Amplitude for N-gluon superstring scattering

We consider scattering processes involving N gluonic massless states of open superstrings with a certain Regge slope alpha('). At the semiclassical level, the string world-sheet sweeps a disk and N gluons are created or annihilated at the boundary. We present exact expressions for the corresponding amplitudes, valid to all orders in alpha('), for the so-called maximally helicity violating configurations, with N=4, 5 and N=6. We also obtain the leading O(alpha('2)) string corrections to the zero-slope N-gluon Yang-Mills amplitudes.