Large-scale 3D galaxy correlation function and non-Gaussianity

TL;DR

This paper analyzes the large-scale 3D galaxy correlation function, incorporating relativistic effects and primordial non-Gaussianity, highlighting the importance of a relativistic approach for accurate cosmological measurements.

Contribution

It provides a comprehensive analysis of the 3D galaxy correlation function including all relativistic effects and their interplay with primordial non-Gaussianity and modified gravity models.

Findings

The correlation function exhibits nonzero dipole and octupole moments.

Relativistic effects and primordial non-Gaussianity have comparable impacts on multipoles.

Modified gravity models influence large-scale correlations and non-Gaussian signals.

Abstract

We investigate the properties of the 2-point galaxy correlation function at very large scales, including all geometric and local relativistic effects -- wide-angle effects, redshift space distortions, Doppler terms and Sachs-Wolfe type terms in the gravitational potentials. The general three-dimensional correlation function has a nonzero dipole and octupole, in addition to the even multipoles of the flat-sky limit. We study how corrections due to primordial non-Gaussianity and General Relativity affect the multipolar expansion, and we show that they are of similar magnitude (when f_NL is small), so that a relativistic approach is needed. Furthermore, we look at how large-scale corrections depend on the model for the growth rate in the context of modified gravity, and we discuss how a modified growth can affect the non-Gaussian signal in the multipoles.