Δ _mix parameter in the overlap on domain-wall mixed action

A direct calculation of the mixed action parameter Δ _mix with valence overlap fermions on a domain-wall fermion sea is presented. The calculation is performed on four ensembles of the 2+1 flavor domain-wall gauge configurations: 243×64 (am _l=0.005, a=0.114fm) and 323×64 (am _l=0.004, 0.006, 0.008, a=0.085fm). For pion masses close to 300 MeV we find Δ _mix=0.030(6)GeV4 at a=0.114fm and Δ _mix=0.033(12)GeV4 at a=0.085fm. The results are quite independent of the lattice spacing and they are significantly smaller than the results for valence domain-wall fermions on asqtad sea or those of valence overlap fermions on clover sea. Combining the results extracted from these two ensembles, we get Δ _mix=0.030(6)(5)GeV4, where the first error is statistical and the second is the systematic error associated with the fitting method.