Vus and neutron beta decay

Abstract

We discuss the effect of the recent change of $V_{\mathrm{us}}$ by three standard deviations on the standard model predictions for neutron beta decay observables. We also discuss the effect the experimental error bars of $V_{\mathrm{us}}$ have on such predictions. Refined precision tests of the standard model will be made by a combined effort to improve measurements in neutron beta decay and in strangeness-changing decays. By itself the former will yield very precise measurements of $V_{\mathrm{ud}}$ and make also very precise predictions for $V_{\mathrm{us}}$.