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Electroweak decays of hadrons are one of the most important topics in modern particle physics due to their extremely rich phenomenology. In particular, they offer vast possibilities for testing the Standard Model (SM) of elementary particles, exploring CP violation, studying quark mixing, searching for New Physics beyond the SM, etc. These decays are characterized by an interplay between electroweak and strong interactions. In the SM, the structure of the electroweak interaction is well defined and rather simple. However, the strong interaction that binds quarks and gluons inside hadrons is not well understood, and this complexity overshadows the simplicity of the electroweak interaction.
The strong interaction is studied within the framework of Quantum Chromodynamics (QCD). From the technical point of view, at the typical (low) energies of these decays, the coupling of the strong interaction is large, and the matrix elements of hadronic transitions between the initial and final states can not be evaluated by using perturbative methods.Therefore, theoretical calculations of these processes require the use of nonperturbative methods, including basically lattice QCD, QCD sum rules, and phenomenological models. Amongst the last is the Covariant Constituent Quark Model which has been developed by our group as an effective quantum field approach to describe hadrons and their transitions, based on a covariant Lagrangian describing the coupling of a hadron with its constituent quarks.
The model has been successfully applied to a large number of decays involving mesons, hadrons, and multiquark states. In this seminar, we will discuss the model and its application in the studies of the semileptonic decays of $D$ meson and $\Lambda_b$ baryon, the rare radiative decay $B_s\to \ell^+\ell^-\gamma$, and possible New Physics effects in the decays $B_c\to J/\psi(\eta_c)\tau\nu$ in the light of experimental flavor anomalies in $B$ physics.