title: Can Spacetime be a Condensate?

abstract:
  We explore further the proposal that general relativity is the hydrodynamic
limit of some fundamental theories of the microscopic structure of spacetime
and matter, i.e., spacetime described by a differentiable manifold is an
emergent entity and the metric or connection forms are collective variables
valid only at the low energy, long wavelength limit of such micro-theories. In
this view it is more relevant to find ways to deduce the microscopic
ingredients of spacetime and matter from their macroscopic attributes than to
find ways to quantize general relativity because it would only give us the
equivalent of phonon physics, not the equivalents of atoms or quantum
electrodyanmics. It may turn out that spacetime is merely a representation of
collective state of matter in some limiting regime of interactions, which is
the view expressed by Sakharov. In this talk, working within the conceptual
framework of geometro-hydrodynamics, we suggest a new way to look at the nature
of spacetime inspired by Bose-Einstein Condensate (BEC) physics. We ask the
question whether spacetime could be a condensate, even without the knowledge of
what the `atom of spacetime' is. We begin with a summary of the main themes for
this new interpretation of cosmology and spacetime physics, and the `bottom-up'
approach to quantum gravity. We then describe the `Bosenova' experiment of
controlled collapse of a BEC and our cosmology-inspired interpretation of its
results. We discuss the meaning of a condensate in different context. We
explore how far this idea can sustain, its advantages and pitfalls, and its
implications on the basic tenets of physics and existing programs of quantum
gravity.


title: Phantom shell around black hole and global geometry

abstract:
  We describe the possible scenarios for the evolution of a thin spherically
symmetric self-gravitating phantom shell around the Schwarzschild black hole.
The general equations describing the motion of the shell with a general form of
equation of state are derived and analyzed. The different types of space-time
R- and T-regions and shell motion are classified depending on the parameters of
the problem. It is shown that in the case of a positive shell mass there exist
three scenarios for the shell evolution with an infinite motion and two
distinctive types of collapse. Analogous scenarios were classified for the case
of a negative shell mass. In particular this classification shows that it is
impossible for the physical observer to detect the fantom energy flow. We
shortly discuss the importance of our results for astrophysical applications.


title: General covariance and the objectivity of space-time point-events

abstract:
  "The last remnant of physical objectivity of space-time" is disclosed, beyond
the Leibniz equivalence, in the case of a continuous family of spatially
non-compact models of general relativity. The {\it physical individuation} of
point-events is furnished by the intrinsic degrees of freedom of the
gravitational field, (viz, the {\it Dirac observables}) that represent - as it
were - the {\it ontic} part of the metric field. The physical role of the {\it
epistemic} part (viz. the {\it gauge} variables) is likewise clarified. At the
end, a peculiar four-dimensional {\it holistic and structuralist} view of
space-time emerges which includes elements common to the tradition of both {\it
substantivalism} and {\it relationism}. The observables of our models undergo
real {\it temporal change} and thereby provide a counter-example to the thesis
of the {\it frozen-time} picture of evolution.
  Invited Contribution to the ESF 2004 Oxford Conference on Space-Time


title: On the twin paradox in a universe with a compact dimension

abstract:
  We consider the twin paradox of special relativity in a universe with a
compact spatial dimension. Such topology allows two twin observers to remain
inertial yet meet periodically. The paradox is resolved by considering the
relationship of each twin to a preferred inertial reference frame which exists
in such a universe because global Lorentz invariance is broken. The twins can
perform "global" experiments to determine their velocities with respect to the
preferred reference frame (by sending light signals around the cylinder, for
instance). Here we discuss the possibility of doing so with local experiments.
Since one spatial dimension is compact, the electrostatic field of a point
charge deviates from $1/r^2$. We show that although the functional form of the
force law is the same for all inertial observers, as required by local Lorentz
invariance, the deviation from 1/r2 is observer-dependent. In particular, the
preferred observer measures the largest field strength for fixed distance from
the charge.


title:
Black hole head-on collisions and gravitational waves with fixed
  mesh-refinement and dynamic singularity excision

abstract:
  We present long-term-stable and convergent evolutions of head-on black hole
collisions and extraction of gravitational waves generated during the merger
and subsequent ring-down. The new ingredients in this work are the use of fixed
mesh-refinement and dynamical singularity excision techniques. We are able to
carry out head-on collisions with large initial separations and demonstrate
that our excision infrastructure is capable of accommodating the motion of the
individual black holes across the computational domain as well as their their
merger. We extract gravitational waves from these simulations using the
Zerilli-Moncrief formalism and find the ring-down radiation to be, as expected,
dominated by the l=2, m=0 quasi-normal mode. The total radiated energy is about
0.1 % of the total ADM mass of the system.


title:
Conformally symmetric vacuum solutions of the gravitational field
  equations in the brane-world models

abstract:
  A class of exact solutions of the gravitational field equations in the vacuum
on the brane are obtained by assuming the existence of a conformal Killing
vector field, with non-static and non-central symmetry. In this case the
general solution of the field equations can be obtained in a parametric form in
terms of the Bessel functions. The behavior of the basic physical parameters
describing the non-local effects generated by the gravitational field of the
bulk (dark radiation and dark pressure) is also considered in detail, and the
equation of state satisfied at infinity by these quantities is derived. As a
physical application of the obtained solutions we consider the behavior of the
angular velocity of a test particle moving in a stable circular orbit. The
tangential velocity of the particle is a monotonically increasing function of
the radial distance and, in the limit of large values of the radial coordinate,
tends to a constant value, which is independent on the parameters describing
the model. Therefore a brane geometry admitting a one-parameter group of
conformal motions may provide an explanation for the dynamics of the neutral
hydrogen clouds at large distances from the galactic center, which is usually
explained by postulating the existence of the dark matter.


title: Does the Holographic Principle determine the Gravitational Interaction?

abstract:
  It is likely that the holographic principle will be a consequence of the
would be theory of quantum gravity. Thus, it is interesting to try to go in the
opposite direction: can the holographic principle fix the gravitational
interaction? It is shown that the classical gravitational interaction is well
inside the set of potentials allowed by the holographic principle. Computations
clarify which role such a principle could have in lowering the value of the
cosmological constant computed in QFT to the observed one.


title:
Indirect Visibility of Gravitational Waves in Magnetohydrodynamic
  Plasmas

abstract:
  We propose a mechanism to make gravitational waves (GWs) visible in the
electromagnetic domain. Gravitational waves that propagate through a strongly
magnetized plasma interact with the plasma through its anisotropic
stress-energy tensor and excite magnetohydrodynamic (MHD) wave modes. In
catastrophic events such as the merger of a double neutron star binary, a large
fraction of the total binding energy of the system is released in the form of
GWs observable by LIGO, and the amount of energy transferred to the MHD waves
is substantial. These modes, however, are excited at the same frequency as the
GW and are not directly observable. In this paper we investigate radiation
processes that operate in the presence of the gravitationally excited MHD waves
and radiate in the radio regime accessible to LOFAR. We present order of
magnitude estimates for the spectral flux of a merger detectable by a LOFAR.


title: On the structure of the post-Newtonian expansion in general relativity

abstract:
  In the continuation of a preceding work, we derive a new expression for the
metric in the near zone of an isolated matter system in post-Newtonian
approximations of general relativity. The post-Newtonian metric, a solution of
the field equations in harmonic coordinates, is formally valid up to any order,
and is cast in the form of a particular solution of the wave equation, plus a
specific homogeneous solution which ensures the asymptotic matching to the
multipolar expansion of the gravitational field in the exterior of the system.
The new form provides some insights on the structure of the post-Newtonian
expansion in general relativity and the gravitational radiation reaction terms
therein.


title:
Non-minimal coupling for the gravitational and electromagnetic fields: A
  general system of equations

abstract:
  We establish a new self-consistent system of equations for the gravitational
and electromagnetic fields. The procedure is based on a non-minimal non-linear
extension of the standard Einstein-Hilbert-Maxwell action. General properties
of a three-parameter family of non-minimal linear models are discussed. In
addition, we show explicitly, that a static spherically symmetric charged
object can be described by a non-minimal model, second order in the derivatives
of the metric, when the susceptibility tensor is proportional to the
double-dual Riemann tensor


title: A new time-machine model with compact vacuum core

abstract:
  We present a class of curved-spacetime vacuum solutions which develope closed
timelike curves at some particular moment. We then use these vacuum solutions
to construct a time-machine model. The causality violation occurs inside an
empty torus, which constitutes the time-machine core. The matter field
surrounding this empty torus satisfies the weak, dominant, and strong energy
conditions. The model is regular, asymptotically-flat, and
topologically-trivial. Stability remains the main open question.


title: Towards a new approach to quantum gravity phenomenology

abstract:
  The idea that quantum gravity manifestations would be associated with a
violation of Lorentz invariance is very strongly bounded and faces serious
theoretical challenges. This leads us to consider an alternative line of
thought for such phenomenological search. We discuss the underlying viewpoint
and briefly mention its possible connections with current theoretical ideas. We
also outline the challenges that the experimental search of the effects would
seem to entail.


title: Hydrodynamics and global structure of rotating Schwarzschild black holes

abstract:
  Exploiting a rotating Schwarzschild black hole metric, we study hydrodynamic
properties of perfect fluid whirling inward toward the black holes along a
conical surface. On the equatorial plane of the rotating Schwarzschild black
hole, we derive radial equations of motion with effective potentials and the
Euler equation for steady state axisymmetric fuid. Moreover, numerical analysis
is performed to figure out effective potentials of particles on the rotating
Schwarzschild manifolds in terms of angular velocity, total energy and angular
momentum per unit rest mass. Higher dimensional global embeddings are also
constructed inside and outside the event horizons of the rotating Schwarzschild
black holes.


title: Blowup of smooth solutions for relativistic Euler equations

abstract:
  We study the singularity formation of smooth solutions of the relativistic
Euler equations in $(3+1)$-dimensional spacetime for both finite initial energy
and infinite initial energy. For the finite initial energy case, we prove that
any smooth solution, with compactly supported non-trivial initial data, blows
up in finite time. For the case of infinite initial energy, we first prove the
existence, uniqueness and stability of a smooth solution if the initial data is
in the subluminal region away from the vacuum. By further assuming the initial
data is a smooth compactly supported perturbation around a non-vacuum constant
background, we prove the property of finite propagation speed of such a
perturbation. The smooth solution is shown to blow up in finite time provided
that the radial component of the initial "generalized" momentum is sufficiently
large.


title: Exploring Fifth Force Interactions with 18th Century Technology

abstract:
  Many theories which unify gravity with the other known forces of nature
predict the existence of an intermediate-range ``fifth force'' similar to
gravity. Such a force could be manifest as a deviation from the gravitational
inverse-square law. Currently, at distances near $10^{-1}$m, the inverse-square
law is known to be correct to about one part per thousand. I present the design
of an experiment that will improve this limit by two orders of magnitude. This
is accomplished by constructing a torsion pendulum and source mass apparatus
that are particularly insensitive to Newtonian gravity and, simultaneously,
maximally sensitive to violations of the same.


title: The Schwarzschild black hole as a point particle

abstract:
  The description of a point mass in general relativity (GR) is given in the
framework of the field formulation of GR where all the dynamical fields,
including the gravitational field, are considered in a fixed background
spacetime. With the use of stationary (not static) coordinates non-singular at
the horizon, the Schwarzschild solution is presented as a point-like field
configuration in a whole background Minkowski space. The requirement of a
stable $\eta$-causality stated recently in [J.B.Pitts and W.C.Schieve, Found.
Phys., v. 34, 211 (2004)] is used essentially as a criterion for testing
configurations.


title: The affine gauge theory in the quantum phase space CP(N-1)

abstract:
  In the present article I propose a non-linear relativistic 4-d field model
originated by the internal dynamics in CP(N-1). There is no initially
distinction between `particle' and `field', and the space-time manifold is
derivable. The main idea is to base the theory on the relative amplitudes
solely. Quantum measurements will be described in terms of the parallel
transport of the local dynamical variables and a specific gauge reduction of
the full state vector to the Qubit coherent state. I will discuss here field
equations of quantum particle arising in the dynamical space-time.


title:
Metric-scalar gravity with torsion and the measurability of the
  non-minimal coupling

abstract:
  The "measurability" of the non-minimal coupling is discussed by considering
the correction to the Newtonian static potential in the semi-classical
approach. The coefficient of the "gravitational Darwin term" (GDT) gets
redefined by the non-minimal torsion-scalar couplings. Based on a similar
analysis of the GDT in the effective field theory approach to non-minimal
scalar we conclude that for reasonable values of the couplings the correction
is very small.


title:
Variable Eddington Factor and Radiating Slowly Rotating Bodies in
  General Relativity

abstract:
  We present an extension to a previous work to study the collapse of a
radiating, slow-rotating self-gravitating relativistic configuration. In order
to simulate dissipation effects due to the transfer of photons and/or neutrinos
within the matter configuration, we introduce the flux factor, the variable
Eddington factor and a closure relation between them. Rotation in General
Relativity is considered in the slow rotation approximation, i.e. tangential
velocity of every fluid element is much less than the speed of light and the
centrifugal forces are little compared with the gravitational ones. Solutions
are properly matched, up to the first order in the Kerr parameter, to the
exterior Kerr-Vaidya metric and the evolution of the physical variables are
obtained inside the matter configuration. To illustrate the method we work out
three models with different equations of state and several closure relations.
We have found that, for the closure relations considered, the matching
conditions implies that a total diffusion regime can not be attained at the
surface of the configuration. It has also been obtained that the eccentricity
at the surface of radiating configurations is greater for models near the
diffusion approximation than for those in the free streaming out limit. At
least for the static ``seed'' equations of state considered, the simulation we
performed show that these models have differential rotation and that the more
diffusive the model is, the slower it rotates.


title:
Matters of Gravity, the newsletter of the Topical Group on Gravitation
  of the Americal Physical Society

abstract:
  GGR News:
  Message from the Chair, by Jim Isenberg
  Einstein@Home, by Bernard Schutz
  We hear that..., by Jorge Pullin
  100 Years ago, by Jorge Pullin
  Research Briefs:
  What's new in LIGO, by David Shoemaker
  Frame-dragging in the news in 2004, by Cliff Will
  Cosmic (super)strings and LIGO, by Xavier Siemens
  Conference reports:
  The first gulf coast gravity conference, by Richard Price
  Imagining the future, by Shane Larson
  VI Mexican School, by Alejandro Corichi


title: Energy Transport in the Vaidya System

abstract:
  Energy transport mechanisms can be generated by imposing relations between
null tetrad Ricci components. Several kinds of mass and density transport
generated by these relations are studied for the generalized Vaidya system.


title: Relativistic superfluid hydrodynamics

abstract:
  Relativistic Riemannian superfluid hydrodynamics used in general relativity
to investigate superfluids in pulsars is extended to non-Riemannian background
spacetime endowed with Cartan torsion. From the Gross-Pitaeviskii (GP) it is
shown that in the weak field Cartan torsion approximation, the torsion vector
is orthogonal to the superfluid plane wave velocity. Torsion vector is also
shown to be aligned along the vortex direction in the superfluid. The
background torsion is shown to induce rotation on the fluid as happens with the
acoustic torsion in the analogue non-Riemannian non-relativistic superfluid
models. The torsion part of the current would be connected to the normal part
of the superfluid velocity while the Riemannian part of the velocity would be
connected to the superfluid velocity itself. Magnus effect and the rotation of
the superfluid are analysed. Since the Kalb-Ramond field is easily associated
with torsion our method seems to be equivalent to the vortex-cosmic string
relativistic superfluid method developed by Carter and Langlois to investigate
rotating neutron stars.


title: Superradiance from BEC vortices: a numerical study

abstract:
  The scattering of sound wave perturbations from vortex excitations of
Bose-Einstein condensates(BEC) is investigated by numerical integration of the
associated Klein-Gordon equation. It is found that, at sufficiently high
angular speeds, sound wave-packets can extract a sizeable fraction of the
vortex energy through a mechanism of superradiant scattering. It is conjectured
that this superradiant regime may be detectable in BEC experiments.


title: Coexisting vacua and effective gravity

abstract:
  Our Universe may be a domain separated by physical phase boundaries from
other domain-Universes with different vacuum energy density and matter content.
The coexistence of different quantum vacua is perhaps regulated by the exchange
of global fermionic charges or by fermion zero modes on the phase boundary. An
example would be a static de-Sitter Universe embedded in an asymptotically flat
spacetime.


title: Space-time: emerging vs. existing

abstract:
  The concept of the space-time as emerging in the world phase transition, vs.
a priori exiting, is put forward. The theory of gravity with two basic
symmetries, the global affine one and the general covariance, is developed.
Implications for the Universe are indicated.


title: Measures and metrics in uniform gravitational fields

abstract:
  A partially alternative derivation of the expression for the time dilation
effect in a uniform static gravitational field is obtained by means of a
thought experiment in which rates of clocks at rest at different heights are
compared using as reference a clock bound to a free falling reference system
(FFRS). Derivations along these lines have already been proposed, but generally
introducing some shortcut in order to make the presentation elementary. The
treatment is here exact: the clocks whose rates one wishes to compare are let
to describe their world lines (Rindler's hyperbolae) with respect to the FFRS,
and the result is obtained by comparing their lengths in space-time. The
exercise may nonetheless prove pedagogically instructive insofar as it shows
that the some results of General Relativity (GR) can be obtained in terms of
physical and geometrical reasoning without having recourse to the general
formalism. The corresponding GR metric is derived, to the purpose of making a
comparison with solutions of Einstein field equation and with other metrics.
For this reasons this paper also compels to deal with a few subtle points
inherent in the very foundations of GR.


title:
Strong cosmic censorship: the role of nearly extreme nonrotating black
  holes

abstract:
  In this paper it is argued that even invoking the dominant energy condition,
the Einstein's field equations admit nonglobally hyperbolic, asymptotically de
Sitter spacetimes with locally naked singularities and with Cauchy horizons
failing to be surfaces of infinite gravitational blueshift; what is more, it is
shown the existence of space-time solutions containing Cauchy horizons expected
to be stable against small linear nonstationary axisymmetric perturbations in
an open set of the physical parameter space where the positive cosmological
constant is nearly zero. The price to pay is a violation at ultrahigh densities
of Le Chatelier's principle. Given an equation of state, the line of thought
introduces black-hole Cauchy horizon instability criteria in terms of the
associated adiabatic index, revealing a connection between this subject and the
stability theory of relativistic stars. This is used to put forward a
tentative, limited formulation of the strong cosmic censorship principle inside
black holes (once called dark stars).


title: Relating Quantum Information to Charged Black Holes

abstract:
  Quantum non-cloning theorem and a thought experiment are discussed for
charged black holes whose global structure exhibits an event and a Cauchy
horizon. We take Reissner-Norstr\"{o}m black holes and two-dimensional dilaton
black holes as concrete examples. The results show that the quantum non-cloning
theorem and the black hole complementarity are far from consistent inside the
inner horizon. The relevance of this work to non-local measurements is briefly
discussed.


title:
Conformally coupled scalar solitons and black holes with negative
  cosmological constant

abstract:
  We present arguments for the existence of both globally regular and black
hole solutions of the Einstein equations with a conformally coupled scalar
field, in the presence of a negative cosmological constant, for space-time
dimensions greater than or equal to four. These configurations approach
asymptotically anti-de Sitter spacetime and are indexed by the central value of
the scalar field. We also study the stability of these solutions, and show
that, at least for all the solutions studied numerically, they are linearly
stable.


title: On the essential constants in Riemannian geometries

abstract:
  In the present work the problem of distinguishing between essential and
spurious (i.e., absorbable) constants contained in a metric tensor field in a
Riemannian geometry is considered. The contribution of the study is the
presentation of a sufficient and necessary criterion, in terms of a covariant
statement, which enables one to determine whether a constant is essential or
not. It turns out that the problem of characterization is reduced to that of
solving a system of partial differential equations of the first order. In any
case, the metric tensor field is assumed to be smooth with respect to the
constant to be tested. It should be stressed that the entire analysis is purely
of local character.


title: Wormholes and Time Travel? Not Likely

abstract:
  Wormholes have been advanced as both a method for circumventing the
limitations of the speed of light as well as a means for building a time
machine (to travel to the past). Thus it is argued that General Relativity may
allow both of these possibilities. In this note I argue that traversable
wormholes connecting otherwise causally disconnected regions, violate two of
the most fundamental principles physics, namely local energy conservation and
the energy-time uncertainty principle.


title: On the cylindrically symmetric Einstein-Vlasov system

abstract:
  For the cylindrically symmetric ''asymptotically flat'' Einstein equations in
the case of electro-vacuum it is known that solutions exist globally and also
that this class of spacetimes is causally geodesically complete. Hence strong
cosmic censorship holds for this class. An interesting question is whether
these results can be generalized to include spacetimes with phenomenological
matter, e.g. collisionless matter described by the Vlasov equation. Spherically
symmetric asymptotically flat solutions of the Einstein-Vlasov system with
small initial data are known to be causally geodesically complete. For
arbitrary (in size) data it has been shown that if a singularity occurs, the
first one occurs at the center of symmetry. In this paper we begin to study the
question of global existence for the cylindrically symmetric Einstein-Vlasov
system with general (in size) data and we show that if a singularity occurs at
all, the first one occurs at the axis of symmetry.


title:
Viable inhomogeneous model universe without dark energy from primordial
  inflation

abstract:
  A new model of the observed universe, using solutions to the full Einstein
equations, is developed from the hypothesis that our observable universe is an
underdense bubble, with an internally inhomogeneous fractal bubble distribution
of bound matter systems, in a spatially flat bulk universe. It is argued on the
basis of primordial inflation and resulting structure formation, that the
clocks of the isotropic observers in average galaxies coincide with clocks
defined by the true surfaces of matter homogeneity of the bulk universe, rather
than the comoving clocks at average spatial positions in the underdense bubble
geometry, which are in voids. This understanding requires a systematic
reanalysis of all observed quantities in cosmology. I begin such a reanalysis
by giving a model of the average geometry of the universe, which depends on two
measured parameters: the present matter density parameter, Omega_m, and the
Hubble constant, H_0. The observable universe is not accelerating. Nonetheless,
inferred luminosity distances are larger than naively expected, in accord with
the evidence of distant type Ia supernovae. The predicted age of the universe
is 15.3 +/-0.7 Gyr. The expansion age is larger than in competing models, and
may account for observed structure formation at large redshifts.


title:
Wave zone extraction of gravitational radiation in three-dimensional
  numerical relativity

abstract:
  We present convergent gravitational waveforms extracted from
three-dimensional, numerical simulations in the wave zone and with causally
disconnected boundaries. These waveforms last for multiple periods and are very
accurate, showing a peak error to peak amplitude ratio of 2% or better. Our
approach includes defining the Weyl scalar Psi_4 in terms of a three-plus-one
decomposition of the Einstein equations; applying, for the first time, a novel
algorithm due to Misner for computing spherical harmonic components of our wave
data; and using fixed mesh refinement to focus resolution on non-linear sources
while simultaneously resolving the wave zone and maintaining a causally
disconnected computational boundary. We apply our techniques to a (linear)
Teukolsky wave, and then to an equal mass, head-on collision of two black
holes. We argue both for the quality of our results and for the value of these
problems as standard test cases for wave extraction techniques.


title: $\mathcal{N}=1$ SUGRA Noether Charges

abstract:
  In this work a generic set of boundary conditions for $\mathcal{N}=1$ SUGRA
is proposed. This conditions defines that Hamiltonian charges equals Noether
ones, including supercharge.


title: Deformed black strings in 5-dimensional Einstein-Yang-Mills theory

abstract:
  We construct the first examples of deformed non-abelian black strings in a
5-dimensional Einstein-Yang-Mills model. Assuming all fields to be independent
of the extra coordinate, we construct deformed black strings, which in the
4-dimensional picture correspond to axially symmetric non-abelian black holes
in gravity-dilaton theory. These solutions thus have deformed S^2 x R horizon
topology. We study fundamental properties of the black strings and find that
for all choices of the gravitational coupling two branches of solutions exist.
The limiting behaviour of the second branch of solutions however depends
strongly on the choice of the gravitational coupling.


title: Dynamically generated embeddings of spacetime

abstract:
  We discuss how embeddings in connection with the Campbell-Magaard (CM)
theorem can have a physical interpretation. We show that any embedding whose
local existence is guaranteed by the CM theorem can be viewed as a result of
the dynamical evolution of initial data given in a four-dimensional spacelike
hypersurface. By using the CM theorem, we establish that for any analytic
spacetime, there exist appropriate initial data whose Cauchy development is a
five-dimensional vacuum space into which the spacetime is locally embedded. We
shall see also that the spacetime embedded is Cauchy stable with respect these
the initial data.


title:
Electromagnetic radiation due to naked singularity formation in
  self-similar gravitational collapse

abstract:
  Dynamical evolution of test fields in background geometry with a naked
singularity is an important problem relevant to the Cauchy horizon instability
and the observational signatures different from black hole formation. In this
paper we study electromagnetic perturbations generated by a given current
distribution in collapsing matter under a spherically symmetric self-similar
background. Using the Green's function method, we construct the formula to
evaluate the outgoing energy flux observed at the future null infinity. The
contributions from "quasi-normal" modes of the self-similar system as well as
"high-frequency" waves are clarified. We find a characteristic power-law time
evolution of the outgoing energy flux which appears just before naked
singularity formation, and give the criteria as to whether or not the outgoing
energy flux diverges at the future Cauchy horizon.


title: On the Entropy Increase in the Black Hole Formation

abstract:
  The entropy increases enormously when a star collapses into a black hole.
This entropy increase is interpreted as the decrease of the temperature due to
the increase of the volume. Through these investigation the microscopic states
of the black hole entropy is naturally understood as the statistical states of
the enlarged phase space.


title: Localized Particle States and Dynamics Gravitational Effects

abstract:
  Scalar particles--i.e., scalar-field excitations--in de Sitter space exhibit
behavior unlike either classical particles in expanding space or quantum
particles in flat spacetime. Their energies oscillate forever, and their
interactions are spread out in energy. Here it is shown that these features
characterize not only normal-mode excitations spread out over all space, but
localized particles or wave packets as well. Both one-particle and coherent
states of a massive, minimally coupled scalar field in de Sitter space,
associated with classical wave packets, are constructed explicitly. Their
energy expectation values and corresponding Unruh-DeWitt detector response
functions are calculated. Numerical evaluation of these quantities for a simple
set of classical wave packets clearly displays these novel features. Hence,
given the observed accelerating expansion of the Universe, it is possible that
observation of an ultralow-mass scalar particle could yield direct confirmation
of distinct predictions of quantum field theory in curved spacetime.


title: Understanding Our Universe: Current Status and Open Issues

abstract:
  Last couple of decades have been the golden age for cosmology. High quality
data confirmed the broad paradigm of standard cosmology but have thrusted upon
us a preposterous composition for the universe which defies any simple
explanation, thereby posing probably the greatest challenge theoretical physics
has ever faced. Several aspects of these developments are critically reviewed,
concentrating on conceptual issues and open questions. [Topics discussed
include: Cosmological Paradigm, Growth of structures in the universe, Inflation
and generation of initial perturbations, Temperature anisotropies of the CMBR,
Dark energy, Cosmological Constant, Deeper issues in cosmology.]


title: Canonical quantization and black hole perturbations

abstract:
  We examine the possibility of a constraint-free quantization of linearized
gravity, based on the Teukolsky equation for black hole perturbations. We
exhibit a simple quadratic (but complex) Lagrangian for the Teukolsky equation,
leading to the interpretation that the elementary excitations (gravitons bound
to the Kerr black hole) are unstable.


title: Some uniqueness results for dynamical horizons

abstract:
  We first show that the intrinsic, geometrical structure of a dynamical
horizon is unique. A number of physically interesting constraints are then
established on the location of trapped and marginally trapped surfaces in the
vicinity of any dynamical horizon. These restrictions are used to prove several
uniqueness theorems for dynamical horizons. Ramifications of some of these
results to numerical simulations of black hole spacetimes are discussed.
Finally several expectations on the interplay between isometries and dynamical
horizons are shown to be borne out.


title:
The leader operators of the $(d+1)$-dimensional relativistic rotating
  oscillators

abstract:
  The main pairs of leader operators of the quantum models of relativistic
rotating oscillators in arbitrary dimensions are derived. To this end one
exploits the fact that these models generate P\"{o}schl-Teller radial problems
with remarkable properties of supersymmetry and shape invariance.


title:
The separate universe and the back reaction of long wavelength
  fluctuations

abstract:
  We investigate the backreaction of cosmological long wavelength perturbations
on the evolution of the Universe. By applying the renormalization group method
to a Friedmann-Robertson-Walker universe with long wavelength fluctuations, we
demonstrate that the renormalized solution with the backreaction effect is
equivalent to that of the separate universe. Then, using the effective
Friedmann equation, we show that only non-adiabatic mode of long wavelength
fluctuations affects the expansion law of the spatially averaged universe.


title: The nature of spacetime singularities

abstract:
  Present knowledge about the nature of spacetime singularities in the context
of classical general relativity is surveyed. The status of the BKL picture of
cosmological singularities and its relevance to the cosmic censorship
hypothesis are discussed. It is shown how insights on cosmic censorship also
arise in connection with the idea of weak null singularities inside black
holes. Other topics covered include matter singularities and critical collapse.
Remarks are made on possible future directions in research on spacetime
singularities.


title: A 3+1 perspective on null hypersurfaces and isolated horizons

abstract:
  The isolated horizon formalism recently introduced by Ashtekar et al. aims at
providing a quasi-local concept of a black hole in equilibrium in an otherwise
possibly dynamical spacetime. In this formalism, a hierarchy of geometrical
structures is constructed on a null hypersurface. On the other side, the 3+1
formulation of general relativity provides a powerful setting for studying the
spacetime dynamics, in particular gravitational radiation from black hole
systems. Here we revisit the kinematics and dynamics of null hypersurfaces by
making use of some 3+1 slicing of spacetime. In particular, the additional
structures induced on null hypersurfaces by the 3+1 slicing permit a natural
extension to the full spacetime of geometrical quantities defined on the null
hypersurface. This 4-dimensional point of view facilitates the link between the
null and spatial geometries. We proceed by reformulating the isolated horizon
structure in this framework. We also reformulate previous works, such as
Damour's black hole mechanics, and make the link with a previous 3+1 approach
of black hole horizon, namely the membrane paradigm. We explicit all
geometrical objects in terms of 3+1 quantities, putting a special emphasis on
the conformal 3+1 formulation. This is in particular relevant for the initial
data problem of black hole spacetimes for numerical relativity. Illustrative
examples are provided by considering various slicings of Schwarzschild and Kerr
spacetimes.


title: Continuous distribution of frequencies and deformed dispersion relations

abstract:
  The possibilities that, in the realm of the detection of the so--called
deformed dispersion relation, a light source with a continuous distribution of
frequencies offers is discussed. It will be proved that the presence of finite
coherence length entails the emergence of a new term in the interference
pattern. This is a novel trait, which renders a new possibility in the quest
for bounds associated with these deformed dispersion relations.


title:
Brane Formation and Cosmological Constraint on the Number of Extra
  Dimensions

abstract:
  Special relativity is generalized to extra dimensions and quantized energy
levels of particles are obtained. By calculating the probability of particles'
motion in extra dimensions at high temperature of the early universe, it is
proposed that the branes may have not existed since the very beginning of the
universe, but formed later. Meanwhile, before the formation, particles of the
universe may have filled in the whole bulk, not just on the branes. This
scenario differs from that in the standard big bang cosmology in which all
particles are assumed to be in the 4D spacetime. So, in brane models, whether
our universe began from a 4D big bang singularity is questionable. A
cosmological constraint on the number of extra dimensions is also given which
favors $N\geq 7$.


title:
Quantum Mechanics without spacetime V - Why a quantum theory of gravity
  should be non-linear-

abstract:
  If there exists a formulation of quantum mechanics which does not refer to a
background classical spacetime manifold, it then follows as a consequence,
(upon making one plausible assumption), that a quantum description of gravity
should be necessarily non-linear. This is true independent of the mathematical
structure used for describing such a formulation of quantum mechanics. A
specific model which exhibits this non-linearity is constructed, using the
language of noncommutative geometry. We derive a non-linear Schrodinger
equation for the quantum dynamics of a particle; this equation reduces to the
standard linear Schrodinger equation when the mass of the particle is much
smaller than Planck mass. It turns out that the non-linear equation found by us
is very similar to a non-linear Schrodinger equation found by Doebner and
Goldin in 1992 from considerations of unitary representaions of the
infinite-dimensional group of diffeomorphisms in three spatial dimensions. Our
analysis suggests that the diffusion constant introduced by Doebner and Goldin
depends on the mass of the particle, and that this constant tends to zero in
the limit in which the particle mass is much smaller than Planck mass, so that
in this limit the non-linear theory reduces to standard linear quantum
mechanics. A similar effective non-linear Schrodinger equation was also found
for the quantum dynamics of a system of D0-branes, by Mavromatos and Szabo.


title:
Linear stability of Einstein-Gauss-Bonnet static spacetimes. Part I:
  tensor perturbations

abstract:
  We study the stability under linear perturbations of a class of static
solutions of Einstein-Gauss-Bonnet gravity in $D=n+2$ dimensions with spatial
slices of the form $\Sigma_{\k}^n \times {\mathbb R}^+$, $\Sigma_{\k}^n$ an
$n-$manifold of constant curvature $\k$. Linear perturbations for this class of
space-times can be generally classified into tensor, vector and scalar types.
The analysis in this paper is restricted to tensor perturbations.


title:
The Evaluation of the M{\o}ller Energy Complex in Difference Coordinate
  Representations

abstract:
  The M{\o}ller energy complex of Schwarzschild black hole solution in several
coodinates are evaluated. Our results show that the M{\o}ller energy complex is
independent of not only the purely spatial transformation, but also the shift
of time coordinate. So, we could conclude that a shift of time coordinates will
not change the energy which is obtained by using the definition of M{\o}ller
energy complex.


title:
Merger of binary neutron stars with realistic equations of state in full
  general relativity

abstract:
  We present numerical results of three-dimensional simulations for the merger
of binary neutron stars (BNSs) in full general relativity. Hybrid equations of
state (EOSs) are adopted to mimic realistic nuclear EOSs. In this approach, we
divide the EOSs into two parts, i.e., the thermal part and the cold part. For
the cold part, we assign a fitting formula for realistic EOSs of cold nuclear
matter slightly modifying the formula developed by Haensel and Potekhin. We
adopt the SLy and FPS EOSs for which the maximum allowed ADM mass of cold and
spherical neutron stars (NSs) is ~ 2.04Mo and 1.80Mo, respectively. Simulations
are performed for BNSs of the total ADM mass in the range between 2.4Mo and
2.8Mo with the rest-mass ratio Q_M to be in the range 0.9 < Q_M < 1. It is
found that if the total ADM mass of the system is larger than a threshold
M_{thr}, a black hole (BH) is promptly formed in the merger irrespective of the
mass ratios. In the other case, the outcome is a hypermassive NS of a large
ellipticity, which results from the large adiabatic index of the realistic EOSs
adopted. The value of M_{thr} depends on the EOS: ~ 2.7Mo and ~ 2.5Mo for the
SLy and FPS EOSs, respectively. Gravitational waves are computed in terms of a
gauge-invariant wave extraction technique. In the formation of the hypermassive
NS, quasiperiodic gravitational waves of a large amplitude and of frequency
between 3 and 4 kHz are emitted. The estimated emission time scale is < 100 ms,
after which the hypermassive NS collapses to a BH. Because of the long emission
time, the effective amplitude may be large enough to be detected by advanced
laser interferometric gravitational wave detectors if the distance to the
source is smaller than ~ 100 Mpc.


title: The String Coupling Accelerates the Expansion of the Universe

abstract:
  Generic cosmological models in non-critical string theory have a
time-dependent dilaton background at a late epoch. The cosmological
deceleration parameter Q_0 is given by the square of the string coupling,
g_s^2, up to a negative sign. Hence the expansion of the Universe must
accelerate eventually, and the observed value of Q_0 coresponds to g_s^2 ~ 0.6.
In this scenario, the string coupling is asymptotically free at large times,
but its present rate of change is imperceptibly small.


title: LISA source confusion: identification and characterization of signals

abstract:
  The Laser Interferometer Space Antenna (LISA) is expected to detect
gravitational radiation from a large number of compact binary systems. We
present a method by which these signals can be identified and have their
parameters estimated. Our approach uses Bayesian inference, specifically the
application of a Markov chain Monte Carlo method. The simulation study that we
present here considers a large number of sinusoidal signals in noise, and our
method estimates the number of periodic signals present in the data, the
parameters for these signals and the noise level. The method is significantly
better than classical spectral techniques at performing these tasks and does
not use stopping criteria for estimating the number of signals present.


title: Embedding G\"{o}del's universe in five dimensions

abstract:
  According to the Campbell-Magaard theorem, any analytical spacetime can be
locally and analytically embedded into a five-dimensional pseudo-Riemannian
Ricci-flat manifold. We find explicitly this embedding for Godel's universe.
The embedding space is Ricci-flat and has a non-Lorentzian signature of type
(++--). We also show that the embedding found is global.


title:
Regular and Black Hole Solutions in the Einstein-Skyrme Theory with
  Negative Cosmological Constant

abstract:
  We study spherically symmetric regular and black hole solutions in the
Einstein-Skyrme theory with a negative cosmological constant. The Skyrme field
configuration depends on the value of the cosmological constant in a similar
manner to effectively varying the gravitational constant. We find the maximum
value of the cosmological constant above which there exists no solution. The
properties of the solutions are discussed in comparison with the asymptotically
flat solutions. The stability is investigated in detail by solving the linearly
perturbed equation numerically. We show that there exists a critical value of
the cosmological constant above which the solution in the branch representing
unstable configuration in the asymptotically flat spacetime turns to be
linearly stable.


title:
Complete adiabatic waveform templates for a test-mass in the
  Schwarzschild spacetime: VIRGO and Advanced LIGO studies

abstract:
  Post-Newtonian expansions of the binding energy and gravitational wave flux
truncated at the {\it same relative} post-Newtonian order form the basis of the
{\it standard adiabatic} approximation to the phasing of gravitational waves
from inspiralling compact binaries. Viewed in terms of the dynamics of the
binary, the standard approximation is equivalent to neglecting certain
conservative post-Newtonian terms in the acceleration. In an earlier work, we
had proposed a new {\it complete adiabatic} approximant constructed from the
energy and flux functions. At the leading order it employs the 2PN energy
function rather than the 0PN one in the standard approximation, so that,
effectively the approximation corresponds to the dynamics where there are no
missing post-Newtonian terms in the acceleration. In this paper, we compare the
overlaps of the standard and complete adiabatic templates with the exact
waveform in the adiabatic approximation of a test-mass motion in the
Schwarzschild spacetime, for the VIRGO and the Advanced LIGO noise spectra. It
is found that the complete adiabatic approximants lead to a remarkable
improvement in the {\it effectualness} at lower PN ($<$ 3PN) orders, while
standard approximants of order $\geq$ 3PN provide a good lower-bound to the
complete approximants for the construction of effectual templates. {\it
Faithfulness} of complete approximants is better than that of standard
approximants except for a few post-Newtonian orders. Standard and complete
approximants beyond the adiabatic approximation are also studied using the
Lagrangian templates of Buonanno, Chen and Vallisneri.


title: Dark Energy and Viscous Cosmology

abstract:
  Singularities in the dark energy universe are discussed, assuming that there
is a bulk viscosity in the cosmic fluid. In particular, it is shown how the
physically natural assumption of letting the bulk viscosity be proportional to
the scalar expansion in a spatially flat FRW universe can drive the fluid into
the phantom region (w < -1), even if lies in the quintessence region (w > -1)
in the non-viscous case.


title: Local conditions for the generalized covariant entropy bound

abstract:
  A set of sufficient conditions for the generalized covariant entropy bound
given by Strominger and Thompson is as follows: Suppose that the entropy of
matter can be described by an entropy current $s^a$. Let $k^a$ be any null
vector along $L$ and $s\equiv -k^a s_a$. Then the generalized bound can be
derived from the following conditions: (i) $s'\leq 2\pi T_{ab}k^ak^b$, where
$s'=k^a\grad_a s$ and $T_{ab}$ is the stress energy tensor; (ii) on the initial
2-surface $B$, $s(0)\leq -{1/4}\theta(0)$, where $\theta$ is the expansion of
$k^a$. We prove that condition (ii) alone can be used to divide a spacetime
into two regions: The generalized entropy bound holds for all light sheets
residing in the region where $s<-{1/4}\theta$ and fails for those in the region
where $s>-{1/4}\theta$. We check the validity of these conditions in FRW flat
universe and a scalar field spacetime. Some apparent violations of the entropy
bounds in the two spacetimes are discussed. These holographic bounds are
important in the formulation of the holographic principle.


title: A characterisation of Schwarzschildean initial data

abstract:
  A theorem providing a characterisation of Schwarzschildean initial data sets
on slices with an asymptotically Euclidean end is proved. This characterisation
is based on the proportionality of the Weyl tensor and its D'Alambertian that
holds for some vacuum Petrov Type D spacetimes (e.g. the Schwarzschild
spacetime, the C-metric, but not the Kerr solution). The 3+1 decomposition of
this proportionality condition renders necessary conditions for an initial data
set to be a Schwarzschildean initial set. These conditions can be written as
quadratic expressions of the electric and magnetic parts of the Weyl tensor
--and thus, involve only the freely specifiable data. In order to complete our
characterisation, a study of which vacuum static Petrov type D spacetimes admit
asymptotically Euclidean slices is undertaken. Furthermore, a discussion of the
ADM 4-momentum for boost-rotation symmetric spacetimes is given. Finally, a
generalisation of our characterisation, valid for Schwarzschildean
hyperboloidal initial data sets is put forward.


title: Non-Boltzmann Statistics as an Alternative to Holography

abstract:
  An intriguing question related to black hole thermodynamics is that the
entropy of a region shall scale as the area rather than the volume. In this
essay we propose that the microscopical degrees of freedom contained in a given
region of space, are statistically related in such a way that obey a
non-standard statistics, in which case an holographic hypothesis would be not
needed. This could provide us with some insight about the nature of degrees of
freedom of the geometry and/or the way in which gravitation plays a role in the
statistic correlation between the degrees of freedom of a system.


title:
Einstein-aether theory, violation of Lorentz invariance, and
  metric-affine gravity

abstract:
  We show that the Einstein-aether theory of Jacobson and Mattingly (J&M) can
be understood in the framework of the metric-affine (gauge theory of) gravity
(MAG). We achieve this by relating the aether vector field of J&M to certain
post-Riemannian nonmetricity pieces contained in an independent linear
connection of spacetime. Then, for the aether, a corresponding geometrical
curvature-square Lagrangian with a massive piece can be formulated
straightforwardly. We find an exact spherically symmetric solution of our
model.


title:
Global parameter-space correlations of coherent searches for continuous
  gravitational waves

abstract:
  The space of phase-parameters (sky-position, frequency, spindowns) of a
coherent matched-filtering search for continuous gravitational waves from
isolated neutron stars shows strong global correlations (``circles in the
sky''). In the local limit this can be analysed in terms of a parameter-space
metric, but the global properties are less well studied. In this work we report
on our recent progress in understanding these global correlations analytically
for short to intermediate (less than a month, say) observation times and
neglecting spindowns. The location of these correlation-circles in
parameter-space is found to be determined mostly by the orbital velocity of the
earth, while the spin-motion of the detector and the antenna-patterns only
contribute significantly to the amplitude of the detection statistic along
these circles.


title: Induced Matter Theory & Heisenberg-like Uncertainty Relations

abstract:
  We show that a differential variant of the Heisenberg uncertainty relations
emerges naturally from induced matter theory, as a sum of line elements in both
momentum and Minkowski spaces.


title: Physical singularity in the regular spacetime and fundamental length

abstract:
  It is shown that formally regular solutions in 5D Kaluza-Klein gravity have
singularities. This phenomenon is connected with the existence of a minimal
length in nature. The calculation of the derivative of the $G_{55}$ metric
component leads to the appearance of the Dirac's $\delta-$function. In this
case the Ricci scalar becomes singular since there is a square of this
derivative.


title:
Better Lunar Ranges with Fewer Photons - Resolving the Lunar
  Retro-reflectors

abstract:
  Because of lunar librations, the retroreflectors left on the moon do not, in
general, face directly at the Earth. Usually this is regarded as a
disadvantage. It results in a spread of arrival times, because each cube that
comprises the retroreflector is at a slightly different distance from the
earth. However, we can turn this same effect into an advantage. Using pulses
and detectors somewhat faster than those currently used for lunar ranging, we
can resolve at least some of the structure of a retroreflector, at least when
the libration angles are large. This additional structure in the transfer
function means that a unique mm level fit can be obtained with many fewer
photons. Fitting to the expected reflector transfer function in general
requires fewer photons than straight averaging, and smoothly reduces to
averaging in the cases where no structure can be resolved. The gains from
resolving the reflectors are largest at large libration angles, exactly the
case where averaging is most inefficient. In these cases the number of photons
needed can be reduced by an order of magnitude or more. Analysis shows that
angles for which the gain is very high happen several times each month, with
the details depending on the exact librations. Experimental validation of this
technique should be possible with existing SLR stations and mockups of the
lunar reflectors.


title:
A Generalization of the Kodama State for Arbitrary Values of the Immirzi
  Parameter

abstract:
  The Kodama State for Lorentzian gravity presupposes a particular value for
the Immirzi-parameter, namely $\beta=-i$. However, the derivation of black hole
entropy in Loop Quantum Gravity suggests that the Immirzi parameter is a fixed
value whose magnitude is on the order of unity but larger than one. Since the
Kodama state has de-Sitter spacetime as its classical limit, to get the proper
radiation temperature, the Kodama state should be extended to incorporate a
more physical value for $\beta$. Thus, we present an extension of the Kodama
state for arbitrary values of the Immirzi parameter, $\beta$, that reduces to
the ordinary Chern-Simons state for the particular value $\beta=-i$. The state
for real values of $\beta$ is free of several of the outstanding problems that
cast doubts on the original Kodama state as a ground state for quantum general
relativity. We show that for real values of $\beta$, the state is invariant
under large gauge transformations, it is CPT invariant (but not CP invariant),
and it is expected to be delta-function normalizable with respect to the
kinematical inner product. To aid in the construction, we first present a
general method for solving the Hamiltonian constraint for imaginary values of
$\beta$ that allows one to use the simpler self-dual and anti-self-dual forms
of the constraint as an intermediate step.


title: The generalized F-statistic: multiple detectors and multiple GW pulsars

abstract:
  The F-statistic, derived by Jaranowski, Krolak & Schutz (1998), is the
optimal (frequentist) statistic for the detection of nearly periodic
gravitational waves from known neutron stars, in the presence of stationary,
Gaussian detector noise. The F-statistic was originally derived for the case of
a single detector, whose noise spectral density was assumed constant in time,
and for a single known neutron star. Here we show how the F-statistic can be
straightforwardly generalized to the cases of 1) a network of detectors with
time-varying noise curves, and 2) a population of known sources. Fortunately,
all the important ingredients that go into our generalized F-statistics are
already calculated in the single-source/single-detector searches that are
currently implemented, e.g., in the LIGO Software Library, so implementation of
optimal multi-detector, multi-source searches should require negligible
additional cost in computational power or software development.


title: Detecting Galactic Binaries with LISA

abstract:
  One of the main sources of gravitational waves for the LISA space-borne
interferometer are galactic binary systems. The waveforms for these sources are
represented by eight parameters, of which four are extrinsic, and four are
intrinsic to the system. Geometrically, these signals exist in an 8-d parameter
space. By calculating the metric tensor on this space, we calculate the number
of templates needed to search for such sources. We show in this study that
below a particular monochromatic frequency, we can ignore one of the intrinsic
parameters and search over a 7-d space. Beyond this frequency, we have a sudden
change in dimensionality of the parameter space from 7 to 8 dimensions, which
results in a change in the scaling of the growth of template number as a
function of monochromatic frequency.


title: Causally pathological spacetimes are physically relevant

abstract:
  We argue that in the context of string theory, the usual restriction to
globally hyperbolic spacetimes should be considerably relaxed. We exhibit an
example of a spacetime which only satisfies the causal condition, and so is
arbitrarily close to admitting closed causal curves, but which has a
well-behaved dual description, free of paradoxes.


title: Noncommutative Unification of General Relativity and Quantum Mechanics

abstract:
  In Gen. Rel. Grav. (36, 111-126 (2004); in press, gr-qc/0410010) we have
proposed a model unifying general relativity and quantum mechanics based on a
noncommutative geometry. This geometry was developed in terms of a
noncommutative algebra A defined on a transformation groupoid given by the
action of a group G on a space E. Owing to the fact that G was assumed to be
finite it was possible to compute the model in full details. In the present
paper we develop the model in the case when G is a noncompact group. It turns
out that also in this case the model works well. The case is important since to
obtain physical effects predicted by the model we should assume that G is a
Lorentz group or some of its representations. We show that the generalized
Einstein equation of the model has the form of the eigenvalue equation for the
generalized Ricci operator, and all relevant operators in the quantum sector of
the model are random operators; we study their dynamics. We also show that the
model correctly reproduces general relativity and the usual quantum mechanics.
It is interesting that the latter is recovered by performing the measurement of
any observable. In the act of such a measurement the model ``collapses'' to the
usual quantum mechanics.


title:
Gravitational radiation reaction and inspiral waveforms in the adiabatic
  limit

abstract:
  We describe progress evolving an important limit of binary orbits in general
relativity, that of a stellar mass compact object gradually spiraling into a
much larger, massive black hole. These systems are of great interest for
gravitational wave observations. We have developed tools to compute for the
first time the radiated fluxes of energy and angular momentum, as well as
instantaneous snapshot waveforms, for generic geodesic orbits. For special
classes of orbits, we compute the orbital evolution and waveforms for the
complete inspiral by imposing global conservation of energy and angular
momentum. For fully generic orbits, inspirals and waveforms can be obtained by
augmenting our approach with a prescription for the self force in the adiabatic
limit derived by Mino. The resulting waveforms should be sufficiently accurate
to be used in future gravitational-wave searches.


title:
Equations of motion according to the asymptotic post-Newtonian scheme
  for general relativity in the harmonic gauge

abstract:
  The asymptotic scheme of post-Newtonian approximation defined for general
relativity (GR) in the harmonic gauge by Futamase & Schutz (1983) is based on a
family of initial data for the matter fields of a perfect fluid and for the
initial metric, defining a family of weakly self-gravitating systems. We show
that Weinberg's (1972) expansion of the metric and his general expansion of the
energy-momentum tensor ${\bf T}$, as well as his expanded equations for the
gravitational field and his general form of the expanded dynamical equations,
apply naturally to this family. Then, following the asymptotic scheme, we
derive the explicit form of the expansion of ${\bf T}$ for a perfect fluid, and
the expanded fluid-dynamical equations. (These differ from those written by
Weinberg.) By integrating these equations in the domain occupied by a body, we
obtain a general form of the translational equations of motion for a 1PN
perfect-fluid system in GR. To put them into a tractable form, we use an
asymptotic framework for the separation parameter $\eta $, by defining a family
of well-separated 1PN systems. We calculate all terms in the equations of
motion up to the order $\eta ^3$ included. To calculate the 1PN correction
part, we assume that the Newtonian motion of each body is a rigid one, and that
the family is quasi-spherical, in the sense that in all bodies the inertia
tensor comes close to being spherical as $\eta \to 0$. Apart from corrections
that cancel for exact spherical symmetry, there is in the final equations of
motion one additional term, as compared with the Lorentz-Droste
(Einstein-Infeld-Hoffmann) acceleration. This term depends on the spin of the
body and on its internal structure.


title:
Testing general relativity and probing the merger history of massive
  black holes with LISA

abstract:
  Observations of binary inspirals with LISA will allow us to place bounds on
alternative theories of gravity and to study the merger history of massive
black holes (MBH). These possibilities rely on LISA's parameter estimation
accuracy. We update previous studies of parameter estimation including
non-precessional spin effects. We work both in Einstein's theory and in
alternative theories of gravity of the scalar-tensor and massive-graviton
types. Inclusion of non-precessional spin terms in MBH binaries has little
effect on the angular resolution or on distance determination accuracy, but it
degrades the estimation of the chirp mass and reduced mass by between one and
two orders of magnitude. The bound on the coupling parameter of scalar-tensor
gravity is significantly reduced by the presence of spin couplings, while the
reduction in the graviton-mass bound is milder. LISA will measure the
luminosity distance of MBHs to better than ~10% out to z~4 for a (10^6+10^6)
Msun binary, and out to z~2 for a (10^7+10^7) Msun binary. The chirp mass of a
MBH binary can always be determined with excellent accuracy. Ignoring spin
effects, the reduced mass can be measured within ~1% out to z=10 and beyond for
a (10^6+10^6) Msun binary, but only out to z~2 for a (10^7+10^7) Msun binary.
Present-day MBH coalescence rate calculations indicate that most detectable
events should originate at z~2-6: at these redshifts LISA can be used to
measure the two black hole masses and their luminosity distance with sufficient
accuracy to probe the merger history of MBHs. If the low-frequency LISA noise
can only be trusted down to 10^-4 Hz, parameter estimation for MBHs (and LISA's
ability to perform reliable cosmological observations) will be significantly
degraded.


title: Relic Gravitational Waves and Cosmology

abstract:
  This is an expanded version of my talk given at the international conference
"Zeldovich-90". I start with a brief recollection of interactions with
Zeldovich in the context of the study of relic gravitational waves. I then
summarise the principles and early results on the quantum-mechanical generation
of cosmological perturbations. The expected amplitudes of relic gravitational
waves are different in different frequency windows, and therefore the
techniques and prospects of their detection are different. One section of the
paper describes the present state of efforts in direct detection of relic
gravitational waves. Another section is devoted to indirect detection via the
anisotropy and polarisation measurements of the cosmic microwave background
radiation (CMB). It is emphasized throughout the paper that the conclusions on
the existence and expected amount of relic gravitational waves are based on a
solid theoretical foundation and the best available cosmological observations.
I also explain in great detail what went wrong with the so-called `inflationary
gravitational waves', whose amount is predicted by inflationary theorists to be
negligibly small, thus depriving them of any observational significance.


title:
A resolution of spacetime singularity and black hole paradoxes through
  avoidance of trapped surface formation in Einstein gravity

abstract:
  The occurrence of a spacetime singularity indicates the breakdown of Einstein
gravitation theory in these extreme regimes. We consider here the singularity
issue and various black hole paradoxes at classical and quantum levels. It is
pointed out that a possible resolution to these problems could be arrived at by
avoiding the formation of trapped surfaces during a continual gravitational
collapse. A class of perfect fluid collapse models is constructed which
realizes such a possibility. While the pressure could be negative in the
interior of the cloud, the weak energy condition is satisfied. The collapsing
star radiates away most of its matter as the process of gravitational collapse
evolves, so as to avoid the formation of trapped surfaces and the spacetime
singularity. The collapsing interior is matched to an exterior which is a
generalized Vaidya spacetime to complete the model.


title:
Frame Dragging Effect on Moment of Inertia and Radius of Gyration of
  Neutron Star

abstract:
  Accurate to the first order in the uniform angular velocity, the general
relativity frame dragging effect of the moments of inertia and radii of
gyration of two kinds of neutron stars are calculated in a relativistic
$\sigma-\omega$ model. The calculation shows that the dragging effect will
diminish the moments of inertia and radii of gyration.


title: Induced Phantom and 5D Attractor Solution in Space-Time-Matter Theory

abstract:
  In Spacetime-Matter theory we assume that the 4D induced matter of the $5D $
Ricci-flat bouncing cosmological solutions contains a perfect fluid as well as
an induced scalar field. Then we show that the conventional 4D quintessence and
phantom models of dark energy could be recovered from the $5D$ cosmological
solutions. By using the phase-plane analysis to study the stability of
evolution of the $5D$ models, we find that the conventional 4D late-time
attractor solution is also recovered. This attractor solution shows that the
scale factors of the phantom dominated universes in both the 4D and $5D$
theories will reach infinity in a finite time and the universes will be ended
at a new kind of spacetime singularity at which everything will be annihilated.
We also find that the repulsive force of the phantom may provide us with a
mechanics to explain the bounce.


title: The Large Footprints of H-Space on Asymptotically Flat Space-Times

abstract:
  We show that certain structures defined on the complex four dimensional space
known as H-Space have considerable relevance for its closely associated
asymptotically flat real physical space-time. More specifically for every
complex analytic curve on the H-space there is an asymptotically shear-free
null geodesic congruence in the physical space-time. There are specific
geometric structures that allow this world-line to be chosen in a unique
canonical fashion giving it physical meaning and significance.


title: Delocalization of brane gravity by a bulk black hole

abstract:
  We investigate the analogue of the Randall-Sundrum brane-world in the case
when the bulk contains a black hole. Instead of the static vacuum Minkowski
brane of the RS model, we have an Einstein static vacuum brane. We find that
the presence of the bulk black hole has a dramatic effect on the gravity that
is felt by brane observers. In the RS model, the 5D graviton has a stable
localized zero-mode that reproduces 4D gravity on the brane at low energies.
With a bulk black hole, there is no such solution -- gravity is delocalized by
the 5D horizon. However, the brane does support a discrete spectrum of
metastable massive bound states, or quasinormal modes, as was recently shown to
be the case in the RS scenario. These states should dominate the high frequency
component of the bulk gravity wave spectrum on a cosmological brane. We expect
our results to generalize to any bulk spacetime containing a Killing horizon.


title:
Non-Relativistic Limit of Dirac Equations in Gravitational Field and
  Quantum Effects of Gravity

abstract:
  Based on unified theory of electromagnetic interactions and gravitational
interactions, the non-relativistic limit of the equation of motion of a charged
Dirac particle in gravitational field is studied. From the Schrodinger equation
obtained from this non-relativistic limit, we could see that the classical
Newtonian gravitational potential appears as a part of the potential in the
Schrodinger equation, which can explain the gravitational phase effects found
in COW experiments. And because of this Newtonian gravitational potential, a
quantum particle in earth's gravitational field may form a gravitationally
bound quantized state, which had already been detected in experiments. Three
different kinds of phase effects related to gravitational interactions are
discussed in this paper, and these phase effects should be observable in some
astrophysical processes. Besides, there exists direct coupling between
gravitomagnetic field and quantum spin, radiation caused by this coupling can
be used to directly determine the gravitomagnetic field on the surface of a
star.


title: Pseudo-Newtonian Potential for Charged Particle in Kerr-Newman Geometry

abstract:
  We consider the equatorial circular motion of a test particle of specific
charge q/m << 1 in the Kerr-Newman geometry of a rotating charged black hole.
We find the particle's conserved energy and conserved projection of the angular
momentum on the black hole's axis of rotation as corrections, in leading order
of q/m, to the corresponding energy and angular momentum of a neutral particle.
We determine the centripetal force acting on the test particle and,
consequently, we find a classical pseudo-Newtonian potential with which one can
mimic this general relativistic problem.


title:
Simulation of the White Dwarf -- White Dwarf galactic background in the
  LISA data

abstract:
  LISA (Laser Interferometer Space Antenna) is a proposed space mission, which
will use coherent laser beams exchanged between three remote spacecraft to
detect and study low-frequency cosmic gravitational radiation. In the low-part
of its frequency band, the LISA strain sensitivity will be dominated by the
incoherent superposition of hundreds of millions of gravitational wave signals
radiated by inspiraling white-dwarf binaries present in our own galaxy. In
order to estimate the magnitude of the LISA response to this background, we
have simulated a synthesized population that recently appeared in the
literature. We find the amplitude of the galactic white-dwarf binary background
in the LISA data to be modulated in time, reaching a minimum equal to about
twice that of the LISA noise for a period of about two months around the time
when the Sun-LISA direction is roughly oriented towards the Autumn equinox.
Since the galactic white-dwarfs background will be observed by LISA not as a
stationary but rather as a cyclostationary random process with a period of one
year, we summarize the theory of cyclostationary random processes and present
the corresponding generalized spectral method needed to characterize such
process. We find that, by measuring the generalized spectral components of the
white-dwarf background, LISA will be able to infer properties of the
distribution of the white-dwarfs binary systems present in our Galaxy.


title:
A Vaidya-type radiating solution in Einstein-Gauss-Bonnet gravity and
  its application to braneworld

abstract:
  We consider a Vaidya-type radiating spacetime in Einstein gravity with the
Gauss-Bonnet combination of quadratic curvature terms. Simply generalizing the
known static black hole solutions in Einstein-Gauss-Bonnet gravity, we present
an exact solution in arbitrary dimensions with the energy-momentum tensor given
by a null fluid form. As an application, we derive an evolution equation for
the ``dark radiation'' in the Gauss-Bonnet braneworld.


title: Effects of Gauss-Bonnet term on the final fate of gravitational collapse

abstract:
  We obtain a general spherically symmetric solution of a null dust fluid in $n
(\geq 4)$-dimensions in Gauss-Bonnet gravity. This solution is a generalization
of the $n$-dimensional Vaidya-(anti)de Sitter solution in general relativity.
For $n=4$, the Gauss-Bonnet term in the action does not contribute to the field
equations, so that the solution coincides with the Vaidya-(anti)de Sitter
solution. Using the solution for $n \ge 5$ with a specific form of the mass
function, we present a model for a gravitational collapse in which a null dust
fluid radially injects into an initially flat and empty region. It is found
that a naked singularity is inevitably formed and its properties are quite
different between $n=5$ and $n \ge 6$. In the $n \ge 6$ case, a massless
ingoing null naked singularity is formed, while in the $n=5$ case, a massive
timelike naked singularity is formed, which does not appear in the general
relativistic case. The strength of the naked singularities is weaker than that
in the general relativistic case. These naked singularities can be globally
naked when the null dust fluid is turned off after a finite time and the field
settles into the empty asymptotically flat spacetime.


title: Black hole evaporation: A paradigm

abstract:
  A paradigm describing black hole evaporation in non-perturbative quantum
gravity is developed by combining two sets of detailed results: i) resolution
of the Schwarzschild singularity using quantum geometry methods; and ii)
time-evolution of black holes in the trapping and dynamical horizon frameworks.
Quantum geometry effects introduce a major modification in the traditional
space-time diagram of black hole evaporation, providing a possible mechanism
for recovery of information that is classically lost in the process of black
hole formation. The paradigm is developed directly in the Lorentzian regime and
necessary conditions for its viability are discussed. If these conditions are
met, much of the tension between expectations based on space-time geometry and
structure of quantum theory would be resolved.


title: The quantum black hole

abstract:
  The quantum nature of a black hole is revealed using the simplest terms that
one learns in undergraduate and beginning graduate courses. The exposition
demonstrates -- vividly -- the importance and power of the quantum oscillator
in contemporary research in theoretical physics.


title: An Issue to the Cosmological Constant Problem

abstract:
  According to general relativity, the present analysis shows on geometrical
grounds that the cosmological constant problem is an artifact due to the
unfounded link of this fundamental constant to vacuum energy density of quantum
fluctuations.


title: Modeling the spectrum of gravitational waves in the primordial Universe

abstract:
  Recent observations from type Ia Supernovae and from cosmic microwave
background (CMB) anisotropies have revealed that most of the matter of the
Universe interacts in a repulsive manner, composing the so-called dark energy
constituent of the Universe. The analysis of cosmic gravitational waves (GW)
represents, besides the CMB temperature and polarization anisotropies, an
additional approach in the determination of parameters that may constrain the
dark energy models and their consistence. In recent work, a generalized
Chaplygin gas model was considered in a flat universe and the corresponding
spectrum of gravitational waves was obtained. The present work adds a massless
gas component to that model and the new spectrum is compared to the previous
one. The Chaplygin gas is also used to simulate a $\Lambda$-CDM model by means
of a particular combination of parameters so that the Chaplygin gas and the
$\Lambda$-CDM models can be easily distinguished in the theoretical scenarios
here established. The lack of direct observational data is partialy solved when
the signature of the GW on the CMB spectra is determined.


title: Classification of Cosmological Trajectories

abstract:
  In the context of effective Friedmann equation we classify the cosmologies in
multi-scalar models with an arbitrary scalar potential $V$ according to their
geometric properties. It is shown that all flat cosmologies are geodesics with
respect to a conformally rescaled metric on the `augmented' target space.
Non-flat cosmologies with V=0 are also investigated. It is shown that geodesics
in a `doubly-augmented' target space yield cosmological trajectories for any
curvature $k$ when projected onto a given hypersurface.


title:
N-dimensional gravitational collapse of Type I matter fields with
  non-zero radial pressure

abstract:
  We study the gravitational collapse of Type I matter field in $N$ dimensional
spacetime with radial pressure $p_{r}$ as a function of $r $. We find that for
a given smooth initial data set satisfying physical requirements, naked
singularities exist for spacetime dimensions N=4 and 5 while for $N \geq 6$
Cosmic Censorship Conjecture withholds its ground. We, also, study the collapse
with linear equation of state and find that, similar to dust collapse with
appropriate choice of initial data naked singularities occur in all dimensions.


title: Wave and Particle Scattering Properties of High Speed Black Holes

abstract:
  The light-like limit of the Kerr gravitational field relative to a distant
observer moving rectilinearly in an arbitrary direction is an impulsive plane
gravitational wave with a singular point on its wave front. By colliding
particles with this wave we show that they have the same focussing properties
as high speed particles scattered by the original black hole. By colliding
photons with the gravitational wave we show that there is a circular disk,
centered on the singular point on the wave front, having the property that
photons colliding with the wave within this disk are reflected back and travel
with the wave. This result is approximate in the sense that there are observers
who can see a dim (as opposed to opaque) circular disk on their sky. By
colliding plane electromagnetic waves with the gravitational wave we show that
the reflected electromagnetic waves are the high frequency waves.


title: Smooth transitions from Schwarzschild vacuum to de Sitter space

abstract:
  We provide an infinity of spacetimes which contain part of both the
Schwarzschild vacuum and de Sitter space. The transition, which occurs below
the Schwarzschild event horizon, involves only boundary surfaces (no surface
layers). An explicit example is given in which the weak and strong energy
conditions are satisfied everywhere (except in the de Sitter section) and the
dominant energy condition is violated only in the vicinity of the boundary to
the Schwarzschild section. The singularity is avoided by way of a change in
topology in accord with a theorem due to Borde..


title: The disinformation problem for black holes (conference version)

abstract:
  Basic properties of black holes are explained in terms of trapping horizons.
It is shown that matter and information will escape from an evaporating black
hole. A general scenario is outlined whereby a black hole evaporates completely
without singularity, event horizon or loss of energy or information.


title: The disinformation problem for black holes (pop version)

abstract:
  The supposed information paradox for black holes is based on the fundamental
misunderstanding that black holes are usefully defined by event horizons.
Understood in terms of locally defined trapping horizons, the paradox
disappears: information will escape from an evaporating black hole. According
to classical properties of trapping horizons, a general scenario is outlined
whereby a black hole evaporates completely without singularity, event horizon
or loss of energy or information.


title: Rebuttal to a Paper on Wormholes

abstract:
  In a recent paper on wormholes (gr-qc/0503097), the author of that paper
demonstrated that he didn't know what he was talking about. In this paper I
correct the author's naive erroneous misconceptions.


title: De Sitter Thermodynamics from Diamonds's Temperature

abstract:
  The thermal time hypothesis proposed by Rovelli [1] regards the physical
basis for the flow of time as thermodynamical and provides a definition of the
temperature for some special cases. We verify this hypothesis in the case of de
Sitter spacetime by relating the uniformly accelerated observer in de Sitter
spacetime to the diamond in Minkowski spacetime. Then, as an application of it,
we investigate the thermal effect for the uniformly accelerated observer with a
finite lifetime in dS spacetime, which generalizes the corresponding result for
the case of Minkowski spacetime [2].
  Furthermore, noticing that a uniformly accelerated dS observer with a finite
lifetime corresponds to a Rindler observer with a finite lifetime in the
embedding Minkowski spacetime, we show that the
global-embedding-Minkowski-spacetime (GEMS) picture of spacetime thermodynamics
is valid in this case. This is a rather nontrivial and unexpected
generalization of the GEMS picture, as well as a further verification of both
the thermal time hypothesis and the GEMS picture.


title:
Relativistic conservation laws and integral constraints for large
  cosmological perturbations

abstract:
  For every mapping of a perturbed spacetime onto a background and with any
vector field $\xi$ we construct a conserved covariant vector density $I(\xi)$,
which is the divergence of a covariant antisymmetric tensor density, a
"superpotential". $ I(\xi)$ is linear in the energy-momentum tensor
perturbations of matter, which may be large; $I(\xi)$ does not contain the
second order derivatives of the perturbed metric. The superpotential is
identically zero when perturbations are absent.
  By integrating conserved vectors over a part $\Si$ of a hypersurface $S$ of
the background, which spans a two-surface $\di\Si$, we obtain integral
relations between, on the one hand, initial data of the perturbed metric
components and the energy-momentum perturbations on $\Si$ and, on the other
hand, the boundary values on $\di\Si$. We show that there are as many such
integral relations as there are different mappings, $\xi$'s, $\Si$'s and
$\di\Si$'s. For given boundary values on $\di\Si$, the integral relations may
be interpreted as integral constraints (e.g., those of Traschen) on local
initial data including the energy-momentum perturbations. Conservation laws
expressed in terms of Killing fields $\Bar\xi$ of the background become
"physical" conservation laws.
  In cosmology, to each mapping of the time axis of a Robertson-Walker space on
a de Sitter space with the same spatial topology there correspond ten
conservation laws. The conformal mapping leads to a straightforward
generalization of conservation laws in flat spacetimes. Other mappings are also
considered. ...


title:
A time-domain MCMC search and upper limit technique for gravitational
  waves of uncertain frequency from a targeted neutron star

abstract:
  It is computationally expensive to search the large parameter space
associated with a gravitational wave signal of uncertain frequency, such as
might be expected from the possible pulsar generated by SN1987A. To address
this difficulty we have developed a Markov Chain Monte Carlo method that
performs a time-domain Bayesian search for a signal over a 4 Hz frequency band
and a spindown of magnitude of up to $1\ee{-9}$ Hz/s. We use Monte Carlo
simulations to set upper limits on signal amplitude with this technique, which
we intend to apply to a gravitational wave search.


title: Quantum Gravitational Collapse

abstract:
  We apply the recent results in Loop Quantum Cosmology and in the resolution
of Black Hole singularity to the gravitational collapse of a star. We study the
dynamic of the space time in the interior of the Schwarzschild radius. In
particular in our simple model we obtain the evolution of the matter inside the
star and of the gravity outside the region where the matter is present. The
boundary condition identify an unique time inside and outside the region where
the matter is present. We consider a star during the collapse in the particular
case in which inside the collapsing star we take null pressure, homogeneity and
isotropy. The space-time outside the matter is homogeneous and anisotropic. We
show that the space time is singularity free and that we can extend dynamically
the space-time beyond the classical singularity.


title:
Non-singular solutions in multidimensional model with scalar fields and
  exponential potential

abstract:
  Using developed earlier our methods for multidimensional models
\cite{M1,M2,M3} a family of cosmological-type solutions in D-dimensional model
with two sets of scalar fields \vec{\phi} and \vec{\psi} and exponential
potential depending upon \vec{\phi} is considered. The solutions are defined on
a product of n Ricci-flat spaces. The fields from \vec{\phi} have positive
kinetic terms and \vec{\psi} are "phantom" fields with negative kinetic terms.
For vector coupling constant obeying 0< \vec{\lambda}^2 < (D-1)/(D-2) a
subclass of non-singular solutions is singled out. The solutions from this
subclass are regular for all values of synchronous "time" \tau \in (- \infty, +
\infty). For \vec{\lambda}^2 < 1/(D-2) we get an asymptotically accelerated and
isotropic expansion for large values of \tau.


title: The Tolman-Bondi--Vaidya Spacetime: matching timelike dust to null dust

abstract:
  The Tolman-Bondi and Vaidya solutions are two solutions to Einstein equations
which describe dust particles and null fluid, respectively. We show that it is
possible to match the two solutions in one single spacetime, the
Tolman-Bondi--Vaidya spacetime. The new spacetime is divided by a null surface
with Tolman-Bondi dust on one side and Vaidya fluid on the other side. The
differentiability of the spacetime is discussed. By constructing a specific
solution, we show that the metric across the null surface can be at least $C^1$
and the stress-energy tensor is continuous.


title:
Variable placement of templates technique in a 2D parameter space for
  binary inspiral searches

abstract:
  In the search for binary systems inspiral signal in interferometric
gravitational waves detectors, one needs the generation and placement of a grid
of templates. We present an original technique for the placement in the
associated parameter space, that makes use of the variation of size of the
isomatch ellipses in order to reduce the number of templates necessary to cover
the parameter space. This technique avoids the potentially expensive
computation of the metric at every point, at the cost of having a small number
of ``holes'' in the coverage, representing a few percent of the surface of the
parameter space, where the match is slightly lower than specified. A study of
the covering efficiency, as well as a comparison with a very simple regular
tiling using a single ellipse is made. Simulations show an improvement varying
between 6% and 30% for the computing cost in this comparison.


title: Decay of Solutions of the Wave Equation in the Kerr Geometry

abstract:
  We consider the Cauchy problem for the scalar wave equation in the Kerr
geometry for smooth initial data supported outside the event horizon. We prove
that the solutions decay in time in L^\infty_loc. The proof is based on a
representation of the solution as an infinite sum over the angular momentum
modes, each of which is an integral of the energy variable on the real line.
This integral representation involves solutions of the radial and angular ODEs
which arise in the separation of variables.


title: Excised acoustic black holes: the scattering problem in the time domain

abstract:
  The scattering process of a dynamic perturbation impinging on a draining-tub
model of an acoustic black hole is numerically solved in the time domain.
Analogies with real black holes of General Relativity are explored by using
recently developed mathematical tools involving finite elements methods,
excision techniques, and constrained evolution schemes for strongly hyperbolic
systems. In particular it is shown that superradiant scattering of a
quasi-monochromatic wavepacket can produce strong amplification of the signal,
offering the possibility of a significant extraction of rotational energy at
suitable values of the angular frequency of the vortex and of the central
frequency of the wavepacket. The results show that theoretical tools recently
developed for gravitational waves can be brought to fruition in the study of
other problems in which strong anisotropies are present.


title:
False discovery rate: setting the probability of false claim of
  detection

abstract:
  When testing multiple hypothesis in a survey --e.g. many different source
locations, template waveforms, and so on-- the final result consists in a set
of confidence intervals, each one at a desired confidence level. But the
probability that at least one of these intervals does not cover the true value
increases with the number of trials. With a sufficiently large array of
confidence intervals, one can be sure that at least one is missing the true
value. In particular, the probability of false claim of detection becomes not
negligible. In order to compensate for this, one should increase the confidence
level, at the price of a reduced detection power. False discovery rate control
is a relatively new statistical procedure that bounds the number of mistakes
made when performing multiple hypothesis tests. We shall review this method,
discussing exercise applications to the field of gravitational wave surveys.


title: A First Comparison Between LIGO and Virgo Inspiral Search Pipelines

abstract:
  This article reports on a project that is the first step the LIGO Scientific
Collaboration and the Virgo Collaboration have taken to prepare for the mutual
search for inspiral signals. The project involved comparing the analysis
pipelines of the two collaborations on data sets prepared by both sides,
containing simulated noise and injected events. The ability of the pipelines to
detect the injected events was checked, and a first comparison of how the
parameters of the events were recovered has been completed.


title: Optical metrics and birefringence of anisotropic media

abstract:
  The material tensor of linear response in electrodynamics is constructed out
of products of two symmetric second rank tensor fields which in the
approximation of geometrical optics and for uniaxial symmetry reduce to
"optical" metrics, describing the phenomenon of birefringence. This
representation is interpreted in the context of an underlying internal
geometrical structure according to which the symmetric tensor fields are
vectorial elements of an associated two-dimensional space.


title: Semiclassical States for Constrained Systems

abstract:
  The notion of semi-classical states is first sharpened by clarifying two
issues that appear to have been overlooked in the literature. Systems with
linear and quadratic constraints are then considered and the group averaging
procedure is applied to kinematical coherent states to obtain physical
semi-classical states. In the specific examples considered, the technique turns
out to be surprisingly efficient, suggesting that it may well be possible to
use kinematical structures to analyze the semi-classical behavior of physical
states of an interesting class of constrained systems.


title:
On the effects of the Dvali-Gabadadze-Porrati braneworld gravity on the
  orbital motion of a test particle

abstract:
  In this paper we explicitly work out the secular perturbations induced on all
the Keplerian orbital elements of a test body to order O(e^2) in the
eccentricity e by the weak-field long-range modifications of the usual
Newton-Einstein gravity due to the Dvali-Gabadadze-Porrati (DGP) braneworld
model. The Gauss perturbative scheme is used. It turns out that the argument of
pericentre and the mean anomaly are affected by secular rates which are
independent of the semimajor axis of the orbit of the test particle. The first
nonvaishing eccentricity-dependent corrections are of order O(e^2). For
circular orbits the Lue-Starkman (LS) effect on the pericentre is obtained.
Some observational consequences are discussed for the Solar System planetary
mean longitudes lambda which would undergo a 1.2\cdot 10^-3 arcseconds per
century braneworld secular precession. According to recent data analysis over
92 years for the EPM2004 ephemerides, the 1-sigma formal accuracy in
determining the Martian mean longitude amounts to 3\cdot 10^-3 milliarcseconds,
while the braneworld effect over the same time span would be 1.159
milliarcseconds. The major limiting factor is the 2.6\cdot 10^-3 arcseconds per
century systematic error due to the mismodelling in the Keplerian mean motion
of Mars. A suitable linear combination of the mean longitudes of Mars and Venus
may overcome this problem. The formal, 1-sigma obtainable observational
accuracy would be \sim 7%. The systematic error due to the present-day
uncertainties in the solar quadrupole mass moment, the Keplerian mean motions,
the general relativistic Schwarzschild field and the asteroid ring would amount
to some tens of percent.


title:
The One-Loop Effective Action in phi^4 Theory Coupled Non-Linearly with
  Curvature Power and Dynamical Origin of Cosmological Constant

abstract:
  The functional formulation and one-loop effective action for scalar
self-interacting theory non-linearly coupled with some power of the curvature
are studied. After the explicit one-loop renormalization at weak curvature, we
investigated numerically the phase structure for such unusual phi^4 theory. It
is demonstrated the possibility of curvature-induced phase transitions for
positive values of the curvature power, while for negative values the radiative
symmetry breaking does not take place. The dynamical mechanism for the
explanation of the current smallness of the cosmological constant is presented
for several models from the class of theories under consideration.


title: Is the Schwarzschild black hole really stable?

abstract:
  The stability of the Schwarzschild black hole is studied. Regge and Wheeler
treated the problem first at 1957 and obtained the dynamical equations for the
small perturbation. There are two kinds of perturbations: odd one and even one.
Using the Painlev\'{e} coordinate, we reconsider the odd perturbation and find
that: the white-hole-connected universe(r>2m, see text) is unstable. Because
the odd perturbation may be regarded as the angular perturbation, therefore,
the physical mean to it may be that the white-hole-connected universe is
unstable with respect to the rotating perturbation.


title: New vacuum Robinson--Trautman metrics

abstract:
  This paper has been withdrawn by the author. The metrics presented are known
since 1969 (and are referred to as C-metrics)


title: Dark Energy Dominance and Cosmic Acceleration in First Order Formalism

abstract:
  The current accelerated universe could be produced by modified gravitational
dynamics as it can be seen in particular in its Palatini formulation. We
analyze here a specific non-linear gravity-scalar system in the first order
Palatini formalism which leads to a FRW cosmology different from the purely
metric one. It is shown that the emerging FRW cosmology may lead either to an
effective quintessence phase (cosmic speed-up) or to an effective phantom
phase. Moreover, the already known gravity assisted dark energy dominance
occurs also in the first order formalism. Finally, it is shown that a dynamical
theory able to resolve the cosmological constant problem exists also in this
formalism, in close parallel with the standard metric formulation.