tau-universality violation with light neutralinos

In a supersymmetric model with the lightest supersymmetric particle (LSP), chi in the range of a few hundred MeV's, the decay tau --> mu chi chi is allowed. We investigate the departure from tau universality caused by this decay which can be triggered by neutrino masses. It is found that universality violation in this way can be greater than both nonuniversal electroweak radiative corrections and supersymmetric one-loop corrections over a considerable region of the parameter space allowed by experiments so far. Thus it suggests a method of constraining the parameter space with light LSP's using data from tau factories.