IceCube PeV-EeV Neutrinos and Secret Interactions of Neutrinos

TL;DR

The study investigates whether IceCube's PeV–EeV neutrinos constrain secret neutrino–neutrino interactions with the cosmic neutrino background. It derives the νν cross section for MeV–GeV mediators, using s ≈ 2 m_ν ε_ν to map mediator parameters to IceCube energies and assesses attenuation and cascade scenarios within a Boltzmann-equation framework, including Γ_X ≈ g^2 m_X/(4π). The results place constraints on the coupling g as a function of the mediator mass m_X and show that a cascade pathway can reproduce a PeV flux while reducing higher-energy neutrinos, though it often requires sizable couplings that lab bounds disfavor. The work provides a novel astrophysical probe of hidden neutrino interactions and makes falsifiable predictions for future observatories such as the Askaryan Radio Array (ARA) that could detect the predicted suppression of >PeV neutrinos.

Abstract

We show that the PeV neutrinos detected by IceCube put unique constraints on "secret" interactions of neutrinos with the cosmic neutrino background (C$ν$B). The coupling must be $g <0.03$ for the mediating boson mass $m_{X} \lesssim 2$ MeV, $g/m_{X} < 5$ GeV$^{-1}$ for $m_{X} \gtrsim 20$ MeV, and $g/m_{X} < 0.07$ GeV$^{-1}$ in between. We also investigate the possibility that neutrino cascades degrade high-energy neutrinos to PeV energies by upgrading C$ν$B where the energy flux of PeV neutrinos can coincide with the Waxman-Bahcall bound or the cosmogenic neutrino flux for protons, thanks to energy conservation. However a large coupling is required, which is disfavored by laboratory decay constraints. The suppression of PeV-EeV neutrinos is a testable prediction for the Askaryan Radio Array.

Figures (2)

• Figure 1: Constraints on the hidden interactions of neutrinos with the coupling constant $g$ and the boson mass $m_{X}$, with and without resonance using the second and the last term in Eq. (\ref{['eq:signunu']}), respectively. The shaded (blue) regions are excluded by the observed (future) IceCube signal with Eq. (\ref{['eq:att']}). We illustrate spiky constraints for a given neutrino energy, although we use $\sigma_{\nu\nu}^{\rm eff}$ for the resonance constraints. Also shown are the constraints by the $Z$-decay width for the light vector mediator Laha+13 and by the $\tau$-decay rate. The left regions of the vertical lines are relevant to BBN and supernovae.
• Figure 2: The observed spectra of cosmogenic neutrinos with ( orange solid line) and without ( blue solid line) the non-standard neutrino interactions in Eq. (\ref{['eq:signunu']}) with $g=0.5$ and $m_X=80$ MeV. Also shown are the Pop III model with $30$ times higher rate $R(z)$ at $z>8$, and the 2$X$ model with two bosons, $g_1=0.65$, $m_{X_1}=130$ MeV, $g_2=0.04$, and $m_{X_2}=7$ MeV.