  Using a method mixing Mellin-Barnes representation and Borel resummation we
show how to obtain hyperasymptotic expansions from the (divergent) formal power
series which follow from the perturbative evaluation of arbitrary "$N$-point"
functions for the simple case of zero-dimensional $\phi^4$ field theory. This
hyperasymptotic improvement appears from an iterative procedure, based on
inverse factorial expansions, and gives birth to interwoven non-perturbative
partial sums whose coefficients are related to the perturbative ones by an
interesting resurgence phenomenon. It is a non-perturbative improvement in the
sense that, for some optimal truncations of the partial sums, the remainder at
a given hyperasymptotic level is exponentially suppressed compared to the
remainder at the preceding hyperasymptotic level. The Mellin-Barnes
representation allows our results to be automatically valid for a wide range of
the phase of the complex coupling constant, including Stokes lines. A numerical
analysis is performed to emphasize the improved accuracy that this method
allows to reach compared to the usual perturbative approach, and the importance
of hyperasymptotic optimal truncation schemes.
