title: Role of Horizons in Semiclassical Gravity: Entropy and the Area Spectrum

abstract:
  In any space-time, it is possible to have a family of observers who have
access to only part of the space-time manifold, because of the existence of a
horizon. We demand that \emph{physical theories in a given coordinate system
must be formulated entirely in terms of variables that an observer using that
coordinate system can access}. In the coordinate frame in which these observers
are at rest, the horizon manifests itself as a (coordinate) singularity in the
metric tensor. Regularization of this singularity removes the inaccessible
region, and leads to the following consequences: (a) The non-trivial
topological structure for the effective manifold allows one to obtain the
standard results of quantum field theory in curved space-time. (b) In case of
gravity, this principle requires that the effect of the unobserved degrees of
freedom should reduce to a boundary contribution $A_{\rm boundary}$ to the
gravitational action. When the boundary is a horizon, $A_{\rm boundary}$
reduces to a single, well-defined term proportional to the area of the horizon.
Using the form of this boundary term, it is possible to obtain the full
gravitational action in the semiclassical limit. (c) This boundary term must
have a quantized spectrum with uniform spacing, $\Delta
A_{boundary}=2\pi\hbar$, in the semiclassical limit. This, in turn, yields the
following results for semiclassical gravity: (i) The area of any one-way
membrane is quantized. (ii) The information hidden by a one-way membrane
amounts to an entropy, which is always one-fourth of the area of the membrane
in the leading order. (iii) In static space-times, the action for gravity can
be given a purely thermodynamic interpretation and the Einstein equations have
a formal similarity to laws of thermodynamics.


title:
The three perspectives on the quantum-gravity problem and their
  implications for the fate of Lorentz symmetry

abstract:
  Each approach to the quantum-gravity problem originates from expertise in one
or another area of theoretical physics. The particle-physics perspective
encourages one to attempt to reproduce in quantum gravity as much as possible
of the successes of the Standard Model of particle physics, and therefore, as
done in String Theory, the core features of quantum gravity are described in
terms of graviton-like exchange in a background classical spacetime. From the
general-relativity perspective it is natural to renounce to any reference to a
background spacetime, and to describe spacetime in a way that takes into
account the in-principle limitations of measurements. The Loop Quantum Gravity
approach and the approaches based on noncommutative geometry originate from
this general-relativity perspective. The condensed-matter perspective, which
has been adopted in a few recent quantum-gravity proposals, naturally leads to
scenarios in which some familiar properties of spacetime are only emergent,
just like, for example, some emergent collective degrees of freedom are
relevant to the description of certain physical systems only near a critical
point. Both from the general-relativity perspective and from the
condensed-matter perspective it is natural to explore the possibility that
quantum gravity might have significant implications for the fate of Lorentz
symmetry in the Planckian regime. From the particle-physics perspective there
is instead no obvious reason to renounce to exact Lorentz symmetry, although
(``spontaneous'') Lorentz symmetry breaking is of course possible. A
fast-growing phenomenological programme looking for Planck-scale departures
from Lorentz symmetry can contribute to this ongoing debate.


title: Trapped surfaces and symmetries

abstract:
  We prove that strictly stationary spacetimes cannot contain closed trapped
nor marginally trapped surfaces. The result is purely geometric and holds in
arbitrary dimension. Other results concerning the interplay between
(generalized) symmetries and trapped submanifolds are also presented.


title: Elastic Stars in General Relativity: II. Radial perturbations

abstract:
  We study radial perturbations of general relativistic stars with elastic
matter sources. We find that these perturbations are governed by a second order
differential equation which, along with the boundary conditions, defines a
Sturm-Liouville type problem that determines the eigenfrequencies. Although
some complications arise compared to the perfect fluid case, leading us to
consider a generalisation of the standard form of the Sturm-Liouville equation,
the main results of Sturm-Liouville theory remain unaltered. As an important
consequence we conclude that the mass-radius curve for a one-parameter sequence
of regular equilibrium models belonging to some particular equation of state
can be used in the same well-known way as in the perfect fluid case, at least
if the energy density and the tangential pressure of the background solutions
are continuous. In particular we find that the fundamental mode frequency has a
zero for the maximum mass stars of the models with solid crusts considered in
Paper I of this series.


title: Electromagnetic waves in NUT space: Solutions to the Maxwell equations

abstract:
  In this paper, using the Newman-Penrose formalism, we find the Maxwell
equations in NUT space and after separation into angular and radial components
solve them analytically. All the angular equations are solved in terms of
Jaccobi polynomials. The radial equations are transformed into Hypergeometric
and Heun's equations with the right hand sides including terms of different
order in the frequency of the perturbation which allow solutions in the
expansion of this parameter.


title:
Components of the gravitational force in the field of a gravitational
  wave

abstract:
  Gravitational waves bring about the relative motion of free test masses. The
detailed knowledge of this motion is important conceptually and practically,
because the mirrors of laser interferometric detectors of gravitational waves
are essentially free test masses. There exists an analogy between the motion of
free masses in the field of a gravitational wave and the motion of free charges
in the field of an electromagnetic wave. In particular, a gravitational wave
drives the masses in the plane of the wave-front and also, to a smaller extent,
back and forth in the direction of the wave's propagation. To describe this
motion, we introduce the notion of `electric' and `magnetic' components of the
gravitational force. This analogy is not perfect, but it reflects some
important features of the phenomenon. Using different methods, we demonstrate
the presence and importance of what we call the `magnetic' component of motion
of free masses. It contributes to the variation of distance between a pair of
particles. We explicitely derive the full response function of a 2-arm laser
interferometer to a gravitational wave of arbitrary polarization. We give a
convenient description of the response function in terms of the spin-weighted
spherical harmonics. We show that the previously ignored `magnetic' component
may provide a correction of up to 10 %, or so, to the usual `electric'
component of the response function. The `magnetic' contribution must be taken
into account in the data analysis, if the parameters of the radiating system
are not to be mis-estimated.


title: A homogeneous brane-world universe

abstract:
  A homogeneous, Kantowski-Sachs type, bouncing brane-world universe is
presented. The bulk has a positive cosmological constant and the Killing
algebra $so(1,3)\oplus so(3)$. The totality of the source terms of the
effective Einstein equation combine to a solid with different radial and
tangential pressures.


title: Comments on astro-ph/0305039 and gr-qc/0309036

abstract:
  The main results of papers gr-qc/0307026 and gr-qc/0312068 are formulated.
These results are opposite to conclusions of paper astro-ph/0305039 and
comments gr-qc/0309036.


title: Kinematical bound in asymptotically translationally invariant spacetimes

abstract:
  We present positive energy theorems in asymptotically translationally
invariant spacetimes which can be applicable to black strings and charged
branes. We also address the bound property of the tension and charge of branes.


title:
Interacting scalar and spinor fields in Bianchi type I universe filled
  with magneto-fluid

abstract:
  Self-consistent system of spinor, scalar and BI gravitational fields in
presence of magneto-fluid and $\Lambda$-term is considered. Assuming that the
expansion of the BI universe is proportional to the $\sigma_1^1$ component of
the shear tensor, exact solutions for the metric functions, as well as for
scalar and spinor fields are obtained. For a non-positive $\Lambda$ the
initially anisotropic space-time becomes isotropic one in the process of
expansion, whereas, for $\Lambda > 0$ an oscillatory mode of expansion of the
BI model occurs.


title: PDE System Approach to Large Extra Dimensions

abstract:
  We explore some fundational issues regarding the splitting of D-dimensional
EFE's w.r.t timelike and spacelike (D-1)-dimensional hypersurfaces, first
without and then with thin matter sheets such as branes. We begin to implement
methodology, that is well-established for the GR CP and IVP, in the new field
of GR-based braneworlds, identifying and comparing many different choices of
procedure. We abridge fragmentary parts of the literature of embeddings,
putting the Campbell--Magaard theorem into context. We recollect and refine
arguments why York and not elimination methods are used for the GR IVP. We
compile a list of numerous mathematical and physical impasses to using timelike
splits, whereas spacelike splits are known to be well-behaved. We however
pursue both options to make contact with the current braneworld literature
which is almost entirely based on timelike splits. We look at the
Shiromizu-Maeda -Sasaki braneworld by means of reformulations which emphasize
different aspects from the original formulation. We show that what remains of
the York method in the timelike case generalizes heuristic bulk construction
schemes. We formulate timelike (brane) versions of the thin sandwich
conjecture. We discuss whether it is plausible to remove singularities by
timelike embeddings. We point out how the braneworld geodesic postulates lead
to further difficulties with the notion of singularities than in GR where these
postulates are simpler. Having argued for the use of the spacelike split, we
study how to progress to the construction of more general data sets for spaces
partially bounded by branes. Boundary conditions are found and algorithms
provided. Working with (finitely) thick branes would appear to facilitate such
a study.


title: Energy-momentum and angular momentum of Goedel universes

abstract:
  We discuss the Einstein energy-momentum complex and the Bergmann-Thomson
angular momentum complex in general relativity and calculate them for
space-time homogeneous Goedel universes. The calculations are performed for a
dust acausal model and for a scalar-field causal model. It is shown that the
Einstein pseudotensor is traceless, not symmetric, the gravitational energy is
"density" is negative and the gravitational Poynting vector vanishes.
Significantly, the total (gravitational and matter) energy "density" fro the
acausal model is zero while for the casual model it is negative.The
Bergmann-Thomson angular momentum complex does not vanish for both G\"odel
models.


title:
Matters of Gravity, the newsletter of the APS Topical Group on
  Gravitation, Fall 2003

abstract:
  Contents:
  Community news:
  - We hear that... by Jorge Pullin
  Research briefs:
  - Update on a busy year for LIGO, by Stan Whitcomb
  - First year results from WMAP, by Rachel Bean
  - Short range searches for non-Newtonian gravity, by M. Varney and J. Long
  Conference reports:
  - Xth Brazilian school of cosmology and gravitation, by Mario Novello
  - 6th East coast gravity meeting, by David Fiske
  - 5th Edoardo Amaldi meeting, by Alain Brillet
  - Pacific coast gravity meeting, by Charles Torre
  - Astrophysics of gravitational wave sources, by Joan Centrella
  - Gravitational interaction of compact objects, by M. Choptuik, E. Flanagan,
L. Lehner
  - PriceFest, by John Whelan
  - Gravitation: a decennial perspective, by Jorge Pullin


title:
Universal temperature corrections to the free energy for the
  gravitational field

abstract:
  The temperature correction to the free energy of the gravitational field is
considered which does not depend on the Planck energy physics. The leading
correction may be interpreted in terms of the temperature dependent effective
gravitational constant G_{eff}. The temperature correction to G_{eff}^{-1}
appears to be valid for all temperatures T<< E_{Planck}. It is universal since
it is determined only by the number of fermionic and bosonic fields with masses
m<< T, does not contain the Planck energy scale E_{Planck} which determines the
gravitational constant at T=0, and does not depend on whether or not the
gravitational field obeys the Einstein equations. That is why this universal
modification of the free energy for gravitational field can be used to study
thermodynamics of quantum systems in condensed matter (such as quantum liquids
superfluid 3He and 4He), where the effective gravity emerging for fermionic
and/or bosonic quasiparticles in the low-energy corner is quite different from
the Einstein gravity.


title:
Possibilities for Measurement and Compensation of Stray DC Electric
  Fields Acting on Drag-Free Test Masses

abstract:
  DC electric fields can combine with test mass charging and thermal dielectric
voltage noise to create significant force noise acting on the drag-free test
masses in the LISA (Laser Interferometer Space Antenna) gravitational wave
mission. This paper proposes a simple technique to measure and compensate
average stray DC potentials at the mV level, yielding substantial reduction in
this source of force noise. We discuss the attainable resolution for both
flight and ground based experiments.


title: Properties of global monopoles with an event horizon

abstract:
  We investigate the properties of global monopoles with an event horizon. We
find that there is an unstable circular orbit even if a particle does not have
an angular momentum when the core mass is negative. We also obtain the
asymptotic form of solutions when the event horizon is much larger than the
core radius of the monopole, and discuss if they could be a model of galactic
halos.


title: Quark stars admitting a one-parameter group of conformal motions

abstract:
  An exact analytical solution describing the interior of a charged strange
quark star is found under the assumption of spherical symmetry and the
existence of a one-parameter group of conformal motions. The solution describes
a unique static charged configuration of quark matter with radius $R=9.46$ km
and total mass $M=2.86M_{\odot}$.


title:
Curvature singularities and abstract boundary singularity theorems for
  space-time

abstract:
  The abstract boundary construction of Scott and Szekeres is a general and
flexible way to define singularities in General Relativity. The abstract
boundary construction also proves of great utility when applied to questions
about more general boundary features of space-time. Within this construction an
essential singularity is a non-regular boundary point which is accessible by a
curve of interest (e.g. a geodesic) within finite (affine) parameter distance
and is not removable. Ashley and Scott proved the first theorem linking
abstract boundary essential singularities with the notion of causal geodesic
incompleteness for strongly causal, maximally extended space-times. The
relationship between this result and the classical singularity theorems of
Penrose and Hawking has enabled us to obtain abstract boundary singularity
theorems. This paper describes essential singularity results for maximally
extended space-times and presents our recent efforts to establish a
relationship between the strong curvature singularities of Tipler and Krolak
and abstract boundary essential singularities.


title: Decay of spin-1/2 field around Reissner-Nordstrom black hole

abstract:
  To find what influence the charge of the black hole $Q$ will bring to the
evolution of the quasinormal modes, we calculate the quasinormal frequencies of
the neutrino field (charge $e=0$) perturbations and those of the massless Dirac
field ($e\neq 0$) perturbations in the RN metric. The influences of $Q$, $e$,
the momentum quantum number $l$, and the mode number $n$ are discussed. Among
the conclusions, the most important one is that, at the stage of quasinormal
ringing, the larger when the black hole and the field have the same kind of
charge ($eQ>0$), the quasinormal modes of the massless charged Dirac field
decay faster than those of the neutral ones, and when $eQ<0$, the massless
charged Dirac field decays slower.


title: Heuristic approach to the Schwarzschild geometry

abstract:
  In this article I present a simple Newtonian heuristic for deriving a
weak-field approximation for the spacetime geometry of a point particle. The
heuristic is based on Newtonian gravity, the notion of local inertial frames
[the Einstein equivalence principle], plus the use of Galilean coordinate
transformations to connect the freely falling local inertial frames back to the
``fixed stars''. Because of the heuristic and quasi-Newtonian manner in which
the spacetime geometry is obtained, we are at best justified in expecting it to
be a weak-field approximation to the true spacetime geometry. However, in the
case of a spherically symmetric point mass the result is coincidentally an
exact solution of the full vacuum Einstein field equations -- it is the
Schwarzschild geometry in Painleve--Gullstrand coordinates.
  This result is much stronger than the well-known result of Michell and
Laplace whereby a Newtonian argument correctly estimates the value of the
Schwarzschild radius -- using the heuristic presented in this article one
obtains the entire Schwarzschild geometry. The heuristic also gives sensible
results -- a Riemann flat geometry -- when applied to a constant gravitational
field. Furthermore, a subtle extension of the heuristic correctly reproduces
the Reissner--Nordstrom geometry and even the de Sitter geometry. Unfortunately
the heuristic construction is not truly generic. For instance, it is incapable
of generating the Kerr geometry or anti-de Sitter space.
  Despite this limitation, the heuristic does have useful pedagogical value in
that it provides a simple and direct plausibility argument for the
Schwarzschild geometry.


title:
Relativistic stars in differential rotation: bounds on the dragging rate
  and on the rotational energy

abstract:
  For general relativistic equilibrium stellar models (stationary axisymmetric
asymptotically flat and convection-free) with differential rotation, it is
shown that for a wide class of rotation laws the distribution of angular
velocity of the fluid has a sign, say "positive", and then both the dragging
rate and the angular momentum density are positive. In addition, the "mean
value" (with respect to an intrinsic density) of the dragging rate is shown to
be less than the mean value of the fluid angular velocity (in full general,
without having to restrict the rotation law, nor the uniformity in sign of the
fluid angular velocity); this inequality yields the positivity and an upper
bound of the total rotational energy.


title: Equation of Motion of Small Bodies in Relativity

abstract:
  There is proven a theorem, to the effect that a material body in general
relativity, in a certain limit of sufficiently small size and mass, moves along
a geodesic.


title: An approach to solve Slavnov-Taylor identity in D4 N=1 supergravity

abstract:
  We consider a particular solution to Slavnov-Taylor identity in
four-dimensional supergravity. The consideration is performed for pure
supergravity, no matter superfields are included. The solution is obtained by
inserting dressing functions into ghost part of the classical action for
supergravity.As a consequence, physical part of the effective action is local
invariant with respect to diffeomorphism and structure groups of transformation
for dressed effective superfields of vielbein and spin connection.


title: Small Black Holes in Randall-Sundrum type I Scenario

abstract:
  An approximation method to study the properties of a small black hole located
on the TeV brane in the Randall-Sundrum type I scenario is presented. The
method enables us to find the form of the metric close to the matter
distribution when its asymptotic form is given. The short range solution is
found as an expansion in the ratio between the Schwarzschild radius of the
black hole and the curvature length of the bulk. Long range properties are
introduced using the linearized gravity solution as an asymptotic boundary
condition. The solution is found up to first order. It is valid in the region
close to the horizon but is not valid on the horizon. The regularity of the
horizon is still under study.


title:
Comment on 'Large-scale non-locality in "doubly special relativity" with
  an energy-dependent speed of light'

abstract:
  We show that some of the recent results reported in gr-qc/0308049 are based
on assumptions which are in contrast with general properties of ``Doubly
Special Relativity'' and/or with Planck-scale physics models.


title: Field propagation in the Schwarzschild-de Sitter black hole

abstract:
  We present an exhaustive analysis of scalar, electromagnetic and
gravitational perturbations in the background of a Schwarzchild-de Sitter
spacetime. The field propagation is considered by means of a semi-analytical
(WKB) approach and two numerical schemes: the characteristic and general
initial value integrations. The results are compared near the extreme regime,
and a unifying picture is established for the dynamics of different spin
fields. Although some of the results just confirm usual expectations, a few
surprises turn out to appear, as the dependence on the non-characteristic
initial conditions of the non-vanishing asymptotic value for l=0 mode scalar
fields.


title: Field propagation in de Sitter black holes

abstract:
  We present an exhaustive analysis of scalar, electromagnetic and
gravitational perturbations in the background of Schwarzchild-de Sitter and
Reissner-Nordstrom-de Sitter spacetimes. The field propagation is considered by
means of a semi-analytical (WKB) approach and two numerical schemes: the
characteristic and general initial value integrations. The results are compared
near the extreme cosmological constant regime, where analytical results are
presented. A unifying picture is established for the dynamics of different spin
fields.


title: Dynamics of radiating braneworlds

abstract:
  If the observable universe is a braneworld of Randall-Sundrum type, then
particle interactions at high energies will produce 5-dimensional gravitons
that escape into the bulk. As a result, the Weyl energy density on the brane
does not behave like radiation in the early universe, but does so only later,
in the low energy regime. Recently a simple model was proposed to describe this
modification of the Randall-Sundrum cosmology. We investigate the dynamics of
this model, and find the exact solution of the field equations. We use a
dynamical systems approach to analyze global features of the phase space of
solutions.


title: Generalised Wick Transform in Dimensionally Reduced Gravity

abstract:
  In the context of canonical quantum gravity, we study an alternative real
quantisation scheme, which is arising by relating simpler Riemannian quantum
theory to the more complicated physical Lorentzian theory - the generalised
Wick transform. On the symmetry reduced models, homogenous Bianchi cosmology
and 2+1 gravity, we investigate its generalised construction principle,
demonstrate that the emerging quantum theory is equivalent to the one obtained
from standard quantisation and how to obtain physical states in Lorentzian
gravity from Wick transforming solutions of Riemannian quantum theory.


title: Stationary Black Holes with Static and Counterrotating Horizons

abstract:
  We show that rotating dyonic black holes with static and counterrotating
horizon exist in Einstein-Maxwell-dilaton theory when the dilaton coupling
constant exceeds the Kaluza-Klein value. The black holes with static horizon
bifurcate from the static black holes. Their mass decreases with increasing
angular momentum, their horizons are prolate.


title: Asymptotic Regimes of Magnetic Bianchi Cosmologies

abstract:
  We consider the asymptotic dynamics of the Einstein-Maxwell field equations
for the class of non-tilted Bianchi cosmologies with a barotropic perfect fluid
and a pure homogeneous source-free magnetic field, with emphasis on models of
Bianchi type VII_{0}, which have not been previously studied. Using the
orthonormal frame formalism and Hubble-normalized variables, we show that, as
is the case for the previously studied class A magnetic Bianchi models, the
magnetic Bianchi VII_{0} cosmologies also exhibit an oscillatory approach to
the initial singularity. However, in contrast to the other magnetic Bianchi
models, we rigorously establish that typical magnetic Bianchi VII_{0}
cosmologies exhibit the phenomena of asymptotic self-similarity breaking and
Weyl curvature dominance in the late-time regime.


title: A Cosmological Model of Holographic Brane Gravity

abstract:
  A cosmological scenario with two branes (A and B) moving in a 5-dimensional
bulk is considered. As in the case of ecpyrotic and born-again braneworld
models it is possible that the branes collide. The energy-momentum tensor is
taken to describe a perfect barotropic fluid on the A-brane and a
phenomenological time-dependent "cosmological constant" on the B-brane. The
A-brane is identified with our Universe and its cosmological evolution in the
approximation of a homogeneous and isotropic brane is analysed. The dynamics of
the radion (a scalar field on the brane) contains information about the proper
distance between the branes. It is demonstrated that the deSitter type
solutions are obtained for late time evolution of the braneworld and
accelerative behaviour is anticipated at the present time.


title:
Hamiltonian study of the Generalized scalar-tensor theory with potential
  in a Bianchi type I model

abstract:
  We study the generalized scalar tensor theory with a potential in the Bianchi
type I model by using the ADM formalism. We examine the conditions for the
Universe to be in expansion, isotropic and with a positive potential at late
time in the Brans-Dicke and Einstein frames. In particular, we analyse the two
important cases where metric functions tend, in an asymptotic way, toward power
or exponential laws in the Einstein frame.


title:
Dynamical study of the hyperextended scalar-tensor theory in the empty
  Bianchi type I model

abstract:
  The dynamics of the hyperextended scalar-tensor theory in the empty Bianchi
type I model is investigated. We describe a method giving the sign of the first
and second derivatives of the metric functions whatever the coupling function.
Hence, we can predict if a theory gives birth to expanding, contracting,
bouncing or inflationary cosmology. The dynamics of a string inspired theory
without antisymetric field strength is analysed. Some exact solutions are
found.


title:
Sufficient conditions for curvature invariants to avoid divergencies in
  Hyperextended Scalar Tensor theory for Bianchi models

abstract:
  We look for sufficient conditions such that the scalar curvature, Ricci and
Kretchmann scalars be bounded in Hyperextended Scalar Tensor theory for Bianchi
models. We find classes of gravitation functions and Brans-Dicke coupling
functions such that the theories thus defined avoid the singularity. We compare
our results with these found by Rama in the framework of the Generalised Scalar
Tensor theory for the FLRW models.


title:
Noether Symmetry of the Hyperextended Scalar Tensor theory for the FLRW
  models

abstract:
  We study in which conditions the Hyperextended Scalar Tensor theory in an
FLRW background admits a Noether symmetry and derive the vectors field
generating it.


title: Dynamics of Pure Shape, Relativity and the Problem of Time

abstract:
  A new approach to the dynamics of the universe based on work by O Murchadha,
Foster, Anderson and the author is presented. The only kinematics presupposed
is the spatial geometry needed to define configuration spaces in purely
relational terms. A new formulation of the relativity principle based on
Poincare's analysis of the problem of absolute and relative motion (Mach's
principle) is given. The enire dynamics is based on shape and nothing else. It
leads to much stronger predictions than standard Newtonian theory. For the
dynamics of Riemannian 3-geometries on which matter fields also evolve,
implementation of the new relativity principle establishes unexpected links
between special relativity, general relativity and the gauge principle. They
all emerge together as a self-consistent complex from a unified and completely
relational approach to dynamics. A connection between time and scale invariance
is established. In particular, the representation of general relativity as
evolution of the shape of space leads to unique definition of simultaneity.
This opens up the prospect of a solution of the problem of time in quantum
gravity on the basis of a fundamental dynamical principle.


title:
Analytic determination of the asymptotic quasi-normal mode spectrum of
  small Schwarzschild-de Sitter black holes

abstract:
  Following the monodromy technique performed by Motl and Neitzke, we consider
the analytic determination of the highly damped (asymptotic) quasi-normal modes
of small Schwarzschild-de Sitter (SdS) black holes. We comment the result as
compared to the recent numerical data of Konoplya and Zhidenko.


title:
On the discrepancy between two approaches to the equilibrium problem for
  spinning particles

abstract:
  We show that the absence of equilibrium states of two uncharged spinning
particles located on the symmetry axis, revealed in an approximate approach
recently employed by Bonnor, can be explained by a non-general character of his
approximation scheme which lacks an important arbitrary parameter representing
a strut. The absence of this parameter introduces an artificial restriction on
the particles' angular momenta, making it impossible to find a physical
solution to the balance equations.


title:
The impact of the new CHAMP and GRACE Earth gravity models on the
  measurement of the general relativistic Lense--Thirring effect with the
  LAGEOS and LAGEOS II satellites

abstract:
  Among the effects predicted by the General Theory of Relativity for the
orbital motion of a test particle, the post-Newtonian gravitomagnetic
Lense-Thirring effect is very interesting and, up to now, there is not yet an
undisputable experimental direct test of it. To date, the data analysis of the
orbits of the existing geodetic LAGEOS and LAGEOS II satellites has yielded a
test of the Lense-Thirring effect with a claimed accuracy of 20%-30%. According
to some scientists such estimates could be optimistic. Here we wish to discuss
the improvements obtainable in this measurement, in terms of reliability of the
evaluation of the systematic error and reduction of its magnitude, due to the
new CHAMP and GRACE Earth gravity models.

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


title:
Exact solutions of the Hyperextended Scalar Tensor theory with potential
  in the Bianchi type I model

abstract:
  The Hyperextended Scalar Tensor theory with a potential is defined by three
free functions: the gravitational function, the Brans-Dicke coupling function
and the potential. Starting from the expression of the 3-volume and the
potential as function of the proper time, we determine the exact solutions of
this theory. We study two important cases corresponding to power and
exponential laws for the 3-volume and the potential.


title:
Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar
  field in the Bianchi type I model

abstract:
  In this paper we study the isotropisation of a Generalized Scalar-Tensor
theory with a massive scalar field. We find it depends on a condition on the
Brans-Dicke coupling function and the potential and show that asymptotically
the metric functions always tend toward a power or exponential law of the
proper time. These results generalise and unify these of De Sitter in the case
of a cosmological constant and of Cooley and Kitada in the case of an
exponential potential.


title:
Isotropisation of the minimally coupled scalar-tensor theory with a
  massive scalar field and a perfect fluid in the Bianchi type I model

abstract:
  We look for necessary conditions such that minimally coupled scalar-tensor
theory with a massive scalar field and a perfect fluid in the Bianchi type I
model isotropises. Then we derive the dynamical asymptotical properties of the
Universe.


title:
Isotropisation of Bianchi class A models with curvature for a minimally
  coupled scalar tensor theory

abstract:
  We look for necessary isotropisation conditions of Bianchi class $A$ models
with curvature in presence of a massive and minimally coupled scalar field when
a function $\ell$ of the scalar field tends to a constant, diverges
monotonically or with sufficiently small oscillations. Isotropisation leads the
metric functions to tend to a power or exponential law of the proper time $t$
and the potential respectively to vanish as $t^{-2}$ or to a constant.
Moreover, isotropisation always requires late time accelerated expansion and
flatness of the Universe.


title: A reciprocal Wald theorem for varying gravitational function

abstract:
  We study when a cosmological constant is a natural issue if it is mimicked by
the potential of a massive Hyperextended Scalar Tensor theory with a perfect
fluid for Bianchi type I and V models. We then deduce a reciprocal Wald theorem
giving the conditions such that the potential tends to a non vanishing constant
when the gravitational function varies. We also get the conditions allowing the
potentiel to vanish or diverge.


title: Mini Black Holes and the Relic Gravitational Waves Spectrum

abstract:
  In this paper we explore the impact of an era -right after reheating-
dominated by mini black holes and radiation on the spectrum of the relic
gravitational waves. This era may lower the spectrum several orders of
magnitude.


title: Wyman's solution, self-similarity and critical behaviour

abstract:
  We show that the Wyman's solution may be obtained from the four-dimensional
Einstein's equations for a spherically symmetric, minimally coupled, massless
scalar field by using the continuous self-similarity of those equations. The
Wyman's solution depends on two parameters, the mass $M$ and the scalar charge
$\Sigma$. If one fixes $M$ to a positive value, say $M_0$, and let $\Sigma^2$
take values along the real line we show that this solution exhibits critical
behaviour. For $\Sigma^2 >0$ the space-times have eternal naked singularities,
for $\Sigma^2 =0$ one has a Schwarzschild black hole of mass $M_0$ and finally
for $-M_0^2 \leq \Sigma^2 < 0$ one has eternal bouncing solutions.


title: Is Mass Quantized?

abstract:
  The cosmological constant combined with Planck's constant and the speed of
light implies a quantum of mass of approximately 2 x 10^{-65}g. This follows
either from a generic dimensional analysis, or from a specific analysis where
the cosmological constant appears in 4D spacetime as the result of a
dimensional reduction from higher dimensional relativity (such as 5D
induced-matter and membrane theory). In the latter type of theory, all the
particles in the universe can be in higher-dimensional contact.


title:
Palatini approach to Born-Infeld-Einstein theory and a geometric
  description of electrodynamics

abstract:
  The field equations associated with the Born-Infeld-Einstein action are
derived using the Palatini variational technique. In this approach the metric
and connection are varied independently and the Ricci tensor is generally not
symmetric. For sufficiently small curvatures the resulting field equations can
be divided into two sets. One set, involving the antisymmetric part of the
Ricci tensor $R_{\stackrel{\mu\nu}{\vee}}$, consists of the field equation for
a massive vector field. The other set consists of the Einstein field equations
with an energy momentum tensor for the vector field plus additional
corrections. In a vacuum with $R_{\stackrel{\mu\nu}{\vee}}=0$ the field
equations are shown to be the usual Einstein vacuum equations. This extends the
universality of the vacuum Einstein equations, discussed by Ferraris et al.
\cite{Fe1,Fe2}, to the Born-Infeld-Einstein action. In the simplest version of
the theory there is a single coupling constant and by requiring that the
Einstein field equations hold to a good approximation in neutron stars it is
shown that mass of the vector field exceeds the lower bound on the mass of the
photon. Thus, in this case the vector field cannot represent the
electromagnetic field and would describe a new geometrical field. In a more
general version in which the symmetric and antisymmetric parts of the Ricci
tensor have different coupling constants it is possible to satisfy all of the
observational constraints if the antisymmetric coupling is much larger than the
symmetric coupling. In this case the antisymmetric part of the Ricci tensor can
describe the electromagnetic field, although gauge invariance will be broken.


title: Calculation of the Self Force using the Extended-Object Approach

abstract:
  We present here the extended-object approach for the explanation and
calculation of the self-force phenomenon. In this approach, one considers a
charged extended object of a finite size $\epsilon$ that accelerates in a
nontrivial manner, and calculates the total force exerted on it by the
electromagnetic field (whose source is the charged object itself). We show that
at the limit $\epsilon \to 0$ this overall electromagnetic field yields a
universal result, independent on the object's shape, which agrees with the
standard expression for the self force acting on a point-like charge. This
approach has already been considered by many authors, but previous analyses
ended up with expressions for the total electromagnetic force that include
$O(1/\epsilon)$ terms which do not have the form required by
mass-renormalization. (In the special case of a spherical charge distribution,
this $\propto 1/\epsilon $ term was found to be 4/3 times larger than the
desired quantity.) We show here that this problem was originated from a too
naive definition of the notion of ''total electromagnetic force'' used in
previous analyses. Based on energy-momentum conservation combined with proper
relativistic kinematics, we derive here the correct notion of total
electromagnetic force. This completely cures the problematic $O(1/\epsilon)$
term, for any object's shape, and yields the correct self force at the limit
$\epsilon \to 0$. In particular, for a spherical charge distribution, the above
''4/3 problem'' is resolved.


title: Massive-Field Approach to the Scalar Self Force in Curved Spacetime

abstract:
  We derive a new regularization method for the calculation of the (massless)
scalar self force in curved spacetime. In this method, the scalar self force is
expressed in terms of the difference between two retarded scalar fields: the
massless scalar field, and an auxiliary massive scalar field. This field
difference combined with a certain limiting process gives the expression for
the scalar self-force. This expression provides a new self force calculation
method.


title: A moving medium simulation of Schwarzschild black hole optics

abstract:
  An explicit fluid flow simulation of electromagnetic wave propagation in the
gravitational field of a Schwarzschild black hole is given. The fluid has a
constant refractive index and a spherically symmetric inward directed flow. The
resulting form of the metric leads to a new coordinate system in which the
Schwarzschild vacuum is written in Gordon's form. It is shown that a closely
related coordinate system interpolates between the Kerr-Schild and
Painleve-Gullstrand coordinates.


title:
On the possibility of testing the Weak Equivalence Principle with
  artificial Earth satellites

abstract:
  In this paper we examine the possibility of testing the equivalence
principle, in its weak form, by analyzing the orbital motion of a pair of
artificial satellites of different composition moving along orbits of identical
shape and size in the gravitational field of Earth. It turns out that the
obtainable level of accuracy is, realistically, of the order of 10^-10 or
slightly better. It is limited mainly by the fact that, due to the unavoidable
orbital injection errors, it would not be possible to insert the satellites in
orbits with exactly the same radius and that such difference could be known
only with a finite precision. The present-day level of accuracy, obtained with
torsion balance Earth-based measurements and the analysis of Earth-Moon motion
in the gravitational field of Sun with the Lunar Laser Ranging technique, is of
the order of 10^-13. The proposed space-based missions STEP, \muSCOPE, GG and
SEE aim to reach a 10^-15-10^-18 precision level.

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


title:
The Planck Length Scale and Einstein Mass-Energy Obtained from the
  Sciama-Mach Large Number Relationship

abstract:
  If a physical significance should be attributed to the cosmological large
number relationship obtained from Sciama's formulation of Mach's Principle,
then a number of interesting physical conclusions may be drawn. The Planck
length is naturally obtained as the amplitude of waves in a medium whose
properties are implied by the relationship. The relativistic internal energy
associated with a rest mass is explicitly related to the gravitational
potential energy of the Universe, and consistency with the Einstein photon
energy is demonstrated. Broader cosmological consequences of this formulation
are addressed.


title:
Teukolsky evolution of particle orbits around Kerr black holes in the
  time domain: elliptic and inclined orbits

abstract:
  We extend the treatment of the problem of the gravitational waves produced by
a particle of negligible mass orbiting a Kerr black hole using black hole
perturbation theory in the time domain, to elliptic and inclined orbits. We
model the particle by smearing the singularities in the source term using
narrow Gaussian distributions. We compare results (energy and angular momentum
fluxes) for such orbits with those computed using the frequency domain
formalism.


title:
Time Delay in Gravitational Lensing by a Charged Black Hole of String
  Theory

abstract:
  We calculate the time delay between different relativistic images formed by
the gravitational lensing produced by the
Gibbons-Maeda-Garfinkle-Horowitz-Stromiger (GMGHS) charged black hole of
heterotic string theory. Modeling the supermassive central objects of some
galaxies as GMGHS black holes, numerical values of the time delays are
estimated and compared with the correspondient Reissner-Nordstrom black holes .
The time difference amounts to hours, thus being measurable and permiting to
distinguish between General Relativity and String Theory charged black holes.


title: Jerk, snap, and the cosmological equation of state

abstract:
  Taylor expanding the cosmological equation of state around the current epoch
is the simplest model one can consider that does not make any a priori
restrictions on the nature of the cosmological fluid. Most popular cosmological
models attempt to be ``predictive'', in the sense that once somea priori
equation of state is chosen the Friedmann equations are used to determine the
evolution of the FRW scale factor a(t). In contrast, a retrodictive approach
might usefully take observational dataconcerning the scale factor, and use the
Friedmann equations to infer an observed cosmological equation of state. In
particular, the value and derivatives of the scale factor determined at the
current epoch place constraints on the value and derivatives of the
cosmological equation of state at the current epoch. Determining the first
three Taylor coefficients of the equation of state at the current epoch
requires a measurement of the deceleration, jerk, and snap -- the second,
third, and fourth derivatives of the scale factor with respect to time.
Higher-order Taylor coefficients in the equation of state are related to
higher-order time derivatives of the scale factor. Since the jerk and snap are
rather difficult to measure, being related to the third and fourth terms in the
Taylor series expansion of the Hubble law, it becomes clear why direct
observational constraints on the cosmological equation of state are so
relatively weak; and are likely to remain weak for the foreseeable future.


title: A charged rotating cylindrical shell

abstract:
  We give an example of a spacetime having an infinite thin rotating
cylindrical shell constituted by a charged perfect fluid as a source. As the
interior of the shell the Bonnor--Melvin universe is considered, while its
exterior is represented by Datta--Raychaudhuri spacetime. We discuss the energy
conditions and we show that our spacetime contains closed timelike curves.
Trajectories of charged test particles both inside and outside the cylinder are
also examined. Expression for the angular velocity of a circular motion inside
the cylinder is given.


title:
Cosmological models described by a mixture of van der Waals fluid and
  dark energy

abstract:
  The Universe is modeled as a binary mixture whose constituents are described
by a van der Waals fluid and by a dark energy density. The dark energy density
is considered either as the quintessence or as the Chaplygin gas. The
irreversible processes concerning the energy transfer between the van der Waals
fluid and the gravitational field are taken into account. This model can
simulate: (a) an inflationary period where the acceleration grows exponentially
and the van der Waals fluid behaves like an inflaton; (b) an inflationary
period where the acceleration is positive but it decreases and tends to zero
whereas the energy density of the van der Waals fluid decays; (c) a decelerated
period which corresponds to a matter dominated period with a non-negative
pressure; and (d) a present accelerated period where the dark energy density
outweighs the energy density of the van der Waals fluid.


title:
Quasinormal modes of Schwarzschild black holes in four and higher
  dimensions

abstract:
  We make a thorough investigation of the asymptotic quasinormal modes of the
four and five-dimensional Schwarzschild black hole for scalar, electromagnetic
and gravitational perturbations. Our numerical results give full support to all
the analytical predictions by Motl and Neitzke, for the leading term. We also
compute the first order corrections analytically, by extending to higher
dimensions, previous work of Musiri and Siopsis, and find excellent agreement
with the numerical results. For generic spacetime dimension number D the
first-order corrections go as $\frac{1}{n^{(D-3)/(D-2)}}$. This means that
there is a more rapid convergence to the asymptotic value for the five
dimensional case than for the four dimensional case, as we also show
numerically.


title: Cosmological magnetic fields: generation during inflation and evolution

abstract:
  This paper concerns the generation and evolution of the cosmological
(large-scale $\sim Mpc$) magnetic fields in an inflationary universe. The
universe during inflation is represented by de Sitter space-time. We started
with the Maxwell equations in spatially flat Friedmann-Robertson-Walker (FRW)
Cosmologies. Then we calculated the wave equations of the magnetic field and
electric field for the evolution. We consider the input current that was
produced from a massless charged scalar complex field. This field minimally
coupled to both gravity and the electromagnetic fields. The Lagrangian for
massless scalar electrodynamics is then
$L=\sqrt{-g}(D_\mu\phi(D^\mu\phi)^*-{1/4}F_{\mu\nu}F^{\mu\nu})$ . The complex
scalar field couples to electromagnetism through the usual gauge covariant
derivative $D_\mu=\partial_\mu-ieA_\mu$ . After the quantum field theoretical
deduction for the current, we put it back into the wave equation of the
magnetic field.
  After solving this wave equation, our result is $a^2B\sim
\frac{eH}{\sqrt{2}k^2}\mid\sin\sqrt{2}k\eta\mid$ . At the time $\eta_{RH}$ we
have $B_{RH}=\frac{e}{k_{phys}}$. This may imply that the breaking of the
conformal invariance due to the minimal coupling of a massless charged scalar
complex field to both gravitational and electromagnetic fields is not
sufficient for the production of seed galactic magnetic fields during
inflation. But since we are interested in the large-scale cosmological magnetic
field, this could be still a candidate, because of the $1/k$ factor.


title: Black hole hydrodynamics

abstract:
  The curved geometry of a spacetime manifold arises as a solution of
Einstein's gravitational field equation. We show that the metric of a
spherically symmetric gravitational field configuration can be viewed as an
optical metric created by the moving material fluid with nontrivial dielectric
and magnetic properties. Such a "hydrodynamical" approach provides a simple
physical interpretation of a horizon.


title:
A proof of Price's law for the collapse of a self-gravitating scalar
  field

abstract:
  A well-known open problem in general relativity, dating back to 1972, has
been to prove Price's law for an appropriate model of gravitational collapse.
This law postulates inverse-power decay rates for the gravitational radiation
flux on the event horizon and null infinity with respect to appropriately
normalized advanced and retarded time coordinates. It is intimately related
both to astrophysical observations of black holes and to the fate of observers
who dare cross the event horizon. In this paper, we prove a well-defined (upper
bound) formulation of Price's law for the collapse of a self-gravitating scalar
field with spherically symmetric initial data. We also allow the presence of an
additional gravitationally coupled Maxwell field. Our results are obtained by a
new mathematical technique for understanding the long-time behavior of large
data solutions to the resulting coupled non-linear hyperbolic system of
p.d.e.'s in 2 independent variables. The technique is based on the interaction
of the conformal geometry, the celebrated red-shift effect, and local energy
conservation; we feel it may be relevant for the problem of non-linear
stability of the Kerr solution. When combined with previous work of the first
author (gr-qc/0307013) concerning the internal structure of charged black
holes, which assumed the validity of Price's law, our results can be applied to
the strong cosmic censorship conjecture for the Einstein-Maxwell-real scalar
field system with complete spacelike asymptotically flat spherically symmetric
initial data. Under Christodoulou's C^0 formulation, the conjecture is proven
to be false.


title:
Could gauge gravitational degrees of freedom play the role of
  environment in "extended phase space" version of quantum geometrodynamics?

abstract:
  In the context of the recently proposed formulation of quantum
geometrodynamics in extended phase space we discuss the problem how the
behavior of the Universe, initially managed by quantum laws, has become
classical. In this version of quantum geometrodynamics we quantize gauge
gravitational degrees of freedom on an equal basis with physical degrees of
freedom. As a consequence of this approach, a wave function of the Universe
depends not only on physical fields but also on gauge degrees of freedom. From
this viewpoint, one should regard the physical Universe as a subsystem whose
properties are formed in interaction with the subsystem of gauge degrees of
freedom. We argue that the subsystem of gauge degrees of freedom may play the
role of environment, which, being taken into account, causes the density matrix
to be diagonal. We show that under physically reasonable fixing of gauge
condition the density matrix describing the physical subsystem of the Universe
may have a Gaussian peak in some variable, but it could take the Gaussian form
only within a spacetime region where a certain gauge condition is imposed. If
spacetime manifold consists of regions covered by different coordinate charts
the Universe cannot behave in a classical manner nearby borders of these
regions. Moreover, in this case the Universe could not stay in the same quantum
state, but its state would change in some irreversible way.


title: Generalized Quantum Theory of Recollapsing Homogeneous Cosmologies

abstract:
  A sum-over-histories generalized quantum theory is developed for homogeneous
minisuperspace type A Bianchi cosmological models, focussing on the particular
example of the classically recollapsing Bianchi IX universe. The decoherence
functional for such universes is exhibited. We show how the probabilities of
decoherent sets of alternative, coarse-grained histories of these model
universes can be calculated. We consider in particular the probabilities for
classical evolution defined by a suitable coarse-graining. For a restricted
class of initial conditions and coarse grainings we exhibit the approximate
decoherence of alternative histories in which the universe behaves classically
and those in which it does not. For these situations we show that the
probability is near unity for the universe to recontract classically if it
expands classically. We also determine the relative probabilities of
quasi-classical trajectories for initial states of WKB form, recovering for
such states a precise form of the familiar heuristic "J d\Sigma" rule of
quantum cosmology, as well as a generalization of this rule to generic initial
states.


title:
Bounds on the dragging rate and on the rotational mass-energy in slowly
  and differentially rotating relativistic stars

abstract:
  For relativistic stars rotating slowly and differentially with a positive
angular velocity, some properties in relation to the positiveness of the rate
of rotational dragging and of the angular momentum density are derived. Also, a
new proof for the bounds on the rotational mass-energy is given.


title:
Formation of a galaxy with a central black hole in the Lemaitre-Tolman
  model

abstract:
  We construct two models of the formation a galaxy with a central black hole,
starting from a small initial fluctuation at recombination. This is an
application of previously developed methods to find a Lemaitre-Tolman model
that evolves from a given initial density or velocity profile to a given final
density profile. We show that the black hole itself could be either a collapsed
object, or a non-vacuum generalisation of a full Schwarzschild-Kruskal-Szekeres
wormhole. Particular attention is paid to the black hole's apparent and event
horizons.


title: On homothetic cosmological dynamics

abstract:
  We consider the homogeneous and isotropic cosmological fluid dynamics which
is compatible with a homothetic, timelike motion, equivalent to an equation of
state $\rho + 3P = 0$. By splitting the total pressure $P$ into the sum of an
equilibrium part $p$ and a non-equilibrium part $\Pi$, we find that on
thermodynamical grounds this split is necessarily given by $p = \rho$ and $\Pi
= - (4/3)\rho$, corresponding to a dissipative stiff (Zel'dovich) fluid.


title:
Non-Unitary and Unitary Transitions in Generalized Quantum Mechanics and
  Information Problem Solving

abstract:
  The present work is a study of the unitarity problem for Quantum Mechanics at
Planck Scale considered as Quantum Mechanics with Fundamental Length (QMFL).In
the process QMFL is described as deformation of a well-known Quantum Mechanics
(QM). Similar to previous works of the author, the basic approach is based on
deformation of the density matrix (density pro-matrix) with concurrent
development of the wave function deformation in the respective Schrodinger
picture. It is demonstrated that the existence of black holes in the suggested
approach in the end twice results in nonunitary transitions (first after the
Big Bang of QMFL to QM, and then when on trapping of the matter into the black
hole the situation is just the opposite - from QM to QMFL)and hence in recovery
of the unitarity. In parallel this problem is considered in the deformation
terms of Heisenberg algebra, showing the identity of the basic results. From
this an explicit solution for Hawking's informaion paradox has been derived


title: Spinning strings, cosmic dislocations and chronology protection

abstract:
  A massless scalar field is quantized in the background of a spinning string
with cosmic dislocation. By increasing the spin density toward the dislocation
parameter, a region containing closed timelike curves (CTCs) eventually forms
around the defect. Correspondingly, the propagator tends to the ordinary cosmic
string propagator, leading therefore to a mean-square field fluctuation, which
remains well behaved throughout the process, unlike the vacuum expectation
value of the energy-momentum tensor, which diverges due to a subtle mechanism.
These results suggest that back reaction leads to the formation of a "horizon"
that protects from the appearance of CTCs.


title: Self-accelerated Universe

abstract:
  It is widely believed that the large redshifts for distant supernovae are
explained by the vacuum energy dominance, or, in other words, by the
cosmological constant in Einstein's equations, which is responsible for the
anti-gravitation effect. A tacit assumption is that particles move along a
geodesic for the background metric. This is in the same spirit as the consensus
regarding the uniform Galilean motion of a free electron. However, there is a
runaway solution to the Lorentz--Dirac equation governing the behavior of a
radiating electron, in addition to the Galilean solution. Likewise, a runaway
solution to the entire system of equations, both gravitation and matter
equations of motion including, may provide an alternative explanation for the
accelerated expansion of the Universe, without recourse to the hypothetic
cosmological constant.


title: Vacuum type I spacetimes and aligned Papapetrou fields: symmetries

abstract:
  We analyze type I vacuum solutions admitting an isometry whose Killing
2--form is aligned with a principal bivector of the Weyl tensor, and we show
that these solutions belong to a family of type I metrics which admit a group
$G_3$ of isometries. We give a classification of this family and we study the
Bianchi type for each class. The classes compatible with an aligned Killing
2--form are also determined. The Szekeres-Brans theorem is extended to non
vacuum spacetimes with vanishing Cotton tensor.


title: The Graviton as a Bound State and the Cosmological Constant Problem

abstract:
  The graviton is pictured as a bound state of a fermion and anti-fermion with
the spacetime metric assumed to be a composite object of spinor fields, based
on a globally Lorentz invariant action proposed by Hebecker and Wetterich. The
additional degrees of freedom beyond those of the graviton are described by
Goldstone boson gravitational degrees of freedom. If we assume that the fermion
is a light neutrino with mass $m_nu\sim 10^{-3}$ eV, then we obtain the
effective vacuum density ${\bar\rho}_\lambda\sim (10^{-3} eV)^4$, which agrees
with the estimates for the cosmological constant from WMAP and SNIa data.


title:
Do Rotations Beyond the Cosmological Horizon Affect the Local Inertial
  Frame?

abstract:
  If perturbations beyond the horizon have the velocities prescribed everywhere
then the dragging of inertial frames near the origin is suppressed by an
exponential factor. However if perturbations are prescribed in terms of their
angular momenta there is no such suppression.
  We resolve this paradox and in doing so give new explicit results on the
dragging of inertial frames in closed, flat and open universe with and without
a cosmological constant.


title: Toroidal Perturbations of Friedmann-Robertson-Walker Universes

abstract:
  Explicit expressions are found for the axisymmetric metric perturbations of
the closed, flat and open FRW universes caused by toroidal motions of the
cosmic fluid. The perturbations are decomposed in vector spherical harmonics on
2-spheres, but the radial dependence is left general. Solutions for general
odd-parity $l$-pole perturbations are given for either angular velocities or
angular momenta prescribed. In particular, in case of closed universes the
solutions require a special treatment of the Legendre equation.


title: Geodesic deviation in pp-wave spacetimes of quadratic curvature gravity

abstract:
  We write the equation of geodesic deviations in the spacetime of $pp$-waves
in terms of the Newman-Penrose scalars and apply it to study gravitational
waves in quadratic curvature gravity. We show that quadratic curvature gravity
$pp$-waves can have a transverse helicity-0 polarization mode and two
transverse helicity-2 general relativity-like wave polarizations. A concrete
example is given in which we analyze the wave polarizations of an exact
impulsive gravitational wave solution to quadratic curvature gravity.


title: Periodic distribution of galaxies in generalized scalar tensor theory

abstract:
  With the help of Nordtvedt's scalar tensor theory an exact analytical model
of a non-minimally coupled scalar field cosmology in which the gravitational
coupling $G$ and the Hubble factor $H$ oscillate during the radiation era is
presented. A key feature is that the oscillations are confined to the early
stages of the radiation dominated era with $G$ approaching its present constant
value while $H$ becoming a monotonically decreasing function of time. The Brans
Dicke parameter $\omega$ is chosen to be a function of Brans Dicke scalar field
so that no conflict with observational constraints regarding its present value
arises.


title: The Energy for 2+1 Dimensional Black Hole Solutions

abstract:
  The energy distributions of four 2+1 dimensional black hole solutions were
obtained by using the Einstein and M{\o}ller energy-momentum complexes. while
$r \to \infty$, the energy distributions of these four solutions become
divergence.


title: Boson stars with negative cosmological constant

abstract:
  We consider boson star solutions in a $D$-dimensional, asymptotically anti-de
Sitter spacetime and investigate the influence of the cosmological term on
their properties. We find that for $D>4$ the boson star properties are close to
those in four dimensions with a vanishing cosmological constant. A different
behavior is noticed for the solutions in the three dimensional case. We
establish also the non-existence of static, spherically symmetric black holes
with a harmonically time-dependent complex scalar field in any dimension
greater than two.


title: Asymptotic behavior of future-complete cosmological space-times

abstract:
  This work discusses the apriori possible asymptotic behavior to the future,
for (vacuum) space-times which are geodesically complete to the future and
which admit a foliation by compact constant mean curvature Cauchy surfaces.


title:
A $T_0$-discrete universe model with five low-energy fundamental
  interactions and the coupling constants hierarchy

abstract:
  A quantum model of universe is constructed in which values of dimensionless
coupling constants of the fundamental interactions (including the cosmological
constant) are determined via certain topological invariants of manifolds
forming finite ensembles of 3D Seifert fibrations. The characteristic values of
the coupling constants are explicitly calculated as the set of rational numbers
(up to the factor $2\pi$) on the basis of a hypothesis that these values are
proportional to the mean relative fluctuations of discrete volumes of manifolds
in these ensembles. The discrete volumes are calculated using the standard
Alexandroff procedure of constructing $T_0$-discrete spaces realized as nerves
corresponding to characteristic canonical triangulations which are compatible
with the Milnor representation of Seifert fibered homology spheres being the
building material of all used 3D manifolds. Moreover, the determination of all
involved homology spheres is based on the first nine prime numbers ($p_1=2,
>..., p_9=23$). The obtained hierarchy of coupling constants at the present
evolution stage of universe well reproduces the actual hierarchy of the
experimentally observed dimensionless low-energy coupling constants.


title:
Space-Time Uncertainty from Higher-Dimensional Determinism (or: How
  Heisenberg was right in 4D because Einstein was right in 5D)

abstract:
  Heisenberg's uncertainty relation is commonly regarded as defining a level of
unpredictability that is fundamentally incompatible with the deterministic laws
embodied in classical field theories such as Einstein's general relativity. We
here show that this is not necessarily the case. Using 5D as an example of
dimensionally-extended relativity, we employ a novel metric to derive the
standard quantum rule for the action and a form of Heisenberg's relation that
applies to real and virtual particles. The philosophical implications of these
technical results are somewhat profound.


title: Constraints On Cosmic Dynamics

abstract:
  Observationally, the universe appears virtually critical. Yet, there is no
simple explanation for this state. In this article we advance and explore the
premise that the dynamics of the universe always seeks equilibrium conditions.
Vacuum-induced cosmic accelerations lead to creation of matter-energy modes at
the expense of vacuum energy. Because they gravitate, such modes constitute
inertia against cosmic acceleration. On the other extreme, the would-be
ultimate phase of local gravitational collapse is checked by a phase transition
in the collapsing matter fields leading to a de Sitter-like fluid deep inside
the black hole horizon, and at the expense of the collapsing matter fields. As
a result, the universe succumbs to neither vacuum-induced run-away
accelerations nor to gravitationally induced spacetime curvature singularities.
Cosmic dynamics is self-regulating. We discuss the physical basis for these
constraints and the implications, pointing out how the framework relates and
helps resolve standing puzzles such as "why did cosmic inflation end?", "why is
Lambda small now?" and "why does the universe appear persistently critical?".
The approach does, on the one hand, suggest a future course for cosmic
dynamics, while on the other hand it provides some insight into the physics
inside black hole horizons. The interplay between the background vacuum and
matter fields suggests an underlying symmetry that links spacetime acceleration
with spacetime collapse and global (cosmic) dynamics with local (black hole)
dynamics.


title:
The Periodic Standing-Wave Approximation: Overview and Three Dimensional
  Scalar Models

abstract:
  The periodic standing-wave method for binary inspiral computes the exact
numerical solution for periodic binary motion with standing gravitational
waves, and uses it as an approximation to slow binary inspiral with outgoing
waves. Important features of this method presented here are: (i) the
mathematical nature of the ``mixed'' partial differential equations to be
solved, (ii) the meaning of standing waves in the method, (iii) computational
difficulties, and (iv) the ``effective linearity'' that ultimately justifies
the approximation. The method is applied to three dimensional nonlinear scalar
model problems, and the numerical results are used to demonstrate extraction of
the outgoing solution from the standing-wave solution, and the role of
effective linearity.


title: Peaks in the Hartle-Hawking Wave Function from Sums over Topologies

abstract:
  Recent developments in ``Einstein Dehn filling'' allow the construction of
infinitely many Einstein manifolds that have different topologies but are
geometrically close to each other. Using these results, we show that for many
spatial topologies, the Hartle-Hawking wave function for a spacetime with a
negative cosmological constant develops sharp peaks at certain calculable
geometries. The peaks we find are all centered on spatial metrics of constant
negative curvature, suggesting a new mechanism for obtaining local homogeneity
in quantum cosmology.


title:
Is the Energy Density of the Cosmic Quaternionic Field a Possible
  Candidate for the Black Energy?

abstract:
  We try to show that the energy density of the cosmic quaternionic field might
be a possible candidate for the black energy.


title:
WKB metastable quantum states of a de Sitter--Reissner-Nordstroem dust
  shell

abstract:
  We study the dynamics of a spherically symmetric dust shell separating two
spacetime domains, the 'interior' one being a part of the de Sitter spacetime
and the exterior one having the 'extremal' Reissner-Nordstroem geometry.
Extending the ideas of previous works on the subject, we show that the it is
possible to determine the (metastable) WKB quantum states of this gravitational
system.


title: Null K\"ahler structures, Symmetries and Integrability

abstract:
  We review the integrable systems which arise as symmetry reductions of
Plebanski's heavenly equations, and their generalisations. We also show that
all four-dimensional null Kahler-Einstein (or type N hyper-heavenly) metrics
with symmetry can be found from solutions to a variable coefficient
generalisation of the dispersionless Kadomtsev-Petviashvili equation.


title:
Classical and Quantum Decay of Oscillatons: Oscillating Self-Gravitating
  Real Scalar Field Solitons

abstract:
  The oscillating gravitational field of an oscillaton of finite mass M causes
it to lose energy by emitting classical scalar field waves, but at a rate that
is non-perturbatively tiny for small GMm, where m is the scalar field mass:
d(GM)/dt ~ -3797437.776333015 e^[-39.433795197160163/(GMm)]/(GMm)^2.
Oscillatons also decay by the quantum process of the annihilation of scalarons
into gravitons, which is only perturbatively small in GMm, giving by itself
d(GM)/dt ~ - 0.008513223934732692 G m^2 (GMm)^5. Thus the quantum decay is
faster than the classical one for Gmm < 39.4338/[ln(1/Gm^2)}-7ln(GMm)+19.9160].
The time for an oscillaton to decay away completely into free scalarons and
gravitons is ~ 2/(G^5 m^11) ~ 10^324 yr (1 meV/m)^11. Oscillatons of more than
one real scalar field of the same mass generically asymptotically approach a
static-geometry U(1) boson star configuration with GMm = GM_0 m, at the rate
d(GM/c^3)/dt ~ [(C/(GMm)^4)e^{-alpha/(GMm)}+Q(m/m_{Pl})^2(GMm)^3]
[(GMm)^2-(GM_0 m)^2], with GM_0 m depending on the magnitudes and relative
phases of the oscillating fields, and with the same constants C, alpha, and Q
given numerically above for the single-field case that is equivalent to GM_0 m
= 0.


title: Is a classical Euclidean TOE reasonable?

abstract:
  We analyze both the feasibility and reasonableness of a classical Euclidean
Theory of Everything (TOE), which we understand as a TOE based on an Euclidean
space and an absolute time over which deterministic models of particles and
forces are built. The possible axiomatic complexity of a TOE in such a
framework is considered and compared to the complexity of the assumptions
underlying the Standard Model. Current approaches to relevant (for our
purposes) reformulations of Special Relativity, General Relativity, inertia
models and Quantum Theory are summarized, and links between some of these
reformulations are exposed. A qualitative framework is suggested for a research
program on a classical Euclidean TOE. Within this framework an underlying basis
is suggested, in particular, for the Principle of Relativity and Principle of
Equivalence. A model for gravity as an inertial phenomenon is proposed. Also, a
basis for quantum indeterminacy and wave function collapse is suggested in the
framework.


title: Reflection from black holes

abstract:
  Black holes are presumed to have an ideal ability to absorb and keep matter.
Whatever comes close to the event horizon, a boundary separating the inside
region of a black hole from the outside world, inevitably goes in and remains
inside forever. This work shows, however, that quantum corrections make
possible a surprising process, reflection: a particle can bounce back from the
event horizon. For low energy particles this process is efficient, black holes
behave not as holes, but as mirrors, which changes our perception of their
physical nature. Possible ways for observations of the reflection and its
relation to the Hawking radiation process are outlined.


title: Dirty black holes: Quasinormal modes

abstract:
  In this paper, we investigate the asymptotic nature of the quasinormal modes
for "dirty" black holes -- generic static and spherically symmetric spacetimes
for which a central black hole is surrounded by arbitrary "matter" fields. We
demonstrate that, to the leading asymptotic order, the [imaginary] spacing
between modes is precisely equal to the surface gravity, independent of the
specifics of the black hole system.
  Our analytical method is based on locating the complex poles in the first
Born approximation for the scattering amplitude. We first verify that our
formalism agrees, asymptotically, with previous studies on the Schwarzschild
black hole. The analysis is then generalized to more exotic black hole
geometries. We also extend considerations to spacetimes with two horizons and
briefly discuss the degenerate-horizon scenario.


title: Features of Motion Around Charged D-Stars

abstract:
  The motion of light and a neutral test particle around the charged D-star has
been studied. The difference of the deficit angle of light from the case in
asymptotically flat spacetime is in a factor $(1-\epsilon^2)$. The motion of a
test particle is affected by the deficit angle and the charge. Through the
phase analysis, we prove the existence of the periodic solution to the equation
of motion and the effect of the deficit angle and the charge to the critical
point and its type. We also give the conditions under which the critical point
is a stable center and an unstable saddle point.


title: Black hole initial data from a non-conformal decomposition

abstract:
  We present an alternative approach to setting initial data in general
relativity. We do not use a conformal decomposition, but instead express the
3-metric in terms of a given unit vector field and one unknown scalar field. In
the case of axisymmetry, we have written a program to solve the resulting
nonlinear elliptic equation. We have obtained solutions, both numerically and
from a linearized analytic method, for a general perturbation of Schwarzschild.


title: Particle creation in the oscillatory phase of inflaton

abstract:
  A thermal squeezed state representation of inflaton is constructed for a flat
Friedmann-Robertson-Walker background metric and the phenomenon of particle
creation is examined during the oscillatory phase of inflaton, in the
semiclassical theory of gravity. An approximate solution to the semiclassical
Einstein equation is obtained in thermal squeezed state formalism by
perturbatively and is found obey the same power-law expansion as that of
classical Einstein equation. In addition to that the solution shows oscillatory
in nature except on a particular condition. It is also noted that, the
coherently oscillating nonclassical inflaton, in thermal squeezed vacuum state,
thermal squeezed state and thermal coherent state, suffer particle production
and the created particles exhibit oscillatory behavior. The present study can
account for the post inflation particle creation due to thermal and quantum
effects of inflaton in a flat FRW universe.


title: Homogeneous Plane-wave Spacetimes and their Stability

abstract:
  We consider the stability of spatially homogeneous plane-wave spacetimes. We
carry out a full analysis for plane-wave spacetimes in (4+1) dimensions, and
find there are two cases to consider; what we call non-exceptional and
exceptional. In the non-exceptional case the plane waves are stable to
(spatially homogeneous) vacuum perturbations as well as a restricted set of
matter perturbations. In the exceptional case we always find an instability.
Also we consider the Milne universe in arbitrary dimensions and find it is also
stable provided the strong energy condition is satisfied. This implies that
there exists an open set of stable plane-wave solutions in arbitrary
dimensions.


title:
Lorentz Invariance and the semiclassical approximation of loop quantum
  gravity

abstract:
  It is shown that the field equations derived from an effective interaction
hamiltonian for Maxwell and gravitational fields in the semiclassical
approximation of loop quantum gravity using rotational invariant states (such
as weave states) are Lorentz invariant. To derive this result, which is in
agreement with the observational evidence, we use the geometrical properties of
the electromagnetic field.


title: Vacuum dominance and holography

abstract:
  A cosmological event horizon develops in a vacuum-dominated Friedmann
universe. The Schwarschild radius of the vacuum energy within the horizon
equals the horizon radius. Black hole thermodynamics and the holographic
conjecture indicate a finite number of degrees of freedom within the horizon.
The average energy per degree of freedom equals the energy of a massless
quantum with wavelength of the horizon circumference. This suggests identifying
the degrees of freedom with the presence or absence, in each Planck area on one
horizon quadrant, of a 0S2 vibrational mode of the horizon with the z axis
passing through that area. Pressure waves on the horizon (the superposition of
0S2 vibrational modes) can be envisioned to propagate into the observable
universe within the horizon at the speed of light. So, the vacuum energy and
pressure throughout the observable universe could (in principle) be determined
from the vacuum equation of state.


title: Dynamics in Stationary, Non-Globally Hyperbolic Spacetimes

abstract:
  Classically, the dynamics in a non-globally hyperbolic spacetime is ill
posed. Previously, a prescription was given for defining dynamics in static
spacetimes in terms of a second order operator acting on a Hilbert space
defined on static slices. The present work extends this result by giving a
similar prescription for defining dynamics in stationary spacetimes obeying
certain mild assumptions. The prescription is defined in terms of a first order
operator acting on a different Hilbert space from the one used in the static
prescription. It preserves the important properties of the earlier one: the
formal solution agrees with the Cauchy evolution within the domain of
dependence, and smooth data of compact support always give rise to smooth
solutions. In the static case, the first order formalism agrees with second
order formalism (using specifically the Friedrichs extension). Applications to
field quantization are also discussed.


title: Time Delay Interferometry with Moving Spacecraft Arrays

abstract:
  Space-borne interferometric gravitational wave detectors, sensitive in the
low-frequency (millihertz) band, will fly in the next decade. In these
detectors the spacecraft-to-spacecraft light-travel-times will necessarily be
unequal, time-varying, and (due to aberration) have different time delays on
up- and down-links. Reduction of data from moving interferometric laser arrays
in solar orbit will in fact encounter non-symmetric up- and downlink light time
differences that are about 100 times larger than has previously been
recognized. The time-delay interferometry (TDI) technique uses knowledge of
these delays to cancel the otherwise dominant laser phase noise and yields a
variety of data combinations sensitive to gravitational waves. Under the
assumption that the (different) up- and downlink time delays are constant, we
derive the TDI expressions for those combinations that rely only on four
inter-spacecraft phase measurements. We then turn to the general problem that
encompasses time-dependence of the light-travel times along the laser links. By
introducing a set of non-commuting time-delay operators, we show that there
exists a quite general procedure for deriving generalized TDI combinations that
account for the effects of time-dependence of the arms. By applying our
approach we are able to re-derive the ``flex-free'' expression for the
unequal-arm Michelson combinations $X_1$, first presented in \cite{STEA}, and
obtain the generalized expressions for the TDI combinations called Relay,
Beacon, Monitor, and Symmetric Sagnac.


title: Energy and Momentum in Spacetime Homogeneous G$\ddot{o}$del-type Metrics

abstract:
  Using Einstein and Papapetrou energy-momentum complexes, we explicitly
calculate the energy and momentum distribution associated with spacetime
homogeneous G$\ddot{o}$del-type metrics. We obtain that the two definitions of
energy-momentum complexes do not provide the same result for these type of
metrics. However, it is shown that the results obtained are reduced to the
energy-momentum densities of G$\ddot{o}$del metric already available in the
literature


title:
Classification of Static Plane Symmetric Spacetimes according to their
  Matter Collineations

abstract:
  In this paper we classify static plane symmetric spacetimes according to
their matter collineations. These have been studied for both cases when the
energy-momentum tensor is non-degenerate and also when it is degenerate. It
turns out that the non-degenerate case yields either {\it four}, {\it five},
{\it six}, {\it seven} or {\it ten} independent matter collineations in which
{\it four} are isometries and the rest are proper. There exists three
interesting cases where the energy-momentum tensor is degenerate but the group
of matter collineations is finite-dimensional. The matter collineations in
these cases are either {\it four}, {\it six} or {\it ten


title:
Critical velocities $c/\sqrt 3$ and $c/\sqrt 2$ in general theory of
  relativity

abstract:
  We consider a few thought experiments of radial motion of massive particles
in the gravitational fields outside and inside various celestial bodies: Earth,
Sun, black hole. All other interactions except gravity are disregarded. For the
outside motion there exists a critical value of coordinate velocity ${\rm v}_c
= c/\sqrt 3$: particles with ${\rm v} < {\rm v}_c$ are accelerated by the
field, like Newtonian apples, particles with ${\rm v} > {\rm v}_c$ are
decelerated like photons. Particles moving inside a body with constant density
have no critical velocity; they are always accelerated. We consider also the
motion of a ball inside a tower, when it is thrown from the top (bottom) of the
tower and after classically bouncing at the bottom (top) comes back to the
original point. The total time of flight is the same in these two cases if the
initial proper velocity $v_0$ is equal to $c/\sqrt 2$.


title:
Gravitational perturbations on local experiments in a satellite : The
  dragging of inertial frame in the HYPER project

abstract:
  We consider a nearly free falling Earth satellite where atomic wave
interferometers are tied to a telescope pointing towards a faraway star. They
measure the acceleration and the rotation relatively to the local inertial
frame.
  We calculate the rotation of the telescope due to the aberrations and the
deflection of the light in the gravitational field of the Earth. We show that
the deflection due to the quadrupolar momentum of the gravity is not negligible
if one wants to observe the Lense-Thirring effect of the Earth.
  We consider some perturbation to the ideal device and we discuss the orders
of magnitude of the phase shifts due to the residual tidal gravitational field
in the satellite and we exhibit the terms which must be taken into account to
calculate and interpret the full signal.
  Within the framework of a geometric model, we calculate the various periodic
components of the signal which must be analyzed to detect the Lense-Tirring
effect. We discuss the results which support a reasonable optimism.
  As a conclusion we put forward the necessity of a more complete, realistic
and powerful model in order to obtain a final conclusion on the theoretical
feasibility of the experiment as far as the observation of the Lense-Thirring
effect is involved.


title: Principal null directions of perturbed black holes

abstract:
  The properties of principal null directions of a perturbed black hole are
investigated. It shown that principal null directions are directly observable
quantities characterizing the space-time. A definition of a perturbed
space-time, generalizing that given by Stewart and Walker is proposed. This
more general framework allows one to include descriptions of a given space-time
other than by a pair $(M,g)$ where $M$ is a four-dimensional differential
manifold and $g$ a Lorentz metric. Examples of alternative characterizations
are the curvature representation of Karlhede and others, the Newman-Penrose
representation or observable quantities involving principal null directions.
The conditions are studied under which the various alternative choices of
observables provide equivalent descriptions of the space-time.


title:
Causal Bulk Viscous LRS Bianchi I Models With Variable Gravitational and
  Cosmological "Constant"

abstract:
  In this paper we have investigated an LRS Bianchi I anisotropic cosmological
model of the universe by taking time varying $G$ and $\Lambda$ in the presence
of bulk viscous fluid source described by full causal non-equilibrium
thermodynamics. We obtain a cosmological constant as a decreasing function of
time and for $m, n > 0$, the value of cosmological ``constant'' for this model
is found to be small and positive which is supported by the results from recent
supernovae observations.


title:
An Integral Spectral Representation of the Propagator for the Wave
  Equation in the Kerr Geometry

abstract:
  We consider the scalar wave equation in the Kerr geometry for Cauchy data
which is smooth and compactly supported outside the event horizon. We derive an
integral representation which expresses the solution as a superposition of
solutions of the radial and angular ODEs which arise in the separation of
variables. In particular, we prove completeness of the solutions of the
separated ODEs.
  This integral representation is a suitable starting point for a detailed
analysis of the long-time dynamics of scalar waves in the Kerr geometry.


title: Bounce Models in Brane Cosmology and a Gravitational Stability Condition

abstract:
  Five-dimensional cosmological models with two 3-branes and with a buck
cosmological constant are studied. It is found that for all the three cases
($\Lambda =0$, $\Lambda >0$, and $\Lambda <0$), the conventional space-time
singularity ``big bang'' could be replaced by a matter singularity ``big
bounce'', at which the ``size'' of the universe and the energy density are
finite while the pressure diverges, and across which the universe evolves from
a pre-existing contracting phase to the present expanding phase. It is also
found that for the $\Lambda >0$ case the brane solutions could give an
oscillating universe model in which the universe oscillates with each cosmic
cycle begins from a ``big bounce'' and ends to a ``big crunch'', with a
distinctive characteristic that in each subsequent cycle the universe expands
to a larger size and then contracts to a smaller (but non-zero) size. By
studying the gravitational force acted on a test particle in the bulk, a
gravitational stability condition is derived and then is used to analyze those
brane models. It predicts that if dark energy takes over ordinary matter,
particles on the brane may become unstable in the sense that they may escape
from our 4D-world and dissolve in the bulk due to the repulsive force of dark
energy.


title:
Improving the sensitivity to gravitational-wave sources by modifying the
  input-output optics of advanced interferometers

abstract:
  We study frequency dependent (FD) input-output schemes for signal-recycling
interferometers, the baseline design of Advanced LIGO and the current
configuration of GEO 600. Complementary to a recent proposal by Harms et al. to
use FD input squeezing and ordinary homodyne detection, we explore a scheme
which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are
sub-optimal among all possible input-output schemes, provide a global noise
suppression by the power squeeze factor, while being realizable by using
detuned Fabry-Perot cavities as input/output filters. At high frequencies, the
two schemes are shown to be equivalent, while at low frequencies our scheme
gives better performance than that of Harms et al., and is nearly fully
optimal. We then study the sensitivity improvement achievable by these schemes
in Advanced LIGO era (with 30-m filter cavities and current estimates of
filter-mirror losses and thermal noise), for neutron star binary inspirals, and
for narrowband GW sources such as low-mass X-ray binaries and known radio
pulsars. Optical losses are shown to be a major obstacle for the actual
implementation of these techniques in Advanced LIGO. On time scales of
third-generation interferometers, like EURO/LIGO-III (~2012), with
kilometer-scale filter cavities, a signal-recycling interferometer with the FD
readout scheme explored in this paper can have performances comparable to
existing proposals. [abridged]


title:
Quasi normal modes: A simple derivation of the level spacing of the
  frequencies

abstract:
  It is known that the imaginary parts of the frequencies of the quasi normal
modes of the Schwarzschild black hole are equally spaced, with the level
spacing dependent only on the surface gravity. We generalize this result to a
wider class of spacetimes and provide a simple derivation of the imaginary
parts of the frequencies. The analysis shows that the result is closely linked
to the thermal nature of horizons and arises from the exponential redshift of
the wave modes close to the horizon.


title:
New derivation of a third post-Newtonian equation of motion for
  relativistic compact binaries without ambiguity

abstract:
  A third post-Newtonian (3 PN) equation of motion for an inspiralling binary
consisting of two spherical compact stars with strong internal gravity is
derived under harmonic coordinate condition using the strong field point
particle limit. The equation of motion is complete in a sense that it is
Lorentz invariant in the post-Newtonian perturbative sense, admits conserved
energy of the orbital motion, and is unambiguous, that is, with no undetermined
coefficient. In this paper, we show explicit expressions of the 3 PN equation
of motion and an energy of the binary orbital motion in case of the circular
orbit (neglecting the 2.5 PN radiation reaction effect) and in the center of
the mass frame. It is argued that the 3 PN equation of motion we obtained is
physically unambiguous. Full details will be reported elsewhere.


title:
Equation of motion for relativistic compact binaries with the strong
  field point particle limit: Third post-Newtonian order

abstract:
  An equation of motion for relativistic compact binaries is derived through
the third post-Newtonian (3 PN) approximation of general relativity. The strong
field point particle limit and multipole expansion of the stars are used to
solve iteratively the harmonically relaxed Einstein equations. We take into
account the Lorentz contraction on the multipole moments defined in our
previous works. We then derive a 3 PN acceleration of the binary orbital motion
of the two spherical compact stars based on a surface integral approach which
is a direct consequence of local energy momentum conservation. Our resulting
equation of motion admits a conserved energy (neglecting the 2.5 PN radiation
reaction effect), is Lorentz invariant and is unambiguous: there exist no
undetermined parameter reported in the previous works. We shall show that our 3
PN equation of motion agrees physically with the Blanchet and Faye 3 PN
equation of motion if $\lambda = - 1987/3080$, where $\lambda$ is the parameter
which is undetermined within their framework. This value of $\lambda$ is
consistent with the result of Damour, Jaranowski, and Sch\"afer who first
completed a 3 PN iteration of the ADM Hamiltonian in the ADMTT gauge using the
dimensional regularization.


title:
Merger of binary neutron stars of unequal mass in full general
  relativity

abstract:
  We present results of three dimensional numerical simulations of the merger
of unequal-mass binary neutron stars in full general relativity. A $\Gamma$-law
equation of state $P=(\Gamma-1)\rho\epsilon$ is adopted, where $P$, $\rho$,
$\varep$, and $\Gamma$ are the pressure, rest mass density, specific internal
energy, and the adiabatic constant, respectively. We take $\Gamma=2$ and the
baryon rest-mass ratio $Q_M$ to be in the range 0.85--1. The typical grid size
is $(633,633,317)$ for $(x,y,z)$ . We improve several implementations since the
latest work. In the present code, the radiation reaction of gravitational waves
is taken into account with a good accuracy. This fact enables us to follow the
coalescence all the way from the late inspiral phase through the merger phase
for which the transition is triggered by the radiation reaction. It is found
that if the total rest-mass of the system is more than $\sim 1.7$ times of the
maximum allowed rest-mass of spherical neutron stars, a black hole is formed
after the merger irrespective of the mass ratios. The gravitational waveforms
and outcomes in the merger of unequal-mass binaries are compared with those in
equal-mass binaries. It is found that the disk mass around the so formed black
holes increases with decreasing rest-mass ratios and decreases with increasing
compactness of neutron stars. The merger process and the gravitational
waveforms also depend strongly on the rest-mass ratios even for the range $Q_M=
0.85$--1.


title:
$\Lambda^{mu}_{\nu}$ geometries from the point of view of different
  observers

abstract:
  $\Lambda^{\mu}_{\nu}$-geometry is a geometry with a variable cosmological
term described by a second-rank symmetric tensor $\Lambda^{\mu}_{\nu}$ whose
asymptotics are Einstein cosmological term $\Lambda \delta ^{\mu}_{\nu}$ at the
origin and $\lambda \delta ^{\mu}_{\nu}$ at infinity (with $\lambda <
\Lambda$).
  It corresponds to extension of the algebraic structure of the Einstein
cosmological term $\Lambda \delta ^{\mu}_{\nu}$ in such a way that a scalar
$\Lambda$ describing vacuum energy density as $\rho_{vac}=8\pi G \Lambda$ (with
$\rho_{vac}$=const by virtue of the Bianchi identities), becomes explicite
related to the appropriate component, $\Lambda^0_0$, of an appropriate
stress-energy tensor, $T^{\mu}_{\nu}=8\pi G\Lambda^{\mu}_{\nu}$ whose vacuum
properties follow from its symmetry, $T_0^0=T_1^1$, and whose variability
follows from the contracted Bianchi identities. In the spherically symmetric
case existence of such geometries in frame of GR follows from imposing on
Einstein equations requirements of finiteness of the ADM mass $m$, and of
regularity of density and pressures. Dependently on parameters $m$ and
$q=\sqrt{\Lambda /\lambda}$, $\Lambda^{\mu}_{\nu}$ geometry describes five
types of configurations. We summarize here the results which tell us how these
configurations look from the point of view of different observers: a static
observer, a Lemaitre co-moving observer, and a Kantowski-Sachs observer.


title: Gravitational Instability of Yang-Mills Cosmologies

abstract:
  The gravitational instability of Yang-Mills cosmologies is numerically
studied with the hamiltonian formulation of the spherically symmetric
Einstein-Yang-Mills equations with SU(2) gauge group. On the short term, the
expansion dilutes the energy densities of the Yang-Mills fluctuations due to
their conformal invariance. In this early regime, the gauge potentials appear
oscillating quietly in an interaction potential quite similar to the one of the
homogeneous case. However, on the long term, the expansion finally becomes
significantly inhomogeneous and no more mimics a conformal transformation of
the metric. Thereafter, the Yang-Mills fluctuations enter a complex non-linear
regime, accompanied by diffusion, while their associated energy contrasts grow.


title: On tilted perfect fluid Bianchi type VI$_0$ self-similar models

abstract:
  We show that the tilted perfect fluid Bianchi VI$_0$ family of self-similar
models found by Rosquist and Jantzen [K. Rosquist and R. T. Jantzen, \emph{%
Exact power law solutions of the Einstein equations}, 1985 Phys. Lett.
\textbf{107}A 29-32] is the most general class of tilted self-similar models
but the state parameter $\gamma $ lies in the interval $(\frac 65,\frac 32) $.
The model has a four dimensional stable manifold indicating the possibility
that it may be future attractor, at least for the subclass of tilted Bianchi
VI$_0$ models satisfying $n_\alpha ^\alpha =0$ in which it belongs. In addition
the angle of tilt is asymptotically significant at late times suggesting that
for the above subclasses of models the tilt is asymptotically extreme.