arXiv subjects

Yong-Zhong Qian

Publications and source records attributed to Yong-Zhong Qian.

81 records · Page 5Linked to original sources

arXiv2002

Constraints on the Variations of the Fundamental Couplings

We reconsider several current bounds on the variation of the fine-structure constant in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories. In particular, we re-examine the bounds established by the Oklo reactor from the resonant neutron capture cross-section of 149Sm. By imposing variations in Λ_{QCD} and the quark masses, as dictated by unified theories, the corresponding bound on the variation of the fine-structure constant can be improved by about 2 orders of magnitude in such theories. In addition, we consider possible bounds on variations due to their effect on long lived α- and β-decay isotopes, particularly 147Sm and 187Re. We obtain a strong constraint on Δα/ α, comparable to that of Oklo but extending to a higher redshift corresponding to the age of the solar system, from the radioactive life-time of 187Re derived from meteoritic studies. We also analyze the astrophysical consequences of perturbing the decay Q values on bound state β-decays operating in the s-process.

hep-ph↗

arXiv2000

Neutrinos and the Supernova Origin of the Elements

Intense fluxes of neutrinos are emitted by the hot neutron star produced in a supernova. The electron neutrino and antineutrino capture reactions on neutrons and protons, respectively, provide heating to drive a wind from the hot neutron star. The same reactions also determine the neutron-richness of the wind material. Nucleosynthesis via rapid neutron capture, the r-process, may occur in the wind material as it expands away from the neutron star. The neutron-richness of the wind material, and hence, the r-process nucleosynthesis therein, are sensitive to mixing between the muon (or tauon) neutrino/antineutrino and the electron (or sterile) neutrino/antineutrino. Indirect arguments and direct tests for the supernova origin of the r-process elements are discussed with a goal to establish supernova r-process nucleosynthesis as an important probe for neutrino mixing.

astro-ph↗

arXiv2000

Recent Progress in Understanding Nucleosynthesis via Rapid Neutron Capture

I discuss the recent progress in our understanding of nucleosynthesis via rapid neutron capture, the r-process, based on meteoritic data for the early solar system and observations of stars at low metallicities. At present, all data require that there be two distinct kinds of r-process events and suggest that supernovae are associated with these events. The diversity of supernova sources for the r-process may depend on whether a neutron star or black hole is formed in an individual supernova. This dependence, if substantiated by future observations discussed here, has important implications for properties of nuclear matter.

astro-ph↗

arXiv1998

Some nuclear physics aspects of core-collapse supernovae

Here I review some nuclear physics aspects of core-collapse supernovae concerning neutrinos. Studies of neutrino emission and interactions in supernovae are crucial to our understanding of the explosion mechanism, the heavy element nucleosynthesis, and pulsar proper motions. I discuss the effects of reduced neutrino opacities in dense nuclear matter on supernova neutrino emission and their implications for the delayed supernova explosion mechanism and the synthesis of neutron-rich heavy elements. I also discuss the effects of parity violation in weak interactions on supernova neutrino emission and their implications for pulsar proper motions.

astro-ph↗

arXiv1997

Neutrino-induced neutron spallation and the site of the r-process

All of the actinides and roughly half the natural abundance of elements with mass number A > 70 come from the rapid neutron capture process, or the r-process. If the r-process, as suggested by many, occurs deep in a supernova, then it is under the influence of an intense neutrino flux. Here we discuss the effects of both charged-current and neutral-current neutrino interactions on the r-process. We show that the multiple-neutron emission induced by both kinds of neutrino interactions can affect the observed r-process abundance pattern significantly. In particular, we find that five nuclei below the r-process abundance peak at A = 195 may be entirely attributed to the neutrino-induced neutron spallation processes following the r-process freeze-out. Furthermore, the deduced neutrino fluence agrees with the conditions in the recent supernova r-process model. These results strongly argue that the r-process occurs in supernovae. They also provide a sensitive probe for the conditions at the supernova r-process site.

nucl-th↗

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↗