2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54457We discuss R-symmetry in locally supersymmetric $N=2$ gauge theories coupled to hypermultiplets, which can be viewed as effective theories of heterotic string models. In this type of supergravities a suitable R-symmetry exists and can be used to topologically twist the theory. The vector multiplet of the dilaton-axion field has a different R-charge assignment with respect to the other vector multiplets.Proceedings of ``Susy95'', Palaiseaux, Ecole Polytechnique, May 95 LaTex, 8 pgsHigh Energy Physics - Theorytext