52 research outputs found
Fermion masses and mixing in models with SO(10) x A_4 symmetry
We study the flavour sector in models where the three families of matter are
unified in a representation of the group. The
necessary ingredients to realize tri-bi-maximal mixing in the lepton sector are
identified systematically. The non-renormalizable operators contributing to the
fermion mass matrices play an important role. We also present a mechanism to
explain the inter-family mass hierarchy of quarks and charged leptons, which
relies on a `universal seesaw' mechanism and is compatible with tri-bi-maximal
mixing.Comment: 24 pages, revte
S4 as a natural flavor symmetry for lepton mixing
Group theoretical arguments seem to indicate the discrete symmetry S4 as the
minimal flavour symmetry compatible with tribimaximal neutrino mixing. We prove
in a model independent way that indeed S4 can realize exact tribimaximal mixing
through different symmetry breaking patterns. We present two models in which
lepton tribimaximal mixing is realized in different ways and for each one we
discuss the superpotential that leads to the correct breaking of the flavor
symmetry.Comment: References added, typos corrected and few irrelevant changing
Just so Higgs boson
8 pages, 4 figures.-- PACS nrs.: 11.30.Qc; 12.60.Fr; 14.80.Cp; 95.35.+d.-- ISI Article Identifier: 000245333000072.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0612280We discuss a minimal extension to the standard model in which there are two Higgs bosons and, in addition to the usual fermion content, two fermion doublets and one fermion singlet. The little hierarchy problem is solved by the vanishing of the one-loop corrections to the quadratic terms of the scalar potential. The electroweak ground state is therefore stable for values of the cut off up to 10 TeV. The Higgs boson mass can take values significantly larger than the current LEP bound and still be consistent with electroweak precision measurements.This work is partially supported by MIUR and the RTN European Program MRTN-CT-2004-503369. F. B. is supported by a MEC postdoctoral grant.Peer reviewe
Quark mixing in the discrete dark matter model
We consider a model in which dark matter is stable as it is charged under a
Z2 symmetry that is residual after an A4 flavour symmetry is broken. We
consider the possibility to generate the quark masses by charging the quarks
appropriately under A4. We find that it is possible to generate the CKM mixing
matrix by an interplay of renormalisable and dimension-six operators. In this
set-up, we predict the third neutrino mixing angle to be large and the dark
matter relic density to be in the correct range. However, low energy
observables - in particular meson-antimeson oscillations - strongly limit the
available parameter space.Comment: 10 pages, 4 figures; version 3 as appeared in Nuclear Physics
Fermion Masses and Mixings in a S4 Based Model
It has been recently claimed that the symmetry group S4 yields to the
Tri-bimaximal neutrino mixing in a "natural" way from the group theory point of
view. Approving of this feature as an indication, we build a supersymmetric
model of lepton and quark masses based on this family symmetry group. In the
lepton sector, a correct mass hierarchy among the charged leptons is achieved
together to a neutrino mass matrix which can be diagonalized by the
Tri-bimaximal pattern. Our model results to be phenomenologically unequivalent
with respect to other proposals based on different flavour groups but still
predicting the Tri-bimaximal mixing. In the quark sector a realistic pattern
for masses and mixing angles is obtained. The flavour structures of the mass
matrices in both the sectors come from the spontaneously symmetry breaking of
S4, due to several scalar fields, which get non-zero vacuum expectation values.
A specific vacuum alignment is required and it is shown to be a natural results
of the minimization of the scalar potential and, moreover, to be stable under
the corrections from the higher order terms.Comment: 25 pages, LaTeX; added references and minor correctio
Phenomenological Consequences of See-Saw in S4 Based Models
It was proposed a flavour model based on the symmetry group S4, managing to
describe fermion masses and mixings. The Weinberg operator has been used in
order to provide the smallness of the neutrino masses, while a set of scalar
fields, getting non-vanishing vacuum expectation values, spontaneously breaks
down S4 and provides the Tri-Bimaximal pattern as the lepton mixing matrix.
Restricting to this setting, in this paper we analyze possible origins for the
effective terms: the type I See-Saw mechanism is the best known approach, but
also the type II and III are discussed. The phenomenology related to these
models is various and the next future experiments could in principle
discriminate among these proposals. Furthermore, we compare our realizations to
two relevant A4 based models, also predicting the Tri-Bimaximal lepton mixing,
and we find that an analysis on the neutrinoless double beta decay parameters
could distinguish among all these realizations. Furthermore a combined
measurement of the effective mass and of the lightest neutrino mass could
indicate in the next future which is the preferred flavour symmetry group. The
introduction of new physics beyond the Standard Model, like heavy right-handed
neutrinos, scalar triplets and fermion triplets, let us investigate on
leptogenesis and this provides constraints in the realization of the models.Comment: 32 pages, 14 figures; added references and minor correctio
Leptogenesis in the presence of exact flavor symmetries
In models with flavor symmetries in the leptonic sector leptogenesis can take
place in a very different way compared to the standard leptogenesis scenario.
We study the generation of a asymmetry in these kind of models in the
flavor symmetric phase pointing out that successful leptogenesis requires (i)
the right-handed neutrinos to lie in different representations of the flavor
group; (ii) the flavons to be lighter at least that one of the right-handed
neutrino representations. When these conditions are satisfied leptogenesis
proceeds due to new contributions to the CP violating asymmetry and -depending
on the specific model- in several stages. We demonstrate the validity of these
arguments by studying in detail the generation of the asymmetry in a
scenario of a concrete flavor model realization.Comment: 25 pages, 7 figures; version 2: A few clarifications added. Version
matches publication in JHE
Impact and Treatment of Sarcopenia in Patients Undergoing Radiotherapy: A Multidisciplinary, AMSTAR-2 Compliant Review of Systematic Reviews and Metanalyses
BackgroundSarcopenia (SP) is defined as the quantitative and functional impairment of skeletal muscles. SP is commonly related to older age and is frequent in patients with cancer. To provide an overview of SP in patients treated with radiotherapy (RT) and to evaluate the current evidence, we analyzed the available systematic reviews and meta-analyses. MethodsReviews were identified using PubMed, Scopus, and Cochrane library databases, without date restriction. Only systematic reviews and meta-analyses on the prognostic impact of SP and on any treatments aimed at reducing SP effect, in patients undergoing RT, were included in this review. The analyses not separately reporting the results in patients treated with RT were excluded. The quality assessment was performed using AMSTAR-2 (A MeaSurement Tool to Assess systematic Reviews). ResultsFrom the 84 papers identified, five reviews met the inclusion criteria with four reports mainly including non-randomized trials. Three reviews on the effect of SP showed a significantly negative impact on overall survival in patients undergoing RT and/or chemoradiation for H&N cancers (HR: 1.63-2.07). Two reviews on interventional studies showed the possibility of 1) improving physical functions through nutritional and physical interventions and 2) avoiding muscle wasting by means of sufficient protein intake. The quality assessment of the included review showed that two and three analyses are classifiable as having low and moderate overall confidence rating, respectively. ConclusionsThe analyzed reviews uniformly confirmed the negative impact of SP in patients with H&N tumors undergoing RT and the possibility of improving muscle mass and function through nutritional and physical interventions. These results justify further research on this topic based on a more uniform SP definition and on a complete evaluation of the potentially confounding parameters
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
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