Using the Milky Way satellites to study interactions between cold dark matter and radiation

TL;DR

This paper demonstrates that incorporating interactions between cold dark matter and radiation in simulations reduces the predicted number of Milky Way satellite galaxies, addressing a key challenge in small-scale structure formation.

Contribution

It introduces a novel simulation approach including dark matter-radiation interactions, improving constraints beyond cosmic microwave background analyses.

Findings

Interactions reduce satellite galaxy counts significantly.

Dark matter-radiation physics is crucial for accurate small-scale predictions.

Constraints on dark matter interactions are substantially improved.

Abstract

The cold dark matter (CDM) model faces persistent challenges on small scales. In particular, taken at face value, the model significantly overestimates the number of satellite galaxies around the Milky Way. Attempts to solve this problem remain open to debate and have even led some to abandon CDM altogether. However, current simulations are limited by the assumption that dark matter feels only gravity. Here, we show that including interactions between CDM and radiation (photons or neutrinos) leads to a dramatic reduction in the number of satellite galaxies, alleviating the Milky Way satellite problem and indicating that physics beyond gravity may be essential to make accurate predictions of structure formation on small scales. The methodology introduced here gives constraints on dark matter interactions that are significantly improved over those from the cosmic microwave background.