Non-thermal production of Wino dark matter via the decay of long-lived particles

A bstract We consider supersymmetric models in which the neutral Wino is the lightest superparticle (LSP), and study the possibility that non-thermally produced Wino plays the role of dark matter. The thermal relic density of Wino is smaller than the present mass density of dark matter if ≲ 2.9 TeV; however, even with smaller Wino mass, the Wino can be the dominant component of dark matter if it is non-thermally produced by the decay of a long-lived particle. In order to study such a possibility in detail, we perform a precise calculation of the present mass density of Wino produced by the decay of a long- lived particle, taking account of the following effects: (i) coannihilation among charged and neutral Winos, and (ii) Sommerfeld effect on the pair annihilation cross section of Winos. We consider several well-motivated cases where the long-lived particle corresponds to cosmological moduli fields, gravitino, or axino, and discuss the implication of the Wino LSP for these cases.