Higgs After the Discovery: A Status Report

TL;DR

This status report tests the 125 GeV Higgs-like resonance against the Standard Model using a Higgs effective-action framework with a small set of couplings and a mapping to simplified new-physics models. It combines ATLAS, CMS, and Tevatron data across $\gamma\gamma$, $ZZ^*$, $WW^*$, and $Vh\to Vb\bar b$ channels to constrain couplings $c_V,c_b,c_\tau,c_c,c_g,c_\gamma,c_{inv}$ and the total width, linking observable rates to these parameters. The analysis finds overall SM compatibility with a slight preference for enhanced $h\to\gamma\gamma$ rates, while allowing modest invisible decays; it also shows how specific scenarios (e.g., top-partner loops, 2HDM, doublet-singlet/triplet extensions, and GM-type models) can fit the data without undermining consistency with other channels. The results guide model-building and point to potential new physics scenarios that could be tested with future collider data, particularly in the diphoton channel and extended Higgs sectors.

Abstract

Recently, the ATLAS and CMS collaborations have announced the discovery of a 125 GeV particle, commensurable with the Higgs boson. We analyze the 2011 and 2012 LHC and Tevatron Higgs data in the context of simplified new physics models, paying close attention to models which can enhance the diphoton rate and allow for a natural weak-scale theory. Combining the available LHC and Tevatron data in the ZZ* 4-lepton, WW* 2-lepton, diphoton, and b-bbar channels, we derive constraints on the effective low-energy theory of the Higgs boson. We map several simplified scenarios to the effective theory, capturing numerous new physics models such as supersymmetry, composite Higgs, dilaton. We further study models with extended Higgs sectors which can naturally enhance the diphoton rate. We find that the current Higgs data are consistent with the Standard Model Higgs boson and, consequently, the parameter space in all models which go beyond the Standard Model is highly constrained.

Figures (9)

• Figure 1: The combined signal strength $\hat{\mu}_{ii} \equiv R_{ii}$ and the corresponding error for the Higgs search channels used in our analysis.
• Figure 2: The allowed parameter space of the effective theory given in Eq. \ref{['eq:1']}, derived from the LHC and Tevatron constraints for $m_h = 125$ GeV. We display the $1\sigma$ allowed regions for the rates in Eqs. \ref{['eq:4']}-\ref{['eq:last']}: $R_{\gamma \gamma}$ (purple), $R_{ZZ}$ (blue), $R_{WW}$ (light grey), $R_{\gamma \gamma jj}$ (beige), and $R_{b \bar{b}}$ (orange). The "Combined" region (green) shows the 95% CL preferred region arising from all channels. The crossing of the dashed lines is the SM point. The $\bigotimes$ corresponds to the best fit point. The top-left plot characterizes models in which loops containing beyond the SM fields contribute to the effective 5-dimensional $h \, G_{\mu \nu}^a G_{\mu \nu}^a$ and $h \, A_{\mu \nu} A_{\mu \nu}$ operators, while leaving the lower-dimension Higgs couplings in Eq. \ref{['eq:1']} unchanged relative to the SM prediction. The red-line shows the trajectory $\delta c_{\gamma} = 2/9 \delta c_{g}$ characteristic for top partners. The top right plot characterizes composite Higgs models. The bottom plots characterize top partner models where only scalars and fermions with the same charge and color as the top quark contribute to the effective 5-dimensional operators, which implies the relation $\delta c_\gamma = (2/9) \delta c_g$. In the bottom-right plot, the shaded region is 95% CL excluded by monojet searches at the LHC.
• Figure 3: Best fit regions in the $c_i$-$m_i$ plane, assuming $m_h = 125$ GeV for the scalar top partner ( top-left), fermionic top partner ( top-right) and vector $W$-partner ( bottom-left). Shown are $68\%$ (darker green) and $95\%$ CL (lighter green) regions. The dashed curves are for constant $R_{\gamma\gamma}^{\rm incl}$, Eq. \ref{['eq.Rgg']}, while the red curve is where a single partner is improving the naturalness of the SM, Eqs. \ref{['eq.cs.natural']}, \ref{['eq.cf.natural']}, \ref{['eq.crho.natural']}. The bottom-right image shows the constraints for $m_h = 125$ GeV, for top partner models, i.e. $\delta c_{\gamma} = 2/9 \delta c_{g}$. The three bands show the 1$\sigma$ allowed regions for $R_{bb}^{VH}$, $R_{\gamma\gamma}^{\rm incl.}$, and $R_{ZZ}^{\rm incl.}$ channels. The three curves show the theoretical predictions as a function of $\delta c_{g}$ for each channel. Only 3 channels are shown, but all channels are included. The green shaded region shows the 95% CL experimental preferred region.
• Figure 4: Constraints for the Simplest Higgs model ( left) and the Twin Higgs model ( right) assuming $m_h = 125$ GeV. The three bands show the 1$\sigma$ allowed regions for $R_{bb}^{VH}$, $R_{\gamma\gamma}^{\rm incl.}$, and $R_{ZZ}^{\rm incl.}$ channels. The three curves show the theoretical predictions as a function of $\xi$ for each channel. Only 3 channels are shown, but all channels are included. The green vertical lines show the 95% CL experimental preferred region.
• Figure 5: Left: The difference between the $\chi^2$ of the dilaton model and the $\chi^2$ of the SM as a function of the parameter $c_\phi$. At the best fit point around $c_\phi \simeq 0.27$, the $\chi^2$ of the dilaton model is larger by 5.2 units compared with the SM, indicating that the dilaton model always fits the data worse than the SM. Right: The favored region at 68% CL (Darker) and 95% CL (Lighter) for the $125$ GeV resonance being a mixture of the SM Higgs and a dilaton. The best fit occurs along the line $\alpha =0$ corresponding to a pure SM Higgs. The dashed lines show contours of constant $R_{\gamma \gamma}$.