Type IIB R4H4g-4 conjectures

We propose SL(2, Z) (and SL(3, Z))-invariant conjectures for all (RH4g-4)-H-4 couplings of Type IIB strings on R-10 (and R-8 x T-2), generalizing conjectures of Green and Gutperle (and Kiritsis and Pioline) for the R-4 coupling. A strong check for our conjectures is that on T-2 at weak coupling, they reproduce the multiloop scattering amplitudes which had been previously computed using N = 2 strings in the N = 4 topological formalism. Applications to (p,q) string production in a background H field, generalizing Schwinger's computation for pair production in a constant F field, are suggested. (C) 1998 Elsevier Science B.V.