Higgs precision study of the 750 GeV diphoton resonance and the 125 GeV standard model Higgs boson with Higgs-singlet mixing

We interpret the potential observation of the 750 GeV diphoton resonance at the LHC in models, in which an $SU(2)$ isospin-singlet scalar boson mixes with the standard model (SM) Higgs boson through an angle $\alpha$. Allowing the singlet scalar boson to have renormalizable couplings to vectorlike leptons and quarks and introducing sizable decay width of the 750 GeV diphoton resonance into non-SM particles such as dark matters, we can explain the large production cross section $\sigma (H_2)\times B(H_2\to \gamma \gamma )$ as well as the apparent large total width of the boson without conflicts from the results obtained by previous global fits to the SM Higgs boson data.

Figure 1

The decay width ${\mathrm{\Gamma }}_{H_2}$ (upper left), $\sigma (gg\to H_2)\times B(H_2\to \gamma \gamma )$ (upper right), and the ratios $C_{H_1}^{g,\gamma }$ (lower) as functions of $\sin \alpha$. We have taken $S^{g(Q)}=3$, $S^{\gamma (F)}=10\times S^{g(Q)}=30$, and ${\mathrm{\Gamma }}_{H_2}^{\mathrm{non}-\mathrm{SM}}=40\mathrm{GeV}$. In the lower frames, the solid (dashed) lines are for ${\eta }^{g(Q)}={\eta }^{\gamma (F)}=2/3(1)$.

Figure 2

The non-SM decay width ${\mathrm{\Gamma }}_{H_2}^{\mathrm{non}-\mathrm{SM}}$ (upper left), $\sigma (gg\to H_2)\times B(H_2\to \gamma \gamma )$ (upper right), and the ratios $C_{H_1}^{g,\gamma }$ (lower) as functions of $\sin \alpha$. We have taken $S_{H_2}^{g(Q)}=3$, $S_{H_2}^{\gamma (F)}=30$, and ${\mathrm{\Gamma }}_{H_2}=45\mathrm{GeV}$. In the upper-right and lower frames, the physical condition ${\mathrm{\Gamma }}_{H_2}^{\mathrm{non}-\mathrm{SM}}>0$ is imposed.