  We study those dimension 6 effective operators which generate flavor-changing
quark-gluon transitions of the third generation quarks, with t -> g + u(c) 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(c). 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.
