Remarks on the Heavy-Quark Symmetry in the Complex Plane
  Hadronic systems built from a heavy quark and a cloud of light quarks and massless gluons posess the Isgur-Wise symmetry resulting in certain relations between various form factors. These relations can not be valid in the entire complex plane. We identify contributions which unavoidably violate strongly the symmetry in the time-like domain near thresholds. A possible connection with the heavy-quark phenomenology is discussed in brief. 
P. Ball, H.G. Dosch and M.A. Shifman