Neutrino Masses from Loop-induced $d \geq 7$ Operators

TL;DR

This paper introduces a novel loop-induced mechanism for generating tiny neutrino masses via higher-dimensional operators, specifically dimension-seven, at the TeV scale, avoiding artificial parameter assumptions.

Contribution

It presents concrete models where neutrino masses arise from one-loop dimension-seven operators induced at the TeV scale with an exact $Z_2$ symmetry, offering a new approach beyond traditional dimension-five mechanisms.

Findings

Neutrino masses are naturally generated without fine-tuning.

The model achieves sufficient suppression through loop factors and scale ratios.

Implications for collider experiments and dark matter are discussed.

Abstract

We propose a new scenario where neutrino masses are generated via operators with the mass dimension higher than five, which are induced at the loop level. The scenario is demonstrated with concrete models where neutrino masses are generated via a one-loop dimension-seven operator which is induced through TeV scale dynamics under the exact $Z_{2}$ symmetry. Tiny neutrino masses are naturally induced from the TeV scale dynamics without introducing any artificial assumption on magnitudes of coupling constants. The combination of one-loop factor $1/(4\pi)^2$ and the factor of the ratio $(v/\Lambda)^2$ between the electroweak scale $v$ and new physics scale $\Lambda$ provides sufficient suppression as compared to the model based on the dimension-five operator induced at the tree level. The reproduction of the data for neutrino masses and mixings are discussed under the constraint from experiments for lepton flavour violation. We also mention phenomenological implications at collider experiments and dark matter candidates.