title:
Retarded coordinates based at a world line, and the motion of a small
  black hole in an external universe

abstract:
  In the first part of this article I present a system of retarded coordinates
based at an arbitrary world line of an arbitrary curved spacetime. The
retarded-time coordinate labels forward light cones that are centered on the
world line, the radial coordinate is an affine parameter on the null generators
of these light cones, and the angular coordinates are constant on each of these
generators. The spacetime metric in the retarded coordinates is displayed as an
expansion in powers of the radial coordinate and expressed in terms of the
world line's acceleration vector and the spacetime's Riemann tensor evaluated
at the world line. The formalism is illustrated in two examples, the first
involving a comoving world line of a spatially-flat cosmology, the other
featuring an observer in circular motion in the Schwarzschild spacetime. The
main application of the formalism is presented in the second part of the
article, in which I consider the motion of a small black hole in an empty
external universe. I use the retarded coordinates to construct the metric of
the small black hole perturbed by the tidal field of the external universe, and
the metric of the external universe perturbed by the presence of the black
hole. Matching these metrics produces the MiSaTaQuWa equations of motion for
the small black hole.


title:
Global classical solutions to the spherically symmetric
  Nordstr\"om-Vlasov system

abstract:
  Classical solutions of the spherically symmetric Nordstr\"{o}m-Vlasov system
are shown to exist globally in time. The main motivation for investigating the
mathematical properties of the Nordstr\"{o}m-Vlasov system is its relation to
the Einstein-Vlasov system. The former is not a physically correct model, but
it is expected to capture some of the typical features of the latter, which
constitutes a physically satisfactory, relativistic model but is mathematically
much more complex. We show that classical solutions of the spherically
symmetric Nordstr\"{o}m-Vlasov system exist globally in time for compactly
supported initial data under the additional condition that there is a lower
bound on the modulus of the angular momentum of the initial particle system. We
emphasize that this is not a smallness condition and that our result holds for
arbitrary large initial data satisfying this hypothesis.


title: Universalization as a physical guiding principle

abstract:
  In this essay, I wish to share a novel perspective based on the principle of
universalization in arriving at the relativistic and quantum world from the
classical world. I also delve on some insightful discussion on going
``beyond''.


title: Einstein constraints on n dimensional compact manifolds

abstract:
  We give a general survey of the solution of the Einstein constraints by the
conformal method on n dimensional compact manifolds. We prove some new results
about solutions with low regularity (solutions in $H_{2}$ when n=3), and
solutions with unscaled sources.


title: Gravitoelectromagnetism: A Brief Review

abstract:
  The main theoretical aspects of gravitoelectromagnetism ("GEM") are
presented. Two basic approaches to this subject are described and the role of
the gravitational Larmor theorem is emphasized. Some of the consequences of GEM
are briefly mentioned.


title:
Rejection Properties of Stochastic-Resonance-Based Detectors of Weak
  Harmonic Signals

abstract:
  In (V. Galdi et al., Phys. Rev. E57, 6470, 1998) a thorough characterization
in terms of receiver operating characteristics (ROCs) of stochastic-resonance
(SR) detectors of weak harmonic signals of known frequency in additive gaussian
noise was given. It was shown that strobed sign-counting based strategies can
be used to achieve a nice trade-off between performance and cost, by comparison
with non-coherent correlators. Here we discuss the more realistic case where
besides the sought signal (whose frequency is assumed known) further unwanted
spectrally nearby signals with comparable amplitude are present. Rejection
properties are discussed in terms of suitably defined false-alarm and
false-dismissal probabilities for various values of interfering signal(s)
strength and spectral separation.


title: Quantizing speeds with the cosmological constant

abstract:
  Considering the Barrett-Crane spin foam model for quantum gravity with
(positive) cosmological constant, we show that speeds must be quantized and we
investigate the physical implications of this effect such as the emergence of
an effective deformed Poincare symmetry.


title: New conservation laws for electromagnetic fields in gravity

abstract:
  A recently found (gr-qc/0303036) 2-index, symmetric, trace-free,
divergence-free tensor is introduced for arbitrary source-free electromagnetic
fields. The tensor can be constructed for any test Maxwell field in Einstein
spaces (including proper vacuum), and more importantly for any Einstein-Maxwell
spacetime. The tensor is explicitly given and analyzed in some special
situations, such as general null electromagnetic fields, Reissner-Nordstr\"om
solution, or classical electrodynamics. We present an explicit example where
the conserved currents derived from the energy-momentum tensor using symmetries
are trivial, but those derived from the new tensor are not.


title: Gravity on Conformal Superspace

abstract:
  The configuration space of general relativity is superspace - the space of
all Riemannian 3-metrics modulo diffeomorphisms. However, it has been argued
that the configuration space for gravity should be conformal superspace - the
space of all Riemannian 3-metrics modulo diffeomorphisms and conformal
transformations. Taking this conformal nature seriously leads to a new theory
of gravity which although very similar to general relativity has some very
different features particularly in cosmology and quantisation. It should
reproduce the standard tests of general relativity. The cosmology is studied in
some detail. The theory is incredibly restrictive and as a result admits an
extremely limited number of possible solutions. The problems of the standard
cosmology are addressed and most remarkably the cosmological constant problem
is resolved in a natural way. The theory also has several attractive features
with regard to quantisation particularly regarding the problem of time.


title: On the structure of the new electromagnetic conservation laws

abstract:
  New electromagnetic conservation laws have recently been proposed: in the
absence of electromagnetic currents, the trace of the Chevreton superenergy
tensor, $H_{ab}$ is divergence-free in four-dimensional (a) Einstein spacetimes
for test fields, (b) Einstein-Maxwell spacetimes. Subsequently it has been
pointed out, in analogy with flat spaces, that for Einstein spacetimes the
trace of the Chevreton superenergy tensor $H_{ab}$ can be rearranged in the
form of a generalised wave operator $\square_L$ acting on the energy momentum
tensor $T_{ab}$ of the test fields, i.e., $H_{ab}=\square_LT_{ab}/2$. In this
letter we show, for Einstein-Maxwell spacetimes in the full non-linear theory,
that, although, the trace of the Chevreton superenergy tensor $H_{ab}$ can
again be rearranged in the form of a generalised wave operator $\square_G$
acting on the electromagnetic energy momentum tensor, in this case the result
is also crucially dependent on Einstein's equations; hence we argue that the
divergence-free property of the tensor $H_{ab}=\square_GT_{ab}/2$ has
significant independent content beyond that of the divergence-free property of
$T_{ab}$.


title: Gravity and the Thermodynamics of Horizons

abstract:
  Spacetimes with horizons show a resemblance to thermodynamic systems and it
is possible to associate the notions of temperature and entropy with them.
Several aspects of this connection are reviewed in a manner appropriate for
broad readership. The approach uses two essential principles: (a) the physical
theories must be formulated for each observer entirely in terms of variables
any given observer can access and (b) consistent formulation of quantum field
theory requires analytic continuation to the complex plane. These two
principles, when used together in spacetimes with horizons, are powerful enough
to provide several results in a unified manner. Since spacetimes with horizons
have a generic behaviour under analytic continuation, standard results of
quantum field theory in curved spacetimes with horizons can be obtained
directly (Sections III to VII). The requirements (a) and (b) also put strong
constraints on the action principle describing the gravity and, in fact, one
can obtain the Einstein-Hilbert action from the thermodynamic considerations.
The latter part of the review (Sections VIII to X) investigates this deeper
connection between gravity, spacetime microstructure and thermodynamics of
horizons. This approach leads to several interesting results in the
semiclassical limit of quantum gravity, which are described.


title:
Toward the search for gravitational waves from inspiralling compact
  binaries in TAMA300 data during 2003: data quality and stability

abstract:
  We present the preliminary results of the analysis to search for inspiraling
compact binaries using TAMA300 DT8 data which was taken during 2003. We compare
the quality and the stability of the data with that taken during DT6 in 2001.
We find that the DT8 data has better quality and stability than the DT6 data.


title: Geodesics in the Generalized Schwarzschild Solution

abstract:
  Since Schwarzshild discovered the point-mass solution to Einstein's equations
that bears his name, many equivalent forms of the metric have been catalogued.
Using an elementary coordinate transformation, we derive the most general form
for the stationary, spherically-symmetric vacuum metric, which contains one
free function. Different choices for the function correspond to common
expressions for the line element. From the general metric, we obtain particle
and photon trajectories, and use them to specify several time coordinates
adapted to physical situations. The most general form of the metric is only
slightly more complicated than the Schwarzschild form, which argues effectively
for teaching the general line element in place of the diagonal metric.


title: 35 Years of Testing Relativistic Gravity: Where do we go from here?

abstract:
  This paper addresses the motivation, technology and recent results in the
tests of the general theory of relativity (GR) in the solar system. We
specifically discuss Lunar Laser Ranging (LLR), the only technique available to
test the Strong Equivalence Principle (SEP) and presently the most accurate
method to test for the constancy of the gravitational constant, G. The new
Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) will enable
tests of the Weak and Strong Equivalence Principles with a sensitivity
approaching 10e-14, translating to a test of the SEP violation parameter, \eta,
to a precision of ~3x10e-5. In addition, the (v/c)^2 general relativistic
effects would be tested to better than 0.1%, and measurements of the relative
change in the gravitational constant, \dot{G}/G, would be ~0.1% the inverse age
of the universe.
  We also discuss the Laser Astrometric Test Of Relativity (LATOR) mission that
will be able to improve the value of the PPN parameter \gamma to accuracy of 1
part in 10e8 and will measure effects of the next post-Newtonian order (1/c^4)
of light deflection resulting from gravity's intrinsic non-linearity, as well
as measure a variety of other relativistic effects. LATOR will lead to very
robust advances in the tests of fundamental physics: this mission could
discover a violation or extension of GR, or reveal the presence of an
additional long range interaction in the physical law. There are no analogs to
the LATOR experiment; it is unique and is a natural culmination of solar system
gravity experiments.


title: A criterion for bubble formation in de Sitter universe

abstract:
  The influence of the shape of scalar field potential on the outcome of vacuum
decay in de Sitter universe is studied. Sufficient condition for vacuum decay
via bubble formation, described by Coleman - de Luccia instanton, is revisited
and necessary condition is found. Both conditions require that the curvature of
the potential is greater than 4 $\times$ (Hubble constant)$^2$, but while the
sufficient condition states that this inequality is to be valid at the top of
the barrier, the necessary condition requires that it holds at least somewhere
throughout the barrier. The conditions leave a 'grey zone' in parameter space,
which however seems to be forbidden for quartic potential as well as for
quadratic potential with a narrow peak proposed by Linde in the context of open
inflation.


title:
Inflationary Dilatonic de Sitter Universe from Super Yang - Mills Theory
  Perturbed by Scalars and Spinors

abstract:
  In this paper a quantum N = 4 super Yang-Mills theory perturbed by
dilaton-coupled scalars and spinor fields is considered. The induced effective
action for such a theory is calculated on a dilaton-gravitational background
using the conformal anomaly found via the AdS/CFT correspondence. Considering
such an effective action (using the large N method) as a quantum correction to
the classical gravity action with cosmological constant, we study the effect
from the dilaton on the scale factor (this corresponds to an inflationary
universe without dilaton). It is shown that, depending on the initial
conditions for the dilaton, the dilaton may slow down or accelerate the
inflation process. At late times the dilaton is decaying exponentially.
Different possible cases corresponding to a dilatonic dS Universe are analyzed
with respect to the equations of motion.


title:
Conformal invariance of massless Duffin-Kemmer-Petiau theory in
  Riemannian space-times

abstract:
  We investigate the conformal invariance of massless Duffin-Kemmer-Petiau
theory coupled to riemannian space-times. We show that, as usual, in the
minimal coupling procedure only the spin 1 sector of the theory -which
corresponds to the electromagnetic field- is conformally invariant. We show
also that the conformal invariance of the spin 0 sector can be naturally
achieved by introducing a compensating term in the lagrangian. Such a procedure
-besides not modifying the spin 1 sector- leads to the well-known conformal
coupling between the scalar curvature and the massless Klein-Gordon-Fock field.
Going beyond the riemannian spacetimes, we briefly discuss the effects of a
nonvanishing torsion in the scalar case.


title:
Influence On The Physical Universe By Wormhole Generated Extra
  Dimensional space

abstract:
  We use the Gu-Huang model for a special case when the universe is seven
dimensional. In the core of extra dimension we place a modified
Gidding-Strominger wormhole. This wormhole is separated by a thin wall from the
extra dimensional space. The wormhole content is assumed to satisfy the
adiabatic gas law. The wormhole pressure penetrates into the extra dimension.
We then solve the Einstein equation assuming that the real universe and the
extra dimension contains only inextendable fluid with negligible local
pressure. We show the physical universe expands because the time dependent
Hubble parameter is positive. Under certain condition the deacceleration
parameter, $q_0$, is also positive. But the most significant outcome of our
investigation is the fact that $q_0$ fluctuates. If we can detect by
observation that the acceleration fluctuates, our model will be an alternative
explanation without the help of dark energy. We could however link dark energy
with work done by wormhole pressure.


title: $\Delta-$String: A Hybrid Between Einstein's and String Paradigmes

abstract:
  Superthin and superlong solutions in 5D Kaluza-Klein gravity are considered.
It is shown that they can be cosidered as a hybrid between Einstein's and
string paradigmes.


title: Bianchi type I cosmology with scalar and spinor fields

abstract:
  We consider a system of interacting spinor and scalar fields in a
gravitational field given by a Bianchi type-I cosmological model filled with
perfect fluid. The interacting term in the Lagrangian is chosen in the form of
derivative coupling, i.e., ${\cal L}_{\rm int} = \frac{\lambda}{2}
\vf_{,\alpha}\vf^{,\alpha} F$, with $F$ being a function of the invariants $I$
an $J$ constructed from bilinear spinor forms $S$ and $P$. We consider the
cases when $F$ is the power or trigonometric functions of its arguments.
Self-consistent solutions to the spinor, scalar and BI gravitational field
equations are obtained. The problems of initial singularity and asymptotically
isotropization process of the initially anisotropic space-time are studied. It
is also shown that the introduction of the Cosmological constant
($\Lambda$-term) in the Lagrangian generates oscillations of the BI model,
which is not the case in absence of $\Lambda$ term. Unlike the case when spinor
field nonlinearity is induced by self-action, in the case in question, wehere
nonlinearity is induced by the scalar field, there exist regular solutions even
without broken dominant energy condition.


title:
Wave polarizations for a beam-like gravitational wave in quadratic
  curvature gravity

abstract:
  We compute analytically the tidal field and polarizations of an exact
gravitational wave generated by a cylindrical beam of null matter of finite
width and length in quadratic curvature gravity. We propose that this wave can
represent the gravitational wave that keep up with the high energy photons
produced in a gamma ray burst (GRB) source.


title:
Constraints on Non-Newtonian Gravity from Recent Casimir Force
  Measurements

abstract:
  Corrections to Newton's gravitational law inspired by extra dimensional
physics and by the exchange of light and massless elementary particles between
the atoms of two macrobodies are considered. These corrections can be described
by the potentials of Yukawa-type and by the power-type potentials with
different powers. The strongest up to date constraints on the corrections to
Newton's gravitational law are reviewed following from the E\"{o}tvos- and
Cavendish-type experiments and from the measurements of the Casimir and van der
Waals force. We show that the recent measurements of the Casimir force gave the
possibility to strengthen the previously known constraints on the constants of
hypothetical interactions up to several thousand times in a wide interaction
range. Further strengthening is expected in near future that makes Casimir
force measurements a prospective test for the predictions of fundamental
physical theories.


title: Nonzero cosmological constant and the many vacua world

abstract:
  The idea of the quantum state of the Universe described by some density
matrix, i.e mixture of at least two vacua, the trivial symmetric and the
nontrivial one with spontaneously broken symmetry is discussed. Nonzero
cosmological constant necessarily arises for such a state and has the
observable value if one takes the axion mass for the vacuum expectation value.
The Higgs model, Nambu's model and discrete symmetry breaking are considered.
Human observers can observe only the world on the nonsymmetric vacuum, the
world on the other vacuum is some dark matter. Gravity is due to action of two
worlds. Tachyons nonobservable for visible matter can be present in the dark
matter, leading to some effects of nonlocality in the space of the Universe.


title:
New Concept for Testing General Relativity: The Laser Astrometric Test
  of Relativity (LATOR) Mission

abstract:
  This paper discusses new Fundamental physics experiment that will test
relativistic gravity at the accuracy better than the effects of the second
order in the gravitational field strength, ~G^2. The Laser Astrometric Test Of
Relativity (LATOR) mission uses laser interferometry between two
micro-spacecraft whose lines of sight pass close by the Sun to accurately
measure deflection of light in the solar gravity. The key element of the
experimental design is a redundant geometry optical truss provided by a
long-baseline (100 m) multi-channel stellar optical interferometer placed on
the International Space Station (ISS). The spatial interferometer is used for
measuring the angles between the two spacecraft and for orbit determination
purposes. LATOR will not only improve the value of the parameterized
post-Newtonian (PPN) $\gamma$ to unprecedented levels of accuracy of 1 part in
10e8, it will also reach ability to measure effects of the next post-Newtonian
order (1/c^4) of light deflection resulting from gravity's intrinsic
non-linearity. The solar quadrupole moment parameter, J2, will be measured with
high precision, as well as a variety of other relativistic effects including
Lense-Thirring precession. LATOR will lead to very robust advances in the tests
of Fundamental physics: this mission could discover a violation or extension of
general relativity, or reveal the presence of an additional long range
interaction in the physical law. There are no analogs to the LATOR experiment;
it is unique and is a natural culmination of solar system gravity experiments.


title: Full causal dissipative cosmologies with stiff matter

abstract:
  The general solution of the gravitational field equations for a full causal
bulk viscous stiff cosmological fluid, with bulk viscosity coefficient
proportional to the energy density to the power 1/4, is obtained in the flat
Friedmann-Robertson-Walker geometry. The solution describes a non-inflationary
Universe, which starts its evolution from a singular state. The time variation
of the scale factor, deceleration parameter, viscous pressure, viscous
pressure-thermodynamic pressure ratio, comoving entropy and Ricci and
Kretschmann invariants is considered in detail.


title: Quasi-Black Holes from Extremal Charged Dust

abstract:
  One can construct families of static solutions that can be viewed as
interpolating between nonsingular spacetimes and those containing black holes.
Although everywhere nonsingular, these solutions come arbitrarily close to
having a horizon. To an observer in the exterior region, it becomes
increasingly difficulty to distinguish these from a true black hole as the
critical limiting solution is approached. In this paper we use the
Majumdar-Papapetrou formalism to construct such quasi-black hole solutions from
extremal charged dust. We study the gravitational properties of these
solutions, comparing them with the the quasi-black hole solutions based on
magnetic monopoles. As in the latter case, we find that solutions can be
constructed with or without hair.


title:
Dimensional regularization of the third post-Newtonian dynamics of point
  particles in harmonic coordinates

abstract:
  Dimensional regularization is used to derive the equations of motion of two
point masses in harmonic coordinates. At the third post-Newtonian (3PN)
approximation, it is found that the dimensionally regularized equations of
motion contain a pole part [proportional to 1/(d-3)] which diverges as the
space dimension d tends to 3. It is proven that the pole part can be
renormalized away by introducing suitable shifts of the two world-lines
representing the point masses, and that the same shifts renormalize away the
pole part of the "bulk" metric tensor g_munu(x). The ensuing, finite
renormalized equations of motion are then found to belong to the general
parametric equations of motion derived by an extended Hadamard regularization
method, and to uniquely determine the heretofore unknown 3PN parameter lambda
to be: lambda = - 1987/3080. This value is fully consistent with the recent
determination of the equivalent 3PN static ambiguity parameter, omega_s = 0, by
a dimensional-regularization derivation of the Hamiltonian in
Arnowitt-Deser-Misner coordinates. Our work provides a new, powerful check of
the consistency of the dimensional regularization method within the context of
the classical gravitational interaction of point particles.


title:
Noncommutative Unification of General Relativity and Quantum Mechanics.
  A Finite Model

abstract:
  We construct a model unifying general relativity and quantum mechanics in a
broader structure of noncommutative geometry. The geometry in question is that
of a transformation groupoid given by the action of a finite group G on a space
E. We define the algebra of smooth complex valued functions on the groupoid,
with convolution as multiplication, in terms of which the groupoid geometry is
developed. Owing to the fact that the group G is finite the model can be
computed in full details. We show that by suitable averaging of noncommutative
geometric quantities one recovers the standard space-time geometry. The quantum
sector of the model is explored in terms of the regular representation of the
groupoid algebra, and its correspondence with the standard quantum mechanics is
established.


title: Astrophysical Implications of Higher-Dimensional Gravity

abstract:
  We review the implications of modern higher-dimensional theories of gravity
for astrophysics and cosmology. In particular, we discuss the latest
developments of space-time-matter theory in connection with dark matter,
particle dynamics and the cosmological constant, as well as related aspects of
quantum theory. There are also more immediate tests of extra dimensions,
notably involving perturbations of the cosmic 3K microwave background and the
precession of a supercooled gyroscope in Earth orbit. We also outline some
general features of embeddings, and include pictures of the big bang as viewed
from a higher dimension.


title: Quantum Gravity Phenomenology, Lorentz Invariance and Discreteness

abstract:
  Contrary to what is often stated, a fundamental spacetime discreteness need
not contradict Lorentz invariance. A causal set's discreteness is in fact
locally Lorentz invariant, and we recall the reasons why. For illustration, we
introduce a phenomenological model of massive particles propagating in a
Minkowski spacetime which arises from an underlying causal set. The particles
undergo a Lorentz invariant diffusion in phase space, and we speculate on
whether this could have any bearing on the origin of high energy cosmic rays.


title: Black Hole fragmentation and holography

abstract:
  We discuss the entropy change due to fragmentation for black hole solutions
in various dimensions. We find three different types of behavior. The entropy
may decrease, increase or have a mixed behavior, characterized by the presence
of a threshold mass. For two-dimensional (2D) black holes we give a complete
characterization of the entropy behavior under fragmentation, in the form of
sufficient conditions imposed on the function J, which defines the 2D
gravitational model. We compare the behavior of the gravitational solutions
with that of free field theories in d dimensions. This excludes the possibility
of finding a gravity/field theory realization of the holographic principle for
a broad class of solutions, including asymptotically flat black holes. We find
that the most natural candidates for holographic duals of the black hole
solutions with mixed behavior are field theories with a mass gap. We also
discuss the possibility of formulating entropy bounds that make reference only
to the energy of a system.


title:
Non CMC Conformal Data Sets Which Do Not Produce Solutions of the
  Einstein Constraint Equations

abstract:
  The conformal formulation provides a method for constructing and
parametrizing solutions of the Einstein constraint equations by mapping freely
chosen sets of conformal data to solutions, provided a certain set of coupled,
elliptic determined PDEs (whose expression depends on the chosen conformal
data) admit a unique solution. For constant mean curvature (CMC) data, it is
known in almost all cases which sets of conformal data allow these PDEs to have
solutions, and which do not. For non CMC data, much less is known. Here we
exhibit the first class of non CMC data for which we can prove that no
solutions exist.


title:
Simultaneity, radar 4-coordinates and the 3+1 point of view about
  accelerated observers in special relativity

abstract:
  After a review of the 1+3 point of view on non-inertial observers and of the
problems of rotating reference frames, we underline that was is lacking in
their treatment is a good global notion of simultaneity due to the restricted
validity of the existing 4-coordinates associated to an accelerated observer
(like the Fermi normal ones). We show that the relativistic Hamiltonian 3+1
point of view, based on a 3+1 splitting of Minkowski space-time with a
foliation whose space-like leaves are both simultaneity and Cauchy surfaces,
allows to find a solution to such problems, if we take into account M$\o$ller's
definition of allowed 4-coordinate transformations extended to radar
4-coordinates. Rigidly rotating relativistic reference frames are shown not to
exist. We give explicit foliations, with simultaneity surfaces (also space-like
hyper-planes) non orthogonal to the non-inertial observer world-line, which
correspond to a good notion of simultaneity for suitable (mutually balancing)
translational and rotational accelerations. This allows to evaluate the
simultaneity-dependent one-way speed of light and to give the 3+1 description
of both the rotating disk and the Sagnac effect. It is also shown how a GPS
system of spacecrafts may establish a grid of admissible radar 4-coordinates
and how the ACES mission can employ a variant of this method adapted to Earth's
rotation in the evaluation of the one-way time transfer to detect the deviation
from Einstein convention on the synchronization of inertial clocks implied by
such a notion of simultaneity. We show that in parametrized Minkowski theories
all the admissible notions of simultaneity are gauge equivalent ({\it
conventionality of simultaneity}) and, as an example, we describe Maxwell
theory in non-inertial systems with any admissible notion of simultaneity.


title: Quantum Theory from Quantum Gravity

abstract:
  We provide a mechanism by which, from a background independent model with no
quantum mechanics, quantum theory arises in the same limit in which spatial
properties appear. Starting with an arbitrary abstract graph as the microscopic
model of spacetime, our ansatz is that the microscopic dynamics can be chosen
so that 1) the model has a low low energy limit which reproduces the
non-relativistic classical dynamics of a system of N particles in flat
spacetime, 2) there is a minimum length, and 3) some of the particles are in a
thermal bath or otherwise evolve stochastically. We then construct simple
functions of the degrees of freedom of the theory and show that their
probability distributions evolve according to the Schroedinger equation. The
non-local hidden variables required to satisfy the conditions of Bell's theorem
are the links in the fundamental graph that connect nodes adjacent in the graph
but distant in the approximate metric of the low energy limit. In the presence
of these links, distant stochastic fluctuations are transferred into universal
quantum fluctuations.


title: Constraints on alternative models to dark energy

abstract:
  The recent observations of type Ia supernovae strongly support that the
universe is accelerating now and decelerated in the recent past. This may be
the evidence of the breakdown of the standard Friemann equation. We consider a
general modified Friedmann equation. Three different models are analyzed in
detail. The current supernovae data and the Wilkinson microwave anisotropy
probe data are used to constrain these models. A detailed analysis of the
transition from the deceleration phase to the acceleration phase is also
performed.


title: Noise reduction in gravitational wave interferometers using feedback

abstract:
  We show that the quantum locking scheme recently proposed by Courty {\it et
al.} [Phys. Rev. Lett. {\bf 90}, 083601 (2003)] for the reduction of back
action noise is able to significantly improve the sensitivity of the next
generation of gravitational wave interferometers.


title:
Linear and nonlinear optics of surface plasmon toy-models of black holes
  and wormholes

abstract:
  Experimental and theoretical studies of linear and nonlinear optics of
surface plasmon toy wormholes and black holes have been performed. These models
are based on dielectric microdroplets on the metal surfaces and on nanoholes
drilled in thin metal films. Toy surface plasmon black holes and wormholes are
shown to exhibit strongly enhanced nonlinear optical behavior in the frequency
range near the surface plasmon resonance of a metal-liquid interface. Various
possibilities to emulate such nontrivial gravitation theory effects as Hawking
radiation and Cauchy horizons are discussed.


title:
On Problem of Mass Origin and Self-Energy Divergence in Relativistic
  Mechanics and Gravitational Physics

abstract:
  The classical problem of self-energy divergence was studied in the framework
of Lagrangian formulation of Relativistic Mechanics. The conclusion was made
that a revision of mass-energy concept is needed for the development of
singularity-free gravitational and electromagnetic field theory. Perspectives
of the development of unified field theory are discussed.


title:
Quasi normal modes in Schwarzschild-DeSitter spacetime: A simple
  derivation of the level spacing of the frequencies

abstract:
  It is known that the imaginary parts of the quasi normal mode (QNM)
frequencies for the Schwarzschild black hole are evenly spaced with a spacing
that depends only on the surface gravity. On the other hand, for massless
minimally coupled scalar fields, there exist no QNMs in the pure DeSitter
spacetime. It is not clear what the structure of the QNMs would be for the
Schwarzschild-DeSitter (SDS) spacetime, which is characterized by two different
surface gravities. We provide a simple derivation of the imaginary parts of the
QNM frequencies for the SDS spacetime by calculating the scattering amplitude
in the first Born approximation and determining its poles. We find that, for
the usual set of boundary conditions in which the incident wave is scattered
off the black hole horizon, the imaginary parts of the QNM frequencies have a
equally spaced structure with the level spacing depending on the surface
gravity of the black hole. Several conceptual issues related to the QNM are
discussed in the light of this result and comparison with previous work is
presented.


title: Propagation in a thermal graviton background

abstract:
  It is well known that radiative corrections evaluated in nontrivial
backgrounds lead to effective dispersion relations which are not Lorentz
invariant. Since gravitational interactions increase with energy,
gravity-induced radiative corrections could be relevant for the trans-Planckian
problem. As a first step to explore this possibility, we compute the one-loop
radiative corrections to the self-energy of a scalar particle propagating in a
thermal bath of gravitons in Minkowski spacetime. We obtain terms which
originate from the thermal bath and which indeed break the Lorentz invariance
that possessed the propagator in the vacuum. Rather unexpectedly, however, the
terms which break Lorentz invariance vanish in the high three-momentum limit.
We also found that the imaginary part, which gives the rate of approach to
thermal equilibrium, vanishes at one loop.


title: Spin Foam Models of Quantum Spacetime

abstract:
  Spin foam models are a new approach to a formulation of quantum gravity which
is fully background independent, non-perturbative, and covariant, in the spirit
of path integral formulations of quantum field theory. In this thesis we
describe in details the general ideas and formalism of spin foam models, and
review many of the results obtained recently in this approach. We concentrate,
for the case of 3-dimensional quantum gravity, on the Turaev-Viro model, and,
in the 4-dimensional case, which is our main concern, on the Barrett-Crane
model. In particular, for the Barrett-Crane model: we describe the general
ideas behind its construction, and review what has been achieved up to date,
discuss in details its links with the classical formulations of gravity as
constrained topological field theory; we show a derivation of the model from a
lattice gauge theory perspective, in the general case of manifold with
boundaries, presenting also a few possible variations of the procedure used,
discussing the problems they present; we analyse in details the classical and
quantum geometry; we also describe how, from the same perspective, a spin foam
model that couples quantum gravity to any gauge theory may be constructed;
finally, we describe a general scheme for causal spin foam models, how the
Barrett-Crane model can be modified to implement causality and to fit in such a
scheme, and the resulting link with the quantum causal set approach to quantum
gravity.


title: Statefinder parameters for interacting dark energy

abstract:
  We argue that the recently introduced "statefinder parameters" (Sahni et al.,
JETP Lett. 77, 201 (2003)), that include the third derivative of the cosmic
scale factor, are useful tools to characterize interacting quitessence models.
We specify the statefinder parameters for two classes of models that solve, or
at least alleviate, the coincidence problem.


title:
A Note on Segre Types of Second Order Symmetric Tensors in 5-D
  Brane-world Cosmology

abstract:
  Recent developments in string theory suggest that there might exist extra
spatial dimensions, which are not small nor compact. The framework of most
brane cosmological models is that in which the matter fields are confined on a
brane-world embedded in five dimensions (the bulk). Motivated by this we
reexamine the classification of the second order symmetric tensors in 5--D, and
prove two theorems which collect together some basic results on the algebraic
structure of these tensors in 5-dimensional space-times. We also briefly
indicate how one can obtain, by induction, the classification of symmetric
two-tensors (and the corresponding canonical forms) on n-dimensional spaces
from the classification on 4-dimensional spaces. This is important in the
context of 11--D supergravity and 10--D superstrings.


title: Forward Modeling of Space-borne Gravitational Wave Detectors

abstract:
  Planning is underway for several space-borne gravitational wave observatories
to be built in the next ten to twenty years. Realistic and efficient forward
modeling will play a key role in the design and operation of these
observatories. Space-borne interferometric gravitational wave detectors operate
very differently from their ground based counterparts. Complex orbital motion,
virtual interferometry, and finite size effects complicate the description of
space-based systems, while nonlinear control systems complicate the description
of ground based systems. Here we explore the forward modeling of space-based
gravitational wave detectors and introduce an adiabatic approximation to the
detector response that significantly extends the range of the standard low
frequency approximation. The adiabatic approximation will aid in the
development of data analysis techniques, and improve the modeling of
astrophysical parameter extraction.


title: Gravitational Waves and the Sagnac Effect

abstract:
  We consider light waves propagating clockwise and other light waves
propagating counterclockwise around a closed path in a plane (theoretically
with the help of stationary mirrors). The time difference between the two light
propagating path orientations constitutes the Sagnac effect. The general
relativistic expression for the Sagnac effect is discussed. It is shown that a
gravitational wave incident to the light beams at an arbitrary angle will not
induce a Sagnac effect so long as the wave length of the weak gravitational
wave is long on the length scale of the closed light beam paths. The
gravitational wave induced Sagnac effect is thereby null.


title: Holography: 2-D or not 2-D?

abstract:
  As was recently pointed out by Cadoni, a certain class of two-dimensional
gravitational theories will exhibit (black hole) thermodynamic behavior that is
reminiscent of a free field theory. In the current letter, a direct
correspondence is established between these two-dimensional models and the
strongly curved regime of (arbitrary-dimensional) anti-de Sitter gravity. On
this basis, we go on to speculatively argue that two-dimensional gravity may
ultimatley be utilized for identifying and perhaps even understanding
holographic dualities.


title:
The Coupling of a Linearized Gravitational Wave to Electromagnetic
  Fields and Relevant Noise Issues

abstract:
  According to electrodynamical equations in curved spacetime we consider the
coupling of a linearized weak gravitational wave (GW) to a Gaussian beam
passing through a static magnetic field. It is found that unlike the properties
of the "left-circular" and "right-circular" waves of the tangential
perturbative photon fluxes in the cylindrical polar coordinates, the resultant
effect of the tangential and radial perturbations can produce the unique
nonvanishing photon flux propagating along the direction of the electric field
of the Gaussian beam. This result might provide a larger detecting space for
the high-frequency GWs in GHz band. Moreover, we also discuss the relevant
noise issues.


title: Time Uncertainty in Quantum Gravitational Systems

abstract:
  It is generally argued that the combined effect of Heisenberg principle and
general relativity leads to a minimum time uncertainty. Most of the analyses
supporting this conclusion are based on a perturbative approach to
quantization. We consider a simple family of gravitational models, including
the Einstein-Rosen waves, in which the (non-linearized) inclusion of gravity
changes the normalization of time translations by a monotonic energy-dependent
factor. In these circumstances, it is shown that a maximum time resolution
emerges non-perturbatively only if the total energy is bounded. Perturbatively,
however, there always exists a minimum uncertainty in the physical time.


title: Rotating Black String and Effective Teukolsky Equation in Braneworld

abstract:
  In the Randall-Sundrum two-brane model (RS1), a Kerr black hole on the brane
can be naturally identified with a section of rotating black string. To
estimate Kaluza-Klein (KK) corrections on gravitational waves emitted by
perturbed rotating black strings, we give the effective Teukolsky equation on
the brane which is separable equation and hence numerically manageable. In this
process, we derive the master equation for the electric part of the Weyl tensor
$E_{\mu\nu}$ which would be also useful to discuss the transition from black
strings to localized black holes triggered by Gregory-Laflamme instability.


title: Melvin solution with a dilaton potential

abstract:
  We find new Melvin-like solutions in Einstein-Maxwell-dilaton gravity with a
Liouville-type dilaton potential. The properties of the corresponding solution
in Freedman-Schwarz gauged supergravity model are extensively studied. We show
that this configuration is regular and geodesically complete but do not
preserve any supersymmetry. An exact solution describing travelling waves in
this Melvin-type background is also presented.


title:
Constraints Algebra and Equations of Motion in Bohmian Interpretation of
  Quantum Gravity

abstract:
  It is shown that introducing the quantum effects using deBroglie--Bohm theory
in the canonical formulation of gravity would change the constraints algebra.
The new algebra is derived and shown that it is the clear projection of general
coordinate transformations to the spatial and temporal diffeomorphisms. The
quantum Einstein's equations are derived and it is shown that they are
manifestly covariant under the above diffeomorphisms, as it would be.


title: Perfect Fluid Spacetimes With Two Symmetries

abstract:
  A method of solving perfect fluid Einstein equations with two commuting
spacelike Killing vectors is presented. Given a spacelike 2-dimensional surface
in the 3-dimensional nonphysical Minkowski space the field equations reduce to
a single nonlinear differential equation. An example is discussed.


title: Exact General Relativistic Thick Disks

abstract:
  A method to construct exact general relativistic thick disks that is a simple
generalization of the ``displace, cut and reflect'' method commonly used in
Newtonian, as well as, in Einstein theory of gravitation is presented. This
generalization consists in the addition of a new step in the above mentioned
method. The new method can be pictured as a ``displace, cut, {\it fill} and
reflect'' method. In the Newtonian case, the method is illustrated in some
detail with the Kuzmin-Toomre disk. We obtain a thick disk with acceptable
physical properties. In the relativistic case two solutions of the Weyl
equations, the Weyl gamma metric (also known as Zipoy-Voorhees metric) and the
Chazy-Curzon metric are used to construct thick disks. Also the Schwarzschild
metric in isotropic coordinates is employed to construct another family of
thick disks. In all the considered cases we have non trivial ranges of the
involved parameter that yield thick disks in which all the energy conditions
are satisfied.


title: From 2-Dimensional Surfaces to Cosmological Solutions

abstract:
  We construct perfect fluid metrics corresponding to spacelike surfaces
invariant under a 1-dimensional group of isometries in 3-dimensional Minkowski
space. Under additional assumptions we obtain new cosmological solutions of
Bianchi type II, VI_0 and VII_0. The solutions depend on an arbitrary function
of time, which can be specified in order to satisfy an equation of state.


title: Autoparallel orbits in Kerr Brans-Dicke spacetimes

abstract:
  The bounded orbital motion of a massive spinless test particle in the
background of a Kerr Brans-Dicke geometry is analysed in terms of worldlines
that are auto-parallels of different metric compatible spacetime connections.
In one case the connection is that of Levi-Civita with zero-torsion. In the
second case the connection has torsion determined by the gradient of the
Brans-Dicke background scalar field. The calculations permit in principle to
discriminate between these possibilities.


title:
Local Existence and Continuation Criterion for Solutions of the
  Spherically Symmetric Einstein-Vlasov-Maxwell System

abstract:
  Using the iterative Scheme we prove the local existence and uniqueness of
solutions of the spherically symmetric Einstein-Vlasov-Maxwell system with
small initial data. We prove a continuation criterion to global in-time
solutions.


title:
Quantum Gravity in Everyday Life: General Relativity as an Effective
  Field Theory

abstract:
  This article is meant as a summary and introduction to the ideas of effective
field theory as applied to gravitational systems.
  Contents:
  1. Introduction
  2. Effective Field Theories
  3. Low-Energy Quantum Gravity
  4. Explicit Quantum Calculations
  5. Conclusions


title: Dark Energy

abstract:
  After some remarks about the history and the mystery of the vacuum energy I
shall review the current evidence for a cosmologically significant nearly
homogeneous exotic energy density with negative pressure (`Dark Energy').
Special emphasis will be put on the recent polarization measurements by WMAP
and their implications. I shall conclude by addressing the question: Do the
current observations really imply the existence of a dominant dark energy
component?


title: 5D gravity and the discrepant G measurements

abstract:
  It is shown that 5D Kaluza-Klein theory stabilized by an external bulk scalar
field may solve the discrepant laboratory G measurements. This is achieved by
an effective coupling between gravitation and the geomagnetic field.
Experimental considerations are also addressed.


title: Magnetic tension and gravitational collapse

abstract:
  The gravitational collapse of a magnetised medium is investigated by studying
qualitatively the convergence of a timelike family of non-geodesic worldlines
in the presence of a magnetic field. Focusing on the field's tension we
illustrate how the winding of the magnetic forcelines due to the fluid's
rotation assists the collapse, while shear-like distortions in the distribution
of the field's gradients resist contraction. We also show that the relativistic
coupling between magnetism and geometry, together with the tension properties
of the field, lead to a magneto-curvature stress that opposes the collapse.
This tension stress grows stronger with increasing curvature distortion, which
means that it could potentially dominate over the gravitational pull of the
matter. If this happens, a converging family of non-geodesic lines can be
prevented from focusing without violating the standard energy conditions.


title: A note on quasinormal modes: A tale of two treatments

abstract:
  There is an apparent discrepancy in the literature with regard to the
quasinormal mode frequencies of Schwarzschild-de Sitter black holes in the
degenerate-horizon limit. On the one hand, a Poschl-Teller-inspired method
predicts that the real part of the frequencies will depend strongly on the
orbital angular momentum of the perturbation field whereas, on the other hand,
the degenerate limit of a monodromy-based calculation suggests there should be
no such dependence (at least, for the highly damped modes). In the current
paper, we provide a possible resolution by critically re-assessing the limiting
procedure used in the monodromy analysis.


title: Preparing the State of a Black Hole

abstract:
  Measurements of the mass or angular momentum of a black hole are onerous,
particularly if they have to be frequently repeated, as when one is required to
transform a black hole to prescribed parameters. Irradiating a black hole of
the Kerr-Newman family with scalar or electromagnetic waves provides a way to
drive it to prescribed values of its mass, charge and angular momentum without
the need to repeatedly measure mass or angular momentum throughout the process.
I describe the mechanism, which is based on Zel'dovich-Misner superradiance and
its analog for charged black holes. It represents a possible step in the
development of preparation procedures for quantum black holes.


title:
Ultrarelativistic black hole in an external electromagnetic field and
  gravitational waves in the Melvin universe

abstract:
  We investigate the ultrarelativistic boost of a Schwarzschild black hole
immersed in an external electromagnetic field, described by an exact solution
of the Einstein-Maxwell equations found by Ernst (the ``Schwarzschild-Melvin''
metric). Following the classical method of Aichelburg and Sexl, the
gravitational field generated by a black hole moving ``with the speed of
light'' and the transformed electromagnetic field are determined. The
corresponding exact solution describes an impulsive gravitational wave
propagating in the static, cylindrically symmetric, electrovac universe of
Melvin, and for a vanishing electromagnetic field it reduces to the well known
Aichelburg-Sexl pp-wave. In the boosting process, the original Petrov type I of
the Schwarzschild-Melvin solution simplifies to the type II on the impulse, and
to the type D elsewhere. The geometry of the wave front is studied, in
particular its non-constant Gauss curvature. In addition, a more general class
of impulsive waves in the Melvin universe is constructed by means of a
six-dimensional embedding formalism adapted to the background. A coordinate
system is also presented in which all the impulsive metrics take a continuous
form. Finally, it is shown that these solutions are a limiting case of a family
of exact gravitational waves with an arbitrary profile. This family is
identified with a solution previously found by Garfinkle and Melvin. We thus
complement their analysis, in particular demonstrating that such spacetimes are
of type II and belong to the Kundt class.


title: Aligned electric and magnetic Weyl fields

abstract:
  We analyze the spacetimes admitting a direction for which the relative
electric and magnetic Weyl fields are aligned. We give an invariant
characterization of these metrics and study the properties of its Debever null
vectors. The directions 'observing' aligned electric and magnetic Weyl fields
are obtained for every Petrov type. The results on the no existence of purely
magnetic solutions are extended to the wider class having homothetic electric
and magnetic Weyl fields.


title:
Relating Spin Foams and Canonical Quantum Gravity: A Discrete Step
  Evolution Formulation of Spin Foams

abstract: This article has been replaced by gr-qc/0412011


title: Two-dimensional metric-affine gravity

abstract:
  There is a number of completely integrable gravity theories in two
dimensions. We study the metric-affine approach on a 2-dimensional spacetime
and display a new integrable model. Its properties are described and compared
with the known results of Poincare gauge gravity.


title: Histories Electromagnetism

abstract:
  Working within the HPO (History Projection Operator) Consistent Histories
formalism, we follow the work of Savvidou on (scalar) field theory and that of
Savvidou and Anastopolous on (first-class) constrained systems to write a
histories theory (both classical and quantum) of Electromagnetism. We focus
particularly on the foliation-dependence of the histories phase space/Hilbert
space and the action thereon of the two Poincare groups that arise in histories
field theory. We quantise in the spirit of the Dirac scheme for constrained
systems.


title: Numerical Modeling of Charged Black Holes with Massive Dilaton

abstract:
  In this paper the static, spherically symmetric and electrically charged
black hole solutions in Einstein-Born-Infeld gravity with massive dilaton are
investigated numerically.
  The Continuous Analog of Newton Method (CANM) is used to solve the
corresponding nonlinear multipoint boundary value problems (BVPs). The
linearized BVPs are solved numerically by means of collocation scheme of fourth
order.
  A special class of solutions are the extremal ones. We show that the extremal
horizons within the framework of the model satisfy some nonlinear system of
algebraic equations. Depending on the charge $q$ and dilaton mass $\gamma$, the
black holes can have no more than three horizons. This allows us to construct
some Hermite polynomial of third order. Its real roots describe the number, the
type and other characteristics of the horizons.


title:
Rigorous construction of a Spin Foam Model for Lorentzian BF theory and
  Gravity: The foundations

abstract:
  Spin foam models for gravity or BF theory can be constructed by path integral
formulation of the classical discrete models formulated on simplicial
manifolds. Using this, we discuss the rigorous construction of Lorentzian spin
foam models for gravity and BF theory based on the Gelfand-Naimark theory of
the representations of SL(2,C). First we construct the simplex amplitude for
the BF SL(2,C) model. Next we discuss the implementation of the Barrett-Crane
constraints on this model to derive the spin foam model for gravity. The
non-trivial constraints are the cross simplicity constraints which state that
the sum of the bivectors associated to any two triangles of a quantum
tetrahedron is simple. We do not complete the construction of the model, but
ultimately we derive an equation corresponding to the cross simplicity
constraints that the Lorentzian spin foam model of gravity has to satisfy. In
the appendix we give a simple derivation of the Clebsch-Gordan coefficients for
SL(2,C).


title:
3D simulations of Einstein's equations: symmetric hyperbolicity, live
  gauges and dynamic control of the constraints

abstract:
  We present three-dimensional simulations of Einstein equations implementing a
symmetric hyperbolic system of equations with dynamical lapse. The numerical
implementation makes use of techniques that guarantee linear numerical
stability for the associated initial-boundary value problem. The code is first
tested with a gauge wave solution, where rather larger amplitudes and for
significantly longer times are obtained with respect to other state of the art
implementations. Additionally, by minimizing a suitably defined energy for the
constraints in terms of free constraint-functions in the formulation one can
dynamically single out preferred values of these functions for the problem at
hand. We apply the technique to fully three-dimensional simulations of a
stationary black hole spacetime with excision of the singularity, considerably
extending the lifetime of the simulations.


title: Gravitational Lensing In Case of Massive Particles

abstract:
  Gravitation lensing calculations, which are generally done for light ray, are
extended to that for a massive particle. Many interesting results were
observed. We discuss the scattering cross section along-with many consequential
quantities here. In particular, the case of Schrwarzschild metric was taken as
illustration, though the analysis applies to a wide range of cases, such as
extended black holes.


title:
A new approach to spherically symmetric junction surfaces and the
  matching of FLRW regions

abstract:
  We investigate timelike junctions (with surface layer) between spherically
symmetric solutions of the Einstein-field equation. In contrast to previous
investigations this is done in a coordinate system in which the junction
surface motion is absorbed in the metric, while all coordinates are continuous
at the junction surface.
  The evolution equations for all relevant quantities are derived. We discuss
the no-surface layer case (boundary surface) and study the behaviour for small
surface energies. It is shown that one should expect cases in which the speed
of light is reached within a finite proper time.
  We carefully discuss necessary and sufficient conditions for a possible
matching of spherically symmetric sections.
  For timelike junctions between spherically symmetric space-time sections we
show explicitly that the time component of the Lanczos equation always reduces
to an identity (independently of the surface equation of state).
  The results are applied to the matching of FLRW models. We discuss `vacuum
bubbles' and closed-open junctions in detail. As illustrations several
numerical integration results are presented, some of them indicate that the
junction surface can reach the speed of light within a finite time.


title:
A Graph method for mapping changes in temporal and spatial phenomena
  with relativistic consequences

abstract:
  A cellular automata approach using a Directed Cyclic Graph is used to model
interrelationships of fluctuating time, state and space. This model predicts
phenomena including a constant and maximum speed at which any moving entity can
travel, time dilation effects in accordance with special relativity,
calculation for the Doppler effect, propagation in three spatial dimensions, an
explanation for the non-local feature of collapse and a speculation on the
origin of gravitation. The approach has proven amenable to computer modelling.


title:
A Graph Model for the quantum mechanics of a moving cyclic disturbance
  interacting at a spatial position

abstract:
  An analysis is made of a moving disturbance using a directed cyclic graph.
  A statistical approach is used to calculate the alternative positions in
space and state of the disturbance with a defined observed time. The
probability for a freely moving entity interacting in a particular spatial
position is calculated and a formulation is derived for the minimum locus of
uncertainty in position and momentum. This is found to accord with calculations
for quantum mechanics. The model has proven amenable to computer modelling; a
copy of the "SimulTime" program is available on request.


title: Is Cosmic Coincidence a Consequence of a Law of Nature?

abstract:
  A field theory is proposed where the regular fermionic matter and the dark
fermionic matter are different states of the same "primordial" fermion fields.
In regime of the fermion densities typical for normal particle physics, the
primordial fermions split into three families identified with regular fermions.
When fermion energy density becomes comparable with dark energy density, the
theory allows new type of states. The possibility of such Cosmo-Low Energy
Physics (CLEP) states is demonstrated by means of solutions of the field theory
equations describing FRW universe filled by homogeneous scalar field and
uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state are
drawn into cosmological expansion by means of dynamically changing their own
parameters. One of the features of the fermions in CLEP state is that in the
late time universe their masses increase as a^{3/2}. The energy density of the
cold dark matter consisting of neutrinos in CLEP state scales as a sort of dark
energy; this cold dark matter possesses negative pressure and for the late time
universe its equation of state approaches that of the cosmological constant.
The total energy density of such universe is less than it would be in the
universe free of fermionic matter at all. The (quintessence) scalar field is
coupled to dark matter but its coupling to regular fermionic matter appears to
be extremely strongly suppressed. The key role in obtaining these results
belongs to a fundamental constraint (which is consequence of the action
principle) that plays the role of a new law of nature.


title: Operational indistinguishably of varying speed of light theories

abstract:
  The varying speed of light theories have been recently proposed to solve the
standard model problems and anomalies in the ultra high energy cosmic rays.
These theories try to formulate a new relativity with no assumptions about the
constancy of the light speed. In this regard, we study two theories and want to
show that these theories are not the new theories of relativity, but only
re-descriptions of Einstein's special relativity.


title: Selected Topics in Teleparallel Gravity

abstract:
  Teleparallel gravity can be seen as a gauge theory for the translation group.
As such, its fundamental field is neither the tetrad nor the metric, but a
gauge potential assuming values in the Lie algebra of the translation group.
This gauge character makes of teleparallel gravity, despite its equivalence to
general relativity, a rather peculiar theory. A first important point is that
it does not rely on the universality of free fall, and consequently does not
require the equivalence principle to describe the gravitational interaction.
Another peculiarity is its similarity with Maxwell's theory, which allows an
Abelian nonintegrable phase factor approach, and consequently a global
formulation for gravitation. Application of these concepts to the motion of
spinless particles, as well as to the COW and gravitational Aharonov-Bohm
effects are presented and discussed.


title: Phantom Field and the Fate of Universe

abstract:
  In this paper we analyze the cosmological dynamics of phantom field in a
variety of potentials unbounded from above. We demonstrate that the nature of
future evolution generically depends upon the steepness of the phantom
potential and discuss the fate of Universe accordingly.


title: Low multipole contributions to the gravitational self-force

abstract:
  We calculate the unregularized monopole and dipole contributions to the
self-force acting on a particle of small mass in a circular orbit around a
Schwarzschild black hole. From a self-force point of view, these non-radiating
modes are as important as the radiating modes with l greater than 2. In fact,
we demonstrate how the dipole self-force contributes to the dynamics even at
the Newtonian level. The self-acceleration of a particle is an inherently
gauge-dependent concept, but the Lorenz gauge is often preferred because of its
hyperbolic wave operator. Our results are in the Lorenz gauge and are also
obtained in closed form, except for the even-parity dipole case where we
formulate and implement a numerical approach.


title: Sagnac interferometry and non-Newtonian gravity

abstract:
  Sagnac interferometry has been employed in the context of gravity as a
proposal for the detection of the so called gravitomagnetic effect. In the
present work we explore the possibilities that this experimental device could
open up in the realm of non--Newtonian gravity. It will be shown that this
experimental approach allows us to explore an interval of values of the range
of the new force that up to now remains unexplored, namely, $\lambda\geq
10^{14}$ m.


title: Stability of Generalised Static Black Holes in Higher Dimensions

abstract:
  We discuss the stability of (charged) static black holes in
higher-dimensional spacetimes with and without cosmological constant by using
gauge-invariant master equations of the Schroedinger equation type for black
hole perturbations derived by the authors recently. In particular, we show that
the stability of higher-dimensional Schwarzschild black holes can be proved
with the help of a technique called S-deformation of the master equations. We
also point out that higher-dimensional static black holes might be unstable
only against scalar-type perturbations in the neutral case and in the charged
case with spherically symmetric or flat horizons.


title:
Harmonic-gauge dipole metric perturbations for weak-field circular
  orbits in Schwarzschild spacetime

abstract:
  We calculate the harmonic-gauge even l=1 mode of the linear metric
perturbation (MP) produced by a particle in a weak-field circular orbit around
a Schwarzschild black hole (BH). We focus on the Newtonian limit, i.e. the
limit in which the mass M of the central BH approaches zero (while fixing the
orbital radius and the small-object mass), and obtain explicit expressions for
the MP in this limit. We find that the MP are anomalous in this limit, namely,
they do not approach their standard, Coulomb-like, flat-space values. Instead,
the MP grows on approaching the BH, and this growth becomes worse as M
decreases. This anomalous behavior leads to some pathologies which we briefly
discuss. We also derive here the next-order correction (in the orbital
frequency $\Omega $) to the MP.


title: Group averaging in the (p,q) oscillator representation of SL(2,R)

abstract:
  We investigate refined algebraic quantisation with group averaging in a
finite-dimensional constrained Hamiltonian system that provides a simplified
model of general relativity. The classical theory has gauge group SL(2,R) and a
distinguished o(p,q) observable algebra. The gauge group of the quantum theory
is the double cover of SL(2,R), and its representation on the auxiliary Hilbert
space is isomorphic to the (p,q) oscillator representation. When p>1, q>1 and
p+q == 0 (mod 2), we obtain a physical Hilbert space with a nontrivial
representation of the o(p,q) quantum observable algebra. For p=q=1, the system
provides the first example known to us where group averaging converges to an
indefinite sesquilinear form.


title:
Gravitational collapse from smooth initial data with vanishing radial
  pressure

abstract:
  We study here the spherical gravitational collapse assuming initial data to
be necessarily smooth, as motivated by the requirements based on physical
reasonableness. A tangential pressure model is constructed and analyzed in
order to understand the final fate of collapse explicitly in terms of the
density and pressure parameters at the initial epoch from which the
collapsedevelops. It is seen that both black holes and naked singularities are
produced as collapse end states even when the initial data is smooth. We show
that the outcome is decided entirely in terms of the initial data, as given by
density, pressure and velocity profiles at the initial epoch, from which the
collapse evolves.


title:
Sensitivity limitations in optical speed meter topology of
  gravitational-wave antennae

abstract:
  The possible design of QND gravitational-wave detector based on speed meter
principle is considered with respect to optical losses. The detailed analysis
of speed meter interferometer is performed and the ultimate sensitivity that
can be achieved is calculated. It is shown that unlike the position meter
signal-recycling can hardly be implemented in speed meter topology to replace
the arm cavities as it is done in signal-recycled detectors, such as GEO 600.
It is also shown that speed meter can beat the Standard Quantum Limit (SQL) by
the factor of $\sim 3$ in relatively wide frequency band, and by the factor of
$\sim 10$ in narrow band. For wide band detection speed meter requires quite
reasonable amount of circulating power $\sim 1$ MW. The advantage of the
considered scheme is that it can be implemented with minimal changes in the
current optical layout of LIGO interferometer.


title: Time-Varying Cosmological Term: Emergence and Fate of a FRW Universe

abstract:
  A time-varying cosmological "constant" Lambda is consistent with Einstein's
equation, provided matter and/or radiation is created or destroyed to
compensate for it. Supposing an empty primordial universe endowed with a very
large cosmological term, matter will emerge gradually as Lambda decays.
Provided only radiation or ultrarelativistic matter is initially created, the
universe starts in a nearly de Sitter phase, which evolves towards a FRW regime
as expansion proceeds. If, at some cosmological time, the cosmological term
begins increasing again, as presently observed, expansion will accelerate and
matter and/or radiation will be transformed back into dark energy. It is shown
that such accelerated expansion is a route towards a new kind of gravitational
singular state, characterized by an empty, conformally transitive spacetime in
which all energy is dark.


title: Quantum Creation of a Universe with Quasi-Hyperbolic Spatial Sections

abstract:
  We calculate the probability of creation of a universe with space topology
$S^{1}\times T_{g}$, where $S^{1}$ is the circle and $T_{g}$ is a compact
hyperbolic surface of genus $g\geq 2$. We use the method of path integrals as
applied to quantum cosmology.


title: Interior perfect fluid scalar-tensor solution

abstract:
  We present a new exact perfect fluid interior solution for a particular
scalar-tensor theory. The solution is regular everywhere and has a well defined
boundary where the fluid pressure vanishes. The metric and the dilaton field
match continuously the external solution.


title:
Asymptotics of solutions of the Einstein equations with positive
  cosmological constant

abstract:
  A positive cosmological constant simplifies the asymptotics of forever
expanding cosmological solutions of the Einstein equations. In this paper a
general mathematical analysis on the level of formal power series is carried
out for vacuum spacetimes of any dimension and perfect fluid spacetimes with
linear equation of state in spacetime dimension four. For equations of state
stiffer than radiation evidence for development of large gradients, analogous
to spikes in Gowdy spacetimes, is found. It is shown that any vacuum solution
satisfying minimal asymptotic conditions has a full asymptotic expansion given
by the formal series. In four spacetime dimensions, and for spatially
homogeneous spacetimes of any dimension, these minimal conditions can be
derived for appropriate initial data. Using Fuchsian methods the existence of
vacuum spacetimes with the given formal asymptotics depending on the maximal
number of free functions is shown without symmetry assumptions.


title: The Petrov type of the five-dimensional Myers-Perry metric

abstract:
  We point out that the Myers-Perry metric in five dimensions is algebraically
special. It has Petrov type \underline{22}, which is the Petrov type of the
five-dimensional Schwarzschild metric.


title: Harmonic maps and isometric embeddings of the spacetime

abstract:
  We investigate harmonic maps in the context of isometric embeddings when the
target space is Ricci-flat and has codimension one. With the help of the
Campbell-Magaard theorem we show that any $n$-dimensional ($n\geqslant 3$)
Lorentzian manifold can be isometrically and harmonically embedded in a
(n+1)-dimensional semi-Riemannian Ricci-flat space. We then extend our analysis
to the case when the target space is an Einstein space. Finally, as an example,
we work out the harmonic and isometric embedding of a
Friedmann-Robertson-Walker spacetime in a five-dimensional Ricci-flat space and
proceed to obtain a general scheme to minimally embed any vacuum solution of
general relativity in Ricci-flat spaces with codimension one.


title: On the Microcanonical Entropy of a Black Hole

abstract:
  It has been suggested recently that the microcanonical entropy of a system
may be accurately reproduced by including a logarithmic correction to the
canonical entropy. In this paper we test this claim both analytically and
numerically by considering three simple thermodynamic models whose energy
spectrum may be defined in terms of one quantum number only, as in a
non-rotating black hole. The first two pertain to collections of noninteracting
bosons, with logarithmic and power-law spectra. The last is an area ensemble
for a black hole with equi-spaced area spectrum. In this case, the many-body
degeneracy factor can be obtained analytically in a closed form. We also show
that in this model, the leading term in the entropy is proportional to the
horizon area A, and the next term is ln A with a negative coefficient.


title: Local Scale Invariance and General Relativity

abstract:
  According to the theory of unimodular relativity developed by Anderson and
Finkelstein, the equations of general relativity with a cosmological constant
are composed of two independent equations, one which determines the null-cone
structure of space-time, another which determines the measure structure of
space-time. The field equations that follow from the restricted variational
principle of this version of general relativity only determine the null-cone
structure and are globally scale-invariant and scale-free. We show that the
electromagnetic field may be viewed as a compensating gauge field that
guarantees local scale invariance of these field equations. In this way, Weyl's
geometry is revived. However, the two principle objections to Weyl's theory do
not apply to the present formulation: the Lagrangian remains first order in the
curvature scalar and the non-integrability of length only applies to the
null-cone structure.


title: Physics of Relativistic Perfect Fluids

abstract:
  A criterion is presented and discussed to detect when a divergence-free
perfect fluid energy tensor in the space-time describes an evolution in local
thermal equilibrium.
  This criterion is applied to the class II Szafron-Szekeres perfect fluid
space-times solutions, giving a very simple characterization of those that
describe such thermal evolutions. For all of them, the significant
thermodynamic variables are explicitly obtained.
  Also, the specific condition is given under which the divergence-free perfect
fluid energy tensors may be interpreted as an ideal gas.


title: Ideal Gas Stephani Universes

abstract:
  The Stephani Universes that can be interpreted as an ideal gas evolving in
local thermal equilibrium are determined, and the method to obtain the
associated thermodynamic schemes is given


title:
Eleven spherically symmetric constant density solutions with
  cosmological constant

abstract:
  Einstein's field equations with cosmological constant are analysed for a
static, spherically symmetric perfect fluid having constant density. Five new
global solutions are described.
  One of these solutions has the Nariai solution joined on as an exterior
field. Another solution describes a decreasing pressure model with exterior
Schwarzschild-de Sitter spacetime having decreasing group orbits at the
boundary. Two further types generalise the Einstein static universe.
  The other new solution is unphysical, it is an increasing pressure model with
a geometric singularity.


title:
Increase of the Number of Detectable Gravitational Waves Signals due to
  Gravitational Lensing

abstract:
  This article deals with the gravitational lensing (GL) of gravitational waves
(GW). We compute the increase in the number of detected GW events due to GL.
First, we check that geometrical optics is valid for the GW frequency range on
which Earth-based detectors are sensitive, and that this is also partially true
for what concerns the future space-based interferometer LISA. To infer this
result, both the diffraction parameter and a cut-off frequency are computed.
Then, the variation in the number of GW signals is estimated in the general
case, and applied to some lens models: point mass lens and singular isothermal
sphere (SIS profile). An estimation of the magnification factor has also been
done for the softened isothermal sphere and for the King profile. The results
appear to be strongly model-dependent, but in all cases the increase in the
number of detected GW signals is negligible. The use of time delays among
images is also investigated.


title: Quasinormal modes for Weyl neutrino field in R-N black holes

abstract:
  We employ WKB approximation up to the third order to determine the low-lying
quasinormal modes for Weyl neutrino field in R-N black holes, which are the
most relevant to the evolution of the field around a black hole in the
intermediate stage. It is showed that the quasinormal mode frequencies for Weyl
neutrino field in R-N black holes are different from those in Schwartzchild
black holes owning to the charge-induced additional gravitation, and the
variations of the quasinormal mode frequencies for Weyl neutrino field are
similar to those for integral spin fields in R-N black holes.


title:
Towards a Realistic Neutron Star Binary Inspiral: Initial Data and
  Multiple Orbit Evolution in Full General Relativity

abstract:
  This paper reports on our effort in modeling realistic astrophysical neutron
star binaries in general relativity. We analyze under what conditions the
conformally flat quasiequilibrium (CFQE) approach can generate
``astrophysically relevant'' initial data, by developing an analysis that
determines the violation of the CFQE approximation in the evolution of the
binary described by the full Einstein theory. We show that the CFQE assumptions
significantly violate the Einstein field equations for corotating neutron stars
at orbital separations nearly double that of the innermost stable circular
orbit (ISCO) separation, thus calling into question the astrophysical relevance
of the ISCO determined in the CFQE approach. With the need to start numerical
simulations at large orbital separation in mind, we push for stable and long
term integrations of the full Einstein equations for the binary neutron star
system. We demonstrate the stability of our numerical treatment and analyze the
stringent requirements on resolution and size of the computational domain for
an accurate simulation of the system.


title: Testing the LIGO Inspiral Analysis with Hardware Injections

abstract:
  Injection of simulated binary inspiral signals into detector hardware
provides an excellent test of the inspiral detection pipeline. By recovering
the physical parameters of an injected signal, we test our understanding of
both instrumental calibration and the data analysis pipeline. We describe an
inspiral search code and results from hardware injection tests and demonstrate
that injected signals can be recovered by the data analysis pipeline. The
parameters of the recovered signals match those of the injected signals.


title: Symmetries of distributional domain wall geometries

abstract:
  Generalizing the Lie derivative of smooth tensor fields to
distribution-valued tensors, we examine the Killing symmetries and the
collineations of the curvature tensors of some distributional domain wall
geometries. The chosen geometries are rigorously the distributional thin wall
limit of self gravitating scalar field configurations representing thick domain
walls and the permanence and/or the rising of symmetries in the limit process
is studied. We show that, for all the thin wall spacetimes considered, the
symmetries of the distributional curvature tensors turns out to be the Killing
symmetries of the pullback of the metric tensor to the surface where the
singular part of these tensors is supported. Remarkably enough, for the
non-reflection symmetric domain wall studied, these Killing symmetries are not
necessarily symmetries of the ambient spacetime on both sides of the wall.


title: Lattice Universes in 2+1-dimensional gravity

abstract:
  Lattice universes are spatially closed space-times of spherical topology in
the large, containing masses or black holes arranged in the symmetry of a
regular polygon or polytope. Exact solutions for such spacetimes are found in
2+1 dimensions for Einstein gravity with a non-positive cosmological constant.
By means of a mapping that preserves the essential nature of geodesics we
establish analogies between the flat and the negative curvature cases. This map
also allows treatment of point particles and black holes on a similar footing.


title: Noncommutative Space-Time in DSR theories

abstract:
  Space-time coordinates in DSR theories with two invariant scales based on a
dispersion relation with an energy independent speed of light are introduced by
the demand, that boost and rotation generators are invariant under a
transformation from SR to DSR variables. This turns out to be equivalent to a
recent suggestion postulating the existence of plane wave solutions in DSR
theories. The momentum space representation of coordinates is derived, yielding
a noncommutative space-time and the deformed algebra.


title:
The Mario Schenberg Gravitational Wave Detector: A mathematical model
  for its quadrupolar oscilations

abstract:
  In this work we present a mathematical model for the mechanical response of
the Brazilian Mario SCHENBERG gravitational wave (GW) detector to such waves.
We found the physical parameters that are involved in this response assuming a
linear elastic theory. Adopting this approach we determined the system's
resonance frequencies for the case when six $i$-mode mechanical resonators are
coupled to the antenna surface according to the arrangement suggested by
Johnson and Merkowitz: the truncated icosahedron configuration. This
configuration presents special symmetries that allow for the derivation of an
analytic expression for the mode channels, which can be experimentally
monitored and which are directly related to the tensorial components of the GW.
Using this model we simulated how the system behaves under a gravitational
sinewave quadrupolar force and found the relative amplitudes that result from
this excitation. The mechanical resonators made the signal $\approx 5340$ times
stronger. We found $i+1$ degenerate triplets plus $i$ non-degenerate system
mode resonances within a band around ${3.17-3.24\rm{kHz}}$ that are sensitive
to signals higher than ${\tilde h\sim 10^{-22}\rm{Hz}^{-1/2}}$ when we
considerate the effects of thermal noise only.


title:
Dynamical Determination of the Innermost Stable Circular Orbit of Binary
  Neutron Stars

abstract:
  We determine the innermost stable circular orbit (ISCO) of binary neutron
stars (BNSs) by performing dynamical simulations in full general relativity.
Evolving quasiequilibrium (QE) binaries that begin at different separations, we
bracket the location of the ISCO by distinguishing stable circular orbits from
unstable plunges. We study Gamma=2 polytropes of varying compactions in both
corotational and irrotational equal-mass binaries. For corotatonal binaries we
find an ISCO orbital angular frequency somewhat smaller than that determined by
applying turning-point methods to QE initial data. For the irrotational
binaries the initial data sequences terminate before reaching a turning point,
but we find that the ISCO frequency is reached prior to the termination point.
Our findings suggest that the ISCO frequency varies with compaction but does
not depend strongly on the stellar spin. Since the observed gravitational wave
signal undergoes a transition from a nearly periodic ``chirp'' to a burst at
roughly twice the ISCO frequency, the measurement of its value by laser
interferometers (e.g LIGO) will be important for determining some of the
physical properites of the underlying stars


title: Spacetime or Space and the Problem of Time

abstract:
  GR and other theories have been obtained from 3-space rather than spacetime
principles. I explore consequences of this as regards the Problem of Time.


title: Strings and Branes under Microscope

abstract:
  It is shown that in the standard vacuum 5D Kaluza-Klein gravity there is
wormhole-like solutions which look like strings attached to two D-branes. The
asymptotical behaviour of the corresponding metric is investigated.


title: High frequency sources of gravitational waves

abstract:
  Sources of high frequency gravitational waves are reviewed. Gravitational
collapse, rotational instabilities and oscillations of the remnant compact
objects are potentially important sources of gravitational waves. Significant
and unique information for the various stages of the collapse, the evolution of
protoneutron stars and the details of the equations of state of such objects
can be drawn from careful study of the gravitational wave signal.


title: A modified Ozer-Taha type cosmological model

abstract:
  A modified version of the Ozer and Taha nonsingular cosmological model is
presented on the assumption that the universe's radius is complex if it is
regarded as empty, but it contains matter when the radius is real. It also
predicts the values: Omega_M =rho_M /rho_C \approx 4/3, Omega_V = rho_V /rho_C
\approx 2/3, and Omega_ = rho_ /rho_C << 1 in the present nonrelativistic era,
where rho_M = matter density, rho_V = vacuum density, rho_= negative energy
density and rho_{C} = critical density.


title: On the viability of the Palatini form of 1/R gravity

abstract:
  Recently Flanagan [astro-ph/0308111] has argued that the Palatini form of 1/R
gravity is ruled out by experiments such as electron-electron scattering. His
argument involves adding minimally coupled fermions in the Jordan frame and
transforming to the Einstein frame. This produces additional terms that are
ruled out experimentally.
  Here I argue that this conclusion is false. It is well known that conformally
related theories are mathematically equivalent but not physically equivalent.
As discussed by Magnano and Sokolowski [2] one must decide, in the vacuum
theory, which frame is the physical frame and add the minimally coupled
Lagrangian in this frame. If this procedure is followed the resulting theory is
not ruled out experimentally. The discussions in this paper also show that the
equivalence between the generalized gravitational theories and scalar tensor
theories discussed by Flanagan [gr-qc/0309015] is only mathematical, not
physical.


title: Rapid LISA Astronomy

abstract:
  A simple method is presented for removing the amplitude, frequency and phase
modulations from the Laser Interferometer Space Antenna (LISA) data stream for
sources at any sky location. When combined with an excess power trigger or the
fast chirp transform, the total demodulation procedure allows the majority of
LISA sources to be identified without recourse to matched filtering.


title: (2+1) gravity for higher genus in the polygon model

abstract:
  We construct explicitly a (12g-12)-dimensional space P of unconstrained and
independent initial data for 't Hooft's polygon model of (2+1) gravity for
vacuum spacetimes with compact genus-g spacelike slices, for any g >= 2. Our
method relies on interpreting the boost parameters of the gluing data between
flat Minkowskian patches as the lengths of certain geodesic curves of an
associated smooth Riemann surface of the same genus. The appearance of an
initial big-bang or a final big-crunch singularity (but never both) is verified
for all configurations. Points in P correspond to spacetimes which admit a
one-polygon tessellation, and we conjecture that P is already the complete
physical phase space of the polygon model. Our results open the way for
numerical investigations of pure (2+1) gravity.


title: Space-Time Foam may Violate the Principle of Equivalence

abstract:
  The interactions of different particle species with the foamy space-time
fluctuations expected in quantum gravity theories may not be universal, in
which case different types of energetic particles may violate Lorentz
invariance by varying amounts, violating the equivalence principle. We
illustrate this possibility in two different models of space-time foam based on
D-particle fluctuations in either flat Minkowski space or a stack of
intersecting D-branes. Both models suggest that Lorentz invariance could be
violated for energetic particles that do not carry conserved charges, such as
photons, whereas charged particles such electrons would propagate in a
Lorentz-inavariant way. The D-brane model further suggests that gluon
propagation might violate Lorentz invariance, but not neutrinos. We argue that
these conclusions hold at both the tree (lowest-genus) and loop (higher-genus)
levels, and discuss their implications for the phenomenology of quantum
gravity.


title: Contrasting Quantum Cosmologies

abstract:
  We compare the recent loop quantum cosmology approach of Bojowald and
co-workers with earlier quantum cosmological schemes. Because the weak-energy
condition can now be violated at short distances, and not necessarily with a
high energy density, a number of possible instabilities are suggested: flat
space unstable to expansion or baby universe production. Or else a Machian type
principle is required to prevent such behaviour. Allowing a bounce to prevent
an approaching singularity seems incompatible with other standard notions
concerning the arrow of time and unitarity.
  Preventing rapid oscillations in the wavefunction appears in conflict with
more general scalar-tensor gravity.
  Other approaches such as ``creation from nothing'' or from some quiescent
state, static or time machine, are also assessed on grounds of naturalness and
fine tuning.


title: Remarks on harmonic maps, solitons, and dilaton gravity

abstract:
  Another connection of harmonic maps to gravity is presented. Using 1-soliton
and anti-soliton solutions of the sine-Gordon equation, we construct a pair of
harmonic maps that we express in terms of a particular dilaton field in
Jackiw-Teitelboim gravity. This field satisfies a linearized sine-Gordon
equation. We use it also to construct an explicit transformation that relates
the corresponding solitonic metric to a two dimensional black hole metric.


title: The Penrose Inequality

abstract:
  In 1973, R. Penrose presented an argument that the total mass of a space-time
which contains black holes with event horizons of total area $A$ should be at
least $\sqrt{A/16\pi}$. An important special case of this physical statement
translates into a very beautiful mathematical inequality in Riemannian geometry
known as the Riemannian Penrose inequality. This inequality was first
established by G. Huisken and T. Ilmanen in 1997 for a single black hole and
then by one of the authors (H.B.) in 1999 for any number of black holes. The
two approaches use two different geometric flow techniques and are described
here. We further present some background material concerning the problem at
hand, discuss some applications of Penrose-type inequalities, as well as the
open questions remaining.


title:
Covariant description of parametrized nonrelativistic Hamiltonian
  systems

abstract:
  The various phase spaces involved in the dynamics of parametrized
nonrelativistic Hamiltonian systems are displayed by using Crnkovic and
Witten's covariant canonical formalism. It is also pointed out that in Dirac's
canonical formalism there exists a freedom in the choice of the symplectic
structure on the extended phase space and in the choice of the equations that
define the constraint surface with the only restriction that these two choices
combine in such a way that any pair (of these two choices) generates the same
gauge transformation. The consequence of this freedom on the algebra of
observables is also discussed.


title: Spherical and planar three-dimensional anti-de Sitter black holes

abstract:
  The technique of dimensional reduction was used in a recent paper (Zanchin et
al, Phys. Rev. D66, 064022,(2002)) where a three-dimensional (3D)
Einstein-Maxwell-Dilaton theory was built from the usual four-dimensional (4D)
Einstein-Maxwell-Hilbert action for general relativity. Starting from a class
of 4D toroidal black holes in asymptotically anti-de Sitter (AdS) spacetimes
several 3D black holes were obtained and studied in such a context. In the
present work we choose a particular case of the 3D action which presents
Maxwell field, dilaton field and an extra scalar field, besides gravity field
and a negative cosmological constant, and obtain new 3D static black hole
solutions whose horizons may have spherical or planar topology. We show that
there is a 3D static spherically symmetric solution analogous to the 4D
Reissner-Nordstr\"om-AdS black hole, and obtain other new 3D black holes with
planar topology. From the static spherical solutions, new rotating 3D black
holes are also obtained and analyzed in some detail.


title:
Constraining a possible dependence of Newton's constant on the Earth's
  magnetic field

abstract:
  Some time ago Mbelek and Lachieze-Rey proposed that the discrepancy between
the results of the various measurements of Newton's constant could be explained
by introducing a gravielectric coupling between the Earth's gravitational and
magnetic fields mediated by two scalar fields. A critical assessment of this
model is performed. By calculating the static field configuration of the
relevant scalar around a nucleus in the linearised theory and then folding this
result with the mass density of the nucleus its effective gravitational mass is
determined. Considering test bodies of different materials one finds violations
of the weak equivalence principle for torsion-balance experiments which are
four orders of magnitude beyond the current experimental limit, thus rendering
the model non-viable. The method presented can be applied to generic theories
with gravielectric coupling and seems to rule out in general the explanation of
the discrepant measurements of Newton's constant by such couplings.


title: Nonlinear coupled Alfv\'{e}n and gravitational waves

abstract:
  In this paper we consider nonlinear interaction between gravitational and
electromagnetic waves in a strongly magnetized plasma. More specifically, we
investigate the propagation of gravitational waves with the direction of
propagation perpendicular to a background magnetic field, and the coupling to
compressional Alfv\'{e}n waves. The gravitational waves are considered in the
high frequency limit and the plasma is modelled by a multifluid description. We
make a self-consistent, weakly nonlinear analysis of the Einstein-Maxwell
system and derive a wave equation for the coupled gravitational and
electromagnetic wave modes. A WKB-approximation is then applied and as a result
we obtain the nonlinear Schr\"{o}dinger equation for the slowly varying wave
amplitudes. The analysis is extended to 3D wave pulses, and we discuss the
applications to radiation generated from pulsar binary mergers. It turns out
that the electromagnetic radiation from a binary merger should experience a
focusing effect, that in principle could be detected.


title:
On the trace anomaly and the energy-momentum conservation of quantum
  fields at D=2 in classical curved backgrounds

abstract:
  We study the conformal symmetry and the energy-momentum conservation of
scalar field interacting with a curved background at D=2. We avoid to
incorporate the metric determinant into the measure of the scalar field to
explain the conformal anomaly and the consequent energy-momentum conservation.
Contrarily, we split the scalar field in two other fields, in such a way that
just one of them can be quantized. We show that the same usual geometric
quantities of the anomaly are obtained, which are accompanied by terms
containing the new field of the theory.


title: Hidden connection between general relativity and Finsler geometry

abstract:
  Modern formulation of Finsler geometry of a manifold M utilizes the
equivalence between this geometry and the Riemannian geometry of VTM, the
vertical bundle over the tangent bundle of M, treating TM as the base space. We
argue that this approach is unsatisfactory when there is an indefinite metric
on M because the corresponding Finsler fundamental function would not be
differentiable over TM (even without its zero section) and therefore TM cannot
serve as the base space. We then make the simple observation that for any
differentiable Lorentzian metric on a smooth space-time, the corresponding
Finsler fundamental function is differentiable exactly on a proper subbundle of
TM. This subbundle is then used, in place of TM, to provide a satisfactory
basis for modern Finsler geometry of manifolds with Lorentzian metrics.
Interestingly, this Finslerian property of Lorentzian metrics does not seem to
exist for general indefinite Finsler metrics and thus, Lorentzian metrics
appear to be of special relevance to Finsler geometry. We note that, in
contrast to the traditional formulation of Finsler geometry, having a
Lorentzian metric in the modern setting does not imply reduction to pseudo-
Riemannian geometry because metric and connection are entirely disentangled in
the modern formulation and there is a new indispensable non-linear connection,
necessary for construction of Finsler tensor bundles. It is concluded that
general relativity--without any modification--has a close bearing on Finsler
geometry and a modern Finsler formulation of the theory is an appealing idea...


title: An Einstein-like theory of gravity with a non-newtonian weak-field limit

abstract:
  We propose a model describing Einstein gravity coupled to a scalar field with
an exponential potential. We show that the weak-field limit of the model has
static solutions given by a gravitational potential behaving for large
distances as \ln r . The Newtonian term GM/r appears only as subleading. Our
model can be used to give a phenomenological explanation of the rotation curves
of the galaxies without postulating the presence of dark matter. This can be
achieved only by giving up at galactic scales Einstein equivalence principle.