833 research outputs found
The diffuse neutrino flux from supernovae: upper limit on the electron neutrino component from the non-observation of antineutrinos at SuperKamiokande
I derive an upper bound on the electron neutrino component of the diffuse
supernova neutrino flux from the constraint on the antineutrino component at
SuperKamiokande. The connection between antineutrino and neutrino channels is
due to the similarity of the muon and tau neutrino and antineutrino fluxes
produced in a supernova, and to the conversion of these species into electron
neutrinos and antineutrinos inside the star. The limit on the electron neutrino
flux is 5.5 cm^-2 s^-1 above 19.3 MeV of neutrino energy, and is stronger than
the direct limit from Mont Blanc by three orders of magnitude. It represents
the minimal sensitivity required at future direct searches, and is intriguingly
close to the reach of the Sudbury Neutrino Observatory (SNO) and of the ICARUS
experiment. The electron neutrino flux will have a lower bound if the electron
antineutrino flux is measured. Indicatively, the first can be smaller than the
second at most by a factor of 2-3 depending on the details of the neutrino
spectra at production.Comment: LaTeX, 5 pages, 1 figure. Paper is modified in the presentation (Fig.
1 was replaced with a different plot and Table 1 was expanded), with
unchanged results. References added and correcte
A test of tau neutrino interactions with atmospheric neutrinos and K2K
The presence of a tau component in the flux of atmospheric neutrinos inside
the Earth, due to flavor oscillations, makes these neutrinos a valuable probe
of interactions of the tau neutrino with matter. We study -- analytically and
numerically -- the effects of nonstandard interactions in the nu_e-nu_tau
sector on atmospheric neutrino oscillations, and calculate the bounds on the
exotic couplings that follow from combining the atmospheric neutrino and K2K
data. We find very good agreement between numerical results and analytical
predictions derived from the underlying oscillation physics. While improving on
existing accelerator bounds, our bounds still allow couplings of the size
comparable to the standard weak interaction. The inclusion of new interactions
expands the allowed region of the vacuum oscillation parameters towards smaller
mixing angles, 0.2 ~< sin^2 theta_{23} ~< 0.7, and slightly larger mass squared
splitting, 1.5 * 10^{-3} eV^2 ~< |\Delta m^2_{23}| ~< 4.0 * 10^{-3} eV^2,
compared to the standard case. The impact of the K2K data on all these results
is significant; further important tests of the nu_e-nu_tau exotic couplings
will come from neutrino beams experiments such as MINOS and long baseline
projects.Comment: 8 figures, some typos corrected, minor editing in the reference
Turbulent Supernova Shock Waves and the Sterile Neutrino Signature in Megaton Water Detectors
The signatures of sterile neutrinos in the supernova neutrino signal in
megaton water Cerenkov detectors are studied. Time dependent modulation of the
neutrino signal emerging from the sharp changes in the oscillation probability
due to shock waves is shown to be a smoking gun for the existence of sterile
neutrinos. These modulations and indeed the entire neutrino oscillation signal
is found to be different for the case with just three active neutrinos and the
cases where there are additional sterile species mixed with the active
neutrinos. The effect of turbulence is taken into account and it is found that
the effect of the shock waves, while modifed, remain significant and
measurable. Supernova neutrino signals in water detectors can therefore give
unambiguous proof for the existence of sterile neutrinos, the sensitivity
extending beyond that for terrestial neutrino experiments. In addition the time
dependent modulations in the signal due to shock waves can be used to trace the
evolution of the shock wave inside the supernova.Comment: 28 pages, 11 figure
Large Lepton Asymmetry for Small Baryon Asymmetry and Warm Dark Matter
We propose a resonant leptogenesis scenario in a U(1)_{B-L} gauge extension
of the standard model to generate large lepton asymmetries for cosmological
baryon asymmetry and dark matter. After B-L number is spontaneously broken,
inflaton can pick up a small vacuum expectation value for the mass splits of
three pairs of quasi-degenerately heavy Majorana neutrinos and the masses of
three sterile neutrinos. With thermal mass effects of sphalerons, the observed
small baryon asymmetry can be converted from large lepton asymmetries of
individual flavors although total lepton asymmetry is assumed zero. The mixing
between sterile and active neutrinos is elegantly suppressed by the heavy
Majorana neutrinos. Before the active neutrinos start their strong flavor
conversions, the sterile neutrinos as warm dark matter can be produced by
resonant active-sterile neutrino oscillations to reconcile X-ray and
Lyman-\alpha bounds. Small neutrino masses are naturally realized by seesaw
contributions from the heavy Majorana neutrinos and the sterile neutrinos.Comment: 8 pages. Typos and parameter choice are corrected. Accepted by Phys.
Rev.
Phenomenology in the Zee Model with the A_4 Symmetry
The Zee model generates neutrino masses at the one-loop level by adding
charged SU(2)_L-singlet and extra SU(2)_L-doublet scalars to the standard model
of particle physics. As the origin of the nontrivial structure of the lepton
flavor mixing, we introduce the softly broken A_4 symmetry to the Zee model.
This model is compatible with the tribimaximal mixing which agrees well with
neutrino oscillation measurements. Then, a sum rule m_1 e^{i alpha_12} + 2 m_2
+ 3 m_3 e^{i alpha_32} = 0 is obtained and it results in Delta m^2_31 < 0 and
m_3 > 1.8*10^{-2}eV. The effective mass |(M_nu)_{ee}| for the neutrinoless
double beta decay is predicted as | (M_\nu)_{ee} | > 1.7*10^{-2}eV. The
characteristic particles in this model are SU(2)_L-singlet charged Higgs bosons
s^+_alpha (alpha=xi,eta,zeta) which are made from a 3-representation of A_4.
Contributions of s^+_alpha to the lepton flavor violating decays of charged
leptons are almost forbidden by an approximately remaining Z_3 symmetry; only
BR(tau to ebar mu mu) can be sizable by the flavor changing neutral current
interaction with SU(2)_L-doublet scalars. Therefore, s^+_alpha can be easily
light enough to be discovered at the LHC with satisfying current constraints.
The flavor structures of BR(s^-_alpha to ell nu) are also discussed.Comment: 26 pages, 4 figures, version accepted by PR
Pseudo-Dirac Neutrinos in the New Standard Model
The addition of gauge singlet fermions to the Standard Model Lagrangian
renders the neutrinos massive and allows one to explain all that is
experimentally known about neutrino masses and lepton mixing by varying the
values of the Majorana mass parameters M for the gauge singlets and the
neutrino Yukawa couplings. Here we explore the region of parameter space where
M values are much smaller than the neutrino Dirac masses. In this region,
neutrinos are pseudo-Dirac fermions. We find that current solar data constrain
M values to be less than at least 1E-9 eV, and discuss the sensitivity of
future experiments to tiny gauge singlet fermion masses. We also discuss a
useful basis for analyzing pseudo-Dirac neutrino mixing effects. In particular,
we identify a simple relationship between elements of M and the induced
enlarged mixing matrix and new mass-squared differences. These allow one to
directly relate bounds on the new mass-squared differences to bounds on the
singlet fermion Majorana masses.Comment: 20 Pages, 9 .eps figures, Updated reference
Neutrino Physics with Dark Matter Experiments and the Signature of New Baryonic Neutral Currents
New neutrino states \nu_b, sterile under the Standard Model interactions, can
be coupled to baryons via the isoscalar vector currents that are much stronger
than the Standard Model weak interactions. If some fraction of solar neutrinos
oscillate into \nu_b on their way to Earth, the coherently enhanced elastic
\nu_b-nucleus scattering can generate a strong signal in the dark matter
detectors. For the interaction strength a few hundred times stronger than the
weak force, the elastic \nu_b-nucleus scattering via new baryonic currents may
account for the existing anomalies in the direct detection dark matter
experiments at low recoil. We point out that for solar neutrino energies the
baryon-current-induced inelastic scattering is suppressed, so that the possible
enhancement of new force is not in conflict with signals at dedicated neutrino
detectors. We check this explicitly by calculating the \nu_b-induced deuteron
breakup, and the excitation of 4.4 MeV \gamma-line in ^{12}C.
Stronger-than-weak force coupled to baryonic current implies the existence of
new abelian gauge group U(1)_B with a relatively light gauge boson.Comment: 20 pages, 5 figures. References added, inconsistent treatment of
neutrino oscillations corrected, conclusions unchange
Oscillations of high energy neutrinos in matter: Precise formalism and parametric resonance
We present a formalism for precise description of oscillation phenomena in
matter at high energies or high densities, V > \Delta m^2/2E, where V is the
matter-induced potential of neutrinos. The accuracy of the approximation is
determined by the quantity \sin^2 2\theta_m \Delta V/2\pi V, where \theta_m is
the mixing angle in matter and \Delta V is a typical change of the potential
over the oscillation length (l \sim 2\pi/V). We derive simple and physically
transparent formulas for the oscillation probabilities, which are valid for
arbitrary matter density profiles. They can be applied to oscillations of high
energy (E > 10 GeV) accelerator, atmospheric and cosmic neutrinos in the matter
of the Earth, substantially simplifying numerical calculations and providing an
insight into the physics of neutrino oscillations in matter. The effect of
parametric enhancement of the oscillations of high energy neutrinos is
considered. Future high statistics experiments can provide an unambiguous
evidence for this effect.Comment: LaTeX, 5 pages, 1 figure. Linestyles in the figure corrected to match
their description in the caption; improved discussion of the accuracy of the
results; references added. Results and conclusions unchange
Solar mass-varying neutrino oscillations
We propose that the solar neutrino deficit may be due to oscillations of
mass-varying neutrinos (MaVaNs). This scenario elucidates solar neutrino data
beautifully while remaining comfortably compatible with atmospheric neutrino
and K2K data and with reactor antineutrino data at short and long baselines
(from CHOOZ and KamLAND). We find that the survival probability of solar MaVaNs
is independent of how the suppression of neutrino mass caused by the
acceleron-matter couplings varies with density. Measurements of MeV and lower
energy solar neutrinos will provide a rigorous test of the idea.Comment: 4 pages, 3 figures. Version to appear in PR
Neutrino spin oscillations in gravitational fields
We study neutrino spin oscillations in gravitational fields. The
quasi-classical approach is used to describe the neutrino spin evolution. First
we examine the case of a weak gravitational field. We obtain the effective
Hamiltonian for the description of neutrino spin oscillations. We also receive
the neutrino transition probability when a particle propagates in the
gravitational field of a rotating massive object. Then we apply the general
technique to the description of neutrino spin oscillations in the Schwarzschild
metric. The neutrino spin evolution equation for the case of the neutrino
motion in the vicinity of a black hole is obtained. The effective Hamiltonian
and the transition probability are also derived. We examine the neutrino
oscillations process on different circular orbits and analyze the frequencies
of spin transitions. The validity of the quasi-classical approach is also
considered.Comment: RevTeX4, 9 pages, 1 esp figure; article was revised, some misprints
were corrected, 6 references added; accepted for publication in
Int.J.Mod.Phys.
- …