Solar neutrino oscillations and bounds on neutrino magnetic moment and solar magnetic field

If the observed deficit of solar neutrinos is due to neutrino oscillations, neutrino conversions caused by the interaction of their transition magnetic moments with the solar magnetic field (spin-flavour precession) can still, be present at a subdominant level. In that case, the combined action of neutrino oscillations and spin-flavour precession can lead to a small but observable flux of electron antineutrinos coming from the sun. Non-observation of these (v) over bar (e)'s could set limits on neutrino transition moment mu and the strength and coordinate dependence of the solar magnetic field B-perpendicular to. The sensitivity of the (v) over bar (e) flux to the product muB(perpendicular to) is the strongest in the case of the vacuum oscillation (VO) solution of the solar neutrino problem; in the case of the LOW solution, it is weaker, and it is the weakest for the LMA solution. For different solutions, different characteristics of the solar magnetic field B-perpendicular to(r) are probed: for the VO solution, the (v) over bar (e) flux is determined by the integral of B-perpendicular to(r) over the solar convective zone, for LMA it is determined by the magnitude of B-perpendicular to in the neutrino production region, and for LOW it depends on the competition between this magnitude and the derivative of B-perpendicular to(r) at the surface of the sun. (C) 2002 Elsevier Science B.V. All rights reserved.