Pion Form Factors in Holographic QCD

Abstract

Using a holographic dual model of QCD, we compute the pion electromagnetic form factor F_pi(Q^2) in the spacelike momentum transfer region, as well as pion couplings to vector mesons g_rho^(n) pi pi. Spontaneous and explicit chiral symmetry breaking are intrinsic features of this particular holographic model. We consider variants with both ``hard-wall'' and ``soft-wall'' infrared cutoffs, and find that the F_pi(Q^2) data tend to lie closer to the hard-wall model predictions, although both are too shallow for large Q^2. By allowing the parameters of the soft-wall model (originally fixed by observables such as m_rho) to vary, one finds fits that tend to agree better with F_pi(Q^2). We also compute the pion charge radius <r_pi^2> for a variety of parameter choices, and use the values of f^(n)_rho, g_{rho^(n) pi pi} and m^(n)_rho to observe the saturation of F_pi(0) by rho poles.