Phenomenology of Self-Interacting Dark Matter in a Matter-Dominated Universe

TL;DR

This paper investigates how self-interacting scalar dark matter produced during an early matter-dominated era affects its abundance and observational signatures, considering both freeze-out and freeze-in mechanisms with hidden sector interactions.

Contribution

It introduces the impact of self-interactions within the hidden sector on dark matter production during matter domination, a novel aspect not previously explored.

Findings

Self-interactions significantly alter dark matter abundance calculations.

The early matter-dominated phase impacts observational signatures of dark matter.

Both freeze-out and freeze-in scenarios are affected by hidden sector dynamics.

Abstract

We study production of self-interacting dark matter (DM) during an early matter-dominated phase. As a benchmark scenario, we consider a model where the DM consists of singlet scalar particles coupled to the visible Standard Model (SM) sector via the Higgs portal. We consider scenarios where the initial DM abundance is set by either the usual thermal freeze-out or an alternative freeze-in mechanism, where DM was never in thermal equilibrium with the SM sector. For the first time, we take the effect of self-interactions within the hidden sector into account in determining the DM abundance, reminiscent to the Strongly Interacting Massive Particle (SIMP) scenario. In all cases, the number density of DM may change considerably compared to the standard radiation-dominated case, having important observational and experimental ramifications.