Reheating, thermalization and non-thermal gravitino production in MSSM inflation

Abstract

In the framework of MSSM inflation, matter and gravitino production are here investigated through the decay of the fields which are coupled to the udd inflaton, a gauge invariant combination of squarks. After the end of inflation, the flat direction oscillates about the minimum of its potential, losing at each oscillation about 56% of its energy into bursts of gauge/gaugino and scalar quanta when crossing the origin. These particles then acquire a large inflaton VEV-induced mass and decay perturbatively into the MSSM quanta and gravitinos, transferring the inflaton energy very efficiently via instant preheating. Regarding thermalization, we show that the MSSM degrees of freedom thermalize very quickly, yet not immediately by virtue of the large vacuum expectation value of the inflaton, which breaks the $SU(3)_C\times U(1)_Y$ symmetry into a residual $U(1)$. The energy transfer to the MSSM quanta is very efficient, since full thermalization is achieved after only $\mathcal{O}(40)$ complete oscillations. The udd inflaton thus provides an extremely efficient reheating of the Universe, with a temperature $T_{reh}=\mathcal{O}(10^8\mathrm{GeV})$ that allows for instance several mechanisms of baryogenesis. We also compute the gravitino number density from the perturbative decay of the flat direction and of the SUSY multiplet. We find that the gravitinos are produced in negligible amount and satisfy cosmological bounds such as the Big Bang Nucleosynthesis (BBN) and Dark Matter (DM) constraints.