Type IIB R4H4g-4 conjectures

We propose SL(2, ℤ) (and SL(3, ℤ))-invariant conjectures for all R4H4g-4 couplings of Type IIB strings on ℝ10 (and ℝ8×T2), generalizing conjectures of Green and Gutperle (and Kiritsis and Pioline) for the R4 coupling. A strong check for our conjectures is that on T2 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. © 1998 Elsevier Science B.V.