Duality and four-dimensional black holes

We consider the effects of abelian duality transformations on static, spherically symmetric, asymptotically flat string spacetimes in four dimensions, where the dilaton, axion, metric, and gauge fields are allowed to be nonzero. Independent of the α′ expansion, there is a six-parameter family of such configurations, labelled by the charges characterizing the asymptotic behaviour of the various fields: i.e. their mass, dilaton charge, axion …