Cosmological non-linearities as an effective fluid

By D. Baumann, Alberto Nicolis, L. Senatore, M. Zaldarriaga. 2010

624 citations recorded by the source corpus.

The universe is smooth on large scales but very inhomogeneous on small scales. Why is the spacetime on large scales modeled to a good approximation by the Friedmann equations? Are we sure that small-scale non-linearities do not induce a large backreaction? Related to this, what is the effective theory that describes the universe on large scales? In this paper we make progress in addressing these questions. We show that the effective theory for the long-wavelength universe behaves as a viscous fluid coupled to gravity: integrating out short-wavelength perturbations renormalizes the homogeneous background and introduces dissipative dynamics into the evolution of long-wavelength perturbations. The effective fluid has small perturbations and is characterized by a few parameters like an equation of state, a sound speed and a viscosity parameter. These parameters can be matched to numerical simulations or fitted from observations. We find that the backreaction of small-scale non-linearities is very small, being suppressed by the large hierarchy between the scale of non-linearities and the horizon scale. The effective pressure of the fluid is always positive and much too small to significantly affect the background evolution. Moreover, we prove that virialized scales decouple completely from the large-scale dynamics, at all orders in the post-Newtonian expansion. We propose that our effective theory be used to formulate a well-defined and controlled alternative to conventional perturbation theory, and we discuss possible observational applications. Finally, our way of reformulating results in second-order perturbation theory in terms of a long-wavelength effective fluid provides the opportunity to understand non-linear effects in a simple and physically intuitive way.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/67c7813ea707cdb049acbb58d41cb9ca7d3f0d9e

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Citations in the corpus

The cosmological analysis of the SDSS/BOSS data from the Effective Field Theory of Large-Scale Structure (2019, background): “[1], and this paper which should be understood as a companion, are the completion of a long journey for the EFTofLSS, which started with the initial development of the theory [7, 8, 9] and underwent many important steps in order for it to be compared to observational data.”
The IR-resummed Effective Field Theory of Large Scale Structures (2014, methodology): “This led to the development of the Effective Theory of Large Scale Structure [4, 5].”
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The effective field theory of cosmological large scale structures (2012, methodology): “The effective field theory (EFT) of the long distance universe was initially developed by some of us in [4].”
Limits on wCDM from the EFTofLSS with the PyBird code (2020, methodology): “2The initial formulation of the EFTofLSS was performed in Eulerian space in [7, 8], and subsequently extended to Lagrangian space in [9].”
The Effective Field Theorist's Approach to Gravitational Dynamics (2016, background): “Therefore, virialized structure ‘decouples,’ since its contribution is suppressed compared to non-virialized sources, for which pren ∼ ρv(2) > 0 [151].”
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Consistent modeling of velocity statistics and redshift-space distortions in one-loop perturbation theory (2020, methodology): “In this paper we shall consider 1-loop perturbation theory in both the Eulerian (EPT; [16–27]) and Lagrangian (LPT; [28–39]) formulations, and their extensions as an effective field theories [39–41].”
The Ups and Downs of Early Dark Energy solutions to the Hubble tension: A review of models, hints and constraints circa 2023 (2023, background): “[229] Daniel Baumann, Alberto Nicolis, Leonardo Senatore, and Matias Zaldarriaga, “Cosmological Non-Linearities as an Effective Fluid,” JCAP 07, 051 (2012), arXiv:1004.”
On the statistics of biased tracers in the Effective Field Theory of Large Scale Structures (2015, background): “The Effective Field Theory of Large Scale Structures (EFTofLSS) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16] is a theoretical framework that aims at developing a rigorous analytic understanding of the clustering of LSS, through a perturbative expansion in the size of the fluctuations.”
Inflation and String Theory (2014, background): “This is one of the objectives of the recently developed ‘effective theory of large-scale structure’ [162,163] (see also [164–169]).”
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The Lagrangian-space Effective Field Theory of large scale structures (2013, methodology): “The Baryonic Acoustic Oscillation (BAO) technique and the study of weak lensing by Large Scale Structure (LSS) have emerged as very powerful techniques to constrain the properties of the “dark-energy”.”
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On the renormalization of the effective field theory of large scale structures (2013, background): “The recently developed Effective Field Theory of Large Scale Structure (EFToLSS) [2, 3, 4] successfully addresses all of the above issues.”