Degeneracies in long-baseline neutrino experiments from nonstandard interactions

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 ${ϵ}_{e\mu }$. If ${ϵ}_{e\tau }$ is nonzero, or the diagonal NSI parameter ${ϵ}_{ee}$ 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 ${ϵ}_{e\tau }$, but is not affected by ${ϵ}_{ee}$.

Comments: 5 pages, 6 figures. Version to appear in PRD