The anomalous chromomagnetic dipole moment of the top quark in the standard model and beyond

The anomalous chromomagnetic moment of the top quark arises from one loop corrections to the vertex $\bar{t}tg$. We give explicit formulae for this anomalous coupling in the framework of the standard model, the two Higgs doublet model and the minimal supersymmetric standard model. We compare the results for the anomalous coupling with the bound $-0.03 \leq \Delta \kappa \leq 0.01$emergingfromtheanalysisof$b \to s \gamma$ process with an on-shell bremsstrahlung gluon. This enables us to study the allowed region of parameters of the models under consideration.