title: Initial value formalism for dust collapse

abstract:
  Formulating a dust filled spherically symmetric metric utilizing the 3+1
formalism for general relativity, we show that the metric coefficients are
completely determined by the matter distribution throughout the spacetime.
Furthermore, the metric describes both inhomogeneous dust regions and also
vacuum regions in a single coordinate patch, thus alleviating the need for
complicated matching schemes at the interfaces. In this way, the system is
established as an initial-boundary value problem, which has many benefits for
its numerical evolution. We show the dust part of the metric is equivalent to
the class of Lemaitre-Tolman-Bondi (LTB) metrics under a coordinate
transformation. In this coordinate system, shell crossing singularities (SCS)
are exhibited as fluid shock waves, and we therefore discuss possibilities for
the dynamical extension of shell crossings through the initial point of
formation by borrowing methods from classical fluid dynamics. This paper fills
a void in the present literature associated with these collapse models by fully
developing the formalism in great detail. Furthermore, the applications provide
examples of the benefits of the present model.


title: Selfgravitation in a general-relativistic accretion of steady fluids

abstract:
  The selfgravity of an infalling gas can alter significantly the accretion of
gases. In the case of spherically symmetric steady flows of polytropic perfect
fluids the mass accretion rate achieves maximal value when the mass of the
fluid is 1/3 of the total mass. There are two weakly accreting regimes, one
over-abundant and the other poor in fluid content. The analysis within the
newtonian gravity suggests that selfgravitating fluids can be unstable, in
contrast to the accretion of test fluids.


title: Static Ricci-flat 5-manifolds admitting the 2-sphere

abstract:
  We examine, in a purely geometrical way, static Ricci-flat 5-manifolds
admitting the 2-sphere and an additional hypersurface-orthogonal Killing
vector. These are widely studied in the literature, from different physical
approaches, and known variously as the Kramer - Gross - Perry - Davidson - Owen
solutions. The 2-fold infinity of cases that result are studied by way of new
coordinates (which are in most cases global) and the cases likely to be of
interest in any physical approach are distinguished on the basis of the
nakedness and geometrical mass of their associated singularities. It is argued
that the entire class of solutions has to be considered unstable about the
exceptional solutions: the black string and soliton cases. Any physical theory
which admits the non-exceptional solutions as the external vacuua of a
collapsing object has to accept the possibility of collapse to zero volume
leaving behind the weakest possible, albeit naked, geometrical singularities at
the origin.Finally, it is pointed out that these types of solutions generalize,
in a straightforward way, to higher dimensions.


title: First-order Formalism and Odd-derivative Actions

abstract:
  In this pedagogical note, we discuss obstacles to the usual Palatini
formulations of gauge and gravity theories in presence of odd-derivative order,
Chern-Simons, terms.


title:
Generalized strong curvature singularities and weak cosmic censorship in
  cosmological space-times

abstract:
  This paper is a further development of the approach to weak cosmic censorship
proposed by the authors in Ref. 5. We state and prove a modified version of
that work's main result under significantly relaxed assumptions on the
asymptotic structure of space--time. The result, which imposes strong
constraints on the occurrence of naked singularities of the strong curvature
type, is in particular applicable to physically realistic cosmological models.


title: Modifying the Einstein Equations off the Constraint Hypersuface

abstract:
  A new technique is presented for modifying the Einstein evolution equations
off the constraint hypersurface. With this approach the evolution equations for
the constraints can be specified freely. The equations of motion for the
gravitational field variables are modified by the addition of terms that are
linear and nonlocal in the constraints. These terms are obtained from solutions
of the linearized Einstein constraints.


title:
Averaged Energy Inequalities for the Non-Minimally Coupled Classical
  Scalar Field

abstract:
  The stress energy tensor for the classical non-minimally coupled scalar field
is known not to satisfy the point-wise energy conditions of general relativity.
In this paper we show, however, that local averages of the classical stress
energy tensor satisfy certain inequalities. We give bounds for averages along
causal geodesics and show, e.g., that in Ricci-flat background spacetimes, ANEC
and AWEC are satisfied. Furthermore we use our result to show that in the
classical situation we have an analogue to the phenomenon of quantum interest.
These results lay the foundations for analogous energy inequalities for the
quantised non-minimally coupled fields, which will be discussed elsewhere.


title: Cosmology with an Action Principle

abstract:
  The Friedman universe is re-examined in a context that is non-standard only
in that the properties of matter are postulated in the form of an action
principle. Applications to equilibrium configurations of ideal stars have
already been reported. In this paper we apply the same theory to a fresh
examination of the Friedman universe. The results agree with standard theory in
the case of low densities. A suggestion is made to replace "vacuum energy" by
"external force".


title: Cosmological milestones and gravastars - topics in general relativity

abstract:
  In this thesis, we consider two different problems relevant to general
relativity. Over the last few years, opinions on physically relevant
singularities occurring in FRW cosmologies have considerably changed. We
present an extensive catalogue of such cosmological milestones using
generalized power series both at the kinematical and dynamical level. We define
the notion of "scale factor singularity" and explore its relation to polynomial
and differential curvature singularities. We also extract dynamical information
using the Friedmann equations and derive necessary and sufficient conditions
for the existence of cosmological milestones such as big bangs, big crunches,
big rips, sudden singularities and extremality events. Specifically, we provide
a complete characterization of cosmological milestones for which the dominant
energy condition is satisfied. The second problem looks at one of the very
small number of serious alternatives to the usual concept of an astrophysical
black hole, that is, the gravastar model developed by Mazur and Mottola. By
considering a generalized class of similar models with continuous pressure (no
infinitesimally thin shells) and negative central pressure, we demonstrate that
gravastars cannot be perfect fluid spheres: anisotropic pressures are
unavoidable. We provide bounds on the necessary anisotropic pressure and show
that these transverse stresses that support a gravastar permit a higher
compactness than is given by the Buchdahl-Bondi bound for perfect fluid stars.
We also comment on the qualitative features of the equation of state that such
gravastar-like objects without any horizon must have.


title: An Algorithm for Generating Rotating Brans-Dicke Wormhole Solutions

abstract:
  Using the ansatz of Matos and N\'{u}\~{n}ez, the present article proposes an
algorithm for generating several classes, not all independent, of
asymptotically flat rotating wormhole solutions in the Brans-Dicke Theory. The
algorithm allows us to associate a real number}$n$ \textit{with} \textit{each
static and generated rotating solution. We shall also demonstrate how to match
a rotating wormhole to a flat spacetime at the matter boundaries. The vacuum
string extensions of the solutions are straightforward. The physical
interpretations of the solutions are deferred.


title: Symmetries of the Robinson-Trautman equation

abstract:
  We study point symmetries of the Robinson--Trautman equation. The cases of
one- and two-dimensional algebras of infinitesimal symmetries are discussed in
detail. The corresponding symmetry reductions of the equation are given. Higher
dimensional symmetries are shortly discussed. It turns out that all known exact
solutions of the Robinson--Trautman equation are symmetric.


title:
The generalized second law in phantom dominated universes in the
  presence of black holes

abstract:
  This Letter considers the generalized second law of gravitational
thermodynamics in two scenarios featuring a phantom dominated expansion plus a
black hole. The law is violated in both scenarios.


title: On the space-times admitting two shear-free geodesic null congruences

abstract:
  We analyze the space-times admitting two shear-free geodesic null
congruences. The integrability conditions are presented in a plain tensorial
way as equations on the volume element $U$ of the time-like 2--plane that these
directions define. From these we easily deduce significant consequences. We
obtain explicit expressions for the Ricci and Weyl tensors in terms of $U$ and
its first and second order covariant derivatives. We study the different
compatible Petrov-Bel types and give the necessary and sufficient conditions
that characterize every type in terms of $U$. The type D case is analyzed in
detail and we show that every type D space-time admitting a 2+2 conformal
Killing tensor also admits a conformal Killing-Yano tensor.


title: Future Singularities and Completeness in Cosmology

abstract:
  We review recent work on the existence and nature of cosmological
singularities that can be formed during the evolution of generic as well as
specific cosmological spacetimes in general relativity. We first discuss
necessary and sufficient conditions for the existence of geodesically
incomplete spacetimes based on a tensorial analysis of the geodesic equations.
We then classify the possible singularities of isotropic globally hyperbolic
universes using the Bel-Robinson slice energy that closely monitors the
asymptotic properties of fields near the singularity. This classification
includes all known forms of spacetime singularities in isotropic universes and
also predicts new types.


title:
k-Essence, Avoidance of the Weinberg's Cosmological Constant No-Go
  Theorem and Other Dark Energy Effects of Two Measures Field Theory

abstract:
  The dilaton-gravity sector of the Two Measures Field Theory (TMT) is explored
in detail in the context of cosmology. The dilaton \phi dependence of the
effective Lagrangian appears only as a result of the spontaneous breakdown of
the scale invariance. If no fine tuning is made, the effective \phi-Lagrangian
p(\phi,X) depends quadratically upon the kinetic energy X. Hence TMT may
represent an explicit example of the effective k-essence resulting from first
principles without any exotic term in the fundamental action intended for
obtaining this result. Depending of the choice of regions in the parameter
space, TMT exhibits different possible outputs for cosmological dynamics: a)
Possibility of resolution of the old cosmological constant (CC) problem. From
the point of view of TMT, it becomes clear why the old CC problem cannot be
solved (without fine tuning) in the conventional field theories (i.e theories
with only the measure of integration \sqrt{-g} in the action). b) The power law
inflation without any fine tuning can end with damped oscillations of \phi
around the state with zero CC. d) There is a broad range of the parameters such
that: in the late time universe w=p/\rho <-1 and asymptotically (as t\to\infty)
approaches -1 from below; \rho approaches a cosmological constant. The
smallness of the CC may be achieved without fine tuning of dimensionfull
parameters: either by a seesaw type mechanism or due to a correspondence
principle between TMT and conventional field theories.


title: About Starobinsky inflation

abstract:
  It is believed that soon after the Planck era, space time should have a
semi-classical nature. According to this, the escape from General Relativity
theory is unavoidable. Two geometric counter-terms are needed to regularize the
divergences which come from the expected value. These counter-terms are
responsible for a higher derivative metric gravitation. Starobinsky idea was
that these higher derivatives could mimic a cosmological constant. In this work
it is considered numerical solutions for general Bianchi I anisotropic
space-times in this higher derivative theory. The approach is ``experimental''
in the sense that there is no attempt to an analytical investigation of the
results. It is shown that for zero cosmological constant $\Lambda=0$, there are
sets of initial conditions which form basins of attraction that asymptote
Minkowski space. The complement of this set of initial conditions form basins
which are attracted to some singular solutions. It is also shown, for a
cosmological constant $\Lambda> 0$ that there are basins of attraction to a
specific de Sitter solution. This result is consistent with Starobinsky's
initial idea. The complement of this set also forms basins that are attracted
to some type of singular solution. Because the singularity is characterized by
curvature scalars, it must be stressed that the basin structure obtained is a
topological invariant, i.e., coordinate independent.


title: Electromagnetic and Gravitational Radiation of Graviatoms

abstract:
  Graviatom existence conditions have been found. The graviatoms (quantum
systems around mini-black-holes) satisfying these conditions contain the
following charged particles: the electron, muon, tau lepton, wino, pion and
kaon. Electric dipole and quadrupole and gravitational radiations are
calculated for the graviatoms and compared with Hawking's mini-hole radiation.


title:
Correspondence between kinematical backreaction and scalar field
  cosmologies - the `morphon field'

abstract:
  Spatially averaged inhomogeneous cosmologies in classical general relativity
can be written in the form of effective Friedmann equations with sources that
include backreaction terms. In this paper we propose to describe these
backreaction terms with the help of a homogeneous scalar field evolving in a
potential; we call it the `morphon field'. This new field links classical
inhomogeneous cosmologies to scalar field cosmologies, allowing to reinterpret,
e.g., quintessence scenarios by routing the physical origin of the scalar field
source to inhomogeneities in the Universe. We investigate a one-parameter
family of scaling solutions to the backreaction problem. Subcases of these
solutions (all without an assumed cosmological constant) include
scale-dependent models with Friedmannian kinematics that can mimic the presence
of a cosmological constant or a time-dependent cosmological term. We explicitly
reconstruct the scalar field potential for the scaling solutions, and discuss
those cases that provide a solution to the Dark Energy and coincidence
problems. In this approach, Dark Energy emerges from morphon fields, a
mechanism that can be understood through the proposed correspondence: the
averaged cosmology is characterized by a weak decay (quintessence) or growth
(phantom quintessence) of kinematical fluctuations, fed by `curvature energy'
that is stored in the averaged 3-Ricci curvature. We find that the late-time
trajectories of those models approach attractors that lie in the future of a
state that is predicted by observational constraints.


title:
`Third' Quantization of Vacuum Einstein Gravity and Free Yang-Mills
  Theories

abstract:
  Based on the algebraico-categorical (:sheaf-theoretic and sheaf
cohomological) conceptual and technical machinery of Abstract Differential
Geometry, a new, genuinely background spacetime manifold independent, field
quantization scenario for vacuum Einstein gravity and free Yang-Mills theories
is introduced. The scheme is coined `third quantization' and, although it
formally appears to follow a canonical route, it is fully covariant, because it
is an expressly functorial `procedure'. Various current and future Quantum
Gravity research issues are discussed under the light of 3rd-quantization. A
postscript gives a brief account of this author's personal encounters with
Rafael Sorkin and his work.


title: Moller's Energy in the Dyadosphere of a Charged Black Hole

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0304081, gr-qc/0212018, gr-qc/0501002, gr-qc/9601044, and gr-qc/0109017.
  This paper also has excessive overlap with the following papers also written
by the authors or their collaborators: gr-qc/0603027, gr-qc/0511030,
gr-qc/0512080, gr-qc/0607011, gr-qc/0603108, gr-qc/0601141, gr-qc/0603063,
gr-qc/0608050, gr-qc/0607095, gr-qc/0607082, gr-qc/0511095, gr-qc/0601070,
gr-qc/0505078, gr-qc/0607083, gr-qc/0607116, gr-qc/0612016, and others.


title:
ZM theory IV: Introduction to quantum concepts, Klein-Gordon and Dirac's
  equations

abstract:
  We describe a general approach to the correspondence of ZM theory with
quantum electrodynamics. As a first step, we show the correspondence of helical
clock-field states with plane wave states of the Dirac equation. Specifically,
defining the direction of time as the gradient of the field in the combined
field and space dimensions, for constant gradients, results in states that are
consistent with conventional plane wave Dirac equation eigenfunctions.
Particles and antiparticles, as well as up and down spins are related by axis
inversions. The Dirac wavefunction represents the clock-field and the observer
defined direction of time and spatial coordinate axes rotation relative to the
region of observation. Additional steps showing the correspondence of ZM theory
to quantum mechanics and the Dirac equation are deferred to subsequent papers.


title: Entropy of Microwave Background Radiation in Observable Universe

abstract:
  We show that the cosmological constant at late time places a bound on the
entropy of microwave background radiation deposited in the future event horizon
of a given observer, $S\leq S_{\Lambda_0}^{3/4}$. This bound is independent of
the energy scale of reheating and the FRW evolution after reheating. We also
discuss why the entropy of microwave background in our observable universe has
its present value.


title: Cosmology in three dimensions: steps towards the general solution

abstract:
  We use covariant and first-order formalism techniques to study the properties
of general relativistic cosmology in three dimensions. The covariant approach
provides an irreducible decomposition of the relativistic equations, which
allows for a mathematically compact and physically transparent description of
the 3-dimensional spacetimes. Using this information we review the features of
homogeneous and isotropic 3-d cosmologies, provide a number of new solutions
and study gauge invariant perturbations around them. The first-order formalism
is then used to provide a detailed study of the most general 3-d spacetimes
containing perfect-fluid matter. Assuming the material content to be dust with
comoving spatial 2-velocities, we find the general solution of the Einstein
equations with non-zero (and zero) cosmological constant and generalise known
solutions of Kriele and the 3-d counterparts of the Szekeres solutions. In the
case of a non-comoving dust fluid we find the general solution in the case of
one non-zero fluid velocity component. We consider the asymptotic behaviour of
the families of 3-d cosmologies with rotation and shear and analyse their
singular structure. We also provide the general solution for cosmologies with
one spacelike Killing vector, find solutions for cosmologies containing scalar
fields and identify all the PP-wave 2+1 spacetimes.


title: The black hole horizon as a dynamical system

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 contribution, in which earlier results
are rederived and elaborated upon, we first 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. We demonstrate that, unlike classical black
holes, the quantized black hole has on its horizon an imprint of its (recent)
past history, i.e., quantum hair. The relation between in- and outgoing states
depends on this imprint. As a first step towards the inclusion of non-Abelian
interactions, we then compute the effects of magnetic monopoles both in the
in-states and in the out-states. They completely modify, and indeed simplify,
our algebra.


title: Ideal Stars and General Relativity

abstract:
  We study a system of differential equations that governs the distribution of
matter in the theory of General Relativity. The new element in this paper is
the use of a dynamical action principle that includes all the degrees of
freedom, matter as well as metric. The matter lagrangian defines a relativistic
version of non-viscous, isentropic hydrodynamics. The matter fields are a
scalar density and a velocity potential; the conventional, four-vector velocity
field is replaced by the gradient of the potential and its scale is fixed by
one of the eulerian equations of motion, an innovation that significantly
affects the imposition of boundary conditions. If the density is integrable at
infinity, then the metric approaches the Schwarzschild metric at large
distances. There are stars without boundary and with finite total mass; the
metric shows rapid variation in the neighbourhood of the Schwarzschild radius
and there is a very small core where a singularity indicates that the gas laws
break down. For stars with boundary there emerges a new, critical relation
between the radius and the gravitational mass, a consequence of the stronger
boundary conditions. Tentative applications are suggested, to certain Red
Giants, and to neutron stars, but the investigation reported here was limited
to polytropic equations of state. Comparison with the results of Oppenheimer
and Volkoff on neutron cores shows a close agreement of numerical results.
However, in the model the boundary of the star is fixed uniquely by the
required matching of the interior metric to the external Schwarzschild metric,
which is not the case in the traditional approach.


title: The Momentum 4-Vector in Bulk Viscous Bianchi Type-V Space-time

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0611031, "Generation of Bianchi type V bulk viscous cosmological models
with time dependent Lambda-term," by A. Pradhan, K. Jotania and A. Rai; Phys.
Rev. D 41, 1086 (1990), "Energy associated with a Kerr-Newman black hole," by
K. S. Virbhadra; and gr-qc/0303034, "The energy of the universe in teleparallel
gravity," by T. Vargas.


title:
Constraints on Distance Duality Relation from Sunyaev Zel'dovich Effect
  and Chandra X-ray measurements

abstract:
  We demonstrate that the recent measurements of the angular diameter distance
of 38 cluster of galaxies using Chandra X-ray data and radio observations from
the OVRO and BIMA interferometric arrays place new and independent constraints
on deviations in the duality relation between angular and luminosity distances.
Using only cluster data, we found that the ratio between the two distances
defined as $\eta = D_L/D_A(1+z)^2.$ is bound to be $\eta=0.97\pm0.03$ at 68%
c.l. with no evidence for distance duality violation. Comparing the cluster
angular diameter distance data with luminosity distance data from type Ia
Supernovae, we obtain the model independent constraint $\eta=1.01\pm0.07$ at
68% c.l.. Those results provide an useful check for the cosmological
concordance model and for the presence of systematics in SN-Ia and clusters
data.


title: Chaplygin gas in light of recent Integrated Sachs--Wolfe effect data

abstract:
  We investigate the possibility of constraining Chaplygin dark energy models
with current Integrated Sachs Wolfe effect data. In the case of a flat universe
we found that generalized Chaplygin gas models must have an energy density such
that $\Omega_c >0.55$ and an equation of state $w <-0.6$ at 95% c.l.. We also
investigate the recently proposed Silent Chaplygin models, constraining
$\Omega_c >0.55$ and $w <-0.65$ at 95% c.l.. Better measurements of the CMB-LSS
correlation will be possible with the next generation of deep redshift surveys.
This will provide independent and complementary constraints on unified dark
energy models such as the Chaplygin gas.


title: Collisions of rigidly rotating disks of dust in General Relativity

abstract:
  We discuss inelastic collisions of two rotating disks by using the
conservation laws for baryonic mass and angular momentum. In particular, we
formulate conditions for the formation of a new disk after the collision and
calculate the total energy loss to obtain upper limits for the emitted
gravitational energy.


title: Non-Singular Bouncing Universes in Loop Quantum Cosmology

abstract:
  Non-perturbative quantum geometric effects in Loop Quantum Cosmology predict
a $\rho^2$ modification to the Friedmann equation at high energies. The
quadratic term is negative definite and can lead to generic bounces when the
matter energy density becomes equal to a critical value of the order of the
Planck density. The non-singular bounce is achieved for arbitrary matter
without violation of positive energy conditions. By performing a qualitative
analysis we explore the nature of the bounce for inflationary and Cyclic model
potentials. For the former we show that inflationary trajectories are
attractors of the dynamics after the bounce implying that inflation can be
harmoniously embedded in LQC. For the latter difficulties associated with
singularities in cyclic models can be overcome. We show that non-singular
cyclic models can be constructed with a small variation in the original Cyclic
model potential by making it slightly positive in the regime where scalar field
is negative.


title: Generally covariant quantization and the Dirac field

abstract:
  Canonical Hamiltonian field theory in curved spacetime is formulated in a
manifestly covariant way. Second quantization is achieved invoking a
correspondence principle between the Poisson bracket of classical fields and
the commutator of the corresponding quantum operators. The Dirac theory is
investigated and it is shown that, in contrast to the case of bosonic fields,
in curved spacetime, the field momentum does not coincide with the generators
of spacetime translations. The reason is traced back to the presence of second
class constraints occurring in Dirac theory. Further, it is shown that the
modification of the Dirac Lagrangian by a surface term leads to a momentum
transfer between the Dirac field and the gravitational background field,
resulting in a theory that is free of constraints, but not manifestly
hermitian.


title: On Perturbation Spectra of N-flation

abstract:
  In this note we study the adiabatic perturbation spectrum of N-flation with
power law potential. We show that the scalar spectrum of N-flation is generally
redder than that of its corresponding single field. The result obtained for
that with unequal massive fields is consistent with the recent numerical
investigation of Kim and Liddle.


title: Kerr geometry beyond the Quantum theory

abstract:
  The Dirac electron theory and QED do not take into account gravitational
field, while the corresponding Kerr-Newman solution with parameters of electron
has very strong stringy, topological and non-local action on the Compton
distances, polarizing space-time and deforming the Coulomb field. We discuss
the relation of the electron to the Kerr's microgeon model and argue that the
Kerr geometry may be hidden beyond the Quantum Theory. In particular, we show
that the Foldi-Wouthuysen `mean-position' operator of the Dirac electron is
related to a complex representation of the Kerr geometry, and to a complex
stringy source. Therefore, the complex Kerr geometry may be hidden beyond the
Dirac equation.


title:
Post-Newtonian equation for the energy levels of a Dirac particle in a
  static metric

abstract:
  We study first the Hamiltonian operator H corresponding to the Fock-Weyl
extension of the Dirac equation to gravitation. When searching for stationary
solutions to this equation, in a static metric, we show that just one invariant
Hermitian product appears natural. In the case of a space-isotropic metric, H
is Hermitian for that product. Then we investigate the asymptotic
post-Newtonian approximation of the stationary Schroedinger equation associated
with H, for a slow particle in a weak-field static metric. We rewrite the
expanded equations as one equation for a two-component spinor field. This
equation contains just the non-relativistic Schroedinger equation in the
gravity potential, plus correction terms. Those "correction" terms are of the
same order in the small parameter as the "main" terms, but are numerically
negligible in the case of ultra-cold neutrons in the Earth's gravity.


title: Approximate initial data for binary black holes

abstract:
  We construct approximate analytical solutions to the constraint equations of
general relativity for binary black holes of arbitrary mass ratio in
quasicircular orbit. We adopt the puncture method to solve the constraint
equations in the transverse-traceless decomposition and consider perturbations
of Schwarzschild black holes caused by boosts and the presence of a binary
companion. A superposition of these two perturbations then yields approximate,
but fully analytic binary black hole initial data that are accurate to first
order in the inverse of the binary separation and the square of the black
holes' momenta.


title: Comment on "The Cosmic Time in Terms of the Redshift", by Carmeli et al

abstract:
  The time-redshift relation of Carmeli et al. differs from that of the
standard flat LambdaCDM model by more than 500 million years for 1 < z < 4.5.


title:
The Vector-Tensor nature of Bekenstein's relativistic theory of Modified
  Gravity

abstract:
  Bekenstein's theory of relativistic gravity is conventionally written as a
bi-metric theory. The two metrics are related by a disformal transformation
defined by a dynamical vector field and a scalar field. In this comment we show
that the theory can be re-written as Vector-Tensor theory akin to
Einstein-Aether theories with non-canonical kinetic terms. We discuss some of
the implications of this equivalence.


title:
Low-energy sector of 8-dimensional General Relativity: Electro-Weak
  model and neutrino mass

abstract:
  In a Kaluza-Klein space-time $V^{4}\otimes S^{3}$, we demonstrate that the
dimensional reduction of spinors provides a 4-field, whose associated SU(2)
gauge connections are geometrized. However, additional and gauge-violating
terms arise, but they are highly suppressed by a factor $\beta$, which fixes
the amount of the spinor dependence on extra-coordinates. The application of
this framework to the Electro-Weak model is performed, thus giving a lower
bound for $\beta$ from the request of the electric charge conservation.
Moreover, we emphasize that also the Higgs sector can be reproduced, but
neutrino masses are predicted and the fine-tuning on the Higgs parameters can
be explained, too.


title: On asymptotic behavior of anisotropic Dvali-Gabadadze-Porrati branes

abstract:
  The braneworld model of Dvali-Gabadadze-Porrati (DGP) provides an interesting
alternative to a positive cosmological constant by modifying gravity at large
distances. We investigate the asymptotic behavior of homogeneous and
anisotropic cosmologies on the DGP brane. It is shown that all Bianchi models
except type IX isotropize, as in general relativity, if the so called
$E_{\mu\nu}$ term satisfies some energy condition. Isotropization can proceed
slower in DGP gravity than in general relativity.


title: Tidal fields on braneworlds

abstract:
  We write out the geodesic deviations that take place in a $d\geq 4$
dimensional brane world subspace of a higher dimensional spacetime by splitting
out the brane and the extra space dynamical quantities from a global metric
spacetime of dimension $D\geq 5$. The higher dimensional dynamical quantities
are projected onto two orthogonal subspaces, where one of which is identified
with a $(d-1)$-brane. This is done by using some technics of the conventional
submanifold theory of the Riemannian geometry, applied to pseudo-Riemannian
spaces. Using the splitting technic, we obtain the tidal field on $(d-1)$
branes with an arbitrary number of non compact extra dimensions. Later, we
analise the geodesic deviations seen by an ordinary observer in a $d=4$
dimensional spacetime and show that deviations from general relativity tidal
field due to the existence of the extra dimensions can appear because, (i) -
the dependence of the indunced metric on the brane with the extra coordinates
and (ii) - deviations of the higher dimensional spacetime metric from spherical
symmetry.


title:
10-Dim Einstein spaces made up on basis of 6-Dim Ricci-flat spaces and
  4-Dim Einstein spaces

abstract:
  Some examples of ten-dimensional vacuum Einstein spaces made up on basis of
four-dimensional Ricci-flat spaces and six-dimensional Ricci-flat spaces
defined by solutions of the Sin-Gordon equation are constructed. The properties
of geodesics for such type of the spaces are discussed


title: Relativistic Positioning Systems: The Emission Coordinates

abstract:
  This paper introduces some general properties of the gravitational metric and
the natural basis of vectors and covectors in 4-dimensional emission
coordinates. Emission coordinates are a class of space-time coordinates defined
and generated by 4 emitters (satellites) broadcasting their proper time by
means of electromagnetic signals. They are a constitutive ingredient of the
simplest conceivable relativistic positioning systems. Their study is aimed to
develop a theory of these positioning systems, based on the framework and
concepts of general relativity, as opposed to introducing `relativistic
effects' in a classical framework. In particular, we characterize the causal
character of the coordinate vectors, covectors and 2-planes, which are of an
unusual type. We obtain the inequality conditions for the contravariant metric
to be Lorentzian, and the non-trivial and unexpected identities satisfied by
the angles formed by each pair of natural vectors. We also prove that the
metric can be naturally split in such a way that there appear 2 parameters
(scalar functions) dependent exclusively on the trajectory of the emitters,
hence independent of the time broadcast, and 4 parameters, one for each
emitter, scaling linearly with the time broadcast by the corresponding
satellite, hence independent of the others.


title: Classic field theories of gravitation embedded in ten dimensions

abstract:
  Two classic field theories of metric gravitation are given as
constant-coefficient Exterior Differential Systems (EDS) on the flat
orthonormal frame bundle over ten dimensional space. They are derivable by
variation of Cartan 4-forms, and shown to be well-posed by calculation of their
Cartan characteristic integers. Their solutions are embedded Riemannian
4-spaces. The first theory is generated by torsion 2-forms and Ricci-flat
3-forms and is a constant-coefficient EDS for vacuum tetrad gravity; its Cartan
character table is the same as found for an EDS recently given in terms of
tetrad frame and connection variables [1] [2]. The second constant-coefficient
EDS is generated solely by 2-forms, and has a Cartan form of quadratic
Yang-Mills type. Its solutions lie in torsion free 6-spaces and are fibered
over 3-spaces. We conjecture that these solutions may be classically related to
10-dimensional quantum field theoretic constructions of cosmological vacua [3].


title:
On the Existence of the Logarithmic Correction Term in Black Hole
  Entropy-Area Relation

abstract:
  In this paper we consider a model universe with large extra dimensions to
obtain a modified black hole entropy-area relation. We use the generalized
uncertainty principle to find a relation between the number of spacetime
dimensions and the presence or vanishing of logarithmic prefactor in the black
hole entropy-area relation. Our calculations are restricted to the
microcanonical ensembles and we show that in the modified entropy-area
relation, the microcanonical logarithmic prefactor appears only when spacetime
has an even number of dimensions.


title: Modified GR and Helium Nucleosynthesis

abstract:
  We show that a previously proposed cosmological model based on general
relativity with non vanishing divergence for the energy-momentum tensor is
consistent with the observed values for the nucleosynthesis of helium for some
values of the arbitrary parameter $\alpha$ presented in this model. Further
more values of $\alpha$ can be accommodated if we adopt the Randall-Sundrum
single brane model.


title: Gauge-noninvariance of quantum cosmology and vacuum dark energy

abstract:
  We address the question how to adapt cosmological constant $\Lambda$ for
description of a vacuum dark energy density jumping from the big initial value
to the small today value suggested by observations. We find such a possibility
in the gauge-noninvariance of quantum cosmology which leads to a connection
between a choice of the gauge and quantum spectrum for a certain physical
quantity which can be specified in the framework of the minisuperspace model.
We introduce a particular gauge in which the cosmological constant $\Lambda$ is
quantized and show that making a measurement of $\Lambda$ today one can find
its small value with the biggest probability, while at the beginning of the
evolution, the biggest probability corresponds to its biggest value.
Transitions between quantum levels of $\Lambda$ in the course of the Universe
evolution, could be related to several scales for symmetry breaking.


title: Lorentzian Wormholes in the Friedman-Robertson-Walker Universe

abstract:
  The metric of some Lorentzian wormholes in the background of the FRW universe
is obtained. It is shown that for a de Sitter space-time the new solution is
supported by Phantom Energy. The wave equation for a scalar field in such
backgrounds is separable. The form of the potential for the Schr\"{o}dinger
type one dimensional wave equation is found.


title: The Dirac propagator in the Kerr-Newman metric

abstract:
  We give an alternative proof of the completeness of the Chandrasekhar ansatz
for the Dirac equation in the Kerr-Newman metric. Based on this, we derive an
integral representation for smooth compactly supported functions which in turn
we use to derive an integral representation for the propagator of solutions of
the Cauchy problem with initial data in the above class of functions. As a
by-product, we also obtain the propagator for the Dirac equation in the
Minkowski space-time in oblate spheroidal coordinates.


title: Scattering for massive Dirac fields on the Kerr metric

abstract:
  Starting with the Dirac equation outside the event horizon of a non-extreme
Kerr black hole, we develop a time-dependent scattering theory for massive
Dirac particles. The explicit computation of the modified wave operators at
infinity is done by implementing a time-dependent logarithmic phase shift from
the free dynamics to offset the long range term in the full Hamiltonian due to
the presence of the gravitational force. Analytical expressions for the wave
operators are also given.


title: Energetics of the Einstein-Rosen spacetime

abstract:
  A study covering some aspects of the Einstein--Rosen metric is presented. The
electric and magnetic parts of the Weyl tensor are calculated. It is shown that
there are no purely magnetic E--R spacetimes, and also that a purely electric
E--R spacetime is necessarily static. The geodesics equations are found and
circular ones are analyzed in detail. The super--Poynting and the
``Lagrangian'' Poynting vectors are calculated and their expressions are found
for two specific examples. It is shown that for a pulse--type solution, both
expressions describe an inward radially directed flow of energy, far behind the
wave front. The physical significance of such an effect is discussed.


title:
Stable radiation-controlling boundary conditions for the generalized
  harmonic Einstein equations

abstract:
  This paper is concerned with the initial-boundary value problem for the
Einstein equations in a first-order generalized harmonic formulation. We impose
boundary conditions that preserve the constraints and control the incoming
gravitational radiation by prescribing data for the incoming fields of the Weyl
tensor. High-frequency perturbations about any given spacetime (including a
shift vector with subluminal normal component) are analyzed using the
Fourier-Laplace technique. We show that the system is boundary-stable. In
addition, we develop a criterion that can be used to detect weak instabilities
with polynomial time dependence, and we show that our system does not suffer
from such instabilities. A numerical robust stability test supports our claim
that the initial-boundary value problem is most likely to be well-posed even if
nonzero initial and source data are included.


title:
Formation of a Black String in a Higher Dimensional Vacuum Gravitational
  Collapse

abstract:
  We present a solution to the vacuum Einstein Equations which represents a
collapse of a gravitational wave in 5 dimensions. Depending on the focal length
of the wave, the collapse results, either in a black string covered by a
horizon, or in a naked singularity which can be removed.


title: Generalized Lemaitre-Tolman-Bondi Solutions with Pressure

abstract:
  Utilizing the ADM equations, we derive a metric and reduced field equations
describing a general, spherically symmetric perfect fluid. The metric describes
both the interior perfect fluid region and exterior vacuum Schwarzschild
spacetime in a single coordinate patch. The exterior spacetime is in
generalized Painleve-Gullstrand coordinates which is an infinite class of
coordinate systems. In the static limit the system reduces to a
Tolman-Oppenheimer-Volkoff equation on the interior with the exterior in
Schwarzschild coordinates. We show the coordinate transformation for the
non-static cases to comoving coordinates, where the metric is seen to be a
direct generalization of the Lemaitre-Tolman-Bondi spacetime to include
pressures.


title: Inflaton perturbations in brane-world cosmology with induced gravity

abstract:
  We study cosmological perturbations in the brane models with an induced
Einstein-Hilbert term on a brane. We consider an inflaton confined to a de
Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations
excite Kaluza-Klein modes of bulk metric perturbations with mass $m^2 =
-2(2\ell-1) (\ell +1) H^2$ and $m^2 = -2\ell(2\ell+3) H^2$ where $\ell$ is an
integer. There are two branches ($\pm$ branches) of solutions for the
background spacetime. In the $+$ branch, which includes the self-accelerating
universe, a resonance appears for a mode with $m^2 = 2 H^2$ due to a spin-0
perturbation with $m^2 = 2H^2$. The self-accelerating universe has a distinct
feature because there is also a helicity-0 mode of spin-2 perturbations with
$m^2 = 2H^2$. In the $-$ branch, which can be thought as the Randall-Sundrum
type brane-world with the high energy quantum corrections, there is no
resonance. At high energies, we analytically confirm that four-dimensional
Einstein gravity is recovered, which is related to the disappearance of van
Dam-Veltman-Zakharov discontinuity in de Sitter spacetime.
  On sufficiently small scales, we confirm that the lineariaed gravity on the
brane is well described by the Brans-Dicke theory with $\omega=3Hr_c$ in $-$
branch and $\omega = -3H r_c$ in $+$ branch, respectively, which confirms the
existence of the ghost in $+$ branch. We also study large scale perturbations.
In $+$ branch, the resonance induces a non-trivial anisotropic stress on the
brane via the projection of Weyl tensor in the bulk, but no instability is
shown to exist on the brane.


title:
The new cosmological model founded on the Scale Covariant Theory of
  Gravitation and on the Dirac's Large Number Hypothesis. (Part 1)

abstract:
  The new scale-covariant formulation of the Dirac's Large Number Hypothesis
(LNH) is proposed. The basic equations of LNH are formulated in the
scale-covariant and "G-invariant" (invariant on the transformation law for G)
form. On the basis of the Scale Covariant Theory of Gravitation and Dirac's LNH
the cosmological model is constructed that gives as result the closed static
Einstein's Universe in the gravitational system of units (g.s.u.) and the
closed expanding Universe in the atomic system of units (a.s.u.). The simple
dynamical model of atomic clock is proposed that leads to the same connection
between the a.s.u. and the g.s.u. as the LNH and allows to specify the
parameters of the model. The question about the equivalence of inertial and
gravitational masses in the arbitrary system of units is ivestigated. It is
deduced that the equivalence of inertial and gravitational masses in the
arbitrary system of units takes place only for the unique transformation law
for G even if the equivalence of two kinds of mass in the g.s.u. is assumed. It
is shown that the model predicts the conservation of the black-body spectrum of
the microvave background radiation independently of choice of the
transformation law for G. It is argued that the some paradoxes of the standard
cosmology can be overcomed in the given model without the supposition about the
existence in the past of a phase of inflationary expansion.


title:
Spontaneously Induced Gravity: From Rippled Dark Matter to Einstein
  Corpuscles

abstract:
  Suppose General Relativity, provocatively governed by a dimensional coupling
constant, is a spontaneously induced theory of Gravity. Invoking Zee's
mechanism, we represent the reciprocal Newton constant by a Brans Dicke scalar
field, and let it damped oscillating towards its General Relativistic VEV. The
corresponding cosmological evolution, in the Jordan frame, averagely resembles
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of the theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the strict General Relativity limit. Also
derived is the spherically symmetric static configuration associated with
spontaneously induced General Relativity. At the stiff scalar potential limit,
the exterior Schwarzschild solution is recovered. However, due to level
crossing at the would have been horizon, it now connects with a novel dark core
characterized by a locally varying Newton constant. The theory further predicts
light Einstein-style gravitational corpuscles (elementary particles?) which
become point-like at the GR-limit.


title:
A hybrid approach to black hole perturbations from extended matter
  sources

abstract:
  We present a new method for the calculation of black hole perturbations
induced by extended sources in which the solution of the nonlinear
hydrodynamics equations is coupled to a perturbative method based on
Regge-Wheeler/Zerilli and Bardeen-Press-Teukolsky equations when these are
solved in the frequency domain. In contrast to alternative methods in the time
domain which may be unstable for rotating black-hole spacetimes, this approach
is expected to be stable as long as an accurate evolution of the matter sources
is possible. Hence, it could be used under generic conditions and also with
sources coming from three-dimensional numerical relativity codes. As an
application of this method we compute the gravitational radiation from an
oscillating high-density torus orbiting around a Schwarzschild black hole and
show that our method is remarkably accurate, capturing both the basic
quadrupolar emission of the torus and the excited emission of the black hole.


title:
Realistic Exact Solution for the Exterior Field of a Rotating Neutron
  Star

abstract:
  A new six-parametric, axisymmetric and asymptotically flat exact solution of
Einstein-Maxwell field equations having reflection symmetry is presented. It
has arbitrary physical parameters of mass, angular momentum, mass--quadrupole
moment, current octupole moment, electric charge and magnetic dipole, so it can
represent the exterior field of a rotating, deformed, magnetized and charged
object; some properties of the closed-form analytic solution such as its
multipolar structure, electromagnetic fields and singularities are also
presented. In the vacuum case, this analytic solution is matched to some
numerical interior solutions representing neutron stars, calculated by Berti &
Stergioulas (Mon. Not. Roy. Astron. Soc. 350, 1416 (2004)), imposing that the
multipole moments be the same. As an independent test of accuracy of the
solution to describe exterior fields of neutron stars, we present an extensive
comparison of the radii of innermost stable circular orbits (ISCOs) obtained
from Berti & Stergioulas numerical solutions, Kerr solution (Phys. Rev. Lett.
11, 237 (1963)), Hartle & Thorne solution (Ap. J. 153, 807, (1968)), an
analytic series expansion derived by Shibata & Sasaki (Phys. Rev. D. 58 104011
(1998)) and, our exact solution. We found that radii of ISCOs from our solution
fits better than others with realistic numerical interior solutions.


title: Gravity: A New Holographic Perspective

abstract:
  A general paradigm for describing classical (and semiclassical) gravity is
presented. This approach brings to the centre-stage a holographic relationship
between the bulk and surface terms in a general class of action functionals and
provides a deeper insight into several aspects of classical gravity which have
no explanation in the conventional approach. After highlighting a series of
unresolved issues in the conventional approach to gravity, I show that (i)
principle of equivalence, (ii) general covariance and (iii)a reasonable
condition on the variation of the action functional, suggest a generic
Lagrangian for semiclassical gravity of the form $L=Q_a^{bcd}R^a_{bcd}$ with
$\nabla_b Q_a^{bcd}=0$. The expansion of $Q_a^{bcd}$ in terms of the
derivatives of the metric tensor determines the structure of the theory
uniquely. The zeroth order term gives the Einstein-Hilbert action and the first
order correction is given by the Gauss-Bonnet action. Any such Lagrangian can
be decomposed into a surface and bulk terms which are related holographically.
The equations of motion can be obtained purely from a surface term in the
gravity sector. Hence the field equations are invariant under the
transformation $T_{ab} \to T_{ab} + \lambda g_{ab}$ and gravity does not
respond to the changes in the bulk vacuum energy density. The cosmological
constant arises as an integration constant in this approach. The implications
are discussed.


title: Einstein-Cartan Theory

abstract:
  The Einstein--Cartan Theory (ECT) of gravity is a modification of General
Relativity Theory (GRT), allowing space-time to have torsion, in addition to
curvature, and relating torsion to the density of intrinsic angular momentum.
This modification was put forward in 1922 by Elie Cartan, before the discovery
of spin. Cartan was influenced by the work of the Cosserat brothers (1909), who
considered besides an (asymmetric) force stress tensor also a moments stress
tensor in a suitably generalized continuous medium.


title:
APSIS - an Artificial Planetary System in Space to probe
  extra-dimensional gravity and MOND

abstract:
  A proposal is made to test Newton's inverse-square law using the perihelion
shift of test masses (planets) in free fall within a spacecraft located at the
Earth-Sun L2 point. Such an Artificial Planetary System In Space (APSIS) will
operate in a drag-free environment with controlled experimental conditions and
minimal interference from terrestrial sources of contamination. We demonstrate
that such a space experiment can probe the presence of a "hidden" fifth
dimension on the scale of a micron, if the perihelion shift of a "planet" can
be measured to sub-arc-second accuracy. Some suggestions for spacecraft design
are made.


title:
Rigid upper bounds for the angular momentum and centre of mass of
  non-singular asymptotically anti-de Sitter space-times

abstract:
  We prove upper bounds on angular momentum and centre of mass in terms of the
Hamiltonian mass and cosmological constant for non-singular asymptotically
anti-de Sitter initial data sets satisfying the dominant energy condition. We
work in all space-dimensions larger than or equal to three, and allow a large
class of asymptotic backgrounds, with spherical and non-spherical conformal
infinities; in the latter case, a spin-structure compatibility condition is
imposed. We give a large class of non-trivial examples saturating the
inequality. We analyse exhaustively the borderline case in space-time dimension
four: for spherical cross-sections of Scri, equality together with completeness
occurs only in anti-de Sitter space-time. On the other hand, in the toroidal
case, regular non-trivial initial data sets saturating the bound exist.


title: Evidence for an entropy bound from fundamentally discrete gravity

abstract:
  The various entropy bounds that exist in the literature suggest that
spacetime is fundamentally discrete, and hint at an underlying relationship
between geometry and "information". The foundation of this relationship is yet
to be uncovered, but should manifest itself in a theory of quantum gravity. We
present a measure for the maximal entropy of spherically symmetric spacelike
regions within the causal set approach to quantum gravity. In terms of the
proposal, a bound for the entropy contained in this region can be derived from
a counting of potential "degrees of freedom" associated to the Cauchy horizon
of its future domain of dependence. For different spherically symmetric
spacelike regions in Minkowski spacetime of arbitrary dimension, we show that
this proposal leads, in the continuum approximation, to Susskind's well-known
spherical entropy bound.


title: Tunnelling Effect and Hawking Radiation from a Vaidya Black Hole

abstract:
  In this paper, we extend Parikh' work to the non-stationary black hole. As an
example of the non-stationary black hole, we study the tunnelling effect and
Hawking radiation from a Vaidya black hole whose Bondi mass is identical to its
mass parameter. We view Hawking radiation as a tunnelling process across the
event horizon and calculate the tunnelling probability. We find that the result
is different from Parikh's work because $\frac{dr_{H}}{dv}$ is the function of
Bondi mass m(v).


title:
How often does the Unruh-DeWitt detector click? Regularisation by a
  spatial profile

abstract:
  We analyse within first-order perturbation theory the instantaneous
transition rate of an accelerated Unruh-DeWitt particle detector whose coupling
to a massless scalar field on four-dimensional Minkowski space is regularised
by a spatial profile. For the Lorentzian profile introduced by Schlicht, the
zero size limit is computed explicitly and expressed as a manifestly finite
integral formula that no longer involves regulators or limits. The same
transition rate is obtained for an arbitrary profile of compact support under a
modified definition of spatial smearing. Consequences for the asymptotic
behaviour of the transition rate are discussed. A number of stationary and
nonstationary trajectories are analysed, recovering in particular the Planckian
spectrum for uniform acceleration.


title:
Evolution Operators for Linearly Polarized Two-Killing Cosmological
  Models

abstract:
  We give a general procedure to obtain non perturbative evolution operators in
closed form for quantized linearly polarized two Killing vector reductions of
general relativity with a cosmological interpretation. We study the
representation of these operators in Fock spaces and discuss in detail the
conditions leading to unitary evolutions.


title: Polymer quantization of CGHS model- I

abstract:
  We present a polymer(loop) quantization of a two dimensional theory of
dilatonic gravity known as the CGHS model. We recast the theory as a
parametrized free field theory on a flat 2-dimensional spacetime and quantize
the resulting phase space using techniques of loop quantization. The resulting
(kinematical) Hilbert space admits a unitary representation of the spacetime
diffeomorphism group. We obtain the complete spectrum of the theory using a
technique known as group averaging and perform quantization of Dirac
observables on the resulting Hilbert space. We argue that the algebra of Dirac
observables gets deformed in the quantum theory. Combining the ideas from
parametrized field theory with certain relational observables, evolution is
defined in the quantum theory in the Heisenberg picture. Finally the dilaton
field is quantized on the physical Hilbert space which carries information
about quantum geometry.


title:
High-order corrections to the holographic entropy bound from quantum
  field theory

abstract:
  From the viewpoint of local quantum field theory, this letter investigates
the high-order corrections to the holographic entropy bound. As a result, the
logarithmic correction term appears naturally with the definite coefficient
$-{1/2}$, which thus provides another semi-classical platform to examine such
candidates for quantum gravity as Loop Quantum Gravity and String Theory.


title: Generating anisotropic fluids from vacuum Ernst equations

abstract:
  Starting with any stationary axisymmetric vacuum metric, we build anisotropic
fluids. With the help of the Ernst method, the basic equations are derived
together with the expression for the energy-momentum tensor and with the
equation of state compatible with the field equations. The method is presented
by using different coordinate systems: the cylindrical coordinates $\rho, z$
and the oblate spheroidal ones. A class of interior solutions matching with
stationary axisymmetric asymptotically flat vacuum solutions is found in oblate
spheroidal coordinates. The solutions presented satisfy the three energy
conditions.


title:
Nonlinear Interactions Between Gravitational Radiation and Modified
  Alfven Modes in Astrophysical Dusty Plasmas

abstract:
  We present an investigation of nonlinear interactions between Gravitational
Radiation and modified Alfv\'{e}n modes in astrophysical dusty plasmas.
Assuming that stationary charged dust grains form neutralizing background in an
electron-ion-dust plasma, we obtain the three wave coupling coefficients, and
calculate the growth rates for parametrically coupled gravitational radiation
and modified Alfv\'{e}n-Rao modes. The threshold value of the gravitational
wave amplitude associated with convective stabilization is particularly small
if the gravitational frequency is close to twice the modified Alfv\'en
wave-frequency. The implication of our results to astrophysical dusty plasmas
is discussed.


title: Dark energy from gravitational collapse?

abstract:
  We discuss the status of both cosmological and black hole type singularities
in the framework of the brane-world model of gravity. We point out that the Big
Bang is not properly understood yet. We also show new features of the
gravitational collapse on the brane, the most important being the production of
dark energy during the collapse.


title: A semiclassical tetrahedron

abstract:
  We construct a macroscopic semiclassical state state for a quantum
tetrahedron. The expectation values of the geometrical operators representing
the volume, areas and dihedral angles are peaked around assigned classical
values, with vanishing relative uncertainties.


title: Tetrads in low-energy weak interactions

abstract:
  Tetrads are introduced in order to study the relationship between gravity and
particle interactions, specially in weak processes at low energy. Through
several examples like inverse Muon decay, elastic Neutrino-Electron scattering,
it is explicitly shown how to assign to each vertex of the corresponding
low-order Feynman diagram in a weak interaction, a particular set of tetrad
vectors. The relationship between the tetrads associated to different vertices
is exhibited explicitly to be generated by a SU(2) local gauge transformation.


title: Branes: cosmological surprise and observational deception

abstract:
  Using some supernovae and CMB data, we constrain the Cardassian,
Randall-Sundrum, and Dvali-Gabadadze-Porrati brane-inspired cosmological
models. We show that a transient acceleration and an early loitering period are
usually excluded by the data. Moreover, the three models are equivalent to some
usual quintessence/ghost dark energy models defined by a barotropic index
$\gamma_\phi$ depending on the redshift. We calculate this index for each model
and show that they mimic a universe close to a $\Lambda CDM$ model today.


title: Concepts of Intertial and Gravitational Mass

abstract:
  The general relativistic notion of gravitational and inertial mass is
discussed from the general viewpoint of the tidal forces implicit in the
curvature and the Einstein field equations within ponderable matter. A simple
yet rigorously general derivation is given for the Tolman gravitational mass
viewpoint wherein the computation of gravitational mass requires both a rest
energy contribution (the inertial mass) and a pressure contribution. The
pressure contribution is extremely small under normal conditions which implies
the equality of gravitational and inertial mass to a high degree of accuracy.
However, the pressure contribution is substantial for conformal symmetric
systems such as Maxwell radiation, whose constituent photons are massless.
Implications of the Tolman mass for standard cosmology and standard high energy
particle physics models are briefly explored.


title: On obtaining classical mechanics from quantum mechanics

abstract:
  Constructing a classical mechanical system associated with a given quantum
mechanical one, entails construction of a classical phase space and a
corresponding Hamiltonian function from the available quantum structures and a
notion of coarser observations. The Hilbert space of any quantum mechanical
system naturally has the structure of an infinite dimensional symplectic
manifold (`quantum phase space'). There is also a systematic, quotienting
procedure which imparts a bundle structure to the quantum phase space and
extracts a classical phase space as the base space. This works straight
forwardly when the Hilbert space carries weakly continuous representation of
the Heisenberg group and recovers the linear classical phase space
$\mathbb{R}^{\mathrm{2N}}$. We report on how the procedure also allows
extraction of non-linear classical phase spaces and illustrate it for Hilbert
spaces being finite dimensional (spin-j systems), infinite dimensional but
separable (particle on a circle) and infinite dimensional but non-separable
(Polymer quantization). To construct a corresponding classical dynamics, one
needs to choose a suitable section and identify an effective Hamiltonian. The
effective dynamics mirrors the quantum dynamics provided the section satisfies
conditions of semiclassicality and tangentiality.


title: Binary black-hole evolutions of excision and puncture data

abstract:
  We present a new numerical code developed for the evolution of binary
black-hole spacetimes using different initial data and evolution techniques.
The code is demonstrated to produce state-of-the-art simulations of orbiting
and inspiralling black-hole binaries with convergent waveforms. We also present
the first detailed study of the dependence of gravitational waveforms resulting
from three-dimensional evolutions of different types of initial data. For this
purpose we compare the waveforms generated by head-on collisions of superposed
Kerr-Schild, Misner and Brill-Lindquist data over a wide range of initial
separations.


title: Energy Distribution in Szekeres Type I and II Space Times

abstract:
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0607103, gr-qc/0607119,
gr-qc/0607115, gr-qc/0607102, gr-qc/0602012, gr-qc/0702047, gr-qc/0607089,
gr-qc/0510123, and others.


title: Errata to "Flat Spacetime Vacuum in Loop Quantum Gravity"

abstract:
  We give the correct expressions for the spin network evaluations proposed in
Class. Quant. Grav. 21 (2004) 3909 as the coefficients of the quantum gravity
vacuum wavefunction in the spin network basis.


title: Loop cosmological implications of a non-minimally coupled scalar field

abstract:
  Non-minimal actions with matter represented by a scalar field coupled to
gravity are considered in the context of a homogeneous and isotropic universe.
The coupling is of the form $-\xi/2 \phi^2 R$. The possibility of successful
inflation is investigated taking into account features of loop cosmology. For
that end a conformal transformation is performed. That brings the theory into
the standard minimally coupled form (Einstein frame) with some effective field
and its potential. Both analytical and numerical estimates show that a negative
coupling constant is preferable for successful inflation. Moreover, provided
fixed initial conditions, larger $|\xi|$ leads to a greater number of {\em
e}-folds. The latter is obtained for a reasonable range of initial conditions
and the coupling parameter and indicates a possibility for successful
inflation.


title: Around a theory of a Walker spaces

abstract:
  An examples of a Ricci-flat of four-dimensional spaces with a Walker metrics
and their generalizations are constructed. The properties of corresponding
geodesic equations are discussed.


title: Does the Big Rip survive quantization?

abstract:
  It is known that certain quantum cosmological models present quantum behavior
for large scale factors. Since quantization can suppress past singularities, it
is natural to inquire whether quantum effects can prevent future singularities.
To this end, a Friedmann-Robertson-Walker quantum cosmological model dominated
by a phantom energy fluid is investigated. The classical model displays
accelerated expansion ending in a Big Rip. The quantization is performed in
three different ways, which turn out to lead to the same result, namely there
is a possibility that quantum gravitational effects could not remove the Big
Rip.


title: Structure formation on the brane: A mimicry

abstract:
  We show how braneworld cosmology with bulk matter can explain structure
formation. In this scenario, the nonlocal corrections to the Friedmann
equations supply a Weyl fluid that can dominate over matter at late times due
to the energy exchange between the brane and the bulk. We demonstrate that the
presence of the Weyl fluid radically changes the perturbation equations, which
can take care of the fluctuations required to account for the large amount of
inhomogeneities observed in the local universe. Further, we show how this Weyl
fluid can mimic dark matter. We also investigate the bulk geometry responsible
for the scenario.


title:
Black hole entropy from the boundary conformal structure in 3D gravity
  with torsion

abstract:
  Asymptotic symmetry of the Euclidean 3D gravity with torsion is described by
two independent Virasoro algebras with different central charges. Elements of
this boundary conformal structure are combined with Cardy's formula to
calculate the black hole entropy.


title:
Kerr Solution Consistent Motion of Spin Particles in the General
  Relativity

abstract:
  The paper presents equations determining the particle spin evolution in the
post-Newtonian approximation in the problem of motion of two mass and spin
possessing particles. The equations are derived with the
Einstein-Infeld-Hoffmann method from the condition of metric tensor symmetry.
The consideration uses the condition of coordinate harmonicity and the metric
coincidence nearby the particles with expansions of the Kerr solution written
in the harmonic coordinates. For gyroscopes on satellites Gravity Probe B, for
example, the equations yield a deviation of the axis of revolution, which is,
first, two times as small as that obtained by J.L.Anderson in paper
gr-qc/0511093 and, second, the deviation is of opposite sense. From the
equations it follows that the total angular momentum of the spin particle
system, generally speaking, is not conserved, beginning even with the
post-Newtonian approximation. The results are briefly discussed.


title:
The search for continuous gravitational waves: metric of the
  multi-detector F-statistic

abstract:
  We develop a general formalism for the parameter-space metric of the
multi-detector F-statistic, which is a matched-filtering detection statistic
for continuous gravitational waves. We find that there exists a whole family of
F-statistic metrics, parametrized by the (unknown) amplitude parameters of the
gravitational wave. The multi-detector metric is shown to be expressible in
terms of noise-weighted averages of single-detector contributions, which
implies that the number of templates required to cover the parameter space does
not scale with the number of detectors. Contrary to using a longer observation
time, combining detectors of similar sensitivity is therefore the
computationally cheapest way to improve the sensitivity of coherent
wide-parameter searches for continuous gravitational waves.
  We explicitly compute the F-statistic metric family for signals from isolated
spinning neutron stars, and we numerically evaluate the quality of different
metric approximations in a Monte-Carlo study. The metric predictions are tested
against the measured mismatches and we identify regimes in which the local
metric is no longer a good description of the parameter-space structure.


title: Addressing LISA Science Analysis Challenges

abstract:
  The principal goal of the \emph{LISA Science Analysis Workshop} is to
encourage the development and maturation of science analysis technology in
preparation for LISA science operations. Exactly because LISA is a pathfinder
for a new scientific discipline -- gravitational wave astronomy -- LISA data
processing and science analysis methodologies are in their infancy and require
considerable maturation if they are to be ready to take advantage of LISA data.
Here we offer some thoughts, in anticipation of the LISA Science Analysis
Workshop, on analysis research problems that demonstrate the capabilities of
different proposed analysis methodologies and, simultaneously, help to push
those techniques toward greater maturity. Particular emphasis is placed on
formulating questions that can be turned into well-posed problems involving
tests run on specific data sets, which can be shared among different groups to
enable the comparison of techniques on a well-defined platform.


title: Polymer state approximations of Schroedinger wave functions

abstract:
  It is shown how states of a quantum mechanical particle in the Schroedinger
representation can be approximated by states in the so-called polymer
representation. The result may shed some light on the semiclassical limit of
loop quantum gravity.


title: Probing the cosmological singularity with a particle

abstract:
  We examine the transition of a particle across the singularity of the
compactified Milne (CM) space. Quantization of the phase space of a particle
and testing the quantum stability of its dynamics are consistent to one
another. One type of transition of a quantum particle is described by a quantum
state that is continuous at the singularity. It indicates the existence of a
deterministic link between the propagation of a particle before and after
crossing the singularity. Regularization of the CM space leads to the dynamics
similar to the dynamics in the de Sitter space. The CM space is a promising
model to describe the cosmological singularity deserving further investigation
by making use of strings and membranes.


title: Evidence of the gravitomagnetic field of Mars

abstract:
  According to general relativity, the gravitomagnetic Lense-Thirring force of
Mars would secularly shift the orbital plane of the Mars Global Surveyor (MGS)
spacecraft by an amount of 1.5 m, on average, in the cross-track direction over
5 years. The determined cross-track post-fit residuals of MGS, built up by
neglecting just the gravitomagnetic force in the dynamical force models and
without fitting any empirical cross-track acceleration which could remove the
relativistic signal, amount to 1.6 m, on average, over a 5-years time interval
spanning from 10 February 2000 to 14 January 2005. The discrepancy with the
predictions of general relativity is 6%.


title: Light-cone coordinates based at a geodesic world line

abstract:
  Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007
(2004)], we construct a system of light-cone coordinates based at a geodesic
world line of an arbitrary curved spacetime. The construction involves (i) an
advanced-time or a retarded-time coordinate that labels past or future light
cones centered on the world line, (ii) a radial coordinate that is an affine
parameter on the null generators of these light cones, and (iii) angular
coordinates that are constant on each generator. The spacetime metric is
calculated in the light-cone coordinates, and it is expressed as an expansion
in powers of the radial coordinate in terms of the irreducible components of
the Riemann tensor evaluated on the world line. The formalism is illustrated in
two simple applications, the first involving a comoving world line of a
spatially-flat cosmology, the other featuring an observer placed on the axis of
symmetry of Melvin's magnetic universe.


title: A light-cone gauge for black-hole perturbation theory

abstract:
  The geometrical meaning of the Eddington-Finkelstein coordinates of
Schwarzschild spacetime is well understood: (i) the advanced-time coordinate v
is constant on incoming light cones that converge toward r=0, (ii) the angles
theta and phi are constant on the null generators of each light cone, (iii) the
radial coordinate r is an affine-parameter distance along each generator, and
(iv) r is an areal radius, in the sense that 4 pi r^2 is the area of each
two-surface (v,r) = constant. The light-cone gauge of black-hole perturbation
theory, which is formulated in this paper, places conditions on a perturbation
of the Schwarzschild metric that ensure that properties (i)--(iii) of the
coordinates are preserved in the perturbed spacetime. Property (iv) is lost in
general, but it is retained in exceptional situations that are identified in
this paper. Unlike other popular choices of gauge, the light-cone gauge
produces a perturbed metric that is expressed in a meaningful coordinate
system; this is a considerable asset that greatly facilitates the task of
extracting physical consequences. We illustrate the use of the light-cone gauge
by calculating the metric of a black hole immersed in a uniform magnetic field.
We construct a three-parameter family of solutions to the perturbative
Einstein-Maxwell equations and argue that it is applicable to a broader range
of physical situations than the exact, two-parameter Schwarzschild-Melvin
family.


title: Energy of the Taub Cosmological Solution

abstract:
  We calculate the total energy of Taub's 1951 exact solution for a Bianchi
type IX geometry using several different energy-localization procedures,
including the prescriptions of Einstein, Papapetrou, Landau-Lifshitz and
Moller. We compare these results to those for other anisotropic geometries, and
comment on their relationship to Rosen's conjecture about the total energy of
the universe.


title: Ellipsoidal configurations in the de Sitter spacetime

abstract:
  The cosmological constant $\Lambda$ modifies certain properties of large
astrophysical rotating configurations with ellipsoidal geometries, provided the
objects are not too compact. Assuming an equilibrium configuration and so using
the tensor virial equation with $\Lambda$ we explore several equilibrium
properties of homogeneous rotating ellipsoids. One shows that the bifurcation
point, which in the oblate case distinguishes the Maclaurin ellipsoid from the
Jacobi ellipsoid, is sensitive to the cosmological constant. Adding to that,
the cosmological constant allows triaxial configurations of equilibrium
rotating the minor axis as solutions of the virial equations. The significance
of the result lies in the fact that minor axis rotation is indeed found in
nature. Being impossible for the oblate case, it is permissible for prolate
geometries, with $\Lambda$ zero and positive. For the triaxial case, however,
an equilibrium solution is found only for non-zero positive $\Lambda$. Finally,
we solve the tensor virial equation for the angular velocity and display
special effects of the cosmological constant there.


title: Renormalization by gravity and the Kerr spinning particle

abstract:
  On the basis of the Kerr spinning particle, we show that the mass
renormalization is perfectly performed by gravity for an arbitrary distribution
of source matter. A smooth regularization of the Kerr-Newman solution is
considered, leading to a source in the form of a rotating bag filled by a false
vacuum. It is shown that gravity controls the phase transition to an AdS or dS
false vacuum state inside the bag, providing the mass balance.


title:
Dirac Relaxation of the Israel Junction Conditions: Unified
  Randall-Sundrum Brane Theory

abstract:
  Following Dirac's brane variation prescription, the brane must not be
deformed during the variation process, or else the linearity of the variation
may be lost. Alternatively, the variation of the brane is done, in a special
Dirac frame, by varying the bulk coordinate system itself. Imposing appropriate
Dirac style boundary conditions on the constrained 'sandwiched' gravitational
action, we show how Israel junction conditions get relaxed, but remarkably, all
solutions of the original Israel equations are still respected. The Israel
junction conditions are traded, in the $Z_2$-symmetric case, for a generalized
Regge-Teitelboim type equation (plus a local conservation law), and in the
generic $Z_2$-asymmetric case, for a pair of coupled Regge-Teitelboim
equations. The Randall-Sundrum model and its derivatives, such as the
Dvali-Gabadadze-Porrati and the Collins-Holdom models, get generalized
accordingly. Furthermore, Randall-Sundrum and Regge-Teitelboim brane theories
appear now to be two different faces of the one and the same unified brane
theory. Within the framework of unified brane cosmology, we examine the dark
matter/energy interpretation of the effective energy/momentum deviations from
General Relativity.


title: Geometry and Regularity of Moving Punctures

abstract:
  Significant advances in numerical simulations of black-hole binaries have
recently been achieved using the puncture method. We examine how and why this
method works by evolving a single black hole. The coordinate singularity and
hence the geometry at the puncture are found to change during evolution, from
representing an asymptotically flat end to being a cylinder. We construct an
analytic solution for the stationary state of a black hole in spherical
symmetry that matches the numerical result and demonstrates that the evolution
is not dominated by artefacts at the puncture but indeed finds the analytical
result.


title: A lattice bosonic model as a quantum theory of gravity

abstract:
  A local quantum bosonic model on a lattice is constructed whose low energy
excitations are gravitons described by linearized Einstein action. Thus the
bosonic model is a quantum theory of gravity, at least at the linear level. We
find that the compactification and the discretization of metric tenor are
crucial in obtaining a quantum theory of gravity.


title: Conformal boundary extensions of Lorentzian manifolds

abstract:
  We study the question of local and global uniqueness of completions, based on
null geodesics, of Lorentzian manifolds. We show local uniqueness of such
boundary extensions. We give a necessary and sufficient condition for existence
of unique maximal completions. The condition is verified in several situations
of interest. This leads to existence and uniqueness of maximal spacelike
conformal boundaries, of maximal strongly causal boundaries, as well as
uniqueness of conformal boundary extensions for asymptotically simple
space-times. Examples of applications include the definition of mass, or the
classification of inequivalent extensions across a Cauchy horizon of the Taub
space-time.


title:
Temporal variations in space-time and progenitors of gamma ray burst and
  millisecond pulsars

abstract:
  A time varying space-time metric is shown to be a source of electromagnetic
radiation. The post-Newtonian approximation is used as a realistic model of the
connection between the space-time metric and a time varying gravitational
potential. Large temporal variations in the metric from the coalescence of
colliding black holes and neutron stars are shown to be possible progenitors of
gamma ray burst and millisecond pulsars.


title:
The Holographic Model of Dark Energy and Thermodynamics of Non-Flat
  Accelerated Expanding Universe

abstract:
  Motivated by recent results on non-vanishing spatial curvature \cite{curve}
we employ the holographic model of dark energy to investigate the validity of
first and second laws of thermodynamics in non-flat (closed) universe enclosed
by apparent horizon $R_A$ and the event horizon measured from the sphere of
horizon named $L$. We show that for the apparent horizon the first law is
roughly respected for different epochs while the second laws of thermodynamics
is respected while for $L$ as the system's IR cut-off first law is broken down
and second law is respected for special range of deceleration parameter. It is
also shown that at late-time universe $L$ is equal to $R_A$ and the
thermodynamic laws are hold, when the universe has non-vanishing curvature.
Defining the fluid temperature to be proportional to horizon temperature the
range for coefficient of proportionality is obtained provided that the
generalized second law of thermodynamics is hold.


title:
Numerical evolutions of a black hole-neutron star system in full General
  Relativity: I. Head-on collision

abstract:
  We present the first simulations in full General Relativity of the head-on
collision between a neutron star and a black hole of comparable mass. These
simulations are performed through the solution of the Einstein equations
combined with an accurate solution of the relativistic hydrodynamics equations
via high-resolution shock-capturing techniques. The initial data is obtained by
following the York-Lichnerowicz conformal decomposition with the assumption of
time symmetry. Unlike other relativistic studies of such systems, no limitation
is set for the mass ratio between the black hole and the neutron star, nor on
the position of the black hole, whose apparent horizon is entirely contained
within the computational domain. The latter extends over ~400M and is covered
with six levels of fixed mesh refinement. Concentrating on a prototypical
binary system with mass ratio ~6, we find that although a tidal deformation is
evident the neutron star is accreted promptly and entirely into the black hole.
While the collision is completed before ~300M, the evolution is carried over up
to ~1700M, thus providing time for the extraction of the gravitational-wave
signal produced and allowing for a first estimate of the radiative efficiency
of processes of this type.


title:
Proof of the angular momentum-mass inequality for axisymmetric black
  holes

abstract:
  We prove that extreme Kerr initial data set is a unique absolute minimum of
the total mass in a (physically relevant) class of vacuum, maximal,
asymptotically flat, axisymmetric data for Einstein equations with fixed
angular momentum. These data represent non-stationary, axially symmetric, black
holes. As a consequence, we obtain that any data in this class satisfy the
inequality $\sqrt{J} \leq m$, where $m$ and $J$ are the total mass and angular
momentum of the spacetime.


title:
Proper Weyl Collineations in Kantowski-Sachs and Bianchi Type III
  Space-Times

abstract:
  A study of proper Weyl collineations in Kantowski-Sachs and Bianchi type III
space-times is given by using the rank of the 6X6 Weyl matrix and direct
integration techniques. Studying proper Weyl collineations in each of the above
space-times, it is shown that there exists no such possibility when the above
space-times admit proper Weyl collineations.


title: The effect of geometry on charge confinement in three dimensions

abstract:
  We show that, in contrast to the flat case, the Maxwell theory is not
confining in the background of the three dimensional BTZ black-hole (covering
space). We also study the effect of the curvature on screening behavior of
Maxwell-Chern-Simons model in this space-time.


title: Quantum Gravity and Precision Tests

abstract:
  This article provides a cartoon of the quantization of General Relativity
using the ideas of effective field theory. These ideas underpin the use of
General Relativity as a theory from which precise predictions are possible,
since they show why quantum corrections to standard classical calculations are
small. Quantum corrections can be computed controllably provided they are made
for the weakly-curved geometries associated with precision tests of General
Relativity, such as within the solar system or for binary pulsars. They also
bring gravity back into the mainstream of physics, by showing that its
quantization (at low energies) exactly parallels the quantization of other,
better understood, non-renormalizable field theories which arise elsewhere in
physics. Of course effective field theory techniques do not solve the
fundamental problems of quantum gravity discussed elsewhere in these pages, but
they do helpfully show that these problems are specific to applications on very
small distance scales. They also show why we may safely reject any proposals to
modify gravity at long distances if these involve low-energy problems (like
ghosts or instabilities), since such problems are unlikely to be removed by the
details of the ultimate understanding of gravity at microscopic scales.


title:
Thermodynamics of high dimensional Schwarzschild de Sitter spacetimes:
  variable cosmological constant

abstract:
  We study the thermodynamic properties of high dimensional Schwarzschild de
Sitter spacetimes with the consideration of quantum effects. It is shown that
by considering the cosmological constant as a variable state parameter and
adding an extra term which denotes the vacuum energy, both the differential and
integral mass formulas of the first law of Schwarzschild de Sitter spacetimes
can be directly derived from the general Schwarzschild de Sitter metrics in a
simple and natural way. Furthermore, after taking quantum effects into account,
we can see that the cosmological constant must decrease and the spontaneous
decay of the vacuum energy never makes the entropy of Schwarzschild de Sitter
spacetimes decrease. In addition, though the laws of thermodynamics are very
powerful, at least the third law can not be applied to the Schwarzschild de
Sitter spacetimes. It should be emphasized that these conclusions come into
existence in any dimension.


title:
Quasinormal frequencies of D-dimensional Schwarzschild black holes:
  evaluation via continued fraction method

abstract:
  We adopt Leaver's method to determine quasi normal frequencies of the
Schwarzschild black hole in higher (D >= 10) dimensions. In D-dimensional
Schwarzschild metric, when D increases, more and more singularities, spaced
uniformly on the unit circle |r|=1, approach the horizon at r = r_h = 1. Thus,
a solution satisfying the outgoing wave boundary condition at the horizon must
be continued to some mid point and only then the continued fraction condition
can be applied. This prescription is general and applies to all cases for
which, due to regular singularities on the way from the point of interest to
the irregular singularity, Leaver's method in its original setting breaks down.
We illustrate the method calculating gravitational vector and tensor
quasinormal frequencies of the Schwarzschild black hole in D=11 and D=10
dimensions. We also give the details for the D=9 case, considered in
gr-qc/0511064.


title: On the issue of gravitons

abstract:
  We investigate the problem of whether one can anticipate any features of the
graviton without a detailed knowledge of a full quantum gravity. Assuming that
in linearized gravity the graviton is in a sense similar to the photon, we
derive a curious large number coincidence between the number of gravitons
emitted by a solar planet during its orbital period and the number of its
nucleons. In Einstein's GR the analogy between the graviton and the photon is
ill founded. A generic relationship between quanta of a quantum field and plane
waves of the corresponding classical field is broken in the case of GR. The
graviton cannot be classically approximated by a generic pp wave nor by the
exact plane wave. Most important, the ADM energy is a zero frequency
characteristic of any asymptotically flat spacetime and this means that any
general relationship between energy and frequency is a priori impossible. In
particular the formula $E=\hbar \omega$ does not hold. The graviton must have
features different from those of the photon and these cannot be predicted from
classical general relativity.


title:
Spherical gravitational wave detectors: An approach for real time data
  analysis

abstract:
  We have developed a full model to simulate spherical detectors where all main
sources of noise are considered. We have built a computer code for determining
the source direction and the wave polarization (solution of the inverse
problem) in real time acquisition. The digital filter used is a simple bandpass
filter. The ``data'' used for testing our code was simulated, which considers
both the source signal and detector noise. The detector noise includes the
antenna thermal, back action, phase noise, series noise and thermal from
transducer coupled masses. The simulated noise takes into account all these
noises and the antenna-transducers coupling. The detector transfer function was
calculated for a spherical antenna with six two-mode parametric transducers.
  From the results we determined that spherical detectors are able to locate an
astrophysical source in the sky in real time as long as the signal-to-noise
ratio for a burst signal is equal to or higher than 3.


title: Coupled quintessence and curvature-assisted acceleration

abstract:
  Spatially homogeneous models with a scalar field non-minimally coupled to the
space-time curvature or to the ordinary matter content are analysed with
respect to late-time asymptotic behaviour, in particular to accelerated
expansion and isotropization. It is found that a direct coupling to the
curvature leads to asymptotic de Sitter expansion in arbitrary exponential
potentials, thus yielding a positive cosmological constant although none is
apparent in the potential. This holds true regardless of the steepness of the
potential or the smallness of the coupling constant. For matter-coupled scalar
fields, the asymptotics are obtained for a large class of positive potentials,
generalizing the well-known cosmic no-hair theorems for minimal coupling. In
this case it is observed that the direct coupling to matter does not impact the
late-time dynamics essentially.


title:
On the Equation of Motion for a Fast Moving Small Object in the Strong
  Field Point Particle Limit

abstract:
  We give a straightforward and divergence free derivation of the equation of
motion for a small but finite object in an arbitrary background using strong
field point particle limit. The resulting equation becomes a generalized
geodesic for a non-rotating spherical object which is consisitent with previous
studies.


title:
Calculation of, and bounds for, the multipole moments of stationary
  spacetimes

abstract:
  In this paper the multipole moments of stationary asymptotically flat
spacetimes are considered. We show how the tensorial recursion of Geroch and
Hansen can be replaced by a scalar recursion on R^2. We also give a bound on
the multipole moments. This gives a proof of the "necessary part" of a long
standing conjecture due to Geroch.


title:
The Positive Mass and Isoperimetric Inequalities for Axisymmetric Black
  Holes in four and five dimensions

abstract:
  In this paper we revisit Brill's proof of positive mass for
three-dimensional, time-symmetric, axisymmetric initial data and generalise his
argument in various directions. In 3+1 dimensions, we include an apparent
horizon in the initial data and prove the Riemannian Penrose inequality in a
wide number of cases by an elementary argument. In the case of 4+1 dimensions
we obtain the analogue of Brill's formula for initial data admitting a
generalised form of axisymmetry. Including an apparent horizon in the initial
data, the Riemannian Penrose inequality is again proved for a large class of
cases. The results may have applications in numerical relativity.


title: Anthropic principle in cosmology

abstract:
  A brief explanation of the meaning of the anthropic principle - as a
prescription for the attribution of a priori probability weighting - is
illustrated by various cosmological and local applications, in which the
relevant conclusions are contrasted with those that could be obtained from
(less plausible) alternative prescriptions such as the vaguer and less
restrictive ubiquity principle, or the more sterile and restrictive autocentric
principle.


title:
Proposed observations of gravity waves from the early Universe via
  "Millikan oil drops"

abstract:
  Pairs of Planck-mass drops of superfluid helium coated by electrons (i.e.,
``Millikan oil drops''), when levitated in a superconducting magnetic trap, can
be efficient quantum transducers between electromagnetic (EM) and gravitational
(GR) radiation. This leads to the possibility of a Hertz-like experiment, in
which EM waves are converted at the source into GR waves, and then
back-converted at the receiver from GR waves back into EM waves. Detection of
the gravity-wave analog of the cosmic microwave background using these drops
can discriminate between various theories of the early Universe.


title:
Quintessential inflation from a variable cosmological constant in a 5D
  vacuum

abstract:
  We explore an effective 4D cosmological model for the universe where the
variable cosmological constant governs its evolution and the pressure remains
negative along all the expansion. This model is introduced from a 5D vacuum
state where the (space-like) extra coordinate is considered as noncompact. The
expansion is produced by the inflaton field, which is considered as
nonminimally coupled to gravity. We conclude from experiental data that the
coupling of the inflaton with gravity should be weak, but variable in different
epochs of the evolution of the universe.


title: A possible experimental test of quantized gravity

abstract:
  While it is widely believed that gravity should ultimately be treated as a
quantum theory, there remains a possibility that general relativity should not
be quantized. If this is the case, the coupling of classical gravity to the
expectation value of the quantum stress-energy tensor will naturally lead to
nonlinearities in the Schrodinger equation. By numerically investigating time
evolution in the nonrelativistic "Schrodinger-Newton" approximation, we show
that such nonlinearities may be observable in the next generation of molecular
interferometry experiments.


title:
Uniform discretizations: a quantization procedure for totally
  constrained systems including gravity

abstract:
  We present a new method for the quantization of totally constrained systems
including general relativity. The method consists in constructing discretized
theories that have a well defined and controlled continuum limit. The discrete
theories are constraint-free and can be readily quantized. This provides a
framework where one can introduce a relational notion of time and that
nevertheless approximates in a well defined fashion the theory of interest. The
method is equivalent to the group averaging procedure for many systems where
the latter makes sense and provides a generalization otherwise. In the
continuum limit it can be shown to contain, under certain assumptions, the
``master constraint'' of the ``Phoenix project''. It also provides a
correspondence principle with the classical theory that does not require to
consider the semiclassical limit.


title: de Sitter special relativity

abstract:
  A special relativity based on the de Sitter group is introduced, which is the
theory that might hold up in the presence of a non-vanishing cosmological
constant. Like ordinary special relativity, it retains the quotient character
of spacetime, and a notion of homogeneity. As a consequence, the underlying
spacetime will be a de Sitter spacetime, whose associated kinematics will
differ from that of ordinary special relativity. The corresponding modified
notions of energy and momentum are obtained, and the exact relationship between
them, which is invariant under a re-scaling of the involved quantities,
explicitly exhibited. Since the de Sitter group can be considered a particular
deformation of the Poincar\'e group, this theory turns out to be a specific
kind of deformed (or doubly) special relativity. Some experimental
consequences, as well as the causal structure of spacetime--modified by the
presence of the de Sitter horizon--are briefly discussed.


title: Iso-spectral potential and inflationary quantum cosmology

abstract:
  Using the factorization approach of quantum mechanics, we obtain a family of
isospectral scalar potentials for power law inflationary cosmology. The
construction is based on a scattering Wheeler-DeWitt solution. These
iso-spectrals have new features, they give a mechanism to end inflation, as
well as the possibility to have new inflationary epochs. The procedure can be
extended to other cosmological models.