title:
Where are all the gravastars? Limits upon the gravastar model from
  accreting black holes

abstract:
  The gravastar model, which postulates a strongly correlated thin shell of
anisotropic matter surrounding a region of anti-de Sitter space, has been
proposed as an alternative to black holes. We discuss constraints that
present-day observations of well-known black hole candidates place on this
model. We focus upon two black hole candidates known to have extraordinarily
low luminosities: the supermassive black hole in the Galactic Center,
Sagittarius A*, and the stellar-mass black hole, XTE J1118+480. We find that
the length scale for modifications of the type discussed in Chapline et al.
(2003) must be sub-Planckian.


title:
On the super-fluid property of the relativistic physical vacuum medium
  and the inertial motion of particles

abstract:
  The similarity between the energy spectra of relativistic particles and that
of quasi-particles in super-conductivity BCS theory makes us conjecture that
the relativistic physical vacuum medium as the ground state of the background
field is a super fluid medium, and the rest mass of a relativistic particle is
like the energy gap of a quasi-particle. This conjecture is strongly supported
by the results of our following investigation: a particle moving through the
vacuum medium at a speed less than the speed of light in vacuum, though
interacting with the vacuum medium, never feels friction force and thus
undergoes a frictionless and inertial motion. The profound and intrinsic
relationship between the super fluid property of the relativistic physical
vacuum medium and the energy-momentum conservation law as well as the
relativistic energy-momentum dispersion relation or the principle of
relativity, can be established.


title:
Interaction of plane gravitational waves with a Fabry-Perot cavity in
  the local Lorentz frame

abstract:
  We analyze the interaction of plane '+'-polarized gravitational waves with a
Fabry-Perot cavity in the local Lorentz frame of the cavity input mirror
outside of the range of long-wave approximation with the force of radiation
pressure taken into account. The obtained detector response signal is
represented as a sum of two parts: (i) the phase shift due to displacement of
the movable mirror under the influence of gravitational wave and the force of
light pressure, and (ii) the phase shift due to direct interaction of
gravitational wave with light wave inside the cavity. We obtain formula for the
movable mirror law of motion paying close attention to the phenomena of optical
rigidity, radiative friction and direct coupling of gravitational wave to light
wave. Some issues concerning the detection of high-frequency gravitational
waves and the role of optical rigidity in it are discussed. We also examine in
detail special cases of optical resonance and small detuning from it and
compare our results with the known ones.


title:
Dixon-Souriau equations from a 5-dimensional spinning particle in a
  Kaluza-Klein framework

abstract:
  The dimensional reduction of Papapetrou equations is performed in a
5-dimensional Kaluza-Klein background and Dixon-Souriau results for the motion
of a charged spinning body are obtained. The splitting provides an electric
dipole moment, and, for elementary particles, the induced parity and
time-reversal violations are explained.


title: General relativity, gravitational energy and spin-two field

abstract:
  In my lectures I will deal with three seemingly unrelated problems: i) to
what extent is general relativity exceptional among metric gravity theories?
ii) is it possible to define gravitational energy density applying field-theory
approach to gravity? and iii) can a consistent theory of a gravitationally
interacting spin-two field be developed at all? The connecting link to them is
the concept of a fundamental spin-2 field. A linear spin-2 field encounters
insurmountable inconsistencies when coupled to gravity. After discussing the
inconsistencies of any coupling of the linear spin-2 field to gravity, I
exhibit the origin of the fact that a gauge invariant field has the variational
metric stress tensor which is gauge dependent. I give a general theorem
explaining under what conditions a symmetry of a field Lagrangian becomes also
the symmetry of the stress tensor. It is a conclusion of the theorem that any
attempt to define gravitational energy density in the framework of a field
theory of gravity must fail. Finally I make a very brief introduction to basic
concepts of how a certain kind of a necessarily nonlinear spin-2 field arises
in a natural way from vacuum higher derivative gravity theories. This specific
spin-2 field consistently interacts gravitationally.


title:
Reply to ``On the Systematic Errors in the Detection of the
  Lense-Thirring Effect with a Mars Orbiter '', by Giampiero Sindoni, Claudio
  Paris and Paolo Ialongo

abstract:
  In this note we reply to the criticisms by Sindoni, Paris and Ialongo
concerning some aspects of the recent frame-dragging test performed by Iorio
with the Mars Global Surveyor (MGS) spacecraft in the gravitational field of
Mars.

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


title: Differences between scalar field and scalar density solutions

abstract:
  We explore differences between scalar field, and scalar density solutions by
using Robertson-Walker (RW) metric, and also a non-relativistic Hamiltonian is
derived for a scalar density field in the post-Newtonian approximation. The
results are compared with those of scalar field. The expanding universe in RW
metric, and post-Newtonian solution of Klein-Gordon equation are separately
discussed.


title:
Cylindrical gravitational waves in expanding universes: Models for waves
  from compact sources

abstract:
  New boundary conditions are imposed on the familiar cylindrical gravitational
wave vacuum spacetimes. The new spacetime family represents cylindrical waves
in a flat expanding (Kasner) universe. Space sections are flat and nonconical
where the waves have not reached and wave amplitudes fall off more rapidly than
they do in Einstein-Rosen solutions, permitting a more regular null inifinity.


title:
Frequency noise and intensity noise of next-generation
  gravitational-wave detectors with RF/DC readout schemes

abstract:
  The sensitivity of next-generation gravitational-wave detectors such as
Advanced LIGO and LCGT should be limited mostly by quantum noise with an
expected technical progress to reduce seismic noise and thermal noise. Those
detectors will employ the optical configuration of resonant-sideband-extraction
that can be realized with a signal-recycling mirror added to the Fabry-Perot
Michelson interferometer. While this configuration can reduce quantum noise of
the detector, it can possibly increase laser frequency noise and intensity
noise. The analysis of laser noise in the interferometer with the conventional
configuration has been done in several papers, and we shall extend the analysis
to the resonant-sideband-extraction configuration with the radiation pressure
effect included. We shall also refer to laser noise in the case we employ the
so-called DC readout scheme.


title: Recoil Velocities from Equal-Mass Binary-Black-Hole Mergers

abstract:
  The final evolution of a binary black-hole system gives rise to a recoil
velocity if an asymmetry is present in the emitted gravitational radiation.
Measurements of this effect for non-spinning binaries with unequal masses have
pointed out that kick velocities $\sim~175$ km/s can be reached for a mass
ratio $\simeq 0.36$. However, a larger recoil can be obtained for equal-mass
binaries if the asymmetry is provided by the spins. Using two independent
methods we show that the merger of such binaries yields velocities as large as
$\sim 440$ km/s for black holes having unequal spins that are antialigned and
parallel to the orbital angular momentum.


title: Large Merger Recoils and Spin Flips From Generic Black-Hole Binaries

abstract:
  We report the first results from evolutions of a generic black-hole binary,
i.e. a binary containing unequal mass black holes with misaligned spins. Our
configuration, which has a mass ratio of 2:1, consists of an initially
non-spinning hole orbiting a larger, rapidly spinning hole (specific spin a/m =
0.885), with the spin direction oriented -45 degrees with respect to the
orbital plane. We track the inspiral and merger for ~2 orbits and find that the
remnant receives a substantial kick of 454 km/s, more than twice as large as
the maximum kick from non-spinning binaries. The remnant spin direction is
flipped by 103 degrees with respect to the initial spin direction of the larger
hole. We performed a second run with anti-aligned spins, a/m = +-0.5 lying in
the orbital plane that produces a kick of 1830 km/s off the orbital plane. This
value scales to nearly 4000 km/s for maximally spinning holes. Such a large
recoil velocity opens the possibility that a merged binary can be ejected even
from the nucleus of a massive host galaxy.


title:
The connection between entropy and the absorption spectra of
  Schwarzschild black holes for light and massless scalar fields

abstract:
  We present heuristic arguments suggesting that if EM waves with wavelengths
somewhat larger than the Schwarzschild radius of a black hole were fully
absorbed by it, the second law of thermodynamics would be violated, under the
Bekenstein interpretation of the area of a black hole as a measure of its
entropy. Thus, entropy considerations make the well known fact that large
wavelengths are only marginally absorbed by black holes, a natural consequence
of thermodynamics. We also study numerically the ingoing radial propagation of
a scalar field wave in a Schwarzschild metric, relaxing the standard assumption
which leads to the eikonal equation, that the wave has zero spatial extent. We
find that if these waves have wavelengths larger that the Schwarzschild radius,
they are very substantially reflected, fully to numerical accuracy.
Interestingly, this critical wavelength approximately coincides with the one
derived from entropy considerations of the EM field, and is consistent with
well known limit results of scattering in the Schwarzschild metric. The
propagation speed is also calculated and seen to differ from the value $c$, for
wavelengths larger than $R_{s}$, in the vicinity of $R_{s}$. As in all
classical wave phenomena, whenever the wavelength is larger or comparable to
the physical size of elements in the system, in this case changes in the
metric, the zero extent 'particle' description fails, and the wave nature
becomes apparent.


title:
Asymptotic properties of the development of conformally flat data near
  spatial infinity

abstract:
  Certain aspects of the behaviour of the gravitational field near null and
spatial infinity for the developments of asymptotically Euclidean, conformally
flat initial data sets are analysed. Ideas and results from two different
approaches are combined: on the one hand the null infinity formalism related to
the asymptotic characteristic initial value problem and on the other the
regular Cauchy initial value problem at spatial infinity which uses Friedrich's
representation of spatial infinity as a cylinder. The decay of the Weyl tensor
for the developments of the class of initial data under consideration is
analysed under some existence and regularity assumptions for the asymptotic
expansions obtained using the cylinder at spatial infinity. Conditions on the
initial data to obtain developments satisfying the Peeling Behaviour are
identified. Further, the decay of the asymptotic shear on null infinity is also
examined as one approaches spatial infinity. This decay is related to the
possibility of selecting the Poincar\'e group out of the BMS group in a
canonical fashion. It is found that for the class of initial data under
consideration, if the development peels, then the asymptotic shear goes to zero
at spatial infinity. Expansions of the Bondi mass are also examined. Finally,
the Newman-Penrose constants of the spacetime are written in terms of initial
data quantities and it is shown that the constants defined at future null
infinity are equal to those at past null infinity.


title:
Searching for Massive Black Hole Binaries in the first Mock LISA Data
  Challenge

abstract:
  The Mock LISA Data Challenge is a worldwide effort to solve the LISA data
analysis problem. We present here our results for the Massive Black Hole Binary
(BBH) section of Round 1. Our results cover Challenge 1.2.1, where the
coalescence of the binary is seen, and Challenge 1.2.2, where the coalescence
occurs after the simulated observational period. The data stream is composed of
Gaussian instrumental noise plus an unknown BBH waveform. Our search algorithm
is based on a variant of the Markov Chain Monte Carlo method that uses
Metropolis-Hastings sampling and thermostated frequency annealing. We present
results from the training data sets and the blind data sets. We demonstrate
that our algorithm is able to rapidly locate the sources, accurately recover
the source parameters, and provide error estimates for the recovered
parameters.


title: Dark energy, antimatter gravity and geometry of the Universe

abstract:
  This article is based on two hypotheses. The first one is the existence of
the gravitational repulsion between particles and antiparticles. Consequently,
virtual particle-antiparticle pairs in the quantum vacuum may be considered as
gravitational dipoles. The second hypothesis is that the Universe has geometry
of a four-dimensional hyper-spherical shell with thickness equal to the Compton
wavelength of a pion, which is a simple generalization of the usual geometry of
a 3-hypersphere. It is striking that these two hypotheses lead to a simple
relation for the gravitational mass density of the vacuum, which is in very
good agreement with the observed dark energy density.


title:
Comment to: Corrections to the fine structure constant in the spacetime
  of a cosmic string from the generalized uncertainty principle

abstract:
  In the paper [F. Nasseri, Phys. Lett. B 632 (2006) 151--154], F. Nasseri
supposed that the value of the angular momentum for the Bohr's atom in the
presence of the cosmic string is quantized in units of ℏ. Using this
assumption it was obtained an incorrect expression for Bohr radius in this
scenario. In this comment I want to point out that this assumption is not
correct and present a corrected expression for the Bohr radius in this
background.


title: An overview of the second round of the Mock LISA Data Challenges

abstract:
  The Mock Data Challenges (MLDCs) have the dual purpose of fostering the
development of LISA data-analysis tools and capabilities and of demonstrating
the technical readiness already achieved by the gravitational-wave community in
distilling a rich science payoff from the LISA data. The first round of MLDCs
has just been completed and the second-round data sets are being released
shortly after this workshop. The second-round data sets contain radiation from
an entire Galactic population of stellar-mass binary systems, from
massive--black-hole binaries, and from extreme--mass-ratio inspirals. These
data sets are designed to capture much of the complexity that is expected in
the actual LISA data, and should provide a fairly realistic setting to test
advanced data-analysis techniques, and in particular the global aspect of the
analysis. Here we describe the second round of MLDCs and provide details about
its implementation.


title: Light Cone Structure near Null Infinity of the Kerr Metric

abstract:
  Motivated by our attempt to understand the question of angular momentum of a
relativistic rotating source carried away by gravitational waves, in the
asymptotic regime near future null infinity of the Kerr metric, a family of
null hypersurfaces intersecting null infinity in shearfree (good) cuts are
constructed by means of asymptotic expansion of the eikonal equation. The
geometry of the null hypersurfaces as well asthe asymptotic structure of the
Kerr metric near null infinity are studied. To the lowest order in angular
momentum, the Bondi-Sachs form of the Kerr metric is worked out. The
Newman-Unti formalism is then further developed, with which the Newman-Penrose
constants of the Kerr metric are computed and shown to be zero. Possible
physical implications of the vanishing of the Newman-Penrose constants of the
Kerr metric are also briefly discussed.


title: On the Onset of Inflation in Loop Quantum Cosmology

abstract:
  Using a Liouville measure, similar to the one proposed recently by Gibbons
and Turok, we investigate the probability that single-field inflation with a
polynomial potential can last long enough to solve the shortcomings of the
standard hot big bang model, within the semiclassical regime of loop quantum
cosmology. We conclude that, for such a class of inflationary models and for
natural values of the loop quantum cosmology parameters, a successful
inflationary scenario is highly improbable.


title: Quasi-normal mode analysis in BEC acoustic black holes

abstract:
  We perform a quasi-normal mode analysis of black hole configurations in
Bose-Einstein condensates (BEC). In this analysis we use the full Bogoliubov
dispersion relation, not just the hydrodynamic or geometric approximation. We
restrict our attention to one-dimensional flows in BEC with step-like
discontinuities. For this case we show that in the hydrodynamic approximation
quasi-normal modes do not exist. The full dispersion relation, however, allows
the existence of quasi-normal modes. Remarkably, the spectrum of these modes is
not discrete but continuous.


title: One common solution to the singularity and perihelion problems

abstract:
  Based on the kinetic energy theorem, as one of the fundamental theorems from
the classical mechanics, throughout the first part of the article an attempt
has been made to derive the mathematical model of a material point motion in
the three-dimensional spatial subspace of the integral four-dimensional
space-time continuum and in the field of action of an active force F.
Accordingly, with a view to surmounting the singularity problem on the one
hand, as well as the moving perihelion problem of the planets on the other, as
two acutely vexed questions within Newton's gravity concept, the paper ends
with modification of Newton's gravity concept itself.


title:
Self-organized critical behavior: the evolution of frozen spin networks
  model in quantum gravity

abstract:
  In quantum gravity, we study the evolution of a two-dimensional planar open
frozen spin network, in which the color (i.e. the twice spin of an edge)
labeling edge changes but the underlying graph remains fixed. The mainly
considered evolution rule, the random edge model, is depending on choosing an
edge randomly and changing the color of it by an even integer. Since the change
of color generally violate the gauge invariance conditions imposed on the
system, detailed propagation rule is needed and it can be defined in many ways.
Here, we provided one new propagation rule, in which the involved even integer
is not a constant one as in previous works, but changeable with certain
probability. In random edge model, we do find the evolution of the system under
the propagation rule exhibits power-law behavior, which is suggestive of the
self-organized criticality (SOC), and it is the first time to verify the SOC
behavior in such evolution model for the frozen spin network. Furthermore, the
increase of the average color of the spin network in time can show the nature
of inflation for the universe.


title:
Gravitation, electromagnetism and cosmological constant in purely affine
  gravity

abstract:
  The Ferraris-Kijowski purely affine Lagrangian for the electromagnetic field,
that has the form of the Maxwell Lagrangian with the metric tensor replaced by
the symmetrized Ricci tensor, is dynamically equivalent to the metric
Einstein-Maxwell Lagrangian, except the zero-field limit, for which the metric
tensor is not well-defined. This feature indicates that, for the
Ferraris-Kijowski model to be physical, there must exist a background field
that depends on the Ricci tensor. The simplest possibility, supported by recent
astronomical observations, is the cosmological constant, generated in the
purely affine formulation of gravity by the Eddington Lagrangian. In this paper
we combine the electromagnetic field and the cosmological constant in the
purely affine formulation. We show that the sum of the two affine (Eddington
and Ferraris-Kijowski) Lagrangians is dynamically inequivalent to the sum of
the analogous ($\Lambda$CDM and Einstein-Maxwell) Lagrangians in the
metric-affine/metric formulation. We also show that such a construction is
valid, like the affine Einstein-Born-Infeld formulation, only for weak
electromagnetic fields, on the order of the magnetic field in outer space of
the Solar System. Therefore the purely affine formulation that combines
gravity, electromagnetism and cosmological constant cannot be a simple sum of
affine terms corresponding separately to these fields. A quite complicated form
of the affine equivalent of the metric Einstein-Maxwell-$\Lambda$ Lagrangian
suggests that Nature can be described by a simpler affine Lagrangian, leading
to modifications of the Einstein-Maxwell-$\Lambda$CDM theory for
electromagnetic fields that contribute to the spacetime curvature on the same
order as the cosmological constant.


title: Scalar functions for wave extraction in numerical relativity

abstract:
  Wave extraction plays a fundamental role in the binary black hole simulations
currently performed in numerical relativity. Having a well defined procedure
for wave extraction, which matches simplicity with efficiency, is critical
especially when comparing waveforms from different simulations. Recently,
progress has been made in defining a general technique which uses Weyl scalars
to extract the gravitational wave signal, through the introduction of the {\it
quasi-Kinnersley tetrad}. This procedure has been used successfully in current
numerical simulations; however, it involves complicated calculations. The work
in this paper simplifies the procedure by showing that the choice of the {\it
quasi-Kinnersley tetrad} is reduced to the choice of the time-like vector used
to create it. The space-like vectors needed to complete the tetrad are then
easily identified, and it is possible to write the expression for the Weyl
scalars in the right tetrad, as simple functions of the electric and magnetic
parts of the Weyl tensor.


title: Effect of the Inverse Volume Modification in Loop Quantum Cosmology

abstract:
  It is known that in loop quantum cosmology (LQC) the universe avoids the
singularity by a bounce when the matter density approaches the critical density
$\rho_c$ (the order of Planck density). After incorporating the inverse volume
modifications both in the gravitational and matter part in the improved
framework of LQC, we find that the inverse volume modification can decrease the
bouncing energy scale, and the presence of nonsingular bounce is generic. For
the backward evolution in the expanding branch, in terms of different initial
states the evolution trajectories classify into two classes. One class with
larger initial energy density leads to the occurrence of bounce in the region
$a>a_{ch}$ where $a_{ch}$ marks the different inverse volume modification
region. The other class with smaller initial energy density evolves back into
the region $a<a_{ch}$. In this region, both the energy density for the scalar
field and the bouncing energy scale decrease with the backward evolution.
However, in the deep modification region, because of the inverse volume
modification the scalar field is frozen, such that the bounce is present when
the bouncing energy scale decreases to be equal to the energy density of the
scalar field. Using numerical method, we show the evolution picture for the
second class bounce.


title: Tachyon field in Loop Quantum Cosmology: inflation and evolution picture

abstract:
  Loop quantum cosmology (LQC) predicts a nonsingular evolution of the universe
through a bounce in the high energy region. We show that this is always true in
tachyon matter LQC. Different from the classical Friedman-Robertson-Walker
(FRW) cosmology, the super inflation can appear in the tachyon matter LQC;
furthermore, the inflation can be extended to the region where classical
inflation stops. Using numerical method, we give an evolution picture of the
tachyon field with an exponential potential in the context of LQC. It indicates
that the quantum dynamical solutions have the attractive behavior as the
classical solutions do. The whole evolution of the tachyon field is that in the
distant past, the tachyon field--being in the contracting cosmology--is
accelerates to climb up the potential hill with a negative velocity; then at
the boundary the tachyon field is bounced into an expanding universe with
positive velocity rolling down to the bottom of the potential. In the slow roll
limit, we compare the quantum inflation with the classical case in both an
analytic and numerical way.


title:
On the physical field generated by rotating masses in Poincare-gauge
  theory of gravity

abstract:
  It is shown that the gauge field in Poincare-gauge theory of gravity consists
in two parts: the translational gauge field (t -field), which is generated by
the energy-momentum current of external fields, and the rotational gauge field
(r -field), which is generated by the sum of the angular and spin momentum
currents of external fields. In connection with this the physical field
generating by rotating masses should exist.


title: The Stability of an Isentropic Model for a Gaseous Relativistic Star

abstract:
  We show that the isentropic subclass of Buchdahl's exact solution for a
gaseous relativistic star is stable and gravitationally bound for all values of
the compactness ratio $u [\equiv (M/R)$, where $M$ is the total mass and $R$ is
the radius of the configuration in geometrized units] in the range, $0 < u \leq
0.20$, corresponding to the {\em regular} behaviour of the solution. This
result is in agreement with the expectation and opposite to the earlier claim
found in the literature.


title: No hair theorems for positive \Lambda

abstract:
  We extend all known black hole no-hair theorems to space-times endowed with a
positive cosmological constant $\Lambda.$ Specifically, we prove that static
spherical black holes with $\Lambda>0$ cannot support scalar fields in convex
potentials and Proca-massive vector fields in the region between black hole and
cosmic horizons. We also demonstrate the existence of at least one type of
quantum hair, and of exactly one charged solution for the Abelian Higgs model.
Our method of proof can be applied to investigate other types of quantum or
topological hair on black holes in the presence of a positive $\Lambda.$


title: Hamiltonian Formulation of 5-dimensional Kaluza-Klein Theory

abstract:
  We analyze the consistency of the ADM approach to KK model; we prove that KK
reduction commute with ADM splitting. This leads to a well defined Hamiltonian;
we provide the outcome. The electromagnetic constraint is derived from a
geometrical one and this result enforces the physical meaning of KK model.
Moreover we study the role of the extra scalar field we have in our model;
classical hints from geodesic motion and cosmological solutions suggest that
the scalar field can be an alternative time variable in the relational point of
view.


title: Spin-2 particles in gravitational fields

abstract:
  We give a solution of the wave equation for massless, or massive spin-2
particles propagating in a gravitational background. The solution is covariant,
gauge-invariant and exact to first order in the background gravitational field.
The background contribution is confined to a phase factor from which
geometrical and physical optics can be derived. The phase also describes
Mashhoon's spin-rotation coupling and, in general, the spin-gravity
interaction.


title:
Why do we Still Believe in Newton's Law ? Facts, Myths and Methods in
  Gravitational Physics

abstract:
  An overview of the experimental and observational status in gravitational
physics is given, both for the known tests of general relativity and Newtonian
gravity, but also for the increasing number of results where these theories run
into problems, such as for dark matter, dark energy, and the Pioneer and flyby
anomalies. It is argued that (1) scientific theories should be tested (2)
current theories of gravity are poorly tested in the weak-acceleration regime
(3) the measurements suggest that the anomalous phenomena have a common origin
(4) it is useful to consider the present situation under a historical
perspective and (5) it could well be that we still do not understand gravity.
Proposals for improving the current use of scientific methods are given.
  `We do not know anything - this is the first. Therefore, we should be very
modest - this is the second. Not to claim that we do know when we do not - this
is the third. That's the kind of attitude I'd like to popularize. There is
little hope for success.' (Karl Popper)


title: Equilibrium temperature anisotropy and black-hole analogues

abstract:
  When long-range interactions are present the usual definition of temperature
implies that two systems in thermal equilibrium can be at different
temperatures. This local temperature has physical significance, if the
sub-systems cease to interact, each system will be at their different local
temperatures. This is formally related to redshifting of temperature in general
relativity. We propose experiments to test this effect which are feasible using
current microfabrication techniques. It is also possible to display
thermodynamical analogues to black-hole space-time.


title:
Confinement and stability of the motion of test particles in thick
  branes

abstract:
  We consider the motion of test particles in a thick brane version of
Randall-Sundrum type II model. It is known that gravity alone cannot explain
the confinement of test particles in this kind of brane. In this paper we show
that a stable confinement in a domain wall is possible by admitting a direct
interaction between test particles and a scalar field. This interaction is
implemented by a modification of the Lagrangian of the particle which is
inspired by a Yukawa-type interaction between fermions and scalar fields.


title:
Nearly Divergence of Correlation Length and Perturbation Spectrum in
  String Gas Cosmology

abstract:
  Recently, it has been shown in Ref.[1] that the string thermodynamic
fluctuation may lead to a scale invariant spectrum of scalar metric
perturbation. However, its realization is still in study. In this note we
suppose that the correlation length of metric perturbation, which is
proportional to the sound speed, might be nearly divergent at the critical
point of phase transition. In this case we find that the string gas mechanism
responsible for the generation of primordial perturbation may be applied well.


title: A new method to construct spacetimes with a spacelike circle action

abstract:
  A new general procedure to construct realistic spacetimes is introduced. It
is based on the null congruence on a time-oriented Lorentzian manifold
associated to a certain timelike vector field. As an application, new examples
of stably causal Petrov type D spacetimes which obey the timelike convergence
condition and which admit an isometric spacelike circle action are obtained.


title: Exact Solutions of Regge-Wheeler Equation

abstract:
  The Regge-Wheeler equation describes the axial perturbations of Schwarzschild
metric in linear approximation. We present its exact solutions in terms of the
confluent Heun's functions, the basic properties of the general solution, novel
analytical approach and numerical techniques for study of different boundary
problems which correspond to quasi-normal modes of black holes and other simple
models of compact objects. We depict in more detail the exact solutions of
Regge-Wheeler equation in the Schwarzschild black hole interior and on
Kruscal-Szekeres manifold.


title: Orbital precession due to central-force perturbations

abstract:
  We calculate the precession of Keplerian orbits under the influence of
arbitrary central-force perturbations. Our result is in the form of a
one-dimensional integral that is straightforward to evaluate numerically. We
demonstrate the effectiveness of our formula for the case of the Yukawa
potential. We obtain analytic results for potentials of the form V(r) = \alpha
r^n and V(r) = \alpha \ln(r/\lambda) in terms of the hypergeometric function
{_2F_1} (1/2-n/2,1-n/2; 2; e^2), where e is the eccentricity. Our results
reproduce the known general relativistic (n=-3), constant force (n=1), and
cosmological constant (n=2) precession formulas. Planetary precessions are
often used to constrain the sizes of hypothetical new weak forces--our results
allow for more precise, and often stronger, constraints on such proposed new
forces.


title: Recoiling from a kick in the head-on collision of spinning black holes

abstract:
  Recoil ``kicks'' induced by gravitational radiation are expected in the
inspiral and merger of black holes. Recently the numerical relativity community
has begun to measure the significant kicks found when both unequal masses and
spins are considered. Because understanding the cause and magnitude of each
component of this kick may be complicated in inspiral simulations, we consider
these effects in the context of a simple test problem. We study recoils from
collisions of binaries with initially head-on trajectories, starting with the
simplest case of equal masses with no spin and then adding spin and varying the
mass ratio, both separately and jointly. We find spin-induced recoils to be
significant relative to unequal-mass recoils even in head-on configurations.
Additionally, it appears that the scaling of transverse kicks with spins is
consistent with post-Newtonian theory, even though the kick is generated in the
nonlinear merger interaction, where post-Newtonian theory should not apply.
This suggests that a simple heuristic description might be effective in the
estimation of spin-kicks.


title: The Quest to Understand the Pioneer Anomaly

abstract:
  The Pioneer 10/11 missions, launched in 1972 and 1973, and their navigation
are reviewed. Beginning in about 1980 an unmodeled force of ~ 8 x 10^{-8}
cm/s^2 appeared in the tracking data, it later being verified. The cause
remains unknown, although radiant heat remains a likely origin. A set of
efforts to find the solution are underway: a) analyzing in detail all available
data, b) using data from the New Horizons mission, and c) considering an ESA
dedicated mission.


title: Entropy of a charged black hole in two dimensions without cutoff

abstract:
  By introducing the generalized uncertainty principle (GUP) on quantum density
states, we newly obtain a consistent entropy of a scalar field on the
(1+1)-dimensional Maxwell-dilaton background without an artificial cutoff in
contrast to the results of the brick wall model, which depend on the choice of
the Hawking temperature for the extremal case.


title:
Detecting gravitational waves from inspiraling binaries with a network
  of detectors : coherent strategies by correlated detectors

abstract:
  We discuss the coherent search strategy to detect gravitational waves from
inspiraling compact binaries by a network of correlated laser interferometric
detectors. From the maximum likelihood ratio statistic, we obtain a coherent
statistic which is slightly different from and generally better than what we
obtained in our previous work. In the special case when the cross spectrum of
two detectors normalized by the power spectrum density is constant, the new
statistic agrees with the old one. The quantitative difference of the detection
probability for a given false alarm rate is also evaluated in a simple case.


title: A teleparallel representation of the Weyl Lagrangian

abstract:
  The main result of the paper is a new representation of the Weyl Lagrangian
(massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e.
an orthonormal tetrad of covector fields. We write down a simple Lagrangian -
wedge product of axial torsion with a lightlike element of the coframe - and
show that variation of the resulting action with respect to the coframe
produces the Weyl equation. The advantage of our approach is that it does not
require the use of spinors, Pauli matrices or covariant differentiation. The
only geometric concepts we use are those of a metric, differential form, wedge
product and exterior derivative. Our result assigns a variational meaning to
the tetrad representation of the Weyl equation suggested by J.B.Griffiths and
R.A.Newing.


title: Kaluza-Klein reduction for the Unruh brane

abstract:
  We present a Kaluza-Klein reduction for the Unruh response that a brane, in
an AdS bulk would experience due to its acceleration. The Unruh radiation is
realised as particle production on the brane for each of the Kaluza-Klein
modes. A correction, coming from the massive modes, is calculated for the
standard Unruh effect in Minkowski spacetime and it is found that the response
coming from these modes is exponentially suppressed.


title:
A mathematical framework for a standard theory using extended
  representations of paths and world lines

abstract:
  An analysis using a composition of currently-accepted theories is given.
Starting with a synthesis of what may be generically termed ``paths'', analysis
of representations for these ``paths'' is developed. Foreground and background
interactions are explicitly treated by using a local representation that treats
the two representations equally and symmetrically. A restriction coupling from
the global space-time representation to local interaction source terms is
treated in terms of mass and charge couplings. Rewriting the connection in
terms of the global manifold and the coupled terms yields compatibility with
Dirac and Klein-Gordan equations for electro-weak coupled particles and fields.
Compatibility with currently-accepted theories that includes standard charge
assignments, SU(3) confinement, and a definition for particle flavor
generations is used to constrain and validate the composition and the analysis.


title: Evolutionary Reformulation of Quantum Gravity

abstract:
  We present a critical analysis of the Canonical approach to quantum gravity,
which relies on the ambiguity of implementing a space-time slicing on the
quantum level. We emphasize that such a splitting procedure is consistent only
if a real matter fluid is involved in the dynamics.


title: Is Torsion a Fundamental Physical Field?

abstract:
  The local Lorentz group is introduced in flat space-time, where the resulting
Dirac and Yang-Mills equations are found, and then generalized to curved
space-time: if matter is neglected, the Lorentz connection is identified with
the contortion field, while, if matter is taken into account, both the Lorentz
connection and the spinor axial current are illustrated to contribute to the
torsion of space-time.


title: Electro-weak Model within a 5-dimensional Lorentz group theory

abstract:
  The Electroweak model will be geometrized in a 5-D Riemann-Cartan framework:
U(1) weak hyper-charge group will be worked out in a Klauza-Klein scheme, while
SU(2) weak isospin group will be identified to suitable bein projections of the
contortion field. The possibility of introducing Ashtekar formalism in 5-D
Klauza-Klein theories will be investigated.


title:
Electro-weak Model within the framework of Lorentz gauge theory:
  Ashtekar variables?

abstract:
  The Electroweak (EW) model is geometrized in the framework of a 5D gauge
theory of the Lorentz group, after the implementation of the Kaluza-Klein (KK)
paradigm. The possibility of introducing Ashtekar variables on a 5D KK manifold
is considered on the ground of its geometrical structure.


title: Canonical Realizations of Doubly Special Relativity

abstract:
  Doubly Special Relativity is usually formulated in momentum space, providing
the explicit nonlinear action of the Lorentz transformations that incorporates
the deformation of boosts. Various proposals have appeared in the literature
for the associated realization in position space. While some are based on
noncommutative geometries, others respect the compatibility of the spacetime
coordinates. Among the latter, there exist several proposals that invoke in
different ways the completion of the Lorentz transformations into canonical
ones in phase space. In this paper, the relationship between all these
canonical proposals is clarified, showing that in fact they are equivalent. The
generalized uncertainty principles emerging from these canonical realizations
are also discussed in detail, studying the possibility of reaching regimes
where the behavior of suitable position and momentum variables is classical,
and explaining how one can reconstruct a canonical realization of doubly
special relativity starting just from a basic set of commutators. In addition,
the extension to general relativity is considered, investigating the kind of
gravity's rainbow that arises from this canonical realization and comparing it
with the gravity's rainbow formalism put forward by Magueijo and Smolin, which
was obtained from a commutative but noncanonical realization in position space.


title: The Gravitomagnetic Influence on Gyroscopes and on the Lunar Orbit

abstract:
  Gravitomagnetism--a motional coupling of matter analogous to the Lorentz
force in electromagnetism--has observable consequences for any scenario
involving differing mass currents. Examples include gyroscopes located near a
rotating massive body, and the interaction of two orbiting bodies. In the
former case, the resulting precession of the gyroscope is often called ``frame
dragging,'' and is the principal measurement sought by the Gravity Probe-B
experiment. The latter case is realized in the earth-moon system, and the
effect has in fact been confirmed via lunar laser ranging (LLR) to
approximately 0.1% accuracy--better than the anticipated accuracy of the
Gravity-Probe-B result. This paper shows the connnection between these
seemingly disparate phenomena by employing the same gravitomagnetic term in the
equation of motion to obtain both gyroscopic precession and modification of the
lunar orbit. Since lunar ranging currently provides a part in a thousand fit to
the gravitomagnetic contributions to the lunar orbit, this feature of
post-Newtonian gravity is not adjustable to fit any anomalous result beyond the
0.1% level from Gravity Probe-B without disturbing the existing fit of theory
to the 36 years of LLR data.


title: Papapetrou Energy-Momentum Tensor for Chern-Simons Modified Gravity

abstract:
  We construct a conserved, symmetric energy-momentum (pseudo-)tensor for
Chern-Simons modified gravity, thus demonstrating that the theory is Lorentz
invariant. The tensor is discussed in relation to other gravitational
energy-momentum tensors and analyzed for the Schwarzschild, Reissner-Nordstrom,
and FRW solutions. To our knowledge this is the first confirmation that the
Reissner-Nordstrom and FRW metrics are solutions of the modified theory.


title: An Introduction to Loop Quantum Gravity Through Cosmology

abstract:
  This introductory review is addressed to beginning researchers. Some of the
distinguishing features of loop quantum gravity are illustrated through loop
quantum cosmology of FRW models. In particular, these examples illustrate: i)
how `emergent time' can arise; ii) how the technical issue of solving the
Hamiltonian constraint and constructing the \emph{physical} sector of the
theory can be handled; iii) how questions central to the Planck scale physics
can be answered using such a framework; and, iv) how quantum geometry effects
can dramatically change physics near singularities and yet naturally turn
themselves off and reproduce classical general relativity when space-time
curvature is significantly weaker than the Planck scale.


title:
A variational analysis of Einstein-scalar field Lichnerowicz equations
  on compact Riemannian manifolds

abstract:
  We establish new existence and non-existence results for positive solutions
of the Einstein-scalar field Lichnerowicz equation on compact manifolds. This
equation arises from the Hamiltonian constraint equation for the
Einstein-scalar field system in general relativity. Our analysis introduces
variational techniques, in the form of the mountain pass lemma, to the analysis
of the Hamiltonian constraint equation, which has been previously studied by
other methods.


title: Black hole and holographic dark energy

abstract:
  We discuss the connection between black hole and holographic dark energy. We
examine the issue of the equation of state (EOS) for holographic energy density
as a candidate for the dark energy carefully. This is closely related to the
EOS for black hole, because the holographic dark energy comes from the black
hole energy density. In order to derive the EOS of a black hole, we may use its
dual (quantum) systems. Finally, a regular black hole without the singularity
is introduced to describe an accelerating universe inside the cosmological
horizon. Inspired by this, we show that the holographic energy density with the
cosmological horizon as the IR cutoff leads to the dark energy-dominated
universe with $\omega_{\rm \Lambda}=-1$.


title: Tunneling Effect Near Weakly Isolated Horizon

abstract:
  The tunneling effect near a weakly isolated horizon (WIH) has been studied.
By applying the null geodesic method of Parikh and Wilczek and Hamilton-Jacibi
method of Angheben et al. to a weakly isolated horizon, we recover the
semiclassical emission rate in the tunneling process. We show that the
tunneling effect exists in a wide class of spacetimes admitting weakly isolated
horizons. The general thermodynamic nature of WIH is then confirmed.


title:
Homotheties of Cylindrically Symmetric Static Manifolds and their Global
  Extension

abstract:
  Cylindrically symmetric static manifolds are classified according to their
homotheties and metrics. In each case the homothety vector fields and the
corresponding metrics are obtained explicitly by solving the homothety
equations. It turns out that these metrics admit homothety groups $H_m$, where
$m=4,5,7,11$. This classification is then used to identify the cylindrically
symmetric static spaces admitting the local homotheties, which are globally
prohibited due to their topological construction. Einstein's field equations
are then used to identify the physical nature of the spaces thus obtained.


title: Adaptive Mesh Refinement and Relativistic MHD

abstract:
  We solve the general relativistic magnetohydrodynamics equations using
distributed parallel adaptive mesh refinement. We discuss strong scaling tests
of the code, and present evolutions of Michel accretion and a TOV star.


title:
Phase-space and Black Hole Entropy of Higher Genus Horizons in Loop
  Quantum Gravity

abstract:
  In the context of loop quantum gravity, we construct the phase-space of
isolated horizons with genus greater than 0. Within the loop quantum gravity
framework, these horizons are described by genus g surfaces with N punctures
and the dimension of the corresponding phase-space is calculated including the
genus cycles as degrees of freedom. From this, the black hole entropy can be
calculated by counting the microstates which correspond to a black hole of
fixed area. We find that the leading term agrees with the A/4 law and that the
sub-leading contribution is modified by the genus cycles.


title: Non-Minimally Coupled Cosmology as Geodesic Motion

abstract:
  Recent works showing that homogeneous and isotropic cosmologies involving
scalar fields correspond to geodesics of certain augmented spaces are
generalized to the non-minimal coupling case. As the Maupertuis-Jacobi
principle in classical mechanics, this result allows us, in principle, to infer
some of the dynamical properties of the cosmologies from the geometry of the
associated augmented spaces.


title: A new spectral apparent horizon finder for 3D numerical relativity

abstract:
  We present a new spectral-method-based algorithm for finding apparent
horizons in three-dimensional space-like hypersurfaces without symmetries.
While there are already a wide variety of algorithms for finding apparent
horizons, our new algorithm does not suffer from the same weakness as previous
spectral apparent horizon finders: namely the monopolar coefficient ($\ell=0$
in terms of the spherical harmonics decomposition) needed to be determined by a
root-finding procedure. Hence, this leads to a much faster and more robust
spectral apparent horizon finder. The finder is tested with the Kerr-Schild and
Brill-Lindquist data. Our finder is accurate and is as efficient as the
currently fastest methods developed recently by Schnetter (2003 Class. Quantum
Grav. {\bf 20}, 4719) and Thornburg (2004 Class. Quantum Grav. {\bf 21}, 743).
At typical resolutions it takes only 0.5 second to find the apparent horizon of
a Kerr-Schild black hole with $a=0.9M$ to the accuracy $\sim 10^{-5}$ for the
fractional error in the horizon's location on a 2 GHz processor.


title: Upper limits on gravitational wave emission from 78 radio pulsars

abstract:
  We present upper limits on the gravitational wave emission from 78 radio
pulsars based on data from the third and fourth science runs of the LIGO and
GEO600 gravitational wave detectors. The data from both runs have been combined
coherently to maximise sensitivity. For the first time pulsars within binary
(or multiple) systems have been included in the search by taking into account
the signal modulation due to their orbits. Our upper limits are therefore the
first measured for 56 of these pulsars. For the remaining 22, our results
improve on previous upper limits by up to a factor of 10. For example, our
tightest upper limit on the gravitational strain is 2.6e-25 for PSRJ1603-7202,
and the equatorial ellipticity of PSRJ2124-3358 is less than 10^{-6}.
Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times
greater than the fiducial spin-down limit.


title: Relativistic r-modes and shear viscosity

abstract:
  We derive the relativistic equations for stellar perturbations, including in
a consistent way shear viscosity in the stress-energy tensor, and we
numerically integrate our equations in the case of large viscosity. We consider
the slow rotation approximation, and we neglect the coupling between polar and
axial perturbations. In our approach, the frequency and damping time of the
emitted gravitational radiation are directly obtained. We find that,
approaching the inviscid limit from the finite viscosity case, the continuous
spectrum is regularized. Constant density stars, polytropic stars, and stars
with realistic equations of state are considered. In the case of constant
density stars and polytropic stars, our results for the viscous damping times
agree, within a factor two, with the usual estimates obtained by using the
eigenfunctions of the inviscid limit. For realistic neutron stars, our
numerical results give viscous damping times with the same dependence on mass
and radius as previously estimated, but systematically larger of about 60%.


title: Moving Detectors in Cavities

abstract:
  We consider two-level detectors, coupled to a quantum scalar field, moving
inside cavities. We highlight some pathological resonant effects due to abrupt
boundaries, and decide to describe the cavity by switching smoothly the
interaction by a time-dependent gate-like function. Considering uniformly
accelerated trajectories, we show that some specific choices of non-adiabatic
switching have led to hazardous interpretations about the enhancement of the
Unruh effect in cavities. More specifically, we show that the
emission/absorption ratio takes arbitrary high values according to the emitted
quanta properties and to the transients undergone at the entrance and the exit
of the cavity, {\it independently of the acceleration}. An explicit example is
provided where we show that inertial and uniformly accelerated world-lines can
even lead to the same ``pseudo-temperature''.


title: On the parameters of the Kerr-NUT-(anti-)de Sitter space-time

abstract:
  Different forms of the metric for the Kerr-NUT-(anti-)de Sitter space-time
are being widely used in its extension to higher dimensions. The purpose of
this note is to relate the parameters that are being used to the physical
parameters (mass, rotation, NUT and cosmological constant) in the basic four
dimensional situation.


title: On the onset of cosmological backreaction

abstract:
  Cosmological backreaction has been suggested as an explanation of dark energy
and is heavily disputed since. We combine cosmological perturbation theory with
Buchert's non-perturbative framework, calculate the relevant averaged
observables up to second order in the comoving synchronous gauge, and discuss
their gauge dependence. With the help of an integrability condition the leading
second order contributions follow from the first order calculation.
  We focus on the onset of cosmological backreaction, as a perturbative
treatment is necessarily restricted to the era when the effect is still small.
We demonstrate that the leading contributions to all averaged physical
observables are completely specified on the boundary of the averaged domain.
For any finite domain these surface terms are nonzero in general and thus
backreaction is for real. We map the backreaction effect on an effectively
homogeneous and isotropic fluid. The generic effective equation of state is not
only time dependent, but also depends on scale.


title: Disordered locality in loop quantum gravity states

abstract:
  We show that loop quantum gravity suffers from a potential problem with
non-locality, coming from a mismatch between micro-locality, as defined by the
combinatorial structures of their microscopic states, and macro-locality,
defined by the metric which emerges from the low energy limit. As a result, the
low energy limit may suffer from a disordered locality characterized by
identifications of far away points. We argue that if such defects in locality
are rare enough they will be difficult to detect.


title:
Cylindrically Symmetric, Static, Perfect-Fluid Solutions of Einstein's
  Field Equations

abstract:
  Perfect-fluid, static, cylindrically symmetric solutions of Einstein's field
equations are obtained for the equations of state $\rho+3p=0$ and $\rho=p$. In
the former case, the density and the pressure turn out to be constant while in
the later case, they depend on the radial parameter $r$. Evan's solution
corresponding to the equation of state $\rho=p$ is included in the solutions
discussed here.


title: A class of relativistic stars with a linear equation of state

abstract:
  By assuming a particular mass function we find new exact solutions to the
Einstein field equations with an anisotropic matter distribution. The solutions
are shown to be relevant for the description of compact stars. A distinguishing
feature of this class of solutions is that they admit a linear equation of
state which can be applied to strange stars with quark matter.


title: Energy and Momentum of Bell-Szekeres Space-time in Moller Prescription

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0602105, gr-qc/0307010, and gr-qc/9802050.


title: Dirac-type equations in a gravitational field, with vector wave function

abstract:
  An analysis of the classical-quantum correspondence shows that it needs to
identify a preferred class of coordinate systems, which defines a torsionless
connection. One such class is that of the locally-geodesic systems,
corresponding to the Levi-Civita connection. Another class, thus another
connection, emerges if a preferred reference frame is available. From the
classical Hamiltonian that rules geodesic motion, the correspondence yields two
distinct Klein-Gordon equations and two distinct Dirac-type equations in a
general metric, depending on the connection used. Each of these two equations
is generally-covariant, transforms the wave function as a four-vector, and
differs from the Fock-Weyl gravitational Dirac equation (DFW equation). One
obeys the equivalence principle in an often-accepted sense, whereas the DFW
equation obeys that principle only in an extended sense.


title: Canonical quantization and the spectral action, a nice example

abstract:
  We study the canonical quantization of the theory given by Chamseddine-Connes
spectral action on a particular finite spectral triple with algebra
$M_2(\Cset)\oplus\Cset$. We define a quantization of the natural distance
associated with this noncommutative space and show that the quantum distance
operator has a discrete spectrum. We also show that it would be the same for
any other geometric quantity. Finally we propose a physical Hilbert space for
the quantum theory. This spectral triple had been previously considered by
Rovelli as a toy model, but with a different action which was not
gauge-invariant. The results are similar in both cases, but the
gauge-invariance of the spectral action manifests itself by the presence of a
non-trivial degeneracy structure for our distance operator.


title: Multidomain Spectral Method for the Helically Reduced Wave Equation

abstract:
  We consider the 2+1 and 3+1 scalar wave equations reduced via a helical
Killing field, respectively referred to as the 2-dimensional and 3-dimensional
helically reduced wave equation (HRWE). The HRWE serves as the fundamental
model for the mixed-type PDE arising in the periodic standing wave (PSW)
approximation to binary inspiral. We present a method for solving the equation
based on domain decomposition and spectral approximation. Beyond describing
such a numerical method for solving strictly linear HRWE, we also present
results for a nonlinear scalar model of binary inspiral. The PSW approximation
has already been theoretically and numerically studied in the context of the
post-Minkowskian gravitational field, with numerical simulations carried out
via the "eigenspectral method." Despite its name, the eigenspectral technique
does feature a finite-difference component, and is lower-order accurate. We
intend to apply the numerical method described here to the theoretically
well-developed post-Minkowski PSW formalism with the twin goals of spectral
accuracy and the coordinate flexibility afforded by global spectral
interpolation.


title:
Outgassing, Temperature Gradients and the Radiometer Effect in LISA: A
  Torsion Pendulum Investigation

abstract:
  Thermal modeling of the LISA gravitational reference sensor (GRS) includes
such effects as outgassing from the proof mass and its housing and the
radiometer effect. Experimental data in conditions emulating the LISA GRS are
required to confidently predict the GRS performance. Outgassing and the
radiometer effect are similar in characteristics and are difficult to decouple
experimentally.
  The design of our torsion balance allows us to investigate differential
radiation pressure, the radiometer effect, and outgassing on closely separated
conducting surfaces with high sensitivity. A thermally controlled split copper
plate is brought near a freely hanging plate-torsion pendulum.We have varied
the temperature on each half of the copper plate and have measured the
resulting forces on the pendulum.
  We have determined that to first order the current GRS model for the
radiometer effect, outgassing, and radiation pressure are mostly consistent
with our torsion balance measurements and therefore these thermal effects do
not appear to be a large hindrance to the LISA noise budget. However, there
remain discrepancies between the predicted dependence of these effects on the
temperature of our apparatus.


title:
Supermassive recoil velocities for binary black-hole mergers with
  antialigned spins

abstract:
  Recent calculations of the recoil velocity in binary black hole mergers have
found the kick velocity to be of the order of a few hundred km/s in the case of
non-spinning binaries and about $500 $km/s in the case of spinning
configurations, and have lead to predictions of a maximum kick of up to $1300
$km/s. We test these predictions and demonstrate that kick velocities of at
least $2500 $km/s are possible for equal-mass binaries with anti-aligned spins
in the orbital plane. Kicks of that magnitude are likely to have significant
repercussions for models of black-hole formation, the population of
intergalactic black holes and the structure of host galaxies.


title: High Sensitivity Torsion Balance Tests for LISA Proof Mass Modeling

abstract:
  We have built a highly sensitive torsion balance to investigate small forces
between closely spaced gold coated surfaces. Such forces will occur between the
LISA proof mass and its housing. These forces are not well understood and
experimental investigations are imperative. We describe our torsion balance and
present the noise of the system. A significant contribution to the LISA noise
budget at low frequencies is the fluctuation in the surface potential
difference between the proof mass and its housing. We present first results of
these measurements with our apparatus.


title:
Adiabatic Evolution of three 'Constants' of Motion for Greatly Inclined
  Orbits in Kerr spacetime

abstract:
  General orbits of a particle of small mass $\mu$ around a Kerr black hole of
mass $M$ are characterized by three parameters: the energy, the angular
momentum and the Carter constant. The time-averaged rates of change of the
energy and the angular momentum can be obtained by computing the corresponding
fluxes of gravitational waves emitted by the particle. By contrast, the
time-averaged rate of change of the Carter constant cannot be expressed as a
flux of gravitational waves. Recently a method to compute this rate of change
was proposed by Mino, and we refined it into a simplified form. In this paper
we further extend our previous work to give a new formulation without the aid
of expansion in terms of a small inclination angle.


title: Cosmic String Structure at the Gravitational Radiation Scale

abstract:
  We use our model of the small scale structure on cosmic strings to develop
further the result of Siemens, Olum, and Vilenkin that the gravitational
radiation length scale on cosmic strings is smaller than the previously assumed
$\Gamma G\mu t$. We discuss some of the properties of cosmic string loops at
this cutoff scale, and we argue that recent network simulations point to two
populations of cosmic string loops, one near the horizon scale and one near the
gravitational radiation cutoff.


title: Absolute quantum energy inequalities in curved spacetime

abstract:
  Quantum Energy Inequalities (QEIs) are results which limit the extent to
which the smeared renormalised energy density of the quantum field can be
negative, when averaged along a timelike curve or over a more general timelike
submanifold in spacetime. On globally hyperbolic spacetimes the
minimally-coupled massive quantum Klein--Gordon field is known to obey a
`difference' QEI that depends on a reference state chosen arbitrarily from the
class of Hadamard states. In many spacetimes of interest this bound cannot be
evaluated explicitly. In this paper we obtain the first `absolute' QEI for the
minimally-coupled massive quantum Klein--Gordon field on four dimensional
globally hyperbolic spacetimes; that is, a bound which depends only on the
local geometry. The argument is an adaptation of that used to prove the
difference QEI and utilises the Sobolev wave-front set to give a complete
characterisation of the singularities of the Hadamard series. Moreover, the
bound is explicit and can be formulated covariantly under additional (general)
conditions. We also generalise our results to incorporate adiabatic states.


title:
Lanczos potentials and a definition of gravitational entropy for
  perturbed FLRW space-times

abstract:
  We give a prescription for constructing a Lanczos potential for a
cosmological model which is a purely gravitational perturbation of a
Friedman-Lemaitre-Robertson-Walker space-time. For the radiation equation of
state, we find the Lanczos potential explicitly via Fourier transforms. As an
application, we follow up a suggestion of Penrose and propose a definition of
gravitational entropy for these cosmologies. With this definition, the
gravitational entropy initially is finite if and only if the initial Weyl
tensor is finite.


title: Homogeneous cosmologies and the Maupertuis-Jacobi principle

abstract:
  A recent work showing that homogeneous and isotropic cosmologies involving
scalar fields are equivalent to the geodesics of certain effective manifolds is
generalized to the non-minimally coupled and anisotropic cases. As the
Maupertuis-Jacobi principle in classical mechanics, such result permits us to
infer some dynamical properties of cosmological models from the geometry of the
associated effective manifolds, allowing us to go a step further in the study
of cosmological dynamics. By means of some explicit examples, we show how the
geometrical analysis can simplify considerably the dynamical analysis of
cosmological models.


title: No-Go Theorem for Energy-Momentum Conservation in Curved Spacetime

abstract:
  It is pointed out that in curved spacetime, one cannot define the sum of
energy-momemtum 4-vector over a space-like hypersurface. The difficulty in
finding satisfactory gravitational energy-momentum complex stems from
misunderstanding of this question. The law of conservation of energy-momentum
holds valid only approximately when spacetime is not seriously curved.


title:
Matter Collineations of Static Spacetimes with Maximal Symmetric
  Transverse Spaces

abstract:
  This paper is devoted to study the symmetries of the energy-momentum tensor
for the static spacetimes with maximal symmetric transverse spaces. We solve
matter collineation equations for the four main cases by taking one, two, three
and four non-zero components of the vector $\xi^a$. For one component non-zero,
we obtain only one matter collineation for the non-degenerate case and for two
components non-zero, the non-degenerate case yields maximum three matter
collineations. When we take three components non-zero, we obtain three, four
and five independent matter collineations for the non-degenerate and for the
degenerate cases respectively. This case generalizes the degenerate case of the
static spherically symmetric spacetimes. The last case (when all the four
components are non-zero) provides the generalization of the non-degenerate case
of the static spherically symmetric spacetimes. This gives either four, five,
six, seven or ten independent matter collineations in which four are the usual
Killing vectors and rest are the proper matter collineations. It is mentioned
here that we obtain different constraint equations which, on solving, may
provide some new exact solutions of the Einstein field equations.


title: Gauss-Bonnet brane gravity with a confining potential

abstract:
  A brane scenario is envisaged in which the $m$-dimensional bulk is endowed
with a Gauss-Bonnet term and localization of matter on the brane is achieved by
means of a confining potential. The resulting Friedmann equations on the brane
are modified by various extra terms that may be interpreted as the X-matter,
providing a possible phenomenological explanation for the accelerated expansion
of the universe. The age of the universe in this scenario is studied and shown
to be consistent with the present observational data.


title:
Gravity induced neutrino-antineutrino oscillation: CPT and lepton number
  non-conservation under gravity

abstract:
  We introduce a new effect in the neutrino oscillation phase which shows the
neutrino-antineutrino oscillation is possible under gravity even if the rest
masses of the corresponding eigenstates are same. This is due to CPT violation
and possible to demonstrate if the neutrino mass eigenstates are expressed as a
combination of neutrino and antineutrino eigenstates, as of the neutral kaon
system, with the plausible breaking of lepton number conservation. For Majorana
neutrinos, this oscillation is expected to affect significantly the inner edge
of neutrino dominated accretion disks around a compact object by influencing
the neutrino sphere which controls the accretion dynamics, and then the related
type-II supernova evolution and the r-process nucleosynthesis. On the other
hand, in early universe, in presence of various lepton number violating
processes, this oscillation, we argue, might lead to neutrino asymmetry which
resulted baryogenesis from the B-L symmetry by electro-weak sphaleron
processes.


title:
Warped product spaces and geodesic motion in the neighbourhood of
  hypersurfaces

abstract:
  We study the classical geodesic motions of nonzero rest mass test particles
and photons in five-dimensional warped product spaces. We show that it is
possible to obtain a general picture of these motions, using the natural
decoupling that occurs in such spaces between the motions in the fifth
dimension and the motion in the hypersurfaces. This splitting allows the use of
phase space analysis in order to investigate the possible confinement of
particles and photons to hypersurfaces in five-dimensional warped product
spaces. Using such analysis, we find a novel form of quasi-confinement which is
oscillatory and neutrally stable. We also find that this class of warped
product spaces locally satisfy the Z2 symmetry by default. The importance of
such a confinement is that it is purely due to the classical gravitational
effects, without requiring the presence of brane-type confinement mechanisms.


title: Non-linear vector perturbations in a contracting universe

abstract:
  A number of scalar field models proposed as alternatives to the standard
inflationary scenario involve contracting phases which precede the universe's
present phase of expansion. An important question concerning such models is
whether there are effects which could potentially distinguish them from purely
expanding cosmologies. Vector perturbations have recently been considered in
this context. At first order such perturbations are not supported by a scalar
field. In this paper, therefore, we consider second order vector perturbations.
We show that such perturbations are generated by first order scalar mode-mode
couplings, and give an explicit expression for them. We compare the magnitude
of vector perturbations produced in collapsing models with the corresponding
amplitudes produced during inflation, using a number of suitable power-law
solutions to model the inflationary and collapsing scenarios. We conclude that
the ratios of the magnitudes of these perturbations depend on the details of
the collapsing scenario as well as on how the hot big bang is recovered, but
for certain cases could be large, growing with the duration of the collapse.


title: Some Implications of the Cosmological Constant to Fundamental Physics

abstract:
  In the presence of a cosmological constant, ordinary Poincare' special
relativity is no longer valid and must be replaced by a de Sitter special
relativity, in which Minkowski space is replaced by a de Sitter spacetime. In
consequence, the ordinary notions of energy and momentum change, and will
satisfy a different kinematic relation. Such a theory is a different kind of a
doubly special relativity. Since the only difference between the Poincare' and
the de Sitter groups is the replacement of translations by certain linear
combinations of translations and proper conformal transformations, the net
result of this change is ultimately the breakdown of ordinary translational
invariance. From the experimental point of view, therefore, a de Sitter special
relativity might be probed by looking for possible violations of translational
invariance. If we assume the existence of a connection between the energy scale
of an experiment and the local value of the cosmological constant, there would
be changes in the kinematics of massive particles which could hopefully be
detected in high-energy experiments. Furthermore, due to the presence of a
horizon, the usual causal structure of spacetime would be significantly
modified at the Planck scale.


title:
Bergmann-Thomson energy-momentum complex for solutions more general than
  the Kerr-Schild class

abstract:
  In a very well-known paper, Virbhadra's research group proved that the
Weinberg, Papapetrou, Landau and Lifshitz, and Einstein energy-momentum
complexes ``coincide'' for all metrics of Kerr-Schild class. A few years later,
Virbhadra clarified that this ``coincidence'' in fact holds for metrics more
general than the Kerr-Schild class. In the present paper, this study is
extended for the Bergmann-Thomson complex and it is proved that this complex
also ``coincides'' with those complexes for a more general than the Kerr-Schild
class metric.


title: Quantum noncommutative multidimensional cosmology

abstract:
  We present exact quantum solutions for a noncommutative, multidimensional
cosmological model and show that stabilization of extra dimensions sets in with
the introduction of noncommutativity between the scale factors. An
interpretation is offered to accommodate the notion of time, rendering
comparison with the classical solutions possible.


title:
Search for Continuous Gravitational Waves: simple criterion for optimal
  detector networks

abstract:
  We derive a simple algebraic criterion to select the optimal detector network
for a coherent wide parameter-space (all-sky) search for continuous
gravitational waves. Optimality in this context is defined as providing the
highest (average) sensitivity per computing cost. This criterion is a direct
consequence of the properties of the multi-detector F-statistic metric, which
has been derived recently. Interestingly, the choice of the optimal network
only depends on the noise-levels and duty-cycles of the respective detectors,
and not on the available computing power.


title:
Formation of Five-Dimensional String Solutions from the Gravitational
  Collapse

abstract:
  We study the formation of five-dimensional string solutions including the
Gregory-Laflamme (GL) black string, the Kaluza-Klein (KK) bubble, and the
geometry with a naked singularity from the gravitational collapse. The interior
solutions of five-dimensional Einstein equations describe collapsing
non-isotropic matter clouds. It is shown that the matter cloud always forms the
GL black string solution while the KK bubble solution cannot be formed. The
numerical study seems to suggest that the collapsing matter forms the
geometries with timelike naked curvature singularities, which should be taken
cautiously as the general relativity is not reliable in the strong curvature
regime.


title:
Non-Singular Spherically Symmetric Solution in Einstein-Scalar-Tensor
  Gravity

abstract:
  A static spherically symmetric metric in Einstein-scalar-tensor gravity
theory with a scalar field potential $V[\phi]$ is non-singular for all real
values of the coordinates. It does not have a black hole event horizon and
there is no essential singularity at the origin of coordinates. The weak energy
condition $\rho_\phi > 0$ fails to be satisfied for $r\lesssim 1.3r_S$ (where
$r_S$ is the Schwarzschild radius) but the strong energy condition
$\rho_\phi+3p_\phi > 0$ is satisfied. The classical Einstein-scalar-tensor
solution is regular everywhere in spacetime without a black hole event horizon.
However, the violation of the weak energy condition may signal the need for
quantum physics anti-gravity as $r\to 0$. The non-singular static spherically
symmetric solution is stable against the addition of ordinary matter.


title: Primordial Perturbations Spectra in a Holographic Phase

abstract:
  In this paper, we suppose that the universe begins in a holographic thermal
equilibrium phase with the diverged correlation length, and the phase
transition to the radiation phase of standard cosmology goes with the abrupt
reducing of correlation length. In this case, the primordial perturbations may
be induced by thermal fluctuations in this holographic phase. We calculate the
spectra of this holographic primordial perturbations, and find that the scalar
spectrum has a slightly red tilt and the tensor perturbation amplitude has a
moderate ratio, which may be tested in coming observations. The results plotted
in r-n_s plane is similar to that of large field inflation models. However, for
fixed efolding number, they are generally in different positions.


title:
1/f fluctuations in spinning-particle motions around Schwarzschild black
  hole

abstract:
  We study the properties of chaos in the motions of a spinning test particle
in Schwarzschild spacetime. We characterize the chaos using the power spectrum
of the time series of $z$ components of the particle's position. It is found
that the pattern of the power spectrum shows not only white noise but also
$1/f$-type fluctuation, depending on the value of the total angular momentum
$J$ and the spin $S$ of the test particle. Therefore we succeed in classifying
the chaotic motions, which have been classified as simply chaotic ones in
former works, into the two distinct types. One is $1/f$, and the other is white
noise. Based on this classification, we plot, in the two-dimensional parameter
space $(J,S)$, the phase diagram for the properties of the chaos. This phase
diagram enables us in principle to guess the properties of the system $(J,S)$
by observing the dynamics of the test particle, even if the motion is chaotic.
Furthermore, we detect that the origin of the $1/f$ fluctuation is that the
particle motion stagnates around regular orbits (tori), while traveling back
and forth between them, which is called ``stagnant motion'' or ``sticky
motion'' in Hamiltonian dynamical systems. The point is that the difference of
the property of the chaos or the power spectra is due to the topological
structure of the phase space, which in turn is governed by the physical
parameter set $(J,S)$ of the system. From this point of view, the chaos we
found in this system is not always merely random.


title: Holonomy Transformation in the FRW Metric

abstract:
  In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.


title:
The Momentum Four-Vector in the $e\psi$N Formalism and the Angular
  Momentum Imparted to Test Particles by Gravitational Waves

abstract:
  Since gravitational waves are solutions of Einstein's field equations with a
zero stress-energy tensor, the reality of these waves was questioned. To
demonstrate it, the momentum imparted to test particles by such waves was
evaluated. A closed form expression for this quantity was provided by Qadir and
Sharif, using an extension of the pseudo-Newtonian formalism. That formalism
carried with it the zero component of the momentum vector, which could not be
interpreted as the energy imparted to the test particle. Sharif proposed that
it may represent the angular momentum imparted to test particles by
gravitational waves. In this paper it is shown that this interpretation is not
valid. An alternative explanation has been provided.


title:
The cosmological constant as an eigenvalue of f(R)-gravity Hamiltonian
  constraint

abstract:
  In the framework of ADM formalism, it is possible to find out eigenvalues of
the WDW equation with the meaning of vacuum states, i.e. cosmological
constants, for f(R) theories of gravity, where f(R) is a generic analytic
function of the Ricci curvature scalar R. The explicit calculation is performed
for a Schwarzschild metric where one-loop energy is derived by the zeta
function regularization method and a renormalized running Lambda constant is
obtained.


title: Choreographic solution to the general relativistic three-body problem

abstract:
  We revisit the three-body problem in the framework of general relativity. The
Newtonian N-body problem admits choreographic solutions, where a solution is
called choreographic if every massive particles move periodically in a single
closed orbit. One is a stable figure-eight orbit for a three-body system, which
was found first by Moore (1993) and re-discovered with its existence proof by
Chenciner and Montgomery (2000). In general relativity, however, the periastron
shift prohibits a binary system from orbiting in a single closed curve.
Therefore, it is unclear whether general relativistic effects admit a
choreographic solution such as the figure eight. We carefully examine general
relativistic corrections to initial conditions so that an orbit for a
three-body system can be closed and a figure eight. This solution is still
choreographic. This illustration suggests that the general relativistic N-body
problem also may admit a certain class of choreographic solutions.


title: Hamiltonian reduction of spin-two theory and of solvable cosmologies

abstract:
  The Hamiltonian reduction of the massless spin-two field theory is carried
out following the Faddeev-Jackiw approach. The reduced Hamiltonian contains
only the traceless-transverse fields, but not all of the non-propagating
components can be determined by the constraints of the theory. The reason for
this is found in the fact that the Hamiltonian is not gauge invariant.
Consequences and implications for General Relativity are discussed and
illustrated on the example of Robertson-Walker cosmologies with a scalar field.
Also, it it shown that for those explicitely solvable models, the reduced form
of the dynamics uniquely determines the operator ordering that has to be
adopted in the Wheeler-DeWitt equation in order to maintain consistency.


title: Minimum mass-radius ratio for charged gravitational objects

abstract:
  We rigorously prove that for compact charged general relativistic objects
there is a lower bound for the mass-radius ratio. This result follows from the
same Buchdahl type inequality for charged objects, which has been extensively
used for the proof of the existence of an upper bound for the mass-radius
ratio. The effect of the vacuum energy (a cosmological constant) on the minimum
mass is also taken into account. Several bounds on the total charge, mass and
the vacuum energy for compact charged objects are obtained from the study of
the Ricci scalar invariants. The total energy (including the gravitational one)
and the stability of the objects with minimum mass-radius ratio is also
considered, leading to a representation of the mass and radius of the charged
objects with minimum mass-radius ratio in terms of the charge and vacuum energy
only.


title: A common misconception about LIGO detectors of gravitational waves

abstract:
  A common misconception about laser interferometric detectors of gravitational
waves purports that, because the wavelength of laser light and the length of an
interferometer's arm are both stretched by a gravitational wave, no effect
should be visible, invoking an analogy with cosmological redshift in an
expanding universe. The issue is clarified with the help of a direct
calculation.


title:
The importance of the ''magnetic'' components of gravitational waves in
  the response functions of interferometers

abstract:
  With an enlighting analysis, Baskaran and Grishchuk have recently shown the
presence and importance of the so-called ``magnetic'' components of
gravitational waves (GWs), which have to be taken into account in the context
of the total response functions of interferometers for GWs propagating from
arbitrary directions. In this paper more detailed angular and frequency
dependences of the response functions for the magnetic components are given in
the approximation of wavelength much larger than the linear dimensions of the
interferometer, with a specific application to the parameters of the LIGO and
Virgo interferometers. Our results agree with the work of Baskaran and
Grishchuk in which it has been shown that the identification of ``electric''
and ``magnetic'' contributions is unambiguous in the long-wavelength
approximation. At the end of this paper the angular and frequency dependences
of the total response functions of the LIGO and Virgo interferometers are
given. In the high-frequency regime the division on ``electric'' and
``magnetic'' components becomes ambiguous, thus the full theory of
gravitational waves has to be used. Our results are consistent with the ones of
Baskaran and Grishchuk in this case too.


title:
Matters of Gravity, The Newsletter of the Topical Group in Gravitation
  of the American Physical Society, Volume 29, Winter 2007

abstract:
  GGR News:
  - The View from the NSF, by Beverly Berger
  - GGR Program at the APS meeting in Jacksonville we hear that..., by David
Garfinkle
  - 100 years ago, by David Garfinkle
  Research Briefs:
  - The Double Pulsar, by Michael Kramer
  - Theoretical Approaches to Cosmic Acceleration, by Mark Trodden
  Conference Reports:
  - Numerical Relativity-Data Analysis, by Patrick Brady
  - Note on Numerical Relativity-Data Analysis, by Peter Saulson
  - Unruh and Wald Fest, by Carsten Gundlach and David Garfinkle
  - Will Fest, by Eric Poisson
  - Brane-World Gravity, by Andrew Mennim
  - Gravity and Theoretical Physics, by Marco Cavaglia


title: Cosmic clocks, cosmic variance and cosmic averages

abstract:
  Cosmic acceleration is explained quantitatively, purely in general
relativity, as an apparent effect due to quasilocal gravitational energy
differences that arise in the decoupling of bound systems from the global
expansion of the universe. "Dark energy" is recognised as a misidentification
of those aspects of gravitational energy which by virtue of the equivalence
principle cannot be localised, namely gradients in the energy associated with
the expansion of space and spatial curvature variations in an inhomogeneous
universe, as we observe. Gravitational energy differences between observers in
bound systems, such as galaxies, and volume-averaged comoving locations within
voids in freely expanding space can be so large that the time dilation between
the two significantly affects the parameters of any effective homogeneous
isotropic model one fits to the universe. A new approach to cosmological
averaging is presented, which implicitly solves the Sandage-de Vaucouleurs
paradox. When combined with a nonlinear scheme for cosmological evolution with
back-reaction via the Buchert equations, a new observationally viable
quantitative model of the universe is obtained. The expansion age is increased,
allowing more time for structure formation. The baryon density fraction
obtained from primordial nucleosynthesis bounds can be significantly larger,
yet consistent with primordial lithium abundance measurements. The angular
scale of the first Doppler peak in the CMB anisotropy spectrum fits the new
model despite an average negative spatial curvature at late epochs, resolving
the anomaly associated with ellipticity in the CMB anisotropies. A number of
other testable consequences are discussed, with the potential to profoundly
change the whole of theoretical and observational cosmology. [Abridged]


title: Classical dynamics on triangleland

abstract:
  In Euclidean relational particle mechanics (ERPM) only relative times,
relative angles and relative separations are meaningful, while in similarity
relational particle mechanics (SRPM) only relative times, relative angles and
ratios of relative separations are. These theories are clearly of interest in
the absolute or relative motion debate. In this paper, ERPM and SRPM are
provided in fully reduced form for 3 particles in 2D, i.e. the classical
dynamics on triangleland in 2D with and without scale. Exact solutions to each
of these are then found, and simple Newton--Coulomb-like and harmonic
oscillator-like SRPM models are studied numerically. The mathematics one
arrives at thus overlaps in many ways with that which arises in the absolutist
approach. The ERPM gives standard mathematics, while the SRPM has standard
small-relative-scale behaviour and an unexpected but in itself standard
universal large-relative-scale behaviour. One way in which SRPM is unusual is
that it is a model in which a symmetry principle underlies an unexpected
departure from standard physical behaviour at sufficiently large relative
scales (interpolation between the abovementioned two behaviours). ERPM and SRPM
are also theoretically interesting at the quantum level, both on their own
merit and as toy models for the development of various approaches to the
problems of time and of observables in quantum general relativity.


title: Black Hole Mergers and Unstable Circular Orbits

abstract:
  We describe recent numerical simulations of the merger of a class of equal
mass, non-spinning, eccentric binary black hole systems in general relativity.
We show that with appropriate fine-tuning of the initial conditions to a region
of parameter space we denote the threshold of immediate merger, the binary
enters a phase of close interaction in a near-circular orbit, stays there for
an amount of time proportional to logarithmic distance from the threshold in
parameter space, then either separates or merges to form a single Kerr black
hole. To gain a better understanding of this phenomena we study an analogous
problem in the evolution of equatorial geodesics about a central Kerr black
hole. A similar threshold of capture exists for appropriate classes of initial
conditions, and tuning to threshold the geodesics approach one of the unstable
circular geodesics of the Kerr spacetime. Remarkably, with a natural mapping of
the parameters of the geodesic to that of the equal mass system, the scaling
exponent describing the whirl phase of each system turns out to be quite
similar. Armed with this lone piece of evidence that an approximate
correspondence might exist between near-threshold evolution of geodesics and
generic binary mergers, we illustrate how this information can be used to
estimate the cross section and energy emitted in the ultra relativistic black
hole scattering problem. This could eventually be of use in providing estimates
for the related problem of parton collisions at the Large Hadron Collider in
extra dimension scenarios where black holes are produced.


title: An Awesome Hypothesis for Dark Energy : The Abnormally Weighting Energy

abstract:
  We introduce the Abnormally Weighting Energy (AWE) hypothesis in which dark
energy (DE) is presented as a consequence of the violation of the weak
equivalence principle (WEP) at cosmological scales by some dark sector. Indeed,
this implies a violation of the strong equivalence principle (SEP) for ordinary
matter and consequent cosmic acceleration in the observable frame as well as
variation of the gravitational constant. The consequent DE mechanism build upon
the AWE hypothesis (i) does not require a violation of the strong energy
condition $p<-\rho c^2/3$, (ii) assumes rather non-negligible direct couplings
to the gravitational scalar field (iii) offers a natural convergence mechanism
toward general relativity (iv) accounts fairly for supernovae data from various
couplings and equations of state of the dark sector as well as density
parameters very close to the ones of the concordance model $\Lambda CDM$.
Finally (v), this AWE mechanism typically ends up with an Einstein-de Sitter
expansion regime once the attractor is reached.


title:
Higher dimensional rotating black holes in Einstein-Maxwell theory with
  negative cosmological constant

abstract:
  We present arguments for the existence of charged, rotating black holes with
equal-magnitude angular momenta in an odd number of dimensions $D\geq 5$. These
solutions posses a regular horizon of spherical topology and approach
asymptotically the Anti-de Sitter spacetime background. We analyze their global
charges, their gyromagnetic ratio and their horizon properties.


title: Renormalization-group running cosmologies and the generalized second law

abstract:
  We explore some thermodynamical consequences of accelerated universes driven
by a running cosmological constant (CC) from the renormalization group (RG).
Application of the generalized second law (GSL) of gravitational thermodynamics
to a framework where the running of the CC goes at the expense of energy
transfer between vacuum and matter, strongly restricts the mass spectrum of a
(hypothetical) theory controlling the CC running. We find that quantum effects
driving the running of the CC should be dominated by a trans-planckian mass
field, in marked contrast with the GUT-scale upper mass bound obtained by
analyzing density perturbations for the running CC. The model shows compliance
with the holographic principle.


title: Testing the Metric-Field Equations of Gravitation

abstract:
  Physical consequences from gravitation equations based on Poincar\'{e} ideas
of relativity of space and time in respect of measuring instruments are
considered. The most interesting of them are the possibility of the existence
of stable supermassive configurations $(10^{2} \div 10^{12} M_{\odot})$ which
can exist in galactic centres, and an explanation of the acceleration of the
Universe expansion as a manifestation of the gravitational force properties in
the theory under consideration.


title: Dark Energy Fluid with Time-Dependent, Inhomogeneous Equation of State

abstract:
  The four-dimensional Friedman flat universe, filled with an ideal fluid with
a linear (oscillating) inhomogeneous equation of state (EoS) depending on time,
is studied. The equations of motion are solved. It is shown that in some cases
there appears a quasi-periodic universe, which repeats the cycles of
phantom-type space acceleration. The appearance of future singularities
resulting from various choices for the input parameters is discussed.


title: Detecting Seasonal Changes in the Fundamental Constants

abstract:
  We show that if one or more of the `constants' of Nature can vary then their
values, as measured in the laboratory, should oscillate over the year in a very
particular way. These seasonal changes in the constants could well be detected,
in the near future, with ground-based atomic clocks.


title: Gravitational radiation from collapsing magnetized dust

abstract:
  In this article we study the influence of magnetic fields on the axial
gravitational waves emitted during the collapse of a homogeneous dust sphere.
We found that while the energy emitted depends weakly on the initial matter
perturbations it has strong dependence on the strength and the distribution of
the magnetic field perturbations. The gravitational wave output of such a
collapse can be up to an order of magnitude larger or smaller calling for
detailed numerical 3D studies of collapsing magnetized configurations.


title: A solution for galactic disks with Yukawian gravitational potential

abstract:
  We present a new solution for the rotation curves of galactic disks with
gravitational potential of the Yukawa type. We follow the technique employed by
Toomre in 1963 in the study of galactic disks in the Newtonian theory. This new
solution allows an easy comparison between the Newtonian solution and the
Yukawian one. Therefore, constraints on the parameters of theories of
gravitation can be imposed, which in the weak field limit reduce to Yukawian
potentials. We then apply our formulae to the study of rotation curves for a
zero-thickness exponential disk and compare it with the Newtonian case studied
by Freeman in 1970. As an application of the mathematical tool developed here,
we show that in any theory of gravity with a massive graviton (this means a
gravitational potential of the Yukawa type), a strong limit can be imposed on
the mass (m_g) of this particle. For example, in order to obtain a galactic
disk with a scale length of b ~ 10 kpc, we should have a massive graviton of
m_g << 10^{-59} g. This result is much more restrictive than those inferred
from solar system observations.


title:
Gauge invariant perturbations around symmetry reduced sectors of general
  relativity: applications to cosmology

abstract:
  We develop a gauge invariant canonical perturbation scheme for perturbations
around symmetry reduced sectors in generally covariant theories, such as
general relativity. The central objects of investigation are gauge invariant
observables which encode the dynamics of the system. We apply this scheme to
perturbations around a homogeneous and isotropic sector (cosmology) of general
relativity. The background variables of this homogeneous and isotropic sector
are treated fully dynamically which allows us to approximate the observables to
arbitrary high order in a self--consistent and fully gauge invariant manner.
Methods to compute these observables are given. The question of backreaction
effects of inhomogeneities onto a homogeneous and isotropic background can be
addressed in this framework. We illustrate the latter by considering
homogeneous but anisotropic Bianchi--I cosmologies as perturbations around a
homogeneous and isotropic sector.


title: Black Hole Entropy and the Problem of Universality

abstract:
  A key test of any quantum theory of gravity is its ability to reproduce the
known thermodynamic properties of black holes. A statistical mechanical
description of the Bekenstein-Hawking entropy once seemed remote, but today we
suffer an embarrassment of riches: many different approaches to quantum gravity
yield the same entropy, despite counting very different states. This
``universality'' suggests that some underlying feature of the classical theory
may control the quantum density of states. I discuss the possibility that this
feature is an approximate two-dimensional conformal symmetry near the horizon.


title: Singularity: Raychaudhuri Equation once again

abstract:
  I first recount Raychaudhuri's deep involvement with the singularity problem
in general relativity. I then argue that precisely the same situation has
arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered
his celebrated equation. We thus need a new analogue of the Raychaudhuri
equation in quantum gravity.


title: Data Analysis of Gravitational Waves Using A Network of Detectors

abstract:
  Several large-scale gravitational wave (GW) interferometers have achieved
long term operation at design sensitivity. Questions arise on how to best
combine all available data from detectors of different sensitivities for
detection, consistency check or veto, localization and waveform extraction. We
show that these problems can be formulated using the singular value
decomposition (SVD) method. We present techniques based on the SVD method for
(1) detection statistic, (2) stable solutions to waveforms, (3) null-stream
construction for an arbitrary number of detectors, and (4) source localization
for GWs of unknown waveforms.