Eternal inflation and energy conditions in de Sitter spacetime

TL;DR

This paper investigates the conditions under which eternal inflation occurs, emphasizing the role of quantum fluctuations in violating the Null Energy Condition within de Sitter spacetime.

Contribution

It demonstrates that quantum fluctuations can induce NEC violations necessary for eternal inflation, highlighting the importance of quantum effects over classical matter sources.

Findings

Quantum fluctuations lead to large-scale NEC violations.

Classical or semiclassical NEC violations are absent with light scalar fields.

Backreaction of quantum fluctuations is crucial for understanding eternal inflation.

Abstract

Eternal inflation is shown to require violations of the Null Energy Condition (NEC) on superhorizon scales. With light scalar fields as the matter sources in a de Sitter background, there can be no classical or semiclassical violations of the NEC. However, quantum fluctuations of the energy-momentum tensor, described by an expectation value of four field operators, do lead to large-scale NEC violations. The backreaction of such quantum fluctuations on the inflating spacetime is generally deduced at a heuristic level and leads to the eternal inflation scenario. A rigorous treatment of the backreaction will necessarily include fluctuations of the metric, and several new effects are expected to come into play.