title: In defence of the `Tunneling' wave function of the Universe

abstract:
  The tunneling approach to the wave function of the universe has been recently
criticized by Bousso and Hawking who claim that it predicts a catastrophic
instability of de Sitter space with respect to pair production of black holes.
We show that this claim is unfounded. First, we argue that different horizon
size regions in de Sitter space cannot be treated as independently created, as
they contend. And second, the WKB tunneling wave function is not simply the
`inverse' of the Hartle-Hawking one, except in very special cases. Applied to
the related problem of pair production of massive particles, we argue that the
tunneling wave function leads to a small constant production rate, and not to a
catastrophy as Bousso and Hawking's argument would suggest.


title:
Solution of the Higgs scalar-tensor theory without Higgs particles for
  static stars

abstract:
  Within the scalar-tensor theory of gravity with Higgs mechanism without Higgs
particles, we prove that the excited Higgs potential (the scalar field) vanishs
inside and outside of the stellar matter for static spherically symmetric
configurations. The field equation for the metric (the tensorial gravitational
field) turns out to be essentially the Einsteinian one.


title:
The cosmological background in the Higgs scalar-tensor theory without
  Higgs particles

abstract:
  The scalar background field and its consequences are discussed for the
Friedmann type cosmological solutions of the scalar-tensor theory of gravity
with the Higgs field of the Standard Model as the scalar gravitational field.


title:
Discrete Spectrum of the Deficit Angle and the Differential Structure of
  a Cosmic String

abstract:
  Differential properties of Klein-Gordon and electromagnetic fields on the
space-time of a straight cosmic string are studied with the help of methods of
the differential space theory. It is shown that these fields are smooth in the
interior of the cosmic string space-time and that they loose this property at
the singular boundary except for the cosmic string space-times with the
following deficit angles : Delta=2\pi*(1-1/n), n=1,2,... A connection between
smoothness of fields at the conical singularity and the scalar and
electromagnetic conical bremsstrahlung is discussed. It is also argued that the
smoothness assumption of fields at the singularity is equivalent to the Aliev
and Gal'tsov "quantization" condition leading to the above mentioned discrete
spectrum of the deficit angle.


title: Superselection Sectors in Asymptotic Quantization of Gravity

abstract:
  Using the continuity of the scalar $\Psi_2$ (the mass aspect) at null
infinity through $i_o$ we show that the space of radiative solutions of general
relativity can be thought of a fibered space where the value of $\Psi_2$ at
$i_o$ plays the role of the base space. We also show that the restriction of
the available symplectic form to each ``fiber'' is degenerate. By finding the
orbit manifold of this degenerate direction we obtain the reduced phase space
for the radiation data. This reduced phase space posses a global structure,
i.e., it does not distinguishes between future or past null infinity. Thus, it
can be used as the space of quantum gravitons. Moreover, a Hilbert space can be
constructed on each ``fiber'' if an appropriate definition of scalar product is
provided. Since there is no natural correspondence between the Hilbert spaces
of different foliations they define superselection sectors on the space of
asymptotic quantum states.


title: New Algorithm for Mixmaster Dynamics

abstract:
  We present a new numerical algorithm for evolving the Mixmaster spacetimes.
By using symplectic integration techniques to take advantage of the exact Taub
solution for the scattering between asymptotic Kasner regimes, we evolve these
spacetimes with higher accuracy using much larger time steps than previously
possible. The longer Mixmaster evolution thus allowed enables detailed
comparison with the Belinskii, Khalatnikov, Lifshitz (BKL) approximate
Mixmaster dynamics. In particular, we show that errors between the BKL
prediction and the measured parameters early in the simulation can be
eliminated by relaxing the BKL assumptions to yield an improved map. The
improved map has different predictions for vacuum Bianchi Type IX and magnetic
Bianchi Type VI$_0$ Mixmaster models which are clearly matched in the
simulation.


title: Einstein-Langevin Equations from Running Coupling Constants

abstract:
  The Einstein-Langevin equations take into account the backreaction of quantum
matter fields on the background geometry. We present a derivation of these
equations to lowest order in a covariant expansion in powers of the curvature.
For massless fields, the equations are completely determined by the running
coupling constants of the theory.


title: On the Entropy of Minimally Coupled and Non-minimally Coupled Gravities

abstract:
  We investigate whether the gravitational thermodynamic properties of the
scalar-tensor theory of gravity are affected by the conformal transformation or
not. As an explicit example, we consider an electrically charged static
spherical black hole in the 4-dimensional low energy effective theory of
bosonic string.


title:
Full determination of the $dp$ backward elastic scattering matrix
  element

abstract:
  The model independent analysis of the $dp$ elastic scattering in the
collinear geometry has been performed. It is shown that the measurements of 10
polarization observables of the first and second order realize the complete
experimental program on the determination of the amplitudes of the $dp$
backward elastic scattering reaction.


title: On the black-hole kink

abstract:
  By allowing the light cones to tip over on hypersurfaces according to the
conservation laws of an one-kink in static, Schwarzschild black hole metric, we
show that in the quantum regime there also exist instantons whose finite
imaginary action gives the probability of occurrence of the kink metric
corresponding to single chargeless, nonrotating black hole taking place in
pairs, the holes of each pair being joined on an interior surface, beyond the
horizon.


title: The Tetrad Frame Constraint Algebra

abstract:
  It is shown via the principle of path independence that the (time gauge)
constraint algebra derived in (Class. Quantum Grav. 5 (1988) pg. 1405) for
vielbein General Relativity is a generic feature of any covariant theory
formulated in a vielbein frame. In the process of doing so, the relationship
between the coordinate and orthonormal frame algebera is made explicit.


title: Cosmic Strings and the String Dilaton

abstract:
  The existence of a dilaton (or moduli) with gravitational-strength coupling
to matter imposes stringent constraints on the allowed energy scale of cosmic
strings, $\eta$. In particular, superheavy gauge strings with $\eta \sim
10^{16} GeV$ are ruled out unless the dilaton mass $m_{\phi} \gsim 100 TeV$,
while the currently popular value $m_{\phi} \sim 1 TeV$ imposes the bound $\eta
\lsim 3 \times 10^{11} GeV$. Similar constraints are obtained for global
topological defects. Some non-standard cosmological scenarios which can avoid
these constraints are pointed out.


title:
Role of Regularization in Quantum Corrections to the Scalar-Tensor
  Theories of Gravity

abstract:
  We show that regularizing divergent integrals is crucially important when
applied to the loop diagrams corresponding to quantum corrections to the
coupling of the ``gravitational" scalar field due to the interaction among
matter fields. We use the method of continuous spacetime dimensions to
demonstrate that WEP is a robust property of the Brans-Dicke theory beyond the
classical level, hence correcting our previous assertion of the contrary. The
same technique can be used to yield the violation of WEP when applied to the
scale-invariant theory, thus providing another reason for expecting fifth-
force-type phenomena.


title: Cosmic String in Scalar-Tensor Gravities

abstract:
  We consider a local cosmic string described by the Abelian-Higgs model in the
framework of scalar-tensor gravities. We find the metric of the cosmic string
in the weak-field approximation. The propagation of particles and light is
analysed in this background. This analysis shows that the (unperturbed) cosmic
string in scalar-tensor theories presents some analogous features to the wiggly
cosmic string in General Relativity.


title:
Large quantum gravity effects: Unexpected limitations of the classical
  theory

abstract:
  3-dimensional gravity coupled to Maxwell (or Klein-Gordon) fields is exactly
soluble under the assumption of axi-symmetry. The solution is used to probe
several quantum gravity issues. In particular, it is shown that the quantum
fluctuations in the geometry are large unless the number and frequency of
photons satisfy the inequality $\N(\hbar G\omega)^2 << 1$. Thus, even when
there is a single photon of Planckian frequency, the quantum uncertainties in
the metric are significant. Results hold also for a sector of the 4-dimensional
theory (consisting of Einstein Rosen gravitational waves).


title:
Generation of Source Terms in General Relativity by differential
  structures

abstract:
  In this paper the relation between the choice of a differential structure and
a smooth connection in the tangential bundle is discussed. For the case of an
exotic $S^7$ one obtains corrections to the curvature after the change of the
differential structure, which can not be neglected by a gauge transformation.
In the more interesting case of four dimensions we obtain a correction of the
connection constructed by intersections of embedded surfaces. This correction
produce a source term in the equation of the general relativity theory which
can be interpreted as the energy-momentum tensor of a embedded surface.


title: Uniqueness of stationary, electro-vacuum black holes revisited

abstract:
  In recent years there has been some progress in the understanding of the
global structure of stationary black hole space-times. In this paper we review
some new results concerning the structure of stationary black hole space-times.
In particular we prove a corrected version of the ``black hole rigidity
theorem'', and we prove a uniqueness theorem for static black holes with
degenerate connected horizons. This paper is an expanded version of a lecture
given at the Journ\'ees relativistes in Ascona, May 1996.


title: On rigidity of analytic black holes

abstract:
  We establish global extendibility (to the domain of outer communications) of
locally defined isometries of appropriately regular analytic black holes. This
allows us to fill a gap in the Hawking-Ellis proof of black-hole rigidity.


title: Two-Component Formulation of the Wheeler-DeWitt Equation

abstract:
  The Wheeler-DeWitt equation for the minimally coupled
FRW-massive-scalar-field minisuperspace is written as a two-component
Schr\"odinger equation with an explicitly `time'-dependent Hamiltonian. This
reduces the solution of the Wheeler-DeWitt equation to the eigenvalue problem
for a non-relativistic one-dimensional harmonic oscillator and an infinite
series of trivial algebraic equations whose iterative solution is easily found.
The solution of these equations yields a mode expansion of the solution of the
original Wheeler-DeWitt equation. Further analysis of the mode expansion shows
that in general the solutions of the Wheeler-DeWitt equation for this model are
doubly graded, i.e., every solution is a superposition of two definite-parity
solutions. Moreover, it is shown that the mode expansion of both even and
odd-parity solutions is always infinite. It may be terminated artificially to
construct approximate solutions. This is demonstrated by working out an
explicit example which turns out to satisfy DeWitt's boundary condition at
initial singularity.


title: On the global evolution problem in 2+1 gravity

abstract:
  Existence of global CMC foliations of constant curvature 3-dimensional
maximal globally hyperbolic Lorentzian manifolds, containing a constant mean
curvature hypersurface with $\genus(\Sigma) > 1$ is proved. Constant curvature
3-dimensional Lorentzian manifolds can be viewed as solutions to the 2+1 vacuum
Einstein equations with a cosmological constant. The proof is based on the
reduction of the corresponding Hamiltonian system in constant mean curvature
gauge to a time dependent Hamiltonian system on the cotangent bundle of
Teichm\"uller space. Estimates of the Dirichlet energy of the induced metric
play an essential role in the proof.


title: Spin-weighted Green's functions in a conical space

abstract:
  We give an analysis of the spin-weighted Green's functions well-defined in a
conical space. We apply these results in the case of a straight cosmic string
and in the Rindler space in order to determine generally the Euclidean Green's
functions for the massless spin 1/2 field and for the electromagnetic field. We
give also the corresponding Green's functions at zero temperature. However,
except for the scalar field, it seems that these Euclidean Green's functions do
not correspond to the thermal Feynman Green's functions.


title: Implosion of quadrupole gravitational waves

abstract:
  Einstein's vacuum equations are solved up to the second approximation for
imploding quadrupole gravitational waves. The implosion generates a black hole
singularity irrespective of the strength of the waves.


title:
Distinguished solutions for discontinuous signature change with weak
  junction conditions

abstract:
  We consider discontinuous signature change with the weak junction condition
favoured by Ellis et. al. (1992). We impose certain regularity conditions and
investigate the space of solutions (considered as one-parameter families of
three-dimensional Riemannian manifolds) for dust and scalar field models.


title: Colombeau's Generalized Functions on Arbitrary Manifolds

abstract:
  We extend the Colombeau algebra of generalized functions to arbitrary
(infinitely differentiable, paracompact) n-dimensional manifolds M. Embedding
of continuous functions and distributions is achieved with the help of a family
of n-forms defined on the tangent bundle TM, which form a partition of unity
upon integration over the fibres.


title: Double Darboux method for the Taub continuum

abstract:
  The strictly isospectral double Darboux method is applied to the quantum Taub
model in order to generate a one-parameter family of strictly isospectral
potentials for this case. The family we build is based on a scattering
Wheeler-DeWitt solution first discussed by Ryan and collaborators that we
slightly modified according to a suggestion due to Dunster. The strictly
isospectral Taub potentials possess different (attenuated) scattering states
with respect to the original Taub potential


title: No-Hair Theorems and Black Holes with Hair

abstract:
  The critical steps leading to the uniqueness theorem for the Kerr-Newman
metric are reexamined in the light of the new black hole solutions with
Yang-Mills and scalar hair. Various methods -- including scaling techniques,
arguments based on energy conditions, conformal transformations and divergence
identities -- are reviewed, and their range of application to selfgravitating
scalar and non-Abelian gauge fields is discussed. In particular, the no-hair
theorem is extended to harmonic mappings with arbitrary Riemannian target
manifolds. (This paper is an extended version of an invited lecture held at the
Journ\'ees Relativistes 96.)


title: The mass shell of the universe

abstract:
  The classical field equations of general relativity can be expressed as a
single geodesic equation, describing the free fall of a point particle in
superspace. Based on this formulation, a ``worldline'' quantization of gravity,
analogous to the Feynman-Schwinger treatment of particle propagation, is
proposed, and a hidden mass-shell parameter is identified. We consider the
effective action for the supermetric, which would be induced at one loop. In
certain minisuperspace models, we find that this effective action is stationary
for vanishing cosmological constant.


title:
Slow Roll Inflation in Non-Minimally Coupled Theories: Hyperextended
  Gravity Approach

abstract:
  The slow roll approximation is studied for cosmological models in
Hyperextended Scalar-Tensor Theories of Gravity. A procedure to obtain slow
roll solutions in non-minimally coupled gravity is outlined and some examples
are provided. An integral condition over the functional form of the non-minimal
coupling is imposed in order to obtain intermediate inflationary behavior.


title: Hyperextended Scalar-Tensor Gravity

abstract:
  We study a general Scalar-Tensor Theory with an arbitrary coupling funtion
$\omega (\phi )$ but also an arbitrary dependence of the ``gravitational
constant'' $G(\phi )$ in the cases in which either one of them, or both, do not
admit an analytical inverse, as in the hyperextended inflationary scenario. We
present the full set of field equations and study their cosmological behavior.
We show that different scalar-tensor theories can be grouped in classes with
the same solution for the scalar field.


title: BRST Invariant Boundary Conditions for Gauge Theories

abstract:
  A systematic way of generating sets of local boundary conditions on the gauge
fields in a path integral is presented. These boundary conditions are suitable
for one--loop effective action calculations on manifolds with boundary and for
quantum cosmology. For linearised gravity, the general proceedure described
here leads to new sets of boundary conditions.


title: On Symmetric Gauge Fields for arbitrary Gauge and Symmetry Groups

abstract:
  A classification of the possible symmetric principal bundles with a compact
gauge group, a compact symmetry group and a base manifold which is regularly
foliated by the orbits of the symmetry group is derived. A generalization of
Wang's theorem (classifying the invariant connections) is proven and local
expressions for the gauge potential of an invariant connection are given.


title: Lagrangian perfect fluids and black hole mechanics

abstract:
  The first law of black hole mechanics (in the form derived by Wald), is
expressed in terms of integrals over surfaces, at the horizon and spatial
infinity, of a stationary, axisymmetric black hole, in a diffeomorphism
invariant Lagrangian theory of gravity. The original statement of the first law
given by Bardeen, Carter and Hawking for an Einstein-perfect fluid system
contained, in addition, volume integrals of the fluid fields, over a spacelike
slice stretching between these two surfaces. When applied to the
Einstein-perfect fluid system, however, Wald's methods yield restricted
results. The reason is that the fluid fields in the Lagrangian of a gravitating
perfect fluid are typically nonstationary. We therefore first derive a first
law-like relation for an arbitrary Lagrangian metric theory of gravity coupled
to arbitrary Lagrangian matter fields, requiring only that the metric field be
stationary. This relation includes a volume integral of matter fields over a
spacelike slice between the black hole horizon and spatial infinity, and
reduces to the first law originally derived by Bardeen, Carter and Hawking when
the theory is general relativity coupled to a perfect fluid. We also consider a
specific Lagrangian formulation for an isentropic perfect fluid given by
Carter, and directly apply Wald's analysis. The resulting first law contains
only surface integrals at the black hole horizon and spatial infinity, but this
relation is much more restrictive in its allowed fluid configurations and
perturbations than that given by Bardeen, Carter and Hawking. In the Appendix,
we use the symplectic structure of the Einstein-perfect fluid system to derive
a conserved current for perturbations of this system: this current reduces to
one derived ab initio for this system by Chandrasekhar and Ferrari.


title: Cosmological Einstein-Yang-Mills equations

abstract:
  We use a systematic construction method for invariant connections on
homogeneous spaces to find the Einstein-SU(n)-Yang-Mills equations for
Friedmann-Robertson-Walker and locally rotationally symmetric homogeneous
cosmologies. These connections depend on the choice of a homomorphism from the
isotropy group into the gauge group. We consider here the cases of the gauge
group SU(n) and SO(n) where these homomorphisms correspond to unitary or
orthogonal representations of the isotropy group. For some of the simpler cases
the full system of the evolution equations are derived, for others we only
determine the number of dynamical variables that remain after some mild fixing
of the gauge.


title:
Asymptotically Hyperbolic Non Constant Mean Curvature Solutions of the
  Einstein Constraint Equations

abstract:
  We describe how the iterative technique used by Isenberg and Moncrief to
verify the existence of large sets of non constant mean curvature solutions of
the Einstein constraints on closed manifolds can be adapted to verify the
existence of large sets of asymptotically hyperbolic non constant mean
curvature solutions of the Einstein constraints.


title: Quantum Prediction Algorithms

abstract:
  The consistent histories formulation of the quantum theory of a closed system
with pure initial state defines an infinite number of incompatible consistent
sets, each of which gives a possible description of the physics. We investigate
the possibility of using the properties of the Schmidt decomposition to define
an algorithm which selects a single, physically natural, consistent set. We
explain the problems which arise, set out some possible algorithms, and explain
their properties with the aid of simple models. Though the discussion is framed
in the language of the consistent histories approach, it is intended to
highlight the difficulty in making any interpretation of quantum theory based
on decoherence into a mathematically precise theory.


title: A Comment on The A/4 Black Hole Entropy

abstract:
  Using a simple analysis based on the measurement procedure for a quantized
area we explain the 1/4 factor in the Bekenstein-Hawking black hole formula A/4
for the entropy.


title: The Origin of the Entropy in the Universe

abstract:
  We discuss the entropy generation in quantum tunneling of a relativistic
particle under the influence of a time varying force with the help of squeezing
formalism. It is shown that if one associates classical coarse grained entropy
to the phase space volume, there is an inevitable entropy increase due to the
changes in position and momentum variances. The entropy change can be
quantified by a simple expression $\Delta S=\ln\cosh 2r$, where $r$ is the
squeeze parameter measuring the "height" and "width" of the potential barrier.
We suggest that the universe could have acquired its initial entropy in a
quantum squeeze from "nothing" and briefly discuss the implications of our
proposal.


title:
On a Static Solution to Einstein Equations with incoming and outgoing
  radiation

abstract:
  Einstein equations with $T_{\mu\nu} = k_\mu k_\nu + \ell_\mu \ell_\nu$ where
$k, \ell$ are null are considered with spherical symmetry and staticity. The
solution has naked singularity and is not asymptotically flat. However, it may
be interpreted as an envelope for any static spherical body making it more
massive. Such an interpretation and some of its implications are detailed.


title: Evolution of Close Neutron Star Binaries

abstract:
  We have calculated evolution of neutron star binaries towards the coalescence
driven by gravitational radiation. The hydrodynamical effects as well as the
general relativistic effects are important in the final phase. All corrections
up to post$^{2.5}$-Newtonian order and the tidal effect are included in the
orbital motion. The star is approximated by a simple Newtonian stellar model
called affine star model. Stellar spins and angular momentum are assumed to be
aligned. We have showed how the internal stellar structure affects the stellar
deformation, variations of the spins, and the orbital motion of the binary just
before the contact. The gravitational wave forms from the last a few
revolutions significantly depend on the stellar structure.


title: Structure of the field equations in N = 1 chiral supergravity

abstract:
  We study the structure of linearized field equations in $N = 1$ chiral
supergravity (SUGRA) with a complex tetrad, as a preliminary to introducing
additional auxiliary fields in order that the supersymmetry (SUSY) algebra
close off shell. We follow the first-order formulation we have recently
constructed using the method of the usual $N = 1$ SUGRA. In particular, we see
how the real and imaginary parts of the complex tetrad are coupled to matter
fields in the weak field approximation. Starting from the linearized (free)
theory of $N = 1$ chiral SUGRA, we then construct a Lagrangian which is
invariant under local SUSY transformations to zeroth order of the gravitational
constant, and compare the results with the linearized field equations.


title:
The isometry groups of asymptotically flat, asymptotically empty
  space-times with timelike ADM four-momentum

abstract:
  We give a complete classification of all connected isometry groups, together
with their actions in the asymptotic region, in asymptotically flat,
asymptotically vacuum space--times with timelike ADM four--momentum.


title:
Gravitational waves and pulsating stars: What can we learn from future
  observations?

abstract:
  We present new results for pulsating stars in general relativity. First we
show that the so-called gravitational-wave modes of a neutron star can be
excited when a gravitational wave impinges on the star. Numerical simulations
suggest that the modes may be astrophysically relevant, and we discuss whether
they will be observable with future gravitational-wave detectors. We also
discuss how such observations could lead to estimates of both the radius and
the mass of a neutron star, and thus put constraints on the nuclear equation of
state.


title: Post-Newtonian extension of the Newton-Cartan theory

abstract:
  The theory obtained as a singular limit of General Relativity, if the
reciprocal velocity of light is assumed to tend to zero, is known to be not
exactly the Newton-Cartan theory, but a slight extension of this theory. It
involves not only a Coriolis force field, which is natural in this theory
(although not original Newtonian), but also a scalar field which governs the
relation between Newtons time and relativistic proper time. Both fields are or
can be reduced to harmonic functions, and must therefore be constants, if
suitable global conditions are imposed. We assume this reduction of
Newton-Cartan to Newton`s original theory as starting point and ask for a
consistent post-Newtonian extension and for possible differences to usual
post-Minkowskian approximation methods, as developed, for example, by
Chandrasekhar. It is shown, that both post-Newtonian frameworks are formally
equivalent, as far as the field equations and the equations of motion for a
hydrodynamical fluid are concerned.


title:
Debye Potentials for Maxwell and Dirac Fields from a Generalisation of
  the Killing-Yano Equation

abstract:
  By using conformal Killing-Yano tensors, and their generalisations, we obtain
scalar potentials for both the source-free Maxwell and massless Dirac
equations. For each of these equations we construct, from conformal
Killing-Yano tensors, symmetry operators that map any solution to another.


title: Gravitational Calorimetry

abstract:
  I generalize the quasilocal formulation of thermodynamics of Brown and York
to include dilaton theories of gravity as well as Abelian and Yang-Mills gauge
matter fields with possible dilaton couplings. The resulting formulation is
applicable to a large class of theories including two-dimensional toy models
and the low energy limit of string theory as well as to many types of matter
such as massless scalar fields, electromagnetism, Yang-Mills fields, and matter
induced cosmological constants. I use this formalism to evaluate the
thermodynamic variables for several black hole spacetimes. I find that the
formulation can handle black hole spacetimes that are not asymptotically flat
as well as rotating black hole spacetimes, and black hole spacetimes possessing
a dilaton field, an electric charge, and a magnetic charge.


title:
Gravitational Radiation from the Coalescence of Binary Neutron Stars:
  Effects Due to the Equation of State, Spin, and Mass Ratio

abstract:
  We calculate the gravitational radiation produced by the coalescence of
inspiraling binary neutron stars in the Newtonian regime using 3-dimensional
numerical simulations. The stars are modeled as polytropes and start out in the
point-mass regime at wide separation. The hydrodynamic integration is performed
using smooth particle hydrodynamics (SPH) with Newtonian gravity, and the
gravitational radiation is calculated using the quadrupole approximation. We
have run a number of simulations varying the neutron star radii, equations of
state, spins, and mass ratio. The resulting gravitational waveforms and spectra
are rich in information about the hydrodynamics of coalescence, and show
characteristic dependence on GM/Rc^2, the equation of state, and the mass
ratio.


title: Pair Creation of Dilaton Black Holes in Extended Inflation

abstract:
  Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.


title:
Gravitational waves propagating into Friedmann--Robertson--Walker
  universes

abstract:
  We consider space-times with two isometries which represent gravitational
waves with distinct wavefronts which propagate into exact
Friedmann-Robertson-Walker (FRW) universes. The geometry of possible wavefronts
is analysed in detail in all three types of FRW models. In the spatially flat
and open universes, the wavefronts can be planar or cylindrical; in the closed
case they are toroidal. Exact solutions are given which describe gravitational
waves propagating into the FRW universes with a fluid with a stiff equation of
state. It is shown that the plane-fronted waves may include impulsive or step
(shock) components, while the cylindrical waves in the spatially flat and open
universes and the toroidal waves in closed universes may contain steps. In
general, wavefronts may exist which have an arbitrary finite degree of
smoothness. In all cases, the waves are backscattered. The head-on collision of
such waves is also briefly mentioned.


title: A Harmonic Space Approach to Spherically Symmetric Quantum Gravity

abstract:
  After dimensional reduction the stationary spherically symmetric sector of
Einstein's gravity is identified with an SL(2,R)/SO(2) Sigma model coupled to a
one dimensional gravitational remnant. The space of classical solutions
consists of a one parameter family interpolating between the Schwarzschild and
the Taub-NUT solution. A Dirac Quantization of this system is performed and the
observables -- the Schwarzschild mass and the Taub-NUT charge operator -- are
shown to be self-adjoint operators with a continuous spectrum ranging from
$-\infty$ to $\infty$. The Hilbert space is constructed explicitely using a
harmonic space approach.


title: Quantum theory requires gravity and superrelativity

abstract:
  The ordinary quantum theory points out that general relativity is negligible
for spatial distances up to the Planck scale. Consistency in the foundations of
the quantum theory requires a``soft'' spacetime structure of the general
relativity at essentially longer length. However, for some reasons this appears
to be not enough. A new framework (``superrelativity'') for the desirable
generalization of the foundation of quantum theory is proposed. A generalized
non-linear Klein-Gordon equation has been derived in order to shape a stable
wave packet.


title: Time dependent Green functions from Wheeler De Witt solutions

abstract:
  The aim of this article is twofold. First we examine from a new angle the
question of recovery of time in quantum cosmology. We construct Green functions
for matter fields from the solutions of the Wheeler De Witt equation. For
simplicity we work in a mini-superspace context. By evaluating these Green
functions in a first order development of the energy ``increment'' induced by
matrix elements of field operators, we show that the background geometry is the
solution of Einstein equations driven by the mean matter energy and that it is
this background which determines the time lapses separating the field
operators. Then, by studying higher order corrections, we clarify the nature of
the small dimensionless parameters which guarantee the validity of the
approximations used. In this respect, we show that the formal expansion in the
inverse Planck mass which is sometime presented as the ``standard procedure''
is illegitimate. Secondly, by the present analysis of Green functions, we
prepare the study of quantum matter transitions in quantum cosmology. In a next
article, we show that the time parametrization of transition amplitudes appears
for the same reasons that it appeared in this article. This proves that the
background is dynamically determined by the transition under examination.


title: Time dependent perturbation theory from Wheeler De Witt solutions

abstract:
  We describe radiative processes in Quantum Cosmology, from the solutions of
the Wheeler De Witt equation. By virtue of this constraint equation, the
quantum propagation of gravity is modified by the matter interaction
hamiltonian at the level of amplitudes. In this we generalize previous works
where gravity was coupled only to expectation values of matter operators. By a
``reduction formula'' we show how to obtain transition amplitudes from the
entangled gravity+matter system. Then we show how ``each'' transition among
matter constituents of the universe determines dynamically ``its'' background
from which a time parameter is defined. Finally, we leave the mini-superspace
context by introducing an extended formalism in which the momenta of the
exchanged quanta no longer vanish. Then, the concept of spatial displacement
emerges from radiative processes like the time parametrization did, thereby
unifying the way by which space and time intervals are recovered in quantum
cosmology.


title: Geometro-Stochastically Quantized Fields with Internal Spin Variables

abstract:
  The use of internal variables for the description of relativistic particles
with arbitrary mass and spin in terms of scalar functions is reviewed and
applied to the stochastic phase space formulation of quantum mechanics.
Following Bacry and Kihlberg a four-dimensional internal spin space $\bar S$ is
chosen possessing an invariant measure and being able to represent integer as
well as half integer spins. $\bar S$ is a homogeneous space of the group $SL(2,
C)$ parametrized in terms of spinors $\a\in C_2$ and their complex conjugates
$\bar\a$. The generalized scalar quantum mechanical wave functions may be
reduced to yield irreducible components of definite physical mass and spin
$[m,s]$, with $m\ge 0$ and $s=0, 1/2, 1, 3/2 ...$, with spin described in terms
of the usual $(2s+1)$-component fields. Viewed from the internal space
description of spin this reduction amounts to a restriction of the variable
$\a$ to a compact subspace of $\bar S$, i.e. a ``spin shell'' $S^2_{r=2s}$ of
radius $r=2s$ in $ C_2$. This formulation of single particles or single
antiparticles of type $[m,s]$ is then used to study the geometro- stochastic
(i.e. quantum) propagation of amplitudes for arbitrary spin on a curved
background space-time possessing a metric and axial vector torsion treated as
external fields. A Poincar\'e gauge covariant path integral-like representation
for the probability amplitude (generalized wave function) of a particle with
arbitrary spin is derived satisfying a second order wave equation on the
Hilbert bundle constructed over curved space-time. The implications for the
stochastic nature of polarization effects in the presence of gravitation are
pointed out and the extension to Fock bundles of bosonic and fermionic type is
briefly mentioned.


title:
Postrelativity --- A Paradigm For Quantization With Preferred Newtonian
  Frame

abstract:
  We define a new paradigm --- postrelativity --- based on the hypothesis of a
preferred hidden Newtonian frame in relativistic theories. It leads to a
modification of general relativity with ether interpretation, without
topological problems, black hole and big bang singularities. Semiclassical
theory predicts Hawking radiation with evaporation before horizon formation. In
quantum gravity there is no problem of time and topology. Configuration space
and quasiclassical predictions are different from canonical quantization of
general relativity. Uncertainty of the light cone or an atomic structure of the
ether may solve ultraviolet problems. The similar concept for gauge fields
leads to real, physical gauge potential without Faddeev-Popov ghost fields and
Gribov copy problem.


title: A detailed study of quasinormal frequencies of the Kerr black hole

abstract:
  We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the $n=8$ quasinormal frequency only at the
Schwarzschild limit.


title: Gravitational Forces with Strongly Localized Retardation

abstract:
  We solve the linearized Einstein equations for a specific oscillating mass
distribution and discuss the usual counterarguments against the existence of
observable gravitational retardations in the "near zone", where d/r << 1 (d =
oscillation amplitude of the source, r = distance from the source). We show
that they do not apply in the region d/r \approx 1, and prove that
gravitational forces are retarded in the immediate vicinity of the source. An
experiment to measure this retardation is proposed, which may provide the first
direct experimental observation of propagating gravitational fields.


title: Back-reaction of a conformal field on a three-dimensional black hole

abstract:
  The first order corrections to the geometry of the (2+1)-dimensional black
hole due to back-reaction of a massless conformal scalar field are computed.
The renormalized stress energy tensor used as the source of Einstein equations
is computed with the Green function for the black-hole background with
transparent boundary conditions. This tensor has the same functional form as
the one found in the nonperturbative case which can be exactly solved. Thus, a
static, circularly symmetric and asymptotically anti-de Sitter black hole
solution of the semiclassical equations is found. The corrections to the
thermodynamic quantities are also computed.


title: Are Higher Order Membranes stable in Black Hole Spacetimes?

abstract:
  We continue the study of the existence and stability of static spherical
membrane configurations in curved spacetimes. We first consider higher order
membranes described by a Lagrangian which, besides the Dirac term, includes a
term proportional to the scalar curvature of the world--volume ${}^{(3)}R$.
Notably, in this case, the equations of motion can be reduced to second order
ones and an effective potential analysis can be made. The conditions for
stability are then explicitly derived. We find a self--consistent static
spherical membrane, determining the spacetime generated by the membrane itself.
In this case we find, however, that the total energy of the membrane has to be
negative, and no {\it stable} equilibrium can be achieved. We then generalize
the discussion to a membrane described by a Lagrangian including all possible
second derivative terms. We conclude the paper with some discussion on the
generality of the results obtained.


title: On parameters of the Levi-Civita solution

abstract:
  The Levi-Civita (LC) solution is matched to a cylindrical shell of an
anisotropic fluid. The fluid satisfies the energy conditions when the mass
parameter $\sigma$ is in the range $0 \le \sigma \le 1$. The mass per unit
length of the shell is given explicitly in terms of $\sigma$, which has a
finite maximum. The relevance of the results to the non-existence of horizons
in the LC solution and to gauge cosmic strings is pointed out.


title:
An axiomatic approach to electromagnetic and gravitational radiation
  reaction of particles in curved spacetime

abstract:
  The problem of determining the electromagnetic and gravitational
``self-force'' on a particle in a curved spacetime is investigated using an
axiomatic approach. In the electromagnetic case, our key postulate is a
``comparison axiom'', which states that whenever two particles of the same
charge $e$ have the same magnitude of acceleration, the difference in their
self-force is given by the ordinary Lorentz force of the difference in their
(suitably compared) electromagnetic fields. We thereby derive an expression for
the electromagnetic self-force which agrees with that of DeWitt and Brehme as
corrected by Hobbs. Despite several important differences, our analysis of the
gravitational self-force proceeds in close parallel with the electromagnetic
case. In the gravitational case, our final expression for the (reduced order)
equations of motion shows that the deviation from geodesic motion arises
entirely from a ``tail term'', in agreement with recent results of Mino et al.
Throughout the paper, we take the view that ``point particles'' do not make
sense as fundamental objects, but that ``point particle equations of motion''
do make sense as means of encoding information about the motion of an extended
body in the limit where not only the size but also the charge and mass of the
body go to zero at a suitable rate. Plausibility arguments for the validity of
our comparison axiom are given by considering the limiting behavior of the
self-force on extended bodies.


title: Diagonal quantum Bianchi type IX models in N=1 supergravity

abstract:
  We take the general quantum constraints of N=1 supergravity in the special
case of a Bianchi metric, with gravitino fields constant in the invariant
basis. We construct the most general possible wave function which solves the
Lorentz constraints and study the supersymmetry constraints in the Bianchi
Class A Models. For the Bianchi-IX cases, both the Hartle-Hawking state and
wormhole state are found to exist in the middle fermion levels.


title: Black Hole Radiation inside Apparent Horizon in Quantum Gravity

abstract:
  We study a black hole radiation inside the apparent horizon in quantum
gravity. First we perform a canonical quantization for spherically symmetric
geometry where one of the spatial coordinates is dealt as the time variable
since we would like to consider the interior region of a black hole. Next this
rather general formalism is applied for a specific model where the ingoing
Vaidya metric is used as a simple model of an evaporating black hole. Following
Tomimatsu's idea, we will solve analytically the Wheeler-DeWitt equation in the
vicinity of the apparent horizon and see that mass-loss rate of a black hole by
thermal radiation is equal to the result obtained by Hawking in his
semiclassical treatment. The present formalism may have a wide application in
quantum gravity inside the horizon of a black hole such as mass inflation and
strong cosmic censorship etc.


title: A toy model for slowly growing wormholes as effective topology changes

abstract:
  We present a toy model for growing wormholes as a model of effective
low-energy topology changes. We study the propagation of quantum fields on a
$1+1$ spacetime analogous to the trouser-leg topology change. A low-energy
effective topology change is produced by a physical model which corresponds to
a barrier smoothly changing the tunneling probability between two spatial
regions.


title: Dynamics of Gravitational Waves in 3D: Formulations, Methods, and Tests

abstract:
  The dynamics of gravitational waves is investigated in full 3+1 dimensional
numerical relativity, emphasizing the difficulties that one might encounter in
numerical evolutions, particularly those arising from non-linearities and gauge
degrees of freedom. Using gravitational waves with amplitudes low enough that
one has a good understanding of the physics involved, but large enough to
enable non-linear effects to emerge, we study the coupling between numerical
errors, coordinate effects, and the nonlinearities of the theory. We discuss
the various strategies used in identifying specific features of the evolution.
We show the importance of the flexibility of being able to use different
numerical schemes, different slicing conditions, different formulations of the
Einstein equations (standard ADM vs. first order hyperbolic), and different
sets of equations (linearized vs. full Einstein equations). A non-linear scalar
field equation is presented which captures some properties of the full Einstein
equations, and has been useful in our understanding of the coupling between
finite differencing errors and non-linearites. We present a set of monitoring
devices which have been crucial in our studying of the waves, including Riemann
invariants, pseudo-energy momentum tensor, hamiltonian constraint violation,
and fourier spectrum analysis.


title:
Gravitational waves from binary systems in circular orbits: Does the
  post-Newtonian expansion converge?

abstract:
  Gravitational radiation can be expressed in terms of an infinite series of
radiative, symmetric trace-free (STF) multipole moments which can be connected
to the behavior of the source. We consider a truncated model for gravitational
radiation from binary systems in which each STF mass and current moment of
order l is given by the lowest-order, Newtonian-like l-pole moment of the
orbiting masses; we neglect post-Newtonian corrections to each STF moment.
Specializing to orbits which are circular (apart from the radiation-induced
inspiral), we find an explicit infinite series for the energy flux in powers of
$v/c$, where v is the orbital velocity. We show that the series converges for
all values $v/c < 2/e$ when one mass is much smaller than the other, and $v/c <
4/e$ for equal masses,where e is the base of natural logarithms. These values
include all physically relevant values for compact binary inspiral. This
convergence cannot indicate whether or not the full series (obtained from the
exact moments) will converge. But if the full series does not converge, our
analysis shows that this failure to converge does not originate from summing
over the Newtonian part of the multipole moments.


title:
Cosmological Gravitational Wave in a Gravity with Quadratic Order
  Curvature Couplings

abstract:
  We present a set of equations describing the cosmological gravitational wave
in a gravity theory with quadratic order gravitational coupling terms which
naturally arise in quantum correction procedures. It is known that the
gravitational wave equation in the gravity theories with a general $f(R)$ term
in the action leads to a second order differential equation with the only
correction factor appearing in the damping term. The case for a $R^{ab} R_{ab}$
term is completely different. The gravitational wave is described by a fourth
order differential equation both in time and space. However, curiously, we find
that the contributions to the background evolution are qualitatively the same
for both terms.


title: Quantized gravitational waves in the Milne universe

abstract:
  The quantization of gravitational waves in the Milne universe is discussed.
The relation between positive frequency functions of the gravitational waves in
the Milne universe and those in the Minkowski universe is clarified.
Implications to the one-bubble open inflation scenario are also discussed.


title: Kinematic Self-Similarity

abstract:
  Self-similarity in general relativity is briefly reviewed and the differences
between self-similarity of the first kind and generalized self-similarity are
discussed. The covariant notion of a kinematic self-similarity in the context
of relativistic fluid mechanics is defined. Various mathematical and physical
properties of spacetimes admitting a kinematic self-similarity are discussed.
The governing equations for perfect fluid cosmological models are introduced
and a set of integrability conditions for the existence of a proper kinematic
self-similarity in these models is derived. Exact solutions of the irrotational
perfect fluid Einstein field equations admitting a kinematic self-similarity
are then sought in a number of special cases, and it is found that; (1) in the
geodesic case the 3-spaces orthogonal to the fluid velocity vector are
necessarily Ricci-flat and (ii) in the further specialisation to dust the
differential equation governing the expansion can be completely integrated and
the asymptotic properties of these solutions can be determined, (iii) the
solutions in the case of zero-expansion consist of a class of shear-free and
static models and a class of stiff perfect fluid (and non-static) models, and
(iv) solutions in which the kinematic self-similar vector is parallel to the
fluid velocity vector are necessarily Friedmann-Robertson-Walker (FRW) models.


title:
Comment on `Smooth and Discontinuous Signature Type Change in General
  Relativity'

abstract:
  Kossowski and Kriele derived boundary conditions on the metric at a surface
of signature change. We point out that their derivation is based not only on
certain smoothness assumptions but also on a postulated form of the Einstein
field equations. Since there is no canonical form of the field equations at a
change of signature, their conclusions are not inescapable. We show here that a
weaker formulation is possible, in which less restrictive smoothness
assumptions are made, and (a slightly different form of) the Einstein field
equations are satisfied. In particular, in this formulation it is possible to
have a bounded energy-momentum tensor at a change of signature without
satisfying their condition that the extrinsic curvature vanish.


title: Gravity and Signature Change

abstract:
  The use of proper ``time'' to describe classical ``spacetimes'' which contain
both Euclidean and Lorentzian regions permits the introduction of smooth
(generalized) orthonormal frames. This remarkable fact permits one to describe
both a variational treatment of Einstein's equations and distribution theory
using straightforward generalizations of the standard treatments for constant
signature.


title: Einstein's Equations in the Presence of Signature Change

abstract:
  We discuss Einstein's field equations in the presence of signature change
using variational methods, obtaining a generalization of the Lanczos equation
relating the distributional term in the stress tensor to the discontinuity of
the extrinsic curvature. In particular, there is no distributional term in the
stress tensor, and hence no surface layer, precisely when the extrinsic
curvature is continuous, in agreement with the standard result for constant
signature.


title: Chaos in Static Axisymmetric Spacetimes II : non-vacuum case

abstract:
  We examine the effect of local matter on the chaotic behavior of a
relativistic test particle in non-vacuum static axisymmetric spacetimes. We
find that the sign of the sectional curvature in the geodesic deviation
equation defined by the Riemann curvature does not always become a good tool to
judge the occurrence of chaos in the non-vacuum case. However, we show that the
locally unstable region ( LU region ) defined by the Weyl curvature can provide
information about chaos even in non-vacuum spacetime as well as in vacuum
spacetime. Since the Weyl tensor affects only the shear part of the geodesic
congruence, it works effectively to stretch some directions of geodesic
congruence, which helps to cause the chaotic behavior of geodesics. Actually,
the orbit moving around an unstable periodic orbit (UPO) becomes strongly
chaotic if it passes through an LU region, which means that the LU region can
be used as a good tool to know in which situation the chaos by homoclinic
mixing occurs around a UPO.


title: Does matter differ from vacuum?

abstract:
  A structured collection of thought provoking conclusions about space and time
is given. Using only the Compton wavelength lambda = hbar / m c and the
Schwarzschild radius r_s = 2 G m / c^2, it is argued that neither the
continuity of space-time nor the concepts of space-point, instant, or point
particle have experimental backing at high energies. It is then deduced that
Lorentz, gauge, and discrete symmetries are not precisely fulfilled in nature.
In the same way, using a simple and new Gedankenexperiment, it is found that at
Planck energies, vacuum is fundamentally indistinguishable from radiation and
from matter. Some consequences for supersymmetry, duality, and unification are
presented.


title: Stochastic Gravity

abstract:
  Gravity is treated as a stochastic phenomenon based on fluctuations of the
metric tensor of general relativity. By using a (3+1) slicing of spacetime, a
Langevin equation for the dynamical conjugate momentum and a Fokker-Planck
equation for its probability distribution are derived. The Raychaudhuri
equation for a congruence of timelike or null geodesics leads to a stochastic
differential equation for the expansion parameter $\theta$ in terms of the
proper time $s$. For sufficiently strong metric fluctuations, it is shown that
caustic singularities in spacetime can be avoided for converging geodesics. The
formalism is applied to the gravitational collapse of a star and the
Friedmann-Robertson-Walker cosmological model. It is found that owing to the
stochastic behavior of the geometry, the singularity in gravitational collapse
and the big-bang have a zero probability of occurring. Moreover, as a star
collapses the probability of a distant observer seeing an infinite red shift at
the Schwarzschild radius of the star is zero. Therefore, there is a vanishing
probability of a Schwarzschild black hole event horizon forming during
gravitational collapse.


title: The Case for a Gravitational de Sitter Gauge Theory

abstract:
  With the exception of gravitation, the known fundamental interactions of
Nature are mediated by gauge fields. A comparison of the candidate groups for a
gauge theory possibly describing gravitation favours the Poincar\'e group as
the obvious choice. This theory gives Einstein's equations in a particular
case, and Newton's law in the static non-relativistic limit, being seemingly
sound at the classical level. But it comes out that it is not quantizable. The
usual procedure of adding counterterms to make it a consistent and
renormalizable theory leads to two possible theories, one for each of the two
de Sitter groups, SO(4,1) and SO(3,2). The consequences of changing from the
Poincar\'e to the de Sitter group, as well as the positive aspects,
perspectives and drawbacks of the resulting theory are discussed.


title: Echoing and scaling in Einstein-Yang-Mills critical collapse

abstract:
  We confirm recent numerical results of echoing and mass scaling in the
gravitational collapse of a spherical Yang-Mills field by constructing the
critical solution and its perturbations as an eigenvalue problem. Because the
field equations are not scale-invariant, the Yang-Mills critical solution is
asymptotically, rather than exactly, self-similar, but the methods for dealing
with discrete self-similarity developed for the real scalar field can be
generalized. We find an echoing period Delta = 0.73784 +/- 0.00002 and critical
exponent for the black hole mass gamma = 0.1964 +/- 0.0007.


title: Brans-Dicke wormholes in nonvacuum spacetime

abstract:
  Analytical wormhole solutions in Brans-Dicke theory in the presence of matter
are presented. It is shown that the wormhole throat must not be necessarily
threaded with exotic matter.


title: Hamiltonian thermodynamics of a Lovelock black hole

abstract:
  We consider the Hamiltonian dynamics and thermodynamics of spherically
symmetric spacetimes within a one-parameter family of five-dimensional Lovelock
theories. We adopt boundary conditions that make every classical solution part
of a black hole exterior, with the spacelike hypersurfaces extending from the
horizon bifurcation three-sphere to a timelike boundary with fixed intrinsic
metric. The constraints are simplified by a Kucha\v{r}-type canonical
transformation, and the theory is reduced to its true dynamical degrees of
freedom. After quantization, the trace of the analytically continued Lorentzian
time evolution operator is interpreted as the partition function of a
thermodynamical canonical ensemble. Whenever the partition function is
dominated by a Euclidean black hole solution, the entropy is given by the
Lovelock analogue of the Bekenstein-Hawking entropy; in particular, in the low
temperature limit the system exhibits a dominant classical solution that has no
counterpart in Einstein's theory. The asymptotically flat space limit of the
partition function does not exist. The results indicate qualitative robustness
of the thermodynamics of five-dimensional Einstein theory upon the addition of
a nontrivial Lovelock term.


title: D-Dimensional Radiative Plasma: A Kinetic Approach

abstract:
  The covariant kinetic approach for the radiative plasma, a mixture of a
relativistic moving gas plus radiation quanta (photons, neutrinos, or
gravitons) is generalized to D spatial dimensions. The operational and physical
meaning of Eckart's temperature is reexamined and the D-dimensional expressions
for the transport coefficients (heat conduction, bulk and shear viscosity) are
explicitly evaluated to first order in the mean free time of the radiation
quanta. Weinberg's conclusion that the mixture behaves like a relativistic
imperfect simple fluid (in Eckart's formulation) depends neither on the number
of spatial dimensions nor on the details of the collisional term. The case of
Thomson scaterring is studied in detail, and some consequences for higher
dimensional cosmologies are also discussed.


title: Toposes in General Theory of Relativity

abstract:
  We study in this paper different topos-theoretical approaches to the problem
of construction of General Theory of Relativity. In general case the resulting
space-time theory will be non-classical, different from that of the usual
Einstein theory of space-time. This is a new theory of space-time, created in a
purely logical manner. Four possibitities are investigated: axiomatic approach
to causal theory of space-time, the smooth toposes as a models of Theory of
Relativity, Synthetic Theory of Relativity, and space-time as Grothendieck
topos.


title: Gravitational Geons Revisited

abstract:
  A careful analysis of the gravitational geon solution found by Brill and
Hartle is made. The gravitational wave expansion they used is shown to be
consistent and to result in a gauge invariant wave equation. It also results in
a gauge invariant effective stress-energy tensor for the gravitational waves
provided that a generalized definition of a gauge transformation is used. To
leading order this gauge transformation is the same as the usual one for
gravitational waves. It is shown that the geon solution is a self-consistent
solution to Einstein's equations and that, to leading order, the equations
describing the geometry of the gravitational geon are identical to those
derived by Wheeler for the electromagnetic geon. An appendix provides an
existence proof for geon solutions to these equations.


title: Comment on "Spacetime Information"

abstract:
  A recent paper by Hartle [Phys. Rev. D 51, 1800 (1995)] proposes a definition
of "spacetime information" - the information available about a quantum system's
boundary conditions in the various sets of decohering histories it may display
- and investigates its properties. We note here that Hartle's analysis contains
errors which invalidate several of the conclusions. In particular, the proof
that the proposed definition agrees with the standard definition for ordinary
quantum mechanics is invalid, the evaluations of the spacetime information for
time-neutral generalized quantum theories and for generalized quantum theories
with non-unitary evolution are incorrect, and the argument that spacetime
information is conserved on spacelike surfaces in these last theories is
erroneous. We show however that the proposed definition does, in fact, agree
with the standard definition for ordinary quantum mechanics. Hartle's
definition relies on choosing, case by case, a class of fine-grained consistent
sets of histories. We supply a general definition of the relevant class of sets
that agrees with Hartle's definition in the cases explicitly considered and
that generalizes to other cases.


title:
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems: The
  Black Hole Regime

abstract:
  The Cauchy+characteristic matching (CCM) problem for the scalar wave equation
is investigated in the background geometry of a Schwarzschild black hole.
Previously reported work developed the CCM framework for the coupled
Einstein-Klein-Gordon system of equations, assuming a regular center of
symmetry. Here, the time evolution after the formation of a black hole is
pursued, using a CCM formulation of the governing equations perturbed around
the Schwarzschild background. An extension of the matching scheme allows for
arbitrary matching boundary motion across the coordinate grid. As a proof of
concept, the late time behavior of the dynamics of the scalar field is
explored. The power-law tails in both the time-like and null infinity limits
are verified.


title: Master Equations and Majorana Spinors

abstract:
  I describe how the states of a discrete automata with p sites, each of which
may be off or on, can be represented as Majorana spinors associated to a
spacetime with signature (p,p). Some ideas about the quantization of such
systems are discussed and the relationship to some unconventional formulations
and generalizations of quantum mechanics, particularly Jordan's spinorial
quantum mechanics are pointed out. A connection is made to the problem of time
and the complex numbers in quantum gravity.


title: Integrability of irrotational silent cosmological models

abstract:
  We revisit the issue of integrability conditions for the irrotational silent
cosmological models. We formulate the problem both in 1+3 covariant and 1+3
orthonormal frame notation, and show there exists a series of constraint
equations that need to be satisfied. These conditions hold identically for
FLRW-linearised silent models, but not in the general exact non-linear case.
Thus there is a linearisation instability, and it is highly unlikely that there
is a large class of silent models. We conjecture that there are no spatially
inhomogeneous solutions with Weyl curvature of Petrov type I, and indicate
further issues that await clarification.


title: Local freedom in the gravitational field

abstract:
  In a cosmological context, the electric and magnetic parts of the Weyl
tensor, E_{ab} and H_{ab}, represent the locally free curvature - i.e. they are
not pointwise determined by the matter fields. By performing a complete
covariant decomposition of the derivatives of E_{ab} and H_{ab}, we show that
the parts of the derivative of the curvature which are locally free (i.e. not
pointwise determined by the matter via the Bianchi identities) are exactly the
symmetrised trace-free spatial derivatives of E_{ab} and H_{ab} together with
their spatial curls. These parts of the derivatives are shown to be crucial for
the existence of gravitational waves.


title:
The Electrically Charged Extreme BTZ Black Hole with Self (Anti-self)
  Dual Maxwell Field

abstract:
  Recently M. Kamata and T. Koikawa claimed to obtain the charged version of
the spinning BTZ black hole solution by assuming an (anti-) self dual condition
imposed on the orthonormal basis components of the electric and magnetic
fields. We point out that the Kamata-Koikawa field is not a solution of the
Einstein-Maxwell equations and we find the correct solution of the studied
problem. It is shown that a duality mapping exists among spinning solutions
obtained from electrostatic and magnetostatic fields with the help of the local
transformation $t\longrightarrow t-\omega \theta \theta \longrightarrow \theta
-\omega t.$


title: Singularities in Silent Universes: State of the Art

abstract:
  After a brief overview of the so-called silent models and their present
status, we consider the subclass of Bianchi Type--I models with a magnetic
field source. Due to the presence of the magnetic field, the initial
singularity shows ``oscillatory'' features reminiscent of the Bianchi Type--IX
case. The Bianchi Type--I models with a magnetic field are therefore a
counterexample to the folklore that matter fields can be neglected in the
vicinity of the singularity.


title: Decomposition and unitarity in quantum cosmology

abstract:
  Considering quantum cosmological minisuperspace models with positive
potential, we present evidence that
  (i) despite common belief there are perspectives for defining a unique,
naturally preferred decomposition of the space H of wave functions into two
subspaces H^\pm that generalizes the concept of positive and negative
frequency, and that
  (ii) an underlying unitary evolution within these two subspaces exists and
may be described in analogy to the representation of a geometric object in
local coordinates: it is associated with the choice of a congruence of
classical trajectories endowed with a suitable weight (such a setting is called
WKB-branch).
  The transformation properties of various quantities under a variation of the
WKB-branch provide the tool for defining the decomposition. The construction
leads to formal series whose actual convergence seems to require additional
conditions on the model (related to global geometric issues and possibly to
analyticity). It is speculated that this approach might relate to the refined
algebraic quantization program.


title: Exact Inhomogeneous Cosmological Models

abstract:
  We present new exact inhomogeneous vacuum cosmological solutions of
Einstein's equations. They provide new information about the nature of general
cosmological solutions to Einstein's equations.


title:
Exact Solution for the Metric and the Motion of Two Bodies in (1+1)
  Dimensional Gravity

abstract:
  We present the exact solution of two-body motion in (1+1) dimensional dilaton
gravity by solving the constraint equations in the canonical formalism. The
determining equation of the Hamiltonian is derived in a transcendental form and
the Hamiltonian is expressed for the system of two identical particles in terms
of the Lambert $W$ function. The $W$ function has two real branches which join
smoothly onto each other and the Hamiltonian on the principal branch reduces to
the Newtonian limit for small coupling constant. On the other branch the
Hamiltonian yields a new set of motions which can not be understood as
relativistically correcting the Newtonian motion. The explicit trajectory in
the phase space $(r, p)$ is illustrated for various values of the energy. The
analysis is extended to the case of unequal masses. The full expression of
metric tensor is given and the consistency between the solution of the metric
and the equations of motion is rigorously proved.


title:
An exact self-consistent gravitational shock wave in semiclassical
  gravity

abstract:
  We find a self-consistent pp-gravitational shock wave solution to the
semiclassical Einstein equations resulting from the $1/N$ approach to the
effective action. We model the renormalized matter stress-energy-momentum
tensor by $N$ massless scalar fields in the Minkowski vacuum plus a classical
particle. We show that quantum effects generate a milder singularity at the
position of the particle than the classical solution, but the singularity does
not disappear. At large distances from the particle, the quantum correction
decreases slowly, as $1/\rho^2$ ($\rho$ being the distance to the particle in
the shock wave plane). We argue that this large distance correction is a
necessary consequence of quantum gravity.


title: About Time

abstract:
  The concept of time is discussed in the context of the canonical formulation
of the gravitational field. Using a hypersurface orthogonal foliation, the
arbitrariness of the lapse function is eliminated and the shift vector
vanishes, allowing a consistent definition of time.


title: On Relation between String Theory and Multidimensional Cosmology

abstract:
  It is shown that a transition from a multidimensional cosmological model with
one internal space of the dimension d_1 to the effective tree-level bosonic
string corresponds to an infinite number of the internal dimensions: d_1 ->
infinity.


title:
Fluctuations of the vacuum energy density of quantum fields in curved
  spacetime via generalized zeta functions

abstract:
  For quantum fields on a curved spacetime with an Euclidean section, we derive
a general expression for the stress energy tensor two-point function in terms
of the effective action. The renormalized two-point function is given in terms
of the second variation of the Mellin transform of the trace of the heat kernel
for the quantum fields. For systems for which a spectral decomposition of the
wave opearator is possible, we give an exact expression for this two-point
function. Explicit examples of the variance to the mean ratio $\Delta' =
(<\rho^2>-<\rho>^2)/(<\rho>^2)$ of the vacuum energy density $\rho$ of a
massless scalar field are computed for the spatial topologies of $R^d\times
S^1$ and $S^3$, with results of $\Delta'(R^d\times S^1) =(d+1)(d+2)/2$, and
$\Delta'(S^3) = 111$ respectively. The large variance signifies the importance
of quantum fluctuations and has important implications for the validity of
semiclassical gravity theories at sub-Planckian scales. The method presented
here can facilitate the calculation of stress-energy fluctuations for quantum
fields useful for the analysis of fluctuation effects and critical phenomena in
problems ranging from atom optics and mesoscopic physics to early universe and
black hole physics.


title:
Radiative processes for Rindler and accelerating observers and the
  stress-tensor detector

abstract:
  We consider a monopole detector interacting with a massive scalar field. The
radiative processes are discussed from the accelerated frame point of view.
After this, we obtain the Minkowski vacuum stress tensor measured by the
accelerated observer using a non-gravitational stress tensor detector as
discussed by Ford and Roman (PRD 48, 776 (1993)). Finally, we analyse radiative
processes of the monopole detector travelling in a world line that is inertial
in the infinite past and has a constant proper acceleration in the infinite
future.


title: Analytic Solutions of the Teukolsky Equation and their Properties

abstract:
  The analytical solutions reported in our previous paper are given as series
of hypergeometric or Coulomb wave functions. By using them, we can get the
Teukolsky functions analytically in a desired accuracy. For the computation,
the deep understanding of their properties is necessary. We summarize the main
result: The relative normalization between the solutions with a spin weight s
and -s is given analytically by using the Teukolsky-Starobinsky (T-S)
identities. By examining the asymptotic behaviors of our solution and combined
with the T-S identities and the Wronskian, we found nontrivial identities
between the sums of coefficients of the series. These identities will serve to
make various expression in simpler forms and also become a powerful tool to
test the accuracy of the computation. As an application, we investigated the
absorption rate and the evaporation rate of black hole and obtain interesting
analytic results.


title: An Extension of Multiple Cosmic String Solution: A Proposal

abstract:
  We extend the work done for cosmic strings and show that for a more general
class of locally flat metrics the one loop calculation do not introduce any new
divergences to the VEV of the energy of a scalar particle. We explicitly
perform the calculation for the configuration where we have one cosmic string
in the presence of a dipole made out of cosmic strings.


title:
Enlarged Bound on the Measurability of Distances and Quantum
  $\kappa$-Poincar\`e Group

abstract:
  When quantum mechanical and general relativistic effects are taken into
account in the analysis of distance measurements, one finds a measurability
bound. I observe that some of the structures that have been encountered in the
literature on the Quantum $\kappa$-Poincar\`e Group naturally lead to this
bound.


title: New Proof of the Generalized Second Law

abstract:
  The generalized second law of black hole thermodynamics was proved by Frolov
and Page for a quasi-stationary eternal black hole. However, realistic black
holes arise from a gravitational collapse, and in this case their proof does
not hold. In this paper we prove the generalized second law for a
quasi-stationary black hole which arises from a gravitational collapse.


title: Gravitational interaction to one loop in effective quantum gravity

abstract:
  We carry out the first step of a program conceived, in order to build a
realistic model, having the particle spectrum of the standard model and
renormalized masses, interaction terms and couplings, etc. which include the
class of quantum gravity corrections, obtained by handling gravity as an
effective theory. This provides an adequate picture at low energies, i.e. much
less than the scale of strong gravity (the Planck mass). Hence our results are
valid, irrespectively of any proposal for the full quantum gravity as a
fundamental theory. We consider only non-analytic contributions to the one-loop
scattering matrix elements, which provide the dominant quantum effect at long
distance. These contributions are finite and independent from the finite value
of the renormalization counter terms of the effective lagrangian. We calculate
the interaction of two heavy scalar particles, i.e. close to rest, due to the
effective quantum gravity to the one loop order and compare with similar
results in the literature.


title:
Quantum-to-classical Transition of Cosmological Perturbations for
  Non-vacuum Initial States

abstract:
  Transition from quantum to semiclassical behaviour and loss of quantum
coherence for inhomogeneous perturbations generated from a non-vacuum initial
state in the early Universe is considered in the Heisenberg and the
Schr\"odinger representations, as well as using the Wigner function. We show
explicitly that these three approaches lead to the same prediction in the limit
of large squeezing (i.e. when the squeezing parameter $|r_k|\to \infty$): each
two-modes quantum state (k, -k) of these perturbations is equivalent to a
classical perturbation that has a stochastic amplitude, obeying a non-gaussian
statistics which depends on the initial state, and that belongs to the
quasi-isotropic mode (i.e. it possesses a fixed phase). The Wigner function is
not everywhere positive for any finite $r_k$, hence its interpretation as a
classical distribution function in phase space is impossible without some
coarse graining procedure. However, this does not affect the transition to
semiclassical behaviour since the Wigner function becomes concentrated near a
classical trajectory in phase space when $|r_k|\to \infty$ even without coarse
graining. Deviations of the statistics of the perturbations in real space from
a Gaussian one lie below the cosmic variance level for the N-particles initial
states with N=N(|k|) but may be observable for other initial states without
statistical isotropy or with correlations between different k modes. As a way
to look for this effect, it is proposed to measure the kurtosis of the angular
fluctuations of the cosmic microwave background temperature.


title: Quantum dynamics of non-relativistic particles and isometric embeddings

abstract:
  It is considered, in the framework of constrained systems, the quantum
dynamics of non-relativistic particles moving on a d-dimensional Riemannian
manifold M isometrically embedded in $R^{d+n}$. This generalizes recent
investigations where M has been assumed to be a hypersurface of $R^{d+1}$. We
show, contrary to recent claims, that constrained systems theory does not
contribute to the elimination of the ambiguities present in the canonical and
path integral formulations of the problem. These discrepancies with recent
works are discussed.


title:
Parametrization of U(N)-monopoles on black holes by the moduli space of
  holomorphic vector bundles over two-sphere and black hole entropy

abstract:
  We discuss how to describe U(N)-monopoles on the Schwarzschild and
Reissner-Nordstr\"om black holes by the parameters of the moduli space of
holomorphic vector bundles over S^2. For N = 2,3 we obtain such a description
in an explicit form as well as the expressions for the corresponding monopole
masses. This gives a possibility to adduce some reasonings in favour of
existence of both a 'fine structure' for black holes and the statistical
ensemble tied with it which might generate the black hole entropy. Also there
arises some analogy with the famous K-theory in topology.


title: Head-on collision of unequal mass black holes: close-limit predictions

abstract:
  The close-limit method has given approximations in excellent agreement with
those of numerical relativity for collisions of equal mass black holes. We
consider here colliding holes with unequal mass, for which numerical relativity
results are not available. We try to ask two questions: (i) Can we get
approximate answers to astrophysical questions (ideal mass ratio for energy
production, maximum recoil velocity, etc.), and (ii) can we better understand
the limitations of approximation methods. There is some success in answering
the first type of question, but more with the second, especially in connection
with the issue of measures of the intrinsic mass of the colliding holes, and of
the range of validity of the method.


title: Gravitational Phase Transition in Neutron Stars

abstract:
  The possibility of a gravitational phase transition, especially with respect
to neutron stars is investigated. First, a semiclassical treatment is given,
predicting a gravitational London penetration depth of 12km for neutron stars.
Second, the problem is considered from a Ginzburg-Landau point of view. A
gravitational Meissner effect, a gravitational Aharanov-Bohm type effect and a
gravitational ferromagnetic type phase are predicted. Finally, a field
theoretic consideration predicts a mass term for the graviton below a certain
critical temperature.


title: Building Blocks in Turaev-Viro Theory

abstract:
  We study the form of the Turaev-Viro partition function Z(M) for different
3-manifolds with boundary. We show that for $S^2$ boundaries Z(M) factorizes
into a term which contains the boundary dependence and another which depends
only on the topology of the underlying manifold. From this follows easily the
formula for the connected sum of two manifolds Z(M # N). For general $T_g$
boundaries this factorization holds only in a particular case.


title: QED blue-sheet effects inside black holes

abstract:
  The interaction of the unboundedly blue-shifted photons of the cosmic
microwave background radiation with a physical object falling towards the inner
horizon of a Reissner-Nordstrom black hole is analyzed. To evaluate this
interaction we consider the QED effects up to the second order in the
perturbation expansion. We then extrapolate the QED effects up to a cutoff,
which we introduce at the Planckian level. (Our results are not sensitive to
the cutoff energy.) We find that the energy absorbed by an infalling observer
is finite, and for typical parameters would not lead to a catastrophic heating.
However, this interaction would almost certainly be fatal for a human being, or
other living organism of similar size. On the other hand, we find that smaller
objects may survive the interaction. Our results do not provide support to the
idea that the Cauchy horizon is to be regarded as the boundary of spacetime.


title: Classical Gravity on Fuzzy Space-Time

abstract:
  A review is made of recent efforts to find relations between the commutation
relations which define a noncommutative geometry and the gravitational field
which remains as a shadow in the commutative limit.


title:
Alignment procedure for the VIRGO Interferometer: experimental results
  from the Frascati prototype

abstract:
  A small fixed-mirror Michelson interferometer has been built in Frascati to
experimentally study the alignment method that has been suggested for VIRGO.
The experimental results fully confirm the adequacy of the method. The minimum
angular misalignment that can be detected in the present set-up is 10
nrad/sqrt{Hz}


title:
The Causal Interpretation of Quantum Mechanics and The Singularity
  Problem in Quantum Cosmology

abstract:
  We apply the causal interpretation of quantum mechanics to homogeneous
quantum cosmology and show that the quantum theory is independent of any
time-gauge choice and there is no issue of time. We exemplify this result by
studying a particular minisuperspace model where the quantum potential driven
by a prescribed quantum state prevents the formation of the classical
singularity, independently on the choice of the lapse function. This means that
the fast-slow-time gauge conjecture is irrelevant within the framework of the
causal interpretation of quantum cosmology.


title:
Comments on the Quantum Potential Approach to a Class of Quantum
  Cosmological Models

abstract:
  In this comment we bring attention to the fact that when we apply the
ontological interpretation of quantum mechanics, we must be sure to use it in
the coordinate representation. This is particularly important when canonical
tranformations that mix momenta and coordinates are present. This implies that
some of the results obtained by A. B\l aut and J. Kowalski-Glikman are
incorrect.


title:
Geometrical representation of Euclidean general relativity in the
  canonical formalism

abstract:
  We give an SU(2) covariant representation of the constraints of Euclidean
general relativity in the Ashtekar variables. The guiding principle is the use
of triads to transform all free spatial indices into SU(2) indices. A central
role is played by a special covariant derivative. The Gauss, diffeomorphism and
Hamiltonian constraints become purely algebraic restrictions on the curvature
and the torsion associated with this connection. We introduce coordinates on
the jet space of the dynamical fields which cleanly separate the constraint and
gauge directions from the true physical directions. This leads to a
classification of all local diffeomorphism and Gauss invariant charges.


title:
Scalar gravitational wave from Oppenheimer-Snyder collapse in scalar-
  tensor theories of gravity

abstract:
  Unlike general relativity, scalar-tensor theories of gravity predict scalar
gravitational waves even from a spherically symmetric gravitational collapse.
We solve numerically the generation and propagation of the scalar gravitational
wave from a spherically symmetric and homogeneous dust collapse under the
approximation that we can neglect the back reaction of the scalar wave on the
space-time, and examine how the amplitude, characteristic frequency and wave
form of the observed scalar gravitational wave depend on the initial radius and
mass of the dust and parameters contained in the theory. In the Brans-Dicke
theory, through the observation of the scalar gravitational wave, it is
possible to determine the initial radius and mass and a parameter contained in
the theory. In the scalar-tensor theories, it would be possible to get the
information of the first derivative of the coupling function contained in the
theory because the wave form of the scalar gravitational wave greatly depends
on it.


title: ``Nowhere'' differentiable horizons

abstract:
  It is folklore knowledge amongst general relativists that horizons are well
behaved, continuously differentiable hypersurfaces except perhaps on a
negligible subset one needs not to bother with. We show that this is not the
case, by constructing a Cauchy horizon, as well as a black hole event horizon,
which contain no open subset on which they are differentiable.


title:
Gravitational Radiation from Rotational Instabilities in Compact Stellar
  Cores with Stiff Equations of State

abstract:
  We carry out 3-D numerical simulations of the dynamical instability in
rapidly rotating stars initially modeled as polytropes with n = 1.5, 1.0, and
0.5. The calculations are done with a SPH code using Newtonian gravity, and the
gravitational radiation is calculated in the quadrupole limit. All models
develop the global m=2 bar mode, with mass and angular momentum being shed from
the ends of the bar in two trailing spiral arms. The models then undergo
successive episodes of core recontraction and spiral arm ejection, with the
number of these episodes increasing as n decreases: this results in
longer-lived gravitational wave signals for stiffer models. This instability
may operate in a stellar core that has expended its nuclear fuel and is
prevented from further collapse due to centrifugal forces. The actual values of
the gravitational radiation amplitudes and frequencies depend sensitively on
the radius of the star R_{eq} at which the instability develops.


title: On diffeomorphism invariance for lattice theories

abstract:
  We consider the role of the diffeomorphism constraint in the quantization of
lattice formulations of diffeomorphism invariant theories of connections. It
has been argued that in working with abstract lattices, one automatically takes
care of the diffeomorphism constraint in the quantum theory. We use two systems
in order to show that imposing the diffeomorphism constraint is imperative to
obtain a physically acceptable quantum theory. First, we consider $2+1$ gravity
where an exact lattice formulation is available. Next, general theories of
connections for compact gauge groups are treated, where the quantum theories
are known --for both the continuum and the lattice-- and can be compared.


title: Quantum state correction of relic gravitons from quantum gravity

abstract:
  The semiclassical approach to quantum gravity would yield the Schroedinger
formalism for the wave function of metric perturbations or gravitons plus
quantum gravity correcting terms in pure gravity; thus, in the inflationary
scenario, we should expect correcting effects to the relic graviton
(Zel'dovich) spectrum of the order (H/mPl)^2.


title: CMBR dipole from ultra large scale isocurvature perturbations

abstract:
  The observed CMBR dipole, generally interpreted as the consequence of the
peculiar motion of the Sun with respect to the reference frame of the CMBR, can
also be explained by the presence of ultra large scale (of the order of
$100H_0^{-1}$) isocurvature perturbations. Moreover, the simplest model of
inflation with several scalar fields, namely that of double inflation, with
appropriate parameters, can produce such perturbations.


title: Classical Underpinnings of Gravitationally Induced Quantum Interference

abstract:
  We show that the gravitational modification of the phase of a neutron beam
(the COW experiment) has a classical origin, being due to the time delay which
classical particles experience in traversing a background gravitational field.
Similarly, we show that classical light waves also undergo a phase shift in
traversing a gravitational field. We show that the COW experiment respects the
equivalence principle even in the presence of quantum mechanics.


title: Local and global gravity

abstract:
  Our long experience with Newtonian potentials has inured us to the view that
gravity only produces local effects. In this paper we challenge this quite
deeply ingrained notion and explicitly identify some intrinsically global
gravitational effects. In particular we show that the global cosmological
Hubble flow can actually modify the motions of stars and gas within individual
galaxies, and even do so in a way which can apparently eliminate the need for
galactic dark matter. Also we show that a classical light wave acquires an
observable, global, path dependent phase in traversing a gravitational field.
Both of these effects serve to underscore the intrinsic difference between
non-relativistic and relativistic gravity.


title: Whittaker quantum universes

abstract:
  We show that closed, radiation-filled Friedmann-Robertson-Walker quantum
universes of arbitrary factor ordering obey the Whittaker equation. We also
present the formal Witten factorization as well as the double Darboux strictly
isospectral scheme for the Whittaker equation


title:
Problem of Unitarity and Quantum Corrections in Semiclassical Quantum
  Gravity

abstract:
  Using both the Born-Oppenheimer idea and the de Broglie-Bohm interpretation
of wavefunction we represent in a different way the semiclassical quantum
gravity from the Wheeler-DeWitt equation in an oscillating regime which can
preserve completely the unitary quantum evolution of a matter field at the
expense of a nonlinear gravitational field equation, but has the same
asymptotic limit as the others. We apply the de Broglie-Bohm interpretation to
the nonlinear gravitational field equation to develop a perturbation method to
find the quantum corrections of a matter field to the gravity. The
semiclassical Einstein equation with the quantum corrections is found for a
minimal quantum FRW cosmological model.


title: Exact non-equilibrium solutions of the Einstein-Boltzmann equations. II

abstract:
  We find exact solutions of the Einstein-Boltzmann equations with relaxational
collision term in FRW and Bianchi I spacetimes. The kinematic and thermodynamic
properties of the solutions are investigated. We give an exact expression for
the bulk viscous pressure of an FRW distribution that relaxes towards
collision-dominated equilibrium. If the relaxation is toward collision-free
equilibrium, the bulk viscosity vanishes - but there is still entropy
production. The Bianchi I solutions have zero heat flux and bulk viscosity, but
nonzero shear viscosity. The solutions are used to construct a realisation of
the Weyl Curvature Hypothesis.


title: Rotating matter in general relativity -- stationary state I

abstract:
  Stationary rotating matter configurations in general relativity are
considered. A formalism for general stationary space times is developed.
Axisymmetric systems are discussed by the use of a nonholonomic and nonrigid
frame in the three-space of the time-like Killing trajectories. Two symmetric
and trace-free tensors are constructed. They characterize a class of matter
states in which both the interior Schwarzschild and the Kerr solution are
contained. Consistency relations for this class of perfect fluids are derived.
Incompressible fluids characterized by these tensors are investigated, and one
differentially rotating solution is found.


title: Quasi-Asimptotically Flat Spacetimes and Their ADM Mass

abstract:
  We define spacetimes that are asymptotically flat, except for a deficit solid
angle $\alpha$, and present a definition of their ``ADM'' mass, which is finite
for this class of spacetimes, and, in particular, coincides with the value of
the parameter $M$ of the global monopole spacetime studied by Vilenkin and
Barriola . Moreover, we show that the definition is coordinate independent, and
explain why it can, in some cases, be negative.


title: Black Hole Entropy in the Chern-Simons Formulation of 2+1 Gravity

abstract:
  We examine Carlip's derivation of the 2+1 Minkowskian black hole entropy. A
simplified derivation of the boundary action -valid for any value of the level
k- is given.


title: Einstein equations in the null quasi-spherical gauge

abstract:
  The structure of the full Einstein equations in a coordinate gauge based on
expanding null hypersurfaces foliated by metric 2-spheres is explored. The
simple form of the resulting equations has many applications -- in the present
paper we describe the structure of timelike boundary conditions; the matching
problem across null hypersurfaces; and the propagation of gravitational shocks.


title: Gravitational Theory without the Cosmological Constant Problem

abstract:
  We develop the principle of nongravitating vacuum energy, which is
implemented by changing the measure of integration from $\sqrt{-g}d^{D}x$ to an
integration in an internal space of $D$ scalar fields $\phi_{a}$. As a
consequence of such a choice of the measure, the matter Lagrangian $L_{m}$ can
be changed by adding a constant while no cosmological term is induced. Here we
develop this idea to build a new theory which is formulated through the first
order formalism, i.e. using vielbein $e_{a}^{\mu}$ and spin connection
$\omega_{\mu}^{ab}$ (a,b=1,2,...D) as independent variables. The equations
obtained from the variation of $e_{a}^{\mu}$ and the fields $\phi_{a}$ imply
the existence of a nontrivial constraint. This approach can be made consistent
with invariance under arbitrary diffeomorphisms in the internal space of scalar
fields $\phi_{a}$ (as well as in ordinary space-time), provided that the matter
model is chosen so as to satisfy the above mentioned constraint. If the matter
model is not chosen so as to satisfy automatically this constraint, the
diffeomorphism invariance in the internal space is broken. In this case the
constraint is dynamically implemented by the degrees of freedom that become
physical due to the breaking of the internal diffeomorphism invariance.
However, this constraint always dictates the vanishing of the cosmological
constant term and the gravitational equations in the vacuum coincide with
vacuum Einstein's equations with zero cosmological constant. The requirement
that the internal diffeomorphisms be a symmetry of the theory points towards
the unification of forces in nature like in the Kaluza-Klein scheme.


title: Onset of inflation in inhomogeneous cosmology

abstract:
  We study how the initial inhomogeneities of the universe affect the onset of
inflation in the closed universe. We consider the model of a chaotic inflation
which is driven by a massive scalar field. In order to construct an
inhomogeneous universe model, we use the long wavelength approximation ( the
gradient expansion method ). We show the condition of the inhomogeneities for
the universe to enter the inflationary phase.


title: On Relativistic Perturbations of Second and Higher Order

abstract:
  We present the results of a study of the gauge dependence of spacetime
perturbations. In particular, we consider gauge invariance in general, we give
a generating formula for gauge transformations to an arbitrary order n, and
explicit transformation rules at second order.


title: Some Quantum Aspects of D=3 Space-Time Massive Gravity

abstract:
  We discuss some features of Einstein-Proca gravity in D=3 and 4 space-times.
Our study includes a discussion on the tree-level unitarity and on the issue of
light deflection in 3D gravity in the presence of a mass term.


title:
4-Dimensional Kaluza-Klein Approach to General Relativity in the
  (2,2)-Splitting of Spacetimes

abstract:
  We propose a Kaluza-Klein approach to general relativity of 4-dimensional
spacetimes. This approach is based on the (2,2)-splitting of a generic
4-dimensional spacetime, which is viewed as a local product of a
(1+1)-dimensional base manifold and a 2-dimensional fibre space. In this
Kaluza-Klein formalism we find that general relativity of 4-dimensional
spacetimes can be interpreted in a natural way as a (1+1)-dimensional gauge
theory. In a gauge where the (1+1)-dimensional metric can be written as the
Polyakov metric, the action is describable as a (1+1)-dimensional Yang-Mills
type gauge theory action coupled to a (1+1)-dimensional non-linear sigma field
and a scalar field, subject to the constraint equations associated with the
diffeomorphism invariance of the (1+1)-dimensional base manifold.
Diffeomorphisms along the fibre directions show up as the Yang-Mills type gauge
symmetries, giving rise to the Gauss-law constraints. We also present the
Einstein's equations in the Polyakov gauge and discuss them from the
(1+1)-dimensional gauge theory point of view. Finally we show that this
Kaluza-Klein formalism is closely related to the null hypersurface formalism of
general relativity.


title: Aspherical gravitational monopoles

abstract:
  We show how to construct non-spherically-symmetric extended bodies of uniform
density behaving exactly as pointlike masses. These ``gravitational monopoles''
have the following equivalent properties: (i) they generate, outside them, a
spherically-symmetric gravitational potential $M/|x - x_O|$; (ii) their
interaction energy with an external gravitational potential $U(x)$ is $- M
U(x_O)$; and (iii) all their multipole moments (of order $l \geq 1$) with
respect to their center of mass $O$ vanish identically. The method applies for
any number of space dimensions. The free parameters entering the construction
are: (1) an arbitrary surface $\Sigma$ bounding a connected open subset
$\Omega$ of $R^3$; (2) the arbitrary choice of the center of mass $O$ within
$\Omega$; and (3) the total volume of the body. An extension of the method
allows one to construct homogeneous bodies which are gravitationally equivalent
(in the sense of having exactly the same multipole moments) to any given body.