3,321 research outputs found
Leptogenesis in the two right-handed neutrino model revisited
We revisit leptogenesis in the minimal non-supersymmetric type I see-saw
mechanism with two right-handed (RH) neutrinos, including flavour effects and
allowing both RH neutrinos N_1 and N_2 to contribute, rather than just the
lightest RH neutrino N_1 that has hitherto been considered. By performing scans
over parameter space in terms of the single complex angle z of the orthogonal
matrix R, for a range of PMNS parameters, we find that in regions around z \sim
\pm \pi/2, for the case of a normal mass hierarchy, the N_2 contribution can
dominate the contribution to leptogenesis, allowing the lightest RH neutrino
mass to be decreased by about an order of magnitude in these regions, down to
M_1 \sim 1.3*10^11 GeV for vanishing initial N_2-abundance, with the numerical
results supported by analytic estimates. We show that the regions around z \sim
\pm \pi /2 correspond to light sequential dominance, so the new results in this
paper may be relevant to unified model building.Comment: 41 pages, 10 figures; v2 matches published version in PR
A fuller flavour treatment of N_2-dominated leptogenesis
We discuss N_2-dominated leptogenesis in the presence of flavour dependent effects that have hitherto been neglected, in particular the off-diagonal entries of the flavour coupling matrix that connects the total flavour asymmetries, distributed in different particle species, to the lepton and Higgs doublet asymmetries. We derive analytical formulae for the final asymmetry including the flavour coupling at the N_2-decay stage as well as at the stage of washout by the lightest right-handed neutrino N_1. We point out that in general part of the electron and muon asymmetries can completely escape the wash-out at the production and a total B-L asymmetry can be generated by the lightest RH neutrino wash-out yielding so called phantom leptogenesis. Taking of all these new effects into account can enhance the final asymmetry produced by the decays of the next-to-lightest RH neutrinos by orders of magnitude, opening up new interesting possibilities for N_2-dominated thermal eptogenesis. We illustrate these effects for two models which describe realistic neutrino masses and mixing based on sequential dominance
Active-sterile neutrino oscillations in the early Universe: asymmetry generation at low |delta m^2| and the Landau-Zener approximation
It is well established that active-sterile neutrino oscillations generate
large neutrino asymmetries for very small mixing angles (), negative values of and provided that
. By numerically solving the quantum
kinetic equations, we show that the generation still occurs at much lower
values of . We also describe the borders of the generation at
small mixing angles and show how our numerical results can be analytically
understood within the framework of the Landau-Zener approximation thereby
extending previous work based on the adiabatic limit. This approximate approach
leads to a fair description of the MSW dominated regime of the neutrino
asymmetry evolution and is also able to correctly reproduce its final value. We
also briefly discuss the impact that neutrino asymmetry generation could have
on big bang nucleosynthesis, CMBR and relic neutrinos.Comment: 29 pages, 8 figures; to appear on Phys. ReV. D; figure 7 added, new
curves in figure 5a, new figure
Focus on the origin of matter
The origin of matter in the Universe is a fascinating cosmological puzzle that has triggered a formidable intellectual enterprise, started in 1967 with the prescient paper by Andrej Sakharov (1967 Pisma Zh. Eksp. Teor. Fiz. 5 32; 1967 JETP Lett. 52 4; 1991 Sov. Phys.—Usp. 34 392; 1991 Usp. Fiz. Nauk 161 61) aimed at relating a cosmological observation to the fundamental laws of physics, the goal of baryogenesis. A successful model of baryogenesis should ultimately identify the required source of charge parity violation and the origin of the cosmological matter–antimatter asymmetry. This focus issue is not only a review of the main ideas that have been proposed in baryogenesis but should also bear witness to the great vitality of the field and to show how future experimental results could bring a breakthrough in baryogenesis during the coming years. For this reason we selected, out of the multitude of proposed baryogenesis models, those that will more likely experience a significant experimental test during the coming years
Effective Universal Unrestricted Adversarial Attacks using a MOE Approach
Recent studies have shown that Deep Leaning models are susceptible to
adversarial examples, which are data, in general images, intentionally modified
to fool a machine learning classifier. In this paper, we present a
multi-objective nested evolutionary algorithm to generate universal
unrestricted adversarial examples in a black-box scenario. The unrestricted
attacks are performed through the application of well-known image filters that
are available in several image processing libraries, modern cameras, and mobile
applications. The multi-objective optimization takes into account not only the
attack success rate but also the detection rate. Experimental results showed
that this approach is able to create a sequence of filters capable of
generating very effective and undetectable attacks
Leptogenesis beyond the limit of hierarchical heavy neutrino masses
We calculate the baryon asymmetry of the Universe in thermal leptogenesis
beyond the usual lightest right-handed (RH) neutrino dominated scenario (N_1DS)
and in particular beyond the hierarchical limit (HL), M_1 << M_2 << M_3, for
the RH neutrino mass spectrum. After providing some orientation among the large
variety of models, we first revisit the central role of the N_1DS, with new
insights on the dynamics of the asymmetry generation and then discuss the main
routes departing from it, focusing on models beyond the HL. We study in detail
two examples of `strong-strong' wash-out scenarios: one with `maximal phase'
and the limit of very large M_3, studying the effects arising when
delta_2=(M_2-M_1)/M_1 is small. We extend analytical methods already applied to
the N_1DS showing, for example, that, in the degenerate limit (DL), the
efficiency factors of the RH neutrinos become equal with the single decay
parameter replaced by the sum. Both cases disprove the misconception that close
RH neutrino masses necessarily lead to a final asymmetry enhancement and to a
relaxation of the lower bounds on M_1 and on the initial temperature of the
radiation-dominated expansion. We also explain why leptogenesis tends to favor
normal hierarchy compared to inverted hierarchy for the left-handed neutrino
masses.Comment: 30 pages, 8 figures; corrected typo in Eq. (67); shortened
Introduction, Section 3 and Conclusions; one figure removed; added 2
references; to appear in JCA
Spatially Resolved Chiroptical Spectroscopies Emphasizing Recent Applications to Thin Films of Chiral Organic Dyes
Instrumental techniques able to identify and structurally characterize the aggregation states in thin films of chiral organic π-conjugated materials, from the first-order supramolecular arrangement up to the microscopic and meso-scopic scale, are very helpful for clarifying structure-property relationships. Chiroptical imaging is currently gaining a central role, for its ability of mapping local supramolecular structures in thin films. The present review gives an overview of electronic circular dichroism imaging (ECDi), circularly polarized luminescence imaging (CPLi), and vibrational circular dichroism imaging (VCDi), with a focus on their applications on thin films of chiral organic dyes as case studies
Development of the Decannulation Prediction Tool in Patients With Dysphagia After Acquired Brain Injury
Chiral Oligothiophenes with Remarkable Circularly Polarized Luminescence and Electroluminescence in Thin Films
We report circular polarized electroluminescence (CPEL) in thin films of self-organized oligothiophenes. Four new 1,4-phenylene and 9H-carbazole-based oligothiophenes were ad hoc designed to ensure efficient spontaneous formation of chiral supramolecular order. They were easily synthetized and their chiroptical properties in thin films were measured. Circularly polarized luminescence (CPL) spectra revealed glum in the order of 10-2 on a wide wavelengths range, originating from their self-organized chiral supramolecular organization. These molecules have reasonable properties as organic semiconductors and for this reason they can constitute the active layer of circularlypolarized organic light-emitting diodes (CP-OLEDs). Thus, we could investigate directly their electroluminescence (EL) and CPEL, without resorting to blends, but rather in a simple multilayer device with basic architecture. This is the first example of a CP-OLED with active layer made only of a small organic compound
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