\begin{table}%t2
%\centering
\par
\caption{Parameters $c_0$ and $\alpha$ for the different cosmological
  models.\label{tab:1}}
\begin{tabular}{lrrr}
\hline\hline
model & $\sigma_8$ & $c_0$ & $\alpha$ \\
\hline
$\Lambda$CDM  & 0.90 & $ 9.59\pm0.07$ & $-0.102\pm0.004$ \\
Ratra-Peebles & 0.90 & $10.20\pm0.07$ & $-0.094\pm0.005$ \\
Ratra-Peebles & 0.82 & $ 9.30\pm0.06$ & $-0.108\pm0.005$ \\
SUGRA         & 0.90 & $11.15\pm0.09$ & $-0.094\pm0.006$ \\
SUGRA         & 0.76 & $ 9.46\pm0.07$ & $-0.099\pm0.005$ \\
OCDM          & 0.90 & $14.29\pm0.13$ & $-0.089\pm0.006$ \\
$w=-0.6$      & 0.90 & $11.32\pm0.09$ & $-0.092\pm0.005$ \\
$w=-0.6$      & 0.86 & $10.44\pm0.08$ & $-0.066\pm0.005$ \\
\hline
\end{tabular}
\end{table}