title: Post-Newtonian parameters and constraints on Einstein-aether theory

abstract:
  We analyze the observational and theoretical constraints on ``Einstein-aether
theory", a generally covariant theory of gravity coupled to a dynamical, unit,
timelike vector field that breaks local Lorentz symmetry. The results of a
computation of the remaining post-Newtonian parameters are reported. These are
combined with other results to determine the joint post-Newtonian,
vacuum-Cerenkov, nucleosynthesis, stability, and positive-energy constraints.
All of these constraints are satisfied by parameters in a large two-dimensional
region in the four-dimensional parameter space defining the theory.


title:
Tidal effects on magnetic gyration of a charged particle in Fermi
  coordinates

abstract:
  We examine the gyration motion of a charged particle, viewed from a reference
observer falling along the Z axis into a Schwarzschild black hole. It is
assumed that the magnetic field is constant and uniform along the Z axis, and
that the particle has a circular orbit in the X-Y plane far from the
gravitational source. When the particle as well as the reference observer
approaches the black hole, its orbit is disrupted by the tidal force. The final
plunging velocity increases in the non-relativistic case, but decreases if the
initial circular velocity exceeds a critical value, which is approximately
0.7c. This toy model suggests that disruption of a rapidly rotating star due to
a velocity-dependent tidal force may be quite different from that of a
non-relativistic star. The model also suggested that collapse of the orbit
after the disruption is slow in general, so that the particle subsequently
escapes outside the valid Fermi coordinates.


title: Exact cosmological solutions of scale-invariant gravity theories

abstract:
  We have found new anisotropic vacuum solutions for the scale-invariant
gravity theories which generalise Einstein's general relativity to a theory
derived from the Lagrangian $R^{1+\delta}$. These solutions are expanding
universes of Kasner form with an initial spacetime singularity at $t=0 $ and
exist for $-1/2<\delta <1/4$ but possess different Kasner index relations to
the classic Kasner solution of general relativity to which they reduce when
$\delta =0$. These solutions are unperturbed by the introduction of
non-comoving perfect-fluid matter motions if $p<\rho $ on approach to the
singularity and should not exhibit an infinite sequence of chaotic Mixmaster
oscillations when $\delta >0$.


title: Twisting Null Geodesic Congruences and the Einstein-Maxwell Equations

abstract:
  The purpose of the present work is to extend the earlier results for
asymptotically flat vacuum space-times to asymptotically flat solutions of the
Einstein-Maxwell equations. Once again, in this case, we get a class of
asymptotically shear-free null geodesic congruences depending on a complex
world-line in the same four-dimensional complex space. However in this case
there will be, in general, two distinct but uniquely chosen world-lines. One of
which can be assigned as the complex center-of- charge while the other could be
called the complex center of mass. Rather than investigating the situation
where there are two distinct complex world-lines, we study instead the special
degenerate case where the two world-lines coincide, i.e., where there is a
single unique world-line. This mimics the case of algebraically special
Einstein-Maxwell fields where the degenerate principle null vector of the Weyl
tensor coincides with a Maxwell principle null vector. Again we obtain
equations of motion for this world-line - but explicitly found here only in an
approximation. Though there are ambiguities in assigning physical meaning to
different terms it appears as if reliance on the Kerr and charged Kerr metrics
and classical electromagnetic radiation theory helps considerably in this
identification. In addition, the resulting equations of motion appear to have
many of the properties of a particle with intrinsic spin and an intrinsic
magnetic dipole moment. At first order there is even the classical
radiation-reaction term 2/3{q^{2}}{c^{-3}}ddot{v}, now obtained without any use
of the Lorentz force law but obtained directly from the asymptotic fields
themselves. One even sees the possible suppression, via the Bondi mass loss, of
the classical runaway solutions due to the radiation reaction force.


title: Stable gravastars with generalised exteriors

abstract:
  New spherically symmetric gravastar solutions, stable to radial
perturbations, are found by utilising the construction of Visser and Wiltshire.
The solutions possess an anti--de Sitter or de Sitter interior and a
Schwarzschild--(anti)--de Sitter or Reissner--Nordstr\"{o}m exterior. We find a
wide range of parameters which allow stable gravastar solutions, and present
the different qualitative behaviours of the equation of state for these
parameters.


title: Thermal evolution of a radiating anisotropic star with shear

abstract:
  We study the effects of pressure anisotropy and heat dissipation in a
spherically symmetric radiating star undergoing gravitational collapse. An
exact solution of the Einstein field equations is presented in which the model
has a Friedmann-like limit when the heat flux vanishes. The behaviour of the
temperature profile of the evolving star is investigated within the framework
of causal thermodynamics. In particular, we show that there are significant
differences between the relaxation time for the heat flux and the relaxation
time for the shear stress.


title: `Iconoclastic', Categorical Quantum Gravity

abstract:
  This is a two-part, `2-in-1' paper. In Part I, the introductory talk at
`Glafka--2004: Iconoclastic Approaches to Quantum Gravity' international
theoretical physics conference is presented in paper form (without references).
In Part II, the more technical talk, originally titled ``Abstract Differential
Geometric Excursion to Classical and Quantum Gravity'', is presented in paper
form (with citations). The two parts are closely entwined, as Part I makes
general motivating remarks for Part II.


title: Classical Gravitation as free Membrane Dynamics

abstract:
  The formulation of General Relativity in which the 4-dimensional space-time
is embedded in a flat host space of higher dimension is reconsidered. New
classes of embeddings (modeled after Nash's classical free embeddings) are
introduced. They present the important advantage of being deformable and
therefore physically realistic. Explicit examples of embeddings whose
deformations DO describe gravitational waves around their respective
backgrounds are given for several space-times, including the Schwarzschild
black hole. New variational principles which give back Einstein's General
Relativity are proposed. In this framework, the 4-D space-time is a membrane
moving in a flat host space.


title: A liquid crystal analogue of the cosmic string

abstract:
  We consider the propagation of light in a anisotropic medium with a
topological line defect in the realm of geometrical optics. It is shown that
the effective geometry perceived by light propagating in such medium is that of
a spacial section of the cosmic string spacetime.


title:
Geometrically motivated hyperbolic coordinate conditions for numerical
  relativity: Analysis, issues and implementations

abstract:
  We study the implications of adopting hyperbolic driver coordinate conditions
motivated by geometrical considerations. In particular, conditions that
minimize the rate of change of the metric variables. We analyze the properties
of the resulting system of equations and their effect when implementing
excision techniques. We find that commonly used coordinate conditions lead to a
characteristic structure at the excision surface where some modes are not of
outflow-type with respect to any excision boundary chosen inside the horizon.
Thus, boundary conditions are required for these modes. Unfortunately, the
specification of these conditions is a delicate issue as the outflow modes
involve both gauge and main variables. As an alternative to these driver
equations, we examine conditions derived from extremizing a scalar constructed
from Killing's equation and present specific numerical examples.


title:
General covariance violation and the gravitational dark matter. II.
  Vector graviton

abstract:
  The (four componenet) vector graviton contained in metric, the scalar
component incorporated, is attributed to the violation of the general
covariance to the residual isoharmonic one. In addition to the previously
studied (singlet) scalar graviton, the vector graviton may constitute one more
fraction of the gravitational dark matter. The gravity interactions of the
vector graviton, as well as its impact on the continuous medium are studied.


title: Numerical Relativity at the Frontier

abstract:
  Numerical relativity is an essential tool for solving Einstein's equations of
general relativity for dynamical systems characterized by high velocities and
strong gravitational fields. The implementation of new algorithms that can
solve these nonlinear equations in 3+1 dimensions has enabled us to tackle many
long-standing problems of astrophysical interest, leading to an explosion of
important new results. Numerical relativity has been used to simulate the
evolution of a diverse array of physical systems, including coalescing black
hole and neutron star binaries, rotating and collapsing compact objects (stars,
collisionless clusters, and scalar fields), and magnetic and viscous stars, to
name a few. Numerical relativity has been exploited to address fundamental
points of principle, including critical phenomena and cosmic censorship. It
holds great promise as a guide for interpreting observations of gravitational
waves and gamma-ray bursts and identifying the sources of such radiation.
Highlights of a few recent developments in numerical relativity are sketched in
this brief overview.


title:
Gravitational wave detection by a spherical antenna: the angular
  sensitivity of resonators in the TIGA configuration and its variation with
  sidereal time and galactic longitude

abstract:
  Experimental projects using spherical antennas to detect gravitational waves
are nowdays a concrete reality. The main purpose of this paper is to give a
possible way of interpreting output data from such a system. Responses of the
five fundamental quadrupole modes and of the six resonators in TIGA
collocations are shown as a function of the incoming direction of the incident
wave. Then, for a source lying in the galactic plane, sidereal time and
galactic longitude dependence is given. Thus, once a candidate source of
gravitational waves is considered, we can exactly predict the resonators'
response as a function of time.


title: Spinorial Field and Lyra Geometry

abstract:
  The Dirac field is studied in a Lyra space-time background by means of the
classical Schwinger Variational Principle. We obtain the equations of motion,
establish the conservation laws, and get a scale relation relating the
energy-momentum and spin tensors. Such scale relation is an intrinsic property
for matter fields in Lyra background.


title: Cosmological Co-evolution of Yang-Mills Fields and Perfect Fluids

abstract:
  We study the co-evolution of Yang-Mills fields and perfect fluids in Bianchi
type I universes. We investigate numerically the evolution of the universe and
the Yang-Mills fields during the radiation and dust eras of a universe that is
almost isotropic. The Yang-Mills field undergoes small amplitude chaotic
oscillations, which are also displayed by the expansion scale factors of the
universe. The results of the numerical simulations are interpreted analytically
and compared with past studies of the cosmological evolution of magnetic fields
in radiation and dust universes. We find that, whereas magnetic universes are
strongly constrained by the microwave background anisotropy, Yang-Mills
universes are principally constrained by primordial nucleosynthesis and the
bound is comparatively weak, and Omega_YM < 0.105 Omega_rad.


title:
A post-Keplerian parameter to test gravito-magnetic effects in binary
  pulsar systems

abstract:
  We study the pulsar timing, focusing on the time delay induced by the
gravitational field of the binary systems. In particular, we study the
gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and
post-Keplerian parameters, and we introduce a new post-Keplerian parameter
which is related to the intrinsic angular momentum of the stars. Furthermore,
we evaluate the magnitude of these effects for the binary pulsar systems known
so far. The expected magnitude is indeed small, but the effect is important per
se.


title: Using FEMLAB for Gravitational problems: numerical simulations for all

abstract:
  We discuss the possibility to solve Modern Numerical Relativity problems
using finite element methods (FEM). Adopting a "user friendly" software for
handling totally general systems of nonlinear partial differential equations,
FEMLAB, we model and numerically solve in a short time a Gowdy vacuum
spacetime, representing an inhomogeneous cosmology. Results agree perfectly
with existing simulations in the recent literature based not of FEMs but on
finite differences methods. Possible applications for non relativistic
Astrophysics, General Relativity, elementary particle physics and more general
theories of gravitation like EMDA and branes are discussed.


title: The bound state Aharonov-Bohm effect around a cosmic string revisited

abstract:
  In this article we observe that the self-adjoint extension of the Hamiltonian
of a particle moving around a shielded cosmic string gives rise to a
gravitational analogue of the bound state Aharonov-Bohm effect.


title: Gravitational wave snapshots of generic extreme mass ratio inspirals

abstract:
  Using black hole perturbation theory, we calculate the gravitational waves
produced by test particles moving on bound geodesic orbits about rotating black
holes. The orbits we consider are generic - simultaneously eccentric and
inclined. The waves can be described as having radial, polar, and azimuthal
"voices", each of which can be made to dominate by varying eccentricity and
inclination. Although each voice is generally apparent in the waveform, the
radial voice is prone to overpowering the others. We also compute the radiative
fluxes of energy and axial angular momentum at infinity and through the event
horizon. These fluxes, coupled to a prescription for the radiative evolution of
the Carter constant, will be used in future work to adiabatically evolve
through a sequence of generic orbits. This will enable the calculation of
inspiral waveforms that, while lacking certain important features, will
approximate those expected from astrophysical extreme mass ratio captures
sufficiently well to aid development of measurement algorithms on a relatively
short timescale.


title:
Thermodynamics of static black objects in D dimensional
  Einstein-Gauss-Bonnet gravity with D-4 compact dimensions

abstract:
  We investigate the thermodynamics of static black objects such as black
holes, black strings and their generalizations to D dimensions (`black branes')
in a gravitational theory containing the four dimensional Gauss-Bonnet term in
the action, when D-4 of the dimensions are compactified on a torus. The
entropies of black holes and black branes are compared to obtain information on
the stability of these objects and to find their phase diagrams. We demonstrate
the existence of a critical mass, which depends on the scale of the
compactified dimensions, below which the black hole entropy dominates over the
entropy of the black membrane.


title: Asymptotic Flatness in Rainbow Gravity

abstract:
  A construction of conformal infinity in null and spatial directions is
constructed for the Rainbow-flat space-time corresponding to doubly special
relativity. From this construction a definition of asymptotic DSRness is put
forward which is compatible with the correspondence principle of Rainbow
gravity. Furthermore a result equating asymptotically flat space-times with
asymptotically DSR spacetimes is presented.


title: Can the cosmological constant undergo abrupt changes?

abstract:
  The existence of a simple spherically symmetric and static solution of the
Einstein equations in the presence of a cosmological constant vanishing outside
a definite value of the radial distance is investigated. A particular
succession of field configurations, which are solutions of the Einstein
equations in the presence of the considered cosmological term and auxiliary
external sources, is constructed. Then, it is shown that the associated
succession of external sources tend to zero in the sense of the generalized
functions. The type of weak solution that is found becomes the deSitter
homogeneous space-time for the interior region, and the Schwartzschild space in
the outside zone.


title:
Physics of Gravitational Interaction: Geometry of Space or Quantum Field
  in Space?

abstract:
  Gravity theory is the basis of modern cosmological models. Thirring-Feynman's
tensor field approach to gravitation is an alternative to General Relativity
(GR). Though Field Gravity (FG) approach is still developing subject, it opens
new understanding of gravitational interaction, stimulates novel experiments on
the nature of gravity and gives possibility to construct new cosmological
models in Minkowski space. According to FG, the universal gravity force is
caused by exchange of gravitons - the quanta of gravity field. Energy of this
field is well-defined and excludes the singularity. All classical relativistic
effects are the same as in GR, though there are new effects, such as free fall
of rotating bodies, scalar gravitational radiation, surface of relativistic
compact bodies, which may be tested experimentally. The intrinsic scalar (spin
0) part of gravity field corresponds to "antigravity" and only together with
the pure tensor (spin 2) part gives the usual Newtonian force. Laboratory and
astrophysical experiments for testing new predictions of FG, will be performed
in near future. In particular observations with bar and interferometric
detectors, like Explorer, Nautilus, LIGO and VIRGO, will check the predicted
scalar gravitational waves from supernova explosions.


title: Inextendibility of expanding cosmological models with symmetry

abstract:
  A new criterion for inextendibility of expanding cosmological models with
symmetry is presented. It is applied to derive a number of new results and to
simplify the proofs of existing ones. In particular it shows that the solutions
of the Einstein-Vlasov system with $T^2$ symmetry, including the vacuum
solutions, are inextendible in the future. The technique introduced adds a
qualitatively new element to the available tool-kit for studying strong cosmic
censorship.


title:
A generalization of Hawking's black hole topology theorem to higher
  dimensions

abstract:
  Hawking's theorem on the topology of black holes asserts that cross sections
of the event horizon in 4-dimensional asymptotically flat stationary black hole
spacetimes obeying the dominant energy condition are topologically 2-spheres.
This conclusion extends to outer apparent horizons in spacetimes that are not
necessarily stationary. In this paper we obtain a natural generalization of
Hawking's results to higher dimensions by showing that cross sections of the
event horizon (in the stationary case) and outer apparent horizons (in the
general case) are of positive Yamabe type, i.e., admit metrics of positive
scalar curvature. This implies many well-known restrictions on the topology,
and is consistent with recent examples of five dimensional stationary black
hole spacetimes with horizon topology $S^2 \times S^1$. The proof is inspired
by previous work of Schoen and Yau on the existence of solutions to the Jang
equation (but does not make direct use of that equation).


title:
Can the Acceleration of Our Universe Be Explained by the Effects of
  Inhomogeneities?

abstract:
  No. It is simply not plausible that cosmic acceleration could arise within
the context of general relativity from a back-reaction effect of
inhomogeneities in our universe, without the presence of a cosmological
constant or ``dark energy.'' We point out that our universe appears to be
described very accurately on all scales by a Newtonianly perturbed FLRW metric.
(This assertion is entirely consistent with the fact that we commonly encounter
$\delta \rho/\rho > 10^{30}$.) If the universe is accurately described by a
Newtonianly perturbed FLRW metric, then the back-reaction of inhomogeneities on
the dynamics of the universe is negligible. If not, then it is the burden of an
alternative model to account for the observed properties of our universe. We
emphasize with concrete examples that it is {\it not} adequate to attempt to
justify a model by merely showing that some spatially averaged quantities
behave the same way as in FLRW models with acceleration. A quantity
representing the ``scale factor'' may ``accelerate'' without there being any
physically observable consequences of this acceleration. It also is {\it not}
adequate to calculate the second-order stress energy tensor and show that it
has a form similar to that of a cosmological constant of the appropriate
magnitude. The second-order stress energy tensor is gauge dependent, and if it
were large, contributions of higher perturbative order could not be neglected.
We attempt to clear up the apparent confusion between the second-order stress
energy tensor arising in perturbation theory and the ``effective stress energy
tensor'' arising in the ``shortwave approximation.''


title:
Stochastic Gravitational Wave Measurements with Bar Detectors:
  Dependence of Response on Detector Orientation

abstract:
  The response of a cross-correlation measurement to an isotropic stochastic
gravitational-wave background depends on the observing geometry via the overlap
reduction function. If one of the detectors being correlated is a resonant bar
whose orientation can be changed, the response to stochastic gravitational
waves can be modulated. I derive the general form of this modulation as a
function of azimuth, both in the zero-frequency limit and at arbitrary
frequencies. Comparisons are made between pairs of nearby detectors, such as
LIGO Livingston-ALLEGRO, Virgo-AURIGA, Virgo-NAUTILUS, and EXPLORER-AURIGA,
with which stochastic cross-correlation measurements are currently being
performed, planned, or considered.


title: Does the cosmological constant imply the existence of a minimum mass?

abstract:
  We show that in the framework of the classical general relativity the
presence of a positive cosmological constant implies the existence of a minimal
mass and of a minimal density in nature. These results rigorously follow from
the generalized Buchdahl inequality in the presence of a cosmological constant.


title: Worldline deviations of charged spinning particles

abstract:
  The geodesic deviation equation is generalized to worldline deviation
equations describing the relative accelerations of charged spinning particles
in the framework of Dixon-Souriau equations of motion.


title: Accelerating Universe from Extra Spatial Dimension

abstract:
  We present a simple higher dimensional FRW type of model where the
acceleration is apparently caused by the presence of the extra dimensions.
Assuming an ansatz in the form of the deceleration parameter we get a class of
solutions some of which shows the desirable feature of dimensional reduction as
well as reasonably good physical properties of matter. Interestingly we do not
have to invoke an extraneous scalar field or a cosmological constant to account
for this acceleration. One argues that the terms containing the higher
dimensional metric coefficients produces an extra negative pressure that
apparently drives the inflation of the 4D space with an accelerating phase. It
is further found that in line with the physical requirements our model admits
of a decelerating phase in the early era along with an accelerating phase at
present.Further the models asymptotically mimic a steady state type of universe
although it starts from a big type of singularity. Correspondence to Wesson's
induced matter theory is also briefly discussed and in line with it it is
argued that the terms containing the higher dimensional metric coefficients
apparently creates a negative pressure which drives the inflation of the
3-space with an accelerating phase.


title: On Spacetimes with Constant Scalar Invariants

abstract:
  We study Lorentzian spacetimes for which all scalar invariants constructed
from the Riemann tensor and its covariant derivatives are constant ($CSI$
spacetimes). We obtain a number of general results in arbitrary dimensions. We
study and construct warped product $CSI$ spacetimes and higher-dimensional
Kundt $CSI$ spacetimes. We show how these spacetimes can be constructed from
locally homogeneous spaces and $VSI$ spacetimes. The results suggest a number
of conjectures. In particular, it is plausible that for $CSI$ spacetimes that
are not locally homogeneous the Weyl type is $II$, $III$, $N$ or $O$, with any
boost weight zero components being constant. We then consider the
four-dimensional $CSI$ spacetimes in more detail. We show that there are severe
constraints on these spacetimes, and we argue that it is plausible that they
are either locally homogeneous or that the spacetime necessarily belongs to the
Kundt class of $CSI$ spacetimes, all of which are constructed. The
four-dimensional results lend support to the conjectures in higher dimensions.


title: Lunar Laser Ranging Contributions to Relativity and Geodesy

abstract:
  Lunar laser ranging (LLR) is used to conduct high-precision measurements of
ranges between an observatory on Earth and a laser retro-reflector on the lunar
surface. Over the years, LLR has benefited from a number of improvements both
in observing technology and data modeling, which led to the current accuracy of
post-fit residuals of ~2 cm. Today LLR is a primary technique to study the
dynamics of the Earth-Moon system and is especially important for gravitational
physics, geodesy and studies of the lunar interior. LLR is used to perform
high-accuracy tests of the equivalence principle, to search for a
time-variation in the gravitational constant, and to test predictions of
various alternative theories of gravity. On the geodesy front, LLR contributes
to the determination of Earth orientation parameters, such as nutation,
precession (including relativistic precession), polar motion, and UT1, i.e.
especially to the long-term variation of these effects. LLR contributes to the
realization of both the terrestrial and selenocentric reference frames. The
realization of a dynamically defined inertial reference frame, in contrast to
the kinematically realized frame of VLBI, offers new possibilities for mutual
cross-checking and confirmation. Finally, LLR also investigates the processes
related to the Moon's interior dynamics. Here, we review the LLR technique
focusing on its impact on relativity and give an outlook to further
applications, e.g. in geodesy. We present results of our dedicated studies to
investigate the sensitivity of LLR data with respect to the relativistic
quantities. We discuss the current observational situation and the level of LLR
modeling implemented to date. We also address improvements needed to fully
utilize the scientific potential of LLR.


title:
Exact Solution of a Linear Wave Equation in Cosmological General
  Relativity

abstract:
  A linear second order wave equation is presented based on cosmological
general relativity, which is a space-velocity theory of the expanding Universe.
The wave equation is shown to be exactly solvable, based on the Gaussian
hypergeometric function.


title:
FINDCHIRP: an algorithm for detection of gravitational waves from
  inspiraling compact binaries

abstract:
  Matched-filter searches for gravitational waves from coalescing compact
binaries by the LIGO Scientific Collaboration use the FINDCHIRP algorithm: an
implementation of the optimal filter with innovations to account for unknown
signal parameters and to improve performance on detector data that has
nonstationary and non-Gaussian artifacts. We provide details on the FINDCHIRP
algorithm as used in the search for subsolar mass binaries, binary neutron
stars, neutron star-black hole binaries, and binary black holes.


title: Massless DKP field in Lyra manifold

abstract:
  Massless scalar and vector fields are coupled to Lyra geometry by means of
Duffin-Kemmer-Petiau (DKP) theory. Using Schwinger Variational Principle,
equations of motion, conservation laws and gauge symmetry are implemented. We
find that the scalar field couples to the anholonomic part of the torsion
tensor, and the gauge symmetry of the electromagnetic field is not breaking by
the coupling with torsion.


title: On the regularization ambiguities in loop quantum gravity

abstract:
  One of the main achievements of LQG is the consistent quantization of the
Wheeler-DeWitt equation which is free of UV problems. However, ambiguities
associated to the intermediate regularization procedure lead to an apparently
infinite set of possible theories. The absence of an UV problem is intimately
linked with the ambiguities arising in the quantum theory. Among these
ambiguities there is the one associated to the SU(2) unitary rep. used in the
diffeomorphism covariant pointsplitting regularization of nonlinear funct. of
the connection. This ambiguity is labelled by a halfinteger m and, here, it is
referred to as the m-ambiguity. The aim of this paper is to investigate the
important implications of this ambiguity./ We first study 2+1 gravity quantized
in canonical LQG. Only when the regularization of the quantum constraints is
performed in terms of the fundamental rep. of the gauge group one obtains the
usual TQFT. In all other cases unphysical local degrees of freedom arise at the
level of the regulated theory that conspire against the existence of the
continuum limit. This shows that there is a clear cut choice in the
quantization of the constraints in 2+1 LQG./ We then analyze the effects of the
ambiguity in 3+1 gravity exhibiting the existence of spurious solutions for
higher unit. rep. quantizations of the Hamiltonian constraint. Although the
analysis is not complete in D=3+1--due to the difficulties associated to the
definition of the physical inner product--it provides evidence supporting the
definitions quantum dynamics of loop quantum gravity in terms of the
fundamental representation of the gauge group as the only consistent
possibilities. If the gauge group is SO(3) we find physical solutions
associated to spin-two local excitations.


title: Discrete boundary treatment for the shifted wave equation

abstract:
  We present strongly stable semi-discrete finite difference approximations to
the quarter space problem (x>0, t>0) for the first order in time, second order
in space wave equation with a shift term. We consider space-like (pure outflow)
and time-like boundaries, with either second or fourth order accuracy. These
discrete boundary conditions suggest a general prescription for boundary
conditions in finite difference codes approximating first order in time, second
order in space hyperbolic problems, such as those that appear in numerical
relativity. As an example we construct boundary conditions for the
Nagy-Ortiz-Reula formulation of the Einstein equations coupled to a scalar
field in spherical symmetry.


title:
Probability Theories with Dynamic Causal Structure: A New Framework for
  Quantum Gravity

abstract:
  Quantum theory is a probabilistic theory with fixed causal structure. General
relativity is a deterministic theory but where the causal structure is dynamic.
It is reasonable to expect that quantum gravity will be a probabilistic theory
with dynamic causal structure. The purpose of this paper is to present a
framework for such a probability calculus. We define an operational notion of
space-time, this being composed of elementary regions. Central to this
formalism is an object we call the causaloid. This object captures information
about causal structure implicit in the data by quantifying the way in which the
number of measurements required to establish a state for a composite region is
reduced when there is a causal connection between the component regions. This
formalism puts all elementary regions on an equal footing. It does not require
that we impose fixed causal structure. In particular, it is not necessary to
assume the existence of a background time. Remarkably, given the causaloid, we
can calculate all relevant probabilities and so the causaloid is sufficient to
specify the predictive aspect of a physical theory. We show how certain
causaloids can be represented by suggestive diagrams and we show how to
represent both classical probability theory and quantum theory by a causaloid.
We do not give a causaloid formulation for general relativity though we
speculate that this is possible. The work presented here suggests a research
program aimed at finding a theory of quantum gravity. The idea is to use the
causaloid formalism along with principles taken from the two theories to marry
the dynamic causal structure of general relativity with the probabilistic
structure of quantum theory.


title: Noether charges and black hole mechanics in Einstein-aether theory

abstract:
  The Noether charge method for defining the Hamiltonian of a
diffeomorphism-invariant field theory is applied to "Einstein-aether" theory,
in which gravity couples to a dynamical, timelike, unit-norm vector field.
Using the method, expressions are obtained for the total energy, momentum, and
angular momentum of an Einstein-aether space-time. The method is also used to
discuss the mechanics of Einstein-aether black holes. The derivation of Wald,
and Iyer and Wald, of the first law of black hole thermodynamics fails for this
theory, because the unit vector is necessarily singular at the bifurcation
surface of the Killing horizon. A general identity relating variations of
energy and angular momentum to a surface integral at the horizon is obtained,
but a thermodynamic interpretation, including a definitive expression for the
black hole entropy, is not found.


title:
Limitations of the adiabatic approximation to the gravitational
  self-force

abstract:
  A small body moving in the field of a much larger black hole and subjected to
its own gravity moves on an accelerated world line in the background spacetime
of the large black hole. The acceleration is produced by the body's
gravitational self-force, which is constructed from the body's retarded
gravitational field. The adiabatic approximation to the gravitational
self-force is obtained instead from the half-retarded minus half-advanced
field; it is known to produce the same dissipative effects as the true
self-force. We argue that the adiabatic approximation is limited, because it
discards important conservative terms which lead to the secular evolution of
some orbital elements. We argue further that this secular evolution has
measurable consequences; in particular, it affects the phasing of the orbit and
the phasing of the associated gravitational wave. Our argument rests on a
simple toy model involving a point electric charge moving slowly in the weak
gravitational field of a central mass; the charge is also subjected to its
electromagnetic self-force. In this simple context the true self-force is known
explicitly and it can cleanly be separated into conservative and
radiation-reaction pieces. We observe that the conservative part of the
self-force produces a secular regression of the orbit's periapsis. We explain
how the conclusions reached on the basis of the toy model can be extended to
the gravitational self-force, and to fast motions and strong fields. While the
limitations of the adiabatic approximation are quite severe in a post-Newtonian
context in which the motion is slow and the gravitational field weak, they
appear to be less so for rapid motions and strong fields.


title:
Exact Solutions of Regge-Wheeler Equation and Quasi-Normal Modes of
  Compact Objects

abstract:
  The well-known Regge-Wheeler equation describes the axial perturbations of
Schwarzschild metric in the linear approximation. From a mathematical point of
view it presents a particular case of the confluent Heun equation and can be
solved exactly, due to recent mathematical developments. We present the basic
properties of its general solution. A novel analytical approach and numerical
techniques for study the boundary problems which correspond to quasi-normal
modes of black holes and other simple models of compact objects are developed.


title:
On globally static and stationary cosmologies with or without a
  cosmological constant and the Dark Energy problem

abstract:
  In the framework of spatially averaged inhomogeneous cosmologies in classical
General Relativity, effective Einstein equations govern the regional and the
global dynamics of averaged scalar variables of cosmological models. A
particular solution may be characterized by a cosmic equation of state. In this
paper it is pointed out that a globally static averaged dust model is
conceivable without employing a compensating cosmological constant. Much in the
spirit of Einstein's original model we discuss consequences for the global, but
also for the regional properties of this cosmology. We then consider the wider
class of globally stationary cosmologies that are conceivable in the presented
framework. All these models are based on exact solutions of the averaged
Einstein equations and provide examples of cosmologies in an out-of-equilibrium
state, which we characterize by an information-theoretical measure. It is shown
that such cosmologies preserve high-magnitude kinematical fluctuations and so
tend to maintain their global properties. The same is true for a
$\Lambda-$driven cosmos in such a state despite of exponential expansion. We
outline relations to inflationary scenarios, and put the Dark Energy problem
into perspective. Here, it is argued, on the grounds of the discussed
cosmologies, that a classical explanation of Dark Energy through backreaction
effects is theoretically conceivable, if the matter-dominated Universe emerged
from a non-perturbative state in the vicinity of the stationary solution. We
also discuss a number of caveats that furnish strong counter arguments in the
framework of structure formation in a perturbed Friedmannian model.


title:
Perturbative and Numerical Analysis of Tilted Cosmological Models of
  Bianchi type V

abstract:
  Cosmological models of Bianchi type V and I containing a perfect fluid with a
linear equation of state plus cosmological constant are investigated using a
tetrad approach where our variables are the Riemann tensor, the Ricci rotation
coefficients and a subset of the tetrad vector components. This set, in the
following called S, describes a spacetime when its elements are constrained by
certain integrability conditions and due to a theorem by Cartan this set gives
a complete local description of the spacetime. The system obtained by imposing
the integrability conditions and Einstein's equations can be reduced to an
integrable system of five coupled first order ordinary differential equations.
The general solution is tilted and describes a fluid with expansion, shear and
vorticity. With the help of standard bases for Bianchi V and I the full line
element is found in terms of the elements in S. We then construct the solutions
to the linearized equations around the open Friedmann model. The full system is
also studied numerically and the perturbative solutions agree well with the
numerical ones in the appropriate domains. We also give some examples of
numerical solutions in the non-perturbative regime.


title: The power spectrum of the circular noise

abstract:
  The circular noise is important in connection to Mach's principle, and also
as a possible probe of the Unruh effect. In this letter the power spectrum of
the detector following the Trocheries-Takeno motion in the Minkowski vacuum is
analytically obtained in the form of an infinite series. A mean distribution
function and corresponding energy density are obtained for this particular
detected noise. The analogous of a non constant temperature distribution is
obtained. And in the end, a brief discussion about the equilibrium
configuration is given.


title: Geodesic Nucleation and Evolution of a de Sitter Brane

abstract:
  Within the framework of Geodesic Brane Gravity, the deviation from General
Relativity is parameterized by the conserved bulk energy. The corresponding
geodesic evolution/nucleation of a de-Sitter brane is shown to be exclusively
driven by a double-well Higgs potential, rather than by a plain cosmological
constant. The (hairy) horizon serves then as the locus of unbroken $Z_{2}$
symmetry. The quartic structure of the scalar potential, singled out on
finiteness grounds of the total (including the dark component) energy density,
chooses the Hartle-Hawking no-boundary proposal.


title:
Post-Newtonian Freely Specifiable Initial Data for Binary Black Holes in
  Numerical Relativity

abstract:
  Construction of astrophysically realistic initial data remains a central
problem when modelling the merger and eventual coalescence of binary black
holes in numerical relativity. The objective of this paper is to provide
astrophysically realistic freely specifiable initial data for binary black hole
systems in numerical relativity, which are in agreement with post-Newtonian
results. Following the approach taken by Blanchet, we propose a particular
solution to the time-asymmetric constraint equations, which represent a system
of two moving black holes, in the form of the standard conformal decomposition
of the spatial metric and the extrinsic curvature. The solution for the spatial
metric is given in symmetric tracefree form, as well as in Dirac coordinates.
We show that the solution differs from the usual post-Newtonian metric up to
the 2PN order by a coordinate transformation. In addition, the solutions,
defined at every point of space, differ at second post-Newtonian order from the
exact, conformally flat, Bowen-York solution of the constraints.


title:
Search for gravitational waves from binary black hole inspirals in LIGO
  data

abstract:
  We report on a search for gravitational waves from binary black hole
inspirals in the data from the second science run of the LIGO interferometers.
The search focused on binary systems with component masses between 3 and 20
solar masses. Optimally oriented binaries with distances up to 1 Mpc could be
detected with efficiency of at least 90%. We found no events that could be
identified as gravitational waves in the 385.6 hours of data that we searched.


title:
Cosmological particle production and the precision of the WKB
  approximation

abstract:
  Particle production by slow-changing gravitational fields is usually
described using quantum field theory in curved spacetime. Calculations require
a definition of the vacuum state, which can be given using the adiabatic (WKB)
approximation. I investigate the best attainable precision of the resulting
approximate definition of the particle number. The standard WKB ansatz yields a
divergent asymptotic series in the adiabatic parameter. I derive a novel
formula for the optimal number of terms in that series and demonstrate that the
error of the optimally truncated WKB series is exponentially small. This
precision is still insufficient to describe particle production from vacuum,
which is typically also exponentially small. An adequately precise
approximation can be found by improving the WKB ansatz through perturbation
theory. I show quantitatively that the fundamentally unavoidable imprecision in
the definition of particle number in a time-dependent background is equal to
the particle production expected to occur during that epoch. The results are
illustrated by analytic and numerical examples.


title:
Post-Minkowski action for point particles and a helically symmetric
  binary solution

abstract:
  Two Fokker actions and corresponding equations of motion are obtained for two
point particles in a post-Minkowski framework, in which the field of each
particle is given by the half-retarded + half-advanced solution to the
linearized Einstein equations. The first action is parametrization invariant,
the second a generalization of the affinely parametrized quadratic action for a
relativistic particle. Expressions for a conserved 4-momentum and angular
momentum tensor are obtained in terms of the particles' trajectories in this
post-Minkowski approximation. A formal solution to the equations of motion is
found for a binary system with circular orbits. For a bound system of this
kind, the post-Minkowski solution is a toy model that omits nonlinear terms of
relevant post-Newtonian order; and we also obtain a Fokker action that is
accurate to first post-Newtonian order, by adding to the post-Minkowski action
a term cubic in the particle masses. Curiously, the conserved energy and
angular momentum associated with the Fokker action are each finite and
well-defined for this bound 2-particle system despite the fact that the total
energy and angular momentum of the radiation field diverge. Corresponding
solutions and conserved quantities are found for two scalar charges (for
electromagnetic charges we exhibit the solution found by Schild). For a broad
class of parametrization-invariant Fokker actions and for the affinely
parametrized action, binary systems with circular orbits satisfy the relation
$dE = \Omega dL$ (a form of the first law of thermodynamics), relating the
energy, angular velocity and angular momentum of nearby equilibrium
configurations.


title: Newtonian Gravitomagnetism and analysis of Earth Satellite Results

abstract:
  The possibility of a Newtonian gravitomagnetic field is considered here with
its immediate and far-reaching implications for the interpretation of 2004
LAGEOS experimental results confirming the general relativistic prediction of
Lense-Thirring effect.


title: Supersymmetry of FRW barotropic cosmologies

abstract:
  Barotropic FRW cosmologies are presented from the standpoint of
nonrelativistic supersymmetry. First, we reduce the barotropic FRW system of
differential equations to simple harmonic oscillator differential equations.
Employing the factorization procedure, the solutions of the latter equations
are divided into the two classes of bosonic (nonsingular) and fermionic
(singular) cosmological solutions. We next introduce a coupling parameter
denoted by K between the two classes of solutions and obtain barotropic
cosmologies with dissipative features acting on the scale factors and spatial
curvature of the universe. The K-extended FRW equations in comoving time are
presented in explicit form in the low coupling regime. The standard barotropic
FRW cosmologies correspond to the dissipationless limit K =0


title: The Kasner Brane

abstract:
  Solutions are found to field equations constructed from the
  Pauli, Bach and Gauss-Bonnet quadratic tensors to the Kasner and Kasner brane
spacetimes in up to five dimensions. A double Kasner space is shown to have a
vacuum solution. Brane solutions in which the bulk components of the Einstein
tensor vanish are also looked at and for four branes a solution similar to
radiation Robertson-Walker spacetime is found. Matter trapping of a test scalar
field and a test perfect fluid are investigated using energy conditions.


title: Null energy in plane Kaluza-Klein worlds

abstract:
  We study the energy problem in the $R0X$ spacetimes in 5D. We found that for
the Einstein, Landau-Lifschitz and the Moller complexes are null.


title:
Acceleration of the universe in the Einstein frame of a metric-affine
  f(R) gravity

abstract:
  We show that inflation and current cosmic acceleration can be generated by a
metric-affine f(R) gravity formulated in the Einstein conformal frame, if the
gravitational Lagrangian L(R) contains both positive and negative powers of the
curvature scalar R. In this frame, we give the equations for the expansion of
the homogeneous and isotropic matter-dominated universe in the case
L(R)=R+{R^3}/{\beta^2}-{\alpha^2}/{3R}, where \alpha and \beta are constants.
We also show that gravitational effects of matter in such a universe at very
late stages of its expansion are weakened by a factor that tends to 3/4, and
the energy density of matter \epsilon scales the same way as in the \Lambda-CDM
model only when \kappa*\epsilon<<\alpha.


title:
Comment on "High-order contamination in the tail of gravitational
  collapse''

abstract:
  We confront the predictions of S. Hod, Phys. Rev. D 60, 104053 (1999) for the
late-time decay rate of black hole perturbations with numerical data.
Specifically, we ask two questions: First, are corrections to the Price tail
dominated by logarithmic terms, as predicted by Hod? Second, if there were
logarithmic correction terms, do they take the specific form predicted in Hod's
paper? The answer to both questions is ``no.''


title: Hawking radiation and Quasinormal modes

abstract:
  The spectrum of Hawking radiation by quantum fields in the curved spacetime
is continuous, so the explanation of Hawking radiation using quasinormal modes
can be suspected to be impossible. We find that quasinormal modes do not
explain the relation between the state observed in a region far away from a
black hole and the short distance behavior of the state on the horizon.


title: Mechanism of Gravity Impulse

abstract:
  It is well-known that energy-momentum is the source of gravitational field.
For a long time, it is generally believed that only stars with huge masses can
generate strong gravitational field. Based on the unified theory of
gravitational interactions and electromagnetic interactions, a new mechanism of
the generation of gravitational field is studied. According to this mechanism,
in some special conditions, electromagnetic energy can be directly converted
into gravitational energy, and strong gravitational field can be generated
without massive stars. Gravity impulse found in experiments is generated by
this mechanism.


title: Quantum Spin Dynamics VIII. The Master Constraint

abstract:
  Recently the Master Constraint Programme (MCP) for Loop Quantum Gravity (LQG)
was launched which replaces the infinite number of Hamiltonian constraints by a
single Master constraint. The MCP is designed to overcome the complications
associated with the non -- Lie -- algebra structure of the Dirac algebra of
Hamiltonian constraints and was successfully tested in various field theory
models. For the case of 3+1 gravity itself, so far only a positive quadratic
form for the Master Constraint Operator was derived. In this paper we close
this gap and prove that the quadratic form is closable and thus stems from a
unique self -- adjoint Master Constraint Operator. The proof rests on a simple
feature of the general pattern according to which Hamiltonian constraints in
LQG are constructed and thus extends to arbitrary matter coupling and holds for
any metric signature. With this result the existence of a physical Hilbert
space for LQG is established by standard spectral analysis.


title: Scalar Field Contribution to Rotating Black Hole Entropy

abstract:
  Scalar field contribution to entropy is studied in arbitrary D dimensional
one parameter rotating spacetime by semiclassical method. By introducing the
zenithal angle dependent cutoff parameter, the generalized area law is derived.
The non-rotating limit can be taken smoothly and it yields known results. The
derived area law is then applied to the Banados-Teitelboim-Zanelli (BTZ) black
hole in (2+1) dimension and the Kerr-Newman black hole in (3+1) dimension. The
generalized area law is reconfirmed by the Euclidean path integral method for
the quantized scalar field. The scalar field mass contribution is discussed
briefly.


title: Causal temperature profiles in horizon-free collapse

abstract:
  We investigate the causal temperature profiles in a recent model of a
radiating star undergoing dissipative gravitational collapse without the
formation of an horizon. It is shown that this simple exact model provides a
physically reasonable behaviour for the temperature profile within the
framework of extended irreversible thermodynamics.


title: Master Constraint Operator in Loop Quantum Gravity

abstract:
  We introduce a master constraint operator $\hat{\mathbf{M}}$ densely defined
in the diffeomorphism invariant Hilbert space in loop quantum gravity, which
corresponds classically to the master constraint in the programme. It is shown
that $\hat{\mathbf{M}}$ is positive and symmetric, and hence has its Friedrichs
self-adjoint extension. The same conclusion is tenable for an alternative
master operator $\hat{\mathbf{M'}}$, whose quadratic form coincides with the
one proposed by Thiemann. So the master constraint programme for loop quantum
gravity can be carried out in principle by employing either of the two
operators.


title: A new perspective on Gravity and the dynamics of Spacetime

abstract:
  The Einstein-Hilbert action has a bulk term and a surface term (which arises
from integrating a four divergence). I show that one can obtain Einstein's
equations from the surface term alone. This leads to: (i) a novel, completely
self contained, perspective on gravity and (ii) a concrete mathematical
framework in which the description of spacetime dynamics by Einstein's
equations is similar to the description of a continuum solid in the
thermodynamic limit.


title: Initial data for black hole evolutions

abstract:
  We discuss the initial value problem of general relativity in its recently
unified Lagrangian and Hamiltonian pictures and present a multi-domain
pseudo-spectral collocation method to solve the resulting coupled nonlinear
partial differential equations. Using this code, we explore several approaches
to construct initial data sets containing one or two black holes: We compute
quasi-circular orbits for spinning equal mass black holes and unequal mass
(nonspinning) black holes using the effective potential method with Bowen-York
extrinsic curvature. We compare initial data sets resulting from different
decompositions, and from different choices of the conformal metric with each
other. Furthermore, we use the quasi-equilibrium method to construct initial
data for single black holes and for binary black holes in quasi-circular
orbits. We investigate these binary black hole data sets and examine the limits
of large mass-ratio and wide separation. Finally, we propose a new method for
constructing spacetimes with superposed gravitational waves of possibly very
large amplitude.


title: A "Lorentz-Poincare"-Type Interpretation of Relativistic Gravitation

abstract:
  The nature of 'time', 'space' and 'reality' are to large extent dependent on
our interpretation of Special (SRT) and General Relativity Theory (GRT). In SRT
essentially two distinct interpretations exist; the "geometrical"
interpretation by Einstein based on the Principle of Relativity and the
Invariance of the velocity of light and, the "physical" Lorentz-Poincar\'e
interpretation with underpinning by rod contractions, clock slowing and light
synchronization, see e.g. (Bohm 1965, Bell 1987). It can be questioned whether
the "Lorentz-Poincar\'e"-interpretation of SRT can be continued into GRT. We
have shown that till first Post-Newtonian order this is indeed possible
(Broekaert 2004). This requires the introduction of gravitationally modified
Lorentz transformations, with an intrinsical spatially-variable speed of light
$c(r)$, a scalar scaling field $\Phi$ and induced velocity field $w$. Still the
invariance of the locally observed velocity of light is maintained (Broekaert
2005). The Hamiltonian description of particles and photons recovers the 1-PN
approximation of GRT. At present we show the model does obey the Weak
Equivalence Principle from a fixed perspective, and that the implied
acceleration transformations are equivalent with those of GRT.


title:
On searches for gravitational waves from mini creation event by laser
  interferometric detectors

abstract:
  As an alternative view to the standard big bang cosmology the quasi-steady
state cosmology(QSSC) argues that the universe was not created in a single
great explosion; it neither had a beginning nor will it ever come to an end.
The creation of new matter in the universe is a regular feature occurring
through finite explosive events. Each creation event is called a mini-bang or,
a mini creation event(MCE). Gravitational waves are expected to be generated
due to any anisotropy present in this process of creation. Mini creation event
ejecting matter in two oppositely directed jets is thus a source of
gravitational waves which can in principle be detected by laser interferometric
detectors. In the present work we consider the gravitational waveforms
propagated by linear jets and then estimate the response of laser
interferometric detectors like LIGO and LISA.


title:
Perturbations of Schwarzschild black holes in the Lorenz gauge:
  Formulation and numerical implementation

abstract:
  We reformulate the theory of Schwarzschild black hole perturbations in terms
of the metric perturbation in the Lorenz gauge. In this formulation, each
tensor-harmonic mode of the perturbation is constructed algebraically from 10
scalar functions, satisfying a set of 10 wavelike equations, which are
decoupled at their principal parts. We solve these equations using numerical
evolution in the time domain, for the case of a pointlike test particle set in
a circular geodesic orbit around the black hole. Our code uses characteristic
coordinates, and incorporates a constraint damping scheme. The
axially-symmetric, odd-parity modes of the perturbation are obtained
analytically. The approach developed here is especially advantageous in
applications requiring knowledge of the local metric perturbation near a point
particle; in particular, it offers a useful framework for calculations of the
gravitational self force.


title:
General Relativistic Decompression of Binary Neutron Stars During
  Dynamic Inspiral

abstract:
  We investigate the dynamic stability of inspiraling neutron stars by
performing multiple-orbit numerical relativity simulations of the binary
neutron star inspiral process. By introducing eccentricities in the orbits of
the neutron stars, significant changes in orbital separation are obtained
within orbital timescales. We find that as the binary system evolves from
apastron to periastron (as the binary separation decreases), the central rest
mass density of each star decreases, thus stabilizing the stars against
individual prompt collapse. As the binary system evolves from periastron to
apastron, the central rest mass density increases; the neutron stars
re-compress as the binary separation increases.


title:
Matters of Gravity, the newsletter of the Topical Group in Gravitation
  of APS

abstract:
  GGR News:
  The WYP speakers program, by Richard Price
  We hear that..., by Jorge Pullin
  100 Years ago, by Jorge Pullin
  Research Briefs:
  What's new in LIGO, by David Shoemaker
  Recent developments in the information loss paradox, by Eanna Flanagan
  Gravity Probe B mission ends, by Bob Kahn
  Conference reports:
  6th Edoardo Amaldi Meeting, by Matthew Benacquista
  Workshop on Numerical Relativity, BIRS, by Carsten Gundlach
  8th Capra Meeting on Radiation Reaction, by Leor Barack
  Theory and experiment in quantum gravity, by Elizabeth Winstanley


title: Correspondence between Loop-inspired and Braneworld Cosmology

abstract:
  Braneworld scenarios are motivated by string/M-theory and can be
characterized by the way in which they modify the conventional Friedmann
equations of Einstein gravity. An alternative approach to quantum gravity,
however, is the loop quantum cosmology program. In the semi-classical limit,
the cosmic dynamics in this scenario can also be described by a set of modified
Friedmann equations. We demonstrate that a dynamical correspondence can be
established between these two paradigms at the level of the effective field
equations. This allows qualitatively similar features between the two
approaches to be compared and contrasted as well as providing a framework for
viewing braneworld scenarios in terms of constrained Hamiltonian systems. As
concrete examples of this correspondence, we illustrate the relationships
between different cosmological backgrounds representing scaling solutions.


title: Kerr metric, static observers and Fermi coordinates

abstract:
  The coordinate transformation which maps the Kerr metric written in standard
Boyer-Lindquist coordinates to its corresponding form adapted to the natural
local coordinates of an observer at rest at a fixed position in the equatorial
plane, i.e., Fermi coordinates for the neighborhood of a static observer world
line, is derived and discussed in a way which extends to any uniformly
circularly orbiting observer there.


title: General Covariance and its Implications for Einstein's Space-Times

abstract:
  This is a review of the chrono-geometrical structure of special and general
relativity with a special emphasis on the role of non-inertial frames and of
the conventions for the synchronization of distant clocks. ADM canonical metric
and tetrad gravity are analyzed in a class of space-times suitable to
incorporate particle physics by using Dirac theory of constraints, which allows
to arrive at a separation of the genuine degrees of freedom of the
gravitational field, the Dirac observables describing generalized tidal
effects, from its gauge variables, describing generalized inertial effects. A
background-independent formulation (the rest-frame instant form of tetrad
gravity) emerges, since the chosen boundary conditions at spatial infinity
imply the existence of an asymptotic flat metric. By switching off the Newton
constant in presence of matter this description deparametrizes to the
rest-frame instant form for such matter in the framework of parametrized
Minkowski theories. The problem of the objectivity of the space-time
point-events, implied by Einstein's Hole Argument, is analyzed.


title: Recollapsing Bianchi I brane worlds

abstract:
  We investigate the possibility for a flat Bianchi I brane Universe to
recollaps due to the presence of a negative "dark radiation" and an anisotropic
stress in the form of a homogeneous magnetic field, localized on the brane.


title:
Equations of motion according to the asymptotic post-Newtonian scheme
  for general relativity

abstract:
  We summarize a recent work done on the title's subject. First, we present the
asymptotic scheme of post-Newtonian (PN) approximation for general relativity
in the harmonic gauge. Then, we discuss the definition of the mass centers and
the derivation of equations for their motion, following that scheme. Finally,
we briefly analyze the reason why a new term has thus been found in the
equations of motion.


title: Bogoliubov transformations for amplitudes in black-hole evaporation

abstract:
  The familiar approach to quantum radiation following collapse to a black hole
proceeds via Bogoliubov transformations, and yields probabilities for final
outcomes. In our (complex) approach, we find quantum amplitudes, not just
probabilities, by following Feynman's $+i\epsilon$ prescription. Initial and
final data for Einstein gravity and (say) a massless scalar field are specified
on a pair of asymptotically-flat space-like hypersurfaces $\Sigma_I$ and
$\Sigma_F$; both are diffeomorphic to ${\Bbb R}^3$. Denote by $T$ the (real)
Lorentzian proper-time interval between the surfaces, as measured at spatial
infinity. Then rotate: $T\to{\mid}T{\mid}\exp(-i\theta),0<\theta\leq \pi/2$.
The {\it classical} boundary-value problem is expected to be well-posed on a
region of topology $I\times{\Bbb R}^3$, where $I$ is a closed interval. For a
locally-supersymmetric theory, the quantum amplitude should be dominated by the
semi-classical expression $\exp(iS_{\rm class})$, where $S_{\rm class}$ is the
classical action. One finds the Lorentzian quantum amplitude from the limit
$\theta\to 0_+$. In the usual approach, the only possible such final surfaces
are in the strong-field region shortly before the curvature singularity. In our
approach one can put arbitrary smooth gravitational data on $\Sigma_F$,
provided that it has the correct mass $M$ -- the singularity is by-passed in
the analytic continuation. Here, we consider Bogoliubov transformations and
their possible relation to the probability distribution and density matrix in
the traditional approach. We find that our probability distribution for
configurations of the final scalar field cannot be expressed in terms of the
diagonal elements of some non-trivial density-matrix distribution.


title: Quantum Amplitudes in Black-Hole Evaporation I. Complex Approach

abstract:
  Here we examine the quantum-mechanical decay of a Schwarzschild-like black
hole, formed by gravitational collapse, into almost-flat space-time and weak
radiation at a very late time, in order to evaluate quantum amplitudes (not
just probabilities) for final states. No information is lost in collapse to a
black hole. Boundary data are specified on initial and final hypersurfaces
$\Sigma_{I, F}$, separated by a Lorentzian proper-time interval $T$, as
measured at spatial infinity. For simplicity, consider Einstein gravity coupled
minimally to a massless scalar field $\phi$. In Lorentzian signature, the
classical Dirichlet boundary-value problem, corresponding to specification of
the intrinsic spatial metric $h_{ij} (i,j =1,2,3)$ and $\phi$ on the bounding
surfaces, is badly posed, being a boundary-value problem for a wave-like
(hyperbolic) set of equations. Following Feynman's $+i\epsilon$ prescription,
the problem is made well-posed by rotating the asymptotic time interval $T$
into the complex: $T\to{\mid} T{\mid}\exp(-i\theta)$, with $0<\theta\leq\pi/2$.
After calculating the amplitude for $\theta>0$, one takes the 'Lorentzian
limit' $\theta\to 0_+$ to obtain the Lorentzian quantum amplitude.


title: Quantum Amplitudes in Black-Hole Evaporation II. Spin-0 Amplitude

abstract:
  This work on spin-0 amplitudes in black-hole evaporation is based on the
underlying results and methods outlined in our first paper, "I. Complex
Approach". The main result here, and the model calculation for work on all
higher spins, as described in several further papers, is the computation of the
quantum amplitude (rather than merely the probability) for a given slightly
anisotropic configuration of a scalar field $\phi$ on a space-like hypersurface
$\Sigma_F$ at a very late time $T$. For simplicity, one may take the initial
data for gravity and the massless scalar field at an initial surface $\Sigma_I$
to be spherically symmetric. This applies to perturbations of
spherically-symmetric collapse to a black hole, starting from a diffuse,
nearly-stationary configuration, where the bosonic part of the Lagrangian
consists of Einstein gravity and the massless scalar field. As in Paper I,
Feynman's $+i\epsilon$ approach is taken; this involves a rotation into the
complex: $T\to {\mid}T{\mid} \exp (-i\theta)$, with $0<\theta\leq\pi/2$. A
complex solution of the classical boundary-value problem is expected to exist,
provided $\theta>0$; although for $\theta =0$ (Lorentzian time-separation), the
classical boundary-value problem is badly posed. Once the amplitude is found
for $\theta>0$, one can take the limit $\theta\to 0_+$ to find the Lorentzian
amplitude. The paper also includes a discussion of adiabatic solutions of the
scalar wave equation, needed for the spin-0 calculation.


title: Spin-1 Amplitudes in Black-Hole Evaporation

abstract:
  Our earlier work on the quantum amplitude for a scalar field in black-hole
evaporation, following gravitational collapse, is here extended to Maxwell
theory. Boundary data are specified on initial and final space-like
hypersurfaces $\Sigma_{I,F}$, separated by a large Lorentzian proper-time
interval $T$, as measured at spatial infinity. The initial boundary data may be
chosen (say) to be spherically symmetric, corresponding to a nearly-spherical
configuration prior to gravitational collapse. The final data include the
intrinsic 3-metric and scalar field, restricted to $\Sigma_F$, in addition to
spin-1 data, naturally taken to be the magnetic field $B_i$ on $\Sigma_{I,F}
(i=1,2,3)$. For a locally-supersymmetric theory, the quantum amplitude should
be proportional to $\exp(iS_{\rm class})$, apart from corrections which are
very small when the frequencies in the boundary data are small compared to the
Planck scale. Here, $S_{\rm class}$ is the action of the classical solution.
The Lorentzian amplitude is found by taking the limit $\theta\to 0_+$. By a
method similar to that used in the spin-0 case, one obtains the quantum
amplitude for photon data on $\Sigma_F$. The magnetic boundary conditions are
related by supersymmetry to the natural spin-2 (gravitational-wave) boundary
conditions, which involve fixing the magnetic part of the Weyl tensor.


title: Critical Tests for two Hypotheses used in Gravitation and Cosmology

abstract:
  From more critical tests for gravitational (G) hypotheses it has been proved
that the relative properties of nonlocal (NL) bodies at rest with respect to an
observer depend on the difference of G potential between bodies and observer.
The G energy comes not from the field but from a fraction of the mass-energy of
the bodies. These results are in opposition with two traditional hypotheses
used in Physics. In the classical tests of general relativity their errors are
compensated because they have the same absolute value and opposite signs. The
general theory based on such tests, called non-local relativity, is consistent
with quantum mechanics and with all of the traditional G tests. The new
cosmological scenario, which is radically different from the standard one, has
also been verified from astronomical observations.


title:
General Formula for Comparison of Clock Rates -- Applications to Cosmos
  and Solar System

abstract:
  In this paper we deduce a quite general formula which allows the relation of
clock rates at two different space time points to be discussed. In the case of
a perturbed Robertson-Walker metric, our analysis leads to an equation for the
comparison of clock rates at different cosmic space time points, which includes
the Hubble redshift, the Doppler effect, the gravitational redshift and the
Rees-Sciama effects. In the case of the solar system, when the 2PN metric is
substituted into the general formula, the comparison of the clock rates on both
the earth and a space station could be made. It might be useful for the
discussion on the precise measurements on future ACES and ASTROD.


title: Lattice p-Form Electromagnetism and Chain Field Theory

abstract:
  Since Wilson's work on lattice gauge theory in the 1970s, discrete versions
of field theories have played a vital role in fundamental physics. But there is
recent interest in certain higher dimensional analogues of gauge theory, such
as p-form electromagnetism, including the Kalb-Ramond field in string theory,
and its nonabelian generalizations. It is desirable to discretize such `higher
gauge theories' in a way analogous to lattice gauge theory, but with the
fundamental geometric structures in the discretization boosted in dimension. As
a step toward studying discrete versions of more general higher gauge theories,
we consider the case of p-form electromagnetism. We show that discrete p-form
electromagnetism admits a simple algebraic description in terms of chain
complexes of abelian groups. Moreover, the model allows discrete spacetimes
with quite general geometry, in contrast to the regular cubical lattices
usually associated with lattice gauge theory. After constructing a suitable
model of discrete spacetime for p-form electromagnetism, we quantize the theory
using the Euclidean path integral formalism. The main result is a description
of p-form electromagnetism as a `chain field theory' -- a theory analogous to
topological quantum field theory, but with chain complexes replacing manifolds.
This, in particular, gives a notion of time evolution from one `spacelike
slice' of discrete spacetime to another.


title:
General-relativistic perturbation equations for the dynamics of elastic
  deformable astronomical bodies expanded in terms of generalized spherical
  harmonics

abstract:
  In our previous paper, based on the Carter & Quintana framework and the
Damour-Soffel-Xu scheme, we deduced a complete and closed set of post-Newtonian
dynamical equations for elastically deformable astronomical bodies. In this
paper, we expand the general relativistic perturbation equations of elastic
deformable bodies (field equations, stress-strain relation, Euler equation) in
terms of Generalized Spherical Harmonics. This turns the set of complicated
partial differential equations into a set of ordinary differential equations.
This will be useful for numerical applications that mainly deal with the global
dynamics of the Earth.


title: Spin-2 Amplitudes in Black-Hole Evaporation

abstract:
  Quantum amplitudes for $s=2$ gravitational-wave perturbations of
Einstein/scalar collapse to a black hole are treated by analogy with $s=1$
Maxwell perturbations. The spin-2 perturbations split into parts with odd and
even parity. We use the Regge-Wheeler gauge; at a certain point we make a gauge
transformation to an asymptotically-flat gauge, such that the metric
perturbations have the expected falloff behaviour at large radii. By analogy
with $s=1$, for $s=2$ natural 'coordinate' variables are given by the magnetic
part $H_{ij} (i,j=1,2,3)$ of the Weyl tensor, which can be taken as boundary
data on a final space-like hypersurface $\Sigma_F$. For simplicity, we take the
data on the initial surface $\Sigma_I$ to be exactly spherically-symmetric. The
(large) Lorentzian proper-time interval between $\Sigma_I$ and $\Sigma_F$,
measured at spatial infinity, is denoted by $T$. We follow Feynman's
$+i\epsilon$ prescription and rotate $T$ into the complex: $T\to{\mid}T{\mid}
\exp(-i\theta)$, for $0<\theta\leq\pi/2$. The corresponding complexified {\it
classical} boundary-value problem is expected to be well-posed. The Lorentzian
quantum amplitude is recovered by taking the limit as $\theta\to 0_+$. For
boundary data well below the Planck scale, and for a locally supersymmetric
theory, this involves only the semi-classical amplitude $\exp(iS^{(2)}_{\rm
class}$, where $S^{(2)}_{\rm class}$ denotes the second-variation classical
action. The relations between the $s=1$ and $s=2$ natural boundary data,
involving supersymmetry, are investigated using 2-component spinor language in
terms of the Maxwell field strength $\phi_{AB}=\phi_{(AB)}$ and the Weyl spinor
$\Psi_{ABCD}=\Psi_{(ABCD)}$.


title: Spin-$1\over 2$ amplitudes in black-hole evaporation

abstract:
  We extend to the fermionic spin-1/2 case earlier work on quantum amplitudes
arising from gravitational collapse to a black hole. Boundary data are
specified on initial and final asymptotically-flat space-like hypersurfaces
$\Sigma_{I,F}$, separated by a Lorentzian proper-time interval $T$, measured at
spatial infinity. Following Feynman's $+i\epsilon$ prescription, one makes the
problem well-posed by rotating $T$ into the complex: $T\to{\mid}T{\mid}
\exp(-i\theta)$, with $0<\theta\leq\pi/2$. After calculating the amplitude for
$\theta>0$, one takes the 'Lorentzian limit' $\theta\to 0_+$. In this paper, we
treat quantum amplitudes for the case of fermionic massless spin-1/2 (neutrino)
final boundary data; working in the holomorphic representation, we take these
boundary data to be odd elements of a Grassmann algebra. Making use of boundary
conditions originally developed for local supersymmetry, we find that this
fermionic case can be treated in a way which parallels the bosonic case. With
these boundary conditions, for $\theta > 0$, one obtains a unique fermionic
classical solution, and we calculate its classical action as a functional of
the fermionic data on the late-time surface $\Sigma_F$; the quantum amplitude
follows straightforwardly from this.


title: Photon in Teleparallel Gravity in the Bianchi-type I Space-time

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0105122.
  This paper also has excessive overlap with the following paper also written
by the authors or their collaborators: gr-qc/0502059, gr-qc/0502061,
gr-qc/0510038, gr-qc/0502032, gr-qc/0207026, gr-qc/0506062, gr-qc/0505078, and
others.


title: Creation of Massless Spin-1 Particles in a Godel-type Metric

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


title: Quasi-normal modes of the scalar hairy black hole

abstract:
  We calculate QNMs of the scalar hairy black hole in the AdS background using
Horowitz-Hubeny method for the potential that is not known in analytical form.
For some black hole parameters we found pure imaginary frequencies. Increasing
of the scalar field mass does not cause the imaginary part to vanish, it
reaches some minimum and then increases, thus in the case under consideration
the infinitely long living modes (quasi-resonances) do not appear.


title: Vaidya Space-Time in Black-Hole Evaporation

abstract:
  Recently we have studied, using a boundary-value approach, quantum amplitudes
resulting from gravitational collapse to a black hole. Suitable boundary data
for all fields present are posed on initial and final space-like asymptotically
flat hypersurfaces $\Sigma_{I,F}$. The Lorentzian proper-time separation
between the surfaces, as measured at spatial infinity, is denoted by $T$.
Following Feynman's $+i\epsilon$ approach, we rotate $T$ into the complex:
$T\to {\mid}T{\mid} \exp(-i\theta)$, where $0<\theta\leq\pi/2$. The
corresponding {\it classical} complex boundary-value problem is expected to be
well-posed for $\theta > 0$. The Lorentzian amplitude is found by taking the
limit $\theta \to 0_+$ of the quantum amplitude, itself closely approximated by
the semi-classical expression $\exp(iS_{\rm class})$, where $S_{\rm class}$ is
the classical action. For given weak anisotropic spin-0 and spin-2 boundary
data on $\Sigma_F$, one can compute an effective classical energy-momentum
tensor in the interior, which has been averaged over several wave-lengths of
the radiation. This averaged extra contribution will be spherically symmetric,
equivalent to a null fluid, and describing the radial outward streaming of the
radiation (of quantum origin). The corresponding space-time metric, in this
region containing radially-outgoing radiation, is of the Vaidya form. This, in
turn, justifies the treatment of the adiabatic radial mode equations, for spins
$s=0$ and $s=2$, which is used throughout this larger project.


title: Pressure as a Source of Gravity

abstract:
  The active mass density in Einstein's theory of gravitation in the analog of
Poisson's equation in a local inertial system is proportional to $\rho+3p/c^2$.
Here $\rho$ is the density of energy and $p$ its pressure for a perfect fluid.
By using exact solutions of Einstein's field equations in the static case we
study whether the pressure term contributes towards the mass.


title: Quantum mechanics without spacetime: a case for noncommutative geometry

abstract:
  Quantum mechanics in its presently known formulation requires an external
classical time for its description. A classical spacetime manifold and a
classical spacetime metric are produced by classical matter fields. In the
absence of such classical matter fields, quantum mechanics should be formulated
without reference to a classical time. If such a new formulation exists, it
follows as a consequence that standard linear quantum mechanics is a limiting
case of an underlying non-linear quantum theory. A possible approach to the new
formulation is through the use of noncommuting spacetime coordinates in
noncommutative differential geometry. Here, the non-linear theory is described
by a non-linear Schrodinger equation which belongs to the Doebner-Goldin class
of equations, discovered some years ago. This mass-dependent non-linearity is
significant when particle masses are comparable to Planck mass, and negligible
otherwise. Such a non-linearity is in principle detectable through experimental
tests of quantum mechanics for mesoscopic systems, and is a valuable empirical
probe of theories of quantum gravity. We also briefly remark on the possible
connection our approach could have with loop quantum gravity and string theory.


title: Bogoliubov transformations in black-hole evaporation

abstract:
  Our boundary-value approach to quantum processes in the gravitational
collapse to a black hole leads to quantum amplitudes (not just probabilities)
for transitions between data posed on initial and final hypersurfaces
$\Sigma_{I,F}$, separated by a Lorentzian proper-time interval $T$, measured at
spatial infinity. Following Feynman's $+i\epsilon$ approach, we rotate: $T\to
{\mid}T{\mid} \exp(-i\theta)$, for $0<\theta\leq\pi/2$. The {\it classical}
complexified boundary-value problem is expected to be well-posed for
$0<\theta\leq\pi/2$, with classical action $S_{\rm class}$. For a locally
supersymmetric Lagrangian, containing supergravity, possibly coupled to
supermatter, the resulting quantum amplitude will be proportional to
$\exp(iS_{\rm class})$, apart from possible loop corrections which are
negligible for boundary data with frequencies below the Planck scale. The
Lorentzian quantum amplitude is recovered by taking the limit as $\theta\to
0_+$ of this amplitude. In the present paper, a connection is made between this
boundary value approach and the original approach to quantum evaporation in
gravitational collapse to a black hole, {\it via} Bogoliubov coefficients. This
connection is developed through consideration of the radial equation obeyed by
the (adiabatic) non-spherical classical perturbations. When one studies the
resulting final probability distribution, based on our quantum amplitudes
above, one finds that this distribution can also be interpreted in terms of the
Wigner quasi-probability distribution for harmonic oscillators.


title: Canonical and gravitational stress-energy tensors

abstract:
  It is dealt with the question, under which circumstances the canonical
Noether stress-energy tensor is equivalent to the gravitational (Hilbert)
tensor for general matter fields under the influence of gravity. In the
framework of general relativity, the full equivalence is established for matter
fields that do not couple to the metric derivatives. Spinor fields are included
into our analysis by reformulating general relativity in terms of tetrad
fields, and the case of Poincare gauge theory, with an additional, independent
Lorentz connection, is also investigated. Special attention is given to the
flat limit, focusing on the expressions for the matter field energy
(Hamiltonian). The Dirac-Maxwell system is investigated in detail, with special
care given to the separation of free (kinetic) and interaction (or potential)
energy. Moreover, the stress-energy tensor of the gravitational field itself is
briefly discussed.


title: Acceleration disturbances due to local gravity gradients in ASTROD I

abstract:
  The Astrodynamical Space Test of Relativity using Optical Devices (ASTROD)
mission consists of three spacecraft in separate solar orbits and carries out
laser interferometric ranging. ASTROD aims at testing relativistic gravity,
measuring the solar system and detecting gravitational waves. Because of the
larger arm length, the sensitivity of ASTROD to gravitational waves is
estimated to be about 30 times better than Laser Interferometer Space Antenna
(LISA) in the frequency range lower than about 0.1 mHz. ASTROD I is a simple
version of ASTROD, employing one spacecraft in a solar orbit. It is the first
step for ASTROD and serves as a technology demonstration mission for ASTROD. In
addition, several scientific results are expected in the ASTROD I experiment.
The required acceleration noise level of ASTROD I is 10^-13 m s^-2 Hz^{-1/2} at
the frequency of 0.1 mHz. In this paper, we focus on local gravity gradient
noise that could be one of the largest acceleration disturbances in the ASTROD
I experiment. We have carried out gravitational modelling for the current
test-mass design and simplified configurations of ASTROD I by using an
analytical method and the Monte Carlo method. Our analyses can be applied to
figure out the optimal designs of the test mass and the constructing materials
of the spacecraft, and the configuration of compensation mass to reduce local
gravity gradients.


title:
Dual Nature of the Ricci Scalar, Creation of Spinless and Spin-1/2
  Particles as Well as a New Cosmological Scenario I

abstract:
  In earlier papers, it is found that the Ricci scalar behaves in dual manner
(i) like a matter field and (ii) like a geometrical field. Using dual role of
the Ricci scalar, inhomogeneous cosmological models are derived. The essential
features of these models is capability of these to exhibit gravitational effect
of compact objects also in an expanding universe. Here, production of spinless
and spin-1/2 particles are demonstrated in these models.


title:
The Sagnac Effect in curved space-times from an analogy with the
  Aharonov-Bohm Effect

abstract:
  In the context of the natural splitting, the standard relative dynamics can
be expressed in terms of gravito-electromagnetic fields, which allow to
formally introduce a gravito-magnetic Aharonov-Bohm effect. We showed elsewhere
that this formal analogy can be used to derive the Sagnac effect in flat
space-time as a gravito-magnetic Aharonov-Bohm effect. Here, we generalize
those results to study the General Relativistic corrections to the Sagnac
effect in some stationary and axially symmetric geometries, such as the
space-time around a weakly gravitating and rotating source, Kerr space-time,
G\"{odel} universe and Schwarzschild space-time.


title:
Comment on 'Model-dependence of Shapiro time delay and the "speed of
  gravity/speed of light" controversy'

abstract:
  In a recent paper published in Classical and Quantum Gravity, 2004, vol. 21,
p. 3803 Carlip used a vector-tensor theory of gravity to calculate the Shapiro
time delay by a moving gravitational lens. He claimed that the relativistic
correction of the order of v/c beyond the static part of the Shapiro delay
depends on the speed of light c and, hence, the Fomalont-Kopeikin experiment is
not sensitive to the speed of gravity c_g. In this letter we analyze Carlip's
calculation and demonstrate that it implies a gravitodynamic (non-metric)
system of units based on the principle of the constancy of the speed of gravity
but it is disconnected from the practical method of measurement of astronomical
distances based on the principle of the constancy of the speed of light and the
SI metric (electrodynamic) system of units. Re-adjustment of
theoretically-admissible but practically unmeasurable Carlip's coordinates to
the SI metric system of units used in JPL ephemeris, reveals that the
velocity-dependent correction to the static part of the Shapiro time delay does
depend on the speed of gravity c_g as shown by Kopeikin in Classical and
Quantum Gravity, 2004, vol. 21, p. 1. This analysis elucidates the importance
of employing the metric system of units for physically meaningful
interpretation of gravitational experiments.


title: Causal particle detectors and topology

abstract:
  We investigate particle detector responses in some topologically non-trivial
spacetimes. We extend a recently proposed regularization of the massless scalar
field Wightman function in 4-dimensional Minkowski space to arbitrary
dimension, to the massive scalar field, to quotients of Minkowski space under
discrete isometry groups and to the massless Dirac field. We investigate in
detail the transition rate of inertial and uniformly accelerated detectors on
the quotient spaces under groups generated by $(t,x,y,z)\mapsto(t,x,y,z+2a)$,
$(t,x,y,z)\mapsto(t,-x,y,z)$, $(t,x,y,z)\mapsto(t,-x,-y,z)$,
$(t,x,y,z)\mapsto(t,-x,-y,z+a)$ and some higher dimensional generalizations.
For motions in at constant $y$ and $z$ on the latter three spaces the response
is time dependent. We also discuss the response of static detectors on the RP^3
geon and inertial detectors on RP^3 de Sitter space via their associated global
embedding Minkowski spaces (GEMS). The response on RP^3 de Sitter space, found
both directly and in its GEMS, provides support for the validity of applying
the GEMS procedure to detector responses and to quotient spaces such as RP^3 de
Sitter space and the RP^3 geon where the embedding spaces are Minkowski spaces
with suitable identifications.


title:
Reality conditions for Ashtekar gravity from Lorentz-covariant
  formulation

abstract:
  We show the equivalence of the Lorentz-covariant canonical formulation
considered for the Immirzi parameter $\beta=i$ to the selfdual Ashtekar
gravity. We also propose to deal with the reality conditions in terms of Dirac
brackets derived from the covariant formulation and defined on an extended
phase space which involves, besides the selfdual variables, also their
anti-selfdual counterparts.


title:
On the nonlinear stability of higher-dimensional triaxial Bianchi IX
  black holes

abstract:
  In this paper, we prove that the 5-dimensional Schwarzschild-Tangherlini
solution of the Einstein vacuum equations is orbitally stable (in the fully
non-linear theory) with respect to vacuum perturbations of initial data
preserving triaxial Bianchi IX symmetry. More generally, we prove that
5-dimensional vacuum spacetimes developing from suitable asymptotically flat
triaxial Bianchi IX symmetric data and containing a trapped or marginally
trapped homogeneous 3-surface possess a complete null infinity whose past is
bounded to the future by a regular event horizon, whose cross-sectional volume
in turn satisfies a Penrose inequality, relating it to the final Bondi mass. In
particular, the results of this paper give the first examples of vacuum black
holes which are not stationary exact solutions.


title: Geometry from quantum particles

abstract:
  We investigate the possibility that a background independent quantum theory
of gravity is not a theory of quantum geometry. We provide a way for global
spacetime symmetries to emerge from a background independent theory without
geometry. In this, we use a quantum information theoretic formulation of
quantum gravity and the method of noiseless subsystems in quantum error
correction. This is also a method that can extract particles from a quantum
geometric theory such as a spin foam model.


title: Spacetime topology from the tomographic histories approach: Part II

abstract:
  As an inverse problem, we recover the topology of the effective spacetime
that a system lies in, in an operational way. This means that from a series of
experiments we get a set of points corresponding to events. This continues the
previous work done by the authors. Here we use the existence of upper bound in
the speed of transfer of matter and information to induce a partial order on
the set of events. While the actual partial order is not known in our
operational set up, the grouping of events to (unordered) subsets corresponding
to possible histories, is given. From this we recover the partial order up to
certain ambiguities that are then classified. Finally two different ways to
recover the topology are sketched and their interpretation is discussed.


title: "Swimming" versus "swinging" in spacetime

abstract:
  Wisdom has recently unveiled a new relativistic effect, called ``spacetime
swimming'', where quasi-rigid free bodies in curved spacetimes can "speed up",
"slow down" or "deviate" their falls by performing "local" cyclic shape
deformations. We show here that for fast enough cycles this effect dominates
over a non-relativistic related one, named here ``space swinging'', where the
fall is altered through "nonlocal" cyclic deformations in Newtonian
gravitational fields. We expect, therefore, to clarify the distinction between
both effects leaving no room to controversy. Moreover, the leading contribution
to the swimming effect predicted by Wisdom is enriched with a higher order term
and the whole result is generalized to be applicable in cases where the tripod
is in large red-shift regions.


title: 3D gravity and non-linear cosmology

abstract:
  By the inclusion of an additional term, non-linear in the scalar curvature
$R$, it is tested if dark energy could rise as a geometrical effect in 3D
gravitational formulations. We investigate a cosmological fluid obeying a
non-polytropic equation of state (the van der Waals equation) that is used to
construct the energy-momentum tensor of the sources, representing the
hypothetical inflaton in gravitational interaction with a matter contribution.
  Following the evolution in time of the scale factor, its acceleration, and
the energy densities of constituents it is possible to construct the
description of an inflationary 3D universe, followed by a matter dominated era.
For later times it is verified that, under certain conditions, the non-linear
term in $R$ can generate the old 3D universe in accelerated expansion, where
the ordinary matter is represented by the barotropic limit of the van der Waals
constituent.


title:
Reply to ``Comment on Model-dependence of Shapiro time delay and the
  `speed of gravity/speed of light' controversy''

abstract:
  To determine whether the Shapiro time delay of light passing near a moving
object depends on the ``speed of gravity'' or the ``speed of light,'' one must
analyze observations in a bimetric framework in which these two speeds can be
different. In a recent comment (gr-qc/0510048), Kopeikin has argued that such a
computation -- described in gr-qc/0403060 -- missed a hidden dependence on the
speed of gravity. By analyzing the observables in the relevant bimetric model,
I show that this claim is incorrect, and that the conclusions of gr-qc/0403060
stand.


title:
Mapping spacetimes with LISA: inspiral of a test-body in a `quasi-Kerr'
  field

abstract:
  The future LISA detector will constitute the prime instrument for
high-precision gravitational wave observations.LISA is expected to provide
information for the properties of spacetime in the vicinity of massive black
holes which reside in galactic nuclei.Such black holes can capture stellar-mass
compact objects, which afterwards slowly inspiral,radiating gravitational
waves.The body's orbital motion and the associated waveform carry information
about the spacetime metric of the massive black hole,and it is possible to
extract this information and experimentally identify (or not!) a Kerr black
hole.In this paper we lay the foundations for a practical `spacetime-mapping'
framework. Our work is based on the assumption that the massive body is not
necessarily a Kerr black hole, and that the vacuum exterior spacetime is
stationary axisymmetric,described by a metric which deviates slightly from the
Kerr metric. We first provide a simple recipe for building such a `quasi-Kerr'
metric by adding to the Kerr metric the deviation in the value of the
quadrupole moment. We then study geodesic motion in this metric,focusing on
equatorial orbits. We proceed by computing `kludge' waveforms which we compare
with their Kerr counterparts. We find that a modest deviation from the Kerr
metric is sufficient for producing a significant mismatch between the
waveforms, provided we fix the orbital parameters. This result suggests that an
attempt to use Kerr waveform templates for studying EMRIs around a non-Kerr
object might result in serious loss of signal-to-noise ratio and total number
of detected events. The waveform comparisons also unveil a `confusion' problem,
that is the possibility of matching a true non-Kerr waveform with a Kerr
template of different orbital parameters.


title:
Conformal Yano-Killing tensor for the Kerr metric and conserved
  quantities

abstract:
  Properties of (skew-symmetric) conformal Yano--Killing tensors are reviewed.
Explicit forms of three symmetric conformal Killing tensors in Kerr spacetime
are obtained from the Yano--Killing tensor. The relation between spin-2 fields
and solutions to the Maxwell equations is used in the construction of a new
conserved quantity which is quadratic in terms of the Weyl tensor. The formula
obtained is similar to the functional obtained from the Bel--Robinson tensor
and is examined in Kerr spacetime. A new interpretation of the conserved
quantity obtained is proposed.


title:
How the orbital period of a test particle is modified by the
  Dvali-Gabadadze-Porrati gravity?

abstract:
  In addition to the pericentre \omega, the mean anomaly M and, thus, the mean
longitude \lambda, also the orbital period Pb and the mean motion $n$ of a test
particle are modified by the Dvali-Gabadadze-Porrati gravity. While the
correction to Pb depends on the mass of the central body and on the geometrical
features of the orbital motion around it, the correction to $n$ is independent
of them, up to terms of second order in the eccentricity $e$. The latter one
amounts to about 2\times 10^-3 arcseconds per century. The present-day accuracy
in determining the mean motions of the inner planets of the Solar System from
radar ranging and differential Very Long Baseline Interferometry is
10^-2-5\times 10^-3 arcseconds per century, but it should be improved in the
near future when the data from the spacecraft to Mercury and Venus will be
available.

categories: gr-qc astro-ph hep-ph hep-th physics.space-ph


title:
On Boundedness of the Admissible Time Slowing Down by the Gravitational
  Field

abstract:
  It is shown that there exists, in the field theory of gravitation, contrary
to the General Theory of Relativity (GTR), a bound for admissible time slowing
down by the gravitational field which excludes a possibility of unbounded
compression of matter by the gravity forces.


title:
The Cosmological Constant as an Eigenvalue of a Sturm-Liouville Problem
  and its Renormalization

abstract:
  We discuss the case of massive gravitons and their relation with the
cosmological constant, considered as an eigenvalue of a Sturm-Liouville
problem. A variational approach with Gaussian trial wave functionals is used as
a method to study such a problem. We approximate the equation to one loop in a
Schwarzschild background and a zeta function regularization is involved to
handle with divergences. The regularization is closely related to the
subtraction procedure appearing in the computation of Casimir energy in a
curved background. A renormalization procedure is introduced to remove the
infinities together with a renormalization group equation.