hi_class code

hiclass-code.net · code · wiki · papers using it

hi_class is an Einstein-Boltzmann solver for dark energy and modified gravity. It extends CLASS to Horndeski's theory — the most general scalar-tensor theory whose equations of motion remain second order — and computes any linear cosmological observable: FRW distances, CMB temperature and polarization, matter power and number-count spectra, and their cross-correlations.

Gravity can be given to the code in two ways. The effective-theory approach parametrizes the α-functions and the dark-energy equation of state directly, independently of any underlying theory. The covariant approach starts from a Lagrangian — the Horndeski functions G_i — and the code solves for the background and derives the α-functions from it.

• hi_class_public — the code, its wiki, and the sources of hiclass-code.net. Current release 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 hi_class.ini

hi_class.ini documents every option, and sixteen worked examples ship in gravity_models/ — Galileons, nKGB, quintessence, Brans-Dicke, α-attractors, the conformally coupled cubic Galileon and the beyond-Horndeski models.

From Python, the wrapper is on PyPI:

pip install hiclassy

If you use hi_class, please cite both code papers:

• hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System — JCAP 08 (2017) 019
• hi_class: Background Evolution, Initial Conditions and Approximation Schemes — JCAP 02 (2020) 008

The code is registered as ascl:1808.010.

Bug reports and feature requests are welcome on the issue tracker; questions are best asked on the hi_class forum.