\[G_{\ell}\left(\eta,\rho\right)\sim\frac{\rho^{-\ell}}{(\ell+\frac{1}{2})%
\lambda_{\ell}(\eta)C_{\ell}\left(\eta\right)}\*\sum_{k=2\ell+1}^{\infty}(-1)^%
{k}b_{k}t^{k/2}K_{k}\left(\textstyle 2\sqrt{t}\right),\]