Pion form factors from lattice QCD with exact chiral symmetry

We calculate pion vector and scalar form factors in two-flavor lattice QCD and study the chiral behavior of the vector and scalar radii 〈r〉V,S. For a direct comparison with chiral perturbation theory (ChPT), chiral symmetry is exactly preserved by employing the overlap quark action. We utilize the all-to-all quark propagator in order to calculate the scalar form factor including the contributions of disconnected diagrams. A detailed comparison with ChPT reveals that two-loop contributions are important to describe the chiral behavior of the radii in our region of the pion mass Mπ & 290 MeV. From chiral extrapolation based on two-loop ChPT, we obtain 〈r〉V = 0.409(23)(37) fm2 and 〈r〉S =0.617(79)(66) fm2, which are consistent with phenomenological analyses.