Measuring Anisotropies in the Cosmic Neutrino Background

Abstract

Neutrino capture on tritium has emerged as a promising method for detecting the cosmic neutrino background (CvB). We show that relic neutrinos are captured most readily when their spin vectors are anti-aligned with the polarization axis of the tritium nuclei and when they approach along the direction of polarization. As a result, CvB observatories may measure anisotropies in the cosmic neutrino velocity and spin distributions by polarizing the tritium targets. A small dipole anisotropy in the CvB is expected due to the peculiar velocity of the lab frame with respect to the cosmic frame and due to late-time gravitational effects. The PTOLEMY experiment, a tritium observatory currently under construction, should observe a nearly isotropic background. This would serve as a strong test of the cosmological origin of a potential signal. The polarized-target measurements may also constrain non-standard neutrino interactions that would induce larger anisotropies and help discriminate between Majorana versus Dirac neutrinos.

7 pages, 2 figures

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Cited by in corpus (6)

• Discriminating between Thermal and Nonthermal Cosmic Relic Neutrinos through Annual Modulation at PTOLEMY
• Influence of local structure on relic neutrino abundances and anisotropies
• Impact of the cosmic neutrino background on black hole superradiance
• Multi-Messenger Astrophysics with the Cosmic Neutrino Background
• A study of the relativistic corrections to polarized tritium $\beta$-decay
• Status and Perspectives of Neutrino Physics