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 ${\cal
O}$(1) MeV, much smaller than radiative splitting of 355 MeV. The scenario is
realized in the minimal supersymmetric standard model by small gaugino mixing.
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 ~1 TeV Higgsino DM, and (b)
Sommerfeld-Ramsauer-Townsend effect saturate at lower velocities $v/c \lesssim
10^{-3}$. As a result, annihilation signals can be large enough to be observed
from the galactic center and/or dwarf galaxies, while relative signal sizes can
vary depending on the location of Sommerfeld peaks and RT dips. In addition, at
collider experiments, stable chargino signature can be searched for to probe
the model in the future. DM direct detection signal, however, depends on the
Wino mass; even no detectable signal can be induced if the Wino is heavier than
about 10 TeV.
