Seasonal oscillation of the solar neutrino flux: Effects of twisting toroidal magnetic fields in the Sun

An intriguing possibility is explored that the solar neutrino data could be used as a probe to the magnetic field structure in the Sun. Various cyclic phenomena occurring on the surface of the Sun have been accounted for by the so-called dynamo mechanism. According to this, a self-generating mechanism of solar cyclic activities gives rise to twisting toroidal magnetic fields in the convective zone. Although its magnitude is not known, the orientation of the twist is certainly opposite in northern and southern hemispheres of the Sun. We show by numerical calculation that the solar neutrino flux, being sensitive to the twist, could exhibit observable seasonal oscillation, provided that the twist is sizable in magnitude and the neutrinos have reasonably large magnetic moments. This oscillation is ascribed to the fact that the Earth's orbit is slightly inclined to the Sun's equator, and that solor neutrinos pass through the northern (southern) hemisphere of the Sun around September (March). We also argue that similar seasonal oscillation could be exhibited in the azimuthal asymmetry of recoiling electrons scattered by the solar neutrinos which are expected to be observed in the super-Kamiokande detector.