Flavor Violating Transitions of Charged Leptons from a Seesaw Mechanism of Dimension Seven

TL;DR

This paper investigates lepton flavor violating processes arising from a dimension-seven neutrino mass generation mechanism, analyzing the flavor structure and numerical constraints, with implications for tau lepton decays.

Contribution

It provides a systematic parametrization of flavor matrices in a dimension-seven seesaw model and explores the parameter space affecting charged lepton flavor violation.

Findings

Tau decays are heavily suppressed by current constraints.

Some parameter regions allow tau decays near two orders below experimental bounds.

Muon decay constraints significantly restrict flavor violation in the model.

Abstract

A mechanism has been suggested recently to generate the neutrino mass out of a dimension-seven operator. This is expected to relieve the tension between the occurrence of a tiny neutrino mass and the observability of other physics effects beyond it. Such a mechanism would inevitably entail lepton flavor violating effects. We study in this work the radiative and purely leptonic transitions of the light charged leptons. In so doing we make a systematic analysis of the flavor structure by providing a convenient parametrization of the mass matrices in terms of independent physical parameters and diagonalizing them explicitly. We illustrate our numerical results by sampling over two CP phases and one Yukawa coupling which are the essential parameters in addition to the heavy lepton mass. We find that with the stringent constraints coming from the muon decays and the muon-electron conversion in nuclei taken into account the decays of the tau lepton are severely suppressed in the majority of parameter space. There exist, however, small regions in which some tau decays can reach a level that is about 2 orders of magnitude below their current bounds.