title: Wave Propagation in Nontrivial Backgrounds

abstract:
  It is well known that waves propagating in a nontrivial medium develop
``tails''. However, the exact form of the late-time tail has so far been
determined only for a narrow class of models. We present a systematic analysis
of the tail phenomenon for waves propagating under the influence of a {\it
general} scattering potential $V(x)$. It is shown that, generically, the
late-time tail is determined by spatial {\it derivatives} of the potential. The
central role played by derivatives of the scattering potential appears not to
be widely recognized. The analytical results are confirmed by numerical
calculations.


title:
Slow flows of an relativistic perfect fluid in a static gravitational
  field

abstract:
  Relativistic hydrodynamics of an isentropic fluid in a gravitational field is
considered as the particular example from the family of Lagrangian
hydrodynamic-type systems which possess an infinite set of integrals of motion
due to the symmetry of Lagrangian with respect to relabeling of fluid particle
labels. Flows with fixed topology of the vorticity are investigated in
quasi-static regime, when deviations of the space-time metric and the density
of fluid from the corresponding equilibrium configuration are negligibly small.
On the base of the variational principle for frozen-in vortex lines dynamics,
the equation of motion for a thin relativistic vortex filament is derived in
the local induction approximation.


title: On the potentials yielding cosmological scaling solutions

abstract:
  In the present work we perform a phase-plane analysis of the complete
dynamical system corresponding to a flat FRW cosmological models with a perfect
fluid and a self-interacting scalar field and show that every positive and
monotonous potential which is asymptotically exponential yields a scaling
solution as a global attractor.


title:
Experimental feasibility of measuring the gravitational redshift of
  light using dispersion in optical fibers

abstract:
  This paper describes a new class of experiments that use dispersion in
optical fibers to convert the gravitational frequency shift of light into a
measurable phase shift or time delay. Two conceptual models are explored. In
the first model, long counter-propagating pulses are used in a vertical fiber
optic Sagnac interferometer. The second model uses optical solitons in
vertically separated fiber optic storage rings. We discuss the feasibility of
using such an instrument to make a high precision measurement of the
gravitational frequency shift of light.


title: Baryonic and Non-Baryonic Dark Matter

abstract:
  Cosmological nucleosynthesis calculations imply that there should be both
non-baryonic and baryonic dark matter. Recent data suggest that some of the
non-baryonic dark matter must be "hot" (i.e. massive neutrinos) and there may
also be evidence for "cold" dark matter (i.e. WIMPs). If the baryonic dark
matter resides in galactic halos, it is likely to be in the form of compact
objects (i.e. MACHOs) and these would probably be the remnants of a first
generation of pregalactic or protogalactic Population III stars. Many
candidates have been proposed - brown dwarfs, red dwarfs, white dwarfs or black
holes - and at various times each of these has been in vogue. We review the
many types of observations which can be used to constrain or exclude both
baryonic and non-baryonic dark matter candidates.


title: False Vacuum Black Holes and Universes

abstract:
  We construct a black hole whose interior is the false vacuum and whose
exterior is the true vacuum of a classical field theory. From the outside the
metric is the usual Schwarzschild one, but from the inside the space is de
Sitter with a cosmological constant determined by the energy of the false
vacuum. The parameters of the field potential may allow for the false vacuum to
exist for more than the present age of the universe. A potentially relevant
effective field theory within the context of QCD results in a Schwarzschild
radius of about 200 km.


title:
An asymptotic analysis of spherically symmetric perfect fluid
  self-similar solutions

abstract:
  The asymptotic properties of self-similar spherically symmetric perfect fluid
solutions with equation of state p=alpha mu (-1<alpha<1) are described. We
prove that for large and small values of the similarity variable, z=r/t, all
such solutions must have an asymptotic power-law form. Some of them are
associated with an exact power-law solution, in which case they are
asymptotically Friedmann or asymptotically Kantowski-Sachs for 1>alpha >-1 or
asymptotically static for 1>alpha >0. Others are associated with an approximate
power-law solution, in which case they are asymptotically quasi-static for
1>alpha >0 or asymptotically Minkowski for 1>alpha >1/5. We also show that
there are solutions whose asymptotic behaviour is associated with finite values
of z and which depend upon powers of ln z. These correspond either to a second
family of asymptotically Minkowski solutions for 1>alpha>1/5 or to solutions
that are asymptotically Kasner for 1>alpha>-1/3. There are some other
asymptotic power-law solutions associated with negative alpha, but the physical
significance of these is unclear. The asymptotic form of the solutions is given
in all cases, together with the number of associated parameters.


title: Moduli fields and brane tensions: generalizing the junction conditions

abstract:
  Taking the Randall-Sundrum models as background scenario, we derive
generalized Israel-Lanczos-Sen thin-shell junction conditions for systems in
which several bulk scalar fields are non-minimally coupled to gravity. We
demonstrate that the form of the junction conditions (though arguably not the
physics) depends on the choice of frame. We show that generally (in any frame
except the Einstein frame) the presence of a thin shell induces discontinuities
in the normal derivative of the scalar field, even in the absence of any direct
interaction between the thin shell and the scalar field. For some exceptional
scalar field configurations the discontinuities in the derivatives of the
metric and the scalar fields can feed back into each other and so persist even
in the absence of any thin shell of stress-energy.


title: The Speed of Light and the Fine Structure Constant

abstract:
  The fine structure constant $\alpha $ includes the speed of light as given by
$\alpha =\frac{e^{2}}{4\pi \epsilon_{0}c\hbar}$. It is shown here that,
following a $TH\epsilon \mu $ formalism, interpreting the permittivity
$\epsilon_{0}$ and permeabiliy $\mu_{0}$ of free space under Lorentz local and
position invariance, this is not the case. The result is a new expression as
$\alpha =\frac{e^{2}}{4\pi \hbar}$ in a new system of units for the charge that
preserves local and position invariance. Hence, the speed of light does not
explicitly enter in the constitution of the fine structure constant. The new
expressions for the Maxwell's equations are derived and some cosmological
implications discussed.


title: Planck-Length Phenomenology

abstract:
  This author's recent proposal of interferometric tests of
Planck-scale-related properties of space-time is here revisited from a strictly
phenomenological viewpoint. The results announced previously are rederived
using elementary dimensional considerations. The dimensional analysis is then
extended to the other two classes of experiments (observations of neutral kaons
at particle accelerators and observations of the gamma rays we detect from
distant astrophysical sources) which have been recently considered as
opportunities to explore "foamy" properties of space-time. The emerging picture
suggests that there is an objective and intuitive way to connect the
sensitivities of these three experiments with the Planck length. While in
previous studies the emphasis was always on some quantum-gravity scenario and
the analysis was always primarily aimed at showing that the chosen scenario
would leave a trace in a certain class of doable experiments, the analysis here
reported takes as starting point the experiments and, by relating in a direct
quantitative way the sensitivities to the Planck length, provides a
model-independent description of the status of Planck-length phenomenology.


title: Hierarchies of invariant spin models

abstract:
  In this paper we present classes of state sum models based on the recoupling
theory of angular momenta of SU(2) (and of its q-counterpart $U_q(sl(2))$, q a
root of unity). Such classes are arranged in hierarchies depending on the
dimension d, and include all known closed models, i.e. the Ponzano-Regge state
sum and the Turaev-Viro invariant in dimension d=3, the Crane-Yetter invariant
in d=4. In general, the recoupling coefficient associated with a d-simplex
turns out to be a $\{3(d-2)(d+1)/2\}j$ symbol, or its q-analog. Each of the
state sums can be further extended to compact triangulations $(T^d,\partial
T^d)$ of a PL-pair $(M^d,\partial M^d)$, where the triangulation of the
boundary manifold is not keeped fixed. In both cases we find out the algebraic
identities which translate complete sets of topological moves, thus showing
that all state sums are actually independent of the particular triangulation
chosen. Then, owing to Pachner's theorems, it turns out that classes of
PL-invariant models can be defined in any dimension d.


title:
Entrainment of an inertial reference frame by an accelerated gravitating
  shell

abstract:
  For the example of an accelerated shell we show that omission of the
energy-momentum tensor (EMT) of the body that causes the acceleration and the
tensions due to this acceleration can lead to a paradoxical result; Namely, the
entrainment of an inertial frame by the accelerated shell in the direction
opposite to that of the acceleration. We consider several models and
demonstrate that the correct result can be obtained only if all components of
the full EMT are adequately taken into account, and the problem statement is
physically correct.


title: Hyperfluid - a model of classical matter with hypermomentum

abstract:
  A variational theory of a continuous medium is developed the elements of
which carry momentum and hypermomentum (hyperfluid). It is shown that the
structure of the sources in metric-affine gravity is predetermined by the
conservation identities and, when using the Weyssenhoff ansatz, these
explicitly yield the hyperfluid currents.


title: On a model of an unconstrained hyperfluid

abstract:
  A hyperfluid is a classical continuous medium carrying hypermomentum. We
modify the earlier developed variational approach to a hyperfluid in such a way
that the Frenkel type constraints imposed on the hypermomentum current are
eliminated. The resulting self-consistent model is different from the
Weyssenhoff type one. The essential point is a conservation of the
hypermomentum current such that the final metrical and canonical
energy-momentum forms coincide.


title: Spin-driven inflation

abstract:
  Following recent studies of Ford, we suggest -- in the framework of general
relativity -- an inflationary cosmological model with the self-interacting
spinning matter. A generalization of the standard fluid model is discussed and
estimates of the physical parameters of the evolution are given.


title: Trans-Planckian Modes, Back-Reaction, and the Hawking Process

abstract:
  Hawking's prediction of black-hole evaporation depends on the application of
known physics to fantastically high energies -- well beyond the Planck scale.
Here, I show that before these extreme regimes are reached, another physical
effect will intervene: the quantum backreaction on the collapsing matter and
its effect on the geometry through which the quantum fields propagate. These
effects are estimated by a simple thought experiment. When this is done, it
appears that there are no matrix elements allowing the emission of Hawking
quanta: black holes do not radiate.


title: On the Numerical Stability of the Einstein Equations

abstract:
  We perform a von Neumann stability analysis on a common discretization of the
Einstein equations. The analysis is performed on two formulations of the
Einstein equations, namely, the standard ADM formulation and the
conformal-traceless (CT) formulation. The eigenvalues of the amplification
matrix are computed for flat space as well as for a highly nonlinear plane wave
exact solution. We find that for the flat space initial data, the condition for
stability is simply $\frac {\Delta t}{\Delta z} \leq 1$. However, a von Neumann
analysis for highly nonlinear plane wave initial data shows that the standard
ADM formulation is unconditionally unstable, while the conformal-traceless (CT)
formulation is stable for $0.25 \leq \frac {\Delta t}{\Delta z} < 1$.


title: Extremal Black holes and the limits of the third law

abstract:
  Recent results of quantum field theory on a curved spacetime suggest that
extremal black holes are not thermal objects and that the notion of zero
temperature is ill-defined for them. If this is correct, one may have to go to
a full semiclassical theory of gravity, including backreaction, in order to
make sense of the third law of black hole thermodynamics. Alternatively, it is
possible that we shall have to drastically revise the status of extremality in
black hole thermodynamics.


title: The rotational modes of relativistic stars: Analytic results

abstract:
  We study the r-modes and rotational ``hybrid'' modes of relativistic stars.
As in Newtonian gravity, the spectrum of low-frequency rotational modes is
highly sensitive to the stellar equation of state. If the star and its
perturbations obey the same one-parameter equation of state (as with isentropic
stars), there exist {\it no pure r-modes at all} - no modes whose limit, for a
star with zero angular velocity, is an axial-parity perturbation. Rotating
stars of this kind similarly have no pure g-modes, no modes whose spherical
limit is a perturbation with polar parity and vanishing perturbed pressure and
density. We compute the post-Newtonian corrections to the $l=m$ r-modes of
isentropic and non-isentropic uniform density stars.


title: Quantum gravity as a theory of quantized area bits fitting together

abstract:
  Non-Abelian Gauss law is interpreted in terms of area bits described in a
local frame which fit together into closed surfaces and the Non-Abelian Stokes
law in terms of length bits described in a local frame which fit together into
closed loops. A new equation relating the area variables and the phase space
variables (or equivalently, angular momentum variables of the lattice
Yang-Mills theory and phase space variables of the continuum theory) is
obtained. Canonical quantization applied to these variables implies area
quantization. A complete orthonormal basis of states satisfying the Gauss
constraint is obtained.It has the interpretation of quantized area bits with
undefined orientations and edges but fitting together into closed surfaces.


title: Gravitational Wave Damping of Neutron Star Wobble

abstract:
  We calculate the effect of gravitational wave (gw) back-reaction on realistic
neutron stars (NS's) undergoing torque-free precession. By `realistic' we mean
that the NS is treated as a mostly-fluid body with an elastic crust, as opposed
to a rigid body. We find that gw's damp NS wobble on a timescale tau_{theta}
approx 2 x 10^5 yr [10^{-7}/(DId/I_0)]^2 (kHz/ nu_s)^4, where nu_s is the spin
frequency and DId is the piece of the NS's inertia tensor that "follows" the
crust's principal axis (as opposed to its spin axis). We give two different
derivations of this result: one based solely on energy and angular momentum
balance, and another obtained by adding the Burke-Thorne radiation reaction
force to the Newtonian equations of motion. This problem was treated long ago
by Bertotti and Anile (1973), but their claimed result is wrong. When we
convert from their notation to ours, we find that their tau_{theta} is too
short by a factor of order 10^5 for typical cases of interest, and even has the
wrong sign for DId negative. We show where their calculation went astray.


title: Causal Implication and the Origin of Time Dilation

abstract:
  We discuss the emergence of time dilation as a normal feature expected of any
system where a central processor may have to wait one or more clock cycles
before concluding a local calculation. We show how the process of causal
implication in a typical Newtonian cellular automaton leads naturally to
Lorentz transformations and invariant causal structure.


title: An exact solution for 2+1 dimensional critical collapse

abstract:
  We find an exact solution in closed form for the critical collapse of a
scalar field with cosmological constant in 2+1 dimensions. This solution agrees
with the numerical simulation done by Pretorius and Choptuik of this system.


title: Global phase time and path integral for string cosmological models

abstract:
  A global phase time is identified for homogeneous and isotropic cosmological
models yielding from the low energy effective action of closed bosonic string
theory. When the Hamiltonian constraint allows for the existence of an
intrinsic time, the quantum transition amplitude is obtained by means of the
usual path integral procedure for gauge systems.


title: Tidal Forces in Cold Black Hole Spacetimes

abstract:
  We investigate here the behavior of a few spherically symmetric static
acclaimed black hole solutions in respect of tidal forces in the geodesic
frame. It turns out that the forces diverge on the horizon of cold black holes
(CBH) while for ordinary ones, they do not. It is pointed out that Kruskal-like
extensions do not render the CBH metrics nonsingular. We present a CBH that is
available in the Brans-Dicke theory for which the tidal forces do not diverge
on the horizon and in that sense it is a better one.


title:
Conversion of conventional gravitational-wave interferometers into QND
  interferometers by modifying their input and/or output optics

abstract:
  The LIGO-II gravitational-wave interferometers (ca. 2006--2008) are designed
to have sensitivities at about the standard quantum limit (SQL) near 100 Hz.
This paper describes and analyzes possible designs for subsequent, LIGO-III
interferometers that can beat the SQL. These designs are identical to a
conventional broad-band interferometer (without signal recycling), except for
new input and/or output optics. Three designs are analyzed: (i) a
"squeezed-input interferometer" (conceived by Unruh based on earlier work of
Caves) in which squeezed vacuum with frequency-dependent (FD) squeeze angle is
injected into the interferometer's dark port; (ii) a "variational-output"
interferometer (conceived in a different form by Vyatchanin, Matsko and
Zubova), in which homodyne detection with FD homodyne phase is performed on the
output light; and (iii) a "squeezed-variational interferometer" with squeezed
input and FD-homodyne output. It is shown that the FD squeezed-input light can
be produced by sending ordinary squeezed light through two successive
Fabry-Perot filter cavities before injection into the interferometer, and
FD-homodyne detection can be achieved by sending the output light through two
filter cavities before ordinary homodyne detection. With anticipated technology
and with laser powers comparable to that planned for LIGO-II, these
interferometers can beat the amplitude SQL by factors in the range from 3 to 5,
corresponding to event rate increases between ~30 and ~100 over the rate for a
SQL-limited interferometer.


title: Stochastic backgrounds of gravitational waves

abstract:
  We review the motivations for the search of stochastic backgrounds of
gravitational waves and we compare the experimental sensitivities that can be
reached in the near future with the existing bounds and with the theoretical
predictions.


title:
Gravitational instabilities in helicity-1 waves propagating through
  matter in equilibrium

abstract:
  It is shown that the interaction of helicity-1 waves of gravity and matter in
a thin slab configuration produces new types of instabilities. Indeed, a
transverse spin-2 helicity-1 mode interacts strongly with the shear motion of
matter. This mode is unstable above a critical wavelength which reminds the
Jeans wavelength but with the speed of sound interchanged by the speed of
light. The two instabilities are of course different. For the case analyzed, a
plane parallel configuration, Jeans instability appears through a density wave
perturbation, the material collapsing into a set of plane-parallel slabs. On
the other hand, the helicity-1 wave instability induces a transverse motion in
the fluid that tends to shear in the material along the node of the
perturbation.


title:
The Energy Distribution in a Static Spherically Symmetric Nonsingular
  Black Hole Space-Time

abstract:
  We calculate the energy distribution in a static spherically symmetric
nonsingular black hole space-time by using the Tolman's energy-momentum
complex. All the calculations are performed in quasi-Cartesian coordinates. The
energy distribution is positive everywhere and be equal to zero at origin. We
get the same result as obtained by Y-Ching Yang by using the Einstein's and
Weinberg's prescriptions.


title:
A quasilocal Hamiltonian for gravity with classical and quantum
  applications

abstract:
  I modify the quasilocal energy formalism of Brown and York into a purely
Hamiltonian form. As part of the reformulation, I remove their restriction that
the time evolution of the boundary of the spacetime be orthogonal to the leaves
of the time foliation. Thus the new formulation allows an arbitrary evolution
of the boundary which physically corresponds to allowing general motions of the
set of observers making up that boundary. I calculate the rate of change of the
quasilocal energy in such situations, show how it transforms with respect to
boosts of the boundaries, and use the Lanczos-Israel thin shell formalism to
reformulate it from an operational point of view. These steps are performed
both for pure gravity and gravity with attendant matter fields. I then apply
the formalism to characterize naked black holes and study their properties,
investigate gravitational tidal heating, and combine it with the path integral
formulation of quantum gravity to analyze the creation of pairs of charged and
rotating black holes. I show that one must use complex instantons to study this
process though the probabilities of creation remain real and consistent with
the view that the entropy of a black hole is the logarithm of the number of its
quantum states.


title:
Making classical and quantum canonical general relativity computable
  through a power series expansion in the inverse cosmological constant

abstract:
  We consider general relativity with a cosmological constant as a perturbative
expansion around a completely solvable diffeomorphism invariant field theory.
This theory is the $\Lambda\to\infty$ limit of general relativity. This allows
an explicit perturbative computational setup in which the quantum states of the
theory and the classical observables can be explicitly computed. The zeroth
order corresponds to highly degenerate space-times with vanishing volume.
Perturbations give rise to space-times with non-vanishing volumes in a natural
way. The spectrum of area- and volume-related observables constructed by
coupling the theory to matter can be directly assessed. An unexpected
relationship arises at a quantum level between the discrete spectrum of the
volume operator and the allowed values of the cosmological constant.


title:
The large cosmological constant approximation to classical and quantum
  gravity: model examples

abstract:
  We have recently introduced an approach for studying perturbatively classical
and quantum canonical general relativity. The perturbative technique appears to
preserve many of the attractive features of the non-perturbative quantization
approach based on Ashtekar's new variables and spin networks. With this
approach one can find perturbatively classical observables (quantities that
have vanishing Poisson brackets with the constraints) and quantum states
(states that are annihilated by the quantum constraints). The relative ease
with which the technique appears to deal with these traditionally hard problems
opens several questions about how relevant the results produced can possibly
be. Among the questions is the issue of how useful are results for large values
of the cosmological constant and how the approach can deal with several
pathologies that are expected to be present in the canonical approach to
quantum gravity. With the aim of clarifying these points, and to make our
construction as explicit as possible, we study its application in several
simple models. We consider Bianchi cosmologies, the asymmetric top, the coupled
harmonic oscillators with constant energy density and a simple quantum
mechanical system with two Hamiltonian constraints. We find that the technique
satisfactorily deals with the pathologies of these models and offers promise
for finding (at least some) results even for small values of the cosmological
constant. Finally, we briefly sketch how the method would operate in the full
four dimensional quantum general relativity case.


title:
Relativistic phase shifts for Dirac particles interacting with weak
  gravitational fields in matter-wave interferometers

abstract:
  We present a second-quantized field theory of massive spin one-half particles
or antiparticles in the presence of a weak gravitational field treated as a
spin two external field in a flat Minkowski background. We solve the
difficulties which arise from the derivative coupling and we are able to
introduce an interaction picture. We derive expressions for the scattering
amplitude and for the outgoing spinor to first-order. In several appendices,
the link with the canonical approach in General Relativity is established and a
generalized stationary phase method is used to calculate the outgoing spinor.
We show how our expressions can be used to calculate and discuss phase shifts
in the context of matter-wave interferometry (especially atom or antiatom
interferometry). In this way, many effects are introduced in a unified
relativistic framework, including spin-gravitation terms: gravitational red
shift, Thomas precession, Sagnac effect, spin-rotation effect, orbital and spin
Lense-Thirring effects, de Sitter geodetic precession and finally the effect of
gravitational waves. A new analogy with the electromagnetic interaction is
pointed out.


title: The Energy Distribution of the Bianchi Type I Universe

abstract:
  We calculate the energy distribution of an anisotropic model of universe,
based on the Bianchi type I metric, in the Tolman's prescription. The energy
due to the matter plus gravitational field is equal to zero. This result agrees
with the results of Banerjee and Sen and Xulu. Also, our result supports the
viewpoint of Tryon and Rosen.


title: The Energy of a Dyonic Dilaton Black Hole

abstract:
  We calculate the energy distribution of a dyonic dilaton black hole by using
the Tolman's energy-momentum complex. All the calculations are performed in
quasi-Cartesian coordinates. The energy distribution of the dyonic dilaton
black hole depends on the mass, electric charge, magnetic charge and asymptotic
value of the dilaton. We get the same result as obtained by Y-Ching Yang,
Ching-Tzung Yeh, Rue-Ron Hsu and Chin-Rong Lee by using the Einstein's
prescription.


title: Darboux cosmological fluids in comoving time

abstract:
  The barotropic indices and the corresponding FRW scale factors of the
so-called Darboux cosmological fluids are presented in the comoving time axis,
which is the natural one for the phenomenology related to the cosmological
data. Some useful comments on the features of the plots are included


title: The asymptotic regimes of tilted Bianchi II cosmologies

abstract:
  In this paper we give, for the first time, a complete description of the
dynamics of tilted spatially homogeneous cosmologies of Bianchi type II. The
source is assumed to be a perfect fluid with equation of state $p = (\gamma -1)
\mu$, where $\gamma$ is a constant. We show that unless the perfect fluid is
stiff, the tilt destabilizes the Kasner solutions, leading to a Mixmaster-like
initial singularity, with the tilt being dynamically significant. At late times
the tilt becomes dynamically negligible unless the equation of state parameter
satisfies $\gamma > {10/7}$. We also find that the tilt does not destabilize
the flat FL model, with the result that the presence of tilt increases the
likelihood of intermediate isotropization.


title: Loop Quantum Gravity and Asymptotically Flat Spaces

abstract:
  After motivating why the study of asymptotically flat spaces is important in
loop quantum gravity, we review the extension of the standard framework of this
theory to the asymptotically flat sector based on the GNS construction. In
particular, we provide a general procedure for constructing new Hilbert spaces
for loop quantum gravity on non-compact spatial manifolds. States in these
Hilbert spaces can be interpreted as describing fluctuations around fiducial
fixed backgrounds. When the backgrounds are chosen to approximate classical
asymptotically flat 3-geometries this gives a natural framework in which to
discuss physical applications of loop quantum gravity, especially its
semi-classical limit. We present three general proposals for the construction
of suitable backgrounds, including one approach that can lead to quantum
gravity on anti-DeSitter space as described by the Chern-Simons state.


title:
Black hole formation from massive scalar field collapse in the
  Einstein-de Sitter universe

abstract:
  We study the spherically symmetric collapse of a real, minimally coupled,
massive scalar field in an asymptotically Einstein-de Sitter spacetime
background. By means of an eikonal approximation for the field and metric
functions, we obtain a simple analytical criterion---involving the physical
size and mass scales (the field's inverse Compton wavelength and the spacetime
gravitational mass) of the initial matter configuration---for generic
(non-time-symmetric) initial data to collapse to a black hole. This analytical
condition can then be used to place constraints on the initial primordial black
hole spectrum, by considering spherical density perturbations that re-entered
the horizon during an early matter-dominated phase that immediately followed
inflation.


title: Response to Fackerell's Article

abstract:
  E. D. Fackerell claims: 1) that Alley and Yilmaz treatment of parallel slabs
in general relativity is wrong because the Yilmaz metric used is not a solution
of the field equations of general relativity; 2) he also claims that the
correct treatment of the parallel slab problem in general relativity must be
based on the so-called Taub metric. We show below that both of Fackerell's
claims are false. His first claim is based on his failure to distinguish the
matter-free regions and the regions with matter. His second claim is based on
his failure to recognize that for the Taub metric the left-hand side, hence
also the right-hand side of the field equations, are identically zero
everywhere. Thus no material systems can be treated via the Taub metric.


title: Sensitivity of a VIRGO pair to stochastic GW backgrounds

abstract:
  The sensitivity of a pair of VIRGO interferometers to gravitational waves
backgrounds (GW) of cosmological origin is analyzed for the cases of maximal
and minimal overlap of the two detectors. The improvements in the detectability
prospects of scale-invariant and non-scale-invariant logarithmic energy spectra
of relic GW are discussed.


title:
Local existence proofs for the boundary value problem for static
  spherically symmetric Einstein-Yang-Mills fields with compact gauge groups

abstract:
  We prove local existence and uniqueness of static spherically symmetric
solutions of the Einstein-Yang-Mills equations for an arbitrary compact
semisimple gauge group in the so-called regular case. By this we mean the
equations obtained when the rotation group acts on the principal bundle on
which the Yang-Mills connection takes its values in a particularly simple way
(the only one ever considered in the literature). The boundary value problem
that results for possible asymptotically flat soliton or black hole solutions
is very singular and just establishing that local power series solutions exist
at the center and asymptotic solutions at infinity amounts to a nontrivial
algebraic problem. We discuss the possible field equations obtained for
different group actions and solve the algebraic problem on how the local
solutions depend on initial data at the center and at infinity.


title: Singularity in 2+1 dimensional AdS-scalar black hole

abstract:
  We study the spacetime singularity in 2+1 dimensional AdS-scalar black hole
with circular symmetry using a quasi-homogeneous model. We show that this is a
spacelike, scalar curvature, deformationally strong singularity.


title: Chaotic Inflation with Time-Variable Space Dimensions

abstract:
  Assuming the space dimension is not constant but decreases during the
expansion of the Universe, we study chaotic inflation with the potential
$m^2\phi^2/2$. Our investigations are based on a model Universe with variable
space dimensions. We write down field equations in the slow-roll approximation,
and define slow-roll parameters by assuming the number of space dimensions
decreases continuously as the Universe expands. The dynamical character of the
space dimension shifts the initial and final value of the inflaton field to
larger values. We obtain an upper limit for the space dimension at the Planck
length. This result is in agreement with previous works for the effective time
variation of the Newtonian gravitational constant in a model Universe with
variable space dimensions.


title:
Generalized Second Law of Black Hole Thermodynamics and Quantum
  Information Theory

abstract:
  We propose a quantum version of a gedanken experiment which supports the
generalized second law of black hole thermodynamics. A quantum measurement of
particles in the region outside of the event horizon decreases the entropy of
the outside matter due to the entanglement of the inside and outside particle
states. This decrease is compensated, however, by the increase in the detector
entropy. If the detector is conditionally dropped into the black hole depending
on the experimental outcome, the decrease of the matter entropy is more than
compensated by the increase of the black hole entropy via the increase of the
black hole mass which is ultimately attributed to the work done by the
measurement.


title:
Trajectories for the Wave Function of the Universe from a Simple
  Detector Model

abstract:
  Inspired by Mott's (1929) analysis of particle tracks in a cloud chamber, we
consider a simple model for quantum cosmology which includes, in the total
Hamiltonian, model detectors registering whether or not the system, at any
stage in its entire history, passes through a series of regions in
configuration space. We thus derive a variety of well-defined formulas for the
probabilities for trajectories associated with the solutions to the
Wheeler-DeWitt equation. The probability distribution is peaked about classical
trajectories in configuration space. The ``measured'' wave functions still
satisfy the Wheeler-DeWitt equation, except for small corrections due to the
disturbance of the measuring device. With modified boundary conditions, the
measurement amplitudes essentially agree with an earlier result of Hartle
derived on rather different grounds. In the special case where the system is a
collection of harmonic oscillators, the interpretation of the results is aided
by the introduction of ``timeless'' coherent states -- eigenstates of the
Hamiltonian which are concentrated about entire classical trajectories.


title: A new approach to electromagnetic wave tails on a curved spacetime

abstract:
  We present an alternative method for constructing the exact and approximate
solutions of electromagnetic wave equations whose source terms are arbitrary
order multipoles on a curved spacetime. The developed method is based on the
higher-order Green's functions for wave equations which are defined as
distributions that satisfy wave equations with the corresponding order
covariant derivatives of the Dirac delta function as the source terms. The
constructed solution is applied to the study of various geometric effects on
the generation and propagation of electromagnetic wave tails to first order in
the Riemann tensor. Generally the received radiation tail occurs after a time
delay which represents geometrical backscattering by the central gravitational
source. It is shown that the truly nonlocal wave-propagation correction (the
tail term) takes a universal form which is independent of multipole order. In a
particular case, if the radiation pulse is generated by the source during a
finite time interval, the tail term after the primary pulse is entirely
determined by the energy-momentum vector of the gravitational field source: the
form of the tail term is independent of the multipole structure of the
gravitational source. We apply the results to a compact binary system and
conclude that under certain conditions the tail energy can be a noticeable
fraction of the primary pulse energy. We argue that the wave tails should be
carefully considered in energy calculations of such systems.


title: A Note in Cosmology and Loop Quantum Gravity

abstract:
  One possible description of the very early stages of the evolution of the
universe is provided by Chaotic Inflationary Cosmology. For that model the role
of the inflaton field is played by quantum gravitational effects. We study if
such a picture may arise within the framework of Loop Quantum gravity by
studying a simple model. While we were unable to reach definitive conclusions
we believe the general approach proposed in this paper may prove fruitful in
the future.


title: Quantum Computation toward Quantum Gravity

abstract:
  The aim of this paper is to enlight the emerging relevance of Quantum
Information Theory in the field of Quantum Gravity. As it was suggested by J.
A. Wheeler, information theory must play a relevant role in understanding the
foundations of Quantum Mechanics (the "It from bit" proposal). Here we suggest
that quantum information must play a relevant role in Quantum Gravity (the "It
from qubit" proposal). The conjecture is that Quantum Gravity, the theory which
will reconcile Quantum Mechanics with General Relativity, can be formulated in
terms of quantum bits of information (qubits) stored in space at the Planck
scale. This conjecture is based on the following arguments: a) The holographic
principle, b) The loop quantum gravity approach and spin networks, c) Quantum
geometry and black hole entropy. Here we present the quantum version of the
holographic principle by considering each pixel of area of an event horizon as
a qubit. This is possible if the horizon is pierced by spin networks' edges of
spin 1\2, in the superposed state of spin "up" and spin "down".


title:
Time-Dependent Automorphism Inducing Diffeomorphisms In Vacuum Bianchi
  Cosmologies And The Complete Closed Form Solutions For Type II & V

abstract:
  We investigate the set of spacetime general coordinate transformations
(G.C.T.) which leave the line element of a generic Bianchi Type Geometry,
quasi-form invariant; i.e. preserve manifest spatial Homogeneity. We find that
these G.C.T.'s, induce special time-dependent automorphic changes, on the
spatial scale factor matrix $\gamma_{\alpha\beta}(t)$ -along with corresponding
changes on the lapse function $N(t)$ and the shift vector $N^{\alpha}(t)$.
These changes, which are Bianchi Type dependent, form a group and are, in
general, different from those induced by the group SAut(G) -advocated in
earlier investigations as the relevant symmetry group-, they are used to
simplify the form of the line element -and thus simplify Einstein's equations
as well-, without losing generality.
  As far as this simplification procedure is concerned, the transformations
found, are proved to be essentialy unique. For the case of Bianchi Types II and
V, where the most general solutions are known -Taub's and Joseph's,
respectively-, it is explicitly verified that our transformations and only
those, suffice to reduce the generic line element, to the previously known
forms. It becomes thus possible, -for these Types- to give in closed form, the
most general solution, containing all the necessary ``gauge'' freedom.


title: Cosmological Constant or Cosmological Potential

abstract:
  In the framework of a model of minimal of dilatonic gravity (MDG) with
cosmological potential we consider: the relations of MDG with nonlinear gravity
and string theory; natural cosmological units, defined by cosmological
constant; the properties of cosmological factor, derived from solar system and
Earth-surface gravitational experiments; universal anty-gravitational
interactions, induced by positive cosmological constant and by Nordtved effect;
a new formulation of cosmological constant problem using the ratio of
introduced cosmological action and Planck constant $\sim 10 ^{122}$;qualitative
analysis of this huge number based on classical action of effective Bohr
hydrogen atoms; inverse cosmological problem: to find cosmological potential
which yields given evolution of the RW Universe; and comment other general
properties of MDG.


title: Loop Quantum Cosmology III: Wheeler-DeWitt Operators

abstract:
  In the framework of loop quantum cosmology anomaly free quantizations of the
Hamiltonian constraint for Bianchi class A, locally rotationally symmetric and
isotropic models are given. Basic ideas of the construction in (non-symmetric)
loop quantum gravity can be used, but there are also further inputs because the
special structure of symmetric models has to be respected by operators. In
particular, the basic building blocks of the homogeneous models are point
holonomies rather than holonomies necessitating a new regularization procedure.
In this respect, our construction is applicable also for other
(non-homogeneous) symmetric models, e.g. the spherically symmetric one.


title: Loop Quantum Cosmology IV: Discrete Time Evolution

abstract:
  Using general features of recent quantizations of the Hamiltonian constraint
in loop quantum gravity and loop quantum cosmology, a dynamical interpretation
of the constraint equation as evolution equation is presented. This involves a
transformation from the connection to a dreibein representation and the
selection of an internal time variable. Due to the discrete nature of
geometrical quantities in loop quantum gravity also time turns out to be
discrete leading to a difference rather than differential evolution equation.
Furthermore, evolving observables are discussed in this framework which enables
an investigation of physical spectra of geometrical quantities. In particular,
the physical volume spectrum is proven to equal the discrete kinematical volume
spectrum in loop quantum cosmology.


title: Angular Momentum in Loop Quantum Gravity

abstract:
  An angular momentum operator in loop quantum gravity is defined using
spherically symmetric states as a non-rotating reference system. It can be
diagonalized simultaneously with the area operator and has the familiar
spectrum. The operator indicates how the quantum geometry of non-rotating
isolated horizons can be generalized to rotating ones and how the recent
computations of black hole entropy can be extended to rotating black holes.


title: Twisting Lightlike Solutions of the Kerr-Schild Class

abstract:
  Using a complex representation of the Debney-Kerr-Schild (DKS) solutions and
the Kerr theorem we give a method to construct boosted Kerr geometries. In the
ultrarelativistic case this method yelds twisting solutions having, contrary to
the known pp-wave limiting solutions, a non-zero value of the total angular
momentum. The solutions show that twist plays a crucial role in removing
singularity and smoothing shock wave in the ultrarelativistic limit. Two
different physical situations are discussed.


title: The Topological Origin of Black Hole Entropy

abstract:
  In gravitational thermodynamics, the origin of a black hole's entropy is the
topology of its instanton or constrained instanton. We prove that the entropy
of an arbitrary nonrotating black hole is one quarter the sum of the products
of the Euler characteristics of its horizons with their respective areas. The
Gauss-Bonnet-like form of the action is not only crucial for the evaluation,
but also for the existence of the entropy. This result covers all previous
results on the entropy of a nonrotating black hole with a regular instanton.
The argument can be readily extended into the lower or higher dimensional
model. The problem of quantum creation of such a black hole is completely
resolved.


title:
Scattering of particles by neutron stars: Time-evolutions for axial
  perturbations

abstract:
  The excitation of the axial quasi-normal modes of a relativistic star by
scattered particles is studied by evolving the time dependent perturbation
equations. This work is the first step towards the understanding of more
complicated perturbative processes, like the capture or the scattering of
particles by rotating stars. In addition, it may serve as a test for the
results of the full nonlinear evolution of binary systems.


title:
Gravitational waves from extreme mass ratio inspirals: Challenges in
  mapping the spacetime of massive, compact objects

abstract:
  In its final year of inspiral, a stellar mass ($1 - 10 M_\odot$) body orbits
a massive ($10^5 - 10^7 M_\odot$) compact object about $10^5$ times, spiralling
from several Schwarzschild radii to the last stable orbit. These orbits are
deep in the massive object's strong field, so the gravitational waves that they
produce probe the strong field nature of the object's spacetime. Measuring
these waves can, in principle, be used to ``map'' this spacetime, allowing
observers to test whether the object is a black hole or something more exotic.
Such measurements will require a good theoretical understanding of wave
generation during inspiral. In this article, I discuss the major theoretical
challenges standing in the way of building such maps from gravitational-wave
observations, as well as recent progress in producing extreme mass ratio
inspirals and waveforms.


title:
Gravitational Wave Chirp Search: Economization of PN Matched Filter Bank
  via Cardinal Interpolation

abstract:
  The final inspiral phase in the evolution of a compact binary consisting of
black holes and/or neutron stars is among the most probable events that a
network of ground-based interferometric gravitational wave detectors is likely
to observe. Gravitational radiation emitted during this phase will have to be
dug out of noise by matched-filtering (correlating) the detector output with a
bank of several $10^5$ templates, making the computational resources required
quite demanding, though not formidable. We propose an interpolation method for
evaluating the correlation between template waveforms and the detector output
and show that the method is effective in substantially reducing the number of
templates required. Indeed, the number of templates needed could be a factor
$\sim 4$ smaller than required by the usual approach, when the minimal overlap
between the template bank and an arbitrary signal (the so-called {\it minimal
match}) is 0.97. The method is amenable to easy implementation, and the various
detector projects might benefit by adopting it to reduce the computational
costs of inspiraling neutron star and black hole binary search.


title: Scalar field collapse in three-dimensional AdS spacetime

abstract:
  We describe results of a numerical calculation of circularly symmetric scalar
field collapse in three spacetime dimensions with negative cosmological
constant. The procedure uses a double null formulation of the Einstein-scalar
equations. We see evidence of black hole formation on first implosion of a
scalar pulse if the initial pulse amplitude $A$ is greater than a critical
value $A_*$. Sufficiently near criticality the apparent horizon radius $r_{AH}$
grows with pulse amplitude according to the formula $r_{AH} \sim
(A-A_*)^{0.81}$.


title: Energy Localization Invariance of Tidal Work in General Relativity

abstract:
  It is well known that, when an external general relativistic (electric-type)
tidal field E(t) interacts with the evolving quadrupole moment I(t) of an
isolated body, the tidal field does work on the body (``tidal work'') -- i.e.,
it transfers energy to the body -- at a rate given by the same formula as in
Newtonian theory: dW/dt = -1/2 E dI/dt. Thorne has posed the following
question: In view of the fact that the gravitational interaction energy between
the tidal field and the body is ambiguous by an amount of order E(t)I(t), is
the tidal work also ambiguous by this amount, and therefore is the formula
dW/dt = -1/2 E dI/dt only valid unambiguously when integrated over timescales
long compared to that for I(t) to change substantially? This paper completes a
demonstration that the answer is no; dW/dt is not ambiguous in this way. More
specifically, this paper shows that dW/dt is unambiguously given by -1/2 E
dI/dt independently of one's choice of how to localize gravitational energy in
general relativity. This is proved by explicitly computing dW/dt using various
gravitational stress-energy pseudotensors (Einstein, Landau-Lifshitz, Moller)
as well as Bergmann's conserved quantities which generalize many of the
pseudotensors to include an arbitrary function of position. A discussion is
also given of the problem of formulating conservation laws in general
relativity and the role played by the various pseudotensors.


title: Effective equations in quantum cosmology

abstract:
  We develop a general framework for effective equations of expectation values
in quantum cosmology and pose for them the quantum Cauchy problem with
no-boundary and tunneling wavefunctions. Cosmological configuration space is
decomposed into two sectors that give qualitatively different contributions to
the radiation currents in effective equations. The field-theoretical sector of
inhomogeneous modes is treated by the method of Euclidean effective action,
while the quantum mechanical sector of the spatially homogeneous inflaton is
handled by the technique of manifest quantum reduction to gauge invariant
cosmological perturbations. We apply this framework in the model with a big
negative non-minimal coupling, which incorporates a recently proposed low
energy (GUT scale) mechanism of the quantum origin of the inflationary Universe
and study the effects of the quantum inflaton mode.


title: Instability of a membrane intersecting a black hole

abstract:
  The stability of a Nambu-Goto membrane at the equatorial plane of the
Reissner-Nordstr{\o}m-de Sitter spacetime is studied. The covariant
perturbation formalism is applied to study the behavior of the perturbation of
the membrane. The perturbation equation is solved numerically. It is shown that
a membrane intersecting a charged black hole, including extremely charged one,
is unstable and that the positive cosmological constant strengthens the
instability.


title: On the stability of cosmological metrics in Einstein-Cartan cosmologies

abstract:
  Two metric perturbations in Einstein-Cartan cosmology are examined.The first
case is the scalar mode perturbation of de Sitter metric in Einstein-Cartan
cosmology.In this case small perturbations of de Sitter metric shows that this
metric is unstable for a universe with spin-torsion density and dilaton
fields.In the second case we show that the Friedmann metric in the same space
is also unstable under the small perturbations.


title: Self force on charges in the spacetime of spherical shells

abstract:
  We study the self force acting on static electric or scalar charges inside or
outside a spherical, massive, thin shell. The regularization of the self force
is done using the recently-proposed Mode Sum Regularization Prescription. In
all cases the self force acting on the charge is repulsive. We find that in the
scalar case the force is quadratic in the mass of the shell, and is a second
post-Newtonian effect. For the electric case the force is linear in the shell's
mass, and is a first post-Newtonian effect. When the charge is outside the
shell our results correct the known zero self force in the scalar case or the
known repulsive, inverse-cubic force law in the electric case, for the finite
size of the shell. When the charge is near the center of the shell the charge
undergoes harmonic oscillations.


title:
An excess power statistic for detection of burst sources of
  gravitational radiation

abstract:
  We examine the properties of an excess power method to detect gravitational
waves in interferometric detector data. This method is designed to detect
short-duration (< 0.5 s) burst signals of unknown waveform, such as those from
supernovae or black hole mergers. If only the bursts' duration and frequency
band are known, the method is an optimal detection strategy in both Bayesian
and frequentist senses. It consists of summing the data power over the known
time interval and frequency band of the burst. If the detector noise is
stationary and Gaussian, this sum is distributed as a chi-squared (non-central
chi-squared) deviate in the absence (presence) of a signal. One can use these
distributions to compute frequentist detection thresholds for the measured
power. We derive the method from Bayesian analyses and show how to compute
Bayesian thresholds. More generically, when only upper and/or lower bounds on
the bursts duration and frequency band are known, one must search for excess
power in all concordant durations and bands. Two search schemes are presented
and their computational efficiencies are compared. We find that given
reasonable constraints on the effective duration and bandwidth of signals, the
excess power search can be performed on a single workstation. Furthermore, the
method can be almost as efficient as matched filtering when a large template
bank is required. Finally, we derive generalizations of the method to a network
of several interferometers under the assumption of Gaussian noise.


title: Simple excision of a black hole in 3+1 numerical relativity

abstract:
  We describe a simple implementation of black hole excision in 3+1 numerical
relativity. We apply this technique to a Schwarzschild black hole with octant
symmetry in Eddington-Finkelstein coordinates and show how one can obtain
accurate, long-term stable numerical evolutions.


title: Class of Eistein-Maxwell Dilatons

abstract:
  The functional potential formalism is used to analyze stationary axisymmetric
spaces in the Einstein-Maxwell-Dilaton theory. Performing a Legendre
transformation, a ``Hamiltonian''is obtained, which allows to rewrite the
dynamical equations in terms of three complex functions only. Using an ansatz
resembling the one used by the harmonic maps ansatz, we express these three
functions in terms of the harmonic parameters, studying the cases where these
parameters are real, and when they are complex. For each case, the set of
equations in terms of these harmonic parameters is derived, and several classes
of solutions to the Einstein-Maxwell with arbitrary coupling constant to a
dilaton field are presented. Most of the known solutions of charged and
dilatonic black holes are contained as special cases and can be non-trivially
generalized in different ways.


title: Deviations from Einstein's Gravity at Large and Short Distances

abstract:
  In this talk I will describe some recent results on the sensitivity of
resonant mass detectors shaped as a hollow sphere to scalar gravitational
radiation. Detection of this type of gravitational radiation will signal
deviations from Einstein's gravity at large distances. I will then discuss a
class of experiments aiming at finding deviations from Einstein's gravity at
distances below 1 cm. I will review the main experimental difficulties in
performing such experiments and evaluate the effects to be taken in account.


title: Holonomy in the Schwarzschild-Droste Geometry

abstract:
  Parallel transport of vectors in curved spacetimes generally results in a
deficit angle between the directions of the initial and final vectors. We
examine such holonomy in the Schwarzschild-Droste geometry and find a number of
interesting features that are not widely known. For example, parallel transport
around circular orbits results in a quantized band structure of holonomy
invariance. We also examine radial holonomy and extend the analysis to spinors
and to the Reissner-Nordstr\"om metric, where we find qualitatively different
behavior for the extremal ($Q = M$) case. Our calculations provide a toolbox
that will hopefully be useful in the investigation of quantum parallel
transport in Hilbert-fibered spacetimes.


title: Black holes: new horizons

abstract:
  This is a review of current black-hole theory, concentrating on local,
dynamical aspects.


title: Energy for N-Body Motion in Two Dimensional Gravity

abstract:
  A general definition of energy is given, via the N\"other theorem, for the
N-body problem in (1+1) dimensional gravity. Within a first-order Lagrangian
framework, the density of energy of a solution relative to a background is
identified with the superpotential of the theory. For specific applications we
reproduce the expected Hamiltonian for the motion of N particles in a curved
spacetime. This Hamiltonian agrees with that found through an ADM-like
prescription for the energy when the latter is applicable but it also extends
to a wider class of solutions provided a suitable background is chosen.


title: Energy-momentum of the gravitational field in the teleparallel geometry

abstract:
  The Hamiltonian formulation of the teleparallel equivalent of general
relativity without gauge fixing has recently been established in terms of the
Hamiltonian constraint and a set of six primary constraints. Altogether, they
constitute a set of first class constraints. In view of the constraint
structure we establish definitions for the energy, momentum and angular
momentum of the gravitational field. In agreement with previous investigations,
the gravitational energy-momentum density follows from a total divergence that
arises in the constraints. This definition is applied successfully to the
calculation of the irreducible mass of the Kerr black hole. The definition of
the algular momentum of the gravitational field follows from the integral form
of primary constraints that satisfy the angular momentum algebra.


title: Gravitational Radiation Theory and Light Propagation

abstract:
  The paper gives an introduction to the gravitational radiation theory of
isolated sources and to the propagation properties of light rays in radiative
gravitational fields. It presents a theoretical study of the generation,
propagation, back-reaction, and detection of gravitational waves from
astrophysical sources. After reviewing the various quadrupole-moment laws for
gravitational radiation in the Newtonian approximation, we show how to
incorporate post-Newtonian corrections into the source multipole moments, the
radiative multipole moments at infinity, and the back-reaction potentials. We
further treat the light propagation in the linearized gravitational field
outside a gravitational wave emitting source. The effects of time delay,
bending of light, and moving source frequency shift are presented in terms of
the gravitational lens potential. Time delay results are applied in the
description of the procedure of the detection of gravitational waves.


title: Quasi-spherical approximation for rotating black holes

abstract:
  We numerically implement a quasi-spherical approximation scheme for computing
gravitational waveforms for coalescing black holes, testing it against angular
momentum by applying it to Kerr black holes. As error measures, we take the
conformal strain and specific energy due to spurious gravitational radiation.
The strain is found to be monotonic rather than wavelike. The specific energy
is found to be at least an order of magnitude smaller than the 1% level
expected from typical black-hole collisions, for angular momentum up to at
least 70% of the maximum, for an initial surface as close as $r=3m$.


title: No-go theorem for false vacuum black holes

abstract:
  We study the possibility of non-singular black hole solutions in the theory
of general relativity coupled to a non-linear scalar field with a positive
potential possessing two minima: a `false vacuum' with positive energy and a
`true vacuum' with zero energy. Assuming that the scalar field starts at the
false vacuum at the origin and comes to the true vacuum at spatial infinity, we
prove a no-go theorem by extending a no-hair theorem to the black hole
interior: no smooth solutions exist which interpolate between the local de
Sitter solution near the origin and the asymptotic Schwarzschild solution
through a regular event horizon or several horizons.


title:
Group-theoretical structure of quantum measurements and equivalence
  principle

abstract:
  The transverse group associated to some continuous quantum measuring
processes is analyzed in the presence of nonvanishing gravitational fields.
This is done considering, as an exmaple, the case of a particle whose
coordinates are being monitored. Employing the so called restricted path
integral formalism, it will be shown that the measuring process could always
contain information concerning the gravitational field. In other words, it
seems that with the presence of a measuring process the equivalence principle
may, in some cases, break down. The relation between the breakdown of the
equivalence principle, at quantum level, and the fact that the gravitational
field could act always as a decoherence environment, is also considered. The
phenomena of quantum beats of quantum optics will allow us to consider the
possibility that the experimental corroboration of the equivalence principle at
quantum level could be taken as an indirect evidence in favor of the
quantization of the gravitational field, i.e., the quantum properties of this
field avoid the violation of the equivalence principle.


title:
Dirac Spinor in Bianchi-I Universe with Time Dependent Gravitational and
  Cosmological Constants

abstract:
  Self-consistent system of nonlinear spinor field and Bianchi I (BI)
gravitational one with time dependent gravitational constant ($G$) and
cosmological constant ($\Lambda$) has been studied. The initial and the
asymptotic behaviors of the field functions and the metric one have been
thoroughly investigated. Given $\Lambda = \Lambda_0/\tau^2$, with $\tau =
\sqrt{-g}$, $G$ has been estimated as a function of $\tau$. The role of perfect
fluid at the initial state of expansion and asymptotical isotropization process
of the initailly anisotropic universe has been elucidated.


title: Minimal Model of Dilatonic Gravity and Cosmological Constant

abstract:
  We consider: minimal scalar-tensor model of gravity with Brans-Dicke factor
$\omega(\Phi)\equiv 0$ and cosmological factor $\Pi(\Phi)$; restrictions on it
from gravitational experiments; qualitative analysis of new approach to
cosmological constant problem based on the huge amount of action in Universe;
determination of $\Pi(\Phi)$ using time evolution of scale factor of Universe.


title:
On the Growth of the Number of Hyperbolic Gravitational Instantons with
  respect to Volume

abstract:
  In this paper, we show that the number of hyperbolic gravitational instantons
grows superexponentially with respect to volume. As an application, we show
that the Hartle-Hawking wave function for the universe is infinitely peaked at
a certain closed hyperbolic 3-manifold.


title: Back Reaction Problem in the Inflationary Universe

abstract:
  We investigate the back reaction of cosmological perturbations on an
inflationary universe using the renormalization-group method. The second-order
zero mode solution which appears by the nonlinearity of the Einstein equation
is regarded as a secular term of a perturbative expansion, we renormalized a
constant of integration contained in the background solution and absorbed the
secular term to this constant in a gauge-invariant manner. The resultant
renormalization-group equation describes the back reaction effect of
inhomogeneity on the background universe. For scalar type classical
perturbation, by solving the renormalization-group equation, we find that the
back reaction of the long wavelength fluctuation works as a positive spatial
curvature, and the short wavelength fluctuation works as a radiation fluid. For
the long wavelength quantum fluctuation, the effect of back reaction is
equivalent to a negative spatial curvature.


title: Circular Cosmic String Loop in Brans-Dicke Theory

abstract:
  The gravitational field of a stationary circular cosmic string loop
,externally supported against collapse, is investigated in the context of
Brans-Dicke theory in the weak field approximation of the field equations. The
solution is quasi-conformally related to the corresponding solution in
Einstein's General Relativity(GR) and goes over to the corresponding solution
in GR when the Brans-Dicke parameter $\omega $ becomes infinitely large.


title:
Einstein Manifolds, Abelian Instantons, Bundle Reduction, and the
  Cosmological Constant

abstract:
  The anti-self-dual projection of the spin connections of certain
four-dimensional Einstein manifolds can be Abelian in nature. These
configurations signify bundle reductions. By a theorem of Kobayashi and Nomizu
such a process is predicated on the existence of a covariantly constant field.
It turns out that even without fundamental Higgs fields and other physical
matter, gravitational self-interactions can generate this mechanism if the
cosmological constant is non-vanishing. This article identifies the order
parameter, and clarifies how these Abelian instanton solutions are associated
with a Higgs triplet which causes the bundle reduction from SO(3) gauge group
to U(1).


title: Accelerating Universes with Scaling Dark Matter

abstract:
  Friedmann-Robertson-Walker universes with a presently large fraction of the
energy density stored in an $X$-component with $w_X<-1/3$, are considered. We
find all the critical points of the system for constant equations of state in
that range. We consider further several background quantities that can
distinguish the models with different $w_X$ values. Using a simple toy model
with a varying equation of state, we show that even a large variation of $w_X$
at small redshifts is very difficult to observe with $d_L(z)$ measurements up
to $z\sim 1$. Therefore, it will require accurate measurements in the range
$1<z<2$ and independent accurate knowledge of $\Omega_{m,0}$ (and/or
$\Omega_{X,0}$) in order to resolve a variable $w_X$ from a constant $w_X$.


title:
Scattering of massive Dirac fields on the Schwarzschild black hole
  spacetime

abstract:
  With a generally covariant equation of Dirac fields outside a black hole, we
develop a scattering theory for massive Dirac fields. The existence of modified
wave operators at infinity is shown by implementing a time-dependent
logarithmic phase shift from the free dynamics to offset a long-range mass
term. The phase shift we obtain is a matrix operator due to the existence of
both positive and negative energy wave components.


title: Quantization of Dirac fields in static spacetime

abstract:
  On a static spacetime, the solutions of the Dirac equation are generated by a
time-independent Hamiltonian. We study this Hamiltonian and characterize the
split into positive and negative energy. We use it to find explicit expressions
for advanced and retarded fundamental solutions and for the propagator.
Finally, we use a fermion Fock space based on the positive/negative energy
split to define a Dirac quantum field operator whose commutator is the
propagator.


title: Quantum metric fluctuations and Hawking radiation

abstract:
  In this Letter we study the gravitational interactions between outgoing
configurations giving rise to Hawking radiation and in-falling configurations.
When the latter are in their ground state, the near horizon interactions lead
to collective effects which express themselves as metric fluctuations and which
induce dissipation, as in Brownian motion. This dissipation prevents the
appearance of trans-Planckian frequencies and leads to a description of Hawking
radiation which is very similar to that obtained from sound propagation in
condensed matter models.


title:
Data conditioning for gravitational wave detectors: A Kalman filter for
  regressing suspension violin mode

abstract:
  Interferometric gravitational wave detectors operate by sensing the
differential light travel time between free test masses. Correspondingly, they
are sensitive to anything that changes the physical distance between the test
masses, including physical motion of the masses themselves. In ground-based
detectors the test masses are suspended as pendula and, consequently, thermal
or other excitations of the suspension wires' violin modes lead to a strong,
albeit narrow-band, ``signal'' in the detector wave-band that can confound
attempts to observe gravitational waves.
  Here we describe the design of a Kalman filter that determines the
time-dependent vibrational state of a detector's suspension ``violin'' modes
from the detector output. From the estimated state we can predict that
component of the detector output due to suspension excitations, thermal or
otherwise, and subtractively remove those disturbances from the detector
output. We demonstrate the filter's effectiveness both through numerical
simulations and application to real data taken on the LIGO 40 M prototype
detector.


title: The warp drive: hyper-fast travel within general relativity

abstract:
  It is shown how, within the framework of general relativity and without the
introduction of wormholes, it is possible to modify a spacetime in a way that
allows a spaceship to travel with an arbitrarily large speed. By a purely local
expansion of spacetime behind the spaceship and an opposite contraction in
front of it, motion faster than the speed of light as seen by observers outside
the disturbed region is possible. The resulting distortion is reminiscent of
the ``warp drive'' of science fiction. However, just as it happens with
wormholes, exotic matter will be needed in order to generate a distortion of
spacetime like the one discussed here.


title: Moving-mirror entropy

abstract:
  We consider a quantized scalar field in a two-dimensional Minkowski spacetime
with a moving mirror and propose a definition of moving-mirror entropy
associated with temporarily inaccessible information about the future.


title: Phase space path integral in curved space

abstract:
  Phase space path integral is worked out in a riemannian geometry, by
employing a prescription for the infinitesimal propagator that takes riemannian
normal coordinates and momenta on an equal footing. The operator ordering
induced by this prescription leads to the DeWitt curvature coupling in the
Schrodinger equation.


title: Motions and world-line deviations in Einstein-Maxwell theory

abstract:
  We examine the motion of charged particles in gravitational and
electro-magnetic background fields. We study in particular the deviation of
world lines, describing the relative acceleration between particles on
different space-time trajectories. Two special cases of background fields are
considered in detail: (a) pp-waves, a combination of gravitational and
electro-magnetic polarized plane waves travelling in the same direction; (b)
the Reissner-Nordstr{\o}m solution. We perform a non-trivial check by computing
the precession of the periastron for a charged particle in the
Reissner-Nordstr{\o}m geometry both directly by solving the geodesic equation,
and using the world-line deviation equation. The results agree to the order of
approximation considered.


title: Brans-Dicke brane cosmology

abstract:
  A five dimensional brane cosmology with non-minimally coupled scalar field to
gravity has been considered in a Jordan-Brans-Dicke frame. We derive an
effective four dimensional field equations on a 3+1 dimensional brane where the
fifth dimension has been assumed to have an orbifold symmetry. We have noticed
that the evolution equation for the matter component stuck to the brane is
non-trivially coupled to the scalar field living on the brane and the bulk.
Finally we discuss some cosmological consequences of this set-up.


title: Expansion-induced contribution to the precession of binary orbits

abstract:
  We point out the existence of new effects of global spacetime expansion on
local binary systems. In addition to a possible change of orbital size, there
is a contribution to the precession of elliptic orbits, to be added to the
well-known general relativistic effect in static spacetimes, and the
eccentricity can change. Our model calculations are done using geodesics in a
McVittie metric, representing a localized system in an asymptotically
Robertson-Walker spacetime; we give a few numerical estimates for that case,
and indicate ways in which the model should be improved.


title: The Limits of Information

abstract:
  Black holes have their own thermodynamics including notions of entropy and
temperature and versions of the three laws. After a light introduction to black
hole physics, I recollect how black hole thermodynamics evolved in the 1970's,
while at the same time stressing conceptual points which were given little
thought at that time, such as why the entropy should be linear in the black
hole's surface area. I also review a variety of attempts made over the years to
provide a statistical mechanics for black hole thermodynamics. Finally, I
discuss the origin of the information bounds for ordinary systems that have
arisen as applications of black hole thermodynamics.

categories: gr-qc astro-ph cond-mat.stat-mech hep-th


title:
The Nature of Singularity in Bianchi I Cosmological String Gravity Model
  with Second Order Curvature Corrections

abstract:
  We investigate Bianchi I cosmological model in the theory of a dilatonM field
coupled to gravity through a Gauss-Bonnet term. Two type ofM cosmological
singularity are distinguished. The former is analogous toM the Einstein gravity
singularity, the latter (which does not appear inM classical General
Relativity) occurs when the main determinant of theM system of field equations
vanishes. An analogy between the latterM cosmological singularity and the
singularity inside a black hole withM a dilatonic hair is discussed. Initial
conditions, leading to theseM two types of cosmological singularity are found
via numericalM integration of the equation of motion.


title: Spin foam model for Lorentzian General Relativity

abstract:
  We present a spin foam formulation of Lorentzian quantum General Relativity.
The theory is based on a simple generalization of an Euclidean model defined in
terms of a field theory over a group. Its vertex amplitude turns out to be the
one recently introduced by Barrett and Crane. As in the case of its Euclidean
relatives, the model fully implements the desired sum over 2-complexes which
encodes the local degrees of freedom of the theory.


title: Cylindrically symmetric perfect-fluid universes

abstract:
  The aim of this paper is to examine some obtained exact solutions of the
Einstein-Maxwell equations, especially their properties from a chronological
point of view. Each our spacetime is stationary cylindrically symmetric and it
is filled up with an perfect fluid that is electrically charged. There are two
classes of solutions and examples of each of them are investigated. We give
examples of the first class both for the vanishing as well as for the
non-vanishing Lorentz force.


title: Process Physics: Modelling Reality as Self-Organising Information

abstract:
  The new Process Physics models reality as self-organising relational
information and takes account of the limitations of logic, discovered by Godel
and extended by Chaitin, by using the concept of self-referential noise. Space
and quantum physics are emergent and unified, and described by a Quantum
Homotopic Field Theory of fractal topological defects embedded in a three
dimensional fractal process-space.


title: Imprints of accretion on gravitational waves from black holes

abstract:
  Black holes are superb sources of gravitational wave signals, for example
when they are born in stellar collapse. We explore the subtleties that may
emerge if mass accretion events increase significantly the mass of the black
hole during its gravitational wave emission. We find the familiar
damped-oscillatory radiative decay but now both decay rate and frequencies are
modulated by the mass accretion rate. Any appreciable increase in the horizon
mass during emission reflects on the instantaneous signal frequency, which
shows a prominent negative branch in the dot[f](f) evolution diagram. The
features of the frequency evolution pattern reveal key properties of the
accretion event, such as the total accreted mass and the accretion rate. For
slow accretion rates the frequency evolution follows verbatim the accretion
rate, as expected from dimensional arguments. In view of the possibility of
detection of black hole ``ringing'' by the upcoming gravitational wave
experiments, the deciphering of the late time frequency dynamics may provide
direct insight into otherwise obscured aspects of the black hole birth process.


title: Quantum Birth of a Hot Universe

abstract:
  We consider quantum birth of a hot Universe in the framework of quantum
qeometrodynamics in the minisuperspace model. The energy spectrum of the
Universe in the pre-de-Sitter domain naturally explains the cosmic microwave
background (CMB) anisotropy. The false vacuum where the Universe tunnels from
the pre-de-Sitter domain is assumed to be of a Grand Unification Theory (GUT)
scale. The probability of the birth of a hot Universe from a quantum level
proves to be about $10^{-10^{14}}$. In the presence of matter with a negative
pressure (quintessence) it is possible for open and flat universes to be born
as well as closed ones.


title: Third Quantization of Brans-Dicke Cosmology

abstract:
  We study the third quantization of a Brans-Dicke toy model, we calculate the
number density of the universes created from nothing and found that it has a
Planckian form. Also, we calculated the uncertainty relation for this model by
means of functional Schr"odinger equation and we found that fluctuations of the
third-quantized universe field tends to a finite limit in the course of cosmic
expansion.


title: Quantum Cosmology in Bergmann-Wagoner Scalar-tensor Gravitational Theory

abstract:
  The Wheeler-DeWitt equation is solved for the Bergmann-Wagoner scalar-tensor
gravitational theory in the case of Friedmann-Robertson- Walker cosmological
model. We present solutions for several cosmological functions: i)
\lambda(\phi)=0, ii) \lambda(\phi)=3\Lambda_0\phi and iii) a more complex
\lambda(\phi), that depends on the choice of the coupling function, considering
closed, flat and hyperbolic Friedmann universes (k=1, 0, -1). In the first two
cases we show particular quantum wormhole solutions. Also, classical solutions
are considered for some scalar-tensor theories, and we study the third
quantization of some minisuperspace models.


title: Vacuum polarization of a scalar field in wormhole spacetimes

abstract:
  An analitical approximation of $<\phi^2>$ for a scalar field in a static
spherically symmetric wormhole spacetime is obtained. The scalar field is
assumed to be both massive and massless, with an arbitrary coupling $\xi$ to
the scalar curvature, and in a zero temperature vacuum state.


title: Time evolution in the presence of gravity

abstract:
  We present a suggestion on the interpretation of canonical time evolution
when gravitation is present, based on the nonlinear gauge approach to gravity.
Essentially, our proposal consists of an internal-time concept, with the time
variable taken from the dynamical fields characteristic of the nonlinear
realization of the internal time-translational symmetry. Physical time
evolution requires the latter symmetry to be broken. After disregarding other
breaking mechanisms, we appeal to the Jordan-Brans-Dicke action, conveniently
interpreted, to achieve that goal. We show that nontrivial time evolution
follows, the special relativistic limit being recovered in the absence of
gravity.


title:
Black Holes and Naked Singularities in Low Energy Limit of String
  Gravity with Modulus Field

abstract:
  We show that the black hole solutions of the effective string theory action,
where one-loop effects that couple the moduli to gravity via a Gauss-Bonnet
term are taken into account, admit primary scalar hair. The requirement of
absence of naked singularities imposes an upper bound on the scalar charges.


title:
Models of Universe with a Delayed Big-Bang singularity. III. Solving the
  horizon problem for an off-center observer

abstract:
  This paper is the third of a series dedicated to the study of the Delayed
Big-Bang (DBB) class of inhomogeneous cosmological models of
Lema\^itre-Tolman-Bondi type. In the first work, it was shown that the
geometrical properties of the DBB model are such that the horizon problem can
be solved, without need for any inflationary phase, for an observer situated
sufficiently near the symmetry center of the model to justify the ``centered
earth'' approximation. In the second work, we studied, in a peculiar subclass
of the DBB models, the extent to which the values of the dipole and quadrupole
moments measured in the cosmic microwave background radiation (CMBR)
temperature anisotropies can support a cosmological origin. This implies a
relation between the location of the observer in the universe and the model
parameter value: the farther the observer from the symmetry center, the closer
our current universe to a local homogeneous pattern. However, in this case, the
centered earth approximation is no longer valid and the results of the first
work do not apply. We show here that the horizon problem can be solved, in the
DBB model, also for an off-center observer, which improves the consistency of
this model regarding the assumption of a CMBR large scale anisotropy
cosmological origin.


title:
How much of the outgoing radiation can be intercepted by
  Schwarzschildean black holes?

abstract:
  The Schwarzschild spacetime is for electromagnetic waves like a nonuniform
medium with a varying refraction index. A fraction of an outgoing radiation
scatters off the curvature of the geometry and can be intercepted by a
gravitational center. The amount of the intercepted energy is bounded above by
the backscattered energy of an initially outgoing pulse of electromagnetic
radiation, which in turn depends on the initial energy, the Schwarzschild
radius and the pulse location. Its magnitude depends on the frequency spectrum:
it becomes negligible in the short wave limit but can be significant in the
long wave regime.


title: Principle of equivalence and wave-particle duality in quantum gravity

abstract:
  This talk presents: (a) A quantum-mechanically induced violation of the
principle of equivalence, and (b) Gravitationally-induced modification to the
wave particle duality. In this context I note that the agreement between the
predictions of general relativity and observations of the energy loss due to
gravitational waves emitted by binary pulsars is just as impressive as the
agreement between prediction of quantum electrodynamics and the measured value
of Lamb shift in atoms. However, general relativity has not yet yielded to a
successful quantised theory. There is a widespread belief that the two thories
are incompatible at some deep level. The question is: where? Here, I show that
the conceptual foundations of the theory of general relativity and quantum
mechanics are so rich that they suggest concrete modifications into each other
in the interface region. Specifically, I consider quantum states that have no
classical counterpart and show that such states must carry an inherent
violation of the principle of equivalence. On the other hand, I show that when
gravitational effects are incorporated into the quantum measurement process one
must induce a gravitationally induced modification to the de Broglie's
wave-particle duality. The reported changes into the foundations of the two
theories are far from in-principle modifications. These are endowed with
serious implications for the understanding of the early universe and, in
certain instances, can be explored in terrestrial laboratories.


title: Scalar-tensor gravity in an accelerating universe

abstract:
  We consider scalar-tensor theories of gravity in an accelerating universe.
The equations for the background evolution and the perturbations are given in
full generality for any parametrization of the Lagrangian, and we stress that
apparent singularities are sometimes artifacts of a pathological choice of
variables. Adopting a phenomenological viewpoint, i.e., from the observations
back to the theory, we show that the knowledge of the luminosity distance as a
function of redshift up to z ~ (1-2), which is expected in the near future,
severely constrains the viable subclasses of scalar-tensor theories. This is
due to the requirement of positive energy for both the graviton and the scalar
partner. Assuming a particular form for the Hubble diagram, consistent with
present experimental data, we reconstruct the microscopic Lagrangian for
various scalar-tensor models, and find that the most natural ones are obtained
if the universe is (marginally) closed.


title: High quality factor measured in fused silica

abstract:
  We have measured the mechanical dissipation in a sample of fused silica drawn
into a rod. The sample was hung from a multiple-bob suspension, which isolated
it from rubbing against its support, from recoil in the support structure, and
from seismic noise. The quality factor, Q, was measured for several modes with
a high value of 57 million found for mode number 2 at 726 Hz. This result is
about a factor 2 higher than previous room temperature measurements. The
measured Q was strongly dependent on handling, with a pristine flame-polished
surface yielding a Q 3-4 times higher than a surface which had been knocked
several times against a copper tube.


title: Inertial mass and the quantum vacuum fields

abstract:
  Even when the Higgs particle is finally detected, it will continue to be a
legitimate question to ask whether the inertia of matter as a reaction force
opposing acceleration is an intrinsic or extrinsic property of matter. General
relativity specifies which geodesic path a free particle will follow, but
geometrodynamics has no mechanism for generating a reaction force for deviation
from geodesic motion. We discuss a different approach involving the
electromagnetic zero-point field (ZPF) of the quantum vacuum. It has been found
that certain asymmetries arise in the ZPF as perceived from an accelerating
reference frame. In such a frame the Poynting vector and momentum flux of the
ZPF become non-zero. Scattering of this quantum radiation by the quarks and
electrons in matter can result in an acceleration-dependent reaction force.
Both the ordinary and the relativistic forms of Newton's second law, the
equation of motion, can be derived from the electrodynamics of such
ZPF-particle interactions. Conjectural arguments are given why this interaction
should take place in a resonance at the Compton frequency, and how this could
simultaneously provide a physical basis for the de Broglie wavelength of a
moving particle. This affords a suggestive perspective on a deep connection
between electrodynamics, the origin of inertia and the quantum wave nature of
matter.


title: Notes on Isolated Horizons

abstract:
  A general analysis for characterizing and classifying `isolated horizons' is
presented in terms of null tetrads and spin coefficients. The freely
specifiable spin coefficients corresponding to isolated horizons are identified
and specific symmetry classes are enumerated. For isolated horizons admitting
at least one spatial isometry, a standard set of spherical coordinates are
introduced and associated metric is obtained. An angular momentum is also
defined.


title: Nonlinear Connections and Nearly Autoparallel Maps in General Relativity

abstract:
  We apply the method of moving anholonomic frames, with associated nonlinear
connections, in (pseudo) Riemannian spaces and examine the conditions when
various types of locally anisotropic (la) structures (Lagrange, Finsler like
and more general ones) could be modeled in general relativity. New classes of
solutions of the Einstein equations with generic local anisotropy are
constructed. We formulate the theory of nearly autoparallel (na) maps and
introduce the tensorial na-integration as the inverse operation to both
covariant derivation and deformation of connections by na-maps. The problem of
redefinition of the Einstein gravity theory on na-backgrounds, provided with a
set of na-map invariant conditions and local conservation laws, is analyzed.
There are illustrated some examples of generation of vacuum Einstein fields by
Finsler like metrics and chains of na-maps.


title:
Locally Anisotropic Structures and Nonlinear Connections in Einstein and
  Gauge Gravity

abstract:
  We analyze local anisotropies induced by anholonomic frames and associated
nonlinear connections in general relativity and extensions to affine Poincare
and de Sitter gauge gravity and different types of Kaluza-Klein theories. We
construct some new classes of cosmological solutions of gravitational field
equations describing Friedmann-Robertson-Walker like universes with rotation
(ellongated and flattened) ellipsoidal or torus symmetry.


title: On the consistency of a repulsive gravity phase in the early Universe

abstract:
  We exploit the possibility of existence of a repulsive gravity phase in the
evolution of the Universe. A toy model with a free scalar field minimally
coupled to gravity, but with the "wrong sign" for the energy and negative
curvature for the spatial section, is studied in detail. The background
solutions display a bouncing, non-singular Universe. The model is well-behaved
with respect to tensor perturbations. But, it exhibits growing models with
respect to scalar perturbations whose maximum occurs in the bouncing. Hence,
large inhomogeneties are produced. At least for this case, a repulsive phase
may destroy homogeneity, and in this sense it may be unstable. A newtonian
analogous model is worked out; it displays qualitatively the same behaviour.
The generality of this result is discussed. In particular, it is shown that the
addition of an attractive radiative fluid does not change essentially the
results. We discuss also a quantum version of the classical repulsive phase,
through the Wheeler-de Witt equation in mini-superspace, and we show that it
displays essentially the same scenario as the corresponding attractive phase.


title: Fundamental units of length and time

abstract:
  Ideal rods and clocks are defined as an infinitesimal symmetry of the
spacetime. Since no a priori geometric structure is considered, all the
possible models of spacetime are obtained.


title: Dyonic Wormholes in 5D Kaluza-Klein Theory

abstract:
  New spherically symmetric dyonic solutions, describing a wormhole-like class
of spacetime configurations in five-dimensional Kaluza-Klein theory, are given
in an explicit form. For this type of solution the electric and magnetic fields
cause a significantly different global structure. For the electric dominated
case, the solution is everywhere regular but, when the magnetic strength
overcomes the electric contribution, the mouths of the wormhole become singular
points. When the electric and magnetic charge parameters are identical, the
throats ``degenerate'' and the solution reduces to the trivial embedding of the
four-dimensional massless Reissner-Nordstr{\"o}m black hole solution. In
addition, their counterparts in eleven-dimensional supergravity are constructed
by a non-trivial uplifting.


title:
Non-dopplerian cosmological redshift parameters in a model of
  graviton-dusty universe

abstract:
  Possible effects are considered which would be caused by a hypothetical
superstrong interaction of photons or massive bodies with single gravitons of
the graviton background. If full cosmological redshift magnitudes are caused by
the interaction, then the luminosity distance in a flat non-expanding universe
as a function of redshift is very similar to the specific function which fits
supernova cosmology data by Riess et al. From another side, in this case every
massive body, slowly moving relatively to the background, would experience a
constant acceleration, proportional to the Hubble constant, of the same order
as a small additional acceleration of Pioneer 10, 11.


title: Solving the Initial Value Problem of two Black Holes

abstract:
  We solve the elliptic equations associated with the Hamiltonian and momentum
constraints, corresponding to a system composed of two black holes with
arbitrary linear and angular momentum. These new solutions are based on a
Kerr-Schild spacetime slicing which provides more physically realistic
solutions than the initial data based on conformally flat metric/maximal
slicing methods. The singularity/inner boundary problems are circumvented by a
new technique that allows the use of an elliptic solver on a Cartesian grid
where no points are excised, simplifying enormously the numerical problem.


title: Testing A (Stringy) Model of Quantum Gravity

abstract:
  I discuss a specific model of space-time foam, inspired by the modern
non-perturbative approach to string theory (D-branes). The model views our
world as a three brane, intersecting with D-particles that represent stringy
quantum gravity effects, which can be real or virtual. In this picture, matter
is represented generically by (closed or open) strings on the D3 brane
propagating in such a background. Scattering of the (matter) strings off the
D-particles causes recoil of the latter, which in turn results in a distortion
of the surrounding space-time fluid and the formation of (microscopic, i.e.
Planckian size) horizons around the defects. As a mean-field result, the
dispersion relation of the various particle excitations is modified, leading to
non-trivial optical properties of the space time, for instance a non-trivial
refractive index for the case of photons or other massless probes. Such models
make falsifiable predictions, that may be tested experimentally in the
foreseeable future. I describe a few such tests, ranging from observations of
light from distant gamma-ray-bursters and ultra high energy cosmic rays, to
tests using gravity-wave interferometric devices and terrestrial particle
physics experients involving, for instance, neutral kaons.


title: Bianchi I Quantum cosmology in the Bergmann-Wagoner theory

abstract:
  The Wheeler-DeWitt equation is considered in the context of generalized
scalar-tensor theories of gravitation for Bianchi type I cosmology. Exact
solutions are found for two selfinteracting potentials and arbitary coupling
function. The WKB wavefunctions are obtained and a family of solutions
satisfying the Hawking-Page regularity conditions of wormholes are found.


title: Grazing Collisions of Black Holes via the Excision of Singularities

abstract:
  We present the first simulations of non-headon (grazing) collisions of binary
black holes in which the black hole singularities have been excised from the
computational domain. Initially two equal mass black holes $m$ are separated a
distance $\approx10m$ and with impact parameter $\approx2m$. Initial data are
based on superposed, boosted (velocity $\approx0.5c$) solutions of single black
holes in Kerr-Schild coordinates. Both rotating and non-rotating black holes
are considered. The excised regions containing the singularities are specified
by following the dynamics of apparent horizons. Evolutions of up to $t \approx
35m$ are obtained in which two initially separate apparent horizons are present
for $t\approx3.8m$. At that time a single enveloping apparent horizon forms,
indicating that the holes have merged. Apparent horizon area estimates suggest
gravitational radiation of about 2.6% of the total mass. The evolutions end
after a moderate amount of time because of instabilities.


title:
Quantization of massless fields over the static Robertson-Walker space
  of constant negative curvature

abstract:
  Taking the ${\Bbb R}^1 \times H^3$ space as an example, we develop the new
method of quantization of fields over symmetric spaces. We construct the
quantized massless fields of an arbitrary spin over the ${\Bbb R}^1 \times H^3$
space by the resolution over the systems of "plane waves" which are solutions
of the corresponding wave equations. The propagators of these fields are ${\Bbb
R}^1 \times SO(3,1)$-invariant and causal. For spin 0 and 1/2 fields the
propagators are obtained in the explicit form.


title:
Does the third law of black hole thermodynamics really have a serious
  failure?

abstract:
  The almost perfect correspondence between certain laws of classical black
hole mechanics and the ordinary laws of thermodynamics is spoiled by the
failure of the conventional back hole analogue of the third law. Our aim here
is to contribute to the associated discussion by flashing light on some simple
facts of black hole physics. However, no attempt is made to lay to rest the
corresponding long lasting debate. Instead, merely some evidence is provided to
make it clear that although the borderline between extremal and non-extremal
black holes is very thin they are essentially different. Hopefully, a careful
investigation of the related issues will end up with an appropriate form of the
third law and hence with an unblemished setting of black hole thermodynamics.