Large tree-level CP violation in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$→${\mathit{tt}\mathit{¯}\mathit{H}}^0$ in the two-Higgs-doublet model

We find a large CP violation effect within the two-Higgs-doublet model for the reaction ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$→tt¯${\mathit{H}}^0$ at future linear colliders. The CP asymmetry arises already at the tree level as a result of interference between diagrams with ${\mathit{H}}^0$ emission from t (and t¯) and its emission from a ${\mathit{Z}}^0$ and can be about 10–20 %. In the best case one needs a few hundred ${\mathit{tt}\mathit{¯}\mathit{H}}^0$ events to observe CP violation at the 3σ level. © 1996 The American Physical Society.