19,424 research outputs found
Some Comments on the Spin of the Chern - Simons Vortices
We compute the spin of both the topological and nontopological solitons of
the Chern - Simons - Higgs model by using our approach based on constrained
analysis. We also propose an extension of our method to the non - relativistic
Chern - Simons models. The spin formula for both the relativistic and
nonrelativistic theories turn out to be structurally identical. This form
invariance manifests the topological origin of the Chern - Simons term
responsible for inducing fractional spin. Also, some comparisons with the
existing results are done.Comment: 12 pages, Late
Spin of Chern-Simons vortices
We discuss a novel method of obtaining the fractional spin of abelian and
nonabelian Chern-Simons vortices. This spin is interpreted as the difference
between the angular momentum obtained by modifying Schwinger's energy momentum
tensor by the Gauss constraint, and the canonical (Noether) angular momentum.
It is found to be a boundary term depending only on the gauge field and, hence,
is independent of the matter sector to which the Chern-Simons term couples.
Addition of the Maxwell term does not alter the fractional spin.Comment: 11 pages, Latex file, no figure
Contribution from unresolved discrete sources to the Extragalactic Gamma-Ray Background (EGRB)
The origin of the extragalactic gamma-ray background (EGRB) is still an open
question, even after nearly forty years of its discovery. The emission could
originate from either truly diffuse processes or from unresolved point sources.
Although the majority of the 271 point sources detected by EGRET (Energetic
Gamma Ray Experiment Telescope) are unidentified, of the identified sources,
blazars are the dominant candidates. Therefore, unresolved blazars may be
considered the main contributor to the EGRB, and many studies have been carried
out to understand their distribution, evolution and contribution to the EGRB.
Considering that gamma-ray emission comes mostly from jets of blazars and that
the jet emission decreases rapidly with increasing jet to line-of-sight angle,
it is not surprising that EGRET was not able to detect many large inclination
angle active galactic nuclei (AGNs). Though Fermi could only detect a few large
inclination angle AGNs in the first three months' survey, it is expected to
detect many such sources in the near future. Since non-blazar AGNs are expected
to have higher density as compared to blazars, these could also contribute
significantly to the EGRB. In this paper we discuss contributions from
unresolved discrete sources including normal galaxies, starburst galaxies,
blazars and off-axis AGNs to the EGRB.Comment: 11 pages, 4 figures, accepted for publication in RA
Ultrapure glass optical waveguide development in microgravity by the sol-gel process
Multicomponent, homogeneous, noncrystalline oxide gels can be prepared by the sol-gel process and these gels are promising starting materials for melting glasses in the space environment. The sol-gel process referred to here is based on the polymerization reaction of alkoxysilane with other metal alkoxy compounds or suitable metal salts. Many of the alkoxysilanes or other metal alkoxides are liquids and thus can be purified by distillation. The use of gels offers several advantages such as high purity and lower melting times and temperatures. The sol-gel process is studied for utilization in the preparation of multicomponent ultrapure glass batches for subsequent containerless melting of the batches in space to prepare glass blanks for optical waveguides
Analytical approach to the transition to thermal hopping in the thin- and thick-wall approximations
The nature of the transition from the quantum tunneling regime at low
temperatures to the thermal hopping regime at high temperatures is investigated
analytically in scalar field theory. An analytical bounce solution is
presented, which reproduces the action in the thin-wall as well as thick-wall
limits. The transition is first order for the case of a thin wall while for the
thick wall case it is second order.Comment: Latex file, 22 pages, 4 Postscript figure
Duality and cosmological compactification of superstrings with unbroken supersymmetry
The cosmological compactification of D=10, N=1 supergravity-super-Yang-Mills
theory obtained from superstring theory is studied. The constraint of unbroken
N=1 supersymmetry is imposed. A duality transformation is performed on the
resulting consistency conditions. The original equations as well as the
transformed equations are solved numerically to obtain new configurations with
a nontrivial scale factor and a dynamical dilaton. It is shown that various
classes of solutions are possible, which include cosmological solutions with no
initial singularity.Comment: Latex2e file, 24 pages including 10 figures as tex file
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