title:
Analytical approach to critical scalar field collapse in three
  dimensions

abstract:
  In the quest of the critical solution for scalar field collapse in 2+1
gravity with a negative cosmological constant, we present a one parameter
family of solutions with continuous self similar (CSS) behaviour near the
central singularity. We also discuss linear perturbations on this background,
leading to black hole formation, and determine the critical exponent.


title: Static charged fluid spheres in general relativity

abstract:
  Interior perfect fluid solutions for the Reissner-Nordstrom metric are
studied on the basis of a new classification scheme. It specifies which two of
the fluid's characteristics are given functions and picks up accordingly one of
the three main field equations, the other two being universal. General formulae
are found for charged de Sitter solutions, the case of constant energy
component of the energy-momentum tensor, the case of known pressure (including
charged dust) and the case of linear equation of state. Explicit new global
solutions, mainly in elementary functions, are given as illustrations. Known
solutions are briefly reviewed and corrected.


title: Fuchsian analysis of S^2xS^1 and S^3 Gowdy spacetimes

abstract:
  The Gowdy spacetimes are vacuum solutions of Einstein's equations with two
commuting Killing vectors having compact spacelike orbits with T^3, S^2xS^1 or
S^3 topology. In the case of T^3 topology, Kichenassamy and Rendall have found
a family of singular solutions which are asymptotically velocity dominated by
construction. In the case when the velocity is between zero and one, the
solutions depend on the maximal number of free functions. We consider the
similar case with S^2xS^1 or S^3 topology, where the main complication is the
presence of symmetry axes. We use Fuchsian techniques to show the existence of
singular solutions similar to the T^3 case. We first solve the analytic case
and then generalise to the smooth case by approximating smooth data with a
sequence of analytic data. However, for the metric to be smooth at the axes,
the velocity must be 1 or 3 there, which is outside the range where the
constructed solutions depend on the full number of free functions. A plausible
explanation is that in general a spiky feature may develop at the axis, a
situation which is unsuitable for a direct treatment by Fuchsian methods.


title:
Generally covariant Fresnel equation and the emergence of the light cone
  structure in linear pre-metric electrodynamics

abstract:
  We study the {\em propagation of electromagnetic waves} in a spacetime devoid
of a metric but equipped with a {\em linear} electromagnetic spacetime relation
$H\sim\chi\cdot F$. Here $H$ is the electromagnetic excitation $({\cal D},{\cal
H})$ and $F$ the field strength $(E,B)$, whereas $\chi$ (36 independent
components) characterizes the electromagnetic permittivity/permeability of
spacetime. We derive analytically the corresponding Fresnel equation and show
that it is always quartic in the wave covectors. We study the `Fresnel tensor
density' ${\cal G}^{ijkl}$ as (cubic) function of $\chi$ and identify the
leading part of $\chi$ (20 components) as indispensable for light propagation.
Upon requiring electric/magnetic reciprocity of the spacetime relation, the
leading part of $\chi$ induces the {\em light cone} structure of spacetime (9
components), i.e., the spacetime metric up to a function. The possible
existence of an Abelian {\em axion} field (1 component of $\chi$) and/or of a
{\em skewon} field (15 components) and their effect on light propagation is
discussed in some detail. The newly introduced skewon field is expected to be
T-odd and related to dissipation.


title:
Covariant Hamiltonian boundary conditions in General Relativity for
  spatially bounded spacetime regions

abstract:
  We investigate the covariant Hamiltonian symplectic structure of General
Relativity for spatially bounded regions of spacetime with a fixed time-flow
vector. For existence of a well-defined Hamiltonian variational principle
taking into account a spatial boundary, it is necessary to modify the standard
Arnowitt-Deser-Misner Hamiltonian by adding a boundary term whose form depends
on the spatial boundary conditions for the gravitational field. The most
general mathematically allowed boundary conditions and corresponding boundary
terms are shown to be determined by solving a certain equation obtained from
the symplectic current pulled back to the hypersurface boundary of the
spacetime region. A main result is that we obtain a covariant derivation of
Dirichlet, Neumann, and mixed type boundary conditions on the gravitational
field at a fixed boundary hypersurface, together with the associated
Hamiltonian boundary terms. As well, we establish uniqueness of these boundary
conditions under certain assumptions motivated by the form of the symplectic
current. Our analysis uses a Noether charge method which extends and unifies
several results developed in recent literature for General Relativity. As an
illustration of the method, we apply it to the Maxwell field equations to
derive allowed boundary conditions and boundary terms for existence of a
well-defined Hamiltonian variational principle for an electromagnetic field in
a fixed spatially bounded region of Minkowski spacetime.


title:
Properties of the symplectic structure of General Relativity for
  spatially bounded spacetime regions

abstract:
  We continue a previous analysis of the covariant Hamiltonian symplectic
structure of General Relativity for spatially bounded regions of spacetime. To
allow for near complete generality, the Hamiltonian is formulated using any
fixed hypersurface, with a boundary given by a closed spacelike 2-surface. A
main result is that we obtain Hamiltonians associated to Dirichlet and Neumann
boundary conditions on the gravitational field coupled to matter sources, in
particular a Klein-Gordon field, an electromagnetic field, and a set of
Yang-Mills-Higgs fields. The Hamiltonians are given by a covariant form of the
Arnowitt-Deser-Misner Hamiltonian modified by a surface integral term that
depends on the particular boundary conditions. The general form of this surface
integral involves an underlying ``energy-momentum'' vector in the spacetime
tangent space at the spatial boundary 2-surface. We give examples of the
resulting Dirichlet and Neumann vectors for topologically spherical 2-surfaces
in Minkowski spacetime, spherically symmetric spacetimes, and stationary
axisymmetric spacetimes. Moreover, we show the relation between these vectors
and the ADM energy-momentum vector for a 2-surface taken in a limit to be
spatial infinity in asymptotically flat spacetimes. We also discuss the
geometrical properties of the Dirichlet and Neumann vectors and obtain several
striking results relating these vectors to the mean curvature and normal
curvature connection of the 2-surface. Most significantly, the part of the
Dirichlet vector normal to the 2-surface depends only the spacetime metric at
this surface and thereby defines a geometrical normal vector field on the
2-surface. Properties and examples of this normal vector are discussed.


title:
Static axially symmetric solutions of Einstein-Yang-Mills equations with
  a negative cosmological constant: the regular case

abstract:
  Numerical solutions of the Einstein-Yang-Mills equations with a negative
cosmological constant are constructed. These axially symmetric solutions
approach asymptotically the anti-de Sitter spacetime and are regular
everywhere. They are characterized by the winding number $n>1$, the mass and
the non-Abelian magnetic charge. The main properties of the solutions and the
differences with respect to the asymptotically flat case are discussed. The
existence of axially symmetric monopole and dyon solutions in fixed anti-de
Sitter spacetime is also discussed.


title:
Hoop conjecture for colliding black holes : non-time-symmetric initial
  data

abstract:
  The hoop conjecture is well confirmed in momentarily static spaces, but it
has not been investigated systematically for the system with relativistic
motion. To confirm the hoop conjecture for non-time-symmetric initial data, we
consider the initial data of two colliding black holes with momentum and search
an apparent horizon that encloses two black holes. In testing the hoop
conjecture, we use two definitions of gravitational mass : one is the ADM mass
and the other is the quasi-local mass defined by Hawking. Although both
definitions of gravitational mass give fairly consistent picture of the hoop
conjecture, the hoop conjecture with the Hawking mass can judge the existence
of an apparent horizon for wider range of parameters of the initial data
compared to the ADM mass.


title: Vacuum Non Singular Black Hole in Tetrad Theory of Gravitation

abstract:
  The field equations of a special class of tetrad theory of gravitation have
been applied to tetrad space having three unknown functions of radial
coordinate. The spherically symmetric vacuum stress-energy momentum tensor with
one assumption concerning its specific form generates two non-trivial different
exact analytic solutions for these field equations. For large $r$, the exact
analytic solutions coincide with the Schwarzschild solution, while for small
$r$, they behave in a manner similar to the de Sitter solution and describe a
spherically symmetric black hole singularity free everywhere. The solutions
obtained give rise to two different tetrad structures, but having the same
metric, i.e., a static spherically symmetric nonsingular black hole metric. We
then, calculated the energy associated with these two exact analytic solutions
using the superpotential method. We find that unless the time-space components
of the tetrad go to zero faster than $ \displaystyle{1 \over \sqrt{r}}$ at
infinity, the two solutions give different results. This fact implies that the
time-space components of the tetrad must vanish faster than $\displaystyle{1
\over \sqrt{r}}$ at infinity.


title:
The collision of two slowly rotating, initially non boosted, black holes
  in the close limit

abstract:
  We study the collision of two slowly rotating, initially non boosted, black
holes in the close limit. A ``punctures'' modification of the Bowen - York
method is used to construct conformally flat initial data appropriate to the
problem. We keep only the lowest nontrivial orders capable of giving rise to
radiation of both gravitational energy and angular momentum. We show that even
with these simplifications an extension to higher orders of the linear
Regge-Wheeler-Zerilli black hole perturbation theory, is required to deal with
the evolution equations of the leading contributing multipoles. This extension
is derived, together with appropriate extensions of the Regge-Wheeler and
Zerilli equations. The data is numerically evolved using these equations, to
obtain the asymptotic gravitational wave forms and amplitudes. Expressions for
the radiated gravitational energy and angular momentum are derived and used
together with the results of the numerical evolution to provide quantitative
expressions for the relative contribution of different terms, and their
significance is analyzed.


title: Isotropic evolution of a JBD anisotropic Bianchi universe

abstract:
  I study the dynamical effects due to the Brans-Dicke scalar $\phi$-field at
the early stages of a supposedly anisotropic Universe expansion in the
scalar-tensor cosmology of Jordan-Brans-Dicke. This is done considering the
behaviour of the general solutions for the homogeneous model of Bianchi type
VII in the vacuum case. I conclude that the Bianchi-VII$_0$ model shows an
isotropic expansion and that its only physical solution is equivalent to a
Friedman-Robertson-Walker spacetime whose evolution can, depending on the value
of the JBD coupling constant, begin in a singularity and, after expanding
(inflating, if $\omega>0$), shrink to another, or starting in a non-singular
state, collapse to a singularity. I also conclude that the general
Bianchi-VII$_h$ (with $h\neq 0$) models show strong curvature singularities
producing a complete collapse of the homogeinity surfaces to 2D-manifolds, to
1D-manifolds or to single points. Our analysis depends crucially on the
introduction of the so-called intrinsic time, $\Phi$, as the product of the JBD
scalar field $\phi$ times a mean scale factor $a^3=a_1a_2a_3$, in which the
finite-cosmological-time evolution of this universe unfolds into an infinite
$\Phi$-range. These universes isotropize from an anisotropic initial state,
thence I conclude that they are stable against anisotropic perturbations.


title:
Inertial Forces as Viewed from the ADM Slicing and their behaviour for
  Particles in Non-Circular Geodesics

abstract:
  Considering the definition of inertial forces acting on a test particle,
following non-circular geodesics, in static and stationary space times we show
that the centrifugal force reversal occurs only in the case of particles
following prograde orbits around black holes. We first rewrite the covariant
expressions for the acceleration components in terms of the lapse function,
shift vector and the 3-metric $\gm_{ij}$, using the ADM 3+1 splitting and use
these, for different cases as given by pure radial motion, pure azimuthal
motion and the general non-circular motion. It is found that the reversal
occurs only when the azimuthal angular velocity of the particle supersedes the
radial velocity, which indeed depends upon the physical parameters $E$, $l$ and
the Kerr parameter $a$.


title:
Comment on ``Strength and genericity of singularities in Tolman-Bondi-de
  Sitter collapse'' and a note on central singularities

abstract:
  It has been claimed that the Lemaitre-Tolman-Bondi-de Sitter solution always
admits future-pointing radial time-like geodesics emerging from the
shell-focussing singularity, regardless of the nature of the (regular) initial
data. This is despite the fact that some data rule out the emergence of future
pointing radial null geodesics. We correct this claim and show that in general
in spherical symmetry, the absence of radial null geodesics emerging from a
central singularity is sufficient to prove that the singularity is censored.


title: Born-Infeld generalization of the Reissner-Nordstrom black hole

abstract:
  In this work we study the trajectories of test particles in a geometry that
is the nonlinear electromagnetic generalization of the Reissner-Nordstrom
solution. The studied spacetime is a Einstein-Born-Infeld solution, nonsingular
outside a regular event horizon and characterized by three parameters: mass
$M$, charge $Q$ and the Born-Infeld parameter $b$ related to the magnitude of
the electric field at the origin. Asymptotically it is a Reissner-Nordstrom
solution


title: Dynamics of Inflationary Universes with Positive Spatial Curvature

abstract:
  If the spatial curvature of the universe is positive, then the curvature term
will always dominate at early enough times in a slow-rolling inflationary
epoch. This enhances inflationary effects and hence puts limits on the possible
number of e-foldings that can have occurred, independently of what happened
before inflation began and in particular without regard for what may have
happened in the Planck era. We use a simple multi-stage model to examine this
limit as a function of the present density parameter $\Omega_0$ and the epoch
when inflation ends.


title: Causality in Inflationary Universes with Positive Spatial Curvature

abstract:
  We show that in the case of positively-curved Friedmann-Lema\^{\i}tre
universes $(k=+1)$, an inflationary period in the early universe will for most
initial conditions not solve the horizon problem, no matter how long inflation
lasts. It will only do so for cases where inflation starts in an almost static
state, corresponding to an extremely high value of $\Omega_{\Lambda}$,
$\Omega_{\Lambda} \gg 1$, at the beginning of inflation. For smaller values, it
is not possible to solve the horizon problem because the relevant integral
asymptotes to a finite value (as happens also in the de Sitter universe in a
$k=+1$ frame). Thus, for these cases, the causal problems associated with the
near-isotropy of the Cosmic Background Radiation have to be solved already in
the Planck era. Furthermore both compact space sections and event horizons will
exist in these universes even if the present cosmological constant dies away in
the far future, raising potential problems for M-theory as a theory of gravity.


title:
Strong curvature singularities in quasispherical asymptotically de
  Sitter dust collapse

abstract:
  We study the occurrence, visibility, and curvature strength of singularities
in dust-containing Szekeres spacetimes (which possess no Killing vectors) with
a positive cosmological constant. We find that such singularities can be
locally naked, Tipler strong, and develop from a non-zero-measure set of
regular initial data. When examined along timelike geodesics, the singularity's
curvature strength is found to be independent of the initial data.


title:
Computation of gravitational waves from inspiraling binary neutron stars
  in quasiequilibrium circular orbits : Formulation and calibration

abstract:
  Gravitational waves from binary neutron stars in quasiequilibrium circular
orbits are computed using an approximate method which we propose in this paper.
In the first step of this method, we prepare general relativistic irrotational
binary neutron stars in a quasiequilibrium circular orbit, neglecting
gravitational waves. We adopt the so-called conformal flatness approximation
for a three-metric to obtain the quasiequilibrium states in this paper. In the
second step, we compute gravitational waves, solving linear perturbation
equations in the background spacetime of the quasiequilibrium states. Comparing
numerical results with post Newtonian waveforms and luminosity of gravitational
waves from two point masses in circular orbits, we demonstrate that this method
can produce accurate waveforms and luminosity of gravitational waves. It is
shown that the effects of tidal deformation of neutron stars and strong general
relativistic gravity modify the post Newtonian results for compact binary
neutron stars in close orbits. We indicate that the magnitude of a systematic
error in quasiequilibrium states associated with the conformal flatness
approximation is fairly large for close and compact binary neutron stars.
Several formulations for improving the accuracy of quasiequilibrium states are
proposed.


title:
Spherically symmetric scalar vacuum: no-go theorems, black holes and
  solitons

abstract:
  We prove some theorems characterizing the global properties of static,
spherically symmetric configurations of a self-gravitating real scalar field in
general relativity (GR) in various dimensions, with an arbitrary potential $V$,
not necessarily positive-definite. The results are extended to sigma models,
scalar-tensor and curvature-nonlinear theories of gravity. We show that the
list of all possible types of space-time causal structure in the models under
study is the same as for a constant scalar field, namely, Minkowski (or AdS),
Schwarzschild, de Sitter and Schwarzschild - de Sitter, and all horizons are
simple. In particular, these theories do not admit regular black holes with any
asymptotics. Some special features of (2+1)D gravity are revealed. We give
examples of two types of asymptotically flat configurations with positive mass
in GR, admitted by the above theorems: (i) a black hole with nontrivial
``scalar hair'' and (ii) a particlelike solution with a regular centre; in both
cases, the potential $V$ must be at least partly negative. We also discuss the
global effects of conformal mappings that connect different theories. Such
effects are illustrated for solutions with a conformal scalar field in GR.


title: Applications of the theory of evolution equations to general relativity

abstract:
  The theory of evolution equations has been applied in various ways in general
relativity. Following some general considerations about this, some illustrative
examples of the use of ordinary differential equations in general relativity
are presented. After this recent applications of Fuchsian equations are
described, with particular attention to work on the structure of singularities
of solutions of the Einstein equations coupled to a massless scalar field. Next
the relations between analytical and numerical studies of the Einstein
equations are discussed. Finally an attempt is made to identify fruitful
directions for future research within the analytic approach to the study of the
Einstein equations.


title: The time travel paradox

abstract:
  We define the time travel paradox in physical terms and prove its existence
by constructing an explicit example. We argue further that in theories -- such
as general relativity -- where the spacetime geometry is subject to nothing but
differential equations and initial data no paradoxes arise.


title: Metric structure and dimensionality over a Borel set via uniform spaces

abstract:
  We introduce a pregeometry that provides a metric and dimensionality over a
Borel set (Wheeler's "bucket of dust") without assuming probability amplitudes
for adjacency. Rather, a non-trivial metric is produced over a Borel set X per
a uniformity base generated via the discrete topological group structures over
X. We show that entourage multiplication in this uniformity base mirrors the
underlying group structure. One may exploit this fact to create an entourage
sequence of maximal length whence a fine metric structure. Unlike the
statistical approaches of graph theory, this method can suggest dimensionality
over low-order sets. An example over Z2 x Z4 produces 3-dimensional polyhedra
embedded in E4.


title: Admissible Lichnerowicz coordinates for the Schwarzschild metric

abstract:
  Global harmonic coordinates for the complete Schwarzschild metric are found
for a more general case than that addressed in a previous work by Quan-Hui Liu.
The supplementary constant that appears, in addition to the mass, is related to
the stress quadrupole moment of a singular energy--momentum tensor. Similar
calculations are also carried out in q--harmonic coordinates.


title:
A numerical testbed for singularity excision in moving black hole
  spacetimes

abstract:
  We evolve a scalar field in a fixed Kerr-Schild background geometry to test
simple $(3+1)$-dimensional algorithms for singularity excision. We compare both
centered and upwind schemes for handling the shift (advection) terms, as well
as different approaches for implementing the excision boundary conditions, for
both static and boosted black holes. By first determining the scalar field
evolution in a static frame with a $(1+1)$-dimensional code, we obtain the
solution to very high precision. This solution then provides a useful testbed
for simulations in full $(3+1)$ dimensions. We show that some algorithms which
are stable for non-boosted black holes become unstable when the boost velocity
becomes high.


title: Vacuum Non Singular Black Hole Solutions in Tetrad Theory of Gravitation

abstract:
  Starting from a spherically symmetric tetrad with three unknown functions of
the radial coordinate, a general solution of M{\o}ller's field equations in
case of spherical symmetry nonsingular black hole is derived. The previously
obtained solutions are verified as special cases of the general solution. The
general solution is characterized by an arbitrary function and two constants of
integration. The general solution gives no more than the spherically symmetric
nonsingular black hole solution. The energy content of the general solution
depends on the asymptotic behavior of the arbitrary function, and is different
from the standard one.


title:
Matters of Gravity, the newsletter of the APS Topical Group on
  Gravitation, Spring 2001

abstract:
  Contents:
  We hear that... by Jorge Pullin
  * Reflections of a decade:
  Matters of Gravity and the Topical Group in Gravitation, by Beverly Berger
  10 Years in Gravitational Wave Detection, by Peter Saulson
  Ten years of general relativity, some reflections, by Carlo Rovelli
  Tabletop gravity experiments, by Jens Gundlach
  String Theory: the past ten years, by Gary Horowitz
  * Conference reports:
  Fourth Capra Meeting on Radiation Reaction, by Lior Burko
  Workshop on Numerical Relativity, by Michael Koppitz
  Workshop on Canonical & Quantum Gravity III by J. Lewandowski
  and J. Wisniewski


title: Gravitational Condensate Stars: An Alternative to Black Holes

abstract:
  A new solution for the endpoint of gravitational collapse is proposed. By
extending the concept of Bose-Einstein condensation to gravitational systems, a
cold, compact object with an interior de Sitter condensate phase and an
exterior Schwarzschild geometry of arbitrary total mass M is constructed. These
are separated by a phase boundary with a small but finite thickness of fluid
with eq. of state p=+\rho, replacing both the Schwarzschild and de Sitter
classical horizons. The new solution has no singularities, no event horizons,
and a global time. Its entropy is maximized under small fluctuations and is
given by the standard hydrodynamic entropy of the thin shell, instead of the
Bekenstein-Hawking entropy. Unlike black holes, a collapsed star of this kind
is thermodynamically stable and has no information paradox.


title: Some Restrictions on Symmetry Groups of Axially Symmetric Spacetimes

abstract:
  Lie transformation groups containing a one-dimensional subgroup acting
cyclically on a manifold are considered. The structure of the group is found to
be considerably restricted by the existence of a one-dimensional subgroup whose
orbits are circles. The results proved do not depend on the dimension of the
manifold nor on the existence of a metric, but merely on the fact that the Lie
group acts globally on the manifold. Firstly some results for the general case
of an $m+1$-dimensional Lie group are derived: those commutators of the
associated Lie algebra involving the generator of the cyclic subgroup, $X_0$
say, are severely restricted and, in a suitably chosen basis, take a simple
form. The Jacobi identities involving $X_0$ are then applied to show there are
further restrictions on the structure of the Lie algebra. All Lie algebras of
dimensions 2 and 3 compatible with cyclic symmetry are obtained. In the
two-dimensional case the group must be Abelian. For the three-dimensional case,
the Bianchi type of the Lie algebra must be I, II, III, VII$_0$, VIII or IX and
furthermore in all cases the vector $X_0$ forms part of a basis in which the
algebra takes its canonical form. Finally four-dimensional Lie algebras
compatible with cyclic symmetry are considered and the results are related to
the Petrov-Kruchkovich classification of all four-dimensional Lie algebras.


title: On the Symmetries of the Edgar-Ludwig Metric

abstract:
  The conformal Killing equations for the most general (non-plane wave)
conformally flat pure radiation field are solved to find the conformal Killing
vectors. As expected fifteen independent conformal Killing vectors exist, but
in general the metric admits no Killing or homothetic vectors. However for
certain special cases a one-dimensional group of homotheties or motions may
exist and in one very special case, overlooked by previous investigators, a
two-dimensional homethety group exists. No higher dimensional groups of motions
or homotheties are admitted by these metrics.


title: Has the Universe always expanded ?

abstract:
  We consider a cosmological setting for which the currently expanding era is
preceded by a contracting phase, that is, we assume the Universe experienced at
least one bounce. We show that scalar hydrodynamic perturbations lead to a
singular behavior of the Bardeen potential and/or its derivatives (i.e. the
curvature) for whatever Universe model for which the last bounce epoch can be
smoothly and causally joined to the radiation dominated era. Such a Universe
would be filled with non-linear perturbations long before nucleosynthesis, and
would thus be incompatible with observations. We therefore conclude that no
observable bounce could possibly have taken place in the early universe if
Einstein gravity together with hydrodynamical fluids is to describe its
evolution, and hence, under these conditions, that the Universe has always
expanded.


title: Anisotropic cosmologies containing isotropic background radiation

abstract:
  We present an anisotropic cosmological model based on a new exact solution of
Einstein equations. The matter content consists of an anisotropic scalar field
minimally coupled to gravity and of two isotropic perfect fluids that represent
dust matter and radiation. The spacetime is described by a spatially
homogeneous, Bianchi type III metric with a conformal expansion. The model
respects the evolution of the scale factor predicted by standard cosmology, as
well as the isotropy of the cosmic microwave background. Remarkably, the
introduction of the scalar field, apart from explaining the spacetime
anisotropy, gives rise to an energy density that is close to the critical
density. As a consequence, the model is quasiflat during the entire history of
the universe. Using these results, we are also able to construct approximate
solutions for shear-free cosmological models with rotation. We finally carry
out a quantitative discussion of the validity of such solutions, showing that
our approximations are acceptably good if the angular velocity of the universe
is within the observational bounds derived from rotation of galaxies.


title: Black Holes with Less Entropy Than A/4

abstract:
  One can increase one-quarter the area of a black hole, A/4, to exceed the
total thermodynamic entropy, S, by surrounding the hole with a perfectly
reflecting shell and adiabatically squeezing it inward. A/4 can be made to
exceed S by a factor of order unity before the shell enters the Planck regime,
though practical limitations are much more restrictive. One interpretation is
that the black hole entropy resides in its thermal atmosphere, and the shell
restricts the atmosphere so that its entropy is less than A/4.


title:
On the possibility of an astronomical detection of chromaticity effects
  in microlensing by wormhole-like objects

abstract:
  We study the colour changes induced by blending in a wormhole-like
microlensing scenario with extended sources. The results are compared with
those obtained for limb darkening. We assess the possibility of an actual
detection of the colour curve using the difference image analysis method.


title:
Stability criterion for self-similar solutions with perfect fluids in
  general relativity

abstract:
  A stability criterion is derived for self-similar solutions with perfect
fluids which obey the equation of state $P=k\rho$ in general relativity. A wide
class of self-similar solutions turn out to be unstable against the so-called
kink mode. The criterion is directly related to the classification of sonic
points. The criterion gives a sufficient condition for instability of the
solution. For a transonic point in collapse, all primary-direction nodal-point
solutions are unstable, while all secondary-direction nodal-point solutions and
saddle-point ones are stable against the kink mode. The situation is reversed
in expansion. Applications are the following: the expanding flat Friedmann
solution for $1/3 \le k < 1$ and the collapsing one for $0< k \le 1/3$ are
unstable; the static self-similar solution is unstable; nonanalytic
self-similar collapse solutions are unstable; the Larson-Penston (attractor)
solution is stable for this mode for $0<k\alt 0.036$, while it is unstable for
$0.036\alt k $; the Evans-Coleman (critical) solution is stable for this mode
for $0<k\alt 0.89$, while it is unstable for $0.89\alt k$. The last application
suggests that the Evans-Coleman solution for $0.89\alt k $ is {\em not
critical} because it has at least two unstable modes.


title: Charged perfect fluid and scalar field coupled to gravity

abstract:
  Charged perfect fluid with vanishing Lorentz force and massless scalar field
is studied in the case of stationary cylindrically symmetric spacetime. The
scalar field can depend both on radial and longitudinal coordinates. Solutions
are found and classified according to scalar field gradient and magnetic field
relationship. Their physical and geometrical properties are examined and
discussion of particular cases, directly generalizing G\"{o}del-type
spacetimes, is presented.


title:
Testing Scalar-Tensor Gravity Using Space Gravitational-Wave
  Interferometers

abstract:
  We calculate the bounds which could be placed on scalar-tensor theories of
gravity of the Jordan, Fierz, Brans and Dicke type by measurements of
gravitational waveforms from neutron stars (NS) spiralling into massive black
holes (MBH) using LISA, the proposed space laser interferometric observatory.
Such observations may yield significantly more stringent bounds on the
Brans-Dicke coupling parameter \omega than are achievable from solar system or
binary pulsar measurements. For NS-MBH inspirals, dipole gravitational
radiation modifies the inspiral and generates an additional contribution to the
phase evolution of the emitted gravitational waveform. Bounds on \omega can
therefore be found by using the technique of matched filtering. We compute the
Fisher information matrix for a waveform accurate to second post-Newtonian
order, including the effect of dipole radiation, filtered using a currently
modeled noise curve for LISA, and determine the bounds on \omega for several
different NS-MBH canonical systems. For example, observations of a 1.4 solar
mass NS inspiralling to a 1000 solar mass MBH with a signal-to-noise ratio of
10 could yield a bound of \omega > 240,000, substantially greater than the
current experimental bound of \omega > 3000.


title: Gluing and wormholes for the Einstein constraint equations

abstract:
  We establish a general gluing theorem for constant mean curvature solutions
of the vacuum Einstein constraint equations. This allows one to take connected
sums of solutions or to glue a handle (wormhole) onto any given solution. Away
from this handle region, the initial data sets we produce can be made as close
as desired to the original initial data sets. These constructions can be made
either when the initial manifold is compact or asymptotically Euclidean or
asymptotically hyperbolic, with suitable corresponding conditions on the
extrinsic curvature. In the compact setting a mild nondegeneracy condition is
required. In the final section of the paper, we list a number ways this
construction may be used to produce new types of vacuum spacetimes.


title: Wave function of the Universe and Chern-Simons Perturbation Theory

abstract:
  The Chern-Simons exact solution of four-dimensional quantum gravity with
nonvanishing cosmological constant is presented in metric variable as the
partition function of a Chern-Simons theory with nontrivial source. The
perturbative expansion is given, and the wave function is computed to the
lowest order of approximation for the Cauchy surface which is topologically a
3-sphere. The state is well-defined even at degenerate and vanishing values of
the dreibein. Reality conditions for the Ashtekar variables are also taken into
account; and remarkable features of the Chern-Simons state and their relevance
to cosmology are pointed out.


title:
On certain quasi-local spin-angular momentum expressions for large
  spheres near the null infinity

abstract:
  The recently suggested quasi-local spin-angular momentum expressions, based
on the Bramson superpotential and on the holomorphic or anti-holomorphic spinor
fields, are calculated for large spheres near the future null infinity of
asymptotically flat Einsten-Maxwell spacetimes. It is shown that although the
expression based on the anti-holomorphic spinors is finite and unambiguously
defined only in the center-of-mass frame (i.e. it diverges in general), the
corresponding Pauli-Lubanski spin is always finite, free of ambiguities, and is
built only from the gravitational data. Thus it defines a gravitational spin
expression at the future null infinity. The construction based on the
holomorphic spinors diverges in presence of outgoing gravitational radiation.
For stationary spacetimes both constructions reduce to the `standard'
expression.


title: Comments on the Stress-Energy Tensor Operator in Curved Spacetime

abstract:
  Hollands and Wald's technique based on *-algebras of Wick products of field
operators is strightforwardly generalized to define the stress-energy tensor
operator in curved globally hyperbolic spacetimes. In particular, the locality
and covariance requirement is generalized to Wick products of differentiated
quantum fields. The proposed stress-energy tensor operator is conserved and
reduces to the classical form if field operators are replaced by classical
fields satisfying the equation of motion. The definition is based on the
existence of convenient counterterms given by certain local Wick products of
differentiated fields. They are independent from the arbitrary length scale
(and any quantum state) and they classically vanish on solutions of field
equation. The averaged stress-energy tensor with respect to Hadamard quantum
states can be obtained by an improved point-splitting renormalization procedure
which makes use of the nonambiguous part of the Hadamard parametrix only that
is completely determined by the local geometry and the parameters which appear
in the Klein-Gordon operator. The averaged stress-energy tensor also coincides
with that found by employing the local $\zeta$-function approach.


title: Bounding the mass of the graviton using binary pulsar observations

abstract:
  The close agreement between the predictions of dynamical general relativity
for the radiated power of a compact binary system and the observed orbital
decay of the binary pulsars PSR B1913+16 and PSR B1534+12 allows us to bound
the graviton mass to be less than 7.6 x 10^{-20} eV with 90% confidence. This
bound is the first to be obtained from dynamic, as opposed to static-field,
relativity. The resulting limit on the graviton mass is within two orders of
magnitude of that from solar system measurements, and can be expected to
improve with further observations.


title: Polarized Spacetime Foam

abstract:
  An approximate model of a spacetime foam is presented. It is supposed that in
the spacetime foam each quantum handle is like to an electric dipole and
therefore the spacetime foam is similar to a dielectric. If we neglect of
linear sizes of the quantum handle then it can be described with an operator
containing a Grassman number and either a scalar or a spinor field. For both
fields the Lagrangian is presented. For the scalar field it is the dilaton
gravity + electrodynamics and the dilaton field is a dielectric permeability.
The spherically symmetric solution in this case give us the screening of a bare
electric charge surrounded by a polarized spacetime foam and the energy of the
electric field becomes finite one. In the case of the spinor field the
spherically symmetric solution give us a ball of the polarized spacetime foam
filled with the confined electric field. It is shown that the full energy of
the electric field in the ball can be very big.


title: Why do naked singularities form in gravitational collapse?

abstract:
  We investigate what are the key physical features that cause the development
of a naked singularity, rather than a black hole, as the end-state of spherical
gravitational collapse. We show that sufficiently strong shearing effects near
the singularity delay the formation of the apparent horizon. This exposes the
singularity to an external observer, in contrast to a black hole, which is
hidden behind an event horizon due to the early formation of an apparent
horizon.


title: Quantum Einstein's Equations and Constraints Algebra

abstract:
  In this paper we shall address this problem: Is quantum gravity constraints
algebra closed and what are the quantum Einstein equations. We shall
investigate this problem in the de-Broglie--Bohm quantum theory framework. It
is shown that the constraint algebra is weakly closed and the quantum
Einstein's equations are derived.


title: Discrete Quantum Causal Dynamics

abstract:
  We give a mathematical framework to describe the evolution of an open quantum
systems subjected to finitely many interactions with classical apparatuses. The
systems in question may be composed of distinct, spatially separated subsystems
which evolve independently but may also interact. This evolution, driven both
by unitary operators and measurements, is coded in a precise mathematical
structure in such a way that the crucial properties of causality, covariance
and entanglement are faithfully represented. We show how our framework may be
expressed using the language of (poly)categories and functors. Remarkably,
important physical consequences - such as covariance - follow directly from the
functoriality of our axioms.
  We establish strong links between the physical picture we propose and linear
logic. Specifically we show that the refined logical connectives of linear
logic can be used to describe the entanglements of subsystems in a precise way.
Furthermore, we show that there is a precise correspondence between the
evolution of a given system and deductions in a certain formal logical system
based on the rules of linear logic.
  This framework generalizes and enriches both causal posets and the histories
approach to quantum mechanics.


title: Oscillation and Instabilities of Relativistic Stars

abstract:
  In this short review we discuss the relevance of ongoing research into
stellar oscillations and associated instabilities for the detection of
gravitational waves and the future field of ``gravitational-wave astronomy''.


title: Time inversion, Self-similar evolution, and Issue of time

abstract:
  We investigate the question, "how does time flow?" and show that time may
change by inversions as well. We discuss its implications to a simple class of
linear systems. Instead of introducing any unphysical behaviour, inversions can
lead to a new multi- time scale evolutionary path for the linear system
exhibiting late time stochastic fluctuations. We explain how stochastic
behaviour is injected into the linear system as a combined effect of an
uncertainty in the definition of inversion and the irrationality of the golden
mean number. We also give an ansatz for the nonlinear stochastic behaviour of
(fractal) time which facilitates us to estimate the late and short time limits
of a two-time correlation function relevant for the stochastic fluctuations in
linear systems. These fluctuations are shown to enjoy generic 1/f spectrum. The
implicit functional definition of the fractal time is shown to satisfy the
differential equation dx=dt. We also discuss the relevance of intrinsic time in
the present formalism, study of which is motivated by the issue of time in
quantum gravity.


title: Modelling Space with an Atom of Quantum Geometry

abstract:
  Within the context of loop quantum gravity there are several operators which
measure geometry quantities. This work examines two of these operators, volume
and angle, to study quantum geometry at a single spin network vertex - ``an
atom of geometry.'' Several aspects of the angle operator are examined in
detail including minimum angles, level spacing, and the distribution of angles.
The high spin limit of the volume operator is also studied for monochromatic
vertices. The results show that demands of the correct scaling relations
between area and volume and requirements of the expected behavior of angles in
three dimensional flat space require high-valence vertices with total spins of
approximately 10^20.


title: Quantum Collapse of a Small Dust Shell

abstract:
  The full quantum mechanical collapse of a small relativistic dust shell is
studied analytically, asymptotically and numerically starting from the exact
finite dimensional classical reduced Hamiltonian recently derived by
H\'aj{\'\i}\v{c}ek and Kucha\v{r}. The formulation of the quantum mechanics
encounters two problems. The first is the multivalued nature of the Hamiltonian
and the second is the construction of an appropriate self adjoint momentum
operator in the space of the shell motion which is confined to a half line. The
first problem is solved by identifying and neglecting orbits of small action in
order to obtain a single valued Hamiltonian. The second problem is solved by
introducing an appropriate lapse function. The resulting quantum mechanics is
then studied by means of analytical and numerical techniques. We find that the
region of total collapse has very small probability. We also find that the
solution concentrates around the classical Schwarzschild radius. The present
work obtains from first principles a quantum mechanics for the shell and
provides numerical solutions, whose behavior is explained by a detailed WKB
analysis for a wide class of collapsing shells.


title:
Quantum Cosmology for the General Bianchi Type II, VI(Class A) and
  VII(Class A) vacuum geometries

abstract:
  The canonical quantization of the most general minisuperspace actions --i.e.
with all six scale factor as well as the lapse function and the shift vector
present-- describing the vacuum type II, VI and VII geometries, is considered.
The reduction to the corresponding physical degrees of freedom is achieved
through the usage of the linear constraints as well as the quantum version of
the entire set of classical integrals of motion.


title: Lectures on Quantum Cosmology

abstract:
  The problems encountered in trying to quantize the various cosmological
models, are brought forward by means of a concrete example. The Automorphism
groups are revealed as the key element through which G.C.T.'s can be used for a
general treatment of these problems. At the classical level, the time dependent
automorphisms lead to significant simplifications of the line element for the
generic spatially homogeneous geometry, without loss of generality. At the
quantum level, the ''frozen'' automorphisms entail an important reduction of
the configuration space --spanned by the 6 components of the scale factor
matrix-- on which the Wheeler-DeWitt equation, is to be based. In this spirit
the canonical quantization of the most general minisuperspace actions --i.e.
with all six scale factor as well as the lapse function and the shift vector
present-- describing the vacuum type II, I geometries, is considered. The
reduction to the corresponding physical degrees of freedom is achieved through
the usage of the linear constraints as well as the quantum version of the
entire set of all classical integrals of motion.


title:
X-matter induced cosmological scenarios in the relativistic theory of
  gravity

abstract:
  It was shown, that the presence of the so-called X-matter with an equation of
state, which lies between limits of the strong and weak energy conditions,
allows the variety of the cosmological scenarios in the relativistic theory of
gravity. In spite of the fixed negative sign of the cosmological term in the
field equations with massive graviton, it is possible to obtain the solutions
with accelerated and complicated loitering expansion of the universe. The
numerical estimation of the universe's age agrees with the modern observational
data if the upper limit of the graviton's mass is 10^{-71} g


title: Constraints on Spatial distributions of Negative Energy

abstract:
  This paper initiates a program which seeks to study the allowed spatial
distributions of negative energy density in quantum field theory. Here we deal
with free fields in Minkowski spacetime. Known restrictions on time integrals
of the energy density along geodesics, the averaged weak energy condition and
quantum inequalities are reviewed. These restrictions are then used to discuss
some possible constraints on the allowable spatial distributions of negative
energy. We show how some geometric configurations can either be ruled out or
else constrained. We also construct some explicit examples of allowed
distributions. Several issues related to the allowable spatial distributions
are also discussed. These include spacetime averaged quantum inequalities in
two-dimensional spacetime, the failure of generalizations of the averaged weak
energy condition to piecewise geodesics, and the issue of when the local energy
density is negative in the frame of all observers.


title: Gravitational dipole radiations from binary systems

abstract:
  We investigate the possibility of generating sizeable dipole radiations in
relativistic theories of gravity. Optimal parameters to observe their effects
through the orbital period decay of binary star systems are discussed.
Constraints on gravitational couplings beyond general relativity are derived.


title: Questioning the Equivalence Principle

abstract:
  The Equivalence Principle (EP) is not one of the ``universal'' principles of
physics (like the Action Principle). It is a heuristic hypothesis which was
introduced by Einstein in 1907, and used by him to construct his theory of
General Relativity. In modern language, the (Einsteinian) EP consists in
assuming that the only long-range field with gravitational-strength couplings
to matter is a massless spin-2 field. Modern unification theories, and notably
String Theory, suggest the existence of new fields (in particular, scalar
fields: ``dilaton'' and ``moduli'') with gravitational-strength couplings. In
most cases the couplings of these new fields ``violate'' the EP. If the field
is long-ranged, these EP violations lead to many observable consequences
(variation of ``constants'', non-universality of free fall, relative drift of
atomic clocks,...). The best experimental probe of a possible violation of the
EP is to compare the free-fall acceleration of different materials.


title: Phase Space of Compact Bianchi Models with Fluid

abstract:
  The structure of phase space is determined for spatially compact and locally
homogeneous universe models with fluid. Analysis covers models with all
possible space topologies except for those covered by S^3, H^3 or S^2xR which
have no moduli freedom. We show that space topology significantly affects the
number of dynamical degrees of freedom of the system. In particular, we give a
detailed proof of the result that for the systems modeled on the Thurston types
H^2xR and SL_2, which have locally the Bianchi type III or VIII symmetry, the
number of dynamical degrees of freedom increases without bound when the space
topology becomes more and more complicated, which was first pointed out by
Koike, Tanimoto and Hosoya in an incomplete form.


title:
Evolution equations for the perturbations of slowly rotating
  relativistic stars

abstract:
  We present a new derivation of the equations governing the oscillations of
slowly rotating relativistic stars. Previous investigations have been mostly
carried out in the Regge-Wheeler gauge. However, in this gauge the process of
linearizing the Einstein field equations leads to perturbation equations which
as such cannot be used to perform numerical time evolutions. It is only through
the tedious process of combining and rearranging the perturbation variables in
a clever way that the system can be cast into a set of hyperbolic first order
equations, which is then well suited for the numerical integration. The
equations remain quite lengthy, and we therefore rederive the perturbation
equations in a different gauge, which has been first proposed by Battiston et
al. (1970). Using the ADM formalism, one is immediately lead to a first order
hyperbolic evolution system, which is remarkably simple and can be numerically
integrated without many further manipulations. Moreover, the symmetry between
the polar and the axial equations becomes directly apparent.


title: Quantum Gravity on the Classical Background: Group Analysis, Part II

abstract:
  Quantization of gravitational field in the neighbourhood of arbitrary
nontrivial solution of Einstein equations is considered, the 2nd order of
perturbation theory is calculated. The expression for quantum corrections of
the field operator and explicit view of Hamiltonian are represented.


title: Quantum Gravity on the Classical Background: Group Analysis, Part I

abstract:
  Quantization of gravitational field in the neighbourhood of exact solution of
Einstein equation is considered. The method of Bogoliubov group variables is
used.


title: Entropic Dynamics

abstract:
  I explore the possibility that the laws of physics might be laws of inference
rather than laws of nature. What sort of dynamics can one derive from
well-established rules of inference? Specifically, I ask: Given relevant
information codified in the initial and the final states, what trajectory is
the system expected to follow? The answer follows from a principle of
inference, the principle of maximum entropy, and not from a principle of
physics. The entropic dynamics derived this way exhibits some remarkable formal
similarities with other generally covariant theories such as general
relativity.


title: R=0 spacetimes and self-dual Lorentzian wormholes

abstract:
  A two-parameter family of spherically symmetric, static Lorentzian wormholes
is obtained as the general solution of the equation $\rho=\rho_t=0$, where
$\rho = T_{ij} u^iu^j$, $\rho_t = (T_{ij} - {1\over2} T g_{ij}) u^iu^j$, and
$u^i u_i =- 1$. This equation characterizes a class of spacetimes which are
``self dual'' (in the sense of electrogravity duality). The class includes the
Schwarzschild black hole, a family of naked singularities, and a disjoint
family of Lorentzian wormholes, all of which have vanishing scalar curvature
(R=0). Properties of these spacetimes are discussed. Using isotropic
coordinates we delineate clearly the domains of parameter space for which
wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be
obtained. A model for the required ``exotic'' stress-energy is discussed, and
the notion of traversability for the wormholes is also examined.


title: The Time Vector: An Analysis of Continuity and Change

abstract:
  This paper sets out to explain: 1. Why the speed of light c is a constant and
is the maximum speed at which any moving entity can travel. 2. Why time elapsed
is different for a moving entity relative to a stationary entity. 3. Why there
has been confusion between the wave and particle nature of an entity. 4. The
relation between the speed of light c, Planck's constant k and time 5. An
expression for Mass using this notation 6. The derivation for De Broglie's
theorem 7. Indeterminacy of position


title: A Grassmann representation of the Hubble parameter

abstract:
  The Riccati equation for the Hubble parameter H of barotropic FRW cosmologies
in conformal time for \kappa \neq 0 spatial geometries and in comoving time for
the \kappa =0 geometry, respectively, is generalized to odd Grassmannian time
parameters. We obtain a system of simple differential equations for the four
supercomponents (two of even type and two of odd type) of the Hubble superfield
function {\cal H} that is explicitly solved. The second even Hubble component
does not have an evolution governed by general relativity although there are
effects of the latter upon it


title:
Pfaff systems theory and the unifications of gravitation and
  electromagnetism

abstract:
  We show in the framework of Pfaff systems theory, the functional dependences
of the general analytic solutions of a suitable system of involutive
differential equations describing the differences between the analytic
solutions of the conformal and "Poincar\'e" Lie equations. Then we ascribe to
the infinitesimal variations of the parametrizing functionals some physical
meanings as the electromagnetic and gravitation potentials. We also deduce
their corresponding fields of interactions together with the differential
equations they must satisfy. Then we discuss on various possible physical
interpretations.


title:
Thermal noise in interferometric gravitational wave detectors due to
  dielectric optical coatings

abstract:
  We report on thermal noise from the internal friction of dielectric coatings
made from alternating layers of Ta2O5 and SiO2 deposited on fused silica
substrates. We present calculations of the thermal noise in gravitational wave
interferometers due to optical coatings, when the material properties of the
coating are different from those of the substrate and the mechanical loss angle
in the coating is anisotropic. The loss angle in the coatings for strains
parallel to the substrate surface was determined from ringdown experiments. We
measured the mechanical quality factor of three fused silica samples with
coatings deposited on them. The loss angle of the coating material for strains
parallel to the coated surface was found to be (4.2 +- 0.3)*10^(-4) for
coatings deposited on commercially polished slides and (1.0 +- 0.3)*10^{-4} for
a coating deposited on a superpolished disk. Using these numbers, we estimate
the effect of coatings on thermal noise in the initial LIGO and advanced LIGO
interferometers. We also find that the corresponding prediction for thermal
noise in the 40 m LIGO prototype at Caltech is consistent with the noise data.
These results are complemented by results for a different type of coating,
presented in a companion paper.


title:
Excess Mechanical Loss Associated with Dielectric Mirror Coatings on
  Test Masses in Interferometric Gravitational Wave Detectors

abstract:
  Interferometric gravitational wave detectors use mirrors whose substrates are
formed from materials of low intrinsic mechanical dissipation. The two most
likely choices for the test masses in future advanced detectors are fused
silica or sapphire. These test masses must be coated to form mirrors, highly
reflecting at 1064nm. We have measured the excess mechanical losses associated
with adding dielectric coatings to substrates of fused silica and calculate the
effect of the excess loss on the thermal noise in an advanced interferometer.


title:
On all possible static spherically symmetric EYM solitons and black
  holes

abstract:
  We prove local existence and uniqueness of static spherically symmetric
solutions of the Einstein-Yang-Mills equations for any action of the rotation
group (or SU(2)) by automorphisms of a principal bundle over space-time whose
structure group is a compact semisimple Lie group G. These actions are
characterized by a vector in the Cartan subalgebra of g and are called regular
if the vector lies in the interior of a Weyl chamber. In the irregular cases
(the majority for larger gauge groups) the boundary value problem that results
for possible asymptotically flat soliton or black hole solutions is more
complicated than in the previously discussed regular cases. In particular,
there is no longer a gauge choice possible in general so that the Yang-Mills
potential can be given by just real-valued functions. We prove the local
existence of regular solutions near the singularities of the system at the
center, the black hole horizon, and at infinity, establish the parameters that
characterize these local solutions, and discuss the set of possible actions and
the numerical methods necessary to search for global solutions. That some
special global solutions exist is easily derived from the fact that su(2) is a
subalgebra of any compact semisimple Lie algebra. But the set of less trivial
global solutions remains to be explored.


title:
The embedding of the spacetime in five dimensions: an extension of
  Campbell-Magaard theorem

abstract:
  We extend Campbell-Magaard embedding theorem by proving that any
n-dimensional semi-Riemannian manifold can be locally embedded in an
(n+1)-dimensional Einstein space. We work out some examples of application of
the theorem and discuss its relevance in the context of modern
higher-dimensional spacetime theories.


title: Classical self-forces in a space with a dispiration

abstract:
  We derive the gravitational and electrostatic self-energies of a particle at
rest in the background of a cosmic dispiration (topological defect), finding
that the particle may experience potential steps, well potentials or potential
barriers depending on the nature of the interaction and also on certain
properties of the defect. The results may turn out to be useful in cosmology
and condensed matter physics.


title:
Dynamical instability of new-born neutron stars as sources of
  gravitational radiation

abstract:
  The dynamical instability of new-born neutron stars is studied by evolving
the linearized hydrodynamical equations. The neutron stars considered in this
paper are those produced by the accretion induced collapse of rigidly rotating
white dwarfs. A dynamical bar-mode (m=2) instability is observed when the ratio
of rotational kinetic energy to gravitational potential energy $\beta$ of the
neutron star is greater than the critical value $\beta_d \approx 0.25$. This
bar-mode instability leads to the emission of gravitational radiation that
could be detected by gravitational wave detectors. However, these sources are
unlikely to be detected by LIGO II interferometers if the event rate is less
than $10^{-6}$ per year per galaxy. Nevertheless, if a significant fraction of
the pre-supernova cores are rapidly rotating, there would be a substantial
number of neutron stars produced by the core collapse undergoing bar-mode
instability. This would greatly increase the chance of detecting the
gravitational radiation.


title: A possible gauge formulation for gravity?

abstract:
  A possible Yang-Mills like lagrangian formulation for gravity is explored.
The starting point consists on two next assumptions. First, the metric is
assumed as a real map from a given gauge group. Second, a gauge invariant
lagrangian density is considered with the condition that it is related to the
Einstein one up to a bound term. We study a stationary solution of the abelian
case for the spherical symmetry, which is connected to the M\"oller's Maxwell
like formulation for gravity. Finally, it is showed the consistence of this
formulation with the Newtonian limit.


title:
Quantum Thermal Effect of Dirac Particles in a Non-uniformly
  Rectilinearly Accelerating Kinnersley Black Hole

abstract:
  The Hawking radiation of Dirac particles in an arbitrarily rectilinearly
accelerating Kinnersley black hole is studied by using a method of the
generalized tortoise coordinate transformation. Both the location and the
temperature of the event horizon depend on the time and polar angle. The
Hawking thermal radiation spectrum of Dirac particles is also derived.
  PACS numbers: 97.60.Lf, 04.70.Dy


title: Conformal Symmetry and Cosmological Entropy Production

abstract:
  Introducing an effective refraction index of an isotropic cosmic medium, we
investigate the cosmological fluid dynamics which is consistent with a
conformal, timelike symmetry of a corresponding ``optical'' metric. We
demonstrate that this kind of symmetry is compatible with the existence of a
negative viscous pressure and, consequently, with cosmological entropy
production. We establish an exactly solvable model according to which the
viscous pressure is a consequence of a self-interacting one-particle force
which is self-consistently exerted on the microscopic particles of a
relativistic gas. Furthermore, we show that a sufficiently high decay rate of
the refraction index of an ultrarelativistic cosmic medium results in an
inflationary expansion of the universe.


title: Inflation and Global Equivalence

abstract:
  This article investigates an extension of General Relativity based upon a
class of lifted metrics on the cotangent bundle of space-time. The dynamics of
the theory is determined by a fixed section of the cotangent bundle,
representing the momentum of a fluid flow, and Einstein's equations for the
fluid applied to the induced space-time metric on the submanifold of the
cotangent bundle defined by the image of the section. This construction is
formally analogous to the extension of Galilean Relativity by Special
Relativity, and is shown to reduce to General Relativity as the gravitational
constant approaches zero. By examining the consequences of the model for
homogeneous cosmologies, it is demonstrated that this construction globalizes
the equivalence principle, in that, the perfect fluid model of Special
Relativity is sufficient to predict both the inflationary and the current era.


title: Conditional probabilities in Ponzano-Regge minisuperspace

abstract:
  We examine the Hartle-Hawking no-boundary initial state for the Ponzano-Regge
formulation of gravity in three dimensions. We consider the behavior of
conditional probabilities and expectation values for geometrical quantities in
this initial state for a simple minisuperspace model consisting of a
two-parameter set of anisotropic geometries on a 2-sphere boundary. We find
dependence on the cutoff used in the construction of Ponzano-Regge amplitudes
for expectation values of edge lengths. However, these expectation values are
cutoff independent when computed in certain, but not all, conditional
probability distributions. Conditions that yield cutoff independent expectation
values are those that constrain the boundary geometry to a finite range of edge
lengths. We argue that such conditions have a correspondence to fixing a range
of local time, as classically associated with the area of a surface for
spatially closed cosmologies. Thus these results may hint at how classical
spacetime emerges from quantum amplitudes.


title: Magnetic Brane-worlds

abstract:
  We investigate brane-worlds with a pure magnetic field and a perfect fluid.
We extend earlier work to brane-worlds, and find new properties of the Bianchi
type I brane-world. We find new asymptotic behaviours on approach to the
singularity and classify the critical points of the dynamical phase space. It
is known that the Einstein equations for the magnetic Bianchi type I models are
in general oscillatory and are believed to be chaotic, but in the brane-world
model this chaotic behaviour does not seem to be possible.


title:
Regular Sources of the Kerr-Schild class for Rotating and Nonrotating
  Black Hole Solutions

abstract:
  A unified approach to regular interiors of black holes with smooth matter
distributions in the core region is given. The approach is based on a class of
Kerr-Schild metrics representing minimal deformations of the Kerr-Newman
solution, and allows us to give a common treatment for (charged and uncharged)
rotating and nonrotating black holes. It is shown that the requirement of
smoothness of the source constraints the structure of the core region in many
respects: in particular, for Schwarzschild holes a de Sitter core can be
selected, which is surrounded by a smooth shell giving a leading contribution
to the total mass of the source. In the rotating, noncharged case the source
has a similar structure, taking the form of a (anisotropic and rotating) de
Sitter-like core surrounded by a rotating elliptic shell. The Kerr singular
ring is regularized by anisotropic matter rotating in the equatorial plane, so
that the negative sheet of the Kerr geometry is absent. In the charged case the
sources take the form of ``bags'', which can have de Sitter or anti de Sitter
interiors and a smooth domain wall boundary, with a tangential stress providing
charge confinement. The ADM and Tolman relations are used to calculate the
total mass of the sources.


title: Some Properties of a New Solution of the Ernst Equation

abstract:
  From a particularly simple solution of the Ernst equation, we build a
solution of the vacuum stationary axisymmetric Einstein equations depending on
three parameters. The parameters are associated to the total mass of the source
and its angular momentum. The third parameter produces a topological
deformation of the ergosphere making it a two-sheet surface, and for some of
its values forbids the Penrose process.


title: Mechanism for a Decaying Cosmological Constant

abstract:
  A mechanism is introduced to reduce a large cosmological constant to a
sufficiently small value consistent with observational upper limit. The basic
ingradient in this mechanism is a distinction which has been made between the
two unit systems used on cosmology and particle physics. We have used a
conformal invariant gravitational model to define a particular conformal frame
in terms of the large scale properties of the universe. It is then argued that
the contributions of mass scales in particle physics to the vacuum energy
density should be considered in a different conformal frame. In this manner a
cancellation mechanism is presented in which the conformal factor plays a key
role to relax the large effective cosmological constant.


title:
Extended hierarchical search (EHS) algorithm for detection of
  gravitational waves from inspiraling compact binaries

abstract:
  Pattern matching techniques like matched filtering will be used for online
extraction of gravitational wave signals buried inside detector noise. This
involves cross correlating the detector output with hundreds of thousands of
templates spanning a multi-dimensional parameter space, which is very expensive
computationally. A faster implementation algorithm was devised by Mohanty and
Dhurandhar [1996] using a hierarchy of templates over the mass parameters,
which speeded up the procedure by about 25 to 30 times. We show that a further
reduction in computational cost is possible if we extend the hierarchy paradigm
to an extra parameter, namely, the time of arrival of the signal. In the first
stage, the chirp waveform is cut-off at a relatively low frequency allowing the
data to be coarsely sampled leading to cost saving in performing the FFTs. This
is possible because most of the signal power is at low frequencies, and
therefore the advantage due to hierarchy over masses is not compromised.
Results are obtained for spin-less templates up to the second post-Newtonian
(2PN) order for a single detector with LIGO I noise power spectral density. We
estimate that the gain in computational cost over a flat search is about 100.


title:
An origin of the Universe determined by quantum physics and relativistic
  gravity

abstract:
  We discuss the evolution of the Universe from what might be called its
quantum origin. We apply the uncertainty principle to the origin of the
Universe with characteristic time scale equal to the Planck time to obtain its
initial temperature and density. We establish that the subsequent evolution
obeying the Einstein equation gives the present temperature of the microwave
background close to the observed value. The same origin allows the possibility
that the Universe started with exactly the critical density, Omega =1, and
remained at the critical density during evolution. Many other important
features of the observed Universe, including homogeneity and isotropy, Hubble's
constant at origin, its minimum age, present density etc. are all predictions
of our theory. We discuss also the testability of our theory.


title:
High Temperature Matter and Gamma Ray Spectra from Microscopic Black
  Holes

abstract:
  The relativistic viscous fluid equations describing the outflow of high
temperature matter created via Hawking radiation from microscopic black holes
are solved numerically for a realistic equation of state. We focus on black
holes with initial temperatures greater than 100 GeV and lifetimes less than 6
days. The spectra of direct photons and photons from $\pi^0$ decay are
calculated for energies greater than 1 GeV. We calculate the diffuse gamma ray
spectrum from black holes distributed in our galactic halo. However, the most
promising route for their observation is to search for point sources emitting
gamma rays of ever-increasing energy.


title: Newtonian Counterparts of Spin 2 Massless Discontinuities

abstract:
  Massive spin 2 theories in flat or cosmological ($\Lambda \ne 0$) backgrounds
are subject to discontinuities as the masses tend to zero. We show and explain
physically why their Newtonian limits do not inherit this behaviour. On the
other hand, conventional ``Newtonian cosmology'', where $\Lambda $ is a
constant source of the potential, displays discontinuities: e.g. for any finite
range, $\Lambda$ can be totally removed.


title: Entropy and Area of Black Holes in Loop Quantum Gravity

abstract:
  Simple arguments related to the entropy of black holes strongly constrain the
spectrum of the area operator for a Schwarzschild black hole in loop quantum
gravity. In particular, this spectrum is fixed completely by the assumption
that the black hole entropy is maximum. Within the approach discussed, one
arrives in loop quantum gravity at a quantization rule with integer quantum
numbers $n$ for the entropy and area of a black hole.


title:
Isometric embeddings of black hole horizons in three-dimensional flat
  space

abstract:
  The geometry of a two-dimensional surface in a curved space can be most
easily visualized by using an isometric embedding in flat three-dimensional
space. Here we present a new method for embedding surfaces with spherical
topology in flat space when such a embedding exists. Our method is based on
expanding the surface in spherical harmonics and minimizing for the differences
between the metric on the original surface and the metric on the trial surface
in the space of the expansion coefficients. We have applied this method to
study the geometry of back hole horizons in the presence of strong,
non-axisymmetric, gravitational waves (Brill waves). We have noticed that, in
many cases, although the metric of the horizon seems to have large deviations
from axisymmetry, the intrinsic geometry of the horizon is almost axisymmetric.
The origin of the large apparent non-axisymmetry of the metric is the
deformation of the coordinate system in which the metric was computed.


title: Dirichlet Boundary Value Problems of the Ernst Equation

abstract:
  We demonstrate how the solution to an exterior Dirichlet boundary value
problem of the axisymmetric, stationary Einstein equations can be found in
terms of generalized solutions of the Backlund type. The proof that this
generalization procedure is valid is given, which also proves conjectures about
earlier representations of the gravitational field corresponding to rotating
disks of dust in terms of Backlund type solutions.


title: Critical phenomena in Newtonian gravity

abstract:
  We investigate the stability of self-similar solutions for a gravitationally
collapsing isothermal sphere in Newtonian gravity by means of a normal mode
analysis. It is found that the Hunter series of solutions are highly unstable,
while neither the Larson-Penston solution nor the homogeneous collapse one have
an analytic unstable mode. Since the homogeneous collapse solution is known to
suffer the kink instability, the present result and recent numerical
simulations strongly support a proposition that the Larson-Penston solution
will be realized in astrophysical situations. It is also found that the Hunter
(A) solution has a single unstable mode, which implies that it is a critical
solution associated with some critical phenomena which are analogous to those
in general relativity. The critical exponent $\gamma$ is calculated as
$\gamma\simeq 0.10567$. In contrast to the general relativistic case, the order
parameter will be the collapsed mass. In order to obtain a complete picture of
the Newtonian critical phenomena, full numerical simulations will be needed.


title: Quasinormal modes of the electrically charged dilaton black hole

abstract:
  We sketch the results of calculations of the quasinormal frequencies of the
electrically charged dilaton black hole. At the earlier phase of evaporation (Q
is less than 0.7-0.8M), the dilaton black hole "rings" with the complex
frequencies which differ negligibly from those of the Reissner-Nordstrom black
hole. The spectrum of the frequencies weakly depends upon the dilaton coupling.


title: The Lemaitre-Schwarzschild Problem Revisited

abstract:
  The Lemaitre and Schwarzschild analytical solutions for a relativistic
spherical body of constant density are linked together through the use of the
Weyl quadratic invariant. The critical radius for gravitational collapse of an
incompressible fluid is shown to vary continuously from 9/8 of the
Schwarzschild radius to the Schwarzschild radius itself while the internal
pressures become locally anisotropic.


title: What are the equations of motion of classical physics?

abstract:
  Action at a distance in Newtonian physics is replaced by finite propagation
speeds in classical physics, the physics defined by the field theories of
Maxwell and Einstein. As a result, the differential equations of motion in
Newtonian physics are replaced in classical physics by functional differential
equations, where the delay associated with the finite propagation speed (the
speed of light) is taken into account. Newtonian equations of motion, with
post-Newtonian corrections, are often used to approximate the functional
differential equations of motion. Some mathematical issues related to the
problem of extracting the ``correct'' approximate Newtonian equations of motion
are discussed.


title:
Is Many Likelier than Few? A Critical Assessment of the Self-Indicating
  Assumption

abstract:
  We analyze the arguments allegedly supporting the so-called Self-Indication
Assumption (SIA), as an attempt to reject counterintuitive consequences of the
Doomsday Argument of Carter, Leslie, Gott and others. Several arguments
purportedly supporting this assumption are demonstrated to be either flawed or,
at best, inconclusive. Therefore, no compelling reason for accepting SIA exists
so far, and it should be regarded as an ad hoc hypothesis with several rather
strange and implausible physical and epistemological consequences. Accordingly,
if one wishes to reject the controversial consequences of the Doomsday
Argument, a route different from SIA has to be found.


title: GPS observables in general relativity

abstract:
  I present a complete set of gauge invariant observables, in the context of
general relativity coupled with a minimal amount of realistic matter (four
particles). These observables have a straightforward and realistic physical
interpretation. In fact, the technology to measure them is realized by the
Global Positioning System: they are defined by the physical reference system
determined by GPS readings. The components of the metric tensor in this
physical reference system are gauge invariant quantities and, remarkably, their
evolution equations are local.


title: Radiation-balanced simulations for binary inspiral

abstract:
  The late stage of the inspiral of two black holes may have important
non-Newtonian effects that are unrelated to radiation reaction. To understand
these effects we approximate a slowly inspiralling binary by a stationary
solution to Einstein's equations in which the holes orbit eternally. Radiation
reaction is nullified by specifying a boundary condition at infinity containing
equal amounts of ingoing and outgoing radiation. The computational problem is
then converted from an evolution problem with initial data to a boundary value
problem. In addition to providing an approximate inspiral waveform via
extraction of the outgoing modes, our approximation can give alternative
initial data for numerical relativity evolution. We report results on
simplified models and on progress in building 3D numerical solutions.


title:
Restoration of Angular Lie Algebra Symmetries from a Covariant
  Hamiltonian

abstract:
  The sO(3) and the Lorentz algebra symmetries breaking with gauge curvatures
are studied by means of a covariant Hamiltonian. The restoration of these
algebra symmetries in flat and curved spaces is performed and led to the
apparition of a monopole field. Then in the context of the Lorentz algebra we
consider an application to the gravitoelectromagnetism theory. In this last
case a qualitative relation giving a mass spectrum for dyons is established.

categories: gr-qc hep-th math-ph math.MP physics.class-ph


title:
Comparing the inspiral of irrotational and corotational binary neutron
  stars

abstract:
  We model the adiabatic inspiral of relativistic binary neutron stars in a
quasi-equilibrium (QE) approximation, and compute the gravitational wavetrain
from the late phase of the inspiral. We compare corotational and irrotational
sequences and find a significant difference in the inspiral rate, which is
almost entirely caused by differences in the binding energy. We also compare
our results with those of a point-mass post-Newtonian calculation. We
illustrate how the late inspiral wavetrain computed with our QE numerical
scheme can be matched to the subsequent plunge and merger waveform calculated
with a fully relativistic hydrodynamics code.


title:
Adjusted ADM systems and their expected stability properties: constraint
  propagation analysis in Schwarzschild spacetime

abstract:
  In order to find a way to have a better formulation for numerical evolution
of the Einstein equations, we study the propagation equations of the
constraints based on the Arnowitt-Deser-Misner formulation. By adjusting
constraint terms in the evolution equations, we try to construct an
"asymptotically constrained system" which is expected to be robust against
violation of the constraints, and to enable a long-term stable and accurate
numerical simulation. We first provide useful expressions for analyzing
constraint propagation in a general spacetime, then apply it to Schwarzschild
spacetime. We search when and where the negative real or non-zero imaginary
eigenvalues of the homogenized constraint propagation matrix appear, and how
they depend on the choice of coordinate system and adjustments. Our analysis
includes the proposal of Detweiler (1987), which is still the best one
according to our conjecture but has a growing mode of error near the horizon.
Some examples are snapshots of a maximally sliced Schwarzschild black hole. The
predictions here may help the community to make further improvements.


title:
Radiation from accelerated perfect or dispersive mirrors following
  prescribed relativistic asymptotically inertial trajectories

abstract:
  We address the question of radiation emission from both perfect and
dispersive mirrors following prescribed relativistic trajectories. The
trajectories considered are asymptotically inertial: the mirror starts from
rest and eventually reverts to motion at uniform velocity. This enables us to
provide a description in terms of in and out states. We calculate exactly the
Bogolubov alpha and beta coefficients for a specific form of the trajectory,
and stress the analytic properties of the amplitudes and the constraints
imposed by unitarity. A formalism for the description of emission of radiation
from a dispersive mirror is presented.


title:
Radiation from perfect mirrors starting from rest and the black body
  spectrum

abstract:
  We address the question of radiation emission from a perfect mirror that
starts from rest and follows the trajectory z=-ln(cosht) till t->Infinity. We
show that a correct derivation of the black body spectrum via the calculation
of the Bogolubov amplitudes requires consideration of the whole trajectory and
not just of its asymptotic part.


title: Adaptive thermal compensation of test masses in advanced LIGO

abstract:
  As the first generation of laser interferometric gravitational wave detectors
near operation, research and development has begun on increasing the
instrument's sensitivity while utilizing the existing infrastructure. In the
Laser Interferometer Gravitational Wave Observatory (LIGO), significant
improvements are being planned for installation in ~2007, increasing strain
sensitivity through improved suspensions and test mass substrates, active
seismic isolation, and higher input laser power. Even with the highest quality
optics available today, however, finite absorption of laser power within
transmissive optics, coupled with the tremendous amount of optical power
circulating in various parts of the interferometer, result in critical
wavefront deformations which would cripple the performance of the instrument.
Discussed is a method of active wavefront correction via direct thermal
actuation on optical elements of the interferometer. A simple nichrome heating
element suspended off the face of an affected optic will, through radiative
heating, remove the gross axisymmetric part of the original thermal distortion.
A scanning heating laser will then be used to remove any remaining
non-axisymmetric wavefront distortion, generated by inhomogeneities in the
substrate's absorption, thermal conductivity, etc. A proof-of-principle
experiment has been constructed at MIT, selected data of which are presented.


title: Inflationary spacetimes are not past-complete

abstract:
  Many inflating spacetimes are likely to violate the weak energy condition, a
key assumption of singularity theorems. Here we offer a simple kinematical
argument, requiring no energy condition, that a cosmological model which is
inflating -- or just expanding sufficiently fast -- must be incomplete in null
and timelike past directions. Specifically, we obtain a bound on the integral
of the Hubble parameter over a past-directed timelike or null geodesic. Thus
inflationary models require physics other than inflation to describe the past
boundary of the inflating region of spacetime.


title: Harmonic coordinate method for simulating generic singularities

abstract:
  This paper presents both a numerical method for general relativity and an
application of that method. The method involves the use of harmonic coordinates
in a 3+1 code to evolve the Einstein equations with scalar field matter. In
such coordinates, the terms in Einstein's equations with the highest number of
derivatives take a form similar to that of the wave equation. The application
is an exploration of the generic approach to the singularity for this type of
matter. The preliminary results indicate that the dynamics as one approaches
the singularity is locally the dynamics of the Kasner spacetimes.


title:
The mass of spacelike hypersurfaces in asymptotically anti-de Sitter
  space-times

abstract:
  We give a Hamiltonian definition of mass for spacelike hypersurfaces in
space-times with metrics which are asymptotic to the anti-de Sitter one, or to
a class of generalizations thereof. We show that our definition provides a
geometric invariant for a spacelike hypersurface embedded in a space-time.


title: Angular momentum effects in Michelson-Morley type experiments

abstract:
  The effect of the angular momentum density of a gravitational source on the
times of flight of light rays in an interferometer is analyzed. The calculation
is made imagining that the interferometer is at the equator of the gravity
source and, as long as possible, the metric, provided it is stationary and
axisymmetric, is not approximated. Finally, in order to evaluate the size of
the effect in the case of the Earth a weak field approximation is introduced.
For laboratory scales and non-geodesic paths the correction turns out to be
comparable with the sensitivity expected in gravitational waves interferometric
detectors, whereas it drops under the threshold of detectability when using
free (geodesic) light rays.


title:
Classical and Quantum Solutions of 2+1 Dimensional Gravity under De
  Broglie-Bohm Interpretation

abstract:
  We have studied classical and quantum solutions of 2+1 dimensional Einstein
gravity theory. Quantum theory is defined through the local conserved angular
momentum and mass operators in the case of spherically symmetric space-time.
The de Broglie-Bohm interpretation is applied for the wave function and we
derive the differential equations for metrics. Metrics including quantum effect
are obtained in solving these equations and we compare them with classical
metrics. Especially the quantum effect on the closed de Sitter universe is
evaluated quantitatively.


title: Spherical Universes with Anisotropic Pressure

abstract:
  Einstein's equations are solved for spherically symmetric universes composed
of dust with tangential pressure provided by angular momentum, L(R), which
differs from shell to shell. The metric is given in terms of the shell label,
R, and the proper time, tau, experienced by the dust particles. The general
solution contains four arbitrary functions of R - M(R), L(R), E(R) and r(0,R).
The solution is described by quadratures, which are in general elliptic
integrals. It provides a generalization of the Lemaitre-Tolman-Bondi solution.
We present a discussion of the types of solution, and some examples. The
relationship to Einstein clusters and the significance for gravitational
collapse is also discussed.


title:
Dynamics of a self gravitating light-like matter shell: a
  gauge-invariant Lagrangian and Hamiltonian description

abstract:
  A complete Lagrangian and Hamiltonian description of the theory of
self-gravitating light-like matter shells is given in terms of
gauge-independent geometric quantities. For this purpose the notion of an
extrinsic curvature for a null-like hypersurface is discussed and the
corresponding Gauss-Codazzi equations are proved. These equations imply Bianchi
identities for spacetimes with null-like, singular curvature. Energy-momentum
tensor-density of a light-like matter shell is unambiguously defined in terms
of an invariant matter Lagrangian density. Noether identity and
Belinfante-Rosenfeld theorem for such a tensor-density are proved. Finally, the
Hamiltonian dynamics of the interacting system: ``gravity + matter'' is derived
from the total Lagrangian, the latter being an invariant scalar density.


title: Progress on stochastic background search codes for LIGO

abstract:
  One of the types of signals for which the LIGO interferometric gravitational
wave detectors will search is a stochastic background of gravitational
radiation. We review the technique of searching for a background using the
optimally-filtered cross-correlation statistic, and describe the state of plans
to perform such cross-correlations between the two LIGO interferometers as well
as between LIGO and other gravitational-wave detectors, in particular the
preparation of software to perform such data analysis.


title: Performance of a 1200m long suspended Fabry-Perot cavity

abstract:
  Using one arm of the Michelson interferometer and the power recycling mirror
of the interferometric gravitational wave detector GEO600, we created a
Fabry-Perot cavity with a length of 1200 m. The main purpose of this experiment
was to gather first experience with the main optics, its suspensions and the
corresponding control systems. The residual displacement of a main mirror is
about 150 nm rms. By stabilising the length of the 1200 m long cavity to the
pre-stabilised laser beam we achieved an error point frequency noise of 0.1
mHz/sqrt(Hz) at 100 Hz Fourier frequency. In addition we demonstrated the
reliable performance of all included subsystems by several 10-hour-periods of
continuous stable operation. Thus the full frequency stabilisation scheme for
GEO600 was successfully tested.


title: Is Einstein's equivalence principle valid for a quantum particle?

abstract:
  Einstein's equivalence principle in classical physics is a rule stating that
the effect of gravitation is locally equivalent to the acceleration of an
observer. The principle determines the motion of test particles uniquely
(modulo very broad general assumptions). We show that the same principle
applied to a quantum particle described by a wave function on a Newtonian
gravitational background determines its motion with a similar degree of
uniqueness.


title: Fluid flow and inertial forces in black hole space times

abstract:
  We discuss the nature of the radial and azimuthal components of centrifugal
force associated with fluid flows in the equatorial plane of black hole space
times. The equations of motion are solved for the radial and azimuthal
components of the 3-velocity V^i which are then used in evaluating the nature
of the various components of inertial accelerations. It is shown that the
reversal of centrifugal force is governed mainly by the dominance of the
azimuthal velocity and the reversal occurs for r, mostly at 2m <~ r <~ 3m,
depending upon the boundary condition.


title:
Exact Solution of Photon Equation in a Nonstationary Godel-Type
  Cosmological Universe

abstract:
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: gr-qc/0207026, gr-qc/0502059,
gr-qc/0502061, and gr-qc/0510038.


title:
Optimum Placement of Post-1PN GW Chirp Templates Made Simple at any
  Match Level via Tanaka-Tagoshi Coordinates

abstract:
  A simple recipe is given for constructing a maximally sparse regular lattice
of spin-free post-1PN gravitational wave chirp templates subject to a given
minimal match constraint, using Tanaka-Tagoshi coordinates.


title: Equilibrium configurations in the dynamics of irrotational dust matter

abstract:
  Irrotational dust solutions of Einstein's equations are suitable models to
describe the general-relativistic aspects of the gravitational instability
mechanism for the formation of cosmic structures. In this paper we study their
state space by considering the local initial-value problem formulated in the
covariant fluid approach. We consider a wide range of models, from homogeneous
and isotropic to highly inhomogeneous irrotational dust models, showing how
they constitute equilibrium configurations (invariant sets) of the dynamics.
Moreover, we give the characterization of such configurations, which provides
an initial-data characterization of the models under consideration.


title:
Relating Covariant and Canonical Approaches to Triangulated Models of
  Quantum Gravity

abstract:
  In this paper explore the relation between covariant and canonical approaches
to quantum gravity and $BF$ theory. We will focus on the dynamical
triangulation and spin-foam models, which have in common that they can be
defined in terms of sums over space-time triangulations. Our aim is to show how
we can recover these covariant models from a canonical framework by providing
two regularisations of the projector onto the kernel of the Hamiltonian
constraint. This link is important for the understanding of the dynamics of
quantum gravity. In particular, we will see how in the simplest dynamical
triangulations model we can recover the Hamiltonian constraint via our
definition of the projector. Our discussion of spin-foam models will show how
the elementary spin-network moves in loop quantum gravity, which were
originally assumed to describe the Hamiltonian constraint action, are in fact
related to the time-evolution generated by the constraint. We also show that
the Immirzi parameter is important for the understanding of a continuum limit
of the theory.


title:
Sufficient condition for Blackhole formation in spherical gravitational
  collapse

abstract:
  A sufficient condition for the validity of Cosmic Censorship in spherical
gravitational collapse is formulated and proved. The condition relies on an
attractive mathematical property of the apparent horizon, which holds if
''minimal'' requirements of physical reasonableness are satisfied by the matter
model.


title: Ricci Collineations in Friedmann-Robertson-Walker Spacetimes

abstract:
  Ricci collineations and Ricci inheritance collineations of
Friedmann-Robertson-Walker spacetimes are considered. When the Ricci tensor is
non-degenerate, it is shown that the spacetime always admits a fifteen
parameter group of Ricci inheritance collineations; this is the maximal
possible dimension for spacetime manifolds. The general form of the vector
generating the symmetry is exhibited. It is also shown, in the generic case,
that the group of Ricci collineations is six-dimensional and coincides with the
isometry group. In special cases the spacetime may admit either one or four
proper Ricci collineations in addition to the six isometries. These special
cases are classified and the general form of the vector fields generating the
Ricci collineations is exhibited. When the Ricci tensor is degenerate, the
groups of Ricci inheritance collineations and Ricci collineations are
infinite-dimensional. General forms for the generating vectors are obtained.
Similar results are obtained for matter collineations and matter inheritance
collineations.


title: Probability for Primordial Black Holes in Higher Derivative Theories

abstract:
  The probability for quantum creation of an inflationary universe with a pair
of black holes in higher derivative theories has been studied. Considering a
gravitational action which includes quadratic ($\alpha R^{2}$) and/or cubic
term ($\beta R^{3}$) in scalar curvature in addition to a cosmological constant
($\Lambda$) in semiclassical approximation with Hartle-Hawking boundary
condition, the probability has been evaluated. The action of the instanton
responsible for creating such a universe, with spatial section with
$S^{1}XS^{2}$ topology, is found to be less than that with a spatial $S^{3}$
topology, unless $\alpha < - \frac{1}{8 \Lambda}$ in $R^{2}$-theory. In the
$R^{3}$ theory, however, there exists a set of solutions without a cosmological
constant when $\beta R^{2} = 1$ and $\alpha = - 3 \sqrt{\beta}$ which admit
primordial black holes (PBH) pair in an inflationary universe scenario. We note
further that when $\beta R^{2} \neq 1$, one gets PBH pairs in the two cases :
(i) with $\alpha$ and $\Lambda$ both positive and (ii) with $\Lambda$ positive
and $\alpha$ negative satisfying a constraint $6 | \alpha | \Lambda > 1$.
However, the relative probability for creation of an inflationary universe with
a pair of black holes in the $R^{3}$-theory suppresses when $\alpha > - 2
\sqrt{\beta} $ or $|\alpha| < 2 \sqrt{\beta} $. However, if the above
constraints are relaxed one derives interesting results leading to a universe
with PBH in $R^{3}$-theory without cosmological constant. PACS No(s). :
04.20.Jb, 04.60.+n, 98.80.Hw


title: Remarks on a solvable cosmological model

abstract:
  We present an exact analytical solution of the Einstein equations with
cosmological constant in a spatially flat Robertson-Walker metric. This is
interpreted as an isotropic Lemaitre-type version of the cosmological Friedmann
model. Implications in the recent discovered cosmic acceleration of the
universe and in the theory of an inflationary model of the universe are in
view. Some properties of this solution are pointed out as a result of numerical
investigations of the model.