K0 form factor at order p6 of chiral perturbation theory Original Research Article

This paper describes the calculation of the electromagnetic form factor of the K0 meson at order p6 of chiral perturbation theory which is the next-to-leading order correction to the well-known p4 result achieved by Gasser and Leutwyler. On the one hand, at order p6 the chiral expansion contains 1- and 2-loop diagrams which are discussed in detail. Especially, a numerical procedure for calculating the irreducible 2-loop graphs of the sunset topology is presented. On the other hand, the chiral Lagrangian L(6) produces a direct coupling of the K0 current with the electromagnetic field tensor. Due to this coupling one of the unknown parameters of L(6) occurs in the contribution to the K0 charge radius.