title:
Probability Interpretation for Klein-Gordon Fields and the Hilbert Space
  Problem in Quantum Cosmology

abstract:
  We give an explicit construction of a positive-definite invariant
inner-product for the Klein-Gordon fields, thus solving the old problem of the
probability interpretation of Klein-Gordon fields without having to restrict to
the subspaces of the positive-frequency solutions. Our method has a much wider
domain of application and may be used to obtain the most general invariant
inner-product on the solution space of a broad class of Klein-Gordon type
evolution equations. We explore its consequences for the solutions of the
Wheeler-DeWitt equation associated with the FRW-massive-real-scalar-field
models.


title: Casimir energy density in closed hyperbolic universes

abstract:
  The original Casimir effect results from the difference in the vacuum
energies of the electromagnetic field, between that in a region of space with
boundary conditions and that in the same region without boundary conditions. In
this paper we develop the theory of a similar situation, involving a scalar
field in spacetimes with compact spatial sections of negative spatial
curvature.


title: The Integral Formulae for a Cylindrical Black Hole

abstract:
  Here we derive the mass formulae for a cylindrical black hole solution with
positive cosmological constant and surrounded by dust. The expressions are
generalising those found by Smarr for the mass and momentum of a Kerr black
hole.


title:
A cosmological model in Weyl-Cartan spacetime: II. Magnitude-redshift
  relation

abstract:
  In this second part of our series of articles on alternative cosmological
models we investigate the observational consequences for the new Weyl-Cartan
model proposed earlier. We review the derivation of the magnitude-redshift
relation within the standard FLRW model and characterize its dependence on the
underlying cosmological model. With this knowledge at hand we derive the
magnitude-redshift relation within our new Weyl-Cartan model. We search for the
best-fit parameters by using the combined data set of 92 SNe of type Ia as
compiled by Wang, which is based on recent supernova data of Perlmutter et al.
and Riess et al. Additionally, we compare our best-fit parameters with the
results of several other groups which performed similar analysis within the
standard cosmological model as well as in non-standard models.


title:
Quantum Mechanical Probability Interpretation In The Mini-superspace
  Model Of Higher Order Gravity Theory

abstract:
  It has been shown that inclusion of higher order curvature invariant terms in
the Robertson-Walker minisuperspace model of the Einstein-Hilbert action leads
to Schrodinger like equation, whose corresponding effective action is
hermitian. Thus, it is possible to write the continuity equation in a straight
forward manner, which reveals a quantum mechanical probability interpretation
of the theory.


title:
Radiation from perfect mirrors following prescribed relativistic
  trajectories

abstract:
  The question is examined of a mirror which starts from rest and either (i)
accelerates for some time and eventually reverts to motion at constant
velocity, or (ii) continues accelerating forever. A sharp distinction is made
between cases (i) and (ii) concerning the spectrum of the emitted radiation,
and the qualitative difference between the two cases is pointed out. The
Bogolubov coefficients are calculated for a trajectory of type (i). A type (ii)
trajectory is entirely unphysical as far as any realistic mirror is concerned,
however it is of interest in that it has been used as a simple analog of black
hole collapse. The spectrum emitted for the type (ii) trajectory z=-ln(cosht)
is examined and it is shown that it is indeed that of a black body.
Inconsistencies in previous derivations of the above result are pointed out.


title: Strings in the Einstein's paradigm of matter

abstract:
  Spherically symmetric solutions with a flux of electric and magnetic fields
in Kaluza-Klein gravity are considered. It is shown that under the condition
(electric charge $q$) $\approx$ (magnetic charge $Q$) ($q>Q$) these solutions
are like a flux tube stretched between two Universes. The longitudinal size of
this tube depends on the value of $\delta = 1 - Q/q$. The cross section of the
tube can be chosen $\approx l_{Pl}$. In this case this flux tube looks like a
1-dimensional object (thread) stretched between two Universes. The propagation
of gravitational waves on the thread is considered. The corresponding equations
are very close to the classical string equations. This result allows us to say
that the thread between two Universes is similar to the string attached to two
$D-$branes.


title:
Quantum mechanics without spacetime II : noncommutative geometry and the
  free point particle

abstract:
  In a recent paper we have suggested that a formulation of quantum mechanics
should exist, which does not require the concept of time, and that the
appropriate mathematical language for such a formulation is noncommutative
differential geometry. In the present paper we discuss this formulation for the
free point particle, by introducing a commutation relation for a set of
noncommuting coordinates. The sought for background independent quantum
mechanics is derived from this commutation relation for the coordinates. We
propose that the basic equations are invariant under automorphisms which map
one set of coordinates to another- this is a natural generalization of
diffeomorphism invariance when one makes a transition to noncommutative
geometry. The background independent description becomes equivalent to standard
quantum mechanics if a spacetime manifold exists, because of the proposed
automorphism invariance. The suggested basic equations also give a quantum
gravitational description of the free particle.


title: Can black holes exist in an accelerating universe?

abstract:
  This letter deals with an analysis of the space-time static metric that
corresponds to a quintessential state equation with constant characteristic
parameter. Following a procedure parallel to as it is used in the case of de
Sitter space, we have tried to generalize the metric components that correspond
to the quintessential case to also embrace black-hole terms and shown that this
is not possible. We argue therefore that, in the absence of a cosmological
constant, black holes seem to be prevented in a cosmological space-time which
is asymptotically accelerating when the acceleration is driven by a
quintessence-like field.


title: An Alternative to Inflation

abstract:
  Inflationary models are generally credited with explaining the large scale
homogeneity, isotropy, and flatness of our universe as well as accounting for
the origin of structure (i.e., the deviations from exact homogeneity) in our
universe. We argue that the explanations provided by inflation for the
homogeneity, isotropy, and flatness of our universe are not satisfactory, and
that a proper explanation of these features will require a much deeper
understanding of the initial state of our universe. On the other hand,
inflationary models are spectacularly successful in providing an explanation of
the deviations from homogeneity. We point out here that the fundamental
mechanism responsible for providing deviations from homogeneity -- namely, the
evolutionary behavior of quantum modes with wavelength larger than the Hubble
radius -- will operate whether or not inflation itself occurs. However, if
inflation did not occur, one must directly confront the issue of the initial
state of modes whose wavelength was larger than the Hubble radius at the time
at which they were "born". Under some simple hypotheses concerning the "birth
time" and initial state of these modes (but without any "fine tuning"), it is
shown that non-inflationary fluid models in the extremely early universe would
result in the same density perturbation spectrum and amplitude as inflationary
models, although there would be no "slow roll" enhancement of the scalar modes.


title: A Mission to Test the Pioneer Anomaly

abstract:
  Analysis of the radio tracking data from the Pioneer 10/11 spacecraft has
consistently indicated the presence of an anomalous small Doppler frequency
drift. The drift can be interpreted as being due to a constant acceleration of
a_P= (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed towards the Sun. Although it is
suspected that there is a systematic origin to the effect, none has been found.
The nature of this anomaly has become of growing interest in the fields of
relativistic cosmology, astro- and gravitational physics as well as in the
areas of spacecraft design and high-precision navigation. We present a concept
for a designated deep-space mission to test the discovered anomaly. A number of
critical requirements and design considerations for such a mission are outlined
and addressed.


title: Kerr-Schild type initial data for black holes with angular momenta

abstract:
  Generalizing previous work we propose how to superpose spinning black holes
in a Kerr-Schild initial slice. This superposition satisfies several physically
meaningful limits, including the close and the far ones. Further we consider
the close limit of two black holes with opposite angular momenta and explicitly
solve the constraint equations in this case. Evolving the resulting initial
data with a linear code, we compute the radiated energy as a function of the
masses and the angular momenta of the black holes.


title: Relativistic stellar aberration for the Space Interferometry Mission

abstract:
  This paper analyses the relativistic stellar aberration requirements for the
Space Interferometry Mission (SIM). We address the issue of general
relativistic deflection of light by the massive self-gravitating bodies.
Specifically, we present estimates for corresponding deflection angles due to
the monopole components of the gravitational fields of a large number of
celestial bodies in the solar system. We study the possibility of deriving an
additional navigational constraints from the need to correct for the
gravitational bending of light that is traversing the solar system. It turns
out that positions of the outer planets presently may not have a sufficient
accuracy for the precision astrometry. However, SIM may significantly improve
those simply as a by-product of its astrometric program. We also consider
influence of the higher gravitational multipoles, notably the quadrupole and
the octupole ones, on the gravitational bending of light. Thus, one will have
to model and account for their influence while observing the sources of
interest in the close proximity of some of the outer planets, notably the
Jupiter and the Saturn. Results presented here are different from the ones
obtained elsewhere by the fact that we specifically account for the
differential nature of the future SIM astrometric campaign (e.g. observations
will be made over the instrument's field of regard with the size of
15$^\circ$). This, in particular, lets us to obtain a more realistic estimate
for the accuracy of determination of the parameterized post-Newtonian (PPN)
parameter $\gamma$. Thus, based on a very conservative assumptions, we conclude
that accuracy of $\sigma_\gamma \sim 10^{-5}$ is achievable in the experiments
conducted in the solar gravity field.


title: Relativistic stellar aberration for the Space Interferometry Mission (2)

abstract:
  We address the issue of relativistic stellar aberration requirements for the
Space Interferometry Mission (SIM). Motivated by the importance of this issue
for SIM, we have considered a problem of relative astrometric observations of
two stars separated by angle $\theta$ on the sky with a single baseline
interferometer. While a definitive answer on the stellar aberration issue may
be obtained only in numerical simulations based on the accurate astrometric
model of the instrument, one could still derive realistic conclusions by
accounting for the main expected properties of SIM. In particular, we have
analysied how the expected astrometric accuracy of determination of positions,
parallaxes and proper motions will constrain the accuracy of the spaceraft
navigation. We estimated the astrometric errors introduced by imperfect
metrology (variations of the calibration term across the tile of interest),
errors in the baseline length estimations, and those due to orbital motion of
the spacecraft. We also estimate requirements on the data sampling rate
necessary to apply on-board in order to correct for the stellar aberration. We
have shown that the worst case observation scenario is realized for the motion
of the spacecraft in the direction perpendicular to the tile. This case of
motion will provide the most stringent requirement on the accuracy of knowledge
of the velocity's magnitude. We discuss the implication of the results obtained
for the future mission analysis.


title:
Relativistic stellar aberration for the Space Interferometry Mission:
  parallax analysis

abstract:
  This paper is a continuation of our previous analysis (i.e. Turyshev 2002a,
2002b) of the relativistic stellar aberration requirements for the Space
Interferometry Mission (SIM). Here we have considered a problem of how the
expected astrometric accuracy of parallax determination will constrain the
accuracy of the spacecraft navigation. We show that effect of the spacecraft's
navigational errors on the accuracy of parallax determination with SIM will be
negligible. We discuss the implication of the results obtained for the future
mission analysis.


title: Hyperbolicity of the BSSN system of Einstein evolution equations

abstract:
  We discuss an equivalence between the Baumgarte-Shapiro-Shibata-Nakamura
(BSSN) formulation of the Einstein evolution equations, a subfamiliy of the
Kidder--Scheel--Teukolsky formulation, and other strongly or symmetric
hyperbolic first order systems with fixed shift and densitized lapse. This
allows us to show under which conditions the BSSN system is, in a sense to be
discussed, hyperbolic. This desirable property may account in part for the
empirically observed better behavior of the BSSN formulation in numerical
evolutions involving black holes.


title:
Asymptotics of a proposed delay-differential equation of motion for
  charged particles

abstract:
  We study the behavior in the remote past and future of solutions of an
equation of motion for charged particles proposed by F. Rohrlich, for the
special case in which the motion is in one spatial dimension.
  We show that if an external force is applied for a finite time, some
solutions exhibit the property of ``preacceleration'', meaning that the
particle accelerates before the force is applied, but that there do exist
solutions without preacceleration. However, most solutions without
preacceleration exhibit ``postacceleration'' into the infinite future (i.e.,
the particle accelerates after the force is removed). Some may consider such
behavior as sufficiently "unphysical" to rule out the equation.
  More encouragingly, we show that analogs of the unphysical ``runaway''
solutions of the Lorentz-Dirac equation do not occur for solutions of
Rohrlich's equation. We show that when the external force eventually vanishes,
the proper acceleration vanishes asymptotically in the future, and the
coordinate velocity becomes asymptotically constant.


title: Twilight for the energy conditions?

abstract:
  The tension, if not outright inconsistency, between quantum physics and
general relativity is one of the great problems facing physics at the turn of
the millennium. Most often, the problems arising in merging Einstein gravity
and quantum physics are viewed as Planck scale issues (10^{19} GeV, 10^{-34} m,
10^{-45} s), and so safely beyond the reach of experiment. However, over the
last few years it has become increasingly obvious that the difficulties are
more widespread: There are already serious problems of deep and fundamental
principle at the semi-classical level, and worse, certain classical systems
(inspired by quantum physics, but in no sense quantum themselves) exhibit
seriously pathological behaviour. One manifestation of these pathologies is in
the so-called ``energy conditions'' of general relativity. Patching things up
in the gravity sector opens gaping holes elsewhere; and some ``fixes'' are more
radical than the problems they are supposed to cure.


title: Conservation Laws in Doubly Special Relativity

abstract:
  Motivated by various theoretical arguments that the Planck energy (Ep - 10^19
GeV) - should herald departures from Lorentz invariance, and the possibility of
testing these expectations in the not too distant future, two so-called "Doubly
Special Relativity" theories have been suggested -- the first by
Amelino-Camelia (DSR1) and the second by Smolin and Magueijo (DSR2). These
theories contain two fundamental scales -- the speed of light and an energy
usually taken to be Ep. The symmetry group is still the Lorentz group, but in
both cases acting nonlinearly on the energy-momentum sector. Accordingly, since
energy and momentum are no longer additive quantities, finding their values for
composite systems (and hence finding the correct conservation laws) is a
nontrivial matter. Ultimately it is these possible deviations from simple
linearly realized relativistic kinematics that provide the most promising
observational signal for empirically testing these models. Various
investigations have narrowed the conservation laws down to two possibilities
per DSR theory. We derive unique exact results for the energy-momentum of
composite systems in both DSR1 and DSR2, and indicate the general strategy for
arbitrary nonlinear realizations of the Lorentz group.


title:
Quantum geometrodynamical description of the Universe in different
  reference frames

abstract:
  Several years ago the so-called quantum geometrodynamics in extended phase
space was proposed. The main role in this version of quantum geometrodynamics
is given to a wave function that carries information about geometry of the
Universe as well as about a reference frame in which this geometry is studied.
We consider the evolution of a physical object (the Universe) in ``physical''
subspace of extended configurational space, the latter including gauge and
ghost degrees of freedom. A measure of the ``physical'' subspace depends on a
chosen reference frame, in particular, a small variation of a gauge-fixing
function results in changing the measure. Thus, a transition to another gauge
condition (another reference frame) leads to non-unitary transformation of a
physical part of the wave function. From the viewpoint of the evolution of the
Universe in the ``physical'' subspace a transition to another reference frame
is an irreversible process that may be important when spacetime manifold has a
nontrivial topology.


title: Wave equations for the perturbations of a charged black hole

abstract:
  A pair of simple wave equations is presented for the symmetric gravitational
and electromagnetic perturbations of a charged black hole. One of the equations
is uncoupled, and the other has a source term given by the solution of the
first equation. The derivation is presented in full detail for either axially
symmetric or stationary perturbations, and is quite straightforward. This
result is expected to have important applications in astrophysical models.


title: Protecting the Holographic Principle: Inflation

abstract:
  A scenario where inflation emerges as a response to protect the holographic
principle is described. A two fluid model in a closed universe inflation
picture is assumed, and a possible explanation for secondary exponential
expansion phases as those currently observed is given.


title: Time without time: a stochastic clock model

abstract:
  We study a classical reparametrization-invariant system, in which ``time'' is
not a priori defined. It consists of a nonrelativistic particle moving in five
dimensions, two of which are compactified to form a torus. There, assuming a
suitable potential, the internal motion is ergodic or more strongly irregular.
We consider quasi-local observables which measure the system's ``change'' in a
coarse-grained way. Based on this, we construct a statistical timelike
parameter, particularly with the help of maximum entropy method and Fisher-Rao
information metric. The emergent reparametrization-invariant ``time'' does not
run smoothly but is simply related to the proper time on the average. For
sufficiently low energy, the external motion is then described by a unitary
quantum mechanical evolution in accordance with the Schr\"odinger equation.


title: On the spin of gravitational bosons

abstract:
  We unearth spacetime structure of massive vector bosons, gravitinos, and
gravitons. While the curvatures associated with these particles carry a
definite spin, the underlying potentials cannot be, and should not be,
interpreted as single spin objects. For instance, we predict that a spin
measurement in the rest frame of a massive gravitino will yield the result 3/2
with probability one half, and 1/2 with probability one half. The simplest
scenario leaves the Riemannian curvature unaltered; thus avoiding conflicts
with classical tests of the theory of general relativity. However, the quantum
structure acquires additional contributions to the propagators, and it gives
rise to additional phases.


title: Stability properties of a formulation of Einstein's equations

abstract:
  We study the stability properties of the Kidder-Scheel-Teukolsky (KST)
many-parameter formulation of Einstein's equations for weak gravitational waves
on flat space-time from a continuum and numerical point of view. At the
continuum, performing a linearized analysis of the equations around flat
spacetime, it turns out that they have, essentially, no non-principal terms. As
a consequence, in the weak field limit the stability properties of this
formulation depend only on the level of hyperbolicity of the system. At the
discrete level we present some simple one-dimensional simulations using the KST
family. The goal is to analyze the type of instabilities that appear as one
changes parameter values in the formulation. Lessons learnt in this analysis
can be applied in other formulations with similar properties.


title: Reply to "On scaling solutions with a dissipative fluid"

abstract:
  In this paper we show that the claims in [Class. Quantum Grav. 19 (2002)
3067, gr-qc/0203081] related to our analysis in [Phys. Rev. D 62, 063508
(2000), astro-ph/0005070] are wrong.


title: A Machian Model of Dark Energy

abstract:
  Einstein believed that Mach's principle should play a major role in finding a
meaningful spacetime geometry, though it was discovered later that his field
equations gave some solutions which were not Machian. It is shown, in this
essay, that the kinematical $\Lambda$ models, which are invoked to solve the
cosmological constant problem, are in fact consistent with Mach's ideas. One
particular model in this category is described which results from the
microstructure of spacetime and seems to explain the current observations
successfully and also has some benefits over the conventional models. This
forces one to think whether the Mach's ideas and the cosmological constant are
interrelated in some way.


title: The CWKB Method of Particle Production in Periodic Potential

abstract:
  In this work we study the particle production in time dependent periodic
potential using the method of complex time WKB (CWKB) approximation. In the
inflationary cosmology at the end of inflationary stage, the potential becomes
time dependent as well as periodic. Reheating occurs due to particle production
by the oscillating inflaton field. Using CWKB we obtain almost identical
results on catastrophic particle production as obtained by others.


title: The CWKB Method of Particle Production Near Chronology Horizon

abstract:
  In this paper we investigate the phenomenon of particle production of massles
scalar field, in a model of spacetime where the chronology horizon could be
formrd, using the method of complex time WKB approximation (CWKB). For the
purpose, we take two examples in a model of spacetime, one already discussed by
Sushkov, to show that the mode of particle production near chronology horizon
possesses the similar characteristic features as are found while discussing
particle production in time dependent curved background. We get identical
results as that obtained by Sushkov in this direction. We find, in both the
examples studied, that the total number of particles remain finite at the
moment of the formation of the chronology horizon.


title: The Fulling-Davies-Unruh Effect is Mandatory: The Proton's Testimony

abstract:
  We discuss the decay of accelerated protons and illustrate how the
Fulling-Davies-Unruh effect is indeed mandatory to maintain the consistency of
standard Quantum Field Theory. The confidence level of the Fulling-Davies-Unruh
effect must be the same as that of Quantum Field Theory itself.


title:
Self-force of a scalar field for circular orbits about a Schwarzschild
  black hole

abstract:
  The foundations are laid for the numerical computation of the actual
worldline for a particle orbiting a black hole and emitting gravitational
waves. The essential practicalities of this computation are here illustrated
for a scalar particle of infinitesimal size and small but finite scalar charge.
This particle deviates from a geodesic because it interacts with its own
retarded field $\psi^\ret$. A recently introduced Green's function $G^\SS$
precisely determines the singular part, $\psi^\SS$, of the retarded field. This
part exerts no force on the particle. The remainder of the field $\psi^\R =
\psi^\ret - \psi^\SS$ is a vacuum solution of the field equation and is
entirely responsible for the self-force. A particular, locally inertial
coordinate system is used to determine an expansion of $\psi^\SS$ in the
vicinity of the particle. For a particle in a circular orbit in the
Schwarzschild geometry, the mode-sum decomposition of the difference between
$\psi^\ret$ and the dominant terms in the expansion of $\psi^\SS$ provide a
mode-sum decomposition of an approximation for $\psi^\R$ from which the
self-force is obtained. When more terms are included in the expansion, the
approximation for $\psi^\R$ is increasingly differentiable, and the mode-sum
for the self-force converges more rapidly.


title: On Conformally Flat Stationary Axisymmetric Spacetimes

abstract:
  It is shown that within conformally flat stationary axisymmetric spacetimes,
besides of the static family, there exists a new class of metrics, which is
always stationary and axisymmetric. All these spacetimes, the static and the
stationary ones, are endowed with an arbitrary function depending on the two
non--Killingian coordinates. The explicit form of this function can be
determined once the coupled matter, i.e., the energy--momentum tensor is given.
One might hope possible extensions of this result to black holes on two--branes
in four dimensions.


title:
Is it possible to improve the present LAGEOS-LAGEOS II Lense-Thirring
  experiment?

abstract:
  The Lense-Thirring effect is currently being measured by means of a
combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and
the perigee of LAGEOS II. The total error is of the order of 20%. The most
insidious systematic error is due to the mismodelled even zonal harmonics of
the geopotential and amounts to 12.9%, according to EGM96 model. The role and
the importance of the LAGEOS--LAGEOS II Lense--Thirring experiment is
investigated. Using other suitable combinations with orbital elements of the
other existing laser-ranged satellites does not yield significative
improvements except for one combination including the nodes of LAGEOS, LAGEOS
II and Ajisai and the perigee of LAGEOS II. The related systematic error due to
the mismodelled even zonal part of the geopotential reduces to almost 10.7%.

categories: gr-qc astro-ph physics.geo-ph physics.space-ph


title: Binary Black Holes in Quasi-Stationary Circular Orbits

abstract:
  We propose a method of determining solutions to the constraint equations of
General Relativity approximately describing binary black holes in
quasi-stationary circular orbits. Black holes with arbitrary linear momenta are
constructed in the manner suggested by Brandt and Brugmann. The
quasi-stationary circular orbits are determined by local minima in the ADM mass
in a manner similar to Baumgarte and Cook; however, rather than fixing the area
of the apparent horizon, we fix the value of the bare masses of the holes. We
numerically generate an evolutionary sequence of quasi-stationary circular
orbits up to and including the innermost stable circular orbit. We compare our
results with post-Newtonian expectations as well as the results of Cook and
Baumgarte. We also generate additional numerical results describing the
dynamics of the geometry due to the emission of gravitational radiation.


title: Construction of hyperboloidal initial data

abstract:
  I describe the conformal method for constructing solutions of the
hyperboloidal constraint equations as well as the conditions needed on the free
data in order to have regularity up to boundary for the solutions to the
constraint equations. A brief discussion of the Einstein evolution equations in
the unphysical setting is given.


title: Cosmic Evolution as Inertial Motion in the Field Space of GR

abstract:
  The identification of a cosmic scale function with the volume integral of a
spacelike hypersurface defines the cosmic evolution in General Relativity as a
collective motion along a geodesic in the field space of the metric components,
considered as the coset of the affine group over the Lorentz one.
  The Friedmann equations are derived out of the homogeneous approximation by
the Gibbs averaging exact equations over the relative constant spatial volume.
  A direct correspondence between the collective cosmic motion and Special
  Relativity is established, to solve the problem of time and energy by analogy
with the solution of this problem for a relativistic particle by Poincare and
Einstein.
  A geometrical time interval is introduced into quantum theory of the
relativistic collective motion by the canonical Levi-Civita -- type
transformation in agreement with the correspondence principle with quantum
field theory. In this context the problem of quantum cosmological creation of
visible matter is formulated.
  We show that latest observational data can testify to the relative
measurement standard, and the cosmic evolution as an inertial motion along
geodesic in the field space.


title:
On arithmetic detection of grey pulses with application to Hawking
  radiation

abstract:
  Micron-sized black holes do not necessarily have a constant horizon
temperature distribution. The black hole remote-sensing problem means to find
out the `surface' temperature distribution of a small black hole from the
spectral measurement of its (Hawking) grey pulse. This problem has been
previously considered by Rosu, who used Chen's modified Moebius inverse
transform. Here, we hint on a Ramanujan generalization of Chen's modified
Moebius inverse transform that may be considered as a special wavelet
processing of the remote-sensed grey signal coming from a black hole or any
other distant grey source


title:
Exploiting gauge and constraint freedom in hyperbolic formulations of
  Einstein's equations

abstract:
  We present new many-parameter families of strongly and symmetric hyperbolic
formulations of Einstein's equations that include quite general algebraic and
live gauge conditions for the lapse. The first system that we present has 30
variables and incorporates an algebraic relationship between the lapse and the
determinant of the three metric that generalizes the densitized lapse
prescription. The second system has 34 variables and uses a family of live
gauges that generalizes the Bona-Masso slicing conditions. These systems have
free parameters even after imposing hyperbolicity and are expected to be useful
in 3D numerical evolutions. We discuss under what conditions there are no
superluminal characteristic speeds.


title:
The new cosmological scenario and dark matter fixed by general
  experimental facts

abstract:
  Both from gravitational (G) experiments and from a new theoretical approach
based on a particle model it is proved that the classical invariability of the
bodies, after a change of relative rest-position with respect to other bodies,
it is not true. The same holds for the traditional hypotheses based on the
classical one. The new relationships are strictly linear. From them it is
proved that a universe expansion must be associated with a G expansion of every
particle in it, in just the same proportion. It does not change the relative
distances, indefinitely. From the relative viewpoint, globally, the universe
must be rather static. According to the new cosmic scenario, galaxies must be
evolving, indefinitely, in rather closed cycles between luminous and black
states. The new kind of linear black hole must absorb radiation until it can
explode after releasing new H gas that would trigger new luminous period of
star clusters and galaxies. Statistically, most of the galaxies must be in cool
states. The last ones should account for all of them, the higher velocities of
the galaxies in clusters, the radiation coming from intergalactic space,
including the low temperature black-body background observed in the CMBR.


title: Bosonic and fermionic behavior in gravitational configurations

abstract:
  We extend Dirac's approach about the quantization of the electric charge to
the case of gravitational configurations. The spacetime curvature is used to
define a phase-like object which allows us to extract information about the
behavior of the corresponding spacetime. We show that all spacetimes that
satisfy certain simple symmetry condition and for which the Petrov type is the
same whitin a specific region, quantization conditions can be derived that
impose constraints on the possible values of the parameters entering the
respective metrics. As a general result we obtain that for the gravitational
configurations described by those metrics, the behavior under rotations can be
only of bosonic or fermionic nature.


title:
A five dimensional model of varying effective gravitational and fine
  structure constants

abstract:
  We explore the possibility that the reported time variation of the fine
structure constant $\alpha$ is due to a coupling between electromagnetism and
gravitation. This may reconcile the claimed results on $\alpha$ with the upper
limit from the Oklo naturel Uranium fission reactor.


title:
The Holography of Gravity encoded in a relation between Entropy, Horizon
  area and Action for gravity

abstract:
  I provide a general proof of the conjecture that one can attribute an entropy
to the area of {\it any} horizon. This is done by constructing a canonical
ensemble of a subclass of spacetimes with a fixed value for the temperature
$T=\beta^{-1}$ and evaluating the {\it exact} partition function $Z(\beta)$.
For spherically symmetric spacetimes with a horizon at $r=a$, the partition
function has the generic form $Z\propto \exp[S-\beta E]$, where $S= (1/4) 4\pi
a^2$ and $|E|=(a/2)$. Both $S$ and $E$ are determined entirely by the
properties of the metric near the horizon. This analysis reproduces the
conventional result for the black-hole spacetimes and provides a simple and
consistent interpretation of entropy and energy for De Sitter spacetime. For
the Rindler spacetime the entropy per unit transverse area turns out to be
$(1/4)$ while the energy is zero. Further, I show that the relationship between
entropy and area allows one to construct the action for the gravitational field
on the bulk and thus the full theory. In this sense, gravity is intrinsically
holographic.


title:
Long-wavelength approximation for string cosmology with barotropic
  perfect fluid

abstract:
  The field equations derived from the low energy string effective action with
a matter tensor describing a perfect fluid with a barotropic equation of state
are solved iteratively using the long-wavelength approximation, i.e. the field
equations are expanded by the number of spatial gradients. In the zero order, a
quasi-isotropic solution is presented and compared with the general solution of
the pure dilaton gravity. Possible cosmological models are analyzed from the
point of view of the pre-big bang scenario. The second order solutions are
found and their growing and decaying parts are studied.


title:
On the existence of conformally coupled scalar field hair for black
  holes in (anti-)de Sitter space

abstract:
  The Einstein-conformally coupled scalar field system is studied in the
presence of a cosmological constant. We consider a massless or massive scalar
field with no additional self-interaction, and spherically symmetric black hole
geometries. When the cosmological constant is positive, no scalar hair can
exist and the only solution is the Schwarzschild-de Sitter black hole. When the
cosmological constant is negative, stable scalar field hair exists provided the
mass of the scalar field is not too large.


title: Nonlinear realizations of Lorentz symmetry

abstract:
  This paper withdrawn -- it has been revised and merged with gr-qc/0205067
(Conservation laws in "Doubly Special Relativities"; Simon Judes and Matt
Visser)


title: Curvature singularity of the distributional BTZ black hole geometry

abstract:
  For the non-rotating BTZ black hole, the distributional curvature tensor
field is found. It is shown to have singular parts proportional to a
$\delta$-distribution with support at the origin. This singularity is related,
through Einstein field equations, to a point source. Coordinate invariance and
independence on the choice of differentiable structure of the results are
addressed.


title:
A Fortran Code for Null Geodesic Solutions in the Lemaitre-Tolman-Bondi
  Spacetime

abstract:
  This paper describes the Fortran 77 code SIMU, version 1.1, designed for
numerical simulations of observational relations along the past null geodesic
in the Lemaitre-Tolman-Bondi (LTB) spacetime. SIMU aims at finding scale
invariant solutions of the average density, but due to its full modularity it
can be easily adapted to any application which requires LTB's null geodesic
solutions. In version 1.1 the numerical output can be read by the GNUPLOT
plotting package to produce a fully graphical output, although other plotting
routines can be easily adapted. Details of the code's subroutines are
discussed, and an example of its output is shown.


title: Plasma waves driven by gravitational waves in an expanding universe

abstract:
  In a Friedmann-Robertson-Walker (FRW) cosmological model with zero spatial
curvature, we consider the interaction of the gravitational waves with the
plasma in the presence of a weak magnetic field. Using the relativistic
hydromagnetic equations it is verified that large amplitude magnetosonic waves
are excited, assuming that both, the gravitational field and the weak magnetic
field do not break the homogeneity and isotropy of the considered FRW
spacetime.


title:
Solution of Massless Spin One Wave Equation in Robertson-Walker
  Space-time

abstract:
  We generalize the quantum spinor wave equation for photon into the curved
space-time and discuss the solutions of this equation in Robertson-Walker
space-time and compare them with the solution of the Maxwell equations in the
same space-time.


title: Consequences of a Killing symmetry in spacetime's local structure

abstract:
  In this paper we discuss the consequences of a Killing symmetry on the local
geometrical structure of four-dimensional spacetimes. We have adopted the point
of view introduced in recent works where the exterior derivative of the Killing
plays a fundamental role. Then, we study some issues related with this approach
and clarify why in many circumstances its use has advantages with respect to
other approaches. We also extend the formalism developed in the case of vacuum
spacetimes to the general case of an arbitrary energy-momentum content.
Finally, we illustrate our framework with the case of spacetimes with a
gravitating electromagnetic field.


title: Gravity wave analogs of black holes

abstract:
  It is demonstrated that gravity waves of a flowing fluid in a shallow basin
can be used to simulate phenomena around black holes in the laboratory. Since
the speed of the gravity waves as well as their high-wavenumber dispersion
(subluminal vs. superluminal) can be adjusted easily by varying the height of
the fluid (and its surface tension) this scenario has certain advantages over
the sonic and dielectric black hole analogs, for example, although its use in
testing quantum effects is dubious. It can be used to investigate the various
classical instabilities associated with black (and white) holes experimentally,
including positive and negative norm mode mixing at horizons. PACS: 04.70.-s,
47.90.+a, 92.60.Dj, 04.80.-y.


title: Quantum Geometric Description of Cosmological Models

abstract:
  This is a written version of the review talk given at the meeting on
"Interface of Gravitational and Quantum Realms" at IUCAA, Pune during December
2001. The talk reviewed the recent work of Martin Bojowald on Loop Quantum
Cosmology.


title: Multidimensional Black Hole Solutions In Model With Perfect Fluid

abstract:
  A family of black-hole solutions in the model with 1-component perfect fluid
is obtained. The metric of any solution contains (n -1) Ricci-flat "internal
space" metrics and for certain equations of state coincides with the metric of
black brane (or black hole) solution in the model with antisymmetric form.
Certain examples (e.g. imitating M2 and M5 black branes) are considered. The
post-Newtonian parameters beta and gamma corresponding to the 4-dimensional
section of the metric are calculated.


title: Jacobi-like bar mode instability of relativistic rotating bodies

abstract:
  We perform some numerical study of the secular triaxial instability of
rigidly rotating homogeneous fluid bodies in general relativity. In the
Newtonian limit, this instability arises at the bifurcation point between the
Maclaurin and Jacobi sequences. It can be driven in astrophysical systems by
viscous dissipation. We locate the onset of instability along several constant
baryon mass sequences of uniformly rotating axisymmetric bodies for compaction
parameter $M/R = 0-0.275$. We find that general relativity weakens the Jacobi
like bar mode instability, but the stabilizing effect is not very strong.
According to our analysis the critical value of the ratio of the kinetic energy
to the absolute value of the gravitational potential energy $(T/|W|)_{\rm
crit}$ for compaction parameter as high as 0.275 is only 30% higher than the
Newtonian value. The critical value of the eccentricity depends very weakly on
the degree of relativity and for $M/R=0.275$ is only 2% larger than the
Newtonian value at the onset for the secular bar mode instability. We compare
our numerical results with recent analytical investigations based on the
post-Newtonian expansion.


title: Quantum gravity corrections to particle interactions

abstract:
  An heuristic semiclassical procedure that incorporates quantum gravity
induced corrections in the description of photons and spin 1/2 fermions is
reviewed. Such modifications are calculated in the framework of loop quantum
gravity and they arise from the granular structure of space at short distances.
The resulting effective theories are described by power counting
nonrenormalizable actions which exhibit Lorentz violations at Planck length
scale. The modified Maxwell and Dirac equations lead to corrections of the
energy momentum relations for the corresponding particle at such scale. An
action for the relativistic point particle exhibiting such modified dispersion
relations is constructed and the first steps towards the study of a consistent
coupling between these effective theories are presented.


title: Vacuum selection by inflation as the origin of the dark energy

abstract:
  I propose a new mechanism to account for the observed tiny but finite dark
energy in terms of a non-Abelian Higgs theory, which has infinitely many
perturbative vacua characterized by a winding number, in the framework of
inflationary cosmology. Inflation homogenizes field configuration and
practically realizes a perturbative vacuum with vanishing winding number, which
is expressed by a superposition of eigenstates of the Hamiltonian with
different vacuum energy density. As a result, we naturally find a nonvanishing
vacuum energy density with fairly large probability, under the assumption that
the cosmological constant vanishes in some vacuum state. Since the predicted
magnitude of dark energy is exponentially suppressed by the instanton action,
we can fit observation without introducing any tiny parameters.


title:
The Scalar Ether-Theory of Gravitation and its First Test in Celestial
  Mechanics

abstract:
  The motivations for investigating a theory of gravitation based on a concept
of "ether" are discussed-- a crucial point is the existence of an alternative
interpretation of special relativity, named the Lorentz-Poincar\'e ether
theory. The basic equations of one such theory of gravity, based on just one
scalar field, are presented. To check this theory in celestial mechanics, an
"asymptotic" scheme of post-Newtonian (PN) approximation is summarized and its
difference with the standard PN scheme is emphasized. The derivation of PN
equations of motion for the mass centers, based on the asymptotic scheme, is
outlined. They are implemented for the major bodies of the solar system and the
prediction for Mercury is compared with an ephemeris based on general
relativity.


title: Black Hole Remnants and Dark Matter

abstract:
  We argue that, when the gravity effect is included, the generalized
uncertainty principle (GUP) may prevent black holes from total evaporation in a
similar way that the standard uncertainty principle prevents the hydrogen atom
from total collapse. Specifically we invoke the GUP to obtain a modified
Hawking temperature, which indicates that there should exist non-radiating
remnants (BHR) of about Planck mass. BHRs are an attractive candidate for cold
dark matter. We investigate an alternative cosmology in which primordial BHRs
are the primary source of dark matter.


title: Perturbations of an exact solution for 2+1 dimensional critical collapse

abstract:
  We find the perturbation spectrum of a family of spherically symmetric and
continuously self-similar (CSS) exact solutions that appear to be relevant for
the critical collapse of scalar field matter in 2+1 spacetime dimensions. The
rate of exponential growth of the unstable perturbation yields the critical
exponent. Our results are compared to the numerical simulations of Pretorius
and Choptuik and are inconclusive: We find a CSS solution with exactly one
unstable mode, which suggests that it may be the critical solution, but another
CSS solution which has three unstable modes fits the numerically found critical
solution better.


title:
Reconcile Planck-scale discreteness and the Lorentz-Fitzgerald
  contraction

abstract:
  A Planck-scale minimal observable length appears in many approaches to
quantum gravity. It is sometimes argued that this minimal length might conflict
with Lorentz invariance, because a boosted observer could see the minimal
length further Lorentz contracted. We show that this is not the case within
loop quantum gravity. In loop quantum gravity the minimal length (more
precisely, minimal area) does not appear as a fixed property of geometry, but
rather as the minimal (nonzero) eigenvalue of a quantum observable. The boosted
observer can see the same observable spectrum, with the same minimal area. What
changes continuously in the boost transformation is not the value of the
minimal length: it is the probability distribution of seeing one or the other
of the discrete eigenvalues of the area. We discuss several difficulties
associated with boosts and area measurement in quantum gravity. We compute the
transformation of the area operator under a local boost, propose an explicit
expression for the generator of local boosts and give the conditions under
which its action is unitary.


title:
Uniqueness of Self-Similar Asymptotically Friedmann-Robertson-Walker
  Spacetime in Brans-Dicke theory

abstract:
  We investigate spherically symmetric self-similar solutions in Brans-Dicke
theory. Assuming a perfect fluid with the equation of state $p=(\gamma-1)\mu (1
\le \gamma<2)$, we show that there are no non-trivial solutions which approach
asymptotically to the flat Friedmann-Robertson-Walker spacetime if the energy
density is positive. This result suggests that primordial black holes in
Brans-Dicke theory cannot grow at the same rate as the size of the cosmological
particle horizon.


title: Variational Principles in General Relativity

abstract:
  This thesis details an effort to generate astrophysically interesting
solutions to the two-body problem in General Relativity. The thesis consists of
two main parts. The first part presents an analytical variational principle for
describing binary neutron stars undergoing irrotational fluid flow. The
variational principle is a powerful tool for generating accurate estimates of
orbital parameters for neutron stars in quasi-equilibrium orbits. The second
part of the thesis details the numerical application of the variational
principle by solving the initial value problem for binary black holes in quasi-
equilibrium circular orbits. The analysis draws from the novel ``puncture''
method of describing the black holes, and relies on nonlinear adaptive
multigrid techniques for generating numerical results. We arrive at two
important conclusions. First, the analytical variational principle describing
binary neutron stars in irrotational motion provides a road map for future
numerical simulations, and also lends credence to previous simulations by other
authors. Second, the numerical application and description of binary black
holes in quasi-equilibrium circular orbits simplifies the analyses of previous
authors, and allows for the imposition of realistic boundary data in
simulations with relatively high grid densities. Both the variational principle
and its application are used to generate accurate estimates of the orbital
parameters.


title: New Vistas in Braneworld Cosmology

abstract:
  Traditionally, higher-dimensional cosmological models have sought to provide
a description of the fundamental forces in terms of a unifying geometrical
construction. In this essay we discuss how, in their present incarnation,
higher-dimensional `braneworld' models might provide answers to a number of
cosmological puzzles including the issue of dark energy and the nature of the
big-bang singularity.


title: Non-unitary HD gravity classically equivalent to Einstein gravity

abstract:
  Runaway solutions can be avoided in fourth order gravity by a doubling of the
matter operator algebra with a symmetry constraint with respect to the exchange
of observable and hidden degrees of freedom together with the change in sign of
the ghost and the dilaton fields. The theory is classically equivalent to
Einstein gravity, while its non-unitary Newtonian limit is compatible with the
wavelike properties of microscopic particles and the classical behavior of
macroscopic bodies, as well as with a trans-Planckian regularization of
collapse singularities. A unified reading of ordinary and black hole entropy
emerges as entanglement entropy with hidden degrees of freedom.


title: Gravity sans singularities

abstract:
  Basis and limitations of singularity theorems for Gravity are examined. As
singularity is a critical situation in course of time, study of time paths, in
full generality of Equivalence principle, provides two mechanisms to prevent
singularity. Resolution of singular Time translation generators into space of
its orbits, and essential higher dimensions for Relativistic particle
interactions has facets to resolve any real singularity problem. Conceptually,
these varied viewpoints have a common denominator: arbitrariness in the
definition of `energy' intrinsic to the space of operation in each case, so as
to render absence of singularity a tautology for self-consistency of the
systems.


title: Recoil and Ring--Down Effects in Gravitation

abstract:
  We construct a model of a relativistic fireball or light--like shell of
matter by considering a spherically symmetric moving gravitating mass
experiencing an impulsive deceleration to rest. We take this event to be
followed by the mass undergoing a deformation leading to the emission of
gravitational radiation while it returns to a spherically symmetric state. We
find that the fireball is accompanied by an impulsive gravitational wave.


title: Room temperature GW bar detector with opto-mechanical readout

abstract:
  We present the full implementation of a room-temperature gravitational wave
bar detector equipped with an opto-mechanical readout. The mechanical
vibrations are read by a Fabry--Perot interferometer whose length changes are
compared with a stable reference optical cavity by means of a resonant laser.
The detector performance is completely characterized in terms of spectral
sensitivity and statistical properties of the fluctuations in the system output
signal. The new kind of readout technique allows for wide-band detection
sensitivity and we can accurately test the model of the coupled oscillators for
thermal noise. Our results are very promising in view of cryogenic operation
and represent an important step towards significant improvements in the
performance of massive gravitational wave detectors.


title:
Generalized de Sitter solution in multidimensional cosmology with static
  internal spaces

abstract:
  A multidimensional cosmological model with space-time consisting of n (n>1)
Einstein spaces M_i is investigated in the presence of a cosmological constant
Lambda and a homogeneous minimally coupled free scalar field. Generalized de
Sitter solution was found for Lambda > 0 and Ricci-flat external space for the
case of static internal spaces with fine tuning of parameters.


title: Five dimensional relativity and two times

abstract:
  It is possible that null paths in 5D appear as the timelike paths of massive
particles in 4D, where there is an oscillation in the fifth dimension around
the hypersurface we call spacetime. A particle in 5D may be regarded as
multiply imaged in 4D, and the 4D weak equivalence principle may be regarded as
a symmetry of the 5D metric.


title: Strong-coupled Relativity without Relativity

abstract:
  GR can be interpreted as a theory of evolving 3-geometries. A recent such
formulation, the 3-space approach of Barbour, Foster and \'{O} Murchadha, also
permits the construction of a limited number of other theories of evolving
3-geometries, including conformal gravity and strong gravity. In this paper, we
use the 3-space approach to construct a 1-parameter family of theories which
generalize strong gravity. The usual strong gravity is the strong-coupled limit
of GR, which is appropriate near singularities and is one of very few regimes
of GR which is amenable to quantization. Our new strong gravity theories are
similar limits of scalar-tensor theories such as Brans--Dicke theory, and are
likewise appropriate near singularities. They represent an extension of the
regime amenable to quantization, which furthermore spans two qualitatively
different types of inner product.
  We find that strong gravity theories permit coupling only to ultralocal
matter fields and that they prevent gauge theory. Thus in the classical
picture, gauge theory breaks down (rather than undergoing unification) as one
approaches the GR initial singularity.


title:
Is there a Darwinian Evolution of the Cosmos? - Some Comments on Lee
  Smolin's Theory of the Origin of Universes by Means of Natural Selection

abstract:
  For Lee Smolin, our universe is only one in a much larger cosmos (the
Multiverse) - a member of a growing community of universes, each one being born
in a bounce following the formation of a black hole. In the course of this, the
values of the free parameters of the physical laws are reprocessed and slightly
changed. This leads to an evolutionary picture of the Multiverse, where
universes with more black holes have more descendants. Smolin concludes, that
due to this kind of Cosmological Natural Selection our own universe is the way
it is. The hospitality for life of our universe is seen as an offshot of this
self-organized process. - This paper outlines Smolin's hypothesis, its
strength, weakness and limits, its relationship to the anthropic principle and
evolutionary biology, and comments on the hypothesis from different points of
view: physics, biology, philosophy of science, philosophy of nature, and
metaphysics. Some of the main points are: (1) There is no necessary connection
between black holes and life. In principle, life and Cosmological Natural
Selection could be independent of each other. Smolin might explain the
so-called fine-tuning of physical constants, but life remains an epiphenomenon.
(2) The Darwinian analogy is an inadequate model transfer. The fitness of
Smolin's universes is not constrained by its environment, but by only one
internal factor: the numbers of black holes. Furthermore, although Smolin's
universes have different reproduction rates, they are not competing against
each other. (3) Smolin's central claim cannot be falsified.


title:
Nongeodesic motion of spinless particles in the teleparallel
  gravitational wave background

abstract:
  The motion of spinless particles in Riemann-Cartan (RC) $U_{4}$ and
teleparallel spacetimes is revisited on the light of gravitational waves
hitting on the spinless test particles. It is shown that in the case Cartan
contortion is totally skew-symmetric the spinless particles follow geodesics
but if this symmetry is dropped they are able to follow nongeodesic worldlines
in torsionic background. The case of totally skew contortion and spinning
particles may appear either in $T_{4}$ or $U_{4}$ spacetimes. We consider
$T_{4}$ nongeodesic motion of spinless test particles in the field of
gravitational waves (GW). It is shown that the general contortion obeys a
tensor wave constraint and the analysis of a ring of spinless test particles as
in General Relativity (GR) hit by the GW leads to damping contortion effects on
the nongeodesic motion is undertaken. It is also shown that the contortion and
gravitational waves possess a difference of phase of $\frac{\pi}{2}$ and a
contortion at the surface of the Earth of $10^{-24} s^{-1}$ computed by Nitsch
in the realm of teleparallelism is used to obtain a deviation of the lenght of
the separation of test spinless particles compatible with the GR result. To
obtain this result data from GW LISA detector is used.


title: Interface of Gravitational and Quantum Realms

abstract:
  The talk centers around the question: Can general-relativistic description of
physical reality be considered complete? On the way I argue how -- unknown to
many a physicists, even today -- the ``forty orders of magnitude argument''
against quantum gravity phenomenology was defeated more than a quarter of a
century ago, and how we now stand at the possible verge of detecting a signal
for the spacetime foam, and studying the gravitationally-modified wave particle
duality using superconducting quantum interference devices.


title:
Detection template families for gravitational waves from the final
  stages of binary--black-hole inspirals: Nonspinning case

abstract:
  We investigate the problem of detecting gravitational waves from binaries of
nonspinning black holes with masses m = 5--20 Msun, moving on quasicircular
orbits, which are arguably the most promising sources for first-generation
ground-based detectors. We analyze and compare all the currently available
post--Newtonian approximations for the relativistic two-body dynamics; for
these binaries, different approximations predict different waveforms. We then
construct examples of detection template families that embed all the
approximate models, and that could be used to detect the true
gravitational-wave signal (but not to characterize accurately its physical
parameters). We estimate that the fitting factor for our detection families is
>~0.95 (corresponding to an event-rate loss <~15%) and we estimate that the
discretization of the template family, for ~10^4 templates, increases the loss
to <~20%.


title:
Canonical quantization of constrained theories on discrete space-time
  lattices

abstract:
  We discuss the canonical quantization of systems formulated on discrete
space-times. We start by analyzing the quantization of simple mechanical
systems with discrete time. The quantization becomes challenging when the
systems have anholonomic constraints. We propose a new canonical formulation
and quantization for such systems in terms of discrete canonical
transformations. This allows to construct, for the first time, a canonical
formulation for general constrained mechanical systems with discrete time. We
extend the analysis to gauge field theories on the lattice. We consider a
complete canonical formulation, starting from a discrete action, for lattice
Yang--Mills theory discretized in space and Maxwell theory discretized in space
and time. After completing the treatment, the results can be shown to coincide
with the results of the traditional transfer matrix method. We then apply the
method to BF theory, yielding the first lattice treatment for such a theory
ever. The framework presented deals directly with the Lorentzian signature
without requiring an Euclidean rotation. The whole discussion is framed in such
a way as to provide a formalism that would allow a consistent, well defined,
canonical formulation and quantization of discrete general relativity, which we
will discuss in a forthcoming paper.


title:
Model of Thermal Wavefront Distortion in Interferometric
  Gravitational-Wave Detectors I: Thermal Focusing

abstract:
  We develop a steady-state analytical and numerical model of the optical
response of power-recycled Fabry-Perot Michelson laser gravitational-wave
detectors to thermal focusing in optical substrates. We assume that the thermal
distortions are small enough that we can represent the unperturbed intracavity
field anywhere in the detector as a linear combination of basis functions
related to the eigenmodes of one of the Fabry-Perot arm cavities, and we take
great care to preserve numerically the nearly ideal longitudinal phase
resonance conditions that would otherwise be provided by an external
servo-locking control system. We have included the effects of nonlinear thermal
focusing due to power absorption in both the substrates and coatings of the
mirrors and beamsplitter, the effects of a finite mismatch between the
curvatures of the laser wavefront and the mirror surface, and the diffraction
by the mirror aperture at each instance of reflection and transmission. We
demonstrate a detailed numerical example of this model using the MATLAB program
Melody for the initial LIGO detector in the Hermite-Gauss basis, and compare
the resulting computations of intracavity fields in two special cases with
those of a fast Fourier transform field propagation model. Additional
systematic perturbations (e.g., mirror tilt, thermoelastic surface
deformations, and other optical imperfections) can be included easily by
incorporating the appropriate operators into the transfer matrices describing
reflection and transmission for the mirrors and beamsplitter.


title:
On the fate of Lorentz symmetry in loop quantum gravity and
  noncommutative spacetimes

abstract:
  I analyze the deformation of Lorentz symmetry that holds in certain
noncommutative spacetimes and the way in which Lorentz symmetry is broken in
other noncommutative spacetimes. I also observe that discretization of areas
does not necessarily require departures from Lorentz symmetry. This is due to
the fact that Lorentz symmetry has no implications for exclusive measurement of
the area of a surface, but it governs the combined measurements of the area and
the velocity of a surface. In a quantum-gravity theory Lorentz symmetry can be
consistent with area discretization, but only when the observables ``area of
the surface" and "velocity of the surface" enjoy certain special properties. I
argue that the status of Lorentz symmetry in the loop-quantum-gravity approach
requires careful scrutiny, since areas are discretized within a formalism that,
at least presently, does not include an observable "velocity of the surface".
In general it may prove to be very difficult to reconcile Lorentz symmetry with
area discretization in theories of canonical quantization of gravity, because a
proper description of Lorentz symmetry appears to require that the
fundamental/primary role be played by the surface's world-sheet, whose
"projection" along the space directions of a given observer describes the
observable area, whereas the canonical formalism only allows the introduction
as primary entities of observables defined at a fixed (common) time, and the
observers that can be considered must share that time variable.


title: The 550 AU Mission: A Critical Discussion

abstract:
  We have studied the science rationale, goals and requirements for a mission
aimed at using the gravitational lensing from the Sun as a way of achieving
high angular resolution and high signal amplification. We find that such a
mission concept is plagued by several practical problems. Most severe are the
effects due to the plasma in the solar atmosphere which cause refraction and
scattering of the propagating rays. These effects limit the frequencies that
can be observed to those above $\sim$100-200 GHz and moves the optical point
outwards beyond the vacuum value of $\geq$ 550 AU. Density fluctuations in the
inner solar atmosphere will further cause random pathlength differences for
different rays. The corrections for the radiation from the Sun itself will also
be a major challenge at any wavelength used. Given reasonable constraints on
the spacecraft (particularly in terms of size and propulsion) source selection
as well as severe navigational constraints further add to the difficulties for
a potential mission.


title: Black holes: A physical route to the Kerr metric

abstract:
  As a consequence of Birkhoff's theorem, the exterior gravitational field of a
spherically symmetric star or black hole is always given by the Schwarzschild
metric. In contrast, the exterior gravitational field of a rotating
(axisymmetric) star differs, in general, from the Kerr metric, which describes
a stationary, rotating black hole.
  In this paper, I discuss the possibility of a quasi-stationary transition
from rotating equilibrium configurations of normal matter to rotating black
holes.


title: Thermodynamical Properties of Horizons

abstract:
  We show, by using Regge calculus, that the entropy of any finite part of a
Rindler horizon is, in the semi-classical limit, one quarter of the area of
that part. We argue that this result implies that the entropy associated with
any horizon of spacetime is, in semi-classical limit, one quarter of its area.
As an example, we derive the Bekenstein-Hawking entropy law for the
Schwarzschild black hole.


title: Bulk shape of brane-world black holes

abstract:
  We propose a method to extend into the bulk asymptotically flat static
spherically symmetric brane-world metrics. We employ the multipole (1/r)
expansion in order to allow exact integration of the relevant equations along
the (fifth) extra coordinate and make contact with the parameterized
post-Newtonian formalism. We apply our method to three families of solutions
previously appeared as candidates of black holes in the brane world and show
that the shape of the horizon is very likely a flat ``pancake'' for
astrophysical sources.


title: One Loop Vaccum Polarization in a Locally de Sitter Background

abstract:
  We compute the one loop vacuum polarization from massless, minimally coupled
scalar QED in a locally de Sitter background. Gauge invariance is maintained
through the use of dimensional regularization, whereas conformal invariance is
explicitly broken by the scalar kinetic term as well as through the conformal
anomaly. A fully renormalized result is obtained. The one loop corrections to
the linearized, effective field equations do not vanish when evaluated
on-shell. In fact the on-shell one loop correction depends quadratically on the
inflationary scale factor, similar to a photon mass. The contribution from the
conformal anomaly is insignificant by comparison.


title:
Charged wormholes with non-minimally coupled scalar fields. Existence
  and stability

abstract:
  Static, spherically symmetric, traversable wormhole solutions with electric
or magnetic charges are shown to exist in general relativity in the presence of
scalar fields nonminimally coupled to gravity. These wormholes, however, turn
out to be unstable under spherically symmetric perturbations. The instability
is related to blowing-up of the effective gravitational constant on a certain
sphere.


title: Higher dimensional gravity invariant under the Poincare group

abstract:
  It is shown that the Stelle-West Grignani-Nardelli-formalism allows, both
when odd dimensions and when even dimensions are considered, constructing
actions for higher dimensional gravity invariant under local Lorentz rotations
and under local Poincar\`{e} translations. It is also proved that such actions
have the same coefficients as those obtained by Troncoso and Zanelli in ref.
Class. Quantum Grav. 17 (2000) 4451.


title: A phase transition model for metric fluctuations in vacuum

abstract:
  Regarding metric fluctuations as generating {\it roughness} on the fabric of
the otherwise smooth vacuum, it is shown that in its simplest form, the effect
can be described by the scalar $\phi^4$ model. The model exhibits a second
order phase transition between a smooth (low-temperature) phase and a rough
(high-temperature) one, corroborating the absence of metric fluctuations at low
energies. In the rough phase near the critical point, vacuum is characterized
by a power-law behavior for the fluctuating field with critical exponent $\beta
\approx 0.33$.


title: Static Negative Energies Near a Domain Wall

abstract:
  We show that a system of a domain wall coupled to a scalar field has static
negative energy density at certain distances from the domain wall. This system
provides a simple, explicit example of violation of the averaged weak energy
condition and the quantum inequalities by interacting quantum fields. Unlike
idealized systems with boundary conditions or external background fields, this
calculation is implemented precisely in renormalized quantum field theory with
the energy necessary to support the background field included
self-consistently.


title:
The r-modes in accreting neutron stars with magneto-viscous boundary
  layers

abstract:
  We explore the dynamics of the r-modes in accreting neutron stars in two
ways. First, we explore how dissipation in the magneto-viscous boundary layer
(MVBL) at the crust-core interface governs the damping of r-mode perturbations
in the fluid interior. Two models are considered: one assuming an
ordinary-fluid interior, the other taking the core to consist of superfluid
neutrons, type II superconducting protons, and normal electrons. We show,
within our approximations, that no solution to the magnetohydrodynamic
equations exists in the superfluid model when both the neutron and proton
vortices are pinned. However, if just one species of vortex is pinned, we can
find solutions. When the neutron vortices are pinned and the proton vortices
are unpinned there is much more dissipation than in the ordinary-fluid model,
unless the pinning is weak. When the proton vortices are pinned and the neutron
vortices are unpinned the dissipation is comparable or slightly less than that
for the ordinary-fluid model, even when the pinning is strong. We also find in
the superfluid model that relatively weak radial magnetic fields ~ 10^9 G (10^8
K / T)^2 greatly affect the MVBL, though the effects of mutual friction tend to
counteract the magnetic effects. Second, we evolve our two models in time,
accounting for accretion, and explore how the magnetic field strength, the
r-mode saturation amplitude, and the accretion rate affect the cyclic evolution
of these stars. If the r-modes control the spin cycles of accreting neutron
stars we find that magnetic fields can affect the clustering of the spin
frequencies of low mass x-ray binaries (LMXBs) and the fraction of these that
are currently emitting gravitational waves.


title: Dynamical instability of differentially rotating stars

abstract:
  We study the dynamical instability against bar-mode deformation of
differentially rotating stars. We performed numerical simulation and linear
perturbation analysis adopting polytropic equations of state with the
polytropic index $n=1$. It is found that rotating stars of a high degree of
differential rotation are dynamically unstable even for the ratio of the
kinetic energy to the gravitational potential energy of $O(0.01)$.
Gravitational waves from the final nonaxisymmetric quasistationary states are
calculated in the quadrupole formula. For rotating stars of mass $1.4M_{\odot}$
and radius several 10 km, gravitational waves have frequency several 100 Hz and
effective amplitude $\sim 5 \times 10^{-22}$ at a distance of $\sim 100$ Mpc.


title: A fast apparent horizon algorithm

abstract:
  I present a fast algorithm to find apparent horizons. This algorithm uses an
explicit representation of the horizon surface, allowing for arbitrary horizon
resolutions and, in principle, shapes. Novel in this approach is that the
tensor quantities describing the horizon live directly on the horizon surface,
yet are represented using Cartesian coordinate components. This eliminates
coordinate singularities, and leads to an efficient implementation. The
apparent horizon equation is then solved as a nonlinear elliptic equation with
standard methods. I explain in detail the coordinate systems used to store and
represent the tensor components of the intermediate quantities, and describe
the grid boundary conditions and the treatment of the polar coordinate
singularities. Last I give as examples apparent horizons for single and
multiple black hole configurations.


title:
Hypercomplex Numbers, Associated Metric Spaces, and Extension of
  Relativistic Hyperboloid

abstract:
  We undertake to develop a successful framework for commutative-associative
hypercomplex numbers with the view to explicate and study associated geometric
and generalized-relativistic concepts, basing on an interesting possibility to
introduce appropriate multilinear metric forms in the treatment. The scalar
polyproduct, which extends the ordinary scalar product used in bilinear
(Euclidean and pseudo-Euclidean) theories, has been proposed and applied to be
a generalized metric base for the approach. A fundamental concept of
multilinear isometry is proposed. This renders possible to muse upon various
relativistic physical applications based on anisotropic {\it versus} ordinary
spatially-rotational case.


title: Coupling gravitomagnetism-spin and Berry's phase

abstract:
  Resorting to Berry's phase, a new idea to detect, at quantum level, the
gravitomagnetic field of any metric theory of gravity, is put forward.
  It is found in this proposal that the magnitude of the gravitomagnetic field
appears only in the definition of the adiabatic regime, but not in the
magnitude of the emerging geometric phase. In other words, the physical
parameter to be observed does not involve, in a direct way, (as in the usual
proposals) the tiny magnitude of the gravitomagnetic field.


title:
Generalized Uncertainty Principle and deformed dispersion relation
  induced by nonconformal metric fluctuations

abstract:
  Considering the existence of nonconformal stochastic fluctuations in the
metric tensor a generalized uncertainty principle and a deformed dispersion
relation (associated to the propagation of photons) are deduced. Matching our
model with the so called quantum kappa--Poincare group will allow us to deduce
that the fluctuation--dissipation theorem could be fulfilled without needing a
restoring mechanism associated with the intrinsic fluctuations of spacetime. In
other words, the loss of quantum information is related to the fact that the
spacetime symmetries are described by the quantum kappa--Poincare group, and
not by the usual Poincare symmetries. An upper bound for the free parameters of
this model will also be obtained.


title: Gravitational and torsion waves in linearised teleparallel gravity

abstract:
  Spin-2, spin-1 and spin-0 modes in linearised teleparallelism are obtained
where the totally skew-symmetric complex contortion tensor generates scalar
torsion waves and the symmetric contortion in the last two indices generates
gravitational waves as gravitational perturbations of flat spacetime with
contortion tensor. A gedanken experiment with this gravitational-torsion wave
hitting a ring of spinless particles is proposed which allows us to estimate
the contortion of the Earth by making use of data from LISA GW detector. This
value coincides with previous value obtained by Nitsch in teleparallelism using
another type of experiment.


title: Introduction to Isolated Horizons in Numerical Relativity

abstract:
  We present a coordinate-independent method for extracting mass (M) and
angular momentum (J) of a black hole in numerical simulations. This method,
based on the isolated horizon framework, is applicable both at late times when
the black hole has reached equilibrium, and at early times when the black holes
are widely separated. We show how J and M can be determined in numerical
simulations in terms of only those quantities which are intrinsic to the
apparent horizon. We also present a numerical method for finding the rotational
symmetry vector field (required to calculate J) on the horizon.


title: Analysis of a Shell System in General Relativity

abstract:
  This Thesis concerns a thin fluid shell embedded in its own gravitational
field. The starting point is a work of Hajicek and Kijowski, where the
hamiltonian formalism for shell(s) (with no symmetry) in Einstein gravity is
developed. An open problem at the end of that paper is to show how the
hamiltonian formalism defines a regular constrained system: the hamiltonian and
the constraints must be differentiable functionals on the phase space, so that
their Poisson Brackets are well defined objects. On the contrary, some
constraints at the shell result to be non differentiable functionals on the
phase space. This problem is tackled, in the present thesis, by following the
reduction procedure suggested by Teitelboim and Henneaux: the singular
constraints are solved and the solution is substituted back into the
hamiltonian. The resulting hamiltonian is shown to lead to equivalent dynamics,
without singular constraints. Besides, the final reduced system (hamiltonian
plus canonical constraints) is shown to be fully differentiable on the reduced
phase space.


title:
Collision of spinning black holes in the close limit: The parallel spin
  case

abstract:
  In this paper we consider the collision of black holes with parallel spins
using first order perturbation theory of rotating black holes (Teukolsky
formalism). The black holes are assumed to be close to each other, initially
non boosted and spinning slowly. We estimate the properties of the
gravitational radiation released from such an collision. The same problem was
studied recently by Gleiser {\em et al.} in the context of the Zerilli
perturbation formalism and our results for waveforms, energy and angular
momentum radiated agree very well with the results presented in that work.


title:
Force measurements of a superconducting-film actuator for a cryogenic
  interferometric gravitational-wave detector

abstract:
  We measured forces applied by an actuator with a YBCO film at near 77 K for
the Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. An
actuator consisting of both a YBCO film of 1.6 micrometers thickness and 0.81
square centimeters area and a solenoid coil exerted a force of up to 0.2 mN on
a test mass. The presented actuator system can be used to displace the mirror
of LCGT for fringe lock of the interferometer.


title:
Survival of the black hole's Cauchy horizon under non-compact
  perturbations

abstract:
  We study numerically the evolution of spactime, and in particular of a
spacetime singularity, inside a black hole under a class of perturbations of
non-compact support. We use a very simplified toy model of a spherical charged
black hole which is perturbed nonlinearly by a self-gravitating, spherical
scalar field. The latter grows logarithmically with advanced time along an
outgoing characteristic hypersurface. We find that for that class of
perturbations a portion of the Cauchy horizon survives as a non-central, null
singularity.


title: Notes on static cylindrical shells

abstract:
  Static cylindrical shells made of various types of matter are studied as
sources of the vacuum Levi-Civita metrics. Their internal physical properties
are related to the two essential parameters of the metrics outside. The total
mass per unit length of the cylinders is always less than 1/4. The results are
illustrated by a number of figures.


title: Horizons and Geodesics of Black Ellipsoids

abstract:
  We analyze the horizon and geodesic structure of a class of 4D off--diagonal
metrics with deformed spherical symmetries, which are exact solutions of the
vacuum Einstein equations with anholonomic variables. The maximal analytic
extension of the ellipsoid type metrics are constructed and the Penrose
diagrams are analyzed with respect to adapted frames. We prove that for small
deformations (small eccentricities) there are such metrics that the geodesic
behaviour is similar to the Schwarzcshild one. We conclude that some vacuum
static and stationary ellipsoid configurations may describe black ellipsoid
objects.

categories: gr-qc astro-ph hep-th math-ph math.DG math.MP


title:
Horizons and Geodesics of Black Ellipsoids with Anholonomic Conformal
  Symmetries

abstract:
  The horizon and geodesic structure of static configurations generated by
anisotropic conformal transforms of the Schwarzschild metric is analyzed. We
construct the maximal analytic extension of such off--diagonal vacuum metrics
and conclude that for small deformations there are different classes of vacuum
solutions of the Einstein equations describing "black ellipsoid" objects. This
is possible because, in general, for off--diagonal metrics with deformed
non--spherical symmetries and associated anholonomic frames the conditions of
the uniqueness black hole theorems do not hold.


title: Perturbations and Stability of Black Ellipsoids

abstract:
  We study the perturbations of two classes of static black ellipsoid solutions
of four dimensional vacuum Einstein equations. Such solutions are described by
generic off--diagonal metrics which are generated by anholonomic transforms of
diagonal metrics. The analysis is performed in the approximation of small
eccentricity deformations of the Schwarzschild solution. We conclude that such
anisotropic black hole objects may be stable with respect to the perturbations
parametrized by the Schrodinger equations in the framework of the
one--dimensional inverse scattering theory.


title: LISA data analysis I: Doppler demodulation

abstract:
  The orbital motion of the Laser Interferometer Space Antenna (LISA) produces
amplitude, phase and frequency modulation of a gravitational wave signal. The
modulations have the effect of spreading a monochromatic gravitational wave
signal across a range of frequencies. The modulations encode useful information
about the source location and orientation, but they also have the deleterious
affect of spreading a signal across a wide bandwidth, thereby reducing the
strength of the signal relative to the instrument noise. We describe a simple
method for removing the dominant, Doppler, component of the signal modulation.
The demodulation reassembles the power from a monochromatic source into a
narrow spike, and provides a quick way to determine the sky locations and
frequencies of the brightest gravitational wave sources.


title:
Thermodynamics of black holes with an infinite effective area of a
  horizon

abstract:
  In some kinds of classical dilaton theory there exist black holes with (i)
infinite horizon area $A$ or infinite $F$ (the coefficient at curvature in
Lagrangian) and (ii) zero Hawking temperature $T_{H}$. For a generic static
black hole, without an assumption about spherical symmetry, we show that
infinite $A$ is compatible with a regularity of geometry in the case $T_{H}=0$
only. We also point out that infinite $T_{H}$ is incompatible with the
regularity of a horizon of a generic static black hole, both for finite or
infinite $A$. Direct application of the standard Euclidean approach in the case
of an infinite ''effective'' area of the horizon $A_{eff}=AF$ leads to
inconsistencies in the variational principle and gives for a black hole entropy
$S$ an indefinite expression, formally proportional to $T_{H}A_{eff}$. We show
that treating a horizon as an additional boundary (that is, adding to the
action some terms calculated on the horizon) may restore self-consistency of
the variational procedure, if $F$ near the horizon grows not too rapidly. We
apply this approach to Brans-Dicke black holes and obtain the same answer S=0
as for ''usual'' (for example, Reissner-Nordstr\"{o}m) extreme classical black
holes. We also consider the exact solution for a conformal coupling, when $A$
is finite but $F$ diverges and find that in the latter case both the standard
and modified approach give rise to an infinite action. Thus, this solution
represents a rare exception of a black hole without nontrivial thermal
properties.


title: Rotating cylindrical shell source for Lewis spacetime

abstract:
  Rotating thin-shell-like sources for the stationary cylindrically symmetric
vacuum solutions (Lewis) are constructed and studied. It is found, by imposing
the non existence of timelike curves in the exterior of the shell, and that the
source satisfies the weak, dominant and strong energy conditions that the
parameters, commonly denoted by $a$ and $\sigma$, are restricted to $0 \le
\sigma \le 1/4$ when $a > 0$, or $1/4 \le \sigma \le 1/2$ when $a < 0$.


title: Topology change in quantum gravity

abstract:
  A particular approach to topology change in quantum gravity is reviewed,
showing that several aspects of Stephen's work are intertwined with it in an
essential way. Speculations are made on possible implications for the causal
set approach to quantum gravity.


title: The Aichelburg-Sexl Boost of Domain-Walls and Cosmic Strings

abstract:
  We consider the application of the Aichelburg-Sexl boost to plane and line
distributions of matter. Our analysis shows that for a domain wall the
space-time after the boost is flat except on a null hypersurface which is the
history of a null shell. For a cosmic string we study the influence of the
boost on the conical singularity and give the new value of the conical deficit.


title:
General relativistic model for experimental measurement of the speed of
  propagation of gravity by VLBI

abstract:
  A relativistic sub-picosecond model of gravitational time delay in radio
astronomical observations is worked out and a new experimental test of general
relativity is discussed in which the effect of retardation of gravity
associated with its finite speed can be observed. As a consequence, the speed
of gravity can be measured by differential VLBI observations. Retardation in
propagation of gravity is a central part of the Einstein theory of general
relativity which has not been tested directly so far. The idea of the proposed
gravitational experiment is based on the fact that gravity in general
relativity propagates with finite speed so that the deflection of light caused
by the body must be sensitive to the ratio of the body's velocity to the speed
of gravity. The interferometric experiment can be performed, for example,
during the very close angular passage of a quasar by Jupiter. Due to the finite
speed of gravity and orbital motion of Jupiter, the variation in its
gravitational field reaches observer on Earth not instantaneously but at the
retarded instant of time and should appear as a velocity-dependent excess time
delay in addition to the well-known Shapiro delay, caused by the static part of
the Jupiter's gravitational field. Such Jupiter-QSO encounter events take place
once in a decade. The next such event will occur on September 8, 2002 when
Jupiter will pass by quasar J0842+1835 at the angular distance 3.7 arcminutes.
If radio interferometric measurement of the quasar coordinates in the sky are
done with the precision of a few picoseconds (about 5 microarcseconds) the
effect of retardation of gravity and its speed of propagation may be measured
with an accuracy about 10%.


title:
LISA data analysis: The monochromatic binary detection and initial guess
  problems

abstract:
  We consider the detection and initial guess problems for the LISA
gravitational wave detector. The detection problem is the problem of how to
determine if there is a signal present in instrumental data and how to identify
it. Because of the Doppler and plane-precession spreading of the spectral power
of the LISA signal, the usual power spectrum approach to detection will have
difficulty identifying sources. A better method must be found. The initial
guess problem involves how to generate {\it a priori} values for the parameters
of a parameter-estimation problem that are close enough to the final values for
a linear least-squares estimator to converge to the correct result. A useful
approach to simultaneously solving the detection and initial guess problems for
LISA is to divide the sky into many pixels and to demodulate the Doppler
spreading for each set of pixel coordinates. The demodulated power spectra may
then be searched for spectral features. We demonstrate that the procedure works
well as a first step in the search for gravitational waves from monochromatic
binaries.


title: Isolated Horizons in 2+1 Gravity

abstract:
  Using ideas employed in higher dimensional gravity, non-expanding, weakly
isolated and isolated horizons are introduced and analyzed in 2+1 dimensions.
While the basic definitions can be taken over directly from higher dimensions,
their consequences are somewhat different because of the peculiarities
associated with 2+1 dimensions. Nonetheless, as in higher dimensions, we are
able to: i) analyze the horizon geometry in detail; ii) introduce the notions
of mass, charge and angular momentum of isolated horizons using geometric
methods; and, iii) generalize the zeroth and the first laws of black hole
mechanics. The Hamiltonian methods also provide, for the first time,
expressions of total angular momentum and mass of charged, rotating black holes
and their relation to the analogous quantities defined at the horizon. We also
construct the analog of the Newman-Penrose framework in 2+1 dimensions which
should be useful in a wide variety of problems in 2+1 dimensional gravity.


title:
Some Heuristic Semiclassical Derivations of the Planck Length, the
  Hawking Effect and the Unruh Effect

abstract:
  The formulae for Planck length, Hawking temperature and Unruh-Davies
temperature are derived by using only laws of classical physics together with
the Heisenberg principle. Besides, it is shown how the Hawking relation can be
deduced from the Unruh relation by means of the principle of equivalence; the
deep link between Hawking effect and Unruh effect is in this way clarified.


title: Phenomenological equation of state and late-time cosmic acceleration

abstract:
  Assuming a flat Friedmann-Robertson-Walker cosmology with a single perfect
fluid, we propose a pressure-density ratio that evolves as a specific universal
function of the scale parameter. We show that such a ratio can indeed be
consistent with several observational constraints including those pertaining to
late-time accelerated expansion. Generic dynamical scalar field models of Dark
energy (with quadratic kinetic terms in their Lagrange density) are shown to be
in accord with the proposed equation-of-state ratio, provided the current
matter density parameter $\Omega_{m0} < 0.23$ - a value {\it not} in agreement
with recent measurements.


title: Poincare ball embeddings of the optical geometry

abstract:
  It is shown that optical geometry of the Reissner-Nordstrom exterior metric
can be embedded in a hyperbolic space all the way down to its outer horizon.
The adopted embedding procedure removes a breakdown of flat-space embeddings
which occurs outside the horizon, at and below the Buchdahl-Bondi limit
(R/M=9/4 in the Schwarzschild case). In particular, the horizon can be captured
in the optical geometry embedding diagram. Moreover, by using the compact
Poincare ball representation of the hyperbolic space, the embedding diagram can
cover the whole extent of radius from spatial infinity down to the horizon.
Attention is drawn to advantages of such embeddings in an appropriately curved
space: this approach gives compact embeddings and it distinguishes clearly the
case of an extremal black hole from a non-extremal one in terms of topology of
the embedded horizon.


title: Tunneling in quantum cosmology: numerical study of particle creation

abstract:
  We consider a minisuperspace model for a closed universe with small and
positive cosmological constant, filled with a massive scalar field conformally
coupled to gravity. In the quantum version of this model, the universe may
undergo a tunneling transition through an effective barrier between regions of
small and large scale factor. We solve numerically the minisuperspace
Wheeler--De Witt equation with tunneling boundary conditions for the wave
function of the universe, and find that tunneling in quantum cosmology is quite
different from that in quantum mechanics. Namely, the matter degree of freedom
gets excited under the barrier, provided its interaction with the scale factor
is not too weak, and makes a strong back reaction onto tunneling. In the
semiclassical limit of small values of cosmological constant, the matter energy
behind the barrier is close to the height of the barrier: the system ``climbs
up'' the barrier, and then evolves classically from its top. These features are
even more pronounced for inhomogeneous modes of matter field. Extrapolating to
field theory we thus argue that high momentum particles are copiously created
in the tunneling process. Nevertheless, we find empirical evidence for the
semiclassical-type scaling with the cosmological constant of the wave function
under and behind the barrier.


title: Dynamical N-body Equlibrium in Circular Dilaton Gravity

abstract:
  We obtain a new exact equilibrium solution to the N-body problem in a
one-dimensional relativistic self-gravitating system. It corresponds to an
expanding/contracting spacetime of a circle with N bodies at equal proper
separations from one another around the circle. Our methods are
straightforwardly generalizable to other dilatonic theories of gravity, and
provide a new class of solutions to further the study of (relativistic)
one-dimensional self-gravitating systems.


title: On the Geometrical Character of Gravitation

abstract:
  The issue of whether some manifestations of gravitation in the quantum
domain, are indicative or not of a non-geometrical aspect in gravitation is
discussed. We examine some examples that have been considered in this context,
providing a critical analysis of previous interpretations. The analysis of
these examples is illustrative about certain details in the interpretation of
quantum mechanics. We conclude that there are, at this time, no indications of
such departure from the geometrical character of gravitation.


title: Fermions in conformally invariant geometrodynamics

abstract:
  Dynamic equations that are the simplest conformally invariant generalization
of Einstein equations with cosmological term are considered. Dimensions and
Weyl weights of the additional geometrical fields (the vector and the
antisymmetric tensor) appearing in the scheme are such, that they admit an
unexpected interpretation. It is proved that the fields can be interpreted as
observed, generated by bispinor degrees of freedom. The vacuum polarization
density matrix leads to different probabilities of different helicity particle
generation.


title: Optimal Strategies for Sinusoidal Signal Detection

abstract:
  We derive and study optimal and nearly-optimal strategies for the detection
of sinusoidal signals hidden in additive (Gaussian and non-Gaussian) noise.
Such strategies are an essential part of algorithms for the detection of the
gravitational Continuous Wave
  (CW) signals produced by pulsars. Optimal strategies are derived for the case
where the signal phase is not known and the product of the signal frequency and
the observation time is non-integral.


title:
Derivation of the General Case Sagnac Result using Non-time-orthogonal
  Analysis

abstract:
  The experimentally determined Sagnac fringe shift dependency on angular
velocity and enclosed area is derived from the rotating reference frame using
non-time-orthogonal tensor analysis. The relationship for the most general
case, in which the area enclosed is not circular and does not have the axis of
rotation passing through its center, is determined. It is submitted that this
quantitative result, along with a related thought experiment, can not be found
using the conventional approach of local co-moving Lorentz frames.


title: On the topology of vacuum spacetimes

abstract:
  We prove that there are no restrictions on the spatial topology of
asymptotically flat solutions of the vacuum Einstein equations in
(n+1)-dimensions. We do this by gluing a solution of the vacuum constraint
equations on an arbitrary compact manifold to an asymptotically Euclidean
solution of the constraints on R^n. For any compact manifold which does not
admit a metric of positive scalar curvature, this provides for the existence of
asymptotically flat vacuum spacetimes with no maximal slices. Our main theorem
is a special case of a more general gluing construction for nondegenerate
solutions of the vacuum constraint equations which have some restrictions on
the mean curvature, but for which the mean curvature is not necessarily
constant. This generalizes the construction [IMP] (gr-qc/0109045), which is
restricted to constant mean curvature data.