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arXiv · 1104.2933

The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes

Diego Blas·Julien Lesgourgues·Thomas Tram
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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 10'000 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.

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Diego Blas, Julien Lesgourgues, Thomas Tram. 2011-04-14. The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes. https://doi.org/10.1088/1475-7516/2011/07/034

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