COSMOLOGICAL QUARK-HADRON PHASE-TRANSITION AND THE EFFECT OF VISCOSITY

It is generally believed that the first-order cosmological quark-hadro n phase transition would have occurred when the temperature of the uni verse was around T-c similar to 200 MeV. The main object of this work is to trace the temperature evolution of the universe during this phas e transition. We treat the quark-gluon plasma as an imperfect fluid an d solve the dynamical equation numerically taking into account the eff ect of the bulk viscosity. We find that, as the phase transition proce eds, the supercooled universe is not reheated back to the critical tem perature. The effect of the bulk viscosity is found to reduce the amou nt of supercooling.