20 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
Non-Abelian family symmetries in Pati-Salam unification
We present a framework of underlying SU(3) x SU(3) family symmetries
consistent with Pati-Salam unification and discuss advantages that can justify
introducing multiple non-Abelian factors. Advantages include improved vacuum
alignment and increased predictivity. We explore in this framework deviations
from tri-bi-maximal neutrinos, such as relatively large theta13.Comment: 11 pages, final version for publication in JHE
Ultraviolet Completion of Flavour Models
Effective Flavour Models do not address questions related to the nature of
the fundamental renormalisable theory at high energies. We study the
ultraviolet completion of Flavour Models, which in general has the advantage of
improving the predictivity of the effective models. In order to illustrate the
important features we provide minimal completions for two known A4 models. We
discuss the phenomenological implications of the explicit completions, such as
lepton flavour violating contributions that arise through the exchange of
messenger fields.Comment: 18 pages, 8 figure
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
Discrete family symmetry, Higgs mediators and theta_{13}
We present a new (supersymmetric) framework for obtaining an excellent
description of quark, charged lepton and neutrino masses and mixings from a
Delta(6n^2) family symmetry with multiplet assignments consistent with an
underlying SO(10) Grand Unification. It employs a Higgs mediator sector in
place of the usual Froggatt-Nielsen messengers, with quark and lepton
messengers, and provides significant improvements over existing models of this
type having unsuppressed Yukawa couplings to the third generation and a
simplified vacuum alignment mechanism. The neutrino mass differences are
naturally less hierarchical than those of the quarks and charged leptons.
Similarly the lepton mixing angles are much larger than those in the quark
sector and have an approximate tri-bi-maximal (TB) mixing form for theta_{12}
and theta_{23}. However the mixing angle theta_{13} is naturally much larger
than in pure TB mixing and can be consistent with the value found in recent
experiments. The magnitude of theta_{13} is correlated with a the predicted
deviation of theta_{23} from bi-maximal mixing. The model has light familon
fields that can significantly modify the associated SUSY phenomenology.Comment: v3: accepted 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
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
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