Constraining anomalous Higgs interactions

TL;DR

The paper addresses constraining anomalous Higgs interactions in a model-independent way by employing a SM gauge-invariant dimension-six effective Lagrangian. It performs a global $\chi^2$ fit to Higgs signal-strength data from Tevatron and LHC (7 and 8 TeV), using two benchmark scenarios for the relevant operators ${\cal O}_{GG}$, ${\cal O}_{BB}$, ${\cal O}_{WW}$, ${\cal O}_B$, ${\cal O}_W$ and accounting for theoretical uncertainties via pull terms. The analysis finds a preference for suppressed gluon-fusion production $\sigma^{ano}_{gg}/\sigma^{SM}_{gg} \approx 0.4$ and an enhanced diphoton branching ratio $\mathrm{BR}^{ano}_{\gamma\gamma}/\mathrm{BR}^{SM}_{\gamma\gamma} \approx 2.9$, with $\mathrm{BR}^{ano}_{WW}/\mathrm{BR}^{SM}_{WW}$ and $\mathrm{BR}^{ano}_{ZZ}/\mathrm{BR}^{SM}_{ZZ}$ near unity, and the best-fit values constrain $f_W$ to be small while $f_{WW}=f_{BB}$ lies in two narrow ranges. The work highlights degeneracies due to interference between SM and new-physics contributions and shows these can be alleviated by including 8 TeV data and, in the future, measurements of triple gauge couplings and EW precision observables. Overall, the study demonstrates that current collider data begin to constrain the Higgs–gauge sector in a model-independent EFT framework and guide expectations for future analyses.

Abstract

The recently announced Higgs discovery marks the dawn of the direct probing of the electroweak symmetry breaking sector. Sorting out the dynamics responsible for electroweak symmetry breaking now requires probing the Higgs interactions and searching for additional states connected to this sector. In this work we analyze the constraints on Higgs couplings to the standard model gauge bosons using the available data from Tevatron and LHC. We work in a model--independent framework expressing the departure of the Higgs couplings to gauge bosons by dimension--six operators. This allows for independent modifications of its couplings to gluons, photons and weak gauge bosons while still preserving the Standard Model (SM) gauge invariance. Our results indicate that best overall agreement with data is obtained if the cross section of Higgs production via gluon fusion is suppressed with respect to its SM value and the Higgs branching ratio into two photons is enhanced, while keeping the production and decays associated to couplings to weak gauge bosons close to their SM prediction.

Figures (5)

• Figure 1: The left (central, right) panel exhibits $\Delta \chi^2$ as a function of $f_{g}$ ($f_{W}$, $f_{WW}$) in the framework of scenario I. Each panel contains three lines: the dotted (dashed) line was obtained using only the LHC 7 TeV (LHC 7 TeV and Tevatron) data while the solid line stands for the result using all the available data. In each panel $\Delta \chi^2$ is marginalized over the two undisplayed parameters.
• Figure 2: $\Delta \chi^2$ as a function of $f_{g}$ (left panel) and $f_{WW}=f_{BB}$ (right panel) for the full combined analysis. The solid lines correspond to scenario I in which $\Delta\chi^2$ is marginalized over the two undisplayed parameters in each panel: $f_{WW}=f_{BB}$ and $f_{W}=f_{B}$ in the left panel, and $f_{g}$ and $f_{W}=f_{B}$ in the right panel. The dashed lines correspond to scenario II, i.e. imposing first the prior $f_{W}=f_{B}=0$ and then marginalizing over $f_{WW}=f_{BB}$ (left) and $f_g$ (right).
• Figure 3: 68%, 90%, 95%, and 99% CL (2dof) allowed regions of the plane $f_{WW} \otimes f_g$ (upper right panel), $f_{W} \otimes f_g$ (upper left panel) and $f_{W} \otimes f_{WW}$ (lower panel) using all available data. These results are obtained for scenario I and after marginalization over the undisplayed parameter in each panel. The best fit points are indicated by a star while the second local minima are indicated with a dot.
• Figure 4: $\Delta \chi^2$ as a function of Higgs branching ratios into electroweak gauge bosons (left panel) and the cross section for different production processes (right panel) normalized to the SM values. In the left panel the solid (dashed, dotted) line stands for the branching ratio into $\gamma\gamma$ ($W^+ W^-$, $ZZ$), while, in the right panel, the solid (dashed, dotted) line represents the gluon fusion (VBF, VH) production cross section.
• Figure 5: Allowed regions for several combinations of Higgs branching ratios and production cross section. In each panel $\Delta\chi^2$ is marginalized with respect to the combination of couplings independent of the two displayed observables. As in Figure \ref{['fig:correl_I']} the regions are shown at 68%, 90%, 95%, and 99% CL (2dof).