Renormalization functions for Nf=2 and Nf=4 twisted mass fermions

Abstract

© 2017 American Physical Society. We present results on the renormalization functions of the quark field and fermion bilinears with up to one covariant derivative. For the fermion part of the action, we employ the twisted mass formulation with Nf=2 and Nf=4 degenerate dynamical quarks, while in the gluon sector, we use the Iwasaki-improved action. The simulations for Nf=4 have been performed for pion masses in the range of 390-760 MeV and at three values of the lattice spacing, a, corresponding to β=1.90, 1.95, 2.10. The Nf=2 action includes a clover term with csw=1.57551 at β=2.10, and three ensembles at different values of mπ. The evaluation of the renormalization functions is carried out in the RI′ scheme using a momentum source. The nonperturbative evaluation is complemented with a perturbative computation, which is carried out at one-loop level and to all orders in the lattice spacing, a. For each renormalization function computed nonperturbatively, we subtract the corresponding lattice artifacts to all orders in a, so that a large part of the cutoff effects is eliminated. The renormalization functions are converted to the MS scheme at a reference energy scale of μ=2 GeV after taking the chiral limit.