Estimation of an Upper Limit on the Density of Relic Neutrinos in the Sun via the Solar $^8$B Neutrino Flux

TL;DR

This paper investigates the potential to set an upper limit on relic neutrino density in the Sun by analyzing the solar $^8$B neutrino flux and its consistency with standard solar and neutrino oscillation models.

Contribution

It introduces a method to estimate an upper bound on relic neutrino density through solar neutrino flux measurements and discusses the implications of neutrino capture on beta-decaying nuclei in the Sun.

Findings

No deviations from standard solar model predictions observed.

Upper limits on relic neutrino density derived.

Analysis supports current neutrino oscillation understanding.

Abstract

Relic neutrinos from the early universe are predicted to have a relatively large number density, but extremely low energies. Hence, the only possible interaction proceeds via neutrino capture on beta-decaying nuclei. In case relic neutrinos are captured by beta-decaying nuclei in the Sun, the neutrinos normally emerging from the decay of these nuclei will be missing from the overall number of solar neutrinos registered in neutrino experiments. Within the Sun, ${}^8\mathrm{B}$ and three nuclei from the CNO cycle are found to be suitable for this kind of process. Their cross section as well as the possible impact on the observed number of solar neutrinos are discussed. Assuming standard neutrino oscillations, no deviations of neutrino flux measurements from the predictions of the solar standard model are observed and upper limits are derived accordingly.