title: The Energy of Bianchi Type I and II Universes in Teleparallel Gravity

abstract:
  For certain models, the energy of the universe which includes the energy of
both the matter and the gravitational fields is obtained by using the
quasilocal energy-momentum in teleparallel gravity. It is shown that in the
case of the Bianchi type I and II universes, not only the total energy but also
the quasilocal energy-momentum for any region vanishes independently of the
three dimensionless coupling constants of teleparallel gravity.


title: An approximate global solution of Einstein's equations for a finite body

abstract:
  We obtain an approximate global stationary and axisymmetric solution of
Einstein's equations which can be considered as a simple star model: a
self-gravitating perfect fluid ball with constant mass density rotating in
rigid motion. Using the post-Minkowskian formalism (weak-field approximation)
and considering rotation as a perturbation (slow-rotation approximation), we
find approximate interior and exterior (asymptotically flat) solutions to this
problem in harmonic and quo-harmonic coordinates. In both cases, interior and
exterior solutions are matched, in the sense of Lichnerowicz, on the surface of
zero pressure to obtain a global solution. The resulting metric depends on
three arbitrary constants: mass density, rotational velocity and the star
radius at the non-rotation limit. The mass, angular momentum, quadrupole moment
and other constants of the exterior metric are determined by these three
parameters. It is easy to show that this type of fluid cannot be a source of
the Kerr metric


title: Brane-World Black Holes and Energy-Momentum Vector

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
hep-th/0308158, "Braneworld cosmological models with anisotropy," by A. Campos,
R. Maartens, D. Matravers and C.F. Sopuerta; and gr-qc/0205028, "Gravitational
Energy of Kerr and Kerr Anti-de Sitter Space-times in the Teleparallel
Geometry," by J. F. da Rocha-neto and K. H. Castello-Branco.


title:
Multidimensional cosmology with anisotropic fluid: acceleration and
  variation of G

abstract:
  A multidimensional cosmological model describing the dynamics of n+1
  Ricci-flat factor-spaces M_i in the presence of a one-component anisotropic
fluid is considered. The pressures in all spaces are proportional to the
density: p_i = w_i \rho, i = 0,...,n. Solutions with accelerated expansion of
our 3-space M_0 and small enough variation of the gravitational constant G are
found. These solutions exist for two branches of the parameter w_0. The first
branch describes superstiff matter with w_0 > 1, the second one may contain
phantom matter with w_0 < - 1, e.g., when G grows with time.


title:
Reply to Comment on ``Can gravity distinguish between Dirac and Majorana
  neutrinos?''

abstract:
  This is a reply to a comment (gr-qc/0610098) written by Nieves and Pal about
our paper (gr-qc/0605153) published in Phys. Rev. Lett. 97, 041101 (2006).


title:
Relativistic generalization of the inertial and gravitational masses
  equivalence principle

abstract:
  The Newtonian approximation for the gravitational field equation should not
necessarily involve admission of non-relativistic properties of the source
terms in Einstein's equations: it is sufficient to merely consider the
weak-field condition for gravitational field. When a source has electromagnetic
nature, one simply {\em cannot} ignore its intrinsically relativistic
properties, since there cannot be invented any non-relativistic approximation
which would describe electromagnetic stress-energy tensor adequately, even at
large distances where the fields become naturally weak. But the test particle
on which gravitational field is acting, should be treated as non-relativistic
(this premise is required for introduction of the Newtonian potential
$\Phi_{\rm N}$ from the geodesic equation).


title:
Bianchi Type III String Cosmological Models with Time Dependent Bulk
  Viscosity

abstract:
  Bianchi type III string cosmological models with bulk viscous fluid for
massive string are investigated. To get the determinate model of the universe,
we have assumed that the coefficient of bulk viscosity ($\xi$) is inversely
proportional to the expansion ($\theta$) in the model and expansion ($\theta$)
in the model is proportional to the shear ($\sigma$). This leads to $B = \ell
C^{n}$, $\ell$ and $n$ are constants. The behaviour of the model in presence
and absence of bulk viscosity, is discussed. The physical implications of the
models are also discussed in detail.


title: Higher dimensional VSI spacetimes

abstract:
  We present the explicit metric forms for higher dimensional vanishing scalar
invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes
belong to the higher dimensional Kundt class. We determine all of the VSI
spacetimes which admit a covariantly constant null vector, and we note that in
general in higher dimensions these spacetimes are of Ricci type III and Weyl
type III. The Ricci type N subclass is related to the chiral null models and
includes the relativistic gyratons and the higher dimensional pp-wave
spacetimes. The spacetimes under investigation are of particular interest since
they are solutions of supergravity or superstring theory.


title: Covariant generalization of cosmological perturbation theory

abstract:
  We present an approach to cosmological perturbations based on a covariant
perturbative expansion between two worldlines in the real inhomogeneous
universe. As an application, at an arbitrary order we define an exact scalar
quantity which describes the inhomogeneities in the number of e-folds on
uniform density hypersurfaces and which is conserved on all scales for a
barotropic ideal fluid. We derive a compact form for its conservation equation
at all orders and assign it a simple physical interpretation. To make a
comparison with the standard perturbation theory, we develop a method to
construct gauge-invariant quantities in a coordinate system at arbitrary order,
which we apply to derive the form of the n-th order perturbation in the number
of e-folds on uniform density hypersurfaces and its exact evolution equation.
On large scales, this provides the gauge-invariant expression for the curvature
perturbation on uniform density hypersurfaces and its evolution equation at any
order.


title:
The two-body problem: analytical results in a toy-model of relativistic
  gravity

abstract:
  The two body problem in a scalar theory of gravity is investigated. We focus
on the closest theory to General Relativity (GR), namely Nordstr\"om's theory
of gravity (1913). The gravitational field can be exactly solved for any
configuration of point-particles. We then derive the exact equations of motion
of two inspiraling bodies including the exact self-forces terms. We prove that
there is no innermost circular orbit (ICO) in the exact theory whereas we find
(order-dependent) ICOs if post-Newtonian (PN) truncations are used. We
construct a solution of the two body problem in an iterative (non-PN) way,
which can be viewed as a series in powers of $(v/c)^{5}$. Besides this rapid
convergence, each order also provides non-perturbative information. Starting
from a circular Newtonian-like orbit, the first iteration already yields the
4.5 PN radiation reaction. These results not only shed light on some
non-perturbative effects of relativistic gravity, but may also be useful to
test numerical codes.


title: Regular black holes and black universes

abstract:
  We give a comparative description of different types of regular static,
spherically symmetric black holes (BHs) and discuss in more detail their
particular type, which we suggest to call black universes. The latter have a
Schwarzschild-like causal structure, but inside the horizon there is an
expanding Kantowski-Sachs universe and a de Sitter infinity instead of a
singularity. Thus a hypothetic BH explorer gets a chance to survive. Solutions
of this kind are naturally obtained if one considers static, spherically
symmetric distributions of various (but not all) kinds of phantom matter whose
existence is favoured by cosmological observations. It also looks possible that
our Universe has originated from phantom-dominated collapse in another universe
and underwent isotropization after crossing the horizon. An explicit example of
a black-universe solution with positive Schwarzschild mass is discussed.


title: An Extensive Search for Overtones in Schwarzschild Black Holes

abstract:
  In this paper we show that with standard methods it is possible to obtain
highly precise results for QNMs. In particular, secondary modes are obtained by
numerical integration. We compare several results making a detailed analysis.


title: Planck-scale modified dispersion relations and Finsler geometry

abstract:
  A common feature of all Quantum Gravity (QG) phenomenology approaches is to
consider a modification of the mass shell condition of the relativistic
particle to take into account quantum gravitational effects. The framework for
such approaches is therefore usually set up in the cotangent bundle (phase
space). However it was recently proposed that this phenomenology could be
associated with an energy dependent geometry that has been coined ``rainbow
metric". We show here that the latter actually corresponds to a Finsler
Geometry, the natural generalization of Riemannian Geometry. We provide in this
way a new and rigorous framework to study the geometrical structure possibly
arising in the semiclassical regime of QG. We further investigate the
symmetries in this new context and discuss their role in alternative scenarios
like Lorentz violation in emergent spacetimes or Deformed Special
Relativity-like models.


title:
Current tests of alternative gravity theories: the Modified Newtonian
  Dynamics case

abstract:
  We address the possibility of taking advantage of high accuracy gravitational
space experiments in the Solar System and complementary cosmological tests to
distinguish between the usual general relativistic theory from the alternative
modified Newtonian dynamics paradigm.


title:
Massive particles' Hawking radiation via tunneling from the G.H Dilaton
  black hole

abstract:
  In the past, Hawking radiation was viewed as a tunneling process and the
barrier was just created by the outgoing particle itself. In this paper,
Parikh's recent work is extended to the case of massive particles' tunneling.
We investigate the behavior of the tunneling massive particles from a
particular black hole solution-G.H Dilaton black hole which is obtained from
the string theory, and calculate the emission rate at which massive particles
tunnel across the event horizon. We obtain that the result is also consistent
with an underlying unitary theory. Furthermore, the result takes the same
functional form as that of massless particles.


title: Angular momentum conservation for uniformly expanding flows

abstract:
  Angular momentum has recently been defined as a surface integral involving an
axial vector and a twist 1-form, which measures the twisting around of
space-time due to a rotating mass. The axial vector is chosen to be a
transverse, divergence-free, coordinate vector, which is compatible with any
initial choice of axis and integral curves. Then a conservation equation
expresses rate of change of angular momentum along a uniformly expanding flow
as a surface integral of angular momentum densities, with the same form as the
standard equation for an axial Killing vector, apart from the inclusion of an
effective energy tensor for gravitational radiation.


title: A note on the black hole remnant

abstract:
  Analyzing the tunneling probability of a Schwarzschild black hole with a
negative log-area correction to Bekenstein-Hawking entropy, I argue that this
correction may be closely related to a black hole remnant. The value for the
minimal black hole mass is also discussed.


title:
Comment to ``Quantization of FRW spacetimes in the presence of a
  cosmological constant and radiation''

abstract:
  The quantization of the Friedmann-Robertson-Walker spacetime in the presence
of a negative cosmological constant was used in a recent paper to conclude that
there are solutions that avoid singularities (big bang--big crunch) at the
quantum level. We show that a proper study of their model{\sl does not prevent}
the occurrence of singularities at the quantum level, in fact the quantum
probability of such event is larger than the classical one. Our numerical
simulations based on the powerful variational sinc collocation method (VSCM)
also show that the precision of the results of that paper is much lower than
the 20 significant digits reported by the authors.


title:
Upper limits to surface force disturbances on LISA proof masses and the
  possibility of observing galactic binaries

abstract:
  We report on the measurement of parasitic surface force noise on a hollow
replica of a LISA (Laser Interferometer Space Antenna for the observation of
gravitational waves) proof mass surrounded by a faithful representation of its
in flight surroundings, namely the capacitive sensor used to detect proof-mass
motion. Parasitic forces are detected through the corresponding torque exerted
on the proof mass and measured with a torsion pendulum in the frequency range
0.1 30 mHz. The sensor electrodes, electrode housing and associated readout
electronics have the same nominal design as for the flight hardware, including
4 mm gaps around the proof mass along the sensitive laser interferometry axis.
We show that the measured upper limit for surface forces would allow detection
of a number of galactic binaries signals with signal to noise ratio up to
approximately 40 for 1 year integration. We also discuss how the flight test
under development, LISA Pathfinder, will substantially improve this limit,
approaching the performance required for LISA.


title:
Generation of Bianchi Type V Bulk Viscous Cosmological Models with Time
  Dependent $\Lambda$-Term

abstract:
  Bianchi type V bulk viscous fluid cosmological models are investigated with
dynamic cosmological term $\Lambda(t)$. Using a generation technique (Camci
{\it et al.}, 2001), it is shown that the Einstein's field equations are
solvable for any arbitrary cosmic scale function. Solutions for particular
forms of cosmic scale functions are also obtained. The cosmological constant is
found to be decreasing function of time, which is supported by results from
recent type Ia supernovae observations. Some physical and geometrical aspects
of the models are also discussed.


title: Some Bianchi Type III String Cosmological Models with Bulk Viscosity

abstract:
  We investigate the integrability of cosmic strings in Bianchi III space-time
in presence of a bulk viscous fluid by applying a new technique. The behaviour
of the model is reduced to the solution of a single second order nonlinear
differential equation. We show that this equation admits an infinite family of
solutions. Some physical consequences from these results are also discussed.


title: P-Structures, P-Geometry and Observer's Perceptive Space

abstract:
  Mathematical theory of an observer is elaborated upon the basis of
A.Poincare's ideas on the nature of geometry and the role of observer's
perceptive space. The said theory is generalizing reference frames theory in
GR. Physical structure (P-structure) and corresponding physical geometry
(P-geometry) notions, representing properties invariance of some physical
objects and their relations, are introduced. P-structure of classical physical
time and its corresponding chronogeometry is considered as an example. Some
quantitative characteristics of observer's visual space geometry are
experimentally determined. The affine model of visual geometry is offered to
interpret experimentally sampled data. The connection of the obtained results
with some problems of theoretical physics is being discussed.


title: Child Universes in the Laboratory

abstract:
  Although cosmology is usually considered an observational science, where
there is little or no space for experimentation, other approaches can (and have
been) also considered. In particular, we can change rather drastically the
above, more passive, observational perspective and ask the following question:
could it be possible, and how, to create a universe in a laboratory? As a
matter of fact, this seems to be possible, according to at least two different
paradigms; both of them help to evade the consequences of singularity theorems.
In this contribution we will review some of these models and we will also
discuss possible extensions and generalizations, by paying a critical attention
to the still open issues as, for instance, the detectability of child universes
and the properties of quantum tunnelling processes.


title:
Conditions for nonexistence of static or stationary, Einstein-Maxwell,
  non-inheriting black-holes

abstract:
  We consider asymptotically-flat, static and stationary solutions of the
Einstein equations representing Einstein-Maxwell space-times in which the
Maxwell field is not constant along the Killing vector defining stationarity,
so that the symmetry of the space-time is not inherited by the electromagnetic
field. We find that static degenerate black hole solutions are not possible
and, subject to stronger assumptions, nor are static, non-degenerate or
stationary black holes. We describe the possibilities if the stronger
assumptions are relaxed.


title:
Torsion pendulum facility for direct force measurements of LISA GRS
  related disturbances

abstract:
  A four mass torsion pendulum facility for testing of the LISA GRS is under
development in Trento. With a LISA-like test mass suspended off-axis with
respect to the pendulum fiber, the facility allows for a direct measurement of
surface force disturbances arising in the GRS. We present here results with a
prototype pendulum integrated with very large-gap sensors, which allows an
estimate of the intrinsic pendulum noise floor in the absence of sensor related
force noise. The apparatus has shown a torque noise near to its mechanical
thermal noise limit, and would allow to place upper limits on GRS related
disturbances with a best sensitivity of 300 fN/Hz^(1/2) at 1mHz, a factor 50
from the LISA goal. Also, we discuss the characterization of the gravity
gradient noise, one environmental noise source that could limit the apparatus
performances, and report on the status of development of the facility.


title:
Cosmological constant, semiclassical gravity, and foundations of quantum
  mechanics

abstract:
  The old cosmological-constant (CC) problem indicates an inconsistency of the
usual formulation of semiclassical gravity. The usual formulation of
semiclassical gravity also seems to be inconsistent with the conventional
interpretation of quantum mechanics based on the discontinuous wave-function
collapse. By reformulating semiclassical gravity in terms of Bohmian
deterministic particle trajectories, the resulting semiclassical theory avoids
both the old CC problem and the discontinuous collapse problem of the usual
semiclassical theory. The relevance to the new CC problem and to particle
creation by classical gravitational fields is also discussed.


title: Different faces of the phantom

abstract:
  The SNe type Ia data admit that the Universe today may be dominated by some
exotic matter with negative pressure violating all energy conditions. Such
exotic matter is called {\it phantom matter} due to the anomalies connected
with violation of the energy conditions. If a phantom matter dominates the
matter content of the universe, it can develop a singularity in a finite future
proper time. Here we show that, under certain conditions, the evolution of
perturbations of this matter may lead to avoidance of this future singularity
(the Big Rip). At the same time, we show that local concentrations of a phantom
field may form, among other regular configurations, black holes with
asymptotically flat static regions, separated by an event horizon from an
expanding, singularity-free, asymptotically de Sitter universe.


title:
Multipole moments as a tool to infer from gravitational waves the
  geometry around an axisymmetric body

abstract:
  A binary system, composed of a compact object orbiting around a massive
central body, will emit gravitational waves which will depend on the central
body's spacetime geometry. We expect that the gravitational wave observables
will somehow ``encode'' the information about the spacetime structure. On the
other hand, it has been known for some time that the geometry around an
axisymmetric body can be described by its (Geroch-Hansen) multipole moments.
Therefore one can speculate that using the multipole moments can prove to be a
helpful tool for extracting this information. We will try to demonstrate this
in this talk, following the procedure described by [F. D. Ryan, Phys. Rev. D
{\bf 52} 5707 (1995)] and [T. P. Sotiriou and T. A. Apostolatos, Phys. Rev. D
{\bf 71} 044005 (2005)].


title: The metric-affine formalism of f(R) gravity

abstract:
  Recently a class of alternative theories of gravity which goes under the name
f(R) gravity, has received considerable attention, mainly due to its
interesting applications in cosmology. However, the phenomenology of such
theories is not only relevant to cosmological scales, especially when it is
treated within the framework of the so called Palatini variation, an
independent variation with respect to the metric and the connection, which is
not considered a priori to be the Levi-Civita connection of the metric. If this
connection has its standard geometrical meaning the resulting theory will be a
metric-affine theory of gravity, as will be discussed in this talk. The general
formalism will be presented and several aspects of the theory will be covered,
mainly focusing on the enriched phenomenology that such theories exhibit with
respect to General Relativity, relevant not only to large scales (cosmology)
but also to small scales (e.g. torsion).


title:
Gravitational Waves generated during inflation from a 5D vacuum theory
  of gravity in a de Sitter expansion

abstract:
  In this letter we study the generation of gravitational waves during
inflation from a 5D vacuum theory of gravity. Within this formalism, on an
effective 4D de Sitter background, we recover the typical results obtained with
4D inflationary theory in general relativity, for the amplitude of
gravitational waves generated during inflation. We also obtain a range of
values for the amplitude of tensor to scalar ratio which is in agreement with
COBE observations.


title: Time-dependent Spherically-symmetric 5-D Vacuum Solutions

abstract:
  Vacuum 5-D Einstein equations with spherical symmetry and t-dependence are
considered. For the case of separating variables several classes of exact
solutions are obtained. Effective matter, induced by geometrical scalar field
is analyzed.


title: Black hole interior from loop quantum gravity

abstract:
  In this paper we calculate modifications to the Schwarzschild solution by
using a semiclassical analysis of loop quantum black hole. We obtain a metric
inside the event horizon that coincides with the Schwarzschild solution near
the horizon but that is substantially different at the Planck scale. In
particular we obtain a bounce of the two-sphere for a minimum value of the
radius and that it is possible to have another event horizon close to the r=0
point.


title:
Asymptotic generators of fermionic charges and boundary conditions
  preserving supersymmetry

abstract:
  We use a covariant phase space formalism to give a general prescription for
defining Hamiltonian generators of bosonic and fermionic symmetries in
diffeomorphism invariant theories, such as supergravities. A simple and general
criterion is derived for a choice of boundary condition to lead to conserved
generators of the symmetries on the phase space. In particular, this provides a
criterion for the preservation of supersymmetries. For bosonic symmetries
corresponding to diffeomorphisms, our prescription coincides with the method of
Wald et al.
  We then illustrate these methods in the case of certain supergravity theories
in $d=4$. In minimal AdS supergravity, the boundary conditions such that the
supercharges exist as Hamiltonian generators of supersymmetry transformations
are unique within the usual framework in which the boundary metric is fixed. In
extended ${\mathcal N}=4$ AdS supergravity, or more generally in the presence
of chiral matter superfields, we find that there exist many boundary conditions
preserving ${\mathcal N}=1$ supersymmetry for which corresponding generators
exist. These choices are shown to correspond to a choice of certain arbitrary
boundary ``superpotentials,'' for suitably defined ``boundary superfields.'' We
also derive corresponding formulae for the conserved bosonic charges, such as
energy, in those theories, and we argue that energy is always positive, for any
supersymmetry-preserving boundary conditions. We finally comment on the
relevance and interpretation of our results within the AdS-CFT correspondence.


title:
Dynamical Emergence of Instantaneous 3-Spaces in a Class of Models of
  General Relativity

abstract:
  The Hamiltonian structure of General Relativity (GR), for both metric and
tetrad gravity in a definite continuous family of space-times, is fully
exploited in order to show that: i) the "Hole Argument" can be bypassed by
means of a specific "physical individuation" of point-events of the space-time
manifold $M^4$ in terms of the "autonomous degrees of freedom" of the vacuum
gravitational field ("Dirac observables"), while the "Leibniz equivalence" is
reduced to differences in the "non-inertial appearances" (connected to "gauge"
variables) of the same phenomena. ii) the chrono-geometric structure of a
solution of Einstein equations for given, gauge-fixed, initial data (a
"3-geometry" satisfying the relevant constraints on the Cauchy surface), can be
interpreted as an "unfolding" in mathematical global time of a sequence of
"achronal 3-spaces" characterized by "dynamically determined conventions" about
distant simultaneity. This result stands out as an important "conceptual
difference" with respect to the standard chrono-geometrical view of Special
Relativity (SR) and allows, in a specific sense, for an "endurantist"
interpretations of ordinary "physical objects" in GR.


title:
Using long-baseline interferometric gravitational waves detectors for
  high precision measures of the gravitational acceleration

abstract:
  A derivation of the optical axis lenght fluctations due by tilts of the
mirrors of the Fabry-Perot cavity of long-baseline interferometers for the
detection of gravitational waves in presence of the gravitational field of the
earth is discussed. By comparing with the typical tilt-induced noises it is
shown that this potential signal, which is considered a weak source of noise,
is negligible for the first generation of gravitational waves interferometers,
but, in principle, this effect could be used for high precision measures of the
gravitational acceleration if advanced projects will achieve an high
sensitivity. In that case the precision of the misure could be higher than the
gravimeter realized by the Istituto di Metrologia ``Gustavo Colonnetti''.


title: Unconventional string-like singularities in flat spacetime

abstract:
  The conical singularity in flat spacetime is mostly known as a model of the
cosmic string or the wedge disclination in solids. Its another, equally
important, function is to be a representative of quasiregular singularities.
  From all these of views it seems interesting to find out whether there exist
other similar singularities. To specify what "similar" means I introduce the
notion of the string-like singularity, which is, roughly speaking, an
absolutely mild singularity concentrated on a curve or on a 2-surface S
(depending on whether the space is three- of four-dimensional). A few such
singularities are already known: the aforementioned conical singularity, two
its Lorentzian versions, the "spinning string", the "screw dislocation", and
Tod's spacetime. In all these spacetimes S is a straight line (or a plane) and
one may wonder if this is an inherent property of the string-like
singularities. The aim of this paper is to construct string-like singularities
with less trivial S. These include flat spacetimes in which S is a spiral, or
even a loop. If such singularities exist in nature (in particular, as an
approximation to gravitational field of strings) their cosmological and
astrophysical manifestations must differ drastically from those of the
conventional cosmic strings. Likewise, being realized as topological defects in
crystals such loops and spirals will probably also have rather unusual
properties.


title: Orbifolds, Quantum Cosmology, and Nontrivial Topology

abstract:
  In order to include nontrivial spatial topologies in the problem of quantum
creation of a universe, it seems to be necessary to generalize the sum over
compact, smooth 4-manifolds to a sum over finite-volume, compact 4-orbifolds.
We consider in detail the case of a 4-spherical orbifold with a cone-point
singularity. This allows for the inclusion of a nontrivial topology in the
semiclassical path integral approach to quantum cosmology, in the context of a
Robertson-Walker minisuperspace.


title:
Mechanics of higher-dimensional black holes in asymptotically anti-de
  Sitter space-times

abstract:
  We construct a covariant phase space for Einstein gravity in dimensions d>=4
with negative cosmological constant, describing black holes in local
equilibrium. Thus, space-times under consideration are asymptotically anti-de
Sitter and admit an inner boundary representing an isolated horizon. This
allows us to derive a first law of black hole mechanics that involves only
quantities defined quasi-locally at the horizon, without having to assume that
the bulk space-time is stationary. The first law proposed by Gibbons et al. for
the Kerr-AdS family follows from a special case of this much more general first
law.


title: An Extra Structure of Spacetime: A Space of Points, Areas and Volumes

abstract:
  A theory in which points, lines, areas and volumes are on on the same footing
is investigated. All those geometric objects form a 16-dimensional manifold,
called C-space, which generalizes spacetime. In such higher dimensional space
fundamental interactions can be unified \` a la Kaluza-Klein. The ordinary,
4-dimensional, gravity and gauge fields are incorporated in the metric and spin
connection, whilst the conserved gauge charges are related to the isometries of
curved C-space. It is shown that a conserved generator of an isometry in
C-space contains a part with derivatives, which generalizes orbital angular
momentum, and a part with the generators of Clifford algebra, which generalizes
spin.


title: Stochastic Gravity: Beyond Semiclassical Gravity

abstract:
  The back-reaction of a classical gravitational field interacting with quantum
matter fields is described by the semiclassical Einstein equation, which has
the expectation value of the quantum matter fields stress tensor as a source.
The semiclassical theory may be obtained from the quantum field theory of
gravity interacting with N matter fields in the large N limit. This theory
breaks down when the fields quantum fluctuations are important. Stochastic
gravity goes beyond the semiclassical limit and allows for a systematic and
self-consistent description of the metric fluctuations induced by these quantum
fluctuations. The correlation functions of the metric fluctuations obtained in
stochastic gravity reproduce the correlation functions in the quantum theory to
leading order in an 1/N expansion. Two main applications of stochastic gravity
are discussed. The first, in cosmology, to obtain the spectrum of primordial
metric perturbations induced by the inflaton fluctuations, even beyond the
linear approximation. The second, in black hole physics, to study the
fluctuations of the horizon of an evaporating black hole.


title:
Covariant Schwarzschild perturbations I: Initial value formulation for
  scalars of spin-weight -+ 2

abstract:
  We consider full perturbations to a covariantly defined Schwarzschild
spacetime. By constructing complex quantities, we derive two decoupled,
covariant and gauge-invariant, wave-like equations for spin-weighted scalars.
These arise naturally from the Bianchi identities and comprise a covariant
representation of the Bardeen-Press equations for scalars with spin-weight
$\pm2$. Furthermore, the covariant and gauge-invariant 1+1+2 formalism is
employed, and consequently, the physical interpretation of the energy-momentum
perturbations is transparent. They are written explicitly in terms of the
energy-momentum specified on spacelike three-slices. Ultimately, a Cauchy
problem is constructed whereby, an initial three-slice may be perturbed by an
energy-momentum source, which induces resultant gravitational fields.


title: On the steady states of the spherically symmetric Einstein-Vlasov system

abstract:
  Using both numerical and analytical tools we study various features of
static, spherically symmetric solutions of the Einstein-Vlasov system. In
particular, we investigate the possible shapes of their mass-energy density and
find that they can be multi-peaked, we give numerical evidence and a partial
proof for the conjecture that the Buchdahl inequality $\sup_{r > 0} 2 m(r)/r <
8/9$, $m(r)$ the quasi-local mass, holds for all such steady states--both
isotropic {\em and} anisotropic--, and we give numerical evidence and a partial
proof for the conjecture that for any given microscopic equation of state--both
isotropic {\em and} anisotropic--the resulting one-parameter family of static
solutions generates a spiral in the radius-mass diagram.


title: Inflation from the bang of a white hole induced from a 6D vacuum state

abstract:
  Using ideas of STM theory, but starting from a 6D vacuum state, we propose an
inflationary model where the universe emerges from the blast of a white hole.
Under this approach, the expansion is affected by a geometrical deformation
induced by the gravitational attraction of the hole, which should be
responsible for the k_{R}-non invariant spectrum of galaxies (and likewise of
the matter density) today observed.


title: Cosmological Constant Problems and Renormalization Group

abstract:
  The Cosmological Constant Problem emerges when Quantum Field Theory is
applied to the gravitational theory, due to the enormous magnitude of the
induced energy of the vacuum. The unique known solution of this problem
involves an extremely precise fine-tuning of the vacuum counterpart. We review
a few of the existing approaches to this problem based on the account of the
quantum (loop) effects and pay special attention to the ones involving the
renormalization group.


title: Energy and momentum of the Friedmann and more general universes

abstract:
  Recently some authors concluded that the energy and momentum of the Fiedman
universes, flat and closed, are equal to zero locally and globally (flat
universes) or only globally (closed universes). The similar conclusion was also
done for more general only homogeneous universes (Kasner and Bianchi type I).
Such conclusions originated from coordinate dependent calculations performed
only in comoving Cartesian coordinates by using the so-called {\it
energy-momentum complexes}. But it is known that the energy-momentum complexes
can be reasonably use only in precisely defined asymptotically flat spacetimes
(at null or at spatial infinity) to calculate global energy and momentum. In
this paper we show, by using new coordinate independent expressions on energy
and momentum that the Friedman and more general universes {\it needn't be
energetic nonentity}.


title: Outer Trapped Surfaces in Vaidya Spacetimes

abstract:
  It is proven that in Vaidya spacetimes of bounded total mass, the outer
boundary, in spacetime, of the region containing outer trapped surfaces, is the
event horizon. Further, it is shown that the region containing trapped surfaces
in these spacetimes does not always extend to the event horizon.


title: New View on Quantum Gravity and the Origin of the Universe

abstract:
  This essay is based on a physics lecture given at the Hong Kong University of
Science and Technology on May 24, 2006, Hong Kong. It has 5 sections and one
page of references and suggested reading. The section titles are: 1. Origin of
the Universe and Quantum Gravity 2. Two major paradigms in Physics and Two
directions of Research in Cosmology 3. The Mescoscopic Structures of Spacetime
and Stochastic Gravity 4. One Vein of the Hydro View: Spacetime as Condensate?
5. Implications for the Origin of the Universe and other issues.


title: Black Hole in a Model with Dilaton and Monopole Fields

abstract:
  We present an exact black hole solution in a model having besides gravity a
dilaton and a monopole field. The solution has three free parameters, one of
which can be identified with the monopole charge, and another with the ADM
mass. The metric is asymptotically flat and has two horizons and irremovable
singularity only at $r=0$. The dilaton field is singular only at $r=0$. The
dominant and the strong energy condition are satisfied outside and on the
external horizon. According to a formulation of the no hair conjecture the
solution is "hairy". Also the well know GHS-GM solution is obtained from our
solution for certain values of its parameters.


title: Black Hole in a Model with Dilaton and Monopole Fields II

abstract:
  We present an exact black hole solution in a model having besides gravity a
dilaton and a monopole field, which is a generalization of a black hole
solution we have found. The new solution, as the previous one, has three free
parameters, one of which can be identified with the monopole charge, and
another with the ADM mass. Its metric is asymptotically flat, has two horizon,
irremovable singularity only at $r=0$, and the dilaton field is singular only
at $r=0$. The dominant and the strong energy condition are satisfied outside
and on the external horizon. According to a formulation of the no hair
conjecture the solution is "hairy". Also a reformulation of the model with two
monopole fields is given, which results in the appearance of an additional
symmetry and therefore in the appearance of a conserved dilaton charge.


title:
Black Holes in Models with Dilaton Field and Electric or Electric and
  Magnetic Charges

abstract:
  Exact static spherically symmetric charged black holes in four dimensions are
presented. One of them has only electric charge and another electric and
magnetic charges. In these solutions the metric is asymptotically flat, has two
horizons, irremovable singularity only at $r=0$, and the dilaton field is
singular only at $r=0$. The solution with electric charge only is characterized
by three free parameters, the ADM mass, the electric charge and an additional
free parameter. It can be considered as a modification of the GHS-GM solution
obtained by changing the coupling between dilaton and electromagnetic field.
The general dyonic solution is again characterized by three free parameters,
the ADM mass, the magnetic charge and an additional free parameter, which is
not the electric charge. According to a definition of the no-hair conjecture
the solutions are "hairy".A very interesting special case of the dyonic
solution is characterized by three free parameters, the ADM mass and the
electric and the magnetic charges. The solutions satisfy the dominant as well
as the strong energy condition outside and on the external horizon.


title:
Backreaction and Unruh effect: New insights from exact solutions of
  uniformly accelerated detectors

abstract:
  Using nonperturbative results obtained recently for an uniformly accelerated
Unruh-DeWitt detector, we discover new features in the dynamical evolution of
the detector's internal degree of freedom, and identified the Unruh effect
derived originally from time-dependent perturbation theory as operative in the
ultra-weak coupling and ultra-high acceleration limits. The mutual interaction
between the detector and the field engenders entanglement between them, and
tracing out the field leads to a mixed state of the detector even for a
detector at rest in Minkowski vacuum. Our findings based on this exact solution
shows clearly the differences from the ordinary result where the quantum
field's backreaction is ignored in that the detector no longer behaves like a
perfect thermometer. From a calculation of the evolution of the reduced density
matrix of the detector, we find that the transition probability from the
initial ground state over an infinitely long duration of interaction derived
from time-dependent perturbation theory is existent in the exact solution only
in transient under special limiting conditions corresponding to the Markovian
regime. Furthermore, the detector at late times never sees an exact Boltzmann
distribution over the energy eigenstates of the free detector, thus in the
non-Markovian regime covering a wider range of parameters the Unruh temperature
cannot be identified inside the detector.


title:
A New Variable in General Relativity and Its Applications for Classic
  and Quantum Gravity

abstract:
  A new variable in the Riemannian geometry is introduced by the tetrad and the
Ricci's coefficients of rotation, the characters of curve of the Riemannian
geometry are determined completely by the new variable; for general relativity,
all the Einstein-Hilbert action, the Einstein equation in general relativity
and the Dirac equation in curved spacetime can be expressed by the new
variable, and, further, as well the action of the theory on the interaction of
gravitational, electromagnetic and spinor field (TGESF). All the characters of
transformations of the new variable, the Einstein-Hilbert action and the action
of TGESF under the general coordinate transformations and the local Lorentz
transformations are discussed, respectively. After presenting the method of
introduction of gravitational field in terms of the principle of gauge
invariance based on the Dirac equation, and the ten constraint conditions for
the tetrad are given, the vacuum-vacuum transition amplitude with the
Faddeev-Popov ghost and the terms of external sources of the pure gravitational
field is presented; finally, as well that of TGESF.


title:
Scaling attractors for quintessence in flat universe with cosmological
  term

abstract:
  For evolution of flat universe, we classify late time and future attractors
with scaling behavior of scalar field quintessence in the case of potential,
which, at definite values of its parameters and initial data, corresponds to
exact scaling in the presence of cosmological constant.


title:
Plane Symmetric Solutions of Gravitational Field Equations in Five
  Dimensions

abstract:
  We present the effective field equations obtained from a generalized gravity
action with Euler-Poincare term and a cosmological constant in a $D$
dimensional bulk space-time. A class of plane-symmetric solutions that describe
a 3-brane world embedded in a D=5 dimensional bulk space-time are given.


title:
Classical and quantum radiation from a moving charge in an expanding
  universe

abstract:
  We investigate photon emission from a moving particle in an expanding
universe. This process is analogous to the radiation from an accelerated charge
in the classical electromagnetic theory. Using the framework of quantum field
theory in curved spacetime, we demonstrate that the Wentzel-Kramers-Brillouin
(WKB) approximation leads to the Larmor formula for the rate of the radiation
energy from a moving charge in an expanding universe. Using exactly solvable
models in a radiation-dominated universe and in a Milne universe, we examine
the validity of the WKB formula. It is shown that the quantum effect suppresses
the radiation energy in comparison with the WKB formula.


title:
Then again, how often does the Unruh-DeWitt detector click if we switch
  it carefully?

abstract:
  The transition probability in first-order perturbation theory for an
Unruh-DeWitt detector coupled to a massless scalar field in Minkowski space is
calculated. It has been shown recently that the conventional $i\epsilon$
regularisation prescription for the correlation function leads to non-Lorentz
invariant results for the transition rate, and a different regularisation,
involving spatial smearing of the field, has been advocated to replace it. We
show that the non-Lorentz invariance arises solely from the assumption of
sudden switch-on and switch-off of the detector, and that when the model
includes a smooth switching function the results from the conventional
regularisation are both finite and Lorentz invariant. The sharp switching limit
of the model is also discussed, as well as the falloff properties of the
spectrum for large frequencies.


title: De Sitter stability in quadratic gravity

abstract:
  Quadratic curvature corrections to Einstein-Hilbert action lead in general to
higher-order equations of motion, which can induced instability of some
unperturbed solutions of General Relativity. We study conditions for stability
of de Sitter cosmological solution. We argue that simple form of this condition
known for FRW background in 3+1 dimensions changes seriously if at least one of
these two assumptions is violated. In the present paper the stability
conditions for de Sitter solution have been found for multidimensional FRW
background and for Bianchi I metrics in 3+1 dimensions.


title:
Metric fluctuations from a NKK theory of gravity in a de Sitter
  expansion

abstract:
  A gauge invariant metric fluctuations formalism from a non-compact
Kaluza-Klein (NKK) theory of gravity is presented in this talk notes. In this
analysis we recover the well-known result $\frac{delta \rho}{\rho}\simeq 2\Phi$
obtained typically in the standard 4D semiclassical approach to inflation and
also the spectrum of this fluctuations becomes dependent of the fifth
(space-like) coordinate. This fact allows to establish an interval of values
for the wave number associated with the fifth dimension.


title: On the Existence of Radiation Gauges in Petrov type II spacetimes

abstract:
  The radiation gauges used by Chrzanowski (his IRG/ORG) for metric
reconstruction in the Kerr spacetime seem to be over-specified. Their
specification consists of five conditions: four, which we treat here as valid
gauge conditions, plus an additional condition on the trace of the metric
perturbation. In this work, we utilize a newly developed form of the perturbed
Einstein equations to establish a condition -- on a particular tetrad component
of the stress-energy tensor -- under which the full IRG/ORG can be imposed.
Using gauge freedom, we are able to impose the full IRG for Petrov type II and
type D backgrounds, using a different tetrad for each case. As a specific
example, we work through the process of imposing the IRG in a Schwarzschild
background, using a more traditional approach. Implications for metric
reconstruction using the Teukolsky curvature perturbations in type D spacetimes
are briefly discussed.


title: Unified First Law and Thermodynamics of Apparent Horizon in FRW Universe

abstract:
  In this paper we revisit the relation between the Friedmann equations and the
first law of thermodynamics. We find that the unified first law firstly
proposed by Hayward to treat the "outer"trapping horizon of dynamical black
hole can be used to the apparent horizon (a kind of "inner" trapping horizon in
the context of the FRW cosmology) of the FRW universe. We discuss three kinds
of gravity theorties: Einstein theory, Lovelock thoery and scalar-tensor
theory. In Einstein theory, the first law of thermodynamics is always satisfied
on the apparent horizon. In Lovelock theory, treating the higher derivative
terms as an effective energy-momentum tensor, we find that this method can give
the same entropy formula for the apparent horizon as that of black hole
horizon. This implies that the Clausius relation holds for the Lovelock theory.
In scalar-tensor gravity, we find, by using the same procedure, the Clausius
relation no longer holds. This indicates that the apparent horizon of FRW
universe in the scalar-tensor gravity corresponds to a system of
non-equilibrium thermodynamics. We show this point by using the method
developed recently by Eling {\it et al.} for dealing with the $f(R)$ gravity.


title:
On finding fields and self-force in a gauge appropriate to separable
  wave equations

abstract:
  Gravitational waves from the inspiral of a stellar-size black hole to a
supermassive black hole can be accurately approximated by a point particle
moving in a Kerr background. This paper presents progress on finding the
electromagnetic and gravitational field of a point particle in a black-hole
spacetime and on computing the self-force in a ``radiation gauge.'' The gauge
is chosen to allow one to compute the perturbed metric from a gauge-invariant
component $\psi_0$ (or $\psi_4$) of the Weyl tensor and follows earlier work by
Chrzanowski and Cohen and Kegeles (we correct a minor, but propagating, error
in the Cohen-Kegeles formalism). The electromagnetic field tensor and vector
potential of a static point charge and the perturbed gravitational field of a
static point mass in a Schwarzschild geometry are found, surprisingly, to have
closed-form expressions. The gravitational field of a static point charge in
the Schwarzschild background must have a strut, but $\psi_0$ and $\psi_4$ are
smooth except at the particle, and one can find local radiation gauges for
which the corresponding spin $\pm 2$ parts of the perturbed metric are smooth.
Finally a method for finding the renormalized self-force from the Teukolsky
equation is presented. The method is related to the Mino, Sasaki, Tanaka and
Quinn and Wald (MiSaTaQuWa) renormalization and to the Detweiler-Whiting
construction of the singular field. It relies on the fact that the renormalized
$\psi_0$ (or $\psi_4$) is a {\em sourcefree} solution to the Teukolsky
equation; and one can therefore reconstruct a nonsingular renormalized metric
in a radiation gauge.


title: Generalizing the Kodama State I: Construction

abstract:
  The Kodama State is unique in being an exact solution to all the ordinary
constraints of canonical quantum gravity that also has a well defined
semi-classical interpretation as a quantum version of a classical spacetime,
namely (anti)de Sitter space. However, the state is riddled with difficulties
which can be tracked down to the complexification of the phase space necessary
in its construction. This suggests a generalization of the state to real values
of the Immirzi parameter. In this first part of a two paper series we show that
one can generalize the state to real variables and the result is surprising in
that it appears to open up an infinite class of physical states. We show that
these states closely parallel the ordinary momentum eigenstates of
non-relativistic quantum mechanics with the Levi-Civita curvature playing the
role of the momentum. With this identification, the states inherit many of the
familiar properties of the momentum eigenstates including delta-function
normalizability. In the companion paper we will discuss the physical
interpretation, CPT properties, and an interesting connection between the inner
product and the Macdowell-Mansouri formulation of general relativity.


title: Generalizing the Kodama State II: Properties and Physical Interpretation

abstract:
  In this second part of a two paper series we discuss the properties and
physical interpretation of the generalized Kodama states. We first show that
the states are the three dimensional boundary degrees of freedom of two
familiar 4-dimensional topological invariants: the second Chern class and the
Euler class. Using this, we show that the states have the familiar
interpretation as WKB states, in this case corresponding not only to de Sitter
space, but also to first order perturbations therein. In an appropriate spatial
topology, the de Sitter solution has pure Chern-Simons functional form, and is
the unique state in the class that is identically diffeomorphism and SU(2)
gauge invariant. The q-deformed loop transform of this state yields evidence of
a cosmological horizon when the deformation parameter is a root of untiy. We
then discuss the behavior of the states under discrete symmetries, showing that
the states violate $P$ and $T$ due to the presence of the Immirzi parameter,
but they are $CPT$ invariant. We conclude with an interesting connection
between the physical inner product and the Macdowell Mansouri formulation of
gravity.


title:
Quantum Gravity and Matter: Counting Graphs on Causal Dynamical
  Triangulations

abstract:
  An outstanding challenge for models of non-perturbative quantum gravity is
the consistent formulation and quantitative evaluation of physical phenomena in
a regime where geometry and matter are strongly coupled. After developing
appropriate technical tools, one is interested in measuring and classifying how
the quantum fluctuations of geometry alter the behaviour of matter, compared
with that on a fixed background geometry.
  In the simplified context of two dimensions, we show how a method invented to
analyze the critical behaviour of spin systems on flat lattices can be adapted
to the fluctuating ensemble of curved spacetimes underlying the Causal
Dynamical Triangulations (CDT) approach to quantum gravity. We develop a
systematic counting of embedded graphs to evaluate the thermodynamic functions
of the gravity-matter models in a high- and low-temperature expansion. For the
case of the Ising model, we compute the series expansions for the magnetic
susceptibility on CDT lattices and their duals up to orders 6 and 12, and
analyze them by ratio method, Dlog Pad\'e and differential approximants. Apart
from providing evidence for a simplification of the model's analytic structure
due to the dynamical nature of the geometry, the technique introduced can shed
further light on criteria \`a la Harris and Luck for the influence of random
geometry on the critical properties of matter systems.


title: Towards a closed differential aging formula in special relativity

abstract:
  It is well known that the Lorentzian length of a timelike curve in Minkowski
spacetime is smaller than the Lorentzian length of the geodesic connecting its
initial and final endpoints. The difference is known as the 'differential
aging' and its calculation in terms of the proper acceleration history of the
timelike curve would provide an important tool for the autonomous spacetime
navigation of non-inertial observers. I give a solution in 3+1 dimensions which
holds whenever the acceleration is decomposed with respect to a lightlike
transported frame (lightlike transport will be defined), the analogous and more
natural problem for a Fermi-Walker decomposition being still open.


title: The Symmetric Teleparallel Gravity

abstract:
  We study symmetric teleparallel (STP) gravity model, in which only spacetime
non-metricity is nonzero. First we obtain STP equivalent Einstein-Hilbert
Lagrangian and give an approach for a generic solution in terms of only metric
tensor. Then we obtain a spherically symmetric static solution to the
Einstein's equation in STP space-time and discuss the singularities. Finally,
we study a model given by a Lagrangian 4-form quadratic in non-metricity. Thus,
we seek Schwarzschild-type solutions because of its observational success and
obtain some sets of solutions. Finally, we discuss physical relevance of the
solutions.


title: Angular distances in metric theories

abstract:
  The general expression of the angular distance between two point sources as
measured by an arbitrary observer is given. The modelling presented here is
rigorous, covariant and valid in any space-time. The sources of light may be
located at a finite distance from the observer. The aberration and the
gravitational deflection of light are treated in a unified way. Assuming the
gravitational field to be weak, an explicit expansion of the angular separation
within the post-post-Minkowskian approximation is carried out. The angular
separation within the post-Newtonian approximation truncated at the order
$1/c^3$ is straightforwardly derived.


title: Purely radiative irrotational dust spacetimes

abstract:
  We consider irrotational dust spacetimes in the full non-linear regime which
are "purely radiative" in the sense that the gravitational field satisfies the
covariant transverse conditions div(H) = div(E) = 0. Within this family we show
that the Bianchi class A spatially homogeneous dust models are uniquely
characterised by the condition that $H$ is diagonal in the shear-eigenframe.


title: A new proposal for group field theory I: the 3d case

abstract:
  In this series of papers, we propose a new rendition of 3d and 4d state sum
models based upon the group field theory (GFT) approach to non-perturbative
quantum gravity. We will see that the group field theories investigated in the
literature to date are, when judged from the position of quantum field theory,
an unusual manifestation of quantum dynamics. They are one in which the
Hadamard function for the field theory propagates a-causally the physical
degrees of freedom of quantum gravity. This is fine if we wish to define a
scalar product on the physical state space, but it is not what we generally
think of as originating directly from a field theory. We propose a model in 3d
more in line with standard quantum field theory, and therefore the field theory
precipitates causal dynamics. Thereafter, we couple the model to point matter,
and extract from the GFT the effective non-commutative field theory describing
the matter dynamics on a quantum gravity background. We identify the symmetries
of our new model and clarify their meaning in the GFT setting. We are aided in
this process by identifying the category theory foundations of this GFT which,
moreover, propel us towards a categorified version for the 4d case.


title:
A comment on the new non-conventional gravitational mechanism proposed
  by Jaekel and Reynaud to accommodate the Pioneer anomaly

abstract:
  In this paper we put on the test the new mechanism of gravitational origin
recently put forth by Jaekel and Reynaud in order to explain the Pioneer
anomaly in the framework of their post-Einsteinian metric extension of general
relativity. According to such a proposal, the secular part of the anomalous
acceleration experienced by the twin spacecraft of about 1 nm s^-2 could be
caused by an extra-potential \delta\Phi_P=c^2\chi r^2, with \chi=4 10^-8 AU^-2,
coming from the second sector of the considered model. When applied to the
motion of the planets of the Solar System, it would induce anomalous secular
perihelion advances which amount to tens-hundreds of arcseconds per century for
the outer planets. As for other previously proposed non-conventional
gravitational explanations of the Pioneer anomaly, the answer of the latest
observational determinations of the residual perihelion rates by RAS IAA is
neatly and unambiguously negative. The presence of another possible candidate
to explain the Pioneer anomaly, i.e. the extra-potential \delta\Phi_N, linear
in distance, from the first sector of the Jaekel and Reynaud model, is ruled
out not only by the residuals of the optical data of the outer planets
processed with the recent RAS IAA EPM2004 ephemerides but also by those
produced with other, older dynamical theories like, e.g., the well known NASA
JPL DE200.


title: Kaluza-Klein solitons reexamined

abstract:
  In (4 + 1) gravity the assumption that the five-dimensional metric is
independent of the fifth coordinate authorizes the extra dimension to be either
spacelike or timelike. As a consequence of this, the time coordinate and the
extra coordinate are interchangeable, which in turn allows the conception of
different scenarios in 4D from a single solution in 5D. In this paper, we make
a thorough investigation of all possible 4D scenarios, associated with this
interchange, for the well-known Kramer-Gross-Perry-Davidson-Owen set of
solutions. We show that there are {\it three} families of solutions with very
distinct geometrical and physical properties. They correspond to different sets
of values of the parameters which characterize the solutions in 5D. The
solutions of physical interest are identified on the basis of physical
requirements on the induced-matter in 4D. We find that only one family
satisfies these requirements; the other two violate the positivity of
mass-energy density. The "physical" solutions possess a lightlike singularity
which coincides with the horizon. The Schwarzschild black string solution as
well as the zero moment dipole solution of Gross and Perry are obtained in
different limits. These are analyzed in the context of Lake's geometrical
approach. We demonstrate that the parameters of the solutions in 5D are not
free, as previously considered. Instead, they are totally determined by
measurements in 4D. Namely, by the surface gravitational potential of the
astrophysical phenomena, like the Sun or other stars, modeled in Kaluza-Klein
theory. This is an important result which may help in observations for an
experimental/observational test of the theory.


title: Gravastars supported by nonlinear electrodynamics

abstract:
  Gravastar models have recently been proposed as an alternative to black
holes, mainly to avoid the problematic issues associated with event horizons
and singularities. In this work, a wide variety of gravastar models within the
context of nonlinear electrodynamics are constructed. Using the $F$
representation, specific forms of Lagrangians are considered describing
magnetic gravastars, which may be interpreted as self-gravitating magnetic
monopoles with charge $g$. Using the dual $P$ formulation of nonlinear
electrodynamics, electric gravastar models are constructed by considering
specific structural functions, and the characteristics and physical properties
of the solutions are further explored. These interior nonlinear electrodynamic
geometries are matched to an exterior Schwarzschild spacetime at a junction
interface.


title:
Statefinder diagnosis in a non-flat universe and the holographic model
  of dark energy

abstract:
  In this paper, we study the holographic dark energy model in non-flat
universe from the statefinder viewpoint. We plot the evolutionary trajectories
of the holographic dark energy model for different values of the parameter $c$
as well as for different contributions of spatial curvature, in the statefinder
parameter-planes. The statefinder diagrams characterize the properties of the
holographic dark energy and show the discrimination between this scenario and
other dark energy models. As we show, the contributions of the spatial
curvature in the model can be diagnosed out explicitly by the statefinder
diagrams. Furthermore, we also investigate the holographic dark energy model in
the $w-w'$ plane, which can provide us with a useful dynamical diagnosis
complement to the statefinder geometrical diagnosis.


title:
Massive uncharged and charged particles' tunneling from the
  Horowitz-Strominger Dilaton black hole

abstract:
  Originally, Parikh and Wilczek's work is only suitable for the massless
particles' tunneling. But their work has been further extended to the cases of
massive uncharged and charged particles' tunneling recently. In this paper, as
a particular black hole solution, we apply this extended method to reconsider
the tunneling effect of the H.S Dilaton black hole. We investigate the behavior
of both massive uncharged and charged particles, and respectively calculate the
emission rate at the event horizon. Our result shows that their emission rates
are also consistent with the unitary theory. Moreover, comparing with the case
of massless particles' tunneling, we find that this conclusion is independent
of the kind of particles. And it is probably caused by the underlying
relationship between this method and the laws of black hole thermodynamics.


title:
Light's Bending Angle due to Black Holes: From the Photon Sphere to
  Infinity

abstract:
  The bending angle of light is a central quantity in the theory of
gravitational lensing. We develop an analytical perturbation framework for
calculating the bending angle of light rays lensed by a Schwarzschild black
hole. Using a perturbation parameter given in terms of the gravitational radius
of the black hole and the light ray's impact parameter, we determine an
invariant series for the strong-deflection bending angle that extends beyond
the standard logarithmic deflection term used in the literature. In the
process, we discovered an improvement to the standard logarithmic deflection
term. Our perturbation framework is also used to derive as a consistency check,
the recently found weak deflection bending angle series. We also reformulate
the latter series in terms of a more natural invariant perturbation parameter,
one that smoothly transitions between the weak and strong deflection series. We
then compare our invariant strong deflection bending-angle series with the
numerically integrated exact formal bending angle expression, and find less
than 1% discrepancy for light rays as far out as twice the critical impact
parameter. The paper concludes by showing that the strong and weak deflection
bending angle series together provide an approximation that is within 1% of the
exact bending angle value for light rays traversing anywhere between the photon
sphere and infinity.


title: Reparametrization invariance of the classical metric

abstract:
  There is a statement on the parametrization dependence of the classical
metric in the recent paper of N.E.J. Bjerrum-Bohr, J.F. Donoghue, B.R.
Holstein, gr-qc/0610096. I completely disagree with this statement. Here I show
reparametrization invariance of the classical metric.


title: Late-time oscillatory behaviour for self-gravitating scalar fields

abstract:
  This paper investigates the late-time behaviour of certain cosmological
models where oscillations play an essential role. Rigorous results are proved
on the asymptotics of homogeneous and isotropic spacetimes with a linear
massive scalar field as source. Various generalizations are obtained for
nonlinear massive scalar fields, $k$-essence models and $f(R)$ gravity. The
effect of adding ordinary matter is discussed as is the case of nonlinear
scalar fields whose potential has a degenerate zero.


title: Self--similar and charged radiating spheres: An anisotropic approach

abstract:
  Considering charged fluid spheres as anisotropic sources and the diffusion
limit as the transport mechanism, we suppose that the inner space--time admits
self--similarity. Matching the interior solution with the
Reissner--Nordstr\"om--Vaidya exterior one, we find an extremely compact and
oscillatory final state with a redistribution of the electric charge function
and non zero pressure profiles.


title: Cosmology as a search for overall equilibrium

abstract:
  In this letter we will revise the steps followed by A. Einstein when he first
wrote on cosmology from the point of view of the general theory of relativity.
We will argue that his insightful line of thought leading to the introduction
of the cosmological constant in the equations of motion has only one weakness:
The constancy of the cosmological term, or what is the same, its independence
of the matter content of the universe. Eliminating this feature, I will propose
what I see as a simple and reasonable modification of the cosmological
equations of motion. The solutions of the new cosmological equations give place
to a cosmological model that tries to approach the Einstein static solution.
This model shows very appealing features in terms of fitting current
observations.


title:
A Review of Leading Quantum Gravitational Corrections to Newtonian
  Gravity

abstract:
  In this review we present the theoretical background for treating General
Relativity as an effective field theory and focus on the concrete results of
such a treatment. As a result we present the calculations of the low-energy
leading gravitational corrections to the Newtonian potential between two
sources.


title: Melvin universe as a limit of the C-metric

abstract:
  It is demonstrated that the Melvin universe representing the spacetime with a
strong 'homogeneous' electric field can by obtained from the spacetime of two
accelerated charged black holes by a suitable limiting procedure. The behavior
of various invariantly defined geometrical quantities in this limit is also
studied.


title: The G\"odel Universe: A Practical Travel Guide

abstract:
  We study the G\"odel universe through worldlines associated with motion at
constant speed and constant acceleration orthogonal to the instantaneous
velocity (WSAs). We show that these worldlines can be used to access every
region -- both spatial and temporal -- of the space-time. We capture the
insights they accord in a series of sketches, which extend significantly the
Hawking and Ellis picture of the G\"odel universe.


title:
Is Modified Chaplygin gas along with barotropic fluid responsible for
  acceleration of the Universe?

abstract:
  In this letter, we have considered a model of the universe filled with
modified Chaplygin gas and another fluid (with barotropic equation of state)
and its role in accelerating phase of the universe. We have assumed that the
mixture of these two fluid models is valid from (i) the radiation era to
$\Lambda$CDM for $-1\le\gamma\le 1$ and (ii) the radiation era to quiessence
model for $\gamma<-1$. For these two fluid models, the statefinder parameters
describe different phase of the evolution of the universe.


title: Space-based tests of gravity with laser ranging

abstract:
  Existing capabilities in laser ranging, optical interferometry and metrology,
in combination with precision frequency standards, atom-based quantum sensors,
and drag-free technologies, are critical for the space-based tests of
fundamental physics; as a result, of the recent progress in these disciplines,
the entire area is poised for major advances. Thus, accurate ranging to the
Moon and Mars will provide significant improvements in several gravity tests,
namely the equivalence principle, geodetic precession, PPN parameters $\beta$
and $\gamma$, and possible variation of the gravitational constant $G$. Other
tests will become possible with development of an optical architecture that
would allow proceeding from meter to centimeter to millimeter range accuracies
on interplanetary distances. Motivated by anticipated accuracy gains, we
discuss the recent renaissance in lunar laser ranging and consider future
relativistic gravity experiments with precision laser ranging over
interplanetary distances.


title: Analog Models beyond Kinematics

abstract:
  In this paper I discuss the extension of the analogy between gravitation and
some systems of condensed matter physics from kinematics to dynamics. I will
focus my attention on two applications of the analogy to the dynamics of fluids
that have been recently proposed: the study of backreaction effects and the
calculation of the depletion in Bose-Einstein condensates, showing how this
extension is possible and stressing the main differences with respect to the
gravitational context. I will conclude with some remarks about the actual
reliability of the proposed scheme, pointing out the basis issues that have
still to be addressed.


title:
Grasping rules and semiclassical limit of the geometry in the
  Ponzano-Regge model

abstract:
  We show how the expectation values of geometrical quantities in 3d quantum
gravity can be explicitly computed using grasping rules. We compute the volume
of a labelled tetrahedron using the triple grasping. We show that the large
spin expansion of this value is dominated by the classical expression, and we
study the next to leading order quantum corrections.


title:
Schroedinger equation for joint bidirectional evolution in time:
  astrophysical applications

abstract:
  The theoretical framework established in arXiv:quant-ph/0404103 is extended
to deal with possible astrophysical manifestations of phenomena involving
reverse, as well as forward, causation in time. The basic idea is that
space-time comprises the direct sum of a number of quantized fields, including
a distinct physical vacuum for each space in the sum. It is presumed that these
fields all contribute to, and are influenced by, gravitation, but generally do
not interact electromagnetically, i.e., are mutually invisible. At least one
term in the sum is proposed to consist of matter+vacuum evolving backward in
time; the expectation values of energies, both of matter and vacuum, of this
subspace are by construction negative, with a corresponding change of sign in
classical gravitational and inertial masses.


title:
An approximate global solution to the gravitational field of a perfect
  fluid in slow rotation

abstract:
  Using the Post-Minkowskian formalism and considering rotation as a
perturbation, we compute an approximate interior solution for a stationary
perfect fluid with constant density and axial symmetry. A suitable change of
coordinates allows this metric to be matched to the exterior metric to a
particle with a pole-dipole-quadrupole structure, relating the parameters of
both.


title: What is (not) wrong with scalar gravity?

abstract:
  On his way to General Relativity (GR) Einstein gave several arguments as to
why a special relativistic theory of gravity based on a massless scalar field
could be ruled out merely on grounds of theoretical considerations. We
re-investigate his two main arguments, which relate to energy conservation and
some form of the principle of the universality of free fall. We find that such
a theory-based a priori abandonment not to be justified. Rather, the theory
seems formally perfectly viable, though in clear contradiction with (later)
experiments. This may be of interest to those who teach GR and/or have an
active interest in its history.


title: Inaccessible Singularities in Toral Cosmology

abstract:
  The familiar Bang/Crunch singularities of classical cosmology have recently
been augmented by new varieties: rips, sudden singularities, and so on. These
tend to be associated with final states. Here we consider an alternative
possibility for the initial state: a singularity which has the novel property
of being inaccessible to physically well-defined probes. These singularities
arise naturally in cosmologies with toral spatial sections.


title: Entropy of BTZ black strings in the brick wall approach

abstract:
  During the last few years, exact solutions that describe black holes that are
bound to a two-brane in a four dimensional anti-de Sitter bulk have been
constructed. In situations wherein there is a negative cosmological constant on
the brane, for large masses, these solutions are exactly the rotating BTZ black
holes on the brane and, in fact, describe rotating BTZ black strings in the
bulk. We evaluate the canonical entropy of a free and massless scalar field (at
the Hawking temperature) around the rotating BTZ black string using the brick
wall model. We explicitly show that the Bekenstein-Hawking `area' law is
satisfied both on the brane as well as in the bulk.


title: Entropy of gravitating systems: scaling laws versus radial profiles

abstract:
  Through the consideration of spherically symmetric gravitating systems
consisting of perfect fluids with linear equation of state constrained to be in
a finite volume, an account is given of the properties of entropy at conditions
in which it is no longer an extensive quantity (it does not scale with system's
size). To accomplish this, the methods introduced by Oppenheim [1] to
characterize non-extensivity are used, suitably generalized to the case of
gravitating systems subject to an external pressure. In particular when, far
from the system's Schwarzschild limit, both area scaling for conventional
entropy and inverse radius law for the temperature set in (i.e. the same
properties of the corresponding black hole thermodynamical quantities), the
entropy profile is found to behave like 1/r, being r the area radius inside the
system. In such circumstances thus entropy heavily resides in internal layers,
in opposition to what happens when area scaling is gained while approaching the
Schwarzschild mass, in which case conventional entropy lies at the surface of
the system. The information content of these systems, even if it globally
scales like the area, is then stored in the whole volume, instead of packed on
the boundary.


title: The possibility of a simple derivation of the Schwarzschild metric

abstract:
  In spite of alleged impossibility proofs, "simple derivations" of the
Schwarzschild metric, based solely on Einstein's equivalence principle and
Newton's free fall velocity formula, are presented.


title: Gravitational waveforms from a Lense-Thirring system

abstract:
  The construction of ready to use templates for gravitational waves from
spinning binaries is an important challenge in the investigation of detectable
gravitational wave signals. Here we present a method to evaluate the
gravitational wave polarization states for inspiralling compact binaries in the
extreme mass ratio limit. We discuss the effects caused by the rotation of the
central massive object for eccentric orbits in the Lense-Thirring approximation
and give the formal expressions of the polarization states including higher
order corrections. Our results are in agreement with existing calculations for
the spinless and circular orbit limits.


title: The Friedman Universe with the stochastic cosmological constant

abstract:
  The Friedman Universe with the remnant stochastic scalar field in the hybrid
inflation model is examined. It is shown that the small effective cosmological
constant appears which increases the cosmological expansion.


title: Curvature scalar instability in f(R) gravity

abstract:
  An instability in the presence of matter in theories of gravity which include
a 1/R correction in the gravitational action has been found by Dolgov and
Kawasaki. In the present paper this instability is discussed for f(R) gravity
in general. We focus on the Palatini formalism of the theory and it is shown
that no such instability occurs in this version of f(R) gravity. The reasons
for the appearance of the instability in the metric but not in the Palatini
formalism are fully investigated.


title: Static self-gravitating elastic bodies in Einstein gravity

abstract:
  We prove that given a stress-free elastic body there exists, for sufficiently
small values of the gravitational constant, a unique static solution of the
Einstein equations coupled to the equations of relativistic elasticity. The
solution constructed is a small deformation of the relaxed configuration. This
result yields the first proof of existence of static solutions of the Einstein
equations without symmetries.


title:
Group classification of the Sachs equations for a radiating
  axisymmetric, non-rotating, vacuum space-time

abstract:
  We carry out a Lie group analysis of the Sachs equations for a time-dependent
axisymmetric non-rotating space-time in which the Ricci tensor vanishes. These
equations, which are the first two members of the set of Newman-Penrose
equations, define the characteristic initial-value problem for the space-time.
We find a particular form for the initial data such that these equations admit
a Lie symmetry, and so defines a geometrically special class of such
spacetimes. These should additionally be of particular physical interest
because of this special geometric feature.


title: Kerr-Sen dilaton-axion black hole lensing in the strong deflection limit

abstract:
  In the present work we study numerically quasi-equatorial lensing by the
charged, stationary, axially-symmetric Kerr-Sen dilaton-axion black hole in the
strong deflection limit. In this approximation we compute the magnification and
the positions of the relativistic images. The most outstanding effect is that
the Kerr-Sen black hole caustics drift away from the optical axis and shift in
clockwise direction with respect to the Kerr caustics. The intersections of the
critical curves on the equatorial plane as a function of the black hole angular
momentum are found, and it is shown that they decrease with the increase of the
parameter $Q^{2}/M$. All of the lensing quantities are compared to particular
cases as Schwarzschild, Kerr and Gibbons-Maeda black holes.


title: A symmetry for vanishing cosmological constant

abstract:
  Two different realizations of a symmetry principle that impose a zero
cosmological constant in an extra-dimensional set-up are studied. The symmetry
is identified by multiplication of the metric by minus one. In the first
realization of the symmetry this is provided by a symmetry transformation that
multiplies the coordinates by the imaginary number i. In the second realization
this is accomplished by a symmetry transformation that multiplies the metric
tensor by minus one. In both realizations of the symmetry the requirement of
the invariance of the gravitational action under the symmetry selects out the
dimensions given by D = 2(2n+1), n=0,1,2,... and forbids a bulk cosmological
constant. Another attractive aspect of the symmetry is that it seems to be more
promising for quantization when compared to the usual scale symmetry. The
second realization of the symmetry is more attractive in that it is posible to
make a possible brane cosmological constant zero in a simple way by using the
same symmetry, and the symmetry may be identified by reflection symmetry in
extra dimensions.


title: Effective constraints of loop quantum gravity

abstract:
  Within a perturbative cosmological regime of loop quantum gravity corrections
to effective constraints are computed. This takes into account all
inhomogeneous degrees of freedom relevant for scalar metric modes around flat
space and results in explicit expressions for modified coefficients and of
higher order terms. It also illustrates the role of different scales
determining the relative magnitude of corrections. Our results demonstrate that
loop quantum gravity has the correct classical limit, at least in its sector of
cosmological perturbations around flat space, in the sense of perturbative
effective theory.


title:
Gauge invariant perturbations of Scalar-Tensor Cosmologies: The vacuum
  case

abstract:
  The covariant gauge invariant perturbation theory of scalar cosmological
perturbations is developed for a general Scalar-Tensor
Friedmann-Lemaitre-Robertson-Walker cosmology in a vacuum. The perturbation
equations are then solved exactly in the long wavelength limit for a specific
coupling, potential and background. Differences with the minimally coupled case
are briefly discussed.


title:
Schwarzschild black hole and the generalized second law in
  phantom-dominated universe

abstract:
  We study the conditions required for validity of the generalized second law
in phantom dominated universe in the presence of Schwarzschild black hole. Our
study is independent of the origin of the phantom like behavior of the
considered universe. We also discuss the generalized second law in the
neighborhood of transition (from quintessence to phantom regime) time. We show
that even for a constant equation of state parameter the generalized second law
may be satisfied provided the temperature is not taken as de Sitter
temperature. It is shown that in models with (only) a transition from
quintessence to phantom regime the generalized second law does not hold in the
transition epoch.


title:
Global existence for the spherically symmetric Einstein-Vlasov system
  with outgoing matter

abstract:
  We prove a new global existence result for the asymptotically flat,
spherically symmetric Einstein-Vlasov system which describes in the framework
of general relativity an ensemble of particles which interact by gravity. The
data are such that initially all the particles are moving radially outward and
that this property can be bootstrapped. The resulting non-vacuum spacetime is
future geodesically complete.


title: Gauge Formulation for Higher Order Gravity

abstract:
  This work is an application of the second order gauge theory for the Lorentz
group, where a description of the gravitational interaction is obtained which
includes derivatives of the curvature. We analyze the form of the second field
strenght, $G=\partial F +fAF$, in terms of geometrical variables. All possible
independent Lagrangians constructed with quadratic contractions of $F$ and
quadratic contractions of $G$ are analyzed. The equations of motion for a
particular Lagrangian, which is analogous to Podolsky's term of his Generalized
Electrodynamics, are calculated. The static isotropic solution in the linear
approximation was found, exhibiting the regular Newtonian behaviour at short
distances as well as a meso-large distance modification.


title:
A new expression for the transition rate of an accelerated particle
  detector

abstract:
  We analyse the instantaneous transition rate of an accelerated Unruh-DeWitt
particle detector whose coupling to a quantum field on Minkowski space is
regularised by a finite spatial profile. We show, under mild technical
assumptions, that the zero size limit of the detector response is well defined,
independent of the choice of the profile function, and given by a manifestly
finite integral formula that no longer involves epsilon-regulators or limits.
Applications to specific trajectories are discussed, recovering in particular
the thermal result for uniform acceleration. Extensions of the model to de
Sitter space are also considered.


title: Symmetric Affine Theories and Nonlinear Einstein-Proca System

abstract:
  We review the correspondence between symmetric affine theories and the
nonlinear Einstein-Proca system that was found by Einstein and Schrodinger.
With the use of this correspondence, we investigate static spherically
symmetric solutions in symmetric affine theory with no matter fields. Use of
the correspondence leads to a significant simplification of the calculation. A
special instance of ``no-hair'' theorem for symmetric affine theory is
established.


title: Ruppeiner theory of black hole thermodynamics

abstract:
  The Ruppeiner metric as determined by the Hessian of the Gibbs surface
provides a geometric description of thermodynamic systems in equilibrium. An
interesting example is a black hole in equilibrium with its own Hawking
radiation. In this article, we present results from the Ruppeiner study of
various black hole families from different gravity theories e.g. 2D dilaton
gravity, BTZ, general relativity and higher-dimensional Einstein-Maxwell
gravity.


title:
Dynamical constraints on some orbital and physical properties of the
  WD0137-349 A/B binary system

abstract:
  In this paper I deal with the WD0137-349 binary system consisting of a white
dwarf (WD) and a brown dwarf (BD) in a close circular orbit of about 116 min.
I, first, constrain the admissible range of values for the inclination i by
noting that, from looking for deviations from the third Kepler law, the
quadrupole mass moment Q would assume unlikely large values, incompatible with
zero at more than 1-sigma level for i < 35 deg and i > 43 deg. Then, by
conservatively assuming that the most likely values for i are those that
prevent such an anomalous behavior of Q, i.e. those for which the third Kepler
law is an adequate modeling of the orbital period, I obtain i=39 +/- 2 deg.
Such a result is incompatible with the value i=35 deg quoted in literature by
more than 2 sigma. Conversely, it is shown that the white dwarf's mass range
obtained from spectroscopic measurements is compatible with my experimental
range, but not for i=35 deg. As a consequence, my estimate of $i$ yields an
orbital separation of a=(0.59 +/- 0.05)R_Sun and an equilibrium temperature of
BD of T_eq=(2087 +/- 154)K which differ by 10% and 4%, respectively, from the
corresponding values for i=35 deg.


title:
Friedmann Robertson Walker models with Conformally Coupled Massive
  Scalar Fields are Non-integrable

abstract:
  In this work we use a recently developed nonintegrability theorem of Morales
and Ramis to prove that the Friedmann Robertson Walker cosmological model with
a conformally coupled massive scalar field is nonintegrable.


title: A dynamical system approach to higher order gravity

abstract:
  The dynamical system approach has recently acquired great importance in the
investigation on higher order theories of gravity. In this talk I review the
main results and I give brief comments on the perspectives for further
developments.


title: The Raychaudhuri equations: a brief review

abstract:
  We present a brief review on the Raychaudhuri equations. Beginning with a
summary of the essential features of the original article by Raychaudhuri and
subsequent work of numerous authors, we move on to a discussion of the
equations in the context of alternate non--Riemannian spacetimes as well as
other theories of gravity, with a special mention on the equations in
spacetimes with torsion (Einstein--Cartan--Sciama--Kibble theory). Finally, we
give an overview of some recent applications of these equations in General
Relativity, Quantum Field Theory, String Theory and the theory of relativisitic
membranes. We conclude with a summary and provide our own perspectives on
directions of future research.


title: Gravity and Faster than Light Particles

abstract:
  In this paper I discuss whether superluminal particles exist in the general
relativistic theory of gravity. It seems that the answer to this question is
negative. In truth the result may only represent a difficulty to {\bf special}
but not general relativity, the later allowing both Lorentzian and Euclidian
metrics. An Euclidian metric does not restrict speed. Although only the
Lorentzian metric is stable \cite{Yahaloma}, an Euclidian metric can be created
under special gravitational circumstances and persist in a limited region of
space-time causing possible superluminality.


title:
Some recent results in scalar quantum field theory in globally
  hyperbolic asymptotically flat spacetimes

abstract:
  Some recent results obtained by the author and collaborators about QFT in
asymptotically flat spacetimes at null infinity are summarized and reviewed. In
particular it is focused on the physical properties of ground states in the
bulk induced by the BMS-invariant state defined at null infinity.


title: Dynamical determination of the quadrupole mass moment of a white dwarf

abstract:
  In this letter we dynamically determine the quadrupole mass moment Q of the
magnetic white dwarf WD 0137-349 by analyzing the period of the recently
discovered brown dwarf moving around it in a close 2-hr orbit. It turns out
that a purely Newtonian model for the orbit of WD 0137-349B, assumed circular
and equatorial, is adequate, given the present-day accuracy in knowing the
orbital parameters of such a binary system. Our result is Q=(-1.4615 +/-
0.9004) 10^47 kg m^2 for i=35 deg. It is able to accommodate the 3-sigma
significant discrepancy of (1.0 +/- 0.3) 10^-8 s^-2 between the inverse square
of the phenomenologically determined orbital period and the inverse square of
the calculated Keplerian one. The impact of i, for which a range Delta i of
possible values close to 35 deg is considered, is investigated as well.


title: f(R) actions, cosmic acceleration and local tests of gravity

abstract:
  We study spherically symmetric solutions in f(R) theories and its
compatibility with local tests of gravity. We start by clarifying the range of
validity of the weak field expansion and show that for many models proposed to
address the Dark Energy problem this expansion breaks down in realistic
situations. This invalidates the conclusions of several papers that make
inappropriate use of this expansion. For the stable models that modify gravity
only at small curvatures we find that when the asymptotic background curvature
is large we approximately recover the solutions of Einstein gravity through the
so-called Chameleon mechanism, as a result of the non-linear dynamics of the
extra scalar degree of freedom contained in the metric. In these models one
would observe a transition from Einstein to scalar-tensor gravity as the
Universe expands and the background curvature diminishes. Assuming an adiabatic
evolution we estimate the redshift at which this transition would take place
for a source with given mass and radius. We also show that models of dynamical
Dark Energy claimed to be compatible with tests of gravity because the mass of
the scalar is large in vacuum (e.g. those that also include R^2 corrections in
the action), are not viable.


title: Frankenstein's Glue: Transition functions for approximate solutions

abstract:
  Approximations are commonly employed to find approximate solutions to the
Einstein equations. These solutions, however, are usually only valid in some
specific spacetime region. A global solution can be constructed by gluing
approximate solutions together, but this procedure is difficult because
discontinuities can arise, leading to large violations of the Einstein
equations. In this paper, we provide an attempt to formalize this gluing scheme
by studying transition functions that join approximate solutions together. In
particular, we propose certain sufficient conditions on these functions and
proof that these conditions guarantee that the joined solution still satisfies
the Einstein equations to the same order as the approximate ones. An example is
also provided for a binary system of non-spinning black holes, where the
approximate solutions are taken to be given by a post-Newtonian expansion and a
perturbed Schwarzschild solution. For this specific case, we show that if the
transition functions satisfy the proposed conditions, the joined solution does
not contain any violations to the Einstein equations larger than those already
inherent in the approximations. We further show that if these functions violate
the proposed conditions, then the matter content of the spacetime is modified
by the introduction of a matter-shell, whose stress-energy tensor depends on
derivatives of these functions.


title: An introduction to the mechanics of black holes

abstract:
  These notes provide a self-contained introduction to the derivation of the
zero, first and second laws of black hole mechanics. The prerequisite
conservation laws in gauge and gravity theories are also briefly discussed. An
explicit derivation of the first law in general relativity is performed in
appendix.


title: Thermodynamics and evaporation of the noncommutative black hole

abstract:
  We investigate the thermodynamics of the noncommutative black hole whose
static picture is similar to that of the nonsingular black hole known as the de
Sitter-Schwarzschild black hole. It turns out that the final remnant of
extremal black hole is a thermodynamically stable object. We describe the
evaporation process of this black hole by using the noncommutativity-corrected
Vaidya metric. It is found that there exists a close relationship between
thermodynamic approach and evaporation process.


title: Remarks on the Generalized Chaplygin Gas

abstract:
  We have developed an action formulation for the Generalized Chaplygin Gas
  (GCG). The most general form for the nonrelativistic GCG action is derived
consistent with the equation of state. We have also discussed a relativistic
formulation for GCG by providing a detailed analysis of the Poincare algebra.


title: The interior spacetimes of stars in Palatini f(R) gravity

abstract:
  We study the interior spacetimes of stars in the Palatini formalism of f(R)
gravity and derive a generalized Tolman-Oppenheimer-Volkoff and mass equation
for a static, spherically symmetric star. We show that matching the interior
solution with the exterior Schwarzschild-De Sitter solution in general gives a
relation between the gravitational mass and the density profile of a star,
which is different from the one in General Relativity. These modifications
become neglible in models for which $\delta F(R) \equiv \partial f/\partial R -
1$ is a decreasing function of R however. As a result, both Solar System
constraints and stellar dynamics are perfectly consistent with $f(R) = R -
\mu^4/R$.


title: Wormhole with varying cosmological constant

abstract:
  It has been suggested that the cosmological constant is a variable dynamical
quantity. A class of solution has been presented for the spherically symmetric
space time describing wormholes by assuming the erstwhile cosmological constant
$\Lambda$ to be a space variable scalar, viz., $\Lambda$ = $\Lambda (r) $ . It
is shown that the Averaged Null Energy Condition (ANEC) violating exotic matter
can be made arbitrarily small.


title: Thin Shell Wormhole in Heterotic String Theory

abstract:
  Using 'Cut and Paste' technique, we develop a thin shell wormhole in
heterotic string theory. We determine the surface stresses, which are localized
in the shell, by using Darmois-Israel formalism. The linearized stability of
this thin wormhole is also analyzed.


title: Quantum causal histories in the light of quantum information

abstract:
  We use techniques of quantum information theory to analyze the quantum causal
histories approach to quantum gravity. We show that while it is consistent to
introduce closed timelike curves (CTCs), they cannot generically carry
independent degrees of freedom. Moreover, if the effective dynamics of the
chronology-respecting part of the system is linear, it should be completely
decoupled from the CTCs. In the absence of a CTC not all causal structures
admit the introduction of quantum mechanics. It is possible for those and only
for those causal structures that can be represented as quantum computational
networks. The dynamics of the subsystems should not be unitary or even
completely positive. However, we show that other commonly maid assumptions
ensure the complete positivity of the reduced dynamics.


title: Doubly Spinning Black Rings

abstract:
  We study a method to solve stationary axisymmetric vacuum Einstein equations
numerically. As an illustration, the five-dimensional doubly spinning black
rings that have two independent angular momenta are formulated in a way
suitable for fully nonlinear numerical method. Expanding for small second
angular velocity, the formulation is solved perturbatively upto second order
involving the backreaction from the second spin. The obtained solutions are
regular without conical singularity, and the physical properties are discussed
with the phase diagram of the reduced entropy vs the reduced angular momenta.
Possible extensions of the present approach to constructing the higher
dimensional version of black ring and the ring with the cosmological constant
are also discussed.