CP asymmetries induced by particle widths: Application to top-quark decays

An on-shell unstable particle produced in a tree-level process, such as W in tqW, induces a CP violating signal through its width. This effect arises from an Im(tree)×Re(loop) type of interference. Among tqqq processes (e.g., tbcb) proceeding either through the tree-level tqW or the one-loop tq+(virtual g) reactions, the CP asymmetry is largest for the case tdcd and is of scrO(/2) in Wolfensteins parametrization. The resulting effects are found to be small in the standard model, but are much larger than those obtained for radiative top-quark decays. We also briefly discuss B decays where such a mechanism may cause CP violation in, for example, bse+e-.