Degeneracies in long-baseline neutrino experiments from nonstandard interactions

TL;DR

This paper investigates how nonstandard interactions in neutrino propagation cause parameter degeneracies in long-baseline experiments, complicating the determination of mass hierarchy, CP violation, and mixing angles, with implications for experiments like DUNE.

Contribution

It identifies specific NSI parameters that lead to degeneracies and analyzes their impact on the ability of current and future experiments to resolve neutrino properties.

Findings

Degeneracies can obscure mass hierarchy and CP phase determination.

DUNE can resolve degeneracies if off-diagonal NSI parameter _{} is nonzero.

Certain NSI parameters can cause incorrect hierarchy and CP violation conclusions.

Abstract

We study parameter degeneracies that can occur in long-baseline neutrino appearance experiments due to nonstandard interactions (NSI) in neutrino propagation. For a single off-diagonal NSI parameter, and neutrino and antineutrino measurements at a single L/E, there exists a continuous four-fold degeneracy (related to the mass hierarchy and $\theta_{23}$ octant) that renders the mass hierarchy, octant, and CP phase unknowable. Even with a combination of NO$\nu$A and T2K data, which in principle can resolve the degeneracy, both NSI and the CP phase remain unconstrained because of experimental uncertainties. A wide-band beam experiment like DUNE will resolve this degeneracy if the nonzero off-diagonal NSI parameter is $\epsilon_{e\mu}$. If $\epsilon_{e\tau}$ is nonzero, or the diagonal NSI parameter $\epsilon_{ee}$ is O(1), a wrong determination of the mass hierarchy and of CP violation can occur at DUNE. The octant degeneracy can be further complicated by $\epsilon_{e\tau}$, but is not affected by $\epsilon_{ee}$.