The Laplace transform of the lognormal distribution

Abstract

We study the analytical properties of the Laplace transform of the lognormal distribution. Two integral expressions for the analytic continuation of the Laplace transform of the lognormal distribution are provided, one of which takes the form of a Mellin-Barnes integral. As a corollary, we obtain an integral expression for the characteristic function; we show that the integral expression derived by Leipnik in [11] is incorrect. We present two approximations for the Laplace transform of the lognormal distribution, both valid in $\mathbb{C} \setminus(-\infty,0]$. In the last section, we discuss how one may use our results to compute the density of a sum of independent lognormal random variables.