Extending the Standard Model by a Dark and Visible Scalar Singlet

Sammanfattning: In this thesis, we extend the Higgs sector of the Standard Model by two scalar singlets and impose a discrete Z2 symmetry on each of them, under which, both singlets are odd. One of the two scalar singlets will acquire a vacuum expectation value while the other one does not. This leads to one scalar field mixing with the SM-like Higgs field and one stable scalar singlet. Thus, three scalar bosons are present in this model, two of which have couplings to Standard Model particles while the third boson only gains couplings to the other two scalars. This third scalar is stabilized by the unbroken Z2 symmetry and is a viable dark matter candidate. Using an implementation of the model in MicrOMEGAs, a code for calculating dark matter observables, we study the relic density and compare it to the value observed by the Planck collaboration measurements. We discuss the impact of the model parameters on the relic density and the DM-nucleon scattering cross section and comment on resonance and threshold effects due to the additional scalar.