title: The Innermost Stable Circular Orbit of Binary Black Holes

abstract:
  We introduce a new method to construct solutions to the constraint equations
of general relativity describing binary black holes in quasicircular orbit.
Black hole pairs with arbitrary momenta can be constructed with a simple method
recently suggested by Brandt and Bruegmann, and quasicircular orbits can then
be found by locating a minimum in the binding energy along sequences of
constant horizon area. This approach produces binary black holes in a
"three-sheeted" manifold structure, as opposed to the "two-sheeted" structure
in the conformal-imaging approach adopted earlier by Cook. We focus on locating
the innermost stable circular orbit and compare with earlier calculations. Our
results confirm those of Cook and imply that the underlying manifold structure
has a very small effect on the location of the innermost stable circular orbit.


title: Noether Currents of Charged Spherical Black Holes

abstract:
  We calculate the Noether currents and charges for Einstein-Maxwell theory
using a version of the Wald approach. In spherical symmetry, the choice of time
can be taken as the Kodama vector. For the static case, the resulting combined
Einstein-Maxwell charge is just the mass of the black hole. Using either a
classically defined entropy or the Iyer-Wald selection rules, the entropy is
found to be just a quarter of the area of the trapping horizon. We propose
identifying the combined Noether charge as an energy associated with the Kodama
time. For the extremal black hole case, we discuss the problem of Wald's
rescaling of the surface gravity to define the entropy.


title:
Integrable spherically symmetric p-brane models associated with Lie
  algebras

abstract:
  A classical model of gravity theory with several dilatonic scalar fields and
differential forms admitting an interpretation in terms of intersecting
p-branes is studied in (pseudo)-Riemannian space-time $M =R_+\times
S^{d_0}\times R_t\times M_2^{d_2}...\times M_n^{d_n}$ of dimension D. The
equations of motion of the model are reduced to the Euler-Lagrange equations
for the so-called pseudo-Euclidean Toda-like system. We suppose that the
characteristic vectors related to the configuration of p-branes and their
couplings to the dilatonic scalar fields may be interpreted as the root vectors
of a Lie algebra of the types $A_r, B_r, C_r$. In this case the model is
reducible to one of the open Toda chain's algebraic generalization and is
completely integrable by the known methods. The corresponding general solutions
are presented in explicit form. The particular exact solution describing a
class of nonextremal black holes is obtained and analyzed.


title: Response of massive bodies to gravitational waves

abstract:
  The response of a massive body to gravitational waves is described on the
microscopic level. The results shed a new light on the commonly used oscillator
model. It is shown that apart from the non-resonant tidal motion the energy
transfer from a gravitational wave to an electromagnetically coupled body is in
general restricted to the surface, whereas gravitational coupling gives rise to
bulk excitation of quadrupole modes, but several orders of magnitude smaller.
These results do not contradict standard theory, rather present a different
viewpoint. A microscopic detector making use of the effect is suggested.


title: A Generalized Equivalence Principle

abstract:
  Gauge field theories may quite generally be defined as describing the
coupling of a matter-field to an interaction-field, and they are suitably
represented in the mathematical framework of fiber bundles. Their underlying
principle is the so-called gauge principle, which is based on the idea of
deriving the coupling structure of the fields by satisfying a postulate of
local gauge covariance. The gauge principle is generally considered to be
sufficient to define the full structure of gauge-field theories. This paper
contains a critique of this usual point of view: firstly, by emphazising an
gauge theoretic conventionalism which crucially restricts the conceptual role
of the gauge principle and, secondly, by introducing a new generalized
equivalence principle - the identity of inertial and field charge (as
generalizations of inertial and gravitational mass) - in order to give a
conceptual justification for combining the equations of motion of the
matter-fields and the field equations of the interaction-fields.


title: Comment on "Viscous cosmology in the Kasner metric"

abstract:
  We show in this comment that in an anisotropic Bianchi type I model of the
Kasner form, it is not possible to describe the growth of entropy, if we want
to keep the thermodynamics together with the dominant energy conditions. This
consequence disagrees with the results obtained by Brevik and Pettersen [Phys.
Rev. D 56, 3322 (1997)].


title: Generalized entropy and Noether charge

abstract:
  We find an expression for the generalized gravitational entropy of Hawking in
terms of Noether charge. As an example, the entropy of the Taub-Bolt spacetime
is calculated.


title: Signature Changing Space-times and the New Generalised Functions

abstract:
  A signature changing spacetime is one where an initially Riemannian manifold
with Euclidean signature evolves into the Lorentzian universe we see today.
This concept is motivated by problems in causality implied by the isotropy and
homogeneity of the universe. As initially time and space are indistinguishable
in signature change, these problems are removed. There has been some dispute as
to the nature of the junction conditions across the signature change, and in
particular, whether or not the metric is continuous there. We determine to what
extent the Colombeau algebra of new generalised functions resolves this dispute
by analysing both types of signature change within its framework. A covariant
formulation of the Colombeau algebra is used, in which the usual properties of
the new generalised functions are extended. We find that the Colombeau algebra
is insufficient to preclude either continuous or discontinuous signature
change, and is also unable to settle the dispute over the nature of the
junction conditions.


title:
Approximate equation relevant to axial oscillations on slowly rotating
  relativistic stars

abstract:
  Axial oscillations relevant to the r-mode instability are studied with slow
rotation formalism in general relativity. The approximate equation governing
the oscillations is derived with second-order rotational corrections. The
equation contains an effective 'viscosity-like' term, which originates from
coupling to the polar g-mode displacements. The term plays a crucial role on
the resonance point, where the disturbance on the rotating stars satisfies a
certain condition at the lowest order equation. The effect is significant for
newly born hot neutron stars, which are expected to be subject to the
gravitational radiation driven instability of the r-mode.


title:
Warm inflation: Towards a realistic COBE data power spectrum for matter
  and metric thermal coupled fluctuations

abstract:
  I consider the COBE data coarse-grained field that characterize the now
observable universe for a model of warm inflation which takes into account the
thermal coupled fluctuations of the scalar field with the thermal bath. The
power spectrum for both, matter and metric fluctuations are analyzed. I find
that the amplitude for the fluctuations of the metric when the horizon entry,
should be very small for the expected values of temperature.


title: Closed cosmologies with a perfect fluid and a scalar field

abstract:
  Closed, spatially homogeneous cosmological models with a perfect fluid and a
scalar field with exponential potential are investigated, using dynamical
systems methods. First, we consider the closed Friedmann-Robertson-Walker
models, discussing the global dynamics in detail. Next, we investigate
Kantowski-Sachs models, for which the future and past attractors are
determined. The global asymptotic behaviour of both the
Friedmann-Robertson-Walker and the Kantowski-Sachs models is that they either
expand from an initial singularity, reach a maximum expansion and thereafter
recollapse to a final singularity (for all values of the potential parameter
kappa), or else they expand forever towards a flat power-law inflationary
solution (when kappa^2<2). As an illustration of the intermediate dynamical
behaviour of the Kantowski-Sachs models, we examine the cases of no barotropic
fluid, and of a massless scalar field in detail. We also briefly discuss
Bianchi type IX models.


title:
Entropies of Rotating Charged Black Holes from Conformal Field Theory at
  Killing Horizons

abstract:
  The covariant phase technique is used to compute the constraint algebra of
the stationary axisymmetric charged black hole. A standard Virasoro subalgebra
with corresponding central charge is constructed at a Killing horizon with
Carlip's boundary conditions. For the Kerr-Newman black hole and the
Kerr-Newman-AdS black hole, the density of states determined by conformal
fields theory methods yields the statistical entropy which agrees with the
Bekenstein-Hawking entropy.


title: Generic Tracking of Multiple Apparent Horizons with Level Flow

abstract:
  We report the development of the first apparent horizon locator capable of
finding multiple apparent horizons in a ``generic'' numerical black hole
spacetime. We use a level-flow method which, starting from a single arbitrary
initial trial surface, can undergo topology changes as it flows towards
disjoint apparent horizons if they are present. The level flow method has two
advantages: 1) The solution is independent of changes in the initial guess and
2) The solution can have multiple components. We illustrate our method of
locating apparent horizons by tracking horizon components in a short
Kerr-Schild binary black hole grazing collision.


title: Quantum Lightcone Fluctuations in Theories with Extra Dimensions

abstract:
  The effects of small extra dimensions upon quantum fluctuations of the
lightcone are examined. We argue that compactified extra dimensions modify the
quantum fluctuations of gravitational field so as to induce lightcone
fluctuations. This phenomenon can be viewed as being related to the Casimir
effect. The observable manifestation of the lightcone fluctuations is
broadening of spectral lines from distant sources. In this paper, we further
develop the formalism used to describe the lightcone fluctuations, and then
perform explicit calculations for several models with flat extra dimensions. In
the case of one extra compactified dimension, we find a large effect which
places severe constraints on such models. When there is more than one
compactified dimension, the effect is much weaker and does not place a
meaningful constraint. We also discuss some brane worlds scenarios, in which
gravitons satisfy Dirichlet or Neumann boundary conditions on parallel
four-dimensional branes, separated by one or more flat extra dimensions.


title:
Sub-Microarcsecond Astrometry and New Horizons in Relativistic
  Gravitational Physics

abstract:
  Attaining the limit of sub-microarcsecond optical resolution will completely
revolutionize fundamental astrometry by merging it with relativistic
gravitational physics. Beyond the sub-microarcsecond threshold, one will meet
in the sky a new population of physical phenomena caused by primordial
gravitational waves from early universe and/or different localized astronomical
sources, space-time topological defects, moving gravitational lenses, time
variability of gravitational fields of the solar system and binary stars, and
many others. Adequate physical interpretation of these yet undetectable
sub-microarcsecond phenomena can not be achieved on the ground of the
"standard" post-Newtonian approach (PNA), which is valid only in the near-zone
of astronomical objects having a time-dependent gravitational field. We
describe a new, post-Minkowskian relativistic approach for modeling astrometric
observations having sub-microarcsecond precision and briefly discuss the
light-propagation effects caused by gravitational waves and other phenomena
related to time-dependent gravitational fields. The domain of applicability of
the PNA in relativistic space astrometry is explicitly outlined.


title: Notes on causal differencing in ADM/CADM formulations: a 1D comparison

abstract:
  Causal differencing has shown to be one of the promising and successful
approaches towards excising curvature singularities from numerical simulations
of black hole spacetimes. So far it has only been actively implemented in the
ADM and Einstein-Bianchi 3+1 formulations of the Einstein equations. Recently,
an approach closely related to the ADM one, commonly referred to as as
``conformal ADM'' (CADM) has shown excellent results when modeling waves on
flat spacetimes and black hole spacetimes where singularity avoiding slices are
used to deal with the singularity. In these cases, the use of CADM has yielded
longer evolutions and better outer boundary dependence than those obtained with
the ADM one. If this success translates to the case where excision is
implemented, then the CADM formulation will likely be a prime candidate for
modeling generic black hole spacetimes. In the present work we investigate the
applicability of causal differencing to CADM, presenting the equations in a
convenient way for such a goal and compare its application with the ADM
approach in 1D.


title: Precanonical Perspective in Quantum Gravity

abstract:
  Quantization of general relativity in metric variables using ``precanonical''
quantization based on the De Donder-Weyl covariant Hamiltonian formulation is
outlined. Elements of classical geometry needed to formulate the (Dirac-like)
wave equation emerge from a self-consistency with the underlying quantum
dynamics of the metric. In this sense the formulation can be viewed as
independent from an arbitrarily fixed background.


title:
Compatibility of the expansive nondecelerative universe model with the
  Newton gravitational theory and the general theory of relativity

abstract:
  Applying the Vaidya metrics in the model of Expansive Nondecelerative
Universe (ENU) leads to compatibility of the ENU model both with the classic
Newton gravitational theory and the general theory of relativity in weak fields


title: Black Holes with Zero Mass

abstract:
  We consider the spacetimes corresponding to static Global Monopoles with
interior boundaries corresponding to a Black Hole Horizon and analyze the
behavior of the appropriate ADM mass as a function of the horizon radius r_H.
We find that for small enough r_H, this mass is negative as in the case of the
regular global monopoles, but that for large enough r_H the mass becomes
positive encountering an intermediate value for which we have a Black Hole with
zero ADM mass.


title: Isotropization of two-component fluids

abstract:
  We consider the problem of late-time isotropization in spatially homogeneous
but anisotropic cosmological models when the source of the gravitational field
consists of two non-interacting perfect fluids -- one tilted and one
non-tilted. In particular, we study irrotational Bianchi type V models. By
introducing appropriate dimensionless variables, a full global understanding of
the state space of the gravitational field equations becomes possible. The
issue of isotropization can then be addressed in a simple fashion. We also
discuss implications for the cosmic ``no-hair'' theorem for Bianchi models when
part of the source is a tilted fluid.


title: Classical Geometry from a Physical State in Canonical Quantum Gravity

abstract:
  We construct a weave state which approximates a degenerate 3-metric of rank 2
at large scales. It turns out that a non-degenerate metric region can be
evolved from this degenerate metric by the classical Ashtekar equations, hence
the degeneracy of 3-metrics is not preserved by the evolution of Ashtekar's
equations. As the s-knot state corresponding to this weave is shown to solve
all the quantum constraints in loop quantum gravity, a physical state in
canonical quantum gravity is related to the familiar classical geometry.


title: Gravitating BIon and BIon black hole with dilaton

abstract:
  We construct static and spherically symmetric particle-like and black hole
solutions with magnetic or electric charge in the Einstein-Born-Infeld-dilaton
system, which is a generalization of the Einstein-Maxwell-dilaton (EMD) system
and of the Einstein-Born-Infeld (EBI) system. They have remarkable properties
which are not seen for the corresponding solutions in the EBI and the EMD
system.


title: Equivalent frames in Brans-Dicke theory

abstract:
  We discuss the physical equivalence between the Einstein and Jordan frames in
Brans-Dicke theory. The inequivalence of conformal transformed theories is
clarified with the help of an old equivalence theorem of Chrisholm's.


title:
Equilibrium Configuration of Black Holes and the Inverse Scattering
  Method

abstract:
  The inverse scattering method is applied to the investigation of the
equilibrium configuration of black holes. A study of the boundary problem
corresponding to this configuration shows that any axially symmetric,
stationary solution of the Einstein equations with disconnected event horizon
must belong to the class of Belinskii-Zakharov solutions. Relationships between
the angular momenta and angular velocities of black holes are derived.


title: Quasi-Local Conservation Equations in General Relativity

abstract:
  A set of exact quasi-local conservation equations is derived from the
Einstein's equations using the first-order Kaluza-Klein formalism of general
relativity in the (2,2)-splitting of 4-dimensional spacetime. These equations
are interpreted as quasi-local energy, momentum, and angular momentum
conservation equations. In the asymptotic region of asymptotically flat
spacetimes, it is shown that the quasi-local energy and energy-flux integral
reduce to the Bondi energy and energy-flux, respectively. In spherically
symmetric spacetimes, the quasi-local energy becomes the Misner-Sharp energy.
Moreover, on the event horizon of a general dynamical black hole, the
quasi-local energy conservation equation coincides with the conservation
equation studied by Thorne {\it et al}. We discuss the remaining quasi-local
conservation equations briefly.


title: Gravitational wave bursts from cosmic strings

abstract:
  Cusps of cosmic strings emit strong beams of high-frequency gravitational
waves (GW). As a consequence of these beams, the stochastic ensemble of
gravitational waves generated by a cosmological network of oscillating loops is
strongly non Gaussian, and includes occasional sharp bursts that stand above
the rms GW background. These bursts might be detectable by the planned GW
detectors LIGO/VIRGO and LISA for string tensions as small as $G \mu \sim
10^{-13}$. The GW bursts discussed here might be accompanied by Gamma Ray
Bursts.


title:
Covariant Vortex In Superconducting-Superfluid-Normal Fluid Mixtures
  with Stiff Equation of State

abstract:
  The integrals of motion for a cylindrically symmetric stationary vortex are
obtained in a covariant description of a mixture of interacting
superconductors, superfluids and normal fluids. The relevant integrated
stress-energy coefficients for the vortex with respect to a vortex-free
reference state are calculated in the approximation of a ``stiff'', i.e. least
compressible, relativistic equation of state for the fluid mixture. As an
illustration of the foregoing general results, we discuss their application to
some of the well known examples of ``real'' superfluid and superconducting
systems that are contained as special cases. These include Landau's two-fluid
model, uncharged binary superfluid mixtures, rotating conventional
superconductors and the superfluid neutron-proton-electron plasma in the outer
core of neutron stars.


title: Loops and Knots as Topoi of Substance. Spinoza Revisited

abstract:
  The relationship between modern philosophy and physics is discussed. It is
shown that the latter develops some need for a modernized metaphysics which
shows up as an ultima philosophia of considerable heuristic value, rather than
as the prima philosophia in the Aristotelian sense as it had been intended, in
the first place. It is shown then, that it is the philosophy of Spinoza in
fact, that can still serve as a paradigm for such an approach. In particular,
Spinoza's concept of infinite substance is compared with the philosophical
implications of the foundational aspects of modern physical theory. Various
connotations of sub-stance are discussed within pre-geometric theories,
especially with a view to the role of spin networks within quantum gravity. It
is found to be useful to intro-duce a separation into physics then, so as to
differ between foundational and empirical theories, respectively. This leads to
a straightforward connection bet-ween foundational theories and speculative
philosophy on the one hand, and between empirical theories and sceptical
philosophy on the other. This might help in the end, to clarify some recent
problems, such as the absence of time and causality at a fundamental level. It
is implied that recent results relating to topos theory might open the way
towards eventually deriving logic from physics, and also towards a possible
transition from logic to hermeneutic.


title: Misner-brane cosmology

abstract:
  A brane universe derived from the Randall-Sundrum models is considered in
which an additional Misner-like periodicity is introduced in the extra
direction. This model solves the ambiguity in the choice of the brane world by
identifying the branes with opposite tensions, in such a way that if one enters
the brane with positive tension, one finds oneself emerging from the brane with
negative tension, without having experienced any tension. We show that the
cosmological evolution resulting from this model matches that of the standard
Friedmann scenario, at least in the radiation dominated era, and that there
exist closed timelike curves only in the bulk, but not in the branes which are
chronologically protected from causality violations by quantum-mechanically
stable chronology horizons.


title:
Large-distance behaviour of the graviton two-point function in de Sitter
  spacetime

abstract:
  It is known that the graviton two-point function for the de Sitter invariant
"Euclidean" vacuum in a physical gauge grows logarithmically with distance in
spatially-flat de Sitter spacetime. We show that this logarithmic behaviour is
a gauge artifact by explicitly demonstrating that the same behaviour can be
reproduced by a pure-gauge two-point function.


title: Causal relation between regions I and IV of the Kruskal extension

abstract:
  By extending the exterior Schwarzschild spacetime in two opposite directions
with the Kruskal method, we get an extension which has the same T-X spacetime
diagram as has the conventional Kruskal extension, while allowing its regions I
and IV to correspond to different directions of the original spacetime. We
further extend the exterior Schwarzschild spacetime in all directions and get a
4-dimensional form of the Kruskal extension. The new form of extension includes
the conventional one as a part of itself. From the point of view of the
4-dimensional form, region IV of the conventional extension does not belong to
another universe but is a portion of the same exterior Schwarzschild spacetime
that contains region I. The two regions are causally related: particles can
move from one to the other.


title: Einstein--Proca model: spherically symmetric solutions

abstract:
  The Proca wave equation describes a classical massive spin 1 particle. We
analyze the gravitational interaction of this vector field. In particular, the
spherically symmetric solutions of the Einstein-Proca coupled system are
obtained numerically. Although at infinity the metric field approaches the
usual Schwarzschild (Reissner-Nordstr\"om) limit, we demonstrate the absence of
black hole type configurations.


title: Rigidly rotating dust in general relativity

abstract:
  A solution to the Einstein field equations that represents a rigidly rotating
dust accompanied by a thin matter shell of the same type is found.


title: Post-Newtonian Frames of Reference

abstract:
  A general theory of frames of reference proposed in a preceding publication
is considered here in the framework of the post-Newtonian approximation,
assuming that the frame of reference is centered on a time-like geodesic. The
problem of taking into account the rotation of the frame of reference, which is
usually ignored or incorrectly oversimplified, is here discussed in detail and
solved.


title: Excitation of Neutron Star Oscillations by an Orbiting Particle

abstract:
  The excitation of neutron stars is expected to be an important source of
gravitational radiation. Of fundamental importance is then to investigate
mechanisms that trigger oscillations in neutron stars in order to characterize
the emitted radiation. We present results from a numerical study of the
even-parity gravitational radiation generated from a particle orbiting a
neutron star. We focus our investigation on those conditions on the orbital
parameters that favor the excitation of $w$-modes. We find that, for
astrophysically realistic conditions, there is practically no $w$-mode
contribution to the emitted radiation. Only for particles with
ultra-relativistic orbital speeds $\ge 0.9c$, the $w$-mode does significantly
contribute to the total emitted gravitational energy. We also stress the
importance of setting consistent initial configurations.


title:
Hyperbolic formulations and numerical relativity: Experiments using
  Ashtekar's connection variables

abstract:
  In order to perform accurate and stable long-time numerical integration of
the Einstein equation, several hyperbolic systems have been proposed. We here
present numerical comparisons between weakly hyperbolic, strongly hyperbolic,
and symmetric hyperbolic systems based on Ashtekar's connection variables. The
primary advantage for using this connection formulation in this experiment is
that we can keep using the same dynamical variables for all levels of
hyperbolicity. Our numerical code demonstrates gravitational wave propagation
in plane symmetric spacetimes, and we compare the accuracy of the simulation by
monitoring the violation of the constraints. By comparing with results obtained
from the weakly hyperbolic system, we observe the strongly and symmetric
hyperbolic system show better numerical performance (yield less constraint
violation), but not so much difference between the latter two. Rather, we find
that the symmetric hyperbolic system is not always the best in numerical
performances.
  This study is the premier to present full numerical simulations using
Ashtekar's variables. We also describe our procedures in detail.


title:
Existence of Noncompact Static Spherically Symmetric Solutions of
  Einstein SU(2) Yang Mills Equations with small Cosmological Constant

abstract:
  We consider static spherically symmetric solutions of Einstein's equations
coupled to an SU(2) Yang Mills field that are smooth at the center of spherical
symmetry. We prove that with small cosmological constant there exist solutions
that possess a coordinate singularity at some r that is not maximum. The
singularity can be removed with a Kruskal-like change of coordinates.


title:
Far Field Behavior of Noncompact Static Spherically Symmetric Solutions
  of Einstein SU(2) Yang Mills Equations

abstract:
  The Einstein equations with small positive cosmological constant coupled to
an SU(2) Yang Mills field admits solutions that possess a coordinate
singularity at a noncritical radius. Here, we prove that these solutions are
otherwise globally smooth and that they asymptotically approach Schwarzschild
deSitter space with a vanishing Yang Mills field.


title:
A Classification of Spherically Symmetric Static Solutions of SU(2)
  Einstein Yang Mills Equations with Non-negative Cosmological Constant

abstract:
  We categorize the global structure of spherically symmetric static solutions
of Einstein SU(2) Yang Mills equations with positive cosmological constant that
are smooth at the center of spherical symmetry.


title: Monopole Black Hole Skyrmions

abstract:
  Charged black hole solutions with pion hair are discussed. These can be used
to study monopole black hole catalysis of proton decay. There also exist multi-
black hole skyrmion solutions with BPS monopole behavior.


title: Wormhole with Quantum Throat

abstract:
  A wormhole with a quantum throat on the basis of an approximate model of the
spacetime foam is presented. An effective spinor field is introduced for the
description of the spacetime foam. The consequences of such model of the
wormhole is preventing a "naked'' singularity in the Reissner-Nordstr\"om
solution with $|e|/m > 1$.


title: Large "Dipolar" Vacuum Fluctuations in Quantum Gravity

abstract:
  We study a novel set of gravitational field configurations, called "dipolar
zero modes", which give an exactly null contribution to the Einstein action and
are thus candidates to become large fluctuations in the quantized theory. They
are generated by static unphysical sources satisfying (up to terms of order
G^2) the simple condition Int d^3x T_00(x) = 0. We give two explicit examples
of virtual sources: (i) a "mass dipole" consisting of two separated mass
distributions with different signs; (ii) two concentric "+/- shells". The field
fluctuations can be large even at macroscopic scale. There are some, for
instance, which last ~ 1 s or more and correspond to the field generated by a
virtual source with size ~ 1 cm and mass ~ 10^6 g. This appears paradoxical,
for several reasons, both theoretical and phenomenological. We also give an
estimate of possible suppression effects following the addition to the pure
Einstein action of cosmological or R^2 terms.


title:
Boundary conditions for the spinor field in Rindler spacetime and the
  quantum field theoretical basis of the Unruh effect

abstract:
  We analyse the quantization procedure of the spinor field in the Rindler
spacetime, showing the boundary conditions that should be imposed to the field,
in order to have a well posed theory. Because of these boundary conditions we
argue that this construction and the usual one in Minkowski spacetime are
qualitatively different and can not be compared and consequently the
conventional interpretation of the Unruh effect, that is the thermal nature of
the Minkowski vacuum state from the point of view of an accelerated observer,
is questionable. We also analyse in detail the Unruh quantization scheme and we
show that it is not valid in the whole Minkowski space but only in the double
Rindler wedge, and it cannot be used as a basis for a quantum theoretical proof
of the Unruh effect.


title: Chaplygin-like gas and branes in black hole bulks

abstract:
  We explore the possibility to locate a brane in black hole bulks. We study
explicitly the cases of BHTZ and Schwarzschild-anti de Sitter (AdS) black
holes. Our result is that in these cases branes cannot be supported by brane
tension alone and it is necessary to introduce other forms of matter on the
brane. We find classes of perfect fluid solutions obeying to peculiar state
equations. For the case of BHTZ bulk geometry the state equation takes exactly
the form of a ``Chaplygin gas'', which is relevant in the brane context. In the
Schwarzschild-AdS case we find new state equations which reduce to the
Chaplygin form when the brane is located near the horizon.


title:
A Nearly Minimum Redundant Correlator Interpolation Formula for
  Gravitational Wave Chirp Detection

abstract:
  An absolute lower bound on the number of templates needed to keep the fitting
factor above a prescribed minimal value $\Gamma$ in correlator bank detection
of (newtonian) gravitational wave chirps from unknown inspiraling compact
binary sources is derived, resorting to the theory of quasi-bandlimited
functions in the $L^\infty$ norm. An explicit nearly-minimum redundant
cardinal-interpolation formula for the (reduced, noncoherent) correlator is
introduced. Its computational burden and statistical properties are compared to
those of the plain lattice of (reduced, noncoherent) correlators, for the same
$\Gamma$. Extension to post-newtonian models is outlined.


title: Gaussian superpositions in scalar-tensor quantum cosmological models

abstract:
  A free scalar field minimally coupled to gravity model is quantized and the
Wheeler-DeWitt equation in minisuperspace is solved analytically, exhibiting
positive and negative frequency modes. The analysis is performed for positive,
negative and zero values of the curvature of the spatial section. Gaussian
superpositions of the modes are constructed, and the quantum bohmian
trajectories are determined in the framework of the Bohm-de Broglie
interpretation of quantum cosmology. Oscillating universes appear in all cases,
but with a characteristic scale of the order of the Planck scale. Bouncing
regular solutions emerge for the flat curvature case. They contract classically
from infinity until a minimum size, where quantum effects become important
acting as repulsive forces avoiding the singularity and creating an
inflationary phase, expanding afterwards to an infinite size, approaching the
classical expansion as long as the scale factor increases. These are
non-singular solutions which are viable models to describe the early Universe.


title:
Relativity of spatial scale and of the Hubble flow: The logical
  foundations of relativity and cosmology

abstract:
  Formalising the logical dependence of physical quantities on material
referents of scale, I show that both Hubble's law and the cosmological constant
are in fact exactly replicable by a spatial contraction of referents locally on
earth, and that the Pioneer anomaly is irrefutable indication that this is the
case. The formalism literally embodies Feynman's ``hot-plate'' model,
predictably yielding a logical derivation of the relativity postulates, and
importantly, suffices to demonstrate the inherent logical consistency of
general relativity and quantum mechanics, whose foundations I have shown
separately to be fundamentally computational. I further show that the spatial
contraction of our referents also accounts for considerable planetary and
geological data inexplicable in the standard model, and predicts that the
Hubble flow appears differently or is altogether absent from platforms in deep
space, depending on the local physics.


title: Exact Inflationary Solutions from a Superpotential

abstract:
  We propose a novel, potentially useful generating technique for constructing
exact solutions of inflationary scalar field cosmologies with non-trivial
potentials. The generating scheme uses the so-called superpotential and is
inspired by recent studies of similar equations in supergravity. Some exact
solutions are derived, and the physical meaning of the superpotential in these
models is clarified.


title: Black hole solutions in Euler-Heisenberg theory

abstract:
  We construct static and spherically symmetric black hole solutions in the
Einstein-Euler-Heisenberg (EEH) system which is considered as an effective
action of a superstring theory. We considered electrically charged,
magnetically charged and dyon solutions. We can solve analytically for the
magnetically charged case. We find that they have some remarkable properties
about causality and black hole thermodynamics depending on the coupling
constant of the EH theory $a$ and $b$, though they have central singularity as
in the Schwarzschild black hole.


title: Logarithmic Corrections to Black Hole Entropy from the Cardy Formula

abstract:
  Many recent attempts to calculate black hole entropy from first principles
rely on conformal field theory techniques. By examining the logarithmic
corrections to the Cardy formula, I compute the first-order quantum correction
to the Bekenstein-Hawking entropy in several models, including those based on
asymptotic symmetries, horizon symmetries, and certain string theories. Despite
very different physical assumptions, these models all give a correction
proportional to the logarithm of the horizon size, and agree qualitatively with
recent results from ``quantum geometry'' in 3+1 dimensions. There are some
indications that even the coefficient of the correction may be universal, up to
differences that depend on the treatment of angular momentum and conserved
charges.


title: Wave propagation in linear electrodynamics

abstract:
  The Fresnel equation governing the propagation of electromagnetic waves for
the most general linear constitutive law is derived. The wave normals are found
to lie, in general, on a fourth order surface. When the constitutive
coefficients satisfy the so-called reciprocity or closure relation, one can
define a duality operator on the space of the two-forms. We prove that the
closure relation is a sufficient condition for the reduction of the fourth
order surface to the familiar second order light cone structure. We finally
study whether this condition is also necessary.


title:
Classical and Quantum Surgery of Geometries in an Open Inflationary
  Universe

abstract:
  We study classically and quantum mechanically the Euclidean geometries
compatible with an open inflationary universe of a Lorentzian geometry. The
Lorentzian geometry of the open universe with an ordinary matter state matches
either an open or a closed Euclidean geometry at the cosmological singularity.
With an exotic matter state it matches only the open Euclidean geometry and
describes a genuine instanton regular at the boundary of a finite radius. The
wave functions are found that describe the quantum creation of the open
inflationary universe.


title:
Covariant two point function for minimally coupled scalar field in de
  Sitter space-time

abstract:
  In a recent paper [1], it has been shown that negative norm states are
indispensable for a fully covariant quantization of the minimally coupled
scalar field in de Sitter space. Their presence, while leaving unchanged the
physical content of the theory, offers an automatic and covariant
renormalization of the vacuum energy divergence. This paper is a completion of
our previous work. An explicit construction of the covariant two-point function
of the ``massless'' minimally coupled scalar field in de Sitter space is given,
which is free of any infrared divergence. The associated Schwinger commutator
function and retarded Green's function are calculated in a fully gauge
invariant way, which also means coordinate independent.


title:
On the extension of the concept of Thin Shells to The Einstein-Cartan
  Theory

abstract:
  This paper develops a theory of thin shells within the context of the
Einstein-Cartan theory by extending the known formalism of general relativity.
In order to perform such an extension, we require the general non symmetric
stress-energy tensor to be conserved leading, as Cartan pointed out himself, to
a strong constraint relating curvature and torsion of spacetime. When we
restrict ourselves to the class of space-times satisfying this constraint, we
are able to properly describe thin shells and derive the general expression of
surface stress-energy tensor both in its four-dimensional and in its
three-dimensional intrinsic form. We finally derive a general family of static
solutions of the Einstein-Cartan theory exhibiting a natural family of null
hypersurfaces and use it to apply our formalism to the construction of a null
shell of matter.


title: Thick Domain Walls Intersecting a Black Hole

abstract:
  We discuss the gravitationally interacting system of a thick domain wall and
a black hole. We numerically solve the scalar field equation in the
Schwarzschild spacetime and show that there exist scalar field configurations
representing thick domain walls intersecting the black hole.


title: Semiclassical Cosmological Perturbations Generated during Inflation

abstract:
  Environment interaction may induce stochastic semiclassical dynamics in open
quantum systems. In the gravitational context, stress-energy fluctuations of
quantum matter fields give rise to a stochastic behaviour in the spacetime
geometry. Einstein-Langevin equation is a suitable tool to take these effects
into account when addressing the back-reaction problem in semiclassical
gravity. We analyze within this framework the generation of gravitational
fluctuations during inflation, which are of great interest for large-scale
structure formation in cosmology.


title: Cosmic microwave background anisotropies seeded by incoherent sources

abstract:
  The cosmic microwave background anisotropies produced by active seeds, such
as topological defects, have been computed recently for a variety of models by
a number of authors. In this paper we show how the generic features of the
anisotropies caused by active, incoherent, seeds (that is the absence of
acoustic peaks at small scales) can be obtained semi-analytically, without
entering into the model dependent details of their formation, structure and
evolution.


title:
Anholonomic Soliton-Dilaton and Black Hole Solutions in General
  Relativity

abstract:
  A new method of construction of integral varieties of Einstein equations in
three dimensional (3D) and 4D gravity is presented whereby, under corresponding
redefinition of physical values with respect to anholonomic frames of reference
with associated nonlinear connections, the structure of gravity field equations
is substantially simplified. It is shown that there are 4D solutions of
Einstein equations which are constructed as nonlinear superpositions of soliton
solutions of 2D (pseudo) Euclidean sine-Gordon equations (or of Lorentzian
black holes in Jackiw-Teitelboim dilaton gravity). The Belinski-Zakharov-Meison
solitons for vacuum gravitational field equations are generalized to various
cases of two and three coordinate dependencies, local anisotropy and matter
sources. The general framework of this study is based on investigation of
anholonomic soliton-dilaton black hole structures in general relativity. We
prove that there are possible static and dynamical black hole, black torus and
disk/cylinder like solutions (of non-vacuum gravitational field equations) with
horizons being parametrized by hypersurface equations of rotation ellipsoid,
torus, cylinder and another type configurations. Solutions describing locally
anisotropic variants of the Schwarzschild-- Kerr (black hole), Weyl
(cylindrical symmetry) and Neugebauer--Meinel (disk) solutions with anisotropic
variable masses, distributions of matter and interaction constants are shown to
be contained in Einstein's gravity. It is demonstrated in which manner locally
anisotropic multi-soliton-- dilaton-black hole type solutions can be generated.


title: Cylindrical sources in full Einstein and Brans-Dicke gravity

abstract:
  It was shown by Hiscock that the energy-momentum tensor commonly used to
model local cosmic strings in linearized Einstein gravity can be extended and
used in the full theory, obtaining a metric in the exterior of the source with
the same deficit angle. Here we show that this tensor is an exception within a
family for which a static solution does not exist in full Einstein nor in
Brans-Dicke gravity.


title:
Relative velocity and relative acceleration induced by the torsion in
  (pseudo) Riemannian spaces with torsion and in spaces with an affine
  connection and metrics

abstract:
  The influence of the torsion on the relative velocity and on the relative
acceleration between particles (points) in spaces with an affine connection and
a metric [$(L_n,g)$-spaces] and in (pseudo) Riemannian spaces with torsion
($U_n$-spaces) is considered. Necessary and sufficient conditions as well as
only necessary and only sufficient conditions for vanishing deformation, shear,
rotation and expansion are found. The notion of relative acceleration and the
related to it notions of shear, rotation and expansion accelerations induced by
the torsion are determined. It is shown that the kinematic characteristics
induced by the torsion (shear acceleration, rotation acceleration and expansion
acceleration) could play the same role as the kinematic characteristics induced
by the curvature and can (under given conditions) compensate their action as
well as the action of external forces.
  The change of the rate of change of the length of a deviation vector field is
given in explicit form for $(L_n,g)$- and $U_n$-spaces.
  PACS numbers: 04.90+e, 04.50+h, 12.10.Gq, 03.40.-t


title:
Absence of Static, Spherically Symmetric Black Hole Solutions for
  Einstein-Dirac-Yang/Mills Equations with Complete Fermion Shells

abstract:
  We study a static, spherically symmetric system of (2j+1) massive Dirac
particles, each having angular momentum j, j=1,2,..., in a classical
gravitational and SU(2) Yang-Mills field. We show that for any black hole
solution of the associated Einstein-Dirac-Yang/Mills equations, the spinors
must vanish identically outside of the event horizon.


title: Excitation of Kaluza-Klein modes of U(1) field by parametric resonance

abstract:
  In this paper, based on the theory of parametric resonance, we propose a
cosmological criterion on ways of compactification: we rule out such a model of
compactification that there exists a Kaluza-Klein mode satisfying
$2m_{KK}=\omega_b$, where $m_{KK}$ is mass of the Kaluza-Klein mode and
$\omega_b$ is the frequency of oscillation of the radius of the compact
manifold on which extra dimensions are compactified. This is a restatement of
the criterion proposed previously [S. Mukohyama, Phys. Rev. {\bf D57}, 6191
(1998)]. As an example, we consider a model of compactification by a sphere and
investigate Kaluza-Klein modes of U(1) field. In this case the parametric
resonance is so mild that the sphere model is not ruled out.


title:
Axiomatic approach to radiation reaction of scalar point particles in
  curved spacetime

abstract:
  Several different methods have recently been proposed for calculating the
motion of a point particle coupled to a linearized gravitational field on a
curved background. These proposals are motivated by the hope that the point
particle system will accurately model certain astrophysical systems which are
promising candidates for observation by the new generation of gravitational
wave detectors. Because of its mathematical simplicity, the analogous system
consisting of a point particle coupled to a scalar field provides a useful
context in which to investigate these proposed methods. In this paper, we
generalize the axiomatic approach of Quinn and Wald in order to produce a
general expression for the self force on a point particle coupled to a scalar
field following an arbitrary trajectory on a curved background. Our equation
includes the leading order effects of the particle's own fields, commonly
referred to as ``self force'' or ``radiation reaction'' effects. We then
explore the equations of motion which follow from this expression in the
absence of non-scalar forces.


title: Black holes and closed trapped surfaces: a revision of a classic theorem

abstract:
  It is standard assertion in relativity that, subject to an energy condition
and the cosmic censorship hypothesis, closed trapped surfaces are not visible
from future null infinity. A proof given by Hawking & Ellis in ''The Large
Scale Structure of Space-Time'' is flawed since it is formulated in terms of an
inadequate definition of a weakly asymptotically simple and empty space-time. A
new proof is given based on a more restrictive definition of a weakly
asymptotically simple and empty space-time.


title:
Isotropization of Bianchi type models and a new FRW solution in
  Brans-Dicke theory

abstract:
  Using scaled variables we are able to integrate an equation valid for
isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD)
theory. We analyze known and new solutions for these models in relation with
the possibility that anisotropic models asymptotically isotropize, and/or
possess inflationary properties. In particular, a new solution of curve
($k\neq0$) Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory
is analyzed.


title: On the Tensor Field Inflation in the GR Homogeneous Cosmological Model

abstract:
  The homogeneous cosmological model in GR is proposed, where the vacuum
energy, which can cause the inflation, is described by tensor field rather than
by commonly used in inflationary scenarios scalar field. It is shown that if
the initial values of the field are sufficiently big (comparable with the
Planck units), under the condition of the tensor field's slow change in the
beginning the regime of the quasiexponential inflation can exist. Numerical
solutions for the inflationary stage are obtained that confirm the validity of
the approximate solutions. Inflation takes place under wide range of initial
conditions provided that the tensor field satisfies the condition imposed on
the initial values of the tensor field ${\phi^0}_0(0)\approx -{\phi^i}_i(0)$
(i=1,2,3). That condition also arises from the requirement to satisfy existing
observational data.


title:
On the determination of the last stable orbit for circular general
  relativistic binaries at the third post-Newtonian approximation

abstract:
  We discuss the analytical determination of the location of the Last Stable
Orbit (LSO) in circular general relativistic orbits of two point masses. We use
several different ``resummation methods'' (including new ones) based on the
consideration of gauge-invariant functions, and compare the results they give
at the third post-Newtonian (3PN) approximation of general relativity. Our
treatment is based on the 3PN Hamiltonian of Jaranowski and Sch\"afer. One of
the new methods we introduce is based on the consideration of the (invariant)
function linking the angular momentum and the angular frequency. We also
generalize the ``effective one-body'' approach of Buonanno and Damour by
introducing a non-minimal (i.e. ``non-geodesic'') effective dynamics at the 3PN
level. We find that the location of the LSO sensitively depends on the
(currently unknown) value of the dimensionless quantity $\oms$ which
parametrizes a certain regularization ambiguity of the 3PN dynamics. We find,
however, that all the analytical methods we use numerically agree between
themselves if the value of this parameter is $\oms\simeq-9$. This suggests that
the correct value of $\oms$ is near -9 (the precise value
$\oms^*\equiv-{47/3}+{41/64}\pi^2=-9.3439...$ seems to play a special role). If
this is the case, we then show how to further improve the analytical
determination of various LSO quantities by using a ``Shanks'' transformation to
accelerate the convergence of the successive (already resummed) PN estimates.


title: The interaction force between rotating black holes at equilibrium

abstract:
  We study the previously constructed Riemann problem whose solutions
correspond to equilibrium configurations of black holes. We evaluate the metric
coefficients at the symmetry axis and the interaction force between the black
holes.


title: Quantum cosmology of 5D non-compactified Kaluza-Klein theory

abstract:
  We study the quantum cosmology of a five dimensional non-compactified
Kaluza-Klein theory where the 4D metric depends on the fifth coordinate,
$x^4\equiv l$. This model is effectively equivalent to a 4D non-minimally
coupled dilaton field in addition to matter generated on hypersurfaces
l=constant by the extra coordinate dependence in the four-dimensional metric.
We show that the Vilenkin wave function of the universe is more convenient for
this model as it predicts a new-born 4D universe on the $l\simeq0$ constant
hypersurface.


title:
A Conserved Energy Integral for Perturbation Equations in the Kerr-de
  Sitter Geometry

abstract:
  The analytic proof of mode stability of the Kerr black hole was provided by
Whiting. In his proof, the construction of a conserved quantity for unstable
mode was crucial. We extend the method of the analysis for the Kerr-de Sitter
geometry. The perturbation equations of massless fields in the Kerr-de Sitter
geometry can be transformed into Heun's equations which have four regular
singularities. In this paper we investigate differential and integral
transformations of solutions of the equations. Using those we construct a
conserved quantity for unstable modes in the Kerr-de Sitter geometry, and
discuss its property.


title: Plane-fronted waves in metric-affine gravity

abstract:
  We study plane-fronted electrovacuum waves in metric-affine gravity theories
(MAG) with cosmological constant. Their field strengths are, on the
gravitational side, curvature $R_{\alpha}{}^{\beta}$, nonmetricity
$Q_{\alpha\beta}$, torsion $T^{\alpha}$ and, on the matter side, the
electromagnetic field strength $F$. Our starting point is the work by
Ozsv\'ath, Robinson, and R\'ozga on type N gravitational fields in general
relativity as coupled to null electromagnetic fields.


title: On Proper Time in General Relativity

abstract:
  It is shown how the relation $ds=cd\tau$ between the proper distance $s$ and
the proper time $\tau$ is obtained in general relativity. A general relation in
curved spacetime between $d\tau$ and $dt$ is given. This relation reduces to
the special relativistic one for flat spacetime.


title: Advance of Mercury Perihelion Explained by Cogravity

abstract:
  The theory of General Relativity explaines the advance of Mercury perihelion
using space curvature and the Schwartzschild metric. We demonstrate that this
phenomena can also be interpreted due to the cogravitational field produced by
the apparent motion of the Sun around Mercury giving exactly the same estimate
as derived from the Schwartzschild metric in general relativity theory. This is
a surprising result because the estimate from both theoretical approaches match
exactly the measured value. The discussion and implications of this result is
out of the scope of the present work.


title: Comment on "Formation of primordial black holes by cosmic strings"

abstract:
  We show that in a pioneering paper by Polnarev and Zembowicz, some
conclusions concerning the characteristics of the Turok-strings are generally
not correct. In addition we show that the probability of string collapse given
there, is off by a large prefactor (~1000).


title:
Self-force on a scalar particle in spherically-symmetric spacetime via
  mode-sum regularization: radial trajectories

abstract:
  Recently, we proposed a method for calculating the ``radiation reaction''
self-force exerted on a charged particle moving in a strong field orbit in a
black hole spacetime. In this approach, one first calculates the contribution
to the ``tail'' part of the self force due to each multipole mode of the
particle's self field. A certain analytic procedure is then applied to
regularize the (otherwise divergent) sum over modes. This involves the
derivation of certain regularization parameters using local analysis of the
(retarded) Green's function. In the present paper we present a detailed
formulation of this mode-sum regularization scheme for a scalar charge on a
class of static spherically-symmetric backgrounds (including, e.g., the
Schwarzschild, Reissner-Nordstr\"{o}m, and Schwarzschild-de Sitter spacetimes).
We fully implement the regularization scheme for an arbitrary radial trajectory
(not necessarily geodesic) by explicitly calculating all necessary
regularization parameters in this case.


title: Generalized Bowen--York Initial Data

abstract:
  A class of vacuum initial-data sets is described which are based on certain
expressions for the extrinsic curvature first studied and employed by Bowen and
York. These expressions play a role for the momentum constraint of general
relativity which is analogous to the role played by the Coulomb solution for
the Gauss-law constraint of electromagnetism.


title:
Fast and Accurate Computation Tools for Gravitational Waveforms from
  Binary Sistems with any Orbital Eccentricity

abstract:
  The relevance of orbital eccentricity in the detection of gravitational
radiation from (steady state) binary stars is emphasized. Computationnally
effective fast and accurate)tools for constructing gravitational wave templates
from binary stars with any orbital eccentricity are introduced, including tight
estimation criteria of the pertinent truncation and approximation errors.


title:
Extremely charged static perfect fluid distributions with dilaton in
  curved spacetimes

abstract:
  We examine charged static perfect fluid distributions with a dilaton field in
the frame-work of general relativity. We consider the case that the Einstein
equations reduce to a non-linear version of Poisson equation. We show that
Maxwell equation and an equation for a dilaton imply the relation among the
charge, mass and dilatonic charge densities.


title: Self-Dual Conformal Supergravity and the Hamiltonian Formulation

abstract:
  In terms of Dirac matrices the self-dual and anti-self-dual decomposition of
a conformal supergravity is given and a self-dual conformal supergravity theory
is developed as a connection dynamic theory in which the basic dynamic variabes
include the self-dual spin connection i.e. the Ashtekar connection rather than
the triad. The Hamiltonian formulation and the constraints are obtained by
using the Dirac-Bergmann algorithm.
  PACS numbers: 04.20.Cv, 04.20.Fy,04.65.+e


title: Time-Independent Gravitational Fields

abstract:
  This article reviews, from a global point of view, rigorous results on time
independent spacetimes. Throughout attention is confined to isolated bodies at
rest or in uniform rotation in an otherwise empty universe. The discussion
starts from first principles and is, as much as possible, self-contained.


title: Multipole Moments of Static Spacetimes

abstract:
  This paper reviews work, largely due to W. Simon and the author, on multipole
theory of static spacetimes. The main purpose is to make this work, which lies
at the interface of potential theory, conformal geometry and general
relativity, known to mathematicians and to perhaps motivate them to look at the
open problems which still remain.


title: Light propagation in non linear electrodynamics

abstract:
  Working on the approximation of low frequency, we present the light cone
conditions for a class of theories constructed with the two gauge invariants of
the Maxwell field without making use of average over polarization states.
Different polarization states are thus identified describing birefringence
phenomena. We make an application of the formalism to the case of
Euler-Heisenberg effective Lagrangian and well know results are obtained.


title: The geometry of photon surfaces

abstract:
  The photon sphere concept in Schwarzschild space-time is generalized to a
definition of a photon surface in an arbitrary space-time. A photon sphere is
then defined as an SO(3)xR-invariant photon surface in a static spherically
symmetric space-time. It is proved, subject to an energy condition, that a
black hole in any such space-time must be surrounded by a photon sphere.
Conversely, subject to an energy condition, any photon sphere must surround a
black hole, a naked singularity or more than a certain amount of matter. A
second order evolution equation is obtained for the area of an SO(3)-invariant
photon surface in a general non-static spherically symmetric space-time. Many
examples are provided.


abstract:
  The model of a relativistic free massive point particle is investigated in
the context of a Hamiltonian constraint system. It is shown that de Broglie
oscillation, rest mass and inertia may be described within this model of
Hamiltonian constraint system.


title: Cosmic crystallography in a circle

abstract:
  In a circle (an S^1) with circumference 1 assume m objects distributed
pseudo-randomly. In the universal covering R^1 assume the objects replicated
accordingly, and take an interval L>1. In this interval, make the normalized
histogram of the pair separations which are not an integer. The theoretical
(expected) such histogram is obtained in this report, as well as its difference
to a similar histogram for non-replicated objects. The whole study is of
interest for the cosmic crystallography.


title: Quantum Zeno effect and the detection of gravitomagnetism

abstract:
  In this work we introduce two experimental proposals that could shed some
light upon the inertial properties of intrinsic spin. In particular we will
analyze the role that the gravitomagnetic field of the Earth could have on a
quantum system with spin 1/2. We will deduce the expression for Rabi
transitions, which depend, explicitly, on the coupling between the spin of the
quantum system and the gravitomagnetic field of the Earth. Afterwards, the
continuous measurement of the energy of the spin 1/2 system is considered, and
an expression for the emerging quantum Zeno effect is obtained. Thus, it will
be proved that gravitomagnetism, in connection with spin 1/2 systems, could
induce not only Rabi transitions but also a quantum Zeno effect.


title:
An Accelerated Expansion Model in the Absence of the Cosmological
  Constant

abstract:
  Based on some observations, the apparent energy, associated with gravity, of
vacuums is defined, with that of normal vacuums to be zero and that of the
vacuums losing some energy to be negative. An important application of the
energy is its contribution to Einstein's equation. A cosmological model,
accounting for recent observations of the accelerated expansion of the
universe, in the absence of the cosmological constant, can be well constructed.
In a certain case, the expansion of the universe would be decelerated at its
early epoch and accelerated at its late epoch. The curvature of the universe
would depend on the ratio of matter energy to total energy. The missing mass
problem does no longer exist in this model. Most negative apparent energy
vacuums might be contained in voids, then the spacetime of galaxy clusters or
that of the solar system would not be significantly affected by this kind of
energy.


title: Topologically massive magnetic monopoles

abstract:
  We show that in the Maxwell-Chern-Simons theory of topologically massive
electrodynamics the Dirac string of a monopole becomes a cone in anti-de Sitter
space with the opening angle of the cone determined by the topological mass
which in turn is related to the square root of the cosmological constant. This
proves to be an example of a physical system, {\it a priory} completely
unrelated to gravity, which nevertheless requires curved spacetime for its very
existence. We extend this result to topologically massive gravity coupled to
topologically massive electrodynamics in the framework of the theory of Deser,
Jackiw and Templeton. These are homogeneous spaces with conical deficit. Pure
Einstein gravity coupled to Maxwell-Chern-Simons field does not admit such a
monopole solution.


title: Black hole evolution by spectral methods

abstract:
  Current methods of evolving a spacetime containing one or more black holes
are plagued by instabilities that prohibit long-term evolution. Some of these
instabilities may be due to the numerical method used, traditionally finite
differencing. In this paper, we explore the use of a pseudospectral collocation
(PSC) method for the evolution of a spherically symmetric black hole spacetime
in one dimension using a hyperbolic formulation of Einstein's equations. We
demonstrate that our PSC method is able to evolve a spherically symmetric black
hole spacetime forever without enforcing constraints, even if we add dynamics
via a Klein-Gordon scalar field. We find that, in contrast to
finite-differencing methods, black hole excision is a trivial operation using
PSC applied to a hyperbolic formulation of Einstein's equations. We discuss the
extension of this method to three spatial dimensions.


title:
Exact Solutions in Multidimensional Cosmology with Shear and Bulk
  Viscosity

abstract:
  Multidimensional cosmological model describing the evolution of a fluid with
shear and bulk viscosity in $n$ Ricci-flat spaces is investigated. The
barotropic equation of state for the density and the pressure in each space is
assumed. The second equation of state is chosen in the form when the bulk and
the shear viscosity coefficients are inversely proportional to the volume of
the Universe. The integrability of Einstein equations reads as a colinearity
constraint between vectors which are related to constant parameters in the
first and second equations of state. We give exact solutions in a Kasner-like
form. The processes of dynamical compactification and the entropy production
are discussed. The non-singular $D$-dimensional isotropic viscous solution is
singled out.


title:
Detection of gravitational waves from inspiraling compact binaries using
  non-restricted post-Newtonian approximations

abstract:
  The set up of matched filters for the detection of gravitational waves from
in-spiraling compact binaries is usually carried out using the restricted
post-Newtonian approximation: the filter phase is modelled including
post-Newtonian corrections, whereas the amplitude is retained at the Newtonian
order. Here we investigate the effects of the introduction of post-Newtonian
corrections also to the amplitude and we discuss some of the implications for
signal detection and parameter estimation.


title:
LISA observations of massive black holes binaries using post-Newtonian
  wave-forms

abstract:
  We consider LISA observations of in-spiral signals emitted by massive black
hole binary systems in circular orbit and with negligible spins. We study the
accuracy with which the source parameters can be extracted from the data
stream. We show that the use of waveforms retaining post-Newtonian corrections
not only to the phase but also the amplitude can drastically improve the
estimation of some parameters.


title: Laser interferometer gravitational wave detectors

abstract:
  I give a brief introduction on gravitational wave laser interferometers,
possible detectable sources from the ground and noise in the detectors


title: Removal of interference from gravitational wave spectrum

abstract:
  We develop a procedure to remove interference from gravitational wave
spectrum.
  The method is applied to the data produced by the Glasgow laser
interferometer in 1996 and all the lines corresponding to the interference with
the main supply are removed.


title: Removal of interference from external coherent signals

abstract:
  We present a technique that we call coherent line removal, for removing
external coherent interference from gravitational wave interferometer data. We
illustrate the usefulness of this technique applying it to the the data
produced by the Glasgow laser interferometer in 1996 and removing all those
lines corresponding to the electricity supply frequency and its harmonics. We
also find that this method 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: A Consistent Histories approach to the Unruh effect

abstract:
  Using the HPO approach to consistent histories we re-derive Unruh's result
that an observer constantly accelerating through the Minkowski vacuum appears
to be immersed in a thermal bath. We show that propositions about any symmetry
of the system always form a consistent set and that the probabilities
associated with such propositions are decided by their value in the initial
state. We use this fact to postulate a condition on the decoherence functional
in the HPO set-up. Finally we show that the Unruh effect arises from the fact
that the initial density matrix corresponding to the inertial vacuum can be
written as a thermal density matrix in the Fock basis associated with the
accelerating observer.


title:
On space-times admitting shear-free, irrotational, geodesic null
  congruences

abstract:
  Space-times admitting a shear-free, irrotational, geodesic null congruence
are studied. Attention is focused on those space-times in which the
gravitational field is a combination of a perfect fluid and null radiation.


title:
Perfect fluid space-times admitting a 3-dimensional conformal group
  acting on null orbits

abstract:
  Space-times admitting a 3-dimensional Lie group of conformal motions $C_3$
acting on null orbits are studied. Coordinate expressions for the metric and
the conformal Killing vectors (CKV) are then provided (irrespectively of the
matter content) and all possible perfect fluid solutions are found, although
none of them verifies the weak and dominant energy conditions over the whole
space-time manifold.


title: Self-similar perfect fluids

abstract:
  Space-times admitting an $r$-parameter Lie group of homotheties are studied
for $r > 2$ devoting a special attention to those representing perfect fluid
solutions to Einstein's field equations.


title: Cylindrically symmetric dust spacetime

abstract:
  We present an explicit exact solution of Einstein's equations for an
inhomogeneous dust universe with cylindrical symmetry. The spacetime is
extremely simple but nonetheless it has new surprising features. The universe
is ``closed'' in the sense that the dust expands from a big-bang singularity
but recollapses to a big-crunch singularity. In fact, both singularities are
connected so that the whole spacetime is ``enclosed'' within a single
singularity of general character. The big-bang is not simultaneous for the
dust, and in fact the age of the universe as measured by the dust particles
depends on the spatial position, an effect due to the inhomogeneity, and their
total lifetime has no non-zero lower limit. Part of the big-crunch singularity
is naked. The metric depends on a parameter and contains flat spacetime as a
non-singular particular case. For appropriate values of the parameter the
spacetime is a small perturbation of Minkowski spacetime. This seems to
indicate that flat spacetime may be unstable against some global {\it
non-vacuum} perturbations.


title: Space-times admitting a three-parameter similarity group

abstract:
  Spacetimes admitting a similarity group are considered. Amongst them, special
attention is given to the 3-parameter ones. A classification of such spacetimes
is given based on the Bianchi type of the similarity group $H_3$, and the
general form of the metric is provided in each case assuming the orbits are
non-null.


title:
Self-similar static solutions admitting a two-space of constant
  curvature

abstract:
  A recent result by Haggag and Hajj-Boutros is reviewed within the framework
of self-similar space-times, extending, in some sense, their results and
presenting a family of metrics consisting of all the static spherically
symmetric perfect fluid solutions admitting a homothety.


title: Space-times admitting a three-dimensional conformal group

abstract:
  Perfect fluid space-times admitting a three-dimensional Lie group of
conformal motions containing a two-dimensional Abelian Lie subgroup of
isometries are studied. Demanding that the conformal Killing vector be proper
(i.e., not homothetic nor Killing), all such space-times are classified
according to the structure of their corresponding three-dimensional conformal
Lie group and the nature of their corresponding orbits (that are assumed to be
non-null). Each metric is then explicitly displayed in coordinates adapted to
the symmetry vectors. Attention is then restricted to the diagonal case, and
exact perfect fluid solutions are obtained in both the cases in which the fluid
four-velocity is tangential or orthogonal to the conformal orbits, as well as
in the more general "tilting" case.


title: Removing Line Interference from Gravitational Wave Interferometer Data

abstract:
  We describe a procedure to identify and remove a class of interference lines
from gravitational wave interferometer data. We illustrate the usefulness of
this technique applying it to prototype interferometer data and removing all
those lines corresponding to the external electricity main supply and related
features.


title: Primordial fluctuations of the metric in the warm inflation scenario

abstract:
  I consider a semiclassical expansion of the scalar field in the warm
inflation scenario. I study the evolution for the fluctuations of the metric
around the Friedmann-Robertson-Walker one. The formalism predicts that, in the
power-law expansion universe, the fluctuations of the metric decreases with
time.


title:
DC Cancellation As a Method of Generating a t^2 Response and of Solving
  the Radial Nonobservability Problem in a Concentric Free-Falling Two-Sphere
  Equivalence-Principle Experiment in a Drag-Free Satellite

abstract:
  This paper solves two major problems which have blocked a free-fall
Equivalence-Principle (EP) in a satellite for 25 years: a semimajor-axis error
between the two proof masses cannot be distinguished from an EP violation and
the response to an EP violation only grows as t not t^2. Using the cancellation
method described in this paper, the nonobservability problem can be suppressed
and a t^2 response can be generated which lasts between 10^4 and 10^6 seconds
depending on the cancellation accuracy. t^2 response times between 10^5 and
10^6 seconds are equivalent to a very tall (0.1 to 10 AU) drop tower with a
constant gravitational field of 3/7 ge.


title:
Feynman Clocks, Causal Networks, and The Origin of Hierarchical 'Arrows
  of Time' in Complex Systems. Part 1: 'Conjectures'

abstract:
  A theory of time as 'information' is outlined using new tools such as Feynman
Clocks (FCs), Collective Excitation Networks (CENs), Sequential Excitation
Networks (SENs), and Plateaus of Complexity (POCs). Applications of this
approach range from the Big Bang to the emergence of 'consciousness'.


title: Brane Universe and Standard Cosmology

abstract:
  Brane cosmology takes the unconventional form $H\sim \sqrt{\rho}$. To recover
the standard cosmology, we have to assume that the matter density is much less
than the brane tension. We show that the assumption can be justified even near
the end of inflation if we fine-tune the coupling constant of the inflaton
potential. As a consequence, the standard cosmology is recovered after
inflation.


title: A Comment on Non-Archimedean Character of Quantum Buoyancy

abstract:
  In a gedankenexperiment about the generalized second law (GSL) of black hole
thermodynamics, the buoyant force by black hole atmosphere (the acceleration
radiation) plays an important role, and then it is significant to understand
the nature of the buoyant force.
  Recently, Bekenstein criticizes that the fluid approximation of the
acceleration radiation which is often used in the estimation of the buoyant
force is invalid for the case that the size of the target is much less than a
typical wavelength of the acceleration radiation, due to the diffractive effect
of wave scattering.
  In this letter, we argue that even if it is correct that we should calculate
the buoyant force as a wave scattering process, its implication in the GSL
strongly depends on whether there exists any massless scalar field, that is,
S-wave scattering. By reconsidering the diffractive effect by S-wave
scattering, we show that if some massless scalar field exists, then the GSL can
hold without invoking a new physics, such as an entropy bound for matter.


title: Spin 1/2 Field Theory in the de Sitter space-time

abstract:
  A covariant quantization of the free spinor fields (s=1/2) in 4-dimensional
de Sitter (dS) space-time based on analyticity in the complexified
pseudo-Riemanian manifold is presented. We define the Wigthman two-point
function ${\cal W}(x,y)$, which satisfies the conditions of: a) positivity, b)
locality, c) covariance, and d) normal analyticity. Then the Hilbert space
structure and the field operators $\psi (f)$ are defined. A
coordinate-independent formula for the unsmeared field operator $\psi (x)$ is
also given.


title: The maximal slicing of a Schwarzschild black hole

abstract:
  We describe recent work due to Niall \'O Murchadha and the author (Phys. Rev.
D57, 4728 (1998)) on the late time behaviour of the maximal foliation of the
extended Schwarzschild geometry which results from evolving a time symmetric
slice into the past and future, with time running equally fast at both spatial
ends of the manifold. We study the lapse function of this foliation in the
limit where proper time-at-infinity goes to ${+\infty}$ or ${-\infty}$ and the
slices approach $r=3m/2$.


title: Spacetime Measurements in Kaluza-Klein Gravity

abstract:
  We extend the classical general relativistic theory of measurement to include
the possibility of existence of higher dimensions. The intrusion of these
dimensions in the spacetime interval implies that the inertial mass of a
particle in general varies along its worldline if the observations are analyzed
assuming the existence of only the four spacetime dimensions. The variations of
mass and spin are explored in a simple 5D Kaluza-Klein model.


title: Gamma-ray bursts as the birth-cries of black holes

abstract:
  The origin of cosmic gamma-ray bursts remains one of the most intriguing
puzzles in astronomy. We suggest that purely general relativistic effects in
the collapse of massive stars could account for these bursts. The late
formation of closed trapped surfaces can occur naturally, allowing the escape
of huge energy from curvature-generated fireballs, before these are hidden
within a black hole.


title:
The newest release of the Ortocartan set of programs for algebraic
  calculations in relativity

abstract:
  The program Ortocartan for algebraic calculations in relativity has just been
implemented in the Codemist Standard Lisp and can now be used under the Windows
98 and Linux operating systems. The paper describes the new facilities and
subprograms that have been implemented since the previous release in 1992.
These are: the possibility to write the output as Latex input code and as
Ortocartan's input code, the calculation of the Ellis evolution equations for
the kinematic tensors of flow, the calculation of the curvature tensors from
given (torsion-free) connection coefficients in a manifold of arbitrary
dimension, the calculation of the lagrangian from a given metric by the
Landau-Lifshitz method, the calculation of the Euler-Lagrange equations from a
given lagrangian (only for sets of ordinary differential equations) and the
calculation of first integrals of sets of ordinary differential equations of
second order (the first integrals are assumed to be polynomials of second
degree in the first derivatives of the functions).


title: Exact Solutions to the Motion of Two Charged Particles in Lineal Gravity

abstract:
  We extend the canonical formalism for the motion of $N$-particles in lineal
gravity to include charges. Under suitable coordinate conditions and boundary
conditions the determining equation of the Hamiltonian (a kind of
transcendental equation) is derived from the matching conditions for the
dilaton field at the particles' position. The canonical equations of motion are
derived from this determining equation.
  For the equal mass case the canonical equations in terms of the proper time
can be exactly solved in terms of hyperbolic and/or trigonometric functions. In
electrodynamics with zero cosmological constant the trajectories for repulsive
charges exhibit not only bounded motion but also a countably infinite series of
unbounded motions for a fixed value of the total energy $H_{0}$, while for
attractive charges the trajectories are simply periodic. When the cosmological
constant $\Lambda$ is introduced, the motion for a given $\Lambda$ and $H_{0}$
is classified in terms of the charge-momentum diagram from which we can predict
what type of the motion is realized for a given charge.
  Since in this theory the charge of each particle appears in the form
$e_{1}e_{2}$ in the determining equation, the static balance condition in 1+1
dimensions turns out to be identical with the condition in Newtonian theory. We
generalize this condition to non-zero momenta, obtaining the first exact
solution to the static balance problem that does not obey the
Majumdar-Papapetrou condition.


title: Isolated Horizons: Hamiltonian Evolution and the First Law

abstract:
  A framework was recently introduced to generalize black hole mechanics by
replacing stationary event horizons with isolated horizons. That framework is
significantly extended. The extension is non-trivial in that not only do the
boundary conditions now allow the horizon to be distorted and rotating, but
also the subsequent analysis is based on several new ingredients. Specifically,
although the overall strategy is closely related to that in the previous work,
the dynamical variables, the action principle and the Hamiltonian framework are
all quite different. More importantly, in the non-rotating case, the first law
is shown to arise as a necessary and sufficient condition for the existence of
a consistent Hamiltonian evolution. Somewhat surprisingly, this consistency
condition in turn leads to new predictions even for static black holes. To
complement the previous work, the entire discussion is presented in terms of
tetrads and associated (real) Lorentz connections.


title:
On the nature of the force acting on a charged classical particle
  deviated from its geodesic path in a gravitational field

abstract:
  In general relativity the gravitational field is a manifestation of spacetime
curvature and unlike the electromagnetic field is not a force field. A particle
falling in a gravitational field is represented by a geodesic worldline which
means that no force is acting on it. If the particle is at rest in a
gravitational field, however, its worldline is no longer geodesic and it is
subjected to a force. The nature of that force is an open question in general
relativity. The aim of this paper is to outline an approach toward resolving it
in the case of classical charged particles which was initiated by Fermi in
1921.


title: SO(4,C)-covariant Ashtekar-Barbero gravity and the Immirzi parameter

abstract:
  An so(4,C)-covariant hamiltonian formulation of a family of generalized
Hilbert-Palatini actions depending on a parameter (the so called Immirzi
parameter) is developed. It encompasses the Ashtekar-Barbero gravity which
serves as a basis of quantum loop gravity. Dirac quantization of this system is
constructed. Next we study dependence of the quantum system on the Immirzi
parameter. The path integral quantization shows no dependence on it. A way to
modify the loop approach in the accordance with the formalism developed here is
briefly outlined.


title:
A class of perfect-fluid cosmologies with polarised Gowdy symmetry and a
  Kasner-like singularity

abstract:
  We prove the existence of a class of perfect-fluid cosmologies with polarised
  Gowdy symmetry and a Kasner-like singularity. These solutions of the Einstein
equations depend on four free functions of one space coordinate and are
constructed by solving a system of Fuchsian equations.


title:
On the existence and convergence of polyhomogeneous expansions of
  zero-rest-mass fields

abstract:
  The convergence of polyhomogeneous expansions of zero-rest-mass fields in
asymptotically flat spacetimes is discussed. An existence proof for the
asymptotic characteristic initial value problem for a zero-rest-mass field with
polyhomogeneous initial data is given. It is shown how this non-regular problem
can be properly recast as a set of regular initial value problems for some
auxiliary fields. The standard techniques of symmetric hyperbolic systems can
be applied to these new auxiliary problems, thus yielding a positive answer to
the question of existence in the original problem.


title:
The Long-Time Dynamics of Dirac Particles in the Kerr-Newman Black Hole
  Geometry

abstract:
  We consider the Cauchy problem for the massive Dirac equation in the
non-extreme Kerr-Newman geometry outside the event horizon. We derive an
integral representation for the Dirac propagator involving the solutions of the
ODEs which arise in Chandrasekhar's separation of variables. It is proved that
for initial data in L^\infty_loc near the event horizon with L^2 decay at
infinity, the probability of the Dirac particle to be in any compact region of
space tends to zero as t goes to infinity. This means that the Dirac particle
must either disappear in the black hole or escape to infinity.


title: Detection of Scalar Gravitational Waves

abstract:
  In this talk I review recent progresses in the detection of scalar
gravitational waves. Furthermore, in the framework of the Jordan-Brans-Dicke
theory, I compute the signal to noise ratio for a resonant mass detector of
spherical shape and for binary sources and collapsing stars. Finally I compare
these results with those obtained from laser interferometers and from
Einsteinian gravity.


title:
Contraction and distension by tidal stress and its role as the cause of
  the Hubble redshift

abstract:
  I show that a cumulative contraction or expansion must result from repetitive
tidal action in a curved stress field, depending on the direction of the
curvature. The resulting expansion of solid materials onboard deep space probes
and the corresponding contraction on earth would be of the right magnitude to
account for all aspects of the Pioneer anomaly, leading to the two component
model previously proposed. Importantly, I show via signal path analysis that
the anomaly mathematically implies planetary Hubble flow, and that it is
predicted by the standard model equations when the cosmological constant is
also taken into account at this range. Also shown is that the variations of the
anomaly do not permit a different explanation. The prediction of the Hubble
flow occurring as a result in the view of the shrinking observer is now fully
explained from both quantum and Doppler perspectives, fundamentally challenging
the cosmological ideas of the past century. Lastly, I discuss how the
contraction reconciles the geological evidence of a past expansion of the
earth.


title: Superfluid analogies of cosmological phenomena

abstract:
  Superfluid 3He-A gives example of how chirality, Weyl fermions, gauge fields
and gravity appear in low energy corner together with corresponding symmetries,
including Lorentz symmetry and local SU(N). This supports idea that quantum
field theory (Standard Model or GUT) is effective theory describing low-energy
phenomena. * Momentum space topology of fermionic vacuum provides topological
stability of universality class of systems, where above properties appear. *
BCS scheme for 3He-A incorporates both ``relativistic'' infrared regime and
ultraviolet ``transplanckian'' range: subtle issues of cut-off in quantum field
theory and anomalies can be resolved on physical grounds. This allows to
separate ``renormalizable'' terms in action, treated by effective theory, from
those obtained only in ``transPlanckian'' physics. * Energy density of
superfluid vacuum within effective theory is ~ E_{Planck}^4. Stability analysis
of ground state beyond effective theory leads to exact nullification of vacuum
energy: equilibrium vacuum is not gravitating. In nonequilibrium, vacuum energy
is of order energy density of matter. * 3He-A provides experimental prove for
anomalous nucleation of fermionic charge according to Adler-Bell-Jackiw. *
Helical instability in 3He-A is described by the same equations as formation of
magnetic field by right electrons in Joyce-Shaposhnikov scenario. * Macroscopic
parity violating effect and angular momentum paradox are both desribed by axial
gravitational Chern-Simons action. * High energy dispersion of quasiparticle
spectrum allow to treat problems of vacuum in presence of event horizon, etc.


title: Quantum Geometrodynamics in the Bohm-de Broglie Interpretation

abstract:
  In this thesis the Bohm-de Broglie interpretation of quantum mechanics is
applied to canonical quantum gravity. It is shown that, irrespective of any
regularization or choice of factor ordering of the Wheeler-DeWitt equation, the
unique relevant quantum effect which does not break spacetime is the change of
its signature from lorentzian to euclidean. The other quantum effects are
either trivial or break the four-geometry of spacetime. A Bohm-de Broglie
picture of quantum geometrodynamics is constructed, which allows the
investigation of these latter structures. For instance, it is shown that any
real solution of the Wheeler-De Witt equation yields a generate four-geometry
compatible with the strong gravity limit of General Relativity and the Carroll
group. We prove that quantum geometrodynamics in the Bohm-de Broglie
interpretation is consistent for any quantum potential. As a previous step to
introduce our metodology, we study the quantum theory of fields in Minkowski
spacetime in the Bohm-de Broglie interpretation and exhibit a concrete example
where Lorentz invariance of individual events is broken.


title: Estimating Hawking radiation for exotic black holes

abstract:
  We study about an approximation method of the Hawking radiation. We analyze
an massless scalar field in exotic black hole backgrounds models which have
peculiar properties in black hole thermodynamics (monopole black hole in SO(3)
Einstein-Yang-Mills-Higgs system and dilatoic black hole in
Einstein-Maxwell-dilaton system). A scalar field is assumed not to be couple to
matter fields consisting of a black hole background. Except for extreme black
holes, we can well approximate the Hawking radiaition by `black body' one with
Hawking temperature estimated at a radius of a critical impact parameter.


title: Canonical Gravity, Diffeomorphisms and Objective Histories

abstract:
  This paper discusses the implementation of diffeomorphism invariance in
purely Hamiltonian formulations of General Relativity. We observe that, if a
constrained Hamiltonian formulation derives from a manifestly covariant
Lagrangian, the diffeomorphism invariance of the Lagrangian results in the
following properties of the constrained Hamiltonian theory: the diffeomorphisms
are generated by constraints on the phase space so that a) The algebra of the
generators reflects the algebra of the diffeomorphism group. b) The Poisson
brackets of the basic fields with the generators reflects the space-time
transformation properties of these basic fields. This suggests that in a purely
Hamiltonian approach the requirement of diffeomorphism invariance should be
interpreted to include b) and not just a) as one might naively suppose. Giving
up b) amounts to giving up objective histories, even at the classical level.
This observation has implications for Loop Quantum Gravity which are spelled
out in a companion paper. We also describe an analogy between canonical gravity
and Relativistic particle dynamics to illustrate our main point.


title:
Is Barbero's Hamiltonian formulation a Gauge Theory of Lorentzian
  Gravity?

abstract:
  This letter is a critique of Barbero's constrained Hamiltonian formulation of
General Relativity on which current work in Loop Quantum Gravity is based.
While we do not dispute the correctness of Barbero's formulation of general
relativity, we offer some criticisms of an aesthetic nature. We point out that
unlike Ashtekar's complex SU(2) connection, Barbero's real SO(3) connection
does not admit an interpretation as a space-time gauge field. We show that if
one tries to interpret Barbero's real SO(3) connection as a space-time gauge
field, the theory is not diffeomorphism invariant. We conclude that Barbero's
formulation is not a gauge theory of gravity in the sense that Ashtekar's
Hamiltonian formulation is. The advantages of Barbero's real connection
formulation have been bought at the price of giving up the description of
gravity as a gauge field.


title: Transport along Null Curves

abstract:
  Fermi Transport is useful for describing the behaviour of spins or gyroscopes
following non-geodesic, timelike world lines. However, Fermi Transport breaks
down for null world lines. We introduce a transport law for polarisation
vectors along non-geodesic null curves. We show how this law emerges naturally
from the geometry of null directions by comparing polarisation vectors
associated with two distinct null directions. We then give a spinorial
treatment of this topic and make contact with the geometric phase of quantum
mechanics. There are two significant differences between the null and timelike
cases. In the null case (i) The transport law does not approach a unique smooth
limit as the null curve approaches a null geodesic. (ii) The transport law for
vectors is integrable, i.e the result depends only on the local properties of
the curve and not on the entire path taken. However, the transport of spinors
is not integrable: there is a global sign of topological origin.


title:
Cumulative gravitational lensing in Newtonian perturbations of
  Friedman-Robertson-Walker cosmologies

abstract:
  It is a common assumption amongst astronomers that, in the determination of
the distances of remote sources from their apparent brightness, the cumulative
gravitational lensing due to the matter in all the galaxies is the same, on
average, as if the matter were uniformly distributed throughout the cosmos. The
validity of this assumption is considered here by way of general Newtonian
perturbations of Friedman-Robertson-Walker (FRW) cosmologies. The analysis is
carried out in synchronous gauge, with particular attention to an additional
gauge condition that must be imposed. The mean correction to the apparent
magnitude-redshift relation is obtained for an arbitrary mean density
perturbation. In the case of a zero mean density perturbation, when the
intergalactic matter has a dust equation of state, then there is indeed a
zero-mean first order correction to the apparent magnitude-redshift relation
for all redshifts. Point particle and Swiss cheese models are considered as
particular cases.


title: Two-Dilaton Theories in Two Dimensions from Dimensional Reduction

abstract:
  Dimensional reduction of generalized gravity theories or string theories
generically yields dilaton fields in the lower-dimensional effective theory.
Thus at the level of D=4 theories, and cosmology many models contain more than
just one scalar field (e.g. inflaton, Higgs, quintessence). Our present work is
restricted to two-dimensional gravity theories with only two dilatons which
nevertheless allow a large class of physical applications.
  The notions of factorizability, simplicity and conformal simplicity, Einstein
form and Jordan form are the basis of an adequate classification. We show that
practically all physically motivated models belong either to the class of
factorizable simple theories (e.g. dimensionally reduced gravity, bosonic
string) or to factorizable conformally simple theories (e.g. spherically
reduced Scalar-Tensor theories). For these theories a first order formulation
is constructed straightforwardly. As a consequence an absolute conservation law
can be established.


title: Hermitian extension of the four-dimensional Hooke's law

abstract:
  It has been shown recently that the classical law of elasticity, expressed in
terms of the displacement three-vector and of the symmetric deformation
three-tensor, can be extended to the four dimensions of special and of general
relativity with a physically meaningful outcome. In fact, the resulting stress-
momentum-energy tensor can provide a unified account of both the elastic and
the inertial properties of uncharged matter. The extension of the displacement
vector to the four dimensions of spacetime allows a further possibility. If the
real displacement four-vector is complemented with an imaginary part, the
resulting complex ``displacement'' four-vector allows for a complex, Hermitian
generalisation of the four-dimensional Hooke's law. Let the complex, Hermitian
``stress-momentum-energy'' tensor density built in this way be subjected to the
usual conservation condition. It turns out that, while the real part of the
latter equation is able to account for the motion of electrically charged,
elastic matter, the imaginary part of the same equation can describe the
evolution of the electromagnetic field and of its sources. The Hermitian
extension of Hooke's law is performed by availing of the postulate of
``transposition invariance'', introduced in 1945 by A. Einstein for finding the
nonsymmetric generalisation of his theory of gravitation of 1915.


title:
Is Nothing Sacred? Vacuum Energy, Supersymmetry and Lorentz Breaking
  from Recoiling D branes

abstract:
  Classical superstring vacua have zero vacuum energy and are supersymmetric
and Lorentz-invariant. We argue that all these properties may be destroyed when
quantum aspects of the interactions between particles and non-perturbative
vacuum fluctuations are considered. A toy calculation of string/D-brane
interactions using a world-sheet approach indicates that quantum recoil effects
- reflecting the gravitational back-reaction on space-time foam due to the
propagation of energetic particles - induce non-zero vacuum energy that is
linked to supersymmetry breaking and breaks Lorentz invariance. This model of
space-time foam also suggests the appearance of microscopic event horizons.


title:
Generalized Field Theoretical Approach to General Relativity and
  Conserved Quantities in Anti-de Sitter Spacetimes

abstract:
  A new prescription to calculate the total energies and angular momenta of
asymptotically $(d+1)$-dimensional anti-de Sitter spacetimes is proposed. The
method is based on an extension of the field theoretical approach to General
Relativity to the case where there is an effective cosmological constant. A
$(d-1)$-form $\Omega$ is exhibited which, when integrated on asymptotic
$(d-1)$-dimensional boundary surfaces, yields the values of those conserved
quantities. The calculations are gauge independent once asymptotic conditions
are not violated . Total energies and angular momenta of some known solutions
in four and five dimensions are calculated agreeing with standard results.