On the (b,c) system contribution to superstring amplitudes
Pettorino R., Pezzella F.
We use the sewing procedure in the operator formalism to construct explicitly the two-loop vertex for the (b,c) system of string theories in its more general form, needed to compute amplitudes involving picture-changed states. By using this operator we show that the contribution of the reparametrization ghosts to superstring amplitudes is just the same as their contribution to bosonic string ones. © 1991.