  Possible non-standard couplings which could contribute to the t -> b W
process are studied based on the effective-Lagrangian approach. The
corresponding effective Lagrangian consists of four kinds of dimension-6
effective operators, each of which has an independent coupling constant. In
this analysis, all those couplings are treated as complex numbers and
constraints on them are estimated by using recent experimental data from the
LHC. We point out that the resultant constraints on those couplings are still
not that strong because contributions from some couplings can work oppositely
with each other.
