Quintessential Kination and Thermal Production of Gravitinos and Axinos

TL;DR

This paper studies how a kination-dominated phase affects the thermal production of gravitinos and axinos, showing that their abundances are reduced and can evade constraints or account for dark matter depending on parameters.

Contribution

It introduces a model of kination influence on particle abundances and presents a new calculation of axino production at low temperatures.

Findings

Gravitino abundance decreases with lower transition temperature.

Unstable gravitino constraints are evaded in this model.

Axino abundance can match dark matter requirements at higher initial temperatures.

Abstract

The impact of a kination-dominated phase generated by a quintessential exponential model on the thermal abundance of gravitinos and axinos is investigated. We find that their abundances become proportional to the transition temperature from the kination to the radiation era; since this temperature is significantly lower than the initial ("reheating") temperature, the abundances decrease with respect to their values in the standard cosmology. For values of the quintessential energy-density parameter close to its upper bound, at the eve of nucleosynthesis, we find the following: (i) for unstable gravitinos, the gravitino constraint is totally evaded; (ii) If the gravitino is stable, its thermal abundance is not sufficient to account for the cold dark matter of the universe; (iii) the thermal abundance of axinos can satisfy the cold dark matter constraint for values of the initial temperature well above those required in the standard cosmology. A novel calculation of the axino production rate by scatterings at low temperature is also presented.