INTERPOLATING BLACK-HOLES IN DILATON-AXION GRAVITY

A 2p + 5 parametric family of black holes is constructed in dilaton-ax ion gravity with p vector fields using a holomorphic representation of U-duality in three dimensions. The metric of the non-extremal black h oles has a Reissner-Nordstrom-type structure and generically possesses an internal horizon. However, in the extremal limit the generic solut ion exhibits a dilatonic-type null singularity. The solution thus inte rpolates between the well known Reissner-Nordstrom and charged dilaton ic spacetimes. Only in the case of the orthogonal electric and magneti c charges (if p > 1) may the extremal solution have a non-singular eve nt horizon.