Regular Article - Theoretical Physics
Penguin and box diagrams in unitary gauge
Department of Physics and Center for Theoretical Sciences, National Taiwan University, Taipei, 106, Taiwan
2 Department of Physics and Astronomy, Iowa State University, Ames, IA, 50011, USA
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Published online: 16 October 2009
We evaluate one-loop diagrams in the unitary gauge that contribute to flavor-changing neutral current (FCNC) transitions involving two and four fermions. Specifically, we deal with penguin and box diagrams arising within the standard model (SM) and in nonrenormalizable extensions thereof with anomalous couplings of the W boson to quarks. We show explicitly in the SM the subtle cancellation among divergences from individual unitary-gauge contributions to some of the physical FCNC amplitudes and derive expressions consistent with those obtained using R ξ gauges in the literature. Some of our results can be used more generally in certain models involving fermions and gauge bosons which have interactions similar in form to those we consider.
© Springer-Verlag, 2009