56,787 research outputs found
Centers and Cocenters of -Hecke algebras
In this paper, we give explicit descriptions of the centers and cocenters of
-Hecke algebras associated to finite Coxeter groups.Comment: 13 pages, a mistake in 4.2 is correcte
Generation of high-energy monoenergetic heavy ion beams by radiation pressure acceleration of ultra-intense laser pulses
A novel radiation pressure acceleration (RPA) regime of heavy ion beams from
laser-irradiated ultrathin foils is proposed by self-consistently taking into
account the ionization dynamics. In this regime, the laser intensity is
required to match with the large ionization energy gap when the successive
ionization of high-Z atoms passing the noble gas configurations [such as
removing an electron from the helium-like charge state to
]. While the target ions in the laser wing region are ionized
to low charge states and undergo rapid dispersions due to instabilities, a
self-organized, stable RPA of highly-charged heavy ion beam near the laser axis
is achieved. It is also found that a large supplement of electrons produced
from ionization helps preserving stable acceleration. Two-dimensional
particle-in-cell simulations show that a monoenergetic beam
with peak energy and energy spread of is obtained by
lasers at intensity .Comment: 5 pages, 4 figure
Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi_2Se_3 with scanning tunneling spectroscopy
Scanning tunneling spectroscopic studies of Bi_2Se_3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level (E_F) and the Dirac point (E_D) and diverges as E_F approaches E_D. The Dirac-cone surface state of the host recovers within ~ 2Å spatial distance from impurities, suggesting robust topological protection of the surface state of topological insulators against high-density impurities that preserve time reversal symmetry
Graphene formed on SiC under various environments: Comparison of Si-face and C-face
The morphology of graphene on SiC {0001} surfaces formed in various
environments including ultra-high vacuum, 1 atm of argon, and 10^-6 to 10^-4
Torr of disilane is studied by atomic force microscopy, low-energy electron
microscopy, and Raman spectroscopy. The graphene is formed by heating the
surface to 1100 - 1600 C, which causes preferential sublimation of the Si
atoms. The argon atmosphere or the background of disilane decreases the
sublimation rate so that a higher graphitization temperature is required, thus
improving the morphology of the films. For the (0001) surface, large areas of
monolayer-thick graphene are formed in this way, with the size of these areas
depending on the miscut of the sample. Results on the (000-1) surface are more
complex. This surface graphitizes at a lower temperature than for the (0001)
surface and consequently the growth is more three-dimensional. In an atmosphere
of argon the morphology becomes even worse, with the surface displaying
markedly inhomogeneous nucleation, an effect attributed to unintentional
oxidation of the surface during graphitization. Use of a disilane environment
for the (000-1) surface is found to produce improved morphology, with
relatively large areas of monolayer-thick graphene.Comment: 22 pages, 11 figures, Proceedings of STEG-2 Conference; eliminated
Figs. 4 and 7 from version 1, for brevity, and added Refs. 18, 29, 30, 31
together with associated discussio
The interference in the reaction and the search for the decay
We describe the interference between amplitudes and ,
where meson is considered in the frameworks of the four-quark model and
the model of the scalar molecule. The general expressions for the
differential cross section with the radiative corrections and two angle cuts
are given. The interference patterns are obtained in the spectrum of the
differential cross section by the energy of the photon and in the full cross
section by the energy of the beams.Comment: 21 pages, revtex, 8 ps files of figure
X(1812) in Quarkonia-Glueball-Hybrid Mixing Scheme
Recently a (X(1812)) state with a mass near the threshold of
and has been observed by the BES collaboration in decay. It has been suggested that it is a
state. If it is true, this state fits in a mixing scheme based on quarkonia,
glueball and hybrid (QGH) very nicely where five physical states are predicted.
Together with the known , , , and
states, X(1812) completes the five members in this family. Using known
experimental data on these particles we determine the ranges of the mixing
parameters and predict decay properties for X(1812). We also discuss some
features which may be able to distinguish between four-quark and hybrid mixing
schemes.Comment: 15 pages, 2 figures, 3 table
Exploration of hyperfine interaction between constituent quarks via eta productions
In this work, the different exchange freedom, one gluon, one pion or
Goldstone boson, in constituent quark model is investigated, which is
responsible to the hyperfine interaction between constituent quarks, via the
combined analysis of the eta production processes,
and . With the Goldstone-boson exchange, as well as
the one-gluon or one-pion exchange, both the spectrum and observables, such as,
the differential cross section and polarized beam asymmetry, are fitted to the
suggested values of Particle Data Group and the experimental data. The first
two types of exchange freedoms give acceptable description of the spectrum and
observables while the one pion exchange can not describe the observables and
spectrum simultaneously, so can be excluded. The experimental data for the two
processes considered here strongly support the mixing angles for two lowest S11
sates and D13 states as about -30 and 6 degree respectively.Comment: 7 pages, 4 figures, 4 table
The statistical properties of galaxy morphological types in compact groups of Main galaxies from the SDSS Data Release 4
In order to explore the statistical properties of galaxy morphological types
in compact groups (CGs), we construct a random group sample which has the same
distributions of redshift and number of member galaxies as those of the CG
sample. It turns out that the proportion of early-type galaxies in different
redshift bins for the CG sample is statistically higher than that for random
group sample, and with growing redshift z this kind of difference becomes more
significant. This may be due to the existence of interactions and mergers
within a significant fraction of SDSS CGs. We also compare statistical results
of CGs with those of more compact groups and pairs, but do not observe as large
statistical difference as Hickson (1982)'results.Comment: 12 pages, 9 figure
Constructing the Tree-Level Yang-Mills S-Matrix Using Complex Factorization
A remarkable connection between BCFW recursion relations and constraints on
the S-matrix was made by Benincasa and Cachazo in 0705.4305, who noted that
mutual consistency of different BCFW constructions of four-particle amplitudes
generates non-trivial (but familiar) constraints on three-particle coupling
constants --- these include gauge invariance, the equivalence principle, and
the lack of non-trivial couplings for spins >2. These constraints can also be
derived with weaker assumptions, by demanding the existence of four-point
amplitudes that factorize properly in all unitarity limits with complex
momenta. From this starting point, we show that the BCFW prescription can be
interpreted as an algorithm for fully constructing a tree-level S-matrix, and
that complex factorization of general BCFW amplitudes follows from the
factorization of four-particle amplitudes. The allowed set of BCFW deformations
is identified, formulated entirely as a statement on the three-particle sector,
and using only complex factorization as a guide. Consequently, our analysis
based on the physical consistency of the S-matrix is entirely independent of
field theory. We analyze the case of pure Yang-Mills, and outline a proof for
gravity. For Yang-Mills, we also show that the well-known scaling behavior of
BCFW-deformed amplitudes at large z is a simple consequence of factorization.
For gravity, factorization in certain channels requires asymptotic behavior
~1/z^2.Comment: 35 pages, 6 figure
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