2,687 research outputs found

### The Solar Neutrino Problem: Neither Astrophysics Nor Oscillations?

There is no consistent solar model which can describe all experimental data
on the solar neutrinos. The problem can be formulated essentially in a model
independent way. The key points are the comparison of the Homestake and the
Kamiokande data as well as the comparison of the GALLEX and SAGE results with
minimal signal estimated from the solar luminosity. It is argued than in such a
comparison one should use the Homestake-II data (only after 1986) with caution.
The results of the model independent analysis show strong suppression of the
beryllium neutrino flux. The data can be well described by the resonant flavor
conversion. For the ``low flux model" which can accommodate the Kamiokande
signal, a consistent solution can be found for the neutrino mass squared
difference $\Delta m^2 = (0.3 - 1.0)\cdot 10^{-5}$ eV$^2$ and values of mixing
angle $\sin^2 2\theta > 5 \cdot 10^{-4}$ (``very small mixing solution").Comment: (Talk given at the International Workshop ``Solar Neutrino Problem:
Astrophysics or Oscillations", Gran Sasso, Italy, February 28 - March 1,
1994), 18 pages (7 figures available upon request), LaTeX,
DOE/ER/40561-136-INT94-13-0

### Theory of neutrino masses and mixing

In spite of enormous experimental progress in determination of the neutrino
parameters, theory of neutrino mass and mixing is still on the cross-roads.
Guidelines could be (i) the connection between zero neutrino charges (and
therefore a possibility to be Majorana particle), smallness of the neutrino
mass and large lepton mixing, (ii) joint description of leptons and quarks,
(iii) existence of the right handed (RH) neutrinos without special quantum
numbers. Properties of the RH neutrinos and the UV completion of the seesaw may
turn out to be the key to understand the neutrino mass and mixing. In view of
the LHC results minimalistic scenarios like $\nu$MSM look rather plausible.
Still the GUT's with additional hidden sector, QLC, high scale flavor
symmetries are appealing. Concerning mixing, the main issue is "symmetry or no
symmetry" behind the observed pattern. The symmetry group condition is useful
tool to study consequences of symmetries and to perform "symmetry building".
Sterile neutrinos are challenge but also opportunity for the present
theoretical constructions.Comment: 13 pages, Talk given at the "Pontecorvo 100" Symposium, Pisa, Italy,
September 18 - 20, 201

### Alternatives to the seesaw mechanism

The observed pattern of lepton mixing does not give an evidence of the
seesaw. It is easier to disprove seesaw showing that one of the alternatives
gives dominant contribution to the neutrino mass. We consider alternative
mechanisms based on (i) small (tree level) effective couplings, (ii) small VEV,
(iii) radiative generation of masses, (iv) protection by SUSY breaking scale or
by $\mu$-term, (v) small overlap of wave functions of the left and right handed
neutrino components in extra dimensions. Seesaw can be the mechanism of
suppression of the Dirac mass terms and not dominant mechanism of the neutrino
mass giving just a sub-leading contribution.Comment: 16 pages, latex, 5 figures. Talk given at the Conference ``Seesaw
Mechanism and Neutrino Masses: 25 Years Later'', 10-11 June 2004, Paris.
References added, statement in sec. 6 correcte

### Neutrino Physics after KamLAND

The neutrino anomalies were driving force of the developments in neutrino
physics during the last 30 - 35 years. I will consider status of the anomalies
after the first KamLAND result. The main questions are "What is left?" and
"What is the next?" In the new phase, the phenomenological objectives of
neutrino physics consist of accomplishing the program of reconstruction of the
neutrino mass and flavor spectrum and searches for physics beyond the
``standard'' picture. The latter includes searches for new (sterile) neutrino
states, new neutrino interactions, effects of violation of the fundamental
symmetries in the neutrino sector.Comment: 21 pages, latex, 6 figures. Invited talk given at the International
workshop NOON2003, February 10 - 14, 2003, Kanazawa, Japa

### Neutrino mass hierarchy and matter effects

Matter effects modify the mixing and the effective masses of neutrinos in a
way which depends on the neutrino mass hierarchy. Consequently, for normal and
inverted hierarchies the oscillations and flavor conversion results are
different. Sensitivity to the mass hierarchy appears whenever the matter
effects on the 1-3 mixing and mass splitting become substantial. This happens
in supernovae in wide energy range and in the matter of the Earth. The Earth
density profile is a multi-layer medium where the resonance and parametric
enhancements of oscillations occur. The enhancement is realized in neutrino
(antineutrino) channels for the normal (inverted) mass hierarchy. Multi-megaton
scale under ice (water) atmospheric neutrino detectors with low energy
threshold can establish mass hierarchy with $(3 - 10) \sigma$ confidence level
in few years. The main challenges of these experiments are discussed and
various ways to improve sensitivity are outlined. In particular, inelasticity
measurements will allow to increase significance of the hierarchy
identification by $20 - 50 \%$ .Comment: 15 pages, 19 figures, Talk given at XV Workshop on Neutrino
Telescopes, 11-15 March 2013, Venice, Ital

### Low Scale Left-Right Symmetry and Naturally Small Neutrino Mass

We consider the low scale ($10$ - $100$ TeV) left-right symmetric model with
"naturally" small neutrino masses generated through the inverse seesaw
mechanism. The Dirac neutrino mass terms are taken to be similar to the masses
of charged leptons and quarks in order to satisfy the quark-lepton similarity
condition. The inverse seesaw implies the existence of fermion singlets $S$
with Majorana mass terms as well as the "left" and "right" Higgs doublets.
These doublets provide the portal for $S$ and break the left-right symmetry.
The inverse seesaw allows to realize a scenario in which the large lepton
mixing originates from the Majorana mass matrix of $S$ fields which has certain
symmetry. The model contains heavy pseudo-Dirac fermions, formed by $S$ and the
right-handed neutrinos, which have masses in the $1$ GeV - $100$ TeV range and
can be searched for at current and future colliders such as LHC and FCC-ee as
well as in SHiP and DUNE experiments. Their contribution to neutrinoless double
beta decay is unobservable. The radiative corrections to the mass of the Higgs
boson and the possibility for generating the baryon asymmetry of the Universe
are discussed. Modification of the model with two singlets ($S_L$ and $S_R$)
per generation can provide a viable keV-scale dark matter candidate.Comment: 22 pages, 3 figures; comments and references adde

### Improving the neutrino mass hierarchy identification with inelasticity measurement in PINGU and ORCA

Multi-megaton scale under ice and underwater detectors of atmospheric
neutrinos with few GeV's energy threshold (PINGU, ORCA) open up new
possibilities in the determination of neutrino properties, and in particular
the neutrino mass hierarchy. With a dense array of optical modules it will be
possible to determine the inelasticity, $y$, of the charged current $\nu_\mu$
events in addition to the neutrino energy $E_\nu$ and the muon zenith angle
$\theta_\mu$. The discovery potential of the detectors will substantially
increase with the measurement of $y$. It will enable (i) a partial separation
of the neutrino and antineutrino signals; (ii) a better reconstruction of the
neutrino direction; (iii) the reduction of the neutrino parameters degeneracy;
(iv) a better control of systematic uncertainties; (v) a better identification
of the $\nu_\mu$ events. It will improve the sensitivity to the CP-violation
phase. The three dimensional, $(E_\nu, \theta_\mu, y)$, $\nu_\mu-$oscillograms
with the kinematical as well as the experimental smearing are computed. We
present the asymmetry distributions in the $E_\nu - \theta_\mu$ plane for
different intervals of $y$ and study their properties. We show that the
inelasticity information reduces the effect of degeneracy of parameters by 30%.
With the inelasticity, the total significance of establishing mass hierarchy
may increase by 20% - 50%, thus effectively increasing the volume of the
detector by factor 1.5 - 2.Comment: 19 pages, 10 figure

### Leptonic CP Violation Phases, Quark-Lepton Similarity and Seesaw Mechanism

We explore generic features of the leptonic CP violation in the framework of
the seesaw type I mechanism with similarity of the Dirac lepton and quarks mass
matrices $m_D$. For this, we elaborate on the standard parametrization
conditions which allow to simultaneously obtain the Dirac and Majorana phases.
If the only origin of CP violation is the left-handed (LH) transformation which
diagonalizes $m_D$ (similar to quarks), the leptonic CP violation is suppressed
and the Dirac phase is close to $\pi$ or to $0$ with $\sin \delta_{CP} \approx
(\sin \theta_{13}^q /\sin \theta_{13}) \cos \theta_{23} \sin \delta_q \sim
\lambda^2 \sin \delta_q$. Here $\lambda \sim \theta_C$, is the Cabibbo mixing
angle, and $\theta_{13}^q$ and $\theta_{13}$ are the 1-3 mixing angles of
quarks and leptons respectively. The Majorana phases $\beta_1$ and $\beta_2$
are suppressed as $\lambda^3\sin\delta_q$. For Majorana neutrinos implied by
seesaw, the right-handed (RH) transformations are important. We explore the
simplest extension inspired by Left-Right (L-R) symmetry with small CKM-type CP
violation. In this case, seesaw enhancement of the CP violation occurs due to
strong hierarchy of the eigenvalues of $m_D$ leading to $\delta_{CP} \sim 1$.
The enhancement is absent under the phase factorization conditions which
require certain relations between parameters of the Majorana mass matrix of RH
neutrinos.Comment: 30 pages. v3(typos fixed, matches version published in Nucl. Phys. B

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