Collider Bounds on 2-Higgs Doublet Models with $U(1)_X$ Gauge Symmetries

TL;DR

This paper derives updated collider bounds on the $Z'$ gauge boson in extended 2-Higgs Doublet Models with $U(1)_X$ symmetry, considering various couplings and future collider sensitivities.

Contribution

It provides the first comprehensive collider bounds on $Z'$ in 2HDMs with $U(1)_X$, including different coupling scenarios and future collider prospects.

Findings

Current LHC data constrains $Z'$ masses and couplings.

Different models show varied sensitivity in dijet and dilepton channels.

Future colliders like HL-LHC and HE-LHC could significantly improve bounds.

Abstract

2-Higgs Doublet Models (2HDMs) typically need to invoke an ad-hoc discrete symmetry to avoid severe flavor bounds and in addition feature massless neutrinos, thus falling short of naturally complying with existing data. However, when augmented by an Abelian gauge symmetry naturally incorporating neutrino masses via a type-I seesaw mechanism while at the same time escaping flavor changing interactions, such enlarged 2HDMs become very attractive phenomenologically. In such frameworks, the distinctive element is the $Z'$ gauge boson generated by the spontaneous breaking of the Abelian group $U(1)_X$. In this work, we derive updated collider bounds on it. Several theoretical setups are possible, each with different and sometimes suppressed couplings to quarks and leptons. Thus, complementary data from dijet and dilepton resonance searches need to be considered to fully probe these objects. We employ the corresponding datasets as obtained at the Large Hadron Collider (LHC) at the 13 TeV CMs energy for $\mathcal{L}=12,36$ and $300$ fb$^{-1}$ of luminosity. Moreover, we present the potential sensitivity to such $Z'$s of the High Luminosity LHC (HL-LHC) and High Energy LHC (HE-LHC).