the concept of effective theories appears again to be a highly efficient tool to make progress [@Beneke1]. For the $t\bar t$ threshold such a framework is already provided by the effective theory NRQCD itself, since it automatically achieves an expansion in the off-shellness of the top quark through the non-relativistic expansion in $v$. The NRQCD effective theory formalism can be extended to account for electroweak corrections. For example, including the electroweak radiative corrections to the top quark two-point function in the NRQCD matching conditions one obtains the additional heavy quark bilinear terms[^2] $$\begin{aligned}
 \label{Gtop}
 \delta {\cal L} = \sum_{{\mbox{\scriptsize\boldmath $p$}}} \psip{{\mbox{\scriptsize\boldmath $p$}}}^\dagger \: \frac{i}{2} \Gamma_t\: 
  \psip{{\mbox{\scriptsize\boldmath $p$}}} \ +\  
  \sum_{{\mbox{\scriptsize\boldmath $p$}}}   \chip{{\mbox{\scriptsize\boldmath $p$}}}^\dagger\: \frac{i}{2} \Gamma_t\: \chip{{\mbox{\scriptsize\boldmath $p$}}} \,\end{aligned}$$ in the effective Lagrangian, where $\psip{p}$ and $\chip{p}$ represent Pauli spinor field operators destroying top and antitop quarks, respectively. For simplicity color indices are suppressed throughout this paper. The terms in Eq.(\[Gtop\]) reproduce the replacement rule $E\to E+i\Gamma_t$. They render the effective theory Lagrangian non-hermitian because they describe an absorptive on-shell process that has been integrated out from the theory. Nevertheless, they allow for a correct determination of the total cross section from the forward scattering amplitude using the optical theorem and 