On the interplay of constraints from Bₒ, D, and K meson mixing in Z^ models with implications for b\! \! s transitions

Abstract Within Z^ Z ′ models, neutral meson mixing severely constrains beyond the Standard Model (SM) effects in flavour changing neutral current (FCNC) processes. However, in certain regions of the Z^ Z ′ parameter space, the contributions to meson mixing observables become negligibly small even for large Z^ Z ′ couplings. While this a priori allows for significant new physics (NP) effects in FCNC decays, we discuss how large Z^ Z ′ couplings in one neutral meson sector can generate effects in meson mixing observables of other neutral mesons, through correlations stemming from {SU (2) }L SU (2) L gauge invariance and through Renormalization Group (RG) effects in the SM Effective Field Theory (SMEFT). This is illustrated with the example of Bₛ⁰-Bₛ⁰ B s 0 - B ¯ s 0 mixing, which in the presence of both left- and right-handed Z^ bs Z ′ b s couplings L^bs Δ L bs and R^bs Δ R bs remains SM-like for R^bs 0. 1\, L^bs. Δ R bs ≈ 0. 1 Δ L bs. We show that in this case, large Z^ bs Z ′ b s couplings generate effects in D and K meson mixing observables, but that the D and K mixing constraints and the relation between R^bs <