title:
Coupling of spacetime atoms and spin foam renormalisation from group
  field theory

abstract:
  We study the issue of coupling among 4-simplices in the context of spin foam
models obtained from a group field theory formalism. We construct a
generalisation of the Barrett-Crane model in which an additional coupling
between the normals to tetrahedra, as defined in different 4-simplices that
share them, is present. This is realised through an extension of the usual
field over the group manifold to a five argument one. We define a specific
model in which this coupling is parametrised by an additional real parameter
that allows to tune the degree of locality of the resulting model,
interpolating between the usual Barrett-Crane model and a flat BF-type one.
Moreover, we define a further extension of the group field theory formalism in
which the coupling parameter enters as a new variable of the field, and the
action presents derivative terms that lead to modified classical equations of
motion. Finally, we discuss the issue of renormalisation of spin foam models,
and how the new coupled model can be of help regarding this.


title:
On the use of Ajisai and Jason-1 satellites for tests of General
  Relativity

abstract:
  Here we analyze in detail some aspects of the proposed use of Ajisai and
Jason-1, together with the LAGEOS satellites, to measure the general
relativistic Lense-Thirring effect in the gravitational field of the Earth. A
linear combination of the nodes of such satellites is the proposed observable.
The systematic error due to the mismodelling in the uncancelled even zonal
harmonics would be \sim 1% according to the latest present-day
CHAMP/GRACE-based Earth gravity models. In regard to the non-gravitational
perturbations especially affecting Jason-1, only relatively high-frequency
harmonic perturbations should occur: neither semisecular nor secular bias of
non-gravitational origin should affect the proposed combination: their maximum
impact is evaluated to \sim 4% over 2 years. Our estimation of the
root-sum-square total error is about 4-5% over at least 3 years of data
analysis required to average out the uncancelled tidal perturbations.


title: Finiteness of Lorentzian 10j symbols and partition functions

abstract:
  We give a short and simple proof that the Lorentzian 10j symbol, which forms
a key part of the Barrett-Crane model of Lorentzian quantum gravity, is finite.
The argument is very general, and applies to other integrals. For example, we
show that the Lorentzian and Riemannian causal 10j symbols are finite, despite
their singularities. Moreover, we show that integrals that arise in
Cherrington's work are finite. Cherrington has shown that this implies that the
Lorentzian partition function for a single triangulation is finite, even for
degenerate triangulations. Finally, we also show how to use these methods to
prove finiteness of integrals based on other graphs and other homogeneous
domains.


title: Quasinormal modes of black holes and dissipative open systems

abstract:
  After explaining the physical origin of the quasinormal modes of
perturbations in the background geometry of a black hole, I critically review
the recent proposal for the quantization of the black-hole area based on the
real part of quasinormal modes. As instantons due to the barriers of black-hole
potentials lie at the root of a discrete set of complex quasinormal modes
frequencies, it is likely that the physics of quasinormal modes can be learned
from quantum theory. I propose a connection of a system of quasinormal modes of
black holes with a dissipative open system, in particular, the
Feshbach-Tikochinsky oscillator. This argument is supported in part by the fact
that these two systems have the same group structure SU(1,1) and the same group
representation of Hamiltonians; thereby, their quantum states exhibit the same
behavior.


title: Comments on "Derivation of the Raychaudhuri Equation" by Dadhich

abstract:
  In a recent preprint, gr-qc/0511123, Dadhich has given a brief yet beautiful
exposition on some of the research works by Prof. A.K. Raychaudhuri. Here
Dadhich highlights the fact that the apparently ``self-evident'' assumption of
occurrence of ``trapped surfaces'' may not be realized atleast in some specific
cosmological models though no general proof for non-occurrence of trapped
surfaces exists in the cosmological context. However, Dadhich added, without
sufficient justification, that trapped surfaces should occur for collapse of
isolated bodies. We point out that actually trapped surfaces do not occur even
for collapse of spherically symmetric isolated bodies. Further unlike the
cosmological case, for isolated bodies, an exact proof for generic
non-occurrence of trapped surfaces is available. Thus for isolated bodies, the
above referred apparently ``self-evident'' assumption fails much more acutely
than in cosmology. Many recent astrophysical observations tend to corroborate
the fact trapped surfaces do not occur for isolated bodies. Two recent specific
papers (PRD) are cited to show that when radiative non-diispative collapse can
prevent formation of trapped surfaces.


title: Scaling Laws for the Cosmological Constant

abstract:
  We study the expansion of the universe at late times in the case that the
cosmological constant obeys certain scaling laws motivated by renormalisation
group running in quantum theories. The renormalisation scale is identified with
the Hubble scale and the inverse radii of the event and particle horizon,
respectively. We find de Sitter solutions, power-law expansion and
super-exponential expansion in addition to future singularities of the Big Rip
and Big Crunch type.


title: Stochastic Background from Coalescences of NS-NS Binaries

abstract:
  In this work, numerical simulations were used to investigate the
gravitational stochastic background produced by coalescences occurring up to $z
\sim 5$ of double neutron star systems. The cosmic coalescence rate was derived
from Monte Carlo methods using the probability distributions for forming a
massive binary and to occur a coalescence in a given redshift. A truly
continuous background is produced by events located only beyond the critical
redshift $z_* = 0.23$. Events occurring in the redshift interval $0.027<z<0.23$
give origin to a "popcorn" noise, while those arising closer than $z = 0.027$
produce a shot noise. The gravitational density parameter $\Omega_{gw}$ for the
continuous background reaches a maximum around 670 Hz with an amplitude of
$1.1\times 10^{-9}$, while the "popcorn" noise has an amplitude about one order
of magnitude higher and the maximum occurs around a frequency of 1.2 kHz. The
signal is below the sensitivity of the first generation of detectors but could
be detectable by the future generation of ground based interferometers.
Correlating two coincident advanced-LIGO detectors or two EGO interferometers,
the expected S/N ratio are respectively 0.5 and 10.


title: Explicit solutions for relativistic acceleration and rotation

abstract:
  The Lorentz transformations are represented by Einstein velocity addition on
the ball of relativistically admissible velocities. This representation is by
projective maps. The Lie algebra of this representation defines the
relativistic dynamic equation. If we introduce a new dynamic variable, called
symmetric velocity, the above representation becomes a representation by
conformal, instead of projective maps. In this variable, the relativistic
dynamic equation for systems with an invariant plane, becomes a non-linear
analytic equation in one complex variable. We obtain explicit solutions for the
motion of a charge in uniform, mutually perpendicular electric and magnetic
fields. By assuming the Clock Hypothesis and using these solutions, we are able
to describe the space-time transformations between two uniformly accelerated
and rotating systems.


title: Progress and problems in quantum gravity

abstract:
  From the point of view of an uncompromising field theorist quantum gravity is
beset with serious technical and, above all, conceptual problems with regard
especially to the meaning of genuine "physical" observables. This situation is
not really improved by the appearance of recent attempts to reformulate gravity
within some novel framework.However, the original aim, a background-independent
quantum theory of gravity, can be achieved in a particular area, namely 2d
dilaton quantum gravity without any assumptions beyond standard quantum field
theory. Some important by-products of the research of the "Vienna School"
include the introduction of the concept of Poisson-Sigma models, a verification
of the "virtual Black Hole" and the extensions to N = (1,1) and N = (2,2)
2d-supergravity, for which complete solutions of some old problems have been
possible which are relevant for superstring theory


title:
A vacuum-like configuration in General Relativity as a manifestation of
  a Lorentz-invariant mode of five-dimensional gravity

abstract:
  A Lorentz-invariant cosmological model is constructed within the framework of
five-dimensional gravity. The five-dimensional theorem which is analogical to
the generalized Birkhoff theorem is proved, that corresponds to the Kaluza's
``cylinder condition''. The five-dimensional vacuum Einstein equations have an
integral of motion corresponding to this symmetry, the integral of motion is
similar to the mass function in general relativity (GR). Space closure with
respect to the extra dimensionality follows from the requirement of the absence
of a conical singularity. Thus, the Kaluza-Klein (KK) model is realized
dynamically as a Lorentz-invariant mode of five-dimensional general relativity.
After the dimensional reduction and conformal mapping the model is reduced to
the GR configuration. It contains a scalar field with a vanishing conformally
invariant energy-momentum tensor on the flat space-time background. This zero
mode can be interpreted as a vacuum configuration in GR. As a result the
vacuum-like configuration in GR can be considered as a manifestation of the
Lorentz-invariant empty five-dimensional space.


title: Recurrence Metrics and Time Varying Light Cones

abstract:
  It is shown by explicit construction of new metrics, that General Relativity
can solve the exact Poinc$\acute{a}$re recurrence problem. In these solutions,
the light cone, flips periodically between past and future, due to a
periodically alternating arrow of the proper time. The geodesics in these
universes show periodic Loschmidt's velocity reversion $v \to -v$, at critical
points, which leads to recurrence. However, the matter tensors of some of these
solutions exhibit unusual properties - such as, periodic variations in density
and pressure. While this is to be expected in periodic models, the physical
basis for such a variation is not clear. Present paper therefore can be
regarded as an extension of Tipler's "no go theorem for recurrence in an
expanding universe", to other space-time geometries.


title: Perspectives on Quantum Gravity Phenomenology

abstract:
  The idea that quantum gravity manifestations would be associated with a
violation of Lorentz invariance is very strongly bounded and faces serious
theoretical challenges. Other related ideas seem to be drowning in
interpretational quagmires. This leads us to consider alternative lines of
thought for such phenomenological search. We discuss the underlying viewpoints
and briefly mention their possible connections with other current theoretical
ideas.


title:
Tomographic approach to resolving the distribution of LISA Galactic
  binaries

abstract:
  The space based gravitational wave detector LISA is expected to observe a
large population of Galactic white dwarf binaries whose collective signal is
likely to dominate instrumental noise at observational frequencies in the range
10^{-4} to 10^{-3} Hz. The motion of LISA modulates the signal of each binary
in both frequency and amplitude, the exact modulation depending on the source
direction and frequency. Starting with the observed response of one LISA
interferometer and assuming only doppler modulation due to the orbital motion
of LISA, we show how the distribution of the entire binary population in
frequency and sky position can be reconstructed using a tomographic approach.
The method is linear and the reconstruction of a delta function distribution,
corresponding to an isolated binary, yields a point spread function (psf). An
arbitrary distribution and its reconstruction are related via smoothing with
this psf. Exploratory results are reported demonstrating the recovery of binary
sources, in the presence of white Gaussian noise.


title: Neutrino quasinormal modes of the Reissner-Nordstr\"om black hole

abstract:
  The neutrino quasinormal modes of the Reissner-Nordstr\"om (RN) black hole
are investigated using continued fraction approach. We find, for large angular
quantum number, that the quasinormal frequencies become evenly spaced and the
spacing of the real part depends on the charge of the black hole and that of
the imaginary part is zero. We then find that the quasinormal frequencies in
the complex $\omega$ plane move counterclockwise as the charge increases. They
get a spiral-like shape, moving out of their Schwarzschild value and ``looping
in" towards some limiting frequency as the charge tends to the extremal value.
The number of the spirals increases as the overtone number increases but it
decreases as the angular quantum number increases. We also find that both the
real and imaginary parts are oscillatory functions of the charge, and the
oscillation becomes faster as the overtone number increases but it becomes
slower as the angular quantum number increases.


title: Deterministic models of quantum fields

abstract:
  Deterministic dynamical models are discussed which can be described in
quantum mechanical terms. -- In particular, a local quantum field theory is
presented which is a supersymmetric classical model. The Hilbert space approach
of Koopman and von Neumann is used to study the classical evolution of an
ensemble of such systems. Its Liouville operator is decomposed into two
contributions, with positive and negative spectrum, respectively. The unstable
negative part is eliminated by a constraint on physical states, which is
invariant under the Hamiltonian flow. Thus, choosing suitable variables, the
classical Liouville equation becomes a functional Schroedinger equation of a
genuine quantum field theory. -- We briefly mention an U(1) gauge theory with
``varying alpha'' or dilaton coupling where a corresponding quantized theory
emerges in the phase space approach. It is energy-parity symmetric and,
therefore, a prototype of a model in which the cosmological constant is
protected by a symmetry.


title: Constraining f(R) gravity in the Palatini formalism

abstract:
  Although several models of $f(R)$ theories of gravity within the Palatini
approach have been studied already, the interest was concentrated on those that
have an effect on the late-time evolution of the universe, by the inclusion for
example of terms inversely proportional to the scalar curvature in the
gravitational action. However, additional positive powers of the curvature also
provide interesting early-time phenomenology, like inflation, and the presence
of such terms in the action is equally, if not more, probable. In the present
paper models with both additional positive and negative powers of the scalar
curvature are studied. Their effect on the evolution of the universe is
investigated for all cosmological eras, and various constraints are put on the
extra terms in the actions. Additionally, we examine the extent to which the
new terms in positive powers affect the late-time evolution of the universe and
the related observables, which also determines our ability to probe their
presence in the gravitational action.


title: Thermodynamic Behavior of a Perfect Fluid with Negative Energy Density

abstract:
  Starting from a perfect cosmological fluid represented by the energy momentum
tensor T_uv, one class of frequency metrics that satisfies both Einstein's
general relativistic equation and the perfect fluid condition is: g_uv = e^iwt
N_uv. Mathematically, such metrics indicate spacetime behaves locally like a
simple harmonic oscillator. In the cosmological model presented here these
small spacetime oscillations compress vacuum energy into a standing wave inside
a dynamic Casimir cavity. At peak compression a phase shift occurs and the
standing wave forms into a particle having relativistic mass-energy equal to
the compressive work required to produce it. At this point the newly formed
particle does isobaric work to expand the volume against the external pressure
given T_ii. Equilibrium is achieved when the collision rate on the volume's
internal and external surfaces equalizes. By treating spacetime as a classical
thermodynamic problem and oscillator, such quantities as the mass of the
compressed particle--that of an axion, the radii of the initial and final
volume of compression, and the angular frequency of compression can be
determined. During axion collision the photon frequency of the particle is
calculated to be in the microwave range and inversely equal to that of the
frequency of the spacetime compression that produced the particle. This
suggests axion production is a source for the 2.7K cosmic background radiation
and dark matter that pervades spacetime.


title: The Duality of Time Dilation and Velocity

abstract:
  Time dilation $\frac{1}{\sqrt{1-v^2}}$ and relative velocity $v$ are
observationally indistinguishable in the special theory of relativity, a
duality that carries over into the general theory under Fermi coordinates along
a curve (in coordinate-independent language, in the tangent Minkowski space
along the curve). For example, on a clock stationary at radius $r$, a distant
observer sees time dilation of $\frac{1}{\sqrt{1-v^2}}=\frac{1}{\sqrt{1-2M/r}}$
under the Schwarzschild metric and sees the clock receding with a relative
velocity of $v=\sqrt{2M/r}$ under the Painlev{\'e}-Gullstrand free fall metric.
Duality implies that during gravitational collapse, the intensifying time
dilation observed at the star's center from a fixed radius $r>0$ is
indistinguishable (along a curve) from an increasing relative velocity at which
the center recedes as seen from any direction, implying a local inflation.


title: Exact Vacuum Solutions of Jordan, Brans-Dicke Field Equations

abstract:
  We present the static spherically symmetric vacuum solutions of the Jordan,
Brans-Dicke field equations. The new solutions are obtained by considering a
polar Gaussian, isothermal and radial hyperbolic metrics.


title: The Hole Argument for Covariant Theories

abstract:
  The hole argument was developed by Einstein in 1913 while he was searching
for a relativistic theory of gravitation. Einstein used the language of
coordinate systems and coordinate invariance, rather than the language of
manifolds and diffeomorphism invariance. He formulated the hole argument
against covariant field equations and later found a way to avoid it using
coordinate language.
  In this paper we shall use the invariant language of categories, manifolds
and natural objects to give a coordinate-free description of the hole argument
and a way of avoiding it. Finally we shall point out some important
implications of further extensions of the hole argument to sets and relations
for the problem of quantum gravity.


title:
The Local Effects of Cosmological Variations in Physical 'Constants' and
  Scalar Fields I. Spherically Symmetric Spacetimes

abstract:
  We apply the method of matched asymptotic expansions to analyse whether
cosmological variations in physical `constants' and scalar fields are
detectable, locally, on the surface of local gravitationally bound systems such
as planets and stars, or inside virialised systems like galaxies and clusters.
We assume spherical symmetry and derive a sufficient condition for the local
time variation of the scalar fields that drive varying constants to track the
cosmological one. We calculate a number of specific examples in detail by
matching the Schwarzschild spacetime to spherically symmetric inhomogeneous
Tolman-Bondi metrics in an intermediate region by rigorously construction
matched asymptotic expansions on cosmological and local astronomical scales
which overlap in an intermediate domain. We conclude that, independent of the
details of the scalar-field theory describing the varying `constant', the
condition for cosmological variations to be measured locally is almost always
satisfied in physically realistic situations. The proof of this statement
provides a rigorous justification for using terrestrial experiments and solar
system observations to constrain or detect any cosmological time variations in
the traditional `constants' of Nature.


title: Towards conformal loop quantum gravity

abstract:
  A discussion is given of recent developments in canonical gravity that
assimilates the conformal analysis of gravitational degrees of freedom. The
work is motivated by the problem of time in quantum gravity and is carried out
at the metric and the triad levels. At the metric level, it is shown that by
extending the Arnowitt-Deser-Misner (ADM) phase space of general relativity
(GR), a conformal form of geometrodynamics can be constructed. In addition to
the Hamiltonian and diffeomorphism constraints, an extra first class constraint
is introduced to generate conformal transformations. This phase space consists
of York's mean extrinsic curvature time, conformal three-metric and their
momenta. At the triad level, the phase space of GR is further enlarged by
incorporating spin-gauge as well as conformal symmetries. This leads to a
canonical formulation of GR using a new set of real spin connection variables.
The resulting gravitational constraints are first class, consisting of the
Hamiltonian constraint and the canonical generators for spin-gauge and
conformorphism transformations. The formulation has a remarkable feature of
being parameter-free. Indeed, it is shown that a conformal parameter of the
Barbero-Immirzi type can be absorbed by the conformal symmetry of the extended
phase space. This gives rise to an alternative approach to loop quantum gravity
that addresses both the conceptual problem of time and the technical problem of
functional calculus in quantum gravity.


title:
Series solutions for a static scalar potential in a Salam-Sezgin
  Supergravitational hybrid braneworld

abstract:
  The static potential for a massless scalar field shares the essential
features of the scalar gravitational mode in a tensorial perturbation analysis
about the background solution. Using the fluxbrane construction of [8] we
calculate the lowest order of the static potential of a massless scalar field
on a thin brane using series solutions to the scalar field's Klein Gordon
equation and we find that it has the same form as Newton's Law of Gravity. We
claim our method will in general provide a quick and useful check that one may
use to see if their model will recover Newton's Law to lowest order on the
brane.


title: Further simplification of the constraints of four-dimensional gravity

abstract:
  The super-Hamiltonian of 4-dimensional gravity as simplified by Ashtekar
through the use of gauge potential and densitized triad variables can
furthermore be succinctly expressed as a Poisson bracket between the volume
element and other fundamental gauge-invariant elements of 3-geometry. This
observation naturally suggests a reformulation of non-perturbative quantum
gravity wherein the Wheeler-DeWitt Equation is identical to the requirement of
the vanishing of the corresponding commutator. Moreover, this reformulation
singles out spin network states as the preeminent basis for expansion of all
physical states.


title: Viscous Brane Cosmology with a Brane-Bulk Energy Interchange Term

abstract:
  We assume a flat brane located at y=0, surrounded by an AdS space, and
consider the 5D Einstein equations when the energy flux component of the
energy-momentum tensor is related to the Hubble parameter through a constant Q.
We calculate the metric tensor, as well as the Hubble parameter on the brane,
when Q is small. As a special case, if the brane is tensionless, the influence
from Q on the Hubble parameter is absent. We also consider the emission of
gravitons from the brane, by means of the Boltzmann equation. Comparing the
energy conservation equation derived herefrom with the energy conservation
equation for a viscous fluid on the brane, we find that the entropy change for
the fluid in the emission process has to be negative. This peculiar effect is
related to the fluid on the brane being a non-closed thermodynamic system. The
negative entropy property for non-closed systems is encountered in other areas
in physics also, in particular, in connection with the Casimir effect at finite
temperature.


title: More on wormholes supported by small amounts of exotic matter

abstract:
  Recent papers by Fewster and Roman have emphasized that wormholes supported
by arbitrarily small amounts of exotic matter will have to be incredibly
fine-tuned if they are to be traversable. This paper discusses a wormhole model
that strikes a balance between two conflicting requirements, reducing the
amount of exotic matter and fine-tuning the metric coefficients, ultimately
resulting in an engineering challenge: one requirement can only be met at the
expense of the other. The wormhole model is macroscopic and satisfies various
traversability criteria.


title:
A Finite Element Computation of the Gravitational Radiation emitted by a
  Point-like object orbiting a Non-rotating Black Hole

abstract:
  The description of extreme-mass-ratio binary systems in the inspiral phase is
a challenging problem in gravitational wave physics with significant relevance
for the space interferometer LISA. The main difficulty lies in the evaluation
of the effects of the small body's gravitational field on itself. To that end,
an accurate computation of the perturbations produced by the small body with
respect the background geometry of the large object, a massive black hole, is
required. In this paper we present a new computational approach based on Finite
Element Methods to solve the master equations describing perturbations of
non-rotating black holes due to an orbiting point-like object. The numerical
computations are carried out in the time domain by using evolution algorithms
for wave-type equations. We show the accuracy of the method by comparing our
calculations with previous results in the literature. Finally, we discuss the
relevance of this method for achieving accurate descriptions of
extreme-mass-ratio binaries.


title: Thin-shell wormholes in Einstein-Maxwell theory with a Gauss-Bonnet term

abstract:
  We study five dimensional thin-shell wormholes in Einstein-Maxwell theory
with a Gauss-Bonnet term. The linearized stability under radial perturbations
and the amount of exotic matter are analyzed as a function of the parameters of
the model. We find that the inclusion of the quadratic correction substantially
widens the range of possible stable configurations, and besides it allows for a
reduction of the exotic matter required to construct the wormholes.


title: Cosmology with running parameters

abstract:
  The experimental evidence that the equation of state (EOS) of the dark energy
(DE) could be evolving with time/redshift (including the possibility that it
might behave phantom-like near our time) suggests that there might be dynamical
DE fields that could explain this behavior. We propose, instead, that a
variable cosmological term (including perhaps a variable Newton's gravitational
coupling too) may account in a natural way for all these features.


title:
Dynamics of the spatially homogeneous Bianchi type I Einstein-Vlasov
  equations

abstract:
  We investigate the dynamics of spatially homogeneous solutions of the
Einstein-Vlasov equations with Bianchi type I symmetry by using dynamical
systems methods. All models are forever expanding and isotropize toward the
future; toward the past there exists a singularity. We identify and describe
all possible past asymptotic states; in particular, on the past attractor set
we establish the existence of a heteroclinic network, which is a new type of
feature in general relativity. This illustrates among other things that Vlasov
matter can lead to quite different dynamics of cosmological models as compared
to perfect fluids.


title:
Thermo--inertial bouncing of a relativistic collapsing sphere: A
  numerical model

abstract:
  We present a numerical model of a collapsing radiating sphere, whose boundary
surface undergoes bouncing due to a decreasing of its inertial mass density
(and, as expected from the equivalence principle, also of the ``gravitational''
force term) produced by the ``inertial'' term of the transport equation. This
model exhibits for the first time the consequences of such an effect, and shows
that under physically reasonable conditions this decreasing of the
gravitational term in the dynamic equation may be large enough as to revert the
collapse and produce a bouncing of the boundary surface of the sphere.


title: Hyperboloidal data and evolution

abstract:
  We discuss the hyperboloidal evolution problem in general relativity from a
numerical perspective, and present some new results. Families of initial data
which are the hyperboloidal analogue of Brill waves are constructed
numerically, and a systematic search for apparent horizons is performed.
Schwarzschild-Kruskal spacetime is discussed as a first application of
Friedrich's general conformal field equations in spherical symmetry, and the
Maxwell equations are discussed on a nontrivial background as a toy model for
continuum instabilities.


title: Two Tunnels to Inflation

abstract:
  We investigate the formation via tunneling of inflating (false-vacuum)
bubbles in a true-vacuum background, and the reverse process. Using effective
potentials from the junction condition formalism, all true- and false-vacuum
bubble solutions with positive interior and exterior cosmological constant, and
arbitrary mass are catalogued. We find that tunneling through the same
effective potential appears to describe two distinct processes: one in which
the initial and final states are separated by a wormhole (the Farhi-Guth-Guven
mechanism), and one in which they are either in the same hubble volume or
separated by a cosmological horizon. In the zero-mass limit, the first process
corresponds to the creation of an inhomogenous universe from nothing, while the
second mechanism is equivalent to the nucleation of true- or false-vacuum
Coleman-De Luccia bubbles. We compute the probabilities of both mechanisms in
the WKB approximation using semi-classical Hamiltonian methods, and find that
-- assuming both process are allowed -- neither mechanism dominates in all
regimes.


title: Thermodynamic Geometry and Critical Behavior of Black Holes

abstract:
  Based on the observations that there exists an analogy between the
Reissner-Nordstr\"om-anti-de Sitter (RN-AdS) black holes and the van der
Waals-Maxwell liquid-gas system, in which a correspondence of variables is
$(\phi, q) \leftrightarrow (V,P)$, we study the Ruppeiner geometry, defined as
Hessian matrix of black hole entropy with respect to the internal energy (not
the mass) of black hole and electric potential (angular velocity), for the RN,
Kerr and RN-AdS black holes. It is found that the geometry is curved and the
scalar curvature goes to negative infinity at the Davies' phase transition
point for the RN and Kerr black holes.
  Our result for the RN-AdS black holes is also in good agreement with the one
about phase transition and its critical behavior in the literature.


title:
Spintessence: a possible candidate as a driver of the late time cosmic
  acceleration

abstract:
  In this paper, it is shown completely analytically that a spintessence model
can very well serve the purpose of providing an early deceleration and the
present day acceleration.


title: Closed timelike curves and geodesics of Godel-type metrics

abstract:
  It is shown explicitly that when the characteristic vector field that defines
a Godel-type metric is also a Killing vector, there always exist closed
timelike or null curves in spacetimes described by such a metric. For these
geometries, the geodesic curves are also shown to be characterized by a lower
dimensional Lorentz force equation for a charged point particle in the relevant
Riemannian background. Moreover, two explicit examples are given for which
timelike and null geodesics can never be closed.


title: Phantom universe from CPT symmetric QFT

abstract:
  Inspired by the generalization of quantum theory for the case of
non-Hermitian Hamiltonians with CPT symmetry, we construct a simple classical
cosmological scalar field based model describing a smooth transition from
ordinary dark energy to the phantom one.


title:
Detecting the Cosmic Gravitational Wave Background with the Big Bang
  Observer

abstract:
  The detection of the Cosmic Microwave Background Radiation (CMB) was one of
the most important cosmological discoveries of the last century. With the
development of interferometric gravitational wave detectors, we may be in a
position to detect the gravitational equivalent of the CMB in this century. The
Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic,
making it difficult to distinguish from instrument noise. The contribution from
the CGB can be isolated by cross-correlating the signals from two or more
independent detectors. Here we extend previous studies that considered the
cross-correlation of two Michelson channels by calculating the optimal signal
to noise ratio that can be achieved by combining the full set of interferometry
variables that are available with a six link triangular interferometer. In
contrast to the two channel case, we find that the relative orientation of a
pair of coplanar detectors does not affect the signal to noise ratio. We apply
our results to the detector design described in the Big Bang Observer (BBO)
mission concept study and find that BBO could detect a background with
$\Omega_{gw} > 2.2 \times 10^{-17}$.


title: Quantum Geometrodynamics of the Bianchi IX cosmological model

abstract:
  The canonical quantum theory of gravity -- Quantum Geometrodynamics (QG) is
applied to the homogeneous Bianchi type IX cosmological model. As a result, the
framework for the quantum theory of homogeneous cosmologies is developed. We
show that the theory is internally consistent, and prove that it possesses the
correct classical limit (the theory of general relativity). To emphasize the
special role that the constraints play in this new theory we, compare it to the
traditional ADM square-root and Wheeler-DeWitt quantization schemes. We show
that, unlike the traditional approaches, QG leads to a well-defined Schrodinger
equation for the wave-function of the universe that is inherently coupled to
the expectation value of the constraint equations. This coupling to the
constraints is responsible for the appearance of a coherent spacetime picture.
Thus, the physical meaning of the constraints of the theory is quite different
from Dirac's interpretation. In light of this distinctive feature of the
theory, we readdress the question of the dark energy effects in the Bianchi IX
cosmological model for highly non-classical quantum states. We show that, at
least for this model, for any choice of the initial wave function, the quantum
corrections will not produce the accelerated expansion of the universe.


title:
On non-existence of static vacuum black holes with degenerate components
  of the event horizon

abstract:
  We present a simple proof of the non-existence of degenerate components of
the event horizon in static, vacuum, regular, four-dimensional black hole
spacetimes. We discuss the generalisation to higher dimensions and the
inclusion of a cosmological constant.


title:
Killing vectors in asymptotically flat space--times: II. Asymptotically
  translational Killing vectors and the rigid positive energy theorem in higher
  dimensions

abstract:
  We show that the borderline cases in the proof of the positive energy theorem
for initial data sets, on spin manifolds, in dimensions $n\ge 3$, are only
possible for initial data arising from embeddings in Minkowski space-time.


title:
The classification of static electro--vacuum space--times containing an
  asymptotically flat spacelike hypersurface with compact interior

abstract:
  We show that static electro--vacuum black hole space--times containing an
asymptotically flat spacelike hypersurface with compact interior and with both
degenerate and non--degenerate components of the event horizon do not exist.
This is done by a careful study of the near-horizon geometry of degenerate
horizons, which allows us to eliminate the last restriction of the static
electro-vacuum no-hair theory.


title: GUP in presence of extra dimensions and lifetime of mini black holes

abstract:
  Based on the general considerations of quantum mechanics and gravity the
generalized uncertainty principle (GUP) is determined in higher-dimensional
case and on the brane, respectively. The result is used to evaluate the effect
of GUP on the dynamics of evaporation and lifetime of mini black holes in the
brane-world models.


title: The initial conditions of the Universe and holography

abstract:
  We address the initial conditions for an expanding cosmology using the
holographic principle. For the case of a closed model, the old prescription of
Fishler and Susskind, that uses the particle horizon to encode the bulk degrees
of freedom, can be implemented for accelerated models with enough acceleration.
As a bonus we have singularity free bouncing models. The bound is saturated for
co-dimension one branes dominated universes.


title:
Dirac equation from the Hamiltonian and the case with a gravitational
  field

abstract:
  Starting from an interpretation of the classical-quantum correspondence, we
derive the Dirac equation by factorizing the algebraic relation satisfied by
the classical Hamiltonian, before applying the correspondence. This derivation
applies in the same form to a free particle, to one in an electromagnetic
field, and to one subjected to geodesic motion in a static metric, and leads to
the same, usual form of the Dirac equation--in special coordinates. To use the
equation in the static-gravitational case, we need to rewrite it in more
general coordinates. This can be done only if the usual, spinor transformation
of the wave function is replaced by the 4-vector transformation. We show that
the latter also makes the flat-space-time Dirac equation Lorentz-covariant,
although the Dirac matrices are not invariant. Because the equation itself is
left unchanged in the flat case, the 4-vector transformation does not alter the
main physical consequences of that equation in that case. However, the equation
derived in the static-gravitational case is not equivalent to the standard
(Fock-Weyl) gravitational extension of the Dirac equation.


title: Classical and quantum LTB model for the non-marginal case

abstract:
  We extend the classical and quantum treatment of the Lemaitre-Tolman-Bondi
(LTB) model to the non-marginal case (defined by the fact that the shells of
the dust cloud start with a non-vanishing velocity at infinity). We present the
classical canonical formalism and address with particular care the boundary
terms in the action. We give the general relation between dust time and Killing
time. Employing a lattice regularization, we then derive and discuss for
particular factor orderings exact solutions to all quantum constraints.


title: Quantum gravity as a group field theory: a sketch

abstract:
  We give a very brief introduction to the group field theory approach to
quantum gravity, a generalisation of matrix models for 2-dimensional quantum
gravity to higher dimension, that has emerged recently from research in spin
foam models.


title:
Uniqueness theorem for BMS-invariant states of scalar QFT on the null
  boundary of asymptotically flat spacetimes and bulk-boundary observable
  algebra correspondence

abstract:
  Scalar BMS-invariant QFT defined on the causal boundary $\scri$ of an
asymptotically flat spacetime is discussed. (a)(i) It is noticed that the
natural $BMS$ invariant pure quasifree state $\lambda$ on $\cW(\scri)$,
recently introduced by Dappiaggi, Moretti an Pinamonti, enjoys positivity of
the self-adjoint generator of $u$-translations with respect to {\em every}
Bondi coordinate frame $(u,\z,\bz)$ on $\scri$, $u\in \bR$ being the affine
parameter of the null geodesics forming $\scri$. This fact may be interpreted
as a remnant of spectral condition inherited from Minkowski spacetime. (ii) It
is proved cluster property under $u$-displacements holds for $u$-invariant pure
state on $\cW(\scri)$. (iii) It is proved that there is a unique algebraic pure
quasifree state invariant under $u$-displacements (of a fixed Bondi frame)
having positive self-adjoint generator of $u$-displacements. It coincides with
the GNS-invariant state $\lambda$.(iv) It is showed that in the folium of a
pure $u$-invariant state $\omega$ (not necessarily quasifree) on $\cW(\scri)$,
$\omega$ is the only state invariant under $u$-displacement. (b) It is proved
that the theory can formulated for spacetimes asymptotically flat at null
infinity which admit future time completion. In this case a $*$-isomorphism
$\imath$ exists which identifies the (Weyl) algebra of observables of linear
fields in the bulk with a sub algebra of $\cW(\scri)$. A preferred state on the
field algebra in the bulk is induced by the $BMS$-invariant state $\lambda$.


title: Spinor field and accelerated regimes in cosmology

abstract:
  A self-consistent system of interaction nonlinear spinor and scalar fields
within the scope of a BI cosmological model filled with perfect fluid is
considered. The role of spinor field in the evolution of the Universe is
studied. It is shown that the spinor field nonlinearity can generate a negative
effective pressure, which can be seen as an alternative source for late time
acceleration of the Universe.


title:
Bel-Robinson tensor and dominant energy property in the Bianchi type I
  Universe

abstract:
  Within the framework of Bianchi type-I space-time we study the Bel-Robinson
tensor and its impact on the evolution of the Universe. We use different
definitions of the Bel-Robinson tensor existing in the literature and compare
the results. Finally we investigate the so called "dominant super-energy
property" for the Bel-Robinson tensor as a generalization of the usual dominant
energy condition for energy momentum tensors.
  Keywords: Bianchi type I model, super-energy tensors
  Pacs: 03.65.Pm and 04.20.Ha


title:
Asymptotic Quasinormal Frequencies of Different Spin Fields in
  Spherically Symmetric Black Holes

abstract:
  We consider the asymptotic quasinormal frequencies of various spin fields in
Schwarzschild and Reissner-Nordstr\"om black holes. In the Schwarzschild case,
the real part of the asymptotic frequency is ln3 for the spin 0 and the spin 2
fields, while for the spin 1/2, the spin 1, and the spin 3/2 fields it is zero.
For the non-extreme charged black holes, the spin 3/2 Rarita-Schwinger field
has the same asymptotic frequency as that of the integral spin fields. However,
the asymptotic frequency of the Dirac field is different, and its real part is
zero. For the extremal case, which is relevant to the supersymmetric
consideration, all the spin fields have the same asymptotic frequency, the real
part of which is zero. For the imaginary parts of the asymptotic frequencies,
it is interesting to see that it has a universal spacing of $1/4M$ for all the
spin fields in the single-horizon cases of the Schwarzschild and the extreme
Reissner-Nordstr\"om black holes. The implications of these results to the
universality of the asymptotic quasinormal frequencies are discussed.


title:
Vacuum Fluctuations, Geometric Modular Action and Relativistic Quantum
  Information Theory

abstract:
  A summary of some lines of ideas leading to model-independent frameworks of
relativistic quantum field theory is given. It is followed by a discussion of
the Reeh-Schlieder theorem and geometric modular action of Tomita-Takesaki
modular objects associated with the quantum field vacuum state and certain
algebras of observables. The distillability concept, which is significant in
specifying useful entanglement in quantum information theory, is discussed
within the setting of general relativistic quantum field theory.


title:
Regular and singular solutions for charged dust distributions in the
  Einstein--Maxwell theory

abstract:
  Solutions for the static spherically symmetric extremally charged dust in the
Majumdar--Papapetrou system have been found. For a certain amount of the
allocated mass/charge, the solutions have singularities of a type which could
render them physically unacceptable, since the corresponding physically
relevant quantities are singular as well. These solutions, with a number of
zero-nodes in the metric tensor, are regularized through the $\delta$-shell
formalism, thus redefining the mass/charge distributions. The bifurcating
behaviour of regular solutions found before is no longer present in these
singular solutions, but quantized-like behaviour in the total mass is observed.
Spectrum of regularized solutions restores the equality of the
Tolman--Whittaker and ADM mass, as well the equality of the net charge and ADM
mass, which is the distinctive feature of Majumdar--Papapetrou systems.


title:
Analytic expressions for gravitational inner multipole moments of
  elementary solids and for the force between two rectangular solids

abstract:
  We give analytic expressions for the gravitational inner spherical multipole
moments, q_{lm} with l <= 5, for 11 elementary solid shapes. These moments, in
conjunction with their known rotational and translational properties, can be
used to calculate precisely the moments of complex objects that may be
assembled from the elementary shapes. We also give an analytic expression for
the gravitational force between two rectangular solids at arbitrary
separations. These expressions are useful for computing the gravitational
properties of complex instruments, such as those used in equivalence principle
tests, and in the gravitational balancing of drag-free spacecraft.


title: Magnetic Monopoles and Cosmic Inflation

abstract:
  It is possible that the expansion of the universe began with an inflationary
phase, in which the inflaton driving the process also was a Higgs field capable
of stabilizing magnetic monopoles in a grand-unified gauge theory. If so, then
the smallness of intensity fluctuations observed in the cosmic microwave
background radiation implies that the self-coupling of the inflaton-Higgs field
was exceedingly weak. It is argued here that the resulting broad, flat maximum
in the Higgs potential makes the presence or absence of a topological zero in
the field insignificant for inflation. There may be monopoles present in the
universe, but the universe itself is not in the inflating core of a giant
magnetic monopole.


title: Asymptotic behavior of the warm inflation scenario with viscous pressure

abstract:
  We analyze the dynamics of models of warm inflation with general dissipative
effects. We consider phenomenological terms both for the inflaton decay rate
and for viscous effects within matter. We provide a classification of the
asymptotic behavior of these models and show that the existence of a late-time
scaling regime depends not only on an asymptotic behavior of the scalar field
potential, but also on an appropriate asymptotic behavior of the inflaton decay
rate. There are scaling solutions whenever the latter evolves to become
proportional to the Hubble rate of expansion regardless of the steepness of the
scalar field exponential potential. We show from thermodynamic arguments that
the scaling regime is associated to a power-law dependence of the
matter-radiation temperature on the scale factor, which allows a mild variation
of the temperature of the matter/radiation fluid. We also show that the late
time contribution of the dissipative terms alleviates the depletion of matter,
and increases the duration of inflation.


title:
Changing the Hilbert space structure as a consequence of gauge
  transformations in "extended phase space" version of quantum geometrodynamics

abstract:
  In the earlier works on quantum geometrodynamics in extended phase space it
has been argued that a wave function of the Universe should satisfy a
Schrodinger equation. Its form, as well as a measure in Schrodinger scalar
product, depends on a gauge condition (a chosen reference frame). It is known
that the geometry of an appropriate Hilbert space is determined by introducing
the scalar product, so the Hilbert space structure turns out to be in a large
degree depending on a chosen gauge condition. In the present work we analyse
this issue from the viewpoint of the path integral approach. We consider how
the gauge condition changes as a result of gauge transformations. In this
respect, three kinds of gauge transformations can be singled out: Firstly,
there are residual gauge transformations, which do not change the gauge
condition. The second kind is the transformations whose parameters can be
related by homotopy. Then the change of gauge condition could be described by
smoothly changing function. In particular, in this context time dependent
gauges could be discussed. We also suggest that this kind of gauge
transformations leads to a smooth changing of solutions to the Schrodinger
equation. The third kind of the transformations includes those whose parameters
belong to different homotopy classes. They are of the most interest from the
viewpoint of changing the Hilbert space structure. In this case the gauge
condition and the very form of the Schrodinger equation would change in
discrete steps when we pass from a spacetime region with one gauge condition to
another region with another gauge condition. In conclusion we discuss the
relation between quantum gravity and fundamental problems of ordinary quantum
mechanics.


title:
Irving Segal's axiomatization of spacetime and its cosmological
  consequences

abstract:
  Irving Ezra Segal (1918-1998) has proposed some axioms for mathematical
cosmology. These are here re-examined and Segal's redshift formula and energy
conservation in the Einstein universe are established in full on their basis. A
detailed table of contents appears at the end.


title:
Numerical Simulation of Rotating Accretion Disk Around the Schwarzschild
  Black Hole Using GRH Code

abstract:
  The 2D time dependent solution of thin accretion disk in a close binary
system have been presented on the equatorial plane around the Schwarzschild
black hole. To do that, the special part of the General Relativistic
Hydrodynamical(GRH) equations are solved using High Resolution Shock Capturing
(HRSC) schemes. The spiral shock waves on the accretion disk are modeled using
perfect fluid equation of state with adiabatic indices $\gamma = 1.05, 1.2$ and
5/3. The results show that the spiral shock waves are created for gammas except
the case $\gamma=5/3$. These results consistent with results from Newtonian
hydrodynamic code except close to black hole. Newtonian approximation does not
give good solution while matter closes to black hole. Our simulations
illustrate that the spiral shock waves are created close to black hole and the
location of inner radius of spiral shock wave is around $10M$ and it depends on
the specific heat rates. We also find that the smaller $\gamma$ is the more
tightly the spiral winds.


title: Stability of Self-Similar Spherical Accretion

abstract:
  Spherical accretion flows are simple enough for analytical study, by solution
of the corresponding fluid dynamic equations. The solutions of stationary
spherical flow are due to Bondi. The questions of the choice of a physical
solution and of stability have been widely discussed. The answer to these
questions is very dependent on the problem of boundary conditions, which vary
according to whether the accretor is a compact object or a black hole. We
introduce a particular, simple form of stationary spherical flow, namely,
self-similar Bondi flow, as a case with physical interest in which analytic
solutions for perturbations can be found. With suitable no
matter-flux-perturbation boundary conditions, we will show that acoustic modes
are stable in time and have no spatial instability at r=0. Furthermore, their
evolution eventually becomes ergodic-like and shows no trace of instability or
of acquiring any remarkable pattern.


title: Modified Newtonian Dynamics and Induced gravity

abstract:
  Modified Newtonian dynamics, a successful alternative to the cosmic dark
matter model, proposes that gravitational field deviates from the Newtonian law
when the field strength $g$ is weaker than a critical value $g_0$. We will show
that the dynamics of MOND can be derived from an induced gravity model. New
dynamics is shown to be compatible with the spatial deformation of scalar
fields coupled to the system. Approximate solutions are shown explicitly for a
simple toy model.


title:
Challenges in Signal Analysis of Resonant-Mass Gravitational Wave
  Detectors

abstract:
  An overview of the main points related to data analysis in resonant-mass
gravitational wave detectors will be presented. Recent developments on the data
analysis system for the Brazilian detector SCHENBERG will be emphasized.


title:
Can lightning be a noise source for a spherical gravitational wave
  antenna?

abstract:
  The detection of gravitational waves is a very active research field at the
moment. In Brazil the gravitational wave detector is called Mario SCHENBERG.
Due to its high sensitivity it is necessary to model mathematically all known
noise sources so that digital filters can be developed that maximize the
signal-to-noise ratio. One of the noise sources that must be considered are the
disturbances caused by electromagnetic pulses due to lightning close to the
experiment. Such disturbances may influence the vibrations of the antenna's
normal modes and mask possible gravitational wave signals. In this work we
model the interaction between lightning and SCHENBERG antenna and calculate the
intensity of the noise due to a close lightning stroke in the detected signal.
We find that the noise generated does not disturb the experiment significantly.


title: Consistent discretizations as a road to quantum gravity

abstract:
  We present a brief description of the ``consistent discretization'' approach
to classical and quantum general relativity. We exhibit a classical simple
example to illustrate the approach and summarize current classical and quantum
applications. We also discuss the implications for the construction of a well
defined quantum theory and in particular how to construct a quantum continuum
limit.


title: On totally umbilic submanifolds of semi-Riemannian manifolds

abstract:
  The notion of being totally umbilic is considered for non-degenerate and
degenerate submanifolds of semi-Riemanian manifolds. After some remarks on the
general case, timelike and lightlike totally umbilic submanifolds of Lorentzian
manifolds are discussed, along with their physical interpretation in view of
general relativity. In particular, the mathematical notion of totally umbilic
submanifolds is linked to the notions of photon surfaces and of null strings
which have been used in the physics literature.


title:
Extra symmetry in the field equations in 5D with spatial spherical
  symmetry

abstract:
  We point out that the field equations in 5D, with spatial spherical symmetry,
possess an extra symmetry that leaves them invariant. This symmetry corresponds
to certain simultaneous interchange of coordinates and metric coefficients. As
a consequence a single solution in 5D can generate very different scenarios in
4D, ranging from static configurations to cosmological situations. A new
perspective emanates from our work. Namely, that different astrophysical and
cosmological scenarios in 4D might correspond to the same physics in 5D. We
present explicit examples that illustrate this point of view.


title:
Algebraic decomposition of the electromagnetic constitutive tensor. A
  step toward pre-metric based gravitation?

abstract:
  It is known that the electromagnetic constitutive tensor can be algebraically
decomposed in three parts: the so-called principal part, the axion part and the
skewon part (see gr-qc/0506042). The aim of this paper is to provide a deeper
decomposition of the principal part.


title:
Generalised group field theories and quantum gravity transition
  amplitudes

abstract:
  We construct a generalised formalism for group field theories, in which the
domain of the field is extended to include additional proper time variables, as
well as their conjugate mass variables. This formalism allows for different
types of quantum gravity transition amplitudes in perturbative expansion, and
we show how both causal spin foam models and the usual a-causal ones can be
derived from it, within a sum over triangulations of all topologies. We also
highlight the relation of the so-derived causal transition amplitudes with
simplicial gravity actions.


title: The late-time behaviour of vortic Bianchi type VIII Universes

abstract:
  We use the dynamical systems approach to investigate the Bianchi type VIII
models with a tilted $\gamma$-law perfect fluid. We introduce
expansion-normalised variables and investigate the late-time asymptotic
behaviour of the models and determine the late-time asymptotic states. For the
Bianchi type VIII models the state space is unbounded and consequently, for all
non-inflationary perfect fluids, one of the curvature variables grows without
bound. Moreover, we show that for fluids stiffer than dust ($1<\gamma<2$), the
fluid will in general tend towards a state of extreme tilt. For dust
($\gamma=1$), or for fluids less stiff than dust ($0<\gamma< 1$), we show that
the fluid will in the future be asymptotically non-tilted. Furthermore, we show
that for all $\gamma\geq 1$ the universe evolves towards a vacuum state but
does so rather slowly, $\rho/H^2\propto 1/\ln t$.


title: Black hole entropy, log corrections and quantum ergosphere

abstract:
  Quantum-gravity corrections to the probability of emission of a particle from
a black hole in the Parikh-Wilczek tunneling framework are studied. We consider
the effects of zero-point quantum fluctuations of the metric on the emission
probability for a tunneling shell. Quantum properties of the geometry are
responsible for the formation of a "quantum egosphere" whose effects on the
emission probability can be related to the emergence of a logarithmic
correction to the Bekenstein-Hawking entropy-area formula.


title: Quantum information in loop quantum gravity

abstract:
  A coarse-graining of spin networks is expressed in terms of partial tracing,
thus allowing to use tools of quantum information theory. This is illustrated
by the analysis of a simple black hole model, where the logarithmic correction
of the Bekenstein-Hawking entropy is shown to be equal to the total amount of
correlations on the horizon. Finally other applications of entanglement to
quantum gravity are briefly discussed.


title:
A numerical study of the correspondence between paths in a causal set
  and geodesics in the continuum

abstract:
  This paper presents the results of a computational study related to the
path-geodesic correspondence in causal sets. For intervals in flat spacetimes,
and in selected curved spacetimes, we present evidence that the longest maximal
chains (the longest paths) in the corresponding causal set intervals
statistically approach the geodesic for that interval in the appropriate
continuum limit.


title: Evolution of Non-linear Fluctuations in Preheating after Inflation

abstract:
  We investigate the evolution of the non-linear long wavelength fluctuations
during preheating after inflation. By using the separate universe approach, the
temporal evolution of the power spectrum of the scalar fields and the curvature
variable is obtained numerically. We found that the amplitude of the large
scale fluctuations is suppressed after non-linear evolution during preheating.


title: A theoretical construction of wormhole supported by Phantom Energy

abstract:
  A new solution has been presented for the spherically symmetric space time
describing wormholes with Phantom Energy. The model suggests that the existence
of wormhole is supported by arbitrarily small quantity of Phantom Energy.


title: Group averaging, positive definiteness and superselection sectors

abstract:
  I discuss group averaging as a method for quantising constrained systems
whose gauge group is a noncompact Lie group. Focussing on three case studies, I
address the convergence of the averaging, possible indefiniteness of the
prospective physical inner product and the emergence of superselection sectors.


title:
Comments on conformal masses, asymptotics backgrounds and conservation
  laws

abstract:
  The "conformal mass prescriptions" were used recently to calculate the mass
of spacetimes in higher dimensional and higher curvature theories of gravity.
These definitions are closely related to Komar integrals for spacetimes that
are conformally flat at great distances from the sources. We derive these
relations without using the conformal infinity formalism.


title:
Joint LIGO and TAMA300 Search for Gravitational Waves from Inspiralling
  Neutron Star Binaries

abstract:
  We search for coincident gravitational wave signals from inspiralling neutron
star binaries using LIGO and TAMA300 data taken during early 2003. Using a
simple trigger exchange method, we perform an inter-collaboration coincidence
search during times when TAMA300 and only one of the LIGO sites were
operational. We find no evidence of any gravitational wave signals. We place an
observational upper limit on the rate of binary neutron star coalescence with
component masses between 1 and 3 M_sun of 49 per year per Milky Way equivalent
galaxy at a 90% confidence level. The methods developed during this search will
find application in future network inspiral analyses.


title: Asymptotic twistor Theory and the Kerr Theorem

abstract:
  We first review asymptotic twistor theory with its real subspace of null
asymptotic twistors. This is followed by a description of an asymptotic version
of the Kerr theorem that produces regular asymptotically shear free null
geodesic congruences in arbitrary asymptotically flat Einstein or
Einstein-Maxwell spacetimes.


title: Energy in the Schwarzschild-de Sitter Spacetime

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0301090, gr-qc/0303034, gr-qc/0212018, and gr-qc/9601044.


title:
Accretion disk onto boson stars: a way to supplant black holes
  candidates

abstract:
  The emission spectrum from a simple accretion disk model around a compact
object is compared for the cases of a black hole (BH) and a boson star (BS)
playing the role of the central object. It was found in the past that such a
spectrum presents a hardening at high frequencies; however, here it is shown
that the self-interaction and compactness of the BS have the effect of
softening the spectrum, the less compact the star is, the softer the emission
spectrum at high frequencies. Because the mass of the boson fixes the mass of
the star and the self-interaction the compactness of the star, we find that,
for certain values of the BS parameters, it is possible to produce similar
spectra to those generated when the central object is a BH. This result
presents two important implications: (i) using this simple accretion model, a
BS can supplant a BH in the role of compact object accreting matter, and (ii)
within the assumptions of the present accretion disk model we do not find a
prediction that could help distinguish a BH from a BS with appropriate
parameters of mass and self-interaction.


title: Optical geometry analysis of the electromagnetic self-force

abstract:
  We present an analysis of the behaviour of the electromagnetic self-force for
charged particles in a conformally static spacetime, interpreting the results
with the help of optical geometry. Some conditions for the vanishing of the
local terms in the self-force are derived and discussed.


title: Modified dispersion relations and black hole physics

abstract:
  A modified formulation of energy-momentum relation is proposed in the context
of doubly special relativity. We investigate its impact on black hole physics.
It turns out that such modification will give corrections to both the
temperature and the entropy of black holes. In particular this modified
dispersion relation also changes the picture of Hawking radiation greatly when
the size of black holes approaching the Planck scale. It can prevent black
holes from total evaporation, as a result providing a plausible mechanism to
treat the remnant of black holes as a candidate for dark matter.


title: Thermodynamics of modified black holes from gravity's rainbow

abstract:
  We study the thermodynamics of modified black holes proposed in the context
of gravity's rainbow. A notion of intrinsic temperature and entropy for these
black holes is introduced. In particular for a specific class of modified
Schwarzschild solutions, their temperature and entropy are obtained and
compared with those previously obtained from modified dispersion relations in
deformed special relativity. It turns out that the results of these two
different strategies coincide, and this may be viewed as a support for the
proposal of deformed equivalence principle.


title: Tilt and phantom cosmology

abstract:
  We show that in tilting perfect fluid cosmological models with an
ultra-radiative equation of state, generically the tilt becomes extreme at late
times and, as the tilt instability sets in, observers moving with the tilting
fluid will experience singular behaviour in which infinite expansion is reached
within a finite proper time, similar to that of phantom cosmology (but without
the need for exotic forms of matter).


title:
Proper Projective Symmetry in some well known Conformally flat
  Space-Times

abstract:
  A study of conformally flat but non flat Bianchi type I and cylindrically
symmetric static space-times according to proper projective symmetry is given
by using some algebraic and direct integration techniques. It is shown that the
special class of the above space-times admit proper projective vector fields.


title: On the algebraic classification of spacetimes

abstract:
  We briefly overview the Petrov classification in four dimensions and its
generalization to higher dimensions.


title:
Locally Lorentz-Covariant Theory of Gravity Founded on Inertial Frame of
  Center of Mass

abstract:
  A Locally Lorentz-covariant theory of gravity which is equivalent to general
relativity in weak gravitational field is present. The space-time standard in
local gravitational field is modified in terms of equivalence principle to keep
consistent with that of inertial frame. The static metric in our theory agrees
with Schwarzschild metric at first order approximation. The gravitational
vector potential produced by a moving body is obtained by applying local
Lorentz transformations in gravitational field. On the other hand, we still
regard inertial frame, i.e. center of mass of the system, as the preferred
frame of reference. This is because Newton's laws of motion hold only for
inertial frames. The apsidal motion of binary system and the expansion of the
universe can be explained reasonably when observed from inertial frame. Black
holes and singularities do not exist in our theory.


title: The general solution for relativistic spherical shells

abstract:
  The general exact solution of the Einstein-matter field equations describing
spherically symmetric shells satisfying an equation of state in closed form is
discussed under general assumptions of physical reasonableness. The solutions
split into two classes: a class of "astro-physically interesting" solutions
describing "ordinary" matter with positive density and pressure, and a class of
"phantom-like" solutions with positive density but negative active
gravitational mass, which can also be of interest in several "very strong
fields" regimes. Known results on linear-barotropic equations of state are
recovered as particular cases.


title: Braneworld dynamics with vacuum polarization

abstract:
  We investigate the cosmological dynamics of a brane Universe when quantum
corrections from vacuum polarization are taken into account. New vacuum de
Sitter points existing on Randall-Sundrum brane are described. We show also
that quantum correction can destroy the DGP de Sitter solution on induced
gravity brane.


title: Spherically symmetric dynamical horizons

abstract:
  We determine sufficient and necessary conditions for a spherically symmetric
initial data set to satisfy the dynamical horizon conditions in the spacetime
development. The constraint equations reduce to a single second order linear
master equation, which leads to a systematic construction of all spherically
symmetric dynamical horizons (SSDH) satisfying certain boundedness conditions.
We also find necessary and sufficient conditions for a given spherically
symmetric spacetime to contain a SSDH.


abstract:
  Proceedings of the international Workshop on ``Dynamics and Thermodynamics of
Blackholes and Naked Singularities``, that took place at the Department of
Mathematics of the Politecnico of Milano from 13 to 15 May 2004.


title: A New Generalized Harmonic Evolution System

abstract:
  A new representation of the Einstein evolution equations is presented that is
first order, linearly degenerate, and symmetric hyperbolic. This new system
uses the generalized harmonic method to specify the coordinates, and
exponentially suppresses all small short-wavelength constraint violations.
Physical and constraint-preserving boundary conditions are derived for this
system, and numerical tests that demonstrate the effectiveness of the
constraint suppression properties and the constraint-preserving boundary
conditions are presented.


title: On rotating solitons in general relativity

abstract:
  We review a number of results recently obtained in the area of constructing
rotating solitons in a four dimensional asymptotically flat spacetime. Various
models are examined, special attention being paid to the monopole-antimonopole
and gauged skyrmion configurations, which have a nonvanishing total angular
momentum. For all known examples of rotating solitons, the angular momentum is
fixed by some conserved charge of the matter fields.


title:
Further results on the smoothability of Cauchy hypersurfaces and Cauchy
  time functions

abstract:
  Recently, folk questions on the smoothability of Cauchy hypersurfaces and
time functions of a globally hyperbolic spacetime M, have been solved. Here we
give further results, applicable to several problems:
  (1) Any compact spacelike acausal submanifold H with boundary can be extended
to a spacelike Cauchy hypersurface S. If H were only achronal, counterexamples
to the smooth extension exist, but a continuous extension (in fact, valid for
any compact achronal subset K) is still possible.
  (2) Given any spacelike Cauchy hypersurface S, a Cauchy temporal function T
(i.e., a smooth function with past-directed timelike gradient everywhere, and
Cauchy hypersurfaces as levels) with S equal to one of the levels, is
constructed -thus, the spacetime splits orthogonally as $R \times S$ in a
canonical way. Even more, accurate versions of this result are obtained if the
Cauchy hypersurface S were non-spacelike (including non-smooth, or achronal but
non-acausal).


title: Alternative variables for the dynamics of general relativity

abstract:
  A new form of the dynamical equations of vacuum general relativity is
proposed. This form involves the canonical Hamiltonian structure but non
canonical variables. The new field variables are the electric field
$E^{a}{}_{i}$ and the magnetic field $B^{a}{}_{i}$ which emerge from the
Ashtekar's representation for canonical gravity. The constraint algebra is
studied in terms of the new field variables and the counting of the degrees of
freedom is done. The quantization is briefly outlined.


title: A note on static metrics

abstract:
  Conditions are given which, subject to a genericity condition on the Ricci
tensor, are both necessary and sufficient for a 3-metric to arise from a static
spacetime metric.


title: Hawking Radiation as Tunnelling in Static Black Holes

abstract:
  Hawking radiation can usefully be viewed as a semi-classical tunnelling
process that originates at the black hole horizon. The conservation of energy
implies the effect of self-gravitation. For a static black hole, a generalized
Painleve coordinate system is introduced, and Hawking radiation as tunnelling
under the effect of self-gravitation is investigated. The corrected radiation
is consistent with the underlying unitary theory.


title: New Coordinates for BTZ Black Hole and Hawking Radiation via Tunnelling

abstract:
  Hawking radiation can usefully be viewed as a semi-classical tunnelling
process that originates at the black hole horizon. For the stationary
axisymmetric BTZ black hole, a generalized Painleve coordinate system
(Painleve-BTZ coordinates) is introduced, and Hawking radiation as tunnelling
under the effect of self-gravitation is investigated. The corrected radiation
is obtained which is not precise thermal spectrum. The result is consistent
with the underlying unitary theory. Moreover, Bekenstein-Hawking entropy of BTZ
black hole is not necessarily corrected when we choose appropriate coordinate
system to study the tunnelling effect.


title:
Inflaton and metric fluctuations in the early universe from a 5D vacuum
  state

abstract:
  In this letter we complete a previously introduced formalism to study the
gauge-invariant metric fluctuations from a noncompact Kaluza-Klein theory of
gravity, to study the evolution of the early universe. The evolution of both,
metric and inflaton field fluctuations are reciprocally related. We obtain that
<\delta\rho/\rho_b$ depends on the coupling of $\Phi$ with $\delta\phi$ and the
spectral index of its spectrum is: $0.9483 < n_1 < 1$.


title:
The stable problem of the black-hole connected region in the
  Schwarzschild black hole

abstract:
  The stability of the Schwarzschild black hole is studied. Using the
Painlev\'{e} coordinate, our region can be defined as the black-hole-connected
region(r>2m, see text) of the Schwarzschild black hole or the
white-hole-connected region(r>2m, see text) of the Schwarzschild black hole. We
study the stable problems of the black-hole-connected region. The conclusions
are: (1) in the black-hole-connected region, the initially regular perturbation
fields must have real frequency or complex frequency whose imaginary must not
be greater than -1/4m, so the black-hole-connected regionis stable in
physicist' viewpoint; (2) On the contrary, in the mathematicians' viewpoint,
the existence of the real frequencies means that the stable problem is unsolved
by the linear perturbation method in the black-hole-connected region.


title: Towards the graviton from spinfoams: the 3d toy model

abstract:
  Recently, a proposal has appeared for the extraction of the 2-point function
of linearised quantum gravity, within the spinfoam formalism. This relies on
the use of a boundary state, which introduces a semi-classical flat geometry on
the boundary. In this paper, we investigate this proposal considering a toy
model in the (Riemannian) 3d case, where the semi-classical limit is better
understood. We show that in this limit the propagation kernel of the model is
the one for the harmonic oscillator. This is at the origin of the expected 1/L
behaviour of the 2-point function. Furthermore, we numerically study the short
scales regime, where deviations from this behaviour occur.


title: Quantum Gravity as a quantum field theory of simplicial geometry

abstract:
  This is an introduction to the group field theory approach to quantum
gravity, with emphasis on motivations and basic formalism, more than on recent
results; we elaborate on the various ingredients, both conceptual and formal,
of the approach, giving some examples, and we discuss some perspectives of
future developments.


title:
Solution of the 1D Special Relativistic Hydrodynamics(SRH) Equations
  Using Different Numerical Method and Results from Different Test Problems

abstract:
  In this paper, we have solved 1D special relativistic hydrodynamical
equations using different numerical method in computational gas dynamics. The
numerical solutions of these equations for smooth wave cases give better
solution when we use $Non-TVD$(Total Variable Diminishing) but solution of
discontinuity wave produces some oscillation behind the shock. On the other
hand, $TVD$ type schemes give good approximation at discontinuity cases.
Because $TVD$ schemes completely remove the oscillations, they reduce locally
the accuracy of the solution around the extrema.


title:
Conformally invariant wave-equations and massless fields in de Sitter
  spacetime

abstract:
  Conformally invariant wave equations in de Sitter space, for scalar and
vector fields, are introduced in the present paper. Solutions of their wave
equations and the related two-point functions, in the ambient space notation,
have been calculated. The ``Hilbert'' space structure and the field operator,
in terms of coordinate independent de Sitter plane waves, have been defined.
The construction of the paper is based on the analyticity in the complexified
pseudo-Riemanian manifold, presented first by Bros et al.. Minkowskian limits
of these functions are analyzed. The relation between the ambient space
notation and the intrinsic coordinates is then studied in the final stage.


title: Curvature estimates for stable marginally trapped surfaces

abstract:
  We derive integral and sup-estimates for the curvature of stably marginally
outer trapped surfaces in a sliced space-time. The estimates bound the shear of
a marginally outer trapped surface in terms of the intrinsic and extrinsic
curvature of a slice containing the surface. These estimates are well adapted
to situations of physical insterest, such as dynamical horizons.


title:
Quantum evolution of the Universe in the constrained quasi-Heisenberg
  picture: from quanta to classics?

abstract:
  The quasi-Heisenberg picture of minisuperspace model is considered. The The
quasi-Heisenberg picture of minisuperspace model is considered. The suggested
scheme consists in quantizing of the equation of motion and interprets all
observables including the Universe scale factor as the time-dependent
(quasi-Heisenbeg) operators acting in the space of solutions of the
Wheeler--DeWitt equation. The Klein-Gordon normalization of the wave function
and corresponding to it quantization rules for the equation of motion allow a
time-evolution of the mean values of operators even under constraint H=0 on the
physical states of Universe. Besides, the constraint H=0 appears as the
relation connecting initial values of the quasi-Heisenbeg operators at $t=0$. A
stage of the inflation is considered numerically in the framework of the
Wigner--Weyl phase-space formalism. For an inflationary model of the ``chaotic
inflation'' type it is found that a dispersion of the Universe scale factor
grows during inflation, and thus, does not vanish at the inflation end. It was
found also, that the ``by hand'' introduced dependence of the cosmological
constant from the scale factor in the model with a massless scalar field leads
to the decrease of dispersion of the Universe scale factor. The measurement and
interpretation problems arising in the framework of our approach are
considered, as well.


title: Accurate Evolution of Orbiting Binary Black Holes

abstract:
  We present a detailed analysis of binary black hole evolutions in the last
orbit, and demonstrate consistent and convergent results for the trajectories
of the individual bodies. The gauge choice can significantly affect the overall
accuracy of the evolution. It is possible to reconcile certain gauge dependent
discrepancies by examining the convergence limit. We illustrate these results
using an initial data set recently evolved by Bruegmann (Phys. Rev. Lett. 92,
211101). For our highest resolution and most accurate gauge, we estimate the
duration of this data set's last orbit to be approximately $59 M_{ADM}$.


title: Modified gravity, Dark Energy and MOND

abstract:
  We propose a class of actions for the spacetime metric that introduce
corrections to the Einstein-Hilbert Lagrangian depending on the logarithm of
some curvature scalars. We show that for some choices of these invariants the
models are ghost free and modify Newtonian gravity below a characteristic
acceleration scale given by a_0 = c\mu, where c is the speed of light and \mu
is a parameter of the model that also determines the late-time Hubble constant:
H_0 \sim \mu. In these models, besides the massless spin two graviton, there is
a scalar excitation of the spacetime metric whose mass depends on the
background curvature. This dependence is such that this scalar, although almost
massless in vacuum, becomes massive and effectively decouples when one gets
close to any source and we recover an acceptable weak field limit at short
distances. There is also a (classical) ``running'' of Newton's constant with
the distance to the sources and gravity is easily enhanced at large distances
by a large ratio. We comment on the possibility of building a model with a
MOND-like Newtonian limit that could explain the rotation curves of galaxies
without introducing Dark Matter using this kind of actions. We also explore
briefly the characteristic gravitational phenomenology that these models imply:
besides a long distance modification of gravity they also predict deviations
from Newton's law at short distances. This short distance scale depends on the
local background curvature of spacetime, and we find that for experiments on
the Earth surface it is of order \sim 0.1mm, while this distance would be
bigger in space where the local curvature is significantly lower.


title:
Non-singular, vacuum, stationary space-times with a negative
  cosmological constant

abstract:
  We construct infinite dimensional families of non-singular stationary space
times, solutions of the vacuum Einstein equations with a negative cosmological
constant.


title:
Extended-body approach to the electromagnetic self-force in curved
  spacetime

abstract:
  We offer a novel derivation of the electromagnetic self-force acting on a
charged particle moving in an arbitrary curved spacetime. Our derivation is
based on a generalization from flat spacetime to curved spacetime of the
extended-body approach of Ori and Rosenthal. In this approach the charged
particle is first modeled as a body of finite extension s, the net force acting
on the extended body is computed, and the limit s -> 0 is taken at the end of
the calculation. Concretely our extended body is a dumbbell that consists of
two point charges that are maintained at a constant spacelike separation s. The
net force acting on the dumbbell includes contributions from the mutual forces
exerted on each charge by the field created by the other charge, the individual
self-forces exerted on each charge by its own field, and the external force
which is mostly responsible for the dumbbell's acceleration. These
contributions are added up, in a way that respects the curved nature of the
spacetime, and all diverging terms in the net force are shown to be removable
by mass renormalization. Our end result, in the limit s -> 0, is the standard
expression for the electromagnetic self-force in curved spacetime.


title:
Chandrasekhar separation ansatz and the generalized total angular
  momentum for the Dirac equation in the Kerr-Newman metric

abstract:
  In this paper we compute the square root of the generalized squared total
angular momentum operator $J$ for a Dirac particle in the Kerr-Newman metric.
The separation constant $\lambda$ arising from the Chandrasekahr separation
ansatz turns out to be the eigenvalue of $J$. After proving that $J$ is a
symmetry operator, we show the completeness of Chandrasekhar Ansatz for the
Dirac equation in oblate spheroidal coordinates and derive an explicit formula
for the propagator $e^{-itH}$.


title: Wormhole and C-field

abstract:
  It is well known that a C-field, generated by a certain source equation leads
to interesting changes in the cosmological solutions of Einstein's equations.
In this article we present and analyze a simple Lorentzian vacuum wormhole in
the presence of C-field.


title: Multidimensional global monopole in presence of Electromagnetic Field

abstract:
  We study the gravitational properties of a global monopole in $(D = d + 2)$
dimensional space-time in presence of electromagnetic field.


title: Gauge gravitation theory from the geometric viewpoint

abstract:
  This is the Preface to the special issue of 'International Journal of
Geometric Methods in Modern Physics', v.3, N.1 (2006) dedicated to the 50th
aniversary of gauge gravitation theory. It addresses the geometry underlying
gauge gravitation theories, their higher-dimensional, supergauge and
non-commutatuve extensions.


title: On Israel-Wilson-Perjes black holes

abstract:
  We show, under certain conditions, that regular Israel-Wilson-Perj\'es black
holes necessarily belong to the Majumdar-Papapetrou family.


title: Local Experiments See Cosmologically Varying Constants

abstract:
  We describe a rigorous construction, using matched asymptotic expansions,
which establishes under very general conditions that local terrestrial and
solar-system experiments will measure the effects of varying `constants' of
Nature occurring on cosmological scales to computable precision. In particular,
`constants' driven by scalar fields will still be found to evolve in time when
observed within virialised structures like clusters, galaxies, and planetary
systems. This provides a justification for combining cosmological and
terrestrial constraints on the possible time variation of many assumed
`constants' of Nature, including the fine structure constant and Newton's
gravitation constant.


title:
Hadamard renormalization of the stress-energy tensor for a quantized
  scalar field in a general spacetime of arbitrary dimension

abstract:
  We develop the Hadamard renormalization of the stress-energy tensor for a
massive scalar field theory defined on a general spacetime of arbitrary
dimension. Our formalism could be helpful in treating some aspects of the
quantum physics of extra spatial dimensions. More precisely, for spacetime
dimension up to six, we explicitly describe the Hadamard renormalization
procedure and for spacetime dimension from seven to eleven, we provide the
framework permitting the interested reader to perform this procedure explicitly
in a given spacetime. We complete our study (i) by considering the ambiguities
of the Hadamard renormalization of the stress-energy tensor and the
corresponding ambiguities for the trace anomaly, (ii) by providing the
expressions of the gravitational counterterms involved in the renormalization
process (iii) by discussing the connections between Hadamard renormalization
and renormalization in the effective action. All our results are expanded on
standard bases for Riemann polynomials constructed from group theoretical
considerations and thus given on irreducible forms.


title: The red-shift effect and radiation decay on black hole spacetimes

abstract:
  We consider solutions to the linear wave equation on a (maximally extended)
Schwarzschild spacetime, assuming only that the solution decays suitably at
spatial infinity on a complete Cauchy hypersurface. (In particular, we allow
the support of the solution to contain the bifurcate event horizon.) We prove
uniform decay bounds for the solution in the exterior regions, including the
uniform bound Cv_+^{-1}, where v_+ denotes max{v,1} and v denotes
Eddington-Finkelstein advanced time. We also prove uniform decay bounds for the
flux of energy through the event horizon and null infinity. The estimates near
the event horizon exploit an integral energy identity normalized to local
observers. This estimate can be thought to quantify the celebrated red-shift
effect. The results in particular give an independent proof of the classical
uniform boundedness theorem of Kay and Wald, without recourse to the discrete
isometries of spacetime.


title:
Gravitational collapse due to dark matter and dark energy in the brane
  world scenario

abstract:
  Gravitational collapse of FRW brane world embedded in a conformaly flat bulk
is considered for matter cloud consists of dark matter and dark energy with
equation of state $p=\epsilon \rho$ $(\epsilon<-{1/3})$. The effect of dark
matter and dark energy is being considered first separately and then a
combination of them both with and without interaction. In some cases the
collapse leads to black hole in some other cases naked singularity appears.


title:
The Study of the Pioneer Anomaly: New Data and Objectives for New
  Investigation

abstract:
  Radiometric tracking data from Pioneer 10 and 11 spacecraft has consistently
indicated the presence of a small, anomalous, Doppler frequency drift,
uniformly changing with a rate of ~6 x 10^{-9} Hz/s; the drift can be
interpreted as a constant sunward acceleration of each particular spacecraft of
a_P = (8.74 \pm 1.33) x 10^{-10} m/s^2. This signal is known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. We discuss the efforts
to retrieve the entire data sets of the Pioneer 10/11 radiometric Doppler data.
We also report on the recently recovered telemetry files that may be used to
reconstruct the engineering history of both spacecraft using original project
documentation and newly developed software tools. We discuss possible ways to
further investigate the discovered effect using these telemetry files in
conjunction with the analysis of the much extended Doppler data. We present the
main objectives of new upcoming study of the Pioneer anomaly, namely i)
analysis of the early data that could yield the direction of the anomaly, ii)
analysis of planetary encounters, that should tell more about the onset of the
anomaly, iii) analysis of the entire dataset, to better determine the anomaly's
temporal behavior, iv) comparative analysis of individual anomalous
accelerations for the two Pioneers, v) the detailed study of on-board
systematics, and vi) development of a thermal-electric-dynamical model using
on-board telemetry. The outlined strategy may allow for a higher accuracy
solution for a_P and, possibly, will lead to an unambiguous determination of
the origin of the Pioneer anomaly.


title:
Gravity of a static massless scalar field and a limiting
  Schwarzschild-like geometry

abstract:
  We study a set of static solutions of the Einstein equations in presence of a
massless scalar field and establish their connection to the Kantowski-Sachs
cosmological solutions based on some kind of duality transformations. The
physical properties of the limiting case of an empty hyperbolic spacetime
(pseudo-Schwarzschild geometry) are analyzed in some detail.


title:
On gravitational repulsion effect at extreme conditions in gauge
  theories of gravity

abstract:
  Homogeneous isotropic gravitating models are discussed in the framework of
gauge approach to gravitation. Generalized cosmological Friedmann equations
without specific solutions are deduced for models filled by scalar fields and
usual gravitating matter. Extreme conditions, by which gravitational repulsion
effect takes place, are analyzed.


title: Gravitational field of charged gyratons

abstract:
  We study relativistic gyratons which carry an electric charge. The
Einstein-Maxwell equations in arbitrary dimensions are solved exactly in the
case of a charged gyraton propagating in an asymptotically flat metric.


title: Projective geometry and special relativity

abstract:
  Some concepts of real and complex projective geometry are applied to the
fundamental physical notions that relate to Minkowski space and the Lorentz
group. In particular, it is shown that the transition from an infinite speed of
propagation for light waves to a finite one entails the replacement of a
hyperplane at infinity with a light cone and the replacement of an affine
hyperplane - or rest space - with a proper time hyperboloid. The transition
from the metric theory of electromagnetism to the pre-metric theory is
discussed in the context of complex projective geometry, and ultimately it is
proposed that the geometrical issues are more general than electromagnetism,
namely, they pertain to the transition from point mechanics to wave mechanics.


title: Symmetries of the equations of pre-metric electromagnetism

abstract:
  The equations of pre-metric electromagnetism are summarized and then
formulated as an exterior differential system on the total space of the bundle
of 2-forms over the spacetime manifold. The Harrison-Estabrook method of
computing the symmetries of the system is then applied, with the result that of
the four possible formal algebras of infinitesimal symmetries, the most
physically compelling one is the Lie algebra of infinitesimal projective
transformations of real four-dimensional projective space.


title: Modelling Planck-scale Lorentz violation via analogue models

abstract:
  Astrophysical tests of Planck-suppressed Lorentz violations had been
extensively studied in recent years and very stringent constraints have been
obtained within the framework of effective field theory. There are however
still some unresolved theoretical issues, in particular regarding the so called
"naturalness problem" - which arises when postulating that Planck-suppressed
Lorentz violations arise only from operators with mass dimension greater than
four in the Lagrangian. In the work presented here we shall try to address this
problem by looking at a condensed-matter analogue of the Lorentz violations
considered in quantum gravity phenomenology. Specifically, we investigate the
class of two-component BECs subject to laser-induced transitions between the
two components, and we show that this model is an example for Lorentz
invariance violation due to ultraviolet physics. We shall show that such a
model can be considered to be an explicit example high-energy Lorentz
violations where the ``naturalness problem'' does not arise.


title: Spinors and pre-metric electromagnetism

abstract:
  The basic concepts of the formulation of Maxwellian electromagnetism in the
absence of a Minkowski scalar product on spacetime are summarized, with
particular emphasis on the way that the electromagnetic constitutive law on the
space of bivectors over spacetime supplants the role of the Minkowski scalar
product on spacetime itself. The complex geometry of the space of bivectors is
summarized, with the intent of showing how an isomorphic copy of the Lorentz
group appears in that context. The use of complex 3-spinors to represent
electromagnetic fields is then discussed, as well as the expansion of scope
that the more general complex projective geometry of the space of bivectors
suggests.


title:
The Science, Technology and Mission Design for the Laser Astrometric
  Test of Relativity

abstract:
  The Laser Astrometric Test of Relativity (LATOR) is a Michelson-Morley-type
experiment designed to test the Einstein's general theory of relativity in the
most intense gravitational environment available in the solar system -- the
close proximity to the Sun. By using independent time-series of highly accurate
measurements of the Shapiro time-delay (laser ranging accurate to 1 cm) and
interferometric astrometry (accurate to 0.1 picoradian), LATOR will measure
gravitational deflection of light by the solar gravity with accuracy of 1 part
in a billion, a factor ~30,000 better than currently available. LATOR will
perform series of highly-accurate tests of gravitation and cosmology in its
search for cosmological remnants of scalar field in the solar system. We
present science, technology and mission design for the LATOR mission.


title:
Analysis of inflationary cosmological models in gauge theories of
  gravitation

abstract:
  Inflationary homogeneous isotropic cosmological models filled by scalar
fields and ultrarelativistic matter are examined in the framework of gauge
theories of gravitation. By using quadratic scalar field potential numerical
analysis of flat, open and closed models is curried out. Properties of
cosmological models are investigated in dependence on indefinite parameter of
cosmological equations and initial conditions at a bounce. Fulfilled analysis
demonstrates regular character of all cosmological models.


title: Magnetohydrodynamics and Plasma Cosmology

abstract:
  We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.


title: Global properties of charged dilatonic Gauss-Bonnet black holes

abstract:
  We study the phase space of the spherically symmetric solutions of
Einstein-Maxwell-Gauss-Bonnet system nonminimally coupled to a scalar field and
prove the existence of solutions with unusual asymptotics in addition to
asymptotically flat ones. We also find new dyonic solutions of dilatonic
Einstein-Maxwell theory.


title:
Harrison transformation of hyperelliptic solutions and charged dust
  disks

abstract:
  We use a Harrison transformation on solutions to the stationary axisymmetric
Einstein equations to generate solutions of the Einstein-Maxwell equations. The
case of hyperelliptic solutions to the Ernst equation is studied in detail.
Analytic expressions for the metric and the multipole moments are obtained. As
an example we consider the transformation of a family of counter-rotating dust
disks. The resulting solutions can be interpreted as disks with currents and
matter with a purely azimuthal pressure or as two streams of freely moving
charged particles. We discuss interesting limiting cases as the extreme limit
where the charge becomes identical to the mass, and the ultrarelativistic limit
where the central redshift diverges.