Pion Form Factors in Holographic QCD

TL;DR

This paper uses holographic QCD models to compute pion form factors and couplings, comparing hard-wall and soft-wall approaches, and analyzing their agreement with experimental data and model parameters.

Contribution

It introduces holographic dual models with chiral symmetry breaking to calculate pion form factors and couplings, comparing different IR cutoff implementations.

Findings

Hard-wall model predictions are closer to data for F_pi(Q^2).

Soft-wall model fits improve when parameters are varied.

Pion charge radius and rho pole saturation are analyzed.

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.