Broadening the Higgs Boson with Right-Handed Neutrinos and a Higher Dimension Operator at the Electroweak Scale

TL;DR

This work explores how TeV-scale higher-dimension operators coupling the Higgs to right-handed neutrinos can open new Higgs decay channels, potentially dominating over $h \rightarrow b\bar b$ for certain scales and flavor structures. By employing an effective field theory with the dim-5 operator $O^{(5)}_1 = H^{\dagger} H N N$ and imposing minimal flavor violation, it shows that Higgs decays to right-handed neutrinos can yield long-lived states with macroscopic lifetimes, producing striking displaced-vertex signatures that violate lepton number. The analysis highlights how the flavor symmetry of the right-handed neutrinos (SO(3) vs SU(3)×U(1)′) critically controls the operator coefficients and decay rates, and it discusses naturalness constraints and the resulting collider phenomenology. Overall, the paper identifies a rich, testable Higgs-neutrino interplay at the electroweak scale with potential to probe otherwise inaccessible neutrino parameters via RHN decays at the LHC.

Abstract

The existence of certain TeV suppressed higher-dimension operators may open up new decay channels for the Higgs boson to decay into lighter right-handed neutrinos. These channels may dominate over all other channels if the Higgs boson is light. For a Higgs boson mass larger than $2 m_W$ the new decays are subdominant yet still of interest. The right-handed neutrinos have macroscopic decay lengths and decay mostly into final states containing leptons and quarks. A distinguishing collider signature of this scenario is a pair of displaced vertices violating lepton number. A general operator analysis is performed using the minimal flavor violation hypothesis to illustrate that these novel decay processes can occur while remaining consistent with experimental constraints on lepton number violating processes. In this context the question of whether these new decay modes dominate is found to depend crucially on the approximate flavor symmetries of the right-handed neutrinos.