(P)reheating after minimal Plateau Inflation and constraints from CMB

We have studied the preheating phase for a class of plateau inflationary model considering the four-legs interaction term $(1/2)g^2\phi^2\chi^2$ between the inflaton $(\phi)$ and reheating field $(\chi)$. We specifically focus on the effects of a parameter $\phi_*$ that controls inflationary dynamics and the shape of the inflaton potential. For $\phi_* < M_p$, the departure of the inflaton potential from the usual power-law behavior $\phi^n$ significantly modifies the microscopic behavior of the preheating dynamics. We analyze and compare the efficiency of production, thermalization and the final equation of state of the system for different models under consideration with $n=2,4,6$ for two different values of $\phi_*$. Most importantly as we increase $n$, or decrease $\phi_*$, the preheating occurs very efficiently with the final equation of state to be that of the radiation, $w=1/3$. Specially for $n=2$, the final equation of state turned out to be $w\simeq 0.2$. However, a complete decay of inflaton could not be achieved with the four-legs interaction for any model under consideration. Therefore, in order to complete the reheating process, we perform the perturbative analysis for the second stage of the reheating phase. Taking the end product of the preheating phase as an initial condition we have solved the homogeneous Boltzmann equations for both the fields supplemented by the constraints coming from the subsequent entropy conservation. In so doing, we can calculate the reheating temperature which is otherwise ill-defined right after the end of preheating. The temperature can be uniquely fixed for a given inflaton decay constant and the CMB temperature. We also compare our results with the conventional reheating constraint analysis and discuss the limit of inflaton decay constant from the field theory perspective.