Leptonic Scalars at the LHC

TL;DR

This paper investigates the potential of the LHC to detect leptonic scalars that couple mainly to neutrinos and carry lepton number, focusing on their unique collider signatures and sensitivity compared to other experiments.

Contribution

It provides the first estimate of LHC sensitivity to lepton-number-charged scalars with masses below the electroweak scale, highlighting their collider signatures and complementarity with other experiments.

Findings

LHC can detect leptonic scalars via same-sign dilepton and missing energy signatures.

Projected LHC sensitivity surpasses existing bounds for scalars heavier than ~10 GeV.

Sensitivity is complementary to low-energy and neutrino experiments.

Abstract

We explore the collider prospects of neutrino non-standard interaction with a Standard Model (SM) gauge-singlet leptonic scalar $\phi$ carrying two units of lepton-number-charge. These leptonic scalars are forbidden from interacting with the SM fermions at the renormalizable level and, if one allows for higher-dimensional operators, couple predominantly to SM neutrinos. For masses at or below the electroweak scale, $\phi$ decays exclusively into neutrinos. Its characteristic production signature at hadron collider experiments like the LHC would be via the vector boson fusion process and leads to same-sign dileptons, two forward jets in opposite hemispheres, and missing transverse energy, i.e., $pp \to \ell_\alpha^\pm \ell_\beta^\pm jj + E_T^{\rm miss}$ ($\alpha,\, \beta = e,\, \mu, \tau$). Exploiting the final states of electrons and muons, we estimate, for the first time, the sensitivity of the LHC to these lepton-number-charged scalars. We show that the LHC sensitivity is largely complementary to that of low-energy precision measurements of the decays of charged leptons, charged mesons, $W$, $Z$ and the SM Higgs boson, as well as the neutrino beam experiments like MINOS, and searches for neutrino self-interactions at IceCube and in cosmological observations. For $\phi$ mass larger than roughly 10 GeV, our projected LHC sensitivity would surpass all existing bounds.