Low energy constant and mixed-action effect

Abstract: We present the pion mass and decay constant using the overlap fermion valence on domain wall (DW) fermion sea at several lattice spacings. The mixed action effect in the lattice calculation is also studied, and the result suggests that the mixed action effect with the overlap valence on DW sea would be proportional to the fourth power of the lattice spacing. We obtain the pion decay constant at the physical pion mass and $N_f=2$ chiral limit to be $92.4(3)(2)~{\rm MeV}$ and $87.0(5)(7)~{\rm MeV}$ respectively; and the physical u/d averaged quark mass at $\overline{\textrm{MS}}$ 2 GeV is $3.74(4)(5)(5)(3)~{\rm MeV}$ with the linear ${\cal O}(a^2)$ continuum extrapolation. Using the FLAG value of the NLO low energy constant, we obtain the $N_f=2$ chiral condensate to be $\Sigma^{\overline{\textrm{MS}}(2~{\rm GeV})}=\big(266(2)(1)~{\rm MeV}\big)^3$.