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 $(16,3)$ representation of the $SO(10)\times A_4$ 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

Erratum: constraining flavour symmetries at the EW scale I: the A4 Higgs potential

n/

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 $B-L$ 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 $B-L$ asymmetry in a scenario of a concrete $A_4$ 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 $S_4$ 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 $\lambda^{-2}$ and $\lambda^2$, with $\lambda\simeq0.2$. 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