Eur. Phys. J. C (2025) 85: 401
https://doi.org/10.1140/epjc/s10052-025-14125-w

Regular Article - Theoretical Physics

Displaced heavy neutral lepton from new Higgs doublet

¹ School of Physics and Physical Engineering, Qufu Normal University, 273165, Qufu, Shandong, China
² School of Physics and Technology, University of Jinan, 250022, Jinan, Shandong, China
³ Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology, Guangxi Normal University, 541004, Guilin, Guangxi, China

^a sps_hanzl@ujn.edu.cn

Received: 26 August 2024
Accepted: 26 March 2025
Published online: 9 April 2025

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 ${\mathrm{\Phi }}_{\nu }$ 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 branching ratios of new decays as $H^{\pm }\to {\ell }^{\pm }N$ are not suppressed when $|V_{\ell N}|\gtrsim {10}^{-16}.$ 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 $|V_{\ell N}{|}^2\gtrsim {10}^{-18}$ with $m_N<m_{H^{+}},$ which covers the seesaw predicted value $|V_{\ell N}{|}^2\sim m_{\nu }/m_N.$ We could probe $m_{H^{+}}\lesssim 1100$ GeV at the 14 TeV HL-LHC and $m_{H^{+}}\lesssim 1490$ GeV at the 3 TeV CLIC.