Mixed constraints to inflationary models

Abstract

We show how to constrain inflationary models and reheating by using mixed constraints. In particular we study the physics of the reheating phase after inflation from observational constraints to the inflationary stage. We show that it is possible to determine $\omega$, the equation of state during reheating, by using the reported values of the spectral index and the {\it full} number of $e$-folds $N(n_s,\omega)= N_H(n_s)+N_{re}(n_s,w)\approx 60$, which includes the accelerated expansion and the reheating phase. We show that the reheating number of $e$-folds $N_{re}$ is quite sensitive to this equation of state. Requiring $N_{re}>0$ and a sensible value for the thermalization scale $T_{re}$, demands in general a reheating phase with $\omega\neq 0$. We exemplify the constraints with two particular examples: We show how the Starobinsky model allows only large values of $T_{re}$ if the reheating phase is dominated by dust ($w =0$), and if Primordial Black Hole production is subdominant. For the case of $N=1$ Supergravity inflation, the extra parameter of the potential provides the necessary freedom to afford lower-scale thermalization in a dust-like reheating phase and yet our method serves to determine the rest of the observable parameters.