SELF-DUAL SUPERGRAVITY FROM N=2 STRINGS

A new heterotic N = 2 string with manifest target space supersymmetry is constructed by combining a conventional N = 2 string in the right-m oving sector and a Green-Schwarz-Berkovits type string in the left-mov ing sector. The corresponding sigma model is then obtained by turning on background fields for the massless excitations. We compute the beta functions and we partially check the OPE's of the superconformal alge bra perturbatively in alpha', all in superspace. The resulting field e quations describe N = 1 self-dual supergravity. (C) 1997 Elsevier Scie nce B.V.