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Cited by 375

The DOI matches its Crossref record; 27 of the 27 references it cites were found in a registry or an index.

Dark energy at early times, the Hubble parameter, and the string axiverse

Open access
Karwal, Tanvi, Kamionkowski, Marc·2016·Physical Review D
DOI 10.1103/physrevd.94.103523
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Abstract

Precise measurements of the cosmic microwave background (CMB) power spectrum are in excellent agreement with the predictions of the standard $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ cosmological model. However, there is some tension between the value of the Hubble parameter ${H}_{0}$ inferred from the CMB and that inferred from observations of the Universe at lower redshifts, and the unusually small value of the dark-energy density is a puzzling ingredient of the model. In this paper, we explore a scenario with a new exotic energy density that behaves like a cosmological constant at early times and then decays quickly at some critical redshift ${z}_{c}$. An exotic energy density like this is motivated by some string-axiverse-inspired scenarios for dark energy. By increasing the expansion rate at early times, the very precisely determined angular scale of the sound horizon at decoupling can be preserved with a larger Hubble constant. We find, however, that the Planck temperature power spectrum tightly constrains the magnitude of the early dark-energy density and thus any shift in the Hubble constant obtained from the CMB. If the reionization optical depth is required to be smaller than the Planck 2016 $2\ensuremath{\sigma}$ upper bound $\ensuremath{\tau}\ensuremath{\lesssim}0.0774$, then early dark energy allows a Hubble-parameter shift of at most $1.6\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ (at ${z}_{c}\ensuremath{\simeq}1585$), too small to fully alleviate the Hubble-parameter tension. Only if $\ensuremath{\tau}$ is increased by more than $5\ensuremath{\sigma}$ can the CMB Hubble parameter be brought into agreement with that from local measurements. In the process, we derive strong constraints to the contribution of early dark energy at the time of recombination---it can never exceed $\ensuremath{\sim}2%$ of the radiation/matter density for $10\ensuremath{\lesssim}{z}_{c}\ensuremath{\lesssim}1{0}^{5}$.

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Metadata

Authors
Karwal, T., & Kamionkowski, M.
Venue
Physical Review D
Publisher
American Physical Society (APS)
Published
2016-11-28
Volume
94
Issue
10
ISSN
  • 2470-0010 (ISSN-L)
  • 2470-0029
DOI
10.1103/physrevd.94.103523
OpenAlex
W2487623152
Cited by
375
References
27
FWCI
6.67
Type
journal article
Language
en
Open access
green

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CoChat. (2026). Citation check: Dark energy at early times, the Hubble parameter, and the string axiverse. https://app.cochat.ai/papers/10.1103/physrevd.94.103523
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Karwal, T., & Kamionkowski, M. (2016). Dark energy at early times, the Hubble parameter, and the string axiverse. Physical Review D. https://doi.org/10.1103/physrevd.94.103523

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Contains information from the Semantic Scholar Academic Graph Datasets, made available under the ODC Attribution License (ODC-BY 1.0).

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