Beyond the Standard Model: Composite Higgs and Dark Matter

Abstract

The Standard Model (SM) of particles and interactions provides some of the most extensively tested predictions in science. However, it does not adequately describe quantum gravity, and does not contain a suitable candidate for Dark Matter. Furthermore, the UV sensitivity of the SM Higgs sector suggests that new states beyond the SM might exist at energies not far above the weak scale. This dissertation explores potential scenarios for physics beyond the SM, either in a dark sector or linked to the Higgs sector of the SM. The first part of this work includes two novel classes of composite Higgs models, with far reaching phenomenological consequences. In the first of these, an adjustable tree-level Higgs quartic coupling, allows for a significant reduction in the tuning of the Higgs potential. The quartic in this model originates from the dimensional reduction of a 6D theory, and is the first example of a holographic composite Higgs model with a tree-level quartic. In the second novel class of composite Higgs models, the top and gauge partners responsible for cutting off the Higgs quadratic divergences form a continuum. A concrete example is presented, based on a warped extra dimension with a linear dilaton, where this finite gap appears naturally. Spectral densities are derived for this model, as well as the full Higgs potential for a phenomenologically viable benchmark point, with percent level tuning. The continuum top and gauge partners in this model evade all resonance searches at the LHC and yield qualitatively different collider signals. The second part of this work features two different classes of models for an extended dark sector that undergoes either confinement or bound states formation. It is shown how each of these mechanisms could lead to vast modifications of early universe dynamics, as well as unique signals today. In the first of these, the relic abundance of heavy stable particles charged under a confining gauge group is depleted by a second stage of annihilations near the deconfinement temperature. This mechanism can be used to construct ultra-heavy dark-matter models with masses above the naive unitarity bound. The second contribution is Self-Destructing Dark Matter (SDDM), a new class of dark matter models which are detectable in large neutrino detectors. In this class of models, a component of dark matter can transition from a long-lived state to a short-lived one by scattering off of a nucleus or an electron in the Earth. The short-lived state then decays to SM particles, generating a dark matter signal with a visible energy of order the dark matter mass rather than just its recoil.