10 research outputs found
A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4
We discuss a grand unified model based on SUSY SU(5) in extra dimensions and
on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing
for neutrinos with the accuracy required by the data, also leads to a natural
description of the observed pattern of quark masses and mixings.Comment: 19 page
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
Tri-Bimaximal Lepton Mixing and Leptogenesis
In models with flavour symmetries added to the gauge group of the Standard
Model the CP-violating asymmetry necessary for leptogenesis may be related with
low-energy parameters. A particular case of interest is when the flavour
symmetry produces exact Tri-Bimaximal lepton mixing leading to a vanishing
CP-violating asymmetry. In this paper we present a model-independent discussion
that confirms this always occurs for unflavoured leptogenesis in type I see-saw
scenarios, noting however that Tri-Bimaximal mixing does not imply a vanishing
asymmetry in general scenarios where there is interplay between type I and
other see-saws. We also consider a specific model where the exact Tri-Bimaximal
mixing is lifted by corrections that can be parametrised by a small number of
degrees of freedom and analyse in detail the existing link between low and
high-energy parameters - focusing on how the deviations from Tri-Bimaximal are
connected to the parameters governing leptogenesis.Comment: 29 pages, 6 figures; version 2: references added, minor correction
Towards Minimal S4 Lepton Flavor Model
We study lepton flavor models with the flavor symmetry. We construct
simple models with smaller numbers of flavon fields and free parameters, such
that we have predictions among lepton masses and mixing angles. The model with
a triplet flavon is not realistic, but we can construct realistic models
with two triplet flavons, or one triplet and one doublet flavons.Comment: 18 pages, 4 figures, references are adde
Embedding A4 into SU(3)xU(1) flavor symmetry: Large neutrino mixing and fermion mass hierarchy in SO(10) GUT
We present a common explanation of the fermion mass hierarchy and the large
lepton mixing angles in the context of a grand unified flavor and gauge theory
(GUTF). Our starting point is a SU(3)xU(1) flavor symmetry and a SO(10) GUT, a
basic ingredient of our theory which plays a major role is that two different
breaking pattern of the flavor symmetry are at work. On one side, the dynamical
breaking of SU(3)xU(1) flavor symmetry into U(2)xZ_3 explains why one family is
much heavier than the others. On the other side, an explicit symmetry breaking
of SU(3) into a discrete flavor symmetry leads to the observed tribimaximal
mixing for the leptons. We write an explicit model where this discrete symmetry
group is A4. Naturalness of the charged fermion mass hierarchy appears as a
consequence of the continuous SU(3) flavor symmetry. Moreover, the same
discrete A4-GUT invariant operators are the root of the large lepton mixing,
small Cabibbo angle, and neutrino masses.Comment: 11 pages, uses package "axodraw", "graphicx
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
The 3-3-1 model with S_4 flavor symmetry
We construct a 3-3-1 model based on family symmetry S_4 responsible for the
neutrino and quark masses. The tribimaximal neutrino mixing and the diagonal
quark mixing have been obtained. The new lepton charge \mathcal{L} related to
the ordinary lepton charge L and a SU(3) charge by L=2/\sqrt{3} T_8+\mathcal{L}
and the lepton parity P_l=(-)^L known as a residual symmetry of L have been
introduced which provide insights in this kind of model. The expected vacuum
alignments resulting in potential minimization can origin from appropriate
violation terms of S_4 and \mathcal{L}. The smallness of seesaw contributions
can be explained from the existence of such terms too. If P_l is not broken by
the vacuum values of the scalar fields, there is no mixing between the exotic
and the ordinary quarks at the tree level.Comment: 20 pages, revised versio
Revisiting Bimaximal Neutrino Mixing in a Model with S4 Discrete Symmetry
In view of the fact that the data on neutrino mixing are still compatible
with a situation where Bimaximal mixing is valid in first approximation and it
is then corrected by terms of order of the Cabibbo angle, arising from the
diagonalization of the charged lepton masses, we construct a model based on the
discrete group S4 where those properties are naturally realized. The model is
supersymmetric in 4-dimensions and the complete flavour group is S4 x Z4 x
U(1)_FN, which also allows to reproduce the hierarchy of the charged lepton
spectrum. The only fine tuning needed in the model is to reproduce the small
observed value of r, the ratio between the neutrino mass squared differences.
Once the relevant parameters are set to accommodate r then the spectrum of
light neutrinos shows a moderate normal hierarchy and is compatible, within
large ambiguities, with the constraints from leptogenesis as an explanation of
the baryon asymmetry in the Universe.Comment: 30 pages, 5 figures; added reference
Natural Vacuum Alignment from Group Theory: The Minimal Case
Discrete flavour symmetries have been proven successful in explaining the
leptonic flavour structure. To account for the observed mixing pattern, the
flavour symmetry has to be broken to different subgroups in the charged and
neutral lepton sector. However, cross-couplings via non-trivial contractions in
the scalar potential force the group to break to the same subgroup. We present
a solution to this problem by extending the flavour group in such a way that it
preserves the flavour structure, but leads to an 'accidental' symmetry in the
flavon potential. We have searched for symmetry groups up to order 1000, which
forbid all dangerous cross-couplings and extend one of the interesting groups
A4, T7, S4, T' or \Delta(27). We have found a number of candidate groups and
present a model based on one of the smallest extension of A4, namely Q8 \rtimes
A4. We show that the most general non-supersymmetric potential allows for the
correct vacuum alignment. We investigate the effects of higher dimensional
operators on the vacuum configuration and mixing angles, and give a
see-saw-like UV completion. Finally, we discuss the supersymmetrization of the
model. Additionally, we release the Mathematica package "Discrete" providing
various useful tools for model building such as easily calculating invariants
of discrete groups and flavon potentials.Comment: 33 pages, 7 figures; references added, minor changes, matches version
published in JHE