title: On (Cosmological) Singularity Avoidance in Loop Quantum Gravity

abstract:
  Loop Quantum Cosmology (LQC), mainly due to Bojowald, is not the cosmological
sector of Loop Quantum Gravity (LQG). Rather, LQC consists of a truncation of
the phase space of classical General Relativity to spatially homogeneous
situations which is then quantized by the methods of LQG. Thus, LQC is a
quantum mechanical toy model (finite number of degrees of freedom) for LQG(a
genuine QFT with an infinite number of degrees of freedom) which provides
important consistency checks. However, it is a non trivial question whether the
predictions of LQC are robust after switching on the inhomogeneous fluctuations
present in full LQG. Two of the most spectacular findings of LQC are that 1.
the inverse scale factor is bounded from above on zero volume eigenstates which
hints at the avoidance of the local curvature singularity and 2. that the
Quantum Einstein Equations are non -- singular which hints at the avoidance of
the global initial singularity. We display the result of a calculation for LQG
which proves that the (analogon of the) inverse scale factor, while densely
defined, is {\it not} bounded from above on zero volume eigenstates. Thus, in
full LQG, if curvature singularity avoidance is realized, then not in this
simple way. In fact, it turns out that the boundedness of the inverse scale
factor is neither necessary nor sufficient for curvature singularity avoidance
and that non -- singular evolution equations are neither necessary nor
sufficient for initial singularity avoidance because none of these criteria are
formulated in terms of observable quantities.After outlining what would be
required, we present the results of a calculation for LQG which could be a
first indication that our criteria at least for curvature singularity avoidance
are satisfied in LQG.


title: Unboundedness of Triad -- Like Operators in Loop Quantum Gravity

abstract:
  In this paper we deliver the proofs for the claims, made in a companion
paper, concerning the avoidance of cosmological curvature singularities in in
full Loop Quantum Gravity (LQG).


title: Chaplygin gas dominated anisotropic brane world cosmological models

abstract:
  We present exact solutions of the gravitational field equations in the
generalized Randall-Sundrum model for an anisotropic brane with Bianchi type I
geometry, with a generalized Chaplygin gas as matter source. The generalized
Chaplygin gas, which interpolates between a high density relativistic era and a
non-relativistic matter phase, is a popular dark energy candidate. For a
Bianchi type I space-time brane filled with a cosmological fluid obeying the
generalized Chaplygin equation of state the general solution of the
gravitational field equations can be expressed in an exact parametric form,
with the comoving volume taken as parameter. In the limiting cases of a stiff
cosmological fluid, with pressure equal to the energy density, and for a
pressureless fluid, the solution of the field equations can be expressed in an
exact analytical form. The evolution of the scalar field associated to the
Chaplygin fluid is also considered and the corresponding potential is obtained.
The behavior of the observationally important parameters like shear, anisotropy
and deceleration parameter is considered in detail.


title: Can Brans-Dicke scalar field account for dark energy and dark matter?

abstract:
  By using a linearized non-vacuum late time solution in Brans-Dicke cosmology
we account for the seventy five percent dark energy contribution but not for
approximately twenty-three percent dark matter contribution to the present day
energy density of the universe.


title: Even perturbations of self-similar Vaidya space-time

abstract:
  We study even parity metric and matter perturbations of all angular modes in
self-similar Vaidya space-time. We focus on the case where the background
contains a naked singularity. Initial conditions are imposed describing a
finite perturbation emerging from the portion of flat space-time preceding the
matter-filled region of space-time. The most general perturbation satisfying
the initial conditions is allowed impinge upon the Cauchy horizon (CH), whereat
the perturbation remains finite: there is no ``blue-sheet'' instability.
However when the perturbation evolves through the CH and onto the second future
similarity horizon of the naked singularity, divergence necessarily occurs:
this surface is found to be unstable. The analysis is based on the study of
individual modes following a Mellin transform of the perturbation. We present
an argument that the full perturbation remains finite after resummation of the
(possibly infinite number of) modes.


title: Does Inflation Provide Natural Initial Conditions for the Universe?

abstract:
  If our universe underwent inflation, its entropy during the inflationary
phase was substantially lower than it is today. Because a low-entropy state is
less likely to be chosen randomly than a high-entropy one, inflation is
unlikely to arise through randomly-chosen initial conditions. To resolve this
puzzle, we examine the notion of a natural state for the universe, and argue
that it is a nearly-empty spacetime. If empty space has a small vacuum energy,
however, inflation can begin spontaneously in this background. This scenario
explains why a universe like ours is likely to have begun via a period of
inflation, and also provides an origin for the cosmological arrow of time.


title: A Jordan GNS Construction for the Holonomy-Flux *-algebra

abstract:
  The holonomy-flux *-algebra was recently proposed as an algebra of basic
kinematical observables for loop quantum gravity. We show the conventional GNS
construction breaks down when the the holonomy-flux *-algebra is allowed to be
a Jordan algebra of observables. To remedy this, we give a Jordan GNS
construction for the holonomy-flux *-algebra that is based on trace. This is
accomplished by assuming the holonomy-flux *-algebra is an algebra of
observables that is also a Banach algebra, hence a JB algebra. We show the
Jordan GNS construction produces a state that is invariant under all inner
derivations of the holonomy-flux *-algebra. Implications for the corresponding
Jordan-Schrodinger equation are also discussed.


title: Curvature invariants of static spherically symmetric geometries

abstract:
  We construct all independent local scalar monomials in the Riemann tensor at
arbitrary dimension, for the special regime of static, spherically symmetric
geometries. Compared to general spaces, their number is significantly reduced:
the extreme example is the collapse of all invariants ~ Weyl^k, to a single
term at each k. The latter is equivalent to the Lovelock invariant L_k.
Depopulation is less extreme for invariants involving rising numbers of Ricci
tensors, and also depends on the dimension. The corresponding local
gravitational actions and their solution spaces are discussed.


title: Active Mass Under Pressure

abstract:
  After a historical introduction to Poisson's equation for Newtonian gravity,
its analog for static gravitational fields in Einstein's theory is reviewed. It
appears that the pressure contribution to the active mass density in Einstein's
theory might also be noticeable at the Newtonian level. A form of its
surprising appearance, first noticed by Richard Chase Tolman, was discussed
half a century ago in the Hamburg Relativity Seminar and is resolved here.


title:
Search for gravitational waves from galactic and extra--galactic binary
  neutron stars

abstract:
  We use 373 hours ($\approx$ 15 days) of data from the second science run of
the LIGO gravitational-wave detectors to search for signals from binary neutron
star coalescences within a maximum distance of about 1.5 Mpc, a volume of space
which includes the Andromeda Galaxy and other galaxies of the Local Group of
galaxies. This analysis requires a signal to be found in data from detectors at
the two LIGO sites, according to a set of coincidence criteria. The background
(accidental coincidence rate) is determined from the data and is used to judge
the significance of event candidates. No inspiral gravitational wave events
were identified in our search. Using a population model which includes the
Local Group, we establish an upper limit of less than 47 inspiral events per
year per Milky Way equivalent galaxy with 90% confidence for non-spinning
binary neutron star systems with component masses between 1 and 3 $M_\odot$.


title:
Search for Gravitational Waves from Primordial Black Hole Binary
  Coalescences in the Galactic Halo

abstract:
  We use data from the second science run of the LIGO gravitational-wave
detectors to search for the gravitational waves from primordial black hole
(PBH) binary coalescence with component masses in the range 0.2--$1.0 M_\odot$.
The analysis requires a signal to be found in the data from both LIGO
observatories, according to a set of coincidence criteria. No inspiral signals
were found. Assuming a spherical halo with core radius 5 kpc extending to 50
kpc containing non-spinning black holes with masses in the range 0.2--$1.0
M_\odot$, we place an observational upper limit on the rate of PBH coalescence
of 63 per year per Milky Way halo (MWH) with 90% confidence.


title: Consistent discretizations: the Gowdy spacetimes

abstract:
  We apply the consistent discretization scheme to general relativity
particularized to the Gowdy space-times. This is the first time the framework
has been applied in detail in a non-linear generally-covariant gravitational
situation with local degrees of freedom. We show that the scheme can be
correctly used to numerically evolve the space-times. We show that the
resulting numerical schemes are convergent and preserve approximately the
constraints as expected.


title: Highly Damped Quasinormal Modes of Generic Single Horizon Black Holes

abstract:
  We calculate analytically the highly damped quasinormal mode spectra of
generic single-horizon black holes using the rigorous WKB techniques of
Andersson and Howls\cite{Andersson}. We thereby provide a firm foundation for
previous analysis, and point out some of their possible limitations. The
numerical coefficient in the real part of the highly damped frequency is
generically determined by the behavior of coupling of the perturbation to the
gravitational field near the origin, as expressed in tortoise coordinates. This
fact makes it difficult to understand how the famous $ln(3)$ could be related
to the quantum gravitational microstates near the horizon.


title:
Gravitational Collapse of Massless Scalar Field with Negative
  Cosmological Constant in (2+1) Dimensions

abstract:
  The 2+1-dimensional geodesic circularly symmetric solutions of
Einstein-massless-scalar field equations with negative cosmological constant
are found and their local and global properties are studied. It is found that
one of them represents gravitational collapse where black holes are always
formed.


title:
Perturbed Self-Similar Massless Scalar Field in the Spacetimes with
  Circular Symmetry in 2+1 Gravity

abstract:
  We present in this work the study of the linear perturbations of the
2+1-dimensional circularly symmetric solution, obtained in a previous work,
with kinematic self-similarity of the second kind. We have obtained an exact
solution for the perturbation equations and the possible perturbation modes. We
have shown that the background solution is a stable solution.


title: Experimentally obtaining metrics in general relativity

abstract:
  It seems to be not well known that the metrics of general relativity (GR) can
be obtained without integrating Einstein equations. To that, we need only
define a unit for GR-interval $\Delta s$, and observe 10 geodesics (out of
which at least one must be nonnull). Even without using any unit, we can have
$\kappa g_{\mu\nu}(x^\rho)$, where $\kappa=$const. Our notes attempt to
simplify the articles of E. Kretschmann (1917) and of H.A. Lorentz (1923) about
this last subject. The text of this article in English will soon be available,
in LaTeX. Please ask the author.
  -----
  /Sajne estas malmulte konata ke la metrikoj de /generala relativeco (/GR)
povas esti havataj sen integri Einstein-ajn ekvaciojn. Por tio, ni bezonas
difini nur unuon por /GR-tempo $\Delta s$, kaj observi 10 geodezajn (el kiuj,
almena/u unu devas esti nenulan). E/c sen uzi iun unuon, ni povas havi $\kappa
g_{\mu\nu}(x^\rho)$, kie $\kappa$=konst. Niaj notoj tentas simpligi la
artikolojn de E. Kretschmann (1917) kaj de H.A. Lorentz (1923) pri tiu lasta
afero.


title: Energy Conditions and Junction Conditions

abstract:
  We consider the familiar junction conditions described by Israel for thin
timelike walls in Einstein-Hilbert gravity. One such condition requires the
induced metric to be continuous across the wall. Now, there are many spacetimes
with sources confined to a thin wall for which this condition is violated and
the Israel formalism does not apply. However, we explore the conjecture that
the induced metric is in fact continuous for any thin wall which models
spacetimes containing only positive energy matter. Thus, the usual junction
conditions would hold for all positive energy spacetimes. This conjecture is
proven in various special cases, including the case of static spacetimes with
spherical or planar symmetry as well as settings without symmetry which may be
sufficiently well approximated by smooth spacetimes with well-behaved null
geodesic congruences.


title: Horizon energy and angular momentum from a Hamiltonian perspective

abstract:
  Classical black holes and event horizons are highly non-local objects,
defined in terms of the causal past of future null infinity. Alternative,
(quasi)local definitions are often used in mathematical, quantum, and numerical
relativity. These include apparent, trapping, isolated, and dynamical horizons,
all of which are closely associated to two-surfaces of zero outward null
expansion. In this paper we show that three-surfaces which can be foliated with
such two-surfaces are suitable boundaries in both a quasilocal action and a
phase space formulation of general relativity. The resulting formalism provides
expressions for the quasilocal energy and angular momentum associated with the
horizon. The values of the energy and angular momentum are in agreement with
those derived from the isolated and dynamical horizon frameworks.


title: Entropy: From Black Holes to Ordinary Systems

abstract:
  Several results of black holes thermodynamics can be considered as firmly
founded and formulated in a very general manner. From this starting point we
analyse in which way these results may give us the opportunity to gain a better
understanding in the thermodynamics of ordinary systems for which a
pre-relativistic description is sufficient. First, we investigated the
possibility to introduce an alternative definition of the entropy basically
related to a local definition of the order in a spacetime model rather than a
counting of microstates. We show that such an alternative approach exists and
leads to the traditional results provided an equilibrium condition is assumed.
This condition introduces a relation between a time interval and the reverse of
the temperature. We show that such a relation extensively used in the black
hole theory, mainly as a mathematical trick, has a very general and physical
meaning here; in particular its derivation is not related to the existence of a
canonical density matrix. Our dynamical approach of thermodynamic equilibrium
allows us to establish a relation between action and entropy and we show that
an identical relation exists in the case of black holes. The derivation of such
a relation seems impossible in the Gibbs ensemble approach of statistical
thermodynamics. From these results we suggest that the definition of entropy in
terms of order in spacetime should be more general that the Boltzmann one based
on a counting of microstates. Finally we point out that these results are
obtained by reversing the traditional route going from the Schr\"{o}dinger
equation to statistical thermodynamics.


title: Field Equations of the CP(N-1) Affine Gauge Theory

abstract:
  A non-linear relativistic 4D field model of a quantum particle which emerges
from the internal dynamics in the quantum phase space $CP(N-1)$ is proposed. In
this model there is no distinction between `particle' and its `surrounding
field', and the space-time manifold emerges from the description of the quantum
state. The quantum observables of the `quantum particle field' are described in
terms of the affine parallel transport of the local dynamical variables in
$CP(N-1)$.


title: Classical and quantum general relativity: a new paradigm

abstract:
  We argue that recent developments in discretizations of classical and quantum
gravity imply a new paradigm for doing research in these areas. The paradigm
consists in discretizing the theory in such a way that the resulting discrete
theory has no constraints. This solves many of the hard conceptual problems of
quantum gravity. It also appears as a useful tool in some numerical simulations
of interest in classical relativity. We outline some of the salient aspects and
results of this new framework.


title: Energy Distribution of Black Plane Solutions

abstract:
  We use the Einstein energy-momentum complex to calculate the energy
distribution of static plane-symmetric solutions of the Einstein-Maxwell
equations in 3+1 dimensions with asymptotic anti-de Sitter behavior. This
solution is expressed in terms of three parameters: the mass, electric charge
and cosmological constant. We compare the energy distribution to that of the
Reissner-Nordstrom-anti-de Sitter solution, pointing to qualitative differences
between the models. Finally, we examine these results within the context of the
Cooperstock hypothesis.


title: Gravitational Lensing by Asymptotically Flat Wormholes

abstract:
  Natural wormholes and its astrophysical signatures have been sugested in
various oportunities. By applying the strong field limit of gravitational
lensing theory, we calculate the deflection angle and magnification curves
produced by Morris-Thorne wormholes in asimptotically flat space-times. The
results show that wormholes act like convergent lenses. Therefore, we show that
it is hard to distinguish them from black holes using the deflection's angle of
the gravitational lens effect, in contrast with the results reported by Cramer
et.al. and Safanova et.al. However, we also show that it is possible, in
principle, distinguish them by the magnification curves, in particular, by
observing the position of the peak of the Einstein's ring.


title: Accurate black hole evolutions by fourth-order numerical relativity

abstract:
  We present techniques for successfully performing numerical relativity
simulations of binary black holes with fourth-order accuracy. Our simulations
are based on a new coding framework which currently supports higher order
finite differencing for the BSSN formulation of Einstein's equations, but which
is designed to be readily applicable to a broad class of formulations. We apply
our techniques to a standard set of numerical relativity test problems,
demonstrating the fourth-order accuracy of the solutions. Finally we apply our
approach to binary black hole head-on collisions, calculating the waveforms of
gravitational radiation generated and demonstrating significant improvements in
waveform accuracy over second-order methods with typically achievable numerical
resolution.


title: Interacting Dark Energy and Cosmological Equations of State

abstract:
  Interactions within the cosmic medium modify its equation of state. We
discuss implications of interacting dark energy models both for the spatially
homogenous background and for the perturbation dynamics.


title: Elements of Loop Quantum Cosmology

abstract:
  The expansion of our universe, when followed backward in time, implies that
it emerged from a phase of huge density, the big bang. These stages are so
extreme that classical general relativity combined with matter theories is not
able to describe them properly, and one has to refer to quantum gravity. A
complete quantization of gravity has not yet been developed, but there are many
results about key properties to be expected. When applied to cosmology, a
consistent picture of the early universe arises which is free of the classical
pathologies and has implications for the generation of structure which are
potentially observable in the near future.


title:
The field theoretical formulation of general relativity and gravity with
  non-zero masses of gravitons

abstract:
  It is a review paper. General relativity (GR) is presented in the field
theoretical form, where gravitational field (metric perturbations) together
with other physical fields are propagated in an auxiliary arbitrary curved
background spacetime. Conserved currents are constructed and expressed through
divergences of antisymmetrical tensor densities (superpotentials). This permits
to connect local properties of perturbations with the quasi-local nature of the
conserved quantities in GR. The problem of the non-localization of energy in GR
is presented in exact mathematical expressions. A modification of GR developed
recently by Babak and Grishchuk on the basis of the field formulation of GR is
described. Their theory includes massive of spin-2 and spin-0 gravitons. All
its local weak-field predictions are in agreement with experimental data. The
exact equations of the massive theory eliminate the black hole event horizons
and give an oscillator behavior for the homogeneous isotropic universe.


title: A double-domain spectral method for black hole excision data

abstract:
  In this paper a new double-domain spectral method to compute binary black
hole excision initial data is presented. The method solves a system of elliptic
partial differential equations in the exterior of two excised spheres. At the
surface of these spheres, boundary conditions need to be imposed. As such, the
method can be used to construct arbitrary initial data corresponding to binary
black holes with specific boundary conditions at their apparent horizons. We
give representative examples corresponding to initial data that fulfill the
requirements of the quasi-stationary framework, which combines the thin
sandwich formulation of the constraint equations with the isolated horizon
conditions for black holes in quasi-equilibrium. For all examples considered,
numerical solutions with extremely high accuracy were obtained with moderate
computational effort. Moreover, the method proves to be applicable even when
tending toward limiting cases such as large radius ratios for the black holes.


title: Black Holes Surrounded by Uniformly Rotating Rings

abstract:
  Highly accurate numerical solutions to the problem of Black Holes surrounded
by uniformly rotating rings in axially symmetric, stationary spacetimes are
presented. The numerical methods developed to handle the problem are discussed
in some detail. Related Newtonian problems are described and numerical results
provided, which show that configurations can reach an inner mass-shedding limit
as the mass of the central object increases. Exemplary results for the full
relativistic problem for rings of constant density are given and the
deformation of the event horizon due to the presence of the ring is
demonstrated. Finally, we provide an example of a system for which the angular
momentum of the central Black Hole divided by the square of its mass exceeds
one.


title:
Standard emitters (clocks) and calibrated standard emitters (clocks) in
  spaces with affine connections and metrics

abstract:
  It is shown that the general belief that the frequency and the absolute value
of the velocity of periodic signals sent by a standard emitter do not change on
the world line of the emitter needs to be revised and new conditions for the
existence of a calibrted standard emitter should be taken into account. The
notions of a standard clock and of a calibrated standard clock are introduced
in a space with affine connections and metrics. The variation of the velocity
and of the frequency of a standard clock could be compared with the constant
velocity and the constant frequency of a calibrated standard clock along the
world line of the observer. This calibrated standard clock is transported by
meand of a generalized Fermi-Walker transport along the same world line of the
observer. Some remarks about the synchronization of standard clocks in spaces
with affine connections and metrics are given. PACS numbers: 95.30.Sf;
04.90.+h; 04.20.Cv; 04.90.+e


title:
Gravitational Collapse of Circularly Symmetric Stiff Fluid with
  Self-Similarity in 2+1 Gravity

abstract:
  Linear perturbations of homothetic self-similar stiff fluid solutions,
$S[n]$, with circular symmetry in 2+1 gravity are studied. It is found that,
except for those with $n = 1$ and $n = 3$, none of them is stable and all have
more than one unstable mode. Hence, {\em none of these solutions can be
critical}.


title: Non-linear terms in 2D cosmology

abstract:
  In this work we investigate the behavior of two-dimensional (2D) cosmological
models, starting with the Jackiw-Teitelboim (JT) theory of gravitation. A
geometrical term, non-linear in the scalar curvature $R$, is added to the JT
dynamics to test if it could play the role of dark energy in a 2D expanding
universe. This formulation makes possible, first, the description of an early
(inflationary) 2D universe, when the van der Waals (vdW) equation of state is
used to construct the energy-momentum tensor of the gravitational sources.
Second, it is found that for later times the non-linear term in $R$ can
generate an old 2D universe in accelerated expansion, where an ordinary matter
dominated era evolves into a decelerated/accelerated transition, giving to the
dark energy effects a geometrical origin. The results emerge through numerical
analysis, following the evolution in time of the scale factor, its
acceleration, and the energy densities of constituents.


title: LATOR Covariance Analysis

abstract:
  We present results from a covariance study for the proposed Laser Astrometric
Test of Relativity (LATOR) mission. This mission would send two
laser-transmitter spacecraft behind the Sun and measure the relative
gravitational light bending of their signals using a hundred-meter-baseline
optical interferometer to be constructed on the International Space Station. We
assume that each spacecraft is equipped with a $ < 1.9 \times 10^{-13}
\mathrm{m} \mathrm{s}^2 \mathrm{Hz}^{-1/2} $ drag-free system and assume
approximately one year of data. We conclude that the observations allow a
simultaneous determination of the orbit parameters of the spacecraft and of the
Parametrized Post-Newtonian (PPN) parameter $\gamma$ with an uncertainty of
$2.4 \times 10^{-9}$. We also find a $6 \times 10^{-9}$ determination of the
solar quadrupole moment, $J_2$, as well as the first measurement of the
second-order post-PPN parameter $\delta$ to an accuracy of about $10^{-3}$.


title: Analogue Gravity

abstract:
  Analogue gravity is a research programme which investigates analogues of
general relativistic gravitational fields within other physical systems,
typically but not exclusively condensed matter systems, with the aim of gaining
new insights into their corresponding problems. Analogue models of (and for)
gravity have a long and distinguished history dating back to the earliest years
of general relativity. In this review article we will discuss the history,
aims, results, and future prospects for the various analogue models. We start
the discussion by presenting a particularly simple example of an analogue
model, before exploring the rich history and complex tapestry of models
discussed in the literature. The last decade in particular has seen a
remarkable and sustained development of analogue gravity ideas, leading to some
hundreds of published articles, a workshop, two books, and this review article.
Future prospects for the analogue gravity programme also look promising, both
on the experimental front (where technology is rapidly advancing) and on the
theoretical front (where variants of analogue models can be used as a
springboard for radical attacks on the problem of quantum gravity).


title: What is the present-day status of The Copernican Principle?

abstract:
  I point out that according to the Copernican principle our universe is not
unique. The way to make sense out of this statement is for us to construct a
gravitational instanton that will tunnel out of our vacuum into another, to
form a universe other than our Hubble bubble.


title: Affine Particles and Fields

abstract:
  The covering of the affine symmetry group, a semidirect product of
translations and special linear transformations, in $D \geq 3$ dimensional
spacetime is considered. Infinite dimensional spinorial representations on
states and fields are presented. A Dirac-like affine equation, with infinite
matrices generalizing the $\gamma$ matrices, is constructed.


title: From qubits to black holes: entropy, entanglement and all that

abstract:
  Entropy plays a crucial role in characterization of information and
entanglement, but it is not a scalar quantity and for many systems it is
different for different relativistic observers. Loop quantum gravity predicts
the Bekenstein-Hawking term for black hole entropy and logarithmic correction
to it. The latter originates in the entanglement between the pieces of spin
networks that describe black hole horizon. Entanglement between gravity and
matter may restore the unitarity in the black hole evaporation process. If the
collapsing matter is assumed to be initially in a pure state, then entropy of
the Hawking radiation is exactly the created entanglement between matter and
gravity.


title:
Statefinders, higher-order energy conditions and sudden future
  singularities

abstract:
  We link observational parameters such as the deceleration parameter, the
jerk, the kerk (snap) and higher-order derivatives of the scale factor, called
statefinders, to the conditions which allow to develop sudden future
singularities of pressure with finite energy density. In this context, and
within the framework of Friedmann cosmology, we also propose higher-order
energy conditions which relate time derivatives of the energy density and
pressure which may be useful in general relativity.


title: Repulsive force in the field theory of gravitation

abstract:
  It is shown that the slowing down of the rate of time referencing to the
inertial time leads in the field theory of gravitation to arising of repulsive
forces which remove the cosmological singularity in the evolution of a
homogeneous and isotropic universe and stop the collapse of large masses.


title:
Boundary conditions and symplectic structure in the Chern-Simons
  formulation of (2+1)-dimensional gravity

abstract:
  We propose a description of open universes in the Chern-Simons formulation of
(2+1)-dimensional gravity where spatial infinity is implemented as a puncture.
At this puncture, additional variables are introduced which lie in the
cotangent bundle of the Poincar\'e group, and coupled minimally to the
Chern-Simons gauge field. We apply this description of spatial infinity to open
universes of general genus and with an arbitrary number of massive spinning
particles. Using results of [9] we give a finite dimensional description of the
phase space and determine its symplectic structure. In the special case of a
genus zero universe with spinless particles, we compare our result to the
symplectic structure computed by Matschull in the metric formulation of
(2+1)-dimensional gravity. We comment on the quantisation of the phase space
and derive a quantisation condition for the total mass and spin of an open
universe.


title:
Limit structure of Future Null Infinity tangent -topology of the event
  horizon and gravitational wave tail-

abstract:
  We investigated the relation between the behavior of gravitational wave at
late time and the limit structure of future null infinity tangent which will
determine the topology of the event horizon far in the future. In the present
article, we mainly consider a spacetime with two black holes. Although in most
of cases, the black holes coalesce and its event horizon is topologically a
single sphere far in the future, there are several possibilities that the black
holes never coalesce and such exact solutions as examples. In our formulation,
the tangent vector of future null infinity is, under conformal embedding,
related to the number of black holes far in the future through the
Poincar\'e-Hopf's theorem. Under the conformal embedding, the topology of event
horizon far in the future will be affected by the geometrical structure of the
future null infinity. In this article, we related the behavior of Weyl
curvature to this limit behavior of the generator vector of the future null
infinity. We show if Weyl curvature decays sufficiently slowly at late time in
the neighborhood of future null infinity, two black holes never coalesce.


title: On the thin wall limit of thick planar domain walls

abstract:
  Considering a planar gravitating thick domain wall of the $\lambda \phi^4$
theory, we demonstrate how the Darmois junction conditions written on the
boundaries of the thick wall with the embedding spacetimes reproduce the Israel
junction condition across the wall when one takes its thin wall limit.


title:
A general relativistic effect in quasi-spherical objects as the possible
  origin of relativistic jets

abstract:
  Based on recently reported results, we present arguments that sign changes in
proper acceleration of test particles on the symmetry axis and close to the
r=2M surface of quasi-spherical objects - related to the quadrupole moment of
the source - might be at the origin of relativistic jets of quasars and
micro-quasars.


title: Computing inspirals in Kerr in the adiabatic regime. I. The scalar case

abstract:
  A key source for LISA will be the inspiral of compact objects into
supermassive black holes. Recently Mino has shown that in the adiabatic limit,
gravitational waveforms for these sources can be computed using for the
radiation reaction force the gradient of one half the difference between the
retarded and advanced metric perturbations. Using post-Newtonian expansions, we
argue that the resulting waveforms should be sufficiently accurate for signal
detection with LISA. Data-analysis templates will require higher accuracy,
going beyond adiabaticity; this remains a significant challenge. We describe an
explicit computational procedure for obtaining waveforms based on Mino's
result, for the case of a point particle coupled to a scalar field. We derive
an expression for the time-averaged time derivative of the Carter constant, and
verify that the expression correctly predicts that circular orbits remain
circular while evolving via radiation reaction. The derivation uses detailed
properties of mode expansions, Green's functions and bound geodesic orbits in
the Kerr spacetime, which we review in detail. This paper is about three
quarters review and one quarter new material. The intent is to give a complete
and self-contained treatment of scalar radiation reaction in the Kerr
spacetime, in a single unified notation, starting with the Kerr metric and
ending with formulae for the time evolution of all three constants of the
motion that are sufficiently explicit to be used immediately in a numerical
code.


title: Searching for gravitational waves from known pulsars

abstract:
  We present upper limits on the amplitude of gravitational waves from 28
isolated pulsars using data from the second science run of LIGO. The results
are also expressed as a constraint on the pulsars' equatorial ellipticities. We
discuss a new way of presenting such ellipticity upper limits that takes
account of the uncertainties of the pulsar moment of inertia. We also extend
our previous method to search for known pulsars in binary systems, of which
there are about 80 in the sensitive frequency range of LIGO and GEO 600.


title: Reinterpreting the Pioneer anomaly and its annual residual

abstract:
  In addition to its long-term constancy, the Pioneer (spacecraft) anomaly
appears to only exist for bodies whose mass is less than that of: planets,
moons, comets, and heavy asteroids of known mass. Assuming the observational
evidence is reliable, and not the result of an unknown systematic effect, a
violation of the Weak Principle of Equivalence is implied. To propose an
additional force fails to satisfy this constraint. This paper presents a new
hypothesis involving additional field energy in the form of: a finite number of
lunar sourced constant amplitude (Lorentz invariant) wave-like undulations upon
the gravitational field. Although apparently a futile suggestion, the author's
model overcomes concerns regarding wave dissipation, wave generation, and the
apparent constancy of the anomaly. A shortfall in motion arises because a tiny
proportion of spacecraft kinetic energy is directed into a superposition of
non-translational longitudinal oscillatory components. The restriction of this
effect to low mass bodies is also addressed. Additionally, the annual residual
of the Pioneer anomaly may be attributed to a real 356 day Callisto-Titan wave
resonance. This hypothesis may also be readily applied to other solar system
anomalies including: the Earth flyby anomaly, an apparent absence of small
comets, an apparent paucity of smaller bodies in the Main Belt of asteroids,
and residual doubts concerning the migrating planets hypothesis that addresses
the too rapid formation of the ice giants Uranus and Neptune.


title: Different Approaches for Moller's Energy in the Kasner-type Space-time

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0011027, "Viscous cosmologies in scalar-tensor theories for Kasner type
metrics," by M. Cataldo, S. del Campo and P. Salgado; 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:
Energy of the Universe in Bianchi-type I Models in Moller's Tetrad
  Theory of Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0011027, "Viscous cosmologies in scalar-tensor theories for Kasner type
metrics," by M. Cataldo, S. del Campo and P. Salgado.


title: Gravitational radiation from dynamical black holes

abstract:
  An effective energy tensor for gravitational radiation is identified for
uniformly expanding flows of the Hawking mass-energy. It appears in an energy
conservation law expressing the change in mass due to the energy densities of
matter and gravitational radiation, with respect to a Killing-like vector
encoding a preferred flow of time outside a black hole. In a spin-coefficient
formulation, the components of the effective energy tensor can be understood as
the energy densities of ingoing and outgoing, transverse and longitudinal
gravitational radiation. By anchoring the flow to the trapping horizon of a
black hole in a given sequence of spatial hypersurfaces, there is a locally
unique flow and a measure of gravitational radiation in the strong-field
regime.


title: Physical effects of the Immirzi parameter

abstract:
  The Immirzi parameter is a constant appearing in the general relativity
action used as a starting point for the loop quantization of gravity. The
parameter is commonly believed not to show up in the equations of motion,
because it appears in front of a term in the action that vanishes on shell. We
show that in the presence of fermions, instead, the Immirzi term in the action
does not vanish on shell, and the Immirzi parameter does appear in the
equations of motion. It determines the coupling constant of a four-fermion
interaction. Therefore the Immirzi parameter leads to effects that are
observable in principle, even independently from nonperturbative quantum
gravity.


title: Improved Stack-Slide Searches for Gravitational-Wave Pulsars

abstract:
  We formulate and optimize a computational search strategy for detecting
gravitational waves from isolated, previously-unknown neutron stars (that is,
neutron stars with unknown sky positions, spin frequencies, and spin-down
parameters). It is well known that fully coherent searches over the relevant
parameter-space volumes are not computationally feasible, and so more
computationally efficient methods are called for. The first step in this
direction was taken by Brady & Creighton (2000), who proposed and optimized a
two-stage, stack-slide search algorithm. We generalize and otherwise improve
upon the Brady-Creighton scheme in several ways. Like Brady & Creighton, we
consider a stack-slide scheme, but here with an arbitrary number of
semi-coherent stages and with a coherent follow-up stage at the end. We find
that searches with three semi-coherent stages are significantly more efficient
than two-stage searches (requiring about 2-5 times less computational power for
the same sensitivity) and are only slightly less efficient than searches with
four or more stages. We calculate the signal-to-noise ratio required for
detection, as a function of computing power and neutron star spin-down-age,
using our optimized searches.


title: Multifractal Analysis of Packed Swiss Cheese Cosmologies

abstract:
  The multifractal spectrum of various three-dimensional representations of
Packed Swiss Cheese cosmologies in open, closed, and flat spaces are measured,
and it is determined that the curvature of the space does not alter the
associated fractal structure. These results are compared to observational data
and simulated models of large scale galaxy clustering, to assess the viability
of the PSC as a candidate for such structure formation. It is found that the
PSC dimension spectra do not match those of observation, and possible solutions
to this discrepancy are offered, including accounting for potential luminosity
biasing effects. Various random and uniform sets are also analyzed to provide
insight into the meaning of the multifractal spectrum as it relates to the
observed scaling behaviors.


title: Extended closed inflationary universes

abstract:
  In this paper we study a type of model for closed inflationary universe
models using the Jordan-Brans-Dicke theory. Herein we determine and
characterize the existence of $\Omega>$1, together with the period of
inflation. We have found that our model, which takes into account a
Jordan-Brans-Dicke type of theory, is less restrictive than the one used in
Einstein's theory of general relativity. Our results are compared to those
found in Einstein's theory of Relativity.


title:
Self-Force with a Stochastic Component from Radiation Reaction of a
  Scalar Charge Moving in Curved Spacetime

abstract:
  We give a quantum field theoretical derivation of the scalar
Abraham-Lorentz-Dirac (ALD) equation and the self-force for a scalar charged
particle interacting with a quantum scalar field in curved spacetime. We
regularize the causal Green's function using a quasi-local expansion in the
spirit of effective field theory and obtain a regular expression for the
self-force. The scalar ALD equation obtained in this way for the classical
motion of the particle checks with the equation obtained by Quinn earlier
\cite{Quinn}. We further derive a scalar ALD-Langevin equation with a classical
stochastic force accounting for the effect of quantum fluctuations in the
field, which causes small fluctuations on the particle trajectory. This
equation will be useful for the study of stochastic motion of charges under the
influence of both quantum and classical noise sources, derived either
self-consistently (as done here) or put in by hand (with warnings). We show the
possibility of secular effects from such stochastic influences on the
trajectory that may impact on the present calculations of gravitational
waveform templates.


title:
The densitized lapse ("Taub function") and the Taub time gauge in
  cosmology

abstract:
  The role of the Taub time gauge in cosmology is linked to the use of the
densitized lapse function instead of the lapse function in the variational
principle approach to the Einstein equations. The spatial metric variational
equations then become the Ricci evolution equations, which are then
supplemented by the Einstein constraints which result from the variation with
respect to the densitized lapse and the usual shift vector field. In those
spatially homogeneous cases where the least disconnect occurs between the
general theory and the restricted symmetry scenario, the recent adjustment of
the conformal approach to solving the initial value problem resulting from
densitized lapse considerations is seen to be inherent in the use of
symmetry-adapted metric variables. The minimal distortion shift vector field is
a natural vector potential for the new York thin sandwich initial data approach
to the constraints, which in this case corresponds to the diagonal spatial
metric gauge. For generic spacetimes, the new approach suggests defining a new
minimal distortion shift gauge which agrees with the old gauge in the Taub time
gauge, but which also makes its defining differential equation agree with the
vector potential equation for solving the supermomentum constraint in any time
gauge.


title:
Smooth dynamical (de)-phantomization of a scalar field in simple
  cosmological models

abstract:
  Simple scalar field cosmological models are considered describing gravity
assisted crossing of the phantom divide line. This crossing or
(de)-phantomization characterized by the change of the sign of the kinetic term
of the scalar field is smooth and driven dynamically by the Einstein equations.
Different cosmological scenarios, including the phantom phase of matter are
sketched.


title: Born-Infeld type Gravity

abstract:
  Generalizations of gravitational Born-Infeld type lagrangians are
investigated. Phenomenological constraints (reduction to Einstein-Hilbert
action for small curvature, spin two ghost freedom and absence of Coulomb like
Schwarschild singularity) select one effective lagrangian whose dynamics is
dictated by the tensors g_{\mu\nu} and R_{\mu\nu\rho\sigma}(not R_{\mu\nu} or
the scalar R).


title:
Black Hole Evaporation and Nonequilibrium Thermodynamics for a Radiation
  Field

abstract:
  When a black hole is put in an "empty" space (zero temperature space) on
which there is no matter except the matter of the Hawking radiation (Hawking
field), then an outgoing energy flow from the black hole into the empty space
exists. By the way, an equilibrium between two arbitrary systems can not allow
the existence of an energy (heat) flow from one system to another.
Consequently, in the case of a black hole evaporation in the empty space, the
Hawking field should be in a nonequilibrium state. Hence the total behaviour of
the evaporation, for example the time evolution of the total entropy, should be
analysed with a nonequilibrium thermodynamics for the Hawking field. This
manuscript explains briefly the way of constructing a nonequilibrium
thermodynamic theory for a radiation field, and apply it to a simplified model
of a black hole evaporation to calculate the time evolution of the total
entropy.


title:
Constraint on intermediate-range gravity from earth-satellite and lunar
  orbiter measurements, and lunar laser ranging

abstract:
  In the experimental tests of gravity, there have been considerable interests
in the possibility of intermediate-range gravity. In this paper, we use the
earth-satellite measurement of earth gravity, the lunar orbiter measurement of
lunar gravity, and lunar laser ranging measurement to constrain the
intermediate-range gravity from lambda=1.2*10^{7}m - 3.8*10^{8}m. The limits
for this range are alpha=10^{-8}-5*10^{-8}, which improve previous limits by
about one order of magnitude in the range lambda=1.2*10^{7}m-3.8*10^{8}m.


title: The Holographic Principle and the Early Universe

abstract:
  A scenario is proposed in which the matter-antimatter asymmetry behaves like
a seed for the inflationary phase of the universe. The mechanism which makes
this scenario plausible is the holographic principle: this scheme is supported
by a good prediction of the number of e-folds. It seems that such a mechanism
can only work in the presence of a Hagedorn-like phase transition. The issue of
the "graceful exit" can also be naturally accounted for.


title: Space-Time Structure and Electromagnetism

abstract:
  Two Lagrangian functions are used to construct geometric field theories. One
of these Lagrangians depends on the curvature of space, while the other depends
on curvature and torsion. It is shown that the theory constructed from the
first Lagrangian gives rise to pure gravity, while the theory constructed using
the second Lagrangian gives rise to both gravity and electromagnetism. The two
theories are constructed in a version of absolute parallelism geometry in which
both curvature and torsion are, simultaneously, non-vanishing. One single
geometric object, {\it W-tensor}, reflecting the properties of curvature and
torsion, is defined in this version and is used to construct the second theory.
The main conclusion is that a necessary condition for geometric representation
of electromagnetism is the presence of a non-vanishing torsion in the geometry
used.


title:
Axially symmetric equilibrium regions of
  Friedmann-Lemaitre-Robertson-Walker universes

abstract:
  The study of the matching of stationary and axisymmetric spacetimes with
Friedmann-Lemaitre-Robertson-Walker spacetimes preserving the axial symmetry is
presented. We show, in particular, that any orthogonally transitive stationary
and axisymmetric region in FLRW must be static, irrespective of the matter
content. Therefore, previous results on static regions in FLRW cosmologies
apply. As a result, the only stationary and axisymmetric vacuum region that can
be matched to a (non-static) FLRW spacetime is a spherically symmetric region
of Schwarzschild. This constitutes another uniqueness result for the
Einstein-Straus model (as well as its Oppenheimer-Snyder counterpart), and
hence another indication of its unsuitability as an answer to the influence of
the cosmic expansion on local physics.


title: Plane fronted gravitational waves in Lovelock-Yang-Mills theory

abstract:
  We obtain plane fronted gravitational waves (PFGWs) in arbitrary dimension in
Lovelock gravity, to any order in the Riemann tensor. We exhibit pure gravity
as well as Lovelock-Yang-Mills PFGWs. Lovelock-Maxwell and $pp$ waves arise as
particular cases. The electrovac solutions trivially satisfy the
Lovelock-Born-Infeld field equations. The peculiarities that arise in
degenerate Lovelock theories are also analyzed.


title: Anisotropic Hubble expansion of large scale structures

abstract:
  We investigate the dynamics of an homogenous distribution of galaxies moving
under the cosmological expansion through Euler-Poisson equations system. The
solutions are interpreted with the aim of understanding the cosmic velocity
fields in the Local Super Cluster, and in particular the presence of a bulk
flow. Among several solutions, we shows a planar kinematics with constant
(eternal) and rotational distortion, the velocity field is not potential.


title: Dual interacting cosmologies and late accelerated expansion

abstract:
  In this paper we show that by considering a universe dominated by two
interacting components a superaccelerated expansion can be obtained from a
decelerated one by applying a dual transformation that leaves the Einstein's
field equations invariant.


title: Superselection sectors in the Ashtekar-Horowitz-Boulware model

abstract:
  We investigate refined algebraic quantisation of the constrained Hamiltonian
system introduced by Boulware as a simplified version of the Ashtekar-Horowitz
model. The dimension of the physical Hilbert space is finite and asymptotes in
the semiclassical limit to 1/(2\pi\hbar) times the volume of the reduced phase
space. The representation of the physical observable algebra is irreducible for
generic potentials but decomposes into irreducible subrepresentations for
certain special potentials. The superselection sectors are related to
singularities in the reduced phase space and to the rate of divergence in the
formal group averaging integral. There is no tunnelling into the classically
forbidden region of the unreduced configuration space, but there can be
tunnelling between disconnected components of the classically allowed region.


title: Weak 'Antigravity' Fields in General Relativity

abstract:
  Within the weak-field approximation of general relativity, new exact
solutions are derived for the gravitational field of a mass moving with
arbitrary velocity and acceleration. A mass having a constant velocity greater
than 3^-1/2 times the speed of light gravitationally repels other masses at
rest within a narrow cone. At high Lorentz factors (gamma >> 1), the force of
repulsion in the forward direction is about -8(gamma^5) times the Newtonian
force, offering opportunities for laboratory tests of gravity at extreme
velocities. One such experiment is outlined for the Large Hadron Collider.


title: Exact Relativistic 'Antigravity' Propulsion

abstract:
  The Schwarzschild solution is used to find the exact relativistic motion of a
payload in the gravitational field of a mass moving with constant velocity. At
radial approach or recession speeds faster than 3^-1/2 times the speed of
light, even a small mass gravitationally repels a payload. At relativistic
speeds, a suitable mass can quickly propel a heavy payload from rest nearly to
the speed of light with negligible stresses on the payload.


title:
Reducing reflections from mesh refinement interfaces in numerical
  relativity

abstract:
  Full interpretation of data from gravitational wave observations will require
accurate numerical simulations of source systems, particularly binary black
hole mergers. A leading approach to improving accuracy in numerical relativity
simulations of black hole systems is through fixed or adaptive mesh refinement
techniques. We describe a manifestation of numerical interface truncation error
which appears as slowly converging, artificial reflections from refinement
boundaries in a broad class of mesh refinement implementations, potentially
compromising the effectiveness of mesh refinement techniques for some numerical
relativity applications if left untreated. We elucidate this numerical effect
by presenting a model problem which exhibits the phenomenon, but which is
simple enough that its numerical error can be understood analytically. Our
analysis shows that the effect is caused by variations in finite differencing
error generated across low and high resolution regions, and that its slow
convergence is caused by the presence of dramatic speed differences among
propagation modes typical of 3+1 relativity. Lastly, we resolve the problem,
presenting a class of finite differencing stencil modifications, termed
mesh-adapted differencing (MAD), which eliminate this pathology in both our
model problem and in numerical relativity examples.


title: The gravity lagrangian according to solar system experiments

abstract:
  In this work we show that the gravity lagrangian f(R) at relatively low
curvatures in both metric and Palatini formalisms is a bounded function that
can only depart from the linearity within the limits defined by well known
functions. We obtain those functions by analysing a set of inequalities that
any f(R) theory must satisfy in order to be compatible with laboratory and
solar system observational constraints. This result implies that the recently
suggested f(R) gravity theories with nonlinear terms that dominate at low
curvatures are incompatible with observations and, therefore, cannot represent
a valid mechanism to justify the cosmic speed-up.


title:
Using the INSPIRAL program to search for gravitational waves from
  low-mass binary inspiral

abstract:
  The INSPIRAL program is the LIGO Scientific Collaboration's computational
engine for the search for gravitational waves from binary neutron stars and
sub-solar mass black holes. We describe how this program, which makes use of
the FINDCHIRP algorithm (discussed in a companion paper), is integrated into a
sophisticated data analysis pipeline that was used in the search for low-mass
binary inspirals in data taken during the second LIGO science run.


title: Emergent Universe in Starobinsky Model

abstract:
  We present an emergent universe scenario making use of a new solution of the
Starobinsky model. The solution belongs to a one parameter family of solutions,
where the parameter is determined by the number and the species (spin-values)
of primordial fields. The general features of the model have also been studied.


title: Vacuum energy: quantum hydrodynamics vs quantum gravity

abstract:
  We compare quantum hydrodynamics and quantum gravity. They share many common
features. In particular, both have quadratic divergences, and both lead to the
problem of the vacuum energy, which in the quantum gravity transforms to the
cosmological constant problem. We show that in quantum liquids the vacuum
energy density is not determined by the quantum zero-point energy of the phonon
modes. The energy density of the vacuum is much smaller and is determined by
the classical macroscopic parameters of the liquid including the radius of the
liquid droplet. In the same manner the cosmological constant is not determined
by the zero-point energy of quantum fields. It is much smaller and is
determined by the classical macroscopic parameters of the Universe dynamics:
the Hubble radius, the Newton constant and the energy density of matter. The
same may hold for the Higgs mass problem: the quadratically divergent quantum
correction to the Higgs potential mass term is also cancelled by the
microscopic (trans-Planckian) degrees of freedom due to thermodynamic stability
of the whole quantum vacuum.


title: Accelerating Universes from Short-Range Interactions

abstract:
  We show that short-range interactions between the fundamental particles in
the universe can drive a period of accelerated expansion. This description fits
the early universe. In the present day universe, if one postulates short-range
interactions or a sort of "shielded gravity", the picture may repeat.


title:
The impact of the new Earth gravity model EIGEN-CG03C on the measurement
  of the Lense-Thirring effect with some existing Earth satellites

abstract:
  The impact of the latest combined CHAMP/GRACE/terrestrial measurements Earth
gravity model EIGEN-CG03C on the measurement of the Lense-Thirring effect with
some linear combinations of the nodes of some of the existing Earth's
artificial satellites is presented. The 1-sigma upper bound of the systematic
error in the node-node LAGEOS-LAGEOS II combination is 3.9% (4% with
EIGEN-GRACE02S, \sim 6% with EIGEN-CG01C and \sim 9% with GGM02S), while it is
1$% for the node-only LAGEOS-LAGEOS II-Ajisai-Jason-1 combination (2% with
EIGEN-GRACE02S, 1.6% with EIGEN-CG01C and 2.7% with GGM02S).


title:
Are we far from testing general relativity with the transiting
  extrasolar planet HD 209458b `Osiris'?

abstract:
  In this paper we investigate the possibility of measuring the general
relativistic gravitoelectric contribution P^(GE) to the orbital period P of the
transiting exoplanet HD 209458b 'Osiris'. It turns out that the predicted
magnitude of such an effect is \sim 0.1 s, while the most recent determinations
of the orbital period of HD 209458b with the photometric transit method are
accurate to \sim 0.01 s. The present analysis shows that the major limiting
factor is the \sim 1 m s^-1 sensitivity in the measurement of the projected
semiamplitude of the star's radial velocity K. Indeed, it affects the
determination of the mass m of the planet which, in turn, induces a systematic
error in the Keplerian period P^(0) of \sim 8 s. It is of crucial importance
because P^(0) should be subtracted from the measured period in order to extract
the relativistic correction. The present-day uncertainty in $m$ does not yet
make necessary the inclusion of relativistic corrections in the data-reduction
process of the determination of the system's parameters. The present situation
could change only if improvements of one-two orders of magnitude in the
ground-based Doppler spectroscopy technique occurred.


title: Inhomogeneous perturbations of plane-wave spacetimes

abstract:
  Recently it was shown that the exact cosmological solutions known as the
vacuum plane-wave solutions are late-time attractors for an open set of the
spatially homogeneous Bianchi universes containing a non-inflationary
$\gamma$-law perfect fluid. In this paper we study inhomogeneous perturbations
of these plane-wave spacetimes. By using expansion-normalised scale-invariant
variables we show that these solutions are unstable to generic inhomogeneous
perturbations. The crucial observation for establishing this result is a
divergence of the expansion-normalised frame variables which ultimately leads
to unstable modes.


title:
Quantization of Friedmann cosmological models with two fluids: dust plus
  radiation

abstract:
  The causal interpretation of quantum mechanics is applied to a homogeneous
and isotropic quantum universe, whose matter content is composed by non
interacting dust and radiation. For wave functions which are eigenstates of the
total dust mass operator, we find some bouncing quantum universes which reachs
the classical limit for scale factors much larger than its minimum size.
However these wave functions do not have unitary evolution. For wave functions
which are not eigenstates of the dust total mass operator but do have unitary
evolution, we show that, for flat spatial sections, matter can be created as a
quantum effect in such a way that the universe can undergo a transition from an
exotic matter dominated era to a matter dominated one.


title: Einstein-Planck Formula, Equivalence Principle and Black Hole Radiance

abstract:
  The presence of gravity implies corrections to the Einstein-Planck formula
$E=h \nu$. This gives hope that the divergent blueshift in frequency,
associated to the presence of a black hole horizon, could be smoothed out for
the energy. Using simple arguments based on Einstein's equivalence principle we
show that this is only possible if a black hole emits, in first approximation,
not just a single particle, but thermal radiation.


title: Entropy and Area in Loop Quantum Gravity

abstract:
  Black hole thermodynamics suggests that the maximum entropy that can be
contained in a region of space is proportional to the area enclosing it rather
than its volume. I argue that this follows naturally from loop quantum gravity
and a result of Kolmogorov and Bardzin' on the the realizability of networks in
three dimensions. This represents an alternative to other approaches in which
some sort of correlation between field configurations helps limit the degrees
of freedom within a region. It also provides an approach to thinking about
black hole entropy in terms of states inside rather than on its surface.
Intuitively, a spin network complicated enough to imbue a region with volume
only lets that volume grow as quickly as the area bounding it.


title: Intermediate Asymptotics of the Kerr Quasinormal Spectrum

abstract:
  We study analytically the quasinormal mode spectrum of near-extremal
(rotating) Kerr black holes. We find an analytic expression for these
black-hole resonances in terms of the black-hole physical parameters: its
Bekenstein-Hawking temperature T_{BH} and its horizon's angular velocity
\Omega, which is valid in the intermediate asymptotic regime
1<<\omega<<1/T_{BH}.


title:
Perturbative Analysis of Universality and Individuality in Gravitational
  Waves from Neutron Stars

abstract:
  The universality observed in gravitational wave spectra of non-rotating
neutron stars is analyzed here. We show that the universality in the axial
oscillation mode can be reproduced with a simple stellar model, namely the
centrifugal barrier approximation (CBA), which captures the essence of the
Tolman VII model of compact stars. Through the establishment of scaled
co-ordinate logarithmic perturbation theory (SCLPT), we are able to explain and
quantitatively predict such universal behavior. In addition, quasi-normal modes
of individual neutron stars characterized by different equations of state can
be obtained from those of CBA with SCLPT.


title:
On global existence for the spherically symmetric Einstein-Vlasov system
  in Schwarzschild coordinates

abstract:
  The spherically symmetric Einstein-Vlasov system in Schwarzschild coordinates
(i.e. polar slicing and areal radial coordinate) is considered. An improved
continuation criterion for global existence of classical solutions is given.
Two other types of criteria which prevent finite time blow-up are also given.


title: Stochastic Quantum Gravitational Inflation

abstract:
  During inflation explicit perturbative computations of quantum field theories
which contain massless, non-conformal fields exhibit secular effects that grow
as powers of the logarithm of the inflationary scale factor. Starobinskii's
technique of stochastic inflation not only reproduces the leading infrared
logarithms at each order in perturbation theory, it can sometimes be summed to
reveal what happens when inflation has proceeded so long that the large
logarithms overwhelm even very small coupling constants. It is thus a
cosmological analogue of what the renormalization group does for the
ultraviolet logarithms of quantum field theory, and generalizing this technique
to quantum gravity is a problem of great importance. There are two significant
differences between gravity and the scalar models for which stochastic
formulations have so far been given: derivative interactions and the presence
of constrained fields. We use explicit perturbative computations in two simple
scalar models to infer a set of rules for stochastically formulating theories
with these features.


title: The Mirror Universes

abstract:
  In this paper we investigate the structure of the Mirror Universes. The two
universes are coupled with transformation t to -t. It is shown that for Planck
scale the oscillations of temperature of the universes are observed. For the
Mirror Universes the temperature fields are shifted in phase.
  Key words: Gravity; Universe temperature; Oscillation of temperature.


title: Dynamical SU(2) magnetic monopoles

abstract:
  In our paper Phys. Rev. Lett. 92, 151801 (2004), the oscillations of strongly
deformed Bogomolny-Prasad-Sommerfield magnetic monopoles have been studied on a
fixed Minkowski background. The purpose of the present article is to provide a
more detailed account on the results yielded by our numerical simulations. In
particular, an analysis on the dependence on the strength of the initial
excitation is carried out in order to distinguish features which are already
present for small perturbations from those which are consequences of the
nonlinearity of the system.


title: The Einstein-Vlasov-Maxwell(EVM) System with Spherical Symmetry

abstract:
  We look for the global in time solution of the Cauchy problem corresponding
to the asymptotically flat spherically symmetric EVM system with small initial
data. Using an estimate, we also prove that if solution of the system stated
above develops a singularity at all time, then the first one has to appear at
the center of symmetry.


title: Information Storage in Black Holes

abstract:
  The information loss paradox for Schwarzschild black holes is examined, using
the ADS/CFT correspondence extended to the $M_6 (4,2)$ bulk. It is found that
the only option compatible with the preservation of the quantum unitarity is
when a regular remnant region of the black hole survives to the black hole
evaporation process, where information can be stored and eventually retrieved.


title:
Quasi-circular orbits of conformal thin-sandwich puncture binary black
  holes

abstract:
  I construct initial data for equal-mass irrotational binary black holes using
the conformal thin-sandwich puncture (CTSP) approach. I locate quasi-circular
orbits using the effective-potential method, and estimate the location of the
innermost stable circular orbit (ISCO). The ISCO prediction is consistent with
results for conformal thin-sandwich data produced using excision techniques.
These results also show that the ISCOs predicted by the effective-potential and
ADM-Komar mass-comparison methods agree for conformal thin-sandwich data, just
as they did for Bowen-York data.


title: The cosmic coincidence in Brans-Dicke cosmologies

abstract:
  Among the suggested solutions to the cosmological constant problem, we find
the idea of a dynamic vacuum, with an energy density decaying with the universe
expansion. We investigate the possibility of a variation in the gravitational
constant as well, induced, at the cosmological scale, by the vacuum decay. We
consider an effective Brans-Dicke theory in the spatially flat FLRW spacetime,
finding late time solutions characterized by a constant ratio between the
matter and vacuum energy densities. By using the observed limits for the
universe age, we fix the only free parameter of our solutions, obtaining a
relative matter density in the range 0.25-0.4. In particular, for Ht = 1 we
obtain a relative matter density equals to 1/3. This constitutes a possible
explanation for another problem related to the cosmological term, the cosmic
coincidence problem.


title: On the Riemann extension of rotating Mikowsky space-time metric

abstract:
  Some properties of eight-dimensional Riemann extension of Minkowsky
space-time metric in rotating coordinate system are studied.


title:
Inflaton field governed universe from NKK theory of gravity: stochastic
  approach

abstract:
  We study a nonperturbative single field (inflaton) governed cosmological
model from a 5D Noncompact Kaluza-Klein (NKK) theory of gravity. The inflaton
field fluctuations are estimated for different epochs of the evolution of the
universe. We conclude that the inflaton field has been sliding down its
(quadratic) potential hill along all the evolution of the universe and a mass
of the order of the Hubble parameter. In the model here developed the only free
parameter is the Hubble parameter, which could be reconstructed in future from
Super Nova Acceleration Probe (SNAP) data.


title: The Ellis wormhole with `tachyon matter'

abstract:
  The Ellis wormhole is known to be an exact solution of the Einstein--scalar
system where the scalar field has negative kinetic energy (phantom). We show
here that the same geometry (in 3+1 dimensions) can also be obtained with
`tachyon matter' as a source term in the field equations and a positive
cosmological constant. The kink--like tachyon field profile and the nature of
the tachyon potential are analyzed. It is shown that the field configuration
and the spacetime are stable against linear scalar perturbations. Finally, we
comment on extensions of the 3+1 dimensional Ellis wormhole (with tachyon
matter source) in diverse dimensions (d=2+1 and d>4).


title: Inflationary solutions with a five dimensional complex scalar field

abstract:
  We discuss inflationary solutions of the coupled Einstein-Klein-Gordon
equations for a complex field in a five dimensional spacetime with a compact
$x^5$-dimension. As a new feature, the scalar field contains a dependence on
the extra dimension of the form $\exp(i m x^5) $, corresponding to Kaluza-Klein
excited modes. In a four dimensional picture, a nonzero $m$ implies the
presence of a new term in the scalar field potential. An interesting feature of
these solutions is the possible existence of several periods of oscillation of
the scalar field around the equilibrium value at the minimum of the potential.
These oscillations lead to cosmological periods of accelerated expansion of the
universe.


title: Dynamical dark energy models -- dynamical system approach

abstract:
  We study the Friedmann-Robertson-Walker model with dynamical dark energy
modelled in terms of the equation of state $p_{x}=w_{x}(a(z)) \rho_{x}$ in
which the coefficient $w_{x}$ is parameterized by the scale factor $a$ or
redshift $z$. We use methods of qualitative analysis of differential equations
to investigate the space of all admissible solutions for all initial conditions
on the two-dimensional phase plane. We show advantages of representing this
dynamics as a motion of a particle in the one-dimensional potential $V(a)$. One
of the features of this reduction is the possibility of investigating how
typical are big rip singularities in the future evolution of the model. The
properties of potential function $V$ can serve as a tool for qualitative
classification of all evolution paths. Some important features like resolution
of the acceleration problem can be simply visualized as domains on the phase
plane. Then one is able to see how large is the class of solutions (labelled by
the inset of the initial conditions) leading to the desired property.


title: Plane 5D worlds and simple compactification

abstract:
  We obtain a new kind of exact solution to vaccum Einstein field equations
that contain both Minkowsian world and a special 5D curved spacetime with
particularly free structure. This special world is defined by an arbitrary
function and a space of three parameters. We suggest that this solution could
correct (in principle) certain aspects of the physics in flat spacetime.


title: Covariant conservation of energy momentum in modified gravities

abstract:
  An explicit proof of the vanishing of the covariant divergence of the
energy-momentum tensor in modified theories of gravity is presented. The
gravitational action is written in arbitrary dimensions and allowed to depend
nonlinearly on the curvature scalar and its couplings with a scalar field. Also
the case of a function of the curvature scalar multiplying a matter Lagrangian
is considered. The proof is given both in the metric and in the first-order
formalism, i.e. under the Palatini variational principle. It is found that the
covariant conservation of energy-momentum is built-in to the field equations.
This crucial result, called the generalized Bianchi identity, can also be
deduced directly from the covariance of the extended gravitational action.
Furthermore, we demonstrate that in all of these cases, the freely falling
world lines are determined by the field equations alone and turn out to be the
geodesics associated with the metric compatible connection. The independent
connection in the Palatini formulation of these generalized theories does not
have a similar direct physical interpretation. However, in the conformal
Einstein frame a certain bi-metricity emerges into the structure of these
theories. In the light of our interpretation of the independent connection as
an auxiliary variable we can also reconsider some criticisms of the Palatini
formulation originally raised by Buchdahl.


title: Solution Independent Analysis of Black Hole Entropy in Brick Wall Model

abstract:
  Using the brick wall regularization of 't Hooft, the entropy of non-extreme
and extreme black holes is investigated in a general static, spherically
symmetric spacetime. We classify the singularity in the entropy by introducing
a {\it new} index $\delta $ with respect to the brick wall cut-off $\epsilon $.
The leading contribution to entropy for non-extreme case $(\delta \neq 0)$ is
shown to satisfy the area law with quadratic divergence with respect to the
invariant cut-off $\epsilon_{{\rm inv}}$ while the extreme case $(\delta =0)$
exhibits logarithmic divergence or constant value with respect to $\epsilon $.
The general formula is applied to Reissner-Nordstr\"{o}m, dilaton and
brane-world black holes and we obtain consistent results.


title:
An Exact Solution for Static Scalar Fields Coupled to Gravity in
  $(2+1)$-Dimensions

abstract:
  We obtain an exact solution for the Einstein's equations with cosmological
constant coupled to a scalar, static particle in static, "spherically"
symmetric background in 2+1 dimensions.


title: Production of scalar particles in expanding spacetime

abstract:
  In this paper, we investigate cosmological particle production using quantum
field theory (QFT). We will consider how production of scalar particles can
occur in an expanding universe. By introducing a time-dependent energy
parameter representing the time evolution of the universe, the initial vacuum
state will be excited. Consequently, creation of particles is present. Here,
our focus is mainly creation of minimally coupled scalar particles in Minkowski
spacetime.


title: Application of Theorems on Null-Geodesics on the Solar Limb Effect

abstract:
  A direct and more general calculation of the limb effect connected with
red-shift observations is obtained. Result agrees completely, in its general
form, with that obtained from observations of the solar spectra but with
different value for the maximum effect.


title: Theorems on existence and global dynamics for the Einstein equations

abstract:
  This article is a guide to theorems on existence and global dynamics of
solutions of the Einstein equations. It draws attention to open questions in
the field. The local-in-time Cauchy problem, which is relatively well
understood, is surveyed. Global results for solutions with various types of
symmetry are discussed. A selection of results from Newtonian theory and
special relativity that offer useful comparisons is presented. Treatments of
global results in the case of small data and results on constructing spacetimes
with prescribed singularity structure or late-time asymptotics are given. A
conjectural picture of the asymptotic behaviour of general cosmological
solutions of the Einstein equations is built up. Some miscellaneous topics
connected with the main theme are collected in a separate section.


title: Ghosts, Strong Coupling and Accidental Symmetries in Massive Gravity

abstract:
  We show that the strong self-interaction of the scalar polarization of a
massive graviton can be understood in terms of the propagation of an extra
ghost-like degree of freedom, thus relating strong coupling to the sixth degree
of freedom discussed by Boulware and Deser in their Hamiltonian analysis of
massive gravity. This enables one to understand the Vainshtein recovery of
solutions of massless gravity as being due to the effect of the exchange of
this ghost which gets frozen at distances larger than the Vainshtein radius.
Inside this region, we can trust the two-field Lagrangian perturbatively, while
at larger distances one can use the higher derivative formulation. We also
compare massive gravity with other models, namely deconstructed theories of
gravity, as well as DGP model. In the latter case we argue that the Vainshtein
recovery process is of different nature, not involving a ghost degree of
freedom.


title: Post-Newtonian constraints on f(R) cosmologies in metric formalism

abstract:
  We compute the complete post-Newtonian limit of the metric form of f(R)
gravities using a scalar-tensor representation. By comparing the predictions of
these theories with laboratory and solar system experiments, we find a set of
inequalities that any lagrangian f(R) must satisfy. The constraints imposed by
those inequalities allow us to find explicit bounds to the possible nonlinear
terms of the lagrangian. We conclude that the lagrangian f(R) must be almost
linear in R and that corrections that grow at low curvatures are incompatible
with observations. This result shows that modifications of gravity at very low
cosmic densities cannot be responsible for the observed cosmic speed-up.


title: Post-Newtonian constraints on f(R) cosmologies in Palatini formalism

abstract:
  We compute the complete post-Newtonian limit of the Palatini form of f(R)
gravities using a scalar-tensor representation. By comparing the predictions of
these theories with laboratory and solar system experiments, we find a set of
inequalities that any lagrangian f(R) must satisfy. The constraints imposed by
those inequalities allow us to find explicit functions that bound from above
and from below the possible nonlinear terms of the lagrangian. We conclude that
the lagrangian f(R) must be almost linear in R and that nonlinear corrections
that grow at low curvatures are incompatible with observations. This result
shows that modifications of gravity at very low cosmic densities cannot be
responsible for the observed cosmic speed-up.


title: Gravastars must have anisotropic pressures

abstract:
  One of the very small number of serious alternatives to the usual concept of
an astrophysical black hole is the "gravastar" model developed by Mazur and
Mottola; and a related phase-transition model due to Laughlin et al. We
consider a generalized class of similar models that exhibit continuous pressure
-- without the presence of infinitesimally thin shells. By considering the
usual TOV equation for static solutions with negative central pressure, we find
that gravastars cannot be perfect fluids -- anisotropic pressures in the
"crust" of a gravastar-like object are unavoidable. The anisotropic TOV
equation can then be used to bound the pressure anisotropy. The transverse
stresses that support a gravastar permit a higher compactness than is given by
the Buchdahl--Bondi bound for perfect fluid stars. Finally we comment on the
qualitative features of the equation of state that gravastar material must have
if it is to do the desired job of preventing horizon formation.


title:
Fibered Manifolds, Natural Bundles, Structured Sets, G-Sets and all
  that: The Hole Story from Space Time to Elementary Particles

abstract:
  In this paper we review the hole argument for the space-time points and
elementary particles and generalize the hole argument to include all geometric
object fields and diffeomorphisms; and, by application of forgetful functors to
abstract from differentiability and even continuity, the hole argument is
applied to a much wider class of mathematical objects. We discuss the problem
concerning the individuation of the objects in more general settings such that
fibered manifolds, fibered sets and n-ary relations.


title:
The recollapse problem of closed FRW models in higher-order gravity
  theories

abstract:
  We study the closed universe recollapse conjecture for positively curved FRW
models with a perfect fluid matter source and a scalar field which arises in
the conformal frame of the $R+\alpha R^{2}$ theory. By including ordinary
matter, we extend the analysis of a previous work. We analyze the structure of
the resulted four-dimensional dynamical system with the methods of the center
manifold theory and the normal form theory. It is shown that an initially
expanding closed FRW universe, starting close to the Minkowski spacetime,
cannot avoid recollapse. We discuss the posibility that potentials with a
positive minimum may prevent the recollapse of closed universes.


title: Some effects of the quantum field theory in the early Universe

abstract:
  Effects of the vacuum polarization leading to change of the effective
gravitational constant and particle creation in the early Universe are
discussed. Gauss-Bonnet type coupling to the curvature is considered.
Renormalization methods are generalized for such coupling and the N-dimensional
space-time. Calculations of creation of entropy and visible matter of the
Universe by the gravity of dark matter are made.


title:
On static spherically symmetric solutions of the vacuum Brans-Dicke
  theory

abstract:
  It is shown that among the four classes of the static spherically symmetric
solution of the vacuum Brans-Dicke theory of gravity only two are really
independent. Further by matching exterior and interior (due to physically
reasonable spherically symmetric matter source) scalar fields it is found that
only Brans class I solution with certain restriction on solution parameters may
represent exterior metric for a nonsingular massive object. The physical
viability of the black hole nature of the solution is investigated. It is
concluded that no physical black hole solution different from the Schwarzschild
black hole is available in the Brans-Dicke theory.


title:
A class of exact solutions of Einstein's field equations in higher
  dimensional spacetimes, d${\bm\geq 4}$: Majumdar-Papapetrou solutions

abstract:
  The Newtonian theory of gravitation and electrostatics admit equilibrium
configurations of charged fluids where the charge density can be equal to the
mass density, in appropriate units. The general relativistic analog for charged
dust stars was discovered by Majumdar and by Papapetrou. In the present work we
consider Einstein-Maxwell solutions in d-dimensional spacetimes and show that
there are Majumdar-Papapetrou type solutions for all ${\rm d} \geq 4$. It is
verified that the equilibrium is independent of the shape of the distribution
of the charged matter. It is also showed that for perfect fluid solutions
satisfying the Majumdar-Papapetrou condition with a boundary where the pressure
is zero, the pressure vanishes everywhere, and that the $({\rm
d}-1)$-dimensional spatial section of the spacetime is conformal to a
Ricci-flat space. The Weyl d-dimensional axisymmetric solutions are generalized
to include electric field and charged matter.


title: Rotating Boson Stars and Q-Balls

abstract:
  We consider axially symmetric, rotating boson stars. Their flat space limits
represent spinning Q-balls. We discuss their properties and determine their
domain of existence. Q-balls and boson stars are stationary solutions and exist
only in a limited frequency range. The coupling to gravity gives rise to a
spiral-like frequency dependence of the boson stars. We address the flat space
limit and the limit of strong gravitational coupling. For comparison we also
determine the properties of spherically symmetric Q-balls and boson stars.


title: Maximum mass of a cold compact star

abstract:
  We calculate the maximum mass of the class of compact stars described by
Vaidya-Tikekar \cite{VT01} model. The model permits a simple method of
systematically fixing bounds on the maximum possible mass of cold compact stars
with a given value of radius or central density or surface density. The
relevant equations of state are also determined. Although simple, the model is
capable of describing the general features of the recently observed very
compact stars. For the calculation, no prior knowledge of the equation of state
(EOS) is required. This is in contrast to the earlier calculations for maximum
mass which were done by choosing first the relevant EOSs and using those to
solve the TOV equation with appropriate boundary conditions. The bounds
obtained by us are comparable and, in some cases, more restrictive than the
earlier results.


title: Braneworld resonances

abstract:
  We investigate in detail gravitational waves in an Schwarzschild-anti-de
Sitter bulk spacetime surrounded by an Einstein static brane with generic
matter content. Such a model provides a useful analogy to braneworld cosmology
at various stages of its evolution, and generalizes our previous work
[gr-qc/0504023] on pure tension Einstein-static branes. We find that the
behaviour of tensor-mode perturbations is completely dominated by quasi-normal
modes, and we use a variety of numeric and analytic techniques to find the
frequencies and lifetimes of these excitations. The parameter space governing
the model yields a rich variety of resonant phenomena, which we thoroughly
explore. We find that certain configurations can support a number of lightly
damped `quasi-bound states'. A zero-mode which reproduces 4-dimensional general
relativity is recovered on infinitely large branes. We also examine the problem
in the time domain using Green's function techniques in addition to direct
numeric integration. We conclude by discussing how the quasi-normal resonances
we find here can impact on braneworld cosmology.


title: Volume elements and torsion

abstract:
  We reexamine here the issue of consistency of minimal action formulation with
the minimal coupling procedure (MCP) in spaces with torsion. In Riemann-Cartan
spaces, it is known that a proper use of the MCP requires that the trace of the
torsion tensor be a gradient, $T_\mu=\partial_\mu\theta$, and that the modified
volume element $\tau_\theta = e^\theta \sqrt{g} dx^1\wedge...\wedge dx^n $ be
used in the action formulation of a physical model. We rederive this result
here under considerably weaker assumptions, reinforcing some recent results
about the inadequacy of propagating torsion theories of gravity to explain the
available observational data. The results presented here also open the door to
possible applications of the modified volume element in the geometric theory of
crystalline defects.


title: Gravitational Model of the String

abstract:
  It is shown that an infinite gravitational flux tube solution in 5D
Kaluza-Klein gravity with the cross section in the Planck region after $5D \to
4D$ reduction and isometrical embedding in a Minkowski spacetime can be
considered as a moving infinite string-like object. Such object has a flux of
the electric and magnetic fields. The 4D gravitational waves on the tube are
considered.


title: Particle Creation in de Sitter Space and Time Quantization

abstract: This paper has been withdrawn.


title:
The geometry of a naked singularity created by standing waves near a
  Schwarzschild horizon, and its application to the binary black hole problem

abstract:
  The most promising way to compute the gravitational waves emitted by binary
black holes (BBHs) in their last dozen orbits, where post-Newtonian techniques
fail, is a quasistationary approximation introduced by Detweiler and being
pursued by Price and others. In this approximation the outgoing gravitational
waves at infinity and downgoing gravitational waves at the holes' horizons are
replaced by standing waves so as to guarantee that the spacetime has a helical
Killing vector field. Because the horizon generators will not, in general, be
tidally locked to the holes' orbital motion, the standing waves will destroy
the horizons, converting the black holes into naked singularities that resemble
black holes down to near the horizon radius. This paper uses a spherically
symmetric, scalar-field model problem to explore in detail the following BBH
issues: (i) The destruction of a horizon by the standing waves. (ii) The
accuracy with which the resulting naked singularity resembles a black hole.
(iii) The conversion of the standing-wave spacetime (with a destroyed horizon)
into a spacetime with downgoing waves by the addition of a ``radiation-reaction
field''. (iv) The accuracy with which the resulting downgoing waves agree with
the downgoing waves of a true black-hole spacetime (with horizon). The model
problem used to study these issues consists of a Schwarzschild black hole
endowed with spherical standing waves of a scalar field. It is found that the
spacetime metric of the singular, standing-wave spacetime, and its
radiation-reaction-field-constructed downgoing waves are quite close to those
for a Schwarzschild black hole with downgoing waves -- sufficiently close to
make the BBH quasistationary approximation look promising for
non-tidally-locked black holes.


title: The Topology of Branching Universes

abstract:
  The purpose of this paper is to survey the possible topologies of branching
space-times, and, in particular, to refute the popular notion in the literature
that a branching space-time requires a non-Hausdorff topology.


title:
The averaged tensors of the relative energy-momentum and angular
  momentum in general relativity

abstract:
  There exist at least a few different kind of averaging of the differences of
the energy-momentum and angular momentum in normal coordinates {\bf NC(P)}
which give tensorial quantities. The obtained averaged quantities are
equivalent mathematically because they differ only by constant scalar
dimensional factors. One of these averaging was used in our papers [1-8] giving
the {\it canonical superenergy and angular supermomentum tensors}.
  In this paper we present one other averaging of the energy-momentum and
angular momentum differences which gives tensorial quantities with proper
dimensions of the energy-momentum and angular momentum densities. But these
averaged energy-momentum and angular momentum tensors, closely related to the
canonical superenergy and angular supermomentum tensors, {\it depend on some
fundamental length L}.
  The averaged energy-momentum and angular momentum tensors of the
gravitational field obtained in the paper can be applied, like the canonical
superenergy and angular supermomentum tensors, to coordinate independent local
(and also global) analysis of this field.


title: Dynamics of radiation dominated branes: Vacuum dynamics from radiation

abstract:
  I point out a symmetry, between equations of state for polytropic fluids, in
the equation of motion of a spherically symmetric singular shell embedded in
4-d and 5-d vacuum spacetimes. In particular the equation of motion of a shell
consisting of radiation has the same form as for a vacuum shell or domain wall.


title: How red is a quantum black hole?

abstract:
  Radiating black holes pose a number of puzzles for semiclassical and quantum
gravity. These include the transplanckian problem -- the nearly infinite
energies of Hawking particles created near the horizon, and the final state of
evaporation. A definitive resolution of these questions likely requires robust
inputs from quantum gravity. We argue that one such input is a quantum bound on
curvature. We show how this leads to an upper limit on the redshift of a
Hawking emitted particle, to a maximum temperature for a black hole, and to the
prediction of a Planck scale remnant.


title:
An Ignored Assumption of $\Lambda$CDM Cosmology and An Old Question: Do
  We Live On The "Center" of The Universe?

abstract:
  We point out that $\Lambda$CDM cosmology has an ignored assumption. That is,
the $\Lambda$ component of the universe moves synchronously with ordinary
matters on Hubble scales. If cosmological constant is vacuum energy, this
assumption may be very difficult to be understood.
  We then propose a new mechanism which can explain the accelerating recession
of super-novaes. That is, considering the pressures originating from the random
moving (including Hubble recession) of galaxy clusters and galaxies. We provide
an new analytical solution of Einstein equation which may describe a universe
whose pressures originating from the random moving of galaxy clusters and
galaxies are considered.


title:
Different faces of chaos in FRW models with scalar fields -- geometrical
  point of view

abstract:
  FRW cosmologies with conformally coupled scalar fields are investigated in a
geometrical way by the means of geodesics of the Jacobi metric. In this model
of dynamics, trajectories in the configuration space are represented by
geodesics. Because of the singular nature of the Jacobi metric on the boundary
set $\partial\mathcal{D}$ of the domain of admissible motion, the geodesics
change the cone sectors several times (or an infinite number of times) in the
neighborhood of the singular set $\partial\mathcal{D}$. We show that this
singular set contains interesting information about the dynamical complexity of
the model. Firstly, this set can be used as a Poincar{\'e} surface for
construction of Poincar{\'e} sections, and the trajectories then have the
recurrence property. We also investigate the distribution of the intersection
points. Secondly, the full classification of periodic orbits in the
configuration space is performed and existence of UPO is demonstrated. Our
general conclusion is that, although the presented model leads to several
complications, like divergence of curvature invariants as a measure of
sensitive dependence on initial conditions, some global results can be obtained
and some additional physical insight is gained from using the conformal Jacobi
metric. We also study the complex behavior of trajectories in terms of symbolic
dynamics.


title:
Tidal coupling of a Schwarzschild black hole and circularly orbiting
  moon

abstract:
  We describe the possibility of using LISA's gravitational-wave observations
to study, with high precision, the response of a massive central body to the
tidal gravitational pull of an orbiting, compact, small-mass object. Motivated
by this application, we use first-order perturbation theory to study tidal
coupling for an idealized case: a massive Schwarzschild black hole, tidally
perturbed by a much less massive moon in a distant, circular orbit. We
investigate the details of how the tidal deformation of the hole gives rise to
an induced quadrupole moment in the hole's external gravitational field at
large radii. In the limit that the moon is static, we find, in Schwarzschild
coordinates and Regge-Wheeler gauge, the surprising result that there is no
induced quadrupole moment. We show that this conclusion is gauge dependent and
that the static, induced quadrupole moment for a black hole is inherently
ambiguous. For the orbiting moon and the central Schwarzschild hole, we find
(in agreement with a recent result of Poisson) a time-varying induced
quadrupole moment that is proportional to the time derivative of the moon's
tidal field. As a partial analog of a result derived long ago by Hartle for a
spinning hole and a stationary distant companion, we show that the orbiting
moon's tidal field induces a tidal bulge on the hole's horizon, and that the
rate of change of the horizon shape leads the perturbing tidal field at the
horizon by a small angle.


title: PP-waves with torsion and metric-affine gravity

abstract:
  A classical pp-wave is a 4-dimensional Lorentzian spacetime which admits a
nonvanishing parallel spinor field; here the connection is assumed to be
Levi-Civita. We generalise this definition to metric compatible spacetimes with
torsion and describe basic properties of such spacetimes. We use our
generalised pp-waves for constructing new explicit vacuum solutions of
quadratic metric-affine gravity.