778 research outputs found
Neutron Star Properties with Hyperons
In the light of the recent discovery of a neutron star with a mass accurately
determined to be almost two solar masses, it has been suggested that hyperons
cannot play a role in the equation of state of dense matter in
-equilibrium. We re-examine this issue in the most recent development of
the quark-meson coupling model. Within a relativistic Hartree-Fock approach and
including the full tensor structure at the vector-meson-baryon vertices, we
find that not only must hyperons appear in matter at the densities relevant to
such a massive star but that the maximum mass predicted is completely
consistent with the observation.Comment: Minor correction
In-medium electron-nucleon scattering
In-medium nucleon electromagnetic form factors are calculated in the quark
meson coupling model. The form factors are typically found to be suppressed as
the density increases. For example, at normal nuclear density and , the nucleon electric form factors are reduced by approximately 8%
while the magnetic form factors are reduced by only 1 - 2%. These variations
are consistent with current experimental limits but should be tested by more
precise experiments in the near future.Comment: 14 pages, latex, 3 figure
Octet baryon electromagnetic form factors in nuclear medium
We study the octet baryon electromagnetic form factors in nuclear matter
using the covariant spectator quark model extended to the nuclear matter
regime. The parameters of the model in vacuum are fixed by the study of the
octet baryon electromagnetic form factors. In nuclear matter the changes in
hadron properties are calculated by including the relevant hadron masses and
the modification of the pion-baryon coupling constants calculated in the
quark-meson coupling model. In nuclear matter the magnetic form factors of the
octet baryons are enhanced in the low region, while the electric form
factors show a more rapid variation with . The results are compared with
the modification of the bound proton electromagnetic form factors observed at
Jefferson Lab. In addition, the corresponding changes for the bound neutron are
predicted.Comment: Version accepted for publication in J.Phys. G. Few changes. 40 pages,
14 figures and 8 table
Valence quark and meson cloud contributions for the gamma* Lambda -> Lambda* and gamma* Sigma0 -> Lambda* reactions
We estimate the valence quark contributions for the gamma* Y -> Lambda*
(Y=Lambda, Sigma0) electromagnetic transition form factors. We focus
particularly on the case Lambda*=Lambda(1670) as an analog reaction with gamma*
N -> N(1535). The results are compared with those obtained from chiral unitary
model, where the Lambda* resonance is dynamically generated and thus the
electromagnetic structure comes directly from the meson cloud excitation of the
baryon ground states. The form factors for the case Y=Sigma0 in particular,
depend crucially on the two real phase (sign) combination, a phase between the
Lambda and Lambda* states, and the other, the phase between the Lambda and
Sigma0 radial wave functions. Depending on the combination of these two phases,
the form factors for the gamma* Sigma0 -> Lambda* reaction can be enhanced or
suppressed. Therefore, there is a possibility to determine the phase
combination by experiments.Comment: 17 pages, 7 figure
Resonance Model of for Kaon Production in Heavy Ion Collisions
The elementary production cross sections
and are needed to describe
kaon production in heavy ion collisions. The reactions
were studied previously by a resonance model. The model can explain the
experimental data quite well \cite{tsu}. In this article, the total cross
sections at intermediate energies (from the kaon
production threshold to3 GeV of center-of-mass energy) are
calculated for the first time using the same resonance model. The resonances,
and for the reactions, and
, and for the reactions are taken into account coherently as
the intermediate states in the calculations. Also t-channel vector meson exchange is included. The results show that
exchange is neglegible for the
reactions, whereas this meson does not contribute to the reactions. Furthemore, the
contributions to kaon production in heavy ion collisions are not only
non-neglegible but also very different from the
reactions. An argument valid for cannot be extended to
reactions. Therefore, cross sections for including correctly the different isospins must beComment: ( Replaced with corrections of printing errors in the Table. ) 15
pages, Latex file with 4 figures, 1 figure is included in the text. A
compressed uuencode file for 3 figures is appended. (A figure file format was
changed.) Also available upon reques
mass shift and -nuclear bound state
We calculate mass shift of the meson in nuclear matter arising from
the modification of and meson loop contributions to the
self-energy. The estimate includes the in-medium and meson
masses consistently. The mass shift (scalar potential) calculated is
negative (attractive), and complementary to the attractive potential obtained
from the QCD color van der Waals forces. Some results for the -nuclear
bound state energies are also presented.Comment: 6 pages, talk given at "T(r)opical QCD II", September 26 - October 1,
2010, Cairns, Australi
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