Mixed (cold+warm) dark matter in the bino-wino coannihilation scenario

Abstract

We study phenomenological aspects of the bino-wino coannihilation scenario in high-scale supersymmetry (SUSY)-breaking models. High-scale SUSY-breaking scenarios are considered to be a promising possibility after the discovery of the Higgs boson with a mass around 126 GeV. In this paper, we discuss the bino lightest supersymmetric particle (LSP), accompanied by the (at most) around 30 GeV heavier wino. With suitable mass splitting between the bino and the wino, the bino LSP has the correct relic abundance of dark matter. For a smaller mass splitting, the late-time decay of the gravitino can provide the correct abundance of bino dark matter. It is extremely challenging to find signals from the bino dark matter in direct and indirect detections. By utilizing multijets plus missing transverse momentum events at the LHC, we can constrain the gluino mass and thus probe the bino-wino coannihilation scenario indirectly. The collider experiment, however, cannot search the bino dark matter directly. In this paper, we suggest the direct probe of the bino dark matter. We show that the bino dark matter leaves imprints on the small-scale matter power spectrum when the bino dark matter is produced by the decay of the gravitino. The nonthermal bino dark matter behaves as mixed ($\mathrm{cold}+\mathrm{warm}$) dark matter.