ORIGINAL

Abstract

The first part of the thesis is a recalculation of supernova bounds on neutrino radiative decays. Specifically, we will be looking at supernova 1987A (SN 1987A). The Solar Maximum Mission satellite saw no gamma rays in excess of background from the radiative decays of heavy neutrinos coming from SN 1987A in the Large Magellanic Cloud. We will build a model based on Ref. [1] to calculate the expected gamma ray fluence on Earth, and with the data from the Gamma Ray Spectrometer of the Solar Maximum Mission satellite, compute an upper bound on the mixing angle of sterile neutrinos to electron neutrinos. The second part is about various backgrounds of HUNTER (Heavy Unseen Neutrinos by Total Energy-momentum Reconstruction). The HUNTER project is aiming to find sterile neutrinos in the mass range 30-200 keV/c\(^{2}\) with \(^{131}\) Cs K-captures; preliminary study on backgrounds is essential because the sensitivity of the experiment depends heavily on the amount of background. The emphasis will be on non-physical accidental events and X-ray mis-identification that may result in misleading non-zero neutrino mass. Accidental events will be ruled out by energy-momentum conservation, and we will show that X-ray mis-identification is of negligible effect.