Quark Propagation in the Presence of a A_\mu^aA_a^\mu> Condensate
  There is a good deal of current interest in the condensate g^2A_\mu^aA_a^\mu> which has recently be shown to be the Landau gauge version of a more general gauge-invariant expression. In the present work we consider quark propagation in the presence of such a condensate which we assume to be present in the vacuum. We describe the vacuum as a random medium of gluon fields. We discuss quark propagation in that medium and show that the quark propagator has no on-mass-shell pole indicating that a quark cannot propagate over extended distances. That is, the quark is a nonpropagating mode in the gluon condensate. 
Xiangdong Li and C. M. Shakin