4,636 research outputs found
A family of pseudo-Anosov braids with large conjugacy invariant sets
We show that there is a family of pseudo-Anosov braids independently
parameterized by the braid index and the (canonical) length whose smallest
conjugacy invariant sets grow exponentially in the braid index and linearly in
the length and conclude that the conjugacy problem remains exponential in the
braid index under the current knowledge.Comment: 16 pages, 6 figure
Kaon dispersion relation and flow in relativistic heavy-ion collisions
Within the framework of a relativistic transport model (ART) for heavy-ion
collisions at AGS energies, we examine the effects of kaon dispersion relation
on the transverse flow of kaons and their transverse momentum and azimuthal
angle distributions. We find that the transverse flow is the most sensitive
observable for studying the kaon dispersion relation in dense medium.Comment: 7 pages, latex, 3 figures available upon request from the authors,
Phys. Rev. C (1996) in pres
Pion flow and antiflow in relativistic heavy-ion collisions
Within the framework of a relativistic transport model (ART) for heavy-ion
collisions at AGS energies, we study the transverse flow of pions with respect
to that of nucleons using two complementary approaches. It is found that in
central collisions pions develop a weak flow as a result of the flow of baryon
resonances from which they are produced. On the other hand, they have a weak
antiflow in peripheral collisions due to the shadowing of spectators.
Furthermore, it is shown that both pion flow and antiflow are dominated by
those with large transverse momenta.Comment: Phys. Rev. C, Rapid communication, in press. Figures are available
from the authors upon reques
Medium effects on charged pion ratio in heavy ion collisions
We have recently studied in the delta-resonance--nucleon-hole model the
dependence of the pion spectral function in hot dense asymmetric nuclear matter
on the charge of the pion due to the pion p-wave interaction in nuclear medium.
In a thermal model, this isospin-dependent effect enhances the ratio of
negatively charged to positively charged pions in neutron-rich nuclear matter,
and the effect is comparable to that due to the uncertainties in the
theoretically predicted stiffness of nuclear symmetry energy at high densities.
This effect is, however, reversed if we also take into account the s-wave
interaction of the pion in nuclear medium as given by chiral perturbation
theory, resulting instead in a slightly reduced ratio of negatively charged to
positively charged pions. Relevance of our results to the determination of the
nuclear symmetry energy from the ratio of negatively to positively charged
pions produced in heavy ion collisions is discussed.Comment: 11 pages, 4 figures, contribution to The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energy (IWND2009),
Shanghai, China, 22-25 August, 200
Density slope of the nuclear symmetry energy from the neutron skin thickness of heavy nuclei
Expressing explicitly the parameters of the standard Skyrme interaction in
terms of the macroscopic properties of asymmetric nuclear matter, we show in
the Skyrme-Hartree-Fock approach that unambiguous correlations exist between
observables of finite nuclei and nuclear matter properties. We find that
existing data on neutron skin thickness of Sn isotopes give an
important constraint on the symmetry energy and its
density slope at saturation density . Combining these
constraints with those from recent analyses of isospin diffusion and double
neutron/proton ratio in heavy-ion collisions at intermediate energies leads to
a more stringent limit on approximately independent of . The implication of these new constraints on the of
Pb as well as the core-crust transition density and pressure in neutron
stars is discussed.Comment: 18 pages, 9 figures, 1 table. Significantly expanded to include a
number of details and discussions. Title shortened. Accepted version to
appear in PR
Transition density and pressure in hot neutron stars
Using the momentum-dependent MDI effective interaction for nucleons, we have
studied the transition density and pressure at the boundary between the inner
crust and liquid core of hot neutron stars. We find that their values are
larger in neutrino-trapped neutron stars than in neutrino-free neutron stars.
Furthermore, both are found to decrease with increasing temperature of a
neutron star as well as increasing slope parameter of the nuclear symmetry
energy, except that the transition pressure in neutrino-trapped neutron stars
for the case of small symmetry energy slope parameter first increases and then
decreases with increasing temperature. We have also studied the effect of the
nuclear symmetry energy on the critical temperature above which the inner crust
in a hot neutron star disappears and found that with increasing value of the
symmetry energy slope parameter, the critical temperature decreases slightly in
neutrino-trapped neutron stars but first decreases and then increases in
neutrino-free neutron stars.Comment: 7 pages, 6 figures, version to appear in Phys. Rev.
Isospin- and momentum-dependent effective interactions for the baryon octet and the properties of hybrid stars
The isospin- and momentum-dependent MDI interaction, which has been
extensively used in intermediate-energy heavy-ion reactions to study the
properties of asymmetric nuclear matter, is extended to include the
nucleon-hyperon and hyperon-hyperon interactions by assuming same density,
momentum and isospin dependence as for the nucleon-nucleon interaction. The
parameters in these interactions are determined from the empirical hyperon
single-particle potentials in symmetric nuclear matter at saturation density.
The extended MDI interaction is then used to study in the mean-field
approximation the equation of state of hypernuclear matter and also the
properties of hybrid stars by including the phase transition from the
hypernuclear matter to the quark matter at high densities. In particular, the
effects of attractive and repulsive N interactions and different values
of symmetry energies on the hybrid star properties are investigated.Comment: 13 pages, 12 figures, version to appear in Phys. Rev.
- …