Neutrinos from stellar collapse: Comparison of the effects of three and four flavor mixings

We study the effect of non-vanishing masses and mixings among neutrino flavors on the detection of neutrinos from stellar collapse by a water Cherenkov detector. We consider a framework in which there are four neutrino flavors, including a sterile neutrino, whose mass squared differences and mixings are constrained by the present understanding of solar, atmospheric and laboratory neutrino detection. We also include the effects of high density matter within the supernova core. Unlike in the three flavor scenario, we find that the number of events due to the dominant process involving electron-antineutrinos changes dramatically for some allowed mixing parameters. Furthermore, contributions from charged-current scattering off oxygen nuclei in the detector can be considerably enhanced due to flavor mixing. We also present a comparison between the two possible scenarios, namely, when only three active neutrino flavors are present and when they are accompanied by a fourth sterile neutrino.