18 research outputs found
Quasi-degenerate neutrinos and tri-bi-maximal mixing
Assuming high-energy tri-bi-maximal mixing we study the radiative running of
leptonic mixing angles and obtain limits on the high-energy scale from
requiring consistency with the observed mixing. We construct a model in which a
non-Abelian discrete family symmetry leads both to a quasi-degenerate neutrino
mass spectrum and to near tri-bi-maximal mixing.Comment: 7 pages, to appear in the proceedings of DISCRETE'0
The Messenger Sector of SUSY Flavour Models and Radiative Breaking of Flavour Universality
The flavour messenger sectors and their impact on the soft SUSY breaking
terms are investigated in SUSY flavour models. In the case when the flavour
scale M is below the SUSY breaking mediation scale M_S, the universality of
soft terms, even if assumed at M_S, is radiatively broken. We estimate this
effect in a broad class of models. In the CKM basis that effect gives flavour
off-diagonal soft masses comparable to the tree-level estimate based on the
flavour symmetry.Comment: 24 pages, 3 figures. v3: minor changes in the text, typos corrected,
version accepted for publication in JHE
Beyond MFV in family symmetry theories of fermion masses
Minimal Flavour Violation (MFV) postulates that the only source of flavour
changing neutral currents and CP violation, as in the Standard Model, is the
CKM matrix. However it does not address the origin of fermion masses and mixing
and models that do usually have a structure that goes well beyond the MFV
framework. In this paper we compare the MFV predictions with those obtained in
models based on spontaneously broken (horizontal) family symmetries, both
Abelian and non-Abelian. The generic suppression of flavour changing processes
in these models turns out to be weaker than in the MFV hypothesis. Despite
this, in the supersymmetric case, the suppression may still be consistent with
a solution to the hierarchy problem, with masses of superpartners below 1 TeV.
A comparison of FCNC and CP violation in processes involving a variety of
different family quantum numbers should be able to distinguish between various
family symmetry models and models satisfying the MFV hypothesis.Comment: 34 pages, no figure
Lowering solar mixing angle in inverted hierarchy without charged lepton corrections
In the present work, the inverted hierarchical neutrino mass model which is
characterised by opposite CP parity in the first two mass eigenvalues
, is studied in order to lower the predicted value of solar
mixing angle , from the tri-bimaximal mixing (TBM), without
sacrificing the conditions of maximal atmospheric mixing angle and zero reactor
angle. The present attempt is different from the earlier approach where the
correction from the charged lepton mass matrix is included in the leptonic
mixing matrix to lower the prediction on solar mixing angle. The lowering of
the solar mixing angle without charged lepton correction, can be obtained
through the variation of the input value of a flavour twister term present in
the texture of neutrino mass matrix having a 2-3 symmetry. The present analysis
agrees with the latest experimental bounds on neutrino mass parameters and also
represents an important result on the survival of the inverted hierarchical
neutrino mass models having opposite CP parity in the first two eigenvalues.Comment: 10 pages, two figures. Accepted for publication in Journal of Physics
G:Nuclear and Particle Physic
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
We present a see-saw model for Tri-Bimaximal mixing which is based on a
very economical flavour symmetry and field content and still possesses all the
good features of models. In particular the charged lepton mass
hierarchies are determined by the flavour symmetry itself
without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is
exact in leading order while all the mixing angles receive corrections of the
same order in next-to-the-leading approximation. As a consequence the predicted
value of is within the sensitivity of the experiments which will
take data in the near future. The light neutrino spectrum, typical of
see-saw models, with its phenomenological implications, also including
leptoproduction, is studied in detail.Comment: 20 pages, 2 figure
The Interplay Between GUT and Flavour Symmetries in a Pati-Salam x S4 Model
Both Grand Unified symmetries and discrete flavour symmetries are appealing
ways to describe apparent structures in the gauge and flavour sectors of the
Standard Model. Both symmetries put constraints on the high energy behaviour of
the theory. This can give rise to unexpected interplay when building models
that possess both symmetries. We investigate on the possibility to combine a
Pati-Salam model with the discrete flavour symmetry that gives rise to
quark-lepton complementarity. Under appropriate assumptions at the GUT scale,
the model reproduces fermion masses and mixings both in the quark and in the
lepton sectors. We show that in particular the Higgs sector and the running
Yukawa couplings are strongly affected by the combined constraints of the Grand
Unified and family symmetries. This in turn reduces the phenomenologically
viable parameter space, with high energy mass scales confined to a small region
and some parameters in the neutrino sector slightly unnatural. In the allowed
regions, we can reproduce the quark masses and the CKM matrix. In the lepton
sector, we reproduce the charged lepton masses, including bottom-tau
unification and the Georgi-Jarlskog relation as well as the two known angles of
the PMNS matrix. The neutrino mass spectrum can present a normal or an inverse
hierarchy, and only allowing the neutrino parameters to spread into a range of
values between and , with .
Finally, our model suggests that the reactor mixing angle is close to its
current experimental bound.Comment: 62 pages, 4 figures; references added, version accepted for
publication in JHE
Cascade Textures and SUSY SO(10) GUT
We give texture analyses of cascade hierarchical mass matrices in
supersymmetric SO(10) grand unified theory. We embed cascade mass textures of
the standard model fermion with right-handed neutrinos into the theory, which
gives relations among the mass matrices of the fermions. The related
phenomenologies, such as the lepton flavor violating processes and
leptogenesis, are also investigated in addition to the PMNS mixing angles.Comment: 27 pages, 4 figures, comments and references added, final versio
Discrete Flavour Groups, \theta_13 and Lepton Flavour Violation
Discrete flavour groups have been studied in connection with special patterns
of neutrino mixing suggested by the data, such as Tri-Bimaximal mixing (groups
A4, S4...) or Bi-Maximal mixing (group S4...) etc. We review the predictions
for sin(\theta_13) in a number of these models and confront them with the
experimental measurements. We compare the performances of the different classes
of models in this respect. We then consider, in a supersymmetric framework, the
important implications of these flavour symmetries on lepton flavour violating
processes, like \mu -> e gamma and similar processes. We discuss how the
existing limits constrain these models, once their parameters are adjusted so
as to optimize the agreement with the measured values of the mixing angles. In
the simplified CMSSM context, adopted here just for indicative purposes, the
small tan(beta) range and heavy SUSY mass scales are favoured by lepton flavour
violating processes, which makes it even more difficult to reproduce the
reported muon g-2 discrepancy.Comment: 45 pages, 16 figures, 3 tables; V3 submitted to add an acknowledgment
to a Networ