Instantaneous Bethe-Salpeter View of Goldstone-Type Pseudoscalar Mesons
  Describing the lightest pseudoscalar mesons as bound states of quark and antiquark within the framework of an instantaneous Bethe-Salpeter formalism constructed such as to retain (in contrast to Salpeter's equation) as much information on the relativistic effects provided by the full quark propagator as conceivable allows for a surprisingly simple implementation of their near masslessness mandatory for their interpretability as pseudo-Goldstone bosons related to the spontaneous breaking of the chiral symmetries of quantum chromodynamics. 
Wolfgang Lucha, Franz F. Sch\"oberl
hep-ph nucl-th