Cosmological perturbations for two cold fluids in ΛCDM. Issue 1 (11th December 2020)

• Record Type: Journal Article
• Authors: Rampf, Cornelius; Uhlemann, Cora; Hahn, Oliver
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 503:Issue 1(2021)
• Page Start: 406
• Page End: 425
• Publication Date: 2020-12-11
• Subjects: dark matter -- large-scale structure of Universe -- cosmology: theory; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3605
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The cosmic large-scale structure of our Universe is comprised of baryons and cold dark matter (CDM). Yet it is customary to treat these two components as a combined single-matter fluid with vanishing pressure, which is justified only for sufficiently large scales and late times. Here, we go beyond the single-fluid approximation and develop the perturbation theory for two gravitationally coupled fluids while still assuming vanishing pressure. We mostly focus on perturbative expansions in powers of D (or D + ), the linear structure growth of matter in a ΛCDM Universe with cosmological constant Λ. We derive in particular (1) explicit recursion relations for the two fluid densities, (2) complementary all-order results in the Lagrangian-coordinates approach, as well as (3) the associated component wavefunctions in a semiclassical approach to cosmic large-scale structure. In our companion paper, we apply these new theoretical results to generate novel higher order initial conditions for cosmological hydrodynamical simulations.