36 research outputs found
Modelling tri-bimaximal neutrino mixing
We model tri-bimaximal lepton mixing from first principles in a way that
avoids the problem of the vacuum alignment characteristic of such models. This
is achieved by using a softly broken A4 symmetry realized with an isotriplet
fermion, also triplet under A4. No scalar A4-triplet is introduced. This
represents one possible realization of general schemes characterized by the
minimal set of either three or five physical parameters. In the three parameter
versions mee vanishes, while in the five parameter schemes the absolute scale
of neutrino mass, although not predicted, is related to the two Majorana
phases. The model realization we discuss is potentially testable at the LHC
through the peculiar leptonic decay patterns of the fermionic and scalar
triplets.Comment: some changing, reference adde
Relating quarks and leptons without grand-unification
In combination with supersymmetry, flavor symmetry may relate quarks with
leptons, even in the absence of a grand-unification group. We propose an
SU(3)xSU(2)xU(1) model where both supersymmetry and the assumed A4 flavor
symmetries are softly broken, reproducing well the observed fermion mass
hierarchies and predicting: (i) a relation between down-type quarks and charged
lepton masses, and (ii) a correlation between the Cabibbo angle in the quark
sector, and the reactor angle characterizing CP violation in neutrino
oscillations.Comment: 4 pages, 2 figures, version published in PR
Lepton flavor violation and non-unitary lepton mixing in low-scale type-I seesaw
Within low-scale seesaw mechanisms, such as the inverse and linear seesaw,
one expects (i) potentially large lepton flavor violation (LFV) and (ii)
sizeable non-standard neutrino interactions (NSI). We consider the interplay
between the magnitude of non-unitarity effects in the lepton mixing matrix, and
the constraints that follow from LFV searches in the laboratory. We find that
NSI parameters can be sizeable, up to percent level in some cases, while LFV
rates, such as that for \mu -> e \gamma, lie within current limits, including
the recent one set by the MEG collaboration. As a result the upcoming long
baseline neutrino experiments offer a window of opportunity for complementary
LFV and weak universality tests.Comment: 14 pages, 14 composite figures and 1 table. v2: minor changes,
references added. Accepted for publication in JHE
Tri-bimaximal neutrino mixing and neutrinoless double beta decay
We present a tri-bimaximal lepton mixing scheme where the neutrinoless double
beta decay rate (bb0v) has a lower bound which correlates with the ratio alpha
= Dmsol/Dmatm well determined by current data, as well as with the unknown
Majorana CP phase phi12 characterizing the solar neutrino sub-system. For the
special value phi12 = pi/2 (opposite CP-sign neutrinos) the bb0v rate vanishes
at tree level when Dmsol/Dmatm = 3/80, only allowed at 3 sigma. For all other
cases the rate is nonzero, and lies within current and projected experimental
sensitivities close to phi12=0. We suggest two model realizations of this
scheme in terms of an A4xZ2 and A4xZ4 flavour symmetries.Comment: 4 pages and 3 figure
Inverse tri-bimaximal type-III seesaw and lepton flavor violation
We present a type-III version of inverse seesaw or, equivalently an inverse
version of type-III seesaw. Naturally small neutrino masses arise at low-scale
from the exchange of neutral fermions transforming as hyperchargeless SU(2)
triplets. In order to implement tri-bimaximal lepton mixing we supplement the
minimal SU(3)xSU(2)xU(1) gauge symmetry with an A4-based flavor symmetry. Our
scenario induces lepton flavour violating (LFV) three body decays that can
proceed at the tree level, while radiative li to lj gamma decays and mu-e
conversion in nuclei are also expected to be sizeable. LFV decays are related
by the underlying flavor symmetry and the new fermions are also expected to be
accessible for study at the Large Hadron Collider (LHC)
Discrete dark matter
We propose a new motivation for the stability of dark matter (DM). We suggest
that the same non-abelian discrete flavor symmetry which accounts for the
observed pattern of neutrino oscillations, spontaneously breaks to a Z2
subgroup which renders DM stable. The simplest scheme leads to a scalar doublet
DM potentially detectable in nuclear recoil experiments, inverse neutrino mass
hierarchy, hence a neutrinoless double beta decay rate accessible to upcoming
searches, while reactor angle equal to zero gives no CP violation in neutrino
oscillations.Comment: minor changes to match version accepted in PRD, one reference adde
A new neutrino mass sum rule from inverse seesaw
A class of discrete flavor-symmetry-based models predicts constrained
neutrino mass matrix schemes that lead to specific neutrino mass sum-rules
(MSR). One of these implies in a lower bound on the effective neutrinoless
double beta mass parameter, even for normal hierarchy neutrinos. Here we
propose a new model based on the S4 flavor symmetry that leads to the new
neutrino mass sum-rule and discuss how to generate a nonzero value for the
reactor mixing angle indicated by recent experiments, and the resulting
correlation with the solar mixing angle.Comment: 14 pages, 4 figure
Bi-large neutrino mixing and the Cabibbo angle
Recent measurements of the neutrino mixing angles cast doubt on the validity
of the so-far popular tri-bimaximal mixing ansatz. We propose a parametrization
for the neutrino mixing matrix where the reactor angle seeds the large solar
and atmospheric mixing angles, equal to each other in first approximation. We
suggest such bi-large mixing pattern as a model building standard, realized
when the leading order value of the reactor angle equals the Cabibbo angle.Comment: 4 pages, 2 figs. v2: matches version appearing in Phys.Rev.D, rapid
communication
Predictive Discrete Dark Matter Model
Dark Matter stability can be achieved through a partial breaking of a flavor
symmetry. In this framework we propose a type-II seesaw model where left-handed
matter transforms nontrivially under the flavor group Delta(54), providing
correlations between neutrino oscillation parameters, consistent with the
recent Daya-Bay and RENO reactor angle measurements, as well as lower bounds
for neutrinoless double beta decay. The dark matter phenomenology is provided
by a Higgs-portal.Comment: v1: 4 pages, 2 figures. v2: The discussion is extended to the NH
case, 1 additional figur
Quark-lepton mass relation and CKM mixing in an A(4) extension of the minimal supersymmetric standard model
An interesting mass relation between down-type quarks and charged leptons has been recently predicted within a supersymmetric SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) model based on the A(4) flavor symmetry. Here we propose a simple extension which provides an adequate full description of the quark sector. By adding a pair of vectorlike up quarks, we show how the CKM entries V-ub, V-cb, V-td and V-ts arise from deviations of the unitarity. We perform an analysis including the most relevant observables in the quark sector, such as oscillations and rare decays of kaons, B-d and B-s mesons. In the lepton sector, the model predicts an inverted hierarchy for the neutrino masses, leading to a potentially observable rate of neutrinoless double beta decay