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Abstract Spatial curvature is one of the most fundamental parameters in our current concordance flat ΛCDM model of the Universe. The goal of this work is to investigate how the constraint on the spatial curvature is affected by an assumption on the sound horizon scale. The sound horizon is an essential quantity to use the standard ruler from the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAOs). As an example, we study the curvature constraint in an axion-like Early Dark Energy (EDE) model in light of recent cosmological datasets from Planck, the South Pole Telescope (SPT), and the Atacama Cosmology Telescope (ACT), as well as BAO data compiled in Sloan Digital Sky Survey Data Release 16. We find that, independent of the CMB datasets, the EDE model parameters are constrained only by the CMB power spectra as precisely and consistently as the flat case in previous work, even with the spatial curvature. We also demonstrate that combining CMB with BAO is extremely powerful to constrain the curvature parameter even with a reduction of the sound-horizon scale in an EDE model, resulting in Ω K = -0.0058± 0.0031 in the case of ACT+BAO after marginalizing over the parameters of the EDE model. This constraint is as competitive as the Planck+BAO result in a ΛCDM model, Ω K = -0.0001± 0.0018.
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What is flat ΛCDM, and may we choose it?
Abstract The Universe is neither homogeneous nor isotropic, but it is close enough that we can reasonably approximate it as such on suitably large scales.The inflationary-Λ-Cold Dark Matter (ΛCDM) concordance cosmology builds on these assumptions to describe the origin and evolution of fluctuations. With standard assumptions about stress-energy sources, this system is specified by just seven phenomenological parameters,whose precise relations to underlying fundamental theories are complicated and may depend on details of those fields.Nevertheless, it is common practice to set the parameter that characterizes the spatial curvature, ΩK, exactly to zero.This parameter-fixed ΛCDM is awarded distinguished status as separate model, “flat ΛCDM.”Ipso factothis places the onus on proponents of “curved ΛCDM” to present sufficient evidence that ΩK≠ 0, and is needed as a parameter.While certain inflationary model Lagrangians, with certain values of their parameters, and certain initial conditions, will lead to a present-day universe well-described as containing zero curvature, this does not justify distinguishing that subset of Lagrangians, parameters and initial conditions into a separate model.Absent any theoretical arguments, we cannot use observations that suggest small ΩKto enforce ΩK= 0.Our track record in picking inflationary models and their parametersa priorimakes such a choice dubious, andconcerns about tensions in cosmological parameters and large-angle cosmic-microwave-background anomalies strengthens arguments against this choice.We argue that ΩKmust not be set to zero, and that ΛCDM remains a phenomenological model with at least 7 parameters.
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- Award ID(s):
- 2013718
- PAR ID:
- 10475744
- Publisher / Repository:
- Journal of Cosmology and Astroparticle Physics
- Date Published:
- Journal Name:
- Journal of Cosmology and Astroparticle Physics
- Volume:
- 2023
- Issue:
- 02
- ISSN:
- 1475-7516
- Page Range / eLocation ID:
- 049
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1475-7516/2023/02/049
