1,349 research outputs found
Vacuum stability in stau-neutralino coannihilation in MSSM
The stau-neutralino coannihilation provides a feasible way to accommodate the
observed cosmological dark matter (DM) relic density in the minimal
supersymmetric standard model (MSSM). In such a coannihilation mechanism the
stau mass usually has an upper bound since its annihilation rate becomes small
with the increase of DM mass. Inspired by this observation, we examine the
upper limit of stau mass in the parameter space with a large mixing of staus.
We find that the stau pair may dominantly annihilate into dibosons and hence
the upper bound on the stau mass ( GeV) obtained from the
final states can be relaxed. Imposing the DM relic density constraint and
requiring a long lifetime of the present vacuum, we find that the lighter stau
mass can be as heavy as about 1.4 TeV for the stau maximum mixing. However, if
requiring the present vacuum to survive during the thermal history of the
universe, this mass limit will reduce to about 0.9 TeV. We also discuss the
complementarity of vacuum stability and direct detections in probing this stau
coannihilation scenario.Comment: 12 pages, 6 figure
Controlled polarization rotation of an optical field in multi-Zeeman-sublevel atoms
We investigate, both theoretically and experimentally, the phenomenon of
polarization rotation of a weak, linearly-polarized optical (probe) field in an
atomic system with multiple three-level electromagnetically induced
transparency (EIT) sub-systems. The polarization rotation angle can be
controlled by a circularly-polarized coupling beam, which breaks the symmetry
in number of EIT subsystems seen by the left- and right-circularly-polarized
components of the weak probe beam. A large polarization rotation angle (up to
45 degrees) has been achieved with a coupling beam power of only 15 mW.
Detailed theoretical analyses including different transition probabilities in
different transitions and Doppler-broadening are presented and the results are
in good agreements with the experimentally measured results.Comment: 28pages, 12figure
Mid-infrared computational temporal ghost imaging
Ghost imaging in the time domain allows for reconstructing fast temporal
objects using a slow photodetector. The technique involves correlating random
or pre-programmed probing temporal intensity patterns with the integrated
signal measured after modulation by the temporal object. However, the
implementation of temporal ghost imaging necessitates ultrafast detectors or
modulators for measuring or pre-programming the probing intensity patterns,
which is not universally available in all spectral regions especially in the
mid-infrared range. Here, we demonstrate a frequency downconversion temporal
ghost imaging scheme that enables to extend the operation regime to arbitrary
wavelengths regions where fast modulators and detectors are not available. The
approach modulates a signal with temporal intensity patterns in the
near-infrared and transfers the patterns to an idler via difference-frequency
generation at the wavelength of the temporal object to be retrieved. As a
proof-of-concept, we demonstrate temporal ghost imaging in the mid-infrared.
The scheme is flexible and introduces new possibilities for scan-free
pump-probe imaging and the study of ultrafast dynamics in spectral regions
where ultrafast modulation or detection is challenging such as the mid-infrared
and THz regions
Guided flows in coronal magnetic flux tubes
There is evidence for coronal plasma flows to break down into fragments and
to be laminar. We investigate this effect by modeling flows confined along
magnetic channels. We consider a full MHD model of a solar atmosphere box with
a dipole magnetic field. We compare the propagation of a cylindrical flow
perfectly aligned to the field to that of another one with a slight
misalignment. We assume a flow speed of 200 km/s, and an ambient magnetic field
of 30 G. We find that while the aligned flow maintains its cylindrical symmetry
while it travels along the magnetic tube, the misaligned one is rapidly
squashed on one side, becoming laminar and eventually fragmented because of the
interaction and backreaction of the magnetic field. This model could explain an
observation of erupted fragments that fall back as thin and elongated strands
and end up onto the solar surface in a hedge-like configuration, made by the
Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The
initial alignment of plasma flow plays an important role in determining the
possible laminar structure and fragmentation of flows while they travel along
magnetic channels.Comment: 11 pages, 8 figures, accepted for publication, movies available upon
request to the first autho
Relationship between obesity and structural brain abnormality: Accumulated evidence from observational studies
Body mass index; Structural brain abnormalitiesÍndex de massa corporal; Anormalitats estructurals del cervellÍndice de masa corporal; Anomalías estructurales del cerebroWe aimed to evaluate the relationship between obesity and structural brain abnormalities assessed by magnetic resonance imaging using data from 45 observational epidemiological studies, where five articles reported prospective longitudinal results. In cross-sectional studies’ analyses, the pooled weighted mean difference for total brain volume (TBV) and gray matter volume (GMV) in obese/overweight participants was -11.59 (95 % CI: -23.17 to -0.02) and -10.98 (95 % CI: -20.78 to -1.18), respectively. TBV was adversely associated with BMI and WC, GMV with BMI, and hippocampal volume with BMI, WC, and WHR. WC/WHR are associated with a risk of lacunar and white matter hyperintensity (WMH). In longitudinal studies’ analyses, BMI was not statistically associated with the overall structural brain abnormalities (for continuous BMI: RR = 1.02, 95 % CI: 0.94–1.12; for categorial BMI: RR = 1.18, 95 % CI: 0.75–1.85). Small sample size of prospective longitudinal studies limited the power of its pooled estimates. A higher BMI is associated with lower brain volume while greater WC/WHR, but not BMI, is related to a risk of lacunar infarct and WMH. Future longitudinal research is needed to further elucidate the specific causal relationships and explore preventive measures.This work was supported by the National Natural Science Foundation of China (No. 82070851, 81870556, 81930019, 81770686, 81970591), Beijing Municipal Administration of Hospital’s Youth Program (QML20170204), Excellent Talents in Dongcheng District of Beijing
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