Neutrino Masses from an A4 Symmetry in Holographic Composite Higgs Models

TL;DR

This paper demonstrates that holographic composite Higgs models with A4 symmetry naturally produce realistic lepton masses and mixings, predict light leptonic resonances, and satisfy current experimental constraints, with potential observable lepton flavor violation signals.

Contribution

It introduces a novel holographic composite Higgs model with A4 symmetry that explains lepton masses, mixings, and predicts light leptonic resonances with distinctive collider signatures.

Findings

Hierarchical charged lepton masses and tri-bimaximal mixing are naturally achieved.

Light leptonic resonances could be as low as a few hundred GeV.

Lepton flavor violation processes like mu -> e gamma may be observable in future experiments.

Abstract

We show that holographic composite Higgs Models with a discrete A4 symmetry naturally predict hierarchical charged lepton masses and an approximate tri-bimaximal lepton mixing with the correct scale of neutrino masses. They also satisfy current constraints from electroweak precision tests, lepton flavor violation and lepton mixing in a large region of parameter space. Two phenomenologically relevant features arise in these models. First, an extra suppression on the lepton Yukawa couplings makes the tau 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 tau and a very characteristic collider phenomenology, are quite likely. Second, the discrete symmetry A4 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 mu -> e gamma, may be however observable at future experiments.