Three-point phase correlations: A new measure of non-linear large-scale structure

TL;DR

This paper introduces the line correlation function, a new statistical measure based on phase correlations in the density field, which effectively probes non-linear large-scale structure with advantages over traditional methods.

Contribution

The authors derive an analytical expression for the line correlation function, demonstrating its sensitivity to non-linear gravitational evolution and its robustness compared to standard measures like the bispectrum.

Findings

Line correlation agrees with simulations for r<30 Mpc/h.

Extended predictions match simulations in the strongly non-linear regime (r<2 Mpc/h).

Line correlation is bias-independent and less affected by Gaussian variance.

Abstract

We derive an analytical expression for a novel large-scale structure observable: the line correlation function. The line correlation function, which is constructed from the three-point correlation function of the phase of the density field, is a robust statistical measure allowing the extraction of information in the non-linear and non-Gaussian regime. We show that, in perturbation theory, the line correlation is sensitive to the coupling kernel F_2, which governs the non-linear gravitational evolution of the density field. We compare our analytical expression with results from numerical simulations and find a 1-sigma agreement for separations r<30 Mpc/h. Fitting formulae for the power spectrum and the non-linear coupling kernel at small scales allow us to extend our prediction into the strongly non-linear regime where we find a 1-sigma agreement with the simulations for r<2 Mpc/h. We discuss the advantages of the line correlation relative to standard statistical measures like the bispectrum. Unlike the latter, the line correlation is independent of the bias, in the regime where the bias is local and linear. Furthermore, the variance of the line correlation is independent of the Gaussian variance on the modulus of the density field. This suggests that the line correlation can probe more precisely the non-linear regime of gravity, with less contamination from the power spectrum variance.