2019/08/19 by Tristan L. Smith, Vivian Poulin, Mustafa A. Amin · 2 citations
Physics and Astronomy · #astro-ph.CO #gr-qc #hep-ph
paper · pdf · doi:10.1103/physrevd.101.063523
published as Phys. Rev. D 101, 063523 (2020) · 26 pages, 22 figures, comments welcome
arxiv created 2019/08/19 · arxiv updated 2020/03/25
We present a detailed investigation of a sub-dominant oscillating scalar field ('early dark energy', EDE) in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until \rm log10(zc)∼3.5, reaching ρ\rm EDE(zc)/ρ\rm tot∼10%, and diluting faster than matter afterwards can bring cosmic microwave background (CMB), baryonic acoustic oscillations, supernovae luminosity distances, and the late-time estimate of the Hubble constant from the SH0ES collaboration into agreement. A scalar field potential which scales as V(ϕ) ∝ ϕ2n with 2\lesssim n\lesssim 3.4 around the minimum is preferred at the 68% confidence level, and the \em Planck polarization places additional constraints on the dynamics of perturbations in the scalar field. In particular, the data prefers a potential which flattens at large field displacements. An MCMC analysis of mock data shows that the next-generation CMB observations (i.e., CMB-S4) can unambiguously detect the presence of the EDE at very high significance. This projected sensitivity to the EDE dynamics is mainly driven by improved measurements of the E-mode polarization. We also explore new observational signatures of EDE scalar field dynamics: (i) We find that depending on the strength of the tensor-to-scalar ratio, the presence of the EDE might imply the existence of isocurvature perturbations in the CMB. (ii) We show that a strikingly rapid, scale-dependent growth of EDE field perturbations can result from parametric resonance driven by the anharmonic oscillating field for n≈ 2. This instability and ensuing potentially nonlinear, spatially inhomogenoues, dynamics may provide unique signatures of this scenario.