title: Discrete fields and the Pioneer anomalous acceleration

abstract:
  The dominant contributions from a discrete gravitational interaction produce
the standard potential as an effective continuous field. The sub-dominant
contributions are, in a first approximation, linear on n, the accumulated
number of (discrete) interaction events along the test-body trajectory. For a
nearly radial trajectory n is proportional to the traversed distance and its
effects may have been observed as the Pioneer anomalous constant radial
acceleration, which cannot be observed on the nearly circular planetary orbits.


title:
Discrete interactions and the Pioneer anomalous acceleration:
  Alternative II

abstract:
  The dominant contributions from a discrete gravitational interaction produce
the standard potential as an effective continuous field. The sub-dominant
contributions are, in a first approximation, linear on $n$, the accumulated
number of (discrete) interaction events along the test-body trajectory. For a
nearly radial trajectory $n$ is proportional to the transversed distance and
its effects may have been observed as the Pioneer anomalous constant radial
acceleration, which cannot be observed on the nearly circular planetary orbits.
Here we give calculation details of the alternative II, discussed in
gr-qc/0106046.


title:
Self-existing objects and auto-generated information in
  chronology-violating space-times: A philosophical discussion

abstract:
  Closed time-like curves naturally appear in a variety of chronology-violating
space-times. In these space-times, the Principle of Self-Consistency demands an
harmony between local and global affairs that excludes grandfather-like
paradoxes. However, self-existing objects trapped in CTCs are not seemingly
avoided by the standard interpretation of this principle, usually constrained
to a dynamical framework. In this paper we discuss whether we are committed to
accept an ontology with self-existing objects if CTCs actually occur in the
universe. In addition, the epistemological status of the Principle of
Self-Consistency is analyzed and a discussion on the information flux through
CTCs is presented.


title:
Distribution of Dark Matter around a Central Body, Pioneer Effect and
  Fifth Force

abstract:
  Within the framework of the Projective Unified Field Theory the distribution
of a dark matter gas around a central body is calculated. As a result the
well-known formulas of the Newtonian gravitational interaction are altered.
This dark matter effect leads to an additional radial force (towards the
center) in the equation of motion of a test body, being used for the
explanation of the so-called ``Pioneer effect'', measured in the solar system,
but without a convincing theoretical basis up to now. Further the relationship
of the occurring new force to the so-called ``fifth force'' is discussed.


title: Dark Matter and Rotation Curves of Stars in Galaxies

abstract:
  The dark matter accretion theory (around a central body) of the author on the
basis of his 5-dimensional Projective Unified Field Theory (PUFT) is applied to
the orbital motion of stars around the center of the Galaxy. The departure of
the motion from Newtonian mechanics leads to approximately flat rotation curves
being in rough accordance with the empirical facts. The spirality of the motion
is investigated.


title: Quantum cosmological perfect fluid models

abstract:
  Perfect fluid Friedmann-Robertson-Walker quantum cosmological models for an
arbitrary barotropic equation of state $p = \alpha\rho$ are constructed using
Schutz's variational formalism. In this approach the notion of time can be
recovered. By superposition of stationary states, finite-norm wave-packet
solutions to the Wheeler-DeWitt equation are found. The behaviour of the scale
factor is studied by applying the many-worlds and the ontological
interpretations of quantum mechanics. Singularity-free models are obtained for
$\alpha < 1$. Accelerated expansion at present requires $- 1/3 > \alpha > - 1$.


title: Composition of Lorentz Transformations in Terms of Their Generators

abstract:
  Two-forms in Minkowski space-time may be considered as generators of Lorentz
transformations. Here, the covariant and general expression for the composition
law (Baker-Campbell-Hausdorff formula) of two Lorentz transformations in terms
of their generators is obtained. Every subalgebra of the Lorentz algebra of
such generators, up to one, may be generated by a sole pair of generators. When
the subalgebra is known, the above BCH formula for the two two-forms
simplifies. Its simplified expressions for all such subalgebras are also given.


title:
Gravitational energy-momentum and the Hamiltonian formulation of the
  teleparallel gravity

abstract:
  The transformation properties of the gravitational energy-momentum in the
teleparallel gravity are analyzed. It is proved that the gravitational
energy-momentum in the teleparallel gravity can be expressed in terms of the
Lorentz gauge potential, and therefore is not covariant under local Lorentz
transformations. On the other hand, it can also be expressed in terms of the
translation gauge field strength, and therefore is covariant under general
coordinate transformations. A simplified Hamiltonian formulation of the
teleparallel gravity is given. Its constraint algebra has the same structure as
that of general relativity, which indicates the equivalence between the
teleparallel gravity and general relativity in the Hamiltonian formulation.


title:
On the response of non-linearly coupled, accelerated detectors in
  odd-dimensional flat spacetimes

abstract:
  In this note, we consider the response of a uniformly accelerated monopole
detector that is coupled non-linearly to the nth power of a quantum scalar
field in (D+1)-dimensional flat spacetime. We show that, when (D+1) is even,
the response of the detector in the Minkowski vacuum is characterized by a
Bose-Einstein factor for all n. Whereas, when (D+1) is odd, we find that a
Fermi-Dirac factor appears in the detector response when n is odd, but a
Bose-Einstein factor arises when n is even.


title: The Causality Principle in the Field Theory of Gravitation

abstract:
  The causality principle for the Relativistic Theory of Gravitation (RTG) is
presented. It is a straightforward consequence of the RTG basic postulates. The
necessary conditions for physical solutions of the gravitational field
equations to be fulfilled are given.


title: r-modes in the Tolman VII solution

abstract:
  The r-mode frequencies of the Tolman VII solution for the slowly rotating
non-barotropic approximation within the low frequency regime are estimated. The
relativistic correction to Newtonian r-mode calculations is shown as function
of the tenuity $\frac{R}{M}$ and is shown to be significant only for very
compact neutron stars.


title: The Schroedinger-Newton model as N->Infinity limit of a N color model

abstract:
  The generalization to N colors of a recently proposed non unitary two color
model for the gravitational interaction in non relativistic quantum mechanics
is considered. The N->Infinity limit is proven to be equivalent to the
Schroedinger-Newton model, which, though sharing localization properties with
the N=2 model, cannot produce decoherence.


title:
Detecting a stochastic gravitational wave background with the Laser
  Interferometer Space Antenna

abstract:
  The random superposition of many weak sources will produce a stochastic
background of gravitational waves that may dominate the response of the LISA
(Laser Interferometer Space Antenna) gravitational wave observatory. Unless
something can be done to distinguish between a stochastic background and
detector noise, the two will combine to form an effective noise floor for the
detector. Two methods have been proposed to solve this problem. The first is to
cross-correlate the output of two independent interferometers. The second is an
ingenious scheme for monitoring the instrument noise by operating LISA as a
Sagnac interferometer. Here we derive the optimal orbital alignment for
cross-correlating a pair of LISA detectors, and provide the first analytic
derivation of the Sagnac sensitivity curve.


title: One thing that general relativity says about photons in matter

abstract:
  Let us abandon for a moment the strict epistemological standpoint of quantum
field theory, that eventually comes to declare nonsensical any question about
the photon posed outside the quantum theoretical framework. We can then avail
of the works by Whittaker et al. and by Synge about the particle and the wave
model of the photon in the vacuum of general relativity. We can also rely on
important results found by Gordon and by Pham Mau Quan: thanks to Gordon's
discovery of an effective metric these authors have been able to reduce to the
vacuum case several problems of the electromagnetic theory of dielectrics.
  The joint use of these old findings allows one to conclude that a quantum
theoretical photon in an isotropic dielectric has a classical simile only if
the dielectric is also homogeneous.


title:
Charged null fluid collapse in anti-de Sitter spacetimes and naked
  singularities

abstract:
  We investigate the occurrence of naked singularities in the spherically
symmetric, plane symmetric and cylindrically symmetric collapse of charged null
fluid in an anti-de Sitter background. The naked singularities are found to be
strong in Tipler's sense and thus violate the cosmic censorship conjecture, but
not hoop conjecture.


title: Remarks on evolution of space-times in 3+1 and 4+1 dimensions

abstract:
  A large class of vacuum space-times is constructed in dimension 4+1 from
hyperboloidal initial data sets which are not small perturbations of empty
space data. These space-times are future geodesically complete, smooth up to
their future null infinity, and extend as vacuum space-times through their
Cauchy horizon. Dimensional reduction gives non-vacuum space-times with the
same properties in 3+1 dimensions.


title: Chaos and Gravitational Waves

abstract:
  The gravitational waveforms of a chaotic system will exhibit sensitive
dependence on initial conditions. The waveforms of nearby orbits decohere on a
timescale fixed by the largest Lyapunov exponent of the orbit. The loss of
coherence has important observational consequences for systems where the
Lyapunov timescale is short compared to the chirp timescale. Detectors that
rely on matched filtering techniques will be unable to detect gravitational
waves from these systems.


title: Graceful exit from inflation using quantum cosmology

abstract:
  A massless scalar field without self interaction and string coupled to
gravity is quantized in the framework of quantum cosmology using the Bohm-de
Broglie interpretation. Gaussian superpositions of the quantum solutions of the
corresponding Wheeler-DeWitt equation in minisuperspace are constructed. The
bohmian trajectories obtained exhibit a graceful exit from the inflationary
Pre-Big Bang epoch to the decelerated expansion phase.


title: Cosmological perturbations: a new gauge-invariant approach

abstract:
  A new gauge-invariant approach for describing cosmological perturbations is
developed. It is based on a physically motivated splitting of the stress-energy
tensor of the perturbation into two parts - the bare perturbation and the
complementary perturbation associated with stresses in the background
gravitational field induced by the introduction of the bare perturbation. The
complementary perturbation of the stress-energy tensor is explicitly singled
out and taken to the left side of the perturbed Einstein equations so that the
bare stress-energy tensor is the sole source for the perturbation of the metric
tensor and both sides of these equations are gauge invariant with respect to
infinitesimal coordinate transformations. For simplicity we analyze the
perturbations of the spatially-flat Friedmann-Lemaitre-Robertson-Walker dust
model. A cosmological gauge can be chosen such that the equations for the
perturbations of the metric tensor are completely decoupled for the h_{00},
h_{0i}, and h_{ij} metric components and explicitly solvable in terms of
retarded integrals.


title:
Conditional Symmetries and the Quantization of Bianchi Type I Vacuum
  Cosmologies with and without Cosmological Constant

abstract:
  In this work, the quantization of the most general Bianchi Type I geometry,
with and without a cosmological constant, is considered. In the spirit of
identifying and subsequently removing as many gauge degrees of freedom as
possible, a reduction of the initial 6--dimensional configuration space is
presented. This reduction is achieved by imposing as additional conditions on
the wave function, the quantum version of the --linear in momenta-- classical
integrals of motion (conditional symmetries). The vector fields inferred from
these integrals induce, through their integral curves, motions in the
configuration space which can be identified to the action of the automorphism
group of Type I, i.e. $GL(3,\Re)$. Thus, a wave function depending on one
degree of freedom, namely the determinant of the scale factor matrix, is found.
A measure for constructing the Hilbert space is proposed. This measure respects
the above mentioned symmetries, and is also invariant under the classical
property of covariance under arbitrary scalings of the Hamiltonian (quadratic
constraint).


title: Spin-Rotation Coupling in Muon g-2 Experiments

abstract:
  Spin-rotation coupling, or Mashhoon effect, is a phenomenon associated with
rotating observers. We show that the effect exists and plays a fundamental role
in the determination of the anomalous magnetic moment of the muon.


title: Classical Aspects of Accelerated Unruh-DeWitt Type Monopole Detectors

abstract:
  We have shown the classical correspondence of Unruh effect in the classical
relativistic electron theory in our previous work (gr-qc/0105051). Here we
demonstrate the analogy between the classical relativistic electron theory and
the classical Unruh-DeWitt type monopole detector theory. The field
configuration generated by a uniformly accelerated detector is worked out. The
classical correspondence of Unruh effect for scalar fields is shown by
calculating the modified energy density for the scalar field around the
detector. We conclude that a classical monopole detector cannot find any
evidence about its acceleration unless it has a finite size.


title:
Anholonomic Triads and New Classes of (2+1)-Dimensional Black Hole
  solutions

abstract:
  We apply the method of moving anholonomic frames in order to construct new
classes of solutions of the Einstein equations on (2+1)-dimensional
pseudo-Riemannian spaces. There are investigated black holes with deformed
horizons and renormalized locally anisotropic constants. We speculate on
properties of such anisotropic black holes with characteristics defined by
anholonomic frames and anisotropic interactions of matter and gravity. The
thermodynamics of locally anisotropic black holes is discussed in connection
with a possible statistical mechanics background based on locally anisotropic
variants of Chern-Simons theories.


title: Anholonomic Frames and Thermodynamic Geometry of 3D Black Holes

abstract:
  We study new classes three dimensional black hole solutions of Einstein
equations written in two holonomic and one anholonomic variables with respect
to anholonomic frames Thermodynamic properties of such (2+1)-black holes with
generic local anisotropy (having elliptitic horizons) are studied by applying
geometric methods. The corresponding thermodynamic systems are three
dimensional with entropy S being a hypersurface function on mass M, anisotropy
angle $\theta$ and eccentricity of elliptic deformations $\epsilon >.$
Two-dimensional curved thermodynamic geometries for locally anistropic deformed
black holes are constructed after integration on anisotropic parameter
$\theta$. Two approaches, the first one based on two-dimensional hypersurface
parametric geometry and the second one developed in a
Ruppeiner-Mrugala-Janyszek fashion, are analyzed. The thermodynamic curvatures
are computed and the critical points of curvature vanishing are defined.


title: Constructing the Goedel universe

abstract:
  By a suitable transformation, we derive the rotating Goedel universe from a
static one and we show, how rotation may be implemented geometrically. The
rotation law turns out to be a differential one. By increasing distance from
the rotation axis the velocity of a rotating point will exceed the velocity of
light and the cosmos has a cut-off radius. Thus, closed time-like curves do not
occur in the Goedel universe.


title:
The "physical process" version of the first law and the generalized
  second law for charged and rotating black holes

abstract:
  We investigate both the ``physical process'' version of the first law and the
second law of black hole thermodynamics for charged and rotating black holes.
We begin by deriving general formulas for the first order variation in ADM mass
and angular momentum for linear perturbations off a stationary, electrovac
background in terms of the perturbed non-electromagnetic stress-energy, $\delta
T_{ab}$, and the perturbed charge current density, $\delta j^a$. Using these
formulas, we prove the "physical process version" of the first law for charged,
stationary black holes. We then investigate the generalized second law of
thermodynamics (GSL) for charged, stationary black holes for processes in which
a box containing charged matter is lowered toward the black hole and then
released (at which point the box and its contents fall into the black hole
and/or thermalize with the ``thermal atmosphere'' surrounding the black hole).
Assuming that the thermal atmosphere admits a local, thermodynamic description
with respect to observers following orbits of the horizon Killing field, and
assuming that the combined black hole/thermal atmosphere system is in a state
of maximum entropy at fixed mass, angular momentum, and charge, we show that
the total generalized entropy cannot decrease during the lowering process or in
the ``release process''. Consequently, the GSL always holds in such processes.
No entropy bounds on matter are assumed to hold in any of our arguments.


title: Numerical Relativity: A review

abstract:
  Computer simulations are enabling researchers to investigate systems which
are extremely difficult to handle analytically. In the particular case of
General Relativity, numerical models have proved extremely valuable for
investigations of strong field scenarios and been crucial to reveal unexpected
phenomena. Considerable efforts are being spent to simulate astrophysically
relevant simulations, understand different aspects of the theory and even
provide insights in the search for a quantum theory of gravity. In the present
article I review the present status of the field of Numerical Relativity,
describe the techniques most commonly used and discuss open problems and (some)
future prospects.


title:
On the r-mode spectrum of relativistic stars: Inclusion of the radiation
  reaction

abstract:
  We consider both mode calculations and time evolutions of axial r-modes for
relativistic uniformly rotating non-barotropic neutron stars, using the
slow-rotation formalism, in which rotational corrections are considered up to
linear order in the angular velocity \Omega. We study various stellar models,
such as uniform density models, polytropic models with different polytropic
indices n, and some models based on realistic equations of state. For weakly
relativistic uniform density models, and polytropes with small values of n, we
can recover the growth times predicted from Newtonian theory when standard
multipole formulae for the gravitational radiation are used. However, for more
compact models, we find that relativistic linear perturbation theory predicts a
weakening of the instability compared to the Newtonian results. When turning to
polytropic equations of state, we find that for certain ranges of the
polytropic index n, the r-mode disappears, and instead of a growth, the time
evolutions show a rapid decay of the amplitude. This is clearly at variance
with the Newtonian predictions. It is, however, fully consistent with our
previous results obtained in the low-frequency approximation.


title: Inflation With Oscillations

abstract:
  In this paper we investigate the general features of "Oscillatory Inflation".
In adiabatic approximation, we derive a general formula for the number of
e-foldings $\tilde{N}$ which reduces to the standard expression in case of the
slow role approximation and leads to the Damour-Mukhanov type expression for
the slowly varying adiabatic index. We apply our result to the logarithmic
potential and arrive at a simple and elegant formula for the number of
e-foldings. We evolve the field equations numerically and observe a remarkable
agreement with the analytical result.


title: Geometrodynamics, Inertia and the Quantum Vacuum

abstract:
  Why does {\bf F} equal m{\bf a} in Newton's equation of motion? How does a
gravitational field produce a force? Why are inertial mass and gravitational
mass the same? It appears that all three of these seemingly axiomatic
foundational questions have an answer involving an identical physical process:
interaction between the electromagnetic quantum vacuum and the fundamental
charged particles (quarks and electrons) constituting matter. All three of
these effects and equalities can be traced back to the appearance of a specific
asymmetry in the otherwise uniform and isotropic electromagnetic quantum
vacuum. This asymmetry gives rise to a non-zero Poynting vector from the
perspective of an accelerating object. We call the resulting energy-momentum
flux the {\it Rindler flux}. The key insight is that the asymmetry in an
accelerating reference frame in flat spacetime is identical to that in a
stationary reference frame (one that is not falling) in curved spacetime.
Therefore the same Rindler flux that creates inertial reaction forces also
creates weight. All of this is consistent with the conceptualizaton and
formalism of general relativity. What this view adds to physics is insight into
a specific physical process creating identical inertial and gravitational
forces from which springs the weak principle of equivalence. What this view
hints at in terms of advanced propulsion technology is the possibility that by
locally modifying either the electromagnetic quantum vacuum and/or its
interaction with matter, inertial and gravitational forces could be modified.


title: R-mode Instability of Slowly Rotating Non-isentropic Relativistic Stars

abstract:
  We investigate properties of $r$-mode instability in slowly rotating
relativistic polytropes. Inside the star slow rotation and low frequency
formalism that was mainly developed by Kojima is employed to study axial
oscillations restored by Coriolis force. At the stellar surface, in order to
take account of gravitational radiation reaction effect, we use a near-zone
boundary condition instead of the usually imposed boundary condition for
asymptotically flat spacetime. Due to the boundary condition, complex
frequencies whose imaginary part represents secular instability are obtained
for discrete $r$-mode oscillations in some polytropic models. It is found that
such discrete $r$-mode solutions can be obtained only for some restricted
polytropic models. Basic properties of the solutions are similar to those
obtained by imposing the boundary condition for asymptotically flat spacetime.
Our results suggest that existence of a continuous part of spectrum cannot be
avoided even when its frequency becomes complex due to the emission of
gravitational radiation.


title:
Singularities of the closed RW metric in Regge Calculus: a generalized
  evolution of the 600-cell

abstract:
  An evolution scheme is developed, based on Sorkin algorithm, to evolve the
most complex regular tridimensional polytope, the 600-cell. The solution of
600-cell, already studied before, is generalized by allowing a larger number of
free variables. The singularities of Robertson-Walker (RW) metric are studied
and a reason is given why the evolution of the 600-cell stops when its volume
is still far from zero. A fit of 600-cell's evolution with a continuos metric
is studied by writing a metric generalizing Friedmann's and including the
600-cell evolution too. The result is that the 600-cell meets a
causality-breaking point of space-time. We also shortly discuss the way matter
is introduced in Regge calculus.


title: Thermodynamics of Expansive Nondecelerative Universe

abstract:
  The present contribution deals with thermodynamic aspects of the model of
Expansive Nondecelerative Universe. In this model, in the matter era a
dependence T^CBR ~ E^CBR ~ a(exp -3/4) holds for the energy of cosmic
background radiation, E^CBR and its temperature T^CBR, while the
proportionality of the energy density epsilon^CBR to the gauge factor a can be
expressed as epsilon^CBR ~ a(exp -3). The given relationships comply with
experimental observations of the cosmic background radiation as well as with a
surprising finding that the Universe expansion is not decelerated by
gravitational forces. It is rationalized that the specific entropy is
proportional to a(exp -1/4), i.e. it is gradually decreasing in time.


title: Five-dimensional general relativity and Kaluza-Klein theory

abstract:
  We consider 5D spaces which admit the most symmetric 3D subspaces. 5D vacuum
Einstein equations are constructed and 5D analog of the mass function is found.
The corresponding conservation law leads to 5D analog of Birkhoff's theorem.
Hence the cylinder condition is dynamically implemented for the considered
spaces. For some obtained metrics a period of space with respect to the fifth
coordinate was found. The problem of the dynamical degrees of freedom of the
fields system obtained in the process of dimensional reduction is discussed,
and the problem of their interpretation is considered. One can think that the
parametrization of the scalar field and 4D metric leading to the conformally
invariant 4D theory for interacting gravitational and scalar fields is most
natural and adequate.


title: The Generalized Uncertainty Principle and Black Hole Remnants

abstract:
  In the current standard viewpoint small black holes are believed to emit
radiation as black bodies at the Hawking temperature, at least until they reach
Planck size, after which their fate is open to conjecture. A cogent argument
against the existence of remnants is that, since no evident quantum number
prevents it, black holes should radiate completely away to photons and other
ordinary stable particles and vacuum, like any unstable quantum system. Here we
argue the contrary, that the generalized uncertainty principle may prevent
their total evaporation in exactly the same way that the uncertainty principle
prevents the hydrogen atom from total collapse: the collapse is prevented, not
by symmetry, but by dynamics, as a minimum size and mass are approached.


title: Pair creation of particles and black holes in external fields

abstract:
  It is well known that massive black holes may form through the gravitational
collapse of a massive astrophysical body. Less known is the fact that a black
hole can be produced by the quantum process of pair creation in external
fields. These black holes may have a mass much lower than their astrophysical
counterparts. This mass can be of the order of Planck mass so that quantum
effects may be important. This pair creation process can be investigated
semiclassically using non-perturbative instanton methods, thus it may be used
as a theoretical laboratory to obtain clues for a quantum gravity theory. In
this work, we review briefly the history of pair creation of particles and
black holes in external fields. In order to present some features of the
euclidean instanton method which is used to calculate pair creation rates, we
study a simple model of a scalar field and propose an effective one-loop action
for a two-dimensional soliton pair creation problem. This action is built from
the soliton field itself and the soliton charge is no longer treated as a
topological charge but as a Noether charge. The results are also valid
straightforwardly to the problem of pair creation rate of domain walls in
dimensions greater than 2.


title:
Green's function for a n-dimensional closed, static universe and with a
  spherical boundary

abstract:
  We construct the Hadamard Green's function by using the eigenfunction, which
are obtained by solving the wave equation for the massless conformal scalar
field on the S^n-1 of a n-dimensional closed, static universe. We also consider
the half space case with both the Dirichlet and the Neumann boundary
conditions. Solving of eigenfunction and eigenvalues of the corresponding field
equation is interesting since the Casimir energy could be calculated
analytically by various methods.


title:
Collapsing shells of radiation in higher dimensional space-time and the
  cosmic censorship conjecture

abstract:
  Gravitational collapse of radiation shells in a non self-similar higher
dimensional spherically symmetric spacetime is studied. Strong curvature naked
singularities form for a highly inhomogeneous collapse, violating the cosmic
censorship conjecture. As a special case, self similar models can be
constructed.


title: A Mass Formula for EYM Solitons

abstract:
  The Isolated Horizon formalism, together with a simple phenomenological model
for colored black holes was recently used to predict a formula for the ADM mass
of the solitons of the EYM system in terms of horizon properties of black holes
{\it for all} values of the horizon area. In this note, this formula is tested
numerically --up to a large value of the area-- for spherically symmetric
solutions and shown to yield the known masses of the solitons


title:
Some Mathematical And Numerical Questions Connected With First And
  Second Order Time Dependent Systems Of Partial Differential Equations

abstract:
  There is a tendency to write the equations of general relativity as a first
order symmetric system of time dependent partial differential equations.
However, for numerical reasons, it might be advantageous to use a second order
formulation like one obtained from the ADM equations. Unfortunately, the type
of the ADM equations is not well understood and therefore we shall discuss, in
the next section, the concept of wellposedness. We have to distinguish between
weakly and strongly hyperbolic systems. Strongly hyperbolic systems are well
behaved even if we add lower order terms. In contrast; for every weakly
hyperbolic system we can find lower order terms which make the problem totally
illposed. Thus, for weakly hyperbolic systems, there is only a restricted class
of lower order perturbations which do not destroy the wellposedness. To
identify that class can be very difficult, especially for nonlinear
perturbations. In Section 3 we will show that the ADM equations, linearized
around flat with constant lapse function and shift vector, are only weakly
hyperbolic. However, we can use the trace of the metric as a lapse function to
make the equations into a strongly second order hyperbolic system. Using simple
models we shall, in section 4, demonstrate that approximations of second order
equations have better accuracy properties than the corresponding approximations
of first order equations. Also, we avoid spurious waves which travel against
the characteristic direction. In the last section we discuss some difficulties
connected with the preservation of constraints.


title: Fresh inflation and decoherence of super Hubble fluctuations

abstract:
  I study a stochastic approach to the recently introduced fresh inflation
model for super Hubble scales. I find that the state loses its coherence at the
end of the fresh inflationary period as a consequence of the damping of the
interference function in the reduced density matrix. This fact should be a
consequence of a) the relative evolutions of both the scale factor and the
horizon and b) the additional thermal and dissipative effects. This implies a
relevant difference with respect to supercooled inflationary scenarios which
require a very rapid expansion of the scale factor to give the decoherence of
super Hubble fluctuations.


title:
Comparison between two methods of post-Newtonian expansion for the
  motion in a weak Schwarzschild field

abstract:
  The asymptotic method of post-Newtonian (PN) expansion for weak gravitational
fields, recently developed, is compared with the standard method of PN
expansion, in the particular case of a massive test particle moving along a
geodesic line of a weak Schwarzschild field. First, the expression of the
active mass in Schwarzschild's solution is given for a barotropic perfect
fluid, both for general relativity (GR) and for an alternative, scalar theory.
The principle of the asymptotic method is then recalled and the PN expansion of
the active mass is derived. The PN correction to the active mass is made of the
Newtonian elastic energy, augmented, for the scalar theory, by a term due to
the self-reinforcement of the gravitational field. Third, two equations, both
correct to first order, are derived for the geodesic motion of a mass particle:
a "standard" one and an "asymptotic" one. Finally, the difference between the
solutions of these two equations is numerically investigated in the case of
Mercury. The asymptotic solution deviates from the standard one like the square
of the time elapsed since the initial time. This is due to a practical
shortcoming of the asymptotic method, which is shown to disappear if one
reinitializes the asymptotic problem often enough. Thus, both methods are
equivalent in the case investigated. In a general case, the asymptotic method
seems more natural.


title: Regularizing the r-mode problem for nonbarotropic relativistic stars

abstract:
  We present results for r-modes of relativistic nonbarotropic stars. We show
that the main differential equation, which is formally singular at lowest order
in the slow-rotation expansion, can be regularized if one considers the initial
value problem rather than the normal mode problem. However, a more physically
motivated way to regularize the problem is to include higher order terms. This
allows us to develop a practical approach for solving the problem and we
provide results that support earlier conclusions obtained for uniform density
stars. In particular, we show that there will exist a single r-mode for each
permissible combination of $l$ and $m$. We discuss these results and provide
some caveats regarding their usefulness for estimates of
gravitational-radiation reaction timescales. The close connection between the
seemingly singular relativistic r-mode problem and issues arising because of
the presence of corotation points in differentially rotating stars is also
clarified.


title: Cosmic strings and strings in gravitational waves

abstract:
  We consider strings with the Nambu action as extremal surfaces in a given
space-time, thus, we ignore their back reaction. Especially, we look for
strings sharing one symmetry with the underlying space-time. If this is a
non-null symmetry, the problem of determining the motion of the string can be
dimensionally reduced. We get exact solutions for the following cases: straight
and circle-like strings in a Friedmann background, straight strings in an
anisotropic Kasner background, different types of strings in the metric of a
gravitational wave. The solutions will be discussed.


title: Embeddings in Non-Vacuum Spacetimes

abstract:
  A scheme is discussed for embedding n-dimensional, Riemannian manifolds in an
(n+1)-dimensional Einstein space. Criteria for embedding a given manifold in a
spacetime that represents a solution to Einstein's equations sourced by a
massless scalar field are also discussed. The embedding procedures are
illustrated with a number of examples.


title:
Spacetime geometry from algebra: spin foam models for non-perturbative
  quantum gravity

abstract:
  This is an introduction to spin foam models for non-perturbative quantum
gravity, an approach that lies at the point of convergence of many different
research areas, including loop quantum gravity, topological quantum field
theories, path integral quantum gravity, lattice field theory, matrix models,
category theory, statistical mechanics. We describe the general formalism and
ideas of spin foam models, the picture of quantum geometry emerging from them,
and give a review of the results obtained so far, in both the Euclidean and
Lorentzian case. We focus in particular on the Barrett-Crane model for
4-dimensional quantum gravity.


title: Fermion masses and quantum numbers from extra dimensions

abstract:
  We study the localization of fermions on a brane embedded in a space-time
with $AdS_n \times M^k$ geometry. Quantum numbers of localized fermions are
associated with their rotation momenta around the brane. Fermions with
different quantum numbers have different higher-dimensional profiles. Fermion
masses and mixings, which are proportional to the overlap of higher-dimensional
profiles of the fermions, depend on the fermion quantum numbers.


title: Structure of Extended Space

abstract:
  In present work the generalization of Einstein's special theory of relativity
on 5-dimentional space is considered, in which as fifth coordinates we consider
the interval s of a particle. 5-dimentional vectors in this space are isotropic
both for mass, and for massless of particles.
  In extended space, offered by the authors, there is a possibility in addition
with usual Lorentz transformations, to enter two new transformations, therefore
massive and massless of a particle can reversible converted to each other.


title: Gravitational waves from freely precessing neutron stars

abstract:
  In this paper we model the gravitational wave emission of a freely precessing
neutron star. The aim is to estimate likely source strengths, as a guide for
gravitational wave astronomers searching for such signals. We model the star as
a partly elastic, partly fluid body with quadrupolar deformations of its moment
of inertia tensor. The angular amplitude of the free precession is limited by
the finite breaking strain of the star's crust. The effect of internal
dissipation on the star is important, with the precession angle being rapidly
damped in the case of a star with an oblate deformation. We then go on to study
detailed scenarios where free precession is created and/or maintained by some
astrophysical mechanism. We consider the effects of accretion torques,
electromagnetic torques, glitches and stellar encounters. We find that the
mechanisms considered are either too weak to lead to a signal detectable by an
Advanced LIGO interferometer, or occur too infrequently to give a reasonable
event rate. We therefore conclude that, using our stellar model at least, free
precession is not a good candidate for detection by the forthcoming laser
interferometers.


title: Decoherent histories analysis of the relativistic particle

abstract:
  The Klein-Gordon equation is a useful test arena for quantum cosmological
models described by the Wheeler-DeWitt equation. We use the decoherent
histories approach to quantum theory to obtain the probability that a free
relativistic particle crosses a section of spacelike surface. The decoherence
functional is constructed using path integral methods with initial states
attached using the (positive definite) ``induced'' inner product between
solutions to the constraint equation. The notion of crossing a spacelike
surface requires some attention, given that the paths in the path integral may
cross such a surface many times, but we show that first and last crossings are
in essence the only useful possibilities. Different possible results for the
probabilities are obtained, depending on how the relativistic particle is
quantized (using the Klein-Gordon equation, or its square root, with the
associated Newton-Wigner states). In the Klein-Gordon quantization, the
decoherence is only approximate, due to the fact that the paths in the path
integral may go backwards and forwards in time. We compare with the results
obtained using operators which commute with the constraint (the ``evolving
constants'' method).


title: Structure formation in the Lemaitre-Tolman model

abstract:
  Structure formation within the Lemaitre-Tolman model is investigated in a
general manner. We seek models such that the initial density perturbation
within a homogeneous background has a smaller mass than the structure into
which it will develop, and the perturbation then accretes more mass during
evolution. This is a generalisation of the approach taken by Bonnor in 1956. It
is proved that any two spherically symmetric density profiles specified on any
two constant time slices can be joined by a Lemaitre-Tolman evolution, and
exact implicit formulae for the arbitrary functions that determine the
resulting L-T model are obtained. Examples of the process are investigated
numerically.


title: Quantum cosmology with a curvature squared action

abstract:
  The correct quantum description for a curvature squared term in the action
can be obtained by casting the action in the canonical form with the
introduction of a variable which is the negative of the first derivative of the
field variable appearing in the action, only after removing the total
derivative terms from the action. We present the Wheeler-DeWitt equation and
obtain the expression for the probability density and current density from the
equation of continuity. Furthermore, in the weak energy limit we obtain the
classical Einstein equation. Finally we present a solution of the wave
equation.


title: An alternative derivation of the gravitomagnetic clock effect

abstract:
  The possibility of detecting the gravitomagnetic clock effect using
artificial Earth satellites provides the incentive to develop a more intuitive
approach to its derivation. We first consider two test electric charges moving
on the same circular orbit but in opposite directions in orthogonal electric
and magnetic fields and show that the particles take different times in
describing a full orbit. The expression for the time difference is completely
analogous to that of the general relativistic gravitomagnetic clock effect in
the weak-field and slow-motion approximation. The latter is obtained by
considering the gravitomagnetic force as a small classical non-central
perturbation of the main central Newtonian monopole force. A general expression
for the clock effect is given for a spherical orbit with an arbitrary
inclination angle. This formula differs from the result of the general
relativistic calculations by terms of order c^{-4}.


title: Gravitational Rainbow

abstract:
  It is shown that unlike Einstein's gravity quadratic gravity produces
dispersive photon propagation. The energy-dependent contribution to the
deflection of photons passing by the Sun is computed and subsequently the angle
at which the visible spectrum would be spread over is plotted as a function of
the $R_{\mu\nu}^2-$sector mass.


title: Exact Dissipative Cosmologies with Stiff Fluid

abstract:
  The general solution of the gravitational field equations in the flat
Friedmann-Robertson-Walker geometry is obtained in the framework of the full
Israel-Stewart-Hiscock theory for a bulk viscous stiff cosmological fluid, with
bulk viscosity coefficient proportional to the energy density.


title: Inflationary Cosmologies in an Anisotropic Brane World

abstract:
  A new cosmological solution of the gravitational field equations in the
generalized Randall-Sundrum model for an anisotropic brane with Bianchi I
geometry and with perfect fluid as matter sources is presented. The matter is
described by a scalar field. The solution admits inflationary era and at a
later epoch the anisotropy of the universe washes out. We obtain two classes of
cosmological scenario, in the first case universe evolves from singularity and
in the second case universe expands without singularity.


title: Gravitational collapse of a radiating shell and radiation bursts

abstract:
  We study the collapse of a self-gravitating thick shell of bosons coupled to
a scalar radiation field. Due to the non-adiabaticity of the collapse, the
shell (quantum) internal degrees of freedom absorb energy from the (classical)
gravitational field and are excited. The excitation energy is then emitted in
the form of bursts of (thermal) radiation and the corresponding backreaction on
the trajectory is estimated.


title:
Gravitational singularities via acceleration: the case of the
  Schwarzschild solution and Bach's gamma metric

abstract:
  The so called gamma metric corresponds to a two-parameter family of axially
symmetric, static solutions of Einstein's equations found by Bach. It contains
the Schwarzschild solution for a particular value of one of the parameters,
that rules a deviation from spherical symmetry.
  It is shown that there is invariantly definable singular behaviour beyond the
one displayed by the Kretschmann scalar when a unique, hypersurface orthogonal,
timelike Killing vector exists. In this case, a particle can be defined to be
at rest when its world-line is a corresponding Killing orbit. The norm of the
acceleration on such an orbit proves to be singular not only for metrics that
deviate from Schwarzschild's metric, but also on approaching the horizon of
Schwarzschild metric itself, in contrast to the discontinuous behaviour of the
curvature scalar.


title: Analog gravity from electrodynamics in non-linear media

abstract:
  Working with electrodynamics in the geometrical optics approximation we
derive the expression representing an effectively curved geometry which guides
the propagation of electromagnetic waves in material media whose physical
properties depend on an external electric field. The issue of birefringence is
addressed, and the trajectory of the extraordinary ray is explicitly worked
out. Quite general curves are obtained for the path of the light ray by
suitably setting an electric field.


title: Assisted inflation in Bianchi VI0 cosmologies

abstract:
  Exact models for Bianchi VI0 spacetimes with multiple scalar fields with
exponential potentials have been derived and analysed. It has been shown that
these solutions, when they exist, attract neighbouring solutions in the two
cases corresponding to interacting and non-interacting fields. Unlike the
results obtained in a previous work dealing with the late-time inflationary
behaviour of Bianchi VI0 cosmologies, the knowledge of exact solutions has made
possible to study in detail the occurrence of inflation before the asymptotic
regime. As happened in preceding works, here as well inflation is more likely
to happen with a higher number of non-interacting fields or a lower number of
interacting scalar fields.


title: Space and Observers in Cosmology

abstract:
  I provide a prescription to define space, at a given moment, for an arbitrary
observer in an arbitrary (sufficiently regular) curved space-time. This
prescription, based on synchronicity (simultaneity) arguments, defines a
foliation of space-time, which corresponds to a family of canonically
associated observers. It provides also a natural global reference frame (with
space and time coordinates) for the observer, in space-time (or rather in the
part of it which is causally connected to him), which remains Minkowskian along
his world-line. This definition intends to provide a basis for the problem of
quantization in curved space-time, and/or for non inertial observers.
  Application to Mikowski space-time illustrates clearly the fact that
different observers see different spaces. It allows, for instance, to define
space everywhere without ambiguity, for the Langevin observer (involved in the
Langevin pseudoparadox of twins). Applied to the Rindler observer (with uniform
acceleration) it leads to the Rindler coordinates, whose choice is so justified
with a physical basis. This leads to an interpretation of the Unruh effect, as
due to the observer's dependence of the definition of space (and time). This
prescription is also applied in cosmology, for inertial observers in the
Friedmann - Lemaitre models: space for the observer appears to differ from the
hypersurfaces of homogeneity, which do not obey the simultaneity requirement. I
work out two examples: the Einstein - de Sitter model, in which space, for an
inertial observer, is not flat nor homogeneous, and the de Sitter case.


title:
Maximum Mass-Radius Ratios for Charged Compact General Relativistic
  Objects

abstract:
  Upper limits for the mass-radius ratio and total charge are derived for
stable charged general relativistic matter distributions. For charged compact
objects the mass-radius ratio exceeds the value 4/9 corresponding to neutral
stars. General restrictions for the redshift and total energy (including the
gravitational contribution) are also obtained.


title: Induction and Amplification of Non-Newtonian Gravitational Fields

abstract:
  One obtains a Maxwell-like structure of gravitation by applying the
weak-field approximation to the well accepted theory of general relativity or
by extending Newton's laws to time-dependent systems. This splits gravity in
two parts, namely a gravitoelectric and gravitomagnetic (or cogravitational)
one. Due to the obtained similar structure between gravitation and
electromagnetism, one can express one field by the other one using a coupling
constant depending on the mass to charge ratio of the field source.
Calculations of induced gravitational fields using state-of-the-art fusion
plasmas reach only accelerator threshold values for laboratory testing.
Possible amplification mechanisms are mentioned in the literature and need to
be explored. The possibility of using the principle of equivalence in the weak
field approximation to induce non-Newtonian gravitational fields and the
influence of electric charge on the free fall of bodies are also investigated,
leading to some additional experimental recommendations.


title: Spinor Field in Bianchi type-I Universe: regular solutions

abstract:
  Self-consistent solutions to the nonlinear spinor field equations in General
Relativity has been studied for the case of Bianchi type-I (B-I) space-time. It
has been shown that, for some special type of nonliearity the model provides
regular solution, but this singularity-free solutions are attained at the cost
of broken dominant energy condition in Hawking-Penrose theorem. It has also
been shown that the introduction of $\Lambda$-term in the Lagrangian generates
oscillations of the B-I model, which is not the case in absence of $\Lambda$
term. Moreover, for the linear spinor field, the $\Lambda$ term provides
oscillatory solutions, those are regular everywhere, without violating dominant
energy condition.
  Key words: Nonlinear spinor field (NLSF), Bianch type -I model (B-I),
$\Lambda$ term
  PACS 98.80.C Cosmology


title:
Gravitational Poynting Vector and Gravitational Larmor Theorem in
  Rotating Bodies with Angular Acceleration

abstract:
  The gravitational Poynting vector provides a mechanism for the transfer of
gravitational energy to a system of falling objects. In the following we will
show that the gravitational poynting vector together with the gravitational
Larmor theorem also provides a mechanism to explain how massive bodies acquire
rotational kinetic energy when external mechanical forces are applied on them.


title: Free Fall of a Cylindrical Mass Electrically Charged Bodies

abstract:
  The gravitational Poynting vector provides a mechanism for the transfer of
gravitational energy to a system of falling objects. In the following we will
show that the gravitational poynting vector together with the electromagnetic
Poynting vector provides a mechanism to explain how massive electrically
charged bodies acquire kinetic energy during a free fall. We will demontrate
that falling electrically charged masses violate the Galilean law of universal
free fall. An experiment is suggested to confirm or not the predicted
phenomena.


title:
The compactification of initial data on constant mean curvature time
  slices in spherically symmetric spacetimes

abstract:
  Conformal mappings of surfaces of constant mean curvature onto compact
bounded background spaces are constructed for Minkowski space-time and for
Schwarzschild black hole spacetimes. In the black hole example, it is found
that initial data on these CMC surfaces can be regular on the compact
background space only when a certain condition is satisfied. That condition
implies that the shift vector points inward from all parts of the boundary of
the compact background. It also implies that the second fundamental form of
these surfaces can never be isotropic when black holes are present.


title: On the Motion of Matter in Spacetime

abstract:
  We argue that the geodesic hypothesis based on auto-parallels of the
Levi-Civita connection may need refinement in theories of gravity with
additional scalar fields. This argument is illustrated with a re-formulation of
the Brans-Dicke theory in terms of a spacetime connection with torsion
determined dynamically in terms of the gradient of the Brans-Dicke scalar
field. The perihelion shift in the orbit of Mercury is calculated on the
alternative hypothesis that its world-line is an auto-parallel of such a
connection. If scalar fields couple significantly to matter and spinless test
particles move on such world-lines, current time keeping methods based on the
conventional geodesic hypothesis may need refinement.


title: Initial data for stationary space-times near space-like infinity

abstract:
  We study Cauchy initial data for asymptotically flat, stationary vacuum
space-times near space-like infinity. The fall-off behavior of the intrinsic
metric and the extrinsic curvature is characterized. We prove that they have an
analytic expansion in powers of a radial coordinate. The coefficients of the
expansion are analytic functions of the angles. This result allow us to fill a
gap in the proof found in the literature of the statement that all
asymptotically flat, vacuum stationary space-times admit an analytic
compactification at null infinity. Stationary initial data are physical
important and highly non-trivial examples of a large class of data with similar
regularity properties at space-like infinity, namely, initial data for which
the metric and the extrinsic curvature have asymptotic expansion in terms of
powers of a radial coordinate. We isolate the property of the stationary data
which is responsible for this kind of expansion.


title:
Gravitational Wave Emission by Cataclysmic Variables: numerical models
  of semi-detached binaries

abstract:
  Gravitational wave emission is considered to be the driving force for the
evolution of short-period cataclysmic binary stars, making them a potential
test for the validity of General Relativity. In spite of continuous refinements
of the physical description, a 10% mismatch exists between the theoretical
minimum period ($P_{\rm turn} \simeq 70$ min) and the short-period cut-off
($P_{\rm min} \simeq 80$ min) observed in the period distribution for
cataclysmic variable binaries. A possible explanation for this mismatch was
associated with the use of the Roche model. We here present a systematic
comparison between self-consistent, numerically constructed sequences of
hydrostatic models of binary stars and Roche models of semi-detached binaries.
On the basis of our approach, we also derive a value for the minimum period of
cataclysmic variable binaries. The results obtained through the comparison
indicate that the Roche model is indeed very good, with deviations from the
numerical solution which are of a few percent at most. Our results therefore
suggest that additional sources of angular momentum loss or alternative
explanations need to be considered in order to justify the mismatch.


title: Spacetime Defects: von K\'arm\'an vortex street like configurations

abstract:
  A special arrangement of spinning strings with dislocations similar to a von
K\'arm\'an vortex street is studied. We numerically solve the geodesic
equations for the special case of a test particle moving along twoinfinite rows
of pure dislocations and also discuss the case of pure spinning defects.


title:
Signal recycled laser-interferometer gravitational-wave detectors as
  optical springs

abstract:
  Using the force-susceptibility formalism of linear quantum measurements, we
study the dynamics of signal recycled interferometers, such as LIGO-II. We show
that, although the antisymmetric mode of motion of the four arm-cavity mirrors
is originally described by a free mass, when the signal-recycling mirror is
added to the interferometer, the radiation-pressure force not only disturbs the
motion of that ``free mass'' randomly due to quantum fluctuations, but also and
more fundamentally, makes it respond to forces as though it were connected to a
spring with a specific optical-mechanical rigidity. This oscillatory response
gives rise to a much richer dynamics than previously known for SR
interferometers, which enhances the possibilities for reshaping the noise
curves and, if thermal noise can be pushed low enough, enables the standard
quantum limit to be beaten. We also show the possibility of using servo systems
to suppress the instability associated with the optical-mechanical interaction
without compromising the sensitivity of the interferometer.


title: Search for a Standard Explanation of the Pioneer Anomaly

abstract:
  The data from Pioneer 10 and 11 shows an anomalous, constant, Doppler
frequency drift that can be interpreted as an acceleration directed towards the
Sun of a_P = (8.74 \pm 1.33) x 10^{-8} cm/s^2. Although one can consider a new
physical origin for the anomaly, one first must investigate the contributions
of the prime candidates, which are systematics generated on board. Here we
expand upon previous analyses of thermal systematics. We demonstrate that
thermal models put forth so far are not supported by the analyzed data.
Possible ways to further investigate the nature of the anomaly are proposed.


title: Space-Time--Time: Five-dimensional Kaluza--Weyl Space

abstract:
  Space-time--time couples Kaluza's five-dimensional geometry with Weyl's
conformal space-time geometry to produce an extension that goes beyond what
either of those theories can achieve by itself. Kaluza's ``cylinder condition''
is replaced by an ``exponential expansion constraint'' that causes translations
along the secondary time dimension to induce both the electromagnetic gauge
transformations found in the Kaluza and the Weyl theories and the metrical
gauge transformations unique to the Weyl theory, related as Weyl had
postulated. A space-time--time geodesic describes a test particle whose rest
mass, space-time momentum, and electric charge q, all defined kinematically,
evolve in accord with definite dynamical laws. Its motion is governed by four
apparent forces: the Einstein gravitational force, the Lorentz electromagnetic
force, a force proportional to the electromagnetic potential, and a force
proportional to a scalar field's gradient d(ln phi). The test particles exhibit
quantum behavior: (1) they appear and disappear in full-blown motion at
definite events; (2) all that share an event E of appearance or disappearance
do so with the same charge magnitude |q| = phi(E); (3) conservation of
space-time--time momentum at such an event entails conservation of electric
charge in addition to conservation of space-time momentum, among the
participating particles; (4) at such events the d(ln phi) force infinitely
dominates the other three --- this strongly biases the appearance and
disappearance events to be concentrated deep in the discretely spaced potential
wells of ln phi, and sparse elsewhere.


title:
Nonanalytic extensions of the extreme Reissner-Nordstroem metric in
  terms of weak solutions

abstract:
  A basic extension of the exterior part of the extreme Reissner-Nordstroem
solution in terms of a continuous metric and gauge potential is constructed.
This extension is not smooth at the null hypersurface given by the
Cauchy-Killing horizon which separates isometric copies of the exterior metric.
The Maxwell-Einstein system of equations is satisfied only in a weak sense. The
manifold is topologically incomplete and the spherical symmetry is globally
broken down to an axial symmetry. This behaviour can be attributed to the
effect of a 'topological string', in the sense of a infinitesimally thin closed
stringlike object 'sitting on the rim' of the black hole and holding it open by
means of an accompanying impulsive gravitational wave. The resulting
differentiable manifold and the corresponding horizons are not anymore simply
connected, being 'pierced' by the strings.


title:
Nonlocal Equation of State in Anisotropic Static Fluid Spheres in
  General Relativity

abstract:
  We show that it is possible to obtain credible static anisotropic spherically
symmetric matter configurations starting from known density profiles and
satisfying a nonlocal equation of state. These particular types of equation of
state describe, at a given point, the components of the corresponding
energy-momentum tensor not only as a function at that point, but as a
functional throughout the enclosed configuration. To establish the physical
plausibility of the proposed family of solutions satisfying nonlocal equation
of state, we study the constraints imposed by the junction and energy
conditions on these bounded matter distributions.
  We also show that it is possible to obtain physically plausible static
anisotropic spherically symmetric matter configurations, having nonlocal
equations of state\textit{,}concerning the particular cases where the radial
pressure vanishes and, other where the tangential pressures vanishes. The later
very particular type of relativistic sphere with vanishing tangential stresses
is inspired by some of the models proposed to describe extremely magnetized
neutron stars (magnetars) during the transverse quantum collapse.


title: Coordinate System, Temperature and Gravity

abstract:
  We discuss the problem of applicability of Coordinate Systems (or Frames)
that determine (t,x,y,z) values - the initial notions for most physical
theories. Equipment that measure these values - Clocks and Meters - are based
at Reference System and are the primary measuring units. We discus when and why
physical phenomena might prevent to provide measurements of (t,x,y,z). We show
that Temperature may be the factor that can significantly influence on the
measurements of (t,x,y,z) by Reference System and that action may violate the
usage of Coordinate System. We discuss possible origin of such unmovable
Temperature and assume that it should be Gravity.


title:
Rossby-Haurwitz waves of a slowly and differentially rotating fluid
  shell

abstract:
  Recent studies have raised doubts about the occurrence of r modes in
Newtonian stars with a large degree of differential rotation. To assess the
validity of this conjecture we have solved the eigenvalue problem for
Rossby-Haurwitz waves (the analogues of r waves on a thin-shell) in the
presence of differential rotation. The results obtained indicate that the
eigenvalue problem is never singular and that, at least for the case of a
thin-shell, the analogues of r modes can be found for arbitrarily large degrees
of differential rotation. This work clarifies the puzzling results obtained in
calculations of differentially rotating axi-symmetric Newtonian stars.


title: Decoherence-induced violations of Einstein equivalence principle

abstract:
  In this essay it will be shown that Decoherence Model and Einstein
Equivalence Principle are conceptually incompatible. In other words, assuming
only the validity of the Weak Equivalence Principle the present work concludes
that we face two possibilities: (i) if Decoherence Model provides a correct
description of nature at quantum level, then there are systems which violate
Local Position Invariance, or, (ii) if all the postulates behind Einstein
Equivalence Principle are valid, even on quantum realm, then Decoherence Model
breaks down in curved spacetimes. Finally, the present results are confronted
against Schiff's conjecture.


title: Tidal interaction in binary black hole inspiral

abstract:
  In rotating viscous fluid stars, tidal torque leads to an exchange of spin
and orbital angular momentum. The horizon of a black hole has an effective
viscosity that is large compared to that of stellar fluids, and an effective
tidal torque may lead to important effects in the strong field interaction at
the endpoint of the inspiral of two rapidly rotating holes. In the most
interesting case both holes are maximally rotating and all angular momenta
(orbital and spins) are aligned. We point out here that in such a case (i) the
transfer of angular momentum may have an important effect in modifying the
gravitational wave ``chirp'' at the endpoint of inspiral. (ii) The tidal
transfer of spin energy to orbital energy may increase the amount of energy
being radiated. (iii) Tidal transfer in such systems may provide a mechanism
for shedding excess angular momentum. We argue that numerical relativity, the
only tool for determining the importance of tidal torque, should be more
specifically focused on binary configurations with aligned, large, angular
momenta.


title:
Long term stable integration of a maximally sliced Schwarzschild black
  hole using a smooth lattice method

abstract:
  We will present results of a numerical integration of a maximally sliced
Schwarzschild black hole using a smooth lattice method. The results show no
signs of any instability forming during the evolutions to t=1000m. The
principle features of our method are i) the use of a lattice to record the
geometry, ii) the use of local Riemann normal coordinates to apply the 1+1 ADM
equations to the lattice and iii) the use of the Bianchi identities to assist
in the computation of the curvatures. No other special techniques are used. The
evolution is unconstrained and the ADM equations are used in their standard
form.


title: Exact Bianchi Identity in Regge Gravity

abstract:
  In the continuum the Bianchi identity implies a relationship between
different components of the curvature tensor, thus ensuring the internal
consistency of the gravitational field equations. In this paper an exact form
for the Bianchi identity in Regge's discrete formulation of gravity is derived,
by considering appropriate products of rotation matrices constructed around
null-homotopic paths. It implies an algebraic relationship between deficit
angles belonging to neighboring hinges. As in the continuum, the derived
identity is valid for arbitrarily curved manifolds, without a restriction to
the weak field, small curvature limit, but is in general not linear in the
curvatures.


title: Relativistic static fluid spheres with a linear equation of state

abstract:
  It is shown that almost all known solutions of the kind mentioned in the
title are easily derived in a unified manner when a simple ansatz is imposed on
the metric. The Whittaker solution is an exception, replaced by a new solution
with the same equation of state.


title: Gravitational Waves from Electroweak Phase Transitions

abstract:
  Gravitational waves are generated during first-order phase transitions,
either by turbolence or by bubble collisions. If the transition takes place at
temperatures of the order of the electroweak scale, the frequency of these
gravitational waves is today just within the band of the planned space
interferometer LISA. We present a detailed analysis of the production of
gravitational waves during an electroweak phase transition in different
supersymmetric models where, contrary to the case of the Standard Model, the
transition can be first order. We find that the stochastic background of
gravitational waves generated by bubble nucleation can reach a maximum value
h0^2 Omega_{gw} of order 10^{-10} - 10^{-11}, which is within the reach of the
planned sensitivity of LISA, while turbolence can even produce signals at the
level h0^2 Omega_{gw} \sim 10^{-9}. These values of h0^2 Omega_{gw} are
obtained in the regions of the parameter space which can account for the
generation of the baryon asymmetry at the electroweak scale.


title: Black Holes and String Theory

abstract:
  This is a short summary of my lectures given at the Fourth Mexican School on
Gravitation and Mathematical Physics. These lectures gave a brief introduction
to black holes in string theory, in which I primarily focussed on describing
some of the recent calculations of black hole entropy using the statistical
mechanics of D-brane states. The following overview will also provide the
interested students with an introduction to the relevant literature.


title:
Generalized Tensor Analysis Method Applied to Non-time-orthogonal
  Coordinate Frames

abstract:
  A generalized covariant method of analysis applicable to frames for which
time is not orthogonal to space, such as spacetime around a star possessing
angular momentum or on a rotating disk, is presented. Important aspects of such
an analysis are shown to include i) use of the physically relevant
contravariant or covariant component form for a given vector/tensor, ii)
conversion of physical (measured) components to generalized coordinate
components prior to tensor analysis, iii) use of generalized covariant
constitutive equations during tensor analysis, and iv) conversion of coordinate
components back to physical components after tensor analysis. The method is
then applied to electrodynamics in a rotating frame, and shown to predict the
results of the Wilson/Wilson and Roentgen/Eichenwald experiments.


title: The covariant graviton propagator in de Sitter spacetime

abstract:
  We consider the covariant graviton propagator in de Sitter spacetime in a
gauge with two parameters, alpha and beta, in the Euclidean approach. We give
an explicit form of the propagator with a particular choice of beta but with
arbitrary value of alpha. We confirm that two-point functions of local
gauge-invariant quantities do not increase as the separation of the two points
becomes large.


title:
Massive Complex Scalar Field in a Kerr-Sen Black Hole Background: Exact
  Solution of Wave Equation and Hawking Radiation

abstract:
  The separated radial part of a massive complex scalar wave equation in the
Kerr-Sen geometry is shown to satisfy the generalized spheroidal wave equation
which is, in fact, a confluent Heun equation up to a multiplier. The Hawking
evaporation of scalar particles in the Kerr-Sen black hole background is
investigated by the Damour-Ruffini-Sannan's method. It is shown that quantum
thermal effect of the Kerr-Sen black hole has the same characteras that of the
Kerr-Newman black hole.


title:
Symmetry, singularities and intregrability in complex dynamics VII:
  Integrability Properties of FRW-Scalar Cosmologies

abstract:
  This paper considers some physically interesting cosmological dynamical
systems in the FRW-scalarfield category which are examined for integrability
according to the criterion of Painlev\'e. In the literature these systems have
been examined from the point of view of dynamical systems and the results from
the two disparate methods of analysis are compared. This allows some more
general comments to be made on the use of the Painlev\'e method in covariant
systems.


title: Isolated Horizon, Killing Horizon and Event Horizon

abstract:
  We consider space-times which in addition to admitting an isolated horizon
also admit Killing horizons with or without an event horizon. We show that an
isolated horizon is a Killing horizon provided either (1) it admits a
stationary neighbourhood or (2) it admits a neighbourhood with two independent,
commuting Killing vectors. A Killing horizon is always an isolated horizon. For
the case when an event horizon is definable, all conceivable relative locations
of isolated horizon and event horizons are possible. Corresponding conditions
are given.


title: On the gravitomagnetic effects in cylindrically symmetric spacetimes

abstract:
  Using gyroscopes we generalize results, obtained for the gravitomagnetic
clock effect in the particular case when the exterior spacetime is produced by
a rotating dust cylinder, to the case when the vacuum spacetime is described by
the general cylindrically symmetric Lewis spacetime. Results are contrasted
with those obtained for the Kerr spacetime.


title: Dynamical systems approach to G2 cosmology

abstract:
  In this paper we present a new approach for studying the dynamics of
spatially inhomogeneous cosmological models with one spatial degree of freedom.
By introducing suitable scale-invariant dependent variables we write the
evolution equations of the Einstein field equations as a system of autonomous
partial differential equations in first-order symmetric hyperbolic format,
whose explicit form depends on the choice of gauge. As a first application, we
show that the asymptotic behaviour near the cosmological initial singularity
can be given a simple geometrical description in terms of the local past
attractor on the boundary of the scale-invariant dynamical state space. The
analysis suggests the name ``asymptotic silence'' to describe the evolution of
the gravitational field near the cosmological initial singularity.


title:
A Newtonian Model for the Quantum Gravitational Back-Reaction on
  Inflation

abstract:
  Quantum gravitational back-reaction offers a simultaneous explanation for why
the cosmological constant is so small and a natural model of inflation in which
scalars play no role. In this talk I review previous work and present a simple
model of the mechanism in which the induced stress tensor behaves like negative
vacuum energy with a density proportional to $-\Lambda/{8\pi G} \cdot (G
\Lambda)^2 \cdot H t$. The model also highlights the essential role of
causality in back-reaction.


title: Relation between polymer and Fock excitations

abstract:
  To bridge the gap between background independent, non-perturbative quantum
gravity and low energy physics described by perturbative field theory in
Minkowski space-time, Minkowskian Fock states are located, analyzed and used in
the background independent framework. This approach to the analysis of
semi-classical issues is motivated by recent results of Varadarajan. As in that
work, we use the simpler U(1) example to illustrate our constructions but, in
contrast to that work, formulate the theory in such a way that it can be
extended to full general relativity.


title: Relativistic Static Thin Disks: The Counter-Rotating Model

abstract:
  A detailed study of the Counter-Rotating Model (CRM) for generic finite
static axially symmetric thin disks with nonzero radial pressure is presented.
We find a general constraint over the counter-rotating tangential velocities
needed to cast the surface energy-momentum tensor of the disk as the
superposition of two counter-rotating perfect fluids. We also found expressions
for the energy density and pressure of the counter-rotating fluids. Then we
shown that, in general, there is not possible to take the two counter-rotating
fluids as circulating along geodesics neither take the two counter-rotating
tangential velocities as equal and opposite. An specific example is studied
where we obtain some CRM with well defined counter-rotating tangential
velocities and stable against radial perturbations. The CRM obtained are in
agree with the strong energy condition, but there are regions of the disks with
negative energy density, in violation of the weak energy condition.


title: Velocity-induced collapses of stable neutron stars

abstract:
  The collapse of spherical neutron stars is studied in General Relativity. The
initial state is a stable neutron star to which an inward radial kinetic energy
has been added through some velocity profile. For two different equations of
state and two different shapes of velocity profiles, it is found that neutron
stars can collapse to black holes for high enough inward velocities, provided
that their masses are higher than some minimal value, depending on the equation
of state. For a polytropic equation of state of the form $p=K\rho^\gamma $,
with $\gamma = 2$ it is found to be $1.16 (\frac{K}{0.1})^{0.5} \msol$, whereas
for a more realistic one, it reads $0.36 \msol $. In some cases of collapse
forming a black hole, part of the matter composing the initial neutron star can
be ejected through a shock, leaving only a fraction of the initial mass to form
a black hole. Therefore, black holes of very small masses can be formed and, in
particular, the mass scaling relation, as a function of initial velocity, takes
the form discovered by Choptuik for critical collapses.


title:
Gravitational signals emitted by a point mass orbiting a neutron star: a
  perturbative approach

abstract:
  We compute the energy spectra of the gravitational signals emitted when a
pointlike mass moves on a closed orbit around a non rotating neutron star,
inducing a perturbation of its gravitational field and its internal structure.
The Einstein equations and the hydrodynamical equations are perturbed and
numerically integrated in the frequency domain. The results are compared with
the energy spectra computed by the quadrupole formalism which assumes that both
masses are pointlike, and accounts only for the radiation emitted because the
orbital motion produces a time dependent quadrupole moment. The results of our
perturbative approach show that, in general, the quadrupole formalism
overestimates the amount of emitted radiation, especially when the two masses
are close. However, if the pointlike mass is allowed to move on an orbit so
tight that the keplerian orbital frequency resonates with the frequency of the
fundamental quasi-normal mode of the star (2w_K=w_f), this mode can be excited
and the emitted radiation can be considerably larger than that computed by the
quadrupole approach.


title: Model of graviton-dusty universe

abstract:
  Primary features of a new cosmological model, which is based on conjectures
about an existence of the graviton background and superstrong gravitational
quantum interaction, are considered. An expansion of the universe is impossible
in such the model because of deceleration of massive objects by the graviton
background, which is similar to the one for the NASA deep space probes Pioneer
10, 11. Redshifts of remote objects are caused in the model by interaction of
photons with the graviton background, and the Hubble constant depends on an
intensity of interaction and an equivalent temperature of the graviton
background. Virtual massive gravitons would be dark matter particles. They
transfer energy, lost by luminous matter radiation, which in a final stage may
be collected with black holes and other massive objects.


title: Detecting torsion from LISA and teleparallel gravity

abstract:
  Torsion detection from totally skew symmetric torsion waves in the context of
teleparallel gravity is discussed. A gedanken experiment to detect Cartan's
contortion based on a circle of particles not necessarily spinning is proposed.
It is shown that by making use of previous value of contortion at the surface
of the Earth computed by Nitsch of $10^{-24} s^{-1}$ a relative displacement of
$10^{-21}$ is obtained which is of the order of the gravitational wave of
$10^{-3}Hz$. Since LISA has been designed to work in the mHz regime this GW
detector could be used for an indirect detection of torsion in $T_{4}$.


title: Quantum Information and Quantum Black Holes

abstract:
  First, the relation between black holes and limitations on information of
other systems is developed. After reviewing the relation of entropy to
information, we derive the entropy bound, review its applications to cosmology
and its extensions to higher dimensions, and discuss why black holes behave as
1-D objects when emitting entropy. We also discuss fundamental limitations on
the information of pulses in curved space, and on the rate of disposal of
information into a black hole. We then move on to a discussion of quantum black
holes motivated by the adiabatic invariance of horizon area of classical holes.
We develop an algebraic formalism based on symmetry which gives information on
the area (or mass) spectrum of quantum black holes, and on the degeneracy of
the levels. This last turns out to be consistent with the horizon area-black
hole entropy proportionality while leaving room for corrections.


title:
Automorphism Inducing Diffeomorphisms, Invariant Characterization of
  Homogeneous 3-Spaces and Hamiltonian Dynamics of Bianchi Cosmologies

abstract:
  An invariant description of Bianchi Homogeneous (B.H.) 3-spaces is presented,
by considering the action of the Automorphism Group on the configuration space
of the real, symmetric, positive definite, $3\times 3$ matrices. Thus, the
gauge degrees of freedom are removed and the remaining (gauge invariant)
degrees, are the --up to 3-- curvature invariants. An apparent discrepancy
between this Kinematics and the Quantum Hamiltonian Dynamics of the lower Class
A Bianchi Types, occurs due to the existence of the Outer Automorphism
Subgroup. This discrepancy is satisfactorily removed by exploiting the quantum
version of some classical integrals of motion (conditional symmetries) which
are recognized as corresponding to the Outer Automorphisms.


title: Evolution systems for non-linear perturbations of background geometries

abstract:
  The formulation of the initial value problem for the Einstein equations is at
the heart of obtaining interesting new solutions using numerical relativity and
still very much under theoretical and applied scrutiny. We develop a
specialised background geometry approach, for systems where there is
non-trivial a priori knowledge about the spacetime under study. The background
three-geometry and associated connection are used to express the ADM evolution
equations in terms of physical non-linear deviations from that background.
Expressing the equations in first order form leads naturally to a system
closely linked to the Einstein-Christoffel system, introduced by Anderson and
York, and sharing its hyperbolicity properties. We illustrate the drastic
alteration of the source structure of the equations, and discuss why this is
likely to be numerically advantageous.


title:
Is Noether Symmetric Approach Consistent With Dynamical Equation In
  Non-minimal Scalar-Tensor Theories?

abstract:
  The form of the coupling of the scalar field with gravity and the potential
have been found by applying Noether theorem to two dimensional minisuperspaces
in induced gravity model. It has been observed that though the forms thus
obtained are consistent with all the equations $\pounds_{X}L=0$, yet they do
not satisfy the field equations for $k=\pm 1$, in Robertson-Walker model. It
has been pointed out that this is not due to the degeneracy of the Lagrangian,
since this problem does not appear in $k=0$ case.It has also been shown that
though Noether theorem fails to extract any symmetry from the Lagrangian of
such model for $k=\pm 1$, symmetry exists, which can easily be found by
studying the continuity equation.


title: Noether and some other dynamical symmetries in Kantowski-Sachs model

abstract:
  The forms of coupling of the scalar field with gravity, appearing in the
induced theory of gravity, and the potential are found in the Kantowski-Sachs
model under the assumption that the Lagrangian admits Noether symmetry. The
form thus obtained makes the Lagrangian degenerate. The constrained dynamics
thus evolved due to such degeneracy has been analysed and a solution has also
been presented which is inflationary in behaviour. It has further been shown
that there exists other technique to explore the dynamical symmetries of the
Lagrangian and that is simply by inspecting the field equations. Through this
method, Noether along with some other dynamical symmetries are found, which do
not make the Lagrangian degenerate.


title: Singularities in gravitational collapse with radial pressure

abstract:
  We analyze spherical dust collapse with non-vanishing radial pressure, $\Pi$,
and vanishing tangential stresses. Considering a barotropic equation of state,
$\Pi=\gamma\rho$, we obtain an analytical solution in closed form---which is
exact for $\gamma=-1,0$, and approximate otherwise---near the center of
symmetry (where the curvature singularity forms). We study the formation,
visibility, and curvature strength of singularities in the resulting spacetime.
We find that visible, Tipler strong singularities can develop from generic
initial data. Radial pressure alters the spectrum of possible endstates for
collapse, increasing the parameter space region that contains no visible
singularities, but cannot by itself prevent the formation of visible
singularities for sufficiently low values of the energy density. Known results
from pressureless dust are recovered in the $\gamma=0$ limit.


title: Recurrence metrics and the physics of closed time-like curves

abstract:
  We investigate vacuum solutions of Einstein's equation for a universe with an
S^1 topology of time. Such a universe behaves like a time-machine and has
geodesics which coincide with closed time-like curves (CTCs). A system evolving
along a CTC experiences the Loschmidt velocity reversion and undergoes a
recurrence commensurate with the universal period. We indicate why this
universe is free of the causality paradoxes, usually associated with CTCs.


title: Gravitational self force and gauge transformations

abstract:
  We explore how the gravitational self force (or ``radiation reaction''
force), acting on a pointlike test particle in curved spacetime, is modified in
a gauge transformation. We derive the general transformation law, describing
the change in the self force in terms of the infinitesimal displacement vector
associated with the gauge transformation. Based on this transformation law, we
extend the regularization prescription by Mino et al. and Quinn and Wald
(originally formulated within the harmonic gauge) to an arbitrary gauge. Then
we extend the method of mode-sum regularization (which provides a practical
means for calculating the regularized self force and was recently applied to
the harmonic-gauge gravitational self force) to an arbitrary gauge. We find
that the regularization parameters involved in this method are
gauge-independent. We also explore the gauge transformation of the self force
from the harmonic gauge to the Regge-Wheeler gauge and to the radiation gauge,
focusing attention on the regularity of these gauge transformations. We
conclude that the transformation of the self force to the Regge-Wheeler gauge
in Schwarzschild spacetime is regular for radial orbits and irregular
otherwise, whereas the transformation to the radiation gauge is irregular for
all orbits.


title: Non--Newtonian gravity and coherence properties of light

abstract:
  In this work the possibility of detecting a non--Newtonian contribution to
the gravitational potential by means of its effects upon the first and
second--order coherence properties of light is analyzed. It will be proved
that, in principle, the effects of a fifth force upon the correlation functions
of electromagnetic radiation could be used to detect the existence of new
forces. Some constraints upon the experimental parameters will also be deduced.


title: Classical Analysis of the van Dam - Veltman Discontinuity

abstract:
  We consider the classical theory of a gravitational field with spin 2 and
non-vanishing (Pauli-Fierz) mass in flat spacetime, coupled to electromagnetism
and point particles. We establish the law of light propagation and calculate
the amount of deflection in the background of a spherically symmetric
gravitational field. As the mass tends to zero, the deflection is shown to
converge to 3/4 of the value predicted by the massless theory (linearized
General Relativity), even though the spherically symmetric solution of the
gravitational field equations has no regular limit. This confirms an old
argument of van Dam and Veltman on a purely classical level, but also shows its
subtle nature.


title: The Graviton Production in a Hot Homogeneous Isotropic Universe

abstract:
  It is shown that the RTG predicts an opportunity of the intensive production
of gravitons at the early stage of evolution of the homogeneous isotropic
Universe. A hypothesis is suggested that the produced gas of gravitons could be
just the ``dark matter'' which presently manifests itself as a ``missing mass''
in our Universe.


title: Integrable cases of gravitating static isothermal fluid spheres

abstract:
  It is shown that different approaches towards the solution of the Einstein
equations for a static spherically symmetric perfect fluid with a gamma-law
equation of state lead to an Abel differential equation of the second kind. Its
only integrable cases at present are flat spacetime, de Sitter solution and its
Buchdahl transform, Einstein static universe and the Klein-Tolman solution.


title:
Properties of r modes in rotating magnetic neutron stars. I. Kinematic
  Secular Effects and Magnetic Evolution Equations

abstract:
  The instability of r-mode oscillations in rapidly rotating neutron stars has
attracted attention as a potential mechanism for producing high frequency,
almost periodic gravitational waves. The analyses carried so far have shown the
existence of these modes and have considered damping by shear and bulk
viscosity. However, the magnetohydrodynamic coupling of the modes with a
stellar magnetic field and its role in the damping of the instability has not
been fully investigated yet. Following our introductory paper (Rezzolla, Lamb
and Shapiro 2000), we here discuss in more detail the existence of secular
higher-order kinematical effects which will produce toroidal fluid drifts. We
also define the sets of equations that account for the time evolution of the
magnetic fields produced by these secular velocity fields and show that the
magnetic fields produced can reach equipartition in less than a year. The full
numerical calculations as well as the evaluation of the impact of strong
magnetic fields on the onset and evolution of the r-mode instability will be
presented in a companion paper.


title:
Properties of r modes in rotating magnetic neutron stars. II. Evolution
  of the r modes and stellar magnetic field

abstract:
  The evolution of the r-mode instability is likely to be accompanied by
secular kinematic effects which will produce differential rotation with large
scale drifts of fluid elements, mostly in the azimuthal direction. As first
discussed by Rezzolla, Lamb and Shapiro 2000, the interaction of these secular
velocity fields with a pre-existing neutron star magnetic field could result in
the generation of intense and large scale toroidal fields. Following their
derivation in the companion paper, we here discuss the numerical solution of
the evolution equations for the magnetic field. The values of the magnetic
fields obtained in this way are used to estimate the conditions under which the
r-mode instability might be prevented or suppressed. We also assess the impact
of the generation of large magnetic fields on the gravitational wave
detectability of r-mode unstable neutron stars. Our results indicate that the
signal to noise ratio in the detection of gravitational waves from the r-mode
instability might be considerably decreased if the latter develops in neutron
stars with initial magnetic fields larger than 10^10 G.


title:
Matter waves in a gravitational field: An index of refraction for
  massive particles in general relativity

abstract:
  We consider the propagation of massive-particle de Broglie waves in a static,
isotropic metric in general relativity. We demonstrate the existence of an
index of refraction that governs the waves and that has all the properties of a
classical index of refraction. We confirm our interpretation with a WKB
solution of the general-relativistic Klein-Gordon equation. Finally, we make
some observations on the significance of the optical action.


title: The Weyl tensor two-point function in de Sitter spacetime

abstract:
  We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.


title: New hairy black holes with negative cosmological constant

abstract:
  Black hole solutions with nonspherical event horizon topology are shown to
exist in an Einstein-Yang-Mills theory with negative cosmological constant. The
main characteristics of the solutions are presented and differences with
respect to the spherically symmetric case are studied. The stability of these
configurations is also addressed.


title: Neutrino Oscillations Induced by Gravitational Recoil Effects

abstract:
  Quantum gravitational fluctuations of the space-time background, described by
virtual D branes, may induce neutrino oscillations if a tiny violation of the
Lorentz invariance (or a violation of the equivalence principle) is imposed. In
this framework, the oscillation length of massless neutrinos turns out to be
proportional to M/E^2, where E is the neutrino energy and M is the mass scale
characterizing the topological fluctuations in the vacuum. Such a functional
dependence on the energy is the same obtained in the framework of loop quantum
gravity.


title: Classical History Theory of Vector Fields

abstract:
  We consider the extension of classical history theory to the massive vector
field and electromagnetism. It is argued that the action of the two Poincare
groups introduced by Savvidou suggests that the history fields should have five
components. The extra degrees of freedom introduced to make the fields
five-dimensional result in an extra pair of second class constraints in the
case of the massive vector field, and in an extended gauge group in the case of
electromagnetism. The total gauge transformations depend on two arbitrary
parameters, and contain `internal' and `external' U(1) gauge transformations as
subgroups.


abstract:
  Boost-rotation symmetric vacuum spacetimes with spinning sources which
correspond to gravitational field of uniformly accelerated spinning "particles"
are studied. Regularity conditions and asymptotic properties are analyzed. News
functions are derived by transforming the general spinning boost-rotation
symmetric vacuum metric to Bondi-Sachs coordinates.


title: Cosmic no-hair: non-linear asymptotic stability of de Sitter universe

abstract:
  We study the asymptotic stability of de Sitter spacetime with respect to
non-linear perturbations, by considering second order perturbations of a flat
Robertson-Walker universe with dust and a positive cosmological constant. Using
the synchronous comoving gauge we find that, as in the case of linear
perturbations, the non-linear perturbations also tend to constants,
asymptotically in time. Analysing curvature and other spacetime invariants we
show, however, that these quantities asymptotically tend to their de Sitter
values, thus demonstrating that the geometry is indeed locally asymptotically
de Sitter, despite the fact that matter inhomogeneities tend to constants in
time. Our results support the inflationary picture of frozen amplitude matter
perturbations that are stretched outside the horizon, and demonstrate the
validity of the cosmic no-hair conjecture in the nonlinear inhomogeneous
settings considered here.


title: Quantum Cosmology With R+R^2 Gravity

abstract:
  Canonical quantization of an action containing curvature squared term
requires introduction of an auxiliary variable. Boulware etal[1] prescribed a
technique to choose such a variable, by taking derivative of an action with
respect to the highest derivative of the field variable, present in the
action.It has been shown that[2] this technique can even be applied in
situations where introduction of auxiliary variables are not at all required,
leading to wrong Wheeler-deWitt equation. It has also been pointed out that[2]
Boulware etal's[1] prescription should be taken up only after removing all
removable total derivative terms from the action. Once this is done only a
unique description of quantum dynamics would emerge. For curvature squared term
this technique yields, for the first time, a quantum mechanical probability
interpretation of quantum cosmology, and an effective potential, whose
extremization leads to Einstein's equation. We conclude that Einstein-Hilbert
action should essentially be modified by at least a curvature squared term to
get a quantum mechanical formulation of quantuum cosmology and hence extend our
previous work[2] for such an action along with a scalar field.


title: On choice of connection in loop quantum gravity

abstract:
  We investigate the quantum area operator in the loop approach based on the
Lorentz covariant hamiltonian formulation of general relativity. We show that
there exists a two-parameter family of Lorentz connections giving rise to
Wilson lines which are eigenstates of the area operator. For each connection
the area spectrum is evaluated. In particular, the results of the su(2)
approach turn out to be included in the formalism. However, only one connection
from the family is a spacetime connection ensuring that the 4d diffeomorphism
invariance is preserved under quantization. It leads to the area spectrum
independent of the Immirzi parameter. As a consequence, we conclude that the
su(2) approach must be modified accordingly to the results obtained since it
breaks one of the classical symmetries.


title: Can Black Holes Decay to Naked Singularities?

abstract:
  We investigate thermodynamic properties of two types of asymptotically
anti-de Sitter spacetimes: black holes and singular scalar field spacetimes. We
describe the possibility that thermodynamic phase transitions can transform one
spacetime into another, suggesting that black holes can radiate to naked
singularities.


title: Local contribution of a quantum condensate to the vacuum energy density

abstract:
  We evaluate the local contribution g_[mu nu]L of coherent matter with
lagrangian density L to the vacuum energy density. Focusing on the case of
superconductors obeying the Ginzburg-Landau equation, we express the
relativistic invariant density L in terms of low-energy quantities containing
the pairs density. We discuss under which physical conditions the sign of the
local contribution of the collective wave function to the vacuum energy density
is positive or negative. Effects of this kind can play an important role in
bringing about local changes in the amplitude of gravitational vacuum
fluctuations - a phenomenon reminiscent of the Casimir effect in QED.