Loop bounds on non-standard neutrino interactions

TL;DR

This paper reevaluates bounds on non-standard neutrino interactions, emphasizing their model dependence and showing that naturalness arguments can impose stronger, but not entirely model-independent, constraints.

Contribution

It demonstrates the model dependence of loop-induced bounds on neutrino interactions and discusses conditions to evade these bounds within specific models.

Findings

Naturalness arguments lead to stronger bounds than previous studies.

Model-independent bounds are approximately 0.1, but require fine-tuning.

Large loop contributions can be avoided with specific model conditions.

Abstract

We reconsider the bounds on non-standard neutrino interactions with matter which can be derived by constraining the four-charged-lepton operators induced at the loop level. We find that these bounds are model dependent. Naturalness arguments can lead to much stronger constraints than those presented in previous studies, while no completely model-independent bounds can be derived. We will illustrate how large loop-contributions to four-charged-lepton operators are induced within a particular model that realizes gauge invariant non-standard interactions and discuss conditions to avoid these bounds. These considerations mainly affect the $\mathcal O(10^{-4})$ constraint on the non-standard coupling strength $\eps_{e\mu}$, which is lost. The only model-independent constraints that can be derived are $\mathcal O(10^{-1})$. However, significant cancellations are required in order to saturate this bound.