  We consider an infrared truncated massive minimally coupled scalar field with
a quartic self-interaction in the locally de Sitter background of an inflating
universe. We compute the two-point correlation function of the scalar and the
mean squared fluctuations (variance) of the field variation analytically, at
tree, one- and two-loop order. The one-loop correlator at a fixed comoving
separation asymptotes to zero in the massive case but grows, at late times,
like $-\lambda\ln^2(a)$ in the massless limit, where $a$ is the cosmic scale
factor. For a fixed physical distance, on the other hand, it grows, at late
times, like $-\lambda\ln^3(a)$ in the massless limit. This growth is severely
suppressed in the massive case. In fact, the one-loop correlator asymptotes
effectively to zero for masses larger than half the expansion rate. We find out
also that the tree-order variance of field variation decreases when quantum
corrections are included. Hence, the actual effect that any local observer
perceives in the field strength as fluctuations happen does not deviate from
the average effect as much as the tree-order variance implies.
