16-FERMION AND RELATED TERMS IN M-THEORY ON T-2

Certain one-loop processes in eleven-dimensional supergravity compacti fied on T-2 determine exact, non-perturbative, terms in the effective action of type II string theories compactified on a circle. One exampl e is the modular invariant U(1)-violating interaction of sixteen compl ex spin-1/2 fermions of ten-dimensional type IIB theory. This term, to gether with the (curvature)(4) term, and many other terms of the same dimension are all explicitly related by supersymmetry. (C) 1998 Publis hed by Elsevier Science B.V.