Experimentally distinguishable origin for electroweak symmetry breaking

TL;DR

This paper explores a classically conformal $U(1)$ extension of the Standard Model where electroweak symmetry breaking is radiatively induced, leading to suppressed Higgs couplings and decay modes, distinguishable at future colliders.

Contribution

It introduces a radiative symmetry breaking model with suppressed Higgs couplings, providing a novel way to differentiate it from conventional models through collider measurements.

Findings

Higgs trilinear coupling is highly suppressed in the conformal model.

The decay $h_1 ightarrow h_2 h_2$ is undetectable in the conformal scenario.

Distinct collider signatures can differentiate the conformal model from conventional Higgs potential.

Abstract

We consider a classically conformal $U(1)$ gauge extension of the Standard Model (SM), in which the $U(1)$ gauge symmetry is radiatively broken by the Coleman-Weinberg mechanism. This breaking triggers the electroweak (EW) symmetry breaking through a mixed quartic coupling between the $U(1)$ Higgs field and the SM Higgs doublet. For two Higgs boson mass eigenstates after the symmetry breaking, $h_1$ (SM-like Higgs boson) and $h_2$ (SM singlet-like Higgs boson), we calculate the Higgs boson trilinear coupling ($g_{h_{1} h_{2} h_{2}}$) in the model by setting the Higgs boson mass spectrum to be $M_{h_1} > 2 M_{h_2}$. For a common Higgs mass spectrum and mixing angle between two Higgs fields, we find that $g_{h_{1} h_{2} h_{2}}$ in the classically conformal model is highly suppressed compared to that calculated for the conventional Higgs potential, where the $U(1)$ and EW symmetry breaking originate from the negative squared masses for the Higgs fields at the tree-level. Thus, this coupling suppression is a striking nature of the radiative origin of EW symmetry breaking. We then consider how to distinguish this origin at the proposed International Linear Collider (ILC) via precise measurements of anomalous SM Higgs boson couplings and the search for anomalous SM Higgs boson decay $h_1 \rightarrow h_2 h_2$ followed by $h_2 \to b \bar{b}$. We conclude that once the anomalous couplings are measured at the ILC, the observation of the anomalous Higgs boson decay is promising in the conventional Higgs potential, while this decay process is highly suppressed and undetectable for the classically conformal model.