title: The Froth of the Universe

abstract:
  We consider a model of the Universe based on the equation of state
$p=(1/3)\rho (c/F)^2$, where $F$ is the scale factor. This model behaves as an
inflationary Universe from the beginning and during its early stages, and
behaves as dust matter during the stages of maximum expansion.


title: Field Theory Models without the Cosmological Constant Problem

abstract:
  We study field theory models in the context of a gravitational theory based
on the requirement that the measure of integration in the action is not
necessarily \sqrt{-g} but it is determined dynamically through additional
degrees of freedom, like four scalar fields \phi_{a}. We study three
possibilities for the general structure of the theory: (A) The total action has
the form S=\int\Phi Ld^{4}x where the measure \Phi is built from the scalars
\phi_{a} in such a way that the transformation L\to L+const does not effect
equations of motion. Then an infinite dimensional shifts group of the measure
fields (SGMF) \phi_{a} by arbitrary functions of the Lagrangian density L is a
symmetry group of the action. (B) The total action has the form S=S_{1}+S_{2},
S_{1}=\int\Phi L_{1}d^{4}x, S_{2}=\int\sqrt{-g}L_{2}d^{4}x which is the only
model different from (A) and invariant under SGMF (but now with f_{a}=
f_{a}(L_{1})). Similarly, now only S_{1} satisfies the requirement that the
transformation L_{1}\to L_{1}+const does not effect equations of motion. Both
in the case (A) and in the case (B) it is assumed that L, L_{1}, L_{2} do not
depend on \phi_{a}. (C) The action includes a term which breaks the SGMF
symmetry. It is shown that in the first order formalism in cases (A) and (B)
the CCP is solved: the effective potential vanishes in a true vacuum state
(TVS) without fine tuning. In the case (C), the breaking of the SGMF symmetry
induces a nonzero energy density for the TVS.


title: Quantum Signature of Cosmological Large Scale Structures

abstract:
  We demonstrate that to all large scale cosmological structures where
gravitation is the only overall relevant interaction assembling the system
(e.g. galaxies), there is associated a characteristic unit of action per
particle whose order of magnitude coincides with the Planck action constant
$h$. This result extends the class of physical systems for which quantum
coherence can act on macroscopic scales (as e.g. in superconductivity) and
agrees with the absence of screening mechanisms for the gravitational forces,
as predicted by some renormalizable quantum field theories of gravity. It also
seems to support those lines of thought invoking that large scale structures in
the Universe should be connected to quantum primordial perturbations as
requested by inflation, that the Newton constant should vary with time and
distance and, finally, that gravity should be considered as an effective
interaction induced by quantization.


title: On the geometry of impulsive gravitational waves

abstract:
  We describe impulsive gravitational pp-waves entirely in the distributional
picture. Applying Colombeau's nonlinear framework of generalized functions we
handle the formally ill-defined products of distributions which enter the
geodesic as well as the geodesic deviation equation. Using a universal
regularization procedure we explicitly derive regularization independent
distributional limits. In the special case of impulsive plane waves we compare
our results with the particle motion derived from the continuous form of the
metric.


title:
Exact relativistic stellar models with liquid surface. I. Generalizing
  Buchdahl's $n=1$ polytrope

abstract:
  A family of exact relativistic stellar models is described. The family
generalizes Buchdahl's n=1 polytropic solution. The matter content is a perfect
fluid and, excluding Buchdahl's original model, it behaves as a liquid at low
pressures in the sense that the energy density is non-zero in the zero pressure
limit. The equation of state has two free parameters, a scaling and a stiffness
parameter. Depending on the value of the stiffness parameter the fluid
behaviour can be divided in four different types. Physical quantities such as
masses, radii and surface redshifts as well as density and pressure profiles
are calculated and displayed graphically. Leaving the details to a later
publication, it is noted that one of the equation of state types can quite
accurately approximate the equation of state of real cold matter in the outer
regions of neutron stars. Finally, it is observed that the given equation of
state does not admit models with a conical singularity at the center.


title: Particles as singularities within the unified algebraic field dynamics

abstract:
  We consider a nonlinear generalization of Cauchy-Riemann eqs. to the algebra
of biquaternions. From here we come to "universal generating equations" (1)
which deal with 2-spinor and gauge fields and form the basis of some unified
algebraic field theory. For each solution of eqs.(1) the components of spinor
field satisfy the eikonal and d'Alembert eqs., and the strengths of gauge field
- both Maxwell and Yang-Mills eqs. We reduce eqs.(1) to that of shear-free
geodesic null congruence and integrate them in twistor variables. Particles are
treated as concurrent singularities of the effective metric and the
electromagnetic field. For unisingular solutions the electric charge is
quantized, and the metric is of Schwarzschild or Kerr type. Bisingular
solutions are announced too.


title: Gravitational dust collapse with cosmological constant

abstract:
  We study the fate of gravitational collapse in presence of a cosmological
constant. The junctions conditions between static and non-static space-times
are deduced. Three apparent horizon are formed, but only two have physical
significance, one of them being the black hole horizon and the other the
cosmological horizon. The cosmological constant term slows down the collapse of
matter, limiting also the size of the black hole.


title: Free Boundary Poisson Bracket Algebra in Ashtekar's Formalism

abstract:
  We consider the algebra of spatial diffeomorphisms and gauge transformations
in the canonical formalism of General Relativity in the Ashtekar and ADM
variables. Modifying the Poisson bracket by including surface terms in
accordance with our previous proposal allows us to consider all local
functionals as differentiable. We show that closure of the algebra under
consideration can be achieved by choosing surface terms in the expressions for
the generators prior to imposing any boundary conditions. An essential point is
that the Poisson structure in the Ashtekar formalism differs from the canonical
one by boundary terms.


title: All nonspherical perturbations of the Choptuik spacetime decay

abstract:
  We study the nonspherical linear perturbations of the discretely self-similar
and spherically symmetric solution for a self-gravitating scalar field
discovered by Choptuik in the context of marginal gravitational collapse. We
find that all nonspherical perturbations decay. Therefore critical phenomena at
the threshold of gravitational collapse, originally found in spherical
symmetry, will extend to (at least slightly) nonspherical initial data.


title: Head-On Collision of Neutron Stars As A Thought Experiment

abstract:
  The head-on collision of identical neutron stars from rest at infinity
requires a numerical simulation in full general relativity for a complete
solution. Undaunted, we provide a relativistic, analytic argument to suggest
that during the collision, sufficient thermal pressure is always generated to
support the hot remnant in quasi-static stable equilibrium against collapse
prior to slow cooling via neutrino emission. Our conclusion is independent of
the total mass of the progenitors and holds even if the remnant greatly exceeds
the maximum mass of a cold neutron star.


title: A Second Poincare' Group

abstract:
  Solutions of the sourceless Einstein's equation with weak and strong
cosmological constants are discussed by using In\"on\"u-Wigner contractions of
the de Sitter groups and spaces. The more usual case corresponds to a weak
cosmological-constant limit, in which the de Sitter groups are contracted to
the Poincar\'e group, and the de Sitter spaces are reduced to the Minkowski
space. In the strong cosmological-constant limit, however, the de Sitter groups
are contracted to another group which has the same abstract Lie algebra of the
Poincar\'e group, and the de Sitter spaces are reduced to a 4-dimensional
cone-space of infinite scalar curvature, but vanishing Riemann and Ricci
curvature tensors. In such space, the special conformal transformations act
transitively, and the equivalence between inertial frames is that of special
relativity.


title: Duality Invariance of Cosmological Perturbation Spectra

abstract:
  I show that cosmological perturbation spectra produced from quantum
fluctuations in massless or self-interacting scalar fields during an
inflationary era remain invariant under a two parameter family of
transformations of the homogeneous background fields. This relates slow-roll
inflation models to solutions which may be far from the usual slow-roll limit.
For example, a scale-invariant spectrum of perturbations in a minimally
coupled, massless field can be produced by an exponential expansion with
$a\propto e^{Ht}$, or by a collapsing universe with $a\propto (-t)^{2/3}$.


title:
Entropy of scalar fields in 3+1 dimensional constant curvature black
  hole background

abstract:
  We consider the thermodynamics of minimally coupled massive scalar field in
3+1 dimensional constant curvature black hole background. The brick wall model
of 't Hooft is used. When Scharzschild like coordinates are used it is found
that apart from the usual radial brick wall cut-off parammeter an angular
cut-off parameter is required to regularize the solution. Free energy of the
scalar field is obtained through counting of states using the WKB
approximation. It is found that the free energy and the entropy are
logarithmically divergent in both the cut-off parameters.


title:
On the absence of scalar hair for charged rotating blackholes in non
  minimally coupled theories

abstract:
  In this work we check the validity of the no scalar hair theorem in charged
axisymmetric stationary black holes for a wide class of scalar tensor theories.


title: Chaotic motion in pp-wave spacetimes

abstract:
  We investigate geodesics in non-homogeneous vacuum pp-wave solutions and
demonstrate their chaotic behavior by rigorous analytic and numerical methods.
For the particular class of solutions considered, distinct "outcomes" (channels
to infinity) are identified, and it is shown that the boundary between
different outcomes has a fractal structure. This seems to be the first example
of chaos in exact radiative spacetimes.


title:
An Unexpected Electrovac Solution with the Negative Cosmological
  Constant

abstract:
  An exact solution of the current-free Einstein-Maxwell equations with the
cosmological constant is presented. The solution is of Petrov type D, includes
the negative cosmological constant, and could be a ``background addition'' to
the present-day models of the universe. It has a surprising property such that
its electromagnetic field and cosmological constant are interdependent (this
constant is proportional to the energy density of this field), which may
suggest a new way of measuring the constant in question. The solution describes
a constant electromagnetic background with a preferred direction in the
universe, and defines the entire lifetime of the universe as a simple function
of the negative cosmological constant. According to our solution the absolute
value of this constant should be considerably lower than that recently
estimated, when astrophysical data are taken into account. Our solution is a
special case of that published by Bertotti in 1959. His solution (in terms of
which the cosmological constant and the background electromagnetic field are
independent) and its two other special cases, i.e. the conformally flat
Robinson solution (1959) and the one which is the counterpart of our solution
with the positive cosmological constant, are briefly discussed.


title: On relativistic spin network vertices

abstract:
  Barrett and Crane have proposed a model of simplicial Euclidean quantum
gravity in which a central role is played by a class of Spin(4) spin networks
called "relativistic spin networks" which satisfy a series of physically
motivated constraints. Here a proof is presented that demonstrates that the
intertwiner of a vertex of such a spin network is uniquely determined, up to
normalization, by the representations on the incident edges and the
constraints. Moreover, the constraints, which were formulated for four valent
spin networks only, are extended to networks of arbitrary valence, and the
generalized relativistic spin networks proposed by Yetter are shown to form the
entire solution set (mod normalization) of the extended constraints. Finally,
using the extended constraints, the Barrett-Crane model is generalized to
arbitrary polyhedral complexes (instead of just simplicial complexes)
representing spacetime. It is explained how this model, like the Barret-Crane
model can be derived from BF theory by restricting the sum over histories to
ones in which the left handed and right handed areas of any 2-surface are
equal. It is known that the solutions of classical Euclidean GR form a branch
of the stationary points of the BF action with respect to variations preserving
this condition.


title: The light speed barrier: Bending the rules

abstract:
  Special relativity includes a concealed mechanism for reducing time-dilation
effects in two mutually-receding objects. Forwarding their signals via one or
more intermediate physical relay stages (a "probe chain") allows enhanced
communication and propulsion efficiency. These possibilities are masked by the
mathematical redefinitions of the special theory, which then assigns the
velocity of the signal source a correspondingly lower value by using a
velocity-addition formula. Probe chains reveal the existence of
velocity-dependent curvature within inertial systems, and suggest a mechanism
for indirect radiation from black holes that is strongly reminiscent of Hawking
radiation. The "emitter-theory" force law is mentioned as a possible basis for
a curved-space alternative to special relativity.


title:
Equations of Motion of Spinning Relativistic Particle in Electromagnetic
  and Gravitational Fields

abstract:
  We consider the motion of a spinning relativistic particle in external
electromagnetic and gravitational fields, to first order in the external field,
but to an arbitrary order in spin. The noncovariant spin formalism is crucial
for the correct description of the influence of the spin on the particle
trajectory. We show that the true coordinate of a relativistic spinning
particle is its naive, common coordinate $\r$. Concrete calculations are
performed up to second order in spin included. A simple derivation is presented
for the gravitational spin-orbit and spin-spin interactions of a relativistic
particle. We discuss the gravimagnetic moment (GM), a specific spin effect in
general relativity. It is shown that for the Kerr black hole the gravimagnetic
ratio, i.e., the coefficient at the GM, equals unity (just as for the charged
Kerr hole the gyromagnetic ratio equals two). The equations of motion obtained
for relativistic spinning particle in external gravitational field differ
essentially from the Papapetrou equations.


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

abstract:
  The reported anomalous acceleration may be explained as the recoil of
radiated waste RTG heat scattered by the back of the high gain antenna.


title: Achieving pole-law inflation:the extreme inflation

abstract:
  The pre-big bang's inflationary mechanism, when allowance is made for the
rapid change of Newton's constant, is not actually of pole-law form . We give
examples where pole-law inflation, which requires violation of the weak-energy
condition, is possible but unlikely due to its very unstable character.


title: Gravitational and Anti-gravitational Applications

abstract:
  It is now possible to partially deflect gravitation away from an object so
that the gravitational attraction on the object is reduced. That effect makes
it possible to extract energy from the gravitational field, which makes the
generation of gravito-electric power technologically feasible. Such plants
would be similar to hydro-electric plants and would have their advantages of
not needing fuel and not polluting the environment.
  Physically, the action of deflecting away gravitational attraction, which of
course is directed toward the gravitation source, produces an equal but
opposite reaction on the mechanism that produces the deflection of the
gravitational action [the deflector], a reaction directed away from the
gravitation source.
  The result is the combination of reducing the gravitational attractive
acceleration of the object toward the gravitation source plus the introducing
of a reactive acceleration on the object in the direction away from the
gravitation source.
  Such a deflector, engineered to enable controlled adjustment of the amount
and the direction of its action, could provide for a spacecraft both launch
levitation and deep space travel acceleration. It could provide both levitation
and horizontal motion for a flying vehicle over a planet surface.
  This technology, which uses readily abundantly available materials and
techniques, is ready now for research and engineering refinement.


title: Singularity deep inside the spherical charged black hole core

abstract:
  We study analytically the spacelike singularity inside a
spherically-symmetric, charged black hole coupled to a self-gravitating
spherical massless scalar field. We assume spatial homogeneity, and find a
generic solution in terms of a formal series expansion. This solution is tested
against fully-nonlinear and inhomogeneous numerical simulations. We find full
compliance between our analytical solution and the pointwise behavior of the
singularity in the numerical simulations. This is a strong scalar-curvature
monotonic spacelike singularity, which connects to a weak null singularity at
asymptotically-late advanced time.


title: Solutions of Penrose's Equation

abstract:
  The computational use of Killing potentials which satisfy Penrose's equation
is discussed. Penrose's equation is presented as a conformal Killing-Yano
equation and the class of possible solutions is analyzed. It is shown that
solutions exist in spacetimes of Petrov type O, D or N. In the particular case
of the Kerr background, it is shown that there can be no Killing potential for
the axial Killing vector.


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

abstract:
  Recently, Anderson et al. presented possible evidence for an anomalous
acceleration acting on spacecrafts. Furthermore, the motions of several planets
and comets are known to experience unexplained disturbances. A transneptunian
comet or asteroid belt might be the common origin of these anomalies.


title: A Proof of Uniqueness of the Taub-bolt Instanton

abstract:
  We show that the Riemannian Schwarzschild and the ``Taub-bolt'' instanton
solutions are the only spaces (M,g) such that
  1) M is a 4-dimensional, simply connected manifold with a Riemannian,
Ricci-flat C^2-metric g which admits (at least) a 1-parameter group of
isometries H without isolated fixed points on M.
  2) The quotient (M L)/H (where L is the set of fixed points of H) is an
asymptotically flat manifold, and the length of the Killing field corresponding
to H tends to a constant at infinity.


title: Naked singularities and Seifert's conjecture

abstract:
  It is shown that for a general nonstatic spherically symmetric metric of the
Kerr-Schild class several energy-momentum complexes give the same energy
distribution as in the Penrose prescription, obtained by Tod. This result is
useful for investigating the Seifert conjecture for naked singularities. The
naked singularity forming in the Vaidya null dust collapse supports the Seifert
conjecture. Further, an example and a counterexample to this conjecture are
presented in the Einstein massless scalar theory.


title:
Algebrodynamical Approach in Field Theory: Bisingular Solution and its
  Modifications

abstract:
  The criterion of differentiability of functions of quaternion variable is
used as the basis of some algebraic field theory. Its necessary consequences
are free Maxwell and Yang-Mills equations. The differentiability equations may
be integrated in twistor variables and are reduced to algebraic ones. In the
article we present bisingular solution and its topological modifications.
Related EM-fields appear to be just the well-known Born solution and its
modifications with singular structure of ring-like and toroidal topology.
General problems of the algebrodynamical approach are discussed.


title: Quantum gravity correction, evolution of scalar field and inflation

abstract:
  We take the first nontrivial coefficient of the Schwinger-DeWitt expansion as
a leading correction to the action of the second-derivative metric-dilaton
gravity. To fix the ambiguities related with an arbitrary choice of the gauge
fixing condition and the parametrization for the quantum field, one has to use
the classical equations of motion. As a result, the only corrections are the
ones to the potential of the scalar field. It turns out that the parameters of
the initial classical action may be chosen in such a way that the potential
satisfies most of the conditions for successful inflation.


title: On the self-consistence of electrodynamics in the early universe

abstract:
  The issue of a self-consistent solution of Maxwell-Einstein equations
achieves a very simple form when all quantum effects are neglected but a weak
vacuum polarization due to an external magnetic field is taken into account.
  From a semi-classical point of view this means to deal with an appropriate
limit of the one-loop effective Lagrangian for electrodynamics. When the
corresponding stress-energy tensor is considered as a source of the
gravitational field a surprisingly bouncing behavior is obtained. The present
toy model leads to important new features which should have taken place in the
early universe.


title:
Energy-momentum tensor of quasiparticles in the effective gravity in
  superfluids

abstract:
  The problem of the energy-momentum conservation for matter in the
gravitational field is discussed on the example of the effective gravity, which
arises in superfluids. The "gravitational" field experienced by the
relativistic-like massless quasiparticles which form the "matter" (phonons in
superfluid 4He and low-energy fermions in superfluid 3He-A), is induced by the
flow of the superfluid "vacuum". It appears that the energy-momentum
conservation law for quasiparticles, has the covariant form
T^{\mu}_{\nu;\mu}=0. "Pseudotensor" of the energy-momentum for the
"gravitational field" (superfluid condensate) appears to depend on "matter". In
the presence of the stationary "gravitational" (superfluid) field the real
thermodynamic temperature T is constant in the true dissipationless equilibrium
state with no entropy production, while the "relativistic" temperature
T/\sqrt{g_{00}} is space dependent in agreement with Tolman's law. In the
presence of the event horizon the true dissipationless equilibrium state does
not exist. The quasiequilibrium dissipative motion across the horizon is
considered. The inflationary stage of the expansion of the Universe can be
modelled using the expanding Bose-condendsate.


title: On Waylen's regular axisymmetric similarity solutions

abstract:
  We review the similarity solutions proposed by Waylen for a regular
time-dependent axisymmetric vacuum space-time, and show that the key equation
introduced to solve the invariant surface conditions is related by a Baecklund
transform to a restriction on the similarity variables. We further show that
the vacuum space-times produced via this path automatically possess a (possibly
homothetic) Killing vector, which may be time-like.


title:
Anti-self-dual Maxwell solutions on hyperk\"ahler manifold and N=2
  supersymmetric Ashtekar gravity

abstract:
  Anti-self-dual (ASD) Maxwell solutions on 4-dimensional hyperk\"ahler
manifolds are constructed. The N=2 supersymmetric half-flat equations are
derived in the context of the Ashtekar formulation of N=2 supergravity. These
equations show that the ASD Maxwell solutions have a direct connection with the
solutions of the reduced N=2 supersymmetric ASD Yang-Mills equations with a
special choice of gauge group. Two examples of the Maxwell solutions are
presented.


title: Normal frames and linear transports along paths in vector bundles

abstract:
  The theory of linear transports along paths in vector bundles, generalizing
the parallel transports generated by linear connections, is developed. The
normal frames for them are defined as ones in which their matrices are the
identity matrix or their coefficients vanish. A number of results, including
theorems of existence and uniqueness, concerning normal frames are derived.
Special attention is paid to the important case when the bundle's base is a
manifold. The normal frames are defined and investigated also for derivations
along paths and along tangent vector fields in the last case. It is proved that
normal frames always exist at a single point or along a given (smooth) path. On
other subsets normal frames exist only as an exception if (and only if) certain
additional conditions, derived here, are satisfied. Gravity physics and gauge
theories are pointed out as possible fields for application of the results
obtained.


title: Nonperturbative gravito-magnetic fields

abstract:
  In a cold matter universe, the linearized gravito-magnetic tensor field
satisfies a transverse condition (vanishing divergence) when it is purely
radiative. We show that in the nonlinear theory, it is no longer possible to
maintain the transverse condition, since it leads to a non-terminating chain of
integrability conditions. These conditions are highly restrictive, and are
likely to hold only in models with special symmetries, such as the known
Bianchi and $G_2$ examples. In models with realistic inhomogeneity, the
gravito-magnetic field is necessarily non-transverse at second and higher
order.


title:
Quantum geometrodynamics in extended phase space - I. Physical problems
  of interpretation and mathematical problems of gauge invariance

abstract:
  The paper is the first of two parts of the work devoted to the investigation
of constructing quantum theory of a closed universe as a system without
asynptotic states. In Part I the role of asymptotic states in quantum theory of
gravity is discussed, that enables us to argue that mathematically correct
quantum geometrodynamics of a closed universe has to be gauge-noninvariant. It
is shown that a gauge-noninvariant quantum geometrodynamics is consistent with
the Copenhagen interpretation. The proposed version of the theory is thought of
as describing the integrated system ``the physical object + observation
means''. It is also demonstrated that introducing the observer into the theory
causes the appearance of time in it.


title: Black Hole Creation in 2+1 Dimensions

abstract:
  When two point particles, coupled to three dimensional gravity with a
negative cosmological constant, approach each other with a sufficiently large
center of mass energy, then a BTZ black hole is created. An explicit solution
to the Einstein equations is presented, describing the collapse of two massless
particles into a non-rotating black hole. Some general arguments imply that
massive particles can be used as well, and the creation of a rotating black
hole is also possible.


title:
The classification of static vacuum space-times containing an
  asymptotically flat spacelike hypersurface with compact interior

abstract:
  We prove non-existence of static, vacuum, appropriately regular,
asymptotically flat black hole space-times with degenerate (not necessarily
connected) components of the event horizon. This finishes the classification of
static, vacuum, asymptotically flat domains of outer communication in an
appropriate class of space-times, showing that the domains of outer
communication of the Schwarzschild black holes exhaust the space of
appropriately regular black hole exteriors.


title: On Accelerated Black Holes

abstract:
  The static and stationary C-metric are revisited in a generic framework and
their interpretations studied in some detail. Specially those with two event
horizons, one for the black hole and another for the acceleration. We found
that: i) The spacetime of an accelerated static black hole is plagued by either
conical singularities or lack of smoothness and compactness of the black hole
horizon; ii) By using standard black hole thermodynamics we show that
accelerated black holes have higher Hawking temperature than Unruh temperature
of the accelerated frame; iii) The usual upper bound on the product of the mass
and acceleration parameters <1/sqrt(27) is just a coordinate artifact. The main
results are extended to accelerated rotating black holes with no significant
changes.


title: AENEAS - A Custom-built Parallel Supercomputer for Quantum Gravity

abstract:
  Accurate Quantum Gravity calculations, based on the simplicial lattice
formulation, are computationally very demanding and require vast amounts of
computer resources. A custom-made 64-node parallel supercomputer capable of
performing up to $2 \times 10^{10}$ floating point operations per second has
been assembled entirely out of commodity components, and has been operational
for the last ten months. It will allow the numerical computation of a variety
of quantities of physical interest in quantum gravity and related field
theories, including the estimate of the critical exponents in the vicinity of
the ultraviolet fixed point to an accuracy of a few percent.


title: Relaxational effects in radiating stellar collapse

abstract:
  Relaxational effects in stellar heat transport can in many cases be
significant. Relativistic Fourier-Eckart theory is inherently quasi-stationary,
and cannot incorporate these effects. The effects are naturally accounted for
in causal relativistic thermodynamics, which provides an improved approximation
to kinetic theory. Recent results, based on perturbations of a static star,
show that relaxation effects can produce a significant increase in the central
temperature and temperature gradient for a given luminosity. We use a simple
stellar model that allows for non-perturbative deviations from staticity, and
confirms qualitatively the predictions of the perturbative models.


title: Resolving the singularity of the Hawking-Turok type instanton

abstract:
  We point out that the singular instanton of Hawking-Turok type, in which the
singularity occurs due to the divergence of a massless scalar field, can be
generated by Euclideanized regular $p$-brane solutions in string (or M-) theory
upon compactification to four dimensions.


title: Canonical Quasilocal Energy and Small Spheres

abstract:
  Consider the definition E of quasilocal energy stemming from the
Hamilton-Jacobi method as applied to the canonical form of the gravitational
action. We examine E in the standard "small-sphere limit," first considered by
Horowitz and Schmidt in their examination of Hawking's quasilocal mass. By the
term "small sphere" we mean a cut S(r), level in an affine radius r, of the
lightcone belonging to a generic spacetime point. As a power series in r, we
compute the energy E of the gravitational and matter fields on a spacelike
hypersurface spanning S(r). Much of our analysis concerns conceptual and
technical issues associated with assigning the zero-point of the energy. For
the small-sphere limit, we argue that the correct zero-point is obtained via a
"lightcone reference," which stems from a certain isometric embedding of S(r)
into a genuine lightcone of Minkowski spacetime. Choosing this zero-point, we
find agreement with Hawking's quasilocal mass expression, up to and including
the first non-trivial order in the affine radius. The vacuum limit relates the
quasilocal energy directly to the Bel-Robinson tensor.


title:
Coherent Line Removal: Filtering out harmonically related line
  interference from experimental data, with application to gravitational wave
  detectors

abstract:
  We describe a new technique for removing troublesome interference from
external coherent signals present in the gravitational wave spectrum. The
method works when the interference is present in many harmonics, as long as
they remain coherent with one another. The method can remove interference even
when the frequency changes. We apply the method to the data produced by the
Glasgow laser interferometer in 1996 and the entire series of wide lines
corresponding to the electricity supply frequency and its harmonics are
removed, leaving the spectrum clean enough to detect possible signals
previously masked by them. We also study the effects of the line removal on the
statistics of the noise in the time domain. We find that this technique seems
to reduce the level of non-Gaussian noise present in the interferometer and
therefore, it can raise the sensitivity and duty cycle of the detectors.


title: The form of cosmic string cusps

abstract:
  We classify the possible shapes of cosmic string cusps and how they transform
under Lorentz boosts. A generic cusp can be brought into a form in which the
motion of the cusp tip lies in the plane of the cusp. The cusp whose motion is
perpendicular to this plane, considered by some authors, is a special case and
not the generic situation.
  We redo the calculation of the energy in the region where the string overlaps
itself near a cusp, which is the maximum energy that can be released in
radiation. We take into account the motion of a generic cusp and the resulting
Lorentz contraction of the string core. The result is that the energy scales as
$\sqrt {rL}$ instead of the usual value of $r^{1/3} L^{2/3}$, where $r$ is the
string radius and $L$ and is the typical length scale of the string. Since $r
<< L $ for cosmological strings, the radiation is strongly suppressed and could
not be observed.


title: Dynamic black-hole entropy

abstract:
  We consider two non-statistical definitions of entropy for dynamic
(non-stationary) black holes in spherical symmetry. The first is analogous to
the original Clausius definition of thermodynamic entropy: there is a first law
containing an energy-supply term which equals surface gravity times a total
differential. The second is Wald's Noether-charge method, adapted to dynamic
black holes by using the Kodama flow. Both definitions give the same answer for
Einstein gravity: one-quarter the area of the trapping horizon.


title:
Effective chiral model of a plane-symmetric gravitational field:
  properties and exact solutions

abstract:
  An effective chiral model of a plane-symmetric gravitational field is
considered. Isometries of the target space of the model are described and exact
solutions corresponding to the isometric ansatz method are obtained. New exact
solutions are found using the method of functional parameters. The solutions
obtained are B\"acklund transforms of solutions of the d'Alembert equation to
those of the Einstein equations.


title: Singularities and isotropy in a Brans-Dicke Bianchi-type VII universe

abstract:
  We study the dynamical effects in the scale factors due to the scalar
$\phi$-field at the early stages of a supposedly anisotropic Universe expansion
in connection with the problem of the initial singularity in the scalar-tensor
cosmology of Jordan-Brans-Dicke. This is done by considering the behaviour of
the general analytical solutions for the homogeneous model of Bianchi type VII
in the vacuum case. We conclude that the Bianchi-VII$_0$ model shows an
isotropic expansion and that its only physical solution is equivalent to a
Friedman-Robertson-Walker spacetime whose evolution begins in a singularity and
ends in another; moreover, we obtain that the general Bianchi-VII$_h$ (with
$h\neq 0$) models show strong curvature singularities that produces a complete
collapse of the homogeinity surfaces to a 2-plane, to a string-like
one-dimensional manifold, or to a single point.


title: Moving Observers, Non-orthogonal Boundaries, and Quasilocal Energies

abstract:
  The popular Hamilton-Jacobi method first proposed by Brown and York for
defining quasilocal quantities such as energy for spatially bound regions
assumes that the spatial boundary is orthogonal to the foliation of the
spacetime. Such a restriction is undesirable for both theoretical and
computational reasons. We remove the orthogonality assumption and show that it
is more natural to focus on the foliation of the spatial boundary rather than
the foliation of the entire spatially bound region. Reference spacetimes which
define additional terms in the action are discussed in detail. To demonstrate
this new formulation, we calculate the quasilocal energies seen by observers
who are moving with respect to a Schwarzschild black hole.


title:
Static Solutions of the Einstein Equations for Spherically Symmetric
  Elastic Bodies

abstract:
  The paper is concerned with the Einstein equations for a spherically
symmetric static distribution of anisotropic matter. The equations are cast
into a system of Fuchsian type ODE for certain scalar invariants of the strain.
And then the existence and regularity of this ODE is studied under general
constitutive relation. In the case the constitutive relation is given by a
quadratic form of strain, it is also shown that the solutions stay regular up
to the boundary of the material ball.


title: Pair Creation of Black Holes in Anti-de Sitter Space Background (I)

abstract:
  For a spherically symmetric vacuum model with a negative cosmological
constant, a complex constrained instanton is considered as the seed for the
quantum pair creation of Schwarzschild-anti-de Sitter black holes. The relative
creation probability is found to be the exponential of the negative of the
black hole entropy. The black hole entropy is known to be one quarter of the
black hole horizon area. In the absence of a general no-boundary proposal for
open creation, the constrained instanton approach is used in treating both the
open and closed pair creations of black holes.


title: Pair Creation of Black Hole in Anti-de Sitter Space Background

abstract:
  In the absence of a general no-boundary proposal for open creation, the
complex constrained instanton is used as the seed for the open pair creations
of black holes in the Kerr-Newman-anti-de Sitter family. The relative
probability of the chargeless and nonrotating black hole pair is the
exponential of the negative of the entropy, and that of the charged and (or)
rotating black hole pair is the exponential of the negative of one quarter of
the sum of the outer and inner black hole horizon areas.


title: Modular Quantum Cosmology

abstract:
  We study solutions of the Wheeler-DeWitt equation corresponding to an
S-modular invariant N=1 supergravity model and a closed homogeneous and
isotropic Friedmann-Robertson-Walker spacetime. The issues of inflation and of
the cosmological constant problem are addressed with the help of the relevant
wave functions. We find that topological type inflation is consistent from the
quantum mechanical point of view and that a solution for the cosmological
constant problem along the lines of the strong CP problem naturally arises.


title: The Case for Hyperbolic Theories of Dissipation in Relativistic Fluids

abstract:
  In this paper we highlight the fact that the physical content of hyperbolic
theories of relativistic dissipative fluids is, in general, much broader than
that of the parabolic ones. This is substantiated by presenting an ample range
of dissipative fluids whose behavior noticeably departs from Navier-Stokes'.


title:
A Prosaic Explanation for the Anomalous Accelerations Seen in Distant
  Spacecraft

abstract:
  Anderson, et al. (gr-qc/9808081) have recently reported the discovery of an
apparent anomalous, weak, long-range acceleration in the Pioneer 10/11 and
Ulysses spacecraft. I believe that this result can be explained by
non-isotropic radiative cooling of the spacecraft electronics through passive
radiators on the spacecraft surface. These radiators are preferentially placed
on the anti-solar side of the spacecraft to avoid heating by solar radiation.
The power transmitted through these radiator panels can explain the observed
acceleration within the observational errors.


title:
Human Gravity-Gradient Noise in Interferometric Gravitational-Wave
  Detectors

abstract:
  Among all forms of routine human activity, the one which produces the
strongest gravity-gradient noise in interferometric gravitational-wave
detectors (e.g. LIGO) is the beginning and end of weight transfer from one foot
to the other during walking. The beginning and end of weight transfer entail
sharp changes (timescale tau ~ 20msec) in the horizontal jerk (first time
derivative of acceleration) of a person's center of mass. These jerk pairs,
occuring about twice per second, will produce gravity-gradient noise in LIGO in
the frequency band 2.5 Hz <~ f <~ 1/(2 tau) ~= 25 Hz with the form sqrt{S_h(f)}
\~0.6 X 10^{-23} Hz^{-1/2} (f/10Hz)^{-6} (sum_i (r_i/10m)^{-6})^{1/2}. Here the
sum is over all the walking people, r_i is the distance of the i'th person from
the nearest interferometer test mass, and we estimate this formula to be
accurate to within a factor 3. To ensure that this noise is neglible in
advanced LIGO interferometers, people should be prevented from coming nearer to
the test masses than r ~= 10m. A r ~= 10m exclusion zone will also reduce to an
acceptable level gravity gradient noise from the slamming of a door and the
striking of a fist against a wall. The dominant gravity-gradient noise from
automobiles and other vehicles is probably that from decelerating to rest. To
keep this below the sensitivity of advanced LIGO interferometers will require
keeping vehicles at least 30 meters from all test masses.


title: An Exact Universal Gravitational Lensing Equation

abstract:
  We first define what we mean by gravitational lensing equations in a general
space-time. A set of exact relations are then derived that can be used as the
gravitational lens equations in all physical situations. The caveat is that
into these equations there must be inserted a function, a two-parameter family
of solutions to the eikonal equation, not easily obtained, that codes all the
relevant (conformal) space-time information for this lens equation
construction. Knowledge of this two-parameter family of solutions replaces
knowledge of the solutions to the geodesic equations.
  The formalism is then applied to the Schwarzschild lensing problem


title:
A Charged Inflaton leaves Behind a Fractal Primeval Structure of
  Electromagnetic Fields

abstract:
  The inflaton field is assumed to possess electric charge. The effect of the
charge upon inflation is studied using a parameter \omega_0 that acts as a
measure of the quantity of inflaton present. It is shown that at the end of
inflation the charged inflaton should produce a fractal electromagnetic
structure, which could act as a seed for the development of macroscopic
galactic structures. Another consequence would be the presence nowadays of
residual electromagnetic fields that would encompass galaxies, clusters, and
larger structures.


title:
Superluminal propagation of light in gravitational field and non-causal
  signals: some comments

abstract:
  We examine the recent statement by A. Dolgov and I. Novikov that superluminal
propagation of light, which is induced by the quantum corrections to the photon
propagation in gravitational field, permits non-causal signal propagation. For
this purpose we examine the possibility of the existence of non-causal signals
in the model case, when characteristic cone of the signal is outside the usual
light cone in Minkowski space-time, as it take place in the case of the photon
propagation in gravitation field with quantum corrections taking into account.
In such model the signal propagates along invariant intervals. It is shown that
there are no non-causal signals in the considered model. The recent statement
of A. Dolgov and I. Novikov was obtained by using additional supposition that
velocity of the signal with respect to the emitter is independent from its
motion. Such supposition does not valid in the case of the photon propagation
in gravitational field.


title:
The Active Gravitational Mass of a Heat Conducting Sphere Out of
  Hydrostatic Equilibrium

abstract:
  We obtain an expression for the active gravitational mass of a relativistic
heat conducting fluid, just after its departure from hydrostatic equilibrium,
on a time scale of the order of relaxation time. It is shown that an increase
of a characteristic parameter leads to larger (smaller) values of active
gravitational mass of collapsing (expanding) spheres, enhacing thereby the
instability of the system.


title: 't Hooft's Polygon Approach Hyperbolically Revisited

abstract:
  The initial data in the polygon approach to (2+1)D gravity coupled to point
particles are constrained by the vertex equations and the particle equations.
We establish the hyperbolic nature of the vertex equations and derive some
consequences. In particular we are able to identify the hyperbolic group of
motions as discrete analogues of the diffeomorphisms in the continuum theory.
We show that particles can be included ``hyperbolically'' as well, but they
spoil the gauge invariance. Finally we derive consistent sets of initial data.


title:
Towards a classification of static electro-vacuum space-times containing
  an asymptotically flat spacelike hypersurface with compact interior

abstract:
  We show that static electro-vacuum black hole space-times containing an
asymptotically flat spacelike hypersurface with compact interior and with both
degenerate and non-degenerate components of the event horizon do not exist,
under the supplementary hypothesis that all degenerate components of the event
horizon have charges of the same sign. This extends previous uniqueness
theorems of Simon and Masood-ul-Alam (where only non-degenerate horizons were
allowed) and Heusler (where only degenerate horizons were allowed).


title:
Minimal conditions for the creation of a Friedman-Robertson-Walker
  universe from a "bounce"

abstract:
  We investigate the minimal conditions under which the creation of our
universe might arise due to a "bounce" from a previous collapse, rather than an
explosion from a big-bang singularity. Such a bounce is sometimes referred to
as a Tolman wormhole. We subject the bounce to a general model-independent
analysis along the lines of that applied to the Morris-Thorne traversable
wormholes, and show that there is always an open temporal region surrounding
the bounce over which the strong energy condition (SEC) must be violated. On
the other hand, all the other energy conditions can easily be satisfied. In
particular, we exhibit an inflation-inspired model in which a big bounce is
"natural".


title: Propagating spin modes in canonical quantum gravity

abstract:
  One of the main results in canonical quantum gravity is the introduction of
spin network states as a basis on the space of kinematical states. To arrive at
the physical state space of the theory though we need to understand the
dynamics of the quantum gravitational states. To this aim we study a model in
which we allow for the spins, labeling the edges of spin networks, to change
according to simple rules. The gauge invariance of the theory, restricting the
possible values for the spins, induces propagating modes of spin changes. We
investigate these modes under various assumptions about the parameters of the
model.


title:
Self-dual SU(2) invariant Einstein metrics and modular dependence of
  theta-functions

abstract:
  We simplify Hitchin's description of SU(2)-invariant self-dual Einstein
metrics, making use of the tau-function of related four-pole Schlesinger
system.


title: Superluminal censorship

abstract:
  We argue that ``effective'' superluminal travel, potentially caused by the
tipping over of light cones in Einstein gravity, is always associated with
violations of the null energy condition (NEC). This is most easily seen by
working perturbatively around Minkowski spacetime, where we use linearized
Einstein gravity to show that the NEC forces the light cones to contract
(narrow). Given the NEC, the Shapiro time delay in any weak gravitational field
is always a delay relative to the Minkowski background, and never an advance.
Furthermore, any object travelling within the lightcones of the weak
gravitational field is similarly delayed with respect to the minimum traversal
time possible in the background Minkowski geometry.


title: Exact solutions of Einstein's equations with ideal gas sources

abstract:
  We derive a new class of exact solutions characterized by the
Szekeres-Szafron metrics (of class I), admitting in general no isometries. The
source is a fluid with viscosity but zero heat flux (adiabatic but irreversible
evolution) whose equilibrium state variables satisfy the equations of state of:
(a) ultra-relativistic ideal gas, (b) non-relativistic ideal gas, (c) a mixture
of (a) and (b). Einstein's field equations reduce to a quadrature that is
integrable in terms of elementary functions (cases (a) and (c)) and elliptic
integrals (case (b)). Necessary and sufficient conditions are provided for the
viscous dissipative stress and equilibrium variables to be consistent with the
theoretical framework of Extended Irreversible Thermodynamics and Kinetic
Theory of the Maxwell-Boltzmann and radiative gases. Energy and regularity
conditions are discussed. We prove that a smooth matching can be performed
along a spherical boundary with a FLRW cosmology or with a Vaidya exterior
solution. Possible applications are briefly outlined.


title: Scalar Fields as Dark Matter in Spiral Galaxies

abstract:
  We present a model for the dark matter in spiral galaxies, which is a result
of a static and axial symmetric exact solution of the Einstein-Dilaton theory.
We suposse that dark matter is a scalar field endowed with a scalar potential.
We obtain that a) the effective energy density goes like $1/(r^2+r_{c}^{2})$
and b) the resulting circular velocity profile of tests particles is in good
agreement with the observed one.


title: Tolman wormholes violate the strong energy condition

abstract:
  For an arbitrary Tolman wormhole, unconstrained by symmetry, we shall define
the bounce in terms of a three-dimensional edgeless achronal spacelike
hypersurface of minimal volume. (Zero trace for the extrinsic curvature plus a
"flare-out" condition.) This enables us to severely constrain the geometry of
spacetime at and near the bounce and to derive general theorems regarding
violations of the energy conditions--theorems that do not involve geodesic
averaging but nevertheless apply to situations much more general than the
highly symmetric FRW-based subclass of Tolman wormholes. [For example: even
under the mildest of hypotheses, the strong energy condition (SEC) must be
violated.] Alternatively, one can dispense with the minimal volume condition
and define a generic bounce entirely in terms of the motion of test particles
(future-pointing timelike geodesics), by looking at the expansion of their
timelike geodesic congruences. One re-confirms that the SEC must be violated at
or near the bounce. In contrast, it is easy to arrange for all the other
standard energy conditions to be satisfied.


title: On the gravitational redshift

abstract:
  The purpose of this paper is twofold - to demonstrate that in the
gravitational redshift it is the frequency a photon that is constant, and to
describe the mechanism responsible for the change of its wavelength.


title: Geodesic Deviation in Regge Calculus

abstract:
  Geodesic deviation is the most basic manifestation of the influence of
gravitational fields on matter. We investigate geodesic deviation within the
framework of Regge calculus, and compare the results with the continuous
formulation of general relativity on two different levels. We show that the
continuum and simplicial descriptions coincide when the cumulative effect of
the Regge contributions over an infinitesimal element of area is considered.
This comparison provides a quantitative relation between the curvature of the
continuous description and the deficit angles of Regge calculus. The results
presented might also be of help in developing generic ways of including matter
terms in the Regge equations.


title: Anomaly-induced effective action for gravity and inflation

abstract:
  In the very early Universe the matter may be described by the free radiation,
that is by the set of massless fields with negligible interactions between
them. Then the dominating quantum effect is the trace anomaly which comes from
the renormalization of the conformal invariant part of the vacuum action. The
anomaly-induced effective action can be found with accuracy to an arbitrary
conformal functional which vanishes for the special case of the conformally
flat metric. This gives the solid basis for the study of the conformally-flat
cosmological solutions, first of which was discovered by Mamaev and
Mostepanenko and by Starobinski in 1980. Treating the anomaly-induced action as
quantum correction to the Einstein-Hilbert term we explore the possibility to
have inflationary solutions, investigate their dependence on the initial data
and discuss the restrictions in considering the density perturbations. The
shape of inflationary solutions strongly depends on the underlying gauge model
of the elementary particles physics. Two special cases are considered: Minimal
Standard Model and the matter sector of N=8, D=4 supergravity. It turns out
that inflation is almost inevitable consequence of the great difference between
Planck mass and the mass of the heaviest massive particle.


title: Behavior of Quasilocal Mass Under Conformal Transformations

abstract:
  We show that in a generic scalar-tensor theory of gravity, the ``referenced''
quasilocal mass of a spatially bounded region in a classical solution is
invariant under conformal transformations of the spacetime metric. We first
extend the Brown-York quasilocal formalism to such theories to obtain the
``unreferenced'' quasilocal mass and prove it to be conformally invariant. The
appropriate reference term in this case is defined by generalizing the
Hawking-Horowitz prescription, which was originally proposed for general
relativity. For such a choice of reference term, the referenced quasilocal mass
for a general spacetime solution is obtained. This expression is shown to be a
conformal invariant provided the conformal factor is a monotonic function of
the scalar field. We apply this expression to the case of static spherically
symmetric solutions with arbitrary asymptotics to obtain the referenced
quasilocal mass of such solutions. Finally, we demonstrate the conformal
invariance of our quasilocal mass formula by applying it to specific cases of
four-dimensional charged black hole spacetimes, of both the asymptotically flat
and non-flat kinds, in conformally related theories.


title: The Interior Field of a Magnetized Einstein-Maxwell Object

abstract:
  Using the Harmonic map ansatz, we reduce the axisymmetric, static
Einstein-Maxwell equations coupled with a magnetized perfect fluid to a set of
Poisson-like equations. We were able to integrate the Poisson equations in
terms of an arbitrary function $M=M(\rho,\zeta)$ and some integration
constants. The thermodynamic equation restricts the solutions to only some
state equations, but in some cases when the solution exists, the interior
solution can be matched with the corresponding exterior one.


title:
Quantum geometrodynamics in extended phase space - II. The Bianchi IX
  model

abstract:
  The mathematically correct approach to constructing quantum geometrodynamics
of a closed universe formulated in Part I is realized on the cosmological
Bianchi-IX model with scalar fields. The physical adequacy of the obtained
gauge-noninvariant theory to existing concepts about possible cosmological
scenarios is shown. It is demonstrated that the Wheeler-DeWitt quantum
geometrodynamics based on general quantum theoretical principles with
probability interpretation of a closed universe wave function does not exist.
The problem of the creation of the Universe is considered as a computational
problem of a quantum reduction of the singular state "Nothing" to one of
possible initial physical quantum states.


title:
The N-body Problem in Tetrad Gravity: a First Step towards the Unified
  Description of the Four Interactions

abstract:
  After a review of the canonical reduction to the rest-frame Wigner-covariant
instant form of standard theories in Minkowski spacetime, a new formulation of
tetrad gravity is introduced. Its canonical reduction, also in presence of N
scalar particles, is done. The modification of the ADM formulation to solve the
deparametrization problem of general relativity (how to recover the rest-frame
instant form for G=0), is presented.


title: A Spinorial Hamiltonian Approach to Ricci-Flat Geometry

abstract:
  The author has removed this paper, following the publication of a more
complete version.


title:
Non-occurrence of Trapped Surfaces and Black Holes in Spherical
  Gravitational Collapse

abstract:
  We point out that although the pioneering work of Oppenheimer and Snyder
(OS), technically, indicated the formation of an event horizon for a collapsing
homogeneous dust ball of mass $M_b$ and radius $R_b$, the Eqs. (32) and (36) of
their paper actually demand that no trapped surface is formed $ 2GM_b/ R_b c^2
\le 1$, and $M_b \equiv 0$! Anybody may verify it. Further, by analyzing the
general inhomogeneous dust solutions of Tolman in a proper physical
perspective, we show that, all dust solutions are characterized by $M_b=0$.
Next, for a collapsing fluid endowed with radiation pressure, we discover that
the collapse equations obey the same Global Constraint $2GM /R c^2 \le 1$ and
which specifically shows that, contrary to the traditional intuitive Newtonian
idea, which equates the gravitational mass ($M_b$) with the fixed baryonic mass
($M_0$), the trapped surfaces are not allowed in general theory of relativity
(GTR). For continued collapse, the final gravitational mss $M_f \to 0$ as $R\to
0$. Thus we confirm Einstein's and Rosen's idea that Event Horizons and
Schwarzschild Singularities are unphysical and can not occur in Nature. This,
in turn, implies that, if there would be any continued collapse, the initial
gravitational mass energy of the fluid must be radiated away $Q\to M_i c^2$.
This also implies that, gravitational collapse of massive stars should give
rise to Ultra Compact Objects and emission of energy much more than what is
obtained in Supernova Events


title:
de Broglie-Bohm interpretation for wave function of
  Reissner-Nordstrom-de Sitter black hole

abstract:
  We study the canonical quantum theory of the Reissner-Nordstrom-de Sitter
black hole(RNdS). We obtain an exact general solution of the Wheeler-DeWitt
equation for the spherically symmetric geometry with electro-magnetic field. We
investigate the wave function form a viewpoint of the de Broglie-Bohm
interpretation. The de Broglie-Bohm interpretation introduces a rigid
trajectory on the minisuperspace without assuming an outside observer or
causing collapse of the wave function. In our analysis, we obtain the boundary
condition for the wave function which corresponds to the classical RNdS black
hole and describe the quantum fluctuations near the horizons quantitatively.


title: Asymptotic Schwarzschild Spacetimes

abstract:
  It is shown that if an asymptotically flat spacetime is asymptotically
stationary, in the sense that $\Lie_{\xi} g_{ab}$ vanishes at the rate $\sim
t^{-3}$ for asymptotically timelike vector field $\xi^a$, and the
energy-momentum tensor vanishes at the rate $\sim t^{-4}$, then the spacetime
is an asymptotically Schwarzschild spacetime. This gives a new aspect of the
uniqueness theorem of a black hole.


title:
Solutions of Schlesinger system and Ernst equation in terms of
  theta-functions

abstract:
  We discuss the relationship between Schlesinger system and stationary
axisymmetric Einstein's equation on the level of algebro-geometric solutions.
In particular, we calculate all metric coefficients corresponding to solutions
of Ernst equation in terms of theta-functions.


title:
Analytic Solutions of The Wheeler-DeWitt Equation in Spherically
  Symmetric Space-time

abstract:
  We study the quantum theory of the Einstein-Maxwell action with a
cosmological term in the spherically symmetric space-time, and explored quantum
black hole solutions in Reissner-Nordstrom-de Sitter geometry. We succeeded to
obtain analytic solutions to satisfy both the energy and momentum constraints.


title: The String Deviation Equation

abstract:
  The relative motion of many particles can be described by the geodesic
deviation equation. This can be derived from the second covariant variation of
the point particle's action. It is shown that the second covariant variation of
the string action leads to a string deviation equation.


title:
Limits to Quantum Gravity Effects from Observations of TeV Flares in
  Active Galaxies

abstract:
  We have used data from the TeV gamma-ray flare associated with the active
galaxy Markarian 421 observed on 15 May 1996 to place bounds on the possible
energy-dependence of the speed of light in the context of an effective quantum
gravitational energy scale. The possibility of an observable time dispersion in
high energy radiation has recently received attention in the literature, with
some suggestions that the relevant energy scale could be less than the Planck
mass and perhaps as low as 10^16 GeV. The limits derived here indicate this
energy scale to be in excess of 4x10^16 GeV at the 95% confidence level. To the
best of our knowledge, this constitutes the first convincing limit on such
phenomena in this energy regime.


title: Stability of Gravitational and Electromagnetic Geons

abstract:
  Recent work on gravitational geons is extended to examine the stability
properties of gravitational and electromagnetic geon constructs. All types of
geons must possess the property of regularity, self-consistency and
quasi-stability on a time-scale much longer than the period of the comprising
waves. Standard perturbation theory, modified to accommodate time-averaged
fields, is used to test the requirement of quasi-stability. It is found that
the modified perturbation theory results in an internal inconsistency. The
time-scale of evolution is found to be of the same order in magnitude as the
period of the comprising waves. This contradicts the requirement of slow
evolution. Thus not all of the requirements for the existence of
electromagnetic or gravitational geons are met though perturbation theory. From
this result it cannot be concluded that an electromagnetic or a gravitational
geon is a viable entity. The broader implications of the result are discussed
with particular reference to the problem of gravitational energy.


title:
Simple Formulas for Generating Chern-Simons Basic Invariant Polynomials
  by Repeated Exterior Differentiation

abstract:
  Simple formulas are given for generating Chern-Simons basic invariant
polynomials by repeated exterior differentiation for n-dimensional
differentiable manifolds having a general linear connection.


title: Microtorsion

abstract:
  The problem of unification of electro-magnetism and gravitation in four
dimensions; some new ideas involving torsion. A metric consisting of a
combination of symmetric and anti-symmetric parts is postulated and, in the
framework of general covariance, used to derive the free-field electro-magnetic
stress-energy tensor and the source tensor.


title:
Non-Existence of Black Hole Solutions for a Spherically Symmetric,
  Static Einstein-Dirac-Maxwell System

abstract:
  We consider for j=1/2, 3/2,... a spherically symmetric, static system of
(2j+1) Dirac particles, each having total angular momentum j. The Dirac
particles interact via a classical gravitational and electromagnetic field.
  The Einstein-Dirac-Maxwell equations for this system are derived. It is shown
that, under weak regularity conditions on the form of the horizon, the only
black hole solutions of the EDM equations are the Reissner-Nordstrom solutions.
In other words, the spinors must vanish identically. Applied to the
gravitational collapse of a "cloud" of spin-1/2-particles to a black hole, our
result indicates that the Dirac particles must eventually disappear inside the
event horizon.


title: Gravitational field of vacuumless defects

abstract:
  It has been recently shown that topological defects can arise in symmetry
breaking models where the scalar field potential $V(\phi)$ has no minima and is
a monotonically decreasing function of $|\phi|$. Here we study the
gravitational fields produced by such vacuumless defects in the cases of both
global and gauge symmetry breaking. We find that a global monopole has a
strongly repulsive gravitational field, and its spacetime has an event horizon
similar to that in de Sitter space. A gauge monopole spacetime is essentially
that of a magnetically charged black hole. The gravitational field of a global
string is repulsive and that of a gauge string is attractive at small distances
and repulsive at large distances. Both gauge and global string spacetimes have
singularities at a finite distance from the string core.


title: Einstein-Cartan-Heisenberg Theory of Gravity with Dynamical Torsion

abstract:
  On the basis of an algebraic relation between torsion and a classical spinor
field a new interpretation of Einstein-Cartan gravity interacting with
classical spinor field is proposed. In this approach the spinor field becomes
an auxiliary field and the dynamical equation for this field (the Heisenberg
equation) is a dynamical, gravitational equation for torsion. The simplest
version of this theory is examined where the metric degrees of freedom are
frozen and only torsion plays a role. A spherically symmetric solution of this
theory is examined. This solution can be interpreted, in the spirit of
Wheeler's ideas of ``charge without charge'' and ``mass without mass'', as a
geometrical model for an uncharged and massless particle with spin (``spin
without spin'').


title:
Conformal ``thin sandwich'' data for the initial-value problem of
  general relativity

abstract:
  The initial-value problem is posed by giving a conformal three-metric on each
of two nearby spacelike hypersurfaces, their proper-time separation up to a
multiplier to be determined, and the mean (extrinsic) curvature of one slice.
The resulting equations have the {\it same} elliptic form as does the
one-hypersurface formulation. The metrical roots of this form are revealed by a
conformal ``thin sandwich'' viewpoint coupled with the transformation
properties of the lapse function.


title: Black Holes Without Singularities

abstract:
  We study the properties of a completely integrable deformation of the CGHS
dilaton gravity model in two dimensions. The solution is shown to represent a
singularity free black hole that at large distances asymptoticaly joins to the
CGHS solution.


title:
On the method of effective nonlinear sigma model in plane- and
  axially-symmetric vacuum spacetimes

abstract:
  In present article effective nonlinear sigma model (NSM) is considered.
  Einstein equation solution, corresponded to the chiral fields determined by
functional parameter method, are presented.
  Effective NSM of stationary axially-symmetric gravitational field is
constructed. Motion equations are solved exactly by functional parameter
method. Einstein equations solution are constructed.
  For particular dependences of functional parameter graphics of solutions are
presented. Metric coefficients behaviour is shown to be similar as functional
parameter one.


title: General relativistic cosmology with no beginning of time

abstract:
  We find that general relativity can be naturally free of cosmological
singularities. Several nonsingular models are currently available that either
assume ad hoc matter contents, or are nonsingular only over a sector of
solution space of zero measure, or depart drastically from general relativity
at high energies. After much uncertainty over whether cosmological inflation
could help solve the initial-singularity problem, the prevailing belief today
is that general relativistic cosmology, with inflation or without, is
endemically singular. This belief was reinforced by recent singularity theorems
that take account specifically of inflation. Here, a viable inflationary
cosmology is worked out that is naturally free of singularities despite the
fact that 1) it uses only classical general relativity, 2) it assumes only the
most generic inflationary matter contents, and 3) it is a theory of the
chaotic-inflation type. That type of inflation is the most widely accepted
today, as it demands the least fine-tuning of initial conditions. It is also
shown how, by dropping the usual simplification of minimal coupling between
matter and geometry, the null energy condition can be violated and the relevant
singularity theorems circumvented.


title:
The Detectability of Relic (Squeezed) Gravitational Waves by Laser
  Interferometers

abstract:
  It is shown that the expected amplitudes and specific correlation properties
of the relic (squeezed) gravitational wave background may allow the
registration of the relic gravitational waves by the first generation of
sensitive gravity-wave detectors.


title:
Second-Order Black Hole Perturbations: A Computer Algebra Approach, I -
  The Schwarzschild Spacetime

abstract:
  This article outlines our derivation of the second order perturbations to a
Schwarzschild black hole, highlighting our use of, and necessary reliance on,
computer algebra. The particular perturbation scenario that is presented here
is the case of the linear quadrapole seeding the second order quadrapole. This
problem amounts to finding the second order Zerilli wave equation, and in
particular the effective source term due to the linear quadrapole. With one
minor exception, our calculations confirm the earlier findings of Gleiser,
et.al. On route to these results we also illustrate that, with the aid of
computer algebra, the linear Schwarzschild problem can be solved in a very
direct manner (i.e., without resorting to the usual function transformations),
and it is this ``direct method'' that drives the higher order perturbation
analysis. The calculations were performed using the GRTensorII computer algebra
package, running on the Maple V platform, along with several new Maple routines
that we have written specifically for these types of problems. Although we have
chosen to consider only the ``quadrapole-quadrapole'' calculation in this
article, the GRTensor environment, with the inclusion of these new routines,
would allow this analysis to be repeated for a far more general problem. These
routines, along with Maple worksheets that reproduce our calculations, are
publicly available at the GRTensor website: www.astro.queensu.ca/~grtensor .
The interested reader is invited to download and use them to reproduce our
results and experiment.


title:
Searching for electrovac solutions to Einstein--Maxwell equations with
  the help of computer algebra system GRG-EC

abstract:
  An example of application of the specialized computer algebra system Grg-EC
to the searching for solutions to the source-free Maxwell and Einstein--Maxwell
equations is demonstrated. The solution involving five arbitrary functions of
two variables is presented in explicit form (up to quadratures). An emphasis is
made on the characterizing of the software utilized.


title: Causal propagation of geometrical fields in relativistic cosmology

abstract:
  We employ the extended 1+3 orthonormal frame formalism for fluid spacetime
geometries $({\cal M}, {\bf g}, {\bf u})$, which contains the Bianchi field
equations for the Weyl curvature, to derive a 44-D evolution system of
first-order symmetric hyperbolic form for a set of geometrically defined
dynamical field variables. Describing the matter source fields
phenomenologically in terms of a barotropic perfect fluid, the propagation
velocities $v$ (with respect to matter-comoving observers that Fermi-propagate
their spatial reference frames) of disturbances in the matter and the
gravitational field, represented as wavefronts by the characteristic 3-surfaces
of the system, are obtained. In particular, the Weyl curvature is found to
account for two (non-Lorentz-invariant) Coulomb-like characteristic eigenfields
propagating with $v = 0$ and four transverse characteristic eigenfields
propagating with $|v| = 1$, which are well known, and four
(non-Lorentz-invariant) longitudinal characteristic eigenfields propagating
with $|v| = \sfrac{1}{2}$. The implications of this result are discussed in
some detail and a parallel is drawn to the propagation of irregularities in the
matter distribution. In a worked example, we specialise the equations to
cosmological models in locally rotationally symmetric class II and include the
constraints into the set of causally propagating dynamical variables.


title: Space-time distributions

abstract:
  The space-time foliation Sigma compatible with the gravitational field g on a
4-manifold M determines a fibration pi of M, pi : M -> N is a surjective
submersion over the 1-dimensional leaves space N. M is then written as a
disjoint union of the leaves of Sigma, which are 3-dimensional spacelike
surfaces on M.
  The decomposition, TM=Sigma + T^0 M, also implies that we can define a lift
of the curves on N to curves (non-spacelike) on M.
  The stable causality condition M coincides with Sigma being a causal
space-time distribution, generated by an exact timelike 1-form omega^0 = dt
where t is some real function on M. In this case M is written as a disjoint
union of a family of spacelike 3-surfaces of constant t, which cover D^+(S) of
a initial 3-surface S of M.


title: A Stationary Asymptotically Einstein Static Universe Solution

abstract:
  Here I present a stationary cylindrically symmetric asymptotically Einstein
static universe solution with the matter consisting of a cosmological and
rotating dust term which admits predicted black hole event horizon.


title: Vortices and extreme black holes: the question of flux expulsion

abstract:
  It has been claimed that extreme black holes exhibit a phenomenon of flux
expulsion for abelian Higgs vortices, irrespective of the relative width of the
vortex to the black hole. Recent work by two of the authors showed a subtlety
in the treatment of the event horizon, which cast doubt on this claim. We
analyse in detail the vortex/extreme black hole system, showing that while flux
expulsion can occur, it does not do so in all cases. We give analytic proofs
for both expulsion and penetration of flux, in each case deriving a bound for
that behaviour. We also present extensive numerical work backing up, and
refining, these claims, and showing in detail how a vortex can end on a black
hole in all situations. We also calculate the backreaction of the vortex on the
geometry, and comment on the more general vortex-black hole system.


title: Anisotropic Null String Cosmologies

abstract:
  We study string propagation in an anisotropic, cosmological background. We
solve the equations of motion and the constraints by performing a perturbative
expansion of the string coordinates in powers of c^2, the world-sheet speed of
light. To zeroth order the string is approximated by a tensionless string
(since c is proportional to the string tension T). We obtain exact, analytical
expressions for the zeroth and the first order solutions and we discuss some
cosmological implications.


title:
Production and Detection of Cosmic Gravitational Wave Background in
  String Cosmology

abstract:
  String cosmology models predict a cosmic background of gravitational waves
produced during a period of dilaton-driven inflation. I describe the
background, present astrophysical and cosmological bounds on it, and discuss in
some detail how it may be possible to detect it with large operating and
planned gravitational wave detectors. The possible use of smaller detectors is
outlined.


title: Can induced gravity isotropize Bianchi I, V, or IX Universes?

abstract:
  We analyze if Bianchi I, V, and IX models in the Induced Gravity (IG) theory
can evolve to a Friedmann--Roberson--Walker (FRW) expansion due to the
non--minimal coupling of gravity and the scalar field. The analytical results
that we found for the Brans-Dicke (BD) theory are now applied to the IG theory
which has $\omega \ll 1$ ($\omega$ being the square ratio of the Higgs to
Planck mass) in a cosmological era in which the IG--potential is not
significant. We find that the isotropization mechanism crucially depends on the
value of $\omega$. Its smallness also permits inflationary solutions. For the
Bianch V model inflation due to the Higgs potential takes place afterwads, and
subsequently the spontaneous symmetry breaking (SSB) ends with an effective FRW
evolution. The ordinary tests of successful cosmology are well satisfied.


title: On the Numerical Integration of Einstein's Field Equations

abstract:
  Many numerical codes now under development to solve Einstein's equations of
general relativity in 3+1 dimensional spacetimes employ the standard ADM form
of the field equations. This form involves evolution equations for the raw
spatial metric and extrinsic curvature tensors. Following Shibata and Nakamura,
we modify these equations by factoring out the conformal factor and introducing
three ``connection functions''. The evolution equations can then be reduced to
wave equations for the conformal metric components, which are coupled to
evolution equations for the connection functions. We evolve small amplitude
gravitational waves and make a direct comparison of the numerical performance
of the modified equations with the standard ADM equations. We find that the
modified form exhibits much improved stability.


title:
Ground State Energy of Massive Scalar Field in the Background of Finite
  Thickness Cosmic String

abstract:
  We calculate the ground state energy of a massive scalar field in the
background of a cosmic string of finite thickness (Gott-Hiscock metric). Using
zeta functional regularization we discuss the renormalization and the relevant
heat kernel coefficients in detail. The finite (non local) part of the ground
state energy is calculated in 2+1 dimensions in the approximation of a small
mass density of the string. By a numerical calculation it is shown to vanish as
a function of the radius of the string and of the parameter $\xi$ of the
nonconformal coupling.


title: A variational principle for time of arrival of null geodesics

abstract:
  Normally the issue or question of the time of arrival of light rays at an
observer coming from a given source is associated with Fermat's Principle of
Least Time which yields paths of extremal time. We here investigate a related
but different problem. We consider an observer receiving light from an extended
source that has propagated in an arbitrary gravitational field. It is assumed
from the start that the propagation is along null geodesics. Each point of the
extended source is sending out a light-cones worth of null rays and the
question arises which null rays from the source arrive first at the observer.
Stated in an a different fashion, a pulse of light comes from the source with a
wave-front as the leading edge, which rays are associated with that leading
edge. In vacuum flat-space we have, from Huygen's principle, that the rays
normal to the source constitute the leading edge and hence arrive first at an
observer. We here investigate this issue in the presence of a gravitational
field. Though it is not obvious, since the rays bend and are focused by the
gravitational field and could even cross, in fact it is the normal rays that
arrive earliest. We give two proofs both involving the extemization of the time
of arrival, one based on an idea of Schrodinger for the derivation of
gravitational frequency shifts and the other based on V.I. Arnold's theory of
generating families.


title: A family of exact solutions for unpolarized Gowdy models

abstract:
  Unpolarized Gowdy models are inhomogeneous cosmological models that depend on
time and one spatial variable and have complicated nonlinear equations of
motion. There are two topologies associated with these models, a three-torus
and a one-sphere cross a two-sphere. The three-torus models have been used for
numerical studies because it seems difficult to find analytic solutions to
their nonlinear Einstein equations. The one-sphere cross tow-sphere models have
even more complicated equations, but at least one family of analytic solutions
can be given as a reinterpretation of known solutions. Various properties of
this family of solutions are studied.


title:
Direct generation of spinning Einstein--Maxwell fields from static
  fields

abstract:
  I present a new method to generate rotating solutions of the
Einstein--Maxwell equations from static solutions, and briefly discuss its
general properties.


title: Extension of bundles of null directions

abstract:
  The geometry of P, the bundle of null directions over an Einstein space-time,
is studied. The full set of invariants of the natural G-structure on P is
constructed using the Cartan method of equivalence. This leads to an extension
of P which is an elliptic fibration over the space-time. Examples are given
which show that such an extension, although natural, is not unique. A
reinterpretation of the Petrov classification in terms of the fibres of an
extension of P is presented.


title: Stability of degenerate Cauchy horizons in black hole spacetimes

abstract:
  In the multihorizon black hole spacetimes, it is possible that there are
degenerate Cauchy horizons with vanishing surface gravities. We investigate the
stability of the degenerate Cauchy horizon in black hole spacetimes. Despite
the asymptotic behavior of spacetimes (flat, anti-de Sitter, or de Sitter), we
find that the Cauchy horizon is stable against the classical perturbations, but
unstable quantum mechanically.


title:
Numerical models of irrotational binary neutron stars in general
  relativity

abstract:
  We report on general relativistic calculations of quasiequilibrium
configurations of binary neutron stars in circular orbits with zero vorticity.
These configurations are expected to represent realistic situations as opposed
to corotating configurations. The Einstein equations are solved under the
assumption of a conformally flat spatial 3-metric (Wilson-Mathews
approximation). The velocity field inside the stars is computed by solving an
elliptical equation for the velocity scalar potential. Results are presented
for sequences of constant baryon number (evolutionary sequences). Although the
central density decreases much less with the binary separation than in the
corotating case, it still decreases. Thus, no tendency is found for the stars
to individually collapse to black hole prior to merger.


title: Quantum gravitational fluctuations and the semi-classical limit

abstract:
  An attempt is made to go beyond the standard semi-classical approximation for
gravity in the Born-Oppenheimer decomposition of the wave-function in
minisuperspace. New terms are included which correspond to quantum
gravitational fluctuations on the background metric. Their existence renders
the definition of the semi-classical limit rather delicate and can lead to the
avoidance of the singularities the classical theory predicts in cosmology and
in the gravitational collapse of compact objects.


title: Quantifying excitations of quasinormal mode systems

abstract:
  Computations of the strong field generation of gravitational waves by black
hole processes produce waveforms that are dominated by quasinormal (QN)
ringing, a damped oscillation characteristic of the black hole. We describe
here the mathematical problem of quantifying the QN content of the waveforms
generated. This is done in several steps: (i) We develop the mathematics of QN
systems that are complete (in a sense to be defined) and show that there is a
quantity, the ``excitation coefficient,'' that appears to have the properties
needed to quantify QN content. (ii) We show that incomplete systems can (at
least sometimes) be converted to physically equivalent complete systems. Most
notably, we give a rigorous proof of completeness for a specific modified model
problem. (iii) We evaluate the excitation coefficient for the model problem,
and demonstrate that the excitation coefficient is of limited utility. We
finish by discussing the general question of quantification of QN excitations,
and offer a few speculations about unavoidable differences between normal mode
and QN systems.


title: Spinning ring wormholes: a classical model for elementary particles?

abstract:
  Static horizonless solutions to the Einstein--Maxwell field equations, with
only a circular cosmic string singularity, are extended to exact rotating
asymptotically flat solutions. The possible interpretation of these field
configurations as spinning elementary particles or as macroscopic rotating
cosmic rings is discussed.


title: From the DeDonder-Weyl Hamiltonian formalism to quantization of Gravity

abstract:
  An approach to quantization of fields and gravity based on the De Donder-Weyl
covariant Hamiltonian formalism is outlined. It leads to a hypercomplex
extension of quantum mechanics in which the algebra of complex numbers is
replaced by the space-time Clifford algebra and all space-time variables enter
on equal footing. A covariant hypercomplex analogue of the Schr\"odinger
equation is formulated. Elements of quantization of General Relativity within
the present framework are sketched.


title: Open and Closed Creations of Black Holes

abstract:
  We study pair creation of Kerr-Newman-anti-de Sitter and Kerr-Newman-de
Sitter black holes.


title: Why the Quantum Must Yield to Gravity

abstract:
  After providing an extensive overview of the conceptual elements -- such as
Einstein's `hole argument' -- that underpin Penrose's proposal for
gravitationally induced quantum state reduction, the proposal is constructively
criticised. Penrose has suggested a mechanism for objective reduction of
quantum states with postulated collapse time T = h/E, where E is an
ill-definedness in the gravitational self-energy stemming from the profound
conflict between the principles of superposition and general covariance. Here
it is argued that, even if Penrose's overall conceptual scheme for the
breakdown of quantum mechanics is unreservedly accepted, his formula for the
collapse time of superpositions reduces to T --> oo (E --> 0) in the strictly
Newtonian regime, which is the domain of his proposed experiment to corroborate
the effect. A suggestion is made to rectify this situation. In particular,
recognising the cogency of Penrose's reasoning in the domain of full `quantum
gravity', it is demonstrated that an appropriate experiment which could in
principle corroborate his argued `macroscopic' breakdown of superpositions is
not the one involving non-rotating mass distributions as he has suggested, but
a Leggett-type SQUID or BEC experiment involving superposed mass distributions
in relative rotation. The demonstration thereby brings out one of the
distinctive characteristics of Penrose's scheme, rendering it empirically
distinguishable from other state reduction theories involving gravity. As an
aside, a new geometrical measure of gravity-induced deviation from quantum
mechanics in the manner of Penrose is proposed, but now for the canonical
commutation relations [Q, P] = ih.


title: The Levi-Civita spacetime as a limiting case of the Gamma spacetime

abstract:
  It is shown that the Levi-Civita metric can be obtained from a family of the
Weyl metric, the Gamma metric, by taking the limit when the length of its
Newtonian image source tends to infinity. In this process a relationship
appears between two fundamental parameters of both metrics.


title: Formation of a rotating hole from a close limit head-on collision

abstract:
  Realistic black hole collisions result in a rapidly rotating Kerr hole, but
simulations to date have focused on nonrotating final holes. Using a new
solution of the Einstein initial value equations we present here waveforms and
radiation for an axisymmetric Kerr-hole-forming collision starting from small
initial separation (the ``close limit'' approximation) of two identical
rotating holes. Several new features are present in the results: (i) In the
limit of small separation, the waveform is linear (not quadratic) in the
separation. (ii) The waveforms show damped oscillations mixing quasinormal
ringing of different multipoles.


title:
Do naked singularities generically occur in generalized theories of
  gravity?

abstract:
  A new mechanism for causing naked singularities is found in an effective
superstring theory. We investigate the gravitational collapse in a spherically
symmetric Einstein-Maxwell-dilaton system in the presence of a pure
cosmological constant "potential", where the system has no static black hole
solution. We show that once gravitational collapse occurs in the system, naked
singularities necessarily appear in the sense that the field equations break
down in the domain of outer communications. This suggests that in generalized
theories of gravity, the non-minimally coupled fields generically cause naked
singularities in the process of gravitational collapse if the system has no
static or stationary black hole solution.


title:
Exact solution to the homogeneous Maxwell equations in the field of a
  gravitational wave in linearized theory

abstract:
  We present the exact solution to the linearized Maxwell equations in
space-time slightly curved by a gravitational wave. We show that in general,
even dealing with a first-order theory in the strength of the gravitational
field, the solution can not be written as the sum of the flat space-time one
and a weak perturbation due to the external field. Such an impossibility arises
when either the frequency of the gravitational wave is too low or too high with
respect to the one of the electromagnetic field. We also provide an application
of the solution to the case of an electromagnetic field bounced between two
parallel conducting planes.


title: Nearness through an extra dimension

abstract:
  It is shown that if our visible universe is a thin trapped shell in a
five-dimensional universe, all matter in it may be connected almost
instantaneously through the fifth dimension. What appears to be action at a
distance is then understood as undetectable ultrafast communication.


title: Inflationary cosmology of the extreme cosmic string

abstract:
  Starting with a study of the cosmological solution to the Einstein equations
for the internal spacetime of an extreme supermassive cosmic string kink, and
by evaluating the probability measure for the formation of such a kink in
semiclassical approximation using a minisuperspace with the appropriate
symmetry, we have found a set of arguments in favor of the claim that the
kinked extreme string can actually be regarded as a unbounded chain of pairs of
Planck- sized universes. Once one such universe pairs is created along a
primordial phase transition at the Planck scale, it undergoes an endless
process of continuous self-regeneration driven by chaotic inflation in each of
the universes forming the pair.


title:
The "Pioneer effect" as a manifestation of the cosmic expansion in the
  solar system

abstract:
  It is proposed that the recently reported anomalous acceleration acting on
the Pioneers spacecrafts should be a consequence of the existence of some local
curvature in light geodesics when using the coordinate speed of light in an
expanding spacetime. This suggests taht this "Pioneer effect" is nothing else
but the detection of cosmological expansion in the solar system.


title: Time-Dependent Vacuum Energy Induced by D-Particle Recoil

abstract:
  We consider cosmology in the framework of a `material reference system' of D
particles, including the effects of quantum recoil induced by closed-string
probe particles. We find a time-dependent contribution to the cosmological
vacuum energy, which relaxes to zero as $\sim 1/ t^2$ for large times $t$. If
this energy density is dominant, the Universe expands with a scale factor $R(t)
\sim t^2$. We show that this possibility is compatible with recent
observational constraints from high-redshift supernovae, and may also respect
other phenomenological bounds on time variation in the vacuum energy imposed by
early cosmology.


title: The equivalence principle in classical mechanics and quantum mechanics

abstract:
  We discuss our understanding of the equivalence principle in both classical
mechanics and quantum mechanics. We show that not only does the equivalence
principle hold for the trajectories of quantum particles in a background
gravitational field, but also that it is only because of this that the
equivalence principle is even to be expected to hold for classical particles at
all.


title: Computation of the conformal algebra of 1+3 decomposable spacetimes

abstract:
  The conformal algebra of a 1+3 decomposable spacetime can be computed from
the conformal Killing vectors (CKV) of the 3-space. It is shown that the
general form of such a 3-CKV is the sum of a gradient CKV and a Killing or
homothetic 3-vector. It is proved that spaces of constant curvature always
admit such conformal Killing vectors. As an example, the complete conformal
algebra of a G\"odel-type spacetime is computed. Finally it is shown that this
method can be extended to compute the conformal algebra of more general
non-decomposable spacetimes.


title: The Quantum Commutator of a Perfect Fluid

abstract:
  A perfect fluid is quantized by the canonical method. The constraints are
found and this allows the Dirac brackets to be calculated. Replacing the Dirac
brackets with quantum commutators formally quantizes the system. There is a
momentum operator in the denominator of some coordinate quantum commutators. It
is shown that it is possible to multiply throughout by this momentum operator.
Factor ordering differences can result in a viscosity term. The resulting
quantum commutator algebra is \vspace{1.0truein}
\bc$v_{4}(v_{3}v_{2}-v_{2}v_{3})=-i,$\ec
\bc$v_{4}(v_{1}v_{3}-v_{3}v_{1})=-iv_{3},$\ec \bc$v_{4}v_{1}-v_{1}v_{4}=-i,$\ec
\bc$v_{5}v_{2}-v_{2}v_{5}=-i$.\ec


title: An Expansion Term In Hamilton's Equations

abstract:
  For any given spacetime the choice of time coordinate is undetermined. A
particular choice is the absolute time associated with a preferred vector
field. Using the absolute time Hamilton's equations are
  $- (\delta H_{c})/(\delta q)=\dot{\pi}+\Theta\pi,
  $+ (\delta H_{c})/(\delta \pi)=\dot{q}$,
  where $\Theta = V^{a}_{.;a}$ is the expansion of the vector field. Thus there
is a hitherto unnoticed term in the expansion of the preferred vector field.
Hamilton's equations can be used to describe fluid motion. In this case the
absolute time is the time associated with the fluid's co-moving vector. As
measured by this absolute time the expansion term is present. Similarly in
cosmology, each observer has a co-moving vector and Hamilton's equations again
have an expansion term. It is necessary to include the expansion term to
quantize systems such as the above by the canonical method of replacing Dirac
brackets by commutators. Hamilton's equations in this form do not have a
corresponding sympletic form. Replacing the expansion by a particle number
$N\equiv exp(-\int\Theta d \ta)$ and introducing the particle numbers conjugate
momentum $\pi^{N}$ the standard sympletic form can be recovered with two extra
fields N and $\pi^N$. Briefly the possibility of a non-standard sympletic form
and the further possibility of there being a non-zero Finsler curvature
corresponding to this are looked at.


title:
Critical Collapse Beyond Spherical Symmetry: General Perturbations of
  the Roberts Solution

abstract:
  This paper studies the non-spherical perturbations of the continuously
self-similar critical solution of the gravitational collapse of a massless
scalar field (the Roberts solution). The exact analysis of the perturbation
equations reveals that there are no growing non-spherical perturbation modes.


title: The extensions of gravitational soliton solutions with real poles

abstract:
  We analyse vacuum gravitational "soliton" solutions with real poles in the
cosmological context. It is well known that these solutions contain
singularities on certain null hypersurfaces. Using a Kasner seed solution, we
demonstrate that these may contain thin sheets of null matter or may be simple
coordinate singularities, and we describe a number of possible extensions
through them.