Elastic form factors of nucleon excitations in lattice QCD

The recent development of the parity-expanded variational analysis (PEVA) technique makes lattice QCD studies of the form factors of baryon excitations possible. In this paper, we present 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 pion masses, these states are dominated by behaviour consistent with constituent quark models for the N(1535) and N(1650), respectively. At pion masses approaching the physical point, meson-baryon contributions are observed to play an increasing role. We also study the lowest-lying localised 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 analysis with those from a conventional variational analysis exposes the necessity of the PEVA approach in baryon excited-state studies.