Studies On The Scalar-portal Based Dark Matter Models

Among the SM extended new physics models, the Higgs-portal singlet scalar dark matter（HSDM） model is a very simple one. In this extension, only a real singlet scalar s is added to the SM, which is account for the DM candidate and couples to the SM Higgs only. With the aid of 2Z parity which is needed for the stability of the scalar DM, the number of model parameters are reduced to three, which are the mass of the scalar DM sm, the Higgs-DM coupling sk and the scalar self-interaction coupling sl.First, we analyzed constraints on the HSDM from DM related observations. Since the DM self-interaction is not related to these constraints, only the parameters sm and sk have been take into account in this case. We induced the relation between the sm and sk by implement the constraints of the DM relic density at the first place. Thus the sm becomes the only free parameter in the HSDM. Then the constraints from the DM direct detection experiments XENON100 and LUX and the latest experiments results of the LHC Run I had been taken into account, which resulted that only the resonant mass region（53GeV 63GeVs￡m ￡） and large mass region（ 185 GeVsm 3） for the HSDM are viable.Then, we discussed the effects of scalar DM self-scattering processes on the astrophysical large scale structures（LSS）. Other than the DM self-interaction, also the Sommerfeld effects have been considered in this work. And we found that both the resonant and the large mass region in the HSDM are allowed by the LSS constraints. If one wish to constrain the DM resonant mass region through this means, the detectability of the ratio of DM self-scattering cross section and the DM mass should be 7 20cm1/ g-, and which for the large mass region is 10 2c¹0 m / g-.After that, the collider signatures of the HSDM have been studied. The primary DM production channel-vector boson fusion（VBF） channel and the relatively clean channel-mono-Z channel have been considered for the hadron collider LHC and 100 TeV future circular collider（FCC）. We simulated the signal and background of these two channels in the computer with the help of MadGraph 5 and codes related. Therefore, one can detect the HSDM resonant mass region through FCC, XENON1 T and LSS observations, and only XENON1 T can reach the large mass region. If one impose constraints from the perturbativity and the electroweak vacuum stability in the early Universe, the resonant mass region is totally excluded and the high mass region is reduced to 1.1TeV 2.0TeVsm ￡￡.The first data at the LHC Run 2 with 13 TeV collision energy was released in the late of year 2015. The data shows an excess over the SM expectation in diphoton final state at the diphoton invariant mass around 750 GeV. And we presented a new model containing a real or pseudo- scalar to give an explanation. In this model, the new real（pseudo） scalar with mass of 750 GeV and couples to a SM top- or bottom-like fermion partner. The（pseudo） scalar is mainly produced by the gluon-gluon fusion, and decays to the diphoton at the fermion partner intermediated one-loop level. We obtained the viable parameter space for this model after considering constraints from the LHC Run II diphoton excess and others of LHC Run I. Based on the above knowledge, we constructed a new kind of dark matter model named the new scalar-portal dark matter（NSDM） model where the mass of the new scalar is 750 GeV. Since the DM only couples to the new scalar, only the DM mass DMm and the DM-scalar coupling y have been added to this NSDM model. Once the constraints from the DM relic density and DM direct detection experiments XENON100 and LUX have been taken into consideration, and with the requirement of perturbativity, we can get the viable DM mass range as 400 GeV <m_DM <3TeV.