Einstein-Cartan pseudoscalaron inflation, reheating and nonthermal leptogenesis

Abstract

We study the postinflationary dynamics of an Einstein-Cartan-Holst gravity-motivated inflationary scenario, known as Einstein-Cartan pseudoscalaron inflation, coupled to a type-I seesaw extension of the Standard Model with three heavy right-handed Majorana neutrinos. In particular, we show that nonthermal leptogenesis emerges as a necessary and self-consistent mechanism for generating the observed baryon asymmetry of the Universe, mainly because of the universal coupling of the inflaton to the additional heavy Majorana fermions. The resulting framework provides theoretical predictions that are fully compatible with the latest cosmological constraints from the Cosmic Microwave Background, Baryon Acoustic Oscillations, and Big Bang Nucleosynthesis, as well as with neutrino oscillation experiments, for a wide range of the fundamental Barbero-Immirzi model parameter $\gamma$, which controls the inflationary and postinflationary phases. In particular, for $\gamma \sim -1/100$ and a lightest Majorana-neutrino mass of order $10^{13}$ GeV, we find a scalar spectral index $n_s \sim 0.970$, a tensor-to-scalar ratio $r \sim 0.004$, for a number of e-folds before the end of inflation $N_e \lesssim 60$, and a baryon-to-entropy ratio $n_B/s \sim 8.7 \times 10^{-11}$.