Propagation of Superluminal PeV IceCube Neutrinos: A High Energy Spectral Cutoff or New Constraints on Lorentz Invariance Violation

TL;DR

This paper uses IceCube neutrino observations to set stringent limits on Lorentz invariance violation, exploring how superluminal neutrinos could cause a high-energy spectral cutoff and constraining their possible velocities.

Contribution

It provides the first comprehensive constraints on LIV parameters for neutrinos using Monte Carlo simulations of energy losses, and links superluminal neutrinos to observed spectral features.

Findings

LIV parameter $oldsymbol{ extstyle oldsymbol{ ext{delta}}_{ u e} extless 5.2 imes 10^{-21}}$

Upper limit on neutrino superluminal velocity fraction $oldsymbol{ extstyle 1.0 imes 10^{-20}}$

Spectral cutoff at 2 PeV consistent with superluminal neutrino hypothesis

Abstract

The IceCube observation of cosmic neutrinos with $E_{\nu} > 60$ TeV, most of which are likely of extragalactic origin, allows one to severely constrain Lorentz invariance violation (LIV) in the neutrino sector, allowing for the possible existence of superluminal neutrinos. The subsequent neutrino energy loss by vacuum $e^+e^-$ pair emission (VPE) is strongly dependent on the strength of LIV. In this paper we explore the physics and cosmology of superluminal neutrino propagation. We consider a conservative scenario for the redshift distribution of neutrino sources. Then by propagating a generic neutrino spectrum, using Monte Carlo techniques to take account of energy losses from both VPE and redshifting, we obtain the best present constraints on LIV parameters involving neutrinos. We find that $\delta_{\nu e} = \delta_{\nu} - \delta_e \le 5.2 \times 10^{-21}$. Taking $\delta_e \le 5 \times 10^{-21}$, we then obtain an upper limit on the superluminal velocity fraction for neutrinos alone of $1.0 \times 10^{-20}$. Interestingly, by taking $\delta_{\nu e} = 5.2 \times 10^{-21}$, we obtain a cutoff in the predicted neutrino spectrum above 2 PeV that is consistent with the lack of observed neutrinos at those energies, and particularly at the Glashow resonance energy of 6.3 PeV. Thus, such a cutoff could be the result of neutrinos being slightly superluminal, with $\delta_{\nu}$ being $(0.5 \ {\rm to} \ 1.0) \times 10^{-20}$.