Abstract: I explore a new-physics interpretation of the recent D0 result on the dimuon asymmetry in B decays. An exhaustive simultaneous analysis of the B_s and B_d mixing complexes points towards new CP phases with negative signs in the corresponding mixing amplitudes. The result can be accommodated in the Minimal Supersymmetric Standard Model. Finally, I discuss a GUT model, in which the atmospheric neutrino mixing angle drives new -&gt;s transitions.<br>