entropy via the Bekenstein-Hawking formula hints a possible selection between
the two configurations. Application to the charged black hole are discussed.


title:
Null Result for the Violation of Equivalence Principle with Free-Fall
  Rotating Gyroscopes

abstract:
  The differential acceleration between a rotating mechanical gyroscope and a
non-rotating one is directly measured by using a double free-fall
interferometer, and no apparent differential acceleration has been observed at
the relative level of 2x10{-6}. It means that the equivalence principle is
still valid for rotating extended bodies, i.e., the spin-gravity interaction
between the extended bodies has not been observed at this level. Also, to the
limit of our experimental sensitivity, there is no observed asymmetrical effect
or anti-gravity of the rotating gyroscopes as reported by hayasaka et al.


title: Scalar Non-Luminous Matter in Galaxies

abstract:
  As a candidate for dark matter in galaxies, we study an SU(3) triplet of
complex scalar fields which are non-minimally coupled to gravity. In the
spherically symmetric static spacetime where the flat rotational velocity
curves of stars in galaxies can be explained, we find simple solutions of
scalar fields with SU(3) global symmetry broken to U(1) X U(1), in an
exponential scalar potential, which will be useful in a quintessence model of
the late-time acceleration of the Universe.


title: Light Sheets and the Covariant Entropy Conjecture

abstract:
  We examine the holography bound suggested by Bousso in his covariant entropy
conjecture, and argue that it is violated because his notion of light sheet is
too generous. We suggest its replacement by a weaker bound.


title: New black holes in the brane-world?

abstract:
  It is known that the Einstein field equations in five dimensions admit more
general spherically symmetric black holes on the brane than four-dimensional
general relativity. We propose two families of analytic solutions (with
g_tt\not=-1/g_rr), parameterized by the ADM mass and the PPN parameter beta,
which reduce to Schwarzschild for beta=1. Agreement with observations requires
|\beta-1| |\eta|<<1. The sign of eta plays a key role in the global causal
structure, separating metrics which behave like Schwarzschild (eta<0) from
those similar to Reissner-Nordstroem (eta>0). In the latter case, we find a
family of black hole space-times completely regular.


title: Generalized observers and velocity measurements in General Relativity

abstract:
  To resolve some unphysical interpretations related to velocity measurements
by static observers, we discuss the use of generalized observer sets, give a
prescription for defining the speed of test particles relative to those
observers and show that, for any locally inertial frame, the speed of a freely
falling material particle is always less than the speed of light at the
Schwarzschild black hole surface.


title:
Covariant Self-force Regularization of a Particle Orbiting a
  Schwarzschild Black Hole - Mode Decomposition Regularization -

abstract:
  Covariant structure of the self-force of a particle in a general curved
background has been made clear in the cases of scalar [Quinn], electromagnetic
[DeWittBrehme], and gravitational charges [QuinnWald]. Namely, what we need is
the part of the self-field that is non-vanishing off and within the past
light-cone of particle's location, the so-called tail. The radiation reaction
force in the absence of external fields is entirely contained in the tail. In
this paper, we develop mathematical tools for the regularization and propose a
practical method to calculate the self-force of a particle orbiting a
Schwarzschild black hole.


title: Rotation intrinsic spin coupling--the parallelism description

abstract:
  For the Dirac particle in the rotational system, the rotation induced inertia
effect is analogously treated as the modification of the "spin connection" on
the Dirac equation in the flat spacetime, which is determined by the equivalent
tetrad. From the point of view of parallelism description of spacetime, the
obtained torsion axial-vector is just the rotational angular velocity, which is
included in the "spin connection". Furthermore the axial-vector spin coupling
induced spin precession is just the rotation-spin(1/2) interaction predicted by
Mashhoon. Our derivation treatment is straightforward and simplified in the
geometrical meaning and physical conception, however the obtained conclusions
are consistent with that of the other previous work.


title:
Higher Dimensional Cosmological Model in Space-Time-Mass (STM) Theory of
  Gravitation

abstract:
  A new class of non-static higher dimensional vacuum solutions in space-time
-mass (STM) theory of gravity is found. This solution represent expanding
universe without big bang singularity and the higher dimension of these models
shrinks as they expands.


title:
The generality of inflation in some closed FRW models with a scalar
  field

abstract:
  The generality of inflation in closed FRW Universe is studied for the models
with a scalar field on a brane and with a complex scalar field. The results
obtained are compared with the previously known results for the model with a
scalar field and a perfect fluid. The influence of the measure chosen in the
initial condition space on the ratio of inflationary solution is described.


title: New embedding of Schwarzschild geometry. I. Exterior solution

abstract:
  We propose a global minimal embedding of the Schwarzschild theory in a
five-dimensional flat space by using two surfaces. Covariant field equations
are deduced for the gravitational forces.


title: Deparametrization and quantization of the Taub universe

abstract:
  Previous analysis about the deparametrization and path integral quantization
of cosmological models are extended to models which do not admit an intrinsic
time. The formal expression for the transition amplitude is written down for
the Taub anisotropic universe with a clear notion of time. The relation
existing between the deparametrization associated to gauge fixation required in
the path integral approach and the procedure of reduction of the Wheeler-De
Witt equation is also studied.


title: Higher dimensional radiation collapse and cosmic censorship

abstract:
  We study the occurrence of naked singularities in the spherically symmetric
collapse of radiation shells in a higher dimensional spacetime. The necessary
conditions for the formation of a naked singularity or a black hole are
obtained. The naked singularities are found to be strong in the Tipler's sense
and thus violating cosmic censorship conjecture.


title: Topological Vacuum of the Closed Universe as a Gauging Factor

abstract:
  The only known general base to eliminate the vacuum divergencies of quantized
matter fields in quantum geometrodynamics is the fermion-boson supersymmetry.
The topological effect of the closed Universe -- discretization of the vacuum
fluctuations spectra -- allows to formulate the conditions of cancellation of
the divergencies. In the center of attention of this work is the fact that
these conditions result in the considerable restrictions on the gauge and
factor-ordering ambiguities peculiar to the equations of the theory and, in the
limits of the isotropic model of the Universe, remove these ambiguities
completely.


title: Quintessence Model With Double Exponential Potential

abstract:
  We have reinvestigated the quintessence model with minimally coupled scalar
field in the context of recent Supernova observation at $z=1.7$. By assuming
the form of the scale factor which gives both the early time deceleration and
late time acceleration, consistent with the observations, we show that one
needs a double exponential potential. We have also shown that the equation of
state and the behaviour of dark energy density are reasonably consistent with
earlier constraints obtained by different authors. This work shows again the
importance of double exponential potential for a quintessence field.


title:
Multidimensional Homogeneous Cosmological Models in Wesson Theory of
  Gravitation

abstract:
  Higher dimensional solutions are obtained for a homogeneous, spatially
isotropic cosmological model in Wesson theory of gravitation. Some cosmological
parameter are also calculated for this model.


title:
Robertson-Walker Type Lyttleton-Bondi Universe in Five Dimensional
  General Theory of Relativity

abstract:
  We study the Robertson-Walker type model in the Lyttleton-Bondi universe in
five dimensional general theory of relativity. Some exact and physical
properties of solutions are discussed.


title:
Numerical Tests of Evolution Systems, Gauge Conditions, and Boundary
  Conditions for 1D Colliding Gravitational Plane Waves

abstract:
  We investigate how the accuracy and stability of numerical relativity
simulations of 1D colliding plane waves depends on choices of equation
formulations, gauge conditions, boundary conditions, and numerical methods, all
in the context of a first-order 3+1 approach to the Einstein equations, with
basic variables some combination of first derivatives of the spatial metric and
components of the extrinsic curvature tensor. Hyperbolic schemes, specifically
variations on schemes proposed by Bona and Masso and Anderson and York, are
compared with variations of the Arnowitt-Deser-Misner formulation.
Modifications of the three basic schemes include raising one index in the
metric derivative and extrinsic curvature variables and adding a multiple of
the energy constraint to the extrinsic curvature evolution equations. Redundant
variables in the Bona-Masso formulation may be reset frequently or allowed to
evolve freely. Gauge conditions which simplify the dynamical structure of the
system are imposed during each time step, but the lapse and shift are reset
periodically to control the evolution of the spacetime slicing and the
longitudinal part of the metric. We show that physically correct boundary
conditions, satisfying the energy and momentum constraint equations,
generically require the presence of some ingoing eigenmodes of the
characteristic matrix. Numerical methods are developed for the hyperbolic
systems based on decomposing flux differences into linear combinations of
eigenvectors of the characteristic matrix. These methods are shown to be
second-order accurate, and in practice second-order convergent, for smooth
solutions, even when the eigenvectors and eigenvalues of the characteristic
matrix are spatially varying.


title:
Recent Improvements in Testing General Relativity with Satellite Laser
  Ranging

abstract:
  In this work some aspects of the detection of certain general relativistic
effects in the weak gravitational field of the Earth via laser-ranged data to
some existing or proposed geodetic satellites are examined. The focus is on the
Lense-Thirring drag of the orbit of a test body, the gravitomagnetic clock
effect and the gravitoelectric perigee shift. The impact of some sources of
systematic errors is investigated. An experiment whose goal is the measurement
of the PPN parameters beta and gamma in the terrestrial field with LAGEOS
satellites at a level of 10^(-3)is presented. A modified version of the
proposed LARES mission is examined.

categories: gr-qc astro-ph physics.geo-ph physics.space-ph


title: Coframe energy-momentum current. Algebraic properties

abstract:
  The coframe (teleparallel) description of gravity is known as a viable
alternative to GR. One of advantages of this model is the existence of a
conserved energy-momentum current witch is covariant under all symmetries of
the three-parameter Lagrangian. In this paper we study the relation between the
covector valued current and the energy-momentum tensor. Algebraic properties of
the conserved current for different values of parameters are derived. It is
shown that the tensor corresponding to the coframe current is traceless and, in
contrast to the electromagnetic field, has in general a non vanishing
antisymmetric part. The symmetric part is also non zero for all values of the
parameters. Consequently, the conserved current involves the energy-momentum as
well as the rotational (spin) properties of the field.


title:
From Poincare to affine invariance: How does the Dirac equation
  generalize?

abstract:
  A generalization of the Dirac equation to the case of affine symmetry, with
SL(4,R) replacing SO(1,3), is considered. A detailed analysis of a Dirac-type
Poincare-covariant equation for any spin j is carried out, and the related
general interlocking scheme fulfilling all physical requirements is
established. Embedding of the corresponding Lorentz fields into
infinite-component SL(4,R) fermionic fields, the constraints on the SL(4,R)
vector-operator generalizing Dirac's gamma matrices, as well as the minimal
coupling to (Metric-)Affine gravity are studied. Finally, a symmetry breaking
scenario for SA(4,R) is presented which preserves the Poincare symmetry.


title:
A finite spin-foam-based theory of three and four dimensional quantum
  gravity

abstract:
  Starting from Ooguri's construction for $BF$ theory in three (and four)
dimensions, we show how to construct a well defined theory with an infinite
number of degrees of freedom. The spin network states that are kept invariant
by the evolution operators of the theory are exact solutions of the Hamiltonian
constraint of quantum gravity proposed by Thiemann. The resulting theory is the
first example of a well defined, finite, consistent, spin-foam based theory in
a situation with an infinite number of degrees of freedom. Since it solves the
quantum constraints of general relativity it is also a candidate for a theory
of quantum gravity. It is likely, however, that the solutions constructed
correspond to a spurious sector of solutions of the constraints. The richness
of the resulting theory makes it an interesting example to be analyzed by
forthcoming techniques that construct the semi-classical limit of spin network
quantum gravity.


title: Fundamental time asymmetry from nontrivial space topology

abstract:
  It is argued that a fundamental time asymmetry could arise from the global
structure of the space manifold. The proposed mechanism relies on the CPT
anomaly of certain chiral gauge theories defined over a multiply connected
space manifold. The resulting time asymmetry (microscopic arrow of time) is
illustrated by a simple thought experiment. The effect could, in principle,
play a role in determining the initial conditions of the big bang.


title:
Stationary Cylindrically Symmetric Solution Approaching Einstein's
  Cosmological Solution

abstract:
  Here we describe a stationary cylindrically symmetric solution of Einstein's
equation with matter consisting of a positive cosmological and rotating dust
term. The solution approaches Einstein static universe solution.


title:
How the Geometric Calculus Resolves the Ordering Ambiguity of Quantum
  Theory in Curved Space

abstract:
  The long standing problem of the ordering ambiguity in the definition of the
Hamilton operator for a point particle in curved space is naturally resolved by
using the powerful geometric calculus based on Clifford Algebra. The momentum
operator is defined to be the vector derivative (the gradient) multiplied by
$-i$; it can be expanded in terms of basis vectors $\gamma_\mu$ as $p = -i
\gamma^\mu \p_\mu$. The product of two such operators is unambiguous, and such
is the Hamiltonian which is just the D'Alambert operator in curved space; the
curvature scalar term is not present in the Hamiltonian if we confine our
consideration to scalar wave functions only. It is also shown that $p$ is
Hermitian and self-adjoint operator: the presence of the basis vectors
$\gamma^\mu$ compensates the presence of $\sqrt{|g|}$ in the matrix elements
and in the scalar product. The expectation value of such operator follows the
classical geodetic line.


title: Simulating the dynamics of relativistic stars via a light-cone approach

abstract:
  We present new numerical algorithms for the coupled Einstein-perfect fluid
system in axisymmetry. Our framework uses a foliation based on a family of
light cones, emanating from a regular center, and terminating at future null
infinity. This coordinate system is well adapted to the study of the dynamical
spacetimes associated with isolated relativistic compact objects such as
neutron stars. In particular, the approach allows the unambiguous extraction of
gravitational waves at future null infinity and avoids spurious outer boundary
reflections. The code can accurately maintain long-term stability of polytropic
equilibrium models of relativistic stars. We demonstrate global energy
conservation in a strongly perturbed neutron star spacetime, for which the
total energy radiated away by gravitational waves corresponds to a significant
fraction of the Bondi mass. As a first application we present results in the
study of pulsations of axisymmetric relativistic stars, extracting the
frequencies of the different fluid modes in fully relativistic evolutions of
the Einstein-perfect fluid system and making a first comparison between the
gravitational news function and the predicted wave using the approximations of
the quadrupole formula.


title: Embeddings in Spacetimes Sourced by Scalar Fields

abstract:
  The extension of the Campbell-Magaard embedding theorem to general relativity
with minimally-coupled scalar fields is formulated and proven. The result is
applied to the case of a self-interacting scalar field for which new embeddings
are found, and to Brans-Dicke theory. The relationship between Campbell-Magaard
theorem and the general relativity, Cauchy and initial value problems is
outlined.


title: Lighthouses of Gravitational Wave Astronomy

abstract:
  Gravitational wave detectors capable of making astronomical observations
could begin to operate within the next year, and over the next 10 years they
will extend their reach out to cosmological distances, culminating in the space
mission LISA. A prime target of these observatories will be binary systems,
especially those whose orbits shrink measurably during an observation period.
These systems are standard candles, and they offer independent ways of
measuring cosmological parameters. LISA in particular could identify the epoch
at which star formation began and, working with telescopes making
electromagnetic observations, measure the Hubble flow at redshifts out to 4 or
more with unprecedented accuracy.


title: Higher Dimensional Static Cosmological Model in Lyra Manifold

abstract:
  A static conformally flat spherically symmetric perfect fluid cosmological
model in Lyra geometry is investigatd.


title: Virtual black hole phenomenology from 2d dilaton theories

abstract:
  Equipped with the tools of (spherically reduced) dilaton gravity in first
order formulation and with the results for the lowest order S-matrix for s-wave
gravitational scattering (P. Fischer, D. Grumiller, W. Kummer, and D.
Vassilevich, gr-qc/0105034) new properties of the ensuing cross-section are
discussed. We find CPT invariance, despite of the non-local nature of our
effective theory and discover pseudo-self-similarity in its kinematic sector.
  After presenting the Carter-Penrose diagram for the corresponding virtual
black hole geometry we encounter distributional contributions to its
Ricci-scalar and a vanishing Einstein-Hilbert action for that configuration.
Finally, a comparison is done between our (Minkowskian) virtual black hole and
Hawking's (Euclidean) virtual black hole bubbles.


title: Inflationary phase in Generalized Brans-Dicke theory

abstract:
  We find a solution for exponential inflation in a Brans-Dicke generalized
model, where the coupling "constant " is variable. While in General Relativity
the equation of state is p is equal to minus rho, here we find p proportional
to rho, where the proportionality constant is smaller than -2/3. The negativity
of cosmic pressure implies acceleration of the expansion, even with lambda < 0
>.


title:
Static Generalized Brans-Dicke Universe and Gravitational Waves
  Amplification

abstract:
  We find a static solution for the scale-factor in a Brans-Dicke generalized
theory where the scalar field and the coupling constant vary with time. We find
also that in the early Universe there may be amplification of gravitational
waves.


title:
Amplification of Gravitational Waves During Inflation in Brans-Dicke
  Theory

abstract:
  We show that Gravitational Waves are exponetially amplified in the
inflationary phase in Brans-Dicke theory, so that it would be possible to
detect them and in this way verify several features of physical reality.


title:
Estimate on the deceleration parameter in a Universe with variable fine
  structure constant

abstract:
  We determine a cosmological model that include a positive acceleration of the
Universe and a time decreasing fine structure constant. The present day
deceleration parameter is estimated by us, according to our model and the
available experimental data .


title: On a time varying fine structure constant

abstract:
  By employing Dirac LNH, and a further generalization by Berman (GLNH), we
estimate how should vary the total number of nucleons, the energy density,
Newton Gravitational constant, the cosmological constant, the magnetic
permeability and electric permitivity, of the Universe,in order to account for
the experimentally observed time variation of the fine structure constant. As a
bonus,we find an acceptable value for the deceleration parameter of the present
Universe, compatible with the Supernovae observations.


title: Relativity and c/sqrt{3}

abstract:
  We define the critical coordinate velocity v_c. A particle moving radially in
Schwarzschild background with this velocity, v_c= c/sqrt 3, is neither
accelerated, nor decelerated if gravitational field is weak, r_g << r, where
r_g is the gravitational radius, while r is the current one.
  We find that the numerical coincidence of v_c with velocity of sound in
ultrarelativistic plasma, u_s, is accidental, since two velocities are
different if the number of spatial dimensions is not equal to 3


title:
Gravitational signals emitted by a point mass orbiting a neutron star:
  effects of stellar structure

abstract:
  The effects that the structure of a neutron star would have on the
gravitational emission of a binary system are studied in a perturbative regime,
and in the frequency domain. Assuming that a neutron star is perturbed by a
point mass moving on a close, circular orbit, we solve the equations of stellar
perturbations in general relativity to evaluate the energy lost by the system
in gravitational waves. We compare the energy output obtained for different
stellar models with that found by assuming that the perturbed object is a black
hole with the same mass, and we discuss the role played by the excitation of
the stellar modes. Ouresults indicate that the stellar structure begins to
affect the emitted power when the orbital velocity is v >0.2c (about 185 Hz for
a binary system composed of two canonical neutron stars). We show that the
differences between different stellar models and a black hole are due mainly to
the excitation of the quasinormal modes of the star. Finally, we discuss to
what extent and up to which distance the perturbative approach can be used to
describe the interaction of a star and a pointlike massive body.


title: Decoherence and gravitational backgrounds

abstract:
  We study the decoherence process associated with the scattering of stochastic
gravitational waves. We discuss the case of macroscopic systems, such as the
planetary motion of the Moon around the Earth, for which gravitational
scattering is found to dominate decoherence though it has a negligible
influence on damping. This contrast is due to the very high effective
temperature of the background of gravitational waves in our galactic
environment.


title: Curvature and Torsion Quintessence

abstract:
  The issues of quintessence and cosmic acceleration can be discussed in the
framework of higher order curvature and torsion theories of gravity. We can
define effective pressure and energy density directly connected to the
curvature or to the torsion fields and then ask for the conditions to get an
accelerated expansion. Exact accelerated expanding solutions can be achieved
for several fourth order curvature or torsion theories so that we obtain an
alternative scheme to the standard quintessence scalar field, minimally coupled
to gravity, usually adopted. We discuss also conformal transformations in order
to see the links of quintessence between the Jordan and Einstein frames.
Furthermore, we take into account a torsion fluid whose effects become relevant
at large scale. Specifically, we investigate a model where a totally
antisymmetric torsion field is taken into account discussing the conditions to
obtain quintessence. We obtain exact solutions also in this case where dust
dominated Friedmann behavior is recovered as soon as torsion effects are not
relevant.


title: Cold Dark Matter from Dark Energy

abstract:
  Dark energy/matter unification is first demonstrated within the framework of
a simplified model.
  Geodetic evolution of a cosmological constant dominated bubble Universe, free
of genuine matter, is translated into a specific FRW cosmology whose
effectively induced dark component highly resembles the cold dark matter
ansatz. The realistic extension constitutes a dark soliton which bridges past
(radiation and/or matter dominated) and future (cosmological constant
dominated)
  Einstein regimes; its experimental signature is a moderate redshift dependent
cold dark matter deficiency function.


title:
Existence of Local Covariant Time Ordered Products of Quantum Fields in
  Curved Spacetime

abstract:
  We establish the existence of local, covariant time ordered products of local
Wick polynomials for a free scalar field in curved spacetime. Our time ordered
products satisfy all of the hypotheses of our previous uniqueness theorem, so
our construction essentially completes the analysis of the existence,
uniqueness and renormalizability of the perturbative expansion for nonlinear
quantum field theories in curved spacetime. As a byproduct of our analysis, we
derive a scaling expansion of the time ordered products about the total
diagonal that expresses them as a sum of products of polynomials in the
curvature times Lorentz invariant distributions, plus a remainder term of
arbitrary low scaling degree.


title: Null Energy Condition Violations in Eternal Inflation

abstract:
  The usual scenario of ``eternal inflation'' involves an approximately de
Sitter spacetime undergoing upward fluctuations of the local expansion rate
$H$. This spacetime requires frequent violations of the Null Energy Condition
(NEC). We investigate the fluctuations of the energy-momentum tensor of the
scalar field in de Sitter space as a possible source of such violations. We
find that fluctuations of the energy-momentum tensor smeared in space and time
are well-defined and may provide the NEC violations. Our results for slow-roll
inflation are consistent with the standard calculations of inflationary density
fluctuations. In the diffusive regime where quantum fluctuations dominate the
slow-roll evolution, the magnitude of smeared energy-momentum tensor
fluctuations is large enough to create frequent NEC violations.


title: A Non-Metric Approach to Space, Time and Gravitation

abstract:
  In this thesis, a non-standard geometric framework, the "quasi-metric"
framework (QMF), is used to define relativistic space-time. The QMF consists of
a 4-dimensional space-time manifold equipped with two one-parameter families of
Lorentzian 4-metrics ${\bf g}_t$ and ${\bf {\bar g}}_t$ parametrized by a
(unique) global time function $t$. The global time function represents one
extra degenerate time dimension and it defines a "distinguished" foliation of
quasi-metric space-time into spatial hypersurfaces. The metric family ${\bf
{\bar g}}_t$ is found as solutions of field equations, whereas the metric
family ${\bf g}_t$ is found via a local transformation ${\bf {\bar
g}}_t{\rightarrow}{\bf g}_t$ and is used in the equations of motion. The role
of the degenerate dimension is to describe global scale changes between
gravitational and non-gravitational systems. In particular, this yields an
alternative description of the expansion of the Universe. In this thesis, a
quasi-metric theory of gravity is constructed. Like General Relativity, the
field equations have two independent propagating dynamical degrees of freedom.
However, the existence of a distinguished dynamical foliation of quasi-metric
space-time into spatial hypersurfaces makes the field equations unsuitable for
a standard PPN-analysis. This implies that the experimental status of the
theory is not completely clear at this point in time. But the non-metric part
of the theory may be tested rather independently. That is, the theory predicts
that gravitational fields in vacuum and gravitationally bound bodies made of
ideal gas expand like the expansion of the Universe. Several observations
suggest this; e.g., the "Pioneer effect", the mean acceleration of the Moon,
the spin-down of the Earth, palaeo-tidal records, etc. Thus quasi-metric
relativity has experimental support where metric theories fail.


title: Analogue models of and for gravity

abstract:
  Condensed matter systems, such as acoustics in flowing fluids, light in
moving dielectrics, or quasiparticles in a moving superfluid, can be used to
mimic aspects of general relativity. More precisely these systems (and others)
provide experimentally accessible models of curved-space quantum field theory.
As such they mimic kinematic aspects of general relativity, though typically
they do not mimic the *dynamics*. Although these analogue models are thereby
limited in their ability to duplicate all the effects of Einstein gravity they
nevertheless are extremely important -- they provide black hole analogues (some
of which have already been seen experimentally) and lead to tests of basic
principles of curved-space quantum field theory. Currently these tests are
still in the realm of *gedanken-experiments*, but there are plausible candidate
models that should lead to laboratory experiments in the not too distant
future.


title: Hyperbolic theories of dissipation: Why and when do we need them?

abstract:
  We illustrate and emphasize the relevance of hyperbolic theories of
dissipation in different physical scenarios. Particular attention is paid to
self-gravitating systems where the relaxation time may become large enough as
to require a description of the transient regime. It is argued that even
outside that regime, hyperbolic theories may be needed to provide an accurate
description of dissipative processes.


title:
Formation of Complex Matter Structures and Mutual Relations Between the
  Mass of Elementary Particles

abstract:
  The model of Expansive Nondecelerative Universe leads to a conclusion stating
that at the end of radiation era the Jeans mass was equal to the upper mass
limit of a black hole and, at the same time, the effective gravitational range
of nucleons was identical to their Compton wavelength. At that time nucleons
started to exert gravitational impact on their environment which enabled to
large scale structures become formed. Moreover, it is shown that there is a
deep relationships between the inertial mass of various leptons and bosons and
that such relations can be extended also into the realm of other kinds of
elementary particles.


title:
Coulomb and quantum oscillator problems in conical spaces with arbitrary
  dimensions

abstract:
  The Schr\"odinger equations for the Coulomb and the Harmonic oscillator
potentials are solved in the cosmic-string conical space-time. The spherical
harmonics with angular deficit are introduced.
  The algebraic construction of the harmonic oscillator eigenfunctions is
performed through the introduction of non-local ladder operators. By exploiting
the hidden symmetry of the two-dimensional harmonic oscillator the eigenvalues
for the angular momentum operators in three dimensions are reproduced.
  A generalization for N-dimensions is performed for both Coulomb and harmonic
oscillator problems in angular deficit space-times.
  It is thus established the connection among the states and energies of both
problems in these topologically non-trivial space-times.


title: A Thermodynamic Sector of Quantum Gravity

abstract:
  The connection between gravity and thermodynamics is explored. Examining a
perfect fluid in gravitational equilibrium we find that the entropy is extremal
only if Einstein's equations are satisfied. Conversely, one can derive part of
Einstein's equations from ordinary thermodynamical considerations. This allows
the theory of this system to be recast in such a way that a sector of general
relativity is purely thermodynamical and should not be quantized.


title:
Dual variables and a connection picture for the Euclidean Barrett-Crane
  model

abstract:
  The partition function of the SO(4)- or Spin(4)-symmetric Euclidean
Barrett-Crane model can be understood as a sum over all quantized geometries of
a given triangulation of a four-manifold. In the original formulation, the
variables of the model are balanced representations of SO(4) which describe the
quantized areas of the triangles. We present an exact duality transformation
for the full quantum theory and reformulate the model in terms of new variables
which can be understood as variables conjugate to the quantized areas. The new
variables are pairs of S^3-values associated to the tetrahedra. These
S^3-variables parameterize the hyperplanes spanned by the tetrahedra (locally
embedded in R^4), and the fact that there is a pair of variables for each
tetrahedron can be viewed as a consequence of an SO(4)-valued parallel
transport along the edges dual to the tetrahedra. We reconstruct the parallel
transport of which only the action of SO(4) on S^3 is physically relevant and
rewrite the Barrett-Crane model as an SO(4) lattice BF-theory living on the
2-complex dual to the triangulation subject to suitable constraints whose form
we derive at the quantum level. Our reformulation of the Barrett-Crane model in
terms of continuous variables is suitable for the application of various
analytical and numerical techniques familiar from Statistical Mechanics.


title: Charged Rotating Black Holes in Equilibrium

abstract:
  Axially symmetric, stationary solutions of the Einstein-Maxwell equations
with disconnected event horizon are studied by developing a method of explicit
integration of the corresponding boundary-value problem. This problem is
reduced to non-leaner system of algebraic equations which gives relations
between the masses, the angular momenta, the angular velocities, the charges,
the distance parameters, the values of the electromagnetic field potential at
the horizon and at the symmetry axis. A found solution of this system for the
case of two charged non-rotating black holes shows that in general the total
mass depends on the distance between black holes. Two-Killing reduction
procedure of the Einstein-Maxwell equations is also discussed.


title: Gravitational Wave Induced Vibrations of Slender Structures in Space

abstract:
  This paper explores the interaction of weak gravitational fields with slender
elastic materials in space and estimates their sensitivities for the detection
of gravitational waves with frequencies between $10^{-4}$ and 1 Hz. The dynamic
behaviour of such slender structures is ideally suited to analysis by the
simple theory of Cosserat rods. Such a description offers a clean conceptual
separation of the vibrations induced by bending, shear, twist and extension and
the response to gravitational tidal accelerations can be reliably estimated in
terms of the constitutive properties of the structure. The sensitivity
estimates are based on a truncation of the theory in the presence of thermally
induced homogeneous Gaussian stochastic forces.


title: Semiglobal Numerical Calculations of Asymptotically Minkowski Spacetimes

abstract:
  This talk reports on recent progress toward the semiglobal study of
asymptotically flat spacetimes within numerical relativity. The development of
a 3D solver for asymptotically Minkowski-like hyperboloidal initial data has
rendered possible the application of Friedrich's conformal field equations to
astrophysically interesting spacetimes. As a first application, the whole
future of a hyperboloidal set of weak initial data has been studied, including
future null and timelike infinity. Using this example we sketch the numerical
techniques employed and highlight some of the unique capabilities of the
numerical code. We conclude with implications for future work.


title:
Creation of scalar and Dirac particles in the presence of a time varying
  electric field in an anisotropic Bianchi I universe

abstract:
  In this article we compute the density of scalar and Dirac particles created
by a cosmological anisotropic Bianchi type I universe in the presence of a time
varying electric field. We show that the particle distribution becomes thermal
when one neglects the electric interaction.


title: Report on A5. Computer Methods

abstract:
  Session A5 on numerical methods contained talks on colliding black holes,
critical phenomena, investigation of singularities, and computer algebra.


title:
A New Transition between Discrete and Continuous Self-Similarity in
  Critical Gravitational Collapse

abstract:
  We analyze a bifurcation phenomenon associated with critical gravitational
collapse in a family of self-gravitating SU(2) $\sigma$-models. As the
dimensionless coupling constant decreases, the critical solution changes from
discretely self-similar (DSS) to continuously self-similar (CSS). Numerical
results provide evidence for a bifurcation which is analogous to a heteroclinic
loop bifurcation in dynamical systems, where two fixed points (CSS) collide
with a limit cycle (DSS) in phase space as the coupling constant tends to a
critical value.


title:
Self-similar spherically symmetric solutions of the massless
  Einstein-Vlasov system

abstract:
  We construct the general spherically symmetric and self-similar solution of
the Einstein-Vlasov system (collisionless matter coupled to general relativity)
with massless particles, under certain regularity conditions. Such solutions
have a curvature singularity by construction, and their initial data on a
Cauchy surface to the past of the singularity can be chosen to have compact
support in momentum space. They can also be truncated at large radius so that
they have compact support in space, while retaining self-similarity in a
central region that includes the singularity. However, the Vlasov distribution
function can not be bounded. As a simpler illustration of our techniques and
notation we also construct the general spherically symmetric and static
solution, for both massive and massless particles.


title: On the effective inertial mass density of a dissipative fluid

abstract:
  It is shown that the effective inertial mass density of a dissipative fluid
just after leaving the equilibrium, on a time scale of the order of relaxation
time, reduces by a factor which depends on dissipative variables. Prospective
applications of this result to cosmological and astrophysical scenarios are
discussed.


title:
Possible Cosmological Implications of Time Varying Fine Structure
  Constant

abstract:
  We make use of Dirac LNH and results for a time varying fine structure
constant in order to derive possible laws of variation for speed of light, the
number of nucleons in the Universe, energy density and gravitational constant.
By comparing with experimental bounds on G variation, we find that the
deceleration paramenter of the present Universe is negative. This is coherent
with recent Supernovae observations.


title: Relativistic Gravity With a Dynamical Preferred Frame

abstract:
  While general relativity possesses local Lorentz invariance, both canonical
quantum gravity and string theory suggest that Lorentz invariance may be broken
at high energies. Broken Lorentz invariance has also been postulated as an
explanation for astrophysical anomalies such as the missing GZK cutoff.
Therefore, we seek an effective field theory description of gravity where
Lorentz invariance is broken. We will construct a candidate theory and then
briefly discuss some of the implications.


title:
Optimal detection of burst events in gravitational wave interferometric
  observatories

abstract:
  We consider the problem of detecting a burst signal of unknown shape. We
introduce a statistic which generalizes the excess power statistic proposed by
Flanagan and Hughes and extended by Anderson et al. The statistic we propose is
shown to be optimal for arbitrary noise spectral characteristic, under the two
hypotheses that the noise is Gaussian, and that the prior for the signal is
uniform. The statistic derivation is based on the assumption that a signal
affects only affects N samples in the data stream, but that no other
information is a priori available, and that the value of the signal at each
sample can be arbitrary. We show that the proposed statistic can be implemented
combining standard time-series analysis tools which can be efficiently
implemented, and the resulting computational cost is still compatible with an
on-line analysis of interferometric data. We generalize this version of an
excess power statistic to the multiple detector case, also including the effect
of correlated noise. We give full details about the implementation of the
algorithm, both for the single and the multiple detector case, and we discuss
exact and approximate forms, depending on the specific characteristics of the
noise and on the assumed length of the burst event. As a example, we show what
would be the sensitivity of the network of interferometers to a delta-function
burst.


title:
Quantum Thermal Effect of Dirac Particles in a Non-uniformly
  Rectilinearly Accelerating Black Hole with Electronic Charge, Magnetic Charge
  and Cosmological Constant

abstract:
  The Hawking radiation of Dirac particles in an arbitrarily rectilinearly
accelerating Kinnersley black hole with electro-magnetic charge and
cosmological constant is investigated by using method of the generalized
tortoise coordinate transformation. Both the location and the temperature of
the event horizon depend on the time and the polar angle. The Hawking thermal
radiation spectrum of Dirac particles is also derived.
  PACS numbers: 04.70.Dy, 97.60.Lf


title: Inertial forces - a la Newton in General Relativity

abstract:
  In this we briefly cover the covariant approach to describe inertial forces
in general relativity and in particular look at the behaviour of the cumulative
drag index for stationary Kerr geometry.


title: Momentum space topology of fermion zero modes on brane

abstract:
  We discuss fermion zero modes within the 3+1 brain -- the domain wall between
the two vacua in 4+1 spacetime. We do not assume relativistic invariance in 4+1
spacetime, or any special form of the 4+1 action. The only input is that the
fermions in bulk are fully gapped and are described by nontrivial
momentum-space topology. Then the 3+1 wall between such vacua contains chiral
3+1 fermions. The bosonic collective modes in the wall form the gauge and
gravitational fields. In principle, this universality class of fermionic vacua
can contain all the ingredients of the Standard Model and gravity.


title:
Frequencies of f-modes in differentially rotating relativistic stars and
  secular stability limits

abstract:
  We have computed the eigenfrequencies of f-modes for a constant-rest-mass
sequences of rapidly rotating relativistic inviscid stars in differential
rotation. The frequencies have been calculated neglecting the metric
perturbations (the relativistic Cowling approximation) and expressed as a
function of the ratio between the rotational kinetic energy and the absolute
value of the gravitational energy of the stellar model beta=T/|W|. The zeros
and the end-points of these sequences mark respectively the onset of the
secular instability driven by gravitational radiation-reaction and the maximum
value of beta at which an equilibrium model exists. In differentially rotating
stars the secular stability limits appear at a beta larger than those found for
uniformly rotating stars. Differential rotation, on the other hand, also allows
for the existence of equilibrium models at values of beta larger than those for
uniformly rotating stars, moving the end-point of the sequences to larger beta.
As a result, for some degrees of differential rotation, the onset of the
secular instability for f-modes is generally favoured by the presence of
differential rotation.


title: Bounding the graviton mass with binary pulsar observations

abstract:
  By comparing the observed orbital decay of the binary pulsars PSRB1913+16 and
PSRB1534+12 to that predicted by general relativity due to gravitational-wave
emission, we are able to bound the mass of the graviton to be less than
$7.6\times10^{-20} \text{eV}/c^2$ at 90% confidence. This is the first such
bound to be derived from dynamic gravitational fields. It is approximately two
orders of magnitude weaker than the static-field bound from solar system
observations, and will improve with further observations.


title: Adding Twist to Anisotropic Fluids

abstract:
  We present a solution generating technique for anisotropic fluids which
preserves specific Killing symmetries. Anisotropic matter distributions that
can be used with the one parameter Ehlers-Geroch transform are discussed.
Example spacetimes that support the appropriate anisotropic stress-energy are
found and the transformation applied. The 3+1 black string solution is one of
the spacetimes with the appropriate matter distribution. Use of the transform
with a black string seed is discussed.


title: Full Causal Bulk Viscous Cosmological Models with Variable G and Lambda

abstract:
  We study the evolution of a flat Friedmann-Robertson- Walker Universe, filled
with a bulk viscous cosmological fluid, in the presence of variable
gravitational and cosmological constants. The dimensional analysis of the model
suggest a proportionality between the bulk viscous pressure of the dissipative
fluid and the energy density. With the use of this assumption and with the
choice of the standard equations of state for the bulk viscosity coefficient,
temperature and relaxation time, the general solution of the field equations
can be obtained, with all physical parameters having a power-law time
dependence. The symmetry analysis of this model, performed by using Lie group
techniques, confirms the unicity of the solution for this functional form of
the bulk viscous pressure.


title: Parametric gravity wave detector

abstract:
  Since 1978 superconducting coupled cavities have been proposed as a sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the esulting motion, induces the transition of some
energy from an initially excited cavity mode to an empty one. The energy
transfer is maximum when the frequency of the wave is equal to the frequency
difference of the two cavity modes. In 1984 Reece, Reiner and Melissinos built
a detector of the type proposed, and used it as a transducer of harmonic
mechanical motion, achieving a sensitivity to fractional deformations of the
order dx/x ~ 10^(-18). In this paper the working principles of the detector are
discussed and the last experimental results summarized. New ideas for the
development of a realistic gravitational waves detector are considered; the
outline of a possible detector design and its expected sensitivity are also
shown.


title: Towards a Theory of Quantum Black Hole

abstract:
  We describe some specific quantum black hole model. It is pointed out that
the origin of a black hole entropy is the very process of quantum gravitational
collapse. The quantum black hole mass spectrum is extracted from the mass
spectrum of the gravitating source. The classical analog of quantum black hole
is constructed.


title: Analytical approach to critical collapse in 2+1 dimensions

abstract:
  We present a family of time-dependent solutions to 2+1 gravity with negative
cosmological constant and a massless scalar field as source. These solutions
are continuously self-similar near the central singularity. We analyze linear
perturbations of these solutions, and discuss the subtle question of boundary
conditions. We find two growing modes, one of which corresponds to the
linearization of static singular solutions, while the other describes black
hole formation.


title: Toward a Quantization of Null Dust Collapse

abstract:
  Spherically symmetric, null dust clouds, like their time-like counterparts,
may collapse classically into black holes or naked singularities depending on
their initial conditions. We consider the Hamiltonian dynamics of the collapse
of an arbitrary distribution of null dust, expressed in terms of the physical
radius, $R$, the null coordinates, $V$ for a collapsing cloud or $U$ for an
expanding cloud, the mass function, $m$, of the null matter, and their
conjugate momenta. This description is obtained from the ADM description by a
Kucha\v{r}-type canonical transformation. The constraints are linear in the
canonical momenta and Dirac's constraint quantization program is implemented.
Explicit solutions the constraints are obtained for both expanding and
contracting null dust clouds with arbitrary mass functions.


title: Quasi-Metric Relativity

abstract:
  This is a survey of a new type of relativistic space-time framework; the
so-called quasi-metric framework. The basic geometric structure underlying
quasi-metric relativity is quasi-metric space-time; this is defined as a
4-dimensional differentiable manifold ${\cal N}$ equipped with two
one-parameter families ${\bf {\bar g}}_t$ and ${\bf g}_t$ of Lorentzian
4-metrics parametrized by a global time function $t$. The metric family ${\bf
{\bar g}}_t$ is found from field equations, whereas the metric family ${\bf
g}_t$ is used to propagate sources and to compare predictions to experiments. A
linear and symmetric affine connection compatible with the family ${\bf g}_t$
is defined, giving rise to equations of motion.
  Furthermore a quasi-metric theory of gravity, including field equations and
local conservation laws, is presented. Just as for General Relativity, the
field equations accommodate two independent propagating dynamical degrees of
freedom. On the other hand, the particular structure of quasi-metric geometry
allows only a partial coupling of space-time geometry to the active
stress-energy tensor. Besides, the field equations are defined from projections
of physical and geometrical tensors with respect to a "preferred" foliation of
quasi-metric space-time into spatial hypersurfaces. The dynamical nature of
this foliation makes the field equations unsuitable for a standard
PPN-analysis. This implies that the experimental status of the theory is not
completely clear at this point in time. The theory seems to be consistent with
a number of cosmological observations and it satisfies all the classical solar
system tests, though. Moreover, in its non-metric sector the new theory has
experimental support where General Relativity fails or is irrelevant.


title: The Collapse of Large Extra Dimensions

abstract:
  In models of spacetime that are the product of a four-dimensional spacetime
with an ``extra'' dimension, there is the possibility that the extra dimension
will collapse to zero size, forming a singularity. We ask whether this collapse
is likely to destroy the spacetime. We argue, by an appeal to the
four-dimensional cosmic censorship conjecture, that--at least in the case when
the extra dimension is homogeneous--such a collapse will lead to a singularity
hidden within a black string. We also construct explicit initial data for a
spacetime in which such a collapse is guaranteed to occur and show how the
formation of a naked singularity is likely avoided.


title: Bulk scalar field in the braneworld can mimic the 4D inflaton dynamics

abstract:
  Based on the recently proposed scenario of inflation driven by a bulk scalar
field in the braneworld of the Randall-Sundrum (RS) type, we investigate the
dynamics of a bulk scalar field on the inflating braneworld. We derive the late
time behavior of the bulk scalar field by analyzing the property of the
retarded Green function. We find that the late time behavior is basically
dominated by a single (or a pair of) pole(s) in the Green function irrespective
of the initial condition and of the signature of $m^{2}=V''(\phi)$, where
$V(\phi)$ is the potential of the bulk scalar field. Including the lowest order
back-reaction to the geometry, this late time behavior can be well approximated
by an effective 4-dimensional scalar field with $m^2_{\mathrm{eff}}=m^2/2$. The
mapping to the 4-dimensional effective theory is given by a simple scaling of
the potential with a redefinition of the field. Our result supports the picture
that the scenario of inflation driven by a bulk scalar field works in a quite
similar way to that in the standard 4-dimensional cosmology.


title: Spinors and Space-Time Anisotropy

abstract:
  This is the first monograph on the geometry of anisotropic spinor spaces and
its applications in modern physics. The main subjects are the theory of gravity
and matter fields in spaces provided with off--diagonal metrics and associated
anholonomic frames and nonlinear connection structures, the algebra and
geometry of distinguished anisotropic Clifford and spinor spaces, their
extension to spaces of higher order anisotropy and the geometry of gravity and
gauge theories with anisotropic spinor variables. The book summarizes the
authors' results and can be also considered as a pedagogical survey on the
mentioned subjects.


title: Quantum effects in a rotating spacetime

abstract:
  The behavior of a arbitrary coupled quantum scalar field is studied in the
background of the G\"odel spacetime. Closed forms are derived for the effective
action and the vacuum expectation value of quadratic field fluctuations by
using $\zeta$-function regularization. Based on these results, we argue that
causality violation presented in this spacetime can not be removed by quantum
effects.


title: Hamiltonian Analysis of Poincar\'e Gauge Theory: Higher Spin Modes

abstract:
  We examine several higher spin modes of the Poincar\'e gauge theory (PGT) of
gravity using the Hamiltonian analysis. The appearance of certain undesirable
effects due to non-linear constraints in the Hamiltonian analysis are used as a
test. We find that the phenomena of field activation and constraint bifurcation
both exist in the pure spin 1 and the pure spin 2 modes. The coupled spin-$0^-$
and spin-$2^-$ modes also fail our test due to the appearance of constraint
bifurcation. The ``promising'' case in the linearized theory of PGT given by
Kuhfuss and Nitsch (KRNJ86) likewise does not pass. From this analysis of these
specific PGT modes we conclude that an examination of such nonlinear constraint
effects shows great promise as a strong test for this and other alternate
theories of gravity.


title:
The most general axially symmetric electrovac spacetime adimitting
  separable equations of motion

abstract:
  We obtain the most general solution of the Einstein electro - vacuum equation
for the stationary axially symmetric spacetime in which the Hamilton-Jacobi and
Klein - Gordon equations are separable. The most remarkable feature of the
solution is its invariance under the duality transformation involving mass and
NUT parameter, and the radial and angle coordinates. It is the general solution
for a rotating (gravitational dyon) particle which is endowed with both
gravoelectric and gravomagnetic charges, and there exists a duality
transformation from one to the other. It also happens to be a transform of the
Kerr - NUT solution. Like the Kerr family, it is also possible to make this
solution radiating which asymptotically conforms to the Vaidya null radiation.


title: Graviton-photon conversion on spin 0 and 1/2 particles

abstract:
  The differential cross-sections for scattering of gravitons into photons on
bosons and fermions are calculated in linearized quantum gravity. They are
found to be strongly peaked in the forward direction and become constant at
high energies. Numerically, they are very small as expected for such
gravitational interactions.


title:
Conformal Killing Vectors in Spherically Symmetric, Inhomogeneous,
  Shear-free, Separable Metric Spacetimes

abstract:
  In this paper, we find all the Conformal Killing Vectors (CKVs) and their Lie
Algebra for the recently reported [cqg1] spherically symmetric, shear-free
separable metric spacetimes with non-vanishing energy or heat flux. We also
solve the geodesic equatios of motion for the spacetime under consideration.


title: Spherical Gravitational Collapse with Heat Flux and Cosmic Censorship

abstract:
  In this paper, we investigate the nature of the singularity in the
spherically symmetrical, shear-free, gravitational collapse of a star with heat
flux using a separable metric [cqg1]. For any non-singular, regular, radial
density profile for a star described by this metric, eq. (2.1), the singularity
of the gravitational collapse is not naked locally. Our results here
unequivocally support the Strong Cosmic Censorship Hypothesis.


title: Spherically Symmetric, Self-Similar Spacetimes

abstract:
  Self-similar spacetimes are of importance to cosmology and to gravitational
collapse problems. We show that self-similarity or the existence of a
homothetic Killing vector field for spherically symmetric spacetimes implies
the separability of the spacetime metric in terms of the co-moving coordinates
and that the metric is, uniquely, the one recently reported in [cqg1]. The
spacetime, in general, has non-vanishing energy-flux and shear. The spacetime
admits matter with any equation of state.


title:
Gauge invariance in teleparallel gravity theories: A solution to the
  background structure problem

abstract:
  We deal with the problem of identifying a background structure and its
perturbation in tetrad theories of gravity. Starting from a peculiar trivial
principal bundle we define a metric which depends only on the gauge connection.
We find the allowed four-dimensional structure groups; two of them turn out to
be the translation group T_4 and the unitary group U(2). When the curvature
vanishes the metric reduces to its background form which coincides with
Minkowski flat metric for the T_4 case and with the Einstein static universe
metric for the U(2) case. The perturbation has a coordinate independent
definition and allows for the introduction of observables distinguished from
those obtained from the metric alone. Finally, we show that any teleparallel
theory of gravity, and hence general relativity, can be considered as a gauge
theory over the groups introduced.


title: Summary of Session D1(ii), String Theory and Supergravity

abstract:
  The talks presented in the string theory and supergravity session of the GR16
conference in Durban, South Africa are described below for the proceedings.


title: Quantum Geometry and Gravity: Recent Advances

abstract:
  Over the last three years, a number of fundamental physical issues were
addressed in loop quantum gravity. These include: A statistical mechanical
derivation of the horizon entropy, encompassing astrophysically interesting
black holes as well as cosmological horizons; a natural resolution of the
big-bang singularity; the development of spin-foam models which provide
background independent path integral formulations of quantum gravity and
`finiteness proofs' of some of these models; and, the introduction of
semi-classical techniques to make contact between the background independent,
non-perturbative theory and the perturbative, low energy physics in Minkowski
space. These developments spring from a detailed quantum theory of geometry
that was systematically developed in the mid-nineties and have added a great
deal of optimism and intellectual excitement to the field.
  The goal of this article is to communicate these advances in general physical
terms, accessible to researchers in all areas of gravitational physics
represented in this conference.