Instanton Action for Type II Hypermultiplets

We analyze the hypermultiplet moduli space describing the universal sector of type IIA theory compactified on a Calabi-Yau threefold. The classical moduli space is described in terms of the coset SU(2, 1)/U(2). The flux quantization condition of the antisymmetric tensor field of M-theory implies discrete identifications for the scalar fields describing this four-dimensional quaternionic geometry. Non-perturbative corrections of the classical theory are described in terms of a membrane-fivebrane instanton action which we construct herein.