Averaging Robertson-Walker cosmologies

作者：Brown Iain A^*; Robbers Georg; Behrend Juliane

来源：Journal of Cosmology and Astroparticle Physics, 2009, 2009(4): 016.

DOI：10.1088/1475-7516/2009/04/016

• cosmological perturbation theory
• dark energy theory

The cosmological backreaction arises when one directly averages the Einstein equations to recover an effective Robertson-Walker cosmology, rather than assuming a background a priori. While usually discussed in the context of dark energy, strictly speaking any cosmological model should be recovered from such a procedure. We apply the scalar spatial averaging formalism for the first time to linear Robertson-Walker universes containing matter, radiation and dark energy. The formalism employed is general and incorporates systems of multiple fluids with ease, allowing us to consider quantitatively the universe from deep radiation domination up to the present day in a natural, unified manner. Employing modified Boltzmann codes we evaluate numerically the discrepancies between the assumed and the averaged behaviour arising from the quadratic terms, finding the largest deviations for an Einstein-de Sitter universe, increasing rapidly with Hubble rate to a 0.01% effect for h = 0.701. For the Lambda CDM concordance model, the backreaction is of the order of Omega(0)(eff) approximate to 4 x 10(-6), with those for dark energy models being within a factor of two or three. The impacts at recombination are of the order of 10(-8) and those in deep radiation domination asymptote to a constant value. While the effective equations of state of the backreactions in Einstein-de Sitter, concordance and quintessence models are generally dust-like, a backreaction with an equation of state omega(eff) < -1/3 can be found for strongly phantom models.

• 出版日期2009-4