LAUSR

Whether an additional light scalar exists is an interesting topic in particle physics beyond the Standard Model (SM), as we do not know as yet the nature of physics beyond the SM in the low mass region in view of the inconsistent results of the ATLAS and CMS collaborations in their search for light resonances around 95 GeV in the diphoton channel. We study a light scalar in the Minimal Dilaton Model (MDM). Under the theoretical and the latest experimental constraints, we sort the selected data samples into two scenarios according to the diphoton rate of the light scalar: the large-diphoton scenario (with \begin{document}$\sigma_{\gamma\gamma}/{\rm SM}\gtrsim0.2$\end{document} ) and the small-diphoton scenario (with \begin{document}$\sigma_{\gamma\gamma}/{\rm SM}\lesssim0.2$\end{document} ), which are favored by the CMS and ATLAS results, respectively. We compare the two scenarios, test the characteristics of the model parameters, the scalar couplings, production and decay, and consider how they could be further discerned at colliders. We draw the following conclusions for the two scenarios: (i) The large-diphoton scenario has in general a small Higgs-dilaton mixing angle ( \begin{document}$|\sin\theta_S|\lesssim0.2$\end{document} ) and a small dilaton vacuum expectation value (VEV) \begin{document}$f$\end{document} ( \begin{document}$0.5\lesssim\eta\equiv v/f\lesssim1$\end{document} ), and the small-diphoton scenario has large mixing ( \begin{document}$|\sin\theta_S|\gtrsim0.4$\end{document} ) or large VEV ( \begin{document}$\eta\equiv v/f\lesssim0.3$\end{document} ). (ii) The large-diphoton scenario in general predicts small \begin{document}$s\gamma\gamma$\end{document} coupling ( \begin{document}$|C_{s\gamma\gamma}/{\rm SM}|\lesssim0.3$\end{document} ) and large \begin{document}$sgg$\end{document} coupling ( \begin{document}$0.6\lesssim|C_{sgg}/{\rm SM}|\lesssim1.2$\end{document} ), while the small-diphoton scenario predicts small \begin{document}$sgg$\end{document} coupling ( \begin{document}$|C_{sgg}/{\rm SM}|\lesssim0.5$\end{document} ). (iii) The large-diphoton scenario can interpret the small diphoton excess seen by CMS at its central value, when \begin{document}$m_s\simeq95$\end{document} GeV, \begin{document}$\eta\simeq0.6$\end{document} and \begin{document}$|\sin\theta_S|\simeq0$\end{document} . (iv) The large-diphoton scenario in general predicts a negative correlation between the Higgs couplings \begin{document}$|C_{h\gamma\gamma}/{\rm SM}|$\end{document} and \begin{document}$|C_{hgg}/{\rm SM}|$\end{document} , while the small-diphoton scenario predicts that both couplings are smaller than 1, or \begin{document}$|C_{h\gamma\gamma}/{\rm SM}|\lesssim0.9 \lesssim|C_{hgg}/{\rm SM}|$\end{document} .