Light sterile neutrinos, spin flavour precession and the solar neutrino experiments

Abstract

We generalize to three active flavours a previous two flavour model for the resonant spin flavour conversion of solar neutrinos to sterile ones, a mechanism which is added to the well known LMA one. The transition magnetic moments from the muon and tau neutrinos to the sterile play the dominant role in fixing the amount of active flavour suppression. We also show, through numerical integration of the evolution equations, that the data from all solar neutrino experiments except Borexino exhibit a clear preference for a sizable magnetic field either in the convection zone or in the core and radiation zone. This is possibly related to the fact that the data from the first set are average ones taken during a period of mostly intense solar activity, whereas in contrast Borexino data were taken during a period of quiet sun. We argue that the solar neutrino experiments are capable of tracing the possible modulation of the solar magnetic field. Those monitoring the high energy neutrinos, namely the 8 B flux, appear to be sensitive to a field modulation either in the convection zone or in the core and radiation zone. Those monitoring the low energy fluxes will be sensitive to the second type of solar field profiles only. In this way Borexino alone may play an essential role, since it examines both energy sectors, although experimental redundancy from other experiments will be most important.

Improving LMA predictions with non standard interactions

“…In section 3 we investigate the influence of the NSI couplings on these rates in order to find whether and how the fits can be improved with respect to the LMA ones. We concentrate in particular on the elimination of the upturn in the SuperKamiokande spectrum predicted by LMA for energies below 8-10 MeV not supported by the data [27,28,29,30] and on the Chlorine rate whose LMA prediction exceeds the data by 2σ [32,33]. We find that there are quite limited possibilities for the NSI couplings allowing for such fit improvements.…”

“…Although LMA is generally accepted as the dominant solution to the solar neutrino problem [25,26], not only its robustness has been challenged by NSI, as it can shift the LMA solution to the dark side region of parameter space [22], but also some inconsistencies remain regarding its agreement with the data [27,28]. In fact, while the SuperKamiokande (SK) energy spectrum appears to be flat [29,30], the LMA prediction shows a clear negative slope in the same energy range.…”

Improving LMA predictions with non-standard interactions: neutrino decay in solar matter?

“…In section 3 we investigate the influence of the NSI couplings on these rates in order to find whether and how the fits can be improved with respect to the LMA ones. We concentrate in particular on the elimination of the upturn in the SuperKamiokande spectrum predicted by LMA for energies below 8-10 MeV not supported by the data [27][28][29][30] and on the Chlorine rate whose LMA prediction exceeds the data by 2σ [32,33]. We find the intriguing result that only imaginary diagonal couplings in the matter Hamiltonian provide a suitable solution to the problem.…”

“…(6)]. This may occur as a consequence of the vacuum mixing angle (oscillations) [25,26] or the magnetic moment for instance [27,28]. On the other hand, in the case of NSI the interaction potentials [eq.…”

“…Furthermore all cases in the third column of table Comparison between the LMA predictions for solar event rates and the NSI ones with −i|ε e P µµ | = −i 1.5 × 10 −3 . For details of the χ 2 analysis see for instance [27].…”