Mixing and CP violation in the D 0 and B 0 s systems

Neutral meson mixing provides excellent tests of the Standard Model (SM) and probes of new physics (NP): CP violation involving K –K mixing (ǫK) predicted the third generation; ∆mK predicted the charmmass; ∆mB predicted the top mass to be heavy. While 31 years passed between the discovery of theKL (1956) and the discovery of B –B mixing (1987), after 19 years, in 2006, the B s –B 0 s mixing frequency was measured [1] and now the observation of D –D mixing [2, 3] is on the verge of being well established. This talk focuses on the implications of these last two sets of measurements. Almost all extensions of the SM aimed at solving the hierarchy problem also contain new sources of CP violation and flavor conversion. If there is NP at the TeV scale, flavor physics already imposes strong constraints on it. Generic TeV-scale NP models violate the experimental bounds from K and B mixing and flavor-changing neutral current (FCNC) decay measurements by several orders of magnitude. Thus, new flavor physics has to either (i) originate at a much higher scale than 1TeV and be decoupled; or (ii) originate from electroweak symmetry breaking (EWSB) related NP with non-trivial structure [4, 5]. Many models with TeV-scale new particles could have given rise to significant deviations from the SM predictions for B s mixing. For example, due to its large mass, the top quark may couple strongly to the NP sector, and in some scenarios it affects B s mixing, but not B or K mixing [4, 6]. Large D mixing is predicted by quark-squark alignment models [7], since in order not to violate the ∆mK bound, Cabibbo mixing must mostly come from the up sector, predicting ∆m/Γ ∼ O(λ2) if mg̃,q̃ ∼ 1TeV.