On the Tail Probabilities of Aggregated Lognormal Random Fields with Small Noise

We develop asymptotic approximations for the tail probabilities of integrals of lognormal random fields. We consider the asymptotic regime that the variance of the random field converges to zero. Under this setting, the integral converges to its limiting value. This analysis is of interest in considering short-term portfolio risk analysis (such as daily performance), for which the variances of log-returns could be as small as a few percent.