1,721,132 research outputs found
Flavor symmetry L-e-L-mu-L-tau, atmospheric neutrino mixing, and CP violation in the lepton sector
No full textThe PMNS neutrino mixing matrix is given, in general,
by the product of two unitary matrices
associated with the diagonalization of the charged lepton
and neutrino mass matrices.
Assuming that the active flavor
neutrinos possess a
Majorana mass matrix which is
diagonalized by a
bimaximal mixing matrix, we
give the allowed forms of the
charged lepton mixing matrix and
the corresponding implied forms of the
charged lepton mass matrix.
We then assume that the
origin of bimaximal mixing is a weakly
broken flavor symmetry
corresponding to the conservation of the non--standard lepton charge
.
The latter does not predict, in general, the
atmospheric neutrino mixing to be maximal.
We study the impact of
this fact on the allowed forms of the charged lepton
mixing matrix and on the
neutrino mixing observables, analyzing the
case of --violation in detail.
When compared with the case of exact
bimaximal mixing, the deviations
from zero and from maximal atmospheric neutrino mixing
are typically more sizable if
one assumes just conservation.
In fact, can be as small
as 0.007 and atmospheric neutrino mixing
can take any value inside its currently allowed range.
We discuss under which conditions the atmospheric neutrino mixing angle
is larger or smaller than .
We present also a simple see--saw realization
of the implied light neutrino Majorana
mass matrix and consider leptogenesis in this
scenario
On the Connection of Leptogenesis with Low Energy CP-Violation and LFV Charged Lepton Decays
Full text linkThe biunitary parametrization of the neutrino Dirac mass matrix m(D) of the seesaw mechanism of neutrino mass generation is considered in detail. Assuming a hierarchical structure of m(D) and of the heavy Majorana neutrino masses M-1,M-2,M-3>0, M-110(3)M(1)), we find that, in order to produce the observed baryon asymmetry of the Universe via leptogenesis, the scale of m(D) should be given by the up-quark masses, m(D)similar tom(up). It is also possible to reproduce the low-energy neutrino mixing phenomenology for m(D)similar tom(up) if one of the heavy Majorana neutrinos is much heavier than the other two and there exists only a rather mild hierarchy between the masses of the latter (M(2)congruent to10 M-1). In the case of a strong hierarchy between M-3 and M-1,M-2, successful leptogenesis requires a mild hierarchy between M-1 and M-2 as well. In this scenario, the effective Majorana mass in neutrinoless double beta decay depends on the CP violating phase controlling the leptogenesis if m(D1) is negligible. The lepton flavor violating decays mu-->e+gamma, tau-->mu+gamma and tau-->e+gamma are considered and a characteristic relation between their decay rates is predicted. The CP violation effects in neutrino oscillations can be observable. In general, there is no direct connection between the latter and CP violation in leptogenesis. If the CP violating phases of the seesaw model satisfy certain relations, the baryon asymmetry of the Universe and the rephasing invariant J(CP) which determines the magnitude of the CP violation effects in neutrino oscillations depend on the same CP violating phase and their signs are correlated
On the CP violation associated with Majorana neutrinos and neutrinoless double-beta decay
Full text linkAssuming 3-ν mixing and massive Majorana neutrinos, we analyze the possibility of establishing the existence of CP violation associated with Majorana neutrinos in the lepton sector by (i) measuring of the effective Majorana mass |m| in neutrinoless double beta decay with a sufficient precision and (ii) by measuring of, or obtaining a stringent upper limit on, the lightest neutrino mass m1. Information on m1 can be obtained in the 3H β-decay experiment KATRIN and from astrophysical and cosmological observations. Proving that the indicated CP violation takes place requires, in particular, a relative experimental error on the measured value of |m| not bigger than 20%, a “theoretical uncertainty” in the value of |m| due to an imprecise knowledge of the corresponding nuclear matrix elements smaller than a factor of 2, a value of tan2θ0.55, and values of the relevant Majorana CP-violating phases typically within the intervals of – and –. In the case of, e.g., quasi-degenerate neutrino mass spectrum it requires also that the neutrino masses have values not smaller than 0.7 eV
The See-Saw Mechanism, Neutrino Yukawa Couplings, LFV Decays l_i --> l_j + gamma and Leptogenesi
No full textThe LFV charged lepton decays , and and thermal leptogenesis
are analysed in the MSSM with see-saw mechanism of neutrino mass
generation and soft SUSY breaking with universal boundary
conditions. The case of hierarchical heavy Majorana neutrino mass
spectrum, , is investigated. Leptogenesis
requires GeV. Considering the natural range of
values of the heaviest right-handed Majorana neutrino mass, GeV, and assuming that the soft SUSY breaking
universal gaugino and/or scalar masses have values in the range of
GeV, we derive the combined constraints, which
the existing stringent upper limit on the decay
rate and the requirement of successful thermal leptogenesis impose
on the neutrino Yukawa couplings, heavy Majorana neutrino masses and
SUSY parameters. Results for the three possible types of light
neutrino mass spectrum -- normal and inverted hierarchical and
quasi-degenerate -- are obtained
U_{PMNS} = U_ell^dagger U_nu
No full textWe consider corrections to vanishing U_{e3} and maximal atmospheric neutrino mixing originating from the relation U = U_ell^dagger U_nu, where U is the PMNS mixing matrix and U_ell (U_nu) is associated with the diagonalization of the charged lepton (neutrino) mass matrix. We assume that in the limit of U_ell or U_nu being the unit matrix, one has U_{e3} = 0 and theta_{23} = pi/4, while the solar neutrino mixing angle is a free parameter. Well-known special cases of the indicated scenario are the bimaximal and tri-bimaximal mixing schemes. If U_{e3} \neq 0 and theta_{23} \neq pi/4 due to corrections from the charged leptons, |U_{e3}| can be sizable (close to the existing upper limit) and we find that the value of the solar neutrino mixing angle is linked to the magnitude of CP violation in neutrino oscillations. In the alternative case of the neutrino sector correcting U_{e3} = 0 and theta_{23} = pi/4, we obtain a generically smaller |U_{e3}| than in the first case. Now the magnitude of CP violation in neutrino oscillations is connected to the value of the atmospheric neutrino mixing angle theta_{23}. We find that both cases are in agreement with present observations. We also introduce parametrization independent "sum-rules" for the oscillation parameters
On Deviations from Bimaximal Neutrino Mixing
Full text linkThe PMNS neutrino mixing matrix is in general a product
of two unitary matrices
and
arising from the diagonalization of
the charged lepton and neutrino mass matrices,
.
Assuming that is a bimaximal mixing matrix,
we investigate the possible forms of .
We identify three possible
generic structures of ,
which are compatible with
the existing data on neutrino mixing. One corresponds to a hierarchical ``CKM--like'' matrix. In this case
relatively large values of
the solar neutrino mixing angle ,
and of ,
are typically predicted,
\tan^2\theta_{\rm sol} \gtap 0.42,
|U_{e3}|^2 \gtap 0.02,
while the atmospheric
neutrino mixing angle can
deviate noticeably from ,
\sin^22\theta_{\rm atm} \gtap 0.95.
The second corresponds to
one of the mixing angles in
being equal to ,
and predicts practically maximal atmospheric
neutrino mixing
.
Large atmospheric neutrino
mixing, \sin^22\theta_{\rm atm} \gtap 0.95,
is naturally predicted by the third possible
generic structure of ,
which corresponds to all three
mixing angles in being large.
We focus especially on the case of
CP--nonconservation, analyzing it in detail.
We show how the CP--violating
phases, arising from the diagonalization
of the neutrino and charged lepton mass matrices, contribute to the measured
neutrino mixing observables
Leptonic unitary triangles and boomerangs
No full textWe review the idea of leptonic unitary triangles and extend the concept of the recently proposed unitary boomerangs to the lepton sector. Using a convenient parameterization of the lepton mixing, we provide approximate expressions for the side lengths and the angles of the six different triangles and give examples of leptonic unitary boomerangs. Possible applications of the leptonic unitary boomerangs are also briefly discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Large |Ue3| and tribimaximal mixing
No full textWe investigate in a model-independent way to what extent one can perturb tri-bimaximal mixing in order to generate a sizable value of |U_{e3}|, while at the same time keeping solar neutrino mixing near its measured value, which is close to sin2 theta_{12} = 1/3. Three straightforward breaking mechanisms to generate |U_{e3}| of
about 0.1 are considered. For charged lepton corrections, the suppression of a sizable contribution to sin2 theta_{12} can be achieved if CP violation in neutrino oscillations is almost maximal. Generation of the indicated value of |U_{e3}| of about 0.1 through renormalization group corrections requires the neutrinos to be quasi-degenerate in mass. The consistency with the allowed range of sin2 theta_{12} together with large running of |U_{e3}| forces one of the Majorana phases to be close to pi. This implies large cancellations in the effective Majorana mass governing neutrino-less double beta, constraining it to lie near its minimum allowed value of m_0 cos 2 theta_{12}, where m_0 is greater than about 0.1 eV. Finally, explicit breaking of the neutrino mass matrix in the inverted hierarchical and quasi-degenerate neutrino mass spectrum cases is similarly correlated with the effective Majorana mass, although to a lesser extent. The implied values for the atmospheric neutrino mixing angle theta_{23} are given in all cases
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