164 research outputs found
Signals of New Gauge Bosons in Gauged Two Higgs Doublet Model
Recently a gauged two Higgs doublet model, in which the two Higgs doublets
are embedded into the fundamental representation of an extra local
group, is constructed. Both the new gauge bosons and are electrically neutral. While can be singly produced at
colliders, , which is heavier, must be pair produced. We
explore the constraints of using the current Drell-Yan type data
from the Large Hadron Collider. Anticipating optimistically that can
be discovered via the clean Drell-Yan type signals at high luminosity upgrade
of the collider, we explore the detectability of extra heavy fermions in the
model via the two leptons/jets plus missing transverse energy signals from the
exotic decay modes of . For the pair production in
a future 100 TeV proton-proton collider, we demonstrate certain kinematical
distributions for the two/four leptons plus missing energy signals have
distinguishable features from the Standard Model background. In addition,
comparisons of these kinematical distributions between the gauged two Higgs
doublet model and the littlest Higgs model with T-parity, the latter of which
can give rise to the same signals with competitive if not larger cross
sections, are also presented.Comment: 39 pages, 23 figures, 7 tables and two new appendixes, to appear in
EPJ
The Effects of the PEM Fuel Cell Performance with the Waved Flow Channels
The objective of this study is to use a new style of waved flow channel instead of the plane surface channel in the proton exchange membrane fuel cell (PEMFC). The velocity, concentration, and electrical performance with the waved flow channel in PEMFC are investigated by numerical simulations. The results show that the waved channel arises when the transport benefits through the porous layer and improves the performance of the PEMFC. This is because the waved flow channel enhances the forced convection and causes the more reactant gas flow into the gas diffusion layer (GDL). The performance which was compared to a conventional straight gas flow channel increases significantly with the small gap size when it is smaller than 0.5 in the waved flow channel. The performance is decreased at the high and low velocities as the force convection mechanism is weakened and the reactant gas supply is insufficient. The pressure drop is increased as the gap size becomes smaller, and the wave number decreases. (gap size) δ > 0.3 has a reasonable pressure drop. Consequently, compared to a conventional PEMFC, the waved flow channel improves approximately 30% of power density
Attosecond Time-Domain Measurement of Core-Level-Exciton Decay in Magnesium Oxide.
Excitation of ionic solids with extreme ultraviolet pulses creates localized core-level excitons, which in some cases couple strongly to the lattice. Here, core-level-exciton states of magnesium oxide are studied in the time domain at the Mg L_{2,3} edge with attosecond transient reflectivity spectroscopy. Attosecond pulses trigger the excitation of these short-lived quasiparticles, whose decay is perturbed by time-delayed near-infrared pulses. Combined with a few-state theoretical model, this reveals that the infrared pulse shifts the energy of bright (dipole-allowed) core-level-exciton states as well as induces features arising from dark core-level excitons. We report coherence lifetimes for the two lowest core-level excitons of 2.3±0.2 and 1.6±0.5 fs and show that these are primarily a consequence of strong exciton-phonon coupling, disclosing the drastic influence of structural effects in this ultrafast relaxation process
Observational connection of non-thermal X-ray emission from pulsars with their timing properties and thermal emission
The origin and radiation mechanisms of high energy emissions from pulsars
have remained mysterious since their discovery. Here we report, based on a
sample of 68 pulsars, observational connection of non-thermal X-ray emissions
from pulsars with their timing properties and thermal emissions, which may
provide some constraints on theoretical modeling. Besides strong correlations
with the spin-down power and the magnetic field strength at the light
cylinder , the non-thermal X-ray luminosity in 0.5 - 8 keV, , represented by the power-law component in the spectral model, is found to
be strongly correlated with the highest possible electric field strength in the
polar gap, , of the pulsar. The spectral power index of that power-law component is also found, for the first time in the
literature, to strongly correlate with , and , thanks to the large sample. In addition, we found that can be
well described by , where
and are the surface temperature and the emitting-region radius of the
surface thermal emission, represented by the black-body component in the
spectral model. , on the other hand, can be well described only
when timing variables are included, and the relation is
plus a constant. These relations strongly suggest the existence of connections
between surface thermal emission and electron-positron pair production in
pulsar magnetospheres.Comment: 13 pages, 11 figures, accepted by MNRA
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