Fundamental Models for Composite Dark Matter and Higgs

In this thesis, concrete extensions of the Standard Model valid up to high energies are presented. Starting from the scenario of Vectorlike Confinement, we perform a systematic search of renormalizable models, where Dark Matter candidates arise as composite particles of a new confining gauge interaction. In particular we investigate the possibility that Dark Matter is made by composite states analog to the QCD baryons and stable thanks to an accidental symmetry, exactly as the proton is stable thanks to the baryon number conservation. The lightest state charged under this U(1) symmetry is neutral, so that our scenario may explain in a simple way both stability and neutrality of Dark Matter. Cosmology suggests that the Dark Matter thermal relic abundance can be reproduced if the mass scale of these states is around 100 TeV. We show that, despite its high mass, composite Dark Matter is characterized by an interesting phenomenology, with observable electric and magnetic dipole moments leading to a peculiar spin-independent cross section. The electric dipole moment of the Dark Matter candidate arises exactly as the neutron electric dipole and it is proportional to a CP-violating coupling induced by the theta-angle of the new strong sector. In some theories, a Majorana Dark Matter can appear, with challenging spin-dependent cross section or inelastic scatterings. Each model predicts also a set of lighter composite states, analog to the pions in QCD, possibly accessible at colliders. The possibility that the Dark Matter abundance in the Universe is made by a scalar composite particle analog to pions in QCD is also investigated. This possibility turns out to be less theoretically motivated, but it is interesting from a phenological point of view: Dark Matter may show up at collider not directly but through LHC signatures from unstable particles of the same composite sector. Finally, we extend the Vectorlike Confinement scenario introducing fundamental scalars with the aim of generating a composite sector that includes a composite Higgs. The partial compositeness mechanism arises automatically from our Lagrangian where fundamental Yukawa couplings between the new particles and the Standard Model fermions are allowed. Despite being aware that the idea of introducing fundamental scalars is unconventional and gives rise to many theoretical problems, we argue that this seems to be unavoidable if we want to construct a fundamental theory of composite Higgs with partial compositeness. Under certain assumptions on the dynamics of the scalars, successful models can be realized thanks to the fact that the Standard Model fermions quantum numbers admit a minimal enough “square root".