N=8 BPS black holes preserving 1/8 supersymmetry

In the context of N = 8 supergravity we consider BPS black holes that prese rve 1/8 supersymmetry. It was shown in a previous paper that, module U-dual ity transformations of E-7(7), the most general solution of this type can b e reduced to a black hole of the ST U model. In this paper we analyse this solution in detail, considering in particular its embedding in one of the p ossible special Kahler manifolds compatible with the consistent truncations to N = 2 supergravity, this manifold being the moduli space of the T-6/Z(3 ) orbifold, that is SU(3, 3)/SU(3) x U(3). This construction requires a cru cial use of the solvable Lie algebra formalism. Once the group-theoretical analysis is done, starting from a static, spherically symmetric ansatz, we find an exact solution for all the scalars (both dilaton- and axion-like) a nd for gauge fields, together with their already known charge-dependent fix ed values, which yield a U-duality-invariant entropy. We also give a comple te translation dictionary between the solvable Lie algebra and the special Kahler formalisms in order to allow a more immediate comparison with other papers on similar issues. Although the explicit solution is given in a simp lified case where the equations turn out to be more manageable, it encodes all the features of the more general one, namely it has non-vanishing entro py and the scalar fields have a non-trivial radial dependence.