title: Looking back in time beyond the big bang

abstract:
  String theory can (in principle) describe gravity at all curvature scales,
and can be applied to cosmology to look back in time beyond the Planck epoch.
The duality symmetries of string theory suggest a cosmological picture in which
the imprint of a primordial, pre-big bang phase could still be accessible to
present observations. The predictive power of such a scenario relies, however,
on our ability to connect in a smooth way the pre-big bang to the present
cosmological regime. Classical radiation back reaction seems to play a key role
to this purpose, by isotropizing and turning into a final expansion any state
of anisotropic contraction possibly emerging from the pre-big bang at the
string scale.


title: Cosmic acceleration: Inhomogeneity versus vacuum energy

abstract:
  In this essay, I present an alternative explanation for the cosmic
acceleration which appears as a consequence of recent high redshift Supernova
data. In the usual interpretation, this cosmic acceleration is explained by the
presence of a positive cosmological constant or vacuum energy, in the
background of Friedmann models. Instead, I will consider a Local Rotational
Symmetric (LRS) inhomogeneous spacetime, with a barotropic equation of state
for the cosmic matter. Within this framework the kinematical acceleration of
the cosmic fluid or, equivalently, the inhomogeneity of matter, is just the
responsible of the SNe Ia measured cosmic acceleration. Although in our model
the Cosmological Principle is relaxed, it maintains local isotropy about our
worldline in agreement with the CBR experiments.


title:
Black hole formation in the Friedmann universe: Formulation and
  computation in numerical relativity

abstract:
  We study formation of black holes in the Friedmann universe. We present a
formulation of the Einstein equations under the constant mean curvature
time-slicing condition. Our formalism not only gives us the analytic solution
of the perturbation equations for non-linear density and metric fluctuations on
superhorizon scales, but also allows us to carry out a numerical relativity
simulation for black hole formation after the scale of the density fluctuations
is well within the Hubble horizon scale. We perform a numerical simulation of
spherically symmetric black hole formation in the radiation-dominated,
spatially flat background universe for a realistic initial condition supplied
from the analytic solution. It is found that the initial metric perturbation
has to be non-linear (the maximum value of 3D conformal factor $\psi_0$ at
$t=0$ should be larger than $\sim 1.4$) for a black hole to be formed, but the
threshold amplitude for black hole formation and the final black hole mass
considerably depend on the initial density (or metric) profile of the
perturbation: The threshold value of $\psi_0$ at $t=0$ for formation of a black
hole is smaller for a high density peak surrounded by a low density region than
for that surrounded by the average density region of the flat universe. This
suggests that it is necessary to take into account the spatial correlation of
density fluctuations in the study of primordial black hole formation.


title:
A generalization of Mach's principle: effect of the velocity relative to
  surrounding matter

abstract:
  We postulate that all the presently known kinematic effects on physical
quantities related to a material particle (e.g., masss increase) are due to its
velocity relative to surrounding matter, and not to the observer's reference
frame. The minimal velocity (i.e., the velocity that minimizes these
quantities) relative to a single large body being a function of the distance to
and mass of the body. In consequence, the minimal velocity is a function of
position, and the reference frame associated to this velocity is strictly of
local validity. We further assume that, at any given point, light propagates
isotropically solely in the minimal-velocity local frame existing at the point.
We obtain the following results: (i) After showing the compatibility of the
gravitational field eqs. with our assumptions, we find the functional
dependance of the minimal velocity on the distance to and mass of a single
large body. (ii) A permanent gravitational field is the convective rate of
change of the minimal velocity field. (iii) A Lorentz transformation connects
the values of quantities related to a particle, for two different velocities of
the particle relative to its minimal-velocity local frame. However, a Lorentz
transformation does not connect this frame with any other moving uniformly with
respect to it. (iv) The experimentally detected effects of kinematic, as well
as gravitational, mass increase and time dilation are derived. This is, they
all are due to the presence of the nearby (single) large mass. (v) Fizeau's
experiment, Michelson's experiment, aberration of fixed stars are taken account
of. (vi) Michelson's experiment performed from an vehicle orbiting the earth,
or the sun, should detect the orbital velocity of the vehicle.


title: Cosmic Acceleration With A Positive Cosmological Constant

abstract:
  We have considered a cosmological model with a phenomenological model for the
cosmological constant of the form $\Lambda=\bt\fr{\ddot R}{R}$, $ \bt$ is a
constant. For age parameter consistent with observational data the Universe
must be accelerating in the presence of a positive cosmological constant. The
minimum age of the Universe is $H_0^{-1}$, where $H_0$ is the present Hubble
constant. The cosmological constant is found to decrease as $t^{-2}$. Allowing
the gravitational constant to change with time leads to an ever increasing
gravitational constant at the present epoch. In the presence of a viscous fluid
this decay law for $\Lambda$ is equivalent to the one with $\Lambda=3\alpha
H^2$ ($\alpha=\rm const.$) provided $\alpha=\fr{\bt}{3(\bt-2)}$. The
inflationary solution obtained from this model is that of the de-Sitter type.


title:
Perturbative evolution of conformally flat initial data for a single
  boosted black hole

abstract:
  The conformally flat families of initial data typically used in numerical
relativity to represent boosted black holes are not those of a boosted slice of
the Schwarzschild spacetime. If such data are used for each black hole in a
collision, the emitted radiation will be partially due to the ``relaxation'' of
the individual holes to ``boosted Schwarzschild'' form. We attempt to compute
this radiation by treating the geometry for a single boosted conformally flat
hole as a perturbation of a Schwarzschild black hole, which requires the use of
second order perturbation theory. In this we attempt to mimic a previous
calculation we did for the conformally flat initial data for spinning holes. We
find that the boosted black hole case presents additional subtleties, and
although one can evolve perturbatively and compute radiated energies, it is
much less clear than in the spinning case how useful for the study of
collisions are the radiation estimates for the ``spurious energy'' in each
hole. In addition to this we draw some lessons on which frame of reference
appears as more favorable for computing black hole collisions in the close
limit approximation.


title:
A New Exact Solution of the Einstein Equations as Revised
  Schwarzschild's Solution Without Black Holes

abstract:
  This paper has been withdrawn by the author due to the triviality of the
considered coordinate transformations. A consistent treatment, based on the
extended physical radial coordinate, is presented in the publications of the
author 2000 - 2003.


title: Charge and the topology of spacetime

abstract:
  A new class of electrically charged wormholes is described in which the outer
two sphere is not spanned by a compact coorientable hypersurface. These
wormholes can therefore display net electric charge from the source free
Maxwell's equation. This extends the work of Sorkin on non-space orientable
manifolds, to spacetimes which do not admit a time orientation. The work is
motivated by the suggestion that quantum theory can be explained by modelling
elementary particles as regions of spacetime with non-trivial causal structure.
The simplest example of an electrically charged spacetime carries a spherical
symmetry.


title: On the (non) existence of a gravitomagnetic Dynamo

abstract:
  Due to the resemblance between Maxwell and the gravitomagnetic equations
obtained in the weak field and slow motion limit of General Relativity, one can
ask if it is possible to amplify a seed intrinsic rotation or spin motion by a
gravitomagetic dynamo, in analogy with the well-known dynamo effect. Using the
Galilean limits of the gravitomagnetic equations, the answer to this question
is negative, due to the fact that a "magnetic" Galilean limit for the
gravitomagnetic equations is physically inconsistent.


title: Dual geometries and spacetime singularities

abstract:
  The notion of geometrical duality is discussed in the context of both
Brans-Dicke theory and general relativity. It is shown that, in some particular
solutions, the spacetime singularities that arise in usual Riemannian general
relativity may be avoided in its dual representation (Weyl-type general
relativity). This dual representation provides a singularity-free picture of
the World that is physicaly equivalent to the canonical general relativistic
one.


title: Sensitivity of wide band detectors to quintessential gravitons

abstract:
  There are no reasons why the energy spectra of the relic gravitons, amplified
by the pumping action of the background geometry, should not increase at high
frequencies. A typical example of this behavior are quintessential inflationary
models where the slopes of the energy spectra can be either blue or mildly
violet. In comparing the predictions of scenarios leading to blue and violet
graviton spectra we face the problem of correctly deriving the sensitivities of
the interferometric detectors. Indeed, the expression of the signal-to-noise
ratio not only depends upon the noise power spectra of the detectors but also
upon the spectral form of the signal and, therefore, one can reasonably expect
that models with different spectral behaviors will produce different
signal-to-noise ratios. By assuming monotonic (blue) spectra of relic gravitons
we will give general expressions for the signal-to-noise ratio in this class of
models. As an example we studied the case of quintessential gravitons. The
minimum achievable sensitivity to $h^2_{0} \Omega_{GW}$ of different pairs of
detectors is computed, and compared with the theoretical expectations.


title: Inflationary Brans-Dicke Quantum Universe

abstract:
  The formulation of Brans-Dicke (BD) gravity with matter in the Einstein frame
is realized as Einstein gravity with dilaton and dilaton coupled matter. We
calculate the one-loop 4d anomaly-induced effective action due to N dilaton-
coupled massless fermions on the time-dependent conformally flat background
with non-trivial dilaton. Using that complete effective action the
(fourth-order) quantum corrected equations of motion are derived. One special
solution of these equations representing an inflationary Universe (with
exponential scale factor) and (much slower) expanding BD dilaton is given.
Similarly, the 2d quantum BD Universe with time-dependent dilaton is
constructed. In the last case the dynamics is completely due to quantum
effects.


title: A geodesically complete space-time with a crushing null hypersurface

abstract: Withdrawn; conclusion that the singularity is strong is incorrect.


title: Compactification, Vacuum Energy and Quintessence

abstract:
  We study the possibility that the vacuum energy density of scalar and
internal-space gauge fields arising from the process of dimensional reduction
of higher dimensional gravity theories plays the role of quintessence. We show
that, for the multidimensional Einstein-Yang-Mills system compactified on a $R
\times S^3 \times S^d$ topology, there are classically stable solutions such
that the observed accelerated expansion of the Universe at present can be
accounted for without upsetting structure formation scenarios or violating
observational bounds on the vacuum energy density.


title: Invariants of spin networks with boundary in Quantum Gravity and TQFT's

abstract:
  The search for classical or quantum combinatorial invariants of compact
n-dimensional manifolds (n=3,4) plays a key role both in topological field
theories and in lattice quantum gravity. We present here a generalization of
the partition function proposed by Ponzano and Regge to the case of a compact
3-dimensional simplicial pair $(M^3, \partial M^3)$. The resulting state sum
$Z[(M^3, \partial M^3)]$ contains both Racah-Wigner 6j symbols associated with
tetrahedra and Wigner 3jm symbols associated with triangular faces lying in
$\partial M^3$. The analysis of the algebraic identities associated with the
combinatorial transformations involved in the proof of the topological
invariance makes it manifest a common structure underlying the 3-dimensional
models with empty and non empty boundaries respectively. The techniques
developed in the 3-dimensional case can be further extended in order to deal
with combinatorial models in n=2,4 and possibly to establish a hierarchy among
such models. As an example we derive here a 2-dimensional closed state sum
model including suitable sums of products of double 3jm symbols, each one of
them being associated with a triangle in the surface.


title:
An Exact Solution of the Einstein Equations Without Singularities and
  Experimental Tests of the Existence of Black Holes

abstract:
  This paper has been withdrawn by the author due to the triviality of the
considered coordinate transformations. A consistent treatment, based on the
extended physical radial coordinates, is presented in the publications of the
author 2000 - 2003.


title: Nonlinear Graviton as a Limit of sl(N;C) Chiral Fields as N--> infty

abstract:
  An example of a sequence of the sl(N;C) chiral fields, for N$\geq 2$, tending
to the complex heavenly metric (nonlinear graviton) of the type [4]x[-] when N
--> infinity is given.


title:
Adaptive mesh refinement approach to construction of initial data for
  black hole collisions

abstract:
  The initial data for black hole collisions is constructed using a
conformal-imaging approach and a new adaptive mesh refinement technique, a
fully threaded tree (FTT). We developed a second-order accurate approach to the
solution of the constraint equations on a non-uniformly refined high resolution
Cartesian mesh including second-order accurate treatment of boundary conditions
at the black hole throats. Results of test computations show convergence of the
solution as the numerical resolution is increased. FTT-based mesh refinement
reduces the required memory and computer time by several orders of magnitude
compared to a uniform grid. This opens up the possibility of using Cartesian
meshes for very high resolution simulations of black hole collisions.


title: Superenergy tensors for a massive scalar field

abstract:
  We define a general class of superenergy tensors of even rank 2(n+1) for a
real massive scalar field propagating in Minkowski spacetime. In the case where
n=1, we establish that this class is a two-parameter family, which reduces to a
unique tensor W(up to a constant factor) when the complete symmetry on the four
indices is required. We show that the superenergy density
$W^{\al\ba\ga\da}u_{\al}u_{\ba}u_{\ga}u_{\da}$ relative to any timelike unit
vector $u$ is positive definite and that the supermomentum density
$W^{\al\ba\ga\da}u_{\ba}u_{\ga}u_{\da}$ is a timelike or a null vector
($W^{\al\ba\ga\da}$ stands for W). Next, we find an infinite set of conserved
tensors $U_{(p,q)}$ of rank 2+p+q, that we call weak superenergy tensors of
order n when p=q=n. We show that $U_{(1,1)}$ and W yield the same total
superenergy and the same total supermomentum. Then, using the canonical
quantization scheme, we construct explicitly the superhamiltonian and the
supermomentum operators corresponding to W and to each weak superenergy tensor
$U_{(n,n)}$. Finally, we exhibit a two-parameter family of superenergy tensors
for an electromagnetic field and for a gravitational field.


title: Inspiralling black holes: the close limit

abstract:
  Using several approximations, we calculate an estimate of the gravitational
radiation emitted when two equal mass black holes coalesce at the end of their
binary inspiral. We find that about 1% of the mass energy of the pair will
emerge as gravitational waves during the final ringdown and a negligible
fraction of the angular momentum will be radiated.


title: Self-Referential Noise as a Fundamental Aspect of Reality

abstract:
  Noise is often used in the study of open systems, such as in classical
Brownian motion and in Quantum Dynamics, to model the influence of the
environment. However generalising results from G\"{o}del and Chaitin in
mathematics suggests that systems that are sufficiently rich that
self-referencing is possible contain intrinsic randomness. We argue that this
is relevant to modelling the universe, even though it is by definition a closed
system. We show how a three-dimensional process-space may arise, as a Prigogine
dissipative structure, from a non-geometric order-disorder model driven by,
what is termed, self-referential noise.


title: Is Supernovae Data in Favour of Isotropic Cosmologies?

abstract:
  Most of the observational claims in cosmology are based on the assumption
that the universe is isotropic and homogeneous so they essentially test
different types of Friedmann models. This also refers to recent observations of
supernovae Ia, which, within the framework of Friedmann cosmologies give strong
support to negative pressure matter and also weaken the age conflict. In this
essay we drop the assumption of homogeneity, though temporarily leaving the
assumption of isotropy with respect to one point, and show that supernovae data
can be consistent with a model of the universe with inhomogeneous pressure
known as the Stephani model. Being consistent with supernovae data we are able
to get the age of the universe in this model to be about 3.8 Gyr more than in
its Friedmann counterpart.


title: A `warp drive' with more reasonable total energy requirements

abstract:
  I show how a minor modification of the Alcubierre geometry can dramatically
improve the total energy requirements for a `warp bubble' that can be used to
transport macroscopic objects. A spacetime is presented for which the total
negative mass needed is of the order of a few solar masses, accompanied by a
comparable amount of positive energy. This puts the warp drive in the mass
scale of large traversable wormholes. The new geometry satisfies the quantum
inequality concerning WEC violations and has the same advantages as the
original Alcubierre spacetime.


title: Quasi-local first law of black-hole dynamics

abstract:
  A property well known as the first law of black hole is a relation among
infinitesimal variations of parameters of stationary black holes. We consider a
dynamical version of the first law, which may be called the first law of black
hole dynamics. The first law of black hole dynamics is derived without assuming
any symmetry or any asymptotic conditions. In the derivation, a definition of
dynamical surface gravity is proposed. In spherical symmetry it reduces to that
defined recently by one of the authors (SAH).


title: Large quantum gravity effects and nonlocal variables

abstract:
  We reconsider here the model where large quantum gravity effects were first
found, but now in its Null Surface Formulation (NSF). We find that although the
set of coherent states for $Z$, the basic variable of NSF, is as restricted as
it is the one for the metric, while some type of small deviations from these
states may cause huge fluctuations on the metric, the corresponding
fluctuations on $Z$ remain small.


title: An Introduction to Spin Foam Models of Quantum Gravity and BF Theory

abstract:
  In loop quantum gravity we now have a clear picture of the quantum geometry
of space, thanks in part to the theory of spin networks. The concept of `spin
foam' is intended to serve as a similar picture for the quantum geometry of
spacetime. In general, a spin network is a graph with edges labelled by
representations and vertices labelled by intertwining operators. Similarly, a
spin foam is a 2-dimensional complex with faces labelled by representations and
edges labelled by intertwining operators. In a `spin foam model' we describe
states as linear combinations of spin networks and compute transition
amplitudes as sums over spin foams. This paper aims to provide a self-contained
introduction to spin foam models of quantum gravity and a simpler field theory
called BF theory.


title: Conservation Laws for Large Perturbations on Curved Backgrounds

abstract:
  Backgrounds are pervasive in almost every application of general relativity.
Here we consider the Lagrangian formulation of general relativity for large
perturbations with respect to a curved background spacetime. We show that
Noether's theorem combined with Belinfante's "symmetrization" method applied to
the group of displacements provide a conserved vector, a "superpotential" and a
energy-momentum that are independent of any divergence added to the Hilbert
Lagrangian of the perturbations. The energy-momentum is symmetrical and
divergenceless only on backgrounds that are Einstein spaces in the sense of
A.Z.Petrov.


title: Isolated Horizons: the Classical Phase Space

abstract:
  A Hamiltonian framework is introduced to encompass non-rotating (but possibly
charged) black holes that are ``isolated'' near future time-like infinity or
for a finite time interval. The underlying space-times need not admit a
stationary Killing field even in a neighborhood of the horizon; rather, the
physical assumption is that neither matter fields nor gravitational radiation
fall across the portion of the horizon under consideration. A precise notion of
non-rotating isolated horizons is formulated to capture these ideas. With these
boundary conditions, the gravitational action fails to be differentiable unless
a boundary term is added at the horizon. The required term turns out to be
precisely the Chern-Simons action for the self-dual connection. The resulting
symplectic structure also acquires, in addition to the usual volume piece, a
surface term which is the Chern-Simons symplectic structure. We show that these
modifications affect in subtle but important ways the standard discussion of
constraints, gauge and dynamics. In companion papers, this framework serves as
the point of departure for quantization, a statistical mechanical calculation
of black hole entropy and a derivation of laws of black hole mechanics,
generalized to isolated horizons. It may also have applications in classical
general relativity, particularly in the investigation of of analytic issues
that arise in the numerical studies of black hole collisions.


title:
Wave functions for arbitrary operator ordering in the de Sitter
  minisuperspace approximation

abstract:
  We derive exact series solutions for the Wheeler-DeWitt equation
corresponding to a spatially closed Friedmann-Robertson-Walker universe with
cosmological constant for arbitrary operator ordering of the scale factor of
the universe. The resulting wave functions are those relevant to the
approximation which has been widely used in two-dimensional minisuperspace
models with an inflationary scalar field for the purpose of predicting the
period of inflation which results from competing boundary condition proposals
for the wave function of the universe. The problem that Vilenkin's tunneling
wave function is not normalizable for general operator orderings, is shown to
persist for other values of the spatial curvature, and when additional matter
degrees of freedom such as radiation are included.


title: What is the Homogeneity of our Universe Telling Us?

abstract:
  The universe we observe is homogeneous on super-horizon scales, leading to
the ``cosmic homogeneity problem''. Inflation alleviates this problem but
cannot solve it within the realm of conservative extrapolations of classical
physics. A probabilistic solution of the problem is possible but is subject to
interpretational difficulties. A genuine deterministic solution of the
homogeneity problem requires radical departures from known physics.


title:
Space-times which are asymptotic to certain Friedman-Robertson-Walker
  space-times at timelike infinity

abstract:
  We define space-times which are asymptotic to radiation dominant
Friedman-Robertson-Walker space-times at timelike infinity and study the
asymptotic structure. We discuss the local asymptotic symmetry and give a
definition of the total energy from the electric part of the Weyl tensor.


title: False vacuum decay in de Sitter space-time

abstract:
  We suggest a technique that explicitly accounts for the structure of an
initial state of quantum field in the semiclassical calculations of path
integral in curved space-time, and consider decay of metastable state
(conformal vacuum of scalar particles above false classical vacuum) in
background de Sitter space-time as an example. Making use of this technique, we
justify the Coleman-De Luccia approach to the calculation of the decay
probability. We propose an interpretation of the Hawking-Moss instanton as a
limiting case of constrained instantons. We find that an inverse process of the
transition from true vacuum to false one is allowed in de Sitter space-time,
and calculate the corresponding probability.


title: Effective Levi-Civita Dilaton theory from Metric Affine Dilaton Gravity

abstract:
  We show how a Metric Affine theory of Dilaton gravity can be reduced to an
effective Riemannian Dilaton gravity model. A simple generalization of the
Obukhov-Tucker-Wang theorem to Dilaton gravity is then presented.


title:
Finite Temperature Resonant Tunneling in False Vacuum Decay and the
  Lee-Yang Theorem

abstract:
  We consider the cosmological model of a self-interacting $\phi^4 - \phi^2$
quantum scalar field and extend our previous results, [3], on resonant
tunneling and consequent particle production, to the case of finite
temperature. Using the mathematical equivalence between, the Euclidean path
integral of a $\phi^4 - \phi^2$ quantum field theory (in the saddle point
approximation), on one hand, and the partition function of a 4-dimensional
ferromagnet (in the Ising model approximation), on the other, we derive the
following results. Tunneling is a first order phase transition. The creation of
metastable bound states of instanton-antinstanton pairs under the barrier
,(i.e. resonant tunneling), is the seed that gives rise to particle production.
Through the application of the Lee-Yang theorem for phase transitions, (as well
as demonstrating the underlying connection this has with the poles of the
S-matrix element in the quantum scattering theory), we show that the
fluctuations around the dominant escape paths of instantons (i.e. fluctuations
of the bubble wall) with momenta comparable to the scale curvature of the
bubble, drive the mechanism for resonant tunneling in false vacuum decay. We
also identify the temperature dependence of the parameters in the potential
term, (or equivalently, of the instanton bubbles), for a wide range of
temperatures Finally, we show that the picture of a dilute instanton
gas,remains valid even at finite temperatures, as this gas becomes more and
more dilute with the increase of the temperature. This suppression continues
until we reach the critical temperature, at which point there is only one
instanton left, with an infinitely thick wall.


title: Search for semiclassical-gravity effects in relativistic stars

abstract:
  We discuss the possible influence of gravity in the neutronization process,
$p^+ e^- \to n \nu_e$, which is particularly important as a cooling mechanism
of neutron stars. Our approach is semiclassical in the sense that leptonic
fields are quantized on a classical background spacetime, while neutrons and
protons are treated as excited and unexcited nucleon states, respectively. We
expect gravity to have some influence wherever the energy content carried by
the in-state is barely above the neutron mass. In this case the emitted
neutrinos would be soft enough to have a wavelength of the same order as the
space curvature radius.


title: Predictability crisis in inflationary cosmology and its resolution

abstract:
  Models of inflationary cosmology can lead to variation of observable
parameters ("constants of Nature") on extremely large scales. The question of
making probabilistic predictions for today's observables in such models has
been investigated in the literature. Because of the infinite thermalized volume
resulting from eternal inflation, it has proven difficult to obtain a
meaningful and unambiguous probability distribution for observables, in
particular due to the gauge dependence. In the present paper, we further
develop the gauge-invariant procedure proposed in a previous work for models
with a continuous variation of "constants". The recipe uses an unbiased
selection of a connected piece of the thermalized volume as sample for the
probability distribution. To implement the procedure numerically, we develop
two methods applicable to a reasonably wide class of models: one based on the
Fokker-Planck equation of stochastic inflation, and the other based on direct
simulation of inflationary spacetime. We present and compare results obtained
using these methods.


title: Origin of the inflationary Universe

abstract:
  We give a consistent description of how the inflationary Universe emerges in
quantum cosmology. This involves two steps: Firstly, it is shown that a
sensible probability peak can be obtained from the cosmological wave function.
This is achieved by going beyond the tree level of the semiclassical expansion.
Secondly, due to decoherence interference terms between different semiclassical
branches are negligibly small. The results give constraints on the particle
content of a unified theory.


title: Relativistic Charged Spheres II: Regularity and Stability

abstract:
  We present new results concerning the existence of static, electrically
charged, perfect fluid spheres that have a regular interior and are arbitrarily
close to a maximally charged black-hole state. These configurations are
described by exact solutions of Einstein's field equations. A family of these
solutions had already be found (de Felice et al., 1995) but here we generalize
that result to cases with different charge distribution within the spheres and
show, in an appropriate parameter space, that the set of such physically
reasonable solutions has a non zero measure. We also perform a perturbation
analysis and identify the solutions which are stable against adiabatic radial
perturbations. We then suggest that the stable configurations can be considered
as classic models of charged particles. Finally our results are used to show
that a conjecture of Kristiansson et al. (1998) is incorrect.


title: Some exact non-vacuum Bianchi VI0 and VII0 instantons

abstract:
  We report some new exact instantons in general relativity. These solutions
are K\"ahler and fall into the symmetry classes of Bianchi types VI0 and VII0,
with matter content of a stiff fluid. The qualitative behaviour of the
solutions is presented, and we compare it to the known results of the
corresponding self-dual Bianchi solutions. We also give axisymmetric Bianchi
VII0 solutions with an electromagnetic field.


title: The Bright Side of Dark Matter

abstract:
  We show that it is not possible in the absence of dark matter to construct a
four-dimensional metric that explains galactic observations. In particular, by
working with an effective potential it is shown that a metric which is
constructed to fit flat rotation curves in spiral galaxies leads to the wrong
sign for the bending of light i.e. repulsion instead of attraction. Hence,
without dark matter the motion of particles on galactic scales cannot be
explained in terms of geodesic motion on a four- dimensional metric. This
reveals a new bright side to dark matter: it is indispensable if we wish to
retain the cherished equivalence principle.


title:
On the generalization of the Schwarzschild and de Sitter Static
  Solutions With and Without Singularities

abstract:
  This paper has been withdrawn by the author due to the triviality of the
considered coordinate transformations. A consistent treatment, based on the
extended physical radial coordinate, is presented in the publications of the
author 2000 - 2003.


title: A new conformal duality of spherically symmetric space-times

abstract:
  A contribution linear in r to the gravitational potential can be created by a
suitable conformal duality transformation: the conformal factor is 1/(1+r)^2
and r will be replaced by r/(1+r), where r is the Schwarzschild radial
coordinate. Thus, every spherically symmetric solution of conformal Weyl
gravity is conformally related to an Einstein space. This result finally
resolves a long controversy about this topic.
  As a byproduct, we present an example of a spherically symmetric Einstein
space which is a limit of a sequence of Schwarzschild-de Sitter space-times but
which fails to be expressable in Schwarzschild coordinates. This example also
resolves a long controversy.


title: Experimental test for extra dimensions in Kaluza-Klein gravity

abstract:
  5D Kaluza-Klein gravity has several nonasymptotically flat solutions which
generally, possessed both electric and magnetic charges. In this paper we
suggest that these solutions can act as quantum virtual handles (wormholes) in
spacetime foam models. By applying a sufficently large, external electric
and/or magnetic field it may be possible to ``inflate'' these solutions from a
quantum to a classical state. This effect would lead to a possible experimental
signal for higher dimensions in multidimensional gravity.


title: Inflationary cosmology with scalar field and radiation

abstract:
  We present a simple, exact and self-consistent cosmology with a
phenomenological model of quantum creation of radiation due to decay of the
scalar field. The decay drives a non-isentropic inflationary epoch, which exits
smoothly to the radiation era, without reheating. The initial vacuum for
radiation is a regular Minkowski vacuum. The created radiation obeys standard
thermodynamic laws, and the total entropy produced is consistent with the
accepted value. We analyze the difference between the present model and a model
with decaying cosmological constant previously considered.


title: Cones and causal structures on topological and differentiable manifolds

abstract:
  General definitions for causal structures on manifolds of dimension d+1>2 are
presented for the topological category and for any differentiable one.
  Locally, these are given as cone structures via local (pointwise)
homeomorphic or diffeomorphic abstraction from the standard null cone variety
in R^{d+1}. Weak and strong local cone (LC) structures refer to the cone itself
or a manifold thickening of the cone respectively.
  After introducing cone (C-)causality, a causal complement with reasonable
duality properties can be defined. The most common causal concepts of
space-times are generalized to the present topological setting. A new notion of
precausality precludes inner boundaries within future/past cones.
  LC-structures, C-causality, a topological causal complement, and precausality
may be useful tools in conformal and background independent formulations of
(algebraic) quantum field theory and quantum gravity.


title: Nonrelativistic Geodesic Motion

abstract:
  We show that any second order dynamic equation on a configuration space $X\to
R$ of nonrelativistic mechanics can be seen as a geodesic equation with respect
to some (nonlinear) connection on the tangent bundle $TX\to X$ of relativistic
velocities. We compare relativistic and nonrelativistic geodesic equations, and
study the Jacobi vector fields along nonrelativistic geodesics.


title:
Analytic solution of the Regge-Wheeler differential equation for black
  hole pertubations in radial coordinate and time domains

abstract:
  An analytic solution of the Regge-Wheeler (RW) equation has been found via
the Frobenius method at the regular singularity of the horizon 2M, in the form
of a time and radial coordinate dependent series. The RW partial differential
equation, derived from the Einstein field equations, represents the first order
perturbations of the Schwarzschild metric. The known solutions are numerical in
time domain or approximate and asymptotic for low or high frequencies in
Fourier domain. The former is of scarce relevance for comprehension of the
geodesic equations for a body in the black hole field, while the latter is
mainly useful for the description of the emitted gravitational radiation.
Instead a time domain solution is essential for the determination of radiation
reaction of the falling particle into the black hole, i.e. the influence of the
emitted radiation on the motion of the perturbing mass in the black hole field.
To this end, a semi-analytic solution of the inhomogeneous RW equation with the
source term (Regge-Wheeler-Zerilli equation) shall be the next development.


title: Observable effects from extra dimensions

abstract:
  For any multidimensional theory with compactified internal spaces, conformal
excitations of the internal space metric result in gravitational excitons in
the external spacetime. These excitations contribute either to dark matter or
to cross sections of usual particles.


title: Tunnelling with Bianchi IX Instantons

abstract:
  Within the context of finding the initial conditions of the universe we
consider gravitational instantons falling into the Bianchi IX classification.
That is, a Euclidean four-manifold with a metric that satisfies Einstein's
equations with an induced metric on S^3 submanifolds that is homogeneous but
anisotropic. As well as finding regular solutions to the field equations with a
tunnelling scalar field, we also look at the case of singular instantons with a
view to applying the results to generic potentials. The study is in agreement
with the prejudice that instantons with higher symmetry have a lower Euclidean
action, even when we consider the singular class of solutions. It is also found
that the Euclidean action can diverge for simple potentials, showing that the
Hawking Turok instanton had finite action owing to its symmetry.


title: A Phase Space Approach to Gravitational Enropy

abstract:
  We examine the definition S = ln Omega as a candidate "gravitational entropy"
function. We calculate its behavior for gravitationl and density perturbations
in closed, open and flat cosmologies and find that in all cases it increases
monotonically. Using the formalism to calculate the gravitational entropy
produced during inflation gives the canonical answer. We compare the behavior
of S with the behavior of the square of the Weyl tensor. Applying the formalism
to black holes has proven more problematical.


title: Measuring the foaminess of space-time with gravity-wave interferometers

abstract:
  By analyzing a gedanken experiment designed to measure the distance $l$
between two spatially separated points, we find that this distance cannot be
measured with uncertainty less than $(ll_P^2)^{1/3}$, considerably larger than
the Planck scale $l_P$ (or the string scale in string theories), the
conventional wisdom uncertainty in distance measurements. This limitation to
space-time measurements is interpreted as resulting from quantum fluctuations
of space-time itself. Thus, at very short distance scales, space-time is
"foamy." This intrinsic foaminess of space-time provides another source of
noise in the interferometers. The LIGO/VIRGO and LISA generations of
gravity-wave interferometers, through future refinements, are expected to reach
displacement noise levels low enough to test our proposed degree of foaminess
in the structure of space-time. We also point out a simple connection to the
holographic principle which asserts that the number of degrees of freedom of a
region of space is bounded by the area of the region in Planck units.


title:
Best Approximation to a Reversible Process in Black-Hole Physics and the
  Area Spectrum of Spherical Black Holes

abstract:
  The assimilation of a quantum (finite size) particle by a
Reissner-Nordstr\"om black hole inevitably involves an increase in the
black-hole surface area. It is shown that this increase can be minimized if one
considers the capture of the lightest charged particle in nature. The
unavoidable area increase is attributed to two physical reasons: the Heisenberg
quantum uncertainty principle and a Schwinger-type charge emission (vacuum
polarization). The fundamental lower bound on the area increase is $4 \hbar$,
which is smaller than the value given by Bekenstein for neutral particles.
Thus, this process is a better approximation to a reversible process in
black-hole physics. The universality of the minimal area increase is a further
evidence in favor of a uniformly spaced area spectrum for spherical quantum
black holes. Moreover, this universal value is in excellent agreement with the
area spacing predicted by Mukhanov and Bekenstein and independently by Hod.


title: Gravitational Radiation from Triple Star Systems

abstract:
  We have studied the main features of the gravitational radiation generated by
an astrophysical system constituted of three compact objects attracting one
another (only via gravitational interaction) in such a manner that stable
orbits do exist. We have limited our analysis to systems that can be treated
with perturbative methods. We show the profile of the gravitational waves
emitted by such systems. These results can be useful within the framework of
the new gravitational astronomy which will be made feasible by means of the new
generation of gravitational detectors such as LISA in a no longer far future.


title: Non-universal gravitational couplings of neutrinos in matter

abstract:
  When neutrinos travel through a normal matter medium, the electron neutrinos
couple differently to gravity compared to the other neutrinos, due to the
presence of electrons in the medium and the absence of the other charged
leptons. The matter-induced gravitational couplings of the neutrinos under such
conditions are calculated and their contribution to the neutrino index of
refraction in the presence of a gravitational potential is determined.


title: Generalized Reissner-Nordstr\"om solution in Metric-Affine Gravity

abstract:
  We present the generalized Reissner-Nordstr\"om solution of the field
equations of metric-affine gravity (MAG), endowed with electric and magnetic
charges, as well as with gravito-electric and gravito-magnetic charges and a
cosmological constant term. Moreover, the case $M=e_o$, i.e. mass equal to
electric charge and $\lambda=0$, corresponds to an electrically and
magnetically charged monopole. Also further multipole solutions are obtained.
The charge assignments of the solutions is discussed.


title:
Quantum mechanical path integrals and thermal radiation in static curved
  spacetimes

abstract:
  The propagator of a spinless particle is calculated from the quantum
mechanical path integral formalism in static curved spacetimes endowed with
event-horizons. A toy model, the Gui spacetime, and the 2D and 4D Schwarzschild
black holes are considered. The role of the topology of the coordinates
configuration space is emphasised in this framework. To cover entirely the
above spacetimes with a single set of coordinates, tortoise coordinates are
extended to complex values. It is shown that the homotopic properties of the
complex tortoise configuration space imply the thermal behaviour of the
propagator in these spacetimes. The propagator is calculated when end points
are located in identical or distinct spacetime regions separated by one or
several event-horizons. Quantum evolution through the event-horizons is shown
to be unitary in the fifth variable.


title: Schroedinger Wheeler-DeWitt Equation In Multidimensional Cosmology

abstract:
  We study multidimensional cosmology to obtain the wavefunction of the
universe using wormhole dominance proposal. Using a prescription for time we
obtain the Schroedinger-Wheeler-DeWitt equation without any reference to WD
equation and WKB ansatz for WD wavefunction. It is found that the
Hartle-Hawking or wormhole-dominated boundary conditions serve as a seed for
inflation as well as for Gaussian type ansatz to Schroedinger-Wheeler-DeWitt
equation.


title: Time in Quantum Gravity

abstract:
  The Wheeler-DeWitt equation in quantum gravity is timeless in character. In
order to discuss quantum to classical transition of the universe, one uses a
time prescription in quantum gravity to obtain a time contained description
starting from Wheeler-DeWitt equation and WKB ansatz for the WD wavefunction.
The approach has some drawbacks. In this work, we obtain the time-contained
Schroedinger-Wheeler-DeWitt equation without using the WD equation and the WKB
ansatz for the wavefunction. We further show that a Gaussian ansatz for SWD
wavefunction is consistent with the Hartle-Hawking or wormhole dominance
proposal boundary condition. We thus find an answer to the small scale boundary
conditions.


title:
Quantum Gravity Equation In Schroedinger Form In Minisuperspace
  Description

abstract:
  We start from classical Hamiltonian constraint of general relativity to
obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter
prescription demanding that geometry itself determines the time, not the matter
field, such that the time so defined being equivalent to the time that enters
into the Schroedinger equation. Without any reference to the Wheeler-DeWitt
equation and without invoking the expansion of exponent in WKB wavefunction in
powers of Planck mass, we obtain an equation for quantum gravity in
Schroedinger form containing time. We restrict ourselves to a minisuperspace
description. Unlike matter field equation our equation is equivalent to the
Wheeler-DeWitt equation in the sense that our solutions reproduce also the
wavefunction of the Wheeler-DeWitt equation provided one evaluates the
normalization constant according to the wormhole dominance proposal recently
proposed by us.


title: Time reversal and negative energies in general relativity

abstract:
  The significance of past-pointing four-vectors and negative energies in
general relativity is discussed. The sign of the energy is not absolute, but
relative to the four-velocity of the observer, and every particle/observer
always measures its own mass as positive. It is shown that the description of
the interaction of past-pointing and future-pointing matter in general
relativity requires two metric tensors for self-consistency. This aspect of
general relativity might account for the observations that led to the proposal
of "dark energy" and non-baryonic "dark matter".


title:
Noncanonical Quantization of Gravity. I. Foundations of Affine Quantum
  Gravity

abstract:
  The nature of the classical canonical phase-space variables for gravity
suggests that the associated quantum field operators should obey affine
commutation relations rather than canonical commutation relations. Prior to the
introduction of constraints, a primary kinematical representation is derived in
the form of a reproducing kernel and its associated reproducing kernel Hilbert
space. Constraints are introduced following the projection operator method
which involves no gauge fixing, no complicated moduli space, nor any auxiliary
fields. The result, which is only qualitatively sketched in the present paper,
involves another reproducing kernel with which inner products are defined for
the physical Hilbert space and which is obtained through a reduction of the
original reproducing kernel. Several of the steps involved in this general
analysis are illustrated by means of analogous steps applied to one-dimensional
quantum mechanical models. These toy models help in motivating and
understanding the analysis in the case of gravity.


title: Static Gravitational Global Monopoles

abstract:
  Static solutions in spherical symmetry are found for gravitating global
monopoles. Regular solutions lacking a horizon are found for $\eta <
1/\sqrt{8\pi}$, where $\eta$ is the scale of symmetry breaking. Apparently
regular solutions with a horizon are found for $1/\sqrt{8\pi} \le \eta \alt
\sqrt{3/8\pi}$. Though they have a horizon, they are not Schwarzschild. The
solution for $\eta = 1/\sqrt{8\pi}$ is argued to have a horizon at infinity.
The failure to find static solutions for $\eta > \sqrt{3/8\pi} \approx 0.3455$
is consistent with findings that topological inflation begins at $\eta \approx
0.33$.


title:
On average properties of inhomogeneous fluids in general relativity I:
  dust cosmologies

abstract:
  For general relativistic spacetimes filled with irrotational `dust' a
generalized form of Friedmann's equations for an `effective' expansion factor
$a_D (t)$ of inhomogeneous cosmologies is derived. Contrary to the standard
Friedmann equations, which hold for homogeneous-isotropic cosmologies, the new
equations include the `backreaction effect' of inhomogeneities on the average
expansion of the model. A universal relation between `backreaction' and average
scalar curvature is also given. For cosmologies whose averaged spatial scalar
curvature is proportional to $a_D^{-2}$, the expansion law governing a generic
domain can be found. However, as the general equations show, `backreaction'
acts as to produce average curvature in the course of structure formation, even
when starting with space sections that are spatially flat on average.


title: Anisotropic simplicial minisuperspace model

abstract:
  The computation of the simplicial minisuperspace wavefunction in the case of
anisotropic universes with a scalar matter field predicts the existence of a
large classical Lorentzian universe like our own at late times


title:
Observables and gauge invariance in the theory of non-linear spacetime
  perturbations

abstract:
  We discuss the issue of observables in general-relativistic perturbation
theory, adopting the view that any observable in general relativity is
represented by a scalar field on spacetime. In the context of perturbation
theory, an observable is therefore a scalar field on the perturbed spacetime,
and as such is gauge invariant in an exact sense (to all orders), as one would
expect. However, perturbations are usually represented by fields on the
background spacetime, and expanded at different orders into contributions that
may or may not be gauge independent. We show that perturbations of scalar
quantities are observable if they are first order gauge-invariant, even if they
are gauge dependent at higher order. Gauge invariance to first order plays
therefore an important conceptual role in the theory, for it selects the
perturbations with direct physical meaning from those having only a
mathematical status. The so-called ``gauge problem'', and the relationship
between measured fluctuations and gauge dependent perturbations that are
computed in the theory are also clarified.


title: Classical back reaction of low-frequency cosmic gravitational radiation

abstract:
  We study in a Brill-Hartle type of approximation the back reaction of a
superposition of linear gravitational waves on the mean gravitational field up
to second order in the wave amplitudes. The background field is taken as an
Einstein-deSitter geometry. In order to follow inflationary scenarios, the
wavelengths are allowed to exceed the temporary Hubble distance. As in optical
coherence theory, the wave amplitudes are considered as random variables, which
form a homogeneous and isotropic stochastic process, sharing the symmetries of
the background metric. The effective stress-energy tensor for the random waves
is calculated in terms of correlation functions and covers subhorizon as well
as superhorizon modes, the latter give in many cases negative contributions to
energy density and pressure. We discuss solutions of the second-order equations
including pure gravitational radiation universes.


title: Numerical simulations of Gowdy spacetimes on S2XS1XR

abstract:
  Numerical simulations are performed of the approach to the singularity in
Gowdy spacetimes on S2XS1XR. The behavior is similar to that of Gowdy
spacetimes on T3XR. In particular, the singularity is asymptotically velocity
term dominated, except at isolated points where spiky features develop.


title: The generalized Reissner-Nordstrom Solution Without Singularities

abstract:
  This paper has been withdrawn by the author due to the triviality of the
considered coordinate transformations. A consistent treatment, based on the
extended physical radial coordinate, is presented in the publications of the
author 2000 - 2003.


title: Degeneracy of the b-boundary in General Relativity

abstract:
  The b-boundary construction by B. Schmidt is a general way of providing a
boundary to a manifold with connection. It has been shown to have undesirable
topological properties however. C. J. S. Clarke gave a result showing that for
space-times, non-Hausdorffness is to be expected in general, but the argument
contains some errors. We show that under somewhat different conditions on the
curvature, the b-boundary will be non-Hausdorff, and illustrate the degeneracy
by applying the conditions to some well known exact solutions of general
relativity.


title:
A 3+1 Computational Scheme for Dynamic Spherically Symmetric Black Hole
  Spacetimes -- II: Time Evolution

abstract:
  This is the second in a series of papers describing a 3+1 computational
scheme for the numerical simulation of dynamic black hole spacetimes. We
discuss the numerical time-evolution of a given black-hole-containing initial
data slice in spherical symmetry. We avoid singularities via the "black-hole
exclusion" or "horizon boundary condition" technique, where the slices meet the
black hole's singularity, but on each slice a spatial neighbourhood of the
singularity is excluded from the domain of the numerical computations.
  After first discussing some of the key design choices which arise with the
black hole exclusion technique, we then give a detailed description of our
numerical evolution scheme for spherically symmetric scalar field evolution,
assuming that a black hole is already present on the initial slice. We use a
free evolution, with Eddington-Finkelstein-like coordinates and the inner
boundary placed at a fixed coordinate radius well inside the horizon.
  Our numerical scheme is based on the method of lines (MOL), where spacetime
PDEs are first finite differenced in space only, yielding a system of coupled
ODEs for the time evolution of the field variables along the spatial-grid-point
world lines. These ODEs are then time-integrated by standard methods. We use
4th order finite differencing in both space and time, with 5 and/or 6 point
spatial molecules (off-centered near the grid boundaries), and a Runge-Kutta
time integrator. The spatial grid is smoothly nonuniform, but not adaptive.
  We present numerical black hole + scalar field evolutions showing that this
scheme is stable, can evolve "forever" (we have gone to t > 4000m), and is very
accurate. At a resolution Delta_r/r = 3% near the horizon, typical errors in
g_ij(K_ij) at t=100m are <= 1e-5(3e-7), and the energy constraint is < 3e-5.


title: Virtual dipoles and large fluctuations in quantum gravity

abstract:
  The positive energy theorem precludes the possibility of Minkowski flat space
decaying by any mechanism. In certain circumstances, however, large quantum
fluctuations of the gravitational field could arise---not only at the Planck
scale, but also at larger scales. This is because there exists a set of
localised weak field configurations which satisfy the condition int d4x
sqrt{g}R = 0 and thus give a null contribution to the Einstein action. Such
configurations can be constructed by solving Einstein field equations with
unphysical dipolar sources. We discuss this mechanism and its modification in
the presence of a cosmological term and/or an external field.


title: Dynamical system analysis for the Einstein-Yang-Mills equations

abstract:
  Local solutions of the static, spherically symmetric Einstein-Yang-Mills
(EYM) equations with SU(2) gauge group are studied on the basis of dynamical
systems methods. This approach enables us to classify EYM solutions in the
origin neighborhood, to prove the existence of solutions with the oscillating
metric as well as the existence of local solutions for all known formal power
series expansions, to study the extendibility of solutions, and to find two new
local singular solutions.


title: Scale Symmetry Spontaneously Broken by Asymptotic Behavior

abstract:
  Conserved quantities are obtained and analyzed in the new models with global
scale invariance recently proposed. Such models allow for non tivial scalar
field potentials and masses for particles, so that the scale symmetry must be
broken somehow. We get to this conclusion by showing that the infrared behavior
of the conserved currents is singular so that there are no conserved charges
associated with the global scale symmetry. The scale symmetry plays
nevertheless a crucial role in determining the structure of the theory and it
implies that in some high field regions the potentials become flat.


title: Gravitational waves and massless particle fields

abstract:
  These notes address the planar gravitational wave solutions of general
relativity in empty space-time, and analyze the motion of test particles in the
gravitational wave field. Next we consider related solutions of the Einstein
equations for the gravitational field accompanied by long-range wave fields of
scalar, spinor and vector type, corresponding to particles of spin s=(0,1/2,1).
The motion of test masses in the combined gravitational and scalar, spinor or
vector wave fields is discussed.


title: Parity Violating Gravitational Coupling Of Electromagnetic Fields

abstract:
  A manifestly gauge invariant formulation of the coupling of the Maxwell
theory with an Einstein Cartan geometry is given, where the space time torsion
originates from a massless Kalb-Ramond field augmented by suitable U(1) Chern
Simons terms.We focus on the situation where the torsion violates parity, and
relate it to earlier proposals for gravitational parity violation.


title: Chaos around the superposition of a black-hole and a thin disk

abstract:
  Motivated by the strong astronomical evidences supporting that huge
black-holes might inhabit the center of many active galaxies, we have studied
the integrability of oblique orbits of test particles around the exact
superposition of a black-hole and a thin disk. We have considered the
relativistic and the Newtonian limits. Exhaustive numerical analyses were
performed, and bounded zones of chaotic behavior were found for both limits. An
intrinsic relativistic gravitational effect is detected: the chaoticity of
trajectories that do not cross the disk.


title:
A Microscopic Recoil Model for Light-Cone Fluctuations in Quantum
  Gravity

abstract:
  We present a microscopic model for light-cone fluctuations ``in vacuo'',
which incorporates a treatment of quantum-gravitational recoil effects induced
by energetic particles. Treating defects in space-time as solitons in string
theory, we derive an energy-dependent refractive index and a stochastic spread
in the arrival times of mono-energetic photons due to quantum diffusion through
space-time foam, as found previously using an effective Born-Infeld action.
Distant astrophysical sources provide sensitive tests of these possible
quantum-gravitational phenomena.


title: Geodesic Completeness of Orthogonally Transitive Cylindrical Spacetimes

abstract:
  In this paper a theorem is derived in order to provide a wide sufficient
condition for an orthogonally transitive cylindrical spacetime to be
singularity-free. The applicability of the theorem is tested on examples
provided by the literature that are known to have regular curvature invariants.


title: Single-exterior black holes

abstract:
  We discuss quantum properties of the single-exterior, geon-type black (and
white) holes that are obtained from the Kruskal spacetime and the spinless
Banados-Teitelboim-Zanelli hole via a quotient construction that identifies the
two exterior regions. For the four-dimensional geon, the Hartle-Hawking type
state of a massless scalar field is thermal in a limited sense, but there is a
discrepancy between Lorentzian and Riemannian derivations of the geon entropy.
For the three-dimensional geon, the state induced for a free conformal scalar
field on the conformal boundary is similarly thermal in a limited sense, and
the correlations in this state provide support for the holographic hypothesis
in the context of asymptotically anti-de Sitter black holes in string theory.


title: The Coupling of Gravity to Spin and Electromagnetism

abstract:
  The coupled Einstein-Dirac-Maxwell equations are considered for a static,
spherically symmetric system of two fermions in a singlet spinor state. Stable
soliton-like solutions are shown to exist, and we discuss the regularizing
effect of gravity from a Feynman diagram point of view.


title: Twisted spinors on Schwarzschild and Reissner-Nordstrom black holes

abstract:
  We describe twisted configurations of spinor field on the Schwarzschild and
Reissner-Nordstr\"om black holes that arise due to existence of the twisted
spinor bundles over the standard black hole topology. From a physical point of
view the appearance of spinor twisted configurations is linked with the natural
presence of Dirac monopoles that play the role of connections in the complex
line bundles corresponding to the twisted spinor bundles. Possible application
to the Hawking radiation is also outlined.


title:
Energy Absorption by the Dilaton Field around a Rotating Black Hole in a
  Binary System

abstract:
  In this paper we analyze a binary system consisting of a star and a rotating
black hole. The electromagnetic radiation emitted by the star interacts with
the background of the black hole and stimulates the production of dilaton
waves. We then estimate the energy transferred from the electromagnetic
radiation of the star to the dilaton field as a function of the frequency. The
resulting picture is a testable signature of the existence of dilaton fields as
predicted by string theory in an astrophysical context.


title: A Hierarchy of Dynamic States of Relaxation

abstract:
  We define a hierarchy of dynamic relaxed gas spheres as solutions of the
Poisson equation coupled to a hierarchy of approximations of the Liouville
equation leading, when this equation is satisfied, to the well-known isothermal
gas spheres in the static case, but also to a new form of dynamic maximum
relaxation. The two previous steps of the hierarchy correspond to an increasing
degree of local relaxation at the center of the configuration.


title: Mode decomposition and renormalization in semiclassical gravity

abstract:
  We compute the influence action for a system perturbatively coupled to a
linear scalar field acting as the environment. Subtleties related to
divergences that appear when summing over all the modes are made explicit and
clarified. Being closely connected with models used in the literature, we show
how to completely reconcile the results obtained in the context of stochastic
semiclassical gravity when using mode decomposition with those obtained by
other standard functional techniques.


title: Strongly gravitating empty spaces

abstract:
  We use various results concerning isometry groups of Riemannian and
pseudo-Riemannian manifolds to prove that there are spaces on which
differential structure can act as a source of gravitational force (Brans
conjecture). The result is important for the analysis of the possible physical
meaning of differential calculus. Possible astrophysical consequences are
discussed.


title:
Tensor mass and particle number peak at the same location in the
  scalar-tensor gravity boson star models - an analytical proof

abstract:
  Recently in boson star models in framework of Brans-Dicke theory, three
possible definitions of mass have been identified, all identical in general
relativity, but different in scalar-tensor theories of gravity.It has been
conjectured that it's the tensor mass which peaks, as a function of the central
density, at the same location where the particle number takes its maximum.This
is a very important property which is crucial for stability analysis via
catastrophe theory. This conjecture has received some numerical support. Here
we give an analytical proof of the conjecture in framework of the generalized
scalar-tensor theory of gravity, confirming in this way the numerical
calculations.


title:
Four-Index Equations for Gravitation and the Gravitational
  Energy-Momentum Tensor

abstract:
  A new treatment of the gravitational energy on the basis of 4-index
gravitational equations is reviewed. The gravitational energy for the
Schwarzschild field is considered.


title: De Sitter Space and Spatial Topology

abstract:
  Morrow-Jones and Witt have shown that generic spatial topologies admit
initial data that evolve to locally de Sitter spacetimes under Einstein's
equations. We simplify their arguments, make them a little more general, and
solve for the global time evolution of the wormhole initial data considered by
them. Finally we give explicit examples of locally de Sitter domains of
development whose universal covers cannot be embedded in de Sitter space.


title:
Lema\^{i}tre-Tolman-Bondi model: fractality, bang time, and Hubble law
  I. Initial conditions and compatibility of density and velocity laws

abstract:
  We start a systematic study of the Lema\^{i}tre-Tolman-Bondi (LTB) model as
applied to the large scale structure and its evolution. Here we study three
possible initial conditions of the LTB models which are asymptotically FRW at
large scales: bang time, fractal density (with fractal dimension D=2), and
velocity law. Any two of these determine the third one. Fractal density and
simultaneous bang time provide a quantitative estimate for the scale beyond
which the deflection from the linear Hubble law is small. This border may be
identified with the zero-velocity surface. For fractal density and linear
Hubble law it is shown that the bang time is necessarily non-simultaneous.


title: Cosmological Constant and the Final Anthropic Hypothesis

abstract:
  The influence of recent detections of a finite vacuum energy ("cosmological
constant") on our formulation of anthropic conjectures, particularly the
so-called Final Anthropic Principle is investigated. It is shown that non-zero
vacuum energy implies the onset of a quasi-exponential expansion of our
causally connected domain ("the universe") at some point in the future, a stage
similar to the inflationary expansion at the very beginning of time. The
transition to this future inflationary phase of cosmological expansion will
preclude indefinite survival of intelligent species in our domain, because of
the rapid shrinking of particle horizons and subsequent depletion of energy
necessary for information processes within the horizon of any observer.
Therefore, to satisfy the Final Anthropic Hypothesis (reformulated to apply to
the entire ensemble of universes), it is necessary to show that (i) chaotic
inflation of Linde (or some similar model) provides a satisfactory description
of reality, (ii) migration between causally connected domains within the
multiverse is physically permitted, and (iii) the time interval left to the
onset of the future inflationary phase is sufficient for development of the
technology necessary for such inter-domain travel. These stringent requirements
diminish the probability of the Final Anthropic Hypothesis being true.


title: Nonlinear Lagrangians of the Ricci type

abstract:
  The Euler-Lagrange equations for some class of gravitational actions are
calculated by means of Palatini principle. Polynomial structures with Einstein
metrics appear among extremals of this variational problem.


title: Eigenvalues as Dynamical Variables

abstract:
  We review some work done with C. Rovelli on the use of the eigenvalues of the
Dirac operator on a curved spacetime as dynamical variables, the main
motivation coming from their invariance under the action of diffeomorphisms.
The eigenvalues constitute an infinite set of ``observables'' for general
relativity and can be taken as variables for an invariant description of the
gravitational field dynamics.


title: FRW-Type Universe With Vacuum Energy Density

abstract:
  We have considered a cosmological model with a cosmological constant of the
form $\Lambda=3\alpha\frac{\dot R^2}{R^2}+\bt\frac{\ddot R}{R} \alpha, \bt=\rm
const.$ The cosmological constant is found to decrease as $t^{-2}$ and the rate
of particle creation is smaller than the Steady State value. We have found that
this behavior gives $\frac{\Lambda_{Pl}}{\Lambda_p}=10^{120}$ where
$\Lambda_{Pl}$ is the value of $\Lambda$ at Planck time. Solutions with
$\bt=3\alpha$ in the radiation dominated era and $\bt=6\alpha$ in the matter
dominated era are equivalent to the FRW results. We have found an inflationary
solution of the de-Sitter type with $\bt=3-3\alpha$. Some problems of the
Standard Model may be resolved with the presence of the above cosmological
constant in the Einstein's equation. Since observations suggest a contribution
of the vacuum energy density in the range $0.40<\Omega^\Lambda<0.76$, one gets
$4<\beta<12$. If $\alpha=0$ the minimum age of the universe is found to be
$H_p^{-1}$ ($H_p$ is the present Hubble constant) with $\beta=\infty$.


title: Structure Formation in Non-singular Higher Curvature Cosmology

abstract:
  We propose novel structure formation scenarios based on a non-singular higher
curvature cosmological model. The model is motivated by the $R^2$ coupling of a
scalar field appearing in the string theory, and in our scenarios the universe
has no beginning and no end. We give two examples with explicit parameter
values which are consistent with present observations of the cosmological
structure. In the first example, the origin of structures are generated as the
adiabatic perturbation during the chaotic inflation, while in the second the
isocurvature non-Gaussian perturbation from the superinflating era is
responsible for the structure. In the second case it is possible to generate
primordial supermassive blackholes whose scale is comparable to what is
expected in the galactic nuclei.


title:
Does the generalized second law require entropy bounds for a charged
  system?

abstract:
  We calculate the net change in generalized entropy occurring when one carries
out the gedanken experiment in which a box initially containing energy $E$,
entropy $S$ and charge $Q$ is lowered adiabatically toward a
Reissner-Nordstr\"{o}m black hole and then dropped in. This is an extension of
the work of Unruh-Wald to a charged system (the contents of the box possesses a
charge $Q$). Their previous analysis showed that the effects of acceleration
radiation prevent violation of the generalized second law of thermodynamics. In
our more generic case, we show that the properties of the thermal atmosphere
are equally important when charge is present. Indeed, we prove here that an
equilibrium condition for the the thermal atmosphere and the physical
properties of ordinary matter are sufficient to enforce the generalized second
law. Thus, no additional assumptions concerning entropy bounds on the contents
of the box need to be made in this process. The relation between our work and
the recent works of Bekenstein and Mayo, and Hod (entropy bound for a charged
system) are also discussed.


title:
Exact static solutions in four dimensional Einstein-Maxwell-Dilaton
  gravity

abstract:
  Classes of exact static solutions in four-dimensional
Einstein-Maxwell-Dilaton gravity are found. Besides of the well-known solutions
previously found in the literature, new solutions are presented.It's shown that
spherically symmetric solutions, except the case of charged dilaton black hole,
represent globally naked strong curvature singularities.


title:
General Non-Static Spherically Symmetric Solutions of Einstein Vaccum
  Field Equations with Lambda

abstract:
  1- It is shown that the upper bound for $\alpha$ in the general solutions of
spherically symmetric vacuum field equations(gr-qc/9812081,$\Lambda$=0) is
nearly 10^3.This has been obtained by comparing the theoretical prediction for
bending of light and precession of perihelia with observation. For a
significant range of possible values of$\alpha$ ($\alpha$ >2) the metric is
free of coordinate singularity. 2- It is checked that the singularity in the
non-static spherically symmetric solution of Einstein field equations with
$\Lambda$ (JHEP04(1999)011,$\alpha$ = 0)at the origin is intrinsic. 3- Using
the techniques of these two works, ageneral class of non-static solutions is
presented. They are smooth and finite everywhere and have an extension larger
than Schwarzschild metric. 4- The geodesic equations of a freely material
particle for the general case are solved which reveals a Schwarzschild
-deSitter type potential field.


title: On the (im)possibility of warp bubbles

abstract:
  Various objections against Alcubierre's warp drive geometry are reviewed.
Superluminal warp bubbles seem an unlikey possibility within the framework of
general relativity and quantum field theory, although subluminal bubbles may
still be possible.


title:
Nonminimal Derivative Couplings and Inflation in Generalized Theories of
  Gravity

abstract:
  We study extended theories of gravity where nonminimal derivative couplings
of the form $R^{kl}\phi_{, k}\phi_{, l}$ are present in the Lagrangian. We show
how and why the other couplings of similar structure may be ruled out and then
deduce the field equations and the related cosmological models. Finally, we get
inflationary solutions which do follow neither from any effective scalar field
potential nor from a cosmological constant introduced ``by hand'', and we show
the de Sitter space--time to be an attractor solution.


title: Quasilocal Energy for Spin-net Gravity

abstract:
  The Hamiltonian of a gravitational system defined in a region with boundary
is quantized. The classical Hamiltonian, and starting point for the
regularization, is required by functional differentiablity of the Hamiltonian
constraint. The boundary term is the quasilocal energy of the system and
becomes the ADM mass in asymptopia. The quantization is carried out within the
framework of canonical quantization using spin networks. The result is a gauge
invariant, well-defined operator on the Hilbert space induced from the state
space on the whole spatial manifold. The spectrum is computed. An alternate
form of the operator, with the correct naive classical limit, but requiring a
restriction on the Hilbert space, is also defined. Comparison with earlier work
and several consequences are briefly explored.


title: Metrics with distributional curvature

abstract:
  This paper considers metrics whose curvature tensor makes sense as a
distribution. A class of such metrics, the regular metrics, was defined and
studied by Geroch and Traschen. Here, we generalize their definition to form a
wider class: semi-regular metrics. We then examine in detail two metrics that
are semi-regular but not regular: (i) Minkowski spacetime minus a wedge and
(ii) a certain traveling wave metric.


title:
Is the squeezing of relic gravitational waves produced by inflation
  detectable?

abstract:
  Grishchuk has shown that the stochastic background of gravitational waves
produced by an inflationary phase in the early Universe has an unusual
property: it is not a stationary Gaussian random process. Due to squeezing, the
phases of the different waves are correlated in a deterministic way, arising
from the process of parametric amplification that created them. The resulting
random process is Gaussian but non-stationary. This provides a unique signature
that could in principle distinguish a background created by inflation from
stationary stochastic backgrounds created by other types of processes. We
address the question: could this signature be observed with a gravitational
wave detector? Sadly, the answer appears to be "no": an experiment which could
distinguish the non-stationary behavior would have to last approximately the
age of the Universe at the time of measurement. This rules out direct detection
by ground and space based gravitational wave detectors, but not indirect
detections via the electromagnetic Cosmic Microwave Background Radiation
(CMBR).


title:
Analytic approximation and an improved method for computing the
  stress-energy of quantized scalar fields in Robertson-Walker spacetimes

abstract:
  An improved method is given for the computation of the stress-energy tensor
of a quantized scalar field using adiabatic regularization. The method works
for fields with arbitrary mass and curvature coupling in Robertson-Walker
spacetimes and is particularly useful for spacetimes with compact spatial
sections. For massless fields it yields an analytic approximation for the
stress-energy tensor that is similar in nature to those obtained previously for
massless fields in static spacetimes.


title:
de Broglie-Bohm Interpretatin for Analytic Solutions of The
  Wheeler-DeWitt Equation in Spherically Symmetric Space-time

abstract:
  We discuss the implications of a wave function for quantum gravity, which
involves nothing but 3-dimensional geometries as arguments and is invariant
under general coordinate transformations. We derive an analytic wave function
from the Wheeler-DeWitt equation for spherically symmetric space-time with the
coordinate system arbitrary. The de Broglie-Bohm interpretation of quantum
mechanics is applied to the wave function. In this interpretation,
deterministic dynamics can be yielded from a wave function in fully quantum
regions as well as in semiclassical ones. By introducing a coordinate system
additionally, we obtain a cosmological black hole picture in compensation for
the loss of general covariance. Our analysis shows that the de Broglie-Bohm
interpretation gives quantum gravity an appropriate prescription to introduce
coordinate systems naturally and extract information from a wave function as a
result of breaking general covariance.


title:
Generalized Lagrangian of N = 1 supergravity and its canonical
  constraints with the real Ashtekar variable

abstract:
  We generalize the Lagrangian of N = 1 supergravity (SUGRA) by using an
arbitrary parameter $\xi$, which corresponds to the inverse of Barbero's
parameter $\beta$. This generalized Lagrangian involves the chiral one as a
special case of the value $\xi = \pm i$. We show that the generalized
Lagrangian gives the canonical formulation of N = 1 SUGRA with the real
Ashtekar variable after the 3+1 decomposition of spacetime. This canonical
formulation is also derived from those of the usual N = 1 SUGRA by performing
Barbero's type canonical transformation with an arbitrary parameter $\beta
(=\xi^{-1})$. We give some comments on the canonical formulation of the theory.


title:
Non-Archimedean character of quantum buoyancy and the generalized second
  law of thermodynamics

abstract:
  Quantum buoyancy has been proposed as the mechanism protecting the
generalized second law when an entropy--bearing object is slowly lowered
towards a black hole and then dropped in. We point out that the original
derivation of the buoyant force from a fluid picture of the acceleration
radiation is invalid unless the object is almost at the horizon, because
otherwise typical wavelengths in the radiation are larger than the object. The
buoyant force is here calculated from the diffractive scattering of waves off
the object, and found to be weaker than in the original theory. As a
consequence, the argument justifying the generalized second law from buoyancy
cannot be completed unless the optimal drop point is next to the horizon. The
universal bound on entropy is always a sufficient condition for operation of
the generalized second law, and can be derived from that law when the optimal
drop point is close to the horizon. We also compute the quantum buoyancy of an
elementary charged particle; it turns out to be negligible for energetic
considerations. Finally, we speculate on the significance of the absence from
the bound of any mention of the number of particle species in nature.


title: Noncommutative Geometry for Pedestrians

abstract:
  A short historical review is made of some recent literature in the field of
noncommutative geometry, especially the efforts to add a gravitational field to
noncommutative models of space-time and to use it as an ultraviolet regulator.
An extensive bibliography has been added containing reference to recent review
articles as well as to part of the original literature.


title: Self-Screening Hawking Atmosphere in the Presence of a Bulk Viscosity

abstract:
  The recent theory of 't Hooft [ Nucl. Phys. Suppl. {\bf 68}, 174 (1998)]
models the black hole as a system endowed with an envelope of matter that obeys
an equation of state in the form $ p=(\gamma -1)\rho$, and acts as a source in
Einstein's equations. The present paper generalizes the 't Hooft theory so as
to take into account a bulk viscosity $\zeta$ in the fluid. It is shown that
even a slight positive value of $\zeta$ will suffice to yield complete
agreement with the Hawking formula for the entropy of the black hole, if the
value of the constant $\gamma$ takes a value that is slightly less than 4/3.
The value $\gamma=4/3$ corresponds to a radiation fluid.


title: Wormholes, Classical Limit and Dynamical Vacuum in Quantum Cosmology

abstract:
  First a Friedmann-Robertson-Walker (FRW) universe filled with dust and a
conformally invariant scalar field is quantized. For the closed model we find a
discrete set of wormhole quantum states. In the case of flat spacelike sections
we find states with classical behaviour at small values of the scale factor and
quantum behaviour for large values of the scale factor. Next we study a FRW
model with a conformally invariant scalar field and a nonvanishing cosmological
constant dynamically introduced by regarding the vacuum as a perfect fluid. The
ensuing Wheeler-DeWitt equation turns out to be a bona fide Schrodinger
equation, and we find that there are realizable states with a definite value of
the cosmological constant. Once again we find finite-norm solutions to the
Wheeler-DeWitt equation with definite values of the cosmological constant that
represent wormholes, suggesting that in quantum cosmological models with a
simple matter content wormhole states are a common occurrence.


title:
Asymptotically constrained and real-valued system based on Ashtekar's
  variables

abstract:
  We present a set of dynamical equations based on Ashtekar's extension of the
Einstein equation. The system forces the space-time to evolve to the manifold
that satisfies the constraint equations or the reality conditions or both as
the attractor against perturbative errors. This is an application of the idea
by Brodbeck, Frittelli, Huebner and Reula who constructed an asymptotically
stable (i.e., constrained) system for the Einstein equation, adding dissipative
forces in the extended space. The obtained systems may be useful for future
numerical studies using Ashtekar's variables.


title:
On the Brown-York quasilocal energy, gravitational charge, and black
  hole horizons

abstract:
  We study a recently proposed horizon defining identity for certain black hole
spacetimes. It relates the difference of the Brown-York quasilocal energy and
the Komar charge at the horizon to the total energy of the spacetime. The
Brown-York quasilocal energy is evaluated for some specific choices of
spacetime foliations. With a certain condition imposed on the matter
distribution, we prove this identity for spherically symmetric static black
hole solutions of general relativity. For these cases, we show that the
identity can be derived from a Gauss-Codacci condition that any
three-dimensional timelike boundary embedded around the hole must obey. We also
demonstrate the validity of the identity in other cases by explicitly applying
it to several static, non-static, asymptotically flat, and asymptotically
non-flat black hole solutions. These include the asymptotically FRW solutions
and the case of a black hole with a global monopole charge.


title: Detection of gravitational waves using a network of detectors

abstract:
  We formulate the data analysis problem for the detection of the Newtonian
coalescing-binary signal by a network of laser interferometric gravitational
wave detectors that have arbitrary orientations, but are located at the same
site. We use the maximum likelihood method for optimizing the detection
problem. We show that for networks comprising of up to three detectors, the
optimal statistic is essentially the magnitude of the network correlation
vector constructed from the matched network-filter. Alternatively, it is simply
a linear combination of the signal-to-noise ratios of the individual detectors.
This statistic, therefore, can be interpreted as the signal-to-noise ratio of
the network. The overall sensitivity of the network is shown to increase
roughly as the square-root of the number of detectors in the network. We
further show that these results continue to hold even for the restricted
post-Newtonian filters. Finally, our formalism is general enough to be extended
to address the problem of detection of such waves from other sources by some
other types of detectors, e.g., bars or spheres, or even by networks of
spatially well-separated detectors.


title:
The Theory of Caustics and Wavefront Singularities with Physical
  Applications

abstract:
  This is intended as an introduction to and review of the work of V, Arnold
and his collaborators on the theory of Lagrangian and Legendrian submanifolds
and their associated maps. The theory is illustrated by applications to
Hamilton-Jacobi theory and the eikonal equation, with an emphasis on null
surfaces and wavefronts and their associated caustics and singularities.


title: Exact Solutions of Relativistic Two-Body Motion in Lineal Gravity

abstract:
  We develop the canonical formalism for a system of $N$ bodies in lineal
gravity and obtain exact solutions to the equations of motion for N=2. The
determining equation of the Hamiltonian is derived in the form of a
transcendental equation, which leads to the exact Hamiltonian to infinite order
of the gravitational coupling constant. In the equal mass case explicit
expressions of the trajectories of the particles are given as the functions of
the proper time, which show characteristic features of the motion depending on
the strength of gravity (mass) and the magnitude and sign of the cosmological
constant. As expected, we find that a positive cosmological constant has a
repulsive effect on the motion, while a negative one has an attractive effect.
However, some surprising features emerge that are absent for vanishing
cosmological constant. For a certain range of the negative cosmological
constant the motion shows a double maximum behavior as a combined result of an
induced momentum-dependent cosmological potential and the gravitational
attraction between the particles. For a positive cosmological constant, not
only bounded motions but also unbounded ones are realized. The change of the
metric along the movement of the particles is also exactly derived.


title:
Electromagnetic Zero Point Field as Active Energy Source in the
  Intergalactic Medium

abstract:
  For over twenty years the possibility that the electromagnetic zero point
field (ZPF) may actively accelerate electromagnetically interacting particles
in regions of extremely low particle density (as those extant in intergalactic
space (IGS) with n < 1 particle/m^3 has been studied and analyzed. This
energizing phenomenon has been one of the few contenders for acceleration of
cosmic rays (CR), particularly at ultrahigh energies. The recent finding by the
AGASA collaboration (Phys. Rev. Lett., 81, 1163, 1998) that the CR energy
spectrum does not display any signs of the Greisen-Zatsepin-Kuzmin cut-off
(that should be present if these CR particles were indeed generated in
localized ultrahigh energies CR sources, as e.g., quasars and other highly
active galactic nuclei), may indicate the need for an acceleration mechanism
that is distributed throughout IGS as is the case with the ZPF. Other
unexplained phenomena that receive an explanation from this mechanism are the
generation of X-ray and gamma-ray backgrounds and the existence of Cosmic
Voids. However recently, a statistical mechanics kind of challenge to the
classical (not the quantum) version of the zero-point acceleration mechanism
has been posed (de la Pena and Cetto, The Quantum Dice, 1996). Here we briefly
examine the consequences of this challenge and a prospective resolution.


title:
Gauge-invariant and coordinate-independent perturbations of stellar
  collapse I: the interior

abstract:
  Small non-spherical perturbations of a spherically symmetric but
time-dependent background spacetime can be used to model situations of
astrophysical interest, for example the production of gravitational waves in a
supernova explosion. We allow for perfect fluid matter with an arbitrary
equation of state p=p(rho,s), coupled to general relativity. Applying a general
framework proposed by Gerlach and Sengupta, we obtain covariant field
equations, in a 2+2 reduction of the spacetime, for the background and a
complete set of gauge-invariant perturbations, and then scalarize them using
the natural frame provided by the fluid. Building on previous work by Seidel,
we identify a set of true perturbation degrees of freedom admitting free
initial data for the axial and for the l>1 polar perturbations. The true
degrees of freedom are evolved among themselves by a set of coupled wave and
transport equations, while the remaining degrees of freedom can be obtained by
quadratures. The polar l=0,1 perturbations are discussed in the same framework.
They require gauge fixing and do not admit an unconstrained evolution scheme.


title:
Progress in Establishing a Connection Between the Electromagnetic
  Zero-Point Field and Inertia

abstract:
  We report on the progress of a NASA-funded study being carried out at the
Lockheed Martin Advanced Technology Center in Palo Alto and the California
State University in Long Beach to investigate the proposed link between the
zero-point field of the quantum vacuum and inertia. It is well known that an
accelerating observer will experience a bath of radiation resulting from the
quantum vacuum which mimics that of a heat bath, the so-called Davies-Unruh
effect. We have further analyzed this problem of an accelerated object moving
through the vacuum and have shown that the zero-point field will yield a
non-zero Poynting vector to an accelerating observer. Scattering of this
radiation by the quarks and electrons constituting matter would result in an
acceleration-dependent reaction force that would appear to be the origin of
inertia of matter (Rueda and Haisch 1998a, 1998b). In the subrelativistic case
this inertia reaction force is exactly newtonian and in the relativistic case
it exactly reproduces the well known relativistic extension of Newton's Law.
This analysis demonstrates then that both the ordinary, F=ma, and the
relativistic forms of Newton's equation of motion may be derived from Maxwell's
equations as applied to the electromagnetic zero-point field. We expect to be
able to extend this analysis in the future to more general versions of the
quantum vacuum than just the electromagnetic one discussed herein.


title: Remark on formation of colored black holes via fine tuning

abstract:
  In a recent paper (gr-qc/9903081) Choptuik, Hirschmann, and Marsa have
discovered the scaling law for the lifetime of an intermediate attractor in the
formation of n=1 colored black holes via fine tuning. We show that their result
is in agreement with the prediction of linear perturbation analysis. We also
briefly comment on the dependence of the mass gap across the threshold on the
radius of the event horizon.


title: Static charged perfect fluid with the Weyl-Majumdar relation

abstract:
  Static charged perfect fluid distributions have been studied. It is shown
that if the norm of the timelike Killing vector and the electrostatic potential
have the Weyl-Majumdar relation, then the background spatial metric is the
space of constant curvature, and the field equations reduces to a single
non-linear partial differential equation. Furthermore, if the linear equation
of state for the fluid is assumed, then this equation becomes a Helmholtz
equation on the space of constant curvature. Some explicit solutions are given.


title: Nonlocal Phenomena from Noncommutative Pre-Planckian Regime

abstract:
  A model unifying general relativity with quantum mechanics is further
developed. It is based on a noncommutative geometry which supposedly modelled
the universe in its pre-Planckian epoch. The geometry is totally nonlocal with
no time and no space in their usual meaning. They emerge only in the transition
process from the noncommutative epoch to the standard space-time physics.
Observational aspects of this model are discussed. It is shown that various
nonlocal phenomena can be explained as remnants of the primordial
noncommutative epoch. In particular, we explain the Einstein-Podolsky-Rosen
experiment, the horizon problem in cosmology, and the appearance of
singularities in general relativity.


title: Asymptotic Behaviour of Inhomogeneous String Cosmologies

abstract:
  The asymptotic behaviour at late times of inhomogeneous axion-dilaton
cosmologies is investigated. The space-times considered here admit two abelian
space-like Killing vectors. These space-times evolve towards an anisotropic
universe containing gravitational radiation. Furthermore, a peeling-off
behaviour of the Weyl tensor and the antisymmetric tensor field strength is
found. The relation to the pre-big-bang scenario is briefly discussed.


title: Starobinsky Model in Schroedinger Description

abstract:
  In the Starobinsky inflationary model inflation is driven by quantum
corrections to the vacuum Einstein equation. We reduce the Wheeler-DeWitt
equation corresponding to the Starobinsky model to a Schroedinger form
containing time. The Schroedinger equation is solved with a Gaussian ansatz.
Using the prescription for the normalization constant of the wavefunction given
in our previous work, we show that the Gaussian ansatz demands Hawking type
initial conditions for the wavefunction of the universe. The wormholes induce
randomness in initial states suggesting a basis for time-contained description
of the Wheeler-DeWitt equation.


title:
Direct Detection of Primordial Gravitational Waves in a BSI Inflationary
  Model

abstract:
  We investigate the possibility for a direct detection by future space
interferometers of the stochastic gravitational wave (GW) background generated
during the inflationary stage in a class of viable $\Lambda$CDM BSI models. At
frequencies around $10^{-3}$Hz, maximal values $\Omega_{gw}(\nu)\sim 3\times
10^{-15}$ are found, an improvement of about one order of magnitude compared to
single-field, slow-roll inflationary models. This is presumably not sufficient
in order to be probed in the near future.


title:
The Hadamard Condition for Dirac Fields and Adiabatic States on
  Robertson-Walker Spacetimes

abstract:
  We characterise the homogeneous and isotropic gauge invariant and quasifree
states for free Dirac quantum fields on Robertson-Walker spacetimes in any even
dimension. Using this characterisation, we construct adiabatic vacuum states of
order $n$ corresponding to some Cauchy surface. We then show that any two such
states (of sufficiently high order) are locally quasi-equivalent. We propose a
microlocal version of the Hadamard condition for spinor fields on arbitrary
spacetimes, which is shown to entail the usual short distance behaviour of the
twopoint function. The polarisation set of these twopoint functions is
determined from the Dencker connection of the spinorial Klein-Gordon operator
which we show to equal the (pull-back) of the spin connection. Finally it is
demonstrated that adiabatic states of infinite order are Hadamard, and that
those of order $n$ correspond, in some sense, to a truncated Hadamard series
and will therefore allow for a point splitting renormalisation of the expected
stress-energy tensor.


title:
Universal gravitation as a complex-dynamical process, renormalised
  Planckian units, and the spectrum of elementary particles

abstract:
  The new, complex-dynamical mechanism of the universal gravitation naturally
incorporating dynamical quantization, wave-particle duality, and relativity of
physically emerging space and time (quant-ph/9902015,16) provides the realistic
meaning and fundamentally substantiated modification of the Planckian units of
mass, length, and time approaching them closely to the extreme values observed
for already discovered elementary particles. This result suggests the important
change of research strategy in high-energy/particle physics, displacing it
towards the already attained energy scales and permitting one to exclude the
existence of elementary objects in the inexplicably large interval of
parameters separating the known, practically more than sufficient set of
elementary species and the conventional, mechanistically exaggerated values of
the Planckian units. This conclusion is supported by the causally complete
(physically and mathematically consistent) picture of the fundamental levels of
reality derived, without artificial introduction of any structure or
'principle', from the unreduced analysis of the (generic) interaction process
between two primal, physically real, but a priori structureless entities, the
electromagnetic and gravitational protofields. The naturally emerging
phenomenon of universal dynamic redundance (multivaluedness) of interaction
process gives rise to the intrinsically unified hierarchy of unreduced dynamic
complexity of the world, starting from the lowest levels of elementary objects,
and explains the irreducible limitations of the basically single-valued
approach of the canonical science leading to the well-known 'mysteries',
separations, and loss of certainty.