A Light Scalar in the Minimal Dilaton Model in Light of LHC Constraints

Abstract

Whether an additional light scalar exists is an interesting topic beyond the Standard Model (SM), while nowadays we do not know exactly physics beyond the SM in the low mass region, e.g., the Atlas and CMS collaborations get inconsistent results at around 95 GeV in searching for light resonances in diphoton channel. Considering these, we study a light scalar in the Minimal Dilaton Model (MDM). Under the theoretical and latest experimental constraints, we sort the surviving samples into two scenarios according to the diphoton rate of the light scalar: the large-diphoton scenario (with $/SM\gtrsim0.2$) and the small-diphoton scenario (with $/SM\lesssim0.2$), which are favored by CMS and Atlas results respectively. We compare the two scenarios, check the characteristics in model parameters, scalar couplings, production and decay, and consider further distinguishing them at colliders. Finally, we get the following conclusions for the two scenarios: (i) The formal usually has small Higgs-dilaton mixing angle ($|\sin\theta_S|\lesssim0.2$) and small dilaton vacuum expectation value (VEV) $f$ ($0.5\lesssim\eta\equiv v/f\lesssim1$), and the later usually has large mixing ($|\sin\theta_S|\gtrsim0.4$) or large VEV ($\eta\equiv v/f\lesssim0.3$). (ii) The former usually predicts small $s\gamma\gamma$ coupling ($|C_{s\gamma\gamma}/SM|\lesssim0.3$) and large $sgg$ coupling ($0.6\lesssim|C_{sgg}/SM|\lesssim1.2$), while the later usually predicts small $sgg$ coupling ($|C_{sgg}/SM|\lesssim0.5$). (iii) The former can interpret the small diphoton excess by CMS at its central value, when $m_s\simeq$95GeV, $\eta\simeq0.6$ and $|\sin\theta_S|\simeq0$. (iv) The former usually predicts a negative correlation between Higgs couplings $|C_{h\gamma\gamma}/SM|$ and $|C_{hgg}/SM|$, while the later usually predicts the two couplings both smaller than 1, or $|C_{h\gamma\gamma}/SM|\lesssim0.9 \lesssim|C_{hgg}/SM|$.