Infrared behaviour of propagators and running coupling in the conformal   window of QCD
  Using the Dyson-Schwinger approach we investigate Landau gauge QCD with a relatively large number of chiral quark flavours. A self-consistent treatment on the propagator level enables us to study unquenching effects via the quark loop diagram in the gluon equation. Above the critical number of fermion flavours the non-perturbative running coupling develops a plateau over a wide momentum range. Correspondingly, the propagators follow a power law behaviour in this momentum range indicating conformal behaviour. Our value $N_f^{crit}=4.5$ is strongly sensitive to the details of the quark-gluon vertex calling for more detailed investigations in future studies. 
Markus Hopfer, Christian S. Fischer, Reinhard Alkofer
hep-ph