Predicting \u03b4PMNS, \u03b823PMNS and fermion mass ratios from flavour GUTs with CSD2

Stefan Antusch,Charanjit K Khosa,Christian Hohl,Vasja Susič

doi:10.1007/jhep12(2018)025

Stefan Antusch, Charanjit K Khosa + Show 2 more

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https://doi.org/10.1007/jhep12(2018)025

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Abstract

Constrained Sequential neutrino Dominance of type 2 (referred to as CSD2) is an attractive building block for flavour Grand Unified Theories (GUTs) because it predicts a non-zero leptonic mixing angle θ13PMNS, a deviation of θ23PMNS from π/4, as well as a leptonic Dirac CP phase δPMNS which is directly linked to the CP violation relevant for generating the baryon asymmetry via the leptogenesis mechanism. When embedded into GUT flavour models, these predictions are modified in a specific way, depending on which GUT operators are responsible for generating the entries of fermion Yukawa matrices. In this paper, we systematically investigate and classify the resulting predictions from supersymmetric SU(5) based flavour models by fitting the known fermion mass and mixing data, in order to provide a roadmap for future model building. Interestingly, the promising models predict the lepton Dirac CP phase δPMNS between 230° and 290°, and the quark CP phase δCKM in accordance with a right-angled unitarity triangle (αUT = 90°). Also, our model setup predicts the quantities θ23PMNS and md/ms with less uncertainty than current experimental precision, and allowing with future sensitivity to discriminate between them.

Highlights

Grand Unified Theories (GUTs) offer an attractive framework for model building beyond the Standard Model (SM)
Constrained Sequential neutrino Dominance of type 2 is an attractive building block for flavour Grand Unified Theories (GUTs) because it predicts a non-zero leptonic mixing angle θ1P3MNS, a deviation of θ2P3MNS from π/4, as well as a leptonic Dirac CP phase δPMNS which is directly linked to the CP violation relevant for generating the baryon asymmetry via the leptogenesis mechanism
Having specified the implementation of the model at the GUT scale and how observables are compared to experimental data in section 3, we investigate the following two questions: first, which tuples of CG coefficients listed in table 1, in combination with one of the two Constrained Sequential Dominance 2” (CSD2) neutrino Yukawa couplings, are compatible with the experimental data

Summary

Introduction

Grand Unified Theories (GUTs) offer an attractive framework for model building beyond the Standard Model (SM). Fermion unification in the large GUT representations, on top of gauge coupling unification, makes them a natural environment for addressing the flavour puzzle, i.e. the question about the origin of the observed fermion masses, mixings and CP violating phases. In this work we will focus on the framework of SU(5) based GUTs. Depending on the GUT gauge group and on the choice of the GUT-Higgs representations involved in the GUT operators for the Yukawa matrices, the unification of fermions in GUT-matter representations leads to a variety of close connections between the elements of the Yukawa matrices, and between the masses and mixings in the quark and lepton sectors (cf [4, 5]). In particular towards understanding the observed charged fermion mass hierarchies and the large mixing in the lepton sector, family symmetries are often considered in addition to the unifying gauge symmetry. In such a “flavour GUT” scenario, the vacuum expectation values (VEVs) of the family symmetry breaking fields (known as “flavons”) play a crucial role in generating the Yukawa couplings

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Conclusion