Theory for symmetry violation experiments in molecules

The Standard Model of particle physics (SM) provides a very accurate description of our visible universe at the smallest scale; however, it is incomplete. Fundamental questions, such as the dominance of matter over antimatter in the universe, remain unanswered in the SM and motivate searches for physics beyond the Standard Model (BSM). Physics BSM can be revealed by testing discrete symmetries with high-precision experiments performed at low energy. The precision of SM and BSM parameters in these experiments can be increased by using molecules, as the molecular electronic structure leads to an enhanced symmetry-violating experimental signal. In the first part of this thesis, we discuss the motivation and approach to searching for BSM physics with molecules, focusing on the role of electronic-structure calculations to connect the low-energy observables with the fundamental particle physics parameters. In the second part, we present studies for ongoing and future experiments. In particular, we identify promising molecular candidates such as the polyatomic molecules BaCH$_3$, YbCH$_3$, and the diatomic molecules LaS, LaO, and LuO, and calculate their sensitivity to symmetry-violation effects using electronic-structure methods. In addition to being highly sensitive to symmetry-violation signals, these molecules also possess important experimental advantages, which make them ideal for high-precision experiments. In this way, this thesis highlights the relevance of theory for the interpretation and planning of BSM-physics searches at low energy and contributes to constructing a bridge between the different domains involved.