Analytic representation of $F_K/F_\pi$ in two loop chiral perturbation theory

Understand

We present an analytic representation of $F_K/F_\pi$ as calculated in three-flavour two-loop chiral perturbation theory, which involves expressing three mass scale sunsets in terms of Kamp\'e de F\'eriet series.

• We demonstrate how approximations may be made to obtain relatively compact analytic representations.
• An illustrative set of fits using lattice data is also presented, which shows good agreement with existing fits.