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.
See the Documentation folder 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 introducing Hi-COLA (pre-print version), 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 is set up to natively operate with Vainshtein screening. However, with a few specific settings, K-mouflage models can also be simulated -- see our paper on K-mouflage in Hi-COLA (pre-print here).
How does the accuracy of Hi-COLA fare relative to other approximate tools for LSS? You can find a detailed comparison exercise in this paper (pre-print version here).
Hi-COLA remains under active development. You can contact the Hi-COLA team at team.hicola@gmail.com, or at our individual emails (see papers linked above).