Cosmological simulations with self-interacting dark matter – II. Halo shapes versus observations

Abstract

If dark matter has a large self-interaction scattering cross section, then interactions among dark-matter particles will drive galaxy and cluster halos to become spherical in their centers. Work in the past has used this effect to rule out velocity-independent, elastic cross sections larger than σ/m 0.02 cm 2 /g based on comparisons to the shapes of galaxy cluster lensing potentials and X-ray isophotes. In this paper, we use cosmological simulations to show that these constraints were off by more than an order of magnitude because (a) they did not properly account for the fact that the observed ellipticity gets contributions from the triaxial mass distribution outside the core set by scatterings, (b) the scatter in axis ratios is large and (c) the core region retains more of its triaxial nature than estimated before. Including these effects properly shows that the same observations now allow dark matter self-interaction cross sections at least as large as σ/m = 0.1 cm 2 /g. We show that constraints on self-interacting dark matter from strong-lensing clusters are likely to improve significantly in the near future, but possibly more via central densities and core sizes than halo shapes.

Direct detection portals for self-interacting dark matter

“…• Self-interactions within dwarf halos can modify the DM distribution in line with observations for σ/m X ∼ 1 cm 2 /g [13][14][15][16]. The shaded bands in Figs.…”

“…For symmetric DM, where X andX are populated equally in the early Universe, the 2 In principle, since numerical simulations follow the trajectories and velocities of each "particle," these dependencies can be straight-forwardly accounted for. However, SIDM simulations thus far have been restricted to cross sections with a v-dependence that is either constant [14,15] or motivated within the classical limit (m X v/m φ 1) [13,16] and with isotropic angular dependence. relic density is determined by standard freeze-out, requiring a thermally-averaged cross section σv ann ≈ 6 × 10 −26 cm 3 /s.…”

BeyondΛCDM: Problems, solutions, and the road ahead

“…The detection of a halo with a mass much less than 10 9 M would be a dramatic confirmation of Dark matter may also have a self-interaction, which could potentially be very large. The present constraint on the interaction strength of dark matter comes from the shapes of clusters, and is fairly weak, < 0.1 cm 2 /g [373]. Interacting dark matter could explain why dwarfs have cores [374] (where the dark matter density becomes constant towards the center of the halo).…”

Testing dark matter clustering with redshift space distortions

“…The analysis is intended to be a purely phenomenological assessment of what growth data can say about the clustering strength, but related effects can arise in models such as self interacting dark matter, e.g. [17][18][19][20][21] multiple dark matter, e.g. [22][23][24][25][26][27], atomic dark matter [28], resonant dark matter [29], cannibal dark matter [30], etc.…”