Boltzmann Equation and Its Cosmological Applications

Abstract

We review the derivation of the Boltzmann equation and its cosmological applications in this paper. A novel derivation of the Boltzmann equation, especially the collision term, is discussed in detail in the language of quantum field theory without any assumption of a finite temperature system. We also discuss the integrated Boltzmann equation, incorporating the temperature parameter as an extension of the standard equation. Among a number of its cosmological applications, we mainly target two familiar examples, the dynamics of the dark matter abundance through the freeze-out/in process and a baryogenesis scenario. The formulations in those systems are briefly discussed with techniques in their calculations.