Electromagnetic form factors of vector mesons in Einstein-dilaton holographic QCD

Abstract

We investigate the electromagnetic form factors of the $ρ$ meson family within a holographic QCD framework based on Einstein-dilaton gravity with confining backgrounds. We obtain the elastic and transition form factors using a spectral decomposition of the three-point isospin current correlator and an independent approach based on the Kaluza-Klein expansion. Furthermore, we establish a holographic dictionary of the current matrix element. The elastic form factors are in agreement with available lattice QCD results, whereas the transition form factors, not yet determined within lattice QCD, are predictions of the model. For the elastic case, the electric form factor for the $ρ$ meson family exhibits a zero at $q^{2} = 6\, m_{ρ^{n}}^{2}$ and in particular for the ground state $q^{2} = 3.61\,\text{GeV}^{2}$, consistent with light-front and Dyson-Schwinger calculations. We also compute strong couplings between vector meson states and find some approximate selection rules. In the elastic case and low-$q^{2}$ regime, we calculate dimensionless electric radius, magnetic and quadrupole moments and compare with other approaches. In the high-$q^{2}$ regime, the form factors follow the expected scaling behavior, and the model predicts their asymptotic normalization. The results in the high-$q^{2}$ regime lead to superconvergence relations and establish a new sum rule involving masses, decay constants and couplings.