Comments on atmospheric neutrino oscillation scenarios with large nu_mu <-> nu_e transitions

TL;DR

This paper critically evaluates scenarios with large muon-to-electron neutrino oscillations, concluding that certain proposed models are inconsistent with existing atmospheric and reactor neutrino data.

Contribution

It provides a quantitative analysis showing that threefold maximal mixing and combined three-neutrino models with large muon-electron oscillations are incompatible with current experimental evidence.

Findings

Threefold maximal mixing is disfavored by data.

Combined three-neutrino models with large nu_mu<->nu_e mixing are ruled out.

Super-Kamiokande data strongly constrains oscillation scenarios.

Abstract

The evidence for $\nu_\mu$ disappearance in the Super-Kamiokande atmospheric neutrino experiment and the negative searches for $\nu_e$ disappearance in the CHOOZ reactor experiment can be easily reconciled by assuming oscillations with large amplitude in the $\nu_\mu\leftrightarrow\nu_\tau$ channel and small (or null) amplitude in the $\nu_\mu\leftrightarrow\nu_e$ channel. It has been claimed, however, that some oscillation scenarios with large $\nu_\mu\leftrightarrow\nu_e$ mixing can also be constructed in agreement with the present data. We investigate quantitatively two such scenarios: (a) threefold maximal mixing; and (b) attempts to fit all sources of evidence for oscillations (solar, atmospheric, and accelerator) with three neutrinos. By using mainly Super-Kamiokande data, we show that the case (a) is disfavored, and that the case (b) is definitely ruled out.