Flavor effects in thermal leptogenesis

We review recent developments in leptogenesis on flavor effects. Their account discloses an important connection between the matter-antimatter asymmetry of the Universe and CP violation at low energies. Besides, they modify the upper bound on the neutrino masses holding in the unflavored case. In this respect, it is important to identify the exact condition for flavor effects to be relevant and for the `fully flavored' Boltzmann equations to be valid.Comment: 3 pages, no figure ; contribution to the proceedings of NOW 2006, Conca Specchiulla, Sep. 9-16, 200

The minimal scenario of leptogenesis

We review the main features and results of thermal leptogenesis within the type I seesaw mechanism, the minimal extension of the Standard Model explaining neutrino masses and mixing. After presenting the simplest approach, the vanilla scenario, we discuss various important developments in recent years, such as the inclusion of lepton and heavy neutrino flavour effects, a description beyond a hierarchical heavy neutrino mass spectrum and an improved kinetic description within the density matrix and the closed-time-path formalisms. We also discuss how leptogenesis can ultimately represent an important phenomenological tool to test the seesaw mechanism and the underlying model of new physics.Comment: 37 pages, 4 figures; invited review chapter for the "Focus on the Origin of Matter" issue published in the New Journal of Physic

Reconciling leptogenesis with observable mu --> e gamma rates

We perform a detailed analysis of thermal leptogenesis in the framework of seesaw models which approximately conserve lepton number. These models are known to allow for large Yukawa couplings and a low seesaw scale in agreement with neutrino mass constraints, and hence to lead to large lepton flavour violating rates that can be probed experimentally. Although large Yukawa couplings lead to (inverse) decay rates much larger than the Hubble expansion rate, we show that the leptogenesis washout induced is generically small if the mass splitting between the right-handed neutrinos is small enough. As a result, large lepton flavour violating rates are compatible with successful leptogenesis. We emphasize that this scenario does not require any particular flavour structure. A small splitting is natural and radiatively stable in this context because it is protected by the lepton number symmetry.Comment: One section added, a few equations and sentences rewritten, references added, results unchange

On the Role of Low-Energy CP Violation in Leptogenesis

The link between low-energy CP violation and leptogenesis became more accessible with the understanding of flavor effects. However, a definite well-motivated model where such a link occurs was still lacking. Adjoint SU(5) is a simple grand unified theory where neutrino masses are generated through the Type I and Type III seesaw mechanisms, and the lepton asymmetry is generated by the fermionic triplet responsible for the Type III seesaw. We focus exclusively on the case of inverted hierarchy for neutrinos, and we show that successful flavored leptogenesis in this theory strongly points towards low-energy CP violation. Moreover, since the range of allowed masses for the triplet is very restricted, we find that the discovery at the LHC of new states present in the theory, together with proton decay and unification of gauge couplings, can conspire to provide a hint in favor of leptogenesis.Comment: 12 pages, 6 figure

Diffuse gamma-ray constraints on dark matter revisited. I: the impact of subhalos

We make a detailed analysis of the indirect diffuse gamma-ray signals from dark matter annihilation in the Galaxy. We include the prompt emission, as well as the emission from inverse Compton scattering whenever the annihilation products contain light leptons. We consider both the contribution from the smooth dark matter halo and that from substructures. The main parameters for the latter are the mass function index and the minimal subhalo mass. We use recent results from N-body simulations to set the most reasonable range of parameters, and find that the signal can be boosted by a factor ranging from 2 to 15 towards the Galactic poles, slightly more towards the Galactic anticenter, with an important dependence on the subhalo mass index. This uncertainty is however much less than that of the extragalactic signal studied in the literature. We derive upper bounds on the dark matter annihilation cross section using the isotropic gamma-ray emission measured by Fermi-LAT, for two directions in the sky, the Galactic anticenter and the Galactic pole(s). The former represents the lowest irreducible signal from dark matter annihilation, and the latter is robust as the astrophysical background, dominated by the hadronic contribution, is rather well established in that direction. Finally, we show how the knowledge of the minimal subhalo mass, which formally depends on the dark matter particle interactions with normal matter, can be used to derive the mass function index.Comment: 32 pages. V2: changes to match the version accepted for publication in JCA

Leptogenesis with heavy neutrino flavours: from density matrix to Boltzmann equations

Leptogenesis with heavy neutrino flavours is discussed within a density matrix formalism. We write the density matrix equation, describing the generation of the matter-antimatter asymmetry, for an arbitrary choice of the right-handed (RH) neutrino masses. For hierarchical RH neutrino masses lying in the fully flavoured regimes, this reduces to multiple-stage Boltzmann equations. In this case we recover and extend results previously derived within a quantum state collapse description. We confirm the generic existence of phantom terms. However, taking into account the effect of gauge interactions, we show that they are washed out at the production with a wash-out rate that is halved compared to that one acting on the total asymmetry. In the N_1-dominated scenario they cancel without contributing to the final baryon asymmetry. In other scenarios they do not in general and they have to be taken into account. We also confirm that there is a (orthogonal) component in the asymmetry produced by the heavier RH neutrinos which completely escapes the washout from the lighter RH neutrinos and show that phantom terms additionally contribute to it. The other (parallel) component is washed out with the usual exponential factor, even for weak washout. Finally, as an illustration, we study the two RH neutrino model in the light of the above findings, showing that phantom terms can contribute to the final asymmetry also in this case.Comment: 39 pages, 5 figures; v2: added Appendix and discussion in 2.2 on lepton-antilepton flavour compositions difference (eq. (28) is a new result); footnotes 4 and 5; new effect of gauge interactions in inducing wash-out of phantom terms but with halved wash-out rate compared to the total asymmetry wash-out rate; matches JCAP versio

The Contribution of Blazars to the Extragalactic Diffuse Gamma-ray Background and Their Future Spatial Resolution

We examine the constraints on the luminosity-dependent density evolution model for the evolution of blazars given the observed spectrum of the diffuse gamma-ray background (DGRB), blazar source-count distribution, and the blazar spectral energy distribution sequence model, which relates the observed the blazar spectrum to its luminosity. We show that the DGRB observed by the Large Area Telescope (LAT) aboard the Fermi Gamma Ray Space Telescope can be produced entirely by gamma-ray emission from blazars and nonblazar active galactic nuclei, and that our blazar evolution model is consistent with and constrained by the spectrum of the DGRB and flux source-count distribution function of blazars observed by Fermi-LAT. Our results are consistent with previous work that used EGRET spectral data to forecast the Fermi-LAT DGRB. The model includes only three free parameters, and forecasts that >~ 95% of the flux from blazars will be resolved into point sources by Fermi-LAT with 5 years of observation, with a corresponding reduction of the flux in the DGRB by a factor of ~2 to 3 (95% confidence level), which has implications for the Fermi-LAT's sensitivity to dark matter annihilation photons.Comment: 13 pages, 7 figures; v3: minor changes, matches version to appear in Phys. Rev.