\subsubsection{The leptonic weak mixing angle}

Determinations of the weak mixing angle $\sintw$ are made from a variety of measurements, such as the leptonic and hadronic forward-backward asymmetries or the $\tau$ polarization in ${\rm Z} \to \tau\tau$ decays. These measurements will be performed with high statistics at the occasion of the line-shape scan without polarized beams.  
\\ 

The single most precise measurement, however, comes from the inclusive left-right beam-polarization asymmetry $\ALR$. This quantity can be measured from the total cross-section asymmetry upon reversal of the polarization of the $\epem$ system. For the same level of polarization in collisions as that observed at LEP, and assuming that a fraction of the bunches can be selectively depolarized, a simultaneous measurement~\cite{Blondel:1987wr} of the beam polarization and of the left-right  asymmetry $\ALR$ can be envisioned at TLEP. For one year of data taking with a luminosity of $10^{35}~\cms$, a precision on $\ALR$ of the order of $10^{-5}$ -- or a precision on $\sintw$ of the order of $10^{-6}$ -- is achievable. Other beam polarization asymmetries for selected final states, like for example $A_{\rm FB}^{\rm pol,f}$, would allow precise measurements of the Electroweak couplings, and become an interesting tool for flavour selection.\\
\textbf{\textit{A precision of $\boldsymbol{\it 10^{-6}}$ on $\boldsymbol{\it \sin^2\theta^{eff}_W}$  is a reasonable goal for the measurement of the leptonic weak mixing angle at TLEP.}}

