Predicting the tau strange branching ratios and implications for V-us

Hadronic τ decays provide several ways to extract the Cabbibo-Kobashi-Maskawa (CKM) matrix element Vus. The most precise determination involves using inclusive τ decays and requires as input the total branching ratio into strange final states. Recent results from B-factories have led to a discrepancy of about 3.4σ from the value of Vus implied by CKM unitarity and direct determination from Kaon semi-leptonic modes. In this paper we predict the three leading strange τ branching ratios, using dispersive parameterizations of the hadronic form factors and taking as experimental input the measured Kaon decay rates and the τ → Kπντ decay spectrum. We then use our results to reevaluate Vus , for which we find |Vus| = 0.2207 ± 0.0027, in better agreement with CKM unitarity.