Higher-derivative couplings in string theory: Dualities and the B field

The first quantum correction to the IIA string effective action arises at the eight-derivative level and takes the schematic form (t8t8−18ϵ10ϵ10)R4+B2∧X8. This correction, however, cannot be complete by itself, as it is neither supersymmetric nor T-duality covariant. We reexamine these eight-derivative couplings and conjecture that the simple replacement R→R(Ω+), where Ω+=Ω+12H is the connection with torsion, nearly completely captures their dependence on the B field. The exception is in the odd-odd spin structure sector, where additional terms are needed. We present here a complete result at the level of the five-point function and a partial one for the six-point function. Further evidence for this conjecture comes from considering T-duality as well as heterotic/IIA duality beyond leading order. Finally, we discuss the eleven-dimensional lift of the modified one-loop type IIA couplings.