title: Stochastic gravitoelectromagnetic inflation

abstract:
  Gravitoelectromagnetic inflation was recently introduced to describe, in an
unified manner, electromagnetic, gravitatory and inflaton fields in the early
(accelerated) inflationary universe from a 5D vacuum state. In this paper, we
study a stochastic treatment for the gravitoelectromagnetic components
$A_B=(A_{\mu},\phi)$, on cosmological scales. We focus our study on the seed
magnetic fields on super Hubble scales, which could play an important role in
large scale structure formation of the universe.


title: Eigenmode frequency distribution of rapidly rotating neutron stars

abstract:
  We use perturbation theory and the relativistic Cowling approximation to
numerically compute characteristic oscillation modes of rapidly rotating
relativistic stars which consist of a perfect fluid obeying a polytropic
equation of state. We present a code that allows the computation of modes of
arbitrary order. We focus here on the overall distribution of frequencies. As
expected, we find an infinite pressure mode spectrum extending to infinite
frequency. In addition we obtain an infinite number of inertial mode solutions
confined to a finite, well-defined frequency range which depends on the
compactness and the rotation frequency of the star. For non-axisymmetric modes
we observe how this range is shifted with respect to the axisymmetric ones,
moving towards negative frequencies and thus making all m>2 modes unstable. We
discuss whether our results indicate that the star's spectrum must have a
continuous part, as opposed to simply containing an infinite number of discrete
modes.


title:
Covariance properties and regularization of conserved currents in tetrad
  gravity

abstract:
  We discuss the properties of the gravitational energy-momentum 3-form within
the tetrad formulation of general relativity theory. We derive the covariance
properties of the quantities describing the energy-momentum content under
Lorentz transformations of the tetrad. As an application, we consider the
computation of the total energy (mass) of some exact solutions of Einstein's
general relativity theory which describe compact sources with asymptotically
flat spacetime geometry. As it is known, depending on the choice of tetrad
frame, the formal total integral for such configurations may diverge. We
propose a natural regularization method which yields finite values for the
total energy-momentum of the system and demonstrate how it works on a number of
explicit examples.


title: Oppenheimer-Volkoff Equation in Relativistic MOND Theory

abstract:
  In this paper, we discuss the internal and external metric of the
semi-realistic stars in relativistic MOND theory. We show the
Oppenheimer-Volkoff equation in relativistic MOND theory and get the metric and
pressure inside the stars to order of post-Newtonian corrections. We study the
features of motion around the static, spherically symmetric stars by
Hamilton-Jacobi mothod, and find there are only some small corrections in
relativistic MOND theory.


title: Parametrization of the equation of state and the expanding universe

abstract:
  The structure of the equation of state $\omega$ could be very complicate in
nature while a few linear models have been successful in cosmological
predictions. Linear models are treated as leading approximation of a complete
Taylor series in this paper. If the power series converges quickly, one can
freely truncate the series order by order. Detailed convergent analysis on the
choices of the expansion parameters is presented in this paper. The related
power series for the energy density function, the Hubble parameter and related
physical quantities of interest are also computed in this paper.


title: The Proca-field in Loop Quantum Gravity

abstract:
  In this paper we investigate the Proca-field in the framework of Loop Quantum
Gravity. It turns out that the methods developed there can be applied to the
symplectically embedded Proca-field, giving a rigorous, consistent,
non-perturbative quantization of the theory. This can be achieved by
introducing a scalar field, which has completely different properties than the
one used in spontaneous symmetry breaking. The analysis of the kernel of the
Hamiltonian suggests that the mass term in the quantum theory has a different
role than in the classical theory.


title: Physics in the Real Universe: Time and Spacetime

abstract:
  The Block Universe idea, representing spacetime as a fixed whole, suggests
the flow of time is an illusion: the entire universe just is, with no special
meaning attached to the present time. This view is however based on
time-reversible microphysical laws and does not represent macro-physical
behaviour and the development of emergent complex systems, including life,
which do indeed exist in the real universe. When these are taken into account,
the unchanging block universe view of spacetime is best replaced by an evolving
block universe which extends as time evolves, with the potential of the future
continually becoming the certainty of the past. However this time evolution is
not related to any preferred surfaces in spacetime; rather it is associated
with the evolution of proper time along families of world lines


title: Non-chaotic dynamics in general-relativistic and scalar-tensor cosmology

abstract:
  In the context of scalar-tensor models of dark energy and inflation, the
dynamics of vacuum scalar-tensor cosmology are analysed without specifying the
coupling function or the scalar field potential. A conformal transformation to
the Einstein frame is used and the dynamics of general relativity with a
minimally coupled scalar field are derived for a generic potential. It is shown
that the dynamics are non-chaotic, thus settling an existing debate.


title: A Note on Black Hole Temperature and Entropy

abstract:
  We propose intuitive derivations of the Hawking temperature and the
Bekenstein-Hawking entropy of a Schwarzschild black hole.


title:
Aspects of Graviton Detection: Graviton Emission and Absorption by
  Atomic Hydrogen

abstract:
  Graviton absorption cross sections and emission rates for hydrogen are
calculated by both semi-classical and field theoretic methods. We point out
several mistakes in the literature concerning spontaneous emission of gravitons
and related phenomena, some of which are due to a subtle issue concerning gauge
invariance of the linearized interaction Hamiltonian.


title: Circular orbits and spin in black-hole initial data

abstract:
  The construction of initial data for black-hole binaries usually involves the
choice of free parameters that define the spins of the black holes and
essentially the eccentricity of the orbit. Such parameters must be chosen
carefully to yield initial data with the desired physical properties. In this
paper, we examine these choices in detail for the quasiequilibrium method
coupled to apparent-horizon/quasiequilibrium boundary conditions. First, we
compare two independent criteria for choosing the orbital frequency, the
"Komar-mass condition" and the "effective-potential method," and find excellent
agreement. Second, we implement quasi-local measures of the spin of the
individual holes, calibrate these with corotating binaries, and revisit the
construction of non-spinning black hole binaries. Higher-order effects, beyond
those considered in earlier work, turn out to be important. Without those,
supposedly non-spinning black holes have appreciable quasi-local spin;
furthermore, the Komar-mass condition and effective potential method agree only
when these higher-order effects are taken into account. We compute a new
sequence of quasi-circular orbits for non-spinning black-hole binaries, and
determine the innermost stable circular orbit of this sequence.


title: Dynamics of a self--gravitating magnetized source

abstract:
  We consider a magnetized degenerate gas of fermions as the matter source of a
homogeneous but anisotropic Bianchi I spacetime with a Kasner--like metric. We
examine the dynamics of this system by means of a qualitative and numerical
study of Einstein-Maxwell field equations which reduce to a non--linear
autonomous system. For all initial conditions and combinations of free
parameters the gas evolves from an initial anisotropic singularity into an
asymptotic state that is completely determined by a stable attractor. Depending
on the initial conditions the anisotropic singularity is of the ``cigar'' or
``plate'' types.


title: A Classification of Plane Symmetric Kinematic Self-Similar Solutions

abstract:
  In this paper we provide a classification of plane symmetric kinematic
self-similar perfect fluid and dust solutions. In the perfect fluid and dust
cases, kinematic self-similar vectors for the tilted, orthogonal and parallel
cases have been explored in the first, second, zeroth and infinite kinds with
different equations of state. We obtain total of eleven plane symmetric
kinematic self-similar solutions out of which six are independent. The perfect
fluid case gives two solutions for infinite tilted and infinite orthogonal
kinds. In the dust case, we have four independent solutions in the first
orthogonal, infinite tilted, infinite orthogonal and infinite parallel kinds.
The remaining cases provide contradiction. It is interesting to mention that
some of these solutions turn out to be vacuum.


title: On smoothness-asymmetric null infinities

abstract:
  We discuss the existence of asymptotically Euclidean initial data sets to the
vacuum Einstein field equations which would give rise (modulo an existence
result for the evolution equations near spatial infinity) to developments with
a past and a future null infinity of different smoothness. For simplicity, the
analysis is restricted to the class of conformally flat, axially symmetric
initial data sets. It is shown how the free parameters in the second
fundamental form of the data can be used to satisfy certain obstructions to the
smoothness of null infinity. The resulting initial data sets could be
interpreted as those of some sort of (non-linearly) distorted Schwarzschild
black hole. Its developments would be so that they admit a peeling future null
infinity, but at the same time have a polyhomogeneous (non-peeling) past null
infinity.


title: A look inside the theory of the linear approximation

abstract:
  We introduce in the framework of the linear approximation of General
relativity a natural distinction between General gauge transformations
generated by any vector field and those Special ones for which this vector
field is a gradient. This allows to introduce geometrical objects that are not
invariant under General gauge transformations but they are under Special ones.
We develop then a formalism that strengthens the analogy of the formalisms of
the electromagnetic and the gravitational theories in a Special relativity
framework. We are thus able to define the energy-momentum tensor of the
gravitational field and to fully analyze the gravitational field of isolated
point masses or continuous distributions of them obtained by linear
superpositions.


title: `Hidden' Symmetries of Higher Dimensional Rotating Black Holes

abstract:
  We demonstrate that the rotating black holes in an arbitrary number of
dimensions and without any restrictions on their rotation parameters possess
the same `hidden' symmetry as the 4-dimensional Kerr metric. Namely, besides
the spacetime symmetries generated by the Killing vectors they also admit the
(antisymmetric) Killing-Yano and symmetric Killing tensors.


title: Quantum cosmology from three different perspectives

abstract:
  Our review is devoted to three promising research lines in quantum cosmology
and the physics of the early universe. The nonperturbative renormalization
programme is making encouraging progress that we here assess from the point of
view of cosmological applications: Lagrangian and Hamiltonian form of pure
gravity with variable G and Lambda; power-law inflation for pure gravity; an
accelerating universe without dark energy. In perturbative quantum cosmology,
on the other hand, diffeomorphism-invariant boundary conditions lead naturally
to a singularity-free one-loop wave function of the universe. Last, but not
least, in the braneworld picture one discovers the novel concept of
cosmological wave function of the bulk space-time. Its impact on quantum
cosmology and singularity avoidance is still, to a large extent, unexplored.


title: Gravitational wave background in perfect fluid quantum cosmologies

abstract:
  We discuss the gravitational wave background produced by bouncing models
based on a full quantum evolution of a universe filled with a perfect fluid.
Using an ontological interpretation for the background wave function allows us
to solve the mode equations for the tensorial perturbations, and we find the
spectral index as a function of the fluid equation of state.


title: Propagating torsion in the Einstein frame

abstract:
  The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume
element so that it is compatible with the connection. The condition of
connection compatibility gives constraints on torsion, which are also necessary
for the consistence of torsion, minimal coupling, and electromagnetic gauge
invariance. To solve the problem of positivity of energy associated with the
torsionic scalar, we reformulate this theory in the Einstein conformal frame.
In the presence of the electromagnetic field, we obtain the
Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different
factor in the torsionic kinetic term.


title: About Poynting vector in axially symmetric stationary spacetimes

abstract:
  We dispose of some objections raised by Manko et al. (gr-qc/0604091) on a
recently published paper on the role of Poynting vector in the ocurrence of
vorticity in electrovaccum spacetimes (2006, Class. Quantum Grav. 23, 2395)


title: On the Zero-energy Universe

abstract:
  We consider the energy of the Universe, from the pseudo-tensor point of
view(Berman,1981). We find zero values, when the calculations are well-done.The
doubts concerning this subject are clarified, with the novel idea that the
justification for the calculation lies in the association of the equivalence
principle, with the nature of co-motional observers, as demanded in Cosmology.
In Section 4, we give a novel calculation for the zero-total energy result.


title:
Stability analysis of self-similar behaviors in perfect fluid
  gravitational collapse

abstract:
  Stability of self-similar solutions for gravitational collapse is an
important problem to be investigated from the perspectives of their nature as
an attractor, critical phenomena and instability of a naked singularity. In
this paper we study spherically symmetric non-self-similar perturbations of
matter and metrics in spherically symmetric self-similar backgrounds. The
collapsing matter is assumed to be a perfect fluid with the equation of state
$P=\alpha\rho$. We construct a single wave equation governing the
perturbations, which makes their time evolution in arbitrary self-similar
backgrounds analytically tractable. Further we propose an analytical
application of this master wave equation to the stability problem by means of
the normal mode analysis for the perturbations having the time dependence given
by $\exp{(i\omega\log|t|)}$, and present some sufficient conditions for the
absence of non-oscillatory unstable normal modes with purely imaginary
$\omega$.


title: Functional evolution of quantum cylindrical waves

abstract:
  Kucha{\v{r}} showed that the quantum dynamics of (1 polarization) cylindrical
wave solutions to vacuum general relativity is determined by that of a free
axially-symmetric scalar field along arbitrary axially-symmetric foliations of
a fixed flat 2+1 dimensional spacetime. We investigate if such a dynamics can
be defined {\em unitarily} within the standard Fock space quantization of the
scalar field.
  Evolution between two arbitrary slices of an arbitrary foliation of the flat
spacetime can be built out of a restricted class of evolutions (and their
inverses). The restricted evolution is from an initial flat slice to an
arbitrary (in general, curved) slice of the flat spacetime and can be
decomposed into (i) `time' evolution in which the spatial Minkowskian
coordinates serve as spatial coordinates on the initial and the final slice,
followed by (ii) the action of a spatial diffeomorphism of the final slice on
the data obtained from (i). We show that although the functional evolution of
(i) is unitarily implemented in the quantum theory, generic spatial
diffeomorphisms of (ii) are not. Our results imply that a Tomanaga-Schwinger
type functional evolution of quantum cylindrical waves is not a viable concept
even though, remarkably, the more limited notion of functional evolution in
Kucha{\v{r}}'s `half parametrized formalism' is well-defined.


title:
Why Gravitational Contraction Must be Accompanied by Emission of
  Radiation Both in Newtonian and Einstein Gravity

abstract:
  By using virial theorem, Helmholtz and Kelvin showed that the contraction of
a bound self-gravitating system must be accompanied by release of radiation
energy irrespective of the details of the contraction process. This happens
because the total Newtonian energy of the system E_N (and not just the
Newtonian gravitational potential energy E_g^N) decreases for such contraction.
In the era of General Relativity (GR) too, it is justifiably believed that
gravitational contraction must release radiation energy. However no GR version
of (Newtonian) Helmholtz- Kelvin (HK) process has ever been derived. Here, for
the first time, we derive the GR version of the appropriate virial theorem and
Helmholtz Kelvin mechanism by simply equating the well known expressions for
the gravitational mass and the Inertial Mass of a spherically symmetric static
fluid. Simultaneously, we show that the GR counterparts of global ``internal
energy'', ``gravitational potential energy'' and ``binding energy'' are
actually different from what have been used so far. Existence of this GR HK
process asserts that, in Einstein gravity too, gravitational collapse must be
accompanied by emission of radiation irrespective of the details of the
collapse process. Consequently, all studies of strictly adibatic gravitational
collapse are only of academic interest.


title:
Cosmological solutions for the Universe filled with matter in various
  states and gauge invariance

abstract:
  We explore at phenomenological level a model of the Universe filled with
various kinds of matter characterized by different equations of state. We show
that introducing of each kind of matter is equivalent to a certain choice of a
gauge condition, the gauge condition describing a medium with a given equation
of state. The case of a particular interest is when one kind of matter (de
Sitter false vacuum) dominates at the early stage of the Universe evolution
while another kind (radiation, or ultrarelativistic gas) dominates at its later
stage. We can, therefore, consider different asymptotic regimes for the early
and later stages of the Universe existence. These regimes are described by
solutions to the Wheeler - DeWitt equation for the Universe with matter in that
given state, and, at the same time, in the "extended phase space" approach to
quantum geometrodynamics the regimes are described by solutions to a
Schrodinger equation associated with a choice of some gauge condition. It is
supposed that, from the viewpoint of the observer located at the later stage of
the Universe evolution, solutions for a Lambda-dominated early Universe would
decay.


title: Collapsing Inhomogeneous Dust Fluid in the Background of Dark Energy

abstract:
  In the present work, gravitational collapse of an inhomogeneous spherical
star model, consisting of inhomogeneous dust fluid (dark matter) in the
background of dark energy is considered. The collapsing process is examined
first separately for both dark matter and dark energy and then under the
combined effect of dark matter and dark energy with or without interaction. The
dark energy is considered in the form of perfect fluid and both marginally and
non-marginally bound cases are considered for the collapsing model. Finally
dark energy in the form of anisotropic fluid is investigated and it is found to
be similar to ref. [12]


title: Generating potentials via difference equations

abstract:
  The condition for pressure isotropy, for spherically symmetric gravitational
fields with charged and uncharged matter, is reduced to a recurrence equation
with variable, rational coefficients. This difference equation is solved in
general using mathematical induction leading to an exact solution to the
Einstein field equations which extends the isotropic model of John and Maharaj.
The metric functions, energy density and pressure are well behaved which
suggests that this model could be used to describe a relativistic sphere. The
model admits a barotropic equation of state which approximates a polytrope
close to the stellar centre.


title: Charged analogue of Finch-Skea stars

abstract:
  We present solutions to the Einstein-Maxwell system of equations in
spherically symmetric gravitational fields for static interior spacetimes with
a specified form of the electric field intensity. The condition of pressure
isotropy yields three category of solutions. The first category is expressible
in terms of elementary functions and does not have an uncharged limit. The
second category is given in terms of Bessel functions of half-integer order.
These charged solutions satisfy a barotropic equation of state and contain
Finch-Skea uncharged stars. The third category is obtained in terms of modified
Bessel functions of half-integer order and does not have an uncharged limit.
The physical features of the charged analogue of the Finch-Skea stars are
studied in detail. In particular the condition of causality is satisfied and
the speed of sound does not exceed the speed of light. The physical analysis
indicates that this analogue is a realistic model for static charged
relativistic perfect fluid spheres.


title:
A Markov Chain Monte Carlo approach to the study of massive black hole
  binary systems with LISA

abstract:
  The Laser Interferometer Space Antenna (LISA) will produce a data stream
containing a vast number of overlapping sources: from strong signals generated
by the coalescence of massive black hole binary systems to much weaker
radiation form sub-stellar mass compact binaries and extreme-mass ratio
inspirals. It has been argued that the observation of weak signals could be
hampered by the presence of loud ones and that they first need to be removed to
allow such observations. Here we consider a different approach in which sources
are studied simultaneously within the framework of Bayesian inference. We
investigate the simplified case in which the LISA data stream contains
radiation from a massive black hole binary system superimposed over a (weaker)
quasi-monochromatic waveform generated by a white dwarf binary. We derive the
posterior probability density function of the model parameters using an
automatic Reversible Jump Markov Chain Monte Carlo algorithm (RJMCMC). We show
that the information about the sources and noise are retrieved at the expected
level of accuracy without the need of removing the stronger signal. Our
analysis suggests that this approach is worth pursuing further and should be
considered for the actual analysis of the LISA data.


title:
The operator product expansion for perturbative quantum field theory in
  curved spacetime

abstract:
  We present an algorithm for constructing the Wilson operator product
expansion (OPE) for perturbative interacting quantum field theory in general
Lorentzian curved spacetimes, to arbitrary orders in perturbation theory. The
remainder in this expansion is shown to go to zero at short distances in the
sense of expectation values in arbitrary Hadamard states. We also establish a
number of general properties of the OPE coefficients: (a) they only depend
(locally and covariantly) upon the spacetime metric and coupling constants, (b)
they satisfy an associativity property, (c) they satisfy a renormalization
group equation, (d) they satisfy a certain microlocal wave front set condition,
(e) they possess a ``scaling expansion''. The latter means that each OPE
coefficient can be written as a sum of terms, each of which is the product of a
curvature polynomial at a spacetime point, times a Lorentz invariant Minkowski
distribution in the tangent space of that point. The algorithm is illustrated
in an example.


title: One Local Solution of the Wheeler-DeWitt equation

abstract:
  We can obtain one solution of the Hamiltonian constraint equation in the
local sense. The form of the state is suggested from the up-to-down method in
our previous work. The up-to-down method works for different way in treating
the general metrics. In the mini-superspace approach there appears additional
constraint in the 4-dimensional quantum gravity Hilbert space. However, in the
general treatment of the metrics this method works as only solving technique.


title: A Unified View of the Basic Forces

abstract:
  In this essay we wish to seek a unifying thread between the basic forces. We
propose that there exists a universal force which is shared by all that
physically exists. Universality is characterized by the two properties: (i)
universal linkage and (ii) long range. They uniquely identify Einstein gravity
as the unversal force. All other forces then arise as these properties are
peeled off. For instance, relaxing (i) but retaining (ii) will lead to Maxwell
electromagnetic force. This unified outlook makes interesting suggestions and
predictions: if there exists a new force, it can only be a short range
non-abelian vector or a scalar field, and there should exist in an appropriate
space duality relations between weak and electric, and between strong and
gravity.


title: Local freedom in the gravitational field revisited

abstract:
  Maartens {\it et al.}\@ gave a covariant characterization, in a 1+3 formalism
based on a perfect fluid's velocity, of the parts of the first derivatives of
the curvature tensor in general relativity which are ``locally free'', i.e. not
pointwise determined by the fluid energy momentum and its derivative. The full
decomposition of independent curvature derivative components given in earlier
work on the spinor approach to the equivalence problem enables analogous
general results to be stated for any order: the independent matter terms can
also be characterized. Explicit relations between the two sets of results are
obtained. The 24 Maartens {\it et al.} locally free data are shown to
correspond to the $\nabla \Psi$ quantities in the spinor approach, and the
fluid terms are similarly related to the remaining 16 independent quantities in
the first derivatives of the curvature.


title:
A New Theory of Cosmology That Preserves the Generally Recognized
  Symmetries of Cosmos, Explains the Origin of the Energy for Matter Field, but
  Excludes the Existence of the Big Bang

abstract:
  While the generally recognized symmetries of cosmos are preserved,
conservation laws for gravitational system are reconsidered and the Lagrangian
density of pure gravitational field is revised. From these considerations, some
of the theoretical foundations of the current cosmology are extended or
revised, and a new theory of cosmology is established. This new theory leads to
the following distinct properties of cosmos: the energy of matter field might
originate from the gravitational field; the big bang might not have occurred;
the fields of the dark energy and some parts of the dark matter would not be
matter fields but might be gravitational fields, they would only interact with
gravitational force but could not interact with other forces. These distinct
properties can be tested by future experiments and observations.


title:
Mode-sum regularization of the scalar self-force: Formulation in terms
  of a tetrad decomposition of the singular field

abstract:
  We examine the motion in Schwarzschild spacetime of a point particle endowed
with a scalar charge. The particle produces a retarded scalar field which
interacts with the particle and influences its motion via the action of a
self-force. We exploit the spherical symmetry of the Schwarzschild spacetime
and decompose the scalar field in spherical-harmonic modes. Although each mode
is bounded at the position of the particle, a mode-sum evaluation of the
self-force requires regularization because the sum does not converge: the
retarded field is infinite at the position of the particle. The regularization
procedure involves the computation of regularization parameters, which are
obtained from a mode decomposition of the Detweiler-Whiting singular field;
these are subtracted from the modes of the retarded field, and the result is a
mode-sum that converges to the actual self-force. We present such a computation
in this paper. There are two main aspects of our work that are new. First, we
define the regularization parameters as scalar quantities by referring them to
a tetrad decomposition of the singular field. Second, we calculate four sets of
regularization parameters (denoted schematically by A, B, C, and D) instead of
the usual three (A, B, and C). As proof of principle that our methods are
reliable, we calculate the self-force acting on a scalar charge in circular
motion around a Schwarzschild black hole, and compare our answers with those
recorded in the literature.


title: On Doppler tracking in cosmological spacetimes

abstract:
  We give a rigorous derivation of the general-relativistic formula for the
two-way Doppler tracking of a spacecraft in Friedmann-Lemaitre-Robertson-Walker
and in McVittie spacetimes. The leading order corrections of the so-determined
acceleration to the Newtonian acceleration are due to special-relativistic
effects and cosmological expansion. The latter, although linear in the Hubble
constant, is negligible in typical applications within the Solar System.


title:
Robust vetoes for gravitational-wave burst triggers using known
  instrumental couplings

abstract:
  The search for signatures of transient, unmodelled gravitational-wave (GW)
bursts in the data of ground-based interferometric detectors typically uses
`excess-power' search methods. One of the most challenging problems in the
burst-data-analysis is to distinguish between actual GW bursts and spurious
noise transients that trigger the detection algorithms. In this paper, we
present a unique and robust strategy to `veto' the instrumental glitches. This
method makes use of the phenomenological understanding of the coupling of
different detector sub-systems to the main detector output. The main idea
behind this method is that the noise at the detector output (channel H) can be
projected into two orthogonal directions in the Fourier space -- along, and
orthogonal to, the direction in which the noise in an instrumental channel X
would couple into H. If a noise transient in the detector output originates
from channel X, it leaves the statistics of the noise-component of H orthogonal
to X unchanged, which can be verified by a statistical hypothesis testing. This
strategy is demonstrated by doing software injections in simulated Gaussian
noise. We also formulate a less-rigorous, but computationally inexpensive
alternative to the above method. Here, the parameters of the triggers in
channel X are compared to the parameters of the triggers in channel H to see
whether a trigger in channel H can be `explained' by a trigger in channel X and
the measured transfer function.


title:
The effect of a fifth large-scale space-time dimension on orbital
  dynamics

abstract:
  A model based on simple assumptions about 4-dimensional space-time being
closed and isotropic, and embedded in a 5th large-scale dimension, r,
representing the radius of curvature of space-time, has been used in an
application of Newton's Second Law to describe a system with angular momentum.
It has been found that the equations of MOND used to explain the rotation
curves of galaxies appear as a limit within this derivation and that there is a
universal acceleration constant, ao, with a value, again consistent with that
used by MOND. This approach does not require modification of Newtonian
dynamics, only its extension into a fifth large-scale dimension. The transition
from the classical Newtonian dynamics to the MOND regime emerges naturally and
without the introduction of arbitrary fitting functions, if this 5-dimensional
model is adopted. The paper also includes the derivation of an effect in
5-dimensional orbital dynamics which is in reasonable agreement with the
observed Pioneer Anomaly.


title: On a Possible Indicator of Homogeneity of the Universe

abstract:
  A new method is described for recognising internal non-randomness in deep
galaxy surveys.


title:
Perturbations and quasi-normal modes of black holes in Einstein-Aether
  theory

abstract:
  We develop a new method for calculation of quasi-normal modes of black holes,
when the effective potential, which governs black hole perturbations, is known
only numerically in some region near the black hole. This method can be applied
to perturbations of a wide class of numerical black hole solutions. We apply it
to the black holes in the Einstein-Aether theory, a theory where general
relativity is coupled to a unit time-like vector field, in order to observe
local Lorentz symmetry violation. We found that in the non-reduced
Einstein-Aether theory, real oscillation frequency and damping rate of
quasi-normal modes are larger than those of Schwarzschild black holes in the
Einstein theory.


title: Cosmological Consequences of Anti-gravitation

abstract:
  The dynamics of a universe with an anti-gravitating contribution to the
matter content is examined. The modified Friedmann equations are derived, and
it is shown that anti-gravitating radiation is the slowest component to dilute
when the universe expands. Assuming an interaction between both kinds of matter
which becomes important at Planckian densities, it is found that the universe
undergoes a periodic cycle of contraction and expansion. Furthermore, the
possibility of energy loss in our universe through separation of both types of
matter is discussed.


title:
Entropy of the Randall-Sundrum brane world with the generalized
  uncertainty principle

abstract:
  By introducing the generalized uncertainty principle, we calculate the
entropy of the bulk scalar field on the Randall-Sundrum brane background
without any cutoff. We obtain the entropy of the massive scalar field
proportional to the horizon area. Here, we observe that the mass contribution
to the entropy exists in contrast to all previous results, which is independent
of the mass of the scalar field, of the usual black hole cases with the
generalized uncertainty principle.


title: MCMC Exploration of Supermassive Black Hole Binary Inspirals

abstract:
  The Laser Interferometer Space Antenna will be able to detect the inspiral
and merger of Super Massive Black Hole Binaries (SMBHBs) anywhere in the
Universe. Standard matched filtering techniques can be used to detect and
characterize these systems. Markov Chain Monte Carlo (MCMC) methods are ideally
suited to this and other LISA data analysis problems as they are able to
efficiently handle models with large dimensions. Here we compare the posterior
parameter distributions derived by an MCMC algorithm with the distributions
predicted by the Fisher information matrix. We find excellent agreement for the
extrinsic parameters, while the Fisher matrix slightly overestimates errors in
the intrinsic parameters.


title: Diagonal Forms of a Dual Scale Cosmology

abstract:
  A hybrid metric with off-diagonal temporal-radial behavior that was
constructed to conveniently parameterized the early and late time behaviors of
the universe is shown to have diagonal forms consistent with Robertson-Walker
and deSitter geometries. The dynamics of the energy content of the cosmology as
parameterized by the classical thermal fraction is briefly discussed as
motivation for the comparison of the observables predicted by various
micoscopic models of the early evolution of the universe.


title: Quantization of strings and branes coupled to BF theory

abstract:
  BF theory is a topological theory that can be seen as a natural
generalization of 3-dimensional gravity to arbitrary dimensions. Here we show
that the coupling to point particles that is natural in three dimensions
generalizes in a direct way to BF theory in d dimensions coupled to
(d-3)-branes. In the resulting model, the connection is flat except along the
membrane world-sheet, where it has a conical singularity whose strength is
proportional to the membrane tension. As a step towards canonically quantizing
these models, we show that a basis of kinematical states is given by `membrane
spin networks', which are spin networks equipped with extra data where their
edges end on a brane.


title: Inhomogeneous spacetimes as a dark energy model

abstract:
  Tolman-Bondi inhomogeneous spacetimes are used as a cosmological model for
type Ia supernova data. It is found that with certain parameter choices the
model fits the data as well as the standard $\Lambda$CDM cosmology does.


title: Cosmology: a bird's eye view

abstract:
  In this essay we discuss the difference in views of the Universe as seen by
two different observers. While one of the observers follows a geodesic
congruence defined by the geometry of the cosmological model, the other
observer follows the fluid flow lines of a perfect fluid with a linear equation
of state. We point out that the information these observers collect regarding
the state of the Universe can be radically different; while one observes a
non-inflating ever-expanding ever-lasting universe, the other observer can
experience a dynamical behaviour reminiscent to that of quintessence or even
that of a phantom cosmology leading to a 'big rip' singularity within finite
time (but without the need for exotic forms of matter).


title: Scalar Metric fluctuations in space time matter inflation

abstract:
  Using the Ponce de Leon background metric, which describes a 5D universe in
an apparent vacuum: $\bar{G}_{AB}=0$, we study the effective 4D evolution of
both, the inflaton and gauge-invariant scalar metric fluctuations, in the
recently introduced model of space time matter inflation.


title: Long distance modifications of gravity in four dimensions

abstract:
  We discuss some general characteristics of modifications of the 4D
Einstein-Hilbert action that become important for low space-time curvatures. In
particular we focus on the chameleon-like behaviour of the massive
gravitational degrees of freedom. Generically there is at least one extra
scalar that is light on cosmic scales, but for certain models it becomes heavy
close to any mass source.


title: Cosmological Model for the Very Early Universe in B.D. Theory

abstract:
  Following a paper by Berman and Marinho Jr (2001), where it was established
an equation of state (p=-(1/3)rho), for the very early Universe, under which,
Einstein's equations with lambda=0, render a scale-factor proportional to the
time coordinate, and under which, Berman(2006, 2006a) showed that in the
non-null lambda case, the Universe entered automatically into an exponential
inflationary phase, we now study the corresponding effect in Brans-Dicke
Cosmology. We find that the resulting models are similar to those in General
Relativity Cosmology.


title:
Probing Spacetime Foam with Photons: Suppression of Observable Effects
  due to Uncertainty in Optical Paths

abstract:
  It was recently proposed to use extra-galactic point sources to constrain
space-time quantum fluctuations in the universe. In these proposals, the
fundamental "fuzziness" of distance caused by space-time quantum fluctuations
have been directly identified with fluctuations in optical paths. Phase-front
corrugations deduced from these optical-path fluctuations are then applied to
light from extragalactic point sources, and used to constrain various models of
quantum gravity. In particular, the so-called random-walk model has been
claimed to be ruled out by existing astrophysical observations from the Hubble
Space Telescope. However, when a photon propagates in three spatial dimensions,
it does not follow a specific ray, but would rather sample a finite,
three-dimensional region around that ray -- thereby averaging over space-time
quantum fluctuations all through that region. We use a simple, random-walk type
model to demonstrate that, once the appropriate wave optics is applied, the
averaging of neighboring space-time fluctuations will cause much less
distortions on the phase front. In our model, the extra suppression factor due
to diffraction is (Planck Length)/(Wavelength), which is at least 19 orders of
magnitude for astronomical observations.


title: Generalized Friedmann Equations for a Finite Thick Brane

abstract:
  We present the generalized Friedmann equations describing the cosmological
evolution of a finite thick brane immeresed in a five-dimensional Schwarzschild
Anti-de Sitter spacetime. A linear term in the density in addition to a
quatratic one arises in the Friedmann equation, leading to the standard
cosmological evolution at late times without introducing an ad hoc tension term
for the brane. The effective four-dimensional cosmological constant is then
uplifted similar to the KKLT effect and vanishes for a brane thickness equal to
the AdS curvature size, up to the third order of the thickness. The
four-dimensional gravitational constant is then equal to the five-dimensional
one divided by the AdS curvature radius, similar to that derived by dimensional
compactification. An accelerating brane cosmology may emerge at late times
provided there is either a negative transverse pressure component in the brane
energy-momentum tensor or the effective brane cosmological constant is
positive.


title: Existence of Wormholes in Einstein-Kalb-Ramond space time

abstract:
  In recent, Kar.S et.al [ Phys Rev D 67,044005 (2003) ] have obtained static
spherically symmetric solutions of the Einstein-Kalb-Ramond field equations. We
have shown that their solutions, indeed, represent Wormholes.


title: Motion of Isolated bodies

abstract:
  It is shown that sufficiently smooth initial data for the Einstein-dust or
the Einstein-Maxwell-dust equations with non-negative density of compact
support develop into solutions representing isolated bodies in the sense that
the matter field has spatially compact support and is embedded in an exterior
vacuum solution.


title: On the Buchdahl inequality for spherically symmetric static shells

abstract:
  A classical result by Buchdahl \cite{Bu1} shows that for static solutions of
the spherically symmetric Einstein-matter system, the total ADM mass M and the
area radius R of the boundary of the body, obey the inequality $2M/R\leq 8/9.$
The proof of this inequality rests on the hypotheses that the energy density is
non-increasing outwards and that the pressure is isotropic. In this work
neither of Buchdahl's hypotheses are assumed. We consider non-isotropic
spherically symmetric shells, supported in $[R_0,R_1], R_0>0,$ of matter models
for which the energy density $\rho\geq 0,$ and the radial- and tangential
pressures $p\geq 0$ and $q,$ satisfy $p+q\leq\Omega\rho, \Omega\geq 1.$ We show
a Buchdahl type inequality for shells which are thin; given an $\epsilon<1/4$
there is a $\kappa>0$ such that $2M/R_1\leq 1-\kappa$ when $R_1/R_0\leq
1+\epsilon.$ It is also shown that for a sequence of solutions such that
$R_1/R_0\to 1,$ the limit supremum of $2M/R_1$ of the sequence is bounded by
$((2\Omega+1)^2-1)/(2\Omega+1)^2.$ In particular if $\Omega=1,$ which is the
case for Vlasov matter, the boumd is $8/9.$ The latter result is motivated by
numerical simulations \cite{AR2} which indicate that for non-isotropic shells
of Vlasov matter $2M/R_1\leq 8/9,$ and moreover, that the value 8/9 is
approached for shells with $R_1/R_0\to 1$. In \cite{An2} a sequence of shells
of Vlasov matter is constructed with the properties that $R_1/R_0\to 1,$ and
that $2M/R_1$ equals 8/9 in the limit. We emphasize that in the present paper
no field equations for the matter are used, whereas in \cite{An2} the Vlasov
equation is important.


title: Area and Entropy: A New Perspective

abstract:
  We consider a spacelike two-plane originally at rest with respect to
electromagnetic radiation in equilibrium. We find that if the plane is moved
with respect to the radiation, the plane shrinks such that the maximum amount
of entropy carried by radiation through the plane is, in natural units, exactly
one-half of the decrease in the area of the plane. This result suggests that
the equivalence between area and entropy may not be limited in black holes, nor
even in the spacetime horizons only, but the equivalence between horizon area
and entropy may be a special case of some general and simple, still
undiscovered fundamental principle of nature.


title: On the Mechanism of Hawking Radiation

abstract:
  In this paper we derived Hawking radiation as a tuneling of massless
particles through a non-singular horizon in the s-wave approximation. The back
reaction of emitted modes on the background black hole geometry is
self-consistently taken into account. This is arXive copy of the paper
published in the Russian journal "Gravitation and Cosmology" in 1999.


title:
Imprints of Relic Gravitational Waves in Cosmic Microwave Background
  Radiation

abstract:
  A strong variable gravitational field of the very early Universe inevitably
generates relic gravitational waves by amplifying their zero-point quantum
oscillations. We begin our discussion by contrasting the concepts of relic
gravitational waves and inflationary `tensor modes'. We explain and summarize
the properties of relic gravitational waves that are needed to derive their
effects on CMB temperature and polarization anisotropies. The radiation field
is characterized by four invariants I, V, E, B. We reduce the radiative
transfer equations to a single integral equation of Voltairre type and solve it
analytically and numerically. We formulate the correlation functions
C^{XX'}_{\ell} for X, X'= T, E, B and derive their amplitudes, shapes and
oscillatory features. Although all of our main conclusions are supported by
exact numerical calculations, we obtain them, in effect, analytically by
developing and using accurate approximations. We show that the TE correlation
at lower \ell's must be negative (i.e. an anticorrelation), if it is caused by
gravitational waves, and positive if it is caused by density perturbations.
This difference in TE correlation may be a signature more valuable
observationally than the lack or presence of the BB correlation, since the TE
signal is about 100 times stronger than the expected BB signal. We discuss the
detection by WMAP of the TE anticorrelation at \ell \approx 30 and show that
such an anticorrelation is possible only in the presence of a significant
amount of relic gravitational waves (within the framework of all other common
assumptions). We propose models containing considerable amounts of relic
gravitational waves that are consistent with the measured TT, TE and EE
correlations.


title:
Supermassive black holes or boson stars? Hair counting with
  gravitational wave detectors

abstract:
  The evidence for supermassive Kerr black holes in galactic centers is strong
and growing, but only the detection of gravitational waves will convincingly
rule out other possibilities to explain the observations. The Kerr spacetime is
completely specified by the first two multipole moments: mass and angular
momentum. This is usually referred to as the ``no-hair theorem'', but it is
really a ``two-hair'' theorem. If general relativity is the correct theory of
gravity, the most plausible alternative to a supermassive Kerr black hole is a
rotating boson star. Numerical calculations indicate that the spacetime of
rotating boson stars is determined by the first three multipole moments
(``three-hair theorem''). LISA could accurately measure the oscillation
frequencies of these supermassive objects. We propose to use these measurements
to ``count their hair'', unambiguously determining their nature and properties.


title: Relativistic MHD with Adaptive Mesh Refinement

abstract:
  This paper presents a new computer code to solve the general relativistic
magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh
refinement (AMR). The fluid equations are solved using a finite difference
Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger.
Hyperbolic divergence cleaning is used to control the $\nabla\cdot {\bf B}=0$
constraint. We present results from three flat space tests, and examine the
accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel
solution. The AMR simulations substantially improve performance while
reproducing the resolution equivalent unigrid simulation results. Finally, we
discuss strong scaling results for parallel unigrid and AMR runs.


title:
Explicit Constructions of the Fedosov star on some Lorentzian
  Space-Times

abstract:
  This paper has been withdrawn by the author due to the fact that the results
were found to be done previously.


title:
Embedding the Reissner-Nordstrom spacetime in Euclidean and Minkowski
  spaces

abstract:
  We examine embedding diagrams of hypersurfaces in the Reissner-Nordstrom
black hole spacetime. These embedding diagrams serve as useful tools to
visualize the geometry of the hypersurfaces and of the whole spacetime in
general.


title:
Affine Histories in Quantum Gravity: Introduction and the Representation
  for a Cosmological Model

abstract:
  It is shown how consistent histories quantum cosmology can be realised
through Isham's Histories Projection Operator consistent histories scheme. This
is done by using an affine algebra instead of a canonical one and also by using
cocycle representations. A regularisation scheme allows us to find a history
Hamiltonian which exists as a proper self-adjoint operator. The role of a
cocycle choice is also discussed.


title: A Higher Dimensional Stationary Rotating Black Hole Must be Axisymmetric

abstract:
  A key result in the proof of black hole uniqueness in 4-dimensions is that a
stationary black hole that is ``rotating''--i.e., is such that the stationary
Killing field is not everywhere normal to the horizon--must be axisymmetric.
The proof of this result in 4-dimensions relies on the fact that the orbits of
the stationary Killing field on the horizon have the property that they must
return to the same null geodesic generator of the horizon after a certain
period, $P$. This latter property follows, in turn, from the fact that the
cross-sections of the horizon are two-dimensional spheres. However, in
spacetimes of dimension greater than 4, it is no longer true that the orbits of
the stationary Killing field on the horizon must return to the same null
geodesic generator. In this paper, we prove that, nevertheless, a higher
dimensional stationary black hole that is rotating must be axisymmetric. No
assumptions are made concerning the topology of the horizon cross-sections
other than that they are compact. However, we assume that the horizon is
non-degenerate and, as in the 4-dimensional proof, that the spacetime is
analytic.


title:
Gauge-invariant Formulation of the Second-order Cosmological
  Perturbations

abstract:
  Gauge invariant treatments of the second order cosmological perturbation in a
four dimensional homogeneous isotropic universe filled with the perfect fluid
are completely formulated without any gauge fixing. We derive all components of
the Einstein equations in the case where the first order vector and tensor
modes are negligible. These equations imply that the tensor and the vector mode
of the second order metric perturbations may be generated by the scalar-scalar
mode coupling of the linear order perturbations as the result of the non-linear
effects of the Einstein equations.

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


title:
Second-order Gauge Invariant Cosmological Perturbation Theory: --
  Einstein equations in terms of gauge invariant variables --

abstract:
  Along the general framework of the gauge invariant perturbation theory
developed in the papers [K. Nakamura, Prog. Theor. Phys. {\bf 110} (2003), 723;
{\it ibid}, {\bf 113} (2005), 481.], we formulate the second order gauge
invariant cosmological perturbation theory in a four dimensional homogeneous
isotropic universe. We consider the perturbations both in the universe
dominated by the single perfect fluid and in that dominated by the single
scalar field. We derive the all components of the Einstein equations in the
case where the first order vector and tensor modes are negligible. All
equations are derived in terms of gauge invariant variables without any gauge
fixing. These equations imply that the second order vector and tensor modes may
be generated due to the mode-mode coupling of the linear order scalar
perturbations. We also briefly discuss the main progress of this work by the
comparison with some literatures.


title: Brans-Dicke theory: Jordan vs Einstein Frame

abstract:
  It is well known that, in contrast to general relativity, there are two
conformally related frames, the Jordan frame and the Einstein frame, in which
the Brans-Dicke theory, a prototype of generic scalar-tensor theory, can be
formulated. There is a long standing debate on the physical equivalence of the
formulations in these two different frames. It is shown here that gravitational
deflection of light to second order accuracy may observationally distinguish
the two versions of the Brans-Dicke theory.


title:
A late time acceleration of the universe with two scalar fields : many
  possibilities

abstract:
  In the present work, an attempt has been made to explain the recent cosmic
acceleration with two mutually interacting scalar fields, one being the
Brans-Dicke scalar field and the other a quintessence scalar field. Conditions
have been derived for which the quintessence scalar field has an early
oscillation and it grows during a later time to govern the dynamics of the
universe.


title:
Does Cassini allow to measure relativistic orbital effects in the
  Saturnian system of satellites?

abstract:
  In this paper we address the following question: do the recent advances in
the orbit determination of the major natural satellites of Saturn obtained with
the analysis of the first data sets from the Cassini mission allow to detect
the general relativistic gravitoelectric orbital precessions of such moons? The
answer is still negative. The present-day down-track accuracy would be adequate
for Mimas, Enceladus, Thetys, Dione, Rhea and Titan and inadequate for
Hyperion, Iapetus and Phoebe. Instead, the size of the systematic errors
induced by the mismodelling in the key parameters of the Saturnian
gravitational field like the even zonal harmonics Jl are larger than the
relativistic down-track shifts by about one order of magnitude, mainly for the
inner satellites like Mimas, Enceladus, Thetys, Dione, Rhea, Titan and
Hyperion. Iapetus and Phoebe are not sensibly affected by such kind of
perturbations. Moreover, the bias due to the uncertainty in Saturn's GM is
larger than the relativistic down-track effects for all such moons. Proposed
linear combinations of the satellites' orbital elements would allow to cancel
out the impact of the mismodelling in the low-degree even zonal harmonics and
GM, but the combined down-track errors would be larger than the combined
relativistic signature.


title: Casimir Effect in $E^3$ closed spaces

abstract:
  As it is well known the topology of space is not totally determined by
Einstein's equations. It is considered a massless scalar quantum field in a
static Euclidean space of dimension 3. The expectation value for the energy
density in all compact orientable Euclidean 3-spaces are obtained in this work
as a finite summation of Epstein type zeta functions. The Casimir energy
density for these particular manifolds is independent of the type of coupling
with curvature. A numerical plot of the result inside each Dirichlet region is
obtained.


title: Avoidance of future singularities in loop quantum cosmology

abstract:
  We consider the fate of future singularities in the effective dynamics of
loop quantum cosmology. Non-perturbative quantum geometric effects which lead
to $\rho^2$ modification of the Friedmann equation at high energies result in
generic resolution of singularities whenever energy density $\rho$ diverges at
future singularities of Friedmann dynamics. Such quantum effects lead to the
avoidance of a Big Rip, which is followed by a recollapsing universe stable
against perturbations. Resolution of sudden singularity, the case when pressure
diverges but energy density approaches a finite value depends on the ratio of
the latter to a critical energy density of the order of Planck. If the value of
this ratio is greater than unity, the universe escapes the sudden future
singularity and becomes oscillatory.


title:
How to bypass Birkhoff through extra dimensions (a simple framework for
  investigating the gravitational collapse in vacuum)

abstract:
  It is fair to say that our current mathematical understanding of the dynamics
of gravitational collapse to a black hole is limited to the spherically
symmetric situation and, in fact, even in this case much remains to be learned.
The reason is that Einstein's equations become tractable only if they are
reduced to a 1+1 dimensional system of partial differential equations. Due to
this technical obstacle, very little is known about the collapse of pure
gravitational waves because by Birkhoff's theorem there is no spherical
collapse in vacuum. In this essay we describe a new cohomogeneity-two symmetry
reduction of the vacuum Einstein equations in five and higher odd dimensions
which evades Birkhoff's theorem and admits time dependent asymptotically flat
solutions. We argue that this model provides an attractive 1+1 dimensional
geometric setting for investigating the dynamics of gravitational collapse in
vacuum.


title: Gravitational holography and trapped surfaces

abstract:
  We have previously discussed the characteristics of the gravitational waves
(GW) and have, theoretically, shown that, like the corresponding
electromagnetic (EM) waves, they also demonstrate, under certain conditions,
holographic properties. In this work we have expanded this discussion and show
that the assumed gravitational holographic images may, theoretically, be
related to another property of GW's which is their possible relation to
singular (or nonsingular) trapped surfaces. We also show that this possibility
may be, theoretically, related even to weak GW's.


title:
Geometrodynamics in a spherically symmetric, static crossflow of null
  dust

abstract:
  The spherically symmetric, static spacetime generated by a crossflow of
non-interacting radiation streams, treated in the geometrical optics limit
(null dust) is equivalent to an anisotropic fluid forming a radiation
atmosphere of a star. This reference fluid provides a preferred / internal
time, which is employed as a canonical coordinate. Among the advantages we
encounter a new Hamiltonian constraint, which becomes linear in the momentum
conjugate to the internal time (therefore yielding a functional Schr\"{o}dinger
equation after quantization), and a strongly commuting algebra of the new
constraints.


title: From spacetime foam to holographic foam cosmology

abstract:
  Due to quantum fluctuations, spacetime is foamy on small scales. For maximum
spatial resolution of the geometry of spacetime, the holographic model of
spacetime foam stipulates that the uncertainty or fluctuation of distance $l$
is given, on the average, by $(l l_P^2)^{1/3}$ where $l_P$ is the Planck
length. Applied to cosmology, it predicts that the cosmic energy is of critical
density and the cosmic entropy is the maximum allowed by the holographic
principle. In addition, it requires the existence of unconventional (dark)
energy/matter and accelerating cosmic expansion in the present era. We will
argue that a holographic foam cosmology of this type has the potential to
become a full fledged competitor (with distinct testable consequences) for
scalar driven inflation.


title: Quasinormal ringing of Kerr black holes: The excitation factors

abstract:
  Distorted black holes radiate gravitational waves. In the so-called ringdown
phase radiation is emitted in a discrete set of complex quasinormal
frequencies, whose values depend only on the black hole's mass and angular
momentum. Ringdown radiation could be detectable with large signal-to-noise
ratio by the Laser Interferometer Space Antenna LISA. If more than one mode is
detected, tests of the black hole nature of the source become possible. The
detectability of different modes depends on their relative excitation, which in
turn depends on the cause of the perturbation (i.e. on the initial data). A
``universal'', initial data-independent measure of the relative mode excitation
is encoded in the poles of the Green's function that propagates small
perturbations of the geometry (``excitation factors''). We compute for the
first time the excitation factors for general-spin perturbations of Kerr black
holes. We find that for corotating modes with $l=m$ the excitation factors tend
to zero in the extremal limit, and that the contribution of the overtones
should be more significant when the black hole is fast rotating. We also
present the first analytical calculation of the large-damping asymptotics of
the excitation factors for static black holes, including the Schwarzschild and
Reissner-Nordstrom metrics. This is an important step to determine the
convergence properties of the quasinormal mode expansion.


title: Gauss-Bonnet brane-world cosmology without $Z_{2}$-symmetry

abstract:
  We consider a single 3-brane situated between two bulk spacetimes that posses
the same cosmological constant, but whose metrics do not posses a
$Z_{2}$-symmetry. On each side of the brane, the bulk is a solution to
Gauss-Bonnet gravity. This asymmetry modifies junction conditions, and so new
terms arise in the Friedmann equation. If these terms become dominant, these
behave cosmological constant at early times for some case, and might remove the
initial singularity for other case. However, we show that these new terms can
not become dominant ones under usual conditions when our brane is outside an
event horizon. We also show that any brane-world scenarios of this type revert
to a $Z_{2}$-symmetric form at late times, and hence rule out certain proposed
scenarios.


title: Can inhomogeneties accelerate the cosmic volume expansion?

abstract:
  If expanding and contracting regions coexist in the universe, the speed of
the cosmic volume expansion can be accelerated. We construct simple
inhomogeneous dust-filled universe models in which the speed of the cosmic
volume expansion is accelerated for finite periods. These models are
constructed by removing spherical domains from the Einstein-de Sitter universe
and filling each domain with a Lemaitre-Tolman-Bondi dust sphere possessing the
same gravitational mass as the removed region. This represents an exact
solution of the Einstein equations. We find that acceleration of the cosmic
volume expansion is realized in some cases when the size of the contracting
region is comparable to the horizon radius of the Einstein-de Sitter universe
though this model is very different from the universe observed today. This
result implies that non-linear general relativistic effects of inhomogeneities
are very important to realize the acceleration of the cosmic volume expansion.


title: Analogue spacetime based on 2-component Bose-Einstein condensates

abstract:
  Analogue spacetimes are powerful models for probing the fundamental physical
aspects of geometry - while one is most typically interested in ultimately
reproducing the pseudo-Riemannian geometries of interest in general relativity
and cosmology, analogue models can also provide useful physical probes of more
general geometries such as pseudo-Finsler spacetimes. In this chapter we shall
see how a 2-component Bose-Einstein condensate can be used to model a specific
class of pseudo-Finsler geometries, and after suitable tuning of parameters,
both bi-metric pseudo-Riemannian geometries and standard single metric
pseudo-Riemannian geometries, while independently allowing the quasi-particle
excitations to exhibit a "mass". Furthermore, when extrapolated to extremely
high energy the quasi-particles eventually leave the phononic regime and begin
to act like free bosons. Thus this analogue spacetime exhibits an analogue of
the "Lorentz violation" that is now commonly believed to occur at or near the
Planck scale defined by the interplay between quantum physics and gravitational
physics. In the 2-component Bose-Einstein analogue spacetime we will show that
the mass generating mechanism for the quasi-particles is related to the size of
the Lorentz violations. This relates the "mass hierarchy" to the so-called
"naturalness problem". In short the analogue spacetime based on 2-component
Bose-Einstein condensates exhibits a very rich mathematical and physical
structure that can be used to investigate many issues of interest to the
high-energy physics, cosmology, and general relativity communities.


title:
Curvature profiles as initial conditions for primordial black hole
  formation

abstract:
  This work is part of an ongoing research programme to study possible
Primordial Black Hole (PBH) formation during the radiation dominated era of the
early universe. Working within spherical symmetry, we specify an initial
configuration in terms of a curvature profile, which represents initial
conditions for the large amplitude metric perturbations, away from the
homogeneous Friedmann Robertson Walker model, which are required for PBH
formation. Using an asymptotic quasi-homogeneous solution, we relate the
curvature profile with the density and velocity fields, which at an early
enough time, when the length scale of the configuration is much larger than the
cosmological horizon, can be treated as small perturbations of the background
values. We present general analytic solutions for the density and velocity
profiles. These solutions enable us to consider in a self-consistent way the
formation of PBHs in a wide variety of cosmological situations with the
cosmological fluid being treated as an arbitrary mixture of different
components with different equations of state. We show that the analytical
solutions for the density and velocity profiles as functions of the initial
time are pure growing modes. We then use two different parametrisation for the
curvature profile and follow numerically the evolution of a range of initial
configuration.


title:
Towards the graviton from spinfoams: higher order corrections in the 3d
  toy model

abstract:
  We consider the recent calculation gr-qc/0508124 of the graviton propagator
in the spinfoam formalism. Within the 3d toy model introduced in gr-qc/0512102,
we test how the spinfoam formalism can be used to construct the perturbative
expansion of graviton amplitudes. Although the 3d graviton is a pure gauge, one
can choose to work in a gauge where it is not zero and thus reproduce the
structure of the 4d perturbative calculations. We compute explicitly the next
to leading and next to next to leading orders, corresponding to one-loop and
two-loop corrections. We show that while the first arises entirely from the
expansion of the Regge action around the flat background, the latter receives
contributions from the microscopic, non Regge-like, quantum geometry.
Surprisingly, this new contribution reduces the magnitude of the next to next
to leading order. It thus appears that the spinfoam formalism is likely to
substantially modify the conventional perturbative expansion at higher orders.
  This result supports the interest in this approach. We then address a number
of open issues in the rest of the paper. First, we discuss the boundary state
ansatz, which is a key ingredient in the whole construction. We propose a way
to enhance the ansatz in order to make the edge lengths and dihedral angles
conjugate variables in a mathematically well-defined way. Second, we show that
the leading order is stable against different choices of the face weights of
the spinfoam model; the next to leading order, on the other hand, is changed in
a simple way, and we show that the topological face weight minimizes it.
Finally, we extend the leading order result to the case of a regular, but not
equilateral, tetrahedron.


title: New 'phase' of quantum gravity

abstract:
  The emergence of loop quantum gravity over the past two decades has
stimulated a great resurgence of interest in unifying general relativity and
quantum mechanics. Amongst a number of appealing features of this approach are
the intuitive picture of quantum geometry using spin networks and powerful
mathematical tools from gauge field theory. However, the present form of loop
quantum gravity suffers from a quantum ambiguity, due to the presence of a free
(Barbero-Immirzi) parameter. Following recent progress on the conformal
decomposition of gravitational fields, we present a new phase space for general
relativity. In addition to spin-gauge symmetry, the new phase space also
incorporates conformal symmetry making the description parameter free. The
Barbero-Immirzi ambiguity is shown to occur only if the conformal symmetry is
gauge-fixed prior to quantization. By withholding its full symmetries, the new
phase space offers a promising platform for the future development of loop
quantum gravity. This paper aims to provide an exposition, at a reduced
technical level, of the above theoretical advances and their background
developments. Further details are referred to cited references.


title: Exploring Extra Dimensions in Spectroscopy Experiments

abstract:
  We propose an idea in spectroscopy to search for extra spatial dimensions as
well as to detect the possible deviation from Newton's inverse-square law at
small scale, and we take high-Z hydrogenic systems and muonic atoms as
illustrations. The relevant experiments might help to explore more than two
extra dimensions scenario in ADD's brane world model and to set constraints for
fundamental parameters such as the size of extra dimensions.


title:
Comparative analysis of the electrogravitational Kepler problem in GRT
  and RTG

abstract:
  In the framework of Einstein's General Relativity Theory and of the
Relativistic Theory of Gravitation, the equations governing the trajectories of
charged particles in the field created by a charged mass point are given. An
analysis of the shape of the trajectories in both theories is presented. The
first and the second order approximate solutions of the electrogravitational
Kepler problem are found in the two theories and the results are compared with
each other. I have pointed out the differences between the predictions in the
two theories.


title: A construction of full qed using finite dimensional Hilbert space

abstract:
  While causal perturbation theory and lattice regularisation allow treatment
of the ultraviolet divergences in qed, they do not resolve the issues of
constructive field theory, or show the validity of qed except as a perturbation
theory. I present a rigorous construction of quantum and classical
electrodynamics from fundamental principles of quantum theory. Hilbert space of
dimension N is justified from statements about measurements with finite range
and resolution. Using linear combinations of basis kets, a continuum of kets,
|x> for x in R^3, is constructed such that the inner product can be expressed
as a finite sum or as an integral. Vectors are smooth wave functions such that
differential operators are defined and the choice of basis has no affect on
underlying physics. Quantum field operators, phi(x) for x in R^4, are
constructed from creation and annihilation operators on Fock space, obey
quantum covariance and locality, and are suitable for a description of particle
interactions under the Feynman-St\"uckelberg interpretation. It is shown that
the formulation is consistent and that any dependency on a lattice arises from
measurement, not from underlying physics. In consequence, and because the
continuum is constructed from linear combinations of basis kets, it is not
required to take the limit N-->oo. Quantum fields are defined on a continuum,
and are operator valued functions, not distributions. The interacting Dirac
equation, Maxwell's equations and the Lorentz force law are derived, showing
that qed is a complete theory of the electromagnetic interaction, not just a
perturbation theory and that bare mass and charge are the physical values. Up
to the accuracy of measurement, predictions of perturbation theory are
identical to those of standard qed with all loop divergences removed. The
standard perturbation expansion is asymptotic to the finite expansion given
here.


title: Fluid observers and tilting cosmology

abstract:
  We study perfect fluid cosmological models with a constant equation of state
parameter $\gamma$ in which there are two naturally defined time-like
congruences, a geometrically defined geodesic congruence and a non-geodesic
fluid congruence. We establish an appropriate set of boost formulae relating
the physical variables, and consequently the observed quantities, in the two
frames. We study expanding spatially homogeneous tilted perfect fluid models,
with an emphasis on future evolution with extreme tilt. We show that for
ultra-radiative equations of state (i.e., $\gamma>4/3$), generically the tilt
becomes extreme at late times and the fluid observers will reach infinite
expansion within a finite proper time and experience a singularity similar to
that of the big rip. In addition, we show that for sub-radiative equations of
state (i.e., $\gamma < 4/3$), the tilt can become extreme at late times and
give rise to an effective quintessential equation of state. To establish the
connection with phantom cosmology and quintessence, we calculate the effective
equation of state in the models under consideration and we determine the future
asymptotic behaviour of the tilting models in the fluid frame variables using
the boost formulae. We also discuss spatially inhomogeneous models and tilting
spatially homogeneous models with a cosmological constant.


title:
Path integral representation of the evolution operator for the Dirac
  equation

abstract:
  A path integral representation of the evolution operator for the
four-dimensional Dirac equation is proposed. A quadratic form of the canonical
momenta regularizes the original representation of the path integral in the
electron phase space. This regularization allows to obtain a representation of
the path integral over trajectories in the configuration space, i.e. in the
Minkowsky space. This form of the path integral is useful for the formulation
of perturbation theory in an external electromagnetic field.


title:
Uniqueness of Petrov type D spatially inhomogeneous irrotational silent
  models

abstract:
  The consistency of the constraint with the evolution equations for spatially
inhomogeneous and irrotational silent (SIIS) models of Petrov type I, demands
that the former are preserved along the timelike congruence represented by the
velocity of the dust fluid, leading to \emph{new} non-trivial constraints. This
fact has been used to conjecture that the resulting models correspond to the
spatially homogeneous (SH) models of Bianchi type I, at least for the case
where the cosmological constant vanish. By exploiting the full set of the
constraint equations as expressed in the 1+3 covariant formalism and using
elements from the theory of the spacelike congruences, we provide a direct and
simple proof of this conjecture for vacuum and dust fluid models, which shows
that the Szekeres family of solutions represents the most general class of SIIS
models. The suggested procedure also shows that, the uniqueness of the SIIS of
the Petrov type D is not, in general, affected by the presence of a non-zero
pressure fluid. Therefore, in order to allow a broader class of Petrov type I
solutions apart from the SH models of Bianchi type I, one should consider more
general ``silent'' configurations by relaxing the vanishing of the vorticity
and the magnetic part of the Weyl tensor but maintaining their ``silence''
properties i.e. the vanishing of the curls of $E_{ab},H_{ab}$ and the pressure
$p$.


title:
Black hole formation in the head-on collision of ultrarelativistic
  charges

abstract:
  We study black hole formation in the head-on collision of ultrarelativistic
charges. The metric of charged particles is obtained by boosting the
Reissner-Nordstr\"om spacetime to the speed of light. Using the slice at the
instant of collision, we study formation of the apparent horizon (AH) and
derive a condition indicating that a critical value of the electric charge is
necessary for formation to take place. Evaluating this condition for
characteristic values at the LHC, we find that the presence of charge decreases
the black hole production rate in accelerators. We comment on possible
limitations of our approach.


title: Universal field equations for metric-affine theories of gravity

abstract:
  We show that almost all metric--affine theories of gravity yield Einstein
equations with a non--null cosmological constant $\Lambda$. Under certain
circumstances and for any dimension, it is also possible to incorporate a Weyl
vector field $W_\mu$ and therefore the presence of an anisotropy. The viability
of these field equations is discussed in view of recent astrophysical
observations.


title:
From de Sitter to de Sitter: A non-singular inflationary universe driven
  by vacuum

abstract:
  A semi-classical analysis of vacuum energy in the expanding spacetime
suggests that the cosmological term decays with time, with a concomitant matter
production. For early times we find, in Planck units, $\Lambda \approx H^4$,
where H is the Hubble parameter. The corresponding cosmological solution has no
initial singularity, existing since an infinite past. During an infinitely long
period we have a quasi-de Sitter, inflationary universe, with $H \approx 1$.
However, at a given time, the expansion undertakes a phase transition, with H
and $\Lambda$ decreasing to nearly zero in a few Planck times, producing a huge
amount of radiation. On the other hand, the late-time scenario is similar to
the standard model, with the radiation phase followed by a dust era, which
tends asymptotically to a de Sitter universe, with vacuum dominating again.


title: Emergent Universe with Exotic Matter

abstract:
  A general framework for an emergent universe scenario has been given which
makes use of an equation of state. The general features of the model have also
been studied and possible primordial composition of the universe have been
suggested.


title: Catching Super Massive Black Hole Binaries Without a Net

abstract:
  The gravitational wave signals from coalescing Supermassive Black Hole
Binaries are prime targets for the Laser Interferometer Space Antenna (LISA).
With optimal data processing techniques, the LISA observatory should be able to
detect black hole mergers anywhere in the Universe. The challenge is to find
ways to dig the signals out of a combination of instrument noise and the large
foreground from stellar mass binaries in our own galaxy. The standard procedure
of matched filtering against a grid of templates can be computationally
prohibitive, especially when the black holes are spinning or the mass ratio is
large. Here we develop an alternative approach based on Metropolis-Hastings
sampling and simulated annealing that is orders of magnitude cheaper than a
grid search. We demonstrate our approach on simulated LISA data streams that
contain the signals from binary systems of Schwarzschild Black Holes, embedded
in instrument noise and a foreground containing 26 million galactic binaries.
The search algorithm is able to accurately recover the 9 parameters that
describe the black hole binary without first having to remove any of the bright
foreground sources, even when the black hole system has low signal-to-noise.


title: Robinson-Trautman spacetimes in higher dimensions

abstract:
  As an extension of the Robinson-Trautman solutions of D=4 general relativity,
we investigate higher dimensional spacetimes which admit a hypersurface
orthogonal, non-shearing and expanding geodesic null congruence. Einstein's
field equations with an arbitrary cosmological constant and possibly an aligned
pure radiation are fully integrated, so that the complete family is presented
in closed explicit form. As a distinctive feature of higher dimensions, the
transverse spatial part of the general line element must be a Riemannian
Einstein space, but it is otherwise arbitrary. On the other hand, the remaining
part of the metric is - perhaps surprisingly - not so rich as in the standard
D=4 case, and the corresponding Weyl tensor is necessarily of algebraic type D.
While the general family contains (generalized) static
Schwarzschild-Kottler-Tangherlini black holes and extensions of the Vaidya
metric, there is no analogue of important solutions such as the C-metric.


title: Leading quantum gravitational corrections to QED

abstract:
  We consider the leading post-Newtonian and quantum corrections to the
non-relativistic scattering amplitude of charged spin-1/2 fermions in the
combined theory of general relativity and QED. The coupled Dirac-Einstein
system is treated as an effective field theory. This allows for a consistent
quantization of the gravitational field. The appropriate vertex rules are
extracted from the action, and the non-analytic contributions to the 1-loop
scattering matrix are calculated in the non-relativistic limit. The
non-analytical parts of the scattering amplitude are known to give the long
range, low energy, leading quantum corrections, are used to construct the
leading post-Newtonian and quantum corrections to the two-particle
non-relativistic scattering matrix potential for two massive fermions with
electric charge.


title:
Quantization of diffeomorphism invariant theories of connections with a
  non-compact structure group - an example

abstract:
  A simple diffeomorphism invariant theory of connections with the non-compact
structure group R of real numbers is quantized. The theory is defined on a
four-dimensional 'space-time' by an action resembling closely the self-dual
Plebanski action for general relativity. The space of quantum states is
constructed by means of projective techniques by Kijowski. Except this point
the applied quantization procedure is based on Loop Quantum Gravity methods.


title:
Higher-order spin effects in the dynamics of compact binaries I.
  Equations of motion

abstract:
  We derive the equations of motion of spinning compact binaries including the
spin-orbit (SO) coupling terms one post-Newtonian (PN) order beyond the
leading-order effect. For black holes maximally spinning this corresponds to
2.5PN order. Our result for the equations of motion essentially confirms the
previous result by Tagoshi, Ohashi and Owen. We also compute the spin-orbit
effects up to 2.5PN order in the conserved (Noetherian) integrals of motion,
namely the energy, the total angular momentum, the linear momentum and the
center-of-mass integral. We obtain the spin precession equations at 1PN order
beyond the leading term, as well. Those results will be used in a future paper
to derive the time evolution of the binary orbital phase, providing more
accurate templates for LIGO-Virgo-LISA type interferometric detectors.


title:
Higher-order spin effects in the dynamics of compact binaries II.
  Radiation field

abstract:
  Motivated by the search for gravitational waves emitted by binary black
holes, we investigate the gravitational radiation field of point particles with
spins within the framework of the multipolar-post-Newtonian wave generation
formalism. We compute: (i) the spin-orbit (SO) coupling effects in the binary's
mass and current quadrupole moments one post-Newtonian (1PN) order beyond the
dominant effect, (ii) the SO contributions in the gravitational-wave energy
flux and (iii) the secular evolution of the binary's orbital phase up to 2.5PN
order. Crucial ingredients for obtaining the 2.5PN contribution in the orbital
phase are the binary's energy and the spin precession equations, derived in
paper I of this series. These results provide more accurate gravitational-wave
templates to be used in the data analysis of rapidly rotating Kerr-type
black-hole binaries with the ground-based detectors LIGO, Virgo, GEO 600 and
TAMA300, and the space-based detector LISA.


title: Time Delay Predictions in a Modified Gravity Theory

abstract:
  The time delay effect for planets and spacecraft is obtained from a fully
relativistic modified gravity theory including a fifth force skew symmetric
field by fitting to the Pioneer 10/11 anomalous acceleration data. A possible
detection of the predicted time delay corrections to general relativity for the
outer planets and future spacecraft missions is considered. The time delay
correction to GR predicted by the modified gravity is consistent with the
observational limit of the Doppler tracking measurement reported by the Cassini
spacecraft on its way to Saturn, and the correction increases to a value that
could be measured for a spacecraft approaching Neptune and Pluto.


title: Geometrical Origin of the Cosmological Term

abstract:
  Nonmetricity derived from a scalar field is shown to exist as a cosmic field,
without direct coupling to matter. It leads to a variable cosmological term, a
term that dominates the expansion in the early universe but dies away at later
time.


title: Transition from quintessence to phantom phase in quintom model

abstract:
  Assuming the Hubble parameter is a continuous and differentiable function of
comoving time, we investigate necessary conditions for quintessence to phantom
phase transition in quintom model. For power-law and exponential potential
examples, we study the behavior of dynamical dark energy fields and Hubble
parameter near the transition time, and show that the phantom-divide-line w=-1
is crossed in these models.


title:
Perspectives in measuring the PPN parameters beta and gamma in the
  Earth's gravitational fields with the CHAMP/GRACE models

abstract:
  The current bounds on the PPN parameters gamma and beta are of the order of
10^-4-10^-5. Various missions aimed at improving such limits by several orders
of magnitude have more or less recently been proposed like LATOR, ASTROD,
BepiColombo and GAIA. They involve the use of various spacecraft, to be
launched along interplanetary trajectories, for measuring the effects of the
solar gravity on the propagation of electromagnetic waves. In this paper we
investigate what is needed to measure the combination nu=(2+2gamma-beta)/3 of
the post-Newtonian gravitoelectric Einstein perigee precession of a test
particle to an accuracy of about 10^-5 with a pair of drag-free spacecraft in
the Earth's gravitational field. It turns out that the latest gravity models
from the dedicated CHAMP and GRACE missions would allow to reduce the
systematic error of gravitational origin just to this demanding level of
accuracy. In regard to the non-gravitational errors, the spectral noise density
of the drag-free sensors required to reach such level of accuracy would amounts
to 10^-8-10^-9 cm s^-2 Hz^-1/2 over very low frequencies. Although not yet
obtainable with the present technologies, such level of compensation is much
less demanding than those required for, e.g., LISA. As a by-product, an
independent measurement of the post-Newtonian gravitomagnetic Lense-Thirring
effect with a 0.9% accuracy would be possible as well. The forthcoming Earth
gravity models from CHAMP and GRACE will further reduce the systematic
gravitational errors in both of such tests.


title: On the Energy of Vaidya Space-time

abstract:
  In this paper we calculate the energy distribution of six cases of
Vaidya-solutions in the M{\o}ller prescription. Except the energy complex of
M{\o}ller for the monopole solution vanishes everywhere, for other solutions
have non-zero energy component, only the energy distributions of the de Sitter
and anti-de Sitter solution are independent on $v$. For the radiating dyon
solution, the difference in energy complex between M{\o}ller's and Einstein's
prescription is like the case of Reissner-Nordstr\"{o}m solution.


title:
Spectral Analysis of Radial Dirac Operators in the Kerr-Newman Metric
  and its Applications to Time-periodic Solutions

abstract:
  We investigate the existence of time-periodic solutions of the Dirac equation
in the Kerr-Newman background metric. To this end, the solutions are expanded
in a Fourier series with respect to the time variable $t$ and the Chandrasekhar
separation ansatz is applied so that the question of existence of a
time-periodic solution is reduced to the solvability of a certain coupled
system of ordinary differential equations. First, we prove the already known
result that there are no time-periodic solutions in the non-extreme case. Then
it is shown that in the extreme case for fixed black hole data there is a
sequence of particle masses $(m_N)_{N\in\mathbb N}$ for which a time-periodic
solution of the Dirac equation does exist. The period of the solution depends
only on the data of the black hole described by the Kerr-Newman metric.


title: Quantum Modified Null Trajectories in Schwarzschild Spacetime

abstract:
  The photon vacuum polarization effect in curved spacetime leads to
birefringence, i.e. the photon velocity becomes greater than (or less than) the
speed of light depending on its polarization. We investigate this phenomenon in
a Schwarzschild curved spacetime.


title: Killing horizons kill horizon degrees

abstract:
  Frequently it is argued that the microstates responsible for the
Bekenstein-Hawking entropy should arise from some physical degrees of freedom
located near or on the black hole horizon. In this Essay we elucidate that
instead entropy may emerge from the conversion of physical degrees of freedom,
attached to a generic boundary, into unobservable gauge degrees of freedom
attached to the horizon. By constructing the reduced phase space it can be
demonstrated that such a transmutation indeed takes place for a large class of
black holes, including Schwarzschild.


title: A modification of the Chen-Nester quasilocal expressions

abstract:
  Chen and Nester proposed four boundary expressions for the quasilocal
quantities using the covariant Hamiltonian formalism. Based on these four
expressions, there is a simple generalization that one can consider, so that a
two parameter set of boundary expressions can be constructed. Using these
modified expressions, a nice result for gravitational energy-momentum can be
obtained in holonomic frames.


title: Classical pseudotenors and positivity in small regions

abstract:
  We have studied the famous classical pseudotensors in the small region limit,
both inside matter and in vacuum. A recent work [Deser et al.1999 CQG 16, 2815]
had found one combination of the Einstein and Landau-Lifshitz expressions which
yields the Bel-Robinson tensor in vacuum. Using similar methods we found
another independent combination of the Bergmann-Thomson, Papapetrou and
Weinberg pseudotensors with the same desired property. Moreover we have
constructed an infinite number of additional new holonomic pseudotensors
satisfying this important positive energy requirement, all seem quite
artificial. On the other hand we found that Moller's 1961 tetrad-teleparallel
energy-momentum expression naturally has this Bel-Robinson property.


title:
On static shells and the Buchdahl inequality for the spherically
  symmetric Einstein-Vlasov system

abstract:
  In a previous work \cite{An1} matter models such that the energy density
$\rho\geq 0,$ and the radial- and tangential pressures $p\geq 0$ and $q,$
satisfy $p+q\leq\Omega\rho, \Omega\geq 1,$ were considered in the context of
Buchdahl's inequality. It was proved that static shell solutions of the
spherically symmetric Einstein equations obey a Buchdahl type inequality
whenever the support of the shell, $[R_0,R_1], R_0>0,$ satisfies $R_1/R_0<1/4.$
Moreover, given a sequence of solutions such that $R_1/R_0\to 1,$ then the
limit supremum of $2M/R_1$ was shown to be bounded by
$((2\Omega+1)^2-1)/(2\Omega+1)^2.$ In this paper we show that the hypothesis
that $R_1/R_0\to 1,$ can be realized for Vlasov matter, by constructing a
sequence of static shells of the spherically symmetric Einstein-Vlasov system
with this property. We also prove that for this sequence not only the limit
supremum of $2M/R_1$ is bounded, but that the limit is
$((2\Omega+1)^2-1)/(2\Omega+1)^2=8/9,$ since $\Omega=1$ for Vlasov matter.
Thus, static shells of Vlasov matter can have $2M/R_1$ arbitrary close to
$8/9,$ which is interesting in view of \cite{AR2}, where numerical evidence is
presented that 8/9 is an upper bound of $2M/R_1$ of any static solution of the
spherically symmetric Einstein-Vlasov system.


title: Understanding Gravity: Some Extra Dimensional Perspectives

abstract:
  Gravity is one of the most inexplicable forces of nature, controlling
everything, from the expansion of the Universe to the ebb and flow of ocean
tides. The search for the laws of motion and gravitation began more than two
thousand years ago but still we do not have the complete picture of it. In this
article, we have outlined how our understanding of gravity is changing
drastically with time and how the previous explanations have shaped the most
recent developments in the field like superstrings and braneworlds.


title: Can Gravity Distinguish Between Dirac and Majorana Neutrinos?

abstract:
  We show that spin-gravity interaction can distinguish between Dirac and
Majorana neutrino wave packets propagating in a Lense-Thirring background.
Using time-independent perturbation theory and gravitational phase to generate
a perturbation Hamiltonian with spin-gravity coupling, we show that the
associated matrix element for the Majorana neutrino differs significantly from
its Dirac counterpart. This difference can be demonstrated through significant
gravitational corrections to the neutrino oscillation length for a two-flavour
system, as shown explicitly for SN1987A.


title:
Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed
  Interferometer

abstract:
  The Laser Interferometer Space Antenna (LISA) is being designed to detect and
study in detail gravitational waves from sources throughout the Universe such
as massive black hole binaries. The conceptual formulation of the LISA
space-borne gravitational wave detector is now well developed. The
interferometric measurements between the sciencecraft remain one of the most
important technological and scientific design areas for the mission.
  Our work has concentrated on developing the interferometric technologies to
create a LISA-like optical signal and to measure the phase of that signal using
commercially available instruments. One of the most important goals of this
research is to demonstrate the LISA phase timing and phase reconstruction for a
LISA-like fringe signal, in the case of a high fringe rate and a low signal
level. We present current results of a test-bed interferometer designed to
produce an optical LISA-like fringe signal previously discussed in the
literature.


title: A Demonstration of LISA Laser Communication

abstract:
  Over the past few years questions have been raised concerning the use of
laser communications links between sciencecraft to transmit phase information
crucial to the reduction of laser frequency noise in the LISA science
measurement. The concern is that applying medium frequency phase modulations to
the laser carrier could compromise the phase stability of the LISA fringe
signal. We have modified the table-top interferometer presented in a previous
article by applying phase modulations to the laser beams in order to evaluate
the effects of such modulations on the LISA science fringe signal. We have
demonstrated that the phase resolution of the science signal is not degraded by
the presence of medium frequency phase modulations.


title:
The influence of differential rotation on the detectability of
  gravitational waves from the r-mode instability

abstract:
  Recently, it was shown that differential rotation is an unavoidable feature
of nonlinear r-modes. We investigate the influence of this differential
rotation on the detectability of gravitational waves emitted by a newly born,
hot, rapidly-rotating neutron star, as it spins down due to the r-mode
instability. We conclude that gravitational radiation may be detected by the
advanced laser interferometer detector LIGO if the amount of differential
rotation at the time the r-mode instability becomes active is not very high.


title: Quantum Structure of Space Near a Black Hole Horizon

abstract:
  We describe a midi-superspace quantization scheme for generic single horizon
black holes in which only the spatial diffeomorphisms are fixed. The remaining
Hamiltonian constraint yields an infinite set of decoupled eigenvalue
equations: one at each spatial point. The corresponding operator at each point
is the product of the outgoing and ingoing null convergences, and describes the
scale invariant quantum mechanics of a particle moving in an attractive $1/X^2$
potential. The variable $X$ that is analoguous to particle position is the
square root of the conformal mode of the metric. We quantize the theory via
Bohr quantization, which by construction turns the Hamiltonian constraint
eigenvalue equation into a finite difference equation. The resulting spectrum
gives rise to a discrete spatial topology exterior to the horizon. The spectrum
approaches the continuum in the asymptotic region.