The relic neutrino composition as seen from Earth

TL;DR

The paper demonstrates that gravitational effects from cosmic structures alter the relic neutrino background near Earth, enriching it with muon and tau neutrinos while reducing the electron neutrino fraction.

Contribution

It reveals how gravitational fields modify the relic neutrino composition, highlighting the dominance of heavier neutrino states near Earth, which was not previously understood.

Findings

Relic neutrino background is enriched with muon and tau neutrinos near Earth.

Electron neutrino fraction in the relic background is reduced to about 20%.

Gravitational fields influence the local composition of cosmic neutrino backgrounds.

Abstract

Being generated, the relic neutrino background contained equal fractions of electron $\nu_e$, muon $\nu_\mu$, and taon $\nu_\tau$ neutrinos. We show that the gravitational field of our Galaxy and other nearby cosmic objects changes this composition near the Solar System, enriching it with the heaviest neutrino $nu_3$. This mass state is almost free of the electron component (only $\sim 2\%$ of $\nu_e$) and contains more muon component than the tau one. As a result, the relic background becomes enriched with taon and particularly muon neutrinos. The electron relic neutrinos are the rarest for a terrestrial observer: instead of $1/3$, the relic background may contain only $\gtrsim 20\%$ of them.