310,347 research outputs found
Possible signatures for tetraquarks from the decays of ,
Based on the recent proposal for the tetraquarks with the mixing scheme, we
investigate fall-apart decays of into two lowest-lying
mesons. This mixing scheme suggests that and are the
tetraquarks with the mixtures of two spin configurations of diquark and
antidiquark. Due to the relative sign differences in the mixtures, the
couplings of fall-apart decays into two mesons are strongly enhanced for
but suppressed for . We report that this expectation is
supported by their experimental decays. In particular, the ratios of the
associated partial decay widths, which depend on some kinematical factors and
the couplings, are found to be around , , which seems to agree with the experimental ratios reasonably well.
This agreement can be interpreted as the tetraquark signatures for .Comment: 6 pages, no figures, more references are added, the version to be
published in EPJ
Z_{12-I} Orbifold Compactification toward SUSY Standard Model
We explain the orbifold compactification in string models and present a
Z_{12-I} orbifold compactification toward supersymmetric standard models. We
also point out an effective R-parity from this string construction. The VEVs of
gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at
LHC", Cairo, 11-14 March 200
Effective Action for the Scalar Field Theory with Higher Vertices
We derive a new kind of recursion relation to obtain the
one-particle-irreducible (1PI) Feynman diagrams for the effective action. By
using this method, we have obtained the graphical representation of the
four-loop effective action in case of the general bosonic field theory which
have vertices higher than the four-point vertex
20 K superconductivity in heavily electron doped surface layer of FeSe bulk crystal
A superconducting transition temperature Tc as high as 100 K was recently
discovered in 1 monolayer (1ML) FeSe grown on SrTiO3 (STO). The discovery
immediately ignited efforts to identify the mechanism for the dramatically
enhanced Tc from its bulk value of 7 K. Currently, there are two main views on
the origin of the enhanced Tc; in the first view, the enhancement comes from an
interfacial effect while in the other it is from excess electrons with strong
correlation strength. The issue is controversial and there are evidences that
support each view. Finding the origin of the Tc enhancement could be the key to
achieving even higher Tc and to identifying the microscopic mechanism for the
superconductivity in iron-based materials. Here, we report the observation of
20 K superconductivity in the electron doped surface layer of FeSe. The
electronic state of the surface layer possesses all the key spectroscopic
aspects of the 1ML FeSe on STO. Without any interface effect, the surface layer
state is found to have a moderate Tc of 20 K with a smaller gap opening of 4
meV. Our results clearly show that excess electrons with strong correlation
strength alone cannot induce the maximum Tc, which in turn strongly suggests
need for an interfacial effect to reach the enhanced Tc found in 1ML FeSe/STO.Comment: 5 pages, 4 figure
Minimax bounds for estimation of normal mixtures
This paper deals with minimax rates of convergence for estimation of density
functions on the real line. The densities are assumed to be location mixtures
of normals, a global regularity requirement that creates subtle difficulties
for the application of standard minimax lower bound methods. Using novel
Fourier and Hermite polynomial techniques, we determine the minimax optimal
rate - slightly larger than the parametric rate - under squared error loss. For
Hellinger loss, we provide a minimax lower bound using ideas modified from the
squared error loss case.Comment: Published in at http://dx.doi.org/10.3150/13-BEJ542 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Compositional changes on GaN surfaces under low-energy ion bombardment studied by synchrotron-based spectroscopies
We have investigated compositional changes on GaNsurfaces under Ar-ion bombardment using synchrotron-based high-resolution x-rayphotoemission (PES) and near-edge x-ray absorption fine structure(NEXAFS)spectroscopy. The low-energy ion bombardment of GaN produces a Ga-rich surface layer which transforms into a metallic Ga layer at higher bombarding energies. At the same time, the photoemissionspectra around N 1s core levels reveal the presence of both uncoordinated nitrogen and nitrogen interstitials, which we have analyzed in more details by x-rayabsorption measurements at N K edge. We have demonstrated that PES and NEXAFS provide a powerful combination for studying the compositional changes on GaNsurfaces. A mechanism for the relocation and loss of nitrogen during ion bombardment in agreement with some recent experimental and theoretical studies of defect formation in GaN has been proposed.P.N.K.D. is grateful for the financial
support of the Australian Research Council
New identities involving q-Euler polynomials of higher order
In this paper we give new identities involving q-Euler polynomials of higher
order.Comment: 11 page
Is Lavelle-McMullan transformation a really new symmetry in QED?
Lavelle-McMullan symmetry of QED is examined at classical and quantum levels.
It is shown that Lavelle-McMullan symmetry does not give any new non-trivial
information in QED by examining the Ward-Takahashi identities. Being inspired
by the examination of Ward-Takahashi identity, we construct the generalized
non-local and non-covariant symmetries of QED.Comment: LATEX, 9 pages, two figures generated by Feynma
- …