Elastic form factors of nucleon excitations in lattice QCD

First principles calculations of the form factors of baryon excitations are now becoming accessible through advances in lattice-QCD techniques. In this paper, we explore the utility of the parity-expanded variational analysis (PEVA) technique in calculating the Sachs electromagnetic form factors for excitations of the proton and neutron. We study the two lowest-lying odd-parity excitations and demonstrate that at heavier quark masses, these states are dominated by behavior consistent with constituent quark models for the N^*(1535 ) and N^*(1650 ), respectively. We also study the lowest-lying localized even-parity excitation and find that its form factors are consistent with a radial excitation of the ground-state nucleon. A comparison of the results from the PEVA technique with those from a conventional variational analysis exposes the necessity of the PEVA approach in baryon excited-state studies.