55,686 research outputs found
The vacuum preserving Lie algebra of a classical W-algebra
We simplify and generalize an argument due to Bowcock and Watts showing that
one can associate a finite Lie algebra (the `classical vacuum preserving
algebra') containing the M\"obius subalgebra to any classical
\W-algebra. Our construction is based on a kinematical analysis of the
Poisson brackets of quasi-primary fields. In the case of the \W_\S^\G-algebra
constructed through the Drinfeld-Sokolov reduction based on an arbitrary
subalgebra of a simple Lie algebra \G, we exhibit a natural
isomorphism between this finite Lie algebra and \G whereby the M\"obius
is identified with .Comment: 11 pages, BONN-HE-93-25, DIAS-STP-93-13. Some typos had been removed,
no change in formula
Studying Gaugino Mass in Semi-Direct Gauge Mediation
We study gaugino mass generation in the context of semi-direct gauge
mediation models, where the messengers are charged under both the hidden sector
and the standard model gauge groups while they do not play important roles in
dynamical supersymmetry breaking. We clarify the cancellation of the leading
contributions of the supersymmetry breaking effects to the gaugino mass in this
class of models in terms of the macroscopic effective theory of the hidden
sector dynamics. We also consider how to retrofit the model so that we obtain
the non-vanishing leading contribution to the gaugino mass.Comment: 14 page
Numerical Study on GRB-Jet Formation in Collapsars
Two-dimensional magnetohydrodynamic simulations are performed using the
ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB
jet, taking account of realistic equation of state, neutrino cooling and
heating processes, magnetic fields, and gravitational force from the central
black hole and self gravity. It is found that neutrino heating processes are
not so efficient to launch a jet in this study. It is also found that a jet is
launched mainly by B_\phi fields that are amplified by the winding-up effect.
However, since the ratio of total energy relative to the rest mass energy in
the jet is not so high as several hundred, we conclude that the jets seen in
this study are not be a GRB jet. This result suggests that general relativistic
effects, which are not included in this study, will be important to generate a
GRB jet. Also, the accretion disk with magnetic fields may still play an
important role to launch a GRB jet, although a simulation for much longer
physical time (\sim 10-100 s) is required to confirm this effect. It is shown
that considerable amount of 56Ni is synthesized in the accretion disk. Thus
there will be a possibility for the accretion disk to supply sufficient amount
of 56Ni required to explain the luminosity of a hypernova. Also, it is shown
that neutron-rich matter due to electron captures with high entropy per baryon
is ejected along the polar axis. Moreover, it is found that the electron
fraction becomes larger than 0.5 around the polar axis near the black hole by
\nu_e capture at the region. Thus there will be a possibility that r-process
and r/p-process nucleosynthesis occur at these regions. Finally, much neutrons
will be ejected from the jet, which suggests that signals from the neutron
decays may be observed as the delayed bump of afterglow or gamma-rays.Comment: 54 pages with 19 postscript figures. Accepted for publication in ApJ.
High resolution version is available at
http://www2.yukawa.kyoto-u.ac.jp/~nagataki/collapsar.pd
Explosive Nucleosynthesis in GRB Jets Accompanied by Hypernovae
Two-dimensional hydrodynamic simulations are performed to investigate
explosive nucleosynthesis in a collapsar using the model of MacFadyen and
Woosley (1999). It is shown that 56Ni is not produced in the jet of the
collapsar sufficiently to explain the observed amount of a hypernova when the
duration of the explosion is \sim 10 sec, which is considered to be the typical
timescale of explosion in the collapsar model. Even though a considerable
amount of 56Ni is synthesized if all explosion energy is deposited initially,
the opening angles of the jets become too wide to realize highly relativistic
outflows and gamma-ray bursts in such a case. From these results, it is
concluded that the origin of 56Ni in hypernovae associated with GRBs is not the
explosive nucleosynthesis in the jet. We consider that the idea that the origin
is the explosive nucleosynthesis in the accretion disk is more promising. We
also show that the explosion becomes bi-polar naturally due to the effect of
the deformed progenitor. This fact suggests that the 56Ni synthesized in the
accretion disk and conveyed as outflows are blown along to the rotation axis,
which will explain the line features of SN 1998bw and double peaked line
features of SN 2003jd. Some fraction of the gamma-ray lines from 56Ni decays in
the jet will appear without losing their energies because the jet becomes
optically thin before a considerable amount of 56Ni decays as long as the jet
is a relativistic flow. We show that abundance of nuclei whose mass number \sim
40 in the ejecta depends sensitively on the energy deposition rate. So it may
be determined by observations of chemical composition in metal poor stars which
model is the proper one as a model of a gamma-ray burst accompanied by a
hypernova.Comment: 29 pages with 16 figures. ApJ, accepte
New N=1 Extended Superconformal Algebras with Two and Three Generators
In this paper we consider extensions of the super Virasoro algebra by one and
two super primary fields. Using a non-explicitly covariant approach we compute
all SW-algebras with one generator of dimension up to 7 in addition to the
super Virasoro field. In complete analogy to W-algebras with two generators
most results can be classified using the representation theory of the super
Virasoro algebra. Furthermore, we find that the SW(3/2, 11/2)-algebra can be
realized as a subalgebra of SW(3/2, 5/2) at c = 10/7. We also construct some
new SW-algebras with three generators, namely SW(3/2, 3/2, 5/2), SW(3/2, 2, 2)
and SW(3/2, 2, 5/2).Comment: 30 pages (Plain TeX), BONN-HE-92-0
Dissipation of Magnetohydrodynamic Waves on Energetic Particles: Impact on Interstellar Turbulence and Cosmic Ray Transport
The physical processes involved in diffusion of Galactic cosmic rays in the
interstellar medium are addressed. We study the possibility that the nonlinear
MHD cascade sets the power-law spectrum of turbulence which scatters charged
energetic particles. We find that the dissipation of waves due to the resonant
interaction with cosmic ray particles may terminate the Kraichnan-type cascade
below wavelengths 10^13 cm. The effect of this wave dissipation has been
incorporated in the GALPROP numerical propagation code in order to asses the
impact on measurable astrophysical data. The energy-dependence of the
cosmic-ray diffusion coefficient found in the resulting self-consistent model
may explain the peaks in the secondary to primary nuclei ratios observed at
about 1 GeV/nucleon.Comment: 15 pages, 20 figures, 1 table, emulateapj.cls; To be published in ApJ
10 May 2006, v.64
Large-scale structure formation for power spectra with broken scale invariance
We have simulated the formation of large-scale structure arising from
COBE-normalized spectra computed by convolving a primordial double-inflation
perturbation spectrum with the CDM transfer function. Due to the broken scale
invariance ('BSI') characterizing the primordial perturbation spectrum, this
model has less small-scale power than the (COBE-normalized) standard CDM model.
The particle-mesh code (with cells and particles) includes a
model for thermodynamic evolution of baryons in addition to the usual
gravitational dynamics of dark matter. It provides an estimate of the local gas
temperature. In particular, our galaxy-finding procedure seeks peaks in the
distribution of gas that has cooled. It exploits the fact that ``cold"
particles trace visible matter better than average and thus provides a natural
biasing mechanism. The basic picture of large-scale structure formation in the
BSI model is the familiar hierarchical clustering scenario. We obtain particle
in cell statistics, the galaxy correlation function, the cluster abundance and
the cluster-cluster correlation function and statistics for large and small
scale velocity fields. We also report here on a semi-quantitative study of the
distribution of gas in different temperature ranges. Based on confrontation
with observations and comparison with standard CDM, we conclude that the BSI
scenario could represent a promising modification of the CDM picture capable of
describing many details of large-scale structure formation.Comment: 15 pages, Latex using mn.sty, uuencoded compressed ps-file with 15
figures by anonymous ftp to ftp://ftp.aip.de/incoming/mueller/bsi.u
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