Hadronic Tau Decay Based Determinations of |V_us|

TL;DR

This paper reviews sum rule methods using hadronic tau decay data to determine |V_us|, addressing recent updates, convergence issues, and the impact of unmeasured modes, leading to reduced discrepancies with unitarity expectations.

Contribution

It introduces improved sum rule techniques and incorporates recent data updates, enhancing the accuracy of |V_us| determinations from tau decays.

Findings

Discrepancies with 3-family unitarity are reduced.

Switching to D=2 OPE treatments improves self-consistency.

Updated strange branching fractions influence the results.

Abstract

I review sum rule determinations of |V_us| employing hadronic tau decay data, taking into account recent HFAG updates of exclusive tau branching fractions and paying special attention to the impact of the slow convergence of the relevant integrated D=2 OPE series and the potential role of contributions of as-yet-unmeasured higher multiplicity modes to the strange inclusive spectral distribution. In addition to conventional flavor-breaking sum rule determinations, information obtainable from mixed tau-electroproduction sum rules having much reduced OPE uncertainties, and from sum rules based on the inclusive strange decay distribution alone, is also considered. Earlier discrepancies with the expectations of 3-family unitarity are found to be reduced, both the switch to D=2 OPE treatments favored by self-consistency tests and the increase in the strange branching fractions playing a role in this reduction.