EHLERS-HARRISON TRANSFORMATIONS AND BLACK-HOLES IN DILATON-AXION GRAVITY WITH MULTIPLE VECTOR-FIELDS

Dilaton-axion gravity with p U(1) vector fields is studied on space-ti mes admitting a timelike Killing vector field. A three-dimensional a m odel is derived in terms of Kahler geometry, and a holomorphic represe ntation of the SO(2,2+p) global symmetry is constructed. A general sta tic black hole solution depending on 2p+5 parameters is obtained via S O(2,2+p) covariantization of the Schwarzschild solution. The metric in the curvature coordinates looks like the variable mass Reissner-Nords trom one and generically possesses two horizons. The inner horizon is pushed to the singularity if electric and magnetic SO(p) charge vector s are parallel. For nonparallel charges the inner horizon has a finite area except for an extremal limit when this property is preserved onl y for orthogonal charges. Extremal dyon configurations with orthogonal charges have finite horizon radii continuously varying from zero to t he Arnowitt-Deser-Misner mass. The new general solution is endowed wit h a Newman-Unti-Tamburino parameter, asymptotic values of dilaton and axion, and a gauge parameter which can be used to ascribe any given va lue to one of the scalar charges.