Error bounds and exponential improvement for the asymptotic expansion of the Barnes G-function

In this paper, we establish new integral representations for the remainder term of the known asymptotic expansion of the logarithm of the Barnes G-function. Using these representations, we obtain explicit and numerically computable error bounds for the asymptotic series, which are much simpler than those obtained earlier by other authors. We find that along the imaginary axis, suddenly infinitely many exponentially small terms appear in the asymptotic expansion of the Barnes G-function. Employing one of our representations for the remainder term, we derive an exponentially improved asymptotic expansion for the logarithm of the Barnes G-function, which shows that the appearance of these exponentially small terms is in fact smooth, thereby proving the Berry transition property of the asymptotic series of the G-function.