Astrophysical/Nuclear Physics Explanations

There is clearly a discrepancy between the existing data and the predictions of the standard solar model (SSM). One can consider nonstandard solar models (NSSM), which differ by significant changes in the input parameters or due to the inclusion of additional effects not included in the SSM. However, it is difficult to account for the data by purely astrophysical and/or nuclear physics explanations, because they generally predict a larger suppression of the higher energy B-8 neutrinos compared to the Be-7 neutrinos, since the B-8 is made after and from Be-7.

Analyses have been made of generic cool sun models; models with lower nuclear cross sections ; and of explicit nonstandard models . More generally, one can make a model independent analysis of essentially all NSSM by allowing the magnitudes of each flux component to be a free parameter. One can also use the observed Kamiokande rate to predict the rates observed in the gallium experiments.

• Cool Sun Models, [ref].
  • Many nonstandard solar models manifest themselves for neutrinos by a lower core temperature TC (with respect to the SSM prediction [ref] 1.6 x 10^7 K). In all reasonable models the B-8 flux is more temperature sensitive (e.g., TC^18) than Be-7 (e.g., TC^8), implying a larger suppression for Kamiokande than Homestake, contrary to the data. (For large deviations from the SSM, the pp flux must be chosen to give the correct solar luminosity.)
  • Expected temperature dependence (postscript file, 7K)

    

  • Suppression factors for each type of experiment (description, from [ref]).

    

• Low S17 , [ref]; nonstandard TC and cross sections [ref]; explicit nonstandard models , [ref]. (description)

• Model Independent Analysis [ref].
  (description, from [ref]).

  Almost the most general NSSM can be parametrized as far as the solar neutrinos are concerned by the overall magnitudes of each of the flux components: pp, Be-7, B-8, and CNO. Unlike MSW, no known astrophysical or nuclear mechanism can distort the shape of the B-8 spectrum significantly [ref].

  Constraints on individual experiments, 7/94, updated from [ref]. (description, from [ref]). (postscript file, 9K)

  

  The combined fit to the Be-7 and B-8 fluxes, relative to the SSM predictions, shows that the Be-7 flux is depleted much more than the B-8 flux. Not only is this far from all realistic standard and nonstandard solar models, but it is also a very poor fit to the data. In the fit, the chis for each value of the Be-7 and B-8 fluxes is minimized with respect to the other fluxes, subject to the luminosity constraint .

  Constraints from combined fit, 7/94, updated from [ref]. (description, from [ref]). (postscript file, 37K)

  

  The same conclusion, i.e., that the Be-7 flux is much more strongly depleted than the B-8 flux, can be obtained from any two of the three classes of solar neutrino experiments:

  Constraints on flux components, 7/94, from [ref]. (description, from [ref]).

  

• Gallium Predictions for nonstandard models agreeing with Kamiokande

  Even disregarding the Homestake results, it is difficult to reconcile the observed Kamiokande and gallium rates in any NSSM. The figure displays the predictions for the gallium experiments of a number of explicit NSSM which agree with Kamiokande (which determines the B-8 flux). They all predict rates in excess of 100 SNU, well above the combined observations.

  Predictions for gallium, 7/94, updated from [ref]. (postscript file, 11K)

  

• Standard Solar Model Predictions
• Current data and comparison with standard solar model predictions
• MSW interpretation
• References
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