title: Coleman-Weinberg SO(10) GUT Theories as Inflationary Models

abstract:
  The flat-space limit of the one-loop effective potential for SO(10) GUT
theories in spatially flat Friedmann-Robertson-Walker cosmologies is applied to
study the dynamics of the early universe. The numerical integration of the
corresponding field equations shows that, for such grand unified theories, a
sufficiently long inflationary stage is achieved for suitable choices of the
initial conditions. However, a severe fine tuning of these initial conditions
is necessary to obtain a large $e$-fold number. In the direction with residual
symmetry $SU(4)_{PS} \otimes SU(2)_{L} \otimes SU(2)_{R}$, one eventually finds
parametric resonance for suitable choices of the free parameters of the
classical potential. This phenomenon leads in turn to the end of inflation.


title: Quantum Geodesics

abstract:
  Classical methods of differential geometry are used to construct equations of
motion for particles in quantum, electrodynamic and gravitational fields. For a
five dimensional geometrical system, the equivalence principle can be extended.
Local transformations generate the effects of electromagnetic and quantum
fields. A combination of five dimensional coordinate transformations and
internal conformal transformations leads to a quantum Kaluza-Klein metric. The
theories of Weyl and Kaluza can be interrelated when charged particle quantum
mechanics is included. Measurements of trajectories are made relative to an
observers' space that is defined by the motion of neutral particles. It is
shown that a preferred set of null geodesics describe valid classical and
quantum trajectories. These are tangent to the probability density four vector.
This construction establishes a generally covariant basis for geodesic motion
of quantum states.


title: Quantum-conformal Field theory

abstract:
  A theoretical study is made of conformal factors in certain types of physical
theories based on classical differential geometry. Analysis of quantum versions
of Weyl's theory suggest that similar field equations should be available in
four, five and more dimensions. Various conformal factors are associated with
the wave functions of source and test particles. This allows for quantum field
equations to be developed. The curvature tensors are calculated and separated
into gravitational, electromagnetic and quantum components. Both four and five
dimensional covariant theories are studied. Nullity of the invariant five
scalar of curvature leads to the Klein-Gordon equation. The mass is associated
with an eigenvalue of the differential operator of the fifth dimension.
Different concepts of interaction are possible and may apply in a quantum
gravitational theory.


title: On the constraint algebra of quantum gravity in the loop representation

abstract:
  Although an important issue in canonical quantization, the problem of
representing the constraint algebra in the loop representation of quantum
gravity has received little attention. The only explicit computation was
performed by Gambini, Garat and Pullin for a formal point-splitting
regularization of the diffeomorphism and Hamiltonian constraints. It is shown
that the calculation of the algebra simplifies considerably when the
constraints are expressed not in terms of generic area derivatives but rather
as the specific shift operators that reflect the geometric meaning of the
constraints.


title: A new approach to quantization of gravity. 2+1-dimensional example

abstract:
  In this paper the quantization of the 2$+$1-dimensional gravity couplet to
the massless Dirac field is carried out. The problem is solved by the
application of the new Dynamic Quantization Method [1,2]. It is well-known that
in general covariant theories such as gravitation, a Hamiltonian is any linear
combination of the first class constraints, which can be considered as gauge
transformation generators. To perform quantization, the Dirac field modes with
gauge invariant creation and annihilation operators are selected. The
regularization of the theory is made by imposing an infinite set of the second
class constraints: almost all the gauge invariant creation and annihilation
operators (except for a finite number) are put equal to zero. As a result the
regularized theory is gauge invariant. The gauge invariant states are built by
using the remained gauge invariant fermion creation operators similar to the
usual construction of the states in any Fock space. The developed dynamic
quantization method can construct a mathematically correct perturbation theory
in a gravitational constant.


title:
A Semi-Analytical Method for the Evaluation of the Power Spectrum of a
  Rotating Observer

abstract:
  In this letter we propose a semi-analitical method of evaluation of the power
spectrum of a circular moving Unruh-type detector using the method of residue
and compare the spectrum with the already known result in the relativistic
limit.


title: The Goldberg--Kerr Approach to Lorentz Covariant Gravity

abstract:
  The approach to asymptotic electromagnetic fields introduced by Goldberg and
Kerr is used to study various aspects of Lorentz Covariant Gravity. Retarded
multipole moments of the source, the central objects of this study, are
defined, and a sequence of conservation equations for these are derived. These
equations are used extensively throughout the paper. The solution of the
linearized Einstein equation is obtained in terms of the retarded moments for a
general bound source, correct to $O(r^{-4})$. This is used to obtain the
peeling--off of the linearized field, and to study the geometric optics
approximation for the field and for the energy-momentum pseudotensor of the
field. It is shown that the energy-momentum 4-vector splits into the `total
radiated 4-momentum' and the `bound 4-momentum of the source', similar to the
case of the electromagnetic field. In the case of a source which has only
retarded pole, dipole and quadrupole moments, a decomposition into arbitrary
functions of a null coordinate is obtained which allows comparison with the
solutions for linearized gravity obtained by other authors.


title: Quantizing Regge calculus

abstract:
  A discretized version of canonical gravity in (3+1)-d introduced in a
previous paper is further developed, introducing the Liouville form and the
Poisson brackets, and studying them in detail in an explicit parametrization
that shows the nature of the variables when the second class constraints are
imposed. It is then shown that, even leaving aside the difficult question of
imposing the first class constraints on the states, it is impossible to
quantize the model directly, using complex variables and leaving the second
class constraints to fix the metric of the quantum Hilbert, because one cannot
find a metric which makes the area variables hermitean.


title: Skein spaces and spin structures

abstract:
  This paper relates skein spaces based on the Kauffman bracket and spin
structures. A spin structure on an oriented 3-manifold provides an isomorphism
between the skein space for parameter A and the skein space for parameter -A.
  There is an application to Penrose's binor calculus, which is related to the
tensor calculus of representations of SU(2). The perspective developed here is
that this tensor calculus is actually a calculus of spinors on the plane, and
the matrices a re determined by a type of spinor transport which generalises to
links in any 3-manifold.
  A second application shows that there is a skein space which is the algebra
of functions on the set of spin structures for the 3-manifold.


title: Poincare Sections of Hamiltonian Systems

abstract:
  A set of Maplev R.3 software routines, for plotting 2D/3D projections of
Poincar\'e surfaces-of-section of Hamiltonian dynamical systems, is presented.
The package consists of a plotting-command plus a set of facility-commands for
a quick setup of the Hamilton equations of motion, initial conditions for
numerical experiments, and for the zooming of plots.


title: The geometry of quantum spin networks

abstract:
  The discrete picture of geometry arising from the loop representation of
quantum gravity can be extended by a quantum deformation. The operators for
area and volume defined in the q-deformation of the theory are partly
diagonalized. The eigenstates are expressed in terms of q-deformed spin
networks. The q-deformation breaks some of the degeneracy of the volume
operator so that trivalent spin-networks have non-zero volume. These
computations are facilitated by use of a technique based on the recoupling
theory of SU(2)_q, which simplifies the construction of these and other
operators through diffeomorphism invariant regularization procedures.


title: Hawking Radiation Entropy and Horizon Divergences

abstract:
  We review the problem of divergences in one--loop thermodynamical quantities
for matter fields in thermal equilibrium on a black hole background. We discuss
a number of results obtained for various thermodynamical quantities. Then we
discuss the ansatz called ``literal interpretation" of zeroth law of black hole
mechanics and try to explain the diseases of the conical defect procedure in
light of this ansatz. Finally, an analysis of the consequences implied by our
ansatz on the calculation of the partition function is made.


title: Dynamics of Gravitating Magnetic Monopoles

abstract:
  According to previous work on magnetic monopoles, static regular solutions
are nonexistent if the vacuum expectation value of the Higgs field $\eta$ is
larger than a critical value $\eta_{{\rm cr}}$, which is of the order of the
Planck mass. In order to understand the properties of monopoles for
$\eta>\eta_{{\rm cr}}$, we investigate their dynamics numerically. If $\eta$ is
large enough ($\gg\eta_{{\rm cr}}$), a monopole expands exponentially and a
wormhole structure appears around it, regardless of coupling constants and
initial configuration. If $\eta$ is around $\eta_{{\rm cr}}$, there are three
types of solutions, depending on coupling constants and initial configuration:
a monopole either expands as stated above, collapses into a black hole, or
comes to take a stable configuration.


title: Dynamic Monopoles and Spacetime Structure

abstract:
  According to previous work on magnetic monopoles, static regular solutions
are nonexistent if the vacuum expectation value of the Higgs field $\eta$ is
larger than a critical value $\eta_{{\rm cr}}$, which is of the order of the
Planck mass. In order to understand the properties of monopoles for
$\eta>\eta_{{\rm cr}}$, we investigate their dynamics numerically and classify
those dynamical solutions into three types as follows. If $\eta$ is larger than
another critical value $\eta_{{\rm inf}}~(>\eta_{{\rm cr}})$, a monopole
inflates and a wormhole structure appears around it. In the case of $\eta_{{\rm
cr}}<\eta<\eta_{{\rm inf}}$, inflation does not occur and the dynamics depend
on the ratio of the Higgs self coupling constant $\lambda$ and the gauge
coupling constant $e^2$: if $\lambda/e^2\stackrel{<}{\sim}1$, a monopole just
shrinks and becomes a black hole; otherwise, a monopole approaches a stable
configuration.


title:
Non-minimal coupling, boundary terms and renormalization of the
  Einstein-Hilbert action

abstract:
  A consistent variational procedure applied to the gravitational action
requires according to Gibbons and Hawking a certain balance between the volume
and boundary parts of the action. We consider the problem of preserving this
balance in the quantum effective action for the matter non-minimally coupled to
metric. It is shown that one has to add a special boundary term to the matter
action analogous to the Gibbons-Hawking one. This boundary term modifies the
one-loop quantum corrections to give a correct balance for the effective action
as well. This means that the boundary UV divergences do not require independent
renormalization and are automatically renormalized simultaneously with their
volume part. This result is derived for arbitrary non-minimally coupled matter.
The example of 2D Maxwell field is considered in much detail. The relevance of
the results obtained to the problem of the renormalization of the black hole
entropy is discussed.


title:
On the oscillation spectra of ultracompact stars: An extensive survey of
  gravitational-wave modes

abstract:
  An extensive survey of gravitational-wave modes for uniform density stars is
presented. The study covers stars ranging in compactness from $R/M=100$ to the
limit of stability in general relativity: $R/M = 9/4$. We establish that polar
and axial gravitational-wave modes exist for all these stellar models.
Moreover, there are two distinct families of both axial and polar modes. We
discuss the physics of these modes and argue that one family is primarily
associated with the interior of the star, while the second family is mainly
associated with the stellar surface. We also show that the problem of axial
perturbations has all the essential features of the polar problem as far as
gravitational waves are concerned. This means that the axial problem is much
more important than has previously been assumed. We also find some surprising
features, such as avoided crossings between the polar gravitational-wave modes
and the Kelvin f-mode as the star becomes very compact. This seems to suggest
that the f-mode should be considered on equal footing with the polar w-modes
for ultracompact stars. All modes may have the main character of trapped modes
inside the curvature potential barrier for $R/M < 3$.


title: Quantum Origin of Noise and Fluctuations in Cosmology

abstract:
  We address two basic issues in the theory of galaxy formation from
fluctuations of quantum fields: 1) the nature and origin of noise and
fluctuations and 2) the conditions for using a classical stochastic equation
for their description. On the first issue, we derive the influence functional
for a $\lambda \phi^4 $ field in a zero-temperature bath in de Sitter universe
and obtain the correlator for the colored noises of vacuum fluctuations. This
exemplifies a new mechanism we propose for colored noise generation which can
act as seeds for galaxy formation with non-Gaussian distributions. For the
second issue, we present a (functional) master equation for the inflaton field
in de Sitter universe. By examining the form of the noise kernel we study the
decoherence of the long-wavelength sector and the conditions for it to behave
classically.


title: Exact Gravitational Shock Wave Solution of Higher Order Theories

abstract:
  We find an {\it exact} pp--gravitational wave solution of the fourth order
gravity field equations. Outside the (delta--like) source this {\it not} a
vacuum solution of General Relativity. It represents the contribution of the
massive, $m=(-\beta)^{-1/2}$, spin--two field associated to the Ricci squared
term in the gravitational Lagrangian. The fourth order terms tend to make
milder the singularity of the curvature at the point where the particle is
located. We generalize this analysis to $D$--dimensions, extended sources, and
higher than fourth order theories. We also briefly discuss the scattering of
fields by this kind of plane gravitational waves.


title: Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology

abstract:
  Quantum fields are investigated in the (2+1)-open-universes with non-trivial
topologies by the method of images. The universes are locally de Sitter
spacetime and anti-de Sitter spacetime. In the present article we study
spacetimes whose spatial topologies are a torus with a cusp and a sphere with
three cusps as a step toward the more general case. A quantum energy momentum
tensor is obtained by the point stripping method. Though the cusps are no
singularities, the latter cusps cause the divergence of the quantum field. This
suggests that only the latter cusps are quantum mechanically unstable. Of
course at the singularity of the background spacetime the quantum field
diverges. Also the possibility of the divergence of topological effect by a
negative spatial curvature is discussed. Since the volume of the negatively
curved space is larger than that of the flat space, one see so many images of a
single source by the non-trivial topology. It is confirmed that this divergence
does not appear in our models of topologies. The results will be applicable to
the case of three dimensional multi black hole\cite{BR}.


title:
A quadratic curvature Lagrangian of Paw{\l}owski and R\c{a}czka: a
  finger exercise with MathTensor

abstract:
  Recently Paw{\l}owski and R\c{a}czka proposed a unified model for the
fundamental interactions which does not contain a physical Higgs field. The
gravitational field equation of their model is rederived under heavy use of the
computer algebra system Mathematica and its package MathTensor.


title: Higher dimensional Chern-Simons supergravity

abstract:
  A Chern-Simons action for supergravity in odd-dimensional spacetimes is
proposed. For all odd dimensions, the local symmetry group is a non trivial
supersymmetric extension of the Poincar\'e group. In $2+1$ dimensions the gauge
group reduces to super-Poincar\'e, while for $D=5$ it is super-Poincar\'e with
a central charge. In general, the extension is obtained by the addition of a
1-form field which transforms as an antisymmetric fifth-rank tensor under
Lorentz rotations. Since the Lagrangian is a Chern-Simons density for the
supergroup, the supersymmetry algebra closes off shell without the need of
auxiliary fields.


title: Gravity, Geometry, and Equivalence

abstract:
  We show that the energy-momentum four-vector of a planet, p = mu, is
conserved during geodesic motion. Therefore, there is no exchange of
energy-momentum with the gravitational field. We discuss the meaning of a
gravitational field which is free of energy, momentum, and stress.


title:
Nonperturbative Amplifications of Inhomogeneities in a Self-Reproducing
  Universe

abstract:
  We investigate the distribution of energy density in a stationary
self-reproducing inflationary universe. We show that the main fraction of
volume of the universe in a state with a given density at any given moment of
proper time t is concentrated near the centers of deep exponentially wide
spherically symmetric wells in the density distribution. Since this statement
is very surprising and counterintuitive, we perform our investigation by three
different analytical methods to verify our conclusions, and then confirm our
analytical results by computer simulations. If one assumes that we are typical
observers living in the universe at a given moment of time, then our results
may imply that we should live near the center of a deep and exponentially large
void, which we will call infloid. Validity of this particular interpretation of
our results is not quite clear since it depends on the as-yet unsolved problem
of measure in quantum cosmology. Therefore at the moment we would prefer to
consider our results simply as a demonstration of nontrivial properties of the
hypersurface of a given time in the fractal self-reproducing universe, without
making any far-reaching conclusions concerning the structure of our own part of
the universe. Still we believe that our results may be of some importance since
they demonstrate that nonperturbative effects in quantum cosmology, at least in
principle, may have significant observational consequences, including an
apparent violation of the Copernican principle.


title: Some Thermodynamic Aspects of Black Holes and Singularities

abstract:
  We review and correct the classical critical exponents characterizing the
transition from negative to positive black hole's heat capacity at high
charge--angular momentum. We discuss the stability properties of black holes as
a thermodynamic system in equilibrium with a radiation bath (canonical
ensamble) by using the Helmholtz free energy potential. We finally analytically
extend the analysis to negative mass holes and study its thermodynamical
stability behavior.


title: Extended knots and the space of states of quantum gravity

abstract:
  In the loop representation the quantum constraints of gravity can be solved.
This fact allowed significant progress in the understanding of the space of
states of the theory. The analysis of the constraints over loop dependent
wavefunctions has been traditionally based upon geometric (in contrast to
analytic) properties of the loops. The reason for this preferred way is
twofold: for one hand the inherent difficulties associated with the analytic
loop calculus, and on the other our limited knowledge about the analytic
properties of knots invariants. Extended loops provide a way to overcome the
difficulties at both levels. For one hand, a systematic method to construct
analytic expressions of diffeomorphism invariants (the extended knots) in terms
of the Chern-Simons propagators can be developed. Extended knots are simply
related to ordinary knots (at least formally). The analytic expressions of knot
invariants could be produced then in a generic way. On the other hand, the
evaluation of the Hamiltonian over extended loop wavefunctions can be
thoroughly accomplished in the extended loop framework. These two ingredients
promote extended loops as a potential resort for answering important questions
about quantum gravity.


title:
Gauging kinematical and internal symmetry groups for extended systems:
  the Galilean one-time and two-times harmonic oscillators

abstract:
  The possible external couplings of an extended non-relativistic classical
system are characterized by gauging its maximal dynamical symmetry group at the
center-of-mass. The Galilean one-time and two-times harmonic oscillators are
exploited as models. The following remarkable results are then obtained: 1) a
peculiar form of interaction of the system as a whole with the external gauge
fields; 2) a modification of the dynamical part of the symmetry
transformations, which is needed to take into account the alteration of the
dynamics itself, induced by the {\it gauge} fields. In particular, the
Yang-Mills fields associated to the internal rotations have the effect of
modifying the time derivative of the internal variables in a scheme of minimal
coupling (introduction of an internal covariant derivative); 3) given their
dynamical effect, the Yang-Mills fields associated to the internal rotations
apparently define a sort of Galilean spin connection, while the Yang-Mills
fields associated to the quadrupole momentum and to the internal energy have
the effect of introducing a sort of dynamically induced internal metric in the
relative space.


title:
Analytic approximations to the spacetime of a critical gravitational
  collapse

abstract:
  We present analytic expressions that approximate the behavior of the
spacetime of a collapsing spherically symmetric scalar field in the critical
regime first discovered by Choptuik. We find that the critical region of
spacetime can usefully be divided into a ``quiescent'' region and an
``oscillatory'' region, and a moving ``transition edge'' that separates the two
regions. We find that in each region the critical solution can be well
approximated by a flat spacetime scalar field solution. A qualitative nonlinear
matching of the solutions across the edge yields the right order of magnitude
for the oscillations of the discretely self-similar critical solution found by
Choptuik.


title: The Evolution of Distorted Rotating Black Holes III: Initial Data

abstract:
  In this paper we study a new family of black hole initial data sets
corresponding to distorted ``Kerr'' black holes with moderate rotation
parameters, and distorted Schwarzschild black holes with even- and odd-parity
radiation. These data sets build on the earlier rotating black holes of Bowen
and York and the distorted Brill wave plus black hole data sets. We describe
the construction of this large family of rotating black holes. We present a
systematic study of important properties of these data sets, such as the size
and shape of their apparent horizons, and the maximum amount of radiation that
can leave the system during evolution. These data sets should be a very useful
starting point for studying the evolution of highly dynamical black holes and
can easily be extended to 3D.


title: $2+1$ Covariant Lattice Theory and t'Hooft's Formulation

abstract:
  We show that 't Hooft's representation of (2+1)-dimensional gravity in terms
of flat polygonal tiles is closely related to a gauge-fixed version of the
covariant Hamiltonian lattice theory. 't Hooft's gauge is remarkable in that it
leads to a Hamiltonian which is a linear sum of vertex Hamiltonians, each of
which is defined modulo $2 \pi$. A cyclic Hamiltonian implies that ``time'' is
quantized. However, it turns out that this Hamiltonian is {\it constrained}. If
one chooses an internal time and solves this constraint for the ``physical
Hamiltonian'', the result is not a cyclic function. Even if one quantizes {\it
a la Dirac}, the ``internal time'' observable does not acquire a discrete
spectrum. We also show that in Euclidean 3-d lattice gravity, ``space'' can be
either discrete or continuous depending on the choice of quantization. Finally,
we propose a generalization of 't Hooft's gauge for Hamiltonian lattice
formulations of topological gravity dimension 4.


title:
Isometries and embedding of the thermodynamic phase space of an ideal
  gas

abstract:
  In this work we find the Killing vector fields of the riemannian submanifolds
of the thermodynamic phase space of an ideal gas and show that the isometry
group corresponding to them is homomorphic to the euclidean group $E(2)$. We
also give the embedding of these submanifolds in the euclidean space $(R^{3},\
delta)$.


title:
From vacuum field equations on principal bundles to Einstein equations
  with fluids

abstract:
  In the present work we show that the Einstein equations on $M$ without
cosmological constant and with perfect fluid as source, can be obtained from
the field equations for vacuum with cosmological constant on the principal
fibre bundle $P(\frac{1}{I} M,U(1))$, $M$ being the space-time and $I$ the
radius of the internal space $U(1)$.


title:
Quantization of Point Particles in 2+1 Dimensional Gravity and
  Space-Time Discreteness

abstract:
  By investigating the canonical commutation rules for gravitating quantized
particles in a 2+1 dimensional world it is found that these particles live on a
space-time lattice. The space-time lattice points can be characterized by three
integers. Various representations are possible, the details depending on the
topology chosen for energy-momentum space. We find that an $S_2\times S_1$
topology yields a physically most interesting lattice within which first
quantization of Dirac particles is possible. An $S_3$ topology also gives a
lattice, but does not allow first quantized particles.


title: Spacetime modes of relativistic stars

abstract:
  The problem of relativistic stellar pulsations is studied in a somewhat ad
hoc approximation that ignores all fluid motions. This {\em Inverse Cowling
Approximation} (ICA) is motivated by two observations: 1) For highly damped
($w$-mode) oscillations the fluid plays very little role. 2) If the fluid
motion is neglected the problem for polar oscillation modes becomes similar to
that for axial modes. Using the ICA we find a polar mode spectrum that has all
features of the $w$-mode spectrum of the full problem. Moreover, in the limit
of superdense stars, we find the ICA spectrum to be qualitatively similar to
that of the axial modes. These results clearly show the importance of general
relativity for the pulsation modes of compact stars, and that there are modes
whose existence do not depend on motions of the fluid at all; pure
``spacetime'' modes.


title: Primordial Density Fluctuations in Phase Coupling Gravity

abstract:
  In this paper we study the evolution of density perturbations in the
framework of Phase Coupling Gravity theory at the very early universe. We show
that these perturbation display an exponential-like behaviour.


title: Relativistic Numerical Method for Close Neutron Star Binaries

abstract:
  We describe a numerical method for calculating the (3+1) dimensional general
relativistic hydrodynamics of a coalescing neutron-star binary system. The
relativistic field equations are solved at each time slice with a spatial
3-metric chosen to be conformally flat. Against this solution to the general
relativistic field equations the hydrodynamic variables and gravitational
radiation are allowed to respond. The gravitational radiation signal is derived
via a multipole expansion of the metric perturbation to the hexadecapole order
including both mass and current moments and a correction for the slow motion
approximation. Using this expansion, the effect of gravitational radiation on
the system evolution can also be recovered by introducing an acceleration term
in the matter evolution.


title: Gravitational kinks in two spacetime dimensions

abstract:
  The properties of gravitational kinks are studied within some simple models
of two dimensional gravity. In spacetimes of cylindrical topology we prove the
existence of kinks of constant curvature with arbitrary kink numbers. In
$R^1\times R^1$ spacetimes $m=1$ kink solutions of the equation $R=0$ are
found, whereas $|m|>1$ flat kinks are proved not to exist. We give a detailed
analysis of the behaviour of gravitational kinks under coordinate
transformations. Viewed as nonsingular black holes $|m|>1$ kink solutions are
found within a simple dilaton gravity theory. The general form of the potential
function is determined from the demand that the theory possesses an arbitrary
number of inequivalent kink configurations.


title: Comment on "Instabilities in Close Neutron Star Binaries"

abstract:
  In a recent Physical Review Letter, Wilson and Mathews presented some
interesting numerical calculations of a system of two equally massive neutron
stars in strong-field gravity. In particular they estimated the innermost
stable circular orbit in their system. Here we point out a possibly important
consequence of their results: Their calculated configurations have total
angular momentum $J$ and total mass $M$ too large to form any Kerr black hole:
$J>M^2$, in constrast to previous calculations of the innermost stable circular
orbit.


title: Black holes have no short hair

abstract:
  We show that in all theories in which black hole hair has been discovered,
the region with non-trivial structure of the non-linear matter fields must
extend beyond 3/2 the horizon radius, independently of all other parameters
present in the theory. We argue that this is a universal lower bound that
applies in every theory where hair is present. This {\it no short hair
conjecture} is then put forward as a more modest alternative to the original
{\it no hair conjecture}, the validity of which now seems doubtful.


title: New no-scalar-hair theorem for black-holes

abstract:
  A new no-hair theorem is formulated which rules out a very large class of
non-minimally coupled finite scalar dressing of an asymptotically flat, static,
and spherically symmetric black-hole. The proof is very simple and based in a
covariant method for generating solutions for non-minimally coupled scalar
fields starting from the minimally coupled case. Such method generalizes the
Bekenstein method for conformal coupling and other recent ones. We also discuss
the role of the finiteness assumption for the scalar field.


title: Canonical quantization of the relativistic particle in static spacetimes

abstract:
  We perform the canonical quantization of a relativistic spinless particle
moving in a curved and static spacetime. We show that the classical theory
already describes at the same time both particle and antiparticle. The analyses
involves time-depending constraints and we are able to construct the
two-particle Hilbert space. The requirement of a static spacetime is necessary
in order to have a well defined Schr\"odinger equation and to avoid problems
with vacuum instabilities. The severe ordering ambiguities we found are in
essence the same ones of the well known non-relativistic case.


title: Extensible Black Hole Embeddings for Apparently Forbidden Periodicities

abstract:
  Imposing extendibility on Kasner-Fronsdal black hole local isometric
embedding is equivalent to removing conic singularities in Kruskal
representation. Allowing for globally non-trivial (living in $M_{5}\times
S_{1}$) embeddings, parameterized by $k$, extendibility can be achieved for
apparently forbidden frequencies $\omega_{1}(k)\le\omega (k)\le \omega_{2}(k)$.
The Hawking-Gibbons limit, say $\displaystyle{\omega_{1,2}(0)= {1\over{4M}}}$
for Schwarzschild geometry, is respected. The corresponding Kruskal sheets are
viewed as slices in some Kaluza-Klein background. Euclidean $k$ discreteness,
dictated by imaginary time periodicity, is correlated with twistor flux
quantization.


title:
Coherent interaction of a monochromatic gravitational wave with both
  elastic bodies and electromagnetic circuits

abstract:
  The interaction of a gravitational wave with a system made of an RLC circuit
forming one end of a mechanical harmonic oscillator is investigated. We show
that, in some configurations, the coherent interaction of the wave with both
the mechanical oscillator and the RLC circuit gives rise to a mechanical
quality factor increase of the electromagnetic signal. When this system is used
as an amplifier of gravitational periodic signals in the frequency range
50-1000 Hz, at ultracryogenic temperatures and for sufficiently long
integration times (up to 4 months), a sensitivity of 10^(-24)-10^(-27) on the
amplitude of the metric could be achieved when thermal noise, shot noise and
amplifier back--action are considered.


title: Pauli-Lubanski scalar in the Polygon Approach to 2+1-Dimensional Gravity

abstract:
  In this paper we derive an expression for the conserved Pauli-Lubanski scalar
in 't Hooft's polygon approach to 2+1-dimensional gravity coupled to point
particles. We find that it is represented by an extra spatial shift $\Delta$ in
addition to the usual identification rule (being a rotation over the cut). For
two particles this invariant is expressed in terms of 't Hooft's phase-space
variables and we check its classical limit.


title: The Near-Linear Regime of Gravitational Waves in Numerical Relativity

abstract:
  We report on a systematic study of the dynamics of gravitational waves in
full 3D numerical relativity. We find that there exists an interesting regime
in the parameter space of the wave configurations: a near-linear regime in
which the amplitude of the wave is low enough that one expects the geometric
deviation from flat spacetime to be negligible, but nevertheless where
nonlinearities can excite unstable modes of the Einstein evolution equations
causing the metric functions to evolve out of control. The implications of this
for numerical relativity are discussed.


title:
Coordinate Conditions and Their Implementation in 3D Numerical
  Relativity

abstract:
  We put forth a few ideas on coordinate conditions and their implementation in
numerical relativity. Coordinate conditions are important for the long time
scale simulations of relativistic systems, e.g., for the determination of
gravitational waveforms from astrophysical events to be measured by LIGO/VIRGO.
We demonstrate the importance of, and propose methods for, the {\it active
enforcement} of coordinate properties. In particular, the constancy of the
determinant of the spatial 3-metric is investigated as such a property. We
propose an exceedingly simple but powerful idea for implementing elliptic
coordinate conditions that not only makes possible the use of complicated
elliptic conditions, but is also {\it orders of magnitude} more efficient than
existing methods for large scale 3D simulations.


title:
A Hamiltonian Lattice Theory for Homogeneous Curved Spacetimes in 2+1
  Dimensions

abstract:
  We propose an exact Hamiltonian lattice theory for (2+1)-dimensional
spacetimes with homogeneous curvature. By gauging away the lattice we find a
generalization of the ``polygon representation'' of (2+1)-dimensional gravity.
We compute the holonomies of the Lorentz connection ${\bf A}_i = \omega_i^a
{\bf L}_a + e_i^a {\bf K}_a$ and find that the cycle conditions are satisfied
only in the limit $\Lambda \to 0$. This implies that, unlike in
(2+1)-dimensional Einstein gravity, the connection ${\bf A}$ is not flat. If
one modifies the theory by taking the cycle conditions as constraints, then one
finds that the constraints algebra is first-class only if the Poisson bracket
structure is deformed. This suggests that a finite theory of quantum gravity
would require either a modified action including higher-order curvature terms,
or a deformation of the commutator structure of the metric observables.


title:
The Lanczos potential for the Weyl curvature tensor: existence, wave
  equation and algorithms

abstract:
  In the last few years renewed interest in the 3-tensor potential $L_{abc} $
proposed by Lanczos for the Weyl curvature tensor has not only clarified and
corrected Lanczos's original work, but generalised the concept in a number of
ways. In this paper we carefully summarise and extend some aspects of these
results, and clarify some misunderstandings in the literature. We also clarify
some comments in a recent paper by Dolan and Kim; in addition, we correct some
internal inconsistencies in their paper and extend their results.
  The following new results are also presented. The (computer checked)
complicated second order partial differential equation for the 3-potential, in
arbitrary gauge, for Weyl candidates satisfying Bianchi-type equations is given
-- in those $n $-dimensional spaces (with arbitrary signature) for which the
potential exists; this is easily specialised to Lanczos potentials for the Weyl
curvature tensor. It is found that it is {\it only} in 4-dimensional spaces
(with arbitrary signature and gauge), that the non-linear terms disappear and
that the awkward second order derivative terms cancel; for 4-dimensional
spacetimes (with Lorentz signature), this remarkably simple form was originally
found by Illge, using spinor methods. It is also shown that, for most
4-dimensional vacuum spacetimes, any 3-potential in the Lanczos gauges which
satisfies a simple homogeneous wave equation must be a Lanczos potential for
the Weyl curvature tensor of the background vacuum spacetime. This result is
used to prove that the form of a {\it possible} Lanczos potential proposed by
Dolan and Kim for a class of vacuum spacetimes is in fact a genuine Lanczos
potential for these spacetimes.


title: Mixed Elliptic and Hyperbolic Systems for the Einstein Equations

abstract:
  We analyse the mathematical underpinnings of a mixed hyperbolic-elliptic form
of the Einstein equations of motion in which the lapse function is determined
by specified mean curvature and the shift is arbitrary. We also examine a new
recently-published first order symmetric hyperbolic form of the equations of
motion. This paper is dedicated to Andre Lichnerowicz on the occasion of his
80th birthday and will appear in a volume edited by G. Ferrarese.


title: 3+1 General Relativity in Hyperbolic Form

abstract:
  This paper focuses on the imposition of boundary conditions for numerical
relativity simulations of black holes. This issue is used to motivate the
discussion of a new hyperbolic formulation of 3+1 general relativity. The paper
will appear in the Proceedings of the Les Houches School on Astrophysical
Sources of Gravitational Radiation, 1995, edited by J.-A. Marck and J.-P.
Lasota to be published by Springer-Verlag.


title: Problems in Black Hole Entropy interpretation

abstract:
  In this work some proposals for black hole entropy interpretation are exposed
and investigated. In particular I will firstly consider the so called
``entanglement entropy" interpretation, in the framework of the brick wall
model, and the divergence problem arising in the one loop calculations of
various thermodynamical quantities, like entropy, internal energy and heat
capacity. It is shown that the assumption of equality of entanglement entropy
and Bekenstein-Hawking one appears to give inconsistent results. These will be
a starting point for a different interpretation of black hole entropy based on
peculiar topological structures of manifolds with ``intrinsic" thermodynamical
features. It is possible to show an exact relation between black hole
gravitational entropy (tree level contribution in path integral approach) and
topology of these Euclidean space-times. The expression for the Euler
characteristic, through the Gauss-Bonnet integral, and the one for entropy for
gravitational instantons are proposed in a form which makes the relation
between these self evident. Using this relations I shall propose a
generalization of Bekenstein-Hawking entropy in which the former and Euler
characteristic are related in the equation: $S=\chi A/8$. The results, quoted
above, are more largely exposed in previous works. Finally I'll try to expose
some conclusions and hypotheses about possible further development of this
research.


title: Relaxation dominated cosmological expansion

abstract:
  The behavior near the singularity of an isotropic, homogeneous cosmological
model with a viscous fluid source is investigated. This turns out to be a
relaxation dominated regime. Full extended irreversible thermodynamics is used,
and comparison with results of the truncated theory is made. New singular
behaviors are found and it is shown that a relaxation dominated inflationary
epoch may exist for fluids with small heat capacity.


title: The Rotating Quantum Vacuum

abstract:
  We derive conditions for rotating particle detectors to respond in a variety
of bounded spacetimes and compare the results with the folklore that particle
detectors do not respond in the vacuum state appropriate to their motion.
Applications involving possible violations of the second law of thermodynamics
are briefly addressed.


title: Validity of the Semiclassical Approximation and Back=reaction

abstract:
  Studying two-dimensional evaporating dilatonic black holes, we show that the
semiclassical approximation, based on the background field approach, is valid
everywhere in regions of weak curvature (including the horizon), as long as one
takes into account the effects of back-reaction of the Hawking radiation on the
background geometry.


title:
Algorithms for computer algebra calculations in spacetime I. The
  calculation of curvature

abstract:
  We examine the relative performance of algorithms for the calculation of
curvature in spacetime. The classical coordinate component method is compared
to two distinct versions of the Newman-Penrose tetrad approach for a variety of
spacetimes, and distinct coordinates and tetrads for a given spacetime. Within
the system GRTensorII, we find that there is no single preferred approach on
the basis of speed. Rather, we find that the fastest algorithm is the one that
minimizes the amount of time spent on simplification. This means that arguments
concerning the theoretical superiority of an algorithm need not translate into
superior performance when applied to a specific spacetime calculation. In all
cases it is the global simplification strategy which is of paramount
importance. An appropriate simplification strategy can change an untractable
problem into one which can be solved essentially instantaneously.


title: Fundamental thermodynamical equation of a self-gravitating system

abstract:
  The features of the fundamental thermodynamical relation (expressing entropy
as function of state variables) that arise from the self-gravitating character
of a system are analyzed. The models studied include not only a spherically
symmetric hot matter shell with constant particle number but also a black hole
characterized by a general thermal equation of state. These examples illustrate
the formal structure of thermodynamics developed by Callen as applied to a
gravitational configuration as well as the phenomenological manner in which
Einstein equations largely determine the thermodynamical equations of state. We
consider in detail the thermodynamics and quasi-static collapse of a
self-gravitating shell. This includes a discussion of intrinsic stability for a
one-parameter family of thermal equations of state and the interpretation of
the Bekenstein bound. The entropy growth associated with a collapsing sequence
of equilibrium states of a shell is computed under different boundary
conditions in the quasi-static approximation and compared with black hole
entropy. Although explicit expressions involve empirical coefficients, these
are constrained by physical conditions of thermodynamical origin. The absence
of a Gibbs-Duhem relation and the associated scaling laws for self-gravitating
matter systems are presented.


title: Gravitational Constraint Combinations Generate a Lie Algebra

abstract:
  We find a first--order partial differential equation whose solutions are all
ultralocal scalar combinations of gravitational constraints with Abelian
Poisson brackets between themselves. This is a generalisation of the Kucha\v{r}
idea of finding alternative constraints for canonical gravity. The new scalars
may be used in place of the hamiltonian constraint of general relativity and,
together with the usual momentum constraints, replace the Dirac algebra for
pure gravity with a true Lie algebra: the semidirect product of the Abelian
algebra of the new constraint combinations with the algebra of spatial
diffeomorphisms.


title:
Studies in Structure Formation in theories with a repulsive long range
  gravitational force

abstract:
  This article reports on emergence of structures in a class of alternative
theories of gravity. These theories do not have any horizon, flatness, initial
cosmological singularity and (possibly) quantization problems. The model is
characterised by a dynamically induced gravitational constant with a ``wrong''
sign corresponding to repulsive gravitation on the large scale. A non - minimal
coupling of a scalar field in the model can give rise to non - topological
solitons in the theory. This results in domains (gravity - balls) inside which
an effective, canonical, attractive gravitational constant is induced. We
consider simulations of the formation and evolution of such solutions. Starting
with a single gravity - ball, we consider its fragmentation into smaller (lower
mass) balls - evolving by mutual repulsion. After several runs, we have been
able to identify two parameters: the strength of the long range gravitational
constant and the size of the gravity balls, which can be used to generate
appropriate two point correlations of the distribution of these balls.


title: Reply Comment: Comparison of Approaches to Classical Signature Change

abstract:
  We contrast the two approaches to ``classical" signature change used by
Hayward with the one used by us (Hellaby and Dray). There is (as yet) no
rigorous derivation of appropriate distributional field equations. Hayward's
distributional approach is based on a postulated modified form of the field
equations. We make an alternative postulate. We point out an important
difference between two possible philosophies of signature change --- ours is
strictly classical, while Hayward's Lagrangian approach adopts what amounts to
an imaginary proper ``time" on one side of the signature change, as is
explicitly done in quantum cosmology. We also explain why we chose to use the
Darmois-Israel type junction conditions, rather than the Lichnerowicz type
junction conditions favoured by Hayward. We show that the difference in results
is entirely explained by the difference in philosophy (imaginary versus real
Euclidean ``time"), and not by the difference in approach to junction
conditions (Lichnerowicz with specific coordinates versus Darmois with general
coordinates).


title: Planary Symmetric Static Worlds with Massless Scalar Sources

abstract:
  Motivated by the recent wave of investigations on plane domain wall
spacetimes with nontrivial topologies, the present paper deals with (probably)
the most simple source field configuration which can generate a spatially
planary symmetric static spacetime, namely a minimally coupled massless scalar
field that depends only upon a spacelike coordinate, $z$. It is shown that the
corresponding exact solutions $({\cal M}, {\bf{\rm g}}_{\pm})$ are
algebraically special, type $D - [S - 3T]_{(11)}$, and represent globally
pathologic spacetimes with a $G_{4}$ - group of motion acting on ${\bf{\rm
R}}^{2} \times {\bf{\rm R}}$ orbits. In spite of the model simplicity, these
$\phi$ - generated worlds possess naked timelike singularities (reached within
a finite universal time by normal non-spacelike geodesics), are completely free
of Cauchy surfaces and contain into the $t$ - leveled sections points which can
not be jointed by ${\rm C}^{1}$ - trajectories images of oblique non-spacelike
geodesics. Finally, we comment on the possibility of deriving from $({\cal M},
{\bf{\rm g}}_{\pm})$ two other physically interesting ^^ ^^ $\phi$ -
generated'' spacetimes, by appropiate jonction conditions in the $(z = 0)$ -
plane.


title: Dirac versus reduced quantization and operator ordering

abstract:
  We show an equivalence between Dirac quantization and the reduced phase space
quantization. The equivalence of the both quantization methods determines the
operator ordering of the Hamiltonian. Some examples of the operator ordering
are shown in simple models.


title:
Action functionals of single scalar fields and arbitrary--weight
  gravitational constraints that generate a genuine Lie algebra

abstract:
  We discuss the issue initiated by Kucha\v{r} {\it et al}, of replacing the
usual Hamiltonian constraint by alternative combinations of the gravitational
constraints (scalar densities of arbitrary weight), whose Poisson brackets
strongly vanish and cast the standard constraint-system for vacuum gravity into
a form that generates a true Lie algebra. It is shown that any such
combination---that satisfies certain reality conditions---may be derived from
an action principle involving a single scalar field and a single Lagrange
multiplier with a non--derivative coupling to gravity.


title:
Energy of General Spherically Symmetric Solution in Tetrad Theory of
  Gravitation

abstract:
  We find the most general, spherically symmetric solution in a special class
of tetrad theory of gravitation. The tetrad gives the Schwarzschild metric. The
energy is calculated by the superpotential method and by the Euclidean
continuation method. We find that unless the time-space components of the
tetrad go to zero faster than ${1/\sqrt{r}}$ at infinity, the two methods give
results different from each other, and that these results differ from the
gravitational mass of the central gravitating body. This fact implies that the
time-space components of the tetrad describing an isolated spherical body must
vanish faster than ${1/\sqrt{r}}$ at infinity.


title: Black Hole in Thermal Equilibrium with a Spin-2 Quantum Field

abstract:
  An approximate form for the vacuum averaged stress-energy tensor of a
conformal spin-2 quantum field on a black hole background is employed as a
source term in the semiclassical Einstein equations. Analytic corrections to
the Schwarzschild metric are obtained to first order in $\epsilon =
{\hbar}/M^2$, where $M$ denotes the mass of the black hole. The approximate
tensor possesses the exact trace anomaly and the proper asymptotic behavior at
spatial infinity, is conserved with respect to the background metric and is
uniquely defined up to a free parameter $\hat c_2$, which relates to the
average quantum fluctuation of the field at the horizon. We are able to
determine and calculate an explicit upper bound on $\hat c_2$ by requiring that
the entropy due to the back-reaction be a positive increasing function in $r$.
A lower bound for $\hat c_2$ can be established by requiring that the metric
perturbations be uniformly small throughout the region $2M \leq r < r_o$, where
$r_o$ is the radius of perturbative validity of the modified metric. Additional
insight into the nature of the perturbed spacetime outside the black hole is
provided by studying the effective potential for test particles in the vicinity
of the horizon.


title: Scientific Knowledge from the Perspective of Quantum Cosmology

abstract:
  Existing physical theories do not predict every feature of our experience but
only certain regularities of that experience. That difference between what
could be observed and what can be predicted is one kind of limit on scientific
knowledge. Such limits are inevitable if the world is complex and the laws
governing the regularities of that world are simple. Another kind of limit on
scientific knowledge arises because even simple theories may require
intractable or impossible computations to yield specific predictions. A third
kind of limit concerns our ability to know theories through the process of
induction and test. Quantum cosmology -- that part of science concerned with
the quantum origin of the universe and its subsequent evolution -- displays all
three kinds of limits. This paper briefly describes quantum cosmology and
discusses these limits. The place of the other sciences in this most
comprehensive of physical frameworks is described.


title: Gravitational Helioseismology?

abstract:
  The magnitudes of the external gravitational perturbations associated with
the normal modes of the Sun are evaluated to determine whether these solar
oscillations could be observed with the proposed Laser Interferometer Space
Antenna (LISA), a network of satellites designed to detect gravitational
radiation. The modes of relevance to LISA---the $l=2$, low-order $p$, $f$ and
$g$-modes---have not been conclusively observed to date. We find that the
energy in these modes must be greater than about $10^{30} \rm{ergs}$ in order
to be observable above the LISA detector noise. These mode energies are larger
than generally expected, but are much smaller than the current observational
upper limits. LISA may be confusion-limited at the relevant frequencies due to
the galactic background from short-period white dwarf binaries. Present
estimates of the number of these binaries would require the solar modes to have
energies above about $10^{33} \rm{ergs}$ to be observable by LISA.


title: Binary inspiral, gravitational radiation, and cosmology

abstract:
  Observations of binary inspiral in a single interferometric gravitational
wave detector can be cataloged according to signal-to-noise ratio $\rho$ and
chirp mass $\cal M$. The distribution of events in a catalog composed of
observations with $\rho$ greater than a threshold $\rho_0$ depends on the
Hubble expansion, deceleration parameter, and cosmological constant, as well as
the distribution of component masses in binary systems and evolutionary
effects. In this paper I find general expressions, valid in any homogeneous and
isotropic cosmological model, for the distribution with $\rho$ and $\cal M$ of
cataloged events; I also evaluate these distributions explicitly for relevant
matter-dominated Friedmann-Robertson-Walker models and simple models of the
neutron star mass distribution. In matter dominated Friedmann-Robertson-Walker
cosmological models advanced LIGO detectors will observe binary neutron star
inspiral events with $\rho>8$ from distances not exceeding approximately
$2\,\text{Gpc}$, corresponding to redshifts of $0.48$ (0.26) for $h=0.8$
($0.5$), at an estimated rate of 1 per week. As the binary system mass
increases so does the distance it can be seen, up to a limit: in a matter
dominated Einstein-deSitter cosmological model with $h=0.8$ ($0.5$) that limit
is approximately $z=2.7$ (1.7) for binaries consisting of two
$10\,\text{M}_\odot$ black holes. Cosmological tests based on catalogs of the
kind discussed here depend on the distribution of cataloged events with $\rho$
and $\cal M$. The distributions found here will play a pivotal role in testing
cosmological models against our own universe and in constructing templates for
the detection of cosmological inspiraling binary neutron stars and black holes.


title: Classical Spacetime from Quantum Gravity

abstract:
  We show how classical spacetime emerges from quantum gravity through the
study of a quantum FRW cosmological model coupled to a free massive scalar
field using a new asymptotic expansion method of the Wheeler-DeWitt equation.
It is shown that the coherent states of the nonadiabatic basis of a particular
generalized invariant give rise to the quantum back reaction of matter field
proportional to classical energy and the Einstein-Hamilton-Jacobi with matter
becomes equivalent to the classical Einstein equation.


title: Nonperturbative solutions for canonical quantum gravity: an overview

abstract:
  In this paper we will make a survey of solutions to the Wheeler-Dewitt
equation which have been found up to now in Ashtekar's formulation for
canonical quantum gravity. Roughly speaking they are classified into two
categories, namely, Wilson-loop solutions and topological solutions. While the
program of finding solutions which are composed of Wilson loops is still in its
infancy, it is expected to be developed in the near future. Topological
solutions are the only solutions at present which we can give their
interpretation in terms of spacetime geometry. While the analysis made here is
formal in the sense that we do not deal with rigorously regularized constraint
equations, these topological solutions are expected to exist even in the fully
regularized theory and they are considered to yield vacuum states of quantum
gravity. We also make an attempt to review the spin network states as
intuitively as possible. In particular, the explicit formulae for two kinds of
measures on the space of spin network states are given.


title: Propagation-Based General Relativity

abstract:
  It is assumed that the radial propagation of light with respect to the naive
coordinate system of the observer is uniform and isotropic and that the
physical rate of propagation of light is the same for all observers. In
accelerated frames of reference, these assumptions lead to the findings that
the measured value of $c$ is a function of the gravitational energy per unit
mass (GEPUM) of the observer, and that this is due to the physical
characteristics of the standard measuring-devices being a function of their
GEPUM. The consequences of these findings include observers who at rest with
respect to each other assigning different values to the same physical
separation, the mixed metric tensor ${g^\mu}_\nu$ describing how gravitation
affects measuring-devices, and the De-Broglie wavelength being a function of an
object's GEPUM. How the measured values of various types of physical quantities
are affected is described. The Schwarzschild solution is re-examined: The
physical size of radial coordinate $2m$ is 0, a traveler must perceive himself
to go an infinite distance to reach the radial coordinate of $2m$, and
gravitational self-potential energy reaches a minimal value at the radial
coordinate $3m$. Therefore, black holes do not exist in this theory.


title: Matters of Gravity, Newsletter of the APS TGG on gravitation, number 7

abstract:
  Contents:
  Editorial, J. Pullin
  Report from the APS TGG, Beverly Berger
  We hear that..., J. Pullin
  LIGO project status, S. Whitcomb
  General relativity survives another test, C. Will
  Macroscopic deviations from Hawking radiation? L. Smolin
  Event horizons and topological censorship, E. Seidel
  Critical behavior in black hole collapse, J. Horne
  Third Texas Workshop on 3D Numerical Relativity, P. Laguna
  ICGC-95, M.A.H. MacCallum
  The Josh Goldberg Symposium, P. Saulson
  Summer school in Bad Honnef, H.-P. Nollert
  Fifth Annual Midwest Relativity Conference, J. Romano
  Volga-7 '95, A. Aminova, D. Brill.


title:
Defining a Research Environment: LIGO and the Gravitational Physics
  Research Community

abstract:
  The LIGO Research Community (LRC) is an independent organization of
researchers interested in the scientific opportunities created by the
construction and operation of the Laser Interferometer Gravitational-wave
Observatory (LIGO). Membership is open to all interested individuals,
irrespective of any other affiliations (including affiliation with the LIGO
project, VIRGO or other gravitational-wave detector projects). The LRC has
begun a study project designed to {\em identify} the ways that an operating
LIGO will affect the research environment in gravitational physics, {\em
decide} what we want that environment to look like, and recommend (to LIGO and
the NSF) the steps to be taken now to develop that environment in the future.
Contributions from LRC members and from the broader gravitational physics
research community are actively solicited.


title:
Hamiltonian thermodynamics of the Reissner-Nordstr\"om-anti-de Sitter
  black hole

abstract:
  We consider the Hamiltonian dynamics and thermodynamics of spherically
symmetric Einstein-Maxwell spacetimes with a negative cosmological constant. We
impose boundary conditions that enforce every classical solution to be an
exterior region of a Reissner-Nordstr\"om-anti-de Sitter black hole with a
nondegenerate Killing horizon, with the spacelike hypersurfaces extending from
the horizon bifurcation two-sphere to the asymptotically anti-de Sitter
infinity. The constraints are simplified by a canonical transformation, which
generalizes that given by Kucha\v{r} in the spherically symmetric vacuum
Einstein theory, and the theory is reduced to its true dynamical degrees of
freedom. After quantization, the grand partition function of a thermodynamical
grand canonical ensemble is obtained by analytically continuing the Lorentzian
time evolution operator to imaginary time and taking the trace. A~similar
analysis under slightly modified boundary conditions leads to the partition
function of a thermodynamical canonical ensemble. The thermodynamics in each
ensemble is analyzed, and the conditions that the (grand) partition function be
dominated by a classical Euclidean black hole solution are found. When these
conditions are satisfied, we recover in particular the Bekenstein-Hawking
entropy. The limit of a vanishing cosmological constant is briefly discussed.
  (This paper is dedicated to Karel Kucha\v{r} on the occasion of his sixtieth
birthday.)


title:
Gravitational Interaction of Spinning Bodies, Center-of-Mass Coordinate
  and Radiation of Compact Binary Systems

abstract:
  Spin-orbit and spin-spin effects in the gravitational interaction are treated
in a close analogy with the fine and hyperfine interactions in atoms. The
proper definition of the cener-of-mass coordinate is discussed. The technique
developed is applied then to the gravitational radiation of compact binary
stars. Our result for the spin-orbit correction differs from that obtained by
other authors. New effects possible for the motion of a spinning particle in a
gravitational field are pointed out. The corresponding corrections, nonlinear
in spin, are in principle of the same order of magnitude as the ordinary
spin-spin interaction.


title: Energy of a spherically symmetric charged dilaton black hole

abstract:
  The energy associated with a static and spherically symmetric charged dilaton
black hole is obtained for arbitrary value of the coupling parameter (which
regulates the strength of the coupling of the dilaton to the Maxwell field)
$\beta$. The energy distribution depends on $\beta$, whereas the total energy
is independent of this and is given by the mass parameter of the black hole.


title:
Exact solutions of Reissner-Nordstr\"om type in Einstein-Yang-Mills
  --systems with arbitrary gauge groups and space-time dimensions

abstract:
  We present a class of solutions in Einstein-Yang-Mills-systems with arbitrary
gauge groups and space-time dimensions, which are symmetric under the action of
the group of spatial rotations. Our approach is based on the dimensional
reduction method for gauge and gravitational fields and relates symmetric
EYM-solutions to certain solutions of two-dimensional
Einstein-Yang-Mills-Higgs-dilaton theory. Application of this method to
four-dimensional spherically symmetric (pseudo)riemannian space-time yields, in
particular, new solutions describing both a magnetic and an electric charge in
the center of a black hole. Moreover, we give an example of a solution with
nonabelian gauge group in six-dimensional space-time. We also comment on the
stability of the obtained solutions.


title: The String Model of Gravity

abstract:
  The string model of gravitational force is proposed where the string forms
the mediation of the gravitational interaction between two gravitating bodies.
It reproduces the Newtonian results in the first-order approximation and it
predicts in the higher-oder approximations the existence of oscillations of the
gravitational field between two massive bodies. It can be easily generalized to
the two-body interaction in particle physics.


title: Schroedinger Equation of the Schwarzschild Black Hole

abstract:
  We describe the gravitational degrees of freedom of the Schwarzschild black
hole by one free variable. We introduce an equation which we suggest to be the
Schroedinger equation of the Schwarzschild black hole corresponding to this
model. We solve the Schroedinger equation explicitly and obtain the mass
spectrum of the black hole as such as it can be observed by an observer very
far away and at rest relative to the black hole. Our equation implies that
there is no singularity inside the Schwarzschild black hole, and that the black
hole has a certain ground state in which its mass is non-zero.


title: On the Stability of Spherical Membranes in Curved Spacetimes

abstract:
  We study the existence and stability of spherical membranes in curved
spacetimes. For Dirac membranes in the Schwarzschild--de Sitter background we
find that there exists an equilibrium solution. By fine--tuning the
dimensionless parameter $\Lambda M^2,$ the static membrane can be at any
position outside the black hole event horizon, even at the stretched horizon,
but the solution is unstable. We show that modes having $l=0$ (and for $\Lambda
M^2<16/243$ also $l=1$) are responsible for the instability. We also find that
spherical higher order membranes (membranes with extrinsic curvature
corrections), contrary to what happens in flat Minkowski space, {\it do} have
equilibrium solutions in a general curved background and, in particular, also
in the ``plain'' Schwarzschild geometry (while Dirac membranes do not have
equilibrium solutions there). These solutions, however, are also unstable. We
shall discuss a way of by--passing these instability problems, and we also
relate our results to the recent ideas of representing the black hole event
horizon as a relativistic bosonic membrane.


title: Twistors and Nearly Autoparallel Maps

abstract:
  In this work a proposal for definition of twistors on generic curved spaces
is exposed and investigated. We consider superpositions of nearly autoparallel
and nearly geodesic maps (nearly conformal maps, nc-maps) of
(pseudo-)Riemannian spaces as generalizations of conformal transforms. We
introduce the nearly autoparallel twistor equations being compatible on nc-flat
spaces and study nearly autoparallel twistor structures generating curved
spaces and vacuum Einstein equations.


title: Quantum Decoherence in a Four-Dimensional Black Hole Background

abstract:
  We display a logarithmic divergence in the density matrix of a scalar field
in the presence of an Einstein-Yang-Mills black hole in four dimensions. This
divergence is related to a previously-found logarithmic divergence in the
entropy of the scalar field, which cannot be absorbed into a renormalization of
the Hawking-Bekenstein entropy of the black hole. As the latter decays, the
logarithmic divergence induces a non-commutator term $\nd{\delta H}\rho$ in the
quantum Liouville equation for the density matrix $\rho$ of the scalar field,
leading to quantum decoherence. The order of magnitude of $\nd{\delta H}$ is
$\mu^2/M_P$, where $\mu$ is the mass of the scalar particle.


title: A New Class of Inhomogeneous Cosmological Solutions

abstract:
  Beginning with a special form of the Einstein-Rosen metric, we find new
cosmological solutions of the Einstein equations, having two
hypersurface-orthogonal Killing vectors , with ideal fluid. The equation of
state is in the most cases of the form $p = \gamma \rho$.


title: On the Gauge Aspects of Gravity

abstract:
  We give a short outline, in Sec.\ 2, of the historical development of the
gauge idea as applied to internal ($U(1),\, SU(2),\dots$) and external
($R^4,\,SO(1,3),\dots$) symmetries and stress the fundamental importance of the
corresponding conserved currents. In Sec.\ 3, experimental results with neutron
interferometers in the gravitational field of the earth, as inter- preted by
means of the equivalence principle, can be predicted by means of the Dirac
equation in an accelerated and rotating reference frame. Using the Dirac
equation in such a non-inertial frame, we describe how in a gauge- theoretical
approach (see Table 1) the Einstein-Cartan theory, residing in a Riemann-Cartan
spacetime encompassing torsion and curvature, arises as the simplest
gravitational theory. This is set in contrast to the Einsteinian approach
yielding general relativity in a Riemannian spacetime. In Secs.\ 4 and 5 we
consider the conserved energy-momentum current of matter and gauge the
associated translation subgroup. The Einsteinian teleparallelism theory which
emerges is shown to be equivalent, for spinless matter and for
electromagnetism, to general relativity. Having successfully gauged the
translations, it is straightforward to gauge the four-dimensional affine group
$R^4 \semidirect GL(4,R)$ or its Poincar\'e subgroup $R^4\semidirect SO(1,3)$.
We briefly report on these results in Sec.\ 6 (metric-affine geometry) and in
Sec.\ 7 (metric-affine field equations (\ref{zeroth}, \ref{first},
\ref{second})). Finally, in Sec.\ 8, we collect some models, currently under
discussion, which bring life into the metric-affine gauge framework developed.


title:
On the Relation Between Quadratic and Linear Curvature Lagrangians in
  Poincar\'e Gauge Gravity

abstract:
  We discuss the choice of the Lagrangian in the Poincar\'e gauge theory of
gravity. Drawing analogies to earlier de Sitter gauge models, we point out the
possibility of deriving the Einstein-Cartan Lagrangian {\it without}
cosmological term from a {\it modified} quadratic curvature invariant of {\it
topological} type.


title: Ricci Tensor of Diagonal Metric

abstract:
  Efficient formulae of Ricci tensor for an arbitrary diagonal metric are
presented.


title: Modified Relativity from the kappa-deformed Poincare Algebra

abstract:
  The theory of the $\kappa$-deformed Poincare algebra is applied to the
analysis of various phenomena in special relativity, quantum mechanics and
field theory. The method relies on the development of series expansions in
$\kappa^{-1}$ of the generalised Lorentz transformations, about the
special-relativistic limit. Emphasis is placed on the underlying assumptions
needed in each part of the discussion, and on in principle limits for the
deformation parameter, rather than on rigorous numerical bounds. In the case of
the relativistic Doppler effect, and the Michelson-Morley experiment,
comparisons with recent experiemntal tests yield the relatively weak lower
bounds on $\kappa c$ of 90eV and 250 keV, respectively. Corrections to the
Casimir effect and the Thomas precession are also discussed.


title: Anisotropic universes with conformal motion

abstract:
  By imposing natural geometrical and kinematical conditions on a conformal
Killing vector in Bianchi I spacetime, we show that a class of axisymmetric
metrics admits a conformal motion. This class contains new exact solutions of
Einstein's equations, including anisotropic radiation universes that isotropise
at late times.


title:
Detectability of gravitational wave events by spherical resonant-mass
  antennas

abstract:
  We have calculated signal-to-noise ratios for eight spherical resonant-mass
antennas interacting with gravitational radiation from inspiralling and
coalescing binary neutron stars and from the dynamical and secular bar-mode
instability of a rapidly rotating star. We find that by using technology that
could be available in the next several years, spherical antennas can detect
neutron star inspiral and coalescence at a distance of 15 Mpc and the dynamical
bar-mode instability at a distance of 2 Mpc.


title: Path Integrals and Instantons in Quantum Gravity

abstract:
  While there does not at this time exist a complete canonical theory of full
3+1 quantum gravity, there does appear to be a satisfactory canonical
quantization of minisuperspace models. The method requires no `choice of time
variable' and preserves the systems' explicit reparametrization invariance. In
the following study, this canonical formalism is used to derive a path integral
for quantum minisuperspace models. As it comes from a well-defined canonical
starting point, the measure and contours of integration are specified by this
construction. The properties of the resulting path integral are analyzed, both
exactly and in the semiclassical limit. Particular attention is paid to the
role of the (unbounded) Euclidean action and Euclidean instantons are argued to
contribute as $e^{-|S_E|/\hbar}$.


title: Quantum Black Hole Model and Hawking's Radiation

abstract:
  The black hole model with a self-gravitating charged spherical symmetric dust
thin shell as a source is considered. The Schroedinger-type equation for such a
model is derived. This equation appeared to be a finite differences equation. A
theory of such an equation is developed and general solution is found and
investigated in details. The discrete spectrum of the bound state energy levels
is obtained. All the eigenvalues appeared to be infinitely degenerate. The
ground state wave functions are evaluated explicitly. The quantum black hole
states are selected and investigated. It is shown that the obtained black hole
mass spectrum is compatible with the existence of Hawking's radiation in the
limit of low temperatures both for large and nearly extreme Reissner-Nordstrom
black holes. The above mentioned infinite degeneracy of the mass (energy)
eigenvalues may appeared helpful in resolving the well known information
paradox in the black hole physics.


title: Some remarks on finite-gap solutions of the Ernst equation

abstract:
  It is shown that the class of algebro-geometrical (finite-gap) solutions of
the Ernst equation constructed several years ago in [D.Korotkin,
Theor.Math.Phys., 77 (1989), p. 1018] contains the solutions recently
constructed by R.Meinel and G.Neugebauer as a subset.


title: Consistency of matter field equations in Ashtekar formulation

abstract:
  The chiral Lagrangian including more than two spin-3/2 fields becomes complex
in general when the self-dual connection satisfies its equation of motion, and
the imaginary part of the chiral Lagrangian gives the additional equation for
spin-3/2 fields which gives rise to the inconsistency. This inconsistency can
be removed by taking the tetrad to be complex and defining the total Lagrangian
which is the sum of the chiral Lagrangian and its complex conjugate. It is
possible to establish the right (left)-handed supersymmetry in its total
Lagrangian as in the case of the chiral Lagrangian. We also comment on the
canonical formulation of the total Lagrangian.


title:
Geometry Eigenvalues and Scalar Product from Recoupling Theory in Loop
  Quantum Gravity

abstract:
  We summarize the basics of the loop representation of quantum gravity and
describe the main aspects of the formalism, including its latest developments,
in a reorganized and consistent form. Recoupling theory, in its graphical
Temperley-Lieb-Kauffman formulation, provides a powerful calculation tool in
this context. We describe its application to the loop representation in detail.
Using recoupling theory, we derive general expressions for the spectrum of the
quantum area and the quantum volume operators. We compute several volume
eigenvalues explicitly. We introduce a scalar product with respect to which
area and volume are symmetric operators, and (the trivalent expansions of) the
spin network states are orthogonal.


title:
Gravitational waveforms from inspiralling compact binaries to
  second-post-Newtonian order

abstract:
  The two independent ``plus" and ``cross" polarization waveforms associated
with the gravitational waves emitted by inspiralling, non-spinning, compact
binaries are presented, ready for use in the data analysis of signals received
by future laser interferometer gravitational-wave detectors such as LIGO and
VIRGO. The computation is based on a recently derived expression of the
gravitational field at the second-post-Newtonian approximation of general
relativity beyond the dominant (Newtonian) quadrupolar field. The use of these
theoretical waveforms to make measurements of astrophysical parameters and to
test the nature of relativistic gravity is discussed.


title: Bubble fluctuations in $\Omega<1$ inflation

abstract:
  In the context of the open inflationary universe, we calculate the amplitude
of quantum fluctuations which deform the bubble shape. These give rise to
scalar field fluctuations in the open Friedman-Robertson-Walker universe which
is contained inside the bubble. One can transform to a new gauge in which
matter looks perfectly smooth, and then the perturbations behave as tensor
modes (gravitational waves of very long wavelength). For $(1-\Omega)<<1$, where
$\Omega$ is the density parameter, the microwave temperature anisotropies
produced by these modes are of order $\delta T/T\sim H(R_0\mu l)^{-1/2}
(1-\Omega)^{l/2}$. Here, $H$ is the expansion rate during inflation, $R_0$ is
the intrinsic radius of the bubble at the time of nucleation, $\mu$ is the
bubble wall tension and $l$ labels the different multipoles ($l>1$). The
gravitational backreaction of the bubble has been ignored. In this
approximation, $G\mu R_0<<1$, and the new effect can be much larger than the
one due to ordinary gravitational waves generated during inflation (unless, of
course, $\Omega$ gets too close to one, in which case the new effect
disappears).


title:
Constraints and Reality Conditions in the Ashtekar Formulation of
  General Relativity

abstract:
  We show how to treat the constraints and reality conditions in the
$SO(3)$-ADM (Ashtekar) formulation of general relativity, for the case of a
vacuum spacetime with a cosmological constant. We clarify the difference
between the reality conditions on the metric and on the triad. Assuming the
triad reality condition, we find a new variable, allowing us to solve the gauge
constraint equations and the reality conditions simultaneously.


title: On $2D$ quantum gravity coupled to a $\s$-model

abstract:
  This contribution is a review of the method of isomonodromic quantization of
dimensionally reduced gravity. Our approach is based on the complete separation
of variables in the isomonodromic sector of the model and the related
``two-time" Hamiltonian structure. This allows an exact quantization in the
spirit of the scheme developed in the framework of integrable systems. Possible
ways to identify a quantum state corresponding to the Kerr black hole are
discussed. In addition, we briefly describe the relation of this model with
Chern Simons theory.


title: Kinetic theory for particle production

abstract:
  Recently, the phenomenological description of cosmological particle
production processes in terms of effective viscous pressures has attracted some
attention. Using a simple creation rate model we discuss the question to what
extent this approach is compatible with the kinetic theory of a relativistic
gas. We find the effective viscous pressure approach to be consistent with this
model for homogeneous spacetimes but not for inhomogeneous ones.


title: Reconstructing the inflaton potential for an almost flat COBE spectrum

abstract:
  Using the Hubble parameter as new `inverse time' coordinate ($H$-formalism),
a new method of reconstructing the inflaton potential is developed also using
older results which, in principle, is applicable to any order of the slow-roll
approximation. In first and second order, we need three observational data as
inputs: the scalar spectral index $n_s$ and the amplitudes of the scalar and
the tensor spectrum. We find constraints between the values of $n_s$ and the
corresponding values for the wavelength $\lambda $. By imposing a dependence
$\lambda (n_s)$, we were able to reconstruct and visualize inflationary
potentials which are compatible with recent COBE and other astrophysical
observations. >From the reconstructed potentials, it becomes clear that one
cannot find only one special value of the scalar spectral index $n_s$.


title: A Mechanism for a small but nonzero cosmological constant

abstract:
  Based on a thoeretical model in which scalar fields play crucial roles, we
propose a mechanism to better understand a cosmological constant expected to be
small (nearly comparable with the critical density) but nonzero as suggested
strongly by the recent observations. We emphasize that a step further is needed
beyond the simplest scenario of a decaying cosmological constant, according to
which the effective $\Lambda$ is not a true constant but decays like $t^{-2}$,
thus explaining why any effect of $\Lambda$ which is assumed to be of the
Planckian order of magnitude in the earliest Universe is at most 120 orders
smaller today ($t\sim 10^{60}$ in units of the Planck time), without any
extreme fine-tuning of the parameters. In addition to the overall smooth
fall-off $\sim t^{-2}$, the total energy density, the sum of the contributions
from the ordinary matter and the scalar fields, must show some leveling-off
behavior, hence mimicking a truly constant $\Lambda$ to fit the observations.
We find that the desired behavior can be obtained by introducing two scalar
fields interacting with each other in a specific manner. Many aspects of this
model are discussed in detail, including the real origin of the whole
mechanism, and how the parameters and the initial conditions of the theory can
be determined by the cosomological parameters at the present epoch as well as
the past history of the Universe.


title: Free Quantum Fields on the Poincare' Group

abstract:
  A class of free quantum fields defined on the Poincare' group, is described
by means of their two-point vacuum expectation values. They are not equivalent
to fields defined on the Minkowski spacetime and they are "elementary" in the
sense that they describe particles that transform according to irreducible
unitary representations of the symmetry group, given by the product of the
Poincare' group and of the group SL(2, C) considered as an internal symmetry
group. Some of these fields describe particles with positive mass and arbitrary
spin and particles with zero mass and arbitrary helicity or with an infinite
helicity spectrum. In each case the allowed SL(2, C) internal quantum numbers
are specified. The properties of local commutativity and the limit in which one
recovers the usual field theories in Minkowski spacetime are discussed. By
means of a superposition of elementary fields, one obtains an example of a
field that present a broken symmetry with respect to the group Sp(4, R), that
survives in the short-distance limit. Finally, the interaction with an
accelerated external source is studied and and it is shown that, in some
theories, the average number of particles emitted per unit of proper time
diverges when the acceleration exceeds a finite critical value.


title: About the Significance of Quasinormal Modes of Black Holes

abstract:
  Quasinormal modes have played a prominent role in the discussion of
perturbations of black holes, and the question arises whether they are as
significant as normal modes are for self adjoint systems, such as harmonic
oscillators. They can be significant in two ways: Individual modes may dominate
the time evolution of some perturbation, and a whole set of them could be used
to completely describe this time evolution. It is known that quasinormal modes
of black holes have the first property, but not the second. It has recently
been suggested that a discontinuity in the underlying system would make the
corresponding set of quasinormal modes complete. We therefore turn the
Regge-Wheeler potential, which describes perturbations of Schwarzschild black
holes, into a series of step potentials, hoping to obtain a set of quasinormal
modes which shows both of the above properties. This hope proves to be futile,
though: The resulting set of modes appears to be complete, but it does not
contain any individual mode any more which is directly obvious in the time
evolution of initial data. Even worse: The quasinormal frequencies obtained in
this way seem to be extremely sensitive to very small changes in the underlying
potential. The question arises whether - and how - it is possible to make any
definite statements about the significance of quasinormal modes of black holes
at all, and whether it could be possible to obtain a set of quasinormal modes
with the desired properties in another way.


title: Ehrenfest's Principle and the Problem of Time in Quantum Gravity

abstract:
  We elaborate on a proposal made by Greensite and others to solve the problem
of time in quantum gravity. The proposal states that a viable concept of time
and a sensible inner product can be found from the demand for the Ehrenfest
equations to hold in quantum gravity. We derive and discuss in detail exact
consistency conditions from both Ehrenfest equations as well as from the
semiclassical approximation. We also discuss consistency conditions arising
from the full field theory. We find that only a very restricted class of
solutions to the Wheeler-DeWitt equation fulfills all consistency conditions.
We conclude that therefore this proposal must either be abandoned as a means to
solve the problem of time or, alternatively, be used as an additional boundary
condition to select physical solutions from the Wheeler-DeWitt equation.


title: Topologically massive gravito-electrodynamics: exact solutions

abstract:
  We construct two classes of exact solutions to the field equations of
topologically massive electrodynamics coupled to topologically massive gravity
in 2 + 1 dimensions. The self-dual stationary solutions of the first class are
horizonless, asymptotic to the extreme BTZ black-hole metric, and regular for a
suitable parameter domain. The diagonal solutions of the second class, which
exist if the two Chern-Simons coupling constants exactly balance, include
anisotropic cosmologies and static solutions with a pointlike horizon.


title: Volume and Quantizations

abstract:
  The aim of this letter is to indicate the differences between the
Rovelli-Smolin quantum volume operator and other quantum volume operators
existing in the literature. The formulas for the operators are written in a
unifying notation of the graph projective framework. It is clarified whose
results apply to which operators and why.


title: Interpolating Between Topologies: Casimir Energies

abstract:
  A set of models is considered which, in a certain sense, interpolates between
1+1 free quantum field theories on topologically distinct backgrounds. The
intermediate models may be termed free quantum field theories, though they are
certainly not local. Their ground state energies are computed and shown to be
finite. The possible relevance to changing spacetime topologies is discussed.


title:
Asymptotic Behavior of the Einstein-Yang-Mills-Dilaton System for a
  Closed Friedmann-Lemaitre Universe

abstract:
  We study the coupled Einstein-Yang-Mills-Dilaton (EYMD) equations for a
Fried\-mann-Le\-mai\-tre universe with constant curvature $k=1$. Our detailed
analysis is restricted to the case where the dilaton potential and the
cosmological constant vanish. Also assuming a static gauge field, we present
analytical and numerical results on the behavior of solutions of the EYMD
equations. For different values of the dilaton coupling constant we analyze the
phase portrait for the time evolution of the dilaton field and give the
behavior of the scale factor. It turns out that there are no inflationary
stages in this model.


title:
Gravitational waves from a spinning particle in circular orbits around a
  rotating black hole

abstract:
  Using the Teukolsky and Sasaki-Nakamura formalisms for the perterbations
around a Kerr black hole, we calculate the energy flux of gravitational waves
induced by a {\it spinning} particle of mass $\mu$ and spin $S$ moving in
circular orbits near the equatorial plain of a rotating black hole of mass $M
(\gg \mu)$ and spin $Ma$. The calculations are performed by using the recently
developed post-Newtonian expansion technique of the Teukolsky equation. To
evaluate the source terms of perturbations caused by a {\it spinning} particle,
we used the equations of motion of a spinning particle derived by Papapetrou
and the energy momentum tensor of a spinning particle derived by Dixon. We
present the post-Newtonian formula of the gravitational wave luminosity up to
the order $(v/c)^5$ beyond the quadrupole formula including the linear order of
particle spin. The results obtained in this paper will be an important
guideline to the post-Newtonian calculation of the inspiral of two spinning
compact objects.


title:
Circles in the Sky: Finding Topology with the Microwave Background
  Radiation

abstract:
  If the universe is finite and smaller than the distance to the surface of
last scatter, then the signature of the topology of the universe is writ on the
microwave background sky. Previous efforts to search for this topology have
focused on one particular model: a toroidal flat universe. We show how both the
high degree of spatial symmetry of this topology and the integrability of its
geodesics make it unreliable as a paradigmatic example, and discuss why
topology on scales significantly smaller than the horizon are not ruled out by
previous analyses focussing on this special case. We show that in these small
universes the microwave background will be identified at the intersections of
the surface of last scattering as seen by different ``copies'' of the observer.
Since the surface of last scattering is a sphere, these intersections will be
circles, regardless of the background geometry or topology. We therefore
propose a statistic that is sensitive to all small finite homogeneous
topologies. Here, small means that the distance to the surface of last scatter
is smaller than the ``periodicity scale'' of the universe.


title: On the Completeness of the Black Hole Singularity in 2d Dilaton Theories

abstract:
  The black hole of the widely used ordinary 2d--dilaton model (DBH) deviates
from the Schwarzschild black hole (SBH) of General Relativity in one important
feature: Whereas non-null extremals or geodesics show the expected
incompleteness this turns out {\it not to be the case for the null extremals}.
After a simple analysis in Kruskal coordinates for singularities with power
behavior of this -- apparently till now overlooked -- property we discuss the
global structure of a large family of generalized dilaton theories which does
not only contain the DBH and SBH but also other proposed dilaton theories as
special cases. For large ranges of the parameters such theories are found to be
free from this defect and exhibit global SBH behavior.


title: A real alternative to quantum gravity in loop space

abstract:
  We show that the Hamiltonian of four-dimensional Lorentzian gravity, defined
on a space of real, SU(2)-valued connections, in spite of its non-polynomiality
possesses a natural quantum analogue in a lattice-discretized formulation of
the theory. This opens the way for a systematic investigation of its spectrum.
The unambiguous and well-defined scalar product is that of the SU(2)-gauge
theory. We also comment on various aspects of the continuum theory.


title: On Divergence of Decoherence Factor in Quantum Cosmology

abstract:
  To discuss the quantum to classical transition in quantum cosmology, we study
the decoherence factor and the peak of the Wigner function, which respectively
represent the degree of decoherence and the degree to which the classical
motion of the Universe is defined, in a Robertson-Walker universe model coupled
with a scalar field. It is known that the decoherence factor is divergent in
some cases. This implies that perfect decoherence occurs, and classical
correlation criterion fails. In this paper we discuss the divergence of the
decoherence factor in some detail and obtain the constraints for decoherence
factor to be convergent, making use of the arbitrariness defining the reduced
density matrix. The result is discussed in connection with the arbitrariness of
{\it system/environment} splitting.


title: Focusing and the Holographic Hypothesis

abstract:
  The ``screen mapping" introduced by Susskind to implement 't Hooft's
holographic hypothesis is studied. For a single screen time, there are an
infinite number of images of a black hole event horizon, almost all of which
have smaller area on the screen than the horizon area. This is consistent with
the focusing equation because of the existence of focal points. However, the
{\it boundary} of the past (or future) of the screen obeys the area theorem,
and so always gives an expanding map to the screen, as required by the
holographic hypothesis. These considerations are illustrated with several
axisymmetric static black hole spacetimes.


title: Qualitative Analysis of Causal Cosmological Models

abstract:
  The Einstein's field equations of Friedmann-Robertson-Walker universes filled
with a dissipative fluid described by both the {\em truncated} and {\em
non-truncated} causal transport equations are analyzed using techniques from
dynamical systems theory. The equations of state, as well as the phase space,
are different from those used in the recent literature. In the de Sitter
expansion both the hydrodynamic approximation and the non-thermalizing
condition can be fulfilled simultaneously. For $\Lambda=0$ these expansions
turn out to be stable provided a certain parameter of the fluid is lower than
1/2. The more general case $\Lambda>0$ is studied in detail as well.


title: Generating new perfect-fluid solutions from known ones

abstract:
  Stationary perfect-fluid configurations of Einstein's theory of gravity are
studied. It is assumed that the 4-velocity of the fluid is parallel to the
stationary Killing field, and also that the norm and the twist potential of the
stationary Killing field are functionally independent. It has been pointed out
earlier by one of us (I.R.) that for these perfect-fluid geometries some of the
basic field equations are invariant under an $SL(2,R)$ transformation. Here it
is shown that this transformation can be applied to generate possibly new
perfect-fluid solutions from existing known ones only for the case of
barotropic equation of state $\rho+3p=0$. In order to study the effect of this
transformation, its application to known perfect-fluid solutions is presented.
In this way, different previously known solutions could be written in a singe
compact form. A new derivation of all Petrov type D stationary axisymmetric
rigidly rotating perfect-fluid solutions with an equation of state
$\rho+3p=constant$ is given in an appendix.


title: Quantum Theory of Gravity I: Area Operators

abstract:
  A new functional calculus, developed recently for a fully non-perturbative
treatment of quantum gravity, is used to begin a systematic construction of a
quantum theory of geometry. Regulated operators corresponding to areas of
2-surfaces are introduced and shown to be self-adjoint on the underlying
(kinematical) Hilbert space of states. It is shown that their spectra are {\it
purely} discrete indicating that the underlying quantum geometry is far from
what the continuum picture might suggest. Indeed, the fundamental excitations
of quantum geometry are 1-dimensional, rather like polymers, and the
3-dimensional continuum geometry emerges only on coarse graining. The full
Hilbert space admits an orthonormal decomposition into finite dimensional
sub-spaces which can be interpreted as the spaces of states of spin systems.
Using this property, the complete spectrum of the area operators is evaluated.
The general framework constructed here will be used in a subsequent paper to
discuss 3-dimensional geometric operators, e.g., the ones corresponding to
volumes of regions.


title: Two-dimensional black holes in accelerated frames: Spacetime structure

abstract:
  Analytical extensions and resulting Penrose diagrams are given for the
solutions of a simple 2d dilaton gravity theory describing black holes which
are static as viewed by asymptotically accelerated observers.


title: Comment on Entropy in Two-dimensional Dilaton Gravity

abstract:
  The thermodynamic second law in the evaporating black hole space-time is
examined in the context of two-dimensional dilaton black hole. The dynamical
evolution of entropy is investigated by using the analytical perturbation
method and the numerical method. It is shown that the thermodynamic second law
holds in the vicinity of infalling shell %analytically and in the region far
from the infalling shell %numerically in the case of semi-classical CGHS model.
The analysis of the general models is also presented and its implication is
discussed.


title:
On the Exponentially Large Probability of Transition through the
  Lavrelashvili-Rubakov-Tinyakov Wormhole

abstract:
  The model consisting of gravitational, scalar and axionic fields is
considered. It is shown that the action of the Lavrelashvili-Rubakov-Tinyakov
wormhole can be made arbitrarily negative by varying the parameters of the
model. This means that semiclassically calculated probability of transition
through this wormhole is not exponentially small (as usual) but exponentially
large.