Stars as Laboratories for Fundamental Physics - MPP Theory Group

Solar Neutrinos 353
While helium and metal diffusion increases the neutrino fluxes, the
changes are roughly within the claimed errors of previous standard solar
model predictions. Many improvements of input physics over the years
have left the neutrino flux predictions of Bahcall and his collaborators
surprisingly stable over 25 years (Bahcall 1989, 1995). Bahcall (1994)
has compiled the central temperature predictions from a heterogeneous
set of 12 standard solar models without diffusion calculated by different
authors since 1988. The temperature predictions are almost uniformly
distributed on the interval 15.40−15.72×10 6 K, i.e. these authors agree
with each other on the value 15.56×10 6 K within ±1%.
Thus, in spite of differences in detail there exists a broad consensus
on what one means with a standard solar model. Therefore, the neutrino
fluxes of the Bahcall and Pinsonneault (1995) model with element
diffusion (Tab. 10.1 and Fig. 10.1) can be taken to be representative.
The general agreement on a standard solar model does not guarantee, of
course, that there might not exist problems related to incorrect standard
assumptions or incorrect input parameters common to all such
models.
10.2.3 Uncertainties of Standard Neutrino Predictions
a) Opacities
In order to compare the neutrino flux predictions with the experimental
measurements one needs to develop a sense for the reliability of the
calculations. Naturally, it is impossible to quantify the probability
for the operation of some hitherto unknown physical effect that might
spoil the predictions; an error analysis can only rely on the recognized
uncertainties of standard input physics. Very detailed error analyses
can be found for the standard solar models of Bahcall and Pinsonneault
(1992) and of Turck-Chièze and Lopes (1993).
As for solar modelling, the dominating uncertainty arises from the
radiative opacities which largely determine the temperature profile of
the Sun. A reduction of the Rosseland mean opacity in the central
region by 10% reduces the temperature by about 1%.
There is not a one-to-one correspondence between the central solar
temperature T c and the neutrino fluxes because it is not possible to
adjust T c and leave all else equal. Conversely, one must modify some
input parameters and evolve a self-consistent solar model. Still, if one
allows all input parameters to vary according to a distribution determined
by their measured or assumed uncertainties one finds a strong