How massless neutrinos affect the cosmic microwave background damping tail

By Z. Hou, R. Keisler, Lloyd Knox, M. Millea, C. Reichardt. 2011

250 citations recorded by the source corpus.

We explore the physical origin and robustness of constraints on the energy density in relativistic species prior to and during recombination, often expressed as constraints on an effective number of neutrino species, Neff. Constraints from current data combination of Wilkinson Microwave Anisotropy Probe (WMAP) and South Pole Telescope (SPT) are almost entirely due to the impact of the neutrinos on the expansion rate, and how those changes to the expansion rate alter the ratio of the photon diffusion scale to the sound horizon scale at recombination. We demonstrate that very little of the constraining power comes from the early Integrated Sachs-Wolfe (ISW) effect, and also provide a first determination of the amplitude of the early ISW effect. Varying the fraction of baryonic mass in Helium, Yp, also changes the ratio of damping to sound-horizon scales. We discuss the physical effects that prevent the resulting near-degeneracy between Neff and Yp from being a complete one. Examining light element abundance measurements, we see no significant evidence for evolution of Neff and the baryon-to-photon ratio from the epoch of big bang nucleosynthesis to decoupling. Finally, we consider measurements of the distance-redshift relation at low to intermediate redshifts and their implications for the value of Neff.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/13ae9a6b5c692e4cc33a706e29e846ef515debb6

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Citations in the corpus

Sounds Discordant: Classical Distance Ladder and ΛCDM-based Determinations of the Cosmological Sound Horizon (2018, background): “One of the hindrances to adjustment of Neff is that it leads to a change in the ratio of sound horizon to damping scales (Hu & White 1996; Bashinsky & Seljak 2004; Hou et al. 2013), a change that is not preferred by CMB data.”
Early Dark Energy can Resolve the Hubble Tension. (2018, unknown): “[58].”
The Simons Observatory: science goals and forecasts (2018, background): “However, this degeneracy is mitigated by effects on the polarization and on the phase of the acoustic oscillations (Bashinsky and Seljak 2004; Hou et al. 2013; Baumann et al. 2016a).”
CONSTRAINTS ON COSMOLOGY FROM THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM OF THE 2500 deg2 SPT-SZ SURVEY (2012, background): “However, the parameters are not fully degenerate due to several additional effects of varying Neff as discussed in Hou et al. (2013).”
A tale of two modes: neutrino free-streaming in the early universe (2017, background): “To understand why, note that the absence of a free-streaming phase shift [12, 15, 19, 20] for models in this corner of parameter space is compensated by adjusting the angular diameter distance to the last scattering surface (via a change in H0).”
Neutrino decoupling beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation (2018, background): “it amounts to a reduction of the power in the high-` spectra [3, 55, 56].”
The Atacama Cosmology Telescope: cosmological parameters from three seasons of data (2013, unknown): “Extra relativistic energy density damps the small-scale CMB power – see Hou et al. (2013) for a concise recent review, and the discussions in Hu & Dodelson (2002); Hu et al. (2001); Bashinsky & Seljak (2004); Tegmark (2005); Lesgourgues & Pastor (2006); Hannestad (2010).”