arXiv subjects

George M. Fuller

Publications and source records attributed to George M. Fuller.

132 records · Page 8Linked to original sources

arXiv1996

Evidence for an Intense Neutrino Flux during $r$-Process Nucleosynthesis?

We investigate the possibility that neutrino capture on heavy nuclei competes with beta decay in the environment where the $r$-Process elements are synthesized. We find that such neutrino capture is not excluded by existing abundance determinations. We show that inclusion of significant neutrino capture on the (neutron number) N=82 waiting point nuclei can allow the inferred abundances of these species to provide a good fit to steady weak (beta decay plus neutrino capture) flow equilibrium. In fact, for particular choices of neutrino flux conditions, this fit is improved over the case where nuclei change their charge by beta decay alone. However, this improved fit can be realized only if neutrino capture plays a negligible role in nuclear decay back toward stability. We discuss the implications of these considerations for current proposed sites and models for $r$-Process nucleosynthesis.

astro-ph↗

arXiv1996

Can a ``natural'' three-generation neutrino mixing scheme satisfy everything?

We examine the potential for a ``natural'' three-neutrino mixing scheme to satisfy available data and astrophysical arguments. By ``natural'' we mean no sterile neutrinos, and a neutrino mass hierarchy similar to that of the charged leptons. We seek to satisfy (or solve): 1. Accelerator and reactor neutrino oscillation constraints, including LSND; 2. The atmospheric muon neutrino deficit problem; 3. The solar neutrino problem; 4. Supernova $r$-process nucleosynthesis in neutrino-heated supernova ejecta; 5. Cold+hot dark matter models. We argue that putative supernova $r$-process nucleosynthesis bounds on two-neutrino flavor mixing can be applied directly to three-neutrino mixing in the case where one vacuum neutrino mass eigenvalue difference dominates the others. We show that in this ``one mass scale dominance'' limit, a natural three-neutrino oscillation solution meeting all the above constraints exists only if the atmospheric neutrino data {\em and} the LSND data can be explained with one neutrino mass difference. In this model, an explanation for the solar neutrino data can be effected by employing the {\em other} independent neutrino mass difference. Such a solution is only marginally allowed by the current data, and proposed long-baseline neutrino oscillation experiments can definitively rule it out. If it were ruled out, the simultaneous solution of the above constraints by neutrino oscillations would then require sterile neutrinos and/or a neutrino mass hierarchy of a different nature than that of the charged leptons.

astro-ph↗

arXiv1995

Do experiments and astrophysical considerations suggest an inverted neutrino mass hierarchy?

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 $\sim 5\ {\rm eV}$, 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 $m_{ν_e} \approx m_{ν_s} \approx 2.7\ {\rm eV}$ (where $ν_e$ is split from a sterile species, $ν_s$, by $\sim {10}^{-6} \ {\rm eV}$) and $m_{ν_τ} \approx m_{ν_μ} \approx 1.1\ {\rm eV}$ (where these species are split by $\sim {10}^{-2} \ {\rm eV}$). We discuss alternative neutrino mass spectra that are allowed if we decline to adopt certain experiments or astrophysical models.

astro-ph↗

arXiv1995

Matter-enhanced antineutrino flavor transformation and supernova nucleosynthesis

Matter-enhanced antineutrino flavor transformation between $\barν_e$ and $\barν_{μ(τ)}$ can occur in supernovae if the vacuum masses for these species satisfy $m_{\barν_e}>m_{\barν_{μ(τ)}}$. For $δm^2> 1$ eV$^2$, such flavor transformation can affect the electron fraction $Y_e$ in the neutrino-heated supernova ejecta. We point out that such flavor transformation will not drive $Y_e>0.5$ at the $r$-process nucleosynthesis epoch in the best available supernova model for such nucleosynthesis. Consequently, there is no obvious conflict between matter-enhanced antineutrino flavor transformation $\barν_e\rightleftharpoons\barν_{μ(τ)}$ and $r$-process nucleosynthesis in the neutrino-heated supernova ejecta.

astro-ph↗

arXiv1994

Comment on The Preprint ``Neutrino Flavor Evolution Near A Supernova's Core'' (Astro-Ph 9405008) by J. Pantaleone

The revised version of the widely circulated preprint ``Neutrino Flavor Evolution Near A Supernova's Core'' by J. Pantaleone (astro-ph 9405008 on the Bulletin Board, Indiana University preprint IUHET-276) is wrong. It contains two errors which lead to incorrect conclusions regarding neutrino flavor transformation in the supernova environment. In this short note we discuss these errors.

astro-ph↗

arXiv1994

Neutrino-Neutrino Scattering and Matter-Enhanced Neutrino Flavor Transformation in Supernovae

We examine matter-enhanced neutrino flavor transformation ($ν_{τ(μ)}\rightleftharpoonsν_e$) in the region above the neutrino sphere in Type II supernovae. Our treatment explicitly includes contributions to the neutrino-propagation Hamiltonian from neutrino-neutrino forward scattering. A proper inclusion of these contributions shows that they have a completely negligible effect on the range of $ν_e$-$ν_{τ(μ)}$ vacuum mass-squared difference, $δm^2$, and vacuum mixing angle, $θ$, or equivalently $\sin^22θ$, required for enhanced supernova shock re-heating. When neutrino background effects are included, we find that $r$-process nucleosynthesis from neutrino-heated supernova ejecta remains a sensitive probe of the mixing between a light $ν_e$ and a $ν_{τ(μ)}$ with a cosmologically significant mass. Neutrino-neutrino scattering contributions are found to have a generally small effect on the $(δm^2,\ \sin^22θ)$ parameter region probed by $r$-process nucleosynthesis. We point out that the nonlinear effects of the neutrino background extend the range of sensitivity of $r$-process nucleosynthesis to smaller values of $δm^2$.

astro-ph↗