Minimal flavour violation: an effective field theory approach

Abstract

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 γ. 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 β-enhanced Higgs-mediated FCNC amplitudes, discussing in particular their impact in B → ℓ + ℓ − , ∆M B and B → X s γ. As a byproduct, we derive some two-loop tan β-enhanced supersymmetric contributions to B → X s γ previously unknown.

Model-independent constraints on ΔF= 2 operators and the scale of new physics

“…The bound we obtained is in agreement with ref. [18], taking into account the present experimental information. If a non-standard Higgs boson is seen at hadron colliders, this implies an upper bound on the a i couplings and/or tan β.…”

“…[18], for ∆m K and D 0 −D 0 mixing we take F SM = |V td V ts | 2 ). This condition is realized in models in which right-handed currents also contribute to FCNC processes, but with the same hierarchical structure in the mixing angles as in the SM left-handed currents.…”

Constraints on supersymmetric flavour models fromb→sγ

“…14a. where 1,2,... 5,6 are ordered lightest to heaviest. Analogously for the 3rd generation sleptons we have (Mẽ 1 , Mẽ 4 ) = (246, 477) GeV, in the CMSSM as shown by the two (red) curves in panel b.…”

“…As a consequence, it is often assumed that one can impose vanishing off-diagonal terms at the GUT scale in the soft squared mass and trilinear mass matrices [5]. In addition, when the trilinear terms are diagonal, the off-diagonal terms in the squark mass matrices generated radiatively at the EW scale can be rotated to the MFV form defined in [6] with the same unitary matrices diagonalizing the Yukawa matrices. In FS with supergravity [2,7,8], the scalar fields breaking such symmetries (flavons) generate off-diagonal terms at the GUT scale in the supersymmetric sector that are correlated to those of the fermion sector in a model dependent way.…”

Complete next-to-leading order gluino contributions to and

“…Bounds on the Little Higgs Model with T-parity have also been presented [36]. Finally, model-independent analyses in the effective field theory approach without [37] and with the assumption of minimal flavor violation [10,11] also show the strong constraining power of theB → X s γ branching fraction. While within the perturbative SM calculation NNLL precision has been achieved [14,15], also within supersymmetric theories higher order calculations have been pushed forward in recent years.…”