I=2 ππ scattering from fully-dynamical mixed-action lattice QCD

We compute the I=2 pi pi scattering length at pion masses of m(pi)similar to 294, 348, and 484 MeV in fully-dynamical lattice QCD using Luscher's finite-volume method. The calculation is performed with domain-wall valence-quark propagators on asqtad-improved MILC configurations with staggered sea quarks at a single lattice spacing, b similar to 0.125 fm. Chiral perturbation theory is used to perform the extrapolation of the scattering length from lattice quark masses down to the physical value, and we find m(pi)a(2)=-0.0426 +/- 0.0006 +/- 0.0003 +/- 0.0018, in good agreement with experiment. The I=2 pi pi scattering phase shift is calculated to be delta=-43 +/- 10 +/- 5 degrees at vertical bar p vertical bar similar to 544 MeV for m(pi) similar to 484 MeV.