Solar cycle effects in future measurements of low-energy atmospheric neutrinos

We study the impact of time-dependent solar cycles in the atmospheric neutrino rate at DUNE, HyperKamiokande (HK), and JUNO, focusing in particular on the flux below 1 GeV. Including the effect of neutrino oscillations for the upward-going component that travels through the Earth, we find that across the solar cycle the amplitude of time variation is about +/- 5% at DUNE, +/- 4% at JUNO, and +/- 1% at HK. We find significant variance in the ratio of upward-going events to downward-going ones in all three experiments, though the overall event rates vary significantly across the three. Over the 11-year solar cycle, we find that the estimated statistical significance for observing time modulation of atmospheric neutrinos is 4.8 sigma for DUNE and 2.0 sigma for HK and JUNO. Flux measurements at all three experiments will be important for understanding systematics in the low-energy atmospheric flux as well as for understanding the effect of oscillations in low-energy atmospheric neutrinos.