Neutrinos emitted from near the surface of the hot proto-neutron star produced by a supernova explosion may be subject to significant gravitational redshift at late times. Electron antineutrinos (ν̄e) decouple deeper in the gravitational potential well of the neutron star than do the electron neutrinos (νe), so that the ν̄e experience a larger redshift effect than do the νe. We show how this differential redshift can increase the electron fraction Ye in the neutrino-heated ejecta from the neutron star. Any r-process nucleosynthesis originating in the neutrino-heated ejecta would require a low Ye, implying that the differential redshift effect cannot be too large. In turn, this effect may allow nucleosynthesis to probe the nuclear equation of state parameters which set the neutron star radius and surface density scale height at times of order tph ≈ 10s to 25s after core bounce.

In astrophysical environments with intense neutrino fluxes, neutrino-neutrino forward scattering contributes both diagonal and off-diagonal potentials to the flavor-basis Hamiltonian that governs neutrino flavor evolution. We examine a special case where adiabatic flavor evolution can produce an off-diagonal potential from neutrino-neutrino forward scattering that dominates over both the corresponding diagonal term and the potential from neutrino-matter forward scattering. In this case, we find a solution that, unlike the ordinary Mikeyhev-Smirnov-Wolfenstein scenario, has both neutrinos and antineutrinos maximally mixed in medium over appreciable ranges of neutrino and antineutrino energy. Employing the measured solar and atmospheric neutrino mass-squared differences, we identify the conditions on neutrino fluxes that are required for this solution to exist deep in the supernova environment, where it could affect the neutrino signal, heavy-element nucleosynthesis, and even the revival of the supernova shock. We speculate on how this solution might or might not be attained in realistic supernova evolution. Though this solution is ephemeral in time and/or space in supernovae, it may signal the onset of subsequent appreciable flavor mixing for both neutrinos and antineutrinos. © 2006 The American Physical Society.

We study supernova neutrino burst signals in large water erenkov detectors, examining the effects of mixing between νe and either νμ or ντ and taking account of charged current νe capture on oxygen in the detector. We show that the characteristic count rates and angular distributions from supernova neutrino-induced events can depend sensitively on the degree of neutrino flavor mixing. This sensitivity results from the different average energies expected in supernova models for νe on the one hand and νμ and ντ on the other, the steep increase in the O16(νe,e-)F16 cross section with neutrino energy, and the backward-peaked nature of the exit channel electron in this reaction. Neutrino flavor-mixing effects would be identifiable in the super Kamiokande detector for the neutrino burst of a galactic supernova. © 1994 The American Physical Society.

Matter-enhanced antineutrino flavor transformation between ν̄e and ν̄μ(τ) can occur in supernovas if the vacuum masses for these species satisfy mν̄e>mν̄μ(τ). For δm2>1 eV2, such flavor transformation can affect the electron fraction Ye in the neutrino-heated supernova ejecta. We point out that such flavor transformations will not drive Ye>0.5 at the r-process nucleosynthesis epoch in the best available supernova model for such nucleosynthesis. Consequently, there is no obvious conflict between the matter-enhanced antineutrino flavor transformation ν̄eν̄μ(τ) and r-process nucleosynthesis in the neutrino-heated supernova ejecta. © 1995 The American Physical Society.

A light sterile neutrino species has been introduced to explain simultaneously the solar and atmospheric neutrino puzzles and the results of the LSND experiment, while providing for a hot component of dark matter. Employing this scheme of neutrino masses and mixings, we show how matter-enhanced active-sterile (Formula presented) neutrino transformation followed by active-active (Formula presented) neutrino transformation can solve robustly the neutron deficit problem encountered by models of (Formula presented) nucleosynthesis associated with neutrino-heated supernova ejecta. © 2000 The American Physical Society.

We present results of 3-neutrino flavor evolution simulations for the neutronization burst from an O-Ne-Mg core-collapse supernova. We find that nonlinear neutrino self-coupling engineers a single spectral feature of stepwise conversion in the inverted neutrino mass hierarchy case and in the normal mass hierarchy case, a superposition of two such features corresponding to the vacuum neutrino mass-squared differences associated with solar and atmospheric neutrino oscillations. These neutrino spectral features offer a unique potential probe of the conditions in the supernova environment and may allow us to distinguish between O-Ne-Mg and Fe core-collapse supernovae.

We can understand many recently discovered features of flavor evolution in dense, self-coupled supernova neutrino and antineutrino systems with a simple, physical scheme consisting of two quasistatic solutions. One solution closely resembles the conventional, adiabatic single-neutrino Mikheyev-Smirnov- Wolfenstein (MSW) mechanism, in that neutrinos and antineutrinos remain in mass eigenstates as they evolve in flavor space. The other solution is analogous to the regular precession of a gyroscopic pendulum in flavor space, and has been discussed extensively in recent works. Results of recent numerical studies are best explained with combinations of these solutions in the following general scenario: (1) Near the neutrino sphere, the MSW-like many-body solution obtains. (2) Depending on neutrino vacuum mixing parameters, luminosities, energy spectra, and the matter density profile, collective flavor transformation in the nutation mode develops and drives neutrinos away from the MSW-like evolution and toward regular precession. (3) Neutrino and antineutrino flavors roughly evolve according to the regular precession solution until neutrino densities are low. In the late stage of the precession solution, a stepwise swapping develops in the energy spectra of νe and νμ/ντ. We also discuss some subtle points regarding adiabaticity in flavor transformation in dense-neutrino systems. © 2007 The American Physical Society.

The recent results from the Los Alamos neutrino oscillation experiment, together with assumptions of neutrino oscillation solutions for the solar and atmospheric neutrino deficit problems, may place powerful constraints on any putative scheme for neutrino masses and mixings. Assuming the validity of these experiments and assumptions, we argue that a nearly unique spectrum of neutrino masses emerges as a fit, if two additional astrophysical arguments are adopted: (1) the sum of the light neutrino masses is ∼5 eV, as large scale structure simulations with mixed cold plus hot dark matter seem to suggest; and (2) r-process nucleosynthesis originates in neutrino-heated ejecta from type II supernovae. In this fit, the masses of the neutrinos must satisfy mνemνs2.7 eV (where νe is split from a sterile species νs by ∼10-6 eV) and mντmνμ1.1 eV (where these species are split by ∼10-2 eV). We discuss alternative neutrino mass spectra that are allowed if we decline to adopt certain experiments or astrophysical models. © 1995 The American Physical Society.