Fits to non-supersymmetric SO(10) models with type I and II seesaw mechanisms using renormalization group evolution

Tommy Ohlsson,Marcus Pernow

doi:10.1007/jhep06(2019)085

Tommy Ohlsson, Marcus Pernow

Open Access

https://doi.org/10.1007/jhep06(2019)085

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Abstract

We consider numerical fits to non-supersymmetric SO(10)-based models in which neutrino mass is generated by the type-I or type-II seesaw mechanism or a combination of both. The fits are performed with a sophisticated top-down procedure, taking into account the renormalization group equations of the gauge and Yukawa couplings, integrating out relevant degrees of freedom at their corresponding mass scales, and using recent data for the Standard Model observables. We find acceptable fits for normal neutrino mass ordering only and with neutrino mass generated by either type-I seesaw only or a combination of types I and II seesaw in which type-I seesaw is dominant. Furthermore, we find predictions from the best fit regarding the small neutrino masses, the effective neutrinoless double beta decay mass, and the leptonic CP-violating phase. Finally, we show that the fits are rather insensitive to the chosen value of the unification scale.

Highlights

Scenarios [24, 25], which concluded that models with type-II seesaw only do not yield acceptable fits, but that type-II seesaw in combination with type-I seesaw provides good fits
The more complete procedure is to use a top-down approach, which involves randomly sampling the parameters of the SO(10) Yukawa sector at MGUT and evolving each parameter down to the electroweak scale MZ using the renormalization group equations (RGEs), where they are compared to experimental values of the observables, as has been done in refs. [18, 21,22,23]
The results of the fits show that the known observables of the SM with normal neutrino mass ordering are well accommodated by the model with the type-I seesaw mechanism (χ2 14.8), and that including the type-II seesaw mechanism improves the fit by a small amount to χ2 14.7

Summary

Introduction

Scenarios [24, 25], which concluded that models with type-II seesaw only do not yield acceptable fits, but that type-II seesaw in combination with type-I seesaw provides good fits. Most of the previous fits have been performed with a bottom-up approach, by first evolving the experimental values of the SM observables up to the GUT scale MGUT using the renormalization group equations (RGEs) and fitting the SO(10) Yukawa sector to the evolved data at that scale This procedure involves several approximations, since the renormalization group (RG) evolution in general depends on parameters which are not known a priori, such as the mass scales of right-handed neutrinos (where they are integrated out) and the matching conditions at intermediate breaking steps. The novelty of this work is the combination of the type-I and type-II seesaw mechanisms with a proper and complete treatment of the RG evolution, including integrating out right-handed neutrinos at their respective mass scales.

Methods

Results

Conclusion