LMA and sterile neutrinos: a case for resonance spin flavour precession

Abstract

Open questions remain after the confirmation of LMA as the dominant solution to the solar neutrino deficit. These are the apparent time modulation of the solar neutrino event rates in the Homestake, Gallium and SuperKamiokande experiments, possibly related to solar magnetic activity, the discrepancy between the event rate in the Homestake experiment and its theoretical prediction and the absence of the electron spectrum upturn in SuperKamiokande at energies below 6-8 MeV. We search for a possible understanding of these questions in the context of resonant spin flavour precession to sterile neutrinos, assuming a class of magnetic field profiles anchored in the upper radiation/lower convection zone. We consider the simplest such model beyond the standard 2ν flavour LMA one, with one single magnetic moment transition between active and sterile state and vanishing vacuum mixing. The preferred mass square difference is ∆m 2 10 = O(10 −8 eV 2 ). The Ga rate appears to be the most sensitive of all to solar activity. It is also found that a field profile extending within a longer region in the radial direction is favoured over another with a shorter span, and leads to a stronger suppression than in the LMA case of the intermediate energy neutrinos and some of the 8 B ones.

Spin-flavor oscillations of neutrinos in rapidly varying external fields

“…[10] where an attempt was made to reproduce the data of the major solar neutrino experiments using the peak profiles of the solar magnetic field. Different approach to the solar neutrino problem was made in Ref.…”

Solar Neutrinos: Spin Flavour Precession and Lma

“…The kinetic energy threshold of 250 keV and maximum of 664 keV ensures that this experiment is directed mainly at 7 Be neutrino flux (E Be = 0.86MeV ). The reduced rate for Borexino is, in standard notation (4) and is shown in fig.2 as a function of the peak field B 0 . It is seen that in the pp + 7 Be dominated modulation the rate decreases faster for increasing B 0 , thus exhibiting more sensitivity to solar activity than in the pp case: the more sensitive 7 Be flux is to the peak field, the more sensitive will the event rate be.…”

“…The typical density profile of the sun requires the mass square difference associated to resonant conversion from active to nonactive neutrinos to be of the order of 10 −8 eV 2 [4], [5]. This excludes the solar and atmospheric mass square differences, ∆m , and therefore conversion toν µ orν τ .…”

“…It is seen that the strongly § For details see ref. [4]. adiabatic LMA transition, whose location is determined for each energy by ∆m 2 21 , takes place in the solar core.…”

Perturbative approach to the spin-flavor precession of Majorana-type solar neutrinos

“…This can also be responsible for the solar electron neutrino deficit. The SFP effect has been investigated by several studies in different aspects [23][24][25][26][27][28][29][30].…”