Status of the Hadronic tau Decay Determination of |V_{us}|

TL;DR

This paper updates the determination of |V_{us}| from hadronic tau decays, highlighting discrepancies with unitarity expectations and discussing theoretical uncertainties and alternative methods.

Contribution

It provides an updated analysis of |V_{us}| from tau decays and examines the impact of different sum rule approaches on the results.

Findings

Current strange branching fractions yield |V_{us}| values 2-3 sigma below unitarity

Theoretical uncertainties significantly affect the |V_{us}| determination

Alternative sum rule methods produce smaller theoretical uncertainties

Abstract

We update the hadronic tau determination of |V_{us}|, showing that current strange branching fractions produce results 2-3 sigma lower than 3-family unitarity expectations. Issues related to the size of theoretical uncertainties and results from an alternate, mixed tau-electroproduction sum rule determination (which, by construction, produces a much smaller theoretical uncertainty), are also considered.