Neutrino oscillation measurements with KamLAND and JUNO in the presence of scalar NSI

Abstract: Determination of neutrino mass ordering and precision measurement of neutrino oscillation parameters are the foremost goals of the JUNO experiment. Here, we explore the effects of scalar non-standard interactions (sNSI) on the electron neutrino survival probability measured by JUNO. sNSI appears as a correction to the neutrino mass term in the Hamiltonian. We have considered the simplest scenario where there is only one NSI ($\eta_{ee}$) present in the theory. Our results show that sNSI can have significant effect on neutrino oscillation probabilities at the medium- and long-baseline reactor experiments. We fit KamLAND data assuming non-zero sNSI in theory and find that {\it estimates of $\Delta m^2_{21}$ and $\theta_{12}$ from KamLAND deviate significantly from their standard best-fit values} if one assumes sNSI in the theory. $\eta_{ee} \in [-1.0, 1.0]$ is allowed by KamLAND. JUNO cannot constrain sNSI but it can robustly measure $\Delta m^2_{21}$ and $\theta_{12}$ even when they differ widely from their current best-fit values. {\it Our works highlight the necessity of global analysis of constraints on sNSI and standard two-flavour oscillation parameters before arduous three-flavour questions such as neutrino mass ordering or CP violation in their presence is attempted.