Kinetic Field Theory: Exact free evolution of Gaussian phase-space correlations

TL;DR

This paper introduces an exact method using diagrammatic techniques to describe the evolution of Gaussian phase-space correlations in cosmic structure formation, improving upon previous perturbative approaches.

Contribution

It develops a diagrammatic framework to exactly treat correlations between all phase-space coordinates, enabling precise calculation of density cumulants in cosmic structure evolution.

Findings

Derived explicit expressions for phase-space density cumulants of arbitrary order.

Demonstrated the use of Feynman rules for non-linear coupling of free streaming kinematics.

Provided a foundation for future perturbation theory investigations.

Abstract

In recent work we developed a description of cosmic large scale structure formation in terms of non-equilibrium ensembles of classical particles, with time evolution obtained in the framework of a statistical field theory. In these works, the initial Gaussian correlations between particles have so far been treated perturbatively or restricted to pure momentum correlations. Here we treat the correlations between all phase-space coordinates exactly by adopting a diagrammatic language for the different forms of correlations, directly inspired by the Mayer cluster expansion. We will demonstrate that explicit expressions for phase-space density cumulants of arbitrary $n$-point order, which fully capture the non-linear coupling of free streaming kinematics due to initial correlations, can be obtained from a simple set of Feynman rules. These cumulants will be the foundation for further investigations of interacting perturbation theory.