Horizon regularity and dilaton coupling quantization in EMD dyons
  Four-dimensional Einstein-Maxwell-Dilaton theory admits asymptotically flat extremal dyonic solutions for an infinite discrete sequence of the coupling constant values. The quantization condition arises as consequence of regularity of the dilaton function at the event horizon. These dyons satisfy the no-force condition and have flat reduced three spaces like true BPS configurations, but no supersymmetric embeddings are known except for some cases of lower values of the coupling sequence. 
D.V. Gal'tsov
gr-qc hep-th math-ph math.MP