Mixing asymmetries in B meson systems, the D0 like-sign dimuon asymmetry and generic New Physics

The measurement of a large like-sign dimuon asymmetry $A^b_{SL}$ by the D0 experiment at the Tevatron departs noticeably from Standard Model expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to $\Delta B\neq 0$ transitions. In this work we analyse how the natural suppression of $A^b_{SL}$ in the SM can be circumvented by New Physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual $3\times 3$ unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for $A^b_{SL}$ is easily reachable through enhancements of the semileptonic asymmetries $A^d_{SL}$ and $A^s_{SL}$ of both $B^0_d$ - $\bar B^0_d$ and $B^0_s$ - $\bar B^0_s$ systems. Despite being insufficient to reproduce the D0 measurement, such deviations from SM expectations may be probed by the LHCb experiment.