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    Multi-scale perturbation theory. Part I. Methodology and leading-order bispectrum corrections in the matter-dominated era

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    Gallagher_2020_J._Cosmol._Astropart._Phys._2020_011 (1).pdf (1.421Mb)
    Date
    2020
    Author
    Clarksona, Chris
    Gallagher, Christopher S.
    Clifton, Timothy
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    Abstract
    Two-parameter perturbation theory is a scheme tailor-made to consistently include nonlinear density contrasts on small scales (< 100 Mpc), whilst retaining a traditional approach to cosmological perturbations in the long-wavelength universe. In this paper we study the solutions that arise from this theory in a spatially-flat dust-filled cosmology, and what these imply for the bispectrum of matter. This is achieved by using Newtonian perturbation theory to model the gravitational fields of nonlinear structures in the quasi-linear regime, and then using the resulting solutions as source terms for the cosmological equations. We find that our approach results in the leading-order part of the cosmological gravitational potentials being identical to those that result from standard cosmological perturbation theory at second-order, while the dark matter bispectrum itself yields some differences on Hubble scales. This demonstrates that our approach is sufficient to capture most leading-order relativistic effects, but within a framework that is far easier to generalize. We expect this latter property to be particularly useful for calculating leading-order relativistic corrections to the matter power spectrum, as well as for deriving predictions for relativistic effects in alternative theories of gravity.
    URI
    http://doi.org/10.1088/1475-7516/2020/03/011
    http://hdl.handle.net/10566/5958
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