Phenomenology of the Higgs sectors of the munuSSM and the N2HDM

In this thesis the phenomenology of the Higgs sectors of two Beyond the Standard Model (BSM) theories was investigated. The first part of the thesis was dedicated to the mu-from-nu supersymmetric SM (munuSSM). In this model, in addition to the supersymmetric partners of the SM particles, the particle content is augmented by right-handed neutrino superfields. A seesaw mechanism at the electroweak scale is utilized to accurately predict the neutrino masses and their mixings. As a consequence, the scalar partners of the neutrinos mix with the usual Higgs bosons. Our work was focused on the precise prediction of the neutral scalar masses, by calculating the full one-loop corrections, and add partial higher-order corrections from the literature. To obtain the one-loop result, we established an adequate renormalization procedure for the Higgs potential, employing on-shell renormalization conditions when appropriate. In the second part of the thesis, we showed that the Next-to 2 Higgs Doublet Model (N2HDM) is capable of accommodating two experimental excesses measured at the LHC and LEP, which hint to the existence of a second Higgs boson with a mass of about 96GeV. In the munuSSM, the excesses could be accounted for at the 1-sigma level by means of a right-handed sneutrino of this mass. In the N2HDM, an explanation for the excesses was presented which is in perfect agreement with the experimentally measured signal strengths. The signals are reproduced by the help of a real gauge-singlet scalar that acquires its couplings to the SM particles via a substantial mixing with the SM Higgs boson.