2019/12/31 by Matthew Baumgart, Raman Sundrum · 72 citations
Physics and Astronomy · #Ansatz #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #De Sitter universe #Propagator #Quantum field theory #Renormalization #Renormalization group #Resummation #Scalar (mathematics) #Scalar field #Semiclassical physics #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1007/jhep07(2020)119
published in Journal of High Energy Physics 2020(7) (Springer Nature) · 39 pages, 7 figures. v2: Appendix edited for clarity and references added. v3: Discussion of i*epsilon for perturbation theory, and references added
openalex created_date 2019/12/26 · openalex publication_date 2020/07/01 · arxiv created 2020/10/21 · arxiv updated 2020/10/22 · openalex updated_date 2026/08/06
A bstract Light scalars in inflationary spacetimes suffer from logarithmic infrared divergences at every order in perturbation theory. This corresponds to the scalar field values in different Hubble patches undergoing a random walk of quantum fluctuations, leading to a simple toy “landscape” on superhorizon scales, in which we can explore questions relevant to eternal inflation. However, for a sufficiently long period of inflation, the infrared divergences appear to spoil computability. Some form of renormalization group approach is thus motivated to resum the log divergences of conformal time. Such a resummation may provide insight into De Sitter holography. We present here a novel diagrammatic analysis of these infrared divergences and their resummation. Basic graph theory observations and momen- tum power counting for the in-in propagators allow a simple and insightful determination of the leading-log contributions. One thus sees diagrammatically how the superhorizon sector consists of a semiclassical theory with quantum noise evolved by a first-order, interacting classical equation of motion. This rigorously leads to the “Stochastic Inflation” ansatz developed by Starobinsky to cure the scalar infrared pathology nonperturbatively. Our approach is a controlled approximation of the underlying quantum field theory and is systematically improvable.