title:
Can the Pioneer anomaly be of gravitational origin? A phenomenological
  answer

abstract:
  In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.


title:
Vacuum Energy Density for Massless Scalar Fields in Flat Homogeneous
  Spacetime Manifolds with Nontrivial Topology

abstract:
  Although the observed universe appears to be geometrically flat, it could
have one of 18 global topologies. A constant-time slice of the spacetime
manifold could be a torus, Mobius strip, Klein bottle, or others. This global
topology of the universe imposes boundary conditions on quantum fields and
affects the vacuum energy density via Casimir effect. In a spacetime with such
a nontrivial topology, the vacuum energy density is shifted from its value in a
simply-connected spacetime. In this paper, the vacuum expectation value of the
stress-energy tensor for a massless scalar field is calculated in all 17
multiply-connected, flat and homogeneous spacetimes with different global
topologies. It is found that the vacuum energy density is lowered relative to
the Minkowski vacuum level in all spacetimes and that the stress-energy tensor
becomes position-dependent in spacetimes that involve reflections and
rotations.


title: Gravitational energy in stationary spacetimes

abstract:
  Static observers remain on Killing-vector world lines and measure the
rest-mass+kinetic energies of particles moving past them, and the flux of that
mechanical energy through space and time. The total mechanical energy is the
total flux through a spacelike cut at one time. The difference between the
total mass-energy and the total mechanical energy is the total gravitational
energy, which we prove to be negative for certain classes of systems. For
spherical systems, Misner, Thorne and Wheeler define the total gravitational
energy this way.
  To obtain the gravitational energy density analogous to that of
electromagnetism we first use Einstein's equations with integrations by parts
to remove second order derivatives. Next we apply a conformal transformation to
reexpress the scalar 3-curvature of the 3-space. The resulting density is
non-local.
  We repeat the argument for mechanical energies as measured by stationary
observers moving orthogonally to constant time slices like the "zero angular
momentum" observers of Bardeen who exist even within ergospheres.


title: Locality hypothesis and the speed of light

abstract:
  The locality hypothesis is generally considered necessary for the study of
the kinematics of non-inertial systems in special relativity. In this paper we
discuss this hypothesis, showing the necessity of an improvement, in order to
get a more clear understanding of the various concepts involved, like
coordinate velocity and standard velocity of light. Concrete examples are
shown, where these concepts are discussed.


title: The nature of $\Lambda$ and the mass of the graviton: A critical view

abstract:
  The existence of a non-zero cosmological constant $\Lambda$ gives rise to
controversial interpretations. Is $\Lambda$ a universal constant fixing the
geometry of an empty universe, as fundamental as the Planck constant or the
speed of light in the vacuum? Its natural place is then on the left-hand side
of the Einstein equation. Is it instead something emerging from a perturbative
calculus performed on the metric $g\_{\mu\nu}$ solution of the Einstein
equation and to which it might be given a material status of (dark or bright)
"energy"? It should then be part of the content of the right-hand side of the
Einstein equations. The purpose of this paper is not to elucidate the
fundamental nature of $\Lambda$, but instead we aim to present and discuss some
of the arguments in favor of both interpretations of the cosmological constant.
We conclude that if the fundamental of the geometry of space-time is
minkowskian, then the square of the mass of the graviton is proportional to
$\Lambda$; otherwise, if the fundamental state is deSitter/AdS, then the
graviton is massless in the deSitterian sense.


title:
Cylindrically symmetric, static strings with a cosmological constant in
  Brans-Dicke theory

abstract:
  The static, cylindrically symmetric vacuum solutions with a cosmological
constant in the framework of the Brans-Dicke theory are investigated. Some of
these solutions admitting Lorentz boost invariance along the symmetry axis
correspond to local, straight cosmic strings with a cosmological constant. Some
physical properties of such solutions are studied. These strings apply
attractive or repulsive forces on the test particles. A smooth matching is also
performed with a recently introduced interior thick string solution with a
cosmological constant.


title: Quantum Mechanics and the Generalized Uncertainty Principle

abstract:
  The generalized uncertainty principle has been described as a general
consequence of incorporating a minimal length from a theory of quantum gravity.
We consider a simple quantum mechanical model where the operator corresponding
to position has discrete eigenvalues and show how the generalized uncertainty
principle results for minimum uncertainty wave packets.


title: Time paradox in Quantum Gravity

abstract:
  The aim of this work is to review the concepts of time in quantum mechanics
and general relativity to show their incompatibility. We show that the absolute
character of Newtonian time is present in quantum mechanics and also partially
in quantum field theories which consider the Minkowski metric as the background
spacetime. We discuss the problems which this non-dynamical concept of time
causes in general relativity that is characterized by a dynamical spacetime.


title: Regular Charged Solutions in Teleparallel Theory of Gravity

abstract:
  Using a nonlinear electrodynamics coupled to teleparallel theory of gravity,
three regular charged spherically symmetric solutions are obtained. The
nonlinear theory reduces to the Maxwell one in the weak limit and the solutions
correspond to charged spacetimes. The third solution contains an arbitrary
function from which we can generate the other two solutions. The metric
associated with these spacetimes is the same, i.e., a regular charged static
spherically symmetric black hole. In calculating the energy content of the
third solution using the gravitational energy-momentum given by M{\o}ller,
within the framework of the teleparallel geometry, we find that the resulting
form depends on the arbitrary function. Using the regularized expression of the
gravitational energy-momentum we get the value of energy.


title: Non-Singular Cosmology in Modified Gravity

abstract:
  A non-singular cosmology is derived in modified gravity (MOG) with a varying
gravitational coupling strength $G(t)=G_N\xi(t)$. Assuming that the curvature
$k$, the cosmological constant $\Lambda$ and $\rho$ vanish at $t=0$, we obtain
a non-singular universe with a negative pressure, $p_G < 0$. Quantum
fluctuations at $t\sim 0$ produce creation of pairs of particles from the
vacuum explaining the origin of matter. The universe expands for $t\to \infty$
according to the standard radiation and matter dominated solutions. The arrow
of time reverses at $t=0$ always pointing in the direction of increasing
entropy ${\cal S}$ and the entropy is at a minimum value at $t=0$, solving the
conundrum of the Second Law of Thermodynamics. The Hubble radius $H^{-1}(t)$ is
infinite at $t=0$ removing the curvature and particle horizons. The negative
pressure $p_G$ generated by the scalar field $\xi$ at $t\sim 0$ can produce
quantum spontaneous creation of particles explaining the origin of matter and
radiation.


title:
A perturbative approach to Dirac observables and their space-time
  algebra

abstract:
  We introduce a general approximation scheme in order to calculate gauge
invariant observables in the canonical formulation of general relativity. Using
this scheme we will show how the observables and the dynamics of field theories
on a fixed background or equivalently the observables of the linearized theory
can be understood as an approximation to the observables in full general
relativity. Gauge invariant corrections can be calculated up to an arbitrary
high order and we will explicitly calculate the first non--trivial correction.
Furthermore we will make a first investigation into the Poisson algebra between
observables corresponding to fields at different space--time points and
consider the locality properties of the observables.


title:
The Landscape of Theoretical Physics: A Global View; From Point
  Particles to the Brane World and Beyond, in Search of a Unifying Principle

abstract:
  This a book is for those who would like to learn something about special and
general relativity beyond the usual textbooks, about quantum field theory, the
elegant Fock-Schwinger-Stueckelberg proper time formalism, the elegant
description of geometry by means of Clifford algebra, about the fascinating
possibilities the latter algebra offers in reformulating the existing physical
theories, and quantizing them in a natural way. It is shown how Clifford
algebra provides much more: it provides room for new physics, with the
prospects of resolving certain long standing puzzles. The theory of branes and
the idea of how a 3-brane might represent our world is discussed in detail.
Much attention is paid to the elegant geometric theory of branes which employs
the infinite dimensional space of functions describing branes. Clifford algebra
is generalized to the infinite dimensional spaces. In short, this is a book for
anybody who would like to explore how the ``theory of everything'' might
possibly be formulated. The theory that would describe all the known phenomena,
could not be formulated without taking into account ``all'' the theoretical
tools which are available. Foundations of those tools and their functional
interrelations are described in the book.


title:
Electromagnetic perturbations of non-vacuum locally rotationally
  symmetric class II spacetimes

abstract:
  We present a method that yields three decoupled covariant equations for three
complex scalars, which completely govern electromagnetic perturbations of
non-vacuum, locally rotationally symmetric class II spacetimes. One of these
equations is equivalent to the previously established generalized Regge-Wheeler
equation for electromagnetic fields. The remaining two equations are a direct
generalization of the Bardeen-Press equations. The approach undertaken makes
use of the well established 3+1 (and 2+1+1) formalism, and therefore, it is an
ideal setting for specifying interpretable energy-momentum on an initial
spacelike three-slice as the perturbation sources to the resultant
electromagnetic radiation.


title: Canonical theory of the Kantowski-Sachs cosmological models

abstract:
  We briefly discuss the Hamiltonian formalism of Kantowski-Sachs space-times
with vacuum, anisotropic fluid and two cross-streaming radiation field sources.
For these models a cosmological time is introduced. New constraints are found
in which the fluid momenta are separated from the rest of the variables. In
consequence their Poisson brackets give an Abelian algebra.


title:
Results of the search for inspiraling compact star binaries from
  TAMA300's observation in 2000-2004

abstract:
  We analyze the data of TAMA300 detector to search for gravitational waves
from inspiraling compact star binaries with masses of the component stars in
the range 1-3Msolar. In this analysis, 2705 hours of data, taken during the
years 2000-2004, are used for the event search. We combine the results of
different observation runs, and obtained a single upper limit on the rate of
the coalescence of compact binaries in our Galaxy of 20 per year at a 90%
confidence level. In this upper limit, the effect of various systematic errors
such like the uncertainty of the background estimation and the calibration of
the detector's sensitivity are included.


title:
A two-point boundary value problem on a Lorentz manifold arising in A.
  Poltorak's concept of reference frame

abstract:
  In A. Poltorak's concept, the reference frame in General Relativity is a
certain manifold equipped with a connection. The question under consideration
here is whether it is possible to join two events in the space-time by a
time-like geodesic if they are joined by a geodesic of the reference frame
connection that has a time-like initial vector. This question is interpreted as
whether an event belongs to the proper future of another event in the
space-time in case it is so in the reference frame. For reference frames of two
special types some geometric conditions are found under which the answer is
positive.


title:
Black hole fluctuations and dynamics from back-reaction of Hawking
  radiation: Current work and further studies based on stochastic gravity

abstract:
  We give a progress report of our research on spacetime fluctuations induced
by quantum fields in an evaporating black hole and a black hole in
quasi-equilibrium with its Hawking radiation. We note the main issues involved
in these two classes of problems and outline the key steps for a systematic
quantitative investigation. This report contains unpublished new ideas for
further studies.


title: Modified teleparallel gravity: inflation without inflaton

abstract:
  Born-Infeld strategy to smooth theories having divergent solutions is applied
to teleparallel equivalent of General Relativity. Differing from other theories
of modified gravity, modified teleparallelism leads to second order equations,
since teleparallel Lagrangian only contains first derivatives of the vierbein.
We show that Born-Infeld-modified teleparallelism solves the particle horizon
problem in a spatially flat FRW universe by providing an initial exponential
expansion without resorting to an inflaton field.


title: Spacetime is spinorial; new dimensions are timelike

abstract:
  A new theory of fundamental physics is presented; it predicts that the new
dimensions that may be observed by the Large Hadron Collider are timelike.


title: Esquisse d'une synthese

abstract:
  Since antiquity, from Euclid of Alexandria to Galileo Galilei to Immanuel
Kant to Hermann Minkowksi to Albert Einstein, the question of the nature of
space and time has occupied scientists and philosophers. In the
four-dimensional space-time of Einstein's wonderful theory of gravity, the
squared interval, in units such that the speed of light is unity, is the
difference between a squared time increment and the sum of three squares
representing the three dimensions of spatial change. More recently higher
dimensional theories have been proposed, which aim to unify gravity with the
other forces in nature. Such theories typically have a hyperbolic character in
that there is one time variable and many spatial variables (rather than just
three) in the formula for the squared interval. Here a new physical theory is
advanced, based on spinors, which clearly predicts that the basic extra
dimensions are timelike: in its simplest form, there are three timelike and
three spatial degrees of freedom. It is expected that devices such as the Large
Hadron Collider will be sensitive to these new degrees of freedom and thus one
may hope that in the near future, this issue can be settled experimentally


title: Rastall's gravity equations and Mach's Principle

abstract:
  Rastall generalized Einstein's field equations relaxing the Einstein's
assumption that the covariant divergence of the energy-momentum tensor should
vanish. His field equations contain a free parameter alpha and in an empty
space, i.e. if T_{\mu\nu}=0, they reduce to the Einstein's equations of
standard general relativity. We calculate the elements of the metric tensor
given by Rastall' equations for different \alpha assuming that T_{\mu\nu} to be
that of a perfect fluid and analyse these model solutions from the point of
view of Mach's principle. Since the source terms in Rastall's modified gravity
equations include the common energy-momentum tensor T_{\mu\nu} as well as the
expressions of the form (1-\alpha)g_{\mu\nu}T/2, these source terms depend on
metric determined by the mass and momentum distribution of the external space.
Likewise, in the classical limit, the source term of the corresponding Poisson
equation for \alpha\neq 1 depends on the gravitational potential in the sense
of Mach's principle.


title: Alternative Theories of Gravity

abstract:
  This work investigates alternative theories of gravity, the solutions to
their field equations and the constraints that can be imposed upon them from
observation and experiment. Specifically, we consider the cosmologies and
spherically symmetric solutions that can be expected to result from
scalar-tensor and fourth-order theories of gravity. We find exact cosmological
solutions of various different kinds; isotropic and anisotropic, homogeneous
and inhomogeneous. These solutions are used to investigate the behaviour of the
Universes at both late and early times, to investigate the effects of
corrections to general relativity on approach to an initial singularity and to
look for effects which may be observable in the present day Universe. We use
physical processes, such as the primordial nucleosynthesis of the light
elements, to impose constraints upon any deviations from the standard model.
Furthermore, we investigate the vacuum spherically symmetric solutions of these
theories. This environment is of particular interest for considerations of the
local effects of gravity, where the most accurate experiments and observations
of gravitational phenomena can be performed. Exact solutions are obtained for
this situation and their stability analysed. It is found that a variety of new
behaviour is obtainable in these theories that was not previously possible in
the standard model. This new behaviour allows us an extended framework in which
to consider gravitational physics, and its cosmological consequences.


title: Hamiltonian and physical Hilbert space in polymer quantum mechanics

abstract:
  In this paper, a version of polymer quantum mechanics, which is inspired by
loop quantum gravity, is considered and shown to be equivalent, in a precise
sense, to the standard, experimentally tested, Schroedinger quantum mechanics.
The kinematical cornerstone of our framework is the so called polymer
representation of the Heisenberg-Weyl (H-W) algebra, which is the starting
point of the construction. The dynamics is constructed as a continuum limit of
effective theories characterized by a scale, and requires a renormalization of
the inner product. The result is a physical Hilbert space in which the
continuum Hamiltonian can be represented and that is unitarily equivalent to
the Schroedinger representation of quantum mechanics. As a concrete
implementation of our formalism, the simple harmonic oscillator is fully
developed.


title: White dwarfs as test objects of Lorentz violations

abstract:
  In the present work the thermodynamical properties of bosonic and fermionic
gases are analyzed under the condition that a modified dispersion relation is
present. This last condition implies a breakdown of Lorentz symmetry. The
implications upon the condensation temperature will be studied, as well, as
upon other thermodynamical variables such as specific heat, entropy, etc.
Moreover, it will be argued that those cases entailing a violation of time
reversal symmetry of the motion equations could lead to problems with the
concept of entropy. Concerning the fermionic case it will be shown that Fermi
temperature suffers a modification due to the breakdown of Lorentz symmetry.
The results will be applied to white dwarfs and the consequences upon the
Chandrasekhar mass--radius relation will be shown. The possibility of resorting
to white dwarfs for the testing of modified dispersion relations is also
addressed. It will be shown that the comparison of the current observations
against the predictions of our model allows us to discard some values of one of
the parameters appearing in the modifications of the dispersion relation.


title: Gravitational collapse in loop quantum gravity

abstract:
  In this paper we study the gravitational collapse in loop quantum gravity. We
consider the space-time region inside the Schwarzschild black hole event
horizon and we divide this region in two parts, the first one where the matter
(dust matter) is localized and the other (outside) where the metric is
Kantowski-Sachs type. We calculate the state solving Hamiltonian constraint and
we obtain a set of three difference equations that give a regular and natural
evolution beyond the classical singularity point in "r=0" localized.


title:
Strong cosmic censorship for T^2-symmetric cosmological spacetimes with
  collisionless matter

abstract:
  We prove strong cosmic censorship for T^2-symmetric cosmological spacetimes
(with spatial topology T^3 and vanishing cosmological constant Lambda) with
collisionless matter. Gowdy symmetric spacetimes constitute a special case. The
formulation of the conjecture is in terms of generic C^2-inextendibility of the
metric. Our argument exploits a rigidity property of Cauchy horizons, inherited
from Killing fields.


title: Topological charges and quasi-charges in Absolute Parallelism

abstract:
  Absolute Parallelism (AP) has many interesting features: large symmetry group
of equations; field irreducibility with respect to this group; vast list of
consistent second order equations not restricted to Lagrangian ones.
  There is the variant of AP which solutions are free of arising singularities
if D=5; in this case AP acquires topological features of nonlinear sigma-model.
Starting with topological charge, one can also introduce the topological
quasi-charge groups for field configurations having some symmetry. For 4D,
considering symmetrical equipped 0-(sub)manifolds in R^3, we find QC-groups for
some symmetries (subsets of O_3) and describe their morphisms. Differential
3-form of topological charge (dual to topological current) is derived, as well
as O_3-quasi-charge 1-form.
  Results of topological classification of symmetric configurations in 5D case
(alighting on evident parallels with the Standard Model combinatorics of
fundamental particles) are announced. An example of SO_2-symmetric
configuration is considered; (quasi-)charge forms (self-dual and
anti-self-dual) are obtained.
  In conclusion, we propose a variant of experiment with single photon
interference (or with bi-photon non-local correlations) which should verify a
possible non-local (spaghetti-like) 5D ontology of particles.


title: Quantum spectrum and statistic entropy of black hole

abstract:
  Taking the horizon surface of the black hole as a compact membrane and
solving the oscillation equation of this membrane by Klein-Gordon equation, we
derive the frequencies of oscillation modes of the horizon surface, which are
proportional to the radiation temperature of the black hole. However, the
frequencies of oscillation modes are not equidistant. Using the distribution of
obtained frequencies of oscillation mode we compute the statistic entropy of
the black hole and obtain that the statistic entropy of the black hole is
proportional to the area of the horizon. Therefore, it is proven that the
quantum statistic entropy of the black hole is consistent with
Bekenstein-Hawking entropy.


title:
Energy and Momentum of a Stationary Beam of Light in the New General
  Relativity

abstract:
  We give an exact solution to the gravitational field in the new general
relativity. The solution creates Bonnor spacetime. This spacetime describes the
gravitational field of a stationary beam of light. The energy and momentum of
this solution is calculated using the energy-momentum complex given by
M{\o}ller in (1978) within the framework of the Weitzenb{\rm $\ddot{o}$}ck
spacetime.


title: The Dark Side of Gravity

abstract:
  Adopting a non geometrical point of view, we are led to an alternative theory
of the order two and symetric gravitational tensor field of GR. The field is no
more interpreted as the metric of our space-time. The true metric is globally
Minkowskian and describes a flat manifold, a context which justifies a genuine
rehabilitation of the global discrete space-time symetries involved in the
structure of the Lorentz group along with their 'problematic' representations:
the negative energy and tachyonic ones.


title: Cosmological coincidence problem in interacting dark energy models

abstract:
  An interacting dark energy model with interaction term $Q= \lambda_m
H\rho_m+\lambda_dH\rho_d$ is considered. By studying the model near the
transition time, in which the system crosses the w=-1 phantom-divide-line, the
conditions needed to overcome the coincidence problem is investigated. The
phantom model, as a candidate for dark energy, is considered and for two
specific examples, the quadratic and exponential phantom potentials, it is
shown that it is possible the system crosses the w=-1 line, meanwhile the
coincidence problem is alleviated, the two facts that have root in
observations.


title:
PROCRUSTES: A computer algebra package for post-Newtonian calculations
  in General Relativity

abstract:
  We report on a package of routines for the computer algebra system Maple
which supports the explicit determination of the geometric quantities, field
equations, equations of motion, and conserved quantities of General Relativity
in the post-Newtonian approximation. The package structure is modular and
allows for an easy modification by the user. The set of routines can be used to
verify hand calculations or to generate the input for further numerical
investigations.


title:
Particle motion around magnetized black holes: Preston-Poisson
  space-time

abstract:
  We analyze motion of massless and massive particles around black holes
immersed in an asymptotically uniform magnetic field and surrounded by some
mechanical structure, which provides the magnetic field. The space-time is
described by Preston-Poisson metric, which is the generalization of the
well-known Ernst metric with a new parameter, tidal force, characterizing the
surrounding structure. The Hamilton-Jacobi equations allow separation of
variables in the equatorial plane. The presence of tidal force from
surroundings considerably changes parameters of the test particle motion: it
increases the radius of circular orbits of particles, increases the binding
energy of massive particles going from a given circular orbits to the innermost
stable orbit near black hole. In addition, it increases the distance of minimal
approach, time delay and bending angle for a ray of light propagating near
black hole.


title:
Are Dark Matter and Dark Energy the Residue of the Expansion-Reaction to
  the Big Bang ?

abstract:
  We derive the phenomenological Milgrom square-law acceleration, describing
the apparent behavior of dark matter, as the reaction to the Big Bang from a
model based on the Lorentz-Dirac equation of motion traditionally describing
radiation reaction in electromagnetism but proven applicable to expansion
reaction in cosmology. The model is applied within the Robertson-Walker
hypersphere, and suggests that the Hubble expansion exactly cancels the
classical reaction imparted to matter following the Big Bang, leaving behind a
residue proportional to the square of the acceleration. The model further
suggests that the energy density associated with the reaction acceleration is
precisely the critical density for flattening the universe thus providing a
potential explanation of dark energy as well. A test of this model is proposed.


title: Generic Evolutionary Quantum Universe

abstract:
  We consider a Schr\"odinger quantum dynamics for the gravitational field
associated to a generic cosmological model and then we solve the corresponding
eigenvalue problem. We show that, from a phenomenological point of view, an
Evolutionary Quantum Cosmology overlaps the Wheeler-DeWitt approach.


title: The Lorentz force equation as Fermi-Walker transport in geometrodynamics

abstract:
  A new tetrad introduced within the framework of geometrodynamics for non-null
electromagnetic fields allows for the geometrical analysis of the Lorentz force
equation and its solutions in curved spacetimes. When expressed in terms of
this new tetrad, the electromagnetic field displays explicitly maximum
simplification, and the degrees of freedom are manifestly revealed. In our
manuscript we are deducing the Lorentz force equation on purely Riemannian
geometrical grounds. The equation arises on the basis of Frenet-Serret analysis
through the use of our new tetrads and gauge invariance arguments only. The
force is deduced through a geometrical construction that precludes any other
mathematical form other than the one already accepted. Therefore, a significant
and fundamental result such as the first geometrical proof on the necessity of
the force in the equation to have the structure already accepted in physics and
not any other, is given. Through the use of the Frenet-Serret formulae and
gauge invariance arguments we are also able to express in terms of the new
tetrad vectors the Lorentz force equation as a generalized form of Fermi-Walker
transport.


title: Vacuumless cosmic strings in Einstein Cartan theory

abstract:
  The gravitational fields of vacuumless global and gauge strings have been
investigated in the context of Einstein Cartan theory under the weak field
assumption of the field equations. It has been shown that global string and
gauge string can have only repulsive gravitational effect on a test particle.


title: Einstein-Yang-Mills solutions in higher dimensional de Sitter spacetime

abstract:
  We consider particle-like and black holes solutions of the
Einstein-Yang-Mills system with positive cosmological constant in d>4 spacetime
dimensions. These configurations are spherically symmetric and present a
cosmological horizon for a finite value of the radial coordinate, approaching
asymptotically the de Sitter background. In the usual Yang--Mills case we find
that the mass of these solutions, evaluated outside the cosmological horizon at
future/past infinity generically diverges for d>4. Solutions with finite mass
are found by adding to the action higher order gauge field terms belonging to
the Yang--Mills hierarchy. A discussion of the main properties of these
solutions and their differences from those to the usual Yang-Mills model, both
in four and higher dimensions is presented.


title: Self-Renormalization of the Classical Quasilocal Energy

abstract:
  Pointlike objects cause many of the divergences that afflict physical
theories. For instance, the gravitational binding energy of a point particle in
Newtonian mechanics is infinite. In general relativity, the analog of a point
particle is a black hole and the notion of binding energy must be replaced by
quasilocal energy. The quasilocal energy (QLE) derived by York, and elaborated
by Brown and York, is finite outside the horizon but it was not considered how
to evaluate it inside the horizon. We present a prescription for finding the
QLE inside a horizon, and show that it is finite at the singularity for a
variety of types of black hole. The energy is typically concentrated just
inside the horizon, not at the central singularity.


title:
Testing gravity at the Second post-Newtonian level through gravitational
  deflection of massive particles

abstract:
  Expression for second post-Newtonian level gravitational deflection angle of
massive particles is obtained in a model independent framework. Several of its
important implications including the possibility of testing gravitational
theories at that level are discussed.


title: Conformal Yano-Killing tensors for the Taub-NUT metric

abstract:
  Symmetric conformal Killing tensors and (skew-symmetric) conformal
Yano-Killing tensors for Euclidean Taub-NUT metric are given in explicit form.
Relations between Yano and CYK tensors in terms of conformal rescaling are
discussed.


title: Rotating spacetimes with a cosmological constant

abstract:
  We develop solution-generating techniques for stationary metrics with one
angular momentum and axial symmetry, in the presence of a cosmological constant
and in arbitrary spacetime dimension. In parallel we study the related lower
dimensional Einstein-Maxwell-dilaton static spacetimes with a Liouville
potential. For vanishing cosmological constant, we show that the field
equations in more than four dimensions decouple into a four dimensional
Papapetrou system and a Weyl system. We also show that given any four
dimensional 'seed' solution, one can construct an infinity of higher
dimensional solutions parametrised by the Weyl potentials, associated to the
extra dimensions. When the cosmological constant is non-zero, we discuss the
symmetries of the field equations, and then extend the well known works of
Papapetrou and Ernst (concerning the complex Ernst equation) in
four-dimensional general relativity, to arbitrary dimensions. In particular, we
demonstrate that the Papapetrou hypothesis generically reduces a stationary
system to a static one even in the presence of a cosmological constant. We also
give a particular class of solutions which are deformations of the (planar) adS
soliton and the (planar) adS black hole. We give example solutions of these
techniques and determine the four-dimensional seed solutions of the 5
dimensional black ring and the Myers-Perry black hole.


title:
Conserved currents in gravitational models with quasi-invariant
  Lagrangians: Application to teleparallel gravity

abstract:
  Conservation laws in gravitational theories with diffeomorphism and local
Lorentz symmetry are studied. Main attention is paid to the construction of
conserved currents and charges associated with an arbitrary vector field that
generates a diffeomorphism on the spacetime. We further generalize previous
results for the case of gravitational models described by quasi-invariant
Lagrangians, that is, Lagrangians that change by a total derivative under the
action of the local Lorentz group. The general formalism is then applied to the
teleparallel models, for which the energy and the angular momentum of a Kerr
black hole are calculated. The subsequent analysis of the results obtained
demonstrates the importance of the choice of the frame.


title: Magnetovac Cylinder to Magnetovac Torus

abstract:
  A method for mapping known cylindrical magnetovac solutions to solutions in
torus coordinates is developed. Identification of the cylinder ends changes
topology from R1 x S1 to S1 x S1. An analytic Einstein-Maxwell solution for a
toroidal magnetic field in tori is presented. The toroidal interior is matched
to an asymptotically flat vacuum exterior, connected by an Israel boundary
layer.


title:
Using (4+1) split and energy conditions to study the induced matter in
  5D Ricc-flat cosmology

abstract:
  We use $(4+1)$ split to derive the 4D induced energy density $\rho $ and
pressure $p$ of the $5D$ Ricci-flat cosmological solutions which are
characterized by having a bounce instead of a bang. The solutions contain two
arbitrary functions of time $t$ and, therefore, are mathematically rich in
giving various cosmological models. By using four known energy conditions
(null, weak, strong, and dominant) to pick out and study physically meaningful
solutions, we find that the 4D part of the $5D$ solutions asymptotically
approach to the standard 4D FRW models and the expansion of the universe is
decelerating for normal induced matter for which all the four energy conditions
are satisfied. We also find that quintessence might be normal or abnormal,
depending on the parameter $w$ of the equation of state. If $-1\leqslant
w<-1/3$, the expansion of the universe is accelerating and the quintessence is
abnormal because the strong energy condition is violated while other three are
satisfied. For phantom, all the four energy conditions are violated. Before the
bounce all the four energy conditions are violated, implying that the cosmic
matter before the bounce could be explained as a phantom which has a large
negative pressure and makes the universe bouncing. In the early times after the
bounce, the dominant energy condition is violated while the other three are
satisfied, and so the cosmic matter could be explained as a super-luminal
acoustic matter.


title: About Gravitomagnetism

abstract:
  The gravitomagnetic field is the force exerted by a moving body on the basis
of the intriguing interplay between geometry and dynamics which is the analog
to the magnetic field of a moving charged body in electromagnetism. The
existence of such a field has been demonstrated based on special relativity
approach and also by special relativity plus the gravitational time dilation
for two different cases, a moving infinite line and a uniformly moving point
mass, respectively. We treat these two approaches when the applied cases are
switched while appropriate key points are employed. Thus, we demonstrate that
the strength of the resulted gravitomagnetic field in the latter approach is
twice the former. Then, we also discuss the full linearized general relativity
and show that it should give the same strength for gravitomagnetic field as the
latter approach. Hence, through an exact analogy with the electrodynamic
equations, we present an argument in order to indicate the best definition
amongst those considered in this issue in the literature. Finally, we
investigate the gravitomagnetic effects and consequences of different
definitions on the geodesic equation including the second order approximation
terms.


title:
On the parameterization dependence of the energy momentum tensor and the
  metric

abstract:
  We use results by Kirilin to show that in general relativity the nonleading
terms in the energy-momentum tensor of a particle depends on the
parameterization of the gravitational field. While the classical metric that is
calculated from this source, used to define the leading long-distance
corrections to the metric, also has a parameteriztion dependence, it can be
removed by a coordinate change. Thus the classical observables are
parameterization independent. The quantum effects that emerge within the same
calculation of the metric also depend on the parameterization and a full
quantum calculation requires the inclusion of further diagrams. However, within
a given parameterization the quantum effects calculated by us in a previous
paper are well defined. Flaws of Kirilin's proposed alternate metric definition
are described and we explain why the diagrams that we calculated are the
appropriate ones.


title:
General Solutions of Cosmological Equations with Inequalities for
  Perfect Fluid and Scalar Field

abstract:
  Spherically symmetric cosmological equations in the usual FLRW coordinates
are explored, with different sources. The first couples a perfect fluid with a
quintessence scalar field and the second couples a perfect fluid to a tachyonic
scalar field. In both cases, in the inflationary regime, the scale factor a(t)
and its first two time derivatives are positive definite. Both sources in the
matter phase yield a scale factor and its first derivative as positive
definite. In both cases and in each phase, the general solutions of the
differential equations together with the algebraic and differential
inequalities are obtained. As special cases, exponential, hyperbolic, and power
law inflation, as well as power law expansion for the matter phase are all
derived from the general solutions. With recent data on baryonic matter, Hubble
parameter and deceleration parameter, the relative percentages of baryonic
matter, daek matter and dark energy are calculated. The quintessence model
yields: 4% baryonic matter, 18% dark matter, and 78% dark energy. The tachyonic
model gives: 4% baryonic matter, 36% dark matter, and 60% dark energy.


title:
Comment on ``Can gravity distinguish between Dirac and Majorana
  neutrinos?''

abstract: This is a comment on the paper gr-qc/0605153, by Singh, Mobed and Papini.


title:
Determination of the internal structure of neutron stars from
  gravitational wave spectra

abstract:
  In this paper the internal structure of a neutron star is shown to be
inferrable from its gravitational-wave spectrum. Iteratively applying the
inverse scheme of the scaled coordinate logarithmic perturbation method for
neutron stars proposed by Tsui and Leung [Astrophys. J. {\bf 631}, 495 (2005)],
we are able to determine the mass, the radius and the mass distribution of a
star from its quasi-normal mode frequencies of stellar pulsation. In addition,
accurate equation of state of nuclear matter can be obtained from such
inversion scheme. Explicit formulas for the case of axial $w$-mode oscillation
are derived here and numerical results for neutron stars characterized by
different equations of state are shown.


title: Thick brane solution with two scalar fields

abstract:
  A new 5D thick brane solution is presented. We conjecture that the deduced
thick brane is a plane defect in a bulk gauge condensate.


title: The emergence of AdS(2) from quantum fluctuations

abstract:
  We have shown how the quantization of two-dimensional quantum gravity with an
action which contains only a positive cosmological constant and boundary
cosmological constants leads to the emergence of a spacetime which can be
described as a constant negative curvature spacetime with superimposed quantum
fluctuations.


title: Gravitational radiation of accelerated sources

abstract:
  We investigate the gravitational radiation produced by a linearly accelerated
source in general relativity. The investigation is performed by studying the
vacuum C metric, which is interpreted as representing the exterior space-time
of an uniformly accelerating spherically symmetric gravitational source, and is
carried out in the context of the teleparallel equivalent of general
relativity. For an observer sufficiently far from both the (modified)
Schwarzschild and Rindler horizons, which is a realistic situation, we obtain a
simple expression for the total emitted gravitational radiation. We also
briefly discuss on the absolute or relative character of the accelerated
motion.


title:
Collapse and black hole formation in magnetized, differentially rotating
  neutron stars

abstract:
  The capacity to model magnetohydrodynamical (MHD) flows in dynamical,
strongly curved spacetimes significantly extends the reach of numerical
relativity in addressing many problems at the forefront of theoretical
astrophysics. We have developed and tested an evolution code for the coupled
Einstein-Maxwell-MHD equations which combines a BSSN solver with a high
resolution shock capturing scheme. As one application, we evolve magnetized,
differentially rotating neutron stars under the influence of a small seed
magnetic field. Of particular significance is the behavior found for
hypermassive neutron stars (HMNSs), which have rest masses greater the mass
limit allowed by uniform rotation for a given equation of state. The remnant of
a binary neutron star merger is likely to be a HMNS. We find that magnetic
braking and the magnetorotational instability lead to the collapse of HMNSs and
the formation of rotating black holes surrounded by massive, hot accretion tori
and collimated magnetic field lines. Such tori radiate strongly in neutrinos,
and the resulting neutrino-antineutrino annihilation (possibly in concert with
energy extraction by MHD effects) could provide enough energy to power
short-hard gamma-ray bursts. To explore the range of outcomes, we also evolve
differentially rotating neutron stars with lower masses and angular momenta
than the HMNS models. Instead of collapsing, the non-hypermassive models form
nearly uniformly rotating central objects which, in cases with significant
angular momentum, are surrounded by massive tori.


title: Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy

abstract:
  The models that unify dark matter and dark energy based upon the Chaplygin
gas fail owing to the suppression of structure formation by the adiabatic speed
of sound. Including string theory effects, in particular the Kalb-Ramond field,
we show how nonadiabatic perturbations allow a successful structure formation.


title: The Hole Argument. Physical Events and the Superspace

abstract:
  The 'hole argument'(the English translation of German 'Lochbetrachtung') was
formulated by Albert Einstein in 1913 in his search for a relativistic theory
of gravitation. The hole argument was deemed to be based on a trivial error of
Einstein, until 1980 when John Stachel (Talk on Einsteins Search for General
Covariance, 1912-1915 at the GRG meeting in Jena 1980) recognized its highly
non-trivial character. Since then the argument has been intensively discussed
by many physicists and philosophers of science. (See e.g., Earman & Norton
(1987), Gaul & Rovelli (1999), Stachel & Iftime(2005}, and Iftime &
Stachel(2006).)
  I shall provide here a coordinate-free formulation of the argument using the
language of categories and bundles, and generalize the argument for arbitrary
covariant and permutable theories (see Iftime & Stachel(2006). In conclusion I
shall point out a way of avoiding the hole argument, by looking at the
structure of the space of solutions of Einstein's equations on a space-time
manifold. This superspace Q(M) is defined as the orbit space of space-time
solutions on M under the action of the diffeomorphisms of M, and it plays an
important role in the study of the gravitational field and attempts to find a
theory of quantum gravity (QG).


title: Topological rigidity of dimensional reduction to three dimensions

abstract:
  Studying spacetimes with continuous symmetries by dimensional reduction to a
lower dimensional spacetime is a well known technique in field theory and
gravity. Recently, its use has been advocated in numerical relativity as an
efficient computational technique for the numerical study of axisymmetric
asymptotically flat 4-dimensional spacetimes. We prove here that if the
dimensionally reduced spacetime is a physically reasonable 3-dimensional
asymptotically flat or asymptotically anti-de Sitter spacetime, then,
surprisingly, the topology of the higher dimensional spacetime must be one of
two product topologies. Reductions of other topologies result in physically
pathological spacetimes. In particular, reduction of asymptotically flat
4-dimensional spacetimes must lead to pathologies. These results use only the
topological censorship theorem and topological methods and consequently are
independent of the field equations and reduction method.


title: Modified gravity inspired DGP brane cosmology

abstract:
  We consider a DGP brane scenario where a scalar field is present on the brane
through the introduction of a scalar potential, itself motivated by the notion
of modified gravity. This theory predicts that the mass appearing in the
gravitational potential is modified by the addition of the mass of the scalar
field. The cosmological implications that such a scenario entails are examined
and shown to be consistent with a universe expanding with power-law
acceleration.


title: Some properties of accelerating observers in the Schwarzschild space

abstract:
  It is well known that observers will be accelerated when they approach the
planets. Thus, discussing the properties of accelerating observers in the
Schwarzschild space is of sense. For the sake of simplicity, we can construct
these observers' world lines by comparing with the observers in the Hawking
effect and Unruh effect, whose world lines are both hyperbolic curves in the
appropriate coordinates. We do it after defining a certain special null
hypersurface in the Kruskal coordinates. Our result shows that these
accelerating observers defined in our paper can also detect the radiation with
the analogy of the Unruh effect, though locally. Furthermore, we conjecture
that, for any null hypersurface in any spacetime, the corresponding observers
who can at least locally detect the radiation from it can be found.


title: "Dark energy" as conformal dynamics of space

abstract:
  The exact solution for dynamic of conform-flat space homogeneous since
dynamic equation is given. Conform mode of space metric changing in Global time
theory has negative energy density. Swap of energy to this mode from another
ones lead to increasing of Universe homogeneity although probability of this
swap from local objects is negligibly small. Conform mode is corresponding to
"dark energy" in observation astronomy.


title:
Close-slow analysis for head-on collision of two black holes in higher
  dimensions: Bowen-York initial data

abstract:
  Scenarios of large extra dimensions have enhanced the importance for the
study of black holes in higher dimensions. In this paper, we analyze an
axisymmetric system of two black holes. Specifically, the Bowen-York method is
generalized for higher dimensions in order to calculate the initial data for
head-on collision of two equal-mass black holes. Then, the initial data are
evolved adopting the close-slow approximation to study gravitational waves
emitted during the collision. We derive an empirical formula for radiation
efficiency, which depends weakly on the dimensionality. Possible implications
of our results for the black hole formation in particle colliders are
discussed.


title: Cosmic string with two interacting scalar fields

abstract:
  The model of cosmic string formed from two gravitating and interacting scalar
fields is considered. It is shown that the regular solutions exist at special
choice of the model's parameters only.


title: On isotropic metric of Schwarzschild solution of Einstein equation

abstract:
  The known static isotropic metric of Schwarzschild solution of Einstein
equation cannot cover with the range of r<2MG, a new isotropic metric of
Schwarzschild solution is obtained. The new isotropic metric has the
characters: (1) It is dynamic and periodic. (2) It has infinite singularities
of the spacetime. (3) It cannot cover with the range of 0<r<r0; On the other
hand, r0 can be small discretionarily. (4) It seemed as if the range of
negative r could be unavoidable, although this range is meaningless for the
Schwarzschild metric.


title:
Topos-theoretic Relativization of Physical Representability and Quantum
  Gravity

abstract:
  In the current debate referring to the construction of a tenable background
independent theory of Quantum Gravity we introduce the notion of
topos-theoretic relativization of physical representability and demonstrate its
relevance concerning the merging of General Relativity and Quantum Theory. For
this purpose we show explicitly that the dynamical mechanism of physical fields
can be constructed by purely algebraic means, in terms of connection inducing
functors and their associated curvatures, independently of any background
substratum. The application of this mechanism in General Relativity is
constrained by the absolute representability of the theory in the field of real
numbers. The relativization of physical representability inside operationally
selected topoi of sheaves forces an appropriate interpretation of the mechanism
of connection functors in terms of a generalized differential geometric
dynamics of the corresponding fields in the regime of these topoi. In
particular, the relativization inside the topos of sheaves over commutative
algebraic contexts makes possible the formulation of quantum gravitational
dynamics by suitably adapting the functorial mechanism of connections inside
that topos.


title: Classical Nature of the Evolution of Dark Energy Density

abstract:
  By ignoring the local density fluctuations, we construct an uniform
Higgs-field's (inflaton's) quantum theory with varying effective Planck
constant ($\hbar_{v}(t) \propto R(t)^{-3}$) for the evolution of the dark
energy density during the epoch after inflation. With presumable sufficient
inflation in the very early period (time-scale is $t_{inf}$), so that
$\hbar_{v}\to 0$, the state of universe decomposes into some decoherent
components, which could be the essential meaning of phase transition, and each
of them could be well described by classical mechanics for an inharmonic
oscillator in the corresponding potential-well with a viscous force. We find
that the cosmological constant at present is $\Lambda_{now}\approx 2.05\times
10^{-3}$ eV, which is almost independent of the choice of potential for
inflaton, and agrees excellently with the recent observations. In addition, we
find that, during the cosmic epoch after inflation, the dark energy is almost
conserved as well as the matter's energy, therefore the "why now" problem can
be avoided.


title: Duffin-Kemmer-Petiau equation with nonminimal coupling to curvature

abstract:
  The generalized Duffin-Kemmer-Petiau equation in curved space-time is
proposed for non-minimal coupling to the curvature and external fields. The
corresponding scalar and vector fields equation are found. Equations are
presented, which are equivalent to those of a scalar field with conformal
coupling and electromagnetic field with non-minimal coupling to the curvature.
The gauge-invariant Duffin-Kemmer-Petiau equation with non-minimal coupling is
given.


title: Perturbative Quantum Gravity Coupled to Particles in (1+1)-Dimensions

abstract:
  We consider the problem of (1+1)-dimensional quantum gravity coupled to
particles. Working with the canonically reduced Hamiltonian, we obtain its
post-Newtonian expansion for two identical particles. We quantize the
(1+1)-dimensional Newtonian system first, after which explicit energy
corrections to second order in 1/c are obtained. We compute the perturbed
wavefunctions and show that the particles are bound less tightly together than
in the Newtonian case.


title:
Isolation of gravitational waves from displacement noise and utility of
  a time-delay device

abstract:
  Interferometers with kilometer-scale arms have been built for
gravitational-wave detections on the ground; ones with much longer arms are
being planned for space-based detection. One fundamental motivation for long
baseline interferometry is from displacement noise. In general, the longer the
arm length L, the larger the motion the gravitational-wave induces on the test
masses, until L becomes comparable to the gravitational wavelength. Recently,
schemes have been invented, in which displacement noises can be evaded by
employing differences between the influence of test-mass motions and that of
gravitational waves on light propagation. However, in these schemes, such
differences only becomes significant when L approaches the gravitational
wavelength, and shot-noise limited sensitivity becomes worse than that of
conventional configurations by a factor of at least (f L/c)^(-2), for f<c/L.
Such a factor, although can be overcome theoretically by employing high optical
powers, makes these schemes quite impractical. In this paper, we explore the
use of time delay in displacement-noise-free interferometers, which can improve
their shot-noise-limited sensitivity at low frequencies, to a factor of (f
L/c)^(-1) of the shot-noise-limited sensitivity of conventional configurations.


title: Van der Waals quintessence stars

abstract:
  The van der Waals quintessence equation of state is an interesting scenario
for describing the late universe, and seems to provide a solution to the puzzle
of dark energy, without the presence of exotic fluids or modifications of the
Friedmann equations. In this work, the construction of inhomogeneous compact
spheres supported by a van der Waals equation of state is explored. These
relativistic stellar configurations shall be denoted as {\it van der Waals
quintessence stars}. Despite of the fact that, in a cosmological context, the
van der Waals fluid is considered homogeneous, inhomogeneities may arise
through gravitational instabilities. Thus, these solutions may possibly
originate from density fluctuations in the cosmological background. Two
specific classes of solutions, namely, gravastars and traversable wormholes are
analyzed. Exact solutions are found, and their respective characteristics and
physical properties are further explored.


title: Chaotic motion in multi-black hole spacetimes and holographic screens

abstract:
  We investigate the geodesic motion in $D-$dimensional Majumdar-Papapetrou
multi-black hole spacetimes and find that the qualitative features of the D=4
case are shared by the higher dimensional configurations. The motion of
timelike and null particles is chaotic, the phase space being divided into
basins of attraction which are separated by a fractal boundary, with a fractal
dimension $d_B$. The mapping of the geodesic trajectories on a screen placed in
the asymptotic region is also investigated. We find that the fractal properties
of the phase space induces a fractal structure on the holographic screen, with
a fractal dimension $d_B-1$.


title:
The Einstein constraints: uniqueness and non-uniqueness in the conformal
  thin sandwich approach

abstract:
  We study the appearance of multiple solutions to certain decompositions of
Einstein's constraint equations. Pfeiffer and York recently reported the
existence of two branches of solutions for identical background data in the
extended conformal thin-sandwich decomposition. We show that the Hamiltonian
constraint alone, when expressed in a certain way, admits two branches of
solutions with properties very similar to those found by Pfeiffer and York. We
construct these two branches analytically for a constant-density star in
spherical symmetry, but argue that this behavior is more general. In the case
of the Hamiltonian constraint this non-uniqueness is well known to be related
to the sign of one particular term, and we argue that the extended conformal
thin-sandwich equations contain a similar term that causes the breakdown of
uniqueness.


title: Exact solutions in bouncing cosmology

abstract:
  We discuss the effects of a (possibly) negative $(1+z)^6$ type contribution
to the Friedmann equation. No definite answer can be given as to the presence
and magnitude of a particular mechanism, because any test using the general
relation $H(z)$ is able to estimate only the total of all sources of such a
term. That is why we describe four possibilities: 1) geometric effects of loop
quantum cosmology, 2) braneworld cosmology, 3) metric-affine gravity, and 4)
cosmology with spinning fluid. We find the exact solutions for the models with
$\rho^2$ correction in terms of elementary functions, and show all evolutional
paths on their phase plane. Instead of the initial singularity, the generic
feature is now a bounce.


title: Inspiral, merger and ring-down of equal-mass black-hole binaries

abstract:
  We investigate the dynamics and gravitational-wave (GW) emission in the
binary merger of equal-mass black holes as obtained from numerical relativity
simulations. Results from the evolution of three sets of initial data are
explored in detail, corresponding to different initial separations of the black
holes. We find that to a good approximation the inspiral phase of the evolution
is quasi-circular, followed by a "blurred, quasi-circular plunge", then merger
and ring down. We present first-order comparisons between analytical models of
the various stages of the merger and the numerical results. We provide
comparisons between the numerical results and analytical predictions based on
the adiabatic Newtonain, post-Newtonian (PN), and non-adiabatic resummed-PN
models. From the ring-down portion of the GW we extract the fundamental
quasi-normal mode and several of the overtones. Finally, we estimate the
optimal signal-to-noise ratio for typical binaries detectable by GW
experiments.


title: Thin-shell wormholes associated with global cosmic strings

abstract:
  In this article we construct cylindrical thin-shell wormholes in the context
of global cosmic strings. We study the stability of static configurations under
perturbations preserving the symmetry and we find that the throat tends to
collapse or expand, depending only on the direction of the velocity
perturbation.


title: Quantization of static inhomogeneous spacetime

abstract:
  In this paper we can solve a Wheeler-DeWitt equation of the some
inhomogeneous spacetime models as a local solution. From the previous study of
up-to-down method we derived the static restriction relating the problem of the
time. Although static restriction does not commute with the general Hamiltonian
constraint, the Hamiltonian constraint of some mini-superspace models commute
with static restriction. We can quantize such inhomogeneous models. With
obtained result we can success to simplify the general local Hamiltonian
constraint.


title:
Plane Symmetric Inhomogeneous Cosmological Models with a Perfect Fluid
  in General Relativity

abstract:
  In this paper we investigate a class of solutions of Einstein equations for
the plane-symmetric perfect fluid case with shear and vanishing acceleration.
If these solutions have shear, they must necessarily be non-static. We examine
the integrable cases of the field equations systematically. Among the cases
with shear we find three classes of solutions.


title: Binary black hole spectroscopy

abstract:
  We study parameter estimation with post-Newtonian (PN) gravitational
waveforms for the quasi-circular, adiabatic inspiral of spinning binary compact
objects. The performance of amplitude-corrected waveforms is compared with that
of the more commonly used restricted waveforms, in Advanced LIGO and EGO. With
restricted waveforms, the properties of the source can only be extracted from
the phasing. For amplitude-corrected waveforms, the spectrum encodes a wealth
of additional information, which leads to dramatic improvements in parameter
estimation. At distances of $\sim 100$ Mpc, the full PN waveforms allow for
high-accuracy parameter extraction for total mass up to several hundred solar
masses, while with the restricted ones the errors are steep functions of mass,
and accurate parameter estimation is only possible for relatively light stellar
mass binaries. At the low-mass end, the inclusion of amplitude corrections
reduces the error on the time of coalescence by an order of magnitude in
Advanced LIGO and a factor of 5 in EGO compared to the restricted waveforms; at
higher masses these differences are much larger. The individual component
masses, which are very poorly determined with restricted waveforms, become
measurable with high accuracy if amplitude-corrected waveforms are used, with
errors as low as a few percent in Advanced LIGO and a few tenths of a percent
in EGO. The usual spin-orbit parameter $\beta$ is also poorly determined with
restricted waveforms (except for low-mass systems in EGO), but the full
waveforms give errors that are small compared to the largest possible value
consistent with the Kerr bound. This suggests a way of finding out if one or
both of the component objects violate this bound. We also briefly discuss the
effect of amplitude corrections on parameter estimation in Initial LIGO.


title: A singularity theorem based on spatial averages

abstract:
  Inspired by Raychaudhuri's work, and using the equation named after him as a
basic ingredient, a new singularity theorem is proved. Open non-rotating
everywhere expanding universes with non-vanishing spatial average of the matter
variables are severely geodesically incomplete to the past. Another way of
stating the result is that, under the same conditions, any singularity-free
model must have a vanishing spatial average of the energy density (and other
physical variables). This is very satisfactory and provides a clear decisive
difference between singular and non-singular cosmologies.


title: Calibration of Moving Puncture Simulations

abstract:
  We present single and binary black hole simulations that follow the moving
puncture paradigm of simulating black-hole spacetimes without excision, and use
moving boxes mesh refinement. Focussing on binary black hole configurations
where the simulations cover roughly two orbits, we address five major issues
determining the quality of our results: numerical discretization error, finite
extraction radius of the radiation signal, physical appropriateness of initial
data, gauge choice and computational performance. We also compare results we
have obtained with the BAM code described here with the independent LEAN code.


title: Non-uniqueness in conformal formulations of the Einstein constraints

abstract:
  Standard methods in non-linear analysis are used to show that there exists a
parabolic branching of solutions of the Lichnerowicz-York equation with an
unscaled source. We also apply these methods to the extended conformal thin
sandwich formulation and show that if the linearised system develops a kernel
solution for sufficiently large initial data then we obtain parabolic solution
curves for the conformal factor, lapse and shift identical to those found
numerically by Pfeiffer and York. The implications of these results for
constrained evolutions are discussed.


title:
Classical central extension for asymptotic symmetries at null infinity
  in three spacetime dimensions

abstract:
  The symmetry algebra of asymptotically flat spacetimes at null infinity in
three dimensions is the semi-direct sum of the infinitesimal diffeomorphisms on
the circle with an abelian ideal of supertranslations. The associated charge
algebra is shown to admit a non trivial classical central extension of Virasoro
type closely related to that of the anti-de Sitter case.


title: On the accretion-induced QNM excitation of a Schwarzschild black hole

abstract:
  By combining the numerical solution of the nonlinear hydrodynamics equations
with the solution of the linear inhomogeneous Zerilli-Moncrief and
Regge-Wheeler equations we investigate the properties of the gravitational
radiation emitted during the axisymmetric accretion of matter onto a
Schwarzschild black hole. The matter models considered include quadrupolar dust
shells and thick accretion disks, permitting us to simulate situations which
may be encountered at the end stages of stellar gravitational collapse or
binary neutron star merger. We focus on the interference pattern appearing in
the energy spectra of the emitted gravitational waves and on the amount of
excitation of the quasi-normal modes of the accreting black hole. We show that,
quite generically in the presence of accretion, the black hole ringdown is not
a simple superposition of quasi-normal modes, although the fundamental mode is
usually present and often dominates the gravitational-wave signal. We interpret
this as due to backscattering of waves off the non-exponentially decaying part
of the black-hole potential and to the finite spatial extension of the
accreting matter. Our results suggest that the black-hole QNM contributions to
the full gravitational-wave signal should be extremely small and possibly not
detectable in generic astrophysical scenarios involving the accretion of
extended distributions of matter.


title: On the nonsymmetric purely affine gravity

abstract:
  We review the vacuum purely affine gravity with the nonsymmetric connection
and metric. We also examine dynamical effects of the second Ricci tensor and
covariant second-rank tensors constructed from the torsion tensor in the
gravitational Lagrangian.


title: The cosmic snap parameter in f(R) gravity

abstract:
  We derive the expression for the snap parameter in f(R) gravity. We use the
Palatini variational principle to obtain the field equations and regard the
Einstein conformal frame as physical. We predict the present-day value of the
snap parameter for the particular case f(R)=R-const/R, which is the simplest
f(R) model explaining the current acceleration of the universe.


title:
Physical Effects of Extra Dimension and Concomitant Map between Photons
  and Gravitons in Randall-Sundrum Brane-World Scenario

abstract:
  We investigate, in Randall-Sundrum braneworld scenario, the relationship
between perturbations of gravitational and electromagnetic waves in a black
hole neighboorhood, proposing an extra-dimensional braneworld extension of the
traditional formalism. Mutual transformations of electromagnetic and
gravitational fields due to the strong fields in Reissner-Nordstrom black holes
are analyzed from an effective 5-dimensional Randall-Sundrum braneworld
perspective.


title: Is a first order space-time theory possible?

abstract:
  Einstein's general relativity relates the curvature of space time, a second
order differential property, to the stress-energy-momentum tensor. In this
paper we ask whether it is possible to develop a first order theory relating
space-time angles to the energy-momentum vector. We suggest several concepts
that would be relevant, including quantum mechanical concepts that are usually
treated separately. Phenomenological Lorentz covariance arises from both field
and coordinate transformation and the Dirac equation becomes a special case of
the space-time field equation. We reinterpret Kaluza-Klein theory in this
context by considering the compact fifth dimension as the quantum wavefunction
phase. Further directions for development are suggested.


title: A note on causally simple and globally hyperbolic spacetimes

abstract:
  This paper has been withdrawn because the part concerning the definition of
global hyperbolicity has already been included in an expanded and clearer way
in gr-qc/0611138. The remainder will be also extended and posted.


title:
Local spherically symmetric perturbations of spatially flat Friedmann
  models

abstract:
  The spherically symmetric perturbations in the spatially flat Friedman models
are considered. It is assumed that the Friedmannian density and pressure are
related through a linear equation of state. The perturbation is joined smoothly
with an unperturbed Friedmann's background at the sound horizon of
perturbation. Such junction is in accordance with the "birth" of a local
perturbation as a result of the redistribution of matter. The solution of the
Einstein's equations is obtained in linear approximation on a Friedmann's
background near the the sound horizon of perturbation.


title: Particle Radiation From Gibbons-Maeda Black Hole

abstract:
  This paper investigates the particle radiation from Gibbons-Maeda black hole.
Taking into account the self-gravitation of the particle, we calculate the
tunnelling rate of the massless particle across the horizon, then we promote
the work to the radiation of the charged particle. The calculations prove that
the rate of tunnelling equals precisely the exponent of the difference of the
black hole entropy before and after emission and the radiation spectrum
deviates from exact thermal. The conclusion supports the viewpoint of
information conservation.


title:
Accurate and efficient gravitational waveforms for certain galactic
  compact binaries

abstract:
  Stellar-mass compact binaries in eccentric orbits are almost guaranteed
sources of gravitational waves for Laser Interferometer Space Antenna. We
present a prescription to compute accurate and efficient gravitational-wave
polarizations associated with bound compact binaries of arbitrary eccentricity
and mass ratio moving in slowly precessing orbits. We compare our approach with
those existing in the literature and present its advantages.


title: Multiple-event probability in general-relativistic quantum mechanics

abstract:
  We discuss the definition of quantum probability in the context of "timeless"
general--relativistic quantum mechanics. In particular, we study the
probability of sequences of events, or multi-event probability. In conventional
quantum mechanics this can be obtained by means of the ``wave function
collapse" algorithm. We first point out certain difficulties of some natural
definitions of multi-event probability, including the conditional probability
widely considered in the literature. We then observe that multi-event
probability can be reduced to single-event probability, by taking into account
the quantum nature of the measuring apparatus. In fact, by exploiting the
von-Neumann freedom of moving the quantum classical boundary, one can always
trade a sequence of non-commuting quantum measurements at different times, with
an ensemble of simultaneous commuting measurements on the joint
system+apparatus system. This observation permits a formulation of quantum
theory based only on single-event probability, where the results of the "wave
function collapse" algorithm can nevertheless be recovered. The discussion
bears also on the nature of the quantum collapse.


title: Deformation Quantization, Quantization, and the Klein-Gordon Equation

abstract:
  The aim of this proceeding is to give a basic introduction to Deformation
Quantization (DQ) to physicists. We compare DQ to canonical quantization and
path integral methods. It is described how certain issues such as the roles of
associativity, covariance, dynamics, and operator orderings are understood in
the context of DQ. Convergence issues in DQ are mentioned. Additionally, we
formulate the Klein-Gordon (KG) equation in DQ. Original results are discussed
which include the exact construction of the Fedosov star-product on the dS and
AdS space-times. Also, the KG equation is written down for these space-times.
This is a proceedings to the Second International Conference on Quantum
Theories and Renormalization Group in Gravity and Cosmology.


title: Is quantum mechanics based on an invariance principle?

abstract:
  Non-relativistic quantum mechanics for a free particle is shown to emerge
from classical mechanics through an invariance principle under transformations
that preserve the Heisenberg position-momentum inequality. These
transformations are induced by isotropic space dilations. This invariance
imposes a change in the laws of classical mechanics that exactly corresponds to
the transition to quantum mechanics. The Schroedinger equation appears jointly
with a second nonlinear equation describing non-unitary processes. Unitary and
non-unitary evolutions are exclusive and appear sequentially in time. The
non-unitary equation admits solutions that seem to correspond to the collapse
of the wave function.


title:
Quantum out-states holographically induced by asymptotic flatness:
  Invariance under spacetime symmetries, energy positivity and Hadamard
  property

abstract:
  This paper continues the analysis of the quantum states determined by the
universal asymptotic structure of four-dimensional asymptotically flat vacuum
spacetimes at null infinity M. It is now focused on the quantum state lambda_M,
of a massles conformally coupled scalar field phi propagating in M. lambda_M is
``holographically'' induced in the bulk by the universal BMS-invariant state
lambda at infinity scri of M. It is done by means of the correspondence between
observables in the bulk and those on the boundary at null infinity discussed in
previous papers. The induction is possible when some requirements are
fulfilled, in particular the spacetime M and the associated unphysical one are
globally hyperbolic and M admits future time infinity i^+. lambda_M coincides
with Minkowski vacuum if M is Minkowski spacetime. It is now proved that, in
the general case of a curved spacetime M, the state lambda_M enjoys the
following further properties. (1) lambda_M is invariant under the group of
isometries of the bulk spacetime M. (2) lambda_M fulfills a natural
energy-positivity condition with respect to every notion of Killing time (if
any) in the bulk spacetime M: If M admits a complete time-like Killing vector,
the associated one-parameter group of isometries is represented by a
strongly-continuous unitary group in the GNS representation of lambda_M. The
unitary group has positive self-adjoint generator without zero modes in the
one-particle space. (3) lambda_M is (globally) Hadamard in M and thus lambda_M
can be used as starting point for perturbative renormalization procedure of QFT
of phi in M.


title: Hidden Symmetry of Higher Dimensional Kerr-NUT-AdS Spacetimes

abstract:
  It is well known that 4-dimensional Kerr-NUT-AdS spacetime possesses the
hidden symmetry associated with the Killing-Yano tensor. This tensor is
"universal" in the sense that there exist coordinates where it does not depend
on any of the free parameters of the metric. Recently the general higher
dimensional Kerr-NUT-AdS solutions of the Einstein equations were obtained. We
demonstrate that all these metrics with arbitrary rotation and NUT parameters
admit a universal Killing-Yano tensor. We give an explicit presentation of the
Killing-Yano and Killing tensors and briefly discuss their properties.


title:
Bound State of an Electron on a $^4$He Superfluid Droplet as a Test for
  Quantum Gravity

abstract:
  We address the problem of finding a system in which there would be measurable
quantum gravitational effects. Following standard quantum-field methods, we
have calculated the first-order radiative correction of graviton exchange on
the binding energy of an electron with an ultra cold superfluid droplet of
$^4$He with mass about the Planck mass. For two $^4$He droplets with a mass
difference of about one microgram, we show that the relative difference in the
binding energies is about one percent.


title: New directions for gravity-wave physics via "Millikan oil drops"

abstract:
  Pairs of Planck-mass--scale drops of superfluid helium coated by electrons
(i.e., "Millikan oil drops"), when levitated in the presence of strong magnetic
fields and at low temperatures, can be efficient quantum transducers between
electromagnetic (EM) and gravitational (GR) radiation. A Hertz-like experiment,
in which EM waves are converted at the source into GR waves, and then
back-converted at the receiver from GR waves back into EM waves, should be
practical to perform. This would open up observations of the gravity-wave
analog of the CMB from the extremely early Big Bang, and also communications
directly through the interior of the Earth.


title: A Cosmological Model with Dark Spinor Source

abstract:
  In this paper, we discuss the system of Friedman-Robertson-Walker metric
coupling with massive nonlinear dark spinors in detail, where the thermodynamic
movement of spinors is also taken into account. The results show that, the
nonlinear potential of the spinor field can provide a tiny negative pressure,
which resists the Universe to become singular. The solution is oscillating in
time and closed in space, which approximately takes the following form $$
g_{\mu\nu}=\bar R^2(1-\delta\cos t)^2\diag(1,-1,-\sin^2r ,-\sin^2r
\sin^2\theta), $$ with $\bar R= (1\sim 2)\times 10^{12}$ light year, and
$\delta=0.96\sim 0.99$. The present time is about $t\sim 18^\circ$.


title:
Determination of the UV cut-off from the observed value of the Universe
  acceleration

abstract:
  It is shown that using of the equation of motion of the Universe scale factor
allows calculation of the contribution of the vacuum fluctuations to the
acceleration of the Universe expansion. Renormalization of the equation is
needed only in the case of massive particles. Under a known number of the
different kinds of fundamental fields, this provides determination of momentum
of the ultraviolet cut-off from the observed value of acceleration.


title: Some exact solutions in general relativity

abstract:
  In this thesis four separate problems in general relativity are considered,
divided into two separate themes: coordinate conditions and perfect fluid
spheres. Regarding coordinate conditions we present a pedagogical discussion of
how the appropriate use of coordinate conditions can lead to simplifications in
the form of the spacetime curvature -- such tricks are often helpful when
seeking specific exact solutions of the Einstein equations. Regarding perfect
fluid spheres we present several methods of transforming any given perfect
fluid sphere into a possibly new perfect fluid sphere. This is done in three
qualitatively distinct manners: The first set of solution generating theorems
apply in Schwarzschild curvature coordinates, and are phrased in terms of the
metric components: they show how to transform one static spherical perfect
fluid spacetime geometry into another. A second set of solution generating
theorems extends these ideas to other coordinate systems (such as isotropic,
Gaussian polar, Buchdahl, Synge, and exponential coordinates), again working
directly in terms of the metric components. Finally, the solution generating
theorems are rephrased in terms of the TOV equation and density and pressure
profiles. Most of the relevant calculations are carried out analytically,
though some numerical explorations are also carried out.


title: On a Raychaudhuri equation for hot gravitating fluids

abstract:
  We generalize the Raychaudhuri equation for the evolution of a self
gravitating fluid to include an Abelian and non-Abelian hybrid magneto fluid at
a finite temperature. The aim is to utilize this equation for investigating the
dynamics of astrophysical high temperature Abelian and non-Abelian plasmas.


title: Thermodynamical properties of the Universe with dark energy

abstract:
  We have investigated the thermodynamical properties of the Universe with dark
energy. Adopting the usual assumption in deriving the constant co-moving
entropy density that the physical volume and the temperature are independent,
we observed some strange thermodynamical behaviors. However, these strange
behaviors disappeared if we consider the realistic situation that the physical
volume and the temperature of the Universe are related. Based on the well known
correspondence between the Friedmann equation and the first law of
thermodynamics of the apparent horizon, we argued that the apparent horizon is
the physical horizon in dealing with thermodynamics problems. We have
concentrated on the volume of the Universe within the apparent horizon and
considered that the Universe is in thermal equilibrium with the Hawking
temperature on the apparent horizon. For dark energy with $w\ge -1$, the
holographic principle and the generalized second law are always respected.


title:
Non-metric Generalizations of Relativistic Gravitational Theory and
  Observational Data Interpretation

abstract:
  We discuss theoretical formalisms concerning with experimental verification
of General Relativity (GR). Non-metric generalizations of GR are considered and
a system of postulates is formulated for metric-affine and Finsler
gravitational theories. We consider local observer reference frames to be a
proper tool for comparing predictions of alternative theories with each other
and with the observational data. Integral formula for geodesic deviation due to
the deformation of connection is obtained. This formula can be applied for
calculations of such effects as the bending of light and time-delay in presence
of non-metrical effects.


title: Strong gravitational lensing from compact bodies: analytical results

abstract:
  We develop a non--perturbative method that yields analytical expressions for
the deflection angle of light in a general static and spherically symmetric
metric. It is an improvement on a method previously devised by the authors, and
provides a correct description of the photon sphere already to first order. We
also propose an alternative approach that provides general simpler formulas,
although with larger errors. We apply our technique to different metrics and
verify that the error is at most $0.5 %$ for {\sl all} regimes. We show that
our approximation is more accurate than others proposed earlier.


title:
Total recoil: the maximum kick from nonspinning black-hole binary
  inspiral

abstract:
  When unequal-mass black holes merge, the final black hole receives a ``kick''
due to the asymmetric loss of linear momentum in the gravitational radiation
emitted during the merger. The magnitude of this kick has important
astrophysical consequences. Recent breakthroughs in numerical relativity allow
us to perform the largest parameter study undertaken to date in numerical
simulations of binary black hole inspirals. We study non-spinning black-hole
binaries with mass ratios from $q=M_1/M_2=1$ to $q =0.25$ ($\eta = q/(1 + q)^2$
from 0.25 to 0.16). We accurately calculate the velocity of the kick to within
6%, and the final spin of the black holes to within 2%. A maximum kick of
$175.2\pm11$ km s$^{-1}$ is achieved for $\eta = 0.195 \pm 0.005$.


title:
Radar ranging and Doppler tracking in post-Einsteinian metric theories
  of gravity

abstract:
  The study of post-Einsteinian metric extensions of general relativity (GR),
which preserve the metric interpretation of gravity while considering metrics
which may differ from that predicted by GR, is pushed one step further. We give
a complete description of radar ranging and Doppler tracking in terms of the
time delay affecting an electromagnetic signal travelling between the Earth and
a remote probe. Results of previous publications concerning the Pioneer anomaly
are corrected and an annually modulated anomaly is predicted besides the
secular anomaly. Their correlation is shown to play an important role when
extracting reliable information from Pioneer observations. The formalism
developed here provides a basis for a quantitative analysis of the Pioneer
data, in order to assess whether extended metric theories can be the
appropriate description of gravity in the solar system.


title:
Extension of the frequency-range of interferometers for the ''magnetic''
  components of gravitational waves?

abstract:
  Recently, with an enlighting treatment, Baskaran and Grishchuk have shown the
presence and importance of the so-called ``magnetic'' components of
gravitational waves (GWs), which have to be taken into account in the context
of the total response functions of interferometers for GWs propagating from
arbitrary directions. In this paper the analysis of the response functions for
the magnetic components is generalized in its full frequency dependence, while
in the work of Baskaran and Grishchuk the response functions were computed only
in the approximation of wavelength much larger than the linear dimensions of
the interferometer. It is also shown that the response functions to the
magnetic components grow at high frequencies, differently from the values of
the response functions to the well known ordinary components that decrease at
high frequencies. Thus the magnetic components could in principle become the
dominant part of the signal at high frequencies. This is important for a
potential detection of the signal at high frequencies and confirms that the
magnetic contributions must be taken into account in the data analysis. More,
the fact that the response functions of the magnetic components grow at high
frequencies shows that, in principle, the frequency-range of Earth-based
interferometers could extend to frequencies over 10000 Hz.


title: Theoretical corrections on scalar gravitational waves

abstract:
  Following some ideas in the Landau book, some corrections about errors in the
old literature on scalar gravitational waves are given and discussed. Even if
such errors can be considered not important from the point of view of
observations, because they do not alter the interferometric response function
for scalar gravitational waves, the presented analysis is due and very
important for a sake of completeness and for a better understanding of the
linearized theory of Scalar-Tensor Gravity


title: Precession of Pericenter: A More Accurate Approach

abstract:
  In this paper we study the orbits of massive bodies moving in the spacetime
generated by a spherically symmetric and non-rotating distribution of mass.
More specifically, our treatment discusses the more accurate calculation of the
precession of pericenter due to general-relativistic effects. Our result is
accurate up to terms of second order, while the precession met in the
bibliography is accurate only up to first-order terms.


title: Deformation Quantization: From Quantum Mechanics to Quantum Field Theory

abstract:
  The aim of this paper is to give a basic overview of Deformation Quantization
(DQ) to physicists. A summary is given here of some of the key developments
over the past thirty years in the context of physics, from quantum mechanics to
quantum field theory. Also, we discuss some of the conceptual advantages of DQ
and how DQ may be related to algebraic quantum field theory. Additionally, our
previous results are summarized which includes the construction of the Fedosov
star-product on dS/AdS. One of the goals of these results was to verify that DQ
gave the same results as previous analyses of these spaces. Another was to
verify that the formal series used in the conventional treatment converged by
obtaining exact and nonperturbative results for these spaces.


title: Long range gravity tests and the Pioneer anomaly

abstract:
  Experimental tests of gravity performed in the solar system show a good
agreement with general relativity. The latter is however challenged by the
Pioneer anomaly which might be pointing at some modification of gravity law at
ranges of the order of the size of the solar system. As this question could be
related to the puzzles of ``dark matter'' or ``dark energy'', it is important
to test it with care. There exist metric extensions of general relativity which
preserve the well verified equivalence principle while possibly changing the
metric solution in the solar system. Such extensions have the capability to
preserve compatibility with existing gravity tests while opening free space for
the Pioneer anomaly. They constitute arguments for new mission designs and new
space technologies as well as for having a new look at data of already
performed experiments.


title: On solutions of a Heavenly equations and their generalizations

abstract:
  Some solutions of the Heavenly equations and their generalizations are
considered


title: Spherically Symmetric Gravitational Collapse of Perfect Fluids

abstract:
  Formulating a perfect fluid filled spherically symmetric metric utilizing the
3+1 formalism for general relativity, we show that the metric coefficients are
completely determined by the mass-energy distribution, and its time rate of
change on an initial spacelike hypersurface. Rather than specifying
Schwarzschild coordinates for the exterior of the collapsing region, we let the
interior dictate the form of the solution in the exterior, and thus both
regions are found to be written in one coordinate patch. This not only
alleviates the need for complicated matching schemes at the interface, but also
finds a new coordinate system for the Schwarzschild spacetime expressed in
generalized Painleve-Gullstrand coordinates.


title:
Late-time evolution of charged massive Dirac fields in the Kerr-Newman
  background

abstract:
  We investigate both the intermediate late-time tail and the asymptotic tail
behavior of the charged massive Dirac fields in the background of the
Kerr-Newman black hole. We find that the intermediate late-time behavior of
charged massive Dirac fields is dominated by an inverse power-law decaying tail
without any oscillation, which is different from the oscillatory decaying tails
of the scalar field. We note that the dumping exponent depends not only on the
angular quantum numbers $m$, the separation constant $\lambda$ and the rotating
parameter $a$, but also on the product $seQ$ of the spin weight of the Dirac
field and the charges of the black hole and the fields. We also find that the
decay rate of the asymptotically late-time tail is $t^{-5/6}$, and the
oscillation of the tail has the period of $2\pi / \mu$ which is modulated by
two types of long-term phase shifts.


title:
Universal Bound on Dynamical Relaxation Times and Black-Hole Quasinormal
  Ringing

abstract:
  From information theory and thermodynamic considerations a universal bound on
the relaxation time $\tau$ of a perturbed system is inferred, $\tau \geq
\hbar/\pi T$, where $T$ is the system's temperature. We prove that black holes
comply with the bound; in fact they actually {\it saturate} it. Thus, when
judged by their relaxation properties, black holes are the most extreme objects
in nature, having the maximum relaxation rate which is allowed by quantum
theory.

categories: gr-qc astro-ph cond-mat.stat-mech hep-th nucl-th quant-ph


title: Problems and hopes in nonsymmetric gravity

abstract:
  We consider the linearized nonsymmetric theory of gravitation (NGT) within
the background of an expanding universe and near a Schwarzschild mass. We show
that the theory always develops instabilities unless the linearized
nonsymmetric lagrangian reduces to a particular simple form. This form contains
a gauge invariant kinetic term, a mass term for the antisymmetric metric-field
and a coupling with the Ricci curvature scalar. This form cannot be obtained
within NGT. Based on the linearized lagrangian we know to be stable, we
consider the generation and evolution of quantum fluctuations of the
antisymmetric gravitational field (B-field) from inflation up to the present
day. We find that a B-field with a mass m ~ 0.03(H_I/10^(13)GeV)^4 eV is an
excellent dark matter candidate.


title: On the Multiple Deaths of Whitehead's Theory of Gravity

abstract:
  Whitehead's 1922 theory of gravitation continues to attract the attention of
philosophers, despite evidence presented in 1971 that it violates experiment.
We demonstrate that the theory strongly fails five quite different experimental
tests, and conclude that, notwithstanding its meritorious philosophical
underpinnings, Whitehead's theory is truly dead.


title: Emergent Semiclassical Time in Quantum Gravity. I. Mechanical Models

abstract:
  Strategies intended to resolve the problem of time in quantum gravity by
means of emergent or hidden timefunctions are considered in the arena of
relational particle toy models. In situations with `heavy' and `light' degrees
of freedom, two notions of emergent semiclassical WKB time emerge; these are
furthermore equivalent to two notions of emergent classical
`Leibniz--Mach--Barbour' time. I futhermore study the semiclassical approach,
in a geometric phase formalism, extended to include linear constraints, and
with particular care to make explicit those approximations and assumptions
used. I propose a new iterative scheme for this in the cosmologically-motivated
case with one heavy degree of freedom. I find that the usual semiclassical
quantum cosmology emergence of time comes hand in hand with the emergence of
other qualitatively significant terms, including back-reactions on the heavy
subsystem and second time derivatives. I illustrate my analysis by taking it
further for relational particle models with linearly-coupled harmonic
oscillator potentials. As these examples are exactly soluble by means outside
the semiclassical approach, they are additionally useful for testing the
justifiability of some of the approximations and assumptions habitually made in
the semiclassical approach to quantum cosmology. Finally, I contrast the
emergent semiclassical timefunction with its hidden dilational Euler time
counterpart.


title:
Emergent Semiclassical Time in Quantum Gravity. Full Geometrodynamics
  and Minisuperspace Examples

abstract:
  I apply the preceding paper's semiclassical treatment to geometrodynamics.
The analogy between the two papers is quite useful at the level of the
quadratic constraints, while I document the differences between the two due to
the underlying differences in their linear constraints. I provide a specific
minisuperspace example for my emergent semiclassical time scheme and compare it
with the hidden York time scheme. Overall, interesting connections are shown
between Newtonian, Leibniz--Mach--Barbour, WKB and cosmic times, while the
Euler and York hidden dilational times are argued to be somewhat different from
these.


title:
Applications of theorems of Jean Leray to the Einstein-scalar field
  equations

abstract:
  The Einstein-scalar field theory can be used to model gravitational physics
with scalar field matter sources. We discuss the initial value formulation of
this field theory, and show that the ideas of Leray can be used to show that
the Einstein-scalar field system of partial differential equations is
well-posed as an evolutionary system. We also show that one can generate
solutions of the Einstein-scalar field constraint equations using conformal
methods.


title:
Boundary conditions for the Einstein-Christoffel formulation of
  Einstein's equations

abstract:
  Specifying boundary conditions continues to be a challenge in numerical
relativity in order to obtain a long time convergent numerical simulation of
Einstein's equations in domains with artificial boundaries. In this paper, we
address this problem for the Einstein--Christoffel (EC) symmetric hyperbolic
formulation of Einstein's equations linearized around flat spacetime. First, we
prescribe simple boundary conditions that make the problem well posed and
preserve the constraints. Next, we indicate boundary conditions for a system
that extends the linearized EC system by including the momentum constraints and
whose solution solves Einstein's equations in a bounded domain.


title:
Well-Posed Initial-Boundary Value Problem for a Constrained Evolution
  System and Radiation-Controlling Constraint-Preserving Boundary Conditions

abstract:
  A well-posed initial-boundary value problem is formulated for the model
problem of the vector wave equation subject to the divergence-free constraint.
Existence, uniqueness and stability of the solution is proved by reduction to a
system evolving the constraint quantity statically, i.e., the second time
derivative of the constraint quantity is zero. A new set of
radiation-controlling constraint-preserving boundary conditions is constructed
for the free evolution problem. Comparison between the new conditions and the
standard constraint-preserving boundary conditions is made using the
Fourier-Laplace analysis and the power series decomposition in time. The new
boundary conditions satisfy the Kreiss condition and are free from the
ill-posed modes growing polynomially in time.