A NEW MECHANISM FOR LEPTON-FLAVOR VIOLATION TAU-]MU-GAMMA IN THE FLIPPED STRING

We explore a new mechanism for lepton-flavor violation which is manifest in the flipped SU(5) string model, and may be a generic feature of string-derived models. This mechanism generates off-diagonal slepton masses from otherwise flavor diagonal Yukawa matrices when heavy vector-like leptons decouple at a high-mass scale. As an example of lepton-flavor violation, we present an order of magnitude prediction for the branching ratio BR(tau --> mu-gamma) in the flipped string. The result depends crucially on the details of the extra vector-like fermion decoupling, and on the assumed nature and scale of supersymmetry breaking. For natural choices of the parameters we obtain a large BR(tau --> mu-gamma), which we show to be well within the reach of present and future experimental searches.