Core Cosmology Library

The Core Cosmology Library (CCL) is a public standardized library of routines to calculate basic observables used in cosmology. It will be the standard theoretical prediction package used by the LSST Dark Energy Science Collaboration (DESC), although we hope it will have broader applicability.

The core functions of this package include:

  • Background quantities (Hubble parameter \(H(z)\), distances etc.).

  • Linear growth factor \(D(z)\) and growth rate \(f(z)\).

  • Linear matter power spectra \(P(k)\) from Boltzmann codes (CLASS, CAMB), emulators, and approximate fitting functions.

  • Non-linear matter power power spectra using a variety of prescriptions, including emulators, and including the impact of baryonic effects.

  • Angular power spectra \(C_\ell\) and correlation functions \(\xi\) for arbitrary combinations of tracers including number counts, shear, CMB lensing, ISW, thermal SZ, CIB, as well as custom-made tracers.

  • A comprehensive halo model framework able to combine different prescriptions for the halo mass function \({\rm d}n/{\rm d}M\), halo bias \(b(M)\), concentration-mass relation \(c(M)\), mass definitions, and halo profiles, as well as to provide predictions for summary statistics (power spectra, non-Gaussian covariances) of arbitrary quantities.

  • Support for \(\Lambda\) CDM, and \(w_0-w_a\) CDM cosmologies with curvature and massive neutrinos, as well as simple modified gravity extensions (e.g. and \(\mu-\Sigma\)).

The source code is available on github at