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P.A. Sturrock, G. Walther (Stanford University), M.S. Wheatland (University of Sydney, Australia)
If neutrinos have a sufficiently strong magnetic moment, the solar neutrino flux will be modulated by the Sun’s internal magnetic field. We have spectrum-analyzed the Homestake data, looking for evidence of periodic modulation in the range 12.6 – 13.3 y-1 due to structures in the radiative zone that has a sidereal rotation rate in the range 13.6 – 14.3 y-1. We find a peak at 12.88 y-1. The estimated probability of finding such a peak in the search band by chance is about 3%. We also find sidebands at 11.88, 12.88, 14.88 and 15.88 y-1, attributable to a seasonal modulation due to the tilt of the solar axis. The estimated probability of this combination occurring by chance is about 0.2%. We have more recently examined the GALLEX data and find that the strongest peak in the range 1 to 20 cycles per year occurs at 13.10 y-1, close to the value found in the Homestake data. The estimated probability of finding such a periodicity in the search band by chance is less than 0.1%. There is evidence for some other well known solar periodicities in the neutrino data: a peak at 2.32 cycles per year (period = 157 days) in the Homestake data, and a peak at 7.00 cycles per year (period = 52 days) in the GALLEX data. We propose that these periodicities [together with another well known periodicity at 4.67 cycles per year (period = 78 days)] are due to internal r-mode oscillations. We suggest that these modulations in the neutrino flux may be understood in terms of the RSFP (resonant spin flavor precession) mechanism proposed by Akhmedov and others. This interpretation leads to an estimate of \Delta m2 and to a lower limit for the neutrino magnetic moment. This work was supported in part by Air Force grant F49620-95-1-008 and NASA grants NAS 8-37334 and NAGW-5-4038.
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