SIMPle Dark Matter: Self-Interactions and keV Lines

Abstract

We consider a simple supersymmetric hidden sector: pure SU(N) gauge theory. Dark matter is made up of hidden glueballinos with mass $m_X$ and hidden glueballs with mass near the confinement scale $\Lambda$. For $m_X\sim 1\text{TeV}$ and $\Lambda \sim 100\text{MeV}$, the glueballinos freeze out with the correct relic density and self-interact through glueball exchange to resolve small-scale structure puzzles. An immediate consequence is that the glueballino spectrum has a hyperfine splitting of order ${\Lambda }^2/m_X\sim 10\text{keV}$. We show that the radiative decays of the excited state can explain the observed 3.5 keV X-ray line signal from clusters of galaxies, Andromeda, and the Milky Way.

Comments: v1: 6 pages, 2 figures; v2: added references, published version; v3: note added