Cosmological simulations with rare and frequent dark matter self-interactions

TL;DR

This study conducts the first cosmological simulations of frequent dark matter self-interactions, revealing subtle differences from rare interactions and providing new constraints on interaction cross-sections.

Contribution

It introduces the first simulation of frequent dark matter self-interactions and compares their effects to rare interactions, offering new methods to distinguish them.

Findings

Satellite galaxy counts are significantly suppressed in frequent interactions.

Differences between frequent and rare interactions are subtle but can be distinguished using combined measures.

New upper limits on the cross-section for frequent dark matter self-interactions are established.

Abstract

Dark matter (DM) with self-interactions is a promising solution for the small-scale problems of the standard cosmological model. Here we perform the first cosmological simulation of frequent DM self-interactions, corresponding to small-angle DM scatterings. The focus of our analysis lies in finding and understanding differences to the traditionally assumed rare DM (large-angle) self scatterings. For this purpose, we compute the distribution of DM densities, the matter power spectrum, the two-point correlation function and the halo and subhalo mass functions. Furthermore, we investigate the density profiles of the DM haloes and their shapes. We find that overall large-angle and small-angle scatterings behave fairly similarly with a few exceptions. In particular, the number of satellites is considerably suppressed for frequent compared to rare self-interactions with the same cross-section. Overall we observe that while differences between the two cases may be difficult to establish using a single measure, the degeneracy may be broken through a combination of multiple ones. For instance, the combination of satellite counts with halo density or shape profiles could allow discriminating between rare and frequent self-interactions. As a by-product of our analysis, we provide - for the first time - upper limits on the cross-section for frequent self-interactions.