Wheeler propagator

We study the half-advanced and half-retarded Wheeler Green function and its relation to Feynman propagators, first for massless equation, then, for Kl ein-Gordon equations with arbitrary mass parameters, real, imaginary, or co mplex. In all cases the Wheeler propagator lacks an on-shell free propagati on. The Wheeler function has support inside the light-cone (whatever the ma ss). The associated vacuum is symmetric with respect to annihilation and cr eation operators. We show with some examples that perturbative unitarity ho lds, whatever the mass (real or complex). Some possible applications are di scussed.