Relativistic Interpretation of Newtonian Simulations for Cosmic Structure Formation

Understand

The standard numerical tools for studying non-linear collapse of matter are Newtonian $N$-body simulations.

• Previous work has shown that these simulations are in accordance with General Relativity (GR) up to first order in perturbation theory, provided that the effects from radiation can be neglected.
• In this paper we show that the present day matter density receives more than 1$\%$ corrections from radiation on large scales if Newtonian simulations are initialised before $z=50$.
• We provide a relativistic framework in which \emph{unmodified} Newtonian simulations are compatible with linear GR even in the presence of radiation.