Back-Reaction and the Trans-Planckian Problem of Inflation Revisited

TL;DR

This paper revisits the back-reaction of trans-Planckian physics on inflation, suggesting that ultraviolet fluctuations may lead to a cosmological constant renormalization rather than preventing inflation.

Contribution

It clarifies the role of back-reaction effects from high-energy modes, proposing they cause a renormalization of the inflation-driving cosmological constant.

Findings

Back-reaction effects may not hinder inflation.

Ultraviolet fluctuations could lead to a cosmological constant renormalization.

Challenges previous constraints on trans-Planckian effects.

Abstract

It has recently been suggested that Planck scale physics may effect the evolution of cosmological fluctuations in the early stages of cosmological inflation in a non-trivial way, leading to an excited state for modes whose wavelength is super-Planck but sub-Hubble. In this case, the issue of how this excited state back-reacts on the background space-time arises. In fact, it has been suggested that such back-reaction effects may lead to tight constraints on the magnitude of possible deviations from the usual predictions of inflation. In this note we discuss some subtle aspects of this back-reaction issue and point out that rather than preventing inflation, the back-reaction of ultraviolet fluctuations may simply lead to a renormalization of the cosmological constant driving inflation.