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We show that in a large class of models based on anomalous U(1) symmetry which addresses the fermion mass hierarchy problem, leptonic flavor changing processes are induced that are in the experimentally interesting range. The flavor violation occurs through the renormalization group evolution of the soft SUSY breaking parameters between the string scale and the U(1)_A breaking scale. We derive general expressions for the evolution of these parameters in the presence of higher dimensional operators. Several sources for the flavor violation are identified: flavor-dependent contributions to the soft masses from the U(1)_A gaugino, scalar mass corrections proportional to the trace of U(1)_A charge, non-proportional A-terms from vertex corrections, and the U(1)_A D-term. Quantitative estimates for the decays mu -> e gamma and tau -> mu gamma are presented in supergravity models which accommodate the relic abundance of neutralino dark matter.
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We study the contributions of supersymmetric models with a $U(1)$ horizontal symmetry and only spontaneous CP breaking to various lepton flavor observables, such as $mu to egamma$ and the electron electric dipole moment. We show that both a horizontal symmetry and a lack of explicit CP violation can alleviate the existing bounds from such observables. The undetermined $mathcal{O}(1)$ coefficients in such mass matrix models muddle the interpretation of the bounds from various flavor observables. To overcome this, we define a new fine-tuning measure for different observables in such setups. This allows us to study how naturally the observed IR flavor observables can emerge from a given mass matrix model. We use our flavor-naturalness measure in study of our supersymmetric models and quantify the degree of fine tuning required by the bounds from various lepton flavor observables at each mass scale of sleptons, neutralinos, and charginos.
We show that new physics models without new flavor violating interactions can explain the recent anomalies in the $bto sell^+ell^-$ transitions. The $bto sell^+ell^-$ arises from a $Z$ penguin which automatically predicts the $V-A$ structure for the quark currents in the effective operators. This framework can be realized either in a renormalizable $U(1)$ setup or be due to new strongly interacting dynamics. The di-muon resonance searches at the LHC are becoming sensitive to this scenario since the $Z$ is relatively light, and could well be discovered in future searches by ATLAS and CMS.
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