Chiral Dynamics with Quark Degrees of Freedom

Possibility to detect DCC fluctuations is discussed. It is shown that interactions with quark background and dissipative effects due to interactions in the chiral field may result in damping of fluctuations. Since the magnitude of fluctuations depends strongly on the initial state and speed of chiral phase transition accurate evaluation of all modifying processes is required to predict observability of DCCs. The possiblity of producing quark-gluon plasma in relativistic heavy ion collisons is exciting especially from the point of view of observing the chiral and deconfinement phase transitions. Rajagopal and Wilczek have suggested that if chiral restoration is of second order, nonequilibrium dynamics can generate transient domains in which macroscopic pion fields develop. As the chiral field relaxes to the true vaccum in such a domain, it may lead to coherent emission of pions [ 1]. This kind of phenomenon is called a disoriented chiral condensate (DCC). Bjorken and others pointed out that DCC can lead to fluctuations in the charged and neutral pion spectra [ 2]. If we can observe this phenomenon we can say the quark-gluon plasma has been produced, and we see the signs of its hadronization. The possibility to resolve fluctuations of neutral and charged pions critically depends on the size and energy content of these domains. If the domains are roughly pion sized, the effect of DCC is too small to be resolved in experiments. If domains are large enough, the effects of DCC can have measurable consequences. All these signals: the isospin fluctuations, the enhancement of the pion spectrum at low pT , and the suppression of HBT correlations are characteristics of any large coherent source [ 3]. Most dynamical studies [ 4, 5, 6, 7, 8] of DCC have been carried out within 0231-4428/97/ 00.00 Preprint 2 Zhonghan Feng, et al. the framework of the linear sigma model. Using this model, one can study the possibility of DCC formation and the domain size of DCC. The Lagrangian density of the linear sigma model can be written as : L = Lq + LSM = Lq + 1 2 (∂μσ ∂ σ + ∂μ~π ∂ ~π)− U(σ, ~π), (1) where U(σ, ~π) = λ 4 ( σ + ~π − v )2 −Hσ + (