TTP09-38 Lepton flavour violation in the MSSM

We derive new constraints on the quantities delta_{XY}^{ij, X,Y=L,R, which parametrise the flavour-off-diagonal terms of the charged slepton mass matrix in the MSSM. Considering mass and anomalous magnetic moment of the electron we obtain the bound delta^{13}_{LL}*delta^{13}_{RR} < 0.1, which involves the poorly constrained element delta^{13}_{RR}. We improve the predictions for the decays tau → mu gamma, tau → e gamma and mu → e gamma by including two-loop corrections which are enhanced if tan beta is large. The finite renormalisation of the PMNS matrix from soft SUSY-breaking terms is derived and applied to the charged-Higgs-lepton vertex. We find that the experimental bound on BR(tau → e gamma) severely limits the size of the MSSM loop correction to the PMNS element U_{e3}, which is important for the proper interpretation of a future U_{e3} measurement. Subsequently we confront our new values for delta^{ij}_{LL} with a GUT analysis. As a novel feature we consider dimension-5 Yukawa terms, which are needed to fix the Yukawa unification of the first two generations. If universal supersymmetry breaking occurs above the GUT scale, we find the flavour structure of the dimension-5 Yukawa couplings tightly constrained by mu → e gamma.