Probing CP violation in neutrino oscillations with neutrino telescopes

TL;DR

This paper explores how astrophysical neutrino measurements can reveal CP violation in neutrino oscillations, especially if certain mixing parameters are constrained by other experiments, requiring advanced neutrino telescopes.

Contribution

It extends previous analyses by considering multiple source types and demonstrates how neutrino telescopes could establish bounds on CP violation parameters under specific conditions.

Findings

Neutrino telescopes can potentially detect CP violation if $ heta_{13}$ is sufficiently large.

Reducing uncertainties in mixing angles enhances the sensitivity to CP violation.

Larger neutrino detectors are needed to achieve the required measurement precision.

Abstract

Measurements of flavor ratios of astrophysical neutrino fluxes are sensitive to the two yet unknown mixing parameters $\theta_{13}$ and $\delta$ through the combination $\sin\theta_{13}\cos\delta$. We extend previous studies by considering the possibility that neutrino fluxes from more than a single type of sources will be measured. We point out that, if reactor experiments establish a lower bound on $\theta_{13}$, then neutrino telescopes might establish an upper bound on $|\cos\delta|$ that is smaller than one, and by that prove that CP is violated in neutrino oscillations. Such a measurement requires several favorable ingredients to occur: (i) $\theta_{13}$ is not far below the present upper bound; (ii) The uncertainties in $\theta_{12}$ and $\theta_{23}$ are reduced by a factor of about two; (iii) Neutrino fluxes from muon-damped sources are identified, and their flavor ratios measured with accuracy of order 10% or better. For the last condition to be achieved with the planned km^3 detectors, the neutrino flux should be close to the Waxman-Bahcall bound. It motivates neutrino telescopes that are effectively about 10 times larger than IceCube for energies of O(100 TeV), even at the expense of a higher energy threshold.