Kℓ3 and πe3 transition form factors

Kℓ3 and πe3 transition form factors are calculated as an application of Dyson-Schwinger equations. A heuristic one-parameter model of the quark-W-boson vertex is used to highlight their sensitivity to the form of this vertex. The Kℓ3 form factors, f±K, are approximately linear on t ∈ [me2, mμ2] and f+K′(0) ∼ f−K′(0). f−K(0) is a measure of the Euclidean constituent-quark mass ratio: MsEMuE. In the isospin symmetric limit: −f+π(0) = Fπ(t), the electromagnetic pion form factor, and f−π(t) ≡ 0.