%\begin{displaymath}
% \sigma_{\gamma\gamma\rightarrow t\bar{t}}^0 \left(s\right)
%=\frac{2 \pi \beta {\alpha^2} Q^4 N_c}{s} | M |^2
%\end{displaymath}
\begin{displaymath}
 \sigma_{\gamma\gamma\rightarrow t\bar{t}}^0 \left(s\right) 
 =\frac{\sigma_{++}+\sigma_{+-}+\sigma_{-+}+\sigma_{--}}{4}\qquad 
 , \qquad \beta =\wurzel
\end{displaymath}
\begin{displaymath}
\sigma_{++}=\sigma_{--}=\frac{2 \pi \beta {\alpha^2} Q^4 N_c}{s}
\left[ 2\left(1+{\beta}^2\right) 
+ \frac{\left(1-{\beta}^4\right)}{\beta} \ln \left(\frac{1+\beta}
           {1-\beta}\right) \right]
\end{displaymath}
\begin{displaymath}
\sigma_{+-}=\sigma_{-+}=\frac{2 \pi \beta {\alpha^2} Q^4 N_c}{s}
\left[ -10+2{\beta}^2+\frac{5-{\beta}^4}{\beta}
 \ln\left(\frac{1+\beta}{1-\beta}\right) \right]
\end{displaymath}
