Natural Electroweak Symmetry Breaking from Scale Invariant Higgs Mechanism

TL;DR

This work develops a minimal, classically scale-invariant extension of the SM by adding a complex singlet S and three right-handed neutrinos, enabling radiative electroweak symmetry breaking via the Coleman–Weinberg mechanism. The scalar sector yields two CP-even states h and σ and a CP-odd DM candidate χ, with h identified as the 125 GeV Higgs and σ acquiring a radiatively generated mass, while χ is stabilized by CP symmetry. The authors perform a thorough analysis of experimental constraints from Higgs data and EW precision tests, alongside theoretical bounds from unitarity, triviality, and vacuum stability, mapping viable regions in the parameter space and outlining implications for LHC runs and DM searches. They find a preference for small Higgs–singlet mixing (|sin ω| ≲ 0.3), heavy χ (TeV-scale), and a σ mass in the few hundred GeV range, with specific correlations between Mσ and Mχ; inverse identification of the 125 GeV state as σ is disfavored, and a real-singlet variant is excluded. The study highlights concrete collider signatures for σ decays to WW/ZZ and hh, and DM production channels, while signaling the need for a detailed DM relic density and direct-detection analysis to fully establish phenomenological viability.

Abstract

We construct a minimal viable extension of the standard model (SM) with classical scale symmetry. Its scalar sector contains a complex singlet in addition to the SM Higgs doublet. The scale-invariant and CP-symmetric Higgs potential generates radiative electroweak symmetry breaking a la Coleman-Weinberg, and gives a natural solution to the hierarchy problem, free from fine-tuning. Besides the 125GeV SM-like Higgs particle, it predicts a new CP-even Higgs (serving as the pseudo-Nambu-Goldstone boson of scale symmetry breaking) and a CP-odd scalar singlet (providing the dark matter candidate) at weak scale. We systematically analyze experimental constraints from direct LHC Higgs searches and electroweak precision tests, as well as theoretical bounds from unitarity, triviality and vacuum stability. We demonstrate the viable parameter space, and discuss implications for new Higgs and dark matter (DM) searches at the upcoming LHC runs and for the on-going direct detections of DM.

Figures (1)

• Figure 1: Experimental and theoretical constraints on the parameter space of $\,|\sin\omega|-M_\chi^{}\,$ in plots (a)-(b), and of $\,M_\sigma^{}-M_\chi^{}\,$ in plots (c)-(d). In each plot, the red region is excluded by the electroweak precision tests at 95% C.L., while the green region is excluded (95% C.L.) by the global fit of direct Higgs measurements at the LHC and Tevatron (as partially overlapped by the red contour). In plots (c)-(d), the shaded black region is forbidden due to $\,|\sin\omega|\leqslant 1\,$. The scattered blue-dots are simulated in each plot to represent the parameter space, allowed by the triviality, stability and perturbative unitarity bounds. We set two benchmark values of right-handed neutrino masses, $\,M_N^{} = 0.5, 1$ TeV, for the plots (a)(c) and (b)(d), respectively.