Irreducible Constraints on Hadronically Interacting Sub-GeV Dark Matter

TL;DR

This paper establishes stringent, model-independent upper limits on sub-GeV dark matter interactions with nucleons using low-energy effective theory, significantly surpassing previous astrophysical and cosmological constraints.

Contribution

It derives the first comprehensive bounds on hadronically interacting sub-GeV dark matter, considering electromagnetic effects and cosmological constraints within a unified low-energy framework.

Findings

Constraints exclude cross-sections above 10^{-36} cm^2 for keV-100 MeV dark matter.

Electromagnetic interactions from hadronic couplings lead to strong BBN and freeze-in constraints.

Leading-order hadronic couplings are tightly constrained by meson decay data.

Abstract

We derive conservative upper limits on the dark-matter--nucleon scattering cross-section for sub-GeV mass dark matter. Working exclusively within the low-energy chiral effective theory, we derive bounds that are independent of the details of the dark matter interactions in the UV. Dark matter that interacts only hadronically at leading order also inevitably interacts with photons or electrons at next-to-leading-order. We show that these electromagnetic interactions lead to strong constraints from big bang nucleosynthesis and over-production of dark matter via freeze-in at low temperatures, while the leading-order hadronic couplings face stringent constraints from meson decays. Combining these constraints, we rule out both spin-independent and spin-dependent dark-matter--nucleon scattering cross-sections $\gtrsim 10^{-36}\,{\rm cm}^2$ for dark matter masses in the keV - 100 MeV range. These bounds are several orders of magnitude stronger than the existing constraints from astrophysics and cosmology and have significant implications for future low-mass direct detection experiments.