13 research outputs found
Resonant Spin-Flavor Conversion of Supernova Neutrinos: Dependence on Electron Mole Fraction
Detailed dependence of resonant spin-flavor (RSF) conversion of supernova
neutrinos on electron mole fraction Ye is investigated. Supernova explosion
forms a hot-bubble and neutrino-driven wind region of which electron mole
fraction exceeds 0.5 in several seconds after the core collapse. When a higher
resonance of the RSF conversion is located in the innermost region, flavor
change of the neutrinos strongly depends on the sign of 1-2Ye. At an adiabatic
high RSF resonance the flavor conversion of bar{nu}_e -> nu_{mu,tau} occurs in
Ye 0.5 and inverted mass hierarchy.
In other cases of Ye values and mass hierarchies, the conversion of nu_e ->
bar{nu}_{mu,tau} occurs. The final bar{nu}_e spectrum is evaluated in the cases
of Ye 0.5 taking account of the RSF conversion. Based on the
obtained result, time variation of the event number ratios of low bar{nu}_e
energy to high bar{nu}_e energy is discussed. In normal mass hierarchy, an
enhancement of the event ratio should be seen in the period when the electron
fraction in the innermost region exceeds 0.5. In inverted mass hierarchy, on
the other hand, a dip of the event ratio should be observed. Therefore, the
time variation of the event number ratio is useful to investigate the effect of
the RSF conversion.Comment: 16 pages, 33 figures, accepted for publication in Physical Review
Supernova Neutrino Nucleosynthesis of Light Elements with Neutrino Oscillations
Light element synthesis in supernovae through neutrino-nucleus interactions, i.e., the ν-process, is affected by neutrino oscillations in the supernova environment. There is a resonance of 13-mixing in the O/C layer, which increases the rates of charged-current ν-process reactions in the outer He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and 1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing resonance, compared to those without neutrino oscillations. In the case of an inverted mass hierarchy and a non-adiabatic 13-mixing resonance, the increase in the 7Li and 11B yields is much smaller. Observations of the 7Li/11B ratio in stars showing signs of supernova enrichment could thus provide a unique test of neutrino oscillations and constrain their parameters and the mass hierarchy
Supernova Neutrino Nucleosynthesis of Light Elements with Neutrino Oscillations
Light element synthesis in supernovae through neutrino-nucleus interactions,
i.e., the nu-process, is affected by neutrino oscillations in the supernova
environment. There is a resonance of 13-mixing in the O/C layer, which
increases the rates of charged-current nu-process reactions in the outer
He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and
1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing
resonance, compared to those without neutrino oscillations. In the case of an
inverted mass hierarchy and a non-adiabatic 13-mixing resonance, the increase
in the 7Li and 11B yields is much smaller. Observations of the 7Li/11B ratio in
stars showing signs of supernova enrichment could thus provide a unique test of
neutrino oscillations and constrain their parameters and the mass hierarchy.Comment: 5 pages, 3 figures, accepted for publication in Physical Review
Letter
Neutrino-Nucleus Reaction Cross Sections for Light Element Systhesis in Supernova Explosions
The neutrino-nucleus reaction cross sections of 4He and 12C are evaluated using new shell model Hamiltoni-ans. Branching ratios of various decay channels are calculated to evaluate the yields of Li, Be, and B producedthrough the ν -process in supernova explosions. The new cross sections enhance the yields of7Li and11B pro-duced during the supernova explosion of a 16.2 M⊙star model compared to the case using the conventionalcross sections by about 10%. On the other hand, the yield of10B decreases by a factor of two. The yieldsof6Li,9Be, and the radioactive nucleus10 Be are found at a level of ∼ 10−11M⊙. The temperature of νµ,τ-and ¯νµ,τ-neutrinos inferred from the supernova contribution of11B in Galactic chemical evolution models isconstrained to the 4.3 − 6.5 MeV range. The increase in the7Li and11B yields due to neutrino oscillations isdemonstrated with the new cross section
Neutrino-Nucleus Reaction Cross Sections for Light Element Synthesis in Supernova Explosions
The neutrino-nucleus reaction cross sections of 4He and 12C are evaluated
using new shell model Hamiltonians. Branching ratios of various decay channels
are calculated to evaluate the yields of Li, Be, and B produced through the
nu-process in supernova explosions. The new cross sections enhance the yields
of 7Li and 11B produced during the supernova explosion of a 16.2 M_odot star
model compared to the case using the conventional cross sections by about 10%.
On the other hand, the yield of 10B decreases by a factor of two. The yields of
6Li, 9Be, and the radioactive nucleus 10Be are found at a level of 10^{-11}
M_odot. The temperature of nu_{mu,tau}- and bar{nu}_{mu,tau}-neutrinos inferred
from the supernova contribution of 11B in Galactic chemical evolution models is
constrained to the 4.3-6.5 MeV range. The increase in the 7Li and 11B yields
due to neutrino oscillations is demonstrated with the new cross sections.Comment: 19 pages, 30 figures, accepted for publication in Astrophysical
Journal. Typos are correcte
Enhancement of CP Violating terms for Neutrino Oscillation in Earth Matter
We investigate the oscillation in the framework of
three generations when neutrinos pass through the earth. The oscillation
probability is represented by the form, in arbitrary matter profile by using the leptonic CP
phase . We compare our approximate formula in the previous paper with
the formula which includes second order terms of and . Non-perturbative effects of
and can be taken into account in our formula and the precision of the
formula is rather improved around the MSW resonance region. Furthermore, we
compare the earth matter effect of and with that of studied by
other authors. We show that the magnitude of and can reach a few ten %
of around the main three peaks of in the region GeV by numerical
calculation. We give the qualitative understanding of this result by using our
approximate formula. The mantle-core effect, which is different from the usual
MSW effect, appears not only in but also in and , although the
effect is weakened.Comment: 16 pages, 5 figure
Proposal of a Simple Method to Estimate Neutrino Oscillation Probability and CP Violation in Matter
We study neutrino oscillation within the framework of three generations in
matter. We propose a simple method to approximate the coefficients A, B and C
which do not depend on the CP phase \delta in the oscillation probability
P(\nu_e \to \nu_{\mu})=A\cos \delta + B\sin \delta +C. An advantage of our
method is that an approximate formula of the coefficients A, B and C in
arbitrary matter {\it without the usual first order perturbative calculations}
of the small parameter \Delta m_{21}^2/\Delta m_{31}^2 or \sin \theta_{13} can
be derived. Furthermore we show that all the approximate formulas for low,
intermediate and high energy regions given by other authors in constant matter
can be easily derived from our formula. It means that our formula is applicable
over a wide energy region.Comment: 15 pages, 9 figures, accepted version in PL
Neutrino Oscillation Effects on Supernova Light Element Synthesis
Neutrino oscillations affect light element synthesis through the
neutrino-process in supernova explosions. The 7Li and 11B yields produced in a
supernova explosion of a 16.2 solar-mass star model increase by factors of 1.9
and 1.3 in the case of large mixing angle solution with normal mass hierarchy
and sin^{2}2theta_{13} > 0.002 compared with those without the oscillations. In
the case of inverted mass hierarchy or nonadiabatic 13-mixing resonance, the
increment of their yields is much smaller. Neutrino oscillations raise the
reaction rates of charged-current neutrino-process reactions in the region
outside oxygen-rich layers. The number ratio of 7Li/11B could be a tracer of
normal mass hierarchy and relatively large theta_{13}, still satisfying
sin^{2}2theta_{13} < 0.1, through future precise observations in stars having
strong supernova component.Comment: 35 pages, 17 figures, accepted for publication in Astrophysical
Journa
Overall Feature of CP dependence for Neutrino Oscillation Probability in Arbitrary Matter Profile
We study the CP dependence of neutrino oscillation probability for all
channels in arbitrary matter profile within three generations. We show that an
oscillation probability for \nu_e \to \nu_\mu can be written in the form
P(\nu_e \to \nu_\mu) =A_{e\mu} cos \delta + B_{e\mu} sin \delta + C_{e\mu}
without any approximation using the CP phase \delta. This result holds not only
in constant matter but also in arbitrary matter. Another probability for
\nu_\mu \to \nu_\tau can be written in the form P(\nu_\mu \to \nu_\tau)=
A_{\mu\tau} cos \delta + B_{\mu\tau} sin \delta
+ C_{\mu\tau} + D_{\mu\tau} cos 2\delta + E_{\mu\tau} sin 2\delta. The term
which is proportional to sin 2\delta disappear, namely E_{\mu\tau}=0, in
symmetric matter. It means that the probability reduces to the same form as in
constant matter. As for other channels, probabilities in arbitrary matter are
at most the quadratic polynomials of sin \delta and cos \delta as in the above
two channels. In symmetric matter, the oscillation probability for each channel
reduces to the same form with respect to \delta as that in constant matter.Comment: 11 pages, no figures, LaTeX2e, a few misprints have been correcte
Exact Formulas and Simple CP dependence of Neutrino Oscillation Probabilities in Matter with Constant Density
We investigate neutrino oscillations in constant matter within the context of
the standard three neutrino scenario. We derive an exact and simple formula for
the oscillation probability applicable to all channels. In the standard
parametrization, the probability for transition can
be written in the form without any
approximation using CP phase . For
transition, the linear term of is added and the probability can
be written in the form . We give the CP dependences of
the probability for other channels. We show that the probability for each
channel in matter has the same form with respect to as in vacuum. It
means that matter effects just modify the coefficients , , and .
We also give the exact expression of the coefficients for each channel.
Furthermore, we show that our results with respect to CP dependences are
reproduced from the effective mixing angles and the effective CP phase
calculated by Zaglauer and Schwarzer. Through the calculation, a new identity
is obtained by dividing the Naumov-Harrison-Scott identity by the Toshev
identity.Comment: 12 pages, RevTeX4 style, changed title, minor correction