The Cosmic Linear Anisotropy Solving System (CLASS). Part II: Approximation schemes
Abstract
Boltzmann codes are used extensively by several groups for constraining cosmological parameters with Cosmic Microwave Background and Large Scale Structure data. This activity is computationally expensive, since a typical project requires from 10^{4} to 10^{5} Boltzmann code executions. The newly released code CLASS (Cosmic Linear Anisotropy Solving System) incorporates improved approximation schemes leading to a simultaneous gain in speed and precision. We describe here the three approximations used by CLASS for basic ΛCDM models, namely: a baryonphoton tightcoupling approximation which can be set to first order, second order or to a compromise between the two; an ultrarelativistic fluid approximation which had not been implemented in public distributions before; and finally a radiation streaming approximation taking reionisation into account.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 July 2011
 DOI:
 10.1088/14757516/2011/07/034
 arXiv:
 arXiv:1104.2933
 Bibcode:
 2011JCAP...07..034B
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 35 pages, 10 figures, 5 tables. Ultrarelativistic fluid approximation better justified in a new Appendix B. Version accepted in JCAP. Code available at http://classcode.net