Displaced Heavy Neutral Lepton from New Higgs Doublet

TL;DR

This paper explores the potential to detect long-lived heavy neutral leptons from a neutrinophilic Higgs doublet decay at future colliders, offering a new avenue to probe tiny neutrino masses and heavy lepton properties.

Contribution

It introduces a novel decay channel via a new Higgs doublet that enhances detection prospects of heavy neutral leptons at colliders, independent of small mixing parameters.

Findings

Displaced vertex signatures can probe very small mixing parameters ($|V_{\ell N}|^2\gtrsim10^{-19}$).

The study identifies collider mass reach up to 1200 GeV at HL-LHC and 1490 GeV at CLIC.

The proposed method covers the parameter space predicted by the seesaw mechanism.

Abstract

Heavy neutral leptons $N$ are introduced to explain the tiny neutrino masses via the seesaw mechanism. For proper small mixing parameter $V_{\ell N}$, the heavy neutral leptons $N$ become long-lived, which leads to the displaced vertex signature at colliders. In this paper, we consider the displaced heavy neutral lepton from the neutrinophilic Higgs doublet $\Phi_\nu$ decay. The new Higgs doublet with MeV scale VEV can naturally explain the tiny neutrino masses with TeV scale $N$. Different from current experimental searches via the $W^\pm\to \ell^\pm N$ decay, the new decays as $H^\pm\to \ell^\pm N$ are not suppressed by the small mixing parameter $V_{\ell N}$. Therefore, a larger parameter space is expected to be detected at colliders. We then investigate the promising region at the 14 TeV HL-LHC and the 3 TeV CLIC. According to our simulation, the DV signature could probe $|V_{\ell N}|^2\gtrsim10^{-19}$ with $m_N<m_{H^+}$, which covers the seesaw predicted value $|V_{\ell N}|^2\sim m_\nu/m_N$. We could probe $m_{H^+}\lesssim1200$ GeV at the 14 TeV HL-LHC and $m_{H^+}\lesssim1490$ GeV at the 3 TeV CLIC.