Effects of partial quenching and staggered fermions on the scalar   correlator
  We determine the mass of the lightest quark-antiquark scalar meson with I=1 using the simulation with two dynamical Domain Wall Fermions. The conventional exponential fit of the scalar correlator is justified in this case giving the mass 1.58 +/- 0.34 GeV. In general the scalar correlator receives also the bubble contribution, which is the intermediate state with two pseudoscalar mesons. This contribution is sizable at light quark masses and has to be incorporated in the fit of the scalar correlator in order to extract the scalar meson mass. We provide predictions for the bubble contribution in Partially Quenched ChPT, Staggered ChPT and ChPT for Mixed quark actions. We find that the bubble contribution is significantly affected by the unphysical approximations that are employed in simulations. It can render the negative sign and unphysical effective mass 2*Mpi in the scalar correlator with I=1. 
S. Prelovsek