title: Near-Horizon Conformal Symmetry and Black Hole Entropy

abstract:
  Near an event horizon, the action of general relativity acquires a new
asymptotic conformal symmetry. Using two-dimensional dilaton gravity as a test
case, I show that this symmetry results in a chiral Virasoro algebra with a
calculable classical central charge, and that Cardy's formula for the density
of states reproduces the Bekenstein-Hawking entropy. This result lends support
to the notion that the universal nature of black hole entropy is controlled by
conformal symmetry near the horizon.


title:
The "optical lever" intracavity readout scheme for gravitational-wave
  antennae

abstract:
  An improved version of the ``optical bar'' intracavity readout scheme for
gravitational-wave antennae is considered. We propose to call this scheme
``optical lever'' because it can provide significant gain in the signal
displacement of the local mirror similar to the gain which can be obtained
using ordinary mechanical lever with unequal arms. In this scheme displacement
of the local mirror can be close to the signal displacement of the end mirrors
of hypothetical gravitational-wave antenna with arm lengths equal to the
half-wavelength of the gravitational wave.


title: Detection of negative energy: 4-dimensional examples

abstract:
  We study the response of switched particle detectors to static negative
energy densities and negative energy fluxes. It is demonstrated how the
switching leads to excitation even in the vacuum and how negative energy can
lead to a suppression of this excitation. We obtain quantum inequalities on the
detection similar to those obtained for the energy density by Ford and
co-workers and in an `operational' context by Helfer. We revisit the question
`Is there a quantum equivalence principle?' in terms of our model. Finally, we
briefly address the issue of negative energy and the second law of
thermodynamics.


title:
Uniqueness and non-uniqueness of static vacuum black holes in higher
  dimensions

abstract:
  We prove the uniqueness theorem for asymptotically flat static vacuum black
hole solutions in higher dimensional space-times. We also construct infinitely
many non-asymptotically flat regular static black holes on the same spacetime
manifold with the same spherical topology.


title: New embedding of Schwarzschild geometry. II. Interior solution

abstract:
  We embed the Schwarzschild interior solution in a five-dimensional flat space
and show that the systems of the interior and the exterior solution are based
on the same geometrical principles. It turns out that the energy tensor of the
matter has its origin in the five-dimensional structure of the geometry and is
built up by the generalized second fundamental forms. Thus, the matter is
already geometrized. The Codazzi equations are the field equations for the
matter field.


title: On the size of the smallest scales in cosmic string networks

abstract:
  We present a method for the calculation of the gravitational back reaction
cutoff on the smallest scales of cosmic string networks taking into account
that not all modes on strings interact with all other modes. This results in a
small scale structure cutoff that is sensitive to the initial spectrum of
perturbations present on strings. From a simple model, we compute the cutoffs
in radiation- and matter-dominated universes.


title: Quintessence Model and Observational Constraints

abstract:
  The recent observations of type Ia supernovae strongly support that the
universe is accelerating now and decelerated in the recent past. By assuming a
general relation between the quintessence potential and the quintessence
kinetic energy, a general relation is found between the quintessence energy
density and the scale factor. The potential includes both the hyperbolic and
the double exponential potentials. A detailed analysis of the transition from
the deceleration phase to the acceleration phase is then performed. We show
that the current constraints on the transition time, the equation of state and
the energy density of the quintessence field are satisfied in the model.


title: Trilinear generally covariant equations of AP

abstract:
  Field equations for n-frames h_a{}^\mu that are possible in the theory of
absolute parallelism (AP) are considered. The methods of compatibility (or
formal integrability) theory enable us to find the non-Lagrangian equation
having unusual kind of compatibility conditions, guaranteed by two (not one)
identities. This 'unique equation' was not noted explicitly in the
classification by Einstein and Mayer of compatible second order equations of
AP.
  It is shown that some equations of AP (including 'unique equation') can be
written in a trilinear form that contains only the matrix of frame density (of
some weight) H_a{}^\mu and its derivatives and not inverse (coframe density)
matrix. The equations are still regular and involutive for degenerate but
finite matrices H_a{}^\mu if rank H_a{}^\mu > 1.


title: Local criteria for the existence of an accelerated frame of reference

abstract:
  A local criteria for the existence of an accelerated frame of reference is
found. An accelerated frame of reference could exist in all regions where a
non-null (non-isotropic) vector field does not degenerate in a null (isotropic)
vector field.


title: On the problem of equation of state for the $\Lambda$ - field

abstract:
  Recently found accelarated expansion of our Universe is due to the presence
of a new kind of matter called "$\Lambda$ - field" or quintessence. The
limitations on its equation of state are found from the fact of its
unclustering at all scales much smaller than the cosmological horizon. It is
discussed how these limitations affect on the possibility to approximate the
accelarated expansion by such cosmological models as the model of Chaplygin
gas.


title: Reduction of the effective mass of the Reissner-Nordstrom spacetime

abstract:
  We derive the Teixeira, Wolk and Som method, for obtaining electrostatic
solutions from given vacuum solutions, in its inverse form. Then we use it to
obtain the geometrical mass $M_S$ in the Schwarzschild spacetime, and we find
$M_S^2=M^2-Q^2$, where $M$ and $Q$ are, respectively, the mass and charge
parameters of the Reissner-Nordstr\"om spacetime. We compare $M_S$ to the
corresponding active gravitational mass and mass function.


title: Theorems on existence and global dynamics for the Einstein equations

abstract:
  This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local in time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity which offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure are given. A conjectural picture of the
asymptotic behaviour of general cosmological solutions of the Einstein
equations is built up. Some miscellaneous topics connected with the main theme
are collected in a separate section.


title:
Gravitomagnetism in Metric Theories: Analysis of Earth Satellites
  Results, and its Coupling with Spin

abstract:
  Employing the PPN formalism the gravitomagnetic field in different metric
theories is considered in the analysis of the LAGEOS results. It will be shown
that there are several models that predict exactly the same effect that general
relativity comprises. In other words, these Earth satellites results can be
taken as experimental evidence that the orbital angular momentum of a body does
indeed generate space--time geometry, notwithstanding they do not endow general
relativity with an outstanding status among metric theories. Additionally the
coupling spin--gravitomagnetic field is analyzed with the introduction of the
Rabi transitions that this field produces on a quantum system with spin 1/2.
Afterwards, a continuous measurement of the energy of this system is
introduced, and the consequences upon the corresponding probabilities of the
involved gravitomagnetic field will be obtained. Finally, it will be proved
that these proposals allows us, not only to confront against future experiments
the usual assumption of the coupling spin--gravotimagnetism, but also to
measure some PPN parameters and to obtain functional dependences among them.


title: Ephemeral point-events: is there a last remnant of physical objectivity?

abstract:
  For the past two decades, Einstein's Hole Argument (which deals with the
apparent indeterminateness of general relativity due to the general covariance
of the field equations) and its resolution in terms of Leibniz equivalence (the
statement that Riemannian geometries related by active diffeomorphisms
represent the same physical solution) have been the starting point for a lively
philosophical debate on the objectivity of the point-events of space-time. It
seems that Leibniz equivalence makes it impossible to consider the points of
the space-time manifold as physically individuated without recourse to
dynamical individuating fields. Various authors have posited that the metric
field itself can be used in this way, but nobody so far has considered the
problem of explicitly distilling the metrical fingerprint of point-events from
the gauge-dependent components of the metric field. Working in the Hamiltonian
formulation of general relativity, and building on the results of Lusanna and
Pauri (2002), we show how Bergmann and Komar's intrinsic pseudo-coordinates
(based on the value of curvature invariants) can be used to provide a physical
individuation of point-events in terms of the true degrees of freedom (the
Dirac observables) of the gravitational field, and we suggest how this
conceptual individuation could in principle be implemented with a well-defined
empirical procedure. We argue from these results that point-events retain a
significant kind of physical objectivity.


title: Process Physics: From Quantum Foam to General Relativity

abstract:
  Progress in the new information-theoretic process physics is reported in
which the link to the phenomenology of general relativity is made. In process
physics the fundamental assumption is that reality is to be modelled as
self-organising semantic (or internal or relational) information using a
self-referentially limited neural network model. Previous progress in process
physics included the demonstration that space and quantum physics are emergent
and unified, with time a distinct non-geometric process, that quantum phenomena
are caused by fractal topological defects embedded in and forming a growing
three-dimensional fractal process-space, which is essentially a quantum foam.
Other features of the emergent physics were: quantum field theory with emergent
flavour and confined colour, limited causality and the Born quantum measurement
metarule, inertia, time-dilation effects, gravity and the equivalence
principle, a growing universe with a cosmological constant, black holes and
event horizons, and the emergence of classicality. Here general relativity and
the technical language of general covariance is seen not to be fundamental but
a phenomenological construct, arising as an amalgam of two distinct phenomena:
the `gravitational' characteristics of the emergent quantum foam for which
`matter' acts as a sink, and the classical `spacetime' measurement protocol,
but with the later violated by quantum measurement processes. Quantum gravity,
as manifested in the emergent Quantum Homotopic Field Theory of the
process-space or quantum foam, is logically prior to the emergence of the
general relativity phenomenology, and cannot be derived from it.


title:
Mechanics of Continuous Media in $(\bar{L}_n,g)$-spaces. I. Introduction
  and mathematical tools

abstract:
  Basic notions and mathematical tools in continuum media mechanics are
recalled. The notion of exponent of a covariant differential operator is
introduced and on its basis the geometrical interpretation of the curvature and
the torsion in $(\bar{L}_n,g)$-spaces is considered. The Hodge (star) operator
is generalized for $(\bar{L}_n,g)$-spaces. The kinematic characteristics of a
flow are outline in brief. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g; 47.75.+f;
47.90.+a; 83.10.Bb


title:
Mechanics of Continuous Media in $(\bar{L}_n,g)$-Spaces. II. Relative
  velocity and deformations

abstract:
  Basic notions of continuous media mechanics are introduced for spaces with
affine connections and metrics. The physical interpretation of the notion of
relative velocity is discussed. The notions of deformation velocity tensor,
shear velocity, rotation (vortex) velocity, and expansion velocity are
introduced. Different types of flows are considered.
  PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g; 47.75.+f; 47.90.+a; 83.10.Bb


title: Geometrical measurements in three-dimensional quantum gravity

abstract:
  A set of observables is described for the topological quantum field theory
which describes quantum gravity in three space-time dimensions with positive
signature and positive cosmological constant. The simplest examples measure the
distances between points, giving spectra and probabilities which have a
geometrical interpretation. The observables are related to the evaluation of
relativistic spin networks by a Fourier transform.


title:
Null Singularity Formation by Scalar Fields in Colliding Waves and Black
  Holes

abstract:
  It was believed that when gravitational, electromagnetic and scalar waves
interact, a spacelike curvature singularity or Cauchy horizon develops because
of mutual focusing. We show with an exact solution that the collision of
Einstein-Maxwell-Scalar fields, in contrast to previous studies, predicts
singularities on null surfaces and that this is a transition phase between
spacelike singularities and regular horizons. Divergences of tidal forces in
the null singularities is shown to be weaker relative to the spacelike ones.
Using the local isometry between colliding plane waves and black holes, we show
that the inner horizon of Reissner-Nordstrom black hole transforms into a null
singularity when a particular scalar field is coupled to it. We also present an
analytic exact solution, which represents a Reissner-Nordstrom black hole with
scalar hair in between the ergosphere.


title:
Computational Resources to Filter Gravitational Wave Data with
  P-approximant Templates

abstract:
  The prior knowledge of the gravitational waveform from compact binary systems
makes matched filtering an attractive detection strategy. This detection method
involves the filtering of the detector output with a set of theoretical
waveforms or templates. One of the most important factors in this strategy is
knowing how many templates are needed in order to reduce the loss of possible
signals. In this study we calculate the number of templates and computational
power needed for a one-step search for gravitational waves from inspiralling
binary systems. We build on previous works by firstly expanding the
post-Newtonian waveforms to 2.5-PN order and secondly, for the first time,
calculating the number of templates needed when using P-approximant waveforms.
The analysis is carried out for the four main first-generation interferometers,
LIGO, GEO600, VIRGO and TAMA. As well as template number, we also calculate the
computational cost of generating banks of templates for filtering GW data. We
carry out the calculations for two initial conditions. In the first case we
assume a minimum individual mass of $1 M_{\odot}$ and in the second, we assume
a minimum individual mass of $5 M_{\odot}$. We find that, in general, we need
more P-approximant templates to carry out a search than if we use standard PN
templates. This increase varies according to the order of PN-approximation, but
can be as high as a factor of 3 and is explained by the smaller span of the
P-approximant templates as we go to higher masses. The promising outcome is
that for 2-PN templates the increase is small and is outweighed by the known
robustness of the 2-PN P-approximant templates.


title: Asymptotically flat and regular Cauchy data

abstract:
  I describe the construction of a large class of asymptotically flat initial
data with non-vanishing mass and angular momentum for which the metric and the
extrinsic curvature have asymptotic expansions at space-like infinity in terms
of powers of a radial coordinate. I emphasize the motivations and the main
ideas behind the proofs.


title: (Conformal) Killing vectors and their associated bivectors

abstract:
  Fayos and Sopuerta have recently set up a formalism for studying vacuum
spacetimes with an isometry, a formalism that is centred around the bivector
corresponding to the Killing vector and that adapts the tetrad to the bivector.
Steele has generalized their approach to include the homothetic case. Here, we
generalize this formalism to arbitrary spacetimes and to homothetic and
conformal Killing vectors but do not insist on aligning the tetrad with the
bivector. The most efficient way to use the formalism to find conformal Killing
vectors (proper or not) of a given spacetime is to combine it with the notion
of a preferred tetrad. A metric by Kimura is used as an illustrative example.


title:
The back reaction and the effective Einstein's equation for the Universe
  with ideal fluid cosmological perturbations

abstract:
  We investigate the back reaction of cosmological perturbations on the
evolution of the Universe using the renormalization group method. Starting from
the second order perturbed Einstein's equation, we renormalize a scale factor
of the Universe and derive the evolution equation for the effective scale
factor which includes back reaction due to inhomogeneities of the Universe. The
resulting equation has the same form as the standard Friedman-Robertson-Walker
equation with the effective energy density and pressure which represent the
back reaction effect.


title: A detector of gravitational waves based on coupled microwave cavities

abstract:
  Since 1978 superconducting coupled cavities have been proposed as sensitive
detector of gravitational waves. The interaction of the gravitational wave with
the cavity walls, and the resulting motion, induces the transition of some
electromagnetic energy from an initially excited cavity mode to an empty one.
The energy transfer is maximum when the frequency of the wave is equal to the
frequency difference of the two cavity modes. In this paper the basic
principles of the detector are discussed. The interaction of a gravitational
wave with the cavity walls is studied in the proper reference frame of the
detector, and the coupling between two electromagnetic normal modes induced by
the wall motion is analyzed in detail. Noise sources are also considered; in
particular the noise coming from the brownian motion of the cavity walls is
analyzed. Some ideas for the developement of a realistic detector of
gravitational waves are discussed; the outline of a possible detector design
and its expected sensitivity are also shown.


title: An anisotropic cosmological model with isotropic background radiation

abstract:
  We present an exact solution of Einstein equations that describes a Bianchi
type III spacetime with conformal expansion. The matter content is given by an
anisotropic scalar field and two perfect fluids representing dust and isotropic
radiation. Based on this solution, we construct a cosmological model that
respects the evolution of the scale factor predicted in standard cosmology.


title: Spacetime Singularities in (2+1)-Dimensional Quantum Gravity

abstract:
  The effects of spacetime quantization on black hole and big bang/big crunch
singularities can be studied using new tools from (2+1)-dimensional quantum
gravity. I investigate effects of spacetime quantization on singularities of
the (2+1)-dimensional BTZ black hole and the (2+1)-dimensional torus universe.
Hosoya has considered the BTZ black hole, and using a ``quantum generalized
affine parameter'' (QGAP), has shown that, for some specific paths, quantum
effects ``smear'' the singularity. Using generic gaussian wave functions, I
show that both BTZ black hole and the torus universe contain families of paths
that still reach the singularities with a finite QGAP, suggesting that
singularities persist in quantum gravity. More realistic calculations, using
modular invariant wave functions of Carlip and Nelson for the torus universe,
further support this conclusion.


title: Extent of the Immirzi Ambiguity in Quantum General Relativity

abstract:
  The Ashtekar-Barbero formulation of general relativity admits a one-parameter
family of canonical transformations that preserves the expressions of the Gauss
and diffeomorphism constraints. The loop quantization of the connection
formalism based on each of these canonical sets leads to different predictions.
This phenomenon is called the Immirzi ambiguity. It has been recently argued
that this ambiguity could be generalized to the extent of a spatially dependent
function, instead of a parameter. This would ruin the predictability of loop
quantum gravity. We prove that such expectations are not realized, so that the
Immirzi ambiguity introduces exclusively a freedom in the choice of a real
number.


title: Operadic curvature as a tool for gravity

abstract:
  The deformation equation and its integrability condition (Bianchi identity)
of a non-associative deformation in operad algebra are found. Their relation to
the theory of gravity is discussed.


title:
Nonholonomic Mapping Principle for Classical and Quantum Mechanics in
  Spaces with Curvature and Torsion

abstract:
  I explain the geometric basis for the recently-discovered nonholonomic
mapping principle which permits deriving laws of nature in spacetimes with
curvature and torsion from those in flat spacetime, thus replacing and
extending Einstein's equivalence principle. As an important consequence, it
yields a new action principle for determining the equation of motion of a free
spinless point particle in such spacetimes. Surprisingly, this equation
contains a torsion force, although the action involves only the metric. This
force makes trajectories autoparallel rather than geodesic. Its geometric
origin is the closure failure of parallelograms in the presence of torsion, A
simple generalization of the mapping principle transforms path integrals from
flat spacetimes to those with curvature and torsion, thus playing the role of a
quantum equivalence principle, applicable at present only to spaces with
gradient torsion.


title: Gravitational waves from inspiraling binary black holes

abstract:
  Binary black holes are the most promising candidate sources for the first
generation of earth-based interferometric gravitational-wave detectors. We
summarize and discuss the state-of-the-art analytic techniques developed during
the last years to better describe the late dynamical evolution of binary black
holes of comparable masses.


title:
The evolution of primordial black hole masses in the radiation-
  dominated era

abstract:
  We revisit the problem of PBH mass evolution in the radiation-dominated era.
We solve the complete differential equation in the semiclassical regime with
absorption and evaporation terms and show that PBHs can gain very little mass,
if at all, in this era. Relativistic proper motion of PBHs respect to the CMBR,
as a possible loophole in the growth argument, is shown to be unlikely. Finally
we demonstrate that PBHs can not remain in thermodynamical equilibrium with the
ambient radiation, and therefore initially non-evaporating black holes must
enter the evaporating regime, supporting several efforts to look for
observational signatures.


title: Dynamics of Chaotic Inflation with Variable Space Dimension

abstract:
  Within the framework of a model Universe with variable space dimension, we
study chaotic inflation with the potential $m^2\phi^2/2$, and calculate the
dynamical solutions of the inflaton field, variable space dimension, scale
factor, and their interdependence during the inflationary epoch. We show that
the characteristic of the variability of the space dimension causes the
inflationary epoch in the variable space dimension to last longer than the
inflationary epoch in the constant space dimension.


title:
Gravitomagnetic Field of a Rotating Superconductor and of a Rotating
  Superfluid

abstract:
  The quantization of the extended canonical momentum in quantum materials
including the effects of gravitational drag is applied successively to the case
of a multiply connected rotating superconductor and superfluid. Experiments
carried out on rotating superconductors, based on the quantization of the
magnetic flux in rotating superconductors, lead to a disagreement with the
theoretical predictions derived from the quantization of a canonical momentum
without any gravitomagnetic term. To what extent can these discrepancies be
attributed to the additional gravitomagnetic term of the extended canonical
momentum? This is an open and important question. For the case of multiply
connected rotating neutral superfluids, gravitational drag effects derived from
rotating superconductor data appear to be hidden in the noise of present
experiments according to a first rough analysis.


title:
Faster than Light Photons in Gravitational Fields II - Dispersion and
  Vacuum Polarisation

abstract:
  Vacuum polarisation in QED in a background gravitational field induces
interactions which effectively violate the strong equivalence principle and
affect the propagation of light. In the low frequency limit, Drummond and
Hathrell have shown that this mechanism leads to superluminal photon
velocities. To confront this phenomenon with causality, however, it is
necessary to extend the calculation of the phase velocity $\vp(\w)$ to high
frequencies, since it is $\vp(\infty)$ which determines the characteristics of
the effective wave equation and thus the causal structure. In this paper, we
use a recently constructed expression, valid to all orders in a derivative
expansion, for the effective action of QED in curved spacetime to determine the
frequency dependence of the phase velocity and investigate whether superluminal
velocities indeed persist in the high frequency limit.


title:
Gravitomagnetic effects for polar circular geodesic orbits around a
  central rotating body

abstract:
  The gravitomagnetic corrections to the Keplerian period for a circular,
geodesic orbit of a test particle in a polar plane containing the proper
angular momentum J of a central rotating body are considered.


title: Coarse graining in spin foam models

abstract:
  We formulate the problem of finding the low-energy limit of spin foam models
as a coarse-graining problem in the sense of statistical physics. This suggests
that renormalization group methods may be used to find that limit. However,
since spin foams are models of spacetime at Planck scale, novel issues arise:
these microscopic models are sums over irregular, background-independent
lattices. We show that all of these issues can be addressed by the recent
application of the Kreimer Hopf algebra for quantum field theory
renormalization to non-perturbative statistical physics. The main difference
from standard renormalization group is that the Hopf algebra executes block
transformations in parts of the lattice only but in a controlled manner so that
the end result is a fully block-transformed lattice.


title:
Gravitational Waves from the Merger of Binary Neutron Stars in a Fully
  General Relativistic Simulation

abstract:
  We performed 3D numerical simulations of the merger of equal-mass binary
neutron stars in full general relativity using a new large scale supercomputer.
We take the typical grid size as (505,505,253) for (x,y,z) and the maximum grid
size as (633,633,317). These grid numbers enable us to put the outer boundaries
of the computational domain near the local wave zone and hence to calculate
gravitational waveforms of good accuracy (within $\sim 10%$ error) for the
first time. To model neutron stars, we adopt a $\Gamma$-law equation of state
in the form $P=(\Gamma-1)\rho\epsilon$, where P, $\rho$, $\varep$ and $\Gamma$
are the pressure, rest mass density, specific internal energy, and adiabatic
constant. It is found that gravitational waves in the merger stage have
characteristic features that reflect the formed objects. In the case that a
massive, transient neutron star is formed, its quasi-periodic oscillations are
excited for a long duration, and this property is reflected clearly by the
quasi-periodic nature of waveforms and the energy luminosity. In the case of
black hole formation, the waveform and energy luminosity are likely damped
after a short merger stage. However, a quasi-periodic oscillation can still be
seen for a certain duration, because an oscillating transient massive object is
formed during the merger. This duration depends strongly on the initial
compactness of neutron stars and is reflected in the Fourier spectrum of
gravitational waves. To confirm our results and to calibrate the accuracy of
gravitational waveforms, we carried out a wide variety of test simulations,
changing the resolution and size of the computational domain.


title:
Scattering of Spinning Test Particles by Plane Gravitational and
  Electromagnetic Waves

abstract:
  The Mathisson-Papapetrou-Dixon (MPD) equations for the motion of electrically
neutral massive spinning particles are analysed, in the pole-dipole
approximation, in an Einstein-Maxwell plane-wave background spacetime. By
exploiting the high symmetry of such spacetimes these equations are reduced to
a system of tractable ordinary differential equations. Classes of exact
solutions are given, corresponding to particular initial conditions for the
directions of the particle spin relative to the direction of the propagating
background fields. For Einstein-Maxwell pulses a scattering cross section is
defined that reduces in certain limits to those associated with the scattering
of scalar and Dirac particles based on classical and quantum field theoretic
techniques. The relative simplicity of the MPD approach and its use of
macroscopic spin distributions suggests that it may have advantages in those
astrophysical situations that involve strong classical gravitational and
electromagnetic environments.


title: Oscillations of General Relativistic Superfluid Neutron Stars

abstract:
  We develop a general formalism to treat, in general relativity, the nonradial
oscillations of a superfluid neutron star about static (non-rotating)
configurations. The matter content of these stars can, as a first
approximation, be described by a two-fluid model: one fluid is the neutron
superfluid, which is believed to exist in the core and inner crust of mature
neutron stars; the other fluid is a conglomerate of all charged constituents.
We use a system of equations that governs the perturbations both of the metric
and of the matter variables, whatever the equation of state for the two fluids.
The entrainment effect is explicitly included. We also allow for an outer
envelope composed of ordinary fluid. We derive and implement the junction
conditions for the metric and matter variables at the core/envelope interface.
We investigate how the quasinormal modes of a superfluid star are affected by
changes in the entrainment parameter, and unveil a series of avoided crossings
between the various modes. We provide a proof that all modes of a two-fluid
star must radiate gravitationally. We also discuss the future detectability of
pulsations in a superfluid star and argue that it may be possible to use
gravitational-wave data to constrain the parameters of superfluid neutron
stars.


title: Results on the spectrum of R-Modes of slowly rotating relativistic stars

abstract:
  The paper considers the spectrum of axial perturbations of slowly uniformly
rotating general relativistic stars in the framework of Y. Kojima. In a first
step towards a full analysis only the evolution equations are treated but not
the constraint. Then it is found that the system is unstable due to a continuum
of non real eigenvalues. In addition the resolvent of the associated generator
of time evolution is found to have a special structure which was discussed in a
previous paper. From this structure it follows the occurrence of a continuous
part in the spectrum of oscillations at least if the system is restricted to a
finite space as is done in most numerical investigations. Finally, it can be
seen that higher order corrections in the rotation frequency can qualitatively
influence the spectrum of the oscillations. As a consequence different
descriptions of the star which are equivalent to first order could lead to
different results with respect to the stability of the star.


title:
Geodesically complete nondiagonal inhomogeneous cosmological solutions
  in dilatonic gravity with a stiff perfect fluid

abstract:
  New nondiagonal $G_{2}$ inhomogeneous cosmological solutions are presented in
a wide range of scalar-tensor theories with a stiff perfect fluid as a matter
source. The solutions have no big-bang singularity or any other curvature
singularities. The dilaton field and the fluid energy density are everywhere
regular, too. The geodesic completeness of the solutions is investigated.


title:
Asymptotic Behavior of Polarized and Half-Polarized U(1) symmetric
  Vacuum Spacetimes

abstract:
  We use the Fuchsian algorithm to study the behavior near the singularity of
certain families of U(1) Symmetric solutions of the vacuum Einstein equations
(with the U(1) isometry group acting spatially). We consider an analytic family
of polarized solutions with the maximum number of arbitrary functions
consistent with the polarization condition (one of the ``gravitational degrees
of freedom'' is turned off) and show that all members of this family are
asymptotically velocity term dominated (AVTD) as one approaches the
singularity. We show that the same AVTD behavior holds for a family of ``half
polarized'' solutions, which is defined by adding one extra arbitrary function
to those characterizing the polarized solutions. (The full set of non-polarized
solutions involves two extra arbitrary functions). We begin to address the
issue of whether AVTD behavior is independent of the choice of time foliation
by showing that indeed AVTD behavior is seen for a wide class of choices of
harmonic time in the polarized and half-polarized (U(1) Symmetric vacuum)
solutions discussed here. \


title: The number of tensor differential invariants of a Riemannian metric

abstract:
  We determine the number of functionally independent components of tensors
involving higher-order derivatives of a Riemannian metric.


title: Constructing Solutions of the Einstein Constraint Equations

abstract:
  The first step in the building of a spacetime solution of Einstein's
gravitational field equations via the initial value formulation is finding a
solution of the Einstein constraint equations. We recall the conformal method
for constructing solutions of the constraints and we recall what it tells us
about the parameterization of the space of such solutions. One would like to
know how to construct solutions which model particular physical phenomena. One
useful step towards this goal is learning how to glue together known solutions
of the constraint equations. We discuss recent results concerning such gluing.


title:
Cosmological Quantum Jump Dynamics I. The Principle of Cosmic Energy
  Determinacy, Equations of Motion, and Jumps Probabilities

abstract:
  The universe, as a closed system, is for all time in a state with a
determinate value of energy, i.e., in an eigenstate of the Hamiltonian. That is
the principle of cosmic energy determinacy. The Hamiltonian depends on cosmic
time through metric. Therefore there are confluence and branch points of energy
levels. At branch points, quantum jumps must happen to prevent the violation of
energy determinacy. Thus quantum jumps are a reaction against the propensity of
the universe dynamics to that violation. On the basis of this idea, an
internally consistent quantum jump dynamics is developed.


title:
Interaction between a stationary electric charge and a stationary
  magnetic dipole

abstract:
  Using Einstein-Maxwell theory I investigate the gravitational field generated
by an electric charge and a magnetic dipole, both held in fixed positions, but
spinning with prescribed angular momenta. There is a conical singularity
between them representing a strut balancing the gravitational attraction of
their masses. However, there is in general another singularity, which I call a
torsion singularity. I interpret this as a couple needed to maintain the spins
at their prescribed values. It vanishes when the parameters obey a certain
formula.
  A conclusion of the work is that the charge and the magnet must spin relative
to one another unless constrained by a couple.


title: The magnetic dipole interaction in Einstein-Maxwell theory

abstract:
  I derive an exact, static, axially symmetric solution of the Einstein-Maxwell
equations representing two massless magnetic dipoles, and compare it with the
corresponding solution of Einstein's equations for two massless spinning
particles (see gr-qc/0201094). I then obtain an exact stationary solution of
the Einstein-Maxwell equations representing two massless spinning magnets in
balance. The conclusion is that the spin-spin force is analogous to the force
between two magnetic dipoles, but of opposite sign, and that the latter agrees
with the classical value in the first approximation.


title:
General existence proof for rest frame systems in asymptotically flat
  space-time

abstract:
  We report a new result on the nice section construction used in the
definition of rest frame systems in general relativity. This construction is
needed in the study of non trivial gravitational radiating systems. We prove
existence, regularity and non-self-crossing property of solutions of the nice
section equation for general asymptotically flat space times. This proves a
conjecture enunciated in a previous work.


title: Reissner-Nordstrom black hole lensing

abstract:
  In this paper we study the strong gravitational lensing scenario where the
lens is a Reissner-Nordstrom black hole. We obtain the basic equations and show
that, as in the case of Schwarzschild black hole, besides the primary and
secondary images, two infinite sets of relativistic images are formed. We find
analytical expressions for the positions and amplifications of the relativistic
images. The formalism is applied to the case of a low-mass black hole placed at
the galactic halo.


title:
The impact of the static part of the Earth's gravity field on some tests
  of General Relativity with Satellite Laser Ranging

abstract:
  In this paper we calculate explicitly the secular classical precessions of
the node \Omega and the perigee \omega of an Earth artificial satellite induced
by the static, even zonal harmonics of the geopotential up to degree l=20.
Subsequently, their systematic errors induced by the mismodelling in the even
zonal geopotential coefficients J_l are compared to the general relativistic
secular gravitomagnetic and gravitoelectric precessions of the node and the
perigee of the existing laser-ranged geodetic satellites and of the proposed
LARES.

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


title: Black holes and traversible wormholes: a synthesis

abstract:
  A unified framework for black holes and traversible wormholes is described,
where both are locally defined by outer trapping horizons, two-way traversible
for wormholes and one-way traversible for black or white holes. In a
two-dimensional dilaton gravity model, examples are given of: construction of
wormholes from black holes; operation of wormholes for transport, including
back-reaction; maintenance of an operating wormhole; and collapse of wormholes
to black holes. In spherically symmetric Einstein gravity, several exotic
matter models supporting wormhole solutions are proposed: ghost scalar fields,
exotic fluids and pure ghost radiation.


title:
Inertial modes of slowly rotating relativistic stars in the Cowling
  approximation

abstract:
  We study oscillations of slowly rotating relativistic barotropic as well as
non-barotropic polytropic stars in the Cowling approximation, including first
order rotational corrections. By taking into account the coupling between the
polar and axial equations, we find that, in contrast to previous results, the
$m=2$ $r$ modes are essentially unaffected by the continuous spectrum and exist
even for very relativistic stellar models. We perform our calculations both in
the time and frequency domain. In order to numerically solve the infinite
system of coupled equations, we truncate it at some value $l_{\rm max}$.
Although the time dependent equations can be numerically evolved without any
problems, the eigenvalue equations possess a singular structure, which is
related to the existence of a continuous spectrum. This prevents the numerical
computation of an eigenmode if its eigenfrequency falls inside the continuous
spectrum. The properties of the latter depend strongly on the cut-off value
$l_{\rm max}$ and it can consist of several either disconnected or overlapping
patches, which are the broader the more relativistic the stellar model is. By
discussing the dependence of the continuous spectrum as a function of both the
cut-off value $l_{\rm max}$ and the compactness $M/R$, we demonstrate how it
affects the inertial modes. Through the time evolutions we are able to show
that some of the inertial modes can actually exist inside the continuous
spectrum, but some cannot. For more compact and therefore more relativistic
stellar models, the width of the continuous spectrum strongly increases and as
a consequence, some of the inertial modes, which exist in less relativistic
stars, disappear.


title: Existence of non-trivial, vacuum, asymptotically simple space-times

abstract:
  We construct non-trivial vacuum space-times with a global Scri. The
construction proceeds by proving extension results across compact boundaries
for initial data sets, adapting the gluing arguments of Corvino and Schoen.
Another application of the extension results is existence of initial data which
are exactly Schwarzschild both near infinity and near each of the connected
component of the apparent horizon.


title:
Planckian Scattering Beyond the Eikonal Approximation in the Functional
  Approach

abstract:
  In the framework of functional integration the non-leading terms to leading
eikonal behavior of the Planckian-energy scattering amplitude are calculated by
the straight-line path approximation. We show that the allowance for the
first-order correction terms leads to the appearance of retardation effect. The
singular character of the correction terms at short distances is also noted,
and they may be lead ultimately to the appearance of non-eikonal contributions
to the scattering amplitudes.


title: Exact Solutions of Five Dimensional Anisotropic Cosmologies

abstract:
  We solve the five dimensional vacuum Einstein equations for several kinds of
anisotropic geometries. We consider metrics in which the spatial slices are
characterized as Bianchi types-II and V, and the scale factors are dependent
both on time and a non-compact fifth coordinate. We examine the behavior of the
solutions we find, noting for which parameters they exhibit contraction over
time of the fifth scale factor, leading naturally to dimensional reduction. We
explore these within the context of the induced matter model: a Kaluza-Klein
approach that associates the extra geometric terms due to the fifth coordinate
with contributions to the four dimensional stress-energy tensor.


title: Relativistic quantum measurement

abstract:
  Does the measurement of a quantum system necessarily break Lorentz
invariance? We present a simple model of a detector that measures the spacetime
localization of a relativistic particle in a Lorentz invariant manner. The
detector does not select a preferred Lorentz frame as a Newton-Wigner
measurement would do. The result indicates that there exists a Lorentz
invariant notion of quantum measurement and sheds light on the issue of the
localization of a relativistic particle. The framework considered is that of
single-particle mechanics as opposed to field theory. The result may be taken
as support for the interpretation postulate of the spacetime-states formulation
of single-particle quantum theory.


title: The Goldberg-Sachs theorem in linearized gravity

abstract:
  The Goldberg-Sachs theorem has been very useful in constructing algebraically
special exact solutions of Einstein vacuum equation. Most of the physical
meaningful vacuum exact solutions are algebraically special. We show that the
Goldberg-Sachs theorem is not true in linearized gravity. This is a remarkable
result, which gives light on the understanding of the physical meaning of the
linearized solutions.


title: Spin foam quantization of SO(4) Plebanski's action

abstract:
  The goal of this work is two-fold. In the first part of this paper we regard
classical Plebanski's action as a BF action supplemented by constraints. We
introduce a spin foam model for Riemannian general relativity by systematically
implementing these constraints as restrictions on paths in the state-sum of the
BF theory. The spin foam model obtained is precisely the Barrett-Crane model.
This provides a clear-cut connection of the model with a simplicial action.
  In the second part of the paper we study the quantization of the effective
action corresponding to the degenerate sectors of Plebanski's theory and obtain
a very simple spin foam model. This model turns out to be precisely the one
introduced by De Pietri et al. as an alternative to the one proposed by Barrett
and Crane.


title: `Superresonance' from a rotating acoustic black hole

abstract:
  Using the analogy between a shrinking fluid vortex (`draining bathtub'),
modelled as a (2+1) dimensional fluid flow with a sink at the origin, and a
rotating (2+1) dimensional black hole with an ergosphere, it is shown that a
scalar sound wave is reflected from such a vortex with an {\it amplification}
for a specific range of frequencies of the incident wave, depending on the
angular velocity of rotation of the vortex. We discuss the possibility of
observation of this phenomenon, especially for inviscid fluids like liquid
HeII, where vortices with quantized angular momentum may occur.


title: Is there an imprint of Planck scale physics on inflationary cosmology?

abstract:
  We study the effects of the trans-Planckian dispersion relation on the
spectrum of the primordial density perturbations during inflation. In contrast
to the earlier analyses, we do not assume any specific form of the dispersion
relation and allow the initial state of the field to be arbitrary. We obtain
the spectrum of vacuum fluctuations of the quantum field by considering a
scalar field satisfying the linear wave equation with higher spatial derivative
terms propagating in the de Sitter space-time. We show that the power spectrum
does not strongly depend on the dispersion relation and that the form of the
dispersion relation does not play a significant role in obtaining the
corrections to the scale invariant spectrum. We also show that the signatures
of the deviations from the flat scale-invariant spectrum from the CMBR
observations due to quantum gravitational effects cannot be differentiated from
the standard inflationary scenario with an arbitrary initial state.


title: Reconstruction of Black Hole Metric Perturbations from Weyl Curvature

abstract:
  Perturbation theory of rotating black holes is usually described in terms of
Weyl scalars $\psi_4$ and $\psi_0$, which each satisfy Teukolsky's complex
master wave equation and respectively represent outgoing and ingoing radiation.
On the other hand metric perturbations of a Kerr hole can be described in terms
of (Hertz-like) potentials $\Psi$ in outgoing or ingoing {\it radiation
gauges}. In this paper we relate these potentials to what one actually computes
in perturbation theory, i.e $\psi_4$ and $\psi_0$. We explicitly construct
these relations in the nonrotating limit, preparatory to devising a
corresponding approach for building up the perturbed spacetime of a rotating
black hole. We discuss the application of our procedure to second order
perturbation theory and to the study of radiation reaction effects for a
particle orbiting a massive black hole.


title: Bimetric Gravitation and Cosmology in Five Dimension

abstract:
  Lee. et.al. (1976) analysed the bimetric theory with the help of
parameterized post Newtonian (PPN) formalism. They found that the post
Newtonian limit of the theory is identical with that of general theory of
relativity except for their PPN parameter $\alpha_{2}$, on the basis of
cosmological considerations. In the present paper it is pointed out that
feasibility of such considerations are doubtful in five dimensional bimetric
theory of relativity. As the universe is unique and is governed by physical
laws, many different cosmologies are possible. Examples are given for some
possible cosmological models, which are different, that those of Lee. et.al.
This work is an extension in five dimension of a similar one obtained earlier
by Rosen (1977) for four dimensional space-time.


title: Generalized Strong Curvature Singularities and Cosmic Censorship

abstract:
  A new definition of a strong curvature singularity is proposed. This
definition is motivated by the definitions given by Tipler and Krolak, but is
significantly different and more general. All causal geodesics terminating at
these new singularities, which we call generalized strong curvature
singularities, are classified into three possible types; the classification is
based on certain relations between the curvature strength of the singularities
and the causal structure in their neighborhood. A cosmic censorship theorem is
formulated and proved which shows that only one class of generalized strong
curvature singularities, corresponding to a single type of geodesics according
to our classification, can be naked. Implications of this result for the cosmic
censorship hypothesis are indicated.


title: Photon rockets and the Robinson-Trautman geometries

abstract:
  We point out the relation between the photon rocket spacetimes and the
Robinson Trautman geometries. This allows a discussion of the issues related to
the distinction between the gravitational and matter energy radiation that
appear in these metrics in a more geometrical way, taking full advantage of
their asymptotic properties at null infinity to separate the Weyl and Ricci
radiations, and to clearly establish their gravitational energy content. We
also give the exact solution for the generalized photon rockets.


title: Scale invariant gravity and the quasi-static universe

abstract:
  We highlight the fact that the lack of scale invariance in the gravitational
field equations of General Relativity results from the underlying assumption
that the appropriate scale for the gravitational force should be linked to the
atomic scale. We show that many of the problems associated with cosmology and
quantum gravity follow directly from this assumption. An alternative scale
invariant paradigm is proposed, in which the appropriate scale for General
Relativity takes the Universe as its baseline, and the gravitational force does
not have any fixed relationship to forces that apply on the atomic scale. It is
shown that this gives rise to a quasi-static universe, and that the predicted
behaviour of this model can resolve most of the problems associated with the
standard Big Bang model. The replacement of Newton's gravitational constant in
the quasi-static model by a scale-dependent re-normalisation factor is also
able to account for a number of astronomical observations that would otherwise
require ad-hoc explanations. Some of the implications of scale invariant
gravity for Planck scale physics, quantum cosmology, and the nature of time are
discussed.


title:
On future geodesic completeness for the Einstein-Vlasov system with
  hyperbolic symmetry

abstract:
  Spacetimes with collisionless matter evolving from data on a compact Cauchy
surface with hyperbolic symmetry are shown to be timelike and null geodesically
complete in the expanding direction, provided the data satisfy a certain size
restriction.


title: Traceless stress-energy and traversable wormholes

abstract:
  A one-parameter family of static and spherically symmetric solutions to
Einstein equations with a traceless energy-momentum tensor is found. When the
nonzero parameter $\beta$ lies in the open interval $(0,1)$ one obtains
traversable Lorentzian wormholes. One also obtains naked singularities when
either $\beta < 0$ or $\beta > 1$ and the Schwarzschild black hole for $\beta =
1$.


title:
Spin 1 fields in Riemann-Cartan space-times "via" Duffin-Kemmer-Petiau
  theory

abstract:
  We consider massive spin 1 fields, in Riemann-Cartan space-times, described
by Duffin-Kemmer-Petiau theory. We show that this approach induces a coupling
between the spin 1 field and the space-time torsion which breaks the usual
equivalence with the Proca theory, but that such equivalence is preserved in
the context of the Teleparallel Equivalent of General Relativity.


title:
Teukolsky Master Equation: De Rham wave equation for the gravitational
  and electromagnetic fields in vacuum

abstract:
  A new version of the Teukolksy Master Equation, describing any massless field
of different spin $s=1/2,1,3/2,2$ in the Kerr black hole, is presented here in
the form of a wave equation containing additional curvature terms. These
results suggest a relation between curvature perturbation theory in general
relativity and the exact wave equations satisfied by the Weyl and the Maxwell
tensors, known in the literature as the de Rham-Lichnerowicz Laplacian
equations. We discuss these Laplacians both in the Newman-Penrose formalism and
in the Geroch-Held-Penrose variant for an arbitrary vacuum spacetime.
Perturbative expansion of these wave equations results in a recursive scheme
valid for higher orders. This approach, apart from the obvious implications for
the gravitational and electromagnetic wave propagation on a curved spacetime,
explains and extends the results in the literature for perturbative analysis by
clarifying their true origins in the exact theory.


title: Static charged perfect fluid spheres in general relativity

abstract:
  Interior perfect fluid solutions for the Reissner-Nordstrom metric are
studied on the basis of a new classification scheme. General formulas are found
in many cases. Explicit new global solutions are given as illustrations. Known
solutions are briefly reviewed.


title:
Estimates of the total gravitation radiation in the head-on black hole
  collision

abstract:
  We report on calculations of the total gravitational energy radiated in the
head-on black hole collision, where we use the geometry of the
Robinson-Trautman metrics.


title: Quantum Geometry as a Relational Construct

abstract:
  The problem of constructing a quantum theory of gravity is considered from a
novel viewpoint. It is argued that any consistent theory of gravity should
incorporate a relational character between the matter constituents of the
theory.
  In particular, the traditional approach of quantizing a space-time metric is
criticized and two possible avenues for constructing a satisfactory theory are
put forward.


title: The Generalized Jacobi Equation

abstract:
  The Jacobi equation in pseudo-Riemannian geometry determines the linearized
geodesic flow. The linearization ignores the relative velocity of the
geodesics. The generalized Jacobi equation takes the relative velocity into
account; that is, when the geodesics are neighboring but their relative
velocity is arbitrary the corresponding geodesic deviation equation is the
generalized Jacobi equation. The Hamiltonian structure of this nonlinear
equation is analyzed in this paper. The tidal accelerations for test particles
in the field of a plane gravitational wave and the exterior field of a rotating
mass are investigated. In the latter case, the existence of an attractor of
uniform relative radial motion with speed $2^{-1/2}c\approx 0.7 c$ is pointed
out. The astrophysical implications of this result for the terminal speed of a
relativistic jet is briefly explored.


title: Graphical and Kinematical Approach to Cosmological Horizons

abstract:
  We study the apparition of event horizons in accelerated expanding
cosmologies. We give a graphical and analytical representation of the horizons
using proper distances to coordinate the events. Our analysis is mainly
kinematical. We show that, independently of the dynamical equations, all the
event horizons tend in the future infinity to a given expression depending on
the scale factor that we call asymptotic horizon. We also encounter a subclass
of accelerating models without horizon. When the ingoing null geodesics do not
change concavity in its cosmic evolution we recover the de Sitter and
quintessence-Friedmann-Robertson-Walker models.


title: Rest Frame System for Asymptotically Flat Spacetimes

abstract:
  The notion of center of mass for an isolated system has been previously
encoded in the definition of the so called nice sections. In this article we
present a generalization of the proof of existence of solutions to the
linearized equation for nice sections, and formalize a local existence proof of
nice sections relaxing the radiation condition. We report on the differentiable
and non-self-crossing properties of this family of solutions. We also give a
proof of the global existence of nice sections.


title: Vistas in numerical relativity

abstract:
  Upcoming gravitational wave-experiments promise a window for discovering new
physics in astronomy. Detection sensitivity of the broadband laser
interferometric detectors LIGO/VIRGO may be enhanced by matched filtering with
accurate wave-form templates. Where analytic methods break down, we have to
resort to numerical relativity, often in Hamiltonian or various hyperbolic
formulations. Well-posed numerical relativity requires consistency with the
elliptic constraints of energy and momentum conservation. We explore this using
a choice of gauge in the future and a dynamical gauge in the past. Applied to a
polarized Gowdy wave, this enables solving {\em all} ten vacuum Einstein
equations. Evolution of the Schwarzschild metric in 3+1 and, more generally,
sufficient conditions for well-posed numerical relativity continue to be open
challenges.


title: A note on the cylindrical collapse of counter-rotating dust

abstract:
  We find analytical solutions describing the collapse of an infinitely long
cylindrical shell of counter-rotating dust. We show that--for the classes of
solutions discussed herein--from regular initial data a curvature singularity
inevitably develops, and no apparent horizons form, thus in accord with the
spirit of the hoop conjecture.


title: Geometry and topology of singularities in spherical dust collapse

abstract:
  We derive some more results on the nature of the singularities arising in the
collapse of inhomogeneous dust spheres. (i) It is shown that there are
future-pointing radial and non-radial time-like geodesics emerging from the
singularity if and only if there are future-pointing radial null geodesics
emerging from the singularity. (ii) Limits of various space-time invariants and
other useful quantities (relating to Thorne's point-cigar-barrel-pancake
classification and to isotropy/entropy measures) are studied in the approach to
the singularity. (iii) The topology of the singularity is studied from the
point of view of ideal boundary structure. In each case, the different nature
of the visible and censored region of the singularity is emphasized.


title: On the pre-nucleosynthesis cosmological period

abstract:
  Physics, as known from our local, around--earth experience, meets some of its
applicability limits at the time just preceding the period of primeval
nucleosynthesis. Attention is focussed here on the effects of the nucleon size.
Radiation--belonging nucleons are found to produce an extremely high pressure
at kT of the order of some tens or hundreds of MeV. Quark deconfinement at
higher energies would not change the results.


title: The cosmological origin of Higgs particles

abstract:
  A proposal of the cosmological origin of Higgs particles is given. We show,
that the Higgs field could be created from the vacuum quantum conformal
fluctuation of Anti-de Sitter space-time, the spontaneous breaking of vacuum
symmetry, and the mass of Higgs particle are related to the cosmological
constant of our universe,especially the theoretical estimated mass m$_{H}$ of
Higgs particles is m$_{H}=\sqrt{-2\mu ^{2}}$ =$\sqrt{|\Lambda /\pi}$.


title: On Scaling Solutions with a Dissipative Fluid

abstract:
  We study the asymptotic behaviour of scaling solutions with a dissipative
fluid and we show that, contrary to recent claims, the existence of stable
accelerating attractor solution which solves the `energy' coincidence problem
depends crucially on the chosen equations of state for the thermodynamical
variables. We discuss two types of equations of state, one which contradicts
this claim, and one which supports it.


title: Classical black hole evaporation in Randall-Sundrum infinite braneworld

abstract:
  After the gravity induced on the brane in the Randall-Sundrum (RS) infinite
braneworld is briefly reviewed, we discuss the possibility that black holes
evaporate as a result of classical evolution in this model based on the AdS/CFT
correspondence. If this possibility is really the case, the existence of
long-lived solar mass black holes will give the strongest constraint on the
bulk curvature radius. At the same time, we can propose a new method to
simulate the evaporation of a 4D black hole due to the Hawking radiation as a
5D process.


title: A Geometric Anisotropic Model of Space-Time Based on Finsler Metric

abstract:
  In this work we study an anisotropic model of general relativity based on the
framework of Finsler geometry. The observed anisotropy of the microwave
background radiation is incorporated in the Finslerian structure of space-time.
We also examine the electromagnetic (e.m.) field equations in our space. As a
result a modified wave equation of e.m. waves yields.


title: M{\o}ller Energy-Momentum Complex for an Axially Symmetric Scalar Field

abstract:
  We calculate the energy-distribution for an axially symmetric scalar field in
the M{\o}ller prescription. The total energy is given by the parameter m of the
space-time.


title: Comparing initial-data sets for binary black holes

abstract:
  We compare the results of constructing binary black hole initial data with
three different decompositions of the constraint equations of general
relativity. For each decomposition we compute the initial data using a
superposition of two Kerr-Schild black holes to fix the freely specifiable
data. We find that these initial-data sets differ significantly, with the ADM
energy varying by as much as 5% of the total mass. We find that all
initial-data sets currently used for evolutions might contain unphysical
gravitational radiation of the order of several percent of the total mass. This
is comparable to the amount of gravitational-wave energy observed during the
evolved collision. More astrophysically realistic initial data will require
more careful choices of the freely specifiable data and boundary conditions for
both the metric and extrinsic curvature. However, we find that the choice of
extrinsic curvature affects the resulting data sets more strongly than the
choice of conformal metric.


title:
Zoom & Whirl: Eccentric equatorial orbits around spinning black holes
  and their evolution under gravitational radiation reaction

abstract:
  We study eccentric equatorial orbits of a test-body around a Kerr black hole
under the influence of gravitational radiation reaction. We have adopted a well
established two-step approach: assuming that the particle is moving along a
geodesic (justifiable as long as the orbital evolution is adiabatic) we
calculate numerically the fluxes of energy and angular momentum radiated to
infinity and to the black hole horizon, via the Teukolsky-Sasaki-Nakamura
formalism. We can then infer the rate of change of orbital energy and angular
momentum and thus the evolution of the orbit. The orbits are fully described by
a semi-latus rectum $p$ and an eccentricity $e$. We find that while, during the
inspiral, $e$ decreases until shortly before the orbit reaches the separatrix
of stable bound orbits (which is defined by $p_{s}(e)$), in many
astrophysically relevant cases the eccentricity will still be significant in
the last stages of the inspiral. In addition, when a critical value
$p_{crit}(e)$ is reached, the eccentricity begins to increase as a result of
continued radiation induced inspiral. The two values $p_{s}$, $p_{crit}$ (for
given $e$) move closer to each other, in coordinate terms, as the black hole
spin is increased, as they do also for fixed spin and increasing eccentricity.
Of particular interest are moderate and high eccentricity orbits around rapidly
spinning black holes, with $p(e) \approx p_{s}(e)$. We call these
``zoom-whirl'' orbits, because of their characteristic behaviour involving
several revolutions around the central body near periastron. Gravitational
waveforms produced by such orbits are calculated and shown to have a very
particular signature. Such signals may well prove of considerable astrophysical
importance for the future LISA detector.


title: Solution of the vacuum Kerr-Schild problem

abstract:
  The complete solution of the vacuum Kerr-Schild equations in general
relativity is presented, including the space-times with a curved background
metric. The corresponding result for a flat background has been obtained by
Kerr.


title: Kerr-Schild metrics revisited I. The ground state

abstract:
  The Kerr-Schild pencil of metrics $g_{ab}+\La l_al_b$ is investigated in the
generic case when it maps an arbitrary vacuum space-time with metric $g_{ab}$
to a vacuum space-time. The theorem is proved that this generic case, with the
field $l$ shearing, does not contain the shear-free subclass as a smooth limit.
It is shown that one of the K\'ota-Perj\'es metrics is a solution in the
shearing class.


title:
A comment on the inhomogeneous Einstein-Cartan-Kalb-Ramond fields in
  Cosmology

abstract:
  Purely time dependent solutions in four-dimensional
Einstein-Cartan-Kalb-Ramond (ECKR) theory of gravity are shown not to be
possible leading to a trivial vanishing of all Kalb-Ramond fields. This result
seems to contradict previously results obtained by SenGupta et al. (Class. and
Quantum Gravity 19(2002)677) where de Sitter spacetime solution is found as an
example of opticaly active spacetime. It seems that only inhomogeneous KR
fields are possible in four-dimensional torsioned spacetimes.


title: Kerr-Schild metrics revisited II. The complete vacuum solution

abstract:
  The complete solution of Einstein's gravitational equations with a
vacuum-vacuum Kerr-Schild pencil of metrics $g_{ab}+V l_al_b$ is obtained. Our
result generalizes the solution of the Kerr-Schild problem with a flat metric
$g_{ab}$ (represented by the Kerr theorem) to the case when $g_{ab}$ is the
metric of a curved space-time.


title: Vacuum Kerr-Schild metrics generated by nontwisting congruences

abstract:
  The Kerr-Schild pencil of metrics $\tilde g_{ab}=g_{ab}+V l_al_b$, with
$g_{ab}$ and $\tilde g_{ab}$ satisfying the vacuum Einstein equations, is
investigated in the case when the null vector $l$ has vanishing twist. This
class of Kerr-Schild metrics contains two solutions: the Kasner metric and a
metric wich can be obtained from the Kasner metric by a complex coordinate
transformation. Both are limiting cases of the K\'ota-Perj\'es metrics. The
base space-time is a pp-wave.


title:
On the Riemann Function and Irregular Singular Points for Axisymmetric
  Black Hole Collisions at the Speed of Light

abstract:
  The news function providing some relevant information about angular
distribution of gravitational radiation in axisymmetric black hole collisions
at the speed of light had been evaluated in the literature by perturbation
methods, after inverting second-order hyperbolic operators with variable
coefficients in two independent variables. More recent work has related the
appropriate Green function to the Riemann function for such a class of
hyperbolic operators in two variables. The present paper obtains an improvement
in the evaluation of the coefficients occurring in the second-order equation
obeyed by the Riemann function, which might prove useful for numerical
purposes. Eventually, we find under which conditions the original
Green-function calculation reduces to finding solutions of an inhomogeneous
second-order ordinary differential equation with a non-regular singular point.


title: Black holes from high-energy beam--beam collisions

abstract:
  Using a recent technique, proposed by Eardley and Giddings, we extend their
results to the high-energy collision of two beams of massless particles, i.e.
of two finite-front shock waves. Closed (marginally) trapped surfaces can be
determined analytically in several cases even for collisions at non-vanishing
impact parameter in D\ge 4 space-time dimensions. We are able to confirm and
extend earlier conjectures by Yurtsever, and to deal with arbitrary
axisymmetric profiles, including an amusing case of ``fractal'' beams. We
finally discuss some implications of our results in high-energy experiments and
in cosmology.


title:
Timelike and null focusing singularities in spherical symmetry: a
  solution to the cosmological horizon problem and a challenge to the cosmic
  censorship hypothesis

abstract:
  Extending the study of spherically symmetric metrics satisfying the dominant
energy condition and exhibiting singularities of power-law type initiated in
SI93, we identify two classes of peculiar interest: focusing timelike
singularity solutions with the stress-energy tensor of a radiative perfect
fluid (equation of state: $p={1\over 3} \rho$) and a set of null singularity
classes verifying identical properties. We consider two important applications
of these results: to cosmology, as regards the possibility of solving the
horizon problem with no need to resort to any inflationary scenario, and to the
Strong Cosmic Censorship Hypothesis to which we propose a class of physically
consistent counter-examples.


title:
Aspects of noncommutative Lorentzian geometry for globally hyperbolic
  spacetimes

abstract:
  Connes' functional formula of the Riemannian distance is generalized to the
Lorentzian case using the so-called Lorentzian distance, the d'Alembert
operator and the causal functions of a globally hyperbolic spacetime. As a step
of the presented machinery, a proof of the almost-everywhere smoothness of the
Lorentzian distance considered as a function of one of the two arguments is
given. Afterwards, using a $C^*$-algebra approach, the spacetime causal
structure and the Lorentzian distance are generalized into noncommutative
structures giving rise to a Lorentzian version of part of Connes'
noncommutative geometry. The generalized noncommutative spacetime consists of a
direct set of Hilbert spaces and a related class of $C^*$-algebras of
operators. In each algebra a convex cone made of self-adjoint elements is
selected which generalizes the class of causal functions. The generalized
events, called {\em loci}, are realized as the elements of the inductive limit
of the spaces of the algebraic states on the $C^*$-algebras. A partial-ordering
relation between pairs of loci generalizes the causal order relation in
spacetime. A generalized Lorentz distance of loci is defined by means of a
class of densely-defined operators which play the r\^ole of a Lorentzian
metric. Specializing back the formalism to the usual globally hyperbolic
spacetime, it is found that compactly-supported probability measures give rise
to a non-pointwise extension of the concept of events.


title:
On a possible new type of a T odd skewon field linked to
  electromagnetism

abstract:
  In the framework of generally covariant (pre-metric) electrodynamics
(``charge & flux electrodynamics''), the Maxwell equations can be formulated in
terms of the electromagnetic excitation $H=({\cal D}, {\cal H})$ and the field
strength $F=(E,B)$. If the spacetime relation linking $H$ and $F$ is assumed to
be {\em linear}, the electromagnetic properties of (vacuum) spacetime are
encoded into 36 components of the vacuum constitutive tensor density $\chi$. We
study the propagation of electromagnetic waves and find that the metric of
spacetime emerges eventually from the principal part $^{(1)}\chi$ of $\chi$ (20
independent components). In this article, we concentrate on the remaining
skewon part $^{(2)}\chi$ (15 components) and the axion part $^{(3)}\chi$ (1
component). The skewon part, as we'll show for the first time, can be
represented by a 2nd rank traceless tensor $\not S_i{}^j$. By means of the
Fresnel equation, we discuss how this tensor disturbs the light cones.
Accordingly, this is a mechanism for violating Lorentz invariance and time
symmetry. In contrast, the (abelian) axion part $^{(3)}\chi$ does {\em not}
interfere with the light cones.


title: Accelerated Charge Kerr-Schild Metrics in D-Dimensions

abstract:
  We consider the D dimensional Einstein Maxwell theory with a null fluid in
the Kerr-Schild Geometry. We obtain a complete set of differential conditions
that are necessary for finding solutions. We examine the case of vanishing
pressure and cosmological constant in detail. For this specific case, we give
the metric, the electromagnetic vector potential and the fluid energy density.
This is, in fact, the generalization of the well known Bonnor-Vaidya solution
to arbitrary D dimensions. We show that due to the acceleration of charged
sources, there is an energy flux in $D \ge 4$ dimensions and we give the
explicit form of this energy flux formula.


title: Weighing the Milky Way

abstract:
  We describe an experiment to measure the mass of the Milky Way galaxy. The
experiment is based on calculated light travel times along orthogonal
directions in the Schwarzschild metric of the Galactic center. We show that the
difference is proportional to the Galactic mass. We apply the result to light
travel times in a 10cm Michelson type interferometer located on Earth. The mass
of the Galactic center is shown to contribute 10^-6 to the flat space component
of the metric. An experiment is proposed to measure the effect.


title: The LARES mission revisited: an alternative scenario

abstract:
  A new proposal for the implementation of LARES mission is presented. In
particular, a new observable is proposed and alternative scenarios are
discussed.


title: Einstein's Equation in Pictures

abstract:
  This paper gives a self-contained, elementary, and largely pictorial
statement of Einstein's equation.


title: Linear Einstein equations and Kerr-Schild maps

abstract:
  We prove that given a solution of the Einstein equations $g_{ab}$ for the
matter field $T_{ab}$, an autoparallel null vector field $l^{a}$ and a solution
$(l_{a}l_{c}, \mathcal{T}_{ac})$ of the linearized Einstein equation on the
given background, the Kerr-Schild metric $g_{ac}+\lambda l_{a}l_{c}$ ($\lambda
$ arbitrary constant) is an exact solution of the Einstein equation for the
energy-momentum tensor $T_{ac}+\lambda \mathcal{T}_{ac}+\lambda
^{2}l_{(a}\mathcal{T}_{c)b}l^{b}$. The mixed form of the Einstein equation for
Kerr-Schild metrics with autoparallel null congruence is also linear. Some more
technical conditions hold when the null congruence is not autoparallel. These
results generalize previous theorems for vacuum due to Xanthopoulos and for
flat seed space-time due to G\"{u}rses and G\"{u}rsey.


title:
Absorbing boundary conditions for simulation of gravitational waves with
  spectral methods in spherical coordinates

abstract:
  We present a new formulation of the multipolar expansion of an exact boundary
condition for the wave equation, which is truncated at the quadrupolar order.
Using an auxiliary function, that is the solution of a wave equation on the
sphere defining the outer boundary of the numerical grid, the absorbing
boundary condition is simply written as a perturbation of the usual Sommerfeld
radiation boundary condition. It is very easily implemented using spectral
methods in spherical coordinates. Numerical tests of the method show that very
good accuracy can be achieved and that this boundary condition has the same
efficiency for dipolar and quadrupolar waves as the usual Sommerfeld boundary
condition for monopolar ones. This is of particular importance for the
simulation of gravitational waves, which have dominant quadrupolar terms, in
General Relativity.


title:
Do Scalar Tensor Cosmologies naturally explain all the current
  cosmological observations ?

abstract:
  It is shown that the general scalar tensor cosmologies may explain all the
current cosmological observations without the need of invoking any ad hoc
missing energy density. The explanation is based entirely on the internal
dynamics of the theories. Two important predictions of the present analysis
are: the universe is tending towards a matter dominated state with the
dimunition of the dark energy component and the acceleration of the universe,
if any, is slowing down with time.


title:
Remarks on the mathematical origin of wave mechanics and consequences
  for a quantum mechanics in a gravitational field

abstract:
  According to Schroedinger's ideas, classical dynamics of point particles
should correspond to the " geometrical optics " limit of a linear wave
equation, in the same way as ray optics is the limit of wave optics. It is
shown that, using notions of modern wave theory, the " geometrical optics "
analogy leads to the correspondence between a classical Hamiltonian H and a "
quantum " wave equation in a natural and general way. In particular, the
correspondence is unambiguous also in the case where H contains mixed terms
involving momentum and position. In the line of Schroedinger's ideas, it is
also attempted to justify the occurrence, in QM, of eigenvalues problems, not
merely for energy, but also for momentum. It is shown that the wave functions
of pure momentum states can be defined in a physically more satisfying way than
by assuming plane waves. In the case of a spatially uniform force field, such
momentum states have a singularity and move undeformed according to Newton's
second law. The mentioned unambiguous correspondence allows to uniquely extend
the Klein-Gordon relativistic wave equation to the case where a constant
gravitational field is present. It is argued that Schroedinger's wave mechanics
can be extended to the case with a variable gravitational field only if one
accepts that the wave equation is a preferred-frame one. From this viewpoint,
generally-covariant extensions of the wave equations of QM seem rather formal.
Finally, it is conjectured that there is no need for a quantum gravity.


title:
Light propagation in generally covariant electrodynamics and the Fresnel
  equation

abstract:
  Within the framework of generally covariant (pre-metric) electrodynamics, we
specify a local vacuum spacetime relation between the excitation $H=({\cal
D},{\cal H})$ and the field strength $F=(E,B)$. We study the propagation of
electromagnetic waves in such a spacetime by Hadamard's method and arrive, with
the constitutive tensor density $\kappa\sim\partial H/\partial F$, at a Fresnel
equation which is algebraic of 4th order in the wave covector. We determine how
the different pieces of $\kappa$, in particular the axion and the skewon
pieces, affect the propagation of light.


title: Inertial modes in slowly rotating stars : an evolutionary description

abstract:
  We present a new hydro code based on spectral methods using spherical
coordinates. The first version of this code aims at studying time evolution of
inertial modes in slowly rotating neutron stars. In this article, we introduce
the anelastic approximation, developed in atmospheric physics, using the mass
conservation equation to discard acoustic waves. We describe our algorithms and
some tests of the linear version of the code, and also some preliminary linear
results. We show, in the Newtonian framework with differentially rotating
background, as in the relativistic case with the strong Cowling approximation,
that the main part of the velocity quickly concentrates near the equator of the
star. Thus, our time evolution approach gives results analogous to those
obtained by Karino {\it et al.} \cite{karino01} within a calculation of
eigenvectors. Furthermore, in agreement with the work of Lockitch {\it et al.}
\cite{lockandf01}, we found that the velocity seems to always get a
non-vanishing polar part.


title: Scalar-tensor gravity and conformal continuations

abstract:
  Global properties of vacuum static, spherically symmetric configurations are
studied in a general class of scalar-tensor theories (STT) of gravity in
various dimensions. The conformal mapping between the Jordan and Einstein
frames is used as a tool. Necessary and sufficient conditions are found for the
existence of solutions admitting a conformal continuation (CC). The latter
means that a singularity in the Einstein-frame manifold maps to a regular
surface S_(trans) in the Jordan frame, and the solution is then continued
beyond this surface. S_(trans) can be an ordinary regular sphere or a horizon.
In the second case, S_(trans) proves to connect two epochs of a Kantowski-Sachs
type cosmology. It is shown that, in an arbitrary STT, with arbitrary potential
functions $U(\phi)$, the list of possible types of causal structures of vacuum
space-times is the same as in general relativity with a cosmological constant.
This is true even for conformally continued solutions. It is found that when
S_(trans) is an ordinary sphere, one of the generic structures appearing as a
result of CC is a traversable wormhole. Two explicit examples are presented: a
known solution illustrating the emergence of singularities and wormholes, and a
nonsingular 3-dimensional model with an infinite sequence of CCs.


title:
Advantages of modified ADM formulation: constraint propagation analysis
  of Baumgarte-Shapiro-Shibata-Nakamura system

abstract:
  Several numerical relativity groups are using a modified ADM formulation for
their simulations, which was developed by Nakamura et al (and widely cited as
Baumgarte-Shapiro-Shibata-Nakamura system). This so-called BSSN formulation is
shown to be more stable than the standard ADM formulation in many cases, and
there have been many attempts to explain why this re-formulation has such an
advantage. We try to explain the background mechanism of the BSSN equations by
using eigenvalue analysis of constraint propagation equations. This analysis
has been applied and has succeeded in explaining other systems in our series of
works. We derive the full set of the constraint propagation equations, and
study it in the flat background space-time. We carefully examine how the
replacements and adjustments in the equations change the propagation structure
of the constraints, i.e. whether violation of constraints (if it exists) will
decay or propagate away. We conclude that the better stability of the BSSN
system is obtained by their adjustments in the equations, and that the
combination of the adjustments is in a good balance, i.e. a lack of their
adjustments might fail to obtain the present stability. We further propose
other adjustments to the equations, which may offer more stable features than
the current BSSN equations.


title:
Mechanics of Continuous Media in $(\bar{L}_{n},g)$-Spaces. III. Relative
  Accelerations

abstract:
  Basic notions of continuous media mechanics are introduced for spaces with
affine connections and metrics. The physical interpretation of the notion of
relative acceleration is discussed. The notions of deformation acceleration,
shear acceleration, rotation (vortex) acceleration, and expansion acceleration
are introduced. Their corresponding notions, generated by the torsion and
curvature, are considered. A classification is proposed for auto-parallel
vector fields with different kinematic characteristics. Relations between the
kinematic characteristics of the relative acceleration and these of the
relative velocity are found. A summary of the introduced and considered notions
is given. A classification is proposed related to the kinematic characteristics
of the relative velocity and the kinematic characteristics related to the
relative acceleration. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g; 47.75.+f;
47.90.+a; 83.10.Bb


title:
Mechanics of Continuous Media in $(\bar{L}_{n},g)$-Spaces. IV. Stress
  (Tension) Tensor

abstract:
  Basic notions of continuous media mechanics are introduced for spaces with
affine connections and metrics. Stress (tension) tensors are considered,
obtained by the use of the method of Lagrangians with covariant derivatives
(MLCD). On the basis of the covariant Noether's identities for the
energy-momentum tensors, Navier-Stokes' identities are found and generalized
Navier-Cauchy as well as Navier-Stokes' equations are investigated over spaces
with affine connections and metrics. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g;
47.75.+f; 47.90.+a; 83.10.Bb


title:
Hawking Radiation of Weyl Neutrinos in a Rectilinearly Non-uniformly
  Accelerating Kinnersley Black Hole

abstract:
  Quantum thermal effect of Weyl neutrinos in a rectilinearly non-uniformly
accelerating Kinnersley black hole is investigated by using the generalized
tortoise coordinate transformation. The equation that determines the location,
the Hawking temperature of the event horizon and the thermal radiation spectrum
of neutrinos are derived. Our results show that the location and the
temperature of the event horizon depend not only on the time but also on the
angle.


title: Energy and Momentum of a Stationary Beam of Light

abstract:
  The energy-momentum complexes of Einstein, Landau-Lifshitz, Papapetrou, and
Weinberg give the same and meaningful results for the energy and momentum of
the Bonnor spacetime describing the gravitational field of a stationary beam of
light. The results support the Cooperstock hypothesis.


title: Quantum Computing Spacetime

abstract:
  A causal set C can describe a discrete spacetime, but this discrete spacetime
is not quantum, because C is endowed with Boolean logic, as it does not allow
cycles. In a quasi-ordered set Q, cycles are allowed. In this paper, we
consider a subset QC of a quasi-ordered set Q, whose elements are all the
cycles. In QC, which is endowed with quantum logic, each cycle of maximal
outdegree N in a node, is associated with N entangled qubits. Then QC describes
a quantum computing spacetime. This structure, which is non-local and
non-casual, can be understood as a proto-spacetime. Micro-causality and
locality can be restored in the subset U of Q whose elements are unentangled
qubits which we interpret as the states of quantum spacetime. The mapping of
quantum spacetime into proto-spacetime is given by the action of the XOR gate.
Moreover, a mapping is possible from the Boolean causal set into U by the
action of the Hadamard gate. In particular, the causal order defined on the
elements of U induces the causal evolution of spin networks.


title: Physical Processes in Naked Singularity Formation

abstract:
  Gravitational collapse is one of the most fruitful subjects in gravitational
physics. It is well known that singularity formation is inevitable in complete
gravitational collapse. It was conjectured that such a singularity should be
hidden by horizons if it is formed from generic initial data with physically
reasonable matter fields. Many possible counterexamples to this conjecture have
been proposed over the past three decades, although none of them has proved to
be sufficiently generic. In these examples, there appears a singularity that is
not hidden by horizons. This singularity is called a `naked singularity.' The
appearance of a naked singularity represents the formation of an observable
high-curvature, strong-gravity region. In this paper we review examples of
naked singularity formation and recent progress in research of observable
physical processes - gravitational radiation and quantum particle creation -
from a forming naked singularity.


title:
Time transfer and frequency shift to the order 1/c^4 in the field of an
  axisymmetric rotating body

abstract:
  Within the weak-field, post-Newtonian approximation of the metric theories of
gravity, we determine the one-way time transfer up to the order 1/c^4, the
unperturbed term being of order 1/c, and the frequency shift up to the order
1/c^4. We adapt the method of the world-function developed by Synge to the
Nordtvedt-Will PPN formalism. We get an integral expression for the
world-function up to the order 1/c^3 and we apply this result to the field of
an isolated, axisymmetric rotating body. We give a new procedure enabling to
calculate the influence of the mass and spin multipole moments of the body on
the time transfer and the frequency shift up to the order 1/c^4. We obtain
explicit formulas for the contributions of the mass, of the quadrupole moment
and of the intrinsic angular momentum. In the case where the only PPN
parameters different from zero are beta and gamma, we deduce from these results
the complete expression of the frequency shift up to the order 1/c^4. We
briefly discuss the influence of the quadrupole moment and of the rotation of
the Earth on the frequency shifts in the ACES mission.


title: Black Brane Entropy from Brane-Antibrane Systems

abstract:
  In the context of string theory, it is possible to explain the microscopic
origin of the entropy of certain black holes in terms of D-brane systems. To
date, most of the cases studied in detail refer to extremal (supersymmetric) or
near-extremal black holes. In this work we propose a microscopic model for
certain black branes (extended versions of black holes) which would apply to
cases arbitrarily far from extremality, including the Schwarzschild case. The
model is based on a system of D-branes and anti-D-branes, and is able to
reproduce several properties of the corresponding supergravity solution. In
particular, the microscopic entropy agrees with supergravity, except for a
factor of 2^{p/p+1}, where p is the dimension of the brane.


title:
Circular orbits of corotating binary black holes: comparison between
  analytical and numerical results

abstract:
  We compare recent numerical results, obtained within a ``helical Killing
vector'' (HKV) approach, on circular orbits of corotating binary black holes to
the analytical predictions made by the effective one body (EOB) method (which
has been recently extended to the case of spinning bodies). On the scale of the
differences between the results obtained by different numerical methods, we
find good agreement between numerical data and analytical predictions for
several invariant functions describing the dynamical properties of circular
orbits. This agreement is robust against the post-Newtonian accuracy used for
the analytical estimates, as well as under choices of resummation method for
the EOB ``effective potential'', and gets better as one uses a higher
post-Newtonian accuracy. These findings open the way to a significant
``merging'' of analytical and numerical methods, i.e. to matching an EOB-based
analytical description of the (early and late) inspiral, up to the beginning of
the plunge, to a numerical description of the plunge and merger. We illustrate
also the ``flexibility'' of the EOB approach, i.e. the possibility of
determining some ``best fit'' values for the analytical parameters by
comparison with numerical data.


title:
Superconductors as quantum transducers and antennas for gravitational
  and electromagnetic radiation

abstract:
  Superconductors will be considered as macroscopic quantum gravitational
antennas and transducers, which can directly convert upon reflection a beam of
quadrupolar electromagnetic radiation into gravitational radiation, and vice
versa, and thus serve as practical laboratory sources and receivers of
microwave and other radio-frequency gravitational waves. An estimate of the
transducer conversion efficiency on the order of unity comes out of the
Ginzburg-Landau theory for an extreme type II, dissipationless superconductor
with minimal coupling to weak gravitational and electromagnetic radiation
fields, whose frequency is smaller than the BCS gap frequency, thus satisfying
the quantum adiabatic theorem. The concept of ``the impedance of free space for
gravitational plane waves'' is introduced, and leads to a natural
impedance-matching process, in which the two kinds of radiation fields are
impedance-matched to each other around a hundred coherence lengths beneath the
surface of the superconductor. A simple, Hertz-like experiment has been
performed to test these ideas, and preliminary results will be reported. (PACS
nos.: 03.65.Ud, 04.30.Db, 04.30.Nk, 04.80.Nn, 74.60-w, 74.72.Bk)


title:
The classical wormhole solution and wormhole wavefunction with a
  nonlinear Born-Infeld scalar field

abstract:
  On this paper we consider the classical wormhole solution of the Born-Infeld
scalar field. The corresponding classical wormhole solution can be obtained
analytically for both very small and large $\dot{\phi}$. At the extreme limits
of small $\dot{\phi}$ the wormhole solution has the same format as one obtained
by Giddings and Strominger[10]. At the extreme limits of large $\dot{\phi}$ the
wormhole solution is a new one. The wormhole wavefunctions can also be obtained
for both very small and large $\dot{\phi}$. These wormhole wavefunctions are
regarded as solutions of quantum-mechanical Wheeler--Dewitt equation with
certain boundary conditions.


title:
General relativity limit of the scalar-tensor theories for traceless
  matter field

abstract:
  $\omega(\phi) \to \infty$ limit of scalar tensor theories are studied for
traceless matter source. It is shown that the limit $\omega(\phi) \to \infty$
does not reduce a scalar tensor theory to general relativity.
  An exact radiation solution of scalar tensor cosmology under Nordtvedt
conditions is obtained for flat Friedmann universe.


title:
Conservation laws in the teleparallel theory with a positive
  cosmological constant

abstract:
  We study the conservation laws in the teleparallel theory with a positive
cosmological constant, an extension of the teleparallel theory possessing
solutions with de Sitter asymptotics. Demanding that the canonical generators
of the asymptotic symmetry are well defined, we obtain their improved form,
which defines the conserved charges of the theory. The physical interpretation
of the results is discussed.


title: Wormholes, naked singularities and universes of ghost radiation

abstract:
  Both the static and homogeneous metrics describing the spherically symmetric
gravitational field of a crossflow of incoming and outgoing null dust streams
are generalized for the case of the two-component ghost radiation. Static
solutions represent either naked singularities or the wormholes recently found
by Hayward. The critical value of the parameter separating the two
possibilities is given. The wormhole is allowed to have positive mass. The
homogeneous solutions are open universes.


title: Bi-refringence versus bi-metricity

abstract:
  In this article we carefully distinguish the notion of bi-refringence (a
polarization-dependent doubling in photon propagation speeds) from that of
bi-metricity (where the two photon polarizations ``see'' two distinct metrics).
We emphasise that these notions are logically distinct, though there are
special symmetries in ordinary (3+1)-dimensional nonlinear electrodynamics
which imply the stronger condition of bi-metricity.
  To illustrate this phenomenon we investigate a generalized version of
(3+1)-dimensional nonlinear electrodynamics, which permits the inclusion of
arbitrary inhomogeneities and background fields. [For example dielectrics (a la
Gordon), conductors (a la Casimir), and gravitational fields (a la
Landau--Lifshitz).] It is easy to demonstrate that the generalized theory is
bi-refringent: In (3+1) dimensions the Fresnel equation, the relationship
between frequency and wavenumber, is always quartic. It is somewhat harder to
show that in some cases (eg, ordinary nonlinear electrodynamics) the quartic
factorizes into two quadratics thus providing a bi-metric theory. Sometimes the
quartic is a perfect square, implying a single unique effective metric. We
investigate the generality of this factorization process.


title: A cosmological constant from the QCD trace anomaly?

abstract:
  According to recent astrophysical observations the large scale mean pressure
of our present universe is negative suggesting a positive cosmological constant
like term. This article addresses the question of whether non-perturbative
effects of self-interacting quantum fields in curved space-times may yield a
significant contribution. Focusing on the trace anomaly of quantum
chromo-dynamics (QCD), a preliminary estimate of the expected order of
magnitude yields a remarkable coincidence with the empirical data, indicating
the potential relevance of this effect. PACS: 04.62.+v, 12.38.Aw, 12.38.Lg,
98.80.Es.