THERMAL-ACTIVATION RATES IN THE CHIRALLY ASYMMETRIC GROSS-NEVEU MODEL

We address the problem of how to incorporate quantum effects into the calculation of finite-temperature decay rates for a metastable state o f a quantum field theory. To do this, we consider the Gross-Neveu mode l with an explicit chiral symmetry breaking term, which allows for a m etastable state, This theory can be shown to have a ''critical bubble' ' which is a solution to the exact equations of motions (i.e. to all o rders in perturbation theory, including all higher derivative, quantum and thermal corrections). This configuration mediates the thermal act ivation of the metastable vacuum to the true ground state, with a deca y rate Gamma proportional to exp(-F-c/T), where F-c is the free energy of the critical bubble. We then compare this exact calculation to var ious approximations that have been used in previous work. We find that these approximations all overestimate the activation rate, Furthermor e, we study the effect of finite baryon number upon the bubble profile and the activation barriers. We find that beyond a critical baryon nu mber the activation barriers disappear altogether.