$\Theta$ vacua states in heavy ion collisions in presence of dissipation and noise

Abstract

We have studied possible formation of $\Theta$ vacua states in heavy ion collisions. Random phases of the chiral fields were evolved in a finite temperature potential, incorporating the breaking of $U_A(1)$ symmetry. Initial random phases very quickly settle into oscillation around the values dictated by the potential. The simulation study indicate that an initial $\Theta$=0 state do not evolve into a $\Theta$ $\neq$ 0 state. However, an initial $\Theta$ $\neq$ 0 state, if formed in heavy ion collision, can survive, as a coherent superposition of a number of modes.