Dark before light: Testing the cosmic expansion history through the cosmic microwave background

Abstract

The cosmic expansion history proceeds in broad terms from a radiation dominated epoch to matter domination to an accelerated, dark energy dominated epoch. We investigate whether intermittent periods of acceleration (from a canonical, minimally coupled scalar field) are possible in the early universe - between Big Bang nucleosynthesis (BBN) and recombination and beyond. We establish that the standard picture is remarkably robust: anisotropies in the cosmic microwave background consistent with ΛCDM will exclude any extra period of accelerated expansion between 1 z105 (corresponding to 5 × 10-4eV T25eV). © 2011 IOP Publishing Ltd and SISSA.