Very Degenerate Higgsino Dark Matter

We present a study of the Very Degenerate Higgsino Dark Matter (DM), whose mass splitting between the lightest neutral and charged components is O (1) MeV, much smaller than radiative splitting of 355 MeV. The scenario is realized in the minimal supersymmetric standard model by small gaugino mixings. In contrast to the pure Higgsino DM with the radiative splitting only, various observable signatures with distinct features are induced. First of all, the very small mass splitting makes (a) sizable Sommerfeld enhancement and Ramsauer-Townsend (RT) suppression relevant to similar to 1TeV Higgsino DM, and (b) Sommerfeld-Ramsauer-Townsend e ff ect saturate at lower velocities v/c less than or similar to 10(-3). As a result, annihilation signals can be large enough to be observed from the galactic center and/or dwarf galaxies, while the relative signal sizes can vary depending on the locations of Sommerfeld peaks and RT dips. In addition, at collider experiments, stable chargino signatures can be searched for to probe the model in the future. DM direct detection signals, however, depend on the Wino mass; even no detectable signals can be induced if the Wino is heavier than about 10TeV.