Hyperon Beta-Decay Analysis and the Recent KTeV Data

The analysis of hyperon semi-leptonic decay data is addressed with reference to SU(3) breaking and isospin mixing between Lambda^O and Sigma^O. Various approaches to SU(3) breaking are discussed and compared. The phenomenological implications of Lambda^0-Sigma^0 mixing are not to be underestimated: it can induce vector couplings in decays otherwise purely axial and may also modify rates. In regard of the KTeV data on Xi^0O -> Sigma^+ e antineutrino, predictions are presented and the impact of present a future data on the extraction of F and D is also examined. In addition, the implications of the new data for the use of octet baryon beta decays in determining V_us are considered