Direct Detection of Multi-component Secluded WIMPs

TL;DR

This paper investigates how multi-component secluded WIMPs with small mass gaps interact in direct detection experiments, revealing that second-order elastic scattering and long-lived excited states significantly influence detection sensitivity and constraints.

Contribution

It provides detailed calculations of elastic and inelastic cross sections for multi-component WIMPs and explores the impact of small mass splittings on detection constraints.

Findings

Second-order elastic scattering enhances sensitivity across various mass splittings.

Long-lived excited states with fractional abundance above 0.1% are common for small splittings.

Mass splittings below 200 keV lead to stronger constraints due to exothermic de-excitation events.

Abstract

Dark matter candidates comprising several sub-states separated by a small mass gap, and coupled to the Standard Model by (sub-)GeV force carriers, can exhibit non-trivial scattering interactions in direct detection experiments. We analyze the secluded U(1)-mediated WIMP scenario, and calculate the elastic and inelastic cross sections for multi-component WIMP scattering off nuclei. We find that second-order elastic scattering, mediated by virtual excited states, provides strong sensitivity to the parameters of the model for a wide range of mass splittings, while for small splittings the WIMP excited states have lifetimes exceeding the age of the universe, and generically have a fractional relative abundance above 0.1%. This generates even stronger constraints for mass splittings less than 200 keV due to exothermic de-excitation events in detectors.