We discuss the possibility of relating the size and sign of the observed baryon asymmetry of the universe to CP violation observable at low energies, in a framework where the observed baryon asymmetry is produced by leptogenesis through the out of the equilibrium decay of heavy Majorana neutrinos. We identify the CP violating phases entering in leptogenesis as well as those relevant for CP violation at low energies in the minimal seesaw model. We show that although in general there is no relation between these two sets of phases, there are specific frameworks in which such a connection may be established and we give a specific grand unification inspired example where such a connection does exist. We construct weak-basis invariants related to CP violation responsible for leptogenesis, as well as those relevant for CP violation at low energies. * gbranco@thwgs.cern.ch and

Top flavour-changing neutral decays are extremely suppressed within the Standard Model (SM) by the GIM mechanism, but can reach observable rates in some of its extensions. We compute the branching ratios for t → cγ and t → cg in minimal SM extensions where the addition of a vector-like up or down quark singlet breaks the unitarity of the 3 × 3 Cabibbo-Kobayashi-Maskawa (CKM) matrix. The maximum rates obtained indicate to what extent present experimental data allow 3 × 3 CKM unitarity to be broken in these models, and are too small to be observed in the near future. As a by-product, we reproduce the calculation of these branching ratios in the SM, and with an improved set of parameters we obtain values one order of magnitude smaller than the ones usually quoted in the literature. We study the CP asymmetries between the decay rates of the top quark and antiquark, which can be much larger than in the SM, also as a consequence of the partial breaking of 3 × 3 CKM unitarity.

We investigate the scenario of resonant thermal leptogenesis, in which the leptonic asymmetries are generated through renormalization group corrections induced at the leptogenesis scale. In the framework of the standard model extended by three right-handed heavy Majorana neutrinos with masses M 1 = M 2 ≪ M 3 at some high scale, we show that the mass splitting and CP -violating effects induced by renormalization group corrections can lead to values of the CP asymmetries large enough for a successful leptogenesis. In this scenario, the low-energy neutrino oscillation data can also be easily accommodated. The possibility of having an underlying symmetry behind the degeneracy in the right-handed neutrino mass spectrum is also discussed.

We study the possibility that the baryon asymmetry of the universe is generated in a minimal seesaw scenario where two right-handed Majorana neutrinos with degenerate masses are added to the standard model particle content. In the usual framework of thermal leptogenesis, a nonzero CP asymmetry can be obtained through the mass splitting induced by the running of the heavy Majorana neutrino masses from their degeneracy scale down to the seesaw scale. Although, in the light of the present neutrino oscillation data, the produced baryon asymmetry turns out to be smaller than the experimental value, the present mechanism could be viable in simple extensions of the standard model.

Isosinglet fermions naturally arise in a variety of extensions of the Standard Model, in particular in models with extra dimensions. In this paper, we study the effect of the addition of a new isosinglet charged lepton to the standard spectrum, with special emphasis on implications for neutrino asymmetries to be measured at future neutrino factories. Lepton flavour violation in neutral current and lepton universality constraints are extensively discussed. We show that new physics effects in ν e − ν µ CP asymmetries are significantly enhanced due to leptonic maximal mixings but still too small to give a signature at future neutrino factories. A signal for CP asymmetries in ν µ − ν τ channel due to new physics could be observed at 1 − 3 σ if lepton flavour violating τ decays are seen in a very close future in B-factories like BELLE experiment.

O artigo descreve a trajetória científica do físico e padre jesuíta Francisco Xavier Roser, fundador do Departamento de Física da Pontifícia Universidade Católica do Rio de Janeiro, e um dos pioneiros do estudo da radioatividade natural no Brasil. Além de uma nota biográfica, o artigo apresenta e discute os principais aspetos e relevância da atividade científica do Pe. Roser.

We discuss how CP violation generating lepton number asymmetry can be related to CP violation in low energy.Comment: A poster Talk presented at KEKTC5, submitted to the proceeding

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