Effective scalar four-fermion interaction for Ge-phobic exothermic dark matter and the CDMS-II Silicon excess

TL;DR

This paper explores a scalar four-fermion interaction model for Ge-phobic exothermic WIMP dark matter, explaining the CDMS-II Silicon excess while remaining consistent with other experimental constraints and relic density observations.

Contribution

It introduces a novel effective interaction framework for exothermic, Ge-phobic WIMPs that can account for the CDMS-II Silicon excess and includes NLO corrections in the analysis.

Findings

A parameter space where WIMPs explain the CDMS-II Silicon excess.

The model's relic density aligns with cosmological observations.

NLO corrections have a small but sometimes significant impact.

Abstract

We discuss within the framework of effective four-fermion scalar interaction the phenomenology of a Weakly Interacting Massive Particle (WIMP) Dirac Dark Matter candidate which is exothermic (i.e. is metastable and interacts with nuclear targets down-scattering to a lower-mass state) and $Ge$-phobic (i.e. whose couplings to quarks violate isospin symmetry leading to a suppression of its cross section off Germanium targets). We discuss the specific example of the CDMS-II Silicon three-candidate effect showing that a region of the parameter space of the model exists where WIMP scatterings can explain the excess in compliance with other experimental constraints, while at the same time the Dark Matter particle can have a thermal relic density compatible with observation. In this scenario the metastable state $\chi$ and the lowest-mass one $\chi^{\prime}$ have approximately the same density in the present Universe and in our Galaxy, but direct detection experiments are only sensitive to the down-scatters of $\chi$ to $\chi^{\prime}$. We include a discussion of the recently calculated Next-to-Leading Order corrections to Dark Matter-nucleus scattering, showing that their impact on the phenomenology is typically small, but can become sizable in the same parameter space where the thermal relic density is compatible to observation.