1,721,098 research outputs found
A case of subdominant/suppressed “high energy” contribution to the baryon asymmetry of the Universe in flavoured leptogenesis
No full textAbstractThe CP-violation necessary for the generation of the baryon asymmetry of the Universe YB in the “flavoured” leptogenesis scenario can arise from the “low energy” PMNS neutrino mixing matrix U and/or from the “high energy” part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is analysed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. We show that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant “high energy” phases have large CP-violating values, but the purely “high energy” contribution in YB plays a subdominant role in the production of baryon asymmetry compatible with the observations. In some of these regions the purely “high energy” contribution in YB is so strongly suppressed that one can have successful leptogenesis only if the requisite CP-violation is provided by the Majorana phase(s) in the neutrino mixing matrix
The interplay between "low" and "high" energy CP-violation in leptogenesis
No full textWe analyse, within the "flavoured" leptogenesis scenario of baryon asymmetry generation, the interplay of "low energy" CP-violation, originating from the PMNS neutrino mixing matrix U, and "high energy" CP-violation, which can be present in the matrix of neutrino Yukawa couplings, lambda, and can manifest itself only in "high" energy scale processes. The type I see-saw model with three heavy right-handed Majorana neutrinos having a hierarchical spectrum is considered. The "orthogonal" parameterisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. In this approach the matrix R is the source of "high energy" CP-violation. Results for normal hierarchical (NH) and inverted hierarchical (IH) light neutrino mass spectrum are derived in the case of decoupling of the heaviest right-handed Majorana neutrino. It is shown that taking into account the contribution to Y (B) due to the CP-violating phases in the neutrino mixing matrix U can change drastically the predictions for Y (B) , obtained assuming that only "high energy" CP-violation from the R-matrix is operative in leptogenesis. In the case of the IH spectrum, in particular, there exist significant regions in the corresponding parameter space where the purely "high energy" contribution in Y (B) plays a subdominant role in the production of baryon asymmetry compatible with the observations
Revisiting leptogenesis in a SUSY SU(5)×T′ model of flavour
Full text linkAbstractWe investigate the generation of the baryon asymmetry of the Universe within a SUSY SU(5)×T′ model of flavour, which gives rise to realistic masses and mixing patterns for quarks and leptons. The model employs the see-saw mechanism for generation of the light neutrino masses and the baryon asymmetry is produced via leptogenesis. We perform detailed calculations of both the CP violating lepton asymmetries, originating from the decays of the heavy Majorana neutrinos operative in the see-saw mechanism, and of the efficiency factors which account for the lepton asymmetry wash-out processes in the Early Universe. The latter are calculated by solving numerically the system of Boltzmann equations describing the generation and the evolution of the lepton asymmetries. The baryon asymmetry in the model considered is proportional to the JCP factor, which determines the magnitude of CP violation effects in the oscillations of flavour neutrinos. The leptogenesis scale can be sufficiently low, allowing to avoid the potential gravitino problem
Papillary thyroid microcarcinoma: Toward an active surveillance strategy
No full textIn the last decades, the incidence of thyroid cancer (TC) has m ore than doubled, but the disease-specific mortality rate was stable. To date, 30-40% of all TC is represented by papilla ry microcarcinomas (mPTC), an indolent tumor, that probably remained undiagnosed before routine ultrasound use. In 1993, Miyauchi was the first who hypothesized a conservative approach for low-risk mPTC and introduced the co ncept of active surveillance (AS) in its clinical management. The progression rate of mPTC during AS was low and delaying surgery did not impact the efficacy of treatment or outcome. Since then, several authors from all over the world have reported their experience of AS in mPTCs. As suggested by current guidelines, AS can be considered as an alternative to immediate surgery to avoid overtreatment in low-risk mPTC and may be the strategy to avoid complications from unnecessary surgery. In the last years, AS inclusion criteria have been extended to both bigger tumors and to younger/healthier patients. The adoption of AS should take into consideration not only tumor characteris tics but also patient psychological profiles and medical team expertise. Its safety and efficacy have been demonstrated in long-term outcome studies and in other types of tumors; however, skepticism in patients, families and physician s should be overcome by strong recommendations coming from scientific guidelines. This review analyses the seve ral and different experiences of AS and the potential obstacles in implementing it as a routine approach in mPTC pati ents
Radioiodine post-surgical remnant ablation in patients with differentiated thyroid cancer: news from the last 10 years.
No full textDue to the growing incidence of differentiated thyroid carcinoma (DTC) and in particular of small papillary thyroid cancer observed in the last few decades, the indications, the activity of radioiodine (131I) to be administered, and the efficacy of post surgical thyroid 131I remnant ablation (RRA) have been widely discussed. In the last 10 years, the use of recombinant human TSH (rhTSH) or thyroid hormone withdrawal (THW) to stimulate the 131I remnant uptake has also interested many authors. The general agreement is that small (≤1 cm) intrathyroidal unifocal DTC with a favorable histology and no node metastases should not be submitted to RRA because of the low risk of relapse and cancer specific mortality. Conversely, RRA is indicated in patients with a higher risk level since it seems to reduce recurrence rates and mortality. The recent demonstration that the RRA preparation with rhTSH is as effective as THW using either high (100 mCi) or low (30 mCi) 131I activities suggests that rhTSH preparation and low activity of 131I should be considered as the standard of care for both low- and intermediate-risk DTC patients in the near future. Moreover, the use of low 131I activities and rhTSH reduces whole body radiation exposure and improves the quality of life which are very important advantages for DTC patients
Majorana phases and leptogenesis in see-saw models with A(4) symmetry
Full text linkThe related issues of Majorana CP violation in the lepton sector and leptogenesis are investigated in detail in two rather generic supersymmetric models with type I see-saw mechanism of neutrino mass generation and A(4) flavour symmetry, which naturally lead at leading order to tri-bimaximal neutrino mixing. The neutrino sector in this class of models is described at leading order by just two real parameters and one phase. This leads, in particular, to significant low energy constraints on the Majorana phases alpha(21) and alpha(31) in the PMNS matrix, which play the role of leptogenesis CP violating parameters in the generation of the baryon asymmetry of the Universe. We find that it is possible to generate the correct size and sign of the baryon asymmetry in both A(4) models. The sign of the baryon asymmetry is directly related to the signs of sin alpha(21) and/or sin alpha(31)
Decorso del carcinoma papillare della tiroide nei bambini dopo chernobyl trattati con tiroidectomia , radioiodio e terapia soppressiva
No full textRadiative corrections to light neutrino masses in low scale type I seesaw scenarios and neutrinoless double beta decay
Full text linkWe perform a detailed analysis of the one-loop corrections to the light neutrino mass matrix within low scale type I seesaw extensions of the Standard Model and their implications in experimental searches for neutrinoless double beta decay. We show that a sizable contribution to the effective Majorana neutrino mass from the exchange of heavy Majorana neutrinos is always possible, provided one requires a fine-tuned cancellation between the tree-level and one-loop contribution to the light neutrino masses. We quantify the level of fine-tuning as a function of the seesaw parameters and introduce a generalisation of the Casas-Ibarra parametrization of the neutrino Yukawa matrix, which easily allows to include the one-loop corrections to the light neutrino masses. © 2015, The Author(s)
Low energy signatures of the TeV scale seesaw mechanism
No full textWe study a type I see-saw scenario
where the right-handed (RH) neutrinos, responsible
for the light neutrino mass generation, lie
at the electroweak scale. Under certain conditions, the strength of
the charged (CC) and neutral current (NC) weak
interactions of the Standard Model particles with the
heavy RH neutrinos can be large enough
to allow the production of the latter at the LHC,
opening also the possibility of
observing other low energy signatures of the new physics in the electroweak
precision observables as well as in searches for rare leptonic decays
or neutrinoless double beta decay.
In this scenario the flavour structure of the
indicated CC and NC couplings of the heavy RH neutrinos
is essentially determined by the low energy
neutrino parameters,
leading to fairly strong correlations among the
new phenomena.
In particular, we show that the present
bound on the decay rate
makes very difficult the observation of the
heavy RH neutrinos at the LHC or the observation of deviations
from the Standard Model predictions in the electroweak precision data.
We also show that all present experimental
constraints on this scenario
still allow i) for an enhancement of the rate of
neutrinoless double beta decay,
which thus can be in the
range of sensitivity
of the GERDA experiment even when
the light Majorana neutrinos possess
a normal hierarchical mass spectrum,
and ii) for the predicted
decay rate
to be within the sensitivity range of the
MEG experiment
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