Chiral Extrapolation of the Strangeness Changing K pi Form Factor

Understand

We perform a chiral extrapolation of lattice data on the scalar K pi form factor and the ratio of the kaon and pion decay constants within Chiral Perturbation Theory to two loops.

• We determine the value of the scalar form factor at zero momentum transfer, at the Callan-Treiman point and at its soft kaon analog as well as its slope.
• Results are in good agreement with their determination from experiment using the standard couplings of quarks to the W boson.
• The slope is however rather large.