title: Space-time correlations in inflationary spectra, a wave packet analysis

abstract:
  The inflationary mechanism of mode amplification predicts that the state of
each mode with a given wave vector is correlated to that of its partner mode
with the opposite vector. This implies nonlocal correlations which leave their
imprint on temperature anisotropies in the cosmic microwave background. Their
spatial properties are best revealed by using local wave packets. This analysis
shows that all density fluctuations giving rise the large scale structures
originate in pairs which are born near the reheating. In fact each local
density fluctuation is paired with an oppositely moving partner with opposite
amplitude. To obtain these results we first apply a ``wave packet
transformation'' with respect to one argument of the two point correlation
function. A finer understanding of the correlations is then reached by making
use of coherent states. The knowledge of the velocity field is required to
extract the contribution of a single pair of wave packets. Otherwise, there is
a two-folded degeneracy which gives three aligned wave packets arising from two
pairs. The applicability of these methods to observational data is briefly
discussed.


title: First upper limits from LIGO on gravitational wave bursts

abstract:
  We report on a search for gravitational wave bursts using data from the first
science run of the LIGO detectors. Our search focuses on bursts with durations
ranging from 4 ms to 100 ms, and with significant power in the LIGO sensitivity
band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than
1.6 events per day at 90% confidence level. This result is interpreted in terms
of the detection efficiency for ad hoc waveforms (Gaussians and sine-Gaussians)
as a function of their root-sum-square strain h_{rss}; typical sensitivities
lie in the range h_{rss} ~ 10^{-19} - 10^{-17} strain/rtHz, depending on
waveform. We discuss improvements in the search method that will be applied to
future science data from LIGO and other gravitational wave detectors.


title:
Searching for gravitational waves from the Crab pulsar - the problem of
  timing noise

abstract:
  Of the current known pulsars, the Crab pulsar (B0531+21) is one of the most
promising sources of gravitational waves. The relatively large timing noise of
the Crab causes its phase evolution to depart from a simple spin-down model.
This effect needs to be taken in to account when performing time domain
searches for the Crab pulsar in order to avoid severely degrading the search
efficiency. The Jodrell Bank Crab pulsar ephemeris is examined to see if it can
be used for tracking the phase evolution of any gravitational wave signal from
the pulsar, and we present a method of heterodyning the data that takes account
of the phase wander. The possibility of obtaining physical information about
the pulsar from comparisons of the electromagnetically and a gravitationally
observed timing noise is discussed. Finally, additional problems caused by
pulsar glitches are discussed.


title: On the thermodynamics of inhomogeneous perfect fluid mixtures

abstract:
  It is shown that inhomogeneous Szekeres and Stephani universes exist
corresponding to non-dissipative binary mixtures of perfect fluids in local
thermal equilibrium. This result contradicts a recent statement by Z\'arate and
Quevedo (2004 Class. Quantum Grav. {\bf 21} 197, {\it Preprint} gr-qc/0310087),
which affirms that the only Szekeres and Stephani universes compatible with
these fluids are the homogeneous Friedmann-Robertson-Walker models. Thus,
contrarily to their conclusion, their thermodynamic scheme do not gives new
indications of incompatibility between thermodynamics and relativity. Two of
the points that have generated this error are commented.


title: Brane-world gravity

abstract:
  The observable universe could be a 1+3-surface (the "brane") embedded in a
1+3+d-dimensional spacetime (the "bulk"), with standard-model particles and
fields trapped on the brane while gravity is free to access the bulk. At least
one of the d extra spatial dimensions could be very large relative to the
Planck scale, which lowers the fundamental gravity scale, possibly even down to
the electroweak (~ TeV) level. This revolutionary picture arises in the
framework of recent developments in M theory. The 1+10-dimensional M theory
encompasses the known 1+9-dimensional superstring theories, and is widely
considered to be a promising potential route to quantum gravity. General
relativity cannot describe gravity at high enough energies and must be replaced
by a quantum gravity theory, picking up significant corrections as the
fundamental energy scale is approached. At low energies, gravity is localized
at the brane and general relativity is recovered, but at high energies gravity
"leaks" into the bulk, behaving in a truly 1+3+d-dimensional way. This
introduces significant changes to gravitational dynamics and perturbations,
with interesting testable implications for high-energy astrophysics, black
holes and cosmology. Brane-world models offer a phenomenological way to test
some of the novel predictions and corrections to general relativity that are
implied by M theory. This review discusses the geometry, dynamics and
perturbations of simple brane-world models for cosmology and astrophysics,
mainly focusing on warped 5-dimensional brane-worlds based on the
Randall-Sundrum models.


title:
Diffeomorphisms from finite triangulations and absence of 'local'
  degrees of freedom

abstract:
  If the diffeomorphism symmetry of general relativity is fully implemented
into a path integral quantum theory, the path integral leads to a partition
function which is an invariant of smooth manifolds. We comment on the physical
implications of results on the classification of smooth and piecewise-linear
4-manifolds which show that the partition function can already be computed from
a triangulation of space-time. Such a triangulation characterizes the topology
and the differentiable structure, but is completely unrelated to any physical
cut-off. It can be arbitrarily refined without affecting the physical
predictions and without increasing the number of degrees of freedom
proportionally to the volume. Only refinements at the boundary have a physical
significance as long as the experimenters who observe through this boundary,
can increase the resolution of their measurements. All these are consequences
of the symmetries. The Planck scale cut-off expected in quantum gravity is
rather a dynamical effect.


title:
A family of filters to search for frequency dependent gravitational wave
  stochastic backgrounds

abstract:
  We consider a three dimensional family of filters based on broken power law
spectra to search for gravitational wave stochastic backgrounds in the data
from Earth-based laser interferometers. We show that such templates produce the
necessary fitting factor for a wide class of cosmological backgrounds and
astrophysical foregrounds and that the total number of filters required to
search for those signals in the data from first generation laser
interferometers operating at the design sensitivity is fairly small


title:
Quantum features in statistical observations of "timeless" classical
  systems

abstract:
  We pursue the view that quantum theory may be an emergent structure related
to large space-time scales. In particular, we consider classical Hamiltonian
systems in which the intrinsic proper time evolution parameter is related
through a probability distribution to the discrete physical time. This is
motivated by studies of ``timeless'' reparametrization invariant models, where
discrete physical time has recently been constructed based on coarse-graining
local observables. Describing such deterministic classical systems with the
help of path-integrals, primordial states can naturally be introduced which
follow unitary quantum mechanical evolution in suitable limits.


title: Time in quantum gravity by weakening the Hamiltonian constraint

abstract:
  We replace the usual Hamiltonian constraint of quantum gravity H|psi>=0 by a
weaker one <psi|H|psi>=0. This allows |psi> to satisfy the time-dependent
functional Schrodinger equation. In general, only the phase of the wave
function appears to be time independent. The resulting quantum theory has the
correct classical limit and thus provides a viable theory of quantum gravity
that solves the problem of time without introducing additional nongravitational
degrees of freedom.


title:
Classification of Energy Momentum Tensors in $n \geq 5$ Dimensional
  Space-times: a Review

abstract:
  Recent developments in string theory suggest that there might exist extra
spatial dimensions, which are not small nor compact. The framework of a great
number of brane cosmological models is that in which the matter fields are
confined on a brane-world embedded in five dimensions (the bulk). Motivated by
this we review the main results on the algebraic classification of second order
symmetric tensors in 5-dimensional space-times. All possible Segre types for a
symmetric two-tensor are found, and a set of canonical forms for each Segre
type is obtained. A limiting diagram for the Segre types of these symmetric
tensors in 5-D is built. Two theorems which collect together some basic results
on the algebraic structure of second order symmetric tensors in 5-D are
presented. We also show how one can obtain, by induction, the classification
and the canonical forms of a symmetric two-tensor on n-dimensional (n > 5)
spaces from its classification in 5-D spaces, present the Segre types in n-D
and the corresponding canonical forms. This classification of symmetric
two-tensors in any n-D spaces and their canonical forms are important in the
context of n-dimensional brane-worlds context and also in the framework of 11-D
supergravity and 10-D superstrings.


title: Scattering of scalar particles by a black hole

abstract:
  The absorption cross section for scalar particle impact on a Schwarzschild
black hole is found. The process is dominated by two physical phenomena. One of
them is the well-known greybody factor that arises from the energy-dependent
potential barrier outside the horizon that filters the incoming and outgoing
waves. The other is related to the reflection of particles on the horizon
(Kuchiev 2003). This latter effect strongly diminishes the cross section for
low energies, forcing it to vanish in the infrared limit. It is argued that
this is a general property, the absorption cross section vanishes in the
infrared limit for scattering of particles of arbitrary spin.


title: Metric fluctuations and its evolution during inflation

abstract:
  W discuss the evolution of the fluctuations in a symmetric
$\phi_c$-exponential potential which provides a power-law expansion during
inflation using both, the gauge invariant field $\Phi$ and the Sasaki-Mukhanov
field.


title:
The variational principle and effective action for a spherical dust
  shell

abstract:
  The variational principle for a spherical configuration consisting of a thin
spherical dust shell in gravitational field is constructed. The principle is
consistent with the boundary-value problem of the corresponding Euler-Lagrange
equations, and leads to ``natural boundary conditions''. These conditions and
the field equations following from the variational principle are used for
performing of the reduction of this system. The equations of motion for the
shell follow from the obtained reduced action. The transformation of the
variational formula for the reduced action leads to two natural variants of the
effective action. One of them describes the shell from a stationary interior
observer's point of view, another from the exterior one. The conditions of
isometry of the exterior and interior faces of the shell lead to the momentum
and Hamiltonian constraints.


title:
Problem of Cosmological Singularity, Inflationary Cosmology and Gauge
  Theories of Gravitation

abstract:
  Problem of cosmological singularity is discussed in the framework of gauge
theories of gravitation. Generalizing cosmological Friedmann equations (GCFE)
for homogeneous isotropic models including scalar fields and usual gravitating
matter are introduced. It is shown that by certain restrictions on equation of
state of gravitating matter and indefinite parameter of GCFE generic feature of
inflationary cosmological models of flat, open and closed type is their regular
bouncing character.


title: Propagating phase boundaries as sonic horizons

abstract:
  If certain conditions are met, a propagating phase boundary can be a sonic
horizon. Sonic Hawking radiation from such a phase boundary is expected in the
quantum theory. The Hawking temperature for typical values of system parameters
can be as large as $\sim 0.04$ K. Since the setup does not require the physical
transport of material, it evades the seemingly insurmountable difficulties of
the usual proposals to create a sonic horizon in which fluid is required to
flow at supersonic speeds. Issues that are likely to present difficulties that
are particular to this setup are discussed. Hawking evaporation of the sonic
horizon is also expected and is predicted to lead to a deceleration of the
phase boundary.


title: The Hartle-Thorne circular geodesics

abstract:
  The Hartle-Thorne metric is an exact solution of vacuum Einstein field
equations that describes the exterior of any slowly and rigidly rotating,
stationary and axially symmetric body. The metric is given with accuracy up to
the second order terms in the body's angular momentum, and first order in its
quadrupole moment. We give, with the same accuracy, analytic formulae for
circular geodesics in the Hartle-Thorne metrics. They describe angular
velocity, angular momentum, energy, epicyclic frequencies, shear, vorticity and
Fermi-Walker precession. These quantities are relevant to several astrophysical
phenomena, in particular to the observed high frequency, kilohertz Quasi
Periodic Oscillations (kHz QPOs) in the X-ray luminosity from black hole and
neutron star sources. It is believed that kHz QPO data may be used to test the
strong field regime of Einstein's general relativity, and the physics of
super-dense matter of which neutron stars are made of.


title:
Quantum inequalities for the free Rarita-Schwinger fields in flat
  spacetime

abstract:
  Using the methods developed by Fewster and colleagues, we derive a quantum
inequality for the free massive spin-${3\over 2}$ Rarita-Schwinger fields in
the four dimensional Minkowski spacetime. Our quantum inequality bound for the
Rarita-Schwinger fields is weaker, by a factor of 2, than that for the
spin-${1\over 2}$ Dirac fields. This fact along with other quantum inequalities
obtained by various other authors for the fields of integer spin (bosonic
fields) using similar methods lead us to conjecture that, in the flat
spacetime, separately for bosonic and fermionic fields, the quantum inequality
bound gets weaker as the the number of degrees of freedom of the field
increases. A plausible physical reason might be that the more the number of
field degrees of freedom, the more freedom one has to create negative energy,
therefore, the weaker the quantum inequality bound.


title: Structures of gravitational vacuum and their role in the Universe

abstract:
  The production of gravitational vacuum defects and their contribution in
energy density of the Universe are discussed. These topological microstructures
could be produced as the result of defect creation of the Universe from
"nothing" as well as the result of the first relativistic phase transition.
They must be isotropically distributed on background of the expanding Universe.
After Universe inflation these microdefects smoothed, stretched and broke up.
Parts of them have survived and now they are perceived as the structures of
Lambda-term (quintessence) and unclustered dark matter. It is shown that for
phenomenological description of vacuum topological defects of different
dimensions (worm-holes, micromembranes, microstrings and monopoles) the
parametrizational noninvariant members of Wheeler -DeWitt equation can be used.
The mathematical illustration of these processes may be the spontaneous
breaking of local Lorentz-invariance of quasi-classical equations of gravity.
In addition, 3-dimensional topological defects revalues Lambda-term.


title: Isotropic singularity in brane cosmological models

abstract:
  It is argued that the initial cosmological singularity is isotropic in
spatially inhomogeneous brane-world models. This implies that brane cosmology
may naturally give rise to a set of initial data that provide the conditions
for inflation to subsequently take place, consequently offering a plausible
solution to the initial conditions problem in cosmology.


title: Effective Space Quantization in Friedman-Robertson-Walker Models

abstract:
  Quantum--mechanical operators corresponding to canonical momentum and
position of a point--like particle, which follow from the quantum field theory
in the general Riemannian space-time, satisfy generally to a deformation of the
canonical commutation relations with $c^{-2}$ as the parameter of deformation.
For operators of the quasi-Cartesian coordinates in the closed and open
Friedman--Robertson--Walker models, the deformation reproduces the spatial part
of the well--known Snyder formula for quantization of the Minkowsky space-time.
The spatially-flat models are distinguished apart by that the deformation is
reduced exactly to the standard canonical commutation relations, which
correlates remarkably with the fact of the observed flatness of the Universe.
Conditions are briefly discussed for which the deformation could have
cosmological manifestations. Key words: quantum mechanics, cosmology, quantized
space.


title: Isotropic singularity in inhomogeneous brane cosmological models

abstract:
  We discuss the asymptotic dynamical evolution of spatially inhomogeneous
brane-world cosmological models close to the initial singularity. By
introducing suitable scale-invariant dependent variables and a suitable gauge,
we write the evolution equations of the spatially inhomogeneous $G_{2}$ brane
cosmological models with one spatial degree of freedom as a system of
autonomous first-order partial differential equations. We study the system
numerically, and we find that there always exists an initial singularity, which
is characterized by the fact that spatial derivatives are dynamically
negligible. More importantly, from the numerical analysis we conclude that
there is an initial isotropic singularity in all of these spatially
inhomogeneous brane cosmologies for a range of parameter values which include
the physically important cases of radiation and a scalar field source. The
numerical results are supported by a qualitative dynamical analysis and a
calculation of the past asymptotic decay rates. Although the analysis is local
in nature, the numerics indicates that the singularity is isotropic for all
relevant initial conditions. Therefore this analysis, and a preliminary
investigation of general inhomogeneous ($G_0$) models, indicates that it is
plausible that the initial singularity is isotropic in spatially inhomogeneous
brane-world cosmological models and consequently that brane cosmology naturally
gives rise to a set of initial data that provide the conditions for inflation
to subsequently take place.


title: Inflationary Braneworld Driven By Bulk Scalar Field

abstract:
  We have developed a formalism to study an inflationary scenario driven by a
bulk inflaton in the two-brane system. The 4-dimensional low energy effective
action is obtained using the gradient expansion method. It is also found that
the dark radiation and the dark scalar source are expressed by the radion. In
the single-brane limit, we find these dark components disappear. Therefore, it
turns out that the inflation due to the bulk inflaton successfully takes place.
Kaluza-Klein corrections are also taken into account in this case.


title: Dualism between Physical Frames and Time in Quantum Gravity

abstract:
  In this work we present a discussion of the existing links between the
procedures of endowing the quantum gravity with a real time and of including in
the theory a physical reference frame. More precisely, as first step, we
develop the canonical quantum dynamics, starting from the Einstein equations in
presence of a dust fluid and arrive to a Schroedinger evolution. Then, by
fixing the lapse function in the path integral of gravity, we get a
Schroedinger quantum dynamics, of which eigenvalues problem provides the
appearance of a dust fluid in the classical limit. The main issue of our
analysis is to claim that a theory, in which the time displacement invariance,
on a quantum level, is broken, is indistinguishable from a theory for which
this symmetry holds, but a real reference fluid is included.


title:
Can the "brick wall" model present the same results in different
  coordinate representations?

abstract:
  By using the 't Hooft's "brick wall" model and the Pauli-Villars
regularization scheme we calculate the statistical-mechanical entropies arising
from the quantum scalar field in different coordinate settings, such as the
Painlev\'{e} and Lemaitre coordinates. At first glance, it seems that the
entropies would be different from that in the standard Schwarzschild coordinate
since the metrics in both the Painlev\'{e} and Lemaitre coordinates do not
possess the singularity at the event horizon as that in the Schwarzschild-like
coordinate. However, after an exact calculation we find that, up to the
subleading correction, the statistical-mechanical entropies in these
coordinates are equivalent to that in the Schwarzschild-like coordinate. The
result is not only valid for black holes and de Sitter spaces, but also for the
case that the quantum field exerts back reaction on the gravitational field
provided that the back reaction does not alter the symmetry of the spacetime.


title: Dirac quasinormal modes of the Reissner-Nordstr\"om de Sitter black hole

abstract:
  The quasinormal modes of the Reissner-Nordstr\"om de Sitter black hole for
the massless Dirac fields are studied using the P\"oshl-Teller potential
approximation. We find that the magnitude of the imaginary part of the
quasinormal frequencies decreases as the cosmological constant or the orbital
angular momentum increases, but it increases as the charge or the overtone
number increases. An interesting feature is that the imaginary part is almost
linearly related to the real part as the cosmological constant changes for
fixed charge, and the linearity becomes better as the orbital angular momentum
increases. We also prove exactly that the Dirac quasinormal frequencies are the
same for opposite chirality.


title: Semiclassical Instability of the Cauchy Horizon in Self-Similar Collapse

abstract:
  Generic spherically symmetric self-similar collapse results in strong
naked-singularity formation. In this paper we are concerned with particle
creation during a naked-singularity formation in spherically symmetric
self-similar collapse without specifying the collapsing matter. In the generic
case, the power of particle emission is found to be proportional to the inverse
square of the remaining time to the Cauchy horizon (CH). The constant of
proportion can be arbitrarily large in the limit to marginally naked
singularity. Therefore, the unbounded power is especially striking in the case
that an event horizon is very close to the CH because the emitted energy can be
arbitrarily large in spite of a cutoff expected from quantum gravity. Above
results suggest the instability of the CH in spherically symmetric self-similar
spacetime from quantum field theory and seem to support the existence of a
semiclassical cosmic censor. The divergence of redshifts and blueshifts of
emitted particles is found to cause the divergence of power to positive or
negative infinity, depending on the coupling manner of scalar fields to
gravity. On the other hand, it is found that there is a special class of
self-similar spacetimes in which the semiclassical instability of the CH is not
efficient. The analyses in this paper are based on the geometric optics
approximation, which is justified in two dimensions but needs justification in
four dimensions.


title: The general boundary approach to quantum gravity

abstract:
  We present an approach to quantum gravity based on the general boundary
formulation of quantum mechanics, path integral quantization, spin foam models
and renormalization.


title:
A Post-Newtonian diagnostic of quasi-equilibrium binary configurations
  of compact objects

abstract:
  Using equations of motion accurate to the third post-Newtonian (3PN) order
(O(v/c)^6 beyond Newtonian gravity), we derive expressions for the total energy
E and angular momentum J of the orbits of compact binary systems (black holes
or neutron stars) for arbitrary orbital eccentricity. We also incorporate
finite-size contributions such as spin-orbit and spin-spin coupling, and
rotational and tidal distortions, calculated to the lowest order of
approximation, but we exclude the effects of gravitational radiation damping.
We describe how these formulae may be used as an accurate diagnostic of the
physical content of quasi-equilibrium configurations of compact binary systems
of black holes and neutron stars generated using numerical relativity. As an
example, we show that quasi-equilibrium configurations of corotating neutron
stars recently reported by Miller et al. can be fit by our diagnostic to better
than one per cent with a circular orbit and with physically reasonable tidal
coefficients.


title: Generating Gowdy cosmological models

abstract:
  Using the analogy with stationary axisymmetric solutions, we present a method
to generate new analytic cosmological solutions of Einstein's equation
belonging to the class of $T^3$ Gowdy cosmological models. We show that the
solutions can be generated from their data at the initial singularity and
present the formal general solution for arbitrary initial data. We exemplify
the method by constructing the Kantowski-Sachs cosmological model and a
generalization of it that corresponds to an unpolarized $T^3$ Gowdy model.


title:
Searching for Gravitational Waves from the Inspiral of Precessing Binary
  Systems: Astrophysical Expectations and Detection Efficiency of "Spiky''
  Templates

abstract:
  Relativistic spin-orbit and spin-spin couplings has been shown to modify the
gravitational waveforms expected from inspiraling binaries with a black hole
and a neutron star. As a result inspiral signals may be missed due to
significant losses in signal-to-noise ratio, if precession effects are ignored
in gravitational-wave searches. We examine the sensitivity of the anticipated
loss of signal-to-noise ratio on two factors: the accuracy of the precessing
waveforms adopted as the true signals and the expected distributions of
spin-orbit tilt angles, given the current understanding of their physical
origin. We find that the results obtained using signals generated by
approximate techniques are in good agreement with the ones obtained by
integrating the 2PN equations. This shows that a complete account of all
high-order post-Newtonian effects is usually not necessary for the
determination of detection efficiencies. Based on our current astrophysical
expectations, large tilt angles are not favored and as a result the decrease in
detection rate varies rather slowly with respect to the black hole spin
magnitude and is within 20--30% of the maximum possible values.


title: On the Time Reversal Invariance of Classical Electromagnetic Theory

abstract:
  David Albert claims that classical electromagnetic theory is not time
reversal invariant. He acknowledges that all physics books say that it is, but
claims they are "simply wrong" because they rely on an incorrect account of how
the time reversal operator acts on magnetic fields. On that account, electric
fields are left intact by the operator, but magnetic fields are inverted.
Albert sees no reason for the asymmetric treatment, and insists that neither
field should be inverted. I argue, to the contrary, that the inversion of
magnetic fields makes good sense and is, in fact, forced by elementary
geometric considerations. I also suggest a way of thinking about the time
reversal invariance of classical electromagnetic theory -- one that makes use
of the invariant four-dimensional formulation of the theory -- that makes no
reference to magnetic fields at all. It is my hope that it will be of interest
in its own right, Albert aside. It has the advantage that it allows for
arbitrary curvature in the background spacetime structure, and is therefore
suitable for the framework of general relativity. The only assumption one needs
is temporal orientability.


title:
The ultrarelativistic limit of 2D dilaton gravity and its energy
  momentum tensor

abstract:
  The ultrarelativistic limit of twodimensional dilaton gravity is presented
and its associated (anti-)selfdual energy momentum tensor is derived. It is
localized on a null line, although the line element remains twice
differentiable. Relations to the Aichelburg-Sexl spacetime and constant dilaton
vacua are pointed out. Geodesics are found to be smooth for minimally coupled
test particles but non-smooth -- with a finite jump in the acceleration -- for
test particles coupled non-minimally to the dilaton. Quantization on boosted
backgrounds is discussed; no anomalous trace of the energy momentum tensor
arises and the 1-loop flux component can be adjusted to be equal to the
classical flux of the shock wave.


title: Geometry of an accelerated rotating disk

abstract:
  We analyze the geometry of a rotating disk with a tangential acceleration in
the framework of the Special Theory of Relativity, using the kinematic linear
differential system that verifies the relative position vector of time-like
curves in a Fermi reference. A numerical integration of these equations for a
generic initial value problem is made up and the results are compared with
those obtained in other works.


title: Analysis of First LIGO Science Data for Stochastic Gravitational Waves

abstract:
  We present the analysis of between 50 and 100 hrs of coincident
interferometric strain data used to search for and establish an upper limit on
a stochastic background of gravitational radiation. These data come from the
first LIGO science run, during which all three LIGO interferometers were
operated over a 2-week period spanning August and September of 2002. The method
of cross-correlating the outputs of two interferometers is used for analysis.
We describe in detail practical signal processing issues that arise when
working with real data, and we establish an observational upper limit on a
f^{-3} power spectrum of gravitational waves. Our 90% confidence limit is
Omega_0 h_{100}^2 < 23 in the frequency band 40 to 314 Hz, where h_{100} is the
Hubble constant in units of 100 km/sec/Mpc and Omega_0 is the gravitational
wave energy density per logarithmic frequency interval in units of the closure
density. This limit is approximately 10^4 times better than the previous,
broadband direct limit using interferometric detectors, and nearly 3 times
better than the best narrow-band bar detector limit. As LIGO and other
worldwide detectors improve in sensitivity and attain their design goals, the
analysis procedures described here should lead to stochastic background
sensitivity levels of astrophysical interest.


title: On reaction thresholds in doubly special relativity

abstract:
  Two theories of special relativity with an additional invariant scale,
"doubly special relativity" (DSR), are tested with calculations of particle
process kinematics. Using the Judes-Visser modified conservation laws,
thresholds are studied in both theories. In contrast to some linear
approximations, which allow for particle processes forbidden in special
relativity, both the Amelino-Camelia and Maguejo-Smolin frameworks allow no
additional processes. To first order, the Amelino-Camelia framework thresholds
are lowered and the Maguejo-Smolin framework thresholds may be raised or
lowered.


title: Numerical Simulation of General Relativistic Stellar Collapse

abstract:
  We present preliminar results and tests of a new general relativistic code to
simulate the hydrodynamic collapse of a 21 solar masses star. We have assumed
spherical symmetry and used the formalism of Misner and Sharp to construct a
finite-difference scheme to solve the Einstein's equations, energy-momentum
conservation equations and baryonic conservation equation. The code is similar
to the one originally developed by May and White (1967). Here we discuss the
capabilities of the code that make it well suited for numerical relativity on a
personal computer and some caveats based on the experiments we have made with
it.


title:
Comment on "Constraining a possible dependence of Newton's constant on
  the Earth's magnetic field"

abstract:
  Recently A. Rathke has argued that the KK$\psi$ model explanation of the
discrepant measurements of Newton's constant is already ruled out due to
E\"otv\"os experiments by several orders of magnitude. The structure of the
action of the KK$\psi$ model is even qualified as inconsistent in the sense
that it would yield a negative energy of the electromagnetic field. Here, I
refute both claims and emphasize the possibility still open to reconcile the
experimental bounds on the test of the weak equivalence principle (WEP) with
scalar-tensor theories in general by some compensating mechanism.


title:
Some cosmological consequences of the five-dimensional Projective
  Unified Field Theory

abstract:
  The classical observational cosmological tests (Hubble diagram, count of
sources, etc.) are considered for a homogeneous and isotropic model of the
Universe in the framework of the five-dimensional Projective Unified Field
Theory in which gravitation is described by both space-time curvature and some
hypothetical scalar field (sigma-field). It is shown that the presence of the
sigma-field can essentially affect conclusions obtained from the cosmological
tests. The surface brightness-redshift relation can be used as a critical test
for sigma-field effects. It seems reasonable to say that the available
experimental data testify that the sigma-field decreases with time. It is
concluded that the spatial curvature is positive or negative depending on
whether the mass density is larger or smaller than some critical parameter
which is smaller than the critical density and can even take negative values.
It is shown that the increase in the number of the observational cosmological
parameters as compared to the standard Friedmann model can essentially
facilitate coordination of the existing observational data.


title: Some Remarks on the Coupling Prescription of Teleparallel Gravity

abstract:
  By using a nonholonomic moving frame version of the general covariance
principle, an active version of the equivalence principle, an analysis of the
gravitational coupling prescription of teleparallel gravity is made. It is
shown that the coupling prescription determined by this principle is always
equivalent with the corresponding prescription of general relativity, even in
the presence of fermions. An application to the case of a Dirac spinor is made.


title: On Singularity Resolution in Quantum Gravity

abstract:
  We examine the singularity resolution issue in quantum gravity by studying a
new quantization of standard Friedmann-Robertson-Walker geometrodynamics. The
quantization procedure is inspired by the loop quantum gravity programme, and
is based on an alternative to the Schr\"odinger representation normally used in
metric variable quantum cosmology. We show that in this representation for
quantum geometrodynamics there exists a densely defined inverse scale factor
operator, and that the Hamiltonian constraint acts as a difference operator on
the basis states. We find that the cosmological singularity is avoided in the
quantum dynamics. We discuss these results with a view to identifying the
criteria that constitute "singularity resolution" in quantum gravity.


title: Hunting Local Mixmaster Dynamics in Spatially Inhomogeneous Cosmologies

abstract:
  Heuristic arguments and numerical simulations support the Belinskii et al
(BKL) claim that the approach to the singularity in generic gravitational
collapse is characterized by local Mixmaster dynamics (LMD). Here, one way to
identify LMD in collapsing spatially inhomogeneous cosmologies is explored. By
writing the metric of one spacetime in the standard variables of another,
signatures for LMD may be found. Such signatures for the dynamics of spatially
homogeneous Mixmaster models in the variables of U(1)-symmetric cosmologies are
reviewed. Similar constructions for U(1)-symmetric spacetimes in terms of the
dynamics of generic $T^2$-symmetric spacetime are presented.


title:
Towards MIGO, the Matter-wave Interferometric Gravitational-wave
  Observatory, and the Intersection of Quantum Mechanics with General
  Relativity

abstract:
  A dynamical, non-Euclidean spacetime geometry in general relativity theory
implies the possibility of gravitational radiation. Here we explore novel
methods of detecting such radiation from astrophysical sources by means of
matter-wave interferometers (MIGOs), using atomic beams emanating from
supersonic atomic sources that are further cooled and collimated by means of
optical molasses. While the sensitivities of such MIGOs compare favorably with
LIGO and LISA, the sizes of MIGOs can be orders of magnitude smaller, and their
bandwidths wider. Using a pedagogical approach, we place this problem into the
broader context of problems at the intersection of quantum mechanics with
general relativity.


title:
Mergers of Irrotational Neutron Star Binaries in Conformally Flat
  Gravity

abstract:
  We present the first results from our new general relativistic, Lagrangian
hydrodynamics code, which treats gravity in the conformally flat (CF) limit.
The evolution of fluid configurations is described using smoothed particle
hydrodynamics (SPH), and the elliptic field equations of the CF formalism are
solved using spectral methodsin spherical coordinates. The code was tested on
models for which the CF limit is exact, finding good agreement with the
classical Oppenheimer-Volkov solution for a relativistic static spherical star
as well as the exact semi-analytic solution for a collapsing spherical dust
cloud. By computing the evolution of quasi-equilibrium neutron star binary
configurations in the absence of gravitational radiation backreaction, we have
confirmed that these configurations can remain dynamically stable all the way
to the development of a cusp. With an approximate treatment of radiation
reaction, we have calculated the complete merger of an irrotational binary
configuration from the innermost point on an equilibrium sequence through
merger and remnant formation and ringdown, finding good agreement withprevious
relativistic calculations. In particular, we find that mass loss is highly
suppressed by relativistic effects, but that, for a reasonably stiff neutron
star equation of state, the remnant is initially stable against gravitational
collapse because of its strong differential rotation. The gravity wave signal
derived from our numerical calculation has an energy spectrum which matches
extremely well with estimates based solely on quasi-equilibrium results,
deviating from the Newtonian power-law form at frequencies below 1 kHz, i.e.,
within the reach of advanced interferometric detectors.


title: Effective Teukolsky Equation on the Brane

abstract:
  To estimate Kaluza-Klein (KK) corrections on gravitational waves emitted by
perturbed rotating black strings, we give the effective Teukolsky equation on
the brane which is separable equation and hence numerically manageable.


title: Dual curvature tensors and dynamics of gravitomagnetic matter

abstract:
  Gravitomagnetic charge that can also be referred to as the {\it dual mass} or
{\it magnetic mass} is the topological charge in gravity theory. A
gravitomagnetic monopole at rest can produce a stationary gravitomagnetic
field. Due to the topological nature of gravitomagnetic charge, the metric of
spacetime where the gravitomagnetic matter is present will be nonanalytic. In
this paper both the dual curvature tensors (which can characterize the dynamics
of gravitational charge/monopoles) and the antisymmetric gravitational field
equation of gravitomagnetic matter are presented. We consider and discuss the
mathematical formulation and physical properties of the dual curvature tensors
and scalar, antisymmetric source tensors, dual spin connection (including the
low-motion weak-field approximation), dual vierbein field as well as dual
current densities of gravitomagnetic charge. It is shown that the dynamics of
gravitomagnetic charge can be founded within the framework of the above dual
quantities. In addition, the dual relationship between the dynamical theories
of gravitomagnetic charge (dual mass) and gravitoelectric charge (mass) is also
taken into account in the present paper.


title:
A Crystal-based Matter-wave Interferometric Gravitational-wave
  Observatory

abstract:
  It is shown that atom interferometry allows for the construction of MIGO, the
Matter-wave Interferometric Gravitational-wave Observatory. MIGOs of the same
sensitivity as LIGO or LISA are expected to be orders of magnitude smaller than
either one. A design for MIGO using crystalline diffraction gratings is
introduced, and its sensitivity is calculated.


title: Cosmological stretching of perturbations on a cosmic string

abstract:
  We investigate the effects of cosmological expansion on the spectrum of
small-scale structure on a cosmic string. We simulate the evolution of a string
with two modes that differ in wavelength by one order of magnitude. Once the
short mode is inside the horizon, we find that its physical amplitude remains
unchanged, in spite of the fact that its comoving wavelength decreases as the
longer mode enters the horizon. Thus the ratio of amplitude to wavelength for
the short mode becomes larger than it would be in the absence of the long mode.


title:
Gravitational waves interacting with a spinning charged particle in the
  presence of a uniform magnetic field

abstract:
  The equations which determine the response of a spinning charged particle
moving in a uniform magnetic field to an incident gravitational wave are
derived in the linearized approximation to general relativity. We verify that
1) the components of the 4-momentum, 4-velocity and the components of the
spinning tensor, both electric and magnetic moments, exhibit resonances and 2)
the co-existence of the uniform magnetic field and the GW are responsible for
the resonances appearing in our equations. In the absence of the GW, the
magnetic field and the components of the spin tensor decouple and the magnetic
resonances disappear.


title: Loop Quantum Cosmology and Boundary Proposals

abstract:
  For many years, the most active area of quantum cosmology has been the issue
of choosing boundary conditions for the wave function of a universe. Recently,
loop quantum cosmology, which is obtained from loop quantum gravity, has shed
new light on this question. In this case, boundary conditions are not chosen by
hand with some particular physical intuition in mind, but they are part of the
dynamical law. It is then natural to ask if there are any relations between
these boundary conditions and the ones provided before. After discussing the
technical foundation of loop quantum cosmology which leads to crucial
differences to the Wheeler-DeWitt quantization, we compare the dynamical
initial conditions of loop quantum cosmology with the tunneling and the
no-boundary proposal and explain why they are closer to the no-boundary
condition. We end with a discussion of recent developments and several open
problems of loop quantum cosmology.


title:
Instability of a four-dimensional de Sitter black hole with a
  conformally coupled scalar field

abstract:
  We study the stability of new neutral and electrically charged
four-dimensional black hole solutions of Einstein's equations with a positive
cosmological constant and conformally coupled scalar field. The neutral black
holes are always unstable. The charged black holes are also shown analytically
to be unstable for the vast majority of the parameter space of solutions, and
we argue using numerical techniques that the configurations corresponding to
the remainder of the parameter space are also unstable.


title: Neutrino current in a gravitational plane wave collision background

abstract:
  The behaviour of a massless Dirac field on a general spacetime background
representing two colliding gravitational plane waves is discussed in the
Newman-Penrose formalism. The geometrical properties of the neutrino current
are analysed and explicit results are given for the special Ferrari-Ibanez
solution.


title: A Novel Approach to Braneworld

abstract:
  Evaluating Kaluza-Klein (KK) corrections is indispensable to test the
braneworld scenario. In this report, we propose a novel symmetry approach to an
effective 4-dimensional action with KK corrections for the Randall-Sundrum
two-brane system.


title: Gravitational Waves from Rotating Black Strings

abstract:
  In the Randall-Sundrum two-brane model (RS1), a Kerr black hole on the brane
can be naturally identified with a section of rotating black string. To
estimate Kaluza-Klein (KK) corrections on gravitational waves emitted by
perturbed rotating black strings, we give the effective Teukolsky equation on
the brane which is separable equation and hence numerically manageable. In this
process, we derive the master equation for the electric part of the Weyl tensor
$E_{\mu\nu}$ which would be also useful to discuss the transition from black
strings to localized black holes triggered by Gregory-Laflamme instability.


title:
Acceleration of the universe, vacuum metamorphosis, and the large-time
  asymptotic form of the heat kernel

abstract:
  We investigate the possibility that the late acceleration observed in the
rate of expansion of the universe is due to vacuum quantum effects arising in
curved spacetime. The theoretical basis of the vacuum cold dark matter (VCDM),
or vacuum metamorphosis, cosmological model of Parker and Raval is revisited
and improved. We show, by means of a manifestly nonperturbative approach, how
the infrared behavior of the propagator (related to the large-time asymptotic
form of the heat kernel) of a free scalar field in curved spacetime causes the
vacuum expectation value of its energy-momentum tensor to exhibit a resonance
effect when the scalar curvature R of the spacetime reaches a particular value
related to the mass of the field. we show that the back reaction caused by this
resonance drives the universe through a transition to an accelerating expansion
phase, very much in the same way as originally proposed by Parker and Raval.
Our analysis includes higher derivatives that were neglected in the earlier
analysis, and takes into account the possible runaway solutions that can follow
from these higher-derivative terms. We find that the runaway solutions do not
occur if the universe was described by the usual classical FRW solution prior
to the growth of vacuum energy-density and negative pressure (i.e., vacuum
metamorphosis) that causes the transition to an accelerating expansion of the
universe in this theory.


title: Local conservation law and dark radiation in cosmological braneworld

abstract:
  In the context of the Randall-Sundrum (RS) single-brane scenario, we discuss
the bulk geometry and dynamics of a cosmological brane in terms of the local
energy conservation law which exists for the bulk that allows slicing with a
maximally symmetric 3-space. This conservation law enables us to define a local
mass in the bulk. We show that there is a unique generalization of the dark
radiation on the brane, which is given by the local mass. We find there also
exists a conserved current associated with the Weyl tensor, and the
corresponding local charge, which we call the Weyl charge, is given by the sum
of the local mass and a certain linear combination of the components of the
bulk energy-momentum tensor. This expression of the Weyl charge relates the
local mass with the projected Weyl tensor, $E_{\mu\nu}$, which plays a central
role in the geometrical formalism of the RS braneworld. On the brane, in
particular, this gives a decomposition of the projected Weyl tensor into the
local mass and the bulk energy-momentum tensor. Then, as an application of
these results, we consider a null dust model for the bulk energy-momentum
tensor and discuss the black hole formation in the bulk. We investigate the
causal structure by identifying the locus of the apparent horizon and clarify
possible brane trajectories in the bulk. We find that the brane stays always
outside the black hole as long as it is expanding. We also find an upper bound
on the value of the Hubble parameter in terms of the matter energy density on
the brane, irrespective of the energy flux emitted from the brane.


title: Big Crunch Avoidance in k = 1 Semi-Classical Loop Quantum Cosmology

abstract:
  It is well known that a closed universe with a minimally coupled massive
scalar field always collapses to a singularity unless the initial conditions
are extremely fine tuned. We show that the corrections to the equations of
motion for the massive scalar field, given by loop quantum gravity in high
curvature regime, always lead to a bounce independently of the initial
conditions. In contrast to the previous works in loop quantum cosmology, we
note that the singularity can be avoided even at the semi-classical level of
effective dynamical equations with non-perturbative quantum gravity
modifications, without using a discrete quantum evolution.


title: Ashtekar Formulation with Temporal Foliations

abstract: This article has been withdrawn.


title: Numerical simulation of orbiting black holes

abstract:
  We present numerical simulations of binary black hole systems which for the
first time last for about one orbital period for close but still separate black
holes as indicated by the absence of a common apparent horizon. An important
part of the method is the construction of comoving coordinates, in which both
the angular and radial motion is minimized through a dynamically adjusted shift
condition. We use fixed mesh refinement for computational efficiency.


title:
Detection of Weak Gravitational Waves by Interferometric Methods and
  Problem of Invertible Calculations

abstract:
  The fundamental features of the detection of non-stationary undulatory
perturbations of metrics based on the interference effects are considered. The
advantage of the Aharonov-Bohm effect in superconductors for these purposes in
comparison with the ordinary optical interference is demonstrated. Some
circuitries of the interferometric detectors in order to be used with SQUID are
suggested. The possibilities of lowering the noise temperature of the ultraweak
signals detectors based on the analogy between the processes of high-sensitive
measurements and the reversible calculations are discussed.


title: Scalar Gravity and Higgs Mechanism

abstract:
  The role that the auxiliary scalar field $\phi$ played in Brans-Dicke
cosmology is discussed. If a constant vacuum energy is assumed to be the origin
of dark energy, then the corresponding density parameter would be a quantity
varying with $\phi$; and almost all of the fundamental components of our
universe can be unified into the dynamical equation for $\phi$. As a
generalization of Brans-Dicke theory, we propose a new gravity theory with a
complex scalar field $\phi$ which is coupled to the cosmological curvature
scalar. Through such a coupling, the Higgs mechanism is naturally incorporated
into the evolution of the universe, and a running density of the field vacuum
energy is obtained which may release the particle standard model from the
rigorous cosmological constant problem in some sense. Our model predicts a
running mass scale of the fundamental particles in which the gauge symmetry
breaks spontaneously. The running speed of the mass scale in our case could
survive all existing experiments.


title: Cosmological Constant Problem

abstract:
  The cosmological constant problem is reviewed and a possible quantum gravity
resolution is proposed. A space satellite E\"otv\"os experiment for zero-point
vacuum energy is proposed to see whether Casimir vacuum energy falls in a
gravitational field at the same rate as ordinary matter.


title: The interaction between graviton spin and gravitomagnetic fields

abstract:
  This note is devoted to the detailed mathematical treatment of the coupling
of graviton spin to gravitomagnetic fields. The expression (i.e., $\sim
g_{0m}\dot{g}_{0n}(\partial_{m}g_{0n}-\partial_{n}g_{0m})$) for the graviton
spin-gravitomagnetic (S-G) coupling in the Lagrangian/Hamiltonian density of
the weak gravitational fields is presented in this note.


title: Numerical simulations of generic singuarities

abstract:
  Numerical simulations of the approach to the singularity in vacuum spacetimes
are presented here. The spacetimes examined have no symmetries and can be
regarded as representing the general behavior of singularities. It is found
that the singularity is spacelike and that as it is approached, the spacetime
dynamics becomes local and oscillatory.


title: The light cone at infinity

abstract:
  A recent refinement of Penrose's conformal framework for asymptotically flat
space-times is summarized. The key idea concerns advanced and retarded
conformal factors, which allow a rigid description of infinity as a locally
metric light cone. In the new framework, the Bondi-Sachs energy-flux integrals
of ingoing and outgoing gravitational radiation decay at spatial infinity such
that the total radiated energy is finite, and the Bondi-Sachs energy-momentum
has a unique limit at spatial infinity, coinciding with the uniquely rendered
ADM energy-momentum.


title: Quantum process and the foundation of relational theories of space-time

abstract:
  We present current theories about the structure of space and time, where the
building blocks are some fundamental entities (yes-no experiment, quantum
processes, spin net-work, preparticles) that do not presuppose the existence of
space and time. The relations among these objects are the base for a
pregeometry of discrete character, the continuous limit of which gives rise to
the physical properties of the space and time.


title: Quantum evolution of the Universe from $\tau=0$

abstract:
  We have shown that DeWitt constraint H=0 on the physical states of the
Universe does not prevent Heisenberg operators and its mean values to evolve
with time. Mean value from observable, which is singular in classical theory,
is also singular in a quantum case.


title: No-horizon theorem for vacuum gravity with spacelike G1 isometry groups

abstract:
  We show that (3+1) vacuum spacetimes admitting a global, spacelike,
one-parameter Lie group of isometries of translational type cannot contain
apparent horizons. The only assumption made is that of the existence of a
global spacelike Killing vector field with infinite open orbits; the
four-dimensional vacuum spacetime metric is otherwise arbitrary. This result
may thus be viewed as a hoop conjecture theorem for vacuum gravity with one
spacelike translational Killing symmetry.


title: No-horizon theorem for spacetimes with spacelike G1 isometry groups

abstract:
  We consider four-dimensional spacetimes $(M,{\mathbf g})$ which obey the
Einstein equations ${\mathbf G}={\mathbf T}$, and admit a global spacelike
$G_{1}={\mathbb R}$ isometry group. By means of dimensional reduction and local
analyis on the reduced (2+1) spacetime, we obtain a sufficient condition on
${\mathbf T}$ which guarantees that $(M,{\mathbf g})$ cannot contain apparent
horizons. Given any (3+1) spacetime with spacelike translational isometry, the
no-horizon condition can be readily tested without the need for dimensional
reduction. This provides thus a useful and encompassing apparent horizon test
for $G_{1}$-symmetric spacetimes. We argue that this adds further evidence
towards the validity of the hoop conjecture, and signals possible violations of
strong cosmic censorship.


title: Shear-free gravitational collapse is strongly censored

abstract:
  We consider spherically symmetric spacetimes with matter whose timelike flow
is assumed to be shear-free. A number of results on the formation and
visibility of spacetime singularities is proven, with the main one being that
shear-free collapse cannot admit locally naked singularities (which implies
absence of globally naked singularities). We conjecture that shear is a
necessary condition for the occurrence of locally naked singularities in
generic gravitational collapse.


title: Phenomenology of Doubly Special Relativity

abstract:
  Investigations of the possibility that some novel ``quantum" properties of
spacetime might induce a modification dispersion relation focused at first on
scenarios with Planck-scale violations of Lorentz symmetry. More recently
several studies have considered the possibility of a ``doubly special
relativity", in which the modification of the dispersion relation emerges from
a framework with both the Planck scale and the speed-of-light scale as
characteristic scales of a deformation of the Lorentz transformations. For the
schemes with broken Lorentz symmetry at the Planck scale there is a large
literature on the derivation of experimental limits. We provide here a
corresponding analysis for the doubly-special-relativity framework. We find
that the analyses of photon stability, synchrotron radiation, and threshold
conditions for particle production in collision processes, the three contexts
which are considered as most promising for constraining the
broken-Lorentz-symmetry scenario, cannot provide significant constraints on
doubly-special-relativity parameter space. However, certain types of analyses
of gamma-ray bursts are sensitive to the symmetry deformation. A key element of
our study is an observation that removes a possible sign ambiguity for the
doubly-special-relativity framework. This result also allows us to characterize
more sharply the differences between the doubly-special-relativity framework
and the framework of k-Poincare Hopf algebras, two frameworks which are often
confused with each other in the literature.


title: Modern theories of discrete time

abstract:
  We review some modern theories about the structure of space and time, in
particular those related to discrete space and time. Following an
epistemological method we start from theories which discuss discrete space and
time as a mathematical tool to solve physical models. Antother theories look
for physical content of the discrete structure of space and time, based in
relational theories of space and time which are derived from the relations of
some fundamental entities. Finally we present some philosophical positions who
try to find the ontological foundation of the relational theories os space and
time.


title: Moduli of quantum Riemannian geometries on <= 4 points

abstract:
  We classify parallelizable noncommutative manifold structures on finite sets
of small size in the general formalism of framed quantum manifolds and
vielbeins introduced previously. The full moduli space is found for $\le 3$
points, and a restricted moduli space for 4 points. The topological part of the
moduli space is found for $\le 9$ points based on the known atlas of regular
graphs. We also discuss aspects of the quantum theory defined by functional
integration.


title:
Rapid Evaluation of Radiation Boundary Kernels for Time-domain Wave
  Propagation on Blackholes

abstract:
  For scalar, electromagnetic, or gravitational wave propagation on a fixed
Schwarzschild blackhole background, we describe the exact nonlocal radiation
outer boundary conditions (ROBC) appropriate for a spherical outer boundary of
finite radius enclosing the blackhole. Derivation of the ROBC is based on
Laplace and spherical-harmonic transformation of the Regge-Wheeler equation,
the PDE governing the wave propagation, with the resulting radial ODE an
incarnation of the confluent Heun equation. For a given angular index l the
ROBC feature integral convolution between a time-domain radiation boundary
kernel (TDRK) and each of the corresponding 2l+1 spherical-harmonic modes of
the radiating wave. The TDRK is the inverse Laplace transform of a
frequency-domain radiation kernel (FDRK) which is essentially the logarithmic
derivative of the asymptotically outgoing solution to the radial ODE. We
numerically implement the ROBC via a rapid algorithm involving approximation of
the FDRK by a rational function. Such an approximation is tailored to have
relative error \epsilon uniformly along the axis of imaginary Laplace
frequency. Theoretically, \epsilon is also a long-time bound on the relative
convolution error. Via study of one-dimensional radial evolutions, we
demonstrate that the ROBC capture the phenomena of quasinormal ringing and
decay tails. Moreover, carrying out a numerical experiment in which a wave
packet strikes the boundary at an angle, we find that the ROBC yield accurate
results in a three-dimensional setting. Our work is a partial generalization to
Schwarzschild wave propagation and Heun functions of the methods developed for
flatspace wave propagation and Bessel functions by Alpert, Greengard, and
Hagstrom.


title: Gauge-Dependent Cosmological "Constant"

abstract:
  When the cosmological constant of spacetime is derived from the 5D
induced-matter theory of gravity, we show that a simple gauge transformation
changes it to a variable measure of the vacuum which is infinite at the big
bang and decays to an astrophysically-acceptable value at late epochs. We
outline implications of this for cosmology and galaxy formation.


title: Remarks on dimensional reduction of multidimensional cosmological models

abstract:
  Multidimensional cosmological models with factorizable geometry and their
dimensional reduction to effective four-dimensional theories are analyzed on
sensitivity to different scalings. It is shown that a non-correct gauging of
the effective four-dimensional gravitational constant within the dimensional
reduction results in a non-correct rescaling of the cosmological constant and
the gravexciton/radion masses. The relationship between the effective
gravitational constants of theories with different dimensions is discussed for
setups where the lower dimensional theory results via dimensional reduction
from the higher dimensional one and where the compactified space components
vary dynamically.


title: The Cauchy problem on spacetimes that are not globally hyperbolic

abstract:
  The initial value problem is well-defined on a class of spacetimes broader
than the globally hyperbolic geometries for which existence and uniqueness
theorems are traditionally proved. Simple examples are the time-nonorientable
spacetimes whose orientable double cover is globally hyperbolic. These
spacetimes have generalized Cauchy surfaces on which smooth initial data sets
yield unique solutions. A more difficult problem is to characterize the class
of spacetimes with closed timelike curves that admit a well-posed initial value
problem. Examples of spacetimes with closed timelike curves are given for which
smooth initial data at past null infinity has been recently shown to yield
solutions. These solutions appear to be unique, and uniquesness has been proved
in particular cases. Other examples, however, show that confining closed
timelike curves to compact regions is not sufficient to guarantee uniqueness.
An approach to the characterization problem is suggested by the behavior of
congruences of null rays. Interacting fields have not yet been studied, but
particle models suggest that uniqueness (and possibly existence) is likely to
be lost as the strength of the interaction increases.


title: Sagnac effect and pure geometry

abstract:
  We show that the Sagnac effect is not necessarily due to the presence of a
rotating observer, but rather to the closed path of light in space and an even
inertial relative motion between the observer and the physical device forcing
light to move along a closed path.


title: Spatial infinity in higher dimensional spacetimes

abstract:
  Motivated by recent studies on the uniqueness or non-uniqueness of higher
dimensional black hole spacetime, we investigate the asymptotic structure of
spatial infinity in n-dimensional spacetimes($n \geq 4$). It turns out that the
geometry of spatial infinity does not have maximal symmetry due to the
non-trivial Weyl tensor {}^{(n-1)}C_{abcd} in general. We also address static
spacetime and its multipole moments P_{a_1 a_2 ... a_s}. Contrasting with four
dimensions, we stress that the local structure of spacetimes cannot be unique
under fixed a multipole moments in static vacuum spacetimes. For example, we
will consider the generalized Schwarzschild spacetimes which are deformed black
hole spacetimes with the same multipole moments as spherical Schwarzschild
black holes. To specify the local structure of static vacuum solution we need
some additional information, at least, the Weyl tensor {}^{(n-2)}C_{abcd} at
spatial infinity.


title: Gravitational perturbation of traversable wormhole

abstract:
  In this paper, we study the perturbation problem of the scalar,
electromagnetic, and gravitational waves under the traversable Lorentzian
wormhole geometry. The unified form of the potential for the Schr\"odinger type
one-dimensional wave equation is found.


title: Classification of the Weyl Tensor in Higher Dimensions

abstract:
  We discuss the algebraic classification of the Weyl tensor in higher
dimensional Lorentzian manifolds. This is done by characterizing algebraically
special Weyl tensors by means of the existence of aligned null vectors of
various orders of alignment. Further classification is obtained by specifying
the alignment type and utilizing the notion of reducibility. For a complete
classification it is then necessary to count aligned directions, the dimension
of the alignment variety, and the multiplicity of principal directions. The
present classification reduces to the classical Petrov classification in four
dimensions. Some applications are briefly discussed.


title: Quantum singularity of Levi-Civita spacetimes

abstract:
  Quantum singularities in general relativistic spacetimes are determined by
the behavior of quantum test particles. A static spacetime is quantum
mechanically singular if the spatial portion of the wave operator is not
essentially self-adjoint. Here Weyl's limit point-limit circle criterion is
used to determine whether a wave operator is essentially self-adjoint. This
test is then applied to scalar wave packets in Levi-Civita spacetimes to help
elucidate the physical properties of the spacetimes in terms of their metric
parameters.


title: Alignment and algebraically special tensors in Lorentzian geometry

abstract:
  We develop a dimension-independent theory of alignment in Lorentzian
geometry, and apply it to the tensor classification problem for the Weyl and
Ricci tensors. First, we show that the alignment condition is equivalent to the
PND equation. In 4D, this recovers the usual Petrov types. For higher
dimensions, we prove that, in general, a Weyl tensor does not possess aligned
directions. We then go on to describe a number of additional algebraic types
for the various alignment configurations. For the case of second-order
symmetric (Ricci) tensors, we perform the classification by considering the
geometric properties of the corresponding alignment variety.


title: Scalar waves on a naked-singularity background

abstract:
  We obtain global space-time weighted-L^2 (Morawetz) and L^4 (Strichartz)
estimates for a massless chargeless scalar field propagating on a
super-extremal (overcharged) Reissner-Nordstrom background. We begin by
discussing the question of well-posedness of the Cauchy problem for scalar
fields on non-globally hyperbolic manifolds and the role played by the
Friedrichs extension, go over the construction of the function spaces involved,
show how to transform the problem to one about the wave equation on the
Minkowski space with a singular potential, and finally prove that the potential
thus obtained satisfies the various conditions needed in order for the
estimates to hold.


abstract:
  Doppler effect and Hubble effect in different models of space-time in the
case of auto-parallel motion of the observer are considered. The Doppler effect
and shift frequency parameter are specialized for the case of auto-parallel
motion of the observer. The Hubble effect and shift frequency parameter are
considered for the same case. It is shown that by the use of the variation of
the shift frequency parameter during a time perod, considered locally in the
proper frame of reference of an observer, one can directly determine the
centrifugal (centripetal) relative velocity and acceleration as well as the
Coriolis relative velocity and acceleration of an astronomical object moving
relatively to the observer. All results are obtained on purely kinematic basis
without taking into account the dynamic reasons for the considered effect. PACS
numbers: 98.80.Jk; 98.62.Py; 04.90.+e; 04.80.Cc


title: Bianchi identities in higher dimensions

abstract:
  A higher dimensional frame formalism is developed in order to study
implications of the Bianchi identities for the Weyl tensor in vacuum spacetimes
of the algebraic types III and N in arbitrary dimension $n$. It follows that
the principal null congruence is geodesic and expands isotropically in two
dimensions and does not expand in $n-4$ spacelike dimensions or does not expand
at all. It is shown that the existence of such principal geodesic null
congruence in vacuum (together with an additional condition on twist) implies
an algebraically special spacetime. We also use the Myers-Perry metric as an
explicit example of a vacuum type D spacetime to show that principal geodesic
null congruences in vacuum type D spacetimes do not share this property.


title: The Pioneer's Anomalous Doppler Drift as a Berry Phase

abstract:
  The detected anomalous frequency drift acceleration in Pioneer's radar data
finds its explanation in a Berry phase that obtains the quantum state of a
photon that propagates within an expanding space-time. The clock acceleration
is just the adiabatic expansion rate and an analogy between the effect and
Foucault's experiment is fully suggested. In this sense, light rays play a
similar role in the expanding space than Foucault's Pendulum does while
determining Earth's rotation. On the other hand, one could speculate about a
suitable future experiment at "laboratory" scales able to measure the local
cosmological expansion rate using the procedure outlined in this paper.


title: Quantum Foam

abstract:
  Quantum foam, also known as spacetime foam, has its origin in quantum
fluctuations of spacetime. Its physics is intimately linked to that of black
holes and computation. Arguably it is the source of the holographic principle
which severely limits how densely information can be packed in space. Various
proposals to detect the foam are briefly discussed. Its detection will provide
us with a glimpse of the ultimate structure of space and time.


title:
Is the Lorentz signature of the metric of spacetime electromagnetic in
  origin?

abstract:
  We formulate a premetric version of classical electrodynamics in terms of the
excitation H and the field strength F. A local, linear, and symmetric spacetime
relation between H and F is assumed. It yields, if electric/magnetic
reciprocity is postulated, a Lorentzian metric of spacetime thereby excluding
Euclidean signature (which is, nevertheless, discussed in some detail).
Moreover, we determine the Dufay law (repulsion of like charges and attraction
of opposite ones), the Lenz rule (the relative sign in Faraday's law), and the
sign of the electromagnetic energy. In this way, we get a systematic
understanding of the sign rules and the sign conventions in electrodynamics.
The question in the title of the paper is answered affirmatively.


title: Whispering Gallery Resonators and Tests of Lorentz Invariance

abstract:
  The frequencies of a cryogenic sapphire oscillator and a hydrogen maser are
compared to set new constraints on a possible violation of Lorentz invariance.
We give a detailed description of microwave resonators operating in Whispering
Gallery modes and then apply it to derive explicit models for Lorentz violating
effects in our experiment. Models are calculated in the theoretical framework
of Robertson, Mansouri and Sexl and in the standard model extension (SME) of
Kostelecky and co-workers. We constrain the parameters of the Mansouri and Sexl
test theory to $1/2 - \beta_{MS} + \delta_{MS} = (1.2 \pm 2.2) \times 10^{-9}$
and $\beta_{MS} - \alpha_{MS} - 1 = (1.6 \pm 3.0) \times 10^{-7}$ which is of
the same order as the best results from other experiments for the former and
represents a 70 fold improvement for the latter. These results correspond to an
improvement of our previously published limits [Wolf P. et al., Phys. Rev.
Lett. {\bf 90}, 6, 060402, (2003)] by about a factor 2.


title: On black holes as inner boundaries for the constraint equations

abstract:
  General aspects of the boundary value problem for the constraint equations
and their application to black holes are discussed.


title: Dynamical shift conditions for the Z4 and BSSN hyperbolic formalisms

abstract:
  A class of dynamical shift conditions is shown to lead to a strongly
hyperbolic evolution system, both in the Z4 and in the BSSN Numerical
Relativity formalisms. This class generalizes the harmonic shift condition,
where light speed is the only non-trivial characteristic speed, and it is
contained into the multi-parameter family of minimal distortion shift
conditions recently proposed by Lindblom and Scheel. The relationship with the
analogous 'dynamical freezing' shift conditions used in black hole simulations
discussed.


title: Regular and Black Hole Skyrmions with Axisymmetry

abstract:
  It has been known that a B=2 skyrmion is axially symmetric. We consider the
Skyrme model coupled to gravity and obtain static axially symmetric regular and
black hole solutions numerically. Computing the energy density of the skyrmion,
we discuss the effect of gravity to the energy density and baryon density of
the skyrmion.


title: Ether theory of gravitation: why and how?

abstract:
  Gravitation might make a preferred frame appear, and with it a clear
space/time separation--the latter being, a priori, needed by quantum mechanics
(QM) in curved space-time. Several models of gravitation with an ether are
discussed: they assume metrical effects in an heterogeneous ether and/or a
Lorentz-symmetry breaking. One scalar model, starting from a semi-heuristic
view of gravity as a pressure force, is detailed. It has been developed to a
complete theory including continuum dynamics, cosmology, and links with
electromagnetism and QM. To test the theory, an asymptotic scheme of
post-Newtonian approximation has been built. That version of the theory which
is discussed here predicts an internal-structure effect, even at the
point-particle limit. The same might happen also in general relativity (GR) in
some gauges, if one would use a similar scheme. Adjusting the equations of
planetary motion on an ephemeris leaves a residual difference with it; one
should adjust the equations using primary observations. The same effects on
light rays are predicted as with GR, and a similar energy loss applies to
binary pulsars.


title: Shear-free radiating collapse and conformal flatness

abstract:
  Here we study some general properties of spherical shear-free collapse. Its
general solution when imposing conformal flatness is reobtained [1,2] and
matched to the outgoing Vaidya spacetime. We propose a simple model satisfying
these conditions and study its physical consequences. Special attention
deserve, the role played by relaxational processes and the conspicuous link
betweeen dissipation and density inhomogeneity.


title:
Static and dynamic traversable wormhole geometries satisfying the
  Ford-Roman constraints

abstract:
  It was shown by Ford and Roman in 1996 that quantum field theory severely
constrains wormhole geometries on a macroscopic scale. The first part of this
paper discusses a wide class of wormhole solutions that meet these constraints.
The type of shape function used is essentially generic. The constraints are
then discussed in conjunction with various redshift functions. Violations of
the weak energy condition and traversability criteria are also considered. The
second part of the paper analyzes analogous time-dependent (dynamic) wormholes
with the aid of differential forms. It is shown that a violation of the weak
energy condition is not likely to be avoidable even temporarily.


title: Exact Solutions of Einstein's Field Equations

abstract:
  We examine various well known exact solutions available in the literature to
investigate the recent criterion obtained in ref. [20] which should be
fulfilled by any static and spherically symmetric solution in the state of
hydrostatic equilibrium. It is seen that this criterion is fulfilled only by
(i) the regular solutions having a vanishing surface density together with the
pressure, and (ii) the singular solutions corresponding to a non-vanishing
density at the surface of the configuration . On the other hand, the regular
solutions corresponding to a non-vanishing surface density do not fulfill this
criterion. Based upon this investigation, we point out that the exterior
Schwarzschild solution itself provides necessary conditions for the types of
the density distributions to be considered inside the mass, in order to obtain
exact solutions or equations of state compatible with the structure of general
relativity. The regular solutions with finite centre and non-zero surface
densities which do not fulfill the criterion [20], in fact, can not meet the
requirement of the `actual mass' set up by exterior Schwarzschild solution. The
only regular solution which could be possible in this regard is represented by
uniform (homogeneous) density distribution.
  The criterion [20] provides a necessary and sufficient condition for any
static and spherical configuration (including core-envelope models) to be
compatible with the structure of general relativity. Thus, it may find
application to construct the appropriate core-envelope models of stellar
objects like neutron stars and may be used to test various equations of state
for dense nuclear matter and the models of relativistic stellar structures like
star clusters.


title: Holonomy, Aharonov-Bohm effect and phonon scattering in superfluids

abstract:
  In this article we discuss the analogy between superfluids and a spinning
thick cosmic string. We use the geometrical approach to obtain the geometrical
phases for a phonon in the presence of a vortex. We use loop variables for a
geometric description of Aharonov-Bohm effect in these systems. We use holonomy
transformations to characterize globally the "space-time" of a vortex and in
this point of view we study the gravitational analog of the Aharonov-Bohm
effect in this system. We demonstrate that in the general case the
Aharonov-Bohm effect has a contribution both from the rotational and the
translational holonomy. We study also Berrys quantum phase for phonons in this
systems.


title: Accelerated expansion from braneworld models with variable vacuum energy

abstract:
  In braneworld models a variable vacuum energy may appear if the size of the
extra dimension changes during the evolution of the universe. In this scenario
the acceleration of the universe is related not only to the variation of the
cosmological term, but also to the time evolution of $G$ and, possibly, to the
variation of other fundamental "constants" as well. This is because the
expansion rate of the extra dimension appears in different contexts, notably in
expressions concerning the variation of rest mass and electric charge. We
concentrate our attention on spatially-flat, homogeneous and isotropic,
brane-universes where the matter density decreases as an inverse power of the
scale factor, similar (but at different rate) to the power law in FRW-universes
of general relativity.
  We show that these braneworld cosmologies are consistent with the observed
accelerating universe and other observational requirements. In particular, $G$
becomes constant and $\Lambda_{(4)} \approx const \times H^2$ asymptotically in
time. Another important feature is that the models contain no "adjustable"
parameters. All the quantities, even the five-dimensional ones, can be
evaluated by means of measurements in 4D. We provide precise constrains on the
cosmological parameters and demonstrate that the "effective" equation of state
of the universe can, in principle, be determined by measurements of the
deceleration parameter alone. We give an explicit expression relating the
density parameters $\Omega_{\rho}$, $\Omega_{\Lambda}$ and the deceleration
parameter $q$. These results constitute concrete predictions that may help in
observations for an experimental/observational test of the model.


title: Horizons

abstract:
  The gravitational force harbours a fundamental instability against collapse.
In standard General Relativity without Quantum Mechanics, this implies the
existence of black holes as natural, stable solutions of Einstein's equations.
If one attempts to quantize the gravitational force, one should also consider
the question how Quantum Mechanics affects the behaviour of black holes. In
this lecture, we concentrate on the horizon. One would have expected that its
properties could be derived from general coordinate transformations out of a
vacuum state. In contrast, it appears that much new physics is needed. Much of
that is still poorly understood, but one may speculate on the way information
is organized at a horizon, and how refined versions of Quantum Theory may lead
to answers.


title: Axially symmetric rotating traversable wormholes

abstract:
  This paper generalizes the static and spherically symmetric traversable
wormhole geometry to a rotating axially symmetric one with a time-dependent
angular velocity by means of an exact solution. It was found that the violation
of the weak energy condition, although unavoidable, is considerably less severe
than in the static spherically symmetric case. The radial tidal constraint is
more easily met due to the rotation. Similar improvements are seen in one of
the lateral tidal constraints. The magnitude of the angular velocity may have
little effect on the weak energy condition violation for an axially symmetric
wormhole. For a spherically symmetric one, however, the violation becomes less
severe with increasing angular velocity. The time rate of change of the angular
velocity, on the other hand, was found to have no effect at all. Finally, the
angular velocity must depend only on the radial coordinate, confirming an
earlier result.


title:
On The Geometrical and Physical Properties of Spherically Symmetric
  Non-Static Space-Times: Self-Similarity

abstract:
  An exact solution of the Einstein field equations is found under the
assumption of spherically symmetry and the existence of one-parameter group of
homothetic motions. This solution has a singularity at $r = 0$, and has
non-vanishing expansion, acceleration and shear. Tidal forces in radial
direction will not stretch an observer falling in this fluid. If the material
is represented by perfect fluid, we can verify that the solution coincides with
stiff matter case. In this case, the solution has zero expansion. Tidal forces
in radial direction will not stretch an observer falling in this fluid and they
not squeeze him in transverse directions.


title:
The self-energy of a charged particle in the presence of a topological
  defect distribution

abstract:
  In this work we study a charged particle in the presence of both a continuous
distribution of disclinations and a continuous distribution of edge
dislocations in the framework of the geometrical theory of defects. We obtain
the self-energy for a single charge both in the internal and external regions
of either distribution. For both distributions the result outside the defect
distribution is the self-energy that a single charge experiments in the
presence of a single defect.


title: Reissner-Nordstrom Black Holes and Thick Domain Walls

abstract:
  We solve numerically equations of motion for real self-interacting scalar
fields in the background of Reissner-Nordstrom black hole and obtained a
sequence of static axisymmetric solutions representing thick domain walls
charged black hole systems. In the case of extremal Reissner-Nordstrom black
hole solution we find that there is a parameter depending on the black hole
mass and the width of the domain wall which constitutes the upper limit for the
expulsion to occur.


title: Brane-worlds and Cosmology

abstract:
  The Friedmann equation for a FRW-brane-world in a flat bulk is derived and
applied to the accelerated expansion of the universe.


title: The Petrov type of the BMPV metric

abstract:
  We show that the BMPV metric has Petrov type 22. This means that the BMPV
metric is less algebraically special than the five-dimensional Schwarzschild
metric, which has Petrov type \underline{22}.


title:
Direct Observation of Broadband Coating Thermal Noise in a Suspended
  Interferometer

abstract:
  We have directly observed broadband thermal noise in silica/tantala coatings
in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with
the prediction based on indirect, ring-down measurements of coating mechanical
loss, validating that method as a tool for the development of advanced
interferometric gravitational-wave detectors.


title: New Hints from General Relativity

abstract:
  The search for a quantum theory of gravity has followed two parallel but
different paths. One aims at arriving at the final theory starting from a
priori assumptions as to its form and building it from the ground up. The other
tries to infer as much as possible about the unknown theory from the existing
ones and use our current knowledge to constrain the possibilities for the
quantum theory of gravity. Probably the biggest success of the second path has
been the results of black hole thermodynamics. The subject of this essay is a
new, highly promising such result, the application of quasinormal modes in
quantum gravity.


title: Rotating wormhole and scalar perturbation

abstract:
  In this paper, we study the rotational wormhole and scalar perturbation under
the spacetime. We found the Schr\"odinger like equation and consider the
asymptotic solutions for the special cases.


title:
Quantum Field Effect on Symmetry Breaking and Restoration in Anisotropic
  Spacetimes

abstract:
  The one-loop effective potential for $\phi ^4$ theory on a Bianchi type-I
universe is evaluated in the adiabatic approximation. It is used to see the
quantum-field effects on symmetry breaking and restoration in anisotropic
spacetimes. The results show that the fate of symmetry will not be changed in
the cases of conformal coupling or a vanishing scale curvature, and only for
some suitable values of scalar-gravitational coupling could the symmetry be
radiatively broken or restored.


title: "Singularity" of Levi-Civita Spacetimes

abstract:
  Levi-Civita spacetimes have both classical and quantum singularities. The
relationship between the two is used here to study and clarify the physical
aspects of the enigmatic Levi-Civita spacetimes.


title: Energy Distribution of a G\"{o}del-Type Space-Time

abstract:
  We calculate the energy and momentum distributions associated with a
G\"{o}del-type space-time, using the well-known energy-momentum complexes of
Landau and Lifshitz and M{\o}ller. We show that the definitions of Landau and
Lifshitz and M{\o}ller do not furnish a consistent result.


title:
Definition and classification of singularities in GR: classical and
  quantum

abstract:
  We will briefly review the definition and classification of classical and
quantum singularities in general relativity. Examples of classically singular
spacetimes that do not have quantum singularities will be given. We will
present results on quantum singularities in quasiregular spacetimes. We will
also show that a strong repulsive "potential" near the classical singularity
can turn a classically singular spacetime into a quantum mechanically
nonsingular spacetime.


title: Reissner Nordstr$\ddot{o}$m solutions and Energy in teleparallel theory

abstract:
  We give three different spherically symmetric spacetimes for the coupled
gravitational and electromagnetic fields with charged source in the tetrad
theory of gravitation. One of these, contains an arbitrary function and
generates the others. These spacetimes give the Reissner Nordstr$\ddot{o}$m
metric black hole. We then, calculated the energy associated with these
spacetimes using the superpotential method. We find that unless the time-space
components of the tetrad field go to zero faster than ${1/\sqrt{r}}$ at
infinity, one gets different results for the energy.


title: Finite-Temperature Cosmological Phase Transition in a Rotating Spacetime

abstract:
  We use the $\zeta$-function regularization method to evaluate the finite
temperature 1-loop effective potential for $\phi^4$ theory in the Godel
spacetime. It is used to study the effects of temperature and curvature
coupling on the cosmological phase transition in the rotational spacetime. From
our results the critical temperature of symmetry restoration, which is a
function of curvature coupling and magnitude of spacetime rotation, can be
determined.


title: Relativity in rotating frames

abstract: A common error, originally due to Ehrenfest, is corrected.


title: Neutrino Helicity and Chirality Transitions in Schwarzschild Space-Time

abstract:
  We study the helicity and chirality transitions of a high-energy neutrino
propagating in a Schwarzschild space-time background. Using both traditional
Schwarzschild and isotropic spherical co-ordinates, we derive an
ultrarelativistic approximation of the Dirac Hamiltonian to first-order in the
neutrino's rest mass, via a generalization of the Cini-Touschek transformation
that incorporates non-inertial frame effects due to the noncommutative nature
of the momentum states in curvilinear co-ordinates. Under general conditions,
we show that neutrino's helicity is not a constant of the motion in the
massless limit due to space-time curvature, while the chirality transition rate
still retains an overall dependence on mass. We show that the chirality
transition rate generally depends on the zeroth-order component of the
neutrino's helicity transition rate under the Cini-Touschek transformation. It
is also shown that the chiral current for high-energy neutrinos is altered by
corrections due to curvature and frame-dependent effects, but should have no
significant bearing on the chiral anomaly in curved space-time. We determine
the upper bound for helicity and chirality transitions near the event horizon
of a black hole. The special case of a weak-field approximation is also
considered, which includes the gravitational analogue of Berry's phase first
proposed by Cai and Papini. Finally, we propose a method for estimating the
absolute neutrino mass and the number of right-handed chiral states from the
expectation values of the helicity and chirality transition rates in the
weak-field limit.


title: Radiation content of Conformally flat initial data

abstract:
  We study the radiation of energy and linear momentum emitted to infinity by
the headon collision of binary black holes, starting from rest at a finite
initial separation, in the extreme mass ratio limit. For these configurations
we identify the radiation produced by the initially conformally flat choice of
the three geometry. This identification suggests that the radiated energy and
momentum of headon collisions will not be dominated by the details of the
initial data for evolution of holes from initial proper separations
$L_0\geq7M$. For non-headon orbits, where the amount of radiation is orders of
magnitude larger, the conformally flat initial data may provide a relative even
better approximation.


title:
Quantum Field Effects on Cosmological Phase Transition in Anisotropic
  Spacetimes

abstract:
  The one-loop renormalized effective potentials for the massive $\phi^4$
theory on the spatially homogeneous models of Bianchi type I and
Kantowski-Sachs type are evaluated. It is used to see how the quantum field
affects the cosmological phase transition in the anisotropic spacetimes. For
reasons of the mathematical technique it is assumed that the spacetimes are
slowly varying or have specially metric forms. We obtain the analytic results
and present detailed discussions about the quantum field corrections to the
symmetry breaking or symmetry restoration in the model spacetimes.


title: Gravitational collapse in braneworld models with curvature corrections

abstract:
  We study the collapse of a homogeneous braneworld dust cloud in the context
of the various curvature correction scenarios, namely, the induced-gravity, the
Gauss-Bonnet, and the combined induced-gravity and Gauss-Bonnet. In accordance
to the Randall-Sundrum model, and contrary to four-dimensional general
relativity, we show in all cases that the exterior spacetime on the brane is
non-static.


title:
Can a wormhole supported by only small amounts of exotic matter really
  be traversable?

abstract:
  Recent studies have shown that (a) quantum effects may be sufficient to
support a wormhole throat and (b) the total amount of "exotic matter" can be
made arbitrarily small. Unfortunately, using only small amounts of exotic
matter may result in a wormhole that flares out too slowly to be traversable in
a reasonable length of time. Combined with the Ford-Roman constraints, the
wormhole may also come close to having an event horizon at the throat. This
paper examines a model that overcomes these difficulties, while satisfying the
usual traversability conditions. This model also confirms that the total amount
of exotic matter can indeed be made arbitrarily small.


title:
Vacuum solutions of the gravitational field equations in the brane world
  model

abstract:
  We consider some classes of solutions of the static, spherically symmetric
gravitational field equations in the vacuum in the brane world scenario, in
which our Universe is a three-brane embedded in a higher dimensional
space-time. The vacuum field equations on the brane are reduced to a system of
two ordinary differential equations, which describe all the geometric
properties of the vacuum as functions of the dark pressure and dark radiation
terms (the projections of the Weyl curvature of the bulk, generating non-local
brane stresses). Several classes of exact solutions of the vacuum gravitational
field equations on the brane are derived. In the particular case of a vanishing
dark pressure the integration of the field equations can be reduced to the
integration of an Abel type equation. A perturbative procedure, based on the
iterative solution of an integral equation, is also developed for this case.
Brane vacuums with particular symmetries are investigated by using Lie group
techniques. In the case of a static vacuum brane admitting a one-parameter
group of conformal motions the exact solution of the field equations can be
found, with the functional form of the dark radiation and pressure terms
uniquely fixed by the symmetry. The requirement of the invariance of the field
equations with respect to the quasi-homologous group of transformations also
imposes a unique, linear proportionality relation between the dark energy and
dark pressure. A homology theorem for the static, spherically symmetric
gravitational field equations in the vacuum on the brane is also proven.


title: Spin Zero Quantum Relativistic Particles in Einstein Universe

abstract:
  In this letter we have considered the eigenvalues and eigenfunctions of
relativistic massless scalar particle which conformally coupled to the
background of Einstein universe. We found the eigenvalues and eigenfunctions
exactly.


title: Pre-Inflation in the Presence of Conformal Coupling

abstract:
  We consider a massless scalar field, conformally coupled to the Ricci scalar
curvature, in the pre-inflation era of a closed FLRW Universe. The scalar field
potential can be of the form of the Coleman-Weinberg one-loop potential, which
is flat at the origin and drives the inflationary evolution. For positive
values of the conformal parameter \xi, less than the critical value xi_c=(1/6),
the model admits exact solutions with non-zero scale factor and zero initial
Hubble parameter. Thus these solutions can be matched smoothly to the so called
Pre-Big-Bang models. At the end of this pre-inflation era one can match
inflationary solutions by specifying the form of the potential and the whole
solution is of the class C^(1).


title:
Highly Damped Quasinormal Modes of Kerr Black Holes: A Complete
  Numerical Investigation

abstract:
  We compute for the first time very highly damped quasinormal modes of the
(rotating) Kerr black hole. Our numerical technique is based on a decoupling of
the radial and angular equations, performed using a large-frequency expansion
for the angular separation constant_{s}A_{l m}. This allows us to go much
further in overtone number than ever before. We find that the real part of the
quasinormal frequencies approaches a non-zero constant value which does not
depend on the spin s of the perturbing field and on the angular index l:
\omega_R=m\varpi(a). We numerically compute \varpi(a). Leading-order
corrections to the asymptotic frequency are likely to be of order 1/\omega_I.
The imaginary part grows without bound, the spacing between consecutive modes
being a monotonic function of a.