Hadronic Tau Decay Based Determinations of |V_us|
  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. 
Kim Maltman
hep-ph