Thermalization of electron-positron-photon plasmas with an application to GRB

The pair plasma with photon energies in the range 0.1 - 10 MeV is believed to play crucial role in cosmic Gamma- Ray Bursts. Starting from a nonequilibrium configuration we analyze the role of the direct and the inverse binary and triple interactions in reaching thermal equilibrium in a homogeneous isotropic pair plasma. We numerically integrate the relativistic Boltzmann equation with the exact QED collisional integrals taking into account all binary and triple interactions. We show that first, when a detailed balance is reached for all binary interactions on a time scale tk≳ 10-14 sec, photons and electronpositron pairs establish kinetic equilibrium. Subsequently, when triple interactions satisfy the detailed balance on a time scale t eq≳ 10-12 sec, the plasma reaches thermal equilibrium. It is shown that neglecting the inverse triple interactions prevents reaching thermal equilibrium. Our results obtained in the theoretical physics domain also find application in astrophysics and cosmology. © 2008 American Institute of Physics.