What the Atmospheric Neutrino Anomaly is Not

TL;DR

This paper investigates the atmospheric neutrino anomaly, examining alternative explanations and emphasizing the need to verify underlying assumptions and reduce uncertainties to better understand the observed neutrino ratio discrepancy.

Contribution

It systematically explores potential non-neutrino explanations for the anomaly and highlights the importance of confirming assumptions and improving flux estimates.

Findings

Alternatives to neutrino explanations are largely unviable.

Reducing uncertainties in atmospheric neutrino flux is crucial.

Confirmation of neutrino interaction origins is necessary.

Abstract

The atmospheric neutrino anomaly is the apparent reduction of the $\nu_{\mu}/\nu_{e}$ ratio observed in underground detectors. It represents either a reduction in the muon neutrino interaction rate or an excess of the electron neutrino interaction rate, or both. Unable to answer the question of ``What else could it be?'' this paper explores a number of alternatives which do not seem to be viable. Various methods to reduce the apparent muon rate or to increase the apparent electron rate are discussed. Perhaps our bias that the interactions are due to neutrinos of atmospheric origin is incorrect. Both of these assumptions need to be confirmed. Efforts to reduce uncertainties in the estimated atmospheric neutrino flux would also help to narrow the possibilities further.