Standard Solar Model

The various Solar Neutrino Experiments all find that the Sun does not produce as many neutrinos as predicted by theory. However, (many people suggest and try to show that) all three results may be made consistent by noting that the neutrinos are produced in different regions in the core of the Sun.

• The key is that the Branch III reactions occur only near the center of the Sun, where the temperature is the highest. The Davis and Kamiokande results can be explained by making the central temperature of the Sun lower by around 10 %.

• The Gallium experiments can see neutrinos produced throughout the core of the Sun. For more detail, the Gallium experiments are expected to see a total of 132 SNU of which 74 SNU to the first step of the pp-chain, i.e., the proton + proton reaction. That is, it may be consistent with the experiment to say that the higher energy neutrinos are not produced and that what the Gallium experiments see is only the first step of the process (this is okay because the first step of the process is the most important one and is the one that tells you how many reactions occur and therefore how much energy the Sun produces). A lowering of the temperature of the core of the Sun may also explain the Gallium results.

A Lowered Temperature?

It is true that one can lower the neutrino flux by changing the central temperature of the Sun, however, one cannot do this arbitrarily as there are other things which we know about the Sun, e.g., its radius. It is difficult to lower the central temperature of the Sun and reproduce all of the data. But anyway, here are some suggestions:

• Rotating Core ---> rotation supports star ---> lower P ---> lower T
• Magnetic Core ---> Magnetic support ---> lower P ---> lower T
• Change of Composition ---> easier for photons to escape ---> heat escapes more efficiently and heat does not build up ---> lower T
• W(eakly) I(nteracting) M(assive) P(articles), i.e., WIMPs. WIMPs get captured gravitationally by the Sun. WIMPs are efficient transporters of energy in core; more efficient transfer of heat ---> lower T without affecting most observable Solar properties.
• Solar variability ---> neutrino flux varies ---> we are in a low stage (not likely because of GALLEX and SAGE experiments, however).

Presently, it is not clear that any of the above schemes work and perhaps, more radical modeling approaches need to be made.