title:
Post-Newtonian Hydrodynamic Equations Using the (3+1) Formalism in
  General Relativity

abstract:
  Using the (3+1) formalism in general relativity, we perform the
post-Newtonian(PN) approximation to clarify what sort of gauge condition is
suitable for numerical analysis of coalescing compact binary neutron stars and
gravitational waves from them. We adopt a kind of transverse gauge condition to
determine the shift vector. On the other hand, for determination of the time
slice, we adopt three slice conditions(conformal slice, maximal slice and
harmonic slice) and discuss their properties. Using these conditions, the PN
hydrodynamic equations are obtained up through the 2.5PN order including the
quadrupole gravitational radiation reaction. In particular, we describe methods
to solve the 2PN tensor potential which arises from the spatial 3-metric. It is
found that the conformal slice seems appropriate for analysis of gravitational
waves in the wave zone and the maximal slice will be useful for describing the
equilibrium configurations. The PN approximation in the (3+1) formalism will be
also useful to perform numerical simulations using various slice conditions
and, as a result, to provide an initial data for the final merging phase of
coalescing binary neutron stars which can be treated only by fully general
relativistic simulations.


title:
Initial Data for General Relativity Containing a Marginally Outer
  Trapped Torus

abstract:
  Asymptotically flat, time-symmetric, axially symmetric and conformally flat
initial data for vacuum general relativity are studied numerically on $R^3$
with the interior of a standard torus cut out. By the choice of boundary
condition the torus is marginally outer trapped, and thus a surface of minimal
area. Apart from pure scaling the standard tori are parameterized by a radius
$a\in [0,1]$, where $a=0$ corresponds to the limit where the boundary torus
degenerates to a circle and $a=1$ to a torus that touches the axis of symmetry.
Noting that these tori are the orbits of a $U(1)\times U(1)$ conformal isometry
allows for a simple scheme to solve the constraint, involving numerical
solution of only ordinary differential equations.The tori are unstable minimal
surfaces (i.e. only saddle points of the area functional) and thus can not be
apparent horizons, but are always surrounded by an apparent horizon of
spherical topology, which is analyzed in the context of the hoop conjecture and
isoperimetric inequality for black holes.


title: The Statistical Mechanics of the Three-Dimensional Euclidean Black Hole

abstract:
  In its formulation as a Chern-Simons theory, three-dimensional general
relativity induces a Wess-Zumino-Witten action on spatial boundaries. Treating
the horizon of the three-dimensional Euclidean black hole as a boundary, I
count the states of the resulting WZW model, and show that when analytically
continued back to Lorentzian signature, they yield the correct
Bekenstein-Hawking entropy. The relevant states can be understood as ``would-be
gauge'' degrees of freedom that become dynamical at the horizon.


title: Comment on "Comparison of approaches to classical signature change"

abstract:
  This is a comment on a reply (gr-qc/9601040) to a comment (gr-qc/9606045) on
a paper of Hellaby & Dray (gr-qc/9404001), repeating the identification of an
important mistake which is still being denied by the authors: their proposed
solutions do not satisfy the Einstein- Klein-Gordon equations at a change of
signature. Substitution of the proposed solutions into the
Einstein-Klein-Gordon equations in unit normal coordinates yields Dirac delta
terms describing source layers at the junction. Hellaby & Dray's criticisms of
this straightforward calculation are absurd: it does not involve "imaginary
time", it does not involve a "modified form" of the field equations, and it is
"purely classical". Moreover, Hellaby & Dray's latest attempt to lose the delta
terms is mathematically invalid, involving division by zero and products of
distributions, hinging on an identity whose incorrectness may be checked by
substitution.


title:
Comment on "Failure of standard conservation laws at a classical change
  of signature"

abstract:
  Hellaby & Dray (gr-qc/9404001) have recently claimed that matter conservation
fails under a change of signature, compounding earlier claims that the standard
junction conditions for signature change are unnecessary. In fact, if the field
equations are satisfied, then the junction conditions and the conservation
equations are satisfied. The failure is rather that the authors did not make
sense of the field equations and conservation equations, which are singular at
a change of signature.


title: Non-closure of constraint algebra in N=1 supergravity

abstract:
  The algebra of constraints arising in the canonical quantization of N=1
supergravity in four dimensions is investigated. Using the holomorphic action,
the structure functions of the algebra are given and it is shown that the
algebra does not close formally for two chosen operator orderings.


title: Conserved Currents in Supersymmetric Quantum Cosmology?

abstract:
  In this paper we investigate whether conserved currents can be sensibly
defined in supersymmetric minisuperspaces. Our analysis deals with k=1 FRW and
Bianchi class--A models. Supermatter in the form of scalar supermultiplets is
included in the former. Moreover, we restrict ourselves to the first-order
differential equations derived from the Lorentz and supersymmetry constraints.
The ``square-root'' structure of N=1 supergravity was our motivation to
contemplate this interesting research. We show that conserved currents cannot
be adequately established except for some very simple scenarios. Otherwise,
conservation equations may only be obtained from Wheeler-DeWitt--like
equations, which are derived from the supersymmetric algebra of constraints.
Two appendices are included. In appendix A we describe some interesting
features of quantum FRW cosmologies with complex scalar fields when
supersymmetry is present. In particular, we explain how the Hartle-Hawking
state can now be satisfactorily identified. In appendix B we initiate a
discussion about the retrieval of classical properties from supersymmetric
quantum cosmologies.


title: The dualities of 3D dilaton gravity

abstract:
  We investigate Brans-Dicke dilaton gravity theories in 2+1 dimensions. We
show that the reduced field equations for solutions with diagonal metric and
depending only on one spacetime coordinate have a continuous O(2) symmetry.
Using this symmetry we derive general static and cosmological solutions of the
theory. The action of the discrete group O(2,Z) on the space of the solutions
is discussed. Three-dimensional string effective theory and three-dimensional
general relativity are discussed in detail. In particular, we find that the
previously discovered black string solution is dual to a spacetime with a
conical singularity.


title: Constant mean curvature foliations in cosmological spacetimes

abstract:
  Foliations by constant mean curvature hypersurfaces provide a possibility of
defining a preferred time coordinate in general relativity. In the following
various conjectures are made about the existence of foliations of this kind in
spacetimes satisfying the strong energy condition and possessing compact Cauchy
hypersurfaces. Recent progress on proving these conjectures under supplementary
assumptions is reviewed. The method of proof used is explained and the
prospects for generalizing it discussed. The relations of these questions to
cosmic censorship and the closed universe recollapse conjecture are pointed
out.


title: Noether symmetries in Bianchi universes

abstract:
  We use our N\"other Symmetry Approach to study the Einstein equations
minimally coupled with a scalar field, in the case of Bianchi universes of
class A and B. Possible cases, when such symmetries exist, are found and two
examples of exact integration of the equations of motion are given in the cases
of Bianchi AI and BV.


title: Relativistic Physics in Arbitrary Reference Frames

abstract:
  In this paper we give a review of the most general approach to description of
reference frames, the monad formalism. This approach is explicitly general
covariant at each step, permitting to use abstract representation of tensor
quantities; it is applicable also to special relativity when non-inertial
effects are considered in its context; moreover, it involves no hypotheses
whatsoever thus being a completely natural one. For the sake of the reader's
convenience, a synopsis of tensor calculus in pseudo-Riemannian space-time
precedes discussion of the subject, containing expressions rarely encountered
in literature but essentially facilitating the consideration. We give also a
comparison of the monad formalism with the other approaches to description of
reference frames in general relativity. In three chapters we consider
applications of the monad formalism to general relativistic mechanics,
electromagnetic and gravitational fields theory. Alongside of the general
theory, which includes the monad representation of basic equations of motion of
(charged) particles and of fields, several concrete solutions are provided to
clarify the physical role and practical application of reference frames (e.g.,
cases when a rotating electrically charged fluid does not produce any electric
field in its co-moving reference frame, or kinematic magnetic charges arise in
a rotating frame). The cases are discussed when it is unnecessary to introduce
a reference frame, and when such an introduction is essential. Special
attention is dedicated to analogy between gravitation, electromagnetism and
mechanics (e.g., the dragging phenomenon and existence in the Maxwell equations
in rotating frames of terms of the same nature as that of the Coriolis and
centrifugal forces).


title: Pair Creation of Black Holes During Inflation

abstract:
  Black holes came into existence together with the universe through the
quantum process of pair creation in the inflationary era. We present the
instantons responsible for this process and calculate the pair creation rate
from the no boundary proposal for the wave function of the universe. We find
that this proposal leads to physically sensible results, which fit in with
other descriptions of pair creation, while the tunnelling proposal makes
unphysical predictions. We then describe how the pair created black holes
evolve during inflation. In the classical solution, they grow with the horizon
scale during the slow roll-down of the inflaton field; this is shown to
correspond to the flux of field energy across the horizon according to the
First Law of black hole mechanics. When quantum effects are taken into account,
however, it is found that most black holes evaporate before the end of
inflation. Finally, we consider the pair creation of magnetically charged black
holes, which cannot evaporate. In standard Einstein-Maxwell theory we find that
their number in the presently observable universe is exponentially small. We
speculate how this conclusion may change if dilatonic theories are applied.


title:
Invalidity of the relativity principle and a proposal of the twofold
  metric principle

abstract:
  I show that all inertial systems are not equivalent, and the Lorentz
transformation is not the space-time transformation over two inertial systems
moving with relative constant velocity. To do this, I consider imaginary
signals travelling over any inertial system K with arbitrarily large
velocities. The travelling of an imaginary signal over K is just a time lapse
over K. Then I present an example to show that all coordinate systems are not
equivalent when the related theory is restricted over tensor-based coordinate
transformations, i.e., the genereal relativity principle is not valid. Instead
of the relativity principle, I propose the twofold metric principle which may
be roughly stated to assert that the set of equations H(v) describing the
motion of a material body with velocity v> 0 can be obtained from the
corresponding set of equations H(0) for velocity v=0 by replacing, in each
differential equation in H(0), each infinitesimal time variable dt with dt /
\beta(v) , each maximal velocity-critical infinitesimal length variable dr with
beta(v) dr, and each zero velocity-critical infinitesimal length variable dx
with dx, where beta(v) = 1/ sqrt {1- v^2/c^2}. By depending on the twofold
metric principle and the energy-velocity equation, I derive beta(v)mc^2, the
twofold Schwarzshild metric, the centennial procession of planatery orbits and
deflection of light. We also present a reason why the Michelson-Morley
experiment is observed. Several other topics are also studied.


title: The New Scenario of the Initial Evolution of the Universe

abstract:
  We propose that the Universe created from "nothing" with relatively small
particles number and quickly relaxed to quasiequilibrium state at the Planck
parameters. The classic cosmological solution for this Universe with
Lambda-term has two branches divided by the gap. The quantum process of
tunneling between the cosmological solution branches and kinetic of the second
order relativistic phase transition in supersymmetric SU(5) model on the GUT
scale are investigated by numerical methods. Einstein equations was solved
together with the equations of relaxation kinetics. Other quantum
geometrodynamics process (the bounce from singularity) and the Wheeler- De Witt
equation are investigated also. For the formation of observable particles
number the model of the slowly swelling Universe in the result of the multiple
reproduction of cosmological cycles is arised naturally.


title: TT-tensors and conformally flat structures on 3-manifolds

abstract:
  We study transverse-tracefree (TT)-tensors on conformally flat 3-manifolds
$(M,g)$. The Cotton-York tensor linearized at $g$ maps every symmetric
tracefree tensor into one which is TT. The question as to whether this is the
general solution to the TT-condition is viewed as a cohomological problem
within an elliptic complex first found by Gasqui and Goldschmidt and reviewed
in the present paper. The question is answered affirmatively when $M$ is simply
connected and has vanishing 2nd de Rham cohomology.


title:
Limits of space-times in five dimensions and their relation to the Segre
  Types

abstract:
  A limiting diagram for the Segre classification in 5-dimensional space-times
is obtained, extending a recent work on limits of the energy-momentum tensor in
general relativity. Some of Geroch's results on limits of space-times in
general relativity are also extended to the context of five-dimensional
Kaluza-Klein space-times.


title: Black Hole Criticality in the Brans-Dicke Model

abstract:
  We study the collapse of a free scalar field in the Brans-Dicke model of
gravity. At the critical point of black hole formation, the model admits two
distinctive solutions dependent on the value of the coupling parameter. We find
one solution to be discretely self-similar and the other to exhibit continuous
self-similarity.


title:
Be star surveys with CCD photometry. II. NGC 1818 and its neighbouring
  cluster in the LMC

abstract:
  As part of an ongoing photometric survey of young Magellanic Cloud clusters
we identified Be stars in NGC 1818 and a nearby smaller cluster in the Large
Magellanic Cloud. The neighbouring cluster does not contain evolved stars, and
its sparsely populated main sequence does not extend to stars as massive as in
NGC 1818. Both clusters are younger than the surrounding field population and
contain a much higher Be star fraction.
  We present a table with photometry, astrometric positions, and IAU-conform
identifiers of the Be stars. We compare Be star fractions in Magellanic Cloud
clusters and Galactic open clusters and discuss possible constraints on Be star
theories.


title: The ultrarelativistic Reissner-Nordstrom field in the Colombeau algebra

abstract:
  The electromagnetic field of the ultrarelativistic Reissner-Nordstrom
solution shows the physically highly unsatisfactory property of a vanishing
field tensor but a nonzero, i.e., delta-like, energy density. The aim of this
work is to analyze this situation from a mathematical point of view, using the
framework of Colombeau's theory of nonlinear generalized functions. It is shown
that the physically unsatisfactory situation is mathematically perfectly
defined and that one cannot aviod such situations when dealing with
distributional valued field tensors.


title: How to Make a Tiny Black Hole?

abstract:
  This is a brief review of critical phenomena in gravitational collapse. The
conceptual issues are emphasized and some directions for future research are
suggested. The paper is not addressed to the experts in the field -- for them
little will be new. It is rather meant to introduce others into one of the most
rapidly developing areas of research in general relativity with the hope of
attracting them into the subject.


title: Canonical quantum gravity with new variables and loops: a report

abstract:
  This is a brief and updated summary of a talk given at the International
Conference on Gravitation and Cosmology that took place in Poona in December
1995. It is very brief and is mostly intended as a guide to current literature,
or to keep people updated only in very broad terms on the latest developments
in the subject.


title:
A new test of conservation laws and Lorentz invariance in relativistic
  gravity

abstract:
  General relativity predicts that energy and momentum conservation laws hold
and that preferred frames do not exist. The parametrised post-Newtonian
formalism (PPN) phenomenologically quantifies possible deviations from general
relativity. The PPN parameter alpha_3 (which identically vanishes in general
relativity) plays a dual role in that it is associated both with a violation of
the momentum conservation law, and with the existence of a preferred frame. By
considering the effects of alpha_3 neq 0 in certain binary pulsar systems, it
is shown that alpha_3 < 2.2 x 10^-20 (90% CL). This limit improves on previous
results by several orders of magnitude, and shows that pulsar tests of alpha_3
rank (together with Hughes-Drever-type tests of local Lorentz invariance) among
the most precise null experiments of physics.


title: Relativistic Navigation: A Theoretical Foundation

abstract:
  We present a theoretical foundation for relativistic astronomical
measurements in curved space-time. In particular, we discuss a new iterative
approach for describing the dynamics of an astronomical N-body system. To do
this, we generalize the Fock-Chandrasekhar method of the weak-field and
slow-motion approximation (WFSMA) and develop a theory of relativistic
reference frames (RF) for a gravitationally bounded many-extended-body problem.
In any proper RF constructed in the immediate vicinity of an arbitrary body,
the N-body solutions of the gravitational field equations are presented as a
sum of the Riemann-flat inertial space-time, the gravitational field generated
by the body itself, the unperturbed solutions for each body in the system
transformed to the coordinates of this proper RF, and the gravitational
interaction term. We develop the basic concept of a general theory of the
celestial RFs applicable to a wide class of metric theories of gravity with an
arbitrary model of matter distribution. We apply the proposed method to general
relativity. Bodies are described using a perfect fluid model; as such, they
possess any number of internal mass and current multipole moments which
explicitly characterize their internal structure. The obtained relativistic
equations of motion contain an explicit information about the coupling of the
bodies proper multiple moments to the surrounding gravitational field. We
further generalize the proposed method and include two Eddington parameters
$(\gamma,\beta)$. This generalized approach was used to derive the relativistic
equations of satellite motion in the vicinity of the extended bodies. We
discuss the possible future implementation of the proposed formalism in
software codes developed for solar-system orbit determination.


title: Inflationary Models Driven by Adiabatic Matter Creation

abstract:
  The flat inflationary dust universe with matter creation proposed by
Prigogine and coworkers is generalized and its dynamical properties are
reexamined. It is shown that the starting point of these models depends
critically on a dimensionless parameter $\Sigma$, closely related to the matter
creation rate $\psi$. For $\Sigma$ bigger or smaller than unity flat universes
can emerge, respectively, either like a Big-Bang FRW singularity or as a
Minkowski space-time at $t=-\infty$. The case $\Sigma=1$ corresponds to a de
Sitter-type solution, a fixed point in the phase diagram of the system,
supported by the matter creation process. The curvature effects have also been
investigated. The inflating de Sitter is a universal attractor for all
expanding solutions regardless of the initial conditions as well as of the
curvature parameter.


title:
Classical and Quantum Implications of the Causality Structure of
  Two-Dimensional Spacetimes with Degenerate Metrics

abstract:
  The causality structure of two-dimensional manifolds with degenerate metrics
is analysed in terms of global solutions of the massless wave equation. Certain
novel features emerge. Despite the absence of a traditional Lorentzian Cauchy
surface on manifolds with a Euclidean domain it is possible to uniquely
determine a global solution (if it exists), satisfying well defined matching
conditions at the degeneracy curve, from Cauchy data on certain spacelike
curves in the Lorentzian region. In general, however, no global solution
satisfying such matching conditions will be consistent with this data.
Attention is drawn to a number of obstructions that arise prohibiting the
construction of a bounded operator connecting asymptotic single particle
states. The implications of these results for the existence of a unitary
quantum field theory are discussed.


title: Cosmic Microwave Background Dipole induced by double inflation

abstract:
  The observed CMBR dipole is generally interpreted as the consequence of the
peculiar motion of the Sun with respect to the reference frame of the CMBR.
This article proposes an alternative interpretation in which the observed
dipole is the result of isocurvature perturbations on scales larger than the
present Hubble radius. These perturbations are produced in the simplest model
of double inflation, depending on three parameters. The observed dipole and
quadrupole can be explained in this model, while severely constraining its
parameters.


title: Deflationary Models Driven by Matter Creation

abstract:
  A nonsingular deflationary cosmology driven by adiabatic matter creation is
proposed. In this scenario there is no preinflationary stage as happens in
conventional inflationary models. Deflation starts from a de Sitter spacetime
characterized by an arbitrary time scale $H_{I}^{-1}$, which also pins down an
initial value for the temperature of the universe. The model evolves
continuously towards a slightly modified Friedman-Robertson-Walker universe.
The horizon and other well known problems of the standard model are then solved
but, unlike in microscopic models of inflation, there is no supercooling and
subsequent reheating. Entropy generation is concomitant with deflation and if
$H_{I}^{-1}$ is of the order of the Planck time, the present day value of the
radiation temperature is deduced. It is also shown that the ``age problem''
does not exist here. In particular, the theoretically favored FRW flat model is
old enough to agree with the observations even given the high values of $H_{o}$
suggested by recent measurements.


title: The Analysis of Initial Conditions for the LTB Model

abstract:
  The Caushy problem in the LTB model is formulated. The rules of calculating
three undetermined functions which defined a solution in the LTB model are
presented. One example of exact nonhomogeneous model is studied. The limit
transformation to the FRW model is shown.


title: Traversable Wormholes in Geometries of Charged Shells

abstract:
  We construct a static axisymmetric wormhole from the gravitational field of
two charged shells which are kept in equilibrium by their electromagnetic
repulsion. For large separations the exterior tends to the Majumdar-Papapetrou
spacetime of two charged particles. The interior of the wormhole is a
Reissner-Nordstr\"om black hole matching to the two shells. The wormhole is
traversable and connects to the same asymptotics without violation of energy
conditions. However, every point in the Majumdar-Papapetrou region lies on a
closed timelike curve.


title: Superoscillations and trans-Planckian frequencies

abstract:
  Superoscillations can explain the arbitrarily high frequencies' paradox in
black hole radiation


title: The Simplest Exact Solutions in the LTB Model

abstract:
  The rules of calculating three undetermined functions which defined a
solution in the LTB model are used to study the class of exact nonhomogene\-ous
models with $f^2(\mu) = 1$, $\Lambda = 0$. The parameter $\nu(\mu)$ defined the
difference between LTB and FRW models is found out and the limit transformation
to the FRW model is shown. The initial conditions are present throught density
and Habble function at the moment of time $\tau = 0$. Two criteria of
homogeneous of matter distribution are studied. The asimptotic of the present
solution for $\tau \rightarrow +\infty$ is studied.


title: Charge scaling and universality in critical collapse

abstract:
  Consider any 1-parameter family of initial data such that data with parameter
value p > p* form black holes, and data with p < p* do not. As p -> p* from
above ("critical collapse"), the black hole mass scales as M ~ (p-p*)^gamma,
where the critical exponent gamma is the same for all such families of initial
data. So far critical collapse has been investigated only for initial data with
zero charge and zero angular momentum. Here we allow for U(1) charge. In scalar
electrodynamics coupled to gravity, with action R + |(d + iqA) phi|^2 + F^2, we
consider initial data with spherical symmetry and nonvanishing charge. From
dimensional analysis and a previous calculation of Lyapunov exponents, we
predict that in critical collapse the black hole mass scales as M ~
(p-p*)^gamma, and the black hole charge as Q ~ (p-p*)^delta, with gamma = 0.374
+- 0.001 (as for the real scalar field), and delta = 0.883 +- 0.007. We
conjecture that, where there is no mass gap, this behavior generalizes to other
charged matter models, with delta \ge 2 gamma. We suggest the existence of
universality classes with respect to parameters such as q.


title:
Hawking-Unruh Thermal Radiance as Relativistic Exponential Scaling of
  Quantum Noise

abstract:
  The Hawking-Unruh effect of thermal radiance from a black hole or observed by
an accelerated detector is usually viewed as a geometric effect related to the
existence of an event horizon. Here we propose a new viewpoint, that the
detection of thermal radiance in these systems is a local, kinematic effect
arising from the vacuum being subjected to a relativistic exponential scale
transformation. This kinematic effect alters the relative weight of quantum
versus thermal fluctuations (noise) between the two vacua. This approach can
treat conditions which the geometric approach cannot, such as systems which do
not even have an event horizon. An example is the case of an observer whose
acceleration is nonuniform or only asymptotically uniform. Since this approach
is based on concepts and techniques of non-equilibrium statistical mechanics,
it is more adept to dynamical problems, such as the dissipation, fluctuation,
and entropy aspects of particle creation and phase transitions in black hole
collapse and in the early universe.


title:
Near-Thermal Radiation in Detectors, Mirrors and Black Holes: A
  Stochastic Approach

abstract:
  In analyzing the nature of thermal radiance experienced by an accelerated
observer (Unruh effect), an eternal black hole (Hawking effect) and in certain
types of cosmological expansion, one of us proposed a unifying viewpoint that
these can be understood as arising from the vacuum fluctuations of the quantum
field being subjected to an exponential scale transformation. This viewpoint,
together with our recently developed stochastic theory of particle-field
interaction understood as quantum open systems described by the influence
functional formalism, can be used to address situations where the spacetime
possesses an event horizon only asymptotically, or none at all. Examples
studied here include detectors moving at uniform acceleration only
asymptotically or for a finite time, a moving mirror, and a collapsing mass. We
show that in such systems radiance indeed is observed, albeit not in a precise
Planckian spectrum. The deviation therefrom is determined by a parameter which
measures the departure from uniform acceleration or from exact exponential
expansion. These results are expected to be useful for the investigation of
non-equilibrium black hole thermodynamics and the linear response regime of
backreaction problems in semiclassical gravity.


title: Causality violation and singularities

abstract:
  We show that singularities necessarily occur when a boundary of causality
violating set exists in a space-time under the physically suitable assumptions
except the global causality condition in the Hawking-Penrose singularity
theorems. Instead of the global causality condition, we impose some
restrictions on the causality violating sets to show the occurrence of
singularities.


title: Testing for gravitationally preferred directions using the lunar orbit

abstract:
  As gravity is a long-range force, it is {\it a priori} conceivable that the
Universe's global matter distribution select a preferred rest frame for local
gravitational physics. At the post-Newtonian approximation, the phenomenology
of preferred-frame effects is described by two parameters, $\alpha_1$ and
$\alpha_2$, the second of which is already very tightly constrained. Confirming
previous suggestions, we show through a detailed Hill-Brown type calculation of
a perturbed lunar orbit that lunar laser ranging data have the potential of
constraining $\alpha_1$ at the $10^{-4}$ level. It is found that certain
retrograde planar orbits exhibit a resonant sensitivity to external
perturbations linked to a fixed direction in space. The lunar orbit being quite
far from such a resonance exhibits no significant enhancement due to solar
tides. Our Hill-Brown analysis is extended to the perturbation linked to a
possible differential acceleration toward the galactic center. It is, however,
argued that there are strong {\it a priori} theoretical constraints on the
conceivable magnitude of such an effect.


title: Theoretical aspects of gravitational radiation

abstract:
  A central problem in gravitational wave research is the {\it generation
problem}, i.e., the problem of relating the outgoing gravitational wave field
to the structure and motion of the material source. This problem has become, in
recent years, of increased interest in view of the development of a worldwide
network of gravitational wave detectors. We review recent progress in {\it
analytical} methods of tackling the gravitational wave generation problem. In
particular, we describe recent work in an approach which consists of matching a
post-Newtonian expansion of the metric near the material source with a
multipolar-post-Minkowskian expansion of the external metric. The results of
such analytical methods are important notably for providing accurate
theoretical predictions for the most promising targets of the LIGO/VIRGO
interferometric network: the ``chirp'' gravitational waveforms emitted during
the radiation-reaction-driven inspiral of binary systems of compact objects
(neutron stars or black holes).


title:
Gravitational radiation from infall into a black hole: Regularization of
  the Teukolsky equation

abstract:
  The Teukolsky equation has long been known to lead to divergent integrals
when it is used to calculate the gravitational radiation emitted when a test
mass falls into a black hole from infinity. Two methods have been used in the
past to remove those divergent integrals. In the first, integrations by parts
are carried out, and the infinite boundary terms are simply discarded. In the
second, the Teukolsky equation is transformed into another equation which does
not lead to divergent integrals. The purpose of this paper is to show that
there is nothing intrinsically wrong with the Teukolsky equation when dealing
with non-compact source terms, and that the divergent integrals result simply
from an incorrect choice of Green's function. In this paper, regularization of
the Teukolsky equation is carried out in an entirely natural way which does not
involve modifying the equation.


title: Gravitation, experiment and cosmology

abstract:
  The confrontation between general relativity (and its theoretically most
plausible deviations) and experimental or observational results is summarized.
Some discussion is devoted to the various methodologies used in confronting
theory and experiment. Both weak-field (solar system) and strong-field (binary
pulsar) tests are discussed in detail. A special discussion is devoted to the
cosmology of moduli fields, i.e. scalar fields having only
gravitational-strength couplings to matter.


title: Testing the equivalence principle: why and how?

abstract:
  Part of the theoretical motivation for improving the present level of testing
of the equivalence principle is reviewed. The general rationale for optimizing
the choice of pairs of materials to be tested is presented. One introduces a
simplified rationale based on a trichotomy of competing classes of theoretical
models.


title:
Staticity Theorem for Non-Rotating Black Holes with Non-Minimally
  Coupled Self-Interacting Scalar Fields

abstract:
  Self-interacting scalar field configurations which are non-minimally coupled
($\zeta\neq0$) to the gravity of a strictly stationary black hole with
non-rotating horizon are studied. It is concluded that for analytical
configurations the corresponding domain of outer communications is static.


title:
On the Equivalence of Brans-Dicke and Einstein Theories with Static
  Black Holes

abstract:
  A `no-hair' theorem for the Brans-Dicke field, in the domain of outer
communications of a static black hole, is established, when the trace of the
energy-momentum tensor, T, is a definite-sign scalar. This implies that
Brans-Dicke theory of gravitation, for matter with T of definite sign, is
equivalent to Einstein gravity with the constraint T=0.


title: Trans-Planckian Tail in a Theory with a Cutoff

abstract:
  Trans-planckian frequencies can be mimicked outside a black-hole horizon as a
tail of an exponentially large amplitude wave that is mostly hidden behind the
horizon. The present proposal requires implementing a final state condition.
This condition involves only frequencies below the cutoff scale. It may be
interpreted as a condition on the singularity. Despite the introduction of the
cutoff, the Hawking radiation is restored for static observers. Freely falling
observers see empty space outside the horizon, but are "heated" as they cross
the horizon.


title: Production of Global Monopoles through the Nucleation of $O(3)$ Bubbles

abstract:
  First-order cosmological phase transitions are considered in the models with
an $O(3)$-symmetric scalar field, in the high temperature limit. It is shown
that a global monopole can be produced at the center of a bubble when the
bubble is nucleated.


title: Probing Quantum Gravity Through Exactly Soluble Midi-Superspaces I

abstract:
  It is well-known that the Einstein-Rosen solutions to the 3+1 dimensional
vacuum Einstein's equations are in one to one correspondence with solutions of
2+1 dimensional general relativity coupled to axi-symmetric, zero rest mass
scalar fields. We first re-examine the quanization of this midi-superspace
paying special attention to the asymptotically flat boundary conditions and to
certain functional analytic subtleties associated with regularization. We then
use the resulting quantum theory to analyze several conceptual and technical
issues of quantum gravity.


title: Perturbing Supersymmetric Black Hole

abstract:
  An investigation of the perturbations of the Reissner-Nordstr\"{o}m black
hole in the $N=2$ supergravity is presented. We prove in the extremal limit
that the black hole responds to the perturbation of each field in the same
manner. We conjecture that we can match the modes of the graviton, gravitino
and photon because of supersymmetry transformations.


title: Fine-Structure of Choptuik's Mass-Scaling Relation

abstract:
  We conjecture (analytically) and demonstrate (numerically) the existence of a
fine-structure above the power-law behavior of the mass of black-holes that
form in gravitational collapse of spherical massless scalar field. The
fine-structure is a periodic function of the critical-separation $(p-p^*)$. We
predict that the period $\varpi$ is {\it universal} and that it depends on the
previous universal parameters, the critical exponent, $\beta$, and the echoing
period $\Delta$ as $\varpi = \Delta /\beta$.


title:
Anomaly-free formulation of non-perturbative, four-dimensional
  Lorentzian quantum gravity

abstract:
  A Wheeler-Dewitt quantum constraint operator for four-dimensional,
non-perturbative Lorentzian vacuum quantum gravity is defined in the continuum.
The regulated Wheeler-DeWitt constraint operator is densely defined, does not
require any renormalization and the final operator is anomaly-free and at least
symmmetric. The technique introduced here can also be used to produce a couple
of other completely well-defined regulated operators including but not
exhausting a) the Euclidean Wheeler-DeWitt operator, b)the generator of the
Wick rotation transform that maps solutions to the Euclidean Hamiltonian
constraint to solutions to the Lorentzian Hamiltonian constraint, c) length
operators, d) Hamiltonian operators of the matter sector and e) the generators
of the asymptotic Poincar\'e group including the quantum ADM energy.


title: Quantum Spin Dynamics (QSD)

abstract:
  An anomaly-free operator corresponding to the Wheeler-DeWitt constraint of
Lorentzian, four-dimensional, canonical, non-perturbative vacuum gravity is
constructed in the continuum. This operator is entirely free of factor ordering
singularities and can be defined in symmetric and non-symmetric form. We work
in the real connection representation and obtain a well-defined quantum theory.
We compute the complete solution to the Quantum Einstein Equations for the
non-symmetric version of the operator and a physical inner product thereon. The
action of the Wheeler-DeWitt constraint on spin-network states is by
annihilating, creating and rerouting the quanta of angular momentum associated
with the edges of the underlying graph while the ADM-energy is essentially
diagonalized by the spin-network states. We argue that the spin-network
representation is the ``non-linear Fock representation" of quantum gravity,
thus justifying the term ``Quantum Spin Dynamics (QSD)".


title: Quantum Spin Dynamics (QSD) II

abstract:
  We continue here the analysis of the previous paper of the Wheeler-DeWitt
constraint operator for four-dimensional, Lorentzian, non-perturbative,
canonical vacuum quantum gravity in the continuum. In this paper we derive the
complete kernel, as well as a physical inner product on it, for a non-symmetric
version of the Wheeler-DeWitt operator. We then define a symmetric version of
the Wheeler-DeWitt operator. For the Euclidean Wheeler-DeWitt operator as well
as for the generator of the Wick transform from the Euclidean to the Lorentzian
regime we prove existence of self-adjoint extensions and based on these we
present a method of proof of self-adjoint extensions for the Lorentzian
operator. Finally we comment on the status of the Wick rotation transform in
the light of the present results.


title:
Closed formula for the matrix elements of the volume operator in
  canonical quantum gravity

abstract:
  We derive a closed formula for the matrix elements of the volume operator for
canonical Lorentzian quantum gravity in four spacetime dimensions in the
continuum in a spin-network basis. We also display a new technique of
regularization which is state dependent but we are forced to it in order to
maintain diffeomorphism covariance and in that sense it is natural. We arrive
naturally at the expression for the volume operator as defined by Ashtekar and
Lewandowski up to a state independent factor.


title: A length operator for canonical quantum gravity

abstract:
  We construct an operator that measures the length of a curve in
four-dimensional Lorentzian vacuum quantum gravity. We work in a representation
in which a $SU(2)$ connection is diagonal and it is therefore surprising that
the operator obtained after regularization is densely defined, does not suffer
from factor ordering singularities and does not require any renormalization. We
show that the length operator admits self-adjoint extensions and compute part
of its spectrum which like its companions, the volume and area operators
already constructed in the literature, is purely discrete and roughly is
quantized in units of the Planck length. The length operator contains full and
direct information about all the components of the metric tensor which
faciliates the construction of a new type of weave states which approximate a
given classical 3-geometry.


title:
Critical Behaviour and Universality in Gravitational Collapse of a
  Charged Scalar Field

abstract:
  We summarize results from a study of spherically symmetric collapse of a {\it
charged} (complex) massless scalar-field \cite{Hod}. We present an analytic
argument which conjecture the generalization of the mass-scaling relation and
echoing phenomena, originally discovered by Choptuik, for the {\it charged}
case. Furthermore, we study the behaviour of the self-similar critical solution
under {\it external} perturbations -- addition of a cosmological constant
$\Lambda$ and a charge-conjugation $e$. Finally, we study the scaling-relation
of the black-hole charge. Using an analytic argument we conjecture that
black-holes of infinitesimal mass are neutral or obey the relation $Q_{BH} \ll
M_{BH}$. We verify our predictions with numerical results.


title: On the Uniqueness of the Papapetrou--Majumdar Metric

abstract:
  We establish the equality of the ADM mass and the total electric charge for
asymptotically flat, static electrovac black hole spacetimes with completely
degenerate, not necessarily connected horizon.


title:
Experimental investigations of demonstrational model of generator using,
  presumably, energy of physical vacuum

abstract:
  In this article, a developed, manufactured and tested model of a new type
generator is presented, which allows to differentiate and predict, with
probability close to 1, coasting characteristics of the rotor during its
clockwise and counter-clockwise rotation. An explication of the effect on a
base of a new interaction, different from four known ones, is provided.


title: Restrictions on Negative Energy Density in Flat Spacetime

abstract:
  In a previous paper, a bound on the negative energy density seen by an
arbitrary inertial observer was derived for the free massless, quantized scalar
field in four-dimensional Minkowski spacetime. This constraint has the form of
an uncertainty principle-type limitation on the magnitude and duration of the
negative energy density. That result was obtained after a somewhat complicated
analysis. The goal of the current paper is to present a much simpler method for
obtaining such constraints. Similar ``quantum inequality'' bounds on negative
energy density are derived for the electromagnetic field, and for the massive
scalar field in both two and four-dimensional Minkowski spacetime.


title: Algebra of Constraints and Solutions of Quantum Gravity

abstract:
  We construct the regularized Wheeler--De Witt operator demanding that the
algebra of constraints of quantum gravity is anomaly free. We find that for
only a small subset of all wavefunctions being integrals of scalar densities
this condition can be satisfied. It turns out that the resulting operator is
much simpler than the one used in \cite{JK} to find exact solutions of
Wheeler--De Witt equation. We proceed to finding exact solutions of quantum
gravity and we discuss their interpretation making use of the quantum potential
approach to quantum theory.


title: Is there no quantum form of Einstein Gravity?

abstract:
  It is well known that Einstein gravity is non-renormalizable; however this
does not preclude the existence of a quantum form.


title:
A non-strictly hyperbolic system for the Einstein equations with
  arbitrary lapse and shift

abstract:
  We obtain a system for the spatial metric and extrinsic curvature of a
spacelike slice that is hyperbolic non-strict in the sense of Leray and Ohya
and is equivalent to the Einstein equations. Its characteristics are the light
cone and the normal to the slice for any choice of lapse and shift functions,
and it admits a well-posed causal Cauchy problem in a Gevrey class of index
$\alpha=2$. The system becomes quasidiagonal hyperbolic if we posit a certain
wave equation for the lapse function, and we can then relate the results to our
previously obtained first order symmetric hyperbolic system for general
relativity.


title: Multidimensional SU(2) wormhole between two null surfaces

abstract:
  The multidimensional gravity on principal bundle with structural SU(2) gauge
group is considered. The Lorentzian wormhole solution disposed between two null
surfaces is founded in this case. As the nondiagonal components are similar to
a gauge fields (in Kaluza - Klein's sense) then in some sense this solution is
dual to the black hole in 4D Einstein - Yang - MIlls gravity: 4D black hole has
the stationary area outside of event horizon but multidimensional wormhole
inside null surface (on which $ds^2=0$).


title: Flat wormholes from straight cosmic strings

abstract:
  Special multi-cosmic string metrics are analytically extended to describe
configurations of Wheeler-Misner wormholes and ordinary cosmic strings. I
investigate in detail the case of flat, asymptotically Minkowskian,
Wheeler-Misner wormhole spacetimes generated by two cosmic strings, each with
tension $-1/4G$.


title: The Lense--Thirring Effect and Mach's Principle

abstract:
  We respond to a recent paper by Rindler on the ``Anti--Machian'' nature of
the Lense--Thirring effect. We remark that his conclusion depends crucially on
the particular formulation of Mach's principle used.


title: Renormalization group and critical behaviour in gravitational collapse

abstract:
  We present a general framework for understanding and analyzing critical
behaviour in gravitational collapse. We adopt the method of renormalization
group, which has the following advantages. (1) It provides a natural
explanation for various types of universality and scaling observed in numerical
studies. In particular, universality in initial data space and universality for
different models are understood in a unified way. (2) It enables us to perform
a detailed analysis of time evolution beyond linear perturbation, by providing
rigorous controls on nonlinear terms. Under physically reasonable assumptions
we prove: (1) Uniqueness of the relevant mode around a fixed point implies
universality in initial data space. (2) The critical exponent $\beta_{BH}$ and
the unique positive eigenvalue $\kappa$ of the relevant mode is exactly related
by $\beta_{BH} = \beta /\kappa$, where $\beta$ is a scaling exponent. (3) The
above (1) and (2) hold also for discretely self-similar case (replacing ``fixed
point'' with ``limit cycle''). (4) Universality for diffent models holds under
a certain condition.
  According to the framework, we carry out a rather complete (though not
mathematically rigorous) analysis for perfect fluids with pressure proportional
to density, in a wide range of the adiabatic index $\gamma$. The uniqueness of
the relevant mode around a fixed point is established by Lyapunov analyses.
This shows that the critical phenomena occurs not only for the radiation fluid
but also for perfect fluids with $1 < \gamma \lesssim 1.88$. The accurate
values of critical exponents are calculated for the models.


title:
Dynamical Critical Phenomena and Large Scale Structure of the Universe:
  the Power Spectrum for Density Fluctuations

abstract:
  As is well known, structure formation in the Universe at times after
decoupling can be described by hydrodynamic equations. These are shown here to
be equivalent to a generalization of the stochastic Kardar--Parisi--Zhang
equation with time-- dependent viscosity in epochs of dissipation. As a
consequence of the Dynamical Critical Scaling induced by noise and
fluctuations, these equations describe the fractal behavior (with a scale
dependent fractal dimension) observed at the smaller scales for the
galaxy--to--galaxy correlation function and $also$ the Harrison--Zel'dovich
spectrum at decoupling. By a Renormalization Group calculation of the
two--point correlation function between galaxies in the presence of (i) the
expansion of the Universe and (ii) non--equilibrium, we can account, from first
principles, for the main features of the observed shape of the power spectrum.


title: Two-dimensional black holes in accelerated frames: quantum aspects

abstract:
  By considering charged black hole solutions of a one parameter family of two
dimensional dilaton gravity theories, one finds the existence of quantum
mechanically stable gravitational kinks with a simple mass to charge relation.
Unlike their Einsteinian counterpart (i.e. extreme Reissner-Nordstr\"om), these
have nonvanishing horizon surface gravity.


title:
Classical stability of black hole Cauchy horizons in two-dimensional
  asymptotically flat space-times

abstract:
  In this paper we analyse the stability of black hole Cauchy horizons arising
in a class of 2d dilaton gravity models. It is shown that due to the
characteristic asymptotic Rindler form of the metric of these models, time
dependent gravitational perturbations generated in the external region do not
necessarily blow-up when propagated along the Cauchy horizon. There exists, in
fact, a region of nonzero measure in the space of the parameters characterizing
the solutions such that both instability and mass inflation are avoided. This
is a new result concerning asymptotically flat space-times, not shared by the
well-known solutions of General Relativity. Despite this fact, however, quantum
back-reaction seems to produce a scalar curvature singularity there.


title: The Gauss Constraint in the Extended Loop Representation

abstract:
  The Gauss constraint in the extended loop representation for quantum gravity
is studied. It is shown that there exists a sector of the state space that is
rigorously gauge invariant without the generic convergence issues of the
extended holonomies.


title:
Quantum Cosmological Multidimensional Einstein-Yang-Mills Model in a $R
  \times S^3 \times S^d$ Topology

abstract:
  The quantum cosmological version of the multidimensional Einstein-Yang-Mills
model in a $R \times S^3 \times S^d$ topology is studied in the framework of
the Hartle-Hawking proposal. In contrast to previous work in the literature, we
consider Yang-Mills field configurations with non-vanishing time-dependent
components in both $S^3$ and $S^d$ spaces. We obtain stable compactifying
solutions that do correspond to extrema of the Hartle-Hawking wave function of
the Universe. Subsequently, we also show that the regions where 4-dimensional
metric behaves classically or quantum mechanically (i.e. regions where the
metric is Lorentzian or Euclidean) will depend on the number, $d$, of compact
space dimensions.


title: Exact Solution for Relativistic Two-Body Motion in Dilaton Gravity

abstract:
  We present an exact solution to the problem of the relativistic motion of 2
point masses in $(1+1)$ dimensional dilaton gravity. The motion of the bodies
is governed entirely by their mutual gravitational influence, and the spacetime
metric is likewise fully determined by their stress-energy. A Newtonian limit
exists, and there is a static gravitational potential. Our solution gives the
exact Hamiltonian to infinite order in the gravitational coupling constant.


title: Remarks on a Decrumpling Model of the Universe

abstract:
  It is argued that when the dimension of space is a constant integer the full
set of Einstein's field equations has more information than the spatial
components of Einstein's equation plus the energy conservation law. Applying
the former approach to the decrumpling FRW cosmology recently proposed, it is
shown that the spacetime singularity cannot be avoided and that turning points
are absent. This result is in contrast to the decrumpling nonsingular spacetime
model with turning points previously obtained using the latter approach.


title: The Effect of Brick Walls on the Black Hole Radiation

abstract:
  In order to understand the physical effect of the brick wall boundary
condition, we compute the distribution of the zero-point energy of the massless
scalar fields minimally coupled to the Schwarzschild and Reissner-Nordstr\"{o}m
black hole backgrounds. We find that the black hole radiation spectrum depends
on the positions of the brick wall and the observer, and reveals the
interference effect due to the reflected field by the brick wall.


title: Remarks on Renormalization of Black Hole Entropy

abstract:
  We elaborate the renormalization process of entropy of a nonextremal and an
extremal Reissner-Nordstr\"{o}m black hole by using the Pauli-Villars
regularization method, in which the regulator fields obey either the
Bose-Einstein or Fermi-Dirac distribution depending on their spin-statistics.
The black hole entropy involves only two renormalization constants. We also
discuss the entropy and temperature of the extremal black hole.


title: Mixmaster quantum cosmology in terms of physical dynamics

abstract:
  An approach to quantum cosmology, relying on strengths of both canonical and
path integral formalisms, is applied to the cosmological model, Bianchi type
IX. Physical quantum states are constructed on the maximal slice of the
cosmological history. A path integral is derived which evolves observables off
the maximal slice. This result is compared a path integral propagator derived
earlier with conventional Faddeev-Poppov gauge fixing.


title: Relativity at Action or Gamma-Ray Bursts

abstract:
  Gamma ray Bursts (GRBs) - short bursts of few hundred keV $\gamma$-rays -
have fascinated astronomers since their accidental discovery in the sixties.
GRBs were ignored by most relativists who did not expect that they are
associated with any relativistic phenomenon. The recent observations of the
BATSE detector on the Compton GRO satellite have revolutionized our ideas on
these bursts and the picture that emerges shows that GRBs are the most
relativistic objects discovered so far.


title: The scattering matrix approach for the quantum black hole, an overview

abstract:
  If one assumes the validity of conventional quantum field theory in the
vicinity of the horizon of a black hole, one does not find a quantum mechanical
description of the entire black hole that even remotely resembles that of
conventional forms of matter; in contrast with matter made out of ordinary
particles one finds that, even if embedded in a finite volume, a black hole
would be predicted to have a strictly continuous spectrum.
  Dissatisfied with such a result, which indeed hinges on assumptions
concerning the horizon that may well be wrong, various investigators have now
tried to formulate alternative approaches to the problem of ``quantizing" the
black hole. We here review the approach based on the assumption of quantum
mechanical purity and unitarity as a starting point, as has been advocated by
the present author for some time, concentrating on the physics of the states
that should live on a black hole horizon. The approach is shown to be powerful
in not only producing promising models for the quantum black hole, but also new
insights concerning the dynamics of physical degrees of freedom in ordinary
flat space-time.


title:
Maxwell's theory on a post-Riemannian spacetime and the equivalence
  principle

abstract:
  The form of Maxwell's theory is well known in the framework of general
relativity, a fact that is related to the applicability of the principle of
equivalence to electromagnetic phenomena. We pose the question whether this
form changes if torsion and/or nonmetricity fields are allowed for in
spacetime. Starting from the conservation laws of electric charge and magnetic
flux, we recognize that the Maxwell equations themselves remain the same, but
the constitutive law must depend on the metric and, additionally, may depend on
quantities related to torsion and/or nonmetricity. We illustrate our results by
putting an electric charge on top of a spherically symmetric exact solution of
the metric-affine gauge theory of gravity (comprising torsion and
nonmetricity). All this is compared to the recent results of Vandyck.


title: Quantum Entropy of Charged Rotating Black Holes

abstract:
  I discuss a method for obtaining the one-loop quantum corrections to the
tree-level entropy for a charged Kerr black hole. Divergences which appear can
be removed by renormalization of couplings in the tree-level gravitational
action in a manner similar to that for a static black hole.


title: Gravitational radiation from relativistic sources

abstract:
  1. Introduction
  2. Basics and outline of the method
  2.1 Regions around an isolated source
  2.2 The quadrupole formalism
  2.3 Outline of the method
  3. Properties of radiative gravitational fields
  3.1 The field in the exterior domain (D_e)
  3.2 Computing the field nonlinearities in (D_e)
  3.3 The field in the far wave zone D_w
  3.4 Nonlinear effects in the far-zone radiation field
  4. Generation of gravitational waves
  4.1 Post-Newtonian iteration of the field in D_i
  4.2 The multipole moments as integrals over the source
  5. Gravitational radiation reaction effects
  6. Application to inspiralling compact binaries


title: Geometry of Black Holes and Multi-Black-Holes in 2+1 dimensions

abstract:
  Lecture given at ``Raychaudhuri session," ICGC-95 conference, Pune (India),
December 1995.
  Contents:
  I. Introduction
  II. (2+1)-Dimensional Initial Values in Stereographic Projection
  A. The single, non-rotating black hole
  B. Non-rotating multi-black-holes
  C. ``Black Hole" Universe Initial Values
  III. Time Development: Enter the Raychaudhuri Equation
  IV. Time Development in Stereographic Projection
  A. The BTZ black hole spacetime
  B. Multi-Black-Hole Spacetimes
  V. Black Holes with Angular Momentum
  VI. Analogous 3+1-Dimensional Black Holes
  VII. Conclusions


title: Tests of Cosmic Censorship in the Ernst Spacetime

abstract:
  The Ernst spacetime is a solution of the Einstein-Maxwell equations
describing two charged black holes accelerating apart in a uniform electric (or
magnetic) field. As the field approaches a critical value, the black hole
horizon appears to touch the acceleration horizon. We show that weak cosmic
censorship cannot be violated by increasing the field past this critical value:
The event horizon remains intact. On the other hand, strong cosmic censorship
does appear to be violated in this spacetime: For a certain range of
parameters, we find evidence that the inner horizon is classically stable.


title:
Remarks on the issue of time and complex numbers in canonical quantum
  gravity

abstract:
  We develop the idea that, as a result of the arbitrariness of the factor
ordering in Wheeler-DeWitt equation, gauge phases can not, in general, being
completely removed from the wave functional in quantum gravity. The latter may
be conveniently described by means of a remnant complex term in WDW equation
depending of the factor ordering. Taking this equation for granted we can
obtain WKB complex solutions and, therefore, we should be able to derive a
semiclassical time parameter for the Schroedinger equation corresponding to
matter fields in a given classical curved space.


title: Dynamics of a self-gravitating thin cosmic string

abstract:
  We assume that a self-gravitating thin string can be locally described by
what we shall call a smoothed cone. If we impose a specific constraint on the
model of the string, then its central line obeys the Nambu-Goto equations. If
no constraint is added, then the worldsheet of the central line is a totally
geodesic surface.


title: Mass Spectrum for Black Holes in Generic 2-D Dilaton Gravity

abstract:
  Two arguments for the quantization of entropy for black holes in generic 2-D
dilaton gravity are summarized. The first argument is based on reduced
quantization of the only physical observables in the theory, namely the black
hole mass and its conjugate momentum, the Killing time separation. The second
one uses the exact physical mass eigenstates for Euclidean black holes found
via Dirac quantization. Both methods give the same spectrum: the black hole
entropy must be quantized $S= 2\pi n/G$.


title: Analysis of ``Gauge Modes'' in Linearized Relativity

abstract:
  By writing the complete set of $3 + 1$ (ADM) equations for linearized waves,
we are able to demonstrate the properties of the initial data and of the
evolution of a wave problem set by Alcubierre and Schutz. We show that the
gauge modes and constraint error modes arise in a straightforward way in the
analysis, and are of a form which will be controlled in any well specified
convergent computational discretization of the differential equations.


title:
The Schrodinger Wave Functional and Vacuum State in Curved Spacetime II.
  Boundaries and Foliations

abstract:
  In a recent paper, general solutions for the vacuum wave functionals in the
Schrodinger picture were given for a variety of classes of curved spacetimes.
Here, we describe a number of simple examples which illustrate how the presence
of spacetime boundaries influences the vacuum wave functional and how physical
quantities are independent of the choice of spacetime foliation used in the
Schrodinger approach despite the foliation dependence of the wave functionals
themselves.


title: A General Expression for the Quintic Lovelock Tensor

abstract:
  A general expression is given for the quintic Lovelock tensor as well as for
the coefficient of the quintic Lovelock Lagrangian in terms of the
Riemann-Christoffel and Ricci curvature tensors and the Riemann curvature
scalar for n-dimensional differentiable manifolds having a general linear
connection.


title: Black Hole--Scalar Field Interactions in Spherical Symmetry

abstract:
  We examine the interactions of a black hole with a massless scalar field
using a coordinate system which extends ingoing Eddington-Finkelstein
coordinates to dynamic spherically symmetric-spacetimes. We avoid problems with
the singularity by excising the region of the black hole interior to the
apparent horizon. We use a second-order finite difference scheme to solve the
equations. The resulting program is stable and convergent and will run forever
without problems. We are able to observe quasi-normal ringing and power-law
tails as well an interesting nonlinear feature.


title: Electrostatic self-force in (2+1)-dimensional cosmological gravity

abstract:
  Point sources in (2+1)-dimensional gravity are conical singularities that
modify the global curvature of the space giving rise to self-interaction
effects on classical fields. In this work we study the electrostatic
self-interaction of a point charge in the presence of point masses in
(2+1)-dimensional gravity with a cosmological constant.


title: Multi-black holes and instantons in effective string theory

abstract:
  The effective action for string theory which takes into account non-minimal
coupling of moduli admits multi-black hole solutions. The euclidean
continuation of these solutions can be interpreted as an instanton mediating
the splitting and recombination of the throat of extremal magnetically charged
black holes.


title: Computer Algebra Solving of First Order ODEs Using Symmetry Methods

abstract:
  A set of Maple V R.3/4 computer algebra routines for the analytical solving
of 1st. order ODEs, using Lie group symmetry methods, is presented. The set of
commands includes a 1st. order ODE-solver and routines for, among other things:
the explicit determination of the coefficients of the infinitesimal symmetry
generator; the construction of the most general invariant 1st. order ODE under
given symmetries; the determination of the canonical coordinates of the
underlying invariant group; and the testing of the returned results.


title: Non-coordinate time/velocity pairs in special relativity

abstract:
  Motions with respect to one inertial (or ``map'') frame are often described
in terms of the coordinate time/velocity pair (or ``kinematic'') of the map
frame itself. Since not all observers experience time in the same way, other
time/velocity pairs describe map-frame trajectories as well. Such coexisting
kinematics provide alternate variables to describe acceleration. We outline a
general strategy to examine these. For example, Galileo's acceleration
equations describe unidirectional relativistic motion {\it exactly} if one uses
$V=\frac{dx}{dT}$, where $x$ is map-frame position and $T$ is clock time in a
chase plane moving such that $\gamma ^{\prime }=\gamma \sqrt{\frac 2{\gamma
+1}}$. Velocity in the traveler's kinematic, on the other hand, has dynamical
and transformational properties which were lost by coordinate-velocity in the
transition to Minkowski space-time. Its repeated appearance with coordinate
time, when expressing relationships in simplest form, suggests complementarity
between traveler and coordinate kinematic views.


title: The Quantum Theory of General Relativity at Low Energies

abstract:
  In quantum field theory there is now a well developed technique, effective
field theory, which allows one to obtain low energy quantum predictions in
``non-renormalizable'' theories, using only the degrees of freedom and
interactions appropriate for those energies. Whether or not general relativity
is truly fundamental, at low energies it is automatically described as a
quantum effective field theory and this allows a consistent framework for
quantum gravity at ordinary energies. I briefly describe the nature and limits
of the technique.


title:
Creation of multiple de Sitter universes inside a Schwarzschild black
  hole

abstract:
  A classical model for the interior structure of a Schwarzshild black hole
which consists in creating multiple de Sitter universes with lightlike
boundaries is proposed.The interaction of the boundaries is studied and a
scenario leading to disconnected de Sitter universes is described.


title:
Density of kinks after a quench: When symmetry breaks, how big are the
  pieces?

abstract:
  Numerical study of order parameter dynamics in the course of second order
(Landau-Ginzburg) symmetry breaking transitions shows that the density of
topological defects, kinks, is proportional to the fourth root of the rate of
the quench. This confirms the more general theory of domain-size evolution in
the course of symmetry breaking transformations proposed by one of us
\cite{Zurek85}. Using these ideas, it is possible to compute the density of
topological defects from the quench timescale and from the equilibrium scaling
of the correlation length and relaxation time near the critical point.


title: Clock Synchronisation in Inertial Frames and Gravitational Fields

abstract:
  The special relativistic test theory of Mansouri and Sexl is sketched.
Theories based on different clock synchronisations are found to be equivalent
to special relativity, as regards experimental results. The conventionality of
clock synchronisation is shown not to hold, by means of an example, in a simple
accelerated system and through the principle of equivalence in gravitational
fields, especially when the metric is not static. Experimental implications on
very precise clock synchronisation on earth are discussed.


title:
Aberration and the Question of Equivalence of some Ether Theories to
  Special Relativity

abstract:
  In the last two decades, theories explaining the same experiments as well as
special relativity does, were developed by using different synchronization
procedures. All of them are ether-like theories. Most authors believe these
theories to be equivalent to special relativity, but no general proof was ever
brought. By means of a Gedankenexperiment on light aberration, we produce
strong evidence that this is the case for experiments made in inertial systems.


title: Reality conditions for Ashtekar variables as Dirac constraints

abstract:
  We show that the reality conditions to be imposed on Ashtekar variables to
recover real gravity can be implemented as second class constraints a la Dirac.
Thus, counting gravitational degrees of freedom follows accordingly. Some
constraints of the real theory turn out to be non-polynomial, regardless of the
form, polynomial or non-polynomial, taken for the reality conditions. We
comment upon the compatibility of our approach with the recently proposed Wick
transform point of view, as well as on some alternatives for dealing with such
second class constraints.


title: Generalized Symmetries of Impulsive Gravitational Waves

abstract:
  We generalize previous \cite{AiBa2} work on the classification of
($C^\infty$) symmetries of plane-fronted waves with an impulsive profile. Due
to the specific form of the profile it is possible to extend the group of
normal-form-preserving diffeomorphisms to include non-smooth transformations.
This extension entails a richer structure of the symmetry algebra generated by
the (non-smooth) Killing vectors.


title: Inertial frame dragging and Mach's principle in General Relativity

abstract:
  We define a new parameter `cumulative drag index' for a particle in circular
orbit in a stationary, axisymmetric gravitational field and study its behaviour
in the two well known solutions of general relativity {\it viz.}, the Kerr
spacetime and the G\"odel spacetime, wherein the inertial frame dragging has an
important role. As it shows similar behaviour for both co and counter rotating
particles, it may indeed be an indication of the influence of the faraway
universe on local physics and thus Machian.


title:
Non-Invariant Velocity of Light and Clock Synchronisation in Accelerated
  Systems

abstract:
  Clock synchronisation is conventional when inertial systems are involved.
This statement is no longer true in accelerated systems. A demonstration is
given in the case of a rotating platform. We conclude that theories based on
the Einstein's clock synchronisation procedure are unable to explain, for
example, the Sagnac effect on the platform. Implications on very precise clock
synchronisation on earth are discussed.


title:
Quantized fields and temperature in charged dilatonic black hole
  spacetimes

abstract:
  The stress-energy tensor of a quantized scalar field is computed in the
reduced two-dimensional charged dilatonic black hole spacetime of Garfinkle,
Horowitz, and Strominger. In order for the stress-energy of quantized fields to
be regular on the event horizon in both the extreme string metric and the
conformally associated physical metric, it is necessary to assign a nonzero
temperature, T = (8 pi e^{phi_0} M)^{-1}, to the extreme string metric,
contrary to the expectation that this horizonless spacetime would have a
natural temperature of zero.


title: A Decrumpling Model of the Universe

abstract:
  Assuming a cellular structure for the space-time, we propose a model in which
the expansion of the universe is understood as a decrumpling process, much like
the one we know from polymeric surfaces. The dimension of space is then a
dynamical real variable. The generalized Friedmann equation, derived from a
Lagrangian, and the generalized equation of continuity for the matter content
of the universe, give the dynamics of our model universe. This leads to an
oscillatory non-singular model with two turning points for the dimension of
space.


title: Symmetries of Decoherence Functionals

abstract:
  The basic ingredients of the `consistent histories' approach to quantum
theory are a space $\UP$ of `history propositions' and a space $\D$ of
`decoherence functionals'. In this article we consider such history quantum
theories in the case where $\UP$ is given by the set of projectors $\P(\V)$ on
some Hilbert space $\V$. Using an analogue of Wigner's Theorem in the context
of history quantum theories proven earlier, we develop the notion of a
`symmetry of a decoherence functional' and prove that all such symmetries form
a group which we call `the symmetry group of a decoherence functional'. We
calculate---for the case of history quantum mechanics---some of these
symmetries explicitly and relate them to some discussions that have appeared
previously.


title: Symmetry and History Quantum Theory: An analogue of Wigner's Theorem

abstract:
  The basic ingredients of the `consistent histories' approach to quantum
theory are a space $\UP$ of `history propositions' and a space $\D$ of
`decoherence functionals'. In this article we consider such history quantum
theories in the case where $\UP$ is given by the set of projectors $\P(\V)$ on
some Hilbert space $\V$. We define the notion of a `physical symmetry of a
history quantum theory' (PSHQT) and specify such objects exhaustively with the
aid of an analogue of Wigner's theorem. In order to prove this theorem we
investigate the structure of $\D$, define the notion of an `elementary
decoherence functional' and show that each decoherence functional can be
expanded as a certain combination of these functionals. We call two history
quantum theories that are related by a PSHQT `physically equivalent' and show
explicitly, in the case of history quantum mechanics, how this notion is
compatible with one that has appeared previously.


title: Strong Cosmic Censorship and Causality Violation

abstract:
  We investigate the instability of the Cauchy horizon caused by causality
violation in the compact vacuum universe with the topology $B\times {\bf
S}^{1}\times {\bf R}$, which Moncrief and Isenberg considered. We show that if
the occurrence of curvature singularities are restricted to the boundary of
causality violating region, the whole segments of the boundary become curvature
singularities. This implies that the strong cosmic censorship holds in the
spatially compact vacuum space-time in the case of the causality violation.
This also suggests that causality violation cannot occur for a compact
universe.


title: Closed-Flux Solutions to the Constraints for Plane Gravity Waves

abstract:
  The metric for plane gravitational waves is quantized within the Hamiltonian
framework, using a Dirac constraint quantization and the self-dual field
variables proposed by Ashtekar. The z axis (direction of travel of the waves)
is taken to be the entire real line rather than the torus (manifold
coordinatized by (z,t) is RxR rather than $S_1$ x R). Solutions to the
constraints proposed in a previous paper involve open-ended flux lines running
along the entire z axis, rather than closed loops of flux; consequently, these
solutions are annihilated by the Gauss constraint at interior points of the z
axis, but not at the two boundary points. The solutions studied in the present
paper are based on closed flux loops and satisfy the Gauss constraint for all
z.


title: Quasinormal modes of nearly extreme Reissner-Nordstrom black holes

abstract:
  We present detailed calculations of the quasinormal modes of
Reissner-Nordstrom black holes. While the first few, slowly damped, modes
depend on the charge of the black hole in a relatively simple way, we find that
the rapidly damped modes show several peculiar features. The higher modes
generally spiral into the value for the extreme black hole as the charge
increases. We also discuss the possible existence of a purely imaginary mode
for the Schwarzschild black hole: Our data suggest that there is a quasinormal
mode that limits to $\omega M = -2i$ as $Q\to 0$.


title: Statistical Mechanical Entropy of Two-Dimensional Black Holes

abstract:
  We calculate the statistical mechanical entropy associated with boundary
terms in the two-dimensional Euclidean black holes in deSitter gravity.


title: On the parameters of Lewis metric for the Weyl class

abstract:
  We provide physical interpretation for the four parameters of the stationary
Lewis metric restricted to the Weyl class. Matching this spacetime to a
completely anisotropic, rigidly rotating, fluid cilinder, we obtain from the
junction conditions that one of these parameters is proportional to the
vorticity of the source. From the Newtonian approximation a second parameter is
found to be proportional to the energy per unit of length. The remaining two
parameters may be associated to a gravitational analog of the Aharanov-Bohm
effect. We prove, using the Cartan scalars, that the Weyl class metric and
static Levi-Civita metric are locally equivalent, i.e., indistinguishable in
terms of its curvature.


title: On the parameters of Lewis metric for the Lewis class

abstract:
  The physical and geometrical meaning of the four parameters of Lewis metric
for the Lewis class are investigated. Matching this spacetime to a completely
anisotropic, rigidly rotating, fluid cylinder, we obtain from the junction
conditions that the four parameters are related to the vorticity of the source.
Furthermore it is shown that one of the parameters must vanish if one wishes to
reduce the Lewis class to a locally static spacetime. Using the Cartan scalars
it is shown that the Lewis class does not include globally Minkowski as special
class, and that it is not locally equivalent to the Levi-Civita metric. Also it
is shown that, in contrast with the Weyl class, the parameter responsible for
the vorticity appears explicitly in the expression for the Cartan scalars.
Finally, to enhance our understanding of the Lewis class, we analyse the van
Stockum metric.


title: The Levi-Civita spacetime

abstract:
  We consider two exact solutions of Einstein's field equations corresponding
to a cylinder of dust with net zero angular momentum. In one of the cases, the
dust distribution is homogeneous, whereas in the other, the angular velocity of
dust particles is constant [1]. For both solutions we studied the junction
conditions to the exterior static vacuum Levi-Civita spacetime. From this study
we find an upper limit for the energy density per unit length $\sigma$ of the
source equal ${1\over 2}$ for the first case and ${1\over 4}$ for the second
one. Thus the homogeneous cluster provides another example [2] where the range
of $\sigma$ is extended beyond the limit value ${1\over 4}$ previously found in
the literature [3,4]. Using the Cartan Scalars technics we show that the
Levi-Civita spacetime gets an extra symmetry for $\sigma={1\over 2}$ or
${1\over 4}$. We also find that the cluster of homogeneous dust has a superior
limit for its radius, depending on the constant volumetric energy density
$\rho_0$.


title:
Quantum fluctuations of Cosmological Perturbations in Generalized
  Gravity

abstract:
  Recently, we presented a unified way of analysing classical cosmological
perturbation in generalized gravity theories. In this paper, we derive the
perturbation spectrums generated from quantum fluctuations again in unified
forms. We consider a situation where an accelerated expansion phase of the
early universe is realized in a particular generic phase of the generalized
gravity. We take the perturbative semiclassical approximation which treats the
perturbed parts of the metric and matter fields as quantum mechanical
operators. Our generic results include the conventional power-law and
exponential inflations in Einstein's gravity as special cases.


title: Quantum Space-time and Classical Gravity

abstract:
  A method has been recently proposed for defining an arbitrary number of
differential calculi over a given noncommutative associative algebra. As an
example a version of quantized space-time is considered here. It is found that
there is a natural differential calculus using which the space-time is
necessarily flat Minkowski space-time. Perturbations of this calculus are shown
to give rise to non-trivial gravitational fields.


title: Homothetic perfect fluid space-times

abstract:
  A brief summary of results on homotheties in General Relativity is given,
including general information about space-times admitting an r-parameter group
of homothetic transformations for r>2, as well as some specific results on
perfect fluids. Attention is then focussed on inhomogeneous models, in
particular on those with a homothetic group $H_4$ (acting multiply
transitively) and $H_3$. A classification of all possible Lie algebra
structures along with (local) coordinate expressions for the metric and
homothetic vectors is then provided (irrespectively of the matter content), and
some new perfect fluid solutions are given and briefly discussed.


title:
Asymptotic behaviour of a class of inhomogeneous scalar field
  cosmologies

abstract:
  The asymptotic behaviour of a class of inhomogeneous scalar field cosmologies
with a Liouville type of potential is studied. We define a set of new variables
for which the phase space of the system of Einstein equations is bounded. This
allows us to perform a complete analysis of the evolution of these cosmologies.
We also discuss the extension of the cosmic no-hair theorem.


title:
Time machines and the Principle of Self-Consistency as a consequence of
  the Principle of Stationary Action (II): the Cauchy problem for a
  self-interacting relativistic particle

abstract:
  We consider the action principle to derive the classical, relativistic motion
of a self-interacting particle in a 4-D Lorentzian spacetime containing a
wormhole and which allows the existence of closed time-like curves. In
particular, we study the case of a pointlike particle subject to a
`hard-sphere' self-interaction potential and which can traverse the wormhole an
arbitrary number of times, and show that the only possible trajectories for
which the classical action is stationary are those which are globally
self-consistent. Generically, the multiplicity of these trajectories (defined
as the number of self-consistent solutions to the equations of motion beginning
with given Cauchy data) is finite, and it becomes infinite if certain
constraints on the same initial data are satisfied. This confirms the previous
conclusions (for a non-relativistic model) by Echeverria, Klinkhammer and
Thorne that the Cauchy initial value problem in the presence of a wormhole
`time machine' is classically `ill-posed' (far too many solutions). Our results
further extend the recent claim by Novikov et al. that the `Principle of
self-consistency' is a natural consequence of the `Principle of minimal
action.'


title: Evolving test-fields in a black-hole geometry

abstract:
  We consider the initial value problem for a massless scalar field in the
Schwarzschild geometry. When constructed using a complex-frequency approach the
necessary Green's function splits into three components. We discuss all of
these in some detail: 1) The contribution from the singularities (the
quasinormal modes of the black hole) is approximated and the mode-sum is
demonstrated to converge after a certain well defined time in the evolution. A
dynamic description of the mode-excitation is introduced and tested. 2) It is
shown how a straightforward low-frequency approximation to the integral along
the branch cut in the black-hole Green's function leads to the anticipated
power-law fall off at very late times. We also calculate higher order
corrections to this tail and show that they provide an important complement to
the leading order. 3) The high-frequency problem is also considered. We
demonstrate that the combination of the obtained approximations for the
quasinormal modes and the power-law tail provide a complete description of the
evolution at late times. Problems that arise (in the complex-frequency picture)
for early times are also discussed, as is the fact that many of the presented
results generalize to, for example, Kerr black holes.


title: Fuzzy Space-Time

abstract:
  A review is made of recent efforts to define linear connections and their
corresponding curvature within the context of noncommutative geometry. As an
application it is suggested that it is possible to identify the gravitational
field as a phenomenological manifestation of space-time commutation relations
and to thereby clarify its role as an ultraviolet regularizer.


title: Time Evolution in Dynamical Spacetimes

abstract:
  We present a gauge--theoretical derivation of the notion of time, suitable to
describe the Hamiltonian time evolution of gravitational systems. It is based
on a nonlinear coset realization of the Poincar\'e group, implying the time
component of the coframe to be invariant, and thus to represent a metric time.
The unitary gauge fixing of the boosts gives rise to the foliation of spacetime
along the time direction. The three supressed degrees of freedom correspond to
Goldstone--like fields, whereas the remaining time component is a Higgs--like
boson.


title: The moduli space of local homogeneous 3-geometries

abstract:
  For a canonical formulation of quantum gravity, the superspace of all
possible 3-geometries on a Cauchy hypersurface of a 3+1-dimensional Lorentzian
manifold plays a key role. While in the analogous 2+1-dimensional case the
superspace of all Riemannian 2-geometries is well known, the structure of the
superspace of all Riemannian 3-geometries has not yet been resolved at present.
  In this paper, an important subspace of the latter is disentangled: The
superspace of local homogenous Riemannian 3-geometries. It is finite
dimensional and can be factored by conformal scale dilations, with the flat
space as the center of projection. The corresponding moduli space can be
represented by homothetically normalized 3-geometries.
  By construction, this moduli space of the local homogenous 3-geometries is an
algebraic variety. An explicit parametrization is given by characteristic
scalar invariants of the Riemannian 3-geometry.
  Although the moduli space is not locally Euclidean, it is a Hausdorff space.
Nevertheless, its topology is compatible with the non-Hausdorffian topology of
the space of all Bianchi-Lie algebras, which characterize the moduli modulo
differences in their anisotropy.


title:
Detection of Anisotropies in the Gravitational-Wave Stochastic
  Background

abstract:
  By correlating the signals from a pair of gravitational-wave detectors, one
can undertake sensitive searches for a stochastic background of gravitational
radiation. If the stochastic background is anisotropic, then this correlated
signal varies harmonically with the earth's rotation. We calculate how the
harmonics of this varying signal are related to the multipole moments which
characterize the anisotropy, and give a formula for the signal-to-noise ratio
of a given harmonic. The specific case of the two LIGO (Laser Interferometric
Gravitational Observatory) detectors, which will begin operation around the
year 2000, is analyzed in detail. We consider two possible examples of
anisotropy. If the gravitational-wave stochastic background contains a dipole
intensity anisotropy whose origin (like that of the Cosmic Background
Radiation) is motion of our local system, then that anisotropy will be
observable by the advanced LIGO detector (with 90% confidence in one year of
observation) if \Omega_{gw} > 5.3 \times 10^{-8} h_{100}^{-2}. We also study
the signal produced by stochastic sources distributed in the same way as the
luminous matter in the galactic disk, and in the same way as the galactic halo.
The anisotropy due to sources distributed as the galactic disk or as the
galactic halo will be observable by the advanced LIGO detector (with 90%
confidence in one year of observation) if \Omega_{gw} > 1.8 \times 10^{-10}
h_{100}^{-2} or \Omega_{gw} > 6.7 \times 10^{-8} h_{100}^{-2}, respectively.


title:
Topos Theory and Consistent Histories: The Internal Logic of the Set of
  all Consistent Sets

abstract:
  A major problem in the consistent-histories approach to quantum theory is
contending with the potentially large number of consistent sets of history
propositions. One possibility is to find a scheme in which a unique set is
selected in some way. However, in this paper we consider the alternative
approach in which all consistent sets are kept, leading to a type of `many
world-views' picture of the quantum theory. It is shown that a natural way of
handling this situation is to employ the theory of varying sets (presheafs) on
the space $\B$ of all Boolean subalgebras of the orthoalgebra $\UP$ of history
propositions. This approach automatically includes the feature whereby
probabilistic predictions are meaningful only in the context of a consistent
set of history propositions. More strikingly, it leads to a picture in which
the `truth values', or `semantic values' of such contextual predictions are not
just two-valued (\ie true and false) but instead lie in a larger logical
algebra---a Heyting algebra---whose structure is determined by the space $\B$
of Boolean subalgebras of $\UP$.


title: General Relativity as Geometro-Hydrodynamics

abstract:
  In the spirit of Sakharov's `metric elasticity' proposal, we draw a loose
analogy between general relativity and the hydrodynamic state of a quantum gas.
In the `top-down' approach, we examine the various conditions which underlie
the transition from some candidate theory of quantum gravity to general
relativity. Our emphasis here is more on the `bottom-up' approach, where one
starts with the semiclassical theory of gravity and examines how it is modified
by graviton and quantum field excitations near and above the Planck scale. We
mention three aspects based on our recent findings: 1) Emergence of stochastic
behavior of spacetime and matter fields depicted by an Einstein-Langevin
equation. The backreaction of quantum fields on the classical background
spacetime manifests as a fluctuation-dissipation relation. 2) Manifestation of
stochastic behavior in effective theories below the threshold arising from
excitations above. The implication for general relativity is that such
Planckian effects, though exponentially suppressed, is in principle detectable
at sub-Planckian energies. 3) Decoherence of correlation histories and quantum
to classical transition. From Gell-Mann and Hartle's observation that the
hydrodynamic variables which obey conservation laws are most readily decohered,
one can, in the spirit of Wheeler, view the conserved Bianchi identity obeyed
by the Einstein tensor as an indication that general relativity is a
hydrodynamic theory of geometry. Many outstanding issues surrounding the
transition to general relativity are of a nature similar to hydrodynamics and
mesoscopic physics.


title: Pair Production of Topological anti de Sitter Black Holes

abstract:
  The pair creation of black holes with event horizons of non-trivial topology
is described. The spacetimes are all limiting cases of the cosmological $C$
metric. They are generalizations of the $(2+1)$ dimensional black hole and have
asymptotically anti de Sitter behaviour. Domain walls instantons can mediate
their pair creation for a wide range of mass and charge.


title: The Behaviour Of Cosmological Models With Varying-G

abstract:
  We provide a detailed analysis of Friedmann-Robertson-Walker universes in a
wide range of scalar-tensor theories of gravity. We apply solution-generating
methods to three parametrised classes of scalar-tensor theory which lead
naturally to general relativity in the weak-field limit. We restrict the
parameters which specify these theories by the requirements imposed by the
weak-field tests of gravitation theories in the solar system and by the
requirement that viable cosmological solutions be obtained. We construct a
range of exact solutions for open, closed, and flat isotropic universes
containing matter with equation of state $p\leq \frac{1}{3}\rho$ and in vacuum.
We study the range of early and late-time behaviours displayed, examine when
there is a `bounce' at early times, and expansion maxima in closed models.


title: Quantum Histories and Their Implications

abstract:
  Classical mechanics and standard Copenhagen quantum mechanics respect
subspace implications. For example, if a particle is confined in a particular
region $R$ of space, then in these theories we can deduce that it is confined
in regions containing $R$. However, subspace implications are generally
violated by versions of quantum theory that assign probabilities to histories,
such as the consistent histories approach. I define here a new criterion,
ordered consistency, which refines the criterion of consistency and has the
property that inferences made by ordered consistent sets do not violate
subspace relations. This raises the question: do the operators defining our
observations form an ordered consistent history? If so, ordered consistency
defines a version of quantum theory with greater predictive power than the
consistent histories formalism. If not, and our observations are defined by a
non-ordered consistent quantum history, then subspace implications are not
generally valid.


title: Approximate Black Holes for Numerical Relativity

abstract:
  Spherically symmetric solutions in Brans-Dicke theory of relativity with zero
coupling constant, $\omega=0$, are derived in the Schwarzschild line-element.
The solutions are obtained from a cubic transition equation with one small
parameter. The exterior space-time of one family of solutions is arbitrarily
close to the exterior Schwarzschild space-time. These nontopological solitons
have some similarity with soliton stars, and are proposed as candidates for
{\em approximate black holes} for the use in numerical relativity, in
particular for treatment of horizon boundary conditions.


title: Gravitational Wave Detector Sites

abstract:
  Locations and orientations of current and proposed laser-interferometric
gravitational wave detectors are given in tabular form.


title:
Geodesics for impulsive gravitational waves and the multiplication of
  distributions

abstract:
  We consider particle trajectories in the gravitational field of an impulsive
pp-wave. Due to the distributional character of the wave profile one inevitably
encounters an ambiguous point value $\theta(0)$. We show that this ambiguity
may be resolved by imposing covariant constancy of the square of the tangent.
Our result is consistent with Colombeau's multiplication of distributions.


title: Cosmological Perturbations of Ultrarelativistic Plasmas

abstract:
  Scalar cosmological perturbations of a weakly self-interacting plasma mixed
with a perfect radiation fluid are investigated. Effects of this plasma are
considered through order $\lambda^{3/2}$ of perturbative thermal-field-theory
in the radiation dominated universe. The breakdown of thermal perturbation
theory at vastly subhorizon scales is circumvented by a Pad\'e approximant
solution. Compared to collisionless plasmas the phase speed and subhorizon
damping of the plasma density perturbations are changed. An example for a
self-interacting thermal field is provided by the neutrinos with effective
4-fermion interactions.


title: An Exact Solution with $f^2 = 1$ and $\Lambda \ne 0$ in the LTB model

abstract:
  The exact solution in the LTB model with $f^2 = 1$, $\Lambda \ne 0$ is
studied. The initial conditions for the metrical function and its derivatives
generate the solution with complicated structure including the solutions like
"stripping of the shell", "collapce" and "core", or "accretion". In the limit
of big time the solution allows the constant Hubble function and the density,
depending on time. The transformation to the FRW model is shown. Three pictures
are available by e-mail.


title: Nucleating Black Holes via Non-Orientable Instantons

abstract:
  We extend the analysis of black hole pair creation to include non- orientable
instantons. We classify these instantons in terms of their fundamental
symmetries and orientations. Many of these instantons admit the pin structure
which corresponds to the fermions actually observed in nature, and so the
natural objection that these manifolds do not admit spin structure may not be
relevant. Furthermore, we analyse the thermodynamical properties of
non-orientable black holes and find that in the non-extreme case, there are
interesting modifications of the usual formulae for temperature and entropy.


title: A Consistency Condition for the Double Series Approximation Method

abstract:
  The double series approximation method of Bonnor is a means for examining the
gravitational radiation from an axisymmetric isolated source that undergoes a
finite period of oscillation. It involves an expansion of the metric as a
double Taylor series. Here we examine the integration procedure that is used to
form an algorithmic solution to the field equations and point out the
possibility of the expansion method breaking down and predicting a singularity
along the axis of symmetry. We derive a condition on the solutions obtained by
the double series method that must be satisfied to avoid this singularity. We
then consider a source with only a quadrupole moment and verify that to fourth
order in each of the expansion parameters, this condition is satisfied. This is
a reassuring test of the consistency of the expansion procedure. We do,
however, find that the imposition of this condition makes a physical
interpretation of any but the lowest order solutions very difficult. The most
obvious decomposition of the solution into a series of independent physical
effects is shown not to be valid.


title: Evaluation of Bartnik's quasilocal mass function

abstract:
  Bartnik's definition of gravitational quasilocal energy is analyzed. For a
wide class of systems Bartnik's function is given by the ADM mass of some
vacuous extension. As an example we calculate mass of a non central ball in
Schwarzschild geometry. The ratio mass to volume becomes singular in the limit
of small volumes.


title: A geometric definition of Lie derivative for Spinor Fields

abstract:
  Relying on the general theory of Lie derivatives a new geometric definition
of Lie derivative for general spinor fields is given, more general than
Kosmann's one. It is shown that for particular infinitesimal lifts, i.e. for
Kosmann vector fields, our definition coincides with the definition given by
Kosmann more than 20 years ago.