Adam J. Christopherson, J. C. Hidalgo, Karim A. Malik
Often in cosmology Newtonian physics is used to model the dynamics of matter inhomogeneities. For pressureless dark matter, or 'dust', this approach gives the correct results, but for scenarios in which the fluid has pressure this is no longer the case. In this article, we explicitly highlight the relationship between the variables in Newtonian and cosmological perturbation theory, showing exact equivalence for pressureless matter, and giving the relativistic corrections for matter with pressure. As an example, we focus on the scalar field dark matter model, which has recently gained popularity but which has non-zero pressure perturbations. We discuss some problems which may arise when modelling this theory with numerical simulations, and when using CMB Boltzmann codes.
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http://arxiv.org/abs/1207.1870
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