title: Spontaneous Symmetry Breaking in the Brane-World

abstract:
  A simplified Randall-Sundrum-like model in 6 dimensions is discussed. The
extra two dimensions correspond to the cone. The effective four-dimensional
scalar self-interacting theory is studied at one-loop level. The contributions
due to 6-dimensional parameters in four-dimensional beta-functions appear.
Using such beta-functions the one-loop effective potential is calculated. The
possibility of spontaneous symmetry breaking due to extra dimensions is
demonstrated.


title: Cosmological models and centre manifold theory

abstract:
  Centre manifold theory is applied to some dynamical systems arising from
spatially homogeneous cosmological models. Detailed information is obtained
concerning the late-time behaviour of solutions of the Einstein equations of
Bianchi type III with collisionless matter. In addition some statements in the
literature on solutions of the Einstein equations coupled to a massive scalar
field are proved rigorously.


title: Analog Electromagnetism in a Symmetrized $^3$He-A

abstract:
  We derive a low temperature effective action for the order parameter in a
symmetrized phase A of helium 3, where the Fermi velocity equals the
transversal velocity of low energy fermionic quasiparticles. The effective
action has a form of the electromagnetic action. This analog electromagnetism
is a part of the program to derive analog gravity and the standard model as a
low energy effective theory in a condensed matter system. For the analog gauge
field to satisfy the Maxwell equations interactions in $^3$He require special
tuning that leads to the symmetric case.


title:
General Relativistic Rossby-Haurwitz waves of a slowly and
  differentially rotating fluid shell

abstract:
  We show that, at first order in the angular velocity, the general
relativistic description of Rossby-Haurwitz waves (the analogues of r-waves on
a thin shell) can be obtained from the corresponding Newtonian one after a
coordinate transformation. As an application, we show that the results recently
obtained by Rezzolla and Yoshida (2001) in the analysis of Newtonian
Rossby-Haurwitz waves of a slowly and differentially rotating, fluid shell
apply also in General Relativity, at first order in the angular velocity.


title: Quantum states of elementary three-geometry

abstract:
  We introduce a quantum volume operator $K$ in three--dimensional Quantum
Gravity by taking into account a symmetrical coupling scheme of three SU(2)
angular momenta. The spectrum of $K$ is discrete and defines a complete set of
eigenvectors which is alternative with respect to the complete sets employed
when the usual binary coupling schemes of angular momenta are considered. Each
of these states, that we call quantum bubbles, represents an interference of
extended configurations which provides a rigorous meaning to the heuristic
notion of quantum tetrahedron. We study the generalized recoupling coefficients
connecting the symmetrical and the binary basis vectors, and provide an
explicit recursive solution for such coefficients by analyzing also its
asymptotic limit.


title: Hydrodynamics of galactic dark matter

abstract:
  We consider simple hydrodynamical models of galactic dark matter in which the
galactic halo is a self-gravitating and self-interacting gas that dominates the
dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static
perfect fluid satisfying the field equations of General Relativity, visible
barionic matter can be treated as ``test particles'' in the geometry of this
field. We show that the assumption of an empirical ``universal rotation curve''
that fits a wide variety of galaxies is compatible, under suitable
approximations, with state variables characteristic of a non-relativistic
Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit.
Consistency criteria lead to a minimal bound for particle masses in the range
$30 \hbox{eV} \leq m \leq 60 \hbox{eV}$ and to a constraint between the central
temperature and the particles mass. The allowed mass range includes popular
supersymmetric particle candidates, such as the neutralino, axino and
gravitino, as well as lighter particles ($m\approx$ keV) proposed by numerical
N-body simulations associated with self-interactive CDM and WDM structure
formation theories.


title: On Principle of Universality of Gravitational Interactions

abstract:
  In this work, the experiment is discussed on the verification of the
principle of universality of gravitational interactions and some related
problems of gravity theory and physics of elementary particles. The meaning of
this proposal lies in the fact that the self-consistency of General Relativity,
as it turns out, presuppose the existence of the nongravitating form of energy.
Theory predicts that electrons are particles that transfer the nongravitating
form of energy.


title:
The Relation of Thermal Fluctuation and Information-Entropy for
  One-Dimensional Rindler Oscillator

abstract:
  Within the framework of thermo-field-dynamics (TFD), the
information-entropies associated with the measurements of position and momentum
for one-dimensional Rindler oscillator are derived, and the connection between
its information-entropy and thermal fluctuation is obtained. A conclusion is
drawn that the thermal fluctuation leads to the loss of information.


title: Remarks on the distributional Schwarzschild geometry

abstract:
  This work is devoted to a mathematical analysis of the distributional
Schwarzschild geometry. The Schwarzschild solution is extended to include the
singularity; the energy momentum tensor becomes a delta-distribution supported
at r=0. Using generalized distributional geometry in the sense of Colombeau's
(special) construction the nonlinearities are treated in a mathematically
rigorous way. Moreover, generalized function techniques are used as a tool to
give a unified discussion of various approaches taken in the literature so far;
in particular we comment on geometrical issues.


title: Classical Radiation Formula in the Rindler Frame

abstract:
  In a preceding paper [T. Hirayama, Prog. Theor. Phys. 106 (2001), 71], the
power of the classical radiation emitted by a moving charge was evaluated in
the Rindler frame. In this paper, we give a simpler derivation of this
radiation formula, including an estimation of the directional dependence of the
radiation. We find that the splitting of the energy-momentum tensor into a
bound part I' and an emitted part II' is consistent with the three conditions
introduced in the preceding paper, also for each direction within the future
light cone.


title: Future Global in time einsteinian spacetimes with U(1) isometry group

abstract:
  We prove that spacetimes satisfying the vacuum Einstein equations on a
manifold of the form $\Sigma \times U(1)\times R$ where $\Sigma $ is a compact
surface of genus $G>1$ and where the Cauchy data is invariant with respect to
U(1) and sufficiently small exist for an infinite proper time in the expanding
direction.


title:
In the Search of Singularity-Free Cosmological Models in Effective
  Actions

abstract:
  Fundamental theories, like strings, supergravity, Kaluza-Klein, lead after
dimensional reduction and a suitable choice of field configurations, to an
effective action in four dimensions where gravity is coupled non-mininally to
one scalar field, and minimally to another scalar field. These scalar fields
couple non-trivially between themselves. A radiation field is also considered
in this effective action. All the possibilities connected to those fundamental
theories are labeled by two parameters $n$ (related to the non-trivial coupling
of the scalar fields) and $\omega$, connected to the coupling of the
Brans-Dicke like field to gravity. Exact solutions are found, exhibiting a
singulariy-free behaviour, from the four dimensional point of view, for some
values of those parameter. The flatness and horizon problems for these
solutions are also analyzed. It is discussed to which extent the solutions
found are non-singular from the point of view of the original frames. This
reveals to be a much complex problem.


title: Dirac observables and the phase space of general relativity

abstract:
  In the canonical approach to general relativity it is customary to
parametrize the phase space by initial data on spacelike hypersurfaces.
However, if one seeks a theory dealing with observations that can be made by a
single localized observer, it is natural to use a different description of the
phase space. This results in a different set of Dirac observables from that
appearing in the conventional formulation. It also suggests a possible solution
to the problem of time, which has been one of the obstacles to the development
of a satisfactory quantum theory of gravity.


title: Cosmological term as a source of mass

abstract:
  In the spherically symmetric case the dominant energy condition together with
the requirements of regularity at the center, asymptotic flatness and
fineteness of the ADM mass, defines the family of asymptotically flat globally
regular solutions to the Einstein minimally coupled equations which includes
the class of metrics asymptotically de Sitter at approaching the regular
center. The source term corresponds to an r-dependent cosmological term given
by the second rank symmetric tensor invariant under boosts in the radial
direction and evolving from de Sitter vacuum in the origin to Minkowski vacuum
at infinity. Space-time symmetry changes smoothly from the de Sitter group at
the center to the Lorentz group at infinity through the radial boosts in
between. The standard formula for the ADM mass relates it to the de Sitter
vacuum replacing a central singularity at the scale of symmetry restoration.
For masses exceeding a certain critical value m_{crit} de Sitter-Schwarzschild
geometry describes a vacuum nonsingular black hole, while beyond m_{crit} it
describes a G-lump which is a vacuum selfgravitating particlelike structure
without horizons. Quantum energy spectrum of G-lump is shifted down by the
binding energy, and zero-point vacuum mode is fixed at the value corresponding
to the Hawking temperature from the de Sitter horizon.


title: Metric and Curvature in Gravitational Phase Space

abstract:
  At a fixed point in spacetime (say, x_0), gravitational phase space consists
of the space of symmetric matrices F^{ab} [corresponding to the canonical
momentum pi^{ab}(x_0) and of symmetric matrices {G_{ab}}[corresponding to the
canonical metric g_{ab}(x_0), where 1 \leq a,b \leq n, and, crucially, the
matrix {G_{ab}} is necessarily positive definite, i.e. \sum u^a G_{ab}u^b > 0
whenever \sum (u^a)^2 > 0. In an alternative quantization procedure known as
Metrical Quantization, the first and most important ingredient is the
specification of a suitable metric on classical phase space. Our choice of
phase space metrics, guided by a recent study of Affine Quantum Gravity, leads
to gravitational phase space geometries which possess constant scalar curvature
and may be regarded as higher dimensional analogs of the Poincare plane, which
applies when n=1. This result is important because phase spaces endowed with
such symmetry lead naturally via the procedures of Metrical Quantization to
acceptable Hilbert spaces of high dimension.


title: Spacetime Warps for Spinning Particles Possible?

abstract:
  By incorporating spinning particles into the framework of classical General
Relativity, the theory is changed insofar, as, though using holonome
coordinates, the connexion becomes asymmetrical. This implies, that partial
derivatives do not commute any longer. Hence, the class of functions under
consideration has to be extended. A non-minimal extension leads to the
possibility of spacetime warps for spinning particles.


title: Vacuum polarization on the spinning circle

abstract:
  Vacuum polarization of a massive scalar field in the background of a
two-dimensional version of a spinning cosmic string is investigated. It is
shown that when the `radius of the universe' is such that spacetime is globally
hyperbolic the vacuum fluctuations are well behaved, diverging though on the
`chronology horizon'. Naive use of the formulae when spacetime is nonglobally
hyperbolic leads to unphysical results. It is also pointed out that the set of
normal modes used previously in the literature to address the problem gives
rise to two-point functions which do not have a Hadamard form, and therefore
are not physically acceptable. Such normal modes correspond to a locally (but
not globally) Minkowski time, which appears to be at first sight a natural
choice of time to implement quantization.


title:
Innermost circular orbit of binary black holes at the third
  post-Newtonian approximation

abstract:
  The equations of motion of two point masses have recently been derived at the
3PN approximation of general relativity. From that work we determine the
location of the innermost circular orbit or ICO, defined by the minimum of the
binary's 3PN energy as a function of the orbital frequency for circular orbits.
We find that the post-Newtonian series converges well for equal masses. Spin
effects appropriate to corotational black-hole binaries are included. We
compare the result with a recent numerical calculation of the ICO in the case
of two black holes moving on exactly circular orbits (helical symmetry). The
agreement is remarkably good, indicating that the 3PN approximation is adequate
to locate the ICO of two black holes with comparable masses. This conclusion is
reached with the post-Newtonian expansion expressed in the standard Taylor
form, without using resummation techniques such as Pad\'e approximants and/or
effective-one-body methods.


title:
Post-Newtonian approximation for isolated systems calculated by matched
  asymptotic expansions

abstract:
  Two long-standing problems with the post-Newtonian approximation for isolated
slowly-moving systems in general relativity are: (i) the appearance at high
post-Newtonian orders of divergent Poisson integrals, casting a doubt on the
soundness of the post-Newtonian series; (ii) the domain of validity of the
approximation which is limited to the near-zone of the source, and prevents
one, a priori, from incorporating the condition of no-incoming radiation, to be
imposed at past null infinity. In this article, we resolve the problem (i) by
iterating the post-Newtonian hierarchy of equations by means of a new
(Poisson-type) integral operator that is free of divergencies, and the problem
(ii) by matching the post-Newtonian near-zone field to the exterior field of
the source, known from previous work as a multipolar-post-Minkowskian expansion
satisfying the relevant boundary conditions at infinity. As a result, we obtain
an algorithm for iterating the post-Newtonian series up to any order, and we
determine the terms, present in the post-Newtonian field, that are associated
with the gravitational-radiation reaction onto an isolated slowly-moving matter
system.


title: Gravitation and Nonlocality

abstract:
  The physical basis of the standard theory of general relativity is examined
and a nonlocal theory of accelerated observers is described that involves a
natural generalization of the hypothesis of locality. The nonlocal theory is
confronted with experiment via an indirect approach. The implications of the
results for gravitation are briefly discussed.


title: Algebraic approach to time-delay data analysis for LISA

abstract:
  Cancellation of laser frequency noise in interferometers is crucial for
attaining the requisite sensitivity of the triangular 3-spacecraft LISA
configuration. Raw laser noise is several orders of magnitude above the other
noises and thus it is essential to bring it down to the level of other noises
such as shot, acceleration, etc. Since it is impossible to maintain equal
distances between spacecrafts, laser noise cancellation must be achieved by
appropriately combining the six beams with appropriate time-delays. It has been
shown in several recent papers that such combinations are possible. In this
paper, we present a rigorous and systematic formalism based on algebraic
geometrical methods involving computational commutative algebra, which
generates in principle {\it all} the data combinations cancelling the laser
frequency noise. The relevant data combinations form the first module of
syzygies, as it is called in the literature of algebraic geometry. The module
is over a polynomial ring in three variables, the three variables corresponding
to the three time-delays around the LISA triangle. Specifically, we list
several sets of generators for the module whose linear combinations with
polynomial coefficients generate the entire module. We find that this formalism
can also be extended in a straight forward way to cancel Doppler shifts due to
optical bench motions. The two modules are infact isomorphic.
  We use our formalism to obtain the transfer functions for the six beams and
for the generators. We specifically investigate monochromatic gravitational
wave sources in the LISA band and carry out the maximisiation over linear
combinations of the generators of the signal-to-noise ratios with the frequency
and source direction angles as parameters.


title: Pair of null gravitating shells I. Space of solutions and its symmetries

abstract:
  The dynamical system constituted by two spherically symmetric thin shells and
their own gravitational field is studied. The shells can be distinguished from
each other, and they can intersect. At each intersection, they exchange energy
on the Dray, 't Hooft and Redmount formula. There are bound states: if the
shells intersect, one, or both, external shells can be bound in the field of
internal shells. The space of all solutions to classical dynamical equations
has six components; each has the trivial topology but a non trivial boundary.
Points within each component are labeled by four parameters. Three of the
parameters determine the geometry of the corresponding solution spacetime and
shell trajectories and the fourth describes the position of the system with
respect to an observer frame. An account of symmetries associated with
spacetime diffeomorphisms is given. The group is generated by an infinitesimal
time shift, an infinitesimal dilatation and a time reversal.


title:
Pair of null gravitating shells II. Canonical theory and embedding
  variables

abstract:
  The study of the two shell system started in our first paper ``Pair of null
gravitating shells I'' (gr-qc/0112060) is continued. An action functional for a
single shell due to Louko, Whiting and Friedman is generalized to give
appropriate equations of motion for two and, in fact, any number of spherically
symmetric null shells, including the cases when the shells intersect. In order
to find the symplectic structure for the space of solutions described in paper
I, the pull back to the constraint surface of the Liouville form determined by
the action is transformed into new variables. They consist of Dirac
observables, embeddings and embedding momenta (the so-called Kucha\v{r}
decomposition). The calculation includes the integration of a set of coupled
partial differential equations. A general method of solving the equations is
worked out.


title: Pair of null gravitating shells III. Algebra of Dirac's observables

abstract:
  The study of the two-shell system started in ``Pair of null gravitating
shells I and II'' (gr-qc/0112060--061) is continued. The pull back of the
Liouville form to the constraint surface, which contains complete information
about the Poisson brackets of Dirac observables, is computed in the singular
double-null Eddington-Finkelstein (DNEF) gauge. The resulting formula shows
that the variables conjugate to the Schwarzschild masses of the intershell
spacetimes are simple combinations of the values of the DNEF coordinates on
these spacetimes at the shells. The formula is valid for any number of in- and
out-going shells. After applying it to the two-shell system, the symplectic
form is calculated for each component of the physical phase space; regular
coordinates are found, defining it as a symplectic manifold. The symplectic
transformation between the initial and final values of observables for the
shell-crossing case is written down.


title: Determination of Cosmological Constant from Gauge Theory of Gravity

abstract:
  Combining general relativity and gravitational gauge theory, the cosmological
constant is determined theoretically. The cosmological constant is related to
the average vacuum energy of gravitational gauge field. Because the vacuum
energy of gravitational gauge field is negative, the cosmological constant is
positive, which generates repulsive force on stars to make the expansion rate
of the Universe accelerated. A rough estimation of it gives out its magnitude
of the order of $10^{-52} m^{-2}$, which is well constant with experimental
results.


title: Naked Singularities in Spherically Symmetric, Self-Similar Spacetimes

abstract:
  We show that all known naked singularities in spherically symmetric
self-similar spacetimes arise as a result of singular initial matter
distribution. This is a result of the peculiarity of the coordinate
transformation that takes these spacetimes into a separable form. Therefore,
these examples of naked singularities are of no apparent consequence to
astrophysical observations or theories.


title:
The dark matter and the condensed description by the gravitational
  fields in the field theory

abstract:
  In this work the approach for a description of the physical systems about
whiches it is not possible to get basicly the total information is suggested.
  As a result the differential equations, the solutions of which characterize
the physical system, must bieng obtained from the demand of the minimality of
the generalized variance.
  As the understanding of the particles trajectory absents in the quantum
theory we shall consider that the Riemannian space-time is the effective one,
postulating the metric tensor on the base of the reduced density matrix of the
gravitational fields.


title: The de Sitter/Anti- de Sitter Black Holes phase transition?

abstract:
  We investigate the Schwarzschild-Anti-deSitter (SAdS) and SdS BH
thermodynamics in 5d higher derivative gravity. The interesting feature of
higher derivative gravity is the possibility for negative (or zero) SdS (or
SAdS) BH entropy which depends on the parameters of higher derivative terms.
The appearence of negative entropy may indicate a new type instability where a
transition between SdS (SAdS) BH with negative entropy to SAdS (SdS) BH with
positive entropy would occur or where definition of entropy should be modified.


title: Hoop Conjecture and Cosmic Censorship in the Brane-World

abstract:
  The initial data of gravity for a cylindrical matter distribution confined on
the brane is studied in the framework of the single brane Randall-Sundrum
scenario. In this scenario, 5-dimensional aspect of gravity appears in the
short range gravitational interaction. We found that the sufficiently thin
configuration of matter leads to the formation of the marginal surface even if
the configuration is infinitely long. This means that the hoop conjecture
proposed by Thorne does not hold in the Randall-Sundrum scenario; Even if a
mass $M$ does not get compacted into a region whose circumference in every
direction is ${\cal C}\le 4\pi GM$, black holes with horizons can form in the
Randall-Sundrum scenario.


title: Cosmic inventory of energy densities: issues and concerns

abstract:
  The dynamics of our universe is characterised by the density parameters for
cosmological constant ($\Omega_V$), nonbaryonic darkmatter($\Omega_{\rm
wimp}$), radiation ($\Omega_R$) and baryons ($\Omega_B$). To these parameters
-- which describe the smooth background universe -- one needs to add at least
another dimensionless number ($\sim 10^{-5}$) characterising the strength of
primordial fluctuations in the gravitational potential, in order to ensure
formation of structures by gravitational instability.
  I discuss several issues related to the description of the universe in terms
of these numbers and argue that we do not yet have a fundamental understanding
of these issues.


title: The black hole tunnel phenomenon

abstract:
  The potentials of spin-weighted wave equations in various Kerr-Newman black
holes are analyzed. They all form singular potential barriers at the event
horizon. Applying the WKB approximation it is shown that no particle can tunnel
out of the interior of a static black hole. However, photons inside a
non-extremely rotating Kerr black hole may tunnel out into the outer space,
whereas neutrinos, electrons, and gravitons may not. If the rotation is
extremal, any particle may tunnel out, under restrictive conditions. It is
unknown whether photons and gravitons may tunnel out if the black hole is
charged and rotating.


title: Discrete scalar field and general relativity

abstract:
  What is the nature - continuous or discrete - of matter and of its
fundamental interactions? The physical meaning, the properties and the
consequences of a discrete scalar field are discussed; limits for the validity
of a mathematical description of fundamental physics in terms of continuum
fields are a natural outcome of discrete fields with discrete interactions. Two
demarcating points (a near and a far) define a domain where no difference
between the discrete and the standard continuum field formalisms can be
experimentally detected. Discrepancies, however, can be observed as a
continuous-interaction is always stronger below the near point and weaker above
the far point than a discrete one. The connections between the discrete scalar
field and gravity from general relativity are discussed. Whereas vacuum
solutions of general relativity can be retrieved from discrete scalar field
solutions, this cannot be extended to solutions in presence of massive sources
as they require a true tensor metric field. Contact is made, on passing, with
the problem of dark matter and the rotation curve of galaxies, with inflation
and the accelerated expansion, the apparent anomaly in the Pioneer spacecraft
acceleration, the quantum Hall effect, high-$T_{c}$ superconductivity, quark
confinement, and with Tsallis generalized one-parameter statistics as some
possible manifestation of discrete interaction and of an essentially discrete
world.


title: Asymptotically Non-Static Kerr-deSitter Spacetime With No Event Horizon

abstract:
  We present our derivations for Kerr-deSitter metric in a proper comoving
coordinate system.It asymptotically approaches to the deSitter metric in
Robertson-walker form.This has been done by considring the stationary
axially-symmetric spacetime in which motion of particle is integrable.That is
the Hamilton-Jacobi and Klein-Gordon equations are separable.In this form it is
asymptotically consistent with comoving frame.


title: The kinematical frame of Loop Quantum Gravity I

abstract:
  In loop quantum gravity in the connection representation, the quantum
configuration space $\bar{\mathcal{A}/\mathcal{G}}$, which is a compact space,
is much larger than the classical configuration space $\mathcal{A}/%
\mathcal{G}$ of connections modulo gauge transformations. One finds that $%
\bar{\mathcal{A}/\mathcal{G}}$ is homeomorphic to the space $Hom(%
\mathcal{L}_{\ast},G))/Ad$. We give a new, natural proof of this result,
suggesting the extension of the hoop group $\mathcal{L}_{\ast}$ to a larger,
compact group $\mathcal{M}(\mathcal{L}_{\ast})$ that contains $%
\mathcal{L}_{\ast}$ as a dense subset. This construction is based on almost
periodic functions. We introduce the Hilbert algebra $L_{2}(\mathcal{M}(%
\mathcal{L}_{\ast}))$ of $\mathcal{M}(\mathcal{L}_{\ast})$ with respect to the
Haar measure $\xi $ on $\mathcal{M}(\mathcal{L}_{\ast})$. The measure $% \xi $
is shown to be invariant under 3-diffeomorphisms. This is the first step in a
proof that $L_{2}(\mathcal{M}(\mathcal{L}_{\ast}))$ is the appropriate Hilbert
space for loop quantum gravity in the loop representation. In a subsequent
paper, we will reinforce this claim by defining an extended loop transform and
its inverse.


title:
Anomalous dispersion of density waves in the early universe with
  positive cosmological constant

abstract:
  Density perturbations in the flat (K=0) Robertson-Walker universe with
radiation ($p=\epsilon/3$) and positive cosmological constant ($\Lambda>0$) are
investigated. The phenomenon of anomalous dispersion of acoustic waves on
$\Lambda$ is discussed.


title: How Is the Maximum Entropy of a Quantized Surface Related to Its Area?

abstract:
  The maximum entropy of a quantized surface is demonstrated to be proportional
to the surface area in the classical limit. The result is valid in loop quantum
gravity, and in a somewhat more general class of approaches to surface
quantization. The maximum entropy is calculated explicitly for some specific
cases.


title:
Slowly decaying tails of massive scalar fields in spherically symmetric
  spacetimes

abstract:
  We study the dominant late-time behaviors of massive scalar fields in static
and spherically symmetric spacetimes. Considering the field evolution in the
far zone where the gravitational field is weak, we show under which conditions
the massive field oscillates with an amplitude that decays slowly as $t^{-5/6}$
at very late times, as previously found in (say) the Schwarzschild case. Our
conclusion is that this long-lived oscillating tail is generally observed at
timelike infinity in black hole spacetimes, while it may not be able to survive
if the central object is a normal star. We also discuss that such a remarkable
backscattering effect is absent for the field near the null cone at larger
spatial distances.


title:
Are spacetime horizons higher dimensional sources of energy fields? (The
  black hole case)

abstract:
  We explore the possibility that spacetime horizons in 4D general relativity
can be treated as manifestations of higher dimensions that induce fields on our
4D spacetime. In this paper we discuss the black hole event horizon, as an
example (we leave the cosmological case for future discussion). Starting off
from the field equations of gravity in 5D and some conditions on the metric we
construct a spacetime whose imbedding is a 4D generalization of the
Schwarzchild metric. The external region of the imbedded spacetime is found to
contain two distinct fields. We discuss the properties of the fields and the
potential implications. Taken as they are, the results suggest that the
collapse of matter to form a horizon may have non-local consequences on the
geometry of spacetime. In general, the use of horizon-confined mass as a
coordinate suggests three potential features of our universe. The first is that
the observed 4D spacetime curvature and ordinary matter fields may be hybrid
features of 5D originating from the mixing of coordinates. Secondly, because
the fifth coordinate induces physical fields on the 4D hyperface, the global
metric of the universe may not be asymptotically flat. And finally, associating
matter with an independent dimension points towards a theory of nature that is
scale invariant.


title: Geometrical Aspects of Cosmic Magnetic Fields

abstract:
  We discuss how the vector nature of magnetic fields, and the geometrical
interpretation of gravity introduced by general relativity, lead to a special
coupling between magnetism and spacetime curvature. This magneto-geometrical
interaction effectively transfers the tension properties of the field into the
spacetime fabric, triggering a variety of effects with potentially far-reaching
implications.


title: Exploring the global topology of the universe

abstract:
  In this talk work done by our group on cosmic topology is reviewed. It ranges
from early attempts to solve a famous controversy about quasars through the
multiplicity of images, to quantum cosmology in this context and an application
to QED renormalization.


title: Cosmic Shells

abstract:
  When a potential for a scalar field has two local minima there arise
spherical shell-type solutions of the classical field equations due to
gravitational attraction. We establish such solutions numerically in a space
which is asymptotically de Sitter. It generically arises when the energy scale
characterizing the scalar field potential is much less than the Planck scale.
It is shown that the mirror image of the shell appears in the other half of the
Penrose diagram. The configuration is smooth everywhere with no physical
singularity.


title: On gravitational interaction of fermions

abstract:
  We discuss some aspects of the gravitational interaction of the relativistic
quantum particles with spin 1/2. The exact Foldy-Wouthuysen transformation is
constructed for the Dirac particle coupled to the static spacetime metric. The
quasi-relativistic limit of the theory is then analyzed. Using the analogous
method, we obtain the exact Cini-Touschek transformation and discuss the
ultra-relativistic limit of the fermion theory. We show that the
Foldy-Wouthuysen transformation is not uniquely defined, and the corresponding
ambiguity is deeply rooted in the relativistic quantum theory.


title:
Post-Newtonian gravitational radiation and equations of motion via
  direct integration of the relaxed Einstein equations. II. Two-body equations
  of motion to second post-Newtonian order, and radiation-reaction to 3.5
  post-Newtonian order

abstract:
  We derive the equations of motion for binary systems of compact bodies in the
post-Newtonian (PN) approximation to general relativity. Results are given
through 2PN order (order (v/c)^4 beyond Newtonian theory), and for
gravitational radiation reaction effects at 2.5PN and 3.5PN orders. The method
is based on a framework for direct integration of the relaxed Einstein
equations (DIRE) developed earlier, in which the equations of motion through
3.5PN order can be expressed in terms of Poisson-like potentials that are
generalizations of the instantaneous Newtonian gravitational potential, and in
terms of multipole moments of the system and their time derivatives. All
potentials are well defined and free of divergences associated with integrating
quantities over all space. Using a model of the bodies as spherical,
non-rotating fluid balls whose characteristic size s is small compared to the
bodies' separation r, we develop a method for carefully extracting only terms
that are independent of the parameter s, thereby ignoring tidal interactions,
spin effects, and internal self-gravity effects. Through 2.5PN order, the
resulting equations agree completely with those obtained by other methods; the
new 3.5PN back-reaction results are shown to be consistent with the loss of
energy and angular momentum via radiation to infinity.


title: The quantum theory of a quadratic gravity action for heterotic strings

abstract:
  The wave function for the quadratic gravity theory derived from the heterotic
string effective action is deduced to first order in ${{e^{-\Phi}}\over
{g_4^2}}$ by solving a perturbed second-order Wheeler-DeWitt equation, assuming
that the potential is slowly varying with respect to $\Phi$. Predictions for
inflation based on the solution to the second-order Wheeler-DeWitt equation
continue to hold for this theory. It is shown how formal expressions for the
average paths in minisuperspace $\{< a(t) >, < \Phi(t)> \}$ determine the
shifts from the classical solutions to $a_{cl}(t)$ and $\Phi_{cl}(t)$, which
occur only at third order in the expansion of the integrals representing the
expectation values.


title:
Topological derivation of Black Hole entropy by analogy with a chain
  polymer

abstract:
  The generic crease set of an event horizon possesses anisotropic structure
though most of black holes are dynamically stable. This fact suggests that a
generic almost spherical black hole has a very crumpled crease set in a
microscopic scale though the crease set is similar to a point-wise crease set
in a macroscopic scale. In the present article, we count the number of such
micro-states of an almost spherical black hole by analogy with an elastic chain
polymer. This estimation of black hole entropy reproduces the well-known
Bekenstein-Hawking entropy of a Schwarzschild black hole.


title: Quantum Space-Time as a Quantum Causal Set

abstract:
  A recently proposed algebraic representation of the causal set model of the
small-scale structure of space-time of Sorkin et al. is briefly reviewed and
expanded. The algebraic model suggested, called quantum causal set, is
physically interpreted as a locally finite, causal and quantal version of the
kinematical structure of general relativity: the 4-dimensional Lorentzian
space-time manifold and its continuous local orthochronous Lorentz symmetries.
We discuss various possible dynamical scenarios for quantum causal sets mainly
by using sheaf-theoretic ideas, and we entertain the possibility of
constructing an inherently finite and genuinely smooth space-time background
free quantum theory of gravity. At the end, based on the quantum causal set
paradigm, we anticipate and roughly sketch out a potential future development
of a noncommutative topology, sheaf and topos theory suitable for quantum
space-time structure and its dynamics.


title: Angular momentum effects in weak gravitational fields

abstract:
  It is shown that, contrary to what is normally expected, it is possible to
have angular momentum effects on the geometry of space time at the laboratory
scale, much bigger than the purely Newtonian effects. This is due to the fact
that the ratio between the angular momentum of a body and its mass, expressed
as a length, is easily greater than the mass itself, again expressed as a
length.


title: Conformal geodesics on vacuum space-times

abstract:
  We discuss properties of conformal geodesics on general, vacuum, and warped
product space-times and derive a system of conformal deviation equations. The
results are used to show how to construct on the Schwarzschild-Kruskal
space-time global conformal Gauss coordinates which extends smoothly and
without degeneracy to future and past null infinity.


title: Geometrical approach to light in inhomogeneous media

abstract:
  Electromagnetism in an inhomogeneous dielectric medium at rest is described
using the methods of differential geometry. In contrast to a general
relativistic approach the electromagnetic fields are discussed in
three-dimensional space only. The introduction of an appropriately chosen
three-dimensional metric leads to a significant simplification of the
description of light propagation in an inhomogeneous medium: light rays become
geodesics of the metric and the field vectors are parallel transported along
the rays. The new metric is connected to the usual flat space metric
diag[1,1,1] via a conformal transformation leading to new, effective values of
the medium parameters leading to an effective constant value of the index of
refraction n=1. The corresponding index of refraction is thus constant and so
is the effective velocity of light. Space becomes effectively empty but curved.
All deviations from straight line propagation are now due to curvature. The
approach is finally used for a discussion of the Riemann-Silberstein vector, an
alternative, complex formulation of the electromagnetic fields.


title: A Possible Test for Quadratic Gravity in $d \ge 4$ dimensions

abstract:
  In this letter we consider the Einsteinian strengths and dynamical degrees of
freedom for quadratic gravity. We show that purely metric quadratic gravity
theories are much stronger in Einsteinian sense than the competitive quadratic
gravity theories which admit torsion.


title: Gravity as a Bend of 4D Elastic Plate

abstract:
  Gravity is treated as manifestation of bending of 4D plate at the variational
functionals level. Some estimates of elastic constants of space-time are made.
Field lagrangians and Einstein equations are discussed in view point of the
approach.


title: Radiative spacetimes

abstract:
  The question of existence of general, asymptotically flat radiative
spacetimes and examples of explicit classes of radiative solutions of
Einstein's field equations are discussed in the light of some new developments.
The examples are cylindrical waves, Robinson-Trautman and type N spacetimes and
especially boost-rotation symmetric spacetimes representing uniformly
accelerated particles or black holes.


abstract:
  This is the account of the workshop Exact solutions and their interpretation
at the 16-th International Conference on General Relativity and Gravitation
held in Durban, July 15-21, 2001. Work reported in 32 oral contributions
spanned a wide variety of topics, ranging from exact radiative spacetimes to
cosmological solutions. Two invited review talks, on the role of exact
solutions in string theory and in cosmology, are also described.


title: Quantum Space-Time: Deformed Symmetries Versus Broken Symmetries

abstract:
  Several recent studies have concerned the faith of classical symmetries in
quantum space-time. In particular, it appears likely that quantum (discretized,
noncommutative,...) versions of Minkowski space-time would not enjoy the
classical Lorentz symmetries. I compare two interesting cases: the case in
which the classical symmetries are "broken", i.e. at the quantum level some
classical symmetries are lost, and the case in which the classical symmetries
are "deformed", i.e. the quantum space-time has as many symmetries as its
classical counterpart but the nature of these symmetries is affected by the
space-time quantization procedure. While some general features, such as the
emergence of deformed dispersion relations, characterize both the
symmetry-breaking case and the symmetry-deformation case, the two scenarios are
also characterized by sharp differences, even concerning the nature of the new
effects predicted. I illustrate this point within an illustrative calculation
concerning the role of space-time symmetries in the evaluation of
particle-decay amplitudes. The results of the analysis here reported also show
that the indications obtained by certain dimensional arguments, such as the
ones recently considered in hep-ph/0106309 may fail to uncover some key
features of quantum space-time symmetries.


title: Hamiltonian and Volume Operators

abstract:
  2+1 gravity coupled to a massless scalar field has an initial singularity
when the spatial slices are compact. The quantized model is used here to
investigate several issues of quantum gravity. The spectrum of the volume
operator is studied at the initial singularity. The energy spectrum is
obtained. Dynamics of the universe is also investigated.


title: Space time and rotations

abstract:
  The paper considers the problem of finding the metric of space time around a
rotating, weakly gravitating body. Both external and internal metric tensors
are consistently found, together with an appropriate source tensor. All tensors
are calculated at the lowest meaningful approximation in a power series. The
two physical parameters entering the equations (the mass and the angular
momentum per unit mass) are assumed to be such that the mass effects are
negligible with respect to the rotation effects. A non zero Riemann tensor is
obtained. The order of magnitude of the effects at the laboratory scale is such
as to allow for experimental verification of the theory.


title:
Exact Foldy-Wouthuysen transformation for spin 0 particle in curved
  space

abstract:
  Up to now, the only known exact Foldy- Wouthuysen transformation (FWT) in
curved space is that concerning Dirac particles coupled to static spacetime
metrics. Here we construct the exact FWT related to a real spin-0 particle for
the aforementioned spacetimes. This exact transformation exists independently
of the value of the coupling between the scalar field and gravity. Moreover,
the gravitational Darwin term written for the conformal coupling is one third
of the relevant term in the fermionic case.


title: Gravitational quasinormal modes for Anti-de Sitter black holes

abstract:
  Quasinormal mode spectra for gravitational perturbations of black holes in
four dimensional de Sitter and anti-de Sitter space are investigated. The
anti-de Sitter case is relevant to the ADS-CFT correspondence in superstring
theory. The ADS-CFT correspondence suggests a prefered set of boundary
conditions.


title: Wave Tails in Time Dependent Backgrounds

abstract:
  It is well-known that waves propagating under the influence of a scattering
potential develop ``tails''. However, the study of late-time tails has so far
been restricted to time-independent backgrounds. In this paper we explore the
late-time evolution of spherical waves propagating under the influence of a
{\it time-dependent} scattering potential. It is shown that the tail structure
is modified due to the temporal dependence of the potential. The analytical
results are confirmed by numerical calculations.


title: Axially Symmetric, Spatially Homothetic Spacetimes

abstract:
  We show that the existence of appropriate spatial homothetic Killing vectors
is directly related to the separability of the metric functions for axially
symmetric spacetimes. The density profile for such spacetimes is (spatially)
arbitrary and admits any equation of state for the matter in the spacetime.
When used for studying axisymmetric gravitational collapse, such solutions do
not result in a locally naked singularity.


title: Cosmology models with \Omega_M-dependent cosmological constant

abstract:
  We investigate the evolution of the scale factor in a cosmological model in
which the cosmological constant is given by the scalar arisen by the
contraction of the stress-energy tensor.


title: Mass loss by a scalar charge in an expanding universe

abstract:
  We study the phenomenon of mass loss by a scalar charge -- a point particle
that acts a source for a noninteracting scalar field -- in an expanding
universe. The charge is placed on comoving world lines of two cosmological
spacetimes: a de Sitter universe, and a spatially-flat, matter-dominated
universe. In both cases, we find that the particle's rest mass is not a
constant, but that it changes in response to the emission of monopole scalar
radiation by the particle. In de Sitter spacetime, the particle radiates all of
its mass within a finite proper time. In the matter-dominated cosmology, this
happens only if the charge of the particle is sufficiently large; for smaller
charges the particle first loses some of its mass, but then regains it all
eventually.


title: Instability of scalar charges in 1+1D and 2+1D

abstract:
  We study the phenomenon of mass loss by a scalar charge -- a point particle
which acts as a source for a (non-interacting) scalar field -- in
(1+1)-dimensional and (2+1)-dimensional flat spacetime. We find that such
particles are unstable against self interaction: they lose their mass through
the emission of monopole radiation. This is in sharp contrast with scalar
charges in (3+1)-dimensional flat spacetime, where no such phenomenon occurs.


title: Spacetime foam

abstract:
  Spacetime is composed of a fluctuating arrangement of bubbles or loops called
spacetime foam, or quantum foam. We use the holographic principle to deduce its
structure, and show that the result is consistent with gedanken experiments
involving spacetime measurements. We propose to use laser-based atom
interferometry techniques to look for spacetime fluctuations. Our analysis
makes it clear that the physics of quantum foam is inextricably linked to that
of black holes. A negative experimental result, therefore, might have
non-trivial ramifications for semiclassical gravity and black hole physics.


title: The Thomas precession and the transformation to rotating frames

abstract:
  The Thomas precession is calculated using three different transformations to
the rotating frame. It is shown that for sufficiently large values of $v/c$,
important differences in the predicted angle of precession appear, depending on
the transformation used. For smaller values of $v/c$ these differences might be
measured by extending the time of observation.


title: On the Penrose Inequality for general horizons

abstract:
  For asymptotically flat initial data of Einstein's equations satisfying an
energy condition, we show that the Penrose inequality holds between the ADM
mass and the area of an outermost apparent horizon, if the data are restricted
suitably. We prove this by generalizing Geroch's proof of monotonicity of the
Hawking mass under a smooth inverse mean curvature flow, for data with
non-negative Ricci scalar. Unlike Geroch we need not confine ourselves to
minimal surfaces as horizons. Modulo smoothness issues we also show that our
restrictions on the data can locally be fulfilled by a suitable choice of the
initial surface in a given spacetime.


title: On the spinning C-metric

abstract:
  Physical interpretation of some stationary and non-stationary regions of the
spinning C-metric is presented. They represent different spacetime regions of a
uniformly accelerated Kerr black hole.
  Stability of geodesics corresponding to equilibrium points in a general
stationary spacetime with an additional symmetry is also studied and results
are then applied to the spinning C-metric.


title: Spherically symmetric scalar field collapse in any dimension

abstract:
  We describe a formalism and numerical approach for studying spherically
symmetric scalar field collapse for arbitrary spacetime dimension d and
cosmological constant Lambda. The presciption uses a double null formalism, and
is based on field redefinitions first used to simplify the field equations in
generic two-dimensional dilaton gravity. The formalism is used to construct
code in which d and Lambda are input parameters. The code reproduces known
results in d = 4 and d = 6 with Lambda = 0. We present new results for d = 5
with zero and negative Lambda.


title:
On a class of stable, traversable Lorentzian wormholes in classical
  general relativity

abstract:
  It is known that Lorentzian wormholes must be threaded by matter that
violates the null energy condition. We phenomenologically characterize such
exotic matter by a general class of microscopic scalar field Lagrangians and
formulate the necessary conditions that the existence of Lorentzian wormholes
imposes on them. Under rather general assumptions, these conditions turn out to
be strongly restrictive. The most simple Lagrangian that satisfies all of them
describes a minimally coupled massless scalar field with a reversed sign
kinetic term. Exact, non-singular, spherically symmetric solutions of
Einstein's equations sourced by such a field indeed describe traversable
wormhole geometries. These wormholes are characterized by two parameters: their
mass and charge. Among them, the zero mass ones are particularly simple,
allowing us to analytically prove their stability under arbitrary space-time
dependent perturbations. We extend our arguments to non-zero mass solutions and
conclude that at least a non-zero measure set of these solutions is stable.


title: Simplicial Euclidean and Lorentzian Quantum Gravity

abstract:
  One can try to define the theory of quantum gravity as the sum over
geometries. In two dimensions the sum over {\it Euclidean} geometries can be
performed constructively by the method of {\it dynamical triangulations}. One
can define a {\it proper-time} propagator. This propagator can be used to
calculate generalized Hartle-Hawking amplitudes and it can be used to
understand the the fractal structure of {\it quantum geometry}. In higher
dimensions the philosophy of defining the quantum theory, starting from a sum
over Euclidean geometries, regularized by a reparametrization invariant cut off
which is taken to zero, seems not to lead to an interesting continuum theory.
The reason for this is the dominance of singular Euclidean geometries.
Lorentzian geometries with a global causal structure are less singular. Using
the framework of dynamical triangulations it is possible to give a constructive
definition of the sum over such geometries, In two dimensions the theory can be
solved analytically. It differs from two-dimensional Euclidean quantum gravity,
and the relation between the two theories can be understood. In three
dimensions the theory avoids the pathologies of three-dimensional Euclidean
quantum gravity. General properties of the four-dimensional discretized theory
have been established, but a detailed study of the continuum limit in the
spirit of the renormalization group and {\it asymptotic safety} is till
awaiting.


title: Exact impulsive gravitational waves in spacetimes of constant curvature

abstract:
  Exact solutions exist which describe impulsive gravitational waves
propagating in Minkowski, de Sitter, or anti-de Sitter universes. These may be
either nonexpanding or expanding. Both cases in each background are reviewed
here from a unified point of view. All the main methods for their construction
are described systematically: the Penrose "cut and paste" method, explicit
construction of continuous coordinates, distributional limits of sandwich
waves, embedding from higher dimensions, and boosts of sources or limits of
infinite accelerations.
  Attention is concentrated on the most interesting specific solutions. In
particular, the nonexpanding impulsive waves that are generated by null
multipole particles are described. These generalize the well-known
Aichelburg-Sexl and Hotta-Tanaka monopole solutions. Also described are the
expanding spherical impulses that are generated by snapping and colliding
strings. Geodesics and some other properties of impulsive wave spacetimes are
also summarized.


title: Uncertainty in Measurements of Distance

abstract:
  Ng and van Dam have argued that quantum theory and general relativity give a
lower bound of L^{1/3} L_P^{2/3} on the uncertainty of any distance, where L is
the distance to be measured and L_P is the Planck length. Their idea is roughly
that to minimize the position uncertainty of a freely falling measuring device
one must increase its mass, but if its mass becomes too large it will collapse
to form a black hole. Here we show that one can go below the Ng-van Dam bound
by attaching the measuring device to a massive elastic rod. Relativistic
limitations on the rod's rigidity, together with the constraint that its length
exceeds its Schwarzschild radius, imply that zero-point fluctuations of the rod
give an uncertainty greater than or equal to L_P.


title: Quantum Radion on de Sitter branes

abstract:
  The quantum fluctuation of the relative location of two (n-1)-dimensional de
Sitter branes (i.e., of n spacetime dimensions) embedded in the
(n+1)-dimensional anti-de Sitter bulk, which we shall call the quantum radion,
is investigated at the linear perturbation level. The quantization of the
radion is done by deriving the effective action of the radion. Assuming the
positive tension brane is our universe, the effect of the quantum radion is
evaluated by using the effective Einstein equations on the brane in which the
radion contributes to the effective energy momentum tensor at the linear order
of the radion amplitude. Specifically, the rms effective energy density arising
from the quantum radion is compared with the background energy density. It is
found out that this ratio remains small for reasonable values of the parameters
of the model even without introducing a stabilizing mechanism for radion,
although the radion itself has a negative mass squared and is unstable. The
reason behind this phenomenon is also discussed.


title: Relativistic Multipoles and the Advance of the Perihelia

abstract:
  In order to shed some light in the meaning of the relativistic multipolar
expansions we consider different static solutions of the axially symmetric
vacuum Einstein equations that in the non relativistic limit have same
Newtonian moments. The motion of test particles orbiting around different
deformed attraction centers with the same Newtonian limit is studied paying
special attention to the advance of the perihelion. We find discrepancies in
the fourth order of the dimensionless parameter (mass of the attraction
center)/(semilatus rectum). An evolution equation for the difference of the
radial coordinate due to the use of different general relativistic multipole
expansions is presented.


title: Curvature Quintessence

abstract:
  The issues of quintessence and cosmic acceleration can be discussed in the
framework of higher order theories of gravity. We can define effective pressure
and energy density directly connected to the Ricci scalar of curvature of a
generic fourth order theory and then ask for the conditions to get an
accelerated expansion. Exact accelerated expanding solutions can be achieved
for several fourth order theories so that we get an alternative scheme to the
standard quintessence scalar field, minimally coupled to gravity, usually
adopted. We discuss also conformal transformations in order to see the links of
quintessence between the Jordan and Einstein frames.


title: Classical Black Hole Production in High-Energy Collisions

abstract:
  We investigate classical formation of a D-dimensional black hole in a high
energy collision of two particles. The existence of an apparent horizon is
related to the solution of an unusual boundary-value problem for Poisson's
equation in flat space. For sufficiently small impact parameter, we construct
solutions giving such apparent horizons in D=4. These supply improved estimates
of the classical cross-section for black hole production, and of the mass of
the resulting black holes. We also argue that a horizon can be found in a
region of weak curvature, suggesting that these solutions are valid starting
points for a semiclassical analysis of quantum black hole formation.


title:
Decay of massive scalar hair in the background of a black hole with a
  global monopole

abstract:
  The late-time tail behaviors of massive scalar fields are examined
analytically in the background of a black hole with a global monopole. It is
found that the presence of a solid deficit angle in the background metric makes
the massive scalar fields decay faster in the intermediate times. However, the
asymptotically late-time tail is not affected and it has the same decay rate of
$t^{-5/6}$ as in the Schwarzschild and nearly extreme Reissner-Nordstr\"{o}m
backgrounds.


title:
Cosmological Constant, Conical Defect and Classical Tests of General
  Relativity

abstract:
  We investigate the perihelion shift of the planetary motion and the bending
of starlight in the Schwarzschild field modified by the presence of a
$\Lambda$-term plus a conical defect. This analysis generalizes an earlier
result obtained by Islam (Phys. Lett. A 97, 239, 1983) to the case of a pure
cosmological constant. By using the experimental data we obtain that the
parameter $\epsilon$ characterizing the conical defect is less than $10^{-9}$
and $10^{-7}$, respectively, on the length scales associated with such
phenomena. In particular, if the defect is generated by a cosmic string, these
values correspond to limits on the linear mass densities of $10^{19}g/cm$ and
$10^{21}g/cm$, respectively.


title: What is wrong with Schwarzschild's coordinates?

abstract:
  A strict derivation of the Schwarzschild metric, based solely on Newton's law
of free fall and the equivalence principle, is presented. In the light of it,
regarding Schwarzschild's coordinates as representing the point of view of a
distant observer resting relative to the source of a centrally symmetric
gravitational field, proves illegitimate. Such point of view is better
represented by the Painleve-Gullstrand system of coordinates, which agrees with
Schwarzschild's system with respect to its spatial coordinates and time scale,
but disagrees with respect to the relation of simultaneity. A duality of the
Schwarzschild solution and its time-irreversibility is suggested. The physical
meaning of the coordinate singularity at the Schwarzschild radius is clarified.


title: Experimental measurement of photothermal effect in Fabry-Perot cavities

abstract:
  We report the experimental observation of the photothermal effect. The
measurements are performed by modulating the laser power absorbed by the
mirrors of two high-finesse Fabry-Perot cavities. The results are very well
described by a recently proposed theoretical model [M. Cerdonio, L. Conti, A.
Heidmann and M. Pinard, Phys. Rev. D 63 (2001) 082003], confirming the
correctness of such calculations. Our observations and quantitative
characterization of the photothermal effect demonstrate its critical importance
for high sensitivity interferometric displacement measurements, as those
necessary for gravitational wave detection.


title: Super-Relativity and State-Dependent Gauge Fields

abstract:
  State-dependent gauge principle invoked to realize the relativity to a
measuring device, has been proposed. Self-consistent global (cosmic) potential
forms the state space of the fundamental field and its connection, agreed with
Fubini-Study metric of $CP(N-1)$, serves as state-dependent gauge potential. In
this framework the linearity of the ordinary quantum mechanics appears as a
`tangent approximation' to the totally nonlinear underlying pre-dynamical
`functional' field theory on $CP(N-1)$.


title:
Post-Newtonian SPH calculations of binary neutron star coalescence. III.
  Irrotational systems and gravitational wave spectra

abstract:
  Using our new post-Newtonian (PN) smoothed particle hydrodynamics (SPH) code,
we have studied numerically the mergers of neutron star binaries with
irrotational initial configurations. Here we describe a new method for
constructing numerically accurate initial conditions for irrotational binary
systems with circular orbits in PN gravity. We then compute the 3D hydrodynamic
evolution of these systems until the two stars have completely merged, and we
determine the corresponding GW signals. We present results for systems with
different binary mass ratios, and for neutron stars represented by polytropes
with $\Gamma=2$ or $\Gamma=3$. Compared to mergers of corotating binaries, we
find that irrotational binary mergers produce similar peak GW luminosities, but
they shed almost no mass at all to large distances. The dependence of the GW
signal on numerical resolution for calculations performed with N>10^5 SPH
particles is extremely weak, and we find excellent agreement between runs
utilizing N=10^5 and N=10^6 SPH particles (the largest SPH calculation ever
performed to study such irrotational binary mergers). We also compute GW energy
spectra based on all calculations reported here and in our previous works. We
find that PN effects lead to clearly identifiable features in the GW energy
spectrum of binary neutron star mergers, which may yield important information
about the nuclear equation of state at extreme densities.


title: Classical formulation of Cosmic Censorship Hypothesis

abstract:
  Spacetimes admitting appropriate spatial homothetic Killing vectors are
called spatially homothetic spacetimes. Such spacetimes conform to the fact
that gravity has no length-scale for matter inhomogeneities. The matter density
for such spacetimes is (spatially) arbitrary and the matter generating the
spacetime admits {\it any} equation of state. Spatially homothetic spacetimes
necessarily possess energy-momentum fluxes. We first discuss spherically
symmetric and axially symmetric examples of such spacetimes that do not form
naked singularities for regular initial data. We then show that the Cosmic
Censorship Hypothesis is {\em equivalent} to the statement that gravity has no
length-scale for matter properties.


title: Stability of Sigma-Model Strings and Textures

abstract:
  In flat space-time, sigma-model strings and textures are both unstable to
collapse and subsequent decay. With sufficient cosmological expansion, however,
they are stable in a generalized sense: a small perturbation will cause them to
change their shape, but they do not decay. The current rate of expansion is
sufficient to stabilize strings, but not textures.


title:
On spacetimes with 3-parameter isometry group in string-inspired theory
  of gravity

abstract:
  Cylindrically symmetric stationary spacetimes are examined in the framework
of string-inpired generalized theory of gravity. In four dimensions this theory
contains a dilatonic scalar field in addition to gravity. A charged perfect
fluid representing fermionic matter is also considered. Explicit solution is
given and a discussion of the geometrical properties of the solutions found is
carried out.


title: Alternative Space-Time for the Point Mass

abstract:
  Schwarzschild's actual exterior solution (Gs) is resurrected and together
with the manifold M is shown to constitute a space-time possessing all the
properties historically thought to be required of a point mass. On the other
hand, the metric that today is ascribed to Schwarzschild, but which was in fact
first obtained by Droste and Weyl, is shown to give rise to a space-time that
is neither equivalent to Schwarzschild's nor derivable from the "historical"
properties of a point mass. Consequently, the point-mass interpretation of the
Kruskal-Fronsdal space-time (Mw, Gkf) can no longer be justified on the basis
that it is an extension of Droste and Weyl's space-time. If such an
interpretation is to be maintained, it can only be done by showing that the
properties of (Mw, Gkf) are more in accord with what a point-mass space-time
should possess than those of (M, Gs). To do this, one must first explain away
three seeming incongruities associated with (Mw, Gkf): its global
nonstationarity, the two-dimensional nature of the singularity, and the fact
that for a finite interval of time it has no singularity at all. Finally, some
of the consequences of choosing (M,Gs) as a model of a point-mass are
discussed.


title: Axial symmetry and conformal Killing vectors

abstract:
  Axisymmetric spacetimes with a conformal symmetry are studied and it is shown
that, if there is no further conformal symmetry, the axial Killing vector and
the conformal Killing vector must commute. As a direct consequence, in
conformally stationary and axisymmetric spacetimes, no restriction is made by
assuming that the axial symmetry and the conformal timelike symmetry commute.
Furthermore, we prove that in axisymmetric spacetimes with another symmetry
(such as stationary and axisymmetric or cylindrically symmetric spacetimes) and
a conformal symmetry, the commutator of the axial Killing vector with the two
others mush vanish or else the symmetry is larger than that originally
considered. The results are completely general and do not depend on Einstein's
equations or any particular matter content.


title:
On the existence of self-similar spherically symmetric wave maps coupled
  to gravity

abstract:
  We present a detailed analytical study of spherically symmetric self-similar
solutions in the SU(2) sigma model coupled to gravity. Using a shooting
argument we prove that there is a countable family of solutions which are
analytic inside the past self-similarity horizon. In addition, we show that for
sufficiently small values of the coupling constant these solutions possess a
regular future self-similarity horizon and thus are examples of naked
singularities. One of the solutions constructed here has been recently found as
the critical solution at the threshold of black hole formation.


title:
Azimuthal electric field in a static rotationally symmetric
  (2+1)-dimensional spacetime

abstract:
  The fundamental metrics, which describe any static three-dimensional
Einstein-Maxwell spacetime (depending only on a unique spacelike coordinate),
are found. In this case there are only three independent components of the
electromagnetic field: two for the vector electric field and one for the scalar
magnetic field. It is shown that we can not have any superposition of these
components of the electric and magnetic fields in this kind of static
gravitational field. One of the electrostatic Einstein-Maxwell solutions is
related to the magnetostatic solution by a duality mapping, while the second
electrostatic gravitational field must be solved separately. Solutions induced
by the more general (2+1)-Maxwell tensor on the static cylindrically symmetric
spacetimes are studied and it is shown that all of them are also connected by
duality mappings.


title: Temperature Evolution Law of Imperfect Relativistic Fluids

abstract:
  The first-order general relativistic theory of a generic dissipative
(heat-conducting, viscous, particle-creating) fluid is rediscussed from a
unified covariant frame-independent point of view. By generalizing some
previous works in the literature, we derive a formula for the temperature
variation rate, which is valid both in Eckart's (particle) and in the
Landau-Lifshitz (energy) frames. Particular attention is paid to the case of
gravitational particle creation and its possible cross-effect with the bulk
viscosity mechanism.


title:
Convergence of Scalar-Tensor theories toward General Relativity and
  Primordial Nucleosynthesis

abstract:
  In this paper, we analyze the conditions for convergence toward General
Relativity of scalar-tensor gravity theories defined by an arbitrary coupling
function $\alpha$ (in the Einstein frame). We show that, in general, the
evolution of the scalar field $(\phi)$ is governed by two opposite mechanisms:
an attraction mechanism which tends to drive scalar-tensor models toward
Einstein's theory, and a repulsion mechanism which has the contrary effect. The
attraction mechanism dominates the recent epochs of the universe evolution if,
and only if, the scalar field and its derivative satisfy certain boundary
conditions. Since these conditions for convergence toward general relativity
depend on the particular scalar-tensor theory used to describe the universe
evolution, the nucleosynthesis bounds on the present value of the coupling
function, $\alpha_0$, strongly differ from some theories to others. For
example, in theories defined by $\alpha \propto \mid\phi\mid$ analytical
estimates lead to very stringent nucleosynthesis bounds on $\alpha_0$
($\lesssim 10^{-19}$). By contrast, in scalar-tensor theories defined by
$\alpha \propto \phi$ much larger limits on $\alpha_0$ ($\lesssim 10^{-7}$) are
found.


title: Gravitational waves and dynamics of compact binary systems

abstract:
  Part A of this article is devoted to the general investigation of the
gravitational-wave emission by post-Newtonian sources. We show how the
radiation field far from the source, as well as its near-zone inner
gravitational field, can (in principle) be calculated in terms of the matter
stress-energy tensor up to any order in the post-Newtonian expansion. Part B
presents some recent applications to the problems of the dynamics and
gravitational-wave flux of compact binary systems. The precision reached in
these developments corresponds to the third post-Newtonian approximation.


title:
Illustrating Stability Properties of Numerical Relativity in
  Electrodynamics

abstract:
  We show that a reformulation of the ADM equations in general relativity,
which has dramatically improved the stability properties of numerical
implementations, has a direct analogue in classical electrodynamics. We
numerically integrate both the original and the revised versions of Maxwell's
equations, and show that their distinct numerical behavior reflects the
properties found in linearized general relativity. Our results shed further
light on the stability properties of general relativity, illustrate them in a
very transparent context, and may provide a useful framework for further
improvement of numerical schemes.


title:
Evolution of Kerr-Schild type initial data for binary black holes using
  the horizon penetrating Teukolsky equation

abstract:
  We use the Kerr-Schild type Teukolsky equation (horizon penetrating) to
evolve binary black hole initial data as proposed by Bishop {\em et al.} in the
close limit. Our results are in agreement with those recently obtained by
Sarbach {\em et al.} from the Zerilli equation evolution of the same initial
data.


title: Black holes

abstract:
  This paper is concerned with several not-quantum aspects of black holes, with
emphasis on theoretical and mathematical issues related to numerical modeling
of black hole space-times. Part of the material has a review character, but
some new results or proposals are also presented. We review the experimental
evidence for existence of black holes. We propose a definition of black hole
region for any theory governed by a symmetric hyperbolic system of equations.
Our definition reproduces the usual one for gravity, and leads to the one
associated with the Unruh metric in the case of Euler equations. We review the
global conditions which have been used in the Scri-based definition of a black
hole and point out the deficiencies of the Scri approach. Various results on
the structure of horizons and apparent horizons are presented, and a new proof
of semi-convexity of horizons based on a variational principle is given. Recent
results on the classification of stationary singularity-free vacuum solutions
are reviewed. Two new frameworks for discussing black holes are proposed: a
"naive approach", based on coordinate systems, and a "quasi-local approach",
based on timelike boundaries satisfying a null convexity condition. Some
properties of the resulting black holes are established, including an area
theorem, topology theorems, and an approximation theorem for the location of
the horizon.


title: Geometry of General Hypersurfaces in Spacetime: Junction Conditions

abstract:
  We study imbedded hypersurfaces in spacetime whose causal character is
allowed to change from point to point. Inherited geometrical structures on
these hypersurfaces are defined by two methods: first, the standard rigged
connection induced by a rigging vector (a vector not tangent to the
hypersurface anywhere); and a second, more physically adapted, where each
observer in spacetime induces a new type of connection that we call the rigged
metric connection. The generalisation of the Gauss and Codazzi equations are
also given. With the above machinery, we attack the problem of matching two
spacetimes across a general hypersurface. It is seen that the preliminary
junction conditions allowing for the correct definition of Einstein's equations
in the distributional sense reduce to the requirement that the first
fundamental form of the hypersurface be continuous. The Bianchi identities are
then proven to hold in the distributional sense. Next, we find the proper
junction conditions which forbid the appearance of singular parts in the
curvature. Finally, we derive the physical implications of the junction
conditions: only six independent discontinuities of the Riemann tensor are
allowed. These are six matter discontinuities at non-null points of the
hypersurface. For null points, the existence of two arbitrary discontinuities
of the Weyl tensor (together with four in the matter tensor) are also allowed.


title:
On a Classical, Geometric Origin of Magnetic Moments, Spin-Angular
  Momentum and the Dirac Gyromagnetic Ratio

abstract:
  By treating the real Maxwell Field and real linearized Einstein equations as
being imbedded in complex Minkowski space, one can interpret magnetic moments
and spin-angular momentum as arising from a charge and mass monopole source
moving along a complex world line in the complex Minkowski space. In the
circumstances where the complex center of mass world-line coincides with the
complex center of charge world-line, the gyromagnetic ratio is that of the
Dirac electron.


title: Numerical Approaches to Spacetime Singularities

abstract:
  This Living Review updates a previous version which its itself an update of a
review article. Numerical exploration of the properties of singularities could,
in principle, yield detailed understanding of their nature in physically
realistic cases. Examples of numerical investigations into the formation of
naked singularities, critical behavior in collapse, passage through the Cauchy
horizon, chaos of the Mixmaster singularity, and singularities in spatially
inhomogeneous cosmologies are discussed.


title: Global Hyperbolicity and Completeness

abstract:
  We prove global hyperbolicity of spacetimes under generic regularity
conditions on the metric. We then show that these spacetimes are timelike and
null geodesically complete if the gradient of the lapse and the extrinsic
curvature $K$ are integrable. This last condition is required only for the
tracefree part of $K$ if the universe is expanding.


title: From vacuum nonsingular black hole to variable cosmological constant

abstract:
  We outline the class of globally regular spherically symmetric solutions to
the minimally coupled GR equations asymptotically de Sitter in the origin and
asymptotically Schwarzschild at infinity. A source term connects smoothly de
Sitter vacuum at the regular center with Minkowski vacuum at infinity and
corresponds to anisotropic spherically symmetric vacuum defined macroscopically
by the algebraic structure of its stress-energy tensor invariant under boosts
in the radial direction. De Sitter-Schwarzschild geometry describes a vacuum
nonsingular black hole which evolves, in the course of Hawking evaporation,
towards a self-gravitating particle-like structure without horizons, G-lump.
Space-time symmetry changes smoothly from the de Sitter group in the center to
the Lorentz group at infinity, and the standard formula for the ADM mass
relates it to the de Sitter vacuum replacing a singularity at the scale of
symmetry restoration. This class of metrics is easily extended to the case of a
nonzero background cosmological constant. A source term connects then smoothly
two de Sitter vacua with different values of cosmological constant which makes
possible to associate anisotropic spherically symmetric vacuum with an
r-dependent cosmological term.


title: Gravitation and the Local Symmetry Group of Spacetime

abstract:
  According to general relativity, the interaction of a matter field with
gravitation requires the simultaneous introduction of a tetrad field, which is
a field related to translations, and a spin connection, which is a field
assuming values in the Lie algebra of the Lorentz group. These two fields,
however, are not independent. By analyzing the constraint between them, it is
concluded that the relevant local symmetry group behind general relativity is
provided by the Lorentz group. Furthermore, it is shown that the minimal
coupling prescription obtained from the Lorentz covariant derivative coincides
exactly with the usual coupling prescription of general relativity. Instead of
the tetrad, therefore, the spin connection is to be considered as the
fundamental field representing gravitation.


title: The Inflaton and its Mass

abstract:
  In the context of the two fluid model of space-time fluctuations proposed to
tame the transplanckian problem encountered in black hole physics, it is
postulated that the inflaton is the fluctuation of mode density, ``the vapor
component'' of the model. The mass of the inflaton is occasioned by the
exchange of degrees of freedom between the ``vapor'' and the ``liquid'', the
planckian ``soup'' in which usual ``cisplanckian'' fields propagate. This
exchange between vacuum fluctuations is modeled after its counterpart in the
real world i.e. black hole evaporation. In order of magnitude, a very rough
semiquantitative estimate, would situate the mass somewhere between $10^{-10}$
and $10^{-5}$ planck masses, the largest uncertainty being the mass of the
planckian black hole fluctuation i.e. the entropy that one ascribes to it.


title: Analog black holes in flowing dielectrics

abstract:
  We show that a flowing dielectric medium with a linear response to an
external electric field can be used to generate an analog geometry that has
many of the formal properties of a Schwarzschild black hole for light rays, in
spite of birefringence. We also discuss the possibility of generating these
analog black holes in the laboratory.


title: New conformally flat initial data for spinning black holes

abstract:
  We obtain an explicit solution of the momentum constraint for conformally
flat, maximal slicing, initial data which gives an alternative to the purely
longitudinal extrinsic curvature of Bowen and York. The new solution is
related, in a precise form, with the extrinsic curvature of a Kerr slice. We
study these new initial data representing spinning black holes by numerically
solving the Hamiltonian constraint. They have the following features: i)
Contain less radiation, for all allowed values of the rotation parameter, than
the corresponding single spinning Bowen-York black hole. ii) The maximum
rotation parameter $J/m^2$ reached by this solution is higher than that of the
purely longitudinal solution allowing thus to describe holes closer to a
maximally rotating Kerr one. We discuss the physical interpretation of these
properties and their relation with the weak cosmic censorship conjecture.
Finally, we generalize the data for multiple black holes using the ``puncture''
and isometric formulations.


title: Laser-interferometer gravitational-wave optical-spring detectors

abstract:
  Using a quantum mechanical approach, we show that in a gravitational-wave
interferometer composed of arm cavities and a signal recycling cavity, e.g.,
the LIGO-II configuration, the radiation-pressure force acting on the mirrors
not only disturbs the motion of the free masses randomly due to quantum
fluctuations, but also and more fundamentally, makes them respond to forces as
though they were connected to an (optical) spring with a specific rigidity.
This oscillatory response gives rise to a much richer dynamics than previously
known, which enhances the possibilities for reshaping the LIGO-II's noise
curves. However, the optical-mechanical system is dynamically unstable and an
appropriate control system must be introduced to quench the instability.


title:
Dynamics of spherically symmetric spacetimes: hydrodynamics and
  radiation

abstract:
  Using the 3+1 formalism of general relativity we obtain the equations
governing the dynamics of spherically symmetric spacetimes with arbitrary
sources. We then specialize for the case of perfect fluids accompanied by a
flow of interacting massless or massive particles (e.g. neutrinos) which are
described in terms of relativistic transport theory. We focus in three types of
coordinates: 1) isotropic gauge and maximal slicing, 2) radial gauge and polar
slicing, and 3) isotropic gauge and polar slicing.


title: Brane World, Mass Hierarchy and the Cosmological Constant

abstract:
  The brane world based on the 6D gravitational model is examined. It is
regarded as a higher dimensional version of the 5D model by Randall and Sundrum
>. The obtained analytic solution is checked by the numerical method. The mass
hierarchy is examined. Especially the {\it geometrical see-saw} mass relation,
between the Planck mass, the cosmological constant, and the neutrino mass, is
suggested. Comparison with the 5D model is made.


title:
Stationary and Axisymmetric Perfect-Fluid Solutions with Conformal
  Motion

abstract:
  Stationary and axisymmetric perfect-fluid metrics are studied under the
assumption of the existence of a conformal Killing vector field and in the
general case of differential rotation. The possible Lie algebras for the
conformal group and corresponding canonical line-elements are explicitly given.
It turns out that only four different cases appear, the abelian and other three
called I, II and III. We explicitly find all the solutions in the abelian and I
cases. For the abelian case the general solution depends on an arbitrary
function of a single variable and the perfect fluid satisfies the equation of
state rho = p+const. This class of metrics is the one presented recently by one
of us. The general solution for case I is a new Petrov type D metric, with the
velocity vector outside the 2-space spanned by the two principal null
directions and a barotropic equation of state rho +3p=0. For the cases II and
III, the general solution has been found only under the further assumption of a
natural separation of variables Ansatz. The conformal Killing vectors in the
solutions that come out here are, in fact, homothetic. No barotropic equation
of state exists in these metrics unless for a new Petrov type D solution
belonging to case II and with rho +3p=0 which cannot be interpreted as an
axially symmetric solution and such that the velocity vector points in the
direction of one of the Killing vectors. This solution has the previously
unknown curious property that both commuting Killing vectors are timelike
everywhere.


title: Cosmological Singularities

abstract:
  An overview is provided of the singularity theorems in cosmological contexts
at a level suitable for advanced graduate students. The necessary background
from tensor and causal geometry to understand the theorems is supplied, the
mathematical notion of a cosmology is described in some detail and issues
related to the range of validity of general relativity are also discussed.


title: On geometry behind Birkhoff theorem

abstract:
  This is an elementary geometrical proof of Birkhoff theorem. It is hardly
important, but the pictures behind are quite nice.


title: Black Hole Relics in String Gravity: Last Stages of Hawking Evaporation

abstract:
  One of the most intriguing problem of modern physics is the question of the
endpoint of black hole evaporation. Based on Einstein-dilaton-Gauss-Bonnet four
dimensional string gravity model we show that black holes do not disappear and
that the end of the evaporation process leaves some relic. The possibility of
experimental detection of the remnant black holes is investigated. If they
really exist, such objects could be a considerable part of the non baryonic
dark matter in our Universe.


title:
Life in an Energy Eigenstate: Decoherent Histories Analysis of a Model
  Timeless Universe

abstract:
  Inspired by quantum cosmology, in which the wave function of the universe is
annihilated by the total Hamiltonian, we consider the internal dynamics of a
simple particle system in an energy eigenstate. Such a system does not possess
a uniquely defined time parameter and all physical questions about it must be
posed without reference to time. We consider in particular the question, what
is the probability that the system's trajectory passes through a set of regions
of configuration space without reference to time? We first consider the
classical case, where the answer has a variety of forms in terms of a phase
space probability distribution function. We then consider the quantum case, and
we analyze this question using the decoherent histories approach to quantum
theory, adapted to questions which do not involve time. When the histories are
decoherent, the probabilities approximately coincide with the classical case,
with the phase space probability distribution replaced by the Wigner function
of the quantum state. For some initial states, decoherence requires an
environment, and we compute the required influence functional and examine some
of its properties. Special attention is given to the inner product used in the
construction (the induced or Rieffel inner product), the construction of class
operators describing the histories, and the extent to which reparametrization
invariance is respected. Our results indicate that simple systems without an
explicit time parameter may be quantized using the decoherent histories
approach, and the expected classical limit extracted. The results support, for
simple models, the usual heuristic proposals for the probability distribution
function associated with a semiclassical wave function satisfying the
Wheeler-DeWitt equation.


title:
Gravitational Stability of inflaton and torsion in
  Einstein-Cartan-Klein-Gordon cosmology with kinky potentials

abstract:
  Gravitational stability of torsion and inflaton field in a four-dimensional
spacetime de Sitter solution in scalar-tensor cosmology where Cartan torsion
propagates is investigated in detail. Inflaton and torsion evolution equations
are derived by making use of a Lagrangean method. Stable and unstable modes for
torsion and inflatons are found to be dependent of the background torsion and
inflaton fields. Present astrophysical observations favour a stable mode for
torsion since this would explain why no relic torsion imprint has been found on
the Cosmic Background Radiation in the universe.


title:
On Consistence of Material Coupling in a GL(3,R) Gauge Formulation of
  Gravity

abstract:
  A covariant scheme for material coupling with $GL(N,R)$ gauge formulation of
gravity is studied. We revisit a known idea of a Yang-Mills type construction,
where quadratical power of cosmological constant have to be considered in
consistence with vacuum Einstein's gravity. Then, matter coupling with gravity
is introduced and some constraints on fields and background appear. Finally,
exploring the N=3 case we elucidate that introduction of auxiliary fields
decreases the number of these constraints.


title: Construction of Sources for Majumdar-Papapetrou Spacetimes

abstract:
  We study Majumdar-Papapetrou solutions for the 3+1 Einstein-Maxwell
equations, with charged dust acting as the external source for the fields. The
spherically symmetric solution of G\"{u}rses is considered in detail. We
introduce new parameters that simplify the construction of class $C^1$,
singularity-free geometries. The arising sources are bounded or unbounded, and
the redshift of light signals allows an observer at spatial infinity to
distinguish these cases. We find out an interesting affinity between the
conformastatic metric and some homothetic, matter and Ricci collineations. The
associated non-Noetherian symmetries provide us with distinctive solutions that
can be used to construct non-singular sources for Majumdar-Papapetrou
spacetimes.}


title: On the geometric foundation of classical gauge gravitation theory

abstract:
  A number of recent works in E-print arXiv have addressed the foundation of
gauge gravitation theory again. As is well known, differential geometry of
fibre bundles provides the adequate mathematical formulation of classical field
theory, including gauge theory on principal bundles. Gauge gravitation theory
is formulated on the natural bundles over a world manifold whose structure
group is reducible to the Lorentz group. It is the metric-affine gravitation
theory where a metric (tetrad) gravitational field is a Higgs field.


title: Dilatonic Black Holes Time Stability

abstract:
  The stability under small time perturbations of the dilatonic black hole
solution near the determinant curvature singularity is proved. This fact gives
the additional arguments that the investigated topological configuration can
realise in nature. In the frames of this model primordial black hole remnants
are examined as time stable objects, which can form an significant part of a
dark matter in the Universe.


title: Angular Momentum and Energy-Momentum Densities as Gauge Currents

abstract:
  If we replace the general spacetime group of diffeomorphisms by
transformations taking place in the tangent space, general relativity can be
interpreted as a gauge theory, and in particular as a gauge theory for the
Lorentz group. In this context, it is shown that the angular momentum and the
energy-momentum tensors of a general matter field can be obtained from the
invariance of the corresponding action integral under transformations taking
place, not in spacetime, but in the tangent space, in which case they can be
considered as gauge currents.


title:
Boundary terms in the Barrett-Crane spin foam model and consistent
  gluing

abstract:
  We extend the lattice gauge theory-type derivation of the Barrett-Crane spin
foam model for quantum gravity to other choices of boundary conditions,
resulting in different boundary terms, and re-analyze the gluing of 4-simplices
in this context. This provides a consistency check of the previous derivation.
Moreover we study and discuss some possible alternatives and variations that
can be made to it and the resulting models.


title: New Non-Diagonal Singularity-Free Cosmological Perfect-Fluid Solution

abstract:
  We present a new non-diagonal G2 inhomogeneous perfect-fluid solution with
barotropic equation of state p=rho and positive density everywhere. It
satisfies the global hyperbolicity condition and has no curvature singularity
anywhere. This solution is very simple in form and has two arbitrary constants.


title: Einstein-Dirac theory on gauge-natural bundles

abstract:
  We present a clear-cut example of the importance of the functorial approach
of gauge-natural bundles and the general theory of Lie derivatives for
classical field theory, where the sole correct geometrical formulation of
Einstein (-Cartan) gravity coupled with Dirac fields gives rise to an
unexpected indeterminacy in the concept of conserved quantities.


title:
Light deflection and time delay in the gravitational field of a spinning
  mass

abstract:
  In this paper we consider the possibility of measuring the corrections
induced by the square of the parameter a_g of the Kerr metric to the general
relativistic deflection of electromagnetic waves and time delay in an Earth
based experiment. It turns out that, while at astronomical scale the well known
gravitoelectric effects are far larger than the gravitomagnetic ones, at
laboratory scale the situation is reversed: the gravitomagnetic effects exceed
definitely the gravitoelectric ones which are totally negligible. By using a
small rapidly rotating sphere as gravitating source on the Earth the deflection
of a grazing light ray amounts to 10^{-13} rad and the time delay is
proportional to 10^{-23} s. These figures are determined by the upper limit in
the attainable values of a_g due to the need of preventing the body from
exploding under the action of the centrifugal forces. Possible criticisms to
the use of the Kerr metric at a_g^2 level are discussed.


title:
Constraints to a Yukawa gravitational potential from laser data to
  LAGEOS satellites

abstract:
  In this paper we investigate the possibility of constraining the hypothesis
of a fifth force at the length scale of two Earth's radii by investigating the
effects of a Yukawa gravitational potential on the orbits of the laser--ranged
LAGEOS satellites. The existing constraints on the Yukawa coupling $\alpha$,
obtained by fitting the LAGEOS orbit, are of the order of | \alpha | <
10^{-5}-10^{-8} for distances of the order of 10^9 cm. Here we show that with a
suitable combination of the orbital residuals of the perigee \omega of LAGEOS
II and the nodes \Omega of LAGEOS II and LAGEOS it should be possible to
constrain \alpha at a level of 4 X 10^{-12} or less. Various sources of
systematic errors are accounted for, as well. Their total impact amounts to 1 X
10^{-11} during an observational time span of 5 years. In the near future, when
the new data on the terrestrial gravitational field will be available from the
CHAMP and GRACE missions, these limits will be further improved. The use of the
proposed LARES laser--ranged satellite would yield an experimental accuracy in
constraining \alpha of the order of 1 X 10^{-12}.


title:
Stationary axisymmetric SU(2) Einstein-Yang-Mills fields with restricted
  circularity conditions are Abelian

abstract:
  In this paper we prove that in a stationary axisymmetric SU(2)
Einstein-Yang-Mills theory the most reasonable circularity conditions that can
be considered for the Yang-Mills fields imply in fact that the field is of
embedded Abelian type, or else that the metric is not asymptotically flat.


title: Instability of wormholes with a nonminimally coupled scalar field

abstract:
  Static, spherically symmetric, traversable wormholes, induced by massless,
nonminimally coupled scalar fields in general relativity, are shown to be
unstable under spherically symmetric perturbations. The instability is related
to blowing-up of the effective gravitational constant on a certain sphere.


title:
Rotational Dragging Effect on Statistical Thermodynamics of
  (2+1)-dimensional Rotating de Sitter Space

abstract:
  Brief comments on a plausible holographic relationship between the opposite
rotational dragging effect of a (2+1)-dimensional rotating de Sitter space and
the non-unitarity of a boundary conformal field theory are given. In addition
to the comments, we study how the opposite rotational dragging effect affects
the statistical-mechanical quantities in the rotating de Sitter space in
comparison with a BTZ black hole.


title: New Properties of Matter in (A)dS and their Consequences

abstract:
  I review briefly, primarily for relativists, a series of recent results,
obtained with A. Waldron, on the novel behavior of massive higher (s>1) spin
systems in constant curvature backgrounds. We find that the cosmological
constant Lambda, together with the mass parameter, define a "phase plane" in
which partially massless gauge invariant lines separate allowed regions from
forbidden, non-unitary, ones. These lines represent short multiplet systems,
with missing lower helicities, removed by novel local gauge invariances, and
(despite having nonvanishing m) propagating on the light cone. In the limit of
an infinite tower of these higher spin bosons and fermions, unitarity requires
Lambda to vanish.