35 research outputs found
Solar Neutrinos Almost Independently of Solar Models
No full textRecent solar neutrino results together with the assumption of a stationary Sun imply severe constraints on the individual components of the total neutrino flux : and (at 1 level), the constraint on being in strong disagreement with . We study a large variety of non-standard solar models with low inner temperatures, finding that the temperature profiles T(m) follow the homology relationship: T(m)=k, so that they are specified just by the central temperature . There is no value of which can account for all the available experimental results and also if we restrict to consider just Gallium and Kamiokande results the fit is poor. Finally we discuss what can be learned from new generation experiments, planned for the detection of monochromatic solar neutrinos, about the properties of neutrinos and of the Sun
Element Diffusion in the Solar Interior
No full textWe study the diffusion of helium and other heavy elements in the solar interior, using the flow equations developed by Burgers (1969) for a multi-component fluid. The set of equations is solved exactly, including the residual heat flow terms. No approximation is made about the relative concentrations and no restriction is placed on the number of elements considered. For helium diffusion, we compare our results with those obtained by Bahcall and Loeb (1990) using a simplified treatment with heat flows neglected. We find that the inclusion of the residual heat flow terms leads to a significant increase in the helium diffusion velocity. However, we also find that the temperature and charge-dependence of the Coulomb logarithm has the opposite effect, leading to a decrease in the helium diffusion velocity. By coincidence, the two effects partially cancel each other out throughout most of the solar interior. Our complete treatment of element diffusion could be directly incorporated in a standard stellar evolution code, but, for convenience, we also give simple analytical fits of our numerical results. Burgers, J.M. 1969, Flow equations for composite gases(Academic Press, New York). Bahcall, J.N., and Loeb, A. 1990, Ap.J.,360, 267
Updated opacities from the opacity project
No full textUsing the code autostructure, extensive calculations of inner-shell atomic data have been made for the chemical elements He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, Mn, Fe and Ni. The results are used to obtain updated opacities from the Opacity Project (OP). A number of other improvements on earlier work have also been included. Rosseland-mean opacities from the OP are compared with those from OPAL. Differences of 5-10 per cent occur. The OP gives the 'Z-bump', at log(T) 5.2, to be shifted to slightly higher temperatures. The opacities from the OP, as functions of temperature and density, are smoother than those from OPAL. The accuracy of the integrations used to obtain mean opacities can depend on the frequency mesh used. Tests involving variation of the numbers of frequency points show that for typical chemical mixtures the OP integrations are numerically correct to within 0.1 per cent. The accuracy of the interpolations used to obtain mean opacities for any required values of temperature and density depends on the temperature-density meshes used. Extensive tests show that, for all cases of practical interest, the OP interpolations give results correct to better than 1 per cent. Prior to a number of recent investigations which have indicated a need for downward revisions in the solar abundances of oxygen and other elements, there was good agreement between properties of the Sun deduced from helioseismology and from stellar evolution models calculated using OPAL opacities. The revisions destroy that agreement. In a recent paper, Bahcall et al. argue that the agreement would be restored if opacities for the regions of the Sun with 2 × 106T 5 × 106 K (0.7-0.4 R) were larger than those given by OPAL by about 10 per cent. In the region concerned, the present results from the OP do not differ from those of OPAL by more than 2.5 per cent
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Improved Limit on Charge Conservation Drive from {sup 71} Ga Solar Neutrino Experiments
No full textMolecular hydrogen in galaxies
No full textThis study aims to understand the key role played by molecular hydrogen in the evolution of galaxies, with a view to constraining its radial distribution in the Galaxy and the CO→H(_2) conversion factor α(_20).The star formation rate is shown to be correlated with the surface density of H(_2). A correlation between the molecular hydrogen fraction and the metallicity of a region allows the time evolution of H(_2) to be described. This leads to a modified 'Schmidt Law' of the SFR which explains quite naturally the production of galactic metallicity gradients and the constancy of the SFR in the absence of infall. A consistent closed model of the chemical evolution of the Galaxy is proposed to solve the G-dwarf problem, the stellar age-metallicity relation and the metallicity gradient, leading to the prediction of some initial amount of pre-disc processing of gas into visible and dark matter. It is found that a constant yield of metals is more appropriate than a yield proportional to metallicity. Possible time variations of the returned fraction, the dark matter fraction and the SFR are also studied. For consistency, we suggest that dark matter in the solar neighbourhood could be totally baryonic provided the Miller-Scalo IMF is modified at the lower end, that is, the dark matter resides in low mass stars or brown dwarfs. The production of metallicity gradients in spiral galaxies is shown to be a direct consequence of the radial variation of the total surface density of matter and the age of the disc. The role of molecular gas in the evolution of the Oort Cloud of comets is examined. It is shown that comet showers with a mean interval of ̴̱ 30My cannot be produced using perturbations of the Oort Cloud by known stars or molecular clouds. If there is indeed an apparent 30My periodicity in the terrestrial mass extinction and geological records, we argue that astronomically induced processes are unlikely to be the primary cause. Evidence is presented that the lifetime of the molecular gas phase is ≤ 2.lO(_8)y, and arguments, particularly from CO observations of the Virgo galaxy cluster, favouring longer lifetimes are shown to be not well founded. We suggest that the ICM in Virgo reduces the value of α(_20) as compared to isolated galaxies. From the above considerations, the radial distribution of in the Galaxy is derived and shown to agree in the inner Galaxy with that derived from ɤ-ray analysis. In the solar neighbourhood we find α(_20) = 2.5±0.5, and present evidence that α(_20) varies as a function of Galactocentric radius and from galaxy to galaxy
Updated Solution To The Solar Neutrino Problem Based On Non-standard Neutrino Interactions
No full textWe present an updated version of the solution to the solar neutrino problem based on non-standard flavor changing neutrino interactions (FCNI) and non-universal flavor diagonal neutrino interactions (FDNI). We find a good fit not only to the total rates measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration. © 2001 Elsevier Science B.V.1001-36264Bergmann, S., Guzzo, M.M., De Holanda, P.C., Krastev, P.I., Nunokawa, H., (2000) Phys. Rev. D, 62, p. 073001. , (hep-ph/0004049)Cleveland, T.B., (1998) Astrophys. J., 496, p. 505. , (Homestake Collaboration)Hampel, W., (1999) Phys. Lett., 447, p. 127. , (GALLEX Collaboration)Abdurashitov, J.N., (1999) Phys. Rev. C, 60, p. 055801. , (SAGE Collaboration)Fukuda, Y., (1999) Phys. Rev. Lett., 82, p. 1810. , (SuperKamiokande Collaboration)Wolfenstein, L., (1978) Phys. Rev., 17, p. 2369Guzzo, M.M., Masiero, A., Petcov, S.T., (1991) Phys. Lett., 260, p. 154Barger, V., Phillips, R.J.N., Whisnant, K., (1991) Phys. Rev. D, 44, p. 1629Roulet, E., (1991) Phys. Rev. D, 44, p. 935Degl'Innocenti, S., Ricci, B., (1993) Mod. Phys. Lett., 8, p. 471Fogli, G.L., Lisi, E., (1994) Astroparticle Phys., 2, p. 91P.I. Krastev, J.N. Bahcall, FCNC solutions to the solar neutrino problem, , hep-ph/9703267Bergmann, S., (1998) Nucl. Phys., 515, p. 363. , [hep-ph/9707398]Resonant neutrino conversion induced by non-orthogonal massless neutrinos was first discussed by J.W.F. Valle in Phys. Lett. B 199, 432 (1987). However this mechanism can not induce a large effect on the solar neutrinos due to the stringent constraints on the model parametersBahcall, J.N., Basu, S., Pinsonneault, M.H., (1998) Phys. Lett., 433, p. 1. , see also J.N. Bahcall's home page, http://www.sns.ias.edu/ ∼jnbFogli, G.L., Lisi, E., Montanino, D., (1994) Phys. Rev. D, 49, p. 3226Fogli, G.L., Lisi, E., (1995) Astropart. Phys., 3, p. 185Gonzalez-Garcia, M.C., (1998) Phys. Rev. D, 58, p. 033004. , For recent analysis, see e.gGonzalez-Garcia, M.C., Nunokawa, H., Peres, O.L.G., Valle, J.W.F., (1999) Nucl. Phys., 543, p. 3. , [hep-ph/9807305]N. Fornengo, M.C. Gonzalez-Garcia, J.W.F. Valle, hep-ph/0002147Athanassopoulos, C., (1996) Phys. Rev. Lett., 77, p. 3082Athanassopoulos, C., (1998) Phys. Rev. Lett., 81, p. 1774. , (LSND Collaboration)Bergmann, S., Grossman, Y., (1999) Phys. Rev. D, 59, p. 093005. , [hep-ph/9809524]Bergmann, S., Grossman, Y., Pierce, D.M., (2000) Phys. Rev. D, 61, p. 53005. , [hep-ph/9909390
Measurement of double beta decay of ¹⁰⁰Mo to excited states in the NEMO 3 experiment
No full textThe double beta decay of ¹⁰⁰Mo to the 0_{1}^{+} and 2_{1}^{+} excited states of ¹⁰⁰Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of ¹⁰⁰Mo to the excited 0_{1}^{+} state is measured to be T_{1/2}^{2v} = [5.7_{-0.9}^{+1.3} (stat.) ± 0.8 (syst.)] x 10²⁰ y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0_{1}^{+} state has been found. The corresponding half-life limit is T_{1/2}^{0v} (0⁺→0_{1}^{+}) > 8.9 x 10²² y (at 90% C.L.). The search for the double beta decay to the 2_{1}^{+} excited state has allowed the determination of limits on the half-life for the two neutrino mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.1 x 10²¹ y (at 90% C.L.) and for the neutrinoless mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.6 x 10²³ y (at 90% C.L.)
