Neutral top-pion and the rare top decays $t\to c l_{i} l_{j}$

Abstract

We study the rare top decays $t\to c l_{i} l_{j}(l=\tau,\mu,or e)$ 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 $m_{\pi_{t}}=150 GeV$ and the parameter $\epsilon=0.08$, the branching ratio $Br$(t$\to c \tau \tau)$ can reach $7.1\times10^{-7}$. 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$) is in the range of 1.8$\times10^{-10}\sim1.7\times10^{-8}$.