A bstract We point out that hints of deviations from unitarity in the first row CKM matrix may be explained by presence a single vector-like top. study how stringent experimental constraints arising CP Violation kaon sector and meson mixing such as $$ {D}^0\hbox{-} {\overline{D}}^0,{K}^0\hbox{-} {\overline{K}}^0 D</mml...