Flavor universality in elementary particle processes at low and high energiesKorajac, Arman (Avtor) Kamenik, Jernej (Mentor) beyond the Standard ModelNew Physicsflavor-violating processescollider studiesdineutrino couplingslow-energy theoryCP violationleptoquarksFCCPersistent indications of lepton flavor universality violation observed in bottom-quark transitions have motivated a plethora of models addressing the relevant deviations from the expected Standard Model (SM) result. This dissertation focuses on different strategies of observing flavor non-universal patterns in diverse Beyond the Standard Model realizations. We utilize simultaneously high-energy and low-energy data to constrain the parameter space of models addressing such issues and propose novel search strategies at present and at future colliders. Specifically, we propose an analysis of extracting New Physics (NP) information from collider searches targeting events with high missing transverse energy (MET) values and tagged $b$-jets as signatures. In the context of the Standard Model Effective Field Theory (SMEFT), we show that such an analysis imposes constraints on the SMEFT operators that are comparable in magnitude to those obtained via high-$p_T$ dilepton searches. Afterwards, we compare our results with the exclusion bounds derived from low-energy experiments, specifically including the decays $\Upsilon(1S) \to $ invisibles and $B \to K^{(\ast)} \nu \bar{\nu}$. Additionally, our attention is linked towards light-generation quarks, with a particular emphasis on investigating CP violation within the SMEFT. The studied inclusion of the singlet and triplet left-handed semileptonic operators for the first two quark generations leads to contributions in semileptonic and leptonic decays of $K, D$ mesons, pions, and nuclear beta decay. We implement the flavor covariant description in the low-energy couplings, identify universal CP phases of New Physics and give an explicit description of up- and down-quark transitions simultaneously. As a result, we can predict the maximal effects of such flavored NP in $D$ decays from stringent $K$ decay constraints and vice-versa. Furthermore, a long-standing candidate for the explanation of charged-current $B$-anomalies is a TeV-scale $U_1 \sim \left(\mathbf{3}, \mathbf{1}, 2/3\right)$ leptoquark, mainly coupled to the third generation. We study its production by lepton-quark fusion at the Large Hadron Collider, considering next-to-leading-order effects from its interactions with gluons and photons. We derive high-energy bounds on the parameters of the 4321 Lagrangian using the most recent resonant leptoquark production search performed by the CMS Collaboration. We also employ recent advances in $b$, $c$, and $s$ quark tagging together with novel statistical analysis techniques within the context of the FCC-ee collider environment. We show that it is possible to place phenomenologically relevant bounds on flavor-violating Higgs and $Z$ decays to quarks using these methods. We show that searches for $h\to bs, cu$ decays at FCC-ee can probe new parameter space not excluded by indirect, low-energy searches.20242024-05-23 12:49:33Doktorsko delo/naloga156396VisID: 139799COBISS_ID: 192034563sl