Electromagnetic nucleon-to-delta transition in chiral effective-field theory

We perform a relativistic chiral effective-field theory calculation of pion electroproduction off the nucleon (e(-)N -> e(-)N pi) in the Delta(1232)-resonance region. After fixing the three low-energy constants, corresponding to the magnetic (M1), electric (E2), and Coulomb (C2) gamma N Delta couplings, our calculation provides a prediction for the momentum transfer and pion-mass dependence of the gamma N Delta form factors. The prediction for the pion-mass dependence resolves the discrepancy between the recent lattice QCD results and the experimental value for the C2/M1 ratio at low Q(2).