Pion form factor in improved holographic QCD backgrounds

We extend a recent numerical calculation of the pion electromagnetic form factor Fπ(Q2) 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, Fπ for large Q2 is shallower than data, an effect that can be cured by relaxing the fit to one of the static observables, particularly the decay constant fπ.