This work covers two searches for exotic physics in proton-proton scattering at
CERN’s Large Hadron Collider, utilising data from the CMS experiment taken at
a centre of mass energy of 13 TeV. The first analysis involves a search for Dark
Matter in association with the decay products of a new scalar coupled exclusively to
the dark sector called the Dark Higgs. The other search is for a heavy Higgs boson
that decays into a top-antitop pair. The analysis on the Dark Higgs signal utilises
the relations between the scalar transverse momentum sum of jets, HT and the
negative vector sum of jet momentum Hmiss to separate signal from background. T
The result from 35.9 fb−1 of data from 2016 is presented. No deviation from the Standard Model prediction is observed, and the first experimental limits on Dark Higgs models ever are set, with Dark Matter mediator masses of up to 1700 GeV and Dark Matter particle masses up to 300 GeV can be excluded at 95% C.L. In the search for heavy scalar and pseudoscalar Higgs bosons, the invariant top-antitop mass is explored together with an angular observable sensitive to the correlation between the spin of the top quark and the spin of the antitop quark. For this search, 41.5 fb−1 of 2017 data has been used. Expected upper limits on the coupling between the heavy Higgs boson and the top quark are set for different hypotheses for the mass of the heavy Higgs boson, which are consistent with the expected limits from the same analysis on 2016 data.