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ΛCDM or self-interacting neutrinos: How CMB data can tell the two models apart

Author(s): Park, Minsu; Kreisch, Christina D; Dunkley, Jo; Hadzhiyska, Boryana; Cyr-Racine, Francis-Yan

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Abstract: Of the many proposed extensions to the ΛCDM paradigm, a model in which neutrinos self-interact until close to the epoch of matter-radiation equality has been shown to provide a good fit to current cosmic microwave background (CMB) data, while at the same time alleviating tensions with late-time measurements of the expansion rate and matter fluctuation amplitude. Interestingly, CMB fits to this model either pick out a specific large value of the neutrino interaction strength, or are consistent with the extremely weak neutrino interaction found in ΛCDM, resulting in a bimodal posterior distribution for the neutrino self-interaction cross section. In this paper, we explore why current cosmological data select this particular large neutrino self-interaction strength, and by consequence, disfavor intermediate values of the self-interaction cross section. We show how it is the l ≳ 1000 CMB temperature anisotropies, most recently measured by the Planck satellite, that produce this bimodality. We also establish that smaller scale temperature data, and improved polarization data measuring the temperature-polarization cross-correlation, will best constrain the neutrino self-interaction strength. We forecast that the upcoming Simons Observatory should be capable of distinguishing between the models
Publication Date: 20-Sep-2019
Electronic Publication Date: 20-Sep-2019
Citation: Park, Minsu, Kreisch, Christina D, Dunkley, Jo, Hadzhiyska, Boryana, Cyr-Racine, Francis-Yan. (<mml:math xmlns:mml="" display="inline"><mml:mi mathvariant="normal">Λ</mml:mi><mml:mi>CDM</mml:mi></mml:math> or self-interacting neutrinos: How CMB data can tell the two models apart. Physical Review D, 100 (6), 10.1103/physrevd.100.063524
DOI: doi:10.1103/physrevd.100.063524
ISSN: 2470-0010
EISSN: 2470-0029
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: Physical Review D
Version: Author's manuscript

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