  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 wino mass is smaller than 2.9
TeV; however, even with smaller Wino mass, Wino can be the dominant component
of dark matter if it is non-thermally produced by the decay of an exotic
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 exotic-particle
decay, 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
exotic particle corresponds to cosmological moduli fields, gravitino, or axino,
and discuss the implication of the Wino LSP for these cases.
