Low energy constants of S U (2 ) partially quenched chiral perturbation theory from Nf=2 +1 domain wall QCD

We have performed fits of the pseudoscalar masses and decay constants, from a variety of the RBC-UKQCD Collaboration's domain wall fermion ensembles, to S U (2 ) partially quenched chiral perturbation theory at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). We report values for nine NLO and eight linearly independent combinations of NNLO partially quenched low-energy constants, which we compare to other lattice and phenomenological determinations. We discuss the size of successive terms in the chiral expansion and use our large set of low-energy constants to make predictions for mass splittings due to QCD isospin-breaking effects and the S-wave π π scattering lengths. We conclude that, for the range of pseudoscalar masses explored in this work, 115 MeV ≲mPS≲430 MeV , the NNLO S U (2 ) expansion is quite robust and can fit lattice data with percent-scale accuracy.