Chiral Dynamics in the Meson Sector at two Loops

Abstract

I give a very short introduction to Chiral Perturbation Theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of $V_{us}$ in more detail. One major conclusion is that all needed $p^6$ low energy constants can be obtained from experiment via the scalar form-factor in $K_{\ell 3}$ decays.

Comments: 5 pages, Talk presented at CIPANP 2003, Conference on the Intersections of Particle and Nuclear Physics, New York May 19-24, 2003