296 research outputs found
A consistent model for leptogenesis, dark matter and the IceCube signal
We discuss a left-right symmetric extension of the Standard Model in which
the three additional right-handed neutrinos play a central role in explaining
the baryon asymmetry of the Universe, the dark matter abundance and the ultra
energetic signal detected by the IceCube experiment. The energy spectrum and
neutrino flux measured by IceCube are ascribed to the decays of the lightest
right-handed neutrino , thus fixing its mass and lifetime, while the
production of in the primordial thermal bath occurs via a freeze-in
mechanism driven by the additional interactions. The constraints
imposed by IceCube and the dark matter abundance allow nonetheless the heavier
right-handed neutrinos to realize a standard type-I seesaw leptogenesis, with
the asymmetry dominantly produced by the next-to-lightest neutrino .
Further consequences and predictions of the model are that: the
production implies a specific power-law relation between the reheating
temperature of the Universe and the vacuum expectation value of the
triplet; leptogenesis imposes a lower bound on the reheating temperature of the
Universe at 7\times10^9\,\mbox{GeV}. Additionally, the model requires a
vanishing absolute neutrino mass scale .Comment: 19 pages, 4 figures. Constraints from cosmic-ray antiprotons and
gamma rays added, with hadrophobic assignment of the matter multiplets to
satisfy bounds. References added. Matches version published in JHE
Strong thermal leptogenesis and the N2-dominated scenario
We briefly review the main aspects of leptogenesis, pointing out the main reasons that draw attention to the so-called N2-dominated scenario. We consider the conditions that stem out when the final asymmetry is required to be fully independent of the initial conditions. We show that in this scenario, called strong thermal leptogenesis, when barring special cancellations in the seesaw formula and in the flavoured decay parameters, a lightest neutrino mass m1 ≳ 10 meV for normal ordering and m1 ≳ 3 meV for inverted ordering are favoured. We then focus on the S O(10)-inspired leptogenesis models that naturally realise N2-dominated leptogenesis. We show how the combination with the strong thermal leptogenesis conditions yields important predictions on neutrino parameters. Finally, we briefly comment on the power of forthcoming neutrino experiments to either support or severely corner these leptogenesis scenarios
The radial metallicity gradients in the Milky Way thick disk as fossil signatures of a primordial chemical distribution
In this letter we examine the evolution of the radial metallicity gradient
induced by secular processes, in the disk of an -body Milky Way-like galaxy.
We assign a [Fe/H] value to each particle of the simulation according to an
initial, cosmologically motivated, radial chemical distribution and let the
disk dynamically evolve for 6 Gyr. This direct approach allows us to take into
account only the effects of dynamical evolution and to gauge how and to what
extent they affect the initial chemical conditions. The initial [Fe/H]
distribution increases with R in the inner disk up to R ~ 10 kpc and decreases
for larger R. We find that the initial chemical profile does not undergo major
transformations after 6 Gyr of dynamical evolution. The final radial chemical
gradients predicted by the model in the solar neighborhood are positive and of
the same order of those recently observed in the Milky Way thick disk.
We conclude that: 1) the spatial chemical imprint at the time of disk
formation is not washed out by secular dynamical processes, and 2) the observed
radial gradient may be the dynamical relic of a thick disk originated from a
stellar population showing a positive chemical radial gradient in the inner
regions.Comment: 10 pages, 5 figures, Accepted for publication on Astrophysical
Journal Letter
Point Defects in Two-Dimensional Indium Selenide as Tunable Single-Photon Sources
In the past few years remarkable interest has been kindled by the development of nonclassical light sources and, in particular, of single-photon emitters (SPE), which represent fundamental building blocks for optical quantum technology. In this Letter, we analyze the stability and electronic properties of an InSe monolayer with point defects with the aim of demonstrating its applicability as an SPE. The presence of deep defect states within the InSe band gap is verified when considering substitutional defects with atoms belonging to group IV, V, and VI. In particular, the optical properties of Ge as substitution impurity of Se predicted by solving the Bethe-Salpeter equation on top of the GW corrected electronic states show that transitions between the valence band maximum and the defect state are responsible for the absorption and spontaneous emission processes, so that the latter results in a strongly peaked spectrum in the near-infrared. These properties, together with a high localization of the involved electronic states, appear encouraging in the quest for novel SPE materials
First-Principles Calculations of Exciton Radiative Lifetimes in Monolayer Graphitic Carbon Nitride Nanosheets: Implications for Photocatalysis
In this work, we report on the exciton radiative lifetimes of graphitic carbon nitride monolayers in the triazine-based (gC3N4-t) and heptazine-based (gC3N4-h) forms, as obtained by means of ground-state plus excited-state ab initio calculations. By analyzing the exciton fine structure, we highlight the presence of dark states and show that the photogenerated electron-hole (e-h) pairs in gC3N4-h are remarkably long-lived, with an effective radiative lifetime of 260 ns. This fosters the employment of gC3N4-h in photocatalysis and makes it attractive for the emerging field of exciton devices. Although very long intrinsic radiative lifetimes are an important prerequisite for several applications, pristine carbon nitride nanosheets show very low quantum photoconversion efficiency, mainly due to the lack of an efficient e-h separation mechanism. We then focus on a vertical heterostructure made of gC3N4-t and gC3N4-h layers, which shows a type-II band alignment and looks promising for achieving net charge separation
Active Surface Structure of SnO2 Catalysts for CO2 Reduction Revealed by Ab Initio Simulations
Tin oxide (SnO2) is an efficient catalyst for the CO2 reduction reaction (CO2RR) to formic acid; however, the understanding of the SnO2 surface structure under working electrocatalytic conditions and the nature of catalytically active sites is a current matter of debate. Here, we employ ab initio density functional theory calculations to investigate how the selectivity and reactivity of SnO2 surfaces toward the CO2RR change at varying surface stoichiometry (i.e., reduction degree). Our results show that SnO2(110) surfaces are not catalytically active for the CO2RR or hydrogen evolution reaction, but rather they reduce under an applied external bias, originating surface structures exposing few metal tin layers, which are responsible for formic acid selectivity
Sistemas de manejo de solo e de rotação de culturas: implicações na emissão de óxido nitroso do solo.
Orientador: Henrique Pereira dos Santos
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