Weak magnetic field corrections to light vector or axial mesons mixings and vector meson dominance

Abstract

Weak magnetic field induced corrections to effective coupling constants describing light vector mesons mixings and vector meson dominance (VMD) are derived. The magnetic field must be weak with respect to an effective quark mass $M^*$ such that: $eB_0/{M^*}^2< 1$ or $eB_0/{M^*}^2<<1$.For that, a flavor SU(2) quark-quark interaction due to non perturbative one gluon exchange is considered. By means of methods usually applied to the Nambu Jona Lasinio (NJL) and Global Color Models (GCM), leading light vector/axial mesons couplings to a background electromagnetic field are derived. The corresponding effective coupling constants are resolved in the structureless mesons and longwavelength limits. Some of the resulting coupling constants are redefined such as to become magnetic field induced corrections to vector or axial mesons couplings. Due to the approximated chiral symmetry of the model, light axial mesons mixings induced by the magnetic field are also obtained. Some numerical estimates are presented for the coupling constants and for some of the corresponding momentum dependent vertices. The contributions of the induced VMD and vector mesons mixing couplings for the low momentum pion electromagnetic form factor and for the (off shell) charge symmetry violation potential at the constituent quark level are estimated. The relative overall weak magnetic field-induced anisotropic corrections are of the order of $(eB_0/{M^*}^2)^n$, where $n=2$ or $n=1$ respectively.