Consistency constraints on m_s from QCD dispersion relations and chiral perturbation theory in K_(l3) decays

We use both old and new theoretical developments in QCD dispersion relation constraints on the scalar form factor in the decay K --> \pi l \nu_l to obtain constraints on the strange quark mass. The perturbative QCD side of the calculation incorporates up to four-loop corrections, while the hadronic side uses a recently developed parameterization constructed explicitly to satisfy the dispersive constraints. Using chiral perturbation theory (\chiPT) as a model for soon-to-be measured data, we find a series of lower bounds on m_s increasing with the accuracy to which one believes \chiPT to represent the full QCD result.