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's second adiabatic mode and point out that the adiabatic nature of a perturbation is a gauge dependent statement.
| Original language | English |
|---|---|
| Article number | 013 |
| Journal | Journal of Cosmology and Astroparticle Physics |
| Volume | 2018 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 9 Mar 2018 |
Funding
Santoni for comments on the draft. E.P. and S.J. are supported by the Delta-ITP consortium, a program of the Netherlands organization for scientific research (NWO) that is funded by the Dutch Ministry of Education, Culture and Science (OCW). S.J. would like to thank Hassan Firouzjahi and Ali Akbar Abolhasani for useful discussions and continuous encouragements. S.J. also thanks Utrecht University for the warm hospitality during the completion of this project. The work of S.J. is also supported by the Iranian National Elites Foundation(BMN).
Keywords
- cosmological perturbation theory
- inflation
- nongaussianity
- physics of the early universe
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