Neutral top-pion and the rare top decays $t\to c{l}_i{l}_j$

Abstract

We study the rare top decays $t\to c{l}_i{l}_j(l=\tau ,\mu ,ore)$ in the framework of topcolor-assisted technicolor($TC2$) models. We find that the neutral top-pion ${\pi }_t^0$ can produce significant contributions to these processes via the flavor changing couplings ${\pi }_t^0\bar{t}c$ and ${\pi }_t^0{l}_i{l}_j$. For the ${\pi }_t^0$ mass $m_{{\pi }_t}=150GeV$ and the parameter $\epsilon =0.08$, the branching ratio $Br$(t$\to c\tau \tau )$ can reach $7.1\times 10^{-7}$. Taking into account the constraints of the present experimental limit of the process $\mu \to e\gamma$ on the free parameters of $TC2$ models, we find that the value of $Br$($t\to c\tau \mu$)$\approx$$Br$($t\to c\tau e$) is in the range of 1.8$\times 10^{-10}\sim 1.7\times 10^{-8}$.

To be published in Phys. D