R-SYMMETRY AND THE TOPOLOGICAL TWIST OF N=2 EFFECTIVE SUPERGRAVITIES OF HETEROTIC STRINGS

We discuss R symmetries in locally supersymmetric N = 2 gauge theories coupled to hypermultiplets which can be thought of as effective theor ies of heterotic superstring models. In this type of supergravities a suitable R symmetry exists and can be used to topologically twist the theory: the vector multiplet containing the dilaton-axion field has di fferent R charge assignments with respect to the other vector multiple ts. Correspondingly a system of coupled instanton equations emerges, m ixing gravitational and Yang-Mills instantons with triholomorphic hype rinstantons and axion instantons. For the tree level classical special manifolds ST(n) = SU(1, 1)/U(1) x SO(2,n)/[SO(2) x SO(n)] R symmetry with the specified properties is a continuous symmetry, but for the qu antum-corrected manifolds <(ST)over cap (n)> a discrete R group of ele ctric-magnetic duality rotations is sufficient and we argue that it ex ists.