2,518 research outputs found
The width of for large in chiral quark soliton model
In the chiral quark soliton model the smallness of width is due to
the cancellation of the coupling constants which are of different order in
. We show that taking properly into account the flavor structure of
relevant SU(3) representations for arbitrary number of colors enahnces the
nonleading term by an additional factor of , making the cancellation
consistent with the counting. Moreover, we show that, for the same
reason, width is suppressed by a group-theoretical factor with respect to and discuss the dependence of the
phase space factors for these two decays.Comment: 9 pages, 3 eps figures, in v2 reference added, minor typos correcte
Hyperon Beta-Decay and Axial Charges of the Lambda in view of Strongly Distorted Baryon Wave-Functions
Within the collective coordinate approach to chiral soliton models we suggest
that breaking of SU(3) flavor symmetry mainly resides in the baryon
wave-functions while the charge operators maintain a symmetric structure.
Sizable symmetry breaking in the wave-functions is required to reproduce the
observed spacing in the spectrum of the (1/2)^+ baryons. The matrix elements of
the flavor symmetric charge operators nevertheless yield g_A/g_V ratios for
hyperon beta-decay which agree with the empirical data approximately as well as
the successful F&D parameterization of the Cabibbo scheme. Demanding the
strangeness component in the nucleon to vanish in the two flavor limit of the
model, determines the structure of the singlet axial charge operator and yields
the various quark flavor components of the axial charge of the \Lambda-hyperon.
The suggested picture gains support from calculations in a realistic model
using pion and vector meson degrees of freedom to build up the soliton.Comment: 14 pages, minor revisions, paper accepted for publication in Nucl.
Phys.
Parton distributions in the chiral quark model: a continuum computation
We compute the parton distributions for the chiral quark model. We present a
new technique for performing such computations based on Green functions. This
approach avoids a discretization of the spectrum. It therefore does not need
any smoothing procedures.
The results are similar to those of other groups, however the distributions
peak at smaller .Comment: 19 pages, 8 Figures, LaTeX, some typos corrected, some additional
comments in the conclusion
Faddeev approach to the octet and decuplet baryons
A relativistic Faddeev model for the baryon octet is extended to treat the
baryon decuplet. We find that after determining the model parameters in the
mesonic sector the masses of both nucleon and delta deviate by less than 5\%
from the experimental data and show only a very weak dependence on the
constituent quark mass.Comment: 9 page
Magnetic Moments of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model
We investigate the magnetic moments of the SU(3) octet baryons in the
framework of the semibosonized Nambu--Jona--Lasinio model. The
rotational corrections and strange quark mass in linear order are taken
into account. We derive general relations between magnetic moments of the SU(3)
octet baryons, based on the symmetry of our model. These relations indicate
that higher order corrections such as and are
relatively small. The magnetic moments of the octet baryons predicted by our
model are quantitatively in a good agreement with experimental results within
about 15.Comment: 17 pages, RevTex, 1 postscript figur
Performance potential for simulating spin models on GPU
Graphics processing units (GPUs) are recently being used to an increasing
degree for general computational purposes. This development is motivated by
their theoretical peak performance, which significantly exceeds that of broadly
available CPUs. For practical purposes, however, it is far from clear how much
of this theoretical performance can be realized in actual scientific
applications. As is discussed here for the case of studying classical spin
models of statistical mechanics by Monte Carlo simulations, only an explicit
tailoring of the involved algorithms to the specific architecture under
consideration allows to harvest the computational power of GPU systems. A
number of examples, ranging from Metropolis simulations of ferromagnetic Ising
models, over continuous Heisenberg and disordered spin-glass systems to
parallel-tempering simulations are discussed. Significant speed-ups by factors
of up to 1000 compared to serial CPU code as well as previous GPU
implementations are observed.Comment: 28 pages, 15 figures, 2 tables, version as publishe
Advances in Hyaluronan Biology: Signaling, Regulation, and Disease Mechanisms
Hyaluronan is an extracellular glycosaminoglycan polymer consisting of linear disaccharide units containing alternating glucuronate and N-acetylglucosamine.Many cell types make hyaluronan, which unlike most other macromolecules is assembled at the plasmamembrane and concurrently translocated through the hyaluronan synthase enzyme. The normal function of large hyaluronan polymers (\u3e1MDa) in tissue cushioning, hydration, and lubrication is well established. The aberrant accumulation and degradation of hyaluronan and the receptor-mediated signaling of smaller hyaluronan fragments have also been extensively implicated in a variety of pathological states including inflammation and cancer. More recently, the discovery that hyaluronan can either be a structural matrix component or appear as smaller processed polymers and oligomers that differentially engage a diverse range of signaling receptors has created an exciting paradigm shift and reenergized hyaluronan research in a broad range of fields. In this special issue, eight review articles focus on summarizing the latest contributions to understanding hyaluronan synthesis and catabolism and the regulation of hyaluronan functions. Seven novel primary research articles also investigate multiple roles of hyaluronan in disease progression and targeting
Binary tree summation Monte Carlo simulation for Potts models
In this talk, we briefly comment on Sweeny and Gliozzi methods, cluster Monte
Carlo method, and recent transition matrix Monte Carlo for Potts models. We
mostly concentrate on a new algorithm known as "binary tree summation". Some of
the most interesting features of this method will be highlighted - such as
simulating fractional number of Potts states, as well as offering the partition
function and thermodynamic quantities as functions of temperature in a single
run.Comment: 9 pages, 2 figures, for StatPhys-Taiwan 2002 conferenc
The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years
Using a sample of 98 galaxy clusters recently imaged in the near infra-red
with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from
the ESO archive, we measure how the stellar mass of the most massive galaxies
in the universe, namely Brightest Cluster Galaxies (BCG), increases with time.
Most of the BCGs in this new sample lie in the redshift range ,
which has been noted in recent works to mark an epoch over which the growth in
the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a
subsample of 102 systems that includes only those clusters that have estimates
of the cluster mass. We combine the BCGs in this subsample with BCGs from the
literature, and find that the growth in stellar mass of BCGs from 10 billion
years ago to the present epoch is broadly consistent with recent semi-analytic
and semi-empirical models. As in other recent studies, tentative evidence
indicates that the stellar mass growth rate of BCGs may be slowing in the past
3.5 billion years. Further work in collecting larger samples, and in better
comparing observations with theory using mock images is required if a more
detailed comparison between the models and the data is to be made.Comment: 15 pages, 8 tables, 7 figures - Accepted for publication in MNRA
Phase transition in the transverse Ising model using the extended coupled-cluster method
The phase transition present in the linear-chain and square-lattice cases of
the transverse Ising model is examined. The extended coupled cluster method
(ECCM) can describe both sides of the phase transition with a unified approach.
The correlation length and the excitation energy are determined. We demonstrate
the ability of the ECCM to use both the weak- and the strong-coupling starting
state in a unified approach for the study of critical behavior.Comment: 10 pages, 7 eps-figure
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