title:
Some remarks on a nongeometrical interpretation of gravity and the
  flatness problem

abstract:
  In a nongeometrical interpretation of gravity, the metric
$g_{\mu\nu}(x)=\eta_{\mu\nu}+\Phi_{\mu\nu}(x)$ is interpreted as an {\em
effective} metric, whereas $\Phi_{\mu\nu}(x)$ is interpreted as a fundamental
gravitational field, propagated in spacetime which is actually flat. Some
advantages and disadvantages of such an interpretation are discussed. The main
advantage is a natural resolution of the flatness problem.


title:
On the gravitational field of a point mass in Einstein Universe
  background

abstract:
  Some properties of an exact solution due to Vaidya, describing the
gravitational field produced by a point particle in the background of the
static Einstein universe are examined. The maximal analytic extension and the
nature of the singularities of the model are discussed. By using the Euclidean
approach, some quantum aspects are analysed and the thermodynamics of this
spacetime is also discussed.


title: Phases of the Brans-Dicke Cosmology with Matter

abstract:
  We study the cosmology of the Brans-Dicke theory with perfect fluid type
matter. In our previous work, we found exact solutions for any Brans-Dicke
parameter $\omega$ and for general parameter $\gamma$ of equation of state. In
this paper we further study the cosmology of these solutions by analyzing them
according to their asymptotic behaviors. The cosmology is classified into 19
phases according to the values of $\gamma$ and $\omega$. The effect of the
cosmological constant to the Brans-Dicke theory is a particular case of our
model. We give plot of time evolution of the scale factor by numerical
investigations. We also give a comparison of the solutions for the theories
with and without matter.


title: Stellar Pulsations excited by a scattered mass

abstract:
  We compute the energy spectra of the gravitational signals emitted when a
mass m is scattered by the gravitational field of a star of mass M >> m. We
show that, unlike black holes in similar processes, the quasi-normal modes of
the star are excited, and that the amount of energy emitted in these modes
depends on how close the exciting mass can get to the star.


title: Time Machines Constructed from Anti-de Sitter Space

abstract:
  In this paper time machines are constructed from anti-de Sitter space. One is
constructed by identifying points related via boost transformations in the
covering space of anti-de Sitter space and it is shown that this Misner-like
anti-de Sitter space is just the Lorentzian section of the complex space
constructed by Li, Xu, and Liu in 1993. The others are constructed by gluing an
anti-de Sitter space to a de Sitter space, which could describe an anti-de
Sitter phase bubble living in a de Sitter phase universe. Self-consistent vacua
for a massless conformally coupled scalar field are found for these time
machines, whose renormalized stress-energy tensors are finite and solve the
semi-classical Einstein equations. The extensions to electromagnetic fields and
massless neutrinos are discussed. It is argued that, in order to make the
results consistent with Euclidean quantization, a new renormalization procedure
for quantum fields in Misner-type spaces (Misner space, Misner-like de Sitter
space, and Misner-like anti-de Sitter space) is required. Such a
"self-consistent" renormalization procedure is proposed. With this
renormalization procedure, self-consistent vacua exist for massless conformally
coupling scalar fields, electromagnetic fields, and massless neutrinos in these
Misner-type spaces.


title: Inhomogeneous Einstein-Rosen String Cosmology

abstract:
  Families of anisotropic and inhomogeneous string cosmologies containing
non-trivial dilaton and axion fields are derived by applying the global
symmetries of the string effective action to a generalized Einstein-Rosen
metric. The models exhibit a two-dimensional group of Abelian isometries. In
particular, two classes of exact solutions are found that represent
inhomogeneous generalizations of the Bianchi type VI_h cosmology. The
asymptotic behaviour of the solutions is investigated and further applications
are briefly discussed.


title: Causal continuity in degenerate spacetimes

abstract:
  A change of spatial topology in a causal, compact spacetime cannot occur when
the metric is globally Lorentzian. One can however construct a causal metric
from a Riemannian metric and a Morse function on the background cobordism
manifold, which is Lorentzian almost everywhere except that it is degenerate at
each critical point of the function. We investigate causal structure in the
neighbourhood of such a degeneracy, when the auxiliary Riemannian metric is
taken to be Cartesian flat in appropriate coordinates. For these geometries, we
verify Borde and Sorkin's conjecture that causal discontinuity occurs if and
only if the Morse index is 1 or n-1.


title: A new look at relativity transformations

abstract:
  A free system, considered to be a comparison system, allows for the notion of
objective existence and inertial frame. Transformations connecting inertial
frames are shown to be either Lorentz or generalized Galilei.


title: Perturbative analysis of non-singular cosmological model

abstract:
  A stability analysis is made for a non-singular pre-big-bang like
cosmological model based on 1-loop corrected string effective action. Its
homogeneous and isotropic solution realizes non-singular transition from de
Sitter universe to Friedmann-like universe, via super inflation phase. We are
interested in whether the non-singular nature of the solution would be stable
or not in more general inhomogeneous case. Perturbative analysis is made for
scalar, vector, and tensor linear perturbations, and instability is found for
tensor-type perturbation.


title: The Universe out of an Elementary Particle?

abstract:
  We consider a model of an elementary particle as a 2 + 1 dimensional brane
evolving in a 3 + 1 dimensional space. Introducing gauge fields that live in
the brane as well as normal surface tension can lead to a stable "elementary
particle" configuration. Considering the possibility of non vanishing vacuum
energy inside the bubble leads, when gravitational effects are considered, to
the possibility of a quantum decay of such "elementary particle" into an
infinite universe. Some remarkable features of the quantum mechanics of this
process are discussed, in particular the relation between possible boundary
conditions and the question of instability towards Universe formation is
analyzed.


title: Scale Invariance, Mass and Cosmology

abstract:
  The possibility of mass in the context of scale-invariant, generally
covariant theories, is discussed. The realizations of scale invariance which
are considered, are in the context of a gravitational theory where the action,
in the first order formalism, is of the form $S = \int L_{1} \Phi d^4x$ + $\int
L_{2}\sqrt{-g}d^4x$ where $\Phi$ is a density built out of degrees of freedom
independent of gravity, which we call the "measure fields". For global scale
invariance, a "dilaton" $\phi$ has to be introduced, with non-trivial
potentials $V(\phi)$ = $f_{1}e^{\alpha\phi}$ in $L_1$ and $U(\phi)$ =
$f_{2}e^{2\alpha\phi}$ in $L_2$. This leads to non-trivial mass generation and
potential for $\phi$. Mass terms for an arbitrary matter field can appear in a
scale invariant form both in $L_1$ and in $L_2$ where they are coupled to
different exponentials of the field $\phi$. Implications of these results for
cosmology having in mind in particular inflationary scenarios, models of the
late universe and modified gravitational theories are discussed.


title:
On certain quasi-local spin-angular momentum expressions for small
  spheres

abstract:
  The Ludvigsen-Vickers and two recently suggested quasi-local spin-angular
momentum expressions, based on holomorphic and anti-holomorphic spinor fields,
are calculated for small spheres of radius $r$ about a point $o$. It is shown
that, apart from the sign in the case of anti-holomorphic spinors in
non-vacuum, the leading terms of all these expressions coincide. In non-vacuum
spacetimes this common leading term is of order $r^4$, and it is the product of
the contraction of the energy-momentum tensor and an average of the approximate
boost-rotation Killing vector that vanishes at $o$ and of the 3-volume of the
ball of radius $r$. In vacuum spacetimes the leading term is of order $r^6$,
and the factor of proportionality is the contraction of the Bel-Robinson tensor
and an other average of the same approximate boost-rotation Killing vector.


title: Adiabatic Hadamard States for Dirac Quantum Fields on Curved Space

abstract:
  In this paper we propose a definition of quasifree Hadamard states for spinor
fields on a curved space-time by specifying the Polarisation Set of the
two-point function. We prove that the thermal equilibrium state on an
ultrastatic space-time is Hadamard. We then construct an adiabatic vacuum state
on a general globally hyperbolic Lorentz manifold using a factorisation of the
spinorial Klein-Gordon operator. This state is pure. In what constitutes the
main part of the paper, we show that it is also Hadamard. As a side result, we
obtain the propagation of singularities of the spinorial Klein-Gordon operator.
Some notation and results are collected in the Appendix.


title:
Ground State Energy of Massive Scalar Field in the Global Monopole
  Background

abstract:
  We consider the ground state energy of scalar massive field in the spacetime
of a pointlike global monopole. Using zeta function regularization method we
obtain the heat kernel coefficients for this system. We show that the
coefficient $B_1$ contains additional contribution due to the non-trivial
topological structure of the spacetime. Taking into account the heat kernel
coefficients we obtain that the ground state energy of the scalar field is
zero. We also discuss our result using dimensional considerations.


title: Simplicial Brill wave initial data

abstract:
  Regge calculus is used to construct initial data for vacuum axisymmetric
Brill waves at a moment of time symmetry. We argue that only a tetrahedral
lattice can successfully reproduce the continuum solution, and develop a
simplicial axisymmetric lattice based on the co-ordinate structure of the
continuum metric. This is used to construct initial data for Brill waves in an
otherwise flat spacetime, and for the distorted black hole spacetime of
Bernstein. These initial data sets are shown to be second order accurate
approximations to the corresponding continuum solutions.


title:
The inverse problem for pulsating neutron stars: A ``fingerprint
  analysis'' for the supranuclear equation of state

abstract:
  We study the problem of detecting, and infering astrophysical information
from, gravitational waves from a pulsating neutron star. We show that the fluid
f and p-modes, as well as the gravitational-wave w-modes may be detectable from
sources in our own galaxy, and investigate how accurately the frequencies and
damping rates of these modes can be infered from a noisy gravitational-wave
data stream. Based on the conclusions of this discussion we propose a strategy
for revealing the supranuclear equation of state using the neutron star
fingerprints: the observed frequencies of an f and a p-mode. We also discuss
how well the source can be located in the sky using observations with several
detectors.


title: SL(2,R) model with two Hamiltonian constraints

abstract:
  We describe a simple dynamical model characterized by the presence of two
noncommuting Hamiltonian constraints. This feature mimics the constraint
structure of general relativity, where there is one Hamiltonian constraint
associated with each space point. We solve the classical and quantum dynamics
of the model, which turns out to be governed by an SL(2,R) gauge symmetry,
local in time. In classical theory, we solve the equations of motion, find a
SO(2,2) algebra of Dirac observables, find the gauge transformations for the
Lagrangian and canonical variables and for the Lagrange multipliers. In quantum
theory, we find the physical states, the quantum observables, and the physical
inner product, which is determined by the reality conditions. In addition, we
construct the classical and quantum evolving constants of the system. The model
illustrates how to describe physical gauge-invariant relative evolution when
coordinate time evolution is a gauge.


title: The Quantum Interest Conjecture

abstract:
  Although quantum field theory allows local negative energy densities and
fluxes, it also places severe restrictions upon the magnitude and extent of the
negative energy. The restrictions take the form of quantum inequalities. These
inequalities imply that a pulse of negative energy must not only be followed by
a compensating pulse of positive energy, but that the temporal separation
between the pulses is inversely proportional to their amplitude. In an earlier
paper we conjectured that there is a further constraint upon a negative and
positive energy delta-function pulse pair. This conjecture (the quantum
interest conjecture) states that a positive energy pulse must overcompensate
the negative energy pulse by an amount which is a monotonically increasing
function of the pulse separation. In the present paper we prove the conjecture
for massless quantized scalar fields in two and four-dimensional flat
spacetime, and show that it is implied by the quantum inequalities.


title:
Data analysis strategies for the detection of gravitational waves in
  non-Gaussian noise

abstract:
  In order to analyze data produced by the kilometer-scale gravitational wave
detectors that will begin operation early next century, one needs to develop
robust statistical tools capable of extracting weak signals from the detector
noise. This noise will likely have non-stationary and non-Gaussian components.
To facilitate the construction of robust detection techniques, I present a
simple two-component noise model that consists of a background of Gaussian
noise as well as stochastic noise bursts. The optimal detection statistic
obtained for such a noise model incorporates a natural veto which suppresses
spurious events that would be caused by the noise bursts. When two detectors
are present, I show that the optimal statistic for the non-Gaussian noise model
can be approximated by a simple coincidence detection strategy. For simulated
detector noise containing noise bursts, I compare the operating characteristics
of (i) a locally optimal detection statistic (which has nearly-optimal behavior
for small signal amplitudes) for the non-Gaussian noise model, (ii) a standard
coincidence-style detection strategy, and (iii) the optimal statistic for
Gaussian noise.


title:
Gravitational waves from inspiraling compact binaries: Validity of the
  stationary-phase approximation to the Fourier transform

abstract:
  We prove that the oft-used stationary-phase method gives a very accurate
expression for the Fourier transform of the gravitational-wave signal produced
by an inspiraling compact binary. We give three arguments. First, we
analytically calculate the next-order correction to the stationary-phase
approximation, and show that it is small. This calculation is essentially an
application of the steepest-descent method to evaluate integrals. Second, we
numerically compare the stationary-phase expression to the results obtained by
Fast Fourier Transform. We show that the differences can be fully attributed to
the windowing of the time series, and that they have nothing to do with an
intrinsic failure of the stationary-phase method. And third, we show that these
differences are negligible for the practical application of matched filtering.


title: Simulation of Panleve-Gullstrand black hole in thin 3He-A film

abstract:
  The quasi-stationary superfluid state is constructed, which exhibits the
event horizon and Hawking radiation.


title: The relations among two transversal submanifolds and global manifold

abstract:
  In Riemann geometry, the relations among two transversal submanifolds and
global manifold are discussed. By replacing the normal vector of a submanifold
with the tangent vector of another submanifold, the metric tensors, Christoffel
symbols and curvature tensors of the three manifolds are linked together. When
the inner product of the two tangent vectors vanishes, some corollaries of
these relations give the most important second fundamental form and
Gauss-Codazzi equation in the conventional submanifold theory. As a special
case, the global manifold is Euclidean is considered. It is pointed out that,
in order to obtain the nonzero energy-momentum tensor of matter field in a
submanifold, there must be the contributions of the above inner product and the
other submanifold. In general speaking, a submanifold is closely related to the
matter fields of the other submanifold through the above inner product. This
conclusion is in agreement with the Kaluza-Klein theory and it can be applied
to generalize the models of direct product of manifolds in string and D-brane
theories to the more general cases --- nondirect product manifolds.


title: Stability of Flat Space to Singular Instantons

abstract:
  Hawking and the author have proposed a class of singular, finite action
instantons for defining the initial conditions for inflation. Vilenkin has
argued they are unacceptable. He exhibited an analogous class of asymptotically
flat instantons which on the face of it lead to an instability of Minkowski
space. However, all these instantons must be defined by introducing a
constraint into the path integral, which is then integrated over. I show that
with a careful definition these instantons do not possess a negative mode.
Infinite flat space is therefore stable against decay via singular instantons.


title:
Spherical gravitational collapse: tangential pressure and related
  equations of state

abstract:
  We derive an equation for the acceleration of a fluid element in the
spherical gravitational collapse of a bounded compact object made up of an
imperfect fluid. We show that non-singular as well as singular solutions arise
in the collapse of a fluid initially at rest and having only a tangential
pressure. We obtain an exact solution of Einstein equations, in the form of an
infinite series, for collapse under tangential pressure with a linear equation
of state. We show that if a singularity forms in the tangential pressure model,
the conditions for the singularity to be naked are exactly the same as in the
model of dust collapse.


title: Oscillating non-singular relativistic spherical model

abstract:
  A particular choice of the time function in the recently presented spherical
solution by Dadhich [1] leads to a singularity free cosmological model which
oscillates between two regular states. The energy-stress tensor involves
anisotropic pressure and a heat flux term but is consistent with the usual
energy conditions (strong, weak and dominant). By choosing the parameters
suitably one can make the model consistent with observational data. An
interesting feature of the model is that it involves blue shifts as in the
quasi steady state model [2] but without violating general relativity.


title: The No-Negative Mode Theorem in False Vacuum Decay with Gravity

abstract:
  The so-called negative mode problem in the path integral approach to the
false vacuum decay with the effect of gravity has been an unsolved problem.
Several years ago, we proposed a conjecture which is to be proved in order to
give a consistent solution to the negative mode problem. We called it the
``no-negative mode conjecture''. In the present paper, we give a proof of this
conjecture for rather general models. Recently, we also proposed the
``no-supercritical supercurvature mode conjecture'' that claims the absence of
supercritical supercurvature modes in the one-bubble open inflation model. In
the same paper, we clarified the equivalence between the ``no-negative mode
conjecture'' and the ``no-supercritical supercurvature mode conjecture''.
Hence, the latter is also proved at the same time when the former is proved.


title:
The degree of generality of inflation in FRW models with massive scalar
  field and hydrodynamical matter

abstract:
  Friedmann-Robertson-Walker cosmological models with a massive scalar field
are studied in the presence of hydrodynamical matter in the form of a perfect
fluid. The ratio of the number of solutions without inflation to the total
number of solutions is evaluated, depending on the fluid density. It is shown
that in a closed model this ratio can reach 60%, by contrast to $\sim 30 %$ in
models without fluid.


title: Search techniques for gravitational waves from black-hole ringdowns

abstract:
  Of all the astronomical sources of gravitational radiation, the ringdown
waveform arising from a small perturbation of a spinning black hole is perhaps
the best understood: for the late stages of such a perturbation, the waveform
is simply an exponentially-damped sinusoid. Searching interferometric
gravitational wave antenna data for these should be relatively easy. In this
paper, I present the results of a single-filter search for ringdown waveforms
arising from a 50 solar mass black hole with 98% of its maximum spin angular
momentum using data from the Caltech 40-meter prototype interferometer. This
search illustrates the techniques that may be used in analyzing data from
future kilometer-scale interferometers and describes some of the difficulties
present in the analysis of interferometer data. Most importantly, it
illustrates the use of coincident events in the output of two independent
interferometers (here simulated by 40-meter data at two different times) to
substantially reduce the spurious event rate. Such coincidences will be
essential tools in future gravitational wave searches in kilometer-scale
interferometers.


title: Entropy, topology of two-dimensional extreme black holes

abstract:
  Through direct thermodynamic calculations we have shown that different
classical entropies of two-dimensional extreme black holes appear due to two
different treatments, namely Hawking's treatment and Zaslavskii's treatment.
Geometrical and topological properties corresponding to these different
treatments are investigated. Quantum entropies of the scalar fields on the
backgrounds of these black holes concerning different treatments are also
exhibited. Different results of entropy and geometry lead us to argue that
there are two kinds of extreme black holes in the nature. Explanation of black
hole phase transition has also been given from the quantum point of view.


title: The gauge invariance of general relativistic tidal heating

abstract:
  When a self-gravitating body (e.g., a neutron star or black hole) interacts
with an external tidal field (e.g., that of a binary companion), the
interaction can do work on the body, changing its mass-energy. The details of
this "tidal heating" are analyzed using the Landau-Lifshitz pseudotensor and
the local asymptotic rest frame of the body. It is shown that the work done on
the body is gauge-invariant, while the body-tidal-field interaction energy
contained within the body's local asymptotic rest frame is gauge dependent.
This is analogous to Newtonian theory, where the interaction energy is shown to
depend on how one localizes gravitational energy, but the work done on the body
is independent of that localization.


title:
Near Field Behavior of Static Spherically Symmetric Solutions of
  Einstein SU(2) Yang Mills Equations with Cosmological Constant

abstract:
  We consider static spherically symmetric solutions of the Einstein equations
with cosmological constant coupled to the SU(2) Yang Mills equations. We prove
that most solutions can be continued back to the origin of spherical symmetry
and that the qualitative behavior of solutions near this origin does not depend
on the value of the cosmological constant.


title: The Equation of Atom Motion in an External Gravitational Field

abstract:
  It is shown that the motion of a multielectron atom in an external
gravitational field in a good approximation is described by system of the
Mathisson-Papapetrou equations, if we put as a classical angular momentum of
the atom the expectation value of the operator of the full angular momentum of
the system, which includes spins of the nucleus and electrons, and orbital
momentums of the electrons in the atom.


title:
Dipole perturbations of the Reissner-Nordstrom solution. II. The axial
  case

abstract:
  We study the linear metric perturbations of the Reissner-Nordstr\"{o}m
solution for the case of axial perturbation modes. We find that the well-known
perturbative analysis fails for the case of dipole $(l=1)$ perturbations,
although valid for higher multipoles. We define new radial functions, with
which the perturbation formalism is generalized to all multipole orders,
including the dipole. We then complete the solution by constructing the
perturbed metric and Maxwell tensors.


title: Numerical Study of Inhomogeneous Pre-Big-Bang Inflationary Cosmology

abstract:
  We study numerically the inhomogeneous pre-big-bang inflation in a
spherically symmetric space-time. We find that a large initial inhomogeneity
suppresses the onset of the pre-big-bang inflation. We also find that even if
the pre-big-bang inflationary stage is realized, the initial inhomogeneities
are not homogenized. Namely, during the pre-big-bang inflation
``hairs''(irregularities) do not fall, in sharp contrast to the usual
(potential energy dominated) inflation where initial inhomogeneity and
anisotropy are damped and thus the resulting universe is less sensitive to
initial conditions.


title: Canonical and path integral quantisation of string cosmology models

abstract:
  We discuss the quantisation of a class of string cosmology models that are
characterized by scale factor duality invariance. We compute the amplitudes for
the full set of classically allowed and forbidden transitions by applying the
reduce phase space and the path integral methods. We show that these approaches
are consistent. The path integral calculation clarifies the meaning of the
instanton-like behaviour of the transition amplitudes that has been first
pointed out in previous investigations.


title: Instability of two-dimensional heterotic stringy black holes

abstract:
  We solve the eigenvalue problem of general relativity for the case of charged
black holes in two-dimensional heterotic string theory, derived by McGuigan et
al. For the case of $m^{2}>q^{2}$, we find a physically acceptable
time-dependent growing mode; thus the black hole is unstable. The extremal case
$m^{2}=q^{2}$ is stable.


title:
Exponential Decay for Small Non-Linear Perturbations of Expanding Flat
  Homogeneous Cosmologies

abstract:
  It is shown that during expanding phases of flat homogeneous cosmologies all
small enough non-linear perturbations decay exponentially. This result holds
for a large class of perfect fluid equations of state, but notably not for very
``stiff'' fluids as the pure radiation case.


title: On the factor ordering problem in stochastic inflation

abstract:
  The stochastic approach to inflation suffers from ambiguities due to the
arbitrary choice of the time variable and due to the choice of the factor
ordering in the corresponding Fokker-Planck equation. Here it is shown that
both ambiguities can be removed if we require that the factor ordering should
be set in such a way that physical results are invariant with respect to time
reparametrizations. This requirement uniquely selects the so-called Ito factor
ordering. Additional ambiguities associated with non-trivial kinetic terms of
the scalar fields are also discussed, as well as ways of constraining these
ambiguities.


title: The Inner Structure of Black Holes

abstract:
  We study the gravitational collapse of a self-gravitating charged
scalar-field. Starting with a regular spacetime, we follow the evolution
through the formation of an apparent horizon, a Cauchy horizon and a final
central singularity. We find a null, weak, mass-inflation singularity along the
Cauchy horizon, which is a precursor of a strong, spacelike singularity along
the $r=0$ hypersurface. The inner black hole region is bounded (in the future)
by singularities. This resembles the classical inner structure of a
Schwarzschild black hole and it is remarkably different from the inner
structure of a charged static Reissner-Nordstr\"om or a stationary rotating
Kerr black holes.


title:
Non-Static Spherically Symmetric solution of Einstein vacuum Field
  Equations with $Lambda$

abstract:
  The Schwarzschild-deSitter metric is the known solution of Einstein field
equations with cosmological constant term for vacuum spherically symmetric
space around a point mass M. Recently it has been reported that in a
$Lamda$-dominant world the Schwarzschild type coordinate systems are
disqualified by redshift-magnitude test as a proper frame of
reference(gr-qc/9812092). We derive the solution in a FRW type coordinate
system which is qualified according to the mentioned test. Asymptotically it
approachs to the non-static form of deSitter metric. The obtained metric is
transformable to Schwarzschild-deSitter metric. It is an analytic function of
$r$ for all values except $r=0$which is singular. This is carried out with no
making use of Eddington-Finkelstein coordinates and without entering any cross
term in the metric.


title: Radiative falloff in Schwarzschild-de Sitter spacetime

abstract:
  We consider the time evolution of a scalar field propagating in
Schwarzschild-de Sitter spacetime. At early times, the field behaves as if it
were in pure Schwarzschild spacetime; the structure of spacetime far from the
black hole has no influence on the evolution. In this early epoch, the field's
initial outburst is followed by quasi-normal oscillations, and then by an
inverse power-law decay. At intermediate times, the power-law behavior gives
way to a faster, exponential decay. At late times, the field behaves as if it
were in pure de Sitter spacetime; the structure of spacetime near the black
hole no longer influences the evolution in a significant way. In this late
epoch, the field's behavior depends on the value of the curvature-coupling
constant xi. If xi is less than a critical value 3/16, the field decays
exponentially, with a decay constant that increases with increasing xi. If xi >
3/16, the field oscillates with a frequency that increases with increasing xi;
the amplitude of the field still decays exponentially, but the decay constant
is independent of xi.


title:
Matters of Gravity, the newsletter of the APS Topical Group on
  Gravitation

abstract:
  Contents:
  Editorial
  Correspondents
  News:
  - Topical Group News, by Jim Isenberg
  - We hear that..., by Jorge Pullin
  - The Chandra Satellite, by Beverly Berger
  Research Briefs:
  - Analytical event horizons of merging black holes, by Simonetta Frittelli
  - LIGO project update, by David Shoemaker
  - Bicentenary of the Cavendish Experiment, by Riley Newman
  Conference reports:
  - Eighth Midwest meeting, by Richard Hammond
  - GWDAW 98, by Sam Finn
  - Bad Honnef seminar, by Alan Randall.


title: A comment on gr-qc/9901053

abstract:
  In eprint gr-qc/9901053 Gen Yoneda and Hisa-aki Shinkai have made several
claims disputing our results in gr-qc/9710004, and gr-qc/9804019. We show here
that these claims are not correct.


title: Integrating Singular Functions on the Sphere

abstract:
  We obtain rigorous results concerning the evaluation of integrals on the two
sphere using complex methods. It is shown that for regular as well as singular
functions which admit poles, the integral can be reduced to the calculation of
residues through a limiting procedure.


title: Null Surfaces and the Bach Equations

abstract:
  It is shown that the integrability conditions that arise in the Null Surface
Formulation (NSF) of general relativity (GR) impose a field equation on the
local null surfaces which is equivalent to the vanishing of the Bach tensor.
This field equation is written explicitly to second order in a perturbation
expansion.
  The field equation is further simplified if asymptotic flatness is imposed on
the underlying space-time. The resulting equation determines the global null
surfaces of asymptotically flat, radiative space-times. It is also shown that
the source term of this equation is constructed from the free Bondi data at
future null infinity.
  Possible generalizations of this field equation are analyzed. In particular
we include other field equations for surfaces that have already appeared in the
literature which coincide with ours at a linear level. We find that the other
equations do not yield null surfaces for GR.


title: Quanta of Geometry and Rotating Black Holes

abstract:
  In the loop approach to quantum gravity the spectra of operators
corresponding to such geometrical quantities as length, area and volume become
quantized. However, the size of arising quanta of geometry in Planck units is
not fixed by the theory itself: a free parameter, sometimes referred to as
Immirzi parameter, is known to affect the spectrum of all geometrical
operators. In this paper I propose an argument that fixes the value of this
parameter. I consider rotating black holes, in particular the extremal ones.
For such black holes the ``no naked singularity condition'' bounds the total
angular momentum J by A_H/8 pi G, where A_H is the horizon area and G Newton's
constant. A similar bound on J comes from the quantum theory. The requirement
that these two bounds are the same fixes the value of Immirzi parameter to be
unity. A byproduct of this argument is the picture of the quantum extremal
rotating black hole in which all the spin entering the extremal hole is
concentrated in a single puncture.


title:
A Spherically Symmetric Closed Universe as an Example of a 2D Dilatonic
  Model

abstract:
  We study the two-dimensional (2D) dilatonic model describing a massless
scalar field minimally coupled to the spherically reduced Einstein-Hilbert
gravity. The general solution of this model is given in the case when a Killing
vector is present. When interpreted in four dimensions, the solution describes
either a static or a homogeneous collision of incoming and outgoing null dust
streams with spherical symmetry. The homogeneous Universe is closed.


title: Higher-Dimensional Algebra and Planck-Scale Physics

abstract:
  This is a nontechnical introduction to recent work on quantum gravity using
ideas from higher-dimensional algebra. We argue that reconciling general
relativity with the Standard Model requires a `background-free quantum theory
with local degrees of freedom propagating causally'. We describe the insights
provided by work on topological quantum field theories such as quantum gravity
in 3-dimensional spacetime. These are background-free quantum theories lacking
local degrees of freedom, so they only display some of the features we seek.
However, they suggest a deep link between the concepts of `space' and `state',
and similarly those of `spacetime' and `process', which we argue is to be
expected in any background-free quantum theory. We sketch how
higher-dimensional algebra provides the mathematical tools to make this link
precise. Finally, we comment on attempts to formulate a theory of quantum
gravity in 4-dimensional spacetime using `spin networks' and `spin foams'.


title:
Relativistic hydrodynamics on spacelike and null surfaces: Formalism and
  computations of spherically symmetric spacetimes

abstract:
  We introduce a formulation of Eulerian general relativistic hydrodynamics
which is applicable for (perfect) fluid data prescribed on either spacelike or
null hypersurfaces. Simple explicit expressions for the characteristic speeds
and fields are derived in the general case. A complete implementation of the
formalism is developed in the case of spherical symmetry. The algorithm is
tested in a number of different situations, predisposing for a range of
possible applications. We consider the Riemann problem for a polytropic gas,
with initial data given on a retarded/advanced time slice of Minkowski
spacetime. We compute perfect fluid accretion onto a Schwarzschild black hole
spacetime using ingoing null Eddington-Finkelstein coordinates. Tests of fluid
evolution on dynamic background include constant density and TOV stars sliced
along the radial null cones. Finally, we consider the accretion of
self-gravitating matter onto a central black hole and the ensuing increase in
the mass of the black hole horizon.


title: Coalescing Binary Neutron Stars

abstract:
  Coalescing compact binaries with neutron star or black hole components
provide the most promising sources of gravitational radiation for detection by
the LIGO/VIRGO/GEO/TAMA laser interferometers now under construction. This fact
has motivated several different theoretical studies of the inspiral and
hydrodynamic merging of compact binaries. Analytic analyses of the inspiral
waveforms have been performed in the Post-Newtonian approximation. Analytic and
numerical treatments of the coalescence waveforms from binary neutron stars
have been performed using Newtonian hydrodynamics and the quadrupole radiation
approximation. Numerical simulations of coalescing black hole and neutron star
binaries are also underway in full general relativity. Recent results from each
of these approaches will be described and their virtues and limitations
summarized.


title: A regular C^0 singularity is not necessarily weak

abstract:
  Examples of space-times are given which contain scalar curvature
singularities whereat the metric tensor is regular and continuous, but which
are gravitationally strong. Thus the argument that such singularities are
necessarily weak is incomplete; in particular the question of the gravitational
strength of the null Cauchy horizon singularity which occurs in gravitational
collapse remains open.


title: Strengths of singularities in spherical symmetry

abstract:
  Covariant equations characterizing the strength of a singularity in spherical
symmetry are derived and several models are investigated. The difference
between central and non-central singularities is emphasised. A slight
modification to the definition of singularity strength is suggested. The
gravitational weakness of shell crossing singularities in collapsing spherical
dust is proven for timelike geodesics, closing a gap in the proof.


title: Energy Associated with Schwarzschild Black Hole in a Magnetic Universe

abstract:
  In this paper we obtain the energy distribution associated with the Ernst
space-time (geometry describing Schwarzschild black hole in Melvin's magnetic
universe) in Einstein's prescription. The first term is the rest-mass energy of
the Schwarzschild black hole, the second term is the classical value for the
energy of the uniform magnetic field and the remaining terms in the expression
are due to the general relativistic effect. The presence of the magnetic field
is found to increase the energy of the system.


title:
Quantum gravitational processes in a hot ultrarelativistic gas and their
  effect on the isotropic Universe evolution

abstract:
  The variant of quasiclassical (half-quantum) theory of gravity in strong
gravitational field is presented. The exact solution of the problem of the
renormalized energy-momentum tensor calculation is performed in terms of
non-local operator-signed function. The procedure of quasilocalization is
proposed, which leads to the equations of non-equilibrium thermodynamics for
temperature and curvature. The effects of induced particle creation and media
polarization are taking into account and used to solve the problem of
non-Einstein's branches damping. The problem of Universe creation from
"nothing" is also discussed.


title:
Evolving Einstein's Field Equations with Matter: The ``Hydro without
  Hydro'' Test

abstract:
  We include matter sources in Einstein's field equations and show that our
recently proposed 3+1 evolution scheme can stably evolve strong-field
solutions. We insert in our code known matter solutions, namely the
Oppenheimer-Volkoff solution for a static star and the Oppenheimer-Snyder
solution for homogeneous dust sphere collapse to a black hole, and evolve the
gravitational field equations. We find that we can evolve stably static,
strong-field stars for arbitrarily long times and can follow dust sphere
collapse accurately well past black hole formation. These tests are useful
diagnostics for fully self-consistent, stable hydrodynamical simulations in 3+1
general relativity. Moreover, they suggest a successive approximation scheme
for determining gravitational waveforms from strong-field sources dominated by
longitudinal fields, like binary neutron stars: approximate quasi-equilibrium
models can serve as sources for the transverse field equations, which can be
evolved without having to re-solve the hydrodynamical equations (``hydro
without hydro'').


title: N + 1 dimensional quantum mechanical model for a closed universe

abstract:
  A quantum mechanical model for an N + 1 dimensional universe arising from a
quantum fluctuation is outlined. (3 + 1) dimensions are a closed
infinitely-expanding universe and the remaining N - 3 dimensions are compact.
The (3 + 1) non-compact dimensions are modeled by quantizing a canonical
Hamiltonian description of a homogeneous isotropic universe. It is assumed
gravity and the strong-electro-weak (SEW) forces had equal strength in the
initial state. Inflation occurred when the compact N -3 dimensional space
collapsed after a quantum transition from the initial state of the univers,
during its evolution to the present state where gravity is much weaker than the
SEW force. The model suggests the universe has no singularities and the large
size of our present universe is determined by the relative strength of gravity
and the SEW force today. A small cosmological constant, resulting from the zero
point energy of the scalar field corresponding to the compact dimensions, makes
the model universe expand forever.


title: On a Quantum Equivalence Principle

abstract:
  The logical consistency of a description of Quantum Theory in the context of
General Relativity, which includes Minimal Coupling Principle, is analyzed from
the point of view of Feynman's formulation in terms of path integrals. We will
argue from this standpoint and using an argument that claims the incompleteness
of the general-relativistic description of gravitation, which emerges as a
consequence of the gravitationally induced phases of the so called
flavor-oscillation clocks, that the postulates of Quantum Theory are logically
incompatible with the usual Minimal Coupling Principle. It will be shown that
this inconsistency could emerge from the fact that the required geometrical
information to calculate the probability of finding a particle in any point of
the respective manifold does not lie in a region with finite volume.
Afterwards, we put forth a new Quantum Minimal Coupling Principle in terms of a
restricted path integral, and along the ideas of this model not only the
propagator of a free particle is calculated but we also deduce the conditions
under which we recover Feynman's case for a free particle. The effect on
diatomic interstellar molecules is also calculated. The already existing
relation between Restricted Path Integral Formalism and Decoherence Model will
enable us to connect the issue of a Quantum Minimal Coupling Principle with the
collapse of the wave function. From this last remark we will claim that the
geometrical structure of the involved manifold acts as, an always present,
measuring device on a quantum particle. In other words, in this proposal we
connect the issue of a Quantum Minimal Coupling Principle with a claim which
states that gravity could be one of the physical entities driving the collapse
of the wave function.


title: Generalized Einstein theory with fundamental cosmological stress tensor

abstract:
  Careful analysis of parametrized variational principles in mechanics and
field theory leads to a generalization of Einstein theory that includes a
cosmological stress tensor. This generalization also follows by restricting
variations of the metric in the Hilbert action to spacetime diffeomorphisms.
The equation of motion for the generalized theory is the twice-contracted
Bianchi identity while the field equations constitute the stress tensor of the
theory. Gravity is interpreted as a cosmological fluid.


title:
On the spectrum of relativistic Schroedinger equation in finite
  differences

abstract:
  We develop a method for constructing asymptotic solutions of
finite-difference equations and implement it to a relativistic Schroedinger
equation which describes motion of a selfgravitating spherically symmetric dust
shell. Exact mass spectrum of black hole formed due to the collapse of the
shell is determined from the analysis of asymptotic solutions of the equation.


title:
Does the generalized second law hold in the form of time derivative
  expression?

abstract:
  We investigate whether the generalized second law is valid, using two
dimensional black hole spacetime, irrespective of models. A time derivative
form of the generalized second law is formulated and it is shown that the law
might become invalid. The way to resolve this difficulty is also presented and
discussed.


title:
Lorentz Covariant Theory of Light Propagation in Gravitational Fields of
  Arbitrary-Moving Bodies

abstract:
  The Lorentz covariant theory of propagation of light in the (weak)
gravitational fields of N-body systems consisting of arbitrarily moving
point-like bodies with constant masses is constructed. The theory is based on
the Lienard-Wiechert presentation of the metric tensor. A new approach for
integrating the equations of motion of light particles depending on the
retarded time argument is applied. In an approximation which is linear with
respect to the universal gravitational constant, G, the equations of light
propagation are integrated by quadratures and, moreover, an expression for the
tangent vector to the perturbed trajectory of light ray is found in terms of
instanteneous functions of the retarded time. General expressions for the
relativistic time delay, the angle of light deflection, and gravitational red
shift are derived. They generalize previously known results for the case of
static or uniformly moving bodies. The most important applications of the
theory are given. They include a discussion of the velocity dependent terms in
the gravitational lens equation, the Shapiro time delay in binary pulsars, and
a precise theoretical formulation of the general relativistic algorithm of data
processing of radio and optical astrometric measurements in the non-stationary
gravitational field of the solar system. Finally, proposals for future
theoretical work being important for astrophysical applications are formulated.


title:
Space-Time as an Orderparameter Manifold in Random Networks and the
  Emergence of Physical Points

abstract:
  In the following we are going to describe how macroscopic space-time is
supposed to emerge as an orderparameter manifold or superstructure floating in
a stochastic discrete network structure. As in preceeding work (mentioned
below), our analysis is based on the working philosophy that both physics and
the corresponding mathematics have to be genuinely discrete on the primordial
(Planck scale) level. This strategy is concretely implemented in the form of
cellular networks and random graphs. One of our main themes is the development
of the concept of physical (proto)points as densely entangled subcomplexes of
the network and their respective web, establishing something like
(proto)causality. It max perhaps be said that certain parts of our programme
are realisations of some old and qualitative ideas of Menger and more recent
ones sketched by Smolin a couple of years ago. We briefly indicate how this
two-story-concept of space-time can be used to encode the (at least in our
view) existing non-local aspects of quantum theory without violating
macroscopic space-time causality!


title: Hamiltonian analysis of Poincar\'e gauge theory scalar modes

abstract:
  The Hamiltonian constraint formalism is used to obtain the first explicit
complete analysis of non-trivial viable dynamic modes for the Poincar\'e gauge
theory of gravity. Two modes with propagating spin-zero torsion are analyzed.
The explicit form of the Hamiltonian is presented. All constraints are obtained
and classified. The Lagrange multipliers are derived. It is shown that a
massive spin-$0^-$ mode has normal dynamical propagation but the associated
massless $0^-$ is pure gauge. The spin-$0^+$ mode investigated here is also
viable in general. Both modes exhibit a simple type of ``constraint
bifurcation'' for certain special field/parameter values.


title:
On the incompatibility of experiments confirming certain conclusions of
  the general relativity

abstract:
  Qualitativ arguments are presented which show the incompatibility of the
positive results obtaned in experiments on the gravitational redshift of
photones and in experiments investigating the behavior of clocks in the
gravitational field.


title:
Proof of the symmetry of the off-diagonal heat-kernel and Hadamard's
  expansion coefficients in general $C^{\infty}$ Riemannian manifolds

abstract:
  We consider the problem of the symmetry of the off-diagonal heat-kernel
coefficients as well as the coefficients corresponding to the
short-distance-divergent part of the Hadamard expansion in general smooth
(analytic or not) manifolds. The requirement of such a symmetry played a
central r\^{o}le in the theory of the point-splitting one-loop renormalization
of the stress tensor in either Riemannian or Lorentzian manifolds. Actually,
the symmetry of these coefficients has been assumed as a hypothesis in several
papers concerning these issues without an explicit proof. The difficulty of a
direct proof is related to the fact that the considered off-diagonal
heat-kernel expansion, also in the Riemannian case, in principle, may be not a
proper asymptotic expansion. On the other hand, direct computations of the
off-diagonal heat-kernel coefficients are impossibly difficult in nontrivial
cases and thus no case is known in the literature where the symmetry does not
hold. By approximating $C^\infty$ metrics with analytic metrics in common
(totally normal) geodesically convex neighborhoods, it is rigorously proven
that, in general $C^\infty$ Riemannian manifolds, any point admits a
geodesically convex neighborhood where the off-diagonal heat-kernel
coefficients, as well as the relevant Hadamard's expansion coefficients, are
symmetric functions of the two arguments.


title: Segre decomposition of spacetimes

abstract:
  Following a recent work in which it is shown that a spacetime admitting
Lie-group actions may be disjointly decomposed into a a closed subset with no
interior plus a dense finite union of open sets in each of which the character
and dimension of the group orbits as well as the Petrov type are constant, the
aim of this work is to include the Segre types of the Ricci tensor (and hence
of the Einstein tensor) into the decomposition. We also show how this type of
decomposition can be carried out for any type of property of the spacetime
depending on the existence of a continuous endomorphism.


title:
Inhomogeneous String Cosmology Solutions with Regular Spacetime
  Curvature

abstract:
  In this work cosmological models are considered for the low energy string
cosmological effective action (tree level) in the absence of dilaton potential.
A two parametric non-diagonal family of analytic solutions is found. The
curvature is non singular, however the string coupling diverges exponentially.


title: Degenerate Sectors of the Ashtekar Gravity

abstract:
  This work completes the task of solving locally the Einstein-Ashtekar
equations for degenerate data. The two remaining degenerate sectors of the
classical 3+1 dimensional theory are considered. First, with all densitized
triad vectors linearly dependent and second, with only two independent ones. It
is shown how to solve the Einstein-Ashtekar equations completely by suitable
gauge fixing and choice of coordinates. Remarkably, the Hamiltonian weakly
Poisson commutes with the conditions defining the sectors. The summary of
degenerate solutions is given in the Appendix.


title: Low Velocity Gravitational Capture by Long Cosmic Strings

abstract:
  Coupled ordinary differential equations are derived for the distant
gravitational interaction of a compact object of mass M and charge Q with an
initially straight, infinitely long, cosmic string of tension mu << 1/G = 1,
when the relative velocities are very low compared to the speed of light c = 1.
(An intermediate result of this derivation is that any localized force F(t) on
the string that is confined to a single plane perpendicular to the initial
string configuration gives the intersection of the string with this plane --
the point where the force is applied -- the velocity F(t)/(2 mu).)
  The coupled equations are then used to calculate the critical impact
parameter b for marginal gravitational capture as a function of the incident
velocity v. For v<<(1-Q^2/M^2)^(1/3) mu^(2/3), so that the string acts
relatively stiffly, b = (pi/4)[12 mu^3 (1-Q^2/M^2)^4]^(1/5) M v^(-7/5) + O(M
v^(-1/5)). For (1-Q^2/M^2)^(1/3) mu^(2/3) << v << 1 - Q^2/M^2$, so that the
string acts essentially as a test string that stays nearly straight, b =
[(pi/2)(1-Q^2/M^2)]^(1/2) M v^(-1/2) + O(M v^(-2)). Between these two limits
the critical impact parameter is found numerically to fit a simple algebraic
combination of these two formulas to better than 99.5% accuracy.


title: Planetary Perturbation with Cosmological Constant

abstract:
  A contribution of quantum vacuum to the energy momentum tensor is inevitably
experienced in the present universe. One requires the presence of non-zero
cosmological constant ($\Lambda$) to make the various observations consistent.
A case of $\Lambda$ in the Schwarzschild de Sitter space-time shows that
precession of perihelion orbit provides a sensative solar test for non-zero
$\Lambda$. Application of the relations involving $\Lambda$ to the planetery
perturbation indicates the values near to the present bound on $\Lambda$. Also
suggested are some relations in vacuum dominated flat universe with a positive
$\Lambda$.


title: Maximum Mass of Boson Star Formed by Self-Interacting Scalar Fields

abstract:
  We make analytic derivation for maximum masses of stable boson stars formed
by scalar fields with any higher order self-interactions and show that those
are equivalent to numerical results. It is shown that the contribution of the
higher order self-interaction terms to the maximum mass decreases as
$(m/M_p)^2$ power.


title:
Black holes vs. naked singularities formation in collapsing Einstein's
  clusters

abstract:
  Non-static, spherically symmetric clusters of counter-rotating particles, of
the type first introduced by Einstein, are analysed here. The initial data
space can be parameterized in terms of three arbitrary functions, namely;
initial density, velocity and angular momentum profiles. The final state of
collapse, black hole or naked singularity, turns out to depend on the order of
the first non-vanishing derivatives of such functions at the centre. The work
extends recent results by Harada, Iguchi and Nakao.


title: Foundational Problems in Quantum Gravity

abstract:
  Boundary conditions play a crucial role in the path-integral approach to
quantum gravity and quantum cosmology, as well as in the current attempts to
understand the one-loop semiclassical properties of quantum field theories.
Within this framework, one is led to consider boundary conditions completely
invariant under infinitesimal diffeomorphisms on metric perturbations. These
are part of a general scheme, which can be developed for Maxwell theory,
Yang-Mills Theory, Rarita-Schwinger fields and any other gauge theory. A
general condition for strong ellipticity of the resulting field theory on
manifolds with boundary is here proved, following recent work by the authors.
The relevance for Euclidean quantum gravity is eventually discussed.


title:
A model Universe with variable space dimension: its dynamics and wave
  function

abstract:
  Assuming the space dimension is not constant, but varies with the expansion
of the Universe, a Lagrangian formulation for a toy model Universe is given.
There is a free paremeter in the theory, $C$, with which we can fix the
dimension of space at the Planck time. The standard FRW model corresponds to
the limiting case $C \to +\infty$. We study the Wheeler-De Witt equation and
the wave function of the Universe and the probability density in our model
Universe. In the limit of constant space dimension, our wave function
approaches to the Hartle-Hawking wave function or to a modified Linde wave
function.


title: Variational Principles and Cosmological Models in Higher-Order Gravity

abstract:
  This dissertation investigates three main topics, all of which dealing with
alternative, higher-order gravity theories in four dimensions. Firstly, we
study the variational and conformal structure of those theories. Next, we
analyse their Hamiltonian formulation and in particular its relationship with
the famous ADM canonical version of general relativity. Finally, we study
higher-order spatially homogeneous cosmologies and exemplify how Hamiltonian
methods can be utilised to simplify the analysis of the associated field
equations.


title: A Uniqueness Theorem for Constraint Quantization

abstract:
  This work addresses certain ambiguities in the Dirac approach to constrained
systems. Specifically, we investigate the space of so-called ``rigging maps''
associated with Refined Algebraic Quantization, a particular realization of the
Dirac scheme. Our main result is to provide a condition under which the rigging
map is unique, in which case we also show that it is given by group averaging
techniques. Our results comprise all cases where the gauge group is a
finite-dimensional Lie group.


title: Quantum Clocks and the Origin of Time in Complex Systems

abstract:
  The origin and nature of time in complex systems is explored using quantum
(or 'Feynman') clocks and the signals produced by them. Networks of these
clocks provide the basis for the evolution of complex systems. The general
concept of 'time' is translated into the 'lifetimes' of these unstable
configurations of matter. 'Temporal phase transitions' mark the emergence of
classical properties such as irreversibility, entropy, and thermodynamic arrows
of time. It is proposed that the creation of the universe can be modeled as a
quantum clock. Keywords: the problem of time, the arrow of time, time
asymmetry, the many-body problem, cellular networks, complexity, the
Wheeler-DeWitt equation, quantum cosmology, and instantons.


title: Spacetime Duality of BTZ Black Hole

abstract:
  We consider the duality of the quasilocal black hole thermodynamics,
explicitly the quasilocal black hole thermodynamic first law, in BTZ black hole
solution as a special one of the three-dimensional low energy effective string
theory.


title: Cosmic String Loops Collapsing to Black Holes

abstract:
  We examine the question of collapse of Turok's two-parameter family of cosmic
strings. We first perform a classification of the strings according to the
specific time(s) at which the minimal string size is reached during one period.
We then obtain an exact analytical expression for the probability of collapse
to black holes for the Turok strings. Our result has the same general behavior
as previously obtained in the literature but we find, in addition, a numerical
prefactor that changes the result by three orders of magnitude. Finally we show
that our careful computation of the prefactor helps to understand the
discrepancy between previously obtained results and, in particular, that for
"large" values of $G\mu$, there may not even be a discrepancy. We also give a
simple physical argument that can immediately rule out some of the previously
obtained results.


title: Spacetime foam and the electroweak coupling constant

abstract:
  We compute the regularized temperature for a spacetime foam model, consisting
on S^4 instantons, in quantum gravity. Assuming that thermal equilibrium takes
place with some amount of radiation - with thermal fields in the SU(2)xU(1)
gauge theory - we obtain the remarkable result that the squared value of this
temperature exactly coincides with the electroweak coupling constant at the
energy scale of the gauge bosons W. This is consistent with the classical ADM
result that the electrical charge should be equal to its finite gravitational
self energy.


title: Gravitational field of global monopoles in Einstein-Cartan gravity

abstract:
  The gravitational weak field of a global monopole in the Einstein-Cartan
theory of gravity is investigated.To obtain this solution we assume that Cartan
torsion takes the form of the Newtonian gravitational potential.From the
geodesics it is possible to show that the torsionic monopole produces a
repulsive gravitational force.


title:
Large Fluctuations in the Horizon Area and what they can tell us about
  Entropy and Quantum Gravity

abstract:
  We evoke situations where large fluctuations in the entropy are induced, our
main example being a spacetime containing a potential black hole whose
formation depends on the outcome of a quantum mechanical event. We argue that
the teleological character of the event horizon implies that the consequent
entropy fluctuations must be taken seriously in any interpretation of the
quantal formalism. We then indicate how the entropy can be well defined despite
the teleological character of the horizon, and we argue that this is possible
only in the context of a spacetime or ``histories'' formulation of quantum
gravity, as opposed to a canonical one, concluding that only a spacetime
formulation has the potential to compute --- from first principles and in the
general case --- the entropy of a black hole. From the entropy fluctuations in
a related example, we also derive a condition governing the form taken by the
entropy, when it is expressed as a function of the quantal density-operator.


title: Second-order rotational effects on the r-modes of neutron stars

abstract:
  Techniques are developed here for evaluating the r-modes of rotating neutron
stars through second order in the angular velocity of the star. Second-order
corrections to the frequencies and eigenfunctions for these modes are evaluated
for neutron star models. The second-order eigenfunctions for these modes are
determined here by solving an unusual inhomogeneous hyperbolic boundary-value
problem. The numerical techniques developed to solve this unusual problem are
somewhat non-standard and may well be of interest beyond the particular
application here. The bulk-viscosity coupling to the r-modes, which appears
first at second order, is evaluated. The bulk-viscosity timescales are found
here to be longer than previous estimates for normal neutron stars, but shorter
than previous estimates for strange stars. These new timescales do not
substantially affect the current picture of the gravitational radiation driven
instability of the r-modes either for neutron stars or for strange stars.


title: Robust evolution system for Numerical Relativity

abstract:
  The paper combines theoretical and applied ideas which have been previously
considered separately into a single set of evolution equations for Numerical
Relativity. New numerical ingredients are presented which avoid gauge
pathologies and allow one to perform robust 3D calculations. The potential of
the resulting numerical code is demonstrated by using the Schwarzschild black
hole as a test-bed. Its evolution can be followed up to times greater than one
hundred black hole masses.


title:
Dimensionally continued Oppenheimer-Snyder gravitational collapse II:
  solutions in odd dimensions

abstract:
  The Lovelock gravity extends the theory of general relativity to higher
dimensions in such a way that the field equations remain of second order. The
theory has many constant coefficients with no a priori meaning. Nevertheless it
is possible to reduce them to two, the cosmological constant and Newton's
constant. In this process one separates theories in even dimensions from
theories in odd dimensions. In a previous work gravitational collapse in even
dimensions was analysed. In this work attention is given to odd dimensions. It
is found that black holes also emerge as the final state of gravitational
collapse of a regular dust fluid.


title: Remark on the strength of singularities with a C^0 metric

abstract:
  Recently Nolan constructed a spherically-symmetric spacetime admitting a
spacelike curvature singularity with a regular C^0 metric. We show here that
this singularity is in fact weak.


title:
A review on recent results of the $\zeta$-function regularization
  procedure in curved spacetime

abstract:
  Some recent (1997-1998) theoretical results concerning the $\zeta$-function
regularization procedure used to renormalize, at one-loop, the effective
Lagrangian, the field fluctuations and the stress-tensor in curved spacetime
are reviewed.


title: Self-gravitating line sources of weak hypercharge

abstract:
  We explore the role of the Cremmer-Scherk mechanism in the context of low
energy effective string theory by coupling the antisymmetric 3-form gauge
potential to an Abelian gauge potential carrying weak hypercharge. The theory
admits a class of exact self-gravitating solutions in the spontaneously broken
phase in which the dual fields acquire massive perturbative modes. Despite the
massive nature of these fields they admit non-perturbative progressive
longitudinal modes that together with pp-type gravitational waves travel in a
direction of a line source at the speed of light.


title: Maximally Symmetric Cosmological Solutions of Type II Superstrings

abstract:
  We study maximally symmetric cosmological solutions of type II supersymmetric
strings in the presence of the exact, SL(2,Z)-invariant, higher-curvature
corrections to the lowest order effective action. We find that, unlike the case
of type IIA theories, de Sitter solutions exist, at all orders in $\alpha'$,
for type IIB superstrings, when non-perturbative instanton-effects are included
on the basis of SL(2,Z) invariance.


title: Inhomogeneous Multidimensional Cosmologies

abstract:
  Einstein's equations for a 4+n-dimensional inhomogeneous space-time are
presented, and a special family of solutions is exhibited for an arbitrary n.
The solutions depend on two arbitrary functions of time. The time development
of a particular member of this family is studied. This solution exhibits a
singularity at t=0 and dynamical compactification of the n dimensions. It is
shown that the behaviour of the system in the 4-dimensional i.e.
post-compactification phase is constrained by the way in which the compactified
dimensions are stabilized. The fluid that generates the solution is analyzed by
means of the energy conditions.


title: Inflation and initial conditions in the pre-big bang scenario

abstract:
  The pre-big bang scenario describes the evolution of the Universe from an
initial state approaching the flat, cold, empty, string perturbative vacuum.
The choice of such an initial state is suggested by the present state of our
Universe if we accept that the cosmological evolution is (at least partially)
duality-symmetric. Recently, the initial conditions of the pre-big bang
scenario have been criticized as they introduce large dimensionless parameters
allowing the Universe to be "exponentially large from the very beginning". We
agree that a set of initial parameters (such as the initial homogeneity scale,
the initial entropy) larger than those determined by the initial horizon scale,
H^{-1}, would be somewhat unnatural to start with. However, in the pre-big bang
scenario, the initial parameters are all bounded by the size of the initial
horizon. The basic question thus becomes: is a maximal homogeneity scale of
order H^{-1} necessarily unnatural if the initial curvature is small and,
consequently, H^{-1} is very large in Planck (or string) units? In the
impossibility of experimental information one could exclude "a priori", for
large horizons, the maximal homogeneity scale H^{-1} as a natural initial
condition. In the pre-big bang scenario, however, pre-Planckian initial
conditions are not necessarily washed out by inflation and are accessible (in
principle) to observational tests, so that their naturalness could be also
analyzed with a Bayesan approach, in terms of "a posteriori" probabilities.


title: Topological Censorship and Higher Genus Black Holes

abstract:
  Motivated by recent interest in black holes whose asymptotic geometry
approaches that of anti-de Sitter spacetime, we give a proof of topological
censorship applicable to spacetimes with such asymptotic behavior. Employing a
useful rephrasing of topological censorship as a property of homotopies of
arbitrary loops, we then explore the consequences of topological censorship for
horizon topology of black holes. We find that the genera of horizons are
controlled by the genus of the space at infinity. Our results make it clear
that there is no conflict between topological censorship and the non-spherical
horizon topologies of locally anti-de Sitter black holes. More specifically,
let D be the domain of outer communications of a boundary at infinity ``scri.''
We show that the principle of topological censorship (PTC), that every causal
curve in D having endpoints on scri can be deformed to scri, holds under
reasonable conditions for timelike scri, as it is known to do for a simply
connected null scri. We then show that the PTC implies that the fundamental
group of scri maps, via inclusion, onto the fundamental group of D, i.e., every
loop in D is homotopic to a loop in scri. We use this to determine the integral
homology of preferred spacelike hypersurfaces (Cauchy surfaces or analogues
thereof) in the domain of outer communications of any 4-dimensional spacetime
obeying PTC. From this, we establish that the sum of the genera of the
cross-sections in which such a hypersurface meets black hole horizons is
bounded above by the genus of the cut of infinity defined by the hypersurface.
Our results generalize familiar theorems valid for asymptotically flat
spacetimes requiring simple connectivity of the domain of outer communications
and spherical topology for stationary and slowly evolving black holes.


title: Excitation of the odd-parity quasi-normal modes of compact objects

abstract:
  The gravitational radiation generated by a particle in a close unbounded
orbit around a neutron star is computed as a means to study the importance of
the $w$ modes of the neutron star. For simplicity, attention is restricted to
odd parity (``axial'') modes which do not couple to the neutron star's fluid
modes. We find that for realistic neutron star models, particles in unbounded
orbits only weakly excite the $w$ modes; we conjecture that this is also the
case for astrophysically interesting sources of neutron star perturbations. We
also find that for cases in which there is significant excitation of quadrupole
$w$ modes, there is comparable excitation of higher multipole modes.


title:
Remarks on Conserved Quantities and Entropy of BTZ Black Hole Solutions.
  Part I: the General Setting

abstract:
  The BTZ stationary black hole solution is considered and its mass and angular
momentum are calculated by means of Noether theorem. In particular, relative
conserved quantities with respect to a suitably fixed background are discussed.
Entropy is then computed in a geometric and macroscopic framework, so that it
satisfies the first principle of thermodynamics. In order to compare this more
general framework to the prescription by Wald et al. we construct the maximal
extension of the BTZ horizon by means of Kruskal-like coordinates. A discussion
about the different features of the two methods for computing entropy is
finally developed.


title: Stochastic Gravity

abstract:
  We give a summary of the status of current research in stochastic
semiclassical gravity and suggest directions for further investigations. This
theory generalizes the semiclassical Einstein equation to an Einstein-Langevin
equation with a stochastic source term arising from the fluctuations of the
energy-momentum tensor of quantum fields. We mention recent efforts in applying
this theory to the study of black hole fluctuations and backreaction problems,
linear response of hot flat space, and structure formation in inflationary
cosmology. To explore the physical meaning and implications of this stochastic
regime in relation to both classical and quantum gravity, we find it useful to
take the view that semiclassical gravity is mesoscopic physics and that general
relativity is the hydrodynamic limit of certain spacetime quantum
substructures. Three basic issues - stochasticity, collectivity, correlations-
and three processes - dissipation, fluctuations, decoherence- underscore the
transformation from quantum micro structure and interaction to the emergence of
classical macro structure and dynamics. We discuss ways to probe into the high
energy activity from below and make two suggestions: via effective field theory
and the correlation hierarchy. We discuss how stochastic behavior at low energy
in an effective theory and how correlation noise associated with coarse-grained
higher correlation functions in an interacting quantum field could carry
nontrivial information about the high energy sector. Finally we describe
processes deemed important at the Planck scale, including tunneling and pair
creation, wave scattering in random geometry, growth of fluctuations and forms,
Planck scale resonance states, and spacetime foams.


title:
Remarks on Conserved Quantities and Entropy of BTZ Black Hole Solutions.
  Part II: BCEA Theory

abstract:
  The BTZ black hole solution for (2+1)-spacetime is considered as a solution
of a triad-affine theory (BCEA) in which topological matter is introduced to
replace the cosmological constant in the model. Conserved quantities and
entropy are calculated via Noether theorem, reproducing in a geometrical and
global framework earlier results found in the literature using local
formalisms. Ambiguities in global definitions of conserved quantities are
considered in detail. A dual and covariant Legendre transformation is performed
to re-formulate BCEA theory as a purely metric (natural) theory (BCG) coupled
to topological matter. No ambiguities in the definition of mass and angular
momentum arise in BCG theory. Moreover, gravitational and matter contributions
to conserved quantities and entropy are isolated. Finally, a comparison of BCEA
and BCG theories is carried out by relying on the results obtained in both
theories.


title: Dual spacetimes, Mach's Principle and topological defects

abstract:
  By resolving the Riemann curvature relative to a unit timelike vector into
electric and magnetic parts, we define a duality transformation which
interchanges active and passive electric parts. It implies interchange of roles
of Ricci and Einstein curvatures. Further by modifying the vacuum/flat equation
we construct spacetimes dual to the Schwarzschild solution and flat spacetime.
The dual spacetimes describe the original spacetimes with global monopole
charge and global texture. The duality so defined is thus intimately related to
the topological defects and also renders the Schwarzschild field asymptotically
non-flat which augurs well with Mach's Principle.


title:
On the back reaction of gravitational and particle emission and
  absorption from straight thick cosmic strings: A toy model

abstract:
  The emission and absorption of gravitational waves and massless particles of
an infinitely long straight cosmic string with finite thickness are studied. It
is shown in a general term that the back reaction of the emission and
absorption {\em always} makes the symmetry axis of the string singular. The
singularity is a scalar singularity and cannot be removed.


title: A Family of Gravitational Waveforms from Rapidly Rotating Neutron Stars

abstract:
  This note describes fitting formulae for the gravitational waveforms
generated by a rapidly rotating neutron star (e.g., newly-formed in the core
collapse of a supernova) as it evolves from an initial axisymmetric
configuration toward a triaxial ellipsoid.


title: On Group Averaging for SO(n,1)

abstract:
  The technique known as group averaging provides powerful machinery for the
study of constrained systems. However, it is likely to be well defined only in
a limited set of cases. Here, we investigate the possibility of using a
`renormalized' group averaging in certain models. The results of our study may
indicate a general connection between superselection sectors and the rate of
divergence of the group averaging integral.


title:
The state space and physical interpretation of self-similar spherically
  symmetric perfect-fluid models

abstract:
  The purpose of this paper is to further investigate the solution space of
self-similar spherically symmetric perfect-fluid models and gain deeper
understanding of the physical aspects of these solutions. We achieve this by
combining the state space description of the homothetic approach with the use
of the physically interesting quantities arising in the comoving approach. We
focus on three types of models. First, we consider models that are natural
inhomogeneous generalizations of the Friedmann Universe; such models are
asymptotically Friedmann in their past and evolve fluctuations in the energy
density at later times. Second, we consider so-called quasi-static models. This
class includes models that undergo self-similar gravitational collapse and is
important for studying the formation of naked singularities. If naked
singularities do form, they have profound implications for the predictability
of general relativity as a theory. Third, we consider a new class of
asymptotically Minkowski self-similar spacetimes, emphasizing that some of them
are associated with the self-similar solutions associated with the critical
behaviour observed in recent gravitational collapse calculations.


title: A Radiating and Rotating Metric

abstract:
  A non-static solution of Einstein's field equations of General Relativity
representing the gravitational field of an axisymmetric radiation flow is
obtained using the Eddington or the Kerr-Schild form for the metric. A solution
obtained here manifestly corresponds to the Kerr metric with its
mass-parameter, $m$, being an arbitrary function of the advanced (retarded)
null-time coordinate. Then, when $m$ is constant, the solution reduces to the
standard Kerr metric expressed in terms of the used null coordinate. Further,
when the angular momentum parameter, $a$, a constant here, is set to zero, the
solution reduces to the Vaidya metric expressed in terms of the used
null-coordinate.


title: Mode-Coupling in Rotating Gravitational Collapse of a Scalar Field

abstract:
  We present an analytic study of the mode-coupling phenomena for a scalar
field propagating on a rotating Kerr background. Physically, this phenomena is
caused by the dragging of reference frames, due to the black-hole (or star's)
rotation. We find that different modes become mixed during the evolution and
the asymptotic late-time tails are dominated by a mode which, in general, has
an angular distribution different from the original one. We show that a
rotating Kerr black hole becomes `bald' slower than a spherically-symmetric
Schwarzschild black hole.


title:
Mode-coupling in rotating gravitational collapse: Gravitational and
  electromagnetic perturbations

abstract:
  We consider the late-time evolution of {\it gravitational} and
electromagnetic perturbations in realistic {\it rotating} Kerr spacetimes. We
give a detailed analysis of the mode-coupling phenomena in rotating
gravitational collapse. A consequence of this phenomena is that the late-time
tail is dominated by modes which, in general, may have an angular distribution
different from the original one. In addition, we show that different types of
fields have {\it different} decaying rates. This result turns over the
traditional belief (which has been widely accepted during the last three
decades) that the late-time tail of gravitational collapse is universal.


title: Absolute conservation law for black holes

abstract:
  In all 2d theories of gravity a conservation law connects the (space-time
dependent) mass aspect function at all times and all radii with an integral of
the matter fields. It depends on an arbitrary constant which may be interpreted
as determining the initial value together with the initial values for the
matter field. We discuss this for spherically reduced Einstein-gravity in a
diagonal metric and in a Bondi-Sachs metric using the first order formulation
of spherically reduced gravity, which allows easy and direct fixations of any
type of gauge. The relation of our conserved quantity to the ADM and Bondi mass
is investigated. Further possible applications (ideal fluid, black holes in
higher dimensions or AdS spacetimes etc.) are straightforward generalizations.


title:
Spinning C-metric: radiative spacetime with accelerating, rotating black
  holes

abstract:
  The spinning C-metric was discovered by Plebanski and Demianski as a
generalization of the standard C-metric which is known to represent uniformly
accelerated non-rotating black holes. We first transform the spinning C-metric
into Weyl coordinates and analyze some of its properties as Killing vectors and
curvature invariants. A transformation is then found which brings the metric
into the canonical form of the radiative spacetimes with the boost-rotation
symmetry. By analytically continuing the metric across "acceleration horizons",
two new regions of the spacetime arise in which both Killing vectors are
spacelike.
  We show that this metric can represent two uniformly accelerated, spinning
black holes, either connected by a conical singularity, or with conical
singularities extending from each of them to infinity. The radiative character
of the metric is briefly discussed.


title: Metric-affine gauge theory of gravity II. Exact solutions

abstract:
  In continuing our series on metric-affine gravity (see Gronwald IJMP D6
(1997) 263 for Part I), we review the exact solutions in this theory.


title: Chiral supergravity and anomalies

abstract:
  Similarily as in the Ashtekar approach, the translational Chern-Simons term
is, as a generating function, instrumental for a chiral reformulation of simple
(N=1) supergravity. After applying the algebraic Cartan relation between spin
and torsion, the resulting canonical transformation induces not only
decomposition of the gravitational fields into selfdual and antiselfdual modes,
but also a splitting of the Rarita-Schwinger fields into their chiral parts in
a natural way. In some detail, we also analyze the consequences for axial and
chiral anomalies.


title: Vacuumless torsion defects

abstract:
  Vacuumless defects in space-times with torsion may be obtained from vacuum
defects in spacetimes without torsion.This idea is applied to planar domain
walls and global monopoles.In the case of domain walls exponentially decaying
Higgs type potentials are obtained.In the case of global monopoles torsion
string type singularities are obtained like the string singularities in Dirac
monopoles.


title: Self-force approach to synchrotron radiation

abstract:
  We analyze radiation reaction for synchrotron radiation by computing, via a
multipole expansion, the near field evaluated on the world-line of the charge.
We find that the temporal component of the self four-force agrees with the
radiated power, which one calculates in the radiation zone. This is the case
for each mode in the multipole decomposition. We also find agreement with the
Abraham-Lorentz-Dirac equation.


title: Local Existence of Spinor- and Tensor Potentials

abstract:
  We give new simple direct proofs in all spacetimes for the existence of
asymmetric $(n,m+1)$-spinor potentials for completely symmetric
$(n+1,m)$-spinors and for the existence of symmetric $(n,1)$-spinor potentials
for symmetric $(n+1,0)$-spinors. These proofs introduce a `superpotential',
i.e., a potential of the potential, which also enables us to get explicit
statements of the gauge freedom of the original potentials. The main
application for these results is the Lanczos potential $L_{ABCA'}$, of the Weyl
spinor and the electromagnetic vector potential $A_{AA'}$. We also investigate
the possibility of existence of a {\em symmetric} potential $H_{ABA'B'}$ for
the Lanczos potential, and prove that in {\em all Einstein spacetimes} any
symmetric (3,1)-spinor $L_{ABCA'}$ possesses a symmetric potential
$H_{ABA'B'}$. Potentials of this type have been found earlier in investigations
of some very special spinors in restricted classes of spacetimes. All of the
new spinor results are translated into tensor notation, and where possible
given also for four dimensional spaces of arbitrary signature.


title: Thick domain wall universes

abstract:
  We investigate the spacetime of a thick gravitating domain wall for a general
potential $V(\Phi)$. Using general analytical arguments we show that all
nontrivial solutions fall into two categories: those interpretable as an
isolated domain wall with a cosmological event horizon, and those which are
pure false vacuum de Sitter solutions. Although this latter solution is always
unstable to the field rolling coherently to its true vacuum, we show that there
is an additional instability to wall formation if the scalar field does not
couple too strongly to gravity. Using the $\lambda \Phi^4$ and sine-Gordon
models as illustrative examples, we investigate the phase space of the
gravitating domain wall in detail numerically, following the solutions from
weak to strong gravity. We find excellent agreement with the analytic work.
Then, we analyse the domain wall in the presence of a cosmological constant
finding again the two kinds of solutions, wall and de Sitter, even in the
presence of a negative cosmological constant.


title: Late-time decay of scalar perturbations outside rotating black holes

abstract:
  We present an analytic method for calculating the late-time tails of a linear
scalar field outside a Kerr black hole. We give the asymptotic behavior at
timelike infinity (for fixed $r$), at future null infinity, and along the event
horizon (EH). In all three asymptotic regions we find a power-law decay. We
show that the power indices describing the decay of the various modes at fixed
$r$ differ from the corresponding Schwarzschild values. Also, the scalar field
oscillates along the null generators of the EH (with advanced-time frequency
proportional to the mode's magnetic number $m$).


title: Illusions of general relativity in Brans-Dicke gravity

abstract:
  Contrary to common belief, the standard tenet of Brans-Dicke theory reducing
to general relativity when omega tends to infinity is false if the trace of the
matter energy-momentum tensor vanishes. The issue is clarified in a new
approach using conformal transformations. The otherwise unaccountable limiting
behavior of Brans-Dicke gravity is easily understood in terms of the conformal
invariance of the theory when the sources of gravity have radiation-like
properties. The rigorous computation of the asymptotic behavior of the
Brans-Dicke scalar field is straightforward in this new approach.


title:
On the normalization of Killing vectors and energy conservation in
  two-dimensional gravity

abstract:
  We explicitly show that, in the context of a recently proposed 2D dilaton
gravity theory, energy conservation requires the ``natural'' Killing vector to
have, asymptotically, an unusual normalization. The Hawking temperature $T_H$
is then calculated according to this prescription.


title: High-Frequency Gravitational Waves from Hairy Black Holes

abstract:
  We investigated the stability of the spherically symmetric non-abelian
(Bartnik-McKinnon) black hole solution of the SU(2) Einstein-Yang-Mills system
using the multiple-scale analysis. It is found, in contrast with the vacuum
situation, that a spherically symmetric oscillatory perturbation to second
order cannot be constructed. The singular behavior of gravitational waves is
induced by the coupling of the gravitational waves to the Yang-Mills waves.


title: Black hole polarization and new entropy bounds

abstract:
  Zaslavskii has suggested how to tighten Bekenstein's bound on entropy when
the object is electrically charged. Recently Hod has provided a second tighter
version of the bound applicable when the object is rotating. Here we derive
Zaslavskii's optimized bound by considering the accretion of an ordinary
charged object by a black hole. The force originating from the polarization of
the black hole by a nearby charge is central to the derivation of the bound
from the generalized second law. We also conjecture an entropy bound for
charged rotating objects, a synthesis of Zaslavskii's and Hod's. On the basis
of the no hair principle for black holes, we show that this last bound cannot
be tightened further in a generic way by knowledge of ``global'' conserved
charges, e.g., baryon number, which may be borne by the object.


title: Simplicial minisuperspace models in the presence of a scalar field

abstract:
  We generalize simplicial minisuperspace models associated with restricting
the topology of the universe to be that of a cone over a closed connected
combinatorial $3-$manifold by considering the presence of a massive scalar
field. By restricting all the interior edge lengths and all the boundary edge
lengths to be equivalent and the scalar field to be homogenous on the
$3-$space, we obtain a family of two dimensional models that include some of
the most relevant triangulations of the spatial universe. After studying the
analytic properties of the action in the space of complex edge lengths we
determine its classical extrema.
  We then obtain steepest descents contours of constant imaginary action
passing through Lorentzian classical geometries yielding a convergent
wavefunction of the universe, dominated by the contributions coming from these
extrema. By considering these contours we justify semiclassical approximations
based on those classical solutions, clearly predicting classical spacetime in
the late universe. These wavefunctions are then evaluated numerically.
  For all of the models examined we find wavefunctions predicting Lorentzian
oscillatory behaviour in the late universe.


title: Cosmological scaling solutions of non-minimally coupled scalar fields

abstract:
  We study the existence and stability of cosmological scaling solutions of a
non-minimally coupled scalar field evolving in either an exponential or inverse
power law potential. We show that for inverse power law potentials there exist
scaling solutions the stability of which does not depend on the coupling
constant $\xi$. We then study the more involved case of exponential potentials
and show that the scalar field will assymptotically behaves as a barotropic
fluid when $\xi\ll 1$. The general case $\xi\not\ll 1$ is then discussed an we
illustrate these results by some numerical examples.


title:
Cosmic acceleration and a natural solution to the cosmological constant
  problem

abstract:
  We trace the origin of the cosmological constant problem to the assumption
that Newton's constant $G$ sets the scale for cosmology. And then we show that
once this assumption is relaxed, the very same cosmic acceleration which has
served to make the cosmological constant problem so very severe instead then
serves to provide us with its potential resolution. We present an alternate
cosmology, one based on conformal gravity, and show that once given only that
the sign of the vacuum energy density $\Lambda$ is explicitly the negative one
associated with spontaneous breakdown of the scale invariance of the conformal
theory (this actually being the choice of sign for $\Lambda$ which precisely
leads to cosmic acceleration in conformal gravity), then that alone, no matter
how big $\Lambda$ might actually be in magnitude, is sufficient to not only
make its measurable contribution to current era cosmology naturally be of order
one today, but to even do so in a way which is completely compatible with the
recent high $z$ supernovae cosmology data. Cosmology can thus live with either
a fundamental $G$ or with the large (and even potentially negative) $\Lambda$
associated with elementary particle physics phase transitions but not with
both. Also, we distinguish between the free energy and the internal energy,
with it being the former which determines cosmological phase transitions and
the latter which is the source of the gravitational field. Then we show that,
even if we make the standard ad hoc assumption that $\Lambda$ actually is
quenched in standard gravity, vacuum energy is nonetheless still found to
dominate standard cosmology at the time of the phase transition which produced
it. However, within conformal gravity no such difficulty is encountered.


title:
Vacuum Polarization of Massless Spinor Field in Global Monopole
  Spacetime

abstract:
  We calculate the renormalized vacuum average of the energy-momentum tensor of
massless left-handed spinor field in the pointlike global monopole spacetime
using point-separation approach. The general structure of the vacuum average of
the energy-momentum tensor is obtained and expressed in terms of
$<T^0_0>^{ren}$ component, explicit form of which is analyzed in great details
for arbitrary solid angle deficit.


title: Relativistic Spheres

abstract:
  By analyzing the Einstein's equations for the static sphere, we find that
there exists a non-singular static configuration whose radius can approach its
corresponding horizon size arbitrarily.


title:
Isotropic cosmological singularities 1: Polytropic perfect fluid
  spacetimes

abstract:
  We consider the conformal Einstein equations for polytropic perfect fluid
cosmologies which admit an isotropic singularity. For the polytropic index
gamma strictly greater than 1 and less than or equal to 2 it is shown that the
Cauchy problem for these equations is well-posed, that is to say that solutions
exist, are unique and depend smoothly on the data, with data consisting of
simply the 3-metric of the singularity. The analogous result for gamma=1 (dust)
is obtained when Bianchi type symmetry is assumed.


title: Isotropic cosmological singularities 2: The Einstein-Vlasov system

abstract:
  We consider the conformal Einstein equations for massless collisionless gas
cosmologies which admit an isotropic singularity. After developing the general
theory, we restrict to spatially-homogeneous cosmologies. We show that the
Cauchy problem for these equations is well-posed with data consisting of the
limiting particle distribution function at the singularity.


title: Universal Upper Bound to the Entropy of a Charged System

abstract:
  We derive a universal upper bound to the entropy of a charged system. The
entropy bound follows from application of the generalized second law of
thermodynamics to a gedanken experiment in which an entropy-bearing charged
system falls into a charged black hole. This bound is stronger than the
Bekenstein entropy bound for neutral systems.


title: Improved Upper Bound to the Entropy of a Charged System

abstract:
  Recently, we derived an improved universal upper bound to the entropy of a
charged system $S \leq \pi (2E b-q^2)/ \hbar$. There was, however, some
uncertainty in the value of the numerical factor which multiplies the $q^2$
term. In this paper we remove this uncertainty; we rederive this upper bound
from an application of the generalized second law of thermodynamics to a
gedanken experiment in which an entropy-bearing charged system falls into a
Schwarzschild black hole. A crucial step in the analysis is the inclusion of
the effect of the spacetime curvature on the electrostatic self-interaction of
the charged system.


title: Domain Wall Spacetimes and Particle Motion

abstract:
  We present a mathematical framework for generating thick domain wall
solutions to the coupled Einstein-scalar field equations which are (locally)
plane symmetric. This approach leads naturally to two broad classes of
wall-like solutions. The two classes include all previously known thick domain
walls.
  Although one of these classes is static and the other dynamic, the
corresponding Einstein-scalar equations share the same mathematical structure
independent of the assumption of any reflection symmetry. We also exhibit a
class of thick static domain wall spacetimes with different asymptotic vacua.
Our analyses of particle motion in such spacetimes raises the interesting
possibility that static domain walls will possess a unique experimental
signature.


title:
Removing non-stationary, non-harmonic external interference from
  gravitational wave interferometer data

abstract:
  We describe a procedure to identify and remove a class of non-stationary and
non-harmonic interference lines from gravitational wave interferometer data.
  These lines appear to be associated with the external electricity main
supply, but their amplitudes are non-stationary and they do not appear at
harmonics of the fundamental supply frequency. We find an empirical model able
to represent coherently all the non-harmonic lines we have found in the power
spectrum, in terms of an assumed reference signal of the primary supply input
signal. If this signal is not available then it can be reconstructed from the
same data by making use of the coherent line removal algorithm that we have
described elsewhere. All these lines are broadened by frequency changes of the
supply signal, and they corrupt significant frequency ranges of the power
spectrum. The physical process that generates this interference is so far
unknown, but it is highly non-linear and non-stationary. Using our model, we
cancel the interference in the time domain by an adaptive procedure that should
work regardless of the source of the primary interference. We have applied the
method to laser interferometer data from the Glasgow prototype detector, where
all the features we describe in this paper were observed. The algorithm has
been tuned in such a way that the entire series of wide lines corresponding to
the electrical interference are removed, leaving the spectrum clean enough to
detect signals previously masked by them. Single-line signals buried in the
interference can be recovered with at least 75 % of their original signal
amplitude.