title:
Active laser frequency stabilization and resolution enhancement of
  interferometers for the measurement of gravitational waves in space

abstract:
  Laser frequency stabilization is notably one of the major challenges on the
way to a space-borne gravitational wave observatory. The proposed Laser
Interferometer Space Antenna (LISA) is presently under development in an ESA,
NASA collaboration. We present a novel method for active laser stabilization
and phase noise suppression in such a gravitational wave detector. The proposed
approach is a further evolution of the "arm locking" method, which in essence
consists of using an interferometer arm as an optical cavity, exploiting the
extreme long-run stability of the cavity size in the frequency band of
interest. We extend this method by using the natural interferometer arm length
differences and existing interferometer signals as additional information
sources for the reconstruction and active suppression of the quasi-periodic
laser frequency noise, enhancing the resolution power of space-borne
gravitational wave detectors.


title: Are We Living in a Higher Dimensional Universe?

abstract:
  It is a brief review of the physical theories embodying the idea of extra
dimensions, starting from the pre-historic times to the present day. Here we
have classified the developments into three eras, such as Pre-Einstein,
Einstein and Kaluza-Klein. Here the views and flow of thoughts are emphasized
rather rigorous mathematical details. Majour developments in Quantum field
theory and Particle physics are outlined. Some well known higher dimensional
approaches to unification are discussed. This is concluded with some examples
for visualizing extra dimensions and a short discussion on the cosmological
implications and possible existence of the same.


title: Formation and evaporation of non-singular black holes

abstract:
  Regular (non-singular) space-times are given which describe the formation of
a (locally defined) black hole from an initial vacuum region, its quiescence as
a static region, and its subsequent evaporation to a vacuum region. The static
region is Bardeen-like, supported by finite density and pressures, vanishing
rapidly at large radius and behaving as a cosmological constant at small
radius. The dynamic regions are Vaidya-like, with ingoing radiation of positive
energy flux during collapse and negative energy flux during evaporation, the
latter balanced by outgoing radiation of positive energy flux and a surface
pressure at a pair creation surface. The black hole consists of a compact
space-time region of trapped surfaces, with inner and outer boundaries which
join circularly as a single smooth trapping horizon.


title: Simultaneity in special and general relativity

abstract:
  We present some basic facts concerning simultaneity in both special and
general relativity. We discuss Weyl's proof of the consistence of Einstein's
synchronization convention and consider the general relativistic problem of
assigning a time function to a congruence of timelike curves.


title: Nonsingular Black Holes and Degrees of Freedom in Quantum Gravity

abstract:
  Spherically symmetric space-times provide many examples for interesting black
hole solutions, which classically are all singular. Following a general
program, space-like singularities in spherically symmetric quantum geometry, as
well as other inhomogeneous models, are shown to be absent. Moreover, one sees
how the classical reduction from infinitely many kinematical degrees of freedom
to only one physical one, the mass, can arise, where aspects of quantum
cosmology such as the problem of initial conditions play a role.


title: Quantum evaporation of a naked singularity

abstract:
  We investigate here quantum effects in gravitational collapse of a scalar
field model which classically leads to a naked singularity. We show that
non-perturbative semi-classical modifications near the singularity, based on
loop quantum gravity, give rise to a strong outward flux of energy. This leads
to the dissolution of the collapsing cloud before the singularity can form.
Quantum gravitational effects thus censor naked singularities by avoiding their
formation. Further, quantum gravity induced mass flux has a distinct feature
which may lead to a novel observable signature in astrophysical bursts.


title: On the black hole limit of rotating fluid bodies in equilibrium

abstract:
  Recently, it was shown that the extreme Kerr black hole is the only candidate
for a (Kerr) black hole limit of stationary and axisymmetric, uniformly
rotating perfect fluid bodies with a zero temperature equation of state. In
this paper, necessary and sufficient conditions for reaching the black hole
limit are presented.


title:
On the nature of initial singularities for solutions of the
  Einstein-Vlasov-scalar field system with surface symmetry

abstract:
  Global existence results in the past time direction of cosmological models
with collisionless matter and a massless scalar field are presented. It is
shown that the singularity is crushing and that the Kretschmann scalar diverges
uniformly as the singularity is approached. In the case without Vlasov matter,
the singularity is velocity dominated and the generalized Kasner exponents
converge at each spatial point as the singularity is approached.


title:
Decoupling of the general scalar field mode and the solution space for
  Bianchi type I and V cosmologies coupled to perfect fluid sources

abstract:
  The scalar field degree of freedom in Einstein's plus Matter field equations
is decoupled for Bianchi type I and V general cosmological models. The source,
apart from the minimally coupled scalar field with arbitrary potential V(Phi),
is provided by a perfect fluid obeying a general equation of state p =p(rho).
The resulting ODE is, by an appropriate choice of final time gauge affiliated
to the scalar field, reduced to 1st order, and then the system is completely
integrated for arbitrary choices of the potential and the equation of state.


title: Spatial Hypersurfaces in Causal Set Cosmology

abstract:
  Within the causal set approach to quantum gravity, a discrete analog of a
spacelike region is a set of unrelated elements, or an antichain. In the
continuum approximation of the theory, a moment-of-time hypersurface is well
represented by an inextendible antichain. We construct a richer structure
corresponding to a thickening of this antichain containing non-trivial
geometric and topological information. We find that covariant observables can
be associated with such thickened antichains and transitions between them, in
classical stochastic growth models of causal sets. This construction highlights
the difference between the covariant measure on causal set cosmology and the
standard sum-over-histories approach: the measure is assigned to completed
histories rather than to histories on a restricted spacetime region. The
resulting re-phrasing of the sum-over-histories may be fruitful in other
approaches to quantum gravity.


title: Power-law Inflation in Spacetimes without Symmetry

abstract:
  We consider models of accelerated cosmological expansion described by the
Einstein equations coupled to a nonlinear scalar field with a suitable
exponential potential. We show that homogeneous and isotropic solutions are
stable under small nonlinear perturbations without any symmetry assumptions.
Our proof is based on results on the nonlinear stability of de Sitter spacetime
and Kaluza-Klein reduction techniques.


title: Creation of Photons in Anisotropic Space-Times

abstract:
  This paper has been removed by arXiv administrators because of excessive
overlap with gr-qc/0506062.


title: A matched expansion approach to practical self-force calculations

abstract:
  We discuss a practical method to compute the self-force on a particle moving
through a curved spacetime. This method involves two expansions to calculate
the self-force, one arising from the particle's immediate past and the other
from the more distant past. The expansion in the immediate past is a covariant
Taylor series and can be carried out for all geometries. The more distant
expansion is a mode sum, and may be carried out in those cases where the wave
equation for the field mediating the self-force admits a mode expansion of the
solution. In particular, this method can be used to calculate the gravitational
self-force for a particle of mass mu orbiting a black hole of mass M to order
mu^2, provided mu/M << 1. We discuss how to use these two expansions to
construct a full self-force, and in particular investigate criteria for
matching the two expansions. As with all methods of computing self-forces for
particles moving in black hole spacetimes, one encounters considerable
technical difficulty in applying this method; nevertheless, it appears that the
convergence of each series is good enough that a practical implementation may
be plausible.


title: Nonlocal Effective Field Equations for Quantum Cosmology

abstract:
  The possibility that the strength of gravitational interactions might slowly
increase with distance, is explored by formulating a set of effective field
equations, which incorporate the gravitational, vacuum-polarization induced,
running of Newton's constant $G$. The resulting long distance (or large time)
behaviour depends on only one adjustable parameter $\xi$, and the implications
for the Robertson-Walker universe are calculated, predicting an accelerated
power-law expansion at later times $t \sim \xi \sim 1/H$.


title: Physics Related with Co-moving Coordinate System

abstract:
  We derive the metric of an expanding universe with zero accelerations by pure
kinematic method. By doing so we expatiate physics related with co-moving
coordinate system in details. The most important discovery or our study is, in
an expanding universe with zero accelerations, the red-shift of photons from
distance galaxies is determined by the co-moving coordinate of the source
galaxy instead of the scale factor's time dependence.
  Our discovery is consistent with the current observed super-novaes's
luminosity-distance v.s. red-shift relations.


title: A Mission to Explore the Pioneer Anomaly

abstract:
  The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of $\sim 20-70$ astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
$\sim(5.99 \pm 0.01)\times 10^{-9}$ Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of $a_P = (8.74 \pm
1.33)\times 10^{-10} {\rm m/s^2}$. This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.


title: Gauge Approach to Gravitation and Regular Big Bang Theory

abstract:
  Field theoretical scheme of regular Big Bang in 4-dimensional physical
space-time, built in the framework of gauge approach to gravitation, is
discussed. Regular bouncing character of homogeneous isotropic cosmological
models is ensured by gravitational repulsion effect at extreme conditions
without quantum gravitational corrections. The most general properties of
regular inflationary cosmological models are examined. Developing theory is
valid, if energy density of gravitating matter is positive and energy dominance
condition is fulfilled.


title: Gravitomagnetism and the Speed of Gravity

abstract:
  Experimental discovery of the gravitomagnetic fields generated by
translational and/or rotational currents of matter is one of primary goals of
modern gravitational physics. The rotational (intrinsic) gravitomagnetic field
of the Earth is currently measured by the Gravity Probe B. The present paper
makes use of a parametrized post-Newtonian (PN) expansion of the Einstein
equations to demonstrate how the extrinsic gravitomagnetic field generated by
the translational current of matter can be measured by observing the
relativistic time delay caused by a moving gravitational lens. We prove that
measuring the extrinsic gravitomagnetic field is equivalent to testing
relativistic effect of the aberration of gravity caused by the Lorentz
transformation of the gravitational field. We unfold that the recent Jovian
deflection experiment is a null-type experiment testing the Lorentz invariance
of the gravitational field (aberration of gravity), thus, confirming existence
of the extrinsic gravitomagnetic field associated with orbital motion of
Jupiter with accuracy 20%. We comment on erroneous interpretations of the
Jovian deflection experiment given by a number of researchers who are not
familiar with modern VLBI technique and subtleties of JPL ephemeris. We propose
to measure the aberration of gravity effect more accurately by observing
gravitational deflection of light by the Sun and processing VLBI observations
in the geocentric frame with respect to which the Sun is moving with velocity
30 km/s.


title: Deviation equations in spaces with torsion

abstract:
  The most general form of the deviation equations in spaces with linear
connection with arbitrary torsion is derived.


title:
Mass and angular momentum of asymptotically AdS or flat solutions in the
  topologically massive gravity

abstract:
  We study the conserved charges of supersymmetric solutions in the
topologically massive gravity theory for both asymptotically flat and constant
curvature geometries.


title:
Multi-block simulations in general relativity: high order
  discretizations, numerical stability, and applications

abstract:
  The need to smoothly cover a computational domain of interest generically
requires the adoption of several grids. To solve the problem of interest under
this grid-structure one must ensure the suitable transfer of information among
the different grids involved. In this work we discuss a technique that allows
one to construct finite difference schemes of arbitrary high order which are
guaranteed to satisfy linear numerical and strict stability. The technique
relies on the use of difference operators satisfying summation by parts and
{\it penalty techniques} to transfer information between the grids. This allows
the derivation of semidiscrete energy estimates for problems admitting such
estimates at the continuum. We analyze several aspects of this technique when
used in conjuction with high order schemes and illustrate its use in one, two
and three dimensional numerical relativity model problems with non-trivial
topologies, including truly spherical black hole excision.


title: First and Second Order Perturbations of Hypersurfaces

abstract:
  In this paper we find the first and second order perturbations of the induced
metric and the extrinsic curvature of a non-degenerate hypersurface $\Sigma$ in
a spacetime $(M,g)$, when the metric $g$ is perturbed arbitrarily to second
order and the hypersurface itself is allowed to change perturbatively (i.e. to
move within spacetime) also to second order. The results are fully general and
hold in arbitrary dimensions and signature. An application of these results for
the perturbed matching theory between spacetimes is presented.


title:
Covariant Newtonian and Relativistic dynamics of (magneto)-elastic solid
  model for neutron star crust

abstract:
  This work develops the dynamics of perfectly elastic solid model for
application to the outer crust of a magnetised neutron star. Particular
attention is given to the Noether identities responsible for energy-momentum
conservation, using a formulation that is fully covariant, not only (as is
usual) in a fully relativistic treatment but also (sacrificing accuracy and
elegance for economy of degrees of gravitational freedom) in the technically
more complicated case of the Newtonian limit. The results are used to obtain
explicit (relativistic and Newtonian) formulae for the propagation speeds of
generalised (Alfven type) magneto-elastic perturbation modes.


title: Generalized harmonic spatial coordinates and hyperbolic shift conditions

abstract:
  We propose a generalization of the condition for harmonic spatial coordinates
analogous to the generalization of the harmonic time slices introduced by Bona
et al., and closely related to dynamic shift conditions recently proposed by
Lindblom and Scheel, and Bona and Palenzuela. These generalized harmonic
spatial coordinates imply a condition for the shift vector that has the form of
an evolution equation for the shift components. We find that in order to
decouple the slicing condition from the evolution equation for the shift it is
necessary to use a rescaled shift vector. The initial form of the generalized
harmonic shift condition is not spatially covariant, but we propose a simple
way to make it fully covariant so that it can be used in coordinate systems
other than Cartesian. We also analyze the effect of the shift condition
proposed here on the hyperbolicity of the evolution equations of general
relativity in 1+1 dimensions and 3+1 spherical symmetry, and study the possible
development of blow-ups. Finally, we perform a series of numerical experiments
to illustrate the behavior of this shift condition.


title: Cylindrically symmetric wormholes

abstract:
  This paper discusses traversable wormholes that differ slightly but
significantly from those of the Morris-Thorne type under the assumption of
cylindrical symmetry. The throat is a piecewise smooth cylindrical surface
resulting in a shape function that is not differentiable at some value. It is
proposed that the regular derivative be replaced by a one-sided derivative at
this value. The resulting wormhole geometry satisfies the weak energy
condition.


title:
Staticity, Self-Similarity and Critical Phenomena in a Self-Gravitating
  Nonlinear Sigma Model

abstract:
  The main part of the thesis deals with continuously and discretely
self-similar solutions and type II critical phenomena in a family of
self-gravitating non-linear sigma-models. The phenomena strongly depend on the
dimensionless coupling constant. For small couplings we numerically construct
continuously self-similar (CSS) solutions and analyze their stability
properties. For large couplings we construct a discretely self-similar (DSS)
solution with one unstable mode. We argue that at some critical coupling the
DSS solution bifurcates from the first CSS excitation in a heteroclinic loop
bifurcation. We study critical phenomena between dispersal and singularity
formation (at very small couplings) respectively black hole formation (for
larger couplings). We give numerical evidence that for very small couplings the
generic end state of ``intermediately strong'' data is the stable CSS ground
state. For small couplings the critical solution is the first CSS excitation
whereas for strong couplings the threshold of black hole formation is governed
by the DSS solution. We describe the phenomena occurring at intermediate
couplings where the critical solution changes from CSS to DSS.
  Content and references are at the state of October 2001.


title:
Role of the Brans-Dicke scalar in the holographic description of dark
  energy

abstract:
  We study cosmological application of the holographic energy density in the
Brans-Dicke theory. Considering the holographic energy density as a dynamical
cosmological constant, it is more natural to study it in the Brans-Dicke theory
than in general relativity. Solving the Friedmann and Brans-Dicke field
equations numerically, we clarify the role of Brans-Dicke field during
evolution of the universe. When the Hubble horizon is taken as the IR cutoff,
the equation of state ($w_{\Lmd}$) for the holographic energy density is
determined to be 5/3 when the Brans-Dicke parameter $\omg$ goes infinity. This
means that the Brans-Dicke field plays a crucial role in determining the
equation of state. For the particle horizon IR cutoff, the Brans-Dicke scalar
mediates a transition from $w_{\Lmd} = -1/3$ (past) to $w_{\Lmd} = 1/3$
(future). If a dust matter is present, it determines future equation of state.
In the case of future event horizon cutoff, the role of the Brans-Dicke scalar
and dust matter are turned out to be trivial, whereas the holographic energy
density plays an important role as a dark energy candidate with $w_{\Lmd} =-1$.


title:
Improving the efficiency of the detection of gravitational wave signals
  from inspiraling compact binaries: Chebyshev interpolation

abstract:
  Inspiraling compact binaries are promising sources of gravitational waves for
ground and space-based laser interferometric detectors. The time-dependent
signature of these sources in the detectors is a well-characterized function of
a relatively small number of parameters; thus, the favored analysis technique
makes use of matched filtering and maximum likelihood methods. Current analysis
methodology samples the matched filter output at parameter values chosen so
that the correlation between successive samples is 97% for which the filtered
output is closely correlated. Here we describe a straightforward and practical
way of using interpolation to take advantage of the correlation between the
matched filter output associated with nearby points in the parameter space to
significantly reduce the number of matched filter evaluations without
sacrificing the efficiency with which real signals are recognized. Because the
computational cost of the analysis is driven almost exclusively by the matched
filter evaluations, this translates directly into an increase in computational
efficiency, which in turn, translates into an increase in the size of the
parameter space that can be analyzed and, thus, the science that can be
accomplished with the data. As a demonstration we compare the present "dense
sampling" analysis methodology with our proposed "interpolation" methodology,
restricted to one dimension of the multi-dimensional analysis problem. We find
that the interpolated search reduces by 25% the number of filter evaluations
required by the dense search with 97% correlation to achieve the same
efficiency of detection for an expected false alarm probability. Generalized to
higher dimensional space of a generic binary including spins suggests an order
of magnitude increase in computational efficiency.


title: Cylindrical solutions in braneworld gravity

abstract:
  In this article we investigate exact cylindrically symmetric solutions to the
modified Einstein field equations in the brane world gravity scenarios. It is
shown that for the special choice of the equation of state $2U+P=0$ for the
dark energy and dark pressure, the solutions found could be considered formally
as solutions of the Einstein-Maxwell equations in 4-D general relativity.


title: On wormholes with arbitrarily small quantities of exotic matter

abstract:
  Recently several models of traversable wormholes have been proposed which
require only arbitrarily small amounts of negative energy to hold them open
against self-collapse. If the exotic matter is assumed to be provided by
quantum fields, then quantum inequalities can be used to place constraints on
the negative energy densities required. In this paper, we introduce an
alternative method for obtaining constraints on wormhole geometries, using a
recently derived quantum inequality bound on the null-contracted stress-energy
averaged over a timelike worldline. The bound allows us to perform a simplified
analysis of general wormhole models, not just those with small quantities of
exotic matter. We then use it to study, in particular, the models of Visser,
Kar, and Dadhich (VKD) and the models of Kuhfittig. The VKD models are
constrained to be either submicroscopic or to have a large discrepancy between
throat size and curvature radius. A recent model of Kuhfittig is shown to be
non-traversable. This is due to the fact that the throat of his wormhole flares
outward so slowly that light rays and particles, starting from outside the
throat, require an infinite lapse of affine parameter to reach the throat.


title: Evolution of Binary Black Hole Spacetimes

abstract:
  We describe early success in the evolution of binary black hole spacetimes
with a numerical code based on a generalization of harmonic coordinates.
Indications are that with sufficient resolution this scheme is capable of
evolving binary systems for enough time to extract information about the orbit,
merger and gravitational waves emitted during the event. As an example we show
results from the evolution of a binary composed of two equal mass, non-spinning
black holes, through a single plunge-orbit, merger and ring down. The resultant
black hole is estimated to be a Kerr black hole with angular momentum parameter
a~0.70. At present, lack of resolution far from the binary prevents an accurate
estimate of the energy emitted, though a rough calculation suggests on the
order of 5% of the initial rest mass of the system is radiated as gravitational
waves during the final orbit and ringdown.


title: Spectroscopy of an AdS Reissner-Nordstrom black hole

abstract:
  In the framework of black hole spectroscopy, we extend the results obtained
for a charged black hole in an asymptotically flat spacetime to the scenario
with non vanishing negative cosmological constant. In particular, exploiting
Hamiltonian techniques, we construct the area spectrum for an AdS
Reissner-Nordstrom black hole.


title:
The gravitation energy for a cylindrically and spherically symmetrical
  system

abstract:
  It has been shown that t00 component of the energy-momentum pseudotensor in
the case of cylindrically symmetrical static gravitational field cannot be
interpreted as energy density of the gravitation field. An approach has been
suggested allows one to express the energy density of the cylindrically or
spherically symmetrical static gravitation field in terms of the metric tensor
components. The approach based on the consideration of the process of
isothermal compression of a cylinder consisted of incoherent matter.


title:
Quantum superposition principle and gravitational collapse: Scattering
  times for spherical shells

abstract:
  A quantum theory of spherically symmetric thin shells of null dust and their
gravitational field is studied. In Nucl. Phys. 603 (2001) 515 (hep-th/0007005),
it has been shown how superpositions of quantum states with different
geometries can lead to a solution of the singularity problem and black hole
information paradox: the shells bounce and re-expand and the evolution is
unitary. The corresponding scattering times will be defined in the present
paper. To this aim, a spherical mirror of radius R_m is introduced. The
classical formula for scattering times of the shell reflected from the mirror
is extended to quantum theory. The scattering times and their spreads are
calculated. They have a regular limit for R_m\to 0 and they reveal a resonance
at E_m = c^4R_m/2G. Except for the resonance, they are roughly of the order of
the time the light needs to cross the flat space distance between the observer
and the mirror. Some ideas are discussed of how the construction of the quantum
theory could be changed so that the scattering times become considerably
longer.


title:
A note on the extendability of compact hypersurfaces to smooth Cauchy
  hypersurfaces

abstract:
  This paper has been withdrawn because the new one gr-qc/0512095 includes all
its results (as well as those in gr-qc/0511016) in a clearer way.


title:
Universality of Highly Damped Quasinormal Modes for Single Horizon Black
  Holes

abstract:
  It has been suggested that the highly damped quasinormal modes of black holes
provide information about the microscopic quantum gravitational states
underlying black hole entropy. This interpretation requires the form of the
highly damped quasinormal mode frequency to be universally of the form:
$\hbar\omega_R = \ln(l)kT_{BH}$, where $l$ is an integer, and $T_{BH}$ is the
black hole temperature. We summarize the results of an analysis of the highly
damped quasinormal modes for a large class of single horizon, asymptotically
flat black holes.


title: Gravitational dynamics in s+1+1 dimensions

abstract:
  We present the concomitant decomposition of an (s+2)-dimensional spacetime
both with respect to a timelike and a spacelike direction. The formalism we
develop is suited for the study of the initial value problem and for canonical
gravitational dynamics in brane-world scenarios. The bulk metric is replaced by
two sets of variables. The first set consist of one tensorial (the induced
metric $g_{ij}$), one vectorial ($M^{i}$) and one scalar ($M$) dynamical
quantity, all defined on the s-space. Their time evolutions are related to the
second fundamental form (the extrinsic curvature $K_{ij}$), the normal
fundamental form ($\mathcal{K}^{i}$) and normal fundamental scalar
($\mathcal{K}$), respectively. The non-dynamical set of variables is given by
the lapse function and the shift vector, which however has one component less.
The missing component is due to the externally imposed constraint, which states
that physical trajectories are confined to the (s+1)-dimensional brane. The
pair of dynamical variables ($g_{ij}$, $K_{ij}$), well-known from the
ADM-decomposition is supplemented by the pairs ($M^{i}$, $\mathcal{K}^{i}$) and
($M$, $\mathcal{K}$) due to the bulk curvature. We give all projections of the
junction condition across the brane and prove that for a perfect fluid brane
neither of the dynamical variables has jump across the brane. Finally we
complete the set of equations needed for gravitational dynamics by deriving the
evolution equations of $K_{ij}$, $\mathcal{K}^{i}$ and $\mathcal{K}$ on a brane
with arbitrary matter.


title: Accelerating and rotating black holes

abstract:
  An exact solution of Einstein's equations which represents a pair of
accelerating and rotating black holes (a generalised form of the spinning
C-metric) is presented. The starting point is a form of the Plebanski-Demianski
metric which, in addition to the usual parameters, explicitly includes
parameters which describe the acceleration and angular velocity of the sources.
This is transformed to a form which explicitly contains the known special cases
for either rotating or accelerating black holes. Electromagnetic charges and a
NUT parameter are included, the relation between the NUT parameter $l$ and the
Plebanski-Demianski parameter $n$ is given, and the physical meaning of all
parameters is clarified. The possibility of finding an accelerating NUT
solution is also discussed.


title: Some Statistical Mechanical Properties of Photon Black Holes

abstract:
  We show that if the total internal energy of a black hole is constructed as
the sum of $N$ photons all having a fixed wavelength chosen to scale with the
Schwarzschild radius as $\lambda=\alpha R_{s}$, then $N$ will scale with
$R_{s}^{2}$. A statistical mechanical calculation of the configuration proposed
yields (\alpha = 4 \pi^2 / \ln(2)) and a total entropy of the system $S=k_{B}N
\ln(2)$, in agreement with the Bekenstein entropy of a black hole . It is shown
that the critical temperature for Bose-Einstein condensation for relativistic
particles of $\lambda=\alpha R_{s}$ is always well below the Hawking
temperature of a black hole, in support of the proposed internal configuration.
We then examine our results from the point of view of recent loop quantum
gravity ideas and find that a natural consistency of both approaches appears.
  We show that the Jeans criterion for gravitational instability can be
generalised to the special and general relativistic regimes and holds for any
type of mass--energy distribution.


abstract:
  Ultrarelativistic circular orbits of spinning particles in a Schwarzschild
field described by the Mathisson-Papapetrou equations are considered. The
preliminary estimates of the possible synchrotron electromagnetic radiation of
highly relativistic protons and electrons on these orbits in the gravitational
field of a black hole are presented


title:
Gravitational ultrarelativistic spin-orbit interaction and the weak
  equivalence principle

abstract:
  It is shown that the gravitational ultrarelativistic spin-orbit interaction
violates the weak equivalence principle in the traditional sense. This fact is
a direct consequence of the Mathisson-Papapetrou equations in the frame of
reference comoving with a spinning test particle. The widely held assumption
that the deviation of a spinning test body from a geodesic trajectory is caused
by tidal forces is not correct


title:
Gravitational ultrarelativistic interaction of classical particles in
  the context of unification of interactions

abstract:
  The response of the ultrarelativistic particle with spin in a Schwarzschild
field to the gravitomagnetic components as measured by the comoving observer is
investigated. The dependence of the particle's spin-orbit acceleration on the
Lorentz \gamma - factor and the spin orientation is studied. The concrete
circular ultrarelativistic orbit of radius r=3m is considered as a partial
solution of the Mathisson-Papapetrou equations and as the corresponding
high-energy quantum state of the Dirac particle. Numerical estimates for
protons and electrons near black holes are given. A tendency of gravitational
and electromagnetic interactions to approach in quantitative terms at
ultrarelativistic velocities is discussed


title: Polynomial form of the Hilbert-Einstein action

abstract:
  Configuration space of general relativity is extended by inclusion of the
determinant of the metric as a new independent variable. As the consequence the
Hilbert-Einstein action takes a polynomial form.


title: The nearly Newtonian regime in Non-Linear Theories of Gravity

abstract:
  The present paper reconsiders the Newtonian limit of models of modified
gravity including higher order terms in the scalar curvature in the
gravitational action. This was studied using the Palatini variational principle
in [Meng X. and Wang P.: Gen. Rel. Grav. {\bf 36}, 1947 (2004)] and
[Dom\'inguez A. E. and Barraco D. E.: Phys. Rev. D {\bf 70}, 043505 (2004)]
with contradicting results. Here a different approach is used, and problems in
the previous attempts are pointed out. It is shown that models with negative
powers of the scalar curvature, like the ones used to explain the present
accelerated expansion, as well as their generalization which include positive
powers, can give the correct Newtonian limit, as long as the coefficients of
these powers are reasonably small. Some consequences of the performed analysis
seem to raise doubts for the way the Newtonian limit was derived in the purely
metric approach of fourth order gravity [Dick R.: Gen. Rel. Grav. {\bf 36}, 217
(2004)]. Finally, we comment on a recent paper [Olmo G. J.: Phys. Rev. D {\bf
72}, 083505 (2005)] in which the problem of the Newtonian limit of both the
purely metric and the Palatini formalism is discussed, using the equivalent
Brans--Dicke theory, and with which our results partly disagree.


title:
A cosmic equation of state for the inhomogeneous Universe: can a global
  far-from-equilibrium state explain Dark Energy?

abstract:
  A system of effective Einstein equations for spatially averaged scalar
variables of inhomogeneous cosmological models can be solved by providing a
`cosmic equation of state'. Recent efforts to explain Dark Energy focus on
`backreaction effects' of inhomogeneities on the effective evolution of
cosmological parameters in our Hubble volume, avoiding a cosmological constant
in the equation of state. In this Letter it is argued that, if kinematical
backreaction effects are indeed of the order of the averaged density (or larger
as needed for an accelerating domain of the Universe), then the state of our
regional Hubble volume would have to be in the vicinity of a
far-from-equilibrium state that balances kinematical backreaction and average
density. This property, if interpreted globally, is shared by a stationary
cosmos with effective equation of state $p_{\rm eff} = -1/3 \rho_{\rm eff}$. It
is concluded that a confirmed explanation of Dark Energy by kinematical
backreaction may imply a paradigmatic change of cosmology.


title:
Semi-classical States, Effective Dynamics and Classical Emergence in
  Loop Quantum Cosmology

abstract:
  We construct physical semi-classical states annihilated by the Hamiltonian
constraint operator in the framework of loop quantum cosmology as a method of
systematically determining the regime and validity of the semi-classical limit
of the quantum theory. Our results indicate that the evolution can be
effectively described using continuous classical equations of motion with
non-perturbative corrections down to near the Planck scale below which the
universe can only be described by the discrete quantum constraint. These
results, for the first time, provide concrete evidence of the emergence of
classicality in loop quantum cosmology and also clearly demarcate the domain of
validity of different effective theories. We prove the validity of modified
Friedmann dynamics incorporating discrete quanum geometry effects which can
lead to various new phenomenological applications. Furthermore the
understanding of semi-classical states allows for a framework for interpreting
the quantum wavefunctions and understanding questions of a semi-classical
nature within the quantum theory of loop quantum cosmology.


title: Gravitational waves from a dust disk around a Schwarzschild black hole

abstract:
  We investigate gravitational waves from a dust disk around a Schwarzschild
black hole to focus on whether we can extract any of its physical properties
from a direct detection of gravitational waves. We adopt a black hole
perturbation approach in a time domain, which is a satisfactory approximation
to illustrate a dust disk in a supermassive black hole. We find that we can
determine the radius of the disk by using the power spectrum of gravitational
waves and that our method to extract the radius works for a disk of arbitrary
density distribution. Therefore we believe a possibility exists for determining
the radius of the disk from a direct observation of gravitational waves
detected by the Laser Interferometer Space Antenna.


title:
Maximally extended, explicit and regular coverings of the Schwarzschild
  - de Sitter vacua in arbitrary dimension

abstract:
  Maximally extended, explicit and regular coverings of the Schwarzschild - de
Sitter family of vacua are given, first in spacetime (generalizing a result due
to Israel) and then for all dimensions $D$ (assuming a $D-2$ sphere). It is
shown that these coordinates offer important advantages over the well known
Kruskal - Szekeres procedure.


title:
Gravitating global monopoles in extra dimensions and the brane world
  concept

abstract:
  Multidimensional configurations with Minkowski external space-time and a
spherical global monopole in extra dimensions are discussed in the context of
the brane world concept. The monopole is formed with a hedgehog-like set of
scalar fields \phi^i with a symmetry-breaking potential V depending on the
magnitude \phi^2 = \phi^i \phi^i. All possible kinds of globally regular
configurations are singled out without specifying the shape of V(\phi). These
variants are governed by the maximum value \phi_m of the scalar field,
characterizing the energy scale of symmetry breaking. If \phi_m < \phi_cr
(where \phi_cr is a critical value of \phi related to the multidimensional
Planck scale), the monopole reaches infinite radii while in the ``strong field
regime'', when \phi_m\geq \phi_cr, the monopole may end with a cylinder of
finite radius or possess two regular centers. The warp factors of monopoles
with both infinite and finite radii may either exponentially grow or tend to
finite constant values far from the center. All such configurations are shown
to be able to trap test scalar matter, in striking contrast to RS2 type 5D
models. The monopole structures obtained analytically are also found
numerically for the Mexican hat potential with an additional parameter acting
as a cosmological constant.


title: Geodesics around Weyl-Bach's Ring Solution

abstract:
  We explore some of the gravitational features of a uniform ring both in the
Newtonian potential theory and in General Relativity. We use a spacetime
associated to a Weyl static solution of the vacuum Einstein's equations with
ring like singularity. The Newtonian motion for a test particle in the
gravitational field of the ring is studied and compared with the corresponding
geodesic motion in the given spacetime. We have found a relativistic peculiar
attraction: free falling particle geodesics are lead to the inner rim but never
hit the ring.


title: Horizon Entropy in Modified Gravity

abstract:
  We present an observation about the proposal that four-dimensional
modification of general relativity may explain the observed cosmic acceleration
today. Assuming that the thermodynamical nature of gravity theory continues to
hold in modified gravity theories, we derive the modified horizon entropy
formula from the modified Friedmann equation. We argue that our results imply
that there are conceptual problems in some models of four-dimensional
modification of general relativity.


title:
Global existence of solutions for the relativistic Boltzmann equation on
  the flat Robertson-Walker space-time for arbitrarily large intial data

abstract:
  We prove a global result in time for the initial value problem for the
relativistic Boltzmann equation on the flat Robertson-Walker sapace time, in
the functional framework appropriate to the coupling with Einstein's equations.
We had nowhere to restrict the size of the initial data which can hence be
taken arbitrarily large.


title:
Consistency Check on Volume and Triad Operator Quantisation in Loop
  Quantum Gravity I

abstract:
  The volume operator plays a pivotal role for the quantum dynamics of Loop
Quantum Gravity (LQG). It is essential in order to construct Triad operators
that enter the Hamiltonian constraint and which become densely defined
operators on the full Hilbert space even though in the classical theory the
triad becomes singular when classical GR breaks down. The expression for the
volume and triad operators derives from the quantisation of the fundamental
electric flux operator of LQG by a complicated regularisation procedure. In
fact, there are two inequivalent volume operators available in the literature
and, moreover, both operators are unique only up to a finite, multiplicative
constant which should be viewed as a regularisation ambiguity. Now on the one
hand, classical volumes and triads can be expressed directly in terms of fluxes
and this fact was used to construct the corresponding volume and triad
operators. On the other hand, fluxes can be expressed in terms of triads and
therefore one can also view the volume operator as fundamental and consider the
flux operator as a derived operator. In this paper we examine whether the
volume, triad and flux quantisations are consistent with each other. The
results of this consistency analysis are rather surprising. Among other
findings we show: 1. The regularisation constant can be uniquely fixed. 2. One
of the volume operators can be ruled out as inconsistent. 3. Factor ordering
ambiguities in the definition of triad operators are immaterial for the
classical limit of the derived flux operator. The results of this paper show
that within full LQG triad operators are consistently quantized. In this paper
we present ideas and results of the consistency check. In a companion paper we
supply detailed proofs.


title:
Consistency Check on Volume and Triad Operator Quantisation in Loop
  Quantum Gravity II

abstract:
  In this paper we provide the techniques and proofs for the resuls presented
in our companion paper concerning the consistency check on volume and triad
operator quantisation in Loop Quantum Gravity.


title: Loop Quantum Geometry: A primer

abstract:
  This is the written version of a lecture given at the ``VI Mexican School of
Gravitation and Mathematical Physics" (Nov 21-27, 2004, Playa del Carmen,
Mexico), introducing the basics of Loop Quantum Geometry. The purpose of the
written contribution is to provide a Primer version, that is, a first entry
into Loop Quantum Gravity and to present at the same time a friendly guide to
the existing pedagogical literature on the subject. This account is geared
towards graduate students and non-experts interested in learning the basics of
the subject.


title: The Newtonian limit at intermediate energies

abstract:
  We study the metric solutions for the gravitational equations in Modified
Gravity Models (MGMs). In models with negative powers of the scalar curvature,
we show that the Newtonian Limit (NL) is well defined as a limit at
intermediate energies, in contrast with the usual low energy interpretation.
Indeed, we show that the gravitational interaction is modified at low densities
or low curvatures.


title: On the puzzle of Bremsstrahlung as described by coaccelerated observers

abstract:
  We consider anew some puzzling aspects of the equivalence of the quantum
field theoretical description of Bremsstrahlung from the inertial and
accelerated observer's perspectives. More concretely, we focus on the seemingly
paradoxical situation that arises when noting that the radiating source is in
thermal equilibrium with the thermal state of the quantum field in the wedge in
which it is located, and thus its presence does not change there the state of
the field, while it clearly does not affect the state of the field on the
opposite wedge. How then is the state of the quantum field on the future wedge
changed, as it must in order to account for the changed energy momentum tensor
there? This and related issues are carefully discussed.


title:
First preliminary tests of the general relativistic gravitomagnetic
  field of the Sun and new constraints on a Yukawa-like fifth force from
  planetary data

abstract:
  The general relativistic Lense-Thirring precessions of the perihelia of the
inner planets of the Solar System are about 10^-3 arcseconds per century.
Recent improvements in planetary orbit determination may yield the first
observational evidence of such a tiny effect. Indeed, corrections to the known
perihelion rates of -0.0036 +/- 0.0050, -0.0002 +/- 0.0004 and 0.0001 +/-
0.0005 arcseconds per century were recently estimated by E.V. Pitjeva for
Mercury, the Earth and Mars, respectively, on the basis of the EPM2004
ephemerides and a set of more than 317,000 observations of various kinds. The
predicted relativistic Lense-Thirring precessions for these planets are
-0.0020, -0.0001 and -3 10^-5 arcseconds per century, respectively and are
compatible with the determined perihelia corrections. The relativistic
predictions fit better than the zero-effect hypothesis, especially if a
suitable linear combination of the perihelia of Mercury and the Earth, which a
priori cancels out any possible bias due to the solar quadrupole mass moment,
is considered. However, the experimental errors are still large. Also the
latest data for Mercury processed independently by Fienga et al. with the INPOP
ephemerides yield preliminary insights about the existence of the solar
Lense-Thirring effect. The data from the forthcoming planetary mission
BepiColombo will improve our knowledge of the orbital motion of this planet
and, consequently, the precision of the measurement of the Lense-Thirring
effect. As a by-product of the present analysis, it is also possible to
constrain the strength of a Yukawa-like fifth force to a 10^-12-10^-13 level at
scales of about one Astronomical Unit (10^11 m).


title:
Global Existence of Solutions for the Einstein-Boltzmann System with
  Cosmological Constant in the Robertson-Walker Space-time

abstract:
  We prove a global in time existence theorem for the initial values problem
for the Einstein-Boltzmann system with cosmological constant and arbitrarily
large initial data, in the spatially homogeneous case, in a Robertson-Walker
space-time.


title: Casimir effect in a two dimensional signature changing spacetime

abstract:
  We study the Casimir effect for free massless scalar fields propagating on a
two-dimensional cylinder with a metric that admits a change of signature from
Lorentzian to Euclidean. We obtain a nonzero pressure, on the hypersurfaces of
signature change, which destabilizes the signature changing region and so
alters the energy spectrum of scalar fields. The modified region and spectrum,
themselves, back react on the pressure. Moreover, the central term of
diffeomorphism algebra of corresponding infinite conserved charges changes
correspondingly.


title:
Unambiguous spin-gauge formulation of canonical general relativity with
  conformorphism invariance

abstract:
  We present a parameter-free gauge formulation of general relativity in terms
of a new set of real spin connection variables. The theory is constructed by
extending the phase space of the recently formulated conformal geometrodynamics
for canonical gravity to accommodate a spin gauge description. This leads to a
further enlarged set of first class gravitational constraints consisting of a
reduced Hamiltonian constraint and the canonical generators for spin gauge and
conformorphism transformations. Owing to the incorporated conformal symmetry,
the new theory is shown to be free from an ambiguity of the Barbero-Immirzi
type.


title: A Proposed Test of the Local Causality of Spacetime

abstract:
  A theory governing the metric and matter fields in spacetime is {\it locally
causal} if the probability distribution for the fields in any region is
determined solely by physical data in the region's past, i.e. it is independent
of events at space-like separated points. General relativity is manifestly
locally causal, since the fields in a region are completely determined by
physical data in its past. It is natural to ask whether other possible theories
in which the fundamental description of space-time is classical and geometric
-- for instance, hypothetical theories which stochastically couple a classical
spacetime geometry to a quantum field theory of matter -- might also be locally
causal.
  A quantum theory of gravity, on the other hand, should allow the creation of
spacetimes which violate local causality at the macroscopic level. This paper
describes an experiment to test the local causality of spacetime, and hence to
test whether or not gravity behaves as quantum theories of gravity suggest, in
this respect. The experiment will either produce direct evidence that the
gravitational field is not locally causal, and thus weak confirmation of
quantum gravity, or else identify a definite limit to the domain of validity of
quantum theory.


title: A quantum-like description of the planetary systems

abstract:
  The Titius-Bode law for planetary distances is reviewed. A model describing
the basic features of this rule in the "quantum-like" language of a wave
equation is proposed. Some considerations about the 't Hooft idea on the
quantum behaviour of deterministic systems with dissipation are discussed.


title: Gravitating Stationary Dyons and Rotating Vortex Rings

abstract:
  We construct dyons, and electrically charged monopole-antimonopole pairs and
vortex rings in Yang-Mills-Higgs theory coupled to Einstein gravity. The
solutions are stationary, axially symmetric and asymptotically flat. The dyons
with magnetic charge $n\ge 2$ represent non-static solutions with vanishing
angular momentum. The electrically charged monopole-antimonopole pairs and
vortex rings, in contrast, possess vanishing magnetic charge, but finite
angular momentum, equaling $n$ times their electric charge.


title: Extra dimensions, preferred frames and ether-drift experiments

abstract:
  Models with extra space-time dimensions produce, tipically, a 4D effective
theory whose vacuum is not exactly Lorentz invariant but can be considered a
physical medium whose refractive index is determined by the gravitational
field. This leads to a version of relativity with a preferred frame and to look
for experimental tests with the new generation of ether-drift experiments using
rotating cryogenic optical resonators. Considering various types of cosmic
motion, we formulate precise predictions for the modulations of the signal
induced by the Earth's rotation and its orbital revolution around the Sun. We
also compare with recent experimental results that might represent the first
modern experimental evidence for a preferred frame.


title:
Energy distribution of Kerr spacetime using Moller energy momentum
  complex

abstract:
  Using the energy momentum complex given by M{\o}ller in 1978 based on the
absolute parallelism, the energy distribution in Kerr spacetime is evaluated.
The energy with this spacetime is found to be the same as it was earlier
evaluated using different definitions mainly based on the metric tensor.


title: Black Hole Horizons and Thermodynamics: A Quantum Approach

abstract:
  We focus on quantization of the metric of a black hole restricted to the
Killing horizon with universal radius $r_0$. After imposing spherical symmetry
and after restriction to the Killing horizon, the metric is quantized employing
the chiral currents formalism. Two ``components of the metric'' are indeed
quantized: The former behaves as an affine scalar field under changes of
coordinates, the latter is instead a proper scalar field. The action of the
symplectic group on both fields is realized in terms of certain horizon
diffeomorphisms. Depending on the choice of the vacuum state, such a
representation is unitary. If the reference state of the scalar field is a
coherent state rather than a vacuum, spontaneous breaking of conformal symmetry
arises and the state contains a Bose-Einstein condensate. In this case the
order parameter fixes the actual size of the black hole with respect to $r_0$.
Both the constructed state together with the one associated with the affine
scalar are thermal states (KMS) with respect to Schwarzschild Killing time when
restricted to half horizon. The value of the order parameter fixes the
temperature at the Hawking value as well. As a result, it is found that the
quantum energy and entropy densities coincide with the black hole mass and
entropy, provided the universal parameter $r_0$ is suitably chosen, not
depending on the size of the actual black hole in particular.


title: Where has all the information gone?

abstract:
  The existence of spacetime singularities is irrelevant for the irreversible
appearance of black holes. However, confirmation of the latter's unitary
dynamics would require the preparation of a coherent superposition of a
tremendous number of appropriate ``Everett worlds''.


title: Using Early Data to Illuminate the Pioneer Anomaly

abstract:
  Analysis of the radio tracking data from the Pioneer 10/11 spacecraft at
distances between about 20 - 70 AU from the Sun has consistently indicated the
presence of an unmodeled, small, constant, Doppler blue shift drift of order 6
\times 10^{-9} Hz/s. After accounting for systematics, this drift can be
interpreted as a constant acceleration of a_P= (8.74 \pm 1.33) \times 10^{-8}
cm/s^2 directed towards the Sun, or perhaps as a time acceleration of a_t =
(2.92 \pm 0.44)\times 10^{-18} s/s^2. Although it is suspected that there is a
systematic origin to this anomaly, none has been unambiguously demonstrated. We
review the current status of the anomaly, and then point out how the analysis
of early data, which was never analyzed in detail, could allow a more clear
understanding of the origin of the anomaly, be it a systematic or a
manifestation of unsuspected physics.


title:
Spin Gauge Theory of Gravity in Clifford Space: A Realization of
  Kaluza-Klein Theory in 4-Dimensional Spacetime

abstract:
  A theory in which 4-dimensional spacetime is generalized to a larger space,
namely a 16-dimensional Clifford space (C-space) is investigated. Curved
Clifford space can provide a realization of Kaluza-Klein theory. A covariant
Dirac equation in curved C-space is explored. The generalized Dirac field is
assumed to be a polyvector-valued object (a Clifford number) which can be
written as a superposition of four independent spinors, each spanning a
different left ideal of Clifford algebra. The general transformations of a
polyvector can act from the left and/or from the right, and form a large gauge
group which may contain the group U(1)xSU(2)xSU(3) of the standard model. The
generalized spin connection in C-space has the properties of Yang-Mills gauge
fields. It contains the ordinary spin connection related to gravity (with
torsion), and extra parts describing additional interactions, including those
described by the antisymmetric Kalb-Ramond fields.


title:
Accelerated Detector - Quantum Field Correlations: From Vacuum
  Fluctuations to Radiation Flux

abstract:
  In this paper we analyze the interaction of a uniformly accelerated detector
with a quantum field in (3+1)D spacetime, aiming at the issue of how kinematics
can render vacuum fluctuations the appearance of thermal radiance in the
detector (Unruh effect) and how they engender flux of radiation for observers
afar. Two basic questions are addressed in this study: a) How are vacuum
fluctuations related to the emitted radiation? b) Is there emitted radiation
with energy flux in the Unruh effect? We adopt a method which places the
detector and the field on an equal footing and derive the two-point correlation
functions of the detector and of the field separately with full account of
their interplay. From the exact solutions, we are able to study the complete
process from the initial transient to the final steady state, keeping track of
all activities they engage in and the physical effects manifested. We derive a
quantum radiation formula for a Minkowski observer. We find that there does
exist a positive radiated power of quantum nature emitted by the detector, with
a hint of certain features of the Unruh effect. We further verify that the
total energy of the dressed detector and a part of the radiated energy from the
detector is conserved. However, this part of the radiation ceases in steady
state. So the hint of the Unruh effect in radiated power is actually not
directly from the energy flux that the detector experiences in Unruh effect.
Since all the relevant quantum and statistical information about the detector
(atom) and the field can be obtained from the results presented here, they are
expected to be useful, when appropriately generalized, for addressing issues of
quantum information processing in atomic and optical systems, such as quantum
decoherence, entanglement and teleportation.


title: Determination of Gravitomagnetic Field through GRBs or X-ray Pulsars

abstract:
  In gauge theory of gravity, there is direct coupling between the spin of a
particle and gravitomagnetic field. In the surface of a neutron star or near
black hole, the coupling energy between spin and gravitomagnetic field can be
large and detectable. Precise measurement of the position of spectrum lines of
the corresponding emission or absorption can help us to determine the
gravitomagnetic field and electromagnetic field simultaneously. The ratio
$\frac{\Delta E_e}{\Delta E_p}$ can be served as a quantitative criteria of
black hole. In GRBs or X-ray pulsar, absorption spectral lines of electron were
observed. If the absorption spectral lines of electron and proton can be
observed simultaneously, using the method given in this paper, we can determine
the gravitomagnetic field in the surface of the star, and discriminate black
hole from neutron star.


title:
Frame dragging and bending of Light in Kerr and Kerr-(anti) de Sitter
  spacetimes

abstract:
  The equations of general relativity in the form of timelike and null
geodesics that describe motion of test particles and photons in Kerr spacetime
are solved exactly including the contribution from the cosmological constant.
We then perform a systematic application of the exact solutions obtained to the
following cases. The exact solutions derived for null, spherical, polar and
non-polar orbits are applied for the calculation of frame dragging
(Lense-Thirring effect) for the orbit of a photon around the galactic centre,
assuming that the latter is a Kerr black hole for various values of the Kerr
parameter including those supported by recent observations. Unbound null polar
orbits are investigated, and an analytical expression for the deviation angle
of a polar photon orbit from the gravitational Kerr field is derived. In
addition, we present the exact solution for timelike and null equatorial
orbits. In the former case, we derive an analytical expression for the
precession of the point of closest approach (perihelion, periastron) for the
orbit of a test particle around a rotating mass whose surrounding curved
spacetime geometry is described by the Kerr field. In the latter case, we
calculate an exact expression for the deflection angle for a light ray in the
gravitational field of a rotating mass (the Kerr field). We apply this
calculation for the bending of light from the gravitational field of the
galactic centre for various values of the Kerr parameter and the impact factor.


title: Accelerating Universe via Spatial Averaging

abstract:
  We present a model of an inhomogeneous universe that leads to accelerated
expansion after taking spatial averaging. The model universe is the
Tolman-Bondi solution of the Einstein equation and contains both a region with
positive spatial curvature and a region with negative spatial curvature. We
find that after the region with positive spatial curvature begins to
re-collapse, the deceleration parameter of the spatially averaged universe
becomes negative and the averaged universe starts accelerated expansion. We
also discuss the generality of the condition for accelerated expansion of the
spatially averaged universe.


title: The Cosmological Constant Emerging From Local Poincare Invariance

abstract:
  The Poincare Gauge Theory of gravitation with a Lagrangian quadratic in the
field strengths is applied to a classical cosmological model. It predicts a
constant value of the non-riemannian curvature scalar, which acts as a
cosmological constant. As the value of the scalar depends on the context,
vacuum solutions may differ from the predictions based on Einstein's constant.
The corresponding deviations from General Relativity are discussed on the basis
of exact solutions for the field of a mass point.


title: Energy in the Einstein-Aether Theory

abstract:
  We investigate the energy of a theory with a unit vector field (the "aether")
coupled to gravity. Both the Weinberg and Einstein type energy-momentum
pseudotensors are employed. In the linearized theory we find expressions for
the energy density of the 5 wave modes. The requirement that the modes have
positive energy is then used to constrain the theory. In the fully non-linear
theory we compute the total energy of an asymptotically flat spacetime. The
resulting energy expression is modified by the presence of the aether due to
the non-zero value of the unit vector at infinity and its 1/r falloff. The
question of non-linear energy positivity is also discussed, but not resolved.


title: A canonical formalism of f(T)-type gravity in terms of Lie derivatives

abstract:
  A canonical formalism of f(R)-type gravity is proposed, resolving the problem
in the formalism of Buchbinder and Lyakhovich(BL). The new coordinates
corresponding to the time derivatives of the metric are taken to be its Lie
derivatives which is the same as in BL. The momenta canonically conjugate to
them and Hamiltonian density are defined similarly to the formalism of
Ostrogradski. It is shown that our method surely resolves the problem of BL.


title:
On a choice of the Bondi radial coordinate and news function for the
  axisymmetric two-body problem

abstract:
  In the Bondi formulation of the axisymmetric vacuum Einstein equations, we
argue that the ``surface area'' coordinate condition determining the ``radial''
coordinate can be considered as part of the initial data and should be chosen
in a way that gives information about the physical problem whose solution is
sought. For the two-body problem, we choose this coordinate by imposing a
condition that allows it to be interpreted, near infinity, as the (inverse of
the) Newtonian potential. In this way, two quantities that specify the problem
-- the separation of the two particles and their mass ratio -- enter the
equations from the very beginning. The asymptotic solution (near infinity) is
obtained and a natural identification of the Bondi "news function" in terms of
the source parameters is suggested, leading to an expression for the radiated
energy that differs from the standard quadrupole formula but agrees with recent
non-linear calculations. When the free function of time describing the
separation of the two particles is chosen so as to make the new expression
agree with the classical result, closed-form analytic expressions are obtained,
the resulting metric approaching the Schwarzschild solution with time. As all
physical quantities are defined with respect to the flat metric at infinity,
the physical interpretation of this solution depends strongly on how these
definitions are extended to the near-zone and, in particular, how the "time"
function in the near-zone is related to Bondi's null coordinate.


title:
On global models for isolated rotating axisymmetric charged bodies;
  uniqueness of the exterior field

abstract:
  A relatively recent study by Mars and Senovilla provided us with a uniqueness
result for the exterior vacuum gravitational field generated by an isolated
distribution of matter in axial rotation in equilibrium in General Relativity.
The generalisation to exterior electrovacuum gravitational fields, to include
charged rotating objects, is presented here.


title: Stability analysis of dynamic thin shells

abstract:
  We analyze the stability of generic spherically symmetric thin shells to
linearized perturbations around static solutions. We include the momentum flux
term in the conservation identity, deduced from the ''ADM'' constraint and the
Lanczos equations. Following the Ishak-Lake analysis, we deduce a master
equation which dictates the stable equilibrium configurations. Considering the
transparency condition, we study the stability of thin shells around black
holes, showing that our analysis is in agreement with previous results.
Applying the analysis to traversable wormhole geometries, by considering
specific choices for the form function, we deduce stability regions, and find
that the latter may be significantly increased by considering appropriate
choices for the redshift function.


title: Planetary and Light Motions From Newtoinian Theory: An Amusing Exercise

abstract:
  We attempt to see how closely we can formally obtain the planetary and light
path equations of General Relativity by employing certain operations on the
familiar Newtonian equation. This article is intended neither as an alternative
to nor as a tool for grasping Einstein's General Relativity. Though the
exercise is understandable by readers at large, it is especially recommended to
the teachers of Relativity for an appreciative understanding of its peculiarity
as well as its pedagogical value in the teaching of differential equations.


title: Negative Energies and a Constantly Accelerating Flat Universe

abstract:
  It has been shown that in the context of General Relativity (GR) enriched
with a new set of discrete symmetry reversal conjugate metrics, negative energy
states can be rehabilitated while avoiding the well-known instability issues.
We review here some cosmological implications of the model and confront them
with the supernovae and CMB data. The predicted flat universe constantly
accelerated expansion phase is found to be in rather good agreement with the
most recent cosmological data.


title: Hydrodynamics in Class B Warped Spacetimes

abstract:
  We discuss certain general features of type B warped spacetimes which have
important consequences on the material content they may admit and its
associated dynamics. We show that, for Warped B spacetimes, if shear and
anisotropy are nonvanishing, they have to be proportional. We also study some
of the physics related to the warping factor and of the underlying decomposable
metric. Finally we explore the only possible cases compatible with a type B
Warped geometry which satisfy the dominant energy conditions. As an example of
the above mentioned consequences we consider a radiating fluid and two
non-spherically symmetric metrics which depend upon an arbitrary parameter,
such that if the parameter vanishes the spherical symmetry is recovered.


title:
Self-force on a scalar charge in radial infall from rest using the
  Hadamard-WKB expansion

abstract:
  We present an analytic method based on the Hadamard-WKB expansion to
calculate the self-force for a particle with scalar charge that undergoes
radial infall in a Schwarzschild spacetime after being held at rest until a
time t = 0. Our result is valid in the case of short duration from the start.
It is possible to use the Hadamard-WKB expansion in this case because the value
of the integral of the retarded Green's function over the particle's entire
past trajectory can be expressed in terms of two integrals over the time period
that the particle has been falling. This analytic result is expected to be
useful as a check for numerical prescriptions including those involving mode
sum regularization and for any other analytical approximations to self-force
calculations.


title:
Towards a wave-extraction method for numerical relativity: IV. Testing
  the quasi-Kinnersley method in the Bondi-Sachs framework

abstract:
  We present a numerical study of the evolution of a non-linearly disturbed
black hole described by the Bondi--Sachs metric, for which the outgoing
gravitational waves can readily be found using the news function. We compare
the gravitational wave output obtained with the use of the news function in the
Bondi--Sachs framework, with that obtained from the Weyl scalars, where the
latter are evaluated in a quasi-Kinnersley tetrad. The latter method has the
advantage of being applicable to any formulation of Einstein's
equations---including the ADM formulation and its various descendants---in
addition to being robust. Using the non-linearly disturbed Bondi--Sachs black
hole as a test-bed, we show that the two approaches give wave-extraction
results which are in very good agreement. When wave extraction through the Weyl
scalars is done in a non quasi-Kinnersley tetrad, the results are markedly
different from those obtained using the news function.


title: Energy-Momentum Distribution in Weyl Metrics

abstract:
  In this paper, we evaluate energy and momentum density distributions for the
Weyl metric by using the well-known prescriptions of Einstein, Landau-Lifshitz,
Papaterou and M$\ddot{o}$ller. The metric under consideration is the static
axisymmetric vacuum solution to the Einstein field equations and one of the
field equations represents the Laplace equation. Curzon metric is the special
case of this spacetime. We find that the energy density is different for each
prescription. However, momentum turns out to be constant in each case.


title: Quantum corrections to spin effects in general relativity

abstract:
  Quantum power corrections to the gravitational spin-orbit and spin-spin
interactions, as well as to the Lense-Thirring effect, were found for particles
of spin 1/2. These corrections arise from diagrams of second order in Newton
gravitational constant G with two massless particles in the unitary cut in the
t-channel. The corrections obtained differ from the previous calculation of the
corrections to spin effects for rotating compound bodies with spinless
constituents.


title:
Gravity-induced birefringence within the framework of Poincare gauge
  theory

abstract:
  Gauge theories of gravity provide an elegant and promising extension of
general relativity. In this paper we show that the Poincar\'e gauge theory
exhibits gravity-induced birefringence under the assumption of a specific gauge
invariant nonminimal coupling between torsion and Maxwell's field. Furthermore
we give for the first time an explicit expression for the induced phaseshift
between two orthogonal polarization modes within the Poincar\'e framework.
Since such a phaseshift can lead to a depolarization of light emitted from an
extended source this effect is, in principle, observable. We use white dwarf
polarimetric data to constrain the essential coupling constant responsible for
this effect.


title:
Black holes in which the electrostatic or scalar equation is solvable in
  closed form

abstract:
  We show that the method used in the Schwarzschild black hole for finding the
elementary solution of the electrostatic equation in closed form cannot extend
in higher dimensions. By contrast, we prove the existence of static,
spherically symmetric geometries with a non-degenerated horizon in which the
static scalar equation can be solved in closed form. We give the explicit
results in 6 dimensions. We determine moreover the expressions of the
electrostatic potential and of the static scalar field for a point source in
the extremal Reissner-Nordstrom black holes in higher dimensions.


title: Validity of semiclassical gravity in the stochastic gravity approach

abstract:
  In semiclassical gravity the back-reaction of the classical gravitational
field interacting with quantum matter fields is described by the semiclassical
Einstein equations. A criterion for the validity of semiclassical gravity based
on the stability of the solutions of the semiclassical Einstein equations with
respect to quantum metric perturbations is discussed. The two-point quantum
correlation functions for the metric perturbations can be described by the
Einstein-Langevin equation obtained in the framework of stochastic gravity.
These correlation functions agree, to leading order in the large $N$ limit,
with the quantum correlation functions of the theory of gravity interacting
with $N$ matter fields. The Einstein-Langevin equations exhibit runaway
solutions and methods to deal with these solutions are discussed. The validity
criterion is used to show that flat spacetime as a solution of semiclassical
gravity is stable and, consequently, a description based on semiclassical
gravity is a valid approximation in that case.


abstract:
  Dynamics of a self-gravitating shell of matter is derived from the Hilbert
variational principle and then described as an (infinite dimensional,
constrained) Hamiltonian system. A method used here enables us to define
singular Riemann tensor of a non-continuous connection {\em via} standard
formulae of differential geometry, with derivatives understood in the sense of
distributions. Bianchi identities for the singular curvature are proved. They
match the conservation laws for the singular energy-momentum tensor of matter.
Rosenfed-Belinfante and Noether theorems are proved to be still valid in case
of these singular objects. Assumption about continuity of the four-dimensional
spacetime metric is widely discussed.


title: Schwarzschild-De Sitter black holes in 4+1 dimensional bulk

abstract:
  We construct a static solution for 4+1 dimensional bulk such that the 3+1
dimensional world has a linear warp factor and describes the
Schwarzschild-dS_{4} black hole. For m=0 this four dimensional universe and
Friedmann Robertson Walker universe are related with an explicit coordinate
transformation. We emphasize that for linear warp factors the effect of bulk on
the brane world shows up as the dS_{4} background which is favored by the big
bang cosmology.


title: Gravitational collapse disturbs the dS/CFT correspondence?

abstract:
  We study the gravitational collapse in five-dimensional de Sitter (dS)
spacetime and discuss the existence of the conformal boundaries at future
timelike infinity from the perspective of the dS/CFT correspondence. We
investigate the motion of a spherical dust shell and the black hole area
bounds. The latter includes the analysis of the trapping horizon and the
initial data with spindle-shaped matter distribution. In all above analyses we
find the evidences that guarantee the existence of the conformal boundaries at
future timelike infinity which are essential to apply the dS/CFT
correspondence.


title: Simple model of big-crunch/big-bang transition

abstract:
  We present classical and quantum dynamics of a test particle in the
compactified Milne space. Background spacetime includes one compact space
dimension undergoing contraction to a point followed by expansion. Quantization
consists in finding a self-adjoint representation of the algebra of particle
observables. Our model offers some insight into the nature of the cosmic
singularity.


title: Structure, Individuality and Quantum Gravity

abstract:
  After reviewing various interpretations of structural realism, I adopt here a
definition that allows both relations between things that are already
individuated (which I call ``relations between things'') and relations that
individuate previously un-individuated entities ("things between relations").
Since both space-time points in general relativity and elementary particles in
quantum theory fall into the latter category, I propose a principle of maximal
permutability as a criterion for the fundamental entities of any future theory
of ``quantum gravity''; i.e., a theory yielding both general relativity and
quantum field theory in appropriate limits. Then I review of a number of
current candidates for such a theory. First I look at the effective field
theory and asymptotic quantization approaches to general relativity, and then
at string theory. Then a discussion of some issues common to all approaches to
quantum gravity based on the full general theory of relativity argues that
processes, rather than states should be taken as fundamental in any such
theory. A brief discussion of the canonical approach is followed by a survey of
causal set theory, and a new approach to the question of which space-time
structures should be quantized ends the paper.


title: Evaporation induced traversability of the Einstein--Rosen wormhole

abstract:
  Suppose, the Universe comes into existence (as classical spacetime) already
with an empty spherically symmetric macroscopic wormhole present in it.
Classically the wormhole would evolve into a part of the Schwarzschild space
and thus would not allow any signal to traverse it. I consider semiclassical
corrections to that picture and build a model of an evaporating wormhole. The
model is based on the assumption that the vacuum polarization and its
backreaction on the geometry of the wormhole are weak. The lack of information
about the era preceding the emergence of the wormhole results in appearance of
three parameters which -- along with the initial mass -- determine the
evolution of the wormhole. For some values of these parameters the wormhole
turns out to be long-lived enough to be traversed and to transform into a time
machine.


title: Higher Dimensional Generalizations of the Kerr Black Hole

abstract:
  A brief introduction is given to rotating black holes in more than four
spacetime dimensions.


title:
Upper limits from the LIGO and TAMA detectors on the rate of
  gravitational-wave bursts

abstract:
  We report on the first joint search for gravitational waves by the TAMA and
LIGO collaborations. We looked for millisecond-duration unmodelled
gravitational-wave bursts in 473 hr of coincident data collected during early
2003. No candidate signals were found. We set an upper limit of 0.12 events per
day on the rate of detectable gravitational-wave bursts, at 90% confidence
level. From simulations, we estimate that our detector network was sensitive to
bursts with root-sum-square strain amplitude above approximately 1-3x10^{-19}
Hz^{-1/2} in the frequency band 700-2000 Hz. We describe the details of this
collaborative search, with particular emphasis on its advantages and
disadvantages compared to searches by LIGO and TAMA separately using the same
data. Benefits include a lower background and longer observation time, at some
cost in sensitivity and bandwidth. We also demonstrate techniques for
performing coincidence searches with a heterogeneous network of detectors with
different noise spectra and orientations. These techniques include using
coordinated signal injections to estimate the network sensitivity, and tuning
the analysis to maximize the sensitivity and the livetime, subject to
constraints on the background.


title: Weyl electrovacuum solutions and gauge invariance

abstract:
  It is argued that in Weyl electrovacuum solutions the linear term in the
metric cannot be eliminated just on grounds of gauge invariance. Its importance
is stressed.


title:
Lunar Laser Ranging Tests of the Equivalence Principle with the Earth
  and Moon

abstract:
  A primary objective of the Lunar Laser Ranging (LLR) experiment is to provide
precise observations of the lunar orbit that contribute to a wide range of
science investigations. Time series of the highly accurate measurements of the
distance between the Earth and Moon provide unique information used to
determine whether, in accordance with the Equivalence Principle (EP), both of
these celestial bodies are falling towards the Sun at the same rate, despite
their different masses, compositions, and gravitational self-energies. Current
LLR solutions give $(-1.0 \pm 1.4) \times 10^{-13}$ for any possible inequality
in the ratios of the gravitational and inertial masses for the Earth and Moon,
$\Delta(M_G/M_I)$. This result, in combination with laboratory experiments on
the weak equivalence principle, yields a strong equivalence principle (SEP)
test of $\Delta(M_G/M_I)_{\tt SEP} = (-2.0 \pm 2.0) \times 10^{-13}$. Such an
accurate result allows other tests of gravitational theories. The result of the
SEP test translates into a value for the corresponding SEP violation parameter
$\eta$ of $(4.4 \pm 4.5)\times10^{-4}$, where $\eta = 4\beta -\gamma -3$ and
both $\gamma$ and $\beta$ are parametrized post-Newtonian (PPN) parameters. The
PPN parameter $\beta$ is determined to be $\beta - 1 = (1.2 \pm 1.1) \times
10^{-4}$. Focusing on the tests of the EP, we discuss the existing data, and
characterize the modeling and data analysis techniques. The robustness of the
LLR solutions is demonstrated with several different approaches that are
presented in the text. We emphasize that near-term improvements in the LLR
ranging accuracy will further advance the research of relativistic gravity in
the solar system, and, most notably, will continue to provide highly accurate
tests of the Equivalence Principle.


title: The Field Theory of Gravitation and The Rest Mass of Particles

abstract:
  It is shown in this work that all free physical fields should have a nonzero
rest mass according to the field theory of gravitation.


title:
Dirac Analysis and Integrability of Geodesic Equations for Cylindrically
  Symmetric Spacetimes

abstract:
  Dirac's constraint analysis and the symplectic structure of geodesic
equations are obtained for the general cylindrically symmetric stationary
spacetime. For this metric, using the obtained first order Lagrangian, the
geodesic equations of motion are integrated, and found some solutions for
Lewis, Levi-Civita, and Van Stockum spacetimes.


title: Gravitational Instability of a Kink

abstract:
  We study the equilibria of a self-gravitating scalar field in the region
outside a reflecting barrier. By introducing a potential difference between the
barrier and infinity, we create a kink which cannot decay to a zero energy
state. In the realm of small amplitude, the kink decays to a known static
solution of the Einstein-Klein-Gordon equation. However, for larger kinks the
static equilibria are degenerate, forming a system with two energy levels. The
upper level is unstable and, under small perturbations, decays to the lower
energy stable equilibrium. Under large perturbations, the unstable upper level
undergoes collapse to a black hole. The equilibrium of the system provides a
remarkably simple and beautiful illustration of a turning point instability.


title:
Hydrodynamic covariant symplectic structure from bilinear Hamiltonian
  functions

abstract:
  Starting from generic bilinear Hamiltonians, constructed by covariant vector,
bivector or tensor fields, it is possible to derive a general symplectic
structure which leads to holonomic and anholonomic formulations of Hamilton
equations of motion directly related to a hydrodynamic picture. This feature is
gauge free and it seems a deep link common to all interactions,
electromagnetism and gravity included. This scheme could lead toward a full
canonical quantization.


title:
Dimension-Dependence of the Critical Exponent in Spherically Symmetric
  Gravitational Collapse

abstract:
  We study the critical behaviour of spherically symmetric scalar field
collapse to black holes in spacetime dimensions other than four. We obtain
reliable values for the scaling exponent in the supercritical region for
dimensions in the range $3.5\leq D\leq 14$. The critical exponent increases
monotonically to an asymptotic value at large $D$ of $\gamma\sim0.466$. The
data is well fit by a simple exponential of the form: $\gamma \sim
0.466(1-e^{-0.408 D})$.


title:
Bounds on the energy densities of ground states on static spacetimes of
  compact objects

abstract:
  In this paper we investigate quantum fields propagating on given, static,
spherically symmetric spacetimes, which are isometric to a part of the
Schwarzschild spacetime. Without specifying the internal geometry we show, that
there exist bounds on the energy densities of ground states of a quantum scalar
field on such spacetimes. The bounds (from above and below) come from the
so-called Quantum Energy Inequalities, and are centered around the energy
density of the Boulware state (the ground state for Schwarzschild spacetime).
The specific value of the bound from below depends critically on the distance
$\ell$ from the horizon, where the spacetimes of compact objects cease to be
isometric to the Schwarzschild spacetime. In the limit of small $\ell$ we
prove, that the energy densities of ground states cannot be below the Boulware
level.


title: Conformally Flat Metric, Position-Dependent Mass and Cold Dark Matter

abstract:
  The maximal acceleration (MA) problem associated with the position-dependent
rest mass concept is considered. New arguments in favor of the mass-dependent
maximal acceleration (MDMA) are put forward. The hypothesis that there exists a
maximal force with the numerical value equal to the inverse Einstein's
gravitation constant is advanced. The Lagrangian and Hamiltonian classical
dynamics of a point-like particle with the coordinate-dependent mass is given.
The effective Lagrangian for the pure gravitational interaction of a test
particle is proposed. Within the scope of this model the typical spiral galaxy
rotation is described. It is shown that by this model the peculiar form of the
corresponding rotation curve is as a whole reproduced without recourse to the
dark matter concept. Also, it is demonstrated that the canonical quantization
of this model leads directly to the Dirac oscillator model for a particle with
Plank's mass.


title: Boundary conditions in first order gravity: Hamiltonian and Ensemble

abstract:
  In this work two different boundary conditions for first order gravity,
corresponding to a null and a negative cosmological constant respectively, are
studied. Both boundary conditions allows to obtain the standard black hole
thermodynamics. Furthermore both boundary conditions define a canonical
ensemble. Additionally the quasilocal energy definition is obtained for the
null cosmological constant case.


title:
Integrability of Some Charged Rotating Supergravity Black Hole Solutions
  in Four and Five Dimensions

abstract:
  We study the integrability of geodesic flow in the background of some
recently discovered charged rotating solutions of supergravity in four and five
dimensions. Specifically, we work with the gauged multicharge
Taub-NUT-Kerr-(Anti) de Sitter metric in four dimensions, and the $U(1)^3$
gauged charged-Kerr-(Anti) de Sitter black hole solution of N = 2 supergravity
in five dimensions. We explicitly construct the Killing tensors that permit
separation of the Hamilton-Jacobi equation in these spacetimes. These results
prove integrability for a large class of previously known supergravity
solutions, including several BPS solitonic states. We also derive first-order
equations of motion for particles in these backgrounds and examine some of
their properties. Finally, we also examine the Klein-Gordon equation for a
scalar field in these spacetimes and demonstrate separability.


title:
The combination of de Broglie's Harmony of the Phases and Mie's theory
  of gravity results in a Principle of Equivalence for Quantum Gravity

abstract:
  Under a Lorentz-transformation, Mie's 1912 gravitational mass behaves
identical as de Broglie's 1923 clock-like frequency. The same goes for Mie's
inertial mass and de Broglie's wave-like frequency. This allows the
interpretation of de Broglie's "Harmony of the Phases" as a "Principle of
Equivalence" for Quantum Gravity. Thus, the particle-wave duality can be given
a realist interpretation. The "Mie-de Broglie" interpretation suggests a
correction of Hamilton's variational principle in the quantum domain. The
equivalence of the masses can be seen as the classical "limit" of the quantum
equivalence of the phases.


title: The Arrow of Time and the Initial Conditions of the Universe

abstract:
  The existence of a thermodynamic arrow of time in the present universe
implies that the initial state of the observable portion of our universe at (or
near) the ``big bang'' must have been very ``special''. We argue that it is not
plausible that these special initial conditions have a dynamical origin.


title: One-parameter teleparallel limit of Poincare gravity

abstract:
  Poincare gauge theories that, in the absence of spinning matter, reduce to
the one-parameter teleparallel theory are investigated with respect to their
mathematical consistency and experimental viability. It is argued that the
theories can be consistently coupled to the known standard model particles.
Moreover, we establish the result that in the classical limit, such theories
share a large class of solutions with general relativity, containing, among
others, the four classical black hole solutions (Schwarzschild,
Reisner-Nordstrom, Kerr and Kerr-Newman), as well as the complete class of
Friedman-Robertson-Walker cosmological solutions, thereby extending older
viability results that were restricted to the correct Newtonian limit and to
the existence of the Schwarzschild solution.


title:
Integrability of Particle Motion and Scalar Field Propagation in
  Kerr-(Anti) de Sitter Black Hole Spacetimes in All Dimensions

abstract:
  We study the Hamilton-Jacobi and massive Klein-Gordon equations in the
general Kerr-(Anti) de Sitter black hole background in all dimensions. Complete
separation of both equations is carried out in cases when there are two sets of
equal black hole rotation parameters. We analyze explicitly the symmetry
properties of these backgrounds that allow for this Liouville integrability and
construct a nontrivial irreducible Killing tensor associated with the enlarged
symmetry group which permits separation. We also derive first-order equations
of motion for particles in these backgrounds and examine some of their
properties. This work greatly generalizes previously known results for both the
Myers-Perry metrics, and the Kerr-(Anti) de Sitter metrics in higher
dimensions.


title: Frequency and surface dependence of the mechanical loss in fused silica

abstract:
  We have compiled measurements of the mechanical loss in fused silica from
samples spanning a wide range of geometries and resonant frequency in order to
model the known variation of the loss with frequency and surface-to-volume
ratio. This improved understanding of the mechanical loss has contributed
significantly to the design of advanced interferometric gravitational wave
detectors, which require ultra-low loss materials for their test mass mirrors.


title: Length Uncertainty in a Gravity's Rainbow Formalism

abstract:
  It is commonly accepted that the combination of quantum mechanics and general
relativity gives rise to the emergence of a minimum uncertainty both in space
and time. The arguments that support this conclusion are mainly based on
perturbative approaches to the quantization, in which the gravitational
interactions of the matter content are described as corrections to a classical
background. In a recent paper, we analyzed the existence of a minimum time
uncertainty in the framework of doubly special relativity. In this framework,
the standard definition of the energy-momentum of particles is modified
appealing to possible quantum gravitational effects, which are not necessarily
perturbative. Demanding that this modification be completed into a canonical
transformation determines the implementation of doubly special relativity in
position space and leads to spacetime coordinates that depend on the
energy-momentum of the particle. In the present work, we extend our analysis to
the quantum length uncertainty. We show that, in generic cases, there actually
exists a limit in the spatial resolution, both when the quantum evolution is
described in terms of the auxiliary time corresponding to the Minkowski
background or in terms of the physical time. These two kinds of evolutions can
be understood as corresponding to perturbative and non-perturbative
descriptions, respectively. This result contrasts with that found for the time
uncertainty, which can be made to vanish in all models with unbounded physical
energy if one adheres to a non-perturbative quantization.


title:
Robustness of a high-resolution central scheme for hydrodynamic
  simulations in full general relativity

abstract:
  A recent paper by Lucas-Serrano et al. indicates that a high-resolution
central (HRC) scheme is robust enough to yield accurate hydrodynamical
simulations of special relativistic flows in the presence of ultrarelativistic
speeds and strong shock waves. In this paper we apply this scheme in full
general relativity (involving {\it dynamical} spacetimes), and assess its
suitability by performing test simulations for oscillations of rapidly rotating
neutron stars and merger of binary neutron stars. It is demonstrated that this
HRC scheme can yield results as accurate as those by the so-called
high-resolution shock-capturing (HRSC) schemes based upon Riemann solvers.
Furthermore, the adopted HRC scheme has increased computational efficiency as
it avoids the costly solution of Riemann problems and has practical advantages
in the modeling of neutron star spacetimes. Namely, it allows simulations with
stiff equations of state by successfully dealing with very low-density
unphysical atmospheres. These facts not only suggest that such a HRC scheme may
be a desirable tool for hydrodynamical simulations in general relativity, but
also open the possibility to perform accurate magnetohydrodynamical simulations
in curved dynamic spacetimes.


title:
Finitary Topos for Locally Finite, Causal and Quantal Vacuum Einstein
  Gravity

abstract:
  Previous work on applications of Abstract Differential Geometry (ADG) to
discrete Lorentzian quantum gravity is brought to its categorical climax by
organizing the curved finitary spacetime sheaves of quantum causal sets
involved therein, on which a finitary (:locally finite), singularity-free,
background manifold independent and geometrically prequantized version of the
gravitational vacuum Einstein field equations were seen to hold, into a topos
structure. This topos is seen to be a finitary instance of both an elementary
and a Grothendieck topos, generalizing in a differential geometric setting, as
befits ADG, Sorkin's finitary substitutes of continuous spacetime topologies.
The paper closes with a thorough discussion of four future routes we could take
in order to further develop our topos-theoretic perspective on ADG-gravity
along certain categorical trends in current quantum gravity research.


title: Black holes and fundamental physics

abstract:
  We give a review of classical, thermodynamic and quantum properties of black
holes relevant to fundamental physics.


title: The Exact Solution of the Riemann Problem in Relativistic MHD

abstract:
  We discuss the procedure for the exact solution of the Riemann problem in
special relativistic magnetohydrodynamics (MHD). We consider both initial
states leading to a set of only three waves analogous to the ones in
relativistic hydrodynamics, as well as generic initial states leading to the
full set of seven MHD waves. Because of its generality, the solution presented
here could serve as an important test for those numerical codes solving the MHD
equations in relativistic regimes.


title: On foundations of Poincar\'{e}-gauged theory of gravity

abstract:
  Foundations of the Poincar\'{e}-gauge theory of gravity are developed. It is
shown that the Poincar\'{e}-gauge field consists of two components: the
translational gauge field ($t$-field), which is generated by the
energy-momentum current of external fields, and the rotational gauge field
($r$-field), which is generated by the sum of the angular and spin momentum
currents of external fields. Therefore, a physical field generated by the
angular momentum of a rotating mass should exist.


title:
Modified Friedmann-Leme\^{\i}tre equation for dilaton-spin dark matter
  in Weyl-Cartan space

abstract:
  It is proposed to consider dark matter as a perfect dilaton-spin fluid (with
particles endowed with intrinsic spin and dilaton charge) in the framework of a
gravitational theory with a Weyl-Cartan geometrical structure. The modified
Friedmann-Lema\^{\i}tre equation (with a cosmological term) is obtained for the
homogeneous and isotropic Universe filled with the dilaton-spin dark matter. On
the basis of this equation, we develop a nonsingular cosmological model
starting from an inflation-like stage (for super-stiff equation of state),
passing radiation-dominated and matter-dominated decelerating stages and
turning into a post-Friedmann accelerating era.