Quark mass and chiral condensate from the Wilson twisted mass lattice   quark propagator
  In this work, we report about the determination of nonperturbative OPE parameters from fits of continuum perturbation theory to the Landau gauge quark propagator. The propagators are computed numerically using lattice QCD with Nf=2 dynamical Wilson twisted mass fermions. We use four different values of the lattice spacing ranging from about 0.1 fm to about 0.05 fm as well as several quark masses per lattice spacing. This allows us to obtain continuum results for the chiral condensate and the average up/down quark mass. The main results are the average up/down quark mass m_q = 3.0(4)(2) MeV at the physical point and a value of the chiral condensate of -(299(26)(29) MeV)^3 in the chiral limit, both in the MSbar scheme at 2 GeV. We have also studied nonperturbative contaminations of our results at small values of the momenta, which are often interpreted as the contribution of the gluon condensate A^2. We do see contributions from such terms, which are, however, not stable over the order in perturbation theory. 
Florian Burger, Vittorio Lubicz, Michael M\"uller-Preussker, Silvano   Simula, Carsten Urbach
hep-lat hep-ph