Constraints on multi-scalar models

The Standard Model of particle physics is one of the most successful theories ever developed. Although the Standard Model provides an accurate description of known elementary particles and their interactions, it leaves several fundamental questions unanswered, including the origin of the baryon asymmetry of the Universe, the nature of Dark Matter, and the mechanism responsible for generating neutrino masses. These shortcomings provide strong motivation for considering extensions of the Standard Model.

In the first part of this work, we present a comprehensive study of perturbative unitarity bounds in the gauge-scalar sectors of models containing additional scalar doublets, neutral singlets, or charged singlets. Such scalar sectors arise naturally in many Beyond the Standard Model scenarios and are particularly common in theories that address the dark matter problem.

We derive a complete classification of these models and identify a minimal set of scattering matrices that contains all the information required to determine the perturbative unitarity constraints. We also developed a Mathematica package, BounDS, which automates the implementation of these results. This work has been published in the International Journal of Modern Physics A (IJMPA).

In the second part of this work, we investigate CP Violation (CPV) in couplings, focusing on the potential role of a complex top Yukawa coupling as a source of CPV. We analyse how such couplings could arise in effective field theory frameworks and study their phenomenological consequences for Higgs decays and interactions.