44,538 research outputs found
Density-functional investigation of rhombohedral stacks of graphene: topological surface states, nonlinear dielectric response, and bulk limit
A DFT-based investigation of rhombohedral (ABC)-type graphene stacks in
finite static electric fields is presented. Electronic band structures and
field-induced charge densities are compared with related literature data as
well as with own results on (AB) stacks. It is found, that the undoped
AB-bilayer has a tiny Fermi line consisting of one electron pocket around the
K-point and one hole pocket on the line K-. In contrast to (AB) stacks,
the breaking of translational symmetry by the surface of finite (ABC) stacks
produces a gap in the bulk-like states for slabs up to a yet unknown critical
thickness , while ideal (ABC) bulk (-graphite)
is a semi-metal. Unlike in (AB) stacks, the ground state of (ABC) stacks is
shown to be topologically non-trivial in the absence of external electric
field. Consequently, surface states crossing the Fermi level must unavoidably
exist in the case of (ABC)-type stacking, which is not the case in (AB)-type
stacks. These surface states in conjunction with the mentioned gap in the
bulk-like states have two major implications. First, electronic transport
parallel to the slab is confined to a surface region up to the critical layer
number . Related implications are expected for stacking domain
walls and grain boundaries. Second, the electronic properties of (ABC) stacks
are highly tunable by an external electric field. In particular, the dielectric
response is found to be strongly nonlinear and can e.g. be used to discriminate
slabs with different layer numbers. Thus, (ABC) stacks rather than (AB) stacks
with more than two layers should be of potential interest for applications
relying on the tunability by an electric field.Comment: 36 pages, 17 figure
Partition Function Expansion on Region-Graphs and Message-Passing Equations
Disordered and frustrated graphical systems are ubiquitous in physics,
biology, and information science. For models on complete graphs or random
graphs, deep understanding has been achieved through the mean-field replica and
cavity methods. But finite-dimensional `real' systems persist to be very
challenging because of the abundance of short loops and strong local
correlations. A statistical mechanics theory is constructed in this paper for
finite-dimensional models based on the mathematical framework of partition
function expansion and the concept of region-graphs. Rigorous expressions for
the free energy and grand free energy are derived. Message-passing equations on
the region-graph, such as belief-propagation and survey-propagation, are also
derived rigorously.Comment: 10 pages including two figures. New theoretical and numerical results
added. Will be published by JSTAT as a lette
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
Constraining supersymmetry from the satellite experiments
In this paper we study the detectability of -rays from dark matter
annihilation in the subhalos of the Milky Way by the satellite-based
experiments, EGRET and GLAST. We work in the frame of supersymmetric extension
of the standard model and assume the lightest neutralino being the dark matter
particles. Based on the N-body simulation of the evolution of dark matter
subhalos we first calculate the average intensity distribution of this new
class of -ray sources by neutralino annihilation. It is possible to
detect these -ray sources by EGRET and GLAST. Conversely, if these
sources are not detected the nature of the dark matter particls will be
constrained by these experiments, which, however, depending on the
uncertainties of the subhalo profile.Comment: 19 pages, 5 gigures; references added, more discussions adde
, and molecules
We investigate theoretically baryon systems made of three hadrons which
contain one nucleon and one D meson, and in addition another meson, or . The systems are studied using the Fixed Center Approximation
to the Faddeev equations. The study is made assuming scattering of a or a
on a cluster, which is known to generate the ,
or the scattering of a nucleon on the cluster, which has been shown
to generate a hidden charm resonance named X(3700). We also investigate the
configuration of scattering of on the cluster, which is known to
generate the . In all cases we find bound states, with the
system, of exotic nature, more bound than the .Comment: 9 figure
The unified Skyrmion profiles and Static Properties of Nucleons
An unified approximated solution for symmetric Skyrmions was proposed for the
SU(2) Skyrme model for baryon numbers up to 8,which take the hybrid form of a
kink-like solution and that given by the instanton method. The Skyrmion
profiles are examined by computing lowest soliton energy as well as the static
properties of nucleons within the framework of collective quantization, with a
good agreement with the exact numeric results. The comparisons with the
previous computations as well as the experimental data are also given.Comment: 6 pages, 3 figures, 3 tables, Created by LaTex Syste
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