Systematics of Adiabatic Modes: Flat Universes
Abstract
Adiabatic modes are cosmological perturbations that are locally indistinguishable from a (large) change of coordinates. At the classical level, they provide model independent solutions. At the quantum level, they lead to soft theorems for cosmological correlators. We present a systematic derivation of adiabatic modes in spatially-flat cosmological backgrounds with asymptotically-perfect fluids. We find several new adiabatic modes including vector, time-dependent tensor and time-dependent scalar modes. The new vector and tensor modes decay with time in standard cosmologies but are the leading modes in contracting universes. We present a preliminary derivation of the related soft theorems. In passing, we discuss a distinction between classical and quantum adiabatic modes, we clarify the subtle nature of Weinberg second adiabatic mode and point out that the adiabatic nature of a perturbation is a gauge dependent statement.
Keywords
Cite
@article{arxiv.1710.02177,
title = {Systematics of Adiabatic Modes: Flat Universes},
author = {Enrico Pajer and Sadra Jazayeri},
journal= {arXiv preprint arXiv:1710.02177},
year = {2019}
}