Dark matter coupled to radiation: Limits from the Milky Way satellites

TL;DR

This paper establishes new upper limits on dark matter interactions with photons and neutrinos using Milky Way satellite galaxy data, significantly improving previous constraints and informing future detection efforts.

Contribution

The study derives the most stringent limits to date on DM-radiation scattering cross sections from satellite galaxy observations, considering temperature-independent interactions.

Findings

Limits on DM-photon and DM-neutrino scattering cross sections are improved by an order of magnitude.

Constraints depend linearly on DM mass for masses above 1 MeV and become more stringent at lower masses.

Upcoming surveys will further tighten these bounds, enhancing our understanding of DM interactions.

Abstract

Interactions between dark matter (DM) and relativistic particles at early times suppress structure formation on small scales. In particular, the scattering process transfers heat and momentum from radiation to DM, ultimately reducing the abundance of low-mass DM halos and the dwarf galaxies they host. Herein, we derive limits on DM-photon and DM-neutrino scattering cross section using the Milky Way satellite galaxy population. We consider temperature-independent interactions parameterized by DM mass ($m_\chi$) and DM-radiation interaction cross section ($\sigma_{\chi\text{-}i}$, where $i$ represents the target species). By requiring that the linear matter power spectra be strictly less suppressed than in the case of a thermal-relic warm DM cutoff, we derive the following $95\%$ upper limits at $m_\chi=1$ MeV: $\sigma_{\chi\text{-}\gamma}<1.98\times10^{-38}\text{cm}^2$ and $\sigma_{\chi\text{-}\nu}<3.16\times10^{-38}\text{cm}^2$. Our bounds on $\sigma_{\chi\text{-}i}$ depend linearly on $m_\chi$ for $m_\chi \gtrsim 1~\mathrm{MeV}$ and improve upon previous limits by 1 order of magnitude. The mass dependence of our limit approaches $m_\chi^3$ at lower masses due to the effects of DM sound speed; at $m_{\chi}=100~\mathrm{keV}$, we arrive at an upper limit 3 orders of magnitude more stringent than achieved in previous explorations. Upcoming dwarf galaxy surveys will further improve the sensitivity of similar analyses, complementing laboratory and indirect detection searches for DM-radiation interactions.