We extend a recent numerical calculation of the pion electromagnetic form factor $F_{\pi }(Q^2)$ in holographic QCD to study two important issues regarding the behavior of fields in the bulk. First, we show that using a chiral symmetry-breaking field formally satisfying the boundary conditions of the “soft-wall” model changes numerical results very little from the earlier calculation that ignores these constraints. Second, we use a background field that interpolates between “hard-wall” and soft-wall models to obtain an improved model that reproduces the desirable phenomenological features of both. In all cases, $F_{\pi }$ for large $Q^2$ is shallower than data, an effect that can be cured by relaxing the fit to one of the static observables, particularly the decay constant $f_{\pi }$.

• Received 19 December 2007

DOI:https://doi.org/10.1103/PhysRevD.77.115007