title: Tolman-Bondi Space-Time in Brane World Scenario

abstract:
  In the present work, inhomogeneous Tolman-Bondi type dust space-time is
studied on the brane. There are two sets of solutions of the above model. The
first solution represents either a collapsing model starting from an infinite
volume at infinite past to the singularity or a model starting from a
singularity and expanding for ever having a transition from decelerating phase
to accelerating phase. The first solution shows that the end state of collapse
may be black hole or a naked singularity depending signs of various parameters
involved. The second solution represents a bouncing model where the bounce
occurs at different comoving radii at different epochs.


title: Euclidean solutions in Einstein-Yang-Mills-dilaton theory

abstract:
  We present arguments for the existence of a new type of solutions of the
Euclidean Einstein-Yang-Mills-dilaton theory in $d=4$ dimensions. Possesing
nonvanishing nonabelian charges, these nonselfdual configurations have no
counterparts on the Lorentzian section. They provide, however, new saddle
points in the Euclidean path integral.


title:
Energy Distribution of the Universe in the Bianchi type II Cosmological
  Models

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/9910015, gr-qc/0008034, and hep-th/0308070.
  This paper also has excessive overlap with the following papers also written
by the authors or their collaborators: gr-qc/0601070 and gr-qc/0509047.


title: Tidal Dynamics in Kerr Spacetime

abstract:
  The motion of free nearby test particles relative to a stable equatorial
circular geodesic orbit about a Kerr source is investigated. It is shown that
the nonlinear generalized Jacobi equation can be transformed in this case to an
autonomous form. Tidal dynamics beyond the critical speed c/sqrt(2) is studied.
We show, in particular, that a free test particle vertically launched from the
circular orbit parallel or antiparallel to the Kerr rotation axis is tidally
accelerated if its initial relative speed exceeds c/sqrt(2). Possible
applications of our results to high-energy astrophysics are briefly mentioned.


title: Genuine covariant description of Hamiltonian dynamics

abstract:
  After reviewing the covariant description of Hamiltonian dynamics, some
applications are done to the non-relativistic isotropic three-dimensional
harmonic oscillator, Rovelli's model, and SO(3,1) BF theories.


title: Aspects of spacetime-symmetry violations

abstract:
  The violation of spacetime symmetries provides a promising candidate signal
for underlying physics, possibly arising at the Planck scale. This talk gives
an overview over various aspects in the field, including some mechanisms for
Lorentz breakdown, the SME test framework, and phenomenological signatures for
such effects.


title:
On the Analytic Structure of a Family of Hyperboloidal Beams of
  Potential Interest for Advanced LIGO

abstract:
  For the baseline design of the advanced Laser Interferometer
Gravitational-wave Observatory (LIGO), use of optical cavities with
non-spherical mirrors supporting flat-top ("mesa") beams, potentially capable
of mitigating the thermal noise of the mirrors, has recently drawn a
considerable attention. To reduce the severe tilt-instability problems
affecting the originally conceived nearly-flat, "Mexican-hat-shaped" mirror
configuration, K. S. Thorne proposed a nearly-concentric mirror configuration
capable of producing the same mesa beam profile on the mirror surfaces.
Subsequently, Bondarescu and Thorne introduced a generalized construction that
leads to a one-parameter family of "hyperboloidal" beams which allows
continuous spanning from the nearly-flat to the nearly-concentric mesa beam
configurations. This paper is concerned with a study of the analytic structure
of the above family of hyperboloidal beams. Capitalizing on certain results
from the applied optics literature on flat-top beams, a physically-insightful
and computationally-effective representation is derived in terms of
rapidly-converging Gauss-Laguerre expansions. Moreover, the functional relation
between two generic hyperboloidal beams is investigated. This leads to a
generalization (involving fractional Fourier transform operators of complex
order) of some recently discovered duality relations between the nearly-flat
and nearly-concentric mesa configurations. Possible implications and
perspectives for the advanced LIGO optical cavity design are discussed.


title: Doubly Special Relativity: A New Relativity or Not?

abstract:
  Double Special Relativity theories are the relativistic theories in which the
transformations between inertial observers are characterized by two
observer-independent scales of the light speed and the Planck length. We study
two main examples of these theories and want to show that these theories are
not the new theories of relativity, but only are re-descriptions of Einstein's
special relativity in the non-conventional coordinates.


title:
Invariance under complex transformations, and its relevance to the
  cosmological constant problem

abstract:
  In this paper we study a new symmetry argument that results in a vacuum state
with strictly vanishing vacuum energy. This argument exploits the well-known
feature that de Sitter and Anti- de Sitter space are related by analytic
continuation. When we drop boundary and hermiticity conditions on quantum
fields, we get as many negative as positive energy states, which are related by
transformations to complex space. The paper does not directly solve the
cosmological constant problem, but explores a new direction that appears
worthwhile.


title: Dynamics of Generalized Assisted Inflation

abstract:
  We study the dynamics of multiple scalar fields and a barotropic fluid in an
FLRW-universe. The scalar potential is a sum of exponentials. All critical
points are constructed and these include scaling and de Sitter solutions. A
stability analysis of the critical points is performed for generalized assisted
inflation, which is an extension of assisted inflation where the fields
mutually interact. Effects in generalized assisted inflation which differ from
assisted inflation are emphasized. One such a difference is that an
(inflationary) attractor can exist if some of the exponential terms in the
potential are negative.


title: Evolution of 3D Boson Stars with Waveform Extraction

abstract:
  Numerical results from a study of boson stars under nonspherical
perturbations using a fully general relativistic 3D code are presented together
with the analysis of emitted gravitational radiation. We have constructed a
simulation code suitable for the study of scalar fields in space-times of
general symmetry by bringing together components for addressing the initial
value problem, the full evolution system and the detection and analysis of
gravitational waves. Within a series of numerical simulations, we explicitly
extract the Zerilli and Newman-Penrose scalar $\Psi_4$ gravitational waveforms
when the stars are subjected to different types of perturbations. Boson star
systems have rapidly decaying nonradial quasinormal modes and thus the complete
gravitational waveform could be extracted for all configurations studied. The
gravitational waves emitted from stable, critical, and unstable boson star
configurations are analyzed and the numerically observed quasinormal mode
frequencies are compared with known linear perturbation results. The
superposition of the high frequency nonspherical modes on the lower frequency
spherical modes was observed in the metric oscillations when perturbations with
radial and nonradial components were applied. The collapse of unstable boson
stars to black holes was simulated. The apparent horizons were observed to be
slightly nonspherical when initially detected and became spherical as the
system evolved. The application of nonradial perturbations proportional to
spherical harmonics is observed not to affect the collapse time. An unstable
star subjected to a large perturbation was observed to migrate to a stable
configuration.


title: Quantum Mechanical Fluctuations at the End of Inflation

abstract:
  During the inflationary phase of the early universe, quantum fluctuations in
the vacuum generate particles as they stretch beyond the Hubble length. These
fluctuations are thought to result in the density fluctuations and
gravitational radiation that we can try to observe today. It is possible to
calculate the quantum-mechanical evolution of these fluctuations during
inflation and the subsequent expansion of the universe until the present day.
The present calculation of this evolution directly exposes the particle
creation during accelerated expansion and while a fluctuation is larger than
the Hubble length. Because all fluctuations regardless of their scale today
began as the vacuum state in the early universe, the current quantum mechanical
state of fluctuations is correlated on different scales and in different
directions.


title:
Hamilton's equations of motion from the SU(1,1)/U(1) symmetry of
  Schwarzschild radial dynamics

abstract:
  Particles moving on a radial ray with respect to a Schwarzschild mass are
shown to have SU(1,1)/U(1) dynamical symmetry. This symmetry is used to
identify a global time variable shared by all test particles moving on a radial
ray. With this time variable, Hamilton's equations for particles on a radial
ray have the form of the harmonic oscillator. The SU(1,1)/U(1) symmetry, in
conjunction with the well defined time variable and observer, assists in
determining the quantization of the motion of the test particles.


title: Physics of dark energy particles

abstract:
  We consider the astrophysical and cosmological implications of the existence
of a minimum density and mass due to the presence of the cosmological constant.
If there is a minimum length in nature, then there is an absolute minimum mass
corresponding to a hypothetical particle with radius of the order of the Planck
length. On the other hand, quantum mechanical considerations suggest a
different minimum mass. These particles associated with the dark energy can be
interpreted as the ``quanta'' of the cosmological constant. We study the
possibility that these particles can form stable stellar-type configurations
through gravitational condensation, and their Jeans and Chandrasekhar masses
are estimated. From the requirement of the energetic stability of the minimum
density configuration on a macroscopic scale one obtains a mass of the order of
10^55 g, of the same order of magnitude as the mass of the universe. This mass
can also be interpreted as the Jeans mass of the dark energy fluid. Furthermore
we present a representation of the cosmological constant and of the total mass
of the universe in terms of `classical' fundamental constants.


title: Exact models for isotropic matter

abstract:
  We study the Einstein-Maxwell system of equations in spherically symmetric
gravitational fields for static interior spacetimes. The condition for pressure
isotropy is reduced to a recurrence equation with variable, rational
coefficients. We demonstrate that this difference equation can be solved in
general using mathematical induction. Consequently we can find an explicit
exact solution to the Einstein-Maxwell field equations. The metric functions,
energy density, pressure and the electric field intensity can be found
explicitly. Our result contains models found previously including the neutron
star model of Durgapal and Bannerji. By placing restrictions on parameters
arising in the general series we show that the series terminate and there exist
two linearly independent solutions. Consequently it is possible to find exact
solutions in terms of elementary functions, namely polynomials and algebraic
functions.


title:
Radiative Symmetry Breaking and Dynamical Origin of Cosmological
  Constant in $\phi^4$ Theory with Non-Linear Curvature Coupling

abstract:
  A scalar self-interacting theory non-linearly coupled with some power of the
curvature have a possibility to explain the current smallness of the
cosmological constant. Here one concentrate on a massless scalar field in the
four-dimensional Fridmann-Robertson-Walker (FRW) spacetime with flat spatial
part. One show the phase structure of radiative symmetry breaking and review a
dynamical resolution of the cosmological constant problem.


title: The universe out of a monopole in the laboratory?

abstract:
  To explore the possibility that an inflationary universe can be created out
of a stable particle in the laboratory, we consider the classical and quantum
dynamics of a magnetic monopole in the thin-shell approximation. Classically
there are three types of solutions: stable, collapsing and inflating monopoles.
We argue that the transition from a stable monopole to an inflating one could
occur either by collision with a domain wall or by quantum tunneling.


title: Black Holes and Generalized Scalar Field

abstract:
  We study the possibility of occurrence of scalar hair with a non-canonical
kinetic term for a static, spherically symmetric asymptotically flat black hole
spacetime. We first obtain a general equation for this purpose and then
consider various examples for the kinetic term $F(X)$ with
$X=-{1\over{2}}\partial^{\mu}\phi\partial_{\mu}\phi$. Our study shows that for
a tachyon field with a positive potential, which naturally arises in open
string theory, asymptotically flat a static black hole solution does not exist.


title: Quantum Nature of the Big Bang

abstract:
  Some long standing issues concerning the quantum nature of the big bang are
resolved in the context of homogeneous isotropic models with a scalar field.
Specifically, the known results on the resolution of the big bang singularity
in loop quantum cosmology are significantly extended as follows: i) the scalar
field is shown to serve as an internal clock, thereby providing a detailed
realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac
observables and semi-classical states are constructed rigorously; iii) the
Hamiltonian constraint is solved numerically to show that the big bang is
replaced by a big bounce. Thanks to the non-perturbative, background
independent methods, unlike in other approaches the quantum evolution is
deterministic across the deep Planck regime.


title: Strong field gravitational lensing in scalar tensor theories

abstract:
  Strong field gravitational lensing in the Brans-Dicke theory has been
studied. The deflection angle for photons passing very close to the photon
sphere is estimated for the static spherically symmetric space-time of the
theory and the position and magnification of the relativistic images are
obtained. Modeling the super massive central object of the galaxy by the
Brans-Dicke space-time, numerical values of different strong lensing observable
are estimated. It is found that against the expectation there is no significant
scalar field effect in the strong field observable lensing parameters. This
observation raises question on the potentiality of the strong field lensing to
discriminate different gravitational theories.


title:
Algebrodynamics in complex space-time and the complex-quaternionic
  origin of Minkowski geometry

abstract:
  We present a scheme of biquaternionic algebrodymamics based on a nonlinear
generalization of the Cauchy-Riemann holomorphy conditions considered therein
as fundamental field equations. The automorphism group SO(3,C) of the
biquaternion algebra acts as a proper Lorentz group on a real space whose
coordinates are bilinear in the complex coordinates of biquaternionic vector
space. A new invariant of Lorentz transformations then arises - the geometric
phase. This invariant can be responsible for the quantum properties of
particles associated in this approach with field singularities. Some new
notions are introduced, related to ``hidden'' complex dynamics: ``observable''
space-time, the ensemble of identical correlated particles-singularities
(``duplicons'') and others.


title: Could the Pioneer anomaly have a gravitational origin?

abstract:
  If the Pioneer anomaly has a gravitational origin, it would, according to the
equivalence principle, distort the motions of the planets in the Solar System.
Since no anomalous motion of the planets has been detected, it is generally
believed that the Pioneer anomaly can not originate from a gravitational source
in the Solar System. However, this conclusion becomes less obvious when
considering models that either imply modifications to gravity at long range or
gravitational sources localized to the outer Solar System, given the
uncertainty in the orbital parameters of the outer planets. Following the
general assumption that the Pioneer spacecraft move geodesically in a
spherically symmetric spacetime metric, we derive the metric disturbance that
is needed in order to account for the Pioneer anomaly. We then analyze the
residual effects on the astronomical observables of the three outer planets
that would arise from this metric disturbance, given an arbitrary metric theory
of gravity. Providing a method for comparing the computed residuals with actual
residuals, our results imply that the presence of a perturbation to the
gravitational field necessary to induce the Pioneer anomaly is in conflict with
available data for the planets Uranus and Pluto, but not for Neptune. We
therefore conclude that the motion of the Pioneer spacecraft must be
non-geodesic. Since our results are model independent within the class of
metric theories of gravity, they can be applied to rule out any model of the
Pioneer anomaly that implies that the Pioneer spacecraft move geodesically in a
perturbed spacetime metric, regardless of the origin of this metric
disturbance.


title: Avoidance of singularities in spherically symmetric charged dust

abstract:
  In spherically symmetric charged dust, just like in electrically neutral
dust, two kinds of singularity may be present: the Big Bang/Crunch (BB/BC)
singularity, and shell crossings. Quite unlike in neutral dust, the BB/BC
singularity may be avoided. When the absolute value of the charge density r is
everywhere small compared to the mass-energy density d (|r| < D = \sqrt{G} d /
c^2), the conditions that allow the model to avoid the BB/BC singularity
necessarily lead to shell crossings. There exist sets of initial conditions
that allow us to avoid both singularities (when either |r| > D everywhere, or
|r| = D at the center of symmetry while |r| < D elsewhere). In those cases,
both kinds of singularity may be avoided for a sufficiently long period that a
body of charged dust may go through the tunnel between the singularities in the
maximally extended Reissner -- Nordstrom spacetime, to emerge into another
asymptotically flat region. An explicit example of such a configuration is
presented and discussed. It does not contradict any astrophysical constraints.


title:
An exhaustive classification of aligned Petrov type D purely magnetic
  perfect fluids

abstract:
  We prove that aligned Petrov type D purely magnetic perfect fluids are
necessarily locally rotationally symmetric and hence are all explicitly known.


title: Huygens-Fresnel Principle in Superspace

abstract:
  We first roughly present a summary of the optico-mechanical analogy, which
has always been so profitable in physics. Then we put forward a
geometrodynamical formulation of gravity suitable to our intentions, both
formally and conceptually. We present difficulties in some approaches to
canonically quantize gravity which can be amended by the idea put forward in
this paper, which we introduce in the last section. It consists basically in
trying to find an intermediary between the quantization step going from the
classical superhamiltonian constraint to the Wheeler-DeWitt equation. This is
accomplished by inputting interference beyond the WKB approximation, through a
type of Huygens-Fresnel Principle (HFP) in superspace.


title:
Using Muonic Hydrogen in Optical Spectroscopy Experiment to Detect Extra
  Dimensions

abstract:
  Considering that gravitational force might deviate from Newton's
inverse-square law (ISL) and become much stronger in small scale, we propose a
kind of optical spectroscopy experiment to detect this possible deviation and
take electronic, muonic and tauonic hydrogen atoms as examples. This experiment
might be used to indirectly detect the deviation of ISL down to nanometer scale
and to explore the possibility of three extra dimensions in ADD's model, while
current direct gravity tests cannot break through micron scale and go beyond
two extra dimensions scenario.


title: Some Aspects of Virtual Black Holes

abstract:
  In this paper we shall consistently third quantize modified gravity. Then we
shall analyse certain aspects of virtual black holes in this third quantized
modified gravity. We will see how a statistical mechanical origin for the
Bekenstein-Hawking entropy naturally arises in this model. Furthermore, in this
model the area and thus the entropy of a real macroscopic black hole is
quantized. Virtual black holes cause loss of quantum coherence and this gives
an intrinsic entropy to all physical systems which can be used to define a
direction of time and hence provide a solution to the problem of time.


title: Solar System planetary orbital motions and dark matter

abstract:
  In this paper we explicitly work out the effects that a spherically symmetric
distribution of dark matter with constant density would induce on the Keplerian
orbital elements of the Solar System planets and compare them with the latest
results in planetary orbit determination from the EPM2004 ephemerides. It turns
out that the longitudes of perihelia and the mean longitudes are affected by
secular precessions. The resulting upper bounds on dark matter density,
obtained from the EPM2004 formal errors in the determined mean longitude shifts
over 90 years, lie in the range 10^-19-10^-20 g cm^-3 with a peak of 10^-22 g
cm^-3 for Mars. Suitable combinations of the planetary mean longitudes and
perihelia, which cancel out the aliasing impact of some of the unmodelled or
mismodelled forces of the dynamical models of EPM2004, yield a global upper
bound of 7 10^-20 g cm^-3 and 4 10^-19 g cm^-3, respectively.


title: Compensation of Strong Thermal Lensing in High Optical Power Cavities

abstract:
  In an experiment to simulate the conditions in high optical power advanced
gravitational wave detectors such as Advanced LIGO, we show that strong thermal
lenses form in accordance with predictions and that they can be compensated
using an intra-cavity compensation plate heated on its cylindrical surface. We
show that high finesse ~1400 can be achieved in cavities with internal
compensation plates, and that the cavity mode structure can be maintained by
thermal compensation. It is also shown that the measurements allow a direct
measurement of substrate optical absorption in the test mass and the
compensation plate.


title: Extended quintessence, inflation, and stable de Sitter spaces

abstract:
  A new gauge-invariant criterion for stability against inhomogeneous
perturbations of de Sitter space is applied to scenarios of dark energy and
inflation in scalar-tensor gravity. The results extend previous studies.


title:
On the influence of the global cosmological expansion on the local
  dynamics in the Solar System

abstract:
  In this expository paper we address the question of whether, and to what
extent, the cosmological expansion influences the dynamics on small scales (as
compared to cosmological ones), particularly in our Solar System. We
distinguish between dynamical and kinematical effects and critically review the
status of both as presented in the current literature.


title: ZM theory I: Introduction and Lorentz covariance

abstract:
  We consider defining time as a function of a cyclical field, an abstraction
of a clock. The definition of time corresponds to a novel interpretation of the
relationship between space-time coordinates of observers at different locations
in space. As a first test of the utility of this definition, we show that it
leads to a Lorentz covariant description of space-time. This derivation of
Lorenz covariance provides a starting point for considering more general
constructions that relate to physical laws. The definition of time couples time
to space, making time not orthogonal to space, and making dynamics a result of
geometry, providing a vehicle for curved space-time theories that generalize
general relativity.


title: Quantum Riemannian Geometry and Black Holes

abstract:
  Black Holes have always played a central role in investigations of quantum
gravity. This includes both conceptual issues such as the role of classical
singularities and information loss, and technical ones to probe the consistency
of candidate theories. Lacking a full theory of quantum gravity, such studies
had long been restricted to black hole models which include some aspects of
quantization. However, it is then not always clear whether the results are
consequences of quantum gravity per se or of the particular steps one had
undertaken to bring the system into a treatable form. Over a little more than
the last decade loop quantum gravity has emerged as a widely studied candidate
for quantum gravity, where it is now possible to introduce black hole models
within a quantum theory of gravity. This makes it possible to use only quantum
effects which are known to arise also in the full theory, but still work in a
rather simple and physically interesting context of black holes. Recent
developments have now led to the first physical results about non-rotating
quantum black holes obtained in this way. Restricting to the interior inside
the Schwarzschild horizon, the resulting quantum model is free of the classical
singularity, which is a consequence of discrete quantum geometry taking over
for the continuous classical space-time picture. This fact results in a change
of paradigm concerning the information loss problem. The horizon itself can
also be studied in the quantum theory by imposing horizon conditions at the
level of states. Thereby one can illustrate the nature of horizon degrees of
freedom and horizon fluctuations. All these developments allow us to study the
quantum dynamics explicitly and in detail which provides a rich ground to test
the consistency of the full theory.


title: Dynamics of Scalar Field in Polymer-like Representation

abstract:
  In recent twenty years, loop quantum gravity, a background independent
approach to unify general relativity and quantum mechanics, has been widely
investigated. We consider the quantum dynamics of a real massless scalar field
coupled to gravity in this framework. A Hamiltonian operator for the scalar
field can be well defined in the coupled diffeomorphism invariant Hilbert
space, which is both self-adjoint and positive. On the other hand, the
Hamiltonian constraint operator for the scalar field coupled to gravity can be
well defined in the coupled kinematical Hilbert space. There are 1-parameter
ambiguities due to scalar field in the construction of both operators. The
results heighten our confidence that there is no divergence within this
background independent and diffeomorphism invariant quantization approach of
matter coupled to gravity. Moreover, to avoid possible quantum anomaly, the
master constraint programme can be carried out in this coupled system by
employing a self-adjoint master constraint operator on the diffeomorphism
invariant Hilbert space.


title: Finite cosmology and a CMB cold spot

abstract:
  The standard cosmological model posits a spatially flat universe of infinite
extent. However, no observation, even in principle, could verify that the
matter extends to infinity. In this work we model the universe as a finite
spherical ball of dust and dark energy, and obtain a lower limit estimate of
its mass and present size: the mass is at least 5 x 10^23 solar masses and the
present radius is at least 50 Gly. If we are not too far from the dust-ball
edge we might expect to see a cold spot in the cosmic microwave background, and
there might be suppression of the low multipoles in the angular power spectrum.
Thus the model may be testable, at least in principle. We also obtain and
discuss the geometry exterior to the dust ball; it is Schwarzschild-de Sitter
with a naked singularity, and provides an interesting picture of cosmogenesis.
Finally we briefly sketch how radiation and inflation eras may be incorporated
into the model.


title: Holographic Dark Energy and the Universe Expansion Acceleration

abstract:
  By incorporating the holographic principle in a time-depending Lambda-term
cosmology, new physical bounds on the arbitrary parameters of the model can be
obtained. Considering then the dark energy as a purely geometric entity, for
which no equation of state has to be introduced, it is shown that the resulting
range of allowed values for the parameters may explain both the coincidence
problem and the universe accelerated expansion, without resorting to any kind
of additional structures.


title:
A multi-block infrastructure for three-dimensional time-dependent
  numerical relativity

abstract:
  We describe a generic infrastructure for time evolution simulations in
numerical relativity using multiple grid patches. After a motivation of this
approach, we discuss the relative advantages of global and patch-local tensor
bases. We describe both our multi-patch infrastructure and our time evolution
scheme, and comment on adaptive time integrators and parallelisation. We also
describe various patch system topologies that provide spherical outer and/or
multiple inner boundaries.
  We employ penalty inter-patch boundary conditions, and we demonstrate the
stability and accuracy of our three-dimensional implementation. We solve both a
scalar wave equation on a stationary rotating black hole background and the
full Einstein equations. For the scalar wave equation, we compare the effects
of global and patch-local tensor bases, different finite differencing
operators, and the effect of artificial dissipation onto stability and
accuracy. We show that multi-patch systems can directly compete with the
so-called fixed mesh refinement approach; however, one can also combine both.
For the Einstein equations, we show that using multiple grid patches with
penalty boundary conditions leads to a robustly stable system. We also show
long-term stable and accurate evolutions of a one-dimensional non-linear gauge
wave. Finally, we evolve weak gravitational waves in three dimensions and
extract accurate waveforms, taking advantage of the spherical shape of our grid
lines.


title: Energy Distribution in a Schwarzschild-like Spacetime

abstract:
  In this paper, utilizing M{\o}ller's energy-momentum complex, we explicitly
evaluate the energy and momentum density associated with a metric describing a
four-dimensional, Schwarzschild-like, spacetime derived from an effective
gravity coupled with a U(1) gauge field in the context of a D3-brane dynamics
in the classical regime, i.e., between the asymptotic and the Planck regime.


title: Analytical formulas for gravitational lensing

abstract:
  In this paper we discuss a new method which can be used to obtain arbitrarily
accurate analytical expressions for the deflection angle of light propagating
in a given metric. Our method works by mapping the integral into a rapidly
convergent series and provides extremely accurate approximations already to
first order. We have derived a general first order formula for a generic
spherically symmetric static metric tensor and we have tested it in four
different cases.


title:
Energy distribution in the dyadosphere of a Reissner-Nordstrom black
  hole in Moller's prescription

abstract:
  The energy and momentum distributions in the dyadosphere of a
Reissner-Nordstrom black hole are evaluated. The Moller's energy-momentum
complex is employed for this computation. The spacetime under study is modified
due to the effects of vacuum fluctuations in the dyadosphere. Therefore, the
corrected Reissner-Nordstrom black hole metric takes into account the first
contribution of the weak field limit of one-loop QED. Furthermore, a comparison
and a consequent connection between our results that those already existing in
the literature is provided. We hypothesize that when the energy distribution is
of specific form there is a relation that connects the coefficients in the
Einstein's prescription with those in the Moller's prescription.


title: On time variation of G in multidimensional models with two curvatures

abstract:
  Expressions for G-dot are considered in a multidimensional model with an
Einstein internal space and a multicomponent perfect fluid. In the case of two
non-zero curvatures without matter, a mechanism for prediction of small G-dot
is suggested. The result is compared with exact
  (1+3+6)-dimensional solutions. A two-component example with two matter
sources (dust + 5-brane) and two Ricci-flat factor spaces is also considered.


title:
Final fate of spherically symmetric gravitational collapse of a dust
  cloud in Einstein-Gauss-Bonnet gravity

abstract:
  We give a model of the higher-dimensional spherically symmetric gravitational
collapse of a dust cloud in Einstein-Gauss-Bonnet gravity. A simple formulation
of the basic equations is given for the spacetime $M \approx M^2 \times
K^{n-2}$ with a perfect fluid and a cosmological constant. This is a
generalization of the Misner-Sharp formalism of the four-dimensional
spherically symmetric spacetime with a perfect fluid in general relativity. The
whole picture and the final fate of the gravitational collapse of a dust cloud
differ greatly between the cases with $n=5$ and $n \ge 6$. There are two
families of solutions, which we call plus-branch and the minus-branch
solutions. Bounce inevitably occurs in the plus-branch solution for $n \ge 6$,
and consequently singularities cannot be formed. Since there is no trapped
surface in the plus-branch solution, the singularity formed in the case of
$n=5$ must be naked. In the minus-branch solution, naked singularities are
massless for $n \ge 6$, while massive naked singularities are possible for
$n=5$. In the homogeneous collapse represented by the flat
Friedmann-Robertson-Walker solution, the singularity formed is spacelike for $n
\ge 6$, while it is ingoing-null for $n=5$. In the inhomogeneous collapse with
smooth initial data, the strong cosmic censorship hypothesis holds for $n \ge
10$ and for $n=9$ depending on the parameters in the initial data, while a
naked singularity is always formed for $5 \le n \le 8$. These naked
singularities can be globally naked when the initial surface radius of the dust
cloud is fine-tuned, and then the weak cosmic censorship hypothesis is
violated.


title: Leading Log Solution for Inflationary Yukawa

abstract:
  We generalize Starobinskii's stochastic technique to the theory of a
massless, minimally coupled scalar interacting with a massless fermion in a
locally de Sitter geometry. The scalar is an ``active'' field that can engender
infrared logarithms. The fermion is a ``passive'' field that cannot cause
infrared logarithms but which can carry them, and which can also induce new
interactions between the active fields. The procedure for dealing with passive
fields is to integrate them out, then stochastically simplify the resulting
effective action following Starobinski\u{\i}. Because Yukawa theory is
quadratic in the fermion this can be done explicitly using the classic solution
of Candelas and Raine. We check the resulting stochastic formulation against an
explicit two loop computation. We also derive a nonperturbative, leading log
result for the stress tensor. Because the scalar effective potential induced by
fermions is unbounded below, back-reaction from this model might dynamically
cancel an arbitrarily large cosmological constant.


title: A Comment on Emergent Gravity

abstract:
  This paper is a set of notes that we wrote concerning the first version of
Emergent Gravity [gr-qc/0602022]. It is our version of an exercise that we
proposed to some of our students. The idea was to find mathematical errors and
inconsistencies on some recent articles published in scientific journals and in
the arXiv, and we did.


title: A New Result on the Dynamical Symmetry of Spherical Collapse

abstract:
  A dynamical symmetry for spherical collapse has been studied using a linear
transformation of the initial data set (mass and kinetic energy function) and
the area radius. With proper choice of the initial area radius, the evolution
as well as the physical parameters namely energy density and shear remain
invariant both initially and at any time instant. Finally, it is found that the
final outcome of collapse depends on the initial choice of the area radius.


title:
Particles Under Extreme Conditions: Part I Quantum Modified Null
  Trajectories in Schwarzschild Spacetime. Part II Superfluid Behaviour of the
  2+1d NJL Model at High Density

abstract:
  In part I we study quantum modified photon trajectories in a Schwarzschild
blackhole spacetime. The photon vacuum polarization effect in curved spacetime
leads to birefringence, i.e. the photon velocity becomes c+/-dc depending on
its polarization. This velocity shift then results in modified photon
trajectories. In this work we give an introduction to this quantum effect in
relativity and we study its effects in Schwarzschild spacetime for critical
orbits. Some key results are that the critical orbits are shifted depending on
polarization and the event horizon remains fixed.
  In Part II we use the 2+1d Nambu-Jona-Lasino NJL model to study the
superfluid behaviour of two-dimensional quark matter. We begin with an
introduction to QCD its symmetries and the NJL model. We then go on to study
the 2+1d NJL model. We show that at high density the 2+1d NJL model represents
a relativistic gapless thin film BCS superfluid.


title: Highly Irregular Quantum Constraints

abstract:
  Motivated by a recent paper of Louko and Molgado, we consider a simple system
with a single classical constraint R(q)=0. If q_l denotes a generic solution to
R(q)=0, our examples include cases where R'(q_l)\ne 0 (regular constraint) and
R'(q_l)=0 (irregular constraint) of varying order as well as the case where
R(q)=0 for an interval, such as a \leq q \leq b. Quantization of irregular
constraints is normally not considered; however, using the projection operator
formalism we provide a satisfactory quantization which reduces to the
constrained classical system when \hbar \to 0. It is noteworthy that irregular
constraints change the observable aspects of a theory as compared to strictly
regular constraints.


title:
Simulation of Binary Black Hole Spacetimes with a Harmonic Evolution
  Scheme

abstract:
  A numerical solution scheme for the Einstein field equations based on
generalized harmonic coordinates is described, focusing on details not provided
before in the literature and that are of particular relevance to the binary
black hole problem. This includes demonstrations of the effectiveness of
constraint damping, and how the time slicing can be controlled through the use
of a source function evolution equation. In addition, some results from an
ongoing study of binary black hole coalescence, where the black holes are
formed via scalar field collapse, are shown. Scalar fields offer a convenient
route to exploring certain aspects of black hole interactions, and one
interesting, though tentative suggestion from this early study is that behavior
reminiscent of "zoom-whirl" orbits in particle trajectories is also present in
the merger of equal mass, non-spinning binaries, with appropriately fine-tuned
initial conditions.


title: Path integral in area tensor Regge calculus and complex connections

abstract:
  Euclidean quantum measure in Regge calculus with independent area tensors is
considered using example of the Regge manifold of a simple structure. We go
over to integrations along certain contours in the hyperplane of complex
connection variables. Discrete connection and curvature on classical solutions
of the equations of motion are not, strictly speaking, genuine connection and
curvature, but more general quantities and, therefore, these do not appear as
arguments of a function to be averaged, but are the integration (dummy)
variables. We argue that upon integrating out the latter the resulting measure
can be well-defined on physical hypersurface (for the area tensors
corresponding to certain edge vectors, i.e. to certain metric) as positive and
having exponential cutoff at large areas on condition that we confine ourselves
to configurations which do not pass through degenerate metrics.


title:
Gravitational Recoil during Binary Black Hole Coalescence using the
  Effective One Body Approach

abstract:
  Using the Effective One Body approach, that includes nonperturbative resummed
estimates for the damping and conservative parts of the compact binary
dynamics, we compute the recoil during the late inspiral and the subsequent
plunge of non-spinning black holes of comparable masses moving in
quasi-circular orbits. Further, using a prescription that smoothly connects the
plunge phase to a perturbed single black hole, we obtain an estimate for the
total recoil associated with the binary black hole coalescence. We show that
the crucial physical feature which determines the magnitude of the terminal
recoil is the presence of a ``burst'' of linear momentum flux emitted slightly
before coalescence. When using the most natural expression for the linear
momentum flux during the plunge, together with a Taylor-expanded $(v/c)^4$
correction factor, we find that the maximum value of the terminal recoil is
$\sim 74$ km/s and occurs for a mass ratio $m_2/m_1 \simeq 0.38$. We comment,
however, on the fact that the above `best bet estimate' is subject to strong
uncertainties because the location and amplitude of the crucial peak of linear
momentum flux happens at a moment during the plunge where most of the
simplifying analytical assumptions underlying the Effective One Body approach
are no longer justified. Changing the analytical way of estimating the linear
momentum flux, we find maximum recoils that range between 49 and 172 km/s.
(Abridged)


title: A topological theory of the Physical Vacuum

abstract:
  This article examines how the physical presence of field energy and
particulate matter could influence the topological properties of space time.
The theory is developed in terms of vector and matrix equations of exterior
differential forms. The topological features and the dynamics of such exterior
differential systems are studied with respect to processes of continuous
topological evolution. The theory starts from the sole postulate that field
properties of a Physical Vacuum (a continuum) can be defined in terms of a
vector space domain, of maximal rank, infinitesimal neighborhoods, that
supports a Basis Frame as a 4 x 4 matrix of C2 functions with non-zero
determinant. The basis vectors of such Basis Frames exhibit differential
closure. The particle properties of the Physical Vacuum are defined in terms of
topological defects (or compliments) of the field vector space defined by those
points where the maximal rank, or non-zero determinant, condition fails. The
topological universality of a Basis Frame over infinitesimal neighborhoods can
be refined by particular choices of a subgroup structure of the Basis Frame,
[B]. It is remarkable that from such a universal definition of a Physical
Vacuum, specializations permit the deduction of the field structures of all
four forces, from gravity fields to Yang Mills fields, and associate the origin
of topological charge and topological spin to the Affine torsion coefficients
of the induced Cartan Connection matrix [C] of 1-forms.


title:
Matters of Gravity, The Newsletter of The Topical Group in Gravitation
  of the American Physical Society, Volume 27, Spring 2006

abstract:
  GGR News:
  GGR program at the APS April meeting in Dallas
  We hear that..., 100 years ago, by Jorge Pullin
  Research Briefs:
  What's new in LIGO, by David Shoemaker
  LISA Pathfinder, by Paul McNamara
  Recent progress in binary black hole simulations, by Thomas Baumgarte
  Conference reports:
  Workshop on Emergence of Spacetime, by Olaf Dreyer
  Quantum gravity subprogram at the Isaac Newton Institute, by Jorma Louko
  Global problems in Math Relativity at the Newton Institute, by Jim Isenberg
  Loops '05, by Thomas Thiemann
  Numrel 2005, by Scott Hawley and Richard Matzner
  Apples With Apples Workshop in Argentina, by Sascha Husa


title:
Categorical Geometry and the Mathematical Foundations of Quantum General
  Relativity

abstract:
  We explore the possibility of replacing point set topology by higher category
theory and topos theory as the foundation for quantum general relativity. We
discuss the BC model and problems of its interpretation, and connect with the
construction of causal sites.


title:
Homothetic Self-Similar Solutions of the Three-Dimensional Brans-Dicke
  Gravity

abstract:
  All homothetic self-similar solutions of the Brans-Dicke scalar field in
three-dimensional spacetime with circular symmetry are found in closed form.

categories: gr-qc astro-ph hep-ph hep-th math-ph math.MP


title: Singular sources in the Demianski-Newman spacetimes

abstract:
  The analysis of singular regions in the NUT solutions carried out in the
recent paper (Manko and Ruiz, 2005 Class. Quantum Grav. 22, p.3555) is now
extended to the Demianski-Newman vacuum and electrovacuum spacetimes. We show
that the effect which produces the NUT parameter in a more general situation
remains essentially the same as in the purely NUT solutions: it introduces the
semi-infinite singularities of infinite angular momenta and positive or
negative masses depending on the interrelations between the parameters; the
presence of the electromagnetic field additionally endows the singularities
with electric and magnetic charges. The exact formulae describing the mass,
charges and angular momentum distributions in the Demianski-Newman solutions
are obtained and concise general expressions P_n=(m+i\nu)(ia)^n,
Q_n=(q+ib)(ia)^n for the entire set of the respective Beig-Simon multipole
moments are derived. These moments correspond to a unique choice of the
integration constant in the expression of the metric function \omega which is
different from the original choice made by Demianski and Newman.


title:
On the Exact Solutions of the Regge-Wheeler Equation in the
  Schwarzschild Black Hole Interior

abstract:
  We solve exactly the Regge-Wheeler equation for axial perturbations of the
Schwarzschild metric in the black hole interior in terms of Heun functions and
give a description of the spectrum and the eigenfunctions of the interior
problem. The phenomenon of attraction and repulsion of the discrete eigenvalues
of gravitational waves is discovered.


title: A New Quasi-local Mass and Positivity

abstract:
  We use an idea of Wang and Yau to give a new definition of quasi-local mass
for a topological sphere in an initial date set. The new definition modifies
Brown-York's definition by using certain spinor norm as lapse function. And it
requires mean curvature of the topological sphere satisfies apparent horizon
conditions, the topological sphere can be isometrically into Euclidean 3-space
and mean curvature of the initial date set does not change sign. The positivity
holds if we further assume the image of the topological sphere in Euclidean
3-space has nonnegative mean curvature.


title: Theoretical basis for a solution to the cosmic coincidence problem

abstract:
  Following a short discussion of some unresolved issues in the standard model
of cosmology (considered to be a generic $\Lambda$CDM model with flat geometry
and an early period of inflation), an update on the current state of research
regarding the problem of negative energy is provided. Arguments are then given
to the effect that traditional assumptions concerning the behavior of negative
action matter give rise to violations of both the principle of relativity and
the principle of inertia. An alternative set of axioms is proposed that would
govern the behavior of negative action matter if it is to be considered a
viable element of physical theories upon which cosmological models are build. A
simple framework, based on general relativity and the proposed axioms, is
elaborated which enables the formulation of quantitative predictions concerning
the interaction between positive and negative action bodies. Based on those
developments, a solution is proposed to the problem of the discrepancy between
current experimental and theoretical values of vacuum energy density (in any
cosmological model), which may also constitute a solution to the problem of the
unexplained coincidence between the (model dependent) experimental values of
vacuum energy density and present day average matter energy density. It is also
shown how irreversibility naturally arises in cosmological models derived in
this context.


title: Quantum Gowdy $T^3$ model: A unitary description

abstract:
  The quantization of the family of linearly polarized Gowdy $T^3$ spacetimes
is discussed in detail, starting with a canonical analysis in which the true
degrees of freedom are described by a scalar field that satisfies a
Klein-Gordon type equation in a fiducial time dependent background. A time
dependent canonical transformation, which amounts to a change of the basic
(scalar) field of the model, brings the system to a description in terms of a
Klein-Gordon equation on a background that is now static, although subject to a
time dependent potential. The system is quantized by means of a natural choice
of annihilation and creation operators. The quantum time evolution is
considered and shown to be unitary, allowing both the Schr\"odinger and
Heisenberg pictures to be consistently constructed. This has to be contrasted
with previous treatments for which time evolution failed to be implementable as
a unitary transformation. Possible implications for both canonical quantum
gravity and quantum field theory in curved spacetime are commented.


title: ZM theory II: Hamilton's and Lagrange's equations of motion

abstract:
  We show that considering time measured by an observer to be a function of a
cyclical field (an abstract version of a clock) is consistent with Hamilton's
and Lagrange's equations of motion for a one dimensional space manifold. The
derivation may provide a simple understanding of the conventions that are used
in defining the relationship between independent and dependent variables in the
Lagrangian and Hamiltonian formalisms. These derivations of the underlying
principles of classical mechanics are steps on the way to discussions of
physical laws and interactions in ZM theory.


title:
Reconstructing Quantum Geometry from Quantum Information: Area
  Renormalisation, Coarse-Graining and Entanglement on Spin Networks

abstract:
  After a brief review of spin networks and their interpretation as wave
functions for the (space) geometry, we discuss the renormalisation of the area
operator in loop quantum gravity. In such a background independent framework,
we propose to probe the structure of a surface through the analysis of the
coarse-graining and renormalisation flow(s) of its area. We further introduce a
procedure to coarse-grain spin network states and we quantitatively study the
decrease in the number of degrees of freedom during this process. Finally, we
use these coarse-graining tools to define the correlation and entanglement
between parts of a spin network and discuss their potential interpretation as a
natural measure of distance in such a state of quantum geometry.


title: An introduction to relativistic hydrodynamics

abstract:
  This lecture provides some introduction to perfect fluid dynamics within the
framework of general relativity. The presentation is based on the
Carter-Lichnerowicz approach. It has the advantage over the more traditional
approach of leading very straightforwardly to important conservation laws, such
as the relativistic generalizations of Bernoulli's theorem or Kelvin's
circulation theorem. It also permits to get easily first integrals of motion
which are particularly useful for computing equilibrium configurations of
relativistic stars in rotation or in binary systems. The presentation is
relatively self-contained and does not require any a priori knowledge of
general relativity. In particular, the three types of derivatives involved in
relativistic hydrodynamics are introduced in detail: this concerns the Lie,
exterior and covariant derivatives.


title: Does Smoothing Matter?

abstract:
  We study how inhomogeneities modify large scale parameters in General
Relativity. For a particular model, we obtain exact results: we compare an
infinite string of extremal black holes to a corresponding smooth line with the
same mass and charge in five dimensions. We find that the effective energy
density does not differ significantly.


title: Bayesian Probabilities and the Histories Algebra

abstract:
  We attempt a justification of a generalisation of the consistent histories
programme using a notion of probability that is valid for all complete sets of
history propositions. This consists of introducing Cox's axioms of probability
theory and showing that our candidate notion of probability obeys them. We also
give a generalisation of Bayes' theorem and comment upon how Bayesianism should
be useful for the quantum gravity/cosmology programmes.


title: Shear dynamics in Bianchi I cosmologies with R^n-gravity

abstract:
  We give the equations governing the shear evolution in Bianchi spacetimes for
general f(R)-theories of gravity. We consider the case of R^n-gravity and
perform a detailed analysis of the dynamics in Bianchi I cosmologies which
exhibit local rotational symmetry. We find exact solutions and study their
behaviour and stability in terms of the values of the parameter n. In
particular, we found a set of cosmic histories in which the universe is
initially isotropic, then develops shear anisotropies which approaches a
constant value.


title: Tachyonic Quintessential Inflation

abstract:
  We study the possibility to construct an observationally viable scenario
where both early Inflation and the recently detected accelerated expansion of
the universe can be explained by using a single scalar field associated with
the Tachyon. The Reheating phase becomes crucial to enable us to have a
consistent cosmology and also to get a second accelerated expansion period. A
discussion using an exponential potential is presented.


title: Generalized inverse mean curvature flows in spacetime

abstract:
  Motivated by the conjectured Penrose inequality and by the work of Hawking,
Geroch, Huisken and Ilmanen in the null and the Riemannian case, we examine
necessary conditions on flows of two-surfaces in spacetime under which the
Hawking quasilocal mass is monotone. We focus on a subclass of such flows which
we call uniformly expanding, which can be considered for null as well as for
spacelike directions. In the null case, local existence of the flow is
guaranteed. In the spacelike case, the uniformly expanding condition leaves a
1-parameter freedom, but for the whole family, the embedding functions satisfy
a forward-backward parabolic system for which local existence does not hold in
general. Nevertheless, we have obtained a generalization of the weak
(distributional) formulation of this class of flows, generalizing the
corresponding step of Huisken and Ilmanen's proof of the Riemannian Penrose
inequality.


title: Relationalism vs. Bayesianism

abstract:
  We compare and contrast the basic principles of two philosophies: Bayesianism
and relationalism. These two philosophies are both based upon criteria of
rationality. The analogy invoked in such a comparison seems rather apt when
discussing tentative proofs of quantum nonlocality. We argue that Bayesianism
is almost to quantum theory, what general covariance is to general relativity.
This is because the Bayesian interpretation of quantum theory can be given a
relational flavour.


title: The Pioneer Anomaly: Seeking an explanation in newly recovered data

abstract:
  The Pioneer 10 and 11 spacecraft yielded very accurate navigation that was
limited only by a small, anomalous frequency drift of their carrier signals
received by the NASA Deep Space Network (DSN). This discrepancy, evident in the
data for both spacecraft, was interpreted as an approximately constant
acceleration and has become known as the Pioneer anomaly. The origin of this
anomaly is yet unknown. Recent efforts to explain the effect included a search
for independent confirmation, analyses of conventional mechanisms, even ideas
rooted in new physics, and proposals for a dedicated mission. We assert that
before any discussion of new physics and (or) a dedicated mission can take
place, one must analyze the entire set of radiometric Doppler data received
from Pioneer 10 and 11. We report on our efforts to recover and utilize the
complete set of radio Doppler and telemetry records of both spacecraft. The
collection of radio Doppler data for both missions is now complete; we are
ready to begin its evaluation. We also made progress utilizing the recently
recovered Pioneer telemetry data. We present a strategy for studying the effect
of on-board generated small forces with this telemetry data, in conjunction
with the analysis of the entire set of the Pioneer Doppler data. We report on
the preparations for the upcoming analysis of the newly recovered data with the
ultimate goal of determining the origin of the Pioneer anomaly. Finally, we
discuss implications of our on-going research of the Pioneer anomaly for other
missions, most notably for New Horizons, NASA's recently launched mission to
Pluto.


title:
Fedosov Observables on Constant Curvature Manifolds and the Klein-Gordon
  Equation

abstract:
  In this paper we construct the set of quantum mechanical observables in the
Fedosov *-formalism (a coordinate invariant way to do quantum mechanics on any
manifold M) of a single free particle that lives on a constant curvature
manifold with metric signature (p,q). This was done for most but not all
constant curvature manifolds. We show that the algebra of all observables in
n=p+q dimensions is SO(p+1,q+1) in a nonperturbative calculation. A subgroup of
this group is identified as the analogue of the Poincare group in Minkowski
space i.e. it is the space of symmetries on the manifolds considered. We then
write down a Klein-Gordon (KG) equation given by the the equation
p^2|phi>=m^2|phi> for the set of allowed physical states. This result is
consistent with previous results on AdS. Furthermore we lay out the standard
scheme for the free KG field from the single particle theory. Furthermore we
argue that this scheme will work on a general space-time.


title: Gravitoelectromagnetic inflation from a 5D vacuum state: a new formalism

abstract:
  We propose a novel formalism for inflation from a 5D vacuum state which could
explain both, seeds of matter and magnetic fields in the early universe.


title: Tunnelling, Temperature and Taub-NUT Black Holes

abstract:
  We investigate quantum tunnelling methods for calculating black hole
temperature, specifically the null geodesic method of Parikh and Wilczek and
the Hamilton-Jacobi Ansatz method of Angheben et al. We consider application of
these methods to a broad class of spacetimes with event horizons, inlcuding
Rindler and non-static spacetimes such as Kerr-Newman and Taub-NUT. We obtain a
general form for the temperature of Taub-NUT-Ads black holes that is
commensurate with other methods. We examine the limitations of these methods
for extremal black holes, taking the extremal Reissner-Nordstrom spacetime as a
case in point.


title: Thick brane solution in the presence of two interacting scalar fields

abstract:
  It is shown that two gravitating scalar fields may form a thick brane in 5D
spacetime. The necessary condition for the existence of such a regular solution
is that the scalar fields potential must have local and global minima.


title:
How can Brane World physics influence Axion temperature dependence,
  initial vacuum states, and permissible solutions to the Wheeler-De Witt
  equation?

abstract:
  We are investigating if the Jeans instability criteria mandading a low
entropy,low temperature initial pre inflation state configuration can be
recociled with thermal conditions of temperature at or above ten to the 12
power Kelvin, or higher,when cosmic inflation physics takes over. We justify
this by pointing to the Akshenkar, Pawlowski, and Singh (2006) article about a
prior universe being modeled via their quantum bounce which states that this
prior universe geometrically can be modeled via a discretized Wheeler - De Witt
equation. This allows a way of getting around the fact that conventional
cosmological CMB is limited by a barrier as of a red shift limit of about z =
1000,as to photons, and to come up with a working model of quintessence scalar
fields which permits relic generation of dark matter/dark energy as well as
relic gravitons.


title: Doubly Special Relativity: facts and prospects

abstract:
  In this short review of Doubly Special Relativity I describe first the
relations between DSR and (quantum) gravity. Then I show how, in the case of a
field theory with curved momentum space, the Hopf algebra of symmetries
naturally emerges. I conclude with some remarks concerning DSR phenomenology
and description of open problems.


title: Generic weak isolated horizons

abstract:
  Weak isolated horizon boundary conditions have been relaxed supposedly to
their weakest form such that both zeroth and the first law of black hole
mechanics still emerge, thus making the formulation more amenable for
applications in both analytic and numerical Relativity. As an additional gain
it explicitly brings the non-extremal and extremal black holes at the same
footing.


title: Superluminal behavior and the Minkowski space-time

abstract:
  Bessel X-waves, or Bessel beams, have been extensively studied in last years,
especially with regard to the topic of superluminality in the propagation of a
signal. However, in spite of many efforts devoted to this subject, no definite
answer has been found, mainly for lack of an exact definition of signal
velocity. The purpose of the present work is to investigate the field of
existence of Bessel beams in order to overcome the specific question related to
the definition of signal velocity. Quite surprisingly, this field of existence
can be represented in the Minkowski space-time by a Super-Light Cone which
wraps itself around the well-known Light Cone. So, the change in the upper
limit of the light velocity does not modify the fundamental low of the
relativity and the causal principle.


title: Crossing of the w=-1 Barrier in Two-Fluid Viscous Modified Gravity

abstract:
  Singularities in the dark energy late universe are discussed, under the
assumption that the Lagrangian contains the Einstein term R plus a modified
gravity term of the form R^\alpha, where \alpha is a constant. It is found,
similarly as in the case of pure Einstein gravity [I. Brevik and O. Gorbunova,
Gen. Rel. Grav. 37 (2005), 2039], that the fluid can pass from the quintessence
region (w>-1) into the phantom region (w<-1) as a consequence of a bulk
viscosity varying with time. It becomes necessary now, however, to allow for a
two-fluid model, since the viscosities for the two components vary differently
with time. No scalar fields are needed for the description of the passage
through the phantom barrier.


title: Method of comparison equations for cosmological perturbations

abstract:
  We apply the method of comparison equations to study cosmological
perturbations during inflation, obtaining the full power spectra of scalar and
tensor perturbations to first and to second order in the slow-roll parameters.
We compare our results with those derived by means of other methods, in
particular the Green's function method and the improved WKB approximation, and
find agreement for the slow-roll structure. The method of comparison equations,
just as the improved WKB approximation, can however be applied to more general
situations where the slow-roll approximation fails.


title: On the Moller Energy Associated with Black Holes

abstract:
  This paper has been removed by arXiv administrators because of overlap with
gr-qc/9601044, gr-qc/0212018, hep-th/0310151, gr-qc/0011066, gr-qc/0404001,
gr-qc/0304081, gr-qc/0501002, and gr-qc/0109017.
  This paper also has excessive overlap with the following papers also written
by the authors or their collaborators: gr-qc/0606022, gr-qc/0512080,
gr-qc/0511030, gr-qc/0603063, gr-qc/0603108, gr-qc/0511095, gr-qc/0607095,
gr-qc/0608050, gr-qc/0601141, gr-qc/0607011, gr-qc/0607082, gr-qc/0603044,
gr-qc/0607083, and others.


title:
Integration of the Friedmann equation for universes of arbitrary
  complexity

abstract:
  An explicit and complete set of constants of the motion are constructed
algorithmically for Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) models
consisting of an arbitrary number of non-interacting species. The inheritance
of constants of the motion from simpler models as more species are added is
stressed. It is then argued that all FLRW models admit what amounts to a unique
candidate for a gravitational epoch function (a dimensionless scalar invariant
derivable from the Riemann tensor without differentiation which is monotone
throughout the evolution of the universe). The same relations that lead to the
construction of constants of the motion allow an explicit evaluation of this
function. In the simplest of all models, the $\Lambda$CDM model, it is shown
that the epoch function exists for all models with $\Lambda > 0$, but for
almost no models with $\Lambda \leq 0$.


title: Counting of Black Hole Microstates

abstract:
  The entropy of a black hole can be obtained by counting states in loop
quantum gravity. The dominant term depends on the Immirzi parameter involved in
the quantization and is proportional to the area of the horizon, while there is
a logarithmic correction with coefficient -1/2.


title: Signals for Lorentz Violation in Post-Newtonian Gravity

abstract:
  The pure-gravity sector of the minimal Standard-Model Extension is studied in
the limit of Riemann spacetime. A method is developed to extract the modified
Einstein field equations in the limit of small metric fluctuations about the
Minkowski vacuum, while allowing for the dynamics of the 20 independent
coefficients for Lorentz violation. The linearized effective equations are
solved to obtain the post-newtonian metric. The corresponding post-newtonian
behavior of a perfect fluid is studied and applied to the gravitating many-body
system. Illustrative examples of the methodology are provided using bumblebee
models. The implications of the general theoretical results are studied for a
variety of existing and proposed gravitational experiments, including lunar and
satellite laser ranging, laboratory experiments with gravimeters and torsion
pendula, measurements of the spin precession of orbiting gyroscopes, timing
studies of signals from binary pulsars, and the classic tests involving the
perihelion precession and the time delay of light. For each type of experiment
considered, estimates of the attainable sensitivities are provided. Numerous
effects of local Lorentz violation can be studied in existing or near-future
experiments at sensitivities ranging from parts in 10^4 down to parts in
10^{15}.


title: Conformally related massless fields in dS, AdS and Minkowski spaces

abstract:
  In this paper we write down the equation for a scalar conformally coupled
field simultaneously for de Sitter (dS), anti-de Sitter (AdS) and Minkowski
spacetime in d-dimensions. The curvature dependence appears in a very simple
way through a conformal factor. As a consequence the process of curvature free
limit, including wave functions limit and two-points functions, turns to be a
straightforward issue. We determine a set of modes, that we call de Sitter
plane waves, which become ordinary plane waves when the curvature vanishes.


title: Local Photon and Graviton Mass and its Consequences

abstract:
  We show that non-zero masses for a spin-1 graviton (called graviphoton) leads
to considerable gravitomagnetic fields around rotating mass densities, which
are not observed. The solution to the problem is found by an equivalent
graviphoton mass which depends on the local mass density to ensure the
principle of equivalence. This solution, derived from Einstein-Proca equations,
has important consequences such as a correction term for the Cooper-pair mass
anomaly reported by Tate among many others. Similar results were obtained for
the photon mass which is then proportional to the charge density in matter. For
the case of coherent matter the predicted effects have been experimentally
observed by the authors.


title: Experimental Detection of the Gravitomagnetic London Moment

abstract:
  It is well known that a rotating superconductor produces a magnetic field
proportional to its angular velocity. The authors conjectured earlier, that in
addition to this so-called London moment, also a large gravitomagnetic field
should appear to explain an apparent mass increase of Niobium Cooper-pairs.
This phenomenon was indeed observed and induced acceleration fields outside the
superconductor in the order of about 10^-4 g were found. The field appears to
be directly proportional to the applied angular acceleration of the
superconductor following our theoretical motivations. If confirmed, a
gravitomagnetic field of measurable magnitude was produced for the first time
in a laboratory environment. These results may open up a new experimental
window on testing general relativity and its consequences using coherent
matter.


title: Excising das All: Evolving Maxwell waves beyond scri

abstract:
  We study the numerical propagation of waves through future null infinity in a
conformally compactified spacetime. We introduce an artificial cosmological
constant, which allows us some control over the causal structure near null
infinity. We exploit this freedom to ensure that all light cones are tilted
outward in a region near null infinity, which allows us to impose
excision-style boundary conditions in our finite difference code. In this
preliminary study we consider electromagnetic waves propagating in a static,
conformally compactified spacetime.


title:
General Relativistic Effects of Gravity in Quantum Mechanics -- A Case
  of Ultra-Relativistic, Spin 1/2 Particles --

abstract:
  We present a general relativistic framework for studying gravitational
effects in quantum mechanical phenomena. We concentrate our attention on the
case of ultra-relativistic, spin-1/2 particles propagating in Kerr spacetime.
The two-component Weyl equation with general relativistic corrections is
obtained in the case of a slowly rotating, weak gravitational field. Our
approach is also applied to neutrino oscillations in the presence of a
gravitational field. The relative phase of two different mass eigenstates is
calculated in radial propagation, and the result is compared with those of
previous works.


title:
Interior Kerr solutions with the Newman-Janis algorithm starting with
  static physically reasonable space-times

abstract:
  We present a simple approach for obtaining Kerr interior solutions with the
help of the Newman-Janis algorithm (NJA) starting with static space-times
describing physically sensible interior Schwarzschild solutions. In this
context, the Darmois-Israel (DI) junction conditions are analyzed. Starting
from the incompressible Schwarzschild solution, a class of Kerr interior
solutions is presented, together with a discussion of the slowly rotating
limit. The energy conditions are discussed for the solutions so obtained.
Finally, the NJA algorithm is applied to the static, anisotropic, conformally
flat solutions found by Stewart leading to interior Kerr solutions with oblate
spheroidal boundary surfaces.


title: Radial quantization in rotating space-times

abstract:
  We present a solution to the time discontinuity paradox in rotating reference
frames by postulating that time is periodic. A kinematic restriction is
enforced that requires the discontinuity to be an integral number of the
periodicity of time. Quantized radii emerge for which the associated tangential
velocities are less than the speed of light. Using the de Broglie relationship,
we show that quantum theory may determine the periodicity of time. A rotating
Kerr black hole and a rigidly rotating disk of dust are also considered.


title: Gravitational Radiation from Two-Body Systems

abstract:
  Thanks to the new generation of gravitational wave detectors LIGO and VIRGO,
the theory of general relativity will face new and important confrontations to
observational data with unprecedented precision. Indeed the detection and
analysis of the gravitational waves from compact binary star systems requires
beforehand a very precise solution of the two-body problem within general
relativity. The approximation currently used to solve this problem is the
post-Newtonian one, and must be pushed to high order in order to describe with
sufficient accuracy (given the sensitivity of the detectors) the inspiral phase
of compact bodies, which immediately precedes their final merger. The resulting
post-Newtonian ``templates'' are currently known to 3.5PN order, and are used
for searching and deciphering the gravitational wave signals in VIRGO and LIGO.


title:
A simple accretion model of a rotating gas sphere onto a Schwarzschild
  black hole

abstract:
  We construct a simple accretion model of a rotating pressureless gas sphere
onto a Schwarzschild black hole. We show how to build analytic solutions in
terms of Jacobi elliptic functions. This construction represents a general
relativistic generalisation of the Newtonian accretion model first proposed by
Ulrich (1976). In exactly the same form as it occurs for the Newtonian case,
the flow naturally predicts the existence of an equatorial rotating accretion
disc about the hole. However, the radius of the disc increases monotonically
without limit as the flow reaches its maximum allowed angular momentum.


title: Klein-Gordon equation and the stable problem in the Rindler space-time

abstract:
  The Klein-Gordon equation in the Rindler space-time is studied carefully. It
is shown that the stable properties depend on using what time coordinate to
define the initial time. If we use the Rindler time, the scalar field is
stable. Alternatively, if we use the Minkowski time, the scalar field may be
regarded unstable to some extent. Furthermore, the complete extension of the
Rindler space time is the Minkowski space time, we could also study the stable
problem of the Rindler space time by the Klein-Gordon equation completely in
the Minkowski coordinates system. The results support that the Rindler space
time is really unstable. This in turn might cast some lights on the stable
problem of the Schwarzschild black-hole, which not only in many aspects shares
the similar geometrical properties with the Rindler space time but also has the
very same situation in stable study as that in Rindler space time. So, it is
not unreasonable to infer that the Schwarzschild black hole might really be
unstable in comparison with the case in Rindler space time. Of course, one must
go further to get the conclusion definitely.


title: The Ernst equation and ergosurfaces

abstract:
  We show that analytic solutions $\mcE$ of the Ernst equation with non-empty
zero-level-set of $\Re \mcE$ lead to smooth ergosurfaces in space-time. In
fact, the space-time metric is smooth near a "Ernst ergosurface" $E_f$ if and
only if $\mcE$ is smooth near $E_f$ and does not have zeros of infinite order
there.


title: Birefringence in nonlinear anisotropic dielectric media

abstract:
  Light propagation is investigated in the context of local anisotropic
nonlinear dielectric media at rest with the dielectric coefficients
$\epsilon^\mu{}_\nu = \epsilon^\mu{}_\nu (\vec{E},\vec{B})$ and constant $\mu$,
in the limit of geometrical optics. Birefringence was examined and the general
conditions for its occurrence were presented. A toy model is exhibited, in
which uniaxial birefringent media with nonlinear dielectric properties could be
driven by external fields in such way that birefringence may be artificially
controlled. The effective geometry interpretation is also addressed.


title:
Loop cosmological dynamics and dualities with Randall-Sundrum
  braneworlds

abstract:
  The discrete quantum geometric effects play an important role in dynamical
evolution in the loop quantum cosmology. These effects which are significant at
the high energies lead to the quadratic energy density modifications to the
Friedmann equation, as in the Randall-Sundrum braneworld scenarios but with a
negative sign. We investigate the scalar field dynamics in this scenario and
show the existence of a phase of super-inflation independent of the inverse
scale factor modifications as found earlier. In this regime the scalar field
mimics the dynamics of a phantom field and vice versa. We also find various
symmetries between the expanding phase, the contracting phase and the phantom
phase in the loop quantum cosmology. We then construct the scaling solutions in
the loop quantum cosmology and show their dual relationship with those of the
Randall-Sundrum cosmology.


title:
On the Gravitational Energy Associated with Spacetimes of Diagonal
  Metric

abstract:
  This paper also has excessive overlap with the following papers also written
by the authors or their collaborators: gr-qc/0608014, gr-qc/0511095,
gr-qc/0505078, gr-qc/0502060, gr-qc/0603027, gr-qc/0606028, gr-qc/0607109,
gr-qc/0607110, gr-qc/0508018, gr-qc/0502031, and others.


title: Closed timelike curves in asymmetrically warped brane universes

abstract:
  In asymmetrically warped spacetimes different warp factors are assigned to
space and to time. We discuss causality properties of these warped brane
universes and argue that scenarios with two extra dimensions may allow for
timelike curves which can be closed via paths in the extra-dimensional bulk. In
particular, necessary and sufficient conditions on the metric for the existence
of closed timelike curves are presented. We find a six-dimensional warped
metric which satisfies the CTC conditions, and where the null, weak and
dominant energy conditions are satisfied on the brane (although only the former
remains satisfied in the bulk). Such scenarios are interesting, since they open
the possibility of experimentally testing the chronology protection conjecture
by manipulating on our brane initial conditions of gravitons or hypothetical
gauge-singlet fermions (sterile neutrinos) which then propagate in the extra
dimensions.


title:
Quantum information cannot be completely hidden in correlations:
  implications for the black-hole information paradox

abstract:
  The black-hole information paradox has fueled a fascinating effort to
reconcile the predictions of general relativity and those of quantum mechanics.
Gravitational considerations teach us that black holes must trap everything
that falls into them. Quantum mechanically the mass of a black hole leaks away
as featureless (Hawking) radiation, but if the black hole vanishes, where is
the information about the matter that made it? We treat the states of the
in-fallen matter quantum mechanically and show that the black-hole information
paradox becomes more severe. Our formulation of the paradox rules out one of
the most conservative resolutions: that the state of the in-falling matter
might be hidden in correlations between semi-classical Hawking radiation and
the internal states of the black hole. As a consequence, either unitarity or
Hawking's semi-classical predictions must break down. Any resolution of the
black-hole information crisis must elucidate one of these possibilities.


title: Orbifolds in Numerical Relativity

abstract:
  Numerical Relativity has been using orbifolds for a long time, although they
appear under different names in the literature. We review orbifolds previously
used in simulations also discuss some that have not been used yet but are
likely to be useful in the future.


title:
Rotating star initial data for a constrained scheme in numerical
  relativity

abstract:
  A new numerical code for computing stationary axisymmetric rapidly rotating
stars in general relativity is presented. The formulation is based on a fully
constrained-evolution scheme for 3+1 numerical relativity using the Dirac gauge
and maximal slicing. We use both the polytropic and MIT bag model equations of
state to demonstrate that the code can construct rapidly rotating neutron star
and strange star models. We compare numerical models obtained by our code and a
well-established code, which uses a different gauge condition, and show that
the two codes agree to high accuracy.


title: The weakly perturbed Schwarzschild lens in the strong deflection limit

abstract:
  We investigate the strong deflection limit of gravitational lensing by a
Schwarzschild black hole embedded in an external gravitational field. The study
of this model, analogous to the Chang & Refsdal lens in the weak deflection
limit, is important to evaluate the gravitational perturbations on the
relativistic images that appear in proximity of supermassive black holes hosted
in galactic centers. By a simple dimensional argument, we prove that the tidal
effect on the light ray propagation mainly occurs in the weak field region far
away from the black hole and that the external perturbation can be treated as a
weak field quadrupole term. We provide a description of relativistic critical
curves and caustics and discuss the inversion of the lens mapping. Relativistic
caustics are shifted and acquire a finite diamond shape. Sources inside the
caustics produce four sequences of relativistic images. On the other hand,
retro-lensing caustics are only shifted while remaining point-like to the
lowest order.


title: Exact scaling solutions and fixed points for general scalar field

abstract:
  We show that the most general dark energy model that possesses a scaling
solution $\rho_\phi\propto a^n$ is the k-essence model, which includes both of
the quintessence and tachyon models. The exact scaling solutions are then
derived. The potential that gives the tracking solution in which dark energy
exactly tracks the background matter field is the inverse squared potential.
The quintessence field with exponential potential can be obtained from the
k-essence field with the inverse squared potential. We also find the fixed
points and study their main properties, whereby the scalar field dominant fixed
point is identified.


title: Phase transition between the BTZ black hole and AdS space

abstract:
  In three dimensions, a phase transition occurs between the non-rotating BTZ
black hole and the massless BTZ black hole. Further, introducing the mass of a
conical singularity, we show that a transition between the non-rotating BTZ
black hole and thermal AdS space is also possible.


title: Perturbations of a Schwarzschild black hole. Notes on Zerilli's approach

abstract:
  Modelling the free fall (and radiative phenomenology) of a massive particle,
charged or not, in a static and spherically symmetric black hole is a classic,
good relativistic dare that produced a remarkable series of papers, mainly in
the seventies of the past century. Some formal topics about the mathematical
machinery required to perform the task are unfortunately still not very clear;
however, with the help of modern computer algebra techniques, some results can
at least be tested and corrected.


title:
Covariance, Geometricity, Setting, and Dynamical Structures on
  Cosmological Manifold

abstract:
  The treatment of the principle of general covariance based on coordinate
systems, i.e., on classical tensor analysis suffers from an ambiguity. A more
preferable formulation of the principle is based on modern differential
geometry: the formulation is coordinate-free. Then the principle may be called
``principle of geometricity.'' In relation to coordinate transformations, there
had been confusions around such concepts as symmetry, covariance, invariance,
and gauge transformations. Clarity has been achieved on the basis of a
group-theoretical approach and the distinction between absolute and dynamical
objects. In this paper, we start from arguments based on structures on
cosmological manifold rather than from group-theoretical ones, and introduce
the notion of setting elements. The latter create a scene on which dynamics is
performed. The characteristics of the scene and dynamical structures on it are
considered.


title: Interferometers for Displacement-Noise-Free Gravitational-Wave Detection

abstract:
  We propose a class of displacement- and laser-noise free
gravitational-wave-interferometer configurations, which does not sense
non-geodesic mirror motions and laser noises, but provides non-vanishing
gravitational-wave signal. Our interferometer consists of 4 mirrors and 2
beamsplitters, which form 4 Mach-Zehnder interferometers. By contrast to
previous works, no composite mirrors are required. Each mirror in our
configuration is sensed redundantly, by at least two pairs of incident and
reflected beams. Displacement- and laser-noise free detection is achieved when
output signals from these 4 interferometers are combined appropriately. Our
3-dimensional interferometer configuration has a low-frequency response
proportional to f^2, which is better than the f^3 achievable by previous
2-dimensional configurations.


title:
Radiation Pressure Supported Stars in Einstein Gravity: Eternally
  Collapsing Objects

abstract:
  Even when we consider Newtonian stars, i.e., stars with surface gravitational
redshift, z<< 1, it is well known that, theoretically, it is possible to have
stars, supported against self-gravity, almost entirely by radiation pressure.
However, such Newtonian stars must necessarily be supermassive. We point out
that this requirement for excessive large M, in Newtonian case, is a
consequence of the occurrence of low z<< 1. On the other hand, if we remove
such restrictions, and allow for possible occurrence highly general
relativistic regime, z >> 1, we show that, it is possible to have radiation
pressure supported stars at arbitrary value of M. Since radiation pressure
supported stars necessarily radiate at the Eddington limit, in Einstein
gravity, they are never in strict hydrodynamical equilibrium. Further, it is
believed that sufficiently massive or dense objects undergo continued
gravitational collapse to the Black Hole stage characterized by z =infty. Thus,
late stages of Black Hole formation, by definition, will have, z >> 1, and
hence would be examples of quasi-stable general relativistic RPSSs. This result
is also supported by with our previous finding that that trapped surfaces are
not formed in gravitational collapse and the value of the integration constant
in the vacuum Schwarzschild solution is zero. Hence the supposed observed BHs
are actually ECOs.


title:
Phasing of gravitational waves from inspiralling eccentric binaries at
  the third-and-a-half post-Newtonian order

abstract:
  We obtain an efficient description for the dynamics of nonspinning compact
binaries moving in inspiralling eccentric orbits to implement the phasing of
gravitational waves from such binaries at the 3.5 post-Newtonian (PN) order.
Our computation heavily depends on the phasing formalism, presented in [T.
Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D \textbf{70}, 064028 (2004)],
and the 3PN accurate generalized quasi-Keplerian parametric solution to the
conservative dynamics of nonspinning compact binaries moving in eccentric
orbits, available in [R.-M. Memmesheimer, A. Gopakumar, and G. Sch\"afer, Phys.
Rev. D \textbf{70}, 104011 (2004)]. The gravitational-wave (GW) polarizations
$h_{+}$ and $h_{\times}$ with 3.5PN accurate phasing should be useful for the
earth-based GW interferometers, current and advanced, if they plan to search
for gravitational waves from inspiralling eccentric binaries. Our results will
be required to do \emph{astrophysics} with the proposed space-based GW
interferometers like LISA, BBO, and DECIGO.


title:
The flight of the bumblebee: solutions from a vector-induced spontaneous
  Lorentz symmetry breaking model

abstract:
  The vacuum solutions arising from a spontaneous breaking of Lorentz symmetry
due to the acquisition of a vacuum expectation value by a vector field are
derived. These include the purely radial Lorentz symmetry breaking (LSB),
radial/temporal LSB and axial/temporal LSB scenarios. It is found that the
purely radial LSB case gives rise to new black hole solutions. Whenever
possible, Parametrized Post-Newtonian (PPN) parameters are computed and
compared to observational bounds, in order to constrain the Lorentz symmetry
breaking scale.


title: Spherical Solutions in Einstein-Aether Theory: Static Aether and Stars

abstract:
  The time independent spherically symmetric solutions of General Relativity
(GR) coupled to a dynamical unit timelike vector are studied. We find there is
a three-parameter family of solutions with this symmetry. Imposing asymptotic
flatness restricts to two parameters, and requiring that the aether be aligned
with the timelike Killing field further restricts to one parameter, the total
mass. These "static aether" solutions are given analytically up to solution of
a transcendental equation. The positive mass solutions have spatial geometry
with a minimal area 2-sphere, inside of which the area diverges at a curvature
singularity occurring at an extremal Killing horizon that lies at a finite
affine parameter along a radial null geodesic. Regular perfect fluid star
solutions are shown to exist with static aether exteriors, and the range of
stability for constant density stars is identified.


title: The Parametric Transition of Strange Matter Rings to a Black Hole

abstract:
  It is shown numerically that strange matter rings permit a continuous
transition to the extreme Kerr black hole. The multipoles as defined by Geroch
and Hansen are studied and suggest a universal behaviour for bodies approaching
the extreme Kerr solution parametrically. The appearance of a `throat region',
a distinctive feature of the extreme Kerr spacetime, is observed. With regard
to stability, we verify for a large class of rings, that a particle sitting on
the surface of the ring never has enough energy to escape to infinity along a
geodesic.


title: Superluminal motion in (semi)classical relativity

abstract:
  The possibility is discussed of superluminal motion of non-tachyonic (i.e.
moving with the instantaneous speed v<c) bodies within general relativity. It
is shown that in some occasions quantum field theory apparently prohibits such
motion, but not - to all appearance - in the general case.


title:
Formalism for testing theories of gravity using lensing by compact
  objects. III: Braneworld gravity

abstract:
  Braneworld gravity is a model that endows physical space with an extra
dimension. In the type II Randall-Sundrum braneworld gravity model, the extra
dimension modifies the spacetime geometry around black holes, and changes
predictions for the formation and survival of primordial black holes. We
develop a comprehensive analytical formalism for far-field black hole lensing
in this model, using invariant quantities to compute all geometric optics
lensing observables. We then make the first analysis of wave optics in
braneworld lensing, working in the semi-classical limit. We show that wave
optics offers the only realistic way to observe braneworld effects in black
hole lensing. We point out that if primordial braneworld black holes exist,
have mass M, and contribute a fraction f of the dark matter, then roughly 3e5 x
f (M/1e-18 Msun)^(-1) of them lie within our Solar System. These objects, which
we call "attolenses," would produce interference fringes in the energy spectra
of gamma-ray bursts at energies ~100 (M/1e-18 Msun)^(-1) MeV (which will soon
be accessible with the GLAST satellite). Primordial braneworld black holes
spread throughout the universe could produce similar interference effects; the
probability for "attolensing" may be non-negligible. If interference fringes
were observed, the fringe spacing would yield a simple upper limit on M.
Detection of a primordial black hole with M <~ 1e-19 Msun would challenge
general relativity and favor the braneworld model. Further work on lensing
tests of braneworld gravity must proceed into the physical optics regime, which
awaits a description of the full spacetime geometry around braneworld black
holes.


title: Conformal decomposition in canonical general relativity

abstract:
  A new canonical transformation is found that enables the direct canonical
treatment of the conformal factor in general relativity. The resulting
formulation significantly simplifies the previously presented conformal
geometrodynamics. It provides a further theoretical basis for the conformal
approach to loop quantum gravity and offers a generic framework for the
conformal analysis of spacetime dynamics.


title: Energy Associated with the Gibbons-Maeda Dilaton Space-Time

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
hep-th/0311050, gr-qc/0306101, gr-qc/9601044, gr-qc/0511106, gr-qc/0303034, and
gr-qc/0212018.


title:
Propagation of Light in the Field of Stationary and Radiative
  Gravitational Multipoles

abstract:
  Extremely high precision of near-future radio/optical interferometric
observatories like SKA, Gaia, SIM and the unparalleled sensitivity of LIGO/LISA
gravitational-wave detectors demands more deep theoretical treatment of
relativistic effects in the propagation of electromagnetic signals through
variable gravitational fields of the solar system, oscillating and precessing
neutron stars, coalescing binary systems, exploding supernova, and colliding
galaxies. Especially important for future gravitational-wave observatories is
the problem of propagation of light rays in the field of multipolar
gravitational waves emitted by a localized source of gravitational radiation.
Present paper suggests physically-adequate and consistent mathematical solution
of this problem in the first post-Minkowskian approximation of General
Relativity which accounts for all time-dependent multipole moments of an
isolated astronomical system.


title:
New spherically symmetric monopole and regular solutions in
  Einstein-Born-Infeld theories

abstract:
  In this work a new asymptotically flat solution of the coupled
Einstein-Born-Infeld equations for a static spherically symmetric space-time is
obtained. When the intrinsic mass is zero the resulting spacetime is regular
everywhere, in the sense given by B. Hoffmann and L. Infeld in 1937, and the
Einstein-Born-Infeld theory leads to the identification of the gravitational
with the electromagnetic mass. This means that the metric, the electromagnetic
field and their derivatives have not discontinuities in all the manifold. In
particular, there are not conical singularities at the origin, in contrast to
well known monopole solution studied by B. Hoffmann in 1935. The lack of
uniqueness of the action function in Non-Linear-Electrodynamics is discussed.


title:
Rotating charged Black Holes in Einstein-Born-Infeld theories and their
  ADM mass

abstract:
  In this work, the solution of the Einstein equations for a slowly rotating
black hole with Born-Infeld charge is obtained. Geometrical properties and
horizons of this solution are analyzed. The conditions when the ADM mass (as in
the nonlinear static cases) and the ADM angular momentum of the system have
been modified by the non linear electromagnetic field of the black hole, are
considered.


title: Properties of gravitational waves in Cosmological General Relativity

abstract:
  The 5D Cosmological General Relativity theory developed by Carmeli reproduces
all of the results that have been successfully tested for Einstein's 4D theory.
However the Carmeli theory because of its fifth dimension, the velocity of the
expanding universe, predicts something different for the propagation of gravity
waves on cosmological distance scales. This analysis indicates that
gravitational radiation may not propagate as an unattenuated wave where effects
of the Hubble expansion are felt. In such cases the energy does not travel over
such large length scales but is evanescent and dissipated into the surrounding
space as heat.


title: Deformed Density Matrix and Quantum Entropy of the Black Hole

abstract:
  In the present work the approach - density matrix deformation - earlier
developed by the author to study a quantum theory of the Early Universe
(Planck's scales) is applied to study a quantum theory of black holes. On this
basis the author investigates the information paradox problem, entropy of the
black hole remainders after evaporation, and consistency with the holographic
principle. The possibility for application of the proposed approach to the
calculation of quantum entropy of a black hole is considered.


title: New Minimal Distortion Shift Gauge

abstract:
  Based on the recent understanding of the role of the densitized lapse
function in Einstein's equations and of the proper way to pose the thin
sandwich problem, a slight readjustment of the minimal distortion shift gauge
in the 3+1 approach to the dynamics of general relativity allows this shift
vector to serve as the vector potential for the longitudinal part of the
extrinsic curvature tensor in the new approach to the initial value problem,
thus extending the initial value decomposition of gravitational variables to
play a role in the evolution as well. The new shift vector globally minimizes
the changes in the conformal 3-metric with respect to the spacetime measure
rather than the spatial measure on the time coordinate hypersurfaces, as the
old shift vector did.