title: Cosmological milestones and energy conditions

abstract:
  Until recently, the physically relevant singularities occurring in FRW
cosmologies had traditionally been thought to be limited to the "big bang", and
possibly a "big crunch". However, over the last few years, the zoo of
cosmological singularities considered in the literature has become considerably
more extensive, with "big rips" and "sudden singularities" added to the mix, as
well as renewed interest in non-singular cosmological events such as "bounces"
and "turnarounds". In this talk, we present an extensive catalogue of such
cosmological milestones, both at the kinematical and dynamical level. First,
using generalized power series, purely kinematical definitions of these
cosmological events are provided in terms of the behaviour of the scale factor
a(t). The notion of a "scale-factor singularity" is defined, and its relation
to curvature singularities (polynomial and differential) is explored. Second,
dynamical information is extracted by using the Friedmann equations (without
assuming even the existence of any equation of state) to place constraints on
whether or not the classical energy conditions are satisfied at the
cosmological milestones. Since the classification is extremely general, and
modulo certain technical assumptions complete, the corresponding results are to
a high degree model-independent.


title: Braneworld gravitational collapse from a radiative bulk

abstract:
  We study the fate of a collapsing star on the brane in a generalized
braneworld gravity with bulk matter. Specifically, we investigate for the
possibility of having a static exterior for a collapsing star in the radiative
bulk scenario. Here, the nonlocal correction due to bulk matter is manifest in
an induced mass that adds up to the physical mass of the star resulting in an
effective mass. A Schwarzschild solution for the exterior in terms of this
effective mass is obtained, which reveals that even if the star exchanges
energy with the bulk, the exterior may appear to be static to a braneworld
observer located outside the collapsing region. The possible explanation of the
situation from the discussion on the role of bulk matter is provided. The
nature of bulk matter and the corresponding bulk geometry have also been
obtained and analyzed, which gives a complete picture of both brane and bulk
viewpoints.


title:
Evolution of high-frequency gravitational waves in some cosmological
  models

abstract:
  We investigate Isaacson's high-frequency gravitational waves which propagate
in some relevant cosmological models, in particular the FRW spacetimes. Their
time evolution in Fourier space is explicitly obtained for various metric forms
of (anti--)de Sitter universe. Behaviour of high-frequency waves in the
anisotropic Kasner spacetime is also described.


title:
Brane world solutions of perfect fluid in the background of a bulk
  containing dust or cosmological constant

abstract:
  The paper presents some solutions to the five dimensional Einstein equations
due to a perfect fluid on the brane with pure dust filling the entire bulk in
one case and a cosmological constant (or vacuum) in the bulk for the second
case. In the first case, there is a linear relationship between isotropic
pressure, energy density and the brane tension, while in the second case, the
perfect fluid is assumed to be in the form of chaplygin gas. Cosmological
solutions are found both for brane and bulk scenarios and some interesting
features are obtained for the chaplygin gas on the brane which are distinctly
different from the standard cosmology in four dimensions.


title: Stationary Cylindrical Anisotropic Fluid

abstract:
  We present the whole set of equations with regularity and matching conditions
required for the description of physically meaningful stationary cylindrically
symmmetric distributions of matter, smoothly matched to Lewis vacuum spacetime.
A specific example is given. The electric and magnetic parts of the Weyl tensor
are calculated, and it is shown that purely electric solutions are necessarily
static. Then, it is shown that no conformally flat stationary cylindrical fluid
exits, satisfying regularity and matching conditions.


title: Second-order gravitational self-force

abstract:
  We derive an expression for the second-order gravitational self-force that
acts on a self-gravitating compact-object moving in a curved background
spacetime. First we develop a new method of derivation and apply it to the
derivation of the first-order gravitational self-force. Here we find that our
result conforms with the previously derived expression. Next we generalize our
method and derive a new expression for the second-order gravitational
self-force. This study also has a practical motivation: The data analysis for
the planned gravitational wave detector LISA requires construction of waveforms
templates for the expected gravitational waves. Calculation of the two leading
orders of the gravitational self-force will enable one to construct highly
accurate waveform templates, which are needed for the data analysis of
gravitational-waves that are emitted from extreme mass-ratio binaries.


title: Proper Conformal Vector fields in Bianchi Type I Space-Times

abstract:
  Direct integration technique is used to study the proper conformal vector
fields in non conformally flat Bianchi type-1 space-times. Using the above
mentioned technique we have shown that a very special class of the above
space-time admits proper conformal vector fields.


title: Seeding of Primordial Perturbations During a Decelerated Expansion

abstract:
  A scalar field with a modified dispersion relation may seed, under certain
conditions, the primordial perturbations during a decelerated expansion. In
this note we examine whether and how these perturbations can be responsible for
the structure formation of observable universe. We discuss relevant
difficulties and possible solutions.


title:
Improved test of Lorentz Invariance in Electrodynamics using Rotating
  Cryogenic Sapphire Oscillators

abstract:
  We present new results from our test of Lorentz invariance, which compares
two orthogonal cryogenic sapphire microwave oscillators rotating in the lab. We
have now acquired over 1 year of data, allowing us to avoid the short data set
approximation (less than 1 year) that assumes no cancelation occurs between the
$\tilde{\kappa}_{e-}$ and $\tilde{\kappa}_{o+}$ parameters from the photon
sector of the standard model extension. Thus, we are able to place independent
limits on all eight $\tilde{\kappa}_{e-}$ and $\tilde{\kappa}_{o+}$ parameters.
Our results represents up to a factor of 10 improvement over previous non
rotating measurements (which independently constrained 7 parameters), and is a
slight improvement (except for $\tilde{\kappa}_{e-}^{ZZ}$) over results from
previous rotating experiments that assumed the short data set approximation.
Also, an analysis in the Robertson-Mansouri-Sexl framework allows us to place a
new limit on the isotropy parameter $P_{MM}=\delta-\beta+{1/2}$ of
$9.4(8.1)\times10^{-11}$, an improvement of a factor of 2.


title: Generalized Puisieux series expansion for cosmological milestones

abstract:
  We use generalized Puisieux series expansions to determine the behaviour of
the scale factor in the vicinity of typical cosmological milestones occurring
in a FRW universe. We describe some of the consequences of this generalized
Puisieux series expansion on other physical observables.


title:
Self-gravitating stationary spherically symmetric systems in
  relativistic galactic dynamics

abstract:
  We study equilibrium states in relativistic galactic dynamics which are
described by solutions of the Einstein-Vlasov system for collisionless matter.
We recast the equations into a regular three-dimensional system of autonomous
first order ordinary differential equations on a bounded state space. Based on
a dynamical systems analysis we derive new theorems that guarantee that the
steady state solutions have finite radii and masses.


title:
A comparison between matter wave and light wave interferometers for the
  detection of gravitational waves

abstract:
  We calculate and compare the response of light wave interferometers and
matter wave interferometers to gravitational waves. We find that metric matter
wave interferometers will not challenge kilometric light wave interferometers
such as Virgo or LIGO, but could be a good candidate for the detection of very
low frequency gravitational waves.


title:
Thermodynamics second law and $\omega=-1$ crossing(s) in interacting
  holographic dark energy model

abstract:
  By the assumption that the thermodynamics second law is valid, we study the
possibility of $\omega=-1$ crossing in interacting holographic dark energy
model. Depending on the choice of the horizon and the interaction, the
transition from quintessence to phantom regime and subsequently from phantom to
quintessence phase may be possible. The second transition avoids the big rip
singularity. We compute the dark energy density at transition time and show
that by choosing appropriate parameters we can alleviate the coincidence
problem.


title:
Bel-Robinson energy and the nature of singularities in isotropic
  cosmologies

abstract:
  We review our recent work on the classification of finite time singularities
that arise in isotropic universes. This scheme is based on the exploitation of
the Bel Robinson energy in a cosmological setting. We comment on the relation
between geodesic completeness and the Bel Robinson energy and present evidence
that relates the divergence of the latter to the existence of closed trapped
surfaces.


title: Averaging anisotropic cosmologies

abstract:
  We examine the effects of spatial inhomogeneities on irrotational anisotropic
cosmologies by looking at the average properties of anisotropic pressure-free
models. Adopting the Buchert scheme, we recast the averaged scalar equations in
Bianchi-type form and close the standard system by introducing a propagation
formula for the average shear magnitude. We then investigate the evolution of
anisotropic average vacuum models and those filled with pressureless matter. In
the latter case we show that the backreaction effects can modify the familiar
Kasner-like singularity and potentially remove Mixmaster-type oscillations. The
presence of nonzero average shear in our equations also allows us to examine
the constraints that a phase of backreaction-driven accelerated expansion might
put on the anisotropy of the averaged domain. We close by assessing the status
of these and other attempts to define and calculate `average' spacetime
behaviour in general relativity.


title: A simple expression for the ADM mass

abstract:
  We show by an almost elementary calculation that the ADM mass of an
asymptotically flat space can be computed as a limit involving a rate of change
of area of a closed 2-surface. The result is essentially the same as that given
by Brown and York. We will prove this result in two ways, first by direct
calculation from the original formula as given by Arnowitt, Deser and Misner
and second as a corollary of an earlier result by Brewin for the case of
simplicial spaces.


title: General Logarithmic Corrections to Bekenstein-Hawking Entropy

abstract:
  Recently, there has been a lot of attention devoted to resolving the quantum
corrections to the Bekenstein-Hawking entropy of the black hole. In particular,
the coefficient of the logarithmic term in the black hole entropy correction
has been of great interest. In this paper, the black hole is corresponded to a
canonical ensemble in statistics by radiant spectrum, resulted from the black
hole tunneling effect studies and the partition function of ensemble is
derived. Then the entropy of the black hole is calculated. When the first order
approximation is taken into account, the logarithmic term of entropy correction
is consistent with the result of the generalized uncertainty principle. In our
calculation, there are no uncertainty factors. The prefactor of the logarithmic
correction and the one if fluctuation is considered are the same. Our result
shows that if the thermal capacity is negative, there is no divergent term. We
provide a general method for further discussion on quantum correction to
Bekenstein-Hawking entropy. We also offer a theoretical basis for comparing
string theory and loop quantum gravitaty and deciding which one is more
reliable.


title: On the orbit of the LARES satellite

abstract:
  This paper is motivated by the recent possibility to find an inexpensive
launching vehicle for the LARES satellite, however at an altitude much lower
than originally planned for the LAGEOS III/LARES satellite.
  We present here a preliminary error analysis corresponding to a lower,
quasi-polar, orbit, in particular we analyze the effect on the LARES node of
the Earth's static gravitational field, and in particular of the Earth's even
zonal harmonics, the effect of the time dependent Earth's gravitational field,
and in particular of the K1 tide, and the effect of particle drag.


title:
Tensor Potential Description of Matter and Space, II Semi-guage and the
  Law of Conservation

abstract:
  Considered a unified field theory approach describing matter and space
(metric tensor) by means of a 3-index tensor $P^{i}_{jk}$. It is shown that if
the Lagrangian has partial U(1) gauge (semi-gauge) of the type
$P^{i}_{jk}->P^{i}_{jk}+a \delta{^i_j} \phi{_{,k}}+b \delta{^i_k}
\phi{_{,j}}+cg_{jk}g^{mi} \phi{_{,m}}$ where a,b,c are constants, then the
Euler equations of motion contain the covariant low of conservation in the form
$J^{k}_{;k}=0$.


title:
Composite dark energy: cosmon models with running cosmological term and
  gravitational coupling

abstract:
  In the recent literature on dark energy (DE) model building we have learnt
that cosmologies with variable cosmological parameters can mimic more
traditional DE pictures exclusively based on scalar fields (e.g. quintessence
and phantom). In a previous work we have illustrated this situation within the
context of a renormalization group running cosmological term, Lambda. Here we
analyze the possibility that both the cosmological term and the gravitational
coupling, G, are running parameters within a more general framework (a variant
of the so-called ``LXCDM models'') in which the DE fluid can be a mixture of a
running Lambda and another dynamical entity X (the ``cosmon'') which may behave
quintessence-like or phantom-like. We compute the effective EOS parameter, w,
of this composite fluid and show that the LXCDM can mimic to a large extent the
standard LCDM model while retaining features hinting at its potential composite
nature (such as the smooth crossing of the cosmological constant boundary
w=-1). We further argue that the LXCDM models can cure the cosmological
coincidence problem. All in all we suggest that future experimental studies on
precision cosmology should take seriously the possibility that the DE fluid can
be a composite medium whose dynamical features are partially caused and
renormalized by the quantum running of the cosmological parameters.


title: Cold black holes and conformal continuations

abstract:
  We study Einstein gravity minimally coupled to a scalar field in a static,
spherically symmetric space-time in four dimensions. Black hole solutions are
shown to exist for a phantom scalar field whose kinetic energy is negative.
These ``scalar black holes'' have an infinite horizon area and zero Hawking
temperature and are termed ``cold black holes'' (CBHs). The relevant explicit
solutions are well-known in the massless case (the so-called anti-Fisher
solution), and we have found a particular example of a CBH with a nonzero
potential $V(\phi)$. All CBHs with $V(\phi) \not \equiv 0$ are shown to behave
near the horizon quite similarly to those with a massless field. The above
solutions can be converted by a conformal transformation to Jordan frames of a
general class of scalar-tensor theories of gravity, but CBH horizons in one
frame are in many cases converted to singularities in the other, which gives
rise to a new type of conformal continuation.


title:
Nonholonomic Ricci Flows and Running Cosmological Constant: I. 4D
  Taub-NUT Metrics

abstract:
  In this work we construct and analyze exact solutions describing Ricci flows
and nonholonomic deformations of four dimensional (4D) Taub-NUT spacetimes. It
is outlined a new geometric techniques of constructing Ricci flow solutions.
Some conceptual issues on spacetimes provided with generic off-diagonal metrics
and associated nonlinear connection structures are analyzed. The limit from
gravity/Ricci flow models with nontrivial torsion to configurations with the
Levi-Civita connection is allowed in some specific physical circumstances by
constraining the class of integral varieties for the Einstein and Ricci flow
equations.


title:
Nonholonomic Ricci Flows and Running Cosmological Constant: 3D Taub-NUT
  Metrics

abstract:
  The common assertion that the Ricci flows of Einstein spaces with
cosmological constant can be modelled by certain classes of nonholonomic frame,
metric and linear connection deformations resulting in nonhomogeneous Einstein
spaces is examined in the light of the role played by topological three
dimensional (3D) Taub-NUT-AdS/dS spacetimes.


title: Black hole evolution with the BSSN system by pseudo-spectral methods

abstract:
  We present a new pseudo-spectral code for the simulation of evolution systems
that are second order in space. We test this code by evolving a non-linear
scalar wave equation. These non-linear waves can be stably evolved using very
simple constant or radiative boundary conditions, which we show to be
well-posed in the scalar wave case. The main motivation for this work, however,
is to evolve black holes for the first time with the BSSN system by means of a
spectral method. We use our new code to simulate the evolution of a single
black hole using all applicable methods that are usually employed when the BSSN
system is used together with finite differencing methods. In particular, we use
black hole excision and test standard radiative and also constant outer
boundary conditions. Furthermore, we study different gauge choices such as
$1+\log$ and constant densitized lapse. We find that these methods in principle
do work also with our spectral method. However, our simulations fail after
about $100M$ due to unstable exponentially growing modes. The reason for this
failure may be that we evolve the black hole on a full grid without imposing
any symmetries. Such full grid instabilities have also been observed when
finite differencing methods are used to evolve excised black holes with the
BSSN system.


title: Solution generating theorems for perfect fluid spheres

abstract:
  The first static spherically symmetric perfect fluid solution with constant
density was found by Schwarzschild in 1918. Generically, perfect fluid spheres
are interesting because they are first approximations to any attempt at
building a realistic model for a general relativistic star. Over the past 90
years a confusing tangle of specific perfect fluid spheres has been discovered,
with most of these examples seemingly independent from each other. To bring
some order to this collection, we develop several new transformation theorems
that map perfect fluid spheres into perfect fluid spheres. These transformation
theorems sometimes lead to unexpected connections between previously known
perfect fluid spheres, sometimes lead to new previously unknown perfect fluid
spheres, and in general can be used to develop a systematic way of classifying
the set of all perfect fluid spheres. In addition, we develop new ``solution
generating'' theorems for the TOV, whereby any given solution can be
``deformed'' to a new solution. Because these TOV-based theorems work directly
in terms of the pressure profile and density profile it is relatively easy to
impose regularity conditions at the centre of the fluid sphere.


title: Scattering of cosmic strings by black holes: loop formation

abstract:
  We study the deformation of a long cosmic string by a nearby rotating black
hole. We examine whether the deformation of a cosmic string, induced by the
gravitational field of a Kerr black hole, may lead to the formation of a loop
of cosmic string. The segment of the string which enters the ergosphere of a
rotating black hole gets deformed and, if it is sufficiently twisted, it can
self-intersect chopping off a loop of cosmic string. We find that the formation
of a loop, via this mechanism, is a rare event. It will only arise in a small
region of the collision phase space, which depends on the string velocity, the
impact parameter and the black hole angular momentum. We conclude that
generically, the cosmic string is simply scattered or captured by the rotating
black hole.


title: Singularities of varying light speed cosmologies

abstract:
  We study the possible singularities of isotropic cosmological models that
have a varying speed of light as well as a varying gravitational constant. The
field equations typically reduce to two dimensional systems which are then
analyzed both by dynamical systems techniques in phase space and by applying
the method of asymptotic splittings. In the general case we find initially
expanding closed models which recollapse to a future singularity and open
universes that are eternally expanding towards the future. The precise nature
of the singularities is also discussed.


title:
Measuring mass moments and electromagnetic moments of a massive,
  axisymmetric body, through gravitational waves

abstract:
  The electrovacuum around a rotating massive body with electric charge density
is described by its multipole moments (mass moments, mass-current moments,
electric moments, and magnetic moments). A small uncharged test particle
orbiting around such a body moves on geodesics if gravitational radiation is
ignored. The waves emitted by the small body carry information about the
geometry of the central object, and hence, in principle, we can infer all its
multipole moments. Due to its axisymmetry the source is characterized now by
four families of scalar multipole moments: its mass moments $M_l$, its
mass-current moments $S_l$, its electrical moments $E_l$ and its magnetic
moments $H_l$, where $l=0,1,2,...$. Four measurable quantities, the energy
emitted by gravitational waves per logarithmic interval of frequency, the
precession of the periastron (assuming almost circular orbits), the precession
of the orbital plane (assuming almost equatorial orbits), and the number of
cycles emitted per logarithmic interval of frequency, are presented as power
series of the newtonian orbital velocity of the test body. The power series
coefficients are simple polynomials of the various moments.


title: Inside an evaporating two-dimensional charged black hole

abstract:
  We investigate the inner structure of an evaporating charged black hole,
within the context of semiclassical dilaton gravity in two dimensions. The
matter fields are charged, allowing the evaporation of both the mass and charge
of the black hole. We find that the semiclassical effects cause the inner
horizon to expand (by a finite factor), rather than to shrink to a point
singularity. Although this expansion is a quantum phenomenon, the overall
expansion factor is found to be independent of the magnitude of the quantum
terms in the effective theory.


title: Brane Cosmology in an Arbitrary Number of Dimensions

abstract:
  We derive the effective cosmological equations for a non-$\mathbb{Z}_2$
symmetric codimension one brane embedded in an arbitrary D-dimensional bulk
spacetime, generalizing the $D=5,6$ cases much studied previously. As a
particular case, this may be considered as a regularized codimension (D-4)
brane avoiding the problem of curvature divergence on the brane. We apply our
results to the case of spherical symmetry around the brane and to partly
compactified AdS-Schwarzschild bulks.


title: Gravitationally Collapsing Shells in (2+1) Dimensions

abstract:
  We study gravitationally collapsing models of pressureless dust, fluids with
pressure, and the generalized Chaplygin gas (GCG) shell in (2+1)-dimensional
spacetimes. Various collapse scenarios are investigated under a variety of the
background configurations such as anti-de Sitter(AdS) black hole, de Sitter
(dS) space, flat and AdS space with a conical deficit. As with the case of a
disk of dust, we find that the collapse of a dust shell coincides with the
Oppenheimer-Snyder type collapse to a black hole provided the initial density
is sufficiently large. We also find -- for all types of shell -- that collapse
to a naked singularity is possible under a broad variety of initial conditions.
For shells with pressure this singularity can occur for a finite radius of the
shell. We also find that GCG shells exhibit diverse collapse scenarios, which
can be easily demonstrated by an effective potential analysis.


title: Gravitation Physics at BGPL

abstract:
  We report progress on a program of gravitational physics experiments using
cryogenic torsion pendula undergoing large-amplitude torsion oscillation. This
program includes tests of the gravitational inverse square law and of the weak
equivalence principle. Here we describe our ongoing search for
inverse-square-law violation at a strength down to $10^{-5}$ of standard
gravity. The low-vibration environment provided by the Battelle Gravitation
Physics Laboratory (BGPL) is uniquely suited to this study.


title:
Kerr-Newman Solution and Energy in Teleparallel Equivalent of Einstein
  Theory

abstract:
  An exact charged axially symmetric solution of the coupled gravitational and
electromagnetic fields in the teleparallel equivalent of Einstein theory is
derived. It is characterized by three parameters ``$ $the gravitational mass
$M$, the charge parameter $Q$ and the rotation parameter $a$" and its
associated metric gives Kerr-Newman spacetime. The parallel vector field and
the electromagnetic vector potential are axially symmetric. We then, calculate
the total energy using the gravitational energy-momentum. The energy is found
to be shared by its interior as well as exterior. Switching off the charge
parameter we find that no energy is shared by the exterior of the Kerr-Newman
black hole.


title:
A comment on the paper "On the orbit of the LARES satellite", by I.
  Ciufolini

abstract:
  In this note we comment on a recent paper by I.Ciufolini about the
possibility of placing the proposed terrestrial satellite LARES in a
low-altitude, nearly polar orbit in order to measure the general relativistic
Lense-Thirring effect with its node. Ciufolini claims that, for a departure of
4 deg in the satellite's inclination $i$ from the ideal polar configuration
(i=90 deg), the impact of the errors in the even zonal harmonics of the
geopotential, modelled with EIGEN-GRACE02S, would be nearly zero allowing for a
few-percent measurement of the Lense-Thirring effect. Instead, we find that,
with the same Earth gravity model and for the same values of the inclination,
the upper bound of the systematic error due to the mismodelling in the even
zonals amounts to 64% of the relativistic effect investigated.

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


title: The Relation between Cosmic Temperature and Scale Factor

abstract:
  This submission has been withdrawn by arXiv admins because it contains
inappropriate overlap with arXiv:physics/0603087.


title: Solution generating theorems: perfect fluid spheres and the TOV equation

abstract:
  We report several new transformation theorems that map perfect fluid spheres
into perfect fluid spheres. In addition, we report new ``solution generating''
theorems for the TOV, whereby any given solution can be ``deformed'' to a new
solution.


title: Initial data sets for the Schwarzschild spacetime

abstract:
  A characterisation of initial data sets for the Schwarzschild spacetime is
provided. This characterisation is obtained by performing a 3+1 decomposition
of a certain invariant characterisation of the Schwarzschild spacetime given in
terms of concomitants of the Weyl tensor. This procedure renders a set of
necessary conditions --which can be written in terms of the electric and
magnetic parts of the Weyl tensor and their concomitants-- for an initial data
set to be a Schwarzschild initial data set. Our approach also provides a
formula for a static Killing initial data set candidate --a KID candidate.
Sufficient conditions for an initial data set to be a Schwarzschild initial
data set are obtained by supplementing the necessary conditions with the
requirement that the initial data set possesses a stationary Killing initial
data set of the form given by our KID candidate. Thus, we obtain an algorithmic
procedure of checking whether a given initial data set is Schwarzschildean or
not.


title: The Lukash Plane-Wave Attractor and Relative Energy

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0411070, "Structure and stability of the Lukash plane-wave spacetime," by
John D. Barrow and Christos G. Tsagas; and gr-qc/0205028, "Gravitational Energy
of Kerr and Kerr Anti-de Sitter Space-times in the Teleparallel Geometry," by
J. F. da Rocha-neto and K. H. Castello-Branco.


title:
Comment on the choice of time in a two-component formulation of the
  Wheeler--DeWitt equation

abstract:
  The two-component formalism in quantum cosmology is revisited with a
particular emphasis on the identification of time. Its relation with the
appearance of imaginary eigenvalues is established. It is explicitly shown how
a good choice of the global time prevents this peculiarity.


title: Violating general covariance

abstract:
  The explicit violation of the general covariance on the whole and its minimal
violation to the unimodular covariance specifically is considered. The proper
extension of General Relativity is shown to describe consistently the massive
scalar graviton together with the massless tensor one, as the parts of the
metric. The bearing of the scalar graviton to the dark matter and dark energy
is indicated.


title: Duality invariance and cosmological dynamics

abstract:
  A duality transformation that interrelates expanding and contracting
cosmological models is shown to single out a duality invariant, interacting
two-component description of any irrotational, geodesic and shearfree cosmic
medium with vanishing three curvature scalar. We apply this feature to a system
of matter and radiation, to a mixture of dark matter and dark energy, to
minimal and conformal scalar fields, and to an enlarged Chaplygin gas model of
the cosmic substratum. We extend the concept of duality transformations to
cosmological perturbations and demonstrate the invariance of adiabatic pressure
perturbations under these transformations.


title: The Mock LISA Data Challenges: An overview

abstract:
  The LISA International Science Team Working Group on Data Analysis
(LIST-WG1B) is sponsoring several rounds of mock data challenges, with the
purposeof fostering the development of LISA data analysis capabilities, and of
demonstrating technical readiness for the maximum science exploitation of the
LISA data. The first round of challenge data sets were released at the Sixth
LISA Symposium. We briefly describe the objectives, structure, and time-line of
this programme.


title: A How-To for the Mock LISA Data Challenges

abstract:
  The LISA International Science Team Working Group on Data Analysis
(LIST-WG1B) is sponsoring several rounds of mock data challenges, with the
purpose of fostering development of LISA data-analysis capabilities, and of
demonstrating technical readiness for the maximum science exploitation of the
LISA data. The first round of challenge data sets were released at this
Symposium. We describe the models and conventions (for LISA and for
gravitational-wave sources) used to prepare the data sets, the file format used
to encode them, and the tools and resources available to support challenge
participants.


title: Emergence of gravity from interacting simplices

abstract:
  We consider a statistical model of interacting 4-simplices fluctuating in an
N-dimensional target space. We argue that a gravitational theory may arise as a
low energy effective theory in a strongly interacting phase where the simplices
form clusters with an emergent space and time with the Euclidean signature. In
the large N limit, two possible phases are discussed, that is, `gravitational
Coulomb phase' and `gravitational Higgs phase'.


title: Prolegomena to any future Quantum Gravity

abstract:
  I shall discuss some "conditions of possibility" of a quantum theory of
gravity, stressing the need for solutions to some of fundamental problems
confronting any attempt to apply some method of quantization to the field
equations of general relativity.


title:
GravEn: Software for the simulation of gravitational wave detector
  network response

abstract:
  Physically motivated gravitational wave signals are needed in order to study
the behaviour and efficacy of different data analysis methods seeking their
detection. GravEn, short for Gravitational-wave Engine, is a MATLAB software
package that simulates the sampled response of a gravitational wave detector to
incident gravitational waves. Incident waves can be specified in a data file or
chosen from among a group of pre-programmed types commonly used for
establishing the detection efficiency of analysis methods used for LIGO data
analysis. Every aspect of a desired signal can be specified, such as start time
of the simulation (including inter-sample start times), wave amplitude, source
orientation to line of sight, location of the source in the sky, etc. Supported
interferometric detectors include LIGO, GEO, Virgo and TAMA.


title:
A First Comparison of SLOPE and Other LIGO Burst Event Trigger
  Generators

abstract:
  A number of different methods have been proposed to identify unanticipated
burst sources of gravitational waves in data arising from LIGO and other
gravitational wave detectors. When confronted with such a wide variety of
methods one is moved to ask if they are all necessary, i.e. given detector data
that is assumed to have no gravitational wave signals present, do they
generally identify the same events with the same efficiency, or do they each
'see' different things in the detector? Here we consider three different
methods, which have been used within the LIGO Scientific Collaboration as part
of its search for unanticipated gravitational wave bursts. We find that each of
these three different methods developed for identifying candidate gravitational
wave burst sources are, in fact, attuned to significantly different features in
detector data, suggesting that they may provide largely independent lists of
candidate gravitational wave burst events.


title: Conformal Properties of Charges in Scalar-Tensor Gravities

abstract:
  We study the behavior under conformal transformations of energy and other
charges in generic scalar-tensor models. This enables us to conclude that the
ADM/AD masses are invariant under field redefinitions mixing metric and scalar
despite the permitted slow asymptotic falloff of massless scalars.


title:
Dynamical constraints on the quadrupole mass moment of the HD 209458
  star

abstract:
  The aim of this paper is to dynamically constrain the quadrupole mass moment
J_2 of the main-sequence HD 209458 star. The adopted method is the
confrontation between the measured orbital period of its transiting planet
Osiris and a model of it. Osiris is assumed to move along an equatorial and
circular orbit. Our estimate, for given values of the stellar mass M and radius
R and by assuming the validity of general relativity, is J_2=(3.5 +/- 385.1)
10^-5. Previous fiducial evaluations based on indirect, spectroscopic
measurements yielded J_2\sim 10^-6: such a value is compatible with our result.


title:
Input spectrum for heterodyne detection in advanced gravitational wave
  detectors without non-stationary shot-noise

abstract:
  Future interferometric gravitational wave detectors will make use of the
coupling between shot noise and radiation pressure noise that produces a
squeezed output for the quantum noise at the dark-port of the interferometer
allowing these interferometers to operate with a sensitivity that exceeds the
standard quantum limit at certain frequencies. The ability of the detector to
take advantage of this squeezed output state depends in part on the readout
system used. With the phase modulated laser input planned for these
interferometers the quantum-noise limited sensitivity is slightly better when
homodyne (rather than heterodyne) detection is used. We show that by modifying
the laser input spectrum for these interferometers, readout with heterodyne
detection can be made to have the same quantum-noise limited sensitivity as
readout with homodyne detection.


title:
Electric S-brane solutions with a parallel charge density form on a
  Ricci-flat factor space

abstract:
  We generalize the previously studied cosmological solutions in D-dimensional
gravity with an antisymmetric (p+2)-form to the case when the spatial part of
the metric is Ricci-flat rather than flat. These generalized solutions are
characterized by a parallel self-dual or anti-self-dual charge density form Q
of rank 2m and satisfy the condition Q^2 >0. As with the previous flat-space
case, these electric, S-brane solutions only exist when D=4m+1 = 5, 9, 13, ...
and p= 2m -1 = 1, 3, 5, .... We further generalize these solutions by adding
Ricci-flat factor-spaces which are not covered by branes.


title: Yang-Mills condensate dark energy coupled with matter and radiation

abstract:
  The coincidence problem is studied for the dark energy model of effective
Yang-Mills condensate in a flat expanding universe during the matter-dominated
stage. The YMC energy $\rho_y(t)$ is taken to represent the dark energy, which
is coupled either with the matter, or with both the matter and the radiation
components. The effective YM Lagrangian is completely determined by quantum
field theory up to 1-loop order. It is found that under very generic initial
conditions and for a variety of forms of coupling, the existence of the scaling
solution during the early stages and the subsequent exit from the scaling
regime are inevitable. The transition to the accelerating stage always occurs
around a redshift $z\simeq (0.3\sim 0.5)$. Moreover, when the Yang-Mills
condensate transfers energy into matter or into both matter and radiation, the
equation of state $w_y$ of the Yang-Mills condensate can cross over -1 around
$z\sim 2$, and takes on a current value $\simeq -1.1$. This is consistent with
the recent preliminary observations on supernovae Ia. Therefore, the
coincidence problem can be naturally solved in the effective YMC dark energy
models.


title:
Approximation to the Second Order Approximation of Einstein Field
  Equations with a Cosmological Constant in a Flat Background

abstract:
  Einstein field equations with a cosmological constant are approximated to the
second order in the perturbation to a flat background metric. The final result
is a set of Einstein-Maxwell-Proca equations for gravity in the weak field
regime. This approximation procedure implements the breaking of gauge symmetry
in general relativity. A brief discussion of the physical consequences (Pioneer
anomalous deceleration) is proposed in the framework of the gauge theory of
gravity.


title: Generation of Closed Timelike Curves with Rotating Superconductors

abstract:
  The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced
from the gravitomagnetic London moment in rotating superconductors. It is shown
that theoretically it is possible to generate Closed Timelike Curves (CTC) with
rotating SCRs. The possibility to use these CTC's to travel in time as
initially idealized by G\"{o}del is investigated. It is shown however, that
from a technology and experimental point of view these ideas are impossible to
implement in the present context.


title:
Reconstruction of source location in a network of gravitational wave
  interferometric detectors

abstract:
  This paper deals with the reconstruction of the direction of a gravitational
wave source using the detection made by a network of interferometric detectors,
mainly the LIGO and Virgo detectors. We suppose that an event has been seen in
coincidence using a filter applied on the three detector data streams. Using
the arrival time (and its associated error) of the gravitational signal in each
detector, the direction of the source in the sky is computed using a chi^2
minimization technique. For reasonably large signals (SNR>4.5 in all
detectors), the mean angular error between the real location and the
reconstructed one is about 1 degree. We also investigate the effect of the
network geometry assuming the same angular response for all interferometric
detectors. It appears that the reconstruction quality is not uniform over the
sky and is degraded when the source approaches the plane defined by the three
detectors. Adding at least one other detector to the LIGO-Virgo network reduces
the blind regions and in the case of 6 detectors, a precision less than 1
degree on the source direction can be reached for 99% of the sky.


title: The causal hierarchy of spacetimes

abstract:
  The full causal ladder of spacetimes is constructed, and their updated main
properties are developed. Old concepts and alternative definitions of each
level of the ladder are revisited, with emphasis in minimum hypotheses. The
implications of the recently solved ``folk questions on smoothability'', and
alternative proposals (as recent isocausality), are also summarized.


title:
Asymptotic symmetries on Kerr--Newman horizon without anomaly of
  diffeomorphism invariance

abstract:
  We analyze asymptotic symmetries on the Killing horizon of the
four-dimensional Kerr--Newman black hole. We first derive the asymptotic
Killing vectors on the Killing horizon, which describe the asymptotic
symmetries, and find that the general form of these asymptotic Killing vectors
is the universal one possessed by arbitrary Killing horizons. We then construct
the phase space associated with the asymptotic symmetries. It is shown that the
phase space of an extreme black hole either has the size comparable with a
non-extreme black hole, or is small enough to exclude degeneracy, depending on
whether or not the global structure of a Killing horizon particular to an
extreme black hole is respected. We also show that the central charge in the
Poisson brackets algebra of these asymptotic symmetries vanishes, which implies
that there is not an anomaly of diffeomorphism invariance. By taking into
account other results in the literature, we argue that the vanishing central
charge on a black hole horizon, in an effective theory, looks consistent with
the thermal feature of a black hole. We furthermore argue that the vanishing
central charge implies that there are infinitely many classical configurations
that are associated with the same macroscopic state, while these configurations
are distinguished physically.


title: Dipolar Particles in General Relativity

abstract:
  The dynamics of "dipolar particles", i.e. particles endowed with a
four-vector mass dipole moment, is investigated using an action principle in
general relativity. The action is a specific functional of the particle's world
line, and of the dipole moment vector, considered as a dynamical variable. The
first part of the action is inspired by that of a particle with spin moving on
an arbitrary gravitational background. The second part is intended to describe,
at some effective level, the internal non-gravitational force linking together
the "microscopic" constituents of the dipole. We find that some solutions of
the equations of motion and evolution of the dipolar particles correspond to an
equilibrium state for the dipole moment in a gravitational field. Under some
hypothesis we show that a fluid of dipolar particles, supposed to constitute
the dark matter, reproduces the modified Newtonian dynamics (MOND) in the non
relativistic limit. We recover the main characteristics of a recently proposed
quasi-Newtonian model of "gravitational polarization".


title: Black hole entropy quantization

abstract:
  Ever since the pioneer works of Bekenstein and Hawking, black hole entropy
has been known to have a quantum origin. Furthermore, it has long been argued
by Bekenstein that entropy should be quantized in discrete (equidistant) steps
given its identification with horizon area in (semi-)classical general
relativity and the properties of area as an adiabatic invariant. This lead to
the suggestion that black hole area should also be quantized in equidistant
steps to account for the discrete black hole entropy. Here we shall show that
loop quantum gravity, in which area is {\it not} quantized in equidistant steps
can nevertheless be consistent with Bekenstein's equidistant entropy proposal
in a subtle way. For that we perform a detailed analysis of the number of
microstates compatible with a given area and show consistency with the
Bekenstein framework when an oscillatory behavior in the entropy-area relation
is properly interpreted.


title: Exact solution of inflationary model with minimum length

abstract:
  Within the inflationary scenario, Planck scale physics should have affected
the comoving modes' initial conditions and early evolution, thereby potentially
affecting the inflationary predictions for the cosmic microwave background
(CMB). This issue has been studied extensively on the basis of various models
for how quantum field theory (QFT) is modified and finally breaks down towards
the Planck scale. In one model, in particular, an ultraviolet cutoff was
implemented into QFT through generalized uncertainty relations which have been
motivated from general quantum gravity arguments and from string theory. Here,
we improve upon prior numerical and semi-analytical results by presenting the
exact mode solutions for both de Sitter and power-law inflation in this model.
This provides an explicit map from the modes' initial conditions, which are
presumably set by quantum gravity, to the modes' amplitudes at horizon crossing
and thus to the inflationary predictions for the CMB. The solutions' particular
behaviour close to the cutoff scale suggests unexpected possibilities for how
the degrees of freedom of QFT emerge from the Planck scale.


title: Positive energy theorem implies constraints on static steller models

abstract:
  Using the positive energy theorem, we derive some constraints on static
steller models in asymptotically flat spacetimes in a general setting without
imposing spherical symmetry. We show that there exist no regular solutions
under certain conditions on the equation of state. As the contraposition, we
obtain some constraints on the pressure and adiabatic index.


title:
Horizon-less Spherically Symmetric Vacuum-Solutions in a Higgs
  Scalar-Tensor Theory of Gravity

abstract:
  The exact static and spherically symmetric solutions of the vacuum field
equations for a Higgs Scalar-Tensor theory (HSTT) are derived in Schwarzschild
coordinates. It is shown that in general there exists no Schwarzschild horizon
and that the fields are only singular (as naked singularity) at the center
(i.e. for the case of a pont-particle). However, the Schwarzschild solution as
in usual general relativity (GR) is obtained for the vanishing limit of Higgs
field excitations.


title: Mutual information challenges entropy bounds

abstract:
  We consider some formulations of the entropy bounds at the semiclassical
level. The entropy S(V) localized in a region V is divergent in quantum field
theory (QFT). Instead of it we focus on the mutual information
I(V,W)=S(V)+S(W)-S(V\cup W) between two different non-intersecting sets V and
W. This is a low energy quantity, independent of the regularization scheme. In
addition, the mutual information is bounded above by twice the entropy
corresponding to the sets involved. Calculations of I(V,W) in QFT show that the
entropy in empty space cannot be renormalized to zero, and must be actually
very large. We find that this entropy due to the vacuum fluctuations violates
the FMW bound in Minkowski space. The mutual information also gives a precise,
cutoff independent meaning to the statement that the number of degrees of
freedom increases with the volume in QFT. If the holographic bound holds, this
points to the essential non locality of the physical cutoff. Violations of the
Bousso bound would require conformal theories and large distances. We speculate
that the presence of a small cosmological constant might prevent such a
violation.


title:
Stationary axisymmetric exteriors for perturbations of isolated bodies
  in general relativity, to second order

abstract:
  Perturbed stationary axisymmetric isolated bodies, e.g. stars, represented by
a matter-filled interior and an asymptotically flat vacuum exterior joined at a
surface where the Darmois matching conditions are satisfied, are considered.
The initial state is assumed to be static. The perturbations of the matching
conditions are derived and used as boundary conditions for the perturbed Ernst
equations in the exterior region. The perturbations are calculated to second
order. The boundary conditions are overdetermined: necessary and sufficient
conditions for their compatibility are derived. The special case of
perturbations of spherical bodies is given in detail.


title: Holography and non-locality in a closed vacuum-dominated universe

abstract:
  A closed vacuum-dominated Friedmann universe is asymptotic to a de Sitter
space with a cosmological event horizon for any observer. The holographic
principle says the area of the horizon in Planck units determines the number of
bits of information about the universe that will ever be available to any
observer. The wavefunction describing the probability distribution of mass
quanta associated with bits of information on the horizon is the boundary
condition for the wavefunction specifying the probability distribution of mass
quanta throughout the universe. Local interactions between mass quanta in the
universe cause quantum transitions in the wavefunction specifying the
distribution of mass throughout the universe, with instantaneous non-local
effects throughout the universe.


title: Rainbow universe

abstract:
  The formalism of rainbow gravity is studied in a cosmological setting. We
consider the very early universe which is radiation dominated. A novel
treatment in our paper is to look for an ``averaged'' cosmological metric
probed by radiation particles themselves. Taking their cosmological evolution
into account, we derive the modified Friedmann-Robertson-Walker(FRW) equations
which is a generalization of the solution presented by Magueijo and Smolin.
Based on this phenomenological cosmological model we argue that the spacetime
curvature has an upper bound such that the cosmological singularity is absent.
These modified $FRW$ equations can be treated as effective equations in the
semi-classical framework of quantum gravity and its analogy with the one
recently proposed in loop quantum cosmology is also discussed.


abstract:
  The kinematics of particles moving in rainbow spacetime is studied in this
paper. In particular the geodesics of a massive particle in rainbow flat
spacetime is obtained when the semi-classical effect of its own energy on the
background is taken into account. We show that in general the trajectory of a
freely falling particle remains unchanged which is still a straight line as in
the flat spacetime. The implication to the Unruh effect in rainbow flat
spacetime is also discussed.


title:
Coherent Bayesian inference on compact binary inspirals using a network
  of interferometric gravitational wave detectors

abstract:
  Presented in this paper is a Markov chain Monte Carlo (MCMC) routine for
conducting coherent parameter estimation for interferometric gravitational wave
observations of an inspiral of binary compact objects using data from multiple
detectors. The MCMC technique uses data from several interferometers and infers
all nine of the parameters (ignoring spin) associated with the binary system,
including the distance to the source, the masses, and the location on the sky.
The Metropolis-algorithm utilises advanced MCMC techniques, such as importance
resampling and parallel tempering. The data is compared with time-domain
inspiral templates that are 2.5 post-Newtonian (PN) in phase and 2.0 PN in
amplitude. Our routine could be implemented as part of an inspiral detection
pipeline for a world wide network of detectors. Examples are given for
simulated signals and data as seen by the LIGO and Virgo detectors operating at
their design sensitivity.


title: Thick planar domain wall: its thin wall limit and dynamics

abstract:
  We consider a planar gravitating thick domain wall of the $\lambda \phi^4$
theory as a spacetime with finite thickness glued to two vacuum spacetimes on
each side of it. Darmois junction conditions written on the boundaries of the
thick wall with the embedding spacetimes reproduce the Israel junction
condition across the wall in the limit of infinitesimal thickness. The thick
planar domain wall located at a fixed position is then transformed to a new
coordinate system in which its dynamics can be formulated. It is shown that the
wall's core expands as if it were a thin wall. The thickness in the new
coordinates is not constant anymore and its time dependence is given.


title:
Black hole solutions of dimensionally reduced Einstein-Gauss-Bonnet
  gravity with a cosmological constant

abstract:
  We study the phase space of the spherically symmetric solutions of the system
obtained from the dimensional reduction of the six-dimensional
Einstein-Gauss-Bonnet action with a cosmological constant. We show that all the
physical solutions have anti-de Sitter asymptotic behavior.


title: The Simplification of Spinor Connection and Classical Approximation

abstract:
  The standard spinor connection in curved space-time is represented in a
compact form. In this form the calculation is complicated, and its physical
effects are concealed. In this paper, we split spinor connection into two
vectors $\Upsilon_\mu$ and $\Omega_\mu$, where $\Upsilon_\mu$ is only related
to geometrical calculations, but $\Omega_\mu$ leads to dynamical effects, which
couples with the spin of a spinor. The representation depends only on metric
but is independent of Dirac matrices, so it is valid for both Weyl spinors and
Dirac spinor. In the new form, we can clearly define classical concepts for a
spinor and then derive its complete classical dynamics. By detailed calculation
we find the classical approximation is just Newtonian second law. The dynamical
connection $\Omega_\mu$ couples with the spin of a particle with a tiny energy
in weak field, which provides location and navigation functions for a spinor.
This term may be also important to form magnetic field of a celestial star.
From the results, we find the spinor has marvelous structure and wonderful
property, and the interaction between spinor and gravity is subtle. This study
may be also helpful to clarify the relations between relativity, quantum
mechanics and classical mechanics.


title: An Electrical Spinning Particle In Einstein's Unified Field Theory

abstract:
  Previous work on exact solutions has been shown that sources need to be
appended to the field equation of Einstein's unified field theory in order to
achieve physically meaningful results,such sources can be included in a
variational formulation by Borchsenius and moffat.The resulting field equations
and conservation identities related to the theory that can be used to derive
the equations of structure and motion of a pole-dipole particle according to an
explicitly covariant approach by Dixon6.In this present paper it is shown
that,under certain conditions for the energy tensor of the spinning
particle,the equations of structure and motion in an electromagnetic field turn
out to be formly identical to those occurring in Einstein-Maxwell theory.


title: Diversity of universes created by pure gravity

abstract:
  We show that a number of problems of modern cosmology may be solved in the
framework of multidimensional gravity with high-order curvature invariants,
without invoking other fields. We use a method employing a slow-change
approximation, able to work with rather a general form of the gravitational
action, and consider Kaluza-Klein type space-times with one or several extra
factor spaces. A vast choice of effective theories suggested by the present
framework may be stressed: even if the initial Lagrangian is entirely fixed,
one obtains quite different models for different numbers, dimensions and
topologies of the extra factor spaces. As examples of problems addressed we
consider (i) explanation of the present accelerated expansion of the Universe,
with a reasonably small cosmological constant, and the problem of its fine
tuning is considered from a new point of view; (ii) the mechanism of closed
wall production in the early Universe; such walls are necessary for massive
primordial black hole formation which is an important stage in some scenarios
of cosmic structure formation; (iii) sufficient particle production rate at the
end of inflation; (iv) it is shown that our Universe may contain spatial
domains with a macroscopic size of extra dimensions. We also discuss chaotic
attractors appearing at possible nodes of the kinetic term of the effective
scalar field Lagrangian.


title: Titania-doped tantala/silica coatings for gravitational-wave detection

abstract:
  Reducing thermal noise from optical coatings is crucial to reaching the
required sensitivity in next generation interferometric gravitational-waves
detectors. Here we show that adding TiO$_2$ to Ta$_2$O$_5$ in
Ta$_2$O$_5$/SiO$_2$ coatings reduces the internal friction and in addition
present data confirming it reduces thermal noise. We also show that
TiO$_2$-doped Ta$_2$O$_5$/SiO$_2$ coatings are close to satisfying the optical
absorption requirements of second generation gravitational-wave detectors.


title:
The Synchronization of Clock Rate and the Equality of Durations Based on
  the Poincar\'{e}-Einstein-Landau Conventions

abstract:
  There are two important basic questions in the measurement of time. The first
one is how to define the simultaneity of two events occurring at two different
places. The second one is how to define the equality of two durations. The
first question has been solved by Einstein, Landau and others on the convention
that the velocity of light is isotropic and it is a constant in empty space.
But no body has answered the second question until today. In this paper, on the
same convention about the velocity of light given by Poincar\'{e}, Einstein,
Landau and others, we find the solution to the definition of the equality of
two durations. Meanwhile, we also find answer to the question about the
definition of the synchronization of rate of clocks located at different
places. 04.20.Cv, 04.20.-q


title: Numerical implementation of isolated horizon boundary conditions

abstract:
  We study the numerical implementation of a set of boundary conditions derived
from the isolated horizon formalism, and which characterize a black hole whose
horizon is in quasi-equilibrium. More precisely, we enforce these geometrical
prescriptions as inner boundary conditions on an excised sphere, in the
numerical resolution of the Conformal Thin Sandwich equations. As main results,
we firstly establish the consistency of including in the set of boundary
conditions a "constant surface gravity" prescription, interpretable as a lapse
boundary condition, and secondly we assess how the prescriptions presented
recently by Dain et al. for guaranteeing the well-posedness of the Conformal
Transverse Traceless equations with quasi-equilibrium horizon conditions extend
to the Conformal Thin Sandwich elliptic system. As a consequence of the latter
analysis, we discuss the freedom of prescribing the expansion associated with
the ingoing null normal at the horizon.


title:
The Kerr theorem, Kerr-Schild formalizm and multiparticle Kerr-Schild
  solutions

abstract:
  We consider an extended version of the Kerr theorem incorporated in the
Kerr-Schild formalism. It allows one to construct the series of exact solutions
of the Einstein-Maxwell field equations from a holomorphic generating function
$F$ of twistor variables. The exact multiparticle Kerr-Schild solutions are
obtained from generating function of the form $F=\prod_i^k F_i, $ where $F_i$
are partial generating functions for the spinning particles $ i=1...k$.
Gravitational and electromagnetic interaction of the spinning particles occurs
via the light-like singular twistor lines. As a result, each spinning particle
turns out to be `dressed' by singular pp-strings connecting it to other
particles. Physical interpretation of this solution is discussed.


title: Holographic dark energy and late cosmic acceleration

abstract:
  It has been persuasively argued that the number of the effective degrees of
freedom of a macroscopic system is proportional to its area rather than to its
volume. This entails interesting consequences for cosmology. Here we present a
model based on this "holographic principle" that accounts for the present stage
of accelerated expansion of the Universe and significantly alleviates the
coincidence problem also for non-spatially flat cosmologies. Likewise, we
comment on a recently proposed late transition to a fresh decelerated phase.


title: Multipole structure of current vectors in curved spacetime

abstract:
  A method is presented which allows the exact construction of conserved (i.e.
divergence-free) current vectors from appropriate sets of multipole moments.
Physically, such objects may be taken to represent the flux of particles or
electric charge inside some classical extended body. Several applications are
discussed. In particular, it is shown how to easily write down the class of all
smooth and spatially-bounded currents with a given total charge. This
implicitly provides restrictions on the moments arising from the smoothness of
physically reasonable vector fields. We also show that requiring all of the
moments to be constant in an appropriate sense is often impossible; likely
limiting the applicability of the Ehlers-Rudolph-Dixon notion of quasirigid
motion. A simple condition is also derived that allows currents to exist in two
different spacetimes with identical sets of multipole moments (in a natural
sense).


title: 5-dimensional special relativistic hydrodynamics and cosmology

abstract:
  5-dimensional special relativity can be considered as the 5-dimensional
extension of Carmeli's cosmological special relativity, as well as the flat
specialization of 5-d brane world theory. To this framework we add a
5-dimensional perfect fluid stress-energy tensor, and unify the equations of
perfect hydrodynamics in a single 5-dimensional tensor conservation law. This
picture permits to interpret particle production phenomena as cosmological
effects, in the spirit of open system cosmology. The source of particle
production vanishes if the fluid is isentropic. Moreover the hydrodynamical
equations can be interpreted in terms of a scale factor, giving rise to a set
of equations which simulate in a sense Friedmann cosmology.


title: Classical aspects of lightlike dimensional reduction

abstract:
  Some aspects of lightlike dimensional reduction in flat spacetime are studied
with emphasis to classical applications. Among them the Galilean transformation
of shadows induced by inertial frame changes is studied in detail by proving
that, (i) the shadow of an object has the same shape in every
orthogonal-to-light screen, (ii) if two shadows are simultaneous in an
orthogonal-to-light screen then they are simultaneous in any such screen. In
particular, the Galilean group in 2+1 dimensions is recognized as an exact
symmetry of Nature which acts on the shadows of the events instead that on the
events themselves. The group theoretical approach to lightlike dimensional
reduction is used to solve the reconstruction problem of a trajectory starting
from its acceleration history or from its projected (shadow) trajectory. The
possibility of obtaining a Galilean projected physics starting from a
Poincar\'e invariant physics is stressed through the example of relativistic
collisions. In particular, it is shown that the projection of a relativistic
collision between massless particles gives a non-relativistic collision in
which the kinetic energy is conserved.


title: Noether symmetry approach in pure gravity with variable G and Lambda

abstract:
  We find exact cosmological solutions when the Newton parameter and the
cosmological term are dynamically evolving in a renormalization-group improved
Hamiltonian approach. In our derivation we use the Noether symmetry approach,
leading to an interesting variable transformation which yields exact and
general integration of the cosmological equations. The functional dependence of
Lambda on G is determined by the method itself, therefore generalizing previous
results on symmetry principles in cosmology. We find new functional relations
between Lambda and G, jointly with power-law inflation for pure gravity.


title: On the evolution of universes in quadratic theories of gravity

abstract:
  We use a dynamical systems approach to investigate Bianchi type I and II
universes in quadratic theories of gravity. Due to the complicated nature of
the equations of motion we focus on the stability of exact solutions and find
that there exists an isotropic FRW universe acting as a past attractor. This
may indicate that there is an isotropisation mechanism at early times for these
kind of theories. We also discuss the Kasner universes, elucidate the
associated centre manifold structure, and show that there exists a set of
non-zero measure which has the Kasner solutions as a past attractor. Regarding
the late-time behaviour, the stability shows a dependence of the parameters of
the theory. We give the conditions under which the de Sitter solution is stable
and also show that for certain values of the parameters there is a possible
late-time behaviour with phantom-like behaviour. New types of anisotropic
inflationary behaviour are found which do not have counterparts in general
relativity.


title: Classical String in Curved Backgrounds

abstract:
  The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.


title:
Measurement of Gravitomagnetic and Acceleration Fields Around Rotating
  Superconductors

abstract:
  It is well known that a rotating superconductor produces a magnetic field
proportional to its angular velocity. The authors conjectured earlier, that in
addition to this so-called London moment, also a large gravitomagnetic field
should appear to explain an apparent mass increase of Niobium Cooper-pairs. A
similar field is predicted from Einstein's general relativity theory and the
presently observed amount of dark energy in the universe. An experimental
facility was designed and built to measure small acceleration fields as well as
gravitomagnetic fields in the vicinity of a fast rotating and accelerating
superconductor in order to detect this so-called gravitomagnetic London moment.
This paper summarizes the efforts and results that have been obtained so far.
Measurements with Niobium superconductors indeed show first signs which appear
to be within a factor of 2 of our theoretical prediction. Possible error
sources as well as the experimental difficulties are reviewed and discussed. If
the gravitomagnetic London moment indeed exists, acceleration fields could be
produced in a laboratory environment.


title: Extending cosmological natural selection

abstract:
  The purpose of this paper is to propose an extension to Lee Smolin's
hypothesis that our own universe belongs to a population of universes evolving
by natural selection. Smolin's hypothesis explains why the parameters of
physics possess the values we observe them to possess, but depends upon the
contingent fact that the universe is a quantum relativistic universe. It is
proposed that the prior existence of a quantum relativistic universe can itself
be explained by postulating that a process of cosmogenic drift evolves
universes towards stable ('rigid') mathematical structures.


title: Physical Diffeomorphisms in Loop Quantum Gravity

abstract:
  We investigate the action of diffeomorphisms in the context of Hamiltonian
Gravity. By considering how the diffeomorphism-invariant Hilbert space of Loop
Quantum Gravity should be constructed, we formulate a physical principle by
demanding, that the gauge-invariant Hilbert space is a completion of gauge-
(i.e. diffeomorphism-)orbits of the classical (configuration) variables,
explaining which extensions of the group of diffeomorphisms must be implemented
in the quantum theory. It turns out, that these are at least a subgroup of the
stratified analytic diffeomorphisms. Factoring these stratified diffeomorphisms
out, we obtain that the orbits of graphs under this group are just labelled by
their knot classes, which in turn form a countable set. Thus, using a physical
argument, we construct a separable Hilbert space for diffeomorphism invariant
Loop Quantum Gravity, that has a spin-knot basis, which is labelled by a
countable set consisting of the combination of knot-classes and spin quantum
numbers. It is important to notice, that this set of diffeomorphism leaves the
set of piecewise analytic edges invariant, which ensures, that one can
construct flux-operators and the associated Weyl-operators. A note on the
implications for the treatment of the Gauss- and the Hamilton-constraint of
Loop Quantum Gravity concludes our discussion.


title: The Asymptotic Safety Scenario in Quantum Gravity -- An Introduction

abstract:
  The asymptotic safety scenario in quantum gravity is reviewed, according to
which a renormalizable quantum theory of the gravitational field is feasible
which reconciles asymptotically safe couplings with unitarity. All presently
known evidence is surveyed: (a) from the 2+\eps expansion, (b) from the
perturbation theory of higher derivative gravity theories and a `large N'
expansion in the number of matter fields, (c) from the 2-Killing vector
reduction, and (d) from truncated flow equations for the effective average
action. Special emphasis is given to the role of perturbation theory as a guide
to `asymptotic safety'. Further it is argued that as a consequence of the
scenario the selfinteractions appear two-dimensional in the extreme
ultraviolet. Two appendices discuss the distinct roles of the ultraviolet
renormalization in perturbation theory and in the flow equation formalism.


title:
Numerical relativity with characteristic evolution, using six angular
  patches

abstract:
  The characteristic approach to numerical relativity is a useful tool in
evolving gravitational systems. In the past this has been implemented using two
patches of stereographic angular coordinates. In other applications, a
six-patch angular coordinate system has proved effective. Here we investigate
the use of a six-patch system in characteristic numerical relativity, by
comparing an existing two-patch implementation (using second-order finite
differencing throughout) with a new six-patch implementation (using either
second- or fourth-order finite differencing for the angular derivatives). We
compare these different codes by monitoring the Einstein constraint equations,
numerically evaluated independently from the evolution. We find that, compared
to the (second-order) two-patch code at equivalent resolutions, the errors of
the second-order six-patch code are smaller by a factor of about 2, and the
errors of the fourth-order six-patch code are smaller by a factor of nearly 50.


title: Entropy of quantum-corrected black holes

abstract:
  The approximate renormalized one-loop effective action of the quantized
massive scalar, spinor and vector field in a large mass limit, i.e., the lowest
order of the DeWitt-Schwinger expansion involves the coincidence limit of the
Hadamard-DeWitt coefficient a3. Building on this and using Wald's approach we
shall construct the general expression describing entropy of the
spherically-symmetric static black hole being the solution of the
semi-classical field equations. For the concrete case of the quantum-corrected
Reissner-Nordstrom black hole this result coincides, as expected, with the
entropy obtained by integration of the first law of black hole thermodynamics
with a suitable choice of the integration constant. The case of the extremal
quantum corrected black hole is briefly considered.


title: Randall-Sundrum with Kalb-Ramond field: return of the hierarchy problem?

abstract:
  We show that when the antisymmetric Kalb-Ramond field is included in the
Randall-Sundrum scenario, although the hierarchy problem can be solved, it
requires an extreme fine tuning of the Kalb-Ramond field (about 1 part in
$10^{62}$). We interpret this as the return of the problem in disguise.
Further, we show that the Kalb-Ramond field induces a small negative
cosmological constant on the visible brane.


title: Entanglement as a source of black hole entropy

abstract:
  We review aspects of black hole thermodynamics, and show how entanglement of
a quantum field between the inside and outside of a horizon can account for the
area-proportionality of black hole entropy, provided the field is in its ground
state. We show that the result continues to hold for Coherent States and
Squeezed States, while for Excited States, the entropy scales as a power of
area less than unity. We also identify location of the degrees of freedom which
give rise to the above entropy.


title:
Uniform discretizations: a new approach for the quantization of totally
  constrained systems

abstract:
  We discuss in detail the uniform discretization approach to the quantization
of totally constrained theories. This approach allows to construct the
continuum theory of interest as a well defined, controlled, limit of well
behaved discrete theories. We work out several finite dimensional examples that
exhibit behaviors expected to be of importance in the quantization of gravity.
We also work out the case of BF theory. At the time of quantization, one can
take two points of view. The technique can be used to define, upon taking the
continuum limit, the space of physical states of the continuum constrained
theory of interest. In particular we show in models that it agrees with the
group averaging procedure when the latter exists. The technique can also be
used to compute, at the discrete level, conditional probabilities and the
introduction of a relational time. Upon taking the continuum limit one can show
that one reproduces results obtained by the use of evolving constants, and
therefore recover all physical predictions of the continuum theory. This second
point of view can also be used as a paradigm to deal with cases where the
continuum limit does not exist. There one would have discrete theories that at
least at certain scales reproduce the semiclassical properties of the theory of
interest. In this way the approach can be viewed as a generalization of the
Dirac quantization procedure that can handle situations where the latter fails.


title: New Insights into Uniformly Accelerated Detector in a Quantum Field

abstract:
  We obtained an exact solution for a uniformly accelerated Unruh-DeWitt
detector interacting with a massless scalar field in (3+1) dimensions which
enables us to study the entire evolution of the total system, from the initial
transient to late-time steady state. We find that the Unruh effect as derived
from time-dependent perturbation theory is valid only in the transient stage
and is totally invalid for cases with proper acceleration smaller than the
damping constant. We also found that, unlike in (1+1)D results, the (3+1)D
uniformly accelerated Unruh-DeWitt detector in a steady state does emit a
positive radiated power of quantum nature at late-times, but it is not
connected to the thermal radiance experienced by the detector in the Unruh
effect proper.


title: Graviton mediated photon-photon scattering in general relativity

abstract:
  In this paper we consider photon-photon scattering due to self-induced
gravitational perturbations on a Minkowski background. We focus on four-wave
interaction between plane waves with weakly space and time dependent
amplitudes, since interaction involving a fewer number of waves is excluded by
energy-momentum conservation. The Einstein-Maxwell system is solved
perturbatively to third order in the field amplitudes and the coupling
coefficients are found for arbitrary polarizations in the center of mass
system. Comparisons with calculations based on quantum field theoretical
methods are made, and the small discrepances are explained.


title: Nieh-Yan Invariant and Fermions in Ashtekar-Barbero-Immirzi Formalism

abstract:
  In order to introduce an interaction between gravity and fermions in the
Ashtekar-Barbero-Immirzi formalism without affecting classical dynamics a
non-minimal term is necessary. The non-minimal term together with the Holst
modification to the Hilbert-Palatini action reconstruct the Nieh-Yan invariant.
As a consequence the Immirzi parameter, differently from the minimal coupling
approach, does not affect the classical dynamics, which is described by the
Einstein-Cartan action.


title: Modified Ostrogradski formulation of field theory

abstract:
  We present a method for the Hamiltonian formulation of field theories that
are based on Lagrangians containing second derivatives. The new feature of our
formalism is that all four partial derivatives of the field variables are
initially considered as independent fields, in contrast to the conventional
Ostrogradski method, where only the velocity is turned into an independent
field variable. The consistency of the formalism is demonstrated by simple
unconstrained and constrained second order scalar field theories. Its
application to General Relativity is briefly outlined.


title: A Solar System Test of Mach's Principle with Gravimetric Data

abstract:
  We present a new test for a possible Mach-Sciama dependence of the
Gravitational constant G. According to Ernst Mach (1838-1916), the
gravitational interaction depends on the distribution of masses in the
universe. A corresponding hypothesis of Sciama (1953) on the gravitational
constant, $c^2/G = \sum m_i/r_i$, can be tested since the elliptic earth orbit
should then cause minute annual variations in G. The test is performed by
analyzing the gravity signals of a network of superconducting gravimeters (SG)
which reach a precision of $10^{-10} m/s^2$. After reducing the signal by
modelling tidal, meteorologic and geophysical effects, no significant evidence
for the above dependence is found.


title: Is the pioneer anomaly a counter example to the dark matter hypothesis?

abstract:
  The Hubble law is extended to massive particles based on the de Broglie
wavelength. Due to the expansion of the universe the wavelength of an unbound
particle would increase according to its cosmological redshift. Based on the
navigation anomalies of the Pioneer 10 & 11 spacecraft it is postulated that an
unbound massive particle has a cosmological redshift z = (c / v_0) H_0 t, where
c is the speed of light in vacuum, v_0 is the initial velocity of the particle,
H_0 is Hubble's constant and t is the duration of time that the particle has
been unbound. The increase in wavelength of the particle corresponds to a
decrease in its speed by delta_v = - c H_0 t. Furthermore, it is hypothesized
that the solar system has escaped the gravity of the Galaxy as evidenced by its
orbital speed and radial distance and by the visible mass within the solar
system radius. This means that spacecraft which become unbound to the solar
system would also be galactically unbound and subject to the Hubble law. This
hypothesis and the extended Hubble law may explain the anomalous acceleration
found to be acting upon the unbound Pioneer 10 & 11 spacecraft. Thus, the
Pioneer anomaly may be a counter example to the dark matter hypothesis.
  Because photons have a speed which make them unbound to the Galaxy, it is
predicted that the navigation beam in open space would undergo a cosmological
redshift in its frequency which would be detectable with modern clocks.


title: Geometric Flows and Black Holes

abstract:
  Motivated by the newest progress in geometric flows both in mathematics and
physics, we apply the geometric evolution equation to study some black-hole
problems. Our results show that, under certain conditions, the geometric
evolution equations satisfy the Birkhoff theorem, and surprisingly, in the case
of spherically symmetric metric field, the Einstein equation, the Ricci flow,
and the hyperbolic geometric flow in vacuum spacetime have the same black-hole
solutions, especially in the case of $\Lambda=0$, they all have the
Schwarzschild solution. In addition, these results can be generalized to a kind
of more general geometric flow.


title:
On linear electromagnetic constitutive laws that define almost-complex
  structures

abstract:
  It is shown that not all linear electromagnetic constitutive laws will define
almost-complex structure on the bundle of 2-forms on the spacetime manifold
when composed with the Poincare duality isomorphism, but only a restricted
class of them that includes linear spatially isotropic and some bi-isotropic
laws. Although this does not trivialize the formulation of the basic equations
equations of pre-metric electromagnetism, it does affect their reduction to
metric electromagnetism by its effect on the types of media that are reducible,
and possibly its effect on the way that such media support the propagation of
electromagnetic waves.


title:
Isolated, slowly evolving, and dynamical trapping horizons: geometry and
  mechanics from surface deformations

abstract:
  We study the geometry and dynamics of both isolated and dynamical trapping
horizons by considering the allowed variations of their foliating two-surfaces.
This provides a common framework that may be used to consider both their
possible evolutions and their deformations as well as derive the well-known
flux laws. Using this framework, we unify much of what is already known about
these objects as well as derive some new results. In particular we characterize
and study the "almost-isolated" trapping horizons known as slowly evolving
horizons. It is for these horizons that a dynamical first law holds and this is
analogous and closely related to the Hawking-Hartle formula for event horizons.


title: Gravitational Perfect Fluid Collapse With Cosmological Constant

abstract:
  In this paper, the effect of a positive cosmological constant on spherically
symmetric collapse with perfect fluid has been investigated. The matching
conditions between static exterior and non-static interior spacetimes are given
in the presence of a cosmological constant. We also study the apparent horizons
and their physical significance. It is concluded that the cosmological constant
slows down the collapse of matter and hence limit the size of the black hole.
This analysis gives the generalization of the dust case to the perfect fluid.
We recover the results of the dust case for $p=0$.


title: Does PIONEER measure local spacetime expansion?

abstract:
  There is a longstanding mystery connected with the radiotracking of distant
interplanetary spaceprobes like ULYSSES, Galileo and especially the two NASA
probes PIONEER 10 and 11. Comparing radiosignals outgoing from the earth to the
probe and ingoing again from the probes do show anomalous frequency shifts
which up to now have been explained as caused by anomalous non-Newtonian
decelerations of these probes recognizable at solar distances beyond 5 AU. In
this paper we study cosmological conditions for the transfer of radiosignals
between the Earth and these distant probes. Applying general relativity, we
derive both the geodetic deceleration as well as the cosmological redshift and
compare the resulting frequency shift with the observed effect. We find that
anomalous decelerations do act on these probes which are of cosmological
nature, but these are, as expected from standard cosmology, much too low to
explain the observed effect. In contrast, the cosmological redshift of
radiophotons suffered during the itinerary to the probe and back due to the
local spacetime expansion reveals a frequency shift which by its magnitude is
in surprisingly good agreement with the long registered phenomenon, and thus
explains the phenomenon well, except for the sign of the effect. Problems of a
local Hubble expansion may give the reason for this.


title: Can (dG/dt)/G Bound the Local Cosmological Dynamics?

abstract:
  It is argued that constraints on time variation of the gravitational constant
(dG/dt)/G, e.g. derived from the lunar laser ranging, cannot be immediately
applied to restrict the cosmological expansion at planetary scales, as it was
done by Williams, Turyshev, and Boggs [PRL, 93, 261101 (2004),
arXiv:gr-qc/0411113].


title:
On the geometrization of the electro-magnetic interaction for a spinning
  particle

abstract:
  We outline that, in a Kaluza-Klein framework, not only the electro-magnetic
field can be geometrized, but also the dynamics of a charged spinning particle
can be inferred from the motion in a 5-dimensional space-time. This result is
achieved by the dimensional splitting of Papapetrou equations and by proper
identifications of 4-dimensional quantities.


title: The electro-weak model as a phenomenological issue of multidimensions

abstract:
  We consider Kaluza-Klein theories as candidates for the unification of
gravity and the electro-weak model. In particular, we fix how to reproduce
geometrically the interaction between fermions and gauge bosons, in the low
energy limit.


title:
On Cosmological Spacetime Structure and Symmetry: Manifold as a Lie
  Group, Spinor Structure and Symmetry Group, Minkowski Metric, and
  Unnecessariness of Double-Valued Representations

abstract:
  It is shown that cosmological spacetime manifold has the structure of a Lie
group and a spinor space. This leads naturally to the Minkowski metric on
tangent spaces and the Lorentzian metric on the manifold and makes it possible
to dispense with double-valued representations.


title: Relativistic Gravitational Collapse of a Cylindrical Shell of Dust

abstract:
  The gravitational collapse of a thick cylindrical shell of dust matter is
investigated. It is found that a spacetime singularity forms on the symmetry
axis and that it is necessarily naked, i.e., observable in principle. We
propose a physically reasonable boundary condition at this naked singularity to
construct the solution including its causal future. This boundary condition
enables us to construct the unique continuation of spacetime beyond the naked
singularity and ensures that the dust shell passes through the naked
singularity. When the cylindrical shell leaves its symmetry axis away, the
naked singularity disappears, and regularity is recovered. We construct
numerical solutions with this feature. This result implies that the gravity
produced by a thick cylindrical shell of dust is too weak to bind the shell
even if it engenders the formation of a curvature singularity which is so
strong as to satisfy the limiting focusing condition. For this reason, this
naked singularity is very weak in the extended spacetime; the metric tensor is
$C^{1-}$ even at the naked singularity, and the extended spacetime is complete
for almost all geodesics. This feature is also seen for singular hypersurfaces.
Such an extended spacetime can be regarded as phenomenological in the sense
that it is valid if the relevant microphysics length scale is sufficiently
small compared to the scale of interest.


title:
From polytropic to barotropic perfect fluids in general-relativistic
  hydrodynamics

abstract:
  Two general-relativistic hydrodynamical models are considered: a model of
self-gravitating static configurations of perfect fluid and a model of steady
accretion of fluid onto a black hole. We generalise analytic results obtained
for the original polytropic versions of these models onto a wider class of
barotropic equations of state. The knowledge about the polytropic solutions is
used to establish bounds on certain characteristic quantities appearing in both
cases.


title:
The dependence of test-mass thermal noises on beam shape in
  gravitational-wave interferometers

abstract:
  In second-generation, ground-based interferometric gravitational-wave
detectors such as Advanced LIGO, the dominant noise at frequencies $f \sim 40$
Hz to $\sim 200$ Hz is expected to be due to thermal fluctuations in the
mirrors' substrates and coatings which induce random fluctuations in the shape
of the mirror face. The laser-light beam averages over these fluctuations; the
larger the beam and the flatter its light-power distribution, the better the
averaging and the lower the resulting thermal noise. In semi-infinite mirrors,
scaling laws for the influence of beam shape on the four dominant types of
thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and
substrate thermoelastic) have been suggested by various researchers and derived
with varying degrees of rigour. Because these scaling laws are important tools
for current research on optimizing the beam shape, it is important to firm up
our understanding of them. This paper (1) gives a summary of the prior work and
of gaps in the prior analyses, (2) gives a unified and rigorous derivation of
all four scaling laws, and (3) explores, relying on work by J. Agresti,
deviations from the scaling laws due to finite mirror size.


title:
Breakdown of self-similar evolution in homogeneous perfect fluid
  collapse

abstract:
  The stability analysis of self-similar solutions is an important approach to
confirm whether they act as an attractor in general non-self-similar
gravitational collapse. Assuming that the collapsing matter is a perfect fluid
with the equation of state $P=\alpha\rho$, we study spherically symmetric
non-self-similar perturbations in homogeneous self-similar collapse described
by the flat Friedmann solution. In the low pressure approximation $\alpha \ll
1$, we analytically derive an infinite set of the normal modes and their growth
(or decay) rate. The existence of one unstable normal mode is found to conclude
that the self-similar behavior in homogeneous collapse of a sufficiently low
pressure perfect fluid must terminate and a certain inhomogeneous density
profile can develop with the lapse of time.


title: Cosmological Effects of Nonlinear Electrodynamics

abstract:
  It will be shown that a given realization of nonlinear electrodynamics, used
as source of Einstein's equations, generates a cosmological model with
interesting features, namely a phase of current cosmic acceleration, and the
absence of an initial singularity, thus pointing to a way to solve two
important problems in cosmology.


title:
Vanishing Cosmological Constant in Modified Gauss-Bonnet Gravity with
  Conformal Anomaly

abstract:
  We consider dark energy cosmology in a de Sitter universe filled with quantum
conformal matter. Our model represents a Gauss-Bonnet model of gravity with
contributions from quantum effects. To the General Relativity action an
arbitrary function of the GB invariant, f(G), is added, and taking into account
quantum effects from matter the cosmological constant is studied. For the
considered model the conditions for a vanishing cosmological constant are
considered. Creation of a de Sitter universe by quantum effects in a GB
modified gravity is discussed.


title:
The constraint equations for the Einstein-scalar field system on compact
  manifolds

abstract:
  We study the constraint equations for the Einstein-scalar field system on
compact manifolds. Using the conformal method we reformulate these equations as
a determined system of nonlinear partial differential equations. By introducing
a new conformal invariant, which is sensitive to the presence of the initial
data for the scalar field, we are able to divide the set of free conformal data
into subclasses depending on the possible signs for the coefficients of terms
in the resulting Einstein-scalar field Lichnerowicz equation. For many of these
subclasses we determine whether or not a solution exists. In contrast to other
well studied field theories, there are certain cases, depending on the mean
curvature and the potential of the scalar field, for which we are unable to
resolve the question of existence of a solution. We consider this system in
such generality so as to include the vacuum constraint equations with an
arbitrary cosmological constant, the Yamabe equation and even (all cases of)
the prescribed scalar curvature problem as special cases.


title:
Detecting extreme mass ratio inspiral events in LISA data using the
  Hierarchical Algorithm for Clusters and Ridges (HACR)

abstract:
  One of the most exciting prospects for the Laser Interferometer Space Antenna
(LISA) is the detection of gravitational waves from the inspirals of
stellar-mass compact objects into supermassive black holes. Detection of these
sources is an extremely challenging computational problem due to the large
parameter space and low amplitude of the signals. However, recent work has
suggested that the nearest extreme mass ratio inspiral (EMRI) events will be
sufficiently loud that they might be detected using computationally cheap,
template-free techniques, such as a time-frequency analysis. In this paper, we
examine a particular time-frequency algorithm, the Hierarchical Algorithm for
Clusters and Ridges (HACR). This algorithm searches for clusters in a power map
and uses the properties of those clusters to identify signals in the data. We
find that HACR applied to the raw spectrogram performs poorly, but when the
data is binned during the construction of the spectrogram, the algorithm can
detect typical EMRI events at distances of up to $\sim2.6$Gpc. This is a little
further than the simple Excess Power method that has been considered
previously. We discuss the HACR algorithm, including tuning for single and
multiple sources, and illustrate its performance for detection of typical EMRI
events, and other likely LISA sources, such as white dwarf binaries and
supermassive black hole mergers. We also discuss how HACR cluster properties
could be used for parameter extraction.


title: Testing General Relativity with Atom Interferometry

abstract:
  The unprecedented precision of atom interferometry will soon lead to
laboratory tests of general relativity to levels that will rival or exceed
those reached by astrophysical observations. We propose such an experiment that
will initially test the equivalence principle to 1 part in 10^15 (300 times
better than the current limit), and 1 part in 10^17 in the future. It will also
probe general relativistic effects--such as the non-linear three-graviton
coupling, the gravity of an atom's kinetic energy, and the falling of light--to
several decimals. Further, in contrast to astrophysical observations,
laboratory tests can isolate these effects via their different functional
dependence on experimental variables.

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


title: Gravity coupled to a scalar field in extra dimensions

abstract:
  In d+1 dimensions we solve the equations of motion for the case of gravity
minimally or conformally coupled to a scalar field. For the minimally coupled
system the equations can either be solved directly or by transforming vacuum
solutions, as shown before in 3+1 dimensions by Buchdahl. In d+1 dimensions the
solutions have been previously found directly by Xanthopoulos and Zannias. Here
we first rederive these earlier results, and then extend Buchdahl's method of
transforming vacuum solutions to d+1 dimensions. We also review the conformal
coupling case, in which d+1 dimensional solutions can be found by extending
Bekenstein's method of conformal transformation of the minimal coupling
solution. Combining the extended versions of Buchdahl transformations and
Bekenstein transformations we can in arbitrary dimensions always generate
solutions of both the minimal and the conformal equations from known vacuum
solutions.


title: Absolute Being vs Relative Becoming

abstract:
  Contrary to our immediate and vivid sensation of past, present, and future as
continually shifting non-relational modalities, time remains as tenseless and
relational as space in all of the established theories of fundamental physics.
Here an empirically adequate generalized theory of the inertial structure is
discussed in which proper time is causally compelled to be tensed within both
spacetime and dynamics. This is accomplished by introducing the inverse of the
Planck time at the conjunction of special relativity and Hamiltonian mechanics,
which necessitates energies and momenta to be invariantly bounded from above,
and lengths and durations similarly bounded from below, by their respective
Planck scale values. The resulting theory abhors any form of preferred
structure, and yet captures the transience of now along timelike worldlines by
causally necessitating a genuinely becoming universe. This is quite unlike the
scenario in Minkowski spacetime, which is prone to a block universe
interpretation. The minute deviations from the special relativistic effects
such as dispersion relations and Doppler shifts predicted by the generalized
theory remain quadratically suppressed by the Planck energy, but may
nevertheless be testable in the near future, for example via observations of
oscillating flavor ratios of ultrahigh energy cosmic neutrinos, or of altering
pulse rates of extreme energy binary pulsars.