Cannibalism's lingering imprint on the matter power spectrum

Abstract

The early universe may have contained internally thermalized dark sectors that were decoupled from the Standard Model. In such scenarios, the relic dark thermal bath, composed of the lightest particle in the dark sector, can give rise to an epoch of early matter domination prior to Big Bang Nucleosynthesis, which has a potentially observable impact on the smallest dark matter structures. This lightest dark particle can easily and generically have number-changing self-interactions that give rise to "cannibal" behavior. We consider cosmologies where an initially sub-dominant cannibal species comes to temporarily drive the expansion of the universe, and we provide a simple map between the particle properties of the cannibal species and the key features of the enhanced dark matter perturbation growth in such cosmologies. We further demonstrate that cannibal self-interactions can determine the small-scale cutoff in the matter power spectrum even when the cannibal self-interactions freeze out prior to cannibal domination.

Dark matter self-interactions in the matter power spectrum

“…This requires a modification of the publicly available code to include self-interactions, allowing DM to interpolate between perfect fluid and free streaming behavior. Related work can be found in [12][13][14]. While our analysis differs in several aspects our findings are consistent with the results presented in [12].…”

Smallest remnants of early matter domination

“…Such a cosmology can have a profound impact of the production of dark matter (DM), favouring regions of theory space that are radically different from naive expectations [21,22,[24][25][26][27][28][29][30][31][32]. An EMD phase would also produce potentially observable relics in the spatial distribution of dark matter (DM) on the very smallest scales which would be easily distinguishable from that expected in ΛCDM if one observes them [33][34][35][36][37][38][39][40][41]. These smallest structures are gravitationally bound clumps of DM (microhalos).…”