Constraints on Asymmetric Dark Matter Self Annihilation Cross Sections

Abstract

The evolution of the relic density for asymmetric dark matter incorporating self annihilation processes in both the shear-dominated universe and Gauss–Bonnet braneworld is investigated. Under the same conditions where the ratio of final asymmetry to the initial asymmetry $R\equiv {\Delta }_{-\infty }/{\Delta }_{\text{in}}$ is identical, the shear-dominated universe, due to its enhanced Hubble expansion rate, leads to an earlier freeze-out point of wash-out asymmetry process and allows a higher upper limit on the self annihilation cross section. Conversely, the Gauss–Bonnet braneworld, with a weakened Hubble expansion rate, delays the freeze-out point and permits a lower upper limit on the self annihilation cross section. The wino mass $M_2$ for sneutrino and higgsino asymmetric dark matter are further constrained in both scenarios, showing that, compared to the standard model, the lower limit of $M_2$ is smaller in the shear-dominated universe but higher in the Gauss–Bonnet braneworld.