Time evolution of thermodynamic temperature in the early stage of universe

We consider a scalar field φφ which acts as a potential function to generate a (thermo)dynamic temperature field making it a possible time evolution description of this fundamental thermal property in the framework of inflationary models of the early universe. The dynamics contains a dynamical phase transition dividing the energy propagation into a dissipative and a non-dissipative process involving a spontaneous symmetry breaking mechanism. It has been found in the energy density dominated by the potential energy (including the effect of the new scalar field) inflation regime that the inflation field ϕϕ decays into the new field in a post-inflationary reheating process. This condition arises during the oscillating period of the inflation field while the new field and the temperature increase as a result of the conversion of the inflation’s energy in heat. Thus, we show that the concept of the temperature as a thermodynamic parameter can be introduced in a natural way in cosmological models remaining within the framework of classical field theory.