Low energy constants of SU(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 SU(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 pi pi scattering lengths. We conclude that, for the range of pseudoscalar masses explored in this work, 115 MeV less than or similar to m(PS) less than or similar to 430 MeV, the NNLO SU(2) expansion is quite robust and can fit lattice data with percent-scale accuracy.