Behavior of the zero modes in the Light-front for pseudo scalar particles: pion case

Abstract

Light-front Quantum Field Theory (LFQFT) stands as an optimal framework for delving into the intricate substructure of hadronic bound states. In this study, we employ a Light-Front Constituent Quark Model (LFCQM) to investigate the pion's internal structure. This model has previously demonstrated significant success in describing the properties of pseudoscalar mesons. A crucial consideration within the light-front formalism is the dependence on the chosen reference frame, stemming from the explicit breaking of covariance. Herein, we meticulously analyze the contribution of zero modes to the pion's electromagnetic current. Subsequently, we explore the impact of these zero modes on observable quantities, including electromagnetic form factors, the pion's electromagnetic radius, and its weak decay constant, $f_π$. Furthermore, we comprehensively investigate the behavior of zero modes and their dependence on both the momentum transfer, $Q^2$, and the model's intrinsic parameters, such as constituent quark masses ($m_{(q,\bar{q})}$) and the regulator mass ($m_R$). Our findings reveal a substantial dependence of light-front zero modes on the specific frame employed for the calculation of the electromagnetic current. Interestingly, we observe that the maximal contribution of the zero mode occurs at a specific four-momentum transfer, denoted as $Q^2 = -q^2 = q_Z^{2(Max.)}$.