Vus from Kl3 Decays

Abstract

Important progress made this year, both in theory and in experiment, helped solving the problem of 2 sigma-deviation from the unitarity of the first row elements in the CKM matrix. Today we have, |Vus|^2 + |Vud|^2 + |Vub|^2-1 = -0.0008(13), -0.0010(13), or -0.0005(13), depending on whether the q^2-dependence of the relevant Kl3 form factor is considered as pole-like, linear or quadratic function, and on the Leutwyler-Roos value of f+(0)=0.961(8), whose validity has recently been reinforced by lattice studies. In this talk we summarize the recent developments.

Comments: Contributed to 32nd International Conference on High-Energy Physics (ICHEP 04), Beijing, China, 16-22 Aug 2004; minor typos corrected