title: Linearized warp drive and the energy conditions

abstract:
  ''Warp drive'' spacetimes are useful as ''gedanken-experiments'' and as a
theoretician's probe of the foundations of general relativity. Applying
linearized gravity to the weak-field warp drive, i.e., for non-relativistic
warp-bubble velocities, we find that the occurrence of energy condition
violations in this class of spacetimes is generic to the form of the geometry
under consideration and is not simply a side-effect of the ''superluminal''
properties. Using the linearized construction it is now possible to compare the
warp field energy with the mass-energy of the spaceship, and applying the
''volume integral quantifier'', extremely stringent conditions on the warp
drive spacetime are found.


title:
The 3-dimensional Einstein-Klein-Gordon system in characteristic
  numerical relativity

abstract:
  We incorporate a massless scalar field into a 3-dimensional code for the
characteristic evolution of the gravitational field. The extended 3-dimensional
code for the Einstein--Klein--Gordon system is calibrated to be second order
convergent. It provides an accurate calculation of the gravitational and scalar
radiation at infinity. As an application, we simulate the fully nonlinear
evolution of an asymmetric scalar pulse of ingoing radiation propagating toward
an interior Schwarzschild black hole and compute the backscattered scalar and
gravitational outgoing radiation patterns. The amplitudes of the scalar and
gravitational outgoing radiation modes exhibit the predicted power law scaling
with respect to the amplitude of the initial data. For the scattering of an
axisymmetric scalar field, the final ring down matches the complex frequency
calculated perturbatively for the $\ell=2$ quasinormal mode.


title:
Classification of Static, Spherically Symmetric Solutions of the
  Einstein-Yang-Mills Theory with Positive Cosmological Constant

abstract:
  We give a complete classification of all static, spherically symmetric
solutions of the SU(2) Einstein-Yang-Mills theory with a positive cosmological
constant. Our classification proceeds in two steps. We first extend solutions
of the radial field equations to their maximal interval of existence. In a
second step we determine the Carter-Penrose diagrams of all 4-dimensional
space-times constructible from such radial pieces. Based on numerical studies
we sketch a complete phase space picture of all solutions with a regular
origin.


title: Holographic Gravity and the Surface term in the Einstein-Hilbert Action

abstract:
  Certain peculiar features of Einstein-Hilbert (EH) action provide clues
towards a holographic approach to gravity which is independent of the detailed
microstructure of spacetime. These features of the EH action include: (a) the
existence of second derivatives of dynamical variables; (b) a non trivial
relation between the surface term and the bulk term; (c) the fact that surface
term is non analytic in the coupling constant, when gravity is treated as a
spin-2 perturbation around flat spacetime and (d) the form of the variation of
the surface term under infinitesimal coordinate transformations. The surface
term can be derived directly from very general considerations and using (d) one
can obtain Einstein's equations {\it just from the surface term of the action}.
Further one can relate the bulk term to the surface term and derive the full EH
action based on purely thermodynamic considerations. The features (a), (b) and
(c) above emerge in a natural fashion in this approach. It is shown that action
$A_{grav}$ splits into two terms $-S+\beta E$ in a natural manner \textit{in
any stationary spacetime with horizon}, where $E$ is essentially an integral
over ADM energy density and $S$ arises from the integral of the surface gravity
over the horizon. This analysis shows that the true degrees of freedom of
gravity reside in the surface term of the action, making gravity intrinsically
holographic. It also provides a close connection between gravity and gauge
theories, and highlights the subtle role of the singular coordinate
transformations.


title: Influence functional approach to decoherence during Inflation

abstract:
  We show how the quantum to classical transition of the cosmological
fluctuations produced during inflation can be described by means of the
influence functional and the master equation. We split the inflaton field into
the system-field (long-wavelength modes), and the environment, represented by
its own short-wavelength modes. We compute the decoherence times for the
system-field modes and compare them with the other time scales of the model.


title: Scalar field perturbation on six-dimensional ultra-spinning black holes

abstract:
  We have studied the scalar field perturbations on six-dimensional
ultra-spinning black holes. We have numerically calculated the quasinormal
modes of rotating black holes. Our results suggest that such perturbations are
stable.


title:
Lightlike limit of the boosted Kerr black holes in higher-dimensional
  spacetimes

abstract:
  Deriving the gravitational field of the high-energy objects is an important
theme because the black holes might be produced in particle collisions in the
brane world scenario. In this paper, we develop a method for boosting the
metric of the stationary objects and taking the lightlike limit in
higher-dimensional spacetimes, using the Kerr black hole as one example. We
analytically construct the metric of lightlike Kerr black holes and find that
this method contains no ambiguity in contrast to the four-dimensional case. We
discuss the possible implications of our results in the brane world context.


title: Anti-de Sitter 3-dimensional Gravity with Torsion

abstract:
  Using the canonical formalism, we study the asymptotic symmetries of the
topological 3-dimensional gravity with torsion. In the anti-de Sitter sector,
the symmetries are realized by two independent Virasoro algebras with classical
central charges. In the simple case of the teleparallel vacuum geometry, the
central charges are equal to each other and have the same value as in general
relativity, while in the general Riemann-Cartan geometry, they become
different.


title: Decay of charged fields in de Sitter spacetime

abstract:
  We study the decay of charged scalar and spinor fields around
Reissner-Nordstrom black holes in de Sitter spacetime through calculations of
quasinormal frequencies of the fields. The influence of the parameters of the
black hole (charge, mass), of the decaying fields (charge, spin), and of the
spacetime (cosmological constant) on the decay is analyzed. The analytic
formula for calculation quasinormal frequencies for a large multipole number
(eikonal approximation) is derived both for the spinor and scalar fieldss.


title:
Maximizing curves for the charged-particle action in globally hyperbolic
  spacetimes

abstract:
  In a globally hyperbolic spacetime any pair of chronologically related events
admits a connecting geodesic. We present two theorems which prove that, more
generally, under weak assumptions, given a charge-to-mass ratio there is always
a connecting solution of the Lorentz force equation having that ratio. A
geometrical interpretation of the charged-particle action is given which shows
that the constructed solutions are maximizing.


title: Charge Tempered Cosmological Model

abstract:
  The main purpose of this work is to obtain the metric of a Charge Tempered
Cosmological Model, a slightly modified Standard Cosmological Model by a small
excess of charge density, distributed uniformly in accordance with the
Cosmological Principle, the global Coulomb interaction incorporated in this
metric. The particularity of this model is that the commoving observer
referential where the metric belongs is non inertial, which consequence is that
clocks at different position can not be synchronized. The new metric is
constrained to k goint to 0, with dependence on a charge parameter, and related
to a modified Friedmann equation, but it is constrained to a positive
deceleration parameter and the hyperbolic solution . Nevertheless, there are
corrections to do, valid just for a long range distances. For example, the red
shift has, now, dependences on the gravitational potential together the
recessional motion. In any way, this model accepts as well the cosmological
constant and its physical counterpart, the dark energy.


title: Computability at the Planck scale

abstract:
  We consider the issue of computability at the most fundamental level of
physical reality: the Planck scale. To this aim, we consider the theoretical
model of a quantum computer on a non commutative space background, which is a
computational model for quantum gravity. In this domain, all computable
functions are the laws of physics in their most primordial form, and non
computable mathematics finds no room in the physical world. Moreover, we show
that a theorem that classically was considered true but non computable, at the
Planck scale becomes computable but non decidable. This fact is due to the
change of logic for observers in a quantum-computing universe: from standard
quantum logic and classical logic, to paraconsistent logic.


title: f-symbols in Robertson-Walker space-times

abstract:
  In a Robertson-Walker space-time a spinning particle model is investigated
and we show that in a stationary case, there exists a class of new structures
called f-symbols which can generate reducible Killing tensors and supersymmetry
algebras.


title: Anisotropic cosmological models with perfect fluid and dark energy

abstract:
  We consider a self-consistent system of Bianchi type-I (BI) gravitational
field and a binary mixture of perfect fluid and dark energy. The perfect fluid
is taken to be the one obeying the usual equation of state, i.e., $p = \zeta
\ve$, with $\zeta \in [0, 1]$ whereas, the dark energy density is considered to
be either the quintessence or the Chaplygin gas. Exact solutions to the
corresponding Einstein equations are obtained.


title: Physics of Deformed Special Relativity

abstract:
  In many different ways, Deformed Special Relativity (DSR) has been argued to
provide an effective limit of quantum gravity in almost-flat regime.
Unfortunately DSR is up to now plagued by many conceptual problems (in
particular how it describes macroscopic objects) which forbids a definitive
physical interpretation and clear predictions. Here we propose a consistent
framework to interpret DSR. We extend the principle of relativity: the same way
that Special Relativity showed us that the definition of a reference frame
requires to specify its speed, we show that DSR implies that we must also take
into account its mass. We further advocate a 5-dimensional point of view on DSR
physics and the extension of the kinematical symmetry from the Poincare group
to the Poincare-de Sitter group (ISO(4,1)). This leads us to introduce the
concept of a pentamomentum and to take into account the renormalization of the
DSR deformation parameter kappa. This allows the resolution of the "soccer ball
problem" (definition of many-particle-states) and provides a physical
interpretation of the non-commutativity and non-associativity of the addition
the relativistic quadrimomentum.


title: On characteristic initial data for a star orbiting a black hole

abstract:
  We take further steps in the development of the characteristic approach to
enable handling the physical problem of a compact self-gravitating object, such
as a neutron star, in close orbit around a black hole. We examine different
options for setting the initial data for this problem and, in order to shed
light on their physical relevance, we carry out short time evolution of this
data. To this end we express the matter part of the characteristic gravity code
so that the hydrodynamics are in conservation form. The resulting gravity plus
matter relativity code provides a starting point for more refined future
efforts at longer term evolution. In the present work we find that,
independently of the details of the initial gravitational data, the system
quickly flushes out spurious gravitational radiation and relaxes to a
quasi-equilibrium state with an approximate helical symmetry corresponding to
the circular orbit of the star.


title: Absolute Parallelism: Spherical Symmetry and Singularities

abstract:
  Observing the list of compatible second order equations of Absolute
Parallelism (AP) found by Einstein and Mayer (for D=4), we have indicated the
one-parameter class of equations taking on 3-linear form (when contra-frame
density of some weight is in use).
  Spherically symmetric solutions to these equations are considered, and we try
not to add any \delta-sources (ie, $\delta(r)$-sources of unknown nature)
during integrations concerned with high symmetry. Using two different ways to
fix radius and time, we have found that only non-static solutions (except for
trivial one, of course) are possible. If D=5, such solutions, looking like a
single wave (or a file of single waves) moving along the radius, could serve as
(a base of) an expanding cosmological model.
  It is interesting that the one coordinate choice used leads to the first
order system, which is closely similar to gas-dynamic equations for Chaplygin
gas, with solutions being free of gradient catastrophe. On the contrary, the
other coordinates used show the possibility of solutions with arising ("weak")
singularities (it is still not clear whether the measure of such solutions is
not zero).


title: Gravitational Collapse End States

abstract:
  Recent developments on the final state of a gravitationally collapsing
massive matter cloud are summarized and reviewed here. After a brief background
on the problem, we point out how the black hole and naked singularity end
states arise naturally in spherical collapse. We see that it is the geometry of
trapped surfaces that governs this phenomena.


title:
The prospects for extended phase space approach to quantization of
  gravity

abstract:
  A brief review of main features of the new approach named ``quantum
geometrodynamics in extended phase space'' is given and its possible prospects
are discussed. Gauge degrees of freedom are treated as a subsystem of the
Universe which affects the evolution of the physical subsystem. Three points
can be singled out when the gauge subsystem shows itself as a real constituent
of the Universe: a chosen gauge condition determines the form of equation for
the physical part of wave function, the form of density matrix and the measure
in physical subspace. An example is considered when a physically relevant
choice of gauge condition leads to almost diagonal density matrix. The analogy
between a transition to another reference frame (another basis in physical
subspace) and a transition to accelerating reference frame in Rindler space is
suggested.


title: Cosmological effects in the local static frame

abstract:
  What is the influence of cosmology (the expansion law and its acceleration,
the cosmological constant...) on the dynamics and optics of a local system like
the solar system, a galaxy, a cluster, a supercluster...? The answer requires
the solution of Einstein equation with the local source, which tends towards
the cosmological model at large distance. There is, in general, no analytic
expression for the corresponding metric, but we calculate here an expansion in
a small parameter, which allows to answer the question. First, we derive a
static expression for the pure cosmological (Friedmann-Lema\^itre) metric,
whose validity, although local, extends in a very large neighborhood of the
observer. This expression appears as the metric of an osculating de Sitter
model. Then we propose an expansion of the cosmological metric with a local
source, which is valid in a very large neighborhood of the local system. This
allows to calculate exactly the (tiny) influence of cosmology on the dynamics
of the solar system: it results that, contrary to some claims, cosmological
effects fail to account for the unexplained acceleration of the Pioneer probe
by several order of magnitudes. Our expression provide estimations of the
cosmological influence in the calculations of rotation or dispersion velocity
curves in galaxies, clusters, and any type of cosmic structure, necessary for
precise evaluations of dark matter and/or cosmic flows. The same metric can
also be used to estimate the influence of cosmology on gravitational optics in
the vicinity of such systems.


title:
Space isotropy and weak equivalence principle in a scalar theory of
  gravity

abstract:
  We consider a preferred-frame bimetric theory in which the scalar
gravitational field both influences the metric and has direct dynamical
effects. A modified version ("v2") is built, by assuming now a
locally-isotropic dilation of physically measured distances, as compared with
distances evaluated with the Euclidean space metric. The dynamical equations
stay unchanged: they are based on a consistent formulation of Newton's second
law in a curved space-time. To obtain a local conservation equation for energy
with the new metric, the equation for the scalar field is modified: now its
l.h.s. is the flat wave operator. Fluid dynamics is formulated and the
asymptotic scheme of post-Newtonian approximation is adapted to v2. The latter
also explains the gravitational effects on light rays, as did the former
version (v1). The violation of the weak equivalence principle found for
gravitationally-active bodies at the point-particle limit, which discarded v1,
is proved to not exist in v2. Thus that violation was indeed due to the
anisotropy of the space metric assumed in v1.


title: The coplanarity of planetary orbits places bounds on dynamical aether

abstract:
  OBITUARY The Article and we have been friends for more than half a year. With
it, we shared many experiences, both in planetary dynamics and field theory.
This research is something I shall always remember with a smile on my face, and
a pain in my heart.
  Today is a day of sadness and mourning for the loss of our ill-born Article.
After more thorough medical examination we came to the conclusion that the
precession of planetary orbits cannot be used to bound anything except human
fantasy.
  Yet it can also be viewed as a day of celebration! Why? Because without it,
we would never have been touched by the shared experiences on physics's
eventful journey. Whilst it will now forever be absent in Arxive, it will be
with us always in spirit. As it might have said, "I have a long journey to
take, and must bid the company farewell" (Sir Walter Raleigh). I say three
things:
  Gone? - Yes!
  Forgotten? - Never!
  Remembered? - Always! by K.G.Z.


title: A note on spherically symmetric naked singularities in general dimension

abstract:
  We discuss generalizations of the recent theorem by Dafermos (hep-th/0403033)
forbidding a certain class of naked singularities in the spherical collapse of
a scalar field. Employing techniques similar to the ones Dafermos used, we
consider extending the theorem (1) to higher dimensions, (2) by including more
general matter represented by a stress-energy tensor satisfying certain
assumptions, and (3) by replacing the spherical geometry by a toroidal or
higher genus (locally hyperbolic) one. We show that the extension to higher
dimensions and a more general topology is straightforward; on the other hand,
replacing the scalar field by a more general matter content forces us to shrink
the class of naked singularities we are able to exclude. We then show that the
most common matter theories (scalar field interacting with a non-abelian gauge
field and a perfect fluid satisfying certain conditions) obey the assumptions
of our weaker theorem, and we end by commenting on the applicability of our
results to the five-dimensional AdS scenarii considered recently in the
literature.


abstract:
  Newtonian limit of Extended Theories of Gravity (in particular, higher--order
and scalar--tensor theories) is theoretically discussed taking into account
recent observational and experimental results.


title: Noncommutativity in quantum cosmology and the Hierarchy problem

abstract:
  We study the quantum cosmology of an empty (4+1)-dimensional Kaluza-Klein
cosmology with a negative cosmological constant and a FRW type metric with two
scale factors, one for 4-D universe and the other for one compact extra
dimension. By assuming the noncommutativity in the corresponding
mini-superspace we suggest a solution for the Hierarchy problem, at the level
of Wheeler-DeWitt equation.


title:
Radial geodesics as a microscopic origin of black hole entropy. I:
  Confined under the Schwarzschild horizon

abstract:
  Causal radial geodesics with a positive interval in the Schwarzschild metric
include a subset of trajectories completely confined under a horizon, which
compose a thermal statistical ensemble with the Hawking-Gibbons temperature.
The Bekenstein--Hawking entropy is given by an action at corresponding
geodesics of particles with a summed mass equal to that of black hole in the
limit of large mass.


title: Cosmological dynamics in tomographic probability representation

abstract:
  The probability representation for quantum states of the universe in which
the states are described by a fair probability distribution instead of wave
function (or density matrix) is developed to consider cosmological dynamics.
The evolution of the universe state is described by standard positive
transition probability (tomographic transition probability) instead of the
complex transition probability amplitude (Feynman path integral) of the
standard approach. The latter one is expressed in terms of the tomographic
transition probability. Examples of minisuperspaces in the framework of the
suggested approach are presented. Possibility of observational applications of
the universe tomographs are discussed.


title:
On the equation of state of a flat FRW model filled with a bulk viscous
  fluid

abstract:
  In this paper, we study the equation of state admissible for a flat FRW
models filled with a bulk viscous fluid by using the Lie group method. It is
founded that the model admits scaling symmetries iff the bulk viscous parameter
$\gamma =1/2$. In this case, it is found that the main quantities follow a
power law solution and in particular the bulk viscous pressure $\Pi $ has the
same order of magnitude as the energy density $\rho ,$ in such a way that it is
possible to formulate the equation of state $\Pi =\varkappa \rho ,$ where
$\varkappa \in \mathbb{R}^{-}$ (i.e. is a negative numerical constant)$.$ If we
assume such relationship we find again that the model is scale invariant iff
$\gamma =1/2.$ We conclude that the model accepts a scaling symmetry iff
$\gamma =1/2$ and that for this value of the viscous parameter, $\Pi =\varkappa
\rho ,$ but the hypothesis $\Pi =\varkappa \rho $ does not imply $\gamma =1/2,$
and that the model is scale invariant.


title:
Measuring the LISA test mass magnetic proprieties with a torsion
  pendulum

abstract:
  Achieving the low frequency LISA sensitivity requires that the test masses
acting as the interferometer end mirrors are free-falling with an unprecedented
small degree of deviation. Magnetic disturbances, originating in the
interaction of the test mass with the environmental magnetic field, can
significantly deteriorate the LISA performance and can be parameterized through
the test mass remnant dipole moment $\vec{m}_r$ and the magnetic susceptibility
$\chi$. While the LISA test flight precursor LTP will investigate these effects
during the preliminary phases of the mission, the very stringent requirements
on the test mass magnetic cleanliness make ground-based characterization of its
magnetic proprieties paramount. We propose a torsion pendulum technique to
accurately measure on ground the magnetic proprieties of the LISA/LTP test
masses.


title: A discrete curvature on a planar graph

abstract:
  Given a planar graph derived from a spherical, euclidean or hyperbolic
tessellation, one can define a discrete curvature by combinatorial properties,
which after embedding the graph in a compact 2d-manifold, becomes the Gaussian
curvature.


title: One loop photon-graviton mixing in an electromagnetic field: Part 1

abstract:
  Photon-graviton mixing in an electromagnetic field is a process of potential
interest for cosmology and astrophysics. At the tree level it has been studied
by many authors. We consider the one-loop contribution to this amplitude
involving a charged spin 0 or spin 1/2 particle in the loop and an arbitrary
constant field. In the first part of this article, the worldline formalism is
used to obtain a compact two-parameter integral representation for this
amplitude, valid for arbitrary photon energies and background field strengths.
The calculation is manifestly covariant througout.


title: Dark Matter and Potential fields

abstract:
  A general concept of potential field is introduced. The potential field that
one puts in correspondence with dark matter, has fundamental geometrical
interpretation (parallel transport) and has intrinsically inherent in local
symmetry. The equations of dark matter field are derived that are invariant
with respect to the local transformations. It is shown how to reduce these
equations to the Maxwell equations. Thus, the dark matter field may be
considered as generalized electromagnetic field and a simple solution is given
of the old problem to connect electromagnetic field with geometrical properties
of the physical manifold itself. It is shown that gauge fixing renders
generalized electromagnetic field effectively massive while the Maxwell
electromagnetic field remains massless. To learn more about interactions
between matter and dark matter on the microscopical level (and to recognize the
fundamental role of internal symmetry) the general covariant Dirac equation is
derived in the Minkowski space--time which describe the interactions of spinor
field with dark matter field.


title:
Radial geodesics as a microscopic origin of black hole entropy. II:
  Features of Reissner--Nordstrom black hole

abstract:
  The entropy of charged black hole is calculated by using the partition
function evaluated at radial geodesics confined under horizons. We establish
two quantum phase states inside the black hole and a transition between them.


title: The Spherically Symmetric Standard Model with Gravity

abstract:
  Spherical reduction of generic four-dimensional theories is revisited. Three
different notions of "spherical symmetry" are defined. The following sectors
are investigated: Einstein-Cartan theory, spinors, (non-)abelian gauge fields
and scalar fields. In each sector a different formalism seems to be most
convenient: the Cartan formulation of gravity works best in the purely
gravitational sector, the Einstein formulation is convenient for the Yang-Mills
sector and for reducing scalar fields, and the Newman-Penrose formalism seems
to be the most transparent one in the fermionic sector. Combining them the
spherically reduced Standard Model of particle physics together with the
usually omitted gravity part can be presented as a two-dimensional (dilaton
gravity) theory.


title: Super-energy and Killing-Yano tensors

abstract:
  In this paper we investigate a class of basic super-energy tensors, namely
those constructed from Killing-Yano tensors, and give a generalization of
super-energy tensors for cases when we start not with a single tensor, but with
a pair of tensors.


title: The general Penrose inequality: lessons from numerical evidence

abstract:
  Formulation of the Penrose inequality becomes ambiguous when the past and
future apparent horizons do cross. We test numerically several natural
possibilities of stating the inequality in punctured and boosted single- and
double- black holes, in a Dain-Friedrich class of initial data and in
conformally flat spheroidal data.The Penrose inequality holds true in vacuum
configurations for the outermost element amongst the set of disjoint future and
past apparent horizons (as expected)and (unexpectedly) for each of the
outermost past and future apparent horizons, whenever these two bifurcate from
an outermost minimal surface, regardless of whether they intersect or remain
disjoint. In systems with matter the conjecture breaks down only if matter does
not obey the dominant energy condition.


title: Modeling the Black Hole Excision Problem

abstract:
  We analyze the excision strategy for simulating black holes. The problem is
modeled by the propagation of quasi-linear waves in a 1-dimensional spatial
region with timelike outer boundary, spacelike inner boundary and a horizon in
between. Proofs of well-posed evolution and boundary algorithms for a second
differential order treatment of the system are given for the separate pieces
underlying the finite difference problem. These are implemented in a numerical
code which gives accurate long term simulations of the quasi-linear excision
problem. Excitation of long wavelength exponential modes, which are latent in
the problem, are suppressed using conservation laws for the discretized system.
The techniques are designed to apply directly to recent codes for the Einstein
equations based upon the harmonic formulation.


title:
The physical meaning of the "boost-rotation symmetric" solutions within
  the general interpretation of Einstein's theory of gravitation

abstract:
  The answer to the question, what physical meaning should be attributed to the
so-called boost-rotation symmetric exact solutions to the field equations of
general relativity, is provided within the general interpretation scheme for
the ``theories of relativity'', based on group theoretical arguments, and set
forth by Erich Kretschmann already in the year 1917.


title:
Characterization of disturbance sources for LISA: torsion pendulum
  results

abstract:
  A torsion pendulum allows ground-based investigation of the purity of
free-fall for the LISA test masses inside their capacitive position sensor.
This paper presents recent improvements in our torsion pendulum facility that
have both increased the pendulum sensitivity and allowed detailed
characterization of several important sources of acceleration noise for the
LISA test masses. We discuss here an improved upper limit on random force noise
originating in the sensor. Additionally, we present new measurement techniques
and preliminary results for characterizing the forces caused by the sensor's
residual electrostatic fields, dielectric losses, residual spring-like
coupling, and temperature gradients.


title: Holography for the Lorentz Group Racah Coefficients

abstract:
  A known realization of the Lorentz group Racah coefficients is given by an
integral of a product of 6 ``propagators'' over 4 copies of the hyperbolic
space. These are ``bulk-to-bulk'' propagators in that they are functions of two
points in the hyperbolic space. It is known that the bulk-to-bulk propagator
can be constructed out of two bulk-to-boundary ones. We point out that there is
another way to obtain the same object. Namely, one can use two bulk-to-boundary
and one boundary-to-boundary propagator. Starting from this construction and
carrying out the bulk integrals we obtain a realization of the Racah
coefficients that is ``holographic'' in the sense that it only involves
boundary objects. This holographic realization admits a geometric
interpretation in terms of an ``extended'' tetrahedron.


title: Cosmological Singularities, Billiards and Lorentzian Kac-Moody Algebras

abstract:
  The structure of the general, inhomogeneous solution of (bosonic)
Einstein-matter systems in the vicinity of a cosmological singularity is
considered. We review the proof (based on ideas of
Belinskii-Khalatnikov-Lifshitz and technically simplified by the use of the
Arnowitt-Deser-Misner Hamiltonian formalism) that the asymptotic behaviour, as
one approaches the singularity, of the general solution is describable, at each
(generic) spatial point, as a billiard motion in an auxiliary Lorentzian space.
For certain Einstein-matter systems, notably for pure Einstein gravity in any
spacetime dimension D and for the particular Einstein-matter systems arising in
String theory, the billiard tables describing asymptotic cosmological behaviour
are found to be identical to the Weyl chambers of some Lorentzian Kac-Moody
algebras. In the case of the bosonic sector of supergravity in 11 dimensional
spacetime the underlying Lorentzian algebra is that of the hyperbolic Kac-Moody
group E_{10}, and there exists some evidence of a correspondence between the
general solution of the Einstein-three-form system and a null geodesic in the
infinite dimensional coset space E_{10} / K (E_{10}), where K (E_{10}) is the
maximal compact subgroup of E_{10}.


title:
Tachyon fields with effects of quantum matter in an Anti-de Sitter
  Universe

abstract:
  We consider an Anti-de Sitter universe filled by quantum conformal matter
with the contribution from the usual tachyon and a perfect fluid. The model
represents the combination of a trace-anomaly annihilated and a tachyon driven
Anti-de Sitter universe. The influence exerted by the quantum effects and by
the tachyon on the AdS space is studied. The radius corresponding to this
universe is calculated and the effect of the tachyon potential is discussed, in
particular, concerning to the possibility to get an accelerated scale factor
for the proposed model (implying an accelerated expansion of the AdS type of
universe). Fulfillment of the cosmological energy conditions in the model is
also investigated


title: Feynman loops and three-dimensional quantum gravity

abstract:
  This paper explores the idea that within the framework of three-dimensional
quantum gravity one can extend the notion of Feynman diagram to include the
coupling of the particles in the diagram with quantum gravity. The paper
concentrates on the non-trivial part of the gravitational response, which is to
the large momenta propagating around a closed loop. By taking a limiting case
one can give a simple geometric description of this gravitational response.
This is calculated in detail for the example of a closed Feynman loop in the
form of a trefoil knot. The results show that when the magnitude of the
momentum passes a certain threshold value, non-trivial gravitational
configurations of the knot play an important role.
  The calculations also provide some new information about a limit of the
coloured Jones polynomial which may be of independent mathematical interest.


title: Mechanics of multidimensional isolated horizons

abstract:
  Recently a multidimensional generalization of Isolated Horizon framework has
been proposed by Lewandowski and Pawlowski (gr-qc/0410146). Therein the
geometric description was easily generalized to higher dimensions and the
structure of the constraints induced by the Einstein equations was analyzed. In
particular, the geometric version of the zeroth law of the black hole
thermodynamics was proved. In this work we show how the IH mechanics can be
formulated in a dimension--independent fashion and derive the first law of BH
thermodynamics for arbitrary dimensional IH. We also propose a definition of
energy for non--rotating horizons.


title: Excising a boosted rotating black hole with overlapping grids

abstract:
  We use the overlapping grids method to construct a fourth order accurate
discretization of a first order reduction of the Klein-Gordon scalar field
equation on a boosted spinning black hole blackground in axisymmetry. This
method allows us to use a spherical outer boundary and excise the singularity
from the domain with a spheroidal inner boundary which is moving with respect
to the main grid. We discuss the use of higher order accurate energy conserving
schemes to handle the axis of symmetry and compare it with a simpler technique
based on regularity conditions. We also compare the single grid long term
stability property of this formulation of the wave equation with that of a
different first order reduction.


title:
Radial geodesics as a microscopic origin of black hole entropy. III:
  Exercise with the Kerr-Newman black hole

abstract:
  We specify an angular motion on geodesics to reduce the problem to the case
of radial motion elaborated in previous chapters. An appropriate value of
entropy for a charged and rotating black hole is obtained by calculating the
partition function on thermal geodesics confined under horizons. The quantum
aggregation is classified in a similar way to the Reissner--Nordstrom black
hole.


title: The KKW Generalized Analysis for a Magnetic Stringy Black Hole

abstract:
  We apply the Keski-Vakkuri, Kraus and Wilczek (KKW) generalized analysis to a
magnetic stringy black hole solution to compute its temperature and entropy.
The solution that we choose in the Einstein-dilaton-Maxwell theory is the dual
solution known as the magnetic black hole solution. Our results show that the
expressions of the temperature and entropy of this non-Schwarzschild-type black
hole are not the Hawking temperature and the Bekenstein-Hawking entropy,
respectively. In addition, the extremal magnetic stringy black hole is not
frozen because it has a constant non-zero temperature.


title: Slice Energy and Conformal Frames in Theories of Gravitation

abstract:
  We examine and compare the behaviour of the scalar field slice energy in
different classes of theories of gravity, in particular higher-order and
scalar-tensor theories. We find a universal formula for the energy and compare
the resulting conservation laws with those known in general relativity. This
leads to a comparison between the inflaton, the dilaton and other forms of
scalar fields present in these generalized theories. It also shows that all
such conformally-related, generalized theories of gravitation allow for the
energy on a slice to be invariably defined and its fundamental properties be
insensitive to conformal transformations.


title: On Useful Conformal Tranformations In General Relativity

abstract:
  Local conformal transformations are known as a useful tool in various
applications of the gravitational theory, especially in cosmology. We describe
some new aspects of these transformations, in particular using them for
derivation of Einstein equations for the cosmological and Schwarzschild
metrics. Furthermore, the conformal transformation is applied for the
dimensional reduction of the Gauss-Bonnet topological invariant in $d=4$ to the
spaces of lower dimensions.


title:
Cosmological perturbations of brane-induced gravity and the vDVZ
  discontinuity on FLRW space-times

abstract:
  We investigate the cosmological perturbations of the brane-induced
(Dvali-Gabadadze-Porrati) model which exhibits a van Dam-Veltman-Zakharov
(vDVZ) discontinuity when linearized over a Minkowski background. We show that
the linear brane scalar cosmological perturbations over an arbitrary
Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time have a well defined limit
when the radius of transition between 4D and 5D gravity is sent to infinity
with respect to the background Hubble radius. This radius of transition plays
for the brane-induced gravity model a role equivalent to the Compton wavelength
of the graviton in a Pauli-Fierz theory, as far as the vDVZ discontinuity is
concerned. This well defined limit is shown to obey the linearized 4D
Einstein's equations whenever the Hubble factor is non vanishing. This shows
the disappearance of the vDVZ discontinuity for general FLRW background, and
extends the previously know result for maximally-symmetric space-times of non
vanishing curvature. Our reasoning is valid for matter with simple equation of
state such as a scalar field, or a perfect fluid with adiabatic perturbations,
and involves to distinguish between space-times with a vanishing scalar
curvature and space-times with a non vanishing one. We also discuss the
validity of the linear perturbation theory, in particular for those FLRW
space-times where the Ricci scalar is vanishing only on a set of zero measure.
In those cases, we argue that the linear perturbation theory breaks down when
the Ricci scalar vanishes (and the radius of transition is sent to infinity),
in a way similar to what has been found to occur around sources on a Minkowski
background.


title:
Boundary conditions for Einstein's field equations: Analytical and
  numerical analysis

abstract:
  Outer boundary conditions for strongly and symmetric hyperbolic formulations
of 3D Einstein's field equations with a live gauge condition are discussed. The
boundary conditions have the property that they ensure constraint propagation
and control in a sense made precise in this article the physical degrees of
freedom at the boundary. We use Fourier-Laplace transformation techniques to
find necessary conditions for the well posedness of the resulting
initial-boundary value problem and integrate the resulting three-dimensional
nonlinear equations using a finite-differencing code. We obtain a set of
constraint-preserving boundary conditions which pass a robust numerical
stability test. We explicitly compare these new boundary conditions to
standard, maximally dissipative ones through Brill wave evolutions. Our
numerical results explicitly show that in the latter case the constraint
variables, describing the violation of the constraints, do not converge to zero
when resolution is increased while for the new boundary conditions, the
constraint variables do decrease as resolution is increased. As an application,
we inject pulses of ``gravitational radiation'' through the boundaries of an
initially flat spacetime domain, with enough amplitude to generate strong
fields and induce large curvature scalars, showing that our boundary conditions
are robust enough to handle nonlinear dynamics.
  We expect our boundary conditions to be useful for improving the accuracy and
stability of current binary black hole and binary neutron star simulations, for
a successful implementation of characteristic or perturbative matching
techniques, and other applications. We also discuss limitations of our approach
and possible future directions.


title: Boundary Conditions for the Einstein Evolution System

abstract:
  New boundary conditions are constructed and tested numerically for a general
first-order form of the Einstein evolution system. These conditions prevent
constraint violations from entering the computational domain through timelike
boundaries, allow the simulation of isolated systems by preventing physical
gravitational waves from entering the computational domain, and are designed to
be compatible with the fixed-gauge evolutions used here. These new boundary
conditions are shown to be effective in limiting the growth of constraints in
3D non-linear numerical evolutions of dynamical black-hole spacetimes.


title: A quantum mass-spectrum of Kerr black hole: superstrings

abstract:
  Using thermal quantization of geodesics confined under horizons and
reasonable conjecture on massless modes, we evaluate quantum spectrum of Kerr
black hole masses compatible with superstring symmetries.


title: Rotating embedded black holes: Entropy and Hawking's radiation

abstract:
  In this paper we derive a class of rotating embedded black holes. Then we
study Hawking's radiation effects on these embedded black holes. The surface
gravity, entropy and angular velocity are given for each of these black holes.


title:
Multiresolution techniques for the detection of gravitational-wave
  bursts

abstract:
  We present two search algorithms that implement logarithmic tiling of the
time-frequency plane in order to efficiently detect astrophysically unmodeled
bursts of gravitational radiation. The first is a straightforward application
of the dyadic wavelet transform. The second is a modification of the windowed
Fourier transform which tiles the time-frequency plane for a specific Q. In
addition, we also demonstrate adaptive whitening by linear prediction, which
greatly simplifies our statistical analysis. This is a methodology paper that
aims to describe the techniques for identifying significant events as well as
the necessary pre-processing that is required in order to improve their
performance. For this reason we use simulated LIGO noise in order to illustrate
the methods and to present their preliminary performance.


title:
Energy and Momentum Distributions of the Magnetic Solution to (2+1)
  Einstein-Maxwell Gravity

abstract:
  We use Moeller's energy-momentum complex in order to explicitly evaluate the
energy and momentum density distributions associated with the three-dimensional
magnetic solution to the Einstein-Maxwell equations. The magnetic spacetime
under consideration is a one-parametric solution describing the distribution of
a radial magnetic field in a three-dimensional AdS background, and representing
the superposition of the magnetic field with a 2+1 Einstein static
gravitational field.


title: Radiation of Quantized Black Hole

abstract:
  The maximum entropy of a quantized surface is demonstrated to be proportional
to the surface area in the classical limit. The general structure of the
horizon spectrum and the value of the Barbero-Immirzi parameter are found. The
discrete spectrum of thermal radiation of a black hole fits naturally the Wien
profile. The natural widths of the lines are very small as compared to the
distances between them. The total intensity of the thermal radiation is
calculated.


title: On one fundamental property of gravitational field in the field theory

abstract:
  It is shown that the universal property of gravitational field to slow down
the rate of time leads in the field theory to a fundamental property --
generation of effective forces of repulsion.


title: Plans for the LIGO-TAMA Joint Search for Gravitational Wave Bursts

abstract:
  We describe the plans for a joint search for unmodelled gravitational wave
bursts being carried out by the LIGO and TAMA collaborations using data
collected during February-April 2003. We take a conservative approach to
detection, requiring candidate gravitational wave bursts to be seen in
coincidence by all four interferometers. We focus on some of the complications
of performing this coincidence analysis, in particular the effects of the
different alignments and noise spectra of the interferometers.


title: Observable form of pulses emitted from relativistic collapsing objects

abstract:
  In this work, we discuss observable characteristics of the radiation emitted
from a surface of a collapsing object. We study a simplified model in which a
radiation of massless particles has a sharp in time profile and it happens at
the surface at the same moment of comoving time. Since the radiating surface
has finite size the observed radiation will occur during some finite time. Its
redshift and bending angle are affected by the strong gravitational field. We
obtain a simple expression for the observed flux of the radiation as a function
of time. To find an explicit expression for the flux we develop an analytical
approximation for the bending angle and time delay for null rays emitted by a
collapsing surface. In the case of the bending angle this approximation is an
improved version of the earlier proposed Beloborodov-Leahy-approximation. For
rays emitted at $R > 2R_g$ the accuracy of the proposed improved approximations
for the bending angle and time delay is of order (or less) than 2-3%. By using
this approximation we obtain an approximate analytical expression for the
observed flux and study its properties.


title: Cosmic String Spacetime in Dilaton Gravity and Flat Rotation Curves

abstract:
  In dilaton gravity theories, we consider a string-like topological defect
formed during U(1) gauge symmetry-breaking phase transition in the early
Universe, and far from the cosmic string we have vacuum solutions of the
generalized Einstein equation. We discuss how they can be related to the
flatness of galactic rotation curves.


title:
Classical evolution and quantum generation in generalized gravity
  theories including string corrections and tachyon: Unified analyses

abstract:
  We present cosmological perturbation theory based on generalized gravity
theories including string theory correction terms and a tachyonic complication.
The classical evolution as well as the quantum generation processes in these
variety of gravity theories are presented in unified forms. These apply both to
the scalar- and tensor-type perturbations. Analyses are made based on the
curvature variable in two different gauge conditions often used in the
literature in Einstein's gravity; these are the curvature variables in the
comoving (or uniform-field) gauge and the zero-shear gauge. Applications to
generalized slow-roll inflations and its consequent power spectra are derived
in unified forms which include wide range of inflationary scenarios based on
Einstein's gravity and others.


title:
Relativistic-Newtonian correspondence of the zero-pressure but weakly
  nonlinear cosmology

abstract:
  It is well known that couplings occur among the scalar-, vector-, and
tensor-type perturbations of Friedmann world model in the second perturbational
order. Here, we prove that, except for the gravitational wave contribution, the
relativistic zero-pressure irrotational fluid perturbed to second order in a
flat Friedmann background coincides exactly with the Newtonian result. Since we
include the cosmological constant, our results are relevant to currently
favoured cosmology. As we prove that the Newtonian hydrodynamic equations are
valid in all cosmological scales to the second order, our result has an
important practical implication that one can now use the large-scale Newtonian
numerical simulation more reliably even as the simulation scale approaches and
even goes beyond the horizon. That is, our discovery shows that, in the
zero-pressure case, except for the gravitational wave contribution, there are
no relativistic correction terms even near and beyond the horizon to the
second-order perturbation.


title:
Second order perturbations of a zero-pressure cosmological medium:
  Proofs of the relativistic-Newtonian correspondence

abstract:
  The dynamic world model and its linear perturbations were first studied in
Einstein's gravity. In the system without pressure the relativistic equations
coincide exactly with the later known ones in Newton's gravity. Here we prove
that, except for the gravitational wave contribution, even to the second-order
perturbations, equations for the relativistic irrotational zero-pressure fluid
in a flat Friedmann background coincide exactly with the previously known
Newtonian equations. Thus, to the second order, we correctly identify the
relativistic density and velocity perturbation variables, and we expand the
range of applicability of the Newtonian medium without pressure to all
cosmological scales including the super-horizon scale. In the relativistic
analyses, however, we do not have a relativistic variable which corresponds to
the Newtonian potential to the second order. Mixed usage of different gauge
conditions is useful to make such proofs and to examine the result with
perspective. We also present the gravitational wave equation to the second
order. Since our correspondence includes the cosmological constant, our results
are relevant to currently favoured cosmology. Our result has an important
practical implication that one can use the large-scale Newtonian numerical
simulation more reliably even as the simulation scale approaches near horizon.


title:
Third order perturbations of a zero-pressure cosmological medium: Pure
  general relativistic nonlinear effects

abstract:
  We consider a general relativistic zero-pressure irrotational cosmological
medium perturbed to the third order. We assume a flat Friedmann background but
include the cosmological constant. We ignore the rotational perturbation which
decays in expanding phase. In our previous studies we discovered that, to the
second-order perturbation, except for the gravitational wave contributions, the
relativistic equations coincide exactly with the previously known Newtonian
ones. Since the Newtonian second-order equations are fully nonlinear, any
nonvanishing third and higher order terms in the relativistic analyses are
supposed to be pure relativistic corrections. In this work we derive such
correction terms appearing in the third order. Continuing our success in the
second-order perturbations we take the comoving gauge. We discover that the
third-order correction terms are of $\phi_v$-order higher than the second-order
terms where $\phi_v$ is a gauge-invariant combination related to the
three-space curvature perturbation in the comoving gauge; compared with the
Newtonian potential we have $\delta \Phi \sim {3 \over 5} \phi_v$ to the linear
order. Therefore, the pure general relativistic effects are of $varphi_v$-order
higher than the Newtonian ones. The corrections terms are independent of the
horizon scale and depend only on the linear order gravitational potential
perturbation strength. From the temperature anisotropy of cosmic microwave
background we have ${\delta T \over T} \sim {1 \over 3} \delta \Phi \sim {1
\over 5} \phi_v \sim 10^{-5}$. Therefore, our present result reinforces our
previous important practical implication that near current era one can use the
large-scale Newtonian numerical simulation more reliably even as the simulation
scale approaches near the horizon.


title: Old and new research on the Absolute Parallelism theory

abstract:
  Compatible equations, Singularities of solutions, Topological charges and
quasi-charges.
  PhD thesis (translated frorm Russian).
  The book shows the sights of Absolute Parallelism (AP), and contains useful
information on the problem of singularities, compatibility theory, homotopy
groups (also relative and k-ad), topological quasi-charge groups and their
morphisms. AP is a single (frame) field theory proposed by Einstein some 80
years ago; it embraces symmetries of both Special and General Relativity.
  The compatibility theory, if applied to the cases when the frame matrix
degenerates, gives a covariant test on singularities of solutions. This gives a
single variant (missed in Einstein-Mayer's list of compatible equations), the
unique 5D equation (nothing, nor D, can be changed), which solutions are free
of emerging singularities. SO4-symmetrical nonstationary solutions give rise to
a cosmological model (relativistic surfing; anti-Milne model in FRW framework)
with a specific reduction of the extra-dimension.
  Topological classification of localized field configurations, combinatorics
of topological quasi-charges (quanta), is discussed in an attempt to imagine
the Standard Model (and quantum theory itself; and, perhaps, to make some
qualitative predictions, like the absence of spin zero elementary quanta).


title:
The Gravitational Field of Massive Non-Charged Point Source in General
  Relativity

abstract:
  Utilizing various gauges of the radial coordinate we give a description of
static spherically symmetric space-times with point singularity at the center
and vacuum outside the singularity. We show that in general relativity (GR)
there exist a two-parameters family of such solutions to the Einstein equations
which are physically distinguishable but only some of them describe the
gravitational field of a single massive point particle with nonzero bare mass
$M_0$. In particular, the widespread Hilbert's form of Schwarzschild solution,
which depends only on the Keplerian mass $M<M_0$, does not solve the Einstein
equations with a massive point particle's stress-energy tensor as a source.
Novel normal coordinates for the field and a new physical class of gauges are
proposed, in this way achieving a correct description of a point mass source in
GR. We also introduce a gravitational mass defect of a point particle and
determine the dependence of the solutions on this mass defect. The result can
be described as a change of the Newton potential $\phi_{{}_N}=-G_{{}_N}M/r$ to
a modified one: $\phi_{{}_G}=-G_{{}_N}M/ (r+G_{{}_N} M/c^2\ln{{M_0}\over M})$
and a corresponding modification of the four-interval. In addition we give
invariant characteristics of the physically and geometrically different classes
of spherically symmetric static space-times created by one point mass. These
space-times are analytic manifolds with a definite singularity at the place of
the matter particle.


title: Non-stationary rotating black holes: Entropy and Hawking's radiation

abstract:
  We derive a class of non-stationary embedded rotating black holes and study
the Hawking's radiation effects on these embedded black holes. The surface
gravity, entropy and angular velocity, which are three important properties of
black holes, are presented for each of these embedded black holes.


title: Massive spinor fields in flat spacetimes with non-trivial topology

abstract:
  The vacuum expectation value of the stress-energy tensor is calculated for
spin $1\over 2$ massive fields in several multiply connected flat spacetimes.
We examine the physical effects of topology on manifolds such as $R^3 \times
S^1$, $R^2\times T^2$, $R^1 \times T^3$, the Mobius strip and the Klein bottle.
We find that the spinor vacuum stress tensor has the opposite sign to, and
twice the magnitude of, the scalar tensor in orientable manifolds. Extending
the above considerations to the case of Misner spacetime, we calculate the
vacuum expectation value of spinor stress-energy tensor in this space and
discuss its implications for the chronology protection conjecture.


title: Canonical structure of 3D gravity with torsion

abstract:
  We study the canonical structure of the topological 3D gravity with torsion,
assuming the anti-de Sitter asymptotic conditions. It is shown that the Poisson
bracket algebra of the canonical generators has the form of two independent
Virasoro algebras with classical central charges. In contrast to the case of
general relativity with a cosmological constant, the values of the central
charges are different from each other.


title: Varying Couplings in Electroweak Theory

abstract:
  We extend the theory of Kimberly and Magueijo for the spacetime variation of
the electroweak couplings in the unified Glashow-Salam-Weinberg model of the
electroweak interaction to include quantum corrections. We derive the effective
quantum-corrected dilaton evolution equations in the presence of a background
cosmological matter density that is composed of weakly interacting and
non-weakly-interacting non-relativistic dark-matter components.


title: Introduction to Quantum-Gravity Phenomenology

abstract:
  After a brief review of the first phase of development of Quantum-Gravity
Phenomenology, I argue that this research line is now ready to enter a more
advanced phase: while at first it was legitimate to resort to heuristic
order-of-magnitude estimates, which were sufficient to establish that
sensitivity to Planck-scale effects can be achieved, we should now rely on
detailed analyses of some reference test theories. I illustrate this point in
the specific example of studies of Planck-scale modifications of the
energy/momentum dispersion relation, for which I consider two test theories.
Both the photon-stability analyses and the Crab-nebula synchrotron-radiation
analyses, which had raised high hopes of ``beyond-Plankian'' experimental
bounds, turn out to be rather ineffective in constraining the two test
theories. Examples of analyses which can provide constraints of rather wide
applicability are the so-called ``time-of-flight analyses'', in the context of
observations of gamma-ray bursts, and the analyses of the cosmic-ray spectrum
near the GZK scale.


title: Mining metrics for buried treasure

abstract:
  The same but different: That might describe two metrics. On the surface
CLASSI may show two metrics are locally equivalent, but buried beneath one may
be a wealth of further structure. This was beautifully described in a paper by
M.A.H. MacCallum in 1998. Here I will illustrate the effect with two flat
metrics -- one describing ordinary Minkowski spacetime and the other describing
a three-parameter family of Gal'tsov-Letelier-Tod spacetimes. I will dig out
the beautiful hidden classical singularity structure of the latter (a structure
first noticed by Tod in 1994) and then show how quantum considerations can
illuminate the riches. I will then discuss how quantum structure can help us
understand classical singularities and metric parameters in a variety of exact
solutions mined from the Exact Solutions book.


title: Quantum theory of scalar field in isotropic world

abstract:
  Fock representations are constructed for a free scalar field in the closed
and quasi-Euclidean isotropic cosmological models. Invariance of their cyclic
vector (vacuum) under isometries and the correspondence principle single out a
class of unitarily equivalent representations.


title: Five-dimensional black strings in Einstein-Gauss-Bonnet gravity

abstract:
  We consider black-string-type solutions in five-dimensional
Einstein-Gauss-Bonnet gravity. Numerically constructed solutions under static,
axially symmetric and translationally invariant metric ansatz are presented.
The solutions are specified by two asymptotic charges: mass of a black string
and a scalar charge associated with the radion part of the metric. Regular
black string solutions are found if and only if the two charges satisfy a
fine-tuned relation, and otherwise the spacetime develops a singular event
horizon or a naked singularity. We can also generate bubble solutions from the
black strings by using a double Wick rotation.


title:
Comments on the paper by S. Samuel "On the speed of gravity and the
  Jupiter/Quasar measurement"

abstract:
  Recent review article by S. Samuel "On the speed of gravity and the
Jupiter/Quasar measurement" published in the International Journal of Modern
Physics D13, 1753 (2004) provides the reader with a misleading "theory" of the
relativistic time delay in general theory of relativity. Furthermore, it
misquotes original publications by Kopeikin and Fomalont & Kopeikin related to
the measurement of the speed of gravity by VLBI. We summarize the general
relativistic principles of the Lorentz-invariant theory of propagation of light
in time-dependent gravitational field, derive Lorentz-invariant expression for
the relativistic time delay, and finally explain why Samuel's "theory" is
conceptually incorrect and confuses the speed of gravity with the speed of
light.


title:
Charged Axially Symmetric Solution, Energy and Angular Momentum in
  Tetrad Theory of Gravitation

abstract:
  Charged axially symmetric solution of the coupled gravitational and
electromagnetic fields in the tetrad theory of gravitation is derived. The
metric associated with this solution is an axially symmetric metric which is
characterized by three parameters ``$ $the gravitational mass $M$, the charge
parameter $Q$ and the rotation parameter $a$". The parallel vector fields and
the electromagnetic vector potential are axially symmetric. We calculate the
total exterior energy. The energy-momentum complex given by M{\o}ller in the
framework of the Weitzenb$\ddot{o}$ck geometry ``$ ${\it characterized by
vanishing the curvature tensor constructed from the connection of this
geometry}" has been used. This energy-momentum complex is considered as a
better definition for calculation of energy and momentum than those of general
relativity theory. The energy contained in a sphere is found to be consistent
with pervious results which is shared by its interior and exterior. Switching
off the charge parameter, one finds that no energy is shared by the exterior of
the charged axially symmetric solution. The components of the momentum density
are also calculated and used to evaluate the angular momentum distribution. We
found no angular momentum contributes to the exterior of the charged axially
symmetric solution if zero charge parameter is used.


title: WANDs of the Black Ring

abstract:
  Necessary conditions for various algebraic types of the Weyl tensor are
determined. These conditions are then used to find Weyl aligned null directions
for the black ring solution. It is shown that the black ring solution is
algebraically special, of type I_i, while locally on the horizon the type is
II. One exceptional subclass - the Myers-Perry solution - is of type D.


title: Perspective on gravitational self-force analyses

abstract:
  A point particle of mass $\mu$ moving on a geodesic creates a perturbation
$h_{ab}$, of the spacetime metric $g_{ab}$, that diverges at the particle.
Simple expressions are given for the singular $\mu/r$ part of $h_{ab}$ and its
distortion caused by the spacetime. This singular part $h^\SS_{ab}$ is
described in different coordinate systems and in different gauges. Subtracting
$h^\SS_{ab}$ from $h_{ab}$ leaves a regular remainder $h^\R_{ab}$. The
self-force on the particle from its own gravitational field adjusts the world
line at $\Or(\mu)$ to be a geodesic of $g_{ab}+h^\R_{ab}$; this adjustment
includes all of the effects of radiation reaction. For the case that the
particle is a small non-rotating black hole, we give a uniformly valid
approximation to a solution of the Einstein equations, with a remainder of
$\Or(\mu^2)$ as $\mu\to0$.
  An example presents the actual steps involved in a self-force calculation.
Gauge freedom introduces ambiguity in perturbation analysis. However,
physically interesting problems avoid this ambiguity.


title:
Canonical Quantization of the Electromagnetic Field on the Kerr
  Background

abstract:
  We investigate the canonical quantization of the electromagnetic field on the
Kerr background. We give new expressions for the expectation value of the
electromagnetic stress-energy tensor in various vacua states and give a
physical interpretation of the separate terms appearing in them. We numerically
calculate the luminosity in these states. We also study the form of the
renormalized stress-energy tensor close to the horizon when the electromagnetic
field is in the past Boulware state.


title: Pioneer's Anomaly and the Solar Quadrupole Moment

abstract:
  The trajectories of test particles moving in the gravitational field of a
non-spherically symmetric mass distribution become affected by the presence of
multipole moments. In the case of hyperbolic trajectories, the quadrupole
moment of an oblate mass induces a displacement of the trajectory towards the
mass source, an effect that can be interpreted as an additional acceleration
directed towards the source. Although this additional acceleration is not
constant, we perform a general relativistic analysis in order to evaluate the
possibility of explaining Pioneer's anomalous acceleration by means of the
observed Solar quadrupole moment, within the range of accuracy of the observed
anomalous acceleration. We conclude that the Solar quadrupole moment generates
an acceleration which is of the same order of magnitude of Pioneer's constant
acceleration only at distances of a few astronomical units.


title: The Search for Gravitational Waves

abstract:
  Experiments aimed at searching for gravitational waves from astrophysical
sources have been under development for the last 40 years, but only now are
sensitivities reaching the level where there is a real possibility of
detections being made within the next five years. In this article a history of
detector development will be followed by a description of current detectors
such as LIGO, VIRGO, GEO 600, TAMA 300, Nautilus and Auriga. Preliminary
results from these detectors will be discussed and related to predicted
detection rates for some types of sources. Experimental challenges for detector
design are introduced and discussed in the context of detector developments for
the future.


title:
Gravitational wave extraction based on Cauchy-characteristic extraction
  and characteristic evolution

abstract:
  We implement a code to find the gravitational news at future null infinity by
using data from a Cauchy code as boundary data for a characteristic code. This
technique of Cauchy-characteristic Extraction (CCE) allows for the unambiguous
extraction of gravitational waves from numerical simulations.


title: Covariant Linear Perturbations in a Concordance Model

abstract:
  We present the complete solution of the first order metric and density
perturbation equations in a spatially flat (K=0), Friedmann-Robertson-Walker
(FRW) universe filled with pressureless ideal fluid, in the presence of
cosmological constant. We use covariant linear perturbation formalism and the
comoving gauge condition to obtain the field and conservation equations. The
solution contains all modes of the perturbations, i.e. scalar, vector and
tensor modes, and we show that our results are in agreement with the Sachs &
Wolfe metric perturbation formalism.


title:
The stability of Killing-Cauchy horizons in colliding plane wave
  space-times

abstract:
  It is confirmed rigorously that the Killing-Cauchy horizons, which sometimes
occur in space-times representing the collision and subsequent interaction of
plane gravitational waves in a Minkowski background, are unstable with respect
to bounded perturbations of the initial waves, at least for the case in which
the initial waves have constant aligned polarizations.


title:
Post-Newtonian accurate parametric solution to the dynamics of spinning
  compact binaries in eccentric orbits: The leading order spin-orbit
  interaction

abstract:
  We derive Keplerian-type parametrization for the solution of post-Newtonian
(PN) accurate conservative dynamics of spinning compact binaries moving in
eccentric orbits. The PN accurate dynamics that we consider consists of the
third post-Newtonian accurate conservative orbital dynamics influenced by the
leading order spin effects, namely the leading order spin-orbit interactions.
The orbital elements of the representation are explicitly given in terms of the
conserved orbital energy, angular momentum and a quantity that characterizes
the leading order spin-orbit interactions in Arnowitt, Deser, and Misner-type
coordinates. Our parametric solution is applicable in the following two
distinct cases: (i) the binary consists of equal mass compact objects, having
two arbitrary spins, and (ii) the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. As
an application of our parametrization, we present gravitational wave
polarizations, whose amplitudes are restricted to the leading quadrupolar
order, suitable to describe gravitational radiation from spinning compact
binaries moving in eccentric orbits. The present parametrization will be
required to construct `ready to use' reference templates for gravitational
waves from spinning compact binaries in inspiralling eccentric orbits. Our
parametric solution for the post-Newtonian accurate conservative dynamics of
spinning compact binaries clearly indicates, for the cases considered, the
absence of chaos in these systems. Finally, we note that our parametrization
provides the first step in deriving a fully second post-Newtonian accurate
`timing formula', that may be useful for the radio observations of relativistic
binary pulsars like J0737-3039.


title: Anderson's localization in a random metric: applications to cosmology

abstract:
  It is considered an equation for the Lyapunov exponent $% \gamma $ in a
random metric for a scalar propagating wave field. At first order in frequency
this equation is solved explicitly. The localization length $L_{c}$ (reciprocal
of Re($\gamma $)) is obtained as function of the metric-fluctuation-distance
$\Delta R$ (function of disorder) and the frequency $\omega $ of the wave.
Explicitly, low-frequencies propagate longer than high, that is $L_{c}\omega
^{2}=C^{te}$. Direct applications with cosmological quantities like background
radiation microwave ($\lambda \sim 1/2\times 10^{-3}$ [m]) and the
Universe-length (`localization length' $L_{c}\sim 1.6\times 10^{25}$ [m])
permits to evaluate the metric-fluctuations-distance as $\Delta R\sim 10^{-35}$
[m], a number at order of the Planck's length.


title: Gravitational collapse of homogeneous scalar fields

abstract:
  Conditions under which gravity coupled to self interacting scalar field
determines singularity formation are found and discussed. It is shown that,
under a suitable matching with an external space, the boundary, if collapses
completely, may give rise to a naked singularity. Issues related to the
strength of the singularity are discussed.


title: Simple quantum cosmology: Vacuum energy and initial state

abstract:
  A static non-singular 10-dimensional closed Friedmann universe of Planck
size, filled with a perfect fluid with an equation of state with w = -2/3, can
arise spontaneously by a quantum fluctuation from nothing in 11-dimensional
spacetime. A quantum transition from this state can initiate the inflationary
quantum cosmology outlined in Ref. 2 [General Relativity and Gravitation 33,
1415, 2001 - gr-qc/0103021]. With no fine-tuning, that cosmology predicts about
60 e-folds of inflation and a vacuum energy density depending only on the
number of extra space dimensions (seven), G, h, c and the ratio between the
strength of gravity and the strength of the strong force. The fraction of the
total energy in the universe represented by this vacuum energy depends on the
Hubble constant. Hubble constant estimates from WMAP, SDSS, the Hubble Key
Project and Sunyaev-Zeldovich and X-ray flux measurements range from 60 to 72
km/(Mpc sec). With a mid-range Hubble constant of 65 km/(Mpc sec), the model in
Ref. 2 predicts Omega-sub-Lambda = 0.7


title:
Physics of the interior of a spherical, charged black hole with a scalar
  field

abstract:
  We analyse the physics of nonlinear gravitational processes inside a
spherical charged black hole perturbed by a self-gravitating massless scalar
field. For this purpose we created an appropriate numerical code. Throughout
the paper, in addition to investigation of the properties of the mathematical
singularities where some curvature scalars are equal to infinity, we analyse
the properties of the physical singularities where the Kretschmann curvature
scalar is equal to the planckian value. Using a homogeneous approximation we
analyse the properties of the spacetime near a spacelike singularity in
spacetimes influenced by different matter contents namely a scalar field,
pressureless dust and matter with ultrarelativistic isotropic pressure. We also
carry out full nonlinear analyses of the scalar field and geometry of spacetime
inside black holes by means of an appropriate numerical code with adaptive mesh
refinement capabilities. We use this code to investigate the nonlinear effects
of gravitational focusing, mass inflation, matter squeeze, and these effects
dependence on the initial boundary conditions. It is demonstrated that the
position of the physical singularity inside a black hole is quite different
from the positions of the mathematical singularities. In the case of the
existence of a strong outgoing flux of the scalar field inside a black hole it
is possible to have the existence of two null singularities and one central
$r=0$ singularity simultaneously.


title: Absence of pre-classical solutions in Bianchi I loop quantum cosmology

abstract:
  Loop quantum cosmology, the symmetry reduction of quantum geometry for the
study of various cosmological situations, leads to a difference equation for
its quantum evolution equation. To ensure that solutions of this equation act
in the expected classical manner far from singularities, additional
restrictions are imposed on the solution. In this paper, we consider the
Bianchi I model, both the vacuum case and the addition of a cosmological
constant, and show using generating function techniques that only the zero
solution satisfies these constraints. This implies either that there are
technical difficulties with the current method of quantizing the evolution
equation, or else loop quantum gravity imposes strong restrictions on the
physically allowed solutions.


title: Torsion Gravity: a Reappraisal

abstract:
  The role played by torsion in gravitation is critically reviewed. After a
description of the problems and controversies involving the physics of torsion,
a comprehensive presentation of the teleparallel equivalent of general
relativity is made. According to this theory, curvature and torsion are
alternative ways of describing the gravitational field, and consequently
related to the same degrees of freedom of gravity. However, more general
gravity theories, like for example Einstein-Cartan and gauge theories for the
Poincare and the affine groups, consider curvature and torsion as representing
independent degrees of freedom. By using an active version of the strong
equivalence principle, a possible solution to this conceptual question is
reviewed. This solution favors ultimately the teleparallel point of view, and
consequently the completeness of general relativity. A discussion of the
consequences for gravitation is presented.


title: Naked shell singularities on the brane

abstract:
  By utilizing non-standard slicings of 5-dimensional Schwarzschild and
Schwarzschild-AdS manifolds based on isotropic coordinates, we generate static
and spherically symmetric braneworld spacetimes containing shell-like naked
null singularities. For planar slicings, we find that the brane-matter sourcing
the solution is a perfect fluid with an exotic equation of state and a pressure
singularity where the brane crosses the bulk horizon. From a relativistic point
of view, such a singularity is required to maintain matter infinitesimally
above the surface of a black hole. From the point of view of the AdS/CFT
conjecture, the singular horizon can be seen as one possible quantum correction
to a classical black hole geometry. Various generalizations of planar slicings
are also considered for a Ricci-flat bulk, and we find that singular horizons
and exotic matter distributions are common features.


title: Bulk viscous FWR with time varying constants revisited

abstract:
  We study a full causal bulk viscous cosmological model with flat FRW
symmetries and where the ``constants'' $G,c$ and $\Lambda $ vary. We take into
account the possible effects of a $c-$variable into the curvature tensor in
order to outline the field equations. Using the Lie method we find the possible
forms of the ``constants'' $G$ and $c$ that make integrable the field equations
as well as the equation of state for the viscous parameter. It is found that
$G,c$ and $\Lambda $ follow a power law solution verifying the relationship
$G/c^{2}=\kappa .$ Once these possible forms have been obtained we calculate
the thermodynamical quantities of the model in order to determine the possible
values of the parameters that govern the quantities, finding that only a
growing $G$ and $c$ are possible while $% \Lambda $ behaves as a negative
decreasing function.


title: CMC-Slicings of Kottler-Schwarzschild-de Sitter Cosmologies

abstract:
  There is constructed, for each member of a one-parameter family of
cosmological models, which is obtained from the Kottler-Schwarzschild-de Sitter
spacetime by identification under discrete isometries, a slicing by spherically
symmetric Cauchy hypersurfaces of constant mean curvature. These slicings are
unique up to the action of the static Killing vector. Analytical and numerical
results are found as to when different leaves of these slicings do not
intersect, i.e. when the slicings form foliations.


title: Can Lightcone Fluctuations be Probed with Cosmological Backgrounds?

abstract:
  Finding signatures of quantum gravity in cosmological observations is now
actively pursued both from the theoretical and the experimental side. Recent
work has concentrated on finding signatures of light-cone fluctuations in the
CMB. Because in inflationary scenarios a Gravitational Wave Background (GWB) is
always emitted much before the CMB, we can ask, in the hypothesis where this
GWB could be observed, what is the imprint of light cone fluctuations on this
GWB. We show that due to the flat nature of the GWB spectrum, the effect of
lightcone fluctuations are negligible.


title: What kind of noncommutative geometry for quantum gravity ?

abstract:
  We give a brief account of the description of the standard model in
noncommutative geometry as well as the thermal time hypothesis, questioning
their relevance for quantum gravity.


title: Projectiles, pendula, and special relativity

abstract:
  The kind of flat-earth gravity used in introductory physics appears in an
accelerated reference system in special relativity. From this viewpoint, we
work out the special relativistic description of a ballistic projectile and a
simple pendulum, two examples of simple motion driven by earth-surface gravity.
The analysis uses only the basic mathematical tools of special relativity
typical of a first-year university course.


title:
Conformal geometrodynamics: True degrees of freedom in a truly canonical
  structure

abstract:
  The standard geometrodynamics is transformed into a theory of conformal
geometrodynamics by extending the ADM phase space for canonical general
relativity to that consisting of York's mean exterior curvature time, conformal
three-metric and their momenta. Accordingly, an additional constraint is
introduced, called the conformal constraint. In terms of the new canonical
variables, a diffeomorphism constraint is derived from the original momentum
constraint. The Hamiltonian constraint then takes a new form. It turns out to
be the sum of an expression that previously appeared in the literature and
extra terms quadratic in the conformal constraint. The complete set of the
conformal, diffeomorphism and Hamiltonian constraints are shown to be of first
class through the explicit construction of their Poisson brackets. The extended
algebra of constraints has as subalgebras the Dirac algebra for the
deformations and Lie algebra for the conformorphism transformations of the
spatial hypersurface. This is followed by a discussion of potential
implications of the presented theory on the Dirac constraint quantization of
general relativity. An argument is made to support the use of the York time in
formulating the unitary functional evolution of quantum gravity. Finally, the
prospect of future work is briefly outlined.


title: Black Holes with Skyrme Hair

abstract:
  This paper is intended to give a review of the recent developments on black
holes with Skyrme hair. The Einstein-Skyrme system is known to possess black
hole solutions with Skyrme hair. The spherically symmetric black hole skyrmion
with B=1 was the first discovered counter example of the no-hair conjecture for
black holes. Recently we found the B=2 axially symmetric black hole skyrmion.
In this system, the black hole at the center of the skyrmion absorbs the baryon
number partially, leaving fractional charge outside the horizon. Therefore the
baryon number is no longer conserved. We examine the B=1, 2 black hole
solutions in detail in this paper. The model has a natural extension to the
gauged version which can describe monopole black hole skyrmions. Callan and
Witten discussed the monopole catalysis of proton decay within the Skyrme
model. We apply the idea to the Einstein-Maxwell-Skyrme system and obtain
monopole black hole skyrmions. Remarkably there exist multi-black hole skyrmion
solutions in which the gravitational, electromagnetic, and strong forces
between the monopoles are all in balance. The solutions turn out to be stable
under spherically symmetric linear perturbations.


title: A mystery of conformal coupling

abstract:
  An origin and necessity of so called conformal (or,Penrose-Chernikov-Tagirov)
coupling of scalar field to the metric of n-dimensional Riemannian space-time
is discussed in brief. The corresponding general-relativistic field equation
implies a one-particle (quantum mechanical) Schrodinger Hamiltonian which
depends on the space-time dimensionality n, contrary to the Hamiltonian
constructed by quantization of geodesic motion, which is the same for any value
of n. In general, the Hamiltonians can coincide only for n = 4, the
dimensionality of the ordinarily observed Universe. In view of the fundamental
role of a scalar field in various cosmological models, this fact may be of
interest for models of brane worlds where n > 4 .


title: Fundamental decoherence in quantum gravity

abstract:
  A recently introduced discrete formalism allows to solve the problem of time
in quantum gravity in a relational manner. Quantum mechanics formulated with a
relational time is not exactly unitary and implies a fundamental mechanism for
decoherence of quantum states. The mechanism is strong enough to render the
black hole information puzzle unobservable.


title:
Non-Riemannian effective spacetime effects on Hawking radiation in
  superfluids

abstract:
  Riemannian effective spacetime description of Hawking radiation in $^{3}He-A$
superfluids is extended to non-Riemannian effective spacetime. An example is
given of non-Riemannian effective geometry of the rotational motion of the
superfluid vacuum around the vortex where the effective spacetime Cartan
torsion can be associated to the Hawking giving rise to a physical
interpretation of effective torsion recently introduced in the literature in
the form of an acoustic torsion in superfluid $^{4}He$ (PRD-70(2004),064004).
Curvature and torsion singularities of this $^{3}He-A$ fermionic superfluid are
investigated. This Lense-Thirring effective metric, representing the superfluid
vacuum in rotational motion, is shown not support Hawking radiation when the
isotropic $^{4}He$ is restored at far distances from the vortex axis. Hawking
radiation can be expressed also in topological solitons (moving domain walls)
in fermionic superfluids in non-Riemannian (teleparallel) $(1+1)$ dimensional
effective spacetime. A teleparallel solution is proposed where the
quasiparticle speed is determined from the teleparallel geometry.


title:
Uniformly Accelerated Charge in a Quantum Field: From Radiation Reaction
  to Unruh Effect

abstract:
  We present a stochastic theory for the nonequilibrium dynamics of charges
moving in a quantum scalar field based on the worldline influence functional
and the close-time-path (CTP or in-in) coarse-grained effective action method.
We summarize (1) the steps leading to a derivation of a modified
Abraham-Lorentz-Dirac equation whose solutions describe a causal semiclassical
theory free of runaway solutions and without pre-acceleration patholigies, and
(2) the transformation to a stochastic effective action which generates
Abraham-Lorentz-Dirac-Langevin equations depicting the fluctuations of a
particle's worldline around its semiclassical trajectory. We point out the
misconceptions in trying to directly relate radiation reaction to vacuum
fluctuations, and discuss how, in the framework that we have developed, an
array of phenomena, from classical radiation and radiation reaction to the
Unruh effect, are interrelated to each other as manifestations at the
classical, stochastic and quantum levels. Using this method we give a
derivation of the Unruh effect for the spacetime worldline coordinates of an
accelerating charge. Our stochastic particle-field model, which was inspired by
earlier work in cosmological backreaction, can be used as an analog to the
black hole backreaction problem describing the stochastic dynamics of a black
hole event horizon.


title:
Exact uncertainty principle and quantization: implications for the
  gravitational field

abstract:
  The quantization of the gravitational field is discussed within the exact
uncertainty approach. The method may be described as a Hamilton-Jacobi
quantization of gravity. It differs from previous approaches that take the
classical Hamilton-Jacobi equation as their starting point in that it
incorporates some new elements, in particular the use of a formalism of
ensembles in configuration space and the postulate of an exact uncertainty
relation. These provide the fundamental elements needed for the transition from
the classical theory to the quantum theory.


title:
Well-posedness of the scale-invariant tetrad formulation of the vacuum
  Einstein equations

abstract:
  We show that with a small modification, the formulation of the Einstein
equations of Uggla et al, which uses tetrad variables normalised by the
expansion, is a mixed symmetric hyperbolic/parabolic system. Well-posedness of
the Cauchy problem follows from a standard theorem.


title: Metric of a tidally distorted, nonrotating black hole

abstract:
  The metric of a tidally distorted, nonrotating black hole is presented in a
light-cone coordinate system that penetrates the event horizon and possesses a
clear geometrical meaning. The metric is expressed as an expansion in powers of
r/R << 1, where r is a measure of distance from the black hole and R is the
local radius of curvature of the external spacetime; this is assumed to be much
larger than M, the mass of the black hole. The metric is calculated up to a
remainder of order (r/R)^4, and it depends on a family of tidal gravitational
fields which characterize the hole's local environment. The coordinate system
allows an easy identification of the event horizon, and expressions are derived
for its surface gravity and the rates at which the tidal interaction transfers
mass and angular momentum to the black hole.


title: Dynamics of Asymptotic Diffeomorphisms in (2+1)-Dimensional Gravity

abstract:
  In asymptotically anti-de Sitter gravity, diffeomorphisms that change the
conformal boundary data can be promoted to genuine physical degrees of freedom.
I show that in 2+1 dimensions, the dynamics of these degrees of freedom is
described by a Liouville action, with the correct central charge to reproduce
the entropy of the BTZ black hole.


title:
The Equivalence Principle as a Stepping Stone from Special to General
  Relativity: A Socratic Dialog

abstract:
  In this paper we show how the student can be led to an understanding of the
connection between special relativity and general relativity by considering the
time dilation effect of clocks placed on the surface of the Earth. This paper
is written as a Socratic dialog between a lecturer Sam and a student Kim.


title:
Quasi-spherical gravitational collapse and the role of initial data,
  anisotropy and inhomogeneity

abstract:
  In this paper, the role of anisotropy and inhomogeneity has been studied in
quasi-spherical gravitational collapse. Also the role of initial data has been
investigated in characterizing the final state of collapse. Finally, a linear
transformation on the initial data set has been presented and its impact has
been discussed.


title: The field-to-particle transition problem

abstract:
  We formulate in an intuitive manner several conceptual aspects of the
field-to-particle transition problem which intends to extract physical
properties of elementary particles from specific field configurations. We
discuss the possibility of using the conceptual basis of the holographic
principle and the mathematical fundaments of nonlinear sigma models for the
field-to-particle transition. It is shown that certain classical gravitational
configurations in vacuum may contain physical parameters with discrete values,
and that they behave under rotations as particle-like objects.


title: Gravitation and Duality Symmetry

abstract:
  By generalizing the Hodge dual operator to the case of soldered bundles, and
working in the context of the teleparallel equivalent of general relativity, an
analysis of the duality symmetry in gravitation is performed. Although the
basic conclusion is that, at least in the general case, gravitation is not dual
symmetric, there is a particular theory in which this symmetry shows up. It is
a self dual (or anti-self dual) teleparallel gravity in which, due to the fact
that it does not contribute to the interaction of fermions with gravitation,
the purely tensor part of torsion is assumed to vanish. The ensuing fermionic
gravitational interaction is found to be chiral. Since duality is intimately
related to renormalizability, this theory may eventually be more amenable to
renormalization than teleparallel gravity or general relativity.


title: Testing the Newton law at long distances

abstract:
  Experimental tests of Newton law put stringent constraints on potential
deviations from standard theory with ranges from the millimeter to the size of
planetary orbits. Windows however remain open for short range deviations, below
the millimeter, as well as long range ones, of the order of or larger than the
size of the solar system. We discuss here the relation between long range tests
of the Newton law and the anomaly recorded on Pioneer 10/11 probes.


title: Relic gravitational waves and the generalized second law

abstract:
  The generalized second law of gravitational thermodynamics is applied to the
present era of accelerated expansion of the Universe. In spite of the fact that
the entropy of matter and relic gravitational waves inside the event horizon
diminish, the mentioned law is fulfilled provided that the expression for the
entropy density of the gravitational waves satisfies a certain condition.


title: Cosmic string scaling in flat space

abstract:
  We investigate the evolution of infinite strings as a part of a complete
cosmic string network in flat space. We perform a simulation of the network
which uses functional forms for the string position and thus is exact to the
limits of computer arithmetic. Our results confirm that the wiggles on the
strings obey a scaling law described by universal power spectrum. The average
distance between long strings also scales accurately with the time. These
results suggest that small-scale structure will also scale in expanding
universe, even in the absence of gravitational damping.


title: The basics of gravitational wave theory

abstract:
  Einstein's special theory of relativity revolutionized physics by teaching us
that space and time are not separate entities, but join as ``spacetime''. His
general theory of relativity further taught us that spacetime is not just a
stage on which dynamics takes place, but is a participant: The field equation
of general relativity connects matter dynamics to the curvature of spacetime.
Curvature is responsible for gravity, carrying us beyond the Newtonian
conception of gravity that had been in place for the previous two and a half
centuries. Much research in gravitation since then has explored and clarified
the consequences of this revolution; the notion of dynamical spacetime is now
firmly established in the toolkit of modern physics. Indeed, this notion is so
well established that we may now contemplate using spacetime as a tool for
other science. One aspect of dynamical spacetime -- its radiative character,
``gravitational radiation'' -- will inaugurate entirely new techniques for
observing violent astrophysical processes. Over the next one hundred years,
much of this subject's excitement will come from learning how to exploit
spacetime as a tool for astronomy. This article is intended as a tutorial in
the basics of gravitational radiation physics.


title: Novel Cauchy-horizon instability

abstract:
  The evolution of weak discontinuity is investigated on horizons in the
$n$-dimensional static solutions in the Einstein-Maxwell-scalar-$\Lambda$
system, including the Reissner-Nordstr\"om-(anti) de Sitter black hole. The
analysis is essentially local and nonlinear. We find that the Cauchy horizon is
unstable, whereas both the black-hole event horizon and the cosmological event
horizon are stable. This new instability, the so-called kink instability, of
the Cauchy horizon is completely different from the well-known
``infinite-blueshift'' instability. The kink instability makes the analytic
continuation beyond the Cauchy horizon unstable.


title: Hamiltonian Relaxation

abstract:
  Due to the complexity of the required numerical codes, many of the new
formulations for the evolution of the gravitational fields in numerical
relativity are not tested on binary evolutions. We introduce in this paper a
new testing ground for numerical methods based on the simulation of binary
neutron stars. This numerical setup is used to develop a new technique, the
Hamiltonian relaxation (HR), that is benchmarked against the currently most
stable simulations based on the BSSN method. We show that, while the length of
the HR run is somewhat shorter than the equivalent BSSN simulation, the HR
technique improves the overall quality of the simulation, not only regarding
the satisfaction of the Hamiltonian constraint, but also the behavior of the
total angular momentum of the binary. The latest quantity agrees well with
post-Newtonian estimations for point-mass binaries in circular orbits.


title: Rotating Fluids with Self-Gravitation in Bounded Domains

abstract:
  In this paper, we study the steady solutions of Euler-Poisson equations in
bounded domains with prescribed angular velocity. This models a rotating
Newtonian star consisting of a compressible perfect fluid with given equation
of state $P=e^S\rho^{\gamma}$. When the domain is a ball and the angular
velocity is constant, we obtain both existence and non-existence theorems,
depending on the adiabatic gas constant $\gamma$. In addition we obtain some
interesting properties of the solutions; e.g., monotonicity of the radius of
the star with both angular velocity and central density. We also prove that the
radius of a rotating spherically symmetric star, with given constant angular
velocity and constant entropy, is uniformly bounded independent of the central
density . This is physically striking and in sharp contrast to the case of the
nonrotating star. For general domains and variable angular velocities, both an
existence result for the isentropic equations of state and non-existence result
for the non-isentropic equation of state are also obtained.


title: Fluctuations, gravity, and the quantum potential

abstract:
  We show how the quantum potential arises in various ways and trace its
connection to quantum fluctuations and Fisher information along with its
realization in terms of Weyl curvature. It is a quantization factor for certain
classical systems as well as an expression for quantum matter in gravity
theories of Weyl-Dirac type. We extract theories and examples from the
literature, providing connections and interpretations, and make a few new
observations.