| Summary: | This dissertation presents two studies performed with data from Super-Kamiokande, a 50 kT water Cherenkov detector located 1,000 meters below Mt. Ikenoyama in Gifu, Japan, which has been operating since 1996. The first study searches for Earth matter effects in atmospheric neutrino oscillations. Earth matter effects have never before been confirmed in a measurement of atmospheric neutrinos, and observing them is an important step toward measuring the neutrino mass hierarchy, since atmospheric neutrino measurements gain sensitivity to neutrino mass hierarchy through Earth matter effects. We find that our data agrees very well with standard matter effects, and excludes vacuum oscillations at a significance of 1.6σ. The second study searches for boosted dark matter by looking for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic Center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic Center and Sun are calculated. These limits can constrain general boosted dark matter theories, as is demonstrated by calculating limits for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay.
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