Direct Detection of Light "Ge-phobic" Exothermic Dark Matter

TL;DR

This paper compares light exothermic dark matter detection data under different halo models, showing that isospin-violating couplings, especially 'Ge-phobic', can reconcile experimental results with bounds.

Contribution

It introduces the concept of 'Ge-phobic' isospin-violating couplings in exothermic dark matter, providing a novel way to reconcile conflicting experimental constraints.

Findings

Isospin-violating couplings reduce germanium sensitivity.

'Ge-phobic' exoDM aligns CDMS-II-Si with bounds.

Halo-independent analysis supports 'Ge-phobic' viability.

Abstract

We present comparisons of direct dark matter (DM) detection data for light WIMPs with exothermic scattering with nuclei (exoDM), both assuming the Standard Halo Model (SHM) and in a halo model - independent manner. Exothermic interactions favor light targets, thus reducing the importance of upper limits derived from xenon targets, the most restrictive of which is at present the LUX limit. In our SHM analysis the CDMS-II-Si and CoGeNT regions become allowed by these bounds, however the recent SuperCDMS limit rejects both regions for exoDM with isospin-conserving couplings. An isospin-violating coupling of the exoDM, in particular one with a neutron to proton coupling ratio of $-0.8$ (which we call "Ge-phobic"), maximally reduces the DM coupling to germanium and allows the CDMS-II-Si region to become compatible with all bounds. This is also clearly shown in our halo-independent analysis.