A Proposal To Constrain Self-Interacting Dark Matter

Usually, I prefer to wait until an experiment or observation has results before discussing a proposal. But this time, the theoretical analysis in the paper and the state of existing knowledge, is sufficient.

The key theoretical conclusion is that structure formation happens later in self-interacting dark matter models than it does with the Lambda CDM Standard Model of Cosmology's simple cold dark matter model.

If this theoretical analysis is correct, however, we can pretty much rule out self-interacting dark matter models, because we know that structure formation has been observed to take place earlier than predicted in the LambdaCDM model, as is the case generically in gravity based models attempting to describe phenomena attributed to dark matter.

Observations of the high redshift universe provide a promising avenue for constraining the nature of the dark matter (DM). This will be even more true following the now successful launch of the James Webb Space Telescope (JWST). We run cosmological simulations of galaxy formation as a part of the Effective Theory of Structure Formation (ETHOS) project to compare the properties of high redshift galaxies in Cold (CDM) and alternative DM models which have varying relativistic coupling and self-interaction strengths. 

Phenomenologically, the interacting DM scenarios result in a cutoff in the linear power spectrum on small-scales, followed by a series of "dark acoustic oscillations" (DAOs). We find that DM interactions suppress the abundance of galaxies below M⋆∼10^8M⊙ for the models considered. The cutoff in the linear power spectrum generally causes a delay in structure formation relative to CDM. Objects in ETHOS that end up at the same final masses as their CDM counterparts are characterised by a more vigorous phase of early star formation. While galaxies with M⋆≲10^6M⊙ make up more than 60 per cent of star formation in CDM at z≈10, they contribute only about half the star formation density in ETHOS. These differences in star formation diminish with decreasing redshift. We find that the effects of DM self-interactions are negligible compared to effects of relativistic coupling (i.e. the effective initial conditions for galaxy formation) in all properties of the galaxy population we examine. Finally, we show that the clustering strength of galaxies at high redshifts depends sensitively on DM physics, although these differences are manifest on scales that may be too small to be measurable by JWST.

Ali Kurmus, et al., "The feasibility of constraining DM interactions with high-redshift observations by JWST" arXiv:2203.04985 (March 9, 2022) (Submitted to MNRAS).