Leptoquark mechanism of neutrino masses within the grand unification framework

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 nonsupersymmetric 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 -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 -R 2 scenarios when the LQ masses are roughly between 10 12 and 5 × 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 -R 2 scenario in the models of unification that we discuss. If one furthermore assumes the presence of the type II seesaw 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. a

The role of the S 3 GUT leptoquark in flavor universality and collider searches

“…We can thus identify y of eq. (2.1) with y 45 / √ 2, where y 45 is related to the difference in masses between charged fermions and down-type quarks [52]. This follows from the fact that there are actually two operators that contribute towards the charged fermion and down-type quark masses in this SU(5) model [91].…”

“…(2.1) since we assume that S 3 and its interactions originate from the GUT construction presented in ref. [52] where the baryon number violating diquark couplings are forbidden due to the grand unified symmetry. 1 The main goal of our study is to address the puzzles observed in neutral current LFU tests in the R K ratio (and related anomalies in b → sµ + µ − ) as well as in charged-current LFU ratios R D ( * ) .…”

“…To insure that the LHC accessible leptoquarks S 3 andR 2 are not in conflict with stringent limits on matter stability it is necessary that both S 3 andR 2 do not couple to the quark-quark pairs either directly or through the mixing with other scalars in a specific model of unification. It turns out that one can meet this requirement in an SU(5) model that comprises 5-, 15-, 24-, and 45-dimensional scalar representations [52]. The decomposition of the scalar sector of that model is…”

“…To this end, we take all scalar fields in the model that mediate proton decay at tree-level to reside at or above 10 12 GeV. These fields are Ψ T , ∆ 5 , and ∆ 6 [52]. We furthermore set the masses of both S 3 andR 2 at 1 TeV and constrain all remaining scalar fields to be at or above one scale we simply denote m that is to be determined through the requirement that the gauge coupling unification takes place at the one-loop level.…”

Surveying the SO(10) model landscape: The left-right symmetric case

“…Within the context of GUTs, neutrino masses may also be generated at the loop level under the presence of heavy leptoquarks [79]. We here omit this possibility.…”