Breakdown of Semiclassical Methods in de Sitter Space

Abstract

Massless interacting scalar fields in de Sitter space have long been known to experience large fluctuations over length scales larger than Hubble distances. A similar situation arises in condensed matter physics in the vicinity of a critical point, and in this better-understood situation these large fluctuations indicate the failure in this regime of mean-field methods. We argue that for non-Goldstone scalars in de Sitter space, these fluctuations can also be interpreted as signaling the complete breakdown of the semi-classical methods widely used throughout cosmology. By power-counting the infrared properties of Feynman graphs in de Sitter space we find that for a massive scalar interacting through a λϕ^4$ interaction, control over the loop approximation is lost for masses smaller than m \simeq \sqrt λH/2π, where H is the Hubble scale. We briefly discuss some potential implications for inflationary cosmology.

24 pages, 7 figures, v2; added references, clarified the resummation discussion

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Cited by in corpus (8)

• The IR stability of de Sitter: Loop corrections to scalar propagators
• On the proper treatment of massless fields in Euclidean de Sitter space
• On Features and Nongaussianity from Inflationary Particle Production
• On the Perturbative Stability of Quantum Field Theories in de Sitter Space
• Cosmological UV/IR Divergences and de-Sitter Spacetime
• One-loop corrections to the power spectrum in general single-field inflation
• Large-Scale Suppression from Stochastic Inflation
• On 1-loop diagrams in AdS space and the random disorder problem