100,471 research outputs found
BES Recent Results and Future Plans
We report the preliminary R values for all the 85 energy points scanned in
the energy region of 2-5 GeV with the upgraded Beijing Spectrometer (BESII) at
Beijing Electron Positron Collider (BEPC). Preliminary results from the J/psi
data collected with both BESI and BESII are presented. Measurements of the
branching fraction of the psi(2S) decays and the psi(2S) resonance parameters
are reported. The future plans, i.e. significantly upgrade the machine and
detector are also discussed.Comment: Talk given at APPAC2000, 6 pages, 8 figure
An octonion algebra originating in combinatorics
C.H. Yang discovered a polynomial version of the classical Lagrange identity
expressing the product of two sums of four squares as another sum of four
squares. He used it to give short proofs of some important theorems on
composition of delta-codes (now known as T-sequences). We investigate the
possible new versions of his polynomial Lagrange identity. Our main result
shows that all such identities are equivalent to each other.Comment: 11 pages, A simpler proof of the main theorem, due to Alberto
Elduque, is inserted. The paper will appear in the Proc. Amer. Math. So
Topological Weyl and Node-Line Semimetals in Ferromagnetic Vanadium-Phosphorous-Oxide -VOPO Compound
We propose that the topological semimetal features can co-exist with
ferromagnetic ground state in vanadium-phosphorous-oxide -VOPO
compound from first-principles calculations. In this magnetic system with
inversion symmetry, the direction of magnetization is able to manipulate the
symmetric protected band structures from a node-line type to a Weyl one in the
presence of spin-orbital-coupling. The node-line semimetal phase is protected
by the mirror symmetry with the reflection-invariant plane perpendicular to
magnetic order. Within mirror symmetry breaking due to the magnetization along
other directions, the gapless node-line loop will degenerate to only one pair
of Weyl points protected by the rotational symmetry along the magnetic axis,
which are largely separated in momentum space. Such Weyl semimetal phase
provides a nice candidate with the minimum number of Weyl points in a condensed
matter system. The results of surface band calculations confirm the non-trivial
topology of this proposed compound. This findings provide a realistic candidate
for the investigation of topological semimetals with time-reversal symmetry
breaking, particularly towards the realization of quantum anomalous Hall effect
in Weyl semimetals.Comment: 5 pages, 4 figure
General response theory of topologically stable Fermi points and its implications for disordered cases
We develop a general response theory of gapless Fermi points with nontrivial
topological charges for gauge and nonlinear sigma fields, which asserts that
the topological character of the Fermi points is embodied as the terms with
discrete coefficients proportional to the corresponding topological charges.
Applying the theory to the effective non-linear sigma models for topological
Fermi points with disorders in the framework of replica approach, we derive
rigorously the Wess-Zumino terms with the topological charges being their
levels in the two complex symmetry classes of A and AIII. Intriguingly, two
nontrivial examples of quadratic Fermi points with the topological charge `2'
are respectively illustrated for the classes A and AIII. We also address a
qualitative connection of topological charges of Fermi points in the real
symmetry classes to the topological terms in the non-linear sigma models, based
on the one-to-one classification correspondence.Comment: 8 pages and 2 figures, revised version with appendi
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