title: A note on the Deser-Tekin charges

abstract:
  Perturbed equations for an arbitrary metric theory of gravity in $D$
dimensions are constructed in the vacuum of this theory. The nonlinear part
together with matter fields are a source for the linear part and are treated as
a total energy-momentum tensor. A generalized family of conserved currents
expressed through divergences of anti-symmetrical tensor densities
(superpotentials) linear in perturbations is constructed. The new family
generalizes the Deser and Tekin currents and superpotentials in quadratic
curvature gravity theories generating Killing charges in dS and AdS vacua. As
an example, the mass of the $D$-dimensional Schwarzschild black hole in an
effective AdS spacetime (a solution in the Einstein-Gauss-Bonnet theory) is
examined.


title:
Geometric spin foams, Yang-Mills theory and background-independent
  models

abstract:
  We review the dual transformation from pure lattice gauge theory to spin foam
models with an emphasis on a geometric viewpoint. This allows us to give a
simple dual formulation of SU(N) Yang-Mills theory, where spin foam surfaces
are weighted with the exponentiated area. In the case of gravity, we introduce
a symmetry condition which demands that the amplitude of an individual spin
foam depends only on its geometric properties and not on the lattice on which
it is defined. For models that have this property, we define a new sum over
abstract spin foams that is independent of any choice of lattice or
triangulation. We show that a version of the Barrett-Crane model satisfies our
symmetry requirement.


title:
A first comparison of search methods for gravitational wave bursts using
  LIGO and Virgo simulated data

abstract:
  We present a comparative study of 6 search methods for gravitational wave
bursts using simulated LIGO and Virgo noise data. The data's spectra were
chosen to follow the design sensitivity of the two 4km LIGO interferometers and
the 3km Virgo interferometer. The searches were applied on replicas of the data
sets to which 8 different signals were injected. Three figures of merit were
employed in this analysis: (a) Receiver Operator Characteristic curves, (b)
necessary signal to noise ratios for the searches to achieve 50 percent and 90
percent efficiencies, and (c) variance and bias for the estimation of the
arrival time of a gravitational wave burst.


title: Gravity and the Quantum Vacuum Inertia Hypothesis

abstract:
  In previous work it has been shown that the electromagnetic quantum vacuum,
or electromagnetic zero-point field, makes a contribution to the inertial
reaction force on an accelerated object. We show that the result for inertial
mass can be extended to passive gravitational mass. As a consequence the weak
equivalence principle, which equates inertial to passive gravitational mass,
appears to be explainable. This in turn leads to a straightforward derivation
of the classical Newtonian gravitational force. We call the inertia and
gravitation connection with the vacuum fields the quantum vacuum inertia
hypothesis. To date only the electromagnetic field has been considered. It
remains to extend the hypothesis to the effects of the vacuum fields of the
other interactions. We propose an idealized experiment involving a cavity
resonator which, in principle, would test the hypothesis for the simple case in
which only electromagnetic interactions are involved. This test also suggests a
basis for the free parameter $\eta(\nu)$ which we have previously defined to
parametrize the interaction between charge and the electromagnetic zero-point
field contributing to the inertial mass of a particle or object.


title: The LTP Experiment on the LISA Pathfinder Mission

abstract:
  We report on the development of the LISA Technology Package (LTP) experiment
that will fly on board the LISA Pathfinder mission of the European Space Agency
in 2008. We first summarize the science rationale of the experiment aimed at
showing the operational feasibility of the so called Transverse-Traceless
coordinate frame within the accuracy needed for LISA. We then show briefly the
basic features of the instrument and we finally discuss its projected
sensitivity and the extrapolation of its results to LISA.


title: Conformal regularization of Einstein's field equations

abstract:
  To study asymptotic structures, we regularize Einstein's field equations by
means of conformal transformations. The conformal factor is chosen so that it
carries a dimensional scale that captures crucial asymptotic features. By
choosing a conformal orthonormal frame we obtain a coupled system of
differential equations for a set of dimensionless variables, associated with
the conformal dimensionless metric, where the variables describe ratios with
respect to the chosen asymptotic scale structure. As examples, we describe some
explicit choices of conformal factors and coordinates appropriate for the
situation of a timelike congruence approaching a singularity. One choice is
shown to just slightly modify the so-called Hubble-normalized approach, and one
leads to dimensionless first order symmetric hyperbolic equations. We also
discuss differences and similarities with other conformal approaches in the
literature, as regards, e.g., isotropic singularities.


title: Universal criterion for black hole stability

abstract:
  It is shown that a non-rotating macroscopic black hole with very large
horizon area can remain in stable thermal equilibrium with Hawking radiation
provided {\it its mass, as a function of horizon area, exceeds its
microcanonical entropy, i.e., its entropy when isolated, without thermal
radiation or accretion, and having a constant horizon area} (in appropriate
units). The analysis does not use properties of specific classical spacetimes,
but depends only on the plausible assumption that the mass is a function of the
horizon area for large areas.


title: Report on the first binary black hole inspiral search in LIGO data

abstract:
  The LIGO Scientific Collaboration is currently engaged in the first search
for binary black hole inspiral signals in real data. We are using the data from
the second LIGO science run and we focus on inspiral signals coming from binary
systems with component masses between 3 and 20 solar masses. We describe the
analysis methods used and report on preliminary estimates for the sensitivities
of the LIGO instruments during the second science run.


title:
A general solution for classical sequential growth dynamics of Causal
  Sets

abstract:
  A classical precursor to a full quantum dynamics for causal sets has been
forumlated in terms of a stochastic sequential growth process in which the
elements of the causal set arise in a sort of accretion process. The transition
probabilities of the Markov growth process satisfy certain physical
requirements of causality and general covariance, and the generic solution with
all transition probabilities non-zero has been found. Here we remove the
assumption of non-zero probabilities, define a reasonable extension of the
physical requirements to cover the case of vanishing probabilities, and find
the completely general solution to these physical conditions. The resulting
family of growth processes has an interesting structure reminiscent of an
``infinite tower of turtles'' cosmology.


title: Veto Studies for LIGO Inspiral Triggers

abstract:
  LIGO recently conducted its third scientific data run, S3. Here we summarize
the veto and data quality studies conducted by the LIGO Scientific
Collaboration in connection with the search for binary inspiral signals in the
S3 data. LIGO's interferometer channels and physical environmental monitors
were monitored, and events in these channels coincident with inspiral triggers
were examined.


title: Perturbative approach to the structure of rapidly rotating neutron stars

abstract:
  We construct models of rotating stars using the perturbative approach
introduced by J. Hartle in 1967, and a set of equations of state proposed to
model hadronic interactions in the inner core of neutron stars. We integrate
the equations of stellar structure to third order in the angular velocity and
show, comparing our results to those obtained with fully non linear codes, to
what extent third order corrections are needed to accurately reproduce the
moment of inertia of a star which rotates at rates comparable to that of the
fastest isolated pulsars.


title: Observables in Extended Percolation Models of Causal Set Cosmology

abstract:
  Classical sequential growth models for causal sets provide an important step
towards the formulation of a quantum causal set dynamics. The covariant
observables in a class of these models known as generalised percolation have
been completely characterised in terms of physically well-defined ``stem sets''
and yield an insight into the nature of observables in quantum causal set
cosmology. We discuss a recent extension of generalised percolation and show
that the characterisation of covariant observables in terms of stem sets is
also complete in this extension.


title: Dust-shell Universe in the modified gravity scenario

abstract:
  The dynamics of the dust-shell model of universe is exactly solved for the
modified Schwarzschild solution. This solution is used to derive the cosmology
corresponding to the modified gravity.


title: Characterizing the Galactic Gravitational Wave Background with LISA

abstract:
  We present a Monte Carlo simulation for the response of the Laser
Interferometer Space Antenna (LISA) to the galactic gravitational wave
background. The simulated data streams are used to estimate the number and type
of binary systems that will be individually resolved in a 1-year power
spectrum. We find that the background is highly non-Gaussian due to the
presence of individual bright sources, but once these sources are identified
and removed, the remaining signal is Gaussian. We also present a new estimate
of the confusion noise caused by unresolved sources that improves on earlier
estimates.


title: Note on Quantum Newtonian Cosmology

abstract:
  It is well known that, for pressureless matter, Newtonian and relativistic
cosmologies are equivalent. We show that this equivalence breaks down in the
quantum level. In addition, we find some cases for which quantum Newtonian
cosmology can be related to quantum cosmology in (2+1) dimensions. Two exact
solutions for the wave function of the Newtonian universe are also obtained.


title: On a thermodynamic basis for inflationary cosmology

abstract:
  Modifying the standard hot big bang model of cosmology with an inflationary
event has been very successful in resolving most of the outstanding
cosmological problems. The various inflationary mechanisms proposed depend on
the production of expansion from exotic phenomena, false vacuum, scalar fields
or other exotic particle behaviour within an environment of astronomically high
energy, making such proposals relatively inaccessible for verification by
experimental tests. Though descriptive of how space has been expanding, the
models do not give a complete and consistent mathematical or physical
explanation that compels space appearance and propels its expansion. Here we
describe another mechanism for achieving exponential inflation based
substantially on already tested physics and equations, particularly the
thermodynamic equation, dS = dE/T and relate this to the creation event.


title: Angular Momentum of the BTZ Black Hole in the Teleparallel Geometry

abstract:
  We carry out the Hamiltonian formulation of the three- dimensional
gravitational teleparallelism without imposing the time gauge condition, by
rigorously performing the Legendre transform. Definition of the gravitational
angular momentum arises by suitably interpreting the integral form of the
constraint equation Gama^ik=0 as an angular momentum equation. The
gravitational angular momentum is evaluated for the gravitational field of a
rotating BTZ black hole.


title:
Dynamical instability of fluid spheres in the presence of a cosmological
  constant

abstract:
  The equations describing the adiabatic, small radial oscillations of general
relativistic stars are generalized to include the effects of a cosmological
constant. The generalized eigenvalue equation for the normal modes is used to
study the changes in the stability of the homogeneous sphere induced by the
presence of the cosmological constant. The variation of the critical adiabatic
index as a function of the central pressure is studied numerically for
different trial functions. The presence of a large cosmological constant
significantly increases the value of the critical adiabatic index. The
dynamical stability condition of the homogeneous star in the Schwarzschild-de
Sitter geometry is obtained and several bounds on the maximum allowable value
for a cosmological constant are derived from stability considerations.


title: The Transplanckian Question and the Casimir Effect

abstract:
  It is known that, through inflation, Planck scale phenomena should have left
an imprint in the cosmic microwave background. The magnitude of this imprint is
expected to be suppressed by a factor $\sigma^n$ where $\sigma\approx 10^{-5}$
is the ratio of the Planck length to the Hubble length during inflation. While
there is no consensus about the value of $n$, it is generally thought that $n$
will determine whether the imprint is observable. Here, we suggest that the
magnitude of the imprint may not be suppressed by any power of $\sigma$ and
that, instead, $\sigma$ may merely quantify the amount of fine tuning required
to achieve an imprint of order one. To this end, we show that the UV/IR scale
separation, $\sigma$, in the analogous case of the Casimir effect plays exactly
this role.


title: The gravitational energy-momentum tensor and the gravitational pressure

abstract:
  In the framework of the teleparallel equivalent of general relativity it is
possible to establish the energy-momentum tensor of the gravitational field.
This tensor has the following essential features: (1) it is identified directly
in Einstein's field equations; (2) it is conserved and traceless; (3) it yields
expressions for the energy and momentum of the gravitational field; (4)it is
free of second (and highest) derivatives of the field variables; (5) the
gravitational and matter energy-momentum tensors take place in the field
equations on the same footing; (6) it is unique. However, it is not symmetric.
We show that the spatial components of this tensor yield a consistent
definition of the gravitational pressure.


title: Gravitational helicity interaction

abstract:
  For gravitational deflections of massless particles of given helicity from a
classical rotating body, we describe the general relativity corrections to the
geometric optics approximation. We compute the corresponding scattering cross
sections for neutrinos, photons and gravitons to lowest order in the
gravitational coupling constant. We find that the helicity coupling to
spacetime geometry modifies the ray deflection formula of the geometric optics,
so that rays of different helicity are deflected by different amounts. We also
discuss the validity range of the Born approximation.


title:
Response of the common mode of interferometric detectors to a stochastic
  background of massive scalar radiation

abstract:
  We compute the angular pattern and the overlap reduction functions for the
geodesic and non-geodesic response of the common mode of two interferometers
interacting with a stochastic, massive scalar background. We also discuss the
possible overlap between common and differential modes. We find that the
cross-correlated response of two common modes to a non-relativistic background
may be higher than the response of two differential modes to the same
background.


title: De Sitter and double irregular domain walls

abstract:
  A new method to obtain thick domain wall solutions to the coupled Einstein
scalar field system is presented. The procedure allows the construction of
irregular walls from well known ones, such that the spacetime associated to
them are physically different. As consequence of the approach, we obtain two
irregular geometries corresponding to thick domain walls with $dS$ expansion
and topological double kink embedded in $AdS$ spacetime. In particular, the
double brane can be derived from a fake superpotential.


title: A Remark on Boundary Effects in Static Vacuum Initial Data sets

abstract:
  Let (M, g) be an asymptotically flat static vacuum initial data set with
non-empty compact boundary. We prove that (M, g) is isometric to a spacelike
slice of a Schwarzschild spacetime under the mere assumption that the boundary
of (M, g) has zero mean curvature, hence generalizing a classic result of
Bunting and Masood-ul-Alam. In the case that the boundary has constant positive
mean curvature and satisfies a stability condition, we derive an upper bound of
the ADM mass of (M, g) in terms of the area and mean curvature of the boundary.
Our discussion is motivated by Bartnik's quasi-local mass definition.


title:
Constraining nuclear equations of state using gravitational waves from
  hypermassive neutron stars

abstract:
  Latest general relativistic simulations for merger of binary neutron stars
with realistic equations of state (EOSs) show that a hypermassive neutron star
of an ellipsoidal figure is formed after the merger if the total mass is
smaller than a threshold value which depends on the EOSs. The effective
amplitude of quasiperiodic gravitational waves from such hypermassive neutron
stars is $\sim 6$--$7 \times 10^{-21}$ at a distance of 50 Mpc, which may be
large enough for detection by advanced laser interferometric gravitational wave
detectors although the frequency is high $\sim 3$ kHz. We point out that the
detection of such signal may lead to constraining the EOSs for neutron stars.


title: Comments on Space-Time

abstract:
  What happens to the entropy increase principle as the Universe evolve to form
the big-crunch singularity? What happens to the uncertainity relations along
the process of gravitational collapses? What is the quantum mechanical
description of a Radon atom in a rigid box when the distance of consecutive
nodes and antinodes of $\psi$ is equal to or less than the diameter of the
atom? What is the position-space wave function of two finite volume massive
bosons if we take contact interaction into account? How a photon produce
electron-positron pair with finite volume concentrate rest masses? What are the
charges of the electron-positron pairs forming loops in the vacuum? How two
particles with three-momentums $k_1, k_2$ $(k_1 \neq k_2)$ produced to form a
loop at a space-time point always arrive at another spacial point
simultaneously? What is the microscopic explanation in terms of particle
exchanges of the force in the Casimir effect? What is the mechanism of the
collapse of the momentum-space wave function of a particle knocking out an
elctron from an atom? What is meant by $|\Psi> = {c_1 (t)}|\Psi_{U^{238}}> +
{c_2 (t)}|\Psi_{Th^{234}}> ~?$ Quantum mechanically the region between the
rigid walls (which is equiprobable in classical mechanics) is non-homogeneous
for a particle in a rigid box. A photon can not reproduce Maxwell's equations
apart from moving with velocity $c$. How can a process involving only a few
photons be described starting from the Maxwell's equations? The large scale
structure of the Universe is homogeneous.
  What is the screen in our brains to view objects, as they are, of sizes
larger than our brains?


title: Time-reparametrization invariance in eternal inflation

abstract:
  I address some recently raised issues regarding the time-parametrization
dependence in stochastic descriptions of eternal inflation. To clarify the role
of the choice of the time gauge, I show examples of gauge-dependent as well as
gauge-independent statements about physical observables in eternally inflating
spacetimes. In particular, the relative abundance of thermalized and inflating
regions is highly gauge-dependent. The unbounded growth of the 3-volume of the
inflating regions is found in certain time gauges, such as the proper time or
the scale factor gauge. Yet in the same spacetimes there exist time foliations
with a finite and monotonically decreasing 3-volume, which I demonstrate by an
explicit construction. I also show that there exists no "correct" choice of the
time gauge that would yield an unbiased stationary probability distribution for
observables in thermalized regions.


title: Special Relativity: A Centenary Perspective

abstract:
  This article is a partly pedagogical, partly historical and partly technical
review of special relativity and its experimental foundations, in honor of the
centenary of Einstein's annus mirabilis.


title: Was Einstein Right? Testing Relativity at the Centenary

abstract:
  We review the experimental evidence for Einstein's special and general
relativity. A variety of high precision null experiments verify the weak
equivalence principle and local Lorentz invariance, while gravitational
redshift and other clock experiments support local position invariance.
Together these results confirm the Einstein Equivalence Principle which
underlies the concept that gravitation is synonymous with spacetime geometry,
and must be described by a metric theory. Solar system experiments that test
the weak-field, post-Newtonian limit of metric theories strongly favor general
relativity. The Binary Pulsar provides tests of gravitational-wave damping and
of strong-field general relativity. Recently discovered binary pulsar systems
may provide additional tests. Future and ongoing experiments, such as the
Gravity Probe B Gyroscope Experiment, satellite tests of the Equivalence
principle, and tests of gravity at short distance to look for extra spatial
dimensions could constrain extensions of general relativity. Laser
interferometric gravitational-wave observatories on Earth and in space may
provide new tests of gravitational theory via detailed measurements of the
properties of gravitational waves.


title:
Thermodynamics of de Sitter black holes with a conformally coupled
  scalar field

abstract:
  We study the thermodynamics of de Sitter black holes with a conformally
coupled scalar field. The geometry is that of the ``lukewarm''
Reissner-Nordstrom-de Sitter black holes, with the event and cosmological
horizons at the same temperature. This means that the region between the event
and cosmological horizons can form a regular Euclidean instanton. The entropy
is modified by the non-minimal coupling of the scalar field to the geometry,
but can still be derived from the Euclidean action, provided suitable
modifications are made to deal with the electrically charged case. We use the
first law as derived from the isolated horizons formalism to compute the local
horizon energies for the event and cosmological horizons.


title: Chaplygin gas with non-adiabatic pressure perturbations

abstract:
  Perturbations in a Chaplygin gas, characterized by an equation of state $p =
-A/\rho$, may acquire non-adiabatic contributions if spatial variations of the
parameter $A$ are admitted. This feature is shown to be related to a specific
internal structure of the Chaplygin gas. We investigate how perturbations of
this type modify the adiabatic sound speed and influence the time dependence of
the gravitational potential which gives rise to the Integrated Sachs-Wolfe
effect in the anisotropy spectrum of the cosmic microwave background.


title: Evolution of density perturbations in a realistic universe

abstract:
  Prompted by the recent more precise determination of the basic cosmological
parameters and growing evidence that the matter-energy content of the universe
is now dominated by dark energy and dark matter we present the general solution
of the equation that describes the evolution of density perturbations in the
linear approximation. It turns out that as in the standard CDM model the
density perturbations grow very slowly during the radiation dominated epoch and
their amplitude increases by a factor of about 4000 in the matter and later
dark energy dominated epoch of expansion of the universe.


title:
Coherent States of Harmonic Oscillator and Generalized Uncertainty
  Principle

abstract:
  In this paper dynamics and quantum mechanical coherent states of a simple
harmonic oscillator are considered in the framework of Generalized Uncertainty
Principle(GUP). Equations of motion for simple harmonic oscillator are derived
and some of their new implications are discussed. Then coherent states of
harmonic oscillator in the case of GUP are compared with relative situation in
ordinary quantum mechanics. It is shown that in the framework of GUP there is
no considerable difference in definition of coherent states relative to
ordinary quantum mechanics. But, considering expectation values and variances
of some operators, based on quantum gravitational arguments one concludes that
although it is possible to have complete coherency and vanishing broadening in
usual quantum mechanics, gravitational induced uncertainty destroys complete
coherency in quantum gravity and it is not possible to have a monochromatic ray
in principle.


title: The Area Metric Reality Constraint in Classical General Relativity

abstract:
  A classical foundation for an idea of reality condition in the context of
spin foams (Barrett-Crane models) is developed. I extract classical real
general relativity (all signatures) from complex general relativity by imposing
the area metric reality constraint; the area metric is real iff a
non-degenerate metric is real or imaginary. First I review the Plebanski theory
of complex general relativity starting from a complex vectorial action. Then I
modify the theory by adding a Lagrange multiplier to impose the area metric
reality condition and derive classical real general relativity. I investigate
two types of action: Complex and Real. All the non-trivial solutions of the
field equations of the theory with the complex action correspond to real
general relativity. Half the non-trivial solutions of the field equations of
the theory with the real action correspond to real general relativity.
Discretization of the area metric reality constraint in the context of
Barrett-Crane theory is discussed. In the context of Barrett-Crane theory the
area metric reality condition is equivalent to the condition that the scalar
products of the bivectors associated to the triangles of a four simplex be
real. The Plebanski formalism for the degenerate case and Palatini formalism
are also briefly discussed by including the area metric reality condition.


title:
Spin Foams for the Real, Complex Orthogonal Groups in 4D and the
  bivector scalar product reality constraint

abstract:
  The Barrett-Crane model for the SO(4,C) general relativity is systematically
derived. This procedure makes rigorous the calculation of the Barrett-Crane
intertwiners from the Barrett-Crane constraints of both real and complex
Riemannian general relativity. The reality of the scalar products of the
complex bivectors associated with the triangles of a flat four simplex is
equivalent to the reality of the associated flat geometry. Spin foam models in
4D for the real and complex orthogonal gauge groups are discussed in a unified
manner from the point of view of the bivector scalar product reality
constraints. Many relevant issues are discussed and generalizations of the
ideas are introduced. The asymptotic limit of the SO(4,C) general relativity is
discussed. The asymptotic limit is controlled by the SO(4,C) Regge calculus
which unifies the Regge calculus theories for all the real general relativity
cases. The spin network functionals for the 3+1 formulation of the spin foams
are discussed. The field theory over group formulation for the Barrett-Crane
models is discussed briefly. I introduce the idea of a mixed Lorentzian
Barrett-Crane model which mixes the intertwiners for the Lorentzian
Barrett-Crane models. A mixed propagator is calculated. I also introduce a
multi-signature spin foam model for real general relativity which is made by
splicing together the four simplex amplitudes for the various signatures.
Further research that is to be done is listed and discussed.


title:
Electromagnetic Dipole Radiation Fields, Shear-Free Congruences and
  Complex Center of Charge World Lines

abstract:
  We show that for asymptotically vanishing Maxwell fields in Minkowski space
with non-vanishing total charge, one can find a unique geometric structure, a
null direction field, at null infinity. From this structure a unique complex
analytic world-line in complex Minkowski space that can be found and then
identified as the complex center of charge. By ''sitting'' - in an imaginary
sense, on this world-line both the (intrinsic) electric and magnetic dipole
moments vanish. The (intrinsic) magnetic dipole moment is (in some sense)
obtained from the `distance' the complex the world line is from the real space
(times the charge). This point of view unifies the asymptotic treatment of the
dipole moments For electromagnetic fields with vanishing magnetic dipole
moments the world line is real and defines the real (ordinary center of
charge). We illustrate these ideas with the Lienard-Wiechert Maxwell field. In
the conclusion we discuss its generalization to general relativity where the
complex center of charge world-line has its analogue in a complex center of
mass allowing a definition of the spin and orbital angular momentum - the
analogues of the magnetic and electric dipole moments.


title:
Asymptotics of Solutions of a Perfect Fluid Coupled with a Cosmological
  Constant in Four-Dimensional Spacetime with Toroidal Symmetry

abstract:
  Asymptotics of solutions of a perfect fluid when coupled with a cosmological
constant in four-dimensional spacetime with toroidal symmetry are studied. In
particular, it is found that the problem of self-similar solutions of the first
kind for a fluid with the equation of state, $p = k \rho$, can be reduced to
solving a master equation of the form, $$ 2 F(q, k)\frac{q''(\xi)}{q'(\xi)} -
G(q,k) q'(\xi) = \frac{4}{\xi}. $$ For $k = 0$ and $k = -1/3$ the general
solutions are obtained and their main local and global properties are studied
in detail.


title:
Nonholonomic Deformations of Disk Solutions and Algebroid Symmetries in
  Einstein and Extra Dimension Gravity

abstract:
  In this article we consider nonholonomic deformations of disk solutions in
general relativity to generic off-diagonal metrics defining knew classes of
exact solutions in 4D and 5D gravity. These solutions possess Lie algebroid
symmetries and local anisotropy and define certain generalizations of manifolds
with Killing and/ or Lie algebra symmetries. For Lie algebroids, there are
structures functions depending on variables on a base submanifold and it is
possible to work with singular structures defined by the 'anchor' map. This
results in a number of new physical implications comparing with the usual
manifolds possessing Lie algebra symmetries defined by structure constants. The
spacetimes investigated here have two physically distinct properties: First,
they can give rise to disk type configurations with angular/ time/ extra
dimension gravitational polarizations and running constants. Second, they
define static, stationary or moving disks in nontrivial solitonic backgrounds,
with possible warped factors, additional spinor and/or noncommutative
symmetries. Such metrics may have nontrivial limits to 4D gravity with
vanishing, or nonzero torsion. The work develops the results of Ref.
gr-qc/0005025 and emphasizes the solutions with Lie algebroid symmetries
following similar constructions for solutions with noncommutative symmetries
gr-qc/0307103.

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


title: Spacetime in Semiclassical Gravity

abstract:
  This article will summarize selected aspects of the semiclassical theory of
gravity, which involves a classical gravitational field coupled to quantum
matter fields. Among the issues which will be discussed are the role of quantum
effects in black hole physics and in cosmology, the effects of quantum
violations of the classical energy conditions, and inequalities which constrain
the extent of such violations. We will also examine the first steps beyond
semiclassical gravity, when the effects of spacetime geometry fluctuations
start to appear.


title: Point Charge Self-Energy in the General Relativity

abstract:
  Singularities in the metric of the classical solutions to the Einstein
equations (Schwarzschild, Kerr, Reissner -- Nordstr\"om and Kerr -- Newman
solutions) lead to appearance of generalized functions in the Einstein tensor
that are not usually taken into consideration. The generalized functions can be
of a more complex nature than the Dirac $\d$-function. To study them, a
technique has been used based on a limiting solution sequence. The solutions
are shown to satisfy the Einstein equations everywhere, if the energy-momentum
tensor has a relevant singular addition of non-electromagnetic origin. When the
addition is included, the total energy proves finite and equal to $mc^2$, while
for the Kerr and Kerr--Newman solutions the angular momentum is $mc {\bf a}$.
As the Reissner--Nordstr\"om and Kerr--Newman solutions correspond to the point
charge in the classical electrodynamics, the result obtained allows us to view
the point charge self-energy divergence problem in a new fashion.


title: Compact anisotropic spheres with prescribed energy density

abstract:
  New exact interior solutions to the Einstein field equations for anisotropic
spheres are found. We utilise a procedure that necessitates a choice for the
energy density and the radial pressure. This class contains the constant
density model of Maharaj and Maartens (Gen. Rel. Grav., Vol 21, 899-905, 1989)
and the variable density model of Gokhroo and Mehra (Gen. Rel. Grav., Vol 26,
75-84, 1994) as special cases. These anisotropic spheres match smoothly to the
Schwarzschild exterior and gravitational potentials are well behaved in the
interior. A graphical analysis of the matter variables is performed which
points to a physically reasonable matter distribution.


title: On the Quantum-Corrected Black Hole Thermodynamics

abstract:
  Bekenstein-Hawking Black hole thermodynamics should be corrected to
incorporate quantum gravitational effects. Generalized Uncertainty
Principle(GUP) provides a perturbational framework to perform such
modifications. In this paper we consider the most general form of GUP to find
black holes thermodynamics in microcanonical ensemble. Our calculation shows
that there is no logarithmic pre-factor in perturbational expansion of entropy.
This feature will solve part of controversies in literatures regarding
existence or vanishing of this pre-factor.


title:
Asymptotic Properties of Difference Equations for Isotropic Loop Quantum
  Cosmology

abstract:
  In loop quantum cosmology, a difference equation for the wave function
describes the evolution of a universe model. This is different from the
differential equations that arise in Wheeler-DeWitt quantizations, and some
aspects of general properties of solutions can appear differently. Properties
of particular interest are boundedness and the presence of small-scale
oscillations. Continued fraction techniques are used to show in different
matter models the presence of special initial conditions leading to bounded
solutions, and an explicit expression for these initial values is derived.


title:
Timelike and Spacelike Matter Inheritance Vectors in Specific Forms of
  Energy-Momentum Tensor

abstract:
  This paper is devoted to the investigation of the consequences of timelike
and spacelike matter inheritance vectors in specific forms of energy-momentum
tensor, i.e., for string cosmology (string cloud and string fluid) and perfect
fluid. Necessary and sufficient conditions are developed for a spacetime with
string cosmology and perfect fluid to admit a timelike matter inheritance
vector, parallel to $u^a$ and spacelike matter inheritance vector, parallel to
$x^a$. We compare the outcome with the conditions of conformal Killing vectors.
This comparison provides us the conditions for the existence of matter
inheritance vector when it is also a conformal Killing vector. Finally, we
discuss these results for the existence of matter inheritance vector in the
special cases of the above mentioned spacetimes.


title: On Physical Properties of Cylindrically Symmetric Self-Similar Solutions

abstract:
  This paper is devoted to discuss some of the features of self-similar
solutions of the first kind. We consider the cylindrically symmetric solutions
with different homotheties. We are interested in evaluating the quantities
acceleration, rotation, expansion, shear, shear invariant and expansion rate.
These kinematical quantities are discussed both in co-moving as well as in
non-co-moving coordinates (only in radial direction). Finally, we would discuss
the singularity feature of these solutions. It is expected that these
properties would help in exploring some interesting features of the
self-similar solutions.


title: Kinematic Self-Similar Cylindrically Symmetric Solutions

abstract:
  This paper is devoted to find out cylindrically symmetric kinematic
self-similar perfect fluid and dust solutions. We study the cylindrically
symmetric solutions which admit kinematic self-similar vectors of second,
zeroth and infinite kinds, not only for the tilted fluid case but also for the
parallel and orthogonal cases. It is found that the parallel case gives
contradiction both in perfect fluid and dust cases. The orthogonal perfect
fluid case yields a vacuum solution while the orthogonal dust case gives
contradiction. It is worth mentioning that the tilted case provides solution
both for the perfect as well as dust cases.


title: Lie symmetries for equations in conformal geometries

abstract:
  We seek exact solutions to the Einstein field equations which arise when two
spacetime geometries are conformally related. Whilst this is a simple method to
generate new solutions to the field equations, very few such examples have been
found in practice. We use the method of Lie analysis of differential equations
to obtain new group invariant solutions to conformally related Petrov type D
spacetimes. Four cases arise depending on the nature of the Lie symmetry
generator. In three cases we are in a position to solve the master field
equation in terms of elementary functions. In the fourth case special solutions
in terms of Bessel functions are obtained. These solutions contain known models
as special cases.


title:
Stellar explosion in the weak field approximation of the Brans-Dicke
  theory

abstract:
  We treat a very crude model of an exploding star, in the weak field
approximation of the Brans-Dicke theory, in a scenario that resembles some
characteristics data of a Type Ia Supernova. The most noticeable feature, in
the electromagnetic component, is the relationship between the absolute
magnitude at maximum brightness of the star and the decline rate in one
magnitude from that maximum. This characteristic has become one of the most
accurate method to measure luminosity distances to objects at cosmological
distances. An interesting result is that the active mass associated with the
scalar field is totally radiated to infinity, representing a mass loss in the
ratio of the "tensor" component to the scalar component of 1 to $(2 \omega +
3)$ ($\omega$ is the Brans-Dicke parameter), in agreement with a general result
of Hawking. Then, this model shows explicitly, in a dynamical case, the
mechanism of radiation of scalar field, which is necessary to understand the
Hawking result.


title: Gravitational wave burst vetoes in the LIGO S2 and S3 data analyses

abstract:
  The LIGO detectors collected about 4 months of data in 2003-2004 during two
science runs, S2 and S3. Several environmental and auxiliary channels that
monitor the instruments' physical environment and overall interferometric
operation were analyzed in order to establish the quality of the data as well
as the presence of transients of non-astrophysical origin. This analysis
allowed better understanding of the noise character of the instruments and the
establishment of correlations between transients in these channels and the one
recording the gravitational wave strain. In this way vetoes for spurious burst
were identified. We present the methodology we followed in this analysis and
the results from the S2 and S3 veto analysis within the context of the search
for gravitational wave bursts.


title: On the anomalous acceleration of Pioneer spacecraft

abstract:
  The anomalous acceleration of Pioneer 10 and 11 spacecraft of (8.74 \pm 1.33)
\times 10^{-8} cm. s^{-2} fits with a theoretical prediction of a minimal
acceleration in nature of about 7.61 \times 10^{-8} cm. s^{-2}


title: Displacement- and Timing-Noise Free Gravitational-Wave Detection

abstract:
  Motivated by a recently-invented scheme of displacement-noise-free
gravitational-wave detection, we demonstrate the existence of
gravitational-wave detection schemes insusceptible to both displacement and
timing (laser) noises, and are thus realizable by shot-noise-limited laser
interferometry. This is possible due to two reasons: first, gravitational waves
and displacement disturbances contribute to light propagation times in
different manners; second, for an N-detector system, the number of signal
channels is of the order O(N^2), while the total number of timing- and
displacement-noise channels is of the order O(N).


title:
Test of constancy of speed of light with rotating cryogenic optical
  resonators

abstract:
  A test of Lorentz invariance for electromagnetic waves was performed by
comparing the resonance frequencies of two optical resonators as a function of
orientation in space. In terms of the Robertson-Mansouri-Sexl theory, we obtain
$\beta-\delta-1/2=(+0.5\pm 3\pm 0.7) E-10$, a ten-fold improvement compared to
the previous best results. We also set a first upper limit for a so far unknown
parameter of the Standard Model Extension test theory,
$|(\tilde{\kappa}_{e-})^{ZZ}| < 2\cdot E-14$.


title:
The Huygens principle and cosmological gravitational waves in the
  Regge-Wheeler gauge

abstract:
  We study the propagation of axial gravitational waves in Friedman universes.
The evolution equation is obtained in the Regge-Wheeler gauge. The
gravitational waves obey the Huygens principle in the radiation dominated era,
but in the matter dominated universe their propagation depends on their
wavelengths, with the scale fixed essentially by the Hubble radius. Short waves
practically satisfy the Huygens principle while long waves can backscatter off
the curvature of a spacetime.


title:
Potential-density pairs for axisymmetric galaxies: the influence of
  scalar fields

abstract:
  We present a formulation for potential-density pairs to describe axisymmetric
galaxies in the Newtonian limit of scalar-tensor theories of gravity. The
scalar field is described by a modified Helmholtz equation with a source that
is coupled to the standard Poisson equation of Newtonian gravity. The net
gravitational force is given by two contributions: the standard Newtonian
potential plus a term stemming from massive scalar fields. General solutions
have been found for axisymmetric systems and the multipole expansion of the
Yukawa potential is given. In particular, we have computed potential-density
pairs of galactic disks for an exponential profile and their rotation curves.


title: The White Dwarf -- White Dwarf galactic background in the LISA data

abstract:
  LISA (Laser Interferometer Space Antenna) is a proposed space mission, which
will use coherent laser beams exchanged between three remote spacecraft to
detect and study low-frequency cosmic gravitational radiation. In the low-part
of its frequency band, the LISA strain sensitivity will be dominated by the
incoherent superposition of hundreds of millions of gravitational wave signals
radiated by inspiraling white-dwarf binaries present in our own galaxy. In
order to estimate the magnitude of the LISA response to this background, we
have simulated a synthesized population that recently appeared in the
literature. We find the amplitude of the galactic white-dwarf binary background
in the LISA data to be modulated in time, reaching a minimum equal to about
twice that of the LISA noise for a period of about two months around the time
when the Sun-LISA direction is roughly oriented towards the Autumn equinox.
Since the galactic white-dwarfs background will be observed by LISA not as a
stationary but rather as a cyclostationary random process with a period of one
year, we summarize the theory of cyclostationary random processes, present the
corresponding generalized spectral method needed to characterize such process,
and make a comparison between our analytic results and those obtained by
applying our method to the simulated data. We find that, by measuring the
generalized spectral components of the white-dwarf background, LISA will be
able to infer properties of the distribution of the white-dwarfs binary systems
present in our Galaxy.


title: On Hawking Radiation as Tunneling with Back-Reaction

abstract:
  Recently, Angheben et.al. [hep-th/0503081] have presented a refined method
for calculating the (tree-level) black hole temperature by way of the tunneling
paradigm. In the current letter, we demonstrate how their formalism can be
suitably adapted to accommodate the (higher-order) effects of the gravitational
back-reaction.


title: Constraint damping in the Z4 formulation and harmonic gauge

abstract:
  We show that by adding suitable lower-order terms to the Z4 formulation of
the Einstein equations, all constraint violations except constant modes are
damped. This makes the Z4 formulation a particularly simple example of a
lambda-system as suggested by Brodbeck et al. We also show that the Einstein
equations in harmonic coordinates can be obtained from the Z4 formulation by a
change of variables that leaves the implied constraint evolution system
unchanged. Therefore the same method can be used to damp all constraints in the
Einstein equations in harmonic gauge.


title: Cosmological Solutions in Macroscopic Gravity

abstract:
  In the macroscopic gravity approach to the averaging problem in cosmology,
the Einstein field equations on cosmological scales are modified by appropriate
gravitational correlation terms. We present exact cosmological solutions to the
equations of macroscopic gravity for a spatially homogeneous and isotropic
macroscopic space-time and find that the correlation tensor is of the form of a
spatial curvature term. We briefly discuss the physical consequences of these
results.


title: Empirical Foundations of Relativistic Gravity

abstract:
  In 1859, Le Verrier discovered the mercury perihelion advance anomaly. This
anomaly turned out to be the first relativistic-gravity effect observed. During
the 141 years to 2000, the precisions of laboratory and space experiments, and
astrophysical and cosmological observations on relativistic gravity have been
improved by 3 orders of magnitude. In 1999, we envisaged a 3-6 order
improvement in the next 30 years in all directions of tests of relativistic
gravity. In 2000, the interferometric gravitational wave detectors began their
runs to accumulate data. In 2003, the measurement of relativistic Shapiro
time-delay of the Cassini spacecraft determined the relativistic-gravity
parameter gammaγ with a 1.5-order improvement. In October 2004, Ciufolini
and Pavlis reported a measurement of the Lense-Thirring effect on the LAGEOS
and LAGEOS2 satellites to 10 percent of the value predicted by general
relativity. In April 2004, Gravity Probe B was launched and has been
accumulating science data for more than 170 days now. MICROSCOPE is on its way
for a 2007 launch to test Galileo equivalence principle to 10-15. STEP
(Satellite Test of Equivalence Principle), and ASTROD (Astrodynamical Space
Test of Relativity using Optical Devices) are in the good planning stage.
Various astrophysical tests and cosmological tests of relativistic gravity will
reach precision and ultra-precision stages. Clock tests and atomic
interferometry tests of relativistic gravity will reach an ever-increasing
precision. These will give revived interest and development both in
experimental and theoretical aspects of gravity, and may lead to answers to
some profound questions of gravity and the cosmos.


title: Weyl-Dirac theory predictions on galactic scales

abstract:
  We consider the Weyl-Dirac theory within the framework of the weak field
approximation and show that the resulting gravitational potential differs from
that of Newtonian by a repulsive correction term increasing with distance. The
scale of the correction term appears to be determined by the time variation
rate of the gravitational coupling. It is shown that if the time variation rate
of gravitational coupling is adopted from observational bounds, the theory can
explain the rotation curves of typical spiral galaxies without resorting to
dark matter. To check the consistency of our theoretical model with observation
we use Likelihood analysis to find the best-fit values for the free parameters.
The mean value for the most important free parameter, $\beta\times 10^{14}
(1/yr)$, using the Top-Hat and Gaussian priors are
$6.38^{+2.44}_{-3.46}_{-6.71}^{+6.18}$ and
$5.72_{-1.18}^{+1.22}_{-2.69}^{+2.90}$, respectively. Although the interval for
which $\beta$ is defined is wide, our results show that the goodness of the fit
is, by and large, not sensitive to this quantity. The intergalactic effects and
gravitational lensing of clusters of galaxies are estimated and seem to be
consistent with observational data.


title: Twin Paradox and the logical foundation of relativity theory

abstract:
  We study the foundation of space-time theory in the framework of first-order
logic (FOL). Since the foundation of mathematics has been successfully carried
through (via set theory) in FOL, it is not entirely impossible to do the same
for space-time theory (or relativity). First we recall a simple and streamlined
FOL-axiomatization SpecRel of special relativity from the literature. SpecRel
is complete with respect to questions about inertial motion. Then we ask
ourselves whether we can prove usual relativistic properties of accelerated
motion (e.g., clocks in acceleration) in SpecRel. As it turns out, this is
practically equivalent to asking whether SpecRel is strong enough to "handle"
(or treat) accelerated observers. We show that there is a mathematical
principle called induction (IND) coming from real analysis which needs to be
added to SpecRel in order to handle situations involving relativistic
acceleration. We present an extended version AccRel of SpecRel which is strong
enough to handle accelerated motion, in particular, accelerated observers.
Among others, we show that the Twin Paradox becomes provable in AccRel, but it
is not provable without IND.


title: Algebraic expansions for curvature coupled scalar field models

abstract:
  A late time asymptotic perturbative analysis of curvature coupled complex
scalar field models with accelerated cosmological expansion is carried out on
the level of formal power series expansions. For this, algebraic analogues of
the Einstein scalar field equations in Gaussian coordinates for space-time
dimensions greater than two are postulated and formal solutions are constructed
inductively and shown to be unique. The results obtained this way are found to
be consistent with already known facts on the asymptotics of such models. In
addition, the algebraic expansions are used to provide a prospect of the large
time behaviour that might be expected of the considered models.


title:
The holographic mapping of the Standard Model onto the black hole
  horizon, Part I: Abelian vector field, scalar field and BEH Mechanism

abstract:
  Interactions between outgoing Hawking particles and ingoing matter are
determined by gravitational forces and Standard Model interactions. In
particular the gravitational interactions are responsible for the unitarity of
the scattering against the horizon, as dictated by the holographic principle,
but the Standard Model interactions also contribute, and understanding their
effects is an important first step towards a complete understanding of the
horizon's dynamics. The relation between in- and outgoing states is described
in terms of an operator algebra. In this paper, the first of a series, we
describe the algebra induced on the horizon by U(1) vector fields and scalar
fields, including the case of an Englert-Brout-Higgs mechanism, and a more
careful consideration of the transverse vector field components.


title:
Stress tensor for massive fields on flat spaces of spatial topology
  R^2\times{S^1}

abstract:
  We calculate the expectation values of the energy-momentum tensor
T_{{\mu}{\nu}} for massive scalar and spinor fields, in the Minkowski-like
vacuum states on the two flat spaces which are quotients of Minkowski space
under the discrete isometries (t,x,y,z)\mapsto(t,x,y,z+2a) and
(t,x,y,z)\mapsto(t,-x,-y,z+a).
  The results on the first space confirm the literature.
  The results on the second space are new. We note some qualitative differences
between the massless and massive fields in the limits of large a and large
x^2+y^2.


title:
Extending Sibgatullin's ansatz for the Ernst potential to generate a
  richer family of axially symmetric solutions of Einstein's equations

abstract:
  The scope of this talk is to present some preliminary results on an effort,
currently in progress, to generate an exact solution of Einstein's equation,
suitable for describing spacetime around a rotating compact object.
Specifically, the form of the Ernst potential on the symmetry axis and its
connection with the multipole moments is discussed thoroughly. The way to
calculate the multipole moments of spacetime directly from the value of the
Ernst potential on the symmetry axis is presented. Finally, a mixed ansatz is
formed for the Ernst potential including parameters additional to the ones
dictated by Sibgatullin. Thus, we believe that this talk can also serve as a
comment on choosing the appropriate ansatz for the Ernst potential.


title: Quantum Cosmological Origin of Universes

abstract:
  A direct pathway from Hilbert's ``Foundation of Physics'' to Quantum Gravity
is established through Dirac's Hamiltonian reduction of General Relativity and
Bogoliubov's transformation by analogy with a similar pathway passed by QFT in
20th century. The cosmological scale factor appears on this pathway as a zero
mode of the momentum constraints treated as a global excitation of the Landau
superfluid liquid type. This approach would be considered as the foundation of
the well--known Lifshitz cosmological perturbation theory, if it did not
contain the double counting of the scale factor as an obstruction to the Dirac
Hamiltonian method. After avoiding this ``double counting'' the Hamiltonian
cosmological perturbation theory does not contain the time derivatives of
gravitational potentials that are responsible for the CMB ``primordial power
spectrum'' in the inflationary model.
  The Hilbert -- Dirac -- Bogoliubov Quantum Gravity gives us another
possibility to explain this ``spectrum'' and other topical problems of
cosmology by the cosmological creation of both universes and particles from
Bogoliubov's vacuum. We listed the set of theoretical and observational
arguments in favor of that the CMB radiation can be a final product of
primordial vector W-, Z- bosons cosmologically created from the vacuum when
their Compton length coincides with the universe horizon. The equations
describing longitudinal vector bosons in SM, in this case, are close to the
equations of the inflationary model used for description of the ``power
primordial spectrum'' of the CMB radiation.


title:
Acoustic peaks in the CMB: a matter of standard causal boundary
  conditions on primordial density anisotropies

abstract:
  The pattern of acoustic peaks in the sub-horizon power spectrum of primordial
density anisotropies at recombination can be naturally understood in the
framework of standard Friedmann-Robertson-Walker cosmology (without inflation)
as a consequence of the boundary conditions imposed by the causal horizon on
the statistical two-points correlation functions: the sub-horizon spectrum is
discrete (harmonic), with comoving modes located at $k_n = n
\frac{\pi}{H^{-1}_{eq}}$, $n = 1,2,...$, because the causally connected patch
of the universe at recombination is compact, with comoving radius
$H^{-1}_{eq}$. The results presented in this paper complement those presented
in [1], where it was shown that the scale invariance of the primordial density
anisotropies over comoving scales of cosmological size is also a consequence of
the boundary conditions imposed by causality. Together these results lay an
appealing theoretical alternative to the inflationary paradigm as the ultimate
answer for the origin of cosmological structures in standard cosmology.


title:
Large volume quantum correction in loop quantum cosmology: Graviton
  illusion?

abstract:
  The leading quantum correction to Einstein-Hilbert Hamiltonian coming from
large volume vacuum isotropic loop quantum cosmology, is independent of
quantization ambiguity parameters. It is shown here that this correction can be
viewed as finite volume gravitational Casimir energy due to one-loop `graviton'
contributions. In vacuum case sub-leading quantum corrections and in non-vacuum
case even leading quantum correction depend on ambiguity parameters. It may be
recalled that these are in fact analogous features of perturbative quantum
gravity where it is well-known that pure gravity (on-shell) is one-loop finite
whereas higher-loops contributions are not even renormalizable. These features
of the quantum corrections coming from non-perturbative quantization, sheds a
new light on a major open issue; how to communicate between non-perturbative
and perturbative approaches of quantum gravity.


title:
Scalar hairy black holes and scalarons in the isolated horizons
  formalism

abstract:
  The Isolated Horizons (IH) formalism, together with a simple phenomenological
model for colored black holes has been used to predict non-trivial formulae
that relate the ADM mass of the solitons and hairy Black Holes of
Gravity-Matter system on the one hand, and several horizon properties of the
black holes in the other. In this article, the IH formalism is tested
numerically for spherically symmetric solutions to an Einstein-Higgs system
where hairy black holes were recently found to exist. It is shown that the mass
formulae still hold and that, by appropriately extending the current model, one
can account for the behavior of the horizon properties of these new solutions.
An empirical formula that approximates the ADM mass of hairy solutions is put
forward, and some of its properties are analyzed.


title:
Statistical Entropy and Superradiance in 2+1 Dimensional Acoustic Black
  Holes

abstract:
  We study ``draining bathtub'' as an acoustic analogue of a three-dimensional
rotating black hole. Rotating fluid near the sonic horizon necessarily gives
rise to the superradiant modes, which are partially responsible for the
thermodynamic quantities in this rotating vortex-like hole. Using the recently
suggested thin-layer method overcoming some difficulties from the well-known
brick-wall method, we explicitly calculate the free energy of the system by
treating the superradiance carefully and obtain the desirable entropy formula.


title: Status of the joint LIGO--TAMA300 inspiral analysis

abstract:
  We present the status of the joint search for gravitational waves from
inspiraling neutron star binaries in the LIGO Science Run 2 and TAMA300 Data
Taking Run 8 data, which was taken from February 14 to April 14, 2003, by the
LIGO and TAMA collaborations. In this paper we discuss what has been learned
from an analysis of a subset of the data sample reserved as a ``playground''.
We determine the coincidence conditions for parameters such as the coalescence
time and chirp mass by injecting simulated Galactic binary neutron star signals
into the data stream. We select coincidence conditions so as to maximize our
efficiency of detecting simulated signals. We obtain an efficiency for our
coincident search of 78 %, and show that we are missing primarily very distant
signals for TAMA300. We perform a time slide analysis to estimate the
background due to accidental coincidence of noise triggers. We find that the
background triggers have a very different character from the triggers of
simulated signals.


title: On the non-linearity of the subsidiary systems

abstract:
  In hyperbolic reductions of the Einstein equations the evolution of gauge
conditions or constraint quantities is controlled by subsidiary systems. We
point out a class of non-linearities in these systems which may have the
potential of generating catastrophic growth of gauge resp. constraint
violations in numerical calculations.


title: On the integrability of spherical gravitational waves in vacuum

abstract:
  The general class of Robinson-Trautman metrics that describe gravitational
radiation in the exterior of bounded sources in four space-time dimensions is
shown to admit zero curvature formulation in terms of appropriately chosen
two-dimensional gauge connections. The result, which is valid for either type
II or III metrics, implies that the gravitational analogue of the
Lienard-Wiechert fields of Maxwell equations form a new integrable sector of
Einstein equations for any value of the cosmological constant. The method of
investigation is similar to that used for integrating the Ricci flow in two
dimensions. The zero modes of the gauge symmetry (factored by the center)
generate Kac's K_2 simple Lie algebra with infinite growth.


title: Tetrade Spin Foam Model

abstract:
  We propose a spin foam model of four-dimensional quantum gravity which is
based on the integration of the tetrads in the path integral for the Palatini
action of General Relativity. In the Euclidian gravity case we show that the
model can be understood as a modification of the Barrett-Crane spin foam model.
Fermionic matter can be coupled by using the path integral with sources for the
tetrads and the spin connection, and the corresponding state sum is based on a
spin foam where both the edges and the faces are colored independently with the
irreducible representations of the spacetime rotations group.


title: Interacting viscous mixtures

abstract:
  Gravitational and hydrodynamical perturbations are analysed in a relativistic
plasma containing a mixture of interacting fluids characterized by a
non-negligible bulk viscosity coefficient. The energy-momentum transfer between
the cosmological fluids, as well as the fluctuations of the bulk viscosity
coefficients, are analyzed simultaneously with the aim of deriving a
generalized set of evolution equations for the entropy and curvature
fluctuations. For typical length scales larger than the Hubble radius, the
fluctuations of the bulk viscosity coefficients and of the decay rate provide
source terms for the evolution of both the curvature and the entropy
fluctuations. According to the functional dependence of the bulk viscosity
coefficient on the energy densities of the fluids composing the system, the
mixing of entropy and curvature perturbations is scrutinized both analytically
and numerically.


title: False vacuum decay with gravity in a critical case

abstract:
  The vacuum decay in a de Sitter universe is studied within semiclassical
approximation for the class of effective inflaton potentials whose curvature at
the top is close to a critical value. By comparing the actions of the Hawking -
Moss instanton and the Coleman - de Luccia instanton(s) the mode of vacuum
decay is determined. The case when the fourth derivative of the effective
potential at its top is less than a critical value is discussed.


title: Mechanical Dissipation in Silicon Flexures

abstract:
  The thermo-mechanical properties of silicon make it of significant interest
as a possible material for mirror substrates and suspension elements for future
long-baseline gravitational wave detectors. The mechanical dissipation in 92um
thick <110> single-crystal silicon cantilevers has been observed over the
temperature range 85 K to 300 K, with dissipation approaching levels down to
phi = 4.4E-7.


title:
Running of the Spectral Index and Violation of the Consistency Relation
  Between Tensor and Scalar Spectra from trans-Planckian Physics

abstract:
  One of the firm predictions of inflationary cosmology is the consistency
relation between scalar and tensor spectra. It has been argued that such a
relation -if experimentally confirmed- would offer strong support for the idea
of inflation. We examine the possibility that trans-Planckian physics violates
the consistency relation in the framework of inflation with a cut-off proposed
in astro-ph/0009209. We find that despite the ambiguity that exists in choosing
the action, Planck scale physics modifies the consistency relation
considerably. It also leads to the running of the spectral index. For modes
that are larger than our current horizon, the tensor spectral index is
positive. For a window of k values with amplitudes of the same order of the
modes which are the precursor to structure formation, the behavior of tensor
spectral index is oscillatory about the standard Quantum Field theory result,
taking both positive and negative values. There is a hope that in the light of
future experiments, one can verify this scenario of short distance physics.


title: Relativistic Compact Objects in Isotropic Coordinates

abstract:
  We present a matrix method for obtaining new classes of exact solutions for
Einstein's equations representing static perfect fluid spheres. By means of a
matrix transformation, we reduce Einstein's equations to two independent
Riccati type differential equations for which three classes of solutions are
obtained. One class of the solutions corresponding to the linear barotropic
type fluid with an equation of state $p=\gamma \rho $ is discussed in detail.


title:
Static Einstein's Universe as a Quantum Solution of Causal Quantum
  Gravity

abstract:
  We shall in the framework of Bohmian quantum gravity show that it is possible
to find a {\it pure} quantum state which leads to the static Einstein universe
whose classical counterpart is flat space--time. We obtain the solution not
only in the long--wavelength approximation but also exactly.


title: Classical and Quantum Limits in Bohmian Quantum Cosmology

abstract:
  In this paper we have investigated the classical limit in Bohmian quantum
cosmology. It is observed that in the quantum regime where the quantum
potential is greater than the classical one, one has an expansion in terms of
negative powers of the Planck constant. But in the classical limit there are
regions having positive powers of the Planck constant, and regions having
negative powers and also regions having both. The conclusion is that the
Bohmian classical limit cannot be obtained by letting the Planck constant goes
to zero.


title: The ringing wormholes

abstract:
  We investigate the response of the traversable wormholes to the external
perturbations through finding their characteristic frequencies and time-domain
profiles. The considered solution describes traversable wormholes between the
branes in the two brane Randall-Sundrum model and was previously found within
Einstein gravity with a conformally coupled scalar field. The evolution of
perturbations of a wormhole is similar to that of a black hole and represents
damped oscillations (ringing) at intermediately late times, which are
suppressed by power law tails (proportional to t^{-2} for monopole
perturbations) at asymptotically late times.


abstract:
  A world-wide network of interferometric gravitational wave detectors is
currently operational. The detectors in the network are still in their
commissioning phase and are expected to achieve their design sensitivity over
the next year or so. Each detector is a complex instrument involving many
subsystems and each subsystem is a source of noise at the output of the
detector. Therefore, in addition to recording the main gravitational wave data
channel at the output of the interferometer, the state of each detector
subsystem is monitored and recorded. This subsidiary data is both large in
volume as well as complex in nature. We require an online monitoring and
analysis tool which can process all the data channels for various noise
artefacts and summarize the results of the analysis in a manner that can be
accessed and interpreted conveniently.
  In this paper we describe the GEO600 Online Detector Characterization System
(GODCS), which is the tool that is being used to monitor the output of the
GEO600 gravitational wave detector situated near Hannover in Germany. We
describe the various algorithms that we use and how the results of several
algorithms can be combined to make meaningful statements about the state of the
detector. This paper will be useful to researchers in the area of gravitational
wave astronomy as a record of the various analyses and checks carried out to
ensure the quality and reliability of the data before searching the data for
the presence of gravitational waves.


title:
Motion of Classical Impurities in the Homogeneous Bose-Einstein
  Condensate

abstract:
  Motion of classical point-like impurities in the homogeneous Einstein
condensate of bosons is studied in the framework of second quantization method.
A toy model is proposed and its general solution within the Bogoliubov
approximation is obtained. The effective Minkowski space-time structure arises
naturally in this non-relativistic quantum many-body system in the low energy
regime. This is shown to be true in this model. Several examples are discussed
in order to illustrate our model. The homogeneous condensate produces an
effective Yukawa type attractive force between impurities sitting in
condensate. Landau's criterion is naturally derived in a case of linear motion
of impurity. The analytic expressions for spectra of Bogoliubov excitations
produced by the accelerated motions of impurities are obtained. A quick look at
the analytic expression reveals that the spectrum of gapless excitations
emitted by the linearly accelerated impurity {\it is not thermal}. If the
homogeneous condensate is the physically correct model for Minkowski space-time
then it follows that the apparent thermal response of the simple linearly
accelerated detector models may be the result of improper regularization.


title: Uniqueness and Non-uniqueness in the Einstein Constraints

abstract:
  The conformal thin sandwich (CTS) equations are a set of four of the Einstein
equations, which generalize the Laplace-Poisson equation of Newton's theory. We
examine numerically solutions of the CTS equations describing perturbed
Minkowski space, and find only one solution. However, we find {\em two}
distinct solutions, one even containing a black hole, when the lapse is
determined by a fifth elliptic equation through specification of the mean
curvature. While the relationship of the two systems and their solutions is a
fundamental property of general relativity, this fairly simple example of an
elliptic system with non-unique solutions is also of broader interest.


title: Acoustic analogues of black hole singularities

abstract:
  We search for acoustic analogues of a spherical symmetric black hole with a
pointlike source. We show that the gravitational system has a dynamical
counterpart in the constrained, steady motion of a fluid with a planar source.
The equations governing the dynamics of the gravitational system can be exactly
mapped in those governing the motion of the fluid. The different meaning that
singularities and sources have in fluid dynamics and in general relativity is
also discussed. Whereas in the latter a pointlike source is always associated
with a (curvature) singularity in the former the presence of sources does not
necessarily imply divergences of the fields.


title: Timelike and Spacelike Ricci Collineation Vectors in String Fluid

abstract:
  We study the consequences of the existence of timelike and spacelike Ricci
collineation vectors (RCVs) for string fluid in the context of general
relativity. Necessary and sufficient conditions are derived for a space-time
with string fluid to admit a timelike RCV, parallel to $u^a$, and a spacelike
RCV, parallel to $n^a$. In these cases, some results obtained are discussed.


title: Geometric Time Delay Interferometry

abstract:
  The space-based gravitational-wave observatory LISA, a NASA-ESA mission to be
launched after 2012, will achieve its optimal sensitivity using Time Delay
Interferometry (TDI), a LISA-specific technique needed to cancel the otherwise
overwhelming laser noise in the inter-spacecraft phase measurements. The TDI
observables of the Michelson and Sagnac types have been interpreted physically
as the virtual measurements of a synthesized interferometer. In this paper, I
present Geometric TDI, a new and intuitive approach to extend this
interpretation to all TDI observables. Unlike the standard algebraic formalism,
Geometric TDI provides a combinatorial algorithm to explore exhaustively the
space of second-generation TDI observables (i.e., those that cancel laser noise
in LISA-like interferometers with time-dependent armlengths). Using this
algorithm, I survey the space of second-generation TDI observables of length
(i.e., number of component phase measurements) up to 24, and I identify
alternative, improved forms of the standard second-generation TDI observables.
The alternative forms have improved high-frequency gravitational-wave
sensitivity in realistic noise conditions (because they have fewer nulls in the
gravitational-wave and noise response functions), and are less susceptible to
instrumental gaps and glitches (because their component phase measurements span
shorter time periods).


title: Relativistic Motion of Spinning Particles in a Gravitational Field

abstract:
  The relative motion of a classical relativistic spinning test particle is
studied with respect to a nearby free test particle in the gravitational field
of a rotating source. The effects of the spin-curvature coupling force are
elucidated and the implications of the results for the motion of rotating
plasma clumps in astrophysical jets are discussed.


title: Uniqueness of diffeomorphism invariant states on holonomy-flux algebras

abstract:
  Loop quantum gravity is an approach to quantum gravity that starts from the
Hamiltonian formulation in terms of a connection and its canonical conjugate.
Quantization proceeds in the spirit of Dirac: First one defines an algebra of
basic kinematical observables and represents it through operators on a suitable
Hilbert space. In a second step, one implements the constraints. The main
result of the paper concerns the representation theory of the kinematical
algebra: We show that there is only one cyclic representation invariant under
spatial diffeomorphisms.
  While this result is particularly important for loop quantum gravity, we are
rather general: The precise definition of the abstract *-algebra of the basic
kinematical observables we give could be used for any theory in which the
configuration variable is a connection with a compact structure group. The
variables are constructed from the holonomy map and from the fluxes of the
momentum conjugate to the connection. The uniqueness result is relevant for any
such theory invariant under spatial diffeomorphisms or being a part of a
diffeomorphism invariant theory.


title: Energy and Hamiltonian in first order gravity

abstract:
  In this work the definition of a quasilocal energy for four dimensional first
order gravity is developed. Using this an action principle which is adequate
for the canonical ensemble is obtained. The microcanonical action principle is
obtained as well.


title: Physical interpretation of NUT solution

abstract:
  We show that the well-known NUT solution can be correctly interpreted as
describing the exterior field of two counter-rotating semi-infinite sources
possessing negative masses and infinite angular momenta which are attached to
the poles of a static finite rod of positive mass.


title:
Absence of the Kasner singularity in the effective dynamics from loop
  quantum cosmology

abstract:
  In classical general relativity, the generic approach to the initial
singularity is usually understood in terms of the BKL scenario. In this
scenario, along with the Bianchi IX model, the exact, singular, Kasner solution
of vacuum Bianchi I model also plays a pivotal role. Using an effective
classical Hamiltonian obtained from loop quantization of vacuum Bianchi I
model, exact solution is obtained which is non-singular due to a discreteness
parameter. The solution is parameterized in exactly the same manner as the
usual Kasner solution and reduces to the Kasner solution as discreteness
parameter is taken to zero. At the effective Hamiltonian level, the avoidance
of Kasner singularity uses a mechanism distinct from the `inverse volume'
modifications characteristic of loop quantum cosmology.


title: A Slowly Rotating Charged Black Hole in Five Dimensions

abstract:
  Black hole solutions in higher dimensional Einstein and Einstein-Maxwell
gravity have been discussed by Tangherlini as well as Myers and Perry a long
time ago. These solutions are the generalizations of the familiar
Schwarzschild, Reissner-Nordstrom and Kerr solutions of four-dimensional
general relativity. However, higher dimensional generalization of the
Kerr-Newman solution in four dimensions has not been found yet. As a first step
in this direction I shall report on a new solution of the Einstein-Maxwell
system of equations that describes an electrically charged and slowly rotating
black hole in five dimensions.


title:
Topology of event horizon in axially symmetric spacetime: Classification
  of Maxwell set with symmetry

abstract:
  The crease set of an event horizon is studied in a spacetime with discrete or
continuous symmetry. It determines possible topologies on spatial sections of
an event horizon. We thereby investigate the classification of stable
topological structure of the crease sets in a spacetime with any symmetry. In
practice, we show the classification of the crease set in axially symmetric
spacetime. By that we realize the topological structure of axially symmetric
event horizons. We will finc that many new topological structures become stable
which is not stable without symmetry.


title: Superfluid Analog of the Davies-Unruh Effect

abstract:
  We produce an analog of the Davies-Unruh effect for superfluid helium four.
There are two temperatures which result--one is associated with ordinary, or
first, sound and the other with second sound.


title: Multi Shell Model for Majumdar-Papapetrau Spacetimes

abstract:
  Exact solutions to static and non-static Einstein-Maxwell equations in the
presence of extremely charged dust embedded on thin shells are constructed.
Singularities of multi-black hole Majumdar-Papapetrou and Kastor-Trashen
solutions are removed by placing the matter on thin shells. Double spherical
thin shell solution is given as an illustration and the matter densitiies on
the shells are derived.


title:
Spatially Compact Solutions and Stabilization in
  Einstein-Yang-Mills-Higgs Theories

abstract:
  New solutions to the static, spherically symmetric Einstein-Yang-Mills-Higgs
equations with the Higgs field in the triplet resp. doublet representation are
presented. They form continuous families parametrized by $\alpha=M_W/M_Pl$
($M_W$ resp. $M_Pl$ denoting the W-boson resp. the Planck mass). The
corresponding spacetimes are regular and have spatially compact sections. A
particularly interesting class with the Yang-Mills amplitude being nodeless is
exhibited and is shown to be linearly stable with respect to spherically
symmetric perturbations. For some solutions with nodes of the Yang-Mills
amplitude a new stabilization phenomenon is found, according to which their
unstable modes disappear as $\alpha$ increases (for the triplet) or decreases
(for the doublet).


title:
New thought experiment to test the generalized second law of
  thermodynamics

abstract:
  We propose an extension of the original thought experiment proposed by
Geroch, which sparked much of the actual debate and interest on black hole
thermodynamics, and show that the generalized second law of thermodynamics is
in compliance with it.


title:
Particle acoustic detection in gravitational wave aluminum resonant
  antennas

abstract:
  The results on cosmic rays detected by the gravitational antenna NAUTILUS
have motivated an experiment (RAP) based on a suspended cylindrical bar, which
is made of the same aluminum alloy as NAUTILUS and is exposed to a high energy
electron beam. Mechanical vibrations originate from the local thermal expansion
caused by warming up due to the energy lost by particles crossing the material.
The aim of the experiment is to measure the amplitude of the fundamental
longitudinal vibration at different temperatures. We report on the results
obtained down to a temperature of about 4 K, which agree at the level of about
10% with the predictions of the model describing the underlying physical
process.


title:
Spacelike Ricci Inheritance Vectors in a Model of String Cloud and
  String Fluid Stress Tensor

abstract:
  We study the consequences of the existence of spacelike Ricci inheritance
vectors (SpRIVs) parallel to $x^a$ for model of string cloud and string fluid
stress tensor in the context of general relativity. Necessary and sufficient
conditions are derived for a spacetime with a model of string cloud and string
fluid stress tensor to admit a SpRIV and a SpRIV which is also a spacelike
conformal Killing vector (SpCKV). Also, some results are obtained.


title: Quadrupole formula for Kaluza-Klein modes in the braneworld

abstract:
  The quadrupole formula in four-dimensional Einstein gravity is a useful tool
to describe gravitational wave radiation. We derive the quadrupole formula for
the Kaluza-Klein (KK) modes in the Randall-Sundrum braneworld model. The
quadrupole formula provides transparent representation of the exterior weak
gravitational field induced by localized sources. We find that a general
isolated dynamical source gives rise to the 1/r^2 correction to the leading 1/r
gravitational field. We apply the formula to an evaluation of the effective
energy carried by the KK modes from the viewpoint of an observer on the brane.
Contrary to the ordinary gravitational waves (zero mode), the flux of the
induced KK modes by the non-spherical part of the quadrupole moment vanishes at
infinity and only the spherical part contributes to the flux. Since the effect
of the KK modes appears in the linear order of the metric perturbations, the
effective energy flux observed on the brane is not always positive, but can
become negative depending on the motion of the localized sources.


title: Generalized macroscopic Schrodinger equation in scale relativity

abstract:
  The scale transformation laws produce, on the motion equations of gravitating
bodies and under some peculiar assumptions, effects which are anologous to
those of a "macroscopic quantum mechanics". When we consider time and space
scales such that the description of the trajectories of these bodies
(planetesimals in the case of planetary system formation, interstellar gas and
dust in the case of star formation, etc...) is in the shape of
non-differentiable curves, we obtain fractal curves of fractal dimension 2.
Continuity and non-differentiability yield a fractal space and a symmetry
breaking of the differential time element which gives a doubling of the
velocity fields. The application of a geodesics principle leads to motion
equations of Schrodinger-type. When we add an outside gravitational field, we
obtain a Schrodinger-Poisson system. We give here the derivation of the
Schrodinger equation for chaotic systems, i.e., with time scales much longer
than their Lyapounov chaos-time.


title: Gowdy $T^3$ Cosmological Models in N=1 Supergravity

abstract:
  We investigate the canonical quantization of supergravity N=1 in the case of
a midisuperspace described by Gowdy $T^3$ cosmological models. The quantum
constraints are analyzed and the wave function of the universe is derived
explicitly. Unlike the minisuperspace case, we show the existence of physical
states in midisuperspace models. The analysis of the wave function of the
universe leads to the conclusion that the classical curvature singularity
present in the evolution of Gowdy models is removed at the quantum level due to
the presence of the Rarita-Schwinger field.


title: Radiation transport equations in non-Riemannian space-times

abstract:
  The transport equations for polarized radiation transfer in non-Riemannian,
Weyl-Cartan type space-times are derived, with the effects of both torsion and
non-metricity included. To obtain the basic propagation equations we use the
tangent bundle approach. The equations describing the time evolution of the
Stokes parameters, of the photon distribution function and of the total
polarization degree can be formulated as a system of coupled first order
partial differential equations. As an application of our results we consider
the propagation of the cosmological gamma ray bursts in spatially homogeneous
and isotropic spaces with torsion and non-metricity. For this case the exact
general solution of the equation for the polarization degree is obtained, with
the effects of the torsion and non-metricity included. The presence of a
non-Riemannian geometrical background in which the electromagnetic fields
couple to torsion and/or non-metricity affect the polarization of photon beams.
Consequently, we suggest that the observed polarization of prompt cosmological
gamma ray bursts and of their optical afterglows may have a propagation effect
component, due to a torsion/non-metricity induced birefringence of the vacuum.
A cosmological redshift and frequency dependence of the polarization degree of
gamma ray bursts also follows from the model, thus providing a clear
observational signature of the torsional/non-metric effects. On the other hand,
observations of the polarization of the gamma ray bursts can impose strong
constraints on the torsion and non-metricity and discriminate between different
theoretical models.


title: On Hawking Radiation as Tunneling with Logarithmic Corrections

abstract:
  There has been recent speculation that the tunneling paradigm for Hawking
radiation could -- after quantum-gravitational effects have suitably been
incorporated -- provide a means for resolving the (black hole) information loss
paradox. A prospective quantum-gravitational effect is the logarithmic-order
correction to the Bekenstein-Hawking entropy/area law. In this letter, it is
demonstrated that, even with the inclusion of the logarithmic correction (or,
indeed, the quantum correction up to any perturbative order), the tunneling
formalism is still unable to resolve the stated paradox. Moreover, we go on to
show that the tunneling framework effectively constrains the coefficient of
this logarithmic term to be non-negative. Significantly, the latter observation
implies the necessity for including the canonical corrections in the quantum
formulation of the black hole entropy.


title: Birkhoff's theorem in Lovelock gravity

abstract:
  We show that the generic solutions of the Lovelock equations with spherical,
planar or hyperbolic symmetry are locally isometric to the corresponding static
Lovelock black hole. As a consequence, these solutions are locally static: they
admit an additional Killing vector that can either be space-like or time-like,
depending on the position. This result also holds in the presence of an abelian
gauge field, in which case the solutions are locally isometric to a charged
static black hole.


title: Semiclassical quantisation of space-times with apparent horizons

abstract:
  Coherent or semiclassical states in canonical quantum gravity describe the
classical Schwarzschild space-time. By tracing over the coherent state
wavefunction inside the horizon, a density matrix is derived.
Bekenstein-Hawking entropy is obtained from the density matrix, modulo the
Immirzi parameter. The expectation value of the area and curvature operator is
evaluated in these states. The behaviour near the singularity of the curvature
operator shows that the singularity is resolved. We then generalise the results
to space-times with spherically symmetric apparent horizons.


title: Quasi-local energy-momentum and energy flux at null infinity

abstract:
  The null infinity limit of the gravitational energy-momentum and energy flux
determined by the covariant Hamiltonian quasi-local expressions is evaluated
using the NP spin coefficients. The reference contribution is considered by
three different embedding approaches. All of them give the expected Bondi
energy and energy flux.


title:
Planck Fluctuations, Measurement Uncertainties and the Holographic
  Principle

abstract:
  Starting from a critical analysis of recently reported surprisingly large
uncertainties in length and position measurements deduced within the framework
of quantum gravity, we embark on an investigation both of the correlation
structure of Planck scale fluctuations and the role the holographic hypothesis
is possibly playing in this context. While we prove the logical independence of
the fluctuation results and the holographic hypothesis (in contrast to some
recent statements in that direction) we show that by combining these two topics
one can draw quite strong and interesting conclusions about the fluctuation
structure and the microscopic dynamics on the Planck scale. We further argue
that these findings point to a possibly new and generalized form of quantum
statistical mechanics of strongly (anti)correlated systems of degrees of
freedom in this fundamental regime.


title: Holographic dark energy and cosmic coincidence

abstract:
  In this Letter we demonstrate that any interaction of pressureless dark
matter with holographic dark energy, whose infrared cutoff is set by the Hubble
scale, implies a constant ratio of the energy densities of both components thus
solving the coincidence problem. The equation of state parameter is obtained as
a function of the interaction strength. For a variable degree of saturation of
the holographic bound the energy density ratio becomes time dependent which is
compatible with a transition from decelerated to accelerated expansion.


title:
Mathisson-Papapetrou equations in metric and gauge theories of gravity
  in a Lagrangian formulation

abstract:
  We present a simple method to derive the semiclassical equations of motion
for a spinning particle in a gravitational field. We investigate the cases of
classical, rotating particles (pole-dipole particles), as well as particles
with intrinsic spin. We show that, starting with a simple Lagrangian, one can
derive equations for the spin evolution and momentum propagation in the
framework of metric theories of gravity and in theories based on a
Riemann-Cartan geometry (Poincare gauge theory), without explicitly referring
to matter current densities (spin and energy-momentum). Our results agree with
those derived from the multipole expansion of the current densities by the
conventional Papapetrou method and from the WKB analysis for elementary
particles.


title: Generalized Korn's inequality and conformal Killing vectors

abstract:
  Korn's inequality plays an important role in linear elasticity theory. This
inequality bounds the norm of the derivatives of the displacement vector by the
norm of the linearized strain tensor. The kernel of the linearized strain
tensor are the infinitesimal rigid-body translations and rotations (Killing
vectors). We generalize this inequality by replacing the linearized strain
tensor by its trace free part. That is, we obtain a stronger inequality in
which the kernel of the relevant operator are the conformal Killing vectors.
The new inequality has applications in General Relativity.


title: Discrete space-time

abstract:
  We review recent efforts to construct gravitational theories on discrete
space-times, usually referred to as the ``consistent discretization'' approach.
The resulting theories are free of constraints at the canonical level and
therefore allow to tackle many problems that cannot be currently addressed in
continuum quantum gravity. In particular the theories imply a natural method
for resolving the big bang (and other types) of singularities and predict a
fundamental mechanism for decoherence of quantum states that might be relevant
to the black hole information paradox. At a classical level, the theories may
provide an attractive new path for the exploration of issues in numerical
relativity. Finally, the theories can make direct contact with several
kinematical results of continuum loop quantum gravity. We review in broad terms
several of these results and present in detail as an illustration the classical
treatment with this technique of the simple yet conceptually challenging model
of two oscillators with constant energy sum.


title:
An exact solution of the five-dimensional Einstein equations with
  four-dimensional de Sitter-like expansion

abstract:
  We present an exact solution to the Einstein field equations which is Ricci
and Riemann flat in five dimensions, but in four dimensions is a good model for
the early vacuum-dominated universe.


title: Lagrange formulation of the symmetric teleparallel gravity

abstract:
  We develop a symmetric teleparallel gravity model in a space-time with only
the non-metricity is nonzero, in terms of a Lagrangian quadratic in the
non-metricity tensor. We present a detailed discussion of the variations that
may be used for any gravitational formulation. We seek Schwarzschild-type
solutions because of its observational significance and obtain a class of
solutions that includes Schwarzschild-type, Schwarzschild-de Sitter-type and
Reissner-Nordstr\"{o}m-type solutions for certain values of the parameters. We
also discuss the physical relevance of these solutions.


title: A note on the peeling theorem in higher dimensions

abstract:
  We demonstrate the ``peeling property'' of the Weyl tensor in higher
dimensions in the case of even dimensions (and with some additional
assumptions), thereby providing a first step towards understanding of the
general peeling behaviour of the Weyl tensor, and the asymptotic structure at
null infinity, in higher dimensions.


title:
Oscillatory regime in the Multidimensional Homogeneous Cosmological
  Models Induced by a Vector Field

abstract:
  We show that in multidimensional gravity vector fields completely determine
the structure and properties of singularity. It turns out that in the presence
of a vector field the oscillatory regime exists in all spatial dimensions and
for all homogeneous models. By analyzing the Hamiltonian equations we derive
the Poincar\'e return map associated to the Kasner indexes and fix the rules
according to which the Kasner vectors rotate. In correspondence to a
4-dimensional space time, the oscillatory regime here constructed overlap the
usual Belinski-Khalatnikov-Liftshitz one.


title:
Towards a wave--extraction method for numerical relativity: III.
  Analytical examples for the Beetle--Burko radiation scalar

abstract:
  Beetle and Burko recently introduced a background--independent scalar
curvature invariant for general relativity that carries information only about
the gravitational radiation in generic spacetimes, in cases where such
radiation is incontrovertibly defined. In this paper we adopt a formalism that
only uses spatial data as they are used in numerical relativity and compute the
Beetle--Burko radiation scalar for a number of analytical examples,
specifically linearized Einstein--Rosen cylindrical waves, linearized
quadrupole waves, the Kerr spacetime, Bowen--York initial data, and the Kasner
spacetime. These examples illustrate how the Beetle--Burko radiation scalar can
be used to examine the gravitational wave content of numerically generated
spacetimes, and how it may provide a useful diagnostic for initial data sets.


title: Upper limits on gravitational wave bursts in LIGO's second science run

abstract:
  We perform a search for gravitational wave bursts using data from the second
science run of the LIGO detectors, using a method based on a wavelet
time-frequency decomposition. This search is sensitive to bursts of duration
much less than a second and with frequency content in the 100-1100Hz range. It
features significant improvements in the instrument sensitivity and in the
analysis pipeline with respect to the burst search previously reported by LIGO.
Improvements in the search method allow exploring weaker signals, relative to
the detector noise floor, while maintaining a low false alarm rate, O(0.1)
microHz. The sensitivity in terms of the root-sum-square (rss) strain amplitude
lies in the range of hrss~10^{-20} - 10^{-19}/sqrt(Hz) No gravitational wave
signals were detected in 9.98 days of analyzed data. We interpret the search
result in terms of a frequentist upper limit on the rate of detectable
gravitational wave bursts at the level of 0.26 events per day at 90% confidence
level. We combine this limit with measurements of the detection efficiency for
given waveform morphologies in order to yield rate versus strength exclusion
curves as well as to establish order-of-magnitude distance sensitivity to
certain modeled astrophysical sources. Both the rate upper limit and its
applicability to signal strengths improve our previously reported limits and
reflect the most sensitive broad-band search for untriggered and unmodeled
gravitational wave bursts to date.


title: Pre-classical solutions of the vacuum Bianchi I loop quantum cosmology

abstract:
  Loop quantization of diagonalized Bianchi class A models, leads to a partial
difference equation as the Hamiltonian constraint at the quantum level. A
criterion for testing a viable semiclassical limit has been formulated in terms
of existence of the so-called pre-classical solutions. We demonstrate the
existence of pre-classical solutions of the quantum equation for the vacuum
Bianchi I model. All these solutions avoid the classical singularity at
vanishing volume.


title:
General covariance violation and the gravitational dark matter. I.
  Scalar graviton

abstract:
  The violation of the general covariance is proposed as a resource of the
gravitational dark matter. The minimal violation of the covariance to the
unimodular one is associated with the massive scalar graviton as the simplest
representative of such a matter. The Lagrangian formalism for the continuous
medium, the perfect fluid in particular, in the scalar graviton environment is
developed. The implications for cosmology are shortly indicated.