Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables

Abstract

We list all possible dimension-six CP-conserving $S{U}_c(3)\times S{U}_L(2)\times U_Y(1)$ invariant operators involving the third-family quarks which could be generated by new physics at a higher scale. Expressions for these operators after electroweak gauge symmetry breaking and the induced effective couplings $Wt\bar{b}$, $Xb\bar{b}$ and $Xt\bar{t}$ $(X=Z,\gamma ,g,H)$ are presented. Analytic expressions for the tree level contributions of all these operators to the observables $R_b$ and $A_{FB}^b$ at LEP I, $\sigma (e^{+}{e}^{-}\to b\bar{b})$ and $A_{FB}^b$ at LEP II, $\sigma (e^{+}{e}^{-}\to t\bar{t})$ and $A_{FB}^t$ at the NLC, as well as $\sigma (p\bar{p}\to t\bar{b}+X)$ at the Tevatron upgrade, are provided. The effects of these operators on different electroweak observables are discussed and numerical examples presented. Numerical analyses show that in the coupling region allowed by $R_b$ and $A_{FB}^b$ at LEP I, some of the new physics operators can still have significant contributions at LEP II, the Tevatron and the NLC.

Comments: 25 pages