title: Mass inflation and chaotic behaviour inside hairy black holes

abstract:
  We analyze the interior geometry of static, spherically symmetric black holes
of the Einstein-Yang-Mills-Higgs theory. Generically the solutions exhibit a
behaviour that may be described as ``mass inflation'', although with a
remarkable difference between the cases with and without a Higgs field. Without
Higgs field the YM field induces a kind of cyclic behaviour leading to repeated
cycles of mass inflation - taking the form of violent explosions - interrupted
by quiescent periods and subsequent approaches to an almost Cauchy horizon.
With the Higgs field no such cycles occur. In addition there are non-generic
families with a Schwarzschild resp. Reissner-Nordstr{\o}m type singularity at
r=0.


title: Post-post-newtonian limit of a dilatonic gravity model

abstract:
  We study a solution of the field equations for dilatonic gravity and obtain
its post-post-newtonian limit. It turns out that terms to this and higher
orders in the expansion may become important in strong gravitational fields,
even though the post-newtonian limit coincides with that of General Relativity.
This suggests that strong gravitational fields can only be studied by exact
solutions of the field equations.


title: A proposed gravitodynamic theory

abstract:
  This paper proposes a gravitodynamic theory because there are similarities
between gravitational theory and electrodynamics. Based on Einstein's principle
of equivalence, two coordinate conditions are proposed into the
four-dimensional line element and transformations. As a consequence,the
equation of motion for gravitational force or inertial force has a form similar
to the equation of Lorentz force on a charge in electrodynamics. The inertial
forces in auniformly rotating system are calculated, which show that the
Coriolis force is produced by a magnetic-type gravitational field. We have also
calculated the Sagnac effect due to the rotation. These experimental facts
strongly support our proposed coordinate conditions. In addition, the
gravitodynamic field equations are briefly discussed. Since only four
gravitational potentials (3 + 1 split) enter the metric tensor, the
gravitodynamic field equations in ``3+1 split" form would be analogous to
Maxwell's equations.


title:
On scattering off the extreme Reissner-Nordstr\"om black hole in N=2
  supergravity

abstract:
  The scattering amplitudes for the perturbed fields of the N=2 supergravity
about the extreme Reissner-Nordstr\"om black hole is examined. Owing to the
fact that the extreme hole is a BPS state of the theory and preserves an
unbroken global supersymmetry(N=1), the scattering amplitudes of the component
fields should be related to each other. In this paper, we derive the formula of
the transformation of the scattering amplitudes.


title: Fisher's arrow of `time' in cosmological coherent phase space

abstract:
  Fisher's arrow of `time' in a cosmological phase space defined as in quantum
optics (i.e., whose points are coherent states) is introduced as follows.
Assuming that the phase space evolution of the universe starts from an initial
squeezed cosmological state towards a final thermal one, a Fokker-Planck
equation for the time-dependent, cosmological Q phase space probability
distribution can be written down. Next, using some recent results in the
literature, we derive an information arrow of time for the Fisher phase space
cosmological entropy based on the Q function. We also mention the application
of Fisher's arrow of time to stochastic inflation models


title:
Time evolution of the perturbations for a complex scalar field in
  Friedmann-Lemaitre universe

abstract:
  We study the time evolution of small classical perturbations in a gauge
invariant way for a complex scalar field in the early zero curvature
Friedmann-Lema\^{\i}tre universe. We, thus, generalize the analysis which has
been done so far for a real scalar field. We give also a derivation of the
Jeans wavenumber in the Newtonian regime starting from the general relativistic
equations, avoiding the so-called Jeans swindle.
  During the inflationary phase, whose length depends on the value of the
bosonic charge, the behavior of the perturbations turns out to be the same as
for a real scalar field. In the oscillatory phase the time evolution of the
perturbations can be determined analytically as long as the bosonic charge of
the corresponding background solution is sufficiently large. This is not
possible for the real scalar field, since the corresponding bosonic charge
vanishes.


title:
The Initial-Value Problem of Spherically Symmetric Wyman Sector
  Nonsymmetric Gravitational Theory

abstract:
  We cast the four-dimensional field equations of the Nonsymmetric
Gravitational Theory (NGT) into a form appropriate for numerical study. In
doing so, we have restricted ourselves to spherically symmetric spacetimes, and
we have kept only the Wyman sector of the theory. We investigate the
well-posedness of the initial-value problem of NGT for a particular data set
consisting of a pulse in the antisymmetric field on an asymptotically flat
space background. We include some analytic results on the solvability of the
initial-value problem which allow us to place limits on the regions of the
parameter space where the initial-value problem is solvable. These results are
confirmed by numerically solving the constraints.


title: Can magnetic fields of astrophysical objects be fundamental ?

abstract:
  We analyze a new class of static exact solutions of Einstein-Maxwell-Dilaton
gravity with arbitrary scalar coupling constant $\alpha$, representing a
gravitational body endowed with electromagnetic dipole moment. This class
possesses mass, dipole and scalar charge parameters. A discussion of the
geodesic motion shows that the scalar field interaction is so weak that it
cannot be measured in gravitational fields like the sun, but it could perhaps
be detected in gravitational fields like pulsars. The scalar force can be
attractive or repulsive. This gives rise to the hypothesis that the magnetic
field of some astrophysical objects could be fundamental.


title: Evaporation of Three Dimensional Black Hole in Quantum Gravity

abstract:
  We discuss an evaporation of (2+1)-dimensional black hole by using quantum
gravity holding in the vicinity of the black hole horizon. It is shown that the
black hole evaporates at a definite rate by emitting matters through the
quantum tunneling effect. A relation of the present formalism to the black hole
entropy is briefly commented.


title: Quantum Instability of Black Hole Singularity in Three Dimensions

abstract:
  We study an internal structure of (2+1)-dimensional black hole with the
neutral scalar matter in the spherically symmetric geometry by using a quantum
theory of gravity which holds in the both vicinities of the singularity and the
apparent horizon. A special attention is paid to the quantum-mechanical
behavior of the singularity in the black hole. We solve analytically the
Wheeler-DeWitt equation of a minisuperspace model where the ingoing Vaidya
metric is used as a simple model representing a dynamical black hole. The wave
function obtained in this way leads to interesting physical phenomena such as
the quantum instability of singularity and the Hawking radiation. It is also
pointed out a similarity between the singularity in (2+1)-dimensional black
hole and the inner Cauchy horizon in (3+1)-dimensional Reissner-Nordstrom
charged black hole.


title:
One Particle Hilbertspace of 2+1 dimensional Gravity using Non commuting
  Coordinates

abstract:
  After a review of multi particle solutions in classical 2+1 dimensional
gravity we will construct a one particle Hilbert space. As we will use a curved
momentum space, the coordinates $x^\mu$ are represented as non commuting
Hermitian operators on this Hilbertspace. Finally we will indicate how to
construct a Schrodinger equation.


title:
Two particle Quantummechanics in 2+1 Gravity using Non Commuting
  Coordinates

abstract:
  We find that the momentum conjugate to the relative distance between two
gravitating particles in their center of mass frame is a hyperbolic angle. This
fact strongly suggests that momentum space should be taken to be a hyperboloid.
We investigate the effect of quantization on this curved momentum space. The
coordinates are represented by non commuting, Hermitian operators on this
hyperboloid. We also find that there is a smallest distance between the two
particles of one half times the Planck length.


title:
Gravitational Lorentz Force and the Description of the Gravitational
  Interaction

abstract:
  In the context of a gauge theory for the translation group, we have obtained,
for a spinless particle, a gravitational analog of the Lorentz force. Then, we
have shown that this force equation can be rewritten in terms of magnitudes
related to either the teleparallel or the riemannian structures induced in
spacetime by the presence of the gravitational field. In the first case, it
gives a force equation, with torsion playing the role of force. In the second,
it gives the usual geodesic equation of General Relativity. The main conclusion
is that scalar matter is able to feel anyone of the above spacetime geometries,
the teleparallel and the metric ones. Furthermore, both descriptions are found
to be completely equivalent in the sense that they give the same physical
trajectory for a spinless particle in a gravitational field.


title: Marginally Trapped Surfaces in the Nonsymmetric Gravitational Theory

abstract:
  We consider a simple, physical approach to the problem of marginally trapped
surfaces in the Nonsymmetric Gravitational Theory (NGT). We apply this approach
to a particular spherically symmetric, Wyman sector gravitational field,
consisting of a pulse in the antisymmetric field variable. We demonstrate that
marginally trapped surfaces do exist for this choice of initial data.


title:
A note on the gauge symmetries of pure Chern-Simons theories with p-form
  gauge fields

abstract:
  The gauge symmetries of pure Chern-Simons theories with p-form gauge fields
are analyzed. It is shown that the number of independent gauge symmetries
depends crucially on the parity of p. The case where p is odd appears to be a
direct generalization of the p=1 case and presents the remarkable feature that
the timelike diffeomorphisms can be expressed in terms of the spatial
diffeomorphisms and the internal gauge symmetries. By constrast, the timelike
diffeomorphisms may be an independent gauge symmetry when p is even. This
happens when the number of fields and the spacetime dimension fulfills an
algebraic condition which is explicitely written.


title:
Reissner-Nordstrom-like solutions of the SU(2) Einstein-Yang/Mills (EYM)
  equations

abstract:
  In this paper we study a new type of solution of the spherically symmetric,
Einstein-Yang/Mills (EYM) equations with SU(2) gauge group. These solutions are
well-behaved in the far-field, and have a Reissner-Nordstrom type essential
singularity at the origin. These solutions display some novel features which
are not present in particle-like, or black-hole solutions. Any spherically
symmetric solution to the EYM equations, defined in the far-field, is either a
particle-like solution, a black-hole solution, or one of these RNL solutions.


title: Notes on the Generalised Second Law of Thermodynamics

abstract:
  Several comments are given to previous proofs of the generalised second law
of thermodynamics: black hole entropy plus ordinary matter entropy never
decreases for a thermally closed system. Arguments in favour of its truism are
given in the spirit of conventional thermodynamics.


title: Coherence and Emergence of Classical Spacetime

abstract:
  Using the coherent-state representation we show that the classical Einstein
equation for the FRW cosmological model with a general minimal scalar field can
be derived from the semiclassical quantum Einstein equation.


title: Quantum Potential and Cosmological Singularities

abstract:
  We apply the de Broglie-Bohm interpretation to the Wheeler-DeWitt equation
for the quantum FRW cosmological model with a minimal massless scalar field. We
find that the quantum FRW cosmological model has quantum potential dominated
solutions that avoid the initial and the final cosmological singularities. It
is suggested that the quantum potential and the back-reaction of geometry and
matter fields may change the property of the cosmological singularities of the
Universe.


title: A simple construction of initial data for multiple black holes

abstract:
  We consider the initial data problem for several black holes in vacuum with
arbitrary momenta and spins on a three space with punctures. We compactify the
internal asymptotically flat regions to obtain a computational domain without
inner boundaries. When treated numerically, this leads to a significant
simplification over the conventional approach which is based on throats and
isometry conditions. In this new setting it is possible to obtain existence and
uniqueness of solutions to the Hamiltonian constraint.


title: Late-time evolution of nonlinear gravitational collapse

abstract:
  We study numerically the fully nonlinear gravitational collapse of a
self-gravitating, minimally-coupled, massless scalar field in spherical
symmetry. Our numerical code is based on double-null coordinates and on free
evolution of the metric functions: The evolution equations are integrated
numerically, whereas the constraint equations are only monitored. The numerical
code is stable (unlike recent claims) and second-order accurate. We use this
code to study the late-time asymptotic behavior at fixed $r$ (outside the black
hole), along the event horizon, and along future null infinity. In all three
asymptotic regions we find that, after the decay of the quasi-normal modes, the
perturbations are dominated by inverse power-law tails. The corresponding power
indices agree with the integer values predicted by linearized theory. We also
study the case of a charged black hole nonlinearly perturbed by a (neutral)
self-gravitating scalar field, and find the same type of behavior---i.e.,
quasi-normal modes followed by inverse power-law tails, with the same indices
as in the uncharged case.


title: Angular Resolution of the LISA Gravitational Wave Detector

abstract:
  We calculate the angular resolution of the planned LISA detector, a
space-based laser interferometer for measuring low-frequency gravitational
waves from galactic and extragalactic sources. LISA is not a pointed
instrument; it is an all-sky monitor with a quadrupolar beam pattern. LISA will
measure simultaneously both polarization components of incoming gravitational
waves, so the data will consist of two time series. All physical properties of
the source, including its position, must be extracted from these time series.
LISA's angular resolution is therefore not a fixed quantity, but rather depends
on the type of signal and on how much other information must be extracted.
Information about the source position will be encoded in the measured signal in
three ways: 1) through the relative amplitudes and phases of the two
polarization components, 2) through the periodic Doppler shift imposed on the
signal by the detector's motion around the Sun, and 3) through the further
modulation of the signal caused by the detector's time-varying orientation. We
derive the basic formulae required to calculate the LISA's angular resolution
$\Delta \Omega_S$ for a given source. We then evaluate $\Delta \Omega_S$ for
two sources of particular interest: monchromatic sources and mergers of
supermassive black holes. For these two types of sources, we calculate (in the
high signal-to-noise approximation) the full variance-covariance matrix, which
gives the accuracy to which all source parameters can be measured. Since our
results on LISA's angular resolution depend mainly on gross features of the
detector geometry, orbit, and noise curve, we expect these results to be fairly
insensitive to modest changes in detector design that may occur between now and
launch. We also expect that our calculations could be easily modified to apply
to a modified design.


title: Dissipative cosmological solutions

abstract:
  The exact general solution to the Einstein equations in a homogeneous
Universe with a full causal viscous fluid source for the bulk viscosity index
$m=1/2$ is found. We have investigated the asymptotic stability of Friedmann
and de Sitter solutions, the former is stable for $m\ge 1/2$ and the latter for
$m\le 1/2$. The comparison with results of the truncated theory is made. For
$m=1/2$, it was found that families of solutions with extrema no longer remain
in the full case, and they are replaced by asymptotically Minkowski evolutions.
These solutions are monotonic.


title: Constraints on Higher Dimensional Models for viable Extended Inflation

abstract:
  We consider two kinds of higher dimensional models which upon dimensional
reduction lead to Jordan-Brans-Dicke type effective actions in four dimensions
with the scale factor of the extra dimensions playing the role of the JBD
field. These models are characterized by the potential for the JBD field which
arises from the process of dimensional reduction, and by the coupling of the
inflaton sector with the JBD field in the Jordan frame. Taking into account the
fact that these models allow the possibility of enough inflation and dynamical
compactification of the extra dimensions, we examine in the context of these
models the other conditions which need to be satisfied for a viable scenario of
extended inflation. We find that the requirements of conforming to general
relativity at the present epoch, and producing suitable bubble spectrums during
inflation lead to constraints on the allowed values taken by the parameters of
these models. A model with a ten dimensional JBD field is able to satisfy the
condition for appropriate density perturbations viewed in the conformal
Einstein frame, with a stringent restriction on the initial value taken by the
scale factor of the extra dimensions.


title: Post-Newtonian Approximation for Spinning Particles

abstract:
  Using an energy-momentum tensor for spinning particles due to Dixon and
Bailey-Israel, we develop the post-Newtonian approximation for N spinning
particles in a self-contained manner. The equations of motion are derived
directly from this energy-momentum tensor. Following the formalism of Epstein-
Wagoner, we also obtain the waveform and the luminosity of the gravitational
wave generated by these particles.


title: Hyperbolic Equations for Vacuum Gravity Using Special Orthonormal Frames

abstract:
  By adopting Nester's higher dimensional special orthonormal frames (HSOF) the
tetrad equations for vacuum gravity are put into first order symmetric
hyperbolic (FOSH) form with constant coefficients, independent of any time
slicing or coordinate specialization.


title:
Vacuum Fluctuations as a Source of Adiabatic Perturbations in Power Law
  Inflationary Cosmology

abstract:
  An analysis of the decoherence of quantum fluctuations shows that production
of classical adiabatic density perturbations may not take place in models of
power-law inflation with power 1< p < 3. Some consequences for models of
extended inflation are pointed out. In general, the condition for decoherence
places new constraint on inflationary models, which does not depend on often
complicated subsequent evolution.


title: A General Expression for the Quartic Lovelock Tensor

abstract:
  A general expression is given for the quartic Lovelock tensor 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. In addition, expressions are given (in the appendix) for the
coefficient of the quartic Lovelock Lagrangian as well as for lower-order
Lovelock tensors and Lovelock Lagrangian coefficients.


title:
Second post-Newtonian gravitational radiation reaction for two-body
  systems: Nonspinning bodies

abstract:
  Starting from the recently obtained 2PN accurate forms of the energy and
angular momentum fluxes from inspiralling compact binaries, we deduce the
gravitational radiation reaction to 2PN order beyond the quadrupole
approximation - 4.5PN terms in the equation of motion - using the refined
balance method proposed by Iyer and Will. We explore critically the features of
their construction and illustrate them by contrast to other possible variants.
The equations of motion are valid for general binary orbits and for a class of
coordinate gauges. The limiting cases of circular orbits and radial infall are
also discussed.


title: Origin of the Thermal Radiation in a Solid-State Analog of a Black-Hole

abstract:
  An effective black-hole-like horizon occurs, for electromagnetic waves in
matter, at a surface of singular electric and magnetic permeabilities. In a
physical dispersive medium this horizon disappears for wave numbers with
$k>k_c$. Nevertheless, it is shown that Hawking radiation is still emitted if
free field modes with $k>k_c$ are in their ground state.


title: The rigidly rotating disk of dust and its black hole limit

abstract:
  The exact global solution of the Einstein equations [Neugebauer & Meinel,
Phys. Rev. Lett. 75 (1995) 3046] describing a rigidly rotating,
self-gravitating disk is discussed. The underlying matter model is a perfect
fluid in the limit of vanishing pressure. The solution represents the
general-relativistic analogue of the classical Maclaurin disk. It was derived
by applying solution techniques from soliton theory to the axisymmetric,
stationary vacuum Einstein equations. In contrast to the Newtonian solution,
there exists an upper limit for the total mass of the disk - if the angular
momentum is fixed. At this limit, a transition to a rotating black hole, i.e.,
to the Kerr solution occurs. Another limiting procedure leads to an interesting
cosmological solution. These results prove conjectures formulated by Bardeen
and Wagoner more than twenty-five years ago.


title: Hamiltonians for Reduced Gravity

abstract:
  A generalised canonical formulation of gravity is devised for foliations of
spacetime with codimension $n\ge1$. The new formalism retains n-dimensional
covariance and is especially suited to 2+2 decompositions of spacetime. It is
also possible to use the generalised formalism to obtain boundary contributions
to the 3+1 Hamiltonian.


title: Decoherence of Vacuum Fluctuations in Cosmology

abstract:
  A calculation of the one-mode occupation numbers for vacuum fluctuations of
massive fields in De Sitter space shows that their use for the generation of
classical density perturbations in inflationary cosmology very much depends on
their masses and conformal couplings. A new mechanism for the decoherence of
relatively massive fields has been identified. A similar analysis of the power
law inflation shows that production of adiabatic density perturbations may not
take place in models with power p < 3.


title: Consistency of dust solutions with div H=0

abstract:
  One of the necessary covariant conditions for gravitational radiation is the
vanishing of the divergence of the magnetic Weyl tensor H_{ab}, while H_{ab}
itself is nonzero. We complete a recent analysis by showing that in
irrotational dust spacetimes, the condition div H=0 evolves consistently in the
exact nonlinear theory.


title:
Hierarchical search strategy for the detection of gravitational waves
  from coalescing binaries: Extension to post-Newtonian wave forms

abstract:
  The detection of gravitational waves from coalescing compact binaries would
be a computationally intensive process if a single bank of template wave forms
(i.e., a one step search) is used. In an earlier paper we had presented a
detection strategy, called a two step search}, that utilizes a hierarchy of
template banks. It was shown that in the simple case of a family of Newtonian
signals, an on-line two step search was about 8 times faster than an on-line
one step search (for initial LIGO). In this paper we extend the two step search
to the more realistic case of zero spin 1.5 post-Newtonian wave forms. We also
present formulas for detection and false alarm probabilities which take
statistical correlations into account. We find that for the case of a 1.5
post-Newtonian family of templates and signals, an on-line two step search
requires about 1/21 the computing power that would be required for the
corresponding on-line one step search. This reduction is achieved when signals
having strength S = 10.34 are required to be detected with a probability of
0.95, at an average of one false event per year, and the noise power spectral
density used is that of advanced LIGO. For initial LIGO, the reduction achieved
in computing power is about 1/27 for S = 9.98 and the same probabilities for
detection and false alarm as above.


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

abstract:
  An update of the ODEtools Maple package, for the analytical solving of 1st
and 2nd order ODEs using Lie group symmetry methods, is presented. The set of
routines includes an ODE-solver and user-level commands realizing most of the
relevant steps of the symmetry scheme. The package also includes commands for
testing the returned results, and for classifying 1st and 2nd order ODEs.


title: Bondi mass in classical field theory

abstract:
  We analyze three classical field theories based on the wave equation: scalar
field, electrodynamics and linearized gravity. We derive certain generating
formula on a hyperboloid and on a null surface for them. The linearized
Einstein equations are analyzed around null infinity. It is shown how the
dynamics can be reduced to gauge invariant quanitities in a quasi-local way.
The quasi-local gauge-invariant ``density'' of the hamiltonian is derived on
the hyperboloid and on the future null infinity. The result gives a new
interpretation of the Bondi mass loss formula. We show also how to define
angular momentum. Starting from affine approach for Einstein equations we
obtain variational formulae for Bondi-Sachs type metrics related with energy
and angular momentum generators. The original van der Burg asymptotic hierarchy
is revisited and the relations between linearized and asymptotic nonlinear
situations are established. We discuss also supertranslations, Newman-Penrose
charges and Janis solutions.


title:
The Application of the Newman-Janis Algorithm in Obtaining Interior
  Solutions of the Kerr Metric

abstract:
  In this paper we present a class of metrics to be considered as new possible
sources for the Kerr metric. These new solutions are generated by applying the
Newman-Janis algorithm (NJA) to any static spherically symmetric (SSS) ``seed''
metric. The continuity conditions for joining any two of these new metrics is
presented. A specific analysis of the joining of interior solutions to the Kerr
exterior is made. The boundary conditions used are those first developed by
Dormois and Israel. We find that the NJA can be used to generate new physically
allowable interior solutions. These new solutions can be matched smoothly to
the Kerr metric. We present a general method for finding such solutions with
oblate spheroidal boundary surfaces. Finally a trial solution is found and
presented.


title: Consistency of Orthodox Gravity

abstract:
  A recent proposal for quantizing gravity is investigated for self
consistency. There are well-known difficulties in dealing with Einstein gravity
when resorting to the perturbative techniques of quantum field theory. This
however does not preclude the existence of a quantum form. This Letter is all
about such a subtle but important difference.


title: Total intrinsic spin for plane gravity waves

abstract:
  A quantity which measures total intrinsic spin along the z axis is
constructed for planar gravity (fields dependent on z and t only), in both the
Ashtekar complex connection formalism and in geometrodynamics. The total spin
is conserved but (surprisingly) is not a surface term. This constant of the
motion coincides with one of four observables previously discovered by Husain
and Smolin. Two more of those observables can be interpreted physically as
raising and lowering operators for total spin.


title: Constants of motion for vacuum general relativity

abstract:
  The 3+1 Hamiltonian Einstein equations, reduced by imposing two commuting
spacelike Killing vector fields, may be written as the equations of the
$SL(2,R)$ principal chiral model with certain `source' terms. Using this
formulation, we give a procedure for generating an infinite number of non-local
constants of motion for this sector of the Einstein equations. The constants of
motion arise as explicit functionals on the phase space of Einstein gravity,
and are labelled by sl(2,R) indices.


title: Large quantum gravity effects: backreaction on matter

abstract:
  We reexamine the large quantum gravity effects discovered by Ashtekar in the
context of 2+1 dimensional gravity coupled to matter. We study an alternative
one-parameter family of coherent states of the theory in which the large
quantum gravity effects on the metric can be diminished, at the expense of
losing coherence in the matter sector. Which set of states is the one that
occurs in nature will determine if the large quantum gravity effects are
actually observable as wild fluctuations of the metric or rapid loss of
coherence of matter fields.


title: Against Many-Worlds Interpretations

abstract:
  A short foreword has been added for the archive version of this article,
which otherwise appears as originally published in 1990, except for the
updating of references. The original abstract follows.
  This is a critical review of the literature on many-worlds interpretations
(MWI), with arguments drawn partly from earlier critiques by Bell and Stein.
The essential postulates involved in various MWI are extracted, and their
consistency with the evident physical world is examined. Arguments are
presented against MWI proposed by Everett, Graham and DeWitt. The relevance of
frequency operators to MWI is examined; it is argued that frequency operator
theorems of Hartle and Farhi-Goldstone-Gutmann do not in themselves provide a
probability interpretation for quantum mechanics, and thus neither support
existing MWI nor would be useful in constructing new MWI. Comments are made on
papers by Geroch and Deutsch that advocate MWI. It is concluded that no
plausible set of axioms exists for an MWI that describes known physics.


title:
Matrix Elements of Thiemann's Hamiltonian Constraint in Loop Quantum
  Gravity

abstract:
  We present an explicit computation of matrix elements of the hamiltonian
constraint operator in non-perturbative quantum gravity. In particular, we
consider the euclidean term of Thiemann's version of the constraint and compute
its action on trivalent states, for all its natural orderings. The calculation
is performed using graphical techniques from the recoupling theory of colored
knots and links. We exhibit the matrix elements of the hamiltonian constraint
operator in the spin network basis in compact algebraic form.


title: Restrictions on negative energy density in a curved spacetime

abstract:
  Recently a restriction ("quantum inequality-type relation") on the
(renormalized) energy density measured by a static observer in a "globally
static" (ultrastatic) spacetime has been formulated by Pfenning and Ford for
the minimally coupled scalar field, in the extension of quantum inequality-type
relation on flat spacetime of Ford and Roman. They found negative lower bounds
for the line integrals of energy density multiplied by a sampling (weighting)
function, and explicitly evaluate them for some specific spacetimes. In this
paper, we study the lower bound on spacetimes whose spacelike hypersurfaces are
compact and without boundary. In the short "sampling time" limit, the bound has
asymptotic expansion. Although the expansion can not be represented by locally
invariant quantities in general due to the nonlocal nature of the integral, we
explicitly evaluate the dominant terms in the limit in terms of the invariant
quantities. We also make an estimate for the bound in the long sampling time
limit.


title:
Controversies in the History of the Radiation Reaction problem in
  General Relativity

abstract:
  This paper examines the historical controversy over whether gravitationally
bound systems, such as binary stars, experienced orbital damping due to the
emission of gravitational radiation, focusing especially on the period of the
1950s, but also discussing the work of Einstein and Rosen in the 1930s on
cylindrical gravitational waves and the later quadrupole formula controversy.


title: On a Three-Dimensional Gravity Model with Higher Derivatives

abstract:
  The purpose of this work is to present a model for 3D massive gravity with
topological and higher-derivative terms. Causality and unitarity are discussed
at tree-level. Power-counting renormalizability is also contemplated.


title:
Some Quantum Aspects of Three-Dimensional Einstein-Chern-Simons-Proca
  Massive Gravity

abstract:
  We present a 3-dimensional model for massive gravity with masses induced by
topological (Chern-Simons) and Proca-like mass terms. Causality and unitarity
are discussed at tree-level. Power-counting renormalizability is also
contemplated.


title: Energy and directional signatures for plane quantized gravity waves

abstract:
  Solutions are constructed to the quantum constraints for planar gravity
(fields dependent on z and t only) in the Ashtekar complex connection
formalism. A number of operators are constructed and applied to the solutions.
These include the familiar ADM energy and area operators, as well as new
operators sensitive to directionality (z+ct vs. z-ct dependence). The
directionality operators are quantum analogs of the classical constraints
proposed for unidirectional plane waves by Bondi, Pirani, and Robinson (BPR).
It is argued that the quantum BPR constraints will predict unidirectionality
reliably only for solutions which are semiclassical in a certain sense. The ADM
energy and area operators are likely to have imaginary eigenvalues, unless one
either shifts to a real connection, or allows the connection to occur other
than in a holonomy. In classical theory, the area can evolve to zero. A quantum
mechanical mechanism is proposed which would prevent this collapse.


title:
Boson Stars in General Scalar-Tensor Gravitation: Equilibrium
  Configurations

abstract:
  We study equilibrium configurations of boson stars in the framework of
general scalar-tensor theories of gravitation. We analyse several possible
couplings, with acceptable weak field limit and, when known, nucleosynthesis
bounds, in order to work in the cosmologically more realistic cases of this
kind of theories. We found that for general scalar-tensor gravitation, the
range of masses boson stars might have is comparable with the general
relativistic case. We also analyse the possible formation of boson stars along
different eras of cosmic evolution, allowing for the effective gravitational
constant far out form the star to deviate from its current value. In these
cases, we found that the boson stars masses are sensitive to this kind of
variations, within a typical few percent. We also study cases in which the
coupling is implicitly defined, through the dependence on the radial
coordinate, allowing it to have significant variations in the radius of the
structure.


title:
Static, massive fields and vacuum polarization potential in Rindler
  space

abstract:
  In Rindler space, we determine in terms of special functions the expression
of the static, massive scalar or vector field generated by a point source. We
find also an explicit integral expression of the induced electrostatic
potential resulting from the vacuum polarization due to an electric charge at
rest in the Rindler coordinates. For a weak acceleration, we give then an
approximate expression in the Fermi coordinates associated with the uniformly
accelerated observer.


title: The ``Nernst Theorem'' and Black Hole Thermodynamics

abstract:
  The Nernst formulation of the third law of ordinary thermodynamics (often
referred to as the ``Nernst theorem'') asserts that the entropy, $S$, of a
system must go to zero (or a ``universal constant'') as its temperature, $T$,
goes to zero. This assertion is commonly considered to be a fundamental law of
thermodynamics. As such, it seems to spoil the otherwise perfect analogy
between the ordinary laws of thermodynamics and the laws of black hole
mechanics, since rotating black holes in general relativity do not satisfy the
analog of the ``Nernst theorem''. The main purpose of this paper is to attempt
to lay to rest the ``Nernst theorem'' as a law of thermodynamics. We consider a
boson (or fermion) ideal gas with its total angular momentum, $J$, as an
additional state parameter, and we analyze the conditions on the single
particle density of states, $g(\epsilon,j)$, needed for the Nernst formulation
of the third law to hold. (Here, $\epsilon$ and $j$ denote the single particle
energy and angular momentum.) Although it is shown that the Nernst formulation
of the third law does indeed hold under a wide range of conditions, some simple
classes of examples of densities of states which violate the ``Nernst theorem''
are given. In particular, at zero temperature, a boson (or fermion) gas
confined to a circular string (whose energy is proportional to its length) not
only violates the ``Nernst theorem'' also but reproduces some other
thermodynamic properties of an extremal rotating black hole.


title: Is "the theory of everything'' merely the ultimate ensemble theory?

abstract:
  We discuss some physical consequences of what might be called ``the ultimate
ensemble theory'', where not only worlds corresponding to say different sets of
initial data or different physical constants are considered equally real, but
also worlds ruled by altogether different equations. The only postulate in this
theory is that all structures that exist mathematically exist also physically,
by which we mean that in those complex enough to contain self-aware
substructures (SASs), these SASs will subjectively perceive themselves as
existing in a physically ``real'' world. We find that it is far from clear that
this simple theory, which has no free parameters whatsoever, is observationally
ruled out. The predictions of the theory take the form of probability
distributions for the outcome of experiments, which makes it testable. In
addition, it may be possible to rule it out by comparing its a priori
predictions for the observable attributes of nature (the particle masses, the
dimensionality of spacetime, etc) with what is observed.


title: Stochastic semiclassical cosmological models

abstract:
  We consider the classical stochastic fluctuations of spacetime geometry
induced by quantum fluctuations of massless non-conformal matter fields in the
Early Universe. To this end, we supplement the stress-energy tensor of these
fields with a stochastic part, which is computed along the lines of the
Feynman-Vernon and Schwinger-Keldysh techniques; the Einstein equation is
therefore upgraded to a so called Einstein-Langevin equation. We consider in
some detail the conformal fluctuations of flat spacetime and the fluctuations
of the scale factor in a simple cosmological modelintroduced by Hartle, which
consists of a spatially flat isotropic cosmology driven by radiation and dust.


title: Universality of the Future Chronological Boundary

abstract:
  The purpose of this note is to establish, in a categorical manner, the
universality of the Geroch-Kronheimer-Penrose causal boundary when considering
the types of causal structures that may profitably be put on any sort of
boundary for a spacetime. Actually, this can only be done for the future causal
boundary (or the past causal boundary) separately; furthermore, only the
chronology relation, not the causality relation, is considered, and the GKP
topology is eschewed. The final result is that there is a unique map, with the
proper causal properties, from the future causal boundary of a spacetime onto
any ``reasonable" boundary which supports some sort of chronological structure
and which purports to consist of a future completion of the spacetime.
Furthermore, the future causal boundary construction is categorically unique in
this regard.


title:
Multidimensional Cosmology with a Generalized Maxwell Field: Integrable
  Cases

abstract:
  We consider multidimensional cosmologies in even-dimensional space-times
(D=2n) containg perfect fluid and a multidimensional generalization of the
Maxwell field, preserving its conformal invariance (the F field, an n-form).
Among models with an isotropic physical 3-space some integrable cases are
found: vacuum models (which are integrable in the general case) and some
perfect fluid models with barotropic equations of state. All of them contain a
component of the F field appearing as an additional scalar in 4 dimensions. A
two-parameter family of spatially flat models and four one-parameter families,
including non-spatially flat models, have been obtained (where the parameters
are constants from the fluid equation of state). All these integrable models
admit the inclusion of a massless scalar field or an additional fluid with
ultrastiff equation of state. Basic properties of vacuum models in the physical
conformal frame are outlined.


title: Dual formulation of spin network evolution

abstract:
  We illustrate the relationship between spin networks and their dual
representation by labelled triangulations of space in 2+1 and 3+1 dimensions.
We apply this to the recent proposal for causal evolution of spin networks. The
result is labelled spatial triangulations evolving with transition amplitudes
given by labelled spacetime simplices. The formalism is very similar to
simplicial gravity, however, the triangulations represent combinatorics and not
an approximation to the spatial manifold. The distinction between future and
past nodes which can be ordered in causal sets also exists here. Spacelike and
timelike slices can be defined and the foliation is allowed to vary. We clarify
the choice of the two rules in the causal spin network evolution, and the
assumption of trivalent spin networks for 2+1 spacetime dimensions and
four-valent for 3+1. As a direct application, the problem of the exponential
growth of the causal model is remedied. The result is a clear and more rigid
graphical understanding of evolution of combinatorial spin networks, on which
further work can be based.


title: "Faster Than Light" Photons in Dilaton Black Hole Spacetimes

abstract:
  We investigate the phenomenon of "faster than light" photons in a family of
dilaton black hole spacetimes. For radially directed photons, we find that
their light-cone condition is modified even though the spacetimes are
spherically symmetric. They also satisfy the "horizon theorem" and the
"polarization sum rule" of Shore. For orbital photons, the dilatonic effect on
the modification of the light-cone condition can become more dominant than the
electromagnetic and the gravitational ones as the orbit gets closer to the
event horizon in the extremal or near-extremal cases.


title:
A Gauge-invariant Analysis of Magnetic Fields in General Relativistic
  Cosmology

abstract:
  We provide a fully general-relativistic treatment of cosmological
perturbations in a universe permeated by a large-scale primordial magnetic
field, using the Ellis-Bruni gauge-invariant formalism. The exact non-linear
equations for general relativistic magnetohydrodynamic evolution are derived. A
number of applications are made: the behaviour of small perturbations to
Friedmann universes are studied; a comparison is made with earlier Newtonian
treatments of cosmological perturbations and some effects of inflationary
expansion are examined.


title: Causal Structures in Linear Spaces

abstract:
  Linear topological spaces with partial ordering (linear kinematics) are
studied. They are defined by a set of 8 axioms implying that topology, linear
structure and ordering are compatible with each other. Most of the results are
valid for both the finite-dimensional and infinite-dimensional case. In
applications to physics, partial ordering is interpreted as the causal
structure. Both Newtonian and the special relativity causal structures are
studied, and some other possible types of causality are discussed.
  Linear topological spaces with pseudometric which satisfies the time
inequality instead of the triangle inequality are studied (3 axioms).
Pseudometric (which is determined by a pseudonorm) is shown to define a
topology on a linear space, it being a continuous mapping in this topology.
Proved that for a space with pseudometric to be a linear kinematics it is
necessary and sufficient that mapping of multiplication by -1 (i.e. time
reversion) be continuous. Minkovskii space of the special relativity theory
proved to be a pseudometric linear kinematics.


title: Space for Both No-Boundary and Tunneling Quantum States of the Universe

abstract:
  At the minisuperspace level of homogeneous models, the bare probability for a
classical universe has a huge peak at small universes for the Hartle-Hawking
`no-boundary' wavefunction, in contrast to the suppression at small universes
for the `tunneling' wavefunction. If the probability distribution is cut off at
the Planck density (say), this suggests that the former quantum state is
inconsistent with our observations. For inhomogeneous models in which
stochastic inflation can occur, it is known that the idea of including a volume
factor in the observational probability distribution can lead to arbitrarily
large universes' being likely. Here this idea is shown to be sufficient to save
the Hartle-Hawking proposal even at the minisuperspace level (for suitable
inflaton potentials), by giving it enough space to be consistent with
observations.


title: The central density of neutron stars in close binaries

abstract:
  Recent numerical simulations of coalescing binary neutron stars conducted by
Wilson, Mathews and Marronetti (WMM) show a rising central energy density of
the stars as the orbital separation shrinks, i.e. the stars are individually
crushed as they near coalescence. They claim this ``star-crushing'' effect is
partially due to a non-linear, first post-Newtonian order enhancement of the
self-gravity of each star caused by the presence of the other star. We present
a concrete calculation which shows, within general relativity, first
post-Newtonian order interactions with the other star leave the central energy
density unchanged as the orbital radius shrinks. The results presented here are
in sharp disagreement with the WMM claim. However, alternative gravitational
theories, such as Brans-Dicke theory, can exhibit a small crushing effect in
the binary constituents as they near coalescence. We show that the absence of
the star-crushing effect at first post-Newtonian order is related to adherence
to the strong equivalence principle.


title:
The central density of a neutron star is unaffected by a binary
  companion at linear order in $\mu/R$

abstract:
  Recent numerical work by Wilson, Mathews, and Marronetti [J. R. Wilson, G. J.
Mathews and P. Marronetti, Phys. Rev. D 54, 1317 (1996)] on the coalescence of
massive binary neutron stars shows a striking instability as the stars come
close together: Each star's central density increases by an amount proportional
to 1/(orbital radius). This overwhelms any stabilizing effects of tidal
coupling [which are proportional to 1/(orbital radius)^6] and causes the stars
to collapse before they merge. Since the claimed increase of density scales
with the stars' mass, it should also show up in a perturbation limit where a
point particle of mass $\mu$ orbits a neutron star. We prove analytically that
this does not happen; the neutron star's central density is unaffected by the
companion's presence to linear order in $\mu/R$. We show, further, that the
density increase observed by Wilson et. al. could arise as a consequence of not
faithfully maintaining boundary conditions.


title: Freely falling 2-surfaces and the quasi-local energy

abstract:
  We derive an expression for effective gravitational mass for any closed
spacelike 2-surface. This effective gravitational energy is defined directly
through the geometrical quantity of the freely falling 2-surface and thus is
well adapted to intuitive expectation that the gravitational mass should be
determined by the motion of test body moving freely in gravitational field. We
find that this effective gravitational mass has reasonable positive value for a
small sphere in the non-vacuum space-times and can be negative for vacuum case.
Further, this effective gravitational energy is compared with the quasi-local
energy based on the $(2+2)$ formalism of the General Relativity. Although some
gauge freedoms exist, analytic expressions of the quasi-local energy for vacuum
cases are same as the effective gravitational mass. Especially, we see that the
contribution from the cosmological constant is the same in general cases.


title: Cosmic Censorship in Quantum Gravity

abstract:
  We study cosmic censorship in the Reissner-Nordstrom charged black hole by
means of quantum gravity holding near the apparent horizons. We consider a
gedanken experiment whether or not a black hole with the electric charge $Q$
less than the mass $M$ ($Q < M$) could increase its charge to go beyond the
extremal limit $Q = M$ by absorbing the external charged matters. If the black
hole charge could exceed the extremal value, a naked singularity would be
liberated from the protection of the outer horizon and visible to distant
observers, which means weak cosmic censorship to be violated in this process.
It is shown that the black hole never exceeds the extremal black hole this way
in quantum gravity as in classical general gravity. An increment of the trapped
external charged matters by the black hole certainly causes the inner Cauchy
horizon to approach the outer horizon, but its relative approaching speed
gradually slows down and stops precisely at the extremal limit. It is quite
remarkable that cosmic censorship remains true even in quantum gravity. This
study is the first attempt of examining weak cosmic censorship beyond the
classical analysis.


title: Thermal Conduction in Systems out of Hydrostatic Equilibrium

abstract:
  We analyse the effects of thermal conduction in a relativistic fluid, just
after its departure from hydrostatic equilibrium, on a time scale of the order
of thermal relaxation time. It is obtained that the resulting evolution will
critically depend on a parameter defined in terms of thermodynamic variables,
which is constrained by causality requirements.


title:
Gravitational waves from pulsating stars: Evolving the perturbation
  equations for a relativistic star

abstract:
  We consider the perturbations of a relativistic star as an initial-value
problem. Having discussed the formulation of the problem (the perturbation
equations and the appropriate boundary conditions at the centre and the surface
of the star) in detail we evolve the equations numerically from several
different sets of initial data. In all the considered cases we find that the
resulting gravitational waves carry the signature of several of the star's
pulsation modes. Typically, the fluid $f$-mode, the first two $p$-modes and the
slowest damped gravitational $w$-mode are present in the signal. This indicates
that the pulsation modes may be an interesting source for detectable
gravitational waves from colliding neutron stars or supernovae. We also survey
the literature and find several indications of mode presence in numerical
simulations of rotating core collapse and coalescing neutron stars. If such
mode-signals can be detected by future gravitational-wave antennae one can hope
to infer detailed information about neutron stars. Since a perturbation
evolution should adequately describe the late time behaviour of a dynamically
excited neutron star, the present work can also be used as a bench-mark test
for future fully nonlinear simulations.


title: Binary Neutron Stars in General Relativity: Quasi-Equilibrium Models

abstract:
  We perform fully relativistic calculations of binary neutron stars in
quasi-equilibrium circular orbits. We integrate Einstein's equations together
with the relativistic equation of hydrostatic equilibrium to solve the initial
value problem for equal-mass binaries of arbitrary separation. We construct
sequences of constant rest mass and identify the innermost stable circular
orbit and its angular velocity. We find that the quasi-equilibrium maximum
allowed mass of a neutron star in a close binary is slightly larger than in
isolation.


title: The Binary Pulsar Is Not the Ultimate Test for the Theory of Gravity

abstract:
  General relativity can be formulated either as in its original geometrical
version (Einstein, 1915) or as a field theory (Feynman, 1962). In the Feynman
presentation of Einstein theory an hypothesis concerning the interaction of
gravity to gravity, which was hidden in the original version, becomes explicit.
This is nothing but the assumed extension of the validity of the equivalence
principle not only for matter-gravity interaction, but also for
gravity-gravity. Recently we have presented a field theory of gravity (from
here on called the NDL theory) which does not contain such a hypothesis. We
have shown that, for this theory, both the cosmological structure and the PPN
approximation for the solar tests are satisfied.
  The proposal of this paper is to go one step further and to show that NDL
theory is able to solve the problem of radiation emission by a binary pulsar in
the same degree of accuracy as it was done in the GR theory. In the
post-Newtonian order of approximation we show that the quadrupole formula of
this theory is equal to the corresponding one in general relativity. Thus, the
unique actual observable distinction of these theories concerns the velocity of
gravitational waves, which becomes then the true ultimate test for gravity
theory.


title:
On the Critical Behaviour of Heat Conducting Sphere out of Hydrostatic
  Equilibrium

abstract:
  We comment further on the behaviour of a heat conducting fluid when a
characteristic parameter of the system approaches a critical value.


title:
Spherical Collapse of a Mass-Less Scalar Field With Semi-Classical
  Corrections

abstract:
  We investigate numerically spherically symmetric collapse of a scalar field
in the semi-classical approximation. We first verify that our code reproduces
the critical phenomena (the Choptuik effect) in the classical limit and black
hole evaporation in the semi classical limit. We then investigate the effect of
evaporation on the critical behavior. The introduction of the Planck length by
the quantum theory suggests that the classical critical phenomena, which is
based on a self similar structure, will disappear. Our results show that when
quantum effects are not strong enough, critical behavior is observed. In the
intermediate regime, evaporation is equivalent to a decrease of the initial
amplitude. It doesn't change the echoing structure of near critical solutions.
In the regime where black hole masses are low and the quantum effects are
large, the semi classical approximation breaks down and has no physical
meaning.


title: Astrophysical Bounds on Global Strings

abstract:
  Global topological defects produce nonzero stress-energy throughout
spacetime, and as a result can have observable gravitational influence on
surrounding matter. Gravitational effects of global strings are used to place
bounds on their cosmic abundance. The minimum separation between global strings
is estimated by considering the defects' contribution to the cosmological
energy density. More rigorous constraints on the abundance of global strings
are constructed by examining the tidal forces such defects will have on
observable astrophysical systems. The small number of observed tidally
disrupted systems indicates there can be very few of these objects in the
observable universe.


title: The gravitational redshift of boson stars

abstract:
  We investigate the possible gravitational redshift values for boson stars
with a self-interaction, studying a wide range of possible masses. We find a
limiting value of $z_{lim} \simeq 0.687$ for stable boson star configurations.
We compare theoretical expectation with the observational capabilities in
several different wavebands, concluding that direct observation of boson stars
by this means will be extremely challenging. X-ray spectroscopy is perhaps the
most interesting possibility.


title: Radiation from a uniformly accelerating harmonic oscillator

abstract:
  We consider a radiation from a uniformly accelerating harmonic oscillator
whose minimal coupling to the scalar field changes suddenly. The exact time
evolutions of the quantum operators are given in terms of a classical solution
of a forced harmonic oscillator. After the jumping of the coupling constant
there occurs a fast absorption of energy into the oscillator, and then a slow
emission follows. Here the absorbed energy is independent of the acceleration
and proportional to the log of a high momentum cutoff of the field. The emitted
energy depends on the acceleration and also proportional to the log of the
cutoff. Especially, if the coupling is comparable to the natural frequency of
the detector ($e^2/(4m) \sim \omega_0$) enormous energies are radiated away
from the oscillator.


title: Internal Structure of a Gauss-Bonnet Black Hole

abstract:
  Black holes are studied in the frames of superstring theory using a
non-trivial numerical integration method. A low energy string action containing
graviton, dilaton, Gauss-Bonnet and Maxwell contributions is considered.
Four-dimensional black hole solutions are studied inside and outside the event
horizon. The internal part of the solutions is shown to have a non-trivial
topology.


title: Entropy in the Kerr-Newman Black Hole

abstract:
  Entropy of the Kerr-Newman black hole is calculated via the brick wall method
with maintaining careful attention to the contribution of superradiant scalar
modes. It turns out that the nonsuperradinat and superradiant modes
simultaneously contribute to the entropy with the same order in terms of the
brick wall cutoff $\epsilon$. In particular, the contribution of the
superradiant modes to the entropy is negative. To avoid divergency in this
method when the angular velocity tends to zero, we propose to intr oduce a
lower bound of angular velocity and to treat the case of the angular momentum
per unit mass $a=0$ separately. Moreover, from the lower bound of the angular
velocity, we obtain the $\theta$-dependence structure of the brick wall cutoff,
which natu rally requires an angular cutoff $\delta$. Finally, if the cutoff
values, $\epsilon$ and $\delta$, satisfy a proper relation between them, the
resulting entropy satisfies the area law.


title:
Indeterministic Quantum Gravity and Cosmology VI. Predynamical Geometry
  of Spacetime Manifold, Supplementary Conditions for Metric, and CPT

abstract:
  This paper is a continuation of the papers [gr-qc/9409010, gr-qc/9505034,
gr-qc/9603022, gr-qc/9609035, gr-qc/9609046]. The introduction of a prior,
i.e., predynamical global geometry of spacetime manifold is substantiated, and
the geometry is specified. The manifold is an infinite four-cylinder, or tube
in the five-dimensional Euclidean space, the orthogonal section of the cylinder
being the unit three-sphere. Supplementary conditions for metric are introduced
geometrically, coordinate-independently, as opposed to coordinate conditions.
Parity and time-reversal transformations are extended to the manifold
specified. PT is equivalent to a rotation through \pi about an axis orthogonal
to the cylinder axis. CPT invariance is discussed.
  Keywords: cosmic time, cosmic space, cylindrical manifold


title: Pushing Einstein's Principles to the Extreme

abstract:
  In these lectures I propose to push Einstein's principle of coordinate
independence to the extreme in order to restrict the possible form of
fundamental equations of motion in physics. I start from nearly tautological
system theoretic axioms. They provide a minimal amount of a priori structure
which is thought to be characteristic of human thinking in general. It is shown
how formal discretizations of Maxwell and Yang Mills theory in flat space and
of general relativity in Ashtekar variables fit into this frame work.


title:
Spherically symmetric solutions in four-dimensional Poincar\'e gravity
  with non-trivial torsion

abstract:
  We study a four-dimensional gauge theory of the Poincar\'e group with
topological action which generalizes some well-known two-dimensional gravity
models. We classify the spherically symmetric solutions and discuss the
perturbative propagation of excitations around flat spacetime.


title: Topological Dynamics and Grand Unified Theory

abstract:
  A formalism is presented to construct a non-perturbative Grand Unified Theory
when gravitational Planck-scale phenomena are included. The fundamental object
on the Planck scale is the three-torus T^3 from which the known properties of
superstrings, such as the geometric action and duality, follow directly. The
low energy theory is 11-dimensional and compactification to a Lorentzian
four-manifold is an automatic feature of the unified model. In particular, the
simply-connected K3 Calabi-Yau manifold follows naturally from the model and
provides a direct link with M-theory. The high energy theory is formulated on a
T^3 lattice with handles which exhibits the necessary symmetry groups for the
standard model, and yields a consistent amplitude for the cosmic microwave
background fluctuations. The equation of motion for the supersymmetric, unified
theory is derived and leads to the Higgs field. This formulation predicts a
remnant, scalar topological defect of mass < 9 m_Planck/46 from the Planck
epoch, which is a candidate for dark matter. Finally, it is shown that if the
universe is quantum-mechanical, its spatial dimension is equal to three and the
laws of nature are Lorentz invariant when gravity can be neglected.


title: The Energy-Momentum Tensor for Cosmological Perturbations

abstract:
  We study the effective energy-momentum tensor (EMT) for cosmological
perturbations and formulate the gravitational back-reaction problem in a gauge
invariant manner. We analyze the explicit expressions for the EMT in the cases
of scalar metric fluctuations and of gravitational waves and derive the
resulting equations of state. The formalism is applied to investigate the
back-reaction effects in chaotic inflation. We find that for long wavelength
scalar and tensor perturbations, the effective energy density is negative and
thus counteracts any pre-existing cosmological constant. For scalar
perturbations during an epoch of inflation, the equation of state is de
Sitter-like.


title:
Indeterministic Quantum Gravity and Cosmology VII. Dynamical Passage
  through Singularities: Black Hole and Naked Singularity, Big Crunch and Big
  Bang

abstract:
  This paper is a continuation of the papers [gr-qc/9409010, gr-qc/9505034,
gr-qc/9603022, gr-qc/9609035, gr-qc/9609046, gr-qc/9704033]. The aim of the
paper is to incorporate singularities---both local (black hole and naked
singularity) and global (big bang and big crunch)---into the dynamics of
indeterministic quantum gravity and cosmology. The question is whether a
singularity is dynamically passable, i.e., whether a dynamical process which
ends with a singularity may be extended beyond the latter. The answer is yes. A
local singularity is trivially passable, while the passableness for a global
singularity may invoke CPT transformation. The passableness of the
singularities implies pulsating black holes and the oscillating universe. For
the local singularity, the escape effect takes place: In a vicinity of the
singularity, quantum matter leaves the gravitational potential well.
  Keywords: tempered singularity, strong singularity, trivial passage, CPT
passage, pulsating black hole, escape effect, oscillating universe


title: Against ``Against Many-Worlds Interpretations''

abstract:
  The paper entitled ``Against Many-Worlds Interpretations'' by A. Kent, which
has recently been submitted to the e-Print archive (gr-qc/9703089) contained
some misconceptions. The claims on Everett's many-worlds interpretation are
quoted and answered.


title:
Perturbations and Critical Behavior in the Self-Similar Gravitational
  Collapse of a Massless Scalar Field

abstract:
  This paper studies the perturbations of the continuously self-similar
critical solution of the gravitational collapse of a massless scalar field
(Roberts solution). The perturbation equations are derived and solved exactly.
The perturbation spectrum is found to be not discrete, but occupying continuous
region of the complex plane. The renormalization group calculation gives the
value of the mass-scaling exponent equal to 1.


title: Canonical Quantization of the Gowdy Model

abstract:
  The family of Gowdy universes with the spatial topology of a three-torus is
studied both classically and quantum mechanically. Starting with the Ashtekar
formulation of Lorentzian general relativity, we introduce a gauge fixing
procedure to remove almost all of the non-physical degrees of freedom. In this
way, we arrive at a reduced model that is subject only to one homogeneous
constraint. The phase space of this model is described by means of a canonical
set of elementary variables. These are two real, homogeneous variables and the
Fourier coefficients for four real fields that are periodic in the angular
coordinate which does not correspond to a Killing field of the Gowdy
spacetimes. We also obtain the explicit expressions for the line element and
reduced Hamiltonian. We then proceed to quantize the system by representing the
elementary variables as linear operators acting on a vector space of analytic
functionals. The inner product on that space is selected by imposing Lorentzian
reality conditions. We find the quantum states annihilated by the operator that
represents the homogeneous constraint of the model and construct with them the
Hilbert space of physical states. Finally, we derive the general form of the
quantum observables of the model.


title: Gravitational Radiation -- A New Window Onto the Universe

abstract:
  A summary is given of the current status and plans for gravitational-wave
searches at all plausible wavelengths, from the size of the observable universe
to a few kilometers. The anticipated scientific payoff from these searches is
described, including expectations for detailed studies of black holes and
neutron stars, high-accuracy tests of general relativity, and hopes for the
discovery of exotic new kinds of objects.


title:
Gravitational Waves and Black Holes: an Introduction to General
  Relativity

abstract:
  In these lectures general relativity is outlined as the classical field
theory of gravity, emphasizing physical phenomena rather than mathematical
formalism. Dynamical solutions representing traveling waves as well as
stationary fields like those of black holes are discussed. Their properties are
investigated by studying the geodesic structure of the corresponding
space-times, as representing the motion of point-like test particles. The
interaction between gravitational, electro-magnetic and scalar fields is also
considered.


title: Estimation of Parameters of Gravitational Waves from Pulsars

abstract:
  The problem of search for nearly periodic gravitational wave sources in the
data from laser interferometric detectors is discussed using a simple model of
the signal. Accuracies of estimation of the parameters and computational
requirements to do the search are assessed.


title: Tensor perturbations in high-curvature string backgrounds

abstract:
  We derive a generalized equation for the evolution of tensor perturbations in
a cosmological background, taking into account higher-curvature contributions
and a tree-level coupling to the dilaton in the string frame. The equation is
obtained by perturbing the gravi-dilaton string effective action, expanded up
to first order in $\alpha'$. The $\alpha'$ corrections can modify the
low-energy perturbation spectrum, but the modifications are shown to be small
when the background curvature keeps constant in the string frame.


title: Relativistic Stellar Pulsations With Near-Zone Boundary Conditions

abstract:
  A new method is presented here for evaluating approximately the pulsation
modes of relativistic stellar models. This approximation relies on the fact
that gravitational radiation influences these modes only on timescales that are
much longer than the basic hydrodynamic timescale of the system. This makes it
possible to impose the boundary conditions on the gravitational potentials at
the surface of the star rather than in the asymptotic wave zone of the
gravitational field. This approximation is tested here by predicting the
frequencies of the outgoing non-radial hydrodynamic modes of non-rotating
stars. The real parts of the frequencies are determined with an accuracy that
is better than our knowledge of the exact frequencies (about 0.01%) except in
the most relativistic models where it decreases to about 0.1%. The imaginary
parts of the frequencies are determined with an accuracy of approximately M/R,
where M is the mass and R is the radius of the star in question.


title: Constraints on Space-Time Torsion from Hughes-Drever Experiments

abstract:
  The coupling of space-time torsion to the Dirac equation leads to effects on
the energy levels of atoms which can be tested by Hughes-Drever type
experiments. Reanalysis of these experiments carried out for testing the
anisotropy of mass and anomalous spin couplings can lead to the till now
tightest constraint on the axial torsion by $K \leq 1.5 . 10^{-15} m^{-1}$.


title:
Should Metric Signature Matter in Clifford Algebra Formulations of
  Physical Theories?

abstract:
  Standard formulation is unable to distinguish between the (+++-) and (---+)
spacetime metric signatures. However, the Clifford algebras associated with
each are inequivalent, R(4) in the first case (real 4 by 4 matrices), H(2) in
the latter (quaternionic 2 by 2). Multivector reformulations of Dirac theory by
various authors look quite inequivalent pending the algebra assumed. It is not
clear if this is mere artifact, or if there is a right/wrong choice as to which
one describes reality. However, recently it has been shown that one can map
from one signature to the other using a "tilt transformation" [see P. Lounesto,
"Clifford Algebras and Hestenes Spinors", Found. Phys. 23, 1203-1237 (1993)].
The broader question is that if the universe is signature blind, then perhaps a
complete theory should be manifestly tilt covariant. A generalized multivector
wave equation is proposed which is fully signature invariant in form, because
it includes all the components of the algebra in the wavefunction (instead of
restricting it to half) as well as all the possibilities for interaction terms.


title:
The influence of cosmological transitions on the evolution of density
  perturbations

abstract:
  We study the influence of the reheating and equality transitions on
superhorizon density perturbations and gravitational waves. Recent criticisms
of the `standard result' for large-scale perturbations in inflationary
cosmology are rectified. The claim that the `conservation law' for the
amplitude of superhorizon modes was empty is shown to be wrong. For sharp
transitions, i.e. the pressure jumps, we rederive the Deruelle-Mukhanov
junction conditions. For a smooth transition we correct a result obtained by
Grishchuk recently. We show that the junction conditions are not crucial,
because the pressure is continuous during the reheating transition. The problem
occurred, because the perturbed metric was not evolved correctly through the
smooth reheating transition. Finally, we derive the `standard result' within
Grishchuks's smooth (reheating) transition.


title: Cosmological and Black Hole Horizon Fluctuations

abstract:
  The quantum fluctuations of horizons in Robertson-Walker universes and in the
Schwarzschild spacetime are discussed. The source of the metric fluctuations is
taken to be quantum linear perturbations of the gravitational field. Lightcone
fluctuations arise when the retarded Green's function for a massless field is
averaged over these metric fluctuations. This averaging replaces the
delta-function on the classical lightcone with a Gaussian function, the width
of which is a measure of the scale of the lightcone fluctuations. Horizon
fluctuations are taken to be measured in the frame of a geodesic observer
falling through the horizon. In the case of an expanding universe, this is a
comoving observer either entering or leaving the horizon of another observer.
In the black hole case, we take this observer to be one who falls freely from
rest at infinity. We find that cosmological horizon fluctuations are typically
characterized by the Planck length. However, black hole horizon fluctuations in
this model are much smaller than Planck dimensions for black holes whose mass
exceeds the Planck mass. Furthermore, we find black hole horizon fluctuations
which are sufficiently small as not to invalidate the semiclassical derivation
of the Hawking process.


title: Chiral Anomaly in Contorted Spacetimes

abstract:
  The Dirac equation in Riemann-Cartan spacetimes with torsion is reconsidered.
As is well-known, only the axial covector torsion $A$, a one-form, couples to
massive Dirac fields. Using diagrammatic techniques, we show that besides the
familiar Riemannian term only the Pontrjagin type four-form $dA\wedge dA$ does
arise additionally in the chiral anomaly, but not the Nieh-Yan term $d ^* A$,
as has been claimed recently. Implications for cosmic strings in
Einstein-Cartan theory as well as for Ashtekar's canonical approach to quantum
gravity are discussed.


title: Effective Nonlocal Euclidean Gravity

abstract:
  A nonlocal form of the effective gravitational action could cure the
unboundedness of euclidean gravity with Einstein action. On sub-horizon length
scales the modified gravitational field equations seem compatible with all
present tests of general relativity and post-Newtonian gravity. They induce a
difference in the effective Newton's constant between regions of space with
vanishing or nonvanishing curvature scalar (or Ricci tensor). In cosmology they
may lead to a value $\Omega<1$ for the critical density after inflation. The
simplest model considered here appears to be in conflict with nucleosynthesis,
but generalizations consistent with all cosmological observations seem
conceivable.


title: Null dust in canonical gravity

abstract:
  We present the Lagrangian and Hamiltonian framework which incorporates null
dust as a source into canonical gravity. Null dust is a generalized Lagrangian
system which is described by six Clebsch potentials of its four-velocity Pfaff
form. The Dirac--ADM decomposition splits these into three canonical
coordinates (the comoving coordinates of the dust) and their conjugate momenta
(appropriate projections of four-velocity). Unlike ordinary dust of massive
particles, null dust therefore has three rather than four degrees of freedom
per space point. These are evolved by a Hamiltonian which is a linear
combination of energy and momentum densities of the dust. The energy density is
the norm of the momentum density with respect to the spatial metric. The
coupling to geometry is achieved by adding these densities to the gravitational
super-Hamiltonian and supermomentum. This leads to appropriate Hamiltonian and
momentum constraints in the phase space of the system. The constraints can be
rewritten in two alternative forms in which they generate a true Lie algebra.
The Dirac constraint quantization of the system is formally accomplished by
imposing the new constraints as quantum operator restrictions on state
functionals. We compare the canonical schemes for null and ordinary dust and
emhasize their differences.


title: The Nonlinear Quantum Gauge Theory-Superrelativity

abstract:
  A new type of a nonlinear gauge quantum theory (superrelativity) has been
proposed. Such theory demands a radical reconstruction of both the quantum
field conception and spacetime structure, and this paves presumably way to the
comprehension of the quantum nature of inertia.


title:
A forgotten argument by Gordon uniquely selects Abraham's tensor as the
  energy-momentum tensor for the electromagnetic field in homogeneous,
  isotropic matter

abstract:
  Given the present status of the problem of the electromagnetic energy tensor
in matter, there is perhaps use in recalling a forgotten argument given in 1923
by W. Gordon. Let us consider a material medium which is homogeneous and
isotropic when viewed in its rest frame. For such a medium, Gordon's argument
allows to reduce the above mentioned problem to an analogous one, defined in a
general relativistic vacuum, in presence of a suitably determined effective
metric. For the latter problem the form of the Lagrangian is known already,
hence the determination of the energy tensor is a straightforward matter. One
just performs the Hamiltonian derivative of the Lagrangian chosen in this way
with respect to the true metric. Abraham's tensor is thus selected as the
electromagnetic energy tensor for a medium which is homogeneous and isotropic
in its rest frame.


title: Why we observe an almost classical spacetime

abstract:
  We argue that, in order to obtain decoherence of spacetime, we should
consider quantum conformal metric fluctuations of spacetime. This could be the
required environment in the problem of selfmeasurement of spacetime in quantum
gravity.


title: A Proposal for the Quantum Theory of Gravity

abstract:
  We propose a model for the quantum theory of gravity. the model has
diffeomorphism invariance, a natural length scale, and (plausibly) propagating
modes. in the new addendum, we alter the model in a way which makes the
propagating modes much easier to approach.


title: Bubble wall perturbations coupled with gravitational waves

abstract:
  We study a coupled system of gravitational waves and a domain wall which is
the boundary of a vacuum bubble in de Sitter spacetime. To treat the system, we
use the metric junction formalism of Israel. We show that the dynamical degree
of the bubble wall is lost and the bubble wall can oscillate only while the
gravitational waves go across it. It means that the gravitational backreaction
on the motion of the bubble wall can not be ignored.


title: Gravito-electromagnetism

abstract:
  We develop and apply a fully covariant 1+3 electromagnetic analogy for
gravity. The free gravitational field is covariantly characterized by the Weyl
gravito-electric and gravito-magnetic spatial tensor fields, whose dynamical
equations are the Bianchi identities. Using a covariant generalization of
spatial vector algebra and calculus to spatial tensor fields, we exhibit the
covariant analogy between the tensor Bianchi equations and the vector Maxwell
equations. We identify gravitational source terms, couplings and potentials
with and without electromagnetic analogues. The nonlinear vacuum Bianchi
equations are shown to be invariant under covariant spatial duality rotation of
the gravito-electric and gravito-magnetic tensor fields. We construct the
super-energy density and super-Poynting vector of the gravitational field as
natural U(1) group invariants, and derive their super-energy conservation
equation. A covariant approach to gravito-electric/magnetic monopoles is also
presented.


title: Static black hole solutions with axial symmetry

abstract:
  We construct a new class of asymptotically flat black hole solutions in
Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole
solutions are static, and they have a regular event horizon. However, they
possess only axial symmetry. Like their regular counterparts, the black hole
solutions are characterized by two integers, the winding number $n$ and the
node number $k$ of the gauge field functions.


title: Critique of the Wheeler-DeWitt equation

abstract:
  The Wheeler-DeWitt equation is based on the use of canonical quantization
rules that may be inconsistent for constrained dynamical systems, such as
minisuperspaces subject to Einstein's equations. The resulting quantum dynamics
has no classical limit and it suffers from the infamous ``problem of time.'' In
this article, it is shown how a dynamical time (an internal clock) can be
constructed by means of a Hamilton-Jacobi formalism, and then used for a
consistent canonical quantization, with the correct classical limit.


title: Finitary Algebraic Superspace

abstract:
  An algebraic scheme is suggested in which discretized spacetime turns out to
be a quantum observable. As an example, a toy model producing spacetimes of
four points with different topologies is presented. The possibility of
incorporating this scheme into the framework of non-commutative differential
geometry is discussed.


title: Ricci Collineations for type B warped space-times

abstract:
  We present the general structure of proper Ricci Collineations (RC) for type
B warped space-times. Within this framework, we give a detailed description of
the most general proper RC for spherically symmetric metrics. As examples,
static spherically symmetric and Friedmann-Robertson-Walker space-times are
considered.


title: On the integrability of halo dipoles in gravity

abstract:
  We stress that halo dipole components are nontrivial in core-halo systems in
both Newton's gravity and General Relativity. To this end, we extend a recent
exact relativistic model to include also a halo dipole component. Next, we
consider orbits evolving in the inner vacuum between a monopolar core and a
pure halo dipole and find that, while the Newtonian dynamics is integrable, its
relativistic counterpart is chaotic. This shows that chaoticity due only to
halo dipoles is an intrinsic relativistic gravitational effect.


title: Detection of Lense-Thirring Effect Due to Earth's Spin

abstract:
  Rotation of a body, according to Einstein's theory of general relativity,
generates a "force" on other matter; in Newton's gravitational theory only the
mass of a body produces a force. This phenomenon, due to currents of mass, is
known as gravitomagnetism owing to its formal analogies with magnetism due to
currents of electric charge. Therefore, according to general relativity,
Earth's rotation should influence the motion of its orbiting satellites.
Indeed, we analysed the laser ranging observations of the orbits of the
satellites LAGEOS and LAGEOS II, using a program developed at NASA/GSFC, and
obtained the first direct measurement of the gravitomagnetic orbital
perturbation due to the Earth's rotation, known as the Lense-Thirring effect.
The accuracy of our measurement is about 25%.


title: Fermion mass gap in the loop representation of quantum gravity

abstract:
  An essential step towards the identification of a fermion mass generation
mechanism at Planck scale is to analyse massive fermions in a given quantum
gravity framework. In this letter the two mass terms entering the Hamiltonian
constraint for the Einstein-Majorana system are studied in the loop
representation of quantum gravity and fermions. One resembles a bare mass gap
because it is not zero for states with zero (fermion) kinetic energy as
opposite to the other that is interpreted as `dressing' the mass. The former
contribution originates from (at least) triple intersections of the loop states
acted on whilst the latter is traced back to every couple of coinciding end
points, where fermions sit. Thus, fermion mass terms get encoded in the
combinatorics of loop states. At last the possibility is discussed of relating
fermion masses to the topology of space.


title: Winding Solutions for the two Particle System in 2+1 Gravity

abstract:
  Using a PASCAL program to follow the evolution of two gravitating particles
in 2+1 dimensions we find solutions in which the particles wind around one
another indefinitely. As their center of mass moves `tachyonic' they form a
Gott-pair. To avoid unphysical boundary conditions we consider a large but
closed universe. After the particles have evolved for some time their momenta
have grown very large. In this limit we quantize the model and find that both
the relevant configuration variable and its conjugate momentum become discrete.


title: On the Schwarzschild field

abstract:
  General relativity is a non-linear theory with the distinguishing feature
that gravitational field energy also acts as gravitational charge density. In
the well-known Schwarzschild solution describing field of an isolated massive
body at rest, the scalar function $\phi$ characterising the field acts as a
gravitational potential as well as it curves space part of spacetime. We
demonstrate explicitly that it is the latter property that accounts for the
non-linear (gravity as its own source) aspect which is not explicit in usual
derivations. It is worth noting that the Einstein vacuum equations ultimately
reduce to the Laplace equation and its first integral which fixes zero of
$\phi$ at infinity. Thus the Schwarzschild field alongwith its asymptotic flat
character is completely determined without application of any boundary
condition by the field equations themselves. That means non-zero constant value
of $\phi$ will have non-vacuous effect. It in fact produces stresses exactly of
the form required to represent a global monopole. By retaining freedom of
choosing zero of $\phi$, which will break asymptotic flatness, we can obtain
the Schwarzschild black hole with global monopole charge. It is the non-linear
aspect responsible for ``curving'' space, which has no Newtonian analogue,
survives even when $\phi$ is constant but not zero.


title: On the Antenna Pattern of an Orbiting Interferometer

abstract:
  The response of an interferometer changing its orientation with respect to a
fixed reference frame is given in terms of the beam-pattern factors and the
polarization-averaged antenna power pattern.


title: On the third law of black hole dynamics

abstract:
  The third law of black hole dynamics states that the surface gravity
(temperature) of black hole cannot be reduced to zero in finite sequence of
physical interactions. We argue that the same is true when surface gravity is
replaced by gravitational charge. We demonstrate that the prescribed window for
infalling energy and radiation pinches off as extremality ($M^2 = a^2 + Q^2 $)
is approached.


title: Boundary States and Black Hole Entropy

abstract:
  Black hole entropy is derived from a sum over boundary states. The boundary
states are labeled by energy and momentum surface densities, and parametrized
by the boundary metric. The sum over state labels is expressed as a functional
integral with measure determined by the density of states. The sum over metrics
is expressed as a functional integral with measure determined by the universal
expression for the inverse temperature gradient at the horizon. The analysis
applies to any stationary, nonextreme black hole in any theory of gravitational
and matter fields.


title: Quantum States of Black Holes

abstract:
  I review the recent progress in providing a statistical foundation for black
hole thermodynamics. In the context of string theory, one can now identify and
count quantum states associated with black holes. One can also compute the
analog of Hawking radiation (in a certain low energy regime) in a manifestly
unitary way. Both extremal and nonextremal black holes are considered,
including the Schwarzschild solution. Some implications of conjectured
non-perturbative string ``duality transformations'' for the description of
black hole states are also discussed.


title: About Black Holes Without Trapping Interior

abstract:
  Physical arguments related with the existence of black hole solutions having
a non trapping interior are discussed. Massive scalar fields interacting with
gravity are considered. Interior asymptotic solutions showing a scalar field
approaching a constant value at the horizon are given. It is argued that the
coupled Einstein-Klein-Gordon equations can be satisfied in the sense of the
generalized functions after removing a particular regularization designed for
matching the interior solution with an external Scwartzschild spacetime. The
scalar field appears as just avoiding the appearance of closed trapped surfaces
while coming from the exterior region. It also follows that the usual space
integral over the temporal- temporal components of energy-momnetum tensor in
the internal region just gives the total proper mass associated to the external
Schwartzschild solution, as it should be expected.


title:
Thermal Particle Creation in Cosmological Spacetimes: A Stochastic
  Approach

abstract:
  The stochastic method based on the influence functional formalism introduced
in an earlier paper to treat particle creation in near-uniformly accelerated
detectors and collapsing masses is applied here to treat thermal and
near-thermal radiance in certain types of cosmological expansions. It is
indicated how the appearance of thermal radiance in different cosmological
spacetimes and in the two apparently distinct classes of black hole and
cosmological spacetimes can be understood under a unifying conceptual and
methodological framework.


title:
Quantum Fields in Curved Spacetime: Non Global Hyperbolicity and
  Locality

abstract:
  We briefly review the current status of the algebraic approach to quantum
field theory on globally hyperbolic spacetimes, both axiomatic -- for general
field theories, and constructive -- for a linear Klein-Gordon model. We recall
the concept of F-locality, introduced in the latter context in BS Kay: Rev.
Math. Phys., Special Issue, 167-195 (1992) and explain how it can be formulated
at an axiomatic level for a general field theory (as a condition on
algebras-with-net-structure) on both globally hyperbolic and non globally
hyperbolic spacetimes. We also discuss the current status of the question
whether/when algebras satisfying F-locality can exist for the Klein-Gordon
model on spacetimes which are chronology violating.


title:
An ansatz for spacetimes of zero gravitational mass : global monopoles
  and textures

abstract:
  We propose a geometric ansatz, a restriction on Euclidean / Minkowski
distance in the embedding space being propotional to distance in the embedded
space, to generate spacetimes with vanishing gravitational mass ($R_{ik} u^i
u^k = 0, u_i u^i = 1 $). It turns out that these spacetimes can represent
global monopoles and textures. Thus the ansatz is a prescription to generate
zero mass spacetimes that could describe topological defects, global monopoles
and textures.


title: Massive scalar field near a cosmic string

abstract:
  The $\zeta$ function of a massive scalar field near a cosmic string is
computed and then employed to find the vacuum fluctuation of the field. The
vacuum expectation value of the energy-momentum tensor is also computed using a
point-splitting approach. The obtained results could be useful also for the
case of self-interacting scalar fields and for the finite-temperature Rindler
space theory.


title:
On the Cosmological Origin of the Homogeneous Scalar Field in Unified
  Theories

abstract:
  We consider the possibility of describing the Higgs effect in unified
theories without the Higgs potential in the presence of the Einstein gravity
with the conformal gravity-scalar coupling under the assumption of homogeneous
matter distribution.
  The scalar field values can be found from the Friedmann equations for the
homogeneous Universe. The considered cosmological mechanism solves the vacuum
density problem (we got $\rho_\phi^{Cosmic}=10^{-34}\rho_{cr}$ instead of
$\rho_\phi^{Higgs}=10^{54}\rho_{cr}$),and exludes the monopole creation and the
domain walls.


title: Spikes in Quantum Regge Calculus

abstract:
  We demonstrate by explicit calculation of the DeWitt-like measure in
two-dimensional quantum Regge gravity that it is highly non-local and that the
average values of link lengths $l, <l^n>$, do not exist for sufficient high
powers of $n$. Thus the concept of length has no natural definition in this
formalism and a generic manifold degenerates into spikes. This might explain
the failure of quantum Regge calculus to reproduce the continuum results of
two-dimensional quantum gravity. It points to severe problems for the Regge
approach in higher dimensions.


title:
Einstein-Yang-Mills Black Hole Interiors: Serious Problems But Simple
  Solution

abstract:
  Recently E. E. Donets, D. V. Galtsov, and the author reported the results of
numerical and analytical investigation of the SU(2) Einstein-Yang-Mills black
hole interior solutions (gr-qc/9612067). It was shown that a generic interior
solution develops a new type of an infinitely oscillating behavior with
exponentially growing amplitude. Numerical data for three sequential
oscillations were presented. The numerical integration technique was not
discussed. Later P. Breitenlohner, G. Lavrelashvili, and D. Maison confirmed
our main results (gr-qc/9703047). But they have made some misleading
statements. In particular, they claimed, discussing the oscillations, that ``as
one performs the numerical integration one quickly runs into serious
problems...'' so that ``it is practically impossible to follow more than one or
two of them numerically'' because ``the numerical integration procedure breaks
down''. It is shown here that trivial logarithmic substitutions and integration
along the integral curve solve these ``serious problems'' easily.


title: A trick for passing degenerate points in Ashtekar formulation

abstract:
  We examine one of the advantages of Ashtekar's formulation of general
relativity: a tractability of degenerate points from the point of view of
following the dynamics of classical spacetime. Assuming that all dynamical
variables are finite, we conclude that an essential trick for such a continuous
evolution is in complexifying variables. In order to restrict the complex
region locally, we propose some `reality recovering' conditions on spacetime.
Using a degenerate solution derived by pull-back technique, and integrating the
dynamical equations numerically, we show that this idea works in an actual
dynamical problem. We also discuss some features of these applications.


title: Geometric structure of the generic static traversable wormhole throat

abstract:
  Traversable wormholes have traditionally been viewed as intrinsically
topological entities in some multiply connected spacetime. Here, we show that
topology is too limited a tool to accurately characterize a generic traversable
wormhole: in general one needs geometric information to detect the presence of
a wormhole, or more precisely to locate the wormhole throat. For an arbitrary
static spacetime we shall define the wormhole throat in terms of a
2-dimensional constant-time hypersurface of minimal area. (Zero trace for the
extrinsic curvature plus a "flare-out" condition.) This enables us to severely
constrain the geometry of spacetime at the wormhole throat and to derive
generalized theorems regarding violations of the energy conditions-theorems
that do not involve geodesic averaging but nevertheless apply to situations
much more general than the spherically symmetric Morris-Thorne traversable
wormhole. [For example: the null energy condition (NEC), when suitably weighted
and integrated over the wormhole throat, must be violated.] The major technical
limitation of the current approach is that we work in a static spacetime-this
is already a quite rich and complicated system.


title: Scalar field fluctuations in Pre-Big-Bang Cosmologies

abstract:
  Jordan-Brans-Dicke theories with a linearized potential for the scalar field
are investigated in the framework of the stochastic approach. The fluctuations
of this field are examined and their backreaction on the classical background
is described. We compute the mode functions and analyze the time evolution of
the variance of the stochastic ensemble corresponding to the full quantum
scalar field in the pre-big-bang regime. We compute fluctuations of the term
discriminating between the two branches of solutions present in the theory. We
find, both analytically and upon direct integration of the stochastic equations
of motion, that the dispersion of these fluctuations grows to achieve the
magnitude of the term separating the two classical solutions. This means that
the ensembles representing classical solutions which belong to different
branches do overlap; this may provide a quantum mechanical realization at the
level of field theory to change among solutions belonging to different
branches.


title:
Quantum Gravity near Apparent Horizon and Two Dimensional Dilaton
  Gravity

abstract:
  We study the Hawking radiation in two dimensional dilaton black hole by means
of quantum gravity holding near the apparent horizon. First of all, we
construct the canonical formalism of the dilaton gravity in two dimensions.
Then the Vaidya metric corresponding to the dilaton black hole is established
where it is shown that the dilaton field takes a form of the linear dilaton.
Based on the canonical formalism and the Vaidya metric, we proceed to analyze
quantum properties of a dynamical black hole. It is found that the mass loss
rate of the Hawking radiation is independent of the black hole mass and at the
same time the apparent horizon recedes to the singularity as shown in other
studies of two dimensional gravity. It is interesting that one can construct
quantum gravity even near the curvature singularity and draw the same
conclusion with respect to the Hawking radiation as the above-mentioned
picture. Unfortunately, the present formalism seems to be ignorant of the
contributions from the functional measures over the gravitational field, the
dilaton and the ghosts.


title: Symmetries and solvable models for evaporating 2D black holes

abstract:
  We study the evaporation process of a 2D black hole in thermal equilibrium
when the ingoing radiation is switched off suddenly. We also introduce global
symmetries of generic 2D dilaton gravity models which generalize the extra
symmetry of the CGHS model.


title: Black Holes: A Window into A New Theory of Space Time

abstract:
  S. Chandrasekhar wrote in the prologue to his book on black holes, "The black
holes of nature are the most perfect macroscopic objects there are in the
universe: the only elements in their construction are our concepts of space and
time." In this contribution I briefly discuss recent developments in
fundamental theory and black holes that vindicate this statement in a modern
perspective. I also include some of my reminiscences of Chandra.