585 research outputs found
Relativistic Transport Theory for Systems Containing Bound States
Using a Lagrangian which contains quarks as elementary degrees of freedom and
mesons as bound states, a transport formalism is developed, which allows for a
dynamical transition from a quark plasma to a state, where quarks are bound
into hadrons. Simultaneous transport equations for both particle species are
derived in a systematic and consistent fashion. For the mesons a formalism is
used which introduces off-shell corrections to the off-diagonal Green
functions. It is shown that these off-shell corrections lead to the appearance
of elastic quark scattering processes in the collision integral. The
interference of the processes and
leads to a modification of the -channel amplitude of quark-antiquark
scattering
One Loop Integrals at Finite Temperature and Density
The technique of decomposing Feynman diagrams at the one loop level into
elementary integrals is generalized to the imaginary time Matsubara formalism.
The three lowest integrals, containing one, two and three fermion lines, are
provided in a form that separates out the real and imaginary parts of these
complex functions, according to the input arguments, in a fashion that is
suitable for numerical evaluation. The forms given can be evaluated for
arbitrary values of temperature, particle mass, particle momenta and chemical
potential.Comment: 32 Pages REVTeX, 9 Figures available as separate fil
Expansion and Hadronization of a Chirally Symmetric Quark--Meson Plasma
Using a chirally symmetric Lagrangian, which contains quarks as elementary
degrees of freedom and mesons as bound states, we investigate the expansion and
hadronization of a fireball, which initially contains only quarks and produces
mesons by collisions. For this model, we study the time scales of expansion and
thermal and chemical equilibration. We find that the expansion progresses
relatively fast, leaving not necessarily enough time to establish thermal and
chemical equilibrium. Mesons are produced in the bulk of the fireball rather
than at a surface, at a temperature below the Mott temperature. Initial density
fluctuations become amplified during the expansion. These observations
challenge the applicability of hydrodynamical approaches to the expansion of a
quark-gluon plasma
Hadronization in the SU(3) Nambu - Jona-Lasinio model
The hadronization process for quarks combining into two mesons, q\bar q\to MM' at temperature T is described within the SU(3) Nambu- Jona-Lasinio model with finite current quark masses. Invariant matrix elements, cross-sections and transition rates are calculated to leading order in a 1/N_c expansion. Four independent classes, u\bar d, u\bar s, u\bar u and s\bar s\to hadrons are analysed, and the yield is found to be dominated by pion production. Threshold behaviour is determined by the exothermic or endothermic nature of the processes constituting the hadronization class. A strong suppression of transition rates is found at the pionic Mott temperature T_{M\pi}=212 MeV, at which the pion becomes a resonant state. The mean time for hadronization is calculated to be 2-4 fm/c near the Mott temperature. The calculation of strangeness changing processes indicates that hadronization accounts for a 1% increase in the absolute value of the kaon to pion ratio at T=150 MeV
Hadronization and Strangeness Production in a Chirally Symmetric Nonequilibrium Model
The expansion and hadronization of a quark meson plasma is studied using an effective chiral interaction Lagrangian. The particles we consider are light as well as strange quarks, which can form pions, kaons and eta mesons via collision processes. The transport equations for the system are solved using a QMD type algorithm. We find that in chemical equilibrium at high temperatures the strange quark mass is considerably higher than the strange current quark mass and becomes even higher if we assume an initial state free of strange quarks. This leads to a considerably higher production threshold. In contrast to simpler scenarios, like thermodynamics of free quarks with their bare mass, we observe that strangeness production in a plasma is hindered and not favoured. The different particle species created during the evolution become separated in coordinate as well as in momentum space. We observe, as at CERN experiments, a larger mean momentum of kaons as compared to pions. Thus the radial collective velocity may as well originate from a plasma expansion and not necessarily from a hadronic scenario
Impact of noise on domain growth in electroconvection
The growth and ordering of striped domains has recently received renewed
attention due in part to experimental studies in diblock copolymers and
electroconvection. One surprising result has been the relative slow dynamics
associated with the growth of striped domains. One potential source of the slow
dynamics is the pinning of defects in the periodic potential of the stripes. Of
interest is whether or not external noise will have a significant impact on the
domain ordering, perhaps by reducing the pinning and increasing the rate of
ordering. In contrast, we present experiments using electroconvection in which
we show that a particular type of external noise decreases the rate of domain
ordering
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