Observations On the Potential Confinement of a Light Fermion
  We consider possible dynamical models for a light fermion confined by a potential field. With the Dirac equation only Lorentz scalar confinement yields normalizable wavefunctions, while with the ``no pair'' variant of the Dirac equation only Lorentz vector confinement has normal Regge behaviour.   A systematic investigation of Regge properties and phenomenological properties is carried out, including calculations of the Isgur-Wise function. We point out that the Isgur-Wise function provides a sensitive test of confinement models. In particular, the slope of the IW function at zero recoil point is found to be $\xi'(1)\simeq -0.90$ for the Dirac equation with scalar confinement, and $\xi'(1)\simeq -1.20$ for the no pair equation with vector confinement. Using heavy-light data alone we argue against scalar confinement. 
M. G. Olsson, S. Veseli, and K. Williams