  The perturbative calculation of the effect of fluctuations in the nonzero
frequency modes of a weakly interacting Bose gas on the condensation
temperature is reviewed. These dynamic modes, discarded in most of the recent
studies, have a temperature-induced energy gap that allows for a perturbative
approach. The simple, yet powerful algorithm used to calculate the effect in a
high-temperature expansion in conjunction with zeta function regularization of
infrared divergences is explained in detail. The algorithm is shown to be
reliable by demonstrating that it reproduces known results for a series of
examples. With two-loop contributions properly included, the dynamic modes are
seen not to lead to a shift in the condensation temperature, thus revising our
earlier finding obtained at one loop.
