Generalized spin-dependent WIMP-nucleus interactions and the DAMA modulation effect

TL;DR

This paper classifies all possible spin-dependent WIMP-nucleus interactions using EFT and explores their compatibility with DAMA's modulation signal, considering non-standard halo velocity distributions and momentum-dependent cross sections.

Contribution

It provides a comprehensive EFT-based classification of spin-dependent WIMP interactions and identifies scenarios that could explain DAMA results with non-Maxwellian halo velocities.

Findings

Certain velocity-dependent interactions can reconcile DAMA with other constraints for WIMPs below 30 GeV.

Compatibility requires non-Maxwellian halo velocity distributions.

Larger WIMP masses are excluded by other detector constraints.

Abstract

Guided by non-relativistic Effective Field Theory (EFT) we classify the most general spin-dependent interactions between a fermionic Weakly Interacting Massive Particle (WIMP) and nuclei, and within this class of models we discuss the viability of an interpretation of the DAMA modulation result in terms of a signal from WIMP elastic scatterings using a halo-independent approach. We find that, although several relativistic EFT's can lead to a spin-dependent cross section, in some cases with an explicit, non-negligible dependence on the WIMP incoming velocity, three main scenarios can be singled out in the non-relativistic limit which approximately encompass them all, and that only differ by their dependence on the transferred momentum. For two of them compatibility between DAMA and other constraints is possible for a WIMP mass below 30 GeV, but only for a WIMP velocity distribution in the halo of our Galaxy which departs from a Maxwellian. This is achieved by combining a suppression of the WIMP effective coupling to neutrons (to evade constraints from xenon and germanium detectors) to an explicit quadratic or quartic dependence of the cross section on the transferred momentum (that leads to a relative enhancement of the expected rate off sodium in DAMA compared to that off fluorine in droplet detectors and bubble chambers). For larger WIMP masses the same scenarios are excluded by scatterings off iodine in COUPP.