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arXiv · 1904.02625

$Λ$CDM or self-interacting neutrinos? - how CMB data can tell the two models apart

Minsu Park·Christina D. Kreisch·Jo Dunkley·Boryana Hadzhiyska·Francis-Yan Cyr-Racine
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Abstract

Of the many proposed extensions to the $Λ$CDM 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 $Λ$CDM, 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 $\ell \gtrsim 1000$ 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.

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Minsu Park, Christina D. Kreisch, Jo Dunkley, Boryana Hadzhiyska, Francis-Yan Cyr-Racine. 2019-04-23. $Λ$CDM or self-interacting neutrinos? - how CMB data can tell the two models apart. https://doi.org/10.1103/physrevd.100.063524

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