Neutrino Flavor Ratios Modified by Cosmic Ray Secondary Acceleration

TL;DR

This paper investigates how secondary acceleration of pions and muons in cosmic rays alters the expected neutrino flavor ratios at Earth, providing a new way to probe cosmic-ray acceleration processes through neutrino observations.

Contribution

It presents a theoretical framework for how secondary acceleration modifies neutrino flavor ratios and spectra, with applications to gamma-ray bursts and implications for IceCube detections.

Findings

Neutrino flavor ratios shift from 1:1:1 to 1:1.8:1.8 at high energies.

A flat excess in the neutrino spectrum is associated with secondary acceleration.

Potential detectability of flavor modifications at PeV--EeV energies by IceCube and future detectors.

Abstract

Acceleration of $\pi$'s and $\mu$'s modifies the flavor ratio at Earth (at astrophysical sources) of neutrinos produced by $\pi$ decay, $\nu_e:\nu_{\mu}:\nu_{\tau}$, from $1:1:1$ ($1:2:0$) to $1:1.8:1.8$ ($0:1:0$) at high energy, because $\pi$'s decay more than $\mu$'s during secondary-acceleration. The neutrino spectrum accompanies a flat excess, differently from the case of energy losses. With the flavor spectra, we can probe timescales of cosmic-ray acceleration and shock dynamics. We obtain general solutions of convection-diffusion equations and apply to gamma-ray bursts, which may have the flavor modification at around PeV -- EeV detectable by IceCube and next-generation experiments.