Breakdown of Semiclassical Methods in de Sitter Space
May, 2010
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Abstract: (arXiv)
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 \lambda \phi^4$ interaction, control over the loop approximation is lost for masses smaller than m \simeq \sqrt \lambda H/2\pi, where H is the Hubble scale. We briefly discuss some potential implications for inflationary cosmology.Note:
- 24 pages, 7 figures, v2/ added references, clarified the resummation discussion
- space-time: de Sitter
- field theory: scalar: massless
- phi**n model: 4
- fluctuation
- approximation: semiclassical
- slow-roll approximation
- critical phenomena
- cosmological model
- condensed matter
- Feynman graph: higher-order
References(76)
Figures(7)