On off-shell bosonic string amplitudes
Cappiello L., Marotta R., Pettorino R., Pezzella F.
We give a simple prescription for computing, in the framework of the bosonic string theory, off-shell one-loop amplitudes with any number of external massless particles, for both the open and closed strings. We discuss their properties and, in particular, for the two-string one-loop amplitudes, we show their transversality.