Frame dependence of form factors in light-front dynamics

TL;DR

This paper investigates how form factors in light-front dynamics depend on the frame of reference, especially under practical truncations, and proposes a way to measure Lorentz symmetry violations.

Contribution

It extends the analysis of form factors to general frames in light-front dynamics, highlighting the small frame dependence in certain models and proposing a metric for Lorentz symmetry violation.

Findings

Frame dependence of meson form factors is small in specific models.

The difference between Drell-Yan and longitudinal frames can measure Lorentz violation.

Practical truncations induce small but notable frame dependence.

Abstract

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.