1,904 research outputs found
The space group classification of topological band insulators
Topological band insulators (TBIs) are bulk insulating materials which
feature topologically protected metallic states on their boundary. The existing
classification departs from time-reversal symmetry, but the role of the crystal
lattice symmetries in the physics of these topological states remained elusive.
Here we provide the classification of TBIs protected not only by time-reversal,
but also by crystalline symmetries. We find three broad classes of topological
states: (a) Gamma-states robust against general time-reversal invariant
perturbations; (b) Translationally-active states protected from elastic
scattering, but susceptible to topological crystalline disorder; (c) Valley
topological insulators sensitive to the effects of non-topological and
crystalline disorder. These three classes give rise to 18 different
two-dimensional, and, at least 70 three-dimensional TBIs, opening up a route
for the systematic search for new types of TBIs.Comment: Accepted in Nature Physic
The effect of cigarette price increase on the cigarette consumption in Taiwan: evidence from the National Health Interview Surveys on cigarette consumption
BACKGROUND: This study uses cigarette price elasticity to evaluate the effect of a new excise tax increase on cigarette consumption and to investigate responses from various types of smokers. METHODS: Our sample consisted of current smokers between 17 and 69 years old interviewed during an annual face-to-face survey conducted by Taiwan National Health Research Institutes between 2000 to 2003. We used Ordinary Least Squares (OLS) procedure to estimate double logarithmic function of cigarette demand and cigarette price elasticity. RESULTS: In 2002, after Taiwan had enacted the new tax scheme, cigarette price elasticity in Taiwan was found to be -0.5274. The new tax scheme brought about an average annual 13.27 packs/person (10.5%) reduction in cigarette consumption. Using the cigarette price elasticity estimate from -0.309 in 2003, we calculated that if the Health and Welfare Tax were increased by another NT$ 3 per pack and cigarette producers shifted this increase to the consumers, cigarette consumption would be reduced by 2.47 packs/person (2.2%). The value of the estimated cigarette price elasticity is smaller than one, meaning that the tax will not only reduce cigarette consumption but it will also generate additional tax revenues. Male smokers who had no income or who smoked light cigarettes were found to be more responsive to changes in cigarette price. CONCLUSIONS: An additional tax added to the cost of cigarettes would bring about a reduction in cigarette consumption and increased tax revenues. It would also help reduce incidents smoking-related illnesses. The additional tax revenues generated by the tax increase could be used to offset the current financial deficiency of Taiwan's National Health Insurance program and provide better public services
Fabrication of Uniform Au–Carbon Nanofiber by Two-Step Low Temperature Decomposition
This paper presents a facile and efficient way to prepare carbon nanofibers ornamented with Au nanoparticles (Au/CNFs). Gold nanoparticles were first deposited in the channels of an anodized aluminum oxide (AAO) membrane by thermal decomposition of HAuCl4and then carbon nanofibers were produced in the same channels loaded with the Au nanoparticles by decomposition of sucrose at 230 °C. An electron microscopy study revealed that the carbon nanofibers, ~10 nm thick and 6 μm long, were decorated with Au nanoparticles with a diameter of 10 nm. This synthetic route can produce uniform Au nanoparticles on CNF surfaces without using any additional chemicals to modify the AAO channels or the CNF surfaces
When Anomaly Mediation is UV Sensitive
Despite its successes---such as solving the supersymmetric flavor
problem---anomaly mediated supersymmetry breaking is untenable because of its
prediction of tachyonic sleptons. An appealing solution to this problem was
proposed by Pomarol and Rattazzi where a threshold controlled by a light field
deflects the anomaly mediated supersymmetry breaking trajectory, thus evading
tachyonic sleptons. In this paper we examine an alternate class of deflection
models where the non-supersymmetric threshold is accompanied by a heavy,
instead of light, singlet. The low energy form of this model is the so-called
extended anomaly mediation proposed by Nelson and Weiner, but with potential
for a much higher deflection threshold. The existence of this high deflection
threshold implies that the space of anomaly mediated supersymmetry breaking
deflecting models is larger than previously thought.Comment: 14 pages, 1 figure (version to appear in JHEP
Emergent quantum confinement at topological insulator surfaces
Bismuth-chalchogenides are model examples of three-dimensional topological
insulators. Their ideal bulk-truncated surface hosts a single spin-helical
surface state, which is the simplest possible surface electronic structure
allowed by their non-trivial topology. They are therefore widely
regarded ideal templates to realize the predicted exotic phenomena and
applications of this topological surface state. However, real surfaces of such
compounds, even if kept in ultra-high vacuum, rapidly develop a much more
complex electronic structure whose origin and properties have proved
controversial. Here, we demonstrate that a conceptually simple model,
implementing a semiconductor-like band bending in a parameter-free
tight-binding supercell calculation, can quantitatively explain the entire
measured hierarchy of electronic states. In combination with circular dichroism
in angle-resolved photoemission (ARPES) experiments, we further uncover a rich
three-dimensional spin texture of this surface electronic system, resulting
from the non-trivial topology of the bulk band structure. Moreover, our study
reveals how the full surface-bulk connectivity in topological insulators is
modified by quantum confinement.Comment: 9 pages, including supplementary information, 4+4 figures. A high
resolution version is available at
http://www.st-andrews.ac.uk/~pdk6/pub_files/TI_quant_conf_high_res.pd
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ALMaQUEST. IV. The ALMA-MaNGA QUEnching and STar Formation (ALMaQUEST) Survey
The ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey is a program
with spatially-resolved CO(1-0) measurements obtained with the Atacama
Large Millimeter Array (ALMA) for 46 galaxies selected from the Mapping Nearby
Galaxies at Apache Point Observatory (MaNGA) DR15 optical integral-field
spectroscopic survey. The aim of the ALMaQUEST survey is to investigate the
dependence of star formation activity on the cold molecular gas content at kpc
scales in nearby galaxies. The sample consists of galaxies spanning a wide
range in specific star formation rate (sSFR), including starburst (SB),
main-sequence (MS), and green valley (GV) galaxies. In this paper, we present
the sample selection and characteristics of the ALMA observations, and showcase
some of the key results enabled by the combination of spatially-matched stellar
populations and gas measurements. Considering the global (aperture-matched)
stellar mass, molecular gas mass, and star formation rate of the sample, we
find that the sSFR depends on both the star formation efficiency (SFE) and the
molecular gas fraction (), although the correlation with the
latter is slightly weaker. Furthermore, the dependence of sSFR on the molecular
gas content (SFE or ) is stronger than that on either the atomic
gas fraction or the molecular-to-atomic gas fraction, albeit with the small HI
sample size. On kpc scales, the variations in both SFE and
within individual galaxies can be as large as 1-2 dex thereby demonstrating
that the availability of spatially-resolved observations is essential to
understand the details of both star formation and quenching processes.STFC
ER
SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA
We study the role of cold gas in quenching star formation in the green valley by analyzing ALMA 12 CO (1-0) observations of three galaxies with resolved optical spectroscopy from the MaNGA survey. We present resolution-matched maps of the star formation rate and molecular gas mass. These data are used to calculate the star formation efficiency (SFE) and gas fraction (f gas ) for these galaxies separately in the central "bulge" regions and outer disks. We find that, for the two galaxies whose global specific star formation rate (sSFR) deviates most from the star formation main sequence, the gas fraction in the bulges is significantly lower than that in their disks, supporting an "inside-out" model of galaxy quenching. For the two galaxies where SFE can be reliably determined in the central regions, the bulges and disks share similar SFEs. This suggests that a decline in f gas is the main driver of lowered sSFR in bulges compared to disks in green valley galaxies. Within the disks, there exist common correlations between the sSFR and SFE and between sSFR and f gas on kiloparsec scales - the local SFE or f gas in the disks declines with local sSFR. Our results support a picture in which the sSFR in bulges is primarily controlled by f gas , whereas both SFE and f gas play a role in lowering the sSFR in disks. A larger sample is required to confirm if the trend established in this work is representative of the green valley as a whole.The work is supported by the Ministry of Science & Technology of Taiwan under the grant MOST 103-2112-M-001-031-MY3 and 106-2112-M-001-034. R.M. and F.B. acknowledge support by the UK Science and Technology Facilities Council (STFC). R.M. acknowledges ERC Advanced Grant 695671 "QUENCH.
(Extra)Ordinary Gauge/Anomaly Mediation
We study anomaly mediation models with gauge mediation effects from
messengers which have a general renormalizable mass matrix with a
supersymmetry-breaking spurion. Our models lead to a rich structure of
supersymmetry breaking terms in the visible sector. We derive sum rules among
the soft scalar masses for each generation. Our sum rules for the first and
second generations are the same as those in general gauge mediation, but the
sum rule for the third generation is different because of the top Yukawa
coupling. We find the parameter space where the tachyonic slepton problem is
solved. We also explore the case in which gauge mediation causes the
anomalously small gaugino masses. Since anomaly mediation effects on the
gaugino masses exist, we can obtain viable mass spectrum of the visible sector
fields.Comment: 24 pages, 10 figure
A SM-like Higgs near 125 GeV in low energy SUSY: a comparative study for MSSM and NMSSM
Motivated by the recent LHC hints of a Higgs boson around 125 GeV, we assume
a SM-like Higgs with the mass 123-127 GeV and study its implication in low
energy SUSY by comparing the MSSM and NMSSM. We consider various experimental
constraints at 2-sigma level (including the muon g-2 and the dark matter relic
density) and perform a comprehensive scan over the parameter space of each
model. Then in the parameter space which is allowed by current experimental
constraints and also predicts a SM-like Higgs in 123-127 GeV, we examine the
properties of the sensitive parameters (like the top squark mass and the
trilinear coupling A_t) and calculate the rates of the di-photon signal and the
VV^* (V=W,Z) signals at the LHC. Our typical findings are: (i) In the MSSM the
top squark and A_t must be large and thus incur some fine-tuning, which can be
much ameliorated in the NMSSM; (ii) In the MSSM a light stau is needed to
enhance the di-photon rate of the SM-like Higgs to exceed its SM prediction,
while in the NMSSM the di-photon rate can be readily enhanced in several ways;
(iii) In the MSSM the signal rates of pp -> h -> VV^* at the LHC are never
enhanced compared with their SM predictions, while in the NMSSM they may get
enhanced significantly; (iv) A large part of the parameter space so far
survived will be soon covered by the expected XENON100(2012) sensitivity
(especially for the NMSSM).Comment: Version in JHEP (refs added
Electroweak Baryogenesis and Dark Matter with an approximate R-symmetry
It is well known that R-symmetric models dramatically alleviate the SUSY
flavor and CP problems. We study particular modifications of existing
R-symmetric models which share the solution to the above problems, and have
interesting consequences for electroweak baryogenesis and the Dark Matter (DM)
content of the universe. In particular, we find that it is naturally possible
to have a strongly first-order electroweak phase transition while
simultaneously relaxing the tension with EDM experiments. The R-symmetry (and
its small breaking) implies that the gauginos (and the neutralino LSP) are
pseudo-Dirac fermions, which is relevant for both baryogenesis and DM. The
singlet superpartner of the U(1)_Y pseudo-Dirac gaugino plays a prominent role
in making the electroweak phase transition strongly first-order. The
pseudo-Dirac nature of the LSP allows it to behave similarly to a Dirac
particle during freeze-out, but like a Majorana particle for annihilation today
and in scattering against nuclei, thus being consistent with current
constraints. Assuming a standard cosmology, it is possible to simultaneously
have a strongly first-order phase transition conducive to baryogenesis and have
the LSP provide the full DM relic abundance, in part of the allowed parameter
space. However, other possibilities for DM also exist, which are discussed. It
is expected that upcoming direct DM searches as well as neutrino signals from
DM annihilation in the Sun will be sensitive to this class of models.
Interesting collider and Gravity-wave signals are also briefly discussed.Comment: 50 pages, 10 figure
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