Parameter Inference from Final-State Entanglement in Higgs Decays

Abstract

The decay out-states of unstable Standard Model (SM) particles provide a unique, well-defined intrinsic quantum-information probe of the SM parameter space. We use Higgs decays as a test case: after tracing out kinematics, we compute entanglement among final-state spins and colors across all decay channels and impose a near-maximal entanglement-entropy criterion. This criterion yields quantitative indications for fundamental parameters. Within the SM, the entanglement entropy exhibits a global maximum close to the observed Higgs mass and the measured $W$ mass, the latter being equivalent to the $SU(2)_L$ gauge coupling. In a two-parameter kappa framework, applying the same criterion points to an SM-like balance between vector and fermion couplings, constraining the ratio of the sector-wide rescalings. These results suggest that entanglement extremality can serve as a complementary handle on fundamental parameters.

Figures (7)

• Figure 1: Spin factors $\mathcal{P}_i$ for each Higgs decay channel as a function of $m_h$.
• Figure 2: Entanglement entropy of Higgs decays as a function of the Higgs mass (left) and $m_W$ (right). The gray band marks the experimentally observed SM values ($1\sigma$), the red band shows the $EE_{\max}$ yield with its $1\sigma$ uncertainty from SM inputs and theory, and the green band indicates the near-maximal-EE region.
• Figure 3: EE in the $\kappa_f$–$\kappa_V$ plane. Green and cyan dotted curves show contours of $\Delta EE/EE_{\max} = 0.5\%$ and $0.1\%$, respectively. The magenta star marks the maximal-EE point, and the white cross denotes the SM point.
• Figure 4: Distributions of the entanglement entropy using analytical formulae for the Higgs decay widths. Upper left: Dependence of the EE on the Higgs mass $m_h$. The black solid line shows results from HDECAY, while the orange dashed line represents the EE calculated using analytical formulae. The orange band indicates $EE_{\max}$ with its $1\sigma$ uncertainty from SM inputs and theoretical uncertainties. Other colored codes follow the same definition as in Fig. \ref{['fig:Higgs_mass-g']}. Upper right: Dependence of the EE on the $W$ boson mass $m_W$. Bottom: EE distribution in the $(\kappa_f, \kappa_V)$ plane.
• Figure 5: Entanglement entropy distribution for Standard Model parameters using $EE = 1 - \sum_{i} {\rm BR}_{i}^2$. Upper left: EE as a function of Higgs mass $m_h$. Upper right: EE as a function of $W$ boson mass $m_W$. Bottom: EE distribution in the $(\kappa_{f}, \kappa_{V})$ plane. Color coding follows the same convention as in Fig. \ref{['fig:Higgs_mass-g']}.