Cosmological Perturbation Theory for streams of relativistic particles

Understand

Motion equations describing streams of relativistic particles and their properties are explored in detail in the framework of Cosmological Perturbation Theory.

• Those equations, derived in any metric both in the linear and nonlinear regimes, express the matter and momentum conservation.
• In this context we extend the setup of adiabatic initial conditions - that was initially performed in the Conformal Newtonian gauge - to the Synchronous gauge.
• The subhorizon limit of the nonlinear motion equations written in a generic perturbed Friedmann-Lema\^{i}tre metric is then derived and analyzed.