title: Gravity, Gauge Theories and Geometric Algebra

abstract:
  A new gauge theory of gravity is presented. The theory is constructed in a
flat background spacetime and employs gauge fields to ensure that all relations
between physical quantities are independent of the positions and orientations
of the matter fields. In this manner all properties of the background spacetime
are removed from physics, and what remains are a set of `intrinsic' relations
between physical fields. The properties of the gravitational gauge fields are
derived from both classical and quantum viewpoints. Field equations are then
derived from an action principle, and consistency with the minimal coupling
procedure selects an action that is unique up to the possible inclusion of a
cosmological constant. This in turn singles out a unique form of spin-torsion
interaction. A new method for solving the field equations is outlined and
applied to the case of a time-dependent, spherically-symmetric perfect fluid. A
gauge is found which reduces the physics to a set of essentially Newtonian
equations. These equations are then applied to the study of cosmology, and to
the formation and properties of black holes. The existence of global solutions
enables one to discuss the properties of field lines inside the horizon due to
a point charge held outside it. The Dirac equation is studied in a black hole
background and provides a quick derivation of the Hawking temperature.


title: Non-asymptotically flat, non-AdS dilaton black holes

abstract:
  We show that previously known non-asymptotically flat static black hole
solutions of Einstein-Maxwell-dilaton theory may be obtained as near-horizon
limits of asymptotically flat black holes. Specializing to the case of the
dilaton coupling constant $\alpha^2 = 3$, we generate from the
non-asymptotically flat magnetostatic or electrostatic black holes two classes
of rotating dyonic black hole solutions. The rotating dyonic black holes of the
``magnetic'' class are dimensional reductions of the five-dimensional
Myers-Perry black holes relative to one of the azimuthal angles, while those of
the ``electric'' class are twisted dimensional reductions of rotating dyonic
Rasheed black strings. We compute the quasi-local mass and angular momentum of
our rotating dyonic black holes, and show that they satisfy the first law of
black hole thermodynamics, as well as a generalized Smarr formula. We also
discuss the construction of non-asymptotically flat multi-extreme black hole
configurations.


title: The Work of Behram Kursunoglu

abstract:
  Talk presented at the 2003 Coral Gables conference in honor and appreciation
of the work of Professor Behram Kursunoglu, general relativist extraordinaire
and founder of the Coral Gables series of conferences, whose untimely death
occurred shortly before the 2003 conference.


title:
Incorporating information from source simulations into searches for
  gravitational-wave bursts

abstract:
  The detection of gravitational waves from astrophysical sources of
gravitational waves is a realistic goal for the current generation of
interferometric gravitational-wave detectors. Short duration bursts of
gravitational waves from core-collapse supernovae or mergers of binary black
holes may bring a wealth of astronomical and astrophysical information. The
weakness of the waves and the rarity of the events urges the development of
optimal methods to detect the waves. The waves from these sources are not
generally known well enough to use matched filtering however; this drives the
need to develop new ways to exploit source simulation information in both
detections and information extraction. We present an algorithmic approach to
using catalogs of gravitational-wave signals developed through numerical
simulation, or otherwise, to enhance our ability to detect these waves. As more
detailed simulations become available, it is straightforward to incorporate the
new information into the search method. This approach may also be useful when
trying to extract information from a gravitational-wave observation by allowing
direct comparison between the observation and simulations.


title: Optics in the Schwarzschild space-time

abstract:
  Realistic modelling of radiation transfer in and from variable accretion
disks around black holes requires the solution of the problem: find the
constants of motion and equation of motion of a light-like geodesic connecting
two arbitrary points in space. Here we give the complete solution of this
problem in the Schwarzschild space-time.


title: SO(1,1) dark energy model and the universe transition

abstract:
  We suggest a scalar model of dark energy with the SO(1,1) symmetry. The model
may be reformulated in terms of a real scalar field $\Phi$ and the scale factor
$a$ so that the Lagrangian may be decomposed as that of the real quintessence
model plus the negative coupling energy term of $\Phi$ to $a$. The existence of
the coupling term $L^c$ leads to a wider range of $w_{\Phi}$ and overcomes the
problem of negative kinetic energy in the phantom universe model. We propose a
power-law expansion model of univese with time-dependent power, which can
describe the phantom universe and the universe transition from ordinary
acceleration to super acceleration.


title:
Local existence and continuation criteria for solutions of the
  Einstein-Vlasov-scalar field system with surface symmetry

abstract:
  We prove in the cases of spherical, plane and hyperbolic symmetry a local in
time existence theorem and continuation criteria for cosmological solutions of
the Einstein-Vlasov-scalar field system, with the sources generated by a
distribution function and a scalar field, subject to the Vlasov and wave
equations respectively. This system describes the evolution of self-gravitating
collisionless matter and scalar waves within the context of general relativity.
In the case where the only source is a scalar field it is shown that a global
existence result can be deduced from the general theorem.


title: Binding energy of static perfect fluids

abstract: Corrected misprints and omissions.


title:
The role of anisotropy and inhomogeneity in Lemaitre-Tolman-Bondi
  collapse

abstract:
  We study the effects of shear and density inhomogeneities in the formation of
naked singularities in spherically symmetric dust space--times. We find that in
general neither of these physical features alone uniquely specifies the end
state of the gravitational collapse. We do this by (i) showing that, for open
sets of initial data, the same initial shear (or initial density contrast) can
give rise to both naked and covered solutions. In particular this can happen
for zero initial shear or zero initial density contrast; (ii) demonstrating
that both shear and density contrast are invariant under a one parameter set of
linear transformations acting on the initial data set and (iii) showing that
asymptotically (near the singularities) one cannot in general establish a
direct relationship between the rate of change of shear (or density contrast)
and the nature of the singularities. However, one can uniquely determine the
nature of the singularity if both the initial shear and initial density
contrast are known.
  These results are important in understanding the effects of the initial
physical state and in particular the role of shear, in determiming the end
state of the gravitational collapse.


title: Perspectives in Fundamental Physics in Space

abstract:
  We discuss the fundamental principles underlying the current physical
theories and the prospects of further improving their knowledge through
experiments in space.


title:
Generalisations of the Einstein-Straus model to cylindrically symmetric
  settings

abstract:
  We study generalisations of the Einstein--Straus model in cylindrically
symmetric settings by considering the matching of a static space-time to a
non-static spatially homogeneous space-time, preserving the symmetry. We find
that such models possess severe restrictions, such as constancy of one of the
metric coefficients in the non-static part. A consequence of this is that it is
impossible to embed static locally cylindrically symmetric objects in
reasonable spatially homogeneous cosmologies.


title: Upper limits on gravitational-wave signals based on loudest events

abstract:
  Searches for gravitational-wave bursts have often focused on the loudest
event(s) in searching for detections and in determining upper limits on
astrophysical populations. Typical upper limits have been reported on event
rates and event amplitudes which can then be translated into constraints on
astrophysical populations. We describe the mathematical construction of such
upper limits.


title:
A chi-squared time-frequency discriminator for gravitational wave
  detection

abstract:
  Searches for known waveforms in gravitational wave detector data are often
done using matched filtering. When used on real instrumental data, matched
filtering often does not perform as well as might be expected, because
non-stationary and non-Gaussian detector noise produces large spurious filter
outputs (events). This paper describes a chi-squared time-frequency test which
is one way to discriminate such spurious events from the events that would be
produced by genuine signals. The method works well only for broad-band signals.
The case where the filter template does not exactly match the signal waveform
is also considered, and upper bounds are found for the expected value of
chi-squared.


title:
On the physical interpretation of singularities in Lanczos-Newman
  electrodynamics

abstract:
  We discuss the physical nature of elementary singularities arising in the
complexified Maxwell field extended into complex spacetime, i.e., in
Lanczos-Newman electrodynamics, which may provide a possible link between
elementary particle physics and general relativity theory. We show that the
translation of the world-line of a bare (e.g., spinless) electric-monopole
singularity into imaginary space is adding a magnetic-dimonopole component to
it, so that it can be interpreted as a pseudoscalar pion-proton interaction
current, consistent which both charge-independent meson theory and zero-order
quantum chromodynamics. On the other hand, the interaction current of an
electric-monopole intrinsic-magnetic-dipole singularity characteristic of a
Dirac electron is obtained by another operation on the world-line, which
however does not seem to have a simple geometric interpretation. Nevertheless,
both operations can be given a covariant interpretation, which shows that the
corresponding interactions necessarily arise on an equal footing, and therefore
provides a connection between elementary particles and singularities in general
relativity.


title: On the possible sources of gravitational wave bursts detectable today

abstract:
  We discuss the possibility that galactic gravitational wave sources might
give burst signals at a rate of several events per year, detectable by
state-of-the-art detectors. We are stimulated by the results of the data
collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which
suggest an excess of coincidences between the two detectors, when the resonant
bars are orthogonal to the galactic plane. Signals due to the coalescence of
galactic compact binaries fulfill the energy requirements but are problematic
for lack of known candidates with the necessary merging rate. We examine the
limits imposed by galactic dynamics on the mass loss of the Galaxy due to GW
emission, and we use them to put constraints also on the GW radiation from
exotic objects, like binaries made of primordial black holes. We discuss the
possibility that the events are due to GW bursts coming repeatedly from a
single or a few compact sources. We examine different possible realizations of
this idea, such as accreting neutron stars, strange quark stars, and the highly
magnetized neutron stars (``magnetars'') introduced to explain Soft Gamma
Repeaters. Various possibilities are excluded or appear very unlikely, while
others at present cannot be excluded.


title:
Equilibrium velocity distribution of low-energy particles in spherically
  symmetric gravitational field

abstract:
  Based on Einstein's theory of gravitation, we discuss the influence of a
spherically symmetric gravitational field on Maxwell's law of velocity
distribution. We derive the equilibrium velocity distribution of low-energy
particles in the spherically symmetric gravitational field and calculate the
escape rate of low-energy particles in a container with a leak placed in the
spherically symmetric gravitational field. They can serve as the tests of
Einstein's theory of gravitation.


title: Cosmic Censorship in Higher Dimensions

abstract:
  We show that the naked singularities arising in dust collapse from smooth
initial data (which include those discovered by Eardley and Smarr,
Christodoulou, and Newman) are removed when we make transition to higher
dimensional spacetimes. The cosmic censorship is then restored for dust
collapse which will always produce a black hole as the collapse end state for
dimensions $D\ge6$, under conditions to be motivated physically such as the
smoothness of initial data from which the collapse develops.


title: Update on Cosmic Censorship Violation in AdS

abstract:
  We reexamine our proposed counterexample (gr-qc/0307102) to cosmic censorship
in anti de Sitter (AdS) space, and find a gap in the construction. We mention
some possible ways to close the gap, but at present the question of whether
cosmic censorship is violated in AdS remains open.


title:
On Traversable Lorentzian Wormholes in the Vacuum Low Energy Effective
  String Theory in Einstein and Jordan Frames

abstract:
  Three new classes (II-IV) of solutions of the vacuum low energy effective
string theory in four dimensions are derived. Wormhole solutions are
investigated in those solutions including the class I case both in the Einstein
and in the Jordan (string) frame. It turns out that, of the eight classes of
solutions investigated (four in the Einstein frame and four in the
corresponding string frame), massive Lorentzian traversable wormholes exist in
five classes. Nontrivial massless limit exists only in class I Einstein frame
solution while none at all exists in the string frame. An investigation of test
scalar charge motion in the class I solution in the two frames is carried out
by using the Plebanski-Sawicki theorem. A curious consequence is that the
motion around the extremal zero (Keplerian) mass configuration leads, as a
result of scalar-scalar interaction, to a new hypothetical "mass" that confines
test scalar charges in bound orbits, but does not interact with neutral test
particles.


title: Static, spherically symmetric solutions of Yang-Mills-Dilaton theory

abstract:
  Static, spherically symmetric solutions of the Yang-Mills-Dilaton theory are
studied. It is shown that these solutions fall into three different classes.
The generic solutions are singular. Besides there is a discrete set of globally
regular solutions further distinguished by the number of nodes of their
Yang-Mills potential. The third class consists of oscillating solutions playing
the role of limits of regular solutions, when the number of nodes tends to
infinity. We show that all three sets of solutions are non-empty. Furthermore
we give asymptotic formulae for the parameters of regular solutions and
confront them with numerical results.


title:
New ways in testing post-Newtonian gravity in the Solar System scenario
  from planetary motion analysis

abstract:
  Here we explore the possibility of extending to the Solar System scenario the
combined residual approach employed for the deterination of the Lense-Thirring
effect in the Earth-LAGEOS satellites system. After calculating the secular
gravitoelectric advance of the mean anomaly, we propose several linear
combinations of the residuals of the nodes, the perihelia and the mean
anomalies of some inner planets in order to measure the gravitoelectric
advance, the Lense-Thirring effect and the solar quadrupole mass moment. The
obtainable accuracies are comparable to those of new complex and expensive
missions involving the launch of one or more spacecrafts. They are 10^-4 for
the PPN parameter beta, 10^-5 for gamma, 10^-9 for the solar J2, 20-30% for the
Lense-Thirring effect. In the case of the solar gravitomagnetic field, it would
be the first attempt to measure its effect on the planetary motions. However,
the improvements in the ephemerides of Mercury thanks to the Messenger and
BepiColombo missions will map into an increasing accuracy of the proposed
tests.


title:
Interpretation of the first order formalism of f(R)-type gravity and the
  corresponding second order formalism

abstract:
  f(R)-type gravity in the first order formalism is interpreted as Einstein
gravity with non-minimal coupling arising from the use of unphysical frame.
Identification of the corresponding second order higher-curvature gravity in
the physical frame is proposed by requiring that the action is the same.


title: Triality between Inflation, Cyclic and Phantom Cosmologies

abstract:
  It is shown that any spatially flat and isotropic universe undergoing
accelerated expansion driven by a self-interacting scalar field can be directly
related to a contracting, decelerating cosmology. The duality is made manifest
by expressing the scale factor and Hubble parameter as functions of the scalar
field and simultaneously interchanging these two quantities. The decelerating
universe can be twinned with a cosmology sourced by a phantom scalar field by
inverting the scale factor and leaving the Hubble parameter invariant. The
accelerating model can be related to the same phantom universe by identifying
the scale factor with the inverse of the Hubble parameter. The duality between
accelerating and decelerating backgrounds can be extended to spatially curved
cosmologies and models containing perfect fluids. A similar triality and
associated scale factor duality is found in the Randall-Sundrum type II
braneworld scenario.


title:
Topological classification of black Hole: Generic Maxwell set and crease
  set of horizon

abstract:
  The crease set of an event horizon or a Cauchy horizon is an important object
which determines qualitative properties of the horizon. In particular, it
determines the possible topologies of the spatial sections of the horizon. By
Fermat's principle in geometric optics, we relate the crease set and the
Maxwell set of a smooth function in the context of singularity theory. We
thereby give a classification of generic topological structure of the Maxwell
sets and the generic topologies of the spatial section of the horizon.


title: Local covariant quantum field theory over spectral geometries

abstract:
  A framework which combines ideas from Connes' noncommutative geometry, or
spectral geometry, with recent ideas on generally covariant quantum field
theory, is proposed in the present work. A certain type of spectral geometries
modelling (possibly noncommutative) globally hyperbolic spacetimes is
introduced in terms of so-called globally hyperbolic spectral triples. The
concept is further generalized to a category of globally hyperbolic spectral
geometries whose morphisms describe the generalization of isometric embeddings.
Then a local generally covariant quantum field theory is introduced as a
covariant functor between such a category of globally hyperbolic spectral
geometries and the category of involutive algebras (or *-algebras). Thus, a
local covariant quantum field theory over spectral geometries assigns quantum
fields not just to a single noncommutative geometry (or noncommutative
spacetime), but simultaneously to ``all'' spectral geometries, while respecting
the covariance principle demanding that quantum field theories over isomorphic
spectral geometries should also be isomorphic. It is suggested that in a
quantum theory of gravity a particular class of globally hyperbolic spectral
geometries is selected through a dynamical coupling of geometry and matter
compatible with the covariance principle.


title: Spin and energy evolution equations for a wide class of extended bodies

abstract:
  We give a surface integral derivation of the leading-order evolution
equations for the spin and energy of a relativistic body interacting with other
bodies in the post-Newtonian expansion scheme. The bodies can be arbitrarily
shaped and can be strongly self-gravitating. The effects of all mass and
current multipoles are taken into account. As part of the computation one of
the 2PN potentials parametrizing the metric is obtained. The formulae obtained
here for spin and energy evolution coincide with those obtained by Damour,
Soffel and Xu for the case of weakly self-gravitating bodies. By combining an
Einstein-Infeld-Hoffman-type surface integral approach with multipolar
expansions we extend the domain of validity of these evolution equations to a
wide class of strongly self-gravitating bodies. This paper completes in a
self-contained way a previous work by Racine and Flanagan on translational
equations of motion for compact objects.


title:
Comment on "Spherically symmetric perfect fluid in area-radial
  coordinates" by Iguchi et al

abstract:
  In this short note we comment about some criticisms - appeared in a recent
paper by Iguchi et al - to our previous works on gravitational collapse of
perfect fluids. We show that those criticisms are incorrect on their own.


title:
Simplification of the Spectral Analysis of the Volume Operator in Loop
  Quantum Gravity

abstract:
  The Volume Operator plays a crucial role in the definition of the quantum
dynamics of Loop Quantum Gravity (LQG). Efficient calculations for dynamical
problems of LQG can therefore be performed only if one has sufficient control
over the volume spectrum. While closed formulas for the matrix elements are
currently available in the literature, these are complicated polynomials in 6j
symbols which in turn are given in terms of Racah's formula which is too
complicated in order to perform even numerical calculations for the
semiclassically important regime of large spins. Hence, so far not even
numerically the spectrum could be accessed. In this article we demonstrate that
by means of the Elliot -- Biedenharn identity one can get rid of all the 6j
symbols for any valence of the gauge invariant vertex, thus immensely reducing
the computational effort. We use the resulting compact formula to study
numerically the spectrum of the gauge invariant 4 -- vertex. The techniques
derived in this paper could be of use also for the analysis of spin -- spin
interaction Hamiltonians of many -- particle problems in atomic and nuclear
physics.

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


title: ICGC-2004 Conference Overview

abstract:
  This is a written, expanded version of the summary talk given at the
conclusion of the ICGC-2004 held at Cochin. Brief introductory remarks are
included to provide a slightly wider context to the theme talks.


title: Non-Riemannian geometry of vortex acoustics

abstract:
  The concept of acoustic metric introduced previously by Unruh (PRL-1981) is
extended to include Cartan torsion by analogy with the scalar wave equation in
Riemann-Cartan (RC) spacetime. This equation describes irrotational
perturbations in rotational non-relativistic fluids. This physical motivation
allows us to show that the acoustic line element can be conformally mapped to
the line element of a stationary torsion loop in non-Riemannian gravity. Two
examples of such sonic analogues are given. The first is when we choose the
static torsion loop in teleparallel gravity. In this case Cartan torsion vector
in the far from the vortex approximation is shown to be proportional to the
quantum vortex number of the superfluid. Also in this case the torsion vector
is shown to be proportional to the superfluid vorticity in the presence of
vortices. Torsion loops in RC spacetime does not favor the formation of
superfluid vortices. It is suggested that the teleparallel model may help to
find a model for superfluid neutron stars vortices based on non-Riemannian
gravity.


title: Non-adiabatic oscillations of compact stars in general relativity

abstract:
  We have developed a formalism to study non-adiabatic, non-radial oscillations
of non-rotating compact stars in the frequency domain, including the effects of
thermal diffusion in the framework of general relativistic perturbation theory.
When a general equation of state depending on temperature is used, the
perturbations of the fluid result in heat flux which is coupled with the
spacetime geometry through the Einstein field equations. Our results show that
the frequency of the first pressure (p) and gravity (g) oscillation modes is
significantly affected by thermal diffusion, while that of the fundamental (f)
mode is basically unaltered due to the global nature of that oscillation. The
damping time of the oscillations is generally much smaller than in the
adiabatic case (more than two orders of magnitude for the p- and g-modes)
reflecting the effect of thermal dissipation. Both the isothermal and adiabatic
limits are recovered in our treatment and we study in more detail the
intermediate regime. Our formalism finds its natural astrophysical application
in the study of the oscillation properties of newly born neutron stars, neutron
stars with a deconfined quark core phase, or strange stars which are all
promising sources of gravitational waves with frequencies in the band of the
first generation and advanced ground-based interferometric detectors.


title: The Electrostatics of Einstein's Unified Field Theory

abstract:
  When sources are added at their right-hand sides, and g_{(ik)} is a priori
assumed to be the metric, the equations of Einstein's Hermitian theory of
relativity were shown to allow for an exact solution that describes the general
electrostatic field of n point charges. Moreover, the injunction of spherical
symmetry of g_{(ik)} in the infinitesimal neighbourhood of each of the charges
was proved to yield the equilibrium conditions of the n charges in keeping with
ordinary electrostatics. The tensor g_{(ik)}, however, cannot be the metric of
the theory, since it enters neither the eikonal equation nor the equation of
motion of uncharged test particles. A physically correct metric that rules both
the behaviour of wave fronts and of uncharged matter is the one indicated by
H\'ely. In the present paper it is shown how the electrostatic solution
predicts the structure of the n charged particles and their mutual positions of
electrostatic equilibrium when H\'ely's physically correct metric is adopted.


title: Static Cylindrical Matter Shells

abstract:
  Static cylindrical shells composed of massive particles arising from matching
of two different Levi-Civita space-times are studied for the shell satisfying
either isotropic or anisotropic equation of state. We find that these solutions
satisfy the energy conditions for certain ranges of the parameters.


title: A supersymmetric D-brane Model of Space-Time Foam

abstract:
  We present a supersymmetric model of space-time foam with two stacks of eight
D8-branes with equal string tensions, separated by a single bulk dimension
containing D0-brane particles that represent quantum fluctuations in the
space-time foam. The ground state configuration with static D-branes has zero
vacuum energy. However, gravitons and other closed-string states propagating
through the bulk may interact with the D0-particles, causing them to recoil and
the vacuum energy to become non zero. This provides a possible origin of dark
energy. Recoil also distorts the background metric felt by energetic massless
string states, which travel at less than the usual (low-energy) velocity of
light. On the other hand, the propagation of chiral matter anchored on the D8
branes is not affected by such space-time foam effects.


title: Gravitational Wave Memory of Gamma-Ray Burst Jets

abstract:
  Gamma-Ray Bursts (GRBs) are now considered as relativistic jets. We analyze
the gravitational waves from the acceleration stage of the GRB jets. We show
that (i) the point mass approximation is not appropriate if the opening
half-angle of the jet is larger than the inverse of the Lorentz factor of the
jet, (ii) the gravitational waveform has many step function like jumps, and
  (iii) the practical DECIGO and BBO may detect such an event if the GRBs occur
in Local group of galaxy. We found that the light curve of GRBs and the
gravitational waveform are anti-correlated so that the detection of the
gravitational wave is indispensable to determine the structure of GRB jets.


title:
An astronomical search for evidence of new physics: Limits on
  gravity-induced birefringence from the magnetic white dwarf RE J0317-853

abstract:
  The coupling of the electromagnetic field directly with gravitational gauge
fields leads to new physical effects that can be tested using astronomical
data. Here we consider a particular case for closer scrutiny, a specific
nonminimal coupling of torsion to electromagnetism, which enters into a
metric-affine geometry of space-time. We show that under the assumption of this
nonminimal coupling, spacetime is birefringent in the presence of such a
gravitational field. This leads to the depolarization of light emitted from
extended astrophysical sources. We use polarimetric data of the magnetic white
dwarf ${RE J0317-853}$ to set strong constraints on the essential coupling
constant for this effect, giving $k^2 \lsim (19 {m})^2 $.


title:
Pure States, Mixed States and Hawking Problem in Generalized Quantum
  Mechanics

abstract:
  This paper is the continuation of a study into the information paradox
problem started by the author in his earlier works. As previously, the key
instrument is a deformed density matrix in quantum mechanics of the early
universe. It is assumed that the latter represents quantum mechanics with
fundamental length. It is demonstrated that the obtained results agree well
with the canonical viewpoint that in the processes involving black holes pure
states go to the mixed ones in the assumption that all measurements are
performed by the observer in a well-known quantum mechanics. Also it is shown
that high entropy for Planck remnants of black holes appearing in the
assumption of the Generalized Uncertainty Relations may be explained within the
scope of the density matrix entropy introduced by the author previously. It is
noted that the suggested paradigm is consistent with the Holographic Principle.
Because of this, a conjecture is made about the possibility for obtaining the
Generalized Uncertainty Relations from the covariant entropy bound at high
energies in the same way as R. Bousso has derived Heisenberg uncertainty
principle for the flat space.


title: Making h(t) for LIGO

abstract:
  The conversion of the read-out from the anti-symmetric port of the LIGO
interferometers into gravitational strain has thus far been performed in the
frequency domain. Here we describe a conversion in the time domain which is
based on the method developed by GEO. We illustrate the method using the
Hanford 4km interferometer during the second LIGO science run (S2).


title: Coordinate Independence and a Physical Metric in Compact Form

abstract:
  A physical metric is constructed as one that gives a coordinate independent
result for the time delay in infinite order in the perturbation expansion in
the gravitational constant. A compact form for the metric is obtained. One
result is that the metric functions are positive definite. Another is an exact
expression for the gravitational red shift. The metric can be used to calculate
general relativity predictions in higher order for any process. A relationship
between the spacetimes of the physical metric and the Schwarzschild metric is
discussed.


title: Entropy of Horizons, Complex Paths and Quantum Tunneling

abstract:
  In any spacetime, it is possible to have a family of observers following a
congruence of timelike curves such that they do not have access to part of the
spacetime. This lack of information suggests associating a (congruence
dependent) notion of entropy with the horizon that blocks the information from
these observers. While the blockage of information is absolute in classical
physics, quantum mechanics will allow tunneling across the horizon. This
process can be analysed in a simple, yet general, manner and we show that the
probability for a system with energy $E$ to tunnel across the horizon is
$P(E)\propto\exp[-(2\pi/\kappa)E)$ where $\kappa$ is the surface gravity of the
horizon. If the surface gravity changes due to the leakage of energy through
the horizon, then one can associate an entropy $S(M)$ with the horizon where
$dS = [ 2\pi / \kappa (M) ] dM$ and $M$ is the active gravitational mass of the
system. Using this result, we discuss the conditions under which, a small patch
of area $\Delta A$ of the horizon contributes an entropy $(\Delta A/4L_P^2)$,
where $L_P^2$ is the Planck area.


title: Local approach to thermodynamics of black holes

abstract:
  Hamiltonian description of gravitational field contained in a spacetime
region with boundary $S$ being a null-like hypersurface (a wave front) is
discussed. Complete generating formula for the Hamiltonian dynamics (with no
surface integrals neglected) is presented. A quasi-local proof of the 1-st law
of black holes thermodynamics is obtained as a consequence, in case when $S$ is
a non-expanding horizon. The 0-th law and Penrose inequalities are discussed
from this point of view.


title: Quasistationary collapse to the extreme Kerr black hole

abstract:
  It is shown that the extreme Kerr black hole is the only candidate for a
black hole limit of rotating fluid bodies in equilibrium.


title:
Asymptotic Analysis of Field Commutators for Einstein-Rosen
  Gravitational Waves

abstract:
  We give a detailed study of the asymptotic behavior of field commutators for
linearly polarized, cylindrically symmetric gravitational waves in different
physically relevant regimes. We also discuss the necessary mathematical tools
to carry out our analysis. Field commutators are used here to analyze
microcausality, in particular the smearing of light cones owing to quantum
effects. We discuss in detail several issues related to the semiclassical limit
of quantum gravity, in the simplified setting of the cylindrical symmetry
reduction considered here. We show, for example, that the small G behavior is
not uniform in the sense that its functional form depends on the causal
relationship between spacetime points. We consider several physical issues
relevant for this type of models such as the emergence of large gravitational
effects.


title:
Modified Gravitational Theory and the Pioneer 10 and 11 Spacecraft
  Anomalous Acceleration

abstract:
  The nonsymmetric gravitational theory leads to a modified acceleration law
that can at intermediate distance ranges account for the anomalous acceleration
experienced by the Pioneer 10 and 11 spacecraft.


title:
Black Hole-Neutron Star Binaries in General Relativity: Quasiequilibrium
  Formulation

abstract:
  We present a new numerical method for the construction of quasiequilibrium
models of black hole-neutron star binaries. We solve the constraint equations
of general relativity, decomposed in the conformal thin-sandwich formalism,
together with the Euler equation for the neutron star matter. We take the
system to be stationary in a corotating frame and thereby assume the presence
of a helical Killing vector. We solve these coupled equations in the background
metric of a Kerr-Schild black hole, which accounts for the neutron star's black
hole companion. In this paper we adopt a polytropic equation of state for the
neutron star matter and assume large black hole--to--neutron star mass ratios.
These simplifications allow us to focus on the construction of quasiequilibrium
neutron star models in the presence of strong-field, black hole companions. We
summarize the results of several code tests, compare with Newtonian models, and
locate the onset of tidal disruption in a fully relativistic framework.


title: Quantum Foam and Quantum Gravity Phenomenology

abstract:
  Spacetime undergoes quantum fluctuations, giving rise to spacetime foam,
a.k.a. quantum foam. We discuss some properties of spacetime foam, and point
out the conceptual interconnections in the physics of quantum foam, black
holes, and quantum computation. We also discuss the phenomenology of quantum
foam, and conclude that it may be difficult, but by no means impossible, to
detect its tiny effects in the not-too-distant future.


title:
Kaluza-Klein gravity in the context of modern embedding theories of
  spacetime

abstract:
  We review and discuss the original Kaluza-Klein theory in the framework of
modern embedding theories of the spacetime, such as the recent induced matter
approach. We show that in spite of their seeming similarity they constitute
rather distinct proposals as far as their geometrical structure is concerned.


title:
Constraint preserving boundary conditions for the linearized BSSN
  formulation

abstract:
  We derive two sets of explicit algebraic constraint preserving boundary
conditions for the linearized BSSN system. The approach can be generalized to
inhomogeneous differential and evolution conditions, the examples of which are
given. The proposed conditions are justified by an energy estimate on the
original BSSN variables.


title:
Dynamical generation of space-time signature by spontaneous symmetry
  breaking

abstract:
  The problem of dynamical generation of 4-D space-time signature at small
scales and its stabilization towards Lorentzian signature at large scales is
studied in the context of Higgs mechanism in a two-time scenario. It is also
shown that Lorentz invariance at small scales can be violated but at large
space-time scales is restored.


title:
Quantum Field Theory Is Not Merely Quantum Mechanics Applied to Low
  Energy Effective Degrees of Freedom

abstract:
  It is commonly assumed that quantum field theory arises by applying ordinary
quantum mechanics to the low energy effective degrees of freedom of a more
fundamental theory defined at ultra-high-energy/short-wavelength scales. We
shall argue here that, even for free quantum fields, there are holistic aspects
of quantum field theory that cannot be properly understood in this manner.
Specifically, the ``subtractions'' needed to define nonlinear polynomial
functions of a free quantum field in curved spacetime are quite simple and
natural from the quantum field theoretic point of view, but are at best
extremely ad hoc and unnatural if viewed as independent renormalizations of
individual modes of the field. We illustrate this point by contrasting the
analysis of the Casimir effect, the renormalization of the stress-energy tensor
in time-dependent spacetimes, and anomalies from the point of quantum field
theory and from the point of view of quantum mechanics applied to the
independent low energy modes of the field. Some implications for the
cosmological constant problem are discussed.


title: Towards a future singularity?

abstract:
  We discuss whether the future extrapolation of the present cosmological state
may lead to a singularity even in case of "conventional" (negative) pressure of
the dark energy field, namely $w=p/\rho \geq -1$. The discussion is based on an
often neglected aspect of scalar-tensor models of gravity: the fact that
different test particles may follow the geodesics of different metric frames,
and the need for a frame-independent regularization of curvature singularities.


title:
Severe constraints on Loop-Quantum-Gravity energy-momentum dispersion
  relation from black-hole area-entropy law

abstract:
  We explore a possible connection between two aspects of Loop Quantum Gravity
which have been extensively studied in the recent literature: the black-hole
area-entropy law and the energy-momentum dispersion relation. We observe that
the original Bekenstein argument for the area-entropy law implicitly requires
information on the energy-momentum dispersion relation. Recent results show
that in first approximation black-hole entropy in Loop Quantum Gravity depends
linearly on the area, with small correction terms which have logarithmic or
inverse-power dependence on the area. Preliminary studies of the
Loop-Quantum-Gravity dispersion relation reported some evidence of the presence
of terms that depend linearly on the Planck length, but we observe that this
possibility is excluded since it would require, for consistency, a contribution
to black-hole entropy going like the square root of the area.


title: About Lorentz invariance in a discrete quantum setting

abstract:
  A common misconception is that Lorentz invariance is inconsistent with a
discrete spacetime structure and a minimal length: under Lorentz contraction, a
Planck length ruler would be seen as smaller by a boosted observer. We argue
that in the context of quantum gravity, the distance between two points becomes
an operator and show through a toy model, inspired by Loop Quantum Gravity,
that the notion of a quantum of geometry and of discrete spectra of geometric
operators, is not inconsistent with Lorentz invariance. The main feature of the
model is that a state of definite length for a given observer turns into a
superposition of eigenstates of the length operator when seen by a boosted
observer. More generally, we discuss the issue of actually measuring distances
taking into account the limitations imposed by quantum gravity considerations
and we analyze the notion of distance and the phenomenon of Lorentz contraction
in the framework of ``deformed (or doubly) special relativity'' (DSR), which
tentatively provides an effective description of quantum gravity around a flat
background. In order to do this we study the Hilbert space structure of DSR,
and study various quantum geometric operators acting on it and analyze their
spectral properties. We also discuss the notion of spacetime point in DSR in
terms of coherent states. We show how the way Lorentz invariance is preserved
in this context is analogous to that in the toy model.


title: Gravitational waves in magnetized relativistic plasmas

abstract:
  We study the propagation of gravitational waves (GW) in a uniformly
magnetized plasma at arbitrary angles to the magnetic field. No a priori
assumptions are made about the temperature, and we consider both a plasma at
rest and a plasma flowing out at ultra-relativistic velocities. In the 3+1
orthonormal tetrad description, we find that all three fundamental
low-frequency plasma wave modes are excited by the GW. Alfven waves are excited
by a x polarized GW, whereas the slow and fast magneto-acoustic modes couple to
the + polarization. The slow mode, however, doesn't interact coherently with
the GW. The most relevant wave mode is the fast magneto-acoustic mode which in
a strongly magnetized plasma has a vanishingly small phase lag with respect to
the GW allowing for coherent interaction over large length scales. When the
background magnetic field is almost, but not entirely, parallel to the GW's
direction of propagation even the Alfven waves grow to first order in the GW
amplitude. Finally, we calculate the growth of the magneto-acoustic waves and
the damping of the GW.


title: The quantum gravitational black hole is neither black nor white

abstract:
  Understanding the end state of black hole evaporation, the microscopic origin
of black hole entropy, the information loss paradox, and the nature of the
singularity arising in gravitational collapse - these are outstanding
challenges for any candidate quantum theory of gravity. Recently, a
midisuperspace model of quantum gravitational collapse has been solved using a
lattice regularization scheme. It is shown that the mass of an eternal black
hole follows the Bekenstein spectrum, and a related argument provides a fairly
accurate estimate of the entropy. The solution also describes a quantized
mass-energy distribution around a central black hole, which in the WKB
approximation, is precisely Hawking radiation. The leading quantum
gravitational correction makes the spectrum non-thermal, thus providing a
plausible resolution of the information loss problem.


title: Rough Solutions of the Einstein Constraint Equations

abstract:
  We construct low regularity solutions of the vacuum Einstein constraint
equations. In particular, on 3-manifolds we obtain solutions with metrics in
$H^s\loc$ with $s>{3\over 2}$. The theory of maximal asymptotically Euclidean
solutions of the constraint equations descends completely the low regularity
setting. Moreover, every rough, maximal, asymptotically Euclidean solution can
be approximated in an appropriate topology by smooth solutions. These results
have application in an existence theorem for rough solutions of the Einstein
evolution equations.


title: Brane Waves

abstract:
  In brane-world cosmology gravitational waves can propagate in the higher
dimensions (i.e., in the `bulk'). In some appropriate regimes the bulk
gravitational waves may be approximated by plane waves. We systematically study
five-dimensional gravitational waves that are algebraically special and of type
N. In the most physically relevant case the projected non-local stress tensor
on the brane is formally equivalent to the energy-momentum tensor of a null
fluid. Some exact solutions are studied to illustrate the features of these
branes; in particular, we show explicity that any plane wave brane can be
embedded into a 5-dimensional Siklos spacetime. More importantly, it is
possible that in some appropriate regime the bulk can be approximated by
gravitational plane waves and thus may act as initial conditions for the
gravitational field in the bulk (thereby enabling the field equations to be
integrated on the brane).


title:
A quasi-physical family of gravity-wave templates for precessing
  binaries of spinning compact objects: Application to double-spin precessing
  binaries

abstract:
  The gravitational waveforms emitted during the adiabatic inspiral of
precessing binaries with two spinning compact bodies of comparable masses,
evaluated within the post-Newtonian approximation, can be reproduced rather
accurately by the waveforms obtained by setting one of the two spins to zero,
at least for the purpose of detection by ground-based gravitational-wave
interferometers. Here we propose to use this quasi-physical family of
single-spin templates to search for the signals emitted by double-spin
precessing binaries, and we find that its signal-matching performance is
satisfactory for source masses (m1,m2) in [3,15]Msun x [3,15]Msun. For this
mass range, using the LIGO-I design sensitivity, we estimate that the number of
templates required to yield a minimum match of 0.97 is ~320,000. We discuss
also the accuracy to which the single-spin template family can be used to
estimate the parameters of the original double-spin precessing binaries.


title:
Modified Gravitational Theory and the Gravity Probe-B Gyroscope
  Experiment

abstract:
  A possible deviation from the precession of the Gravity Probe-B gyroscope
predicted by general relativity is obtained in the nonsymmetric gravity theory.
The time delay of radio signals emitted by spacecraft at planetary distances
from the Sun, in nonsymmetric gravity theory is the same as in general
relativity. A correction to the precession of the gyroscope would provide a
possible experimental signature for the Gravity Probe-B gyroscope experiment.
The Lense-Thirring frame-dragging effect is predicted to be the same as in GR.


title: The Constraint Equations

abstract:
  We review the properties of the constraint equations, from their geometric
origin in hypersurface geometry through to their roles in the Cauchy problem
and the Hamiltonian formulation of the Einstein equations. We then review
properties of the space of solutions and construction techniques, including the
conformal and conformal thin sandwich methods, the thin sandwich method,
quasi-spherical and generalized QS methods, gluing techniques and the
Corvino-Schoen projection.


title: Displacement-Noise-Free Gravitational-Wave Detection

abstract:
  We present a new idea that allows us to detect gravitational waves without
being disturbed by any kind of displacement noise, based on the fact that
gravitational waves and test-mass motions affect the propagations of light
differently. We demonstrate this idea by analyzing a simple toy model
consisting three equally-separated objects on a line. By taking a certain
combination of light travel times between these objects, we construct an
observable free from the displacement of each object which has a reasonable
sensitivity to gravitational waves.


title: Self Creation Cosmology - An Alternative Gravitational Theory

abstract:
  The premature acceptance of the standard cosmological model, the 'LambdaCDM'
paradigm, is questioned; Self Creation Cosmology is offered as an alternative
and shown to be as equally concordant with observed cosmological constraints
and local observations including the EEP. The Brans Dicke theory is modified to
enable the creation of matter and energy out of the self contained
gravitational and scalar fields constrained by the local conservation of energy
so that rest masses vary whereas the observed Newtonian Gravitation 'constant'
does not. There is a conformal equivalence between self-creation and General
Relativity in vacuo, which results in the predictions of the two theories being
equal in the standard tests. In self-creation test particles in vacuo follow
the geodesics of General Relativity. Nevertheless there are three types of
experiment, including the LIGO apparatus & Gravity Probe B geodetic precession,
which are able to distinguish between the two theories. Self-creation is as
consistent with cosmological constraints as the standard paradigm, without the
addition of the undiscovered physics of Inflation, dark non-baryonic matter, or
dark energy. It does demand an exotic equation of state, which requires a false
vacuum energy determined by the field equations. The two conformal frames
conserve energy or energy-momentum and choose photons or atoms as the standard
of measurement respectively. In the former frame the universe is stationary and
eternal with exponentially shrinking rulers and accelerating atomic clocks, and
in the latter frame the universe is freely coasting, expanding linearly from a
Big Bang with rigid rulers and regular atomic clocks. A novel representation of
space-time geometry is suggested. (Abridged)


title: Precise relativistic orbits in Kerr and Kerr-(anti) de Sitter spacetimes

abstract:
  The timelike geodesic equations resulting from the Kerr gravitational metric
element are derived and solved exactly including the contribution from the
cosmological constant. The geodesic equations are derived, by solving the
Hamilton-Jacobi partial differential equation by separation of variables. The
solutions can be applied in the investigation of the motion of a test particle
in the Kerr and Kerr-(anti) de Sitter gravitational fields. In particular, we
apply the exact solutions of the timelike geodesics i) to the precise
calculation of dragging (Lense-Thirring effect) of a satellite's spherical
polar orbit in the gravitational field of Earth assuming Kerr geometry, ii)
assuming the galactic centre is a rotating black hole we calculate the precise
dragging of a stellar polar orbit aroung the galactic centre for various values
of the Kerr parameter including those supported by recent observations. The
exact solution of non-spherical geodesics in Kerr geometry is obtained by using
the transformation theory of elliptic functions. The exact solution of
spherical polar geodesics with a nonzero cosmological constant can be expressed
in terms of Abelian modular theta functions that solve the corresponding
Jacobi's inversion problem.


title: Backreaction in Acoustic Black Holes

abstract:
  The backreaction equations for the linearized quantum fluctuations in an
acoustic black hole are given. The solution near the horizon, obtained within a
dimensional reduction, indicates that acoustic black holes, unlike
Schwarzschild ones, get cooler as they radiate phonons. They show remarkable
analogies with near-extremal Reissner-Nordstrom black holes.


title:
A unified Scenario for modeling the Galactic and Cosmological Dark
  Matter Components

abstract:
  In this work we analyze the viability of use a particular models of scalar
fields in the context of the galactic dark matter problem. These models are
based on a single scalar field, minimally coupled to the gravity in a
asymptotically flat or asymptotically deSitter spacetime. We discuss the
opening possibility of constructing a unified model for both the cosmological
and the galactic dark matter.


title: Quantum effects in Acoustic Black Holes: the Backreaction

abstract:
  We investigate the backreaction equations for an acoustic black hole formed
in a Laval nozzle under the assumption that the motion of the fluid is
one-dimensional. The solution in the near-horizon region shows that as phonons
are (thermally) radiated the sonic horizon shrinks and the temperature
decreases. This contrasts with the behaviour of Schwarzschild black holes, and
is similar to what happens in the evaporation of (near-extremal)
Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by
appropriate boundary conditions the solution is extended in both the asymptotic
regions of the nozzle.


title:
On perfect fluid models in non-comoving observational spherical
  coordinates

abstract:
  We use null spherical (observational) coordinates to describe a class of
inhomogeneous cosmological models. The proposed cosmological construction is
based on the observer past null cone. A known difficulty in using inhomogeneous
models is that the null geodesic equation is not integrable in general. Our
choice of null coordinates solves the radial ingoing null geodesic by
construction. Furthermore, we use an approach where the velocity field is
uniquely calculated from the metric rather than put in by hand. Conveniently,
this allows us to explore models in a non-comoving frame of reference. In this
frame, we find that the velocity field has shear, acceleration and expansion
rate in general. We show that a comoving frame is not compatible with expanding
perfect fluid models in the coordinates proposed and dust models are simply not
possible. We describe the models in a non-comoving frame. We use the dust
models in a non-comoving frame to outline a fitting procedure.


title: Efectos relativistas en los sistemas Galileo, GPS y GLONASS

abstract:
  Nowadays, the Global Navigation Satellite Systems (GNSS), working like global
positioning systems, are the GPS (NAVSTAR) and the GLONASS, which only are
operative when several relativistic effects are corrected. In the next years
the Galileo system will be constructed, copying the GPS System if there is no
an alternative project. In this work, it will be exposed that there is one
alternative to the mere copy by means of the SYPOR project, using relativistic
concepts, and without utilize the Newtonian ideas that are in the basic
conception, so much of the GPS as of the GLONASS. According to the SYPOR
project, the Galileo system would be exact, with no need of corrections, and it
would have additional technological advantages.


title: Critical Collapse of a Complex Scalar Field with Angular Momentum

abstract:
  We report a new critical solution found at the threshold of axisymmetric
gravitational collapse of a complex scalar field with angular momentum. To
carry angular momentum the scalar field cannot be axisymmetric; however, its
azimuthal dependence is defined so that the resulting stress energy tensor and
spacetime metric are axisymmetric. The critical solution found is
non-spherical, discretely self-similar with an echoing exponent of 0.42 (+-
4%), and exhibits a scaling exponent of 0.11 (+- 10%) in near critical
collapse. Our simulations suggest that the solution is universal (within the
imposed symmetry class), modulo a family-dependent constant phase in the
complex plane.


title:
Matching of spatially homogeneous non-stationary space--times to vacuum
  in cylindrical symmetry

abstract:
  We study the matching of LRS spatially homogeneous collapsing dust
space-times with non-stationary vacuum exteriors in cylindrical symmetry. Given
an interior with diagonal metric we prove existence and uniqueness results for
the exterior. The matched solutions contain trapped surfaces, singularities and
Cauchy horizons. The solutions cannot be asymptotically flat and we present
evidence that they are singular on the Cauchy horizons.


title: Quantifying energy condition violations in traversable wormholes

abstract:
  The `theoretical' existence of traversable Lorentzian wormholes in the
classical, macroscopic world is plagued by the violation of the well--known
energy conditions of General Relativity. In this brief article we show : (i)
how the extent of violation can be quantified using certain volume integrals
(ii) whether this `amount of violation' can be minimised for some specific
cut--and--paste geometric constructions. Examples and possibilities are also
outlined.


title: Cosmological Term and Fundamental Physics

abstract:
  A nonvanishing cosmological term in Einstein's equations implies a
nonvanishing spacetime curvature even in absence of any kind of matter. It
would, in consequence, affect many of the underlying kinematic tenets of
physical theory. The usual commutative spacetime translations of the Poincare'
group would be replaced by the mixed conformal translations of the de Sitter
group, leading to obvious alterations in elementary concepts such as time,
energy and momentum. Although negligible at small scales, such modifications
may come to have important consequences both in the large and for the
inflationary picture of the early Universe. A qualitative discussion is
presented which suggests deep changes in Hamiltonian, Quantum and Statistical
Mechanics. In the primeval universe as described by the standard cosmological
model, in particular, the equations of state of the matter sources could be
quite different from those usually introduced.


title: A stable static Universe?

abstract:
  Starting from the assumption that general relativity might be an emergent
phenomenon showing up at low-energies from an underlying microscopic structure,
we re-analyze the stability of a static closed Universe filled with radiation.
In this scenario, it is sensible to consider the effective general-relativistic
configuration as in a thermal contact with an "environment" (the role of
environment can be played, for example, by the higher-dimensional bulk or by
the trans-Planckian degrees of freedom). We calculate the free energy at a
fixed temperature of this radiation-filled static configuration. Then, by
looking at the free energy we show that the static Einstein configuration is
stable under the stated condition.


title:
Structure of Extended Loop Wave Function in Quantum Gravity and Operator
  Formalism

abstract:
  The structure of extended loop wave function is investigated in terms of the
operator formalism. It is found that the extended loop wave function is
characterized by the family number and classified by the partition of the
family number. It is pointed out that the constraints to the extended loop
function in quantum gravity exhibit a hierarchy structure.


title: Quantum Gravity

abstract: General lectures on quantum gravity.


title: Geometry of null hypersurfaces

abstract:
  We review some basic natural geometric objects on null hypersurfaces.
Gauss-Codazzi constraints are given in terms of the analog of canonical ADM
momentum which is a well defined tensor density on the null surface. Bondi
cones are analyzed with the help of this object.


title: The Dynamics of General Relativity

abstract:
  This article--summarizing the authors' then novel formulation of General
Relativity--appeared as Chapter 7 of an often cited compendium edited by L.
Witten in 1962, which is now long out of print. Intentionally unretouched, this
posting is intended to provide contemporary accessibility to the flavor of the
original ideas. Some typographical corrections have been made: footnote and
page numbering have changed--but not section nor equation numbering etc. The
authors' current institutional affiliations are encoded in:
arnowitt@physics.tamu.edu, deser@brandeis.edu, misner@physics.umd.edu .


title: Gravity as the affine Goldstone phenomenon and beyond

abstract:
  The two-phase structure is imposed on the world continuum, with the graviton
emerging as the tensor Goldstone boson during the spontaneous transition from
the affinely connected phase to the metric one. The physics principle of
metarelativity, extending the respective principle of special relativity, is
postulated. The theory of metagravitation as the general nonlinear model
GL(4,R)/SO(1,3) in the arbitrary background continuum is built. The concept of
Metauniverse as the ensemble of the regions of the metric phase inside the
affinely connected phase is introduced, and the possible bearing of the
emerging multiple universes to the fine tuning of our Universe is conjectured.


title: Dark Energy and Condensate Stars: Casimir Energy in the Large

abstract:
  Vacuum fluctuations and the Casimir effect are considered in a cosmological
setting. It is suggested that the dark energy, which recent observations
suggest make up 73% of our universe, is vacuum energy due to a causal boundary
effect at the cosmological horizon. After a discussion of the similarities and
differences between material boundaries in flat spacetime and causal horizons
in general relativity, a simple model with a purely vacuum energy de Sitter
interior and Schwarzschild exterior, separated by a thin boundary layer is
outlined. The boundary layer is a quantum transition region which replaces the
event horizons of the classical de Sitter and Schwarzschild solutions, through
which the vacuum energy changes.


title: Charge conjugation and Lense-Thirring Effect: A new Asymmetry

abstract:
  This essay presents a new asymmetry that arises from the interplay of charge
conjugation and Lense-Thirring effect. When applied to Majorana neutrinos, the
effects predicts nu_e <-> overline{nu}_e oscillations in gravitational
environments with rotating sources. Parameters associated with astrophysical
environments indicate that the presented effect is presently unobservable for
solar neutrinos. But, it will play an important role in supernova explosions,
and carries relevance for the observed matter-antimatter asymmetry in the
universe.


title: Kinematic self-similar solutions in general relativity

abstract:
  The gravitational interaction is scale-free in both Newtonian gravity and
general theory of relativity. The concept of self-similarity arises from this
nature. Self-similar solutions reproduce themselves as the scale changes. This
property results in great simplification of the governing partial differential
equations. In addition, some self-similar solutions can describe the asymptotic
behaviors of more general solutions. Newtonian gravity contains only one
dimensional constant, the gravitational constant, while the general relativity
contains another dimensional constant, the speed of light, besides the
gravitational constant. Due to this crucial difference, incomplete similarity
can be more interesting in general relativity than in Newtonian gravity.
Kinematic self-similarity has been defined and studied as an example of
incomplete similarity in general relativity, in an effort to pursue a wider
application of self-similarity in general relativity. We review the
mathematical and physical aspects of kinematic self-similar solutions in
general relativity.


title: Closed Timelike Curves Re-Examined

abstract:
  Examples are given of the creation of closed timelike curves by choices of
coordinate identifications. Following G\"odel's prescription, it is seen that
flat spacetime can produce closed timelike curves with structure similar to
that of G\"odel. In this context, coordinate identifications rather than exotic
gravitational effects of general relativity are shown to be the source of
closed timelike curves. Removing the periodic time coordinate restriction, the
modified G\"odel family of curves is expressed in a form that retains the
timelike and spacelike character of the coordinates. With these coordinates,
the nature of the timelike curves is clarified. A helicoidal surface unifies
the families of timelike, spacelike and null curves. In all of these, it is
seen that as in ordinary flat spacetime, periodicity in the spatial position
does not naturally carry over into closure in time. Thus, the original source
of serious scientific speculation regarding time machines is seen to be
misconceived.


title: Universality, Gravity, the enigmatic Lambda and Beyond

abstract:
  In this essay, I wish to share a novel perspective which envisions
universalization as a guide from the classical world to relativistic and
quantum world. It is the incorporation of zero mass particle in mechanics which
leads to special relativity while its interaction with a universal field shared
by all particles leads to general relativity. We also give a very simple
classical argument to show that why the universal force has to be attractive.
We try to envisage what sort of directions does this principle of universality
point to for the world beyond general relativity?


title: Smarr's formula for black holes with non-linear electrodynamics

abstract:
  It is known that for nonlinear electrodynamics the First Law of Black Hole
Mechanics holds, however the Smarr's formula for the total mass does not. In
this contribution we discuss the point and determine the corresponding
expressions for the Bardeen black hole solution that represents a nonlinear
magnetic monopole. The same is done for the regular black hole solution derived
by Ayon-Beato and Garcia, showing that in the case that variations of the
electric charge are involved, the Smarr's formula does not longer is valid.


title: Coarse-Grained Back Reaction in Single Scalar Field Driven Inflation

abstract:
  We introduce a self-consistent stochastic coarse-graining method, which
includes both metric and scalar field fluctuations, to investigate the back
reaction of long wavelength perturbations in single-scalar driven inflation, up
to the second (one loop) order. We demonstrate that, although back reaction
cannot be significant during the last 70 e-foldings of inflation with a smooth
potential, there exist non-smooth inflaton potentials which allow significant
back reaction, and are also consistent with cosmological observations. Such
non-smooth potentials may lead to the generation of massive primordial black
holes, which could be further used to constrain/verify these models.


title: On the Energy of Stringy Black Holes

abstract:
  It is well-known that one of the most interesting and challenging problems of
General Relativity is the energy and momentum localization. There are many
attempts to evaluate the energy distribution in a general relativistic system.
One of the methods used for the energy and momentum localization is the one
which used the energy-momentum complexes. After the Einstein work, a large
number of definitions for the energy distribution was given. We mention the
expressions proposed by Landau and Lifshitz, Papapetrou, Bergmann, Weinberg and
M{\o}ller. The Einstein, Landau and Lifshitz, Papapetrou, Bergmann and Weinberg
energy-momentum complexes are restricted to calculate the energy distribution
in quasi-Cartesian coordinates. The energy-momentum complex of M{\o}ller gives
the possibility to make the calculations in any coordinate system. In this
paper we calculate the energy distribution of three stringy black hole
solutions in the M{\o}ller prescription. The M{\o}ller energy-momentum complex
gives us a consistent result for these three situations.
  Keywords: M{\o}ller energy-momentum complex, charged black hole solution in
heterotic string theory PACS: 04. 20 Dw, 04. 70. Bw,


title: Automorphism covariant representations of the holonomy-flux *-algebra

abstract:
  We continue an analysis of representations of cylindrical functions and
fluxes which are commonly used as elementary variables of Loop Quantum Gravity.
We consider an arbitrary principal bundle of a compact connected structure
group and following Sahlmann's ideas define a holonomy-flux *-algebra whose
elements correspond to the elementary variables. There exists a natural action
of automorphisms of the bundle on the algebra; the action generalizes the
action of analytic diffeomorphisms and gauge transformations on the algebra
considered in earlier works. We define the automorphism covariance of a
*-representation of the algebra on a Hilbert space and prove that the only
Hilbert space admitting such a representation is a direct sum of spaces L^2
given by a unique measure on the space of generalized connections. This result
is a generalization of our previous work (Class. Quantum. Grav. 20 (2003)
3543-3567, gr-qc/0302059) where we assumed that the principal bundle is
trivial, and its base manifold is R^d.


title:
Multicomponent perfect fluid with variable parameters in n Ricci-flat
  spaces

abstract:
  D-dimensional cosmological model describing the evolution of a multicomponent
perfect fluid with variable barotropic parameters in n Ricci-flat spaces is
investigated. The equations of motion are integrated for the case, when each
component possesses an isotropic pressure with respect to all spaces. Exact
solutions are presented in the Kasner-like form. Some explicit examples are
given: 4-dimensional model with an isotropic accelerated expansion at late
times and (4+d)-dimensional model describing a compactification of extra
dimensions.


title: Does the Cosmos have two times? Multi-time and cosmic acceleration

abstract:
  We put forward a multi-time theory, in frame of which the cosmic acceleration
is a natural phenomenon without cosmological constant or anything like that.
The main point of this theory is that each of the gravity interaction and
electromagnetic interaction has its own time, respectively. Also we give a
concrete model of this theory which can exactly simulate $\Lambda$CDM. Further
we discuss the possible observations which may improve this theory in the
future.


title: Late-time behavior of massive Dirac fields in a Schwarzschild background

abstract:
  The late-time tail behavior of massive Dirac fields is investigated in the
Schwarzschild black-hole geometry and the result is compared with that of the
massive scalar fields. It is shown that in the intermediate times there are
three kinds of differences between the massive Dirac and scalar fields, (I) the
asymptotic behavior of massive Dirac fields is dominated by a decaying tail
without any oscillation, but the massive scalar field by a oscillatory inverse
power-law decaying tail, (II) the dumping exponent for the massive Dirac field
depends not only on the multiple number of the wave mode but also on the mass
of the Dirac field, while that for the massive scalar field depends on the
multiple number only, and (III) the decay of the massive Dirac field is slower
than that of the massive scalar field.


title: Speed of gravity and gravitomagnetism

abstract:
  A v_J/c correction to the Shapiro time delay seems verified by a 2002 Jovian
observation by VLBI. In this Essay, this correction is interpreted as an effect
of the aberration of light in an optically refractive medium which supplies an
analog of Jupiter's gravity field rather than as a measurement of the speed of
gravity, as it was first proposed by other authors. The variation of the index
of refraction is induced by the Lorentz invariance of the weak gravitational
field equations for Jupiter in a uniform translational slow motion with
velocity v_J=13.5 km/s. The correction on time delay and deflection is due not
to the Kerr (or Lense-Thirring) stationary gravitomagnetic field of Jupiter,
but to its Schwarzschild gravitostatic field when measured from the barycenter
of the solar system.


title: Perfect hypermomentum fluid: variational theory and equations of motion

abstract:
  The variational theory of the perfect hypermomentum fluid is developed. The
new type of the generalized Frenkel condition is considered. The Lagrangian
density of such fluid is stated, and the equations of motion of the fluid and
the Weyssenhoff-type evolution equation of the hypermomentum tensor are
derived. The expressions of the matter currents of the fluid (the canonical
energy-momentum 3-form, the metric stress-energy 4-form and the hypermomentum
3-form) are obtained. The Euler-type hydrodynamic equation of motion of the
perfect hypermomentum fluid is derived. It is proved that the motion of the
perfect fluid without hypermomentum in a metric-affine space coincides with the
motion of this fluid in a Riemann space.


title:
Separability of the Hamilton-Jacobi and Klein-Gordon Equations in
  Kerr-de Sitter Metrics

abstract:
  We study separability of the Hamilton-Jacobi and massive Klein-Gordon
equations in the general Kerr-de Sitter spacetime in all dimensions. Complete
separation of both equations is carried out in 2n+1 spacetime dimensions with
all n rotation parameters equal, in which case the rotational symmetry group is
enlarged from (U(1))^n to U(n). We explicitly construct the additional Killing
vectors associated with the enlarged symmetry group which permit separation. We
also derive first-order equations of motion for particles in these backgrounds
and examine some of their properties.


title: Generating function techniques for loop quantum cosmology

abstract:
  Loop quantum cosmology leads to a difference equation for the wave function
of a universe, which in general has solutions changing rapidly even when the
volume changes only slightly. For a semiclassical regime such small-scale
oscillations must be suppressed, by choosing the parameters of the solution
appropriately. For anisotropic models this is not possible to do numerically by
trial and error; instead, it is shown here for the Bianchi I LRS model how this
can be done analytically, using generating function techniques. Those
techniques can also be applied to more complicated models, and the results
gained allow conclusions about initial value problems for other systems.


title:
Reissner Nordstr\"{o}m Background Metric in Dynamical Co-ordinates:
  Exceptional Behaviour of Hadamard States

abstract:
  We cast the Reissner Nordstrom solution in a particular co-ordinate system
which shows dynamical evolution from initial data. The initial data for the
$E<M$ case is regular. This procedure enables us to treat the metric as a
collapse to a singularity. It also implies that one may assume Wald axioms to
be valid globally in the Cauchy development, especially when Hadamard states
are chosen. We can thus compare the semiclassical behaviour with spherical dust
case, looking upon the metric as well as state specific information as
evolution from initial data. We first recover the divergence on the Cauchy
horizon obtained earlier. We point out that the semiclassical domain extends
right upto the Cauchy horizon. This is different from the spherical dust case
where the quantum gravity domain sets in before. We also find that the
backreaction is not negligible near the central singularity, unlike the dust
case. Apart from these differences, the Reissner Nordstrom solution has a
similarity with dust in that it is stable over a considerable period of time.
The features appearing dust collapse mentioned above were suggested to be
generally applicable within spherical symmetry. Reissner Nordstrom background
(along with the quantum state) generated from initial data, is shown not to
reproduce them.


title: Conformal transformations near Naked Singularities - I

abstract:
  We show that the behaviour of the outgoing radial null geodesic congruence on
the boundary of the trapped region (suitably defined as a four dimensional
region) is related to the property of nakedness in spherical dust collapse. The
argument involves a conformal transformation which justifies the difference in
the Penrose diagrams in the naked and covered dust collapse scenarios.


title:
Asymptotic tails of massive scalar fields in a stationary axisymmetric
  EMDA black hole geometry

abstract:
  The late-time tail behavior of massive scalar fields is studied analytically
in a stationary axisymmetric EMDA black hole geometry. It is shown that the
asymptotic behavior of massive perturbations is dominated by the oscillatory
inverse power-law decaying tail $ t^{-(l+3/2)}\sin(\mu t)$ at the intermediate
late times, and by the asymptotic tail $ t^{-5/6}\sin(\mu t)$ at asymptotically
late times. Our result seems to suggest that the intermediate tails $
t^{-(l+3/2)}\sin(\mu t)$ and the asymptotically tails $t^{-5/6} \sin(\mu t)$
may be quite general features for evolution of massive scalar fields in any
four dimensional asymptotically flat rotating black hole backgrounds.


title:
Conditions for negative specific heat in systems of attracting classical
  particles

abstract:
  We identify conditions for the presence of negative specific heat in
non-relativistic self-gravitating systems and similar systems of attracting
particles.
  The method used, is to analyse the Virial theorem and two soluble models of
systems of attracting particles, and to map the sign of the specific heat for
different combinations of the number of spatial dimensions of the system,
$D$($\geq 2$), and the exponent, $\nu$($\neq 0$), in the force potential,
$\phi=Cr^\nu$. Negative specific heat in such systems is found to be present
exactly for $\nu=-1$, at least for $D \geq 3$. For many combinations of $D$ and
$\nu$ representing long-range forces, the specific heat is positive or zero,
for both models and the Virial theorem. Hence negative specific heat is not
caused by long-range forces as such. We also find that negative specific heat
appears when $\nu$ is negative, and there is no singular point in a certain
density distribution. A possible mechanism behind this is suggested.


title:
Dirac-like approach for consistent discretizations of classical
  constrained theories

abstract:
  We analyze the canonical treatment of classical constrained mechanical
systems formulated with a discrete time. We prove that under very general
conditions, it is possible to introduce nonsingular canonical transformations
that preserve the constraint surface and the Poisson or Dirac bracket
structure. The conditions for the preservation of the constraints are more
stringent than in the continuous case and as a consequence some of the
continuum constraints become second class upon discretization and need to be
solved by fixing their associated Lagrange multipliers. The gauge invariance of
the discrete theory is encoded in a set of arbitrary functions that appear in
the generating function of the evolution equations. The resulting scheme is
general enough to accommodate the treatment of field theories on the lattice.
This paper attempts to clarify and put on sounder footing a discretization
technique that has already been used to treat a variety of systems, including
Yang--Mills theories, BF-theory and general relativity on the lattice.


title: The Dynamic Space of General Relativity in Second Atomization

abstract:
  The notion that the geometry of our space-time is not only a static
background but can be physically dynamic is well established in general
relativity. Geometry can be described as shaped by the presence of matter,
where such shaping manifests itself as gravitational force. We consider here
probabilistic or atomistic models of such space-time, in which the active
geometry emerges from a statistical distribution of 'atoms'. Such atoms are not
to be confused with their chemical counterparts, however the shift of
perspective obtained in analyzing a gas via its molecules rather than its bulk
properties is analogous to this "second atomization". In this atomization,
space-time itself (i.e. the meter and the second) is effectively atomized, so
the atoms themselves must exist in a 'subspace'.
  Here we build a simple model of such a space-time from the ground up,
establishing a route for more complete theories, and enabling a review of
recent work. We first introduce the motivation behind statistical
interpretations and atomism, and look at applications to the realm of dynamic
space-time theories. We then consider models of kinetic media in subspace
compatible with our understanding of light. From the equations governing the
propagation of light in subspace we can build a metric geometry, describing the
dynamic and physical space-time of general relativity. Finally, implications of
the theory on current frontiers of general relativity including cosmology,
black holes, and quantum gravity are discussed.


title:
On the general structure of Ricci collineations for type B warped
  spacetimes

abstract:
  A complete study of the structure of Ricci collineations for type B warped
spacetimes is carried out. This study can be used as a method to obtain these
symetries in such spacetimes. Special cases as 2+2 reducible spacetimes, and
plane and spherical symmetric spacetimes are considered specifically.


title: Twist of stationary black hole/ring in five dimensions

abstract:
  It is unlikely that uniqueness theorem holds for stationary black holes in
higher dimensional spacetimes. However, we will examine the possibility that
the higher multipole moments classify vacuum solutions uniquely. Especially, we
compute the potentials associated with rotational Killing vectors and look at
the dependence on the total mass M and angular momentum J. Consequently, there
is a potential $\sigma$ which we cannot write down in terms of integer power of
M and J explicitly. This may be regarded as an evidence for the uniqueness
using multipole moments generated by $\sigma$.


title: Wormhole Core, Extra Dimensions, and Physical Universe

abstract:
  We created a model of several dimensional physical universe. The extra
dimensions associated with the four dimensional physical universe is assumed to
have modified Gidding-Strominger wormhole core. This core is separated by a
flexible wall, but it allows the adiabatic pressure generated in the wormhole
to penetrate in the extra dimensions. We assume that the extra dimensions are a
contracting Robinson-Walker space. We show that the associated physical
universe accelerates under certain restriction of the parameters introduced.
The extra dimensional space is very large at the begining, however at present
time this space will be very reduced. As a result the physical universe will
appear to us four dimensional the way we observe it now.


title: Gravitational Radiation - Observing the Dark and Dense Universe

abstract:
  Astronomical observations in the electromagnetic window - microwave, radio
and optical - have revealed that most of the Universe is dark. The only reason
we know that dark matter exists is because of its gravitational influence on
luminous matter. It is plausible that a small fraction of that dark matter is
clumped, and strongly gravitating. Such systems are potential sources of
gravitational radiation that can be observed with a world-wide network of
gravitational wave antennas. Electromagnetic astronomy has also revealed
objects and phenomena - supernovae, neutron stars, black holes and the big bang
- that are without doubt extremely strong emitters of the radiation targeted by
the gravitational wave interferometric and resonant bar detectors. In this talk
I will highlight why gravitational waves arise in Einstein's theory, how they
interact with matter, what the chief astronomical sources of the radiation are,
and in which way by observing them we can gain a better understanding of the
dark and dense Universe.


title: Event rate estimates for LISA extreme mass ratio capture sources

abstract:
  One of the most exciting prospects for the LISA gravitational wave
observatory is the detection of gravitational radiation from the inspiral of a
compact object into a supermassive black hole. The large inspiral parameter
space and low amplitude of the signal makes detection of these sources
computationally challenging. We outline here a first cut data analysis scheme
that assumes realistic computational resources. In the context of this scheme,
we estimate the signal-to-noise ratio that a source requires to pass our
thresholds and be detected. Combining this with an estimate of the population
of sources in the Universe, we estimate the number of inspiral events that LISA
could detect. The preliminary results are very encouraging -- with the baseline
design, LISA can see inspirals out to a redshift z=1 and should detect over a
thousand events during the mission lifetime.


title: Dirac Spin Precession in Kerr Spacetime by the parallelism description

abstract:
  In the framework of parallelism general relativity (PGR), the Dirac particle
spin precession in the rotational gravitational field is studied. In terms of
the equivalent tetrad of Kerr frame, we investigate the torsion axial-vector
spin coupling in PGR. In the case of the weak field and slow rotation
approximation, we obtain that the torsion axial-vector has the dipole-like
structure, but different from the gravitomagnetic field, which indicates that
the choice of the Kerr tetrad will influence on the physics interpretation of
the axial-vector spin coupling.


title:
A globally well-behaved simultaneity connection for stationary frames in
  the weak field limit

abstract:
  Local simultaneity conventions are mathematically represented by connections
on the bundle of timelike curves that defines the frame. Those simultaneity
conventions having an holonomy proportional to the Riemann tensor have a
special interest since they exhibit a good global behavior in the weak field
limit. By requiring that the simultaneity convention depends on the the
acceleration, vorticity vector and the angle between them we are able to
restrict considerably the allowed simultaneity conventions. In particular, we
focus our study on the simplest among the allowed conventions. It should be
preferred over Einstein's in flat spacetime and in general if the tidal force
between neighboring particles is weaker than the centrifugal force. It reduces
to the Einstein convention if the vectorial product between the acceleration
and the vorticity vector vanishes. We finally show how to use this convention
in practice.


title:
On the Asymptotic Character of Electromagnetic Waves in a
  Friedmann-Robertson-Walker Universe

abstract:
  Asymptotic properties of electromagnetic waves are studied within the context
of Friedmann-Robertson-Walker (FRW) cosmology. Electromagnetic fields are
considered as small perturbations on the background spacetime and Maxwell's
equations are solved for all three cases of flat, closed and open FRW
universes. The asymptotic character of these solutions are investigated and
their relevance to the problem of cosmological tails of electromagnetic waves
is discussed.


title: Decaying Lambda cosmology, varying G and holography

abstract:
  We discuss a class of uniform and isotropic, spatially flat, decaying Lambda
cosmologies, in the realm of a model where the gravitation constant G is a
function of the cosmological time. Besides the usual de Sitter solution, the
models at late times are characterized by a constant ratio between the matter
and total energy densities. One of them presents a coasting expansion where the
matter density parameter is equal to 1/3, and the age of the universe satisfies
Ht = 1. From considerations in line with the holographic conjecture, it is
argued that, among the non-decelerating solutions, the coasting expansion is
the only acceptable from a thermodynamic viewpoint, and that the time varying
cosmological term must be proportional to the square of the Hubble parameter, a
result earlier obtained using different arguments.


title: On gravitational radiation and the energy flux of matter

abstract:
  A suitable derivative of Einstein's equations in the framework of the
teleparallel equivalent of general relativity (TEGR) yields a continuity
equation for the gravitational energy-momentum. In particular, the time
derivative of the total gravitational energy is given by the sum of the total
fluxes of gravitational and matter fields energy. We carry out a detailed
analysis of the continuity equation in the context of Bondi and Vaidya's
metrics. In the former space-time the flux of the gravitational energy is given
by the well known expression in terms of the square of the news function. It is
known that the energy definition in the realm of the TEGR yields the ADM
(Arnowitt-Deser-Misner) energy for appropriate boundary conditions. Here we
show that the same definition also describes the Bondi energy. The analysis of
the continuity equation in Vaidya's space-time shows that the variation of the
total gravitational energy is given by the energy flux of matter only.


title: Kottler-Lambda-Kerr Spacetime

abstract:
  The static Kottler metric is the Schwarzschild vacuum metric extended to
include a cosmological constant. Angular momentum is added to the Kottler
metric by using Newman and Janis' complexifying algorithm. The new metric is
the Lambda generalization of the Kerr spacetime. It is stationary, axially
symmetric, Petrov type II, and has Kerr-Schild form.


title:
Space Time Covariance of Canonical Quantization of Gravity: A (formal)
  general result and the (rigorous) explicit case of 2+1 Quantum Cosmology

abstract:
  A general classical theorem is presented according to which all invariant
relations among the space time metric scalars, when turned into functions on
the Phase Space of full Pure Gravity (using the Canonical Equations of motion),
become weakly vanishing functions of the Quadratic and Linear Constraints. The
implication of this result is that (formal) Dirac consistency of the Quantum
Operator Constraints (annihilating the wave Function) suffices to guarantee
space time covariance f the ensuing quantum theory: An ordering for each
invariant relation will always exist such that the emanating operator has an
eigenvalue identical to the classical value. The example of 2+1 Quantum
Cosmology is explicitly considered: The four possible ``Cosmological
Solutions'' --two for pure Einstein's equations plus two more when a $\Lambda$
term is present- are exhibited and the corresponding models are quantized. The
invariant relations describing the geometries are explicitly calculated and
promoted to operators whose eigenvalues are their corresponding classical
values.


title: Gravitational wave bursts induced by r-mode spin-down of hybrid stars

abstract:
  We show that sudden variations in the composition and structure of an hybrid
star can be triggered by its rapid spin-down, induced by r-mode instabilities.
The discontinuity of this process is due to the surface tension between
hadronic and quark matter and in particular to the overpressure needed to
nucleate new structures of quark matter in the mixed phase. The consequent
mini-collapses in the star can produce highly energetic gravitational wave
bursts. The possible connection between the predictions of this model and the
burst signal found by EXPLORER and NAUTILUS detectors during the year 2001 is
also investigated.


title:
Rotating neutron stars: an invariant comparison of approximate and
  numerical spacetime models

abstract:
  We compare three different models of rotating neutron star spacetimes: the
Hartle-Thorne (HT) slow-rotation approximation at second order in rotation, the
exact analytic vacuum solution of Manko et al. and a numerical solution of the
full Einstein equations. We integrate the HT structure equations for five
representative equations of state. Then we match the HT models to numerical
solutions of the Einstein equations, imposing that the mass and angular
momentum of the models be the same. We estimate the limits of validity of the
HT expansion computing relative errors in the spacetime's quadrupole moment Q
and in the ISCO radii. We find that ISCO radii computed in the HT approximation
are accurate to better than 1%, even for the fastest observed ms pulsar. At the
same rotational rates the accuracy on Q is of order 20%. In the second part of
the paper we focus on the exterior vacuum spacetimes. We introduce a physically
motivated `quasi-Kinnersley' Newman-Penrose frame. In this frame we evaluate
the speciality index S, a coordinate-independent quantity measuring the
deviation of each model from Petrov Type D. On the equatorial plane this
deviation is smaller than 5%, even for the fastest rotating models. Our main
conclusion is that the HT approximation is very reliable for most astrophysical
applications.


title:
The LISA Time-Delay Interferometry Zero-Signal Solution. I: Geometrical
  Properties

abstract:
  Time-Delay Interferometry (TDI) is the data processing technique needed for
generating interferometric combinations of data measured by the multiple
Doppler readouts available onboard the three LISA spacecraft. Within the space
of all possible interferometric combinations TDI can generate, we have derived
a specific combination that has zero-response to the gravitational wave signal,
and called it the {\it Zero-Signal Solution} (ZSS). This is a two-parameter
family of linear combinations of the generators of the TDI space, and its
response to a gravitational wave becomes null when these two parameters
coincide with the values of the angles of the source location in the sky.
Remarkably, the ZSS does not rely on any assumptions about the gravitational
waveform, and in fact it works for waveforms of any kind. Our approach is
analogous to the data analysis method introduced by G\"ursel & Tinto in the
context of networks of Earth-based, wide-band, interferometric gravitational
wave detectors observing in coincidence a gravitational wave burst. The ZSS
should be regarded as an application of the G\"ursel & Tinto method to the LISA
data.


title:
Discrete symmetries and the muon's gyro-gravitational ratio in g-2
  experiments

abstract:
  We show that recent, persistent discrepancies between theory and experiment
can be interpreted as corrections to the gyro-gravitational ratio of the muon
and lead to improved upper limits on the violation of discrete symmetries in
rotational inertia.


title: Conformal Generators and Doubly Special Relativity Theories

abstract:
  In this paper, the relation between the modified Lorenz boosts, proposed in
the doubly relativity theories and a linear combination of Conformal Group
generators in $R^{1,d-1}$ is investigated. The introduction of a new generator
is proposed in order to deform the Conformal Group to achieve the connection
conjectured. The new generator is obtained trough a formal dimensional
reduction from a free massless particle living in a $R^{2,d}$ space. Due this
treatment it is possible to say that even DSR theories modify light cone
structure in $R^{1,d-1}$, it could remains, in some cases, untouched in
$R^{2,d}$.


title: Inhomogeneous Gravity

abstract:
  We study the inhomogeneous cosmological evolution of the Newtonian
gravitational 'constant' G in the framework of scalar-tensor theories. We
investigate the differences that arise between the evolution of G in the
background universes and in local inhomogeneities that have separated out from
the global expansion. Exact inhomogeneous solutions are found which describe
the effects of masses embedded in an expanding FRW Brans-Dicke universe. These
are used to discuss possible spatial variations of G in different regions. We
develop the technique of matching different scalar-tensor cosmologies of
different spatial curvature at a boundary. This provides a model for the linear
and non-linear evolution of spherical overdensities and inhomogeneities in G.
This allows us to compare the evolution of G and \dot{G} that occurs inside a
collapsing overdense cluster with that in the background universe. We develop a
simple virialisation criterion and apply the method to a realistic lambda-CDM
cosmology containing spherical overdensities. Typically, far slower evolution
of \dot{G} will be found in the bound virialised cluster than in the
cosmological background. We consider the behaviour that occurs in Brans-Dicke
theory and in some other representative scalar-tensor theories.


title: The Papapetrou equations and supplementary conditions

abstract:
  On the bases of the Papapetrou equations with various supplementary
conditions and other approaches a comparative analysis of the equations of
motion of rotating bodies in general relativity is made. The motion of a body
with vertical spin in a circular orbit is considered. An expression for the
spin-orbit force in a post-Newtonian approximation is investigated.


title:
On the well posedness of the Baumgarte-Shapiro-Shibata-Nakamura
  formulation of Einstein's field equations

abstract:
  We give a well posed initial value formulation of the
Baumgarte-Shapiro-Shibata-Nakamura form of Einstein's equations with gauge
conditions given by a Bona-Masso like slicing condition for the lapse and a
frozen shift. This is achieved by introducing extra variables and recasting the
evolution equations into a first order symmetric hyperbolic system. We also
consider the presence of artificial boundaries and derive a set of boundary
conditions that guarantee that the resulting initial-boundary value problem is
well posed, though not necessarily compatible with the constraints. In the case
of dynamical gauge conditions for the lapse and shift we obtain a class of
evolution equations which are strongly hyperbolic and so yield well posed
initial value formulations.


title: Gravity and the quantum potential

abstract:
  We review some material connecting gravity and the quantum potential and
provide a few new observations.


title: On thermodynamic and quantum fluctuations of cosmological constant

abstract:
  We discuss from the condensed-matter point of view the recent idea that the
Poisson fluctuations of cosmological constant about zero could be a source of
the observed dark energy. We argue that the thermodynamic fluctuations of
Lambda are much bigger. Since the amplitude of fluctuations is proportional to
V^{-1/2}, where V is the volume of the Universe, the present constraint on the
cosmological constant provides the lower limit for V, which is much bigger than
the volume within the cosmological horizon.