Search

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 M1 = M2 << M3 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., Comment: 20 pages, 2 figures, final version to appear in Phys. Lett. B

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., Comment: 6 pages, 2 figures, uses RevTeX4, calculations improved, comments added

The possibility of achieving a gauge coupling grand unification by increasing the QCD degrees of freedom at higher energies is investigated. When confronted with precision low-energy data, the generic weak-mixing angle relation sin^2(theta_W) = N/2(N+1) requires N=7 colors at the GUT scale M_U ~ 10^17 GeV. With the exclusive addition of light Higgs doublets to the standard model particle content, such a unification may also occur if N=5 at M_U ~ 10^16 GeV., Comment: 4 pages, 2 figures

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 -> c gamma and t -> c g in minimal SM extensions where the addition of a vector-like up or down quark singlet breaks the unitarity of the 3 x 3 Cabibbo-Kobayashi-Maskawa (CKM) matrix. The maximum rates obtained indicate to what extent present experimental data allow 3 x 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 x 3 CKM unitarity., Comment: LaTeX, 15 pages, 12 PS figures, minor changes. To be published in PLB

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 out of equilibrium decay of heavy Majorana neutrinos. We have shown that although in general such a connection cannot be established, there are specific frameworks where a link does exist. Furthermore, we identify the CP violating phases relevant to leptogenesis and those relevant for low energy CP violation and build weak basis invariant conditions for CP conservation., Comment: Talk given at the RTN meeting : ``Across the Present Energy Frontier : Probing the Origin of Mass'', Corfu, Greece, 10 September- 13 September 2001

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 proceedings

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., Comment: 18 pages, no figures