Leptoquark mechanism of neutrino masses within the grand unification framework

Ilja Doršner,Svjetlana Fajfer,Nejc Košnik

doi:10.1140/epjc/s10052-017-4987-2

Ilja Doršner, Svjetlana Fajfer + Show 1 more

Open Access

https://doi.org/10.1140/epjc/s10052-017-4987-2

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Abstract

We demonstrate the viability of the one-loop neutrino mass mechanism within the framework of grand unification when the loop particles comprise scalar leptoquarks (LQs) and quarks of the matching electric charge. This mechanism can be implemented in both supersymmetric and non-supersymmetric models and requires the presence of at least one LQ pair. The appropriate pairs for the neutrino mass generation via the up-type and down-type quark loops are S_3–R_2 and S_{1,,3}–tilde{R}_2, respectively. We consider two distinct regimes for the LQ masses in our analysis. The first regime calls for very heavy LQs in the loop. It can be naturally realized with the S_{1,,3}–tilde{R}_2 scenarios when the LQ masses are roughly between 10^{12} and 5 times 10^{13} GeV. These lower and upper bounds originate from experimental limits on partial proton decay lifetimes and perturbativity constraints, respectively. Second regime corresponds to the collider accessible LQs in the neutrino mass loop. That option is viable for the S_3–tilde{R}_2 scenario in the models of unification that we discuss. If one furthermore assumes the presence of the type II see-saw mechanism there is an additional contribution from the S_3–R_2 scenario that needs to be taken into account beside the type II see-saw contribution itself. We provide a complete list of renormalizable operators that yield necessary mixing of all aforementioned LQ pairs using the language of SU(5). We furthermore discuss several possible embeddings of this mechanism in SU(5) and SO(10) gauge groups.

Highlights

Leptoquarks (LQs) are colored states that couple quarks to leptons
We demonstrate the viability of the one-loop neutrino mass mechanism within the framework of grand unification when the loop particles comprise scalar leptoquarks (LQs) and quarks of the matching electric charge
If one assumes the presence of the type II seesaw mechanism there is an additional contribution from the S3–R2 scenario that needs to be taken into account beside the type II see-saw contribution itself

Summary

Introduction

Leptoquarks (LQs) are colored states that couple quarks to leptons. They can yield novel physical processes such as proton decay or help explain experimentally observed phenomena that cannot be successfully addressed within the Standard Model (SM) of elementary particle physics. First regime corresponds to a scenario where the LQs behind the neutrino mass generation reside at a very high energy scale One would need to prevent mixing between these LQs and any other LQ in the theory that has “diquark” couplings to ensure stability of matter This might represent a challenge since one needs to mix specific LQ multiplets in order to generate neutrino masses in the first place. We show that both of these issues can be successfully addressed for the S3– R2 and S3–R2 scenarios in Sect. The S1–R2 option, on the other hand, is problematic due to difficulty with suppression of the S1 “diquark” couplings in the simplest of models and we opt not to discuss it in the light LQ regime

Heavy leptoquark regime

Light leptoquark regime

Conclusions