Neutrino masses from an A4 symmetry in holographic composite Higgs models

Abstract

We show that holographic composite Higgs Models with a discrete A 4 symmetry can be built, which naturally predict hierarchical charged lepton masses and an approximate tri-bimaximal lepton mixing with the correct scale of neutrino masses and a characteristic phenomenology. They also satisfy current constraints from electroweak precision tests, lepton flavor violation and lepton mixing in a large region of parameter space. Two features arise in our model phenomenologically relevant. First, an extra suppression on the lepton Yukawa couplings makes the τ lepton more composite than naively expected from its mass. As a consequence new light leptonic resonances, with masses as low as few hundreds of GeV, large couplings to τ and a very characteristic collider phenomenology, are quite likely. Second, the discrete symmetry A 4 together with the model structure provide a double-layer of flavor protection that allows to keep tree-level mediated processes below present experimental limits. One-loop processes violating lepton flavor, like μ → eγ, may be however observable at future experiments. © 2010 SISSA.