## Constraint from

In the Standard Model, oscillations occur through a second order process (a box diagram) with a loop containing W and up-type quarks. The box diagram with the top quark gives the dominant contribution. The oscillation frequency, which is related to the mass difference between the light and the heavy mass eigenstates of the system is expressed, in the Standard Model, as function of and the other elements of CKM matrix:

where is the Inami-Lim function and , is the top mass, is the W mass, and is the perturbative QCD short distance NLO correction. The remaining factor encodes the information of non-perturbative QCD. The experimental values we use are summarized in the Table of Inputs. The representation of this constraint in the plane is given below.

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