Degeneracy between ${\theta }_{23}$ octant and neutrino non-standard interactions at DUNE

Abstract

We expound in detail the degeneracy between the octant of ${\theta }_{23}$ 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 $e-\mu$ (${\epsilon }_{e\mu }$) and $e-\tau$ (${\epsilon }_{e\tau }$) flavors, the ${\nu }_{\mu }\to {\nu }_e$ and ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_e$ appearance probabilities in long-baseline experiments acquire an additional interference term, which depends on one new dynamical CP-phase ${\varphi }_{e\mu /e\tau }$. This term sums up with the well-known interference term related to the standard CP-phase $\delta$ creating a source of confusion in the determination of the octant of ${\theta }_{23}$. We show that for values of the NSI coupling (taken one at-a-time) as small as $few\%$ (relative to the Fermi coupling constant $G_{\mathrm{F}}$), and for unfavorable combinations of the two CP-phases $\delta$ and ${\varphi }_{e\mu /e\tau }$, the discovery potential of the octant of ${\theta }_{23}$ gets completely lost.

Comments: 11 pages, 5 pdf figures. Minor changes in the text. New references added. Accepted in Physics Letters B