Constraints on the form factors for K --> pi l nu and implications for V_us

Richard J. Hill

Published 2006-07-11, updated 2006-12-01Version 2

Rigorous bounds are established for the expansion coefficients governing the shape of semileptonic K-->pi form factors. The constraints enforced by experimental data from tau-->K pi nu eliminate uncertainties associated with model parameterizations in the determination of |V_us|. The results support the validity of a powerful expansion that can be applied to other semileptonic transitions.