Direct Constraints, Flavor Physics, and Flavor Anomalies in Composite Higgs Models

Abstract

Composite Higgs models (CHMs) offer an elegant solution to the naturalness problem of the Standard Model (SM). Their direct effects at particle colliders like the Large Hadron Collider (LHC) are thus of central interest. While no direct effects have been observed so far, there are recent indirect hints for new physics (NP) coming from measurements of rare B meson decays. This thesis studies direct collider constraints on CHMs as well as the question if these models can explain the hints for NP in rare B decays. The first part of this thesis gives a self-contained introduction to all main concepts of CHMs used in the remainder of the work. These concepts are then applied in several phenomenological analyses. In the context of global numerical analyses of two explicit CHMs, the direct constraints on vector, fermion and scalar resonances are studied in detail. The prospects of various decay channels for observing or excluding still viable parameter points of the considered models are discussed. Model independent analyses of the hints for NP in rare B decays are performed in the context of the $B \to K^* μ^+ μ^-$ anomaly as well as the hints for violation of lepton flavor universality (LFU) found in measurements of the observables $R_K$ and $R_{K^*}$. A simple CHM is presented that can explain the anomalies in rare B decays by partially composite left-handed muons. The flavor physics of a much more ambitious model, which is based on a UV completion of effective CHMs called fundamental partial compositeness (FPC), is investigated in detail. Taking into account all relevant constraints from electroweak scale physics and low-energy flavor observables, it is shown that this model can explain the anomalies found in rare B decays.