Strongly interacting dark matter: Self-interactions and keV lines

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 Λ . For m_X∼1 TeV and Λ ∼100 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 Λ²/m_X∼10 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.