Like Sign Top Quark Pair Production at Linear Colliders

In the general two Higgs doublet model with flavor changing neutral Higgs couplings, neutral Higgs bosons may decay dominantly via $t\bar c$ or $\bar tc$ final states. At the linear collider, $e^+e^- \to h^0A^0$ or $H^0A^0$ production processes may result in $b\bar bt\bar c$, $W^+W^-t\bar c$ or $tt\bar c\bar c$ (or $\bar t\bar tcc$) final states. The process $\gamma\gamma \to h^0,\ A^0 \to t\bar c$ is also promising, but $e^+e^- \to (h^0,\ H^0) Z^0 \to t\bar c Z^0$ is relatively suppressed. The possibility of observing like sign lepton pairs, usually the hallmark for neutral meson mixing, is quite interesting since $T^0$ mesons do not even form.