PHYSICAL REVIEW D
In light-front dynamics, form factors are traditionally computed with the "good current" J(+) within the Drell-Yan frame q(+) = 0. Due to truncations imposed in practical calculations, the from factor may acquire frame dependence, which is often neglected. In this work, we explore the form factors in more general frames, preserving the boost covariance. We find the frame dependence of the elastic form factors for mesons is small in basis light-front holography and related models with two-body Fock space truncation. We suggest to use the difference between form factor results from Drell-Yan frame and the "longitudinal frame" as a metric for the violation of the Lorentz symmetry due to Fock space truncation.
Li, Yang; Maris, Pieter; and Vary, James P., Frame dependence of form factors in light-front dynamics (2018). PHYSICAL REVIEW D, 97(5), 1-18.