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arXiv · 1710.02177

Systematics of Adiabatic Modes: Flat Universes

Enrico Pajer·Sadra Jazayeri
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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.

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Enrico Pajer, Sadra Jazayeri. 2017-10-05. Systematics of Adiabatic Modes: Flat Universes. https://doi.org/10.1088/1475-7516%2F2018%2F03%2F013

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