Origins of the isospin violation of dark matter interactions

Abstract

Light dark matter (DM) with a large DM-nucleon spin-independent scattering cross section and moreover proper isospin violation (ISV) fn/fp ≈ −0.7 may provide a way to understand the confusing DM direct detection results. Further using the stringent astrophysical and collider constraints, we systematically investigate the origin of ISV first via general operator analyses and further via specifying three types of mediators: a light Z′ from chiral U(1)X, an approximate spectator Higgs doublet (It can explain the W+jj anomaly simultaneously) and color triplets. In addition, although Z′ from an exotic U(1)X mixing with U(1)Y generates only fn = 0, we can combine it with the conventional Higgs to achieve the proper ISV. As a concrete example, we propose the U(1)X model where the U(1)X charged light sneutrino is an inelastic DM, which dominantly annihilates to light dark states such as Z′ with sub-GeV mass. The model can consistently (with other DM direct detection results) and safely interpret the recent GoGeNT annual modulation result.