B_s(d) - bar B_s(d) mixing constraints on flavor changing decays of t and b quarks

We study those dimension 6 effective operators which generate flavor-changing quark-gluon transitions of the third generation quarks, with t -> g + u© and b -> g + d(s), and which could be of interest for LHC experiments. We analyze the contribution of these operators to B_s(d) - bar B_s(d) mixing and derive limits on the corresponding effective couplings from the existing experimental data. The Standard Model gauge invariance relates these couplings to the couplings controlling t -> g + u©. On this basis we derive upper limits for the branching ratios of these processes. We further show that forthcoming LHC experiments might be able to probe the studied operators and the physics beyond the Standard Model related to them.