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Keywords = relic neutrino capture

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48 pages, 790 KiB  
Review
A Review of Neutrino Decoupling from the Early Universe to the Current Universe
by Kensuke Akita and Masahide Yamaguchi
Universe 2022, 8(11), 552; https://doi.org/10.3390/universe8110552 - 25 Oct 2022
Cited by 9 | Viewed by 2325
Abstract
We review the distortions of spectra of relic neutrinos due to the interactions with electrons, positrons, and neutrinos in the early universe. We solve integro-differential kinetic equations for the neutrino density matrix, including vacuum three-flavor neutrino oscillations, oscillations in electron and positron background, [...] Read more.
We review the distortions of spectra of relic neutrinos due to the interactions with electrons, positrons, and neutrinos in the early universe. We solve integro-differential kinetic equations for the neutrino density matrix, including vacuum three-flavor neutrino oscillations, oscillations in electron and positron background, a collision term and finite temperature corrections to electron mass and electromagnetic plasma up to the next-to-leading order O(e3). After that, we estimate the effects of the spectral distortions in neutrino decoupling on the number density and energy density of the Cosmic Neutrino Background (CνB) in the current universe, and discuss the implications of these effects on the capture rates in direct detection of the CνB on tritium, with emphasis on the PTOLEMY-type experiment. In addition, we find a precise value of the effective number of neutrinos, Neff=3.044. However, QED corrections to weak interaction rates at order O(e2GF2) and forward scattering of neutrinos via their self-interactions have not been precisely taken into account in the whole literature so far. Recent studies suggest that these neglections might induce uncertainties of ±(103104) in Neff. Full article
(This article belongs to the Special Issue Recent Advances in Neutrino Physics: From Theory to Experiments)
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7 pages, 526 KiB  
Article
Impact of Warm Dark Matter on the Cosmic Neutrino Background Anisotropies
by Christopher G. Tully and Gemma Zhang
Universe 2022, 8(2), 118; https://doi.org/10.3390/universe8020118 - 12 Feb 2022
Cited by 4 | Viewed by 2507
Abstract
The Cosmic Neutrino Background (CνB) anisotropies for massive neutrinos are a unique probe of large-scale structure formation. The redshift-distance measure is completely different for massive neutrinos as compared to electromagnetic radiation. The CνB anisotropies in massive neutrinos grow in [...] Read more.
The Cosmic Neutrino Background (CνB) anisotropies for massive neutrinos are a unique probe of large-scale structure formation. The redshift-distance measure is completely different for massive neutrinos as compared to electromagnetic radiation. The CνB anisotropies in massive neutrinos grow in response to non-relativistic motion in gravitational potentials seeded by relatively high k-modes. Differences in the early phases of large-scale structure formation in warm dark matter (WDM) versus cold dark matter (CDM) cosmologies have an impact on the magnitude of the CνB anisotropies for contributions to the angular power spectrum that peak at high k-modes. We take the examples of WDM consisting of 2, 3, or 7 keV sterile neutrinos and show that the CνB anisotropies for 0.05 eV neutrinos drop off at high-l multipole moment in the angular power spectrum relative to CDM. At the same angular scales that one can observe baryonic acoustical oscillations in the CMB, the CνB anisotropies begin to become sensitive to differences in WDM and CDM cosmologies. The precision measurement of high-l multipoles in the CνB neutrino sky map is a potential possibility for the PTOLEMY experiment with thin film targets of spin-polarized atomic tritium superfluid that exhibit significant quantum liquid amplification for non-relativistic relic neutrino capture. Full article
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