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hi_class implements Horndeski's theory in the modern Cosmic Linear Anisotropy Solving System. It computes any linear cosmological observable in seconds — distances, CMB, matter power and number-count spectra — for dark energy and modified gravity models, and interfaces with the standard parameter samplers.
Horndeski is the most general scalar-tensor theory described by second-order equations of motion, and contains many well known models, including covariant Galileons, Brans–Dicke, f(R), k-essence and quintessence. hi_class relies on the Effective Field Theory of Dark Energy formulation developed in Bellini & Sawicki (2014). You can specify a model either through its full covariant Lagrangian or directly through the EFT α-functions — see the model pages below.
Current version: hi_class v3.3.4.4 (built on CLASS v3.3.4).
git clone https://github.com/hiclass-code/hi_class_public.git
cd hi_class_public
make class
./class gravity_models/brans_dicke.iniEvery model shipped in gravity_models/ runs out of the box. See Installation for the Python wrapper and Running hi_class for the input-file anatomy.
| Section | Pages |
|---|---|
| Getting started | Installation · Running hi_class |
| Models | Covariant theories · Parametrized (α) models · Expansion history |
| Reference | Output files · Stability, ICs and precision · Python wrapper |
| Development | Extending hi_class |
| Background | Physics and papers |
For the science overview, animations, publication list and team, visit the website: hiclass-code.net.
If you use hi_class in a project, please cite at least:
- hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System — M. Zumalacárregui, E. Bellini, I. Sawicki, J. Lesgourgues, P. G. Ferreira, JCAP 1708 (2017) 019
- hi_class: Background Evolution, Initial Conditions and Approximation Schemes — E. Bellini, I. Sawicki, M. Zumalacárregui, JCAP 02 (2020) 008
- the original CLASS paper — D. Blas, J. Lesgourgues, T. Tram, JCAP 1107 (2011) 034
Model-specific references are listed on the model pages and collected in Physics and papers.
hi_class is developed by a team of cosmologists — see who develops hi_class. It has been used in 99 scientific publications and counting and validated against similar codes with sub-percent accuracy (Bellini et al. 2017). An earlier version of this wiki was developed by Carlos García-García.