It is well known that the correlation functions of a scalar field in a
quasi-de Sitter space exhibit at the loop level cumulative infra-red effects
proportional to the total number of e-foldings of inflation. Using the in-in
formalism, we explore the behavior of these infra-red effects in the large N
limit of an O(N) invariant scalar field theory with quartic self-interactions.
By resumming all higher-order loop diagrams non-perturbatively, we show that
the connected four-point correlation function, which is a signal of
non-Gaussianity, is non-perturbatively enhanced with respect to its tree-level
value.Comment: 17 pages, v2: minor corrections, to appear in jca
