Gigantic diphoton rate of heavy Higgs bosons in the aligned two Higgs doublet models with small $\tan \beta$

Abstract

We study the implications of the LHC heavy neutral Higgs search data on the aligned two Higgs doublet model with softly broken $Z_2$ symmetry. When $\tan \beta$ is small, the gluon fusion production of the heavy CP-even scalar $H^0$ or the CP-odd scalar $A^0$ becomes large enough to constrain the model by the current $\gamma \gamma$, ${\tau }^{+}{\tau }^{-}$, and $t\bar{t}$ data. By reinvestigating this small $\tan \beta$ region, we find that the indirect constraints like $\Delta \rho$, $b\to s\gamma$, $\Delta M_{B_d}$, $R_b$, ${ϵ}_K$, and the perturbativity of running top Yukawa coupling are rather weak to be $\tan \beta >0.5$. The current heavy Higgs search results are shown to put more significant bounds. If $m_H\simeq m_A$, the $t\bar{t}$ mode excludes $\tan \beta <1.5$ for $m_{H,A}=500-600$GeV in all four types, and the $\gamma \gamma$ and ${\tau }^{+}{\tau }^{-}$ modes exclude $\tan \beta <1-3$ ($\tan \beta <3-10$) for $m_{H,A}=120-340$GeV in Type I, II, and Y (Type X).

Comments: 27 pages, 11 figure, 2 tables