Physics, Astronomy and Astrophysics

We have performed an analysis of fluid instabilities below the neutrinospheres of the collapsed cores of supernova progenitors using a methodology introduced by Bruenn and Dineva [28, 29, 31]. In an extensive survey we found that the rate of lepton diffusion always exceeds the rate of thermal diffusion and as a result we do not anywhere see the neutron finger instability as described by the Livermore group [16, 17]. A new instability, lepto-entropy fingers, extending from a radius of 10--15 km out to the vicinity of the neutrinosphere, driven by the cross-response functions (i.e. the dependence of lepton transport on entropy perturbations and vice versa) was discovered. This instability has a maximum growth rate of the order of 100 s-1 with a scale of approximately 1/20 the distance of a perturbed fluid element from the core center [18]. This instability has probably already been seen in some multi-dimensional core collapse calculations. To test our results predicting the presence of doubly diffusive instabilities below the neutrinosphere of a proto-supernova, we have performed two dimensional hydrodynamic simulations with radial ray neutrino transport. This entailed rewriting RadHyd, which is the merger of EVH-1 hydrodynamics and MGFLD neutrino transport developed by Bruenn and DiNisco [43], for two dimensions. In particular, hydrodynamic evolution along angular arrays was included, as was MPI message passing capabilities, in order to utilize massively parallel computer platform such as FAU's BOCA4 Beowulf cluster. This work was partially funded by a grant from the DOE Office of Science, Scientific Discovery through Advanced Computing Program.

In recent years there have been several neutrino detectors built to detect solar, atmospheric, and cosmic neutrinos. In this dissertation, we used a Monte Carlo approach to model both the SuperKamiokande (SuperK) detector in Japan, and the Sudbury Neutrino Observatory (SNO) in Canada. A neutrino flux produced by a supernova code was implemented to simulate a realistic signal. An analysis of the minimum neutrino mass which could be detected was then performed for SuperK which produced discrepancies for the zero tau mass case when compared to previous work using a smooth emission spectrum as the incident neutrino source. As a result, we reconstructed the neutrino parameters involved in the supernovae explosion mechanism, to correct this discrepancy and determined the minimum mass for a realistic source. The source reconstruction is also useful for empirically determining the explosion mechanism when the next galactic supernova event occurs, since at present, this mechanism is still not entirely understood.