1,690 research outputs found

### Measuring the CP-violating phase by a long base-line neutrino experiment with Hyper-Kamiokande

We study the sensitivity of a long-base-line (LBL) experiment with neutrino
beams from the High Intensity Proton Accelerator (HIPA), that delivers 10^{21}
POT per year, and a proposed 1Mt water-Cherenkov detector, Hyper-Kamiokande
(HK) 295km away from the HIPA, to the CP phase (delta_{M N S}) of the
three-flavor lepton mixing matrix. We examine a combination of the nu_mu
narrow-band beam (NBB) at two different energies, vev{p_pi}=2, 3GeV, and the
bar{nu}_mu NBB at vev{p_pi}=2GeV. By allocating one year each for the two nu_mu
beams and four years for the bar{nu}_mu beam, we can efficiently measure the
nu_mu to nu_e and bar{nu}_mu to bar{nu}_e transition probabilities, as well as
the nu_mu and bar{nu}_mu survival probabilities. CP violation in the lepton
sector can be established at 4sigma (3sigma) level if the MSW
large-mixing-angle scenario of the solar-neutrino deficit is realized, |\dmns|
or |delta{M N S}-180^{circ}| > 30^{circ}, and if 4|U_{e3}|^2 (1-|U_{e3}|^2)
equiv sin^2 2 theta_{CHOOZ} > 0.03 (0.01). The phase delta_{M N S} is more
difficult to constrain by this experiment if there is little CP violation,
delta_{M N S} sim 0^{circ} or 180^{circ}, which can be distinguished at 1sigma
level if sin^2 2 theta_{CHOOZ} >~ 0.01.Comment: 16 pages, 4 figures, 2 tables, we add 1 figure, some refrences, and
minor corrections. PLB published versio

### Precise Formulation of Neutrino Oscillation in the Earth

We give a perturbation theory of neutrino oscillation in the Earth. The
perturbation theory is valid for neutrinos with energy E \gsim 0.5 GeV. It is
formulated using trajectory dependent average potential. Non-adiabatic
contributions are included as the first order effects in the perturbation
theory. We analyze neutrino oscillation with standard matter effect and with
non-standard matter effect. In a three flavor analysis we show that the
perturbation theory gives a precise description of neutrino conversion in the
Earth. Effect of the Earth matter is substantially simplified in this
formulation.Comment: References added, 21 pages, 10 figures, version to appear in PR

### Solar neutrinos and 1-3 leptonic mixing

Effects of the 1-3 leptonic mixing on the solar neutrino observables are
studied and the signatures of non-zero $\theta_{13}$ are identified. For this
we have re-derived the formula for $3\nu$-survival probability including all
relevant corrections and constructed the iso-contours of observables in the
$\sin^2 \theta_{12} - \sin^2 \theta_{13}$ plane. Analysis of the solar neutrino
data gives $\sin^2\theta_{13} = 0.007^{+ 0.080}_{-0.007}$ (90% C.L.) for
$\Delta m^2 = 8 \cdot 10^{-5}$ eV$^2$. The combination of the ratio CC/NC at
SNO and gallium production rate selects $\sin^2\theta_{13} = 0.017 \pm 0.026$
($1\sigma$). The global fit of all oscillation data leads to zero best value of
$\sin^2 \theta_{13}$. The sensitivity ($1\sigma$ error) of future solar
neutrino studies to $\sin^2 \theta_{13}$ can be improved down to 0.01 - 0.02 by
precise measurements of the pp-neutrino flux and the CC/NC ratio as well as
spectrum distortion at high ($E > 4$ MeV) energies. Combination of experimental
results sensitive to the low and high energy parts of the solar neutrino
spectrum resolves the degeneracy of angles $\theta_{13}$ and $\theta_{12}$.
Comparison of $\sin^2 \theta_{13}$ as well as $\sin^2 \theta_{12}$ measured in
the solar neutrinos and in the reactor/accelerator experiments may reveal new
effects which can not be seen otherwise.Comment: 36 pages, latex, 10 figures. Analysis and figures are updated with
new (salt phase II) SNO results, several clarifications added, typos
correcte

### Testing large mixing MSW solutions of the solar neutrino problem through Earth regeneration effects

Large mixing MSW solutions to the solar neutrino problem appear to be
currently favored by the data. We discuss the possibility of discriminating
them by means of present and future experiments. In particular, we show that
the study of energy and time dependence of the Earth regeneration effect can be
useful in this respect.Comment: Talk given at Europhysics Neutrino Oscillation Workshop (NOW 2000),
Conca Specchiulla, Otranto, Lecce, Italy, 9-16 Sep. 200

### Density profiles of supernova matter and determination of neutrino parameters

The flavor conversion of supernova neutrinos can lead to observable
signatures related to the unknown neutrino parameters. As one of the
determinants in dictating the efficiency of resonant flavor conversion, the
local density profile near the MSW resonance in a supernova environment is,
however, not so well understood. In this analysis, variable power-law functions
are adopted to represent the independent local density profiles near the
locations of resonance. It is shown that the uncertain matter density profile
in a supernova, the possible neutrino mass hierarchies, and the undetermined
1-3 mixing angle would result in six distinct scenarios in terms of the
survival probabilities of $\nu_{e}$ and $\bar{\nu_{e}}$. The feasibility of
probing the undetermined neutrino mass hierarchy and the 1-3 mixing angle with
the supernova neutrinos is then examined using several proposed experimental
observables. Given the incomplete knowledge of the supernova matter profile,
the analysis is further expanded to incorporate the Earth matter effect. The
possible impact due to the choice of models, which differ in the average energy
and in the luminosity of neutrinos, is also addressed in the analysis.Comment: 27 pages, 10 figures. text and figures revised, references added, to
appear in Phys. Rev.

### The neutrino ground state in a neutron star

We address a recent claim that the stability of neutron stars implies a lower
bound on the mass of the neutrino. We argue that the result obtained by some
previous authors is due to an improper summation of an infrared-sensitive
series and that a non-perturbative "resummation" of the series yields a finite
and well-behaved result. The stability of neutron stars thus gives no lower
bound on the mass of the neutrino.Comment: 5 pages, 3 figures, Latex (uses espcrc2.sty); contribution to the
proceedings of Neutrino 98, Takayama, Japan, 4-9 June, 199

### Bilarge neutrino mixing from supersymmetry with high-scale nonrenormalizable interactions

We suggest a supersymmetric (SUSY) explanation of neutrino masses and mixing,
where nonrenormalizable interactions in the hidden sector generate lepton
number violating Majorana mass terms for both right-chiral sneutrinos and
neutrinos. It is found necessary to start with a superpotential including an
array of gauge singlet chiral superfields. This leads to nondiagonal $\Delta L
= 2$ mass terms and almost diagonal SUSY breaking $A$-terms. As a result, the
observed pattern of bilarge mixing can be naturally explained by the
simultaneous existence of the seesaw mechanism and radiatively induced masses.
Allowed ranges of parameters in the gauge singlet sector are delineated,
corresponding to each of the cases of normal hierarchy, inverted hierarchy and
degenerate neutrinos.Comment: 19 pages, 5 figures. Minor modifications are made in the title and
the text, some new references are added. To appear in this form in Physical
Review

### Random magnetic fields inducing solar neutrino spin-flavor precession in a three generation context

We study the effect of random magnetic fields in the spin-flavor precession
of solar neutrinos in a three generation context, when a non-vanishing
transition magnetic moment is assumed. While this kind of precession is
strongly constrained when the magnetic moment involves the first family, such
constraints do not apply if we suppose a transition magnetic moment between the
second and third families. In this scenario we can have a large non-electron
anti-neutrino flux arriving on Earth, which can lead to some interesting
phenomenological consequences, as, for instance, the suppression of day-night
asymmetry. We have analyzed the high energy solar neutrino data and the KamLAND
experiment to constrain the solar mixing angle, and solar mass difference, and
we have found a larger shift of allowed values.Comment: 10 pages, 3 figure

### Solar neutrino spectrum, sterile neutrinos and additional radiation in the Universe

Recent results from the SNO, Super-Kamiokande and Borexino experiments do not
show the expected upturn of the energy spectrum of events (the ratio $R \equiv
N_{obs}/N_{SSM}$) at low energies. At the same time, cosmological observations
testify for possible existence of additional relativistic degrees of freedom in
the early Universe: $\Delta N_{eff} = 1 - 2$. These facts strengthen the case
of very light sterile neutrino, $\nu_s$, with $\Delta m^2_{01} \sim (0.7 - 2)
\cdot 10^{-5}$ eV$^2$, which mixes weakly with the active neutrinos. The
$\nu_s$ mixing in the mass eigenstate $\nu_1$ characterized by $\sin^2 2\alpha
\sim 10^{-3}$ can explain an absence of the upturn. The mixing of $\nu_s$ in
the eigenstate $\nu_3$ with $\sin^2 \beta \sim 0.1$ leads to production of
$\nu_s$ via oscillations in the Universe and to additional contribution $\Delta
N_{eff} \approx 0.7 - 1$ before the big bang nucleosynthesis and later. Such a
mixing can be tested in forthcoming experiments with the atmospheric neutrinos
as well as in future accelerator long baseline experiments. It has substantial
impact on conversion of the supernova neutrinos.Comment: 27 pages, LaTeX, 14 eps figures, 3 figures and additional
considerations adde

### On in situ Determination of Earth Matter Density in Neutrino Factory

We point out that an accurate in situ determination of the earth matter
density \rho is possible in neutrino factory by placing a detector at the magic
baseline, L = \sqrt{2} \pi / G_{F} N_{e} where N_{e} denotes electron number
density. The accuracy of matter density determination is excellent in a region
of relatively large theta_{13} with fractional uncertainty \delta \rho / \rho
of about 0.43%, 1.3%, and \lsim 3% at 1 sigma CL at sin^2 2theta_{13}=0.1,
10^{-2}, and 3 x 10^{-3}, respectively. At smaller theta_{13} the uncertainty
depends upon the CP phase delta, but it remains small, 3%-7% in more than 3/4
of the entire region of delta at sin^2 2theta_{13} = 10^{-4}. The results would
allow us to solve the problem of obscured CP violation due to the uncertainty
of earth matter density in a wide range of theta_{13} and delta. It may provide
a test for the geophysical model of the earth, or it may serve as a method for
stringent test of the MSW theory of neutrino propagation in matter once an
accurate geophysical estimation of the matter density is available.Comment: 21 pages, 4 figures, version to appear in PR

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