Leptons in Holographic Composite Higgs Models with Non-Abelian Discrete Symmetries

Abstract

We study leptons in holographic composite Higgs models, namely in models possibly admitting a weakly coupled description in terms of five-dimensional (5D) theories. We introduce two scenarios leading to Majorana or Dirac neutrinos, based on the non-abelian discrete group $S_4\times {\mathbb{Z}}_3$ which is responsible for nearly tri-bimaximal lepton mixing. The smallness of neutrino masses is naturally explained and normal/inverted mass ordering can be accommodated. We analyze two specific 5D gauge-Higgs unification models in warped space as concrete examples of our framework. Both models pass the current bounds on Lepton Flavour Violation (LFV) processes. We pay special attention to the effect of so called boundary kinetic terms that are the dominant source of LFV. The model with Majorana neutrinos is compatible with a Kaluza-Klein vector mass scale $m_{KK}\gtrsim 3.5$ TeV, which is roughly the lowest scale allowed by electroweak considerations. The model with Dirac neutrinos, although not considerably constrained by LFV processes and data on lepton mixing, suffers from a too large deviation of the neutrino coupling to the $Z$ boson from its Standard Model value, pushing $m_{KK}\gtrsim 10$ TeV.

37 pages, 4 figures; v2: Note added in light of recent T2K and MINOS results, figures updated with new limit from MEG, references added, various minor improvements, matches JHEP published version

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• Tri-Bimaximal Neutrino Mixing and Discrete Flavour Symmetries
• Leptons in Composite MFV
• Warped flavor symmetry predictions for neutrino physics
• Dirac Neutrinos with $S_4$ Flavor Symmetry in Warped Extra Dimensions
• Explicit and spontaneous breaking of SU(3) into its finite subgroups
• A 3-3-1 model with right-handed neutrinos based on the $\Delta \left(27\right)$ family symmetry
• A naturally light Higgs without light Top Partners
• A highly predictive $A_4$ flavour 3-3-1 model with radiative inverse seesaw mechanism
• The symmetry approach to quark and lepton masses and mixing
• A 3-3-1 model with low scale seesaw mechanisms
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• Radiative Seesaw-type Mechanism of Fermion Masses and Non-trivial Quark Mixing
• Fermion masses and mixings and some phenomenological aspects of a 3-3-1 model with linear seesaw mechanism
• A novel Randall-Sundrum model with $S_3$ flavor symmetry
• Lepton Flavour Violation in Composite Higgs Models
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• Neutrino Mixing from Wilson Lines in Warped Space
• Muon anomalies and the $SU(5)$ Yukawa relations
• Flavour and CP symmetries in the inverse seesaw
• SU(6) Gauge-Higgs Grand Unification: Minimal Viable Models and Flavor
• Low-scale leptogenesis with flavour and CP symmetries
• Multiscalar $B-L$ extension based on $S_4$ flavor symmetry for neutrino mass and mixing
• Phenomenology of extended multiHiggs doublet models with $S_4$ family symmetry
• Theoretical aspects of charged Lepton Flavour Violation
• Flavour anomalies meet flavour symmetry
• Charged lepton flavour violation in supersymmetric and holographic composite Higgs models with flavour symmetries