Matter Effect on Neutrino Oscillations from the violation of Universality in Neutrino Neutral Current Interactions

The violation of lepton-flavor-universality in the neutrino-Z interactions can lead to extra matter effects on neutrino oscillations at high energies, beyond that due to the usual charged-current interaction of the electron-neutrino. We show that the dominant effect of the violation is a shift in the effective value of \theta_{23}. This is in contrast to the dominant effect of the charged-current interaction which shifts \theta_{12} and \theta_{13}. The shift in \theta_{23} will be difficult to observe if the value of \sin^2(2\theta_{23}) is too close to one. However, if the value of \sin^2(2\theta_{23}) is as small as 0.92, then a Fermilab -> Hyper-Kamiokande experiment can potentially place a constraint on universality violation at the 1% level after 5 years of data taking.