title: Supersymmetric Quantization of Anisotropic Scalar-Tensor Cosmologies

abstract:
  In this paper we show that the spatially homogeneous Bianchi type I and
Kantowski-Sachs cosmologies derived from the Brans-Dicke theory of gravity
admit a supersymmetric extension at the quantum level. Global symmetries in the
effective one-dimensional actions characterize both classical and quantum
solutions. A wide family of exact wavefunctions satisfying the supersymmetric
constraints are found. A connection with quantum wormholes is briefly
discussed.


title:
The radial supersymmetry of the (d+1)-dimensional relativistic rotating
  oscillators

abstract:
  We study the supersymmetry of the radial problems of the models of quantum
relativistic rotating oscillators in arbitrary dimensions, defined as
Klein-Gordon fields in backgrounds with deformed anti-de Sitter metrics. It is
pointed out that the shape invariance of the supersymmetric partner radial
potentials leads to simple operators forms of the Rodrigues formulas for the
normalized radial wave functions.


title: The harmonic gauge condition in the gravitomagnetic equations

abstract:
  It has been asserted in the literature that the analogy between the linear
and first order slow motion approximation of Einstein equations of General
Relativity (gravitomagnetic equations) and the Maxwell-Lorentz equations of
electrodynamics breaks down if the gravitational potentials are time dependent.
  In this work, we show that this assertion is not correct and it has arisen
from an incorrect limit of the usual harmonic gauge condition, which
drastically changes the physical content of the gravitomagnetic equations.


title: A generalized linear Hubble law for an inhomogeneous barotropic Universe

abstract:
  In this work, I present a generalized linear Hubble law for a barotropic
spherically symmetric inhomogeneous spacetime, which is in principle compatible
with the acceleration of the cosmic expansion obtained as a result of high
redshift Supernovae data. The new Hubble function, defined by this law, has two
additional terms besides an expansion one, similar to the usual volume
expansion one of the FLRW models, but now due to an angular expansion. The
first additional term is dipolar and is a consequence of the existence of a
kinematic acceleration of the observer, generated by a negative gradient of
pressure or of mass-energy density. The second one is quadrupolar and due to
the shear. Both additional terms are anisotropic for off-centre observers,
because of to their dependence on a telescopic angle of observation. This
generalized linear Hubble law could explain, in a cosmological setting, the
observed large scale flow of matter, without to have recourse to peculiar
velocity-type newtonian models. It is pointed out also, that the matter dipole
direction should coincide with the CBR dipole one.


title: Mass dependence of the gravitationally-induced wave-function phase

abstract:
  The leading mass dependence of the wave function phase is calculated in the
presence of gravitational interactions. The conditions under which this phase
contains terms depending on both the square of the mass and the gravitational
constant are determined. The observability of such terms is briefly discussed.


title:
The Location and Temperature of Event Horizon for General Black Hole via
  the Method of Damour-Ruffini-Zhao

abstract:
  In this paper, we investigate the general case of black hole on horizon by
the method of Damour-Ruffini-Zhao. The proof of identification of the location
of horizons determined both by Damour-Ruffini-Zhao's (D-R-Z) method and by
equation of null super-surface is given. The formula of temperature on the
horizon for general black holes is obtained and is successfully checked by a
variety of models of black holes.


title:
The Relation Between Technique of Conformal Flat and
  Damour-Ruffini-Zhao's Method

abstract:
  The relation between the technique of conformal flat and
Damour-Ruffini-Zhao's method is investigated in this paper. It is pointed out
that the two methods give the same results when the metric has the form
$g_{\alpha\beta=0},$ with $\alpha=0,1$ and $\beta=2,3$. It is indicated that
the two methods are not equivalent for general case.


title:
General Relativity as a (constrained) Yang-Mills's Theory and a Novel
  Gravity with Torsion

abstract:
  We show that General Relativity (GR) with cosmological constant may be
formulated as a rather simple constrained SO(D-1,2) (or SO(D,1))-Yang-Mills
(YM) theory. Furthermore, the spin connections of the Cartan-Einstein
formulation for GR appear as solutions of a genuine SO(D-1,1)-YM.
  We also present a theory of gravity with torsion as the most natural
extension of this result. The theory comes out to be strictly an YM-theory upon
relaxation of a suitable constraint. This work sets out to enforce the close
connection between YM theories and GR by means of a new construction.


title: A New Interpretation of Compensate Effect

abstract:
  A new interpretation of compensate effect is presented. The Hawking effect in
general space-time can be taken as a compensate effect of the scale
transformation of coordinate time on the horizon in generalized tortoise
coordinates transformation. It is proved that the Hawking temperature is the
pure gauge of compensate field in tortoise coordinates. This interpretation
does not refer to a zero-temperature space-time.


title: The Formation of non-Keplerian Rings of Matter about Compact Stars

abstract:
  The formation of energetic rings of matter in a Kerr spacetime with an
outward pointing acceleration field does not appear to have previously been
noted as a relativistic effect. In this paper we show that such rings are a
gravimagneto effect with no Newtonian analog, and that they do not occur in the
static limit. The energy efficiency of these rings can, depending of the
strength of the acceleration field, be much greater than that of Keplerian
disks. The rings rotate in a direction opposite to that of compact star about
which they form. The size and energy efficiency of the rings depend on the
fundamental parameters of the spacetime as well as the strength the
acceleration field.


title:
Vector-like Einstein's equations for D-dimensional spherical gravity
  with (D-2)-dimensional sphere

abstract:
  We demonstrate how the Einstein's equations for the $D$-dimensional spherical
gravity can be written in the covariant vector-like form. These equations
reveal easily the causal structure of curved spherically symmetric manifolds
and may appear useful in investigation of different models of brane universes.


title: Exact non-singular waves in the anti-de Sitter universe

abstract:
  A class of radiative solutions of Einstein's field equations with a negative
cosmological constant and a pure radiation is investigated. The space-times,
which generalize the Defrise solution, represent exact gravitational waves
which interact with null matter and propagate in the anti-de Sitter universe.
Interestingly, these solutions have homogeneous and non-singular wave-fronts
for all freely moving observers. We also study properties of sandwich and
impulsive waves which can be constructed in this class of space-times.


title: On the use of algebraic programming in the general relativity

abstract:
  This is a review devoted to some results of Algebraic Programming (Computer
Algebra) used in treating several problems of general relativity, based mainly
on already published articles. The article contains the talk given by the
author at The Albert Einstein Institut, Max Planck Institut fur
Gravitationstheorie, Golm, Germany, september 2000


title: When is S=A/4?

abstract:
  Black hole entropy and its relation to the horizon area are considered. More
precisely, the conditions and specifications that are expected to be required
for the assignment of entropy, and the consequences that these expectations
have when applied to a black hole are explored. In particular, the following
questions are addressed: When do we expect to assign an entropy?; when are
entropy and area proportional? and, what is the nature of the horizon? It is
concluded that our present understanding of black hole entropy is somewhat
incomplete, and some of the relevant issues that should be addressed in
pursuing these questions are pointed out.


title:
On the contribution of density perturbations and gravitational waves to
  the lower order multipoles of the Cosmic Microwave Background Radiation

abstract:
  The important studies of Peebles, and Bond and Efstathiou have led to the
formula C_l = const/[l(l +1)] aimed at describing the lower order multipoles of
the CMBR temperature variations caused by density perturbations with the flat
spectrum. Clearly, this formula requires amendments, as it predicts an
infinitely large monopole C_0, and a dipole moment C_1 only 6/2 times larger
than the quadrupole C_2, both predictions in conflict with observations. We
restore the terms omitted in the course of the derivation of this formula, and
arrive at a new expression. According to the corrected formula, the monopole
moment is finite and small, while the dipole moment is sensitive to
short-wavelength perturbations, and numerically much larger than the
quadrupole, as one would expect on physical grounds. At the same time, the
function l(l +1)C_l deviates from a horizontal line and grows with l, for l
\geq 2. We show that the inclusion of the modulating (transfer) function
terminates the growth and forms the first peak, recently observed. We fit the
theoretical curves to the position and height of the first peak, as well as to
the observed dipole, varying three parameters: red-shift at decoupling,
red-shift at matter-radiation equality, and slope of the primordial spectrum.
It appears that there is always a deficit, as compared with the COBE
observations, at small multipoles, l \sim 10. We demonstrate that a reasonable
and theoretically expected amount of gravitational waves bridges this gap at
small multipoles, leaving the other fits as good as before. We show that the
observationally acceptable models permit somewhat `blue' primordial spectra.
This allows one to avoid the infra-red divergence of cosmological
perturbations, which is otherwise present.


title: Distorted Black Holes with Charge

abstract:
  We present new solutions to the Einstein-Maxwell equations representing a
class of charged distorted black holes. These solutions are static-axisymmetric
and are generalizations of the distorted black hole solutions studied by Geroch
and Hartle. Physically, they represent a charged black hole distorted by
external matter fields. We discuss the zeroth and first law for these black
holes. The first law is proved in two different forms, one motivated by the
isolated horizon framework and the other using normalizations at infinity.


title: The kernel of the edth operators on higher-genus spacelike two-surfaces

abstract:
  The dimension of the kernels of the edth and edth-prime operators on closed,
orientable spacelike 2-surfaces with arbitrary genus is calculated, and some of
its mathematical and physical consequences are discussed.


title: The Behavior of Kasner Cosmologies with Induced Matter

abstract:
  We extend the induced matter model, previously applied to a variety of
isotropic cases, to a generalization of Bianchi type-I anisotropic cosmologies.
The induced matter model is a 5D Kaluza-Klein approach in which assumptions of
compactness are relaxed for the fifth coordinate, leading to extra geometric
terms. One interpretation of these extra terms is to identify them as an
``induced matter'' contribution to the stress-energy tensor. In similar spirit,
we construct a five dimensional metric in which the spatial slices possess
Bianchi type-I geometry. We find a set of solutions for the five dimensional
Einstein equations, and determine the pressure and density of induced matter.
We comment on the long-term dynamics of the model, showing that the assumption
of positive density leads to the contraction over time of the fifth scale
factor.


title: Energy Distribution of a Schwarzschild Black Hole in a Magnetic Universe

abstract:
  We obtain the energy distribution of a Schwarzschild black hole in a magnetic
universe in the Tolman prescription.


title: Late time acceleration in Brans Dicke Cosmology

abstract:
  In this work we have investigated the possibility of having a late time
accelerated phase of the universe, suggested by recent supernova observation,
in the context of Brans Dicke (BD) theory with a symmetry breaking potential
and a matter field. We find that a perfect fluid matter field (pressureless and
with pressure) cannot support this acceleration but a fluid with dissipative
pressure can drive this late time acceleration. We have also calculated some
cosmological parameters in our model to match with observations.


title: Energy of a Conformal Scalar Dyon Black Hole

abstract:
  We obtain the energy of a conformal scalar dyon black hole (CSD) by using the
energy-momentum complexes of Tolman and M{\o}ller. The total gravitational
energy is given by the CSD charge in the both prescriptions.


title:
General Electric-Magnetic decomposition of fields, positivity and
  Rainich-like conditions

abstract:
  We show how to generalize the classical electric-magnetic decomposition of
the Maxwell or the Weyl tensors to arbitrary fields described by tensors of any
rank in general $n$-dimensional spacetimes of Lorentzian signature. The
properties and applications of this decomposition are reviewed. In particular,
the definition of tensors quadratic in the original fields and with important
positivity properties is given. These tensors are usually called "super-energy"
(s-e) tensors, they include the traditional energy-momentum, Bel and
Bel-Robinson tensors, and satisfy the so-called Dominant Property, which is a
straightforward generalization of the classical dominant energy condition
satisfied by well-behaved energy-momentum tensors. We prove that, in fact, any
tensor satisfying the dominant property can be decomposed as a finite sum of
the s-e tensors. Some remarks about the conservation laws derivable from s-e
tensors, with some explicit examples, are presented. Finally, we will show how
our results can be used to provide adequate generalizations of the Rainich
conditions in general dimension and for any physical field.


title:
Riemann normal coordinates, Fermi reference system and the geodesic
  deviation equation

abstract:
  We obtain the integral formulae for computing the tetrads and metric
components in Riemann normal coordinates and Fermi coordinate system of an
observer in arbitrary motion. Our approach admits essential enlarging the range
of validity of these coordinates. The results obtained are applied to the
geodesic deviation in the field of a weak plane gravitational wave and the
computation of plane-wave metric in Fermi normal coordinates.


title:
Vacuum polarization of massive scalar fields in the spacetime of the
  electrically charged nonlinear black hole

abstract:
  The approximate renormalized stress-energy tensor of the quantized massive
conformally coupled scalar field in the spacetime of electrically charged
nonlinear black hole is constructed. It is achieved by functional
differentiation of the lowest order of the DeWitt-Schwinger effective action
involving coincidence limit of the Hadamard-Minakshisundaram-DeWitt-Seely
coefficient $a_{3}.$ The result is compared with the analogous result derived
for the Reissner-Nordstr\"om black hole. It is shown that the most important
differences occur in the vicinity of the event horizon of the black hole near
the extremality limit. The structure of the nonlinear black hole is briefly
studied by means of the Lambert functions.


title: Geodesic Deviation in Kaluza-Klein Theories

abstract:
  We study in detail the equations of the geodesic deviation in
multidimensional theories of Kaluza-Klein type. We show that their
4-dimensional space-time projections are identical with the equations obtained
by direct variation of the usual geodesic equation in the presence of the
Lorentz force, provided that the fifth component of the deviation vector
satisfies an extra constraint derived here.


title: Parameterized Absolute Parallelism: A Geometry for Physical Applications

abstract:
  Absolute parallelism (AP) geometry is frequently used for physical
applications. Although it is wider than Riemannian geometry, it has two main
defects. The first is that its path equation does not represent physical
trajectories of any test particle. The second is the identical vanishing of its
curvature tensor. The present work shows that parameterizing this geometry
would solve the two problems. Furthermore, the resulting parameterized
AP-structure is more general than both the conventional AP-structure and the
Riemannian structure. Also, it is shown that it can be reduced to one or the
other, of these two geometric structures, in some special cases. The structure
obtained is more appropriate for physical applications, especially in
constructing field theories gauging gravity.


title: The fate of chaotic binaries

abstract:
  A typical stellar mass black hole with a lighter companion is shown to
succumb to a chaotic precession of the orbital plane. As a result, the optimal
candidates for the direct detection of gravitational waves by Earth based
interferometers can show irregular modulation of the waveform during the last
orbits before plunge. The precession and the subsequent modulation of the
gravitational radiation depends on the mass ratio, eccentricity, and spins. The
smaller the mass of the companion, the more prominent the effect of the
precession. The most important parameters are the spin magnitudes and
misalignments. If the spins are small and nearly aligned with the orbital
angular momentum, then there will be no chaotic precession while increasing
both the spin magnitudes and misalignments increases the erratic precession. A
large eccentricity can be induced by large, misaligned spins but does not seem
to be required for chaos. An irregular precession of the orbital plane will
generate irregularities in the gravitational wave frequency but may have a
lesser effect on the total number of cycles observed.


title: Naked singularities and quantum gravity

abstract:
  There are known models of spherical gravitational collapse in which the
collapse ends in a naked shell-focusing singularity for some initial data. If a
massless scalar field is quantized on the classical background provided by such
a star, it is found that the outgoing quantum flux of the scalar field diverges
in the approach to the Cauchy horizon. We argue that the semiclassical
approximation (i.e. quantum field theory on a classical curved background) used
in these analyses ceases to be valid about one Planck time before the epoch of
naked singularity formation, because by then the curvature in the central
region of the star reaches Planck scale. It is shown that during the epoch in
which the semiclassical approximation is valid, the total emitted energy is
about one Planck unit, and is not divergent. We also argue that back reaction
in this model does not become important so long as gravity can be treated
classically. It follows that the further evolution of the star will be
determined by quantum gravitational effects, and without invoking quantum
gravity it is not possible to say whether the star radiates away on a short
time scale or settles down into a black hole state.


title: The r-mode instability in rotating neutron stars

abstract:
  In this review we summarize the current understanding of the
gravitational-wave driven instability associated with the so-called r-modes in
rotating neutron stars. We discuss the nature of the r-modes, the detailed
mechanics of the instability and its potential astrophysical significance. In
particular we discuss results regarding the spin-evolution of nascent neutron
stars, the detectability of r-mode gravitational waves and mechanisms limiting
the spin-rate of accreting neutron stars in binary systems.


title: Spontaneous loss of charge of the Reissner-Nordstrom black hole

abstract:
  In this paper, we study by a functional method the vacuum instability of a
charged scalar field, when it is quantized in the background of the
Reissner-Nordtrom black hole; we also show that the first stage of the
evaporation process of the black hole can be driven by a Schwinger-like effect.


title: Effective one-body approach to the relativistic two-body problem

abstract:
  The relativistic 2-body problem, much like the non-relativistic one, is
reduced to describing the motion of an effective particle in an external field.
The concept of a relativistic reduced mass and effective particle energy
introduced some 30 years ago to compute relativistic corrections to the Balmer
formula in quantum electrodynamics, is shown to work equally well for classical
electromagnetic and gravitational interaction. The results for the
gravitational 2-body problem have more than academic interest since they apply
to the study of binary pulsars that provide precision tests for general
relativity. They are compared with recent results derived by other methods.


title: Classical and quantum equivalence principle in terms of the path group

abstract:
  A natural mapping of paths in a curved space onto the paths in the
corresponding (tangent) flat space may be used to reduce the curved-space-time
path integral to the flat-space-time path integral. The dynamics of the
particle in a curved space-time is expressed then in terms of an integral over
paths in the flat (Minkowski) space-time. This may be called quantum
equivalence principle. Contrary to the known DeWitt's definition of a
curved-space path integral, the present definition leads to the covariant
equation of motion without a scalar curvature term. The reduction of a
curved-space path integral to the flat-space path integral may be expressed in
terms of a representation of the path group. With the help of this
representation all the results may be generalized to the case of an arbitrary
external field.


title: A new approach to quantum gravity: an overview

abstract: We quantise General Relativity for a class of energy-momentum-stress tensors.


title: Cosmic crystallography: the hyperbolic isometries

abstract:
  All orientation preserving isometries of the hyperbolic three-space are
studied, and the probability density of conjugate pair separations for each
isometry is presented. The study is relevant for the cosmic crystallography,
and is the theoretical counterpart of the mean histograms arising from computer
simulations of the isometries.


title: Relativistic theory for time and frequency transfer to order c^{-3}

abstract:
  This paper is motivated by the current development of several space missions
(e.g. ACES on International Space Station) that will fly on Earth orbit laser
cooled atomic clocks, providing a time-keeping accuracy of the order of
5~10^{-17} in fractional frequency. We show that to such accuracy, the theory
of frequency transfer between Earth and Space must be extended from the
currently known relativistic order 1/c^2 (which has been needed in previous
space experiments such as GP-A) to the next relativistic correction of order
1/c^3. We find that the frequency transfer includes the first and second-order
Doppler contributions, the Einstein gravitational red-shift and, at the order
1/c^3, a mixture of these effects. As for the time transfer, it contains the
standard Shapiro time delay, and we present an expression also including the
first and second-order Sagnac corrections. Higher-order relativistic
corrections, at least O(1/c^4), are numerically negligible for time and
frequency transfers in these experiments, being for instance of order 10^{-20}
in fractional frequency. Particular attention is paid to the problem of the
frequency transfer in the two-way experimental configuration. In this case we
find a simple theoretical expression which extends the previous formula (Vessot
et al. 1980) to the next order 1/c^3. In the Appendix we present the detailed
proofs of all the formulas which will be needed in such experiments.


title: Uniformly accelerating black holes in a de Sitter universe

abstract:
  A class of exact solutions of Einstein's equations is analysed which
describes uniformly accelerating charged black holes in an asymptotically de
Sitter universe. This is a generalisation of the C-metric which includes a
cosmological constant. The physical interpretation of the solutions is
facilitated by the introduction of a new coordinate system for de Sitter space
which is adapted to accelerating observers in this background. The solutions
considered reduce to this form of the de Sitter metric when the mass and charge
of the black holes vanish.


title:
Analytic derivation of the map of null rays passing near a naked
  singularity

abstract:
  Recently the energy emission from a naked singularity forming in spherical
dust collapse has been investigated. This radiation is due to the particle
creation in a curved spacetime. In this discussion, the central role is played
by the mapping formula between the incoming and the outgoing null coordinates.
For the self-similar model, this mapping formula has been derived analytically.
But for the model with $C^{\infty}$ density profile, the mapping formula has
been obtained only numerically. In the present paper, we argue that the
singular nature of the mapping is determined by the local geometry around the
point at which the singularity is first formed. If this is the case, it would
be natural to expect that the mapping formula can be derived analytically. In
the present paper, we analytically rederive the same mapping formula for the
model with $C^{\infty}$ density profile that has been earlier derived using a
numerical technique.


title: Gravitational Collapse in Constant Potential Bath

abstract:
  We analyse here the gravitational collapse of directed null radiation in a
background with a constant potential such as one produced by a star system like
galaxy in which the collapsing object is immersed. Both naked singularities and
black holes are shown to be developing as the final outcome of the collapse. An
interesting feature that emerges is that a part of the naked singularity
spectrum in collapsing Vaidya region gets covered in the corresponding
dual-Vaidya region, which corresponds to the Vaidya directed null radiation
sitting in constant potential bath. The implications of such a result towards
the issue of stability of naked singularities are discussed.


title: The Effect of Sources on the Inner Horizon of Black Holes

abstract:
  Single pulse of null dust and colliding null dusts both transform a regular
horizon into a space-like singularity in the space of colliding waves. The
local isometry between such space-times and black holes extrapolates these
results to the realm of black holes. However, inclusion of particular scalar
fields instead of null dusts creates null singularities rather than space-like
ones on the inner horizons of black holes.


title: Gauge invariance of complex general relativity

abstract:
  In this paper it is implemented how to make compatible the boundary
conditions and the gauge fixing conditions for complex general relativity
written in terms of Ashtekar variables using the Henneaux-Teitelboim-Vergara
approach. Moreover, it is found that at first order in the gauge parameters,
the Hamiltonian action is (on shell) fully gauge-invariant under the gauge
symmetry generated by the first class constraints in the case when spacetime
$\cal M$ has the topology ${\cal M}= R \times \Sigma$ and $\Sigma$ has no
boundary. Thus, the statement that the constraints linear in the momenta do not
contribute to the boundary terms is right, but only in the case when $\Sigma$
has no boundary.


title: Mixmaster chaos

abstract:
  The significant discussion about the possible chaotic behavior of the
mixmaster cosmological model due to Cornish and Levin [J.N. Cornish and J.J.
Levin, Phys. Rev. Lett. 78 (1997) 998; Phys. Rev. D 55 (1997) 7489] is
revisited. We improve their method by correcting nontrivial oversights that
make their work inconclusive to precisely confirm their result: ``The mixmaster
universe is indeed chaotic''.


title: Wideband dual sphere detector of gravitational waves

abstract:
  We present the concept of a sensitive AND broadband resonant mass
gravitational wave detector. A massive sphere is suspended inside a second
hollow one. Short, high-finesse Fabry-Perot optical cavities read out the
differential displacements of the two spheres as their quadrupole modes are
excited. At cryogenic temperatures one approaches the Standard Quantum Limit
for broadband operation with reasonable choices for the cavity finesses and the
intracavity light power. A molybdenum detector of overall size of 2 m, would
reach spectral strain sensitivities of 2x10^-23/Sqrt{Hz} between 1000 Hz and
3000 Hz.


title: Cosmic Censorship: The Role of Quantum Gravity

abstract:
  The cosmic censorship hypothesis introduced by Penrose thirty years ago is
still one of the most important open questions in {\it classical} general
relativity. In this essay we put forward the idea that cosmic censorship is
intrinsically a {\it quantum gravity} phenomena. To that end we construct a
gedanken experiment in which cosmic censorship is violated within the purely
{\it classical} framework of general relativity. We prove, however, that {\it
quantum} effects restore the validity of the conjecture. This suggests that
classical general relativity is inconsistent and that cosmic censorship might
be enforced only by a quantum theory of gravity.


title: Studies of the Schroedinger-Newton Equations in D Dimensions

abstract:
  We investigate a $D$ dimensional generalization of the Schroedinger-Newton
equations, which purport to describe quantum state reduction as resulting from
gravitational effects. For a single particle, the system is a combination of
the Schroedinger and Poisson equations modified so that the probability density
of the wavefunction is the source of the potential in the Schroedinger
equation. For spherically symmetric wavefunctions, a discrete set of energy
eigenvalue solutions emerges for dimensions $D<6$, accumulating at D=6.
Invoking Heisenberg's uncertainty principle to assign timescales of collapse
correspoding to each energy eigenvalue, we find that these timescales may vary
by many orders of magnitude depending on dimension. For example, the time taken
for the wavefunction of a free neutron in a spherically symmetric state to
collapse is many orders of magnitude longer than the age of the universe,
whereas for one confined to a box of picometer-sized cross-sectional dimensions
the collapse time is about two weeks.


title: Uniqueness of the asymptotic AdS3 geometry

abstract:
  We explicitly show that in (2+1) dimensions the general solution of the
Einstein equations with negative cosmological constant on a neigbourhood of
timelike spatial infinity can be obtained from BTZ metrics by coordinate
transformations corresponding geometrically to deformations of their spatial
infinity surface. Thus, whatever the topology and geometry of the bulk, the
metric on the timelike extremities is BTZ.


title: Constraints on Area Variables in Regge Calculus

abstract:
  We describe a general method of obtaining the constraints between area
variables in one approach to area Regge calculus, and illustrate it with a
simple example. The simplicial complex is the simplest tessellation of the
4-sphere. The number of independent constraints on the variations of the
triangle areas is shown to equal the difference between the numbers of
triangles and edges, and a general method of choosing independent constraints
is described. The constraints chosen by using our method are shown to imply the
Regge equations of motion in our example.


title:
Conformal derivative and conformal transports over spaces with
  contravariant and covariant affine connections and metrics

abstract:
  Transports preserving the angle between two contravariant vector fields but
changing their lengths proportional to their own lengths are introduced as
''conformal'' transports and investigated over spaces with contravariant and
covariant affine connections (whose components differ not only by sign) and
metrics. They are more general than the Fermi-Walker transports. In an
analogous way as in the case of Fermi-Walker transports a conformal covariant
differential operator and its conformal derivative are defined and considered
over the above mentioned spaces. Different special types of conformal
transports are determined inducing also Fermi-Walker transports for orthogonal
vector fields as special cases. Conditions under which the length of a non-null
contravariant vector field could swing as a homogeneous harmonic oscillator are
established. The results obtained regardless of any concrete field
(gravitational) theory could have direct applications in such types of
theories.
  PACS numbers: 04.90.+e; 04.50.+h; 12.10.Gq; 02.40.Vh


title: A new approach to quantum gravity: a summary

abstract:
  Quantum Electrodynamics (QED) has been so successful a theory that it is
taken as a model for the production of further quantum theories. However, when
the prescription for quantising electromagnetic interactions that so
successfully resulted in QED is applied to General Relativity the theory
obtained is not renormalizable. We derive a different method of quantising
classical electromagnetism which also results in QED. We call the method the
versatile method. We then apply the versatile method to General Relativity, in
particular the Einstein equation which equates a geometrical description
derivable from the metric to the energy-momentum-stress tensor, or as we shall
call it the matter tensor of the matter field. The method can be applied
provided that there is always a reference frame, which may differ with location
and time, where the matter tensor can be reduced to a mass density with the
other elements zero. We call such matter tensors simple. This restriction means
that the tensor can be put into one to one correspondence with the Dirac
current. When the versatile method of quantising a classical theory is applied
to General Relativity the theory that results is renormalizable. It is in fact
isomorphic to QED, provided that the temporal and a spatial co-ordinate are
exchanged.


title: Analysing Charges in even dimensions

abstract:
  Lanczos-Lovelock theories of gravity, in its first order version, are studied
on asymptotically locally anti de Sitter spaces. It is shown that
thermodynamics satisfies the standard behavior and an expression for entropy is
found for this formalism. Finally a short analysis of the algebra of conserved
charges is displayed.


title:
Hamiltonians for a general dilaton gravity theory on a spacetime with a
  non-orthogonal, timelike or spacelike outer boundary

abstract:
  A generalization of two recently proposed general relativity Hamiltonians, to
the case of a general (d+1)-dimensional dilaton gravity theory in a manifold
with a timelike or spacelike outer boundary, is presented.


title: On Quantum Mechanics in Friedmann-Robertson-Walker Universe

abstract:
  It is shown that only in the space-times admitting a 1+3-foliation by flat
Cauchy hypesurfaces (i.e., in the Bianchi I type space-times the isotropic
version of which the spatially flat Friedmann-Robertson-Walker space-times are)
the canonical quantization of geodesic motion and quantum-mechanics obtained as
an asymptotics of the quantum theory of scalar field lead to the same canonical
commutation relations (CCR). Otherwise, the field-theoretical approach leads to
a deformation of CCR (particularly, operators of coordinates do not commute),
and the Principle of Correspondence is broken in a sense. Thus, the spatially
flat cosmology is distinguished intrinsically in the quantum theory.


title: EinS: a Mathematica package for computations with indexed objects

abstract:
  This preprint contains a description of a package for Mathematica called
EinS. This package allows one to perform various calculations with indexed
objects.


title: Relativity and Nonlocality

abstract:
  The basic physical structure of the relativistic theory of gravitation is
discussed. The significant role that the Hypothesis of Locality plays in
relativity theory is elucidated via the phenomenon of spin-rotation coupling.
The limitations of this hypothesis are critically examined. A nonlocal theory
of accelerated observers is presented and some of its observational
consequences are described.


title: Gravitoelectromagnetism

abstract:
  Gravitoelectromagnetism is briefly reviewed and some recent developments in
this topic are discussed. The stress-energy content of the
gravitoelectromagnetic field is described from different standpoints. In
particular, the gravitational Poynting flux is analyzed and it is shown that
there exists a steady flow of gravitational energy circulating around a
rotating mass.


title: Projective Relativity: Present Status and Outlook

abstract:
  We give a critical analysis of projective relativity theory. Examining
Kaluza's own intention and the following development by Klein, Jordan, Pauli,
Thiry, Ludwig and others, we conclude that projective relativity was abused in
its own terms. Much more in the case of newer higher dimensional Kaluza--Klein
theories with non-Abelian gauge groups. Reviewing the projective formulation of
the Jordan isomorphy theorem yields some hints how one can proceed in a
different direction. We can interpret the condition R5_{\mu\nu}=0 not as a
field equation in a 5-dimensional Riemannian space, e.g. as vacuum
Einstein-Hilbert equation, but can (or should) interpret it as a geometrical
object, a null-quadric. Projective aspects of quantum (field) theory are
discussed under this viewpoint.


title: Impulsive spherical gravitational waves

abstract:
  Penrose's identification with warp provides the general framework for
constructing the continuous form of impulsive gravitational wave metrics. We
present the 2-component spinor formalism for the derivation of the full family
of impulsive spherical gravitational wave metrics which brings out the power in
identification with warp and leads to the simplest derivation of exact
solutions. These solutions of the Einstein vacuum field equations are obtained
by cutting Minkowski space into two pieces along a null cone and re-identifying
them with warp which is given by an arbitrary non-linear holomorphic
transformation. Using 2-component spinor techniques we construct a new metric
describing an impulsive spherical gravitational wave where the vertex of the
null cone lies on a world-line with constant acceleration.


title: Symmetries of homogeneous cosmologies

abstract:
  We reformulate the dynamics of homogeneous cosmologies with a scalar field
matter source with an arbitrary self-interaction potential in the language of
jet bundles and extensions of vector fields. In this framework, the
Bianchi-scalar field equations become subsets of the second Bianchi jet bundle,
$J^2$, and every Bianchi cosmology is naturally extended to live on a variety
of $J^2$. We are interested in the existence and behaviour of extensions of
arbitrary Bianchi-Lie and variational vector fields acting on the Bianchi
variety and accordingly we classify all such vector fields corresponding to
both Bianchi classes $A$ and $B$. We give examples of functions defined on
Bianchi jet bundles which are constant along some Bianchi models (first
integrals) and use these to find particular solutions in the Bianchi total
space. We discuss how our approach could be used to shed new light to questions
like isotropization and the nature of singularities of homogeneous cosmologies
by examining the behaviour of the variational vector fields and also give rise
to interesting questions about the `evolution' and nature of the cosmological
symmetries themselves.


title: Light propagation around a relativistic vortex flow of dielectric medium

abstract:
  We determine the path of the light around a dielectric vortex described by
the relativistic vortex flow of a perfect fluid.


title:
Symmetry, Singularities and Integrability in Complex Dynamics IV:
  Painleve Integrability of Isotropic Cosmologies

abstract:
  We apply the results of singularity analysis to the isotropic cosmological
models in general relativity and string theory with a variety of matter terms.
For some of these models the standard Painlev\'{e} test is sufficient to
demonstrate integrability or nonintegrability in the sense of Painlev\'{e}. For
others of these models it is necessary to use a less algorithmic procedure.


title:
Inflation and nonequilibrium thermodynamics for the fluctuations in the
  infrared sector

abstract:
  In the framework of inflationary cosmology I study some aspects of
nonequilibrium thermodynamics for the matter field fluctuations. The
thermodynamic analysis is developed for de Sitter and power - law expansions of
the universe. In both cases, I find that the heat capacity is negative leading
respectively, to exponential and superexponential growth for the number of
states in the infrared sector for de Sitter and power-law expansions of the
universe. The spectrum for the matter field fluctuations can be understood from
the background effective temperature when the horizon entry.


title: Ever-expanding, Isotropizing, Quadratic Cosmologies

abstract:
  We consider some aspects of the global evolution problem of Hamiltonian
homogeneous, anisotropic cosmologies derived from a purely quadratic action
functional of the scalar curvature. We show that models can isotropize in the
positive asymptotic direction and that quadratic diagonal Bianchi IX models do
not recollapse and may be regular initially. Although the global existence and
isotropization results we prove hold quite generally, they are applied to
specific Bianchi models in an attempt to describe how certain dynamical
properties uncommon to the general relativity case, become generic features of
these quadratic universes. The question of integrability of the models is also
considered. Our results point to the fact that the more general models are not
integrable in the sense of Painlev\'e and for the Bianchi IX case this may be
connected to the validity of a BKL oscillatory picture on approach to the
singularity in sharp contrast with other higher order gravity theories that
contain an Einstein term and show a monotonic evolution towards the initial
singularity.


title: Solid and ocean tides and the detection of some gravitomagnetic effects

abstract:
  The detection of some tiny gravitomagnetic effects in the field of the Earth
by means of artificial satellites is a very demanding task because of the
various other perturbing forces of gravitational and non-gravitational origin
acting upon them. Among the gravitational perturbations a relevant role is
played by the Earth solid and ocean tides. In this communication I outline
their effects on the detection of the Lense-Thirring drag of the orbits of
LAGEOS and LAGEOS II, currently analyzed, and the proposed GP-C experiment
devoted to the measurement of the clock effect.

categories: gr-qc astro-ph physics.geo-ph physics.space-ph


title: On Cyclically Symmetrical Spacetimes

abstract:
  In a recent paper Carot et al. considered the definition of cylindrical
symmetry as a specialisation of the case of axial symmetry. One of their
propositions states that if there is a second Killing vector, which together
with the one generating the axial symmetry, forms the basis of a
two-dimensional Lie algebra, then the two Killing vectors must commute, thus
generating an Abelian group. In this paper a similar result, valid under
considerably weaker assumptions, is derived: any two-dimensional Lie
transformation group which contains a one-dimensional subgroup whose orbits are
circles, must be Abelian. The method used to prove this result is extended to
apply three-dimensional Lie transformation groups. It is shown that the
existence of a one-dimensional subgroup with closed orbits restricts the
Bianchi type of the associated Lie algebra to be I, II, III, VII_0, VIII or IX.
Some results on n-dimensional Lie groups are also derived and applied to show
there are severe restrictions on the structure of the allowed four-dimensional
Lie transformation groups compatible with cyclic symmetry.


title: Why is the black hole entropy (almost) linear in the horizon area?

abstract:
  We show that essentially pure classical thermodynamics is sufficient to
determine Bekenstein's formula for the black hole's entropy, $S=\eta A$. We
base our reasoning on the minimal assumption that since black body radiation is
describable by classical thermodynamics, so is the complete black hole-Hawking
radiation system. Furthermore, we argue that any non-linear correction to the
black hole entropy must be quantum mechanical in nature. The proportionality
coefficient, $\eta=1/4\ell_P^2$, must be calculated within a semi-classical or
full-fledged quantum mechanical framework.


title: Scattering by Black Holes

abstract:
  This is a chapter on Black-hole Scattering that was commissioned for an
Encyclopaedia on Scattering edited by Pike and Sabatier, to be published by
Academic Press. The chapter surveys wave propagation in black-hole spacetimes,
diffraction effects in wave scattering, resonances, quasinormal modes and
related topics.


title: Analog gravity from Bose-Einstein condensates

abstract:
  We analyze prospects for the use of Bose-Einstein condensates as
condensed-matter systems suitable for generating a generic ``effective
metric'', and for mimicking kinematic aspects of general relativity. We extend
the analysis due to Garay et al, [gr-qc/0002015, gr-qc/0005131]. Taking a long
term view, we ask what the ultimate limits of such a system might be. To this
end, we consider a very general version of the nonlinear Schrodinger equation
(with a 3-tensor position-dependent mass and arbitrary nonlinearity). Such
equations can be used for example in discussing Bose-Einstein condensates in
heterogeneous and highly nonlinear systems. We demonstrate that at low momenta
linearized excitations of the phase of the condensate wavefunction obey a
(3+1)-dimensional d'Alembertian equation coupling to a (3+1)-dimensional
Lorentzian-signature ``effective metric'' that is generic, and depends
algebraically on the background field. Thus at low momenta this system serves
as an analog for the curved spacetime of general relativity. In contrast at
high momenta we demonstrate how to use the eikonal approximation to extract a
well-controlled Bogoliubov-like dispersion relation, and (perhaps unexpectedly)
recover non-relativistic Newtonian physics at high momenta. Bose-Einstein
condensates appear to be an extremely promising analog system for probing
kinematic aspects of general relativity.


title: Viscous cosmologies in scalar-tensor theories for Kasner type metrics

abstract:
  In a viscous Bianchi type I metric of the Kasner form, it is well known that
it is not possible to describe an anisotropic physical model of the universe,
which satisfies the second law of thermodynamics and the dominant energy
condition (DEC) in Einstein's theory of gravity. We examine this problem in
scalar-tensor theories of gravity. In this theory we show that it is possible
to describe the growth of entropy, keeping the thermodynamics and the dominant
energy condition.


title:
Gravitational Wavetrains in the Quasi-Equilibrium Approximation: A Model
  Problem in Scalar Gravitation

abstract:
  A quasi-equilibrium (QE) computational scheme was recently developed in
general relativity to calculate the complete gravitational wavetrain emitted
during the inspiral phase of compact binaries. The QE method exploits the fact
that the the gravitational radiation inspiral timescale is much longer than the
orbital period everywhere outside the ISCO. Here we demonstrate the validity
and advantages of the QE scheme by solving a model problem in relativistic
scalar gravitation theory. By adopting scalar gravitation, we are able to
numerically track without approximation the damping of a simple, quasi-periodic
radiating system (an oscillating spherical matter shell) to final equilibrium,
and then use the exact numerical results to calibrate the QE approximation
method. In particular, we calculate the emitted gravitational wavetrain three
different ways: by integrating the exact coupled dynamical field and matter
equations, by using the scalar-wave monopole approximation formula
(corresponding to the quadrupole formula in general relativity), and by
adopting the QE scheme. We find that the monopole formula works well for weak
field cases, but fails when the fields become even moderately strong. By
contrast, the QE scheme remains quite reliable for moderately strong fields,
and begins to breakdown only for ultra-strong fields. The QE scheme thus
provides a promising technique to construct the complete wavetrain from binary
inspiral outside the ISCO, where the gravitational fields are strong, but where
the computational resources required to follow the system for more than a few
orbits by direct numerical integration of the exact equations are prohibitive.


title:
New Five Dimensional Black Holes Classified by Horizon Geometry, and a
  Bianchi VI Braneworld

abstract:
  We introduce two new families of solutions to the vacuum Einstein equations
with negative cosmological constant in 5 dimensions. These solutions are static
black holes whose horizons are modelled on the 3-geometries nilgeometry and
solvegeometry. Thus the horizons (and the exterior spacetimes) can be foliated
by compact 3-manifolds that are neither spherical, toroidal, hyperbolic, nor
product manifolds, and therefore are of a topological type not previously
encountered in black hole solutions. As an application, we use the
solvegeometry solutions to construct Bianchi VI$_{-1}$ braneworld cosmologies.


title:
The dipolar zero-modes of Einstein action: An informal summary with some
  new issues

abstract:
  We recall the main features of metric vacuum fluctuations which have the
global property int d^4x sqrt{g(x)} R(x) = 0, even though R(x) does not vanish
locally. We stress that these fluctuations could mediate an anomalous coupling
between the gravitational field and coherent matter. Some new issues are
discussed: (1) these fluctuations still imply that <T_{mu nu}(x)>=0; (2) they
are not extrema of the action; (3) for finite duration, their volume in phase
space is not zero; (4) vacuum fluctuations of this kind are not allowed in QED;
(5) their null-action property is a nonperturbative feature; (6) any -real-
pure e.m. field generates zero-modes of this kind, too, up to terms of order
G^2.


title:
Theory of Relativistic Reference Frames for High-Precision Astrometric
  Space Missions

abstract:
  Recent modern space missions deliver invaluable information about origin of
our universe, physical processes in the vicinity of black holes and other
exotic astrophysical objects, stellar dynamics of our galaxy, etc. On the other
hand, space astrometric missions make it possible to determine with
unparalleled precision distances to stars and cosmological objects as well as
their physical characteristics and positions on the celestial sphere.
Permanently growing accuracy of space astronomical observations and the urgent
need for adequate data processing algorithms require corresponding development
of an adequate theory of reference frames along with unambiguous description of
propagation of light rays from a source of light to observer. Such a theory
must be based on the Einstein's general relativity and account for numerous
relativistic effects both in the solar system and outside of its boundary. The
main features of the relativistic theory of reference frames are presented in
this work. A hierarchy of the frames is described starting from the perturbed
cosmological Friedmann-Robertson-Walker metric and going to the observer's
frame through the intermediate barycentric and geocentric frames in the solar
system. Microarcsecond astrometry and effects of propagation of light rays in
time-dependent gravitational fields are discussed as well.


title: Resampled random processes in gravitational-wave data analysis

abstract:
  The detection of continuous gravitational-wave signals requires to account
for the motion of the detector with respect to the solar system barycenter in
the data analysis. In order to search efficiently for such signals by means of
the fast Fourier transform the data needs to be transformed from the
topocentric time to the barycentric time by means of resampling. The resampled
data form a non-stationary random process. In this communication we prove that
this non-stationary random process is mathematically well defined, and show
that generalizations of the fundamental results for stationary processes, like
Wiener-Khintchine theorem and Cram\`{e}r representation, exist.


title: New properties of Cauchy and event horizons

abstract:
  We present several recent results concerning Cauchy and event horizons. In
the first part of the paper we review the differentiablity properties of the
Cauchy and the event horizons. In the second part we discuss compact Cauchy
horizons and summarize their main properties.


title:
Searching for continuous gravitational wave signals: the hierarchical
  Hough transform algorithm

abstract:
  It is well known that matched filtering techniques cannot be applied for
searching extensive parameter space volumes for continuous gravitational wave
signals. This is the reason why alternative strategies are being pursued.
Hierarchical strategies are best at investigating a large parameter space when
there exist computational power constraints. Algorithms of this kind are being
implemented by all the groups that are developing software for analyzing the
data of the gravitational wave detectors that will come online in the next
years. In this talk we will report about the hierarchical Hough transform
method that the GEO 600 data analysis team at the Albert Einstein Institute is
developing. The three step hierarchical algorithm has been described elsewhere.
In this talk we will focus on some of the implementational aspects we are
currently concerned with.


title:
Dynamics of a string coupled to gravitational waves II - Perturbations
  propagate along an infinite Nambu-Goto string

abstract:
  The perturbative modes propagating along an infinite string are investigated
within the framework of the gauge invariant perturbation formalism on a
spacetime containing a self-gravitating straight string with a finite
thickness. These modes are not included in our previous analysis. We
reconstruct the perturbation formalism to discuss these modes and solve the
linearized Einstein equation within the first order with respect to the string
oscillation amplitude. In the thin string case, we show that the oscillations
of an infinite string must involve the propagation of cosmic string traveling
wave.


title: On unbounded bodies with finite mass: asymptotic behaviour

abstract:
  There is introduced a class of barotropic equations of state (EOS) which
become polytropic of index $n = 5$ at low pressure. One then studies
asymptotically flat solutions of the static Einstein equations coupled to
perfect fluids having such an EOS. It is shown that such solutions, in the same
manner as the vacuum ones, are conformally smooth or analytic at infinity, when
the EOS is smooth or analytic, respectively.


title:
3+1 spinfoam model of quantum gravity with spacelike and timelike
  components

abstract:
  We present a spinfoam formulation of Lorentzian quantum General Relativity.
The theory is based on a simple generalization of an Euclidean model defined in
terms of a field theory over a group. The model is an extension of a recently
introduced Lorentzian model, in which both timelike and spacelike components
are included. The spinfoams in the model, corresponding to quantized
4-geometries, carry a natural non-perturbative local causal structure induced
by the geometry of the algebra of the internal gauge (sl(2,C)). Amplitudes can
be expressed as integrals over the spacelike unit-vectors hyperboloid in
Minkowski space, or the imaginary Lobachevskian space.


title:
Thermal fluctuations of a quantized massive scalar field in Rindler
  background

abstract:
  Thermal fluctuations for a massive scalar field in the Rindler wedge are
obtained by applying the point-splitting procedure to the zero temperature
Feynman propagator in a conical spacetime. Renormalization is implemented by
removing the zero temperature contribution. It is shown that for a field of non
vanishing mass the thermal fluctuations, when expressed in terms of the local
temperature, do not have Minkowski form. As a by product, Minkowski vacuum
fluctuations seen by an uniformly accelerated observer are determined and
confronted with the literature.


title:
Radiation reaction and the self-force for a point mass in general
  relativity

abstract:
  A point particle of mass m moving on a geodesic creates a perturbation h, of
the spacetime metric g, that diverges at the particle. Simple expressions are
given for the singular m/r part of h and its quadrupole distortion caused by
the spacetime. Subtracting these from h leaves a remainder h^R that is C^1. The
self-force on the particle from its own gravitational field corrects the
worldline at O(m) to be a geodesic of g+h^R. For the case that the particle is
a small non-rotating black hole, an approximate solution to the Einstein
equations is given with error of O(m^2) as m approaches 0.


title: Generating spherically symmetric static perfect fluid solutions

abstract:
  By a choice of new variables the pressure isotropy condition for spherically
symmetric static perfect fluid spacetimes can be made a quadratic algebraic
equation in one of the two functions appearing in it. Using the other variable
as a generating function, the pressure and the density of the fluid can be
expressed algebraically by the function and its derivatives. One of the
functions in the metric can also be expressed similarly, but to obtain the
other function, related to the redshift factor, one has to perform an integral.
Conditions on the generating function ensuring regularity and physicality near
the center are investiagted. Two everywhere physically well behaving example
solutions are generated, one representing a compact fluid body with a zero
pressure surface, the other an infinite sphere.


title:
On line power spectra identification and whitening for the noise in
  interferometric gravitational wave detectors

abstract:
  In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
  Least Squares ones.


title: A Stationary Approximation to the Spacetime of a Compact Object Binary

abstract:
  The gravitational-radiation-induced inspiral of a binary system of compact
objects is considered. A scheme is described to model the regime in which the
gravitational interaction is too strong to use weak-field approximation
methods, but the time scale for decay of the orbits is still long compared to
the orbital period, by numerically solving for a stationary spacetime which
approximates the slowly evolving one. Equilibrium is to be maintained in the
radiating system by imposing a balance of incoming and outgoing radiation at
large distances. Numerical results from non-linear scalar field theory have
shown that such an approach can be effective modelling a slowly evolving
solution to a wave equation.


title:
Diffeomorphism on Horizon as an Asymptotic Isometry of Schwarzschild
  Black Hole

abstract:
  It is argued that the diffeomorphism on the horizontal sphere can be regarded
as a nontrivial asymptotic isometry of the Schwarzschild black hole. We propose
a new boundary condition of asymptotic metrics near the horizon and show that
the condition admits the local time-shift and diffeomorphism on the horizon as
the asymptotic symmetry.


title: Non-vanishing Magnetic Flux through the Slightly-charged Kerr Black Hole

abstract:
  In association with the Blanford-Znajek mechanism for rotational energy
extraction from Kerr black holes, it is of some interest to explore how much of
magnetic flux can actually penetrate the horizon at least in idealized
situations. For completely uncharged Kerr hole case, it has been known for some
time that the magnetic flux gets entirely expelled when the hole is
maximally-rotating. In the mean time, it is known that when the rotating hole
is immersed in an originally uniform magnetic field surrounded by an ionized
interstellar medium (plasma), which is a more realistic situation, the hole
accretes certain amount of electric charge. In the present work, it is
demonstrated that as a result of this accretion charge small enough not to
disturb the geometry, the magnetic flux through this slightly charged Kerr hole
depends not only on the hole's angular momentum but on the hole's charge as
well such that it never vanishes for any value of the hole's angular momentum.


title:
Weyl's spaces with shear-free and expansion-free conformal Killing
  vectors and the motion of a free spinless test particle

abstract:
  Conditions for the existence of shear-free and expansion-free non-null vector
fields in spaces with affine connections and metrics are found. On their basis
Weyl's spaces with shear-free and expansion-free conformal Killing vectors are
considered. The necessary and sufficient conditions are found under which a
free spinless test particle could move in spaces with affine connections and
metrics on a curve described by means of an auto-parallel equation. In Weyl's
spaces with Weyl's covector, constructed by the use of a dilaton field, the
dilaton field appears as a scaling factor for the rest mass density of the test
particle.
  PACS numbers: 02.40.Ky, 04.20.Cv, 04.50.+h, 04.90.+e


title:
N = 3 chiral supergravity compatible with the reality condition and
  higher N chiral Lagrangian density

abstract:
  We obtain N = 3 chiral supergravity (SUGRA) compatible with the reality
condition by applying the prescription of constructing the chiral Lagrangian
density from the usual SUGRA. The $N = 3$ chiral Lagrangian density in
first-order form, which leads to the Ashtekar's canonical formulation, is
determined so that it reproduces the second-order Lagrangian density of the
usual SUGRA especially by adding appropriate four-fermion contact terms. We
show that the four-fermion contact terms added in the first-order chiral
Lagrangian density are the non-minimal terms required from the invariance under
first-order supersymmetry transformations. We also discuss the case of higher N
theories, especially for N = 4 and N = 8.


title: On the Hawking effect

abstract:
  In terms of the Painlev{\'e}-Gullstrand-Lema{\^\i}tre coordinates a rather
general scenario for the gravitational collapse of an object and the subsequent
formation of a horizon is described by a manifestly $C^\infty$-metric. For a
1+1 dimensional model of the collapse the leading contributions to the
Bogoliubov coefficients are calculated explicitely and the Hawking temperature
is recovered. But depending on the particular dynamics of the collapse the
final state represents either evaporation or anti-evaporation. The
generalization of the calculation to 3+1 dimensions is outlined and possible
implications are addressed. PACS-numbers: 04.70.Dy, 04.70.-s, 04.62.+v.


title:
Wormholes and Spacetime Foam: an approach to the Cosmological Constant
  and Entropy

abstract:
  This paper summarizes the contribution presented at the IX Marcel Grossmann
Meeting (Rome, July 2000). A simple model of spacetime foam, made by $N$
Schwarzschild wormholes in a semiclassical approximation, is here proposed. The
Casimir-like energy of the quantum fluctuation of such a model and its
probability of being realized are computed. Implications on the
Bekenstein-Hawking entropy and the cosmological constant are considered. A
proposal for an alternative foamy model formed by $N$ Schwarzschild-Anti-de
Sitter wormholes is here considered.


title: An alternative approach to the galactic dark matter problem

abstract:
  We discuss scenarios in which the galactic dark matter in spiral galaxies is
described by a long range coherent field which settles in a stationary
configuration that might account for the features of the galactic rotation
curves. The simplest possibility is to consider scalar fields, so we discuss in
particular, two mechanisms that would account for the settlement of the scalar
field in a non-trivial configuration in the absence of a direct coupling of the
field with ordinary matter: topological defects, and spontaneous scalarization.


title: Uniqueness of Simultaneity

abstract:
  We consider the problem of uniqueness of certain simultaneity structures in
flat spacetime. Absolute simultaneity is specified to be a non-trivial
equivalence relation which is invariant under the automorphism group Aut of
spacetime. Aut is taken to be the identity-component of either the
inhomogeneous Galilei group or the inhomogeneous Lorentz group. Uniqueness of
standard simultaneity in the first, and absence of any absolute simultaneity in
the second case are demonstrated and related to certain group theoretic
properties. Relative simultaneity with respect to an additional structure X on
spacetime is specified to be a non-trivial equivalence relation which is
invariant under the subgroup in Aut that stabilises X. Uniqueness of standard
Einstein simultaneity is proven in the Lorentzian case when X is an inertial
frame. We end by discussing the relation to previous work of others.


title: Refractive gravitational waves and quantum fluctuations

abstract:
  Refractive gravitational waves are a generalisation of impulsive waves on a
null hypersurface in which the metric is discontinuous but a weaker continuity
condition for areas holds. A simple example of a plane wave is examined in
detail and two arguments are given that this should be considered a solution of
Einstein's vacuum field equations. The study of these waves is motivated by
quantum gravity, where the refractive plane waves are considered as elementary
quantum fluctuations and the `area geometry' of a null hypersurface plays a
primary role.


title:
Binary black holes coalescence: transition from adiabatic inspiral to
  plunge

abstract:
  Using two recent techniques giving non-perturbative re-summed estimates of
the damping and of the conservative part of the dynamics of two-body systems,
we describe the transition between adiabatic inspiral and plunge in binary
non-spinning black holes moving along quasi-circular orbits.


title: Yes, semiclassical zero temperature black holes exist

abstract:
  In a recent paper (gr-qc/0002007), Anderson, Hiscock and Taylor claimed that
"in all physically realistic cases, macroscopic zero temperature black hole
solutions do not exist." We show this conclusion was reached on the basis of an
incorrect calculation.


title:
Stable evolution of a maximally sliced Schwarzschild spacetime using a
  smooth lattice

abstract:
  We will present results of a long term stable evolution, to $t=1000m$, of a
maximally sliced Schwarzschild blackhole using a smooth lattice method.


title: Convex Functions and Spacetime Geometry

abstract:
  Convexity and convex functions play an important role in theoretical physics.
To initiate a study of the possible uses of convex functions in General
Relativity, we discuss the consequences of a spacetime $(M,g_{\mu \nu})$ or an
initial data set $(\Sigma, h_{ij}, K_{ij})$ admitting a suitably defined convex
function. We show how the existence of a convex function on a spacetime places
restrictions on the properties of the spacetime geometry.


title: The Weyl anomaly and the nature of the background geometry

abstract:
  The Weyl anomaly problem is treated within a purely geometrical context.
Arguments are given that hint at a possible classical origin of the conformal
anomaly in the Riemannian nature of the background geometry where the matter
fields play out their dynamics. Some considerations allowing for a possible
resolution of the Weyl anomaly problem are briefly outlined. Following the
spirit of the standard model of the fundamental interactions, it is argued that
the Weyl anomaly should be a consequence of the breaking of the gauge symmetry
at some stage during the evolution of the universe.


title:
Localization of gravitational energy and its potential to evaluation of
  hydrogen atom properties

abstract:
  Vaidya metric as an integral part of the Expansive Nondecelerative Universe
(ENU) model enables to localize the energy of gravitational field and,
subsequently, to find a deep interrelationship between quantum mechanics and
the general theory of relativity. In the present paper, stemming from the ENU
model, ionisation energy and energy of hyperfine splitting of the hydrogen
atom, energy of the elementary quantum of action, as well as the proton and
electron mass are independently expressed through the mass of the planckton, Z
and W bosons and fundamental constants.


title: Finiteness of a spinfoam model for euclidean quantum general relativity

abstract:
  We prove that a certain spinfoam model for euclidean quantum general
relativity, recently defined, is finite: all its all Feynman diagrams converge.
The model is a variant of the Barrett-Crane model, and is defined in terms of a
field theory over SO(4) X SO(4) X SO(4) X SO(4).


title: Gravitational Entropy and Quantum Cosmology

abstract:
  We investigate the evolution of different measures of ``Gravitational
Entropy'' in Bianchi type I and Lema\^itre-Tolman universe models.
  A new quantity behaving in accordance with the second law of thermodynamics
is introduced. We then go on and investigate whether a quantum calculation of
initial conditions for the universe based upon the Wheeler-DeWitt equation
supports Penrose's Weyl Curvature Conjecture, according to which the Ricci part
of the curvature dominates over the Weyl part at the initial singularity of the
universe. The theory is applied to the Bianchi type I universe models with dust
and a cosmological constant and to the Lema\^itre-Tolman universe models. We
investigate two different versions of the conjecture. First we investigate a
local version which fails to support the conjecture. Thereafter we construct a
non-local entity which shows more promising behaviour concerning the
conjecture.


title: Inflation on a single brane - exact solutions

abstract:
  Algorithms are developed for generating a class of exact braneworld
cosmologies, where a self-interacting scalar field is confined to a
positive-tension brane embedded in a bulk containing a negative cosmological
constant. It is assumed that the five-dimensional Planck scale exceeds the
brane tension but is smaller than the four-dimensional Planck mass. It is shown
that the field equations can be expressed as a first-order system. A number of
solutions to the equations of motion are found. The potential resulting in the
perfect fluid model is identified.


title: Geometry of rotating disk and the Sagnac effect

abstract:
  In this paper we demonstrate that subsequent application of Lorentz
transformations to the cylindrical coordinates on a rotating disk leaves the
Euclidean metric invariant. Therefore, the geometry on rotating disk is the
Euclidean geometry, and any experiment which do not involve tidal forces or
Coriolis forces cannot identify either the disk rotates or not. We also show
that, from the point of view of external inertial observer, the difference in
the transit times for the light running along a circle of radius R in the
opposite directions (with respect to the rotation) is 2w/c^2 S, where S is the
area the circle, and w is the angle velocity.


title:
On the scalar sector of the covariant graviton two-point function in de
  Sitter spacetime

abstract:
  We examine the scalar sector of the covariant graviton two-point function in
de Sitter spacetime. This sector consists of the pure-trace part and another
part described by a scalar field. We show that it does not contribute to
two-point functions of gauge-invariant quantities. We also demonstrate that the
long-distance growth present in some gauges is absent in this sector for a wide
range of gauge parameters.


title:
Third post-Newtonian dynamics of compact binaries: Noetherian conserved
  quantities and equivalence between the harmonic-coordinate and
  ADM-Hamiltonian formalisms

abstract:
  A Lagrangian from which derive the third post-Newtonian (3PN) equations of
motion of compact binaries (neglecting the radiation reaction damping) is
obtained. The 3PN equations of motion were computed previously by Blanchet and
Faye in harmonic coordinates. The Lagrangian depends on the harmonic-coordinate
positions, velocities and accelerations of the two bodies. At the 3PN order,
the appearance of one undetermined physical parameter \lambda reflects an
incompleteness of the point-mass regularization used when deriving the
equations of motion. In addition the Lagrangian involves two unphysical
(gauge-dependent) constants r'_1 and r'_2 parametrizing some logarithmic terms.
The expressions of the ten Noetherian conserved quantities, associated with the
invariance of the Lagrangian under the Poincar\'e group, are computed. By
performing an infinitesimal ``contact'' transformation of the motion, we prove
that the 3PN harmonic-coordinate Lagrangian is physically equivalent to the 3PN
Arnowitt-Deser-Misner Hamiltonian obtained recently by Damour, Jaranowski and
Sch\"afer.


title: What can Physics learn from Continuum Mechanics ?

abstract:
  This paper is mostly a collection of ideas already published by various
authors, some of them even a long time ago. Its intention is to bring the
reader to know some rather unknown papers of different fields that merit
interest and to show some relations between them the author claims to have
observed. In the first section, some comments on old unresolved problems in
theoretical physics are collected. In the following, I shall explain what
relation exists between Feynman graphs and the teleparallel theory of Einstein
and Cartan in the late 1920s, and the relation of both to the theories of the
incompressible aether around 1840. Reviewing these developments, we will have a
look at the continuum theory of dislocations developed by Kroener in the 1950s
and some techniques of differential geometry and topology relevant for a modern
description of defects in continous media. I will then illustrate some basic
concepts of nonlinear continuum mechanics and discuss applications to the above
theories. By doing so, I hope to attract attention to the possible relevance of
these facts for `fundamental' physics.


title: Solutions with negative mass for the SU(2) Einstein-Yang-Mills equations

abstract:
  The aim of this note is to clarify the structure of nontrivial global
solutions with nonpositive ADM mass for the static, spherically symmetric
Einstein-Yang-Mills equations with SU(2) gauge group. The presented numerical
results demonstrate that these solutions have zero number of nodes of the gauge
field function. This is a feature that is present neither for particlelike nor
for black hole solutions.


title: Energy Distribution of a Charged Regular Black Hole

abstract:
  We calculate the energy distribution of a charged regular black hole by using
the energy-momentum complexes of Einstein and M{\o}ller.


title:
On fine differentiability properties of horizons and applications to
  Riemannian geometry

abstract:
  We study fine differentiability properties of horizons. We show that the set
of end points of generators of a n-dimensional horizon H (which is included in
a (n+1)-dimensional space-time M) has vanishing n-dimensional Hausdorff
measure. This is proved by showing that the set of end points of generators at
which the horizon is differentiable has the same property. For 1\le k\le n+1 we
show (using deep results of Alberti) that the set of points where the convex
hull of the set of generators leaving the horizon has dimension k is ``almost a
C^2 manifold of dimension n+1-k'': it can be covered, up to a set of vanishing
(n+1-k)-dimensional Hausdorff measure, by a countable number of C^2 manifolds.
We use our Lorentzian geometry results to derive information about the fine
differentiability properties of the distance function and the structure of cut
loci in Riemannian geometry.


title: Gauge fixing and the Hamiltonian for cylindrical spacetimes

abstract:
  We introduce a complete gauge fixing for cylindrical spacetimes in vacuo
that, in principle, do not contain the axis of symmetry. By cylindrically
symmetric we understand spacetimes that possess two commuting spacelike Killing
vectors, one of them rotational and the other one translational. The result of
our gauge fixing is a constraint-free model whose phase space has four
field-like degrees of freedom and that depends on three constant parameters.
Two of these constants determine the global angular momentum and the linear
momentum in the axis direction, while the third parameter is related with the
behavior of the metric around the axis. We derive the explicit expression of
the metric in terms of the physical degrees of freedom, calculate the reduced
equations of motion and obtain the Hamiltonian that generates the reduced
dynamics. We also find upper and lower bounds for this reduced Hamiltonian that
provides the energy per unit length contained in the system. In addition, we
show that the reduced formalism constructed is well defined and consistent at
least when the linear momentum in the axis direction vanishes. Furthermore, in
that case we prove that there exists an infinite number of solutions in which
all physical fields are constant both in the surroundings of the axis and at
sufficiently large distances from it. If the global angular momentum is
different from zero, the isometry group of these solutions is generally not
orthogonally transitive. Such solutions generalize the metric of a spinning
cosmic string in the region where no closed timelike curves are present.


title:
Noether Charges for Self-interacting Quantum Field Theories in Curved
  Spacetimes with a Killing-vector

abstract:
  We consider self-interacting, perturbative quantum field theory in a curved
spacetime background with a Killing vector field. We show that the action of
this spacetime symmetry on interacting field operators can be implemented by a
Noether charge which arises as a surface integral over the time-component of
the interacting Noether current-density associated with the Killing field. The
proof of this involves the demonstration of a corresponding set of Ward
identities. Our work is based on the perturbative construction by Brunetti and
Fredenhagen (Commun.Math.Phys. 208 (2000) 623-661) of self-interacting quantum
field theories in general globally hyperbolic spacetimes.


title:
Quantization of the electromagnetic field outside static black holes and
  its application to low-energy phenomena

abstract:
  We discuss the Gupta-Bleuler quantization of the free electromagnetic field
outside static black holes in the Boulware vacuum. We use a gauge which reduces
to the Feynman gauge in Minkowski spacetime. We also discuss its relation with
gauges used previously. Then we apply the low-energy sector of this field
theory to investigate some low-energy phenomena. First, we discuss the response
rate of a static charge outside the Schwarzschild black hole in four
dimensions. Next, motivated by string physics, we compute the absorption cross
sections of low-energy plane waves for the Schwarzschild and extreme
Reissner-Nordstr\"om black holes in arbitrary dimensions higher than three.


title: Kruskal coordinates as canonical variables for Schwarzschild black holes

abstract:
  We derive a transformation from the usual ADM metric-extrinsic curvature
variables on the phase space of Schwarzschild black holes, to new canonical
variables which have the interpretation of Kruskal coordinates. We explicitly
show that this transformation is non-singular, even at the horizon. The
constraints of the theory simplify in terms of the new canonical variables and
are equivalent to the vanishing of the canonical momenta. Our work is based on
earlier seminal work by Kuchar in which he reconstructed curvature coordinates
and a mass function from spherically symmetric canonical data. The key feature
in our construction of a nonsingular canonical transformation to Kruskal
variables, is the scaling of the curvature coordinate variables by the mass
function rather than by the mass at left spatial infinity.


title:
Search for Periodic Gravitational Wave Sources with the Explorer
  Detector

abstract:
  We have developped a procedure for the search of periodic signals in the data
of gravitational wave detectors. We report here the analysis of one year of
data from the resonant detector Explorer, searching for pulsars located in the
Galactic Center (GC). No signals with amplitude greater than $\bar{h}=
2.9~10^{-24}$, in the range 921.32-921.38 Hz, were observed using data
collected over a time period of 95.7 days, for a source located at
$\alpha=17.70 \pm 0.01$ hours and $\delta=-29.00 \pm 0.05$ degrees. Our
procedure can be extended for any assumed position in the sky and for a more
general all-sky search, even with a frequency correction at the source due to
the spin-down and Doppler effects.


title: Scaling solutions from interacting fluids

abstract:
  We examine the dynamical implications of an interaction between some of the
fluid components of the universe. We consider the combination of three matter
components, one of which is a perfect fluid and the other two are interacting.
The interaction term generalizes the cases found in scalar field cosmologies
with an exponential potential. We find that attracting scaling solutions are
obtained in several regions of parameter space, that oscillating behaviour is
possible, and that new curvature scaling solutions exist. We also discuss the
inflationary behaviour of the solutions and present some of the constraints on
the strength of the coupling, namely those arising from nucleosynthesis.


title:
Fluctuations in the current and energy densities around a magnetic flux
  carrying cosmic string

abstract:
  We calculate the fluctuations in the current and energy densities for the
case of a quantized, minimally coupled, massless, complex scalar field around a
straight and infinitesimally thin cosmic string carrying magnetic flux. At zero
temperature, we evaluate the fluctuations in the current and energy densities
for arbitrary flux and deficit angle. At a finite temperature, we evaluate the
fluctuations in the energy density for the special case wherein the flux is
absent and the deficit angle equals $\pi$. We find that, quite generically, the
dimensionless ratio of the variance to the mean-squared values of the current
and energy densities are of order unity which suggests that the fluctuations
around cosmic strings can be considered to be large.


title: Super-Hubble Nonlinear Perturbations During Inflation

abstract:
  We show that the non-linear evolution of long wavelength perturbations may be
important in a wide class of inflationary scenarios. We develop a solution for
the evolution of such nonlinear perturbations which is exact to first order in
a gradient expansion. As a first application, we demonstrate that in single
field models of inflation there can be no parametric amplification of
super-Hubble modes during reheating. We consider the implications of the
solution for recent discussions of the back-reaction effect of long wavelength
perturbations on the background geometry, give a new derivation of the equation
of motion of stochastic inflation, and demonstrate that if the (generalized)
slow-rolling condition is not satisfied, then inevitably long wavelength vector
modes for gravitational fluctuations will be generated.


title:
(Quantum) Space-Time as a Statistical Geometry of Fuzzy Lumps and the
  Connection with Random Metric Spaces

abstract:
  We develop a kind of pregeometry consisting of a web of overlapping fuzzy
lumps which interact with each other. The individual lumps are understood as
certain closely entangled subgraphs (cliques) in a dynamically evolving network
which, in a certain approximation, can be visualized as a time-dependent random
graph. This strand of ideas is merged with another one, deriving from ideas,
developed some time ago by Menger et al, that is, the concept of probabilistic-
or random metric spaces, representing a natural extension of the metrical
continuum into a more microscopic regime. It is our general goal to find a
better adapted geometric environment for the description of microphysics. In
this sense one may it also view as a dynamical randomisation of the causal-set
framework developed by e.g. Sorkin et al. In doing this we incorporate, as a
perhaps new aspect, various concepts from fuzzy set theory.


title: Sum-Over-Histories Quantization of Relativistic Particle

abstract:
  Sum-over-histories quantization of particle-like theory in curved space is
discussed. It is reviewed that the propagator satisfies the Schrodinger
equation respective wave equation with a Laplace-like operator. The exact
dependence of the operator on the choice of measure is shown.
  Next, modifications needed for a manifold with a boundary are introduced, and
the exact form of the equation for the propagator is derived. It is shown that
the Laplace-like operator contains some distributional terms localized on the
boundary. These terms induce proper boundary conditions for the propagator.
This choice of boundary conditions is explained as a consequence of a
measurement of particles on the boundary.
  The interaction with sources inside of the domain and sources on the boundary
is also discussed.


title: Radion on the de Sitter brane

abstract:
  The radion on the de Sitter brane is investigated at the linear perturbation
level, using the covariant curvature tensor formalism developed by Shiromizu,
Maeda and Sasaki. It is found that if there is only one de Sitter brane with
positive tension, there is no radion and thus the ordinary Einstein gravity is
recoverd on the brane other than corrections due to the massive Kaluza-Klein
modes. As a by-product of using the covariant curvature tensor formalism, it is
immediately seen that the cosmological scalar, vector and tensor type
perturbations all have the same Kaluza-Klein spectrum. On the other hand, if
there are two branes with positive and negative tensions, the gravity on each
brane takes corrections from the radion mode in addition to the Kaluza-Klein
modes and the radion is found to have a negative mass-squared proportional to
the curvature of the de Sitter brane, in contrast to the flat brane case in
which the radion mass vanishes and degenerates with the 4-dimensional graviton
modes. To relate our result with the metric perturbation approach, we derive
the second order action for the brane displacement. We find that the radion
identified in our approach indeed corresponds to the relative displacement of
the branes in the Randall-Sundrum gauge and describes the scalar curvature
perturbations of the branes in the gaussian normal coordinates around the
branes. Implications to the inflationary brane universe are briefly discussed.


title: Teleparallel Gravity and the Gravitational Energy-Momentum Density

abstract:
  In the context of the teleparallel equivalent of general relativity, we show
that the energy-momentum density for the gravitational field can be described
by a true spacetime tensor. It is also invariant under local (gauge)
translations of the tangent space coordinates, but transforms covariantly only
under global Lorentz transformations. When the gauge gravitational field
equation is written in a purely spacetime form, it becomes the teleparallel
equivalent of Einstein's equation, and we recover M{\o}ller's expression for
the canonical gravitational energy-momentum pseudotensor.


title:
Asymptotic behaviour of cylindrical waves interacting with spinning
  strings

abstract:
  We consider a family of cylindrical spacetimes endowed with angular momentum
that are solutions to the vacuum Einstein equations outside the symmetry axis.
This family was recently obtained by performing a complete gauge fixing adapted
to cylindrical symmetry. In the present work, we find boundary conditions that
ensure that the metric arising from this gauge fixing is well defined and that
the resulting reduced system has a consistent Hamiltonian dynamics. These
boundary conditions must be imposed both on the symmetry axis and in the region
far from the axis at spacelike infinity. Employing such conditions, we
determine the asymptotic behaviour of the metric close to and far from the
axis. In each of these regions, the approximate metric describes a conical
geometry with a time dislocation. In particular, around the symmetry axis the
effect of the singularity consists in inducing a constant deficit angle and a
timelike helical structure. Based on these results and on the fact that the
degrees of freedom in our family of metrics coincide with those of cylindrical
vacuum gravity, we argue that the analysed set of spacetimes represent
cylindrical gravitational waves surrounding a spinning cosmic string. For any
of these spacetimes, a prediction of our analysis is that the wave content
increases the deficit angle at spatial infinity with respect to that detected
around the axis.


title: Hairy Black Holes, Horizon Mass and Solitons

abstract:
  Properties of the horizon mass of hairy black holes are discussed with
emphasis on certain subtle and initially unexpected features. A key property
suggests that hairy black holes may be regarded as `bound states' of ordinary
black holes without hair and colored solitons. This model is then used to
predict the qualitative behavior of the horizon properties of hairy black
holes, to provide a physical `explanation' of their instability and to put
qualitative constraints on the end point configurations that result from this
instability. The available numerical calculations support these predictions.
Furthermore, the physical arguments are robust and should be applicable also in
more complicated situations where detailed numerical work is yet to be carried
out.


title: A coherent approach to Spacetime Foam

abstract:
  A coherent superposition of N Schwarzschild wormholes is proposed as a model
for spacetime foam. Following the subtraction procedure for manifolds with
boundaries, we calculate by variational methods the Casimir energy. A proposal
for an alternative foamy model formed by N Schwarzschild-Anti-de Sitter
wormholes is here considered. Finally, a conjecture about the foam evolution is
proposed.


title:
Possible measurement of Quintessence and density parameter using strong
  gravitational lensing events

abstract:
  We propose a possible measurement of the time variability of the vacuum
energy using strong gravitational lensing events. As an example we take an
Einstein cross lens HST 14176+5226 and demonstrate that the measurement of the
velocity dispersion with the accuracy of $\pm$ 5 km/sec will have a chance to
determine the time dependence of the vacuum energy as well as the density
parameter with the accuracy of order 0.1 if one fixes the lens model.


title: Hair from the Isolated Horizon Perspective

abstract:
  The recently introduced Isolated Horizons (IH) formalism has become a
powerful tool for realistic black hole physics. In particular, it generalizes
the zeroth and first laws of black hole mechanics in terms of quasi-local
quantities and serves as a starting point for quantum entropy calculations. In
this note we consider theories which admit hair, and analyze some new results
that the IH provides, when considering solitons and stationary solutions.
Furthermore, the IH formalism allows to state uniqueness conjectures (i.e.
horizon `no-hair conjectures') for the existence of solutions.


title: Searching for continuous gravitational wave sources in binary systems

abstract:
  We consider the problem of searching for continuous gravitational wave
sources orbiting a companion object. This issue is of particular interest
because the LMXB's, and among them Sco X-1, might be marginally detectable with
2 years coherent observation time by the Earth-based laser interferometers
expected to come on line by 2002, and clearly observable by the second
generation of detectors. Moreover, several radio pulsars, which could be deemed
to be CW sources, are found to orbit a companion star or planet, and the
LIGO/VIRGO/GEO network plans to continuously monitor such systems. We estimate
the computational costs for a search launched over the additional five
parameters describing generic elliptical orbits using match filtering
techniques. These techniques provide the optimal signal-to-noise ratio and also
a very clear and transparent theoretical framework. We provide ready-to-use
analytical expressions for the number of templates required to carry out the
searches in the astrophysically relevant regions of the parameter space, and
how the computational cost scales with the ranges of the parameters. We also
determine the critical accuracy to which a particular parameter must be known,
so that no search is needed for it. In order to disentangle the computational
burden involved in the orbital motion of the CW source, from the other source
parameters (position in the sky and spin-down), and reduce the complexity of
the analysis, we assume that the source is monochromatic and its location in
the sky is exactly known. The orbital elements, on the other hand, are either
assumed to be completely unknown or only partly known. We apply our theoretical
analysis to Sco X-1 and the neutron stars with binary companions which are
listed in the radio pulsar catalogue.


title: Scalar-tensor $\sigma$-cosmologies

abstract:
  We show that the scalar-tensor $\sigma$-model action is conformally
equivalent to general relativity with a minimally coupled wavemap with a
particular target metric. Inflation on the source manifold is then shown to
occur in a natural way due both to the arbitrary curvature couplings and the
wavemap self-interactions.


title: Teleparallel Gravity: An Overview

abstract:
  The fundamentals of the teleparallel equivalent of general relativity are
presented, and its main properties described. In particular, the field
equations, the definition of an energy--momentum density for the gravitational
field, the teleparallel version of the equivalence principle, and the dynamical
role played by torsion as compared to the corresponding role played by
curvature in general relativity, are discussed in some details.


title:
Cosmological Models with Nonlinearity of Scalar Field Induced by
  Yang-Mills Field

abstract:
  The exact solutions of Einstein - Yang - Mills and interacting with SO (3) -
Yang-Mills field nonlinear scalar field equations in a class of spatially
homogeneous cosmological Friedmann models are obtained.


title: Quantum Gravity at the Turn of the Millennium

abstract:
  A very brief review is given of the current state of research in quantum
gravity. Over the past fifteen years, two approaches have emerged as the most
promising paths to a quantum theory of gravity: string theory and quantum
geometry. I will discuss the main achievements and open problems of each of
these approaches, and compare their strengths and weaknesses.


title:
Unboundable Spacetimes with Metric Singularities and Matching Metrics
  and Geodesics: A Black-White Hole and a Big Crunch-Bang

abstract:
  Singularity theorems of general relativity utilize the notion of causal
geodesic incompleteness as a criterion of the presence of a spacetime
singularity. The incompleteness of a causal curve implies the end and/or
beginning of the existence of a particle, which is an event. In the commonly
accepted approach, singularities are not incorporated into spacetime. Thus
spacetime turns out to be event-incomplete. With creation from nothing,
singularities are sources of lawlessness. A straightforward way around those
conceptual problems consists in including metric singularities in spacetime and
then matching metrics and causal geodesics at the singularities. To this end, a
spacetime manifold is assumed to be unboundable, so that singularities may only
be interior. The matching the geodesics is achieved through weakening
conditions for their smoothness. This approach is applied to a black-white hole
and a big crunch-bang.


title: Cosmological Consequences of Conformal General Relativity

abstract:
  We consider cosmological consequences of a conformal-invariant unified theory
which is dynamically equivalent to general relativity and is given in a space
with the geometry of similarity. We show that the conformal-invariant theory
offers new explanations for to such problems as the arrow of time, initial
cosmic data, dark matter and accelerating evolution of the universe in the dust
stage.


title:
Black holes with toroidal, cylindrical and planar horizons in anti-de
  Sitter spacetimes in general relativity and their properties

abstract:
  We review the toroidal, cylindrical and planar black hole solutions in
anti-de Sitter spacetimes and present their properties.


title: Radial oscillations of relativistic stars

abstract:
  We present a new survey of the radial oscillation modes of neutron stars.
This study complements and corrects earlier studies of radial oscillations. We
present an extensive list of frequencies for the most common equations of state
and some more recent ones. In order to check the accuracy, we use two different
numerical schemes which yield the same results. The stimulation for this work
comes from the need of the groups that evolve the full nonlinear Einstein
equation to have reliable results from perturbation theory for comparison.