Non-standard cosmological scenarios, Sommerfeld enhancement and asymmetric dark matter

TL;DR

This paper explores how non-standard cosmological models, Sommerfeld enhancement, and asymmetric dark matter interactions influence relic density, revealing complex effects on dark matter freeze-out and providing constraints on model parameters.

Contribution

It introduces a detailed analysis of the combined effects of modified cosmic expansion and Sommerfeld enhancement on asymmetric dark matter relic density, including new constraint relations.

Findings

Sommerfeld enhancement significantly increases annihilation cross sections.

Modified cosmic expansion rate affects the decoupling temperature of dark matter.

Derived upper bounds on asymmetric dark matter mass for s-wave and p-wave annihilations.

Abstract

We discuss the relic density of asymmetric dark matter with long-range interactions in non-standard cosmological scenarios where the extra cosmic energy is introduced. The Hubble expansion rate is modified in non-standard cosmological models, which affects the relic density of dark matter. If the mass of the dark exchanged gauge boson is less than the mass of dark matter particles multiplied by the dark fine-structure constant, the wave function of the incoming particles of dark matter annihilation would be distorted away from the free plane-wave approximation, yielding the significant enhancements to annihilation cross sections, known as Sommerfeld enhancement. Sommerfeld enhancement results the asymmetric dark matter relic density under abundant, while the enhanced cosmic expansion rate increases the relic density of asymmetric dark matter by letting the decoupling from the thermal equilibrium occurs earlier. However, the mixed effect of modified cosmic expansion and the Sommerfeld enhancement on asymmetric dark matter density evolution becomes quite complicated, due to their opposing affects on relic density and contrary strength developments as the temperature fell. We investigated the mixed effects on asymmetric dark matter freeze-out process and current relic abundance, which is significantly different from the standard situation. Further, we calculate the constraint relations of the asymmetric dark matter pertubative annihilation cross section and dark coupling constant with the mass of asymmetric dark matter, the asymmetry factor with the dark coupling constant, when the relic density of asymmetric dark matter falled in the observed region. The upper bounds on the mass of asymmetric dark matter for s-wave and p-wave annihilations are also derived.