2011/04/30 by Diego Blas, Julien Lesgourgues, Thomas Tram · 17 citations
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.1088/1475-7516/2011/07/034
published as JCAP 07 (2011) 034 · 35 pages, 10 figures, 5 tables. Ultra-relativistic fluid approximation better justified in a new Appendix B. Version accepted in JCAP. Code available at http://class-code.net
arxiv created 2011/08/17 · arxiv updated 2015/05/27
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 10'000 to 100'000 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 LambdaCDM models, namely: a baryon-photon tight-coupling approximation which can be set to first order, second order or to a compromise between the two; an ultra-relativistic fluid approximation which had not been implemented in public distributions before; and finally a radiation streaming approximation taking reionisation into account.