The π+π+ scattering length from maximally twisted mass lattice QCD

We calculate the s-wave pion-pion scattering length in the isospin I = 2 channel in lattice QCD for pion masses ranging from 270 MeV to 485 MeV using two flavors of maximally twisted mass fermions at a lattice spacing of 0.086 fm. Additionally, we check for lattice artifacts with one calculation at a finer lattice spacing of 0.067 fm. We use chiral perturbation theory at next-to-leading order to extrapolate our results. At the physical pion mass, we find m(pi)a(pi pi)(I=2) = -0.04385(28)(38) for the scattering length, where the first error is statistical and the second is our estimate of several systematic effects. (C) 2010 Elsevier B.V. All rights reserved.