Delta-baryon electromagnetic form factors in lattice QCD

We develop techniques to calculate the four $\Delta$ electromagnetic form factors using lattice QCD, with particular emphasis on the subdominant electric quadrupole form factor that probes deformation of the $\Delta$ . Results are presented for pion masses down to approximately 350 MeV for three cases: quenched QCD, two flavors of dynamical Wilson quarks, and three flavors of quarks described by a mixed action combining domain-wall valence quarks and dynamical staggered sea quarks. The magnetic moment of the $\Delta$ is compared with chiral effective field theory calculations and the $\Delta$ charge density distributions are discussed.