Pion form factors in holographic QCD

Using a holographic dual model of QCD, we compute the pion electromagnetic form factor Fπ(Q2) in the spacelike momentum transfer region, as well as pion couplings to vector mesons gρ(n)ππ. 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 Fπ(Q2) data tend to lie closer to the hard-wall model predictions, although both are too shallow for large Q2. By allowing the parameters of the soft-wall model (originally fixed by observables such as mρ) to vary, one finds fits that tend to agree better with Fπ(Q2). We also compute the pion charge radius rπ2 for a variety of parameter choices, and use the values of f(n)ρ, gρ(n)ππ and m(n)ρ to observe the saturation of Fπ(0) by ρ poles.

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