title: Gravitomagnetic effects

abstract:
  This paper contains a review of the theory and practice of gravitomagnetism,
with particular attention to the different and numerous proposals which have
been put forward to experimentally or observationally verify its effects. The
basics of the gravitoelectromagnetic form of the Einstein equations is
expounded. Then the Lense-Thirring and clock effects are described, reviewing
the essentials of the theory. Space based and Earth based experiments are
listed. Other effects, such as the coupling of gravitomagnetism with spin, are
described and orders of magnitude are considered to give an idea of the
feasibility of actual experiments.


title:
Method to compute the stress-energy tensor for the massless spin 1/2
  field in a general static spherically symmetric spacetime

abstract:
  A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.


title:
Proposal for a New Michelson-Morley Experiment Using a Single Whispering
  Spherical Mode Resonator

abstract:
  A new Michelson-Morley experiment is proposed by measuring the beat frequency
of two near degenerate modes with orthogonal propagation in a single spherical
resonator. The unique properties of the experiment allow: 1. Substantial common
mode rejection of some noise sources: 2. Simple calculation of the signal if
Special Relativity is violated. We show that optimum filtering may be used to
increase the signal to noise ratio, and to search for a preferred direction of
the speed of light. Using this technique we show that a sensitivity limit of
order 7.10^-19 is possible by integrating data over one month. We propose
methods to veto systematic effects by correlating the output of more than one
experiment.


title: Generalized Uncertainty Relations,Fundamental Length and Density Matrix

abstract:
  It was shown that if in Quantum Theory a fundamental length exists and a
well-known measurement procedure is used, then the density matrix at the Planck
scale cannot be defined in the usual way, because in this case density matrix
trace is strongly less than one.
  Density matrix must be changed by a progenitrix or as we call it throughout
this paper, density pro-matrix. This pro-matrix is a deformed density matrix,
which at low energy limit turns to usual one.
  Below the explicit form of the deformation is described. Implications of
obtained results are summarized as well as their application to the
interpretation of Information Paradox on the Black Holes.


title: On Black Hole Scalar Hair in Asymptotically Anti de Sitter Spacetimes

abstract:
  The unexpected discovery of hairy black hole solutions in theories with
scalar fields simply by considering asymptotically Anti de-Sitter, rather than
asymptotically flat, boundary conditions is analyzed in a way that exhibits in
a clear manner the differences between the two situations.
  It is shown that the trivial Schwarzschild Anti de Sitter becomes unstable in
some of these situations, and the possible relevance of this fact for the
ADS/CFT conjecture is pointed out.


title:
Does a relativistic metric generalization of Newtonian gravity exist in
  2+1 dimensions?

abstract:
  It is shown that, contrary to previous claims, a scalar tensor theory of
Brans-Dicke type provides a relativistic generalization of Newtonian gravity in
2+1 dimensions. The theory is metric and test particles follow the space-time
geodesics. The static isotropic solution is studied in vacuum and in regions
filled with an incompressible perfect fluid. It is shown that the solutions can
be consistently matched at the matter vacuum interface, and that the Newtonian
behavior is recovered in the weak field regime.


title:
Matched filters for coalescing binaries detection on massively parallel
  computers

abstract:
  We discuss some computational problems associated to matched filtering of
experimental signals from gravitational wave interferometric detectors in a
parallel-processing environment. We then specialize our discussion to the use
of the APEmille and apeNEXT processors for this task. Finally, we accurately
estimate the performance of an APEmille system on a computational load
appropriate for the LIGO and VIRGO experiments, and extrapolate our results to
apeNEXT.


title:
Aspects of hidden and manifest SL(2,R) symmetry in 2D near-horizon
  black-hole background

abstract:
  The invariance under unitary representations of the conformal group SL(2,R)
of a quantum particle is rigorously investigated in two-dimensional spacetimes
containing Killing horizons using DFF model. The limit of the near-horizon
approximation is considered. If the Killing horizon is bifurcate the conformal
symmetry is hidden, i.e. it does not arise from geometrical spacetime
isometries, but the whole Hilbert space turns out to be an irreducible unitary
representation of SL(2,R) and the time evolution is embodied in the unitary
representation. In this case the symmetry does not depend on the mass of the
particle and, if the representation is faithful, the conformal observable K
shows thermal properties. If the Killing horizon is nonbifurcate the conformal
symmetry is manifest, i.e. it arises from geometrical spacetime isometries. The
SL(2,R) representation which arises from the geometry selects a hidden
conformal representation. Also in that case the Hilbert space is an irreducible
representation of SL(2,R) and the group conformal symmetries embodies the time
evolution with respect to the local Killing time. However no thermal properties
are involved. The conformal observable K gives rise to Killing time evolution
of the quantum state with respect to another global Killing time present in the
manifold. Mathematical proofs about the developed machinery are supplied and
features of the operator H_g = -({d^2}/{dx^2})+ ({g}/{x^2}), with g=-1/4 are
discussed. It is proven that a statement, used in the recent literature, about
the spectrum of self-adjoint extensions of H_g is incorrect.


title: Boson Stars with Self-Interacting Quantum Scalar Fields

abstract:
  The Klein-Gordon-Einstein equations of classical real scalar fields have
time-dependent solutions (periodic in time). We show that quantum real scalar
fields can form non-oscillating (static) solitonic objects, which are quite
similar to the solutions describing boson stars formed with classical and
quantum complex scalar fields (the latter will be studied in this paper). We
numerically analyze the difference between them concerning the mass of boson
stars. On the other hand, we suggest an interesting test (a viable process that
the boson star may undergo in the early universe) for the formation of boson
stars. That is, it is questioned that after a second-order phase transition (a
simple toy model will be considered here), what is the fate of the boson star
composed of quantum real scalar field.


title:
Fundamental Length,Deformed Density Matrix and New View on the Black
  Hole Information Paradox

abstract:
  In this paper Quantum Mechanics with Fundamental Length is chosen as Quantum
Mechanics at Planck's scale. This is possible due to the presence in the theory
of General Uncertainty Relations (GUR). Here Quantum Mechanics with Fundamental
Length is obtained as a deformation of Quantum Mechanics. The distinguishing
feature of the proposed approach in comparison with previous ones, lies on the
fact that here density matrix subjects to deformation whereas so far
commutators have been deformed. The density matrix obtained by deformation of
quantum-mechanical density one is named throughout this paper density
pro-matrix, which at low energy limit turns to the density matrix. This
transition corresponds to non-unitary one from Quantum Mechanics with GUR to
Quantum mechanics. Below the implications of obtained results are
enumerated.New view on the Black Holes Information Paradox are discussed


title:
Properties of a monolithic sapphire parametric transducer: prospects of
  measuring the standard quantum limit

abstract:
  To measure the standard quantum limit (SQL) a high quality transducer must be
coupled to a high quality mechanical system. Due to its monolithic nature, the
monolithic sapphire transducer (MST) has high quality factors for both types of
resonances. Single loop suspension is shown to yield a mechanical quality
factor of 6.10^8 at 4 K. From standard analysis we show the MST has the
potential to measure noise fluctuations of the mechanical oscillator at the
SQL. also, we point out a new way to determine if the transducer back action is
quantum limited. We show that if the fluctuations are at the quantum limit,
then the amplitude of the oscillation will be amplified by the ratio of the
ringdown time to the measurement time, which is an inherently easier
measurement.


title:
Group of boost and rotation transformations with two
  observer-independent scales

abstract:
  I examine the structure of the deformed Lorentz transformations in one of the
recently-proposed schemes with two observer-independent scales. I develop a
technique for the analysis of general combinations of rotations and deformed
boosts. In particular, I verify explicitly that the transformations form group.


title: Higher Dimensional Wormhole Geometries with Compact Dimensions

abstract:
  This paper studies wormhole solutions to Einstein gravity with an arbitrary
number of time dependent compact dimensions and a matter-vacuum boundary. A new
gauge is utilized which is particularly suited for studies of the wormhole
throat. The solutions possess arbitrary functions which allow for the
description of infinitely many wormhole systems of this type and, at the
stellar boundary, the matter field is smoothly joined to vacuum. It turns out
that the classical vacuum structure differs considerably from the four
dimensional theory and is therefore studied in detail. The presence of the
vacuum-matter boundary and extra dimensions places interesting restrictions on
the wormhole. For example, in the static case, the radial size of a weak energy
condition (WEC) respecting throat is restricted by the extra dimensions. There
is a critical dimension, D=5, where this restriction is eliminated. In the time
dependent case, one \emph{cannot} respect the WEC at the throat as the time
dependence actually tends the solution towards WEC violation. This differs
considerably from the static case and the four dimensional case.


title: On the Intrinsic Parity of Black Holes

abstract:
  We investigate the intrinsic parity of black holes. It appears that discrete
symmetries require the black hole Hilbert space to be larger than suggested by
the usual quantum numbers M (mass), Q (charge) and J (angular momentum). Recent
results on black hole production in trans-Planckian scattering lead to
gravitational effects which do not decouple from low-energy physics. Dispersion
relations incorporating these effects imply that the semi-classical black hole
spectrum is similar in parity even and odd channels. This result can be
generalized to other discrete and continuous symmetries.


title:
Multidimensional Cosmology: Spatially Homogeneous models of dimension
  4+1

abstract:
  In this paper we classify all 4+1 cosmological models where the spatial
hypersurfaces are connected and simply connected homogeneous Riemannian
manifolds. These models come in two categories, multiply transitive and simply
transitive models. There are in all five different multiply transitive models
which cannot be considered as a special case of a simply transitive model. The
classification of simply transitive models, relies heavily upon the
classification of the four dimensional (real) Lie algebras. For the orthogonal
case, we derive all the equations of motion and give some examples of exact
solutions. Also the problem of how these models can be compactified in context
with the Kaluza-Klein mechanism, is addressed.


title: Dynamical Horizons: Energy, Angular Momentum, Fluxes and Balance Laws

abstract:
  Dynamical horizons are considered in full, non-linear general relativity.
Expressions of fluxes of energy and angular momentum carried by gravitational
waves across these horizons are obtained. Fluxes are local, the energy flux is
positive and change in the horizon area is related to these fluxes. The flux
formulae also give rise to balance laws analogous to the ones obtained by Bondi
and Sachs at null infinity and provide generalizations of the first and second
laws of black hole mechanics.


title: Casimir energy for spherical shell in Schwarzchild black hole background

abstract:
  In this paper, we consider the Casimir energy of massless scalar field which
satisfy Dirichlet boundary condition on a spherical shell. Outside the shell,
the spacetime is assumed to be described by the Schwarzschild metric, while
inside the shell it is taken to be the flat Minkowski space. Using zeta
function regularization and heat kernel coefficients we isolate the divergent
contributions of the Casimir energy inside and outside the shell, then using
the renormalization procedure of the bag model the divergent parts are
cancelled, finally obtaining a renormalized expression for the total Casimir
energy.


title:
Possible Development of the Newton Gravitational Theory of Interactions.
  An Alternative Approach to the Gravitational Theory

abstract:
  This work is devoted to the discussion of an idea that gravitational
interactions might be residual interactions of strong and electromagnetic
interactions. Then, absence of the carriers of the gravitational interactions
finds a natural explanation in the framework this idea. Besides, since masses
(charges of the gravitational interactions) of particles are generated in
strong, electromagnetic (and possibly, in other) interactions and if masses of
the particles will be not generated in these interactions (i.e. $m \equiv 0$),
then the gravitational interactions do not appear. That is also indirect
confirmation of the considered idea. Connections between charge of the
gravitational and other interactions are considered.


title: Accelerated Born-Infeld Metrics in Kerr-Schild Geometry

abstract:
  We consider Einstein Born-Infeld theory with a null fluid in Kerr-Schild
Geometry. We find accelerated charge solutions of this theory. Our solutions
reduce to the Plebanski solution when the acceleration vanishes and to the
Bonnor-Vaidya solution as the Born-Infeld parameter b goes to infinity. We also
give the explicit form of the energy flux formula due to the acceleration of
the charged sources.


title:
Projected Spin Networks for Lorentz connection: Linking Spin Foams and
  Loop Gravity

abstract:
  In the search for a covariant formulation for Loop Quantum Gravity, spin
foams have arised as the corresponding discrete space-time structure and, among
the different models, the Barrett-Crane model seems the most promising. Here,
we study its boundary states and introduce cylindrical functions on both the
Lorentz connection and the time normal to the studied hypersurface. We call
them projected cylindrical functions and we explain how they would naturally
arise in a covariant formulation of Loop Quantum Gravity.


title: Generalized Lorentz invariance with an invariant energy scale

abstract:
  The hypothesis that the Lorentz transformations may be modified at Planck
scale energies is further explored. We present a general formalism for theories
which preserve the relativity of inertial frames with a non-linear action of
the Lorentz transformations on momentum space. Several examples are discussed
in which the speed of light varies with energy and elementary particles have a
maximum momenta and/or energy. Energy and momentum conservation are suitably
generalized and a proposal is made for how the new transformation laws apply to
composite systems. We then use these results to explain the ultra high energy
cosmic ray anomaly and we find a form of the theory that explains the anomaly,
and leads also to a maximum momentum and a speed of light that diverges with
energy. We finally propose that the spatial coordinates be identified as the
generators of translation in Minkowski spacetime. In some examples this leads
to a commutative geometry, but with an energy dependent Planck constant.


title:
Note on a reformulation of the strong cosmic censor conjceture based on
  computability

abstract:
  In this letter we provide a reformulation of the strong cosmic censor
conjecture taking into account recent results on Malament--Hogarth space-times.
We claim that the strong version of the cosmic censor conjecture can be
formulated by postulating that a physically relevant space-time is either
globally hyperbolic or possesses the Malament--Hogarth property. But it is
known that a Malament--Hogarth space-time in principle is capable for
performing non-Turing computations such as checking consistency of ZFC set
theory. In this way we get an intimate conjectured link between the cosmic
censorship scenario and computability theory.


title: BritGravII - The Second British Gravity Meeting

abstract:
  The second of the annual BritGrav meetings on current research in
Gravitational Physics in Britain took place at the School of Mathematical
Sciences of Queen Mary, University of London on June 10/11, 2002. 47 plenary
talks of 12min duration were given. We make available the abstracts of the
talks and the references to the electronic preprints at arXiv.org where they
exist.


title:
On the Schroedinger Representation for a Scalar Field on Curved
  Spacetime

abstract:
  It is generally known that linear (free) field theories are one of the few
QFT that are exactly soluble. In the Schroedinger functional description of a
scalar field on flat Minkowski spacetime and for flat embeddings, it is known
that the usual Fock representation is described by a Gaussian measure. In this
paper, arbitrary globally hyperbolic space-times and embeddings of the Cauchy
surface are considered. The classical structures relevant for quantization are
used for constructing the Schroedinger representation in the general case. It
is shown that in this case, the measure is also Gaussian. Possible implications
for the program of canonical quantization of midisuperspace models are pointed
out.


title:
Finslerian Extension of Lorentz Transformations and First-Order
  Censorship Theorem

abstract:
  Granted the post-Lorentzian relativistic kinematic transformations are
described in the Finslerian framework, the uniformity between the actual light
velocity anisotropy change and the anisotropic deformation of measuring rods
can be the reason proper for the null results of the Michelson-Morley-type
experiments at the first-order level.


title: Black Hole Interaction Energy

abstract:
  The interaction energy between two black holes at large separation distance
is calculated. The first term in the expansion corresponds to the Newtonian
interaction between the masses. The second term corresponds to the spin-spin
interaction. The calculation is based on the interaction energy defined on the
two black holes initial data. No test particle approximation is used. The
relation between this formula and cosmic censorship is discussed.


title:
New properties of scalar field dynamics in brane isotropic cosmological
  models

abstract:
  Several aspects of scalar field dynamics on a brane which differs from
corresponding regimes in the standard cosmology are investigated. We consider
asymptotic solution near a singularity, condition for inflation and bounces and
some detail of chaotic behavior in the brane model. Each results are compared
with those known in the standard cosmology.


title: On discretizations of axisymmetric systems

abstract:
  In this paper we discuss stability properties of various discretizations for
axisymmetric systems including the so called cartoon method which was proposed
by Alcubierre, Brandt et.al. for the simulation of such systems on Cartesian
grids. We show that within the context of the method of lines such
discretizations tend to be unstable unless one takes care in the way individual
singular terms are treated. Examples are given for the linear axisymmetric wave
equation in flat space.


title: Some aspects of the numerical treatment of the conformal field equations

abstract:
  Some issues in the numerical treatment of the conformal field equations are
discussed. In particular, the problem of obtaining smooth initial data for the
hyperboloidal initial value problem is described and solution methods are
presented.


title:
Numerical evolution of axisymmetric, isolated systems in General
  Relativity

abstract:
  We describe in this article a new code for evolving axisymmetric isolated
systems in general relativity. Such systems are described by asymptotically
flat space-times which have the property that they admit a conformal extension.
We are working directly in the extended `conformal' manifold and solve
numerically Friedrich's conformal field equations, which state that Einstein's
equations hold in the physical space-time. Because of the compactness of the
conformal space-time the entire space-time can be calculated on a finite
numerical grid. We describe in detail the numerical scheme, especially the
treatment of the axisymmetry and the boundary.


title: Extrinsic Curvature and the Einstein Constraints

abstract:
  The Einstein initial-value equations in the extrinsic curvature (Hamiltonian)
representation and conformal thin sandwich (Lagrangian) representation are
brought into complete conformity by the use of a decomposition of symmetric
tensors which involves a weight function. In stationary spacetimes, there is a
natural choice of the weight function such that the transverse traceless part
of the extrinsic curvature (or canonical momentum) vanishes.


title: Black-hole threshold solutions in stiff fluid collapse

abstract:
  Numerical studies of the gravitational collapse of a stiff (P=rho) fluid have
found the now familiar critical phenomena, namely scaling of the black hole
mass with a critical exponent and continuous self-similarity at the threshold
of black hole formation. Using the equivalence of an irrotational stiff fluid
to a massless scalar field, we construct the critical solution as a scalar
field solution by making a self-similarity ansatz. We find evidence that this
solution has exactly one growing perturbation mode; both the mode and the
critical exponent, gamma ~ 0.94, derived from its eigenvalue agree with those
measured in perfect fluid collapse simulations. We explain why this solution is
seen as a critical solution in stiff fluid collapse but not in scalar field
collapse, and conversely why the scalar field critical solution is not seen in
stiff fluid collapse, even though the two systems are locally equivalent.


title: Post-Newtonian Models of Differentially Rotating Neutron Stars

abstract:
  A self-consistent field method is developed, which can be used to construct
models of differentially rotating stars to first post-Newtonian order. The
rotation law is specified by the specific angular momentum distribution j(m),
where m is the baryonic mass fraction inside the surface of constant specific
angular momentum. The method is then used to compute models of the nascent
neutron stars resulting from the accretion induced collapse of white dwarfs.
The result shows that the ratios of kinetic energy to gravitational binding
energy of the relativistic models are slightly smaller than the corresponding
values of the Newtonian models.


title:
Quasiequilibrium sequences of synchronized and irrotational binary
  neutron stars in general relativity. III. Identical and different mass stars
  with gamma=2

abstract:
  We present the first computations of quasiequilibrium binary neutron stars
with different mass components in general relativity, within the
Isenberg-Wilson-Mathews approximation. We consider both cases of synchronized
rotation and irrotational motion. A polytropic equation of state is used with
the adiabatic index gamma=2. The computations have been performed for the
following combinations of stars: (M/R)_{star 1} vs. (M/R)_{star 2} = 0.12 vs.
(0.12, 0.13, 0.14), 0.14 vs. (0.14, 0.15, 0.16), 0.16 vs. (0.16, 0.17, 0.18),
and 0.18 vs. 0.18, where (M/R) denotes the compactness parameter of infinitely
separated stars of the same baryon number. It is found that for identical mass
binary systems there is no turning point of the binding energy (ADM mass)
before the end point of the sequence (mass shedding point) in the irrotational
case, while there is one before the end point of the sequence (contact point)
in the synchronized case. On the other hand, in the different mass case, the
sequence ends by the tidal disruption of the less massive star (mass shedding
point). It is then more difficult to find a turning point in the ADM mass.
Furthermore, we find that the deformation of each star depends mainly on the
orbital separation and the mass ratio and very weakly on its compactness. On
the other side, the decrease of the central energy density depends on the
compactness of the star and not on that of the companion.


title:
Slowly rotating charged fluid balls and their matching to an exterior
  domain

abstract:
  The slow-rotation approximation of Hartle is developed to a setting where a
charged rotating fluid is present. The linearized Einstein-Maxwell equations
are solved on the background of the Reissner-Nordstrom space-time in the
exterior electrovacuum region. The theory is put to action for the charged
generalization of the Wahlquist solution found by Garcia. The Garcia solution
is transformed to coordinates suitable for the matching and expanded in powers
of the angular velocity. The two domains are then matched along the zero
pressure surface using the Darmois-Israel procedure. We prove a theorem to the
effect that the exterior region is asymptotically flat if and only if the
parameter C_{2}, characterizing the magnitude of an external magnetic field,
vanishes. We obtain the form of the constant C_{2} for the Garcia solution. We
conjecture that the Garcia metric cannot be matched to an asymptotically flat
exterior electrovacuum region even to first order in the angular velocity. This
conjecture is supported by a high precision numerical analysis.


title:
A critical approach to the concept of a polar, low-altitude LARES
  satellite

abstract:
  According to very recent developments of the LARES mission, which would be
devoted to the measurement of the general relativistic Lense--Thirring effect
in the gravitational field of the Earth with Satellite Laser Ranging, it seems
that the LARES satellite might be finally launched in a polar, low--altitude
orbit by means of a relatively low--cost rocket. The observable would be the
node only. In this letter we critically analyze this scenario.


title: A reformulation of the Barrabes-Israel null-shell formalism

abstract:
  We consider a situation in which two metrics are joined at a null
hypersurface. It often occurs that the union of the two metrics gives rise to a
Ricci tensor that contains a term proportional to a Dirac delta-function
supported on the hypersurface. This singularity is associated with a thin
distribution of matter on the hypersurface, and following Barrabes and Israel,
we seek to determine its stress-energy tensor in terms of the geometric
properties of the null hypersurface. While our treatment here does not deviate
strongly from their previous work, it offers a simplification of the
computational operations involved in a typical application of the formalism,
and it gives rise to a stress-energy tensor that possesses a more recognizable
phenomenology. Our reformulation of the null-shell formalism makes systematic
use of the null generators of the singular hypersurface, which define a
preferred flow to which the flow of matter can be compared. This construction
provides the stress-energy tensor with a simple characterization in terms of a
mass density, a mass current, and an isotropic pressure. Our reformulation also
involves a family of freely-moving observers that intersect the surface layer
and perform measurements on it. This construction gives operational meaning to
the stress-energy tensor by fixing the argument of the delta-function to be
proper time as measured by these observers.


title:
The information content of gravitational wave harmonics in compact
  binary inspiral

abstract:
  The nonlinear aspect of gravitational wave generation that produces power at
harmonics of the orbital frequency, above the fundamental quadrupole frequency,
is examined to see what information about the source is contained in these
higher harmonics. We use an order (4/2) post-Newtonian expansion of the
gravitational wave waveform of a binary system to model the signal seen in a
spaceborne gravitational wave detector such as the proposed LISA detector.
Covariance studies are then performed to determine the ultimate accuracy to be
expected when the parameters of the source are fit to the received signal. We
find three areas where the higher harmonics contribute crucial information that
breaks degeneracies in the model and allows otherwise badly-correlated
parameters to be separated and determined. First, we find that the position of
a coalescing massive black hole binary in an ecliptic plane detector, such as
OMEGA, is well-determined with the help of these harmonics. Second, we find
that the individual masses of the stars in a chirping neutron star binary can
be separated because of the mass dependence of the harmonic contributions to
the wave. Finally, we note that supermassive black hole binaries, whose
frequencies are too low to be seen in the detector sensitivity window for long,
may still have their masses, distances, and positions determined since the
information content of the higher harmonics compensates for the information
lost when the orbit-induced modulation of the signal does not last long enough
to be apparent in the data.


title: Manifold dimension of a causal set: Tests in conformally flat spacetimes

abstract:
  This paper describes an approach that uses flat-spacetime dimension
estimators to estimate the manifold dimension of causal sets that can be
faithfully embedded into curved spacetimes. The approach is invariant under
coarse graining and can be implemented independently of any specific curved
spacetime. Results are given based on causal sets generated by random
sprinklings into conformally flat spacetimes in 2, 3, and 4 dimensions, as well
as one generated by a percolation dynamics.


title: Space geometry of rotating platforms: an operational approach

abstract:
  We study the space geometry of a rotating disk both from a theoretical and
operational approach, in particular we give a precise definition of the space
of the disk, which is not clearly defined in the literature. To this end we
define an extended 3-space, which we call relative space: it is recognized as
the only space having an actual physical meaning from an operational point of
view, and it is identified as the 'physical space of the rotating platform'.
Then, the geometry of the space of the disk turns out to be non Euclidean,
according to the early Einstein's intuition; in particular the Born metric is
recovered, in a clear and self consistent context. Furthermore, the
relativistic kinematics reveals to be self consistent, and able to solve the
Ehrenfest's paradox without any need of dynamical considerations or ad hoc
assumptions.


title:
Two-parameter non-linear spacetime perturbations: gauge transformations
  and gauge invariance

abstract:
  An implicit fundamental assumption in relativistic perturbation theory is
that there exists a parametric family of spacetimes that can be Taylor expanded
around a background. The choice of the latter is crucial to obtain a manageable
theory, so that it is sometime convenient to construct a perturbative formalism
based on two (or more) parameters. The study of perturbations of rotating stars
is a good example: in this case one can treat the stationary axisymmetric star
using a slow rotation approximation (expansion in the angular velocity Omega),
so that the background is spherical. Generic perturbations of the rotating star
(say parametrized by lambda) are then built on top of the axisymmetric
perturbations in Omega. Clearly, any interesting physics requires non-linear
perturbations, as at least terms lambda Omega need to be considered. In this
paper we analyse the gauge dependence of non-linear perturbations depending on
two parameters, derive explicit higher order gauge transformation rules, and
define gauge invariance. The formalism is completely general and can be used in
different applications of general relativity or any other spacetime theory.


title: Quantum gravity, shadow states, and quantum mechanics

abstract:
  A program was recently initiated to bridge the gap between the Planck scale
physics described by loop quantum gravity and the familiar low energy world. We
illustrate the conceptual problems and their solutions through a toy model:
quantum mechanics of a point particle. Maxwell fields will be discussed in the
second paper of this series which further develops the program and provides
details.


title: Clifford Residues and Charge Quantization

abstract:
  We derive the quantization of action, particle number, and electric charge in
a Lagrangian spin bundle over M equivalent M_# union D_J, Penrose's conformal
compactification of Minkowsky space, with the world tubes of massive particles
removed.


title:
Mass and Charge in Brane-World and Non-Compact Kaluza-Klein Theories in
  5 Dim

abstract:
  In classical Kaluza-Klein theory, with compactified extra dimensions and
without scalar field, the rest mass as well as the electric charge of test
particles are constants of motion. We show that in the case of a large extra
dimension this is no longer so. We propose the Hamilton-Jacobi formalism,
instead of the geodesic equation, for the study of test particles moving in a
five-dimensional background metric. This formalism has a number of advantages:
(i) it provides a clear and invariant definition of rest mass, without the
ambiguities associated with the choice of the parameters used along the motion
in 5D and 4D, (ii) the electromagnetic field can be easily incorporated in the
discussion, and (iii) we avoid the difficulties associated with the "splitting"
of the geodesic equation. For particles moving in a general 5D metric, we show
how the effective rest mass, as measured by an observer in 4D, varies as a
consequence of the large extra dimension. Also, the fifth component of the
momentum changes along the motion. This component can be identified with the
electric charge of test particles. With this interpretation, both the rest mass
and the charge vary along the trajectory. The constant of motion is now a
combination of these quantities. We study the cosmological variations of charge
and rest mass in a five-dimensional bulk metric which is used to embed the
standard k = 0 FRW universes. The time variations in the fine structure
"constant" and the Thomson cross section are also discussed.


title:
On the Problems of Hazardous Matter and Radiation at Faster than Light
  Speeds in the Warp Drive Space-Time

abstract:
  The problems of hazardous radiation and collisions with matter on a warp
driven ship pose considerable obstacles to this possibility for interstellar
travel. A solution to these problems lies in the Broeck metric. It is
demonstrated that both threats to the ship will be greatly reduced. It is also
shown that the horizon problem no longer exists.


title:
Causal Relationship: a new tool for the causal characterization of
  Lorentzian manifolds

abstract:
  We define and study a new kind of relation between two diffeomorphic
Lorentzian manifolds called {\em causal relation}, which is any diffeomorphism
characterized by mapping every causal vector of the first manifold onto a
causal vector of the second. We perform a thorough study of the mathematical
properties of causal relations and prove in particular that two given
Lorentzian manifolds (say $V$ and $W$) may be causally related only in one
direction (say from $V$ to $W$, but not from $W$ to $V$). This leads us to the
concept of causally equivalent (or {\em isocausal} in short) Lorentzian
manifolds as those mutually causally related. This concept is more general and
of a more basic nature than the conformal relationship, because we prove the
remarkable result that a conformal relation $\f$ is characterized by the fact
of being a causal relation of the {\em particular} kind in which both $\f$ and
$\f^{-1}$ are causal relations. For isocausal Lorentzian manifolds there are
one-to-one correspondences, which sometimes are non-trivial, between several
classes of their respective future (and past) objects. A more important feature
of isocausal Lorentzian manifolds is that they satisfy the same causality
constraints. This indicates that the causal equivalence provides a possible
characterization of the {\it basic causal structure}, in the sense of mutual
causal compatibility, for Lorentzian manifolds. Thus, we introduce a partial
order for the equivalence classes of isocausal Lorentzian manifolds providing a
classification of spacetimes in terms of their causal properties, and a
classification of all the causal structures that a given fixed manifold can
have. A full abstract inside the paper.


title:
Some results concerning the representation theory of the algebra
  underlying loop quantum gravity

abstract:
  Important characteristics of the loop approach to quantum gravity are a
specific choice of the algebra A of observables and of a representation of A on
a measure space over the space of generalized connections. This representation
is singled out by its elegance and diffeomorphism covariance.
  Recently, in the context of the quest for semiclassical states, states of the
theory in which the quantum gravitational field is close to some classical
geometry, it was realized that it might also be worthwhile to study different
representations of the algebra A of observables.
  The content of the present note is the observation that under some mild
assumptions, the mathematical structure of representations of A can be analyzed
rather effortlessly, to a certain extent: Each representation can be labeled by
sets of functions and measures on the space of (generalized) connections that
fulfill certain conditions.
  These considerations are however mostly of mathematical nature. Their
physical content remains to be clarified, and physically interesting examples
are yet to be constructed.


title:
When Do Measures on the Space of Connections Support the Triad Operators
  of Loop Quantum Gravity?

abstract:
  In this work we investigate the question, under what conditions Hilbert
spaces that are induced by measures on the space of generalized connections
carry a representation of certain non-Abelian analogues of the electric flux.
We give the problem a precise mathematical formulation and start its
investigation. For the technically simple case of U(1) as gauge group, we
establish a number of "no-go theorems" asserting that for certain classes of
measures, the flux operators can not be represented on the corresponding
Hilbert spaces.
  The flux-observables we consider play an important role in loop quantum
gravity since they can be defined without recourse to a background geometry,
and they might also be of interest in the general context of quantization of
non-Abelian gauge theories.


title: New Path Equations in Absolute Parallelism Geometry

abstract:
  The Bazanski approach, for deriving the geodesic equations in Riemannian
geometry, is generalized in the absolute parallelism geometry. As a consequence
of this generalization three path equations are obtained. A striking feature in
the derived equations is the appearance of a torsion term with a numerical
coefficients that jumps by a step of one half from equation to another. This is
tempting to speculate that the paths in absolute parallelism geometry might
admit a quantum feature.


title:
Einstein's lifts and topologies: topological investigations on the
  Principle of Equivalence

abstract:
  The gedanken-experiment of Einstein's lift is analyzed in order of
determining whether the free-falling observer inside the lift can detect the
eventual topological non-triviality of space-time


title: Equality of Inertial and Gravitational Masses for Quantum Particle

abstract:
  We investigate the interaction of the gravitational field with a quantum
particle. First, we give the proof of the equality of the inertial and the
gravitational mass for the nonrelativistic quantum particle, independently of
the equivalence principle. Second, we show that the macroscopic body cannot be
described by the many-particle Quantum Mechanics. As an important tool we
generalize the Bargmann's theory of ray representations and explain the
connection with the state vector reduction problem. The Penrose's hypothesis is
discussed, i.e. the hypothesis that the gravitational field may influence the
state vector reduction.


title: Scalar normal modes of higher dimensional gravitating kinks

abstract:
  The scalar normal modes of higher dimensional gravitating kink solutions are
derived. By perturbing to second order the gravity and matter parts of the
action in the background of a five-dimensional kink, the effective Lagrangian
of the scalar fluctuations is derived and diagonalized in terms of a single
degree of freedom which invariant under infinitesimal diffeomorphisms. The
spectrum of the normal modes is discussed and applied to the analysis of short
distance corrections to Newton law.


title:
Finslerian Post-Lorentzian Kinematic Transformations in
  Anisotropic-Space Case

abstract:
  The Finslerian post-Lorentzian kinematic transformations can explicitly be
obtained under uni-directional breakdown of spatial isotropy, provided that the
requirement that the relativistic unit hypersurface (indicatrix or mass shell)
be a space of constant negative curvature is still fulfilled. The method
consists in evaluating respective Finslerian tetrads and then treating them as
the bases of inertial reference frames. The Transport Synchronization has
rigorously been proven, which opens up the ways proper to favour the concept of
one-way light velocity. Transition to the Hamiltonian treatment is
straightforward, so that the Finslerian transformation laws for momenta and
frequences, as well as due Finslerian corrections to Doppler effect, become
clear. An important common feature of the ordinary pseudo-Euclidean theory of
special relativity and of the Finslerian relativistic approach under study is
that they both endeavour to establish a universal prescription for applying the
theory to systems in differing states of motion.


title: Quantum power correction to the Newton law

abstract:
  We have found the graviton contribution to the one-loop quantum correction to
the Newton law. This correction results in interaction decreasing with distance
as 1/r^3 and is dominated numerically by the graviton contribution. The
previous calculations of this contribution to the discussed effect are
demonstrated to be incorrect.


title: Data analysis of continuous gravitational wave: Fourier transform-II

abstract:
  In this paper we obtain the Fourier Transform of a continuous gravitational
wave. We have analysed the data set for (i) one year observation time and (ii)
arbitrary observation time, for arbitrary location of detector and source
taking into account the effects arising due to rotational as well as orbital
motion of the earth. As an application of the transform we considered spin down
and N-component signal analysis.


title:
A Classification of Spherically Symmetric Kinematic Self-Similar
  Perfect-Fluid Solutions

abstract:
  We classify all spherically symmetric spacetimes admitting a kinematic
self-similar vector of the second, zeroth or infinite kind. We assume that the
perfect fluid obeys either a polytropic equation of state or an equation of
state of the form $p=K\mu$, where $p$ and $\mu$ are the pressure and the energy
density, respectively, and $K$ is a constant. We study the cases in which the
kinematic self-similar vector is not only ``tilted'' but also parallel or
orthogonal to the fluid flow. We find that, in contrast to Newtonian gravity,
the polytropic perfect-fluid solutions compatible with the kinematic
self-similarity are the Friedmann-Robertson-Walker solution and general static
solutions. We find three new exact solutions which we call the dynamical
solutions (A) and (B) and $\Lambda$-cylinder solution, respectively.


title: Collapse of a Scalar Field in 2+1 Gravity

abstract:
  We consider the problem of critical gravitational collapse of a scalar field
in 2+1 dimensions with spherical (circular) symmetry. After surveying all the
analytic, continuously self-similar solutions and considering their global
structure, we examine their perturbations with the intent of understanding
which are the critical solutions with a single unstable mode. The critical
solution which we find is the one which agrees most closely with that found in
numerical evolutions. However, the critical exponent which we find does not
seem to agree with the numerical result.


title:
TELEPENSOUTH project: Measurement of the Earth gravitomagnetic field in
  a terrestrial laboratory

abstract:
  We will expose a preliminary study on the feasibility of an experiment
leading to a direct measurement of the gravitomagnetic field generated by the
rotational motion of the Earth. This measurement would be achieved by means of
an appropriate coupling of a TELEscope and a Foucault PENdulum in a laboratory
on ground, preferably at the SOUTH pole. An experiment of this kind was firstly
proposed by Braginski, Polnarev and Thorne, 18 years ago, but it was never
re-analyzed.


title: Hypothetical Gravity Control and Implications for Spacecraft Propulsion

abstract:
  A scientific analysis of the conditions under which gravity could be
controlled and the implications that an hypothetical manipulation of gravity
would have for known schemes of space propulsion have been the scope of a
recent study carried out for the European Space Agency. The underlying
fundamental physical principles of known theories of gravity were analysed and
shown that even if gravity could be modified it would bring somewhat modest
gains in terms of launching of spacecraft and no breakthrough for space
propulsion.


title: Noncommutative Scalar Field Coupled to Gravity

abstract:
  A model for a noncommutative scalar field coupled to gravity is proposed via
an extension of the Moyal product. It is shown that there are solutions
compatible with homogeneity and isotropy to first non-trivial order in the
perturbation of the star-product, with the gravity sector described by a flat
Robertson-Walker metric. We show that in the slow-roll regime of a typical
chaotic inflationary scenario, noncommutativity has negligible impact.


title: Singularity free cosmological solutions of Einstein-Maxwell equations

abstract:
  We report on a new two-parameter class of cosmological solutions to the
Einstein-Maxwell equations. The solutions have everywhere regular curvature
invariants. We prove that the solutions are geodesically complete and globally
hyperbolic.


title:
Collapsing and Expanding Cylindrically Symmetric Fields with Ligh-tlike
  Wave-Fronts in General Relativity

abstract:
  The dynamics of collapsing and expanding cylindrically symmetric
gravitational and matter fields with lightlike wave-fronts is studied in
General Relativity, using the Barrabes-Israel method. As an application of the
general formulae developed, the collapse of a matter field that satisfies the
condition R_{AB}g^{AB} = 0, (A, B = z, phi), in an otherwise flat spacetime
background is studied. In particular, it is found that the gravitational
collapse of a purely gravitational wave or a null dust fluid cannot be realized
in a flat spacetime background. The studies are further specified to the
collapse of purely gravitational waves and the general conditions for such
collapse are found. It is shown that after the waves arrive at the axis, in
general, part of them is reflected to spacelike infinity along the future light
cone, and part of it is focused to form spacetime singularities on the symmetry
axis. The cases where the collapse does not result in the formation of
spacetime singularities are also identified.


title: Particle velocity in noncommutative space-time

abstract:
  We investigate a particle velocity in the $\kappa$-Minkowski space-time,
which is one of the realization of a noncommutative space-time. We emphasize
that arrival time analyses by high-energy $\gamma$-rays or neutrinos, which
have been considered as powerful tools to restrict the violation of Lorentz
invariance, are not effective to detect space-time noncommutativity. In
contrast with these examples, we point out a possibility that {\it low-energy
massive particles} play an important role to detect it.


title: Trapping photons by a line singularity

abstract:
  We present cylindrically symmetric, static solutions of the Einstein field
equations around a line singularity such that the energy momentum tensor
corresponds to infinitely thin photonic shells. Positivity of the energy
density of the thin shell and the line singularity is discussed. It is also
shown that thick shells containing mostly radiation are possible by a numerical
solution.


title: Spin Axioms in Relativistic Continuum Physics

abstract:
  The 24 components of the relativistic spin tensor consist of 3+3 basic spin
fields and 9+9 constitutive fields. Empirically only 3 basic spin fields and 9
constitutive fields are known. This empirem can be expressed by two spin
axioms, one of them identifying 3 spin fields, and the other one 9 constitutive
fields to each other. This identification by the spin axioms is
material-independent and does not mix basic spin fields with constitutive
properties. The approaches to the Weyssenhoff fluid and the Dirac-electron
fluid found in literature are discussed with regard to these spin axioms. The
conjecture is formulated, that another reduction from 6 to 3 basic spin fields
which does not obey the spin axioms introduces special material properties by
not allowed mixing of constitutive and basic fields.


title:
Satellite E\"otv\"os Test of the Weak Equivalence Principle for
  Zero-Point Vacuum Energy

abstract:
  An E\"otv\"os experiment to test the weak equivalence principle (WEP) for
zero-point vacuum energy is proposed using a satellite. Following the
suggestion of Ross for a terrestrial experiment of this type, the acceleration
of a spherical test mass of aluminum would be compared with that of a similar
test mass made from another material. The estimated ratio of the zero-point
vacuum energy density inside the aluminum sphere to the rest mass energy
density is ~ 1.6 X 10^{-14}, which would allow a 1% resolution of a potential
WEP violation observed in a satellite mission test that had a baseline
sensitivity to WEP violations of ~ 10^{-16}. An observed violation of the WEP
for vacuum energy density would constitute a significant clue as to the origin
of the cosmological constant and the source of dark energy, and test a recently
proposed resolution of the cosmological constant problem, based on a model of
nonlocal quantum gravity and quantum field theory.


title: Can a brane fluctuate freely?

abstract:
  No, it cannot in the following sense if a self-gravitating vacuum brane is
concerned. Once we write down the full set of linear perturbation equations of
the system containing a self-gravitating brane, we will see that such a brane
does not have its own dynamical degrees of freedom independent of those of
gravitational waves which propagate in the surrounding spacetime. This
statement seems to contradict with our intuition that a brane fluctuates freely
on a given background spacetime in the lowest order approximation. Based on
this intuition, we usually think that the dynamics of a brane can be
approximately described by the equations derived from the Nambu-Goto action. In
this paper we fill the gap residing between these two descriptions, showing
that the dynamics of a self-gravitating brane is in fact similar to that
described by a non-gravitating brane on a fixed background spacetime when the
weak backreaction condition we propose in this paper is satisfied.


title:
A cross-correlation technique in wavelet domain for detection of
  stochastic gravitational waves

abstract:
  Stochastic gravitational waves (SGW) can be detected by measuring a
cross-correlation of two or more gravitational wave (GW) detectors. In this
paper we describe an optimal SGW search technique in the wavelet domain. It
uses a sign correlation test, which allows calculation of the cross-
correlation significance for non-Gaussian data. We also address the problem of
correlated noise for the GW detectors. A method that allows calculation of the
cross-correlation variance, when data is affected by correlated noise, is
developed. As a part of the optimal search technique a robust estimator for
detector noise spectral amplitude is introduced. It is not sensitive to
outliers and allows application of the search technique to non-stationary data.


title: 8-Spinor Quantum Gravity

abstract:
  Quantum gravity has been so elusive because we have tried to approach it by
two paths which can never meet: quantum mechanics and general relativity. These
contradict each other not only in superdense regimes, but also in the vacuum.
  We explore a straight road to quantum gravity here--the one mandated by
Clifford-algebra covariance. This bridges the gap from microscales--where the
massive Dirac propagator is a sum over null zig-zags--to macroscales--where we
see the energy-momentum current, *T and the resulting Einstein curvature, *G.
For massive particles, *T flows in the "cosmic time" direction,
y^0--centrifugally in an expanding universe.
  Neighboring centrifugal currents of *T present opposite spacetime vorticities
*G to the boundaries of each others' worldtubes, so they advect--i.e. attract,
as we show here by integrating a Spin^c-4 Lagrangian by parts in the spinfluid
regime.
  This boundary integral not only explains why stress-energy *T is the source
for gravitational curvature *G, but also gives a value for the gravitational
constant, kappa(x^0) that depends on the current scale factor of our expanding
Friedmann 3-brane. On the microscopic scale, quantum gravity appears naturally
as the statistical mechanics of null zig-zags of massive particles in
"imaginary time," y^0.


title: Scattering of a Long Cosmic String by a Rotating Black Hole

abstract:
  The scattering of a straight, infinitely long string by a rotating black hole
is considered. We assume that a string is moving with velocity v and that
initially the string is parallel to the axis of rotation of the black hole. We
demonstrate that as a result of scattering, the string is displaced in the
direction perpendicular to the velocity by an amount kappa(v,b), where b is the
impact parameter. The late-time solution is represented by a kink and
anti-kink, propagating in opposite directions at the speed of light, and
leaving behind them the string in a new ``phase''. We present the results of
the numerical study of the string scattering and their comparison with the
weak-field approximation, valid where the impact parameter is large, b/M >> 1,
and also with the scattering by a non-rotating black hole which was studied in
earlier works.


title: Asymptotics of 10j symbols

abstract:
  The Riemannian 10j symbols are spin networks that assign an amplitude to each
4-simplex in the Barrett-Crane model of Riemannian quantum gravity. This
amplitude is a function of the areas of the 10 faces of the 4-simplex, and
Barrett and Williams have shown that one contribution to its asymptotics comes
from the Regge action for all non-degenerate 4-simplices with the specified
face areas. However, we show numerically that the dominant contribution comes
from degenerate 4-simplices. As a consequence, one can compute the asymptotics
of the Riemannian 10j symbols by evaluating a `degenerate spin network', where
the rotation group SO(4) is replaced by the Euclidean group of isometries of
R^3. We conjecture formulas for the asymptotics of a large class of Riemannian
and Lorentzian spin networks in terms of these degenerate spin networks, and
check these formulas in some special cases. Among other things, this conjecture
implies that the Lorentzian 10j symbols are asymptotic to 1/16 times the
Riemannian ones.


title:
Are Post-Newtonian templates faithful and effectual in detecting
  gravitational signals from neutron star binaries?

abstract:
  We compute the overlap function between Post-Newtonian (PN) templates and
gravitational signals emitted by binary systems composed of one neutron star
and one point mass, obtained by a perturbative approach. The calculations are
performed for different stellar models and for different detectors, to estimate
how effectual and faithful the PN templates are, and to establish whether
effects related to the internal structure of neutron stars may possibly be
extracted by the matched filtering technique.


title:
Global existence of solutions to the Einstein-Yang-Mills-dilaton
  equations

abstract:
  This paper has been withdrawn by the author, due to an error in the proof of
lemma 7.4. However, numerical evidence strongly suggest that this lemma is
true.


title:
Radiation Bursts from Particles in the Field of Compact, Impenetrable,
  Astrophysical Objects

abstract:
  The radiation emitted by charged, scalar particles in a Schwarzschild field
with maximal acceleration corrections is calculated classically and in the tree
approximation of quantum field theory. In both instances the particles emit
radiation that has characteristics similar to those of gamma-ray bursters.


title:
The Gravitational Radiaton degrees of freedom in Hyperbolic Systems for
  Numerical Relativity

abstract:
  The gravitational radiation degrees of freedom of freedom are described in
the framework of the 3+1 decomposition of spacetime. The relationship with
eigenfields of the Kidder-Scheel-Teukolsky (KST) equations is established. This
relationship is used to fix a parameter in the KST equations which is related
to the ordering ambiguity of space derivatives in the Ricci tensor, which is
inherent to first order evolution systems, like the ones currently used in
Numerical Relativity applications.


title: Symmetry-preserving matchings

abstract:
  In the literature, the matchings between spacetimes have been most of the
times implicitly assumed to preserve some of the symmetries of the problem
involved. But no definition for this kind of matching was given until recently.
Loosely speaking, the matching hypersurface is restricted to be tangent to the
orbits of a desired local group of symmetries admitted at both sides of the
matching and thus admitted by the whole matched spacetime. This general
definition is shown to lead to conditions on the properties of the preserved
groups. First, the algebraic type of the preserved group must be kept at both
sides of the matching hypersurface. Secondly, the orthogonal transivity of
two-dimensional conformal (in particular isometry) groups is shown to be
preserved (in a way made precise below) on the matching hypersurface. This
result has in particular direct implications on the studies of axially
symmetric isolated bodies in equilibrium in General Relativity, by making up
the first condition that determines the suitability of convective interiors to
be matched to vacuum exteriors. The definition and most of the results
presented in this paper do not depend on the dimension of the manifolds
involved nor the signature of the metric, and their applicability to other
situations and other higher dimensional theories is manifest.


title: Space-Based Gravity Detector for a Space Laboratory

abstract:
  A space-based superconducting gravitational low-frequency wave detector is
considered. Sensitivity of the detector is sufficient to use the detector as a
partner of other contemporary low-frequency detectors like LIGO and LISA. This
device can also be very useful for experimental study of other effects
predicted by theories of gravitation.


title:
Separation of variables and exact solution of the Klein-Gordon and Dirac
  equations in an open universe

abstract:
  We solve the Klein-Gordon and Dirac equations in an open cosmological
universe with a partially horn topology in the presence of a time dependent
magnetic field. Since the exact solution cannot be obtained explicitly for
arbitrary time-dependence of the field, we discuss the asymptotic behavior of
the solutions with the help of the relativistic Hamilton-Jacobi equation.


title: The Interpretation of Quantum Cosmology and the Problem of Time

abstract:
  The development of quantum cosmology, in which Stephen Hawking played a
crucial role, has frequently encountered substantial conceptual and technical
difficulties related to the problem of time in quantum gravity and to general
issues concerning the foundations of quantum theory. In this contribution to
Stephen's 60th Birthday Conference, I describe some recent work in which the
decoherent histories approach to quantum theory is used to quantize simple
cosmological models and perhaps shed some light on some of these difficulties.


title: Uniformly Accelerated Mirrors. Part 1: Mean Fluxes

abstract:
  The Davies-Fulling model describes the scattering of a massless field by a
moving mirror in 1+1 dimensions. When the mirror travels under uniform
acceleration, one encounters severe problems which are due to the infinite blue
shift effects associated with the horizons. On one hand, the Bogoliubov
coefficients are ill-defined and the total energy emitted diverges. On the
other hand, the instantaneous mean flux vanishes. To obtained well-defined
expressions we introduce an alternative model based on an action principle. The
usefulness of this model is to allow to switch on and off the interaction at
asymptotically large times. By an appropriate choice of the switching function,
we obtain analytical expressions for the scattering amplitudes and the fluxes
emitted by the mirror. When the coupling is constant, we recover the vanishing
flux. However it is now followed by transients which inevitably become singular
when the switching off is performed at late time. Our analysis reveals that the
scattering amplitudes (and the Bogoliubov coefficients) should be seen as
distributions and not as mere functions. Moreover, our regularized amplitudes
can be put in a one to one correspondence with the transition amplitudes of an
accelerated detector, thereby unifying the physics of uniformly accelerated
systems. In a forthcoming article, we shall use our scattering amplitudes to
analyze the quantum correlations amongst emitted particles which are also
ill-defined in the Davies-Fulling model in the presence of horizons.


title:
Black-hole horizon and metric singularity at the brane separating two
  sliding superfluids

abstract:
  An analog of black hole can be realized in the low-temperature laboratory.
The horizon can be constructed for the `relativistic' ripplons (surface waves)
living on the brane. The brane is represented by the interface between two
superfluid liquids, 3He-A and 3He-B, sliding along each other without friction.
Similar experimental arrangement has been recently used for the observation and
investigation of the Kelvin-Helmholtz type of instability in superfluids
(cond-mat/0111343). The shear-flow instability in superfluids is characterized
by two critical velocities. The lowest threshold measured in recent experiments
(cond-mat/0111343) corresponds to appearance of the ergoregion for ripplons. In
the modified geometry this will give rise to the black-hole event horizon in
the effective metric experienced by ripplons. In the region behind the horizon,
the brane vacuum is unstable due to interaction with the higher-dimensional
world of bulk superfluids. The time of the development of instability can be
made very long at low temperature. This will allow us to reach and investigate
the second critical velocity -- the proper Kelvin-Helmholtz instability
threshold. The latter corresponds to the singularity inside the black hole,
where the determinant of the effective metric becomes infinite.


title: Problems of G and multidimensional models

abstract:
  The relations for G-dot in multidimensional model with Ricci-flat internal
space and multicomponent perfect fluid are obtained. A two-component example:
dust + 5-brane, is considered.


title: An interpretation of Robinson-Trautman type N solutions

abstract:
  The Robinson-Trautman type N solutions, which describe expanding
gravitational waves, are investigated for all possible values of the
cosmological constant Lambda and the curvature parameter epsilon. The wave
surfaces are always (hemi-)spherical, with successive surfaces displaced in a
way which depends on epsilon. Explicit sandwich waves of this class are studied
in Minkowski, de Sitter or anti-de Sitter backgrounds. A particular family of
such solutions which can be used to represent snapping or decaying cosmic
strings is considered in detail, and its singularity and global structure is
presented.


title: Strings from Flux Tube Solutions in Kaluza-Klein Theory

abstract:
  We calculate dimensional reduction of gravitational flux tube solutions in
the scheme of Kaluza-Klein theory. The fifth dimension is compacified to a
region of Planck size. Assuming the width of the tube to be also Planck size we
obtain string-like object with physical fields originated from an initial 5D
metric. The dynamics of these fields is inner one.


title:
Conceptual tensions between quantum mechanics and general relativity:
  Are there experimental consequences, e.g., superconducting transducers
  between electromagnetic and gravitational radiation?

abstract:
  One of the conceptual tensions between quantum mechanics (QM) and general
relativity (GR) arises from the clash between the spatial nonseparability of
entangled states in QM, and the complete spatial separability of all physical
systems in GR, i.e., between the nonlocality implied by the superposition
principle, and the locality implied by the equivalence principle. Experimental
consequences of this conceptual tension will be explored for macroscopically
coherent quantum fluids, such as superconductors, superfluids, and atomic
Bose-Einstein condensates (BECs), subjected to tidal and Lense-Thirring fields
arising from gravitational radiation. A Meissner-like effect is predicted, in
which the Lense-Thirring field is expelled from the bulk of a quantum fluid.
Superconductors are predicted to be macroscopic quantum gravitational antennas
and transducers, which can directly convert upon reflection a beam of
quadrupolar electromagnetic radiation into gravitational radiation, and vice
versa, and thus serve as both sources and receivers of gravitational waves. An
estimate of the transducer conversion efficiency on the order of unity comes
out of the Ginzburg-Landau theory for an extreme type II, dissipationless
superconductor with minimal coupling to weak gravitational and electromagnetic
radiation fields, whose frequency is smaller than the BCS gap frequency, thus
satisfying the quantum adiabatic theorem. The concept of ``the impedance of
free space for gravitational plane waves'' is introduced, and leads to a
natural impedance-matching process, in which the two kinds of radiation fields
are impedance-matched to each other around a hundred coherence lengths beneath
the surface of the superconductor. A simple, Hertz-like experiment has been
performed to test these ideas, and preliminary results will be reported.


title:
Motion of charged particles around a rotating black hole in a magnetic
  field

abstract:
  We study the effects of an external magnetic field, which is assumed to be
uniform at infinity, on the marginally stable circular motion of charged
particles in the equatorial plane of a rotating black hole. We show that the
magnetic field has its greatest effect in enlarging the region of stability
towards the event horizon of the black hole. Using the Hamilton-Jacobi
formalism we obtain the basic equations governing the marginal stability of the
circular orbits and their associated energies and angular momenta. As
instructive examples, we review the case of the marginal stability of the
circular orbits in the Kerr metric, as well as around a Schwarzschild black
hole in a magnetic field. For large enough values of the magnetic field around
a maximally rotating black hole we find the limiting analytical solutions to
the equations governing the radii of marginal stability. We also show that the
presence of a strong magnetic field provides the possibility of relativistic
motions in both direct and retrograde innermost stable circular orbits around a
Kerr black hole.


title:
On the static solutions in gravity with massive scalar field in three
  dimensions

abstract:
  We investigate circularly symmetric static solutions in three-dimensional
gravity with a minimally coupled massive scalar field. We integrate numerically
the field equations assuming asymptotic flatness, where black holes do not
exist and a naked singularity is present. We also give a brief review on the
massless cases with cosmological constant.


title: The history of the cosmological constant problem

abstract:
  The interesting early history of the cosmological term is reviewed, beginning
with its introduction by Einstein in 1917 and ending with two papers of
Zel'dovich, shortly before the advent of spontaneously broken gauge theories.
Beside classical aspects, I shall also mention some unpublished early remarks
by Pauli on possible contributions of vacuum energies in quantum field theory.


title: Possible time variations of G in scalar-tensor theories of gravity

abstract:
  We estimate the possible variations of the gravitational constant G in the
framework of a generalized (Bergmann-Wagoner-Nordtvedt) scalar-tensor theory of
gravity on the basis of the field equations, without using their special
solutions. Specific estimates are essentially related to the values of other
cosmological parameters (the Hubble and acceleration parameters, the dark
matter density etc.), but the values of G-dot/G compatible with modern
observations do not exceed 10^{-12}.


title:
New Photodetection Method Using Unbalanced Sidebands for Squeezed
  Quantum Noise in Gravitational Wave Interferometer

abstract:
  Homodyne detection is one of the ways to circumvent the standard quantum
limit for a gravitational wave detector. In this paper it will be shown that
the same quantum-non-demolition effect using homodyne detection can be realized
by heterodyne detection with unbalanced RF sidebands. Furthermore, a broadband
quantum-non-demolition readout scheme can also be realized by the unbalanced
sideband detection.


title: Cosmic Evolution and Primordial Black Hole Evaporation

abstract:
  A cosmological model in which primordial black holes (PBHs) are present in
the cosmic fluid at some instant t=t_0 is investigated. The time t_0 is
naturally identified with the end of the inflationary period. The PBHs are
assumed to be nonrelativistic in the comoving fluid, to have the same mass, and
may be subject to evaporation for t>t_0. Our present work is related to an
earlier paper of Zimdahl and Pavon [Phys. Rev. D {\bf 58}, 103506 (1998)], but
in contradistinction to these authors we assume that the (negative) production
rate of the PBHs is zero. This assumption appears to us to be more simple and
more physical. Consequences of the formalism are worked out. In particular, the
four-divergence of the entropy four-vector in combination with the second law
in thermodynamics show in a clear way how the the case of PBH evaporation
corresponds to a production of entropy. Accretion of radiation onto the black
holes is neglected. We consider both a model where two different sub-fluids
interact, and a model involving one single fluid only. In the latter case an
effective bulk viscosity naturally appears in the formalism.


title: Quantum vs stochastic processes and the role of complex numbers

abstract:
  We argue that the complex numbers are an irreducible object of quantum
probability. This can be seen in the measurements of geometric phases that have
no classical probabilistic analogue. Having complex phases as primitive
ingredient implies that we need to accept non-additive probabilities. This has
the desirable consequence of removing constraints of standard theorems about
the possibility of describing quantum theory with commutative variables.
Motivated by the formalism of consistent histories and keeping an analogy with
the theory of stochastic processes, we develop a (statistical) theory of
quantum processes. They are characterised by the introduction of a "density
matrix" on phase space paths -thus including phase information- and fully
reproduce quantum mechanical predictions. In this framework wecan write quantum
differential equations, that could be interpreted as referring to a single
system (in analogy to Langevin's equation). We describe a reconstruction
theorem by which a quantum process can yield the standard Hilbert space
structure if the Markov property is imposed. Finally, we discuss the relevance
of our iresults for the interpretation of quantum theory (a sample space if
possible if probabilities are non-additive) and quantum gravity (the Hilbert
space arises after the consideration of a background causal structure).


title: Extremal Isolated Horizons: A Local Uniqueness Theorem

abstract:
  We derive all the axi-symmetric, vacuum and electrovac extremal isolated
horizons. It turns out that for every horizon in this class, the induced metric
tensor, the rotation 1-form potential and the pullback of the electromagnetic
field necessarily coincide with those induced by the monopolar, extremal
Kerr-Newman solution on the event horizon. We also discuss the general case of
a symmetric, extremal isolated horizon. In particular, we analyze the case of a
two-dimensional symmetry group generated by two null vector fields. Its
relevance to the classification of all the symmetric isolated horizons,
including the non-extremal once, is explained.


title: The horizon and its charges in the first order gravity

abstract:
  In this work the algebra of charges of diffeomorphisms at the horizon of
generic black holes is analyzed within first order gravity. This algebra
reproduces the algebra of diffeomorphisms at the horizon, (Diff(S^1)), without
central extension.


title:
Orbital evolution of a test particle around a black hole: higher-order
  corrections

abstract:
  We study the orbital evolution of a radiation-damped binary in the extreme
mass ratio limit, and the resulting waveforms, to one order beyond what can be
obtained using the conservation laws approach. The equations of motion are
solved perturbatively in the mass ratio (or the corresponding parameter in the
scalar field toy model), using the self force, for quasi-circular orbits around
a Schwarzschild black hole. This approach is applied for the scalar model.
Higher-order corrections yield a phase shift which, if included, may make
gravitational-wave astronomy potentially highly accurate.


title: Analog of the Fizeau Effect in an Effective Optical Medium

abstract:
  Using a new approach, we propose an analog of the Fizeau effect for massive
and massless particles in an effective optical medium derived from the static,
spherically symmetric gravitational field. The medium is naturally perceived as
a dispersive medium by matter de Broglie waves. Several Fresnel drag
coefficients are worked out, with appropriate interpretations of the
wavelengths used. In two cases, it turns out that the coefficients become
independent of the wavelength even if the equivalent medium itself is
dispersive. A few conceptual issues are also addressed in the process of
derivation. It is shown that some of our results complement recent works
dealing with real fluid or optical black holes.


title: Regge Calculus in Teleparallel Gravity

abstract:
  In the context of the teleparallel equivalent of general relativity, the
Weitzenbock manifold is considered as the limit of a suitable sequence of
discrete lattices composed of an increasing number of smaller an smaller
simplices, where the interior of each simplex (Delaunay lattice) is assumed to
be flat. The link lengths between any pair of vertices serve as independent
variables, so that torsion turns out to be localized in the two dimensional
hypersurfaces (dislocation triangle, or hinge) of the lattice. Assuming that a
vector undergoes a dislocation in relation to its initial position as it is
parallel transported along the perimeter of the dual lattice (Voronoi polygon),
we obtain the discrete analogue of the teleparallel action, as well as the
corresponding simplicial vacuum field equations.


title: Bianchi type I cosmology and the Euler-Calogero-Sutherland model

abstract:
  The Bianchi type I cosmological model is brought into a form where the
evolution of observables is governed by the unconstrained Hamiltonian that
coincides with the Hamiltonian describing the relative motion of particles in
the integrable three-body hyperbolic Euler-Calogero-Sutherland system.


title: The Doomsday Argument, Consciousness and Many Worlds

abstract:
  The doomsday argument is a probabilistic argument that claims to predict the
total lifetime of the human race. By examining the case of an individual
lifetime, I conclude that the argument is fundamentally related to
consciousness. I derive a reformulation stating that an infinite conscious
lifetime is not possible even in principle. By considering a hypothetical
conscious computer, running a non-terminating program, I deduce that
consciousness cannot be generated by a single set of deterministic laws.
Instead, I hypothesize that consciousness is generated by a superposition of
brain states that is simultaneously associated with many quasi-classical
histories, each following a different set of deterministic laws. I generalize
the doomsday argument and discover that it makes no prediction in this case.
Thus I conclude that the very fact of our consciousness provides us with
evidence for a many-worlds interpretation of reality in which our future is not
predictable using anthropic reasoning.


title: Degeneracy in exotic gravitational lensing

abstract:
  We present three different theoretically foreseen, but unusual, astrophysical
situations where the gravitational lens equation ends up being the same, thus
producing a degeneracy problem. These situations are (a) the case of
gravitational lensing by exotic stresses (matter violating the weak energy
condition and thus having a negative mass, particular cases of wormholes
solutions can be used as an example), (b) scalar field gravitational lensing
  (i.e. when considering the appearance of a scalar charge in the lensing
scenario), and (c) gravitational lensing in closed universes (with
antipodes).The reasons that lead to this degeneracy in the lens equations, the
possibility of actually encountering it in the real universe, and eventually
the ways to break it, are discussed.


title: Irreversible Processes in Inflationary Cosmological Models

abstract:
  By using the thermodynamic theory of irreversible processes and Einstein
general relativity, a cosmological model is proposed where the early universe
is considered as a mixture of a scalar field with a matter field. The scalar
field refers to the inflaton while the matter field to the classical particles.
The irreversibility is related to a particle production process at the expense
of the gravitational energy and of the inflaton energy. The particle production
process is represented by a non-equilibrium pressure in the energy-momentum
tensor. The non-equilibrium pressure is proportional to the Hubble parameter
and its proportionality factor is identified with the coefficient of bulk
viscosity. The dynamic equations of the inflaton and the Einstein field
equations determine the time evolution of the cosmic scale factor, the Hubble
parameter, the acceleration and of the energy densities of the inflaton and
matter. Among other results it is shown that in some regimes the acceleration
is positive which simulates an inflation. Moreover, the acceleration decreases
and tends to zero in the instant of time where the energy density of matter
attains its maximum value.


title:
Effect of Earth's rotation on the trajectories of free-fall bodies in
  Equivalence Principle Experiment

abstract:
  Owing to Earth's rotation a free-fall body would move in an elliptical orbit
rather than along a straight line forward to the center of the Earth. In this
paper on the basis of the theory for spin-spin coupling between macroscopic
rotating bodies we study violation of the equivalence principle from
long-distance free-fall experiments by means of a rotating ball and a
non-rotating sell. For the free-fall time of 40 seconds, the difference between
the orbits of the two free-fall bodies is of the order of 10^{-9}cm which could
be detected by a SQUID magnetometer owing to such a magnetometer can be used to
measure displacements as small as 10^{-13} centimeters.


title: Dirac equation in spacetimes with torsion and non-metricity

abstract:
  Dirac equation is written in a non-Riemannian spacetime with torsion and
non-metricity by lifting the connection from the tangent bundle to the spinor
bundle over spacetime. Foldy-Wouthuysen transformation of the Dirac equation in
a Schwarzschild background spacetime is considered and it is shown that both
the torsion and non-metricity couples to the momentum and spin of a massive,
spinning particle. However, the effects are small to be observationally
significant.


title: Particle motion in electro-magnetic and gravitational pp-waves

abstract:
  We discuss the motion of neutral and charged particles in a plane
electro-magnetic wave and its accompanying gravitational field.


title: Chaos in a Relativistic 3-body Self-Gravitating System

abstract:
  We consider the 3-body problem in relativistic lineal gravity and obtain an
exact expression for its Hamiltonian and equations of motion. While
general-relativistic effects yield more tightly-bound orbits of higher
frequency compared to their non-relativistic counterparts, as energy increases
we find in the equal-mass case no evidence for either global chaos or a
breakdown from regular to chaotic motion, despite the high degree of
non-linearity in the system. We find numerical evidence for a countably
infinite class of non-chaotic orbits, yielding a fractal structure in the outer
regions of the Poincare plot.


title:
Spatially Averaged Quantum Inequalities Do Not Exist in Four-Dimensional
  Spacetime

abstract:
  We construct a particular class of quantum states for a massless, minimally
coupled free scalar field which are of the form of a superposition of the
vacuum and multi-mode two-particle states. These states can exhibit local
negative energy densities. Furthermore, they can produce an arbitrarily large
amount of negative energy in a given region of space at a fixed time. This
class of states thus provides an explicit counterexample to the existence of a
spatially averaged quantum inequality in four-dimensional spacetime.


title: Independent Confirmation of the Pioneer 10 Anomalous Acceleration

abstract:
  I perform an independent analysis of radio Doppler tracking data from the
Pioneer 10 spacecraft for the time period 1987-1994. All of the tracking data
were taken from public archive sources, and the analysis tools were developed
independently by myself. I confirm that an apparent anomalous acceleration is
acting on the Pioneer 10 spacecraft, which is not accounted for by present
physical models of spacecraft navigation. My best fit value for the
acceleration, including corrections for systematic biases and uncertainties, is
(8.60 +/- 1.34) x 10^{-8} cm s^{-2}, directed towards the Sun. This value
compares favorably to previous results. I examine the robustness of my result
to various perturbations of the analysis method, and find agreement to within
+/- 5%. The anomalous acceleration is reasonably constant with time, with a
characteristic variation time scale of > 70 yr. Such a variation timescale is
still too short to rule out on-board thermal radiation effects, based on this
particular Pioneer 10 data set.


title: Bouncing Braneworlds

abstract:
  We study cosmological braneworld models with a single timelike extra
dimension. Such models admit the intriguing possibility that a contracting
braneworld experiences a natural bounce without ever reaching a singular state.
This feature persists in the case of anisotropic braneworlds under some
additional and not very restrictive assumptions. Generalizing our study to
braneworld models containing an induced brane curvature term, we find that a
FRW-type singularity is once again absent if the bulk extra dimension is
timelike. In this case, the universe either has a non-singular origin or
commences its expansion from a quasi-singular state during which both the
Hubble parameter and the energy density and pressure remain finite while the
curvature tensor diverges. The non-singular and quasi-singular behaviour which
we have discovered differs both qualitatively and quantitatively from what is
usually observed in braneworld models with spacelike extra dimensions and could
have interesting cosmological implications.


title:
Scaling law in signal recycled laser-interferometer gravitational-wave
  detectors

abstract:
  By mapping the signal-recycling (SR) optical configuration to a three-mirror
cavity, and then to a single detuned cavity, we express SR optomechanical
dynamics, input--output relation and noise spectral density in terms of only
three characteristic parameters: the (free) optical resonant frequency and
decay time of the entire interferometer, and the laser power circulating in arm
cavities. These parameters, and therefore the properties of the interferometer,
are invariant under an appropriate scaling of SR-mirror reflectivity, SR
detuning, arm-cavity storage time and input power at beamsplitter. Moreover, so
far the quantum-mechanical description of laser-interferometer
gravitational-wave detectors, including radiation-pressure effects, was only
obtained at linear order in the transmissivity of arm-cavity internal mirrors.
We relax this assumption and discuss how the noise spectral densities change.


title: Practical speed meter designs for QND gravitational-wave interferometers

abstract:
  In the quest to develop viable designs for third-generation optical
interferometric gravitational-wave detectors (e.g., LIGO-III and EURO), one
strategy is to monitor the relative momentum or speed of the test-mass mirrors,
rather than monitoring their relative position. A previous paper analyzed a
straightforward but impractical design for a {\it speed-meter interferometer}
that accomplishes this. This paper describes some practical variants of
speed-meter interferometers. Like the original interferometric speed meter,
these designs {\it in principle} can beat the gravitational-wave standard
quantum limit (SQL) by an arbitrarily large amount, over an arbitrarily wide
range of frequencies. These variants essentially consist of a Michelson
interferometer plus an extra "sloshing" cavity that sends the signal back into
the interferometer with opposite phase shift, thereby cancelling the position
information and leaving a net phase shift proportional to the relative
velocity. {\it In practice}, the sensitivity of these variants will be limited
by the maximum light power $W_{\rm circ}$ circulating in the arm cavities that
the mirrors can support and by the leakage of vacuum into the optical train at
dissipation points. In the absence of dissipation and with a squeezed vacuum of
power squeeze factor ~ 0.1 inserted into the output port so as to keep the
circulating power down, the SQL can be beat by a factor 10 in power at all
frequencies below some chosen $f_{\rm opt}\simeq 100$ Hz, with $W_{\rm
circ}\simeq 800$ kW. Estimates are given of the amount by which vacuum leakage
at dissipation points will debilitate this sensitivity; these losses are 10% or
less over most of the frequency range of interest.


title:
General Relativistic Effects on Quantum Interference and the Principle
  of Equivalence

abstract:
  Using a novel approach, we work out the general relativistic effects on the
quantum interference of de Broglie waves associated with thermal neutrons. The
unified general formula is consistent with special relativistic results in the
flat space limit. It is also shown that the exact geodesic equation contains in
a natural way a gravitational analog of the Aharonov-Bohm effect. We work out
two examples, one in general relativity and the other in heterotic string
theory, in order to obtain the first order gravitational correction terms to
the quantum fringe shift. Measurement of these terms is closely related to the
validity of the equivalence principle at a quantum level.


title:
Sagnac Interferometer as a Speed-Meter-Type, Quantum-Nondemolition
  Gravitational-Wave Detector

abstract:
  According to quantum measurement theory, "speed meters" -- devices that
measure the momentum, or speed, of free test masses -- are immune to the
standard quantum limit (SQL). It is shown that a Sagnac-interferometer
gravitational-wave detector is a speed meter and therefore in principle it can
beat the SQL by large amounts over a wide band of frequencies. It is shown,
further, that, when one ignores optical losses, a signal-recycled Sagnac
interferometer with Fabry-Perot arm cavities has precisely the same
performance, for the same circulating light power, as the Michelson speed-meter
interferometer recently invented and studied by P. Purdue and the author. The
influence of optical losses is not studied, but it is plausible that they be
fairly unimportant for the Sagnac, as for other speed meters. With squeezed
vacuum (squeeze factor $e^{-2R} = 0.1$) injected into its dark port, the
recycled Sagnac can beat the SQL by a factor $ \sqrt{10} \simeq 3$ over the
frequency band $10 {\rm Hz} \alt f \alt 150 {\rm Hz}$ using the same
circulating power $I_c\sim 820$ kW as is used by the (quantum limited)
second-generation Advanced LIGO interferometers -- if other noise sources are
made sufficiently small. It is concluded that the Sagnac optical configuration,
with signal recycling and squeezed-vacuum injection, is an attractive candidate
for third-generation interferometric gravitational-wave detectors (LIGO-III and
EURO).


title: Teleparallel Equivalent of Non-Abelian Kaluza-Klein Theory

abstract:
  Based on the equivalence between a gauge theory for the translation group and
general relativity, a teleparallel version of the non-abelian Kaluza-Klein
theory is constructed. In this theory, only the fiber-space turns out to be
higher-dimensional, spacetime being kept always four-dimensional. The resulting
model is a gauge theory that unifies, in the Kaluza-Klein sense, gravitational
and gauge fields. In contrast to the ordinary Kaluza-Klein models, this theory
defines a natural length-scale for the compact sub-manifold of the fiber space,
which is shown to be of the order of the Planck length.


title: Exact solutions of Dirac equation on a 2D gravitational background

abstract:
  We obtain classes of two dimensional static Lorentzian manifolds, which
through the supersymmetric formalism of quantum mechanics admit the exact
solvability of Dirac equation on these curved backgrounds. Specially in the
case of a modified supersymmetric harmonic oscillator the wave function and
energy spectrum of Dirac equation is given explicitly.


title: Classical gauge theory of gravity

abstract:
  The classical theory of gravity is formulated as a gauge theory on a frame
bundle with spontaneous symmetry breaking caused by the existence of Dirac
fermionic fields. The pseudo-Riemannian metric (tetrad field) is the
corresponding Higgs field. We consider two variants of this theory. In the
first variant, gravity is represented by the pseudo-Riemannian metric as in
general relativity theory; in the second variant, it is represented by the
effective metric as in the Logunov relativistic theory of gravity. The
configuration space, Dirac operator, and Lagrangians are constructed for both
variants.


title: Entropy of A Scalar Field In (3 + 1)-dimensional Taub-NUT Space-Time

abstract:
  In this article we discuss a few aspects of the space-time description of
fields and particles. In sectionn II and III we demonstrate that fields are as
fundamental as particles. In section IV we discuss non-equivalence of the
Schwarzschild coordinates and the Kruskal-Szekeres coordinates. In section V we
discuss that it is not possible to define causal structure in discrete
space-time manifolds. In App.B we show that a line is not just a collection of
points and we will have to introduce one-dimensional line-intervals as
fundamental geometric elements. Similar discussions are valid for area and
volume-elements. In App.C and App.D we make a comparative study of Quantum
Field Theory and Quantum Mechanics and contradictions associated with
probabilistics interpretation of these theories with space-time dimensional
analysis. In App.E and App.F we discuss the geometry of Robertson-Walker model
and electrostatic behavior of dielectrics respectively. In Sup.I we discuss the
regularity of Spin-Spherical harmonics and also derive an energy-spectrum which
is free of back-reaction problem. In Sup.II we discuss that in general the
integral version of Gauss's divergence law in Electrodynamics is not valid and
rederive Gauss's law and Ampere's law. We also show that under duality
transformation magnetic charge conservation law do not remain time reversal
symmetric. In Sup.III we derive the complete equation for viscous compressible
fluids and make a few comments regarding some cotradictions associated with
boundary conditions for fluid dynamics. In Sup.IV we discuss a few aspects on
double slit interference experiments. We conclude this article with a few
questions in Sup.V.


title:
The One-Way Speed of Light on Rotating Earth and the Definition of the
  Meter

abstract:
  Since 1983 the meter is defined to be the "length of the path travelled by
light in vacuum during a time interval of 1/299792458 of a second". If there
was exactly one single consistent method of synchronizing clocks, or if all
corresponding methods were equivalent, one could infer from the validity of
special relativity theory on a definite value of the one-way speed of light c
in inertial frames.
  It is true that sufficiently slowly separated clocks always show middle in
time reflection when sending and receiving light signals. But a simple
consideration proves that the one-way speed of light is not a constant in
rotating systems, in principle detectable with only one clock.
  On basis of a new internal synchronization method, this also affects all
local inertial frames on rotating Earth, too, violating an absolute constancy
of the one-way speed of light. This is not a contradiction to Einstein's
original theory of relativity but to the present definition of the meter. Based
on the constant local average value c of light going there and back, however, a
modification for the definition of the meter is suggested, which would not
depend on synchronization of any distant clocks.
  Appendix: FitzGerald-Lorentz contraction and time dilation, according to
Einstein's generally accepted understanding, should be purely kinematic effects
and would not need any dynamic explanation. But an analysis of Ehrenfest's
paradox of the rotating disk shows that it is not possible to separate exactly
relativistic kinematics from dynamics. The necessity of such a fundamental
restriction is well known for a long time - though only from quantum mechanics
till now.


title:
On a Pregeometric Origin for Spacetime Dimensionality and Metric
  Structure

abstract:
  Motivated by Wheeler's bottom up pregeometry, we introduce a pregeometric
approach that does not assume Wheeler's probability amplitudes for establishing
spacetime neighborhoods. Rather, a non-trivial metric is produced via the
concept of a uniformity base, which is generated with discrete topological
groups over some arbitrary fundamental, denumerable set. We show how the
concept of entourage multiplication for the elements of our uniformity base
mirrors the underlying group structure. This fact is then exploited to create
entourage sequences of maximal length, whence a fine metric structure. The
resulting metric structure is, for certain group structures, consistent with
E4-embeddable graphs. Examples over Z2 x Z4, D4, Z6, D3, Z8, and Z5 are
provided. Euclidean embeddability over Z7 and Q8 is discussed. Unlike the
statistical approaches typical of graph theory, this method generates
dimensionality over low-order sets. Possible applications to the pregeometric
modeling of quantum stochasticity and non-locality/non-separability, wave
function collapse, and the M4 structure of spacetime are provided in the
context of Z2 x Z2 x Z4.


title: Ultralight particle creation during fresh inflation

abstract:
  I study ultralight particle creation which becomes from the Yukawa
interaction between the inflaton and the thermal bath during fresh inflation.
Particle creation is important in the first stages of fresh inflation, when the
nonequilibrium thermal effects are important. I find that the number density of
the ultralight created particles is more important as the scale factor growth
rate is more large (i.e., for $p$ large -- $a \sim t^p$). Ultralight boson
fields created during fresh inflation could be an alternative mechanism to
cosmological constant to explain the discrepancy between the observed $\Omega_m
\simeq 0.2$ and $\Omega_{tot} \simeq 1$, predicted by inflationary models.