We expound in detail the degeneracy between the octant of θ 23 and flavor-changing neutral-current non-standard interactions (NSI's) in neutrino propagation, considering the Deep Underground Neutrino Experiment (DUNE) as a case study. In the presence of such NSI parameters involving the e−μ (ε eμ ) and e−τ (ε eτ ) flavors, the ν μ →ν e and ν¯ μ →ν¯ e appearance probabilities in long-baseline experiments acquire an additional interference term, which depends on one new dynamical CP-phase ϕ eμ/eτ . This term sums up with the well-known interference term related to the standard CP-phase δ creating a source of confusion in the determination of the octant of θ 23 . We show that for values of the NSI coupling (taken one at-a-time) as small as few% (relative to the Fermi coupling constant G F ), and for unfavorable combinations of the two CP-phases δ and ϕ eμ/eτ , the discovery potential of the octant of θ 23 gets completely lost.
Agarwalla, S. K., Chatterjee, S. S., & Palazzo, A. (2016). Degeneracy between θ 23 octant and neutrino non-standard interactions at DUNE. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 762, 64–71. https://doi.org/10.1016/j.physletb.2016.09.020