FIG. 2: Constraints on the effective parameters encoding NP effects in B$_{d}$ – B$_{d}$ mixing and K $^{0}$– K 0 mixing as obtained by the UTfit collaboration [12]. where the c$_{ij}$ are dimensionless couplings. The condition |A Δ F =2 NP | < |A Δ F =2 SM | implies The strong bounds on Λ for generic c$_{ij}$ of order 1 is a manifestation of what in many specific frameworks (supersymmetry, technicolor, etc.) goes under the name of flavor problem : if we insist that the new physics emerges in the TeV region, we have to conclude that it possesses a highly non-generic flavor structure. (iii) In the case of B$_{s}$ – B$_{s}$ mixing, the precise determination of Δ m$_{B}$$_{s}$ does not allow large deviations in modulo with respect to the SM. The constraint is particularly severe if we consider the ratio Δ m$_{B}$$_{d}$/ Δ m$_{B}$$_{s}$ , where hadronic uncertainties cancel to a large extent. However, the constraint on the CP-violating phase is quite poor. Present data from CDF [13] and D0 [14] indicate a large (ii) In the case of B$_{d}$ – B$_{d}$ and K $^{0}$– K 0 mixing, where both CP conserving and CP-violating observables are measured with excellent accuracy, there is still room for a sizable NP contribution (relative to the SM one), provided that it is to a good extent aligned in phase with the SM amplitude [ O (0 . 01) for the K system and O (0 . 3) for the B$_{d}$ system]. This is because the theoretical errors in the observables used to constraint the phases, S$_{B}$$_{d}$$_{→}$$_{ψK}$ and ϵ$_{K}$ , are smaller with respect to the theoretical uncertainties in Δ m$_{B}$$_{d}$ and Δ m$_{K}$ , which constrain the magnitude of the mixing amplitudes. 8 Λ > 4 . 4 TeV | V ∗ $_{ti}$V$_{tj}$ | / | c$_{ij}$ | 1 / 2 ∼      1 . 3 × 10 4 TeV × | c$_{sd}$ | 1 / 2 5 . 1 × 10 2 TeV × | c$_{bd}$ | 1 / 2 1 . 1 × 10 2 TeV × | c$_{bs}$ | 1 / 2 (3.5) d B C 0 1 2 3 4 5 6 ] o [ d B -80 -60 -40 -20 0 20 40 60 80 K m C 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 K C -3 -2 -1 0 1 2 3