New Physics Effect on the Higgs Self-Coupling

TL;DR

This work analyzes one-loop corrections to the Higgs self-coupling $hhh$ in the two-Higgs-doublet model (THDM). It shows that non-decoupling heavy Higgs states can induce large deviations from the SM prediction for the $hhh$ coupling, even when the light Higgs couplings to gauge bosons and fermions remain SM-like, due to quartic-mass contributions from heavy scalars. Analytic results and numerics reveal potential 30–100% deviations for heavy-Higgs masses up to the perturbative unitarity bound, controlled by the soft-breaking parameter $M^2$ and the alignment condition. The findings imply that precise measurements of the Higgs self-coupling at future linear colliders could uncover non-minimal Higgs sectors, highlighting a general non-decoupling mechanism for new physics scenarios.

Abstract

One-loop corrections to the self-coupling constant of the lightest CP-even Higgs boson are studied in the two Higgs doublet model. After renormalization is performed, quartic contributions of heavy particle's mass can appear in the effective coupling. We find that these non-decoupling effects can yield ${\cal O}(100)$ % deviations from the Standard Model prediction, even when all the other couplings of the lightest Higgs boson to gauge bosons and fermions are in good agreement with the Standard Model.

Figures (3)

• Figure 1: The $m_\Phi^4$ behavior in $\Delta\lambda_{hhh}^{THDM}$, where $\Delta\lambda_{hhh}^{THDM}$$\equiv \lambda_{hhh}^{eff}(THDM)-\lambda_{hhh}^{eff}(SM)$. The results of the full one-loop calculation are shown as solid curves, while the quartic mass contributions given in Eq. (\ref{['m4THDM']}) are plotted as dotted curves.
• Figure 2: The decoupling behavior of $\Delta\lambda_{hhh}^{THDM}$, where $\Delta\lambda_{hhh}^{THDM}$ is defined by $\lambda_{hhh}^{eff}(THDM)-\lambda_{hhh}^{eff}(SM)$ calculated in the one-loop diagrammatic approach. The mass of the heavy Higgs bosons $m_{\Phi} (\equiv m_H^{}=m_A^{}=m_{H^\pm}^{})$ is given by $m_{\Phi}^2=\lambda v^2+M^2$.
• Figure 3: The momentum dependence of $\Delta\lambda_{hhh}^{THDM}(q^2) \equiv \lambda_{hhh}^{eff}(THDM)- \lambda_{hhh}^{eff}(SM)$ calculated in the diagrammatic approach, where $\sqrt{q^2}$ is the invariant mass of $h^\ast$ in $h^\ast \to hh$ for each value of $m_\Phi^{}$ ($\equiv m_H^{}=m_A^{}=m_{H^\pm}^{}$), when $m_h=120$ GeV, $\sin(\alpha-\beta)=-1$ and $M=0$.