Effective action approach to heavy particle contributions and Wilsonian renormalization

We consider theories with both light and heavy particles. A method to obtai n an effective low-energy action with respect to the light particle is pres ented. Using Wilsonian renormalization, we obtain effective actions with a finite number of local operators describing possible non-decoupling effects of heavy particles. The validity of the method is first checked by explici t computation of a specific observable, the rho-parameter, in the framework of the effective theory. Then we discuss a procedure to obtain the full ef fective action with respect to light particles in a typical example of the system consisting of a (t, b) doublet, gauge bosons and a Higgs doublet, re garding only the t quark as a heavy particle.