Gauge invariant Boltzmann equation and the fluid limit
Cyril Pitrou
TL;DR
This paper develops a gauge invariant formulation of the collisionless Boltzmann equation up to second order in cosmological perturbations, enabling consistent analysis of fluid limits in cosmology.
Contribution
It introduces a gauge invariant distribution function and brightness, and derives the gauge invariant fluid limit for the collisionless Boltzmann equation.
Findings
Gauge dependence of the distribution function analyzed
Gauge invariant distribution function constructed
Gauge invariant fluid limit derived
Abstract
This article investigates the collisionless Boltzmann equation up to second order in the cosmological perturbations. It describes the gauge dependence of the distribution function and the construction of a gauge invariant distribution function and brightness, and then derives the gauge invariant fluid limit.
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