Kaon electromagnetic form factors in dispersion theory

The electromagnetic form factors of charged and neutral kaons are strongly constrained by their low-energy singularities, in the isovector part from two-pion intermediate states and in the isoscalar contribution in terms of [Formula: see text] and [Formula: see text] residues. The former can be predicted using the respective [Formula: see text] partial-wave amplitude and the pion electromagnetic form factor, while the latter parameters need to be determined from electromagnetic reactions involving kaons. We present a global analysis of time- and spacelike data that implements all of these constraints. The results enable manifold applications: kaon charge radii, elastic contributions to the kaon electromagnetic self energies and corrections to Dashen’s theorem, kaon boxes in hadronic light-by-light (HLbL) scattering, and the [Formula: see text] region in hadronic vacuum polarization (HVP). Our main results are: [Formula: see text] , [Formula: see text] for the charged and neutral radii, [Formula: see text] for the elastic contribution to the violation of Dashen’s theorem, [Formula: see text] for the charged kaon box in HLbL scattering, and [Formula: see text] , [Formula: see text] for the HVP integrals around the [Formula: see text] resonance. The global fit to [Formula: see text] gives [Formula: see text] , [Formula: see text] for the [Formula: see text] resonance parameters including vacuum-polarization effects.