Stringent Tests of Constrained Minimal Flavour Violation through Delta F=2 Transitions

TL;DR

This paper tests the constraints of Constrained Minimal Flavour Violation (CMFV) models on Delta F=2 transitions, revealing tensions with current lattice values and suggesting the need for new sources of flavour violation.

Contribution

It provides a comprehensive analysis of CMFV parameter space using current experimental data and lattice inputs, highlighting potential issues and proposing methods to refine charm contribution estimates.

Findings

CMFV models face tensions with lattice values of decay constants.

|Vcb| and |Vub| need to be higher/lower than current determinations.

Indications of possible new sources of flavour violation.

Abstract

New Physics contributions to Delta F=2 transitions in models with constrained Minimal Flavour Violation (CMFV), are parametrized by a single variable S(v), the value of the real box diagram function. With already precise experimental values of epsilon_K, Delta M_d, Delta M_s, CP-asymmetry S_{psi K_S} and of hat{B}_K entering the evaluation of epsilon_K, the future of CMFV in the Delta F=2 sector depends crucially on the values of |Vcb|, |Vub|, gamma, F_{B_s} sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}}. The ratio xi of the latter two parameters, rather precisely determined from lattice calculations, allows then together with Delta M_s/Delta M_d and S_{psi K_S} to determine the range of gamma in the unitarity triangle independently of the value of S(v). Imposing in addition the constraints from epsilon_K and Delta M_d allows to determine the favorite CMFV values of |Vcb|, |Vub|, F_{B_s} sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}} as functions of S(v) and gamma. The |Vcb|^4 dependence of epsilon_K allows to determine |Vcb| for a given S(v) and gamma with a higher precision than it is presently possible using tree-level decays. The same applies to |Vub|, |Vtd| and |Vts| that are automatically determined as functions of S(v) and gamma. Typically F_{B_s}sqrt{hat B_{B_s}} and F_{B_d} sqrt{hat B_{B_d}} have to be significantly lower than their present lattice values, while |Vcb| has to be significantly higher than its tree-level determination. The region in the space of these three parameters allowed by CMFV indicates visible problems in this class of models and hints for the presence of new sources of flavour violation and/or new local operators in Delta F=2 data that are strongly suppressed in these models. As a byproduct we propose to reduce the present uncertainty in the charm contribution toepsilon_K by using the experimental value of Delta M_K.