91 research outputs found
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
A See-Saw model for fermion masses and mixings
We present a supersymmetric see-saw model giving rise to the most
general neutrino mass matrix compatible with Tri-Bimaximal mixing. We adopt the
flavour symmetry, broken by suitable vacuum expectation values
of a small number of flavon fields. We show that the vacuum alignment is a
natural solution of the most general superpotential allowed by the flavour
symmetry, without introducing any soft breaking terms. In the charged lepton
sector, mass hierarchies are controlled by the spontaneous breaking of the
flavour symmetry caused by the vevs of one doublet and one triplet flavon
fields instead of using the Froggatt-Nielsen U(1) mechanism. The next to
leading order corrections to both charged lepton mass matrix and flavon vevs
generate corrections to the mixing angles as large as .
Applied to the quark sector, the symmetry group can give a
leading order proportional to the identity as well as a matrix with
coefficients in the Cabibbo submatrix. Higher order
corrections produce non vanishing entries in the other entries which
are generically of .Comment: 30 pages, 3 figures, minor changes to match the published versio
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
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
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
Strong coupling, discrete symmetry and flavour
We show how two principles - strong coupling and discrete symmetry - can work
together to generate the flavour structure of the Standard Model. We propose
that in the UV the full theory has a discrete flavour symmetry, typically only
associated with tribimaximal mixing in the neutrino sector. Hierarchies in the
particle masses and mixing matrices then emerge from multiple strongly coupled
sectors that break this symmetry. This allows for a realistic flavour
structure, even in models built around an underlying grand unified theory. We
use two different techniques to understand the strongly coupled physics:
confinement in N=1 supersymmetry and the AdS/CFT correspondence. Both
approaches yield equivalent results and can be represented in a clear,
graphical way where the flavour symmetry is realised geometrically.Comment: 31 pages, 5 figures, updated references and figure
Accidental stability of dark matter
We propose that dark matter is stable as a consequence of an accidental Z2
that results from a flavour-symmetry group which is the double-cover group of
the symmetry group of one of the regular geometric solids. Although
model-dependent, the phenomenology resembles that of a generic Higgs portal
dark matter scheme.Comment: 12 pages, final version, published in JHE
Prolonged RT-PCR test positivity in hemodialysis patients with COVID-19
Background: The weakened immune system of patients on hemodialysis (HD) may prolong SARS-CoV-2 infection compared to the general population. Current international guidelines recommend ending isolation in conjunction with serial testing in moderately and severely immunocompromised subjects. This study aimed to estimate SARS-CoV-2 infectivity by measuring RT-PCR test positivity in HD patients. A comparison between RT-PCR test and cycle threshold (Ct) value has been performed as a secondary endpoint. Methods: A single-center retrospective study was conducted at the University of Modena (Italy) from March 2020 to October 2022. Only patients on chronic HD therapy with COVID-19 were enrolled in the study. In our HD Center, two negative nasopharyngeal reverse transcription polymerase chain reaction (RT-PCR) results were used to end quarantine in this population. SARS-CoV-2 RT-PCR test positivity duration measured the time elapsed from a positive RT-PCR to a second negative test. Ct cut-off of 35 cycles was used to definite “high Ct value,” a condition characterized by a large number of cycles of PCR amplification to register a positive RT-PCR test. Results: During the observational period, 159 cases of SARS-CoV-2 infections were diagnosed in 151 patients. Median age was 70.1 (54.3–81.6) years and males accounted for 59.6% of the COVID-19 population. Median duration of SARS-CoV-2 RT-PCR test positivity on the nasal mucosa accounted for 30 (IQR, 21–40.5) days. Unvaccinated patients experienced significantly longer RT-PCR test positivity compared to vaccinated patients (42 [IQR,31–56] vs. 28 [IQR,20–35.7] days; p = < 0.001). The use of high Ct value, a laboratory surrogate of SARS-CoV-2 replication, anticipated a negative RT-PCR test of 9 (IQR, 6–12) days. Multivariate linear regression analysis showed that increased age (β coefficient 0.31; confidence interval [CI] 95%, 0.14—0.43; p = < 0.001) and the lack of anti-SARS-CoV-2 vaccination (β 0.49 CI95%, 11.9–22.5; p = < 0.001) were predictors of a prolonged RT-PCR positivity. Conclusions: Patients with COVID-19 on HD had prolonged RT-PCR test positivity. The adoption of “high Ct value” criteria led to a significant reduction in the duration of RT-PCR test positivity compared to the use of the classical nucleic acid amplification test. In our study, the lack of SARS-CoV-2 vaccination and older age were independently associated with a longer RT-PCR positivity
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
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