γNΔ form factors and Wigner rotations

For more than 50 years the Δγ nucleon resonance isobar transition form factors G_M^*(q²), G_E^*(q²), and G_C^*(q²) have been studied experimentally, theoretically, and phenomenologically. Although there has been substantial progress in understanding their behavior, there remains much work to be done. The Δ resonance mass position and width remain ambiguous. A major tool used in many investigations is the Jones-Scadron Δ rest frame parametrization of the three ΔNγ form factors. We point out that many studies utilizing this parametrization and related formulations and which utilize the Δ rest frame (c.m. frame) may not account for Wigner rotations and the consequent helicity mixing that ensues when the Δ is not at rest (lab frame) thus adversely affecting the accurate and precise determination of these form factors.