1,721,097 research outputs found
Testability of leptogenesis with three RH-neutrinos below the electroweak scale
No full textThe Standard Model extended with right-handed neutrinos whose masses are below the electroweak scale provides a simultaneous solution for the origin of neutrino masses and of the baryon asymmetry of the Universe, that can be tested in current experiments. If three right-handed neutrinos participate to the processes, their parameter space of solutions extends to very large mixing angles, saturating the current experimental constraints. Solutions with right-handed neutrino masses at the GeV scale can be probed in the decay of mesons at the LHC. For this channel the collision of isotopes of intermediate mass such as Ar provides a better sensitivity per unit of running time compared to collisions with protons
Leptogenesis in natural low-scale seesaw mechanisms
No full textWe explore the hypothesis of having an approximate lepton number conservation as a way to achieve a successful leptogenesis in low-scale seesaw mechanisms. The smallness of the active neutrino masses, as well as a strong degeneracy in the mass spectrum of the heavy sterile states, are both consequence of the assumed approximate symmetry. We propose a minimal extension of the Standard Model in order to implement the idea, and perform an analytical and numerical study to determine the viable solutions in the model and the testability of this leptogenesis scenario in future experiments
Looking for the minimal inverse seesaw realisation
No full textAbstractIn this work we consider a simple extension of the Standard Model involving additional fermionic singlets and assume an underlying inverse seesaw mechanism (with one or more right-handed neutrinos and one or more sterile fermions) for neutrino mass generation. Under the assumption that both sterile states and right-handed neutrinos are present, our goal is to determine which is the minimal inverse seesaw realisation that accounts for neutrino data while at the same time complying with all experimental requirements (electroweak precision tests and laboratory constraints). This study aims at identifying the minimal inverse seesaw realisation for the 3-flavour and for the 3 + more-mixing schemes, the latter giving an explanation for the reactor anomalies and/or providing a possible candidate for the dark matter of the Universe. Based on a perturbative approach, our generic study shows that in the class of inverse seesaw models giving rise to a 3-flavour flavour mixing scheme, only two mass scales are relevant (the light neutrino mass scale, mν and the mass of the right-handed neutrinos, MR) while in the case of a 3+1-mixing scheme, an additional mass scale (μ∈[mν,MR]) is required. For each of the two obtained inverse seesaw frameworks, we conduct a thorough numerical analysis, providing predictions for the hierarchy of the light neutrino spectrum and for the effective mass in neutrinoless double beta decay
Freeze-In Dark Matter within the Seesaw mechanism
Full text linkWe show that the minimal Type-I Seesaw mechanism can successfully account for
the observed dark matter abundance in the form of a keV sterile neutrino. This
population can be produced by the decay of the heavier neutral leptons, with
masses above the Higgs mass scale, while they are in thermal equilibrium in the
early Universe (freeze-in). Moreover, the implementation of the relevant
phenomenological constraints (relic abundance, indirect detection and structure
formation) on this model automatically selects a region of the parameter space
featuring an approximate lepton number symmetry.Comment: 8 pages, 2 figures. v3: matches the version accepted for publication
on Physics Letters
Leptogenesis from Lighter-than-Pion Neutrinos
No full textWe address the Type-I Seesaw mechanism with three right-handed neutrinos and Majorana masses below the pion mass: we identify three distinct potentially viable regions in the parameter space, characterised by the value of the sterile neutrino lifetime, and show that the impact of the sterile neutrino decay products on the abundance of light elements via photodisintegration (together with complementary existing bounds) effectively rules out solutions where the decays take place between BBN and the CMB decoupling. Remarkably, solutions in which all the three heavy neutrinos decay before BBN can generally account for the observed baryon asymmetry of the Universe via freeze-in leptogenesis, without further requirements other than complying with laboratory and cosmological constraints. We conclude that leptogenesis can be tested in pion decay experiments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lepton number violation as a key to low-scale leptogenesis
No full textWe explore the possibility of having a successful leptogenesis through oscillations between new sterile fermion states added to the Standard Model field content in a well motivated framework, naturally giving rise to the required mass splitting between the sterile states through a small total lepton number violation. We propose a framework with only two sterile states forming a pseudo-Dirac state, in which their mass difference as well as the smallness of the neutrino masses are due to two sources of lepton number violation with Δ L=2, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term. We also explore the pure Inverse Seesaw mechanism in its minimal version, requiring at least four new sterile states in order to comply with neutrino data. Our analytical and numerical studies reveal that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between the two sterile states with a ''natural'' origin of the strong degeneracy in their mass spectrum. We also revisit the analytical expression of the baryon asymmetry of the Universe in the weak washout regime of this framework
Neutrino masses, leptogenesis and dark matter from small lepton number violation?
No full textWe consider the possibility of simultaneously addressing the baryon asymmetry of the Universe, the dark matter problem and the neutrino mass generation in minimal extensions of the Standard Model via sterile fermions with (small) total lepton number violation. Within the framework of Inverse and Linear Seesaw models, the small lepton number violating parameters set the mass scale of the active neutrinos, the efficiency of leptogenesis through a small mass splitting between pairs of sterile fermions as well as the mass scale of a sterile neutrino dark matter candidate. We provide an improved parametrization of these seesaw models taking into account existing experimental constraints and derive a linearized system of Boltzmann equations to describe the leptogenesis process, which allows for an efficient investigation of the parameter space. This in particular enables us to perform a systematic study of the strong washout regime of leptogenesis. Our study reveals that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between two sterile states with a natural origin of the (necessary) strong degeneracy in their mass spectrum. The minimal model however requires a non-standard cosmological history to account for the relic dark matter. Finally, we discuss the prospect for neutrinoless double beta decay and for testing, in future experiments, the values of mass and different active-sterile mixings required for successful leptogenesis
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