Higgs At Last

TL;DR

The paper performs a global fit of a Higgs effective Lagrangian to the latest LHC Higgs data and electroweak precision observables, testing whether the 126 GeV state behaves like the SM Higgs. It shows that the leading Higgs couplings $c_V$, $c_t$, $c_b$, and $c_\tau$ are tightly constrained around their SM values, with $c_V$ restricted to about $[0.98,1.08]$ (95% CL) when EW data are included. The loop-induced couplings $c_{gg}$, $c_{\gamma\gamma}$, and $c_{Z\gamma}$ are also well constrained, especially by LHC Higgs rates, while the $c_{Z\gamma}$ bound is comparatively weaker. The study further analyzes loop NP, composite-Higgs scenarios, and 2HDM frameworks, finding no compelling deviations from the SM and placing meaningful bounds on the corresponding new-physics scales; invisible Higgs decays are highly constrained unless production is simultaneously enhanced. Overall, the Higgs EFT approach provides a rigorous, data-driven consistency check of the SM with sizable implications for Beyond-Standard-Model theories.

Abstract

We update the experimental constraints on the parameters of the Higgs effective Lagrangian. We combine the most recent LHC Higgs data in all available search channels with electroweak precision observables from SLC, LEP-1, LEP-2, and the Tevatron. Overall, the data are perfectly consistent with the 126 GeV particle being the Standard Model Higgs boson. The Higgs coupling to W and Z bosons relative to the Standard Model one is constrained in the range [0.98,1.09] at 95% confidence level, independently of the values of other Higgs couplings. Higher-order Higgs couplings to electroweak gauge bosons are also well constrained by a combination of LHC Higgs data and electroweak precision tests.

Figures (5)

• Figure 1: Left: $\chi^2-\chi^2_{\rm min}$ as a function of $c_V$ for a fit to the Higgs (dashed blue), EW (dashed red), and combined (solid black) data, after marginalizing over the remaining parameters of the effective theory. The orange and purple lines visualize the 68% and 95% CL range of $c_V$. Right: Fit of $c_{\gamma \gamma}$ and $c_{Z\gamma}$ to EW data when $c_V$ is fixed to the SM value. The $68\%$ (darker green) and $95\%$ CL (lighter green) allowed regions are displayed. In both plots $\Lambda = 3$ TeV.
• Figure 2: Left: The 68% (darker green) and 95% (lighter green) CL best fit regions in the $c_{\gamma \gamma}$-$c_{g g}$ section of the parameter space. The straight lines correspond to a 1-loop contribution from a quark of electric charge $1/3$ (dashed orange), $2/3$ (dotted red), and $5/3$ (dash-dotted purple). Right: the same for the $c_{\gamma \gamma}$-$c_{Z \gamma}$ section of parameter space. We also show the contours of $\hat{\mu}_{Z \gamma}$ (dashed red), and $\sigma_{WH}/\sigma_{WH}^{\rm SM}$ (dotted blue). The yellow regions are fits without the EW data.
• Figure 3: Left: The 68% (darker green) and 95% (lighter green) CL best fit regions in the $c_V$-$c_f$ parameter space. The yellow regions are fits without the EW data. The color bands are the $1\sigma$ regions preferred by the Higgs data in the $\gamma \gamma$ (purple), $WW$ (blue), $ZZ$ (red), $\tau \tau$ (brown), and $b b$ (mauve) channels. Right: Fit to the parameter $\epsilon= v/f$ in sample composite Higgs models with (black) and without (gray) including EW precision data. The different lines correspond to the $SO(5)/SO(4)$ coset and fermionic representations with $m=0$ and $n=0$ (solid), $n=1$ (dashed) and $n=2$ (dot-dashed)."
• Figure 4: Left: The 68% (darker green) and 95% (lighter green) CL best fit regions in the $c_t$-$c_b=c_\tau$ parameter space. The color bands are the $1\sigma$ regions preferred by the Higgs data in the $\gamma \gamma$ (purple), $VV$ (blue), $\tau \tau$ (brown), and $b b$ (mauve) channels.
• Figure 5: Left: $\chi^2-\chi^2_{\rm min}$ of the fit for the Higgs with the SM-size couplings to the SM matter and an invisible branching fraction to hidden sector new physics states. Right: $68\%$ CL (light green) and $95\%$ CL (dark green) best fit regions to the combined LHC Higgs data in a model where the Higgs invisible branching fraction and the NLO coupling to gluons $c_{gg}$ can be simultaneously varied. The color bands are the $1\sigma$ regions preferred by the Higgs data in the $\gamma \gamma$ (purple), $VV$ (blue), $\tau \tau$ (brown), and $b b$ (mauve) channels. The meshed regions are excluded by direct probes of the invisible Higgs width: the ATLAS $Z+h \to {\rm inv.}$ search (red) ATLAS_Inv, and monojet constraints (black) derived in Djouadi:2012zc using the CMS monojet search Chatrchyan:2012me.