title:
Embedding of exact C*-algebras and continuous fields in the Cuntz
  algebra O_2

abstract:
  We prove that any separable exact C*-algebra is isomorphic to a subalgebra of
the Cuntz algebra ${\cal O}_2.$ We further prove that if $A$ is a simple
separable unital nuclear C*-algebra, then ${\cal O}_2 \otimes A \cong {\cal
O}_2,$ and if, in addition, $A$ is purely infinite, then ${\cal O}_{\infty}
\otimes A \cong A.$
  The embedding of exact C*-algebras in $\OA{2}$ is continuous in the following
sense. If $A$ is a continuous field of C*-algebras over a compact manifold or
finite CW complex $X$ with fiber $A (x)$ over $x \in X,$ such that the algebra
of continuous sections of $A$ is separable and exact, then there is a family of
injective homomorphisms $\phi_x : A (x) \to {\cal O}_2$ such that for every
continuous section $a$ of $A$ the function $x \mapsto \phi_x (a (x))$ is
continuous. Moreover, one can say something about the modulus of continuity of
the functions $x \mapsto \phi_x (a (x))$ in terms of the structure of the
continuous field. In particular, we show that the continuous field $\theta
\mapsto A_{\theta}$ of rotation algebras posesses unital embeddings
$\phi_{\theta}$ in ${\cal O}_2$ such that the standard generators $u (\theta)$
and $v (\theta)$ are mapped to $\operatorname{Lip}^{1/2}$ functions.


title: Analysis in $R^{1,1}$ or the Principal Function Theory

abstract:
  We explore a function theory connected with the principal series
representation of SL(2,R) in contrast to standard complex analysis connected
with the discrete series.
  We construct counterparts for the Cauchy integral formula, the Hardy space,
the Cauchy-Riemann equation and the Taylor expansion.
  Keywords: Complex analysis, Cauchy integral formula, Hardy space, Taylor
expansion, Cauchy-Riemann equations, Dirac operator, group representations,
SL(2,R), discrete series, principal series, wavelet transform, coherent states.


title: On Matrix-Valued Herglotz Functions

abstract:
  We provide a comprehensive analysis of matrix-valued Herglotz functions and
illustrate their applications in the spectral theory of self-adjoint
Hamiltonian systems including matrix-valued Schr\"odinger and Dirac-type
operators. Special emphasis is devoted to appropriate matrix-valued extensions
of the well-known Aronszajn-Donoghue theory concerning support properties of
measures in their Nevanlinna-Riesz-Herglotz representation. In particular, we
study a class of linear fractional transformations M_A(z) of a given n \times n
Herglotz matrix M(z) and prove that the minimal support of the absolutely
continuos part of the measure associated to M_A(z) is invariant under these
linear fractional transformations.
  Additional applications discussed in detail include self-adjoint finite-rank
perturbations of self-adjoint operators, self-adjoint extensions of densely
defined symmetric linear operators (especially, Friedrichs and Krein
extensions), model operators for these two cases, and associated realization
theorems for certain classes of Herglotz matrices.


title: Hilbert norms for graded algebras

abstract:
  This paper presents a solution to a problem from superanalysis about the
existence of Hilbert-Banach superalgebras. Two main results are derived: 1)
There exist Hilbert norms on some graded algebras (infinite-dimensional
superalgebras included) with respect to which the multiplication is continuous.
2) Such norms cannot be chosen to be submultiplicative and equal to one on the
unit of the algebra.


title: Tensor Products of Fell Bundles over Discrete Groups

abstract:
  We prove, by means of the tensor product of Fell bundles, that a Fell bundle
B={B_t}_{t in G} over a discrete group G has nuclear cross-sectional
C^*-algebra, whenever B has the approximation property and the unit fiber B_e
is nuclear. In particular, any twisted partial crossed product of a nuclear
C^*-algebra by an amenable discrete group is nuclear.


title:
Partial dynamical systems and C*-algebras generated by partial
  isometries

abstract:
  A collection of partial isometries whose range and initial projections
satisfy a specified set of conditions often gives rise to a partial
representation of a group. The C*-algebra generated by the partial isometries
is thus a quotient of the universal C*-algebra for partial representations of
the group, from which it inherits a crossed product structure, of an abelian
C*-algebra by a partial action of the group. Questions of faithfulness of
representations, simplicity, and ideal structure of these C*-algebras can then
be addressed in a unified manner from within the theory of partial actions. We
do this here, focusing on two key properties of partial dynamical systems,
namely amenability and topological freeness; they are the essential ingredients
of our main results in which we characterize faithful representations,
simplicity and the ideal structure of crossed products. As applications we
consider three situations involving C*-algebras generated by partial
isometries: partial representations of groups, Toeplitz algebras of
quasi-lattice ordered groups, and Cuntz-Krieger algebras. These C*-algebras
share a crossed product structure which we give here explicitly and which we
use to study them in terms of the underlying partial actions.


title: Cuntz-Krieger algebras for infinite matrices

abstract:
  Given an arbitrary infinite 0--1 matrix A having no identically zero rows, we
define an algebra OA as the universal C*-algebra generated by partial
isometries subject to conditions that generalize, to the infinite case, those
introduced by Cuntz and Krieger for finite matrices. We realize OA as the
crossed product algebra for a partial dynamical system and, based on this
description, we extend to the infinite case some of the main results known to
hold in the finite case, namely the uniqueness theorem, the classification of
ideals, and the simplicity criteria. OA is always nuclear and we obtain
conditions for it to be unital and purely infinite.


title:
A Rohlin Type Theorem for Automorphisms of Certain Purely Infinite
  $C^{\ast}$-Algebras

abstract:
  We show a noncommutative Rohlin type theorem for automorphisms of a certain
class of purely infinite simple $C^{\ast}$-algebras. This class consists of the
purely infinite unital simple $C^{\ast}$-algebras which are in the bootstrap
category ${\cal N}$ and have trivial $K_{1}$-groups.


title: Equivariance and Imprimitivity for Discrete Hopf C*-Coactions

abstract:
  Let U, V, and W be multiplicative unitaries coming from discrete Kac systems
such that W is an amenable normal submultiplicative unitary of V with quotient
U. We define notions for right-Hilbert bimodules of coactions of S_V and
(S_V)^, their restrictions to S_W and (S_U)^, their dual coactions, and their
full and reduced crossed products. If N(A) denotes the imprimitivity bimodule
associated to any coaction of S_V on a C*-algebra A by Ng's imprimitivity
theorem, then for any suitably nondegenerate injective coaction of S_V on a
right-Hilbert A - B bimodule X we establish an isomorphism between two tensor
product bimodules involving N(A), N(B), and certain crossed products of X. This
can be interpreted as a natural transformation between two crossed-product
functors.


title: C*-Crossed Products by Twisted Inverse Semigroup Actions

abstract:
  The notions of Busby-Smith and Green type twisted actions are extended to
discrete unital inverse semigroups. The connection between the two types, and
the connection with twisted partial actions, are investigated. Decomposition
theorems for the twisted crossed products are given.


title:
Can Quantum Cosmology Give Observational Consequences of Many-Worlds
  Quantum Theory?

abstract:
  Although many people have thought that the difference between the Copenhagen
and many-worlds versions of quantum theory was merely metaphysical, quantum
cosmology may allow us to make a physical test to distinguish between them
empirically. The difference between the two versions shows up when the various
components of the wavefunction have different numbers of observers and
observations. In the Copenhagen version, a random observation is selected from
the sample within the component that is selected by wavefunction collapse, but
in the many-worlds version, a random observation is selected from those in all
components. Because of the difference in the samples, probable observations in
one version can be very improbable in the other version.


title: Evolution of thin-wall configurations of texture matter

abstract:
  We consider the free matter of global textures within the framework of the
perfect fluid approximation in general relativity. We examine thermodynamical
properties of texture matter in comparison with radiation fluid and bubble
matter. Then we study dynamics of thin-wall selfgravitating texture objects,
and show that classical motion can be elliptical (finite), parabolical or
hyperbolical. It is shown that total gravitational mass of neutral textures in
equilibrium equals to zero as was expected. Finally, we perform the
Wheeler-DeWitt's minisuperspace quantization of the theory, obtain exact wave
functions and discrete spectra of bound states with provision for spatial
topology.


title: Regularity of Horizons and The Area Theorem

abstract:
  We prove that the area of sections of future event horizons in space-times
satisfying the null energy condition is non-decreasing towards the future under
any one of the following circumstances: 1) the horizon is future geodesically
complete; 2) the horizon is a black hole event horizon in a globally hyperbolic
space-time and there exists a conformal completion with a ``H-regular'' Scri
plus; 3) the horizon is a black hole event horizon in a space-time which has a
globally hyperbolic conformal completion. (Some related results under less
restrictive hypotheses are also established.) This extends a theorem of
Hawking, in which piecewise smoothness of the event horizon seems to have been
assumed. No assumptions about the cosmological constant or its sign are made.
We prove smoothness or analyticity of the relevant part of the event horizon
when equality in the area inequality is attained - this has applications to the
theory of stationary black holes, as well as to the structure of compact Cauchy
horizons. In the course of the proof we establish several new results
concerning the differentiability properties of horizons.


title: Ricci Collineations of the Bianchi Type II, VIII, and IX Space-times

abstract:
  Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX
space-times, associated with the vector fields of the form (i) one component of
$\xi^a(x^b)$ is different from zero and (ii) two components of $\xi^a(x^b)$ are
different from zero, for $a,b=1,2,3,4$, are presented. In subcase (i.b), which
is $\xi^a= (0,\xi^2(x^a),0,0)$, some known solutions are found, and in subcase
(i.d), which is $\xi^a =(0,0,0,\xi^4(x^a))$, choosing $S(t)=const.\times R(t)$,
the Bianchi type II, VIII, and IX space-times is reduced to the
Robertson-Walker metric.


title: One Proposal about the Nature during Our Time and Space

abstract:
  It made that the new symmetric property, the binary law, existed newly in our
time and space at the thing except the symmetric property of the principle of
general relativity which is already known in this paper clear. The introduction
of this symmetric property will have made dealing with the position tensor of
us handy as much as the surprise.


title: Symmetries and conservation laws in histories-based theories

abstract:
  Symmetries are defined in histories-based theories paying special attention
to the class of history theories admitting quasitemporal structure (a
generalization of the concept of `temporal sequences' of `events' using partial
semigroups) and logic structure for `single-time histories'. Symmetries are
classified into orthochronous (those preserving the `temporal order' of
`events') and nonorthochronous. A straightforward criterion for physical
equivalence of histories is formulated in terms of orthochronous symmetries;
this criterion covers various notions of physical equivalence of histories
considered by Gell-Mann and Hartle as special cases. In familiar situations, a
reciprocal relationship between traditional symmetries (Wigner symmetries in
quantum mechanics and Borel-measurable transformations of phase space in
classical mechanics) and symmetries defined in this work is established. In a
restricted class of theories, a definition of conservation law is given in the
history language which agrees with the standard ones in familiar situations; in
a smaller subclass of theories, a Noether type theorem (implying a connection
between continuous symmetries of dynamics and conservation laws) is proved. The
formalism evolved is applied to histories (of particles, fields or more general
objects) in general curved spacetimes. Sharpening the definition of symmetry so
as to include a continuity requirement, it is shown that a symmetry in our
formalism implies a conformal isometry of the spacetime metric.


title:
Is the cosmological singularity really unavoidable in general
  relativity?

abstract:
  The initial singularity problem in standard general relativity is treated on
the light of a viewpoint asserting that this formulation of Einstein's theory
and its conformal formulations are physically equivalent. We show that flat
Friedmann-Robertson-Walker universes and open dust-filled and radiation-filled
universes are singularity free when described in terms of the formulation of
general relativity conformal to the canonical one.


title: Local and global existence theorems for the Einstein equations

abstract:
  This article is a guide to the literature on existence theorems for the
Einstein equations which also draws attention to open problems in the field.
The local in time Cauchy problem, which is relatively well understood, is
treated first. Next global results for solutions with symmetry are discussed. A
selection of results from Newtonian theory and special relativity which offer
useful comparisons is presented. This is followed by a survey of global results
in the case of small data and results on constructing spacetimes with given
singularity structure. The article ends with some miscellaneous topics
connected with the main theme.


title: Quantum Inequalities in Curved Two Dimensional Spacetimes

abstract:
  In quantum field theory there exist states for which the energy density is
negative. It is important that these negative energy densities satisfy
constraints, such as quantum inequalities, to minimize possible violations of
causality, the second law of thermodynamics, and cosmic censorship. In this
paper I show that conformally invariant scalar and Dirac fields satisfy quantum
inequalities in two dimensional spacetimes with a conformal factor that depends
on $x$ only or on $t$ only. These inequalities are then applied to two
dimensional black hole and cosmological spacetimes. It is shown that the bound
on the negative energies diverges to minus infinity as the event horizon or
initial singularity is approached. Thus, neglecting back reaction, negative
energies become unconstrained near the horizon or initial singularity. The
results of this paper also support the hypothesis that the quantum interest
conjecture applies only to deviations from the vacuum polarization energy, not
to the total energy.


title:
How does the electromagnetic field couple to gravity, in particular to
  metric, nonmetricity, torsion, and curvature?

abstract:
  The coupling of the electromagnetic field to gravity is an age-old problem.
Presently, there is a resurgence of interest in it, mainly for two reasons: (i)
Experimental investigations are under way with ever increasing precision, be it
in the laboratory or by observing outer space. (ii) One desires to test out
alternatives to Einstein's gravitational theory, in particular those of a
gauge-theoretical nature, like Einstein-Cartan theory or metric-affine gravity.
A clean discussion requires a reflection on the foundations of electrodynamics.
If one bases electrodynamics on the conservation laws of electric charge and
magnetic flux, one finds Maxwell's equations expressed in terms of the
excitation H=(D,H) and the field strength F=(E,B) without any intervention of
the metric or the linear connection of spacetime. In other words, there is
still no coupling to gravity. Only the constitutive law H= functional(F)
mediates such a coupling. We discuss the different ways of how metric,
nonmetricity, torsion, and curvature can come into play here. Along the way, we
touch on non-local laws (Mashhoon), non-linear ones (Born-Infeld,
Heisenberg-Euler, Plebanski), linear ones, including the Abelian axion (Ni),
and find a method for deriving the metric from linear electrodynamics (Toupin,
Schoenberg). Finally, we discuss possible non-minimal coupling schemes.


title: Attractive and Repulsive Gravity

abstract:
  We discuss the circumstances under which gravity might be repulsive rather
than attractive. In particular we show why our standard solar system distance
scale gravitational intuition need not be a reliable guide to the behavior of
gravitational phenomena on altogether larger distance scales such as
cosmological, and argue that in fact gravity actually gets to act repulsively
on such distance scales. With such repulsion a variety of current cosmological
problems (the flatness, horizon, dark matter, universe age, cosmic acceleration
and cosmological constant problems) are then all naturally resolved.


title:
Gravitational Solitons and Monodromy Transform Approach to Solution of
  Integrable Reductions of Einstein Equations

abstract:
  In this paper the well known Belinskii and Zakharov soliton generating
transformations of the solution space of vacuum Einstein equations with
two-dimensional Abelian groups of isometries are considered in the context of
the so called "monodromy transform approach", which provides some general base
for the study of various integrable space - time symmetry reductions of
Einstein equations. Similarly to the scattering data used in the known spectral
transform, in this approach the monodromy data for solution of associated
linear system characterize completely any solution of the reduced Einstein
equations, and many physical and geometrical properties of the solutions can be
expressed directly in terms of the analytical structure on the spectral plane
of the corresponding monodromy data functions. The Belinskii and Zakharov
vacuum soliton generating transformations can be expressed in explicit form
(without specification of the background solution) as simple
(linear-fractional) transformations of the corresponding monodromy data
functions with coefficients, polynomial in spectral parameter. This allows to
determine many physical parameters of the generating soliton solutions without
(or before) calculation of all components of the solutions. The similar
characterization for electrovacuum soliton generating transformations is also
presented.


title: Transition from inspiral to plunge in binary black hole coalescences

abstract:
  Combining recent techniques giving non-perturbative re-summed estimates of
the damping and conservative parts of the two-body dynamics, we describe the
transition between the adiabatic phase and the plunge, in coalescing binary
black holes with comparable masses moving on quasi-circular orbits. We give
initial dynamical data for numerical relativity investigations, with a fraction
of an orbit left, and provide, for data analysis purposes, an estimate of the
gravitational wave-form emitted throughout the inspiral, plunge and coalescence
phases.


title: Spectral Representation and the Averaging Problem in Cosmology

abstract:
  We investigate the averaging problem in cosmology as the problem of
introducing a distance between spaces.
  We first introduce the spectral distance, which is a measure of closeness
between spaces defined in terms of the spectra of the Laplacian. Then we define
a space S, the space of all spaces equipped with the spectral distance. We
argue that this space S can be regarded as a metric space and that it also
possess other desirable properties. These facts make the space S a suitable
arena for spacetime physics.
  We apply the spectral framework to the averaging problem:
  We sketch the model-fitting procedure in terms of the spectral
representation, and also discuss briefly how to analyze the dynamical aspects
of the averaging procedure with this scheme.
  In these analyses, we are naturally led to the concept of the apparatus- and
the scale-dependent effective evolution of the universe. These observations
suggest that the spectral scheme seems to be suitable for the quantitative
analysis of the averaging problem in cosmology.


title:
Dynamics of a string coupled to gravitational waves - Gravitational wave
  scattering by a Nambu-Goto straight string

abstract:
  We study the perturbative dynamics of an infinite gravitating Nambu-Goto
string within the general-relativistic perturbation framework. We develop the
gauge invariant metric perturbation on a spacetime containing a
self-gravitating straight string with a finite thickness and solve the
linearized Einstein equation. In the thin string case, we show that the string
does not emit gravitational waves by its free oscillation in the first order
with respect to its oscillation amplitude, nevertheless the string actually
bends when the incidental gravitational waves go through it.


title: BTZ Black Hole Entropy in Higher Curvature Gravity

abstract:
  For the BTZ black hole in the Einstein gravity, a statistical entropy has
been calculated. It is equal to the Bekenstein-Hawking entropy. In this
article, its statistical entropy in the higer curvature gravity is calculated
and shown to be equal to one derived by using the Noether charge method. This
suggests that the equivalence between the geometrical and statistical entropies
of the black hole is retained in the general diffeomorphism invariant theories
of gravity. A relation between the cosmic censorship conjecture and the
unitarity of the conformal field theory on the boundary of AdS_3 is also
discussed.


title:
General analysis of self-dual solutions for the
  Einstein-Maxwell-Chern-Simons theory in (1+2) dimensions

abstract:
  The solutions of the Einstein-Maxwell-Chern-Simons theory are studied in
(1+2) dimensions with the self-duality condition imposed on the Maxwell field.
We give a closed form of the general solution which is determined by a single
function having the physical meaning of the quasilocal angular momentum of the
solution. This function completely determines the geometry of spacetime, also
providing the direct computation of the conserved total mass and angular
momentum of the configurations.


title: On the structure of solutions to the static vacuum Einstein equations

abstract:
  A complete characterization is obtained of the asymptotic behavior of
solutions of the static vacuum Einstein equations which have a (pseudo)-compact
horizon or boundary and are complete away from the boundary. It is proved that
the time-symmetric space-like hypersurface has only finitely many ends, each of
which is either asymptotically flat (AF) or parabolic, as in the (static)
Kasner metric. Examples are given with both types of behavior, together with an
extensive discussion and new characterization of Weyl metrics. The asymptotics
result allows one in most circumstances to drop the AF assumption from the
static black hole uniqueness theorems and replace it with just a completeness
assumption.


title: The world is not enough

abstract:
  We show that the 5-dimensional model introduced by Randall and Sundrum is
(half of) a wormhole, and that this is a general result in models of the RS
type. We also discuss the gravitational trapping of a scalar particle in 5-d
spacetimes. Finally, we present a simple model of brane-world cosmology in
which the background is a static anti-de Sitter manifold, and the location of
the two 3-branes is determined by the technique of ``surgical grafting''.


title: Locally Anisotropic Black Holes in Einstein Gravity

abstract:
  By applying the method of moving frames modelling one and two dimensional
local anisotropies we construct new solutions of Einstein equations on
pseudo-Riemannian spacetimes. The first class of solutions describes
non-trivial deformations of static spherically symmetric black holes to locally
anisotropic ones which have elliptic (in three dimensions) and ellipsoidal,
toroidal and elliptic and another forms of cylinder symmetries (in four
dimensions). The second class consists from black holes with oscillating
elliptic horizons.


title:
Second order perturbations of a Schwarzschild black hole: inclusion of
  odd parity perturbations

abstract:
  We consider perturbations of a Schwarzschild black hole that can be of both
even and odd parity, keeping terms up to second order in perturbation theory,
for the $\ell=2$ axisymmetric case. We develop explicit formulae for the
evolution equations and radiated energies and waveforms using the
Regge-Wheeler-Zerilli approach. This formulation is useful, for instance, for
the treatment in the ``close limit approximation'' of the collision of
counterrotating black holes.


title: Atom made from charged elementary black hole

abstract:
  It is believed that there may have been a large number of black holes formed
in the very early universe. These would have quantised masses. A charged
``elementary black hole'' (with the minimum possible mass) can capture
electrons, protons and other charged particles to form a ``black hole atom''.
We find the spectrum of such an object with a view to laboratory and
astronomical observation of them, and estimate the lifetime of the bound
states. There is no limit to the charge of the black hole, which gives us the
possibility of observing Z>137 bound states and transitions at the lower
continuum. Negatively charged black holes can capture protons. For Z>1, the
orbiting protons will coalesce to form a nucleus (after beta-decay of some
protons to neutrons), with a stability curve different to that of free nuclei.
In this system there is also the distinct possibility of single quark capture.
This leads to the formation of a coloured black hole that plays the role of an
extremely heavy quark interacting strongly with the other two quarks. Finally
we consider atoms formed with much larger black holes.


title:
Frequency-domain P-approximant filters for time-truncated inspiral
  gravitational wave signals from compact binaries

abstract:
  Frequency-domain filters for time-windowed gravitational waves from
inspiralling compact binaries are constructed which combine the excellent
performance of our previously developed time-domain P-approximants with the
analytic convenience of the stationary phase approximation without a serious
loss in event rate. These Fourier-domain representations incorporate the ``edge
oscillations'' due to the (assumed) abrupt shut-off of the time-domain signal
caused by the relativistic plunge at the last stable orbit. These new analytic
approximations, the SPP-approximants, are not only `effectual' for detection
and `faithful' for parameter estimation, but are also computationally
inexpensive to generate (and are `faster' by factors up to 10, as compared to
the corresponding time-domain templates). The SPP approximants should provide
data analysts the Fourier-domain templates for massive black hole binaries of
total mass m less than about 40 solar mases, the most likely sources for LIGO
and VIRGO.


title: The inverse scattering method for cylindrical gravitational waves

abstract:
  The initial-value problem for cylindrical gravitational waves is studied
through the development of the inverse scattering method scheme. The inverse
scattering transform in this case can be viewed as a transformation of the
Cauchy data to the data on the symmetry axis. Riemann-Hilbert problem, which
serves as inverse transformation, is formulated in two different ways. We
consider Einstein-Rosen waves to illustrate the method.


title:
The self-force on a static scalar test-charge outside a Schwarzschild
  black hole

abstract:
  The finite part of the self-force on a static scalar test-charge outside a
Schwarzschild black hole is zero. By direct construction of Hadamard's
elementary solution, we obtain a closed-form expression for the minimally
coupled scalar field produced by a test-charge held fixed in Schwarzschild
spacetime. Using the closed-form expression, we compute the necessary external
force required to hold the charge stationary. Although the energy associated
with the scalar field contributes to the renormalized mass of the particle (and
thereby its weight), we find there is no additional self-force acting on the
charge. This result is unlike the analogous electrostatic result, where, after
a similar mass renormalization, there remains a finite repulsive self-force
acting on a static electric test-charge outside a Schwarzschild black hole. We
confirm our force calculation using Carter's mass-variation theorem for black
holes. The primary motivation for this calculation is to develop techniques and
formalism for computing all forces - dissipative and non-dissipative - acting
on charges and masses moving in a black-hole spacetime. In the Appendix we
recap the derivation of the closed-form electrostatic potential. We also show
how the closed-form expressions for the fields are related to the infinite
series solutions.


title: The Central Singularity in Spherical Collapse

abstract:
  The gravitational strength of the central singularity in spherically
symmetric space-times is investigated. Necessary conditions for the singularity
to be gravitationally weak are derived and it is shown that these are violated
in a wide variety of circumstances. These conditions allow conclusions to be
drawn about the nature of the singularity without having to integrate the
geodesic equations. In particular, any geodesic with a non-zero amount of
angular momentum which impinges on the singularity terminates in a strong
curvature singularity.


title: Fermion Stars with an Extra Dimension

abstract:
  Many efforts have been devoted to the studies of the phenomenology in
particle physics with extra dimensions. We propose the degenerate fermion star
in the five dimensions, and study what effects caused by the geometry of extra
dimensions should appear in its structure. We note that Kaluza-Klein excited
modes have effects for the larger scale of extra dimensions and examine the
conditions on which different layers should be caused in the inside of the
stars. We expound how the effects of the extra dimensions appears on physical
quantities.


title: Finite Temperature Field Theory of "Extreme Black Holes"

abstract:
  We treat the model which describes "extreme black holes" moving slowly. We
derive an effective lagrangian in the low energy for this model and then
investigate a statistical behavior of "extreme black holes" in the finite
temperature.


title: Scalar-Tensor Gravity in Two 3-brane System

abstract:
  We derive the low-energy effective action of four-dimensional gravity in the
Randall-Sundrum scenario in which two 3-branes of opposite tension reside in a
five-dimensional spacetime. The dimensional reduction with the Ansatz for the
radion field by Charmousis et al., which solves five-dimensional linearized
field equations, results in a class of scalar-tensor gravity theories. In the
limit of vanishing radion fluctuations, the effective action reduces to the
Brans-Dicke gravity in accord with the results of Garriga and Tanaka:
Brans-Dicke gravity with the corresponding Brans-Dicke parameter $0< \omega <
\infty$ (for positive tension brane) and $-3/2< \omega <0$ (for negative
tension brane). In general the gravity induced a brane belongs to a class of
scalar-tensor gravity with the Brans-Dicke parameter which is a function of the
interval and the radion. In particular, gravity on a positive tension brane
contains an attractor mechanism toward the Einstein gravity.


title:
Time Dispersion and Efficiency of Detection for Signals in Gravitational
  Wave Experiments

abstract:
  Using simulated signals and measured noise with the EXPLORER and NAUTILUS
detectors we find the efficiency of signal detection and the signal arrival
time dispersion versus the signal-to-noise ratio.


title:
4d neutral dilatonic black holes and (4+p) dimensional nondilatonic
  black p-branes

abstract:
  It is shown that, in contrast to the case of extreme 4d dilatonic black
holes, 4d neutral dilatonic black holes with horizon singularities can not be
interpreted as nonsingular nondilatonic black p-branes in (4+p) dimensions,
regardless of the number of extra dimensions p. That is, extra dimensions do
not remove naked singularities of 4d neutral dilatonic black holes.


title:
Analytic treatment of black-hole gravitational waves at the
  algebraically special frequency

abstract:
  We study the Regge-Wheeler and Zerilli equations (RWE and ZE) at the
`algebraically special frequency' $\Omega$, where these equations admit an
exact solution (elaborated here), generating the SUSY relationship between
them. The physical significance of the SUSY generator and of the solutions at
$\Omega$ in general is elucidated as follows. The RWE has no (quasinormal or
total-transmission) modes at all; however, $\Omega$ is nonetheless `special' in
that (a) for the outgoing wave into the horizon one has a `miraculous'
cancellation of a divergence expected due to the exponential potential tail,
and (b) the branch-cut discontinuity at $\omega=\Omega$ vanishes in the
outgoing wave to infinity. Moreover, (a) and (b) are related. For the ZE, its
only mode is the-inverse-SUSY generator, which is at the same time a
quasinormal mode_and_ a total-transmission mode propagating to infinity. The
subtlety of these findings (of general relevance for future study of the
equations on or near the negative imaginary $\omega$-axis) may help explain why
the situation has sometimes been controversial. For finite black-hole rotation,
the algebraically special modes are shown to be totally transmitting, and the
implied singular nature of the Schwarzschild limit is clarified. The analysis
draws on a recent detailed investigation of SUSY in open systems
[math-ph/9909030].


title: Birth of the Brane World

abstract:
  Birth of the brane world is studied using the Hamiltonian approach. It is
shown that an inflating brane world can be created from nothing. The wave
function of the universe obtained from the Wheeler de-Witt equation and the
time-dependent Schr$\ddot{o}$dinger equation for quantized scalar fields on the
brane are the same as in the conventional 4-dimensional quantum cosmology if
the bulk is exactly the Anti-de Sitter spacetime. The effect of the massive
objects in the bulk is also discussed. This analysis tells us the presence of
the extra dimension imprints a nontrivial effect on the quantum cosmology of
the brane world. This fact is important for the analysis of the quantum
fluctuations in the inflationary scenario of the brane world.


title: Creation of an Open Universe from Valley Bounce

abstract:
  It appears difficult to construct a simple model for an open universe based
on the one bubble inflationary scenario. The reason is that one needs a large
mass to avoid the tunneling via the Hawking Moss solution and a small mass for
successful slow-rolling. However, Rubakov and Sibiryakov suggest that the
Hawking Moss solution is not a solution for the false vacuum decay process
since it does not satisfy the boundary condition. Hence, we have reconsidered
the arguments for the defect of the simple polynomial model. We find the valley
bounce belonging to a valley line in the functional space represents the decay
process instead of the Hawking Moss solution. The point is that the valley
bounce gives the appropriate initial condition for the inflation. We show an
open inflation model can be constructed within the polynomial form of the
potential so that the fluctuations can be reconciled with the observations.


title: On Upper Limits for Gravitational Radiation

abstract:
  A procedure with a Bayesan approach for calculating upper limits to
gravitational wave bursts from coincidence experiments with multiple detectors
is described.

categories: gr-qc hep-ex hep-ph math.PR physics.data-an


title: Towards a Deeper Understanding of General Relativity

abstract:
  Standard treatments of general relativity accept the gravitational slowing of
clocks as a primary phenomenon, requiring no further analysis as to cause.
Rejecting this attitude, I argue that one or more of the fundamental
"constants" governing the quantum mechanics of atoms must depend upon position
in a gravitational field. A simple relationship governing the possible
dependencies of e, h, c and m is deduced, and arguments in favor of the choice
of the electron rest mass, m, are presented. The reduction of rest mass is thus
taken to be the sole cause of clock slowing. Importantly, this dependency
implies another effect, heretofore unsuspected, namely, the gravitational
elongation of measuring rods. An alternate ("telemetric") system of measurement
is introduced, leading to a metric that is conformally related to the usual
proper metric. In terms of the new system, many otherwise puzzling phenomena
may be simply understood. In particular,the geometry of the Schwarzschild space
as described by the telemetric system differs profoundly from that described by
proper measurments, leading to a very different understanding of the structure
of black holes. The theory is extended to cosmology,leading to a remarkable
alternate view of the structure and history of the universe.


title: Spacetime perspective of Schwarzschild lensing

abstract:
  We propose a definition of an exact lens equation without reference to a
background spacetime, and construct the exact lens equation explicitly in the
case of Schwarzschild spacetime. For the Schwarzschild case, we give exact
expressions for the angular-diameter distance to the sources as well as for the
magnification factor and time of arrival of the images. We compare the exact
lens equation with the standard lens equation, derived under the
thin-lens-weak-field assumption (where the light rays are geodesics of the
background with sharp bending in the lens plane, and the gravitational field is
weak), and verify the fact that the standard weak-field thin-lens equation is
inadequate at small impact parameter. We show that the second-order correction
to the weak-field thin-lens equation is inaccurate as well. Finally, we compare
the exact lens equation with the recently proposed strong-field thin-lens
equation, obtained under the assumption of straight paths but without the small
angle approximation, i.e., with allowed large bending angles. We show that the
strong-field thin-lens equation is remarkably accurate, even for lightrays that
take several turns around the lens before reaching the observer.


title: The virtual black hole in 2d quantum gravity

abstract:
  As shown recently (W. Kummer, H. Liebl, D.V. Vassilevich, Nucl. Phys. B 544,
403 (1999)) 2d quantum gravity theories --- including spherically reduced
Einstein-gravity --- after an exact path integral of its geometric part can be
treated perturbatively in the loops of (scalar) matter. Obviously the classical
mechanism of black hole formation should be contained in the tree approximation
of the theory. This is shown to be the case for the scattering of two scalars
through an intermediate state which by its effective black hole mass is
identified as a ``virtual black hole''. The present discussion is restricted to
minimally coupled scalars without and with mass. In the first case the
probability amplitude diverges, except the black hole is ``plugged'' by a
suitable boundary condition. For massive scalars a finite S-matrix element is
obtained.


title: Rotating 5D-Kaluza-Klein Space-Times from Invariant Transformations

abstract:
  Using invariant transformations of the five-dimensional Kaluza-Klein (KK)
field equations, we find a series of formulae to derive axial symmetric
stationary exact solutions of the KK theory starting from static ones. The
procedure presented in this work allows to derive new exact solutions up to
very simple integrations. Among other results, we find exact rotating solutions
containing magnetic monopoles, dipoles, quadripoles, etc., coupled to scalar
and to gravitational multipole fields.


title: A proposal for analyzing the classical limit of kinematic loop gravity

abstract:
  We analyze the classical limit of kinematic loop quantum gravity in which the
diffeomorphism and hamiltonian constraints are ignored. We show that there are
no quantum states in which the primary variables of the loop approach, namely
the SU(2) holonomies along {\em all} possible loops, approximate their
classical counterparts. At most a countable number of loops must be specified.
To preserve spatial covariance, we choose this set of loops to be based on
physical lattices specified by the quasi-classical states themselves. We
construct ``macroscopic'' operators based on such lattices and propose that
these operators be used to analyze the classical limit. Thus, our aim is to
approximate classical data using states in which appropriate macroscopic
operators have low quantum fluctuations.
  Although, in principle, the holonomies of `large' loops on these lattices
could be used to analyze the classical limit, we argue that it may be simpler
to base the analysis on an alternate set of ``flux'' based operators. We
explicitly construct candidate quasi-classical states in 2 spatial dimensions
and indicate how these constructions may generalize to 3d. We discuss the less
robust aspects of our proposal with a view towards possible modifications.
Finally, we show that our proposal also applies to the diffeomorphism invariant
Rovelli model which couples a matter reference system to the Hussain Kucha{\v
r} model.


title:
On cosmological perturbations in FRW model with scalar field and false
  vacuum decay

abstract:
  The unconstrained reduced action corresponding to the dynamics of scalar
fluctuations about the Friedmann-Robertson-Walker (FRW) background is derived
using Dirac's method of description of singular Lagrangian systems. The results
are applied to so-called negative mode problem in description of tunneling
transitions with gravity. With our special choice of physical variable, the
kinetic term of the reduced action has a conventional signature for a wide
class of models. In this representation, the existence of a negative mode
justifying the false vacuum decay picture turns out to be manifest. We also
explain how the present result becomes consistent with the previously proved
``no negative mode (supercritical supercurvature mode) theorem''.


title: Can a Particle's Velocity Exceed the Speed of Light in Empty Space?

abstract:
  Relative motion in space with multifractal time (fractional dimension of time
close to integer $d_{t}=1+\epsilon (r,t), \epsilon \ll 1$) for "almost"
inertial frames of reference (time is almost homogeneous and almost isotropic)
is considered. Presence in such space of absolute frames of reference and
violation of conservation laws (though, small because of the smallness of
$\epsilon$) due to the openness of all physical systems and inhomogeneiy of
time are shown. The total energy of a body moving with $v=c$ is obtained to be
finite and modified Lorentz transformations are formulated. The relation for
the total energy (and the whole theory) reduce to the known formula of the
special relativity in case of transition to the usual time with dimension equal
to one.


title: Physical Consequences of Moving Faster than Light in Empty Space

abstract:
  Physical phenomena caused by particle's moving faster than light in a space
with multifractal time with dimension close to integer
($d_{t}=1+\epsilon(r(t),t), |\epsilon| \ll 1$ - time is almost homogeneous and
almost isotropic) are considered. The presence of gravitational field is taken
into account. According to the results of the developed by the author theory, a
particle with the rest energy $E_{0}$ would achieve the velocity of light if
given the energy of about $E \sim 10^{3}E_{0}$


title:
A power filter for the detection of burst sources of gravitational
  radiation in interferometric detectors

abstract:
  We present a filter for detecting gravitational wave signals from burst
sources. This filter requires only minimal advance knowledge of the expected
signal: i.e. the signal's frequency band and time duration. It consists of a
threshold on the total power in the data stream in the specified signal band
during the specified time. This filter is optimal (in the Neyman-Pearson sense)
for signal searches where only this minimal information is available.


title: Reissner-Nordstr\"om-AdS black hole in the GEMS approach

abstract:
  We obtain a (5+2)-dimensional global flat embedding of the (3+1)-dimensional
curved RN-AdS space. Our results include the various limiting cases of global
embedding Minkowski space (GEMS) geometries of the RN, Schwarzschild-AdS in
(5+2)-dimensions, Schwarzschild in (5+1)-dimensions, purely charged space, and
universal covering space of AdS in (4+1)-dimensions, through the successive
truncation procedure of parameters in the original curved space.


title: Critical phenomena in gravitational collapse - Living Reviews

abstract:
  As first discovered by Choptuik, the black hole threshold in the space of
initial data for general relativity shows both surprising structure and
surprising simplicity. Universality, power-law scaling of the black hole mass,
and scale echoing have given rise to the term ``critical phenomena''. They are
explained by the existence of exact solutions which are attractors within the
black hole threshold, that is, attractors of codimension one in phase space,
and which are typically self-similar. This review gives an introduction to the
phenomena, tries to summarize the essential features of what is happening, and
then presents extensions and applications of this basic scenario. Critical
phenomena are of interest particularly for creating surprising structure from
simple equations, and for the light they throw on cosmic censorship and the
generic dynamics of general relativity.


title: Quiescent cosmological singularities

abstract:
  The most detailed existing proposal for the structure of spacetime
singularities originates in the work of Belinskii, Khalatnikov and Lifshitz. We
show rigorously the correctness of this proposal in the case of analytic
solutions of the Einstein equations coupled to a scalar field or stiff fluid.
More specifically, we prove the existence of a family of spacetimes depending
on the same number of free functions as the general solution which have the
asymptotics suggested by the Belinskii-Khalatnikov-Lifshitz proposal near their
singularities. In these spacetimes a neighbourhood of the singularity can be
covered by a Gaussian coordinate system in which the singularity is
simultaneous and the evolution at different spatial points decouples.


title: On Gravity, Holography and the Quantum

abstract:
  The holographic principle states that the number of degrees of freedom
describing the physics inside a volume (including gravity) is bounded by the
area of the boundary (also called the screen) which encloses this volume. A
stronger statement is that these (quantum) degrees of freedom live on the
boundary and describe the physics inside the volume completely. The obvious
question is, what mechanism is behind the holographic principle. Recently, 't
Hooft argued that the quantum degrees of freedom on the boundary are not
fundamental. We argue that this interpretation opens up the possibility that
the mapping between the theory in the bulk (the holographic theory) and the
theory on the screen (the dual theory) is always given by a (generalized)
procedure of stochastic quantization. We show that gravity causes differences
to the situation in Minkowski/Euclidean spacetime and argue that the fictitious
coordinate needed in the stochastic quantization procedure can be spatial. The
diffusion coefficient of the stochastic process is in general a function of
this coordinate. While a mapping of a bulk theory onto a (quantum) boundary
theory can be possible, such a mapping does not make sense in spacetimes in
which the area of the screen is growing with time. This is connected to the
average process in the formalism of stochastic quantization. We show where the
stochastic quantization procedure breaks down and argue, in agreement with `t
Hooft, that the quantum degrees of freedom are not fundamental degrees of
freedom. They appear as a limit of a more complex process.


title:
The collision and snapping of cosmic strings generating spherical
  impulsive gravitational waves

abstract:
  The Penrose method for constructing spherical impulsive gravitational waves
is investigated in detail, including alternative spatial sections and an
arbitrary cosmological constant. The resulting waves include those that are
generated by a snapping cosmic string. The method is used to construct an
explicit exact solution of Einstein's equations describing the collision of two
nonaligned cosmic strings in a Minkowski background which snap at their point
of collision.


title: Fock representations from U(1) holonomy algebras

abstract:
  We revisit the quantization of U(1) holonomy algebras using the abelian C*
algebra based techniques which form the mathematical underpinnings of current
efforts to construct loop quantum gravity. In particular, we clarify the role
of ``smeared loops'' and of Poincare invariance in the construction of Fock
representations of these algebras. This enables us to critically re-examine
early pioneering efforts to construct Fock space representations of linearised
gravity and free Maxwell theory from holonomy algebras through an application
of the (then current) techniques of loop quantum gravity.


title:
Cosmological Constant, Quintessence and Scalar-Tensor Theories of
  Gravity

abstract:
  We show how the scalar field, a candidate of quintessence, in a proposed
model of the scalar-tensor theories of gravity provides a way to understand a
small but nonzero cosmological constant as indicated by recent observations. A
particular emphasis is placed on the effort to inherit the success of the
scenario of a decaying cosmological constant. Discussions of a possible link to
non-Newtonian gravity, the coincidence problem, the issue of time-variability
of coupling constants as well as the chaos-like nature of the solution are also
included in a new perspective.


title: Covariant two-point function for linear gravity in de Sitter space

abstract:
  The Wightman two-point function for the gravitational field in the linear
approximation (the rank-2 ``massless'' tensor field) on de Sitter space has a
pathological behaviour for large separated points (infrared divergence). This
behaviour can be eliminated in the two-point function for the traceless part of
this field if one chooses the Gupta-Bleuler vacuum. But it is not possible to
do the same for the pure trace part (conformal sector). We briefly discuss the
consequences of this pure trace behaviour for inflationary models.


title:
Areas of the Event Horizon and Stationary Limit Surface for a Kerr Black
  Hole

abstract:
  We present an elementary evaluation of the surface areas of the event horizon
and stationary limit surface for an uncharged Kerr black hole. The latter
appears not to have been previously given in the literature, and permits us to
suggest new geometrical / physical interpretations of these areas.


title: Generalised scalar-tensor theory in the Bianchi type I model

abstract:
  We use a conformal transformation to find solutions to the generalised
scalar-tensor theory, with a coupling constant dependent on a scalar field, in
an empty Bianchi type I model. We describe the dynamical behaviour of the
metric functions for three different couplings: two exact solutions to the
field equations and a qualitative one are found. They exhibit non-singular
behaviours and kinetic inflation. Two of them admit both General Relativity and
string theory in the low-energy limit as asymptotic cases.


title:
A remark on Brans-Dicke dust cosmological solutions with negative
  $\omega$

abstract:
  Analysing the Brans-Dicke solutions for the dust phase, we show that, for
negative values of $\omega$, they contain scenarios that display an initial
subluminal expansion followed by an inflationary phase. We discuss these
solutions with respect to the results of the observation of high redshif
supernova as well as the age problem and structure formation. We stablish
possible connections of these solutions with those emerging from string
effective models.


title: On average properties of inhomogeneous cosmologies

abstract:
  The present talk summarizes the recently progressed state of a systematic
re-evaluation of cosmological models that respect the presence of
inhomogeneities. Emphasis is given to identifying the basic steps towards an
effective (i.e. spatially averaged) description of structural evolution, also
unfolding the various facets of a `smoothed--out' cosmology. We shall highlight
some results obtained within Newtonian cosmology, discuss expansion laws in
general relativity within a covariant fluid approach, and put forward some
promising directions of future research.


title: Stochastic Processes and Thermodynamics on Curved Spaces

abstract:
  Our approach views the thermodynamics and kinetics in general relativity and
extended gravitational theories (with generic local anisotropy) from the
perspective of the theory of stochastic differential equations on curved
spaces.
  Nonequilibrium and irreversible processes in black hole thermodynamics are
considered. The paper summarizes the author's contribution to Journees
Relativistes 99 (12--17 September 1999), Weimar, Germany.


title:
Analitical approximation of $<\phi^2>$ for a massive scalar field in
  static spherically symmetric spacetimes

abstract:
  An analitical approximation of $<\phi^2>$ for a massive scalar field in a
zero temperature vacuum state in static spherically symmetric spacetimes is
obtained. The calculations are based on the method for computing vacuum
expectations values for scalar fields in general static spherically symmetric
spacetimes derived by Anderson, Hiscock and Samuel [Phys. Rev. D {\bf 51}, 4337
(1995)]. The analitical approximation is used to compute $<\phi^2>$ in
Schwarzschild and wormhole spacetimes.


title:
Unification of Weak and Gravitational Interactions Stemming from
  Expansive Nondecelerative Universe Model

abstract:
  There is a deep interrelationship of the General Theory of Relativity and
weak interactions in the model of Expansive Nondecelerative Universe. This fact
allows an independent determination of the mass of vector bosons Z and W, as
well as the time of separation of electromagnetic and weak interactions.


title:
Locally Anisotropic Kinetic Processes and Thermodynamics in Curved
  Spaces

abstract:
  The kinetic theory is formulated with respect to anholonomic frames of
reference on curved spacetimes. By using the concept of nonlinear connection we
develop an approach to modelling locally anisotropic kinetic processes and, in
corresponding limits, the relativistic non-equilibrium thermodynamics with
local anisotropy. This lead to a unified formulation of the kinetic equations
on (pseudo) Riemannian spaces and in various higher dimensional models of
Kaluza-Klein type and/or generalized Lagrange and Finsler spaces. The
transition rate considered for the locally anisotropic transport equations is
related to the differential cross section and spacetime parameters of
anisotropy. The equations of states for pressure and energy in locally
anisotropic thermodynamics are derived. The obtained general expressions for
heat conductivity, shear and volume viscosity coefficients are applied to
determine the transport coefficients of cosmic fluids in spacetimes with
generic local anisotropy. We emphasize that such locally anisotropic structures
are induced also in general relativity if we are modelling physical processes
with respect to frames with mixed sets of holonomic and anholonomic basis
vectors which naturally admits an associated nonlinear connection structure.


title: Boson Stars: Alternatives to primordial black holes?

abstract:
  The present surge for the astrophysical relevance of boson stars stems from
the speculative possibility that these compact objects could provide a
considerable fraction of the non-baryonic part of dark matter within the halo
of galaxies. For a very light `universal' axion of effective string models,
their total gravitational mass will be in the most likely range of \sim 0.5
M_\odot of MACHOs. According to this framework, gravitational microlensing is
indirectly ``weighing" the axion mass, resulting in \sim 10^{-10} eV/c^2. This
conclusion is not changing much, if we use a dilaton type self-interaction for
the bosons. Moreover, we review their formation, rotation and stability as
likely candidates of astrophysical importance.


title: About the detection of gravitational wave bursts

abstract:
  Several filtering methods for the detection of gravitational wave bursts in
interferometric detectors are presented. These are simple and fast methods
which can act as online triggers. All methods are compared to matched filtering
with the help of a figure of merit based on the detection of supernovae signals
simulated by Zwerger and Muller.


title:
The Planck quantum hypothesis and the Friedmannian models of flat
  universe

abstract:
  Only one model from an infinite number of the Friedmannian models of flat
expansive isotropic and homogeneous universe satisfies the assumptions
resulting from the Planck quantum hypothesis.


title: Some Recent Progress in Classical General Relativity

abstract:
  In this short survey paper, we discuss certain recent results in classical
gravity. Our main attention is restricted to two topics: the positive mass
conjecture and its extensions to the case with horizons, including the Penrose
conjecture (Part I), and the interaction of gravity with other force fields and
quantum-mechanical particles (Part II).


title: Quantum Evolution of the Bianchi Type I Model

abstract:
  The behaviour of the flat anisotropic model of the Universe with a scalar
field is explored within the framework of quantum cosmology. The principal
moment of the account of an anisotropy is the presence either negative
potential barrier or positive repelling wall. In the first case occur the above
barrier reflection of the wave function of the Universe, in the second one
there is bounce off a potential wall. The further evolution of the Universe
represents an exponential inflating with fast losses of an anisotropy and
approach to the standard cosmological scenario.


title:
Reconstruction of a scalar-tensor theory of gravity in an accelerating
  universe

abstract:
  The present acceleration of the Universe strongly indicated by recent
observational data can be modeled in the scope of a scalar-tensor theory of
gravity. We show that it is possible to determine the structure of this theory
(the scalar field potential and the functional form of the scalar-gravity
coupling) along with the present density of dustlike matter from the following
two observable cosmological functions: the luminosity distance and the linear
density perturbation in the dustlike matter component as functions of redshift.
Explicit results are presented in the first order in the small inverse
Brans-Dicke parameter 1/omega.


title:
The Interaction of Dirac Particles with Non-Abelian Gauge Fields and
  Gravity - Bound States

abstract:
  We consider a spherically symmetric, static system of a Dirac particle
interacting with classical gravity and an SU(2) Yang-Mills field. The
corresponding Einstein-Dirac-Yang/Mills equations are derived. Using numerical
methods, we find different types of soliton-like solutions of these equations
and discuss their properties. Some of these solutions are stable even for
arbitrarily weak gravitational coupling.


title: Gravitational waves from quasi-spherical black holes

abstract:
  A quasi-spherical approximation scheme, intended to apply to coalescing black
holes, allows the waveforms of gravitational radiation to be computed by
integrating ordinary differential equations.


title:
Regular coordinate systems for Schwarzschild and other spherical
  spacetimes

abstract:
  The continuation of the Schwarzschild metric across the event horizon is
almost always (in textbooks) carried out using the Kruskal-Szekeres
coordinates, in terms of which the areal radius r is defined only implicitly.
We argue that from a pedagogical point of view, using these coordinates comes
with several drawbacks, and we advocate the use of simpler, but equally
effective, coordinate systems. One such system, introduced by Painleve and
Gullstrand in the 1920's, is especially simple and pedagogically powerful; it
is, however, still poorly known today. One of our purposes here is therefore to
popularize these coordinates. Our other purpose is to provide generalizations
to the Painleve-Gullstrand coordinates, first within the specific context of
Schwarzschild spacetime, and then in the context of more general spherical
spacetimes.


title: Coordinate Singularities in Harmonically-sliced Cosmologies

abstract:
  Harmonic slicing has in recent years become a standard way of prescribing the
lapse function in numerical simulations of general relativity. However, as was
first noticed by Alcubierre (1997), numerical solutions generated using this
slicing condition can show pathological behaviour. In this paper, analytic and
numerical methods are used to examine harmonic slicings of Kasner and Gowdy
cosmological spacetimes. It is shown that in general the slicings are prevented
from covering the whole of the spacetimes by the appearance of coordinate
singularities. As well as limiting the maximum running times of numerical
simulations, the coordinate singularities can lead to features being produced
in numerically evolved solutions which must be distinguished from genuine
physical effects.


title: How to test vector nature of gravity

abstract:
  The covariant scheme is proposed to couple gravity and electrodynamics in
pseudo-Riemannian four-spaces with electromagnetic connections. Novel dynamics
of the extended charge and electromagnetic dilation-compression of its proper
time can be tested in non-relativistic experiments. The vector equations
acknowledge unified photon waves without metric modulations of flat laboratory
space.


title:
Noncommutative Unification of General Relativity with Quantum Mechanics
  and Canonical Gravity Quantization

abstract:
  The groupoid approach to noncommutative unification of general relativity
with quantum mechanics is compared with the canonical gravity quantization. It
is shown that by restricting the corresponding noncommutative algebra to its
(commutative) subalgebra, which determines the space-time slicing, an algebraic
counterpart of superspace (space of 3-metrics) can be obtained. It turns out
that when this space-time slicing emerges the universe is already in its
commutative regime. We explore the consequences of this result.


title: On the variational principle for dust shells in General Relativity

abstract:
  The variational principle for a thin dust shell in General Relativity is
constructed. The principle is compatible with the boundary-value problem of the
corresponding Euler-Lagrange equations, and leads to ``natural boundary
conditions'' on the shell. These conditions and the gravitational field
equations which follow from an initial variational principle, are used for
elimination of the gravitational degrees of freedom. The transformation of the
variational formula for spherically-symmetric systems leads to two natural
variants of the effective action. One of these variants describes the shell
from a stationary interior observer's point of view, another from the exterior
one. The conditions of isometry of the exterior and interior faces of the shell
lead to the momentum and Hamiltonian constraints. The canonical equivalence of
the mentioned systems is shown in the extended phase space. Some particular
cases are considered.


title: Quantum Isotropization of the Universe

abstract:
  We consider minisuperspace models constituted of Bianchi I geometries with a
free massless scalar field. The classical solutions are always singular (with
the trivial exception of flat space-time), and always anisotropic once they
begin anisotropic. When quantizing the system, we obtain the Wheeler-DeWitt
equation as a four-dimensional massless Klein-Gordon equation. We show that
there are plenty of quantum states whose corresponding bohmian trajectories may
be non-singular and/or presenting large isotropic phases, even if they begin
anisotropic, due to quantum gravitational effects. As a specific example, we
exhibit field plots of bohmian trajectories for the case of gaussian
superpositions of plane wave solutions of the Wheeler-DeWitt equation which
have those properties. These conclusions are valid even in the absence of the
scalar field.


title: Gyroscope precession in cylindrically symmetric spacetimes

abstract:
  We present calculations of gyroscope precession in spacetimes described by
Levi-Civita and Lewis metrics, under different circumstances. By doing so we
are able to establish a link between the parameters of the metrics and
observable quantities, providing thereby a physical interpretation for those
parameters, without specifying the source of the field.


title:
Interpretation of intuitionistic solution of the vacuum Einstein
  equations in smooth topos

abstract:
  The topos theory is a theory which is used for deciding a number of problems
of theory of relativity, gravitation and quantum physics. In the article
spherically symmetric solution of the vacuum Einstein equations in the
Intuitionistic theory of Gravitation at different stages of smooth topos ${\bf
Set}^{\bf L_{op}}$ is considered. Infinitesimal "weak" gravitational field can
be strong at some stagies, for which we have the additional dimensions. For
example, the cosmological constant is not constant with respect to additional
dimensions. Signature of space-time metric can depend of density of vacuum and
cosmological constant.


title:
Approximate Analytical Solutions to the Initial Data Problem of Black
  Hole Binary Systems

abstract:
  We present approximate analytical solutions to the Hamiltonian and momentum
constraint equations, corresponding to systems composed of two black holes with
arbitrary linear and angular momentum. The analytical nature of these initial
data solutions makes them easier to implement in numerical evolutions than the
traditional numerical approach of solving the elliptic equations derived from
the Einstein constraints. Although in general the problem of setting up initial
conditions for black hole binary simulations is complicated by the presence of
singularities, we show that the methods presented in this work provide initial
data with $l_1$ and $l_\infty$ norms of violation of the constraint equations
falling below those of the truncation error (residual error due to
discretization) present in finite difference codes for the range of grid
resolutions currently used. Thus, these data sets are suitable for use in
evolution codes. Detailed results are presented for the case of a head-on
collision of two equal-mass M black holes with specific angular momentum 0.5M
at an initial separation of 10M. A straightforward superposition method yields
data adequate for resolutions of $h=M/4$, and an "attenuated" superposition
yields data usable to resolutions at least as fine as $h=M/8$. In addition, the
attenuated approximate data may be more tractable in a full (computational)
exact solution to the initial value problem.


title: Stability of self-gravitating magnetic monopoles

abstract:
  The stability of a spherically symmetric self-gravitating magnetic monopole
is examined in the thin wall approximation: modeling the interior false vacuum
as a region of de Sitter space; the exterior as an asymptotically flat region
of the Reissner-Nordstr\"om geometry; and the boundary separating the two as a
charged domain wall. There remains only to determine how the wall gets embedded
in these two geometries. In this approximation, the ratio $k$ of the false
vacuum to surface energy densities is a measure of the symmetry breaking scale
$\eta$. Solutions are characterized by this ratio, the charge on the wall $Q$,
and the value of the conserved total energy $M$. We find that for each fixed
$k$ and $Q$ up to some critical value, there exists a unique globally static
solution, with $M\simeq Q^{3/2}$; any stable radial excitation has $M$ bounded
above by $Q$, the value assumed in an extremal Reissner-Nordstr\"om geometry
and these are the only solutions with $M<Q$. As $M$ is raised above $Q$ a black
hole forms in the exterior: (i) for low $Q$ or $k$, the wall is crushed; (ii)
for higher values, it oscillates inside the black hole. If the mass is not too
high these `collapsing' solutions co-exist with an inflating bounce; (iii) for
$k$, $Q$ or $M$ outside the above regimes, there is a unique inflating
solution. In case (i) the course of the bounce lies within a single
asymptotically flat region (AFR) and it resembles closely the bounce exhibited
by a false vacuum bubble (with Q=0). In cases (ii) and (iii) the course of the
bounce spans two consecutive AFRs.


title: Generalised hyperbolicity in space-times with conical singularities

abstract:
  It is shown that the space-time with a conical singularity, which describes a
thin cosmic string, is hyperbolic in the sense that a unique H^1 solution
exists to the initial value problem for the wave equation with a certain class
of initial data.


title: Geometric treatment of the gravitomagnetic clock effect

abstract:
  We have developed a general geometric treatment of the GCE valid for any
stationary axisymmetric metric. The method is based on the remark that the
world lines of objects rotating along spacely circular trajectories are in any
case, for those kind of metrics, helices drawn on the flat bidimensional
surface of a cylinder. Applying the obtained formulas to the special cases of
the Kerr and weak field metric for a spinning body, known results for time
delays and synchrony defects are recovered.


title: Exact Solution for the Exterior Field of a Rotating Neutron Star

abstract:
  A four-parameter class of exact asymptotically flat solutions of the
Einstein-Maxwell equations involving only rational functions is presented. It
is able to describe the exterior field of a slowly or rapidly rotating neutron
star with poloidal magnetic field.


title:
Dynamical study of the empty Bianchi type I model in generalised
  scalar-tensor theory

abstract:
  A dynamical study of the generalised scalar-tensor theory in the empty
Bianchi type I model is made. We use a method from which we derive the sign of
the first and second derivatives of the metric functions and examine three
different theories that can all tend towards relativistic behaviours at late
time. We determine conditions so that the dynamic be in expansion and
decelerated at late time.


title: Exact U(1) symmetric cosmologies with local Mixmaster dynamics

abstract:
  By applying a standard solution generating technique, we transform an
arbitrary vacuum Mixmaster solution on $S^3 \times {\bf R}$ to a new solution
which is spatially inhomogeneous. We thereby obtain a family of exact,
spatially inhomogeneous, vacuum spacetimes which exhibit Belinskii,
Khalatnikov, and Lifshitz (BKL) oscillatory behavior. The solutions are
constructed explicitly by performing the transformations on numerically
generated, homogeneous Mixmaster solutions. Their behavior is found to be
qualitatively like that seen in previous numerical simulations of generic U(1)
symmetric cosmological spacetimes on $T^3 \times {\bf R}$.


title: Can one increase the luminosity of a Schwarzschild black hole?

abstract:
  We illustrate how Hawking's radiance from a Schwarzschild black hole is
modified by the electrostatic self-interaction of the emitted charged
particles. A W.K.B approximation shows that the probability for a
self-interacting charged particle to propagate from the interior to the
exterior of the horizon is increased relative to the corresponding probability
for neutral particles. We also demonstrate how the electric potential of a
charged test object in the black hole's vicinity gives rise to pair creation.
We analyze this phenomenon semiclassically by considering the existence of the
appropriate Klein region. Finally we discuss the possible energy source for the
process.


title:
Divergence of the Quantum Stress Tensor on the Cauchy Horizon in 2-d
  Dust Collapse

abstract:
  We prove that the quantum stress tensor for a massless scalar field in two
dimensional non-selfsimilar Tolman Bondi dust collapse and Vaidya radiation
collapse models diverges on the Cauchy horizon, if the latter exists. The two
dimensional model is obtained by suppressing angular co-ordinates in the
corresponding four dimensional spherical model.


title: How much energy do closed timelike curves in 2+1 spacetimes need?

abstract:
  By noticing that, in open 2+1 gravity, polarized surfaces cannot converge in
the presence of timelike total energy momentum (except for a rotation of 2 pi),
we give a simple argument which shows that, quite generally, closed timelike
curves cannot exist in the presence of such energy condition.


title:
Exotic spacetimes, superconducting strings with linear momentum, and
  (not quite) all that

abstract:
  We derive the general exact vacuum metrics associated with a stationary (non
static), non rotating, cylindrically symmetric source. An analysis of the
geometry described by these vacuum metrics shows that they contain a subfamily
of metrics that, although admitting a consistent time orientation, display
"exotic" properties, such as "trapping" of geodesics and closed causal curves
through every point. The possibility that such spacetimes could be generated by
a superconducting string, endowed with a neutral current and momentum, has
recently been considered by Thatcher and Morgan. Our results, however, differ
from those found by Thatcher and Morgan, and the discrepancy is explained. We
also analyze the general possibility of constructing physical sources for the
exotic metrics, and find that, under certain restrictions, they must always
violate the dominant energy condition (DEC). We illustrate our results by
explicitly analyzing the case of concentric shells, where we find that in all
cases the external vacuum metric is non exotic if the matter in the shells
satisfies the DEC.


title: A Symplectic Hamiltonian Derivation of Quasilocal Energy-Momentum for GR

abstract:
  The various roles of boundary terms in the gravitational Lagrangian and
Hamiltonian are explored. A symplectic Hamiltonian-boundary-term approach is
ideally suited for a large class of quasilocal energy-momentum expressions for
general relativity. This approach provides a physical interpretation for many
of the well-known gravitational energy-momentum expressions including all of
the pseudotensors, associating each with unique boundary conditions. From this
perspective we find that the pseudotensors of Einstein and M{\o}ller (which is
closely related to Komar's superpotential) are especially natural, but the
latter has certain shortcomings. Among the infinite possibilities, we found
that there are really only two Hamiltonian-boundary-term quasilocal expressions
which correspond to {\em covariant} boundary conditions; they are respectively
of the Dirichlet or Neumann type. Our Dirichlet expression coincides with the
expression recently obtained by Katz and coworkers using Noether arguments and
a fixed background. A modification of their argument yields our Neumann
expression.


title: On the gravitational moments of a Dirac particle

abstract:
  We consider the classical theory of the Dirac massive particle in the
Riemann-Cartan spacetime. We demonstrate that the translational and the Lorentz
gravitational moments, obtained by means of the Gordon type decompositions of
the canonical energy-momentum and spin currents, are consistently coupled to
torsion and curvature, as expected.


title:
The use of new coordinates for the template space in hierarchical search
  for gravitational waves from inspiraling binaries

abstract:
  We discuss a method to analyze data from interferometric gravitational wave
detectors focusing on the technique of hierarchical search to detect
gravitational waves from inspiraling binaries. For this purpose, we propose new
coordinates to parameterize the template space. Using our new coordinates, we
develop several new techniques for two step search, which would reduce the
computation cost by large amount. These techniques become more important when
we need to implement a $\chi^2$-test as a detection criterion.


title: On stationary vacuum solutions to the Einstein equations

abstract:
  It is proved that the only geodesically complete stationary vacuum solution
of the Einstein equations is the empty Minkowski space, or a quotient of it by
a discrete group of isometries, generalizing a classical result of
Lichnerowicz. In addition, we obtain an apriori bound on the curvature of
stationary vacuum solutions away from the boundary or horizon.


title:
Integration of the GHP equations in spacetimes admitting a geodesic
  shear-free expanding null congruence

abstract:
  We perform a complete rho-integration of the GHP equations for all spacetimes
that admit a geodesic shear-free expanding null congruence, whose Ricci spinor
is aligned to the congruence and whose Ricci scalar is constant. We also deduce
the system of GHP equations after the integration is completed, and discuss a
few applications.


title:
On String Cosmology and de Sitter inflation with massless dilatons and
  dynamical torsion

abstract:
  Variation of the 4-D string cosmology action with dynamical torsion and
massless dilatons lead to an expression of torsion in terms of massless
dilatons in the case of de Sitter inflation.The solution is approximated
according to the COBE data.


title:
Signal-to-noise ratio for a stochastic background of massive relic
  particles

abstract:
  We estimate the signal-to-noise ratio for two gravitational detectors
interacting with a stochastic background of massive scalar waves. We find that
the present experimental level of sensitivity could be already enough to detect
a signal from a light but non-relativistic component of dark matter, even if
the coupling is weak enough to exclude observable deviations from standard
gravitational interactions, provided the mass is not too far from the
sensitivity and overlapping band of the two detectors.


title: A Metric Theory of Gravity with Condensed Matter Interpretation

abstract:
  We consider a classical condensed matter theory in a Newtonian framework
where conservation laws
  \partial_t \rho + \partial_i (\rho v^i) = 0
  \partial_t (\rho v^j) + \partial_i(\rho v^i v^j + p^{ij}) = 0
  are related with the Lagrange formalism in a natural way. For an ``effective
Lorentz metric'' g_{\mu\nu} it is equivalent to a metric theory of gravity
close to general relativity with Lagrangian
  L = L_{GR}
  - (8\pi G)^{-1}(\Upsilon g^{00}-\Xi (g^{11}+g^{22}+g^{33}))\sqrt{-g}
  We consider the differences between this theory and general relativity (no
nontrivial topologies, stable frozen stars instead of black holes, big bounce
instead of big bang singularity, a dark matter term), quantum gravity, and the
connection with realism and Bohmian mechanics.


abstract:
  We present a metric theory of gravity with Lagrangian
  L = (8\pi G)^{-1}(\Xi g^{ii} - \Upsilon g^{00})\sqrt{-g} + L_{GR} +
L_{matter}
  motivated by classical equations
  \partial_t \rho + \partial_i (\rho v^i) = 0
  \partial_t (\rho v^j) + \partial_i (\rho v^i v^j + p^{ij}) = 0
  for a medium in Newtonian space-time. We obtain stable ``frozen stars''
instead of black holes and a ``big bounce'' instead of a big bang singularity.


title: On the spontaneous breaking of Lorentz invariance

abstract:
  We show that estimates of the Lorentz symmetry violation extracted from
ultra-high energy cosmic rays beyond the GZK cut-off set bounds on the
parameters of a Lorentz-violating extension of the Standard Model. Moreover, we
argue that correlated measurements of the difference in the arrival time of
gamma-ray photons and neutrinos emitted from Active Galactic Nuclei or
Gamma-Ray Bursts may provide a signature for a possible violation of the
Lorentz symmetry. We find that this time delay is energy independent, but that
it has a dependence on the chirality of the particles involved.


title: Stochastic semiclassical fluctuations in Minkowski spacetime

abstract:
  The semiclassical Einstein-Langevin equations which describe the dynamics of
stochastic perturbations of the metric induced by quantum stress-energy
fluctuations of matter fields in a given state are considered on the background
of the ground state of semiclassical gravity, namely, Minkowski spacetime and a
scalar field in its vacuum state. The relevant equations are explicitly derived
for massless and massive fields arbitrarily coupled to the curvature. In doing
so, some semiclassical results, such as the expectation value of the
stress-energy tensor to linear order in the metric perturbations and particle
creation effects, are obtained. We then solve the equations and compute the
two-point correlation functions for the linearized Einstein tensor and for the
metric perturbations. In the conformal field case, explicit results are
obtained. These results hint that gravitational fluctuations in stochastic
semiclassical gravity have a ``non-perturbative'' behavior in some
characteristic correlation lengths.


title: Energy conditions and their cosmological implications

abstract:
  The energy conditions of general relativity permit one to deduce very
powerful and general theorems about the behaviour of strong gravitational
fields and cosmological geometries. However, the energy conditions these
theorems are based on are beginning to look a lot less secure than they once
seemed: (1) there are subtle quantum effects that violate all of the energy
conditions, and more tellingly (2), there are also relatively benign looking
classical systems that violate all the energy conditions. This opens up a
Pandora's box of rather disquieting possibilities --- everything from negative
asymptotic mass, to traversable wormholes, to warp drives, up to and including
time machines.


title:
A testable description of space-time foam as a fundamental stochastic
  gravity-wave background

abstract:
  I develop a phenomenological approach to the description of the noise levels
that the space-time foam of quantum gravity could induce in modern gravity-wave
detectors. Various possibilities are considered, including white noise and
random-walk noise. In particular, I find that the sensitivity level expected
for the planned LIGO and VIRGO interferometers and for the next upgrade of the
NAUTILUS resonant-bar detector corresponds to a white-noise level which can be
naturally associated with the Planck length.


title: General Ether Theory

abstract:
  The paper is an introduction into General Ether Theory (GET). We start with
few assumptions about an universal ``ether'' in a Newtonian space-time which
fulfils
  \partial_t \rho + \partial_i (\rho v^i) = 0
  \partial_t (\rho v^j) + \partial_i(\rho v^i v^j + p^{ij}) = 0
  For an ``effective metric'' $g_{\mu\nu}$ we derive a Lagrangian where the
Einstein equivalence principle is fulfilled:
  L=L_{GR}-(8\pi G)^{-1}(\Upsilon g^{00}-\Xi(g^{11}+g^{22}+g^{33}))\sqrt{-g}
  We consider predictions (stable frozen stars instead of black holes, big
bounce instead of big bang singularity, a dark matter term), quantization
(regularization by an atomic ether, superposition of gravitational fields),
related methodological questions (covariance, EPR criterion, Bohmian
mechanics).


title:
Stochastically Fluctuating Black-Hole Geometry, Hawking Radiation and
  the Trans-Planckian Problem

abstract:
  We study the propagation of null rays and massless fields in a black hole
fluctuating geometry. The metric fluctuations are induced by a small
oscillating incoming flux of energy. The flux also induces black hole mass
oscillations around its average value. We assume that the metric fluctuations
are described by a statistical ensemble. The stochastic variables are the
phases and the amplitudes of Fourier modes of the fluctuations. By averaging
over these variables, we obtain an effective propagation for massless fields
which is characterized by a critical length defined by the amplitude of the
metric fluctuations: Smooth wave packets with respect to this length are not
significantly affected when they are propagated forward in time. Concomitantly,
we find that the asymptotic properties of Hawking radiation are not severely
modified. However, backward propagated wave packets are dissipated by the
metric fluctuations once their blue shifted frequency reaches the inverse
critical length. All these properties bear many resemblences with those
obtained in models for black hole radiation based on a modified dispersion
relation. This strongly suggests that the physical origin of these models,
which were introduced to confront the trans-Planckian problem, comes from the
fluctuations of the black hole geometry.


title: Boson stars in massive dilatonic gravity

abstract:
  We study equilibrium configurations of boson stars in the framework of a
class scalar-tensor theories of gravity with massive gravitational scalar
(dilaton). In particular we investigate the influence of the mass of the
dilaton on the boson star structure. We find that the masses of the boson stars
in presence of dilaton are close to those in general relativity and they are
sensitive to the ratio of the boson mass to the dilaton mass within a typical
few percent. It turns out also that the boson star structure is mainly
sensitive to the mass term of the dilaton potential rather to the exact form of
the potential.


title:
The Angular Scale of Topologically-Induced Flat Spots in the Cosmic
  Microwave Background Radiation

abstract:
  The notion that the topology of the universe need not be that of the
universal covering space of its geometry has recently received renewed
attention. Generic signatures of cosmological topology have been sought, both
in the distribution of objects in the universe, and especially in the
temperature fluctuations of the cosmic microwave background radiation (CMBR).
One signature identified in the horn topology but hypothesized to be generic is
featureless regions or flat spots in the CMBR sky. We show that typical
observation points within the cusped 3-manifold m003 from the Snappea census
have flat spots with an angular scale of about five degrees for $\Omega_0$=0.3.
We expect that this holds for other small volume cusped manifolds with this
$\Omega_0$ value.


title: Monopoles and Dyons in the Pure Einstein-Yang-Mills Theory

abstract:
  In the pure Einstein-Yang-Mills theory in four dimensions there exist
monopole and dyon solutions. The spectrum of the solutions is discrete in
asymptotically flat or de Sitter space, whereas it is continuous in
asymptotically anti-de Sitter space. The solutions are regular everywhere and
specified with their mass, and non-Abelian electric and magnetic charges. In
asymptotically anti-de Sitter space a class of monopole solutions have no node
in non-Abelian magnetic fields, and are stable against spherically symmetric
perturbations.


title: Nonminimal global monopoles and bound orbits

abstract:
  We perform a numerical analysis of the gravitational field of a global
monopole coupled nonminimally to gravity, and find that, for some given
nonminimal couplings (in constrast with the minimal coupling case), there is an
attractive region where bound orbits exist. We exhibit the behavior of the
frequency shifts that would be associated with `rotation curves' of stars in
circular orbits in the spacetimes of such global monopoles.


title: Gravitation, the Quantum, and Bohr's Correspondence Principle

abstract:
  The black hole combines in some sense both the ``hydrogen atom'' and the
``black-body radiation'' problems of quantum gravity. This analogy suggests
that black-hole quantization may be the key to a quantum theory of gravity.
During the last twenty-five years evidence has been mounting that black-hole
surface area is indeed {\it quantized}, with {\it uniformally} spaced area
eigenvalues. There is, however, no general agreement on the {\it spacing} of
the levels. In this essay we use Bohr's correspondence principle to provide
this missing link. We conclude that the fundamental area unit is $4\hbar\ln3$.
This is the unique spacing consistent both with the area-entropy {\it
thermodynamic} relation for black holes, with Boltzmann-Einstein formula in
{\it statistical physics} and with {\it Bohr's correspondence principle}.


title:
Maxwell equation, Shroedinger equation, Dirac equation, Einstein
  equation defined on the multifractal sets of the time and the space

abstract:
  What forms will have an equations of modern physics if the dimensions of our
time and space are fractional? The generalized equations enumerated by title
are presented by help the generalized fractional derivatives of
Riemann-Liouville.


title: Background Estimation in a Gravitational Wave Experiment

abstract:
  The problem to estimate the background due to accidental coincidences in the
search for coincidences in gravitational wave experiments is discussed. The use
of delayed coincidences obtained by orderly shifting the event times of one of
the two detectors is shown to be the most correct


title:
Wave-Particle duality at the Planck scale: Freezing of neutrino
  oscillations

abstract:
  A gravitationally-induced modification to de Broglie wave-particle duality is
presented. At Planck scale, the gravitationally-modified matter wavelength
saturates to a few times the Planck length in a momentum independent manner. In
certain frameworks, this circumstance freezes neutrino oscillations in the
Planck realm. This effect is apart, and beyond, the gravitational red-shift. A
conclusion is drawn that in a complete theory of quantum gravity the notions of
``quantum'' and ``gravity'' shall carry new meanings -- meanings, that are yet
to be deciphered from theory and observations in their entirety.


title:
Active controls in interferometric detectors of gravitational waves:
  inertial damping of the VIRGO superattenuator

abstract:
  The operation of an interferometer for gravitational waves detection requires
sophisticated feedback controls in many parts of the apparatus. The aim of this
lecture is to introduce the types of problems to be faced in this line of
research. The attention is focused on the "inertial damping" of the test mass
suspension of the VIRGO interferometer (the superattenuator): it is a
multidimensional local control aimed to reduce the residual motion of the
suspended mirror associated to the normal modes of the suspension. Its
performance is very important for the locking of the interferometer.


title: Do semiclassical zero temperature black holes exist?

abstract:
  The semiclassical Einstein equations are solved to first order in $\epsilon =
\hbar/M^2$ for the case of a Reissner-Nordstr\"{o}m black hole perturbed by the
vacuum stress-energy of quantized free fields. Massless and massive fields of
spin 0, 1/2, and 1 are considered. We show that in all physically realistic
cases, macroscopic zero temperature black hole solutions do not exist. Any
static zero temperature semiclassical black hole solutions must then be
microscopic and isolated in the space of solutions; they do not join smoothly
onto the classical extreme Reissner-Nordst\"{o}m solution as $\epsilon \to 0$.


title: Gravitational event search with five resonant antennas

abstract:
  Five cryogenic resonant gravitational antennas are now in operation. This is
the first time that such a large number of high sensitive antennas are taking
data and an agreement on data exchange has been signed by the responsible
groups. The data exchanged will consist essentially in lists of ''candidate
events''. In this paper the procedure used by the Rome group in order to obtain
''candidate events'' is presented.
  Some methods of analyzing the data of the "network" of the five antennas are
shown.


title:
Adaptive filtering techniques for interferometric data preparation:
  removal of long-term sinusoidal signals and oscillatory transients

abstract:
  We propose an adaptive denoising scheme for poorly modeled non-Gaussian
features in the gravitational wave interferometric data. Preliminary tests on
real data show encouraging results.


title:
Detection of gravitational waves from inspiraling compact binaries using
  a network of interferometric detectors

abstract:
  We formulate the data analysis problem for the detection of the Newtonian
waveform from an inspiraling compact-binary by a network of arbitrarily
oriented and arbitrarily distributed laser interferometric gravitational wave
detectors. We obtain for the first time the relation between the optimal
statistic and the magnitude of the network correlation vector, which is
constructed from the matched network-filter. This generalizes the calculation
reported in an earlier work (gr-qc/9906064), where the detectors are taken to
be coincident.


title:
Comment on "Relativistic Effects of Light in Moving Media with Extremely
  Low Group Velocity"

abstract:
  In [cond-mat/9906332; Phys. Rev. Lett. 84, 822 (2000)] and [physics/9906038;
Phys. Rev. A 60, 4301 (1999)] Leonhardt and Piwnicki have presented an
interesting analysis of how to use a flowing dielectric fluid to generate a
so-called "optical black hole". Qualitatively similar phenomena using
acoustical processes have also been much investigated. Unfortunately there is a
subtle misinterpretation in the Leonhardt-Piwnicki analysis regarding these
"optical black holes": While it is clear that "optical black holes" can
certainly exist as theoretical constructs, and while the experimental prospects
for actually building them in the laboratory are excellent, the particular
model geometries that Leonhardt and Piwnicki write down as alleged examples of
"optical black holes" are in fact not black holes at all.


title: Principia Physica

abstract:
  A comprehensive physical theory explains all aspects of the physical
universe, including quantum aspects, classical aspects, relativistic aspects,
their relationships, and unification. The central nonlocality principle leads
to a nonlocal geometry that explains entire quantum phenomenology, including
two-slit experiment, Aspect-type experiments, quantum randomness, tunneling,
etc. The infinitesimal aspect of this geometry is a usual (differential)
geometry, various aspects of which are energy-momentum, spin-helicity,
electric, color and flavor charges. Their interactions are governed by a
mathematically automatic field equation - also a grand conservation principle.
New predictions: a new particle property; bending-of-light estimates refined
over relativity's; shape of the universe; a no-gravitational-singularity
theorem, etc. Nonlocal physics is formulated using a nonlocal calculus and
nonlocal differential equations, replacing inadequate local concepts of
Newton's calculus and partial differential equations. Usual quantum formalisms
follow from our theory - the latter doesn't rest on the former.


title: Nonexistence of conformally flat slices of the Kerr spacetime

abstract:
  Initial data for black hole collisions are commonly generated using the
Bowen-York approach based on conformally flat 3-geometries. The standard
(constant Boyer-Lindquist time) spatial slices of the Kerr spacetime are not
conformally flat, so that use of the Bowen-York approach is limited in dealing
with rotating holes. We investigate here whether there exist foliations of the
Kerr spacetime that are conformally flat. We limit our considerations to
foliations that are axisymmetric and that smoothly reduce in the Schwarzschild
limit to slices of constant Schwarzschild time. With these restrictions, we
show that no conformally flat slices can exist.


title: A slowly rotating perfect fluid body in an ambient vacuum

abstract:
  A global model of a slowly rotating perfect fluid ball in general relativity
is presented. To second order in the rotation parameter, the junction surface
is an ellipsoidal cylinder. The interior is given by a limiting case of the
Wahlquist solution, and the vacuum region is not asymptotically flat. The
impossibility of joining an asymptotically flat vacuum region has been shown in
a preceding work.


title: Sonic analog of gravitational black holes in Bose-Einstein condensates

abstract:
  It is shown that, in dilute-gas Bose-Einstein condensates, there exist both
dynamically stable and unstable configurations which, in the hydrodynamic
limit, exhibit a behavior resembling that of gravitational black holes. The
dynamical instabilities involve creation of quasiparticle pairs in positive and
negative energy states, as in the well-known suggested mechanism for black hole
evaporation. We propose a scheme to generate a stable sonic black hole in a
ring trap.


title:
Lanczos potentials and curvature-free connections aligned to a geodesic
  shear-free expanding null congruence

abstract:
  By the method of rho-integration we obtain all Lanczos potentials L_{ABCA'}
of the Weyl spinor that, in a certain sense, are aligned to a geodesic
shear-free expanding null congruence. We also obtain all spinors
H_{ABA'B'}=Q_{AB}o_{A'}o_{B'}, Q_{AB}=Q_{(AB)} satisfying
nabla_{(A}{}^{B'}H_{BC)A'B'}=L_{ABCA'}. We go on to prove that H_{ABA'B'} can
be chosen so that Gamma_{ABCA'}=nabla_{(A}{}^{B'} H_{B)CA'B'} defines a metric
asymmetric curvature-free connection such that L_{ABCA'}=Gamma_{(ABC)A'} is a
Lanczos potential that is aligned to the geodesic shear-free expanding
congruence. These results are a generalization to a large class of
algebraically special spacetimes (including all vacuum ones for which the
principal null direction is expanding) of the curvature-free connection of the
Kerr spacetime found by Bergqvist and Ludvigsen, which was used in a
construction of quasi-local momentum.


title: Acceleration and Special Relativity

abstract:
  This paper has been withdrawn by the author due to similarity to Author's
other paper