Production and decays of a light $\phi^0$ in the LRTH model under the LHC Higgs data

In this paper we study the production and decays of a light pseudoscalar boson $\phi^0$ with $m_{\phi^0} \leq m_h/2$ appeared in the left-right twin Higgs (LRTH) model, and explore its phenomenological consequences when the latest LHC Higgs data are taken into account. We found that (a) the decay rate $Br(h\to \phi^0\phi^0)$ can be as large as $80\%$ and can suppress significantly the visible $\gamma\gamma$ signal rate, but the latest LHC Higgs data put a strong constraint on it: $Br(h \to \phi^0\phi^0) \leq 30\%$ at $3\sigma$ level; (b) the $p$-value of the LRTH model is around $0.6$, smaller than that of the SM in most of the parameter space and approaches the SM value $0.8$ for a sufficiently large $f$ parameter; (c) the neutral pseudoscalar $\phi^0$ dominantly decay into $b\bar{b}$ and the decay rate $Br(\phi^0\to b\bar{b})$ can be larger than $80\%$ for $m_{\phi^0}\leq 60$ GeV, and the second main decay mode is $\phi^0\to \tau^{+}\tau^{-}$ with a branching ratio about $14\%$; and (d) at the future $e^-e^+$ collider with $\sqrt{s}=250$ GeV, the processes $e^{+}e^{-}\to Zh\to Z(\phi^0\phi^0)\to Z(4b,2b2\tau)$ are promising for discovering such a light pseudoscalar $\phi^0$.