Constraints on Light Sterile Neutrinos and Scalar Non-Standard Interactions Using the First Reactor Antineutrino Oscillation Results at JUNO

Abstract: Constraints on light sterile neutrinos and scalar non-standard neutrino interactions are obtained from the first reactor antineutrino results reported by JUNO. The analysis is based on a spectral $χ<sup>2$ fit to the prompt-energy distribution corresponding to 59.1 days of data, including full three-flavor oscillations extended to a $3+1$ framework and effective scalar NSI contributions. The reactor flux is modeled using the Daya Bay measured spectrum, and systematic uncertainties are accounted for through a set of nuisance parameters describing reactor flux normalization, spectral shape, background normalization, and detector response. It is found that JUNO is already sensitive to light sterile neutrinos in the mass-splitting range $$10^{-5} \lesssim Δm^{2_{41}/\text{eV}²} \lesssim 10<sup>{-2}$$, probing mixing amplitudes down to $$\sin² 2θ<em>{14} \sim \mathcal{O}(10<sup>{-1})$$. In addition, a constraint on the scalar NSI parameter $|η</em>{ee}| &lt; \mathcal{O}(10<sup>{-2})$ is obtained, with correlations with solar oscillation parameters. These results demonstrate the potential of JUNO to probe small deviations from the Standard Model resulting from new physics through precision measurements, with significant improvements expected as statistics and systematic control improve.