arXiv subjects
Publications and source records attributed to Da-Shin Lee.
We study the nonequilibrium photon production in the quark-hadron phase transition, using the Friedberg-Lee type solitons as a working model for quark-hadron physics. We propose that to search for nonequilibrium photons in the direct photon measurements of heavy-ion collisions may be a characteristic test of the transition from the quark-gluon to hadronic phases.
We address the problem of how to incorporate quantum effects into the calculation of finite-temperature decay rates for a metastable state of a quantum field theory. To do this, we consider the Gross-Neveu model with an explicit chiral symmetry breaking term, which allows for a metastable 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 orders in perturbation theory, including all higher derivative, quantum and thermal corrections). This configuration mediates the thermal activation of the metastable vacuum to the true ground state, with a decay rate $Γ\propto \exp(-F_c/T)$, where $F_c$ is the free energy of the critical bubble. We then compare this exact calculation to various approximations that have been used in previous work. We find that these approximations all *overestimate* the activation rate. Furthermore, we study the effect of finite baryon number upon the bubble profile and the activation barriers. We find that beyond a critical baryon number the activation barriers disappear altogether.
We study the non-equilibrium dynamics of a symmetry restoring phase transition in a scalar field theory, the ``system'', linearly coupled to another scalar field taken as a ``heat bath''. The ``system'' is initially in an ordered low temperature phase, and the heat bath is at a temperature close to the critical temperature for the system. We estimate the time at which the phase transition to the disordered (symmetric) phase takes place. We derive, and integrate the one-loop effective equations of motion for the order parameter that include the effects of the heat bath. A semiclassical Langevin equation is derived and it is found that it contains a non-dissipative, non-Markovian kernel, the noise term is colored and correlated on time scales determined by the temperature of the heat bath. The range of validity of the Langevin equation and a consistent procedure to incorporate corrections are discussed.