On off-shell bosonic string amplitudes
  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, both for the open and for the closed string. We discuss their properties and, in particular, for the two-string one-loop amplitudes we show their being transverse. 
L. Cappiello, R. Marotta, R. Pettorino and F. Pezzella (Dipartimento   di Scienze Fisiche, Universita' di Napoli and INFN, S...