A taste of dark matter: Flavour constraints on pseudoscalar mediators

TL;DR

This paper explores how light pseudoscalar mediators in dark matter models can be constrained by flavour-changing processes, providing new insights into their detectability and compatibility with existing experimental bounds.

Contribution

It offers a detailed analysis of flavour constraints on pseudoscalar mediators, highlighting their implications for dark matter interactions and experimental detection prospects.

Findings

Flavour constraints limit pseudoscalar mediator masses to above B mesons.

A pseudoscalar can only explain the Galactic Centre excess if its mass exceeds B mesons.

Large direct detection cross sections are incompatible with DAMA modulation explanations.

Abstract

Dark matter interacting via the exchange of a light pseudoscalar can induce observable signals in indirect detection experiments and experience large self-interactions while evading the strong bounds from direct dark matter searches. The pseudoscalar mediator will however induce flavour-changing interactions in the Standard Model, providing a promising alternative way to test these models. We investigate in detail the constraints arising from rare meson decays and fixed target experiments for different coupling structures between the pseudoscalar and Standard Model fermions. The resulting bounds are highly complementary to the information inferred from the dark matter relic density and the constraints from primordial nucleosynthesis. We discuss the implications of our findings for the dark matter self-interaction cross section and the prospects of probing dark matter coupled to a light pseudoscalar with direct or indirect detection experiments. In particular, we find that a pseudoscalar mediator can only explain the Galactic Centre excess if its mass is above that of the B mesons, and that it is impossible to obtain a sufficiently large direct detection cross section to account for the DAMA modulation