6,640 research outputs found
Multipole moments in Kaluza-Klein theories
This paper contains discussion of the problem of motion of extended i.e. non
point test bodies in multidimensional space. Extended bodies are described in
terms of so called multipole moments. Using approximated form of equations of
motion for extended bodies deviation from geodesic motion is derived. Results
are applied to special form of space-time.Comment: 11 pages, AMS-TeX, few misprints corrected, to appear in Classical
and Quantum Gravit
Semileptonic charm decays D \to \pi l \nu_{\l} and from QCD Light-Cone Sum Rules
We present a new calculation of the and form factors from
QCD light-cone sum rules. The scheme for the -quark mass is
used and the input parameters are updated. The results are , and
. Combining the calculated form
factors with the latest CLEO data, we obtain and
where the first and second errors are of experimental origin and the third
error is due to the estimated uncertainties of our calculation. We also
evaluate the form factors and and predict the slope
parameters at . Furthermore, calculating the form factors from the sum
rules at , we fit them to various parameterizations. After analytic
continuation, the shape of the form factors in the whole
semileptonic region is reproduced, in a good agreement with experiment.Comment: 34 pages, 5 figure
Form Factors and Strong Couplings of Heavy Baryons from QCD Light-Cone Sum Rules
We derive QCD light-cone sum rules for the hadronic matrix elements of the
heavy baryon transitions to nucleon. In the correlation functions the
and -baryons are interpolated by three-quark
currents and the nucleon distribution amplitudes are used. To eliminate the
contributions of negative parity heavy baryons, we combine the sum rules
obtained from different kinematical structures. The results are then less
sensitive to the choice of the interpolating current. We predict the
form factor and calculate the widths of the and decays. Furthermore, we consider double
dispersion relations for the same correlation functions and derive the
light-cone sum rules for the and strong
couplings. Their predicted values can be used in the models of charm production
in collisions.Comment: 45 pages, 3 figure
Geodesic Deviation in Kaluza-Klein Theories
We study in detail the equations of the geodesic deviation in
multidimensional theories of Kaluza-Klein type. We show that their
4-dimensional space-time projections are identical with the equations obtained
by direct variation of the usual geodesic equation in the presence of the
Lorentz force, provided that the fifth component of the deviation vector
satisfies an extra constraint derived here.Comment: 5 pages, Revtex, 1 figure. To appear in Phys. Rev. D (Brief Report
A multi-wavelength study of a double intermediate-mass protostar - from large-scale structure to collimated jets
(abridged) We study a previously discovered protostellar source that is
deeply embedded and drives an energetic molecular outflow. The source, UYSO1,
is located close to IRAS 07029-1215 at a distance of ~1 kpc. The
multi-wavelength observations resulted in the detection of a double
intermediate-mass protostar at the location of UYSO1. In addition to the
associated molecular outflow, with a projected size of 0.25 pc, two
intersecting near-infrared jets with projected sizes of 0.4 pc and 0.2 pc were
found. However, no infrared counterparts to the driving sources could be
detected in sensitive near- to far-infrared observations. In interferometric
millimeter observations, UYSO1 was resolved into two continuum sources with
high column densities and gas masses of 3.5 Mo and 1.2 Mo, with a linear
separation of 4200 AU. We report the discovery of a H2O maser toward one of the
two sources. The total luminosity is roughly estimated to be ~50 Lo, shared by
the two components, one of which is driving the molecular outflow that has a
dynamical timescale of less than a few thousand years. The jets of the two
individual components are not aligned. Submillimeter observations show that the
region lacks typical hot-core chemistry. We thus find two protostellar objects,
whose associated circumstellar and parent core masses are high enough to
suggest that they may evolve into intermediate-mass stars. This is corroborated
by their association with a very massive and energetic CO outflow, suggesting
high protostellar accretion rates. The short dynamical timescale of the
outflow, the pristine chemical composition of the cloud core and absence of hot
core tracers, the absence of detectable radio continuum emission, and the very
low protostellar luminosity argue for an extremely early evolutionary stage.Comment: 10 pages, 10 figures, accepted for publication in A&A; minor changes:
typos corrected, revised argument in Section
First Detection of Millimeter Dust Emission from Brown Dwarf Disks
We report results from the first deep millimeter continuum survey targeting
Brown Dwarfs (BDs). The survey led to the first detection of cold dust in the
disks around two young BDs (CFHT-BD-Tau 4 and IC348 613), with deep JCMT and
IRAM observations reaching flux levels of a few mJy. The dust masses are
estimated to be a few Earth masses assuming the same dust opacities as usually
applied to TTauri stars.Comment: 5 pages, accepted for ApJ
The Collapse of Large Extra Dimensions
In models of spacetime that are the product of a four-dimensional spacetime
with an ``extra'' dimension, there is the possibility that the extra dimension
will collapse to zero size, forming a singularity. We ask whether this collapse
is likely to destroy the spacetime. We argue, by an appeal to the
four-dimensional cosmic censorship conjecture, that--at least in the case when
the extra dimension is homogeneous--such a collapse will lead to a singularity
hidden within a black string. We also construct explicit initial data for a
spacetime in which such a collapse is guaranteed to occur and show how the
formation of a naked singularity is likely avoided.Comment: Uses revtex
The electronic structure of amorphous silica: A numerical study
We present a computational study of the electronic properties of amorphous
SiO2. The ionic configurations used are the ones generated by an earlier
molecular dynamics simulations in which the system was cooled with different
cooling rates from the liquid state to a glass, thus giving access to
glass-like configurations with different degrees of disorder [Phys. Rev. B 54,
15808 (1996)]. The electronic structure is described by a tight-binding
Hamiltonian. We study the influence of the degree of disorder on the density of
states, the localization properties, the optical absorption, the nature of
defects within the mobility gap, and on the fluctuations of the Madelung
potential, where the disorder manifests itself most prominently. The
experimentally observed mismatch between a photoconductivity threshold of 9 eV
and the onset of the optical absorption around 7 eV is interpreted by the
picture of eigenstates localized by potential energy fluctuations in a mobility
gap of approximately 9 eV and a density of states that exhibits valence and
conduction band tails which are, even in the absence of defects, deeply located
within the former band gap.Comment: 21 pages of Latex, 5 eps figure
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
More then forty years ago R.I. Pimenov introduced a new geometry --
semi-Riemannian one -- as a set of geometrical objects consistent with a
fibering He suggested the heuristic principle according to
which the physically different quantities (meter, second, coulomb etc.) are
geometrically modelled as space coordinates that are not superposed by
automorphisms. As there is only one type of coordinates in Riemannian geometry
and only three types of coordinates in pseudo-Riemannian one, a multiple
fibered semi-Riemannian geometry is the most appropriate one for the treatment
of more then three different physical quantities as unified geometrical field
theory.
Semi-Euclidean geometry with 1-dimensional fiber and
4-dimensional Minkowski space-time as a base is naturally interpreted as
classical electrodynamics. Semi-Riemannian geometry with the
general relativity pseudo-Riemannian space-time and 1-dimensional
fiber responsible for the electromagnetism, provides the unified field
theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where
the 5-th coordinate appears in nondegenerate Riemannian or pseudo-Riemannian
geometry, the theory based on semi-Riemannian geometry is free from defects of
the former. In particular, scalar field does not arise.
PACS: 04.50.Cd, 02.40.-k, 11.10.KkComment: 16 pages, 2 figures. Submited to Physics of Atomic Nucle
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