Generalized Unitarity Method for Unstable Particles

In theories with unstable particles, unitarity is satisfied by the inclusion of only stable states in sums. Hence cuts are not to be taken through particles. This raises a challenge generalized method, whose aim reconstruct amplitudes analyzing sets cuts. Nevertheless, under some general physical conditions, and perhaps methodological modifications, we prove that method still reliable for one-loop containing resonances. We discuss simple examples which illustrate these features.