How large can the light quark Yukawa couplings be?

The light quark Yukawa couplings are notoriously difficult to measure at the LHC. Current bounds and future projections for the HL-LHC foresee that they can be constrained to be a factor of several hundred times their Standard Model value. The thesis aims to respond to the question on how large they actually can be in UV models. In order to address this question, models will be identified that generate deviations in light quark Yukawa couplings via dimension-six effective operators at tree-level. A particular good choice not studied yet in depth in literature are models with vector-like quarks. The list of possible models is finite and can hence been studied systematically, taking into account potential bounds from flavour physics, Higgs physics and electroweak precision tests. The latter in particular might set important bounds as models with vector-like quarks typically generate also effective operators that modify the quark couplings to W and Z bosons. The thesis will also confront the concrete UV models with an effective field theory description.