Tests of Leptogenesis at Low Energy

The problem of testing leptogenesis from low energy experiments is discussed following three different perspectives. Firstly, we review the prospects that from low energy experiments we could reconstruct the neutrino Yukawa coupling matrix and hence constrain the leptogenesis mechanism. We emphasize the fact that the experimental determination of the phases and mixings in the light neutrino mass matrix is irrelevant for leptogenesis, unless additional information about the texture of the Yukawa coupling matrix is provided by other observables. Secondly, we show how the discovery of an extra gauge boson could bring us important indications for leptogenesis. Thirdly, we discuss the problems one encounters when attempting to build a leptogenesis mechanism at a directly testable scale, presenting an explicit model which avoids these problems.Comment: To appear in the proceedings of 14th Rencontres de Blois: Matter - Anti-matter Asymmetry, Blois, France, 17-22 Jun 2002, 9 page

Leptogenesis from right-handed neutrino decays to right-handed leptons

We investigate what would be the consequences for leptogenesis of the existence of a charged SU(2)_L singlet scalar delta^+. If such a scalar particle exists, it allows the right-handed neutrinos to couple not only to left-handed lepton and Higgs doublets as in ordinary leptogenesis, but also to a right-handed charged lepton and a delta^+. This provides a new source of leptogenesis which can be successful in a non-resonant way at scales as low as TeV. The incorporation of this scenario in left-right symmetric and unified models is discussed.Comment: To appear in the proceedings of 41st Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 11-18 Mar 200

On the stability of particle dark matter

From the particle physics point of view, the most peculiar property of the dark matter particle is its stability on cosmological time scales. We briefly review the possible origins of this characteristic feature for candidates whose relic density results from the thermal freeze-out of their annihilation. We emphasize that each stabilization mechanism implies an all specific phenomenology. The models reviewed include supersymmetric and non-supersymmetric models where the stability is a consequence of grand-unification, models where stability is due to an unbroken gauge group and models where the DM stability is accidental. The latter possibility includes minimal dark matter, hidden vector dark matter and composite DM models.Comment: Talk presented at the "Identification of Dark Matter 2010" conference, July 26-30, Montpellier, Franc

Various realizations of leptogenesis and neutrino mass constraints

Seven types of leptogenesis models which can lead to a successful explanation of baryogenesis are presented. Emphasis is put on the conditions which need to be fulfilled by the neutrino masses as well as by the heavy state masses. The model dependence of these conditions is discussed.Comment: Talk given at International Conference on the Seesaw Mechanism, Paris, France, 10-11 June 2004, 18 page

Neutrino mass matrix solutions and neutrinoless double beta decay

We present a determination of the neutrino mass matrix which holds for values of the neutrinoless double beta decay effective mass m_{ee} larger than the neutrino mass differences. We find eight possible solutions and discuss for each one the corresponding neutrino mass eigenvalues and zero texture. A minimal structure of the perturbations to add to these zero textures to recover the full mass matrix is also determined. Implications for neutrino hot dark matter are discussed for each solution.Comment: 18 page

Predictions of Physical Observables from Minimal Neutrino Structures

We find all possible seesaw textures which can describe in a natural way the currently observed neutrino oscillation pattern in terms of a minimum number of parameters. Natural here means due only to the relative smallness (vanishing) of some parameters in the relevant lagrangian, without special relations or accidental cancellations among them. The corresponding predictions for the mixing angle theta_13 and the effective mass m_ee are given.Comment: 6 pages, 1 figure; to appear in the proceedings of the XXXVIIIth Rencontres de Moriond, "Electroweak Interactions and Unified Theories", Les Arcs, France, 15-22 March 200

Leptogenesis: beyond the minimal type I seesaw scenario

Numerous recent evidences for neutrino masses have established the leptogenesis mechanism as a very natural possible explanation for the baryon asymmetry of the Universe. The explicit realization of this mechanism depends on the neutrino mass model considered. If the right-handed type-I seesaw model of neutrino masses is certainly the most straightforward, it is not the only natural one, especially in the framework of explicit GUT realizations of the seesaw. In this review we discuss in detail the various seesaw scenarios that can implement the leptogenesis mechanism successfully, beyond the paradigm of the pure standard type-I seesaw model. This includes scenarios based on the existence of scalar triplets (type-II), of fermion triplets (type-III) as well as mixed seesaw frameworks.Comment: 42 pages, 13 figures, invited review chapter for the "Focus on the Origin of Matter" issue published in the New Journal of Physics (It is likely that non-seesaw leptogenesis scenarios will be also discussed in this review in a subsequent arXiv version

Baryogenesis from L-violating Higgs-doublet decay in the density-matrix formalism

We compute in the density-matrix formalism the baryon asymmetry generated by the decay of the Higgs doublet into a right-handed (RH) neutrino and a Standard Model lepton. The emphasis is put on the baryon asymmetry produced by the total lepton-number violating decay. From the derivation of the corresponding evolution equations, and from their integration, we find that this contribution is fully relevant for large parts of the parameter space. This confirms the results found recently in the CP-violating decay formalism with thermal corrections and shows in particular that the lepton-number violating processes are important not only for high-scale leptogenesis but also when the RH-neutrino masses are in the GeV range. For large values of the Yukawa couplings, we also find that the strong washout is generically much milder for this total lepton-number violating part than for the usual RH-neutrino oscillation flavour part.Comment: 12 pages, 10 figure

SM Higgs mass bounds from theory

The two-loop Higgs mass upper bounds are reanalyzed. Previous results for a cutoff scale $\Lambda\approx$ few TeV are found to be too stringent. For $\Lambda=10^{19}$ GeV we find $M_H < 180 \pm 4\pm 5$ GeV, the first error indicating the theoretical uncertainty, the second error reflecting the experimental uncertainty due to $m_t = 175 \pm 6$ GeV. We also summarize the lower bounds on $M_H$. We find that a SM Higgs mass in the range of 160 to 170 GeV will certainly allow for a perturbative and well-behaved SM up to the Planck-mass scale $\Lambda_{Pl}\simeq 10^{19}$ GeV, with no need for new physics to set in below this scale.Comment: 6 pages; to appear in the Proceedings of the ``ECFA/DESY Study on Physics and Detectors for the Linear Collider'', ed. R. Settle