TeV-scale Seesaw with Quintuplet Fermions

TL;DR

This paper introduces a novel TeV-scale seesaw model using fermionic quintuplets and scalar quadruplets, enabling neutrino mass generation accessible at the LHC with distinctive multi-lepton signatures.

Contribution

It proposes a new seesaw mechanism involving fermionic quintuplets and scalar quadruplets, providing both tree-level and radiative neutrino mass contributions, and discusses collider phenomenology.

Findings

Achieves neutrino masses ~ 0.1 eV with TeV-scale new particles.

Predicts ~ 500 doubly-charged fermions at the LHC with 5 fb^{-1} luminosity.

Shows the neutral fermion component's instability and stabilization via Z_2 symmetry.

Abstract

We propose a new seesaw model based on fermionic hypercharge zero weak quintuplet in conjunction with additional scalar quadruplet which attains an induced vev. The model provides both tree-level seesaw ~ v^6/M^5 and a loop-suppressed radiative ~ (1 / 16 \pi^2) v^2/M contributions to active neutrino masses. The empirical masses m_\nu ~ 10^{-1} eV can be achieved with M ~ TeV new states, accessible at the LHC. For 5 fb^{-1} of accumulated integrated luminosity at the LHC, there could be ~ 500 doubly-charged \Sigma^{++} or \bar{\Sigma^{++}} fermions with mass M_\Sigma = 400 GeV, leading to interesting multi-lepton signatures. The neutral component of the fermion quintuplet, previously identified as minimal dark matter candidate, becomes unstable in the proposed seesaw setup. The stability can be restored by introducing a Z_2 symmetry, in which case neutrinos get mass only from radiative contributions.