Precision Higgs Measurements: Constraints from New Oblique Corrections

TL;DR

This work analyzes how new colored and charged states contribute to Higgs oblique corrections by modifying loop-induced decays $h\to gg$ and $h\to \gamma\gamma$. It computes the NLO QCD corrections to the Higgs-gluon coupling for particles in arbitrary $SU(3)_c$ representations via the two-loop low-energy Higgs theorem, providing explicit Wilson coefficients $c_f^{NLO}$ and $c_S^{NLO}$ for fundamental and adjoint representations and updating the squark case. Using these results, it derives 5–10% deviation contours in masses and couplings for new scalars and fermions, including MSSM stops/staus, and demonstrates that precise measurements of $hWW$ and $ht\bar t$ are essential to disentangle oblique effects from other Higgs couplings. The study shows that precision Higgs measurements offer complementary constraints to direct searches, enabling sensitivity to TeV-scale physics through loop-induced Higgs processes.

Abstract

New particles entering into self-energies of the Higgs boson would necessarily modify loop-induced couplings of the Higgs, if the new particle carries standard model gauge quantum numbers. For a 1 TeV new particle, deviations in these "Higgs oblique corrections" are generically of the order of v^2/(1 TeV)^2 ~ 5%. We study constraints on masses and couplings of new scalars and fermions that can be derived from 5-10% deviations in the Higgs digluon and diphoton partial widths. To reduce theoretical uncertainties, we present next-to-leading order QCD corrections to the Higgs-to-digluon coupling for scalars and fermions in arbitrary representations of SU(3) color group, by applying the low-energy Higgs theorems at two-loop order. As a by-product we provide a new value for NLO QCD corrections to the top squark contributions to digluon decays that differs from existing literature. We also emphasize that precise measurements of Higgs couplings to W boson and top quark are prerequisite to precise determinations of Higgs oblique corrections from new particles.

Figures (6)

• Figure 1: (a) Higgs oblique corrections from new electroweak particles. (b) Contributions from new electroweak particles to $h\to \gamma\gamma$ and $h\to Z\gamma$. (c) Electroweak oblique corrections from new particles.
• Figure 2: Contours of constant NLO digluon partial width, normalized to the NLO value in the SM, as a function of the new particle mass and its coupling to the Higgs. The orange and yellow region are for deviations within $5\%$ and 10%, respectively. For comparison, we also show in dashed lines the contour of 10% deviation from only retaining the LO effect in new particles.
• Figure 3: Contours of constant diphoton partial width, normalized to the SM value. The color-coding is as in Fig. \ref{['fig:NPeffectgg']}.
• Figure 4: Contours of constant NLO digluon partial width, normalized to the NLO value in the SM, in supersymmetry as a function of $m_{\tilde{t}}$ and $X_t/m_{\tilde{t}}$. We also include contours of 122 GeV $\le m_h \le$ 128 GeV in MSSM. In the bottom row we show masses of the light stop eigenmasses (dashed lines) and heavy stop eigenmasses (solid lines). The constraints from digluon widths are independent of MSSM when new $D$ term contributions can be neglected. The color-coding is as in Fig. \ref{['fig:NPeffectgg']}.
• Figure 5: Contours of constant diphoton partial widths in supersymmetry as a function of $m_{\tilde{\tau}}$ and $X_\tau/m_{\tilde{\tau}}$. We also show masses of the light stau eigenmasses (dashed lines) and heavy stau eigenmasses (solid lines). The color-coding is as in Fig. \ref{['fig:NPeffectgg']}.