2,120 research outputs found
Signals of spinodal phase decomposition in high-energy nuclear collisions
High-energy nuclear collisions produce quark-gluon plasmas that expand and
hadronize. If the associated phase transition is of first order then the
hadronization should proceed through a spinodal phase separation. We explore
here the possibility of identifying the associated clumping by analysis of
suitable N-particle momentum correlations.Comment: 7 pages, incl 4 ps figure
Probing chiral dynamics by charged-pion correlations
The environment generated in the mid-rapidity region of a high-energy nuclear
collision endows the pionic degrees of freedom with a time-dependent effective
mass. Its specific evolution provides a mechanism for the production of
back-to-back charge-conjugate pairs of soft pions which may present an
observable signal of the non-equilibrium dynamics of the chiral order
parameter.Comment: revtex body and 3 eps figures (4 pages total
Quantum Field Treatment of DCC Dynamics
A practical quantum-field treatment is developed for systems endowed with an
effective mass function depending on both space and time and a schematic
application illustrates the quantitative importance of quantum fluctuations in
the dynamics of disoriented chiral condensates.Comment: revtex body and 4 eps figures (4 pages total
Spin-Isospin Modes in Heavy-Ion Collisions I: Nuclear Matter at Finite Temperatures
With a view towards implementation in microscopic transport simulations of
heavy-ion collisions, the properties of spin-isospin modes are studied in
nuclear matter consisting of nucleons and Delta isobars that interact by the
exchange of pi and rho mesons. For a standard p-wave interaction and an
effective g' short-range interaction, the dispersion relations for the spin-
isospin modes, and the associated amplitudes, are calculated at various nuclear
densities and temperatures, within the random-phase approximation. Quantities
of physical interest are then extracted, including the total and partial Delta
decay widths and the Delta cross sections in the nuclear medium. The
self-consistent inclusion of the Delta width has a strong effect on the Delta
cross sections at twice normal nuclear density, as compared with the result of
ignoring the width. Generally, the obtained quantities exhibit a strong density
dependence, but are fairly insensitive to the temperature, at least up to T=25
MeV. Finally, it is described how these in-medium effects may be consistently
included into microscopic transport simulations of nuclear collisions, and the
improvements over previous approaches are discussed.Comment: LaTeX 47 pages, 17 postscript figures in accompanying uuencoded fil
Brownian shape motion on five-dimensional potential-energy surfaces: Nuclear fission-fragment mass distributions
Although nuclear fission can be understood qualitatively as an evolution of
the nuclear shape, a quantitative description has proven to be very elusive. In
particular, until now, there exists no model with demonstrated predictive power
for the fission fragment mass yields. Exploiting the expected strongly damped
character of nuclear dynamics, we treat the nuclear shape evolution in analogy
with Brownian motion and perform random walks on five-dimensional fission
potential-energy surfaces which were calculated previously and are the most
comprehensive available. Test applications give good reproduction of highly
variable experimental mass yields. This novel general approach requires only a
single new global parameter, namely the critical neck size at which the mass
split is frozen in, and the results are remarkably insensitive to its specific
value.Comment: 4 pages, 2 ps figure
Inclusion of Quantum Fluctuations in Wave Packet Dynamics
We discuss a method by which quantum fluctuations can be included in
microscopic transport models based on wave packets that are not energy
eigenstates. By including the next-to-leading order term in the cumulant
expansion of the statistical weight, which corresponds to the wave packets
having Poisson energy distributions, we obtain a much improved global
description of the quantum statistical properties of the many-body system. In
the case of atomic nuclei, exemplified by 12C and 40Ca, the standard
liquid-drop results are reproduced at low temperatures and a phase
transformation to a fragment gas occurs as the temperature is raised. The
treatment can be extended to dynamical scenarios by means of a Langevin force
emulating the transitions between the wave packets. The general form of the
associated transport coefficients is derived and it is shown that the
appropriate microcanonical equilibrium distribution is achieved in the course
of the time evolution. Finally, invoking Fermi's golden rule, we derive
specific expressions for the transport coefficients and verify that they
satisfy the fluctuation-dissipation theorem.Comment: uuencoded revtex body and 8 ps figures (16 pages total
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