Effective field theory of a single scalar pion field for large scale structure in the Universe

TL;DR

This paper develops an effective field theory for a scalar 'pion' field representing large scale structure in the universe, organizing perturbations systematically while matching simulations and exploring new analysis variables.

Contribution

It introduces a systematic EFT framework based on a Goldstone boson of broken spacetime symmetry for modeling cosmic large scale structure.

Findings

Next-to-leading order corrections to the power spectrum are computed.

EFT coefficients are measured from N-body simulations.

The pion field approach aligns with simulation data and offers new analysis variables.

Abstract

We discuss the effective field theory of large scale structure in terms of a single scalar degree of freedom, corresponding to the velocity potential of the matter fluid in a $\Lambda$CDM universe. This cosmic ``pion'' field is nonlinearly related to the overdensity and the gravitational potential, and corresponds to the Goldstone boson of spontaneously broken spacetime symmetry, allowing us to organize perturbation theory in a systematic way while keeping the symmetries manifest. We develop the effective field theory of the pion field to next-to-leading order, and we use it to calculate the corrections to the power spectrum and to check that these are consistent with the consistency relations of spontaneously broken spacetime symmetry. We compare our results against computer simulations for the evolution of large scale structure in the pion field picture, and we make use of N-body simulations to measure EFT coefficients and analyze the growth of additional degrees of freedom in the deep nonlinear regime. We conclude with a discussion of how the pion field picture may help suggest new variables for analyzing simulations and experimental surveys of large scale structure.