Probing Spontaneous CP-Violation through Precision Higgs Observables

Abstract

We investigate the implications of spontaneous CP-violation in the general two Higgs doublet model, which leads to a non-decoupling structure of the Higgs sector. All the masses of the Higgs bosons are purely determined by the vacuum expectation value of the Higgs fields, and are thus constrained to be smaller than ${\cal O}(500)$ GeV by the perturbative unitarity bound. Such a non-decoupling nature predicts sizable deviations from the standard model expectations in the observables of the discovered Higgs boson ($h$). We find that the magnitude of deviations in ${\cal B}_{h \to γγ}$ (${\cal B}_{h \to Zγ}$) are larger than $\sim 10\%~(4\%)$ in the Higgs alignment limit. Moreover, we show that a robust correlation emerges between the deviations in the one-loop corrected $hhh$ coupling and ${\cal B}_{h \to γγ}$ to be, e.g., 200\%~(50\%) and $-10.3\%$ ($-10.8\%$), respectively, under the constraints from theoretical bounds and current experimental data. Using a few benchmark points, we highlight that flavor-violating decays of the additional Higgs bosons can be sizable due to the constrained structure of the Yukawa interactions.

Figures (1)

• Figure 1: Correlation between $\Delta {\cal B}_{h\to \gamma\gamma}$ and $\Delta \kappa_\lambda$ defined in Eq. (\ref{['eq:delta']}) in the Higgs alignment limit. The blue, black, magenta and red curves show the cases with $\Delta m (\equiv m_{H_2}^{} - m_{H^\pm}$)= $-100,$ 0, 100 and 200 GeV, respectively, and $m_{H^\pm} = m_{H_3}$ for all curves. The magenta-dashed lines represent the current upper limit taken by the ATLAS experiments at 95% CL, while the red-dotted line shows the expected upper limit on $\Delta \kappa_\lambda$ at 95% CL given at the HL-LHC. The green dots show the predictions allowed by the theoretical constraints (perturbative unitarity and vacuum stability) and the experimental constraints ($S$, $T$ parameters, $b \to s\gamma$, meson mixings, electron EDM and direct searches for charged and extra neutral Higgs bosons at LHC).