Order and Anarchy hand in hand in 5D SO(10)

TL;DR

This paper updates a 5D SO(10) grand unified model with anarchical Yukawa couplings, solving the doublet-triplet splitting problem, and finds that a normal neutrino mass ordering is naturally compatible with the model's parameters.

Contribution

The paper extends the original model by explicitly solving the doublet-triplet splitting and performs a fit to data, showing natural compatibility with normal neutrino ordering and specific neutrino mass predictions.

Findings

Normal neutrino mass ordering is naturally compatible.

Lightest neutrino mass below 5 meV.

Model predicts no baryon asymmetry via thermal leptogenesis.

Abstract

We update a five-dimensional SO(10) grand unified model of fermion masses and mixing angles originally proposed by Kitano and Li. In our setup Yukawa couplings are anarchical and quark and lepton sectors are diversified by the profiles of the fermion zero modes in the extra dimension. The breaking of SO(10) down to SU(5) \times U(1)_X provides the key parameter that distinguishes the profiles of the different SU(5) components inside the same 16 representation. With respect to the original version of the model, we extend the Higgs sector to explicitly solve the doublet-triplet splitting problem through the missing partner mechanism and we perform a fit to an idealized set of data. By scanning the Yukawa couplings of the model we find that, for large tan\beta, both normal and inverted ordered neutrino spectrum can be accommodated. However, while the case of inverted order requires a severe fine tuning of the Yukawa parameters, the normal ordering is compatible with an anarchical distribution of Yukawa couplings. Thus, in a natural portion of the parameter space, the model predicts a normal ordered neutrino spectrum, the lightest neutrino mass below 5 meV, and |m_{\beta\beta}| in the range 0.1-5 meV. No particular preference is found for the Dirac CP phase in the lepton sector while the right-handed neutrino masses are too small to explain the baryon asymmetry of the universe through thermal leptogenesis.