Probing the Cosmic Neutrino Background and New Physics with TeV-Scale Astrophysical Neutrinos

TL;DR

This paper uses TeV astrophysical neutrino observations to constrain relic neutrino overdensity and explore new neutrino interactions, providing bounds on these phenomena through analysis of IceCube data.

Contribution

It introduces new constraints on relic neutrino overdensity and neutrino self-interactions using high-energy astrophysical neutrino data from IceCube.

Findings

Relic neutrino overdensity constrained to η ≤ 2×10^{14} at 90% confidence.

Current data probes neutrino self-couplings around g ∼ 10^{-2} for MeV-scale mediators.

Limits improve with larger neutrino masses and overdensity scales.

Abstract

We use recent evidence of TeV neutrino events from the most significant astrophysical sources detected by IceCube -- NGC 1068, TXS 0506+056, PKS 1424+240 -- to constrain the local and global overdensity of relic neutrinos and to explore potential new neutrino self-interactions. Assuming a relic neutrino overdensity, such high-energy neutrinos have travelled considerable distances through a sea of relic neutrinos and could have undergone scattering, altering their observed flux on Earth. Considering only Standard Model interactions, we constrain the relic overdensity to $\eta \leq 2 \times 10^{14}$ at the 90$\%$ confidence level, assuming the sum of neutrino masses saturates the cosmological bound, $\sum_i m_i = 0.13$ eV. We demonstrate that this limit improves for larger neutrino masses and study how it depends on the scale of the overdensity region. Considering new interactions between TeV-scale neutrinos and relic neutrinos, mediated by a light boson, we probe couplings of approximately $g \sim 10^{-2}$ with current data for a boson mass around the MeV scale. We demonstrate that this limit improves with larger neutrino masses and the scale of the overdensity region.