2,732 research outputs found
Electrophilic dark matter with dark photon: from DAMPE to direct detection
The electron-positron excess reported by the DAMPE collaboration recently may
be explained by an electrophilic dark matter (DM). A standard model singlet
fermion may play the role of such a DM when it is stablized by some symmetries,
such as a dark gauge symmetry, and dominantly annihilates into the
electron-positron pairs through the exchange of a scalar mediator. The model,
with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively
one expects that in this type of models the DM-nucleon cross section should be
small since there is no tree-level DM-quark interactions. We however find that
at one-loop level, a testable DM-nucleon cross section can be induced for
providing ways to test the electrophilic model. We also find that a
kinetic mixing can generate a sizable DM-nucleon cross section although the
dark photon only has a negligible contribution to the DM
annihilation. Depending on the signs of the mixing parameter, the dark photon
can enhance/reduce the one-loop induced DM-nucleon cross section.Comment: 4 pages, typos are corrected, references are added as well as more
discussions on direct detectio
Leptogenesis parametrized by lepton mass matrices
The conventional seesaw-leptogenesis can simultaneously explain the
suppression of neutrino masses and the generation of cosmic baryon asymmetry,
but usually cannot predict an unambiguous relation between these two sectors.
In this work we shall demonstrate a novel left-right symmetric scenario,
motivated to solve the strong CP problem by parity symmetry, where the present
baryon asymmetry is determined by three charged lepton masses and a
seesaw-suppressed hermitian Dirac neutrino mass matrix up to an overall scale
factor. To produce the observed baryon asymmetry, this scenario requires that
the neutrinos must have a normal hierarchical mass spectrum and their mixing
matrix must contain a sizable Dirac CP phase. Our model can be tested in
neutrino oscillation and neutrinoless double beta decay experiments.Comment: 5 pages, 2 figures. Typos are correcte
Versatile Preparation of Mesoporous Single-Layered Transition-Metal Sulfide/Carbon Composites for Enhanced Sodium Storage
Transition metal sulfides are promise electrochemical energy storage materials due to their abundant active sites, large inter-layer space and high theoretical capacities. Especially for sodium storage. However, the low conductivity and poor cycling stability at high current densities hampered their applications. Herein, we report a versatile dual-templates method to elaborate ordered mesoporous single layered MoS2 /carbon composite with high specific area, uniform pore size and large pore volume. The single layered MoS2 is confined in the carbon matrix. The mesopores between the composite nanorods provide fast electrolyte diffusion. The obtained nanocomposite shows a high sodium storage capability, excellent rate capacity, and very good cycling performance. A 310 mAh g-1 capacity can remains at 5.0 A g-1 after 2500 cycles. Furthermore, a SIB full cell composed the MoS2 /carbon composite anode and a Na3 V2 (PO4 )3 (NVP) cathode maintains a specific capacity of 330 mA h g-1 at 1.0 A g-1 during 100 cycles. The mechanism is investigated by in situ and ex situ characterizations as well as density functional theory (DFT) calculations. This article is protected by copyright. All rights reserved
Time-reversal symmetry breaking superconducting ground state in the doped Mott insulator on the honeycomb lattice
The emergence of superconductivity in doped Mott insulators has been debated
for decades. In this paper, we report the theoretical discovery of a
time-reversal symmetry breaking superconducting ground state in the doped Mott
insulator (described by the well known t-J model) on honeycomb lattice, based
on a recently developed variational method: the Grassmann tensor product state
approach. As a benchmark, we use exact diagonalization and density-matrix
renormalization methods to check our results on small clusters. We find
systematic consistency for the ground-state energy as well as other physical
quantities, such as the staggered magnetization. At low doping, the
superconductivity coexists with antiferromagnetic ordering.Comment: 7 pages, 9 figures (published version
Possible proximity of the Mott insulating Iridate Na2IrO3 to a topological phase: Phase diagram of the Heisenberg-Kitaev model in a magnetic field
Motivated by the recent experimental observation of a Mott insulating state
for the layered Iridate Na2IrO3, we discuss possible ordering states of the
effective Iridium moments in the presence of strong spin-orbit coupling and a
magnetic field. For a field pointing in the [111] direction - perpendicular to
the hexagonal lattice formed by the Iridium moments - we find that a
combination of Heisenberg and Kitaev exchange interactions gives rise to a rich
phase diagram with both symmetry breaking magnetically ordered phases as well
as a topologically ordered phase that is stable over a small range of coupling
parameters. Our numerical simulations further indicate two exotic multicritical
points at the boundaries between these ordered phases.Comment: 5 pages, 6 figure
Physiological Ischemic Training Promotes Brain Collateral Formation and Improves Functions in Patients with Acute Cerebral Infarction
Objectives: To observe the effectiveness and mechanisms of physiological ischemic training (PIT) on brain cerebral collateral formation and functional recovery in patients with acute cerebral infarction.Methods: 20 eligible patients with acute cerebral infarction were randomly assigned to either PIT group (n = 10) or Control group (n = 10). Both groups received 4 weeks of routine rehabilitation therapy, while an additional session of PIT, which consisted of 10 times of maximal voluntary isometric handgrip for 1 min followed by 1 min rest, was prescribed for patients in the PIT groups. Each patient was trained with four sections a day and 5 days a week for 4 weeks. The Fugl-Meyer Assessment (FMA), the Modified Barthel Index (MBI), and the short-form 36-item health survey questionnaire (SF-36) were applied for the evaluation of motor impairment, activity of daily living, and quality of life at the baseline and endpoint. MRI was applied to detect the collateral formation in the brain. The concentration of vascular endothelial growth factor (VEGF) and endothelial progenitor cells (EPCs) number in plasma were also tested at the endpoint.Results: Demographic data were consistent between experimental groups. At the endpoint, the scores of the FMA, MBI, and SF-36 were significantly higher than that at baseline. As compared to the Control group, the score of FMA and SF-36 in PIT group was significantly higher, while no significant difference was detected between groups in terms of MBI. Both groups had significantly higher cerebral blood flow (CBF) level at endpoint as compared to that at baseline. Moreover, the CBF level was even higher in the PIT group as compared to that in the Control group after 4 weeks of training. The same situations were also found in the plasma VEGF and EPCs assessment. In addition, positive correlations were found between FMA score and CBF level (r = 0.686, p < 0.01), CBF level and VEGF concentration (r = 0.675, p < 0.01), and VEGF concentration and EPC number (r = 0.722, p < 0.01).Conclusion: PIT may be effective in increasing the expression of VEGF and recruitment of EPCs and in turn promote the formation of brain collateral circulation. The positive correlations may demonstrate a potential association between biological and functional parameters, and PIT may be able to improve the motor function, activity of daily living, and quality of life in patients with stroke.Interdisciplinary Division of Biomedical Engineerin
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