CP Violation in $t\to W^{+}b$ Decays in Two-Higgs Doublet Model

Abstract

Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in $t\to W^{+}b$ decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from $W$ boson decays in $t\to W^{+}b$, defined by Grzcadkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of $(1-3)\times 10^{-4}$ for $\tan \beta =1.0$, where $\tan \beta$ is the ratio of vacuum expectation values for the two neutral Higgs bosons.

16 pages written in LaTex. 5 figures available upon request