A critical look at V_us determinations from hadronic tau decay data

TL;DR

This paper critically examines methods for determining |V_{us}| from hadronic tau decay data, highlighting issues with theoretical convergence and proposing alternative analyses to improve consistency with unitarity.

Contribution

It provides a detailed review of the challenges in extracting |V_{us}|, emphasizing the slow convergence of the OPE series and exploring new sum rule approaches to reduce uncertainties.

Findings

Slow convergence of the D=2 OPE series affects |V_{us}| determinations.

Alternative sum rule analyses can reduce discrepancies with unitarity.

Self-consistency tests favor methods that align better with three-family unitarity.

Abstract

A critical review of hadronic tau decay data based determinations of |V_{us}| is given, focussing on the impact of the slow convergence of the integrated D=2 OPE series for the conventional flavor-breaking sum rule determination and the potential role of as-yet-unmeasured multiparticle contributions to the strange spectral distribution. Additional information obtainable from analyses of inclusive strange decay data alone, and from mixed electroproduction-tau sum rules with much reduced OPE uncertainties, is also discussed. Self-consistency tests are shown to favor determinations which reduce somewhat discrepancies with 3-family unitarity expectations.