title: Noether's theorem, the stress-energy tensor and Hamiltonian constraints

abstract:
  Noether's theorem is reviewed with a particular focus on an intermediate step
between global and local gauge and coordinate transformations, namely linear
transformations. We rederive the well known result that global symmetry leads
to charge conservation (Noether's first theorem), and show that linear symmetry
allows for the current to be expressed as a four divergence. Local symmetry
leads to identical conservation of the current and allows for the expression of
the charge as two dimensional surface integral (Noether's second theorem). In
the context of coordinate transformations, an additional step (Poincare
symmetry) is of physical interest and leads to the definition of the symmetric
Belinfante stress-energy tensor, which is then shown to be identically zero in
generally covariant first order theories. The intermediate step of linear
symmetry turns out to be important in general relativity when the customary
first order Lagrangian is used, which is covariant only under affine
transformations. In addition, we derive explicitely the canonical stress-energy
tensor in second order theories in its identically conserved form. Finally, we
analyze the relations between the generators of local transformations, the
corresponding currents and the Hamiltonian constraints.


title:
Complete model of a spherical gravitational wave detector with
  capacitive transducers. Calibration and sensitivity optimization

abstract:
  We report the results of a detailed numerical analysis of a real resonant
spherical gravitational wave antenna operating with six resonant two-mode
capacitive transducers read out by superconducting quantum interference devices
(SQUID) amplifiers. We derive a set of equations to describe the
electro-mechanical dynamics of the detector. The model takes into account the
effect of all the noise sources present in each transducer chain: the thermal
noise associated with the mechanical resonators, the thermal noise from the
superconducting impedance matching transformer, the back-action noise and the
additive current noise of the SQUID amplifier. Asymmetries in the detector
signal-to-noise ratio and bandwidth, coming from considering the transducers
not as point-like objects but as sensor with physically defined geometry and
dimension, are also investigated. We calculate the sensitivity for an
ultracryogenic, 30 ton, 2 meter in diameter, spherical detector with optimal
and non-optimal impedance matching of the electrical read-out scheme to the
mechanical modes. The results of the analysis is useful not only to optimize
existing smaller mass spherical detector like MiniGrail, in Leiden, but also as
a technological guideline for future massive detectors. Furthermore we
calculate the antenna patterns when the sphere operates with one, three and six
resonators. The sky coverage for two detectors based in The Netherlands and
Brasil and operating in coincidence is also estimated. Finally, we describe and
numerically verify a calibration and filtering procedure useful for diagnostic
and detection purposes in analogy with existing resonant bar detectors.


title: Towards classification of simple dark energy cosmological models

abstract:
  We characterize a class of simple FRW models filled by both dark energy and
dark matter in notion of a single potential function of the scale factor
$a(t)$; $t$ is the cosmological time. It is representing potential of
fictitious particle - Universe moving in 1-dimensional well $V(a)$ which the
positional variable mimics the evolution of the Universe. Then the class of all
dark energy models (called a multiverse) can be regarded as a Banach space
naturally equipment in the structure of the Sobolev metric. In this paper we
explore notion of $C^{1}$ metric introduced in the multiverse which measure
distance between any two dark energy models. If we choose cold dark matter as a
reference one then we can find how so far apart are different models offering
explanation of present accelerating expansion phase of the Universe. We
consider both models with dark energy (models with the generalized Chaplygin
gas, models with variable coefficient equation of state
$w_{X}=\frac{p_{X}}{\rho_{X}}$ parameterized by redshift $z$, models with
phantom matter) as well as models basing on some modification of the Friedmann
equation (Cardassian models, Dvali-Gabadadze-Porati brane models). We argue
that because observational data still favor the $\Lambda$CDM model all
reasonable dark energy models should belong to the nearby neighborhood of this
model.


title:
The arrow of time: from universe time-asymmetry to local irreversible
  processes

abstract:
  In several previous papers we have argued for a global and non-entropic
approach to the problem of the arrow of time, according to which the ''arrow''
is only a metaphorical way of expressing the geometrical time-asymmetry of the
universe. We have also shown that, under definite conditions, this global
time-asymmetry can be transferred to local contexts as an energy flow that
points to the same temporal direction all over the spacetime. The aim of this
paper is to complete the global and non-entropic program by showing that our
approach is able to account for irreversible local phenomena, which have been
traditionally considered as the physical origin of the arrow of time.


title: Large scale effective theory for cosmological bounces

abstract:
  An exactly solvable bounce model in loop quantum cosmology is identified
which serves as a perturbative basis for realistic bounce scenarios. Its
bouncing solutions are derived analytically, demonstrating why recent numerical
simulations robustly led to smooth bounces under the assumption of
semiclassicality. Several effects, easily included in a perturbative analysis,
can however change this smoothness. The effective theory is not only applicable
to such situations where numerical techniques become highly involved but also
allows one to discuss conceptual issues. For instance, consequences of the
notoriously difficult physical inner product can be implemented at the
effective level. This indicates that even physical predictions from full
quantum gravity can be obtained from perturbative effective equations.


title:
On a recently proposed scalar-tensor-vector metric extension of general
  relativity to explain the Pioneer anomaly

abstract:
  Recently, Brownstein and Moffat proposed a gravitational mechanism to explain
the Pioneer anomaly based on their scalar-tensor-vector (STVG) metric theory of
gravity. In this paper we show that their model, fitted to the presently
available data for the anomalous Pioneer 10/11 acceleration, is in contrast
with the latest determinations of the perihelion extra-rates of Jupiter, Saturn
and Uranus.


title: Codimension-two critical behavior in vacuum gravitational collapse

abstract:
  We consider the critical behavior at the threshold of black hole formation
for the five dimensional vacuum Einstein equations satisfying the
cohomogeneity-two triaxial Bianchi IX ansatz. Exploiting a discrete symmetry
present in this model we predict the existence of a codimension-two attractor.
This prediction is confirmed numerically and the codimension-two attractor is
identified as a discretely self-similar solution with two unstable modes.


title:
Detecting gravitational waves from inspiraling binaries with a network
  of detectors : coherent versus coincident strategies

abstract:
  We compare two strategies of multi-detector detection of compact binary
inspiral signals, namely, the coincidence and the coherent. For simplicity we
consider here two identical detectors having the same power spectral density of
noise, that of initial LIGO, located in the same place and having the same
orientation. We consider the cases of independent noise as well as that of
correlated noise. The coincident strategy involves separately making two
candidate event lists, one for each detector, and from these choosing those
pairs of events from the two lists which lie within a suitable parameter
window, which then are called as coincidence detections. The coherent strategy
on the other hand involves combining the data phase coherently, so as to obtain
a single network statistic which is then compared with a single threshold. Here
we attempt to shed light on the question as to which strategy is better. We
compare the performances of the two methods by plotting the Receiver Operating
Characteristics (ROC) for the two strategies. Several of the results are
obtained analytically in order to gain insight. Further we perform numerical
simulations in order to determine certain parameters in the analytic formulae
and thus obtain the final complete results. We consider here several cases from
the relatively simple to the astrophysically more relevant in order to
establish our results. The bottom line is that the coherent strategy although
more computationally expensive in general than the coincidence strategy, is
superior to the coincidence strategy - considerably less false dismissal
probability for the same false alarm probability in the viable false alarm
regime.


title:
Tachyons described by infinitely degenereate massless-fields and dark
  matters in the universe

abstract:
  A tachyon field having a negative squared-mass $-m_t^2$ can be described in
terms of massless fields degenerating infinitely with respect to helicities.
This picture for tachyons does not contradict causality. It is seen that the
tachyon vector field can be quenched from the interactions with matter fields,
and the effects can be represented by a phase factor. The accelerated expansion
of the universe and the dark energies are interpreted in terms of the phase
factor.


title: The Lense-Thirring effect and the Pioneer anomaly: Solar System tests

abstract:
  We report on a \lessim 1% test of the Lense-Thirring effect with the Mars
Global Surveyor (MGS) spacecraft and on certain features of motion of Uranus,
Neptune and Pluto which contradict the hypothesis that the Pioneer anomaly can
be caused by some gravitational mechanism.

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


title:
On the Sensitivity of a Hollow Sphere as a Multi-modal Resonant
  Gravitational Wave Detector

abstract:
  We present a numerical analysis to simulate the response of a spherical
resonant gravitational wave detector and to compute its sensitivity. Under the
assump- tion of optimal filtering, we work out the sensitivity curve for a
sphere first taking into account only a single transducer, and then using a
coherent analysis of the whole set of transducers.


title: FRW Universe with Variable $G$ and $\Lambda$-Terms

abstract:
  A new class of exact solutions of Einstein's field equations with a perfect
fluid source, variable gravitational coupling $G$ and cosmological term
$\Lambda$ for FRW spacetime is obtained by considering variable deceleration
parameter models for the universe. The nature of the variables $G(t)$,
$\Lambda(t)$ and the energy density $\rho(t)$ have been examined for three
cases : (i) exponential (ii) polynomial and (iii) sinusoidal form. The special
types of models for dust, Zel'dovich and radiating universe are also mentioned
in all these cases. The behaviour of these models of the universe are also
discussed in the light of recent supernovae Ia observations.


title: Global solutions of the Einstein-Maxwell equations in higher dimensions

abstract:
  We consider the Einstein-Maxwell equations in space-dimension $n$. We point
out that the Lindblad-Rodnianski stability proof applies to those equations
whatever the space-dimension $n\ge 3$. In even space-time dimension $n+1\ge 6$
we use the standard conformal method on a Minkowski background to give a simple
proof that the maximal globally hyperbolic development of initial data sets
which are sufficiently close to the data for Minkowski space-time and which are
Schwarzschildian outside of a compact set lead to geodesically complete
space-times, with a complete Scri, with smooth conformal structure, and with
the gravitational field approaching the Minkowski metric along null directions
at least as fast as $r^{-(n-1)/2}$.


title: The dynamics of scalar-tensor cosmology from RS two-brane model

abstract:
  We consider a Randall-Sundrum two-brane cosmological model in the low energy
gradient expansion approximation by Kanno and Soda. It is a scalar-tensor
theory with a specific coupling function and a specific potential. Upon
introducing the FLRW metric and perfect fluid matter on both branes in the
Jordan frame, the effective dynamical equation for the the A-brane (our
Universe) scale factor decouples from the scalar field and B-brane matter
leaving only a non-vanishing integration constant (the dark radiation term). We
find exact solutions for the A-brane scale factor for four types of matter:
cosmological constant, radiation, dust, and cosmological constant plus
radiation. We perform a complementary analysis of the dynamics of the scalar
field (radion) using phase space methods and examine convergence towards the
limit of general relativity. In particular, we find that radion stabilizes at a
certain finite value for suitable negative matter densities on the B-brane.
Observational constraints from Solar system experiments (PPN) and primordial
nucleosynthesis (BBN) are also briefly discussed.


title: Spinning Gravitating Skyrmions

abstract:
  We investigate self-gravitating rotating solutions in the Einstein-Skyrme
theory. These solutions are globally regular and asymptotically flat. We
present a new kind of solutions with zero baryon number, which possess neither
a flat limit nor a static limit.


title:
The Colliding Plane Wave and Energy-Momentum Problems in General
  Relativity and Teleparallel Gravity

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0603075, 0706.3245, gr-qc/0403097, gr-qc/0404108, gr-qc/0303034,
hep-th/0206052, and others.
  This paper has excessive overlap with the following papers also written by
the authors or their collaborators: 0704.0525 and others.


title:
Slice & Dice: Identifying and Removing Bright Galactic Binaries from
  LISA Data

abstract:
  Here we describe a hierarchal and iterative data analysis algorithm used for
searching, characterizing, and removing bright, monochromatic binaries from the
Laser Interferometer Space Antenna (LISA) data streams. The algorithm uses the
F-statistic to provide an initial solution for individual bright sources,
followed by an iterative least squares fitting for all the bright sources.
Using the above algorithm, referred to as Slice & Dice, we demonstrate the
removal of multiple, correlated galactic binaries from simulated LISA data.
Initial results indicate that Slice & Dice may be a useful tool for analyzing
the forthcoming LISA data.


title:
Challenging the paradigm of singularity excision in gravitational
  collapse

abstract:
  A paradigm deeply rooted in modern numerical relativity calculations
prescribes the removal of those regions of the computational domain where a
physical singularity may develop. We here challenge this paradigm by performing
three-dimensional simulations of the collapse of uniformly rotating stars to
black holes without excision. We show that this choice, combined with suitable
gauge conditions and the use of minute numerical dissipation, improves
dramatically the long-term stability of the evolutions. In turn, this allows
for the calculation of the waveforms well beyond what previously possible,
providing information on the black-hole ringing and setting a new mark on the
present knowledge of the gravitational-wave emission from the stellar collapse
to a rotating black hole.


title: When is Enough Good Enough in Gravitational Wave Source Modeling?

abstract:
  A typical approach to developing an analysis algorithm for analyzing
gravitational wave data is to assume a particular waveform and use its
characteristics to formulate a detection criteria. Once a detection has been
made, the algorithm uses those same characteristics to tease out parameter
estimates from a given data set. While an obvious starting point, such an
approach is initiated by assuming a single, correct model for the waveform
regardless of the signal strength, observation length, noise, etc. This paper
introduces the method of Bayesian model selection as a way to select the most
plausible waveform model from a set of models given the data and prior
information. The discussion is done in the scientific context for the proposed
Laser Interferometer Space Antenna.


title: Nonuniform black strings in various dimensions

abstract:
  The nonuniform black strings branch, which emerges from the critical
Gregory-Laflamme string, is numerically constructed in dimensions 6 <= D <= 11
and extended into the strongly non-linear regime. All the solutions are more
massive and less entropic than the marginal string. We find the asymptotic
values of the mass, the entropy and other physical variables in the limit of
large horizon deformations. By explicit metric comparison we verify that the
local geometry around the ``waist'' of our most nonuniform solutions is
cone-like with less than 10% deviation. We find evidence that in this regime
the characteristic length scale has a power-law dependence on a parameter along
the branch of the solutions, and estimate the critical exponent.


title: Causality and matter propagation in 3d spin foam quantum gravity

abstract:
  In this paper we tackle the issue of causality in quantum gravity, in the
context of 3d spin foam models. We identify the correct procedure for
implementing the causality/orientation dependence restriction that reduces the
path integral for BF theory to that of quantum gravity in first order form. We
construct explicitly the resulting causal spin foam model. We then add matter
degrees of freedom to it and construct a causal spin foam model for 3d quantum
gravity coupled to matter fields. Finally, we show that the corresponding spin
foam amplitudes admit a natural approximation as the Feynman amplitudes of a
non-commutative quantum field theory, with the appropriate Feynman propagators
weighting the lines of propagation, and that this effective field theory
reduces to usual QFT in flat space in the no-gravity limit.


title: Numerical Analysis of the Big Bounce in Loop Quantum Cosmology

abstract:
  Loop quantum cosmology homogeneous models with a massless scalar field show
that the big-bang singularity can be replaced by a big quantum bounce. To gain
further insight on the nature of this bounce, we study the semi-discrete loop
quantum gravity Hamiltonian constraint equation from the point of view of
numerical analysis. For illustration purposes, we establish a numerical analogy
between the quantum bounces and reflections in finite difference
discretizations of wave equations triggered by the use of nonuniform grids or,
equivalently, reflections found when solving numerically wave equations with
varying coefficients. We show that the bounce is closely related to the method
for the temporal update of the system and demonstrate that explicit
time-updates in general yield bounces. Finally, we present an example of an
implicit time-update devoid of bounces and show back-in-time, deterministic
evolutions that reach and partially jump over the big-bang singularity.


title: Rigidity of marginally trapped surfaces and the topology of black holes

abstract:
  In a recent paper (gr-qc/0509107) the author and Rick Schoen obtained a
generalization to higher dimensions of a classical result of Hawking concerning
the topology of black holes. It was proved that, apart from certain exceptional
circumstances, cross sections of the event horizon, in the stationary case, and
'weakly outermost' marginally outer trapped surfaces, in the general case, in
black hole spacetimes obeying the dominant energy condition, are of positive
Yamabe type. This implies many well-known restrictions on the topology, and is
consistent with recent examples of five dimensional stationary black hole
spacetimes with horizon topology $S^2 \times S^1$. In the present paper, we
rule out for 'outermost' marginally outer trapped surfaces, in particular, for
cross sections of the event horizon in stationary black hole spacetimes, the
possibility of any such exceptional circumstances (which might have permitted,
e.g., toroidal cross sections). This follows from the main result, which is a
rigidity result for marginally outer trapped surfaces that are not of positive
Yamabe type.


title:
An assessment of the measurement of the Lense-Thirring effect in the
  Earth gravity field, in reply to: ``On the measurement of the Lense-Thirring
  effect using the nodes of the LAGEOS satellites, in reply to ``On the
  reliability of the so far performed tests for measuring the Lense-Thirring
  effect with the LAGEOS satellites'' by L. Iorio,'' by I. Ciufolini and E.
  Pavlis

abstract:
  In this paper we reply to recent claims by Ciufolini and Pavlis about certain
aspects of the measurement of the general relativistic Lense-Thirring effect in
the gravitational field of the Earth. I) The proposal by such authors of using
the existing satellites endowed with some active mechanism of compensation of
the non-gravitational perturbations as an alternative strategy to improve the
currently ongoing Lense-Thirring tests is unfeasible because of the impact of
the uncancelled even zonal harmonics of the geopotential and of some
time-dependent tidal perturbations. II) It is shown that their criticisms about
the possibility of using the existing altimeter Jason-1 and laser-ranged Ajisai
satellites are groundless.III) Ciufolini and Pavlis also claimed that we would
have explicitly proposed to use the mean anomaly of the LAGEOS satellites in
order to improve the accuracy of the Lense-Thirrring tests. We prove that it is
false. In regard to the mean anomaly of the LAGEOS satellites, Ciufolini
himself did use such an orbital element in some previously published tests.
About the latest test performed with the LAGEOS satellites, IV) we discuss the
cross-coupling between the inclination errors and the first even zonal harmonic
as another possible source of systematic error affecting it with an additional
9% bias. V) Finally, we stress the weak points of the claims about the origin
of the two-nodes LAGEOS-LAGEOS II combination used in that test.

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


title: On a time-dependent extra spatial dimension

abstract:
  In the usual brane-world scenario matter fields are confined to the
four-dimensional spacetime, called a 3-brane, embedded in a higher-dimensional
space, usually referred to as the bulk spacetime. In this paper we assume that
the 3-brane is a de Sitter space; there is only one extra spatial dimension,
assumed to be time dependent. By using the form of the brane-world
energy-momentum tensor suggested by Shiromizu et al. in the five-dimensional
Einstein equations, it is proposed that the cosmological expansion of the
3-brane may provide a possible explanation for the collapse of the extra
dimension, as well as for the energy stored in the resulting curled-up
dimension. More precisely, whenever the bulk cosmological constant \Lambda is
negative, the extra spatial dimension rapidly shrinks during the inflation of
the brane. When \Lambda is positive, on the other hand, the extra spatial
dimension either completely follows the cosmological expansion of the brane or
completely ignores it, thereby shrinking relative to the expanding space. This
behavior resembles the all-or-nothing behavior of ordinary systems in an
expanding universe, as recently demonstrated by R.H. Price.


title: Constraining Torsion with Gravity Probe B

abstract:
  It is well-entrenched folklore that torsion gravity theories predict
observationally negligible torsion in the solar system, since torsion (if it
exists) couples only to the intrinsic spin of elementary particles, not to
rotational angular momentum. We argue that this assumption has a logical
loophole which can and should be tested experimentally. In the spirit of
action=reaction, if a rotating mass like a planet can generate torsion, then a
gyroscope should also feel torsion. Using symmetry arguments, we show that to
lowest order, the torsion field around a uniformly rotating spherical mass is
determined by seven dimensionless parameters. These parameters effectively
generalize the PPN formalism and provide a concrete framework for further
testing GR. We construct a parametrized Lagrangian that includes both standard
torsion-free GR and Hayashi- Shirafuji maximal torsion gravity as special
cases. We demonstrate that classic solar system tests rule out the latter and
constrain two observable parameters. We show that Gravity Probe B (GPB) is an
ideal experiment for further constraining torsion theories, and work out the
most general torsion-induced precession of its gyroscope in terms of our
torsion parameters


title: Canonical entropy of three-dimensional BTZ black hole

abstract:
  Recently, Hawking radiation of the black hole has been studied using the
tunnel effect method. It is found that the radiation spectrum of the black hole
is not a strictly pure thermal spectrum. How does the departure from pure
thermal spectrum affect the entropy? This is a very interesting problem. In
this paper, we calculate the partition function by energy spectrum obtained
from tunnel effect. Using the partition function, we compute the black hole
entropy and derive the expression of the black hole entropy after considering
the radiation. And we derive the entropy of charged black hole. In our
calculation, we consider not only the correction to the black hole entropy due
to fluctuation of energy but also the effect of the change of the black hole
charges on entropy. There is no other hypothesis. Our result is more
reasonable.According to the fact that the black hole entropy is not divergent,
we obtain the lower limit of Banados-Teitelboim-Zanelli black hole energy. That
is, the least energy of Banados-Teitelboim-Zanelli black hole, which satisfies
the stationary condition in thermodynamics.


title: Canonical Entropy of charged black hole

abstract:
  Recently, Hawking radiation of the black hole has been studied by using the
tunnel effect method. It is found that the radiation spectrum of the black hole
is not a strictly pure thermal spectrum. How does the departure from pure
thermal spectrum affect the entropy? This is a very interesting problem. In
this paper, we calculate the partition function through energy spectrum
obtained by using the tunnel effect. From the relation between the partition
function and canonical entropy, we can derive the entropy of charged black
hole. In our calculation, we consider not only the correction to the black hole
entropy due to fluctuation of energy, but also the effect of the change in the
black hole charges on entropy. There is not any assumption. This makes our
result more reliable.


title: Loop Quantum Gravity Modification of the Compton Effect

abstract:
  Modified dispersion relations(MDRs) as a manifestation of Lorentz invariance
violation, have been appeared in alternative approaches to quantum gravity
problem. Loop quantum gravity is one of these approaches which evidently
requires modification of dispersion relations. These MDRs will affect the usual
formulation of the Compton effect. The purpose of this paper is to incorporate
the effects of loop quantum gravity MDRs on the formulation of Compton
scattering. Using limitations imposed on MDRs parameters from Ultra High Energy
Cosmic Rays(UHECR), we estimate the quantum gravity-induced wavelength shift of
scattered photons in a typical Compton process. Possible experimental detection
of this wavelength shift will provide strong support for underlying quantum
gravity proposal.


title:
Asymptotic singular behaviour of inhomogeneous cosmologies in
  Einstein-Maxwell-dilaton-axion theory

abstract:
  We present the study of exact inhomogeneous cosmological solutions to a
four-dimensional low energy limit of string theory containing non-minimal
interacting electromagnetic, dilaton and axion fields. We analyze
Einstein-Rosen solutions of Einstein-Maxwell-dilaton-axion equations and show,
by explicitly taken the asymptotic limits, that they have asymptotically
velocity-term dominated (AVTD) singularities.


title: Large-scale structure and the Cardassian fluid

abstract:
  In this paper, we confront the predictions of the power law cardassian model
for the baryon power spectrum with the observations of the SDSS galaxy survey.
We show that they fit only for very unusual values of the cold dark matter or
baryon density parameters, the Hubble parameter or the spectral index of the
initial power spectrum. Moreover, the best-fit Cardassian models turn out to be
phantom models. If one wants to recover the usual values for these constants,
as quoted by the WMAP team, the power law Cardassian model turns out to be
indistinguishable from a LCDM model.


title:
Test of the Pioneer anomaly with the Voyager 2 radio-ranging distance
  measurements to Uranus and Neptune

abstract:
  In this paper we test the hypothesis that the Pioneer anomaly can be of
gravitational origin by comparing the predicted model-independent shifts Delta
a/a for the semimajor axis of Uranus and Neptune with the Voyager 2
radio-technical distance measurements performed at JPL-NASA. As in the case of
other tests based on different methods and data sets (secular perihelion
advance, right ascension/declination residuals over about one century), the
orbits of the investigated planets are not affected by any anomalous
acceleration like that experienced by the Pioneer 10/11 spacecraft.


title: Optimal degeneracy for the signal-recycling cavity in advanced LIGO

abstract:
  As currently designed, the signal-recycling cavity (SRC) in the Advanced-LIGO
interferometer is degenerate. In such a degenerate cavity, the phase fronts of
optical fields become badly distorted when the mirror shapes are slightly
deformed due to mirror figure error and/or thermal aberration, and this causes
significant loss of the signal power and the signal-to-noise ratio (SNR) of a
gravitational wave event. Through a numerical modal simulation of the optical
fields in a simplified model of an Advanced-LIGO interferometer, We investigate
the loss of the SNR and the behavior of both the carrier and signal optical
fields, with the SRC at various levels of degeneracy. We show that the loss of
the SNR is severe with a degenerate SRC, and a nondegenerate SRC can be used to
solve this problem. We identify the optimal level of degeneracy for the SRC,
which is achieved when the cavity Gouy phase is between 0.2 and 1.3 radians. We
also discuss possible alternative designs of the SRC to achieve this optimal
degeneracy.


title: Leopold Halpern and the generalization of general relativity

abstract:
  Leopold Halpern, who was a close associate of both Erwin Schroedinger and
Paul Dirac before making his own mark as a theoretical physicist of the first
rank, died in Tallahassee, Florida on 3 June 2006 after a valiant struggle with
cancer. We give an outline of his life and work, including his progress towards
a unified gauge theory of gravitation and spin.


title: Hamilton-Jacobi Approach for Power-Law Potentials

abstract:
  The classical and relativistic Hamilton-Jacobi approach is applied to the
one-dimensional homogeneous potential, $V(q)=\alpha q^n$, where $\alpha$ and
$n$ are continuously varying parameters. In the non-relativistic case, the
exact analytical solution is determined in terms of $\alpha$, $n$ and the total
energy $E$. It is also shown that the non-linear equation of motion can be
linearized by constructing a hypergeometric differential equation for the
inverse problem $t(q)$. A variable transformation reducing the general problem
to that one of a particle subjected to a linear force is also established. For
any value of $n$, it leads to a simple harmonic oscillator if $E>0$, an
"anti-oscillator" if $E<0$, or a free particle if E=0. However, such a
reduction is not possible in the relativistic case. For a bounded relativistic
motion, the first order correction to the period is determined for any value of
$n$. For $n >> 1$, it is found that the correction is just twice that one
deduced for the simple harmonic oscillator ($n=2$), and does not depend on the
specific value of $n$.


title: Group Integral Techniques for the Spinfoam Graviton Propagator

abstract:
  We consider the proposal of gr-qc/0508124 for the extraction of the graviton
propagator from the spinfoam formalism. We propose a new ansatz for the
boundary state, using which we can write the propagator as an integral over
SU(2). The perturbative expansion in the Planck length can be recast into the
saddle point expansion of this integral. We compute the leading order and
recover the behavior expected from low-energy physics. In particular, we prove
that the degenerate spinfoam configurations are suppressed.


title: Non-spherical collapse of a two fluid star

abstract:
  We obtain the analogue of collapsing Vaidya-like solution to include both a
null fluid and a string fluid, with a linear equation of state ($p_{\bot} = k
\rho$), in non-spherical (plane symmetric and cylindrically symmetric) anti-de
Sitter space-timess. It turns out that the non-spherical collapse of two fluid
in anti-de Sitter space-times, in accordance with cosmic censorship, proceed to
form black holes, i.e., on naked singularity ever forms, violating hoop
conjecture.


title: Local Temperature in Curved Spacetime

abstract:
  A physically meaningful local concept of temperature is introduced in quantum
field theory on curved spacetime and applied to the example of a massless field
on de Sitter space. It turns out in this model that the equilibrium (Gibbs)
states which can be prepared by a geodesic observer have in general a varying
temperature distribution in the neighborhood of the geodesic and may not even
allow for a consistent thermal interpretation close to the horizon. This
result, which can be traced back to the Unruh effect, illustrates the failure
of a global notion of temperature in curved spacetime and reveals the need for
a local concept, as presented here.


title: Kinematic and Weyl singularities

abstract:
  We study the properties of a future singularity encountered by a perfect
fluid observer in tilting spatially homogeneous Bianchi cosmologies. We derive
the boost formulae for the Weyl tensor to establish that, for two observers
that are asymptotically null with respect to each other, their respective Weyl
parameters generally both tend to zero, constant, or infinity together. We
examine three classes of typical examples and one exceptional class. Given the
behaviour of the Weyl parameter, we can predict that the singularity
encountered is a Weyl singularity or a kinematic singularity. The analysis
suggests that the kinematic variables are also useful in indicating a
singularity in these models.


title: Towards a Covariant Loop Quantum Gravity

abstract:
  We review the canonical analysis of the Palatini action without going to the
time gauge as in the standard derivation of Loop Quantum Gravity. This allows
to keep track of the Lorentz gauge symmetry and leads to a theory of Covariant
Loop Quantum Gravity. This new formulation does not suffer from the Immirzi
ambiguity, it has a continuous area spectrum and uses spin networks for the
Lorentz group. Finally, its dynamics can easily be related to Barrett-Crane
like spin foam models.


title: Spherical gravitational collapse in N-dimensions

abstract:
  We investigate here spherically symmetric gravitational collapse in a
spacetime with an arbitrary number of dimensions and with a general {\it type
I} matter field, which is a broad class that includes most of the physically
reasonable matter forms. We show that given the initial data for matter in
terms of the initial density and pressure profiles at an initial surface
$t=t_i$ from which the collapse evolves, there exist rest of the initial data
functions and classes of solutions of Einstein equations which we construct
here, such that the spacetime evolution goes to a final state which is either a
black hole or a naked singularity, depending on the nature of initial data and
evolutions chosen, and subject to validity of the weak energy condition. The
results are discussed and analyzed in the light of the cosmic censorship
hypothesis in black hole physics. The formalism here combines the earlier
results on gravitational collapse in four dimensions in a unified treatment.
Also the earlier work is generalized to higher dimensional spacetimes to allow
a study of the effect of number of dimensions on the possible final outcome of
the collapse in terms of either a black hole or naked singularity. No
restriction is adopted on the number of dimensions, and other limiting
assumptions such as self-similarity of spacetime are avoided, in order to keep
the treatment general. Our methodology allows to consider to an extent the
genericity and stability aspects related to the occurrence of naked
singularities in gravitational collapse.


title: The Dominant Balance at Cosmological Singularities

abstract:
  We define the notion of a finite-time singularity of a vector field and then
discuss a technique suitable for the asymptotic analysis of vector fields and
their integral curves in the neighborhood of such a singularity. Having in mind
the application of this method to cosmology, we also provide an analysis of the
time singularities of an isotropic universe filled with a perfect fluid in
general relativity.


title: Optimal Source Tracking and Beaming of LISA

abstract:
  We revisit the directionally optimal data streams of LISA first introduced in
Nayak etal. It was shown that by using appropriate choice of Time delay
interferometric (TDI) combinations, a monochromatic fixed source in the
barycentric frame can be optimally tracked in the LISA frame. In this work, we
study the beaming properties of these optimal streams. We show that all the
three streams V+, Vx and Vo with maximum, minimum and zero directional SNR
respectively are highly beamed. We study in detail the frequency dependence of
the beaming.


title:
On the equilibrium of a charged massive particle in the field of a
  Reissner-Nordstr\"om black hole

abstract:
  The multiyear problem of a two-body system consisting of a
Reissner-Nordstr\"om black hole and a charged massive particle at rest is here
solved by an exact perturbative solution of the full Einstein-Maxwell system of
equations. The expressions of the metric and of the electromagnetic field,
including the effects of the electromagnetically induced gravitational
perturbation and of the gravitationally induced electromagnetic perturbation,
are presented in closed analytic formulas.


title: (Sort of) Testing relativity with extreme mass ratio inspirals

abstract:
  The inspirals of ``small'' ($1 - 100 M_\odot$) compact bodies through highly
relativistic orbits of massive (several $\times 10^5 M_\odot -$ several $\times
10^6 M_\odot$) black holes are among the most anticipated sources for the LISA
gravitational-wave antenna. The measurement of these waves is expected to map
the spacetime of the larger body with high precision, allowing us to test in
detail the hypothesis that black hole candidates are described by the Kerr
metric of general relativity. In this article, we will briefly describe how
these sources can be used to perform such a test. These proposed measurements
are often described as ``testing relativity''. This description is at best
somewhat glib: Because -- at least to date -- all work related to these
measurements assumes general relativity as the theoretical framework in which
these tests are performed, the measurements cannot be said to ``test
relativity'' in a fundamental way. More accurately, they test the {\it nature
of massive compact bodies within general relativity}. A surprising result for
such a test could point to deviations from general relativity, and would
provide an experimentally motivated direction in which to pursue tests of
gravity theories beyond GR.


title:
Fractal Holography: a geometric re-interpretation of cosmological large
  scale structure

abstract:
  The fractal dimension of large-scale galaxy clustering has been demonstrated
to be roughly $D_F \sim 2$ from a wide range of redshift surveys. If correct,
this statistic is of interest for two main reasons: fractal scaling is an
implicit representation of information content, and also the value itself is a
geometric signature of area. It is proposed that the fractal distribution of
galaxies may thus be interpreted as a signature of holography (``fractal
holography''), providing more support for current theories of holographic
cosmologies. Implications for entropy bounds are addressed. In particular,
because of spatial scale invariance in the matter distribution, it is shown
that violations of the spherical entropy bound can be removed. This holographic
condition instead becomes a rigid constraint on the nature of the matter
density and distribution in the Universe. Inclusion of a dark matter
distribution is also discussed, based on theoretical considerations of possible
universal CDM density profiles.


title:
Accurate time-domain gravitational waveforms for extreme-mass-ratio
  binaries

abstract:
  The accuracy of time-domain solutions of the inhomogeneous Teukolsky equation
is improved significantly. Comparing energy fluxes in gravitational waves with
highly accurate frequency-domain results for circular equatorial orbits in
Schwarzschild and Kerr, we find agreement to within 1% or better, which we
believe can be even further improved. We apply our method to orbits for which
frequency-domain calculations have a relative disadvantage, specifically
high-eccentricity (elliptical and parabolic) "zoom-whirl" orbits, and find the
energy fluxes, waveforms, and characteristic strain in gravitational waves.


title: On A 5-Dimensional Spinning Cosmic String

abstract:
  We present a numerical solution of a stationary 5-dimensional spinning cosmic
string in the Einstein-Yang-Mills (EYM) model, where the extra bulk coordinate
$\psi$ is periodic. It turns out that when $g_{\psi\psi}$ approaches zero,
i.e., a closed time-like curve (CTC) would appear, the solution becomes
singular. When a negative cosmological constant is incorporated in the model,
the solution becomes regular everywhere with angle deficit$<2\pi$. However, the
cosmic string-like object has not all the desired asymptotic properties of the
counterpart Abelian Nielsen-Olesen string. When we use a two point boundary
value routine with the correct cosmic string features far from the core, then
again a negative $\Lambda$ results in an acceptable string-like solution.
  We also investigated the possibility of a Gott space time structure of the
static 5D cosmic string. The matching condition yields no obstruction for an
effective angle deficit. Moreover, by considering the angular momentum in bulk
space, no helical structure of time is necessary. Two opposite moving 5D
strings could, in contrast with the 4D case, fulfil the Gott condition.


title:
Calculation of the Cosmological Constant by Unifying Matter and Dark
  Energy

abstract:
  This paper has been withdrawn by the authors due to the too limited range of
the current version of the model (the dark energy fraction is constant, but it
has to be a function of the scale factor). We will resubmit the paper after
extension.


title: Fishing in Black Holes

abstract:
  The coordinate system $(\bar{x},\bar{t})$ defined by $r = 2m + K\bar{x}- c K
\bar{t}$ and $t=\bar{x}/cK - 1 /cK \int_{r_a}^r (1- 2m/r + K^2)^{1/2} (1 -
2m/r)^{-1}dr$ allow us to write the Schwarzschild metric in the form:
\[ds^2=c^2 d\bar{t}^2 + (W^2/K^2 - 2W/K) d\bar{x}^2 + 2c (1 + W/K)
d\bar{x}d\bar{t} - r^2 (d\theta^2 + cos^2\theta d\phi^2)\] with $W=(1 - 2m/r +
K^2)^{1/2}$, in which the coefficients' pathologies are moved to $r_K =
2m/(1+K^2)$. This new coordinate system is used to study the entrance into a
black hole of a rigid line (a line in which the shock waves propagate with
velocity c).


title: The Arrow of Time Forbids a Positive Cosmological Constant $\Lambda$

abstract:
  Motivated by the mounting evidence for dark energy, here we explore the
consequences of a fundamental cosmological constant $\Lambda$ for our universe.
We show that when the gravitational entropy of a pure DeSitter state ultimately
wins over matter, then the thermodynamic arrow of time in our universe must
reverse in scales of order a Hubble time. We find that due to the dynamics of
gravity and nonlocal entanglement, a finite size system such as a DeSitter
patch with horizon size $H_0^{-1}$ has a finite lifetime $\Delta t$. This
phenomenon arises from the dynamic gravitational instabilities that develop
during a DeSitter epoch and turn catastrophic. A reversed arrow of time is
clearly in disagreement with observations. Thus we are led to conclude: Nature
forbids a fundamental $\Lambda$. Or else general relativity must be modified in
the IR regime when $\Lambda$ dominates the expansion of the Universe.


title: Averaged null energy condition in spacetimes with boundaries

abstract:
  The Averaged Null Energy Condition (ANEC) requires that the average along a
complete null geodesic of the projection of the stress-energy tensor onto the
geodesic tangent vector can never be negative. It is sufficient to rule out
many exotic phenomena in general relativity. Subject to certain conditions, we
show that the ANEC can never be violated by a quantized minimally coupled free
scalar field along a complete null geodesic surrounded by a tubular
neighborhood in which the geometry is flat and whose intrinsic causal structure
coincides with that induced from the full spacetime. In particular, the ANEC
holds in flat space with boundaries, as in the Casimir effect, for geodesics
which stay a finite distance away from the boundary


title: Angular momentum conservation for dynamical black holes

abstract:
  Angular momentum can be defined by rearranging the Komar surface integral in
terms of a twist form, encoding the twisting around of space-time due to a
rotating mass, and an axial vector. If the axial vector is a coordinate vector
and has vanishing transverse divergence, it can be uniquely specified under
certain generic conditions. Along a trapping horizon, a conservation law
expresses the rate of change of angular momentum of a general black hole in
terms of angular momentum densities of matter and gravitational radiation. This
identifies the transverse-normal block of an effective gravitational-radiation
energy tensor, whose normal-normal block was recently identified in a
corresponding energy conservation law. Angular momentum and energy are dual
respectively to the axial vector and a previously identified vector, the
conservation equations taking the same form. Including charge conservation, the
three conserved quantities yield definitions of an effective energy, electric
potential, angular velocity and surface gravity, satisfying a dynamical version
of the so-called first law of black-hole mechanics. A corresponding zeroth law
holds for null trapping horizons, resolving an ambiguity in taking the null
limit.


title: Some analytical models of radiating collapsing spheres

abstract:
  We present some analytical solutions to the Einstein equations, describing
radiating collapsing spheres in the diffusion approximation. Solutions allow
for modeling physical reasonable situations. The temperature is calculated for
each solution, using a hyperbolic transport equation, which permits to exhibit
the influence of relaxational effects on the dynamics of the system.


title: Automatic Bayesian inference for LISA data analysis strategies

abstract:
  We demonstrate the use of automatic Bayesian inference for the analysis of
LISA data sets. In particular we describe a new automatic Reversible Jump
Markov Chain Monte Carlo method to evaluate the posterior probability density
functions of the a priori unknown number of parameters that describe the
gravitational wave signals present in the data. We apply the algorithm to a
simulated LISA data set containing overlapping signals from white dwarf binary
systems (DWD) and to a separate data set containing a signal from an extreme
mass ratio inspiral (EMRI). We demonstrate that the approach works well in both
cases and can be regarded as a viable approach to tackle LISA data analysis
challenges.


title: The Cosmological Constant Problem, an Inspiration for New Physics

abstract:
  We have critically compared different approaches to the cosmological constant
problem, which is at the edge of elementary particle physics and cosmology.
This problem is deeply connected with the difficulties formulating a theory of
quantum gravity. After the 1998 discovery that our universe's expansion is
accelerating, the cosmological constant problem has obtained a new dimension.
We are mainly interested in the question why the cosmological constant is so
small. We have identified four different classes of solutions: a symmetry, a
back-reaction mechanism, a violation of (some of) the building blocks of
general relativity, and statistical approaches. In this thesis we carefully
study all known potential candidates for a solution, but conclude that so far
none of the approaches gives a satisfactory solution. A symmetry would be the
most elegant solution and we study a new symmetry under transformation to
imaginary spacetime.


title: Why Does Gravity Ignore the Vacuum Energy?

abstract:
  The equations of motion for matter fields are invariant under the shift of
the matter lagrangian by a constant. Such a shift changes the energy momentum
tensor of matter by T^a_b --> T^a_b +\rho \delta^a_b. In the conventional
approach, gravity breaks this symmetry and the gravitational field equations
are not invariant under such a shift of the energy momentum tensor. I argue
that until this symmetry is restored, one cannot obtain a satisfactory solution
to the cosmological constant problem. I describe an alternative perspective to
gravity in which the gravitational field equations are [G_{ab} -\kappa T_{ab}]
n^an^b =0 for all null vectors n^a. This is obviously invariant under the
change T^a_b --> T^a_b +\rho \delta^a_b and restores the symmetry under
shifting the matter lagrangian by a constant. These equations are equivalent to
G_{ab} = \kappa T_{ab} + Cg_{ab} where C is now an integration constant so that
the role of the cosmological constant is very different in this approach. The
cosmological constant now arises as an integration constant, somewhat like the
mass M in the Schwarzschild metric, the value of which can be chosen depending
on the physical context. These equations can be obtained from a variational
principle which uses the null surfaces of spacetime as local Rindler horizons
and can be given a thermodynamic interpretation. This approach turns out to be
quite general and can encompass even the higher order corrections to Einstein's
gravity and suggests a principle to determine the form of these corrections in
a systematic manner.


title: Dissipative generalized Chaplygin gas as phantom dark energy

abstract:
  The generalized Chaplygin gas, characterized by the equation of state
$p=-\mathcal{A}/\rho^{\alpha}$, has been considered as a model for dark energy
due its dark-energy-like evolution at late times. When dissipative processes
are taken account, within the framework of the standard Eckart theory of
relativistic irreversible thermodynamics, cosmological analytical solutions are
found. Using the truncated causal version of the Israel-Stewart formalism, a
suitable model was constructed which cross the $w=-1$ barrier. The
future-singularities encounter in both approaches are of a new type, not
included in the classification presented by S. Nojiri, S. D. Odintsov and S.
Tsujikawa, Phys. Rev. D71, 063004 (2005).


title: Tracking quintessence and k-essence in a general cosmological background

abstract:
  We derive conditions for stable tracker solutions for both quintessence and
k-essence in a general cosmological background, H^2 \propto f(\rho). We find
that tracker solutions are possible only when \eta = d ln f /d ln \rho is
constant, aside from a few special cases, which are enumerated. Expressions for
the quintessence or k-essence equation of state are derived as a function of
\eta and the equation of state of the dominant background component.


title:
Modelling the post-Newtonian test-mass gravitational wave flux function
  for compact binary systems using Chebyshev polynomials

abstract:
  We introduce a new method for modelling the gravitational wave flux function
of a test-mass particle inspiralling into an intermediate mass Schwarzschild
black hole which is based on Chebyshev polynomials of the first kind. It is
believed that these Intermediate Mass Ratio Inspiral events (IMRI) are expected
to be seen in both the ground and space based detectors. Starting with the
post-Newtonian expansion from Black Hole Perturbation Theory, we introduce a
new Chebyshev approximation to the flux function, which due to a process called
Chebyshev economization gives a model with faster convergence than either
post-Newtonian or Pad\'e based methods. As well as having excellent convergence
properties, these polynomials are also very closely related to the elusive
minimax polynomial. We find that at the last stable orbit, the error between
the Chebyshev approximation and a numerically calculated flux is reduced, $<
1.8%$, at all orders of approximation. We also find that the templates
constructed using the Chebyshev approximation give better fitting factors, in
general $> 0.99$, and smaller errors, $< 1/10%$, in the estimation of the Chirp
mass when compared to a fiducial exact waveform, constructed using the
numerical flux and the exact expression for the orbital energy function, again
at all orders of approximation. We also show that in the intermediate test-mass
case, the new Chebyshev template is superior to both PN and Pad\'e approximant
templates, especially at lower orders of approximation.


title: Local cosmic strings in Brans-Dicke theory with a cosmological constant

abstract:
  It is known that Vilenkin's phenomenological equation of state for static
straight cosmic strings is inconsistent with Brans-Dicke theory. We will prove
that, in the presence of a cosmological constant, this equation of state is
consistent with Brans-Dicke theory. The general solution of the full nonlinear
field equations, representing the interior of a cosmic string with a
cosmological constant is also presented.


title: Density Perturbations for Running Cosmological Constant

abstract:
  The dynamics of density and metric perturbations is investigated for the
previously developed model where the decay of the vacuum energy into matter (or
vice versa) is due to the renormalization group (RG) running of the
cosmological constant (CC) term. The evolution of the CC depends on the single
parameter \nu, which characterizes the running of the CC produced by the
quantum effects of matter fields of the unknown high energy theory below the
Planck scale. The sign of \nu indicates whether bosons or fermions dominate in
the running. The spectrum of perturbations is computed assuming an adiabatic
regime and an isotropic stress tensor. Moreover, the perturbations of the CC
term are generated from the simplest covariant form suggested by the RG model
under consideration. The corresponding numerical analysis shows that for \nu>0
there is a depletion of the matter power spectrum at low scales (large wave
numbers) as compared to the standard LCDM model, whereas for \nu<0 there is an
excess of power at low scales. We find that the LSS data rule out the range
|\nu|> 10^{-4} while the values |\nu|< 10^{-6} look perfectly acceptable. For
\nu<0 the excess of power at low scales grows rapidly and the bound is more
severe. From the particle physics viewpoint, the values |\nu|\sim 10^{-6}
correspond to the ``desert'' in the mass spectrum above the GUT scale M_X\sim
10^{16} GeV. Our results are consistent with those obtained in other dynamical
models admitting an interaction between dark matter and dark energy. We find
that the matter power spectrum analysis is a highly efficient method to
discover a possible scale dependence of the vacuum energy.


title: The angular momentum of the gravitational field and the Poincare group

abstract:
  We redefine the gravitational angular momentum in the framework of the
teleparallel equivalent of general relativity. In similarity to the
gravitational energy-momentum, the new definition for the gravitational angular
momentum is coordinate independent. By considering the Poisson brackets in the
phase space of the theory, we find that the gravitational energy-momentum and
angular momentum correspond to a representation of the Poincar\'e group. This
result allows us to define Casimir type invariants for the gravitational field.


title:
Coordinates with Non-Singular Curvature for a Time Dependent Black Hole
  Horizon

abstract:
  A naive introduction of a dependency of the mass of a black hole on the
Schwarzschild time coordinate results in singular behavior of curvature
invariants at the horizon, violating expectations from complementarity. If
instead a temporal dependence is introduced in terms of a coordinate akin to
the river time representation, the Ricci scalar is nowhere singular away from
the origin. It is found that for a shrinking mass scale due to evaporation, the
null radial geodesics that generate the horizon are slightly displaced from the
coordinate singularity. In addition, a changing horizon scale significantly
alters the form of the coordinate singularity in diagonal (orthogonal) metric
coordinates representing the space-time. A Penrose diagram describing the
growth and evaporation of an example black hole is constructed to examine the
evolution of the coordinate singularity.


title: Introduction to spectral methods

abstract:
  This proceeding is intended to be a first introduction to spectral methods.
It is written around some simple problems that are solved explicitly and in
details and that aim at demonstrating the power of those methods. The
mathematical foundation of the spectral approximation is first introduced,
based on the Gauss quadratures. The two usual basis of Legendre and Chebyshev
polynomials are then presented. The next section is devoted to one dimensional
equation solvers using only one domain. Three different methods are described.
Techniques using several domains are shown in the last section of this paper
and their various merits discussed.


title:
Double-slit interference pattern from single-slit screen and its
  gravitational analogues

abstract:
  The double slit experiment (DSE) is known as an important cornerstone in the
foundations of physical theories such as Quantum Mechanics and Special
Relativity. A large number of different variants of it were designed and
performed over the years. We perform and discuss here a new verion with the
somewhat unexpected results of obtaining interference pattern from single-slit
screen. This outcome, which shows that the routes of the photons through the
array were changed, leads one to discuss it, using the equivalence principle,
in terms of geodesics mechanics. We show using either the Brill's version of
the canonical formulation of general relativity or the linearized version of it
that one may find corresponding and analogous situations in the framework of
general relativity.


title:
The generalised second law and the black hole evaporation in an empty
  space as a nonequilibrium process

abstract:
  When a black hole is in an empty space on which there is no matter field
except that of the Hawking radiation (Hawking field), then the black hole
evaporates and the entropy of the black hole decreases. The generalised second
law guarantees the increase of the total entropy of the whole system which
consists of the black hole and the Hawking field. That is, the increase of the
entropy of the Hawking field is faster than the decrease of the black hole
entropy. In naive sense, one may expect that the entropy increase of the
Hawking field is due to the self-interaction among the composite particles of
the Hawking field, and that the "self"-relaxation of the Hawking field results
in the entropy increase. Then, when one consider a non-self-interacting matter
field as the Hawking field, it is obvious that the self-relaxation does not
take place, and one may think that the total entropy does not increase.
However, using nonequilibrium thermodynamics which has been developed recently,
we find for the non-self-interacting Hawking field that the rate of entropy
increase of the Hawking field (the entropy emission rate by the black hole)
grows faster than the rate of entropy decrease of the black hole along the
black hole evaporation in the empty space. The origin of the entropy increase
of the Hawking field is the increase of the black hole temperature. Hence an
understanding of the generalised second law in the context of the
nonequilibrium thermodynamics is suggested; even if the self-relaxation of the
Hawking field does not take place, the temperature increase of the black hole
during the evaporation process causes the entropy increase of the Hawking field
to result in the increase of the total entropy.


title:
Dynamical determination of the Kuiper Belt's mass from motions of the
  inner planets of the Solar System

abstract:
  In this paper we dynamically determine the mass of the Kuiper Belt Objects by
exploiting the latest observational determinations of the orbital motions of
the inner planets of the Solar System. Our result, in units of terrestrial
masses, is 0.033 +/- 0.115 by modelling the Classical Kuiper Belt Objects as an
ecliptic ring of finite thickness. A two-rings model yields for the Resonant
Kuiper Belt Objects a value of 0.018 +/- 0.063. Such figures are consistent
with recent determinations obtained with ground and space-based optical
techniques. Some implications for precise tests of Einsteinian and
post-Einsteinian gravity are briefly discussed.


title: Observation of Incipient Black Holes and the Information Loss Problem

abstract:
  We study the formation of black holes by spherical domain wall collapse as
seen by an asymptotic observer, using the functional Schrodinger formalism. To
explore what signals such observers will see, we study radiation of a scalar
quantum field in the collapsing domain wall background. The total energy flux
radiated diverges when backreaction of the radiation on the collapsing wall is
ignored, and the domain wall is seen by the asymptotic observer to evaporate by
non-thermal ``pre-Hawking radiation'' during the collapse process. Evaporation
by pre-Hawking radiation implies that an asymptotic observer can never lose
objects down a black hole. Together with the non-thermal nature of the
radiation, this may resolve the black hole information loss problem.


title:
The recollapse problem of closed isotropic models in second order
  gravity theory

abstract:
  We study the closed universe recollapse conjecture for positively curved
Friedmann-Robertson-Walker (FRW) models in the Jordan frame of the second order
gravity theory. We analyse the late time evolution of the model with the
methods of the dynamical systems. We find that an initially expanding closed
FRW universe, starting close to the Minkowski spacetime, may exhibit
oscillatory behaviour.


title: Spectroscopy of Cosmic topology

abstract:
  Einstein's theory of gravitation that governs the geometry of space-time,
coupled with spectacular advance in cosmological observations, promises to
deliver a `standard model' of cosmology in the near future. However, local
geometry of space constrains, but does not dictate the topology of the cosmos.
hence, Cosmic topology has remained an enigmatic aspect of the `standard model'
of cosmology. Recent advance in the quantity and quality of observations has
brought this issue within the realm of observational query. The breakdown of
statistical homogeneity and isotropy of cosmic perturbations is a generic
consequence of non trivial cosmic topology arising from to the imposed
`crystallographic' periodicity on the eigenstates of the Laplacian. The sky
maps of Cosmic Microwave Background (CMB) anisotropy and polarization most
promising observations that would carry signatures of a violation of
statistical isotropy and homogeneity. Hence, a measurable spectroscopy of
cosmic topology is made possible using the Bipolar power spectrum (BiPS) of the
temperature and polarization that quantifies violation of statistical isotropy.


title: A Measurement of Newton's Gravitational Constant

abstract:
  A precision measurement of the gravitational constant $G$ has been made using
a beam balance. Special attention has been given to determining the
calibration, the effect of a possible nonlinearity of the balance and the
zero-point variation of the balance. The equipment, the measurements and the
analysis are described in detail. The value obtained for G is 6.674252(109)(54)
10^{-11} m3 kg-1 s-2. The relative statistical and systematic uncertainties of
this result are 16.3 10^{-6} and 8.1 10^{-6}, respectively.


title: A brief survey of LISA sources and science

abstract:
  LISA is a planned space-based gravitational-wave (GW) detector that would be
sensitive to waves from low-frequency sources, in the band of roughly $(0.03 -
0.1) {\rm mHz} \lesssim f \lesssim 0.1 {\rm Hz}$. This is expected to be an
extremely rich chunk of the GW spectrum -- observing these waves will provide a
unique view of dynamical processes in astrophysics. Here we give a quick survey
of some key LISA sources and what GWs can uniquely teach us about these
sources. Particularly noteworthy science which is highlighted here is the
potential for LISA to track the moderate to high redshift evolution of black
hole masses and spins through the measurement of GWs generated from massive
black hole binaries (which in turn form by the merger of galaxies and
protogalaxies). Measurement of these binary black hole waves has the potential
to determine the masses and spins of the constituent black holes with
percent-level accuracy or better, providing a unique high-precision probe of an
aspect of early structure growth. This article is based on the ``Astrophysics
Tutorial'' talk given by the author at the Sixth International LISA Symposium.


title:
Loop Quantum Cosmology in Bianchi Type I Models: Analytical
  Investigation

abstract:
  The comprehensive formulation for loop quantum cosmology in the spatially
flat, isotropic model was recently constructed. In this paper, the methods are
extended to the anisotropic Bianchi I cosmology. Both the precursor and the
improved strategies are applied and the expected results are established: (i)
the scalar field again serves as an internal clock and is treated as emergent
time; (ii) the total Hamiltonian constraint is derived by imposing the
fundamental discreteness and gives the evolution as a difference equation; and
(iii) the physical Hilbert space, Dirac observables and semi-classical states
are constructed rigorously. It is also shown that the state in the kinematical
Hilbert space associated with the classical singularity is decoupled in the
difference evolution equation, indicating that the big bounce may take place
when any of the area scales undergoes the vanishing behavior. The investigation
affirms the robustness of the framework used in the isotropic model by
enlarging its domain of validity and provides foundations to conduct the
detailed numerical analysis.


title: A Comment on hep-th/0608078

abstract:
  The above hep-th posting purports -- erroneously -- to be a comment on a Note
by me in gr-qc.


title: Black hole thermodynamics with generalized uncertainty principle

abstract:
  We apply the generalized uncertainty principle to the thermodynamics of a
small black hole. Here we have a black hole system with the UV cutoff. It is
shown that the minimal length induced by the GUP interrupts the
Gross-Perry-Yaffe phase transition for a small black hole. In order to see
whether the black hole remnant takes place a transition to a large black hole,
we introduce a black hole in a cavity (IR system). However, we fail to show the
phase transition of the remnant to the large black hole.


title: Exploring the diffeomorphism invariant Hilbert space of a scalar field

abstract:
  As a toy model for the implementation of the diffeomorphism constraint, the
interpretation of the resulting states, and the treatment of ordering
ambiguities in loop quantum gravity, we consider the Hilbert space of spatially
diffeomorphism invariant states for a scalar field. We give a very explicit
formula for the scalar product on this space, and discuss its structure.
  Then we turn to the quantization of a certain class of diffeomorphism
invariant quantities on that space, and discuss in detail the ordering issues
involved. On a technical level these issues bear some similarity to those
encountered in full loop quantum gravity.


title: Spinor Theory of Gravity

abstract:
  The proposal of this work is to provide an answer to the following question:
is it possible to treat the metric of space-time - that in General Relativity
(GR) describes the gravitational interaction - as an effective geometry? In
other words, to obtain the dynamics of the metric tensor as a consequence of
the dynamics of other fields. In this work we will use a slight modfication of
the non-linear equation of motion of a spinor field proposed some years ago by
Heisenberg, although in a completely distinct context, to obtain a field theory
that provides a framework equivalent to the way GR represents the gravitational
interaction. In particular we exhibit a solution of the equations of motion
that represents the gravitational field of a compact object and compare it with
the corresponding Schwarzschild solution of General Relativity.


title: Loop quantum cosmology and inhomogeneities

abstract:
  Inhomogeneities are introduced in loop quantum cosmology using regular
lattice states, with a kinematical arena similar to that in homogeneous models
considered earlier. The framework is intended to encapsulate crucial features
of background independent quantizations in a setting accessible to explicit
calculations of perturbations on a cosmological background. It is used here
only for qualitative insights but can be extended with further more detailed
input. One can thus see how several parameters occuring in homogeneous models
appear from an inhomogeneous point of view. Their physical roles in several
cases then become much clearer, often making previously unnatural choices of
values look more natural by providing alternative physical roles. This also
illustrates general properties of symmetry reduction at the quantum level and
the roles played by inhomogeneities. Moreover, the constructions suggest a
picture for gravitons and other metric modes as collective excitations in a
discrete theory, and lead to the possibility of quantum gravity corrections in
large universes.


title: The extent of computation in Malament-Hogarth spacetimes

abstract:
  We analyse the extent of possible computations following Hogarth in
Malament-Hogarth (MH) spacetimes, and Etesi and N\'emeti in the special
subclass containing rotating Kerr black holes. Hogarth had shown that any
arithmetic statement could be resolved in a suitable MH spacetime. Etesi and
Nemeti had shown that some \forall \exists relations on natural numbers which
are neither universal nor co-universal, can be decided in Kerr spacetimes, and
had asked specifically as to the extent of computational limits there. The
purpose of this note is to address this question, and further show that MH
spacetimes can compute far beyond the arithmetic: effectively Borel statements
(so hyperarithmetic in second order number theory, or the structure of
analysis) can likewise be resolved: Theorem A. If H is any hyperarithmetic
predicate on integers, then there is an MH spacetime in which any query ? n \in
H ? can be computed. In one sense this is best possible, as there is an upper
bound to computational ability in any spacetime which is thus a universal
constant of the space-time M. Theorem C. Assuming the (modest and standard)
requirement that space-time manifolds be paracompact and Hausdorff, for any MH
spacetime M there will be a countable ordinal upper bound, w(M), on the
complexity of questions in the Borel hierarchy resolvable in it.


title: Quasinormal modes for the Vaidya metric

abstract:
  We consider here scalar and electromagnetic perturbations for the Vaidya
metric in double-null coordinates. Such an approach allows one to go a step
further in the analysis of quasinormal modes for time-dependent spacetimes.
Some recent results are refined, and a new non-stationary behavior
corresponding to some sort of inertia for quasinormal modes is identified. Our
conclusions can enlighten some aspects of the wave scattering by black holes
undergoing some mass accretion processes.


title: Semi-classical States in Homogeneous Loop Quantum Cosmology

abstract:
  Semi-classical states in homogeneous loop quantum cosmology (LQC) are
constructed by two different ways. In the first approach, we firstly construct
an exponentiated annihilation operator. Then a kind of semi-classical
(coherent) state is obtained by solving the eigen-equation of that operator.
Moreover, we use these coherent states to analyze the semi-classical limit of
the quantum dynamics. It turns out that the Hamiltonian constraint operator
employed currently in homogeneous LQC has correct classical limit with respect
to the coherent states. In the second approach, the other kind of
semi-classical state is derived from the mathematical construction of coherent
states for compact Lie groups due to Hall.


title: Collapse Dynamics of a Star of Dark Matter and Dark Energy

abstract:
  In this work, we study the collapse dynamics of an inhomogeneous spherically
symmetric star made of dark matter (DM) and dark energy (DE). The dark matter
is taken in the form of a dust cloud while anisotropic fluid is chosen as the
candidate for dark energy. It is investigated how dark energy modifies the
collapsing process and is examined whether dark energy has any effect on the
Cosmic Censorship Conjecture. The collapsing star is assumed to be of finite
radius and the space time is divided into three distinct regions $\Sigma$ and
$V^{\pm}$, where $\Sigma$ represents the boundary of the star and
$V^{-}(V^{+})$ denotes the interior (exterior) of the star. The junction
conditions for matching $V^{\pm}$ over $\Sigma$ are specified. Role of Dark
energy in the formation of apparent horizon is studied and central singularity
is analyzed.


title: Cosmic Duality in Quintom Universe

abstract:
  In this paper we study the duality in two-field Quintom models of Dark
Energy. We find that an expanding universe dominated by Quintom-A field is dual
to a contracting universe with Quintom-B field.


title: Fermions in three-dimensional spinfoam quantum gravity

abstract:
  We study the coupling of massive fermions to the quantum mechanical dynamics
of spacetime emerging from the spinfoam approach in three dimensions. We first
recall the classical theory before constructing a spinfoam model of quantum
gravity coupled to spinors. The technique used is based on a finite expansion
in inverse fermion masses leading to the computation of the vacuum to vacuum
transition amplitude of the theory. The path integral is derived as a sum over
closed fermionic loops wrapping around the spinfoam. The effects of quantum
torsion are realised as a modification of the intertwining operators assigned
to the edges of the two-complex, in accordance with loop quantum gravity. The
creation of non-trivial curvature is modelled by a modification of the pure
gravity vertex amplitudes. The appendix contains a review of the geometrical
and algebraic structures underlying the classical coupling of fermions to three
dimensional gravity.


title:
Charged massive particle at rest in the field of a Reissner-Nordstr\"om
  black hole

abstract:
  The interaction of a Reissner-Nordstr\"om black hole and a charged massive
particle is studied in the framework of perturbation theory. The particle
backreaction is taken into account, studying the effect of general static
perturbations of the hole following the approach of Zerilli. The solutions of
the combined Einstein-Maxwell equations for both perturbed gravitational and
electromagnetic fields at first order of the perturbation are exactly
reconstructed by summing all multipoles, and are given explicit closed form
expressions. The existence of a singularity-free solution of the
Einstein-Maxwell system requires that the charge to mass ratios of the black
hole and of the particle satisfy an equilibrium condition which is in general
dependent on the separation between the two bodies. If the black hole is
undercritically charged (i.e. its charge to mass ratio is less than one), the
particle must be overcritically charged, in the sense that the particle must
have a charge to mass ratio greater than one. If the charge to mass ratios of
the black hole and of the particle are both equal to one (so that they are both
critically charged, or "extreme"), the equilibrium can exist for any separation
distance, and the solution we find coincides with the linearization in the
present context of the well known Majumdar-Papapetrou solution for two extreme
Reissner-Nordstr\"om black holes. In addition to these singularity-free
solutions, we also analyze the corresponding solution for the problem of a
massive particle at rest near a Schwarzschild black hole, exhibiting a strut
singularity on the axis between the two bodies. The relations between our
perturbative solutions and the corresponding exact two-body solutions belonging
to the Weyl class are also discussed.


title: Interior of a Schwarzschild black hole revisited

abstract:
  The Schwarzschild solution has played a fundamental conceptual role in
general relativity, and beyond, for instance, regarding event horizons,
spacetime singularities and aspects of quantum field theory in curved
spacetimes. However, one still encounters the existence of misconceptions and a
certain ambiguity inherent in the Schwarzschild solution in the literature. By
taking into account the point of view of an observer in the interior of the
event horizon, one verifies that new conceptual difficulties arise. In this
work, besides providing a very brief pedagogical review, we further analyze the
interior Schwarzschild black hole solution. Firstly, by deducing the interior
metric by considering time-dependent metric coefficients, the interior region
is analyzed without the prejudices inherited from the exterior geometry. We
also pay close attention to several respective cosmological interpretations,
and briefly address some of the difficulties associated to spacetime
singularities. Secondly, we deduce the conserved quantities of null and
timelike geodesics, and discuss several particular cases in some detail.
Thirdly, we examine the Eddington-Finkelstein and Kruskal coordinates directly
from the interior solution. In concluding, it is important to emphasize that
the interior structure of realistic black holes has not been satisfactorily
determined, and is still open to considerable debate.


title: The covariant derivatives and energy momentum tensor of spinors

abstract:
  To understand the coupling behavior of the spinor with spacetime, the
explicit form of the energy-momentum tensor of the spinor in curved spacetime
is important. This problem seems to be overlooked for a long time. In this
paper we derive the explicit form of energy momentum tensors and display some
equivalent but simple forms of the covariant derivatives for both the Weyl
spinor and the Dirac bispinor in curved spacetime.


title: Accurate and realistic initial data for black hole-neutron star binaries

abstract:
  This paper is devoted to the computation of compact binaries composed of one
black hole and one neutron star. The objects are assumed to be on exact
circular orbits. Standard 3+1 decomposition of Einstein equations is performed
and the conformal flatness approximation is used. The obtained system of
elliptic equations is solved by means of multi-domain spectral methods. Results
are compared with previous work both in the high mass ratio limit and for one
neutron star with very low compactness parameter. The accuracy of the present
code is shown to be greater than with previous codes. Moreover, for the first
time, some sequences containing one neutron star of realistic compactness are
presented and discussed.


title:
Matters of Gravity, The Newsletter of the Topical Group in Gravitation
  of the American Physical Society, Volume 28, Fall 2006

abstract:
  Research Briefs:
  Singularity Avoidance in Canonical Quantum Gravity, by Viqar Husain
  What's New in LIGO, by David Shoemaker
  Conference reports:
  Scanning New Horizons: GR Beyond 4 dimensions, by Donald Marolf
  Quantum Gravity in the Americas III, by Jorge Pullin
  New Frontiers in Numerical Relativity, by Luciano Rezzolla
  Teaching General Relativity to Undergraduates, by Greg Comer
  Ninth Capra Meeting on Radiation Reaction, by Lior Burko


title: New stable phase of non-uniform charged black strings

abstract:
  Non-uniform black strings coupled to a gauge field are constructed by a
perturbative method in a wide range of spacetime dimensions. At the linear
order of perturbations, we see that the Gregory-Laflamme instability vanishes
at the point where the background solution becomes thermodynamically stable.
The emergence/vanishing of the static mode resembles phase transitions, and in
fact we find that its critical exponent is nearly 1/2, which means a
second-order transition. By employing higher-order perturbations, the physical
properties of the non-uniform black strings are investigated in detail. For
fixed spacetime dimensions, we find the critical charges at which the stability
of non-uniform states changes. For some range of charge, non-uniform black
strings are entropically favored over uniform ones. The gauge charge works as a
control parameter that controls not only the stability of uniform black strings
but also the non-uniform states. In addition, we find that for a fixed
background charge the uniform state is not necessarily the state carrying the
largest tension. The phase diagram and a comparison with the critical dimension
are also discussed.


title:
Testing the Accuracy and Stability of Spectral Methods in Numerical
  Relativity

abstract:
  The accuracy and stability of the Caltech-Cornell pseudospectral code is
evaluated using the KST representation of the Einstein evolution equations. The
basic "Mexico City Tests" widely adopted by the numerical relativity community
are adapted here for codes based on spectral methods. Exponential convergence
of the spectral code is established, apparently limited only by numerical
roundoff error. A general expression for the growth of errors due to finite
machine precision is derived, and it is shown that this limit is achieved here
for the linear plane-wave test. All of these tests are found to be stable,
except for simulations of high amplitude gauge waves with nontrivial shift.


title: Transient chaos in scalar field cosmology on a brane

abstract:
  We study cosmological dynamics of a flat Randall-Sundrum brane with a scalar
field and a negative "dark radiation" term. It is shown that in some situations
the "dark radiation" can mimic spatial curvature and cause a chaotic behavior
which is similar to chaotic dynamics in closed Universe with a scalar field.


title:
Black rings with a small electric charge: gyromagnetic ratios and
  algebraic alignment

abstract:
  We study electromagnetic test fields in the background of vacuum black rings
using Killing vectors as vector potentials. We consider both spacetimes with a
rotating S^1 and with a rotating S^2 and we demonstrate, in particular, that
the gyromagnetic ratio of slightly charged black rings takes the value g=3
(this will in fact apply to a wider class of spacetimes). We also observe that
a S^2-rotating black ring immersed in an external "aligned" magnetic field
completely expels the magnetic flux in the extremal limit. Finally, we discuss
the mutual alignment of principal null directions of the Maxwell 2-form and of
the Weyl tensor, and the algebraic type of exact charged black rings. In
contrast to spherical black holes, charged rings display new distinctive
features and provide us with an explicit example of algebraically general (type
G) spacetimes in higher dimensions. Appendix A contains some global results on
black rings with a rotating 2-sphere. Appendix C shows that g=D-2 in any D>=4
dimensions for test electromagnetic fields generated by a time translation.


title: Solitons as Key Parts to Produce a Universe in the Laboratory

abstract:
  Cosmology is usually understood as an observational science, where
experimentation plays no role. It is interesting, nevertheless, to change this
perspective addressing the following question: what should we do to create a
universe, in a laboratory? It appears, in fact, that this is, in principle,
possible according to at least two different paradigms; both allow to
circumvent singularity theorems, i.e. the necessity of singularities in the
past of inflating domains which have the required properties to generate a
universe similar to ours. The first of them is substantially classical, and is
built up considering solitons which collide with surrounding topological
defects, generating an inflationary domain of space-time. The second is,
instead, partly quantum and considers the possibility of tunnelling of
past-non-singular regions of spacetime into an inflating universe, following a
well-known instanton proposal.
  We are, here, going to review some of these models, as well as highlight
possible extensions, generalizations and the open issues (as for instance the
detectability of child universes and the properties of quantum tunnelling
processes) that still affect the description of their dynamics. In doing so we
will remark how the works on this subject can represent virtual laboratories to
test the role that fundamental principles of physics (particularly, the
interplay of quantum and general relativistic realms) played in the formation
of our universe.


title:
On the extension of Newton's second law to theories of gravitation in
  curved space-time

abstract:
  We investigate the possibility of extending Newton's second law to the
general framework of theories in which special relativity is locally valid, and
in which gravitation changes the flat Galilean space-time metric into a curved
metric. This framework is first recalled, underlining the possibility to
uniquely define a space metric and a local time in any given reference frame,
hence to define velocity and momentum in terms of the local space and time
standards. It is shown that a unique consistent definition can be given for the
derivative of a vector (the momentum) along a trajectory. Then the possible
form of the gravitation force is investigated. It is shown that, if the motion
of free particles has to follow space-time geodesics, then the expression for
the gravity acceleration is determined uniquely. It depends on the variation of
the metric with space and time, and it involves the velocity of the particle.


title: Accurate extraction of the News

abstract:
  We propose a new scheme for extracting gravitational radiation from a
characteristic numerical simulation of a spacetime. This method is similar in
conception to our earlier work but analytical and numerical implementation is
different. The scheme is based on direct transformation to the Bondi
coordinates and the gravitational waves are extracted by calculating the Bondi
news function in Bondi coordinates. The entire calculation is done in a way
which will make the implementation easy when we use uniform Bondi angular grid
at $\mathcal I^+$. Using uniform Bondi grid for news calculation has added
advantage that we have to solve only ordinary differential equations instead of
partial differential equation. For the test problems this new scheme allows us
to extract gravitational radiation much more accurately than the previous
schemes.


title:
Quasiequilibrium sequences of black-hole--neutron-star binaries in
  general relativity

abstract:
  We construct quasiequilibrium sequences of black hole-neutron star binaries
for arbitrary mass ratios by solving the constraint equations of general
relativity in the conformal thin-sandwich decomposition. We model the neutron
star as a stationary polytrope satisfying the relativistic equations of
hydrodynamics, and account for the black hole by imposing equilibrium boundary
conditions on the surface of an excised sphere (the apparent horizon). In this
paper we focus on irrotational configurations, meaning that both the neutron
star and the black hole are approximately nonspinning in an inertial frame. We
present results for a binary with polytropic index n=1, mass ratio
M_{irr}^{BH}/M_{B}^{NS}=5 and neutron star compaction
M_{ADM,0}^{NS}/R_0=0.0879, where M_{irr}^{BH} is the irreducible mass of the
black hole, M_{B}^{NS} the neutron star baryon rest-mass, and M_{ADM,0}^{NS}
and R_0 the neutron star Arnowitt-Deser-Misner mass and areal radius in
isolation, respectively. Our models represent valid solutions to Einstein's
constraint equations and may therefore be employed as initial data for
dynamical simulations of black hole-neutron star binaries.


title: Are Causality Violations Undesirable?

abstract:
  Causality violations are typically seen as unrealistic and undesirable
features of a physical model. The following points out three reasons why
causality violations, which Bonnor and Steadman identified even in solutions to
the Einstein equation referring to ordinary laboratory situations, are not
necessarily undesirable. First, a space-time in which every causal curve can be
extended into a closed causal curve is singularity free--a necessary property
of a globally applicable physical theory. Second, a causality-violating
space-time exhibits a nontrivial topology--no closed timelike curve (CTC) can
be homotopic among CTCs to a point, or that point would not be causally well
behaved--and nontrivial topology has been explored as a model of particles.
Finally, if every causal curve in a given space-time passes through an event
horizon, a property which can be called "causal censorship", then that
space-time with event horizons excised would still be causally well behaved.


title: Is there a black hole minimum mass?

abstract:
  Applying the first and generalised second laws of thermodynamics for a
realistic process of near critical black hole formation, we derive an entropy
bound, which is identical to Bekenstein's one for radiation. Relying upon this
bound, we derive an absolute minimum mass $\sim0.04 \sqrt{g_{*}}m_{\rm Pl}$,
where $g_{*}$ and $m_{\rm Pl}$ is the effective degrees of freedom for the
initial temparature and the Planck mass, respectively. Since this minimum mass
coincides with the lower bound on masses of which black holes can be regarded
as classical against the Hawking evaporation, the thermodynamical argument will
not prohibit the formation of the smallest classical black hole. For more
general situations, we derive a minimum mass, which may depend on the initial
value for entropy per particle. For primordial black holes, however, we show
that this minimum mass can not be much greater than the Planck mass at any
formation epoch of the Universe, as long as $g_{*}$ is within a reasonable
range. We also derive a size-independent upper bound on the entropy density of
a stiff fluid in terms of the energy density.


title: Interpreting the C-metric

abstract:
  The basic properties of the C-metric are well known. It describes a pair of
causally separated black holes which accelerate in opposite directions under
the action of forces represented by conical singularities. However, these
properties can be demonstrated much more transparently by making use of
recently developed coordinate systems for which the metric functions have a
simple factor structure. These enable us to obtain explicit
Kruskal-Szekeres-type extensions through the horizons and construct
two-dimensional conformal Penrose diagrams. We then combine these into a
three-dimensional picture which illustrates the global causal structure of the
space-time outside the black hole horizons. Using both the weak field limit and
some invariant quantities, we give a direct physical interpretation of the
parameters which appear in the new form of the metric. For completeness,
relations to other familiar coordinate systems are also discussed.


title:
Hamiltonian cosmological perturbation theory with loop quantum gravity
  corrections

abstract:
  Cosmological perturbation equations are derived systematically in a canonical
scheme based on Ashtekar variables. A comparison with the covariant derivation
and various subtleties in the calculation and choice of gauges are pointed out.
Nevertheless, the treatment is more systematic when correction terms of
canonical quantum gravity are to be included. This is done throughout the paper
for one characteristic modification expected from loop quantum gravity.


title:
Quantum variational measurement in the next generation
  gravitational-wave detectors

abstract:
  A relatively simple method of overcoming the Standard Quantum Limit in the
next-generation Advanced LIGO gravitational wave detector is considered. It is
based on the quantum variational measurement with a single short (a few tens of
meters) filter cavity. Estimates show that this method allows to reduce the
radiation pressure noise at low frequencies ($<100 \mathrm{Hz}$) to the level
comparable with or smaller than the low-frequency noises of non-quantum origin
(mirrors suspension noise, mirrors internal thermal noise, and gravity
gradients fluctuations).


title: Exact solutions of Brans-Dicke cosmology with decaying vacuum density

abstract:
  We investigate cosmological solutions of Brans-Dicke theory with both the
vacuum energy density and the gravitational constant decaying linearly with the
Hubble parameter. A particular class of them, with constant deceleration
factor, sheds light on the cosmological constant problems, leading to a
presently small vacuum term, and to a constant ratio between the vacuum and
matter energy densities. By fixing the only free parameter of these solutions,
we obtain cosmological parameters in accordance with observations of both the
relative matter density and the universe age. In addition, we have three other
solutions, with Brans-Dicke parameter w = -1 and negative cosmological term,
two of them with a future singularity of big-rip type. Although interesting
from the theoretical point of view, two of them are not in agreement with the
observed universe. The third one leads, in the limit of large times, to a
constant relative matter density, being also a possible solution to the cosmic
coincidence problem.


title:
Normalization conventions for Newton's constant and the Planck scale in
  arbitrary spacetime dimension

abstract:
  We calculate, in d spacetime dimensions, the relationship between the
coefficient 1/K^2 of the Einstein-Hilbert term in the action of general
relativity and the coefficient G_N of the force law that results from the
Newtonian limit of general relativity. The result is
K^2=2[(d-2)/(d-3)]Vol(S^[d-2])G_N, where Vol(S^n) is the volume of the unit
n-sphere. While the d=4 case is an elementary calculation in any general
relativity text, the arbitrary case presented here is slightly less well known.
We discuss the relevance of this result for the definition of the so-called
"reduced Planck mass" and comment very briefly on the implications for brane
world models. [abstract abridged]


title:
Bounds on the basic physical parameters for anisotropic compact general
  relativistic objects

abstract:
  We derive upper and lower limits for the basic physical parameters
(mass-radius ratio, anisotropy, redshift and total energy) for arbitrary
anisotropic general relativistic matter distributions in the presence of a
cosmological constant. The values of these quantities are strongly dependent on
the value of the anisotropy parameter (the difference between the tangential
and radial pressure) at the surface of the star. In the presence of the
cosmological constant, a minimum mass configuration with given anisotropy does
exist. Anisotropic compact stellar type objects can be much more compact than
the isotropic ones, and their radii may be close to their corresponding
Schwarzschild radii. Upper bounds for the anisotropy parameter are also
obtained from the analysis of the curvature invariants. General restrictions
for the redshift and the total energy (including the gravitational
contribution) for anisotropic stars are obtained in terms of the anisotropy
parameter. Values of the surface redshift parameter greater than two could be
the main observational signature for anisotropic stellar type objects.


title: Excited by a quantum field: Does shape matter?

abstract:
  The instantaneous transition rate of an arbitrarily accelerated Unruh-DeWitt
particle detector on four-dimensional Minkowski space is ill defined without
regularisation. We show that Schlicht's regularisation as the zero-size limit
of a Lorentz-function spatial profile yields a manifestly well-defined
transition rate with physically reasonable asymptotic properties. In the
special case of stationary trajectories, including uniform acceleration, we
recover the results that have been previously obtained by a regularisation that
relies on the stationarity. Finally, we discuss evidence for the conjecture
that the zero-size limit of the transition rate is independent of the detector
profile.


title:
Phenomenological description of quantum gravity inspired modified
  classical electrodynamics

abstract:
  We discuss a large class of phenomenological models incorporating quantum
gravity motivated corrections to electrodynamics. The framework is that of
electrodynamics in a birefringent and dispersive medium with non-local
constitutive relations, which are considered up to second order in the inverse
of the energy characterizing the quantum gravity scale. The energy-momentum
tensor, Green functions and frequency dependent refraction indices are
obtained, leading to departures from standard physics. The effective character
of the theory is also emphasized by introducing a frequency cutoff. The
analysis of its effects upon the standard notion of causality is performed,
showing that in the radiation regime the expected corrections get further
suppressed by highly oscillating terms, thus forbiding causality violations to
show up in the corresponding observational effects.