Neutrino Trapping in a Supernova and Ion Screening

Neutrino-nucleus elastic scattering is reduced in dense matter because of correlations between ions. The static structure factor for a plasma of electrons and ions is calculated from Monte Carlo simulations and parameterized with a least squares fit. Our results imply a large increase in the neutrino mean free path. This strongly limits the trapping of neutrinos in a supernova by coherent neutral current interactions.Comment: 9 pages, 1 postscript figure using epsf.st

Signal for supernova νμ\nu_\mu and ντ\nu_\tau neutrinos in water \v{C}erenkov detectors

We suggest that photons with energies between 5 and 10 MeV, generated by the ($\nu,\nu'p\gamma$) and ($\nu,\nu'n\gamma$) reactions on $^{16}$O, constitute a signal which allows a unique identification of supernova $\nu_\mu$ and $\nu_\tau$ neutrinos in water \v{C}erenkov detectors. We calculate the yield of such $\gamma$ events and estimate that a few hundred of them would be detected in Superkamiokande for a supernova at 10 kpc distance.Comment: 8 pages, RevTex 3.0, figures and text available at http://www.krl.caltech.edu/preprints/MAP.htm

Neutrino Interactions in Hot and Dense Matter

We study the charged and neutral current weak interaction rates relevant for the determination of neutrino opacities in dense matter found in supernovae and neutron stars. We establish an efficient formalism for calculating differential cross sections and mean free paths for interacting, asymmetric nuclear matter at arbitrary degeneracy. The formalism is valid for both charged and neutral current reactions. Strong interaction corrections are incorporated through the in-medium single particle energies at the relevant density and temperature. The effects of strong interactions on the weak interaction rates are investigated using both potential and effective field-theoretical models of matter. We investigate the relative importance of charged and neutral currents for different astrophysical situations, and also examine the influence of strangeness-bearing hyperons. Our findings show that the mean free paths are significantly altered by the effects of strong interactions and the multi-component nature of dense matter. The opacities are then discussed in the context of the evolution of the core of a protoneutron star.Comment: 41 pages, 25 figure

Electron capture on iron group nuclei

We present Gamow-Teller strength distributions from shell model Monte Carlo studies of fp-shell nuclei that may play an important role in the pre-collapse evolution of supernovae. We then use these strength distributions to calculate the electron-capture cross sections and rates in the zero-momentum transfer limit. We also discuss the thermal behavior of the cross sections. We find large differences in these cross sections and rates when compared to the naive single-particle estimates. These differences need to be taken into account for improved modeling of the early stages of type II supernova evolution

Neutrino-electron scattering in dense magnetized plasma

We derive exact expressions for the cross section of neutrino scattering on electrons in dense, hot stellar matter, in the presence of strong magnetic fields. Numerical calculations of the scattering cross sections at various densities, temperatures and magnetic fields, are performed. Strong, quantizing magnetic fields modify significantly the angular and energy dependence of the scattering cross section.Comment: Physical Review D, to be published, 18 pages, using REVTEX, without figures. Figures (hardcopy) available upon request from one of the authors ([email protected]

Neutrino Spectroscopy of the Early Phase of Nearby Supernovae

Neutrinos emitted during stellar core collapse up to their trapping phase carry information about the stage from which the Supernova explosion process initiates. The dominant $\nu_e$ emission mechanism is by electron capture on free protons and f-p shell nuclei and the spectrum of these neutrinos is a function of the ambient physical conditions within the core as well as the nuclear equation of state. The number of collapse phase $\nu_e$ which can be detected by Super-Kamioka and Sudbury Neutrino Observatory from a Supernova within 1 kpc, and their generic energy spectra are given.Comment: 9 pages of text and tables plus 2 pages of figures. Accepted for publication in Phys. Rev. Lett. on 11th Jul., 1997. Please e-mail Comments etc. to [email protected]