\[P^{-\mu}_{\nu}\left(\cosh\xi\right)=\frac{1}{\nu^{\mu}}\left(\frac{\xi}{\sinh%
\xi}\right)^{1/2}I_{\mu}\left(\left(\nu+\tfrac{1}{2}\right)\xi\right)\*\left(1%
+O\left(\frac{1}{\nu}\right)\right),\]