Resonance at 125 GeV: Higgs or Dilaton/Radion?

TL;DR

This work investigates whether the 125 GeV resonance is a dilaton from spontaneously broken conformal symmetry, arising in technicolor or in a Higgs-as-a-pNGB framework with UV strong conformal dynamics. It builds a dilaton effective theory with a breaking scale $f$ and parameter $\xi = v^{2}/f^{2}$, incorporating conformal-symmetry-violating effects that render a small dilaton mass and modify couplings. By classifying SM fields as elementary or composite and mapping to RS radion intuition, the authors derive dilaton couplings to massive and massless gauge bosons and fermions, then perform a global fit to LHC/Tevatron Higgs data using observables $\eta_{XX}$ to extract $\xi$, $\epsilon$, $\phi$, and $\psi$. The results show that both technicolor-like and pNGB-like dilatons can fit current data comparably to the SM Higgs, with a preference for larger $\xi$ but a viable $\xi \sim 0.3$ region; future measurements, especially in exclusive channels and in GF versus VBF/associated production, will help corroborate or falsify these scenarios.

Abstract

We consider the possibility that the new particle that has been observed at 125 GeV is not the Standard Model (SM) Higgs, but instead the dilaton associated with an approximate conformal symmetry that has been spontaneously broken. We focus on dilatons that arise from theories of technicolor, or from theories of the Higgs as a pseudo-Nambu-Goldstone boson (pNGB), that involve strong conformal dynamics in the ultraviolet. In the pNGB case, we are considering a framework where the Higgs particle is significantly heavier than the dilaton and has therefore not yet been observed. In each of the technicolor and pNGB scenarios, we study both the case when the SM fermions and gauge bosons are elementary, and the case when they are composites of the strongly interacting sector. Our analysis incorporates conformal symmetry violating effects, which are necessarily present since the dilaton is not massless, and is directly applicable to a broad class of models that stabilize the weak scale and involve strong conformal dynamics. Since the AdS/CFT correspondence relates the radion in Randall-Sundrum (RS) models to the dilaton, our results also apply to RS models with the SM fields localized on the infrared brane, or in the bulk. We identify the parameters that can be used to distinguish the dilatons associated with the several different classes of theories being considered from each other, and from the SM Higgs. We perform a fit to all the available data from several experiments and highlight the key observations to extract these parameters. We find that at present, both the technicolor and pNGB dilaton scenarios provide a good fit to the data, comparable to the SM Higgs. We indicate the future observations that will help to corroborate or falsify each scenario.

Figures (4)

• Figure 1: The $1\sigma$ (yellow) and $2\sigma$(green) CL regions of the plane $(\phi,\xi)$. At each point the $\chi^{2}$ has been minimized w.r.t. $\epsilon$ in the range $0\leq \epsilon \leq 0.6$. The black star corresponds to the best-fit point and the black cross is the location of the SM-Higgs-like dilaton. The dashed line corresponds to the $2\sigma$ contour applying the further constraint $\epsilon\geq0.35$
• Figure 2: The $1\sigma$ (yellow) and $2\sigma$ (green) CL regions of the $(\phi,\,\epsilon)$ plane. In each point the $\chi^{2}$ is minimized w.r.t $\xi$ in the interval $0\leq\xi\leq2$. The solid blue lines are the isolines of the value of $\xi$ that minimizes the $\chi^{2}$. The black star corresponds to the best-fit point and the black cross is the location of the SM-Higgs-like dilaton. The upper gray-shaded region is disfavored by constraints from flavor physics. The lower gray-shaded region is disfavored by the bounds on the dimension of the operator $\mathcal{H}^{\dagger}\mathcal{H}$ and their implications for the solution of the hierarchy problem discussed in Section \ref{['fermioncouplings']}.
• Figure 3: The $1\sigma$ (yellow) and $2\sigma$ (green) CL regions of the $(\phi,\,\psi)$ plane. In each point the $\chi^{2}$ is minimized w.r.t $\xi$ in the interval $0\leq\xi\leq2$. The solid blue lines are the isolines of the value of $\xi$ that minimizes the $\chi^{2}$. The black star corresponds to the best-fit point. The black cross is the location of the SM-Higgs-like dilaton.
• Figure 4: The $1\sigma$ (yellow) and $2\sigma$(green) CL regions of the $(\phi,\,\xi)$ plane. In each point the $\chi^{2}$ is minimized w.r.t $\psi$. The solid blue lines are the isolines of the value of $\psi$ that minimizes the $\chi^{2}$. The black star corresponds to the best-fit point. The black cross is the location of the SM-Higgs-like dilaton.