title:
Extended Analysis of Gravitomagnetic Fields in Rotating Superconductors
  and Superfluids

abstract:
  Applying the Ginzburg-Landau theory including frame dragging effects to the
case of a rotating superconductor, we were able to express the absolute value
of the gravitomagnetic field involved to explain the Cooper pair mass anomaly
previously reported by Tate. Although our analysis predicts large
gravitomagnetic fields originated by superconductive gyroscopes, those should
not affect the measurement of the Earth gravitomagnetic field by the Gravity
Probe-B satellite. However, the hypothesis might be well suited to explain a
mechanical momentum exchange phenomena reported for superfluid helium. As a
possible explanation for those abnormally large gravitomagnetic fields in
quantum materials, the reduced speed of light (and gravity) that was found in
the case of Bose-Einstein condensates is analysed.


title:
Exact Relativistic Static Charged Dust Disks and Non-axisymmetric
  Structures

abstract:
  The well-known ``displace, cut and reflect'' method used to generate disks
from given solutions of Einstein field equations is applied to the
superposition of twoextreme Reissner-Nordstrom black holes to construct disks
made of charged dust and alsonon-axisymmetric planar distributions of charged
dust on the z=0 plane. They are symmetric with respect to twoor one coordinate
axes, depending whether the black holes have equal or unequal masses,
respectively.For these non-axisymmetric distributions of matter we also study
the effective potential for geodesic motion of neutral test particles.


title: Comments on the kinematical structure of loop quantum cosmology

abstract:
  We comment on the presence of spurious observables and on a subtle violation
of irreducibility in loop quantum cosmology.


title:
The Response of Test Masses to Gravitational Waves in the Coordinates of
  a Local Observer

abstract:
  The response of laser interferometers to gravitational waves has been
calculated in a number of different ways, particularly in the
transverse-traceless and the local Lorentz gauges. At first sight, it would
appear that these calculations lead to different results when the separation
between the test masses becomes comparable to the wavelength of the
gravitational wave. In this paper this discrepancy is resolved. We describe the
response of free test masses to plane gravitational waves in the coordinate
frame of a local observer and show that it acquires contributions from three
different effects: the displacement of the test masses, the apparent change in
the photon velocity, and the variation in the clock speed of the local
observer, all of which are induced by the gravitational wave. Only when taken
together do these three effects represent a quantity which is translationally
invariant. This translationally-invariant quantity is identical to the response
function calculated in the transverse-traceless gauge. We thus resolve the
well-known discrepancy between the two coordinates systems, and show that the
results found in the coordinate frame of a local observer are valid for large
separation between the masses.


title: Spacetime Slices and Surfaces of Revolution

abstract:
  Under certain conditions, a $(1+1)$-dimensional slice $\hat{g}$ of a
spherically symmetric black hole spacetime can be equivariantly embedded in
$(2+1)$-dimensional Minkowski space. The embedding depends on a real parameter
that corresponds physically to the surface gravity $\kappa$ of the black hole
horizon.
  Under conditions that turn out to be closely related, a real surface that
possesses rotational symmetry can be equivariantly embedded in 3-dimensional
Euclidean space. The embedding does not obviously depend on a parameter.
However, the Gaussian curvature is given by a simple formula: If the metric is
written $g = \phi(r)^{-1} dr^2 + \phi(r) d\theta^2$, then
$\K_g=-{1/2}\phi''(r)$.
  This note shows that metrics $g$ and $\hat{g}$ occur in dual pairs, and that
the embeddings described above are orthogonal facets of a single phenomenon. In
particular, the metrics and their respective embeddings differ by a Wick
rotation that preserves the ambient symmetry.
  Consequently, the embedding of $g$ depends on a real parameter. The ambient
space is not smooth, and $\kappa$ is inversely proportional to the cone angle
at the axis of rotation. Further, the Gaussian curvature of $\hat{g}$ is given
by a simple formula that seems not to be widely known.


title:
Comment to the reply to "On the thermodynamics of inhomogeneous perfect
  fluid mixtures"

abstract:
  In spite of a recent reply by Quevedo and Z\'arate (gr-qc/0403096), their
assertion that their thermodynamic scheme for a perfect fluid binary mixture is
incompatible with Szekeres and Stephani families of universes, except those of
FRW ones, remains wrong.


title:
Gravitational radiation from inspiralling compact binaries completed at
  the third post-Newtonian order

abstract:
  The gravitational radiation from point particle binaries is computed at the
third post-Newtonian (3PN) approximation of general relativity. Three
previously introduced ambiguity parameters, coming from the Hadamard self-field
regularization of the 3PN source-type mass quadrupole moment, are consistently
determined by means of dimensional regularization, and proved to have the
values xi = -9871/9240, kappa = 0 and zeta = -7/33. These results complete the
derivation of the general relativistic prediction for compact binary inspiral
up to 3.5PN order, and should be of use for searching and deciphering the
signals in the current network of gravitational wave detectors.


title:
A Novel Two-Step Laser Ranging Technique for a Precision Test of the
  Theory of Gravity

abstract:
  All powered spacecraft experience residual systematic acceleration due to
anisotropy of the thermal radiation pressure and fuel leakage. The residual
acceleration limits the accuracy of any test of gravity that relies on the
precise determination of the spacecraft trajectory. We describe a novel
two-step laser ranging technique, which largely eliminates the effects of
non-gravity acceleration sources and enables celestial mechanics checks with
unprecedented precision. A passive proof mass is released from the mother
spacecraft on a solar system exploration mission. Retro-reflectors attached to
the proof mass allow its relative position to the spacecraft to be determined
using optical ranging techniques. Meanwhile, the position of the spacecraft
relative to the Earth is determined by ranging with a laser transponder. The
vector sum of the two is the position, relative to the Earth, of the proof
mass, the measurement of which is not affected by the residual accelerations of
the mother spacecraft. We also describe the mission concept of the Dark Matter
Explorers (DMX), which will demonstrate this technology and will use it to test
the hypothesis that dark matter congregates around the sun. This hypothesis
implies a small apparent deviation from the inverse square law of gravity,
which can be detected by a sensitive experiment. We expect to achieve an
acceleration resolution of $\sim 10^{-14} m/s^2$. DMX will also be sensitive to
acceleration towards the galactic center, which has a value of $\sim 10^{-10}
m/s^2$. Since dark matter dominates the galactic acceleration, DMX can also
test whether dark matter obeys the equivalence principle to a level of 100 ppm
by ranging to several proof masses of different composition from the mother
spacecraft.


title: Comments on "New Brans-Dicke Wormholes"

abstract:
  It is shown that the recently claimed two new Brans-Dicke wormhole solutions
[F. He and S-W. Kim, Phys. Rev. D{\bf 65}, 084022 (2002)] are not really new
solutions. They are just the well known Brans-Dicke solutions of Class I and II
in a different conformal gauge.


title:
Lessons of spin and torsion: Reply to ``Consistent coupling to Dirac
  fields in teleparallelism"

abstract:
  In reply to the criticism made by Mielke in the pereceding Comment [Phys.
Rev. D69 (2004) 128501] on our recent paper, we once again explicitly
demonstrate the inconsistency of the coupling of a Dirac field to gravitation
in the teleparallel equivalent of general relativity. Moreover, we stress that
the mentioned inconsistency is generic for {\it all} sources with spin and is
by no means restricted to the Dirac field. In this sense the
$SL(4,R)$-covariant generalization of the spinor fields in the teleparallel
gravity theory is irrelevant to the inconsistency problem.


title: Goedel type solution in teleparallel gravity

abstract:
  The stationary cosmological model without closed timelike curves of G\"odel
type is obtained for the ideal dust matter source within the framework of the
teleparallel gravity. For a specific choice of the teleparallel gravity
parameters, this solution reproduces the causality violating stationary G\"odel
solution in general relativity, in accordance with the teleparallel equivalent
of general relativity. The relation between the axial-vector torsion and the
cosmic vorticity is clarified.


title: Quantum horizon and thermodynamics of black hole

abstract:
  A semi-classical reasoning leads to the non-commutativity of space and time
coordinates near the horizon of static non-extreme black hole, and renders the
classical horizon spreading to {\it Quantum Horizon} . In terms of the
background metric of the black hole with the {\it Quantum Horizon}, a quantum
field theory in curved space without ultraviolet divergency near the horizon is
formulated. In this formulism, the black hole thermodynamics is reproduced
correctly without both ambiguity and additional hypothesis in the deriving the
hole's Hawking radiations and entropies, and a new interesting prediction on
the number of radiative field modes $N$ is provided. Specifically, the main
results are follows: 1, Hawking radiations rightly emerge as an effect of
quantum tunneling through the quantum horizon, and hence the ambiguities due to
going across the singularity on the classical horizon were got rid of; 2, 't
Hooft's brick wall thickness hypothesis and the boundary condition imposed for
the field considered in his brick wall model were got rid of also, and related
physics has been interpreted; 3, The present theory is parameter free. So, the
theory has power to predict the multiplicity $N$ of radiative field modes
according to the requirement of normalization of Hawking-Bekenstein entropy. It
has been found that $N\simeq 162$, which is just in good agreement with one in
the Minimal Super-symmetric Standard Model. The studies in this paper represent
an attempt to reveal some physics near the horizon at Planck scale. This paper
serves a brief review on the author's works on this subject.


title:
Electromagnetic Fields in the Exterior of an Oscillating Relativistic
  Star -- I. General Expressions and application to a rotating magnetic dipole

abstract:
  Relativistic stars are endowed with intense electromagnetic fields but are
also subject to oscillations of various types. We here investigate the impact
that oscillations have on the electric and magnetic fields external to a
relativistic star in vacuum. In particular, modelling the star as a
relativistic polytrope with infinite conductivity, we consider the solution of
the general relativistic Maxwell equations both in the vicinity of the stellar
surface and far from it, once a perturbative velocity field is specified. In
this first paper we present general analytic expressions that are not
specialized to a particular magnetic field topology or velocity field. However,
as a validating example and an astrophysically important application, we
consider a dipolar magnetic field and the velocity field corresponding to the
rotation of the misaligned dipole. Besides providing analytic expressions for
the electromagnetic fields produced by this configuration, we calculate, for
the first time, the general relativistic energy loss through dipolar
electromagnetic radiation. We find that the widely used Newtonian expression
under-estimates this loss by a factor of 2-6 depending on the stellar
compactness. This correction could have important consequences in the study of
the spin evolution of pulsars.


title: Independent Components of an Indexed Object with Linear Symmetries

abstract:
  The problem of finding independent components of an indexed object (e.g., a
tensor) with arbitrary number of indices and arbitrary linear symmetries is
discussed. It is proved that the number of independent components $f(k)$ is a
polynomial of degree not greater than the number of indices $n$, $k$ being the
dimension of the space. Several algorithms to compute $f(k)$ for arbitrary $k$
are described and discussed. It is shown that in the worst case finding $f(k)$
for arbitrary $k$ requires solving at most P(n) systems of linear equations
with at most $(n!)^2$ equations for at most of $n!$ unknowns, P(n) being the
number of partitions of $n$. As a by-product, an efficient algorithm to
parametrize all components of the object through its independent components is
found and implemented in \Mathematica.


title:
Quasi-equilibrium Binary Black Hole Initial Data for Dynamical
  Evolutions

abstract:
  We present a formalism for constructing quasi-equilibrium binary black hole
initial data suitable for numerical evolution. We construct quasi-equilibrium
models by imposing an approximate helical Killing symmetry appropriate for
quasi-circular orbits. We use the sum of two Kerr-Schild metrics as our
background metric, thereby improving on conformally flat backgrounds that do
not accommodate rotating black holes and providing a horizon-penetrating lapse,
convenient for implementing black hole excision. We set inner boundary
conditions at an excision radius well inside the apparent horizon and construct
these boundary conditions to incorporate the quasi-equilibrium condition and
recover the solution for isolated black holes in the limit of large separation.
We use our formalism both to generate initial data for binary black hole
evolutions and to construct a crude quasi-equilibrium, inspiral sequence for
binary black holes of fixed irreducible mass.


title:
On a Regularity Theorem for Solutions of the Spherically Symmetric
  Einstein-Vlasov-Maxwell System

abstract:
  Using an estimate, we prove that if solution of the spherically symmetric
Einstein-Vlasov-Maxwell system develops a singularity at all time, then the
first one has to appear at the center of symmetry.


title: Stochastic quantisation of locally supersymmetric models

abstract:
  Stochastic quantisation normally involves the introduction of a fictitious
extra time parameter, which is taken to infinity so that the system evolves to
an equilibrium state.In the case of a locally supersymmetric theory, an
interesting new possibility arises due to the existence of a Nicolai map. In
this case it turns out that no additional time parameter is required, as the
existence of the Nicolai map ensures that the same job can be done by the
existing time parameter after Euclideanisation. This provides the quantum
theory with a natural probabilistic interpretation, without any reference to
the concept of an inner product or a Hilbert space structure.


title:
Cosmic Relativity: The Fundamental Theory of Relativity, its
  Implications, and Experimental Tests

abstract:
  In this paper I argue for a reassessment of special relativity. The
fundamental theory of relativity applicable in this Universe has to be
consistent with the existence of the massive Universe, and with the effects of
its gravitational interaction on local physics. A reanalysis of the situation
suggests that all relativistic effects that are presently attributed to
kinematics of relative motion in flat space-time are in fact gravitational
effects of the nearly homogeneous and isotropic Universe. The correct theory of
relativity is the one with a preferred cosmic rest frame. Yet, the theory
preserves Lorentz invariance. I outline the new theory of Cosmic Relativity,
and its implications to local physics, especially to physics of clocks and to
quantum physics. This theory is generally applicable to inertial and
noninertial motion. Most significanlty, experimental evidence support and
favour Cosmic Relativity. There are observed effects that can be consistently
explained only within Cosmic Relativity. The most amazing of these is the
dependence of the time dilation of clocks on their `absolute' velocity relative
to the cosmic rest frame. Important effects on quantum systems include the
physical cause of the Thomas precession responsible for part of the spectral
fine structure, and the phase changes responsible for the spin-statistics
connection. At a deeper level it is conlcuded that relativity in flat
space-time with matter reiterates Mach's principle. There will not be any
relativistic effect in an empty Universe.


title: World-line observables and clocks in General Relativity

abstract:
  A proposal for the issue of time and observables in any parameterized theory
such as general relativity is addressed. Introduction of a gauge potential
3-form A in the theory of relativity enables us to define a gauge-invariant
quantity which can be used by observers as a clock to measure the passage of
time. This dynamical variable increases monotonically and continuously along a
world line. Then we define world line observables to be any covariantly defined
quantity obtained from the field configurations on any such causal past with
dynamical time T.


title: Self-Similar Collapse of Scalar Field with Plane Symmetry

abstract:
  Plane symmetric self-similar solutions to Einstein's four-dimensional theory
of gravity are studied and all such solutions are given analytically in closed
form. The local and global properties of these solutions are investigated and
it is shown that some of the solutions can be interpreted as representing
gravitational collapse of the scalar field. During the collapse, trapped
surfaces are never developed. As a result, no black hole is formed. Although
the collapse always ends with spacetime singularities, it is found that these
singularities are spacelike and not naked.


title:
Collapsing Scalar Field with Kinematic Self-Similarity of the Second
  Kind in 2+1 Gravity

abstract:
  All the 2+1-dimensional circularly symmetric solutions with kinematic
self-similarity of the second kind to the Einstein-massless-scalar field
equations are found and their local and global properties are studied. It is
found that some of them represent gravitational collapse of a massless scalar
field, in which black holes are always formed.


title: A varying-c cosmology

abstract:
  We develop a new model for the Universe based on two key assumptions: first,
the inertial energy of the Universe is a constant, and second, the total energy
of a particle, the inertial plus the gravitational potential energy produced by
the other mass in the Universe, is zero. This model allows the speed of light
and the total mass of the Universe to vary as functions of cosmological time,
where we assume the gravitational constant to be a constant. By means of these
assumptions, the relations between the scale factor and the other parameters
are derived. The Einstein equation, by making it compatible with varying-$c$,
is used and the Friedmann equations in this model are obtained. Assuming the
matter content of the Universe to be perfect fluids, the model fixes $\gamma$
to be 2/3. That is, the whole Universe always exhibits a negative pressure.
Moreover, the behavior of the scale factor is the same for any value of the
curvature. It is also shown that the Universe began from a big bang with zero
initial mass and expands forever even with positive curvature, but it is always
decelerating. At the end, solutions to some famous problems, mainly of the
standard big bang model, and an explanation for the observational data about
the accelerating Universe are provided.


title: Hilbert space built over connections with a non-compact structure group

abstract:
  Quantization of general relativity in terms of SL(2,C)-connections (i.e. in
terms of the complex Ashtekar variables) is technically difficult because of
the non-compactness of SL(2,C). The difficulties concern the construction of a
diffeomorphism invariant Hilbert space structure on the space of cylindrical
functions of the connections. We present here a 'toy' model of such a Hilbert
space built over connections whose structure group is the group of real
numbers. We show that in the case of any Hilbert space built analogously over
connections with any non-compact structure group (this includes some models
presented in the literature) there exists an obstacle which does not allow to
define a *-representation of cylindrical functions on the Hilbert space by the
multiplication map which is the only known way to define a diffeomorphism
invariant representation of the functions.


title:
On the Physical Properties of Spherically Symmetric Self-Similar
  Solutions

abstract:
  In this paper, we are exploring some of the properties of the self-similar
solutions of the first kind. In particular, we shall discuss the kinematic
properties and also check the singularities of these solutions. We discuss
these properties both in co-moving and also in non co-moving (only in the
radial direction) coordinates. Some interesting features of these solutions
turn up.


title: Non-Singular Cosmology and Gauge Theories of Gravitation

abstract:
  The resolution of the problem of cosmological singularity in the framework of
gauge theories of gravitation is discussed. Generalized cosmological Friedmann
equations for homogeneous isotropic models filled by interacting scalar fields
and usual gravitating matter are deduced. It is shown that generic feature of
cosmological models of flat, open and closed type is their regular bouncing
character.


title:
Spherical collapse of a heat conducting fluid in higher dimensions
  without horizon

abstract:
  We consider a scenario where the interior spacetime,described by a heat
conducting fluid sphere is matched to a Vaidya metric in higher
dimensions.Interestingly we get a class of solutions, where following heat
radiation the boundary surface collapses without the appearance of an event
horizon at any stage and this happens with reasonable properties of matter
field.The non-occurrence of a horizon is due to the fact that the rate of mass
loss exactly counterbalanced by the fall of boundary radius.Evidently this
poses a counter example to the so-called cosmic censorship hypothesis.Two
explicit examples of this class of solutions are also given and it is observed
that the rate of collapse is delayed with the introduction of extra
dimensions.The work extends to higher dimensions our previous investigation in
4D.


title: Entropy of Spacelike Two-Surfaces of Spacetime

abstract:
  We argue that every finite piecewise smooth spacelike two-surface of
spacetime possesses an entropy which is, in natural units, one quarter of its
area. However, the thermodynamical properties of a two-surface become apparent
only to the observers having that two-surface as a horizon. Consequences of
this result are discussed.


title: Multidimensional inhomogeneous cosmology in scalar tensor theory

abstract:
  Exact cosmological solutions are obtained for a five dimensional
inhomogeneous fluid distribution along with a Brans-Dicke type of scalar field.
The set includes varied forms of matter field including $\rho+p=0$, where p is
the 3D isotropic pressure. Depending on the signature of 4-space curvature our
solutions admit of indefinite expansion in the usual 3-space and dimensional
reduction of the fifth dimension. Due to the presence of the scalar field the
case $p=-\rho$ does not yield an exponential expansion of the scale factor,
which strikingly differs from our earlier investigations without scalar
field.The \emph{effective} four dimensional values of entropy and matter are
calculated and possible consequences of entropy and matter generation in the 4D
world as a result of dimensional reduction of the extra space are also
discussed. Encouraging to point out that aside from the well known big bang
singularity our inhomogeneous cosmology is spatially regular everywhere.
Further our model seems to suggest an alternative mechanism pointing to a
smooth pass over from a primordial, inhomogeneous cosmological phase to a 4D
homogeneous one.


title: The Conditional Probability Interpretation of the Hamiltonian Constraint

abstract:
  The Conditional Probability Interpretation (CPI), first introduced by Page
and Wootters, is reviewed and refined. It is argued that in it's refined form
the CPI is capable of answering various past criticisms. In particular,
questions involving more than one clock time are described in detail, resolving
the problems raised in Kuchar's ``reduction ad absurdum''. In the case of
Parametrized Particle Dynamics, conventional quantum mechanics is recovered in
the ideal clock limit. When E=0 is among the continuous spectrum of the
Hamiltonian, the induced inner product is used to construct the physical
Hilbert space $\clh_{\rm ph}$ from the generalized eigenvectors in (the
topological dual of) $\clh_{\rm aux}$. This allows the CPI to be applied to
these `continuous-spectrum' cases in a more rigorous fashion than that
described previously. The discrete spectrum case is also treated.


title: A toy model for the coincidence problem

abstract:
  The measured values of the matter energy density and the vacuum energy
density are obtained using an adiabatic black hole percolating model at the
critical point. The percolation of black holes is related with an expanding
isotropic universe filled with the most entropic fluid saturating the
holographic bound.


title:
Novel Properties of Bound States of Klein-Gordon Equation in
  Gravitational Field of Massive Point

abstract:
  We consider for the first time the solutions of Klein-Gordon equation in
gravitational field of {\em a massive} point source in GR. We examine
numerically the basic bounded quantum state and the next few states in the
discrete spectrum for different values of the orbital momentum. A novel feature
of the solutions under consideration is the essential dependence if their
physical properties on the gravitational mass defect of the point source, even
not introduced up to recently. It yields a repulsion or an attraction of the
quantum levels up to their quasi-crossing.


title: Toward a Background Independent Quantum Theory of Gravity

abstract:
  Any canonical quantum theory can be understood to arise from the
compatibility of the statistical geometry of distinguishable observations with
the canonical Poisson structure of Hamiltonian dynamics. This geometric
perspective offers a novel, background independent non-perturbative formulation
of quantum gravity. We invoke a quantum version of the equivalence principle,
which requires both the statistical and symplectic geometries of canonical
quantum theory to be fully dynamical quantities. Our approach sheds new light
on such basic issues of quantum gravity as the nature of observables, the
problem of time, and the physics of the vacuum. In particular, the observed
numerical smallness of the cosmological constant can be rationalized in this
approach.


title: Improved gravitational waveforms from spinning black hole binaries

abstract:
  The standard post-Newtonian approximation to gravitational waveforms, called
T-approximants, from non-spinning black hole binaries are known not to be
sufficiently accurate close to the last stable orbit of the system. A new
approximation, called P-approximants, is believed to improve the accuracy of
the waveforms rendering them applicable up to the last stable orbit. In this
study we apply P-approximants to the case of a test-particle in equatorial
orbit around a Kerr black hole parameterized by a spin parameter q that takes
values between -1 and 1. In order to assess the performance of the two
approximants we measure their effectualness (i.e. larger overlaps with the
exact signal), and faithfulness (i.e. smaller biases while measuring the
parameters of the signal) with the exact (numerical) waveforms. We find that in
the case of prograde orbits, that is orbits whose angular momentum is in the
same sense as the spin angular momentum of the black hole, T-approximant
templates obtain an effectualness of ~ 0.99 for spins q < 0.75. For 0.75 < q <
0.95, the effectualness drops to about 0.82. The P-approximants achieve
effectualness of > 0.99 for all spins up to q = 0.95. The bias in the
estimation of parameters is much lower in the case of P-approximants than
T-approximants. We find that P-approximants are both effectual and faithful and
should be more effective than T-approximants as a detection template family
when q>0. For q<0 both T- and P-approximants perform equally well so that
either of them could be used as a detection template family.


title:
The Effect of the LISA Response Function on Observations of
  Monochromatic Sources

abstract:
  The Laser Interferometer Space Antenna (LISA) is expected to provide the
largest observational sample of binary systems of faint sub-solar mass compact
objects, in particular white-dwarfs, whose radiation is monochromatic over most
of the LISA observational window. Current astrophysical estimates suggest that
the instrument will be able to resolve about 10000 such systems, with a large
fraction of them at frequencies above 3 mHz, where the wavelength of
gravitational waves becomes comparable to or shorter than the LISA arm-length.
This affects the structure of the so-called LISA transfer function which cannot
be treated as constant in this frequency range: it introduces characteristic
phase and amplitude modulations that depend on the source location in the sky
and the emission frequency. Here we investigate the effect of the LISA transfer
function on detection and parameter estimation for monochromatic sources. For
signal detection we show that filters constructed by approximating the transfer
function as a constant (long wavelength approximation) introduce a negligible
loss of signal-to-noise ratio -- the fitting factor always exceeds 0.97 -- for
f below 10mHz, therefore in a frequency range where one would actually expect
the approximation to fail. For parameter estimation, we conclude that in the
range 3mHz to 30mHz the errors associated with parameter measurements differ
from about 5% up to a factor of 10 (depending on the actual source parameters
and emission frequency) with respect to those computed using the long
wavelength approximation.


title:
A note: graviton spin, gravitomagnetic fields and self-interaction of
  non-inertial frame of reference

abstract:
  Three weak gravitational effects associated with the gravitomagnetic fields
are taken into account in this paper: (i) we discuss the background Lorentz
transformation and gauge transformation in a linearized gravity theory, and
obtain the expression for the spin of gravitational field by using the
canonical procedure and Noether theorem; (ii) we point out that by using the
coordinate transformation from the fixed frame to the rotating frame, it is
found that the nature of Mashhoon's spin-rotation coupling is in fact an
interaction between the gravitomagnetic moment of a spinning particle and the
gravitomagnetic fields. The fact that the rotational angular velocity of a
rotating frame can be viewed as a gravitomagnetic field is demonstrated; (iii)
a purely gravitational generalization of Mashhoon's spin-rotation coupling,
i.e., the interaction of the graviton spin with the gravitomagnetic fields is
actually a self-interaction of the spacetime (gravitational fields). In the
present paper, we will show that this self-interaction will also arise in a
non-inertial frame of reference itself: specifically, a rotating frame that
experiences a fluctuation of its rotational frequency (i.e., the change in the
rotational angular frequency) will undergo a weak self-interaction. The
self-interaction of the rotating frame, which can also be called the
self-interaction of the spacetime of the rotating frame, is just the
non-inertial generalization of the interaction of the graviton spin with the
gravitomagnetic fields.


title:
On the possibility of measuring the solar oblateness and some
  relativistic effects from planetary ranging

abstract:
  In this paper we first calculate the post-Newtonian gravitoelectric secular
rate of the mean anomaly of a test particle freely orbiting a spherically
symmetric central mass. Then, we propose a novel approach to suitably combine
the presently available planetary ranging data to Mercury, Venus and Mars in
order to determine, simultaneously and independently of each other, the Sun's
quadrupole mass moment J_2 and the secular advances of the perihelion and the
mean anomaly. This would also allow to obtain the PPN parameters gamma and beta
independently. We propose to analyze the time series of three linear
combinations of the experimental residuals of the rates of the nodes, the
longitudes of perihelia and mean anomalies of Mercury, Venus and Mars built up
in order to absorb the secular precessions induced by the solar oblateness and
the post-Newtonian gravitoelectric forces. The values of the three investigated
parameters can be obtained by fitting the expected linear trends with straight
lines, determining their slopes in arcseconds per century and suitably
normalizing them. According to the present-day EPM2000 ephemerides accuracy,
the obtainable precision would be of the order of 10^-4-10^-5 for the PPN
parameters and, more interestingly, of 10^-9 for J_2. The future BepiColombo
mission should improve the Mercury's orbit by one order of magnitude.


title:
Oscillatory Universes in Loop Quantum Cosmology and Initial Conditions
  for Inflation

abstract:
  Positively-curved, oscillatory universes are studied within the context of
Loop Quantum Cosmology subject to a consistent semi-classical treatment. The
semi-classical effects are reformulated in terms of an effective phantom fluid
with a variable equation of state. In cosmologies sourced by a massless scalar
field, these effects lead to a universe that undergoes ever-repeating cycles of
expansion and contraction. The presence of a self-interaction potential for the
field breaks the symmetry of the cycles and can enable the oscillations to
establish the initial conditions for successful slow-roll inflation, even when
the field is initially at the minimum of its potential with a small kinetic
energy. The displacement of the field from its minimum is enhanced for lower
and more natural values of the parameter that sets the effective quantum
gravity scale. For sufficiently small values of this parameter, the universe
can enter a stage of eternal self-reproduction.


title:
Spin-Statistics connection and the gravity of the Universe: The Cosmic
  connection

abstract:
  I suggest that the Spin-Statistics connection is a consequence of the phase
shifts on quantum scattering amplitudes due to the induced gravitomagnetic
field of the whole Universe at critical density. This connection was recently
brought out in the context of a new theory of relativity in flat space with
matter, called Cosmic Relativity (gr-qc/0406023). This prediction of the
correct gravitational phases is a consequence of any relativistic gravitation
theory in the presence of the massive Universe. This can also be interpreted as
related to the Mach's principle applied to quantum phenomena. Perhaps this is
the simplest valid proof of the Spin-Statistics Theorem, and it finally
identifies the physical origin of the connection.


title: A comment on black hole entropy or does Nature abhor a logarithm?

abstract:
  There has been substantial interest, as of late, in the quantum-corrected
form of the Bekenstein-Hawking black hole entropy. The consensus viewpoint is
that the leading-order correction should be a logarithm of the horizon area;
however, the value of the logarithmic prefactor remains a point of notable
controversy. Very recently, Hod has employed statistical arguments that
constrain this prefactor to be a non-negative integer. In the current paper, we
invoke some independent considerations to argue that the "best guess" for the
prefactor might simply be zero. Significantly, this value complies with the
prior prediction and, moreover, seems suggestive of some fundamental symmetry.


title:
Is timing noise important in the gravitational wave detection of neutron
  stars?

abstract:
  In this paper we ask whether the phenomenon of timing noise long known in
electromagnetic pulsar astronomy is likely to be important in gravitational
wave (GW) observations of spinning-down neutron stars. We find that timing
noise is strong enough to be of importance only in the young pulsars, which
must have larger triaxialities than theory predicts for their GW emission to be
detectable. However, assuming that their GW emission is detectable, we list the
pulsars for which timing noise is important, either because it is strong enough
that its neglect by the observer would render the source undetectable, or else
because it is a measurable feature of the GW signal. We also find that timing
noise places a limit on the observation duration of a coherent blind GW search,
and suggest that hierarchical search techniques might be able to cope with this
problem. Demonstration of the presence or absence of timing noise in the GW
channel would give a new probe of neutron star physics.


title: Spectra of Relic Gravitons and Brans-Dicke Theory

abstract:
  The spectra of relic gravitational waves produced as a result of cosmological
expansion of the inflationary models are derived in Brans-Dicke theory of
gravity.The time dependence of the very early Hubble parameter and matter
energy density are derived from frequency dependent spectrum of relic
gravitational waves.Also it is found that Brans-Dicke scalar field contributes
to the energy density of relic gravitons.


title:
New Hamiltonian formalism and quasi-local conservation equations of
  general relativity

abstract:
  I describe the Einstein's gravitation of 3+1 dimensional spacetimes using the
(2,2) formalism without assuming isometries. In this formalism, quasi-local
energy, linear momentum, and angular momentum are identified from the four
Einstein's equations of the divergence-type, and are expressed geometrically in
terms of the area of a two-surface and a pair of null vector fields on that
surface. The associated quasi-local balance equations are spelled out, and the
corresponding fluxes are found to assume the canonical form of energy-momentum
flux as in standard field theories. The remaining non-divergence-type
Einstein's equations turn out to be the Hamilton's equations of motion, which
are derivable from the {\it non-vanishing} Hamiltonian by the variational
principle. The Hamilton's equations are the evolution equations along the
out-going null geodesic whose {\it affine} parameter serves as the time
function. In the asymptotic region of asymptotically flat spacetimes, it is
shown that the quasi-local quantities reduce to the Bondi energy, linear
momentum, and angular momentum, and the corresponding fluxes become the Bondi
fluxes. The quasi-local angular momentum turns out to be zero for any
two-surface in the flat Minkowski spacetime. I also present a candidate for
quasi-local {\it rotational} energy which agrees with the Carter's constant in
the asymptotic region of the Kerr spacetime. Finally, a simple relation between
energy-flux and angular momentum-flux of a generic gravitational radiation is
discussed, whose existence reflects the fact that energy-flux always
accompanies angular momentum-flux unless the flux is an s-wave.


title:
Physical interpretation of gauge invariant perturbations of spherically
  symmetric space-times

abstract:
  By calculating the Newman-Penrose Weyl tensor components of a perturbed
spherically symmetric space-time with respect to invariantly defined classes of
null tetrads, we give a physical interpretation, in terms of gravitational
radiation, of odd parity gauge invariant metric perturbations. We point out how
these gauge invariants may be used in setting boundary and/or initial
conditions in perturbation theory.


title:
Feynman path integral in area tensor Regge calculus and correspondence
  principle

abstract:
  The quantum measure in area tensor Regge calculus can be constructed in such
the way that it reduces to the Feynman path integral describing canonical
quantisation if the continuous limit along any of the coordinates is taken.
This construction does not necessarily mean that Lorentzian (Euclidean) measure
satisfies correspondence principle, that is, takes the form proportional to
$e^{iS}$ ($e^{-S}$) where $S$ is the action. Requirement to fit this principle
means some restriction on the action, or, in the context of representation of
the Regge action in terms of independent rotation matrices (connections),
restriction on such representation. We show that the representation based on
separate treatment of the selfdual and antiselfdual rotations allows to modify
the derivation and give sense to the conditionally convergent integrals to
implement both the canonical quantisation and correspondence principles. If
configurations are considered such that the measure is factorisable into the
product of independent measures on the separate areas (thus far it was just the
case in our analysis), the considered modification of the measure does not
effect the vacuum expectation values.


title:
Modification of quantum measure in area tensor Regge calculus and
  positivity

abstract:
  A comparative analysis of the versions of quantum measure in the area tensor
Regge calculus is performed on the simplest configurations of the system. The
quantum measure is constructed in such the way that it reduces to the Feynman
path integral describing canonical quantisation if the continuous limit along
any of the coordinates is taken. As we have found earlier, it is possible to
implement also the correspondence principle (proportionality of the Lorentzian
(Euclidean) measure to $e^{iS}$ ($e^{-S}$), $S$ being the action). For that a
certain kind of the connection representation of the Regge action should be
used, namely, as a sum of independent contributions of selfdual and
antiselfdual sectors (that is, effectively 3-dimensional ones). There are two
such representations, the (anti)selfdual connections being SU(2) or SO(3)
rotation matrices according to the two ways of decomposing full SO(4) group, as
SU(2) $\times$ SU(2) or SO(3) $\times$ SO(3). The measure from SU(2) rotations
although positive on physical surface violates positivity outside this surface
in the general configuration space of arbitrary independent area tensors. The
measure based on SO(3) rotations is expected to be positive in this general
configuration space on condition that the scale of area tensors considered as
parameters is bounded from above by the value of the order of Plank unit.


title: FRW cosmological model inside an isolated Schwarzschild black hole

abstract:
  Using the canonical quantum theory of spherically symmetric pure
gravitational systems, we present a direct correspondence between the
Friedmann-Robertson-Walker (FRW) cosmological model in the interior of a
Schwarzschild black hole and the nth energy eigenstate of a linear harmonic
oscillator. Such type of universe has a quantized mass of the order of the
Planck mass and harmonic oscillator wave functions


title:
Gravitational collapse of an isentropic perfect fluid with a linear
  equation of state

abstract:
  We investigate here the gravitational collapse end states for a spherically
symmetric perfect fluid with an equation of state $p=k\rho$. It is shown that
given a regular initial data in terms of the density and pressure profiles at
the initial epoch from which the collapse develops, the black hole or naked
singularity outcomes depend on the choice of rest of the free functions
available, such as the velocities of the collapsing shells, and the dynamical
evolutions as allowed by Einstein equations. This clarifies the role that
equation of state and initial data play towards determining the final fate of
gravitational collapse.


title: Thick shells and stars in Majumdar-Papapetrou general relativity

abstract:
  The Majumdar-Papapetrou system is the subset of the Einstein-Maxwell-charged
dust matter theory, when the charge of each particle is equal to its mass.
Solutions for this system are less difficult to find, in general one does not
need even to impose any spatial symmetry a priori. For instance, any number of
extreme Reissner-Nordstrom solutions (which in vacuum reduce to extreme
Reissner-Nordstrom black holes) located at will is a solution. In matter one
can also find solutions with some ease. Here we find an exact solution of the
Majumdar-Papapetrou system, a spherically symmetric charged thick shell, with
mass m, outer radius r_o, and inner radius r_i. This solution consists of three
regions, an inner Minkowski region, a middle region with extreme charged dust
matter, and an outer Reissner-Nordstrom region. The matching of the regions,
obeying the usual junction conditions for boundary surfaces, is continuous. For
vanishing inner radius, one obtains a Bonnor star, whereas for vanishing
thickness, one obtains an infinitesimally thin shell. For sufficiently high
mass of the thick shell or sufficiently small outer radius, it forms an extreme
Reissner-Nordstrom quasi-black hole, i.e., a star whose gravitational
properties are virtually indistinguishable from a true extreme black hole. This
quasi-black hole has no hair and has a naked horizon, meaning that the Riemann
tensor at the horizon on an infalling probe diverges. At the critical value,
when the mass is equal to the outer radius, m=r_o, there is no smooth manifold.
Above the critical value when m>r_o there is no solution, the shell collapses
into a singularity. Systems with m< r_o are neutrally stable. Many of these
properties are similar to those of gravitational monopoles.


title:
Quantum mechanics without spacetime IV : a noncommutative
  Hamilton-Jacobi equation

abstract:
  It has earlier been argued that there should exist a formulation of quantum
mechanics which does not refer to a background spacetime. In this paper we
propose that, for a relativistic particle, such a formulation is provided by a
noncommutative generalisation of the Hamilton-Jacobi equation. If a certain
form for the metric in the noncommuting coordinate system is assumed, along
with a correspondence rule for the commutation relations, it can be argued that
this noncommutative Hamilton-Jacobi equation is equivalent to standard quantum
mechanics.


title:
On the Electromagnetism of Gravitational System and the Four Dimensional
  Constants (c, h, k, G)

abstract:
  We presented a model for unification of electricity and gravity. We have
found a consistent description of all physical quantities pertaining to the
system. We have provided limiting values for all physical values. These values
are neither zero nor infinity. Our universe is described at all times by the
four dimensional constants $c, \hbar, k, G$ only. The remnant of vacuum remains
at all epochs with different values. The present cosmological puzzles are
justified as due to the consequences of cosmic quantization developed in this
work.


title:
Casimir Energy Density at Planck Time: Cosmic Coincidence or Double
  Solution to the Cosmological Dark Energy Problem?

abstract:
  The Casimir energy density calculated for a spherical shell of radius equal
to the size of the Universe projected back to the Planck time is almost equal
to the present day critical density. Is it just a coincidence, or is it a
solution to the `cosmic dark energy' and the `cosmic coincidence' problems? The
correspondence is too close to be ignored as a coincidence, especially since
this solution fits the conceptual and numerical ideas about the dark energy,
and also answers why this energy is starting to dominate at the present era in
the evolution of the Universe.


title:
Geometric Phase for Fermionic Quasiparticles Scattering by Disgyration
  in Superfluids

abstract:
  We consider a Volovik's analog model for description of a topological defects
in a superfluid and we investigate the scattering of quasiparticles in this
background. The analog of the gravitational Aharonov-Bohm in this system is
found. An analysis of this problem employing loop variables is considered and
corroborates for the existence of the Aharonov-Bohm effect in this system. The
results presented here may be used to study the Aharonov-Bohm effect in
superconductors.


title:
Variation of the velocity and the frequency of a periodic signal along
  the world line of the emitter

abstract:
  The variation of the velocity of a periodic signal and its frequency along
the world line of a standard emitter (at rest with an observer) are considered
in a space with affine connections and metrics. It is shown that the frequency
of the emitted periodic signal is depending on the kinematic characteristics of
the motion of the emitter in space-time related to its shear and expansion
velocities. The same conclusions are valid for a standard clock moving with an
observer.


title: Black Hole Entropy and Dilatations

abstract:
  Dilatations by means of a constant factor can be seen in a double way: as a
simple change of units length or as a conformal mapping of the starting
spacetime into a ``stretched'' one with the same units length. The numerical
value of the black hole entropy depends on the interpretations made for the
stretched manifold. Further, we study the possibility to choose an unusual
``mass dependent'' normalization for the timelike Killing vector for a Kerr
black hole with and without a cosmic string.


title: Vacuum Solutions of Einstein's Equations in Parabolic Coordinates

abstract:
  We present a simple method to obtain vacuum solutions of Einstein's equations
in parabolic coordinates starting from ones with cylindrical symmetries.
Furthermore, a generalization of the method to a more general situation is
given together with a discussion of the possible relations between our method
and the Belinsky-Zakharov soliton-generating solutions.


title: Spin, Acceleration and Gravity

abstract:
  The massless field perturbations of the accelerating Minkowski and
Schwarzschild spacetimes are studied. The results are extended to the
propagation of the Proca field in Rindler spacetime. We examine critically the
possibility of existence of a general spin-acceleration coupling in complete
analogy with the well-known spin-rotation coupling. We argue that such a direct
coupling between spin and linear acceleration does not exist.


title:
Reply to "Bouncing Universes and their perturbations: remarks on a toy
  model"

abstract:
  In this web note, we reply to a recent paper, gr-qc/0404126, confirming a
previous work of ours in which a cosmological bouncing phase was shown to have
the ability of modifying the spectrum of primordial perturbations (PRD 68,
103517 2003), but challenging its physical conditions of validity. Explicitly,
Ref. gr-qc/0404126, besides pretending our Taylor series expansion of the scale
factor close to the bounce amounts to choosing a family of polynomial scale
factors, also claims that the bounce affects the spectrum only if the mass
scale of the scalar field driving the dynamics is of the order of the Planck
mass. We show that these objections are either misleading or incorrect since
the minimum size of the Universe a_0 (value of the scale factor at the bounce)
is either not physically specified, as required in a closed Universe, or
implicitly assumed to be the Planck mass. We calculate this mass and obtain
that, unsurprisingly, for a reasonable value of a_0, i.e. much larger than the
Planck length, the scalar field mass is smaller than the Planck mass.


title: Spinfoam 2d quantum gravity and discrete bundles

abstract:
  In 4 dimensions, general relativity can be formulated as a constrained $BF$
theory; we show that the same is true in 2 dimensions. We describe a spinfoam
quantization of this constrained BF-formulation of 2d riemannian general
relativity, obtained using the Barrett-Crane technique of imposing the
constraint as a restriction on the representations summed over. We obtain the
expected partition function, thus providing support for the viability of the
technique. The result requires the nontrivial topology of the bundle where the
gravitational connection is defined, to be taken into account. For this
purpose, we study the definition of a principal bundle over a simplicial base
space. The model sheds light also on several other features of spinfoam quantum
gravity: the reality of the partition function; the geometrical interpretation
of the Newton constant, and the issue of possible finiteness of the partition
function of quantum general relativity.


title: Time 'betwins'

abstract:
  Discussions on the Langevin Twins 'paradox' are most often based on a
"triangular" diagram which outlines the twins spacetime travels. It won't be
our way, avoiding what we think to be a problem at the basis of numerous
controversies. Our approach relies on a fundamentally different Equivalence
Principle, namely the so-called "Punctual Equivalence Principle", from which we
think that a very conformal aspect proceeds. We present a resolution of this
paradox in the framework of the so-called "scale gravity". This resolution
hinges on a clear determinism of the Twins proper times, in some definite
situations, and a fundamental under-determinism in some other particular ones,
the physical discrimination of which being achieved out of a precise
mathematical description of conformal geometry. Moreover, we find that the time
discrepancy between the twins, could somehow be at the root expression of the
second fundamental law of thermodynamics.


title: Old and new ether-drift experiments: a sharp test for a preferred frame

abstract:
  Motivated by the critical remarks of several authors, we have re-analyzed the
classical ether-drift experiments with the conclusion that the small observed
deviations should not be neglected. In fact, within the framework of Lorentzian
Relativity, they might indicate the existence of a preferred frame relatively
to which the Earth is moving with a velocity v_earth\sim 200$ km/s (value
projected in the plane of the interferometer). We have checked this idea by
comparing with the modern ether-drift experiments, those where the observation
of the fringe shifts is replaced by the difference \Delta \nu in the relative
frequencies of two cavity-stabilized lasers, upon local rotations of the
apparatus or under the Earth's rotation. It turns out that, even in this case,
the most recent data are consistent with the same value of the Earth's
velocity, once the vacuum within the cavities is considered a physical medium
whose refractive index is fixed by General Relativity. We thus propose a sharp
experimental test that can definitely resolve the issue. If the small
deviations observed in the classical ether-drift experiments were not mere
instrumental artifacts, by replacing the high vacuum in the resonating cavities
with a dielectric gaseous medium (e.g. air), the typical measured \Delta\nu\sim
1 Hz should increase by orders of magnitude. This expectation is consistent
with the characteristic modulation of a few kHz observed in the original
experiment with He-Ne masers. However, if such enhancement would not be
confirmed by new and more precise data, the existence of a preferred frame can
be definitely ruled out.


title:
Effects of Quantum Stress Tensor Fluctuations with Compact Extra
  Dimensions

abstract:
  The effects of compact extra dimensions upon quantum stress tensor
fluctuations are discussed. It is argued that as the compactification volume
decrease, these fluctuations increase in magnitude. In principle, this would
have the potential to create observable effects, such as luminosity
fluctuations or angular blurring of distant sources, and lead to constraints
upon Kaluza-Klein theories. However, the dependence of the four-dimensional
Newton's constant upon the compactification volume causes the gravitational
effects of the stress tensor fluctuations to be finite in the limit of small
volume. Consequently, no observational constraints upon Kaluza-Klein theories
are obtained.


title:
Semi-analytical approach for the Vaidya metric in double-null
  coordinates

abstract:
  We reexamine here a problem considered in detail before by Waugh and Lake:
the solutions of spherically symmetric Einstein's equations with a radial flow
of unpolarized radiation (the Vaidya metric) in double-null coordinates. This
problem is known to be not analytically solvable, the only known explicit
solutions correspond to the constant mass case (Schwarzschild solution in
Kruskal-Szekeres form) and the linear and exponential mass functions originally
discovered by Waugh and Lake. We present here a semi-analytical approach that
can be used to discuss some qualitative and quantitative aspects of the Vaidya
metric in double-null coordinates for generic mass functions. We present also a
new analytical solution corresponding to $(1/v)$-mass function.


title:
Quantum effects and superquintessence in the new age of precision
  cosmology

abstract:
  Recent observations of Type Ia supernova at high redshifts establish that the
dark energy component of the universe has (a probably constant) ratio between
pressure and energy density $w=p/\rho=-1.02(^{+0.13}_{-0.19})$. The
conventional quintessence models for dark energy are restricted to the range
$-1\le w < 0$, with the cosmological constant corresponding to $w=-1$.
Conformally coupled quintessence models are the simplest ones compatible with
the marginally allowed superaccelerated regime ($w<-1$). However, they are
known to be plagued with anisotropic singularities.
  We argue here that the extension of the classical approach to the
semiclassical one, with the inclusion of quantum counterterms necessary to
ensure the renormalization, can eliminate the anisotropic singularities
preserving the isotropic behavior of conformally coupled superquintessence
models. Hence, besides of having other interesting properties, they are
consistent candidates to describe the superaccelerated phases of the universe
compatible with the present experimental data.


title:
Conformal quantum effects and the anisotropic singularities of
  scalar-tensor theories of gravity

abstract:
  We show that the inclusion of a term $C_{abcd}C^{abcd}$ in the action can
remove the recently described anisotropic singularity occurring on the
hypersurface $F(\phi)=0$ of scalar-tensor theories of gravity of the type $$
S=\int d^4x \sqrt{-g} {F(\phi)R - \partial_a\phi\partial^a\phi -2V(\phi)}, $$
preserving, by construction, all of their isotropic solutions. We show that, in
principle, a higher order term of this type can arise from considerations about
the renormalizability of the semiclassical approach to the theory. Such result
brings again into consideration the quintessential models recently proposed
based in a conformally coupled scalar field ($F(\phi)=1-{1/6}\phi^2$) with
potential $V(\phi)=\frac{m}{2}\phi^2 -\frac{\Omega}{4}\phi^4$, that have been
discharged as unrealistic precisely by their anisotropic instabilities on the
hypersurface $F(\phi)=0$.


title: On a debate about cosmic censor violation

abstract:
  We review the arguments and counter arguments about the recent proposal for
generic censorship violation. In particular the argument made in gr-qc/0405050
against our proposal for a possible expanding domain wall that could encompass
a large black hole, is shown to have a serious flaw. Other problems of the
original idea are also discussed.


title:
Reducing the mirrors coating noise in laser gravitational-wave antennae
  by means of double mirrors

abstract:
  Recent researches show that the fluctuations of the dielectric mirrors
coating thickness can introduce a substantial part of the future laser
gravitational-wave antennae total noise budget. These fluctuations are
especially large in the high-reflectivity end mirrors of the Fabry-Perot
cavities which are being used in the laser gravitational-wave antennae.
  We show here that the influence of these fluctuations can be substantially
decreased by using additional short Fabry-Perot cavities, tuned in
anti-resonance instead of the end mirrors.


title: Matter and dynamics in closed cosmologies

abstract:
  To systematically analyze the dynamical implications of the matter content in
cosmology, we generalize earlier dynamical systems approaches so that perfect
fluids with a general barotropic equation of state can be treated. We focus on
locally rotationally symmetric Bianchi type IX and Kantowski-Sachs orthogonal
perfect fluid models, since such models exhibit a particularly rich dynamical
structure and also illustrate typical features of more general cases. For these
models, we recast Einstein's field equations into a regular system on a compact
state space, which is the basis for our analysis. We prove that models expand
from a singularity and recollapse to a singularity when the perfect fluid
satisfies the strong energy condition. When the matter source admits Einstein's
static model, we present a comprehensive dynamical description, which includes
asymptotic behavior, of models in the neighborhood of the Einstein model; these
results make earlier claims about ``homoclinic phenomena and chaos'' highly
questionable. We also discuss aspects of the global asymptotic dynamics, in
particular, we give criteria for the collapse to a singularity, and we describe
when models expand forever to a state of infinite dilution; possible initial
and final states are analyzed. Numerical investigations complement the
analytical results.


title:
Code Development of Three-Dimensional General Relativistic Hydrodynamics
  with AMR(Adaptive-Mesh Refinement) and Results From Special and General
  Relativistic Hydrodynamic

abstract:
  In this paper, the general procedure to solve the General Relativistic
Hydrodynamical(GRH) equations with Adaptive-Mesh Refinement (AMR) is presented.
In order to achieve, the GRH equations are written in the conservation form to
exploit their hyperbolic character. The numerical solutions of general
relativistic hydrodynamic equations are done by High Resolution Shock Capturing
schemes (HRSC), specifically designed to solve non-linear hyperbolic systems of
conservation laws. These schemes depend on the characteristic information of
the system. The Marquina fluxes with MUSCL left and right states are used to
solve GRH equations. First, different test problems with uniform and AMR grids
on the special relativistic hydrodynamics equations are carried out to verify
the second order convergence of the code in 1D, 2D and 3D. Results from uniform
and AMR grid are compared. It is found that adaptive grid does a better job
when the number of resolution is increased. Second, the general relativistic
hydrodynamical equations are tested using two different test problems which are
Geodesic flow and Circular motion of particle In order to this, the flux part
of GRH equations is coupled with source part using Strang splitting. The
coupling of the GRH equations is carried out in a treatment which gives second
order accurate solutions in space and time.


title:
A detailed recalculation of the spectrum of radiation emitted during
  gravitational collapse of a spherically symmetric star

abstract:
  We address the question of radiation emitted from a collapsing star. We
consider the simple model of a spherical star consisting of pressure-free dust
and we derive the emission spectrum via a systematic asymptotic expansion of
the complete Bogolubov amplitude. We present a review of standard features of
the problem and we point out certain inconsistencies in previous derivations.


title:
Recalculation of the spectrum of radiation emitted during gravitational
  collapse

abstract:
  We recalculate the spectrum of radiation emitted from a collapsing star. We
consider the simple model of a spherical star consisting of pressure-free dust
and we derive the thermal spectrum via a systematic asymptotic expansion of the
complete Bogolubov amplitude. Inconsistencies in previous derivations are
pointed out.


title:
Advanced VIRGO: detector optimization for gravitational waves by
  inspiralling binaries

abstract:
  For future configurations, we study the relation between the abatement of the
noise sources and the Signal to Noise Ratio (SNR) for coalescing binaries. Our
aim is not the proposition of a new design, but an indication of where in the
bandwidth or for which noise source, a noise reduction would be most efficient.
We take VIRGO as the reference for our considerations, solely applicable to the
inspiralling phase of a coalescing binary. Thus, only neutron stars and small
black holes of few solar masses are encompassed by our analysis. The
contributions to the SNR given by final merge and quasi-normal ringing are
neglected. It is identified that i) the reduction in the mirror thermal noise
band provides the highest gain for the SNR, when the VIRGO bandwidth is divided
according to the dominant noises; ii) it exists a specific frequency at which
lies the potential largest increment in the SNR, and that the enlargement of
the bandwidth, where the noise is reduced, produces a shift of such optimal
frequency to higher values; iii) the abatement of the pendulum thermal noise
provides the largest, but modest, gain, when noise sources are considered
separately. Our recent astrophysical analysis on event rates for neutron stars
leads to a detection rate of one every 148 or 125 years for VIRGO and LIGO,
respectively, while a recently proposed and improved, but still conservative,
VIRGO configuration would provide an increase to 1.5 events per year. Instead,
a bi-monthly event rate, similar to advanced LIGO, requires a 16 times gain. We
analyse the 3D (pendulum, mirror, shot noises) parameter space showing how such
gain could be achieved.


title: A poor man's positive energy theorem: II. Null geodesics

abstract:
  We show that positivity of energy for stationary, or strongly uniformly
Schwarzschildian, asymptotically flat, non-singular domains of outer
communications can be proved using Galloway's null rigidity theorem.


title: Duality between magnetic field and rotation

abstract:
  It is shown that in 5D Kaluza-Klein theory there are everywhere regular
wormhole-like solutions in which the magnetic field at the center is the origin
of a rotation on the peripheral part of these solutions. The time on the
peripheral part is topologically non-trivial and magnetic field is suppressed
in comparison with the electric one.


title: Nonlinear quantum gravity on the constant mean curvature foliation

abstract:
  A new approach to quantum gravity is presented based on a nonlinear
quantization scheme for canonical field theories with an implicitly defined
Hamiltonian. The constant mean curvature foliation is employed to eliminate the
momentum constraints in canonical general relativity. It is, however, argued
that the Hamiltonian constraint may be advantageously retained in the reduced
classical system to be quantized. This permits the Hamiltonian constraint
equation to be consistently turned into an expectation value equation on
quantization that describes the scale factor on each spatial hypersurface
characterized by a constant mean exterior curvature. This expectation value
equation augments the dynamical quantum evolution of the unconstrained
conformal three-geometry with a transverse traceless momentum tensor density.
The resulting quantum theory is inherently nonlinear. Nonetheless, it is
unitary and free from a nonlocal and implicit description of the Hamiltonian
operator. Finally, by imposing additional homogeneity symmetries, a broad class
of Bianchi cosmological models are analyzed as nonlinear quantum
minisuperspaces in the context of the proposed theory.


title: How to make a traversable wormhole from a Schwarzschild black hole

abstract:
  The theoretical construction of a traversable wormhole from a Schwarzschild
black hole is described, using analytic solutions in Einstein gravity. The
matter model is pure phantom radiation (pure radiation with negative energy
density) and the idealization of impulsive radiation is employed.


title:
The three dimensional theory of gravitation based on a temporal scalar
  field in Riemanian geometry

abstract:
  A new approach to the model of the universe based on work by Rippl, Romero,
Tavakol is presented. We have used the scheme for relating the vacuum (D + 1)
dimensional theories to D dimensional theories for setting up a correspondence
between vacuum 4-dimensional Einstein theory with 3-dimensional gravity theory
with temporal scalar field. These ideas we continued by using the 3-dimensional
analog of Jordan, Brans-Dicke theory with temporal scalar field. As the result
space and time are treated in completely different ways. For the case of a
static spherically symmetric field new vacuum static solutions are found.


title: Holonomy and projective symmetry in space-times

abstract:
  It is shown using a space-time curvature classification and decomposition
that for certain holonomy types of a space-time, proper projective vector
fields cannot exist. Existence is confirmed, by example, for the remaining
holonomy types. In all except the most general holonomy type, a local
uniqueness theorem for proper projective symmetry is established.


title: Fundamental limitations on "warp drive" spacetimes

abstract:
  "Warp drive" spacetimes are useful as "gedanken-experiments" that force us to
confront the foundations of general relativity, and among other things, to
precisely formulate the notion of "superluminal" communication. We verify the
non-perturbative violation of the classical energy conditions of the Alcubierre
and Natario warp drive spacetimes and apply linearized gravity to the
weak-field warp drive, testing the energy conditions to first and second order
of the non-relativistic warp-bubble velocity. We are primarily interested in a
secondary feature of the warp drive that has not previously been remarked upon,
if it could be built, the warp drive would be an example of a "reaction-less
drive". For both the Alcubierre and Natario warp drives we find that the
occurrence of significant energy condition violations is not just a high-speed
effect, but that the violations persist even at arbitrarily low speeds.
  An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare the
warp field energy with the mass-energy of the spaceship. There is no hope of
doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For both
the Alcubierre and Natario warp drives we find that even at low speeds the net
(negative) energy stored in the warp fields must be a significant fraction of
the mass of the spaceship.


title: Geometry of crossing null shells

abstract:
  New geometric objects on null thin layers are introduced and their importance
for crossing null-like shells are discussed. The Barrab\`es--Israel equations
are represented in a new geometric form and they split into decoupled system of
equations for two different geometric objects: tensor density ${\bf G}^a{_b}$
and vector field $I$. Continuity properties of these objects through a crossing
sphere are proved. In the case of spherical symmetry Dray--t'Hooft--Redmount
formula results from continuity property of the corresponding object.


title:
Nonlinear Couplings of R-modes: Energy Transfer and Saturation
  Amplitudes at Realistic Timescales

abstract:
  Non-linear interactions among the inertial modes of a rotating fluid can be
described by a network of coupled oscillators. We use such a description for an
incompressible fluid to study the development of the r-mode instability of
rotating neutron stars. A previous hydrodynamical simulation of the r-mode
reported the catastrophic decay of large amplitude r-modes. We explain the
dynamics and timescale of this decay analytically by means of a single three
mode coupling. We argue that at realistic driving and damping rates such large
amplitudes will never actually be reached. By numerically integrating a network
of nearly 5000 coupled modes, we find that the linear growth of the r-mode
ceases before it reaches an amplitude of around 10^(-4). The lowest parametric
instability thresholds for the r-mode are calculated and it is found that the
r-mode becomes unstable to modes with 13<n<15 if modes up to n=30 are included.
Using the network of coupled oscillators, integration times of 10^6 rotational
periods are attainable for realistic values of driving and damping rates.
Complicated dynamics of the modal amplitudes are observed. The initial
development is governed by the three mode coupling with the lowest parametric
instability. Subsequently a large number of modes are excited, which greatly
decreases the linear growth rate of the r-mode.


title: Ghost condensate model of flat rotation curves

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


title:
Particles and vacuum for perturbative and non-perturbative
  Einstein-Rosen gravity

abstract:
  We discuss the connection between the Fock space introduced by Ashtekar and
Pierri for Einstein-Rosen waves and its perturbative counterpart based on the
concept of particle that arises in linearized gravity with a de Donder gauge.
We show that the gauge adopted by Ashtekar and Pierri is a generalization of
the de Donder gauge to full (i.e. non-linearized) cylindrical gravity. This
fact allows us to relate the two descriptions of the Einstein-Rosen waves
analyzed here by means of a simple field redefinition. Employing this
redefinition, we find the highly non-linear relation that exists between the
annihilation and creation-like variables of the two approaches. We next
represent the particle-like variables of the perturbative approach as
regularized operators, introducing a cut-off. These can be expanded in powers
of the annihilation and creation operators of the Ashtekar and Pierri
quantization, each additional power being multiplied by an extra square-root of
the three-dimensional gravitational constant, $\sqrt{G}$. In principle, the
perturbative vacuum may be reached as the limit of a state annihilated by these
regularized operators when the cut-off is removed. This state can be written as
the vacuum of the Ashtekar and Pierri quantization corrected by a perturbative
series in $\sqrt{G}$ with no contributions from particles with energies above
the cut-off. We show that the first-order correction is in fact a state of
infinite norm. This result is interpreted as indicating that the Fock
quantizations in the two approaches are unitarily inequivalent and, in any
case, proves that the perturbative vacuum is not analytic in the interaction
constant. Therefore a standard perturbative quantum analysis fails.


title: Universality of affine formulation in General Relativity theory

abstract:
  Affine variational principle for General Relativity, proposed in 1978 by one
of us (J.K.), is a good remedy for the non-universal properties of the
standard, metric formulation, arising when the matter Lagrangian depends upon
the metric derivatives. Affine version of the theory cures the standard
drawback of the metric version, where the leading (second order) term of the
field equations depends upon matter fields and its causal structure violates
the light cone structure of the metric. Choosing the affine connection (and not
the metric one) as the gravitational configuration, simplifies considerably the
canonical structure of the theory and is more suitable for purposes of its
quantization along the lines of Ashtekar and Lewandowski (see
http://www.arxiv.org/gr-qc/0404018). We show how the affine formulation
provides a simple method to handle boundary integrals in general relativity
theory.


title: Very high frequency gravitational wave background in the universe

abstract:
  Astrophysical sources of high frequency gravitational radiation are
considered in association with a new interest to very sensitive HFGW receivers
required for the laboratory GW Hertz experiment. A special attention is paid to
the phenomenon of primordial black holes evaporation. They act like black body
to all kinds of radiation, including gravitons, and, therefore, emit an
equilibrium spectrum of gravitons during its evaporation. Limit on the density
of high frequency gravitons in the Universe is obtained, and possibilities of
their detection are briefly discussed.


title: Reinstating Schwarzschild's original manifold and its singularity

abstract:
  The content of this review is summarized here through the titles of its
sections, as follows:
  1. Introduction: Schwarzschild's original solution and the ``Schwarzschild
solution''.
  2. The wrong arrow of time of Hilbert's manifold is at the origin of the
Kruskal extension.
  3. An invariant, local, intrinsic quantity that diverges at the Schwarzschild
surface.
  4. The singularity at the Schwarzschild surface is both intrinsic and
physical.
  5. Conclusion.


title: Monolithic Geometric Anti-Spring Blade

abstract:
  In this article we investigate the principle and properties of a vertical
passive seismic noise attenuator conceived for ground based gravitational wave
interferometers. This mechanical attenuator based on a particular geometry of
cantilever blades called monolithic geometric anti springs (MGAS) permits the
design of mechanical harmonic oscillators with very low resonant frequency
(below 100mHz).
  Here we address the theoretical description of the mechanical device,
focusing on the most important quantities for the low frequency regime, on the
distribution of internal stresses, and on the thermal stability.
  In order to obtain physical insight of the attenuator peculiarities, we
devise some simplified models, rather than use the brute force of finite
element analysis. Those models have been used to optimize the design of a
seismic attenuation system prototype for LIGO advanced configurations and for
the next generation of the TAMA interferometer.


title: Semiclassical gravitational effects near a singular magnetic flux

abstract:
  We consider the backreaction of the vacuum polarization effect for a massive
charged scalar field in the presence of a singular magnetic massless string on
the background metric. Using semiclassical approach, we find the first-order
(in $\hbar$ units) metric modifications and the corresponding gravitational
potential and deficit angle. It is shown that, in certain region of values of
coupling constant and magnetic flux, the gravitational potential and deficit
angle can be positive as well as negative over all distances from the string
and can even change its sign. Unlike the case of massless scalar field, the
gravitational corrections were found to have short-range behavior.


title: The Efroimsky formalism adapted to high-frequency perturbations

abstract:
  The Efroimsky perturbation scheme for consistent treatment of gravitational
waves and their influence on the background is summarized and compared with
classical Isaacson's high-frequency approach. We demonstrate that the Efroimsky
method in its present form is not compatible with the Isaacson limit of
high-frequency gravitational waves, and we propose its natural generalization
to resolve this drawback.


title: Rotating Black Holes with Monopole Hair

abstract:
  We study rotating black holes in Einstein-Yang-Mills-Higgs theory. These
black holes emerge from static black holes with monopole hair when a finite
horizon angular velocity is imposed. At critical values of the horizon angular
velocity and the horizon radius, they bifurcate with embedded Kerr-Newman black
holes. The non-Abelian black holes possess an electric dipole moment, but no
electric charge is induced by the rotation. We deduce that gravitating regular
monopoles possess a gyroelectric ratio g_el=2.


title:
Lie symmetries of the energy-momentum tensor for plane symmetric static
  spacetimes

abstract:
  Matter collineations (MCs) are the vector fields along which the
energy-momentum tensor remains invariant under the Lie transport. Invariance of
the metric, the Ricci and the Riemann tensors have been studied extensively and
the vectors along which these tensors remain invariant are called Killing
vectors (KVs), Ricci collineations (RCs) and curvature collineations (CCs),
respectively. In this paper plane symmetric static spacetimes have been studied
for their MCs. Explicit form of MCs together with the Lie algebra admitted by
them has been presented. Examples of spacetimes have been constructed for which
MCs have been compared with their RCs and KVs. The comparison shows that
neither of the sets of RCs and MCs contains the other, in general.


title:
Differing Calculations of the Response of Matter-wave Interferometers to
  Gravitational Waves

abstract:
  There now exists in the literature two different expressions for the phase
shift of a matter-wave interferometer caused by the passage of a gravitation
wave. The first, a commonly accepted expression that was first derived in the
1970s, is based on the traditional geodesic equation of motion (EOM) for a test
particle. The second, a more recently derived expression, is based on the
geodesic deviation EOM. The power-law dependence on the frequency of the
gravitational wave for both expressions for the phase shift is different, which
indicates fundamental differences in the physics on which these calculations
are based. Here we compare the two approaches by presenting a series of
side-by-side calculations of the phase shift for one specific
matter-wave-interferometer configuration that uses atoms as the interfering
particle. By looking at the low-frequency limit of the different expressions
for the phase shift obtained, we find that the phase shift calculated via the
geodesic deviation EOM is correct, and the ones calculated via the geodesic EOM
are not.


title: Hawking temperature from quasi-normal modes

abstract:
  A perturbed black hole has characteristic frequencies (quasi-normal modes).
Here I apply a quantum measurement analysis of the quasi-normal mode frequency
in the limit of high damping. It turns out that a measurement of this mode
necessarily adds noise to it. For a Schwarzschild black hole, this corresponds
exactly to the Hawking temperature. The situation for other black holes is
briefly discussed.


title: Quantum effects can render w<-1 on cosmological scales

abstract:
  We report on a revision of our previous computation of the renormalized
expectation value of the stress-energy tensor of a massless, minimally coupled
scalar with a quartic self-interaction on a locally de Sitter background. This
model is important because it demonstrates that quantum effects can lead to
violations of the weak energy condition on cosmological scales - on average,
not just in fluctuations - although the effect in this particular model is far
too small to be observed. The revision consists of modifying the propagator so
that dimensional regularization can be used when the dimension of the
renormalized theory is not four. Although the finite part of the stress-energy
tensor does not change (in D=4) from our previous result, the counterterms do.
We also speculate that a certain, finite and separately conserved part of the
stress tensor can be subsumed into a natural correction of the initial state
from free Bunch-Davies vacuum.


title: A new geometric invariant on initial data for Einstein equations

abstract:
  For a given asymptotically flat initial data set for Einstein equations a new
geometric invariant is constructed. This invariant measure the departure of the
data set from the stationary regime, it vanishes if and only if the data is
stationary. In vacuum, it can be interpreted as a measure of the total amount
of radiation contained in the data.


title:
Deformed Special Relativity as an effective flat limit of quantum
  gravity

abstract:
  We argue that a (slightly) curved space-time probed with a finite resolution,
equivalently a finite minimal length, is effectively described by a flat
non-commutative space-time. More precisely, a small cosmological constant (so a
constant curvature) leads the kappa-deformed Poincar\'e flat space-time of
deformed special relativity (DSR) theories. This point of view eventually helps
understanding some puzzling features of DSR. It also explains how DSR can be
considered as an effective flat (low energy) limit of a (true) quantum gravity
theory. This point of view leads us to consider a possible generalization of
DSR to arbitrary curvature in momentum space and to speculate about a possible
formulation of an effective quantum gravity model in these terms. It also leads
us to suggest a {\it doubly deformed special relativity} framework for
describing particle kinematics in an effective low energy description of
quantum gravity.


title:
The Onset of Chaotic Motion of a Spinning Particle around the
  Schwarzchild Black Hole

abstract:
  In the Schwarzchild black hole spacetime, we show that chaotic motion can be
triggered by the spin of a particle. Taking the spin of the particle as a
perturbation and using the Melnikov method, we find that the perturbed stable
and unstable orbits are entangled with each other and that illustrates the
onset of chaotic behavior in the motion of the particle.


title: Null Cones and Einstein's Equations in Minkowski Spacetime

abstract:
  If Einstein's equations are to describe a field theory of gravity in
Minkowski spacetime, then causality requires that the effective curved metric
must respect the flat background metric's null cone. The kinematical problem is
solved using a generalized eigenvector formalism based on the Segr\'{e}
classification of symmetric rank 2 tensors with respect to a Lorentzian metric.
Securing the correct relationship between the two null cones dynamically
plausibly is achieved using the naive gauge freedom. New variables tied to the
generalized eigenvector formalism reduce the configuration space to the
causality-respecting part. In this smaller space, gauge transformations do not
form a group, but only a groupoid. The flat metric removes the difficulty of
defining equal-time commutation relations in quantum gravity and guarantees
global hyperbolicity.


title:
Nonsingularity of Flat Robertson-Walker Models in the Special
  Relativistic Approach to Einstein's Equations

abstract:
  Recently the neglected issue of the causal structure in the flat spacetime
approach to Einstein's theory of gravity has been substantially resolved.
Consistency requires that the flat metric's null cone be respected by the null
cone of the effective curved metric. While consistency is not automatic,
thoughtful use of the naive gauge freedom resolves the problem. After briefly
recapitulating how consistent causality is achieved, we consider the flat
Robertson-Walker Big Bang model. The Big Bang singularity in the spatially flat
Robertson-Walker cosmological model is banished to past infinity in Minkowski
spacetime. A modified notion of singularity is proposed to fit the special
relativistic approach, so that the Big Bang becomes nonsingular.


title: Anthropic Reasoning and Quantum Cosmology

abstract:
  Prediction in quantum cosmology requires a specification of the universe's
quantum dynamics and its quantum state. We expect only a few general features
of the universe to be predicted with probabilities near unity conditioned on
the dynamics and quantum state alone. Most useful predictions are of
conditional probabilities that assume additional information beyond the
dynamics and quantum state. Anthropic reasoning utilizes probabilities
conditioned on `us'. This paper discusses the utility, limitations, and
theoretical uncertainty involved in using such probabilities. The predictions
resulting from various levels of ignorance of the quantum state are discussed
including those related to uncertainty in the vacuum of string theory. Some
obstacles to using anthropic reasoning to determine this vacuum are described.


title:
Static circularly symmetric perfect fluid solutions with an exterior BTZ
  metric

abstract:
  In this work we study static perfect fluid stars in 2+1 dimensions with an
exterior BTZ spacetime. We found the general expression for the metric
coefficients as a function of the density and pressure of the fluid. We found
the conditions to have regularity at the origin throughout the analysis of a
set of linearly independent invariants. We also obtain an exact solution of the
Einstein equations, with the corresponding equation of state $p=p(\rho)$, which
is regular at the origin.


title: Post-processed time-delay interferometry for LISA

abstract:
  High-precision interpolation of LISA phase measurements allows signal
reconstruction and formulation of Time-Delay Interferometry (TDI) combinations
to be conducted in post-processing. The reconstruction is based on phase
measurements made at approximately 10 Hz, at regular intervals independent of
the TDI delay times. Interpolation introduces an error less than 1e-8 with
continuous data segments as short as two seconds in duration. Potential
simplifications in the design and operation of LISA are presented.


title:
Thermodynamics of four-dimensional black objects in the warped
  compactification

abstract:
  We reinvestigate the thermodynamics of black objects (holes and strings) in
four-dimensional braneworld models that are originally constructed by Emparan,
Horowitz and Myers based on the anti-de Sitter (AdS) C-metric. After proving
the uniqueness of slicing the AdS C-metric, we derive thermodynamic quantities
of the black objects by means of the Euclidean formulation and find that we
have no necessity of requiring any regularization to calculate their classical
action. We show that there exist the Bekenstein-Hawking law and the
thermodynamic first law. The thermodynamic mass of the localized black hole on
a flat brane is negative, and it differs from the one previously derived. We
discuss the thermodynamic stabilities and show that the BTZ black string is
more stable than the localized black holes in a canonical ensemble, except for
an extreme case. We also find a braneworld analogue of the Hawking-Page
transition between the BTZ black string and thermal AdS branes. The localized
black holes on a de Sitter brane is discussed by considering Nariai instanton,
comparing the study of "black cigar" in the five-dimensional braneworld model.


title: Qualitative Approach to Semi-Classical Loop Quantum Cosmology

abstract:
  Recently the mechanism was found which allows avoidance of the cosmological
singularity within the semi-classical formulation of Loop Quantum Gravity.
Numerical studies show that the presence of self-interaction potential of the
scalar field allows generation of initial conditions for successful slow-roll
inflation. In this paper qualitative analysis of dynamical system,
corresponding to cosmological equations of Loop Quantum Gravity is performed.
The conclusion on singularity avoidance in positively curved cosmological
models is confirmed. Two cases are considered, the massless (with flat
potential) and massive scalar field. Explanation of initial conditions
generation for inflation in models with massive scalar field is given. The
bounce is discussed in models with zero spatial curvature and negative
potentials.


title:
Maximally symmetric subspace decomposition of the Schwarzschild black
  hole

abstract:
  The well-known Schwarzschild black hole was first obtained as a stationary,
spherically symmetric solution of the Einstein's vacuum field equations. But
until thirty years later, efforts were made for the analytic extension from the
exterior area $(r>2GM)$ to the interior one $(r<2GM)$. As a contrast to its
maximally extension in the Kruskal coordinates, we provide a comoving
coordinate system from the view of the observers freely falling into the black
hole in the radial direction. We find an interesting fact that the spatial part
in this coordinate system is maximally symmetric $(E_3)$, i.e., along the world
lines of these observers, the Schwarzschild black hole can be decomposed into a
family of maximally symmetric subspaces.


title: The Quantum Big Bang in Global Time Theory

abstract:
  The it Global Time Theory (GTT) is the further development of the General
Relativity (GR). GTT significantly differs from GR in the general physical
concepts, but retains 90% of the mathematical structure and main results. The
dynamics equations are derived from Lagrangian, and the Hamiltonian of
gravitation is nonzero. The quantum theory of gravitation can be built on the
basis of the Schroedinger equation, as for other fields. The quantum model of
the Big Bang is demonstrated.


title: On the degrees of freedom of a semi-Riemannian metric

abstract:
  A semi-Riemannian metric in a n-manifold has n(n-1)/2 degrees of freedom,
i.e. as many as the number of components of a differential 2-form. We prove
that any semi-Riemannian metric can be obtained as a deformation of a constant
curvature metric, this deformation being parametrized by a 2-form


title: Cosmic Vortexes in Global Time Theory

abstract:
  Introduced herein are the foundations of Global Time Theory (GTT) that
further develop the General Relativity (GR). GTT is significantly different
from GR in the general physical concepts, but retains 90% of the mathematical
structure and main results.Meanwhile, description of the cosmos dynamics in GTT
leads to significant modifications. The dynamics equations are derived from
Lagrangian, and the Hamiltonian of gravitation is nonzero. Detailed solutions
to the cosmic vortexes, that possess a weak principle of superposition and a
huge energy, are derived. The virial theorem of space is formulated and proved.


title:
Construction and enlargement of traversable wormholes from Schwarzschild
  black holes

abstract:
  Analytic solutions are presented which describe the construction of a
traversable wormhole from a Schwarzschild black hole, and the enlargement of
such a wormhole, in Einstein gravity. The matter model is pure radiation which
may have negative energy density (phantom or ghost radiation) and the
idealization of impulsive radiation (infinitesimally thin null shells) is
employed.


title: Energy Density in Expanding Universes as Seen by Unruh's Detector

abstract:
  We consider the response of an Unruh detector to scalar fields in an
expanding space-time. When combining transition elements of the scalar field
Hamiltonian with the interaction operator of detector and field, one finds at
second order in time-dependent perturbation theory a transition amplitude,
which actually dominates in the ultraviolet over the first order contribution.
In particular, the detector response faithfully reproduces the particle number
implied by the stress-energy of a minimally coupled scalar field, which is
inversely proportional to the energy of a scalar mode. This finding disagrees
with the contention that in de Sitter space, the response of the detector drops
exponentially with particle energy and therefore indicates a thermal spectrum.


title:
Inflaton field fluctuations from gauge-invariant metric fluctuations
  during inflation

abstract:
  The evolution of the inflaton field fluctuations from gauge-invariant metric
fluctuations is discused. In particular, the case of a symmetric
$\phi_c$-exponential potential is analyzed.


title:
The discrete energy method in numerical relativity: Towards long-term
  stability

abstract:
  The energy method can be used to identify well-posed initial boundary value
problems for quasi-linear, symmetric hyperbolic partial differential equations
with maximally dissipative boundary conditions. A similar analysis of the
discrete system can be used to construct stable finite difference equations for
these problems at the linear level. In this paper we apply these techniques to
some test problems commonly used in numerical relativity and observe that while
we obtain convergent schemes, fast growing modes, or ``artificial
instabilities,'' contaminate the solution. We find that these growing modes can
partially arise from the lack of a Leibnitz rule for discrete derivatives and
discuss ways to limit this spurious growth.


title:
Two-dimensional Riemannian and Lorentzian geometries from second order
  ODEs

abstract:
  In this note we give an alternative geometrical derivation of the results
recently presented by Garcia-Godinez, Newman and Silva-Ortigoza in [1] on the
class of all two-dimensional riemannian and lorentzian metrics from 2nd order
ODEs which are in duality with the two dimensional Hamilton-Jacobi equation. We
show that, as it happens in the Null Surface Formulation of General Relativity,
the Wuschmann-like condition can be obtained as a requirement of a vanishing
torsion tensor. Furthermore, from these second order ODEs we obtain the
associated Cartan connections.


title: Significance of c/sqrt(2) in Relativistic Physics

abstract:
  In the description of \emph{relative} motion in accelerated systems and
gravitational fields, inertial and tidal accelerations must be taken into
account, respectively. These involve a critical speed that in the first
approximation can be simply illustrated in the case of motion in one dimension.
For one-dimensional motion, such first-order accelerations are multiplied by
$(1-V^2/V_c^2)$, where $V_c=c/\sqrt{2}$ is the critical speed. If the speed of
relative motion exceeds $V_c$, there is a sign reversal with consequences that
are contrary to Newtonian expectations.