The Atacama Cosmology Telescope: limits on dark matter-baryon interactions from DR4 power spectra

TL;DR

This paper uses combined Planck and ACT DR4 data to set new upper limits on dark matter-baryon interactions, tightening constraints on scattering cross sections and exploring velocity-dependent models.

Contribution

It provides the first combined analysis of large-scale and small-scale CMB data to constrain dark matter-baryon elastic scattering, improving existing bounds.

Findings

Tighter bounds on proton scattering cross sections by 40% compared to previous CMB constraints.

Some velocity-dependent models show 2σ deviations from zero cross section, but are not statistically favored.

No statistically significant detection of dark matter-baryon scattering was found.

Abstract

Diverse astrophysical observations suggest the existence of cold dark matter that interacts only gravitationally with radiation and ordinary baryonic matter. Any nonzero coupling between dark matter and baryons would provide a significant step towards understanding the particle nature of dark matter. Measurements of the cosmic microwave background (CMB) provide constraints on such a coupling that complement laboratory searches. In this work we place upper limits on a variety of models for dark matter elastic scattering with protons and electrons by combining large-scale CMB data from the Planck satellite with small-scale information from Atacama Cosmology Telescope (ACT) DR4 data. In the case of velocity-independent scattering, we obtain bounds on the interaction cross section for protons that are 40\% tighter than previous constraints from the CMB anisotropy. For some models with velocity-dependent scattering we find best-fitting cross sections with a 2$\sigma$ deviation from zero, but these scattering models are not statistically preferred over $\Lambda$CDM in terms of model selection.