Generalized mass ordering degeneracy in neutrino oscillation experiments

TL;DR

This paper demonstrates that non-standard neutrino interactions create an exact degeneracy in neutrino oscillation experiments, preventing the determination of neutrino mass ordering and mixing angle octant, and suggests testing this degeneracy via neutrino--nucleus scattering experiments.

Contribution

It reveals an exact degeneracy caused by NSI that affects all neutrino oscillation experiments and proposes a method to test this degeneracy.

Findings

Degeneracy prevents mass ordering determination in presence of NSI.

Degeneracy holds across all matter density profiles and experiment types.

Testable via neutrino--nucleus neutral-current scattering experiments.

Abstract

We consider the impact of neutral-current (NC) non-standard neutrino interactions (NSI) on the determination of the neutrino mass ordering. We show that in presence of NSI there is an exact degeneracy which makes it impossible to determine the neutrino mass ordering and the octant of the solar mixing angle $\theta_{12}$ at oscillation experiments. The degeneracy holds at the probability level and for arbitrary matter density profiles, and hence, solar, atmospheric, reactor, and accelerator neutrino experiments are affected simultaneously. The degeneracy requires order-one corrections from NSI to the NC neutrino--quark interaction and can be tested in neutrino--nucleus NC scattering experiments.