The dynamical models and the Z→bbˉZ \to b \bar{b} asymmetry}

Motivated by the $3.2\sigma(1.4\sigma)$ deviations between the recent experimental value for $A_{FB}^{b}(R_{b})$ and the standard model(SM) prediction, we examine the effect of new physics(NP) on the $Zb \bar{b}$ couplings $g_L^b$ and $g_R^b$. First we focus our attention on the dynamical models. Then, using effective lagrangean techniques, we discuss the corrections of NP to $g_L^b$ and $g_R^b$. We find some kinds of NP might explain the recently experimental data about $R_b$ and $A_{FB}^b$. However, the free parameters of these kinds of NP must be severely constrained.Comment: Latex files, 13 pages and 1 figur

The process e+e−→tˉce^{+}e^{-}\to \bar{t}c in topcolor-assisted technicolor models

We consider the flavor changing neutral current(FCNC) process $e^{+}e^{-}\to\bar{t}c$(or $t\bar{c}$) in the context of topcolor-assisted technicolor(TC2) models. We find that the contributions of charged scalars (technipions and top-pions) and topcolor gauge bosons are negligibly small. The neutral scalars (top-pion $\pi_{t}^{0}$ and top-Higgs $h_{t}^{0}$) can give significant contributions to this process. With reasonable values of the parameters in TC2 models, there will be several tens of the observable $\bar{t}c$ events to be generated in the future $e^{+}e^{-}$ linear colliders.Comment: Latex files, 15 pages and 6 figure