Effective field theory for nonstandard top quark couplings

We present an effective-field-theory calculation of the effect of a dimension-six operator involving the top quark on precision electroweak data via a top-quark loop. We demonstrate the renormalizability, in the modern sense, of the effective field theory. We use the oblique parameter Uˆ to bound the coefficient of the operator, and compare with the bound derived from top-quark decay.