title: Hawking radiation without black hole entropy

abstract:
  In this Letter I point out that Hawking radiation is a purely kinematic
effect that is generic to Lorentzian geometries. Hawking radiation arises for
any test field on any Lorentzian geometry containing an event horizon
regardless of whether or not the Lorentzian geometry satisfies the dynamical
Einstein equations of general relativity. On the other hand, the classical laws
of black hole mechanics are intrinsically linked to the Einstein equations of
general relativity (or their perturbative extension into either semiclassical
quantum gravity or string-inspired scenarios). In particular, the laws of black
hole thermodynamics, and the identification of the entropy of a black hole with
its area, are inextricably linked with the dynamical equations satisfied by the
Lorentzian geometry: entropy is proportional to area (plus corrections) if and
only if the dynamical equations are the Einstein equations (plus corrections).
It is quite possible to have Hawking radiation occur in physical situations in
which the laws of black hole mechanics do not apply, and in situations in which
the notion of black hole entropy does not even make any sense. This observation
has important implications for any derivation of black hole entropy that seeks
to deduce black hole entropy from the Hawking radiation.


title: Microfield Dynamics of Black Holes

abstract:
  The microcanonical treatment of black holes as opposed to the canonical
formulation is reviewed and some major differences are displayed. In particular
the decay rates are compared in the two different pictures.


title: Thermodynamics of entanglement in Schwarzschild spacetime

abstract:
  Extending the analysis in our previous paper, we construct the entanglement
thermodynamics for a massless scalar field on the Schwarzschild spacetime.
Contrary to the flat case, the entanglement energy $E_{ent}$ turns out to be
proportional to area radius of the boundary if it is near the horizon. This
peculiar behavior of $E_{ent}$ can be understood by the red-shift effect caused
by the curved background. Combined with the behavior of the entanglement
entropy, this result yields, quite surprisingly, the entanglement
thermodynamics of the same structure as the black hole thermodynamics. On the
basis of these results, we discuss the relevance of the concept of entanglement
as the microscopic origin of the black hole thermodynamics.


title: Lecture Notes on General Relativity

abstract:
  These notes represent approximately one semester's worth of lectures on
introductory general relativity for beginning graduate students in physics.
Topics include manifolds, Riemannian geometry, Einstein's equations, and three
applications: gravitational radiation, black holes, and cosmology.


title: Limits on Cosmological Magnetic Fields and Other Anisotropic Stresses

abstract:
  We discuss the cosmological evolution of matter sources with small
anisotropic pressures. This includes electric and magnetic fields,
collisionless relativistic particles, gravitons, antisymmetric axion fields in
low-energy string cosmologies, spatial curvature anisotropies, and stresses
arising from simple topological defects. The COBE microwave sky maps are used
to place strong limits on the possible contribution of these sources to the
total density of the universe. We explain why the limits obtained from
primordial nucleosynthesis are generally weaker than those imposed by the
microwave background isotropy. The effect of inflation on all these stresses is
also calculated.


title: A duality relation : global monopole and texture

abstract:
  We resolve the entire gravitational field;i.e. the Riemann curvature into its
electric and magnetic parts. In general, the vacuum Einstein equation is
symmetric in active and passive electric parts. However it turns out that the
Schwarzschild solution, which is the unique spherically symmetric vacuum
solutions can be characterised by a slightly more general equation which is not
symmetric. Then the duality transformation, implying interchange of active and
passive parts will relate the Schwarzschlid particle with the one with global
monopole charge. That is the two are dual of each-other. It further turns out
that flat spacetime is dual to massless global monopole and global texture
spacetimes.


title: Spherical scalar waves and gravity - red shift and backscattering

abstract:
  This article investigates the interaction of a spherically symmetric massless
scalar field with a strong gravitational field. It focuses on the propagation
of waves in regions outside any horizons. The two factors acting on the waves
can be identified as a redshift and a backscattering. The influence of
backscattering on the intensity of the outgoing radiation is studied and
rigorous quantitative upper bounds obtained. These show that the total flux may
be decreased if the sources are placed in a region adjoining an apparent
horizon. Backscattering can be neglected in the case $2m_0 /R<< 1$, that is
when the emitter is located at a distance from a black hole much larger than
the Schwarzschild radius. This backscattering may have noticeable astrophysical
consequences.


title: Technological picture of the Planck scale universe

abstract:
  A picture of the Planck scale universe as a network of mesoscopic (with
respect to that scale) resonators connected through quasi-one-dimensional
waveguides is presented


title: Oscillatory and Power-law Mass Inflation in Non-Abelian Black Holes

abstract:
  Interior structure of non-Abelian black holes is shown to exhibit in a
general case either an oscillating mass-inflationary behavior, or power-law
behavior with a divergent mass function. In both cases no Cauchy horizon forms.


title:
Variational and conformal structure of nonlinear metric-connection
  gravitational lagrangians

abstract:
  We examine the variational and conformal structures of higher order theories
of gravity which are derived from a metric-connection Lagrangian that is an
arbitrary function of the curvature invariants. We show that the constrained
first order formalism when applied to these theories may lead consistently to a
new method of reduction of order of the associated field equations. We show
that the similarity of the field equations which are derived from appropriate
actions via this formalism to those produced by Hilbert varying purely metric
Lagrangians is not merely formal but is implied by the diffeomorphism covariant
property of the associated Lagrangians. We prove that the conformal equivalence
theorem of these theories with general relativity plus a scalar field, holds in
the extended framework of Weyl geometry with the same forms of field and
self-interacting potential but, in addition, there is a new `source term' which
plays the role of a stress. We point out how these results may be further
exploited and address a number of new issues that arise from this analysis.


title:
Proof of the Cosmic No-Hair Conjecture for Quadratic Homogeneous
  Cosmologies

abstract:
  We prove the cosmic no-hair conjecture for all orthogonal Bianchi cosmologies
with matter in the $R+\beta R^2$ theory using the conformally equivalent
Einstein field equations, with the scalar field having the full
self-interacting potential, in the presence of the conformally related matter
fields. We show, in particular, that the Bianchi IX universe asymptotically
approaches de Sitter space provided that initially the scalar three-curvature
does not exceed the potential of the scalar field associated with the conformal
transformation. Our proof relies on rigorous estimates of the possible bounds
of the so-called Moss-Sahni function which obeys certain differential
inequalities and a non-trivial argument which connects the behaviour of that
function to evolution of the spatial part of the scalar curvature.


title: Adiabatic invariants and Mixmaster catastrophes

abstract:
  We present a rigorous analysis of the role and uses of the adiabatic
invariant in the Mixmaster dynamical system. We propose a new invariant for the
global dynamics which in some respects has an improved behaviour over the
commonly used one. We illustrate its behaviour in a number of numerical
results. We also present a new formulation of the dynamics via Catastrophe
Theory. We find that the change from one era to the next corresponds to a fold
catastrophe, during the Kasner shifts the potential is an Implicit Function
Form whereas, as the anisotropy dissipates, the Mixmaster potential must become
a Morse 0--saddle. We compare and contrast our results to many known works on
the Mixmaster problem and indicate how extensions could be achieved. Further
exploitation of this formulation may lead to a clearer understanding of the
global Mixmaster dynamics.


title:
Stationary and static cylindrically symmetric Einstein spaces of the
  Lewis form

abstract:
  The derivation of the general solutions for stationary and static
cylindrically symmetric Einstein spaces of Lewis form is revisited and the
physical and geometrical meaning of the parameters appearing in the resulting
solutions are investigated. It is shown that three of the parameters (and the
value of the cosmological constant) are essential, of which one characterizes
the local gravitational field and appears in the Cartan scalars, while the
remaining two give information about the topological identification made to
produce cylindrical symmetry. Other than the cosmological constant, they can be
related to the parameters of the vacuum Weyl and Lewis classes, whose
interpretation was previously investigated by da Silva et al. (1995a, 1995b).


title: Upper bound for entropy in asymptotically de Sitter space-time

abstract:
  We investigate nature of asymptotically de Sitter space-times containing a
black hole. We show that if the matter fields satisfy the dominant energy
condition and the cosmic censorship holds in the considering space-time, the
area of the cosmological event horizon for an observer approaching a future
timelike infinity does not decrease, i.e. the second law is satisfied. We also
show under the same conditions that the total area of the black hole and the
cosmological event horizon, a quarter of which is the total Bekenstein-Hawking
entropy, is less than $12\pi/\Lambda$, where $\Lambda$ is a cosmological
constant. Physical implications are also discussed.


title: Chaos and Taub-NUT related spacetimes

abstract:
  The occurrence of chaos for test particles moving in a Taub-NUT spacetime
with a dipolar halo perturbation is studied using Poincar\'e sections. We find
that the NUT parameter (magnetic mass) attenuates the presence of chaos.


title: How typical is General Relativity in Brans-Dicke chaotic inflation?

abstract:
  General Relativity is recovered from Brans-Dicke gravity in the limit of
large $\omega$. In this article we investigate theories of Brans-Dicke gravity
with chaotic inflation, allowing for either a constant or variable value of
$\omega$, known as extended and hyperextended inflation respectively. The main
focus of the paper is placed on the latter. The variation $\omega$ with respect
to the Brans-Dicke field is based on higher-order corrections analogous to
those of the dilaton field in string theory, following the simple principle
that the Brans-Dicke and metric fields decouple asymptotically. The question
addressed is whether a large value of $\omega$ is predominant in most regions
of the universe, which would lead to the conclusion that a typical region is
then governed by General Relativity. In these theories we find that it is
possible to construct inflaton potentials that drive the evolution of the
Brans-Dicke field to an appropriate range of values at the end of inflation,
such that a large $\omega$ is indeed typical in an average region of the
universe. However, in general this conclusion does not hold and it is shown
that for a wide class of inflaton potentials General Relativity is not a priori
a typical theory.


title: Can LIGO see compact binaries?

abstract:
  The probability that interferometric detectors such as LIGO and VIRGO will
successfully detect inspiraling compact binaries depends in part on our
knowledge of the expected gravitational wave forms.
  The best approximations to the true wave forms available today are the
post-Newtonian (PN) templates. In this paper we argue that these 2PN templates
are accurate enough for a successful search for compact binaries with the
advanced LIGO interferometer. Results are presented for the 40-meter Caltech
prototype as well as for the inital and advance LIGO detectors.


title: Quantum time machine

abstract:
  The continuation of Misner space into the Euclidean region is seen to imply
the topological restriction that the period of the closed spatial direction
becomes time-dependent. This restriction results in a modified Lorentzian
Misner space in which the renormalized stress-energy tensor for quantized
complex massless scalar fields becomes regular everywhere, even on the
chronology horizon. A quantum-mechanically stable time machine with just the
sub-microscopic size may then be constructed out of the modified Misner space,
for which the semiclassical Hawking's chronology protection conjecture is no
longer an obstruction.


title: A two-dimensional representation of four-dimensional gravitational waves

abstract:
  The Einstein equation in D dimensions, if restricted to the class of
space-times possessing n = D - 2 commuting hypersurface-orthogonal Killing
vectors, can be equivalently written as metric-dilaton gravity in 2 dimensions
with n scalar fields. For n = 2, this results reduces to the known reduction of
certain 4-dimensional metrics which include gravitational waves. Here, we give
such a representation which leads to a new proof of the Birkhoff theorem for
plane-symmetric space--times, and which leads to an explanation, in which sense
two (spin zero-) scalar fields in 2 dimensions may incorporate the (spin two-)
gravitational waves in 4 dimensions. (This result should not be mixed up with
well--known analogous statements where, however, the 4-dimensional space-time
is supposed to be spherically symmetric, and then, of course, the equivalent
2-dimensional picture cannot mimic any gravitational waves.) Finally, remarks
on hidden symmetries in 2 dimensions are made.


title: Third Quantization of Kaluza-Klein Cosmology and Compactification

abstract:
  We study on the third quantization of a Kaluza-Klein toy model. In this model
time ($x$) is defined by the scale factor of universe, and the space coordinate
($y$) is defined by the ratio of the scales of the ordinary space and the
internal space. We calculate the number density of the universes created from
nothing and examine whether the compactification can be explained statistically
by the idea of the third quantization.


title:
Existence of Constant Mean Curvature Hypersurfaces in Asymptotically
  Flat Spacetimes

abstract:
  The problem of existence of spacelike hypersurfaces with constant mean
curvature in asymptotically flat spacetimes is considered for a class of
asymptotically Schwarzschild spacetimes satisfying an interior condition. Using
a barrier construction, a proof is given of the existence of complete
hypersurfaces with constant mean cuvature which intersect null infinity in a
regular cut.


title:
Waveform propagation in black hole spacetimes: evaluating the quality of
  numerical solutions

abstract:
  We compute the propagation and scattering of linear gravitational waves off a
Schwarzschild black hole using a numerical code which solves a generalization
of the Zerilli equation to a three dimensional cartesian coordinate system.
Since the solution to this problem is well understood it represents a very good
testbed for evaluating our ability to perform three dimensional computations of
gravitational waves in spacetimes in which a black hole event horizon is
present.


title: Has the black hole equilibrium problem been solved?

abstract:
  When the term ``black hole'' was originally coined in 1968, it was
immediately conjectured that the only pure vacuum equilibrium states were those
of the Kerr family. Efforts to confirm this made rapid progress during the
``classical phase'' from 1968 to 1975, and some gaps in the argument have been
closed during more recent years. However the presently available demonstration
is still subject to undesirably restrictive assumptions such as non-degeneracy
of the horizon, as well as analyticity and causality in the exterior.


title: On the PPN 1+2 Body Problem

abstract:
  A particulare case of the three-body problem, in the PPN formalism, is
presented. The Hamiltonian function is obtained and the problem is reduced to a
perturbed two-body one.


title: Tail of Gravitational Radiation and Coulomb Final-State Interaction

abstract:
  We present a simple intuitive derivation of the corrections to the intensity
of gravitational radiation due to the so-called tail effect.


title:
Late-Time Evolution of Charged Gravitational Collapse and Decay of
  Charged Scalar Hair - I

abstract:
  We study analytically the asymptotic evolution of charged fields around a
Reissner-Nordstr\"om black-hole. Following the no-hair theorem we focus
attention on the dynamical mechanism by which the charged hair is radiated
away. We find an inverse power-law relaxation of the charged fields at future
timelike infinity, along future null infinity and an oscillatory inverse
power-law relaxation along the future outer horizon. We show that a charged
hair is shedd slower than a neutral one. Our results are also of importance to
the study of mass inflation and the stability of Cauchy horizons during a
dynamical gravitational collapse of charged matter to form a charged black-hole


title:
Self-consistent solutions for low-frequency gravitational background
  radiation

abstract:
  We study in a Brill-Hartle type of approximation the back-reaction of a
superposition of linear gravitational waves in an Einstein-de Sitter background
up to the second order in the small wave amplitudes $h_{ik}$. The wave
amplitudes are assumed to form a homogeneous and isotropic stochastic process.
No restriction for the wavelengths is assumed. The effective stress-energy
tensor $T^{e}_{\mu\nu}$ is calculated in terms of the correlation functions of
the process. We discuss in particular a situation where $T^{e}_{\mu\nu}$ is the
dominant excitation of the background metric. Apart from the Tolman radiation
universe, a solution with the scale factor of the de Sitter universe exists
with $p = -\rho$ as effective equation of state.


title: Persistence Amplitudes from Numerical Quantum Gravity

abstract:
  The Euclidean quantum amplitude to go between data specified on an initial
and a final hypersurface may be approximated by the tree amplitude
exp(-I_{classical}/\hbar), where I_{classical} is the Euclidean action of the
classical solution joining the initial and final data. In certain cases the
tree amplitude is exact. We study I_{classical} hence the quantum amplitude, in
the case of a spherically symmetric Riemannian gravitational field coupled to a
spherically symmetric scalar field. The classical scalar field obeys an
elliptic equation, which we solve using relaxation techniques, in conjunction
with the field equations giving the gravitational field. An example of the
transition from linearity to non-linearity is presented and power law behavior
of the action is demonstrated.


title: Listening for Ringing Black Holes

abstract:
  The gravitational radiation produced by binary black holes during their
inspiral, merger, and ringdown phases is a promising candidate for detection by
the first or second generation of kilometer-scale interferometric gravitational
wave antennas. Waveforms for the last phase, the quasinormal ringing, are well
understood. I discuss the feasibility of detection of the quasinormal ringing
of a black hole based on an analysis of the Caltech 40-meter interferometer
data.


title: Evolution of Cosmological Perturbations in the Long Wavelength Limit

abstract:
  The relation between the long wavelength limit of solutions to the
cosmological perturbation equations and the perturbations of solutions to the
exactly homogeneous background equations is investigated for scalar
perturbations on spatially flat cosmological models. It is shown that a
homogeneous perturbation coincides with the long wavelength limit of some
inhomogeneous perturbation only when the former satisfies an additional
condition corresponding to the momentum constraint if the matter consists only
of scalar fields. In contrast, no such constraint appears if the fundamental
variables describing the matter contain a vector field as in the case of a
fluid. Further, as a byproduct of this general analysis, it is shown that there
exist two universal exact solutions to the perturbation equations in the long
wavelength limit, which are expressed only in terms of the background
quantities. They represent adiabatic growing and decaying modes, and correspond
to the well-known exact solutions for perfect fluid systems and scalar field
systems.


title: Mathematical problems in higher order gravity and cosmology

abstract:
  We discuss the issue of motivating the analysis of higher order gravity
theories and their cosmologies and introduce a rule which states that these
theories may be considered as a vehicle for testing whether certain properties
may be of relevance to quantum theory. We discuss the physicality issue arising
as a consequence of the conformal transformation theorem, the question of
formulating a consistent first order formalism of such theories and also the
isotropization problem for a class of generalized cosmologies. We point out
that this field may have an important role to play in clarifying issues arising
also in general relativity.


title: New Coordinate Systems for Axisymmetric Black Hole Collisions

abstract:
  We describe a grid generation procedure designed to construct new classes of
orthogonal coordinate systems for binary black hole spacetimes. The computed
coordinates offer an alternative approach to current methods, in addition to
providing a framework for potentially more stable and accurate evolutions of
colliding black holes. As a particular example, we apply our procedure to
generate appropriate numerical grids to evolve Misner's axisymmetric initial
data set representing two equal mass black holes colliding head-on. These new
results are compared with previously published calculations, and we find
generally good agreement in both the waveform profiles and total radiated
energies over the allowable range of separation parameters. Furthermore,
because no specialized treatment of the coordinate singularities is required,
these new grids are more easily extendible to unequal mass and spinning black
hole collisions.


title:
Correct statement of a scattering problem for quantum charged scalar
  particles on the Reissner-Nordstr\"{o}m black holes

abstract:
  We study a correct statement of the scattering problem arising for quantum
charged scalar particles on the Reissner-Nordstr\"{o}m black holes when taking
into account the own electric field of black hole. The elements of the
corresponding S-matrix are explored in the form convenient to physical
applications and for applying numerical methods. Some further possible issues
are outlined.


title:
Existence Theorems for Hairy Black Holes in su(N) Einstein-Yang-Mills
  theories

abstract:
  We establish the existence of hairy black holes in su(N) Einstein-Yang-Mills
theories, described by N-1 parameters, corresponding to the nodes of the gauge
field functions.


title:
Numerical treatment of the hyperboloidal initial value problem for the
  vacuum Einstein equations. I. The conformal field equations

abstract:
  This is the first in a series of articles on the numerical solution of
Friedrich's conformal field equations for Einstein's theory of gravity. We will
discuss in this paper why one should be interested in applying the conformal
method to physical problems and why there is good hope that this might even be
a good idea from the numerical point of view. We describe in detail the
derivation of the conformal field equations in the spinor formalism which we
use for the implementation of the equations, and present all the equations as a
reference for future work. Finally, we discuss the implications of the
assumptions of a continuous symmetry.


title:
Irreversible Time Flow in a Two-Dimensional Dilaton Black Hole with
  Matter

abstract:
  We show that an exact solution of two-dimensional dilaton gravity with matter
discovered previously exhibits an irreversible temporal flow towards flat space
with a vanishing cosmological constant. This time flow is induced by the back
reaction of matter on the space-time geometry. We demonstrate that the system
is not in equilibrium if the cosmological constant is non-zero, whereas the
solution with zero cosmological constant is stable. The flow of the system
towards this stable end-point is derived from the renormalization-group flow of
the Zamolodchikov function. This behaviour is interpreted in terms of
non-critical Liouville string, with the Liouville field identified as the
target time.


title:
Numerical treatment of the hyperboloidal initial value problem for the
  vacuum Einstein equations. II. The evolution equations

abstract:
  This is the second in a series of articles on the numerical solution of
Friedrich's conformal field equations for Einstein's theory of gravity. We will
discuss in this paper the numerical methods used to solve the system of
evolution equations obtained from the conformal field equations. In particular
we discuss in detail the choice of gauge source functions and the treatment of
the boundaries. Of particular importance is the process of ``radiation
extraction'' which can be performed in a straightforward way in the present
formalism.


title:
Symmetry reduced Einstein gravity and generalized sigma and chiral
  models

abstract:
  Certain features associated with the symmetry reduction of the vacuum
Einstein equations by two commuting, space-like Killing vector fields are
studied. In particular, the discussion encompasses the equations for the Gowdy
$T^3$ cosmology and cylindrical gravitational waves. We first point out a
relation between the $SL(2,R)$ (or SO(3)) $\sigma$ and principal chiral models,
and then show that the reduced Einstein equations can be obtained from a
dimensional reduction of the standard SL(2,R) sigma-model in three dimensions.
The reduced equations can also be derived from the action of a `generalized'
two dimensional SL(2,R) sigma-model with a time dependent constraint. We give a
Hamiltonian formulation of this action, and show that the Hamiltonian evolution
equations for certain phase space variables are those of a certain
generalization of the principal chiral model. Using these Hamiltonian
equations, we give a prescription for obtaining an infinite set of constants of
motion explicitly as functionals of the space-time metric variables.


title:
Gravity Probe C(lock) - Probing the gravitomagnetic field of the Earth
  by means of a clock experiment

abstract:
  We outline a mission with the aim of directly detecting the gravitomagnetic
field of the Earth. This mission is called Gravity Probe C. Gravity Probe
C(lock) is based on a recently discovered and surprisingly large
gravitomagnetic clock effect. The main idea is to compare the proper time of
two standard clocks in direct and retrograde orbits around the Earth. After one
orbit the proper time difference of two such clocks is predicted to be of the
order of $2\times 10^{-7}$ s. The conceptual difficulty to perform Gravity
Probe C is expected to be comparable to that of the Gravity Probe B--mission.


title: Mixmaster Behavior in Inhomogeneous Cosmological Spacetimes

abstract:
  Numerical investigation of a class of inhomogeneous cosmological spacetimes
shows evidence that at a generic point in space the evolution toward the
initial singularity is asymptotically that of a spatially homogeneous spacetime
with Mixmaster behavior. This supports a long-standing conjecture due to
Belinskii et al. on the nature of the generic singularity in Einstein's
equations.


title: Gravitational Radiation Reaction

abstract:
  We consider the radiation reaction to the motion of a point-like particle of
mass $m$ and specific spin $S$ traveling on a curved background. Assuming
$S=O(Gm)$ and $Gm\ll L$ where $L$ is the length scale of the background
curvature, we divide the spacetime into two regions; the external region where
the metric is approximated by the background metric plus perturbations due to a
point-like particle and the internal region where the metric is approximated by
that of a black hole plus perturbations due to the tidal effect of the
background curvature, and use the technique of the matched asymptotic expansion
to construct an approximate metric which is valid over the entire region. In
this way, we avoid the divergent self-gravity at the position of the particle
and derive the equations of motion from the consistency condition of the
matching. The matching is done to the order necessary to include the effect of
radiation reaction of $O(Gm)$ with respect to the background metric as well as
the effect of spin-induced force. The reaction term of $O(Gm)$ is found to be
completely due to tails of radiation, that is, due to curvature scattering of
gravitational waves. In other words, the reaction force is found to depend on
the entire history of the particle trajectory. Defining a regularized metric
which consists of the back- ground metric plus the tail part of the perturbed
metric, we find the equations of motion reduce to the geodesic equation on this
regularized metric, except for the spin-induced force which is locally
expressed in terms of the curvature and spin tensors. Some implications of the
result and future issues are briefly discussed.


title: Black Hole Perturbation

abstract:
  We present analytic calculations of gravitational waves from a particle
orbiting a black hole. We first review the Teukolsky formalism for dealing with
the gravitational perturbation of a black hole. Then we develop a systematic
method to calculate higher order post-Newtonian corrections to the
gravitational waves emitted by an orbiting particle. As applications of this
method, we consider orbits that are nearly circular, including exactly circular
ones, slightly eccentric ones and slightly inclined orbits off the equatorial
plane of a Kerr black hole and give the energy flux and angular momentum flux
formulas at infinity with higher order post-Newtonian corrections. Using a
different method that makes use of an analytic series representation of the
solution of the Teukolsky equation, we also give a post-Newtonian expanded
formula for the energy flux absorbed by a Kerr black hole for a circular orbit.


title: On the differentiability conditions at spacelike infinity

abstract:
  We consider space-times which are asymptotically flat at spacelike infinity,
i^0. It is well known that, in general, one cannot have a smooth differentiable
structure at i^0, but have to use direction dependent structures. Instead of
the oftenly used C^{>1}-differentiabel structure, we suggest a weaker
differential structure, a C^{1^+} structure. The reason for this is that we
have not seen any completions of the Schwarzschild space-time which is C^{>1}
in both spacelike and null directions at {i^0}. In a C^{1^+} structure all
directions can be treated equal, at the expense of logarithmic singularities at
{i^0}. We show that, in general, the relevant part of the curvature tensor, the
Weyl part, is free from these singularities, and that the (rescaled) Weyl
tensor has a certain symmetry.


title:
Thermodynamics, topology and dimension of initial real tunneling
  manifolds

abstract:
  We develop the argument that initial real tunneling in quantum gravity be
contemplated as a thermodynamical analogous to a black hole condensate in
equilibrium with Hawking's radiation in a box. The total entropy is always
maximized in the Lorentzian sector of the manifold, and, in this sense,
tunneling is predicted.


title: Prediction of a finite bare electrical charge from quantum gravity

abstract:
  In the spirit of general relativity, spacetime should become curved due to
the presence of a particle of a given mass and charge, We try to understand
this fact in the quantum theory of a thin shell of matter. It leads to a
generalization of the potential energy of the shell in the semiclassical
highest dominant order of Planck mass. Rather surprisingly, the quantization of
charge is obtained as a consequence of the existence of bound states and the
quantum of the squared bare electrical charge is $\hbar c/2$


title: Inflation without Slow Roll

abstract:
  We draw attention to the possibility that inflation (i.e. accelerated
expansion) might continue after the end of slow roll, during a period of fast
oscillations of the inflaton field \phi . This phenomenon takes place when a
mild non-convexity inequality is satisfied by the potential V(\phi). The
presence of such a period of \phi-oscillation-driven inflation can
substantially modify reheating scenarios.
  In some models the effect of these fast oscillations might be imprinted on
the primordial perturbation spectrum at cosmological scales.


title: Pre-big bang model has Planck problem

abstract:
  The pre-big bang's kinetic driven inflationary mechanism is not an adequate
form of inflation: the Planck length grows more rapidly than the scale factor.
In order to explain our large universe, the resulting post-big bang universe
requires the same unnatural constants (Planck problem) as those of any other
non-inflationary big bang model.


title: Volume elements of spacetime and a quartet of scalar fields

abstract:
  Starting with a `bare' 4-dimensional differential manifold as a model of
spacetime, we discuss the options one has for defining a volume element which
can be used for physical theories. We show that one has to prescribe a scalar
density \sigma. Whereas conventionally \sqrt{|\det g_{ij}|} is used for that
purpose, with g_{ij} as the components of the metric, we point out other
possibilities, namely \sigma as a `dilaton' field or as a derived quantity from
either a linear connection or a quartet of scalar fields, as suggested by
Guendelman and Kaganovich.


title:
Dynamical Evolution of Boson Stars II: Excited States and
  Self-Interacting Fields

abstract:
  The dynamical evolution of self-gravitating scalar field configurations in
numerical relativity is studied. The previous analysis on ground state boson
stars of non-interacting fields is extended to excited states and to fields
with self couplings.
  Self couplings can significantly change the physical dimensions of boson
stars, making them much more astrophysically interesting (e.g., having mass of
order 0.1 solar mass). The stable ($S$) and unstable ($U$) branches of
equilibrium configurations of boson stars of self-interacting fields are
studied; their behavior under perturbations and their quasi-normal oscillation
frequencies are determined and compared to the non-interacting case.
  Excited states of boson stars with and without self-couplings are studied and
compared. Excited states also have equilibrium configurations with $S$ and $U$
branch structures; both branches are intrinsically unstable under a generic
perturbation but have very different instability time scales. We carried out a
detailed study of the instability time scales of these configurations. It is
found that highly excited states spontaneously decay through a cascade of
intermediate states similar to atomic transitions.


title: Dynamical evolution of boson stars in Brans-Dicke theory

abstract:
  We study the dynamics of a self-gravitating scalar field solitonic object
(boson star) in the Jordan-Brans-Dicke (BD) theory of gravity. We show
dynamical processes of this system such as (i) black hole formation of
perturbed equilibrium configuration on an unstable branch; (ii) migration of
perturbed equilibrium configuration from the unstable branch to stable branch;
(iii) transition from excited state to a ground state. We find that the
dynamical behavior of boson stars in BD theory is quite similar to that in
general relativity (GR), with comparable scalar wave emission. We also
demonstrate the formation of a stable boson star from a Gaussian scalar field
packet with flat gravitational scalar field initial data. This suggests that
boson stars can be formed in the BD theory in much the same way as in GR.


title: Quantum Fields in Schwarzschild-de Sitter Space

abstract:
  In the No-Boundary Universe a primordial black hole is created from a
constrained gravitational instanton. The black hole created is immersed in the
de Sitter background with a positive cosmological constant. The constrained
instanton is characterized not only by the external parameters, the mass
parameter, charge and angular momentum, but also by one more internal
parameter, the identification period in the imaginary time coordinate. Although
the period has no effect on the black hole background, its inverse is the
temperature of the no-boundary state of the perturbation modes perceived by an
observer. By using the Bogoliubov transformation, we show that the perturbation
modes of both scalar and spinor fields are in thermal q equilibrium with the
black hole background at the arbitrary temperature. However, for the two
extreme cases, the de Sitter and the Nariai models, the no-boundary state
remains pure.


title: Quantum geometry with intrinsic local causality

abstract:
  The space of states and operators for a large class of background independent
theories of quantum spacetime dynamics is defined. The SU(2) spin networks of
quantum general relativity are replaced by labelled compact two-dimensional
surfaces. The space of states of the theory is the direct sum of the spaces of
invariant tensors of a quantum group G_q over all compact (finite genus)
oriented 2-surfaces. The dynamics is background independent and locally causal.
The dynamics constructs histories with discrete features of spacetime geometry
such as causal structure and multifingered time. For SU(2) the theory satisfies
the Bekenstein bound and the holographic hypothesis is recast in this
formalism.


title:
Domain with Noncompactified Extra Dimensions in Multidimensional
  Universe with Compactified Extra Dimensions

abstract:
  It is supposed that in our Universe with compactified extra dimensions (ED)
the domains exist with noncompactified ED. Such domain can be a wormhole-like
solution in multidimensional gravity (MD), located between two null surfaces.
With the availability of compactification mechanism this MD domain can be
joined on null surfaces with two black holes filled by gauge field. Solution of
this kind in MD gravity on the principal bundle with structural group SU(3) is
obtained. This solution is wormhole-like object located between two null
surfaces $ds^2=0$. In some sense these solutions are dual to black holes: they
are statical spherically symmetric solutions under null surfaces whereas black
holes are statical spherically symmetric solutions outside of event horizon.


title: Hamiltonians for Compact Homogeneous Universes

abstract:
  We briefly show how we can obtain Hamiltonians for spatially compact locally
homogeneous vacuum spacetimes. The dynamical variables are categorized into the
curvature parameters and the Teichm\"{u}ller parameters. While the
Teichm\"{u}ller parameters usually parameterise the covering group of the
spatial sections, we utilise another suitable parameterization where the
universal cover metric carries all the dynamical variables and with this we
reduce the Hamiltonians. For our models, all dynamical variables possess their
clear geometrical meaning, in contrast to the conventional open models.}


title: Perturbative dynamics of quantum general relativity

abstract:
  The quantum theory of General Relativity at low energy exists and is of the
form called "effective field theory". In this talk I describe the ideas of
effective field theory and its application to General Relativity.


title: Riemannian Space-times of G\"odel Type in Five Dimensions

abstract:
  The five-dimensional (5D) Riemannian G\"odel-type manifolds are examined in
light of the equivalence problem techniques, as formulated by Cartan. The
necessary and sufficient conditions for local homogeneity of these 5D manifolds
are derived. The local equivalence of these homogeneous Riemannian manifolds is
studied. It is found that they are characterized by two essential parameters
$m^2$ and $\omega $: identical pairs $(m^2, \omega)$ correspond to locally
equivalent 5D manifolds. An irreducible set of isometrically nonequivalent 5D
locally homogeneous Riemannian G\"odel-type metrics are exhibited. A
classification of these manifolds based on the essential parameters is
presented, and the Killing vector fields as well as the corresponding Lie
algebra of each class are determined. It is shown that apart from the $(m^2= 4
\omega^2, \omega\not=0)$ and $(m^2\not=0, \omega = 0)$ classes the homogeneous
Riemannian G\"odel-type manifolds admit a seven-parameter maximal group of
isometry ($G_7$). The special class $(m^2= 4 \omega^2, \omega\not=0)$ and the
degenerated G\"odel-type class $(m^2\not=0, \omega=0)$ are shown to have a
$G_9$ as maximal group of motion. The breakdown of causality in these classes
of homogeneous G\"odel-type manifolds are also examined.


title: Cosmological Levinson theorem

abstract:
  If at least some Wheeler-DeWitt solutions can be interpreted as zero-energy
resonances then the total s-wave cross section of the corresponding quantum
universes is infinite


title: From Taub Numbers to the Bondi Mass

abstract:
  Taub numbers are studied on asymptotically flat backgrounds with Killing
symmetries. When the field equations are solved for a background spacetime and
higher order functional derivatives (higher order variational derivatives of
the Hilbert Lagrangean) are solved for perturbations from the background, such
perturbed space-times admit zeroth, first, and second order Taub numbers.
Zeroth order Taub numbers are Komar constants (upto numerical factors) or
Penrose-Goldberg constants of the background. For a Killing symmetry of the
background, first order Taub numbers give the contribution of the linearized
perturbation to the associated backgound quantity, such as the perturbing mass.
Second order Taub numbers give the contribution of second order perturbations
to the background quantity. The Bondi mass is a sum of first and second order
Taubs numbers on a Minkowski background.


title: Gravity and Parity Violation in Spin Gauge Theory

abstract:
  Within a spin-gauge theory of gravity unified with the electroweak
interaction we start with totally symmetric left- and right-handed fermions and
explain the parity violation by symmetry breaking in such a way that the
$W^{\pm}$-bosons couple only to the left-handed leptons. Right-handed neutrinos
exist and couple as the right-handed electrons only to the Z-bosons (and to
gravity). The mass of the neutrinos comes out to be necessarily zero. Therefore
this procedure cannot be transferred to the quarks, because then the u-quark
would become massless too; for this reason parity violation with respect to the
quarks is avoided. On the other hand concerning gravity the u-quark couples
only with u-quarks and the d-quark only with d-quarks, however with the same
strength, so that isotopic effects appear regarding the equivalence principle
in such a way, that the macroscopic gravitational constant depends on the
isotopic composition of the material.


title:
3rd post-Newtonian higher order Hamilton dynamics for two-body
  point-mass systems

abstract:
  The paper presents the conservative dynamics of two-body point-mass systems
up to the third post-Newtonian order ($1/c^6$). The two-body dynamics is given
in terms of a higher order ADM Hamilton function which results from a third
post-Newtonian Routh functional for the total field-plus-matter system. The
applied regularization procedures, together with making use of distributional
differentiation of homogeneous functions, give unique results for the terms in
the Hamilton function apart from the coefficient of the term $(\nu
p_{i}{\pa_{i}})^2r^{-1}$. The result suggests an invalidation of the binary
point-mass model at the third post-Newtonian order.


title: Testing the Equivalence Principle in Quantum Physics

abstract:
  We showed in a previous paper that a wide class of nonmetric theories of
gravity encompassed by the $\chi g$ formalism predict that the speed of light
rays depends on the their polarization direction relative to directions singled
out by the gravitational field. This gravity-induced birefringence of space is
a violation of the Equivalence Principle and is due to the nonmetric coupling
between gravity and electromagnetism. In this paper we analyze the propagation
of light in the gravitational field of a rotating black hole when nonmetric
couplings to curvature are included and compute the time delay between rays
with orthogonal polarizations. We obtain an upper bound on the strength of QED
like and CP violating curvature couplings using time delay data for pulsar PSR
1937+21. By comparison the corresponding coupling strength for QED coupling is
37 orders of magnitude less.


title: An Action for Black Hole Membranes

abstract:
  The membrane paradigm is the remarkable view that, to an external observer, a
black hole appears to behave exactly like a dynamical fluid membrane, obeying
such pre-relativistic equations as Ohm's law and the Navier-Stokes equation. It
has traditionally been derived by manipulating the equations of motion. Here we
provide an action formulation of this picture, clarifying what underlies the
paradigm, and simplifying the derivations. Within this framework, we derive
previous membrane results, and extend them to dyonic black hole solutions. We
discuss how it is that an action can produce dissipative equations. Using a
Euclidean path integral, we show that familiar semi-classical thermodynamic
properties of black holes also emerge from the membrane action. Finally, in a
Hamiltonian description, we establish the validity of a minimum entropy
production principle for black holes.


title: Relativistic Quantum Measurements, Unruh effect and Black Holes

abstract:
  It is shown how the technique of restricted path integrals (RPI) or quantum
corridors (QC) may be applied for the analysis of relativistic measurements.
Then this technique is used to clarify the physical nature of thermal effects
as seen by an accelerated observer in Minkowski space-time (Unruh effect) and
by a far observer in the field of a black hole (Hawking effect). The physical
nature of the "thermal atmosphere" around the observer is analysed in three
cases: a) the Unruh effect, b) an eternal (Kruskal) black hole and c) a black
hole forming in the process of collapse. It is shown that thermal particles are
real only in the case (c). In the case (b) they cannot be distinguished from
real particles but they do not carry away mass of the black hole until some of
these particles are absorbed by the far observer. In the case (a) thermal
particles are virtual.


title:
Solution to the inverse problem for a noisy spherical gravitational wave
  antenna

abstract:
  A spherical gravitational wave antenna is distinct from other types of
gravitational wave antennas in that only a single detector is necessary to
determine the direction and polarization of a gravitational wave. Zhou and
Michelson showed that the inverse problem can be solved using the maximum
likelihood method if the detector outputs are independent and have normally
distributed noise with the same variance. This paper presents an analytic
solution using only linear algebra that is found to produce identical results
as the maximum likelihood method but with less computational burden.
Applications of this solution to gravitational waves in alternative symmetric
metric theories of gravity and impulsive excitations also are discussed.


title: On the weak field approximation of Brans-Dicke theory of gravity

abstract:
  It is shown that in the weak field approximation solutions of Brans-Dicke
equations are simply related to the solutions of General Relativity equations
for the same matter distribution. A simple method is developed which permits to
obtain Brans-Dicke solutions from Einstein solutions when both theories are
considered in their linearized forms. To illustrate the method some examples
found in the literature are discussed.


title:
Equilibrium of Spheres with Local Anisotropy in Postnewtonian Gravity.
  Application to White Dwarfs

abstract:
  Static solutions of white dwarfs with spherical symmetry and local anisotropy
are studied in the post-Newtonian approximation. It is argued that the
condition for equilibrium must be that the total energy is a minimum for given
baryon number and the question whether there is local isotropy or anisotropy
inside the star should follow from that condition, rather than be postulated "a
priori". It is shown show that, in post-Newtonian gravity, there are stable
configurations with local anisotropy for masses above the Chandrasekhar limit.


title: Light bending and perihelion precession: A unified approach

abstract:
  The standard General Relativity results for precession of particle orbits and
for bending of null rays are derived as special cases of perturbation of a
quantity that is conserved in Newtonian physics, the Runge-Lenz vector. First
this method is applied to give a derivation of these General Relativity effects
for the case of the spherically symmetric Schwarzschild geometry. Then the
lowest order correction due to an angular momentum of the central body is
considered. The results obtained are well known, but the method used is rather
more efficient than that found in the standard texts, and it provides a good
occasion to use the Runge-Lenz vector beyond its standard applications in
Newtonian physics.


title: Spherical Black Holes cannot Support Scalar Hair

abstract:
  The static spherically symmetric ``black hole solution" of the Einstein -
conformally invariant massless scalar field equations known as the BBMB (
Bocharova, , Bronikov, Melinkov, Bekenstein) black hole is critically examined.
It is shown that the stress energy tensor is ill-defined at the horizon, and
that its evaluation through suitable regularization yields ambiguous
  results. Consequently, the configuration fails to represent a genuine black
hole solution. With the removal of this solution as a counterexample to the no
hair conjecture, we argue that the following appears to be true: Spherical
black holes cannot carry any kind of classical scalar hair.


title: Critical phenomena in gravitational collapse (review paper)

abstract:
  As first discovered by Choptuik, the black hole threshold in the space of
initial data for general relativity shows both surprising structure and
surprising simplicity. Universality, power-law scaling of the black hole mass,
and scale echoing have given rise to the term "critical phenomena". They are
explained by the existence of exact solutions which are attractors within the
black hole threshold, that is, attractors of codimension one in phase space,
and which are typically self-similar. This review gives an introduction to the
phenomena, tries to summarize the essential features of what is happening, and
then presents extensions and applications of this basic scenario. Critical
phenomena are of interest particularly for creating surprising structure from
simple equations, and for the light they throw on cosmic censorship. They may
have applications in quantum black holes and astrophysics.


title: An Operational Approach To Black Hole Entropy

abstract:
  In this paper we calculate the entropy of a thin spherical shell that
contracts reversibly from infinity down to its event horizon. We find that, for
a broad class of equations of state, the entropy of a non-extremal shell is
one-quarter of its area in the black hole limit. The considerations in this
paper suggest the following operational definition for the entropy of a black
hole: $S_{BH}$ is the equilibrium thermodynamic entropy that would be stored in
the material which gathers to form the black hole, if all of this material were
compressed into a thin layer near its gravitational radius. Since the entropy
for a given mass and area is maximized for thermal equilibrium we expect that
this is the maximum entropy that could be stored in the material before it
crosses the horizon. In the case of an extremal black hole the shell model does
not assign an unambiguous value to the entropy.


title:
Static Axially Symmetric Einstein-Yang-Mills-Dilaton Solutions: II.Black
  Hole Solutions

abstract:
  We discuss the new class of static axially symmetric black hole solutions
obtained recently in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton
theory. These black hole solutions are asymptotically flat and they possess a
regular event horizon. The event horizon is almost spherically symmetric with a
slight elongation along the symmetry axis. The energy density of the matter
fields is angle-dependent at the horizon. The static axially symmetric black
hole solutions satisfy a simple relation between mass, dilaton charge, entropy
and temperature. The black hole solutions are characterized by two integers,
the winding number $n$ and the node number $k$ of the purely magnetic gauge
field. With increasing node number the magnetically neutral black hole
solutions form sequences tending to limiting solutions with magnetic charge
$n$, corresponding to Einstein-Maxwell-dilaton black hole solutions for finite
dilaton coupling constant and to Reissner-Nordstr\o m black hole solutions for
vanishing dilaton coupling constant.


title: On the Classical Limit of the Balanced State Sum

abstract:
  The purpose of this note is to make several advances in the interpretation of
the balanced state sum model by Barrett and Crane in gr-qc/9709028 as a quantum
theory of gravity. First, we outline a shortcoming of the definition of the
model in pointed out to us by Barrett and Baez in private communication, and
explain how to correct it. Second, we show that the classical limit of our
state sum reproduces the Einstein-Hilbert lagrangian whenever the term in the
state sum to which it is applied has a geometrical interpretation. Next we
outline a program to demonstrate that the classical limit of the state sum is
in fact dominated by terms with geometrical meaning. This uses in an essential
way the alteration we have made to the model in order to fix the shortcoming
discussed in the first section. Finally, we make a brief discussion of the
Minkowski signature version of the model.


title: Mixed Boundary Problem for the Traversable Wormhole Models

abstract:
  The conditions of the traversable wormhole joining with the exterior
space-time are considered in details and the mixed boundary problem for the
Einstein equations is formulated. It is shown that, in opposite to some
declarations, the conditions of the wormhole joining with the exterior
space-time have non-dynamical nature and can not be defined by the physical
processes. The role of these conditions in the formation of the causal
structure of space-time is analyzed. It is shown that the causal structure of
the wormhole-type space-time models is independent from both the interior and
exterior energy-momentum tensors. This statement is illustrated in the
particular case of the spherical wormhole joining with flat exterior
space-time. The same conditions, which define the wormhole joining with the
exterior space-time, provide the absence of paradoxes in the models with
causality violation. It is pointed out, that the nature and physical
interpretation of the conditions of wormhole joining with the exterior
space-time and induced boundary conditions for the field variables is one of
the fundamental problems, which arise in the models with causality violation.


title:
Is a `hadronic' shear current one of the sources in metric-affine
  gravity?

abstract:
  The Minkowski space of special relativity can be understood as a flat
4-dimensional affine space enriched by a constant Minkowski metric. If we gauge
the general affine group and `superimpose' the metric, then we arrive at the
metric-affine theory of gravity (MAG). The gravitational potentials are the
spacetime coframe, the metric, and the linear connection. The material
energy-momentum is coupled to the coframe (and the metric), a hypothetical
hypermomentum current to the connection. The hypermomentum splits in a spin, a
dilation, and a shear piece. We collect some evidence in favor of the existence
of a material shear current in the context of Regge type trajectories of
`hadronic' matter, thus supporting the link between particle physics and MAG.


title:
Radiation in Yang-Mills formulation of gravity and a generalized pp-wave
  metric

abstract:
  The variational methods implemented on a quadratic Yang-Mills type Lagrangian
yield two sets of equations interpreted as the field equations and the
energy-momentum tensor for the gravitational field. A covariant condition is
imposed on the energy-momentum tensor to represent the radiation field. A
generalized pp-wave metric is found to simultaneously satisfy both the field
equations and the radiation condition. The result is compared with that of
Lichn\'{e}rowicz.


title: Influence functional in two dimensional dilaton gravity

abstract:
  We evaluate the influence functional for two dimensional models of dilaton
gravity. This functional is exactly computed when the conformal invariance is
preserved, and it can be written as the difference between the Liouville
actions on each closed-time-path branch plus a boundary term. From the
influence action we derive the covariant form of the semiclassical field
equations. We also study the quantum to classical transition in cosmological
backgrounds. In the conformal case we show that the semiclassical approximation
is not valid because there is no imaginary part in the influence action.
Finally we show that the inclusion of the dilaton loop in the influence
functional breaks conformal invariance and ensures the validity of the
semiclassical approximation.


title: A Closed Formula for the Riemann Normal Coordinate Expansion

abstract:
  We derive an integral representation which encodes all coefficients of the
Riemann normal coordinate expansion, and also a closed formula for those
coefficients.


title: Interaction of massless Dirac field with a Poincar\'e gauge field

abstract:
  In this paper we consider a model of Poincar\'e gauge theory (PGT) in which a
translational gauge field and a Lorentz gauge field are actually identified
with the Einstein's gravitational field and a pair of ``Yang-Mills'' field and
its partner, respectively.In this model we re-derive some special solutions and
take up one of them. The solution represents a ``Yang-Mills'' field without its
partner field and the Reissner-Nordstr\"om type spacetime, which are generated
by a PGT-gauge charge and its mass.It is main purpose of this paper to
investigate the interaction of massless Dirac fields with those fields. As a
result, we find an interesting fact that the left-handed massless Dirac fields
behave in the different manner from the right-handed ones. This can be
explained as to be caused by the direct interaction of Dirac fields with the
``Yang-Mills'' field. Accordingly, the phenomenon can not happen in the
behavior of the neutrino waves in ordinary Reissner-Nordstr\"om geometry. The
difference between left- and right-handed effects is calculated quantitatively,
considering the scattering problems of the massless Dirac fields by our
Reissner-Nordstr\"om type black-hole.


title:
Some Aspects of Four Dimensional Black Hole Solutions in Gauss-Bonnet
  Extended String Gravity

abstract:
  An internal singularity of a string four-dimensional black hole with second
order curvature corrections is discussed. A restriction to a minimal size of a
neutral black hole is obtained in the frame of the model considered. Vacuum
polarization of the surrounding space-time caused by this minimal-size black
hole is also discussed.


title: Innermost Stable Circular Orbit of a Spinning Particle in Kerr Spacetime

abstract:
  We study stability of a circular orbit of a spinning test particle in a Kerr
spacetime. We find that some of the circular orbits become unstable in the
direction perpendicular to the equatorial plane, although the orbits are still
stable in the radial direction. Then for the large spin case ($S < \sim O(1)),
the innermost stable circular orbit (ISCO) appears before the minimum of the
effective potential in the equatorial plane disappears. This changes the radius
of ISCO and then the frequency of the last circular orbit.


title: Alternative Gravitational Theories in Four Dimensions

abstract:
  We argue that from the point of view of gauge theory and of an appropriate
interpretation of the interferometer experiments with matter waves in a
gravitational field, the Einstein-Cartan theory is the best theory of gravity
available. Alternative viable theories are general relativity and a certain
teleparallelism model. Objections of Ohanian and Ruffini against the
Einstein-Cartan theory are discussed. Subsequently we list the papers which
were read at the `Alternative 4D Session' and try to order them, at least
partially, in the light of the structures discussed.


title: Conformal relations and Hamiltonian formulation of fourth-order gravity

abstract:
  The conformal equivalence of fourth-order gravity following from a non-linear
Lagrangian L(R) to theories of other types is widely known, here we report on a
new conformal equivalence of these theories to theories of the same type but
with different Lagrangian.
  For a quantization of fourth-order theories one needs a Hamiltonian
formulation of them. One of the possibilities to do so goes back to
Ostrogradski in 1850. Here we present another possibility: A Hamiltonian H
different from Ostrogradski's one is discussed for the Lagrangian L depending
on first and second order drivatives of the position variable q. We add a
suitable divergence to L. Contrary to other approaches no constraint is needed.
One of the canonical equations becomes equivalent to the fourth-order
Euler-Lagrange equation of L.
  Finally, we discuss the stability properties of cosmological models within
fourth-order gravity.


title: Chaotic inflation with a scalar field in non-classical states

abstract:
  We study chaotic inflation driven by a real, massive, homogeneous minimally
coupled scalar field in a flat Robertson-Walker spacetime. The semiclassical
limit for gravity is considered, whereas the scalar field is treated quantum
mechanically by the technique of invariants in order to also investigate the
dynamics of the system for non-classical states of the latter. An inflationary
stage is found to be possible for a large set of initial quantum states,
obviously including the coherent ones. States associated with a vanishing mean
value of the field (such as the vacuum and the thermal) can also lead to
inflation, however for such states we cannot make a definitive prediction due
to the importance of higher order corrections during inflation. The results for
the above coupled system are described and their corrections evaluated
perturbatively.


title: Representations of relativity, quantum gravity and cosmology

abstract:
  We review an attempt to set a suitable foundational principle for consistent
quantization of gravity based on the canonical formulation. It requires
extending the spacetime description of the relativistic postulates to also
encompass an alternative formulation in momentum-energy continuum where the
inertial physical laws can be equivalently described. The extension to
noninertial frames breaks such an equivalence, leaving a new dynamical field
which, together with gravity, allows to construct a canonical scenario where
the Dirac's quantization method leads to consistent definitions of hermitian
ordering for the operators of the canonical quantum theory.


title: Tolman's energy of a stringy charged black hole

abstract:
  Virbhadra and Parikh studied the energy distribution associated with stringy
charged black hole in Einstein's prescription. We study the same using Tolman's
energy-momentum complex and get the same result as obtained by Virbhadra and
Parikh. The entire energy is confined inside the black hole.


title:
Late-Time Evolution of Charged Gravitational Collapse and Decay of
  Charged Scalar Hair - II

abstract:
  We study analytically the initial value problem for a charged massless
scalar-field on a Reissner-Nordstr\"om spacetime. Using the technique of
spectral decomposition we extend recent results on this problem. Following the
no-hair theorem we reveal the dynamical physical mechanism by which the charged
hair is radiated away. We show that the charged perturbations decay according
to an inverse power-law behaviour at future timelike infinity and along future
null infinity. Along the future outer horizon we find an oscillatory inverse
power-law relaxation of the charged fields. We find that a charged black hole
becomes ``bald'' slower than a neutral one, due to the existence of charged
perturbations. Our results are also important to the study of mass-inflation
and the stability of Cauchy horizons during a dynamical gravitational collapse
of charged matter in which a charged black-hole is formed.


title: Radiation Backreaction in Spinning Binaries

abstract:
  The evolution under radiation backreaction of a binary system consisting of a
black hole and a companion is studied in the limiting case when the spin of the
companion is negligible compared with the spin S of the black hole. To first
order in the spin, the motion of the reduced-mass particle excluding radiation
effects, is characterized by three constants: the energy E, the magnitude L of
the angular momentum and the projection L_S of the angular momentum along the
spin S. This motion is quasiperiodic with a period determined by r_{min} and
r_{max}. We introduce a new parametrization, making the integration over a
period of a generic orbit especially simple. We give the averaged losses in
terms of the 'constants of motion' during one period for generic orbits, to
linear order in spin.


title:
Nonholonomic Mapping Principle for Classical Mechanics in Spaces with
  Curvature and Torsion. New Covariant Conservation Law for Energy-Momentum
  Tensor

abstract:
  The lecture explains the geometric basis for the recently-discovered
nonholonomic mapping principle which specifies certain laws of nature in
spacetimes with curvature and torsion from those in flat spacetime, thus
replacing and extending Einstein's equivalence principle. An important
consequence is a new action principle for determining the equation of motion of
a free spinless point particle in such spacetimes. Surprisingly, this equation
contains a torsion force, although the action involves only the metric. This
force changes geodesic into autoparallel trajectories, which are a direct
manifestation of inertia. The geometric origin of the torsion force is a
closure failure of parallelograms. The torsion force changes the covariant
conservation law of the energy-momentum tensor whose new form is derived.


title:
Location of the innermost stable circular orbit of binary neutron stars
  in the post Newtonian approximations of general relativity

abstract:
  In this paper, we present results obtained from our recent studies on the
location of the innermost stable circular orbit (ISCO) for binary neutron stars
(BNSs) in several levels of post Newtonian (PN) approximations. We reach the
following conclusion at present: (1) even in the Newtonian case, there exists
the ISCO for binary of sufficiently stiff equation of state (EOS). If the mass
and the radius of each star are fixed, the angular velocity at the ISCO
$\Omega_{ISCO}$ is larger for softer EOS: (2) when we include the first PN
correction, there appear roughly two kinds of effects. One is the effect to the
self-gravity of each star of binary and the other is to the gravity acting
between two stars. Due to the former one, each star of binary becomes compact
and the tidal effect is less effective. As a result, $\Omega_{ISCO}$ tends to
be increased. On the other hand, the latter one has the property to destabilize
the binary orbit, and $\Omega_{ISCO}$ tends to be decreased. If we take into
account both effects, however, the former effect is stronger than the latter
one, and $\Omega_{ISCO}$ becomes large with increase of the 1PN correction: (3)
the feature mentioned above is more remarkable for softer EOS if the mass and
radius are fixed. This is because for softer EOS, each star has the larger
central density and is susceptible to the GR correction: (4) there has been no
self consistent calculation including all the 2PN effects and only exist
studies in which one merely includes the effect of the 2PN gravity acting
between two stars. In this case, the effect has the property to destabilize the
binary orbit, so that $\Omega_{ISCO}$ is always smaller than that for the
Newtonian case. If we include the PN effect of the self-gravity to each star,
$\Omega_{ISCO}$ will increase.


title: On the energy of the de Sitter-Schwarzschild black hole

abstract:
  Using Einstein's and Weinberg's energy complex, we evaluate the energy
distribution of the vaccum nonsingularity black hole solution. The energy
distribution is positive everywhere and be equal to zero at origin.


title:
Noisy Spherical Resonant Detector of Gravitational Waves: Veto on the
  Longitudinal Part of the Signal

abstract:
  The equations of a resonant sphere in interaction with $N$ secondary radial
oscillators (transducers) on its surface have been found in the context of
Lagrangian formalism. It has been shown the possibility to exert a veto against
spurious events measuring the longitudinal component of a signal. Numerical
simulations has been performed, which take into account thermal noise between
resonators and the sphere surface, for a particular configuration of the
transducers.


title: Invariance of Positive-Frequency Kernels in Generalized FRW Spacetimes

abstract:
  We consider the Klein-Gordon equation in FRW-like spacetimes, with compact
space sections (not necessarily isotropic neither homogeneous). The bi-scalar
kernel allowing to select the positive-frequency part of any solution is
developed on mode solutions, using the eigenfunctions of the three-dimensional
Laplacian. Of course this kernel is not unique but, except (perhaps) when the
scale factor undergoes a special law of evolution, the metric has no more
symmetries (connected with the identity) than those inherited from the space
sections. As a result, all admissible definitions of the positive-frequency
kernel are related one to another by a unitary transformation which commutes
with the connected isometries of spacetime; any such kernel is invariant under
these isometries isometries. A physical interpretation is tentatively
suggested.


title:
New first integral for twisting type-N vacuum gravitational fields with
  two non-commuting Killing vectors

abstract:
  A new first integral for the equations corresponding to twisting type-N
vacuum gravitational fields with two non-commuting Killing vectors is
introduced. A new reduction of the problem to a complex second-order ordinary
differential equation is given. Alternatively, the mentioned first integral can
be used in order to provide a first integral of the second-order complex
equation introduced in a previous treatment of the problem.


title: Self-forces in the Spacetime of Multiple Cosmic Strings

abstract:
  We calculate the electromagnetic self-force on a stationary linear
distribution of four-current in the spacetime of multiple cosmic strings. It is
shown that if the current is infinitely thin and stretched along a line which
is parallel to the strings the problem admits an explicit solution.


title: On the Nature of the Generic Big Bang

abstract:
  Spatially homogeneous but possibly anisotropic cosmologies have two main
types of singularities: (1) asymptotically velocity term dominated (AVTD) -
(reversing the time direction) the universe evolves to the singularity with
fixed anisotropic collapse rates ; (2) Mixmaster-the anisotropic collapse rates
change in a deterministicaly chaotic way. Much less is known about spatially
inhomogeneous universes. It has been claimed that a generic universe would
evolve toward the singularity as a different Mixmaster universe at each spatial
point. I shall discuss how to predict whether a cosmology has an AVTD or
Mixmaster singularity and whether or not our numerical simulations agree with
these predictions.


title:
Comment on the "Influence of Cosmological Transitions on the Evolution
  of Density Perturbations"

abstract:
  A recent paper by Martin and Schwarz [1] argues that the ``standard
inflationary result" has been finally proven. The result itself is formulated
as: ``the closer the inflationary epoch is to the de Sitter space-time, the
less important are large-scale gravitational waves in the CMBR today".
Beginning from the basic equations of Grishchuk [2, 3] the authors say [1] that
Grishchuk's conclusion about approximate equality of metric amplitudes for
gravitational waves and density perturbations ``is wrong because the time
evolution of the scalar metric perturbation through the (smooth) reheating
transition was not calculated correctly". They reiterate a claim about ``big
amplification" of scalar perturbations (in contrast to gravitational waves)
during reheating. The authors say [1] that after appropriate correction they
have recovered the "standard result" within Grishchuk's approach. It is shown
in this Comment that the "big amplification" is a misinterpretation. There is
no difference in the evolution of long-wavelength metric perturbations for
gravitational waves and density perturbations: they both stay approximately
constant. The influence of cosmological transitions on the evolution is none at
all, as long as the wavelength of the perturbation is much larger than the
Hubble radius. It is shown that from the approach of [2, 3] follow the
conclusions of [2, 3] without change. Finally, it is argued that the ``standard
inflationary result" does not follow from the correct evolution and quantum
normalization of density perturbations.


title: Critical Collapse of Skyrmions

abstract:
  We study first order phase transitions in the gravitational collapse of
spherically symmetric skyrmions. Static sphaleron solutions are shown to play
the role of critical solutions separating black-hole spacetimes from
no-black-hole spacetimes. In particular, we find a new type of first order
phase transition where subcritical data do not disperse but evolve towards a
static regular stable solution. We also demonstrate explicitly that the
near-critical solutions depart from the intermediate asymptotic regime along
the unstable manifold of the critical solution.


title: On stable compactification with Casimir-like potential

abstract:
  Multidimensional cosmological models with a higher dimensional space-time
manifold are investigated under dimensional reduction. In the Einstein
conformal frame, the effective potential for the internal scale factors is
obtained. The stable compactification of the internal spaces is achieved due to
the Casimir effect. In the case of more than one internal space a Casimir-like
ansatz for the energy density of the massless scalar field fluctuations is
proposed. Stable configurations with respect to the internal scale factor
excitations are found in the cases of one and two internal spaces.


title: Modelling Gravitational Waves from Inspiralling Compact Binaries

abstract:
  Gravitational waves from inspiralling compact binaries can be reliably
extracted from a noisy detector output only if the template used in the
detection is a faithful representation of the true signal. In this article we
suggest a new approach to constructing faithful signal models.


title: Black Hole Thermodynamics Today

abstract:
  A brief survey of the major themes and developments of black hole
thermodynamics in the 1990's is given, followed by summaries of the talks on
this subject at MG8 together with a bit of commentary, and closing with a look
towards the future.


title: Topological Inflation with Multiple Winding

abstract:
  We analyze the core dynamics of critically coupled, superheavy gauge vortices
in the (2+1) dimensional Einstein-Abelian-Higgs system. By numerically solving
the Eistein and field equations for various values of the symmetry breaking
scale, we identify the regime in which static solutions cease to exist and
topological inflation begins. We explicitly include the topological winding of
the vortices into the calculation and extract the dependence on the winding of
the critical scale separating the static and inflating regimes. Extrapolation
of our results suggests that topological inflation might occur within high
winding strings formed at the Grand Unified scale.


title: Super-Horizon Scale Dynamics of Multi-Scalar Inflation

abstract:
  We consider the dynamics of a multi-component scalar field on super-horizon
scales in the context of inflationary cosmology. We present a method to solve
the perturbation equations on super- horizon scales, i.e., in the long
wavelength limit, by using only the knowledge of spatially homogeneous
background solutions. In doing so, we clarify the relation between the
perturbation equations in the long wavelength limit and the background
equations. Then as a natural extension of our formalism, we provide a strategy
to study super-horizon scale perturbations beyond the standard linear
perturbation theory. Namely we reformulate our method so as to take into
account the nonlinear dynamics of the scalar field.


title:
Interaction of electromagnetic perturbations with infalling observers
  inside spherical charged black holes

abstract:
  The electromagnetic radiation that falls into a Reissner-Nordstr\"{o}m black
hole is known to develop a ``blue sheet'', namely, an infinite concentration of
energy density at the Cauchy horizon. The interaction of these divergent
electromagnetic fields with infalling matter was recently analyzed (L. M. burko
and A. Ori, Phys. Rev. Lett. 74, 1064 (1995)). Here, we give a more detailed
description of that analysis: We consider classical electromagnetic fields
(that were produced during the collapse and then backscattered into the black
hole), and investigate the blue-sheet effects of these fields on infalling
objects within two simplified models of a classical and a quantum absorber.
These effects are found to be finite and even negligible for typical parameters
of a supermassive black hole.


title:
A classical history theory: Geometrodynamics and general field dynamics
  regained

abstract:
  Assuming that the Hamiltonian of a canonical field theory can be written in
the form N H + N^i H_i, and using as the only input the actual choice of the
canonical variables, we derive: (i) The algebra satisfied by H and H_i, (ii)
any constraints, and (iii) the most general canonical representation for H and
H_i. This completes previous work by Hojman, Kuchar and Teitelboim who had to
impose a set of additional postulates, among which were the form of the
canonical algebra and the requirement of path-independence of the dynamical
evolution. A prominent feature of the present approach is the replacement of
the equal-time Poisson bracket with one evaluated at general times. The
resulting formalism is therefore an example of a classical history theory -- an
interesting fact, especially in view of recent work by Isham et al.


title: Quantum Creation of a Black Hole

abstract:
  Using the Hartle-Hawking no-boundary proposal for the wave function of the
universe, we can study the wave function and probability of a single black hole
created at the birth of the universe. The black hole originates from a
constrained gravitational instanton with conical singularities. The wave
function and probability of a universe with a black hole are calculated at the
$WKB$ level. The probability of a black hole creation is the exponential of one
quarter of the sum of areas of the black hole and cosmological horizons. One
quarter of this sum is the total entropy of the universe. We show that these
arguments apply to all kinds of black holes in the de Sitter space background.


title:
Solutions of gauge invariant cosmological perturbations in
  long-wavelength limit

abstract:
  We investigate gauge invariant cosmological perturbations in a spatially flat
Friedman-Robertson-Walker universe with scalar fields. It is well known that
the evolution equation for the gauge invariant quantities has exact solutions
in the long-wavelength limit. We find that these gauge invariant solutions can
be obtained by differentiating the background solution with respect to
parameters contained in the background system. This method is very useful when
we analyze the long-wavelength behavior of cosmological perturbation with
multiple scalar fields.


title: Variation of Area Variables in Regge Calculus

abstract:
  We consider the possibility to use the areas of two-simplexes, instead of
lengths of edges, as the dynamical variables of Regge calculus. We show that if
the action of Regge calculus is varied with respect to the areas of
two-simplexes, and appropriate constraints are imposed between the variations,
the Einstein-Regge equations are recovered.


title: Yang's gravitational theory

abstract:
  Yang's pure space equations (C.N. Yang, Phys. Rev. Lett. v.33, p.445 (1974))
generalize Einstein's gravitational equations, while coming from gauge theory.
We study these equations from a number of vantage points: summarizing the work
done previously, comparing them with the Einstein equations and investigating
their properties. In particular, the initial value problem is discussed and a
number of results are presented for these equations with common energy-momentum
tensors.


title: Spacetime foam as a quantum thermal bath

abstract:
  An effective model for the spacetime foam is constructed in terms of nonlocal
interactions in a classical background. In the weak-coupling approximation, the
evolution of the low-energy density matrix is determined by a master equation
that predicts loss of quantum coherence. Moreover, spacetime foam can be
described by a quantum thermal field that, apart from inducing loss of
coherence, gives rise to effects such as gravitational Lamb and Stark shifts as
well as quantum damping in the evolution of the low-energy observables.


title: Particle Creation Near the Chronology Horizon

abstract:
  We investigate the phenomenon of particle creation of the massless scalar
field in the model of spacetime in which, depending on the model's parameter
$\aout$, the chronology horizon could be formed. The model represents a
two-dimensional curved spacetime with the topology $R^1 \times S^1$ which is
asymptotically flat in the past and in the future. The spacetime is globally
hyperbolic and has no causal pathologies if $\aout<1$, and closed timelike
curves appear in the spacetime if $\aout\ge 1$. We obtain the spectrum of
created particles in the case $\aout<1$. In the limit $\aout \to 1$ this
spectrum gives the number of particles created into mode $n$ near the
chronology horizon. The main result we have obtained is that the number of
scalar particles created into each mode as well as the full number of particles
remain finite at the moment of forming of the chronology horizon.


title:
Effective average action and nonperturbative renormalization group
  equation in higher derivative quantum gravity

abstract:
  We study the exact renormalization group (RG) in $R^2$-gravity in the
effective average action formalism using the background field method. The
truncated evolution equation (where truncation is made to low-derivatives
functionals space) for such a theory in a de Sitter background leads to a set
of nonperturbative RG equations for cosmological and gravitational coupling
constants. The gauge dependence problem is solved by working in the physical
Landau-De Witt gauge corresponding to gauge-fixing independent effective
action. Approximate solution of nonperturbative RG equations reveals the
appearence of antiscreening or screening behaviour of Newtonian coupling,
depending on the higher-derivatives coupling constants. The existence of
unstable
  UV fixed points is also mentioned.


title:
Deconvolving the information from an imperfect spherical gravitational
  wave antenna

abstract:
  We have studied the effects of imperfections in spherical gravitational wave
antenna on our ability to properly interpret the data it will produce. The
results of a numerical simulation are reported that quantitatively describe the
systematic errors resulting from imperfections in various components of the
antenna. In addition, the results of measurements on a room-temperature
prototype are presented that verify it is possible to accurately deconvolve the
data in practice.


title:
Perturbative Quantum Gravity And Newton's Law On A Flat Robertson-Walker
  Background

abstract:
  We derive the Feynman rules for the graviton in the presence of a flat
Robertson-Walker background and give explicit expressions for the propagator in
the physically interesting cases of inflation, radiation domination, and matter
domination. The aforementioned background is generated by a scalar field source
which should be taken to be dynamical. As an elementary application, we compute
the corrections to the Newtonian gravitational force in the present matter
dominated era and conclude -- as expected -- that they are negligible except
for the largest scales.


title: Absolute spacetime: the twentieth century ether

abstract:
  All gauge theories need ``something fixed'' even as ``something changes.''
Underlying the implementation of these ideas all major physical theories make
indispensable use of an elaborately designed spacetime model as the ``something
fixed,'' i.e., absolute. This model must provide at least the following
sequence of structures: point set, topological space, smooth manifold,
geometric manifold, base for various bundles. The ``fine structure'' of
spacetime inherent in this sequence is of course empirically unobservable
directly, certainly when quantum mechanics is taken into account. This issue is
at the basis of the difficulties in quantizing general relativity and has been
approached in many different ways. Here we review an approach taking into
account the non-Boolean properties of quantum logic when forming a spacetime
model. Finally, we recall how the fundamental gauge of diffeomorphisms (the
issue of general covariance vs coordinate conditions) raised deep conceptual
problems for Einstein in his early development of general relativity. This is
clearly illustrated in the notorious ``hole'' argument. This scenario, which
does not seem to be widely known to practicing relativists, is nevertheless
still interesting in terms of its impact for fundamental gauge issues.


title: Novel Geometric Gauge Invariance of Autoparallels

abstract:
  We draw attention to a novel type of geometric gauge invariance relating the
autoparallel equations of motion in different Riemann-Cartan spacetimes with
each other. The novelty lies in the fact that the equations of motion are
invariant even though the actions are not. As an application we use this gauge
transformation to map the action of a spinless point particle in a
Riemann-Cartan spacetime with a gradient torsion to a purely Riemann spacetime,
in which the initial torsion appears as a nongeometric external field. By
extremizing the transformed action in the usual way, we obtain the same
autoparallel equations of motion as those derived in the initial spacetime with
torsion via a recently-discovered variational principle.


title:
Spin effects in gravitational radiation backreaction II. Finite mass
  effects

abstract:
  A convenient formalism for averaging the losses produced by gravitational
radiation backreaction over one orbital period was developed in an earlier
paper. In the present paper we generalize this formalism to include the case of
a closed system composed from two bodies of comparable masses, one of them
having the spin S.
  We employ the equations of motion given by Barker and O'Connell, where terms
up to linear order in the spin (the spin-orbit interaction terms) are kept. To
obtain the radiative losses up to terms linear in the spin, the equations of
motion are taken to the same order. Then the magnitude L of the angular
momentum L, the angle kappa subtended by S and L and the energy E are
conserved. The analysis of the radial motion leads to a new parametrization of
the orbit.
  From the instantaneous gravitational radiation losses computed by Kidder the
leading terms and the spin-orbit terms are taken. Following Apostolatos,
Cutler, Sussman and Thorne, the evolution of the vectors S and L in the
momentary plane spanned by these vectors is separated from the evolution of the
plane in space. The radiation-induced change in the spin is smaller than the
leading-order spin terms in the momentary angular momentum loss. This enables
us to compute the averaged losses in the constants of motion E, L and L_S=L cos
kappa. In the latter, the radiative spin loss terms average to zero. An
alternative description using the orbital elements a,e and kappa is given.
  The finite mass effects contribute terms, comparable in magnitude, to the
basic, test-particle spin terms in the averaged losses.


title: Cosmic Censorship: As Strong As Ever

abstract:
  Spacetimes which have been considered counter-examples to strong cosmic
censorship are revisited. We demonstrate the classical instability of the
Cauchy horizon inside charged black holes embedded in de Sitter spacetime for
all values of the physical parameters. The relevant modes which maintain the
instability, in the regime which was previously considered stable, originate as
outgoing modes near to the black hole event horizon. This same mechanism is
also relevant for the instability of Cauchy horizons in other proposed
counter-examples of strong cosmic censorship.


title: Scaling Behaviour of Conformal Fields in Curved Three-dimensional Space

abstract:
  The limitations of three-dimensional semi-classical gravity are explored in
the context of a conformally invariant theory for a self-interacting scalar
field. The analysis of the theory's scaling behaviour reveals that scalar-loop
effects contribute to the conformal anomaly only at advanced orders allowing
for a range of relevant energy scales which extend to those comparable to the
non-perturbative scale of Planck mass.


title: Black Holes and Two-Dimensional Dilaton Gravity

abstract:
  We study the conditions for 2-dimensional dilaton gravity models to have
dynamical formation of black holes and construct all such models. Furthermore
we present a parametric representation of the general solutions of the black
holes.


title: Dynamical Instability of a two-dimensional Quantum Black Hole

abstract:
  We investigate dynamical instability of a two-dimensional quantum black hole
model considered by Lowe in his study of Hawking evaporation. The model is
supposed to express a black hole in equilibrium with a bath of Hawking
radiation. It turns out that the model has at least one instability modes for a
wide range of parameters, and thus it is unstable.


title:
A small guide to variations in teleparallel gauge theories of gravity
  and the Kaniel-Itin model

abstract:
  Recently Kaniel & Itin proposed a gravitational model with the wave type
equation [\square+\lambda(x)]\vartheta^\alpha=0 as vacuum field equation, where
\vartheta^\alpha denotes the coframe of spacetime. They found that the viable
Yilmaz-Rosen metric is an exact solution of the tracefree part of their field
equation. This model belongs to the teleparallelism class of gravitational
gauge theories. Of decisive importance for the evaluation of the Kaniel-Itin
model is the question whether the variation of the coframe commutes with the
Hodge star. We find a master formula for this commutator and rectify some
corresponding mistakes in the literature. Then we turn to a detailed discussion
of the Kaniel-Itin model.


title: Multidimensional Gravity and Cosmology: Exact Solutions

abstract:
  A short review of recent results on exact solutions in multidimensional
cosmology and overview of reports at workshop in MG8 (held by the author) are
presented.


title:
Gravitational waves from inspiraling compact binaries: Accuracy of the
  post-Newtonian waveforms

abstract:
  The accuracy of the post-Newtonian waveforms, both in standard and Pade form,
is determined by computing their matched-filtering overlap integral with a
reference waveform obtained from black-hole perturbation theory.


title: Complex inflaton field in quantum cosmology

abstract:
  We investigate the cosmological model with the complex scalar
self-interacting inflaton field non-minimally coupled to gravity. The different
geometries of the Euclidean classically forbidden regions are represented. The
instanton solutions of the corresponding Euclidean equations of motion are
found by numerical calculations supplemented by the qualitative analysis of
Lorentzian and Euclidean trajectories. The applications of these solutions to
the no-boundary and tunneling proposals for the wave function of the Universe
are studied. Possible interpretation of obtained results and their connection
with inflationary cosmology is discussed. The restrictions on the possible
values of the new quasi-fundamental constant of the theory-non-zero classical
charge-- are obtained. The equations of motion for the generalized cosmological
model with complex scalar field are written down and investigated. The
conditions of the existence of instanton solutions corresponding to permanent
values of an absolute value of scalar field are obtained.


title: Discrete and finite Genral Relativity

abstract:
  We develop the General Theory of Relativity in a formalism with extended
causality that describes physical interaction through discrete, transversal and
localized pointlike fields. The homogeneous field equations are then solved for
a finite, singularity-free, point-like field that we associate to a ``classical
graviton". The standard Einstein's continuous formalism is retrieved by means
of an averaging process, and its continuous solutions are determined by the
chosen imposed symetry. The Schwarzschild metric is obtained by the imposition
of spherical symmetry on the averaged field.


title: Multidimensional Gravity with p-branes

abstract:
  A short review of recent results of authors on sigma-model approach in
multidimensional gravity with p-branes is presented.


title:
Integration of D-dimensional 2-factor spaces cosmological models by
  reducing to the generalized Emden-Fowler equation

abstract:
  The D-dimensional cosmological model on the manifold $M = R \times M_{1}
\times M_{2}$ describing the evolution of 2 Einsteinian factor spaces, $M_1$
and $M_2$, in the presence of multicomponent perfect fluid source is
considered. The barotropic equation of state for mass-energy densities and the
pressures of the components is assumed in each space. When the number of the
non Ricci-flat factor spaces and the number of the perfect fluid components are
both equal to 2, the Einstein equations for the model are reduced to the
generalized Emden-Fowler (second-order ordinary differential) equation, which
has been recently investigated by Zaitsev and Polyanin within discrete-group
analysis. Using the integrable classes of this equation one generates the
integrable cosmological models. The corresponding metrics are presented. The
method is demonstrated for the special model with Ricci-flat spaces $M_1,M_2$
and the 2-component perfect fluid source.


title: On the Gravitational Back Reaction to Hawking Radiation

abstract:
  We show that a surface term should be added to the Einstein-Hilbert action in
order to properly describe quantum transitions occurring around a black hole.
The introduction of this boundary term has been advocated by Teitelboim and
collaborators and it has been used in the computation of the black hole
entropy. Here, we use it to compute the gravitational corrections to the
transition amplitudes giving rise to Hawking radiation. This surface term
implies that the probability to emit a particle is given by $e^{- \Delta A/4}$
where $\Delta A$ is the change in the area of the black hole horizon induced by
the emission. Its inclusion at the level of the amplitudes therefore relates
quantum black hole radiation to the first law of black hole dynamics. In both
cases indeed, the term expressing the change in area directly results from the
same boundary term introduced for the same reason: to obtain a well defined
action principle.


title:
Evaporation of a Kerr black hole by emission of scalar and higher spin
  particles

abstract:
  We study the evolution of an evaporating rotating black hole, described by
the Kerr metric, which is emitting either solely massless scalar particles or a
mixture of massless scalar and nonzero spin particles. Allowing the hole to
radiate scalar particles increases the mass loss rate and decreases the angular
momentum loss rate relative to a black hole which is radiating nonzero spin
particles. The presence of scalar radiation can cause the evaporating hole to
asymptotically approach a state which is described by a nonzero value of $a_*
\equiv a / M$. This is contrary to the conventional view of black hole
evaporation, wherein all black holes spin down more rapidly than they lose
mass. A hole emitting solely scalar radiation will approach a final asymptotic
state described by $a_* \simeq 0.555$. A black hole that is emitting scalar
particles and a canonical set of nonzero spin particles (3 species of
neutrinos, a single photon species, and a single graviton species) will
asymptotically approach a nonzero value of $a_*$ only if there are at least 32
massless scalar fields. We also calculate the lifetime of a primordial black
hole that formed with a value of the rotation parameter $a_{*}$, the minimum
initial mass of a primordial black hole that is seen today with a rotation
parameter $a_{*}$, and the entropy of a black hole that is emitting scalar or
higher spin particles.


title: Space-time Foam, Casimir energy and black hole pair creation

abstract:
  We conjecture that the neutral black hole pair production is related to the
vacuum fluctuation of pure gravity via the Casimir-like energy. Implications on
the foam-like structure of spacetime are discussed.