Fermionic Dark Matter through a Light Pseudoscalar Portal: Hints from the DAMA Results

TL;DR

This paper explores fermionic dark matter interacting via a light pseudoscalar portal, showing that CP-violating interactions can reconcile DAMA signals with null results from other experiments, and discusses future experimental constraints.

Contribution

It introduces a model with CP-violating pseudoscalar interactions that can explain DAMA results while remaining consistent with other null detection experiments.

Findings

CP-violating interactions dominate at direct detection.

DAMA signal can be compatible with null results for certain coupling ratios.

Future experiments will further test this dark matter model.

Abstract

We study the fermionic dark matter (DM) particle interacting with Standard Model quarks via a light pseudoscalar mediator. We consider separately the scenarios for which the DM-pseudoscalar coupling is $CP$ conserving or $CP$ violating. We show that taking a contact interaction is not suitable, even when the mediator has a mass of the same order of magnitude as the typical momentum transfer at the direct-detection experiments, such that the allowed DAMA region is excluded or considerably modified by the correct relic density requirement. The DAMA result seems to indicate that the $CP$-violating interaction is dominant at direct searches. We find that, if the proton-to-neutron effective coupling ratio is $-60\sim -40$, the exclusion limits set by SuperCDMS, XENON100, and LUX are highly suppressed, and the DAMA signal can thus be easily reconciled with these null measurements. For this model, the allowed region determined by the DAMA signal and correct relic density can successfully satisfy the conditions required by the thermal equilibrium, big bang nucleosynthesis, and DM self-interactions. The results of future measurements on flavor physics will provide important constraints on the related models. Precise measurements performed by COUPP, PICASSO, SIMPLE and KIMS should be able to test this model in the near future.