5,313 research outputs found
Air transparent soundproof window
A soundproof window or wall which is transparent to airflow is presented. The
design is based on two wave theories of diffraction and acoustic metamaterials.
It consists of a three-dimensional array of strong diffraction-type resonators
with many holes centered at each individual resonator. The acoustic performance
levels of two soundproof windows with air holes of and diameters
were measured. Sound waves of 80dB in the frequency range of
were applied to the windows. It was observed that the sound level was reduced
by about dB in the above frequency range with the window and by
about dB in the frequency range of with the
window.
It is an extraordinary acoustic anti-transmission. The geometric factors
which produced the effective negative modulus were obtained.Comment: 4 pages, 6 figures, 1 tabl
Worst-case User Analysis in Poisson Voronoi Cells
In this letter, we focus on the performance of a worst-case mobile user (MU)
in the downlink cellular network. We derive the coverage probability and the
spectral efficiency of the worst-case MU using stochastic geometry. Through
analytical and numerical results, we draw out interesting insights that the
coverage probability and the spectral efficiency of the worst-case MU decrease
down to 23% and 19% of those of a typical MU, respectively. By applying a
coordinated scheduling (CS) scheme, we also investigate how much the
performance of the worst-case MU is improved.Comment: Accepted, IEEE Communications Letter
Cluster X-ray line at from axion-like dark matter
The recently reported X-ray line signal at
from a stacked spectrum of various galaxy clusters and the Andromeda galaxy may
be originating from a decaying dark matter particle of the mass . A
light axion-like scalar is suggested as a natural candidate for dark matter and
its production mechanisms are closely examined. We show that the right amount
of axion relic density with the preferred parameters, and , can be naturally obtainable
from the decay of inflaton. If the axions were produced from the saxion decay,
it could not have constituted the total relic density due to the bound from
structure formation. Nonetheless, the saxion decay is an interesting
possibility, because the line and dark radiation can be
addressed simultaneously, being consistent with the Planck data. Small
misalignment angles of the axion, ranging between depending on the reheating temperature, can also be the source of
axion production. The model with axion misalignment can satisfy the constraints
for structure formation and iso-curvature perturbation.Comment: 14 pages, significant changes in the form, matched to the journal
versio
Diboson Excesses Demystified in Effective Field Theory Approach
We study the collider implication of a neutral resonance which decays to
several diboson final states such as , , and via a
minimal set of effective operators. We consider both CP-even and CP-odd bosonic
states with spin 0, 1, or 2. The production cross sections for the bosonic
resonance states are obtained with the effective operators involving gluons
(and quarks), and the branching fractions are obtained with the operators
responsible for the interactions with electroweak gauge bosons. We demonstrate
that each scenario allows for a broad parameter space which could accommodate
the recently-reported intriguing excesses in the ATLAS diboson final states,
and discuss how the CP states and spin information of the resonance can be
extracted at the LHC run II.Comment: 22 pages, 6 figures, main text slightly modified with results
unchange
Positivity Bounds on Higgs-Portal Dark Matter
We consider the positivity bounds for WIMP scalar dark matter with effective
Higgs-portal couplings up to dimension-8 operators. Taking the superposed
states for Standard Model Higgs and scalar dark matter, we show that the part
of the parameter space for the effective couplings, otherwise unconstrained by
phenomenological bounds, is ruled out by the positivity bounds on the
dimension-8 derivative operators. We find that dark matter relic density,
direct and indirect detection and LHC constraints are complementary to the
positivity bounds in constraining the effective Higgs-portal couplings. In the
effective theory obtained from massive graviton or radion, there appears a
correlation between dimension-8 operators and other effective Higgs-portal
couplings for which the strong constraint from direct detection can be evaded.
Nailing down the parameter space mainly by relic density, direct detection and
positivity bounds, we find that there are observable cosmic ray signals coming
from the dark matter annihilations into a pair of Higgs bosons, or .Comment: 31 pages, 6 figures, v2: one-loop corrections to the positivity
bounds added, version to be published in JHE
- β¦