We update the determination of |V_us| using semielectronic and semimuonic decays of K mesons. A modest improvement of 15% with respect to its present value is obtained for the error bar of this matrix element when we combine the four available semileptonic decays. The combined effects of long-distance radiative corrections and nonlinear terms in the vector form factors can decrease the value of |V_us| by up to 1%. Refined measurements of the decay widths and slope form factors in the semimuonic modes and a more accurate calculation of vector form factors at zero momentum transfer can push the determination of |V_us| at a few of percent level.
@article{arxiv.hep-ph/0111272,
title = {Updating V_us from kaon semileptonic decays},
author = {G. Calderon and G. Lopez Castro},
journal= {arXiv preprint arXiv:hep-ph/0111272},
year = {2009}
}