title:
General behaviour of Bianchi VI_0 solutions with an
  exponential-potential scalar field

abstract:
  The solutions to the Einstein-Klein-Gordon equations without a cosmological
constant are investigated for an exponential potential in a Bianchi VI_0
metric. There exists a two-parameter family of solutions which have a power-law
inflationary behaviour when the exponent of the potential, k, satisfies k^2<2.
In addition, there exists a two-parameter family of singular solutions for all
k^2 values. A simple anisotropic exact solution is found to be stable when
2<k^2.


title: Asymptotic Freedom Cosmology

abstract:
  For a general class of scalar--tensor gravity theories, we discuss how to
recover asymptotic freedom regimes when cosmic time $t\to\pm\infty$. Such a
feature means that the effective gravitational coupling $G_{eff}\to 0$, while
cosmological solutions can asymptotically assume de Sitter or power--law
behaviours. In our opinion, through this mechanism, it is possible to cure some
shortcomings in inflationary and in string--dilaton cosmology.


title:
Oscillating universes as eigensolutions of cosmological Schr\"odinger
  equation

abstract:
  We propose a cosmological model which could explain, in a very natural way,
the apparently periodic structures of the universe, as revealed in a series of
recent observations. Our point of view is to reduce the cosmological
Friedman--Einstein dynamical system to a sort of Schr\"odinger equation whose
bound eigensolutions are oscillating functions. Taking into account the
cosmological expansion, the large scale periodic structure could be easily
recovered considering the amplitudes and the correlation lengths of the galaxy
clusters.


title: Phase diagram of the mean field model of simplicial gravity

abstract:
  We discuss the phase diagram of the balls in boxes model, with a varying
number of boxes. The model can be regarded as a mean-field model of simplicial
gravity. We analyse in detail the case of weights of the form $p(q) =
q^{-\beta}$, which correspond to the measure term introduced in the simplicial
quantum gravity simulations. The system has two phases~: {\em elongated} ({\em
fluid}) and {\em crumpled}. For $\beta\in (2,\infty)$ the transition between
these two phases is first order, while for $\beta \in (1,2]$ it is continuous.
The transition becomes softer when $\beta$ approaches unity and eventually
disappears at $\beta=1$. We then generalise the discussion to an arbitrary set
of weights. Finally, we show that if one introduces an additional kinematic
bound on the average density of balls per box then a new {\em condensed} phase
appears in the phase diagram. It bears some similarity to the {\em crinkled}
phase of simplicial gravity discussed recently in models of gravity interacting
with matter fields.


title:
Distance-redshift relation in an isotropic inhomogeneous universe:
  Spherically symmertic dust-shell universe

abstract:
  The relation between angular diameter distance and redshift in a spherically
symmetric dust-shell universe is studied. This model has large inhomogeneities
of matter distribution on small scales. We have discovered that the relation
agrees with that of an appropriate Friedmann-Lemaitre(FL) model if we set a
``homogeneous'' expansion law and a ``homogeneous'' averaged density field.
This will support the averaging hypothesis that a universe looks like a FL
model in spite of small-scale fluctuations of density field, if its averaged
density field is homogeneous on large scales.


title:
Friedmann Limit of a point mass universe (is not
  Friedmann):Gravinational Lens Effect

abstract:
  We study the distance-redshift relation in a universe filled with point
particles, and discuss what the universe looks like when we make the number of
particles N very large, while fixing the averaged mass density. Using the
Raychaudhuri equation and a simple analysis of the probability of strong
lensing effects, we show that the statistical nature of the amplification is
independent of N, and clarify the appearance of the point particle universe.


title: Integration using invariant operators:Conformally flat radiation metrics

abstract:
  A new method is presented for obtaining the general conformally flat
radiation metric by using the differential operators of Machado Ramos and
Vickers (a generalisation of the GHP operators) which are invariant under null
rotations and spin and boosts. The solution is found by constructing involutive
tables of these derivatives applied to the quantities which arise in the
Karlhede classification of metrics.


title: Fractal local galaxy number counts may imply strong bias

abstract:
  Exact Tolman solutions are used to analyse the implications if the galactic
number has a fractal form out to a distance of about 150 Mpc in a universe
which is homogeneous on the large scale. It is concluded that such a model
requires either a non-linear Hubble law or a very low density if galaxies trace
the total matter distribution.


title: Consistent Sets and Contrary Inferences: Reply to Griffiths and Hartle

abstract:
  It was pointed out recently [A. Kent, Phys. Rev. Lett. 78 (1997) 2874] that
the consistent histories approach allows contrary inferences to be made from
the same data. These inferences correspond to projections $P$ and $Q$,
belonging to different consistent sets, with the properties that $PQ = QP = 0$
and $P \neq 1 -Q$. To many, this seems undesirable in a theory of physical
inferences. It also raises a specific problem for the consistent histories
formalism, since that formalism is set up so as to eliminate contradictory
inferences, i.e. inferences $P$ and $Q$ where $P = 1 - Q$. Yet there seems to
be no sensible physical distinction between contradictory and contrary
inferences.
  It seems particularly hard to defend the asymmetry, since (i) there is a
well-defined quantum histories formalisms which admits both contradictory and
contrary inferences, and (ii) there is also a well-defined formalism, based on
ordered consistent sets of histories, which excludes both.
  In a recent comment, Griffiths and Hartle, while accepting the validity of
the examples given in the above paper, restate their own preference for the
consistent histories formalism. As this brief reply explains, in so doing, they
fail to address the arguments made against their approach to quantum theory.


title:
On detecting the gravitomagnetic field of the earth by means of orbiting
  clocks

abstract:
  Based on the recent finding that the difference in proper time of two clocks
in prograde and retrograde equatorial orbits about the Earth is of the order
10^{-7}s per revolution, the possibility of detecting the terrestrial
gravitomagnetic field by means of clocks carried by satellites is discussed. A
mission taking advantage of this influence of the rotating Earth on the proper
time is outlined and the conceptual difficulties are briefly examined.


title:
No supercritical supercurvature mode conjecture in one-bubble open
  inflation

abstract:
  In the path integral approach to false vacuum decay with the effect of
gravity, there is an unsolved problem, called the negative mode problem. We
show that the appearance of a supercritical supercurvature mode in the
one-bubble open inflation scenario is equivalent to the existence of a negative
mode around the Euclidean bounce solution. Supercritical supercurvature modes
are those whose mode functions diverge exponentially for large spatial radius
on the time constant hypersurface of the open universe. Then we propose a
conjecture that there should be ``no supercritical supercurvature mode''. For a
class of models that contains a wide variety of tunneling potentials, this
conjecture is shown to be correct.


title:
$<T^{\mu}_{\nu}>_{ren}$ of the quantized fields in the Unruh state in
  the Schwarzschild spacetime

abstract:
  The renormalized expectation value of the stress energy tensor of the
conformally invariant massless fields in the Unruh state in the Schwarzschild
spacetime is constructed. It is achieved through solving the conservation
equation in conformal space and utilizing the regularity conditions in the
physical metric. The relations of obtained results to the existing
approximations are analysed.


title: The Inverse Variational Problem for Autoparallels

abstract:
  We study the problem of the existence of a local quantum scalar field theory
in a general affine metric space that in the semiclassical approximation would
lead to the autoparallel motion of wave packets, thus providing a deviation of
the spinless particle trajectory from the geodesics in the presence of torsion.
The problem is shown to be equivalent to the inverse problem of the calculus of
variations for the autoparallel motion with additional conditions that the
action (if it exists) has to be invariant under time reparametrizations and
general coordinate transformations, while depending analytically on the torsion
tensor. The problem is proved to have no solution for a generic torsion in
four-dimensional spacetime. A solution exists only if the contracted torsion
tensor is a gradient of a scalar field. The corresponding field theory
describes coupling of matter to the dilaton field.


title:
Quasiclassical mass spectrum of the black hole model with
  selfgravitating dust shell

abstract:
  We consider a quantum mechanical black hole model introduced in {\it
Phys.Rev.}, {\bf D57}, 1118 (1998) that consists of the selfgravitating dust
shell. The Schroedinger equation for this model is a finite difference equation
with the shift of the argument along the imaginary axis. Solving this equation
in quasiclassical limit in complex domain leads to quantization conditions that
define discrete quasiclassical mass spectrum. One of the quantization
conditions is Bohr-Sommerfeld condition for the bound motion of the shell. The
other comes from the requirement that the wave function is unambiguously
defined on the Riemannian surface on which the coefficients of Schroedinger
equation are regular. The second quantization condition remains valid for the
unbound motion of the shell as well, and in the case of a collapsing null-dust
shell leads to $m\sim\sqrt{k}$ spectrum.


title:
Spontaneous Generation of Torsion Coupling of Electroweak Massive Gauge
  Bosons

abstract:
  We derive the coupling to torsion of massive electroweak vector bosons
generated by the Higgs mechanism.


title: Discrete Riemannian Geometry

abstract:
  Within a framework of noncommutative geometry, we develop an analogue of
(pseudo) Riemannian geometry on finite and discrete sets. On a finite set,
there is a counterpart of the continuum metric tensor with a simple geometric
interpretation. The latter is based on a correspondence between first order
differential calculi and digraphs. Arrows originating from a vertex span its
(co)tangent space. If the metric is to measure length and angles at some point,
it has to be taken as an element of the left-linear tensor product of the space
of 1-forms with itself, and not as an element of the (non-local) tensor product
over the algebra of functions. It turns out that linear connections can always
be extended to this left tensor product, so that metric compatibility can be
defined in the same way as in continuum Riemannian geometry. In particular, in
the case of the universal differential calculus on a finite set, the Euclidean
geometry of polyhedra is recovered from conditions of metric compatibility and
vanishing torsion. In our rather general framework (which also comprises
structures which are far away from continuum differential geometry), there is
in general nothing like a Ricci tensor or a curvature scalar. Because of the
non-locality of tensor products (over the algebra of functions) of forms,
corresponding components (with respect to some module basis) turn out to be
rather non-local objects. But one can make use of the parallel transport
associated with a connection to `localize' such objects and in certain cases
there is a distinguished way to achieve this. This leads to covariant
components of the curvature tensor which then allow a contraction to a Ricci
tensor. In the case of a differential calculus associated with a hypercubic
lattice we propose a new discrete analogue of the (vacuum) Einstein equations.

categories: gr-qc hep-lat hep-th math-ph math.DG math.MP


title:
Numerical Relativity for Inspiraling Binaries in Co-Rotating
  Coordinates: Test Bed for Lapse and Shift Equations

abstract:
  Gravitational-wave data analysis requires a detailed understanding of the
highly relativistic, late stages of inspiral of neutron-star and black-hole
binaries. A promising method to compute the late inspiral and its emitted waves
is numerical relativity in co-rotating coordinates. The coordinates must be
kept co-rotating via an appropriate choice of numerical relativity's lapse and
shift functions. This article proposes a model problem for testing the ability
of various lapse and shift prescriptions to keep the coordinates co-rotating.


title:
Evolution of Nonlinear Perturbations Inside Einstein-Yang-Mills Black
  Holes

abstract:
  We present our results on numerical study of evolution of nonlinear
perturbations inside spherically symmetric black holes in the SU(2)
Einstein-Yang-Mills (EYM) theory. Recent developments demonstrate a new type of
the behavior of the metric for EYM black hole interiors; the generic metric
exhibits an infinitely oscillating approach to the singularity, which is a
spacelike but not of the mixmaster type. The evolution of various types of
spherically symmetric perturbations, propagating from the internal vicinity of
the external horizon towards the singularity is investigated in a
self-consistent way using an adaptive numerical algorithm. The obtained results
give a strong numerical evidence in favor of nonlinear stability of the generic
EYM black hole interiors. Alternatively, the EYM black hole interiors of
S(chwarzschild)-type, which form only a zero measure subset in the space of all
internal solutions are found to be unstable and transform to the generic type
as perturbations are developed.


title: Gravitational Collapse of a Shell of Quantized Matter

abstract:
  The semi-classical collapse, including lowest order back-reaction, of a thin
shell of self-gravitating quantized matter is illustrated. The conditions for
which self-gravitating matter forms a thin shell are first discussed and an
effective Lagrangian for such matter is obtained. The matter-gravity system is
then quantized, the semi-classical limit for gravitation is taken and the
method of adiabatic invariants is applied to the resulting time dependent
matter Hamiltonian. The governing equations are integrated numerically, for
suitable initial conditions, in order to illustrate the effect of
back-reaction, due to the creation of matter, in slowing down the collapse near
the horizon.


title: Black hole mass spectrum vs spectrum of Hawking radiation

abstract:
  We consider a massive selfgravitating shell as a model for collapsing body
and a null selfgravitating shell as a model for quanta of Hawking radiation. It
is show that the mass-energy spectra for the body and the radiation do not
match. The way out of this difficulty is to consider not only out-going
radiation but also the ingoing one. It means that the structure of black hole
is changing during its evaporation resulting in the Bekenstein-Mukhanov
spectrum for large masses.


title:
Black Holes: Classical Properties, Thermodynamics and Heuristic
  Quantization

abstract:
  I discuss the no hair principle, the recently found hairy solutions, generic
properties of nonvacuum spherical static black holes, and the new no scalar
hair theorems. I go into the generic phenomenon of superradiance, first uniform
linear motion superradiance, then Kerr black hole superradiance, and finally
general rotational superradiance and its possible applications in the
laboratory. I show that the horizon area of a nearly stationary black hole can
be regarded as an adiabatic invariant. This invariance suggests that quantum
horizon area is quantized in multiples of a basic unit. Consideration of the
quantum version of the Christodoulou reversible processes provides support for
this idea. Horizon area quantization dictates a definite discrete black hole
mass spectrum, so that Hawking's semiclassical spectrum is predicted to be
replaced by a spectrum of nearly uniformly spaced lines whose envelope is
roughly Planckian. Line natural broadening seems not enough to wash out the
lines. To check on the possibility of line splitting, I present a simple
algebra involving, among other operators, the black hole observables. Under
simple assumptions it also leads to the uniformly spaced area spectrum.


title:
An interferometric gravitational wave detector as a quantum-gravity
  apparatus

abstract:
  As a consequence of the extreme precision of the measurements it performs, an
interferometric gravitational wave detector is a macroscopic apparatus for
which quantum effects are not negligible. I observe that this property can be
exploited to probe some aspects of the interplay between Quantum Mechanics and
Gravity.


title: The Dirac particle on de Sitter background

abstract:
  We show that the Dirac equation on de Sitter background can be analytically
solved in a special static frame where the energy eigenspinors can be expressed
in terms of usual angular spinors known from special relativity, and a pair of
radial wave functions.


title: Nucleosynthesis in a simmering univeerse

abstract:
  Primordial nucleosynthesis is considered a success story of the standard big
bang (SBB) cosmology. The cosmological and elementary particle physics
parameters are believed to be severely constrained by the requirement of
correct abundances of light elements. We explore nucleosynthesis in a class of
models very different from SBB. In these models the cosmological scale factor
increases linearly with time right through the period during which
nucleosynthesis occurs till the present. It turns out that weak interactions
remain in thermal equilibrium upto temperatures which are two orders of
magnitude lower than the corresponding (weak interaction decoupling)
temperature in SBB. Inverse beta decay of the proton can ensure adequate
production of several light elements while producing primordial metalicity much
higher than that produced in SBB. Other attractive features of these models are
the absence of the horizon, flatness and the age problems and consistency with
classical cosmological tests.


title: Comment on ``Theorem for nonrotating singularity-free universes''

abstract:
  We show that Raychaudhuri's recently proposed theorem on nonrotating
universes cannot be used to rule out realistic singularity-free descriptions of
the universe, as suggested by him in PRL 80, 654 (1998).


title:
Quantum Measurement Problem and the Possible Role of the Gravitational
  Field

abstract:
  The quantum measurement problem and various unsuccessful attempts to resolve
it are reviewed. A suggestion by Diosi and Penrose for the half life of the
quantum superposition of two Newtonian gravitational fields is generalized to
an arbitrary quantum superposition of relativistic, but weak, gravitational
fields. The nature of the ``collapse'' process of the wave function is
examined.


title: Real Tunneling and Black Hole Creation

abstract:
  The concept of constrained gravitational instanton is introduced. It is used
to study black hole creation. We discussed the global aspects of the scenario
and the alternative tunnelings.


title: Black Holes

abstract:
  Black holes are among the most intriguing objects in modern physics. Their
influence ranges from powering quasars and other active galactic nuclei, to
providing key insights into quantum gravity. We review the observational
evidence for black holes, and briefly discuss some of their properties. We also
describe some recent developments involving cosmic censorship and the
statistical origin of black hole entropy.


title:
Gyroscopic Precession and Inertial Forces in Axially Symmetric
  Stationary Spacetimes

abstract:
  We study the phenomenon of gyroscopic precession and the analogues of
inertial forces within the framework of general relativity. Covariant
connections between the two are established for circular orbits in stationary
spacetimes with axial symmetry. Specializing to static spacetimes, we prove
that gyroscopic precession and centrifugal force both reverse at the photon
orbits. Simultaneous non-reversal of these in the case of stationary spacetimes
is discussed. Further insight is gained in the case of static spacetime by
considering the phenomena in a spacetime conformal to the original one.
Gravi-electric and gravi-magnetic fields are studied and their relation to
inertial forces is established.


title: Stability Issues in Euclidean Quantum Gravity

abstract:
  It is known that the action of Euclidean Einstein gravity is not bounded from
below and that the metric of flat space does not correspond to a minimum of the
action. Nevertheless, perturbation theory about flat space works well. The deep
dynamical reasons for this reside in the non perturbative behaviour of the
system and have been clarified in part by numerical simulations. Several open
issues remain. We treat in particular those zero modes of the action for which
R(x) is not identically zero, but the integral of sqrt{g(x)} R(x) vanishes.


title: Quantum Black Hole

abstract:
  Creation of a black hole in quantum cosmology is the third way of black hole
formation. In contrast to the gravitational collapse from a massive body in
astrophysics or from the quantum fluctuation of matter fields in the very early
universe, in quantum cosmology scenario the black hole is essentially created
from nothing. The black hole originates from a constrained gravitational
instanton. The probability of creation for all kinds of single black holes in
the Kerr- Newman-de Sitter family, at the semi-classical level, is the
exponential of the total entropy of the universe, or one quarter of the sum of
both the black hole and the cosmological horizon areas. The de Sitter spacetime
is the most probable evolution at the Planckian era.


title:
On a Growing Transverse Mode as a Post-Newtonian Effect in the
  Large-Scale Structure Formation

abstract:
  We point out the existence of a new type of growing transverse mode in the
gravitational instability. This appears as a post-Newtonian effect to Newtonian
dynamics. We demonstrate this existence by formulating the Lagrangian
perturbation theory in the framework of the cosmological post-Newtonian
approximation in general relativity. Such post-Newtonian order effects might
produce characteristic appearances of large-scale structure formation, for
example, through the observation of anisotropy of the cosmic microwave
background radiation (CMB).


title:
Collapsing open isotropic universe generated by nonminimally coupled
  scalar field

abstract:
  We investigated the behavior of an open isotropic universe generated by a
scalar field which couples with background curvature nonminimally with the
coupling constant $\xi$. In particular we focus on the situation where the
initial value for the scalar field $\phi_{\rm in}$ is greater than the critical
value ${\hat \phi}_c$=${m_p}/{\sqrt{8\pi\xi(1-6\xi)}}$. The behavior is similar
to an open de Sitter universe with $k=-1$ with a negative cosmological constant
$\Lambda <0$. It is found that the universe will collapse eventually to a
singularity and thus has a finite extent in time in the future. Furthermore,
there are some cases which shows a rebouncing behavior before the final
collapse.


title: Chaos after Two-Field Inflation

abstract:
  We show that two-field inflation can be followed by an era in which the field
dynamics become chaotic, and discuss the possible consequences of this for
two-field inflationary models. [PASCOS conference proceedings - a short version
of gr-qc/9711035]


title: Scalar Black Holes

abstract:
  A class of exact regular spherically symmetric solutions to the Einstein
equation obeying Dymnikova's definition of the vacuumlike state is considered.
These solutions, which may be interpreted as black holes, are not only
singularity free, but also do not set us thinking about the loss of information
under gravitational collapse. According to the singularity theorems, the
geometries introduced by these solutions inevitably have some causal pathology.
However, if the vacuumlike state is reinterpreted to be a sort of `confinement'
representing a particular phase of matter, this pathology under certain
conditions does not involve actual causality violation. By means of that, the
above class of solutions, and probably much broader variety of solutions
including dynamic ones, may be incorporated into General Relativity. There are
listed other phenomena, such as `hidden mass', that could help to identify the
presence of vacuumlike phase.


title: Overcharging a Black Hole and Cosmic Censorship

abstract:
  We show that, contrary to a widespread belief, one can overcharge a near
extremal Reissner-Nordstrom black hole by throwing in a charged particle, as
long as the backreaction effects may be considered negligible. Furthermore, we
find that we can make the particle's classical radius, mass, and charge, as
well as the relative size of the backreaction terms arbitrarily small, by
adjusting the parameters corresponding to the particle appropriately. This
suggests that the question of cosmic censorship is still not wholly resolved
even in this simple scenario. We contrast this with attempting to overcharge a
black hole with a charged imploding shell, where we find that cosmic censorship
is upheld. We also briefly comment on a number of possible extensions.


title:
Extending the Black Hole Uniqueness Theorems, I. Accelerating Black
  Holes: The Ernst Solution and C-Metric

abstract:
  We present black hole uniqueness theorems for the C-metric and Ernst
solution. The proof follows a similar strategy as that used to prove the
uniqueness of the Kerr-Newman solution, however the presence of an acceleration
horizon provides some critical differences. We also show how to derive the
Bunting/Mazur result (on the positivity of a suitable divergence required in
the proof) using new methods. We briefly explain the importance of the
uniqueness of the Ernst solution in relation to the proposed black hole
monopole pair creation mediated by the related instanton.


title:
Extending the Black Hole Uniqueness Theorems, II. Superstring Black
  Holes

abstract:
  We make use of an internal symmetry of a truncation of the bosonic sector of
the superstring and N=4 supergravity theories to write down an analogue of
Robinson's identity for the black holes of this theory. This allows us to prove
the uniqueness of a restricted class of black hole solutions. In particular, we
can apply the methods of the preceding paper to prove the uniqueness of a class
of accelerating black holes (the Stringy Ernst solution and Stringy C-metric)
which incorporate the possibility of the black hole accelerating within an
electromagnetic flux tube. These solutions and their associated uniqueness may
be useful in future instanton calculations.


title:
Dimensionful deformations of Poincare' symmetries for a Quantum Gravity
  without ideal observers

abstract:
  Quantum Mechanics is revisited as the appropriate theoretical framework for
the description of the outcome of experiments that rely on the use of classical
devices. In particular, it is emphasized that the limitations on the
measurability of (pairs of conjugate) observables encoded in the formalism of
Quantum Mechanics reproduce faithfully the ``classical-device limit'' of the
corresponding limitations encountered in (real or gedanken) experimental
setups. It is then argued that devices cannot behave classically in Quantum
Gravity, and that this might raise serious problems for the search of a class
of experiments described by theories obtained by ``applying Quantum Mechanics
to Gravity.'' It is also observed that using heuristic/intuitive arguments
based on the absence of classical devices one is led to consider some candidate
Quantum-Gravity phenomena involving dimensionful deformations of the Poincare'
symmetries.


title:
Could we observe the discreteness of Quantum-Gravity length and area
  operators ?

abstract:
  Several proposals for Quantum Gravity involve length and area operators with
discrete eigenvalues. I show that the analyses of some simple procedures for
the measurement of areas and lengths suggest that this discreteness
characterizing the formalism might not be observable. I also discuss a possible
relation with the so-called $\kappa$ deformations of Poincare' symmetries.


title:
Energy-momentum tensor for scalar fields coupled to the dilaton in two
  dimensions

abstract:
  We clarify some issues related to the evaluation of the mean value of the
energy-momentum tensor for quantum scalar fields coupled to the dilaton field
in two-dimensional gravity. Because of this coupling, the energy-momentum
tensor for the matter is not conserved and therefore it is not determined by
the trace anomaly. We discuss different approximations for the calculation of
the energy-momentum tensor and show how to obtain the correct amount of Hawking
radiation. We also compute cosmological particle creation and quantum
corrections to the Newtonian potential.


title: Causal Anomalies in Kaluza-Klein Gravity Theories

abstract:
  Causal anomalies in two Kaluza-Klein gravity theories are examined,
particularly as to whether these theories permit solutions in which the
causality principle is violated. It is found that similarly to general
relativity the field equations of the space-time-mass Kaluza-Klein (STM-KK)
gravity theory do not exclude violation of causality of G\"odel type, whereas
the induced matter Kaluza-Klein (IM-KK) gravity rules out noncausal
G\"odel-type models. The induced matter version of general relativity is shown
to be an efficient therapy for causal anomalies that occurs in a wide class of
noncausal geometries. Perfect fluid and dust G\"odel-type solutions of the
STM-KK field equations are studied. It is shown that every G\"odel-type perfect
fluid solution is isometric to the unique dust solution of the STM-KK field
equations. The question as to whether 5-D G\"odel-type non-causal geometries
induce any physically acceptable 4-D energy-momentum tensor is also addressed.


title:
Some Possible Features of General Expressions for Lovelock Tensors and
  for the Coefficients of Lovelock Lagrangians Up to the 15th Order in
  Curvature (and Beyond)

abstract:
  This paper presents some possible features of general expressions for
Lovelock tensors and for the coefficients of Lovelock Lagrangians up to the
15th order in curvature (and beyond) in terms of the Riemann-Christoffel and
Ricci curvature tensors and the Riemann curvature scalar for n-dimensional
differentiable manifolds having a general linear connection.


title: Topological Black Holes in Weyl Conformal Gravity

abstract:
  We present a class of exact solutions of Weyl conformal gravity, which have
an interpretation as topological black holes. Solutions with negative, zero or
positive scalar curvature at infinity are found, the former generalizing the
well-known topological black holes in anti-de Sitter gravity. The rather
delicate question of thermodynamic properties of such objects in Weyl conformal
gravity is discussed; suggesting that the thermodynamics of the found solutions
should be treated within the framework of gravity as an induced phenomenon, in
the spirit of Sakharov's work.


title:
Magnetic Knots as The origin of Spikes in the Gravitational Waves
  Backgrounds

abstract:
  The dynamical symmetries of hot and electrically neutral plasmas in a highly
conducting medium suggest that, after the epoch of the electron-positron
annihilation, magnetohydrodynamical configurations carrying a net magnetic
helicity can be present. The simultaneous conservation of the magnetic flux and
helicity implies that the (divergence free) field lines will possess
inhomogeneous knot structures acting as source seeds in the evolution equations
of the scalar, vector and tensor fluctuations of the background geometry. We
give explicit examples of magnetic knot configurations with finite energy and
we compute the induced metric fluctuations. Since magnetic knots are
(conformally) coupled to gravity via the vertex dictated by the equivalence
principle, they can imprint spikes in the gravitational wave spectrum for
frequencies compatible with the typical scale of the knot corresponding, in our
examples, to a present frequency range of $10^{-11}$--$10^{-12}$ Hertz. At
lower frequencies the spectrum is power-suppressed and well below the COBE
limit. For smaller length scales (i.e. for larger frequencies) the spectrum is
exponentially suppressed and then irrelevant for the pulsar bounds. Depending
upon the number of knots of the configuration, the typical amplitude of the
gravitational wave logarithmic energy spectrum (in critical units) can be even
four orders of magnitude larger than the usual flat (inflationary) energy
spectrum generated thanks to the parametric amplification of the vacuum
fluctuations.


title:
Charged gravitational instantons in five-dimensional
  Einstein-Gauss-Bonnet-Maxwell theory

abstract:
  We study a solution of the Einstein-Gauus-Bonnet theory in 5 dimensions
coupled to a Maxwell field, whose euclidean continuation gives rise to an
instanton describing black hole pair production. We also discuss the dual
theory with a 3-form field coupled to gravity.


title: Matter flows around black holes and gravitational radiation

abstract:
  We develop and calibrate a new method for estimating the gravitational
radiation emitted by complex motions of matter sources in the vicinity of black
holes. We compute numerically the linearized curvature perturbations induced by
matter fields evolving in fixed black hole backgrounds, whose evolution we
obtain using the equations of relativistic hydrodynamics. The current
implementation of the proposal concerns non-rotating holes and axisymmetric
hydrodynamical motions. As first applications we study i) dust shells falling
onto the black hole isotropically from finite distance, ii) initially spherical
layers of material falling onto a moving black hole, and iii) anisotropic
collapse of shells. We focus on the dependence of the total gravitational wave
energy emission on the flow parameters, in particular shell thickness, velocity
and degree of anisotropy. The gradual excitation of the black hole quasi-normal
mode frequency by sufficiently compact shells is demonstrated and discussed. A
new prescription for generating physically reasonable initial data is
discussed, along with a range of technical issues relevant to numerical
relativity.


title: Detecting Event Horizons and Stationary Surfaces

abstract:
  We have investigated the behavior of three curvature invariants for
Schwarzschild, Reissner-Nordstr{\o}m, Kerr, and Kerr-Newman black holes. We
have also studied these invariants for a Schwarzschild-de Sitter space-time,
the $\gamma$ metric, and for a 2+1 charged dimensional black hole. The
invariants are
$I_{1}=R_{\alpha\beta\mu\nu;\lambda}R^{\alpha\beta\mu\nu;\lambda}$,
$I_{2}=R_{\mu\nu;\lambda} R^{\mu\nu;\lambda}$, and
$I_{3}=C_{\alpha\beta\mu\nu;\lambda}C^{\alpha\beta\mu\nu;\lambda}$. For all but
the Kerr-Newman case these invariants serve as either horizon or stationary
surface detectors. The Kerr-Newman case is more complicated. We show that
$I_{1}$ vanishs on the horizon in any space-time with a Schwarzschild like
metric.


title: Quantum field and uniformly accelerated oscillator

abstract:
  We present an exact treatment of the influences on a quantum scalar field in
its Minkowski vacuum state induced by coupling of the field to a uniformly
accelerated harmonic oscillator. We show that there are no radiation from the
oscillator in the point of view of a uniformly accelerating observer. On the
other hand, there are radiations in the point of view of an inertial observer.
It is shown that Einstein-Podolsky-Rosen (EPR) like correlations of Rindler
particles in Minkowski vacuum states are modified by a phase factor in front of
the momentum-symmetric Rindler operators. The exact quantization of a
time-dependent oscillator coupled to a massless scalar field was given.


title: Constraints on Inflation in Einstein-Brans-Dicke Frame

abstract:
  The density perturbation during inflation seeds the large scale structure. We
consider both new inflation-type and chaotic inflation-type potentials in the
framework of Einstein-Brans-Dicke gravity. The density perturbation gives
strong constraints on the parameters in these potentials. For both potentials,
the constraints are not much different from those obtained in the original
inflationary models by using of Einstein gravity.


title: Rigid Singularity Theorem in Globally Hyperbolic Spacetimes

abstract:
  We show the rigid singularity theorem, that is, a globally hyperbolic
spacetime satisfying the strong energy condition and containing past trapped
sets, either is timelike geodesically incomplete or splits isometrically as
space $\times$ time. This result is related to Yau's Lorentzian splitting
conjecture.


title: Defect Formation and Critical Dynamics in the Early Universe

abstract:
  We study the nonequilibrium dynamics leading to the formation of topological
defects in a symmetry-breaking phase transition of a quantum scalar field with
\lambda\Phi^4 self-interaction in a spatially flat, radiation-dominated
Friedmann-Robertson-Walker Universe. The quantum field is initially in a
finite-temperature symmetry-restored state and the phase transition develops as
the Universe expands and cools. We present a first-principles, microscopic
approach in which the nonperturbative, nonequilibrium dynamics of the quantum
field is derived from the two-loop, two-particle-irreducible closed-time-path
effective action. We numerically solve the dynamical equations for the
two-point function and we identify signatures of topological defects in the
infrared portion of the momentum-space power spectrum. We find that the density
of topological defects formed after the phase transition scales as a power law
with the expansion rate of the Universe. We calculate the equilibrium critical
exponents of the correlation length and relaxation time for this model and show
that the power law exponent of the defect density, for both overdamped and
underdamped evolution, is in good agreement with the "freeze-out" scenario of
Zurek. We introduce an analytic dynamical model, valid near the critical point,
that exhibits the same power law scaling of the defect density with the quench
rate. By incorporating the realistic quench of the expanding Universe, our
approach illuminates the dynamical mechanisms important for topological defect
formation. The observed power law scaling of the defect density with the quench
rate, observered here in a quantum field theory context, provides evidence for
the "freeze-out" scenario in three spatial dimensions.


title: Exact Cosmological Solutions of Nonlinear F(R)-Gravity

abstract:
  We report on the cited papers refs. 1 - 18 from the following points of view:
What do we exactly know about solutions when no exact solution (in the sense of
"solution in closed form") is available? In which sense do these solutions
possess a singularity? In which cases do conformal relations and/or dimensional
reductions simplify the deduction? Furthermore, we outline some open questions
worth of being studied in future research.


title: Interpreting a conformally flat pure radiation space-time

abstract:
  A physical interpretation is presented of the general class of conformally
flat pure radiation metrics that has recently been identified by Edgar and
Ludwig. It is shown that, at least in the weak field limit, successive wave
surfaces can be represented as null (half) hyperplanes rolled around a
two-dimensional null cone. In the impulsive limit, the solution reduces to a
pp-wave whose direction of propagation depends on retarded time. In the general
case, there is a coordinate singularity which corresponds to an envelope of the
wave surfaces. The global structure is discussed and a possible vacuum
extension through the envelope is proposed.


title:
Invariant construction of solutions to Einstein's field equations - LRS
  perfect fluids II

abstract:
  The properties of LRS class II perfect fluid space-times are analyzed using
the description of geometries in terms of the Riemann tensor and a finite
number of its covariant derivatives. In this manner it is straightforward to
obtain the plane and hyperbolic analogues to the spherical symmetric case. For
spherically symmetric static models the set of equations is reduced to the
Tolman-Oppenheimer-Volkoff equation only. Some new non-stationary and
inhomogeneous solutions with shear, expansion, and acceleration of the fluid
are presented. Among these are a class of temporally self-similar solutions
with equation of state given by $p=(\gamma-1)\mu, 1<\gamma<2$, and a class of
solutions characterized by $\sigma=-\Theta/6$. We give an example of geometry
where the Riemann tensor and the Ricci rotation coefficients are not sufficient
to give a complete description of the geometry. Using an extension of the
method, we find the full metric in terms of curvature quantities.


title:
Spin effects in gravitational radiation backreaction III. Compact
  binaries with two spinning components

abstract:
  The secular evolution of a spinning, massive binary system in eccentric orbit
is analyzed, expanding and generalizing our previous treatments of the
Lense-Thirring motion and the one-spin limit. The spin-orbit and spin-spin
effects up to the 3/2 post-Newtonian order are considered, both in the
equations of motion and in the radiative losses. The description of the orbit
in terms of the true anomaly parametrization provides a simple averaging
technique, based on the residue theorem, over eccentric orbits. The evolution
equations of the angle variables characterizing the relative orientation of the
spin and orbital angular momenta reveal a speed-up effect due to the
eccentricity. The dissipative evolutions of the relevant dynamical and angular
variables is presented in the form of a closed system of differential
equations.


title: Quantization of generally covariant systems with extrinsic time

abstract:
  A generally covariant system can be deparametrized by means of an
``extrinsic'' time, provided that the metric has a conformal ``temporal''
Killing vector and the potential exhibits a suitable behavior with respect to
it. The quantization of the system is performed by giving the well ordered
constraint operators which satisfy the algebra. The searching of these
operators is enlightned by the methods of the BRST formalism.


title:
On an incompleteness in the general-relativistic description of
  gravitation

abstract:
  The recently introduced mechanism of flavor-oscillation clocks has been used
to emphasize observability of constant gravitational potentials and thereby to
question completeness of the theory of general relativity. An inequality has
been derived to experimentally test the thesis presented.


title: Neutrino oscillation in a space-time with torsion

abstract:
  Using the Einstein-Cartan-Dirac theory, we study the effect of torsion on
neutrino oscillation. We see that torsion cannot induce neutrino oscillation,
but affects it whenever oscillation exists for other reasons. We show that the
torsion effect on neutrino oscillation is as important as the neutrino mass
effect, whenever the ratio of neutrino number density to neutrino energy is
$\sim 10^{69}$ cm$^{-3}$ /eV, or the number density of the matter is $\sim
10^{69}$ cm$^{-3}$.


title: Topological black holes in the dimensionally continued gravity

abstract:
  We investigate the topological black holes in a special class of Lovelock
gravity. In the odd dimensions, the action is the Chern-Simons form for the
anti-de Sitter group. In the even dimensions, it is the Euler density
constructed with the Lorentz part of the anti-de Sitter curvature tensor. The
Lovelock coefficients are reduced to two independent parameters: cosmological
constant and gravitational constant. The event horizons of these topological
black holes may have constant positive, zero or negative curvature. Their
thermodynamics is analyzed and electrically charged topological black holes are
also considered. We emphasize the differences due to the different curvatures
of event horizons. As a comparison, we also discuss the topological black holes
in the higher dimensional Einstein-Maxwell theory with a negative cosmological
constant.


title: Symmetries of asymptotically flat electrovacuum spacetimes and radiation

abstract:
  Symmetries compatible with asymptotic flatness and admitting gravitational
and electromagnetic radiation are studied by using the Bondi-Sachs-van der Burg
formalism. It is shown that in axially symmetric electrovacuum spacetimes in
which at least locally a smooth null infinity in the sense of Penrose exists,
the only second allowable symmetry is either the translational symmetry or the
boost symmetry. Translationally invariant spacetimes with in general a straight
"cosmic string" along the axis of symmetry are non-radiative although they can
have a non-vanishing news function. The boost-rotation symmetric spacetimes are
radiative. They describe "uniformly accelerated charged particles" or black
holes which in general may also be rotating - the axial and an additional
Killing vector are not assumed to be hypersurface orthogonal. The general
functional forms of both gravitational and electromagnetic news functions, and
of the mass aspect and total mass of asymptotically flat boost-rotation
symmetric spacetimes at null infinity are obtained. The expressions for the
mass are new even in the case of vacuum boost-rotation symmetric spacetimes
with hypersurface orthogonal Killing vectors. In Appendices some errors
appearing in previous works are corrected.


title: Creation and Structure of Baby Universes in Monopole Collisions

abstract:
  Under certain circumstances, the collision of magnetic monopoles,
topologically locked-in regions of false vacuum, leads to topological inflation
and the creation of baby universes. The future evolution of initial data
represented by the two incoming monopoles may contain a timelike singularity
but this need not be the case. We discuss the global structure of the spacetime
associated with monopole collisions and also that of topological inflation. We
suggest that topological inflation within magnetic monopoles leads to an
eternally reproducing universe.


title: Generalized Quantum Theory and Black Hole Evaporation

abstract:
  Usually quantum theory is formulated in terms of the evolution of states
through spacelike surfaces. However, a generalization of this formulation is
needed for field theory in spacetimes not foliable by spacelike surfaces, or in
quantum gravity where geometry is not definite but a quantum variable. In
particular, a generalization of usual quantum theory is needed for field theory
in the spacetimes that model the process of black hole evaporation. This paper
discusses a spacetime generalization of usual quantum theory that is applicable
to evaporating black hole spacetimes. In this generalization, information is
not lost in the process of evaporation. Rather, complete information is
distributed about four-dimensional spacetime. Black hole evaporation is thus
not in conflict with the principles of quantum theory when suitably generally
stated. (Talk presented at the 49th Yamada Conference: Black Holes and High
Energy Astrophysics, Kyoto Japan, April 7-10, 1998.)


title: Effective Theories of Coupled Classical and Quantum Variables

abstract:
  We address the issue of coupling variables which are essentially classical to
variables that are quantum. Two approaches are discussed. In the first (based
on collaborative work with L.Di\'osi), continuous quantum measurement theory is
used to construct a phenomenological description of the interaction of a
quasiclassical variable $X$ with a quantum variable $x$, where the
quasiclassical nature of $X$ is assumed to have come about as a result of
decoherence. The state of the quantum subsystem evolves according to the
stochastic non-linear Schr\"odinger equation of a continuously measured system,
and the classical system couples to a stochastic c-number $\x (t)$ representing
the imprecisely measured value of $x$. The theory gives intuitively sensible
results even when the quantum system starts out in a superposition of
well-separated localized states. The second approach involves a derivation of
an effective theory from the underlying quantum theory of the combined
quasiclassical--quantum system, and uses the decoherent histories approach to
quantum theory.


title:
Numerical treatment of the hyperboloidal initial value problem for the
  vacuum Einstein equations. III. On the determination of radiation

abstract:
  We discuss the issue of radiation extraction in asymptotically flat
space-times within the framework of conformal methods for numerical relativity.
Our aim is to show that there exists a well defined and accurate extraction
procedure which mimics the physical measurement process. It operates entirely
intrisically within $\scri^+$ so that there is no further approximation
necessary apart from the basic assumption that the arena be an asymptotically
flat space-time. We define the notion of a detector at infinity by idealising
local observers in Minkowski space. A detailed discussion is presented for
Maxwell fields and the generalisation to linearised and full gravity is
performed by way of the similar structure of the asymptotic fields.


title: Einstein and Brans-Dicke frames in multidimensional cosmology

abstract:
  Inhomogeneous multidimensional cosmological models with a higher dimensional
space-time manifold M= M_0 x M_1 ...x M_n are investigated under dimensional
reduction to a D_0-dimensional effective non-minimally coupled sigma-model
which generalizes the familiar Brans-Dicke model.
  It is argued that the Einstein frame should be considered as the physical
one. The general prescription for the Einstein frame reformulation of known
solutions in the Brans-Dicke frame is given. As an example, the reformulation
is demonstrated explicitly for the generalized Kasner solutions where it is
shown that in the Einstein frame there are no solutions with inflation of the
external space.


title: On the large-scale structure of the inflationary universe

abstract:
  We study the evolution of quantum fluctuations of a scalar field which is
coupled to the geometry, in an exponentially expanding universe.
  We derive an expression for the spectrum of intrinsic perturbations, and it
is shown that the intrinsic degrees of freedom are well behaved in the
infra-red part of the spectrum. We conclude that quantum fluctuations do not
change the dynamics of the spacetime in a way which makes its evolution
non-perturbative and stochastic.
  This result contradicts previous derivations which are based on the study of
a quantum field on a fixed geometry.


title: Superconducting cosmic string in Brans-Dicke theory

abstract:
  In the present work, the gravitational field of superconducting cosmic string
has been investigated in the context of Brans-Dicke theory of gravity. We have
presented two kind of solutions for the spacetime in the far field zone of the
string. When the B-D scalar field is switched off, one of the solutions reduces
to the solution earlier obtained by Moss and Poletti in General Relativity.


title:
Matched filtering of gravitational waves from inspiraling compact
  binaries: Computational cost and template placement

abstract:
  We estimate the number of templates, computational power, and storage
required for a one-step matched filtering search for gravitational waves from
inspiraling compact binaries. These estimates should serve as benchmarks for
the evaluation of more sophisticated strategies such as hierarchical searches.
We use waveform templates based on the second post-Newtonian approximation for
binaries composed of nonspinning compact bodies in circular orbits. We present
estimates for six noise curves: LIGO (three configurations), VIRGO, GEO600, and
TAMA. To search for binaries with components more massive than 0.2M_o while
losing no more than 10% of events due to coarseness of template spacing,
initial LIGO will require about 1*10^11 flops (floating point operations per
second) for data analysis to keep up with data acquisition. This is several
times higher than estimated in previous work by Owen, in part because of the
improved family of templates and in part because we use more realistic (higher)
sampling rates. Enhanced LIGO, GEO600, and TAMA will require computational
power similar to initial LIGO. Advanced LIGO will require 8*10^11 flops, and
VIRGO will require 5*10^12 flops. If the templates are stored rather than
generated as needed, storage requirements range from 1.5*10^11 real numbers for
TAMA to 6*10^14 for VIRGO. We also sketch and discuss an algorithm for placing
the templates in the parameter space.


title: Observable frequency shifts via spin-rotation coupling

abstract:
  The phase perturbation arising from spin-rotation coupling is developed as a
natural extension of the celebrated Sagnac effect. Experimental evidence in
support of this phase shift, however, has yet to be realized due to the
exceptional sensitivity required. We draw attention to the relevance of a
series of experiments establishing that circularly polarized light, upon
passing through a rotating half-wave plate, is changed in frequency by twice
the rotation rate. These experiments may be interpreted as demonstrating the
role of spin-rotation coupling in inducing this frequency shift, thus providing
direct empirical verification of the coupling of the photon helicity to
rotation. A neutron interferometry experiment is proposed which would be
sensitive to an analogous frequency shift for fermions. In this arrangement,
polarized neutrons enter an interferometer containing two spin flippers, one of
which is rotating while the other is held stationary. An observable beating in
the transmitted neutron beam intensity is predicted.


title:
The Bifurcation of the Topological Structure in the Sunspot's Electric
  Topological Current with Locally Gauge-invariant Maxwell-Chern-Simons Term

abstract:
  The topological structure of the electric topological current of the locally
gauge invariant Maxwell-Chern-Simons Model and its bifurcation is studied. The
electric topological charge is quantized in term of winding number. The Hopf
indices and Brouwer degree labeled the local topological structure of the
electric topological current. Using $\Phi $-mapping method and implicity
theory, the electric topological current is found generating or annihilating at
the limit points and splitting or merging at the bifurcate points. The total
electric charge holds invariant during the evolution.


title:
Large Scale Inhomogeneity Versus Source Evolution -- Can We Distinguish
  Them Observationally?

abstract:
  We reconsider the issue of proving large scale spatial homogeneity of the
universe, given isotropic observations about us and the possibility of source
evolution both in numbers and luminosities. Two theorems make precise the
freedom available in constructing cosmological models that will fit the
observations. They make quite clear that homogeneity cannot be proven without
either a fully determinate theory of source evolution, or availability of
distance measures that are independent of source evolution. We contrast this
goal with the standard approach that assumes spatial homogeneity a priori, and
determines source evolution functions on the basis of this assumption.


title: Gravitational Wave Interaction with Normal and Superconducting Circuits

abstract:
  The interaction, in the long--wavelength approximation, of normal and
superconducting electromagnetic circuits with gravitational waves is
investigated. We show that such interaction takes place by modifying the
physical parameters R, L, C of the electromagnetic devices. Exploiting this
peculiarity of the gravitational field we find that a circuit with two plane
and statically charged condensers set at right angles can be of interest as a
detector of periodic gravitational waves.


title:
Indication, from Pioneer 10/11, Galileo, and Ulysses Data, of an
  Apparent Anomalous, Weak, Long-Range Acceleration

abstract:
  Radio metric data from the Pioneer 10/11, Galileo, and Ulysses spacecraft
indicate an apparent anomalous, constant, acceleration acting on the spacecraft
with a magnitude $\sim 8.5\times 10^{-8}$ cm/s$^2$, directed towards the Sun.
Two independent codes and physical strategies have been used to analyze the
data. A number of potential causes have been ruled out. We discuss future
kinematic tests and possible origins of the signal.


title: Self--gravitating cosmic rings

abstract:
  The classical Einstein--Maxwell field equations admit static horizonless
wormhole solutions with only a circular cosmic string singularity. We show how
to extend these static solutions to exact rotating asymptotically flat
solutions. For a suitable range of parameter values, these solutions describe
charged or neutral rotating closed cosmic strings, with a perimeter of the
order of their Schwarzschild radius.


title:
A Statistical Mechanical Interpretation of Black Hole Entropy Based on
  an Orthonormal Frame Action

abstract:
  Carlip has shown that the entropy of the three-dimensional black hole has its
origin in the statistical mechanics of microscopic states living at the
horizon. Beginning with a certain orthonormal frame action, and applying
similar methods, I show that an analogous result extends to the (Euclidean)
black hole in any spacetime dimension. However, this approach still faces many
interesting challenges, both technical and conceptual.


title: Torsion Dilaton and Novel Minimal Coupling Principle

abstract:
  We propose a novel self consistent minimal coupling principle in presence of
torsion dilaton field. This principle yields a new local dilatation symmetry
and predicts the interactions of torsion dilaton with the real matter and with
metric. The soft violation of this symmetry yields a physical dilaton and a
simple relation between Cartan scalar curvature and cosmological constant in
this new model of gravity with propagating torsion. Its relation with
scalar-tensor theories of gravity and a possible use of torsion dilaton in the
inflation scenario is discussed.
  \noindent{PACS number(s): 04.50.+h, 04.40.Nr, 04.62.+v}

categories: gr-qc astro-ph hep-ph hep-th math-ph math.MP


title:
<T^{\mu}_{\nu}>_{ren}> of the quantized conformal fields in the
  Schwarzschild spacetime: Israel-Hartle-Hawking state

abstract:
  The renormalized expectation value of the stress-energy tensor of the
conformally invariant massless field in the Israel-Hartle-Hawking state in the
Schwarzschild spacetime is constructed. It is achieved through solving the
conservation equation in conformal space and utilizing the regularity
conditions in the physical metric. Specifically, the relation of the results of
the present approach to the stress tensor constructed within the framework of
the Hadamard renormalization is analysed. Finally, the semi-analytic models
reconstructing the tangential component of the stress-energy tensor with the
maximal deviation not exceeding 0.7% are constructed.


title:
Boosted static multipole particles as sources of impulsive gravitational
  waves

abstract:
  It is shown that the known solutions for nonexpanding impulsive gravitational
waves generated by null particles of arbitrary multipole structure can be
obtained by boosting the Weyl solutions describing static sources with
arbitrary multipole moments, at least in a Minkowski background. We also
discuss the possibility of boosting static sources in (anti-) de Sitter
backgrounds, for which exact solutions are not known, to obtain the known
solutions for null multipole particles in these backgrounds.


title:
Test-beds and applications for apparent horizon finders in numerical
  relativity

abstract:
  We present a series of test beds for numerical codes designed to find
apparent horizons. We consider three apparent horizon finders that use
different numerical methods: one of them in axisymmetry, and two fully
three-dimensional. We concentrate first on a toy model that has a simple
horizon structure, and then go on to study single and multiple black hole data
sets. We use our finders to look for apparent horizons in Brill wave initial
data where we discover that some results published previously are not correct.
For pure wave and multiple black hole spacetimes, we apply our finders to
survey parameter space, mapping out properties of interesting data sets for
future evolutions.


title: Hamiltonian evolution and quantization for extremal black holes

abstract:
  We present and contrast two distinct ways of including extremal black holes
in a Lorentzian Hamiltonian quantization of spherically symmetric
Einstein-Maxwell theory. First, we formulate the classical Hamiltonian dynamics
with boundary conditions appropriate for extremal black holes only. The
Hamiltonian contains no surface term at the internal infinity, for reasons
related to the vanishing of the extremal hole surface gravity, and quantization
yields a vanishing black hole entropy. Second, we give a Hamiltonian
quantization that incorporates extremal black holes as a limiting case of
nonextremal ones, and examine the classical limit in terms of wave packets. The
spreading of the packets, even the ones centered about extremal black holes, is
consistent with continuity of the entropy in the extremal limit, and thus with
the Bekenstein-Hawking entropy even for the extremal holes. The discussion
takes place throughout within Lorentz-signature spacetimes.


title:
One-loop stress-tensor renormalization in curved background: the
  relation between $\zeta$-function and point-splitting approaches, and an
  improved point-splitting procedure

abstract:
  We conclude the rigorous analysis of a previous paper concerning the relation
between the (Euclidean) point-splitting approach and the local $\zeta$-function
procedure to renormalize physical quantities at one-loop in (Euclidean) QFT in
curved spacetime. The stress tensor is now considered in general
$D$-dimensional closed manifolds for positive scalar operators $-\Delta +
V(x)$. Results obtained in previous works (in the case D=4 and $V(x) =\xi R(x)
+ m^2$) are rigorously proven and generalized. It is also proven that, in
static Euclidean manifolds, the method is compatible with Lorentzian-time
analytic continuations. It is found that, for $D>1$, the result of the $\zeta$
function procedure is the same obtained from an improved version of the
point-splitting method which uses a particular choice of the term $w_0(x,y)$ in
the Hadamard expansion of the Green function. This point-splitting procedure
works for any value of the field mass $m$. Furthermore, in the case D=4 and
$V(x) = \xi R(x)+ m^2$, the given procedure generalizes the Euclidean version
of Wald's improved point-splitting procedure. The found point-splitting method
should work generally, also dropping the hypothesis of a closed manifold, and
not depending on the $\zeta$-function procedure. This fact is checked in the
Euclidean section of Minkowski spacetime for $A = -\Delta + m^2$ where the
method gives rise to the correct stress tensor for $m^2 \geq 0$ automatically.


title:
Spreading of wave packets, Uncertainty Relations and the de Broglie
  Frequency

abstract:
  The spreading of quantum mechanical wave packets is studied in two cases.
Firstly we look at the time behavior of the packet width of a free particle
confined in the observable Universe. Secondly, by imposing the conservation of
the time average of the packet width of a particle driven by a harmonic
oscillator potential, we find a zero-point energy which frequency is the de
Broglie frequency.


title: Generalized power expansions in cosmology

abstract:
  It is given an algorithm to obtain generalized power asymptotic expansions of
the solutions of the Einstein equations arising for several homogeneous
cosmological models. This allows to investigate their behavior near the initial
singularity or for large times. An implementation of this algorithm in the CAS
system Maple V Release 4 is described and detailed calculations for three
equations are shown.


title: Can torsion play a role in angular momentum conservation law?

abstract:
  In Einstein-Cartan theory, by the use of the general Noether theorem, the
general covariant angular-momentum conservation law is obtained with the
respect to the local Lorentz transformations. The corresponding conservative
Noether current is interpreted as the angular momentum tensor of the
gravity-matter system including the spin density. It is pointed out that,
assuming the tetrad transformation given by eq. (15), torsion tensor can not
play a role in the conservation law of angular momentum.


title:
Comment on the exterior solutions and their geometry in scalar-tensor
  theories of gravity

abstract:
  We study series of the stationary solutions with asymptotic flatness
properties in the Einstein-Maxwell-free scalar system because they are locally
equivalent with the exterior solutions in some class of the scalar-tensor
theories of gravity. First, we classify spherical exterior solutions into two
types of the solutions, an apparently black hole type solution and an
apparently worm hole type solution. The solutions contain three parameters, and
we clarify their physical significance. Second, we reduce the field equations
for the axisymmetric exterior solutions. We find that the reduced equations are
partially the same as the Ernst equations. As simple examples, we derive new
series of the static, axisymmetric exterior solutions, which correspond to
Voorhees's solutions. We then show a non-trivial relation between the spherical
exterior solutions and our new solutions. Finally, since null geodesics have
conformally invariant properties, we study the local geometry of the exterior
solutions by using the optical scalar equations and find some anomalous
behaviors of the null geodesics.


title:
Group Theoretical Examination of the Relativistic Wave Equations on
  Curved Spaces. III. Real reducible spaces

abstract:
  The group theoretical approach to the relativistic wave equations on the real
reducible spaces for spin~0, 1/2 and~1 massless particles is considered. The
invariant wave equations which determine the appropriate irreducible
representations are constructed. The coincidence of these equations with the
general-covariant Klein-Gordon, Weyl and Maxwell equations on the corresponding
spaces is shown. The explicit solutions of these equations possessing a
simplicity and physical transparency are obtained in the form of so-called
"plane waves" without using the method of separation of variables. The
invariance properties of these "plane waves" for the spinless particles under
the group $SO(3,1)$ were used for the construction of the invariant spin~0,1/2
and~1 two-point functions on the $H^3$. Secondly quantized spin~0,1/2 and~1
fields on the ${\Bbb R}^{1}\otimes H^{3}$ are constructed; their propagators
which are their (anti)commutators in different points, are expressed in terms
of the mentioned two-point functions. From here the ${\Bbb R}^{1}\otimes
  SO(3,1)$-invariance follows.


title: Invariants of the Riemann tensor for Class B Warped Product Spacetimes

abstract:
  We use the computer algebra system \textit{GRTensorII} to examine invariants
polynomial in the Riemann tensor for class $B$ warped product spacetimes -
those which can be decomposed into the coupled product of two 2-dimensional
spaces, one Lorentzian and one Riemannian, subject to the separability of the
coupling: $ds^2 = ds_{\Sigma_1}^2 (u,v) + C(x^\gamma)^2 ds_{\Sigma_2}^2
(\theta,\phi)$ with $C(x^\gamma)^2=r(u,v)^2 w(\theta,\phi)^2$ and
$sig(\Sigma_1)=0, sig(\Sigma_2)=2\epsilon (\epsilon=\pm 1)$ for class $B_{1}$
spacetimes and $sig(\Sigma_1)=2\epsilon, sig(\Sigma_2)=0$ for class $B_{2}$.
Although very special, these spaces include many of interest, for example, all
spherical, plane, and hyperbolic spacetimes. The first two Ricci invariants
along with the Ricci scalar and the real component of the second Weyl invariant
$J$ alone are shown to constitute the largest independent set of invariants to
degree five for this class. Explicit syzygies are given for other invariants up
to this degree. It is argued that this set constitutes the largest functionally
independent set to any degree for this class, and some physical consequences of
the syzygies are explored.


title:
Physical Acceptability of Isolated, Static, Spherically Symmetric,
  Perfect Fluid Solutions of Einstein's Equations

abstract:
  We ask the following question: Of the exact solutions to Einstein's equations
extant in the literature, how many could represent the field associated with an
isolated static spherically symmetric perfect fluid source? The candidate
solutions were subjected to the following elementary tests: i) isotropy of the
pressure, ii) regularity at the origin, iii) positive definiteness of the
energy density and pressure at the origin, iv) vanishing of the pressure at
some finite radius, v) monotonic decrease of the energy density and pressure
with increasing radius, and vi) subluminal sound speed. A total of 127
candidate solutions were found. Only 16 of these passed all the tests. Of these
16, only 9 have a sound speed which monotonically decreases with radius. The
analysis was facilitated by use of the computer algebra system GRTensorII.


title:
The dynamical stability of the static real scalar field solutions to the
  Einstein-Klein-Gordon equations revisited

abstract:
  We re-examine the dynamical stability of the nakedly singular, static,
spherical ly symmetric solutions of the Einstein-Klein Gordon system. We
correct an earlier proof of the instability of these solutions, and demonstrate
that there are solutions to the massive Klein-Gordon system that are
perturbatively stable.


title: Einstein-Brans-Dicke Cosmology

abstract:
  We studied the Einstein-Brans-Dicke cosmology in detail. The difference of
the evolution of the universe is significant between Einstein-Brans-Dicke
cosmology and standard big-bang model during the radiation-dominated era. The
power-law evolution of the scale factor is fast enough to solve the
cosmological puzzles and slow enough to avoid the graceful exit problem.
However, the constraints from the satisfactory bubble distribution
(beta^2>0.25) and the solar system observations (beta^2<0.002) are mutually
exclusive. This suggests that this kind of inflationary model is ruled out. We
also clarify the distinction between Einstein frame and Jordan frame in
Brans-Dicke theory.


title: Characteristic Surface Data for the Eikonal Equation

abstract:
  A method of solving the eikonal equation, in either flat or curved
space-times, with arbitrary Cauchy data, is extended to the case of data given
on a characteristic surface. We find a beautiful relationship between the
Cauchy and characteristic data for the same solution, namely they are related
by a Legendre transformation. From the resulting solutions, we study and
describe their associated wave-front singularities.


title: Class of colliding plane waves in terms of Jacobi functions

abstract:
  We present a general class of noncolinear colliding wave solutions of the
Einstein-Maxwell equations given in terms of fourth order polynomials, which in
turn can be expressed through Jacobi functions depending on generalized
advanced and retarded time coordinates. The solutions are characterized by six
free parameters. The parameters can be chosen in such a way to avoid the
generic focusing singularity


title: Low Frequency Gravitational Waves from Black Hole MACHO Binaries

abstract:
  Nakamura, Sasaki, Tanaka, and Thorne have recently estimated the initial
distribution of binary MACHOs in the galactic halo assuming that the MACHOs are
primordial half solar mass black holes, and considered their coalescence as a
possible source for ground-based interferometer gravitational wave detectors
such as LIGO. Evolving their binary distribution forward in time to the
present, the low-frequency (10^{-5} < f < 10^{-1} Hz) spectrum of gravitational
waves associated with such a population of compact binaries is calculated. The
resulting gravitational waves would form a strong stochastic background in
proposed space interferometers such as LISA and OMEGA. Low frequency
gravitational waves are likely to become a key tool for determining the
properties of binaries within the dark MACHO population.


title:
The Eikonal Equation in Flat Space: Null Surfaces and Their
  Singularities I

abstract:
  The level surfaces of solutions to the eikonal equation define null or
characteristic surfaces. In this note we study, in Minkowski space, properties
of these surfaces. In particular we are interested both in the singularities of
these ``surfaces'' (which can in general self-intersect and be only piece-wise
smooth) and in the decomposition of the null surfaces into a one parameter
family of two-dimensional wavefronts which can also have self-intersections and
singularities.
  We first review a beautiful method for constructing the general solution to
the flat-space eikonal equation; it allows for solutions either from arbitrary
Cauchy data or for time independent (stationary) solutions of the form
S=t-S_{0}(x,y,z). We then apply this method to obtain global, asymptotically
spherical, null surfaces that are associated with shearing ("bad")
two-dimensional cuts of null infinity; the surfaces are defined from the normal
rays to the cut. This is followed by a study of the caustics and singularities
of these surfaces and those of their associated wavefronts. We then treat the
same set of issues from an alternative point of view, namely from Arnold's
theory of generating families. This treatment allows one to deal
(parametrically) with the regions of self-intersection and non-smoothness of
the null surfaces, regions which are difficult to treat otherwise.
  Finally we generalize the analysis of the singularities to families of
solutions of the eikonal equation.


title: Quasilocal quantities for GR and other gravity theories

abstract:
  From a covariant Hamiltonian formulation, by using symplectic ideas, we
obtain certain covariant boundary expressions for the quasilocal quantities of
general relativity and other geometric gravity theories. The contribution from
each of the independent dynamic geometric variables (the frame, metric or
connection) has two possible covariant forms associated with the selected type
of boundary condition. The quasilocal expressions also depend on a reference
value for each dynamic variable and a displacement vector field. Integrating
over a closed two surface with suitable choices for the vector field gives the
quasilocal energy, momentum and angular momentum. For the special cases of
Einstein's theory and the Poincar\'e Gauge theory our expressions are similar
to some previously known expressions and give good values for the total ADM and
Bondi quantities. We apply our formalism to black hole thermodynamics obtaining
the first law and an associated entropy expression for these general gravity
theories. For Einstein's theory our quasilocal expressions are evaluated on
static spherically symmetric solutions and compared with the findings of some
other researchers. The choices needed for the formalism to associate a
quasilocal expression with the boundary of a region are discussed.


title:
Causal differencing of flux-conservative equations applied to black hole
  spacetimes

abstract:
  We give a general scheme for finite-differencing partial differential
equations in flux-conservative form to second order, with a stencil that can be
arbitrarily tilted with respect to the numerical grid, parameterized by a
"tilt" vector field gamma^A. This can be used to center the numerical stencil
on the physical light cone, by setting gamma^A = beta^A, where beta^A is the
usual shift vector in the 3+1 split of spacetime, but other choices of the tilt
may also be useful. We apply this "causal differencing" algorithm to the
Bona-Masso equations, a hyperbolic and flux-conservative form of the Einstein
equations, and demonstrate long term stable causally correct evolutions of
single black hole systems in spherical symmetry.


title: Simplifying Tensor Polynomials with Indices

abstract:
  We are presenting an algorithm capable of simplifying tensor polynomials with
indices when the building tensors have index symmetry properties. These
properties include simple symmetry, cyclicity and those due to the presence of
partial and covariant derivatives. We are also including some examples using
the Riemann tensor as a paradigm. The algorithm is part of a Mathematica
package called Tools of Tensor Calculus (TTC) [web address:
http://baldufa.upc.es/ttc]


title: Einstein's Equations with Asymptotically Stable Constraint Propagation

abstract:
  We introduce a proposal to modify Einstein's equations by embedding them in a
larger symmetric hyperbolic system. The additional dynamical variables of the
modified system are essentially first integrals of the original constraints.
The extended system of equations reproduces the usual dynamics on the
constraint surface of general relativity, and therefore naturally includes the
solutions to Einstein gravity. The main feature of this extended system is
that, at least for a linearized version of it, the constraint surface is an
attractor of the time evolution. This feature suggests that this system may be
a useful alternative to Einstein's equations when obtaining numerical solutions
to full, non-linear gravity.


title: Spherically symmetric static solution for colliding null dust

abstract:
  The Einstein equations are integrated in the presence of two (incoming and
outgoing) streams of null dust, under the assumptions of spherical symmetry and
staticity. The solution is also written in double null and radiation
coordinates and it is reinterpreted as an anisotropic fluid. Interior matching
with a static fluid and exterior matching with the Vaidya solution along null
hypersurfaces is discussed. The connection with two-dimensional dilaton gravity
is established.


title: Thermodynamics and Evaporation of Closed Black Cosmic Strings

abstract:
  Both the canonical and microcanonical ensembles are utilized to study the
thermodynamic and evaporation properties of a closed black cosmic string whose
spacetime is asymptotically anti deSitter. There are similarities and
differences to the Schwarzschild-anti deSitter and 2+1 BTZ black hole
solutions. It is found that there exist regimes of black string/thermal
radiation equilibrium as well as stable remnant regimes. The relevance to black
hole evaporation is discussed.


title: Quantum Histories

abstract:
  There are good motivations for considering some type of quantum histories
formalism. Several possible formalisms are known, defined by different
definitions of event and by different selection criteria for sets of histories.
These formalisms have a natural interpretation, according to which nature
somehow chooses one set of histories from among those allowed, and then
randomly chooses to realise one history from that set; other interpretations
are possible, but their scientific implications are essentially the same.
  The selection criteria proposed to date are reasonably natural, and certainly
raise new questions. For example, the validity of ordering inferences which we
normally take for granted --- such as that a particle in one region is
necessarily in a larger region containing it --- depends on whether or not our
history respects the criterion of ordered consistency, or merely consistency.
  However, the known selection criteria, including consistency and medium
decoherence, are very weak. It is not possible to derive the predictions of
classical mechanics or Copenhagen quantum mechanics from the theories they
define, even given observational data in an extended time interval. Attempts to
refine the consistent histories approach so as to solve this problem by finding
a definition of quasiclassicality have so far not succeeded.
  On the other hand, it is shown that dynamical collapse models, of the type
originally proposed by Ghirardi-Rimini-Weber, can be re-interpreted as set
selection criteria within a quantum histories framework, in which context they
appear as candidate solutions to the set selection problem. This suggests a new
route to relativistic generalisation of these models, since covariant
definitions of a quantum event are known.


title: Comparison of Exact and perturbative Results for Two Metrics

abstract:
  We compare the exact and perturbative results in two metrics and show that
the spurious effects due to the perturbation method do not survive for
physically relevant quantities such as the vacuum expectation value of the
stress-energy tensor.


title: Quantum fluctuations of some gravitational waves

abstract:
  We review our previous work on the the calculation of the stress-energy
tensor for a scalar particle in the background metric of different types of
spherical impulsive, spherical shock and plane impulsive gravitational waves.


title: Thermodynamics of toroidal black holes

abstract:
  The thermodynamical properties of toroidal black holes in the grand canonical
ensemble are investigated using York's formalism. The black hole is enclosed in
a cavity with finite radius where the temperature and electrostatic potential
are fixed. The boundary conditions allow one to compute the relevant
thermodynamical quantities, e.g. thermal energy, entropy and specific heat.
This black hole is thermodynamically stable and dominates the grand partition
function. This means that there is no phase transition, as the one encountered
for spherical black holes.


title: The quadratic spinor Lagrangian is equivalent to the teleparallel theory

abstract:
  The quadratic spinor Lagrangian is shown to be equivalent to the teleparallel
/ tetrad representation of Einstein's theory. An important consequence is that
the energy-momentum density obtained from this quadratic spinor Lagrangian is
essentially the same as the ``tensor'' proposed by Moller in 1961.


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

abstract:
  Contents:
  Editorial
  News:
  - Topical group news, by Jim Isenberg
  - Summer school in gravitational physics opportunity, by Jim Hartle
  - Bogart, Bergman and (Al)bert, by Clifford Will and Robert Riemer
  - New data-analysis subgroups of the LSC, by Eanna Flanagan
  - Marcel Bardon, a man of vision, by Richard Isaacson
  Research Briefs:
  - Status of the GEO600 project, by Harold Lueck
  - A nonperturbative formulation of string theory?, by Gary Horowitz
  - TAMA project update, by Seiji Kawamura
  - Neohistorical approaches to quantum gravity, by Lee Smolin
  - LIGO project update, by David Shoemaker
  - Gravitational waves from neutron stars, by Eanna Flanagan
  Conference reports
  - Perugia meeting, by Joe Kovalik
  - Nickel and Dime gravity meeting, by Eric Poisson
  - Second international LISA symposium, by Robin Stebbins
  - JILA meeting on seismic isolation et al., by Joe Giaime


title: The asymptotics of an amplitude for the 4-simplex

abstract:
  An expression for the oscillatory part of an asymptotic formula for the
relativistic spin network amplitude for a 4-simplex is given. The amplitude
depends on specified areas for each two-dimensional face in the 4-simplex. The
asymptotic formula has a contribution from each flat Euclidean metric on the
4-simplex which agrees with the given areas. The oscillatory part of each
contribution is determined by the Regge calculus Einstein action for that
geometry.


title: Trapped gravitational wave modes in stars with R>3M

abstract:
  The possibility of trapped modes of gravitational waves appearing in stars
with R>3M is considered. It is shown that the restriction to R<3M in previous
studies of trapped modes, using uniform density models, is not essential.
Scattering potentials are computed for another family of analytic stellar
models showing the appearance of a deep potential well for one model with R>3M.
However, the provided example is unstable, although it has a more realistic
equation of state in the sense that the sound velocity is finite. On the other
hand it is also shown that for some stable models belonging to the same family
but having R<3M, the well is significantly deeper than that of the uniform
density stars. Whether there are physically realistic equations of state which
allow stable configurations with trapped modes therefore remains an open
problem.


title: Exact Solutions for the Intrinsic Geometry of Black Hole Coalescence

abstract:
  We describe the null geometry of a multiple black hole event horizon in terms
of a conformal rescaling of a flat space null hypersurface. For the prolate
spheroidal case, we show that the method reproduces the pair-of-pants shaped
horizon found in the numerical simulation of the head-on-collision of black
holes. For the oblate case, it reproduces the initially toroidal event horizon
found in the numerical simulation of collapse of a rotating cluster. The
analytic nature of the approach makes further conclusions possible, such as a
bearing on the hoop conjecture. From a time reversed point of view, the
approach yields a description of the past event horizon of a fissioning white
hole, which can be used as null data for the characteristic evolution of the
exterior space-time.


title: Asymptotic Isometry and Two Dimensional Anti-de Sitter Gravity

abstract:
  We analyze canonical asymptotic isometry of two dimensional AdS dilaton
gravity in detail.


title: No-scalar hair conjecture in asymptotic de-Sitter spacetime

abstract:
  We discuss the no-hair conjecture in the presence of a cosmological constant.
For the firststep the real scalar field is considered as the matter field and
the spacetime is assumed to be static spherically symmetric. If the scalar
field is massless or has a convex potential such as a mass term, it is proved
that there is no regular black hole solution. For a general positive potential,
we search for black hole solutions which support the scalar field with a double
well potential, and find them by numerical calculations. The existence of such
solutions depends on the values of the vacuum expectation value and the
self-coupling constant of the scalar field. When we take the zero horizon
radius limit, the solution becomes a boson star like solution which we found
before. However new solutions are found to be unstable against the linear
perturbation. As a result we can conclude that the no-scalar hair conjecture
holds in the case of scalar fields with a convex or double well potential.


title: Null Cones in Schwarzschild Geometry

abstract:
  Light cones of Schwarzschild geometry are studied in connection to the Null
Surface Formulation and gravitational lensing. The paper studies the light cone
cut function's singularity structure, gives exact gravitational lensing
equations, and shows that the "pseudo-Minkowski" coordinates are well defined
within the model considered.


title: Nonstandard optics from quantum spacetime

abstract:
  We study light propagation in the picture of semi-classical space-time that
emerges in canonical quantum gravity in the loop representation. In such
picture, where space-time exhibits a polymer-like structure at microscales, it
is natural to expect departures from the perfect non-dispersiveness of ordinary
vacuum. We evaluate these departures, computing the modifications to Maxwell's
equations due to quantum gravity, and showing that under certain circumstances,
non-vanishing corrections appear that depend on the helicity of propagating
waves. These effects could lead to observable cosmological predictions of the
discrete nature of quantum spacetime. In particular, recent observations of
non-dispersiveness in the spectra of gamma-ray bursts at various energies could
be used to constrain the type of semi-classical state that describes the
universe.


title:
Irrotational and Incompressible Ellipsoids in the First Post-Newtonian
  Approximation of General Relativity

abstract:
  First post-Newtonian (1PN) hydrostatic equations for an irrotational fluid
which have been recently derived are solved for an incompressible star. The 1PN
configurations are expressed as a deformation of the Newtonian irrotational
Riemann ellipsoid using Lagrangian displacement vectors introduced by
Chandrasekhar. For the 1PN solutions, we also calculate the luminosity of
gravitational waves in the 1PN approximation using the Blanchet-Damour
formalism. It is found that the solutions of the 1PN equations exhibit
singularities at points where the axial ratios of semi-axes are 1:0.5244:0.6579
and 1:0.2374:0.2963, and the singularities seem to show that at the points, the
irrotational Riemann ellipsoid is unstable to the deformation induced by the
effect of general relativity. For stable cases (a_2/a_1 > 0.5244, where a_1 and
a_2 are the semi-major and minor axes, respectively) we find that when
increasing the 1PN correction, the angular velocity and total angular momentum
increase, while the total energy and luminosity of gravitational waves
decrease. These 1PN solutions will be useful when examining the accuracy of
numerical code for obtaining relativistic irrotational stars.
  We also investigate the validity of an ellipsoidal approximation, in which a
1PN solution is obtained assuming an ellipsoidal figure and neglecting the
deformation. It is found that for $a_2/a_1 > 0.7$, the ellipsoidal
approximation gives a fairly accurate result for the energy, angular momentum,
and angular velocity, although in the approximation we cannot find the
singularities.


title: Pseudotensors and quasilocal energy-momentum

abstract:
  Early energy-momentum investigations for gravitating systems gave reference
frame dependent pseudotensors; later the quasilocal idea was developed.
Quasilocal energy-momentum can be determined by the Hamiltonian boundary term,
which also identifies the variables to be held fixed on the boundary. We show
that a pseudotensor corresponds to a Hamiltonian boundary term. Hence they are
quasilocal and acceptable; each is the energy-momentum density for a definite
physical situation with certain boundary conditions. These conditions are
identified for well-known pseudotensors.


title:
Quantum Scalar Field on the Massless (2+1)-Dimensional Black Hole
  Background

abstract:
  The behavior of a quantum scalar field is studied in the metric ground state
of the (2+1)-dimensional black hole of Ba\~nados, Teitelboim and Zanelli which
contains a naked singularity. The one-loop BTZ partition function and the
associate black hole effective entropy, the expectation value of the quantum
fluctuation as well as the renormalized expectation value of the stress tensor
are explicitly computed in the framework of the $\zeta$-function procedure.
This is done for all values of the coupling with the curvature, the mass of the
field and the temperature of the quantum state. In the massless conformally
coupled case, the found stress tensor is used for determining the quantum back
reaction on the metric due to the scalar field in the quantum vacuum state, by
solving the semiclassical Einstein equations. It is finally argued that, within
the framework of the 1/N expansion, the Cosmic Censorship Hypothesis is
implemented since the naked singularity of the ground state metric is shielded
by an event horizon created by the back reaction.


title: The Quantum Collapse and the Birth of a New Universe

abstract:
  The gravitational collapse and the birth of a new universe are considered in
terms of quantum mechanics. Transitions from annihilation of matter to
deflation in the collapse and from inflation to creation of matter in the birth
of a universe are considered. The creation of a new universe takes place in
another space-time since beyond the event horizon the time coordinate is
inextensible for an external observer. A reasonable probability of this
creation is obtainable only for miniholes. The major part of the mass of such
collapsing compact objects as stars, quasars and active nuclei of galaxies
remains confined in the potential well near the vacuum state.


title: A Godel-Friedman cosmology?

abstract:
  Based on the mathematical similarity between the Friedman open metric and
Godel's metric in the case of nearby distances, we investigate a new scenario
for the Universe's evolution, where the present Friedman universe originates
from a primordial Godel universe by a phase transition during which the
cosmological constant vanishes. Using Hubble's constant and the present matter
density as input, we show that the radius and density of the primordial Godel
universe are close, in order of magnitude, to the present values, and that the
time of expansion coincides with the age of the Universe in the standard
Friedman model. In addition, the conservation of angular momentum provides, in
this context, a possible origin for the rotation of galaxies, leading to a
relation between the masses and spins corroborated by observational data.


title: Wavy Horizons?

abstract:
  We describe the application of a gravity wave-generating technique to certain
higher dimensional black holes. We find that the induced waves generically
destroy the event horizon producing parallelly propagated curvature
singularities.


title: Spinors, Spin Coefficients and Lanczos Potentials

abstract:
  It has been demonstrated, in a number of special situations, that the spin
coefficients of a canonical spinor dyad can be used to define a Lanczos
potential of the Weyl curvature spinor. In this paper we explore some of these
potentials and show that they can be defined directly from the spinor dyad in a
very simple way, but that the results do not generalize significantly, in any
direct manner. A link to metric, asymmetric, curvature-free connections, which
suggests a more natural relationship between the Lanczos potential and spin
coefficients, is also considered.


title:
Data analysis of gravitational-wave signals from spinning neutron stars.
  II. Accuracy of estimation of parameters

abstract:
  We examine the accuracy of estimation of parameters of the gravitational-wave
signals from spinning neutron stars that can be achieved from observations by
Earth-based laser interferometers. We consider a model of the signal consisting
of two narrowband components and including both phase and amplitude modulation.
We calculate approximate values of the rms errors of the parameter estimators
using the Fisher information matrix. We carry out extensive Monte Carlo
simulations and obtain cumulative distribution functions of rms errors of
astrophysically interesting parameters: amplitude of the signal, wobble angle,
position of the source in the sky, frequency, and spindown coefficients. We
consider both all-sky searches and directed searches. We also examine the
possibility of determination of neutron star proper motion. We perform
simulations for all laser-interferometric detectors that are currently under
construction and for several possible lengths of the observation time and sizes
of the parameter space. We find that observations of continuous
gravitational-wave signals from neutron stars by laser-interferometric
detectors will provide a very accurate information about their astrophysical
properties. We derive several simplified models of the signal that can be used
in the theoretical investigations of the data analysis schemes independently of
the physical mechanisms generating the gravitational-wave signal.


title: Spinning BTZ Black Hole versus Kerr Black Hole : A Closer Look

abstract:
  By applying Newman's algorithm, the AdS_3 rotating black hole solution is
``derived'' from the nonrotating black hole solution of Banados, Teitelboim,
and Zanelli (BTZ). The rotating BTZ solution derived in this fashion is given
in ``Boyer-Lindquist-type'' coordinates whereas the form of the solution
originally given by BTZ is given in a kind of an ``unfamiliar'' coordinates
which are related to each other by a transformation of time coordinate alone.
The relative physical meaning between these two time coordinates is carefully
studied. Since the Kerr-type and Boyer-Lindquist-type coordinates for rotating
BTZ solution are newly found via Newman's algorithm, next, the transformation
to Kerr-Schild-type coordinates is looked for. Indeed, such transformation is
found to exist. And in this Kerr-Schild-type coordinates, truely maximal
extension of its global structure by analytically continuing to ``antigravity
universe'' region is carried out.


title: Topological entropy for some isotropic cosmological models

abstract:
  The chaotical dynamics is studied in different Friedmann-Robertson- Walker
cosmological models with scalar (inflaton) field and hydrodynamical matter. The
topological entropy is calculated for some particular cases. Suggested scheme
can be easily generalized for wide class of models. Different methods of
calculation of topological entropy are compared.


title: Symmetric teleparallel general relativity

abstract:
  General relativity can be presented in terms of other geometries besides
Riemannian. In particular, teleparallel geometry (i.e., curvature vanishes) has
some advantages, especially concerning energy-momentum localization and its
``translational gauge theory'' nature. The standard version is metric
compatible, with torsion representing the gravitational ``force''. However
there are many other possibilities. Here we focus on an interesting alternate
extreme: curvature and torsion vanish but the nonmetricity $\nabla g$ does
not---it carries the ``gravitational force''. This {\it symmetric teleparallel}
representation of general relativity covariantizes (and hence legitimizes) the
usual coordinate calculations. The associated energy-momentum density is
essentially the Einstein pseudotensor, but in this novel geometric
representation it is a true tensor.


title: On the Noether charge form of the first law of black hole mechanics

abstract:
  The first law of black hole mechanics was derived by Wald in a general
covariant theory of gravity for stationary variations around a stationary black
hole. It is formulated in terms of Noether charges, and has many advantages. In
this paper several issues are discussed to strengthen the validity of the
Noether charge form of the first law. In particular, a gauge condition used in
the derivation is justified. After that, we justify the generalization to
non-stationary variations done by Iyer-Wald.