Heavy Majorana Neutrinos in the Effective Lagrangian Description: Application to Hadron Colliders

TL;DR

This paper explores how heavy Majorana neutrinos, if present at sub-TeV scales, could signal physics beyond the minimal seesaw mechanism and be detected at colliders through effective interactions leading to distinctive same-sign lepton events.

Contribution

It develops a comprehensive effective Lagrangian framework for heavy Majorana neutrinos and analyzes their collider signatures, especially at the LHC and Tevatron.

Findings

Heavy Majorana neutrinos can produce thousands of same-sign lepton events at the LHC.

Effective operators up to dimension 6 effectively describe neutrino interactions.

Distinctive forward-backward asymmetry signals can help identify these neutrinos.

Abstract

We consider the effects of heavy Majorana neutrinos N with sub-TeV masses. We argue that the mere presence of these particles would be a signal of physics beyond the minimal seesaw mechanism and their interactions are, therefore, best described using an effective Lagrangian. We then consider the complete set of leading effective operators (up to dimension 6) involving the N and Standard Model fields and show that these interactions can be relatively easy to track at high-energy colliders. For example, we find that an exchange of a TeV-scale heavy vector field can yield thousands of characteristic same-sign lepton number violating l^+ l^+ j j events (j=light jet) at the LHC if m_N < 600 GeV, which can also have a distinctive forward-backward asymmetry signal; even the Tevatron has good prospects for this signature if m_N < 300 GeV.