N to Δ electromagnetic transition form factors from lattice QCD -: art. no. 114506

The magnetic dipole, the electric quadrupole, and the Coulomb quadrupole amplitudes for the transition gammaN-->Delta are evaluated both in quenched lattice QCD at beta=6.0 and using two dynamical Wilson fermions simulated at beta=5.6. The dipole transition form factor is accurately determined at several values of momentum transfer. On the lattices studied in this work, the electric quadrupole amplitude is found to be nonzero, yielding a negative value for the ratio R-EM of electric quadrupole to magnetic dipole amplitudes at three values of momentum transfer.