Hi-COLA

A lightweight simulation suite for large-scale structure beyond GR

Hi-COLA is a package that runs fast, approximate N-body simulations of non-linear structure formation in reduced Horndeski gravity (Horndeski theories with luminal gravitational waves).

Hi-COLA is not hard-coded to solve specific Horndeski theories, but is designed to be generic with respect to the reduced Horndeski class. Given an input Lagrangian, Hi-COLA's frontend dynamically constructs the appropriate field equations and consistently solves for the cosmological background, linear growth, and screened fifth force of that theory. This is passed to the backend, an adaptation of the FML library, where a hybrid N-body simulation at significantly reduced computational and temporal cost compared to traditional N-body codes is run. By analysing the particle snapshots, one is able to study the formation of structure through statistics like the matter power spectrum.

Hi-COLA is publicly available on GitHub here.

See the Documentation folder on GitHub for guidance on how to install and use Hi-COLA. There you will find both a quickstart guide and a more detailed user manual.

Also see our paper, where we detail the work gone into creating the first version of Hi-COLA. We encourage the community to use Hi-COLA for their own research, and request that you cite us as detailed in the user manual (a handy bibtex is also provided there). Hi-COLA is provided under a CC BY 4.0 licence.

Hi-COLA remains under active development, with further extensions of the code and applications planned. You can contact the Hi-COLA team at [email protected] .