Impact of scalar NSI on the neutrino mass ordering sensitivity at DUNE, HK and KNO

Abstract: The study of neutrino non-standard interactions (NSI) is a well-motivated phenomenological scenario to explore new physics beyond the Standard Model. The possible scalar coupling of neutrinos ($\nu$) with matter is one of such new physics scenarios that appears as a sub-dominant effect that can impact the $\nu$-oscillations in matter. The presence of scalar NSI introduces an additional contribution directly to the $\nu$-mass matrix in the interaction Hamiltonian and subsequently to the $\nu$-oscillations. This indicates that scalar NSI may have a significant impact on measurements related to $\nu$-oscillations e.g. leptonic CP phase $(\delta_{CP})$, $\theta_{23}$ octant and neutrino mass ordering (MO). The linear scaling of the effects of scalar NSI with matter density also motivates its exploration in long-baseline (LBL) experiments. In this paper, we study the impact of a scalar-mediated NSI on the MO sensitivity of DUNE, HK and HK+KNO, which are upcoming LBL experiments. We study the impact on MO sensitivities at these experiments assuming that scalar NSI parameters are present in nature and is known from other non-LBL experiments. We observe that the presence of diagonal scalar NSI elements can significantly affect the $\nu$-mass ordering sensitivities. We then also combine the data from DUNE with HK and HK+KNO to explore possible synergy among these experiments in a wider parameter space. We also observe a significant enhancement in the MO sensitivities for the combined analysis.