On the adiabatic subtraction of cosmological perturbations

TL;DR

This paper reviews the effects of adiabatic subtraction on cosmological perturbations, highlighting differences between standard and alternative renormalization methods in inflationary models.

Contribution

It compares standard adiabatic subtraction with an alternative approach, showing how the latter removes intermediate-wavelength renormalization effects.

Findings

Standard adiabatic subtraction alters power spectra at intermediate wavelengths.

Alternative prescription by Dabrowski and Dunne eliminates these intermediate effects.

Differences are significant for light fields in de Sitter space.

Abstract

Adiabatic subtraction is a popular method of renormalization of observables in quantum field theories on a curved spacetime. When applied to the computation of the power spectra of light ($m\ll H$) fields on de Sitter space with flat Friedmann-Lema\^{i}tre-Robertson-Walker slices, the standard prescriptions of adiabatic subtraction, traceable back to Parker's work, lead to results that are significantly different from the standard predictions of inflation not only in the ultraviolet ($k\gg aH$) but also at intermediate ($m\ll k/a\lesssim H$) wavelengths. In this paper we review those results and we contrast them with the power spectra obtained using an alternative prescription for adiabatic subtraction applied to quantum field theoretical systems by Dabrowski and Dunne. This prescription eliminates the intermediate-wavelength effects of renormalization that are found when using the standard one.