Models with extended Higgs sectors at future $e^{+}{e}^{-}$ colliders

We discuss the phenomenology of several beyond the Standard Model (SM) extensions that include extended Higgs sectors. The models discussed are the SM extended by a complex singlet field, the 2-Higgs-doublet model with a $CP$-conserving and a $CP$-violating scalar sector, the singlet extension of the 2-Higgs-doublet model, and the next-to-minimal supersymmetric SM extension. All the above models have at least three neutral scalars, with one being the 125 GeV Higgs boson. This common feature allows us to compare the production and decay rates of the other two scalars and therefore to compare their behavior at future electron-positron colliders. Using predictions on the expected precision of the 125 GeV Higgs boson couplings at these colliders we are able to obtain the allowed admixtures of either a singlet or a pseudoscalar to the observed 125 GeV scalar. Therefore, even if no new scalar is found, the expected precision at future electron-positron colliders, such as CLIC, will certainly contribute to a clearer picture of the nature of the discovered Higgs boson.

Figure 1

Mixing angles ${\alpha }_2$ vs ${\alpha }_1$ (left) and $c_b^o$ vs $c_b^e$ (right) for the C2HDM Type I. The blue points are for $Sc1$ but without the constraints from ${\kappa }_{Hgg}$ and ${\kappa }_{H\gamma \gamma }$, the green points are for $Sc1$ including ${\kappa }_{Hgg}$, and the red points are for $Sc3$ including ${\kappa }_{Hgg}$ and ${\kappa }_{H\gamma \gamma }$.

Figure 2

Mixing angles ${\alpha }_2$ vs ${\alpha }_1$ (left) and $c_b^o$ vs $c_b^e$ (right) for the C2HDM Type II. The blue points are for $Sc1$ but without the constraints from ${\kappa }_{Hgg}$ and ${\kappa }_{H\gamma \gamma }$, the green points are for $Sc1$ including ${\kappa }_{Hgg}$, and the red points are for $Sc3$ including ${\kappa }_{Hgg}$ and ${\kappa }_{H\gamma \gamma }$.

Figure 3

$\tan \beta$ as a function of $\sin ({\alpha }_1-\frac{\pi }{2})$ for Type I in $Sc1$ (left) and $Sc3$ (right). The factor $-\frac{\pi }{2}$ is due to a different definition of the rotation angles relative to the 2HDM. Also shown in the color code is the amount of singlet admixture present in $h_{125}$.

Figure 4

$\tan \beta$ as a function of $\sin ({\alpha }_1-\frac{\pi }{2})$ for Type II in $Sc1$ (left) and $Sc3$ (right). The factor $-\frac{\pi }{2}$ is due to a different definition of the rotation angles relative to the 2HDM. Also shown in the color code is the amount of singlet present in $h_{125}$.

Figure 5

${\mu }_t={\sigma }_{\overline{t}th}^{\mathrm{BSM}}/{\sigma }_{\overline{t}th}^{\mathrm{SM}}$ as a function of ${\mu }_V={\sigma }_{VVh}^{\text{BSM}}/{\sigma }_{VVh}^{\mathrm{SM}}={(g_{VVh}^{\mathrm{BSM}}/g_{VVh}^{\mathrm{SM}})}^2$, where $V=W,Z$, for the 2HDM and N2HDM Type I and the CxSM (left) and for the 2HDM and N2HDM Type II and the NMSSM (right) for 1.4 TeV.

Figure 6

Same as Fig. 5, but after imposing the constraints on the Higgs couplings from CLIC@350GeV.

Figure 7

Total rate for $e^{+}{e}^{-}\to \nu \overline{\nu }{H}_i\to \nu \overline{\nu }\gamma \gamma$ as a function of the Higgs boson mass for $\sqrt{s}=350\mathrm{GeV}$. The models presented are the CxSM and the Type I versions of the N2HDM and C2HDM. Also shown is the line for a SM-like Higgs boson. In the left panel we present the results for the lighter Higgs boson, $H_{\downarrow }$, and on the right we show the results for the heavier Higgs boson, $H_{\uparrow }$.

Figure 8

Total rate for $e^{+}{e}^{-}\to Z{H}_{\downarrow }\to Zb\overline{b}$ (left) and for $e^{+}{e}^{-}\to \nu \overline{\nu }{H}_{\downarrow }\to \nu \overline{\nu }b\overline{b}$ (right) as a function of $m_{H_{\downarrow }}$ for $\sqrt{s}=350\mathrm{GeV}$. Plots are shown for the NMSSM and for the Type II versions of the N2HDM and C2HDM. Also shown is the line for a SM-like Higgs boson.

Figure 9

Total rate for $e^{+}{e}^{-}\to \nu \overline{\nu }{H}_{\downarrow }\to \nu \overline{\nu }ZZ$ as a function of the lighter Higgs boson mass for $\sqrt{s}=1.4\mathrm{TeV}$. Left: models CxSM and Type I N2HDM and C2HDM; right: NMSSM and Type II N2HDM and C2HDM. Also shown is the line for a SM-like Higgs boson.

Figure 10

Same as Fig. 9 after imposing the final results for the 350 GeV run.

Figure 11

Total rates for $e^{+}{e}^{-}\to t\overline{t}{H}_{\uparrow }\to t\overline{t}b\overline{b}$ for the Type 1 N2HDM and C2HDM and CxSM. No 350 GeV CLIC constraints (left) and with constraints (right).

Figure 12

Total rate for $e^{+}{e}^{-}\to \nu \overline{\nu }{H}_{\downarrow }\to \nu \overline{\nu }ZZ$ as a function of the lighter Higgs boson mass for $\sqrt{s}=1.4\mathrm{TeV}$. Left: same as the left panel of Fig. 9 after imposing the final results predicted for the LHC@14TeV with $300{\mathrm{fb}}^{-1}$ integrated luminosity; right: same as the left panel of Fig. 9 after imposing the final results predicted for the LHC@14TeV with $3000{\mathrm{fb}}^{-1}$ integrated luminosity.