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7–9 Sept 2020
CERN
Europe/Zurich timezone

Live Talk 6: De Sitter Diagrammar and the Resummation of Time [Matthew Baumgart]

9 Sept 2020, 16:00
1h
CERN

CERN

Virtual meeting on Zoom

Description

Abstract: Light scalars in inflationary spacetimes suffer from infrared logarithmic 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 momentum power counting for the in-in propagators allow a simple and insightful determination of the leading-log infrared divergences. 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 theStochastic 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.

Presentation materials