4,192 research outputs found
Interpreting the galactic center gamma-ray excess in the NMSSM
In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), all
singlet-dominated particles including one neutralino, one CP-odd Higgs boson
and one CP-even Higgs boson can be simultaneously lighter than about 100 GeV.
Consequently, dark matter (DM) in the NMSSM can annihilate into multiple final
states to explain the galactic center gamma-ray excess (GCE). In this work we
take into account the foreground and background uncertainties for the GCE and
investigate these explanations. We carry out a sophisticated scan over the
NMSSM parameter space by considering various experimental constraints such as
the Higgs data, -physics observables, DM relic desnity, LUX experiment and
the dSphs constraints. Then for each surviving parameter point we perform a fit
to the GCE spectrum by using the correlation matrix that incorporates both the
statistical and systematic uncertainties of the measured excess. After
examining the properties of the obtained GCE solutions, we conclude that the
GCE can be well explained by the pure annihilations and with being the lighter singlet-dominated CP-odd Higgs boson and
denoting the singlet-dominated CP-even Higgs boson or SM-like Higgs
boson, and it can also be explained by the mixed annihilation . Among these annihilation channels,
can provide the best
interpretation with the corresponding -value reaching 0.55. We also discuss
to what extent the future DM direct detection experiments can explore the GCE
solutions and conclude that the XENON-1T experiment is very promising in
testing nearly all the solutions.Comment: 31 pages, 7 figure
Charged BTZ-like black hole solutions and the diffusivity-butterfly velocity relation
We show that there exists a class of charged BTZ-like black hole solutions in
Lifshitz spacetime with a hyperscaling violating factor. The charged BTZ is
characterized by a charge-dependent logarithmic term in the metric function. As
concrete examples, we give five such charged BTZ-like black hole solutions and
the standard charged BTZ metric can be regarded as a special instance of them.
In order to check the recent proposed universal relations between diffusivity
and the butterfly velocity, we first compute the diffusion constants of the
standard charged BTZ black holes and then extend our calculation to arbitrary
dimension , exponents and . Remarkably, the case and
is a very special in that the charge diffusion is a constant and
the energy diffusion might be ill-defined, but diverges. We
also compute the diffusion constants for the case that the DC conductivity is
finite but in the absence of momentum relaxation.Comment: 30 pages, 2 figure
A path to precision cosmology: synergy between four promising late-universe cosmological probes
In the next decades, it is necessary to forge new late-universe cosmological
probes to precisely constrain the Hubble constant and the equation of state of
dark energy simultaneously. In this work, we show that the four typical
late-universe cosmological probes, the 21 cm intensity mapping (IM), fast radio
burst (FRB), gravitational wave (GW) standard siren, and strong gravitational
lensing (SGL), are expected to be forged into useful tools in solving the
Hubble tension and exploring dark energy. We propose that the synergy of them
is rather important in cosmology. We simulate the 21 cm IM, FRB, GW, and SGL
data based on the hypothetical observations of the Hydrogen Intensity and
Real-time Analysis eXperiment (HIRAX), the Square Kilometre Array (SKA), the
Einstein Telescope (ET), and the Large Synoptic Survey Telescope (LSST),
respectively. We find that the four probes show obviously different parameter
degeneracy orientations in cosmological constraints, so any combination of them
can break the parameter degeneracies and thus significantly improve the
constraint precision. The joint 21 cm IM+FRB+GW+SGL data can provide the
constraint errors of and in the CDM model, which meet the standard of
precision cosmology, i.e., the constraint precision of parameters is better
than 1%. In addition, the joint data give in the CDM
model, and and in the CDM model,
which are all better than the constraints obtained by the CMB+BAO+SN data. We
show that the synergy between the four late-universe cosmological probes has
magnificent prospects.Comment: 28 pages, 9 figures; accepted for publication in JCA
Slow light by coherent hole burnings
We show that the simultaneous application of a copropagating saturating pump and a counterpropagating coherent beam can be used to burn a narrow spectral hole within the absorption line of the optical transition in a Doppler-broadened medium. The large index of refraction of this hole slows down a light pulse by a factor of about 104. In addition, we propose a method to create two-color slow light pulses with simultaneous gain by employing a bichromatic field to saturate the medium
Elevated CO2 and Warming Altered Grassland Microbial Communities in Soil Top-Layers.
As two central issues of global climate change, the continuous increase of both atmospheric CO2 concentrations and global temperature has profound effects on various terrestrial ecosystems. Microbial communities play pivotal roles in these ecosystems by responding to environmental changes through regulation of soil biogeochemical processes. However, little is known about the effect of elevated CO2 (eCO2) and global warming on soil microbial communities, especially in semiarid zones. We used a functional gene array (GeoChip 3.0) to measure the functional gene composition, structure, and metabolic potential of soil microbial communities under warming, eCO2, and eCO2 + warming conditions in a semiarid grassland. The results showed that the composition and structure of microbial communities was dramatically altered by multiple climate factors, including elevated CO2 and increased temperature. Key functional genes, those involved in carbon (C) degradation and fixation, methane metabolism, nitrogen (N) fixation, denitrification and N mineralization, were all stimulated under eCO2, while those genes involved in denitrification and ammonification were inhibited under warming alone. The interaction effects of eCO2 and warming on soil functional processes were similar to eCO2 alone, whereas some genes involved in recalcitrant C degradation showed no significant changes. In addition, canonical correspondence analysis and Mantel test results suggested that NO3-N and moisture significantly correlated with variations in microbial functional genes. Overall, this study revealed the possible feedback of soil microbial communities to multiple climate change factors by the suppression of N cycling under warming, and enhancement of C and N cycling processes under either eCO2 alone or in interaction with warming. These findings may enhance our understanding of semiarid grassland ecosystem responses to integrated factors of global climate change
Intelligent Hydrogen Fuel Cell Range Extender for Battery Electric Vehicles
Road transport is recognized as having a negative impact on the environment. Policy has focused on replacement of the internal combustion engine (ICE) with less polluting forms of technology, including battery electric and fuel cell electric powertrains. However, progress is slow and both battery and fuel cell based vehicles face considerable commercialization challenges. To understand these challenges, a review of current electric battery and fuel cell electric technologies is presented. Based on this review, this paper proposes a battery electric vehicle (BEV) where components are sized to take into account the majority of user requirements, with the remainder catered for by a trailer-based demountable intelligent fuel cell range extender. The proposed design can extend the range by more than 50% for small BEVs and 25% for large BEVs (the extended range of vehicles over 250 miles), reducing cost and increasing efficiency for the BEV. It enables BEV manufacturers to design their vehicle battery for the most common journeys, decreases charging time to provide convenience and flexibility to the drivers. Adopting a rent and drop business model reduces the demand on the raw materials, bridging the gap in the amount of charging (refueling) stations, and extending the lifespan for the battery pack.
Document type: Articl
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