Separate universe approach and the evolution of nonlinear superhorizon cosmological perturbations

By G. Rigopoulos, E. Shellard. 2003

196 citations recorded by the source corpus.

In this paper we review the separate universe approach for cosmological perturbations and point out that it is essentially the lowest order approximation to a gradient expansion. Using this approach, one can study the nonlinear evolution of inhomogeneous spacetimes and find the conditions under which the long wavelength curvature perturbation can vary with time. When there is one degree of freedom or a well-defined equation of state the nonlinear long wavelength curvature perturbation remains constant. With more degrees of freedom it can vary and this variation is determined by the nonadiabatic pressure perturbation, exactly as in linear theory. We identify combinations of spatial vectors characterizing the curvature perturbation which are invariant under a change of time hypersurfaces.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ef2aaa24841f29c2fd3f5255f27e16331c8e175d

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In Astronomy and Astrophysics

1. D. Baumann
2. D. Green
3. Valentin Assassi
4. Yi Wang
5. T. Battefeld
6. R. Easther
7. L. Senatore
8. E. Pajer

Citations in the corpus

• Non-Gaussianities in multi-field inflation (2006, background): “Note that ζ is conserved on large scales in simple models, even beyond linear order [25, 26] 5.”
• Symmetries and loops in inflation (2012, background): “First of all, at tree level ζ̇ vanishes outside the horizon [1–5] and therefore any loop corrections that generate ζ̇ 6= 0 would be the leading effect.”