title: A No-Go Theorem About Rotation in Relativity Theory

abstract:
  Within the framework of general relativity, in some cases at least, it is a
delicate and interesting question just what it means to say that an extended
body is or is not "rotating". It is so for two reasons. First, one can easily
think of different criteria of rotation. Though they agree if the background
spacetime structure is sufficiently simple, they do not do so in general.
Second, none of the criteria fully answers to our classical intuitions. Each
one exhibits some feature or other that violates those intuitions in a
significant and interesting way. The principal goal of the paper is to make the
second claim precise in the form of a modest no-go theorem.


title: Black Hole in Higher Curvature Gravity and AdS/CFT Correspondence

abstract:
  The classical central charge for the higher curvature gravity in 3-dimensions
is calculated using the Legendre transformation method. The statistical entropy
of BTZ black hole is derived by the Cardy's formula and the result completely
coincides with the Iyer-Wald formula for the geometrical entropy. This
coincidence suggests the generalized AdS/CFT correspondence.


title:
Characteristic numerical relativity applied to hydrodynamic studies of
  neutron stars

abstract:
  We present tests and results of a new axisymmetric, fully general
relativistic code capable of solving the coupled Einstein-matter system for a
perfect fluid matter field. Our implementation is based on the Bondi metric, by
which the spacetime is foliated with a family of outgoing light cones. We use
high-resolution shock-capturing schemes to solve the fluid equations. The code
can accurately maintain long-term stability of a spherically symmetric,
relativistic, polytropic equilibrium model of a neutron star. In axisymmetry,
we demonstrate global energy conservation of a perturbed neutron star in a
compactified spacetime, for which the total energy radiated away by
gravitational waves corresponds to a significant fraction of the Bondi mass.


title:
Radiation from a uniformly accelerated charge in the outskirts of a
  wormhole throat

abstract:
  Using traversable wormholes as theoretical background, we revisit a deep
question of general relativity: Does a uniformly accelerated charged particle
radiate? We particularize to the recently proposed gravitational \v{C}erenkov
radiation, that happens when the spatial part of the Ricci tensor is negative.
If $^{^{(3+1)}}R^i_{\phantom{i}i}< 0$, the matter threading the gravitational
field violates the weak energy condition. In this case, the effective
refractive index for light is bigger than 1, i.e. particles propagates, in that
medium, faster than photons. This leads to a violation of the equivalence
principle.


title: FRW Cosmological Solutions in M-theory

abstract:
  We present the canonical and quantum cosmological investigation of a
four-dimensional, spatially flat, Friedmann-Robertson-Walker (FRW) model that
is derived from the bosonic Neveu-Schwarz/Neveu-Schwarz sector of the
low-energy M-theory effective action. We discuss in detail the phase space of
the classical theory. We find the quantum solutions of the model and obtain the
positive norm Hilbert space of states. Finally, the correspondence between wave
functions and classical solutions is outlined.


title:
Radiation Pressure Induced Instabilities in Laser Interferometric
  Detectors of Gravitational Waves

abstract:
  The large scale interferometric gravitational wave detectors consist of
Fabry-Perot cavities operating at very high powers ranging from tens of kW to
MW for next generations. The high powers may result in several nonlinear
effects which would affect the performance of the detector. In this paper, we
investigate the effects of radiation pressure, which tend to displace the
mirrors from their resonant position resulting in the detuning of the cavity.
We observe a remarkable effect, namely, that the freely hanging mirrors gain
energy continuously and swing with increasing amplitude. It is found that the
`time delay', that is, the time taken for the field to adjust to its
instantaneous equilibrium value, when the mirrors are in motion, is responsible
for this effect. This effect is likely to be important in the optimal operation
of the full-scale interferometers such as VIRGO and LIGO.


title:
Znajek-Damour Horizon Boundary Conditions with Born-Infeld
  Electrodynamics

abstract:
  In this work, the interaction of electromagnetic fields with a rotating
(Kerr) black hole is explored in the context of Born-Infeld (BI) theory of
electromagnetism instead of standard Maxwell theory and particularly BI theory
versions of the four horizon boundary conditions of Znajek and Damour are
derived. Naturally, an issue to be addressed is then whether they would change
from the ones given in Maxwell theory context and if they would, how.
Interestingly enough, as long as one employs the same local null tetrad frame
as the one adopted in the works by Damour and by Znajek to read out physical
values of electromagnetic fields and fictitious surface charge and currents on
the horizon, it turns out that one ends up with exactly the same four horizon
boundary conditions despite the shift of the electrodynamics theory from a
linear Maxwell one to a highly non-linear BI one. Close inspection reveals that
this curious and unexpected result can be attributed to the fact that the
concrete structure of BI equations happens to be such that it is
indistinguishable at the horizon to a local observer, say, in Damour's local
tetrad frame from that of standard Maxwell theory.


title: Gravitational Energy-Momentum in MAG

abstract:
  Energy-momentum (and angular momentum) for the Metric-Affine Gravity theory
is considered from a Hamiltonian perspective (linked with the Noether
approach). The important roles of the Hamiltonian boundary term and the many
choices involved in its selection-which give rise to many different
definitions-are emphasized. For each choice one obtains specific boundary
conditions along with a value for the quasilocal, and (with suitable asymptotic
behavior) total (Bondi and ADM) energy-momentum and angular momentum.
Applications include the first law of black hole thermodynamics-which
identifies a general expression for the entropy. Prospects for a positive
energy proof are considered and quasilocal values for some solutions are
presented.


title: Classical analogous of quantum cosmological perfect fluid models

abstract:
  Quantization in the mini-superspace of a gravity system coupled to a perfect
fluid, leads to a solvable model which implies singularity free solutions
through the construction of a superposition of the wavefunctions. We show that
such models are equivalent to a classical system where, besides the perfect
fluid, a repulsive fluid with an equation of state $p_Q = \rho_Q$ is present.
This leads to speculate on the true nature of this quantization procedure. A
perturbative analysis of the classical system reveals the condition for the
stability of the classical system in terms of the existence of an anti-gravity
phase.


title: Fourth-Order Ricci Gravity

abstract:
  The Euler-Lagrange equations of motion for the most general Ricci type
gravitational Lagrangians are derived by means of a purely metric formalism.


title: Quiescent cosmological singularities

abstract:
  I discuss recent work (gr-qc/0001047) on non-oscillatory singularities in
four dimensional space-times with scalar field or stiff fluid matter, in the
context of the BKL proposal.


title: Anisotropy dissipation in brane-world inflation

abstract:
  We examine the behavior of an anisotropic brane-world in the presence of
inflationary scalar fields. We show that, contrary to naive expectations, a
large anisotropy does not adversely affect inflation. On the contrary, a large
initial anisotropy introduces more damping into the scalar field equation of
motion, resulting in greater inflation. The rapid decay of anisotropy in the
brane-world significantly increases the class of initial conditions from which
the observed universe could have originated. This generalizes a similar result
in general relativity. A unique feature of Bianchi I brane-world cosmology
appears to be that for scalar fields with a large kinetic term the initial
expansion of the universe is quasi-isotropic. The universe grows more
anisotropic during an intermediate transient regime until anisotropy finally
disappears during inflationary expansion.


title:
A generalized Hamiltonian Constraint Operator in Loop Quantum Gravity
  and its simplest Euclidean Matrix Elements

abstract:
  We study a generalized version of the Hamiltonian constraint operator in
nonperturbative loop quantum gravity. The generalization is based on admitting
arbitrary irreducible SU(2) representations in the regularization of the
operator, in contrast to the original definition where only the fundamental
representation is taken. This leads to a quantization ambiguity and to a family
of operators with the same classical limit. We calculate the action of the
Euclidean part of the generalized Hamiltonian constraint on trivalent states,
using the graphical notation of Temperley-Lieb recoupling theory. We discuss
the relation between this generalization of the Hamiltonian constraint and
crossing symmetry.


title: Image distortion in non perturbative gravitational lensing

abstract:
  We introduce the idea of {\it shape parameters} to describe the shape of the
pencil of rays connecting an observer with a source lying on his past
lightcone. On the basis of these shape parameters, we discuss a setting of
image distortion in a generic (exact) spacetime, in the form of three {\it
distortion parameters}. The fundamental tool in our discussion is the use of
geodesic deviation fields along a null geodesic to study how source shapes are
propagated and distorted on the path to an observer. We illustrate this
non-perturbative treatment of image distortion in the case of lensing by a
Schwarzschild black hole. We conclude by showing that there is a
non-perturbative generalization of the use of Fermat's principle in lensing in
the thin-lens approximation.


title:
Image distortion from optical scalars in non perturbative gravitational
  lensing

abstract:
  In a previous article concerning image distortion in non-perturbative
gravitational lensing theory we described how to introduce shape and distortion
parameters for small sources. We also showed how they could be expressed in
terms of the scalar products of the geodesic deviation vectors of the source's
pencil of rays in the past lightcone of an observer. In the present work we
give an alternative approach to the description of the shape and distortion
parameters and their evolution along the null geodesic from the source to the
observer, but now in terms of the optical scalars (the convergence and shear of
null vector field of the observer's lightcone) and the associated optical
equations, which relate the optical scalars to the curvature of the spacetime.


title: Calculating Gravitational Radiation from Collisions

abstract:
  The development of both ground- and space-based gravitational wave detectors
provides new opportunities to observe the radiation from binaries containing
neutron stars and black holes. Numerical simulations in 3-D are essential for
calculating the coalescence waveforms, and comprise some of the most
challenging problems in astrophysics today. This article briefly reviews the
current status of efforts to calculate black hole and neutron star
coalescences, and highlights challenges for the future.


title: Gravitation in Flat Spacetime

abstract:
  A special-relativistic scalar-vector theory of gravitation is presented which
mimics an important class of solutions of Einstein's gravitational field
equations. The theory includes solutions equivalent to Schwarzschild, Kerr,
Reissner-Nordstroem, and Friedman metrics as well as to gravitational waves. In
fact, all the empirical tests until now due to general relativity can be
explained within this flat spacetime theory.


title: Quantum correlation functions and the classical limit

abstract:
  We study the transition from the full quantum mechanical description of
physical systems to an approximate classical stochastic one. Our main tool is
the identification of the closed-time-path (CTP) generating functional of
Schwinger and Keldysh with the decoherence functional of the consistent
histories approach. Given a degree of coarse-graining in which interferences
are negligible, we can explicitly write a generating functional for the
effective stochastic process in terms of the CTP generating functional. This
construction gives particularly simple results for Gaussian processes. The
formalism is applied to simple quantum systems, quantum Brownian motion,
quantum fields in curved spacetime. Perturbation theory is also explained. We
conclude with a discussion on the problem of backreaction of quantum fields in
spacetime geometry.


title: Group Averaging and Refined Algebraic Quantization: Where are we now?

abstract:
  Refined Algebraic Quantization and Group Averaging are powerful methods for
quantizing constrained systems. They give constructive algorithms for
generating observables and the physical inner product. This work outlines the
current status of these ideas with an eye toward quantum gravity. The main goal
is provide a description of outstanding problems and possible research topics
in the field.


title: Chaos in FRW cosmology with various types of a scalar field potential

abstract:
  The results on chaos in FRW cosmology with a massive scalar field are
extended to another scalar field potential. It is shown that for sufficiently
steep potentials the chaos disappears. A simple and rather accurate analytical
criterion for the chaos to disappear is given. On the contrary, for gently
sloping potentials the transition to a strong chaotic regime can occur. Two
examples, concerning asymptotically flat and Damour-Mukhanov potentials are
given.


title:
Tests of strong-field gravity and gravitational radiation damping in
  binary-pulsar systems

abstract:
  This talk reviews the constraints imposed by binary-pulsar data on gravity
theories, and notably on "scalar-tensor" theories which are the most natural
alternatives to general relativity. Because neutron stars have a strong
gravitational binding energy, binary-pulsar tests are qualitatively different
from solar-system experiments: They have the capability of probing models which
are indistinguishable from general relativity in weak gravitational field
conditions. Besides the two most precise binary-pulsar experiments, in the
systems B1913+16 and B1534+12, we also present the results of the various
"null" tests of general relativity provided by several neutron star-white dwarf
binaries, notably those of gravitational radiation damping. [The main interest
of this very short paper is its figure, which also takes into account the
"strong equivalence principle" tests.]


title: A phenomenological approach to quintessence in scalar-tensor gravity

abstract:
  This talk is based on my work in collaboration with B. Boisseau, D. Polarski,
and A.A. Starobinsky. The most natural and best-motivated alternatives to
general relativity are the so-called "scalar-tensor" theories, in which the
gravitational interaction is mediated not only by a (spin-2) graviton, but also
by a (spin-0) scalar field. We study quintessence in this general framework,
and show that the microscopic Lagrangian of the theory can be unambiguously
reconstructed from two observable cosmological functions of the redshift: the
luminosity distance and the linear density perturbation of dustlike matter. We
also analyze the constraints imposed on the theory by the knowledge of only the
first of these functions, as it will probably be available sooner with a good
accuracy. [The main interest of this very short paper is to give the equations
in the "Brans-Dicke" parametrization.]


title: An exact-plane fronted wave solution in metric-affine gravity

abstract:
  We study plane-fronted electrovacuum waves in metric-affine gravity (MAG)
with cosmological constant in the triplet ansatz sector of the theory. 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 $F$. Here we
basically present, after a short introduction into MAG and its triplet subcase,
the results of earlier joint work with Garcia, Macias, and Socorro. Our
solution is based on an exact solution of Ozsvath, Robinson, and Rozga
describing type N gravitational fields in general relativity as coupled to
electromagnetic null-fields.


title: Algebraic integrability of FRW-scalar cosmologies

abstract:
  For dynamical systems of dimension three or more the question of
integrability or nonintegrability is extended by the possibility of chaotic
behaviour in the general solution. We determine the integrability of isotropic
cosmological models in general relativity and string theory with a variety of
matter terms, by a performance of the Painlev\'{e} analysis in an effort to
examine whether or not there exists a Laurent expansion of the solution about a
movable pole which contains the number of arbitrary constants necessary for a
general solution.


title: Embedding variables in finite dimensional models

abstract:
  Global problems associated with the transformation from the Arnowitt, Deser
and Misner (ADM) to the Kucha\v{r} variables are studied. Two models are
considered: The Friedmann cosmology with scalar matter and the torus sector of
the 2+1 gravity. For the Friedmann model, the transformations to the Kucha\v{r}
description corresponding to three different popular time coordinates are shown
to exist on the whole ADM phase space, which becomes a proper subset of the
Kucha\v{r} phase spaces. The 2+1 gravity model is shown to admit a description
by embedding variables everywhere, even at the points with additional symmetry.
The transformation from the Kucha\v{r} to the ADM description is, however,
many-to-one there, and so the two descriptions are inequivalent for this model,
too. The most interesting result is that the new constraint surface is free
from the conical singularity and the new dynamical equations are linearization
stable. However, some residual pathology persists in the Kucha\v{r}
description.


title:
Regularity and stability of electrostatic solutions in Kaluza-Klein
  theory

abstract:
  We investigate the family of electrostatic spherically symmetric solutions of
the five-dimensional Kaluza-Klein theory. Besides black holes and wormholes, a
new class of geodesically complete solutions is identified. A monopole
perturbation is carried out, enabling us to prove analytically the stability of
a large class of solutions, including all black holes and neutral solutions.


title: Parametrization of singularities of the Demia\'{n}ski-Newman spacetimes

abstract:
  We propose a new presentation of the Demia\'{n}ski-Newman (DN) solution of
the axisymmetric Einstein equations. We introduce new dimensionless parameters
$p$, $q$ and $s$, but keeping the Boyer-Lindquist coordinate transformation
used for the Kerr metric in the Ernst method. The family of DN metrics is
studied and it is shown that the main role of $s$ is to determine the
singularities, which we obtain by calculating the Riemann tensor components and
the invariants of curvature. So, $s$ reveals itself as the parameter of the
singular rings on the inner ergosphere.


title: Resonance enhancement of particle production during reheating

abstract:
  We found a consistent equation of reheating after inflation, which shows that
for small quantum fluctuations the frequencies of resonance are slighted
different from the standard ones. Quantum interference is taken into account
and we found that at large fluctuations the process mimics very well the usual
parametric resonance but proceed in a different dynamical way. The analysis is
made in a toy quantum mechanical model and we discuss further its extension to
quantum field theory.


title: Electromagnetic fields around black holes and Meissner effect

abstract:
  The work on black holes immersed in external stationary magnetic fields is
reviewed in both test-field approximation and within exact solutions. In
particular we pay attention to the effect of the expulsion of the flux of
external fields across charged and rotating black holes which are approaching
extremal states. Recently this effect has been shown to occur for black hole
solutions in string theory and Kaluza-Klein theory.


title: Electron-Positron Jets from a Critically Magnetized Black Hole

abstract:
  The curved spacetime surrounding a rotating black hole dramatically alters
the structure of nearby electromagnetic fields. The Wald field which is an
asymptotically uniform magnetic field aligned with the angular momentum of the
hole provides a convenient starting point to analyze the effects of radiative
corrections on electrodynamics in curved spacetime. Since the curvature of the
spacetime is small on the scale of the electron's Compton wavelength, the tools
of quantum field theory in flat spacetime are reliable and show that a rotating
black hole immersed in a magnetic field approaching the quantum critical value
of $B_k=m^2 c^3/(e\hbar) \approx 4.4 \times 10^{13}$~G $\approx
1.3\times10^{-11}$ cm$^{-1}$ is unstable. Specifically, a maximally rotating
three-solar-mass black hole immersed in a magnetic field of $2.3 \times
10^{12}$~G would be a copious producer of electron-positron pairs with a
luminosity of $3 \times 10^{52}$ erg s$^{-1}$.


title: Vacuum spacetimes with an isometry

abstract:
  In vacuum space-times the exterior derivative of a Killing vector field is a
two-form that satisfies Maxwell equations without electromagnetic sources.
Using the algebraic structure of this two-form we have set up a new formalism
for the study of vacuum space-times with an isometry.


title: Distorted charged dilaton black holes

abstract:
  We construct exact static, axisymmetric solutions of Einstein-Maxwell-dilaton
gravity presenting distorted charged dilaton black holes. The thermodynamics of
such distorted black holes is also discussed.


title:
The First Search for Gravitational Waves from Inspiraling Compact
  Binaries using TAMA300 data

abstract:
  We analyzed 6 hours of data from the TAMA300 detector by matched filtering,
searching for gravitational waves from inspiraling compact binaries. We
incorporated a two-step hierarchical search strategy in matched filtering. We
obtained an upper limit of 0.59/hour (C.L.=90%) on the event rate of inspirals
of compact binaries with mass between 0.3M_solar and 10M_solar and with
signal-to-noise ratio greater than 7.2. The distance of 1.4M_solar (0.5M_solar)
binaries which produce the signal-to-noise ratio 7.2 was estimated to be 6.2kpc
(2.9kpc) when the position of the source on the sky and the inclination angle
of the binaries were optimal.


title:
On the existence of a gyroscope in spaces with affine connections and
  metrics

abstract:
  Conditions for the existence of a gyroscope in spaces with affine connections
and metrics are found. They appear as special types of Fermi-Walker transports
for vector fields, lying in a subspace, orthogonal to the velocity vector field
of an observer.
  PACS numbers: 04.20Cv, 04.90.+e, 04.50.+h, 02.40.Ky


title: A Multiple-Grid-Patch Evolution Scheme for 3-D Black Hole Excision

abstract:
  When using black hole excision to numerically evolve a fully generic black
hole spacetime, most 3-D 3+1 codes use an $xyz$-topology (spatial) grid. In
such a grid, an $r = \constant$ excision surface must be approximated by an
irregular and non-smooth "staircase-shaped" excision grid boundary, which may
introduce numerical instabilities into the evolution. In this paper I describe
an alternate scheme, which uses multiple grid patches, each with topology $\{r
\times ({\rm angular coordinates})\}$, to cover the slice outside the $r =
\constant$ excision surface. The excision grid boundary is now smooth, so the
evolution should be less prone to instabilities. With 4th order finite
differencing, this code evolves Kerr initial data to ${\sim} 60M$ using the ADM
equations; I'm currently implementing the BSSN equations in it in the hope that
this will improve the stability.


title: Elimination of Clock Jitter Noise in Spaceborn Laser Interferometers

abstract:
  Space gravitational wave detectors employing laser interferometry between
free-flying spacecraft differ in many ways from their laboratory counterparts.
Among these differences is the fact that, in space, the end-masses will be
moving relative to each other. This creates a problem by inducing a Doppler
shift between the incoming and outgoing frequencies. The resulting beat
frequency is so high that its phase cannot be read to sufficient accuracy when
referenced to state-of-the-art space-qualified clocks. This is the problem that
is addressed in this paper. We introduce a set of time-domain algorithms in
which the effects of clock jitter are exactly canceled. The method employs the
two-color laser approach that has been previously proposed, but avoids the
singularities that arise in the previous frequency-domain algorithms. In
addition, several practical aspects of the laser and clock noise cancellation
schemes are addressed.


title: The gravitational wave symphony of the Universe

abstract:
  The new millennium will see the upcoming of several ground-based
interferometric gravitational wave antennas. Within the next decade a
space-based antenna may also begin to observe the distant Universe. These
gravitational wave detectors will together operate as a network taking data
continuously for several years, watching the transient and continuous phenomena
occurring in the deep cores of astronomical objects and dense environs of the
early Universe where gravity was extremely strong and highly non-linear. The
network will listen to the waves from rapidly spinning non-axisymmetric neutron
stars, normal modes of black holes, binary black hole inspiral and merger,
phase transitions in the early Universe, quantum fluctuations resulting in a
characteristic background in the early Universe. The gravitational wave
antennas will open a new window to observe the dark Universe unreachable via
other channels of astronomical observations.


title:
Deviation equations of Synge and Schild over spaces with affine
  connections and metrics

abstract:
  Deviation equation of Synge and Schild has been investigated over spaces with
affine connections and metrics. It is shown that the condition for the
vanishing of the Lie derivative of a vector field along a given non-null
(non-isotropic) vector field u for obtaining this equation is only a sufficient
(but not necessary) condition. By means of the vector field u and the
projective metric (orthogonal to it) projected deviation equations of Synge and
Schild have been obtained for a vector field, orthogonal to the given vector
field u, as well as for the square of its length. For a given non-isotropic,
auto-parallel and normalized vector field u this equation could have some
simple solutions.
  PACS numbers: 02.90; 04.50+h; 04.90.+e: 04.30.+x


title:
Integrability conditions for vacuum spacetimes with a Killing vector
  field

abstract:
  We present a new approach to the study of vacuum spacetimes with a Killing
symmetry. The central quantity in this approach is the exterior derivative of
the Killing vector field, which is a test electromagnetic field. Considering
the algebraic structure of this quantity we get a new view of the integrability
conditions, which provides a natural way of studying the connections between
the algebraic structure of the spacetime and properties of the Killing
symmetry.


title:
HBO and Periastron Precession around the X-ray Neutron Star
  Magnetosphere

abstract:
  Based on the periastron precession model to account for kHz QPO of the binary
X-ray neutron star, proposed by Stella and Vietri, we ascribe the 15-60 Hz
Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the
orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron
star (NS). The obtained conclusions include: all QPO frequencies increase with
increasing the accretion rate. The theoretical relations between 15-60 Hz QPO
(HBO) frequency and the twin kHz QPOs are similar to the measured empirical
formula. Further, the better fitted NS mass by the proposed model is about 1.9
solar masses for the detected LMXBs.


title: 2+1 gravity, chaos and time machines

abstract:
  2+1 gravity for spacetimes with topology RxT^2 has been much studied. We add
a description of how to extend these spacetimes across a Cauchy horizon into a
region where the torus becomes Lorentzian. The result is a one parameter family
of tori given by a geodesic in the "Teichmueller space" of Lorentzian tori. We
describe this in detail. We also point out that if the modular group is
regarded as part of the gauge group then these spacetimes offer a nice toy
model for the dynamics of Bianchi IX models; in the region where the tori are
spacelike the dynamics is described exactly by a hyperbolic billiard. On the
other hand the modular group acts ergodically on the Teichmueller space of
Lorentzian tori.


title:
Static Anisotropic Solutions to Einstein Equations with a Nonlocal
  Equation of State

abstract:
  We present a general method to obtain static anisotropic spherically
symmetric solutions, satisfying a nonlocal equation of state, from known
density profiles. This equation of state describes, at a given point, the
components of the corresponding energy-momentum tensor not only as a function
at that point, but as a functional throughout the enclosed configuration. In
order to establish the physical aceptability of the proposed static family of
solutions satisfying nonlocal equation of state,\textit{}we study the
consequences imposed by the junction and energy conditions for anisotropic
fluids in bounded matter distribution. It is shown that a general relativistic
spherically symmetric bounded distributions of matter, at least for certain
regions, could satisfy a nonlocal equation of state.


title: Slowly Rotating Boson Fermion Stars

abstract:
  Relativistic prescription is used to study the slow rotation of stars
composed by self-gravitating bosons and fermions (fermions may be considered as
neutrons). Previous results demand that purely boson stars are unable to
display slow rotation, if one uses relativistic prescription with classical
scalar fields. In contrast to this, the present work shows that a combined
boson-neutron star in its ground-state can rotate. Their structure and
stability are analysed under slow rotation approximations.


title: Coarse-grained field wave function in stochastic inflation

abstract:
  The wave function for the matter field fluctuations in the infrared sector is
studied within the framework of inflationary cosmology. These fluctuations are
described by a coarse-grained field which takes into account only the modes
with wavelength much bigger than the size of the Hubble horizon. The case of a
power-law expanding universe is considered and it is found that the relevant
phase-space remains coherent under certain circumstances. In this case the
classical stochastic treatment for matter field fluctuations is not valid,
however, for $p > 4.6$, the system loses its coherence and a classical
stochastic approximation is allowed.


title:
Asymptotic power-law tails of massive scalar fields in
  Reissner-Nordstr\"{o}m background

abstract:
  We investigate dominant late-time tail behaviors of massive scalar fields in
nearly extreme Reissner-Nordstr\"{o}m background. It is shown that the
oscillatory tail of the scalar fields has the decay rate of $t^{-5/6}$ at
asymptotically late times. The physical mechanism by which the asymptotic
$t^{-5/6}$ tail yields and the relation between the field mass and the time
scale when the tail begins to dominate, are discussed in terms of resonance
backscattering due to spacetime curvature.


title: Initial data for two Kerr-like black holes

abstract:
  We prove the existence of a family of initial data for the Einstein vacuum
equation which can be interpreted as the data for two Kerr-like black holes in
arbitrary location and with spin in arbitrary direction. When the mass
parameter of one of them is zero, this family reduces exactly to the Kerr
initial data. The existence proof is based on a general property of the Kerr
metric which can be used in other constructions as well. Further
generalizations are also discussed.


title:
Bursts of Radiation and Recoil Effects in Electromagnetism and
  Gravitation

abstract:
  The Maxwell field of a charge e which experiences an impulsive acceleration
or deceleration is constructed explicitly by subdividing Minkowskian space-time
into two halves bounded by a future null-cone and then glueing the halves back
together with appropriate matching conditions. The resulting retarded radiation
can be viewed as instantaneous electromagnetic bremsstrahlung. If we similarly
consider a spherically symmetric, moving gravitating mass, to experience an
impulsive deceleration, as viewed by a distant observer, then this is
accompanied by the emission of a light-like shell whose total energy measured
by this observer is the same as the kinetic energy of the source before it
stops. This phenomenon is a recoil effect which may be thought of as a limiting
case of a Kinnersley rocket.


title: Extended Kelvin theorem in relativistic magnetohydrodynamics

abstract:
  We prove the existence of a generalization of Kelvin's circulation theorem in
general relativity which is applicable to perfect isentropic
magnetohydrodynamic flow. The argument is based on a new version of the
Lagrangian for perfect magnetohydrodynamics. We illustrate the new conserved
circulation with the example of a relativistic magnetohydrodynamic flow
possessing three symmetries.


title:
2D gravity without test particles is pointless (Comment on
  hep-th/0011136)

abstract:
  Claims of a general Weyl invariance of an arbitrary 2D dilaton theory are
critically discussed.


title: Mass neutrino flavor evolution in spacetime with torsion

abstract:
  In the framework of the spacetime with torsion, we obtain the flavor
evolution equation of the mass neutrino oscillation in vacuum. A comparison
with the result of general relativity case, it shows that the flavor
evolutionary equations in Riemann spacetime and Weitzenb\"ock spacetimes are
equivalent in the spherical symmetric Schwarzschild spacetime, but turns out to
be different in the case of the axial symmetry.


title: The Fundamental Commutator For Massless Particles

abstract:
  It is discussed that the usual Heisenberg commutation relation (CR) is not a
proper relation for massless particles and then an alternative is obtained. The
canonical quantization of the free electromagnetic(EM)fields based on the field
theoretical generalization of this alternative is carried out. Without imposing
the normal ordering condition,the vacuum energy is automatically zero.This can
be considered as a solution to the EM fields vacuum catastrophe and a step
toward managing the cosmologial constant problem at least for the EM fields
contribution to the state of vacuum.


title: Detection of variable frequency signals using a fast chirp transform

abstract:
  The detection of signals with varying frequency is important in many areas of
physics and astrophysics. The current work was motivated by a desire to detect
gravitational waves from the binary inspiral of neutron stars and black holes,
a topic of significant interest for the new generation of interferometric
gravitational wave detectors such as LIGO. However, this work has significant
generality beyond gravitational wave signal detection.
  We define a Fast Chirp Transform (FCT) analogous to the Fast Fourier
Transform (FFT). Use of the FCT provides a simple and powerful formalism for
detection of signals with variable frequency just as Fourier transform
techniques provide a formalism for the detection of signals of constant
frequency. In particular, use of the FCT can alleviate the requirement of
generating complicated families of filter functions typically required in the
conventional matched filtering process. We briefly discuss the application of
the FCT to several signal detection problems of current interest.


title: Canonical Theory of 2+1 Gravity

abstract:
  Recently 2+1 dimensional gravity theory, especially ${\rm AdS_3}$ has been
studied extensively. It was shown to be equivalent to the 2+1 Chern-Simon
theory and has been investigated to understand the black hole thermodynamics,
i.e. Hawking temperature and others. The purpose of this report is to
investigate the canonical formalism of the original 2+1 Einstein gravity theory
instead of the Chern-Simon theory. For the spherically symmetric space-time,
local conserved quantities(local mass and angular momentum) are introduced and
using them canonical quantum theory is defined. Constraints are imposed on
state vectors and solved analytically. The strategy to obtain the solution is
followed by our previous work.


title: Supermassive boson stars: prospects for observational detection

abstract:
  In a recent work (Torres, Capozziello and Lambiase, Physical Review D62,
104012 (2000)), it was shown that a supermassive boson star could provide an
alternative model for the galactic center, usually assumed as a black hole.
Here we comment on some of the possibilities to actually detect this object,
and how can it be distinguished from the standard and other alternative models.


title: Naked singularities in Tolman-Bondi-de Sitter collapse

abstract:
  We study the formation of central naked singularities in spherical dust
collapse with a cosmological constant. We find that the central curvature
singularity is locally naked, Tipler strong, and generic, in the sense that it
forms from a non-zero-measure set of regular initial data. We also find that
the Weyl and Ricci curvature scalars diverge at the singularity, with the
former dominating over the latter, thereby signaling the non-local origin of
the singularity.


title:
The quasi-classical model of the spherical configuration in general
  relativity

abstract:
  We consider the quasi-classical model of the spin-free configuration on the
basis of the self-gravitating spherical dust shell in General Relativity. For
determination of the energy spectrum of the stationary states on the basis of
quasi-classical quantization rules it is required to carry out some
regularization of the system. It is realized by an embedding of the initial
system in the extended system with rotation. Then, the stationary states of the
spherical shells are S-states of the system with the intrinsic momentum. The
quasi-classical treatment of a stability of the configuration is associated
with the Langer modification of a square of the quantum mechanical intrinsic
momentum. It gives value of critical bare mass of the shell determining
threshold of stability. For the shell with the bare mass smaller or equal to
the Planck's mass, the energy spectra of bound states are found. We obtain the
expression for tunneling probability of the shell and construct the
quasi-classical model of the pair creation and annihilation of the shells.


title: Data Processing for LISA's Laser Interferometer Tracking System (LITS)

abstract:
  The purpose of this paper is twofold. First, we will present recent results
on the data processing for LISA, including algorithms for elimination of clock
jitter noise and discussion of the generation of the data averages that will
eventually need to be telemetered to the ground. Second, we will argue, based
partly on these results, that a laser interferometer tracking system (LITS)
that employs independent lasers in each spacecraft is preferable for reasons of
simplicity to that in which the lasers in two of the spacecraft are locked to
the incoming beam from the third.


title: Discrete structures in gravity

abstract:
  Discrete approaches to gravity, both classical and quantum, are reviewed
briefly, with emphasis on the method using piecewise-linear spaces. Models of
3-dimensional quantum gravity involving 6j-symbols are then described, and
progress in generalising these models to four dimensions is discussed, as is
the relationship of these models in both three and four dimensions to
topological theories. Finally, the repercussions of the generalisations are
explored for the original formulation of discrete gravity using edge-length
variables.


title: Essentials of Classical Brane Dynamics

abstract:
  This article provides a self contained overview of the geometry and dynamics
of relativistic brane models, of the category that includes point particle,
string, and membrane representations for phenomena that can be considered as
being confined to a worldsheet of the corresponding dimension (respectively
one, two, and three) in a thin limit approximation in an ordinary 4 dimensional
spacetime background. This category also includes ``brane world'' models that
treat the observed universe as a 3-brane in 5 or higher dimensional background.
The first sections are concerned with purely kinematic aspects: it is shown
how, to second differential order, the geometry (and in particular the inner
and outer curvature) of a brane worldsheet of arbitrary dimension is
describable in terms of the first, second, and third fundamental tensor. The
later sections show how -- to lowest order in the thin limit -- the evolution
of such a brane worldsheet will always be governed by a simple tensorial
equation of motion whose left hand side is the contraction of the relevant
surface stress tensor $ bar T^{\mu\nu}$ with the (geometrically defined) second
fundamental tensor $K_{\mu\nu}{^\rho}$, while the right hand side will simply
vanish in the case of free motion and will otherwise be just the orthogonal
projection of any external force density that may happen to act on the brane.


title:
The Einstein 3-form G_a and its equivalent 1-form L_a in Riemann-Cartan
  space

abstract:
  The definition of the Einstein 3-form G_a is motivated by means of the
contracted 2nd Bianchi identity. This definition involves at first the complete
curvature 2-form. The 1-form L_a is defined via G_a = L^b \wedge #(o_b \wedge
o_a). Here # denotes the Hodge-star, o_a the coframe, and \wedge the exterior
product. The L_a is equivalent to the Einstein 3-form and represents a certain
contraction of the curvature 2-form. A variational formula of Salgado on
quadratic invariants of the L_a 1-form is discussed, generalized, and put into
proper perspective.


title: Covariant Geometric Prequantization of Fields

abstract:
  A geometric prequantization formula for the Poisson-Gerstenhaber bracket of
forms found within the DeDonder-Weyl Hamiltonian formalism earlier is
presented. The related aspects of covariant geometric quantization of field
theories are sketched. In particular, the importance of the framework of
Clifford and spinor bundles and superconnections in this context is underlined.

categories: gr-qc hep-th math-ph math.MP math.SG quant-ph


title: Remarks on vacuum fluctuations around a spinning cosmic string

abstract:
  We apply the point-splitting method to investigate vacuum fluctuations in the
nonglobally hyperbolic background of a spinning cosmic string. Implementing
renormalization by removing the Minkowski contribution it is shown that
although the Green function in the literature satisfies the usual Green
function equation, it leads to pathological physical results.


title: BF Actions for the Husain-Kuchar Model

abstract:
  We show that the Husain-Kuchar model can be described in the framework of BF
theories. This is a first step towards its quantization by standard
perturbative QFT techniques or the spin-foam formalism introduced in the
space-time description of General Relativity and other diff-invariant theories.
The actions that we will consider are similar to the ones describing the
BF-Yang-Mills model and some mass generating mechanisms for gauge fields. We
will also discuss the role of diffeomorphisms in the new formulations that we
propose.


title: The generalized teleparallel structure

abstract:
  It is proposed to describe a teleparallel structure as a combination of a
Riemannian and a symplectic structure. The correspondent invariance group is an
intersection of the orthogonal and the symplectic groups. For a 4D manifold it
turns to be the basic group of the electro-week interaction $U(1)\times SU(2).$


title: On the derivation of the equation of motion in a scalar model

abstract:
  A new method for derivation of the equation of motion from the field equation
is proposed. The problem of embedding the singularities in a field satisfying
the field equations is discussed.


title: Episodic Self-Similarity in Critical Gravitational Collapse

abstract:
  We report on a new behavior found in numerical simulations of spherically
symmetric gravitational collapse in self-gravitating SU(2) sigma models at
intermediate gravitational coupling constants: The critical solution (between
black hole formation and dispersion) closely approximates the continuously
self-similar (CSS) solution for a finite time interval, then departs from this,
and then returns to CSS again. This cycle repeats several times, each with a
different CSS accumulation point. We have preliminary evidence that this same
critical solution is also discretely self-similar (DSS) between the CSS
episodes, but with an echoing period $\Delta$ which varies during the
evolution.


title: Evaluation of neutrinos mass based on ENU model

abstract:
  Based on principles of the Expansive Nondecelerative Universe model that
enables to quantify and localize the gravitational energy density, and stemming
from the see-saw mechanism, the mass of electron, muon and tau neutrinos are
determined in an independent way.


title: Braking--Radiation: An Energy Source for a Relativistic Fireball

abstract:
  If the Schwarzschild black-hole is moving rectilinearly with uniform
3-velocity and suddenly stops, according to a distant observer, then we
demonstrate that this observer will see a spherical light--like shell or
"relativistic fireball" radiate outwards with energy equal to the original
kinetic energy of the black-hole.


title: Torsion waves in metric-affine field theory

abstract:
  The approach of metric-affine field theory is to define spacetime as a real
oriented 4-manifold equipped with a metric and an affine connection. The 10
independent components of the metric tensor and the 64 connection coefficients
are the unknowns of the theory. We write the Yang-Mills action for the affine
connection and vary it both with respect to the metric and the connection. We
find a family of spacetimes which are stationary points. These spacetimes are
waves of torsion in Minkowski space. We then find a special subfamily of
spacetimes with zero Ricci curvature; the latter condition is the Einstein
equation describing the absence of sources of gravitation. A detailed
examination of this special subfamily suggests the possibility of using it to
model the neutrino. Our model naturally contains only two distinct types of
particles which may be identified with left-handed neutrinos and right-handed
antineutrinos.


title: Note on Signature Change and Colombeau Theory

abstract:
  Recent work alludes to various `controversies' associated with signature
change in general relativity. As we have argued previously, these are in fact
disagreements about the (often unstated) assumptions underlying various
possible approaches. The choice between approaches remains open.


title: Cosmic acceleration without quintessence

abstract:
  It is argued that the Brans-Dicke theory may explain the present accelerated
expansion of the universe without resorting to a cosmological constant or
quintessence matter


title: Quantum theory's last challenge

abstract:
  Quantum mechanics is now 100 years old and still going strong. Combining
general relativity with quantum mechanics is the last hurdle to be overcome in
the "quantum revolution".


title: Vacuum Polarization in the Spacetime of a Scalar-Tensor Cosmic String

abstract:
  We study the vacuum polarization effect in the spacetime generated by a
magnetic flux cosmic string in the framework of a scalar-tensor gravity. The
vacuum expectation values of the energy-momentum tensor of a conformally
coupled scalar field are calculated. The dilaton's contribution to the vacuum
polarization effect is shown explicitly.


title:
Relativity in space-times with short-distance structure governed by an
  observer-independent (Planckian) length scale

abstract:
  I show that it is possible to formulate the Relativity postulates in a way
that does not lead to inconsistencies in the case of space-times whose
short-distance structure is governed by an observer-independent length scale.
The consistency of these postulates proves incorrect the expectation that
modifications of the rules of kinematics involving the Planck length would
necessarily require the introduction of a preferred class of inertial
observers. In particular, it is possible for every inertial observer to agree
on physical laws supporting deformed dispersion relations of the type $E^2- c^2
p^2- c^4 m^2 + f(E,p,m;L_p)=0$, at least for certain types of $f$.


title: Properties of the instantaneous Ergo Surface of a Kerr Black Hole

abstract:
  This paper explores properties of the instantaneous ergo surface of a Kerr
black hole. The surface area is evaluated in closed form. In terms of the mass
($m$) and angular velocity ($a$), to second order in $a$, the area of the ergo
surface is given by $16 \pi m^2 + 4 \pi a^2$ (compared to the familiar $16 \pi
m^2 - 4 \pi a^2$ for the event horizon). Whereas the total curvature of the
instantaneous event horizon is $4 \pi$, on the ergo surface it ranges from $4
\pi$ (for $a=0$) to 0 (for $a=m$) due to conical singularities on the axis
($\theta=0,\pi$) of deficit angle $2 \pi (1-\sqrt{1-(a/m)^2})$. A careful
application of the Gauss-Bonnet theorem shows that the ergo surface remains
topologically spherical. Isometric embeddings of the ergo surface in Euclidean
3-space are defined for $0 \leq a/m \leq 1$ (compared to $0 \leq a/m \leq
\sqrt{3}/2$ for the horizon).


title:
Toward a Midisuperspace Quantization of LeMaitre-Tolman-Bondi Collapse
  Models

abstract:
  LeMa\^\i tre-Tolman-Bondi models of spherical dust collapse have been used
and continue to be used extensively to study various stellar collapse
scenarios. It is by now well-known that these models lead to the formation of
black holes and naked singularities from regular initial data. The final
outcome of the collapse, particularly in the event of naked singularity
formation, depends very heavily on quantum effects during the final stages.
These quantum effects cannot generally be treated semi-classically as quantum
fluctuations of the gravitational field are expected to dominate before the
final state is reached. We present a canonical reduction of LeMa\^\i
tre-Tolman-Bondi space-times describing the marginally bound collapse of
inhomogeneous dust, in which the physical radius, $R$, the proper time of the
collapsing dust, $\tau$, and the mass function, $F$, are the canonical
coordinates, $R(r)$, $\tau(r)$ and $F(r)$ on the phase space. Dirac's
constraint quantization leads to a simple functional (Wheeler-DeWitt) equation.
The equation is solved and the solution can be employed to study some of the
effects of quantum gravity during gravitational collapse with different initial
conditions.


title: On Pauli's invention of non-abelian Kaluza-Klein Theory in 1953

abstract:
  There are documents which show that Wolfgang Pauli developed in 1953 the
first consistent generalization of the five-dimensional theory of Kaluza,
Klein, Fock and others to a higher dimensional internal space. Because he saw
no way to give masses to the gauge bosons, he refrained from publishing his
results formally.


title: Quantum-mechanical model of the Kerr-Newman black hole

abstract:
  We consider a Hamiltonian quantum theory of stationary spacetimes containing
a Kerr-Newman black hole. The physical phase space of such spacetimes is just
six-dimensional, and it is spanned by the mass $M$, the electric charge $Q$ and
angular momentum $J$ of the hole, together with the corresponding canonical
momenta. In this six-dimensional phase space we perform a canonical
transformation such that the resulting configuration variables describe the
dynamical properties of Kerr-Newman black holes in a natural manner. The
classical Hamiltonian written in terms of these variables and their conjugate
momenta is replaced by the corresponding self-adjoint Hamiltonian operator and
an eigenvalue equation for the Arnowitt-Deser-Misner (ADM) mass of the hole,
from the point of view of a distant observer at rest, is obtained. In a certain
very restricted sense, this eigenvalue equation may be viewed as a sort of
"Schr\"odinger equation of black holes". Our "Schr\"odinger equation" implies
that the ADM mass, electric charge and angular momentum spectra of black holes
are discrete, and the mass spectrum is bounded from below. Moreover, the
spectrum of the quantity $M^2-Q^2-a^2$, where $a$ is the angular momentum per
unit mass of the hole, is strictly positive when an appropriate self-adjoint
extension is chosen. The WKB analysis yields the result that the large
eigenvalues of $M$, $Q$ and $a$ are of the form $\sqrt{2n}$, where $n$ is an
integer. It turns out that this result is closely related to Bekenstein's
proposal on the discrete horizon area spectrum of black holes.


title:
Gauge-invariant and coordinate-independent perturbations of stellar
  collapse II: matching to the exterior

abstract:
  In Paper I in this series we constructed evolution equations for the complete
gauge-invariant linear perturbations of a time-dependent spherically symmetric
perfect fluid spacetime. A key application of this formalism is the interior of
a collapsing star. Here we derive boundary conditions at the surface of the
star, matching the interior perturbations to the well-known perturbations of
the vacuum Schwarzschild spacetime outside the star.


title:
Scalar, electromagnetic, and gravitational self-forces in weakly curved
  spacetimes

abstract:
  We calculate the self-force experienced by a point scalar charge, a point
electric charge, and a point mass moving in a weakly curved spacetime
characterized by a time-independent Newtonian potential. The self-forces are
calculated by first computing the retarded Green's functions for scalar,
electromagnetic, and (linearized) gravitational fields in the weakly curved
spacetime, and then evaluating an integral over the particle's past world line.
In all three cases the self-force contains both a conservative and a
nonconservative (radiation-reaction) part. The conservative part of the
self-force is directly related to the presence of matter in the spacetime. The
radiation-reaction part of the self-force, on the other hand, is insensitive to
the presence of matter. Our result for the gravitational self-force is
disturbing: a radiation-reaction force should not appear in the equations of
motion at this level of approximation, and it should certainly not give rise to
radiation antidamping. The last section of this paper attempts to make sense of
this result by placing it in the context of the post-Newtonian N-body problem.


title: Differential Geometry from Differential Equations

abstract:
  We first show how, from the general 3rd order ODE of the form
z'''=F(z,z',z'',s), one can construct a natural Lorentzian conformal metric on
the four-dimensional space (z,z',z'',s). When the function F(z,z',z'',s)
satisfies a special differential condition of the form, U[F]=0, the conformal
metric possesses a conformal Killing field, xi = partial with respect to s,
which in turn, allows the conformal metric to be mapped into a three
dimensional Lorentzian metric on the space (z,z',z'') or equivalently, on the
space of solutions of the original differential equation. This construction is
then generalized to the pair of differential equations, z_ss =
S(z,z_s,z_t,z_st,s,t) and z_tt = T(z,z_s,z_t,z_st,s,t), with z_s and z_t, the
derivatives of z with respect to s and t. In this case, from S and T, one can
again, in a natural manner, construct a Lorentzian conformal metric on the six
dimensional space (z,z_s,z_t,z_st,s,t). When the S and T satisfy equations
analogous to U[F]=0, namely equations of the form M[S,T]=0, the 6-space then
possesses a pair of conformal Killing fields, xi =partial with respect to s and
eta =partial with respect to t which allows, via the mapping to the four-space
of z, z_s, z_t, z_st and a choice of conformal factor, the construction of a
four-dimensional Lorentzian metric. In fact all four-dimensional Lorentzian
metrics can be constructed in this manner. This construction, with further
conditions on S and T, thus includes all (local) solutions of the Einstein
equations.


title: Critical Collapse of Collisionless Matter in Spherical Symmetry

abstract:
  We perform a numerical study of the critical regime for the general
relativistic collapse of collisionless matter in spherical symmetry. The
evolution of the matter is given by the Vlasov equation (or Boltzmann equation)
and the geometry by Einstein's equations. This system of coupled differential
equations is solved using a particle-mesh (PM) method. This method approximates
the distribution function which describes the matter in phase space with a set
of particles moving along the characteristics of the Vlasov equation. The
individual particles are allowed to have angular momentum different from zero
but the total angular momentum has to be zero to retain spherical symmetry.
  In accord wih previous work by Rein, Rendall and Schaeffer, our results give
some indications that the critical behaviour in this model is of Type I (the
smallest black hole in each family has a finite mass). For the families of
initial data that we have studied it seems that in the critical regime the
solution is a static spacetime with non-zero radial momentum for the individual
particles. We have also found evidence for scaling laws for the time that the
critical solutions spend in the critical regime.


title:
Black-Hole Uncertainty Entails an Intrinsic Time Arrow. a Note on the
  Hawking-Penrose Controversy

abstract:
  Any theory that states that the basic laws of physics are time-symmetric must
be strictly deterministic. Only determinism enables time reversal of entropy
increase. A contradiction therefore arises between two statements of Hawking. A
simulation of a system under time reversal shows how an intrinsic time arrow
re-emerges, destroying the time reversal, when even slight failure of
determinism occurs.


title: Indeterminism and Time Symmetry are Incompatible: Reply to Rebilas

abstract:
  Rebilas argues that time-reversal can occur even in an indeterministic
system. This hypothesis is untestable, hence lying beyond physics.


title:
Families of exact solutions of a 2D gravity model minimally coupled to
  electrodynamics

abstract:
  Three families of exact solutions for 2-dimensional gravity minimally coupled
to electrodynamics are obtained in the context of ${\cal R}=T$ theory. It is
shown, by supersymmetric formalism of quantum mechanics, that the quantum
dynamics of a neutral bosonic particle on static backgrounds with both varying
curvature and electric field is exactly solvable.


title: Accelerating Photons with Gravitational Radiation

abstract:
  The nature of superluminal photon propagation in the gravitational field
describing radiation from a time-dependent, isolated source (the Bondi-Sachs
metric) is considered in an effective theory which includes interactions which
violate the strong equivalence principle. Such interactions are, for example,
generated by vacuum polarisation in conventional QED in curved spacetime. The
relation of the resulting light-cone modifications to the Peeling Theorem for
the Bondi-Sachs spacetime is explained.


title:
The Role of Elliptic Operators in the Initial-Value Problem for General
  Relativity

abstract:
  The Arnowitt-Deser-Misner (ADM) equations are deeply intertwined with
discrete spectral resolutions of an elliptic operator of Laplace type
associated with the spacelike hypersurfaces which foliate the space-time
manifold, and the non-linearities of the four-dimensional hyperbolic theory are
mapped into the potential term occurring in this operator. The ADM equations
are here re-expressed as a coupled first-order system for the induced metric
and the trace-free part of the extrinsic-curvature tensor, and their
formulation in terms of integral equations is studied.


title: Gravitomagnetism and Relative Observer Clock Effects

abstract:
  The gravitomagnetic clock effect and the Sagnac effect for circularly
rotating orbits in stationary axisymmetric spacetimes are studied from a
relative observer point of view, clarifying their relationships and the roles
played by special observer families. In particular Semer\'ak's recent
characterization of extremely accelerated observers in terms of the two-clock
clock effect is shown to be complemented by a similarly special property of the
single-clock clock effect.


title: Spectrum of Charged Black Holes - The Big Fix Mechanism Revisited

abstract:
  Following an earlier suggestion of the authors(gr-qc/9607030), we use some
basic properties of Euclidean black hole thermodynamics and the quantum
mechanics of systems with periodic phase space coordinate to derive the
discrete two-parameter area spectrum of generic charged spherically symmetric
black holes in any dimension. For the Reissner-Nordstrom black hole we get
$A/4G\hbar=\pi(2n+p+1)$, where the integer p=0,1,2,.. gives the charge
spectrum, with $Q=\pm\sqrt{\hbar p}$. The quantity $\pi(2n+1)$, n=0,1,... gives
a measure of the excess of the mass/energy over the critical minimum (i.e.
extremal) value allowed for a given fixed charge Q. The classical critical
bound cannot be saturated due to vacuum fluctuations of the horizon, so that
generically extremal black holes do not appear in the physical spectrum.
Consistency also requires the black hole charge to be an integer multiple of
any fundamental elementary particle charge: $Q= \pm me$, m=0,1,2,.... As a
by-product this yields a relation between the fine structure constant and
integer parameters of the black hole -- a kind of the Coleman big fix mechanism
induced by black holes. In four dimensions, this relationship is
$e^2/\hbar=p/m^2$ and requires the fine structure constant to be a rational
number. Finally, we prove that the horizon area is an adiabatic invariant, as
has been conjectured previously.


title: Evolution of Black Holes in Brans-Dicke Cosmology

abstract:
  We consider a modified ``Swiss cheese'' model in the Brans-Dicke theory, and
discuss the evolution of black holes in the expanding universe. We define the
black hole radius by the Misner-Sharp mass and find the time evolution for dust
and vacuum universes.


title:
Gravitoelectromagnetism and the Integral Formulation of MAxwell's
  Equations

abstract:
  The integral formulation of Maxwell's equations expressed in terms of an
arbitrary observer family in a curved spacetime is developed and used to
clarify the meaning of the lines of force associated with observer-dependent
electric and magnetic fields.


title: Effect of spins on the quantum entropy of black holes

abstract:
  By using the Newman-Penrose formalism and 't Hooft brick-wall model, the
quantum entropies of the Kerr-Newman black hole due to the Dirac and
electromagnetic fields are calculated and the effects of the spins of the
photons and Dirac particles on the entropies are investigated. It is shown that
the entropies depend only on the square of the spins of the particles and the
contribution of the spins is dependent on the rotation of the black hole,
except that different fields obey different statistics.


title: Detecting Binary Black Holes With Efficient and Reliable Templates

abstract:
  Detecting binary black holes in interferometer data requires an accurate
knowledge of the orbital phase evolution of the system. From the point of view
of data analysis one also needs fast algorithms to compute the templates that
will employed in searching for black hole binaries. Recently, there has been
progress on both these fronts: On the one hand, re-summation techniques have
made it possible to accelerate the convergence of poorly convergent asymptotic
post-Newtonian series and derive waveforms beyond the conventional adiabatic
approximation. We now have a waveform model that extends beyond the inspiral
regime into the plunge phase followed by the quasi-normal mode ringing. On the
other hand, explicit Fourier domain waveforms have been derived that make the
generation of waveforms fast enough so as not to be a burden on the
computational resources required in filtering the detector data. These new
developments should make it possible to efficiently and reliably search for
black hole binaries in data from first interferometers.


title: Electrostatic in Reissner-Nordstrom space-time with a conical defect

abstract:
  We calculate the electrostatic potential generated by a point charge in the
space-time of Reissner-Nordstrom with a conical defect. An expression for the
self-energy is also presented.


title:
Qualitative analysis of a scalar-tensor theory with exponential
  potential

abstract:
  A qualitative analysis of a scalar-tensor cosmological model, with an
exponential potential for the scalar field, is performed. The phase diagram for
the flat case is constructed. It is shown that solutions with an initial and
final inflationary behaviour appear. The conditions for which the scenario
favored by supernova type Ia observations becomes an attractor in the space of
the solutions are established.


title: General approach to the study of vacuum space-times with an isometry

abstract:
  In vacuum space-times the exterior derivative of a Killing vector field is a
2-form (named here as the Papapetrou field) that satisfies Maxwell's equations
without electromagnetic sources. In this paper, using the algebraic structure
of the Papapetrou field, we will set up a new formalism for the study of vacuum
space-times with an isometry, which is suitable to investigate the connections
between the isometry and the Petrov type of the space-time. This approach has
some advantages, among them, it leads to a new classification of these
space-times and the integrability conditions provide expressions that determine
completely the Weyl curvature. These facts make the formalism useful for
application to any problem or situation with an isometry and requiring the
knowledge of the curvature.


title:
Precanonical Quantum Gravity: quantization without the space-time
  decomposition

abstract:
  A nonpertubative approach to quantum gravity using precanonical field
quantization originating from the covariant De Donder-Weyl Hamiltonian
formulation which treats space and time variables on equal footing is
presented. A generally covariant ``multi-temporal'' generalized Schroedinger
equation on the finite dimensional space of metric and space-time variables is
obtained. An important ingredient of the formulation is the ``bootstrap
condition'' which introduces a classical space-time geometry as an approximate
concept emerging as the quantum average in a self-consistent with the
underlying quantum dynamics manner. An independence of the theory from an
arbitrarily fixed background is ensured in this way. The prospects and unsolved
problems of precanonical quantization of gravity are outlined.


title: The Isotropy of Compact Universes

abstract:
  We discuss the problem of the stability of the isotropy of the universe in
the space of ever-expanding spatially homogeneous universes with a compact
spatial topology. The anisotropic modes which prevent isotropy being
asymptotically stable in Bianchi-type $VII_h$ universes with non-compact
topologies are excluded by topological compactness. Bianchi type $V$ and type
$VII_h$ universes with compact topologies must be exactly isotropic. In the
flat case we calculate the dynamical degrees of freedom of Bianchi-type $I$ and
$VII_0$ universes with compact 3-spaces and show that type $VII_0$ solutions
are more general than type $I$ solutions for systems with perfect fluid,
although the type $I$ models are more general than type $VII_0$ in the vacuum
case. For particular topologies the 4-velocity of any perfect fluid is required
to be non-tilted. Various consequences for the problems of the isotropy,
homogeneity, and flatness of the universe are discussed.


title: Discrete Black-Hole Radiation and the Information Loss Paradox

abstract:
  Hawking's black hole information puzzle highlights the incompatibility
between our present understanding of gravity and quantum physics. However,
Hawking's prediction of black-hole evaporation is at a semiclassical level. One
therefore suspects some modifications of the character of the radiation when
quantum properties of the {\it black hole itself} are properly taken into
account. In fact, during the last three decades evidence has been mounting
that, in a quantum theory of gravity black holes may have a discrete mass
spectrum, with concomitant {\it discrete} line emission. A direct consequence
of this intriguing prediction is that, compared with blackbody radiation,
black-hole radiance is {\it less} entropic, and may therefore carry a
significant amount of {\it information}. Using standard ideas from quantum
information theory, we calculate the rate at which information can be recovered
from the black-hole spectral lines. We conclude that the information that was
suspected to be lost may gradually leak back, encoded into the black-hole
spectral lines.


title:
Gravitational radiation, energy and reaction on quasi-spherical black
  holes

abstract:
  Gravitational radiation is locally defined where the wavefronts are roughly
spherical. A local energy tensor is defined for the gravitational radiation.
Including this energy tensor as a source in the truncated Einstein equations
describes gravitational radiation reaction, such as back-reaction on a roughly
spherical black hole. The energy-momentum in a canonical frame is covariantly
conserved. The strain to be measured by a distant detector is simply defined.


title:
Casimir energy and black hole pair creation in Schwarzschild-de Sitter
  spacetime

abstract:
  Following the subtraction procedure for manifolds with boundaries, we
calculate by variational methods, the Schwarzschild-de Sitter and the de Sitter
space energy difference. By computing the one loop approximation for TT tensors
we discover the existence of an unstable mode even for the non-degenerate case.
This result seems to be in agreement with the sub-maximal black hole pair
creation of Bousso-Hawking. The instability can be eliminated by the boundary
reduction method. Implications on a foam-like space are discussed.


title: The 3D Grazing Collision of Two Black Holes

abstract:
  We present results for two colliding black holes (BHs), with angular
momentum, spin, and unequal mass. For the first time gravitational waveforms
are computed for a grazing collision from a full 3D numerical evolution. The
collision can be followed through the merger to form a single BH, and through
part of the ringdown period of the final BH. The apparent horizon is tracked
and studied, and physical parameters, such as the mass of the final BH, are
computed. The total energy radiated in gravitational waves is shown to be
consistent with the total mass of the spacetime and the final BH mass. The
implication of these simulations for gravitational wave astronomy is discussed.


title: Gravitating macroscopic media in general relativity

abstract:
  The problem of construction of a continuous (macroscopic) matter model for a
given point-like (microscopic) matter distribution in general relativity is
formulated. The existing approaches are briefly reviewed and a physical analogy
with the similar problem in classical macroscopic electrodynamics is pointed
out. The procedure by Szekeres in the linearized general relativity on
Minkowski background to construct a tensor of gravitational quadruple
polarization by applying Kaufman's method of molecular moments for derivation
of the polarization tensor in macroscopic electrodynamics and to derive an
averaged field operator by utilizing an analogy between the linearized Bianchi
identities and Maxwell equations, is analyzed. It is shown that the procedure
has some inconsistencies, in particular, (1) it has only provided the terms
linear in perturbations for the averaged field operator which do not contribute
into the dynamics of the averaged field, and (2) the analogy between
electromagnetism and gravitation does break upon averaging. A macroscopic
gravity approach in the perturbation theory up to the second order on a
particular background space-time taken to be a smooth weak gravitational field
is applied to write down a system of macroscopic field equations: Isaacson's
equations with a source incorporating the quadruple gravitational polarization
tensor, Isaacson's energy-momentum tensor of gravitational waves and
energy-momentum tensor of gravitational molecules and corresponding equations
of motion. A suitable set of material relations which relate all the tensors is
proposed.


title: Rotating Hairy Black Holes

abstract:
  We construct stationary black holes in SU(2) Einstein-Yang-Mills theory,
which carry angular momentum and electric charge. Possessing non-trivial
non-abelian magnetic fields outside their regular event horizon, they represent
non-perturbative rotating hairy black holes.


title:
Nonconformal Scalar Field in a Homogeneous Isotropic Space and the
  Method of Hamiltonian Diagonalization

abstract:
  The diagonalization of the metrical Hamiltonian of a scalar field with an
arbitrary coupling with a curvature in N-dimensional homogeneous isotropic
space is performed. The energy spectrum of the corresponding quasiparticles is
obtained. The energies of the quasiparticles corresponding to the diagonal form
of the canonical Hamiltonian are calculated. The modified energy-momentum
tensor with the following properties is constructed. It coincides with the
metrical energy-momentum tensor for conformal scalar field. Under its
diagonalization the energies of relevant particles of a nonconformal field
coincide to the oscillator frequencies and the density of such particles
created in a nonstationary metric is finite. It is shown that the Hamiltonian
calculated with the modified energy-momentum tensor can be constructed as a
canonical Hamiltonian under the special choice of variables.


title: Noninertial quantum mechanical fluctuations

abstract:
  Zero point quantum fluctuations as seen from non-inertial reference frames
are of interest for several reasons. In particular, because phenomena such as
Unruh radiation (acceleration radiation) and Hawking radiation (quantum leakage
from a black hole) depend intrinsically on both quantum zero-point fluctuations
and some appropriate notion of an accelerating vacuum state, any experimental
test of zero-point fluctuations in non-inertial frames is implicitly a test of
the foundations of quantum field theory, and the Unruh and Hawking effects


title: Rotational Instabilities in Post-Collapse Stellar Cores

abstract:
  A core-collapse supernova might produce large amplitude gravitational waves
if, through the collapse process, the inner core can aquire enough rotational
energy to become dynamically unstable. In this report I present the results of
3-D numerical simulations of core collapse supernovae. These simulations
indicate that for some initial conditions the post-collapse inner core is
indeed unstable. However, for the cases considered, the instability does not
produce a large gravitational-wave signal.


title: Superinflation, quintessence, and nonsingular cosmologies

abstract:
  The dynamics of a universe dominated by a self-interacting nonminimally
coupled scalar field are considered. The structure of the phase space and
complete phase portraits are given. New dynamical behaviors include
superinflation ($\dot{H}>0$), avoidance of big bang singularities through
classical birth of the universe, and spontaneous entry into and exit from
inflation. This model is promising for describing quintessence as a
nonminimally coupled scalar field.


title:
Theoretical Necessity of an External Scalar Field in the Kaluza-Klein
  Theory (I)

abstract:
  We show that the principle of least action is generally inconsistent with the
usual Kaluza-Klein program, the higher dimensional Einstein-Hilbert action
being unbounded from below. This inconsistency is also present in other
theories with higher dimensions like supergravity. Hence, we conclude to the
necessity of an external scalar field to compensate this flaw.


title: Comparing quantum black holes and naked singularities

abstract:
  There are models of gravitational collapse in classical general relativity
which admit the formation of naked singularities as well as black holes. These
include fluid models as well as models with scalar fields as matter. Even if
fluid models were to be regarded as unphysical in their matter content, the
remaining class of models (based on scalar fields) generically admit the
formation of visible regions of finite but arbitrarily high curvature. Hence it
is of interest to ask, from the point of view of astrophysics, as to what a
stellar collapse leading to a naked singularity (or to a visible region of very
high curvature) will look like, to a far away observer. The emission of energy
during such a process may be divided into three phases - (i) the classical
phase, during which matter and gravity can both be treated according to the
laws of classical physics, (ii) the semiclassical phase, when gravity is
treated classically but matter behaves as a quantum field, and (iii) the
quantum gravitational phase. In this review, we first give a summary of the
status of naked singularities in classical relativity, and then report some
recent results comparing the semiclassical phase of black holes with the
semiclassical phase of spherical collapse leading to a naked singularity. In
particular, we ask how the quantum particle creation during the collapse
leading to a naked singularity compares with the Hawking radiation from a star
collapsing to form a black hole. It turns out that there is a fundamental
difference between the two cases. A spherical naked star emits only about one
Planck energy during its semiclassical phase, and the further evolution can
only be determined by the laws of quantum gravity. This contrasts with the
semiclassical evaporation of a black hole.


title: Classification of image distortions in terms of Petrov types

abstract:
  An observer surrounded by sufficiently small spherical light sources at a
fixed distance will see a pattern of elliptical images distributed over the
sky, owing to the distortion effect (shearing effect) of the spacetime geometry
upon light bundles. In lowest non-trivial order with respect to the distance,
this pattern is completely determined by the conformal curvature tensor (Weyl
tensor) at the observation event. In this paper we derive formulas that allow
to calculate these distortion patterns in terms of the Newman-Penrose
formalism. Then we represent the distortion patterns graphically for all Petrov
types, and we discuss their dependence on the velocity of the observer.


title: Relativity without relativity

abstract:
  We give a derivation of general relativity and the gauge principle that is
novel in presupposing neither spacetime nor the relativity principle. We
consider a class of actions defined on superspace with two key properties. The
first is 3-coordinate invariance. This is the only postulated symmetry, and it
leads to the standard momentum constraint. The second property is that the
Lagrangian is constructed from a `local' square root of an expression quadratic
in the velocities, `local' because it is taken before integration over 3-space.
It gives rise to quadratic constraints that do not correspond to any symmetry
and are not, in general, propagated by the Euler-Lagrange equations. Therefore
these actions are internally inconsistent. Only one action of this form is well
behaved: the Baierlein-Sharp-Wheeler reparametrisation-invariant action for GR.
  From this viewpoint, spacetime symmetry is emergent. It appears as a `hidden'
symmetry in the (underdetermined) solutions of the evolution equations, without
being manifestly coded into the action itself. In addition, propagation of the
constraints acts as a striking selection mechanism beyond pure gravity. If a
scalar field is included in the configuration space, it must have the same
characteristic speed as gravity. Thus Einstein causality emerges. Finally,
self-consistency requires that any 3-vector field must satisfy Einstein
causality, the equivalence principle and, in addition, the Gauss constraint.
Therefore we recover the standard (massless) Maxwell equations.


title: New matrix formalism for heterotic string theory on a torus

abstract:
  A new Lagrange formalism based on the use of a single scalar (d+1)X(d+1+n)
matrix potential is developed for the low-energy heterotic string theory with n
U(1) gauge fields compactified from d+3 to 3 dimensions on a torus. This
formalism also includes three pairs on-shell defined scalar and vector matrix
potentials of the dimensions (d+1)X(d+1), (d+1)X(d+1+n) and (d+1+n)X(d+1+n).
All these potentials undergo linear transformations when the group of charging
symmetries acts.


title: Gravitomagnetic Barnett Effect

abstract:
  Using the linearized theory of general relativity, the gravitomagnetic
analogue of the Barnett effect is derived. Further theoretical and experimental
investigation is recommended, due to the expected macroscopic values of the
gravitomagnetic field involved in this effect, and to the constraints which
would appear on quantum theories of gravity, currently under development, in
case of non detection of the predicted phenomena.


title: Gravitomagnetism, clocks and geometry

abstract:
  New techniques to evaluate the clock effect using light are described. These
are based on the flatness of the cylindrical surface containing the world lines
of the rays constrained to move on circular trajectories about a spinning mass.
The effect of the angular momentum of the source is manifested in the fact that
inertial observers must be replaced by local non rotating observers. Starting
from this an exact formula for circular trajectories is found. Numerical
estimates for the Earth environment show that light would be a better probe
than actual clocks to evidence the angular momentum influence. The advantages
of light in connection with some principle experiments are shortly reviewed.


title:
On a Peculiar Family of Static, Axisymmetric, Vacuum Solutions of the
  Einstein Equations

abstract:
  The Zipoy-Voorhees family of static, axisymmetric vacuum solutions forms an
interesting family in that it contains the Schwarzschild black hole excepting
which all other members have naked singularity. We analyze some properties of
the region near singularity by studying a natural family of 2-surfaces. We
establish that these have the topology of the 2-sphere by an application of the
Gauss-Bonnet theorem. By computing the area, we establish that the singular
region is `point-like'. Isometric embedding of these surfaces in the three
dimensional Euclidean space is used to distinguish the two types of deviations
from spherical symmetry.


title:
Quantum Phase Transitions and the Breakdown of Classical General
  Relativity

abstract:
  It is proposed that the event horizon of a black hole is a quantum phase
transition of the vacuum of space-time analogous to the liquid-vapor critical
point of a bose fluid. The equations of classical general relativity remain
valid arbitrarily close to the horizon yet fail there through the divergence of
a characteristic coherence length. The integrity of global time, required for
conventional quantum mechanics to be defined, is maintained. The metric inside
the event horizon is different from that predicted by classical general
relativity and may be de Sitter space. The deviations from classical behavior
lead to distinct spectroscopic and bolometric signatures that can, in
principle, be observed at large distances from the black hole.


title: Continuous matter fields in Regge calculus

abstract:
  We find that the continuous matter fields are ill-defined in Regge calculus
in the physical 4D theory since the corresponding effective action has infinite
terms unremovable by the UV renormalisation procedure. These terms are
connected with the singular nature of the curvature distribution in Regge
calculus, namely, with the presence in d>2 dimensions of the (d-3)-dimensional
simplices where the (d-2)-dimensional ones carrying different conical
singularities are meeting. Possible resolution of this difficulty is
discretisation of matter fields in Regge background.


title: Dual Metrics for a Class of Radiative Spacetimes

abstract:
  Second rank non-degenerate Killing tensors for some subclasses of spacetimes
admitting parallel null one-planes are investigated. Lichn\'erowicz radiation
conditions are imposed to provide a physical meaning to spacetimes whose
metrics are described through their associated second rank Killing tensors.
Conditions under which the dual spacetimes retain the same physical properties
are presented.


title: On the Faddeev-Popov determinant in Regge calculus

abstract:
  The functional integral measure in the 4D Regge calculus normalised w.r.t.
the DeWitt supermetric on the space of metrics is considered. The Faddeev-Popov
factor in the measure is shown according to the previous author's work on the
continuous fields in Regge calculus to be generally ill-defined due to the
conical singularities. Possible resolution of this problem is discretisation of
the gravity ghost (gauge) field by, e.g., confining ourselves to the affine
transformations of the affine frames in the simplices. This results in the
singularity of the functional measure in the vicinity of the flat background,
where part of the physical degrees of freedom connected with linklengths become
gauge ones.


title: A Quintessence Scalar Field in Brans-Dicke Theory

abstract:
  It is shown that a minimally coupled scalara field in Brans-Dicke theory
yields a non-decelerated expansion for the present universe for open, flat and
closed Friedmann-Robertson-Walker models.


title: Signature Change on the Brane

abstract:
  We explore the possibility of having a good description of classical
signature change in the brane scenario.


title: Characterizing exact solutions from asymptotic physical concepts

abstract:
  We contribute to the subject of the physical interpretation of exact
solutions by characterizing them through a systematic study in terms of
unambiguous physical concepts coming from systems in linearized gravity. We use
the physical meaning of the leading order behavior of the Weyl spinor
components $\Psi_0^0$, $\Psi_1^0$ and $\Psi_2^0$ and of the Maxwell spinor
components $\phi_0^0$ and $\phi_1^0$ and integrate from future null infinity
inwards the exact field equations. In this way it is assigned an unambiguous
physical meaning to exact solutions. We indicate a method to generalize the
procedure to radiating spacetimes.


title: Cherenkov radiation in a gravitational wave background

abstract:
  A covariant criterion for the Cherenkov radiation emission in the field of a
non-linear gravitational wave is considered in the framework of exact
integrable models of particle dynamics and electromagnetic wave propagation. It
is shown that vacuum interacting with curvature can give rise to Cherenkov
radiation. The conically shaped spatial distribution of radiation is derived
and its basic properties are discussed.


title: Spin, gravity, and inertia

abstract:
  The gravitational effects in the relativistic quantum mechanics are
investigated. The exact Foldy-Wouthuysen transformation is constructed for the
Dirac particle coupled to the static spacetime metric. As a direct application,
we analyze the non-relativistic limit of the theory. The new term describing
the specific spin (gravitational moment) interaction effect is recovered in the
Hamiltonian. The comparison of the true gravitational coupling with the purely
inertial case demonstrates that the spin relativistic effects do not violate
the equivalence principle for the Dirac fermions.


title: Relativistic Quantum Scattering on a Cone

abstract:
  We study the relativistic quantum mechanical scattering of a bosonic particle
by an infinite straight cosmic string, considering the non-minimal coupling
between the bosonic field and the scalar curvature. In this case, an effective
two-dimensional delta-function interaction takes place besides the usual
topological scattering and a renormalization procedure is necessary in order to
treat the problem that appears in connection with the delta-function.


title:
Physical Significance of the Difference between the Brans-Dicke Theory
  and General Relativity

abstract:
  The asymptotic behavior of the scalar field and its physical meaning are
discussed for T=0 and T\neq 0 for the large enough coupling parameter \omega.
The special character of the Brans-Dicke theory is also discussed for local and
cosmological problems in comparison with general relativity and the selection
rules are introduced respectivley. The scalar field by locally-distributed
matter should exhibit the asymptotic behavior \phi = <\phi> +O(1/\omega)
because of the presence of cosmological matter. The scalar field of a proper
cosmological solution should have the asymptotic form \phi =O(\rho /\omega) and
should converge to zero in the continuous limit \rho /\omega \to 0.


title:
Superinflation, quintessence, and the avoidance of the initial
  singularity

abstract:
  We consider the dynamics of a spatially flat universe dominated by a
self-interacting nonminimally coupled scalar field. The structure of the phase
space and complete phase portraits for the conformal coupling case are given.
It is shown that the non-minimal coupling modifies drastically the dynamics of
the universe. New cosmological behaviors are identified, including
superinflation ($\dot{H}>0$), avoidance of big bang singularities through
classical birth of the universe from empty Minkowski space, and spontaneous
entry into and exit from inflation. The relevance of this model to the
description of quintessence is discussed.


title: Large fluctuations of time and change of space-time signature

abstract:
  We consider five-dimensional cylindric spacetime $V^5$ with foliation of
codimension ~1. The leaves of this foliation are four-dimensional
  "parallel" universes. The metric of five-dimensional spacetime and induced
metrics of four-dimensional universes are flat. The "large" fluctuations of the
5-metric are studied. These fluctuations depend only on the coordinate $x^0$,
and under these fluctuations the curvature of $V^5$ is not zero. The
contribution of the fluctuations in the Feynman path integral over
five-dimensional trajectories doesn't change the amplitude of the probability
of the real physical four-dimensional universe. Moreover the large fluctuations
of 5-metric $G_{AB}$ are large fluctuations for physical four-dimensional
universe $V^4$ and change signature of $V^4$. The change of the signature from
$<+--->$ to $<---->$ and inversely occurs in the all 3-dimensional space
simultaneously (in absolute time) and can take arbitrarily large period of
time.


title: The close limit from a null point of view: the advanced solution

abstract:
  We present a characteristic algorithm for computing the perturbation of a
Schwarzschild spacetime by means of solving the Teukolsky equation. We
implement the algorithm as a characteristic evolution code and apply it to
compute the advanced solution to a black hole collision in the close
approximation. The code successfully tracks the initial burst and quasinormal
decay of a black hole perturbation through 10 orders of magnitude and tracks
the final power law decay through an additional 6 orders of magnitude.
Determination of the advanced solution, in which ingoing radiation is absorbed
by the black hole but no outgoing radiation is emitted, is the first stage of a
two stage approach to determining the retarded solution, which provides the
close approximation waveform with the physically appropriate boundary condition
of no ingoing radiation.


title:
Data analysis of gravitational-wave signals from spinning neutron stars.
  IV. An all-sky search

abstract:
  We develop a set of data analysis tools for a realistic all-sky search for
continuous gravitational-wave signals. The methods that we present apply to
data from both the resonant bar detectors that are currently in operation and
the laser interferometric detectors that are in the final stages of
construction and commissioning. We show that with our techniques we shall be
able to perform an all-sky 2-day long coherent search of the narrow-band data
from the resonant bar EXPLORER with no loss of signals with the dimensionless
amplitude greater than $2.8\times10^{-23}$.


title:
Twistor and "weak" gauge structures in the framework of quaternionic
  analysis

abstract:
  The earlier proposed conditions of (bi)quaternionic differentiability are
nonlinear, give rize to the 2-spinor and the self-dual gauge structures and may
be considered as the it generating system of equations (GSE) with respect to
the source-free Maxwell, Yang-Mills and eikonal equations. We present the
general solution of the GSE in terms of twistor variables, analize its rather
specific gauge symmetry and demonstrate the relation of GSE to the equations of
shear-free null congruences and, consequently, - to effective metrics of Kerr-
Shild type. The concept of particles as singularities of physical fields
associated with the solutions of GSE is developed


title: Colliding black holes from a null point of view: the close limit

abstract:
  We present a characteristic algorithm for computing the perturbations of a
Schwarzschild spacetime by means of solving the Teukolsky equations. Our
methods and results are expected to have direct bearing on the study of binary
black holes presently underway using a fully {\em nonlinear} characteristic
code \cite{Gomez98a}.


title: Quantization of Generally Covariant Systems

abstract:
  Finite dimensional models that mimic the constraint structure of Einstein's
General Relativity are quantized in the framework of BRST and Dirac's canonical
formalisms. The first system to be studied is one featuring a constraint
quadratic in the momenta (the "super-Hamiltonian") and a set of constraints
linear in the momenta (the "supermomentum" constraints). The starting point is
to realize that the ghost contributions to the supermomentum constraint
operators can be read in terms of the natural volume induced by the constraints
in the orbits. This volume plays a fundamental role in the construction of the
quadratic sector of the nilpotent BRST charge. It is shown that the quantum
theory is invariant under scaling of the super-Hamiltonian. As long as the
system has an intrinsic time, this property translates in a contribution of the
potential to the kinetic term. In this aspect, the results substantially differ
from other works where the scaling invariance is forced by introducing a
coupling to the curvature. The contribution of the potential, far from being
unnatural, is beautifully justified in the light of the Jacobi's principle.
Then, it is shown that the obtained results can be extended to systems with
extrinsic time. In this case, if the metric has a conformal temporal Killing
vector and the potential exhibits a suitable behavior with respect to it, the
role played by the potential in the case of intrinsic time is now played by the
norm of the Killing vector. Finally, the results for the previous cases are
extended to a system featuring two super-Hamiltonian constraints. This step is
extremely important due to the fact that General Relativity features an
infinite number of such constraints satisfying a non trivial algebra among
themselves.


title: Conformal Cosmology and Supernova Data

abstract:
  We define the cosmological parameters $H_{c,0}$, $\Omega_{m,c}$ and
$\Omega_{\Lambda, c}$ within the Conformal Cosmology as obtained by the
homogeneous approximation to the conformal-invariant generalization of
Einstein's General Relativity theory. We present the definitions of the age of
the universe and of the luminosity distance in the context of this approach. A
possible explanation of the recent data from distant supernovae Ia without a
cosmological constant is presented.


title:
Toward Quantum Gravity I: Newton Gravitation Constant, Cosmological
  Constant, and Classical Tests

abstract:
  This study toward quantum gravity (QG) introduces an SU(N) gauge theory with
the \Theta vacuum term as a trial theory. Newton gravitation constant G_N is
realized as the effective coupling constant for a massive graviton, G_N
/\sqrt{2} = g_f g_g^2/8 M_G^2 \simeq 10^{-38} GeV^{-2} with the gauge boson
mass M_G = M_{Pl} \simeq 10^{19} GeV, the gravitational coupling constant g_g,
and the gravitational factor g_f. This scheme postulates the effective
cosmological constant as the effective vacuum energy represented by massive
gauge bosons, \Lambda_e = 8 \pi G_N M_G^4, and provides a plausible explanation
for the small cosmological constant at the present epoch \Lambda_0 \simeq
10^{-84} GeV^2 and the large value at the Planck epoch \Lambda_{Pl} \simeq
10^{38} GeV^2; the condensation of the singlet gauge field <\phi> triggers the
current anomaly and subtracts the gauge boson mass, M_G^2 = M_{Pl}^2 - g_f
g_g^2 <\phi>^2 = g_f g_g^2 (A_{0}^2 - <\phi>^2), as the vacuum energy.
Relations among QG, general relativity, and Newtonian mechanics are discussed.