2,806 research outputs found
Studying the molecule in the Bethe-Salpeter equation approach
We study the possible bound states of the system in the Bethe-Salpeter
(BS) formalism in the ladder and instantaneous approximations. By solving the
BS equation numerically with the kernel containing one-particle exchange
diagrams and introducing three different form factors (monopole, dipole, and
exponential form factors) at the vertices, we investigate whether the isoscalar
and isovector bound states may exist, respectively. We find that
could be accommodated as a molecule, whereas the
interpretation of as a molecule is disfavored. The bottom
analog of may exist but that of does not.Comment: 17 pages, 6 figures, and 4 table
Can the tension be resolved in extensions to CDM cosmology?
We wish to investigate whether there is an extension to the base CDM
cosmology that can resolve the tension between the Planck observation of the
cosmic microwave background anisotropies and the local measurement of the
Hubble constant. We consider various plausible extended models in this work,
and we use the Planck 2015 observation, combined with the baryon acoustic
oscillation data, the JLA type Ia supernovae data, and the local measurement of
the Hubble constant (by Riess et al. in 2016), to make an analysis. We find
that the holographic dark energy plus sterile neutrino model can reduce the
tension to be at the 1.11 level, but this model is obviously not
favored by the current observations. Among these extended models, the
CDM+ model is most favored by the current observations,
and this model can reduce the tension to be at the 1.87 level. By a
careful test, we conclude that none of these extended models can convincingly
resolve the tension.Comment: 10 pages, 1 figur
Exploring neutrino mass and mass hierarchy in the scenario of vacuum energy interacting with cold dark matter
We investigate the constraints on total neutrino mass in the scenario of
vacuum energy interacting with cold dark matter. We focus on two typical
interaction forms, i.e., and .
To avoid the occurrence of large-scale instability in interacting dark energy
cosmology, we adopt the parameterized post-Friedmann approach to calculate the
perturbation evolution of dark energy. We employ observational data, including
the Planck cosmic microwave background temperature and polarization data,
baryon acoustic oscillation data, a JLA sample of type Ia supernovae
observation, direct measurement of the Hubble constant, and redshift space
distortion data. We find that, compared with those in the CDM model,
much looser constraints on are obtained in the model, whereas slightly tighter constraints are obtained in the
model. Consideration of the possible mass hierarchies
of neutrinos reveals that the smallest upper limit of appears in
the degenerate hierarchy case. By comparing the values of ,
we find that the normal hierarchy case is favored over the inverted one. In
particular, we find that the difference in the
model. In addition, we find that is consistent with the current
observations in the model, and is favored
at more than the level in the model.Comment: 10 pages, 4 figure
Studying the bound state of the system in the Bethe-Salpeter formalism
In this work, we study the molecule in the Bethe-Salpeter (BS)
equation approach. With the kernel containing one-particle-exchange diagrams
and introducing two different form factors (monopole form factor and dipole
form factor) in the vertex, we solve the BS equation numerically in the
covariant instantaneous approximation. We investigate the isoscalar and
isovector systems, and we find cannot be a
molecule
Three-dimensional topological insulators in the octahedron-decorated cubic lattice
We investigate a tight-binding model of the octahedron-decorated cubic
lattice with spin-orbit coupling. We calculate the band structure of the
lattice and evaluate the Z_2 topological indices. According to the Z_2
topological indices and the band structure, we present the phase diagrams of
the lattice with different filling fractions. We find that the and
strong topological insulators occur in some range of parameters at
1/6, 1/2 and 2/3 filling fractions. Additionally, the weak
topological insulator is found at 1/6 and 2/3 filing fractions. We analyze and
discuss the characteristics of these topological insulators and their surfaces
states
Constraints on brane inflation after Planck 2015: Impacts of the latest local measurement of the Hubble constant
We investigate the observational constraints on three typical brane inflation
models by considering the latest local measurement of the Hubble constant in
the global fit. We also employ other observational data, including the Planck
2015 CMB data, the BICEP2/Keck Array B-mode data, and the baryon acoustic
oscillations data, in our analysis. Previous studies have shown that the
addition of the latest local measurement favors a larger spectral
index, and can exert a significant influence on the model selection of
inflation. In this work, we investigate its impacts on the status of brane
inflation models. We find that, when the direct measurement is
considered, the prototype model of brane inflation is still in good agreement
with the current observational data within the level range. For the
KKLMMT model, the consideration of the measurement allows the range of
the parameter to be amplified to , which slightly
alleviates the fine-tuning problem. For the IR DBI model, the addition of the
measurement does not provide a better fit. These results show that the
consideration of the new prior can exert a considerable influence on
the brane inflation models. At last, we show that, when ,
the equilateral non-Gaussianity in the IR DBI inflation model is compatible
with the current CMB data at the 1 level.Comment: 9 pages, 4 figure
X(3872) as a molecular state in the Bethe-Salpeter equation approach
We discuss the possibility that the X(3872) can be a molecular
bound state in the Bethe-Salpeter equation approach in the ladder and
instantaneous approximations. We show that the bound state with
quantum numbers exists. We also calculate the decay width of
channel and compare our result with those
from previous calculations.Comment: 18pages,4 figure
Study of localized violation in and the branching ratio of in the QCD factorization approach
In this work, within the QCD factorization approach, we study the localized
integrated violation in the decay and the
branching fraction of the decay. Both the resonance
and nonresonance contributions are included when we study the localized
asymmetry in the decay. The resonance
contributions from the scalar and vector mesons are
included. For the meson, we apply both the Breit-Wigner and Bugg
models to deal with its propagator, and obtain and in these two models, respectively. We
find that there is no allowed divergence parameters and to
satisfy the experimental data
in the region
and
and the upper limit of
in the Breit-Wigner model,
however, there exists the region and satisfying the data for and
the upper limit of in the Bugg
model. This reveals that the Bugg model is more plausible than the Breit-Wigner
model to describe the propagator of the meson even though the
finite width effects are considered in both models. The large values of
indicate that the contributions from weak annihilation and hard
spectator scattering processes are both large, especially, the weak
annihilation contribution should not be negleted for decays to final states
including a scalar meson.Comment: arXiv admin note: substantial text overlap with arXiv:1811.0216
When coding meets ranking: A joint framework based on local learning
Sparse coding, which represents a data point as a sparse reconstruction code
with regard to a dictionary, has been a popular data representation method.
Meanwhile, in database retrieval problems, learning the ranking scores from
data points plays an important role. Up to now, these two problems have always
been considered separately, assuming that data coding and ranking are two
independent and irrelevant problems. However, is there any internal
relationship between sparse coding and ranking score learning? If yes, how to
explore and make use of this internal relationship? In this paper, we try to
answer these questions by developing the first joint sparse coding and ranking
score learning algorithm. To explore the local distribution in the sparse code
space, and also to bridge coding and ranking problems, we assume that in the
neighborhood of each data point, the ranking scores can be approximated from
the corresponding sparse codes by a local linear function. By considering the
local approximation error of ranking scores, the reconstruction error and
sparsity of sparse coding, and the query information provided by the user, we
construct a unified objective function for learning of sparse codes, the
dictionary and ranking scores. We further develop an iterative algorithm to
solve this optimization problem
Quantum theory of photonic crystals
In this paper, we have firstly presented a new quantum theory to study
one-dimensional photonic crystals. We give the quantum transform matrix,
quantum dispersion relation and quantum transmissivity, and compare them with
the classical dispersion relation and classical transmissivity. By the
calculation, we find the classical and quantum dispersion relation and
transmissivity are identical. The new approach can be studied two-dimensional
and three-dimensional photonic crystals
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