title:
Exotic Low Density Fermion States in the Two Measures Field Theory:
  Neutrino Dark Energy

abstract:
  We study a new field theory effect in the cosmological context in the Two
Measures Field Theory (TMT). TMT is an alternative gravity and matter field
theory where the gravitational interaction of fermionic matter is reduced to
that of General Relativity when the energy density of the fermion matter is
much larger than the dark energy density. In this case also the 5-th force
problem is solved automatically. In the opposite limit, where the magnitudes of
fermionic energy density and scalar field dark energy density become
comparable, nonrelativistic fermions can participate in the cosmological
expansion in a very unusual manner. Some of the features of such states in a
toy model of the late time universe filled with homogeneous scalar field and
uniformly distributed nonrelativistic neutrinos: neutrino mass increases as m ~
a^{3/2}; the neutrino gas equation-of-state approaches w=-1, i.e. neutrinos
behave as a sort of dark energy; the total (scalar field + neutrino)
equation-of-state also approaches w=-1; the total energy density of such
universe is less than it would be in the universe filled with the scalar field
alone. An analytic solution is presented. A domain structure of the dark energy
seems to be possible. We speculate that decays of the CLEP state neutrinos may
be both an origin of cosmic rays and responsible for a late super-acceleration
of the universe. In this sense the CLEP states exhibit simultaneously new
physics at very low densities and for very high particle masses.


title:
Fourth order gravity and experimental constraints on Eddington
  parameters

abstract:
  PPN-limit of higher order theories of gravity represents a still
controversial matter of debate and no definitive answer has been provided, up
to now, about this issue. By exploiting the analogy between scalar-tensor and
fourth-order theories of gravity, one can generalize the PPN-limit formulation.
  By using the definition of the PPN-parameters $\gamma$ and $\beta$ in term of
the $f(R)$ derivatives, we show that a family of third-order polynomial
theories, in the Ricci scalar $R$, turns out to be compatible with the
PPN-limit and the deviation from General Relativity theoretically predicted
agree with experimental data.


title:
Thermodynamics and quantum cosmology -- Continuous topological evolution
  of topologically coherent defects

abstract:
  As a point of departure it is suggested that Quantum Cosmology is a
topological concept independent from metrical constraints. Methods of
continuous topological evolution and topological thermodynamics are used to
construct a cosmological model of the present universe, using the techniques
based upon Cartan's theory of exterior differential systems. Thermodynamic
domains, which are either Open, Closed, Isolated, or in Equilibrium, can be put
into correspondence with topological systems of Pfaff topological dimension 4,
3, 2 and 1. If the environment of the universe is assumed to be a physical
vacuum of Pfaff topological dimension 4, then continuous but irreversible
topological evolution can cause the emergence of topologically coherent defect
structures of Pfaff topological dimension less than 4. As galaxies and stars
exchange radiation but not matter with the environment, they are emergent
topological defects of Pfaff topological dimension 3 which are far from
equilibrium. DeRham topological theory of period integrals over closed but not
exact exterior differential systems leads to the emergence of quantized,
deformable, but topologically coherent, singular macrostates at all scales. The
method leads to the conjecture that dark matter and energy is represented by
those thermodynamic topological defect structures of Pfaff dimension 2 or less.


title: Could quantum gravity be tested with high intensity Lasers?

abstract:
  In quantum gravity theories Planckian behavior is triggered by the energy of
{\it elementary} particles approaching the Planck energy, $E_P$, but it's also
possible that anomalous behavior strikes systems of particles with total energy
near $E_P$. This is usually perceived to be pathological and has been labelled
``the soccer ball problem''. We point out that there is no obvious
contradiction with experiment if {\it coherent} collections of particles with
bulk energy of order $E_P$ do indeed display Planckian behavior, a possibility
that would open a new experimental window. Unfortunately field theory
realizations of deformed special relativity never exhibit a ``soccer ball
problem''; we present several formulations where this is undeniably true. Upon
closer scrutiny we discover that the only chance for Planckian behavior to be
triggered by large coherent energies involves the details of second
quantization. We find a formulation where the quanta have their energy-momentum
(mass-shell) relations deformed as a function of the bulk energy of the
coherent packet to which they belong, rather than the frequency. Given ongoing
developments in Laser technology, such a possibility would be of great
experimental interest.


title: Spacetimes containing slowly evolving horizons

abstract:
  Slowly evolving horizons are trapping horizons that are "almost" isolated
horizons. This paper reviews their definition and discusses several spacetimes
containing such structures. These include certain Vaidya and Tolman-Bondi
solutions as well as (perturbatively) tidally distorted black holes. Taking
into account the associated mass scales, they also suggest that slowly evolving
horizons are the norm rather than the exception in astrophysical processes that
involve stellar-scale black holes.


title:
Energy and Momentum densities of cosmological models, with equation of
  state $\rho=\mu$, in general relativity and teleparallel gravity

abstract:
  We calculated the energy and momentum densities of stiff fluid solutions,
using Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum complexes,
in both general relativity and teleparallel gravity. In our analysis we get
different results comparing the aforementioned complexes with each other when
calculated in the same gravitational theory, either this is in general
relativity and teleparallel gravity. However, interestingly enough, each
complex's value is the same either in general relativity or teleparallel
gravity. Our results sustain that (i) general relativity or teleparallel
gravity are equivalent theories (ii) different energy-momentum complexes do not
provide the same energy and momentum densities neither in general relativity
nor in teleparallel gravity. In the context of the theory of teleparallel
gravity, the vector and axial-vector parts of the torsion are obtained. We show
that the axial-vector torsion vanishes for the space-time under study.


title:
Alternative symplectic structures for SO(3,1) and SO(4) four-dimensional
  BF theories

abstract:
  The most general action, quadratic in the B fields as well as in the
curvature F, having SO(3,1) or SO(4) as the internal gauge group for a
four-dimensional BF theory is presented and its symplectic geometry is
displayed. It is shown that the space of solutions to the equations of motion
for the BF theory can be endowed with symplectic structures alternative to the
usual one. The analysis also includes topological terms and cosmological
constant. The implications of this fact for gravity are briefly discussed.


title:
The conformal factor in the parameter-free construction of spin-gauge
  variables for gravity

abstract:
  The newly found conformal decomposition in canonical general relativity is
applied to drastically simplify the recently formulated parameter-free
construction of spin-gauge variables for gravity. The resulting framework
preserves many of the main structures of the existing canonical framework for
loop quantum gravity related to the spin network and Thiemann's regularization.
However, the Barbero-Immirzi parameter is now converted into the conformal
factor as a canonical variable. It behaves like a scalar field but is somehow
non-dynamical since the effective Hamiltonian constraint does not depend on its
momentum. The essential steps of the mathematical derivation of this
parameter-free framework for the spin-gauge variables of gravity are spelled
out. The implications for the loop quantum gravity programme are briefly
discussed.


title: The use of Generalised Functions and Distributions in General Relativity

abstract:
  In this paper we review the extent to which one can use classical
distribution theory in describing solutions of Einstein's equations. We show
that there are a number of physically interesting cases which cannot be treated
using distribution theory but require a more general concept. We describe a
mathematical theory of nonlinear generalised functions based on Colombeau
algebras and show how this may be applied in general relativity. We end by
discussing the concept of singularity in general relativity and show that
certain solutions with weak singularities may be regarded as distributional
solutions of Einstein's equations.


title:
Towards a Background Independent Formulation of Perturbative Quantum
  Gravity

abstract:
  The recent formulation of locally covariant quantum field theory may open the
way towards a background independent perturbative formulation of Quantum
Gravity.


title: A symmetry for vanishing cosmological constant: Another realization

abstract:
  A more conventional realization of a symmetry which had been proposed towards
the solution of cosmological constant problem is considered. In this study the
multiplication of the coordinates by the imaginary number $i$ in the literature
is replaced by the multiplication of the metric tensor by minus one. This
realization of the symmetry as well forbids a bulk cosmological constant and
selects out $2(2n+1)$ dimensional spaces. On contrary to its previous
realization the symmetry, without any need for its extension, also forbids a
possible cosmological constant term which may arise from the extra dimensional
curvature scalar provided that the space is taken as the union of two $2(2n+1)$
dimensional spaces where the usual 4-dimensional space lies at the intersection
of these spaces. It is shown that this symmetry may be realized through
spacetime reflections that change the sign of the volume element. A possible
relation of this symmetry to the E-parity symmetry of Linde is also pointed
out.


title:
Note on reflection symmetry in stationary axisymmetric electrovacuum
  spacetimes

abstract:
  Recently Kordas (1995, Class. Quantum Grav. 12 2037) and Meinel and
Neugebauer (1995, Class. Quantum Grav. 12 2045) studied the conditions for
reflection symmetry in stationary axisymmetric space--times in vacuum. They
found that a solution to the Einstein field equations is reflectionally
symmetric if their Ernst's potential ${\cal E}(\rho=0,z)= e(z)$ on a portion of
the positive z-axis extending to infinity satisfies the condition
$e_{+}(z){e}_{+}^{*}(-z)=1$. In this note, we formulate an analogous conditions
for two complex Ernst potentials in electrovacuum. We also present the special
case of rational axis potentials.


title: Conformal Klein-Gordon equations and quasinormal modes

abstract:
  Using conformal coordinates associated with conformal relativity --
associated with de Sitter spacetime homeomorphic projection into Minkowski
spacetime -- we obtain a conformal Klein-Gordon partial differential equation,
which is intimately related to the production of quasi-normal modes (QNMs)
oscillations, in the context of electromagnetic and/or gravitational
perturbations around, e.g., black holes. While QNMs arise as the solution of a
wave-like equation with a Poschl-Teller potential, here we deduce and
analytically solve a conformal radial d'Alembert-like equation, from which we
derive QNMs formal solutions, in a proposed alternative to more completely
describe QNMs. As a by-product we show that this radial equation can be
identified with a Schrodinger-like equation in which the potential is exactly
the second Poschl-Teller potential, and it can shed some new light on the
investigations concerning QNMs.


title: Regular and Chaotic Regimes in Scalar Field Cosmology

abstract:
  A transient chaos in a closed FRW cosmological model with a scalar field is
studied. We describe two different chaotic regimes and show that the type of
chaos in this model depends on the scalar field potential. We have found also
that for sufficiently steep potentials or for potentials with large
cosmological constant the chaotic behavior disappears.


title: Junction conditions in General Relativity with spin sources

abstract:
  The junction conditions for General Relativity in the presence of domain
walls with intrinsic spin are derived in three and higher dimensions. A stress
tensor and a spin current can be defined just by requiring the existence of a
well defined volume element instead of an induced metric, so as to allow for
generic torsion sources. In general, when the torsion is localized on the
domain wall, it is necessary to relax the continuity of the tangential
components of the vielbein. In fact it is found that the spin current is
proportional to the jump in the vielbein and the stress-energy tensor is
proportional to the jump in the spin connection. The consistency of the
junction conditions implies a constraint between the direction of flow of
energy and the orientation of the spin. As an application, we derive the
circularly symmetric solutions for both the rotating string with tension and
the spinning dust string in three dimensions. The rotating string with tension
generates a rotating truncated cone outside and a flat space-time with
inevitable frame dragging inside. In the case of a string made of spinning
dust, in opposition to the previous case no frame dragging is present inside,
so that in this sense, the dragging effect can be "shielded" by considering
spinning instead of rotating sources. Both solutions are consistently lifted as
cylinders in the four-dimensional case.


title: Exotic Statistics for Strings in 4d BF Theory

abstract:
  After a review of exotic statistics for point particles in 3d BF theory, and
especially 3d quantum gravity, we show that string-like defects in 4d BF theory
obey exotic statistics governed by the 'loop braid group'. This group has a set
of generators that switch two strings just as one would normally switch point
particles, but also a set of generators that switch two strings by passing one
through the other. The first set generates a copy of the symmetric group, while
the second generates a copy of the braid group. Thanks to recent work of
Xiao-Song Lin, we can give a presentation of the whole loop braid group, which
turns out to be isomorphic to the 'braid permutation group' of Fenn, Rimanyi
and Rourke. In the context 4d BF theory this group naturally acts on the moduli
space of flat G-bundles on the complement of a collection of unlinked unknotted
circles in R^3. When G is unimodular, this gives a unitary representation of
the loop braid group. We also discuss 'quandle field theory', in which the
gauge group G is replaced by a quandle.


title: A Statistical Mechanical Problem in Schwarzschild Spacetime

abstract:
  We use Fermi coordinates to calculate the canonical partition function for an
ideal gas in a circular geodesic orbit in Schwarzschild spacetime. To test the
validity of the results we prove theorems for limiting cases. We recover the
Newtonian gas law subject only to tidal forces in the Newtonian limit.
Additionally we recover the special relativistic gas law as the radius of the
orbit increases to infinity. We also discuss how the method can be extended to
the non ideal gas case.


title:
Some remarks on the notions of general covariance and background
  independence

abstract:
  In the first part of this paper I review some of the difficulties that seem
to obstruct generally valid definitions of "general covariance" and/or
"background independence" The second and more historical part deals with a
rather strange argument that Einstein put forward in his 1913 "Entwurf paper"
with M. Grossmann to discredit scalar theories of gravity in order to promote
general covariance.


title: A solution to the cosmological constant problem

abstract:
  We argue that, when coupled to Einstein's theory of gravity, the Yukawa
theory may solve the cosmological constant problem in the following sense: The
radiative corrections of fermions generate an effective potential for the
scalar field, such that the effective cosmological term Lambda_eff is
dynamically driven to zero. Thence, for any initial positive cosmological
constant Lambda_0, Lambda_eff = 0 is an attractor of the semiclassical Einstein
theory coupled to fermionic and scalar matter fields. When the initial
cosmological term is negative, Lambda_eff=Lambda_0 does not change. Next we
argue that the dark energy of the Universe may be explained by a GUT scale
fermion with a mass, m = 4.3 * 10^15 (Lambda_0/10^13GeV)^(1/2) GeV.
  Finally, we comment on how the inflationary paradigm, BEH mechanism and phase
transitions in the early Universe get modified in the light of our findings.


title: Stability analysis of sonic horizons in Bose-Einstein condensates

abstract:
  We examine the linear stability of various configurations in Bose-Einstein
condensates with sonic horizons. These configurations are chosen in analogy
with gravitational systems with a black hole horizon, a white hole horizon and
a combination of both. We discuss the role of different boundary conditions in
this stability analysis, paying special attention to their meaning in
gravitational terms. We highlight that the stability of a given configuration,
not only depends on its specific geometry, but especially on these boundary
conditions. Under boundary conditions directly extrapolated from those in
standard General Relativity, black hole configurations, white hole
configurations and the combination of both into a black hole--white hole
configuration are shown to be stable. However, we show that under other (less
stringent) boundary conditions, configurations with a single black hole horizon
remain stable, whereas white hole and black hole--white hole configurations
develop instabilities associated to the presence of the sonic horizons.


title: Fundamental decoherence from quantum gravity: a pedagogical review

abstract:
  We present a discussion of the fundamental loss of unitarity that appears in
quantum mechanics due to the use of a physical apparatus to measure time. This
induces a decoherence effect that is independent of any interaction with the
environment and appears in addition to any usual environmental decoherence. The
discussion is framed self consistently and aimed to general physicists. We
derive the modified Schroedinger equation that arises in quantum mechanics with
real clocks and discuss the theoretical and potential experimental implications
of this process of decoherence.


title: Stable phantom energy traversable wormhole models

abstract:
  A possible candidate for the present accelerated expansion of the Universe is
''phantom energy'', which possesses an equation of state of the form
$\omega\equiv p/\rho<-1$, consequently violating the null energy condition. As
this is the fundamental ingredient to sustain traversable wormholes, this
cosmic fluid presents us with a natural scenario for the existence of these
exotic geometries. In this context, we shall construct phantom wormhole
geometries by matching an interior wormhole solution, governed by the phantom
energy equation of state, to an exterior vacuum at a junction interface.
Several physical properties and characteristics of these solutions are further
investigated. The dynamical stability of the transition layer of these phantom
wormholes to linearized spherically symmetric radial perturbations about static
equilibrium solutions is also explored. It is found that the respective stable
equilibrium configurations may be increased by strategically varying the
wormhole throat radius.


title: Coherent and squeezed states in black-hole evaporation

abstract:
  In earlier Letters, we adopted a complex approach to quantum processes in the
formation and evaporation of black holes. Taking Feynman's $+i\epsilon$
prescription, rather than than one of the more usual approaches, we calculated
the quantum amplitude (not just the probability density) for final weak-field
configurations following gravitational collapse to a black hole with subsequent
evaporation. What we have done is to find quantum amplitudes relating to a pure
state at late times following black-hole matter collapse. Such pure states are
then shown to be susceptible to a description in terms of coherent and squeezed
states - in practice, this description is not very different from that for the
well-known highly-squeezed final state of the relic radiation background in
inflationary cosmology. The simplest such collapse model involves Einstein
gravity with a massless scalar field. The Feynman approach involves making the
boundary-value problem for gravity and a massless scalar field well-posed. To
define this, let T be the proper-time separation, measured at spatial infinity,
between two space-like hypersurfaces on which initial (collapse) and final
(evaporation) data are posed. Then, in this approach, one rotates T by a
complex phase exp(-i\delta) into the lower half-plane. In an adiabatic
approximation, the resulting quantum amplitude may be expressed in terms of
generalised coherent states of the quantum oscillator, and a physical
interpretation is given. A squeezed-state representation, as above, then
follows.


title: Horizons and Ergoregions in Superfluids

abstract:
  Ripplons -- gravity-capillary waves on the free surface of a liquid or at the
interfaces between two superfluids -- are the most favourable excitations for
simulation of the general-relativistic effects related to horizons and
ergoregions. The white-hole horizon for the ``relativistic'' ripplons at the
surface of the shallow liquid is easily simulated using the kitchen-bath
hydraulic jump. The same white-hole horizon is observed in quantum liquid --
superfluid 4He. The ergoregion for the ``non-relativistic'' ripplons is
generated in the experiments with two sliding 3He superfluids. The common
property experienced by all these ripplons is the Miles instability inside the
ergoregion or horizon. Because of the universality of the Miles instability,
one may expect that it could take place inside the horizon of the astrophysical
black holes, if there is a preferred reference frame which comes from the
trans-Planckian physics. If this is the case, the black hole would evapotate
much faster than due to the Hawking radiation. Hawking radiation from the
artificial black hole in terms of the quantum tunneling of phonons and ripplons
is also discussed.

categories: gr-qc cond-mat.soft hep-ph physics.flu-dyn


title: Critical Phenomena in Head-on Collisions of Neutron Stars

abstract:
  We found type I critical collapses of compact objects modeled by a polytropic
equation of state (EOS) with polytropic index $\Gamma=2$ without the
ultra-relativistic assumption. The object is formed in head-on collisions of
neutron stars. Further we showed that the critical collapse can occur due to a
change of the EOS, without fine tuning of initial data. This opens the
possibility that a neutron star like compact object, not just those formed in a
collision, may undergo a critical collapse in processes which slowly change the
EOS, such as cooling.


title: Torsion, Dilaton and Gauge Couplings

abstract:
  Non-Abelian gauge fields are traditionally not coupled to torsion due to
violation of gauge invariance. However, it is possible to couple torsion to
Yang-Mills fields while maintaining gauge invariance provided one accepts that
the gauge couplings then become scalar fields. In the past this has been
untenable from experimental constraints at the current epoch for the
electromagnetic field at least. Recent researches on the "landscape" arising
out of string theory provides for many scalar fields which eventually determine
the various low energy parameters including gauge couplings in the universe.
With this scenario, we argue that the very early universe provides a
Riemann-Cartan geometry with non-zero torsion coupling to gauge fields. The
torsion is just the derivative of gauge coupling (scalar) fields. As a result,
in the evolution of the Universe, when the scalar (moduli) fields determine the
geometry of the universe to be Riemannian, torsion goes to zero, implying that
the associated modulus (and hence the gauge coupling) has a constant value. An
equivalent view is that the modulus fixes the gauge coupling at some constant
value causing the torsion to vanish as a consequence. Of course, when torsion
vanishes we recover Einstein's theory for further evolution of the universe.


title: Field equations from a surface term

abstract:
  As is well known, in order for the Einstein--Hilbert action to have a well
defined variation, and therefore to be used for deriving field equation through
the stationary action principle, it has to be amended by the addition of a
suitable boundary term. It has recently been claimed that, if one constructs an
action by adding this term to the matter action, the Einstein field equations
can be derived by requiring this action to be invariant under active
transformations which are normal to a null boundary. In this paper we
re-examine this approach both for the case of pure gravity and in the presence
of matter. We show that in the first case this procedure holds for more general
actions than the Einstein-Hilbert one and trace the basis of this remarkable
attribute. However, it is also pointed out the when matter is rigorously
considered the approach breaks down. The reasons for that are thoroughly
discussed.


title: Mass and temperature limits for blackbody radiation

abstract:
  A spherically symmetric distribution of classical blackbody radiation is
considered, at conditions in which gravitational self-interaction effects
become not negligible. Static solutions to Einstein field equations are
searched for, for each choice of the assumed central energy density. Spherical
cavities at thermodynamic equilibrium, i.e. filled with blackbody radiation,
are then studied, in particular for what concerns the relation among the mass M
of the ball of radiation contained in them and their temperature at center and
at the boundary. For these cavities it is shown, in particular, that: i) there
is no absolute limit to M as well to their central and boundary temperatures;
ii) when radius R is fixed, however, limits exist both for mass and for
boundary energy density rho_B: M <= K M_S(R) and rho_B <= Q/R^2, with K = 0.493
and Q = 0.02718, dimensionless, and M_S(R) the Schwarzschild mass for that
radius. Some implications of the existence and the magnitude of these limits
are considered. Finally the radial profiles for entropy for these systems are
studied, in their dependence on the mass (or central temperature) of the ball
of radiation.


title: Baryon Asymmetry, Inflation and Squeezed States

abstract:
  We use the general formalism of squeezed rotated states to calculate baryon
asymmetry in the wake of inflation through parametric amplification. We base
our analysis on a B and CP violating Lagrangian in an isotropically expanding
universe. The B and CP violating terms originate from the coupling of complex
fields with non-zero baryon number to a complex background inflaton field. We
show that a differential amplification of particle and anti-particle modes
gives rise to baryon asymmetry.


title:
Electromagnetic and gravitational self-force on a relativistic particle
  from quantum fields in curved space

abstract:
  We provide a quantum field theoretical derivation of the
Abraham-Lorentz-Dirac (ALD) equation, describing the motion of an electric
point charge sourcing an electromagnetic field, which back-reacts on the charge
as a self-force, and the Mino-Sasaki-Tanaka-Quinn-Wald (MSTQW) equation
describing the motion of a point mass with self-force interacting with the
linearized metric perturbations caused by the mass off an otherwise vacuous
curved background spacetime. We regularize the formally divergent self-force by
smearing the direct part of the retarded Green's function and using a
quasilocal expansion. We also derive the ALD-Langevin and the MSTQW-Langevin
equations with a classical stochastic force accounting for the effect of the
quantum fluctuations in the field, which causes small fluctuations on the
particle trajectory. These equations will be useful for studying the stochastic
motion of charges and small masses under the influence of both quantum and
classical noise sources, derived either self-consistently or put in by hand
phenomenologically. We also show that history-dependent noise-induced drift
motions could arise from such stochastic sources on the trajectory that could
be a hidden feature of gravitational wave forms hitherto unknown.


title: de Sitter group and Einstein-Hilbert Lagrangian

abstract:
  Axial vector torsion in the Einstein-Cartan space $U_{4}$ is considered here.
By picking a particular term from the SO(4,1) Pontryagin density and then
modifying it in a SO(3,1) invariant way, we get a Lagrangian density with
Lagrange multipliers. Then considering torsion and torsion-less connection as
independent fields, it has been found that $\kappa$ and $\lambda$ of
Einstein-Hilbert Lagrangian, appear as integration constants in such a way that
$\kappa$ has been found to be linked with the topological Nieh-Yan density of
$U_{4}$ space.


title: Gravitational magnetic monopoles and Majumdar-Papapetrou stars

abstract:
  A large amount of work has been dedicated to studying general relativity
coupled to non-Abelian Yang-Mills type theories. It has been shown that the
magnetic monopole, a solution of the Yang-Mills-Higgs equations can be coupled
to gravitation. For a low Higgs mass there are regular solutions, and for a
sufficiently massive monopole the system develops an extremal magnetic
Reissner-Nordstrom quasi-horizon. These solutions, called quasi-black holes,
although non-singular, are arbitrarily close to having a horizon. However, at
the critical value the quasi-black hole turns into a degenerate spacetime. On
the other hand, for a high Higgs mass, a sufficiently massive monopole develops
also a quasi-black hole, but it turns into an extremal true horizon, with
matter fields outside. One can also put a small Schwarzschild black hole inside
the magnetic monopole, an example of a non-Abelian black hole. Surprisingly,
Majumdar-Papapetrou systems, Abelian systems constructed from extremal dust,
also show a resembling behavior. Previously, we have reported that one can find
Majumdar-Papapetrou solutions which can be arbitrarily close of being a black
hole, displaying quasi-black hole behavior. With the aim of better
understanding the similarities between gravitational monopoles and
Majumdar-Papapetrou systems, we study a system composed of two extremal
electrically charged spherical shells (or stars, generically) in the
Einstein--Maxwell--Majumdar-Papapetrou theory. We review the gravitational
properties of the monopoles, and compare with the properties of the double
extremal electric shell system. These quasi-black holes can help in the
understanding of true black holes, and can give insight into the nature of the
entropy of black holes in the form of entanglement.


title: On-ground tests of LISA PathFinder thermal diagnostics system

abstract:
  Thermal conditions in the LTP, the LISA Technology Package, are required to
be very stable, and in such environment precision temperature measurements are
also required for various diagnostics objectives. A sensitive temperature
gauging system for the LTP is being developed at IEEC, which includes a set of
thermistors and associated electronics. In this paper we discuss the derived
requirements applying to the temperature sensing system, and address the
problem of how to create in the laboratory a thermally quiet environment,
suitable to perform meaningful on-ground tests of the system. The concept is a
two layer spherical body, with a central aluminium core for sensor implantation
surrounded by a layer of polyurethane. We construct the insulator transfer
function, which relates the temperature at the core with the laboratory ambient
temperature, and evaluate the losses caused by heat leakage through connecting
wires. The results of the analysis indicate that, in spite of the very
demanding stability conditions, a sphere of outer diameter of the order one
metre is sufficient. We provide experimental evidence confirming the model
predictions.


title: Static elastic shells in Einsteinian and Newtonian gravity

abstract:
  We study the behaviour of a specific system of relativistic elasticity in its
own gravitational field: a static, spherically symmetric shell whose wall is of
arbitrary thickness consisting of hyperelastic material. We give the system of
field equations and boundary conditions within the framework of the Einsteinian
theory of gravity. Furthermore, we analize the situation in the Newtonian
theory of gravity and obtain an existence result valid for small gravitational
constants and pointwise stability by using the implicit function theorem. If
one replaces the elastic material with a fluid, one finds that stable states
can not exist.


title:
Coupling Between the Spin and Gravitational Field and the Equation of
  Motion of the Spin

abstract:
  In general relativity, the equation of motion of the spin is given by the
equation of parallel transport, which is a result of the space-time geometry.
Any result of the space-time geometry can not be directly applied to gauge
theory of gravity. In gauge theory of gravity, based on the viewpoint of the
coupling between the spin and gravitational field, an equation of motion of the
spin is deduced. In the post Newtonian approximation, it is proved that this
equation gives out the same result as that of the equation of parallel
transport. So, in the post Newtonian approximation, gauge theory of gravity
gives out the same prediction on the precession of orbiting gyroscope as that
of general relativity.


title: Bounds for scalar waves on self-similar naked-singularity backgrounds

abstract:
  The stability of naked singularities in self-similar collapse is probed using
scalar waves. It is shown that the multipoles of a minimally coupled massless
scalar field propagating on a spherically symmetric self-similar background
spacetime admitting a naked singularity maintain finite $L^2$ norm as they
impinge on the Cauchy horizon. It is also shown that each multipole obeys a
pointwise bound at the horizon, as does its locally observed energy density.
$L^2$ and pointwise bounds are also obtained for the multipoles of a minimally
coupled massive scalar wave packet.


title:
On The 5D Extra-Force according to Basini-Capozziello-Leon Formalism and
  five important features: Kar-Sinha Gravitational Bending of Light,
  Chung-Freese Superluminal Behaviour, Maartens-Clarkson Black Strings,
  Experimental measures of Extra Dimensions on board International Space
  Station(ISS) and the existence of the Particle $Z$ due to a Higher
  Dimensional spacetime

abstract:
  We use the Conformal Metric as described in Kar-Sinha work on Gravitational
Bending of Light in a 5D Spacetime to recompute the equations of the 5D Force
in Basini-Capozziello-Leon Formalism and we arrive at a result that possesses
some advantages. The equations of the Extra Force as proposed by Leon are now
more elegant in Conformal Formalism and many algebraic terms can be simplified
or even suppressed. Also we recompute the Kar-Sinha Gravitational Bending of
Light affected by the presence of the Extra Dimension and analyze the
Superluminal Chung-Freese Features of this Formalism describing the advantages
of the Chung-Freese BraneWorld when compared to other Superluminal spacetime
metrics(eg:Warp Drive) and we describe why the Extra Dimension is invisible and
how the Extra Dimension could be made visible at least in theory.We also
examine the Maartens-Clarkson Black Holes in 5D(Black Strings) coupled to
massive Kaluza-Klein graviton modes predicted by Extra Dimensions theories and
we study experimental detection of Extra Dimensions on-board LIGO and LISA
Space Telescopes.We also propose the use of International Space Station(ISS) to
measure the additional terms(resulting from the presence of Extra Dimensions)
in the Kar-Sinha Gravitational Bending of Light in Outer Space to verify if we
really lives in a Higher Dimensional Spacetime.Also we demonstrate that
Particle $Z$ can only exists if the 5D spacetime exists.


title: From Local Regge Calculus towards Spin Foam Formalism?

abstract:
  We introduce the basic elements of SO(n)-local theory of Regge Calculus. A
first order formalism, in the sense of Palatini, is defined on the metric-dual
Voronoi complex of a simplicial complex. The Quantum Measure exhibits an
expansion, in four dimensions, in characters of irreducible representation of
SO(4) which has close resemblance and differences as well with the Spin Foam
Formalism. The coupling with fermionic matter is easily introduced which could
have consequences for the Spin Foam Formalism and Loop Quantum Gravity.


title:
Energy Distribution in Reissner-Nordstrom anti-de Sitter black holes in
  Moller Prescription

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0010068, gr-qc/9911018, gr-qc/0303034, and gr-qc/0212018.


title: Torsion, Scalar Field, Mass and FRW Cosmology

abstract:
  In the Einstein-Cartan space $U_4$, an axial vector torsion together with a
scalar field connected to a local scale factor have been considered. By
combining two particular terms from the SO(4,1) Pontryagin density and then
modifying it in a SO(3,1) invariant way, we get a Lagrangian density with
Lagrange multipliers. Then under FRW-cosmological background, where the scalar
field is connected to the source of gravitation, the Euler-Lagrange equations
ultimately give the constancy of the gravitational constant together with only
three kinds of energy densities representing mass, radiation and cosmological
constant. The gravitational constant has been found to be linked with the
geometrical Nieh-Yan density.


title: Quantum Cosmology

abstract:
  Quantum cosmology in general denotes the application of quantum physics to
the whole universe and thus gives rise to many realizations and examples,
covering problems at different mathematical and conceptual levels. It is
related to quantum gravity and more specifically describes the application to
cosmological situations rather than the construction and analysis of quantum
field equations. As there are several different approaches to quantum gravity,
equations for quantum cosmology are not unique. Most investigations have been
performed in the context of canonical quantization, where Wheeler--DeWitt like
equations are the prime object. Applications are mostly conceptual, ranging
from possible resolutions of classical singularities and explanations of the
uniqueness of the universe to the origin of seeds for a classical world and its
initial conditions.


title: Finite Action Klein-Gordon Solutions on Lorentzian Manifolds

abstract:
  The eigenvalue problem for the square integrable solutions is studied usually
for elliptic equations. In this note we consider such a problem for the
hyperbolic Klein-Gordon equation on Lorentzian manifolds. The investigation
could help to answer the question why elementary particles have a discrete mass
spectrum. An infinite family of square integrable solutions for the
Klein-Gordon equation on the Friedman type manifolds is constructed. These
solutions have a discrete mass spectrum and a finite action. In particular the
solutions on de Sitter space are investigated.


title: Quantum gravitational decoherence of matter waves

abstract:
  One of the biggest unsolved problems in physics is the unification of quantum
mechanics and general relativity. The lack of experimental guidance has made
the issue extremely evasive, though various attempts have been made to relate
the loss of matter wave coherence to quantum spacetime fluctuations. We present
a new approach to the gravitational decoherence near the Planck scale, made
possible by recently discovered conformal structure of canonical gravity. This
leads to a gravitational analogue of the Brownian motion whose correlation
length is given by the Planck length up to a scaling factor. With input from
recent matter wave experiments, we show that the minimum value of this factor
to be well within the expected range for quantum gravity theories. This
suggests that the sensitivities of advanced matter wave interferometers may be
approaching the fundamental level due to quantum spacetime fluctuations and
that investigating Planck scale physics using matter wave interferometry may
become a reality in the near future.


title:
The effect of the tortoise coordinate on the stable study of the
  Schwarzschild black hole

abstract:
  Carefully analyze influence of the tortoise coordinates r* and t on the
stable study of the Schwarzschild black hole. Actually, one should be cautious
in using the compact property of the perturbation field: it is true only with
respect with the coordinate r and proper time or "good time", not the tortoise
coordinates r* and t. Therefore, the mathematical proof used in reference [7]
is incorrect because of it relying on the compact property of the perturbation
fields. The Schwarzschild black hole might be unstable[1]-[5]


title: Physics of Quantum Relativity through a Linear Realization

abstract:
  The idea of quantum relativity as a generalized, or rather deformed, version
of Einstein (special) relativity has been taking shape in recent years.
Following the perspective of deformations, while staying within the framework
of Lie algebra, we implement explicitly a simple linear realization of the
relativity symmetry, and explore systematically the resulting physical
interpretations. Some suggestions we make may sound radical, but are arguably
natural within the context of our formulation. Our work may provide a new
perspective on the subject matter, complementary to the previous approach(es),
and may lead to a better understanding of the physics.


title:
Gravitational wave bursts from cosmic (super)strings: Quantitative
  analysis and constraints

abstract:
  We discuss data analysis techniques that can be used in the search for
gravitational wave bursts from cosmic strings. When data from multiple
interferometers are available, we describe consistency checks that can be used
to greatly reduce the false alarm rates. We construct an expression for the
rate of bursts for arbitrary cosmic string loop distributions and apply it to
simple known solutions. The cosmology is solved exactly and includes the
effects of a late-time acceleration. We find substantially lower burst rates
than previous estimates suggest and explain the disagreement. Initial LIGO is
unlikely to detect field theoretic cosmic strings with the usual loop sizes,
though it may detect cosmic superstrings as well as cosmic strings and
superstrings with non-standard loop sizes (which may be more realistic). In the
absence of a detection, we show how to set upper limits based on the loudest
event. Using Initial LIGO sensitivity curves, we show that these upper limits
may result in interesting constraints on the parameter space of theories that
lead to the production of cosmic strings.


title: Decaying Gravity

abstract:
  We consider the possibility of energy being exchanged between the scalar and
matter fields in scalar-tensor theories of gravity. Such an exchange provides a
new mechanism which can drive variations in the gravitational 'constant' G. We
find exact solutions for the evolution of spatially flat
Friedman-Roberston-Walker cosmologies in this scenario and discuss their
behaviour at both early and late times. We also consider the physical
consequences and observational constraints on these models.


title: A self-consistent solution in affine space with scalar field

abstract:
  Conformal connection of scalar field is shown to produce possible
non-metricity in affine connection spaces. In case of self-consistent solution
the non-metricity is a correction to background Riemannian structure with
respect to gravitational constant and its magnitude may be essential in the
early Universe.


title:
Local existence in a class of characteristic problems for the Einstein
  vacuum equations

abstract:
  This paper has been withdrawn by the author due to an error in the use of the
Cauchy-Kowalevski theorem in section 4., theorem 4.1 which does not allow to
prove the final result. When (and if) this error will be cured it will be
replaced by a corrected version of the result.


title:
A variational approach to homogeneous scalar fields in General
  Relativity

abstract:
  A result of existence of homogeneous scalar field solutions between
prescribed configurations is given, using a modified version of
Euler--Maupertuis least action variational principle. Solutions are obtained as
limit of approximating variational problems, solved using techniques introduced
by Rabinowitz.


abstract:
  Global visibility of naked singularities is analyzed here for a class of
spherically symmetric spacetimes, extending previous studies - limited to
inhomogeneous dust cloud collapse - to more physical valid situations in which
pressures are non-vanishing. Existence of nonradial geodesics escaping from the
singularity is shown, and the observability of the singularity from far-away
observers is discussed.


title: Generic degeneracy and entropy in loop quantum gravity

abstract:
  Without imposing the trapping boundary conditions and only from within the
very definition of area it is shown that the loop quantization of area
manifests an unexpected degeneracy in area eigenvalues. This could lead to a
deeper understanding of the microscopic description of a quantum black hole. If
a certain number of semi-classically expected properties of black holes are
imposed on a quantum surface its entropy coincides with the Bekenstein-Hawking
entropy.


title: Bringing Together Gravity and the Quanta

abstract:
  Due to its underlying gauge structure, teleparallel gravity achieves a
separation between inertial and gravitational effects. It can, in consequence,
describe the isolated gravitational interaction without resorting to the
equivalence principle, and is able to provide a tensorial definition for the
energy-momentum density of the gravitational field. Considering the conceptual
conflict between the local equivalence principle and the nonlocal uncertainty
principle, the replacement of general relativity by its teleparallel equivalent
can be considered an important step towards a prospective reconciliation
between gravitation and quantum mechanics.


title: Some bounds extracted from a quantum of area

abstract:
  Asking very elementary relativistic quantum mechanics to meet quantums of
area and time, it is possible to observe at a general level: a) the seesaw
bound for the mass of neutrinos, and b) the need of a gauge group at energies
below Planck mass.


title: Dynamics of Anisotropic Universes

abstract:
  We present a general study of the dynamical properties of Anisotropic Bianchi
Universes in the context of Einstein General Relativity. Integrability results
using Kovalevskaya exponents are reported and connected to general knowledge
about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type
VIII and IX universes are showed to be equivalent in some precise sence.


title: Why is the metric invertible?

abstract:
  We raise, and provide an (unsatisfactory) answer to, the title's question:
why, unlike all other fields, does the gravitational "metric" variable not have
zero vacuum? After formulating, without begging it, we exhibit additions to the
conventional action that express existence of the inverse through a field
equation.


title: Hamiltonian dynamics of extended objects: Regge-Teitelboim model

abstract:
  We consider the Regge-Teitelboim model for a relativistic extended object
embedded in a fixed background Minkowski spacetime, in which the dynamics is
determined by an action proportional to the integral of the scalar curvature of
the worldvolume spanned by the object in its evolution. In appearance, this
action resembles the Einstein-Hilbert action for vacuum General Relativity: the
equations of motion for both are second order; the difference is that here the
dynamical variables are not the metric, but the embedding functions of the
worldvolume. We provide a novel Hamiltonian formulation for this model. The
Lagrangian, like that of General Relativity, is linear in the acceleration of
the extended object. As such, the model is not a genuine higher derivative
theory, a fact reflected in the order of the equations of motion. Nevertheless,
as we will show, it is possible as well as useful to treat it as a `fake'
higher derivative system, enlarging the phase space appropriately. The
corresponding Hamiltonian on this phase space is constructed: it is a
polynomial. The complete set of constraints on the phase space is identified.
The fact that the equations of motion are of second order in derivatives of the
field variables manifests itself in the Hamiltonian formulation through the
appearance of additional constraints, both primary and secondary. These new
constraints are second class. In this formulation, the Lagrange multipliers
implementing the primary constraints get identified as accelerations. This is a
generic feature of any Lagrangian linear in the acceleration possessing
reparametrization invariance.


title: Skyrme Black Holes in the Isolated Horizons Formalism

abstract:
  We study static, spherically symmetric, Skyrme black holes in the context of
the assumption that they can be viewed as bound states between ordinary bare
black holes and solitons. This assumption and results stemming from the
isolated horizons formalism lead to several conjectures about the static black
hole solutions. These conjectures are tested against the Skyrme black hole
solutions. It is shown that, while there is in general good agreement with the
conjectures, a crucial aspect seems to violate one of the conjectures.


title: Gravitational lensing due to dark matter modelled by vector field

abstract:
  The specified constant 4-vector field reproducing the spherically symmetric
stationary metric of cold dark matter halo in the region of flat rotation
curves results in a constant angle of light deflection at small impact
distances. The effective deflecting mass is factor $\pi/2$ greater than the
dark matter mass. The perturbation of deflection picture due to the halo edge
is evaluated.


title:
Networks of cosmological histories, crossing of the phantom divide line
  and potentials with cusps

abstract:
  We discuss the phenomenon of the smooth dynamical gravity induced crossing of
the phantom divide line in a framework of simple cosmological models where it
appears to occur rather naturally, provided the potential of the unique scalar
field has some kind of cusp. The behavior of cosmological trajectories in the
vicinity of the cusp is studied in some detail and a simple mechanical analogy
is presented. The phenomenon of certain complementarity between the smoothness
of the spacetime geometry and matter equations of motion is elucidated. We
introduce a network of cosmological histories and qualitatively describe some
of its properties.


title: Singular Isotropic Cosmologies and Bel-Robinson Energy

abstract:
  We consider the problem of the nature and possible types of spacetime
singularities that can form during the evolution of \emph{FRW} universes in
general relativity. We show that by using, in addition to the Hubble expansion
rate and the scale factor, the Bel-Robinson energy of these universes we can
consistently distinguish between the possible different types of singularities
and arrive at a complete classification of the singularities that can occur in
the isotropic case. We also use the Bel-Robinson energy to prove that known
behaviours of exact flat isotropic universes with given singularities are
generic in the sense that they hold true in every type of spatial geometry.


title:
Cosmo-dynamics and dark energy with a quadratic EoS: anisotropic models,
  large-scale perturbations and cosmological singularities

abstract:
  In general relativity, for fluids with a linear equation of state (EoS) or
scalar fields, the high isotropy of the universe requires special initial
conditions, and singularities are anisotropic in general. In the brane world
scenario anisotropy at the singularity is suppressed by an effective quadratic
equation of state. There is no reason why the effective EoS of matter should be
linear at the highest energies, and a non-linear EoS may describe dark energy
or unified dark matter (Paper I, astro-ph/0512224). In view of this, here we
study the effects of a quadratic EoS in homogenous and inhomogeneous
cosmological models in general relativity, in order to understand if in this
context the quadratic EoS can isotropize the universe at early times. With
respect to Paper I, here we use the simplified EoS P=alpha rho + rho^2/rho_c,
which still allows for an effective cosmological constant and phantom behavior,
and is general enough to analyze the dynamics at high energies. We first study
anisotropic Bianchi I and V models, focusing on singularities. Using dynamical
systems methods, we find the fixed points of the system and study their
stability. We find that models with standard non-phantom behavior are in
general asymptotic in the past to an isotropic fixed point IS, i.e. in these
models even an arbitrarily large anisotropy is suppressed in the past: the
singularity is matter dominated. Using covariant and gauge invariant variables,
we then study linear perturbations about the homogenous and isotropic spatially
flat models with a quadratic EoS. We find that, in the large scale limit, all
perturbations decay asymptotically in the past, indicating that the isotropic
fixed point IS is the general asymptotic past attractor for non phantom
inhomogeneous models with a quadratic EoS. (Abridged)


title: A five-dimensional Schwarzschild-like solution

abstract:
  In recent years, interest in extra dimensions has experienced a dramatic
increase. A common practice has been to look for higher-dimensional
generalizations of four-dimensional solutions to the Einstein equations. In
this vein, we have found a static, spherically symmetric solution to the 5-d
Einstein equations. Certain aspects of this solution are very different from
the 4-d Schwarzschild solution. However, in observationally accessible regions,
the geodesics of the two solutions are essentially the same.


title: Self-dual metrics in Husain's approach

abstract:
  We show that Husain's reduction of the self-dual Einstein equations is
equivalent to the Pleba\'nski equation. The B\"acklund transformation between
these equations is found. Contact symmetries of the Husain-Park equation and
corresponding conservation laws are derived.


title: Torsion, Dirac Field, Dark Matter and Dark Radiation

abstract:
  The role of torsion and a scalar field $\phi$ in gravitation, especially, in
the presence of a Dirac field in the background of a particular class of the
Riemann-Cartan geometry is considered here. Recently, a Lagrangian density with
Lagrange multipliers has been proposed by the author which has been obtained by
picking some particular terms from the SO(4,1) Pontryagin density, where the
scalar field $\phi$ causes the de Sitter connection to have the proper
dimension of a gauge field. In this article the scalar field has been linked to
the dimension of the Dirac field. Here we get the field equations for the Dirac
field and the scalar field in such a way that both of them appear to be
mutually non-interacting. In this scenario the scalar field appears to be a
natural candidate for the dark matter and the dark radiation.


title: Gravitons Enhance Fermions during Inflation

abstract:
  We solve the effective Dirac equation for massless fermions during inflation
in the simplest gauge, including all one loop corrections from quantum gravity.
At late times the result for a spatial plane wave behaves as if the classical
solution were subjected to a time dependent field strength renormalization of
Z_2(t) = 1 - \frac{17}{4 \pi} G H^2 \ln(a) + O(G^2). We show that this also
follows from making the Hartree approximation, although the numerical
coefficients differ.


title:
The Quantum and Statistical Theory of Early Universe and Its Possible
  Applications to Cosmology

abstract:
  The subject of this study is Quantum and Statistical Mechanics of the Early
Universe. In it a new approach to investigation of these two theories - density
matrix deformation - is proposed. The distinguishing feature of the proposed
approach as compared to the previous ones is the fact that here the density
matrix is subjected to deformation, rather than commutators or (that is the
same) Heisenberg's Algebra. The deformation is understood as an extension of a
particular theory by inclusion of one or several additional parameters in such
a way that the initial theory appears in the limiting transition. Some
consequences of this approach for unitarity problem in Early Universe,black
hole entropy, information paradox problem,for symmetry restoration in the
associated deformed field model with scalar field are proposed.


title:
Possible variations of the fine structure constant $\alpha$ and their
  metrological significance

abstract:
  We briefly review the recent experimental results on possible variations of
the fine structure constant $\alpha$ on the cosmological time scale and its
position dependence. We outline the theoretical grounds for the assumption that
$\alpha$ might be variable, mention some phenomenological models incorporating
a variable $\alpha$ into the context of modern cosmology and discuss the
significance of possible $\alpha$ variations for theoretical and practical
metrology.


title: Confinement in Einstein's unified field theory

abstract:
  After recalling the mathematical structure of Einstein's Hermitian extension
of the gravitational theory of 1915, the problem, whether its field equations
should admit of phenomenological sources at their right-hand sides, and how
this addition should be done, is expounded by relying on a thread of essential
insights and achievements by Schr\"odinger, Kursunoglu, Lichnerowicz, H\'ely
and Borchsenius. When sources are appended to all the field equations, from the
latter and from the contracted Bianchi identities a sort of
gravoelectrodynamics appears, that totally departs from the so called
Einstein-Maxwell theory, since its constitutive equation, that rules the link
between inductions and fields, is a very complicated differential relation that
allows for a much wider, still practically unexplored range of possible
occurrences. In this sort of theory one can allow for both an electric and a
magnetic four-current, which are not a physically wrong replica of each other,
like it would occur if both these currents were allowed in Maxwell's vacuum.
Particular static exact solutions show that, due to the peculiar constitutive
equation, while electric charges with a pole structure behave according to
Coulomb's law, magnetic charges with a pole structure interact with forces not
depending on their mutual distance. The latter behaviour was already discovered
by Treder in 1957 with an approximate calculation, while looking for ordinary
electromagnetism in the theory. He also showed that in the Hermitian theory
magnetic charges of unlike sign mutually attract, hence they are permanently
confined entities. The exact solutions confirm this finding, already
interpreted in 1980 by Treder in a chromodynamic sense.


title: Null-stream veto for two co-located detectors: Implementation issues

abstract:
  Time-series data from multiple gravitational wave (GW) detectors can be
linearly combined to form a null-stream, in which all GW information will be
cancelled out. This null-stream can be used to distinguish between actual GW
triggers and spurious noise transients in a search for GW bursts using a
network of detectors. The biggest source of error in the null-stream analysis
comes from the fact that the detector data are not perfectly calibrated. In
this paper, we present an implementation of the null-stream veto in the
simplest network of two co-located detectors. The detectors are assumed to have
calibration uncertainties and correlated noise components. We estimate the
effect of calibration uncertainties in the null-stream veto analysis and
propose a new formulation to overcome this. This new formulation is
demonstrated by doing software injections in Gaussian noise.


title:
Rank deficiency and Tikhonov regularization in the inverse problem for
  gravitational-wave bursts

abstract:
  Coherent techniques for searches of gravitational-wave bursts effectively
combine data from several detectors, taking into account differences in their
responses. The efforts are now focused on the maximum likelihood principle as
the most natural way to combine data, which can also be used without prior
knowledge of the signal. Recent studies however have shown that straightforward
application of the maximum likelihood method to gravitational waves with
unknown waveforms can lead to inconsistencies and unphysical results such as
discontinuity in the residual functional, or divergence of the variance of the
estimated waveforms for some locations in the sky. So far the solutions to
these problems have been based on rather different physical arguments.
Following these investigations, we now find that all these inconsistencies stem
from rank deficiency of the underlying network response matrix. In this paper
we show that the detection of gravitational-wave bursts with a network of
interferometers belongs to the category of ill-posed problems. We then apply
the method of Tikhonov regularization to resolve the rank deficiency and
introduce a minimal regulator which yields a well-conditioned solution to the
inverse problem for all locations on the sky.


title: Metric-affine f(R) theories of gravity

abstract:
  General Relativity assumes that spacetime is fully described by the metric
alone. An alternative is the so called Palatini formalism where the metric and
the connections are taken as independent quantities. The metric-affine theory
of gravity has attracted considerable attention recently, since it was shown
that within this framework some cosmological models, based on some generalized
gravitational actions, can account for the current accelerated expansion of the
universe. However we think that metric-affine gravity deserves much more
attention than that related to cosmological applications and so we consider
here metric-affine gravity theories in which the gravitational action is a
general function of the scalar curvature while the matter action is allowed to
depend also on the connection which is not {\em a priori} symmetric. This
general treatment will allow us to address several open issues such as: the
relation between metric-affine $f(R)$ gravity and General Relativity (in vacuum
as well as in the presence of matter), the implications of the dependence (or
independence) of the matter action on the connections, the origin and role of
torsion and the viability of the minimal-coupling principle.


title: A new way to solve Wheeler-DeWitt equation including black hole universe

abstract:
  One of the unsolved issues in the quantum gravity comes from the
Wheeler-DeWitt equation, which is second order functional derivative equation.
In this paper, we introduce a new method to solve the Wheeler-DeWitt equation.
Usually one treats the state functional of the space of 3-dimensional metrics,
which do not contain timelike metrics. However we can expand this state to the
state which has support on the space of spacetime metrics with using additional
constraint which requires the recovery of 4-dimensional quantum gravity.
Enlarging the support of the state functional of the spacetime metrics, we can
simply solve the usual Wheeler-DeWitt equation with the additional constraint.
Using this method we can solve some unsolved problems, such as the quantization
of the black hole.


title: A New Kind of Uniformly Accelerated Reference Frames

abstract:
  A new kind of uniformly accelerated reference frames with a line-element
different from the M{\o}ller and Rindler ones is presented, in which every
observer at $x, y, z=$consts. has the same constant acceleration. The laws of
mechanics are checked in the new kind of frames. Its thermal property is
studied. The comparison with the M{\o}ller and Rindler uniform accelerated
reference frames is also made.


title:
An effective vacuum refractive index from gravity and the present
  ether-drift experiments

abstract:
  Re-analyzing the data published by the Berlin and Duesseldorf ether-drift
experiments, we have found a clean non-zero daily average for the amplitude of
the signal. The two experimental values, A_0\sim (10.5 \pm 1.3) 10^{-16} and
A_0\sim (12.1\pm 2.2) 10^{-16}$ respectively, are entirely consistent with the
theoretical prediction (9.7\pm 3.5) 10^{-16} that is obtained once the
Robertson-Mansouri-Sexl anisotropy parameter is expressed in terms of
N_{vacuum}, the effective vacuum refractive index that one would get, for an
apparatus placed on the Earth's surface, in a flat-space picture of gravity .


title:
Finite difference schemes for second order systems describing black
  holes

abstract:
  In the harmonic description of general relativity, the principle part of
Einstein's equations reduces to 10 curved space wave equations for the
componenets of the space-time metric. We present theorems regarding the
stability of several evolution-boundary algorithms for such equations when
treated in second order differential form. The theorems apply to a model black
hole space-time consisting of a spacelike inner boundary excising the
singularity, a timelike outer boundary and a horizon in between. These
algorithms are implemented as stable, convergent numerical codes and their
performance is compared in a 2-dimensional excision problem.


title: A teleparallel model for the neutrino

abstract:
  The main result of the paper is a new representation for the Weyl Lagrangian
(massless Dirac Lagrangian). As the dynamical variable we use the coframe, i.e.
an orthonormal tetrad of covector fields. We write down a simple Lagrangian -
wedge product of axial torsion with a lightlike element of the coframe - and
show that variation of the resulting action with respect to the coframe
produces the Weyl equation. The advantage of our approach is that it does not
require the use of spinors, Pauli matrices or covariant differentiation. The
only geometric concepts we use are those of a metric, differential form, wedge
product and exterior derivative. Our result assigns a variational meaning to
the tetrad representation of the Weyl equation suggested by J.B.Griffiths and
R.A.Newing.


title: Spinning-black-hole binaries: The orbital hang up

abstract:
  We present the first fully-nonlinear numerical study of the dynamics of
highly spinning black-hole binaries. We evolve binaries from quasicircular
orbits (as inferred from Post-Newtonian theory), and find that the last stages
of the orbital motion of black-hole binaries are profoundly affected by their
individual spins. In order to cleanly display its effects, we consider two
equal mass holes with individual spin parameters S/m^2=0.757, both aligned and
anti-aligned with the orbital angular momentum (and compare with the spinless
case), and with an initial orbital period of 125M. We find that the aligned
case completes three orbits and merges significantly after the anti-aligned
case, which completes less than one orbit. The total energy radiated for the
former case is ~7% while for the latter it is only ~2%. The final Kerr hole
remnants have rotation parameters a/M=0.89 and a/M=0.44 respectively, showing
the unlikeliness of creating a maximally rotating black hole out of the merger
of two spinning holes.


title:
Quantum Nature of the Big Bang: An Analytical and Numerical
  Investigation

abstract:
  Analytical and numerical methods are developed to analyze the quantum nature
of the big bang in the setting of loop quantum cosmology. They enable one to
explore the effects of quantum geometry both on the gravitational and matter
sectors and significantly extend the known results on the resolution of the big
bang singularity. Specifically, the following results are established for the
homogeneous isotropic model with a massless scalar field: i) the scalar field
is shown to serve as an internal clock, thereby providing a detailed
realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac
observables and semi-classical states are constructed rigorously; iii) the
Hamiltonian constraint is solved numerically to show that the big bang is
replaced by a big bounce. Thanks to the non-perturbative, background
independent methods, unlike in other approaches the quantum evolution is
deterministic across the deep Planck regime. Our constructions also provide a
conceptual framework and technical tools which can be used in more general
models. In this sense, they provide foundations for analyzing physical issues
associated with the Planck regime of loop quantum cosmology as a whole.


title: FRW barotropic zero modes: Dynamical systems observability

abstract:
  The dynamical systems observability properties of barotropic bosonic and
fermionic FRW cosmological oscillators are investigated. Nonlinear techniques
for dynamical analysis have been recently developed in many engineering areas
but their application has not been extended beyond their standard field. This
paper is a small contribution to an extension of this type of dynamical systems
analysis to FRW barotropic cosmologies. We find that determining the Hubble
parameter of barotropic FRW universes does not allow the observability, i.e.,
the determination of neither the barotropic FRW zero mode nor of its derivative
as dynamical cosmological states. Only knowing the latter ones correspond to a
rigorous dynamical observability in barotropic cosmology


title: Introduction to dynamical horizons in numerical relativity

abstract:
  This paper presents a quasi-local method of studying the physics of dynamical
black holes in numerical simulations. This is done within the dynamical horizon
framework, which extends the earlier work on isolated horizons to
time-dependent situations. In particular: (i) We locate various kinds of
marginal surfaces and study their time evolution. An important ingredient is
the calculation of the signature of the horizon, which can be either spacelike,
timelike, or null. (ii) We generalize the calculation of the black hole mass
and angular momentum, which were previously defined for axisymmetric isolated
horizons to dynamical situations. (iii) We calculate the source multipole
moments of the black hole which can be used to verify that the black hole
settles down to a Kerr solution. (iv) We also study the fluxes of energy
crossing the horizon, which describes how a black hole grows as it accretes
matter and/or radiation.
  We describe our numerical implementation of these concepts and apply them to
three specific test cases, namely, the axisymmetric head-on collision of two
black holes, the axisymmetric collapse of a neutron star, and a
non-axisymmetric black hole collision with non-zero initial orbital angular
momentum.


title: Hidden Quantum Gravity in 3d Feynman diagrams

abstract:
  In this work we show that 3d Feynman amplitudes of standard QFT in flat and
homogeneous space can be naturally expressed as expectation values of a
specific topological spin foam model. The main interest of the paper is to set
up a framework which gives a background independent perspective on usual field
theories and can also be applied in higher dimensions. We also show that this
Feynman graph spin foam model, which encodes the geometry of flat space-time,
can be purely expressed in terms of algebraic data associated with the Poincare
group. This spin foam model turns out to be the spin foam quantization of a BF
theory based on the Poincare group, and as such is related to a quantization of
3d gravity in the limit where the Newton constant G_N goes to 0. We investigate
the 4d case in a companion paper where the strategy proposed here leads to
similar results.


title: Detecting Highly Oscillatory Signals by Chirplet Path Pursuit

abstract:
  This paper considers the problem of detecting nonstationary phenomena, and
chirps in particular, from very noisy data. Chirps are waveforms of the very
general form A(t) exp(i\lambda \phi(t)), where \lambda is a (large) base
frequency, the phase \phi(t) is time-varying and the amplitude A(t) is slowly
varying. Given a set of noisy measurements, we would like to test whether there
is signal or whether the data is just noise. One particular application of note
in conjunction with this problem is the detection of gravitational waves
predicted by Einstein's Theory of General Relativity.
  We introduce detection strategies which are very sensitive and more flexible
than existing feature detectors. The idea is to use structured algorithms which
exploit information in the so-called chirplet graph to chain chirplets together
adaptively as to form chirps with polygonal instantaneous frequency. We then
search for the path in the graph which provides the best trade-off between
complexity and goodness of fit. Underlying our methodology is the idea that
while the signal may be extremely weak so that none of the individual empirical
coefficients is statistically significant, one can still reliably detect by
combining several coefficients into a coherent chain. This strategy is general
and may be applied in many other detection problems. We complement our study
with numerical experiments showing that our algorithms are so sensitive that
they seem to detect signals whenever their strength makes them detectable.


title: Testing post-Newtonian theory with gravitational wave observations

abstract:
  The Laser Interferometric Space Antenna (LISA) will observe supermassive
black hole binary mergers with amplitude signal-to-noise ratio of several
thousands. We investigate the extent to which such observations afford
high-precision tests of Einstein's gravity. We show that LISA provides a unique
opportunity to probe the non-linear structure of post-Newtonian theory both in
the context of general relativity and its alternatives.


title: Specific heat of a particle on the cone

abstract:
  This work investigates how a conical singularity can affect the specific heat
of systems. A free nonrelativistic particle confined to the lateral surface of
a cone -- conical box -- is taken as a toy model. Its specific heat is
determined as a function of the deficit angle and the temperature. For a
vanishing deficit angle, the specific heat is that of a particle in a flat disk
where a characteristic temperature separates quantum and classical behaviors,
as usual. By increasing the deficit angle the characteristic temperature
increases also, and eventually another characteristic temperature (which does
not depend on the deficit angle) arises. When the cone gets sufficiently sharp,
at low and intermediate temperatures the azimuthal degree of freedom is
suppressed. At low temperatures the specific heat varies discontinuously with
the deficit angle. Connections between certain theorems regarding common zeros
of the Bessel functions and this discontinuity are reported.


title:
Decelerating and accelerating back-reaction of vacuum to the Universe
  expansion

abstract:
  Back-reaction of the massless scalar field vacuum to the Universe expansion
is considered. Automatic renormalization procedure based on the equations of
motion instead of the Friedman equation is used to avoid the cosmological
constant problem. It is found, that the vacuum tends to decelerate an expansion
of Universe if the conformal acceleration of Universe is equal to zero. In
contract, the vacuum acts as the true cosmological constant in Universe
expanding with the present day acceleration. Estimation for third derivative of
the Universe scale factor with respect to conformal time is presented.


title: Instability of the negative mass Schwarzschild naked singularity

abstract:
  We study the negative mass Schwarzschild spacetime, which has a naked
singularity, and show that it is perturbatively unstable. This is achieved by
first introducing a modification of the well known Regge - Wheeler - Zerilli
approach to black hole perturbations to allow for the presence of a
``kinematic'' singularity that arises for negative masses, and then exhibiting
exact exponentially growing solutions to the linearized Einstein's equations.
The perturbations are smooth everywhere and behave nicely around the
singularity and at infinity. In particular, the first order variation of the
scalar invariants can be made everywhere arbitrarily small as compared to the
zeroth order terms. Our approach is also compared to a recent analysis that
leads to a different conclusion regarding the stability of the negative mass
Schwarzschild spacetime. We also comment on the relevance of our results to the
stability of more general negative mass, nakedly singular spacetimes.


title: Self interaction of spins in binary systems

abstract:
  Beyond point mass effects various contributions add to the radiative
evolution of compact binaries. We present all the terms up to the second
post-Newtonian order contributing to the rate of increase of gravitational wave
frequency and the number of gravitational wave cycles left until the final
coalescence for binary systems with spin, mass quadrupole and magnetic dipole
moments, moving on circular orbit. We evaluate these contributions for some
famous or typical compact binaries and show that the terms representing the
self interaction of individual spins, given for the first time here, are
commensurable with the proper spin-spin contributions for the recently
discovered double pulsar J0737-3039.


title:
Derivation of Source-Free Maxwell and Gravitational Radiation Equations
  by Group Theoretical Methods

abstract:
  We derive source-free Maxwell-like equations in flat spacetime for any
helicity "j" by comparing the transformation properties of the 2(2j+1) states
that carry the manifestly covariant representations of the inhomogeneous
Lorentz group with the transformation properties of the two helicity "j" states
that carry the irreducible representations of this group. The set of
constraints so derived involves a pair of curl equations and a pair of
divergence equations. These reduce to the free-field Maxwell equations for j=1
and the analogous equations coupling the gravito-electric and the
gravito-magnetic fields for j=2.


title: Gravity on the octonion algebra

abstract:
  Gravitational interactions are treated as non-associative part of a
Lagrangian of octonion fields. The Lagrangian is defined in the charge space as
squared curvature with respect to the octonion fields. The applications of
suggested formalism to homogeneous and isotropic space are studied.


title:
Complete classification of purely magnetic, non-rotating and
  non-accelerating perfect fluids

abstract:
  Recently the class of purely magnetic non-rotating dust spacetimes has been
shown to be empty (Wylleman, Class. Quant. Grav. 23, 2727). It turns out that
purely magnetic rotating dust models are subject to severe integrability
conditions as well. One of the consequences of the present paper is that also
rotating dust cannot be purely magnetic when it is of Petrov type D or when it
has a vanishing spatial gradient of the energy density. For purely magnetic and
non-rotating perfect fluids on the other hand, which have been fully classified
earlier for Petrov type D (Lozanovski, Class. Quant. Grav. 19, 6377), the fluid
is shown to be non-accelerating if and only if the spatial density gradient
vanishes. Under these conditions, a new and algebraically general solution is
found, which is unique up to a constant rescaling, which is spatially
homogeneous of Bianchi type $VI_0$, has degenerate shear and is of Petrov type
I($M^\infty)$ in the extended Arianrhod-McIntosh classification.
  The metric and the equation of state are explicitly constructed and
properties of the model are briefly discussed. We finally situate it within the
class of normal geodesic flows with degenerate shear tensor.


title: Thermal stability of radiant black holes

abstract:
  Beginning with a brief sketch of the derivation of Hawking's theorem of
horizon area increase, based on the Raychaudhuri equation, we go on to discuss
the issue as to whether generic black holes, undergoing Hawking radiation, can
ever remain in stable thermal equilibrium with that radiation. We derive a
universal criterion for such a stability, which relates the black hole mass and
microcanonical entropy, both of which are well-defined within the context of
the Isolated Horizon, and in principle calculable within Loop Quantum Gravity.
The criterion is argued to hold even when thermal fluctuations of electric
charge are considered, within a {\it grand} canonical ensemble.


title:
Hamiltonian analysis of the double null 2+2 decomposition of Ashtekar
  variables

abstract:
  We derive a canonical analysis of a double null 2+2 Hamiltonian description
of General Relativity in terms of complex self-dual 2-forms and the associated
SO(3) connection variables. The algebra of first class constraints is obtained
and forms a Lie algebra that consists of two constraints that generate
diffeomorphisms in the two surface, a constraint that generates diffeomorphisms
along the null generators and a constraint that generates self-dual spin and
boost transformations.


title: f(R) Gravity and scalar-tensor theory

abstract:
  In the present paper we will investigate the relation between scalar-tensor
theory and $f(R)$ theories of gravity. Such studies have been performed in the
past for the metric formalism of $f(R)$ gravity; here we will consider mainly
the Palatini formalism, where the metric and the connections are treated as
independent quantities. We will try to investigate under which circumstances
$f(R)$ theories of gravity are equivalent to scalar-tensor theory and examine
the implications of this equivalence, when it exists.


title: Cosmological Singularities and Bel-Robinson Energy

abstract:
  We consider the problem of describing the asymptotic behaviour of
\textsc{FRW} universes near their spacetime singularities in general
relativity. We find that the Bel-Robinson energy of these universes in
conjunction with the Hubble expansion rate and the scale factor proves to be an
appropriate measure leading to a complete classification of the possible
singularities. We show how our scheme covers all known cases of cosmological
asymptotics possible in these universes and also predicts new and distinct
types of singularities. We further prove that various asymptotic forms met in
flat cosmologies continue to hold true in their curved counterparts. These
include phantom universes with their recently discovered big rips, sudden
singularities as well as others belonging to graduated inflationary models.


title:
symmetries of the Ricci tensor of static space times with maximal
  symmetric transverse spaces

abstract:
  Static space times with maximal symmetric transverse spaces are classified
according to their Ricci collineations. These are investigated for
non-degenerate Ricci tensor ($det.(R_{\alpha}) \neq 0$). It turns out that the
only collineations admitted by these spaces can be ten, seven, six or four.
Some new metrics admitting proper Ricci collineations are also investigated.


title: The Homogeneous Scalar Field and the Wet Dark Sides of the Universe

abstract:
  We study the possibility that a generalised real scalar field minimally
coupled to gravity could explain both the galactic and the cosmological dark
components of the universe. Within the framework of Einstein's Relativity we
model static galactic halos by considering the most general action built from
the scalar field and its first derivatives. Although the gravitational
configuration is static, the scalar field may be either static, or homogeneous
and linear in time. In the case of the static scalar field, the models we look
at inevitably posses unphysical negative energies, and we are led to a sort of
no-go result. In the case of the homogeneous scalar field, on the contrary, we
find that compact objects with flat rotational curves and with the mass and the
size of a typical galaxy can be successfully modeled and the Tully-Fisher
relation recovered. We further show that the homogeneous scalar field deduced
from the galactic halo spacetimes has an action compatible with the kinetic
Unified Dark Matter models recently proposed by Scherrer. Therefore, such a
homogeneous kinetic Unified Dark Matter not only may correctly mimic the
galactic dynamics, but could also be used to model the present-day accelerated
expansion in the universe.


title:
Binary black hole detection rates in inspiral gravitational wave
  searches

abstract:
  The signal-to-noise ratios (SNRs) for quasi-circular binary black hole
inspirals computed from restricted post-Newtonian waveforms are compared with
those attained by more complete post-Newtonian signals, which are
superpositions of amplitude-corrected harmonics of the orbital phase. It is
shown that if one were to use the best available amplitude-corrected waveforms
for detection templates, one should expect SNRs in actual searches to be
significantly lower than those suggested by simulations based purely on
restricted waveforms.


title: Stability and thermodynamics of brane black holes

abstract:
  We consider scalar and axial gravitational perturbations of black hole
solutions in brane world scenarios. We show that perturbation dynamics is
surprisingly similar to the Schwarzschild case with strong indications that the
models are stable. Quasinormal modes and late-time tails are discussed. We also
study the thermodynamics of these scenarios verifying the universality of
Bekenstein's entropy bound as well as the applicability of 't Hooft's brickwall
method.


title:
Exact boundary conditions in numerical relativity using multiple grids:
  scalar field tests

abstract:
  Cauchy-Characteristic Matching (CCM), the combination of a central 3+1 Cauchy
code with an exterior characteristic code connected across a time-like
interface, is a promising technique for the generation and extraction of
gravitational waves. While it provides a tool for the exact specification of
boundary conditions for the Cauchy evolution, it also allows to follow
gravitational radiation all the way to infinity, where it is unambiguously
defined.
  We present a new fourth order accurate finite difference CCM scheme for a
first order reduction of the wave equation around a Schwarzschild black hole in
axisymmetry. The matching at the interface between the Cauchy and the
characteristic regions is done by transfering appropriate characteristic/null
variables. Numerical experiments indicate that the algorithm is fourth order
convergent. As an application we reproduce the expected late-time tail decay
for the scalar field.


title:
Well-posedness of formulations of the Einstein equations with dynamical
  lapse and shift conditions

abstract:
  We prove that when the equations are restricted to the principal part the
standard version of the BSSN formulation of the Einstein equations is
equivalent to the NOR formulation for any gauge, and that the KST formulation
is equivalent to NOR for a variety of gauges. We review a family of elliptic
gauge conditions and the implicit parabolic and hyperbolic drivers that can be
derived from them, and show how to make them symmetry-seeking. We investigate
the hyperbolicity of ADM, NOR and BSSN with implicit hyperbolic lapse and shift
drivers. We show that BSSN with the coordinate drivers used in recent "moving
puncture" binary black hole evolutions is ill-posed at large shifts, and
suggest how to make it strongly hyperbolic for arbitrary shifts. For ADM, NOR
and BSSN with elliptic and parabolic gauge conditions, which cannot be
hyperbolic, we investigate a necessary condition for well-posedness of the
initial-value problem.


title: Casimir Effect In Krein Space Quantization

abstract:
  An explicit calculation of Casimir effect through an alternative approach of
field quantization [1, 2], has been presented in this paper. In this method,
the auxiliary negative norm states have been utilized, the modes of which do
not interact with the physical states or real physical world. Naturally these
modes cannot be affected by the physical boundary conditions. Presence of
negative norm states play the rule of an automatic renormalization device for
the theory.


title:
A template bank to search for gravitational waves from inspiralling
  compact binaries I: physical models

abstract:
  Gravitational waves from coalescing compact binaries are searched using the
matched filtering technique. As the model waveform depends on a number of
parameters, it is necessary to filter the data through a template bank covering
the astrophysically interesting region of the parameter space. The choice of
templates is defined by the maximum allowed drop in signal-to-noise ratio due
to the discreteness of the template bank. In this paper we describe the
template-bank algorithm that was used in the analysis of data from the Laser
Interferometer Gravitational Wave Observatory (LIGO) and GEO 600 detectors to
search for signals from binaries consisting of non-spinning compact objects.
Using Monte-Carlo simulations, we study the efficiency of the bank and show
that its performance is satisfactory for the design sensitivity curves of
ground-based interferometric gravitational wave detectors GEO 600, initial
LIGO, advanced LIGO and Virgo. The bank is efficient to search for various
compact binaries such as binary primordial black holes, binary neutron stars,
binary black holes, as well as a mixed binary consisting of a non-spinning
black hole and a neutron star.


title: $\theta$-Term and Cosmological Constant from CJD Action

abstract:
  In the gravity without metric formalism of Capovilla, Jacobson and Dell, the
topological $\theta$-term appears through a canonical transformation.The origin
of this canonical transformation is probed here. It is shown here that when
$\theta$-term appears cosmological $\lambda$-term also appears simultaneously.


title: Generalized Area Law under Multi-parameter Rotating Black Hole Spacetime

abstract:
  We study the statistical mechanics for quantum scalar fields under the
multi-parameter rotating black hole spacetime in arbitrary D dimensions. The
method of analysis is general in the sense that the metric does not depend on
the explicit black hole solutions. The generalized Stefan-Boltzmann's law for
the scalar field is derived by considering the allowed energy region properly.
Then the generalized area law for the scalar field entropy is derived by
introducing the invariant regularization parameter in the Rindler spacetime.
The derived area law is applied to Kerr-AdS black holes in four and five
dimensions. Thermodynamic implication is also discussed.


title:
Macroscopic observables and Lorentz violation in discrete quantum
  gravity

abstract:
  This article concerns the fate of local Lorentz invariance in quantum
gravity, particularly for approaches in which a discrete structure replaces
continuum spacetime. Some features of standard quantum mechanics, presented in
a sum-over-histories formulation, are reviewed, and their consequences for such
theories are discussed. It is argued that, if the individual histories of a
theory give bad approximations to macroscopic continuum properties in some
frames, then it is inevitable that the theory violates Lorentz symmetry.


title: First-Order Logic Foundation of Relativity Theories

abstract:
  Motivation and perspective for an exciting new research direction
interconnecting logic, spacetime theory, relativity--including such
revolutionary areas as black hole physics, relativistic computers, new
cosmology--are presented in this paper. We would like to invite the logician
reader to take part in this grand enterprise of the new century. Besides
general perspective and motivation, we present initial results in this
direction.


title: Gravitational Constant and Torsion

abstract:
  Riemann-Cartan space time $U_{4}$ is considered here. It has been shown that
when we link topological Nieh-Yan density with the gravitational constant then
we get Einstein-Hilbert Lagrangian as a consequence.


title: Nonlinear perturbations of the Kaluza-Klein monopole

abstract:
  We consider the nonlinear stability of the Kaluza-Klein monopole viewed as
the static solution of the five dimensional vacuum Einstein equations. Using
both numerical and analytical methods we give evidence that the Kaluza-Klein
monopole is asymptotically stable within the cohomogeneity-two biaxial Bianchi
IX ansatz recently introduced in \cite{bcs}. We also show that for sufficiently
large perturbations the Kaluza-Klein monopole loses stability and collapses to
a Kaluza-Klein black hole. The relevance of our results for the stability of
BPS states in M/String theory is briefly discussed.


title: Graviton propagator in loop quantum gravity

abstract:
  We compute some components of the graviton propagator in loop quantum
gravity, using the spinfoam formalism, up to some second order terms in the
expansion parameter.


title: Unfinished revolution

abstract:
  Introductive chapter of a book on Quantum Gravity, edited by Daniele Oriti,
to appear with Cambridge University Press.


title:
Reply to "Comment on 'Scalar-tensor gravity coupled to a global monopole
  and flat rotation curves' "

abstract:
  In Brans-Dicke theory of gravity we explain how the extra constant value in
the formula for rotation velocities of stars in a galactic halo can be obtained
due to the global monopole field. We argue on a few points of the preceding
Comment and discuss improvement of our model.


title: Remote quantum states in curved spacetime

abstract:
  It is seen that issues of unitarity raised by the evolution of the wave
function in curved spacetime can be resolved by describing the evolution of
quantum states in Minkowski tangent space. The treatment adheres closely to the
orthodox interpretation that the wave function is not physical but is part of a
mathematical method for the calculation of probabilities of measurement
results. Minkowski tangent space refers to a non-physical configuration space
used to describe quantum mechanics. The teleconnection is defined between
Hilbert spaces at different points in spacetime motivated by arguments from the
probability interpretation. The teleconnection is analogous to a connection
between vector spaces and reduces to the Levi-Civita connection in the limit of
near initial and final measurements. Predictions for quantum theory in curved
spacetime agree with those of classical general relativity.


title:
Upper limits on the gravitational mass loss of the Galaxy and the LIGO
  burst searches

abstract:
  We discuss the relevance, for the search of gravitational-wave bursts, of
upper limits on the total mass loss of the Galaxy which come from various
astronomical observations. For sub-millisecond bursts we obtain limits on the
event rate, as a function of the GW amplitude, which are stronger than the
corresponding upper limits set by LIGO in the S2 run. A detection of a burst
rate saturating these limits, with the sensitivities of present and near-future
runs, would imply that, with some improvement on the accuracy of astronomical
observations of the Galaxy, as foreseen with the GAIA mission, it might be
possible to detect gravitational waves indirectly from their effect on galactic
dynamics.


title: Evolutionary Quantum Dynamics of a Generic Universe

abstract:
  The implications of an Evolutionary Quantum Gravity are addressed in view of
formulating a new dark matter candidate. We consider a Schr\"odinger dynamics
for the gravitational field associated to a generic cosmological model and then
we solve the corresponding eigenvalues problem, inferring its phenomenological
issue for the actual Universe. The spectrum of the super-Hamiltonian is
determined including a free inflaton field, the ultrarelativistic thermal bath
and a perfect gas into the dynamics. We show that, when a Planckian cut-off is
imposed in the theory and the classical limit of the ground state is taken,
then a dark matter contribution can not arise because its critical parameter
$\Omega_{dm}$ is negligible today when the appropriate cosmological
implementation of the model is provided. Thus, we show that, from a
phenomenological point of view, an Evolutionary Quantum Cosmology overlaps the
Wheeler-DeWitt approach and therefore it can be inferred as appropriate to
describe early stages of the Universe without significant traces on the later
evolution. Finally, we provide indications that the horizon paradox can be
solved in the Planck era by the morphology of the Universe wave function.


title: Tachyon Matter in Loop Quantum Cosmology

abstract:
  An analytical approach for studying the cosmological scenario with a
homogeneous tachyon field within the framework of loop quantum gravity is
developed. Our study is based on the semi-classical regime where space time can
be approximated as a continuous manifold, but matter Hamiltonian gets
non-perturbative quantum corrections. A formal correspondence between classical
and loop quantum cosmology is also established. The Hamilton-Jacobi method for
getting exact solutions is constructed and some exact power-law as well as
bouncing solutions are presented.