Quintessential Kination and Leptogenesis

TL;DR

This paper explores how quintessential kination, a cosmological model with kinetic energy dominance, affects thermal leptogenesis, revealing new viable regimes and potential enhancements in lepton asymmetry production compared to standard cosmology.

Contribution

It demonstrates that quintessential kination allows for a broader range of leptogenesis scenarios, including enhanced efficiency and viability across different wash-out regimes, with implications for neutrino mass scales.

Findings

Leptogenesis can be efficient even in super-weak wash-out regimes under kination.

The efficiency of lepton asymmetry production can surpass standard cosmology when T_r is appropriately chosen.

A sufficient window exists for sphaleron processes to convert lepton asymmetry into baryon asymmetry.

Abstract

Thermal leptogenesis induced by the CP-violating decay of a right-handed neutrino (RHN) is discussed in the background of quintessential kination, i.e., in a cosmological model where the energy density of the early Universe is assumed to be dominated by the kinetic term of a quintessence field during some epoch of its evolution. This assumption may lead to very different observational consequences compared to the case of a standard cosmology where the energy density of the Universe is dominated by radiation. We show that, depending on the choice of the temperature T_r above which kination dominates over radiation, any situation between the strong and the super--weak wash--out regime are equally viable for leptogenesis, even with the RHN Yukawa coupling fixed to provide the observed atmospheric neutrino mass scale ~ 0.05 eV. For M< T_r < M/100, i.e., when kination stops to dominate at a time which is not much later than when leptogenesis takes place, the efficiency of the process, defined as the ratio between the produced lepton asymmetry and the amount of CP violation in the RHN decay, can be larger than in the standard scenario of radiation domination. This possibility is limited to the case when the neutrino mass scale is larger than about 0.01 eV. The super--weak wash--out regime is obtained for T_r << M/100, and includes the case when T_r is close to the nucleosynthesis temperature ~ 1 MeV. Irrespective of T_r, we always find a sufficient window above the electroweak temperature T ~ 100 GeV for the sphaleron transition to thermalize, so that the lepton asymmetry can always be converted to the observed baryon asymmetry.