Production of Massive Fermions at Preheating and Leptogenesis

TL;DR

Giudice et al. solve how heavy fermions can be produced non-perturbatively during preheating after chaotic inflation and whether such production can realize leptogenesis. They perform a complete calculation of inflaton decay into very massive fermions, modelling a Dirac fermion with $m(t)=m_X+g\phi(t)$ in a quadratic inflaton potential and analyze it with Bogoliubov transformations and numerical evolution, complemented by analytical estimates. They find efficient production up to masses $M_N\sim 10^{17}-10^{18}$ GeV, enabling a non-thermal population of right-handed neutrinos during preheating and a viable leptogenesis scenario with moderate gravitino constraints on $T_{RH}$. This non-thermal production channel broadens the allowed neutrino-mass parameter space for leptogenesis and provides a robust mechanism to generate the observed baryon asymmetry without requiring solely thermal equilibration.

Abstract

We present a complete computation of the inflaton decay into very massive fermions during preheating. We show that heavy fermions are produced very efficiently up to masses of order 10^{17}-10^{18} GeV; the accessible mass range is thus even broader than the one for heavy bosons. We apply our findings to the leptogenesis scenario, proposing a new version of it, in which the massive right-handed neutrinos, responsible for the generation of the baryon asymmetry, are produced during preheating. We also discuss other production mechanisms of right-handed neutrinos in the early Universe, identifying the neutrino mass parameters for which the observed baryon asymmetry is reproduced.

Figures (4)

• Figure 1: The fraction of the energy density of produced fermions with respect to the total energy density, as a function of the fermion mass $m_X$ in units of the inflaton mass, for various values of $q$.
• Figure 2: The final phase-space density of produced particles for two values of the parameter $q$. The $X$-fermions are taken to be 100 times heavier than the inflaton. At $q=10^5$ the freeze-out of the particle production was reached after the first inflaton oscillation, while for $q=10^8$ it required twenty oscillations.
• Figure 3: The phase-space density of produced particles after $n=1$ and $n=3$ inflaton oscillations for $q=10^6$ and for $X$-fermions 100 times heavier than the inflaton. The distribution at $n=3$ coincides with the final distribution.
• Figure 4: The phase-space density of produced particles after $n=1$ and $n=20$ inflaton oscillations for $q=10^8$ and for $X$-fermions 100 times heavier than the inflaton. The distribution at $n=20$ coincides with the final distribution.