title:
Fine Tuning Free Paradigm of Two Measures Theory: K-Essence, Absence of
  Initial Singularity of the Curvature and Inflation with Graceful Exit to Zero
  Cosmological Constant State

abstract:
  The dilaton-gravity sector of the Two Measures Field Theory (TMT)is explored
in detail in the context of cosmology. The model possesses scale invariance
which is spontaneously broken due to the intrinsic features of the TMT
dynamics. The effective model represents an explicit example of the effective
k-essence resulting from first principles without any exotic term in the
fundamental action. Depending of the choice of regions in the parameter space,
TMT exhibits different possible outputs for cosmological dynamics: a) Absence
of initial singularity of the curvature while its time derivative is singular.
This is a sort of "sudden" singularities studied by Barrow on purely kinematic
grounds. b) Power law inflation in the subsequent stage of evolution. Depending
on the region in the parameter space (but without fine tuning) the inflation
ends with a graceful exit either into the state with zero cosmological constant
(CC) or into the state driven by both a small CC and the field phi with a
quintessence-like potential. c) Possibility of resolution of the old CC
problem. From the point of view of TMT, it becomes clear why the old CC problem
cannot be solved (without fine tuning) in conventional field theories. d) TMT
enables two ways for achieving small CC without fine tuning of dimensionfull
parameters: either by a seesaw type mechanism or due to a correspondence
principle between TMT and conventional field theories (i.e theories with only
the measure of integration sqrt{-g} in the action. e) There is a wide range of
the parameters such that in the late time universe: the equation-of-state
w=p/\rho <-1; w asymptotically (as t\to\infty) approaches -1 from below; \rho
approaches a constant, the smallness of which does not require fine tuning of
dimensionfull parameters.


title:
The gravitational field energy density for symmetrical and asymmetrical
  systems

abstract:
  The relativistic theory of gravitation has the considerable difficulties by
description of the gravitational field energy. Pseudotensor t00 in the some
cases cannot be interpreted as energy density of the gravitational field. In
[1] the approach was proposed, which allow to express the energy density of
such a field through the components of a metric tensor. This approach based on
the consideration of the isothermal compression of the layer consisted of the
incoherent matter. It was employ to the cylindrically and spherically
symmetrical static gravitational field. In presented paper the approach is
developed.


title: Effective Hamiltonian for non-minimally coupled scalar fields

abstract:
  Performing a relativistic approximation as the generalization to a curved
spacetime of the flat space Klein-Gordon equation, an effective Hamiltonian
which includes non-minimial coupling between gravity and scalar field and also
quartic self-interaction of scalar field term is obtained.


title: Reissner-Nordstr\"om anti-de Sitter black holes and energy

abstract:
  We show that the tetrad field whose metric gives the Reissner-Nordstr\"om
anti-de Sitter black holes gives the correct value of energy in M{\o}ller
tetrad theory of gravitation.


title: Energy Momentum Complexes For Bianchi Type II-VIII-IX Universes

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0303009, hep-th/0405047, gr-qc/0412120, gr-qc/0602107, hep-th/0311050,
and gr-qc/0508005.
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0607119, gr-qc/0607103,
gr-qc/0607126, gr-qc/0606080, gr-qc/0607102, gr-qc/0510123, gr-qc/0607110, and
others.


title: Energy Associated with Bianchi Type V10 Universe in Teleparallel Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0011087, gr-qc/0205028, gr-qc/0404108, gr-qc/0212018, and gr-qc/0011027.


title:
Four-Momentum Associated with the Vaidya Black Holes in Teleparallel
  Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
hep-th/0307162, gr-qc/9601044, gr-qc/0510040, gr-qc/0205028, gr-qc/0212018, and
gr-qc/0605145.


title: A f(R) gravity without cosmological constant

abstract:
  In this work we consider the possibility of describing the current evolution
of the universe, without the introduction of any cosmological constant or dark
energy (DE), by modifying the Einstein-Hilbert (EH) action. In the context of
the f(R) gravities within the metric formalism, we show that it is possible to
find an action without cosmological constant which exactly reproduces the
behavior of the EH action with cosmological constant. In addition the f(R)
action is analytical at the origin having Minkowski and Schwarzschild as vacuum
solutions. The found f(R) action is highly non-trivial and must be written in
terms of hypergeometric functions but, in spite of looking somewhat artificial,
it shows that the cosmological constant, or more generally the DE, is not a
logical necessity.


title: Energy And Momentum Associated With Bianchi Type Universes

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0303009, hep-th/0405047, gr-qc/0602107, hep-th/0311050, and others.
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0607115, gr-qc/0607103,
gr-qc/0606080, gr-qc/0607126, gr-qc/0607102, gr-qc/0510123, gr-qc/0607110, and
others.


title:
Symmetric hyperbolic systems for a large class of fields in arbitrary
  dimension

abstract:
  Symmetric hyperbolic systems of equations are explicitly constructed for a
general class of tensor fields by considering their structure as r-fold forms.
The hyperbolizations depend on 2r-1 arbitrary timelike vectors. The importance
of the so-called "superenergy" tensors, which provide the necessary symmetric
positive matrices, is emphasized and made explicit. Thereby, a unified
treatment of many physical systems is achieved, as well as of the sometimes
called "higher order" systems. The characteristics of these symmetric
hyperbolic systems are always physical, and directly related to the null
directions of the superenergy tensor, which are in particular principal null
directions of the tensor field solutions. Generic energy estimates and
inequalities are presented too.


title:
Geometrical (2+1)-gravity and the Chern-Simons formulation: Grafting,
  Dehn twists, Wilson loop observables and the cosmological constant

abstract:
  We relate the geometrical and the Chern-Simons description of
(2+1)-dimensional gravity for spacetimes of topology $R\times S_g$, where $S_g$
is an oriented two-surface of genus $g>1$, for Lorentzian signature and general
cosmological constant and the Euclidean case with negative cosmological
constant. We show how the variables parametrising the phase space in the
Chern-Simons formalism are obtained from the geometrical description and how
the geometrical construction of (2+1)-spacetimes via grafting along closed,
simple geodesics gives rise to transformations on the phase space. We
demonstrate that these transformations are generated via the Poisson bracket by
one of the two canonical Wilson loop observables associated to the geodesic,
while the other acts as the Hamiltonian for infinitesimal Dehn twists. For
spacetimes with Lorentzian signature, we discuss the role of the cosmological
constant as a deformation parameter in the geometrical and the Chern-Simons
formulation of the theory. In particular, we show that the Lie algebras of the
Chern-Simons gauge groups can be identified with the (2+1)-dimensional Lorentz
algebra over a commutative ring, characterised by a formal parameter
$\Theta_\Lambda$ whose square is minus the cosmological constant. In this
framework, the Wilson loop observables that generate grafting and Dehn twists
are obtained as the real and the $\Theta_\Lambda$-component of a Wilson loop
observable with values in the ring, and the grafting transformations can be
viewed as infinitesimal Dehn twists with the parameter $\Theta_\Lambda$.


title: A Partially Gauged Fixed Hamiltonian for Scalar Field Collapse

abstract:
  We derive a partially gauge fixed Hamiltonian for black hole formation via
real scalar field collapse. The class of models considered includes many
theories of physical interest, including spherically symmetric black holes in
$D$ spacetime dimensions. The boundary and gauge fixing conditions are chosen
to be consistent with generalized Painleve-Gullstrand coordinates, in which the
metric is regular across the black hole future horizon. The resulting
Hamiltonian is remarkably simple and we argue that it provides a good starting
point for studying the quantum dynamics of black hole formation.


title:
The Einstein-Hamilton-Jacobi equation: Searching the classical solution
  for barotropic FRW

abstract:
  The dynamical evolution of the scale factor of FRW cosmological model is
presented, when the equation of state of the material content assume the form
$\rm p=\gamma \rho$, $\rm \gamma=constant$, including the cosmological term. We
use the WKB approximation and the relation with the Einstein-Hamilton-Jacobi
equation to obtain the exact solutions.


title: Interacting dark energy in $f(R)$ gravity

abstract:
  The field equations in $f(R)$ gravity derived from the Palatini variational
principle and formulated in the Einstein conformal frame yield a cosmological
term which varies with time. Moreover, they break the conservation of the
energy--momentum tensor for matter, generating the interaction between matter
and dark energy. Unlike phenomenological models of interacting dark energy,
$f(R)$ gravity derives such an interaction from a covariant Lagrangian which is
a function of a relativistically invariant quantity (the curvature scalar $R$).
We derive the expressions for the quantities describing this interaction in
terms of an arbitrary function $f(R)$, and examine how the simplest
phenomenological models of a variable cosmological constant are related to
$f(R)$ gravity. Particularly, we show that $\Lambda c^2=H^2(1-2q)$ for a flat,
homogeneous and isotropic, pressureless universe. For the Lagrangian of form
$R-1/R$, which is the simplest way of introducing current cosmic acceleration
in $f(R)$ gravity, the predicted matter--dark energy interaction rate changes
significantly in time, and its current value is relatively weak (on the order
of 1% of $H_0$), in agreement with astronomical observations.


title: Global monopole, dark matter and scalar tensor theory

abstract:
  In this article, we discuss the space-time of a global monopole field as a
candidate for galactic dark matter in the context of scalar tensor theory.


title:
The Energy Momentum Problem in Teleparallel Gravity For Bianchi Type
  II-VIII-IX Universes

abstract:
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0607110, gr-qc/0607115,
gr-qc/0607119, gr-qc/0607109, gr-qc/0607103, gr-qc/0607089, gr-qc/0602012,
gr-qc/0608024, and others.


title: Remarks on the Wave Function of the Universe in the Dilaton Cosmology

abstract:
  Motivated by previous works, we study semi-classical cosmological solutions
and the wave function of the Wheeler-DeWitt equation in the Bose-Parker-Peleg
model. We obtain the wave function of the universe satisfying the suitable
boundary condition of the redefined fields, which has not been considered in
previous works. For some limiting cases, the Wheeler-DeWitt equation is reduced
to the Liouville equation with a boundary, and its solution can be described by
well-known functions. The consistent requirement of the boundary condition is
related to the avoidance of the curvature singularity.


title:
Conservative discretization of the Einstein-Dirac equations in
  spherically symmetric spacetime

abstract:
  In computational relativity, critical behaviour near the black hole threshold
has been studied numerically for several models in the last decade. In this
paper we present a spatial Galerkin method, suitable for finding numerical
solutions of the Einstein-Dirac equations in spherically symmetric spacetime
(in polar/areal coordinates). The method features exact conservation of the
total electric charge and allows for a spatial mesh adaption based on physical
arclength. Numerical experiments confirm excellent robustness and convergence
properties of our approach. Hence, this new algorithm is well suited for
studying critical behaviour.


title:
Universe With Time Dependent Deceleration Parameter and $\Lambda$ Term
  in General Relativity

abstract:
  A new class of exact solutions of Einstein's field equations with perfect
fluid for an LRS Bianchi type-I spacetime is obtained by using a time dependent
deceleration parameter. We have obtained a general solution of the field
equations from which three models of the universe are derived: exponential,
polynomial and sinusoidal form respectively. The behaviour of these models of
the universe are also discussed in the frame of reference of recent supernovae
Ia observations.


title: Quantum Geometry and its Implications for Black Holes

abstract:
  General relativity successfully describes space-times at scales that we can
observe and probe today, but it cannot be complete as a consequence of
singularity theorems. For a long time there have been indications that quantum
gravity will provide a more complete, non-singular extension which, however,
was difficult to verify in the absence of a quantum theory of gravity. By now
there are several candidates which show essential hints as to what a quantum
theory of gravity may look like. In particular, loop quantum gravity is a
non-perturbative formulation which is background independent, two properties
which are essential close to a classical singularity with strong fields and a
degenerate metric. In cosmological and black hole settings one can indeed see
explicitly how classical singularities are removed by quantum geometry: there
is a well-defined evolution all the way down to, and across, the smallest
scales. As for black holes, their horizon dynamics can be studied showing
characteristic modifications to the classical behavior. Conceptual and physical
issues can also be addressed in this context, providing lessons for quantum
gravity in general. Here, we conclude with some comments on the uniqueness
issue often linked to quantum gravity in some form or another.


title:
Constraints on Gravitational Scaling Dimensions from Non-Local Effective
  Field Equations

abstract:
  Quantum corrections to the classical field equations, induced by a scale
dependent gravitational constant, are analyzed in the case of the static
isotropic metric. The requirement of general covariance for the resulting
non-local effective field equations puts severe restrictions on the nature of
the solutions that can be obtained. In general the existence of vacuum
solutions to the effective field equations restricts the value of the
gravitational scaling exponent $\nu^{-1}$ to be a positive integer greater than
one. We give further arguments suggesting that in fact only for $\nu^{-1}=3$
consistent solutions seem to exist in four dimensions.


title: Observable Effects of Scalar Fields and Varying Constants

abstract:
  We show by using the method of matched asymptotic expansions that a
sufficient condition can be derived which determines when a local experiment
will detect the cosmological variation of a scalar field which is driving the
spacetime variation of a supposed constant of Nature. We extend our earlier
analyses of this problem by including the possibility that the local region is
undergoing collapse inside a virialised structure, like a galaxy or galaxy
cluster. We show by direct calculation that the sufficient condition is met to
high precision in our own local region and we can therefore legitimately use
local observations to place constraints upon the variation of "constants" of
Nature on cosmological scales.


title:
Massive scalar field quasi-normal modes of higher dimensional black
  holes

abstract:
  We study quasinormal spectrum of massive scalar field in the $D$-dimensional
black hole background. We found the qualitatively different dependence on the
field mass of the fundamental modes for $D\geq6$. The behaviour of higher modes
is qualitatively the same for all $D$. Thus for some particular values of mass
(of the field and of the black hole) the spectrum has two dominating
oscillations with a very long lifetime. Also we show that the asymptotically
high overtones do not depend on the field mass. In addition, we present the
generalisation of the Nollert improvement of the continued fraction technique
for the numerical calculation of quasi-normal frequencies of $D$-dimensional
black holes.


title: Topology and Closed Timelike Curves II: Causal structure

abstract:
  Because no closed timelike curve (CTC) on a Lorentzian manifold can be
deformed to a point, any such manifold containing a CTC must have a topological
feature, to be called a timelike wormhole, that prevents the CTC from being
deformed to a point. If all wormholes have horizons, which typically seems to
be the case in space-times without exotic matter, then each CTC must transit
some timelike wormhole's horizon. Therefore, a Lorentzian manifold containing a
CTC may nevertheless be causally well behaving once its horizon's are deleted.
For instance, there may be a Cauchy-like surface through which every timelike
curve passes one and only once before crossing a horizon.


title: Quantum gravitational optics in the field of a gravitomagnetic monopole

abstract:
  Vacuum polarization in QED in a background gravitational field induces
interactions which {\it effectively} modify the classical picture of light rays
as the null geodesics of spacetime. After a short introduction on the main
aspects of the quantum gravitational optics, as a nontrivial example, we study
this effect in the background of NUT space characterizing the spacetime of a
spherical mass endowed with a gravitomagnetic monopole charge, the so called
NUT factor.


title: Quantum Gowdy $T^3$ model: A uniqueness result

abstract:
  Modulo a homogeneous degree of freedom and a global constraint, the linearly
polarised Gowdy $T^3$ cosmologies are equivalent to a free scalar field
propagating in a fixed nonstationary background. Recently, a new field
parameterisation was proposed for the metric of the Gowdy spacetimes such that
the associated scalar field evolves in a flat background in 1+1 dimensions with
the spatial topology of $S^1$, although subject to a time dependent potential.
Introducing a suitable Fock quantisation for this scalar field, a quantum
theory was constructed for the Gowdy model in which the dynamics is implemented
as a unitary transformation. A question that was left open is whether one might
adopt a different, nonequivalent Fock representation by selecting a distinct
complex structure. The present work proves that the chosen Fock quantisation is
in fact unique (up to unitary equivalence) if one demands unitary
implementation of the dynamics and invariance under the group of constant $S^1$
translations. These translations are precisely those generated by the global
constraint that remains on the Gowdy model. It is also shown that the proof of
uniqueness in the choice of complex structure can be applied to more general
field dynamics than that corresponding to the Gowdy cosmologies.


title: On the existence of black hole evaporation yet again

abstract:
  A new argument is presented confirming the point of view that a Schwarzschild
black hole formed during a collapse process does not radiate.


title: Teleparallel Versions of Friedmann and Lewis-Papapetrou Spacetimes

abstract:
  This paper is devoted to investigate the teleparallel versions of the
Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad
and the torsion fields for both the spacetimes. It is shown that the
axial-vector vanishes for the Friedmann models. We discuss the different
possibilities of the axial-vector depending on the arbitrary functions $\omega$
and $\psi$ in the Lewis-Papapetrou metric. The vector related with spin has
also been evaluated.


title: Homoclinic chaos and energy condition violation

abstract:
  In this letter we discuss the connection between so-called homoclinic chaos
and the violation of energy conditions in locally rotationally symmetric
Bianchi type IX models, where the matter is assumed to be non-tilted dust and a
positive cosmological constant. We show that homoclinic chaos in these models
is an artifact of unphysical assumptions: it requires that there exist
solutions with positive matter energy density $\rho>0$ that evolve through the
singularity and beyond as solutions with negative matter energy density
$\rho<0$. Homoclinic chaos is absent when it is assumed that the dust particles
always retain their positive mass.In addition, we discuss more general models:
for solutions that are not locally rotionally symmetric we demonstrate that the
construction of extensions through the singularity, which is required for
homoclinic chaos, is not possible in general.


title: On surface-symmetric spacetimes with collisionless and charged matter

abstract:
  Some future global properties of cosmological solutions for the
Einstein-Vlasov-Maxwell system with surface symmetry are presented. Global
existence is proved, the homogeneous spacetimes are future complete for causal
trajectories, and the same is true for inhomogeneous plane-symmetric solutions
with small initial data. In the latter case some decay properties are also
obtained at late times. Similar but slightly weaker results hold for hyperbolic
symmetry.


title: A Robust Test of General Relativity in Space

abstract:
  LISA may make it possible to test the black-hole uniqueness theorems of
general relativity, also called the no-hair theorems, by Ryan's method of
detecting the quadrupole moment of a black hole using high-mass-ratio
inspirals. This test can be performed more robustly by observing inspirals in
earlier stages, where the simplifications used in making inspiral predictions
by the perturbative and post-Newtonian methods are more nearly correct. Current
concepts for future missions such as DECIGO and BBO would allow even more
stringent tests by this same method. Recently discovered evidence supports the
existence of intermediate-mass black holes (IMBHs). Inspirals of binary systems
with one IMBH and one stellar-mass black hole would fall into the frequency
band of proposed maximum sensitivity for DECIGO and BBO. This would enable us
to perform the Ryan test more precisely and more robustly. We explain why tests
based on observations earlier in the inspiral are more robust and provide
preliminary estimates of possible optimal future observations.


title: Higher dimensional dust collapse with a cosmological constant

abstract:
  The general solution of the Einstein equation for higher dimensional (HD)
spherically symmetric collapse of inhomogeneous dust in presence of a
cosmological term, i.e., exact interior solutions of the Einstein field
equations is presented for the HD Tolman-Bondi metrics imbedded in a de Sitter
background. The solution is then matched to exterior HD Scwarschild-de Sitter.
A brief discussion on the causal structure singularities and horizons is
provided. It turns out that the collapse proceed in the same way as in the
Minkowski background, i.e., the strong curvature naked singularities form and
that the higher dimensions seem to favor black holes rather than naked
singularities.


title: Non-linear Oscillations of Compact Stars and Gravitational Waves

abstract:
  This thesis investigates in the time domain a particular class of second
order perturbations of a perfect fluid non-rotating compact star: those arising
from the coupling between first order radial and non-radial perturbations. This
problem has been treated by developing a gauge invariant formalism based on the
2-parameter perturbation theory (Sopuerta, Bruni and Gualtieri, 2004) where the
radial and non-radial perturbations have been separately parameterized. The
non-linear perturbations obey inhomogeneous partial differential equations,
where the structure of the differential operator is given by the previous
perturbative orders and the source terms are quadratic in the first order
perturbations. In the exterior spacetime the sources vanish, thus the
gravitational wave properties are completely described by the second order
Zerilli and Regge-Wheeler functions.
  As main initial configuration we have considered a first order differentially
rotating and radially pulsating star. Although at first perturbative order this
configuration does not exhibit any gravitational radiation, we have found a new
interesting gravitational signal at non-linear order, in which the radial
normal modes are precisely mirrored. In addition, a resonance effect is present
when the frequencies of the radial pulsations are close to the first axial
w-mode. Finally, we have roughly estimated the damping times of the radial
pulsations due to the non-linear gravitational emission. The coupling near the
resonance results to be a very effective mechanism for extracting energy from
the radial oscillations.


title: A New Action-Derived Form of The Black Hole Metric

abstract:
  Several different but equivalent forms of the spherical black hole
(Schwarzschild) are known, as well as several derivations. Here a novel form is
derived through the power of the action formalism. The method generalizes to
any spherical black hole or brane, and the charged hole case
(Reissner-Nordstrom) is worked out in detail.


title:
Possible Constraints on the Duration of Inflationary Expansion from
  Quantum Stress Tensor Fluctuations

abstract:
  We discuss the effect of quantum stress tensor fluctuations in deSitter
spacetime upon the expansion of a congruence of timelike geodesics. We treat a
model in which the expansion fluctuations begin on a given hypersurface in
deSitter spacetime, and find that this effect tends to grow, in contrast to the
situation in flat spacetime. This growth potentially leads to observable
consequences in inflationary cosmology in the form of density perturbations
which depend upon the duration of the inflationary period. In the context of
our model, the effect may be used to place upper bounds on this duration.


title: Evolving wormhole geometries within nonlinear electrodynamics

abstract:
  In this work, we explore the possibility of evolving (2+1) and
(3+1)-dimensional wormhole spacetimes, conformally related to the respective
static geometries, within the context of nonlinear electrodynamics. For the
(3+1)-dimensional spacetime, it is found that the Einstein field equation
imposes a contracting wormhole solution and the obedience of the weak energy
condition. Nevertheless, in the presence of an electric field, the latter
presents a singularity at the throat, however, for a pure magnetic field the
solution is regular. For the (2+1)-dimensional case, it is also found that the
physical fields are singular at the throat. Thus, taking into account the
principle of finiteness, which states that a satisfactory theory should avoid
physical quantities becoming infinite, one may rule out evolving
(3+1)-dimensional wormhole solutions, in the presence of an electric field, and
the (2+1)-dimensional case coupled to nonlinear electrodynamics.


title: "Massless" vector field in de Sitter Universe

abstract:
  In the present work the massless vector field in the de Sitter (dS) space has
been quantized. "Massless" is used here by reference to conformal invariance
and propagation on the dS light-cone whereas "massive" refers to those dS
fields which contract at zero curvature unambiguously to massive fields in
Minkowski space. Due to the gauge invariance of the massless vector field, its
covariant quantization requires an indecomposable representation of the de
Sitter group and an indefinite metric quantization. We will work with a
specific gauge fixing which leads to the simplest one among all possible
related Gupta-Bleuler structures. The field operator will be defined with the
help of coordinate independent de Sitter waves (the modes) which are simple to
manipulate and most adapted to group theoretical matters. The physical states
characterized by the divergencelessness condition will for instance be easy to
identify. The whole construction is based on analyticity requirements in the
complexified pseudo-Riemanian manifold for the modes and the two-point
function.


title: Non-stationary de Sitter cosmological models

abstract:
  In this note it is proposed a class of non-stationary de Sitter, rotating and
non-rotating, solutions of Einstein's field equations with a cosmological term
of variable function.


title: High reflectivity grating waveguide coatings for 1064nm

abstract:
  We propose thin single-layer grating waveguide structures to be used as
high-reflectivity, but low thermal noise, alternative to conventional coatings
for gravitational wave detector test mass mirrors. Grating waveguide (GWG)
coatings can show a reflectivity of up to 100% with an overall thickness of
less than a wavelength. We theoretically investigate GWG coatings for 1064nm
based on tantala (Ta2O5) on a Silica substrate focussing on broad spectral
response and low thickness.


title:
Analysis of Parametric Oscillatory Instability in Signal Recycled LIGO
  Interferometer

abstract:
  We present the analysis of undesirable effect of parametric oscillatory
instability in signal recycled LIGO interferometer. The basis for this effect
is the excitation of the additional (Stokes) optical mode, with frequency
$\omega_1$, and the mirror elastic mode, with frequency $\omega_m$, when
optical energy stored in the main FP cavity mode, with frequency $\omega_0$,
exceeds the certain threshold and the frequencies are related as
$\omega_0\simeq \omega_1+\omega_m$. We show that possibility of parametric
instability in this interferometer is relatively small due to stronger
sensitivity to detuning. We propose to ``scan'' the frequency range where
parametric instability may take place varying the position of signal recycling
mirror.


title: Classical and quantum wormholes in a flat $\Lambda$-decaying cosmology

abstract:
  We study the classical and quantum wormholes for a flat {\it Euclidean}
Friedmann-Robertson-Walker metric with a perfect fluid including an ordinary
matter source plus a source playing the role of dark energy (decaying
cosmological term). It is shown that classical wormholes exist for this model
and the quantum version of such wormholes are consistent with the Hawking-Page
conjecture for quantum wormholes as solutions of the Wheeler-DeWitt equation.


title: The Projection Operator Method and the Ashtekar-Horowitz-Boulware Model

abstract:
  Motivated by the recent work of Louko and Molgado, we consider the
Ashtekar-Horowitz-Boulware model using the projection operator formalism. This
paper uses the techniques developed in a recent paper of Klauder and Little to
overcome the potential difficulties of this particular model. We also extend
the model by including a larger class of functions than previously considered
and evaluate the classical limit of the model.


title: The spherical symmetry of static stellar systems in general relativity

abstract: Paper withdrawn. Error lemma 7.


title:
Reflection of electromagnetic waves from mixtures of plane gravitational
  and scalar waves

abstract:
  We consider colliding wave packets consisting of hybrid mixtures of
electromagnetic, gravitational and scalar waves. Irrespective of the scalar
field, the electromagnetic wave still reflects from the gravitational wave.
Some reflection processes are given for different choice of packets in which
the Coulomb-like component $\Psi_2$ vanishes. Exact solution for multiple
reflection of an electromagnetic wave from successive impulsive gravitational
waves is obtained in a closed form. It is shown that a succesive sign flip in
the Maxwell spinor arises as a result of encountering with an impulsive train
(i.e. the Dirac's comb curvature) of gravitational waves. Such an observable
effect may be helpful in the detection of gravitational wave bursts.


title:
On Properties of Vacuum Axial Symmetric Spacetime of Gravitomagnetic
  Monopole in Cylindrical Coordinates

abstract:
  We investigate general relativistic effects associated with the
gravitomagnetic monopole moment of gravitational source through the analysis of
the motion of test particles and electromagnetic fields distribution in the
spacetime around nonrotating cylindrical NUT source. We consider the circular
motion of test particles in NUT spacetime, their characteristics and the
dependence of effective potential on the radial coordinate for the different
values of NUT parameter and orbital momentum of test particles. It is shown
that the bounds of stability for circular orbits are displaced toward the event
horizon with the growth of monopole moment of the NUT object. In addition, we
obtain exact analytical solutions of Maxwell equations for magnetized and
charged cylindrical NUT stars.


title:
Equations of motion for a (non-linear) scalar field model as derived
  from the field equations

abstract:
  The problem of derivation of the equations of motion from the field equations
is considered. Einstein's field equations have a specific analytical form: They
are linear in the second order derivatives and quadratic in the first order
derivatives of the field variables. We utilize this particular form and propose
a novel algorithm for thederivation of the equations of motion from the field
equations. It is based on the condition of the balance between the singular
terms of the field equation. We apply the algorithm to a nonlinear Lorentz
invariant scalar field model. We show that it results in the Newton law of
attraction between the singularities of the field moved on approximately
geodesic curves. The algorithm is applicable to the $N$-body problem of the
Lorentz invariant field equations.


title: Relative Energy of the Taub Cosmological Model in Teleparallel Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0303034, "The energy of the universe in teleparallel gravity," by T.
Vargas; and Gen relativ. Grav. 37(6) 1151-1152 (2005), "The taub solution
again," by Robert T. Jantzen.


title: On gravitational flow in the Relativistic Theory of Gravitation

abstract:
  A definition of the gravitational flow and a short description of the recipe
of its calculation are presented.


title: The w = -1 crossing of the quintom model with slowly-varying potentials

abstract:
  Considering the quintom model with arbitrary potential, it is shown that
there always exists a solution which evolves from w > -1 region to w < -1
region. The problem is restricted to the slowly varying potentials, i.e. the
slow-roll approximation. It is seen that the rate of this phase transition only
depends on the energy density of matter at transition time, which itself is
equal to the kinetic part of quintom energy density at that time. The
perturbative solutions of the fields are also obtained.


title: Electromagnetic Effects in Superconductors in Gravitational Field

abstract:
  The general relativistic modifications to the resistive state in
superconductors of second type in the presence of a stationary gravitational
field are studied. Some superconducting devices that can measure the
gravitational field by its red-shift effect on the frequency of radiation are
suggested. It has been shown that by varying the orientation of a
superconductor with respect to the earth gravitational field, a corresponding
varying contribution to AC Josephson frequency would be added by gravity. A
magnetic flux (being proportional to angular velocity of rotation $\Omega$)
through a rotating hollow superconducting cylinder with the radial gradient of
temperature $\nabla_r T$ is theoretically predicted. The magnetic flux is
assumed to be produced by the azimuthal current arising from Coriolis force
effect on radial thermoelectric current. Finally the magnetic flux through the
superconducting ring with radial heat flow located at the equatorial plane
interior the rotating neutron star is calculated. In particular it has been
shown that nonvanishing magnetic flux will be generated due to the general
relativistic effect of dragging of inertial frames on the thermoelectric
current.


title:
The History and Present Status of Quantum Field Theory in Curved
  Spacetime

abstract:
  Quantum field theory in curved spacetime is a theory wherein matter is
treated fully in accord with the principles of quantum field theory, but
gravity is treated classically in accord with general relativity. It is not
expected to be an exact theory of nature, but it should provide a good
approximate description when the quantum effects of gravity itself do not play
a dominant role. A major impetus to the theory was provided by Hawking's
calculation of particle creation by black holes, showing that black holes
radiate as perfect black bodies. During the past 30 years, considerable
progress has been made in giving a mathematically rigorous formulation of
quantum field theory in curved spacetime. Major issues of principle with regard
to the formulation of the theory arise from the lack of Poincare symmetry and
the absence of a preferred vacuum state or preferred notion of ``particles''.
By the mid-1980's, it was understood how all of these difficulties could be
overcome for free (i.e., non-self-interacting) quantum fields by formulating
the theory via the algebraic approach and focusing attention on the local field
observables rather than a notion of ``particles''. However, these ideas, by
themselves, were not adequate for the formulation of interacting quantum field
theory, even at a perturbative level, since standard renormalization
prescriptions in Minkowski spacetime rely heavily on Poincare invariance and
the existence of a Poincare invariant vacuum state. However, during the past
decade, great progress has been made, mainly due to the importation into the
theory of the methods of ``microlocal analysis''. This article will describe
the historical development of the subject and describe some of the recent
progress.


title: Self-reproduction in k-inflation

abstract:
  We study cosmological self-reproduction in models of inflation driven by a
scalar field $\phi$ with a noncanonical kinetic term ($k$-inflation). We
develop a general criterion for the existence of attractors and establish
conditions selecting a class of $k$-inflation models that admit a unique
attractor solution. We then consider quantum fluctuations on the attractor
background. We show that the correlation length of the fluctuations is of order
$c_{s}H^{-1}$, where $c_{s}$ is the speed of sound. By computing the magnitude
of field fluctuations, we determine the coefficients of Fokker-Planck equations
describing the probability distribution of the spatially averaged field $\phi$.
The field fluctuations are generally large in the inflationary attractor
regime; hence, eternal self-reproduction is a generic feature of $k$-inflation.
This is established more formally by demonstrating the existence of stationary
solutions of the relevant FP equations. We also show that there exists a
(model-dependent) range $\phi_{R}<\phi<\phi_{\max}$ within which large
fluctuations are likely to drive the field towards the upper boundary
$\phi=\phi_{\max}$, where the semiclassical consideration breaks down. An exit
from inflation into reheating without reaching $\phi_{\max}$ will occur almost
surely (with probability 1) only if the initial value of $\phi$ is below
$\phi_{R}$. In this way, strong self-reproduction effects constrain models of
$k$-inflation.


title:
Massless spinning test particles in vacuum algebraically special
  spacetimes

abstract:
  The motion of massless spinning test particles is investigated using the
Newman-Penrose formalism within the Mathisson-Papapetrou model extended to
massless particles by Mashhoon and supplemented by the Pirani condition. When
the "multipole reduction world line" lies along a principal null direction of
an algebraically special vacuum spacetime, the equations of motion can be
explicitly integrated. Examples are given for some familiar spacetimes of this
type in the interest of shedding some light on the consequences of this model.


title: Gravitomagnetic Effects in a Conductor in an Applied Magnetic Field

abstract:
  The electromagnetic measurements of general relativistic gravitomagnetic
effects which can be performed within a conductor embedded in the space-time of
slow rotating gravitational object in the presence of magnetic field are
proposed.


title: Remarks on Papapetrou Class of Vacuum Solutions of Einstein Equations

abstract:
  Class of axially symmetric solutions of vacuum Einstein field equations
including the Papapetrou solution as particular case has been found. It has
been shown that the derived solution describes the external axial symmetric
gravitational field of the source with nonvanishing mass. The general solution
is obtained for this class of functions. As an example of physical application,
the spacetime metric outside a line gravitomagnetic monopole has been obtained
from Papapetrou solution of vacuum equations of gravitational field.


title:
Generalized uncertainty principle and correction value to the black hole
  entropy

abstract:
  Recently, there has been much attention devoted to resolving the quantum
corrections to the Bekenstein-Hawking entropy of the black hole. In particular,
many researchers have expressed a vested interest in the coefficient of the
logarithmic term of the black hole entropy correction term. In this paper, we
calculate the correction value of the black hole entropy by utilizing the
generalized uncertainty principle and obtain the correction term caused by the
generalized uncertainty principle. Because in our calculation we think that the
Bekenstein-Hawking area theorem is still valid after considering the
generalized uncertainty principle, we derive that the coefficient of the
logarithmic term of the black hole entropy correction term is negative. This
result is different from the known result at present. Our method is valid not
only for single horizon spacetime but also for double horizons spacetime. In
the whole process, the physics idea is clear and calculation is simple. It
offers a new way for studying the condition that Bekenstein-Hawking area
theorem is valid.


title: The Energy of Marder Space-Time in Moller Prescription

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0212018 and gr-qc/0408043.
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0505078, gr-qc/0607109,
gr-qc/0511095, gr-qc/0607110, gr-qc/0603044, gr-qc/0603027, gr-qc/0607126,
gr-qc/0607116, gr-qc/0502060, gr-qc/0601070, gr-qc/0508018, gr-qc/0606028,
gr-qc/0603063, and others.


title: Phantom fields: bounce solutions in the early Universe and S-branes

abstract:
  The cosmological model with two phantom scalar fields with the special choice
of field's potential is considered. The obtained regular solution describes a
bounce with a subsequent transition to the de Sitter stage of the expansion of
the Universe. This solution also could be interpreted as a S-brane solution.


title: Curvaton Dynamics in Brane-worlds

abstract:
  We study the curvaton dynamics in brane-world cosmologies. Assuming that the
inflaton field survives without decay after the end of inflation, we apply the
curvaton reheating mechanism to Randall-Sundrum and to its curvature
corrections: Gauss-Bonnet, induced gravity and combined Gauss-Bonnet and
induced gravity cosmological models. In the case of chaotic inflation and
requiring suppression of possible short-wavelength generated gravitational
waves, we constraint the parameters of a successful curvaton brane-world
cosmological model. If density perturbations are also generated by the curvaton
field then, the fundamental five-dimensional mass could be much lower than the
Planck mass


title:
Semiclassical approach to the decay of protons in circular motion under
  the influence of gravitational fields

abstract:
  We investigate the possible decay of protons in geodesic circular motion
around neutral compact objects. Weak and strong decay rates and the associated
emitted powers are calculated using a semi-classical approach. Our results are
discussed with respect to distinct ones in the literature, which consider the
decay of accelerated protons in electromagnetic fields. A number of consistency
checks are presented along the paper.


title: Quantum Radiation Reaction and the Green's Function Decomposition

abstract:
  We analyze the change in position (the position shift) of the wave packet of
a charged scalar particle due to radiation reaction in the $\hbar \to 0$ limit
of quantum electrodynamics. In particular, we re-express the formula previously
obtained for the position shift in terms of Green's functions for the
electromagnetic field, thus clarifying the relation between the quantum and
classical derivations of the radiation-reaction force.


title: Weinberg Energy-Momentum Complex for a Stringy Black Hole Solution

abstract:
  In our paper we compute the energy distribution of a magnetic stringy black
hole solution in the Weinberg prescription. The metric under consideration
describes the dual solution in the string frame that is known as the magnetic
stringy black hole solution. The metric is obtained by multiplying the electric
metric in the Einstein frame by a factor . The energy distribution depends on
the mass M and charge Q. Also, we make a discussion of the results and we
compare our result with those obtained in the Einstein and Landau and Lifshitz
prescriptions and investigate the connections between the expressions of the
energy obtained in these prescriptions.


title:
Virialization of matter overdensities within dark energy subsystems:
  special cases

abstract:
  The virialization of matter overdensities within dark energy subsystems is
considered under the restrictive assumptions (i) spherical-symmetric density
profiles, (ii) time-independent quintessence equation of state parameter, w,
and (iii) nothing but gravitational interaction between dark energy scalar
field and matter. In addition, the quintessence subsystem is conceived as made
of ``particles'' whose mutual interaction has intensity equal to G(1+3w) and
scales as the inverse square of their distance. Then the virial theorem is
formulated for subsystems. In the special case of fully clustered quintessence,
energy conservation is assumed with regard to either the whole system (global
energy conservation), or to the matter subsystem within the tidal potential
induced by the quintessence subsystem (partial energy conservation). Further
investigation is devoted to a few special values, w=-1/3, -1/2, -2/3, -1. The
special case of fully clustered (i.e. collapsing together with the matter)
quintessence is studied in detail. The general case of partially clustered
quintessence is considered in terms of a degree of quintessence de-clustering,
\zeta, ranging from fully clustered (\zeta=0) to completely de-clustered
(\zeta=1) quintessence, respectively. The special case of unclustered (i.e.
remaining homogeneous) quintessence is also discussed. The trend exhibited by
the fractional (virialization to turnaround) radius, \eta, as a function of
other parameters, is found to be different from its counterparts reported in
earlier attempts. The reasons of the above mentioned discrepancy are discussed.


title: A Lagrangian description of interacting dark energy

abstract:
  We propose a relativistically covariant model of interacting dark energy
based on the principle of least action. The cosmological term $\Lambda$ in the
gravitational Lagrangian is a function of the trace of the energy--momentum
tensor $T$. We find that the $\Lambda(T)$ gravity is more general than the
Palatini $f(R)$ gravity, and reduces to the latter if we neglect the pressure
of matter. We show that recent cosmological data favor a variable cosmological
constant and are consistent with the $\Lambda(T)$ gravity, without knowing the
specific function $\Lambda(T)$.


title:
Accelerating universe in two-dimensional noncommutative dilaton
  cosmology

abstract:
  We show that the phase transition from the decelerating universe to the
accelerating universe, which is of relevance to the cosmological coincidence
problem, is possible in the semiclassically quantized two-dimensional dilaton
gravity by taking into account the noncommutative field variables during the
finite time. Initially, the quantum-mechanically induced energy from the
noncommutativity among the fields makes the early universe decelerate and
subsequently the universe is accelerating because the dilaton driven cosmology
becomes dominant later.


title:
On singularities, horizons, invariants, and the results of Antoci,
  Liebscher and Mihich (GRG 38, 15 (2006) and earlier)

abstract:
  Antoci et al. have argued that the horizons of the boost-rotation, Kerr and
Schwarzschild solutions are singular, having shown that a certain
invariantly-defined acceleration scalar blows up at the horizons. Their
examples do not satisfy the usual definition of a singularity. It is argued
that using the same term is seriously misleading and it is shown that such
divergent functions are natural concomitants of regular horizons. In particular
it is noted that the divergence is given by the special relativistic
approximation to the overall metric. Earlier work on characterization of
horizons by invariants is revisited, a new invariant criterion for them is
proposed, and the relation of the acceleration invariant to the Cartan
invariants, which are finite at the horizons and completely determine the
spacetimes, is examined for the C-metric, Kerr and Schwarzschild cases. An
appendix considers coordinate identifications at axes and horizons.


title: Electromagnetic field near cosmic string

abstract:
  The retarded Green function of the electromagnetic field in spacetime of a
straight thin cosmic string is found. It splits into a geodesic part
(corresponding to the propagation along null rays) and to the field scattered
on the string. With help of the Green function the electric and magnetic fields
of simple sources are constructed. It is shown that these sources are
influenced by the cosmic string through a self-interaction with their field.
The distant field of static sources is studied and it is found that it has a
different multipole structure than in Minkowski spacetime. On the other hand,
the string suppresses the electric and magnetic field of distant sources--the
field is expelled from regions near the string.


title: Exact non-spherical relativistic star

abstract:
  We obtain Vaidya-like solutions to include both a null fluid and a string
fluid in non-spherical (plane symmetric and cylindrical symmetric) anti-de
Sitter space-times. Assuming that string fluid diffuse, we find exact solutions
of Einstein's field equations. Thus we extend a recent work of Glass and Krisch
\cite {gk} to non-spherical anti-de Sitter space-times.


title: Concerning Measurement of Gravitomagnetism in Electromagnetic Systems

abstract:
  Measurement of gravitomagnetic field is of fundamental importance as a test
of general relativity. Here we present a new theoretical project for performing
such a measurement based on detection of the electric field arising from the
interplay between the gravitomagnetic and magnetic fields in the stationary
axial-symmetric gravitational field of a slowly rotating massive body. Finally
it is shown that precise magnetometers based on superconducting quantum
interferometers could not be designed for measurement of the
gravitomagnetically induced magnetic field in the cavity of a charged capacitor
since they measure the circulation of a vector potential of electromagnetic
field, i.e., an invariant quantity including the sum of electric and magnetic
fields, and the general-relativistic magnetic part will be totally cancelled by
the electric one which is in good agreement with the experimental results.


title: Generalizing Starobinskii's Formalism to Yukawa Theory & to Scalar QED

abstract:
  During inflation quantum effects from massless, minimally coupled scalars and
gravitons can be strengthened so much that perturbation theory breaks down. To
follow the subsequent evolution one must employ a nonperturbative resummation.
Starobinski\u{\i} has developed such a technique for simple scalDuring
inflation quantum effects from massless, minimally coupled scalars and
gravitons can be strengthened so much that perturbation theory breaks down. To
follow the subsequent evolution one must employ a nonperturbative resummation.
Starobinski\u{\i} has developed such a technique for simple scalar theories. I
discuss recent progress in applying this technique to more complicated models.


title:
Global characteristic problem for the Einstein vacuum equations with
  small initial data, (II): The existence proof

abstract:
  This is the second part of our result on a class of global characteristic
problems for the Einstein vacuum equations with small initial data. In the
previous work denoted by (I), our attention was focused on prescribing the
initial data satisfying the costraints imposed by the characteristic problem.
Here we show how the global existence result can be achieved. This part is
heavily based on the global results of D.Christodoulou, S.Klainerman and
S.Klainerman, F.Nicolo`.


title: Magnetic Fields of Spherical Compact Stars in Braneworld

abstract:
  We study the dipolar magnetic field configuration in dependence on brane
tension and present solutions of Maxwell equations in the internal and external
background spacetime of a magnetized spherical star in a Randall-Sundrum II
type braneworld. The star is modelled as sphere consisting of perfect highly
magnetized fluid with infinite conductivity and frozen-in dipolar magnetic
field. With respect to solutions for magnetic fields found in the Schwarzschild
spacetime brane tension introduces enhancing corrections both to the interior
and the exterior magnetic field. These corrections could be relevant for the
magnetic fields of magnetized compact objects as pulsars and magnetars and may
provide the observational evidence for the brane tension through the
modification of formula for magneto-dipolar emission which gives amplification
of electromagnetic energy loss up to few orders depending on the value of the
brane tension.


title: Odd-parity perturbations of self-similar Vaidya spacetime

abstract:
  We carry out an analytic study of odd-parity perturbations of the
self-similar Vaidya space-times that admit a naked singularity. It is found
that an initially finite perturbation remains finite at the Cauchy horizon.
This holds not only for the gauge invariant metric and matter perturbation, but
also for all the gauge invariant perturbed Weyl curvature scalars, including
the gravitational radiation scalars. In each case, `finiteness' refers to
Sobolev norms of scalar quantities on naturally occurring spacelike
hypersurfaces, as well as pointwise values of these quantities.


title:
Application of Discrete Differential Forms to Spherically Symmetric
  Systems in General Relativity

abstract:
  In this article we describe applications of Discrete Differential Forms in
computational GR. In particular we consider the initial value problem in vacuum
space-times that are spherically symmetric. The motivation to investigate this
method is mainly its manifest coordinate independence. Three numerical schemes
are introduced, the results of which are compared with the corresponding
analytic solutions. The error of two schemes converges quadratically to zero.
For one scheme the errors depend strongly on the initial data.


title: Equation of Motion of a Spinning Test Particle in Gravitational Field

abstract:
  Based on the coupling between the spin of a particle and
gravitoelectromagnetic field, the equation of motion of a spinning test
particle in gravitational field is deduced. From this equation of motion, it is
found that the motion of a spinning particle deviates from the geodesic
trajectory, and this deviation originates from the coupling between the spin of
the particle and gravitoelectromagnetic field, which is also the origin of
Lense-Thirring effects. In post-Newtonian approximations, this equation gives
out the same results as those of Papapetrou equation. Effect of the deviation
of geodesic trajectory is detectable.


title:
Towards Quantum Gravity: A Framework for Probabilistic Theories with
  Non-Fixed Causal Structure

abstract:
  General relativity is a deterministic theory with non-fixed causal structure.
Quantum theory is a probabilistic theory with fixed causal structure. In this
paper we build a framework for probabilistic theories with non-fixed causal
structure. This combines the radical elements of general relativity and quantum
theory. The key idea in the construction is physical compression. A physical
theory relates quantities. Thus, if we specify a sufficiently large set of
quantities (this is the compressed set), we can calculate all the others. We
apply three levels of physical compression. First, we apply it locally to
quantities (actually probabilities) that might be measured in a particular
region of spacetime. Then we consider composite regions. We find that there is
a second level of physical compression for the composite region over and above
the first level physical compression for the component regions. Each
application of first and second level physical compression is quantified by a
matrix. We find that these matrices themselves are related by the physical
theory and can therefore be subject to compression. This is the third level of
physical compression. This third level of physical compression gives rise to a
new mathematical object which we call the causaloid. From the causaloid for a
particular physical theory we can calculate verything the physical theory can
calculate. This approach allows us to set up a framework for calculating
probabilistic correlations in data without imposing a fixed causal structure
(such as a background time). We show how to put quantum theory in this
framework (thus providing a new formulation of this theory). We indicate how
general relativity might be put into this framework and how the framework might
be used to construct a theory of quantum gravity.


title:
The tortoise coordinates and the cauchy problem in the stable study of
  the Schwarzschild black hole

abstract:
  Generally, the Schwarzschild black hole was proved stable through two
different methods: the mode-decomposition method and the integral method. In
the paper, we show the integral method can only apply to the initial data
vanishing at both the horizon and the spatial infinity. It can not treat the
initial data only vanishing at the spatial infinity. We give an example to show
the misleading information caused by the use of the tortoise coordinates in the
perturbation equations. Subsequently, the perturbation equation in the
Schwarzschild coordinates is shown not sufficient for the stable study.


title: The stable problem in the Rindler space-time

abstract:
  We carefully study the stable problem of the Rindler space time by the scalar
wave perturbation. Using the two different coordinate systems, the scalar wave
equation is investigated. The results are different in these two cases. They
are analyzed and compared in detail. The conclusions are: (a) the Rindler space
time as a whole is not stable; (b) the Rindler space time could exist stably
only as a part of the Minkowski space time, and the Minkowski space time could
be a real entity independently; (c) there are some defects for the scalar wave
equation written by the Rindler coordinates, and it is unsuitable for
investigation of the stable properties of the Rindler space time. All these
results might shed some lights on the stable properties of the Schwarzschild
black hole. It is natural and not unreasonable for one to infer that: (a)
perhaps the Regge-Wheeler equation is not sufficient to decide the stable
properties; (b) the Schwarzschild black hole as a whole might be really
unstable; (c) the Kruskal space time is stable and can exist as a real physical
entity ; whereas the Schwarzschild black hole could occur only as part of the
Kruskal space time.


title: The effect of the tortoise coordinates on the tunnel effect

abstract:
  The tunnel process of the quantum wave from the light cone is carefully
discussed. They are applied in the massive quantum particles from the
Schwarzschild black hole in the Kruskal metric. The tortoise coordinates
prevent one from understanding the tunnel process, and are investigated with
care. Furthermore, the massive particles could come out of the black hole
either by the Hawking radiation or by the tunnel effect; the tunnel effect
might give more information about the black hole.


title: Nonlinear spinor field in Bianchi type-I cosmology: accelerated regimes

abstract:
  A self-consistent system of interacting nonlinear spinor and scalar fields
within the scope of a Bianchi type-I cosmological model filled with perfect
fluid is considered. Exact self-consistent solutions to the corresponding field
equations are obtained. The role of spinor field in the evolution of the
Universe is studied. It is shown that the spinor field gives rise to an
accelerated mode of expansion of the Universe. At the early stage of evolution
the spinor field nonlinearity generates the acceleration while at the later
stage it is done by the nonzero spinor mass.


title:
Electromagnetic Fields of Charged and Magnetized Cylindrical Conductors
  in NUT Space

abstract:
  We present analytic solutions of Maxwell equations for infinitely long
cylindrical conductors with nonvanishing electric charge and currents in the
external background spacetime of a line gravitomagnetic monopole. It has been
shown that vertical magnetic field arising around cylindrical conducting shell
carrying azimuthal current will be modified by the gravitational field of NUT
source. We obtain that the purely general relativistic magnetic field which has
no any Newtonian analog will be produced around charged gravitomagnetic
monopole.


title: One Loop Corrected Mode Functions for SQED during Inflation

abstract:
  We solve the one loop effective scalar field equations for spatial plane
waves in massless, minimally coupled scalar quantum electrodynamics on a
locally de Sitter background. The computation is done in two different gauges:
a non-de Sitter invariant analogue of Feynman gauge, and in the de Sitter
invariant, Lorentz gauge. In each case our result is that the finite part of
the conformal counterterm can be chosen so that the mode functions experience
no significant one loop corrections at late times. This is in perfect agreement
with a recent, all orders stochastic prediction.


title: Topological Black Holes and Momentum Four Vector

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0303034, "The energy of the universe in teleparallel gravity," by T.
Vargas; and hep-th/0512022, "Topological black holes dressed with a conformally
coupled scalar field and electric charge," by C. Martinez, J. P. Staforelli and
R. Troncoso.


title: Towards absorbing outer boundaries in General Relativity

abstract:
  We construct exact solutions to the Bianchi equations on a flat spacetime
background. When the constraints are satisfied, these solutions represent in-
and outgoing linearized gravitational radiation. We then consider the Bianchi
equations on a subset of flat spacetime of the form [0,T] x B_R, where B_R is a
ball of radius R, and analyze different kinds of boundary conditions on
\partial B_R. Our main results are: i) We give an explicit analytic example
showing that boundary conditions obtained from freezing the incoming
characteristic fields to their initial values are not compatible with the
constraints. ii) With the help of the exact solutions constructed, we determine
the amount of artificial reflection of gravitational radiation from
constraint-preserving boundary conditions which freeze the Weyl scalar Psi_0 to
its initial value. For monochromatic radiation with wave number k and arbitrary
angular momentum number l >= 2, the amount of reflection decays as 1/(kR)^4 for
large kR. iii) For each L >= 2, we construct new local constraint-preserving
boundary conditions which perfectly absorb linearized radiation with l <= L.
(iv) We generalize our analysis to a weakly curved background of mass M, and
compute first order corrections in M/R to the reflection coefficients for
quadrupolar odd-parity radiation. For our new boundary condition with L=2, the
reflection coefficient is smaller than the one for the freezing Psi_0 boundary
condition by a factor of M/R for kR > 1.04. Implications of these results for
numerical simulations of binary black holes on finite domains are discussed.


title: Two-dimensional gravity with a dynamical aether

abstract:
  We investigate the two-dimensional behavior of gravity coupled to a dynamical
unit timelike vector field, i.e. "Einstein-aether theory". The classical
solutions of this theory in two dimensions depend on one coupling constant.
When this coupling is positive the only solutions are (i) flat spacetime with
constant aether, (ii) de Sitter or anti-de Sitter spacetimes with a uniformly
accelerated unit vector invariant under a two-dimensional subgroup of SO(2,1)
generated by a boost and a null rotation, and (iii) a non-constant curvature
spacetime that has no Killing symmetries and contains singularities. In this
case the sign of the curvature is determined by whether the coupling is less or
greater than one. When instead the coupling is negative only solutions (i) and
(iii) are present. This classical study of the behavior of Einstein-aether
theory in 1+1 dimensions may provide a starting point for further
investigations into semiclassical and fully quantum toy models of quantum
gravity with a dynamical preferred frame.


title: Perfect magnetohydrodynamics as a field theory

abstract:
  We propose the generally covariant action for the theory of a self-coupled
complex scalar field and electromagnetism which by virtue of constraints is
equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics
(MHD). We recover from it the Euler equation with Lorentz force, and the
thermodynamic relations for a prefect fluid. The equation of state of the
latter is related to the scalar field's self potential. We introduce 1+3
notation to elucidate the relation between MHD and field variables. In our
approach the requirement that the scalar field be single valued leads to the
quantization of a certain circulation in steps of $\hbar$; this feature leads,
in the classical limit, to the conservation of that circulation. The
circulation is identical to that in Oron's generalization of Kelvin's
circulation theorem to perfect MHD; we here characterize the new conserved
helicity associated with it. We also demonstrate the existence for MHD of two
Bernoulli-like theorems for each spacetime symmetry of the flow and geometry;
one of these is pertinent to suitably defined potential flow. We exhibit the
conserved quantities explicitly in the case that two symmetries are
simultaneously present, and give examples. Also in this case we exhibit a new
conserved MHD circulation distinct from Oron's, and provide an example.


title: Searching for dark matter with helium atom

abstract:
  With the help of the boost operator we can model the interaction between a
weakly interacting particle(WIMP) of dark matter(DAMA) and an atomic nuclei.
Via this "kick" we calculate the total electronic excitation cross section of
the helium atom. The bound spectrum of He is calculated through a
diagonalization process with a configuration interaction (CI) wavefunction
built up from Slater orbitals. All together 19 singly- and doubly-excited
atomic sates were taken with total angular momenta of L=0,1 and 2. Our
calculation may give a rude estimation about the magnitude of the total
excitation cross section which could be measured in later scintillator
experiments. The upper limit of the excitation cross section is $9.7\cdot
10^{-8}$ barn.


title:
Seeking exactly solvable models of traversable wormholes supported by
  phantom energy

abstract:
  The purpose of this paper is to obtain exact solutions of the Einstein field
equations describing traversable wormholes supported by phantom energy. Their
relationship to exact solutions in the literature is also discussed, as well as
the conditions required to determine such solutions.


title: A New Class of LRS Bianchi Type-I Cosmological Models in Lyra's Manifold

abstract:
  LRS Bianchi type-I models have been studied in the cosmological theory based
on Lyra's geometry. A new class of exact solutions has been obtained by
considering a time dependent displacement field for variable deceleration
parameter models of the universe. We have compared our models with those of
Einstein's field theory with the cosmological term $\Lambda$. Our frame of
reference is restricted to the recent Ia observations of supernovae. Some
physical behaviour of the models is also examined in the presence of perfect
fluids.


title: GL(3,R) gauge theory of gravity coupled with an electromagnetic field

abstract:
  Consistency of $GL(3,R)$ gauge theory of gravity coupled with an external
electromagnetic field, is studied. It is shown that possible restrictions on
Maxwell field can be avoided through introduction of auxiliary fields.


title: On Primordial Perturbations of Test Scalar Fields

abstract:
  The primordial perturbations of test scalar fields not affecting the
evolution of background may be very interesting since they can be transferred
to the curvature perturbations by some mechanisms, and thus under certain
condition can be responsible for the structure formation of observable
universe. In this brief report we study the primordial perturbations of test
scalar fields in various (super)accelerated expanding backgrounds.


title: Propagation of a string across the cosmological singularity

abstract:
  Our results concern the transition of a quantum string through the
singularity of the compactified Milne (CM) space. We restrict our analysis to
the string winding around the compact dimension (CD) of spacetime. The CD
undergoes contraction to a point followed by re-expansion. We demonstrate that
both classical and quantum dynamics of considered string are well defined. Most
of presently available calculations strongly suggest that the singularity of a
time dependent orbifold is useless as a model of the cosmological singularity.
We believe that our results bring, to some extent, this claim into question.


title: Electrical Conductivity in General Relativity

abstract:
  The general relativistic kinetic theory including the effect of a stationary
gravitational field is applied to the electromagnetic transport processes in
conductors. Then it is applied to derive the general relativistic Ohm's law
where the gravitomagnetic terms are incorporated. The total electric charge
quantity and charge distribution inside conductors carrying conduction current
in some relativistic cases are considered. The general relativistic Ohm's law
is applied to predict new gravitomagnetic and gyroscopic effects which can, in
principle, be used to detect the Lense-Thirring and rotational fields.


title: Entropy and temperature of black holes in a gravity's rainbow

abstract:
  The linear relation between the entropy and area of a black hole can be
derived from the Heisenberg principle, the energy-momentum dispersion relation
of special relativity, and general considerations about black holes. There
exist results in quantum gravity and related contexts suggesting the
modification of the usual dispersion relation and uncertainty principle. One of
these contexts is the gravity's rainbow formalism. We analyze the consequences
of such a modification for black hole thermodynamics from the perspective of
two distinct rainbow realizations built from doubly special relativity. One is
the proposal of Magueijo and Smolin and the other is based on a canonical
implementation of doubly special relativity put forward recently by the
authors. In these scenarios, we obtain modified expressions for the entropy and
temperature of black holes. We show that, for a family of doubly special
relativity theories satisfying certain properties, the temperature can vanish
in the limit of zero black hole mass. For the Magueijo and Smolin proposal,
this is only possible for some restricted class of models with bounded energy
and unbounded momentum. With the proposal of a canonical implementation, on the
other hand, the temperature may vanish for more general theories; in
particular, the momentum may also be bounded, with bounded or unbounded energy.
This opens new possibilities for the outcome of black hole evaporation in the
framework of a gravity's rainbow.


title:
Measuring coalescing massive binary black holes with gravitational
  waves: The impact of spin-induced precession

abstract:
  The coalescence of massive black holes generates gravitational waves (GWs)
that will be measurable by space-based detectors such as LISA to large
redshifts. The spins of a binary's black holes have an important impact on its
waveform. Specifically, geodetic and gravitomagnetic effects cause the spins to
precess; this precession then modulates the waveform, adding periodic structure
which encodes useful information about the binary's members. Following
pioneering work by Vecchio, we examine the impact upon GW measurements of
including these precession-induced modulations in the waveform model. We find
that the additional periodicity due to spin precession breaks degeneracies
among certain parameters, greatly improving the accuracy with which they may be
measured. In particular, mass measurements are improved tremendously, by one to
several orders of magnitude. Localization of the source on the sky is also
improved, though not as much -- low redshift systems can be localized to an
ellipse which is roughly ${a few} \times 10$ arcminutes in the long direction
and a factor of 2-4 smaller in the short direction. Though not a drastic
improvement relative to analyses which neglect spin precession, even modest
gains in source localization will greatly facilitate searches for
electromagnetic counterparts to GW events. Determination of distance to the
source is likewise improved: We find that relative error in measured luminosity
distance is commonly $\sim 0.2%-0.7%$ at $z \sim 1$. Finally, with the
inclusion of precession, we find that the magnitude of the spins themselves can
typically be determined for low redshift systems with an accuracy of about
$0.1%-10 %$, depending on the spin value, allowing accurate surveys of mass and
spin evolution over cosmic time.


title: The Causal Boundary of spacetimes revisited

abstract:
  We present a new development of the causal boundary of spacetimes, originally
introduced by Geroch, Kronheimer and Penrose. Given a strongly causal spacetime
(or, more generally, a chronological set), we reconsider the GKP ideas to
construct a family of completions with a chronology and topology extending the
original ones. Many of these completions present undesirable features, like
those appeared in previous approaches by other authors. However, we show that
all these deficiencies are due to the attachment of an ``excessively big''
boundary. In fact, a notion of ``completion with minimal boundary'' is then
introduced in our family such that, when we restrict to these minimal
completions, which always exist, all previous objections disappear. The optimal
character of our construction is illustrated by a number of satisfactory
properties and examples.


title:
Invariant conserved currents in gravity theories with local Lorentz and
  diffeomorphism symmetry

abstract:
  We discuss conservation laws for gravity theories invariant under general
coordinate and local Lorentz transformations. We demonstrate the possibility to
formulate these conservation laws in many covariant and noncovariant(ly
looking) ways. An interesting mathematical fact underlies such a diversity:
there is a certain ambiguity in a definition of the (Lorentz-) covariant
generalization of the usual Lie derivative. Using this freedom, we develop a
general approach to construction of invariant conserved currents generated by
an arbitrary vector field on the spacetime. This is done in any dimension, for
any Lagrangian of the gravitational field and of a (minimally or nonminimally)
coupled matter field. A development of the "regularization via relocalization"
scheme is used to obtain finite conserved quantities for asymptotically nonflat
solutions. We illustrate how our formalism works by some explicit examples.


title: The universal 'energy' operator

abstract:
  The "positive square" of any tensor is presented in a universal and unified
manner, valid in Lorentzian manifolds of arbitrary dimension, and independently
of any (anti)-symmetry properties of the tensor. For rank-m tensors, the
positive square has rank 2m. Positive here means future, that is to say,
satisfying the dominant property. The standard energy-momentum and super-energy
tensors are recovered as appropriate parts of the general square. A richer
structure of principal null directions arises.


title: Magnetized black hole as a gravitational lens

abstract:
  We use the Ernst-Schwarzschild solution for a black hole immersed in a
uniform magnetic field to estimate corrections to the bending angle and time
delay due-to presence of weak magnetic fields in galaxies and between galaxies,
and also due-to influence of strong magnetic field near supermassive black
holes. The magnetic field creates a kind of confinement in space, that leads to
increasing of the bending angle and time delay for a ray of light propagating
in the equatorial plane.


title:
Adopting the Uncertainty Principle for the Entropy Estimation of Black
  Holes, de Sitter Space and Rindler Space

abstract:
  By a simple physical consideration and uncertain principle, we derive that
temperature is proportional to the surface gravity and entropy is proportional
to the surface area of the black hole. We apply the same consideration to de
Sitter space and estimate the temperature and entropy of the space, then we
deduce that the entropy is proportional to the boundary surface area. By the
same consideration, we estimate the temperature and entropy in the uniformly
accelerated system (Rindler coordinate). The cases in higher dimensions are
considered.


title:
On a recently proposed metric linear extension of general relativity to
  explain the Pioneer anomaly

abstract:
  Recently, Jaekel and Reynaud put forth a metric linear extension of general
relativity which, in the intentions of its proponents, would be able, among
other things, to provide a gravitational mechanism for explaining the Pioneer
anomaly without contradicting either the equivalence principle or what we know
about the planetary motions. In this paper we perform an independent test of
such an hypothesis by showing that the planets' orbits are, in fact, affected
by the suggested mechanism as well and comparing the resulting effects with the
latest observational determinations. It turns out that the predicted perihelion
precessions, expressed in terms of an adjustable free parameter zeta_P set
equal to the value used to reproduce the magnitude of the Pioneer anomalous
acceleration, are quite different from the observationally determined
extra-advances of such Keplerian element for the inner planets. Conversely, the
values obtained for zeta_P from the determined perihelion extra-rates of the
inner planets turn out to be in disagreement with the value which would be
required to accommodate the Pioneer anomaly. As a consequence, the suggested
explanation of gravitational origin for the Pioneer anomaly, based on the
assumption that zeta_P is constant throughout the Solar System, should be
rejected, at least in its present form.


title: A Maximally Symmetric Vector Propagator

abstract:
  We derive the propagator for a massive vector field on a de Sitter background
of arbitrary dimension. This propagator is de Sitter invariant and possesses
the proper flat spacetime and massless limits. Moreover, the retarded Green's
function inferred from it produces the correct classical response to a test
source. Our result is expressed in a tensor basis which is convenient for
performing quantum field theory computations using dimensional regularization.


title:
Cosmological Models of Universe with Variable Deceleration Parameter in
  Lyra's Manifold

abstract:
  FRW models of the universe have been studied in the cosmological theory based
on Lyra's manifold. A new class of exact solutions has been obtained by
considering a time dependent displacement field for variable deceleration
parameter from which three models of the universe are derived (i) exponential
(ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these
models of the universe are also discussed. Finally some possibilities of
further problems and their investigations have been pointed out.


title: Stabilization of test particles in Induced Matter Kaluza-Klein theory

abstract:
  The stability conditions for the motion of classical test particles in an $%
n $-dimensional Induced Matter Kaluza-Klein theory is studied. We show that
stabilization requires a variance of the strong energy condition for the
induced matter to hold and that it is related to the hierarchy problem.
Stabilization of test particles in a FRW universe is also discussed.


title: Constraining f(R) theories with the energy conditions

abstract:
  A new method to constrain gravitational theories depending on the Ricci
scalar is presented. It is based on the weak energy condition and yields limits
on the parameters of a given theory through the current values of the
derivatives of the scale factor of the Friedmann-Robertson-Walker geometry. A
further constraint depending on the current value of the snap is also given.
Actual constraints (and the corresponding error propagation analysis) are
calculated for two examples, which show that the method is useful in limiting
the possible $f(R)$ theories.


title:
Errata for ``Global existence and scattering for the nonlinear
  Schrodinger equation on Schwarzschild manifolds'', ``Semilinear wave
  equations on the Schwarzschild manifold I: Local Decay Estimates'', and ``The
  wave equation on the Schwarzschild metric II: Local Decay for the spin 2
  Regge Wheeler equation''

abstract:
  In ``Global existence and scattering for the nonlinear Schrodinger equation
on Schwarzschild manifolds'' (math-ph/0002030), ``Semilinear wave equations on
the Schwarzschild manifold I: Local Decay Estimates'' (gr-qc/0310091), and
``The wave equation on the Schwarzschild metric II: Local Decay for the spin 2
Regge Wheeler equation'' (gr-qc/0310066), local decay estimates were proven for
the (decoupled) Schrodinger, wave, and Regge-Wheeler equations on the
Schwarzschild manifold, using commutator methods. Here, we correct a step in
the commutator argument. The corrected argument works either for radial
semilinear equations or general linear equations. This recovers the results in
math-ph/0002030 and gr-qc/0310066, but does not recover the non radial, large
data, semilinear result asserted in the gr-qc/0310091.


title:
A Modified Gravity and its Consequences for the Solar System,
  Astrophysics and Cosmology

abstract:
  A relativistic modified gravity (MOG) theory leads to a self-consistent,
stable gravity theory that can describe the solar system, galaxy and clusters
of galaxies data and cosmology.


title: Towards a Novel no-hair Theorem for Black Holes

abstract:
  We provide strong numerical evidence for a new no-scalar-hair theorem for
black holes in general relativity, which rules out spherical scalar hair of
static four dimensional black holes if the scalar field theory, when coupled to
gravity, satisfies the Positive Energy Theorem. This sheds light on the
no-scalar-hair conjecture for Calabi-Yau compactifications of string theory,
where the effective potential typically has negative regions but where
supersymmetry ensures the total energy is always positive. In theories where
the scalar tends to a negative local maximum of the potential at infinity, we
find the no-scalar-hair theorem holds provided the asymptotic conditions are
invariant under the full anti-de Sitter symmetry group.


title: On the Stability of Planetary Circular Orbits in Noncommutative Spaces

abstract:
  We investigate the effects of space noncommutativity and the generalized
uncertainty principle on the stability of circular orbits of particles in both
a central force potential and Schwarzschild spacetime. We find noncommutative
form of the effective potential which up to first order of noncommutativity
parameter contains an angular momentum dependent extra term. This angular
momentum dependent extra term affects the stability of circular orbits in such
a way that the radius of a stable circular orbit in noncommutative space is
larger than its commutative counterpart. In the case of large angular momentum,
the condition for stability of circular orbits in noncommutative space differs
considerably from commutative case.


title:
Reissner-Nordstr\"{o}m Black Hole Thermodynamics in Noncommutative
  Spaces

abstract:
  This paper considers the effects of space noncommutativity on the
thermodynamics of a Reissner-Nordstr\"{o}m black hole. In the first step, we
extend the ordinary formalism of Bekenstein-Hawking to the case of charged
black holes in commutative space. In the second step we investigate the effects
of space noncommutativity and the generalized uncertainty principle on the
thermodynamics of charged black holes. Finally we compare thermodynamics of
charged black holes in commutative space with thermodynamics of Schwarzschild
black hole in noncommutative space. In this comparison we explore some
conceptual relation between charge and space noncommutativity.


title: Spherical Voids in Newton-Friedmann Universe

abstract:
  We show that the cosmological constant favours significantly the growth of
voids in the universe. This dynamical effect is investigated within a newtonian
approach with an extension to Friedmann-Lema\^{\i}tre model.


title: Deformed dispersion relations and the degree of coherence function

abstract:
  The analysis of the modifications that the presence of a deformed dispersion
relation entails in the roots of the so--called degree of coherence function,
for a beam embodying two different frequencies and moving in a Michelson
interferometer, is carried out. The conditions to be satisfied, in order to
detect this kind of quantum gravity effect, are also obtained.


title:
Transgressing the horizons: Time operator in two-dimensional dilaton
  gravity

abstract:
  We present a Dirac quantization of generic single-horizon black holes in
two-dimensional dilaton gravity. The classical theory is first partially
reduced by a spatial gauge choice under which the spatial surfaces extend from
a black or white hole singularity to a spacelike infinity. The theory is then
quantized in a metric representation, solving the quantum Hamiltonian
constraint in terms of (generalized) eigenstates of the ADM mass operator and
specifying the physical inner product by self-adjointness of a time operator
that is affinely conjugate to the ADM mass. Regularity of the time operator
across the horizon requires the operator to contain a quantum correction that
distinguishes the future and past horizons and gives rise to a quantum
correction in the hole's surface gravity. We expect a similar quantum
correction to be present in systems whose dynamics admits black hole formation
by gravitational collapse.


title: Optical Clocks in Space

abstract:
  The performance of optical clocks has strongly progressed in recent years,
and accuracies and instabilities of 1 part in 10^18 are expected in the near
future. The operation of optical clocks in space provides new scientific and
technological opportunities. In particular, an earth-orbiting satellite
containing an ensemble of optical clocks would allow a precision measurement of
the gravitational redshift, navigation with improved precision, mapping of the
earth's gravitational potential by relativistic geodesy, and comparisons
between ground clocks.


title: Gravitational field of higher dimensional domain walls in Lyra geometry

abstract:
  This paper studies Thick domain wall within the framework of Lyra geometry.
Their exact solutions are obtained in the background of a five dimensional
space-time. The space-time is nonsingular in its both spatial and temporal
behavior. The gravitational field of the wall is shown to be attractive in
nature.


title:
Cosmological models with negative constant deceleration parameter in
  Lyra geometry

abstract:
  Bermann [ Nuovo Cimento B (1983), 74, 182 ] presented a law of variation of
Hubble parameter that yields constant deceleration parameter models of the
Universe. In this paper, we study some cosmological models with negative
constant deceleration parameter within the framework of Lyra geometry.


title: Matched filter for multi-transducers resonant GW antennas

abstract:
  We analyze two kinds of matched filters for data output of a spherical
resonant GW detector. In order to filter the data of a real sphere, a strategy
is proposed, firstly using an omnidirectional in-line filter, which is supposed
to select periodograms with excitations, secondly by performing a directional
filter on such selected periodograms, finding the wave arrival time, direction
and polarization. We point out that, as the analytical simplifications
occurring in the ideal 6 transducers TIGA sphere do not hold for a real sphere,
using a 5 transducers configuration could be a more convenient choice.


title: Topologically massive gravity as a Pais-Uhlenbeck oscillator

abstract:
  We give a detailed account of the free field spectrum and the Newtonian limit
of the linearized "massive" (Pauli-Fierz), "topologically massive"
(Einstein-Hilbert-Chern-Simons) gravity in 2+1 dimensions about a Minkowski
spacetime. For a certain ratio of the parameters, the linearized free theory is
Jordan-diagonalizable and reduces to a degenerate "Pais-Uhlenbeck" oscillator
which, despite being a higher derivative theory, is ghost-free.


title: Homotopy approach to quantum gravity

abstract:
  I construct a finite-dimensional quantum theory from general relativity by a
homotopy method. Its quantum history is made up of at least two levels of
fermionic elements. Its unitary group has the diffeomorphism group as singular
limit. Its gravitational metrical form is the algebraic square. Its spinors are
multivectors.


title:
The Bell-Szekeres Solution and Related Solutions of the Einstein-Maxwell
  Equations

abstract:
  A novel technique for solving some head-on collisions of plane homogeneous
light-like signals in Einstein-Maxwell theory is described. The technique is a
by-product of a re-examination of the fundamental Bell-Szekeres solution in
this field of study. Extensions of the Bell-Szekeres collision problem to
include light-like shells and gravitational waves are described and a family of
solutions having geometrical and topological properties in common with the
Bell-Szekeres solution is derived.


title: A Keplerian gaseous disk around the B0 star R Mon

abstract:
  We present high-angular resolution observations of the circumstellar disk
around the massive Herbig Be star R Mon (M~8 Msun) in the continuum at 2.7mm
and 1.3mm and the CO 1->0 and 2->1 rotational lines. Based on the new 1.3mm
continuum image we estimate a disk mass (gas+dust) of 0.007 Msun and an outer
radius of <150 AU. Our CO images are consistent with the existence of a
Keplerian rotating gaseous disk around this star. Up to our knowledge, this is
the most clear evidence for the existence of Keplerian disks around massive
stars reported thus far. The mass and physical characteristics of this disk are
similar to thoseof the more evolved T Tauri stars and indicate a shorter
timescale for the evolution and dispersal of circumstellar disks around massive
stars which lose most of their mass before the star becomes visible.


title: Analytical formulas for gravitational lensing: higher order calculation

abstract:
  We extend to higher order a recently published method for calculating the
deflection angle of light in a general static and spherically symmetric metric.
Since the method is convergent we obtain very accurate analytical expressions
that we compare with numerical results.


title: On a Completely Antisymmetric Cartan Torsion Tensor

abstract:
  We discuss the general structure of metric geometries, and how metricity
implies the complete antisymmetry of Cartan tensor; an application in the frame
of Lie group theory is given. Interpretations of the completely antisymmetric
torsion in physical models are reviewed.


title: A numerical study of the quasinormal mode excitation of Kerr black holes

abstract:
  We present numerical results from three-dimensional evolutions of scalar
perturbations of Kerr black holes. Our simulations make use of a high-order
accurate multi-block code which naturally allows for fixed adaptivity and
smooth inner (excision) and outer boundaries. We focus on the quasinormal
ringing phase, presenting a systematic method for extraction of the quasinormal
mode frequencies and amplitudes and comparing our results against perturbation
theory.
  The amplitude of each mode depends exponentially on the starting time of the
quasinormal regime, which is not defined unambiguously. We show that this
time-shift problem can be circumvented by looking at appropriately chosen
relative mode amplitudes. From our simulations we extract the quasinormal
frequencies and the relative and absolute amplitudes of corotating and
counterrotating modes (including overtones in the corotating case). We study
the dependence of these amplitudes on the shape of the initial perturbation,
the angular dependence of the mode and the black hole spin, comparing against
results from perturbation theory in the so-called asymptotic approximation. We
also compare the quasinormal frequencies from our numerical simulations with
predictions from perturbation theory, finding excellent agreement. Finally we
study under what conditions the relative amplitude between given pairs of modes
gets maximally excited and present a quantitative analysis of rotational
mode-mode coupling. The main conclusions and techniques of our analysis are
quite general and, as such, should be of interest in the study of ringdown
gravitational waves produced by astrophysical gravitational wave sources.


title: Accelerating Taub-NUT and Eguchi-Hanson solitons in four dimensions

abstract:
  We construct new solutions of the vacuum Einstein field equations in four
dimensions via a solution generating method utilizing the SL(2,R) symmetry of
the reduced Lagrangian. We apply the method to an accelerating version of the
Zipoy-Voorhees solution and generate new solutions which we interpret to be the
accelerating versions of the Zipoy-Voorhees generalisation of the Taub-NUT
solution (with Lorentzian signature) and the Zipoy-Voorhees generalisation of
the Eguchi-Hanson solitons (with Euclidean signature). As an intermediary in
the solution-generating process we obtain charged versions of the accelerated
Zipoy-Voorhees-like families of solutions. Finally we present the accelerating
version of the Taub-NUT solution and discuss its properties.


title: General Relativity at an interface

abstract:
  In this work a simple toy model for a free interface between bulk phases in
space and time is presented, derived from the balance equations for extensive
thermodynamic variables of Meinhold-Heerlein. In this case the free interface
represents geodesics in the space-time, allowing the derivation of the
Einstein's equations for gravitational fields. The effect of the balance
equation is examined and a simple expression for cold dark matter is derived.
The thermodynamically meaning of this model is also discussed.


title: Accelerating Universe Around A Blackhole

abstract:
  We have assumed that in a physical universe a blackhole is created some
where. We conjecture that this blackhole will then separate itself from the
physical universe and will build up an extra dimensional entity associated with
the physical universe. The extra dimensional entity we suppose to be orthogonal
to the physical universe. We further conjecture that this blackhole is a
Schwartzschild blackhole. We assume that this physical universe and the
blackhole span a seven dimensional space with a common time coordinate. We then
generate the Einstein equation. Using the time-blackhole and the time-time
component of the equation we show that the Hubble parameter is positive and
time dependent if we conjecture that both scale factor and the radius of the
blackhole reduces exponetially. Under the same assumption we have also
calculated the deacceleration parameter and shown that under certain constrain
the universe accelerates.


title:
Demonstration of displacement- and frequency-noise free laser
  interferometry using bi-directional Mach-Zehnder interferometers

abstract:
  We have demonstrated displacement- and frequency-noise free laser
interferometry (DFI) by partially implementing a recently proposed optical
configuration using bi-directional Mach-Zehnder interferometers (MZI). This
partial implementation, the minimum necessary to be called DFI, has confirmed
the essential feature of DFI: the combination of two MZI signals can be carried
out in a way which cancels displacement noise of the mirrors while maintaining
gravitational wave signals. The attained maximum displacement noise suppression
allowed a simulated-SNR of 45dB.