title: Radiation and Potential Barriers of a 5D Black String Solution

abstract:
  By using a massless scalar field we examine the effect of an extra dimension
on black hole radiation. Because the equations are coupled, we find that the
structure of the fifth dimension (as for membrane and induced-matter theory)
affects the nature of the radiation observed in four-dimensional spacetime. In
the case of the Schwarzschild-de Sitter solution embedded in a Randall-Sundrum
brane model, the extension of the black hole along the fifth dimension looks
like a black string. Then it is shown that, on the brane, the potential barrier
surrounding the black hole has a quantized as well as a continuous spectrum. In
principle, Hawking radiation may thus provide a probe for higher dimensions.


title:
Globally hyperbolic spacetimes can be defined as "causal" instead of
  "strongly causal"

abstract:
  The classical definition of {\em global hyperbolicity} for a spacetime
$(M,g)$ comprises two conditions: (A) compactness of the diamonds $J^+(p)\cap
J^-(q)$, and (B) strong causality. Here we show that condition (B) can be
replaced just by causality. In fact, we show first that the classical
definition of causal simplicity (which impose to be distinguishing, apart from
the closedness of $J^+(p)$, $J^-(q)$) can be weakened in causal instead of
distinguishing. So, the full consistency of the causal ladder (recently proved
by the authors in a definitive way) yields directly the result.


title:
The Mystery of the Asymptotic Quasinormal Modes of Gauss-Bonnet Black
  Holes

abstract:
  We analyze the quasinormal modes of $D$-dimensional Schwarzschild black holes
with the Gauss-Bonnet correction in the large damping limit and show that
standard analytic techniques cannot be applied in a straightforward manner to
the case of infinite damping. However, by using a combination of analytic and
numeric techniques we are able to calculate the quasinormal mode frequencies in
a range where the damping is large but finite. We show that for this damping
region the famous $\ln(3)$ appears in the real part of the quasinormal mode
frequency. In our calculations, the Gauss-Bonnet coupling, $\alpha$, is taken
to be much smaller than the parameter $\mu$, which is related to the black hole
mass.


title: Proper Matter Collineations of Plane Symmetric Spacetimes

abstract:
  We investigate matter collineations of plane symmetric spacetimes when the
energy-momentum tensor is degenerate. There exists three interesting cases
where the group of matter collineations is finite-dimensional. The matter
collineations in these cases are either four, six or ten in which four are
isometries and the rest are proper.


title:
The Canonical Approach to Quantum Gravity: General Ideas and
  Geometrodynamics

abstract:
  We give an introduction to the canonical formalism of Einstein's theory of
general relativity. This then serves as the starting point for one approach to
quantum gravity called quantum geometrodynamics. The main features and
applications of this approach are briefly summarized.


title: General Relativistic Dynamics of Compact Binary Systems

abstract:
  The equations of motion of compact binary systems have been derived in the
post-Newtonian (PN) approximation of general relativity. The current level of
accuracy is 3.5PN order. The conservative part of the equations of motion
(neglecting the radiation reaction damping terms) is deducible from a
generalized Lagrangian in harmonic coordinates, or equivalently from an
ordinary Hamiltonian in ADM coordinates. As an application we investigate the
problem of the dynamical stability of circular binary orbits against
gravitational perturbations up to the 3PN order. We find that there is no
innermost stable circular orbit or ISCO at the 3PN order for equal masses.


title: Inside the BTZ black hole

abstract:
  We consider static circularly symmetric solution of three-dimensional
Einstein's equations with negative cosmological constant (the BTZ black hole).
The case of zero cosmological constant corresponding to the interior region of
a black hole is analyzed in detail. We prove that the maximally extended BTZ
solution with zero cosmological constant coincides with flat three-dimensional
Minkowskian space-time without any singularity and horizons. The Euclidean
version of this solution is shown to have physical interpretation in the
geometric theory of defects in solids describing combined wedge and screw
dislocations.


title: N-body Gravity and the Schroedinger Equation

abstract:
  We consider the problem of the motion of $N$ bodies in a self-gravitating
system in two spacetime dimensions. We point out that this system can be mapped
onto the quantum-mechanical problem of an N-body generalization of the problem
of the H$_{2}^{+}$ molecular ion in one dimension. The canonical gravitational
N-body formalism can be extended to include electromagnetic charges. We derive
a general algorithm for solving this problem, and show how it reduces to known
results for the 2-body and 3-body systems.


title: Numerical calculations near spatial infinity

abstract:
  After describing in short some problems and methods regarding the smoothness
of null infinity for isolated systems, I present numerical calculations in
which both spatial and null infinity can be studied. The reduced conformal
field equations based on the conformal Gauss gauge allow us in spherical
symmetry to calculate numerically the entire Schwarzschild-Kruskal spacetime in
a smooth way including spacelike, null and timelike infinity and the domain
close to the singularity.


title:
Massive scalar field quasinormal modes of a Schwarzschild black hole
  surrounded by quintessence

abstract:
  We present the quasinormal frequencies of the massive scalar field in the
background of a Schwarzchild black hole surrounded by quintessence with the
third-order WKB method. The mass of the scalar field $u$ plays an important
role in studying the quasinormal frequencies, the real part of the frequencies
increases linearly as mass $u$ increases, while the imaginary part in absolute
value decreases linearly which leads to damping more slowly and the frequencies
having a limited value. Moreover, owing to the presence of the quintessence,
the massive scalar field damps more slowly.


title: On the Matching Conditions for the Collapsing Cylinder

abstract:
  We review the matching conditions for a collapsing anisotropic cylindrical
perfect fluid, recently discussed in the literature (2005 {\it Class. Quantum
Grav.} {\bf 22} 2407). It is shown that radial pressure vanishes on the surface
of the cylinder, contrary to what is asserted in that reference. The origin of
this discrepancy is to be found in a mistake made in one step of the
calculations. Some comments about the relevance of this result in relation to
the momentum of Einstein--Rosen waves are presented.


title:
Fundamental spatiotemporal decoherence: a key to solving the conceptual
  problems of black holes, cosmology and quantum mechanics

abstract:
  Unitarity is a pillar of quantum theory. Nevertheless, it is also a source of
several of its conceptual problems. We note that in a world where measurements
are relational, as is the case in gravitation, quantum mechanics exhibits a
fundamental level of loss of coherence. This can be the key to solving, among
others, the puzzles posed by the black hole information paradox, the formation
of inhomogeneities in cosmology and the measurement problem in quantum
mechanics.


title:
Equilibrium hydrostatic equation and Newtonian limit of the singular
  f(R) gravity

abstract:
  We derive the equilibrium hydrostatic equation of a spherical star for any
gravitational Lagrangian density of the form $L=\sqrt{-g}f(R)$. The Palatini
variational principle for the Helmholtz Lagrangian in the Einstein gauge is
used to obtain the field equations in this gauge. The equilibrium hydrostatic
equation is obtained and is used to study the Newtonian limit for
$f(R)=R-\frac{a^{2}}{3R}$. The same procedure is carried out for the more
generally case $f(R)=R-\frac{1}{n+2}\frac{a^{n+1}}{R^{n}}$ giving a good
Newtonian limit.


title:
Traversable wormholes supported by cosmic accelerated expanding
  equations of state

abstract:
  We explore the possibility that traversable wormholes be supported by
specific equations of state responsible for the present accelerated expansion
of the Universe, namely, phantom energy, the generalized Chaplygin gas, and the
van der Waals quintessence equation of state.


title:
Casimir stress on parallel plates in de Sitter space with signature
  change

abstract:
  The Casimir stress on two parallel plates in a de Sitter background
corresponding to different metric signatures and cosmological constants is
calculated for massless scalar fields satisfying Robin boundary conditions on
the plates. Our calculation shows that for the parallel plates with false
vacuum between and true vacuum outside, the total Casimir pressure leads to an
attraction of the plates at very early universe.


title: Forces in Kerr spacetimes with a repulsive cosmological constant

abstract:
  Forces defined in the framework of optical reference geometry are introduced
in the case of stationary and axially symmetric Kerr black-hole and
naked-singularity spacetimes with a repulsive cosmological constant. Properties
of the forces acting on test particles moving along circular orbits in the
equatorial plane are discussed, whereas it is shown where the gravitational
force vanishes and changes its orientation and where the centrifugal force
vanishes and changes its orientation independently of the velocity of test
particles related to the optical geometry; the Coriolis force does not vanish
for the velocity being non-zero. The spacetimes are classified according to the
number of circular orbits where the gravitational and centrifugal forces
vanish.


title:
Equilibrium conditions of spinning test particles in Kerr-de Sitter
  spacetimes

abstract:
  Equilibrium conditions and spin dynamics of spinning test particles are
discussed in the stationary and axially symmetric Kerr-de Sitter black-hole or
naked-singularity spacetimes. The general equilibrium conditions are
established, but due to their great complexity, the detailed discussion of the
equilibrium conditions and spin dynamics is presented only in the simple and
most relevant cases of equilibrium positions in the equatorial plane and on the
symmetry axis of the spacetimes. It is shown that due to the combined effect of
the rotation of the source and the cosmic repulsion the equilibrium is spin
dependent in contrast to the spherically symmetric spacetimes. In the
equatorial plane, it is possible at the so-called static radius, where the
gravitational attraction is balanced by the cosmic repulsion, for the spinless
particles as well as for spinning particles with arbitrarily large
azimuthal-oriented spin or at any radius outside the ergosphere with a
specifically given spin orthogonal to the equatorial plane. On the symmetry
axis, the equilibrium is possible at any radius in the stationary region and is
given by an appropriately tuned spin directed along the axis. At the static
radii on the axis the spin of particles in equilibrium must vanish.


title: MacDowell-Mansouri gravity and Cartan geometry

abstract:
  The geometric content of the MacDowell-Mansouri formulation of general
relativity is best understood in terms of Cartan geometry. In particular,
Cartan geometry gives clear geometric meaning to the MacDowell-Mansouri trick
of combining the Levi-Civita connection and coframe field, or soldering form,
into a single physical field. The Cartan perspective allows us to view physical
spacetime as tangentially approximated by an arbitrary homogeneous "model
spacetime", including not only the flat Minkowski model, as is implicitly used
in standard general relativity, but also de Sitter, anti de Sitter, or other
models. A "Cartan connection" gives a prescription for parallel transport from
one "tangent model spacetime" to another, along any path, giving a natural
interpretation of the MacDowell-Mansouri connection as "rolling" the model
spacetime along physical spacetime. I explain Cartan geometry, and "Cartan
gauge theory", in which the gauge field is replaced by a Cartan connection. In
particular, I discuss MacDowell-Mansouri gravity, as well as its more recent
reformulation in terms of BF theory, in the context of Cartan geometry.


title: Thermodynamical properties of dark energy

abstract:
  We have investigated the thermodynamical properties of dark energy. Assuming
that the dark energy temperature $T\sim a^{-n}$ and considering that the volume
of the Universe enveloped by the apparent horizon relates to the temperature,
we have derived the dark energy entropy. For dark energy with constant equation
of state $w>-1$ and the generalized Chaplygin gas, the derived entropy can be
positive and satisfy the entropy bound. The total entropy, including those of
dark energy, the thermal radiation and the apparent horizon, satisfies the
generalized second law of thermodynamics. However, for the phantom with
constant equation of state, the positivity of entropy, the entropy bound, and
the generalized second law cannot be satisfied simultaneously.


title: On Loop States in Loop Quantum Gravity

abstract:
  We explicitly construct and characterize all possible independent loop states
in 3+1 dimensional loop quantum gravity by regulating it on a 3-d regular
lattice in the Hamiltonian formalism. These loop states, characterized by the
(dual) angular momentum quantum numbers, describe SU(2) rigid rotators on the
links of the lattice. The loop states are constructed using the Schwinger
bosons which are harmonic oscillators in the fundamental (spin half)
representation of SU(2). Using generalized Wigner Eckart theorem, we compute
the matrix elements of the volume operator in the loop basis. Some simple loop
eigenstates of the volume operator are explicitly constructed.


title: A note on spin two fields in curved backgrounds

abstract:
  We reconsider the consistency constraints on a free massless symmetric, rank
2, tensor field in a background and confirm that they uniquely require it to be
the linear deviation about (cosmological) Einstein gravity. Neither adding
non-minimal higher derivative terms nor changing the gauge transformations by
allowing terms non-analytic in the cosmological constant alters this fact.


title: The significance of matter coupling in f(R) gravity

abstract:
  The way one chooses to couple gravity to matter is an essential
characteristic of any gravitational theory. In theories where the gravitational
field is allowed to have more degrees of freedom than those of General
Relativity (e.g. scalar-tensor theory, f(R) gravity) this issue often becomes
even more important. We concentrate here on f(R) gravity treated within the
Palatini variational principle and discuss how the coupling between matter and
the extra degrees of freedom of gravity (the independent connections in our
case) affects not only the resulting phenomenology but even the geometrical
meaning of fundamental fields.


title: Beyond the Bowen-York extrinsic curvature for spinning black holes

abstract:
  It is well-known that Bowen-York initial data contain spurious radiation.
Although this ``junk'' radiation has been seen to be small for non-spinning
black-hole binaries in circular orbit, its magnitude increases when the black
holes are given spin. It is possible to reduce the spurious radiation by
applying the puncture approach to multiple Kerr black holes, as we demonstrate
for examples of head-on collisions of equal-mass black-hole binaries.


title: Violation of the Equivalence Principle in Modified Theories of Gravity

abstract:
  We study modified theories of gravity of the f(R) type in Palatini formalism.
For a generic f(R) lagrangian, we show that the metric can be solved as the
product of a scalar function times a rank-two tensor (or auxiliary metric). The
scalar function is sensitive to the local energy-momentum density. The
auxiliary metric satisfies a set of equations very similar to Einstein's
equations and, for weak sources, it can be approximated by the Minkowski
metric. According to this, the metric coupled to the matter strongly departs
from the Minkowskian one in the neighbourhood of any microscopic physical
system. As a consequence, new gravitationally-induced interactions arise and
lead to observable effects at microscopic and macroscopic scales. In
particular, test body trajectories experience self-accelerations which depend
on the internal structure and composition of the body. These facts make very
unlikely the viability of Palatini f(R) models designed to change the late-time
cosmic evolution.


title: Chaos and Order in Models of Black Hole Pairs

abstract:
  Chaos in the orbits of black hole pairs has by now been confirmed by several
independent groups. While the chaotic behavior of binary black hole orbits is
no longer argued, it remains difficult to quantify the importance of chaos to
the evolutionary dynamics of a pair of comparable mass black holes. None of our
existing approximations are robust enough to offer convincing quantitative
conclusions in the most highly nonlinear regime. It is intriguing to note that
in three different approximations to a black hole pair built of a spinning
black hole and a non-spinning companion, two approximations exhibit chaos and
one approximation does not. The fully relativistic scenario of a spinning
test-mass around a Schwarzschild black hole shows chaos, as does the
Post-Newtonian Lagrangian approximation. However, the approximately equivalent
Post-Newtonian Hamiltonian approximation does not show chaos when only one body
spins. It is well known in dynamical systems theory that one system can be
regular while an approximately related system is chaotic, so there is no formal
conflict. However,the physical question remains, Is there chaos for comparable
mass binaries when only one object spins? We are unable to answer this question
given the poor convergence of the Post-Newtonian approximation to the fully
relativistic system. A resolution awaits better approximations that can be
trusted in the highly nonlinear regime.


title: The Universal Cut Function and Type II Metrics

abstract:
  In analogy with classical electromagnetic theory, where one determines the
total charge and both electric and magnetic multipole moments of a source from
certain surface integrals of the asymptotic (or far) fields, it has been known
for many years - from the work of Hermann Bondi - that energy and momentum of
gravitational sources could be determined by similar integrals of the
asymptotic Weyl tensor. Recently we observed that there were certain overlooked
structures, {defined at future null infinity,} that allowed one to determine
(or define) further properties of both electromagnetic and gravitating sources.
These structures, families of {complex} `slices' or `cuts' of Penrose's null
infinity, are referred to as Universal Cut Functions, (UCF). In particular, one
can define from these structures a (complex) center of mass (and center of
charge) and its equations of motion - with rather surprising consequences. It
appears as if these asymptotic structures contain in their imaginary part, a
well defined total spin-angular momentum of the source. We apply these ideas to
the type II algebraically special metrics, both twisting and twist-free.


title: The Seeds of Cosmic structure as a door to New Physics

abstract:
  There is something missing in our understanding of the origin of the seeds of
Cosmic Structuture.
  The fact that the fluctuation spectrum can be extracted from the inflationary
scenario through an analysis that involves quantum field theory in curved
space-time, and that it coincides with the observational data has lead to a
certain complacency in the community, which prevents the critical analysis of
the obscure spots in the derivation. The point is that the inhomogeneity and
anisotropy of our universe seem to emerge from an exactly homogeneous and
isotropic initial state through processes that do not break those symmetries.
This article gives a brief recount of the problems faced by the arguments based
on established physics, which comprise the point of view held by a large
majority of researchers in the field.
  The conclusion is that we need some new physics to be able to fully address
the problem. The article then exposes one avenue that has been used to address
the central issue and elaborates on the degree to which, the new approach makes
different predictions from the standard analyses.
  The approach is inspired on Penrose's proposals that Quantum Gravity might
lead to a real, dynamical collapse of the wave function, a process that we
argue has the properties needed to extract us from the theoretical impasse
described above.


title: The Xi-transform for conformally flat space-time

abstract:
  The Xi-transform is a new spinor transform arising naturally in Einstein's
general relativity. Here the example of conformally flat space-time is
discussed in detail. In particular it is shown that for this case, the
transform coincides with two other naturally defined transforms: one a
two-variable transform on the Lie group SU(2, C), the other a transform on the
space of null split octaves. The key properties of the transform are developed.


title: Spherically Symmetric Gravitational Collapse of General Fluids

abstract:
  We express Einstein's field equations for a spherically symmetric ball of
general fluid such that they are conducive to an initial value problem. We show
how the equations reduce to the Vaidya spacetime in a non-null coordinate
frame, simply by designating specific equations of state. Furthermore, this
reduces to the Schwarzschild spacetime when all matter variables vanish. We
then describe the formulation of an initial value problem, whereby a general
fluid ball with vacuum exterior is established on an initial spacelike slice.
As the system evolves, the fluid ball collapses and emanates null radiation
such that a region of Vaidya spacetime develops. Therefore, on any subsequent
spacelike slice there exists three regions; general fluid, Vaidya and
Schwarzschild, all expressed in a single coordinate patch with two
free-boundaries determined by the equations. This implies complicated matching
schemes are not required at the interfaces between the regions, instead, one
simply requires the matter variables tend to the appropriate equations of
state. We also show the reduction of the system of equations to the static
cases, and show staticity necessarily implies zero ``heat flux''. Furthermore,
the static equations include a generalization of the Tolman-Oppenheimer-Volkoff
equations for hydrostatic equilibrium to include anisotropic stresses in
general coordinates.


title:
General Relativistic Radiant Shock Waves in the Post-Quasistatic
  Approximation

abstract:
  An evolution of radiant shock wave front is considered in the framework of a
recently presented method to study self-gravitating relativistic spheres, whose
rationale becomes intelligible and finds full justification within the context
of a suitable definition of the post-quasistatic approximation. The spherical
matter configuration is divided into two regions by the shock and each side of
the interface having a different equation of state and anisotropic phase. In
order to simulate dissipation effects due to the transfer of photons and/or
neutrinos within the matter configuration, we introduce the flux factor, the
variable Eddington factor and a closure relation between them. As we expected
the strength of the shock increases the speed of the fluid to relativistic
values and for some critical ones is larger than light speed. In addition, we
find that energy conditions are very sensible to the anisotropy, specially the
strong one. As a special feature of the model, we find that the contribution of
the matter and radiation to the radial pressure are the same order of magnitude
as in the mant as in the core, moreover, in the core radiation pressure is
larger than matter pressure.


title:
Quasinormal modes of gravitational perturbation around a Schwarzschild
  black hole surrounded by quintessence

abstract:
  In this paper, the quasinormal modes of gravitational perturbation around a
Schwarzschild black hole surrounded by quintessence were evaluated by using the
third-order WKB approximation. Due to the presence of quintessence, the
gravitational wave damps more slowly.


title:
Quasinormal modes of a Schwarzschild black hole surrounded by free
  static spherically symmetric quintessence: Electromagnetic perturbations

abstract:
  In this paper, we evaluated the quasinormal modes of electromagnetic
perturbation in a Schwarzschild black hole surrounded by the static spherically
symmetric quintessence by using the third-order WKB approximation when the
quintessential state parameter $ w_{q}$ in the range of $-1/3<w_{q}<0$. Due to
the presence of quintessence, Maxwell field damps more slowly. And when at
$-1<w_{q}<-1/3$, it is similar to the black hole solution in the ds/Ads
spacetime. The appropriate boundary conditions need to be modified.


title: Quasi-stationary routes to the Kerr black hole

abstract:
  Quasi-stationary (i.e. parametric) transitions from rotating equilibrium
configurations of fluid bodies to rotating black holes are discussed. For the
idealized model of a rotating disc of dust, analytical results derived by means
of the "inverse scattering method" are available. They are generalized by
numerical results for rotating fluid rings with various equations of state. It
can be shown rigorously that a black hole limit of a fluid body in equilibrium
occurs if and only if the gravitational mass becomes equal to twice the product
of angular velocity and angular momentum. Therefore, any quasi-stationary route
from fluid bodies to black holes passes through the extreme Kerr solution.


title:
The asymptotics of stationary electro-vacuum metrics in odd space-time
  dimensions

abstract:
  We show that stationary, asymptotically flat solutions of the electro-vacuum
Einstein equations are analytic at $i^0$, for a large family of gauges, in odd
space-time dimensions higher than seven. The same is true in space-time
dimension five for static vacuum solutions with non-vanishing mass.


title:
The cosmological gravitational wave background from primordial density
  perturbations

abstract:
  We discuss the gravitational wave background generated by primordial density
perturbations evolving during the radiation era. At second-order in a
perturbative expansion, density fluctuations produce gravitational waves. We
calculate the power spectra of gravitational waves from this mechanism, and
show that, in principle, future gravitational wave detectors could be used to
constrain the primordial power spectrum on scales vastly different from those
currently being probed by large-scale structure. As examples we compute the
gravitational wave background generated by both a power-law spectrum on all
scales, and a delta-function power spectrum on a single scale.


title: Eisenhart's theorem and the causal simplicity of Eisenhart's spacetime

abstract:
  We give a causal version of Eisenhart's geodesic characterization of
classical mechanics. We emphasize the geometric, coordinate independent
properties needed to express Eisenhart's theorem in light of modern studies on
the Bargmann structures (lightlike dimensional reduction, pp-waves). The
construction of the space metric, Coriolis 1-form and scalar potential through
which the theorem is formulated is shown in detail, and in particular it is
proved a one-to-one correspondence between Newtonian frames and Abelian
connections on suitable lightlike principal bundles. The relation of
Eisenhart's theorem in the lightlike case with a Fermat type principle is
pointed out. The operation of lightlike lift is introduced and the existence of
minimizers for the classical action is related to the causal simplicity of
Eisenhart's spacetime.


title: Time machines and quantum theory

abstract:
  There is a deep structural link between acausal spacetimes and quantum
theory. As a consequence quantum theory may resolve some "paradoxes" of time
travel. Conversely, non-time-orientable spacetimes naturally give rise to
electric charges and spin half. If an explanation of quantum theory is
possible, then general relativity with time travel could be it.


title: An ASSF and the Teleparallelisim

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0203084, gr-qc/0607138, gr-qc/0011087, gr-qc/0102070, gr-qc/0607138,
gr-qc/0109017, gr-qc/0212018, and gr-qc/9409039.


title: The Effacing Principle in the Post-Newtonian Celestial Mechanics

abstract:
  First post-Newtonian (PN) approximation of the scalar-tensor theory of
gravity is used to discuss the effacing principle in N-body system, that is
dependence of equations of motion of spherically-symmetric bodies comprising
the system on their internal structure. We demonstrate that the effacing
principle is violated by terms which are proportional to the second order
rotational moment of inertia of each body coupled with \beta-1, where \beta is
the measure of non-linearity of gravitational field. In case of general
relativity, where \beta=1, the effacing principle is violated by terms being
proportional to the rotational moment of inertia of the forth order. For
systems made of neutron stars (NS) and/or black holes (BH) these terms
contribute to the orbital equations of motion at the level of the third and
fifth PN approximation respectively.


title: Apparent universality of semiclassical gravity in the far field limit

abstract:
  The universality of semiclassical gravity is investigated by considering the
behavior of the quantities < \phi^2 > and < {T^a}_b >, along with quantum
corrections to the effective Newtonian potential in the far field limits of
static spherically symmetric objects ranging from stars in the weak field
Newtonian limit to black holes. For scalar fields it is shown that when
differences occur they all result from the behavior of a single mode with zero
frequency and angular momentum and are thus due to a combination of infrared
and s-wave effects. An intriguing combination of similarities and differences
between the extreme cases of a Schwarzschild black hole and a star in the weak
field Newtonian limit is explained.


title: Non-minimal Wu-Yang monopole

abstract:
  We discuss new exact spherically symmetric static solutions to non-minimally
extended Einstein-Yang-Mills equations. The obtained solution to the Yang-Mills
subsystem is interpreted as a non-minimal Wu-Yang monopole solution. We focus
on the analysis of two classes of the exact solutions to the gravitational
field equations. Solutions of the first class belong to the
Reissner-Nordstr{\"o}m type, i.e., they are characterized by horizons and by
the singularity at the point of origin. The solutions of the second class are
regular ones. The horizons and singularities of a new type, the non-minimal
ones, are indicated.


title:
Curvature coupling in Einstein-Yang-Mills theory and non-minimal
  self-duality

abstract:
  A self-consistent non-minimal non-Abelian Einstein-Yang-Mills model,
containing three phenomenological coupling constants, is formulated. The ansatz
of a vanishing Yang-Mills induction is considered as a particular case of the
self-duality requirement for the gauge field. Such an ansatz is shown to allow
obtaining an exact solution of the self-consistent set of equations when the
space-time has a constant curvature. An example describing a pure magnetic
gauge field in the de Sitter cosmological model is discussed in detail.


title: There exist consistent temporal logics admitting changes of History

abstract:
  Introducing his Chronology Protection Conjecture Stephen Hawking said that it
seems that there exists a Chronology Protection Agency making the Universe safe
for historians.
  Without taking sides about such a conjecture we show that the Chronology
Protection Agency is not necessary in order to make the Universe unsafe for
historians but safe for logicians.


title:
Constraining models of modified gravity with the double pulsar PSR
  J0737-3039A/B system

abstract:
  In this paper we use Delta P = -1.772341 +/- 13.153788 s between the
phenomenologically determined orbital period P_b of the PSR J0737-3039 double
pulsar system and the purely Keplerian period P^(0)=2\pi\sqrt{a^3/G(m_A+m_B)}
calculated with the system's parameters, determined independently of the third
Kepler law itself, in order to put constraints on some models of modified
gravity (f(R), Yukawa-like fifth force, MOND). The major source of error
affecting Delta P is not the one in the phenomenologically measured period
(\delta P_b=4 10^-6 s), but the systematic uncertainty \delta P^(0) in the
computed Keplerian one due to the relative semimajor axis a mainly caused, in
turn, by the errors in the ratio R of the pulsars' masses and in sin i. We get
|\kappa|< 0.8 10^-26 m^-2 for the parameter that in the f(R) framework is a
measure of the non linearity of the theory, |\alpha|< 5.5 10^-4 for the
fifth-force strength parameter (for \lambda\approx a=0.006 AU). The effects
predicted by the strong-acceleration regime of MOND are far too small to be
constrained with some effectiveness today and in the future as well. In view of
the continuous timing of such an important system, it might happen that in the
near future it will be possible to obtain somewhat tighter constraints.


title:
Future singularity free accelerating expansion with the modified Poisson
  brackets

abstract:
  We show that the second accelerating expansion of the universe appears
smoothly from the decelerating universe remarkably after the initial inflation
in the two-dimensional soluble semi-classical dilaton gravity along with the
modified Poisson brackets of noncommutativity between the relevant fields.
However, the ordinary solution coming from the equations of motion following
the conventional Poisson algebra describes permanent accelerating universe
without any phase change. In this modified model, it turns out that the phase
transition is related to the noncommutative Poisson algebra.


title: Consistency of post-Newtonian waveforms with numerical relativity

abstract:
  General relativity predicts the gravitational wave signatures of coalescing
binary black holes. Explicit waveform predictions for such systems, required
for optimal analysis of observational data, have so far been achieved using the
post-Newtonian (PN) approximation. The quality of this treatment is unclear,
however, for the important late-inspiral portion. We derive late-inspiral
waveforms via a complementary approach, direct numerical simulation of
Einstein's equations. We compare waveform phasing from simulations of the last
$\sim 14$ cycles of gravitational radiation from equal-mass, nonspinning black
holes with the corresponding 2.5PN, 3PN, and 3.5PN orbital phasing. We find
phasing agreement consistent with internal error estimates based on either
approach, suggesting that PN waveforms for this system are effective until the
last orbit prior to final merger.


title: Newtonian Quantum Gravity

abstract:
  A Newtonian approach to quantum gravity is studied. At least for weak
gravitational fields it should be a valid approximation. Such an approach could
be used to point out problems and prospects inherent in a more exact theory of
quantum gravity, yet to be discovered. Newtonian quantum gravity, e.g., shows
promise for prohibiting black holes altogether (which would eliminate
singularities and also solve the black hole information paradox), breaks the
equivalence principle of general relativity, and supports non-local
interactions (quantum entanglement). Its predictions should also be testable at
length scales well above the "Planck scale", by high-precision experiments
feasible even with existing technology. As an illustration of the theory, it
turns out that the solar system, superficially, perfectly well can be described
as a quantum gravitational system, provided that the $l$ quantum number has its
maximum value, $n-1$. This results exactly in Kepler's third law. If also the
$m$ quantum number has its maximum value ($\pm l$) the probability density has
a very narrow torus-like form, centered around the classical planetary orbits.
However, as the probability density is independent of the azimuthal angle
$\phi$ there is, from quantum gravity arguments, no reason for planets to be
located in any unique place along the orbit (or even \textit{in} an orbit for
$m \neq \pm l$). This is, in essence, a reflection of the "measurement problem"
inherent in all quantum descriptions.


title: Quantum Stability of a w < - 1 Phase of Cosmic Acceleration

abstract:
  We consider a massless, minimally coupled scalar with a quartic
self-interaction which is released in Bunch-Davies vacuum in locally de Sitter
background of an inflating universe. It was shown, in this system, that quantum
effects can induce a temporary phase of super-acceleration causing a violation
of the Weak Energy Condition on cosmological scales. In this paper we
investigate the system's stability by studying the behavior of linearized
perturbations in the quantum-corrected effective field equation at one and
two-loop order. We show that the time dependence we infer from the
quantum-corrected mode function is in perfect agreement with the system
developing a positive mass squared. The maximum induced mass remains
perturbatively small and it does not go tachyonic. Thus, the system is stable.


title: Voids of dark energy

abstract:
  We investigate the clustering properties of a dynamical dark energy
component. In a cosmic mix of a pressureless fluid and a light scalar field, we
follow the linear evolution of spherical matter perturbations. We find that the
scalar field tends to form underdensities in response to the gravitationally
collapsing matter. We thoroughly investigate these voids for a variety of
initial conditions, explain the physics behind their formation and consider
possible observational implications. Detection of dark energy voids will
clearly rule out the cosmological constant as the main source of the present
acceleration.


title: Hamiltonian General Relativity in CMB frame

abstract:
  A collection of requirements to the General Relativity that follow from the
WMAP observations of the Cosmic Microwave Background radiation anisotropy as an
inertial frame are discussed. These obligations include the separation of both
the CMB frame from the diffeomorphisms and the diffeo-invariant cosmic
evolution from the local scalar metric component in the manner compatible with
the canonical Hamiltonian approach to the Einstein--Hilbert theory with the
energy constraints. The solution of these constraints in classical and quantum
theories and a fit of units of measurements are discussed in the light of the
last Supernovae data.


title:
Using LISA EMRI sources to test off-Kerr deviations in the geometry of
  massive black holes

abstract:
  Inspirals of stellar-mass compact objects into $\sim 10^6 M_{\odot}$ black
holes are especially interesting sources of gravitational waves for LISA. We
investigate whether the emitted waveforms can be used to strongly constrain the
geometry of the central massive object, and in essence check that it
corresponds to a Kerr black hole (BH). For a Kerr BH, all multipole moments of
the spacetime have a simple, unique relation to $M$ and $S$, the BH's mass and
spin; in particular, the spacetime's mass quadrupole moment is given by $Q=-
S^2/M$. Here we treat $Q$ as an additional parameter, independent of $M$ and
$S$, and ask how well observation can constrain its difference from the Kerr
value. This was already estimated by Ryan, but for simplified (circular,
equatorial) orbits, and neglecting signal modulations due to the motion of the
LISA satellites. Here we consider generic orbits and include these modulations.
We use a family of approximate (post-Newtonian) waveforms, which represent the
full parameter space of Inspiral sources, and exhibit the main qualitative
features of true, general relativistic waveforms. We extend this parameter
space to include (in an approximate manner) an arbitrary value of $Q$, and
construct the Fisher information matrix for the extended parameter space. By
inverting the Fisher matrix we estimate how accurately $Q$ could be extracted
from LISA observations. For 1 year of coherent data from the inspiral of a $10
M_{\odot}$ BH into rotating BHs of masses $10^{5.5} M_{\odot}$, $10^6
M_{\odot}$, or $10^{6.5} M_{\odot}$, we find $\Delta (Q/M^3) \sim 10^{-4}$,
$10^{-3}$, or $10^{-2}$, respectively (assuming total signal-to-noise ratio of
100, typical of the brightest detectable EMRIs). These results depend only
weakly on the eccentricity of the orbit or the BH's spin.


title: Stable dark energy stars: An alternative to black holes?

abstract:
  In this work, a generalization of the Mazur-Mottola gravastar model is
explored, by considering a matching of an interior solution governed by the
dark energy equation of state, $\omega\equiv p/ \rho<-1/3$, to an exterior
Schwarzschild vacuum solution at a junction interface, situated near to where
the event horizon is expected to form. The motivation for implementing this
generalization arises from the fact that recent observations have confirmed an
accelerated cosmic expansion, for which dark energy is a possible candidate.


title:
Tunneling probability for the birth of an asymptotically DeSitter
  universe

abstract:
  In the present work, we quantize a closed Friedmann-Robertson-Walker model in
the presence of a positive cosmological constant and radiation. It gives rise
to a Wheeler-DeWitt equation for the scale factor which has the form of a
Schr\"{o}dinger equation for a potential with a barrier. We solve it
numerically and determine the tunneling probability for the birth of a
asymptotically DeSitter, inflationary universe, initially, as a function of the
mean energy of the initial wave-function. Then, we verify that the tunneling
probability increases with the cosmological constant, for a fixed value of the
mean energy of the initial wave-function. Our treatment of the problem is more
general than previous ones, based on the WKB approximation. That is the case
because we take into account the fact that the scale factor ($a$) cannot be
smaller than zero. It means that, one has to introduce an infinity potential
wall at $a = 0$, which forces any wave-packet to be zero there. That condition
introduces new results, in comparison with previous works.


title: No realistic wormholes from ghost-free scalar-tensor phantom dark energy

abstract:
  It is proved that no wormholes can be formed in viable scalar-tensor models
of dark energy admitting its phantom-like ($w < -1$) behaviour in cosmology,
even in the presence of electric or magnetic fields, if the non-minimal
coupling function $f(\Phi)$ is everywhere positive and the scalar field $\Phi$
itself is not a ghost. Some special static, spherically symmetric wormhole
solutions may exist if $f(\Phi)$ is allowed to reach zero or to become
negative, so that the effective gravitational constant becomes negative in some
region making the graviton a ghost. If $f$ remains non-negative, such solutions
require severe fine tuning and a very peculiar kind of model. If $f < 0$ is
allowed, it is argued (and confirmed by previous investigations) that such
solutions are generically unstable under non-static perturbations, the
instability appearing right near transition surfaces to negative $f$.


title: Surface Geometry of 5D Black Holes and Black Rings

abstract:
  We discuss geometrical properties of the horizon surface of five-dimensional
rotating black holes and black rings. Geometrical invariants characterizing
these 3D geometries are calculated. We obtain a global embedding of the 5D
rotating black horizon surface into a flat space. We also describe the
Kaluza-Klein reduction of the black ring solution (along the direction of its
rotation) which relates this solution to the 4D metric of a static black hole
distorted by the presence of external scalar (dilaton) and vector
(`electromagnetic') field. The properties of the reduced black hole horizon and
its embedding in $\E^3$ are briefly discussed.


title: Kinematic Self-Similar Plane Symmetric Solutions

abstract:
  This paper is devoted to classify the most general plane symmetric spacetimes
according to kinematic self-similar perfect fluid and dust solutions. We
provide a classification of the kinematic self-similarity of the first, second,
zeroth and infinite kinds with different equations of state, where the
self-similar vector is not only tilted but also orthogonal and parallel to the
fluid flow. This scheme of classification yields twenty four plane symmetric
kinematic self-similar solutions. Some of these solutions turn out to be
vacuum. These solutions can be matched with the already classified plane
symmetric solutions under particular coordinate transformations. As a result,
these reduce to sixteen independent plane symmetric kinematic self-similar
solutions.


title: Noncommutative geometry inspired charged black holes

abstract:
  We find a new, non-commutative geometry inspired, solution of the coupled
Einstein-Maxwell field equations describing a variety of charged,
self-gravitating objects, including extremal and non-extremal black holes. The
metric smoothly interpolates between deSitter geometry, at short distance, and
Reissner-Nordstroem geometry far away from the origin. Contrary to the ordinary
Reissner-Nordstroem spacetime there is no curvature singularity in the origin
neither "naked" nor shielded by horizons. We investigate both the Hawking
process and pair creation in this new scenario.


title:
A theory of gravity as a pressure force. II. Lorentz contraction and
  "relativistic" effects

abstract:
  In a foregoing paper, gravity has been interpreted as the pressure force
exerted on matter at the scale of elementary particles by a perfect fluid.
Under the condition that Newtonian gravity must be recovered in the
incompressible case, a scalar field equation has thus been proposed for
gravity, giving a new theory in the compressible case. Here the theory is
reinterpreted so as to describe the relativistic effects, by extending the
Lorentz-Poincar\'e interpretation of special relativity which is first
recalled. Gravitational space-contraction and time-dilatation are postulated,
as a consequence of the principle of local equivalence between the effects of
motion and gravitation. The space-time metric (expressing the proper time along
a trajectory) is hence curved also in the proposed theory. As the result of a
modified Newton law, it is proved that free test particles follow geodesic
lines of this metric. In the spherical static situation, Schwarzschild's
exterior metric is exactly recovered and with it the experimental support of
general relativity, but the interior solution as well as the problematic of
singularities are different in the proposed theory, e.g. the radius of the body
cannot be smaller than the Schwarzschild radius.


title: Extracting Information about EMRIs using Time-Frequency Methods

abstract:
  The inspirals of stellar-mass compact objects into supermassive black holes
are some of the most exciting sources of gravitational waves for LISA.
Detection of these sources using fully coherent matched filtering is
computationally intractable, so alternative approaches are required. In Wen &
Gair (2005), we proposed a detection method based on searching for significant
deviation of power density from noise in a time-frequency spectrogram of the
LISA data. The performance of the algorithm was assessed in Gair & Wen (2005)
using Monte-Carlo simulations on several trial waveforms and approximations to
the noise statistics. We found that typical extreme mass ratio inspirals
(EMRIs) could be detected at distances of up to 1-3 Gpc, depending on the
source parameters. In this paper, we first give an overview of our previous
work in Wen & Gair (2005) and Gair & Wen (2005), and discuss the performance of
the method in a broad sense. We then introduce a decomposition method for LISA
data that decodes LISA's directional sensitivity. This decomposition method
could be used to improve the detection efficiency, to extract the source
waveform, and to help solve the source confusion problem. Our approach to
constraining EMRI parameters using the output from the time-frequency method
will be outlined.


title:
Spin-Spin Interactions in Gauge Theory of Gravity, Violation of Weak
  Equivalence Principle and New Classical Test of General Relativity

abstract:
  For a long time, it is generally believed that spin-spin interactions can
only exist in a theory where Lorentz symmetry is gauged, and a theory with
spin-spin interactions is not perturbatively renormalizable. But this is not
true. By studying the motion of a spinning particle in gravitational field, it
is found that there exist spin-spin interactions in gauge theory of gravity.
Its mechanism is that a spinning particle will generate gravitomagnetic field
in space-time, and this gravitomagnetic field will interact with the spin of
another particle, which will cause spin-spin interactions. So, spin-spin
interactions are transmitted by gravitational field. The form of spin-spin
interactions in post Newtonian approximations is deduced. This result can also
be deduced from the Papapetrou equation. This kind of interactions will not
affect the renormalizability of the theory. The spin-spin interactions will
violate the weak equivalence principle, and the violation effects are
detectable. An experiment is proposed to detect the effects of the violation of
the weak equivalence principle.


title: Multigravity and Space Time Foam

abstract:
  We consider a multigravity approach to spacetime foam. As an application we
give indications on the computation of the cosmological constant, considered as
an eigenvalue of a Sturm-Liouville problem. A variational approach with
Gaussian trial wave functionals is used as a method to study such a problem. We
approximate the equation to one loop in a Schwarzschild background and a zeta
function regularization is involved to handle with divergences. The
regularization is closely related to the subtraction procedure appearing in the
computation of Casimir energy in a curved background. A renormalization
procedure is introduced to remove the infinities together with a
renormalization group equation.


title:
Short note on second-order gauge-invariant cosmological perturbation
  theory

abstract:
  The second order perturbations in Friedmann-Robertson-Walker universe filled
with a perfect fluid are completely formulated in the gauge invariant manner
without any gauge fixing. All components of the Einstein equations are derived
neglecting the first order vector and tensor modes. These equations imply that
the tensor and the vector mode of the second order metric perturbations may be
generated by the non-linear effects of the Einstein equations from the first
order density perturbations.


title: Improved calculation of relic gravitational waves

abstract:
  In this paper, we improve the calculation of the relic gravitational waves
(RGW) in two aspects: First, we investigate the transfer function after
considering the redshift-suppression effect, the accelerating expansion effect,
the damping effect of free-streaming relativistic particles, and the damping
effect of cosmic phase transition, and give a simple approximate analytic
expression, which clearly illustrates the dependent relations on the
cosmological parameters. Second, we develop a numerical method to calculate the
primordial power spectrum of RGW at a very wide frequency range, where the
observed constraints on $n_s$ (the scalar spectral index) and $P_S(k_0)$ (the
amplitude of primordial scalar spectrum) and the Hamilton-Jacobi equation are
used. This method is applied to two kinds of inflationary models, which all
satisfy the current constraints on $n_s$, $\alpha$ (the running of $n_s$) and
$r$ (the tensor-scalar ratio). We plot them in the $r-\Omega_g$ diagram, where
$\Omega_g$ is the strength of RGW, and study their detection by the CMB
experiments and laser interferometers.


title: Lyra black holes

abstract:
  Long ago, since 1951, Lyra proposed a modification of Riemannian geometry.
Based on the Lyra's modification on Riemannian geometry, Sen and Dunn
constructed a field equation which is analogous to Einstein's field equations.
Further more, Sen and Dunn gave series type solution to the static vacuum field
equations. Retaining only a few terms, we have shown that their solutions
correspond to black holes (we call, Lyra black holes). Some interesting
properties of the Lyra black holes are studied.


title: Axisymmetric stationary solutions with arbitrary multipole moments

abstract:
  In this paper, the problem of finding an axisymmetric stationary spacetime
from a specified set of multipole moments, is studied. The condition on the
multipole moments, for existence of a solution, is formulated as a convergence
condition on a power series formed from the multipole moments. The methods in
this paper can also be used to give approximate solutions to any order as well
as estimates on each term of the resulting power series.


title:
A theoretical approach to thermal noise caused by an inhomogeneously
  distributed loss -- Physical insight by the advanced modal expansion

abstract:
  We modified the modal expansion, which is the traditional method used to
calculate thermal noise. This advanced modal expansion provides physical
insight about the discrepancy between the actual thermal noise caused by
inhomogeneously distributed loss and the traditional modal expansion. This
discrepancy comes from correlations between the thermal fluctuations of the
resonant modes. The thermal noise spectra estimated by the advanced modal
expansion are consistent with the results of measurements of thermal
fluctuations caused by inhomogeneous losses.


title:
World-making with extended gravity black holes for cosmic natural
  selection in the multiverse scenario

abstract:
  Physics is facing contingency. Not only in facts but also in laws (the
frontier becoming extremely narrow). Cosmic natural selection is a tantalizing
idea to explain the apparently highly improbable structure of our Universe. In
this brief note I will study the creation of Universes by black holes in
-string inspired- higher order curvature gravity.

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


title: Slowly rotating fluid balls of Petrov type D

abstract:
  The second order perturbative field equations for slowly and rigidly rotating
perfect fluid balls of Petrov type D are solved numerically. It is found that
all the slowly and rigidly rotating perfect fluid balls up to second order,
irrespective of Petrov type, may be matched to a possibly non-asymptotically
flat stationary axisymmetric vacuum exterior. The Petrov type D interior
solutions are characterized by five integration constants, corresponding to
density and pressure of the zeroth order configuration, the magnitude of the
vorticity, one more second order constant and an independent spherically
symmetric second order small perturbation of the central pressure. A
four-dimensional subspace of this five-dimensional parameter space is
identified for which the solutions can be matched to an asymptotically flat
exterior vacuum region. Hence these solutions are completely determined by the
spherical configuration and the magnitude of the vorticity. The physical
properties like equations of state, shapes and speeds of sound are determined
for a number of solutions.


title: Limit to General Relativity in f(R) theories of gravity

abstract:
  We discuss two aspects of f(R) theories of gravity in metric formalism. We
first study the reasons to introduce a scalar-tensor representation for these
theories and the behavior of this representation in the limit to General
Relativity, f(R)--> R. We find that the scalar-tensor representation is well
behaved even in this limit. Then we work out the exact equations for
spherically symmetric sources using the original f(R) representation, solve the
linearized equations, and compare our results with recent calculations of the
literature. We observe that the linearized solutions are strongly affected by
the cosmic evolution, which makes very unlikely that the cosmic speedup be due
to f(R) models with correcting terms relevant at low curvatures.


title: Energy-Momentum Distribution: Some Examples

abstract:
  In this paper, we elaborate the problem of energy-momentum in General
Relativity with the help of some well-known solutions. In this connection, we
use the prescriptions of Einstein, Landau-Lifshitz, Papapetrou and M\"{o}ller
to compute the energy-momentum densities for four exact solutions of the
Einstein field equations. We take the gravitational waves, special class of
Ferrari-Ibanez degenerate solution, Senovilla-Vera dust solution and
Wainwright-Marshman solution. It turns out that these prescriptions do provide
consistent results for special class of Ferrari-Ibanez degenerate solution and
Wainwright-Marshman solution but inconsistent results for gravitational waves
and Senovilla-Vera dust solution.


title:
MHD of rotating compact stars with spectral methods: description of the
  algorithm and tests

abstract:
  A flexible spectral code for the study of general relativistic
magnetohydrodynamics is presented. Aiming at investigating the physics of
slowly rotating magnetized compact stars, this new code makes use of various
physically motivated approximations. Among them, the relativistic anelastic
approximation is a key ingredient of the current version of the code. In this
article, we mainly outline the method, putting emphasis on algorithmic
techniques that enable to benefit as much as possible of the non-dissipative
character of spectral methods, showing also a potential astrophysical
application and providing a few illustrative tests.


title: Hamiltonian theory of brane-world gravity

abstract:
  A brane-world universe consists of a 4-dimensional brane embedded into a
5-dimensional space-time (bulk). We apply the Arnowitt-Deser-Misner
decomposition to the brane-world, which results in a 3+1+1 break-up of the
bulk. We present the canonical theory of brane cosmology based on this
decomposition. The Hamiltonian equations allow for the study of any physical
phenomena in brane gravity. This method gives new prospects for studying the
initial value problem, stability analysis, brane black holes, cosmological
perturbation theory and canonical quantization in brane-worlds.


title:
Constraint-preserving Sommerfeld conditions for the harmonic Einstein
  equations

abstract:
  The principle part of Einstein equations in the harmonic gauge consists of a
constrained system of 10 curved space wave equations for the components of the
space-time metric. A new formulation of constraint-preserving boundary
conditions of the Sommerfeld type for such systems has recently been proposed.
We implement these boundary conditions in a nonlinear 3D evolution code and
test their accuracy.


title: Canonical Analysis of Radiating Atmospheres of Stars in Equilibrium

abstract:
  The spherically symmetric, static spacetime generated by a cross-flow of
non-interacting null dust streams can be conveniently interpreted as the
radiation atmosphere of a star, which also receives exterior radiation.
Formally, such a superposition of sources is equivalent to an anisotropic
fluid. Therefore, there is a preferred time function in the system, defined by
this reference fluid. This internal time is employed as a canonical coordinate,
in order to linearize the Hamiltonian constraint. This turns to be helpful in
the canonical quantization of the geometry of the radiating atmosphere.


title: Minimal metagravity vs. dark matter and/or dark energy

abstract:
  The minimal metagravity theory, explicitly violating the general covariance
but preserving the unimodular one, is applied to study the evolution of the
isotropic homogeneous Universe. The massive scalar graviton, contained in the
theory in addition to the massless tensor one, is treated as a source of the
dark matter and/or dark energy. The modified Friedmann equation for the scale
factor of the Universe is derived. The question wether the minimal metagravity
can emulate the LCDM concordance model, valid in General Relativity, is
discussed.


title: Shortcuts in particle production in a toroidal compactified spacetime

abstract:
  We investigate the particle production in a toroidal compactified spacetime
due to the expansion of a Friedmann cosmological model in R3 x S1 outside a
U(1) local cosmic string. The case of a Friedmann spacetime is also
investigated when torsion is incorporated in the connection. We present a
generalization to toroidal compactification of p extra dimensions, where the
topology is given by R3 x T^p. Some implications are presented and discussed.
Besides the dynamics of spacetime, we also investigate in details the physical
consequences of the topological transformations.


title:
Generalized Chaplygin gas model: constraints from Hubble parameter
  versus Redshift Data

abstract:
  We examine observational constraints on the generalized Chaplygin gas (GCG)
model for dark energy from the 9 Hubble parameter data points, the 115 SNLS Sne
Ia data and the size of baryonic acoustic oscillation peak at redshift,
$z=0.35$. At a 95.4% confidence level, a combination of three data sets gives
$0.67\leq A_s\leq 0.83$ and $-0.21\leq \alpha\leq 0.42$, which is within the
allowed parameters ranges of the GCG as a candidate of the unified dark matter
and dark energy. It is found that the standard Chaplygin gas model ($\alpha=1$)
is ruled out by these data at the 99.7% confidence level.


title:
A model-independent test of spatial variations of the Newtonian
  gravitational constant in some extrasolar planetary systems

abstract:
  In this paper we directly constrain possible spatial variations of the
Newtonian gravitational constant G over ranges 0.01-5 AU in various extrasolar
multi-planet systems. By means of the third Kepler's law we determine the
quantity \Gamma_ XY=G_X/G_Y for each couple of planets X and Y located at
different distances from their parent star: deviations of the measured values
of \Gamma from unity would signal variations of G. The obtained results for
\eta=1-\Gamma are found to be well compatible with zero within the experimental
errors (\eta/\delta\eta= 0.2-0.3). A comparison with an analogous test
previously performed in our Solar System is made.


title: Gravitational Trapping Near Domain Walls and Stable Solitons

abstract:
  In this work, the behavior of test particles near a domain wall of a stable
false vacuum bubble is studied. It is shown that matter is naturally trapped in
the vicinity of a static domain wall, and also, that there is a discontinuity
in the test particle's velocity when crossing the domain wall. The latter is
unexpected as it stands in contrast to Newtonian theory, where infinite forces
are not allowed. The weak field limit is defined in order to show that there is
no conflict with the non-relativistic behavior of gravitational fields and
particle motions under these conditions.


title: Global texture in Lyra geometry

abstract:
  In this paper, we consider global texture with time dependent displacement
vector based on Lyra geometry in normal gauge i.e. displacement vector \phi_i^*
= (\beta_0(t),0,0,0). We investigate gravitational field of global texture
configuration by solving Einstein equations as well as that for the scalar
field due to texture.


title:
Cosmological perturbations in FRW model with scalar field within
  Hamilton-Jacobi formalism and symplectic projector method

abstract:
  The Hamilton-Jacobi analysis is applied to the dynamics of the scalar
fluctuations about the Friedmann-Robertson-Walker (FRW). The gauge conditions
are found from the consistency conditions. The physical degrees of freedom of
the model are obtain by symplectic projector method. The role of the linearly
dependent Hamiltonians and the gauge variables in Hamilton-Jacobi formalism is
discussed.


title:
Gravitational waves from intermediate-mass-ratio inspirals for
  ground-based detectors

abstract:
  We explore the prospects for Advanced LIGO to detect gravitational waves from
neutron stars and stellar mass black holes spiraling into intermediate-mass
($M\sim 50 M_\odot$ to $350 M_\odot$) black holes. We estimate an event rate
for such \emph{intermediate-mass-ratio inspirals} (IMRIs) of up to $\sim
10$--$30 \mathrm{yr}^{-1}$. Our numerical simulations show that if the central
body is not a black hole but its metric is stationary, axisymmetric, reflection
symmetric and asymptotically flat then the waves will likely be tri-periodic,
as for a black hole. We report generalizations of a theorem due to Ryan (1995)
which suggest that the evolutions of the waves' three fundamental frequencies
and of the complex amplitudes of their spectral components encode (in
principle) a full map of the central body's metric, full details of the energy
and angular momentum exchange between the central body and the orbit, and the
time-evolving orbital elements. We estimate that Advanced LIGO can measure or
constrain deviations of the central body from a Kerr black hole with modest but
interesting accuracy.


title:
Gravitational energy-momentum in small regions according to Moller's
  tetrad expression

abstract:
  Moller's tetrad gravitational energy-momentum "tensor" is evaluated for a
small vacuum region using an orthonormal frame adapted to Riemann normal
coordinates. We find that it does satisfy the highly desired property of being
a positive multiple of the Bel-Robinson tensor.


title: On source coupling and the teleparallel equivalent to GR

abstract:
  Alternatives to the usual general relativity (GR) Riemannian framework
include Riemann-Cartan and teleparallel geometry. The ``teleparallel equivalent
of GR" (TEGR, aka GR${}_{||}$) has certain virtues, however there have been
allegations of serious source coupling limitations. Now it is quite
straightforward to show that the coupled dynamical field equations of
Einstein's GR with any source can be accurately represented in terms of any
other connection, in particular teleparallel geometry. Using an argument
similar to one used long ago to show the "effective equivalence" between GR and
the Einstein-Cartan theory, we construct the teleparallel action which is
equivalent to a given Riemanian one; thereby finding the ``effectively
equivalent" coupling principle for all sources, including spinors. No auxiliary
field is required. Can one decide which is the real "physical" geometry?
Invoking the minimal coupling principle may give a unique answer.


title:
The Newman-Janis Algorithm, Rotating Solutions and Einstein-Born-Infeld
  Black Holes

abstract:
  A new metric is obtained by applying a complex coordinate trans- formation to
the static metric of the self-gravitating Born-Infeld monopole. The behaviour
of the new metric is typical of a rotating charged source, but this source is
not a spherically symmetric Born-Infeld monopole with rotation. We show that
the structure of the energy-momentum tensor obtained with this new metric does
not correspond to the typical structure of the energy momentum tensor of
Einstein-Born-Infeld theory induced by a rotating spherically symmetric source.
This also show, that the complex coordinate transformations have the
interpretation given by Newman and Janis only in space-time solutions with
linear sources.


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

abstract:
  The stress-energy tensor for the non-minimally coupled scalar field is known
not to satisfy the pointwise energy conditions, even on the classical level. We
show, however, that local averages of the classical stress-energy tensor
satisfy certain inequalities and give bounds for averages along causal
geodesics. It is shown that in vacuum background spacetimes, ANEC and AWEC are
satisfied. Furthermore we use our result to show that in the classical
situation we have an analogue to the so called quantum interest conjecture.
These results lay the foundations for averaged energy inequalities for the
quantised non-minimally coupled fields.


title: Post-Newtonian expansion for Gauss-Bonnet Gravity

abstract:
  The Parametrized Post-Newtonian expansion of gravitational theories with a
scalar field coupled to the Gauss-Bonnet invariant is performed and
confrontation of such theories with Solar system experiments is discussed.


title: Helically symmetric N-particle solutions in scalar gravity

abstract:
  Within a scalar model theory of gravity, where the interaction between
particles is given by the half-retarded + half-advanced solution of the scalar
wave equation, we consider an N-body problem: we investigate configurations of
N particles which form an equilateral N-angle and are in helical motion about
their common center. We prove that there exists a unique equilibrium
configuration and compute the equilibrium radius explicitly in a post-Newtonian
expansion.


title: Head-on collisions of boson stars

abstract:
  We study head-on collisions of boson stars in three dimensions. We consider
evolutions of two boson stars which may differ in their phase or have opposite
frequencies but are otherwise identical. Our studies show that these phase
differences result in different late time behavior and gravitational wave
output.


title: Cosmological Dark Energy: Prospects for a Dynamical Theory

abstract:
  We present an approach to the problem of vacuum energy in cosmology, based on
dynamical screening of Lambda on the horizon scale. We review first the
physical basis of vacuum energy as a phenomenon connected with macroscopic
boundary conditions, and the origin of the idea of its screening by particle
creation and vacuum polarization effects. We discuss next the relevance of the
quantum trace anomaly to this issue. The trace anomaly implies additional terms
in the low energy effective theory of gravity, which amounts to a non-trivial
modification of the classical Einstein theory, fully consistent with the
Equivalence Principle. We show that the new dynamical degrees of freedom the
anomaly contains provide a natural mechanism for relaxing Lambda to zero on
cosmological scales. We consider possible signatures of the restoration of
conformal invariance predicted by the fluctuations of these new scalar degrees
of freedom on the spectrum and statistics of the CMB, in light of the latest
bounds from WMAP. Finally we assess the prospects for a new cosmological model
in which the dark energy adjusts itself dynamically to the cosmological horizon
boundary, and therefore remains naturally of order H^2 at all times without
fine tuning.


title: Impact of Lorentz Violation on Cosmology

abstract:
  We discuss the impact of Lorentz violation on the cosmology. Firstly, we show
that the Lorentz violation affects the dynamics of the chaotic inflationary
model and gives rise to an interesting feature. Secondly, we propose the
Lorentz violating DGP brane models where the Lorentz violating terms on the
brane accelerate the current universe. We conjecture that the ghost disappears
in the Lorentz violating DGP models.


title: Loop quantum cosmology and the k = - 1 RW model

abstract:
  The loop quantization of the negatively curved k=-1 RW model poses several
technical challenges. We show that the issues can be overcome and a successful
quantization is possible that extends the results of the k=0,+1 models in a
natural fashion. We discuss the resulting dynamics and show that for a universe
consisting of a massless scalar field, a bounce is predicted in the backward
evolution in accordance with the results of the k=0,+1 models. We also show
that the model predicts a vacuum repulsion in the high curvature regime that
would lead to a bounce even for matter with vanishing energy density. We
finally comment on the inverse volume modifications of loop quantum cosmology
and show that, as in the k=0 model, the modifications depend sensitively on the
introduction of a length scale which a priori is independent of the curvature
scale or a matter energy scale.


title: Plebanski Theory and Covariant Canonical Formulation

abstract:
  We establish an equivalence between the Hamiltonian formulation of the
Plebanski action for general relativity and the covariant canonical formulation
of the Hilbert-Palatini action. This is done by comparing the symplectic
structures of the two theories through the computation of Dirac brackets. We
also construct a shifted connection with simplified Dirac brackets, playing an
important role in the covariant loop quantization program, in the Plebanski
framework. Implications for spin foam models are also discussed.


title:
Charged shells in Lovelock gravity: Hamiltonian treatment and physical
  implications

abstract:
  Using a Hamiltonian treatment, charged thin shells in spherically symmetric
spacetimes in d dimensional Lovelock-Maxwell theory are studied. The
coefficients of the theory are chosen to obtain a sensible theory, with a
negative cosmological constant appearing naturally. After writing the action
and the Lagrangian for a spacetime comprised of an interior and an exterior
regions, with a thin shell as a boundary in between, one finds the Hamiltonian
using an ADM description. For spherically symmetric spacetimes, one reduces the
relevant constraints. The dynamic and constraint equations are obtained. The
vacuum solutions yield a division of the theory into two branches, d-2k-1>0
(which includes general relativity, Born-Infeld type theories) and d-2k-1=0
(which includes Chern-Simons type theories), where k gives the highest power of
the curvature in the Lagrangian. An additional parameter, chi, gives the
character of the vacuum solutions. For chi=1 the solutions have a black hole
character. For chi=-1 the solutions have a totally naked singularity character.
The integration through the thin shell takes care of the smooth junction. The
subsequent analysis is divided into two cases: static charged thin shell
configurations, and gravitationally collapsing charged dust shells. Physical
implications are drawn: if such a large extra dimension scenario is correct,
one can extract enough information from the outcome of those collapses as to
know, not only the actual dimension of spacetime, but also which particular
Lovelock gravity, is the correct one.


title: Tomographic entropy and cosmology

abstract:
  The probability representation of quantum mechanics including propagators and
tomograms of quantum states of the universe and its application to quantum
gravity and cosmology are reviewed. The minisuperspaces modeled by oscillator,
free pointlike particle and repulsive oscillator are considered. The notion of
tomographic entropy and its properties are used to find some inequalities for
the tomographic probability determining the quantum state of the universe. The
sense of the inequality as a lower bound for the entropy is clarified.


title: Counting entropy in causal set quantum gravity

abstract:
  The finiteness of black hole entropy suggest that spacetime is fundamentally
discrete, and hints at an underlying relationship between geometry and
"information". The foundation of this relationship is yet to be uncovered, but
should manifest itself in a theory of quantum gravity. We review recent
attempts to define a microscopic measure for black hole entropy and for the
maximum entropy of spherically symmetric spacelike regions, within the causal
set approach to quantum gravity.


title: The (pseudo)issue of the conformal frame revisited

abstract:
  The issue of the equivalence between Jordan and Einstein conformal frames in
scalar-tensor gravity is revisited, with emphasis on implementing running units
in the latter. The lack of affine parametrization for timelike worldlines and
the cosmological constant problem in the Einstein frame are clarified, and a
paradox in the literature about cosmological singularities appearing only in
one frame is solved. While, classically, the two conformal frames are
physically equivalent, they seem to be inequivalent at the quantum level.


title: Spin Flips and Precession in Black-Hole-Binary Mergers

abstract:
  We use the `moving puncture' approach to perform fully non-linear evolutions
of spinning quasi-circular black-hole binaries with individual spins not
aligned with the orbital angular momentum. We evolve configurations with the
individual spins (parallel and equal in magnitude) pointing in the orbital
plane and 45-degrees above the orbital plane. We introduce a technique to
measure the spin direction and track the precession of the spin during the
merger, as well as measure the spin flip in the remnant horizon. The former
configuration completes 1.75 orbits before merging, with the spin precessing by
98-degrees and the final remnant horizon spin flipped by ~72-degrees with
respect to the component spins. The latter configuration completes 2.25 orbits,
with the spins precessing by 151-degrees and the final remnant horizon spin
flipped ~34-degrees with respect to the component spins. These simulations show
for the first time how the spins are reoriented during the final stage of
binary black hole mergers verifying the hypothesis of the spin-flip phenomenon.
We also compute the track of the holes before merger and observe a precession
of the orbital plane with frequency similar to the orbital frequency and
amplitude increasing with time.


title: The modification of the Einstein and Landau-Lifshitz pseudotensrs

abstract:
  Deser et al. proposed a combination of the Einstein and Landau-Lifshitz
pseudotensors such that the second derivatives in vacuum are proportional to
the Bel-Robinson tensor. Stimulated by their work, the present paper discuss
the gravitational energy-momentum expression which has the same desirable
Bel-Robinson tensor property. We find modifications of the Einstein and
Landau-Lifshitz pseudotensors that both give the same coefficient of the
Bel-Robinson tensor in vacuum in holonomic frames.


title: Gravitation and Thermodynamics: The Einstein Equation of State Revisited

abstract:
  We perform an analysis where Einstein's field equation is derived by means of
very simple thermodynamical arguments. Our derivation is based on a
consideration of the properties of a very small, spacelike two-plane in a
uniformly accelerating motion.


title: New Approach to Quantization of Cosmological Models

abstract:
  We propose the new quantization of homogenous cosmological models. Four
fundamental methods are applied to the cosmological model and efficiently
jointed. The Dirac method for constrained systems is used, then the Fock space
is built and the second quantization is carried out. Finally, the
diagonalization ansatz, which is a combination of the Bogoliubov transformation
method and the Heisenberg equation of motion, is formulated. The temperature of
quantum cosmological model is introduced.


title: Slowly rotating fluid balls with linear equation of state

abstract:
  Slowly rotating perfect fluid balls with regular center and asymptotically
flat exterior are considered to second order in the rotation parameter. The
necessary condition for being Petrov type D is given for general perfect fluid
matter. As a special case, fluids with a linear equation of state are
considered. Using a power series expansion at the regular center, it is shown
that the Petrov D condition is inconsistent with the linear equation of state
assumption.


title:
Multi-Domain Spectral Method for Initial Data of Arbitrary Binaries in
  General Relativity

abstract:
  We present a multi-domain spectral method to compute initial data of binary
systems in General Relativity. By utilizing adapted conformal coordinates, the
vacuum region exterior to the gravitational sources is divided up into two
subdomains within which the spectral expansion of the field quantities is
carried out. If a component of the binary is a neutron star, a further
subdomain covering the star's interior is added. As such, the method can be
used to construct arbitrary initial data corresponding to binary black holes,
binary neutron stars or mixed binaries. In particular, it is possible to
describe a black hole component by the puncture ansatz as well as through an
excision technique. First examples are given for binary black hole excision
data that fulfill the requirements of the quasi-stationary framework, which
combines the Conformal Thin Sandwich formulation of the constraint equations
with the Isolated Horizon conditions for black holes in quasi-equilibrium.
These numerical solutions were obtained to extremely high accuracy with
moderate computational effort. Moreover, the method proves to be applicable
even when tending toward limiting cases such as large mass ratios of the binary
components.


title: Proposed split-causality test of the relativity principle

abstract:
  We propose a test of the principle of relativity, involving quantum signals
between two inertial frames. If the principle is upheld, classical causality
will appear to be split in a dramatic and emphatic way. We discuss the
existence of quantum horizons, which are barriers to the transmission of any
form of quantum information. These must occur in any finite time, inter-frame
experiment if quantum causality holds. We conclude with some comments on such
experiments involving entangled states.


title: Dynamic wormhole spacetimes coupled to nonlinear electrodynamics

abstract:
  We explore the possibility of dynamic wormhole geometries, within the context
of nonlinear electrodynamics. The Einstein field equation imposes a contracting
wormhole solution and the obedience of the weak energy condition. Furthermore,
in the presence of an electric field, the latter presents a singularity at the
throat, however, for a pure magnetic field the solution is regular. Thus,
taking into account the principle of finiteness, that a satisfactory theory
should avoid physical quantities becoming infinite, one may rule out evolving
wormhole solutions, in the presence of an electric field, coupled to nonlinear
electrodynamics.


title: Evaporating loop quantum black hole

abstract:
  In this paper we obtain the black hole metric from a semiclassical analysis
of loop quantum black hole. Our solution and the Schwarzschild one tend to
match well at large distances from Planck region. In r=0 the semiclassical
metric is regular and singularity free in contrast to the classical one. By
using the new metric we calculate the Hawking temperature and the entropy. For
the entropy we obtain the logarithmic correction to the classical area law.
Finally we study the mass evaporation process and we show the mass and
temperature tend to zero at infinitive time.


title:
Compact binary inspiral and the science potential of third-generation
  ground-based gravitational wave detectors

abstract:
  We consider EGO as a possible third-generation ground-based gravitational
wave detector and evaluate its capabilities for the detection and
interpretation of compact binary inspiral signals. We identify areas of
astrophysics and cosmology where EGO would have qualitative advantages, using
Advanced LIGO as a benchmark for comparison.


title: The second post-Newtonian order generalized Kepler equation

abstract:
  The radial component of the motion of compact binary systems composed of
neutron stars and/or black holes on eccentric orbit is integrated. We consider
all type of perturbations that emerge up to second post-Newtonian order. These
perturbations are either of relativistic origin or are related to the spin,
mass quadrupole and magnetic dipole moments of the binary components. We derive
a generalized Kepler equation and investigate its domain of validity, in which
it properly describes the radial motion.


title: Global dynamics of cosmological scalar fields -- Part I

abstract:
  We investigate the Liouvillian integrability of Hamiltonian systems
describing a universe filled with a scalar field (possibly complex). The tool
used is the differential Galois group approach, as introduced by Morales-Ruiz
and Ramis. The main result is that the generic systems are non-integrable,
although there still exist some values of parameters for which integrability
remains undecided. We also draw a connection with chaos present in such
cosmological models. The first part of the article deals with minimally coupled
fields, and the second treats the conformal couping.


title: Black Holes and Gravitational Properties of Antimatter

abstract:
  The gravitational properties of antimatter are still a secret of nature. One
outstanding possibility is that there is a gravitational repulsion between
matter and antimatter (in short we call it antigravity). We argue that in the
case of antigravity the collapse of a black hole doesn't end with singularity
and that deep inside the horizon, the gravitational field may be sufficiently
strong to create (from the vacuum) neutrino-antineutrino pairs of all flavours.
The created antineutrinos (neutrinos) should be violently ejected outside the
horizon of a black hole composed from matter (antimatter). Our rudimentary
calculations suggest that both, the supermassive black hole in the centre of
our Galaxy and in the centre of the Andromeda Galaxy may produce a flux of
antineutrinos measurable with the new generation of one cubic kilometre
neutrino telescopes. In addition, we suggest two signatures of antigravity in
the case of microscopic black holes which may be eventually produced at CERN:
the decay products should exhibit a strong matter-antimatter asymmetry and the
Hawking radiation should not be the main mechanism for decay.


title: Thermodynamic Behavior of Field Equations for f(R) Gravity

abstract:
  Recently it has shown that Einstein's field equations can be rewritten into a
form of the first law of thermodynamics both at event horizon of static
spherically symmetric black holes and apparent horizon of
Friedmann-Robertson-Walker (FRW) universe, which indicates intrinsic
thermodynamic properties of spacetime horizon. In the present paper we deal
with the so-called $f(R)$ gravity, whose action is a function of the curvature
scalar $R$. In the setup of static spherically symmetric black hole spacetime,
we find that at the event horizon, the field equations of $f(R)$ gravity can be
written into a form $dE = TdS - PdV + Td\bar{S}$, where $T$ is the Hawking
temperature and $S=Af'(R)/4G$ is the horizon entropy of the black hole, $E$ is
the horizon energy of the black hole, $P$ is the radial pressure of matter, $V$
is the volume of black hole horizon, and $d\bar S$ can be interpreted as the
entropy production term due to nonequilibrium thermodynamics of spacetime. In
the setup of FRW universe, the field equations can also be cast to a similar
form, $dE=TdS +WdV +Td\bar S$, at the apparent horizon, where $W=(\rho-P)/2$,
$E$ is the energy of perfect fluid with energy density $\rho$ and pressure $P$
inside the apparent horizon. Compared to the case of Einstein's general
relativity, an additional term $d\bar S$ also appears here. The appearance of
the additional term is consistent with the argument recently given by Eling
{\it et al.} (gr-qc/0602001) that the horizon thermodynamics is non-equilibrium
one for the $f(R)$ gravity.


title: Non-integrability and Mach's principle in Induced Matter Theory

abstract:
  The geodesic equation in induced matter theory is redefined. It is shown that
the extra forces do not change the four-impulse of massive particles. We show
that the 4D space-time is non-integrable and find the relation between
non-integrability and the Mach's principal.


title: The Search for Massive Black Hole Binaries with LISA

abstract:
  In this work we focus on the search and detection of Massive black hole
binary (MBHB) systems, including systems at high redshift. As well as expanding
on previous works where we used a variant of Markov Chain Monte Carlo (MCMC),
called Metropolis-Hastings Monte Carlo, with simulated annealing, we introduce
a new search method based on frequency annealing which leads to a more rapid
and robust detection. We compare the two search methods on systems where we do
and do not see the merger of the black holes. In the non-merger case, we also
examine the posterior distribution exploration using a 7-D MCMC algorithm. We
demonstrate that this method is effective in dealing with the high correlations
between parameters, has a higher acceptance rate than previously proposed
methods and produces posterior distribution functions that are close to the
prediction from the Fisher Information matrix. Finally, after carrying out
searches where there is only one binary in the data stream, we examine the case
where two black hole binaries are present in the same data stream. We
demonstrate that our search algorithm can accurately recover both binaries, and
more importantly showing that we can safely extract the MBHB sources without
contaminating the rest of the data stream.


title: The Generalized Second Law in Dark Energy Dominated Universes

abstract:
  The generalized second law of gravitational thermodynamics is examined in
scenarios where the dark energy dominates the cosmic expansion. For
quintessence and phantom fields this law is fulfilled but it may fail when the
dark energy is in the form of a Chaplygin gas. However, if a black hole is
allowed in the picture, the law can be violated if the field is of phantom
type.


title:
Can we see gravitational collapse in (quantum) gravity perturbation
  theory?

abstract:
  In this paper, by making use of the perturbative expansion around topological
field theory we are trying to understand why the standard perturbation theory
for General Relativity, which starts with linearized gravity does not see
gravitational collapse. We start with investigating classical equations of
motion. For zero Immirzi parameter the ambiguity of the standard perturbative
expansion is reproduced. This ambiguity is related to the appearance of the
linearized diffeomorphism symmetry, which becomes unlinked from the original
diffeomorphism symmetry. Introducing Immirzi parameter makes it possible to
restore the link between these two symmetries and thus removes the ambiguity,
but at the cost of making classical perturbation theory rather intractable.
Then we argue that the two main sources of complexity of perturbation theory,
infinite number of degrees of freedom and non-trivial curvature of the phase
space of General Relativity could be disentangled when studying {\it quantum}
amplitudes. As an illustration we consider zero order approximation in quantum
perturbation theory. We identify relevant observables, and sketch their
quantization. We find some indications that this zero order approximation might
be described by Doubly Special Relativity.


title:
Formation of Three-Dimensional Black Strings from Gravitational Collapse
  of Dust Cloud

abstract:
  We study the formation of black strings from a gravitational collapse of
cylindrical dust clouds in the three-dimensional low-energy string theory. New
junction conditions for the dilaton as well as two junction conditions for
metrics and extrinsic curvatures between both regions of the clouds are
presented. As a result, it is found that the collapsing dust cloud always
collapses to a black string within a finite collapse time, and then a curvature
singularity formed at origin is cloaked by an event horizon. Moreover, it is
also shown that the collapse process can form a naked singularity within finite
time, regardless of the choice of initial data.


title: Inhomogeneous Quantum Mixmaster: from Classical toward Quantum Mechanics

abstract:
  Starting from the Hamiltonian formulation for the inhomogeneous Mixmaster
dynam- ics, we approach its quantum features through the link of the
quasi-classical limit. We fix the proper operator-ordering which ensures that
the WKB continuity equation overlaps the Liouville theorem as restricted to the
configuration space. We describe the full quantum dynamics of the model in some
details, providing a characterization of the (discrete) spectrum with analytic
expressions for the limit of high occupation number. One of the main
achievements of our analysis relies on the description of the ground state
morphology, showing how it is characterized by a non-vanishing zero-point
energy associated to the Universe anisotropy degrees of freedom


title: Binary black hole merger in the extreme mass ratio limit

abstract:
  We discuss the transition from quasi-circular inspiral to plunge of a system
of two nonrotating black holes of masses $m_1$ and $m_2$ in the extreme mass
ratio limit $m_1m_2\ll (m_1+m_2)^2$. In the spirit of the Effective One Body
(EOB) approach to the general relativistic dynamics of binary systems, the
dynamics of the two black hole system is represented in terms of an effective
particle of mass $\mu\equiv m_1m_2/(m_1+m_2)$ moving in a (quasi-)Schwarzschild
background of mass $M\equiv m_1+m_2$ and submitted to an ${\cal O}(\mu)$
radiation reaction force defined by Pad\'e resumming high-order Post-Newtonian
results. We then complete this approach by numerically computing, \`a la
Regge-Wheeler-Zerilli, the gravitational radiation emitted by such a particle.
Several tests of the numerical procedure are presented. We focus on
gravitational waveforms and the related energy and angular momentum losses. We
view this work as a contribution to the matching between analytical and
numerical methods within an EOB-type framework.


title: Where do moving punctures go?

abstract:
  Currently the most popular method to evolve black-hole binaries is the
``moving puncture'' method. It has recently been shown that when puncture
initial data for a Schwarzschild black hole are evolved using this method, the
numerical slices quickly lose contact with the second asymptotically flat end,
and end instead on a cylinder of finite Schwarzschild coordinate radius. These
slices are stationary, meaning that their geometry does not evolve further. We
will describe these results in the context of maximal slices, and present
time-independent puncture-like data for the Schwarzschild spacetime.


title:
The Effective Lorentzian and Teleparallel Spacetimes Generated by a Free
  Electromagnetic Field

abstract:
  In this paper we show that a free electromagnetic field living in Minkowski
spacetime generates an effective Weitzenbock or an effective Lorentzian
spacetime whose properties aredetermined in details. These results are possible
because we found using the Clifford bundle formalism the noticeable result that
the energy-momentum densities of a free electromagnetic field are sources of
the Hodge duals of exact 2-form fields which satisfy Maxwell like equations.


title: Thermodynamics of Spacetime and Unimodular Relativity

abstract:
  The black hole entropy formula applied to local Rindler horizon at each
spacetime point has been used in the literature to derive the Einstein field
equation as an equation of state of a thermodynamical system of spacetime. In
the present paper we argue that due to the key role of causal structure and
discrete spacetime in this approach the natural framework is unimodular
relativity rather than general relativity. It is shown that the equation of
state is trace free unimodular relativity field equation that uniquely
determines only the traceless stress tensor. Recent generalization to
nonequilibrium thermodynamics is shown to be equivalent to the conformally
related spacetime metrics, and energy-momentum conservation is satisfied
without invoking entropy production. We suggest that the cosmological constant
should possess thermodynamical fluctuations, and at a deeper level the metric
may have statistical origin.


title:
Learning about compact binary merger: the interplay between numerical
  relativity and gravitational-wave astronomy

abstract:
  Activities in data analysis and numerical simulation of gravitational waves
have to date largely proceeded independently. In this work we study how
waveforms obtained from numerical simulations could be effectively used within
the data analysis effort to search for gravitational waves from black hole
binaries. We propose measures to quantify the accuracy of numerical waveforms
for the purpose of data analysis and study how sensitive the analysis is to
errors in the waveforms. We estimate that ~100 templates (and ~10 simulations
with different mass ratios) are needed to detect waves from non-spinning binary
black holes with total masses in the range 100 Msun < M < 400 Msun using
initial LIGO. Of course, many more simulation runs will be needed to confirm
that the correct physics is captured in the numerical evolutions. From this
perspective, we also discuss sources of systematic errors in numerical waveform
extraction and provide order of magnitude estimates for the computational cost
of simulations that could be used to estimate the cost of parameter space
surveys. Finally, we discuss what information from near-future numerical
simulations of compact binary systems would be most useful for enhancing the
detectability of such events with contemporary gravitational wave detectors and
emphasize the role of numerical simulations for the interpretation of eventual
gravitational-wave observations.


title: Closed FRW model in Loop Quantum Cosmology

abstract:
  The basic idea of the LQC applies to every spatially homogeneous cosmological
model, however only the spatially flat (so called $k=0$) case has been
understood in detail in the literature thus far. In the closed (so called: k=1)
case certain technical difficulties have been the obstacle that stopped the
development. In this work the difficulties are overcome, and a new LQC model of
the spatially closed, homogeneous, isotropic universe is constructed. The
topology of the spacelike section of the universe is assumed to be that of
SU(2) or SO(3). Surprisingly, according to the results achieved in this work,
the two cases can be distinguished from each other just by the local properties
of the quantum geometry of the universe. The quantum hamiltonian operator of
the gravitational field takes the form of a difference operator, where the
elementary step is the quantum of the 3-volume derived in the flat case by
Ashtekar, Pawlowski and Singh. The mathematical properties of the operator are
studied: it is essentially self-adjoint, bounded from above by 0, the 0 itself
is not an eigenvalue, the eigenvectors form a basis. An estimate on the
dimension of the spectral projection on any finite interval is provided.