title: Generalized Gravity and a Ghost

abstract:
  We show that generalized gravity theories involving the curvature invariants
of the Ricci tensor and the Riemann tensor as well as the Ricci scalar are
equivalent to multi- scalar-tensor gravities with four derivatives terms. By
expanding the action around a vacuum spacetime, the action is reduced to that
of the Einstein gravity with four derivative terms, and consequently there
appears a massive spin-2 ghost in such generalized gravity theories in addition
to a massive spin-0 field.


title: A tight constraint on some varying speed of light theories

abstract:
  We argue that if the velocity of electromagnetic waves in vacuum, \cem, is
different from the limiting velocity for massive particles, \cst, then, a
proton moving with velocity $\cem < v < \cst$ would radiate Cherenkov
radiation. Because we have seen protons with energy $\sim 10^{19}$ eV coming
from a distance of order more than 1 Mpc, we can put a constraint on $\Delta :=
(\cst - \cem)/\cst$: $\Delta < 10^{-27}$.


title: Mass and angular momenta of Kerr-anti-de Sitter spacetimes

abstract:
  We briefly review how to compute the mass and angular momenta of rotating,
asymptotically anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory of
gravity using superpotentials derived from standard Noether identities. The
calculations depend on the asymptotic form of the metrics only and hence take
no account of the source of the curvature. When the source of curvature is a
black hole, the results can be checked using the first law of black hole
thermodynamics.


title: Thin-shell wormholes in dilaton gravity

abstract:
  In this work we construct charged thin-shell Lorentzian wormholes in dilaton
gravity. The exotic matter required for the construction is localized in the
shell and the energy conditions are satisfied outside the shell. The total
amount of exotic matter is calculated and its dependence with the parameters of
the model is analysed.


title: Relationship between Hawking Radiation and Gravitational Anomalies

abstract:
  We show that in order to avoid a breakdown of general covariance at the
quantum level the total flux in each outgoing partial wave of a quantum field
in a black hole background must be equal to that of a (1+1)-dimensional
blackbody at the Hawking temperature.


title:
PP-waves, Israel's Matching conditions, Brane-world scenarios and BPS
  states in gravity

abstract:
  The matching between two 4-dimensional PP-waves is discussed by using
Israel's matching conditions. Physical consequences on the dynamics of (cosmic)
strings are analyzed. The extension to space-time of arbitrary dimension is
discussed and some interesting features related to the brane world scenario,
BPS states in gravity and Dirac-like quantization conditions are briefly
described.


title: Classical and quantum spinor cosmology with signature change

abstract:
  We study the classical and quantum cosmology of a universe in which the
matter source is a massive Dirac spinor field and consider cases where such
fields are either free or self-interacting. We focus attention on the spatially
flat Robertson-Walker cosmology and classify the solutions of the
Einstein-Dirac system in the case of zero, negative and positive cosmological
constant $\Lambda$. For $\Lambda<0$, these solutions exhibit signature
transitions from a Euclidean to a Lorentzian domain. In the case of massless
spinor fields it is found that signature changing solutions do not exist when
the field is free while in the case of a self-interacting spinor field such
solutions may exist. The resulting quantum cosmology and the corresponding
Wheeler-DeWitt equation are also studied for both free and self interacting
spinor fields and closed form expressions for the wavefunction of the universe
are presented. These solutions suggest a quantization rule for the energy.


title: Big Rip in SO(1,1) phantom universe

abstract:
  For the inverse linear potential, the SO(1,1) field behaves as phantom for
late time and the Big Rip will occur. The field approaches zero as time
approaches the Big Rip, here. For this potential the phantom equation of state
takes the late-time minimum $w_\Phi=-3$. We give some discussions that the Big
Rip in the SO(1,1) model may be treated as either the transition point of
universe from expansion to extract phase or the final state. In the latter
picture of the universe, the field has the $T$ symmetry and the scale factor
possesses the $CT$ symmetry, for which the SO(1,1) charge $\bar{Q}$ plays a
crucial role.


title: Quantum Mechanics and the Metrics of General Relativity

abstract:
  A one-to-one correspondence is established between linearized space-time
metrics of general relativity and the wave equations of quantum mechanics.
Also, the key role of boundary conditions in distinguishing quantum mechanics
from classical mechanics will emerge naturally from the procedure. Finally, we
will find that the methodology will enable us to introduce not only test
charges but also test masses by means of gauges.


title:
Parametric instabilities and their control in advanced interferometer GW
  detectors

abstract:
  A detailed simulation of Advanced LIGO test mass optical cavities shows that
parametric instabilities will excite acoustic modes in the test masses in the
frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical
cavity parameters with fused silica test masses, parametric instability excites
7 acoustic modes in each test mass, with parametric gain R up to 7. For the
alternative sapphire test masses only 1 acoustic mode is excited in each test
mass with R ~ 2. Fine tuning of the test mass radii of curvature cause the
instabilities to sweep through various modes with R as high as ~2000. Sapphire
test mass cavities can be tuned to completely eliminate instabilities using
thermal g-factor tuning with negligible degradation of the noise performance.
In the case of fused silica test mass, instabilities can be minimized but not
eliminated.


title: Cosmic Censorship in Higher dimension II

abstract:
  Generalizing earlier results on dust collapse in higher dimensions, we show
here that cosmic censorship can be restored in gravitational collapse with
tangential pressure present if we take the spacetime dimension to be $N\ge6$.
This is under conditions to be motivated physically, such as the smoothness of
initial data from which the collapse develops. The models considered here
incorporating a non-zero tangential pressure include the Einstein cluster
spacetime.


title:
Gravitational collapse in asymptotically Anti-de Sitter/de Sitter
  backgrounds

abstract:
  We study here the gravitational collapse of a matter cloud with a
non-vanishing tangential pressure in the presence of a non-zero cosmological
term. Conditions for bounce and singularity formation are derived for the
model. It is also shown that when the tangential pressures vanish, the bounce
and singularity conditions reduce to that of the dust case studied earlier. The
collapsing interior is matched with an exterior which is asymptotically de
Sitter or anti de Sitter, depending on the sign of cosmological constant. The
junction conditions for matching the cloud to exterior are specified. The
effect of the cosmological term on apparent horizons is studied in some detail,
and the nature of central singularity is analyzed. We also discuss here the
visibility of the singularity and implications for the cosmic censorship
conjecture.


title: On the Hamiltonian Constraint of Loop Quantum Cosmology

abstract:
  In this paper we construct the Hamiltonian constraint operator of loop
quantum cosmology using holonomies defined for arbitrary irreducible SU(2)
representations labeled by spin J. We show that modifications to the effective
semi-classical equations of motion arise both in the gravitational part of the
constraint as well as matter terms. The modifications are important for
phenomenological investigations of the cosmological imprints of loop quantum
cosmology. We discuss the implications for the early universe evolution.


title: Neutrino Quasinormal Modes of a Kerr-Newman-de Sitter Black Hole

abstract:
  Using the P\"{o}shl-Teller approximation, we evaluate the neutrino
quasinormal modes (QNMs) of a Kerr-Newman-de Sitter black hole. The result
shows that for a Kerr-Newman-de Sitter black hole, massless neutrino
perturbation of large $\Lambda$, positive $m$ and small value of $n$ will decay
slowly.


title: Wormholes supported by a phantom energy

abstract:
  We extend the notion of phantom energy--which is generally accepted for
homogeneously distributed matter with $w<-1$ in the universe--on inhomogeneous
spherically symmetric spacetime configurations. A spherically symmetric
distribution of phantom energy is shown to be able to support the existence of
static wormholes. We find an exact solution describing a static spherically
symmetric wormhole with phantom energy and show that a spatial distribution of
the phantom energy is mainly restricted by the vicinity of the wormhole's
throat. The maximal size of the spherical region, surrounding the throat and
containing the most part of the phantom energy, depends on the
equation-of-state parameter $w$ and cannot exceed some upper limit.


title: Two black hole initial data

abstract:
  Misner initial data are a standard example of time-symmetric initial data
with two apparent horizons. Compact formulae describing such data are presented
in the cases of equal or non-equal masses (i.e. isometric or non-isometric
horizons). The interaction energy in the "Schwarzschild + test particle" limit
of the Misner data is analyzed.


title: Effective State Metamorphosis in Semi-Classical Loop Quantum Cosmology

abstract:
  Modification to the behavior of geometrical density at short scales is a key
result of loop quantum cosmology, responsible for an interesting phenomenology
in the very early universe. We demonstrate the way matter with arbitrary scale
factor dependence in Hamiltonian incorporates this change in its effective
dynamics in the loop modified phase. For generic matter, the equation of state
starts varying near a critical scale factor, becomes negative below it and
violates strong energy condition. This opens a new avenue to generalize various
phenomenological applications in loop quantum cosmology. We show that different
ways to define energy density may yield radically different results, especially
for the case corresponding to classical dust. We also discuss implications for
frequency dispersion induced by modification to geometric density at small
scales.


title:
Accuracy requirements for the calculation of gravitational waveforms
  from coalescing compact binaries in numerical relativity

abstract:
  I discuss the accuracy requirements on numerical relativity calculations of
inspiraling compact object binaries whose extracted gravitational waveforms are
to be used as templates for matched filtering signal extraction and physical
parameter estimation in modern interferometric gravitational wave detectors.
Using a post-Newtonian point particle model for the pre-merger phase of the
binary inspiral, I calculate the maximum allowable errors for the mass and
relative velocity and positions of the binary during numerical simulations of
the binary inspiral. These maximum allowable errors are compared to the errors
of state-of-the-art numerical simulations of multiple-orbit binary neutron star
calculations in full general relativity, and are found to be smaller by several
orders of magnitude. A post-Newtonian model for the error of these numerical
simulations suggests that adaptive mesh refinement coupled with second order
accurate finite difference codes will {\it not} be able to robustly obtain the
accuracy required for reliable gravitational wave extraction on Terabyte-scale
computers. I conclude that higher order methods (higher order finite difference
methods and/or spectral methods) combined with adaptive mesh refinement and/or
multipatch technology will be needed for robustly accurate gravitational wave
extraction from numerical relativity calculations of binary coalescence
scenarios.


title: Newtonian Gravity Predictions For Gravity Probe B

abstract:
  Newtonian gravity and special relativity combine to produce a gravitomagnetic
precession of an orbiting gyroscope that is one fourth as large as predicted by
General Relativity. The geodetic effect is the same in both cases.


title: Intersecting hypersurfaces and Lovelock Gravity

abstract:
  A theory of gravity in higher dimensions is considered. The usual
Einstein-Hilbert action is supplemented with Lovelock terms, of higher order in
the curvature tensor. These terms are important for the low energy action of
string theories.
  The intersection of hypersurfaces is studied in the Lovelock theory. The
study is restricted to hypersurfaces of co-dimension 1, $(d-1)$-dimensional
submanifolds in a $d$-dimensional space-time. It is found that exact thin
shells of matter are admissible, with a mild form of curvature singularity: the
first derivative of the metric is discontinuous across the surface. Also, with
only this mild kind of curvature singularity, there is a possibility of matter
localised on the intersections.
  This gives a classical analogue of the intersecting brane-worlds in high
energy String phenomenology. Such a possibility does not arise in the pure
Einstein-Hilbert case.


title: What does the Letelier-Gal'tsov metric describe?

abstract:
  Recently the structure of the Letelier-Gal'tsov spacetime has become a matter
of some controversy. I show that the metric proposed in \cite{letgal} is
defined only on a dense subset of the whole manifold. In the case when it can
be defined on the remainder by continuity, the resulting spacetime corresponds
to a system of parallel cosmic strings at rest w.r.t. each other.


title: The Einstein-Vlasov system/Kinetic theory

abstract:
  The main purpose of this article is to provide a guide to theorems on global
properties of solutions to the Einstein-Vlasov system. This system couples
Einstein's equations to a kinetic matter model. Kinetic theory has been an
important field of research during several decades in which the main focus has
been on nonrelativistic and special relativistic physics, {\it i.e.} to model
the dynamics of neutral gases, plasmas, and Newtonian self-gravitating systems.
In 1990, Rendall and Rein initiated a mathematical study of the Einstein-Vlasov
system. Since then many theorems on global properties of solutions to this
system have been established. The Vlasov equation describes matter
phenomenologically and it should be stressed that most of the theorems
presented in this article are not presently known for other such matter models
({\it i.e.} fluid models). This paper gives introductions to kinetic theory in
non-curved spacetimes and then the Einstein-Vlasov system is introduced. We
believe that a good understanding of kinetic theory in non-curved spacetimes is
fundamental to good comprehension of kinetic theory in general relativity.


title:
Non-radial strong curvature naked singularities in five dimensional
  perfect fluid self-similar space-time

abstract:
  We study five dimensional(5D) spherically symmetric self-similar perfect
fluid space-time with adiabatic equation of state, considering all the families
of future directed non-spacelike geodesics. The space-time admits globally
strong curvature naked singularities in the sense of Tipler and thus violates
the cosmic censorship conjecture provided a certain algebraic equation has real
positive roots. We further show that it is the weak energy condition (WEC) that
is necessary for visibility of singularities for a finite period of time and
for singularities to be gravitationally strong. We, also, match the solution to
5D Schwarzschild solution using the junction conditions.


title: Testing Lorentz Invariance Violation in Quantum Gravity Theories

abstract:
  Much research has been done in the latter years on the subject of Lorentz
violation induced by Quantum Gravity effects. On the theoretical side it has
been shown that both Loop Quantum Gravity and String Theory predict that
Lorentz violation can be induced at an energy near to the Planck scale. On the
other hand, most of the experimental results in the latter years, have
confirmed that the laws of physics are Lorentz invariant at low energy with
very high accuracy.
  The inclusion of one- and two-loop contributions from a Lorentz violating
Lagrangian dramatically change the above picture: the loop momenta run into the
Planck scale and above and from the "divergent" terms finite Lorentz violating
contributions of order one arise. These can be suppressed through suitable
counterterms in the Lagrangian, originating a strong fine tuning problem.
  A brief discussion of these issues and their possible influence in future
research follows.


title: Can be gravitational waves markers for an extra-dimension?

abstract:
  The main issue of the present letter is to fix specific features (which turn
out being independent of extradimension size) of gravitational waves generated
before a dimensional compactification process. Valuable is the possibility to
detect our prediction from gravitational wave experiment without high energy
laboratory investigation. In particular we show how gravitational waves can
bring information on the number of Universe dimensions. Within the framework of
Kaluza-Klein hypotheses, a different morphology arises between waves generated
before than the compactification process settled down and ordinary
4-dimensional waves. In the former case the scalar and tensor degrees of
freedom can not be resolved. As a consequence if were detected gravitational
waves having the feature here predicted (anomalous polarization amplitudes),
then they would be reliable markers for the existence of an extra dimension.


title:
Asymptotic directional structure of radiative fields in spacetimes with
  a cosmological constant

abstract:
  We analyze the directional properties of general gravitational,
electromagnetic, and spin-s fields near conformal infinity I. The fields are
evaluated in normalized tetrads which are parallelly propagated along null
geodesics which approach a point P of I. The standard peeling-off property is
recovered and its meaning is discussed and refined. When the (local) character
of the conformal infinity is null, such as in asymptotically flat spacetimes,
the dominant term which is identified with radiation is unique. However, for
spacetimes with a non-vanishing cosmological constant the conformal infinity is
spacelike (for Lambda>0) or timelike (for Lambda<0), and the radiative
component of each field depends substantially on the null direction along which
P is approached. The directional dependence of asymptotic fields near such de
Sitter-like or anti-de Sitter-like I is explicitly found and described. We
demonstrate that the corresponding directional structure of radiation has a
universal character that is determined by the algebraic (Petrov) type of the
field. In particular, when Lambda>0 the radiation vanishes only along
directions which are opposite to principal null directions. For Lambda<0 the
directional dependence is more complicated because it is necessary to
distinguish outgoing and ingoing radiation. Near such anti-de Sitter-like
conformal infinity the corresponding directional structures differ, depending
not only on the number and degeneracy of the principal null directions at P but
also on their specific orientation with respect to I. The directional structure
of radiation near (anti-)de Sitter-like infinities supplements the standard
peeling-off property of spin-s fields. This offers a better understanding of
the asymptotic behaviour of the fields near conformal infinity.


title:
Asymptotic directional structure of radiation for fields of algebraic
  type D

abstract:
  The directional behavior of dominant components of algebraically special
spin-s fields near a spacelike, timelike or null conformal infinity is studied.
By extending our previous general investigations we concentrate on fields which
admit a pair of equivalent algebraically special null directions, such as the
Petrov type D gravitational fields or algebraically general electromagnetic
fields. We introduce and discuss a canonical choice of the reference tetrad
near infinity in all possible situations, and we present the corresponding
asymptotic directional structures using the most natural parametrizations.


title: Modern tests of Lorentz invariance

abstract:
  Motivated by ideas about quantum gravity, a tremendous amount of effort over
the past decade has gone into testing Lorentz invariance in various regimes.
This review summarizes both the theoretical frameworks for tests of Lorentz
invariance and experimental advances that have made new high precision tests
possible. The current constraints on Lorentz violating effects from both
terrestrial experiments and astrophysical observations are presented.


title: Neutrino Wave Packet Propagation in Gravitational Fields

abstract:
  We discuss the propagation of neutrino wave packets in a Lense-Thirring
space-time using a gravitational phase approach. We show that the neutrino
oscillation length is altered by gravitational corrections and that neutrinos
are subject to helicity flip induced by stellar rotation. For the case of a
rapidly rotating neutron star, we show that absolute neutrino masses can be
derived, in principle, from rotational contributions to the mass-induced energy
shift, without recourse to mass generation models presently discussed in the
literature.


title: Phantom energy traversable wormholes

abstract:
  It has been suggested that a possible candidate for the present accelerated
expansion of the Universe is ''phantom energy''. The latter possesses an
equation of state of the form $\omega\equiv p/\rho<-1$, consequently violating
the null energy condition. As this is the fundamental ingredient to sustain
traversable wormholes, this cosmic fluid presents us with a natural scenario
for the existence of these exotic geometries. Due to the fact of the
accelerating Universe, macroscopic wormholes could naturally be grown from the
submicroscopic constructions that originally pervaded the quantum foam. One
could also imagine an advanced civilization mining the cosmic fluid for phantom
energy necessary to construct and sustain a traversable wormhole.
  In this context, we investigate the physical properties and characteristics
of traversable wormholes constructed using the equation of state $p=\omega
\rho$, with $\omega<-1$. We analyze specific wormhole geometries, considering
asymptotically flat spacetimes and imposing an isotropic pressure. We also
construct a thin shell around the interior wormhole solution, by imposing the
phantom energy equation of state on the surface stresses. Using the ''volume
integral quantifier'' we verify that it is theoretically possible to construct
these geometries with vanishing amounts of averaged null energy condition
violating phantom energy. Specific wormhole dimensions and the traversal
velocity and time are also deduced from the traversability conditions for a
particular wormhole geometry. These phantom energy traversable wormholes have
far-reaching physical and cosmological implications. For instance, an advanced
civilization may use these geometries to induce closed timelike curves,
consequently violating causality.


title:
Detecting extreme mass ratio inspirals with LISA using time-frequency
  methods

abstract:
  The inspirals of stellar-mass compact objects into supermassive black holes
are some of the most important sources for LISA. Detection techniques based on
fully coherent matched filtering have been shown to be computationally
intractable. We describe an efficient and robust detection method that utilizes
the time-frequency evolution of such systems. We show that a typical extreme
mass ratio inspiral (EMRI) source could possibly be detected at distances of up
to ~2 Gpc, which would mean ~10s of EMRI sources can be detected per year using
this technique. We discuss the feasibility of using this method as a first step
in a hierarchical search.


title:
3-mode detection for widening the bandwidth of resonant gravitational
  wave detectors

abstract:
  We have implemented a novel scheme of signal readout for resonant
gravitational wave detectors. For the first time, a capacitive resonant
transducer has been matched to the signal amplifier by means of a tuned high Q
electrical resonator. The resulting 3-mode detection scheme widens
significantly the bandwidth of the detector. We present here the results
achieved by this signal readout equipped with a two-stage SQUID amplifier. Once
installed on the AURIGA detector, the one-sided spectral sensitivity obtained
with the detector operated at 4.5 K is better than 10^-20 Hz^-1/2 over 110 Hz
and in good agreement with the expectations.


title: N-dimensional geometries and Einstein equations from systems of PDE's

abstract:
  The aim of the present work is twofold: first, we show how all the
$n$-dimensional Riemannian and Lorentzian metrics can be constructed from a
certain class of systems of second-order PDE's which are in duality to the
Hamilton-Jacobi equation and second we impose the Einstein equations to these
PDE's.


title:
Bound states in the dynamics of a dipole in the presence of a conical
  defect

abstract:
  In this work we investigate the quantum dynamics of an electric dipole in a
$(2+1)$-dimensional conical spacetime. For specific conditions, the
Schr\"odinger equation is solved and bound states are found with the energy
spectrum and eigenfunctions determined. We find that the bound states spectrum
extends from minus infinity to zero with a point of accumulation at zero. This
unphysical result is fixed when a finite radius for the defect is introduced.


title:
Topologically general U(1) symmetric Einstein spacetimes with AVTD
  behavior

abstract:
  We use Fuchsian methods to show that, for any two dimensional manifold
$\Sigma^2$, there is a large family of U(1) symmetric solutions of the vacuum
Einstein equations on the manifold $\Sigma \times S^1 \times \mathbb{R}$, each
of which has AVTD behavior in the neighborhood of its singularity.


title: Quantum physical relevance of the Einstein tensor

abstract:
  Taking quantum physics as well as large scale astronomical observations into
account, a spacetime metric is introduced, such that the nonlinear part of the
Einstein tensor contains effects of the order of Planck's constant.


title:
The necessity of non-Riemannian acoustic spacetime in the fluids with
  vorticity

abstract:
  The necessity of a newly proposed (PRD 70 (2004) 64004) non-Riemannian
acoustic spacetime structure called acoustic torsion of sound wave equation in
fluids with vorticity are discussed. It is shown that this structure, although
not always necessary is present in fluids with vorticity even when the
perturbation is rotational. This can be done by solving the Bergliaffa et al
(Physica D (2004)) gauge invariant equations for sound, superposed to a general
background flow, needs to support a non-Riemannian acoustic geometry in
effective spacetime. Bergliaffa et al have previously shown that a Riemannian
structure cannot be associated to this gauge invariant general system.


title: Black Hole Skyrmions with Negative Cosmological Constant

abstract:
  We study spherically symmetric black hole solutions with Skyrme hair in the
Einstein-Skyrme theory with a negative cosmological constant. The dependence of
the skyrmion field configuration on the cosmological constant is examined. The
stability is investigated in detail by solving the linearly perturbed equation
numerically. It is shown that there exist linearly stable solutions in the
branch which represents unstable configuration in the asymptotically flat
spacetime.


title:
Lagrangian Brane Dynamics in General Relativity and
  Einstein-Gauss-Bonnet Gravity

abstract:
  This paper gives a new, simple and concise derivation of brane actions and
brane dynamics in general relativity and in Einstein-Gauss-Bonnet gravity. We
present a unified treatment, applicable to timelike surface layers and
spacelike transition layers, and including consideration of the more difficult
lightlike case.


title: Conditional escape of gravitons from the brane

abstract:
  In this paper we consider a cosmological Friedmann Robertson Walker brane
world imbedded in a 5-dimensional anti-de Sitter Schwarzschild bulk. We show,
using potential diagrams, that for an anti-de Sitter bulk the null geodesics
never return to the brane. Null geodesics do however return for k=+1 when we
include the Schwarzschild like mass and the condition of return is obtained
from the corresponding effective potential. We next obtain the condition for a
gravitational signal to be emitted from a FRW brane with isotropically
distributed matter. We use these results to investigate the conditions under
which shortcuts through the bulk are possible.


title: Phenomenological Quantum Gravity

abstract:
  These notes summarize a set of lectures on phenomenological quantum gravity
which one of us delivered and the other attended with great diligence. They
cover an assortment of topics on the border between theoretical quantum gravity
and observational anomalies. Specifically, we review non-linear relativity in
its relation to loop quantum gravity and high energy cosmic rays. Although we
follow a pedagogic approach we include an open section on unsolved problems,
presented as exercises for the student. We also review varying constant models:
the Brans-Dicke theory, the Bekenstein varying $\alpha$ model, and several more
radical ideas. We show how they make contact with strange high-redshift data,
and perhaps other cosmological puzzles. We conclude with a few remaining
observational puzzles which have failed to make contact with quantum gravity,
but who knows... We would like to thank Mario Novello for organizing an
excellent school in Mangaratiba, in direct competition with a very fine beach
indeed.


title: Space-Time Non-Commutativity near Horizon of a Black Hole

abstract:
  We consider dynamics of a quantum scalar field, minimally coupled to
classical gravity, in the near-horizon region of a Schwarzschild black-hole. It
is described by a static Klein-Gordon operator which in the near-horizon region
reduces to a scale invariant Hamiltonian of the system. This Hamiltonian is not
essentially self-adjoint, but it admits a one-parameter family of self-adjoint
extension. The time-energy uncertainty relation, which can be related to the
thermal black-hole mass fluctuations, requires explicit construction of a time
operator near-horizon. We present its derivation in terms of generators of the
affine group. Matrix elements involving the time operator should be evaluated
in the affine coherent state representation.


title: Relativistic Solenoids

abstract:
  We construct a general relativistic analogy of an infinite solenoid, i.e., of
an infinite cylinder with zero electric charge and non-zero electric current in
the direction tangential to the cylinder and perpendicular to its axis. We
further show that the solution has a good weak-field limit.


title: Optical Design for the Laser Astrometric Test of Relativity

abstract:
  This paper discusses the Laser Astrometric Test Of Relativity (LATOR)
mission. By using a combination of independent time-series of highly accurate
gravitational deflection of light in the immediate proximity to the Sun along
with measurements of the Shapiro time delay on the interplanetary scales (to a
precision respectively better than $10^{-13}$ radians and 1 cm), LATOR will
significantly improve our knowledge of relativistic gravity. The primary
mission objective is to i) measure the key post-Newtonian Eddington parameter
$\gamma$ with accuracy of a part in 10$^9$. $(1-\gamma)$ is a direct measure
for presence of a new interaction in gravitational theory, and, in its search,
LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test.
Other mission objectives include: ii) first measurement of gravity's non-linear
effects on light to $\sim$0.01% accuracy; including both the traditional
Eddington $\beta$ parameter and also the spatial metric's 2nd order potential
contribution (never been measured before); iii) direct measurement of the solar
quadrupole moment $J_2$ (currently unavailable) to accuracy of a part in 200 of
its expected size; iv) direct measurement of the ``frame-dragging'' effect on
light by the Sun's rotational gravitomagnetic field to one percent accuracy.
LATOR's primary measurement pushes to unprecedented accuracy the search for
cosmologically relevant scalar-tensor theories of gravity by looking for a
remnant scalar field in today's solar system. The key element of LATOR is a
geometric redundancy provided by the laser ranging and long-baseline optical
interferometry. We discuss the mission and optical designs of this proposed
experiment.


title:
The Cauchy convergence of T and P-approximant templates for test-mass
  Kerr binary systems

abstract:
  In this work we examine the Cauchy convergence of both post-Newtonian
(T-approximant) and re-summed post-Newtonian (P-approximant) templates for the
case of a test-mass orbiting a Kerr black hole along a circular equatorial
orbit. The Cauchy criterion demands that the inner product between the $n$ and
$n+1$ order approximation approaches unity, as we increase the order of
approximation. In previous works, it has been shown that we achieve greater
fitting factors and better parameter estimation using the P-approximant
templates for both Schwarzschild and Kerr black holes. In this work, we show
that the P-approximant templates also display a faster Cauchy convergence
making them a superior template to the standard post-Newtonian templates.


title: Semiclassical ultraextremal horizons

abstract:
  We examine backreaction of quantum massive fields on multiply-degenerate
(ultraextremal) horizons. It is shown that, under influence of the quantum
backreaction, the horizon of such a kind moves to a new position, near which
the metric does not change its asymptotics, so the ultraextremal black holes
and cosmological spacetimes do exist as self-consistent solutions of the
semiclassical field equations.


title:
On initial conditions and global existence for accelerating cosmologies
  from string theory

abstract:
  We construct a solution satisfying initial conditions for accelerating
cosmologies from string/M-theory. Gowdy symmetric spacetimes with a positive
potential are considered. Also, a global existence theorem for the spacetimes
is shown.


title: Causality condition and reflection on event horizon

abstract:
  A new way to implement the causality condition on the event horizon of black
holes is discovered. The metric of a black hole is shown to be a function of
the complex-valued gravitational radius r_g => r_g + i0. The relation between
this modification of the metric and the causality condition is established
using the analyticity of the S-matrix, which describes scattering of probing
particles on a back hole. The found property of the metric has strong
manifestations in scattering and related phenomena. One of them is the
unexpected effect of reflection of incoming particles on the event horizon,
which strongly reduces the absorption cross section.


title:
Cosmological quintessence accretion onto primordial black holes :
  conditions for their growth to the supermassive scale

abstract:
  In this work we revisit the growth of small primordial black holes (PBHs)
immersed in a quintessential field and/or radiation to the supermassive black
hole (SMBHs) scale. We show the difficulties of scenarios in which such huge
growth is possible. For that purpose we evaluated analytical solutions of the
differential equations (describing mass evolution) and point out the strong
fine tuning for that conclusions. The timescale for growth in a model with a
constant quintessence flux is calculated and we show that it is much bigger
than the Hubble time.The fractional gain of the mass is further evaluated in
other forms, including quintessence and/or radiation. We calculate the
cosmological density $\Omega$ due to quintessence necessary to grow BHs to the
supermassive range and show it to be much bigger than one. We also describe the
set of complete equations analyzing the evolution of the BH+quintessence
universe, showing some interesting effects such the quenching of the BH mass
growth due to the evolution of the background energy. Additional constraints
obtained by using the Holographic Bound are also described. The general
equilibrium conditions for evaporating/accreting black holes evolving in a
quintessence/radiation universe are discussed in the Appendix.


title: Liouville Cosmology

abstract:
  Liouville string theory is a natural framework for discussing the
non-equilibrium evolution of the Universe. It enables non-critical strings to
be treated in mathematically consistent manner, in which target time is
identified with a world-sheet renormalization-group scale parameter, preserving
target-space general coordinate invariance and the existence of an S-matrix. We
review our proposals for a unified treatment of inflation and the current
acceleration of the Universe. We link the current acceleration of the Universe
with the value of the string coupling. In such a scenario, the dilaton plays an
essential background role, driving the acceleration of the Universe during the
present era after decoupling as a constant during inflation.


title:
Using clocks to determine the entropy of black holes and other
  space-time singularities

abstract:
  Space-time singularities, viz. Big bang, Big crunch and black holes have been
shown to follow from the singularity theorems of General relativity. Whether
the entropy at such infinite proper-time objects can be other than zero has
also been a longstanding subject of research. Currently the property most
commonly chosen to calculate their entropy is a multiple of the surface area of
the event horizon and usually gives non-zero entropy values. Though popular,
this choice still leaves some substantial questions unanswered hence the
motivation for alternative methods for entropy derivation. Here, we use a
different property, the proper-time at singularities based on the General
relativity predicted behavior of clocks, to derive their entropy. We find,
firstly within statistical and thermodynamic principles, secondly when this
property is taken into account in the Bekenstein-Hawking formula and thirdly
illustrating with a natural analogue, that the entropy of black holes and all
other gravitational singularities cannot be other than zero as had been earlier
classically speculated.


title:
The intermediate problem for binary black hole inspiral and the periodic
  standing wave approximation

abstract:
  In calculations of the inspiral of binary black holes an intermediate
approximation is needed that can bridge the post-Newtonian methods of the early
inspiral and the numerical relativity computations of the final plunge. We
describe here the periodic standing wave approximation: A numerical solution is
found to the problem of a periodic rotating binary with helically symmetric
standing wave fields, and from this solution an approximation is extracted for
the physically relevant problem of inspiral with outgoing waves. The
approximation underlying this approach has been recently confirmed with
innovative numerical methods applied to nonlinear model problems.


title:
Spherically symmetric, static spacetimes in a tensor-vector-scalar
  theory

abstract:
  Recently, a relativistic gravitation theory has been proposed [J. D.
Bekenstein, Phys. Rev. D {\bf 70}, 083509 (2004)] that gives the Modified
Newtonian Dynamics (or MOND) in the weak acceleration regime. The theory is
based on three dynamic gravitational fields and succeeds in explaining a large
part of extragalactic and gravitational lensing phenomenology without invoking
dark matter. In this work we consider the strong gravity regime of TeVeS. We
study spherically symmetric, static and vacuum spacetimes relevant for a
non-rotating black hole or the exterior of a star. Two branches of solutions
are identified: in the first the vector field is aligned with the time
direction while in the second the vector field has a non-vanishing radial
component. We show that in the first branch of solutions the \beta and \gamma
PPN coefficients in TeVeS are identical to these of general relativity (GR)
while in the second the \beta PPN coefficient differs from unity violating
observational determinations of it (for the choice of the free function $F$ of
the theory made in Bekenstein's paper). For the first branch of solutions, we
derive analytic expressions for the physical metric and discuss their
implications. Applying these solutions to the case of black holes, it is shown
that they violate causality (since they allow for superluminal propagation of
metric, vector and scalar waves) in the vicinity of the event horizon and/or
that they are characterized by negative energy density carried by the fields.


title: Numerical Radiation Reaction for a Scalar Charge in Kerr Circular Orbit

abstract:
  We numerically calculate the dissipative part of the self-force on a scalar
charge moving on a circular, geodesic, equatorial orbit in Kerr spacetime. The
solution to the scalar field equation is computed by separating variables and
is expressed as a mode sum over radial and angular modes. The force is then
computed in two ways: a direct, instantaneous force calculation which uses the
half-retarded-minus-half-advanced field, and an indirect method which uses the
energy and angular momentum flux at the horizon and at infinity to infer the
force. We are able to show numerically and analytically that the force-per-mode
is the same for both methods. To enforce the boundary conditions (ingoing
radiation at the horizon and outgoing radiation at infinity for the retarded
solution) numerical solutions to the radial equation are matched to asymptotic
expansions for the fields at the boundaries. Recursion relations for the
coefficients in the asymptotic expansions are given in an appendix.


title:
A time-domain fourth-order-convergent numerical algorithm to integrate
  black hole perturbations in the extreme-mass-ratio limit

abstract:
  We obtain a fourth order accurate numerical algorithm to integrate the
Zerilli and Regge-Wheeler wave equations, describing perturbations of
nonrotating black holes, with source terms due to an orbiting particle. Those
source terms contain the Dirac's delta and its first derivative. We also
re-derive the source of the Zerilli and Regge-Wheeler equations for more
convenient definitions of the waveforms, that allow direct metric
reconstruction (in the Regge-Wheeler gauge).


title:
Leading order corrections to the cosmological evolution of tensor
  perturbations in braneworld (Short version)

abstract:
  Tensor perturbations in an expanding braneworld of the Randall Sundrum type
are investigated. We consider a model composed of a slow-roll inflation phase
and the succeeding radiation phase. The effect of the presence of an extra
dimension through the transition to the radiation phase is studied, giving an
analytic formula for leading order corrections.


title: Studies on Some Aspects of the Fundamental Theory of Everything

abstract:
  What happens to the entropy increase principle as the Universe evolve to form
the big-crunch singularity? What happens to the uncertainity relations along
the process of gravitational collapses? What is the quantum mechanical
description of a Radon atom in a rigid box when the distance of consecutive
nodes and antinodes of $\psi$ is equal to or less than the diameter of the
atom? What is the position-space wave function of two finite volume massive
bosons if we take contact interaction into account? How a photon produce
electron-positron pair with finite volume concentrate rest masses? What are the
charges of the electron-positron pairs forming loops in the vacuum? How two
particles with three-momentums $k_1, k_2$ $(k_1 \neq k_2)$ produced to form a
loop at a space-time point always arrive at another spacial point
simultaneously? What is the microscopic explanation in terms of particle
exchanges of the force in the Casimir effect? What is the mechanism of the
collapse of the momentum-space wave function of a particle knocking out an
elctron from an atom? What is meant by $|\Psi> = {c_1 (t)}|\Psi_{U^{238}}> +
{c_2 (t)}|\Psi_{Th^{234}}> ~?$ Quantum mechanically the region between the
rigid walls (which is equiprobable in classical mechanics) is non-homogeneous
for a particle in a rigid box ! The large scale structure of the Universe is
homogeneous.


title: Wormholes in vacuum Brans-Dicke theory

abstract:
  It is shown that among the different classes of claimed static wormhole
solutions of the vacuum Brans-Dicke theory only Brans Class I solution with
coupling constant $\omega$ less than -1.5 (excluding the point $\omega =2$)
gives rise to physically viable traversable wormhole geometry. Usability of
this wormhole geometry for interstellar travel has been examined.


title: Dark energy, wormholes, and the Big Rip

abstract:
  The time evolution of a wormhole in a Friedmann universe approaching the Big
Rip is studied. The wormhole is modeled by a thin spherical shell accreting the
superquintessence fluid - two different models are presented. Contrary to
recent claims that the wormhole overtakes the expansion of the universe and
engulfs it before the Big Rip is reached, it is found that the wormhole becomes
asymptotically comoving with the cosmic fluid and the future evolution of the
universe is fully causal.


title: Primordial magnetic seed field amplification by gravitational waves

abstract:
  Using second-order gauge-invariant perturbation theory, a self-consistent
framework describing the non-linear coupling between gravitational waves and a
large-scale homogeneous magnetic field is presented. It is shown how this
coupling may be used to amplify seed magnetic fields to strengths needed to
support the galactic dynamo. In situations where the gravitational wave
background is described by an `almost' Friedmann-Lema{\^i}tre-Robertson-Walker
(FLRW) cosmology we find that the magnitude of the original magnetic field is
amplified by an amount proportional to the magnitude of the gravitational wave
induced shear anisotropy and the square of the field's initial co-moving scale.
We apply this mechanism to the case where the seed field and gravitational wave
background are produced during inflation and find that the magnitude of the
gravitational boost depends significantly on the manner in which the estimate
of the shear anisotropy at the end of inflation is calculated. Assuming a seed
field of $10^{-34}$ $\rm{G}$ spanning a comoving scale of about $10 \rm{kpc}$
today, the shear anisotropy at the end of inflation must be at least as large
as $10^{-40}$ in order to obtain a generated magnetic field of the same order
of magnitude as the original seed. Moreover, contrasting the weak field
approximation to our gauge-invariant approach, we find that while both methods
agree in the limit of high conductivity, their corresponding solutions are
otherwise only compatible in the limit of infinitely long-wavelength
gravitational waves.


title: Generating perfect fluid spheres in general relativity

abstract:
  Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry
describing the interior of a particular idealized general relativistic star --
a static spherically symmetric blob of fluid with position-independent density
-- the general relativity community has continued to devote considerable time
and energy to understanding the general-relativistic static perfect fluid
sphere. Over the last 90 years a tangle of specific perfect fluid spheres has
been discovered, with most of these specific examples seemingly independent
from each other. To bring some order to this collection, in this article we
develop several new transformation theorems that map perfect fluid spheres into
perfect fluid spheres. These transformation theorems sometimes lead to
unexpected connections between previously known perfect fluid spheres,
sometimes lead to new previously unknown perfect fluid spheres, and in general
can be used to develop a systematic way of classifying the set of all perfect
fluid spheres.


title: Hoop Conjecture in Five-dimensios -Violation of Cosmic Censorship-

abstract:
  We study the condition of black hole formation in five-dimensional
space-time. We analytically solve the constraint equations of five-dimensional
Einstein equations for momentarily static and conformally flat initial data of
a spheroidal mass. We numerically search for an apparent horizon in various
initial hypersurfaces and find both necessary and sufficient conditions for the
horizon formation in terms of inequalities relating a geometric quantity and a
mass defined in an appropriate manner. In the case of infinitely thin spheroid,
our results suggest a possibility of naked singularity formation by the spindle
gravitational collapse in five-dimensional space-time.


title: Effective Equations on the 3-Brane World from Type IIB String

abstract:
  The effective field equations on a 3-brane are established considering the
massless bosonic sector of the type IIB string compactified on S^5. The
covariant embedding formalism in a space endowed with Z_2-symmetry is applied.
Recently the derivation of effective equations on the 3-brane, where only
gravity penetrates in the bulk has been performed by Shiromizu, Maeda, and
Sasaki. We extend this analysis to the situation when the bulk contains a set
of fields given by the type IIB string. The notion of the Einstein-Cartan space
is considered in order to avoid extra suppositions about the embedding of these
fields. The interactions between the brane and the bulk fields are understood
in a purely geometric way, which fixes the form of these interactions. Finally,
we present the dynamically equivalent effective equations have expressed
completely in Riemannian terms and make conclusions.


title: Five-Dimensional Charged Rotating Black Holes

abstract:
  We consider charged rotating black holes in 5-dimensional Einstein-Maxwell
theory. These black holes are asymptotically flat, they possess a regular
horizon of spherical topology and two independent angular momenta associated
with two distinct planes of rotation. We discuss their global and horizon
properties, and derive a generalized Smarr formula. We construct these black
holes numerically, focussing on black holes with a single angular momentum, and
with two equal-magnitude angular momenta.


title: Binary black hole initial data from matched asymptotic expansions

abstract:
  We present an approximate metric for a binary black hole spacetime to
construct initial data for numerical relativity. This metric is obtained by
asymptotically matching a post-Newtonian metric for a binary system to a
perturbed Schwarzschild metric for each hole. In the inner zone near each hole,
the metric is given by the Schwarzschild solution plus a quadrupolar
perturbation corresponding to an external tidal gravitational field. In the
near zone, well outside each black hole but less than a reduced wavelength from
the center of mass of the binary, the metric is given by a post-Newtonian
expansion including the lowest-order deviations from flat spacetime. When the
near zone overlaps each inner zone in a buffer zone, the post-Newtonian and
perturbed Schwarzschild metrics can be asymptotically matched to each other. By
demanding matching (over a 4-volume in the buffer zone) rather than patching
(choosing a particular 2-surface in the buffer zone), we guarantee that the
errors are small in all zones. The resulting piecewise metric is made formally
$C^\infty$ with smooth transition functions so as to obtain the finite
extrinsic curvature of a 3-slice. In addition to the metric and extrinsic
curvature, we present explicit results for the lapse and the shift, which can
be used as initial data for numerical simulations. This initial data is not
accurate all the way to the asymptotically flat ends inside each hole, and
therefore must be used with evolution codes which employ black hole excision
rather than puncture methods. This paper lays the foundations of a method that
can be sraightforwardly iterated to obtain initial data to higher perturbative
order.


title:
Detectability of f-mode Unstable Neutron Stars by the Schenberg
  Spherical Antenna

abstract:
  The Brazilian spherical antenna (Schenberg) is planned to detect high
frequency gravitational waves (GWs) ranging from 3.0 kHz to 3.4 kHz. There is a
host of astrophysical sources capable of being detected by the Brazilian
antenna, namely: core collapse in supernova events; (proto)neutron stars
undergoing hydrodynamical instability; f-mode unstable neutron stars, caused by
quakes and oscillations; excitation of the first quadrupole normal mode of 4-9
solar mass black holes; coalescence of neutron stars and/or black holes; exotic
sources such as bosonic or strange matter stars rotating at 1.6 kHz; and
inspiralling of mini black hole binaries. We here address our study in
particular to the neutron stars, which could well become f-mode unstable
producing therefore GWs. We estimate, for this particular source of GWs, the
event rates that in principle can be detected by Schenberg and by the Dutch
Mini-Grail antenna.


title:
The issue of time in generally covariant theories and the Komar-Bergmann
  approach to observables in general relativity

abstract:
  Diffeomorphism-induced symmetry transformations and time evolution are
distinct operations in generally covariant theories formulated in phase space.
Time is not frozen. Diffeomorphism invariants are consequently not necessarily
constants of the motion. Time-dependent invariants arise through the choice of
an intrinsic time, or equivalently through the imposition of time-dependent
gauge fixation conditions. One example of such a time-dependent gauge fixing is
the Komar-Bergmann use of Weyl curvature scalars in general relativity. An
analogous gauge fixing is also imposed for the relativistic free particle and
the resulting complete set time-dependent invariants for this exactly solvable
model are displayed. In contrast with the free particle case, we show that
gauge invariants that are simultaneously constants of motion cannot exist in
general relativity. They vary with intrinsic time.


title:
Reparameterization invariants for anisotropic Bianchi I cosmology with a
  massless scalar source

abstract:
  Intrinsic time-dependent invariants are constructed for classical, flat,
homogeneous, anisotropic cosmology with a massless scalar material source.
Invariance under the time reparameterization-induced canonical symmetry group
is displayed explicitly.


title:
Slowly rotating proto strange stars in Quark mass density- and
  temperature- dependent model

abstract:
  Employing the Quark Mass Denisity- and temperature- dependent model and the
Hartle's method, We have studied the slowly rotating strange star with uniform
angular velocity. The mass-radius relation, the moment of inertia and the frame
dragging for different frequencies are given. We found that we cannot use the
strange star to solve the challenges of Stella and Vietri for the horizontal
branch oscillations and the moment of inertia $I_{45}/(M/M_ s)>2.3$.
Furthermore, we extended the Hartle's method to study the differential rotating
strange star and found that the differential rotation is an effective way to
get massive strange star.


title:
Gravitational-Wave Emission from Rotating Gravitational Collapse in
  three Dimensions

abstract:
  We present the first calculation of gravitational wave emission produced in
the gravitational collapse of uniformly rotating neutron stars to black holes
in fully three-dimensional simulations. The initial stellar models are
relativistic polytropes which are dynamically unstable and with angular
velocities ranging from slow rotation to the mass-shedding limit. An essential
aspect of these simulations is the use of progressive mesh-refinement
techniques which allow to move the outer boundaries of the computational domain
to regions where gravitational radiation attains its asymptotic form. The
waveforms have been extracted using a gauge-invariant approach in which the
numerical spacetime is matched with the non-spherical perturbations of a
Schwarzschild spacetime. Overall, the results indicate that the waveforms have
features related to the properties of the initial stellar models (in terms of
their w-mode oscillations) and of the newly produced rotating black holes (in
terms of their quasi-normal modes). While our waveforms are in good qualitative
agreement with those computed by Stark and Piran in two-dimensional
simulations, our amplitudes are about one order of magnitude smaller and this
difference is mostly likely due to our less severe pressure reduction. For a
neutron star rotating uniformly near mass-shedding and collapsing at 10 kpc,
the signal-to-noise ratio computed uniquely from the burst is S/N ~ 0.25, but
this grows to be S/N <~ 4 in the case of LIGO II.


title: Horizon crossing and inflation with large \eta

abstract:
  I examine the standard formalism of calculating curvature perturbations in
inflation at horizon crossing, and derive a general relation which must be
satisfied for the horizon crossing formalism to be valid. This relation is
satisfied for the usual cases of power-law and slow roll inflation. I then
consider a model for which the relation is strongly violated, and the curvature
perturbation evolves rapidly on superhorizon scales. This model has Hubble slow
roll parameter $\eta = 3$, but predicts a scale-invariant spectrum of density
perturbations. I consider the case of hybrid inflation with large $\eta$, and
show that such solutions do not solve the ``$\eta$ problem'' in supergravity.
These solutions correspond to field evolution which has not yet relaxed to the
inflationary attractor solution, and may make possible new, more natural models
on the string landscape.


title: On the uniqueness of harmonic coordinates

abstract:
  Harmonic coordinate conditions in stationary asymptotically flat spacetimes
with matter sources have more than one solution. The solutions depend on the
degree of smoothness of the metric and its first derivatives, which we wish to
impose across the material boundary, and on the conditions at infinity and at a
suitable point inside the matter. This is illustrated in detail by simple fully
solvable examples of static spherically symmetric spacetimes in global harmonic
coordinates. Examples of stationary electrovacuum spacetimes described simply
in harmonic coordinates are also given. They can represent the exterior fields
of material discs.
  The use of an appropriate background metric considerably simplifies the
calculations.


title: Fermion absorption cross section of a Schwarzschild black hole

abstract:
  We study the absorption of massive spin-half particles by a small
Schwarzschild black hole by numerically solving the single-particle Dirac
equation in Painleve-Gullstrand coordinates. We calculate the absorption cross
section for a range of gravitational couplings Mm/m_P^2 and incident particle
energies E. At high couplings, where the Schwarzschild radius R_S is much
greater than the wavelength lambda, we find that the cross section approaches
the classical result for a point particle. At intermediate couplings we find
oscillations around the classical limit whose precise form depends on the
particle mass. These oscillations give quantum violations of the equivalence
principle. At high energies the cross section converges on the geometric-optics
value of 27 \pi R_S^2/4, and at low energies we find agreement with an
approximation derived by Unruh. When the hole is much smaller than the particle
wavelength we confirm that the minimum possible cross section approaches \pi
R_S^2/2.


title: The Early Universe in Loop Quantum Cosmology

abstract:
  Loop quantum cosmology applies techniques derived for a background
independent quantization of general relativity to cosmological situations and
draws conclusions for the very early universe. Direct implications for the
singularity problem as well as phenomenology in the context of inflation or
bouncing universes result, which will be reviewed here. The discussion focuses
on recent new results for structure formation and generalizations of the
methods.


title: A Route to Understanding of the Pioneer Anomaly

abstract:
  The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. However, while at heliocentric distance of $\sim$ 20--70 AU, the
accuracies of their orbit reconstructions were limited by a small, anomalous,
Doppler frequency drift. This drift can be interpreted as a sunward constant
acceleration of $a_P = (8.74 \pm 1.33)\times 10^{-8}$ cm/s$^2$ which is now
commonly known as the Pioneer anomaly. Here we discuss the Pioneer anomaly and
present the next steps towards understanding of its origin. They are: 1)
Analysis of the entire set of existing Pioneer 10 and 11 data, obtained from
launch to the last telemetry received from Pioneer 10, on 27 April 2002, when
it was at a heliocentric distance of 80 AU. This data could yield critical new
information about the anomaly. If the anomaly is confirmed, 2) Development of
an instrumental package to be operated on a deep space mission to provide an
independent confirmation on the anomaly. If further confirmed, 3) Development
of a deep-space experiment to explore the Pioneer anomaly in a dedicated
mission with an accuracy for acceleration resolution at the level of $10^{-10}$
cm/s$^2$ in the extremely low frequency range. In Appendices we give a summary
of the Pioneer anomaly's characteristics, outline in more detail the steps
needed to perform an analysis of the entire Pioneer data set, and also discuss
the possibility of extracting some useful information from the Cassini mission
cruise data.


title:
Conformal Field Theory, (2+1)-Dimensional Gravity, and the BTZ Black
  Hole

abstract:
  In three spacetime dimensions, general relativity becomes a topological field
theory, whose dynamics can be largely described holographically by a
two-dimensional conformal field theory at the ``boundary'' of spacetime. I
review what is known about this reduction--mainly within the context of pure
(2+1)-dimensional gravity--and discuss its implications for our understanding
of the statistical mechanics and quantum mechanics of black holes.


title: Palatini Formalism of 5-Dimensional Kaluza-Klein Theory

abstract:
  The Einstein field equations can be derived in $n$ dimensions ($n>2$) by the
variations of the Palatini action. The Killing reduction of 5-dimensional
Palatini action is studied on the assumption that pentads and Lorentz
connections are preserved by the Killing vector field. A Palatini formalism of
4-dimensional action for gravity coupled to a vector field and a scalar field
is obtained, which gives exactly the same fields equations in Kaluza-Klein
theory.


title: Hamiltonian analysis of $n$-dimensional Palatini gravity with matter

abstract:
  We consider the Palatini formalism of gravity with cosmological constant
$\Lambda$ coupled to a scalar field $\phi$ in $n$-dimensions. The
$n$-dimensional Einstein equations with $\Lambda$ can be derived by the
variation of the coupled Palatini action provided $n>2$. The Hamiltonian
analysis of the coupled action is carried out by a $1+(n-1)$ decomposition of
the spacetime. It turns out that both Palatini action and Hilbert action lead
to the same geometric dynamics in the presence of $\Lambda$ and $\phi$. While,
the $n$-dimensional Palatini action could not give a connection dynamics
formalism directly.


title: f(R) theory of gravity and conformal continuations

abstract:
  We consider static, spherically symmetric vacuum solutions to the equations
of a theory of gravity with the Lagrangian f(R) where R is the scalar curvature
and f is an arbitrary function. Using a well-known conformal transformation,
the equations of f(R) theory are reduced to the ``Einstein picture'', i.e., to
the equations of general relativity with a source in the form of a scalar field
with a potential. We have obtained necessary and sufficient conditions for the
existence of solutions admitting conformal continuations. The latter means that
a central singularity that exists in the Einstein picture is mapped, in the
Jordan picture (i.e., in the manifold corresponding to the original formulation
of the theory), to a certain regular sphere, and the solution to the field
equations may be smoothly continued beyond it. The value of the curvature R on
the transition sphere corresponds to an extremum of the function f(R). Specific
examples are considered.


title: Ultrarelativistic boost of the black ring

abstract:
  We investigate the ultrarelativistic boost of the five-dimensional
Emparan-Reall non-rotating black ring. Following the classical method of
Aichelburg and Sexl, we determine the gravitational field generated by a black
ring moving ``with the speed of light'' in an arbitrary direction. In
particular, we study in detail two different boosts along axes orthogonal and
parallel to the plane of the ring circle, respectively. In both cases, after
the limit one obtains a five-dimensional impulsive pp-wave propagating in
Minkowski spacetime. The curvature singularity of the original static spacetime
becomes a singular source within the wave front, in the shape of a ring or a
rod according to the direction of the boost. In the case of an orthogonal
boost, the wave front contains also a remnant of the original disk-shaped
membrane as a component of the Ricci tensor (which is everywhere else
vanishing). We also analyze the asymptotic properties of the boosted black ring
at large spatial distances from the singularity, and its behaviour near the
sources. In the limit when the singularity shrinks to a point, one recovers the
well known five-dimensional analogue of the Aichelburg-Sexl ``monopole''
solution.


title: Neutrino optics and oscillations in gravitational fields

abstract:
  We study the propagation of neutrinos in gravitational fields using wave
functions that are exact to first order in the metric deviation. For
illustrative purposes, the geometrical background is represented by the
Lense-Thirring metric. We derive explicit expressions for neutrino deflection,
helicity transitions, flavor oscillations and oscillation Hamiltonian.


title:
The Structure and Interpretation of Cosmology: Part I - General
  Relativistic Cosmology

abstract:
  The purpose of this work is to review, clarify, and critically analyse modern
mathematical cosmology. The emphasis is upon mathematical objects and
structures, rather than numerical computations. This paper concentrates on
general relativistic cosmology. The opening section reviews and clarifies the
Friedmann-Robertson-Walker models of general relativistic cosmology, while
Section 2 deals with the spatially homogeneous models. Particular attention is
paid in these opening sections to the topological and geometrical aspects of
cosmological models. Section 3 explains how the mathematical formalism can be
linked with astronomical observation. In particular, the informal,
observational notion of the celestial sphere is given a rigorous mathematical
implementation. Part II of this work will concentrate on inflationary cosmology
and quantum cosmology.


title:
The structure and interpretation of cosmology: Part II - The concept of
  creation in inflation and quantum cosmology

abstract:
  The purpose of the paper, of which this is part II, is to review, clarify,
and critically analyse modern mathematical cosmology. The emphasis is upon
mathematical objects and structures, rather than numerical computations. Part
II provides a critical analysis of inflationary cosmology and quantum
cosmology, with particular attention to the claims made that these theories can
explain the creation of the universe.


title: Are gauge shocks really shocks?

abstract:
  The existence of gauge pathologies associated with the Bona-Masso family of
generalized harmonic slicing conditions is proven for the case of simple 1+1
relativity. It is shown that these gauge pathologies are true shocks in the
sense that the characteristic lines associated with the propagation of the
gauge cross, which implies that the name ``gauge shock'' usually given to such
pathologies is indeed correct. These gauge shocks are associated with places
where the spatial hypersurfaces that determine the foliation of spacetime
become non-smooth.


title: Flat slice Hamiltonian formalism for dynamical black holes

abstract:
  We give a Hamiltonian analysis of the asymptotically flat spherically
symmetric system of gravity coupled to a scalar field. This 1+1 dimensional
field theory may be viewed as the "standard model" for studying black hole
physics. Our analysis is adapted to the flat slice Painleve-Gullstrand
coordinates. We give a Hamiltonian action principle for this system, which
yields an asymptotic mass formula. We then perform a time gauge fixing that
gives a Hamiltonian as the integral of a local density. The Hamiltonian takes a
relatively simple form compared to earlier work in Schwarzschild gauge, and
therefore provides a setting amenable to full quantisation.


title: K-Causal Structure of Space-Time in General Relativity

abstract:
  Using K-causal relation introduced by Sorkin and Woolgar [26], we gener-
alize results of Garcia-Parrado and Senovilla [8, 9] on causal maps. We also
introduce causality conditions with respect to K-causality which are analogous
to those in classical causality theory and prove their inter relationships. We
introduce a new causality condition following the work of Bombelli and Noldus
[3] and show that this condition lies in between global hyperbolicity and
causal simplicity. This approach is simpler and more general as compared to
traditional causal approach [11, 19] and it has been used by Penrose et.al [20]
in giving a new proof of positivity of mass theorem. C^0 space-time structures
arise in many mathematical and physical situations like conical singularities,
discontinuous matter distributions, phenomena of topology-change in quantum
field theory etc.


title: Cosmological significance of one-loop effective gravity

abstract:
  We study the one-loop effective action for gravity in a cosmological setup to
determine possible cosmological effects of quantum corrections to Einstein
theory. By considering the effect of the universal non-local terms in a toy
model, we show that they can play an important role in the very early universe.
We find that during inflation, the non-local terms are significant, leading to
deviations from the standard inflationary expansion.


title: Relativistic simultaneity and causality

abstract:
  We analyze two types of relativistic simultaneity associated to an observer:
the spacelike simultaneity, given by Landau submanifolds, and the lightlike
simultaneity (also known as observed simultaneity), given by past-pointing
horismos submanifolds. We study some geometrical conditions to ensure that
Landau submanifolds are spacelike and we prove that horismos submanifolds are
always lightlike. Finally, we establish some conditions to guarantee the
existence of foliations in the space-time whose leaves are these submanifolds
of simultaneity generated by an observer.


title:
Comment on Singularity-free Cosmological Solutions with Non-rotating
  Perfect Fluids

abstract:
  A conjecture stated by Raychaudhuri which claims that the only physical
perfect fluid non-rotating non-singular cosmological models are comprised in
the Ruiz-Senovilla and Fernandez-Jambrina families is shown to be incorrect. An
explicit counterexample is provided and the failure of the argument leading to
the result is explicitly pointed out.


title: Boundary term, extended Witten identities and positivity of energy

abstract:
  In terms of two-spinors a chiral formulation of general relativity with the
Ashtekar Lagrangian and its Hamiltonian formalism in which the basic dynamic
variables are the dyad spinors are presented. The extended Witten identities
are derived. A new expression of the Hamiltonian boundary term is obtained.
Using this expression and the extended Witten identities the proof of the
positive energy theorem is extended to a case including momentum and angular
momentum.


title: Friedmann cosmology with decaying vacuum density

abstract:
  Among the several proposals to solve the incompatibility between the observed
small value of the cosmological constant and the huge value obtained by quantum
field theories, we can find the idea of a decaying vacuum energy density,
leading from high values at early times of universe evolution to the small
value observed nowadays. In this paper we consider a variation law for the
vacuum density recently proposed by Schutzhold on the basis of quantum field
estimations in the curved, expanding background, characterized by a vacuum
density proportional to the Hubble parameter. We show that, in the context of
an isotropic and homogeneous, spatially flat model, the corresponding solutions
retain the well established features of the standard cosmology, and, in
addition, are in accordance with the observed cosmological parameters. Our
scenario presents an initial phase dominated by radiation, followed by a dust
era long enough to permit structure formation, and by an epoch dominated by the
cosmological term, which tends asymptotically to a de Sitter universe. Taking
the matter density equals to half of the vacuum energy density, as suggested by
observation, we obtain a universe age given by Ht = 1.1, and a decelerating
parameter equals to -1/2.


title: Deformed dispersion relations and the Hanbury--Brown--Twiss Effect

abstract:
  In the present work we analyze the possibility of detecting some deformed
dispersion relations, emerging in some quantum--gravity models, resorting to
the so--called Hanbury--Brown--Twiss effect. It will be proved that in some
scenarios the possibilities are not pessimistic. Forsooth, for some values of
the corresponding parameters the aforementioned effect could render interesting
outcomes.


title: Classical Gravitational Interactions and Gravitational Lorentz Force

abstract:
  In quantum gauge theory of gravity, the gravitational field is represented by
gravitational gauge field. The field strength of gravitational gauge field has
both gravitational electric component and gravitational magnetic component. In
classical level, gauge theory of gravity gives out classical Newtonian
gravitational interactions in a relativistic form. Besides, it gives out
gravitational Lorentz force which is the gravitational force on a moving object
in gravitational magnetic field. The direction of gravitational Lorentz force
does not along that of classical gravitational Newtonian force. Effects of
gravitational Lorentz force should be detectable, and these effects can be used
to discriminate gravitational magnetic field from ordinary electromagnetic
magnetic field.


title: VSI_i spacetimes and the epsilon-property

abstract:
  We investigate Lorentzian spacetimes where all zeroth and first order
curvature invariants vanish and discuss how this class differs from the one
where all curvature invariants vanish (VSI). We show that for VSI spacetimes
all components of the Riemann tensor and its derivatives up to some fixed order
can be made arbitrarily small. We discuss this in more detail by way of
examples.


title:
A black hole mass threshold from non-singular quantum gravitational
  collapse

abstract:
  Quantum gravity is expected to remove the classical singularity that arises
as the end-state of gravitational collapse. To investigate this, we work with a
toy model of a collapsing homogeneous scalar field. We show that
non-perturbative semi-classical effects of Loop Quantum Gravity cause a bounce
and remove the black hole singularity. Furthermore, we find a critical
threshold scale, below which no horizon forms -- quantum gravity may exclude
very small astrophysical black holes.


title:
Primordial magnetic seed field amplification by gravitational waves:
  comment on gr-qc/0503006

abstract:
  We consider the amplification of cosmological magnetic fields by
gravitational waves as it was recently presented in [gr-qc/0503006]. That study
confined to infinitely conductive environments, arguing that on spatially flat
Friedmann backgrounds the gravito-magnetic interaction proceeds always as if
the universe were a perfect conductor. We explain why this claim is not correct
and then re-examine the Maxwell-Weyl coupling at the limit of ideal
magnetohydrodynamics. We find that the scales of the main results of
[gr-qc/0503006] were not properly assessed and that the incorrect scale
assessment has compromised both the physical and the numerical results of the
paper. This comment aims to clarify these issues on the one hand, while on the
other it takes a closer look at the gauge-invariance and the nonlinearity of
[gr-qc/0503006].


title:
Monodromy-data parameterization of spaces of local solutions of
  integrable reductions of Einstein's field equations

abstract:
  For the fields depending on two of the four space-time coordinates only, the
spaces of local solutions of various integrable reductions of Einstein's field
equations are shown to be the subspaces of the spaces of local solutions of the
``null-curvature'' equations constricted by a requirement of a universal (i.e.
solution independent) structures of the canonical Jordan forms of the unknown
matrix variables. These spaces of solutions of the ``null-curvature'' equations
can be parametrized by a finite sets of free functional parameters -- arbitrary
holomorphic (in some local domains) functions of the spectral parameter which
can be interpreted as the monodromy data on the spectral plane of the
fundamental solutions of associated linear systems. Direct and inverse problems
of such mapping (``monodromy transform''), i.e. the problem of finding of the
monodromy data for any local solution of the ``null-curvature'' equations with
given canonical forms, as well as the existence and uniqueness of such solution
for arbitrarily chosen monodromy data are shown to be solvable unambiguously.
The linear singular integral equations solving the inverse problems and the
explicit forms of the monodromy data corresponding to the spaces of solutions
of the symmetry reduced Einstein's field equations are derived.


title:
Dimensional regularization of the third post-Newtonian gravitational
  wave generation from two point masses

abstract:
  Dimensional regularization is applied to the computation of the gravitational
wave field generated by compact binaries at the third post-Newtonian (3PN)
approximation. We generalize the wave generation formalism from isolated
post-Newtonian matter systems to d spatial dimensions, and apply it to point
masses (without spins), modelled by delta-function singularities. We find that
the quadrupole moment of point-particle binaries in harmonic coordinates
contains a pole when epsilon = d-3 -> 0 at the 3PN order. It is proved that the
pole can be renormalized away by means of the same shifts of the particle
world-lines as in our recent derivation of the 3PN equations of motion. The
resulting renormalized (finite when epsilon -> 0) quadrupole moment leads to
unique values for the ambiguity parameters xi, kappa and zeta, which were
introduced in previous computations using Hadamard's regularization. Several
checks of these values are presented. These results complete the derivation of
the gravitational waves emitted by inspiralling compact binaries up to the
3.5PN level of accuracy which is needed for detection and analysis of the
signals in the gravitational-wave antennas LIGO/VIRGO and LISA.


title:
Noncompact KK theory of gravity: stochastic treatment for a
  nonperturbative inflaton field in a de Sitter expansion

abstract:
  We study a stochastic formalism for a nonperturbative treatment of the
inflaton field in the framework of a noncompact Kaluza-Klein (KK) theory during
an inflationary (de Sitter) expansion, without the slow-roll approximation.


title: Quantum Measurements and the kappa--Poincare Group

abstract:
  The possible description of the vacuum of quantum gravity through the so
called kappa--Poincare group is analyzed considering some of the consequences
of this symmetry in the path integral formulation of nonrelativistic quantum
theory. This study is carried out with two cases, firstly, a free particle, and
finally, the situation of a particle immersed in a homogeneous gravitational
field. It will be shown that the kappa--Poincare group implies the loss of some
of the basic properties associated to Feynman's path integral. For instance,
loss of the group characteristic related to the time dependence of the
evolution operator, or the breakdown of the composition law for amplitudes of
events occurring successively in time. Additionally some similarities between
the present idea and the so called restricted path integral formalism will be
underlined. These analogies advocate the claim that if the kappa--Poincare
group contains some of the physical information of the quantum gravity vacuum,
then this vacuum could entail decoherence. This last result will also allow us
to consider the possibility of analyzing the continuous measurement problem of
quantum theory from a group--theoretical point of view, but now taking into
account the kappa--Poincare symmetries.


title: Relativistic non-equilibrium thermodynamics revisited

abstract:
  Relativistic irreversible thermodynamics is reformulated following the
conventional approach proposed by Meixner in the non-relativistic case. Clear
separation between mechanical and non-mechanical energy fluxes is made. The
resulting equations for the entropy production and the local internal energy
have the same structure as the non-relativistic ones. Assuming linear
constitutive laws, it is shown that consistency is obtained both with the laws
of thermodynamics and causality.


title:
Global existence of solutions for the relativistic Boltzmann equation
  with arbitrarily large initial data on a Bianchi type I space-time

abstract:
  We prove, for the relativistic Boltzmann equation on a Bianchi type I
space-time, a global existence and uniqueness theorem, for arbitrarily large
initial data.


title: Interacting fluids generating identical, dual and phantom cosmologies

abstract:
  We find the group of symmetry transformations generated by interacting fluids
in spatially flat Friedmann-Robertson-Walker (FRW) spacetime which links
cosmologies with the same scale factor {\it (identity)} or with scale factors
$a$ and $a^{-1}$ {\it (duality)}. There exists a duality between contracting
and superaccelerated expanding scenarios associated with {\it (phantom)}
cosmologies. We investigate the action of this symmetry group on
self-interacting minimally(conformally) coupled quintessence and $k$-essence
cosmologies.


title:
Semiclassical approach to black hole absorption of electromagnetic
  radiation emitted by a rotating charge

abstract:
  We consider an electric charge, minimally coupled to the Maxwell field,
rotating around a Schwarzschild black hole. We investigate how much of the
radiation emitted from the swirling charge is absorbed by the black hole and
show that most of the photons escape to infinity. For this purpose we use the
Gupta-Bleuler quantization of the electromagnetic field in the modified Feynman
gauge developed in the context of quantum field theory in Schwarzschild
spacetime. We obtain that the two photon polarizations contribute quite
differently to the emitted power. In addition, we discuss the accurateness of
the results obtained in a full general relativistic approach in comparison with
the ones obtained when the electric charge is assumed to be orbiting a massive
object due to a Newtonian force.


title: Universally Coupled Massive Gravity

abstract:
  We derive Einstein's equations from a linear theory in flat space-time using
free-field gauge invariance and universal coupling. The gravitational potential
can be either covariant or contravariant and of almost any density weight. We
adapt these results to yield universally coupled massive variants of Einstein's
equations, yielding two one-parameter families of distinct theories with spin 2
and spin 0. The Freund-Maheshwari-Schonberg theory is therefore not the unique
universally coupled massive generalization of Einstein's theory, although it is
privileged in some respects. The theories we derive are a subset of those found
by Ogievetsky and Polubarinov by other means. The question of positive energy,
which continues to be discussed, might be addressed numerically in spherical
symmetry. We briefly comment on the issue of causality with two observable
metrics and the need for gauge freedom and address some criticisms by
Padmanabhan of field derivations of Einstein-like equations along the way.


title: Quantum nature of black holes

abstract:
  I reconsider Hawking's analysis of the effects of gravitational collapse on
quantum fields, taking into account interactions between the fields. The
ultra-high energy vacuum fluctuations, which had been considered to be an
awkward peripheral feature of the analysis, are shown to play a key role. By
interactions, they can scatter particles to, or create pairs of particle at,
ultra-high energies. The energies rapidly become so great that quantum gravity
must play a dominant role. Thus the vicinities of black holes are essentially
quantum-gravitational regimes.


title: Quantum character of black holes

abstract:
  Black holes are extreme manifestations of general relativity, so one might
hope that exotic quantum effects would be amplified in their vicinities,
perhaps providing clues to quantum gravity. The commonly accepted treatment of
quantum corrections to the physics around the holes, however, has provided only
limited encouragement of this hope. The predicted corrections have been minor
(for macroscopic holes): weak fluxes of low-energy thermal radiation which
hardly disturb the classical structures of the holes. Here, I argue that this
accepted treatment must be substantially revised. I show that when interactions
among fields are taken into account (they were largely neglected in the earlier
work) the picture that is drawn is very different. Not only low-energy
radiation but also ultra-energetic quanta are produced in the gravitationally
collapsing region. The energies of these quanta grow exponentially quickly, so
that by the time the hole can be said to have formed, they have passed the
Planck scale, at which quantum gravity must become dominant. The vicinities of
black holes are windows on quantum gravity.


title:
Deriving Mathisson - Papapetrou equations from relativistic
  pseudomechanics

abstract:
  It is shown that the equations of motion of a test point particle with spin
in a given gravitational field, so called Mathisson - Papapetrou equations, can
be derived from Euler - Lagrange equations of the relativistic pseudomechanics
-- relativistic mechanics, which side by side uses the conventional (commuting)
and Grassmannian (anticommuting) variables. In this approach the known
difficulties of the Mathisson - Papapetrou equations, namely, the problem of
the choice of supplementary conditions and the problem of higher derivatives
are not appear.


title: Uniqueness of RS2 type thick branes supported by a scalar field

abstract:
  We study thick brane world models as Z_2-symmetric domain walls supported by
a scalar field with an arbitrary potential V(\phi) in 5D general relativity.
Under the global regularity requirement, such configurations (i) have always an
AdS asymptotic far from the brane, (ii) are only possible if V(\phi) has an
alternating sign and (iii) V(\phi) should satisfy a certain fine-tuning type
equality. Thus a thick brane with any admissible V(\phi) is a regularized
version of the RS2 brane immersed in the AdS_5 bulk. The thin brane limit is
realized in a universal manner by including an arbitrary thick brane model in a
one-parameter family, where the parameter "a" is associated with brane
thickness; the asymptotic value of V(\phi) (related to \Lambda_5, the effective
cosmological constant) remains a-independent. The problem of ordinary matter
confinement on the brane is discussed for a test scalar field. Its
stress-energy tensor is found to diverge at the AdS horizon for both thin and
thick branes, making a serious problem for this class of brane world models.


title:
Numerical stability for finite difference approximations of Einstein's
  equations

abstract:
  We extend the notion of numerical stability of finite difference
approximations to include hyperbolic systems that are first order in time and
second order in space, such as those that appear in Numerical Relativity. By
analyzing the symbol of the second order system, we obtain necessary and
sufficient conditions for stability in a discrete norm containing one-sided
difference operators. We prove stability for certain toy models and the
linearized Nagy-Ortiz-Reula formulation of Einstein's equations.
  We also find that, unlike in the fully first order case, standard
discretizations of some well-posed problems lead to unstable schemes and that
the Courant limits are not always simply related to the characteristic speeds
of the continuum problem. Finally, we propose methods for testing stability for
second order in space hyperbolic systems.


title: Big extra dimensions make Lambda too small

abstract:
  I argue that the true quantum gravity scale cannot be much larger than the
Planck length, because if it were then the quantum gravity-induced fluctuations
in $\Lam$ would be insufficient to produce the observed cosmic ``dark energy''.
If one accepts this argument, it rules out scenarios of the ``large extra
dimensions'' type. I also point out that the relation between the lower and
higher dimensional gravitational constants in a Kaluza-Klein theory is
precisely what is needed in order that a black hole's entropy admit a
consistent higher dimensional interpretation in terms of an underlying
spatio-temporal discreteness.


title: Black Strings in Our World

abstract:
  The brane world scenario is a new approach to resolve the problem on how to
compactify the higher dimensional spacetime to our 4-dimensional world. One of
the remarkable features of this scenario is the higher dimensional effects in
classical gravitational interactions at short distances. Due to this feature,
there are black string solutions in our 4-dimensional world. In this paper,
assuming the simplest model of complex minimally coupled scalar field with the
local U(1) symmetry, we show a possibility of black-string formation by merging
processes of type I long cosmic strings in our 4-dimensional world. No fine
tuning for the parameters in the model might be necessary.


title:
Two-dimensional description of D-dimensional static black holes with
  pointlike sources

abstract:
  We derive two-dimensional (2D) solutions of a generic dilaton gravity model
coupled with matter, which describe D-dimensional static black holes with
pointlike sources. The equality between the mass M of the D-dimensional
gravitational solution and the mass m of the source can be preserved also at
the level of the 2D gravity model.


title: On three quantization methods for particle on hyperboloid

abstract:
  We compare the respective efficiencies of three quantization methods (group
theoretical, coherent state and geometric) by quantizing the dynamics of a free
massive particle in two-dimensional de Sitter space. For each case we consider
the realization of the principal series representation of $SO_0(1,2) $ group
and its two-fold covering SU(1,1). We demonstrate that standard technique for
finding an irreducible representation within the geometric quantization scheme
fails. For consistency we recall our earlier results concerning the other two
methods, make some improvements and generalizations.


title: Drawing conformal diagrams for a fractal landscape

abstract:
  Generic models of cosmological inflation and the recently proposed scenarios
of a recycling universe and the string theory landscape predict spacetimes
whose global geometry is a stochastic, self-similar fractal. To visualize the
complicated causal structure of such a universe, one usually draws a conformal
(Carter-Penrose) diagram. I develop a new method for drawing conformal
diagrams, applicable to arbitrary 1+1-dimensional spacetimes. This method is
based on a qualitative analysis of intersecting lightrays and thus avoids the
need for explicit transformations of the spacetime metric. To demonstrate the
power and simplicity of this method, I present derivations of diagrams for
spacetimes of varying complication. I then apply the lightray method to three
different models of an eternally inflating universe (scalar-field inflation,
recycling universe, and string theory landscape) involving the nucleation of
nested asymptotically flat, de Sitter and/or anti-de Sitter bubbles. I show
that the resulting diagrams contain a characteristic fractal arrangement of
lines.


title: Fermionic sectors for the Kodama state

abstract:
  Diffeomorphisms not connected to the identity can act nontrivially on the
quantum state space for gravity. However, in stark contrast to the case of
nonabelian Yang-Mills field theories, for which the quantum state space is
always in 1 dimensional representation of the large gauge transformations, the
quantum state space for gravity can have higher dimensional representations. In
particular, the Kodama state will have 2 dimensional representations, that is
sectors with spin 1/2, for many topologies that admit positive scalar
curvature. The existence of these spin 1/2 states are used to point out a
possible answer to certain criticisms raised recently in the literature.


title:
Using Simulation, Comparison and Grid Search To Find all Possible Binary
  Black Hole Source Parameters For Extreme Mass-Ratio Inspiral Gravitational
  Wave Signals

abstract:
  First, for each case to be tested, a specific target inspiral signal is
selected for parameter extraction. In a future real analysis, the target signal
would be a real signal actually observed by a gravitational wave detector such
as LISA. In this study, however, the target signals are themselves simulations.
Some cases were selected to resemble sources likely to be detected by LISA when
it flies; others were selected to facilitate comparison with previous work
using Fisher matrix techniques. Then, for each target inspiral signal, a grid
search of the input parameter space is conducted to determine the set of input
parameters that produce a simulated inspiral output signal compatible with the
target. In this study, we consider four parameters: the two masses, the spin of
the larger black hole, and the eccentricity of the orbit. Searching through
this four dimensional parameter space requires that hundreds of possible input
source parameter combinations be simulated for each target signal analyzed. For
each input parameter combination, the detailed time history of the phase of the
resulting inspiral is simulated and compared with the phase history of the
target signal. The simulation, comparison, and grid search technique used in
this study requires more work than the Fisher matrix technique used in most
previous studies of this topic. However, this method yields a detailed map of
the acceptable region of input parameter space, in contrast to the
multidimensional ellipsoids of the Fisher matrix method. Nevertheless, the
final results are in general agreement with those obtained previously by the
Fisher matrix method, providing a partly independent confirmation of both
results.


title: Numerical Solutions of Inflating Higher Dimensional Global Defects

abstract:
  We find numerical solutions of Einstein equations and scalar field equation
for a global defect in higher dimensional spacetimes ($\geq 6$). We examine in
detail the relation among the expansion rate $H$ and the symmetry-breaking
scale $\eta$ and the number of extra dimensions $n$ for these solutions. We
find that even if the extra dimensions do not have a cigar geometry, the
expansion rate $H$ grows as $\eta$ increases, which is opposite to what is
needed for the recently proposed mechanism for solving the cosmological
constant problem. We also find that the expansion rate $H$ decreases as $n$
increases.


title: On Energy Conditions and Stability in Effective Loop Quantum Cosmology

abstract:
  In isotropic loop quantum cosmology, non-perturbatively modified dynamics of
a minimally coupled scalar field violates weak, strong and dominant energy
conditions when they are stated in terms of equation of state parameter. The
violation of strong energy condition helps to have non-singular evolution by
evading singularity theorems thus leading to a generic inflationary phase.
However, the violation of weak and dominant energy conditions raises concern,
as in general relativity these conditions ensure causality of the system and
stability of vacuum via Hawking-Ellis conservation theorem. It is shown here
that the non-perturbatively modified kinetic term contributes negative pressure
but positive energy density. This crucial feature leads to violation of energy
conditions but ensures positivity of energy density, as scalar matter
Hamiltonian remains bounded from below. It is also shown that the modified
dynamics restricts group velocity for inhomogeneous modes to remain sub-luminal
thus ensuring causal propagation across spatial distances.


title: A Michelson interferometer in the field of a plane gravitational wave

abstract:
  We treat the problem of a Michelson interferometer in the field of a plane
gravitational wave in the framework of general relativity. The arms of the
interferometer are regarded as the world lines of the light beams, whose motion
is determined by the Hamilton-Jacobi equation for a massless particle. In the
case of a weak monochromatic wave we find that the formula for the delay of a
light beam agrees with the result obtained by solving the linearized coupled
Einstein-Maxwell equations. We also calculate this delay in the next
(quadratic) approximation.