Analytic structure of the Landau gauge gluon propagator
  The results of different non-perturbative studies agree on a power law as the infrared behavior of the Landau gauge gluon propagator. This propagator violates positivity and thus indicates the absence of the transverse gluons from the physical spectrum, i.e. gluon confinement. A simple analytic structure for the gluon propagator is proposed capturing all of its features. We comment also on related investigations for the Landau gauge quark propagator. 
R. Alkofer, W. Detmold, C. S. Fischer and P. Maris