  New physics beyond the Standard Model could appear at long baseline
oscillation experiments as non-standard interactions (NSI) between neutrinos
and matter. If so, determination of the CP-violating phase $\delta_{13}$ is
ambiguous due to interference with additional complex phases. I'll present my
work using both numerical solutions and a perturbative approach to study
oscillation probabilities in the presence of NSI. I'll show how the CP phase
degeneracies are visualized on biprobability plots, and the extent to which the
energy spectrum for a given baseline length can help resolve them. In
particular, this shows how the broad range of energies at DUNE would help
distinguish between maximal, standard CP violation and the absence of CP
violation with large $\epsilon_{e\tau}$.
