GrGadget: an N-body TreePM relativistic code for cosmological simulations

Understand

We present the merging of the Particle-Mesh (PM) relativistic Gevolution code with the TreePM Gadget-4 code, with the aim of studying general relativity effects in cosmology.

• Our code, called GrGadget, is able to track the evolution of metric perturbations in the weak field limit by using Gevolution's implementation of a relativistic PM in the Poisson gauge.
• To achieve this, starting from Gevolution we have written a C++ library called libgevolution, that allows a code to access and use the same abstractions and resources that Gevolution uses for its PM-only N-body simulations.
• The code works under the assumption that particle interactions at short distances can be approximated as Newtonian, so that we can combine the forces computed with a Newtonian Tree with those computed with a relativistic PM.