Janus-Facedness of the Pion: Analytic Instantaneous Bethe-Salpeter   Models
  Inversion enables the construction of interaction potentials underlying - under fortunate circumstances even analytic - instantaneous Bethe-Salpeter descriptions of all lightest pseudoscalar mesons as quark-antiquark bound states of Goldstone-boson nature. 
Wolfgang Lucha
hep-ph nucl-th