The Genuine Type-V Seesaw Model: Phenomenological Introduction

TL;DR

This paper introduces a Type-V seesaw model generating Majorana neutrino masses via a high-dimensional operator, leading to testable predictions at colliders with rich fermionic multiplets and observable lepton flavor violation.

Contribution

It proposes a novel low-energy effective operator-based Type-V seesaw model with multiple fermionic multiplets, providing new collider phenomenology and experimental constraints.

Findings

Lower bounds on heavy fermion masses from CMS data.

Constraints on Yukawa couplings from lepton flavor violation.

Potential signatures at future colliders like long-lived particles.

Abstract

We study a model which generates Majorana neutrino masses at tree-level via low-energy effective operator with mass-dimension-9. Introduction of such a higher dimensional operator brings down the lepton number violating mass scale to TeV making such model potentially testable at present or near future colliders. This model possesses several new $SU(2)_L$ fermionic multiplets, in particular, three generations of triplets, quadruplets and quintuplets, and thus a rich phenomenology at the LHC. As the lepton flavour violation arises very naturally in such setup, we put constraints on the Yukawa couplings and heavy fermion masses from the current experimental bounds on lepton flavour violating processes. We also obtain 95% CL lower bounds on the masses of the triplets, quadruplets and quintuplets using a recent CMS search for multilepton final states with 137 inverse femtobarn integrated luminosity data at 13 TeV center of mass energy. The possibility that the heavy fermions could be long-lived leaving disappearing charge track signatures or displaced vertex at the future colliders like LHeC, FCC-he, MATHUSLA, etc. is also discussed.