U (a, z) = \frac{e^{- \frac{1}{4} z^{2}}}{Γ (\frac{3}{4} + \frac{1}{2} a)} \int_{0}^{\infty} t^{\frac{1}{2} a - \frac{1}{4}} e^{- t} {(z^{2} + 2 t)}^{- \frac{1}{2} a - \frac{1}{4}} d t