Dynamical RG and Critical Phenomena in de Sitter Space.

Perturbative quantum field theory in de Sitter space is known to give rise a variety of contributions that diverge with time (secular terms). Despite significant progress, a complete understanding of the physical origin these divergences remains an outstanding problem. In this paper, we will study the origin of secular divergences in de Sitter space for interacting theories that are near attractive conformal fixed points. We show that the secular divergences are determined by the anomalous dimensions of the same theory in flat space and can be re-summed using the dynamical renormalization group. This behavior is mandatory at the conformal fixed point but we show that it holds away from the fixed point as well. We analyze this problem in general using conformal perturbation theory and study conformally coupled scalar fields in four and $4-\epsilon$ dimensions as examples.