title: Reducing the flexing of the arms of LISA

abstract:
  The joint NASA-ESA mission LISA relies crucially on the stability of the
three spacecraft constellation. All three spacecraft are on heliocentric and
weakly eccentric orbits forming a stable triangle. It has been shown that for
certain spacecraft orbits, the arms keep constant distances to the first order
in the eccentricities. However, exact orbitography shows the so-called
`breathing modes' of the arms where the arms slowly change their lengths over
the time-scale of a year. In this paper we analyse the breathing modes (the
flexing of the arms) with the help of the geodesic deviation equations to
octupole order which are shown to be equivalent to higher order
Clohessy-Wiltshire equations. We show that the flexing of the arms of LISA as
given by the `exact' solution of Keplerian orbits, which gives constant
armlengths to the first order in eccentricity and whose maximum flexing
amplitude is $\sim 115,000$ km, can be improved, by tilting the plane of the
LISA triangle slightly from the proposed orientation of $60^\circ$ with the
ecliptic to obtain a maximum flexing amplitude of $\sim 48,000$ km, reducing it
by a factor of $\sim 2.4$. The reduction factor is even larger if we consider
the corresponding Doppler shifts, for which the reduction factor reaches almost
a factor of 6. We solve the second order equations and obtain the general
solution. We then use the general solution to establish the optimality of the
solutions that we have found.


title: Partial and Complete Observables for Canonical General Relativity

abstract:
  In this work we will consider the concepts of partial and complete
observables for canonical general relativity. These concepts provide a method
to calculate Dirac observables. The central result of this work is that one can
compute Dirac observables for general relativity by dealing with just one
constraint. For this we have to introduce spatial diffeomorphism invariant
Hamiltonian constraints. It will turn out that these can be made to be Abelian.
Furthermore the methods outlined here provide a connection between observables
in the space--time picture, i.e. quantities invariant under space--time
diffeomorphisms, and Dirac observables in the canonical picture.


title: In Defense of Campbell's Theorum as a Frame for New Physics

abstract:
  The Campbell-Magaard theorem is widely seen as a way of embedding Einstein's
4D theory of general relativity in a 5D theory of the Kaluza-Klein type. We
give a brief history of theorem, present a short account of it, and show that
it provides a geometrical frame for new physics related to the unification of
the forces. Anderson's recent vituperative attack on Campbell's theorem
(gr-qc/0409122)is errant.


title:
A Hamiltonian functional for the linearized Einstein vacuum field
  equations

abstract:
  By considering the Einstein vacuum field equations linearized about the
Minkowski metric, the evolution equations for the gauge-invariant quantities
characterizing the gravitational field are written in a Hamiltonian form by
using a conserved functional as Hamiltonian; this Hamiltonian is not the analog
of the energy of the field. A Poisson bracket between functionals of the field,
compatible with the constraints satisfied by the field variables, is obtained.
The generator of spatial translations associated with such bracket is also
obtained.


title:
Contributions from Dilatonic Strings to the Flat Behaviour of the
  Rotational Curves in Galaxies

abstract:
  We analyse the flat behaviour of the rotational curves in some galaxies in
the framework of a dilatonic, current-carrying string. We determine the
expression of the tangential velocity of test objects following a stable
circular equatorial orbit in this spacetime.


title:
New Black Hole Solutions with Axial Symmetry in Einstein-Yang-Mills
  Theory

abstract:
  We construct new black hole solutions in Einstein-Yang-Mills theory. They are
static, axially symmetric and asymptotically flat. They are characterized by
their horizon radius and a pair of integers (k,n), where k is related to the
polar angle and n to the azimuthal angle. The known spherically and axially
symmetric EYM black holes have k=1. For k>1, pairs of new black hole solutions
appear above a minimal value of n, that increases with k. Emerging from
globally regular solutions, they form two branches, which merge and end at a
maximal value of the horizon radius. The difference of their mass and their
horizon mass equals the mass of the corresponding regular solution, as expected
from the isolated horizon framework.


title: General relativity and the spiral of compact binary stars

abstract:
  The theory of general relativity, which is extremely well verified by classic
tests in the solar system as well as by the radiation of the binary pulsar, is
one of the fundamental tools of nowadays astrophysics. It permits the
computation of the gravitational wave form emitted during the inspiral phase of
binary systems of neutron stars and black holes. Based on the so-called
post-Newtonian approximation (developped to high order), the prediction of
general relativity is used as a "template" for searching and analysing the
signals in the network of gravitational-wave detectors VIRGO/LIGO.


title:
A Toy Model for Testing Finite Element Methods to Simulate
  Extreme-Mass-Ratio Binary Systems

abstract:
  Extreme mass ratio binary systems, binaries involving stellar mass objects
orbiting massive black holes, are considered to be a primary source of
gravitational radiation to be detected by the space-based interferometer LISA.
The numerical modelling of these binary systems is extremely challenging
because the scales involved expand over several orders of magnitude. One needs
to handle large wavelength scales comparable to the size of the massive black
hole and, at the same time, to resolve the scales in the vicinity of the small
companion where radiation reaction effects play a crucial role. Adaptive finite
element methods, in which quantitative control of errors is achieved
automatically by finite element mesh adaptivity based on posteriori error
estimation, are a natural choice that has great potential for achieving the
high level of adaptivity required in these simulations. To demonstrate this, we
present the results of simulations of a toy model, consisting of a point-like
source orbiting a black hole under the action of a scalar gravitational field.


title: Overview of Affine Quantum Gravity

abstract:
  The basic principles of Affine Quantum Gravity are presented in a pedagogical
style with a limited number of equations.


title:
Probing anisotropies of gravitational-wave backgroundswith a space-based
  interferometer II: Perturbative reconstruction of a low-frequency skymap

abstract:
  We present a perturbative reconstruction method to make a skymap of
gravitational-wave backgrounds (GWBs) observed via space-based interferometer.
In the presence of anisotropies in GWBs, the cross-correlated signals of
observed GWBs are inherently time-dependent due to the non-stationarity of the
gravitational-wave detector. Since the cross-correlated signal is obtained
through an all-sky integral of primary signals convolving with the antenna
pattern function of gravitational-wave detectors, the non-stationarity of
cross-correlated signals, together with full knowledge of antenna pattern
functions, can be used to reconstruct an intensity map of the GWBs. Here, we
give two simple methods to reconstruct a skymap of GWBs based on the
perturbative expansion in low-frequency regime. The first one is based on
harmonic-Fourier representation of data streams and the second is based on
"direct" time-series data. The latter method enables us to create a skymap in a
direct manner. The reconstruction technique is demonstrated in the case of the
Galactic gravitational wave background observed via planned space
interferometer, LISA. Although the angular resolution of low-frequency skymap
is rather restricted, the methodology presented here would be helpful in
discriminating the GWBs of galactic origins by those of the extragalactic
and/or cosmological origins.


title: An interacting scalar field and the recent cosmic acceleration

abstract:
  In this paper it is shown that the Brans - Dicke scalar field itself can
serve the purpose of providing an early deceleration and a late time
acceleration of the universe without any need of quintessence field if one
considers an interaction, i.e, transfer of energy between the dark matter and
the Brans - Dicke scalar field.


title:
The Renormalized Stress Tensor in Kerr Space-Time: Numerical Results for
  the Hartle-Hawking Vacuum

abstract:
  We show that the pathology which afflicts the Hartle-Hawking vacuum on the
Kerr black hole space-time can be regarded as due to rigid rotation of the
state with the horizon in the sense that when the region outside the
speed-of-light surface is removed by introducing a mirror, there is a state
with the defining features of the Hartle-Hawking vacuum. In addition, we show
that when the field is in this state, the expectation value of the
energy-momentum stress tensor measured by an observer close to the horizon and
rigidly rotating with it corresponds to that of a thermal distribution at the
Hawking temperature rigidly rotating with the horizon.


title: Searches for Black Holes. the Most Recent Results

abstract:
  Black holes were predicted by Einstein General Relativity (GR). Because of
unusual properties of these objects their existence is almost unbelievable.
There are gravitation theories which do not predict the black hole appearance.
By now, astronomers discovered a few hundreds of massive and highly compact
objects with observational features which are very similar to the properties of
black holes predicted by GR. To confirm existence of black holes in the
Universe, a number of groundbased and space experiments are planned to be held
in the coming decade.


title: Observational Features of Black Holes

abstract:
  Recently considered a very attracting possibility to detect retro-MACHOs,
i.e. retro-images of the Sun by a Schwarzschild black hole. In this paper we
discuss glories (mirages) formed near rapidly rotating Kerr black hole horizons
and propose a procedure to measure masses and rotation parameters analyzing
these forms of mirages. In some sense that is a manifestation of gravitational
lens effect in the strong gravitational field near black hole horizon and a
generalization of the retro-gravitational lens phenomenon. We analyze the case
of a Kerr black hole rotating at arbitrary speed for some selected positions of
a distant observer with respect to the equatorial plane of a Kerr black hole.
We discuss glories (mirages) formed near rapidly rotating Kerr black hole
horizons and propose a procedure to measure masses and rotation parameters
analyzing these forms of mirages. Some time ago suggested to search shadows at
the Galactic Center. In this paper we present the boundaries for shadows
calculated numerically. We also propose to use future radio interferometer
RADIOASTRON facilities to measure shapes of mirages (glories) and to evaluate
the black hole spin as a function of the position angle of a distant observer.


title: Black hole mass decreasing due to phantom energy accretion

abstract:
  Solution for a stationary spherically symmetric accretion of the relativistic
perfect fluid with an equation of state p(rho) onto the Schwarzschild black
hole is presented. This solution is a generalization of Michel solution and
applicable to the problem of dark energy accretion. It is shown that accretion
of phantom energy is accompanied with the gradual decrease of the black hole
mass. Masses of all black holes tend to zero in the phantom energy universe
approaching to the Big Rip.


title: On the gravitational field. A suggestion about a possible experiment

abstract:
  After a preliminary discussion of the relevance of the field nature of
gravitation interaction, both for the fundamental interaction of particles and
the topology of space time, a method is proposed to produce and detect a
dynamical gravitational field, allowing the determination of the order of
magnitude of its propagation velocity.


title: Introducing Relativity in Global Navigation Satellite Systems

abstract:
  Today, the Global Navigation Satellite Systems, used as global positioning
systems, are the GPS and the GLONASS. They are based on a Newtonian model and
hence they are only operative when several relativistic effects are taken into
account. The most important relativistic effects (to order 1/c^2) are: the
Einstein gravitational blue shift effect of the satellite clock frequency
(Equivalence Principle of General Relativity) and the Doppler red shift of
second order, due to the motion of the satellite (Special Relativity).
  On the other hand, in a few years the Galileo system will be built, copying
the GPS system unless an alternative project is designed. In this work, it will
be also shown that the SYPOR project, using fully relativistic concepts, is an
alternative to a mere copy of the GPS system. According to this project, the
Galileo system would be exact and there would be no need for relativistic
corrections.


title:
Regularized expression for the gravitational energy-momentum in
  teleparallel gravity and the principle of equivalence

abstract:
  The expression of the gravitational energy-momentum defined in the context of
the teleparallel equivalent of general relativity is extended to an arbitrary
set of real-valued tetrad fields, by adding a suitable reference space
subtraction term. The characterization of tetrad fields as reference frames is
addressed in the context of the Kerr space-time. It is also pointed out that
Einstein's version of the principle of equivalence does not preclude the
existence of a definition for the gravitational energy-momentum density.


title:
Singular Strings in the Rotating Astrophysical Sources: a New Conjecture
  on the QPOs and Jet Phenomena

abstract:
  Stringy and disklike sources of the rotating compact astrophysical objects
are considered on the base of the Kerr geometry. It is argued that analyticity
of the Kerr solutions may result the appearance of singular strings, which may
be the source of two important astrophysical effects: the jets and QPOs
phenomena.


title: Black Hole Statistical Physics: Entropy

abstract:
  We discuss the most interesting approaches to derivation of the
Bekenstein-Hawking entropy formula from a statistical theory.


title:
Self-Similar Structure of the Universe and Fundamental Sense of
  Existence of Large and Small Black Holes in the Nature

abstract:
  The origin of self-similar (according to Y.Kulakov) structure of the Universe
is discussed from a position of the theory of dynamic systems (DS). A probable
nature of the isomorphism of DS configurations of different levels is revealed.
Nucleon DS configuration like black hole (BH) might be acquired by the last as
a result of Hawking radiation of initial BH and serve further as a genome of
the Universe development.


title: Ghost condensate model of flat rotation curves

abstract:
  An effective action of ghost condensate with higher derivatives creates a
source of gravity and mimics a dark matter in spiral galaxies. We present a
spherically symmetric static solution of Einstein--Hilbert equations with the
ghost condensate at large distances, where flat rotation curves are reproduced
in leading order over small ratio of two energy scales characterizing constant
temporal and spatial derivatives of ghost field: $\mu_*^2$ and $\mu_\star^2$,
respectively, with a hierarchy $\mu_\star\ll \mu_*$. We assume that a mechanism
of hierarchy is provided by a global monopole in the center of galaxy. An
estimate based on the solution and observed velocities of rotations in the
asymptotic region of flatness, gives $\mu_*\sim 10^{19}$ GeV and the monopole
scale in a GUT range $\mu_\star\sim 10^{16}$ GeV, while a velocity of rotation
$v_0$ is determined by the ratio: $ \sqrt{2} v_0^2= \mu_\star^2/\mu_*^2$. A
critical acceleration is introduced and naturally evaluated of the order of
Hubble rate, that represents the Milgrom's acceleration.


title:
Nonlinear monopole, regularity conditions and the electromagnetic mass
  in Einstein-Born-Infeld theories

abstract:
  In this work a new asymptotically flat solution of the coupled
Einstein-Born-Infeld equations for a static spherically symmetric space-time is
obtained. When the intrinsic mass is zero the resulting spacetime is regular
everywhere, in the sense given by B. Hoffmann and L. Infeld in 1937, and the
Einstein-Born-Infeld theory leads to the identification of the gravitational
with the electromagnetic mass.


title: Space-time: emerging vs. existing

abstract:
  The concept of the space-time as emerging in the world phase transition, vs.
a priori existing, is put forward. The theory of gravity with two basic
symmetries, the global affine one and the general covariance, is developed.
Implications for the Universe are indicated.


title:
Lagrangian Formalism on Jet-Gauge and Jet-Diffeomorphism Groups: Towards
  a Unification of Gravity with Internal Gauge Interactions

abstract:
  In this talk the description of gauge theories associated with internal
symmetries is extended to the case in which the symmetry group is the
space-time translation group (recovering Einstein's theory) using the standard
jet-bundle formalism. We also reformulate these theories introducing the idea
of jet-gauge and jet-diffeomorphism groups. Finally, we attempt to a simple,
yet non-trivial, mixing of gravity and electromagnetism (or more general
internal interaction) by turning to gauge symmetry a central extension of the
Poincare group.


title: Do Wormholes Fix the Coupling Constants?

abstract:
  If Newtonian gravitation is modified to use surface-to-surface separation
between particles, it can have the strength of nuclear force between nucleons.
This may be justified by possible existence of quantum wormholes in particles.
All gravitational interactions would be between coupled wormholes, emitting
graviton flux in proportional to particle size, allowing for the point-like
treatment above. When the wormholes are 1 Planck length apart, the resultant
force is 10^40 times the normal gravitational strength for nucleons.


title: Energy in Theory of Gravity and Essence of Time

abstract:
  In the framework of the field theory it is shown that a time (viewed as a
scalar temporal field) is an internal property of the physical system, which
defines its causal structure and evolution. A new concept of internal time
allows to solve the energy problem in General Relativity and predicts the
existence of matter outside the time. It is demonstrated that introduction of
the temporal field permits to derive the physical laws of the electromagnetic
field(the general covariant four dimensional Maxwell equations for the electric
and magnetic fields) from the geometrical equations of this field. It means
that the fundamental physical laws are in full correspondence with the essence
of time. On this ground, from the geometrical laws of the gravitational field
the physical evolution equations of this field are derived. Two characteristic
solutions of these equations are obtained (including the Schwarzschild
solution).


title: Cosmic Neutrinos and Quantum Gravity with Extra Dimensions

abstract:
  This paper has been withdrawn by the authors because the authors excluded the
paper from electronic proceedings of the conference.


title:
Plenary talk presented at Workshop on High Energy Physics&Field Theory
  (Protvino, Russia, 2004)

abstract:
  The problems concerning a possible discovery of the mini block holes at
earthly accelerators are discussed.


title: Composite Electric $s$-Brane Solutions with Maximal Charge Densities

abstract:
  In this paper we consider $(n+1)$-dimensional cosmological model with scalar
field and antisymmetric $(p+2)$-form. Using an electric composite $Sp$-brane
ansatz the field equations for the original system reduce to the equations for
a Toda-like system with $n(n-1)/2$ quadratic constraints on the charge
densities. For certain odd dimensions ($D = 4m+1 = 5, 9, 13, ...$) and
$(p+2)$-forms ($p = 2m-1 = 1, 3, 5, ...$) these algebraic constraints can be
satisfied with the maximal number of charged branes (i.e.} all the branes have
non-zero charge densities). These solutions are characterized by self-dual or
anti-self-dual charge density forms $Q$ (of rank $2m$). For these algebraic
solutions with the particular $D$, $p$, $Q$ and non-exceptional dilatonic
coupling constant $\lambda$ we obtain general cosmological solutions to the
field equations and some properties of these solutions are examined. In
particuilar Kasner-like behavior, the existence of attractor solutions.


title: Quantization of Physical Models and Non-Commutative Geometry

abstract:
  Application of the noncommutative geometry to several physical models is
considered.


title: Einstein, Hilbert and Equations of Gravitation

abstract:
  Some highlights of the priority in the discovery of the gravitational field
equations are given.


title:
Analytic Kerr black hole lensing for equatorial observers in the strong
  deflection limit

abstract:
  In this paper we present an analytical treatment of gravitational lensing by
Kerr black holes in the limit of very large deflection angles, restricting to
observers in the equatorial plane. We accomplish our objective starting from
the Schwarzschild black hole and adding corrections up to second order in the
black hole spin. This is sufficient to provide a full description of all
caustics and the inversion of lens mapping for sources near them. On the basis
of these formulae we argue that relativistic images of Low Mass X-ray Binaries
around Sgr A* are very likely to be seen by future X-ray interferometry
missions.


title: XXVII International Workshop on High Energy Physics and Field Theory

abstract: BLACK HOLES ON EARTH AND IN SPACE


title:
Feasibility of a Unitary Quantum Dynamics in the Gowdy $T^3$
  Cosmological Model

abstract:
  It has been pointed out that it is impossible to obtain a unitary
implementation of the dynamics for the polarized Gowdy $T^{3}$ cosmologies in
an otherwise satisfactory, nonperturbative canonical quantization proposed for
these spacetimes. By introducing suitable techniques to deal with
deparametrized models in cosmology that possess an explicit time dependence (as
it is the case for the toroidal Gowdy model), we present in this paper a
detailed analysis about the roots of this failure of unitarity. We investigate
the impediments to a unitary implementation of the evolution by considering
modifications to the dynamics. These modifications may be regarded as
perturbations. We show in a precise manner why and where unitary
implementability fails in our system, and prove that the obstructions are
extremely sensitive to modifications in the Hamiltonian that dictates the time
evolution of the symmetry-reduced model. We are able to characterize to a
certain extent how far the model is from unitarity. Moreover, we demonstrate
that the dynamics can actually be approximated as much as one wants by means of
unitary transformations.


title:
Analytic structure of radiation boundary kernels for blackhole
  perturbations

abstract:
  Exact outer boundary conditions for gravitational perturbations of the
Schwarzschild metric feature integral convolution between a time-domain
boundary kernel and each radiative mode of the perturbation. For both axial
(Regge-Wheeler) and polar (Zerilli) perturbations, we study the Laplace
transform of such kernels as an analytic function of (dimensionless) Laplace
frequency. We present numerical evidence indicating that each such
frequency-domain boundary kernel admits a "sum-of-poles" representation. Our
work has been inspired by Alpert, Greengard, and Hagstrom's analysis of
nonreflecting boundary conditions for the ordinary scalar wave equation.


title: Excess Baggage

abstract:
  Many advances in physics have in common that some idea which was previously
accepted as fundamental, general, and inescapable was subsequently seen to be
consequent, special, and dispensable. The idea was not truly a general feature
of the world, but only perceived to be general because of our special place in
the universe and the limited range of our experience. It was excess baggage
which had to be jettisoned to reach a more a more general perspective. This
article discusses excess baggage from the perspective of quantum cosmology
which aims at a theory of the universe's quantum initial state. We seek to
answer the question `Which features of our current theoretical framework are
fundamental and which reflect our special position in the universe or its
special initial condition?' Past instances of cosmological excess baggage are
reviewed such as the idea that the Earth was at the center of the universe or
that the second law of thermodynamics was fundamental. Examples of excess
baggage in our current understanding of quantum cosmology are the notion that
measurement is central to formulating quantum mechanics, a fundamental quantum
mechanical arrow of time, and the idea that a preferred time is needed to
formulate quantum theory. We speculate on candidates for future excess baggage.
(This article appeared in 1991 but is posted here for accessibility and
possible current interest.)


title: Proper Affine Vector Fields in Bianchi Type I Space-Times

abstract:
  A study of Bianchi type I space-times according to its proper affine vector
field is given by using holonomy and decomposability, the rank of the Rieman
matrix and direct integration techinques. It is shown that the special class of
the above space-times admits proper affine vector fields.


title: A generalized Damour-Navier-Stokes equation applied to trapping horizons

abstract:
  An identity is derived from Einstein equation for any hypersurface H which
can be foliated by spacelike two-dimensional surfaces. In the case where the
hypersurface is null, this identity coincides with the two-dimensional
Navier-Stokes-like equation obtained by Damour in the membrane approach to a
black hole event horizon. In the case where H is spacelike or null and the
2-surfaces are marginally trapped, this identity applies to Hayward's trapping
horizons and to the related dynamical horizons recently introduced by Ashtekar
and Krishnan. The identity involves a normal fundamental form (normal
connection 1-form) of the 2-surface, which can be viewed as a generalization to
non-null hypersurfaces of the Hajicek 1-form used by Damour. This 1-form is
also used to define the angular momentum of the horizon. The generalized
Damour-Navier-Stokes equation leads then to a simple evolution equation for the
angular momentum.


title:
Grafting and Poisson structure in (2+1)-gravity with vanishing
  cosmological constant

abstract:
  We relate the geometrical construction of (2+1)-spacetimes via grafting to
phase space and Poisson structure in the Chern-Simons formulation of
(2+1)-dimensional gravity with vanishing cosmological constant on manifolds of
topology $R\times S_g$, where $S_g$ is an orientable two-surface of genus
$g>1$. We show how grafting along simple closed geodesics \lambda is
implemented in the Chern-Simons formalism and derive explicit expressions for
its action on the holonomies of general closed curves on S_g. We prove that
this action is generated via the Poisson bracket by a gauge invariant
observable associated to the holonomy of $\lambda$. We deduce a symmetry
relation between the Poisson brackets of observables associated to the Lorentz
and translational components of the holonomies of general closed curves on S_g
and discuss its physical interpretation. Finally, we relate the action of
grafting on the phase space to the action of Dehn twists and show that grafting
can be viewed as a Dehn twist with a formal parameter $\theta$ satisfying
$\theta^2=0$.


title:
Energy distribution of the Einstein-Klein-Gordon system for a static
  spherically symmetric spacetime in (2+1)-dimensions

abstract:
  We use Moeller's energy-momentum complex in order to explicitly compute the
energy and momentum density distributions for an exact solution of Einstein's
field equations with a negative cosmological constant minimally coupled to a
static massless scalar field in a static, spherically symmetric background in
(2+1)-dimensions.


title: Soft singularity and the fundamental length

abstract:
  It is shown that some regular solutions in 5D Kaluza-Klein gravity may have
interesting properties if one from the parameters is in the Planck region. In
this case the Kretschman metric invariant runs up to a maximal reachable value
in nature, i.e. practically the metric becomes singular. This observation
allows us to suppose that in this situation the problems with such soft
singularity will be much easier resolved in the future quantum gravity then by
the situation with the ordinary hard singularity (Reissner-Nordstr\"om
singularity, for example). It is supposed that the analogous consideration can
be applied for the avoiding the hard singularities connected with the gauge
charges.


title: From 3-geometry transition amplitudes to graviton states

abstract:
  In various background independent approaches, quantum gravity is defined in
terms of a field propagation kernel: a sum over paths interpreted as a
transition amplitude between 3-geometries, expected to project quantum states
of the geometry on the solutions of the Wheeler-DeWitt equation. We study the
relation between this formalism and conventional quantum field theory methods.
We consider the propagation kernel of 4d Lorentzian general relativity in the
temporal gauge, defined by a conventional formal Feynman path integral, gauge
fixed a\' la Fadeev--Popov. If space is compact, this turns out to depend only
on the initial and final 3--geometries, while in the asymptotically flat case
it depends also on the asymptotic proper time. We compute the explicit form of
this kernel at first order around flat space, and show that it projects on the
solutions of all quantum constraints, including the Wheeler-DeWitt equation,
and yields the correct vacuum and n-graviton states. We also illustrate how the
Newtonian interaction is coded into the propagation kernel, a key open issue in
the spinfoam approach.


title: Observables for the polarized Gowdy model

abstract:
  We give an explicit characterization of all functions on the phase space for
the polarized Gowdy 3-torus spacetimes which have weakly vanishing Poisson
brackets with the Hamiltonian and momentum constraint functions.


title:
Classical Solution of Field Equation of Gravitational Gauge Field and
  Classical Tests of Gauge Theory of Gravity

abstract:
  A systematic method is developed to study classical motion of a mass point in
gravitational gauge field. First, the formulation of gauge theory of gravity in
arbitrary curvilinear coordinates is given. Then in spherical coordinates
system, a spherical symmetric solution of the field equation of gravitational
gauge field is obtained, which is just the Schwarzschild solution. In gauge
theory of gravity, the equation of motion of a classical mass point in
gravitational gauge field is given by Newton's second law of motion. A
relativistic form of the gravitational force on a mass point is deduced in this
paper. Based on the spherical symmetric solution of the field equation and
Newton's second law of motion, we can discuss classical tests of gauge theory
of gravity, including the deflection of light by the sun, the precession of the
perihelia of the orbits of the inner planets and the time delay of radar echoes
passing the sun. It is found that the theoretical predictions of these
classical tests given by gauge theory of gravity are completely the same as
those given by general relativity. From the study in this paper, an important
qualitative conclusion on the nature of gravity is that gravity can be treated
as a kind of physical interactions in flat Minkowski space-time, and the
equation of motion of mass point in gravitational field can be given by
Newton's second law of motion.


title:
Stability of semiclassical gravity solutions with respect to quantum
  metric fluctuations

abstract:
  We discuss the stability of semiclassical gravity solutions with respect to
small quantum corrections by considering the quantum fluctuations of the metric
perturbations around the semiclassical solution. We call the attention to the
role played by the symmetrized two-point quantum correlation function for the
metric perturbations, which can be naturally decomposed into two separate
contributions: intrinsic and induced fluctuations. We show that traditional
criteria on the stability of semiclassical gravity are incomplete because these
criteria based on the linearized semiclassical Einstein equation can only
provide information on the expectation value and the intrinsic fluctuations of
the metric perturbations. By contrast, the framework of stochastic
semiclassical gravity provides a more complete and accurate criterion because
it contains information on the induced fluctuations as well. The
Einstein-Langevin equation therein contains a stochastic source characterized
by the noise kernel (the symmetrized two-point quantum correlation function of
the stress tensor operator) and yields stochastic correlation functions for the
metric perturbations which agree, to leading order in the large N limit, with
the quantum correlation functions of the theory of gravity interacting with N
matter fields. These points are illustrated with the example of Minkowski
spacetime as a solution to the semiclassical Einstein equation, which is found
to be stable under both intrinsic and induced fluctuations.


title:
Dyonic Kerr-Newman black holes, complex scalar field and Cosmic
  Censorship

abstract:
  We construct a gedanken experiment, in which a weak wave packet of the
complex massive scalar field interacts with a four-parameter (mass, angular
momentum, electric and magnetic charges) Kerr-Newman black hole. We show that
this interaction cannot convert an extreme the black hole into a naked
sigularity for any black hole parameters and any generic wave packet
configuration. The analysis therefore provides support for the weak cosmic
censorship conjecture.


title:
On the impossibility of using certain existing spacecraft for the
  measurement of the Lense-Thirring effect in the terrestrial gravitational
  field

abstract:
  In the context of the currently ongoing efforts to improve the accuracy and
reliability of the measurement of the Lense-Thirring effect in the
gravitational field of the Earth it has recently been proposed to use the data
from the existing spacecraft endowed with some active mechanisms of
compensation of the non-gravitational accelerations like GRACE. In this paper
we critically discuss this interesting possibility. Unfortunately, it turns out
to be unpracticable because of the impact of the uncancelled even zonal
harmonic coefficients of the multipolar expansion of the terrestrial
gravitational potential and of some time-dependent tidal perturbations which
would resemble as superimposed linear trends over the necessarily limited
observational time span of the analysis.


title: Anti-Gravitation

abstract:
  The possibility of a symmetry between gravitating and anti-gravitating
particles is examined. The properties of the anti-gravitating fields are
defined by their behavior under general diffeomorphisms. The equations of
motion and the conserved canonical currents are derived, and it is shown that
the kinetic energy remains positive whereas the new fields can make a negative
contribution to the source term of Einstein's field equations. The interaction
between the two types of fields is naturally suppressed by the Planck scale.


title:
Constraint Preserving Boundary Conditions for Hyperbolic Formulations of
  Einstein's Equations

abstract:
  Einstein's system of equations in the ADM decomposition involves two
subsystems of equations: evolution equations and constraint equations. For
numerical relativity, one typically solves the constraint equations only on the
initial time slice, and then uses the evolution equations to advance the
solution in time. Our interest is in the case when the spatial domain is
bounded and appropriate boundary conditions are imposed. A key difficulty,
which we address in this thesis, is what boundary conditions to place at the
artificial boundary that lead to long time stable numerical solutions. We
develop an effective technique for finding well-posed constraint preserving
boundary conditions for constrained first order symmetric hyperbolic systems.
By using this technique, we study the preservation of constraints by some first
order symmetric hyperbolic formulations of Einstein's equations derived from
the ADM decomposition linearized around Minkowski spacetime with arbitrary
lapse and shift perturbations, and the closely related question of their
equivalence with the linearized ADM system. Our main result is the finding of
well-posed maximal nonnegative constraint preserving boundary conditions for
each of the first order symmetric hyperbolic formulations under investigation,
for which the unique solution of the corresponding initial boundary value
problem provides a solution to the linearized ADM system on polyhedral domains.


title: Charged Scalar Self-Mass during Inflation

abstract:
  We compute the one loop self-mass of a charged massless, minimally coupled
scalar in a locally de Sitter background geometry. The computation is done in
two different gauges: the noninvariant generalization of Feynman gauge which
gives the simplest expression for the photon propagator and the de Sitter
invariant gauge of Allen and Jacobson. In each case dimensional regularization
is employed and fully renormalized results are obtained. By using our result in
the linearized, effective field equations one can infer how the scalar responds
to the dielectric medium produced by inflationary particle production. We also
work out the result for a conformally coupled scalar. Although the conformally
coupled case is of no great physical interest the fact that we obtain a
manifestly de Sitter invariant form for its self-mass-squared establishes that
our noninvariant gauge introduces no physical breaking of de Sitter invariance
at one loop order.


title: Is general relativity `essentially understood' ?

abstract:
  The content of Einstein's theory of gravitation is encoded in the properties
of the solutions to his field equations. There has been obtained a wealth of
information about these solutions in the ninety years the theory has been
around. It led to the prediction and the observation of physical phenomena
which confirm the important role of general relativity in physics. The
understanding of the domain of highly dynamical, strong field configurations
is, however, still quite limited. The gravitational wave experiments are likely
to provide soon observational data on phenomena which are not accessible by
other means. Further theoretical progress will require, however, new methods
for the analysis and the numerical calculation of the solutions to Einstein's
field equations on large scales and under general assumptions. We discuss some
of the problems involved, describe the status of the field and recent results,
and point out some open problems.


title: Spinning cosmic strings: a general class of solutions

abstract:
  In this work, we give a general class of solutions of the spinning cosmic
string in Einstein's theory of gravity. After treating same problem in Einstein
Cartan (EC) theory of gravity, the exact solution satisfying both exterior and
interior space-times representing a spin fluid moving along the symmetry axis
is presented in the EC theory. The existence of closed timelike curves in this
spacetime are also examined.


title:
Energy-Momentum in the Viscous Kasner-type Universe in Teleparallel
  Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0011027, "Viscous cosmologies in scalar-tensor theories for Kasner type
metrics," by M. Cataldo, S. del Campo and P. Salgado; and gr-qc/0303034, "The
energy of the universe in teleparallel gravity," by T. Vargas.


title: From Inflation to Dark Energy

abstract:
  It is proposed that after the macroscopic fluctuation of energy density that
is responsible for inflation dies away, a class of microscopic fluctuations,
always present, survives to give the present day dark energy. This latter is
simply a reinterpretation of the causet mechanism of Ahmed, Dodelson, Green and
Sorkin, wherein the emergence of space is dropped but only energy
considerations are maintained. At postinflation times, energy is exchanged
between the "cisplanckian" cosmos and an unknown foam-like transplanckian
reservoir. Whereas during inflation, the energy flows only from the latter to
the former after inflation it fluctuates in sign thereby accounting for the
tiny effective cosmological constant that seems to account for dark energy.


title:
Exact Static Solutions for Scalar Fields Coupled to Gravity in
  $(3+1)$-Dimensions

abstract:
  Einstein's field equations for a spherically symmetric metric coupled to a
massless scalar field are reduced to a system effectively of second order in
time, in terms of the variables $\mu=m/r$ and $y=(\alpha/ra)$, where $a$,
$\alpha$, $r$ and $m$ are as in [W.M. Choptuik, ``Universality and Scaling in
Gravitational Collapse of Massless Scalar Field", \textit{Physical Review
Letters} {\bf{70}} (1993), 9-12]. Solutions for which $\mu $ and $y$ are time
independent may arise either from scalar fields with $\phi_t=0$ or with
$\phi_s=0$ but $\phi$ linear in $t$, called respectively the positive and
negative branches having the Schwarzschild solution characterized by $\phi=0 $
and $\mu_s+\mu=0$ in common. For the positive branch we obtain an exact
solution which have been in fact obtained first in [I.Z. Fisher,``Scalar
mesostatic field with regard for gravitational effects", \textit{Zh. Eksp.
Teor. Fiz.} {\bf{18}} (1948), 636-640, gr-qc/9911008] and rediscovered many
times (see D. Grumiller, ``Quantum dilaton gravity in two dimensions with
matter", PhD thesis, \textit{Technische Universit$\ddot{a}$t, Wien} (2001),
gr-qc/0105078) and we prove that the trivial solution $\mu=0$ is a global
attractor for the region $\mu_s+\mu>0 $, $\mu<1/2$. For the negative branch
discussed first in [M. Wyman, ``Static spherically symmetric scalar fields in
general relativity", \textit{Physical Review D} {\bf{24}} (1981), 839-841]
perturbatively, we prove that $\mu=0$ is a saddle point for the linearized
system, but the non-vacuum solution $\mu=1/4$ is a stable focus and a global
attractor for the region $\mu_s+\mu>0$, $\mu<1/2$.


title: Chaplygin Gravitodynamics

abstract:
  We consider a new approach for gravity theory coupled to Chaplygin matter in
which the {\it{relativistic}} formulation of the latter is of crucial
importance. We obtain a novel form of matter with dust like density $(\sim
(volume)^{-1})$ and negative pressure. We explicitly show that our results are
compatible with a relativistic generalization of the energy conservation
principle, derived here.


title:
To the practical design of the optical lever intracavity topology of
  gravitational-wave detectors

abstract:
  The QND intracavity topologies of gravitational-wave detectors proposed
several years ago allow, in principle, to obtain sensitivity significantly
better than the Standard Quantum Limit using relatively small anount of optical
pumping power. In this article we consider an improved more ``practical''
version of the optical lever intracavity scheme. It differs from the original
version by the symmetry which allows to suppress influence of the input light
amplitude fluctuation. In addition, it provides the means to inject optical
pumping inside the scheme without increase of optical losses.
  We consider also sensitivity limitations imposed by the local meter which is
the key element of the intracavity topologies. Two variants of the local meter
are analyzed, which are based on the spectral variation measurement and on the
Discrete Sampling Variation Measurement, correspondingly. The former one, while
can not be considered as a candidate for a practical implementation, allows, in
principle, to obtain the best sensitivity and thus can be considered as an
ideal ``asymptotic case'' for all other schemes. The DSVM-based local meter can
be considered as a realistic scheme but its sensitivity, unfortunately, is by
far not so good just due to a couple of peculiar numeric factors specific for
this scheme.
  From our point of view search of new methods of mechanical QND measurements
probably based on improved DSVM scheme or which combine the local meter with
the pondermotive squeezing technique, is necessary.


title:
Clifford and Riemann-Finsler Structures in Geometric Mechanics and
  Gravity

abstract:
  The book contains a collection of works on Riemann-Cartan and metric-affine
manifolds provided with nonlinear connection structure and on generalized
Finsler-Lagrange and Cartan-Hamilton geometries and Clifford structures
modelled on such manifolds. The choice of material presented has evolved from
various applications in modern gravity and geometric mechanics and certain
generalizations to noncommutative Riemann-Finsler geometry.
  The authors develop and use the method of anholonomic frames with associated
nonlinear connection structure and apply it to a number of concrete problems:
constructing of generic off-diagonal exact solutions, in general, with
nontrivial torsion and nonmetricity, possessing noncommutative symmetries and
describing black ellipsoid/torus configurations, locally anisotropic wormholes,
gravitational solitons and warped factors and investigation of stability of
such solutions; classification of Lagrange/ Finsler -- affine spaces;
definition of nonholonomic Dirac operators and their applications in
commutative and noncommutative Finsler geometry.


title:
Spacetime metric from local and linear electrodynamics: a new axiomatic
  scheme

abstract:
  We consider spacetime to be a 4-dimensional differentiable manifold that can
be split locally into time and space. No metric, no linear connection are
assumed. Matter is described by classical fields/fluids. We distinguish
electrically charged from neutral matter. Electric charge and magnetic flux are
postulated to be conserved. As a consequence, the inhomogeneous and the
homogeneous Maxwell equations emerge expressed in terms of the excitation H and
the field strength F, respectively. H and F are assumed to fulfill a local and
linear "spacetime relation" with 36 constitutive functions. The propagation of
electromagnetic waves is considered under such circumstances in the geometric
optics limit. We forbid birefringence in vacuum and find the light cone
including its Lorentzian signature. Thus the conformally invariant part of the
metric is recovered. If one sets a scale, one finds the pseudo-Riemannian
metric of spacetime.


title: On the motion of a compact elastic body

abstract:
  We study the problem of motion of a relativistic, ideal elastic solid with
free surface boundary by casting the equations in material form ("Lagrangian
coordinates"). By applying a basic theorem due to Koch, we prove short-time
existence and uniqueness for solutions close to a trivial solution. This
trivial, or natural, solution corresponds to a stress-free body in rigid
motion.


title: The Hamiltonian boundary term and quasi-local energy flux

abstract:
  The Hamiltonian for a gravitating region includes a boundary term which
determines not only the quasi-local values but also, via the boundary variation
principle, the boundary conditions. Using our covariant Hamiltonian formalism,
we found four particular quasi-local energy-momentum boundary term expressions;
each corresponds to a physically distinct and geometrically clear boundary
condition. Here, from a consideration of the asymptotics, we show how a
fundamental Hamiltonian identity naturally leads to the associated quasi-local
energy flux expressions. For electromagnetism one of the four is distinguished:
the only one which is gauge invariant; it gives the familiar energy density and
Poynting flux. For Einstein's general relativity two different boundary
condition choices correspond to quasi-local expressions which asymptotically
give the ADM energy, the Trautman-Bondi energy and, moreover, an associated
energy flux (both outgoing and incoming). Again there is a distinguished
expression: the one which is covariant.


title:
Regular solutions to higher order curvature Einstein--Yang-Mills systems
  in higher dimensions

abstract:
  We study regular, static, spherically symmetric solutions of Yang-Mills
theories employing higher order invariants of the field strength coupled to
gravity in $d$ dimensions. We consider models with only two such invariants
characterised by integers $p$ and $q$. These models depend on one dimensionless
parameter $\alpha$ leading to one-parameter families of regular solutions,
obtainable by numerical solution of the corresponding boundary value problem.
Much emphasis is put on an analytical understanding of the numerical results.


title: Tensorial Spin-s Harmonics

abstract:
  We show how to define and go from the spin-s spherical harmonics to the
tensorial spin-s harmonics. These quantities, which are functions on the sphere
taking values as Euclidean tensors, turn out to be extremely useful for many
calculations in General Relativity. In the calculations, products of these
functions, with their needed decompositions which are given here, often arise
naturally.


title: Fermat Principle in Finsler Spacetimes

abstract:
  It is shown that, on a manifold with a Finsler metric of Lorentzian
signature, the lightlike geodesics satisfy the following variational principle.
Among all lightlike curves from a point (emission event) to a timelike curve
(worldline of receiver), the lightlike geodesics make the arrival time
stationary. Here ``arrival time'' refers to a parametrization of the timelike
curve. This variational principle can be applied (i) to the vacuum light rays
in an alternative spacetime theory, based on Finsler geometry, and (ii) to
light rays in an anisotropic non-dispersive medium with a general-relativistic
spacetime as background.


title: Dirac Cosmology and the Acceleration of the Contemporary Universe

abstract:
  A model is suggested to unify the Einstein GR and Dirac Cosmology. There is
one adjusted parameter $b_2$ in our model. After adjusting the parameter $b_2$
in the model by using the supernova data, we have calculated the gravitational
constant $\bar G$ and the physical quantities of $a(t)$, $q(t)$ and $\rho_r(t)/
\rho_b(t)$ by using the present day quantities as the initial conditions and
found that the equation of state parameter $w_{\theta}$ equals to -0.83, the
ratio of the density of the addition creation $\Omega_{\Lambda}=0.8$ and the
ratio of the density of the matter including multiplication creation, radiation
and normal matter $\Omega_m =0.2$ at present. The results are self-consistent
and in good agreement with present knowledge in cosmology. These results
suggest that the addition creation and multiplication creation in Dirac
cosmology play the role of the dark energy and dark matter.


title:
Cosmological Models with Variable Gravitational and Cosmological
  constants in $R^{2}$ Gravity

abstract:
  We consider the evolution of a flat Friedmann-Roberstson-Walker Universe in a
higher derivative theories, including $\alpha R^{2}$ terms to the
Einstein-Hilbert action in the presence of a variable gravitational and
cosmological constants. We study here the evolution of the gravitational and
cosmological constants in the presence of radiation and matter domination era
of the universe. We present here new cosmological solutions which are
physically interesting for model building.


title:
Detecting gravitational waves from test-mass bodies orbiting a Kerr
  black hole with P-approximant templates

abstract:
  In this study we apply post-Newtonian (T-approximants) and resummed
post-Newtonian (P-approximants) to the case of a test-particle in equatorial
orbit around a Kerr black hole. We compare the two approximants by measuring
their effectualness (i.e. larger overlaps with the exact signal), and
faithfulness (i.e. smaller biases while measuring the parameters of the signal)
with the exact (numerical) waveforms. We find that in the case of prograde
orbits, T-approximant templates obtain an effectualness of ~0.99 for spins q <
0.75. For 0.75 < q < 0.95, the effectualness drops to about 0.82. The
P-approximants achieve effectualness of > 0.99 for all spins up to q = 0.95.
The bias in the estimation of parameters is much lower in the case of
P-approximants than T-approximants. We find that P-approximants are both
effectual and faithful and should be more effective than T-approximants as a
detection template family when q > 0. For q < 0 both T- and P-approximants
perform equally well so that either of them could be used as a detection
template family. However, for parameter estimation, the P-approximant templates
still outperforms the T-approximants.


title: No hair conjecture, nonabelian hierarchies and anti-de Sitter spacetime

abstract:
  We consider globally regular and black holes solutions for the
Einstein-Yang-Mills system with negative cosmological constant in $d-$spacetime
dimensions. We find that the ADM mass of the spherically symmetric solutions
generically diverges for $d>4$. Solutions with finite mass are found by
considering corrections to the YM Lagrangean consisting in higher therm of the
Yang--Mills hierarchy. Such systems can occur in the low energy effective
action of string theory. A discussion of the main properties of the solutions
and the differences with respect to the four dimensional case is presented. The
mass of these configurations is computed by using a counterterm method.


title: The Relative Entropy as an Increasing Function of Time in Cosmology

abstract:
  In this paper, it is shown that the relative entropy is an increasing
function of time in both the linear regime and the non-linear regime during the
large scale structure formation in cosmology.


title: Symmetries and pre-metric electromagnetism

abstract:
  The equations of pre-metric electromagnetism are formulated as an exterior
differential system on the bundle of exterior differential 2-forms over the
spacetime manifold. The general form for the symmetry equations of the system
is computed and then specialized to various possible forms for an
electromagnetic constitutive law, namely, uniform linear, non-uniform linear,
and uniform nonlinear. It is shown that in the uniform linear case, one has
four possible ways of prolonging the symmetry Lie algebra, including
prolongation to a Lie algebra of infinitesimal projective transformations of a
real four-dimensional projective space. In the most general non-uniform linear
case, th effect of non-uniformity on symmetry seems inconclusive in the absence
of further specifics, and in the uniform nonlinear case, the overall difference
from the uniform linear case amounts to a deformation of the electromagnetic
constitutive tensor by the electromagnetic fields strengths, which induces a
corresponding deformation of the symmetry Lie algebra that was obtained in the
uniform linear case.


title: Morgan-Morgan-NUT disk space via the Ehlers transformation

abstract:
  Using the Ehlers transformation along with the gravitoelectromagnetic
approach to stationary spacetimes we start from the Morgan-Morgan disk
spacetime (without radial pressure) as the seed metric and find its
corresponding stationary spacetime. As expected from the Ehlers transformation
the stationary spacetime obtained suffers from a NUT-type singularity and the
new parameter introduced in the stationary case could be interpreted as the
gravitomagnetic monopole charge (or the NUT factor). As a consequence of this
singularity there are closed timelike curves (CTCs) in the singular region of
the spacetime. Some of the properties of this spacetime including its particle
velocity distribution, gravitational redshift, stability and energy conditions
are discussed.


title: Leptogenesis from Spin-Gravity Coupling Following Inflation

abstract:
  The energy levels of the left and the right handed neutrinos is split in the
background of gravitational waves generated during inflation which in presence
of lepton number violating interactions gives rise to a net lepton asymmetry at
equilibrium. Lepton number violation is achieved by the same dimension five
operator which gives rise to neutrino masses after electro-weak symmetry
breaking. A net baryon asymmetry of the same magnitude can be generated from
this lepton asymmetry by electroweak sphaleron processes.


title: Viscous FRW Cosmology in Modified Gravity

abstract:
  We discuss a modified form of gravity implying that the action contains a
power \alpha of the scalar curvature. Coupling with the cosmic fluid is
assumed. As equation of state for the fluid, we take the simplest version where
the pressure is proportional to the density. Based upon a natural ansatz for
the time variation of the scale factor, we show that the equations of motion
are satisfied for general \alpha. Also the condition of conservation of energy
and momentum is satisfied. Moreover, we investigate the case where the fluid is
allowed to possess a bulk viscosity, and find the noteworthy fact that
consistency of the formalism requires the bulk viscosity to be proportional to
the power (2\alpha -1) of the scalar expansion. In Einstein's gravity, where
\alpha=1, this means that the bulk viscosity is proportional to the scalar
expansion. This mathematical result is of physical interest; as discussed
recently by the present authors, there exists in principle a viscosity-driven
transition of the fluid from the quintessence region into the phantom region,
implying a future Big Rip singularity.


title: The Similarity Hypothesis in General Relativity

abstract:
  Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.


title: Quasinormal modes of Unruh's Acoustic Black Hole

abstract:
  We have studied the sound perturbation of Unruh's acoustic geometry and we
present an exact expression for the quasinormal modes of this geometry. We are
obtain that the quasinormal frequencies are pure-imaginary, that give a purely
damped modes.


title: The Gravitational Energy of a Black Hole

abstract:
  An exact energy expression for a physical black hole is derived by
considering the escape of a photon from the black hole. The mass of the black
hole within its horizon is found to be twice its mass as observed at infinity.
This result is important in understanding gravitational waves in black hole
collisions.


title: Coherent Network Detection of Gravitational Waves: The Redundancy Veto

abstract:
  A network of gravitational wave detectors is called redundant if, given the
direction to a source, the strain induced by a gravitational wave in one or
more of the detectors can be fully expressed in terms of the strain induced in
others in the network. Because gravitational waves have only two polarizations,
any network of three or more differently oriented interferometers with similar
observing bands is redundant. For LISA, this ``null'' output is known as the
Sagnac mode, and its use in discriminating between detector noise and a
cosmological gravitational wave background is well understood [1][2]. But the
usefulness of the null veto for ground-based detector networks has been ignored
until now. We show that it should make it possible to discriminate in a
model-independent way between real gravitational waves and accidentally
coincident non-Gaussian noise ``events'' in redundant networks of two or more
broadband detectors (e.g, three LIGO detectors and GEO). It has been shown that
with three detectors, the null output can be used to locate the direction to
the source, and then two other linear combinations of detector outputs give the
optimal ``coherent'' reconstruction of the two polarization components of the
signal. We discuss briefly the implementation of such a detection strategy in
realistic networks.


title: Tensor Potential Description of Matter and Space

abstract:
  A unified field theory for the description of matter in a curved space is
discussed. The description is based on a standard Lagrangianian formalism in a
pseudo-Euclidian 4D continuum using a 3-index tensor as independent variables.
The theory defines gravitational matter as a vector field and contains the
Einstein-Schwarzschild solution for the metric tensor in the case of stationary
spherical symmetry. Maxwell's equations, generalized for curved space, offer an
alternative to the expanding Universe explanation for the red shift phenomenon.
The theory contains a covariant law for conservation of matter and strictly
upports the Mach principle. A perturbation method allows a natural transition
to the special relativity, providing an explanation and the scale of elementary
particles parameters.


title:
Gauge-invariant metric fluctuations from NKK theory of gravity: de
  Sitter expansion

abstract:
  In this paper we study gauge-invariant metric fluctuations from a Noncompact
Kaluza-Klein (NKK) theory of gravity in a de Sitter expansion. We recover the
well known result $\delta\rho/\rho \simeq 2\Phi$, obtained from the standard 4D
semiclassical approach to inflation. The spectrum for these fluctuations should
be dependent of the fifth (spatial-like) coordinate.


title:
Necessary and sufficient conditions for big bangs, bounces, crunches,
  rips, sudden singularities, and extremality events

abstract:
  The physically relevant singularities occurring in FRW cosmologies had
traditionally been thought to be limited to the "big bang", and possibly a "big
crunch". However, over the last few years, the zoo of cosmological
singularities considered in the literature has become considerably more
extensive, with "big rips" and "sudden singularities" added to the mix, as well
as renewed interest in non-singular cosmological events such as "bounces" and
"turnarounds".
  In this article we present a complete catalogue of such cosmological
milestones, both at the kinematical and dynamical level. First, using
generalized power series, purely kinematical definitions of these cosmological
events are provided in terms of the behaviour of the scale factor a(t). The
notion of a "scale-factor singularity'" is defined, and its relation to
curvature singularities (polynomial and differential) is explored. Second,
dynamical information is extracted by using the Friedmann equations (without
assuming even the existence of any equation of state) to place constraints on
whether or not the classical energy conditions are satisfied at the
cosmological milestones. We use these considerations to derive necessary and
sufficient conditions for the existence of cosmological milestones such as
bangs, bounces, crunches, rips, sudden singularities, and extremality events.
Since the classification is extremely general, the corresponding results are to
a high degree model-independent: In particular, we provide a complete
characterization of the class of bangs, crunches, and sudden singularities for
which the dominant energy condition is satisfied.


title: 5D Kaluza-Klein gravity: singularuty and freezing of $5^{th}$ dimension

abstract:
  Some reasonings are presented that the problem of a singularity in general
relativity with the problem of freezing of the $5^{th}$ dimension can be
connected. It is shown that some solutions in the 5D Kaluza-Klein gravity with
the cross section in the Planck region have a region $(\approx l_{Pl})$ where
the metric signature changes from $\{+,-,-,-,- \}$ to $\{-,-,-,-,+ \}$. The
idea is discussed that such switching can not occur following some general
point of view that the Planck length is the minimal length in the nature and
consequently the physical quantities can not change very quickly in the course
of this length. In this case the dynamic of the $G_{55}$ metric component
should be frozen.


title:
Secular increase of the Astronomical Unit and perihelion precessions as
  tests of the Dvali-Gabadadze-Porrati multi-dimensional braneworld scenario

abstract:
  An unexpected secular increase of the Astronomical Unit, the length scale of
the Solar System, has recently been reported by three different research groups
(Krasinsky and Brumberg, Pitjeva, Standish). The latest JPL measurements amount
to 7+-2 m cy^-1. At present, there are no explanations able to accommodate such
an observed phenomenon, neither in the realm of classical physics nor in the
usual four-dimensional framework of the Einsteinian General Relativity. The
Dvali-Gabadadze-Porrati braneworld scenario, which is a multi-dimensional model
of gravity aimed to the explanation of the observed cosmic acceleration without
dark energy, predicts, among other things, a perihelion secular shift, due to
Lue and Starkman, of 5 10^-4 arcsec cy^-1 for all the planets of the Solar
System. It yields a variation of about 6 m cy^-1 for the Earth-Sun distance
which is compatible at 1-sigma level with the observed rate of the Astronomical
Unit. The recently measured corrections to the secular motions of the perihelia
of the inner planets of the Solar System are in agreement, at 1-sigma level,
with the predicted value of the Lue-Starkman effect for Mercury and Mars and at
2-sigma level for the Earth.

categories: gr-qc astro-ph hep-ph hep-th physics.space-ph


title: Growth of a Black Hole

abstract:
  This paper studies the interpretation of physics near a Schwarzschild black
hole. A scenario for creation and growth is proposed that avoids the conundrum
of information loss. In this picture the horizon recedes as it is approached
and has no physical reality. Radiation is likely to occur, but it cannot be
predicted.


title:
Semi-relativistic approximation to gravitational radiation from
  encounters with nonspinning black holes

abstract:
  The capture of compact bodies by black holes in galactic nuclei is an
important prospective source for low frequency gravitational wave detectors,
such as the planned Laser Interferometer Space Antenna. This paper calculates,
using a semirelativistic approximation, the total energy and angular momentum
lost to gravitational radiation by compact bodies on very high eccentricity
orbits passing close to a supermassive, nonspinning black hole; these
quantities determine the characteristics of the orbital evolution necessary to
estimate the capture rate. The semirelativistic approximation improves upon
treatments which use orbits at Newtonian-order and quadrupolar radiation
emission, and matches well onto accurate Teukolsky simulations for low
eccentricity orbits. Formulae are presented for the semirelativistic energy and
angular momentum fluxes as a function of general orbital parameters.


title:
Regularization of the second-order gravitational perturbations produced
  by a compact object

abstract:
  The equations for the second-order gravitational perturbations produced by a
compact-object have highly singular source terms at the point particle limit.
At this limit the standard retarded solutions to these equations are
ill-defined. Here we construct well-defined and physically meaningful solutions
to these equations. These solutions are important for practical calculations:
the planned gravitational-wave detector LISA requires preparation of waveform
templates for the potential gravitational-waves. Construction of templates with
desired accuracy for extreme mass ratio binaries, in which a compact-object
inspirals towards a supermassive black-hole, requires calculation of the
second-order gravitational perturbations produced by the compact-object.


title: On a Petrov-type D homogeneous solution

abstract:
  We present a new two-parameter family of solutions of Einstein gravity with
negative cosmological constant in 2+1 dimensions. These solutions are obtained
by squashing the anti-de Sitter geometry along one direction and posses four
Killing vectors. Global properties as well as the four dimensional
generalization are discussed, followed by the investigation of the geodesic
motion. A simple global embedding of these spaces as the intersection of four
quadratic surfaces in a seven dimensional space is obtained. We argue also that
these geometries describe the boundary of a four dimensional nutty-bubble
solution and are relevant in the context of AdS/CFT correspondence.


title: In an expanding universe, what doesn't expand?

abstract:
  The expansion of the universe is often viewed as a uniform stretching of
space that would affect compact objects, atoms and stars, as well as the
separation of galaxies. One usually hears that bound systems do not take part
in the general expansion, but a much more subtle question is whether bound
systems expand partially. In this paper, a very definitive answer is given for
a very simple system: a classical "atom" bound by electrical attraction. With a
mathemical description appropriate for undergraduate physics majors, we show
that this bound system either completely follows the cosmological expansion, or
-- after initial transients -- completely ignores it. This "all or nothing"
behavior can be understood with techniques of junior-level mechanics. Lastly,
the simple description is shown to be a justifiable approximation of the
relativistically correct formulation of the problem.


title: Dark energy and the future fate of the Universe

abstract:
  We consider the possibility of observing the onset of the late time inflation
of our patch of the Universe. The Hubble size criterion and the event horizon
criterion are applied to several dark energy models to discuss the problem of
future inflation of the Universe. We find that the acceleration has not lasted
long enough to confirm the onset of inflation by present observations for the
dark energy model with constant equation of state, the holographic dark energy
model and the generalized Chaplygin gas (GCG) model. For the flat $\Lambda$CDM
model with $\Omega_{m0}=0.3$, we find that if we use the Hubble size criterion,
we need to wait until the $a_v$ which is the scale factor at the time when the
onset of inflation is observed reaches 3.59 times of the scale factor $a_T$
when the Universe started acceleration, and we need to wait until $a_v=2.3 a_T$
to see the onset of inflation if we use the event horizon criterion. For the
flat holographic dark energy model with $d=1$, we find that $a_v=3.46 a_T$ with
the Hubble horizon and $a_v=2.34 a_T$ with the event horizon, respectively. For
the flat GCG model with the best supernova fitting parameter $\alpha=1.2$, we
find that $a_v=5.50 a_T$ with the Hubble horizon and $a_v=2.08 a_T$ with the
event horizon, respectively.


title: Equation of state and transport processes in self--similar spheres

abstract:
  We study the effect of transport processes (diffusion and free--streaming) on
a collapsing spherically symmetric distribution of matter in a self--similar
space--time. A very simple solution shows interesting features when it is
matched with the Vaidya exterior solution. In the mixed case (diffusion and
free--streaming), we find a barotropic equation of state in the stationary
regime. In the diffusion approximation the gravitational potential at the
surface is always constant; if we perturb the stationary state, the system is
very stable, recovering the barotropic equation of state as time progresses. In
the free--streaming case the self--similar evolution is stationary but with a
non--barotropic equation of state.


title: Self-similar and charged spheres in the diffusion approximation

abstract:
  We study spherical, charged and self--similar distributions of matter in the
diffusion approximation. We propose a simple, dynamic but physically meaningful
solution. For such a solution we obtain a model in which the distribution
becomes static and changes to dust. The collapse is halted with damped mass
oscillations about the absolute value of the total charge.


title: A self-similar dynamics in viscous spheres

abstract:
  We study the evolution of radiating and viscous fluid spheres assuming an
additional homothetic symmetry on the spherically simmetric space--time. We
match a very simple solution to the symmetry equations with the exterior one
(Vaidya). We then obtain a system of two ordinary differential equations which
rule the dynamics, and find a self--similar collapse which is shear--free and
with a barotropic equation of state. Considering a huge set of initial
self--similar dynamics states, we work out a model with an acceptable physical
behavior.


title: Exactly solvable model of wormhole supported by phantom energy

abstract:
  We have found a simple exact solution of spherically-symmetrical Einstein
equations describing a wormhole for an inhomogeneous distribution of the
phantom energy. The equation of state is linear but highly anisotropic: while
the radial pressure is negative, the transversal one is positive. At infinity
the spacetime is not asymptotically flat and possesses on each side of the
bridge a regular cosmological Killing horizon with an infinite area,
impenetrable for any particles. This horizon does not arise if the wormhole
region is glued to the Schwarzschild region. In doing so, the wormhole can
enclose an arbitrary amount of the phantom energy. The configuration under
discussion has a limit in which the phantom energy turns into the string dust,
the areal radius tends to the constant. In this limit, the strong gravitational
mass defect is realized in that the gravitational active mass is finite and
constant while the proper mass integrated over the total manifold is infinite.


title:
A quantum weak energy inequality for the Dirac field in two-dimensional
  flat spacetime

abstract:
  Fewster and Mistry have given an explicit, non-optimal quantum weak energy
inequality that constrains the smeared energy density of Dirac fields in
Minkowski spacetime. Here, their argument is adapted to the case of flat,
two-dimensional spacetime. The non-optimal bound thereby obtained has the same
order of magnitude, in the limit of zero mass, as the optimal bound of Vollick.
In contrast with Vollick's bound, the bound presented here holds for all
(non-negative) values of the field mass.


title:
An exact Lagrangian integral for the Newtonian gravitational field
  strength

abstract:
  An exact expression for the gravitational field strength in a
self-gravitating dust continuum is derived within the Lagrangian picture of
continuum mechanics. From the Euler-Newton system a transport equation for the
gravitational field strength is formulated and then integrated along
trajectories of continuum elements. The resulting integral solves one of the
Lagrangian equations of the corresponding Lagrange-Newton system in general.
Relations to known exact solutions without symmetry in Newtonian gravity are
discussed. The presented integral may be employed to access the
non-perturbative regime of structure formation in Newtonian cosmology, and to
apply iterative Lagrangian schemes to solve the Lagrange-Newton system.


title: Wormholes supported by small amounts of exotic matter: some corrections

abstract:
  It was pointed out by Fewster and Roman that some of the wormhole models
discussed by Kuhfittig suffer from the failure to distinguish proper from
coordinate distances. One of the advantages of "designer wormholes" is that
models can be altered. The purpose of this note is to show that by adjusting
the metric coefficients, some of these problems can be corrected. By doing so,
the basic idea can be retained: wormholes containing only small amounts of
exotic matter can still be traversable.


title:
A variational principle for stationary, axisymmetric solutions of
  Einstein's equations

abstract:
  Stationary, axisymmetric, vacuum, solutions of Einstein's equations are
obtained as critical points of the total mass among all axisymmetric and
$(t,\phi)$ symmetric initial data with fixed angular momentum. In this
variational principle the mass is written as a positive definite integral over
a spacelike hypersurface. It is also proved that if absolute minimum exists
then it is equal to the absolute minimum of the mass among all maximal,
axisymmetric, vacuum, initial data with fixed angular momentum. Arguments are
given to support the conjecture that this minimum exists and is the extreme
Kerr initial data.


title:
Critical Collapse of an Ultrarelativistic Fluid in the $\Gamma\to 1$
  Limit

abstract:
  In this paper we investigate the critical collapse of an ultrarelativistic
perfect fluid with the equation of state $P=(\Gamma-1)\rho$ in the limit of
$\Gamma\to 1$. We calculate the limiting continuously self similar (CSS)
solution and the limiting scaling exponent by exploiting self-similarity of the
solution. We also solve the complete set of equations governing the
gravitational collapse numerically for $(\Gamma-1) = 10^{-2},...,10^{-6}$ and
compare them with the CSS solutions. We also investigate the supercritical
regime and discuss the hypothesis of naked singularity formation in a generic
gravitational collapse. The numerical calculations make use of advanced methods
such as high resolution shock capturing evolution scheme for the matter
evolution, adaptive mesh refinement, and quadruple precision arithmetic. The
treatment of vacuum is also non standard. We were able to tune the critical
parameter up to 30 significant digits and to calculate the scaling exponents
accurately. The numerical results agree very well with those calculated using
the CSS ansatz. The analysis of the collapse in the supercritical regime
supports the hypothesis of the existence of naked singularities formed during a
generic gravitational collapse.


title:
Close-limit analysis for head-on collision of two black holes in higher
  dimensions: Brill-Lindquist initial data

abstract:
  Motivated by the TeV-scale gravity scenarios, we study gravitational
radiation in the head-on collision of two black holes in higher dimensional
spacetimes using a close-limit approximation. We prepare time-symmetric initial
data sets for two black holes (the so-called Brill-Lindquist initial data) and
numerically evolve the spacetime in terms of a gauge invariant formulation for
the perturbation around the higher-dimensional Schwarzschild black holes. The
waveform and radiated energy of gravitational waves emitted in the head-on
collision are clarified. Also, the complex frequencies of fundamental
quasinormal modes of higher-dimensional Schwarzschild black holes, which have
not been accurately derived so far, are determined.


title:
Detecting gravitational waves from precessing binaries of spinning
  compact objects. II. Search implementation for low-mass binaries

abstract:
  Detection template families (DTFs) are built to capture the essential
features of true gravitational waveforms using a small set of phenomenological
waveform parameters. Buonanno, Chen, and Vallisneri [Phys. Rev. D 67, 104025
(2003)] proposed the ``BCV2'' DTF to perform computationally efficient searches
for signals from precessing binaries of compact stellar objects. Here we test
the signal-matching performance of the BCV2 DTF for asymmetric--mass-ratio
binaries, and specifically for double--black-hole binaries with component
masses (m1,m2): (6~12Msun, 1~3Msun), and for black-hole--neutron-star binaries
with component masses (m1,m2) = (10Msun, 1.4Msun); we take all black holes to
be maximally spinning. We find a satisfactory signal-matching performance, with
fitting factors averaging between 0.94 and 0.98. We also scope out the region
of BCV2 parameters needed for a template-based search, we evaluate the template
match metric, we discuss a template-placement strategy, and we estimate the
number of templates needed for searches at the LIGO design sensitivity. In
addition, after gaining more insight in the dynamics of spin--orbit precession,
we propose a modification of the BCV2 DTF that is parametrized by physical
(rather than phenomenological) parameters. We test this modified ``BCV2P'' DTF
for the (10Msun, 1.4Msun) black-hole--neutron-star system, finding a
signal-matching performance comparable to the BCV2 DTF, and a reliable
parameter-estimation capability for target-binary quantities such as the chirp
mass and the opening angle (the angle between the black-hole spin and the
orbital angular momentum).


title:
First all-sky upper limits from LIGO on the strength of periodic
  gravitational waves using the Hough transform

abstract:
  We perform a wide parameter space search for continuous gravitational waves
over the whole sky and over a large range of values of the frequency and the
first spin-down parameter. Our search method is based on the Hough transform,
which is a semi-coherent, computationally efficient, and robust pattern
recognition technique. We apply this technique to data from the second science
run of the LIGO detectors and our final results are all-sky upper limits on the
strength of gravitational waves emitted by unknown isolated spinning neutron
stars on a set of narrow frequency bands in the range 200-$400 $Hz. The best
upper limit on the gravitational wave strain amplitude that we obtain in this
frequency range is $4.43\times 10^{-23}$.


title: Cosmological gravitomagnetism and Mach's principle

abstract:
  The spin axes of gyroscopes experimentally define local non-rotating frames.
But what physical cause governs the time-evolution of gyroscope axes? We
consider linear perturbations of Friedmann-Robertson-Walker cosmologies with
k=0. We ask: Will cosmological vorticity perturbations exactly drag the spin
axes of gyroscopes relative to the directions of geodesics to quasars in the
asymptotic unperturbed FRW space? Using Cartan's formalism with local
orthonormal bases we cast the laws of linear cosmological gravitomagnetism into
a form showing the close correspondence with the laws of ordinary magnetism.
Our results, valid for any equation of state for cosmological matter, are: 1)
The dragging of a gyroscope axis by rotational perturbations of matter beyond
the Hubble-dot radius from the gyroscope is exponentially suppressed, where dot
is the derivative with respect to cosmic time. 2) If the perturbation of matter
is a homogeneous rotation inside some radius around a gyroscope, then exact
dragging of the gyroscope axis by the rotational perturbation is reached
exponentially fast as the rotation radius grows beyond the H-dot radius. 3) For
the most general linear cosmological perturbations the time-evolution of all
gyroscope spin axes exactly follow a weighted average of the energy currents of
cosmological matter. The weight function is the same as in Ampere's law except
that the inverse square law is replaced by the Yukawa force with the Hubble-dot
cutoff. Our results demonstrate (in first order perturbation theory for FRW
cosmologies with k = 0) the validity of Mach's hypothesis that axes of local
non-rotating frames precisely follow an average of the motion of cosmic matter.


title:
Transition from inspiral to plunge in precessing binaries of spinning
  black holes

abstract:
  We investigate the non-adiabatic dynamics of spinning black hole binaries by
using an analytical Hamiltonian completed with a radiation-reaction force,
containing spin couplings, which matches the known rates of energy and angular
momentum losses on quasi-circular orbits. We consider both a straightforward
post-Newtonian-expanded Hamiltonian (including spin-dependent terms), and a
version of the resummed post-Newtonian Hamiltonian defined by the Effective
One-Body approach. We focus on the influence of spin terms onto the dynamics
and waveforms. We evaluate the energy and angular momentum released during the
final stage of inspiral and plunge. For an equal-mass binary the energy
released between 40Hz and the frequency beyond which our analytical treatment
becomes unreliable is found to be, when using the more reliable Effective
One-Body dynamics: 0.6% M for anti-aligned maximally spinning black holes, 5% M
for aligned maximally spinning black hole, and 1.8% M for non-spinning
configurations. In confirmation of previous results, we find that, for all
binaries considered, the dimensionless rotation parameter J/E^2 is always
smaller than unity at the end of the inspiral, so that a Kerr black hole can
form right after the inspiral phase. By matching a quasi-normal mode ringdown
to the last reliable stages of the plunge, we construct complete waveforms
approximately describing the gravitational wave signal emitted by the entire
process of coalescence of precessing binaries of spinning black holes.


title:
Constraint Likelihood analysis for a network of gravitational wave
  detectors

abstract:
  We propose a coherent method for the detection and reconstruction of
gravitational wave signals for a network of interferometric detectors. The
method is derived using the likelihood functional for unknown signal waveforms.
In the standard approach, the global maximum of the likelihood over the space
of waveforms is used as the detection statistic. We identify a problem with
this approach. In the case of an aligned pair of detectors, the detection
statistic depends on the cross-correlation between the detectors as expected,
but this dependence dissappears even for infinitesimally small misalignments.
We solve the problem by applying constraints on thelikelihood functional and
obtain a new class of statistics. The resulting method can be applied to the
data from a network consisting of any number of detectors with arbitrary
detector orientations. The method allows us reconstruction of the source
coordinates and the waveforms of two polarization components of a gravitational
wave. We study the performance of the method with numerical simulation and find
the reconstruction of the source coordinates to be more accurate than in the
standard approach.


title: A cosmological model with complex scalar field

abstract:
  In this paper, we wish to point out the possibility of using a complex scalar
field to account for the inflationary stage and the current acceleration. By
the analysis of the dynamical system and numerical work, we show that the
amplitude of the complex scalar field plays the role of the inflaton whereas
the phase is the quintessence field. The numerical solutions describe
heteroclinic orbits, which interpolate between an unstable critical point and a
late-time de Sitter attractor. Therefore, this model is more natural to explain
the two stages of acceleration.


title: Corvino's construction using Brill waves

abstract:
  For two-black-hole time-symmetric initial data we consider the Corvino
construction of gluing an exact Schwarzschild end. We propose to do this by
using Brill waves. We address the question of whether this method can be used
to reduce the overall energy, which seems to relate to the question of whether
it can reduce the amount of `spurious' gravitational radiation. We find a
positive answer at first order in the inverse gluing radius.


title: Horizon constraints and black hole entropy

abstract:
  To ask a question about a black hole in quantum gravity, one must restrict
initial or boundary data to ensure that a black hole is actually present. For
two-dimensional dilaton gravity, and probably a much wider class of theories as
well, the imposition of a "stretched horizon" constraint alters the algebra of
symmetries at the horizon, introducing a central term. Standard conformal field
theory techniques can then then be used to obtain the asymptotic density of
states, reproducing the Bekenstein-Hawking entropy. The microscopic states
responsible for black hole entropy can thus be viewed as "would-be pure gauge"
states that become physical because the symmetry is altered by the requirement
that a horizon exist.


title: A Note on Real Tunneling Geometries

abstract:
  In the Hartle-Hawking ``no boundary'' approach to quantum cosmology, a real
tunneling geometry is a configuration that represents a transition from a
compact Riemannian spacetime to a Lorentzian universe. I complete an earlier
proof that in three spacetime dimensions, such a transition is ``probable,'' in
the sense that the required Riemannian geometry yields a genuine maximum of the
semiclassical wave function.


title: Analytic solutions for the $\Lambda$-FRW Model

abstract:
  The high precision attained by cosmological data in the last few years has
increased the interest in exact solutions. Analytic expressions for solutions
in the Standard Model are presented here for all combinations of $\Lambda = 0$,
$\Lambda \ne 0$, $\kappa = 0$ and $\kappa \ne 0$, in the presence and absence
of radiation and nonrelativistic matter. The most complete case (here called
the $\Lambda \gamma CDM$ Model) has $\Lambda \ne 0, \kappa \ne 0$, and supposes
the presence of radiation and dust. It exhibits clearly the recent onset of
acceleration. The treatment includes particular models of interest such as the
$\Lambda$CDM Model (which includes the cosmological constant plus cold dark
matter as source constituents).


abstract:
  A static Einstein metric that generalizes the Schwarzschild metric is
considered. The event horizon is not necessarily a sphere and the term $dt\sp2$
is a function on such horizon. That the metric is Einstein establishes a
relation between its terms. One demonstrates that the scalar curvature of the
horizon is constant, and that the term $dt\sp2$ gives rise to (i) the metric of
the horizon being Einstein, or (ii) the scalar curvature of the horizon being
proportional to an eigenvalue of the Laplace operator.


title: Probability for Primordial Black Holes Pair in 1/R Gravity

abstract:
  The probability for quantum creation of an inflationary universe with a pair
of black holes in 1/R - gravitational theory has been studied. Considering a
gravitational action which includes a cosmological constant ($\Lambda$) in
addition to $ \delta R^{- 1} $ term, the probability has been evaluated in a
semiclassical approximation with Hartle-Hawking boundary condition. We obtain
instanton solutions determined by the parameters $\delta$ and $\Lambda$
satisfying the constraint $ \delta \leq \frac{4 \Lambda^{2}}{3}$. However, we
note that two different classes of instanton solutions exists in the region $0
< \delta < \frac{4 \Lambda^{2}}{3}$. The probabilities of creation of such
configurations are evaluated. It is found that the probability of creation of a
universe with a pair of black holes is strongly suppressed with a positive
cosmological constant except in one case when $0 < \delta < \Lambda^{2}$. It is
also found that gravitational instanton solution is permitted even with
$\Lambda = 0$ but one has to consider $\delta < 0$. However, in the later case
a universe with a pair of black holes is less probable.


title: Zero-point length, extra-dimensions and string T-duality

abstract:
  In this paper, we are going to put in a single consistent framework
apparently unrelated pieces of information, i.e. zero-point length,
extra-dimensions, string T-duality. More in details we are going to introduce a
modified Kaluza-Klein theory interpolating between (high-energy) string theory
and (low-energy) quantum field theory. In our model zero-point length is a four
dimensional ``virtual memory'' of compact extra-dimensions length scale. Such a
scale turns out to be determined by T-duality inherited from the underlying
fundamental string theory. From a low energy perspective short distance
infinities are cut off by a minimal length which is proportional to the square
root of the string slope, i.e. \sqrt{\alpha^\prime}. Thus, we provide a
``bridge'' between the ultra-relativistic string domain and the low energy
arena of point-particle quantum field theory.


title: The spacetime metric in particle QED

abstract:
  A small time delay between interactions, which has previously been shown to
remove divergences from QED, is used to show that, if spacetime geometry is
emergent from particle interactions in the manner suggested by Bondi, then
Minkowski metric, which appears in the Schroedinger equation as a requirement
of the probability interpretation, is perturbed in physical measurement,
leading to curved spacetime in accordance with Einstein's equation.


title:
On the non-relativistic limit of the spherically symmetric
  Einstein-Vlasov-Maxwell system

abstract:
  The Einstein-Vlasov-Maxwell (EVM) system can be viewed as a relativistic
generalization of the Vlasov-Poisson (VP) system. As it is proved below, one of
nice property obeys by the first system is that the strong energy condition
holds and this allows to conclude that the above system is physically viable.
We show in this paper that in the context of spherical symmetry, solutions of
the perturbed (EVM) system by $\gamma := 1/c^{2}$, $c$ being the speed of
light, exist and converge uniformly in $L^{\infty}$-norm, as $c$ goes to
infinity on compact time intervals to solutions of the non-relativistic (VP)
system.


title: Wormhole solution and Energy in Teleparallel Theory of Gravity

abstract:
  An exact solution is obtained in the tetrad theory of gravitation. This
solution is characterized by two-parameters $k_1, k_2$ of spherically symmetric
static Lorentzian wormhole which is obtained as a solution of the equation
$\rho=\rho_t=0$ with $\rho=T_{i,j}u^iu^j$, $\rho_t=(T_{ij}-\displaystyle{1
\over 2}Tg_{ij}) u^iu^j$ where $u^iu_i=-1$.
  From this solution which contains an arbitrary function we can generates the
other two solutions obtained before. The associated metric of this spacetime is
a static Lorentzian wormhole and it includes the Schwarzschild black hole, a
family of naked singularity and a disjoint family of Lorentzian wormholes.
Calculate the energy content of this tetrad field using the gravitational
energy-momentum given by M{\o}ller in teleparallel spacetime we find that the
resulting form depends on the arbitrary function and does not depend on the two
parameters $k_1$ and $k_2$ characterize the wormhole. Using the regularized
expression of the gravitational energy-momentum we get the value of energy does
not depend on the arbitrary function.


title:
Exact solutions of SO(3) non-linear sigma model in a conic space
  background

abstract:
  We consider a nonlinear sigma model coupled to the metric of a conic space.
We obtain restrictions for a nonlinear sigma model to be a source of the conic
space. We then study nonlinear sigma model in the conic space background. We
find coordinate transformations which reduce the chiral fields equations in the
conic space background to field equations in Minkowski spacetime. This enables
us to apply the same methods for obtaining exact solutions in Minkowski
spacetime to the case of a conic spacetime. In the case the solutions depend on
two spatial coordinates we employ Ivanov's geometrical ansatz. We give a
general analysis and also present classes of solutions in which there is
dependence on three and four coordinates. We discuss with special attention the
intermediate instanton and meron solutions and their analogous in the conic
space. We find differences in the total actions and topological charges of
these solutions and discuss the role of the deficit angle.


title: Conservation laws for vacuum tetrad gravity

abstract:
  Ten conservation laws in useful polynomial form are derived from a Cartan
form and Exterior Differential System (EDS) for the tetrad equations of vacuum
relativity. The Noether construction of conservation laws for well posed EDS is
introduced first, and an illustration given, deriving 15 conservation laws of
the free field Maxwell Equations from symmetries of its EDS. The Maxwell EDS
and tetrad gravity EDS have parallel structures, with their numbers of
dependent variables, numbers of generating 2-forms and generating 3-forms, and
Cartan character tables all in the ratio of 1 to 4. They have 10 corresponding
symmetries with the same Lorentz algebra, and 10 corresponding conservation
laws.


title: A note on Tachyon dynamics

abstract:
  A suitable splitting of tachyon field equation is able to disclose non
trivial properties of Born-Infeld (some known, some unexpected) and Polyakov
actions; the tachyon equation also can be analyzed in some detail. The analysis
displays an intriguing connection between sine-Gordon theory and some crucial
issues such as the emergence of perturbative string states when a D-Brane and
an anti-D-Brane annihilate and the confinement of charged D-Branes.


title: Braneworld Cosmological Perturbation Theory at Low Energy

abstract:
  Homogeneous cosmology in the braneworld can be studied without solving bulk
equations of motion explicitly. The reason is simply because the symmetry of
the spacetime restricts possible corrections in the 4-dimensional effective
equations of motion. It would be great if we could analyze cosmological
perturbations without solving the bulk. For this purpose, we combine the
geometrical approach and the low energy gradient expansion method to derive the
4-dimensional effective action. Given our effective action, the standard
procedure to obtain the cosmological perturbation theory can be utilized and
the temperature anisotropy of the cosmic background radiation can be computed
without solving the bulk equations of motion explicitly.


title: Black String Perturbations in RS1 Model

abstract:
  We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor $E_{\mu\nu}$. Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.