Infrared-finite amplitudes for massless gauge theories Original Research Article

We present a method to construct infrared-finite amplitudes for gauge theories with massless fermions. Rather than computing S-matrix elements between usual states of the Fock space we construct order-by-order in perturbation theory dressed states that incorporate all long-range interactions. The S-matrix elements between these states are shown to be free from soft and collinear singularities. As an explicit example we consider the process e+e−→2 jets at next-to-leading order in the strong coupling. We verify by explicit calculation that the amplitudes are infrared-finite and recover the well-known result for the total cross section e+e−→ hadrons.