Minimal flavour violation: an effective field theory approach

We present a general analysis of extensions of the Standard Model which satisfy the criterion of Minimal Flavour Violation (MFV). We define this general framework by constructing a low-energy effective theory containing the Standard Model fields, with one or two Higgs doublets and, as the only source of SU(3)(5) flavour symmetry breaking, the background values of fields transforming under the flavour group as the ordinary Yukawa couplings. We analyse present bounds on the effective scale of dimension-six operators, which range between 1 and 10 TeV, with the most stringent constraints imposed by B --> X(s)gamma. In this class of theories, it is possible to relate predictions for FCNC processes in B physics to those in K physics. We compare the sensitivity of various experimental searches in probing the hypothesis of MFV. Within the two-Higgs-doublet scenario, we develop a general procedure to obtain all tan beta-enhanced Higgs-mediated FCNC amplitudes, discussing in particular their impact in B --> l(+)l(-), DeltaM(B) and B --> X(s)gamma. As a byproduct, we derive some two-loop tan beta-enhanced supersymmetric contributions to B --> X(s)gamma previously unknown. (C) 2002 Elsevier Science B.V. All rights reserved.