Neutrino mass ordering in JUNO at risk from scalar NSI induced resonance

The determination of neutrino mass ordering (NMO) is the primary goal of the currently running JUNO reactor experiment. We show that the measurement of NMO at JUNO may severely deteriorate in the presence of non-standard neutrino interactions mediated by a beyond standard model scalar (SNSI). Taking inverted ordering and the lightest neutrino mass at $m_l=0.01$ eV, the NMO sensitivity falls below $2\sigma$ for SNSI parameter values in the range $\eta_{ee}< -7.1\times 10^{-3}$ and $\eta_{ee} > 3.3\times 10^{-3}$. More importantly, for $\eta_{ee} \gtrsim 5.7\times 10^{-3}$ the NMO sensitivity in JUNO is completely lost. We show that this is due to the presence of a hitherto unrecognized resonant enhancement of the mixing angle $\theta_{12}$, which gives rise to a mass ordering degeneracy.