Very Degenerate Higgsino Dark Matter

TL;DR

This paper explores a very degenerate Higgsino dark matter scenario with minimal mass splitting, leading to unique observable signatures in indirect detection, collider experiments, and direct detection depending on model parameters.

Contribution

It introduces a minimal supersymmetric model with small gaugino mixing resulting in very small Higgsino mass splitting, revealing new phenomenological signatures.

Findings

Enhanced annihilation signals from galactic center and dwarf galaxies.

Observable stable chargino signatures at colliders.

Direct detection signals depend on Wino mass, with potential null results if Wino > 10 TeV.

Abstract

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.