We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates. [S0034-6861(98)00704-1]

Including nucleon-nucleon correlations due to both Fermi statistics and nuclear forces, we have developed a general formalism for calculating the neutral-current neutrino-nucleon scattering rates in nuclear matter. We derive corrections to the dynamic structure factors due to both density and spin correlations and find that neutrino-nucleon scattering rates are suppressed by large factors around and above nuclear density. Hence, in particular for the ν µ and ν τ neutrinos, but also for the ν e neutrinos, supernova cores are more "transparent" than previously thought. The many-body corrections increase with density, decrease with temperature, and are roughly independent of incident neutrino energy.In addition, we find that the spectrum of energy transfers in neutrino scattering is considerably broadened by the interactions in the medium. An identifiable component of this broadening comes from the absorption and emission of quanta of collective modes akin to the Gamow-Teller and Giant Dipole resonances in nuclei (zero-sound; spin sound), withČerenkov kinematics.Under the assumption that both the charged-current and the neutralcurrent cross sections are decreased by many-body effects, we calculate a set of ad hoc protoneutron star cooling models to gauge the potential importance of the new opacities to the supernova itself. While the early luminosities are not altered, the luminosities after many hundreds of milliseconds to seconds can be increased by factors that range from 10% to 100%. Such enhancements may have a bearing on the efficacy of the neutrino-driven supernova mechanism, the delay to explosion, the energy of the explosion, and the strength and relative role of convective overturn at late times. However, the actual conse-1 quences, if any, of these new neutrino opacities remain to be determined.

When the neutral current neutrino-neutrino interaction is treated completely, rather than as an interaction among angle-averaged distributions, or as a set of flavor-diagonal effective potentials, the result can be flavor mixing at a speed orders of magnitude faster than that one would anticipate from the measured neutrino oscillation parameters. It is possible that the energy spectra of the three active species of neutrinos emerging from a supernova are nearly identical.Comment: 8 pages, 4 figure

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The Rapid Communications section is intended for the accelerated publication of important new results Si.nce manuscripts submitted to this section are given priority treatment both in the editorial ofhce and in production, authors should explain in their submittal letter why the work justiftes this special handling A Rapid Communication in Physical Review D should be no longer than jtve printed pages and must be accompanied by an abstract Pag. e proofs are sent to authors, but because of the ac celerated schedulepu, blication is not delayed for receipt of corrections unless requested by the author or noted by the editor Bulk viscosity of hot neutron-star matter and the maximum rotation rates of neutron starsThe bulk viscosity of neutron-star matter, arising from the time lag in achieving beta equilibrium as the density is changed, is calculated. In the model used in standard cooling calculations, it is found, for the case of normal neutron matter, that the bulk viscosity goes as the sixth power of the temperature (as compared with a T dependence for the shear viscosity), and that at temperatures above 10 K the bulk viscosity may dominate the dissipation term which regulates the gravitational-wave instability of rapidly rotating neutron stars. This raises the possibility that in the first years of a neutron star's life the star could become unstable as the bulk viscosity decreases through cooling, with potentially observable consequences.