Yu. L. Kalinovsky

1/ N c expansion of the quark condensate at finite temperature

Previously the quark and meson properties in a many quark system at finite temperature have been studied within effective QCD approaches in the Hartree approximation. In the present paper we consider the influence of the mesonic correlations on the quark self-energy and on the quark propagator within a systematic 1/{ital N}{sub {ital c}} expansion. Using a general separable ansatz for the nonlocal interaction, we derive a self-consistent equation for the 1/{ital N}{sub {ital c}} correction to the quark propagator. For a separable model with cutoff form factor, we obtain a decrease of the condensate of the order of 20{percent} at zero temperature. A lowering of the critical temperature for the onset of the chiral restoration transition due to the inclusion of mesonic correlations is obtained with results that seem to be closer to those from lattice calculations. {copyright} {ital 1996 The American Physical Society.}

Anomalous pion decay in effective QCD at finite temperature

Abstract The width of the process π 0 → γγ is calculated within effective QCD at finite temperature. We use two different effective models which describe chiral symmetry breaking and its restoration at finite temperature in SU(2) ƒ : (i) an effective lagrangian with a nonlocal separable interaction kernel, (ii) A- and B-scaledNJL lagrangians which implement the scale anomaly of QCD. We calculate the temperature dependences of the quark and pion masses as well as of the pion-park-antiquark coupling strength below and above the double quark mass threshold. At zero temperature we obtain a fairly good agreement with the experimental value for the decay width. The temperature dependence of the decay width is related to that of the pion mass. Γ π 0 → γγ is enhanced in the vicinity of the Mott temperature ( M π = 2 m q ) for the nonlocal as well as for the A-scaled model and suppressed for the B-scaled model. We compare our results with the SU(2) Nambu-Jona-Lasinio model which is contained as a limiting case in our approach.

Critical scattering and two photon spectra for a quark/meson plasma

Abstract At the Mott transition of a quark/meson plasma, mesons become unbound. This leads to the effect of critical scattering, which is studied by investigating photon pair production due to the process q q →γγ . This process can proceed either via direct annihilation or via the formation of a mesonic resonance. It is shown that the latter channel leads to an enhancement of photon pairs with invariant mass equal to the thermal pion mass. The size of this effect measures the time the temperature stays near the Mott temperature during the evolution. It is particularly pronounced for a first order phase transition. The π0→γγ decay gives a strong background contribution and may make the observation of critical scattering in two-proton spectra of present day heavy ion collision experiments difficult.

Chiral Symmetry Restoration and Anomalous J/ψ Suppression

We investigate the in-medium modification of pseudoscalar and vector mesons within a QCD motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature in the wide mass range from light mesons (π, σρ ) to opencharm mesons (D, D ∗ ). At the chiral/deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (Mott effect). We calculate the in-medium cross section for charmonium breakup processes due to light hadron impact within a chiral Lagrangian approach and show that the Mott effect for the D-mesons effectively reduces the threshold for charmonium breakup and leads to a step-like behaviour of the reaction rate. This is suggested as an explanation of the anomalous J/ψ suppression phenomenon in the NA50 experiment.

Scalar correlations in a quark plasma and low mass dilepton production

We investigate possible consequences of resonant scalar interactions for dilepton production from a quark plasma at the chiral phase transition. It is found that this production mechanism is strongly suppressed compared to the Born process and has no significance for present experiments. {copyright} {ital 1998} {ital The American Physical Society}

Instantaneous chiral quark model for relativistic mesons in a hot and dense medium

Abstract A chiral quark model with covariant instantaneous interactions is formmulatd using relativistic thermodynamic Green functions. The approach is applied to the description of mesons as relativistic bound states in hot and dense quark matter. The Schwinger-Dyson equation for the quark-mass operator and the Salpeter equations for quark-antiquark bound states are obtained for a nonlocal covariant four-point interaction kernel. Special attention is paid to the medium modification of meson properties as a function of their total momentum. Numerical results for the pion mass and the pion decay constant at finite temperature are presented for the special case of a separable interaction. We obtain a “protection” of the pseudoscalar bound state against medium influence due to the finite (thermal) velocity relative to the surrounding matter.