In this paper, motivated by the observation that the Standard Model
predictions are now above the experimental data for the mass difference ΔMs(d)​, we perform a detailed study of Bs(d)​−Bˉs(d)​ mixing and
Bs​→μ+μ− decay in the Z3​-invariant NMSSM with non-minimal
flavour violation, using the recently developed procedure based on the Flavour
Expansion Theorem, with which one can perform a purely algebraic mass-insertion
expansion of an amplitude written in the mass eigenstate basis without
performing any diagrammatic calculations in the interaction/flavour basis.
Specifically, we consider the finite orders of mass insertions for neutralinos
but the general orders for squarks and charginos, under two sets of assumptions
for the squark flavour structures (\textit{i.e.}, while the flavour-conserving
off-diagonal element δ33LR​ is kept in both of these two
sectors, only the flavour-violating off-diagonal elements
δ23LL​ and δi3RR​ (i=1,2) are kept in the
\text{LL} and \text{RR} sectors, respectively). Our analytic results are then
expressed directly in terms of the initial Lagrangian parameters in the
interaction/flavour basis, making it easy to impose the experimental bounds on
them. It is found numerically that the NMSSM effects with the above two
assumptions for the squark flavour structures can accommodate the observed
deviation for ΔMs(d)​, while complying with the experimental
constraints from the branching ratios of Bs​→μ+μ− and B→Xs​γ decays.Comment: 48 pages, 7 figures, and 2 tables; More discussions and references
added, final version to be published in JHE