On the evolution of the neutrino state inside the sun Page: 2 of 34
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The solar neutrino problem (SNP) is a discrepancy between the measured
values of the solar neutrino flux at different energies [1, 2, 3, 4, 5] and the
corresponding predictions of the Standard Solar Model (SSM) . Not only
is the observed flux suppressed, compared to the SSM predictions, but, if the
data from the Homestake experiment are correct, the degree of suppression
varies with energy. The leading explanation of this phenomenon is that
neutrinos have small masses and the mass and flavor bases in the lepton
sector are not aligned, just like in the quark sector. The resulting neutrino
oscillations convert some of the solar electron neutrinos into another neutrino
Neutrino oscillation solutions to the SNP have traditionally been divided
into the so-called Mikheyev-Smirnov-Wolfenstein (MSW) solutions [7, 8, 9]
and the vacuum oscillation (VO) solutions, according to the physical mecha-
nism responsible for the neutrino flavor conversion in each case. In the MSW
case the conversion is caused by neutrino interactions with the solar (and
Earth's) matter, while in the VO case it is due to long-wavelength neutrino
oscillations in vacuum between the Sun and the Earth. Over time, it has
become a tradition to treat the two cases completely separately, showing re-
sults in separate plots (see, for example, [10, 11]) and using different input
formulas and different codes.
Justifying such a complete separation, however, requires a careful analysis
of the magnitude of the solar matter effects and the degree of decoherence of
vacuum oscillations. The separation assumption has been recently reexam-
ined by the author  and it has been found that the solar matter effects are
nonnegligible for the vacuum oscillation solutions with Am2 ? 5 x 1010 eV2.
This conclusion has been subsequently verified by other authors [13, 14, 15],
and the term quasi-vacuum oscillations (QVO) has been coined to refer to
the region where both effects influence the neutrino survival probability .
It must be mentioned that the experimental situation has changed since
the QVO solutions were first introduced. At the time, the most preferred
part of the VO solutions was in the region Am2 < 10-10 eV2. The latest
Super-Kamiokande spectrum data, however, disfavors a large fraction of the
vacuum oscillation region, roughly 2 x 10-" eV2 < Am2 < 4 x 10-10 eV2
[16, 15]. At the same time, the solutions with Am2 > 4 x 10-10 eV2, i. e.
the QVO solutions, remain allowed.
Prior to , the VO solutions had always been studied in the range of the
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Friedland, Alexander. On the evolution of the neutrino state inside the sun, article, January 26, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc778694/m1/2/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.