spin 1/2 fields in curved spacetime

While quantum eld theory in minkowski spacetime relies on the notion of one particlestates, the existence of such states has been controversial in the context of quantum eld theoryin curved spacetime. in this talk we argue that a notion of spin 12 one-particle state exists ingeneral time-dependent curved backgrounds. these particles are localized on two dimensionalsubspaces and in the at spacetime limit simulate spin-up massless dirac particles separatedfrom their spin-down counterparts.