Complete NLO SMEFT Electroweak Corrections to Higgs Decays

TL;DR

The paper tackles the precision prediction problem for Higgs decays within the SMEFT by computing the complete set of NLO electroweak and QCD corrections for all 2- and 3-body Higgs decays in the dimension-6 SMEFT, truncated at ${1\over \Lambda^2}$, using the Warsaw basis. It implements a hybrid renormalization scheme and infrared treatment, delivering a flexible Monte Carlo tool that outputs the total width, branching ratios, and differential distributions, including new NLO results for $h\rightarrow W f\overline{f}'$ and $h\rightarrow Z f\overline{f}$. The results show that incorporating Higgs decays into the Higgstrahlung process $e^+e^-\rightarrow Z h$ at FCC-ee significantly improves sensitivity to SMEFT coefficients (e.g., $C_\phi$, $C_{u\phi}[3,3]$, $C_W$, $C_{\phi D}$) compared to production alone, with mappings to $\delta_Z$ and $\kappa_\lambda$ clarifying Higgs self-coupling constraints. Overall, this work enables robust, high-precision global SMEFT fits at future lepton colliders and tightens constraints on Higgs-vector boson interactions and the Higgs self-coupling, aided by a publicly available Monte Carlo tool.

Abstract

Precise predictions for Higgs decays are a crucial ingredient of the search for beyond the Standard Model (BSM) physics and the Standard Model Effective Field Theory (SMEFT) is a valuable tool for quantifying deviations from the Standard Model (SM). We present the complete set of predictions for the 2- and 3- body Higgs decays at next-to-leading order (NLO), considering QCD and electroweak corrections and including all contributions from the dimension-6 SMEFT operators and with an arbitrary flavor structure. Including the NLO SMEFT results for Higgs decays greatly increases the sensitivity to BSM physics of the $e^+e^-\rightarrow Zh$ process at FCC-ee, as compared with that obtained using only the total cross section.

Figures (4)

• Figure 1: Top: diagrams contributing to $h\rightarrow W l \nu$ at LO in the dimension-6 SMEFT. Bottom: representative virtual and real emission diagrams from SMEFT dimension-6 operators that first arise at one-loop. The circles represent dimension-6 SMEFT insertions.
• Figure 2: Left: $95\%$ confidence level sensitivity to $C_{u \phi}[3,3]$ and $C_\phi$ assuming $\Lambda=1$ TeV. The grey band assumes a $.5\%$ measurement of the total Higgstrahlung cross section, while the other bands assume the precision on the Higgs decays given in Tab. \ref{['tab:fcc']}. The red circle includes all measured Higgs decays. Right: bounds on $C_{W}$ and $C_{\phi D}$.
• Figure 3: Left: $95\%$ confidence level limits on $C_{e u}[1,1,3,3]$ and $C_\phi$. Right: sensitivity to $C_{u \phi}[3,3]$ and $C_{\phi u}[3,3]$. We combine Higgstrahlung production at two energies, $\sqrt{s} = 240$ and $\sqrt{s} = 365$ GeV.
• Figure 4: Bounds on coefficients contributing to $hZZ/hWW$ and tri-linear couplings. Left: SMEFT calculation in terms of $C_{\phi D}$ and $C_\phi$. Right: interpretation in the framework that makes use of the parameters $\delta_Z$ and $\delta \kappa_\lambda$ computed to linear order, with $C_{\phi\square}$ set to $0$.