Electromagnetic form factors of the nucleon in chiral perturbation theory

Abstract

The electromagnetic form factors of the nucleon are calculated at order $q^4$ in the relativistic formulation of baryon chiral perturbation theory. In order to obtain a consistent power counting for the renormalized diagrams we make use of the extended on-mass-shell renormalization scheme which we have discussed in a recent paper. We analyze the Dirac and Pauli form factors, $F_1$ and $F_2$, as well as the electric and magnetic Sachs form factors, $G_E$ and $G_M$. Our results are compared with those obtained in the heavy-baryon approach and in the (relativistic) infrared regularization. In addition, the Sachs form factors are compared with experimental data. We confirm previous findings that a one-loop calculation of the electromagnetic form factors does not generate sufficient curvature for the Sachs form factors $G^p_E$, $G^p_M$, and $G^n_M$. Moreover, the electric form factor of the neutron is very sensitive to higher-order contributions.