Interpretation of precision tests in the Higgs sector in terms of physics beyond the Standard Model

TL;DR

The paper develops a model-independent effective field theory framework using dim-6 operators built from the Higgs and gauge fields to interpret deviations in Higgs couplings as signals of physics beyond the Standard Model. It shows how Higgs-gauge and Higgs-fermion coupling shifts are linked to operator coefficients and how current LHC data constrain these coefficients, revealing correlations predicted by specific ultraviolet completions. Through an explicit mediator analysis, it demonstrates that the data prefer combinations of multiple mediators with characteristic coupling relations rather than a single new field. The work also outlines which Higgs production–decay channels are most informative for breaking degeneracies and stresses the potential of future measurements, including Higgs self-couplings, to sharpen tests of BSM scenarios.

Abstract

We demonstrate how the measurements of the Higgs-fermion and Higgs-gauge boson couplings can be interpreted in terms of physics beyond the Standard Model in a model-independent way. That is, we describe deviations from the Standard Model by effective $d=6$ operators made of Higgs fields and gauge fields, under the hypothesis that the new physics may show up in the Higgs sector only and the effective operators are generated at tree level. While the effective operator coefficients are independent in general, the completion of the theory at high energies will lead to specific correlations which will be recovered between Higgs-fermion and Higgs-gauge boson couplings. We demonstrate that the current measurement of these couplings in terms of tree-level new physics requires several new mediators with specific relationships among different couplings. New insights in the effective theory and mediator spaces can be expected for improved measurements from the inclusive $H \rightarrow ττ$ and the exclusive vector boson fusion-dominated $H \rightarrow γγ$ search channels, as well as the measurement of the Higgs self-couplings, including higher order couplings which do not exist in the Standard Model.

Figures (2)

• Figure 1: Filled contours: measurement of the Higgs-vector boson and Higgs-fermion couplings in terms of $c_V$ and $c_F$ (left panel, "experimental plane"), and $\alpha_\phi^{(1)}$ and $\alpha_{\partial \phi}$ (right panel, "theory plane"). The data are at the 68% and 95% confidence levels, taken from Ref. CMSJuly4. The different lines (rays) represent the correlations among the effective operator coefficients for specific mediators, where in the case of small couplings the SM is recovered. The dashed circle in the right panel shows the perturbative regime (geometric average of couplings smaller than about 0.5), i.e., the region where the effective operator approach is expected to be a good description.
• Figure 2: Value of the individual effective operator coefficient $\alpha_{\phi}^{(1)}\frac{v^2}{2}$ as a function of $R_X^Y$ for different search channels for a fixed relationship $\alpha_{\partial\phi}=\alpha_{\phi}^{(1)}$. The orange shading illustrates the effect of a 20% measurement of $R_X^Y$.