The non-perturbative BRST quartets generated by transverse gluons or   quarks in Landau gauge
  The BRST quartet mechanism is briefly reviewed. A special emphasis is given to the distinction of perturbative versus non-perturbative quartets. The field contents of the non-perturbative BRST quartets generated by transverse gluons or quarks in Landau gauge are presented. Corresponding truncated Bethe-Salpeter equations for the respective first daughter and second parent states are derived. It is discussed in which sense these equations provide evidence for the existence of bound states as daughter states in non-perturbative BRST quartets. It is noted that within the scaling solution of functional approaches the infrared divergence of the quark-gluon vertex is exactly the right one tomake the respective Bethe-Salpeter equation infrared consistent. 
Natalia Alkofer and Reinhard Alkofer
hep-th hep-ph