title:
Metric gravity theories and cosmology. I. Physical interpretation and
  viability

abstract:
  We critically review some concepts underlying current applications of gravity
theories with Lagrangians depending on the full Riemann tensor to cosmology. We
argue that it is impossible to reconstruct the underlying Lagrangian from the
observational data: the Robertson-Walker spacetime is so simple and "flexible"
that any cosmic evolution may be fitted by infinite number of Lagrangians.
Confrontation of a solution with the astronomical data is obstructed by the
existence of many frames of dynamical variables and the fact that initial data
for the gravitational triplet depend on which frame is minimally coupled to
ordinary matter. Prior to any application it is necessary to establish physical
contents and viability of a given gravity theory.


title: Stable Isotropic Cosmological Singularities in Quadratic Gravity

abstract:
  We show that, in quadratic lagrangian theories of gravity, isotropic
cosmological singularities are stable to the presence of small scalar, vector
and tensor inhomogeneities. Unlike in general relativity, a particular exact
isotropic solution is shown to be the stable attractor on approach to the
initial cosmological singularity. This solution is also known to act as an
attractor in Bianchi universes of types I, II and IX, and the results of this
paper reinforce the hypothesis that small inhomogeneous and anisotropic
perturbations of this attractor form part of the general cosmological solution
to the field equations of quadratic gravity. Implications for the existence of
a 'gravitational entropy' are also discussed.


title:
Gravitational Waves from Nonlinear Couplings of Radial and Polar
  Nonradial Modes in Relativistic Stars

abstract:
  The post-bounce oscillations of newly-born relativistic stars are expected to
lead to gravitational-wave emission through the excitation of nonradial
oscillation modes. At the same time, the star is oscillating in its radial
modes, with a central density variation that can reach several percent.
Nonlinear couplings between radial oscillations and polar nonradial modes lead
to the appearance of combination frequencies (sums and differences of the
linear mode frequencies). We study such combination frequencies using a
gauge-invariant perturbative formalism, which includes bilinear coupling terms
between different oscillation modes. For typical values of the energy stored in
each mode we find that gravitational waves emitted at combination frequencies
could become detectable in galactic core-collapse supernovae with advanced
interferometric or wide-band resonant detectors.


title:
"Millikan oil drops" as quantum transducers between electromagnetic and
  gravitational radiation

abstract:
  Pairs of Planck-mass-scale drops of superfluid helium coated by electrons
(i.e., "Millikan oil drops"), when levitated in the presence of strong magnetic
fields and at low temperatures, can be efficient quantum transducers between
electromagnetic (EM) and gravitational (GR) radiation. A Hertz-like experiment,
in which EM waves are converted at the source into GR waves, and then
back-converted at the receiver from GR waves back into EM waves, should be
practical to perform. This would open up observations of the gravity-wave
analog of the Cosmic Microwave Background from the extremely early Big Bang,
and also communications directly through the interior of the Earth.


title: Asymptotic Behavior of Spherically Symmetric Marginally Trapped Tubes

abstract:
  We give conditions on a general stress-energy tensor T_{\alpha \beta} in a
spherically symmetric black hole spacetime which are sufficient to guarantee
that the black hole will contain a (spherically symmetric) marginally trapped
tube which is eventually achronal, connected, and asymptotic to the event
horizon. Price law decay per se is not required for this asymptotic result, and
in this general setting, such decay only implies that the marginally trapped
tube has finite length with respect to the induced metric. We do, however,
impose a smallness condition (B1) which one may obtain in practice by imposing
decay on the T_{vv} component of the stress-energy tensor. We give two
applications of the theorem to self-gravitating Higgs field spacetimes, one
using weak Price law decay, the other certain strong smallness and monotonicity
assumptions.


title: Tikekar superdense stars in electric fields

abstract:
  We present exact solutions to the Einstein-Maxwell system of equations with a
specified form of the electric field intensity by assuming that the
hypersurface \{$t$ = constant\} are spheroidal. The solution of the
Einstein-Maxwell system is reduced to a recurrence relation with variable
rational coefficients which can be solved in general using mathematical
induction. New classes of solutions of linearly independent functions are
obtained by restricting the spheroidal parameter $K$ and the electric field
intensity parameter $\alpha$. Consequently it is possible to find exact
solutions in terms of elementary functions, namely polynomials and algebraic
functions. Our result contains models found previously including the superdense
Tikekar neutron star model [R. Tikekar, \emph{J. Math. Phys.} \textbf{31}, 2454
(1990)] when $K=-7$ and $\alpha=0$. Our class of charged spheroidal models
generalise the uncharged isotropic Maharaj and Leach solutions
  [S. D. Maharaj and P. G. L. Leach, \emph{J. Math. Phys.} \textbf{37}, 430
(1996)]. In particular, we find an explicit relationship directly relating the
spheroidal parameter $K$ to the electromagnetic field.


title: Lorentz violation and the speed of gravitational waves in brane-worlds

abstract:
  Lorentz violation in a brane-world scenario is presented and used to obtain a
relationship between the speed of gravitational waves in the bulk and that on
the brane. Lorentz violating effects would manifest themselves in gravitational
waves travelling with a greater speed in the bulk than on the brane and this
effect is independent of the signature of the extra dimension.


title:
Response to ``Comment on `Primordial magnetic seed field amplification
  by gravitational waves' "

abstract:
  Here we respond to the comment by Tsagas (gr-qc/0503042) on our paper
gr-qc/0503006. We show that the results in that comment are flawed and cannot
be used for drawing conclusion about the nature of magnetic field amplification
by gravitational waves, and give further support that the results of
gr-qc/0503006 are correct.


title:
Landau-Lifshitz and Weinberg Energy-Momentum Complexes for 2+1
  Dimensional Black Hole Solutions

abstract:
  The aim of this paper is to evaluate the energy distribution of some 2+1
black hole solutions applying the Landau-Lifshitz and Weinberg definitions. The
metrics under consideration describe the charged black hole, the solution
coupling to a static scalar field and the static and circularly symmetric exact
solution of the Einstein-massless scalar equation. Further, we compare the
expressions for energy with those obtained using the Einstein and Moller
prescriptions and give a discussion of the results.


title: Reducing orbital eccentricity in binary black hole simulations

abstract:
  Binary black hole simulations starting from quasi-circular (i.e., zero radial
velocity) initial data have orbits with small but non-zero orbital
eccentricities. In this paper the quasi-equilibrium initial-data method is
extended to allow non-zero radial velocities to be specified in binary black
hole initial data. New low-eccentricity initial data are obtained by adjusting
the orbital frequency and radial velocities to minimize the orbital
eccentricity, and the resulting ($\sim 5$ orbit) evolutions are compared with
those of quasi-circular initial data. Evolutions of the quasi-circular data
clearly show eccentric orbits, with eccentricity that decays over time. The
precise decay rate depends on the definition of eccentricity; if defined in
terms of variations in the orbital frequency, the decay rate agrees well with
the prediction of Peters (1964). The gravitational waveforms, which contain
$\sim 8$ cycles in the dominant l=m=2 mode, are largely unaffected by the
eccentricity of the quasi-circular initial data. The overlap between the
dominant mode in the quasi-circular evolution and the same mode in the
low-eccentricity evolution is about 0.99.


title: Black Hole Thermodynamics from Euclidean Horizon Constraints

abstract:
  To explain black hole thermodynamics in quantum gravity, one must introduce
constraints to ensure that a black hole is actually present. I show that for a
large class of black holes, such ``horizon constraints'' allow the use of
conformal field theory techniques to compute the density of states, reproducing
the Bekenstein-Hawking entropy in a nearly model-independent manner. One
standard string theory approach to black hole entropy arises as a special case,
lending support to the claim that the mechanism may be ``universal.'' I argue
that the relevant degrees of freedom are Goldstone-boson-like excitations
arising from the weak breaking of symmetry by the constraints.


title:
Stabilization of internal space in noncommutative multidimensional
  cosmology

abstract:
  We study the cosmological aspects of a noncommutative, multidimensional
universe where the matter source is assumed to be a scalar field which does not
commute with the internal scale factor. We show that such noncommutativity
results in the internal dimensions being stabilized


title: Energy in an Expanding Universe in the Teleparallel Geometry

abstract:
  The main purpose of this paper is to explicitly verify the consistency of the
energy-momentum and angular momentum tensor of the gravitational field
established in the Hamiltonian structure of the Teleparallel Equivalent of
General Relativity (TEGR). In order to reach these objectives, we obtained the
total energy and angular momentum (matter plus gravitational field) of the
closed universe of the Friedmann-Lemaitre-Robertson-Walker (FLRW). The result
is compared with those obtained from the pseudotensors of Einstein and
Landau-Lifshitz. We also applied the field equations (TEGR) in an expanding
FLRW universe. Considering the stress energy-momentum tensor for a perfect
fluid, we found a teleparallel equivalent of Friedmann equations of General
Relativity (GR).


title: Holographic dark energy in Brans-Dicke theory

abstract:
  In this Letter it is shown that when the holographic dark energy is combined
with the Brans-Dicke field equations the transition from decelerated to
accelerated expansion of the Universe can be more easily accounted for than
when resort to the Einstein field equations is made. Likewise, the coincidence
problem of late cosmic acceleration gets more readily softened.


title: The Bousso entropy bound in selfgravitating gas of massless particles

abstract:
  The Bousso entropy bound is investigated in a static spherically symmetric
spacetime filled with an ideal gas of massless bosons or fermions. Especially
lightsheets generated by spheres are considered. Statistical description of the
gas is given. Conditions under which the Bousso bound can be violated are
discussed and it is shown that a possible violating region cannot be
arbitrarily large and it is contained inside a sphere of unit Planck radius if
number of independent polarization states $g_s$ is small enough. It is also
shown that central temperature must exceed the Planck temperature to get a
violation of the Bousso bound for $g_s$ not too large.


title: Scalar Polynomial Singularities in Power-Law Spacetimes

abstract:
  Recently, Helliwell and Konkowski (\texttt{gr-qc/0701149}) have examined the
quantum "healing" of some classical singularities in certain power-law
spacetimes. Here I further examine classical properties of these spacetimes and
show that some of them contain naked strong curvature singularities.


title: Waveless Approximation Theories of Gravity

abstract:
  The analysis of a general multibody physical system governed by Einstein's
equations in quite difficult, even if numerical methods (on a computer) are
used. Some of the difficulties -- many coupled degrees of freedom, dynamic
instability -- are associated with the presence of gravitational waves. We have
developed a number of ``waveless approximation theories'' (WAT) which repress
the gravitational radiation and thereby simplify the analysis. The matter,
according to these theories, evolves dynamically. The gravitational field,
however, is determined at each time step by a set of elliptic equations with
matter sources. There is reason to believe that for many physical systems, the
WAT-generated system evolution is a very accurate approximation to that
generated by the full Einstein theory.


title:
The infinite red-shift surfaces of the Kerr and Kerr-Newman solutions of
  the Einstein field equations

abstract:
  In contrast to the Schwarzschild solution, the infinite red-shift surfaces
and null surfaces of the Kerr solution to the axially-symmetric Einstein field
equations are distinct. Some three-dimensional depictions of these surfaces are
presented here for observers following the time-like Killing vector of the Kerr
and Kerr-Newman solutions. Some similarities of the latter to the
Reissner-Nordstrom solution are also discussed. In the case of the Kerr
solution, the inner infinite red-shift surface terminates at the ring
singularity. This is not the case for the Kerr-Newman solution where the
infinite red-shift surface and the ring singularity have no points in common.
The presence of charge severs the relation between the singularity and the
infinite red-shift surface. This paper is also intended to fill a void in the
literature where few, if any, adequate representations of the infinite
red-shift surfaces and their relation to the singularity and horizons exist.


title: Nonlinear connections and 1+3 splittings of spacetime

abstract:
  The analogy between 1+3 splittings of the spacetime tangent bundle and the
splitting of the tangent bundle to the bundle of linear frames into vertical
and horizontal sub-bundles is described from the unifying standpoint of the
geometry of foliations. The physical nature of the line field on spacetime that
plays the role of vertical sub-bundle is discussed in some detail. The notion
that the complementary spatial bundle is most fundamentally a representation of
the normal bundle to the foliation of spacetime by the integral curves of the
line field is proposed, such that the geometry of space becomes the transverse
geometry of the flow and the integration of the spatial bundle into proper time
simultaneity hypersurfaces becomes a secondary issue to the geometry of space
as the geometry of the leaf space of the foliation. The concept of an adapted
convected frame field is introduced as a means of locally representing the
transversal geometry of a flow in terms of the information that is contained in
the flow and its derivatives, and some discussion is given to the role of the
Bott connection.


title: On the genericity of spacetime singularities

abstract:
  We consider here the genericity aspects of spacetime singularities that occur
in cosmology and in gravitational collapse. The singularity theorems (that
predict the occurrence of singularities in general relativity) allow the
singularities of gravitational collapse to be either visible to external
observers or covered by an event horizon of gravity. It is shown that the
visible singularities that develop as final states of spherical collapse are
generic. Some consequences of this fact are discussed.


title: Uniqueness of the Fock quantization of the Gowdy $T^3$ model

abstract:
  After its reduction by a gauge-fixing procedure, the family of linearly
polarized Gowdy $T^3$ cosmologies admit a scalar field description whose
evolution is governed by a Klein-Gordon type equation in a flat background in
1+1 dimensions with the spatial topology of $S^1$, though in the presence of a
time-dependent potential. The model is still subject to a homogeneous
constraint, which generates $S^1$-translations. Recently, a Fock quantization
of this scalar field was introduced and shown to be unique under the
requirements of unitarity of the dynamics and invariance under the gauge group
of $S^1$-translations. In this work, we extend and complete this uniqueness
result by considering other possible scalar field descriptions, resulting from
reasonable field reparameterizations of the induced metric of the reduced
model. In the reduced phase space, these alternate descriptions can be obtained
by means of a time-dependent scaling of the field, the inverse scaling of its
canonical momentum, and the possible addition of a time-dependent, linear
contribution of the field to this momentum. Demanding again unitarity of the
field dynamics and invariance under the gauge group, we prove that the
alternate canonical pairs of fieldlike variables admit a Fock representation if
and only if the scaling of the field is constant in time. In this case, there
exists essentially a unique Fock representation, provided by the quantization
constructed by Corichi, Cortez, and Mena Marugan. In particular, our analysis
shows that the scalar field description proposed by Pierri does not admit a
Fock quantization with the above unitarity and invariance properties.


title: Is it possible to detect gravitational waves with atom interferometers?

abstract:
  We investigate the possibility to use atom interferometers to detect
gravitational waves. We discuss the interaction of gravitational waves with an
atom interferometer and analyze possible schemes.


title:
Reply to "Comment on 'Quantization of FRW spacetimes in the presence of
  a cosmological constant and radiation'"

abstract:
  The Comment by Amore {\it et al.} [gr-qc/0611029] contains a valid criticism
of the numerical precision of the results reported in a recent paper of ours
[Phys. Rev. D {\bf 73}, 044022 (2006)], as well as fresh ideas on how to
characterize a quantum cosmological singularity. However, we argue that,
contrary to what is suggested in the Comment, the quantum cosmological models
we studied show hardly any sign of singular behavior.


title:
Comment on "The gravitomagnetic influence on gyroscopes and on the lunar
  orbit"

abstract:
  Analysis of the gauge residual freedom in the relativistic theory of lunar
motion demonstrates that lunar laser ranging (LLR) is not currently capable to
detect gravitomagnetic effects.


title: Supersymmetric 3D gravity with torsion: asymptotic symmetries

abstract:
  We study the structure of asymptotic symmetries in N=1+1 supersymmetric
extension of three-dimensional gravity with torsion. Using a natural
generalization of the bosonic anti-de Sitter asymptotic conditions, we show
that the asymptotic Poisson bracket algebra of the canonical generators has the
form of two independent super-Virasoro algebras with different central charges.


title:
An analysis of the shear dynamics in Bianchi I cosmologies with
  $R^n$-gravity

abstract:
  We consider the case of $R^n$-gravity and perform a detailed analysis of the
dynamics in Bianchi I cosmologies which exhibit {\it local rotational symmetry}
(LRS). We find exact solutions and study their behaviour and stability in terms
of the values of the parameter $n$. In particular, we found a set of cosmic
histories in which the universe is initially isotropic, then develops shear
anisotropies which approaches a constant value.


title: Kerr Geodesics, the Penrose Process and Jet Collimation by a Black Hole

abstract:
  We re-examine the possibility that astrophysical jet collimation may arise
from the geometry of rotating black holes and the presence of high-energy
particles resulting from a Penrose process, without the help of magnetic
fields. Our analysis uses the Weyl coordinates, which are revealed better
adapted to the desired shape of the jets. We numerically integrate the
2D-geodesics equations. We give a detailed study of these geodesics and give
several numerical examples. Among them are a set of perfectly collimated
geodesics with asymptotes $\rho =\rho_{1}$ parallel to the $z-$ axis, with
$\rho_{1}$ only depending on the ratios $\frac{\mathcal{Q}}{E^{2}-1}$ and
$\frac{a}{M}$, where $a$ and $M$ are the parameters of the Kerr black hole, $E$
the particle energy and $\mathcal{Q}$ the Carter's constant.


title:
The singular field used to calculate the self-force on non-spinning and
  spinning particles

abstract:
  The singular field of a point charge has recently been described in terms of
a new Green's function of curved spacetime. This singular field plays an
important role in the calculation of the self-force acting upon the particle.
We provide a method for calculating the singular field and a catalog of
expansions of the singular field associated with the geodesic motion of
monopole and dipole sources for scalar, electromagnetic and gravitational
fields. These results can be used, for example, to calculate the effects of the
self-force acting on a particle as it moves through spacetime.


title: 3d Spinfoam Quantum Gravity: Matter as a Phase of the Group Field Theory

abstract:
  An effective field theory for matter coupled to three-dimensional quantum
gravity was recently derived in the context of spinfoam models in
hep-th/0512113. In this paper, we show how this relates to group field theories
and generalized matrix models. In the first part, we realize that the effective
field theory can be recasted as a matrix model where couplings between matrices
of different sizes can occur. In a second part, we provide a family of
classical solutions to the three-dimensional group field theory. By studying
perturbations around these solutions, we generate the dynamics of the effective
field theory. We identify a particular case which leads to the action of
hep-th/0512113 for a massive field living in a flat non-commutative space-time.
The most general solutions lead to field theories with non-linear redefinitions
of the momentum which we propose to interpret as living on curved space-times.
We conclude by discussing the possible extension to four-dimensional spinfoam
models.


title:
Evolving relativistic fluid spacetimes using pseudospectral methods and
  finite differencing

abstract:
  We present a new code for solving the coupled Einstein-hydrodynamics
equations to evolve relativistic, self-gravitating fluids. The Einstein field
equations are solved on one grid using pseudospectral methods, while the fluids
are evolved on another grid by finite differencing. We discuss implementation
details, such as the communication between the grids and the treatment of
stellar surfaces, and present code tests.


title: Quantum collapse of dust shells in 2+1 gravity

abstract:
  This paper considers the quantum collapse of infinitesimally thin dust shells
in 2+1 gravity. In 2+1 gravity a shell is no longer a sphere but a ring of
matter. The classical equation of motion has been considered by Peleg and Steif
and Cristosomo and Olea. The minisuperspace quantum problem can be reduced to
that of a harmonic oscillator in terms of the curvature radius of the shell,
allowing the use of well-known methods to find the motion of coherent wave
packets that give the quantum collapse of the shell. Classically, as the radius
of the shell falls below a certain point, a horizon forms. In the quantum
problem one can define various quantities that give "indications" of horizon
formation. Without proper definitions of a "horizon" in quantum gravity, these
can be nothing but indications.


title:
The complete quantum collapse scenario of 2+1 dust shell: Preliminary
  Calculations

abstract:
  If we consider the gravitational collapse of a material object to a black
hole, we would expect, for ranges of mass where a black hole would form, the
following scenario. A large enough object would collapse classically until an
event horizon forms, and to an external observer the object would be lost fom
view. However, once the horizon has formed the black hole will begin to emit
Hawking radiation and the hole will lose mass and the horizon will shrink. The
final state of this process could be either a zero-mass "black hole" with
consequent information loss, or some sort of "quantum remnant.
  A complete investigation of this process would require: 1) A complete and
consistent theory of quantum gravity coupled to some kind of field that would
provide the Hawking radiation (which could be the gravitational field itself
--gravitons); 2) Some kind of definition of a "horizon" in this quantum
gravity, and; 3) The calculational tools to achieve a description of the
scenario. Lacking these, one may resort to toy models to try to give some sort
of preliminary answer.
  In this paper we will consider the collapse of an infinitesimally thin dust
shell in 2+1 gravity, where an exact minisuperspace quantum solution exists,
and try to make rough estimates of the collapse-Hawking radiation-remnant
formation process.


title: The Maxwell Lagrangian in purely affine gravity

abstract:
  The purely affine Lagrangian for linear electrodynamics, that has the form of
the Maxwell Lagrangian in which the metric tensor is replaced by the
symmetrized Ricci tensor and the electromagnetic field tensor by the tensor of
homothetic curvature, is dynamically equivalent to the Einstein-Maxwell
equations in the metric-affine and metric formulation. We show that this
equivalence is related to the invariance of the Maxwell Lagrangian under
conformal transformations of the metric tensor. We also apply to a purely
affine Lagrangian the Legendre transformation with respect to the tensor of
homothetic curvature to show that the corresponding Legendre term and the new
Hamiltonian density are related to the Maxwell-Palatini Lagrangian for the
electromagnetic field. Therefore the purely affine picture, in addition to
generating the gravitational Lagrangian that is linear in the curvature,
justifies why the electromagnetic Lagrangian is quadratic in the
electromagnetic field.


title: Matching LTB and FRW spacetimes through a null hypersurface

abstract:
  Matching of a LTB metric representing dust matter to a background FRW
universe across a null hypersurface is studied. In general, an unrestricted
matching is possible only if the background FRW is flat or open. There is in
general no gravitational impulsive wave present on the null hypersurface which
is shear-free and expanding. Special cases of the vanishing pressure or energy
density on the hypersurface is discussed. In the case of vanishing energy
momentum tensor of the null hypersurface, i.e. in the case of a null boundary,
it turns out that all possible definitions of the Hubble parameter on the null
hypersurface, being those of LTB or that of FRW, are equivalent, and that a
flat FRW can only be joined smoothly to a flat LTB.


title: Focusing of branes in warped backgrounds

abstract:
  Branes are embedded surfaces in a given background (bulk) spacetime. Assuming
a warped bulk, we investigate, in analogy with the case for geodesics, the
notion of {\em focusing} of families of such embedded, extremal 3--branes in a
five dimensional background . The essential tool behind our analysis, is the
well-known generalised Raychaudhuri equations for surface congruences. In
particular, we find explicit solutions of these equations, which seem to show
that families of 3--branes can focus along lower dimensional submanifolds
depending on where the initial expansions are specified. We conclude with
comments on the results obtained and possibilities about future work along
similar lines.


title: A generalized Schroedinger equation for loop quantum cosmology

abstract:
  A temporally discrete Schroedinger time evolution equation is proposed for
isotropic quantum cosmology coupled to a massless scalar source. The approach
employs dynamically determined intrinsic time and produces the correct
semiclassical limit.


title: Maximum gravitational recoil

abstract:
  Recent calculations of gravitational radiation recoil generated during
black-hole binary mergers have reopened the possibility that a merged binary
can be ejected even from the nucleus of a massive host galaxy. Here we report
the first systematic study of gravitational recoil of equal-mass binaries with
equal, but anti-aligned, spins parallel to the orbital plane. Such an
orientation of the spins is expected to maximize the recoil. We find that
recoil velocity (which is perpendicular to the orbital plane) varies
sinusoidally with the angle that the initial spin directions make with the
initial linear momenta of each hole and scales up to a maximum of ~4000 km/s
for maximally-rotating holes. Our results show that the amplitude of the recoil
velocity can depend sensitively on spin orientations of the black holes prior
to merger.


title: On a Covariant Formulation of the Barbero-Immirzi Connection

abstract:
  The Barbero-Immirzi (BI) connection, as usually introduced out of a spin
connection, is a global object though it does not transform properly as a
genuine connection with respect to generic spin transformations, unless quite
specific and suitable gauges are imposed. We shall here investigate whether and
under which global conditions a (properly transforming and hence global)
SU(2)-connection can be canonically defined in a gauge covariant way. Such
SU(2)-connection locally agrees with the usual BI connection and it can be
defined on pretty general bundles; in particular triviality is not assumed. As
a by-product we shall also introduce a global covariant SU(2)-connection over
the whole spacetime (while for technical reasons the BI connection in the
standard formulation is just introduced on a space slice) which restricts to
the usual BI connection on a space slice.


title: Type O pure radiation metrics with a cosmological constant

abstract:
  In this paper we complete the integration of the conformally flat pure
radiation spacetimes with a non-zero cosmological constant $\Lambda$, and $\tau
\ne 0$, by considering the case $\Lambda +\tau\bar\tau \ne 0$. This is a
further demonstration of the power and suitability of the generalised invariant
formalism (GIF) for spacetimes where only one null direction is picked out by
the Riemann tensor. For these spacetimes, the GIF picks out a second null
direction, (from the second derivative of the Riemann tensor) and once this
spinor has been identified the calculations are transferred to the simpler GHP
formalism, where the tetrad and metric are determined. The whole class of
conformally flat pure radiation spacetimes with a non-zero cosmological
constant (those found in this paper, together with those found earlier for the
case $\Lambda +\tau\bar\tau = 0$) have a rich variety of subclasses with zero,
one, two, three, four or five Killing vectors.


title: Formulation of an Evolutionary Quantum Cosmology

abstract:
  We provide an evolutionary formulation of a generic quantum cosmology. Our
starting point is the request that all quantities living on the slicing have to
be 3-tensors. This statement, when applied to the lapse function and the shift
vector, yields the no longer vanishing behavior of the super-Hamiltonian. Then,
we provide the formulation of an evolutionary quantum cosmology in
correspondence to a generic Universe asymptotically to the initial singularity.


title: Sharp bounds on $2m/r$ of general spherically symmetric static objects

abstract:
  In 1959 Buchdahl \cite{Bu} obtained the inequality $2M/R\leq 8/9$ under the
assumptions that the energy density is non-increasing outwards and that the
pressure is isotropic. Here $M$ is the ADM mass and $R$ the area radius of the
boundary of the static body. The assumptions used to derive the Buchdahl
inequality are very restrictive and e.g. neither of them hold in a simple soap
bubble. In this work we remove both of these assumptions and consider
\textit{any} static solution of the spherically symmetric Einstein equations
for which the energy density $\rho\geq 0,$ and the radial- and tangential
pressures $p\geq 0$ and $p_T,$ satisfy $p+2p_T\leq\Omega\rho, \Omega>0,$ and we
show that $$\sup_{r>0}\frac{2m(r)}{r}\leq
\frac{(1+2\Omega)^2-1}{(1+2\Omega)^2},$$ where $m$ is the quasi-local mass, so
that in particular $M=m(R).$ We also show that the inequality is sharp. Note
that when $\Omega=1$ the original bound by Buchdahl is recovered. The
assumptions on the matter model are very general and in particular any model
with $p\geq 0$ which satisfies the dominant energy condition satisfies the
hypotheses with $\Omega=3.$


title: Dynamics of colliding branes and black brane production

abstract:
  We study the dynamics of colliding domain walls including self-gravity. The
initial data is set up by applying a BPS domain wall in five-dimensional
supergravity, and we evolve the system determining the final outcome of
collisions. After a collision, a spacelike curvature singularity covered by a
horizon is formed in the bulk, resulting in a black brane with trapped domain
walls. This is a generic consequence of collisions, except for non-relativistic
weak field cases, in which the walls pass through one another or multiple
bounces take place without singularity formation. These results show that
incorporating the self-gravity drastically changes a naive picture of colliding
branes.


title: The Cosmology of Tetradic Theory of Gravitation

abstract:
  We consider a special class of the tetrad theory of gravitation which can be
considered as a viable alternative gravitational theories. We investigate
cosmological models based on those theories by examining the possibility of
fitting the recent astronomical measurement of supernova Ia magnitude versus
shift. Our investigations result in a reasonable fit for the supernova data
without introducing a cosmological constant. Thus, cosmological models based on
tetradic theory of gravitation can provide alternatives to dark energy models.


title: Discrete spacetime and its applications

abstract:
  We survey some results about the asymptotic behavior of discrete spacetime
models, which appeared in diverse settings in the physics and math literature.
We then discuss some recent applications, including scheduling in disk drives
and analysis of airplane boarding strategies.


title: The cosmological billiard attractor

abstract:
  This article is devoted to a study of the asymptotic dynamics of generic
solutions of the Einstein vacuum equations toward a generic spacelike
singularity. Starting from fundamental assumptions about the nature of generic
spacelike singularities we derive in a step-by-step manner the cosmological
billiard conjecture: we show that the generic asymptotic dynamics of solutions
is represented by (randomized) sequences of heteroclinic orbits on the
`billiard attractor'. Our analysis rests on two pillars: (i) a dynamical
systems formulation based on the conformal Hubble-normalized orthonormal frame
approach expressed in an Iwasawa frame; (ii) stochastic methods and the
interplay between genericity and stochasticity. Our work generalizes and
improves the level of rigor of previous work by Belinskii, Khalatnikov, and
Lifshitz; furthermore, we establish that our approach and the Hamiltonian
approach to `cosmological billiards', as elaborated by Damour, Hennaux, and
Nicolai, can be viewed as yielding `dual' representations of the asymptotic
dynamics.


title:
Vacuum fluctuations, the size of extra spatial dimensions and
  microscopic black holes at CERN

abstract:
  We have suggested, that the size of extra spatial dimensions (if they exist)
should be related to the quantum vacuum fluctuations; an extra dimension must
be sufficiently large to allow appearance of virtual quark-antiquark pairs,
which are an inherent part of the physical vacuum in quantum chromodynamics. We
argue that the conjecture of extra dimensions with the universal size equal to
the reduced Compton wavelength of a pion is a serious alternative to the
postulated universal mass in the theory of large extra dimensions (LED). Our
conjecture leads to the conclusion that the production of artificial mini black
holes at LHC at CERN is unlikely. It is shown that the recent lower limit on
the mass of a microscopic black hole (established by CMS collaboration at CERN)
may be interpreted as the upper limit (equal to six) for the number of extra
dimensions. Additionally, we challenge the current wisdom that mini black holes
disintegrate through the Hawking radiation. We point that it might be wrong, if
there is a hypothetical repulsion between matter and antimatter; resulting in
the creation of particle-antiparticle pairs from the quantum vacuum and
matter-antimatter asymmetry in the spectrum of radiation.


title: No "big trips" for the universe

abstract:
  It has been claimed in several papers that a phantom energy-dominated
universe can undergo a ``big trip'', i.e., tunneling through a wormhole that
grows faster than the cosmic substratum due to the accretion of phantom energy,
and will reappear on the other mouth of the wormhole. We show that such claims
are unfounded and contradict the Einstein equations.


title: Singularities and Quantum Gravity

abstract:
  Although there is general agreement that a removal of classical gravitational
singularities is not only a crucial conceptual test of any approach to quantum
gravity but also a prerequisite for any fundamental theory, the precise
criteria for non-singular behavior are often unclear or controversial. Often,
only special types of singularities such as the curvature singularities found
in isotropic cosmological models are discussed and it is far from clear what
this implies for the very general singularities that arise according to the
singularity theorems of general relativity. In these lectures we present an
overview of the current status of singularities in classical and quantum
gravity, starting with a review and interpretation of the classical singularity
theorems. This suggests possible routes for quantum gravity to evade the
devastating conclusion of the theorems by different means, including modified
dynamics or modified geometrical structures underlying quantum gravity. The
latter is most clearly present in canonical quantizations which are discussed
in more detail. Finally, the results are used to propose a general scheme of
singularity removal, quantum hyperbolicity, to show cases where it is realized
and to derive intuitive semiclassical pictures of cosmological bounces.


title: Quantum Cooling Evaporation Process in Regular Black Holes

abstract:
  We investigate a universal behavior of thermodynamics and evaporation process
for the regular black holes. We newly observe an important point where the
temperature is maximum, the heat capacity is changed from negative infinity to
positive infinity, and the free energy is minimum. Furthermore, this point
separates the evaporation process into the early stage with negative heat
capacity and the late stage with positive heat capacity. The latter represents
the quantum cooling evaporation process. As a result, the whole evaporation
process could be regarded as the inverse Hawking-Page phase transition.


title:
A generalization of Ryan's theorem: probing tidal coupling with
  gravitational waves from nearly circular, nearly equatorial,
  extreme-mass-ratio inspirals

abstract:
  Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals
(IMRIs)--binaries in which a stellar-mass object spirals into a massive black
hole or other massive, compact body--are important sources of gravitational
waves for LISA and LIGO, respectively. Thorne has speculated that the waves
from EMRIs and IMRIs encode, in principle, all the details of (i) the central
body's spacetime geometry (metric), (ii) the tidal coupling (energy and angular
momentum exchange) between the central body and orbiting object, and (iii) the
evolving orbital elements. Fintan Ryan has given a first partial proof that
this speculation is correct: Restricting himself to nearly circular, nearly
equatorial orbits and ignoring tidal coupling, Ryan proved that the central
body's metric is encoded in the waves. In this paper we generalize Ryan's
theorem. Retaining Ryan's restriction to nearly circular and nearly equatorial
orbits, and dropping the assumption of no tidal coupling, we prove that
Thorne's conjecture is nearly fully correct: the waves encode not only the
central body's metric but also the evolving orbital elements and (in a sense
slightly different from Thorne's conjecture) the evolving tidal coupling.


title: Vacuum less global monopole in Brans-Dicke theory

abstract:
  In the present work, the gravitational field of a vacuum less global monopole
has been investigated in Brans-Dicke theory under weak field assumption of the
field equations. It has been shown that the vacuum less global monopole exerts
attractive gravitational effects on a test particle. It is dissimilar to the
case studied in general relativity.


title: Quantization of four-dimensional Abelian gravity

abstract:
  An abelian version of standard general relativity in the Cartan-Palatini
gauge-like formulation in four dimensions has been introduced. Traditional
canonical analysis utilizing similarities to the akin Husain-Kuchar SU(2)
version of gravity has been performed. The model has been next quantized in the
canonical path-integral Faddeev-Popov formalism yielding abelian BF theory.


title:
A mission to test the Pioneer anomaly: estimating the main systematic
  effects

abstract:
  We estimate the main systematic effects relevant in a mission to test and
characterize the Pioneer anomaly through the flight formation concept, by
launching probing spheres from a mother spacecraft and tracking their motion
via laser ranging.


title: Thermodynamics of a photon gas and deformed dispersion relations

abstract:
  We resort to the methods of statistical mechanics in order to determine the
effects that a deformed dispersion relation has upon the thermodynamics of a
photon gas. The ensuing modifications to the density of states, partition
function, pressure, internal energy, entropy, and specific heat are calculated.
It will be shown that the breakdown of Lorentz invariance can be interpreted as
a repulsive interaction, among the photons. Additionally, it will be proved
that the presence of a deformed dispersion relation entails an increase in the
entropy of the system. In other words, as a consequence of the loss of the
aforementioned symmetry the number of microstates available to the
corresponding equilibrium state grows.


title: A Quick and Dirty Approach to Verify the Pioneer Anomaly

abstract:
  We present source code for the computer algebra system Mathematica that
analyzes the motion of the Pioneer spacecraft using the public available
ephemeris data from JPL's website. Within 15 minutes, the reader can verify
that the Pioneer anomalous acceleration a_p (1) exists in the order of
magnitude of c H_0, (2) is not due to mismodeling of gravitational attraction,
solar pressure or spacecraft attitude maneuvers. The simple code of about 100
lines may easily be extended by the reader to include further tests. Due to the
limitations of our approach, we do not know (1) whether the unknown raw data
were correctly processed to generate the trajectory files (2) how the apparent
mismatch of ephemerides before 1990 had occurred.


title: On curvature homogeneous 4D Lorentzian manifolds

abstract:
  We prove that a four-dimensional Lorentzian manifold that is curvature
homogeneous of order 3, or $\CH_3$ for short, is necessarily locally
homogeneous. We also exhibit and classify four-dimensional Lorentzian, $\CH_2$
manifolds that are not homogeneous.


title: Elastic stars in general relativity: IV. Axial perturbations

abstract:
  This is the fourth paper in a series that attempt to put forward a consistent
framework for modelling solid regions in neutron stars. Here we turn our
attention to axial perturbations of spherically symmetric spacetimes using a
gauge invariant approach due to one of us. Using the formalism developed in the
first paper in the series it turns out that the matter perturbations are neatly
expressible in terms of a ``metric'' tensor field depending only on the speeds
of shear wave propagation along the principal directions in the solid. The
results are applicable to a wide class of elastic materials and does not assume
material isotropy nor quasi-Hookean behaviour. The perturbation equations are
then specialised to a static background and are given by two coupled wave
equations. Our formalism is thus slightly simpler than the previously existing
results of Shumaker & Thorne, where an additional initial value equation needs
to be solved. The simplification is mainly due to the gauge invariance of our
approach and shows up also in somewhat simpler boundary conditions. We also
give a first order formulation suitable for numerical integration of the
quasi-normal mode problem of a neutron star. The relations between the gauge
independent variables and the, in general, gauge dependent perturbed metric and
strain tensor are explicitly given.


title: Non-Metric Gravity I: Field Equations

abstract:
  We describe and study a certain class of modified gravity theories. Our
starting point is Plebanski formulation of gravity in terms of a triple B^i of
2-forms, a connection A^i and a ``Lagrange multiplier'' field Psi^ij. The
generalization we consider stems from presence in the action of an extra term
proportional to a scalar function of Psi^ij. As in the usual Plebanski general
relativity (GR) case, a certain metric can be constructed from B^i. However,
unlike in GR, the connection A^i no longer coincides with the self-dual part of
the metric-compatible spin-connection. Field equations of the theory are shown
to be relations between derivatives of the metric and components of field Psi,
as well as its derivatives, the later being in contrast to the GR case. The
equations are of second order in derivatives. An analog of the Bianchi identity
is still present in the theory, as well as its contracted version tantamount to
energy conservation equation.


title: Electromagnetic Fields of Separable Space-Times

abstract:
  Carter derived the forms of the metric and the vector potentials of the
space-times in which the relativistic Schrodinger equation for the motion of a
charged particle separates. Here we show that on each `spheroidal' surface a
rotation rate exists such that relative to those rotating axes the electric and
magnetic fields are parallel and orthogonal to the spheroid which is thus an
equipotential in those axes. All the finite Carter separable systems without
magnetic monopoles or gravomagnetic NUT monopoles have the same gyromagnetic
ratio as the Dirac electron.


title: Bianchi type I model with two interacting scalar fields

abstract:
  The flat anisotropic model of the early Universe is considered. Two
interacting scalar fields with special form of potential energy are a source of
matter fields. Analytic solutions for inflationary and scalaron stages are
found. It is shown that the solutions tend asymptotically to isotropic
Friedmann model.


title: On constraint-consistency, covariant operators, gauge-invariance, etc

abstract:
  We look at the covariant techniques and the ideas on constraints and
gauge-invariance, which were recently employed in [gr-qc/0702104] to support
earlier work by the same authors. That work was criticised in [gr-qc/0503042].
Using very simple and well known examples we show that, when adopted, the
methods and views of [gr-qc/0702104] lead to basic-level mathematical problems,
with analogous consequences for the physics. We provide a few simple rules that
should help to avoid similar problems in the future.


title: Can f(R) Modified Gravity Theories Mimic a LCDM Cosmology?

abstract:
  We consider f(R) modified gravity theories in the metric variation formalism
and attempt to reconstruct the function f(R) by demanding a background LCDM
cosmology. In particular we impose the following requirements: a. A background
cosmic history H(z) provided by the usual flat LCDM parametrization though the
radiation (w_eff=1/3), matter (w_eff=0) and deSitter (w_eff=-1) eras. b. Matter
and radiation dominate during the `matter' and `radiation' eras respectively
i.e. \Omega_m =1 when w_eff=0 and \Omega_r=1 when w_eff=1/3. We have found that
the cosmological dynamical system constrained to obey the LCDM cosmic history
has four critical points in each era which correspondingly lead to four forms
of f(R). One of them is the usual general relativistic form f(R)=R-2\Lambda.
The other three forms in each era, reproduce the LCDM cosmic history but they
do not satisfy requirement b. stated above. Only one of these forms (different
from general relativity) is found to be an attractor of the dynamical
cosmological evolution. It has (\Omega_DE=1, \Omega_r=0, \Omega_m=0) throughout
the evolution. Its phase space trajectory is numerically obtained.

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


title:
The low dimensional dynamical system approach in General Relativity: an
  example

abstract:
  In this paper we explore one of the most important features of the Galerkin
method, which is to achieve high accuracy with a relatively modest
computational effort, in the dynamics of Robinson-Trautman spacetimes.


title: Hawking radiation from the quantum Lemaitre-Tolman-Bondi model

abstract:
  In an earlier paper, we obtained exact solutions of the Wheeler-DeWitt
equation for the Lemaitre-Tolman-Bondi (LTB) model of gravitational collapse,
employing a lattice regularization. In this paper, we derive Hawking radiation
in non-marginally bound models from our exact solutions. We show that a
non-vanishing energy function does not spoil the (approximate) Planck spectrum
near the horizon. We can also reliably compute corrections to the Bogoliubov
coefficient because our solutions are exact. The corrections are obtained by
going beyond the near horizon region and are shown to introduce additional
greybody factors, which modify the black body spectrum of radiation from the
black hole.


title: Fundamental length scale of quantum spacetime foam

abstract:
  It is argued that the fundamental length scale for the quantum dynamics of
spacetime need not be equal to the Planck length. Possibly, this new length
scale is related to a nonvanishing cosmological constant or vacuum energy
density.


title:
Effective Dynamics for the Cosmological Bounces in Bianchi Type I Loop
  Quantum Cosmology

abstract:
  The detailed formulation for loop quantum cosmology (LQC) in the Bianchi I
model with a massless scalar field was recently constructed. In this paper, its
effective dynamics with the LQC discreteness corrections is studied and the
equations of motion are analytically solved, showing that the big bang
singularity is replaced by the big bounces, which take place up to three times,
once in each diagonal direction, whenever each of the area scale factors
approaches its critical value in the Planck regime measured by the reference of
the scalar field momentum.


title:
Exact Solutions in Five-Dimensional Axi-dilaton Gravity with
  Euler-Poincare Term

abstract:
  We examine the effective field equations that are obtained from the
axi-dilaton gravity action with a second order Euler-Poincare term and a
cosmological constant in all higher dimensions. We solve these equations for
five-dimensional spacetimes possessing homogeneity and isotropy in their
three-dimensional subspaces. For a number of interesting special cases we show
that the solutions fall into two main classes: The first class consists of
time-dependent solutions with spherical or hyperboloidal symmetry which require
certain fine-tuning relations between the coupling constants of the model and
the cosmological constant. Solutions in the second class are locally static and
prove the validity of Birkhoff's staticity theorem in the axi-dilaton gravity.
We also give a special class of static solutions, among them the well-known
black hole solutions in which the usual electric charge is superseded by an
axion charge.


title:
Luminosity distance-redshift relation for the LTB solution near the
  center

abstract:
  Motivated by the inverse problem for the Lemaitre-Tolman-Bondi dust solution,
in which problem the luminosity distance function $D_L(z)$ is taken as an input
to select a specific model, we compute the function $D_L(z)$ of the LTB
solution up to the third order of $z$. To perform the otherwise cumbersome
computation, we introduce a new convenient form of the LTB solution, in which
the solution is explicit and unified. With this form of the LTB solution we
obtain the luminosity distance function with the full generality. We in
particular find that the function exactly coincides with that of a homogeneous
and isotropic dust solution up to second order, if we demand that the solution
be regular at the center.


title:
A New Formulation of General Relativity - Part I: Pre-Radar Charts as
  Generating Functions for Metric and Velocity

abstract:
  In this paper (Part I of a series of three papers) an axiomatic formulation
of GR is given, here use is made of the concept of pre-radar charts. These
charts have "infinitesimally" the same properties as the true radar charts used
in space-time theory. Their existence in GR has far-reaching consequences which
are discussed throughout the papers. For the sake of simplicity and convenience
I consider only such material systems the state of which is defined by a
velocity field, a mass density and a temperature field. But the main results
hold also for more complex systems. It follows from the axiomatics that the
pre-radar charts define an atlas for the space-time manifold and that, in
addition, they generate the metric, the velocity field and the displacement of
the matter. Therefore, they are called generating functions. They act like
"potentials". At the end of the paper it is shown that the existence of
pre-radar charts allows to simplify the original axiomatics drasticly. But the
two versions of GR are equivalent.


title:
A New Formulation of General Relativity - Part II: Pre-Radar Charts and
  Generating Functions in Arbitrary Space-Times

abstract:
  In this paper (Part II), the so-called inverse problem is treated. This means
the question whether it is possible to define pre-radar charts, i.e. generating
functions in arbitrary space-times. This problem is subtle. A local general
constructive solution of it is presented. Sufficient conditions for the
existence of global solutions are given.


title:
A New Formulation of General Relativity - Part III: GR as Scalar Field
  Theory

abstract:
  The aim of this paper (Part III) is formulating GR as a scalar field theory.
The basic structural elements of it are a generating function, a generalized
density and a generalized temperature. One of the axioms of this theory is a
generalized Einstein equation which determines the generating function
directly. It is shown that basic concepts like orientation, time orientation
and isometry are expressible in terms of generating functions. At the end of
the paper six problems are formulated which are still unsolved and can act as a
stimulant for further research.


title: Adiabatic renormalization in theories with modified dispersion relations

abstract:
  We generalize the adiabatic renormalization to theories with dispersion
relations modified at energies higher than a new scale $M_C$. We obtain
explicit expressions for the mean value of the stress tensor in the adiabatic
vacuum, up to the second adiabatic order. We show that for any dispersion
relation the divergences can be absorbed into the bare gravitational constants
of the theory. We also point out that, depending on the renormalization
prescription, the renormalized stress tensor may contain finite trans-Planckian
corrections even in the limit $M_C\to\infty$.


title:
The impact of the Kuiper Belt Objects and of the asteroid ring on future
  high-precision relativistic Solar System tests

abstract:
  We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and
of the asteroid ring on some proposed high-precision tests of Newtonian and
post-Newtonian gravity to be performed in the Solar System by means of
spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination
of some of the inner planets. It turns out that the Classical KBOSs (CKBOS),
which amount to \approx 70% of the observed population of Trans-Neptunian
bodies, induce a systematic secular error of about 1 m after one year in the
transverse direction T of the orbit of a test particle orbiting at 1 AU from
the Sun. For Mercury the ratios of the secular perihelion precessions induced
by CKBOs to the ones induced by the general relativity and the solar oblateness
J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse
perturbation induced on a \approx 1 AU orbit by the asteroid ring, which
globally accounts for the action of the minor asteroids whose mass is about 5
10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2
Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given
the very ambitious goals of many expensive and complex missions aimed to
testing gravitational theories to unprecedented levels of accuracy, these notes
may suggest further and more accurate investigations of such sources of
potentially insidious systematic bias.


title: On the wave equation in spacetimes of Goedel type

abstract:
  We analyze the d'Alembert equation in the Goedel-type spacetimes with
spherical and Lobachevsky sections (with sufficiently rapid rotation). By
separating the $t$ and $x_3$ dependence we reduce the problem to a
group-theoretical one. In the spherical case solutions have discrete
frequencies, and involve spin-weighted spherical harmonics. In the Lobachevsky
case we give simple formulas for obtaining all the solutions belonging to the
$D^\pm_\la$ sectors of the irreducible unitary representations of the reduced
Lorentz group. The wave equation enforces restrictions on $\la$ and the allowed
(here: continuous) spectrum of frequencies.


title: Transition from AdS universe to DS universe in the BPP model

abstract:
  It can be shown that in the BPP model the smooth phase transition from the
asymptotically decelerated AdS universe to the asymptotically accelerated DS
universe is possible by solving the modified semiclassical equations of motion.
This transition comes from noncommutative Poisson algebra, which gives the
constant curvature scalars asymptotically. The decelerated expansion of the
early universe is due to the negative energy density with the negative pressure
induced by quantum back reaction, and the accelerated late-time universe comes
from the positive energy and the negative pressure which behave like dark
energy source in recent cosmological models.


title:
The meaning of systematic errors, a comment to "Reply to On the
  Systematic Errors in the Detection of the Lense-Thirring Effect with a Mars
  Orbiter", by Lorenzo Iorio

abstract:
  This submission has been removed because 'G. Felici' is an apparent
pseudonym, in violation of arXiv policies.


title: Probing Dynamical Dark Energy with Press-Schechter Mass Functions

abstract:
  Measurement of accelerated expansion in the Universe led to propose a new
cosmic fluid as its cause: dark energy. Its various incarnations offer a wealth
of models whose relevance it is important to discriminate via contacts with
observations. I will present my investigations on the influence of dynamical
dark energy models on the formation of non-linear dark matter structures. In
particular, I will focus on structures traced by the mass function of dark
matter haloes.


title: Purely radiative perfect fluids

abstract:
  We study `purely radiative' (div E = div H = 0) and geodesic perfect fluids
with non-constant pressure and show that the Bianchi class A perfect fluids can
be uniquely characterized --modulo the class of purely electric and
(pseudo-)spherically symmetric universes-- as those models for which the
magnetic and electric part of the Weyl tensor and the shear are simultaneously
diagonalizable. For the case of constant pressure the same conclusion holds
provided one also assumes that the fluid is irrotational.


title: The Dirac propagator in the extreme Kerr metric

abstract:
  Starting with the Dirac equation in the extreme Kerr metric we derive an
integral representation for the propagator of solutions of the Cauchy problem
with initial data in the class of smooth compactly supported functions.


title: A new two-sphere singularity in general relativity

abstract:
  The Florides solution, proposed as an alternative to the interior
Schwarzschild solution, represents a static and spherically symmetric geometry
with vanishing radial stresses. It is regular at the center, and is matched to
an exterior Schwarzschild solution. The specific case of a constant energy
density has been interpreted as the field inside an Einstein cluster. In this
work, we are interested in analyzing the geometry throughout the permitted
range of the radial coordinate without matching it to the Schwarzschild
exterior spacetime at some constant radius hypersurface. We find an interesting
picture, namely, the solution represents a three-sphere, whose equatorial
two-sphere is singular, in the sense that the curvature invariants and the
tangential pressure diverge. As far as we know, such singularities have not
been discussed before. In the presence of a large negative cosmological
constant (anti-de Sitter) the singularity is removed.


title:
The Big-Bang Singularity in the framework of a Generalized Uncertainty
  Principle

abstract:
  We analyze the quantum dynamics of the Friedmann-Robertson-Walker Universe in
the context of a Generalized Uncertainty Principle. Since the isotropic
Universe dynamics resembles that of a one-dimensional particle, we quantize it
with the commutation relations associated to an extended formulation of the
Heisenberg algebra. The evolution of the system is described in terms of a
massless scalar field taken as a relational time. We construct suitable wave
packets and analyze their dynamics from a quasi-classical region to the initial
singularity. The appearance of a non singular dynamics comes out as far as the
behavior of the probability density is investigated. Furthermore, reliable
indications arise about the absence of a Big-Bounce, as predicted in recent
issues of Loop Quantum Cosmology.


title: Tachyonic open inflationary universes

abstract:
  We study one-field open inflationary models in a universe dominated by
tachyon matter. In these scenarios, we determine and characterize the existence
of the Coleman-De Lucia (CDL) instanton. Also, we study the Lorentzian regime,
that is, the period of inflation after tunnelling has occurred.


title: Conserved Quantities in Background Independent Theories

abstract:
  We discuss the difficulties that background independent theories based on
quantum geometry encounter in deriving general relativity as the low energy
limit. We follow a geometrogenesis scenario of a phase transition from a
pre-geometric theory to a geometric phase which suggests that a first step
towards the low energy limit is searching for the effective collective
excitations that will characterize it. Using the correspondence between the
pre-geometric background independent theory and a quantum information
processor, we are able to use the method of noiseless subsystems to extract
such coherent collective excitations. We illustrate this in the case of locally
evolving graphs.


title:
Towards adiabatic waveforms for inspiral into Kerr black holes: I. A new
  model of the source for the time domain perturbation equation

abstract:
  We revisit the problem of the emission of gravitational waves from a test
mass orbiting and thus perturbing a Kerr black hole. The source term of the
Teukolsky perturbation equation contains a Dirac delta function which
represents a point particle. We present a technique to effectively model the
delta function and its derivatives using as few as four points on a numerical
grid. The source term is then incorporated into a code that evolves the
Teukolsky equation in the time domain as a (2+1) dimensional PDE. The waveforms
and energy fluxes are extracted far from the black hole. Our comparisons with
earlier work show an order of magnitude gain in performance (speed) and
numerical errors less than 1% for a large fraction of parameter space. As a
first application of this code, we analyze the effect of finite extraction
radius on the energy fluxes. This paper is the first in a series whose goal is
to develop adiabatic waveforms describing the inspiral of a small compact body
into a massive Kerr black hole.


title: Fate of Kaluza-Klein Black Holes: Evaporation or Excision?

abstract:
  We study evaporation process of black strings which are typical examples of
Kaluza-Klein black holes. Taking into account the backreaction of the Hawking
radiation, we deduce the evolution equation for the radion field. By solving
the evolution equation, we find that the shape of the internal space is necked
by the Hawking radiation and the amount of the deformation becomes large as the
evaporation proceeds. Based on this analysis, we speculate that the
Kaluza-Klein black holes would be excised from the Kaluza-Klein spacetime
before the onset of the Gregory-Laflamme instability and therefore before the
evaporation.


title:
Numerical method for binary black hole/neutron star initial data: Code
  test

abstract:
  A new numerical method to construct binary black hole/neutron star initial
data is presented. The method uses three spherical coordinate patches; Two of
these are centered at the binary compact objects and cover a neighborhood of
each object; the third patch extends to the asymptotic region. As in the
Komatsu-Eriguchi-Hachisu method, nonlinear elliptic field equations are
decomposed into a flat space Laplacian and a remaining nonlinear expression
that serves in each iteration as an effective source. The equations are solved
iteratively, integrating a Green's function against the effective source at
each iteration. Detailed convergence tests for the essential part of the code
are performed for a few types of selected Green's functions to treat different
boundary conditions. Numerical computation of the gravitational potential of a
fluid source, and a toy model for a binary black hole field are carefully
calibrated with the analytic solutions to examine accuracy and convergence of
the new code. As an example of the application of the code, an initial data set
for binary black holes in the Isenberg-Wilson-Mathews formulation is presented,
in which the apparent horizons are located using a method described in Appendix
A.


title: Global dynamics of cosmological scalar fields -- Part II

abstract:
  This is the second part of integrability analysis of cosmological models with
scalar fields. Here, we study systems with conformal coupling, and show that
apart from four cases, where explicit first integrals are known, the generic
system is not integrable. We also comment on some chaotic properties of the
system, and the issues of integrability restricted to the real domain.


title: A note on a third order curvature invariant in static spacetimes

abstract:
  We consider here the third order curvature invariant
$I=R_{\mu\nu\rho\sigma;\delta}R^{\mu\nu\rho\sigma;\delta}$ in static spacetimes
${\cal M}=R\times\Sigma$ for which $\Sigma$ is conformally flat. We evaluate
explicitly the invariant for the $N$-dimensional Majumdar-Papapetrou multi
black-holes solution, confirming that $I$ does indeed vanish on the event
horizons of such black-holes. Our calculations show, however, that solely the
vanishing of $I$ is not sufficient to locate an event horizon in
non-spherically symmetric spacetimes. We discuss also some tidal effects
associated to the invariant $I$.


title:
Existence and Nonlinear Stability of Rotating Star Solutions of the
  Compressible Euler-Poisson Equations

abstract:
  We prove existence of rotating star solutions which are steady-state
solutions of the compressible isentropic Euler-Poisson (EP) equations in 3
spatial dimensions, with prescribed angular momentum and total mass. This
problem can be formulated as a variational problem of finding a minimizer of an
energy functional in a broader class of functions having less symmetry than
those functions considered in the classical Auchmuty-Beals paper. We prove the
nonlinear dynamical stability of these solutions with perturbations having the
same total mass and symmetry as the rotating star solution. We also prove local
in time stability of $W^{1, \infty}(\RR^3)$ solutions where the perturbations
are entropy-weak solutions of the EP equations. Finally, we give a uniform (in
time) a-priori estimate for entropy-weak solutions of the EP equations.


title:
Post-Newtonian Approximations, Compact Binaries, and Strong-Field Tests
  of Gravity

abstract:
  This is an extended summary of the two parallel sessions held at MG11: PPN1
``Strong Gravity and Binaries'' (chaired by L.B. and L.G.) and PPN2
``Post-Newtonian Dynamics in Binary Objects'' (chaired by G.S.). The aims and
contents of these sessions were close to each other and overlapping. It is
natural to review both sessions in one joint contribution to the MG11
Proceedings. The summary places the delivered talks in a broader perspective of
current studies in this area. One can find more details in individual
contributions of the respective authors.


title: 3+1 Formalism and Bases of Numerical Relativity

abstract:
  These lecture notes provide some introduction to the 3+1 formalism of general
relativity, which is the foundation of most modern numerical relativity. The
text is rather self-contained, with detailed calculations and numerous
examples. Contents: 1. Introduction, 2. Geometry of hypersurfaces, 3. Geometry
of foliations, 4. 3+1 decomposition of Einstein equation, 5. 3+1 equations for
matter and electromagnetic field, 6. Conformal decomposition, 7. Asymptotic
flatness and global quantities, 8. The initial data problem, 9. Choice of
foliation and spatial coordinates, 10. Evolution schemes.


title: On the Relation between Mass and Charge: A Pure Geometric Approach

abstract:
  A new solution of the field equations of the generalized field theory,
constructed by Mikhail and Wanas in 1977, has been obtained.
  The geometric structure used, in the present application, is an absolute
parallelism (AP)-space with spherical symmetry (type FIGI). The solution
obtained represents a generalized field outside a charged massive central body.
Two schemes have been used to get the physical meaning of the solution: The
first is related to the metric of the Riemannian space associated with the
AP-structure. The second is connected to a covariant scheme known as {\it{Type
Analysis}}. It is shown that the dependence on both schemes for interpreting
the results obtained, is more better than the dependence on the metric of the
Riemannian space associated with the AP-structure.
  In General, if we consider the solution obtained as representing a geometric
model for an elementary charged particle, then the results of the present work
can be summarized in the following points. (i) It is shown that the mass of the
particle is made of two contributions: The first is the gravitational
contribution, and the second is the contribution due to the existence of
charge. (ii) The model allows for the existence of a charged particle whose
mass is completely electromagnetic in origin. (iii) The model prevents the
existence of a charged massless particle. (iv) The electromagnetic
contribution, to the mass, is independent of the sign of the electric charge.
(v) It is shown that the mass of the electron (or a positron) is purely made of
its charge.


title:
Schwarzschild limit of conformal gravity in the presence of macroscopic
  scalar fields

abstract:
  In their original study of conformal gravity, a candidate alternate
gravitational theory, Mannheim and Kazanas showed that in any empty vacuum
region exterior to a localized static spherically symmetric gravitational
source, the geometry would reduce to the standard attractive gravity
Schwarzschild geometry on solar system distance scales. In a recent paper
Flanagan has argued that this would not be the case if the source has
associated with it a macroscopic scalar field which makes a non-zero
contribution to the energy-momentum tensor in the otherwise empty exterior
region. In this paper we examine Flanagan's analysis and show that even with
such long range scalar fields, the standard Schwarzschild phenomenology is
still recovered.


title: Late-time behaviour of the tilted Bianchi type VIh models

abstract:
  We study tilted perfect fluid cosmological models with a constant equation of
state parameter in spatially homogeneous models of Bianchi type VI_h using
dynamical systems methods and numerical experimentation, with an emphasis on
their future asymptotic evolution. We determine all of the equilibrium points
of the type VI_h state space (which correspond to exact self-similar solutions
of the Einstein equations, some of which are new), and their stability is
investigated. We find that there are vacuum plane-wave solutions that act as
future attractors. In the parameter space, a `loophole' is shown to exist in
which there are no stable equilibrium points. We then show that a
Hopf-bifurcation can occur resulting in a stable closed orbit (which we refer
to as the Mussel attractor) corresponding to points both inside the loophole
and points just outside the loophole; in the former case the closed curves act
as late-time attractors while in the latter case these attracting curves will
co-exist with attracting equilibrium points. In the special Bianchi type III
case, centre manifold theory is required to determine the future attractors.
Comprehensive numerical experiments are carried out to complement and confirm
the analytical results presented. We note that the Bianchi type VI_h case is of
particular interest in that it contains many different subcases which exhibit
many of the different possible future asymptotic behaviours of Bianchi
cosmological models.


title: Torsional Oscillations of Slowly Rotating Relativistic Stars

abstract:
  We study the effects of rotation on the torsional modes of oscillating
relativistic stars with a solid crust. Earlier works in Newtonian theory
provided estimates of the rotational corrections for the torsional modes and
suggested that they should become CFS unstable, even for quite low rotation
rates. In this work, we study the effect of rotation in the context of general
relativity using elasticity theory and in the slow-rotation approximation. We
find that the Newtonian picture does not change considerably. The inclusion of
relativistic effects leads only to quantitative corrections. The degeneracy of
modes for different values of $m$ is removed, and modes with $\ell=m$ are
shifted towards zero frequencies and become secularly unstable at stellar
rotational frequencies $\sim$ 20-30 Hz.


title: Detecting LISA sources using time-frequency techniques

abstract:
  The planned Laser Interferometer Space Antenna (LISA) will detect
gravitational wave signals from a wide range of sources. However, disentangling
individual signals from the source-dominated data stream is a challenging
problem and the focus of much current research. The problems are particularly
acute for detection of extreme mass ratio inspirals (EMRIs), for which the
instantaneous signal amplitude is an order of magnitude below the level of the
instrumental noise, and the parameter space of possible signals is too large to
permit fully-coherent matched filtering. One possible approach is to attempt to
identify sources in a time-frequency spectrogram of the LISA data. This is a
computationally cheap method that may be useful as a first stage in a
hierarchical analysis. Initial results, evaluated using a significantly
simplified model of the LISA data stream, suggest that time-frequency
techniques might be able to detect the nearest few tens of EMRI events. In this
proceedings article, we briefly outline the methods that have so far been
applied to the problem, initial results and possible future directions for the
research.


title:
Approximate waveform templates for detection of extreme mass ratio
  inspirals with LISA

abstract:
  The inspirals of compact objects into massive black holes are some of the
most exciting of the potential sources of gravitational waves for the planned
Laser Interferometer Space Antenna (LISA). Observations of such extreme mass
ratio inspirals (EMRIs) will not only reveal to us the properties of black
holes in the Universe, but will allow us to verify that the space-time
structure around massive compact objects agrees with the predictions of
relativity. Detection of EMRI signals via matched filtering and interpretation
of the observations will require models of the gravitational waveforms. The
extreme mass ratio allows accurate waveforms to be computed from black hole
perturbation theory, but this is computationally expensive and has not yet been
fully developed. Ongoing research to scope out LISA data analysis algorithms
requires waveforms that can be generated quickly in large numbers. To fulfil
this purpose, families of approximate, "kludge", EMRI waveforms have been
developed that capture the main features of true EMRI waveforms, but that can
also be generated for a comparatively small computational cost. In this
proceedings article, we briefly outline one such waveform family (the
"numerical kludge"), its accuracy and some possible ways in which it might be
improved in the future. Although accurate parameter extraction will require use
of perturbative waveforms, these approximate waveforms are sufficiently
faithful to the true waveforms that they may be able to play a role in
detection of EMRIs in the LISA data.


title:
Reply to "The meaning of systematic errors, a comment to "Reply to On
  the Systematic Errors in the Detection of the Lense-Thirring Effect with a
  Mars Orbiter", by Lorenzo Iorio'', by G. Felici

abstract:
  In this note we reply to the criticisms by Felici concerning some aspects of
the recent frame-dragging test performed by Iorio with the Mars Global Surveyor
(MGS) spacecraft in the gravitational field of Mars.


title: Asymptotics of flat, radiation universes in quadratic gravity

abstract:
  We consider the asymptotics of flat, radiation-dominated isotropic universes
in four-dimensional theories with quadratic curvature corrections which may
arise when contributions related to the string parameter $\alpha'$ are switched
on. We show that all such universes are singular initially, and calculate all
early time asymptotics using the method of asymptotic splittings. We also
examine the late time asymptotic behaviour of these models and show that there
are no solutions which diverge as $e^{t^2}$, the known radiation solution of
general relativity is essentially the only late time asymptotic possibility in
these models.


title:
de Sitter space and the equivalence between f(R) and scalar-tensor
  gravity

abstract:
  It is shown that, when f'' is non-vanishing, metric f(R) gravity is
completely equivalent to a scalar-tensor theory (with zero Brans-Dicke
parameter) with respect to perturbations of de Sitter space, contrary to
previous expectations. Moreover, the stability conditions of de Sitter space
with respect to homogeneous and inhomogeneous perturbations coincide in most
scalar-tensor theories, as is the case in metric f(R) gravity.


title: Conserving Integrals in [Non-]Metric Theories of Gravitation

abstract:
  In this work I present location to first mentioning to result of Robert
Geroch Preprint deals with conserving quantities of metric gravitational
theories They are constructed from Killing vector fields (if any exists) and
symmetric tensors of arbitrary rank with vanishing divergence I also suggest
alternative approach by introducing spinorial fields allowing to construct
conserved integrals of energy-momentum etc


title: Renormalization Group Approach to Generalized Cosmological models

abstract:
  We revisit here the problem of generalized cosmology using renormalization
group approach. A complete analysis of these cosmologies, where specific models
appear as asymptotic fixed-points, is given here along with their linearized
stability analysis.


title: Inhomogeneous Cosmological Model in Lyra Geometry

abstract:
  Exact solutions are obtained for an inhomogeneous cosmological model in
normal gauge for Lyra geometry. Some properties of the model have also been
discussed.


title:
Gauge invariance of the wave functional in mixed momentum/coordinate
  representations

abstract:
  Starting from the observation that in Yang-Mills theory the Schroedinger
state functional in the momentum representation is not gauge invariant, we
investigate the reversed question: Which are the representations for the
operators of a gauge theory that lead to an invariant wave functional once the
quantum constraints have been imposed upon it? Stated otherwise: Which
representation do we have to use if we wish the constraints of the theory to
eliminate the non-physical degrees of freedom from the states? We use the
framework of geometric quantization to attack this question. In particular, it
is found that in the linear spin-two theory as well as in General Relativity,
gauge invariance cannot be achieved by a pure coordinate (i.e., field)
representation, but that one has to use mixed momentum/coordinate
representations instead. Our results are illustrated by the example of the free
relativistic point-particle as well as by simple cosmological mini-superspace
models in the framework of General Relativity.


title: Rainich theory for type D aligned Einstein-Maxwell solutions

abstract:
  The original Rainich theory for the non-null Einstein-Maxwell solutions
consists of a set of algebraic conditions and the Rainich (differential)
equation. We show here that the subclass of type D aligned solutions can be
characterized just by algebraic restrictions.


title: Vacuum properties of nonsymmetric gravity in de Sitter space

abstract:
  We consider quantum effects of a massive antisymmetric tensor field on the
dynamics of de Sitter space-time. Our starting point is the most general,
stable, linearized Lagrangian arising in nonsymmetric gravitational theories
(NGTs), where part of the antisymmetric field mass is generated by the
cosmological term. We construct a renormalization group (RG) improved effective
action by integrating out one loop vacuum fluctuations of the antisymmetric
tensor field and show that, in the limit when the RG scale goes to zero, the
Hubble parameter -- and thus the effective cosmological constant -- relaxes
rapidly to zero. We thus conclude that quantum loop effects in de Sitter space
can dramatically change the infrared sector of the on-shell gravity, making the
expansion rate insensitive to the original (bare) cosmological constant.


title: Black holes on cosmological branes

abstract:
  While in general relativity black holes can be freely embedded into a
cosmological background, the same problem in brane-worlds is much more
cumbersome. We present here the results obtained so far in the explicit
constructions of such space-times. We also discuss gravitational collapse in
this context.


title: Finite states in four dimensional quantized gravity

abstract:
  This is the first in a series of papers outlining an algorithm to explicitly
construct finite quantum states of the full theory of gravity in Ashtekar
variables. The algorithm is based upon extending some properties of a special
state, the Kodama state for pure gravity with cosmological term, to
matter-coupled models. We then illustrate a presciption for nonperturbatively
constructing the generalized Kodama states, in preparation for subsequent works
in this series. We also introduce the concept of the semiclassical-quantum
correspondence (SQC). We express the quantum constraints of the full theory as
a system of equations to be solved for the constituents of the `phase' of the
wavefunction. Additionally, we provide a variety of representations of the
generalized Kodama states including a generalization of the topological
instanton term to include matter fields, for which we present arguments for the
field-theoretical analogue of cohomology on infinite dimensional spaces. We
demonstrate that the Dirac, reduced phase space and geometric quantization
procedures are all equivalent for these generalized Kodama states as a natural
consequence of the SQC. We relegate the method of the solution to the
constraints and other associated ramifications of the generalized Kodama states
to separate works.


title:
Inspiral, merger and ringdown of unequal mass black hole binaries: a
  multipolar analysis

abstract:
  We study the inspiral, merger and ringdown of unequal mass black hole
binaries by analyzing a catalogue of numerical simulations for seven different
values of the mass ratio (from q=M2/M1=1 to q=4). We compare numerical and
Post-Newtonian results by projecting the waveforms onto spin-weighted spherical
harmonics, characterized by angular indices (l,m). We find that the
Post-Newtonian equations predict remarkably well the relation between the wave
amplitude and the orbital frequency for each (l,m), and that the convergence of
the Post-Newtonian series to the numerical results is non-monotonic. To leading
order the total energy emitted in the merger phase scales like eta^2 and the
spin of the final black hole scales like eta, where eta=q/(1+q)^2 is the
symmetric mass ratio. We study the multipolar distribution of the radiation,
finding that odd-l multipoles are suppressed in the equal mass limit. Higher
multipoles carry a larger fraction of the total energy as q increases. We
introduce and compare three different definitions for the ringdown starting
time. Applying linear estimation methods (the so-called Prony methods) to the
ringdown phase, we find resolution-dependent time variations in the fitted
parameters of the final black hole. By cross-correlating information from
different multipoles we show that ringdown fits can be used to obtain precise
estimates of the mass and spin of the final black hole, which are in remarkable
agreement with energy and angular momentum balance calculations.


title: Orbital phase in inspiralling compact binaries

abstract:
  We derive the rate of change of the mean motion up to the second
post-Newtonian order for inspiralling compact binaries with spin, mass
quadrupole and magnetic dipole moments on eccentric orbits. We give this result
in terms of orbital elements. We also present the related orbital phase for
circular orbits.


title: Hawking radiation as tunneling from Gravity's rainbow

abstract:
  Planck scale corrections arising from deformed special relativity on Hawking
radiation in Parikh and Wilczk's tunneling framework are studied. We calculate
the emission rate of massless particles tunneling though the corrected horizon
of modified black holes from gravity's rainbow. In the tunneling process, when
a particle get across the quantum horizon, the metric fluctuation not only due
to the energy conservation but also quantum effects of the space-time are taken
into account. Our results show that, the emission rate is related to the
changes of the black hole's quantum corrected entropy and consistent with an
underlying unitary theory. In the modified black hole, by using black hole
thermodynamics, a series of quantum correction terms including a logarithmic
term to the Bekenstein-Hawking entropy are obtained. Correspondingly, the
Planck scale corrected emission spectrum is obtained and it deviates from the
thermal spectrum.


title:
Finite states in four dimensional quantum gravity. The isotropic
  minisuperspace Asktekar--Klein--Gordon model

abstract:
  In this paper we construct the generalized Kodama state for the case of a
Klein--Gordon scalar field coupled to Ashtekar variables in isotropic
minisuperspace by a new method. The criterion for finiteness of the state stems
from a minisuperspace reduction of the quantized full theory, rather than the
conventional techniques of reduction prior to quantization. We then provide a
possible route to the reproduction of a semiclassical limit via these states.
This is the result of a new principle of the semiclassical-quantum
correspondence (SQC), introduced in the first paper in this series. Lastly, we
examine the solution to the minisuperspace case at the semiclassical level for
an isotropic CDJ matrix neglecting any quantum corrections and examine some of
the implications in relation to results from previous authors on semiclassical
orbits of spacetime, including inflation. It is suggested that the application
of nonperturbative quantum gravity, by way of the SQC, might potentially lead
to some predictions testable below the Planck scale.


title:
Instanton representation of Plebanski gravity. Gravitational instantons
  from the classical formalism

abstract:
  We present a reformulation of general relativity as a `generalized'
Yang--Mills theory of gravity, using a SO(3,C) gauge connection and the
self-dual Weyl tensor as dynamical variables. This formulation uses Plebanski's
theory as the starting point, and obtains a new action called the instanton
representation (IRPG). This paper has yielded a collection of various new
results, which show that the IRPG is indeed a fundamentally new approach to GR
which should not be confused with existing approaches. Additionally, the IRPG
appears to provide a realization of the relation amongst general relativity,
Yang--Mills theory and instantons.


title: Asymptotic quasinormal modes of scalar field in a gravity's rainbow

abstract:
  In the context of a gravity's rainbow, the asymptotic quasinormal modes of
the scalar perturbation in the quantum modified Schwarzschild black holes are
investigated. By using the monodromy method, we calculated and obtained the
asymptotic quasinormal frequencies, which are dominated not only by the mass
parameter of the spacetime, but also by the energy functions from the modified
dispersion relations. However, the real parts of the asymptotic quasinormal
modes is still $T_H\ln 3$, which is consistent with Hod's conjecture. In
addition, for the quantum corrected black hole, the area spacing is calculated
and the result is independent of the energy functions, in spite of the area
itself is energy dependence. And that, by relating the area spectrum to loop
quantum gravity, the Barbero-Immirzi parameter is given and it remains the same
as from the usual black hole.


title:
Asymptotic properties of black hole solutions in dimensionally reduced
  Einstein-Gauss-Bonnet gravity

abstract:
  We study the asymptotic behavior of the spherically symmetric solutions of
the system obtained from the dimensional reduction of the six-dimensional
Einstein- Gauss-Bonnet action. We show that in general the scalar field that
parametrizes the size of the internal space is not trivial, but nevertheless
the solutions depend on a single parameter. In analogy with other models
containing Gauss-Bonnet terms, naked singularities are avoided if a minimal
radius for the horizon is assumed.


title:
Stability of spherically symmetric solutions in modified theories of
  gravity

abstract:
  In recent years, a number of alternative theories of gravity have been
proposed as possible resolutions of certain cosmological problems or as toy
models for possible but heretofore unobserved effects. However, the
implications of such theories for the stability of structures such as stars
have not been fully investigated. We use our "generalized variational
principle", described in a previous work, to analyze the stability of static
spherically symmetric solutions to spherically symmetric perturbations in three
such alternative theories: Carroll et al.'s f(R) gravity, Jacobson &
Mattingly's "Einstein-aether theory", and Bekenstein's TeVeS. We find that in
the presence of matter, f(R) gravity is highly unstable; that the stability
conditions for spherically symmetric curved vacuum Einstein-aether backgrounds
are the same as those for linearized stability about flat spacetime, with one
exceptional case; and that the "kinetic terms" of vacuum TeVeS are indefinite
in a curved background, leading to an instability.


title: A practical formula for the radiated angular momentum

abstract:
  We present a simple formula for the radiated angular momentum based on a
spin-weighted spherical harmonic decomposition of the Weyl scalar psi_4
representing outgoing radiation in the Kinnersley tetrad. We test our formula
by measuring the radiated angular momentum from three simulations of
non-spinning equal-mass black-hole binary with orbital angular momentum aligned
along the x, y, and z axes respectively. We find that the radiated angular
momentum agrees with the differences in the remnant horizon spins and the
initial angular momentum for each system.


title:
Hamiltonian Approach to Conformal Coupling Scalar Field in the General
  Relativity

abstract:
  The dynamic status of scalar fields is studied in the Hamiltonian approach to
the General Relativity. We show that the conformal coupling of the scalar field
violates the standard geometrical structure of the Einstein equations in GR and
their solutions including the Schwarzschild one and the Newton static
interaction. In order to restore the standard geometrical structure of GR, the
scalar field is mixed with the scale metric component by the Bekenstein type
transformation. This "scalar-scale" mixing converts the conformal coupling
scalar field with conformal weight (n= -1) into the minimal coupling scalar
field with zero conformal weight (n=0) called a "scalar graviton". Cosmological
consequences of the "scalar-scale" mixing are considered in the finite
space-time by extraction of the zero mode (homogeneous) harmonics of a "scalar
graviton". The classical dynamics of "scalar graviton" testifies about a
tremendous contribution of evolution at the beginning in the form of the rigid
state.


title:
Field Equations and Conservation Laws Derived from the Generalized
  Einstein Lagrangian Density for A Gravitational System and Their Implications
  to Cosmology

abstract:
  Based on investigations of the fundamental properties of the generalized
Einstein Lagrangian density for a gravitational system, the theoretical
foundations of the modified Einstein field equations and the Lorentz and
Levi-Civita conservation laws are systematically studied. The theory of
cosmology developed on the basis of these equations and laws is analyzed in
detail. Some new properties and new effects of the cosmos are deduced; these
new properties and new effects could be tested via future experiments and
observations.


title:
Can gravitational dynamics be obtained by diffeomorphism invariance of
  action?

abstract:
  It has recently been suggested that the gravitational dynamics could be
obtained by requiring the action to be invariant under diffeomorphism
transformations. We argue that the action constructed in usual way is
automatically diffeomorphism invariant in nature, which thus invalidates this
alternative perspective to obtain gravitational dynamics. Especially, we also
show what is wrong with the technical derivation of gravitational dynamics in
the alternative approach.


title:
Positive Equation-of-state Parameter in the Accelerating Dilaton
  Cosmology

abstract:
  In a semiclassically quantized two-dimensional cosmological model, it can be
shown that the parameter of the equation of state for the accelerating universe
can be positive due to the negative energy density and the negative pressure,
which is a little different from the conventional wisdom that the parameter is
negative with the positivity of the energy density. Furthermore, we show that
the full parameter composed of the classical and the quantum-mechanical
contributions is positive and finite even though the partial state parameter
from the quantum-mechanical contribution is not positive definite, which means
that the state parameter is not perturbatively additive in this model.


title:
Interactions between Multipolar Nuclear Transitions and Gravitational
  Waves

abstract:
  Interactions between multipolar nuclear transitions and gravitational waves
(GWs) are theoretically investigated. Two nonclassical scenarios of the GW
detection are suggested. We demonstrate in this report that the long-lived
Moessbauer nuclides of multipolar transitions are suitable transducers to
detect the impinging GWs. Shape deformation and spin flip of nucleus are
derived from the Hamiltonian with gravity interaction. The GWs generate a
nuclear quadrupole deformation in analogy with the Stark effect, of which the
electric field generates the dipole deformation of electron orbits. Likewise in
analogy with the nuclear magnetic resonance that the rotating radio-frequency
field flips the nuclear spin, the GWs flip the nuclear spin by the resonant
helicity-rotation-gravity coupling. The high energy states of the quadrupole
deformation in heavy nuclides can dramatically speed up the multipolar
transitions, which may be important for the GW detection particularly in the
low frequency band, ranging from 100 nHz to 1 Hz.


title:
Spherically symmetric solutions in f(R)-gravity via Noether Symmetry
  Approach

abstract:
  We search for spherically symmetric solutions of f(R) theories of gravity via
the Noether Symmetry Approach. A general formalism in the metric framework is
developed considering a point-like f(R)-Lagrangian where spherical symmetry is
required. Examples of exact solutions are given.


title:
First Cross-Correlation Analysis of Interferometric and Resonant-Bar
  Gravitational-Wave Data for Stochastic Backgrounds

abstract:
  Data from the LIGO Livingston interferometer and the ALLEGRO resonant bar
detector, taken during LIGO's fourth science run, were examined for
cross-correlations indicative of a stochastic gravitational-wave background in
the frequency range 850-950 Hz, with most of the sensitivity arising between
905 Hz and 925 Hz. ALLEGRO was operated in three different orientations during
the experiment to modulate the relative sign of gravitational-wave and
environmental correlations. No statistically significant correlations were seen
in any of the orientations, and the results were used to set a Bayesian 90%
confidence level upper limit of Omega_gw(f) <= 1.02, which corresponds to a
gravitational wave strain at 915 Hz of 1.5e-23/rHz. In the traditional units of
h_100^2 Omega_gw(f), this is a limit of 0.53, two orders of magnitude better
than the previous direct limit at these frequencies. The method was also
validated with successful extraction of simulated signals injected in hardware
and software.