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1.
We have developed an algorithm for taking into account the neutrino scattering in the approximation of neutrino heat conduction. We show that in the case of incoherent neutrino scattering (e.g., by electrons), the coefficients of the temperature and chemical potential gradients are averaged over the neutrino energy using functions that can be found by numerically solving integral equations. The coherent scattering by free nucleons and atomic nuclei can be described by introducing a transport cross section. We suggest a new method for calculating the neutrino—electron scattering functions that is based on Fermi—Dirac functions of integer indices.  相似文献   

2.
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).  相似文献   

3.
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.  相似文献   

4.
Neutrinos couple through a weak neutral current to the density of matter, in particular to the neutron density. Density fluctuations, or phonons, in the neutron fluid may be emitted or absorbed by neutrinos passing through the matter. At high densities, temperatures and neutrino energies the neutrino mean free paths for phonon emission and absorption can be 106 cm. Significant changes in the neutrino momentum and energy accompany these processes. We present a model calculation for neutrino scattering by phonons, and representative numerical results for the neutrino mean free path and mean energy and momentum changes fork B T andE v both ranging from 1 to 27 MeV.Research supported by the National Research Council of Canada.  相似文献   

5.
Solution to steady-state, bigroup neutrino transport with isoenergetic and neutrino-electron scattering have been obtained for idealized conditions representative of the outer core or envelope of a star whose inner core is undergoing gravitational collapse. The solutions are presented in a form suitable for comparison with other numerical schemes. The incident neutrino distribution was chosen to be nonequilibrium, and the solutions clearly show the tendency of the neutrinos to equilibrate via neutrino-electron scattering as they propagate through the material. Care is taken to compare solutions obtained by two completely different techniques to ensure that the solutions presented here are accurate and error free. The solutions are compared with those obtained by a simple diffusion scheme, and by a flux limited diffusion scheme. The solutions given by the latter agree well with the solutions derived here, except when the neutrino angular distribution becomes oblate.  相似文献   

6.
The interaction of neutrinos with nuclei in the superdense matter of a collapsing star is studied, taking into account the collective modes and thermal fluctuations of the medium density. It is shown that the elastic neutrino scattering by nuclei with a momentum transfer less than or of the order of the inverse distance between the ions in the nonideal Coulomb plasma, differs considerably from the analogous scattering by a single nucleus. The weak A interaction screening by medium electrons is taken into account. The collision integral and transport cross section of neutrino scattering by nuclei are calculated in terms of macroscopic medium parameters.  相似文献   

7.
Time-dependent neutrino transport out of an optically thick neutronized stellar core is calculated to study the effects of neutrino degeneracy and of source depletion. Neutrino trapping inhibits further neutrino emission until neutrinos peel out of the outer zones of the core, exposing successively inner zones. This inwardly propagating neutrino rarefaction wave can lead toe –+pv+n oscillations in chemical composition. The effect of neutrino Fermi statistics is to retard considrably and disperse neutrino leakage out of the core, making neutrino transport insignificant during fast stages of core collapse.Supported in part by the U.S. Department of Energy under Contract EY-76-C-02-3071.  相似文献   

8.
We have ascertained an important role of rotation effects in a collapsing stellar core using a quasi-one-dimensional hydrodynamic model with a rigorous allowance for the neutrino energy losses including the neutrino opacity stage. However, the neutrino scattering processes are not considered in the neutrino emission kinetics as secondary compared to the absorption processes. The quasi-one-dimensional approximation (with averaging of the expression for the centrifugal force over the polar angle) allows numerical calculations to be performed relatively easily up to the formation of a hydrostatically equilibrium neutron star after a very long stage of collapsar cooling by neutrino emission (about 2 s). We present detailed results of our numerical solution, including the neutrino spectra, with electron neutrinos making a dominant contribution to them and the contribution from electron antineutrinos being smaller by an order of magnitude. In the model under consideration, we solve the equation of matter neutronization kinetics by taking into account the main process of nuclear reactions on free nucleons, although the contribution from iron and helium nuclei is included in the equation of state.  相似文献   

9.
Typically collapsing supernova hydrodynamic computations assume LTE neutrino transport andimpose photon-like behavior, i.e., fix the neutrino chemical potentials at zero. The validity of the latter condition is investigated in the diffusion approximation to transport. A coupled system of diffusion equations for energy and lepton number is solved in a collapsing supernova ambience. The results indicate a substantial growth in the neutrino chemical potential for densities above 1012 gm cm?3. The rate of energy transport is affected significantly by the concomitant increases in Fermi integrals and gradients in chemical potential counter to those of temperature. It is found that the extent of neutrino particle/antiparticle interaction also affects energy diffusion rates. Thus the photon-like condition on neutrino transport may misrepresent supernova energetics substantially. An extension of the usual Sn transport to include lepton characteristics is deemed necessary for a definitive answer to the neutrino transport supernova question.  相似文献   

10.
Possibilities for the development of an r-process in the helium shell of a supernova under the action of free neutrons appearing as a result of inelastic neutrino scattering by 4He nuclei are investigated. The conditions in the outer part of the helium shell in metal-poor stars are shown to be favorable for the reproduction of a weak r-process component.  相似文献   

11.
The properties of the neutrino burst generated by massive 1.5–2M collapsing stellar iron-oxygen cores are discussed. Special attention is given to the neutrino heat conductivity theory which allows us to calculate the transport of neutrinos through the collapsing stellar core up to the formation and during the first seconds of cooling of a hot hydrostatic neutron star. The theoretical predictions seem to be in good agreement with both the KAMIOKANDE II and IMB data on the neutrino burst detected from SN 1987A. The most reliable constraint on the neutrino rest mass is shown to bem v <20–30eV, while the safest upper limit on the neutrino magnetic moment, µ v < 10–11 Bohr magnetons, results rather from the cooling of white dwarfs than from the SN 1987A neutrino data.Presented to the 13th International Conference Neutrino-88, Boston, U.S.A., 5–11 June, 1988.  相似文献   

12.
The collapse of iron-oxygen stars with masses of 2M has been calculated. The commencement of the collapse is due to dissociation of iron-group nuclei into free nucleons. After a while, the collapse proceeds in consequence of intensive energy losses due to neutrino volume radiation. At an intermediate stage of the collapse, the core — opaque with respect to neutrino radiation (neutrino core) — is formed inside the collapsing star. Both the gradual increase of the mass of the neutrino core and the partial absorption of neutrinos radiated from the surface of the neutrino core by the stellar envelope (deposition) were taken into account in our calculations. The kinetics of oxygen burning in the outer layers of the envelope was also allowed for. Neither the deposition, nor the oxygen burning, result in ejection of stellar envelopes.  相似文献   

13.
With the equations of neutrino heat conductivity being used, the neutrino light curve is calculated for the spherically symmetrical collapse of an iron-oxygen 2M star (Figure 1) up to the formation of a hot hydrostatically equilibrium neutron star. The total energy, radiated in the form of muon and electron neutrinos, is 5.8×1053 erg (0.16Mc 2). The mean neutrino particle energy is 12 MeV for all the time the collapse proceeds. The maximum neutrino luminosity value is equal to 3×1053 erg s–1. For a 10M star collapse, the luminosity maximum 3×1054 erg s–1 takes place just at the moment of the formation of a black hole inside the collapsing star. The total radiated energy in this case is about 0.08Mc 2. The set of calculations, allowing for the deposition of momentum by means of neutrino-nuclear coherent scattering, brings us to a conclusion that the envelope outburst is only possible if the scattering cross-section is 50 times larger than the value experimentally accepted (inequality 20)).  相似文献   

14.
We calculate the kinetic coefficients and the transport mean free paths of high-energy particles parallel to the regular magnetic field in the approximation of a large-scale anisotropic random magnetic field by using a nonlinear collision integral, i.e., by taking into account the processes of strong random scattering. We consider the diffusion of solar and Galactic cosmic rays by two-dimensional turbulence. Strong random scattering by two-dimensional turbulence is shown to reduce the parallel transport mean free path several fold. The momentum dependence of the parallel mean free path does not change, Λ∥ ∝ p2?v. In the case of strong random scattering by turbulence formed by several modes, the parallel transport mean free path is Λ∥ ∝ p. We show that two-dimensional turbulence can make a major contribution to the parallel transport mean free paths of cosmic rays in the heliosphere and the interstellar medium.  相似文献   

15.
Four operating neutrino observatories confirm the long standing discrepancy between detected and predicted solar neutrino flux. Among these four experiments the Homestake experiment is taking data for almost 25 years. The reliability of the radiochemical method for detecting solar neutrinos has been tested recently by the GALLEX experiment. All efforts to solve the solar neutrino problem by improving solar, nuclear, and neutrino physics have failed so far. This may also mean that the average solar neutrino flux extracted from the four experiments may not be the proper quantity to explain the production of neutrinos in the deep interior of the Sun. Occasionally it has been emphasized that the solar neutrino flux may vary over time. In this paper we do address relations among specific neutrino fluxes produced in the proton-proton chain that are imposed by the coupled systems of nonlinear partial differential equations of solar structure and kinetic equations by focusing our attention on a statistical interpretation of selected kinetic equations of PPII/PPIII branch reactions of the protonproton chain. A fresh look at the statistical implications for the outcome of kinetic equations for nuclear reactions may shed light on recent claims that the7 Be-neutrino flux of the Sun is suppressed in comparison to the pp- and8B neutrino fluxes and may hint at that the solar neutrino flux is indeed varying over time as shown by the Homestake experiment.  相似文献   

16.
This work deals with the possible solution of the solar neutrino problem in the framework of the resonant neutrino spin-flavor precession scenario. The event rate results from the solar neutrino experiments as well as the recoil electron energy spectrum from SuperKamiokande are used to constrain the free parameters of the neutrino in this model (Δm2 and μν). We consider two kinds of magnetic profiles inside the sun. For both cases, a static and a twisting field are discussed.  相似文献   

17.
《Astroparticle Physics》2002,16(3):205-234
Borexino, a real-time device for low energy neutrino spectroscopy is nearing completion of construction in the underground laboratories at Gran Sasso, Italy (LNGS). The experiment's goal is the direct measurement of the flux of 7Be solar neutrinos of all flavors via neutrino–electron scattering in an ultra-pure scintillation liquid. Seeded by a series of innovations which were brought to fruition by large-scale operation of a 4-ton test detector at LNGS, a new technology has been developed for Borexino. It enables sub-MeV solar neutrino spectroscopy for the first time. This paper describes the design of Borexino, the various facilities essential to its operation, its spectroscopic and background suppression capabilities and a prognosis of the impact of its results towards resolving the solar neutrino problem. Borexino will also address several other frontier questions in particle physics, astrophysics and geophysics.  相似文献   

18.
Nonlinear processes describing the interaction of neutrinos with collective plasma oscillations and the excitation of plasma turbulence by a large neutrino flux is discussed. The excitation considered is the inverse processes of neutrino emission by plasma waves first considered by Tsytovich (V.N. Tsytovich, Soviet Fiz. Dokl. 9 (1965) 1114). The process is similar to a beam plasma instability considered as inverse Landau damping in which the usual electromagnetic interactions are important. In the neutrino beam relaxation the weak interaction can play a similar role. We emphasize here the possibility of another process namely the interaction of an intense neutrino flux with a strongly turbulent plasma. The turbulence can also be assumed to be due to the shock produced at the early stages of a type II supernova (SN) explosion. The scattering of the neutrinos in the turbulent plasma is shown to be sufficient for transferring momentum and energy from the neutrino flux to the plasma causing the shock to continue moving outward and eventually creating the blow-off of the mantle of the star producing type II SN.  相似文献   

19.
In this paper, the neutrino mass has been determined from SN1987a observation in a manner that the simultaneity of neutrino emission is not regarded as the starting point, but is itself defined through the analysis by Monte-Carlo simulation. The result is that the neutrino mass lies in 3–4 eV, possiblym v 3.6 eV. Neutrino luminosity variation and neutrino spectrum are also obtained. Comparison with theories gives further support to the mass determination, and also predicts the mass of progenitor star of SN1987a to be in the range of 12–25M .The project supported by the National Natural Science Foundation of China.  相似文献   

20.
By combining data from cosmic microwave background (CMB) experiments (including the recent WMAP third year results), large scale structure (LSS) and Lyman-α forest observations, we derive upper limits on the sum of neutrino masses of Σmν < 0.17 eV at 95% c.l. We then constrain the hypothesis of a fourth, sterile, massive neutrino. For the third massless +1 massive neutrino case we bound the mass of the sterile neutrino to ms < 0.26 eV at 95% c.l. These results exclude at high significance the sterile neutrino hypothesis as an explanation of the LSND anomaly. We then generalize the analysis to account for active neutrino masses which tightens the limit to ms < 0.23 eV and the possibility that the sterile abundance is not thermal. In the latter case, the constraints in the (mass, density) plane are non-trivial. For a mass of >1 eV or <0.05 eV the cosmological energy density in sterile neutrinos is always constrained to be ων < 0.003 at 95% c.l. However, for a sterile neutrino mass of 0.25 eV, ων can be as large as 0.01.  相似文献   

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