Maximal R-symmetry violating amplitudes in type IIb superstring theory

On-shell superspace techniques are used to quantify R-symmetry violation in type IIB superstring theory amplitudes in a flat background in 10 dimensions. This shows the existence of a particularly simple class of nonvanishing amplitudes in this theory, which violate R symmetry maximally. General properties of the class and some of its extensions are established that at string tree level are shown to determine the first three nontrivial effective field theory contributions to all multiplicity. This leads to a natural conjecture for the exact analytic part of the first two of these.