Abstract
Models of radiative Majorana neutrino masses require new scalars and/or fermions to induce lepton-number-violating interactions. We show that these new particles also generate observable neutrino non-standard interactions (NSI) with matter. We classify radiative models as type-I or II, with type-I models containing at least one Standard Model (SM) particle inside the loop diagram generating neutrino mass, and type- II models having no SM particle inside the loop. While type-II radiative models do not generate NSI at tree-level, popular models which fall under the type-I category are shown, somewhat surprisingly, to generate observable NSI at tree-level, while being consistent with direct and indirect constraints from colliders, electroweak precision data and charged-lepton flavor violation (cLFV). We survey such models where neutrino masses arise at one, two and three loops. In the prototypical Zee model which generates neutrino masses via one-loop diagrams involving charged scalars, we find that diagonal NSI can be as large as (8%, 3.8%, 9.3%) for (εee, εμμ, εττ), while off-diagonal NSI can be at most (10−3%, 0.56%, 0.34%) for (εeμ, εeτ, εμτ). In one-loop neutrino mass models using leptoquarks (LQs), (εμμ, εττ) can be as large as (21.6%, 51.7%), while εee and (εeμ, εeτ, εμτ) can at most be 0.6%. Other two- and three-loop LQ models are found to give NSI of similar strength. The most stringent constraints on the diagonal NSI are found to come from neutrino oscillation and scattering experiments, while the off-diagonal NSI are mostly constrained by low-energy processes, such as atomic parity violation and cLFV. We also comment on the future sensitivity of these radiative models in long-baseline neutrino experiments, such as DUNE. While our analysis is focused on radiative neutrino mass models, it essentially covers all NSI possibilities with heavy mediators.
Highlights
The origin of tiny neutrino masses needed to explain the observed neutrino oscillation data is of fundamental importance in particle physics
We have made a comprehensive analysis of neutrino non-standard interactions generated by new scalars in radiative neutrino mass models
We have proposed a new nomenclature to classify radiative neutrino mass models, viz., the class of models with at least one Standard Model (SM) particle in the loop are dubbed as type-I radiative models, whereas those models with no SM particles in the loop are called type-II radiative models
Summary
The origin of tiny neutrino masses needed to explain the observed neutrino oscillation data is of fundamental importance in particle physics. Most attempts that explain the smallness of these masses assume the neutrinos to be Majorana particles, in which case their masses could arise from effective higher dimensional operators, suppressed by a high energy scale that characterizes lepton number violation. In these radiative neutrino mass models, the tree-level Lagrangian does not generate O1 of eq (1.1), owing to the particle content or symmetries present in the model If such a model has lepton number violation, small. One possible way to avoid such constraints is to have light mediators for NSI [21,22,23] In contrast to these attempts, in this paper we focus on heavy mediators, and study the range of NSI allowed in a class of radiative neutrino mass models.. Somewhat surprisingly, that the strengths of the diagonal NSI can be (20–50)% of the weak interaction strength for the flavor diagonal components in a class of popular models that we term as type-I radiative neutrino mass models, while they are absent at tree-level in another class, termed type-II radiative models
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