Energy Density, Temperature and Entropy Dynamics in Perturbative
  Reheating
  We discuss the perturbative decay of the energy density of a non standard
inflaton field $\rho_{\phi}$ and the corresponding creation of the energy
density of the relativistic fields $\rho_r$ at the end of inflation, in the
perfect fluid description, refining some concepts and providing some new
computations. In particular, the process is characterized by two fundamental
time scales. The first one, $t_\text{max}$, occurs when the energy density
$\rho_r$ reaches its largest value, slightly after the beginning of the
reheating phase. The second one, $t_\text{reh}$, is the time in which the
reheating is completely realized and the thermalization is attained. By
assuming a non-instantaneous reheating phase, we are able to derive the energy
densities and the temperatures of the produced relativistic bath at
$t_\text{max}$ and $t_\text{reh}$, as well as the value of the corresponding
horizon entropy $S_\text{hor}$, for an Equation-of-State (EoS) parameter $w\ne
0$.
