1,578 research outputs found
Topological Insulators and Superconductors from String Theory
Topological insulators and superconductors in different spatial dimensions
and with different discrete symmetries have been fully classified recently,
revealing a periodic structure for the pattern of possible types of topological
insulators and supercondutors, both in terms of spatial dimensions and in terms
of symmetry classes. It was proposed that K-theory is behind the periodicity.
On the other hand, D-branes, a solitonic object in string theory, are also
known to be classified by K-theory. In this paper, by inspecting low-energy
effective field theories realized by two parallel D-branes, we establish a
one-to-one correspondence between the K-theory classification of topological
insulators/superconductors and D-brane charges. In addition, the string theory
realization of topological insulators and superconductors comes naturally with
gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a
gauge field theory of topological nature, such as ones with the Chern-Simons
term or the -term in various dimensions. This sheds light on
topological insulators and superconductors beyond non-interacting systems, and
the underlying topological field theory description thereof. In particular, our
string theory realization includes the honeycomb lattice Kitaev model in two
spatial dimensions, and its higher-dimensional extensions. Increasing the
number of D-branes naturally leads to a realization of topological insulators
and superconductors in terms of holography (AdS/CFT).Comment: 13 pages, 3 figures;references update
Wigner transform and pseudodifferential operators on symmetric spaces of non-compact type
We obtain a general expression for a Wigner transform (Wigner function) on
symmetric spaces of non-compact type and study the Weyl calculus of
pseudodifferential operators on them
Connecting geodesics and security of configurations in compact locally symmetric spaces
A pair of points in a riemannian manifold makes a secure configuration if the
totality of geodesics connecting them can be blocked by a finite set. The
manifold is secure if every configuration is secure. We investigate the
security of compact, locally symmetric spaces.Comment: 27 pages, 2 figure
Unmanned aerial vehicle remote sensing of snow: improving snowmelt prediction
Non-Peer Reviewe
Soil origin and land use history determine C cycling in transplanted soils after 21 years
Non-Peer Reviewe
Response of transplanted Chernozems towards C addition after 21 years of identical climatic, topographic, and management practices
Non-Peer Reviewe
Semidirect product gauge group and quantization of hypercharge
In the Standard Model the hypercharges of quarks and leptons are not
determined by the gauge group alone. We show that, if we choose the semidirect product group
as its gauge group,
the hyperchages are settled to be . In
addition, the conditions for gauge-anomaly cancellation give strong
constraints. As a result, the ratios of the hypercharges are uniquely
determined and the gravitational anomaly is automatically canceled. The
standard charge assignment to quarks and leptons can be properly reproduced.
For exotic matter fields their hypercharges are also discussed.Comment: 17 pages, 2 tables; LaTeX; typos corrected, references added or
replaced, argument in Secs. 2 and 3 revised, results unchanged; to be
published in Phys. Rew.
Social correlates of cigarette smoking among Icelandic adolescents: A population-based cross-sectional study
BACKGROUND: Previous research has shown that between 80 and 90 percent of adult
smokers report having started smoking before 18 years of age. Several studies
have revealed that multiple social factors influence the likelihood of smoking
during adolescence, the period during which the onset of smoking usually occurs.
To better understand the social mechanisms that influence adolescent smoking, we
analyzed the relationship and relative importance of a broad spectrum of social
variables in adolescent smoking in Iceland, a Nordic country with high per-capita
income.
METHODS: We used cross-sectional data from 7,430 14- to 16 year-old
students (approximately 81% of all Icelanders in these age cohorts) in the 2006
Youth in Iceland study. The Youth in Iceland studies are designed to investigate
the role of several cognitive, behavioral, and social factors in the lives of
adolescents, and the data collected are used to inform the design,
implementation, and evaluation of substance use prevention programs that are
being developed by Icelandic social scientists, policy makers, and practitioners.
RESULTS: Our analysis revealed that friends' smoking behavior and attitude toward
smoking were strongly associated with adolescent smoking and other tobacco use,
as well as alcohol consumption during the previous 30 days. Main protective
factors were parent's perceived attitude toward smoking, the quantity of time
spent with parents, absence of serious verbal conflict between parents and
adolescents, and participation in physical activity. Family structure was related
to adolescent smoking to a small extent, but other background factors were not.
CONCLUSION: We conclude that multiple social factors are related to adolescent
smoking. Parents and other primary preventive agents need to be informed about
the complicated nature of the adolescent social world in order to maximize their
impact.Icelandic Alcohol and Drug Prevention CommitteeIcelandic Red CrossCity of ReykjavikSports and Recreational Committee of Reykjavik to the Icelandic Centre for Social Research and AnalysisIcelandic Centre for Research (RANNÍS)Publishe
A generalised Landau-Lifshitz equation for isotropic SU(3) magnet
In the paper we obtain equations for large-scale fluctuations of the mean
field (the field of magnetization and quadrupole moments) in a magnetic system
realized by a square (cubic) lattice of atoms with spin s >= 1 at each site. We
use the generalized Heisenberg Hamiltonian with biquadratic exchange as a
quantum model. A quantum thermodynamical averaging gives classical effective
models, which are interpreted as Hamiltonian systems on coadjoint orbits of Lie
group SU(3).Comment: 15 pages, 1 figur
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