98,151 research outputs found

    Dispelling the Anthropic Principle from the Dimensionality Arguments

    Get PDF
    It is shown that in d=11 supergravity, under a very reasonable ansatz, the nearly flat spacetime in which we are living must be 4-dimensional without appealing to the Anthropic Principle. Can we dispel the Anthropic Principle completely from cosmology?Comment: 7 pages, Essa

    Mass retention efficiencies of He accretion onto carbon-oxygen white dwarfs and type Ia supernovae

    Full text link
    Type Ia supernovae (SNe Ia) play a crucial role in studying cosmology and galactic chemical evolution. They are thought to be thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs) when their masses reach the Chandrasekar mass limit in binaries. Previous studies have suggested that He novae may be progenitor candidates of SNe Ia. However, the mass retention efficiencies during He nova outbursts are still uncertain. In this article, we aim to study the mass retention efficiencies of He nova outbursts and to investigate whether SNe Ia can be produced through He nova outbursts. Using the stellar evolution code Modules for Experiments in Stellar Astrophysics, we simulated a series of multicycle He-layer flashes, in which the initial WD masses range from 0.7 to 1.35 Msun with various accretion rates. We obtained the mass retention efficiencies of He nova outbursts for various initial WD masses, which can be used in the binary population synthesis studies. In our simulations, He nova outbursts can increase the mass of the WD to the Chandrasekar mass limit and the explosive carbon burning can be triggered in the center of the WD; this suggests that He nova outbursts can produce SNe Ia. Meanwhile, the mass retention efficiencies in the present work are lower than those of previous studies, which leads to a lower birthrates of SNe Ia through the WD + He star channel. Furthermore, we obtained the elemental abundances distribution at the moment of explosive carbon burning, which can be used as the initial input parameters in studying explosion models of SNe Ia.Comment: 8 pages, 12 figures, 2 tables, published in Astronomy & Astrophysics (A&A 604, A31, 2017

    Effect of Dzyaloshinskii Moriya interaction on magnetic vortex

    Full text link
    The effect of the Dzyaloshinskii Moriya interaction on the vortex in magnetic microdisk was investigated by micro magnetic simulation based on the Landau Lifshitz Gilbert equation. Our results show that the DM interaction modifies the size of the vortex core, and also induces an out of plane magnetization component at the edge and inside the disk. The DM interaction can destabilizes one vortex handedness, generate a bias field to the vortex core and couple the vortex polarity and chirality. This DM-interaction-induced coupling can therefore provide a new way to control vortex polarity and chirality

    Evidence for Weyl fermions in a canonical heavy-fermion semimetal YbPtBi

    Full text link
    The manifestation of Weyl fermions in strongly correlated electron systems is of particular interest. We report evidence for Weyl fermions in the heavy fermion semimetal YbPtBi from electronic structure calculations, angle-resolved photoemission spectroscopy, magnetotransport and calorimetric measurements. At elevated temperatures where 4f4f-electrons are localized, there are triply degenerate points, yielding Weyl nodes in applied magnetic fields. These are revealed by a contribution from the chiral anomaly in the magnetotransport, which at low temperatures becomes negligible due to the influence of electronic correlations. Instead, Weyl fermions are inferred from the topological Hall effect, which provides evidence for a Berry curvature, and a cubic temperature dependence of the specific heat, as expected from the linear dispersion near the Weyl nodes. The results suggest that YbPtBi is a Weyl heavy fermion semimetal, where the Kondo interaction renormalizes the bands hosting Weyl points. These findings open up an opportunity to explore the interplay between topology and strong electronic correlations.Comment: 19 pages, 5 figures, Supplementary Information available with open access at https://www.nature.com/articles/s41467-018-06782-

    Level sequence and splitting identification of closely-spaced energy levels by angle-resolved analysis of the fluorescence light

    Full text link
    The angular distribution and linear polarization of the fluorescence light following the resonant photoexcitation is investigated within the framework of the density matrix and second-order perturbation theory. Emphasis has been placed on "signatures" for determining the level sequence and splitting of intermediate (partially) overlapping resonances, if analyzed as a function of the photon energy of the incident light. Detailed computations within the multiconfiguration Dirac-Fock method have been performed especially for the 1s22s22p63s  Ji=1/2+γ1(1s22s2p63s)13p3/2  J=1/2,3/21s22s22p63s  Jf=1/2+γ21s^{2}2s^{2}2p^{6}3s\;\, J_{i}=1/2 \,+\, \gamma_{1} \:\rightarrow\: (1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\;\, J=1/2, \, 3/2 \:\rightarrow\: 1s^{2}2s^{2}2p^{6}3s\;\, J_{f}=1/2 \,+\, \gamma_{2} photoexcitation and subsequent fluorescence emission of atomic sodium. A remarkably strong dependence of the angular distribution and linear polarization of the γ2\gamma_{2} fluorescence emission is found upon the level sequence and splitting of the intermediate (1s22s2p63s)13p3/2  J=1/2,3/2(1s^{2}2s2p^{6}3s)_{1}3p_{3/2}\;\, J=1/2, \, 3/2 overlapping resonances owing to their finite lifetime (linewidth). We therefore suggest that accurate measurements of the angular distribution and linear polarization might help identify the sequence and small splittings of closely-spaced energy levels, even if they can not be spectroscopically resolved.Comment: 9 pages, 7 figure
    corecore