738 research outputs found

### Explicit seesaw with nearly bimaximal neutrino mixing and no LSND effect

An explicit model of neutrino texture is presented, where in the 6 times 6
mass matrix the Majorana lefthanded component is zero, the Majorana righthanded
component - diagonal with equal entries, and the Dirac component gets a
hierarchical structure, deformed by nearly bimaximal mixing. If the Majorana
righthanded component dominates over the Dirac component, the familiar seesaw
mechanism leads effectively to the popular, nearly bimaximal oscillations of
active neutrinos. The Dirac component, before its deformation, may be similar
in shape to the charged-lepton and quark mass matrices. Then, parameters for
solar and atmospheric neutrinos may be related to each other, predicting from
the SuperKamiokande value of Delta m_{32}^2 a tiny Delta m_{21}^2, typical for
MSW LOW solar solution (rather than for MSW Large Mixing Angle solution).Comment: Some improvements introduce

### A satisfactory empirical mass sum rule for charged leptons

In the framework of a mass formula proposed previously (transforming in a
specific way three free parameters into three masses), a simple empirical sum
rule for three charged-lepton masses is found, predicting m_\tau = 1776.9926
MeV, when the experimental values of m_e and m_\mu are used as an input. The
experimental value to be compared with is m_\tau = 1776.99^{+0.29}_{-0.26} MeV.
This satisfactory sum rule (equivalent to a simple parameter constraint in the
mass formula) is linear in masses and involves integers as its coefficients.
The author believes that such a simple and precise mass sum rule for charged
leptons may help in the process of developing realistic models for mass spectra
of fundamental fermions. In the second part of the paper, another equivalent
parametrization of the charged-lepton mass formula is described, corresponding
to an oscillatory picture of their mass matrix, where two matrices appear
playing the role of annihilation and creation operators in the generation
space.Comment: 11 page

### Option of three pseudo--Dirac neutrinos

As an alternative for popular see-saw mechanism, the option of three pseudo%
-Dirac neutrinos is discussed, where ${1/2}(m^{(L)} + m^{(R)}) \ll m^{(D)}$ for
their Majorana and Dirac masses. The actual neutrino mass matrix is assumed in
the form of tensor product M^{(\nu)} \otimes {(\{array} {cc} \lambda^{(L)} &
1 1 & \lambda^{(R)} \{array})}, where $M^{(\nu)}$ is a neutrino family mass
matrix ($M^{(\nu) \dagger} = M^{(\nu)}$) and $\lambda^{(L,R)} \equiv
m^{(L,R)}/m^{(D)}$ with $m^{(L)}$, $m^{(R)}$ and $m^{(D)}$ being taken as
universal for three neutrino families. It is shown that three neutrino effects
(deficits of solar $\nu_e$'s and atmospheric $\nu_\mu$'s as well as the
possible LSND excess of $\nu_e$'s in accelerator $\nu_\mu$ beam) can be
nicely described by the corresponding neutrino oscillations, though the LSND
effect may, alternatively, be eliminated (by a parameter choice). Atmospheric
$\nu_\mu$'s oscillate dominantly into $\nu_\tau$'s, while solar $\nu_e$'s -
into (existing here automatically) Majorana sterile counterparts of $\nu_e$'s.
A phenomenological texture for neutrinos, compatible with the proposed
description, is briefly presented.Comment: LaTeX, 10 page

### The four-group Z_2 x Z_2 as a discrete invariance group of effective neutrino mass matrix

Two sets of four 3x3 matrices 1^(3), varphi_1, varphi_2, varphi_3 and 1^(3),
mu_1, mu_2, mu_3 are constructed, forming two unitarily isomorphic reducible
representations 3 of the group Z_2 x Z_2 called often the four-group. They are
related to each other through the effective neutrino mixing matrix U with
s_{13} = 0, and generate four discrete transformations of flavor and mass
active neutrinos, respectively. If and only if s_{13} = 0, the generic form of
effective neutrino mass matrix M becomes invariant under the subgroup Z_2 of
Z_2 x Z_2 represented by the matrices 1^(3) and varphi_3. In the approximation
of m_1 = m_2, the matrix M becomes invariant under the whole Z_2 x Z_2
represented by the matrices 1^(3), varphi_1, varphi_2, varphi_3. The effective
neutrino mixing matrix U with s_{13} = 0 is always invariant under the whole
Z_2 x Z_2 represented in two ways, by the matrices 1^(3), varphi_1, varphi_2,
varphi_3 and 1^(3), mu_1, mu_2, mu_3.Comment: LaTeX, 1+10 pages. The term "irreducible" applied to the considered
doublet representations of the four-group is replaced by the correct term
"not reduced

### Photonic portal to hidden sector and a parity-preserving option

In the case of previously proposed idea of photonic portal to hidden sector,
the parity in this sector may be violated. We discuss here two new options
within our model, where the parity is preserved. The first of them is not
satisfactory, as not diplaying a full relativistic covariance. The second seems
to be satisfactory.Comment: 9 page

### Constructing the off-diagonal part of active-neutrino mass matrix from annihilation and creation matrices in neutrino-generation space

The off-diagonal part of the active-neutrino mass matrix is constructed from
two $3\times 3$ matrices playing the role of annihilation and creation matrices
acting in the neutrino-generation space of $\nu_e, \nu_\mu, \nu_\tau$. The
construction leads to a new relation, $M_{\mu \tau} = 4\sqrt{3} M_{e \mu}$,
which predicts in the case of tribimaximal neutrino mixing that $m_3 - m_1 =
\eta (m_2 - m_1)$ with $\eta = 5.28547$. Then, the maximal possible value of
${\Delta m^2_{32}}/{\Delta m^2_{21}}$ is equal to $\eta^2 -1 = 26.9362$ and
gives $m_1 = 0$. With the experimental estimate ${\Delta m^2_{21}}\sim
8.0\times 10^{-5} {\rm eV}^2$, this maximal value, if realized, predicts
$\Delta m^2_{32} \sim 2.2\times 10^{-3} {\rm eV}^2$, near to the popular
experimental estimation $\Delta m^2_{32} \sim 2.4\times 10^{-3} {\rm eV}^2$.Comment: 9 page

### Oscillations of the mixed pseudo--Dirac neutrinos

Oscillations of three pseudo--Dirac flavor neutrinos $\nu_e, \nu_\mu,
\nu_\tau$ are considered: $0 < m^{(L)} = m^{(R)} \ll m^{(D)}$ for their
Majorana and Dirac masses taken as universal before family mixing. The actual
neutrino mass matrix is assumed to be the tensor product $M^{(\nu)} \otimes
{(\begin{array}{cc} \lambda^{(L)} & 1 1 & \lambda^{(R)} \end{array})}$, where
$M^{(\nu)}$ is a neutrino family mass matrix ($M^{(\nu) \dagger} = M^{(\nu)}$)
and $\lambda^{(L,R)} = m^{(L,R)}/m^{(D)}$. The $M^{(\nu)}$ is tried in a form
proposed previously for charged leptons $e, \mu, \tau$ for which it gives
$m_\tau = 1776.80$ MeV versus $m^{exp}_\tau = 1777.05^{+0.29}_{-0.20}$ MeV
(with the experimental values of $m_e$ and $m_\mu$ used as inputs). However, in
contrast to the charged -lepton case, in the neutrino case its off-diagonal
entries dominate over diagonal. Then, it is shown that three neutrino effects
(the deficits of solar $\nu_e$'s and atmospheric $\nu_\mu$'s as well as the
possible LSND excess of $\nu_e$'s in accelerator $\nu_\mu$ beam) can be
explained by neutrino oscillations though, alternatively, the LSND effect may
be eliminated (by a parameter choice). Atmospheric $\nu_\mu$'s oscillate
dominantly into $\nu_\tau$'s, while solar $\nu_e$'s -- into (automatically
existing) Majorana sterile counterparts of $\nu_e$'s.Comment: 1+13 pages (LaTeX

### Explicit lepton texture

An explicit form of charged--lepton mass matrix, predicting $m_\tau =
1776.80$~MeV from the experimental values of $m_e$ and $m_\mu$ (in good
agreement with the experimental figure $m_\tau = 1777.05^{+0.29}_{-0.26}$
MeV), is applied to three neutrinos $\nu_e$, $\nu_\mu$, $\nu_\tau$ in order
to correlate tentatively their masses and mixing parameters. While for charged
leptons the off--diagonal mass--matrix elements turn out to be small {\it
versus} its diagonal elements, it is suggested that for neutrinos the situation
is inverse. Under such a conjecture, the neutrino masses, lepton \CKM matrix
and neutrino oscillation probabilities are calculated in the corresponding
lowest (and the next to lowest) perturbative order. Then, the nearly maximal
mixing of $\nu_\mu$ and $\nu_\tau$ is predicted in consistency with the
observed deficit of atmospheric $\nu_\mu$'s. However, the predicted deficit of
solar $\nu_e$'s is much too small to explain the observed effect, what
suggests the existence of (at least) one sort, $\nu_s$, of sterile neutrinos,
whose mixing with $\nu_e$ would be responsible for the observed deficit. In the
last Section, promising perspectives for applying the same form of mass matrix
to quarks are outlined. Two independent predictions of $|V_{ub}|/|V_{cb}| =
0.0753 \pm 0.0032$ and unitary angle $\gamma \simeq 70^\circ$ are deduced
from the experimental values of $|V_{us}|$ and $|V_{cb}|$ (with the use of
quark masses $m_s$, $m_c$ and $m_b$).Comment: Latex, 20 page

### Possible LSND effect as a small perturbation of the bimaximal texture for three active neutrinos

A particular form of mixing matrix for three active and one sterile neutrinos
is proposed. Its $3\times 3$ part describing three active neutrinos arises
from the popular bimaximal mixing matrix that works satisfactorily in solar and
atmospheric experiments if the LSND effect is ignored. Then, the sterile
neutrino, effective in the fourth row and fourth column of the proposed mixing
matrix, is responsible for the possible LSND effect by inducing one extra
neutrino mass state to exist actively. The LSND effect, if it exists, turns out
to reveal its {\it perturbative} nature related to small mixing of three active
neutrinos with their sterile partner.Comment: 9 pages, no figure

### Scattering of nucleons on cold-dark-matter particles through photonic portal

In the model of hidden sector proposed recently, protons and neutrons scatter
differently on cold-dark-matter particles. First, we summarize briefly our
model based on a mechanism of "photonic portal" between hidden and
Standard-Model sectors of the Universe. Then, we calculate in an elementary way
the differential cross-sections for scattering of protons and neutrons on
sterile Dirac fermions ("sterinos") playing the role of cold-dark-matter
particles. They interact with nucleons through the photonic portal in a
somewhat involved but natural manner. Due to this portal, the differential
cross-section for protons displays a Coulomb-like forward singularity.Comment: 12 pages, two misprints are correcte

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