Subproject C6: Flavout Physics beyond the SM
Flavour-changing neutral current (FCNC) processes are highly suppressed in the Standard Model, because several suppression factors pile up: they are electroweak loop processes with an extra suppression from small elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. In some processes there are additional suppression factors from helicity or the Glashow-Iliopoulos-Maiani mechanism. Therefore FCNC processes are very sensitive to New Physics, which we expect on general grounds to be associated with new particles with masses at or below the TeV scale. CP-violating processes play a special role in the search for New Physics: in the Standard Model all CP-violating flavour-changing processes involve the same parameter, the complex phase of the CKM matrix, which renders the Standard Model highly predictive and falsifiable.
We address three questions in Project C6:
First, we investigate the Minimal Supersymmetric Standard Model (MSSM) for large values of the parameter tan β. This range is theoretically interesting, because it probes the unification of top and bottom Yukawa couplings. It is further phenomenologically interesting, because there are large effects in flavour physics possible, which moreover involve only relatively few parameters.
Second, we investigate a special version of the MSSM which obeys boundary conditions from a grand unified theory (GUT). This drastically reduces the number of parameters compared to the MSSM. The studied model is also, unlike the MSSM, predictive with respect to the flavour sector, although it does not employ the popular assumption of Minimal Flavour Violation (MFV).
Third, we perform model-independent studies of hadronic two-body B decays using the framework of QCD factorisation. Since many decay channels of hadronic two-body B decays are experimentally studied, analyses in widely-defined classes of models of New Physics are possible.