LHC and the origin of neutrino mass

TL;DR

This paper explores how the LHC can directly probe the origin of neutrino Majorana mass through lepton number violating processes, especially within $L-R$ symmetric theories and grand unified models.

Contribution

It provides a detailed analysis of collider signatures for neutrino mass mechanisms, focusing on $L-R$ symmetry and a specific SU(5) GUT model with hybrid seesaw.

Findings

$W_R$ boson in TeV range can dominate neutrinoless double beta decay

LHC signatures include parity restoration and lepton number violation

A grand unified model predicts a light fermion triplet below TeV scale

Abstract

It is often said that neutrino mass is a window to a new physics beyond the standard model (SM). This is certainly true if neutrinos are Majorana particles since the SM with Majorana neutrino mass is not a complete theory. The classical text-book test of neutrino Majorana mass, the neutrino-less double beta decay depends on the completion, and thus cannot probe neutrino mass. As pointed out already more than twenty five years ago, the colliders such as Tevatron or LHC offer a hope of probing directly the origin of neutrino Majorana mass through lepton number violating production of like sign lepton pairs. I discuss this in the context of all three types of seesaw mechanism. I then discuss in detail the situation in $L-R$ symmetric theories, which led originally to the seesaw and which incorporates naturally both type I and type II. A $W_R$ gauge boson with a mass in a few TeV region could easily dominate the neutrino-less double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. At the end I give an example of a predictive SU(5) grand unified theory that results in a hybrid type I and III seesaw with a light fermion triplet below TeV scale.