Seminarium Teorii Oddziaływań Elementarnych

Based on flavour symmetries only, there are two ways to give rise to an effective description of flavour physics in the quark sector close to the CKM picture: one is based on U(3)q x U(3)u x U(3)d, and the other on U(2)q x U(2)u x U(2)d (or equivalent symmetries). In this context we analyze the current status of flavour physics measurements and we compare their impact, in the specific case of supersymmetry, with the direct searches of new particles at the LHC, present or foreseen. In a complementary view, in absence of some mechanism able to suppress potentially large flavour-changing effects, one must rely on a very high scale of new flavour phenomena in order to explain the observed near-CKM structure. In such a scenario, an interesting question is what energy scales one will be able to probe by means of the precision measurements of rare decays foreseen in the next decade. We find that, in some simple toy models, and depending on the specific process, scales from a few tens of TeV up to thousands of TeV can be explored. A prominent role will be played by the K → πνν decays, whose branching ratios will be measured with high precision for the first time in the next few years. I will review the present status of their prediction in the Standard Model, showing how the dominant source of error presently comes from the determination of the CKM matrix elements.