ENTROPY OF 4-DIMENSIONAL ROTATING BPS BLACK-HOLE DYONS

The known BPS dyon black hole solutions of the N=4 heterotic string in four dimensions with a nonzero angular momentum all have naked singul arities, We show that it is possible to modify a certain class of thes e solutions by the addition of massive Kaluza-Klein fields in such a w ay that the solutions decompactify near the core to five-dimensional b lack hole solutions with regular event horizons. We argue that the deg eneracy of the four-dimensional BPS dyon states is given, for large ch arges, by the five-dimensional geometric entropy.