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We explicitly show that the one loop IR correction to the two--point functionin de Sitter space scalar QFT does not reduce just to the mass renormalization.The proper interpretation of the loop corrections is via particle creationrevealing itself through the generation of the quantum averages $<a^+_p a_p>$,$<a_p a_{-p}>$ and $<a^+_p a^+_{-p}>$, which slowly change in time. We showthat this observation in particular means that loop corrections to correlationfunctions in de Sitter space can not be obtained via analytical continuation ofthose calculated on the sphere.  We find harmonics for which the particle number $<a^+_p a_p>$ dominates overthe anomalous expectation values $<a_p a_{-p}>$ and $<a^+_p a^+_{-p}>$. Forthese harmonics the Dyson--Schwinger equation reduces in the IR limit to thekinetic equation. We solve the latter equation, which allows us to sum up allloop leading IR contributions to the Whiteman function. We perform thecalculation for the principle series real scalar fields both in expanding andcontracting Poincare patches.

IR divergences and kinetic equation in de Sitter space. (Poincare patch; Principal series)