The low-energy effective action for perturbative heterotic strings on K3 × T2 and the d = 4 N = 2 vector-tensor multiplet Original Research Article

We consider d = 4 N = 2 supergravity theories which serve as low-energy effective actions for heterotic strings on K3 × T2. At the perturbative level we construct a new version of the heterotic effective action in which the axion has been traded for an antisymmetric tensor field. In the string frame the antisymmetric tensor does not transform under Poincaré supersymmetry into the dilaton-dilatini system. This indicates that, in this frame, the antisymmetric tensor field and the dilaton are not contained in an N = 2 vector-tensor multiplet. Instead, we find that the heterotic dilaton is part of a compensating hypermultiplet, whereas the antisymmetric tensor is part of the gravitational multiplet. In order to obtain our results we use superconformal techniques. This enables us to comment on the range of applicability of this particular framework.