title: Electromagnetic waves around dilatonic stars and naked singularities

abstract:
  We study the propagation of classical electromagnetic waves on the simplest
four-dimensional spherically symmetric metric with a dilaton background field.
Solutions to the relevant equations are obtained perturbatively in a parameter
which measures the strength of the dilaton field (hence parameterizes the
departure from Schwarzschild geometry). The loss of energy from outgoing modes
is estimated as a back-scattering process against the dilaton background, which
would affect the luminosity of stars with a dilaton field. The radiation
emitted by a freely falling point-like source on such a background is also
studied by analytical and numerical methods.


title:
Formation of cosmological mass condensation within a FRW universe: exact
  general relativistic solutions

abstract:
  Within the framework of an exact general relativistic formulation of gluing
manifolds, we consider the problem of matching an inhomogeneous overdense
region to a Friedmann-Robertson-Walker background universe in the general
spherical symmetric case of pressure-free models. It is shown that, in general,
the matching is only possible through a thin shell, a fact ignored in the
literature. In addition to this, in subhorizon cases where the matching is
possible, an intermediate underdense region will necessarily arise.


title: Linearized Perturbations of a Black Hole: Continuum Spectrum

abstract:
  Linearized perturbations of a Schwarzschild black hole are described, for
each angular momentum $\ell$, by the well-studied discrete quasinormal modes
(QNMs), and in addition a continuum. The latter is characterized by a cut
strength $q(\gamma>0)$ for frequencies $\omega = -i\gamma$. We show that: (a)
$q(\gamma\downarrow0) \propto \gamma$, (b) $q(\Gamma) = 0$ at $\Gamma =
(\ell+2)!/[6(\ell-2)!]$, and (c) $q(\gamma)$ oscillates with period $\sim 1$
($2M\equiv1$). For $\ell=2$, a pair of QNMs are found beyond the cut on the
unphysical sheet very close to $\Gamma$, leading to a large dipole in the
Green's function_near_ $\Gamma$. For a source near the horizon and a distant
observer, the continuum contribution relative to that of the QNMs is small.


title: Spacetime Foam Model of the Schwarzschild Horizon

abstract:
  We consider a spacetime foam model of the Schwarzschild horizon, where the
horizon consists of Planck size black holes. According to our model the entropy
of the Schwarzschild black hole is proportional to the area of its event
horizon. It is possible to express geometrical arguments to the effect that the
constant of proportionality is, in natural units, equal to one quarter.


title: Regular inflationary cosmology and gauge theories of gravitation

abstract:
  Cosmological equations for homogeneous isotropic models filled by scalar
fields and ultrarelativistic matter are investigated in the framework of gauge
theories of gravity. Regular inflationary cosmological models of flat, closed
and open type with dominating ultrarelativistic matter at a bounce are
discussed. It is shown that essential part of inflationary cosmological models
has bouncing character.


title:
Quasi-equilibrium binary black hole sequences for puncture data derived
  from helical Killing vector conditions

abstract:
  We construct a sequence of binary black hole puncture data derived under the
assumptions (i) that the ADM mass of each puncture as measured in the
asymptotically flat space at the puncture stays constant along the sequence,
and (ii) that the orbits along the sequence are quasi-circular in the sense
that several necessary conditions for the existence of a helical Killing vector
are satisfied. These conditions are equality of ADM and Komar mass at infinity
and equality of the ADM and a rescaled Komar mass at each puncture. In this
paper we explicitly give results for the case of an equal mass black hole
binary without spin, but our approach can also be applied in the general case.
We find that up to numerical accuracy the apparent horizon mass also remains
constant along the sequence and that the prediction for the innermost stable
circular orbit is similar to what has been found with the effective potential
method.


title: Spatial and null infinity via advanced and retarded conformal factors

abstract:
  A new approach to space-time asymptotics is presented, refining Penrose's
idea of conformal transformations with infinity represented by the conformal
boundary of space-time. Generalizing examples such as flat and Schwarzschild
space-times, it is proposed that the Penrose conformal factor be a product of
advanced and retarded conformal factors, which asymptotically relate physical
and conformal null (light-like) coordinates and vanish at future and past null
infinity respectively, with both vanishing at spatial infinity. A
correspondingly refined definition of asymptotic flatness at both spatial and
null infinity is given, including that the conformal boundary is locally a
light cone, with spatial infinity as the vertex. It is shown how to choose the
conformal factors so that this asymptotic light cone is locally a metric light
cone. The theory is implemented in the spin-coefficient (or null-tetrad)
formalism by a simple joint transformation of the spin-metric and spin-basis
(or metric and tetrad). The advanced and retarded conformal factors may be used
as expansion parameters near the respective null infinity, together with a
dependent expansion parameter for both spatial and null infinity, essentially
inverse radius. Asymptotic regularity conditions on the spin-coefficients are
proposed, based on the conformal boundary locally being a smoothly embedded
metric light cone. These conditions ensure that the Bondi-Sachs energy-flux
integrals of ingoing and outgoing gravitational radiation decay at spatial
infinity such that the total radiated energy is finite, and that the
Bondi-Sachs energy-momentum has a unique limit at spatial infinity, coinciding
with the uniquely rendered ADM energy-momentum.


title: Non-Abelian gravitating solitons with negative cosmological constant

abstract:
  Static, spherically symmetric solutions with regular origin are investigated
of the Einstein-Yang-Mills theory with a negative cosmological constant
$\Lambda$. A combination of numerical and analytical methods leads to a clear
picture of the `moduli space' of the solutions. Some issues discussed in the
existing literature on the subject are reconsidered and clarified. In
particular the stability of the asymptotically AdS solutions is studied. Like
for the Bartnik-McKinnon (BK) solutions obtained for $\Lambda=0$ there are two
different types of instabilities -- `topological' and `gravitational'. Regions
with any number of these instabilities are identified in the moduli space.
While for BK solutions there is always a non-vanishing equal number of
instabilities of both types, this degeneracy is lifted and there exist stable
solutions, genuine sphalerons with exactly one unstable mode and so on. The
boundaries of these regions are determined.


title:
On the gravitational field (A suggestion about a possible experimental
  research)

abstract:
  After a preliminary discussion of the relevance of the field nature of
gravitation interaction, both for the fundamental interaction of particles and
the topology of space time, a method is proposed to produce and detect a
dynamical gravitational field, allowing the determination of the order of
magnitude of its propagation velocity.


title: Self-phase modulation of spherical gravitational waves

abstract:
  Self-phase modulation of spherical gravitational wavepackets propagating in a
flat space-time in the presence of a tenuous distribution of matter is
considered. Analogies with respect to similar effects in nonlinear optics are
explored. Self phase modulation of waves emitted from a single source can
eventually lead to an efficient energy dilution of the gravitational wave
energy over an increasingly large spectral range. An explicit criterium for the
occurrence of a significant spectral energy dilution is established.


title: Stochastic Gravity: Theory and Applications

abstract:
  Whereas semiclassical gravity is based on the semiclassical Einstein equation
with sources given by the expectation value of the stress-energy tensor of
quantum fields, stochastic semiclassical gravity is based on the
Einstein-Langevin equation, which has in addition sources due to the noise
kernel.In the first part, we describe the fundamentals of this new theory via
two approaches: the axiomatic and the functional. In the second part, we
describe three applications of stochastic gravity theory. First, we consider
metric perturbations in a Minkowski spacetime: we compute the two-point
correlation functions for the linearized Einstein tensor and for the metric
perturbations. Second, we discuss structure formation from the stochastic
gravity viewpoint. Third, we discuss the backreaction of Hawking radiation in
the gravitational background of a quasi-static black hole.


title: World Nematic Crystal Model of Gravity Explaining the Absence of Torsion

abstract:
  We attribute the gravitational interaction between sources of curvature to
the world being a crystal which has undergone a quantum phase transition to a
nematic phase by a condensation of dislocations.
  The model explains why spacetime has no observable torsion and predicts the
existence of curvature sources in the form of world sheets, albeit with
different high-energy properties than those of string models.


title: Traversable Wormholes Construction in 2+1 Dimensions

abstract:
  We study traversable Lorentzian wormholes in the three-dimensional low energy
string theory by adding some matter source involving a dilaton field. It will
be shown that there are two-different types of wormhole solutions such as BTZ
and black string wormholes depending on the dilaton backgrounds, respectively.
We finally obtain the desirable solutions which confine exotic matter near the
throat of wormhole by adjusting NS charge.


title: Nonradial oscillations of quark stars

abstract:
  Recently, it has been reported that a candidate for a quark star may have
been observed. In this article, we pay attention to quark stars with radiation
radii in the reported range. We calculate nonradial oscillations of $f$-, $w$-
and $w_{\rm II}$-modes. Then, we find that the dependence of the $f$-mode
quasi-normal frequency on the bag constant and stellar radiation radius is very
strong and different from that of the lowest $w_{\rm II}$-mode quasi-normal
frequency. Furthermore we deduce a new empirical formula between the $f$-mode
frequency of gravitational waves and the parameter of the equation of state for
quark stars. The observation of gravitational waves both of the $f$-mode and of
the lowest $w_{\rm II}$-mode would provide a powerful probe for the equation of
state of quark matter and the properties of quark stars.


title:
Maximal Slicing for Puncture Evolutions of Schwarzschild and
  Reissner-Nordstr\"om Black Holes

abstract:
  We prove by explicit construction that there exists a maximal slicing of the
Schwarzschild spacetime such that the lapse has zero gradient at the puncture.
This boundary condition has been observed to hold in numerical evolutions, but
in the past it was not clear whether the numerically obtained maximal slices
exist analytically. We show that our analytical result agrees with numerical
simulation. Given the analytical form for the lapse, we can derive that at late
times the value of the lapse at the event horizon approaches the value
${3/16}\sqrt{3} \approx 0.3248$, justifying the numerical estimate of 0.3 that
has been used for black hole excision in numerical simulations. We present our
results for the non-extremal Reissner-Nordstr\"om metric, generalizing previous
constructions of maximal slices.


title: Cosmic Dynamics of Bose-Einstein Condensates

abstract:
  A dynamical correspondence is established between positively curved,
isotropic, perfect fluid cosmologies and quasi-two-dimensional, harmonically
trapped Bose-Einstein condensates by mapping the equations of motion for both
systems onto the one-dimensional Ermakov system. Parameters that characterize
the physical properties of the condensate wavepacket, such as its width,
momentum and energy, may be identified with the scale factor, Hubble expansion
parameter and energy density of the universe, respectively. Different forms of
cosmic matter correspond to different choices for the time-dependent trapping
frequency of the condensate. The trapping frequency that mimics a
radiation-dominated universe is determined.


title: Bulk Viscous cosmological models in Lyra geometry

abstract:
  We have investigated an LRS Bianchi Type I models with bulk viscosity in the
cosmological theory based on Lyra's geometry. A new class of exact solutions
have been obtained by considering a time-dependent displacement field for a
constant value of the deceleration parameter and viscosity coefficient of bulk
viscous fluid is assumed to be a power function of mass density. The physical
behaviour of the models is also discussed.


title:
Some Homogeneous Bianchi Type IX Viscous Fluid Cosmological Models with
  a varying $\Lambda$

abstract:
  Some Bianchi type IX viscous fluid cosmological models are investigated. To
get a solution a supplementary condition between metric potentials is used. The
viscosity coefficient of bulk viscous fluid is assumed to be a power function
of mass density whereas the coefficient of shear viscosity is considered as
proportional to scale of expansion in the model. The cosmological constant
$\Lambda$ is found to be positive and is a decreasing function of time which is
supported by results from recent supernova observations. Some physical and
geometric properties of the models are also discussed.


title: Particle detectors, geodesic motion, and the equivalence principle

abstract:
  It is shown that quantum particle detectors are not reliable probes of
spacetime structure. In particular, they fail to distinguish between inertial
and non-inertial motion in a general spacetime. To prove this, we consider
detectors undergoing circular motion in an arbitrary static spherically
symmetric spacetime, and give a necessary and sufficient condition for the
response function to vanish when the field is in the static vacuum state. By
examining two particular cases, we show that there is no relation, in general,
between the vanishing of the response function and the fact that the detector
motion is, or is not, geodesic. In static asymptotically flat spacetimes,
however, all rotating detectors are excited in the static vacuum. Thus, in this
particular case the static vacuum appears to be associated with a non-rotating
frame. The implications of these results for the equivalence principle are
considered. In particular, we discuss how to properly formulate the principle
for particle detectors, and show that it is satisfied.


title: Einstein spaces in warped geometries in five dimensions

abstract:
  We investigate five dimensional Einstein spaces in warped geometries from the
point of view of the four dimensional physically relevant
Robertson-Walker-Friedman cosmological metric and the Schwarzschild metric. We
show that a four-dimensional cosmology with a closed spacelike section and a
cosmological constant can be imbedded into five-dimensional flat space-time.


title:
The Pioneer anomalous acceleration: can we measure the cosmological
  constant at the scale of the solar system ?

abstract:
  An anomalous constant acceleration of (8.7 \pm 1.3) x 10^-8 cm/s^2 directed
toward the Sun has been discovered by Anderson et al. in the motion of the
Pioneer 10/11 and Galileo spacecrafts. In parallel, the WMAP results have
definitively established the existence of a cosmological constant Lambda=1/
L_U^2, and therefore of an invariant cosmic length-scale L_U=(2.72 \pm 0.10)
Gpc. We show that the existence of this invariant scale definitively implements
Mach's principle in Einstein's theory of general relativity. Then we
demonstrate, in the framework of an exact cosmological solution of Einstein's
field equations which is valid both locally and globally, that the definition
of inertial systems ultimately depends on this length-scale. As a consequence,
usual local coordinates are not inertial, so that the motion of a free body of
speed v is expected to contain an additional constant acceleration
a_P=v^2(\surd3 L_U), which is, using the WMAP five years results, (6.02 \pm
0.34) x 10^-8 cm/s^2 when v \approx c. Such an effect is too small to
contribute significantly to the Pioneer acceleration (since v_Pioneer \approx
12 km/s << c), but could be possibly observed in a dedicated space mission.


title: The Effects of Stress Tensor Fluctuations upon Focusing

abstract:
  We treat the gravitational effects of quantum stress tensor fluctuations. An
operational approach is adopted in which these fluctuations produce
fluctuations in the focusing of a bundle of geodesics. This can be calculated
explicitly using the Raychaudhuri equation as a Langevin equation. The physical
manifestation of these fluctuations are angular blurring and luminosity
fluctuations of the images of distant sources. We give explicit results for the
case of a scalar field on a flat background in a thermal state.


title:
Chaos in a closed Friedmann-Robertson-Walker universe: An imaginary
  approach

abstract:
  In this work we study the existence of mechanisms of transition to global
chaos in a closed Friedmann-Robertson-Walker universe with a massive
conformally coupled scalar field. We propose a complexification of the radius
of the universe so that the global dynamics can be understood. We show
numerically the existence of heteroclinic connections of the unstable and
stable manifolds to periodic orbits associated to the saddle-center equilibrium
points. We find two bifurcations which are crucial in creating non-collapsing
universes both in the real and imaginary version of the models. The techniques
presented here can be employed in any cosmological model.


title:
Tilted Bianchi Type V Bulk Viscous Cosmological Models in General
  Relativity

abstract:
  Conformally flat tilted Bianchi type V cosmological models in presence of a
bulk viscous fluid and heat flow are investigated. The coefficient of bulk
viscosity is assumed to be a power function of mass density. Some physical and
geometric aspects of the models are also discussed.


title:
Constant mean curvature slices in the extended Schwarzschild solution
  and collapse of the lapse: Part I

abstract:
  We give a detailed description of the constant mean curvature foliations in
the Schwarzschild solution; show that the lapse collapses exponentially, and
compute the exponent.


title:
Constant mean curvature slices in the extended Schwarzschild solution
  and collapse of the lapse. Part II

abstract:
  An explicit CMC Schwarzschildean line element is derived near the critical
point of the foliation, the lapse is shown to decay exponentially, and the
coefficient of the exponent is calculated.


title: On the Quasi-Isotropic Inflationary Solution

abstract:
  In this paper we find a solution for a quasi-isotropic inflationary Universe
which allows to introduce in the problem a certain degree of inhomogeneity. We
consider a model which generalize the (flat) FRW one by introducing a first
order inhomogeneous term, whose dynamics is induced by an effective
cosmological constant. The 3-metric tensor is constituted by a dominant term,
corresponding to an isotropic-like component, while the amplitude of the first
order one is controlled by a ``small'' function $\eta(t)$.
  In a Universe filled with ultrarelativistic matter and a real
self-interacting scalar field, we discuss the resulting dynamics, up to first
order in $\eta$, when the scalar field performs a slow roll on a plateau of a
symmetry breaking configuration and induces an effective cosmological constant.
  We show how the spatial distribution of the ultrarelativistic matter and of
the scalar field admits an arbitrary form but nevertheless, due to the required
inflationary e-folding, it cannot play a serious dynamical role in tracing the
process of structures formation (via the Harrison--Zeldovic spectrum). As a
consequence, this paper reinforces the idea that the inflationary scenario is
incompatible with a classical origin of the large scale structures.


title: Equatorial circular orbits in the Kerr-de Sitter spacetimes

abstract:
  Equatorial motion of test particles in the Kerr-de Sitter spacetimes is
considered. Circular orbits are determined, their properties are discussed for
both the black-hole and naked-singularity spacetimes, and their relevance for
thin accretion discs is established.


title: Embedding spherical spacelike slices in a Schwarzschild solution

abstract:
  Given a spherical spacelike three-geometry, there exists a very simple
algebraic condition which tells us whether, and in which, Schwarzschild
solution this geometry can be smoothly embedded. One can use this result to
show that any given Schwarzschild solution covers a significant subset of
spherical superspace and these subsets form a sequence of nested domains as the
Schwarzschild mass increases. This also demonstrates that spherical data offer
an immediate counter example to the thick sandwich `theorem'.


title: Radiation from Bodies with Extreme Acceleration II: Kinematics

abstract:
  When applied to a dipole source subjected to acceleration which is violent
and long lasting (``extreme acceleration''), Maxwell's equations predict
radiative power which augments Larmor's classical radiation formula by a
nontrivial amount. The physical assumptions behind this result are made
possible by the kinematics of a system of geometrical clocks whose tickings are
controlled by cavities which are expanding inertially. For the purpose of
measuring the radiation from such a source we take advantage of the physical
validity of a spacetime coordinate framework (``inertially expanding frame'')
based on such clocks. They are compatible and commensurable with the
accelerated clocks of the accelerated source. By contrast, a common Lorentz
frame with its mutually static clocks won't do: it lacks that commensurability.
Inertially expanding clocks give a physicist a window into the frame of a
source with extreme acceleration. He thus can locate that source and measure
radiation from it without being subjected to such acceleration himself. The
conclusion is that inertially expanding reference frames reveal qualitatively
distinct aspects of nature which would not be accessible if static inertial
frames were the only admissible frames.


title: On the Newtonian Limit in Gravity Models with Inverse Powers of R

abstract:
  I reconsider the problem of the Newtonian limit in nonlinear gravity models
in the light of recently proposed models with inverse powers of the Ricci
scalar.
  Expansion around a maximally symmetric local background with positive
curvature scalar R_0 gives the correct Newtonian limit on length scales <<
R_0^{-1/2} if the gravitational Lagrangian f(R) satisfies |f(R_0)f''(R_0)|<< 1.
I propose two models with f''(R_0)=0.


title:
Formation of Schwarzschild black hole from the scalar field collapse in
  four-dimensions

abstract:
  We obtain a new self-similar solution to the Einstein's equations in
four-dimensions, representing the collapse of a spherically symmetric,
minimally coupled, massless, scalar field. Depending on the value of certain
parameters, this solution represents the formation of naked singularities and
black holes. Since the black holes are identified as the Schwarzschild ones,
one may naturally see how these black holes are produced as remnants of the
scalar field collapse.


title: (2+1)-dimensional quantum gravity, spin networks and asymptotics

abstract:
  A method to evaluate spin networks for (2+1)-dimensional quantum gravity is
given. We analyse the evaluation of spin networks for Lorentzian, Euclidean and
a new limiting case of Newtonian quantum gravity. Particular attention is paid
to the tetrahedron and to the study of its asymptotics. Moreover, we propose
that all this technique can be extended to spin networks for quantum gravity in
any dimension.


title: Extended Lifetime in Computational Evolution of Isolated Black Holes

abstract:
  Solving the 4-d Einstein equations as evolution in time requires solving
equations of two types: the four elliptic initial data (constraint) equations,
followed by the six second order evolution equations. Analytically the
constraint equations remain solved under the action of the evolution, and one
approach is to simply monitor them ({\it unconstrained} evolution).
  The problem of the 3-d computational simulation of even a single isolated
vacuum black hole has proven to be remarkably difficult. Recently, we have
become aware of two publications that describe very long term evolution, at
least for single isolated black holes. An essential feature in each of these
results is {\it constraint subtraction}. Additionally, each of these approaches
is based on what we call "modern," hyperbolic formulations of the Einstein
equations. It is generally assumed, based on computational experience, that the
use of such modern formulations is essential for long-term black hole
stability. We report here on comparable lifetime results based on the much
simpler ("traditional") $\dot g$ - $\dot K$ formulation.
  We have also carried out a series of {\it constrained} 3-d evolutions of
single isolated black holes. We find that constraint solution can produce
substantially stabilized long-term single hole evolutions. However, we have
found that for large domains, neither constraint-subtracted nor constrained
$\dot g$ - $\dot K$ evolutions carried out in Cartesian coordinates admit
arbitrarily long-lived simulations. The failure appears to arise from features
at the inner excision boundary; the behavior does generally improve with
resolution.


title: Embedding Diagrams for the Reissner-Nordstr\"om spacetime

abstract:
  We consider embedding diagrams for the Reissner-Nordstr\"om spacetime. We
embed the $(r-t)$ and $(r-\phi)$ planes into 3-Minkowski/Euclidean space and
discuss the relation between the diagrams and the corresponding curvature
scalar of the 2-metrics


title:
Density Matrix Deformations in Quantum and Statistical Mechanics at
  Planck-Scale

abstract:
  In this work the Quantum and Statistical Mechanics of the Early Universe,
i.e. at Planck scale, is considered as a deformation of the well-known
theories. In so doing the primary object under deformation in both cases is the
density matrix. It is demonstrated that in construction of the deformed quantum
mechanical and statistical density matrices referred to as density pro-matrices
there is a complete analog. The principal difference lies in a nature of the
deformation parameter that is associated with the fundamental length in the
first case and with a maximum temperature in the second case. Consideration is
also given to some direct consequences, specifically the use of the explicitly
specified exponential ansatz in the derivation from the basic principles of a
semiclassical Bekenstein-Hawking formula for the black hole entropy and of the
high-temperature complement to the canonical Gibbs distribution.


title:
Bianchi Type I Magnetofluid Cosmological Models with Variable
  Cosmological Constant Revisited

abstract:
  The behaviour of magnetic field in anisotropic Bianchi type I cosmological
model for bulk viscous distribution is investigated. The distribution consists
of an electrically neutral viscous fluid with an infinite electrical
conductivity. It is assumed that the component $\sigma^{1}_{1}$ of shear tensor
$\sigma^{j}_{i}$ is proportional to expansion ($\theta$) and the coefficient of
bulk viscosity is assumed to be a power function of mass density. Some physical
and geometrical aspects of the models are also discussed in presence and also
in absence of the magnetic field.


title: Covariant Fluid Dynamics: a Long Wave-Length Approximation

abstract:
  In this paper we consider the Long-Wavelength Approximation Scheme (LWAS) in
the framework of the covariant fluid approach to general relativistic dynamics,
specializing to the particular case of irrotational dust matter. We discuss the
dynamics of these models during the approach to any spacelike singularity where
a BKL-type evolution is expected, studying the validity of this approximation
scheme and the role of the magnetic part of the Weyl tensor, $H_{ab}$. Our
analytic results confirm a previous numerical analysis: it is $H_{ab}$ that
destroys the pure Kasner-like approach to the singularity and eventually
produces the bounce to another Kasner phase. Expanding regions evolve as
separate universes where inhomogeneities and anisotropies die away.


title: Asymptotic quasinormal mode spectrum of rotating black holes

abstract:
  Motivated by novel results in the theory of black-hole quantization, we study
{\it analytically} the quasinormal modes (QNM) of ({\it rotating}) Kerr black
holes. The black-hole oscillation frequencies tend to the asymptotic value
$\omega_n=m\Omega+i2\pi T_{BH}n$ in the $n \to \infty$ limit. This simple
formula is in agreement with Bohr's correspondence principle. Possible
implications of this result to the area spectrum of quantum black holes are
discussed.


title: Killing Reduction of 5-Dimensional Spacetimes

abstract:
  In a 5-dimensional spacetime ($M,g_{ab}$) with a Killing vector field $\xi
^a$ which is either everywhere timelike or everywhere spacelike, the collection
of all trajectories of $\xi ^a$ gives a 4-dimensional space $S$. The reduction
of ($M,g_{ab}$) is studied in the geometric language, which is a generalization
of Geroch's method for the reduction of 4-dimensional spacetime. A
4-dimensional gravity coupled to a vector field and a scalar field on $S$ is
obtained by the reduction of vacuum Einstein's equations on $M$, which gives
also an alternative description of the 5-dimensional Kaluza-Klein theory.
Besides the symmetry-reduced action from the Hilbert action on $M$, an
alternative action of the fields on $S$ is also obtained, the variations of
which lead to the same fields equations as those reduced from the vacuum
Einstein equation on $M$.


title: Global aspects of gravitomagnetism

abstract:
  We consider global properties of gravitomagnetism by investigating the
gravitomagnetic field of a rotating cosmic string. We show that although the
gravitomagnetic field produced by such a configuration of matter vanishes
locally, it can be detected globally. In this context we discuss the
gravitational analogue of the Aharonov-Bohm effect.


title:
Maxwell's field coupled nonminimally to quadratic torsion: Induced axion
  field and birefringence of the vacuum

abstract:
  We consider a possible (parity conserving) interaction between the
electromagnetic field $F$ and a torsion field $T^\alpha$ of spacetime. For
generic elementary torsion, gauge invariant coupling terms of lowest order fall
into two classes that are both nonminimal and {\it quadratic} in torsion. These
two classes are displayed explicitly. The first class of the type $\sim F T^2$
yields (undesirable) modifications of the Maxwell equations. The second class
of the type $\sim F^2 T^2$ doesn't touch the Maxwell equations but rather
modifies the constitutive tensor of spacetime. Such a modification can be
completely described in the framework of metricfree electrodynamics. We
recognize three physical effects generated by the torsion: (i) An axion field
that induces an {\em optical activity} into spacetime, (ii) a modification of
the light cone structure that yields {\em birefringence} of the vacuum, and
(iii) a torsion dependence of the {\em velocity of light.} We study these
effects in the background of a Friedmann universe with torsion. {\it File
tor17.tex, 02 August 2003}


title: Gravitational collapse of a Hagedorn fluid in Vaidya geometry

abstract:
  The gravitational collapse of a high-density null charged matter fluid,
satisfying the Hagedorn equation of state, is considered in the framework of
the Vaidya geometry. The general solution of the gravitational field equations
can be obtained in an exact parametric form. The conditions for the formation
of a naked singularity, as a result of the collapse of the compact object, are
also investigated. For an appropriate choice of the arbitrary integration
functions the null radial outgoing geodesic, originating from the shell
focussing central singularity, admits one or more positive roots. Hence a
collapsing Hagedorn fluid could end either as a black hole, or as a naked
singularity. A possible astrophysical application of the model, to describe the
energy source of gamma-ray bursts, is also considered.


title:
Global solutions for the relativistic Boltzmann equation in the
  homogeneous case on the Minkowski space-time

abstract:
  We prove, for the relativistic Boltzmann equation in the homogeneous case, on
the Minkowski space-time, a global in time existence and uniqueness theorem.
The method we develop extends to the cases of some curved space-times such as
the flat Robertson-Walker space-time and some Bianchi type I space-times.


title: Lorentz Violations and Euclidean Signature Metrics

abstract:
  We show that the families of effective actions considered by Jacobson et al.
to study Lorentz invariance violations contain a class of models that represent
pure General Relativity with Euclidean signature. We also point out that some
members of this family of actions preserve Lorentz invariance in a generalized
sense.


title:
A symmetry-breaking mechanism for the Z4 general-covariant evolution
  system

abstract:
  The general-covariant Z4 formalism is further analyzed. The gauge conditions
are generalized with a view to Numerical Relativity applications and the
conditions for obtaining strongly hyperbolic evolution systems are given both
at the first and the second order levels. A symmetry-breaking mechanism is
proposed that allows one, when applied in a partial way, to recover previously
proposed strongly hyperbolic formalisms, like the BSSN and the Bona-Mass\'o
ones. When applied in its full form, the symmetry breaking mechanism allows one
to recover the full five-parameter family of first order KST systems. Numerical
codes based in the proposed formalisms are tested. A robust stability test is
provided by evolving random noise data around Minkowski space-time. A strong
field test is provided by the collapse of a periodic background of plane
gravitational waves, as described by the Gowdy metric.


title: Reheating After Quintessential Inflation and Gravitational Waves

abstract:
  We investigate the dependence of the gravitational wave spectrum from
quintessential inflation on the reheating process. We consider two extreme
reheating processes. One is the gravitational reheating by particle creation in
the expanding universe in which the beginning of the radiation dominated epoch
is delayed due to the presence of the epoch of domination of the kinetic energy
of the inflaton (kination). The other is the instant preheating considered by
Felder et al. in which the Universe becomes radiation dominated soon after the
end of inflation. We find that the spectrum of the gravitational waves at $\sim
100$ MHz is quite sensitive to the reheating process. This result is not
limited to quintessential inflation but applicable to various inflation models.
Conversely, the detection or non-detection of primordial gravitational waves at
$\sim$100 MHz would provide useful information regarding the reheating process
in inflation.


title: Cosmological Issues for Revised Canonical Quantum Gravity

abstract:
  In a recent work we presented a reformulation of the canonical quantum
gravity, based on adding the so-called kinematical term to the gravity-matter
action; this revised approach leads to a self-consistent canonical quantization
of the 3-geometries, referred to the external time as provided via the added
term.
  Here, we show how the kinematical term can be interpreted in terms of a non
relativistic dust fluid which plies the role of a ``real clock' for the quantum
gravity theory, and, in the WKB limit of a cosmological problem, makes account
for a dark matter component which, at present time, could play a dynamical
role.


title: Probing entropy bounds with scalar field spacetimes

abstract:
  We study covariant entropy bounds in dynamical spacetimes with naked
singularities. Specifically we study a spherically symmetric massless scalar
field solution. The solution is an inhomogeneous cosmology with an initial
spacelike singularity, and a naked timelike singularity at the origin. We
construct the entropy flux 4-vector for the scalar field, and show by explicit
computation that the generalized covariant bound $S_{L(B,B')}\le (A(B)-A(B'))/4
$ is violated for light sheets $L(B,B')$ in the neighbourhood of the (evolving)
apparent horizon. We find no violations of the Bousso bound (for which
$A(B')=0$), even though certain sufficient conditions for this bound do not
hold. This result therefore shows that these conditions are not necessary.


title:
Critical Collapse of Cylindrically Symmetric Scalar Field in
  Four-Dimensional Einstein's Theory of Gravity

abstract:
  Four-dimensional cylindrically symmetric spacetimes with homothetic
self-similarity are studied in the context of Einstein's Theory of Gravity, and
a class of exact solutions to the Einstein-massless scalar field equations is
found. Their local and global properties are investigated and found that they
represent gravitational collapse of a massless scalar field. In some cases the
collapse forms black holes with cylindrical symmetry, while in the other cases
it does not. The linear perturbations of these solutions are also studied and
given in closed form. From the spectra of the unstable eigen-modes, it is found
that there exists one solution that has precisely one unstable mode, which may
represent a critical solution, sitting on a boundary that separates two
different basins of attraction in the phase space.


title:
On the exact gravitational lens equation in spherically symmetric and
  static spacetimes

abstract:
  Lensing in a spherically symmetric and static spacetime is considered, based
on the lightlike geodesic equation without approximations. After fixing two
radius values r_O and r_S, lensing for an observation event somewhere at r_O
and static light sources distributed at r_S is coded in a lens equation that is
explicitly given in terms of integrals over the metric coefficients. The lens
equation relates two angle variables and can be easily plotted if the metric
coefficients have been specified; this allows to visualize in a convenient way
all relevant lensing properties, giving image positions, apparent brightnesses,
image distortions, etc. Two examples are treated: Lensing by a
Barriola-Vilenkin monopole and lensing by an Ellis wormhole.


title: Energy in Topologically Massive Gravity

abstract:
  We define conserved gravitational charges in -cosmologically extended-
topologically massive gravity, exhibit them in surface integral form about
their de-Sitter or flat vacua and verify their correctness in terms of two
basic types of solution.


title: Perturbations of global monopoles as a black hole's hair

abstract:
  We study the stability of a spherically symmetric black hole with a global
monopole hair. Asymptotically the spacetime is flat but has a deficit solid
angle which depends on the vacuum expectation value of the scalar field. When
the vacuum expectation value is larger than a certain critical value, this
spacetime has a cosmological event horizon. We investigate the stability of
these solutions against the spherical and polar perturbations and confirm that
the global monopole hair is stable in both cases. Although we consider some
particular modes in the polar case, our analysis suggests the conservation of
the "topological charge" in the presence of the event horizons and violation of
black hole no-hair conjecture in asymptotically non-flat spacetime.


title: Gravitating Fermionic Lumps with a False Vacuum Core

abstract:
  We investigate gravitating lumps with a false vacuum core surrounded by the
true vacuum in a scalar field potential. Such configurations become possible in
the Einstein gravity in the presence of fermions at the core. Gravitational
interactions as well as Yukawa interactions are essential for such lumps to
exist. The mass and size of gravitating lumps sensitively depend on the scale
characterizing the scalar field potential and the density of fermions. These
objects can exist in the universe at various scales.


title:
Collision of High Frequency Plane Gravitational and Electromagnetic
  Waves

abstract:
  We study the head-on collision of linearly polarized, high frequency plane
gravitational waves and their electromagnetic counterparts in the
Einstein-Maxwell theory. The post-collision space-times are obtained by solving
the vacuum Einstein-Maxwell field equations in the geometrical optics
approximation. The head-on collisions of all possible pairs of these systems of
waves is described and the results are then generalised to non-linearly
polarized waves which exhibit the maximum two degrees of freedom of
polarization.


title:
The Gravitational Polarization in General Relativity: Solution to
  Szekeres' Model of Quadrupole Polarization

abstract:
  A model for the static weak-field macroscopic medium is analyzed and the
equation for the macroscopic gravitational potential is derived. This is a
biharmonic equation which is a non-trivial generalization of the Poisson
equation of Newtonian gravity. In case of the strong gravitational quadrupole
polarization it essentially holds inside a macroscopic matter source. Outside
the source the gravitational potential fades away exponentially. The equation
is equivalent to a system of the Poisson equation and the nonhomogeneous
modified Helmholtz equations. The general solution to this system is obtained
by using Green's function method and it does not have a limit to Newtonian
gravity. In case of the insignificant gravitational quadrupole polarization the
equation for macroscopic gravitational potential becomes the Poisson equation
with the matter density renormalized by the factor including the value of the
quadrupole gravitational polarization of the source. The general solution to
this equation obtained by using Green's function method has a limit to
Newtonian gravity.


title: 3D gravity with torsion as a Chern-Simons gauge theory

abstract:
  We show that topological 3D gravity with torsion can be formulated as a
Chern-Simons gauge theory, provided a specific parameter, known as the
effective cosmological constant, is negative. In that case, the boundary
dynamics of the theory corresponding to anti-de Sitter boundary conditions is
described by a conformal field theory with two different central charges.


title: Electron in the Einstein-Weyl space

abstract:
  The classical unified theory of Weyl is revisited. The possibility of stable
extended electron model in the Einstein-Weyl space is suggested.


title: Data Combinations Accounting for LISA Spacecraft Motion

abstract:
  LISA is an array of three spacecraft in an approximately equilateral triangle
configuration which will be used as a low-frequency gravitational wave
detector. We present here new generalizations of the Michelson- and Sagnac-type
time-delay interferometry data combinations. These combinations cancel laser
phase noise in the presence of different up and down propagation delays in each
arm of the array, and slowly varying systematic motion of the spacecraft. The
gravitational wave sensitivities of these generalized combinations are the same
as previously computed for the stationary cases, although the combinations are
now more complicated. We introduce a diagrammatic representation to illustrate
that these combinations are actually synthesized equal-arm interferometers.


title:
The naked singularity in the global structure of critical collapse
  spacetimes

abstract:
  We examine the global structure of scalar field critical collapse spacetimes
using a characteristic double-null code. It can integrate past the horizon
without any coordinate problems, due to the careful choice of constraint
equations used in the evolution. The limiting sequence of sub- and
supercritical spacetimes presents an apparent paradox in the expected Penrose
diagrams, which we address in this paper. We argue that the limiting spacetime
converges pointwise to a unique limit for all r>0, but not uniformly. The r=0
line is different in the two limits. We interpret that the two different
Penrose diagrams differ by a discontinuous gauge transformation. We conclude
that the limiting spacetime possesses a singular event, with a future removable
naked singularity.


title:
A constrained scheme for Einstein equations based on Dirac gauge and
  spherical coordinates

abstract:
  We propose a new formulation for 3+1 numerical relativity, based on a
constrained scheme and a generalization of Dirac gauge to spherical
coordinates. This is made possible thanks to the introduction of a flat
3-metric on the spatial hypersurfaces t=const, which corresponds to the
asymptotic structure of the physical 3-metric induced by the spacetime metric.
Thanks to the joint use of Dirac gauge, maximal slicing and spherical
components of tensor fields, the ten Einstein equations are reduced to a system
of five quasi-linear elliptic equations (including the Hamiltonian and momentum
constraints) coupled to two quasi-linear scalar wave equations. The remaining
three degrees of freedom are fixed by the Dirac gauge. Indeed this gauge allows
a direct computation of the spherical components of the conformal metric from
the two scalar potentials which obey the wave equations. We present some
numerical evolution of 3-D gravitational wave spacetimes which demonstrates the
stability of the proposed scheme.


title: Consistency Conditions for Fundamentally Discrete Theories

abstract:
  The dynamics of physical theories is usually described by differential
equations. Difference equations then appear mainly as an approximation which
can be used for a numerical analysis. As such, they have to fulfill certain
conditions to ensure that the numerical solutions can reliably be used as
approximations to solutions of the differential equation. There are, however,
also systems where a difference equation is deemed to be fundamental, mainly in
the context of quantum gravity. Since difference equations in general are
harder to solve analytically than differential equations, it can be helpful to
introduce an approximating differential equation as a continuum approximation.
In this paper implications of this change in view point are analyzed to derive
the conditions that the difference equation should satisfy. The difference
equation in such a situation cannot be chosen freely but must be derived from a
fundamental theory. Thus, the conditions for a discrete formulation can be
translated into conditions for acceptable quantizations. In the main example,
loop quantum cosmology, we show that the conditions are restrictive and serve
as a selection criterion among possible quantization choices.


title:
Radon transform of Wheeler-De Witt equation and tomography of quantum
  states of the universe

abstract:
  The notion of standard positive probability distribution function (tomogram)
which describes the quantum state of universe alternatively to wave function or
to density matrix is introduced. Connection of the tomographic probability
distribution with the Wigner function of the universe and with the star-product
(deformation) quantization procedure is established.
  Using the Radon transform the Wheeler-De Witt generic equation for the
probability function is written in tomographic form. Some examples of the
Wheeler-DeWitt equation in the minisuperspace are elaborated explicitly for a
homogeneous isotropic cosmological models. Some interpretational aspects of the
probability description of the quantum state are discussed.


title: Gravitational Wave Detection with Michelson Interferometers

abstract:
  Electromagnetic methods recently proposed for detecting gravitational waves
modify the Michelson phase shift analysis (historically employed for special
relativity). We suggest that a frequency modulation analysis is more suited to
general relativity. An incident photon in the presence of a very long
wavelength gravitational wave will have a finite probability of being returned
as a final photon with a frequency shift whose magnitude is equal to the
gravitational wave frequency. The effect is due to the non-linear coupling
between electromagnetic and gravitational waves. The frequency modulation is
derived directly from the Maxwell-Einstein equations.


title: Big smash of the universe

abstract:
  The occurrence of a big smash singularity which ends the universe in a finite
time in the future is investigated in the context of superquintessence, i.e.
dark energy with effective equation of state parameter w<-1. The simplest model
of superquintessence based on a single nonminimally coupled scalar field
exhibits big smash solutions which are attractors in phase space.


title: The first law for slowly evolving horizons

abstract:
  We study the mechanics of Hayward's trapping horizons, taking isolated
horizons as equilibrium states. Zeroth and second laws of dynamic horizon
mechanics come from the isolated and trapping horizon formalisms respectively.
We derive a dynamical first law by introducing a new perturbative formulation
for dynamic horizons in which "slowly evolving" trapping horizons may be viewed
as perturbatively non-isolated.


title: Cauchy horizons in Gowdy space times

abstract:
  We analyse exhaustively the structure of \emph{non-degenerate} Cauchy
horizons in Gowdy space-times, and we establish existence of a large class of
non-polarized Gowdy space-times with such horizons.
  Added in proof: Our results here, together with deep new results of H.
Ringstr\"om (talk at the Miami Waves conference, January 2004), establish
strong cosmic censorship in (toroidal) Gowdy space-times.


title: The spectrum of quantum black holes and quasinormal modes

abstract:
  The spectrum of multiple level transitions of the quantum black hole is
considered, and the line widths calculated. Initial evidence is found for these
higher order transitions in the spectrum of quasinormal modes for Schwarzschild
and Kerr black holes, further bolstering the idea that there exists a
correspondence principle between quantum transitions and classical ``ringing
modes''. Several puzzles are noted, including a fine-tuning problem between the
line width and the level degeneracy. A more general explanation is provided for
why setting the Immirzi parameter of loop quantum gravity from the black hole
spectrum necessarily gives the correct value for the black hole entropy.


title: Loops versus strings

abstract:
  Two popular attempts to understand the quantum physics of gravitation are
critically assessed. The talk on which this paper is based was intended for a
general particle-physics audience.


title: Scale-invariant gravity: Spacetime recovered

abstract:
  The configuration space of general relativity is superspace - the space of
all Riemannian 3-metrics modulo diffeomorphisms. However, it has been argued
that the configuration space for gravity should be conformal superspace - the
space of all Riemannian 3-metrics modulo diffeomorphisms and conformal
transformations. Recently a manifestly 3-dimensional theory was constructed
with conformal superspace as the configuration space. Here a fully
4-dimensional action is constructed so as to be invariant under conformal
transformations of the 4-metric using general relativity as a guide. This
action is then decomposed to a (3+1)-dimensional form and from this to its
Jacobi form. The surprising thing is that the new theory turns out to be
precisely the original 3-dimensional theory. The physical data is identified
and used to find the physical representation of the theory. In this
representation the theory is extremely similar to general relativity. The
clarity of the 4-dimensional picture should prove very useful for comparing the
theory with those aspects of general relativity which are usually treated in
the 4-dimensional framework.


title: Generality of Topological Inflation

abstract:
  Many authors claimed that a large initial inhomogeneity prevents the onset of
inflation and therefore inflation takes place only if the scalar field is
homogeneous or appropriately chosen over the horizon scale. We show that those
arguments do not apply to topological inflation. The core of a defect starts
inflation even if it has much smaller size than the horizon and much larger
gradient energy than the potential, as long as the vacuum expectation value is
large enough ($\gtrsim0.3\mpl$) and the core is not contracting initially. This
is due to stability of false vacuum.


title: A fine quantum mechanism of classical gravity

abstract:
  It is shown that screening the background of super-strong interacting
gravitons ensures the Newtonian attraction, if a part of single gravitons is
pairing and graviton pairs are destructed by collisions with a body. If the
considered quantum mechanism of classical gravity is realized in the nature,
than an existence of black holes contradicts to the equivalence principle. In
such the model, Newton's constant is proportional to $H^{2}/T^{4},$ where $H$
is the Hubble constant, $T$ is an equivalent temperature of the graviton
background. The estimate of the Hubble constant is obtained for the Newtonian
limit: $H=3.026 \cdot 10^{-18} s^{-1}$ (or $94.576 km \cdot s^{-1} \cdot
Mpc^{-1}$).


title: Isotropisation of flat homogeneous universes with scalar fields

abstract:
  Starting from an anisotropic flat cosmological model(Bianchi type $I$), we
show that conditions leading to isotropisation fall into 3 classes,
respectively 1, 2, 3. We look for necessary conditions such that a Bianchi type
$I$ model reaches a stable isotropic state due to the presence of several
massive scalar fields minimally coupled to the metric with a perfect fluid for
class 1 isotropisation. The conditions are written in terms of some functions
$\ell$ of the scalar fields. Two types of theories are studied. The first one
deals with scalar tensor theories resulting from extra-dimensions
compactification, where the Brans-Dicke coupling functions only depend on their
associated scalar fields. The second one is related to the presence of complex
scalar fields. We give the metric and potential asymptotical behaviours
originating from class 1 isotropisation. The results depend on the domination
of the scalar field potential compared to the perfect fluid energy density. We
give explicit examples showing that some hybrid inflation theories do not lead
to isotropy contrary to some high-order theories, whereas the most common forms
of complex scalar fields undergo a class 3 isotropisation, characterised by
strong oscillations of the $\ell$ functions.


title: Stationary Einstein-Maxwell fields in arbitrary dimensions

abstract:
  The Einstein-Maxwell equations in D-dimensions admitting (D-3) commuting
Killing vector fields have been investigated. The existence of the electric,
magnetic and twist potentials have been proved. The system is formulated as the
harmonic map coupled to gravity on three-dimensional base space generalizing
the Ernst system in the four-dimensional stationary Einstein-Maxwell theory.
Some classes of the new exact solutions have been provided, which include the
electro-magnetic generalization of the Myers-Perry solution, which describes
the rotating black hole immersed in a magnetic universe, and the static charged
black ring solution.


title: Deformed density matrix, Density of entropy and Information problem

abstract:
  Quantum Mechanics at Planck scale is considered as a deformation of the
conventional Quantum Mechanics. Similar to the earlier works of the author, the
main object of deformation is the density matrix. On this basis a notion of the
entropy density is introduced that is a matrix value used for a detail study of
the Information Problem at the Universe, and in particular, for the Information
Paradox Problem.


title:
Quasinormal Modes in three-dimensional time-dependent Anti-de Sitter
  spacetime

abstract:
  The massless scalar wave propagation in the time-dependent BTZ black hole
background has been studied. It is shown that in the quasi-normal ringing both
the decay and oscillation time-scales are modified in the time-dependent
background.


title: Quantum Weak Energy Inequalities for the Dirac field in Flat Spacetime

abstract:
  Quantum Weak Energy Inequalities (QWEIs) have been established for a variety
of quantum field theories in both flat and curved spacetimes. Dirac fields are
known (by a result of Fewster and Verch) to satisfy QWEIs under very general
circumstances. However this result does not provide an explicit formula for the
QWEI bound, so its magnitude has not previously been determined. In this paper
we present a new and explicit QWEI bound for Dirac fields of arbitrary mass in
four-dimensional Minkowski space. We follow the methods employed by Fewster and
Eveson for the scalar field, modified to take account of anticommutation
relations. A key ingredient is an identity for Fourier transforms established
by Fewster and Verch. We also compare our QWEI with those previously obtained
for scalar and spin-1 fields.


title: Gravitational hedgehog, stringy hedgehog and stringy sphere

abstract:
  We investigate the solutions of Einstein equations such that a hedgehog
solution is matched to different exterior or interior solutions via a spherical
shell. In the case where both the exterior and the interior regions are
hedgehog solutions or one of them is flat, the resulting spherical shell
becomes a stringy shell. We also consider more general matchings and see that
in this case the shell deviates from its stringy character.


title:
Coincidence and coherent data analysis methods for gravitational wave
  bursts in a network of interferometric detectors

abstract:
  Network data analysis methods are the only way to properly separate real
gravitational wave (GW) transient events from detector noise. They can be
divided into two generic classes: the coincidence method and the coherent
analysis. The former uses lists of selected events provided by each
interferometer belonging to the network and tries to correlate them in time to
identify a physical signal. Instead of this binary treatment of detector
outputs (signal present or absent), the latter method involves first the
merging of the interferometer data and looks for a common pattern, consistent
with an assumed GW waveform and a given source location in the sky. The
thresholds are only applied later, to validate or not the hypothesis made. As
coherent algorithms use a more complete information than coincidence methods,
they are expected to provide better detection performances, but at a higher
computational cost. An efficient filter must yield a good compromise between a
low false alarm rate (hence triggering on data at a manageable rate) and a high
detection efficiency. Therefore, the comparison of the two approaches is
achieved using so-called Receiving Operating Characteristics (ROC), giving the
relationship between the false alarm rate and the detection efficiency for a
given method. This paper investigates this question via Monte-Carlo
simulations, using the network model developed in a previous article.


title:
Detection of a close supernova gravitational wave burst in a network of
  interferometers, neutrino and optical detectors

abstract:
  Trying to detect the gravitational wave (GW) signal emitted by a type II
supernova is a main challenge for the GW community. Indeed, the corresponding
waveform is not accurately modeled as the supernova physics is very complex; in
addition, all the existing numerical simulations agree on the weakness of the
GW emission, thus restraining the number of sources potentially detectable.
Consequently, triggering the GW signal with a confidence level high enough to
conclude directly to a detection is very difficult, even with the use of a
network of interferometric detectors. On the other hand, one can hope to take
benefit from the neutrino and optical emissions associated to the supernova
explosion, in order to discover and study GW radiation in an event already
detected independently. This article aims at presenting some realistic
scenarios for the search of the supernova GW bursts, based on the present
knowledge of the emitted signals and on the results of network data analysis
simulations. Both the direct search and the confirmation of the supernova event
are considered. In addition, some physical studies following the discovery of a
supernova GW emission are also mentioned: from the absolute neutrino mass to
the supernova physics or the black hole signature, the potential spectrum of
discoveries is wide.


title: Generic Cosmic Censorship Violation in anti de Sitter Space

abstract:
  We consider (four dimensional) gravity coupled to a scalar field with
potential V(\phi). The potential satisfies the positive energy theorem for
solutions that asymptotically tend to a negative local minimum. We show that
for a large class of such potentials, there is an open set of smooth initial
data that evolve to naked singularities. Hence cosmic censorship does not hold
for certain reasonable matter theories in asymptotically anti de Sitter
spacetimes. The asymptotically flat case is more subtle. We suspect that
potentials with a local Minkowski minimum may similarly lead to violations of
cosmic censorship in asymptotically flat spacetimes, but we do not have
definite results.


title:
Exact Solutions with Noncommutative Symmetries in Einstein and Gauge
  Gravity

abstract:
  We present new classes of exact solutions with noncommutative symmetries
constructed in vacuum Einstein gravity (in general, with nonzero cosmological
constant), five dimensional (5D) gravity and (anti) de Sitter gauge gravity.
Such solutions are generated by anholonomic frame transforms and parametrized
by generic off-diagonal metrics. For certain particular cases, the new classes
of metrics have explicit limits with Killing symmetries but, in general, they
may be characterized by certain anholonomic noncommutative matrix geometries.
We argue that different classes of noncommutative symmetries can be induced by
exact solutions of the field equations in 'commutative' gravity modeled by a
corresponding moving real and complex frame geometry. We analyze two classes of
black ellipsoid solutions (in the vacuum case and with cosmological constant)
in 4D gravity and construct the analytic extensions of metrics for certain
classes of associated frames with complex valued coefficients. The third class
of solutions describes 5D wormholes which can be extended to complex metrics in
complex gravity models defined by noncommutative geometric structures. The
anholonomic noncommutative symmetries of such objects are analyzed. We also
present a descriptive account how the Einstein gravity can be related to gauge
models of gravity and their noncommutative extensions and discuss such
constructions in relation to the Seiberg-Witten map for the gauge gravity.
Finally, we consider a formalism of vielbeins deformations subjected to
noncommutative symmetries in order to generate solutions for noncommutative
gravity models with Moyal (star) product.


title:
Electromagnetic radiation from collisions at almost the speed of light:
  an extremely relativistic charged particle falling into a Schwarzschild black
  hole

abstract:
  We investigate the electromagnetic radiation released during the high energy
collision of a charged point particle with a four-dimensional Schwarzschild
black hole. We show that the spectra is flat, and well described by a classical
calculation. We also compare the total electromagnetic and gravitational
energies emitted, and find that the former is supressed in relation to the
latter for very high energies. These results could apply to the astrophysical
world in the case charged stars and small charged black holes are out there
colliding into large black holes, and to a very high energy collision
experiment in a four-dimensional world. In this latter scenario the calculation
is to be used for the moments just after the black hole formation, when the
collision of charged debris with the newly formed black hole is certainly
expected. Since the calculation is four-dimensional, it does not directly apply
to Tev-scale gravity black holes, as these inhabit a world of six to eleven
dimensions, although our results should qualitatively hold when extrapolated
with some care to higher dimensions.


title:
Optimization of parameters of a couple generator-receiver for a
  gravitational Hertz experiment

abstract:
  Brief review of principal ideas, estimates and schemes proposed by Russian
research groups in respect of the gravitational radiation generated and
detected in the laboratory condition is presented. Analysis leads to conclusion
that the more promising variant of the laboratory GW-Hertz experiment might be
associated with power electromagnetic and acoustical impulsive or shock waves
travelling and interacting in nonlinear optic-acoustical medium


title: Graviton Production by a Thermal Bath

abstract:
  Thermal fluctuations in the early universe plasma and in very hot
astrophysical objects are an unavoidable source of gravitational waves (GW).
Differently from previous studies on the subject, we approach this problem
using methods based on field theory at finite temperature. Such an approach
allows to probe the infrared region of the spectrum where dissipative effects
are dominant. Incidentally, this region is the most interesting from the point
of view of the detectability perspectives. We find significant deviations from
a Planck spectrum.


title:
Loop variables and gravitational Berry's quantum phase in the space-time
  of a rotating massive body

abstract:
  In this paper we compute the holonomies along curves in the gravitational
field of a slowly rotating massive body. We use our results to study the
gravitational analogue of Aharanov-Bohm effect in this space-time. We also
investigate the behaviour of a scalar quantum particle in this space-time and
determine Berry's quantum phase acquired by this particle when transported
along a closed curve surrounding the body.


title: Radiation from accelerated black holes in an anti-de Sitter universe

abstract:
  We study gravitational and electromagnetic radiation generated by uniformly
accelerated charged black holes in anti-de Sitter spacetime. This is described
by the C-metric exact solution of the Einstein-Maxwell equations with a
negative cosmological constant Lambda. We explicitly find and interpret the
pattern of radiation that characterizes the dependence of the fields on a null
direction from which the (timelike) conformal infinity is approached. This
directional pattern exhibits specific properties which are more complicated if
compared with recent analogous results obtained for asymptotic behavior of
fields near a de Sitter-like infinity. In particular, for large acceleration
the anti-de Sitter-like infinity is divided by Killing horizons into several
distinct domains with a different structure of principal null directions, in
which the patterns of radiation differ.


title: The Trautman-Bondi mass of initial data sets

abstract:
  We give a definition of mass for conformally compactifiable initial data
sets. The asymptotic conditions are compatible with existence of gravitational
radiation, and the compactifications are allowed to be polyhomogeneous. We show
that the resulting mass is a geometric invariant, and we prove positivity
thereof in the case of a spherical conformal infinity. When R(g) - or,
equivalently, the trace of the extrinsic curvature tensor - tends to a negative
constant to order one at infinity, the definition is expressed purely in terms
of three-dimensional or two-dimensional objects.


title: A wormhole-generated physical universe with refined approximation

abstract:
  We improved the approximation of the model of the wormhole generated physical
universe constructed by Choudhury and Pendharkar. We show here that the
negative pressure of the unphysical wormhole can generate the right physical
condition to explain the correct sign of the deacceleration parameter $q_0$.
The negative sign ofsign of $q_0$ implies an accelerating universe.


title: Constructing Phantom Cosmologies from Standard Scalar Field Universes

abstract:
  We illustrate how form-invariance transformations can be used for
constructing phantom cosmologies from standard scalar field universes. First,
we discuss how to relate two flat Friedmann-Robertson-Walker cosmologies with
different barotropic indexes $\gamma$ and $\bar \gamma$. Then, we consider the
particular case $\bar \gamma=-\gamma$, and we show that if the matter content
is interpreted in terms of self-interacting scalar fields, then the
corresponding transformation provides the link between a standard and a phantom
cosmology. After that, we illustrate the method by considering models with
exponential potentials. Finally, we also show that the mentioned duality
persists even if the typical braneworld modifications to the Friedmann equation
are considered.


title: The Emergent Universe: An Explicit Construction

abstract:
  We provide a realisation of a singularity-free inflationary universe in the
form of a simple cosmological model dominated at early times by a single
minimally coupled scalar field with a physically based potential. The universe
starts asymptotically from an initial Einstein static state, which may be large
enough to avoid the quantum gravity regime. It enters an expanding phase that
leads to inflation followed by reheating and a standard hot Big Bang evolution.
We discuss the basic characteristics of this Emergent model and show that none
is at odds with current observations.


title:
Cosmic String Cusps with Small-Scale Structure: Their Forms and
  Gravitational Waveforms

abstract:
  We present a method for the introduction of small-scale structure into
strings constructed from products of rotation matrices. We use this method to
illustrate a range of possibilities for the shape of cusps that depends on the
properties of the small-scale structure. We further argue that the presence of
structure at cusps under most circumstances leads to the formation of loops at
the size of the smallest scales. On the other hand we show that the
gravitational waveform of a cusp remains generally unchanged; the primary
effect of small-scale structure is to smooth out the sharp waveform emitted in
the direction of cusp motion.


title: Decaying Lambda cosmology with varying G

abstract:
  We study a uniform and isotropic cosmology with a decaying vacuum energy
density, in the realm of a model with a time varying gravitational "constant".
We show that, for late times, such a cosmology is in accordance with the
observed values of the cosmological parameters. In particular, we can obtain
the observed ratio between the matter density and the total energy density,
with no necessity of any fine tuning.


title: Axially Symmetric Black Hole Skyrmions

abstract:
  It has been known that a B=2 skyrmion is axially symmetric. We consider the
Skyrme model coupled to gravity and obtain static axially symmetric black hole
solutions numerically. The black hole skyrmion no longer has integer baryonic
charge but has fractional charge outside the horizon as in the spherically
symmetric case. Therefore, the solution represents a black hole partially
swallowing a deuteron. Recent studies of theories with large extra dimensions
suggest an effective Planck scale of order a TeV and thus the deuteron black
hole may be produced in the Linear Hadron Collider (LHC) in future.


title:
Symmetries of the Energy-Momentum Tensor of Spherically Symmetric
  Lorentzian Manifolds

abstract:
  Matter collineations of spherically Symmetric Lorentzian Manifolds are
considered. These are investigated when the energy-momentum tensor is
non-degenerate and also when it is degenerate. We have classified spacetimes
admitting higher symmetries and spacetimes admitting SO(3) as the maximal
isometry group. For the non-degenerate case, we obtain either {\it four}, {\it
six}, {\it seven} or {\it ten} independent matter collineations in which {\it
four} are isometries and the rest are proper. The results of the previous paper
[1] are recovered as a special case. It is worth noting that we have also
obtained two cases where the energy-momentum tensor is degenerate but the group
of matter collineations is finite-dimensional, i.e. {\it four} or {\it ten}.


title:
Solutions of the Einstein Constraint Equations with Apparent Horizon
  Boundaries

abstract:
  We construct asymptotically Euclidean solutions of the vacuum Einstein
constraint equations with an apparent horizon boundary condition. Specifically,
we give sufficient conditions for the constant mean curvature conformal method
to generate such solutions. The method of proof is based on the barrier method
used by Isenberg for compact manifolds without boundary, suitably extended to
accommodate semilinear boundary conditions and low regularity metrics. As a
consequence of our results for manifolds with boundary, we also obtain
improvements to the theory of the constraint equations on asymptotically
Euclidean manifolds without boundary.


title: Minkowski vacuum in background independent quantum gravity

abstract:
  We consider a local formalism in quantum field theory, in which no reference
is made to infinitely extended spacial surfaces, infinite past or infinite
future. This can be obtained in terms of a functional W[f,S] of the field f on
a closed 3d surface S that bounds a finite region R of Minkowski spacetime. The
dependence of W on S is governed by a local covariant generalization of the
Schroedinger equation. Particles' scattering amplitudes that describe
experiments conducted in the finite region R --the lab during a finite time--
can be expressed in terms of W. The dependence of W on the geometry of S
expresses the dependence of the transition amplitudes on the relative location
of the particle detectors. In a gravitational theory, background independence
implies that W is independent from S. However, the detectors' relative location
is still coded in the argument of W, because the geometry of the boundary
surface is determined by the boundary value f of the gravitational field. This
observation clarifies the physical meaning of the functional W defined by non
perturbative formulations of quantum gravity, such as the spinfoam formalism.
In particular, it suggests a way to derive particles' scattering amplitudes
from a spinfoam model. In particular, we discuss the notion of vacuum in a
generally covariant context. We distinguish the nonperturbative vacuum |0_S>,
which codes the dynamics, from the Minkowski vacuum |0_M>, which is the state
with no particles and is recovered by taking appropriate large values of the
boundary metric. We derive a relation between the two vacuum states. We propose
an explicit expression for computing the Minkowski vacuum from a spinfoam
model.


title:
New perspectives in testing the general relativistic Lense--Thirring
  effect

abstract:
  Testing the effects predicted by the General Theory of Relativity, in its
linearized weak field and slow motion approximation, in the Solar System is
difficult because they are very small. Among them the post-Newtonian
gravitomagnetic Lense-Thirring effect, or dragging of the inertial frames, on
the orbital motion of a test particle is very interesting and, up to now, there
is not yet an undisputable experimental direct test of it. Here we illustrate
how it could be possible to measure it with an accuracy of the order of 1%,
together with other tests of Special Relativity and post-Newtonian gravity,
with a joint space based OPTIS/LARES mission in the gravitational field of
Earth. Up to now, the data analysis of the orbits of the existing geodetic
LAGEOS and LAGEOS II satellites has yielded a test of the Lense-Thirring effect
with a claimed accuracy of 20%-30%.


title:
Increasing the bandwidth of resonant gravitational antennas: The case of
  Explorer

abstract:
  Resonant gravitational wave detectors with an observation bandwidth of tens
of hertz are a reality: the antenna Explorer, operated at CERN by the ROG
collaboration, has been upgraded with a new read-out. In this new
configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz
about its frequency of operation of 919 Hz the spectral sensitivity is better
than 10^{-20} /sqrt(Hz) . We describe the detector and its sensitivity and
discuss the foreseable upgrades to even larger bandwidths.


title:
Vacuum spacetimes with a spacelike, hypersurface-orthogonal Killing
  vector: reduced equations in a canonical frame

abstract:
  The Newman-Penrose equations for spacetimes having one spacelike Killing
vector are reduced -- in a geometrically defined "canonical frame'' -- to a
minimal set, and its differential structure is studied. Expressions for the
frame vectors in an arbitrary coordinate basis are given, and
coordinate-independent choices of the metric functions are suggested which make
the components of the Ricci tensor in the direction of the Killing vector
vanish.


title:
Effects of electrical charging on the mechanical Q of a fused silica
  disk

abstract:
  We report on the effects of an electrical charge on mechanical loss of a
fused silica disk. A degradation of Q was seen that correlated with charge on
the surface of the sample. We examine a number of models for charge damping,
including eddy current damping and loss due to polarization. We conclude that
rubbing friction between the sample and a piece of dust attracted by the
charged sample is the most likely explanation for the observed loss.


title: Self-gravitating stringlike configurations from nonlinear electodynamics

abstract:
  We consider static, cylindrically symmetric configurations in general
relativity coupled to nonlinear electrodynamics (NED) with an arbitrary
gauge-invariant Lagrangian of the form $L_{em}= \Phi(F)$, $F =F_{mn}F^{mn}$. We
study electric and magnetic fields with three possible orientations: radial
(R), longitudinal (L) and azimuthal (A), and try to find solitonic stringlike
solutions, having a regular axis and a flat metric at large $r$, with a
possible angular defect. Assuming the function $\Phi(F)$ to be regular at small
$F$, it is shown that a regular axis is impossible in R-fields if there is a
nonzero effective electric charge and in A-fields if there is a nonzero
effective electric current along the axis. Solitonic solutions are only
possible for purely magnetic R-fields and purely electric A-fields, in cases
when $\Phi(F)$ tends to a finite limit at large $F$. For both R- and A-fields,
the desired large $r$ asymptotic is only possible with a non- Maxwell behaviour
of $\Phi(F)$ at small $F$. For L-fields, solutions with a regular axis are
easily obtained (and can be found by quadratures) whereas a desired large $r$
asymptotic is only possible in an exceptional solution; the latter gives rise
to solitonic configurations in case $\Phi(F) = \const \cdot \sqrt{F}$. We give
an explicit example of such a solution.


title:
Orbital evolution of a particle around a black hole: II. Comparison of
  contributions of spin-orbit coupling and the self force

abstract:
  We consider the evolution of the orbit of a spinning compact object in a
quasi-circular, planar orbit around a Schwarzschild black hole in the extreme
mass ratio limit. We compare the contributions to the orbital evolution of both
spin-orbit coupling and the local self force. Making assumptions on the
behavior of the forces, we suggest that the decay of the orbit is dominated by
radiation reaction, and that the conservative effect is typically dominated by
the spin force. We propose that a reasonable approximation for the
gravitational waveform can be obtained by ignoring the local self force, for
adjusted values of the parameters of the system. We argue that this
approximation will only introduce small errors in the astronomical
determination of these parameters.


title: Gravitational and electromagnetic fields near a de Sitter-like infinity

abstract:
  We present a characterization of general gravitational and electromagnetic
fields near de Sitter-like conformal infinity which supplements the standard
peeling behavior. This is based on an explicit evaluation of the dependence of
the radiative component of the fields on the null direction from which infinity
is approached. It is shown that the directional pattern of radiation has a
universal character that is determined by the algebraic (Petrov) type of the
spacetime. Specifically, the radiation field vanishes along directions opposite
to principal null directions.


title: The topology of Schwarzschild's solution and the Kruskal metric

abstract:
  Kruskal's extension solves the problem of the arrow of time of the
``Schwarzschild solution'' through combining two Hilbert manifolds by a
singular coordinate transformation. We discuss the implications for the
singularity problem and the definition of the mass point.
  The analogy set by Rindler between the Kruskal metric and the Minkowski
spacetime is investigated anew. The question is answered, whether this analogy
is limited to a similarity of the chosen "Bildr\"aume'', or can be given a
deeper, intrinsic meaning. The conclusion is reached by observing a usually
neglected difference: the left and right quadrants of Kruskal's metric are
endowed with worldlines of absolute rest, uniquely defined through each event
by the manifold itself, while such worldlines obviously do not exist in the
Minkowski spacetime.


title: Singular Hypersurfaces in Einstein--Gauss--Bonnet Theory of Gravitation

abstract:
  We present a general formalism for describing singular hypersurfaces in the
Einstein theory of gravitation with a Gauss--Bonnet term. The junction
conditions are given in a form which is valid for the most general embedding
and matter content and for coordinates chosen independently on each side of the
hypersurface. The theory is applied to both a time--like and a light--like
hypersurface in brane--cosmology.


title: Summation by parts and dissipation for domains with excised regions

abstract:
  We discuss finite difference techniques for hyperbolic equations in
non-trivial domains, as those that arise when simulating black hole spacetimes.
In particular, we construct dissipative and difference operators that satisfy
the {\it summation by parts} property in domains with excised multiple cubic
regions. This property can be used to derive semi-discrete energy estimates for
the associated initial-boundary value problem which in turn can be used to
prove numerical stability.


title:
Spherical excision for moving black holes and summation by parts for
  axisymmetric systems

abstract:
  It is expected that the realization of a convergent and long-term stable
numerical code for the simulation of a black hole inspiral collision will
depend greatly upon the construction of stable algorithms capable of handling
smooth and, most likely, time dependent boundaries. After deriving single grid,
energy conserving discretizations for axisymmetric systems containing the axis
of symmetry, we present a new excision method for moving black holes using
multiple overlapping coordinate patches, such that each boundary is fixed with
respect to at least one coordinate system. This multiple coordinate structure
eliminates all need for extrapolation, a commonly used procedure for moving
boundaries in numerical relativity.
  We demonstrate this excision method by evolving a massless Klein-Gordon
scalar field around a boosted Schwarzschild black hole in axisymmetry. The
excision boundary is defined by a spherical coordinate system co-moving with
the black hole. Our numerical experiments indicate that arbitrarily high boost
velocities can be used without observing any sign of instability.


title: Trapped surfaces as boundaries for the constraint equations

abstract:
  Trapped surfaces are studied as inner boundary for the Einstein vacuum
constraint equations. The trapped surface condition can be written as a non
linear boundary condition for these equations. Under appropriate assumptions,
we prove existence and uniqueness of solutions in the exterior region for this
boundary value problem. We also discuss the relevance of this result for the
study of black holes collisions.


title:
Improved Test of General Relativity with Radio Doppler Data from the
  Cassini Spacecraft

abstract:
  This paper was withdrawn at the recommendation of the Cassini Radio Science
Team.


title: Discrete Hamiltonian evolution and quantum gravity

abstract:
  We study constrained Hamiltonian systems by utilizing general forms of time
discretization. We show that for explicit discretizations, the requirement of
preserving the canonical Poisson bracket under discrete evolution imposes
strong conditions on both allowable discretizations and Hamiltonians. These
conditions permit time discretizations for a limited class of Hamiltonians,
which does not include homogeneous cosmological models. We also present two
general classes of implicit discretizations which preserve Poisson brackets for
any Hamiltonian. Both types of discretizations generically do not preserve
first class constraint algebras. Using this observation, we show that time
discretization provides a complicated time gauge fixing for quantum gravity
models, which may be compared with the alternative procedure of gauge fixing
before discretization.


title: The critical role of shear in gravitational collapse

abstract:
  We investigate here how the shearing effects present within a collapsing
matter cloud influence the outcome of gravitational collapse in terms of
formation of either a black hole or a naked singularity as the final end state.
For collapse of practically all physically reasonable matter fields, we prove
that it would always end up in a black hole if it is either shear-free or has
homogeneous density. Thus it follows that whenever a naked singularity forms as
end product, the collapsing cloud must necessarily be shearing with
inhomogeneous density. Our consideration brings out the physical forces at work
which could cause a naked singularity to result as collapse end state, rather
than a black hole.


title:
Canonical theory of spherically symmetric spacetimes with
  cross-streaming null dusts

abstract:
  The Hamiltonian dynamics of two-component spherically symmetric null dust is
studied with regard to the quantum theory of gravitational collapse. The
components--the ingoing and outgoing dusts--are assumed to interact only
through gravitation. Different kinds of singularities, naked or "clothed", that
can form during collapse processes are described. The general canonical
formulation of the one-component null-dust dynamics by Bicak and Kuchar is
restricted to the spherically symmetric case and used to construct an action
for the two components. The transformation from a metric variable to the
quasilocal mass is shown to simplify the mathematics. The action is reduced by
a choice of gauge and the corresponding true Hamiltonian is written down.
Asymptotic coordinates and energy densities of dust shells are shown to form a
complete set of Dirac observables. The action of the asymptotic time
translation on the observables is defined but it has been calculated explicitly
only in the case of one-component dust (Vaidya metric).


title: Hubble operator in isotropic loop quantum cosmology

abstract:
  We present a construction of the Hubble operator for the spatially flat
isotropic loop quantum cosmology. This operator is a Dirac observable on a
subspace of the space of physical solutions. This subspace gets selected
dynamically, requiring that its action be invariant on the physical solution
space. As a simple illustrative application of the expectation value of the
operator, we do find a generic phase of (super)inflation, a feature shown by
Bojowald from the analysis of effective Friedmann equation of loop quantum
cosmology.


title:
Interaction of Hawking radiation with static sources in deSitter and
  Schwarzschild-deSitter spacetimes

abstract:
  We study and look for similarities between the response rates $R^{\rm
dS}(a_0, \Lambda)$ and $R^{\rm SdS}(a_0, \Lambda, M)$ of a static scalar source
with constant proper acceleration $a_0$ interacting with a massless,
conformally coupled Klein-Gordon field in (i) deSitter spacetime, in the
Euclidean vacuum, which describes a thermal flux of radiation emanating from
the deSitter cosmological horizon, and in (ii) Schwarzschild-deSitter
spacetime, in the Gibbons-Hawking vacuum, which describes thermal fluxes of
radiation emanating from both the hole and the cosmological horizons,
respectively, where $\Lambda$ is the cosmological constant and $M$ is the black
hole mass. After performing the field quantization in each of the above
spacetimes, we obtain the response rates at the tree level in terms of an
infinite sum of zero-energy field modes possessing all possible angular
momentum quantum numbers. In the case of deSitter spacetime, this formula is
worked out and a closed, analytical form is obtained. In the case of
Schwarzschild-deSitter spacetime such a closed formula could not be obtained,
and a numerical analysis is performed. We conclude, in particular, that $R^{\rm
dS}(a_0, \Lambda)$ and $R^{\rm SdS}(a_0, \Lambda, M)$ do not coincide in
general, but tend to each other when $\Lambda \to 0$ or $a_0 \to \infty$. Our
results are also contrasted and shown to agree (in the proper limits) with
related ones in the literature.


title:
Gravitational radiation from gamma-ray bursts as observational
  opportunities for LIGO and VIRGO

abstract:
  Gamma-ray bursts are believed to originate in core-collapse of massive stars.
  This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.


title: Finding the Origin of the Pioneer Anomaly

abstract:
  Analysis of radio-metric tracking data from the Pioneer 10/11 spacecraft at
distances between 20 - 70 astronomical units (AU) from the Sun has consistently
indicated the presence of an anomalous, small, constant Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 \pm 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
As a result, the nature of this anomaly has become of growing interest. Here we
present a concept for a deep-space experiment that will reveal the origin of
the discovered anomaly and also will characterize its properties to an accuracy
of at least two orders of magnitude below the anomaly's size. The proposed
mission will not only provide a significant accuracy improvement in the search
for small anomalous accelerations, it will also determine if the anomaly is due
to some internal systematic or has an external origin. A number of critical
requirements and design considerations for the mission are outlined and
addressed. If only already existing technologies were used, the mission could
be flown as early as 2010.


title: Cosmological Models Generalising Robertson-Walker Models

abstract:
  Considering the physical 3-space t = constant of the spacetime metrics as
spheroidal and pseudo spheroidal, cosmological models which are generalizations
of Robertson-Walker models are obtained. Specific forms of these general models
as solutions of Einstein's field equations are also discussed in the radiation-
and the matter-dominated eras of the universe.


title: Charges and Energy in Chern-Simons Theories and Lovelock Gravity

abstract:
  Starting from the SO(2,2n) Chern-Simons form in (2n+1) dimensions we
calculate the variation of conserved quantities in Lovelock gravity and
Lovelock-Maxwell gravity through the covariant formalism developed in
gr-qc/0305047. Despite the technical complexity of the Lovelock Lagrangian we
obtain a remarkably simple expression for the variation of the charges ensuing
from the diffeomorphism covariance of the theory. The viability of the result
is tested in specific applications and the formal expression for the entropy of
Lovelock black holes is recovered.


title: Some Further Properties of the Accelerated Kerr-Schild Metrics

abstract:
  We extend the previously found accelerated Kerr-Schild metrics for
Einstein-Maxwell-null dust and Einstein-Born-Infeld-null dust equations to the
cases including the cosmological constant. This way we obtain the
generalization of the charged de Sitter metrics in static space-times. We also
give a generalization of the zero acceleration limit of our previous
Einstein-Maxwell and Einstein-Born-Infeld solutions.


title: Lorentz invariant intrinsic decoherence

abstract:
  Quantum decoherence can arise due to classical fluctuations in the parameters
which define the dynamics of the system. In this case decoherence, and
complementary noise, is manifest when data from repeated measurement trials are
combined. Recently a number of authors have suggested that fluctuations in the
space-time metric arising from quantum gravity effects would correspond to a
source of intrinsic noise, which would necessarily be accompanied by intrinsic
decoherence. This work extends a previous heuristic modification of
Schr\"{o}dinger dynamics based on discrete time intervals with an intrinsic
uncertainty. The extension uses unital semigroup representations of space and
time translations rather than the more usual unitary representation, and does
the least violence to physically important invariance principles. Physical
consequences include a modification of the uncertainty principle and a
modification of field dispersion relations, in a way consistent with other
modifications suggested by quantum gravity and string theory .


title:
The new Earth gravity models and the measurement of the Lense-Thirring
  effect

abstract:
  We examine how the new forthcoming Earth gravity models from the CHAMP and,
especially, GRACE missions could improve the measurement of the general
relativistic Lense-Thirring effect according to the various kinds of
observables which could be adopted. In a very preliminary way, we use the
recently released EIGEN2 CHAMP-only and GRACE01S GRACE-only Earth gravity
models in order to assess the impact of the mismodelling in the even zonal
harmonic coefficients of geopotential which represents one of the major sources
of systematic errors in this kind of measurement.

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


title: Strong Field Gravitational Lensing by a Kerr Black Hole

abstract:
  We consider a Kerr black hole acting as a gravitational deflector within the
geometrical optics, and point source approximations. The Kerr black hole
gravitational lens geometry consisting of an observer and a source located far
away and placed at arbitrary inclinations with respect to the black hole's
equatorial plane is studied in the strong field regime. For this geometry the
null geodesics equations of our interest can go around the black hole several
times before reaching the observer. Such photon trajectories are written in
terms of the angular positions in the observer's sky and therefore become "lens
equations". As a consequence, we found for any image a simple classification
scheme based in two integers numbers: the number of turning points in the polar
coordinate $\theta$, and the number of windings around the black hole's
rotation axis. As an application, and to make contact with the literature, we
consider a supermassive Kerr black hole at the Galactic center as a
gravitational deflector. In this case, we show that our proposed computational
scheme works successfully by computing the positions and magnifications of the
relativistic images for different source-observer geometries. In fact, it is
shown that our general procedure and results for the positions and
magnifications of the images off the black hole's equatorial plane, reduce and
agree with well known cases found in the literature.


title: Spectral Line Removal in the LIGO Data Analysis System (LDAS)

abstract:
  High power in narrow frequency bands, spectral lines, are a feature of an
interferometric gravitational wave detector's output. Some lines are coherent
between interferometers, in particular, the 2 km and 4 km LIGO Hanford
instruments. This is of concern to data analysis techniques, such as the
stochastic background search, that use correlations between instruments to
detect gravitational radiation. Several techniques of `line removal' have been
proposed. Where a line is attributable to a measurable environmental
disturbance, a simple linear model may be fitted to predict, and subsequently
subtract away, that line. This technique has been implemented (as the command
oelslr) in the LIGO Data Analysis System (LDAS). We demonstrate its application
to LIGO S1 data.


title: Dynamics of general relativistic spherically symmetric dust thick shells

abstract:
  We consider a spherical thick shell immersed in two different spherically
symmetric space-times. Using the fact that the boundaries of the thick shell
with two embedding space-times must be nonsingular hypersurfaces, we develop a
scheme to obtain the underlying equation of motion for the thick shell in
general. As a simple example, the equation of motion of a spherical dustlike
shell in vacuum is obtained. To compare our formalism with the thin shell one,
the dynamical equation of motion of the thick shell is then expanded to the
first order of its thickness. It is easily seen that the thin shell limit of
our dynamical equation is exactly that given in the literature for the dynamics
of a thin shell. It turns out that the effect of thickness is to speed up the
collapse of the shell.