Duality of Lorentzian and Euclidean black holes in two-dimensional   string-generated models
  We discuss the properties of lorentzian and euclidean black hole solutions of a generalized 2-dim dilaton-gravity action containing a modulus field, which arises from the compactification of heterotic string models. The duality symmetries of these solutions are also investigated. 
M. Cadoni and S. Mignemi