Borexino as a test of solar matter density fluctuations
This talk summarizes some results of our recent work focusing on the possibility to test solar matter density fluctuations by the future Borexino experiment.
hep-ph↗
arXiv subjects
H. Nunokawa
Publications and source records attributed to H. Nunokawa.
An Updated Analysis on Atmospheric Neutrinos
We have reanalysed the atmospheric neutrino data including new results from Super-Kamiokande and Soudan-II experiments, under the assumption of two-flavor neutrino oscillation. We present the allowed region of oscillation parameters for the $ν_μ\toν_τ$ channel. In performing this re-analysis we also take into account some recent theoretical improvements in the flux calculations.
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Supernova Bounds on Resonant Active-Sterile Neutrino Conversions
We discuss the effects of resonant $ν_e \to ν_s$ and $\barν_e \to \barν_s$ ($ν_s$ is a sterile neutrino) conversions in the dense medium of a supernova. In particular, we assume the sterile neutrino $ν_s$ to be in the hot dark matter few eV mass range. The implications of such a scenario for the supernova shock re-heating, the detected $\barν_e$ signal from SN1987A and for the r-process nucleosynthesis hypothesis are analysed in some detail. The resulting constraints on mixing and mass difference for the $ν_e-ν_s$ system are derived. There is also an allowed region in the neutrino parameter space for which the r-process nucleosynthesis can be enhanced.
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Resonant Neutrino Spin-Flavor Precession and Supernova Nucleosynthesis and Dynamics
We discuss the effects of resonant spin-flavor precession (RSFP) of Majorana neutrinos on heavy element nucleosynthesis in neutrino-heated supernova ejecta and the dynamics of supernovae. In assessing the effects of RSFP, we explicitly include matter-enhanced (MSW) resonant neutrino flavor conversion effects where appropriate. We point out that for plausible ranges of neutrino magnetic moments and proto-neutron star magnetic fields, spin-flavor conversion of $ν_τ$ (or $ν_μ$) with a cosmologically significant mass (1--100 eV) into a light $\bar ν_e$ could lead to an enhanced neutron excess in neutrino-heated supernova ejecta. This could be beneficial for models of $r$-process nucleosynthesis associated with late-time neutrino-heated ejecta from supernovae. Similar spin-flavor conversion of neutrinos at earlier epochs could lead to an increased shock reheating rate and, concomitantly, a larger supernova explosion energy. We show, however, that such increased neutrino heating likely will be accompanied by an enhanced neutron excess which could exacerbate the problem of the overproduction of the neutron number $N = 50$ nuclei in the supernova ejecta from this stage. In all of these scenarios, the average $\barν_e$ energy will be increased over those predicted by supernova models with no neutrino mixings. This may allow the SN1987a data to constrain RSFP-based schemes.
astro-ph↗
Neutrino Conversions in a Polarized Medium
Electron polarization induced by magnetic fields can modify the potentials relevant for describing neutrino conversions in media with magnetic fields. The magnitudes of polarization potentials are determined for different conditions. We show that variations of the electron polarization along the neutrino trajectory can induce resonant conversions in the active-sterile neutrino system, but cannot lead to level crossing in the active-active neutrino system. For neutrino flavour conversions the polarisation leads only to a shift of the standard MSW resonance. For polarizations $λ\lsim 0.04$ the direct modifications of the potential (density) due to the magnetic field pressure are smaller than the modifications due to the polarization effect. We estimate that indeed the typical magnitude of the polarization in the sun or in a supernova are not expected to exceed $10^{-2}$. However even such a small polarization may lead to interesting consequences for supernova physics and for properties of neutrino signals from collapsing stars.
hep-ph↗
The MSW conversion of solar neutrinos and random matter density perturbations
We present a generalization of the resonant neutrino conversion in matter, including a random component in the matter density profile. The study is focused on the effect of such matter perturbations upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \to ν_{μ,τ}$ as well as active-sterile $ν_e \to ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $δm^2$) than the large mixing solution. Future solar neutrino experiments, such as Borexino, could probe solar matter density noise at the few percent level.
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Supernova Bounds on Supersymmetric $R$-parity Violating Interactions
We re-examine resonant massless-neutrino conversions in a dense medium induced by flavour changing neutral current (FCNC) interactions. We show how the observed $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis provide constraints on supersymmetric models with $R$ parity violation, which are much more stringent than those obtained from the laboratory. We also suggest that resonant massless-neutrino conversions may play a positive role in supernova shock reheating. Finally, we examine the constraints on explicit $R$-parity-violating FCNCs in the presence of non-zero neutrino masses in the eV range, as indicated by present hot dark matter observations.
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Resonant Conversion of Massless Neutrinos in Supernovae
It has been noted for a long time that, in some circumstances, {\sl massless} neutrinos may be {\sl mixed} in the leptonic charged current. Conventional neutrino oscillation searches in vacuum are insensitive to this mixing. We discuss the effects of resonant massless-neutrino conversions in the dense medium of a supernova. In particular, we show how the detected $\barν_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis may be used to provide very stringent constraints on the mixing of {\sl massless} neutrinos.
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The effect of random matter density perturbations on the MSW solution to the solar neutrino problem
We consider the implications of solar matter density random noise upon resonant neutrino conversion. The evolution equation describing MSW-like conversion is derived in the framework of the Schrödinger approach. We study quantitatively their effect upon both large and small mixing angle MSW solutions to the solar neutrino problem. This is carried out both for the active-active $ν_e \ra ν_{μ,τ}$ as well as active-sterile $ν_e \ra ν_s$ conversion channels. We find that the small mixing MSW solution is much more stable (especially in $Δm^2$) than the large mixing solution. The possible existence of solar matter density noise at the few percent level could be tested at future solar neutrino experiments, especially Borexino.
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A Natural Explanation of All Solar Neutrino Data by Resonant Spin-Flavor Precession Scenario
It is emphasized that the $E_ν$ (neutrino energy) spectrum of the $ν_e$ survival probability in the Resonant Spin-Flavor Precession (RSFP) scenario has very desirable shape to reconcile all existing solar neutrino data. As the result, the RSFP scenario is shown to have rather broad allowed region to reconcile the data in the ($B,\ Δm^2$) plane, with $B$ being the magnetic field strength inside the Sun. The sensitivity of the allowed region on the different choices of the $B$ profile, and the time variations of the solar neutrino event rates in the RSFP scenario are also discussed in some detail.
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