Self-interacting Dark Matter Energy Density

TL;DR

This paper explores how elastic dark matter self-interactions can dominate early universe energy density, affecting structure formation and aligning with cosmic ray observations, while remaining consistent with nucleosynthesis constraints.

Contribution

It introduces a model where dark matter self-interactions significantly influence early cosmology and structure formation, with implications for cosmic ray excesses and nucleosynthesis constraints.

Findings

Self-interacting dark matter can dominate early universe energy density.

Constraints allow self-interaction strength comparable to strong interactions.

Enhanced small-scale structure formation before star formation.

Abstract

We investigate cosmological implications of an energy density contribution arising by elastic dark matter self-interactions. Its scaling behaviour shows that it can be the dominant energy contribution in the early universe. Constraints from primordial nucleosynthesis give an upper limit on the self-interaction strength which allows for the same strength as standard model strong interactions. Furthermore we explore the cosmological consequences of an early self-interaction dominated universe. Chemical dark matter decoupling requires that self-interacting dark matter particles are rather light (keV range) but we find that super-weak inelastic interactions are predicted by strong elastic dark matter self-interactions. Assuming a second, collisionless cold dark matter component, its natural decoupling scale exceeds the weak scale and is in accord with the electron and positron excess observed by PAMELA and Fermi-LAT. Structure formation analysis reveals a linear growing solution during self-interaction domination, enhancing structures up to ~ 10^(-3) solar masses long before the formation of the first stars.