645 research outputs found
Boost invariant quantum evolution of a meson field at large proper times
We construct asymptotic solutions of the functional Schroedinger equation for
a scalar field in the Gaussian approximation at large proper time. These
solutions describe the late proper time stages of the expansion of a meson gas
with boost invariant boundary conditions. The relevance of these solutions for
the formation of a disoriented chiral condensate in ultra relativistic
collisions is discussed.Comment: 9 pages, LATE
The giant resonances in hot nuclei: linear response calculations
We calculate the isovector response function of hot nuclear matter using
various effective Skyrme interactions. For Skyrme forces with a small effective
mass the strength distribution is found to be nearly independent of
temperature, and shows little collective effects. In contrast effective forces
with an effective mass close to unity produce sizeable collective effects at
zero temperature which disappear at temperatures of a few MeV. We discuss the
relevance of these results for the saturation of the multiplicity of photons
emitted by the giant dipole resonance in hot nuclei beyond =3 MeV observed
in recent experiments.Comment: 6 pages, LaTeX file, 3 figures (not included, available on request)
(Contribution to the 3th IN2P3-Riken Symposium on Heavy Ion Collisions,
Shinrin-Koen, Saitama, Japan, October 1994
Response Function of Hot Nuclear Matter
We investigate the response function of hot nuclear matter to a small
isovector external field using a simplified Skyrme interaction reproducing the
value of the symmetry energy coefficient.
We consider values of the momentum transfer corresponding to the dipole
oscillation in heavy nuclei. We find that while at zero temperature the
particle hole interaction is almost repulsive enough to have a sharp (zero
sound type) collective oscillation, such is no longer the case at temperatures
of a few MeV. As a result a broadening of the dipole resonance occurs, leading
to its quasi disappearence by the time the temperature reaches 5 MeV. The
sensivity of the temperature evolution of the width when modifying the residual
interaction strength is also examined.Comment: 9 pages, IPNO/TH 94-15, DPT-IPN Orsay. Two figures available under
reques
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Mean field theory for collective motion of quantum meson fields
Mean field theory for the time evolution of quantum meson fields is studied
in terms of the functional Schroedinger picture with a time-dependent Gaussian
variational wave functional. We first show that the equations of motion for the
variational wavefunctional can be rewritten in a compact form similar to the
Hartree-Bogoliubov equations in quantum many-body theory and this result is
used to recover the covariance of the theory. We then apply this method to the
O(N) model and present analytic solutions of the mean field evolution equations
for an N-component scalar field. These solutions correspond to quantum
rotations in isospin space and represent generalizations of the classical
solutions obtained earlier by Anselm and Ryskin. As compared to classical
solutions new effects arise because of the coupling between the average value
of the field and its quantum fluctuations. We show how to generalize these
solutions to the case of mean field dynamics at finite temperature. The
relevance of these solutions for the observation of a coherent collective state
or a disoriented chiral condensate in ultra-relativistic nuclear collisions is
discussed.Comment: 31 pages, 2 Postscript figures, uses ptptex.st
Temperature dependence of the response function of hot nuclear matter
The description of collective motion in nuclei at finite temperature using the framework of the random phase approximation is discussed. We focus on the special case of the isovector response function of hot nuclear matter using various effective Skyrme interactions
Continuum HFB calculations with finite range pairing interactions
A new method of calculating pairing correlations in coordinate space with
finite range interactions is presented. In the Hartree-Fock-Bogoliubov (HFB)
approach the mean field part is derived from a Skyrme-type force whereas the
pairing field is constructed with a Gogny force. An iterative scheme is used
for solving the integro-differential HFB equations via the introduction of a
local equivalent potential. The method is illustrated on the case of the
nucleus C. It is shown that the results are insensitive to the cut off
value in the quasiparticle spectrum if this value is above 100 MeV.Comment: 3 figures, in press, Phys. Lett.
A new baryonic equation of state at sub-nuclear densities for core-collapse simulations
We calculate a new equation of state for baryons at sub-nuclear densities
meant for the use in core-collapse simulations of massive stars. The abundance
of various nuclei is obtained together with the thermodynamic quantities. The
formulation is the NSE description and the liquid drop approximation of nuclei.
The model free energy to minimize is calculated by relativistic mean field
theory for nucleons and the mass formula for nuclei with the atomic number up
to ~ 1000. We have also taken into account the pasta phase, thanks to which the
transition to uniform nuclear matter in our EOS occurs in the conventional
manner: nuclei are not dissociated to nucleons but survive right up to the
transition to uniform nuclear matter. We find that the free energy and other
thermodynamical quantities are not very different from those given in the
Shen's EOS, one of the standard EOS's that adopt the single nucleus
approximation. The average mass is systematically different, on the other hand,
which may have an important ramification to the rates of electron captures and
coherent neutrino scatterings on nuclei in supernova cores. It is also
interesting that the root mean square of the mass number is not very different
from the average mass number, since the former is important for the evaluation
of coherent scattering rates on nuclei but has been unavailable so far. The EOS
table is currently under construction, which will include the weak interaction
rates.Comment: 34 pages, 11 figures, Accepted for publication Ap
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