Abstract:
Thermal leptogenesis, in the seesaw model, is a popular mechanism for generating the Baryon Asymmetry of the Universe. It was noticed recently, that including lepton flavour can modify significantly the results. These proceedings aim to discuss why and when flavour matters, in the thermal leptogenesis scenario for hierarchical right-handed neutrinos. No Boltzmann Equations are introduced.

Abstract:
The discovery of neutrino masses makes leptogenesis a very attractive scenario for explaining the puzzle of the baryon asymmetry of the Universe. We present the basic ingredients of leptogenesis, explain the predictive power of this scenario (and its limitations), and describe recent theoretical developments.

Abstract:
In this talk, we studied the implication of the constraint on the reheating temperature coming from the gravitino problem on models of leptogenesis. We point out that in supersymmetric extensions of the standard model, all existing models of neutrino masses and leptogenesis, except the one with right-handed singlet neutrinos are ruled out for a large range of the gravitino mass.

Abstract:
Leptogenesis is a class of scenarios in which the cosmic baryon asymmetry originates from an initial lepton asymmetry generated in the decays of heavy sterile neutrinos in the early Universe. We explain why leptogenesis is an appealing mechanism for baryogenesis. We review its motivations, the basic ingredients, and describe subclasses of effects, like those of lepton flavours, spectator processes, scatterings, finite temperature corrections, the role of the heavier sterile neutrinos and quantum corrections. We then address leptogenesis in supersymmetric scenarios, as well as some other popular variations of the basic leptogenesis framework.

Abstract:
It has been recently shown that the quantum Boltzmann equations may be relevant for the leptogenesis scenario. In particular, they lead to a time-dependent CP asymmetry which depends upon the previous dynamics of the system. This memory effect in the CP asymmetry is particularly important in resonant leptogenesis where the asymmetry is generated by the decays of nearly mass-degenerate right-handed neutrinos. We study the impact of the nontrivial time evolution of the CP asymmetry in resonant leptogenesis, both in the one-flavour case and with flavour effects included. We show that significant qualitative and quantitative differences arise with respect to the case in which the time dependence of the CP asymmetry is neglected.

Abstract:
We study variations of the standard leptogenesis scenario that can arise if an additional mass scale related to the breaking of some new symmetry (as for example a flavor or the B-L symmetry) is present below the mass $M_{N_1}$ of the lightest right-handed Majorana neutrino. Our scheme is inspired by U(1) models of flavor \`a la Froggatt-Nielsen, and involves new vectorlike heavy fields $F$. We show that depending on the specific hierarchy between $M_{N_1}$ and the mass scale of the fields $F$, qualitatively different realizations of leptogenesis can emerge. We compute the CP asymmetries in $N_1$ decays in all the relevant cases, and we conclude that in most situations leptogenesis could be viable at scales much lower than in the standard scenario.

Abstract:
The possibility to explain the CMB measurement of the baryon asymmetry with leptogenesis results in a stringent bound on the neutrino masses such that [(m_1)^2+(m_2)^2+(m_3)^2]^(1/2) < 0.30 eV. We discuss the implications of such a bound for future experiments on the absolute neutrino mass scale.

Abstract:
We consider a class of leptogenesis models in which the lepton asymmetry arises from dark matter annihilation processes which violate CP and lepton number. Importantly, a necessary one-loop contribution to the annihilation matrix element arises from absorptive final state interactions. We elucidate the relationship between this one-loop contribution and the CP-violating phase. As we show, the branching fraction for dark matter annihilation to leptons may be small in these models, while still generating the necessary asymmetry.

Abstract:
After recalling the general virtues of leptogenesis we compare two realizations, Affleck-Dine leptogenesis and thermal leptogenesis, which generically lead to different predictions for neutrino masses. Finally, we describe the progress towards a full quantum mechanical description of the basic non-equilibrium process of leptogenesis beyond the approximations involved in Boltzmann's equations.

Abstract:
Leptogenesis is a class of scenarios in which the cosmic baryon asymmetry originates from an initial lepton asymmetry generated in the decays of heavy sterile neutrinos in the early Universe. We explain why leptogenesis is an appealing mechanism for baryogenesis. We review its motivations and the basic ingredients and describe subclasses of effects, like those of lepton flavours, spectator processes, scatterings, finite temperature corrections, the role of the heavier sterile neutrinos, and quantum corrections. We then address leptogenesis in supersymmetric scenarios, as well as some other popular variations of the basic leptogenesis framework. 1. The Baryon Asymmetry of the Universe 1.1. Observations Up to date no traces of cosmological antimatter have been observed. The presence of a small amount of antiprotons and positrons in cosmic rays can be consistently explained by their secondary origin in cosmic particles collisions or in highly energetic astrophysical processes, but no antinuclei, even as light as antideuterium or as tightly bounded as anti- particles, have ever been detected. The absence of annihilation radiation excludes significant matter-antimatter admixtures in objects up to the size of galactic clusters ~20？Mpc [1]. Observational limits on anomalous contributions to the cosmic diffuse -ray background and the absence of distortions in the cosmic microwave background (CMB) imply that little antimatter is to be found within ~1？Gpc and that within our horizon an equal amount of matter and antimatter can be excluded [2]. Of course, at larger superhorizon scales the vanishing of the average asymmetry cannot be ruled out, and this would indeed be the case if the fundamental Lagrangian is C and CP symmetric and charge invariance is broken spontaneously [3]. Quantitatively, the value of baryon asymmetry of the Universe is inferred from observations in two independent ways. The first way is by confronting the abundances of the light elements, , , , and , with the predictions of Big Bang nucleosynthesis (BBN) [4–9]. The crucial time for primordial nucleosynthesis is when the thermal bath temperature falls below ？MeV. With the assumption of only three light neutrinos, these predictions depend on a single parameter, that is, the difference between the number of baryons and antibaryons normalized to the number of photons: where the subscript means ”at present time.” By using only the abundance of deuterium, that is particularly sensitive to , [4] quotes: In this same range there is also an acceptable agreement among the various abundances, once