2,955 research outputs found
Neutrino oscillations and Big Bang Nucleosynthesis
We outline how relic neutrino asymmetries may be generated in the early
universe via active-sterile neutrino oscillations. We discuss possible
consequences for big bang nucleosynthesis, within the context of a particular
4-neutrino model.Comment: 6 pages. Talk given at NuFACT'01 workshop, Tsukuba, Japan (May 2001
Dark Radiation or Warm Dark Matter from long lived particle decays in the light of Planck
Although Planck data supports the standard \Lambda CDM model, it still allows
for the presence of Dark Radiation corresponding up to about half an extra
standard neutrino species. We propose a scenario for obtaining a fractional
"effective neutrino species" from a thermally produced particle which decays
into a much lighter stable relic plus standard fermions. At lifetimes much
longer than 1 sec, both the relic particles and the non-thermal neutrino
component contribute to Dark Radiation. By increasing the stable-to-unstable
particle mass ratio, the relic particle no longer acts as Dark Radiation but
instead becomes a candidate for Warm Dark Matter with mass O(1keV - 100GeV). In
both cases it is possible to address the lithium problem.Comment: 18 pages, 2 figures; v3 matches version to be published in PL
Leptogenesis within a generalized quark-lepton symmetry
Quark-lepton symmetry has been shown to be inconsistent with baryogenesis via
leptogenesis in natural schemes of the see-saw mechanism. Within the
phenomenological approach of textures, we relax this strict symmetry and
propose weaker conditions, namely models of the neutrino Dirac mass matrix
which have the same hierarchy as the matrix elements of . We call
this guide-line generalized quark-lepton symmetry. We consider
in detail particular cases in which the moduli of the matrix elements of
are equal to those of . Within the phenomenological approach of textures,
we try for the heavy Majorana mass matrix diagonal and off-diagonal forms. We
find that an ansatz for preserving the hierarchy, together with an
off-diagonal model for the heavy Majorana neutrino mass, is consistent with
neutrino masses, neutrino mixing and baryogenesis via leptogenesis for an
intermediate mass scale GeV. The preservation of the
hierarchical structure could come from a possible symmetry scheme.Comment: 12 pages, RevTex4. Title and abstract changed. Revised and enlarged
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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
Quantifying the Overall Efficiency of Circularly Polarized Emitters
An increasing number of circularly polarized luminescence (CPL) molecular emitters has been developed in recent years and many of them are intended for applications in which high overall CPL efficiencies are required. In order to have a complete picture of the efficiency of a CPL emitter, dissymmetry factor (glum) is not enough. In the following we propose a new quantity, named CPL brightness (BCPL), which takes into account absorption extinction coefficient and quantum yield along with the glum factor. We calculated BCPL value for more than 180 compounds reported in the literature and we analyse data distribution for the main classes of CPL molecular emitters. This tool can be employed to put into context new CPL active compounds and to direct the choice of molecular systems for specific CPL applications
Circularly polarized light at the mirror: Caveats and opportunities
Moving from the simple concept that reflection onto a mirror surface changes the handedness of circularly polarized light, we describe what happens to the emergent polarization in two different cases after reflection on a back mirror. In the first case, a regular emitter is taken into account, where reflection has the effect to destroy the emergent polarization. In the second case, we show what could happen when a hypothetical apparently non-reciprocal emitting material undergoes a similar experiment. These simple concepts have important implications in the design of efficient circularly polarized emitting devices
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