Pion Scattering in Wilson Chiral Perturbation Theory

We compute the scattering amplitude in Wilson Chiral Perturbation Theory for two flavors. The lattice spacing effects due to the explicit chiral symmetry breaking are kept through O(a^2), and we consider the regime where the quark mass m is of order a^2 Lambda_^3. Analytic expressions for the scattering lengths in different isospin channels are given. As a result of the O(a^2) terms the scattering lengths do not vanish in the chiral limit. Moreover, additional chiral logarithms proportional to a^2 ln M_pi^2 are present in the one-loop results. These contributions can obscure the continuum chiral logarithms and the determination of low-energy constants from numerical lattice simulations.