Neutrino chemical potential and neutrino heat conductivity with allowance for neutrino scattering

The equations of neutrino hydrodynamics are derived in two different approximations taking into consideration the neutrino scattering from stellar material. In a thermal-conductivity approximation which holds good when neutrino optical depth with respect to absorption exceeds 1, the neutrino scattering is taken into account, analogously with photon radiative conductivity, by introducing the transport cross-section in the neutrino mean free path. In a practically important case when the neutrino optical thickness with respect to scattering is high enough, whereas that concerning absorption is sufficiently low, another approximation of Comptonized neutrinos is valid. In this case, the neutrino and antineutrino chemical potentials are independent of each other. They have to be calculated from equations of continuity established for neutrino and antineutrino alongside with the diffusion equation expressing the law of lepton-charge conservation. The equations of neutrino hydrodynamics are written out both with and without inclusion of muon neutrinos and antineutrinos.The equations obtained are established to deal properly with neutrino diffusion inside collapsing stars.     

Neutrino detection with CLEAN

This article describes CLEAN, an approach to the detection of low-energy solar neutrinos and neutrinos released from supernovae. The CLEAN concept is based on the detection of elastic scattering events (neutrino–electron scattering and neutrino–nuclear scattering) in liquified noble gases such as liquid helium, liquid neon, and liquid xenon, all of which scintillate brightly in the ultraviolet. Key to the CLEAN technique is the use of a thin film of wavelength-shifting fluor to convert the ultraviolet scintillation light to the visible, thereby allowing detection by conventional photomultipliers.

Liquid neon is a particularly promising medium for CLEAN. Because liquid neon has a high scintillation yield, has no long-lived radioactive isotopes, and can be easily purified by use of cold traps, it is an ideal medium for the detection of rare nuclear events. In addition, neon is inexpensive, dense, and transparent to its own scintillation light, making it practical for use in a large self-shielding apparatus. The central region of a full-sized detector would be a stainless steel tank holding approximately 135 metric tons of liquid neon. Inside the tank and suspended in the liquid neon would be several thousand photomultipliers.

Monte Carlo simulations of gamma ray backgrounds have been performed assuming liquid neon as both shielding and detection medium. Gamma ray events occur with high probability in the outer parts of the detector. In contrast, neutrino scattering events occur uniformly throughout the detector. We discriminate background gamma ray events from events of interest based on a spatial maximum likelihood method estimate of event location. Background estimates for CLEAN are presented, as well as an evaluation of the sensitivity of the detector for p–p neutrinos. Given these simulations, the physics potential of the CLEAN approach is evaluated.     

Neutrino transport in supernova models: A multigroup,flux limited diffusion scheme

A multigroup, diffusion scheme is derived from the Boltzmann equation for efficient numerical computation of neutrino transport in a collapsing stellar core. This scheme treats all neutrino scattering processes correctly with a Legendre expansion of the scattering rates. Modifications of the diffusion coefficient and the addition of a flux limiter extend the applicability of the scheme to neutrino transparent regimes and improve the agreement of the solution in both opaque and transparent regimes with those obtained analytically for some test problems. In addition, a more accurate treatment of the neutrino flowAcross shock discontinuities is developed through a shock matching condition. The solutions given by this multigroup, flux-limited diffusion scheme are compared with those of a modifiedS _N code.Supported in part by the National Science Foundation (Grant AST75-05012 and AST 77-17572).     

Neutrino luminosity of stars with different masses

Neutrinos play an important role in stellar evolution. They are produced by nuclear reactions or thermal processes. Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA), we study stellar neutrino luminosity with different masses. The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated. We find that the neutrino flux of a star with 1 M⊙mass at an evolutionary age of 4.61 × 10~9 yr is consistent with that of the Sun. In general, neutrinos are produced by nuclear reactions, and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity. However, neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M_⊙. Although the helium flash does not produce neutrinos, plasma decay, one of the thermal processes, can efficiently make neutrinos during this stage. Due to the high mass-loss rate, a star with a mass of 9 M_⊙does not undergo the helium flash. Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage. At the end of the AGB stage, its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.     

超新星坍缩与中微子泄漏

本文用简化的中微子泄漏模式代替输运方程，计算超新星坍缩过程中的中微子变化，通过调节模式中的参数可改变中微子的俘陷密度，使之达到较为合适的值，还讨论了在中微子俘陷密度到达之前，特定密度区段（10~(-10)－5×10~(11)g／cm~3）内使电子俘获率有显著变化的一种参数方法及研究结果。     

中微子泄漏与超新星爆发

在超新星爆发过程中,中微子的泄漏非常重要.采用一维球对称模型,在不同的中微子泄漏模式下,数值模拟了质量为12 M_⊙、14 M_⊙及15 M_⊙的Ⅱ型超新星爆发过程.结果表明:不同的中微子泄漏模式对超新星塌缩、激波的传播和爆发都具有影响;并给出了最有利于Ⅱ型超新星爆发的相关参数的最佳值.此外还讨论了物态方程与压缩模量对模拟结果的影响.     

Neutrino bursts and gravitational waves experiments

Several experiments have been performed in many countries to observe gravitational waves or neutrino bursts. Since their simultaneous emission may occur in stellar collapses, we evaluate the effect of neutrino bursts on gravitational wave antennas and suggest the usefulness of a time correlation among the different detectors.     

The different transport regimes of pitch-angle scattering of energetic particles

Recently an advanced nonlinear diffusion theory for particle transport across the mean magnetic field has been developed. The method used in the derivation of the latter theory is based on the cosmic ray Fokker-Planck equation. In the present article we use the same approach to describe pitch-angle scattering and parallel spatial diffusion nonlinearly. Furthermore, we derive the quasilinear transport theory, the weakly nonlinear theory as well as the Bohm limit as special cases from our more general approach.     

Second-order scattering approximation to X-ray photon transport at balloon altitudes

A numerical solution of the transport equation, based on the iterative method of expansion in order of scattering, is proposed to evaluate the effect of multiple Compton scattering on the cosmic X-ray spectrum from balloon experiments. Computation up to the second order of scattering is performed in the hard X-ray range (10–200 keV). It is shown that this approximation is sufficient to evaluate the X-ray flux at typical balloon atmospherical depths.INFN sez. Rome. On leave from CNR, Istituto di Astrofisica Spaziale.     

Neutrino emission,population II stars and big-bang cosmology

The spectroscopic determination of the helium abundance in the oldest stars of the galaxy is supported by the theory of stellar evolution when neutrino emission is considered according to the photon-neutrino coupling theory, if it is assumed that the population II stars started their life with a low surface helium content.Receipt delayed by postal strike in Great Britain.     

Properties of Hot Quark Matter with Neutrino Confinement in the NJL Model

Astrophysics - The thermodynamic characteristics of hot β-equilibrium three-flavor quark matter with neutrino confinement are studied in terms of the local SU(3) Nambu-Jona-Lasinio (NJL)...     

Neutrino degeneracy and the primordial abundance of helium and deuterium

Recent observations indicate that the primordial abundance of⁴He could be smaller than 0.24. It may then be necessary to invoke neutrino degeneracy in the early universe to explain the primordial abundances of helium and deuterium. It is shown here that the necessary degeneracy, though small, gives rise to a large asymmetry between the present number densities of neutrinos and antineutrinos. The effect of degeneracy on the upper limit to the neutrino masses is also considered.     

Time-dependentX- andY-functions for an isotropically scattering neutron transport problem in a finite slab

Expressions for time-dependentX- andY-functions for a one-speed neutron transport problem in a finite slab have been derived using a technique combining invariant imbedding method and eigenfunction expansion method. The atmosphere has been considered to scatter isotropically.     

Neutrino fluxes from a core-collapse supernova in a model with three sterile neutrinos

The characteristics of the gravitational collapse of a supernova and the fluxes of active and sterile neutrinos produced during the formation of its protoneutron core have been calculated numerically. The relative yields of active and sterile neutrinos in corematter with different degrees of neutronization have been calculated for various input parameters and various initial conditions. A significant increase in the fraction of sterile neutrinos produced in superdense core matter at the resonant degree of neutronization has been confirmed. The contributions of sterile neutrinos to the collapse dynamics and the total flux of neutrinos produced during collapse have been shown to be relatively small. The total luminosity of sterile neutrinos is considerably lower than the luminosity of electron neutrinos, but their spectrum is considerably harder at high energies.     

Exact solution of the transport equation for imperfect rayleigh scattering in a semi-infinite atmosphere

By performing the one-sided Laplace transform on the matrix integro-differential equation for a semi-infinite plane parallel imperfect Rayleigh scattering atmosphere we derive an integral equation for the emergent intensity matrix. Application of the Wiener-Hopf technique to this integral equation will give the emergent intensity matrix in terms of singularH-matrix and an unknown matrix. The unknown matrix has been determined considering the boundary condition at infinity to be identical with the asymptotic solution for the intensity matrix.     

Seasonal Variations in Solar High-Energy Neutrino Flux and Their Probable Source

Cyclic variations of the solar neutrino flux (Homestake detector data) have been analyzed both from season to season and within different seasons and were compared with the corresponding variations of the large-scale deep-layer solar magnetic field. The analysis revealed a seasonal variation of the flux in the last twenty years with extremes at equinox epochs. The mechanism of this variation can be due to the asymmetry in magnitudes or to the twisting of the large-scale magnetic fields in the southern and northern hemispheres of the Sun in the flux modulation region.