The Trans-Planckian Problem of Inflationary Cosmology

TL;DR

This paper examines how assumptions about physics beyond the Planck scale can influence inflationary cosmology predictions, showing that modifications at super-Planckian scales can lead to significant deviations in the expected fluctuation spectrum.

Contribution

It introduces modified dispersion relations to model super-Planck scale effects and demonstrates their impact on inflationary fluctuation predictions.

Findings

Inflation predictions depend on assumptions about super-Planck scale physics.

Modified dispersion relations can cause deviations from standard inflationary spectra.

Super-Planckian physics may influence observable cosmological fluctuations.

Abstract

In most current models of inflation based on a weakly self-coupled scalar matter field minimally coupled to gravity, the period of inflation lasts so long that, at the beginning of the inflationary period, the physical wavelengths of comoving scales which correspond to the present large-scale structure of the Universe were smaller than the Planck length. Thus, the usual computations of the spectrum of fluctuations in these models involve extrapolating low energy physics (both in the matter and gravitational sector) into regions where this physics is not applicable. In this paper we demonstrate that the usual predictions of inflation for the spectrum of cosmological fluctuations do indeed depend on the hidden assumptions about super-Planck scale physics. We introduce a class of modified dispersion relations to mimic possible effects of super-Planck scale physics, and show that in some cases important deviations from the usual predictions of inflation are obtained. Some implications of this result for the unification of fundamental physics and early Universe cosmology are discussed.