On the calculation of the nucleon electromagnetic form factors in light-front dynamics

Abstract

Abstract In the formulation of light-front dynamics on the quantization plane t + z = 0, there is an asymmetry between the z- and x-, y-axes that leads in practice to a violation of rotational invariance. In the explicitly covariant formulation of light-front dynamics, the nucleon electromagnetic current matrix elements contain, instead of this violation, additive contributions depending on the position of the light-front plane. We show how to extract the physical form factors, excluding these spurious contributions. We also show why the usual approach, taking into account the J + component of the current only, contains these non-physical contributions. We apply our formalism to a simple three-quark model in order to quantitatively estimate the difference between both approaches. This difference can be as large as 50% at high momentum transfer.