Weak sun blamed on WIMPS.

There is something wrong with the sun. For almost two decades now, observers have been monitoring the flux of neutrinos from the sun. Consistently, they have recorded significantly fewer neutrinos than the astrophysicists' model of what goes on in the sun leads them to expect. Neutrinos come from the deepest center of the sun so the lack of the expected number says something about conditions there.

What it may say, according to John Faulkner of the University of California at Santa Cruz (UCSC) and Ron Gilliland of the National Center for Atmospheric Research in Boulder, Colo., is that the sun's core is inhabited by WIMPS (Weakly Interacting Massive Particles). WIMP is a generic term; a specific kind of particle that could fill the bill is a hypothetical one known as a photino. However, another argument, recently published, avers that photinos living in the center of the sun could not be responsible for lessening the neutrino flux.

What WIMPS would do, according to Faulkner and Gilliland, is to cool the center of the sun. Being massive (by particle physics standards) WIMPS stay near the center of the sun, orbiting around in there. As weakly interacting particles, they sometimes collide with other objects and carry away some energy (but not too much), which they then give away to regions outward from the core. Thus they cool the core just enough to slow down the thermonuclear fusion reactions that go on there, and that would lessen the flux of neutrinos.

Faulkner and Gilliland got this scenario from a computer model of the sun's evolution that they calculated some years ago, while Gilliland was a graduate student at UCSC. At the time they finished the calculation, they decided not to publishe it, Faulkner says, because at the moment there seemed to be good astrophysical arguments against WIMPS. Now those arguments have fallen away and there are some unexplained experimental results from the CERN laboratory in Geneva that could indicate that particles like WIMPS, and specifically photinos, really do exist. So now Faulkner and Gilliland are about to publish their solar model.

Meanwhile, the same experiments at CERN prompted Joseph Silk of the University of California at Berkeley, Keith Olive of the Fermi National Accelerator Laboratory in Batavia, Ill., and Mark Srednicki of the University of California at Santa Barbara to consider photinos as candidates for the unseen or dark matter that astrophysicists believe is plentiful in the universe; which would account for the cohesion of clusters of galaxies and also ensure that the universe has a closed geometry. Their report, in the July 8 PHYSICAL REVIEW LETTERS, indicates that if there are a large number of photinos floating around the cosmos, the sun's gravity would continually draw some of them to its interior. As they orbit there, photinos and antiphotinos would meet at a fairly steady rate and annihilate one another. The result of the annihilation would be high-energy (250 million electron-volt) neutrinos. Thus the sun would have an extra flux of neutrinos, and these high-energy neutrinos should be detectable on earth in experiments now running.

While the photinos are moving through the sun, however, Silk, Olive and Srednicki calculate, their cross section or probability for collision with other particles is too low to cool the sun's core significantly. Faulkner and Gilliland calculate that the cross section is large enough. Exactly what you get in such a case depends on what you assume about the behavior of the hypothetical particle. If anyone finds and measures the properties of an actual photino, that might resolve the disagreement.

Photinos are a prediction of the super-symmetry theories, which propose that every particle we now know has an as yet unknown partner. Photinos would be partners to the photons or particles of light. The CERN results may indicate the existence of a squark (partner of a quark) of about 50 billion electron-volts mass. If that is true, it means that photinos of about 4 billion to 10 billion electron-volts are likely to exist.