Abstract
We consider the prospects for multiple dark matter direct detection experiments to determine if the interactions of a dark matter candidate are isospin-violating. We focus on theoretically well-motivated examples of isospin-violating dark matter (IVDM), including models in which dark matter interactions with nuclei are mediated by a dark photon, a Z, or a squark. We determine that the best prospects for distinguishing IVDM from the isospin-invariant scenario arise in the cases of dark photon- or Z-mediated interactions, and that the ideal experimental scenario would consist of large exposure xenon- and neon-based detectors. If such models just evade current direct detection limits, then one could distinguish such models from the standard isospin-invariant case with two detectors with of order 100 ton-year exposure.
Highlights
The most studied scenario for the direct detection of dark matter is through elastic spin-independent (SI) velocityindependent contact scattering with a variety of target nuclei
We consider the scenario of an Isospin-violating dark matter (IVDM) candidate which just escapes current direct detection limits from XENON1T [25] and PandaX-II [26], and we study the exposure which would be needed by two different experiments to discover the dark matter candidate, but determine that its interactions are isospin-violating
We consider three benchmark examples for the interaction of a generic DM candidate with SM quarks. (a) Dark Photon Mediation: The dark matter is a Dirac fermion which interacts through a massive dark photon [28,29,30,31] that kinetically mixes with the SM photon. (b) Z Mediation: The dark matter is a Dirac fermion which interacts through Z exchange. (c) Squark Mediation: The dark matter is a binolike lightest neutralino of the Minimal Supersymmetric Standard Model (MSSM), which interacts with nucleons through squark exchange [32], but flavor violation is not minimal
Summary
The most studied scenario for the direct detection of dark matter is through elastic spin-independent (SI) velocityindependent contact scattering with a variety of target nuclei. Isospin-violating dark matter (IVDM) has been well studied as an approach for resolving the apparent tension between the exclusion limits of some experiments (including CDMS-Ge [6,7], Edelweiss [8], XENON10 [9], XENON100 [10,11] and LUX [12]) and putative signals of other direct detection experiments (DAMA [13], CoGeNT [14,15], CRESST [16], CDMS-Si [17]) Theoretical models for this scenario have been studied in, for example, Refs.
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