9,186 research outputs found
A variant of the Brillouin-Wigner perturbation theory with Epstein-Nesbet partitioning
We present an elementary pedagogical derivation of the Brillouin-Wigner and
the Rayleigh-Schr\"odinger perturbation theories with Epstein-Nesbet
partitioning. A variant of the Brillouin-Wigner perturbation theory is also
introduced, which can be easily extended to the quasi-degenerate case. A main
advantage of the new theory is that the computing time required for obtaining
the successive higher-order results is negligible after the third-order
calculation. We illustrate the accuracy of the new perturbation theory for some
simple model systems like the perturbed harmonic oscillator and the particle in
a box.Comment: 15 page
The doubly virtual transition form factors in the light-front quark model
We report our investigation on the doubly virtual TFFs for the transitions using the light-front quark model (LFQM).
Performing a LF calculation in the exactly solvable manifestly covariant
Bethe-Salpeter (BS) model as the first illustration, we used frame
and found that both LF and manifestly covariant calculations produce exactly
the same results for . This confirms the
absence of the LF zero mode in the doubly virtual TFFs. We then mapped this
covariant BS model to the standard LFQM using the more phenomenologically
accessible Gaussian wave function provided by the LFQM analysis of meson mass
spectra. For the numerical analyses of , we
compared our LFQM results with the available experimental data and the
perturbative QCD (pQCD) and the vector meson dominance (VMD) model predictions.
As , our LFQM result for doubly virtual TFF is
consistent with the pQCD prediction, i.e. , while it differs far from the result of VMD
model which behaves . Our LFQM prediction for shows an
agreement with the very recent experimental data obtained from the BaBar
collaboration for the ranges of GeV.Comment: 7 pages, 6 figures. Slight change of title, Correct some typos;
version to appear in Phys. Rev.D. arXiv admin note: substantial text overlap
with arXiv:1708.0073
Systematic twist expansion of transition form factors in light-front quark model
The light-front quark model analysis of the meson-photon transition form
factor amenable both for the spacelike region ()
and the timelike region () provides a systematic twist expansion of
for the high region. Investigating for the entire kinematic regions of , we
examine the twist-2 and twist-3 distribution amplitudes of
mesons in the light-front quark model and quantify their contributions to . Our numerical results for the normalized
transition form factor
and the decay
width are compared with the available
data checking the sensitivity of our model to the variation of the constituent
quark masses.Comment: 9 pages, 6 figures, Version to appear in Phys.Rev. D. arXiv admin
note: text overlap with arXiv:1708.0073
Spacelike and timelike form factors for the transitions in the light-front quark model
We investigate the transitions both for
the spacelike region and the timelike region using the light-front quark model
(LFQM). In particular, we present the new direct method to explore the timelike
region without resorting to mere analytic continuation from the spacelike
region to the timelike region. Our direct calculation in timelike region shows
the complete agreement not only with the analytic continuation result from the
spacelike region but also with the result from the dispersion relation between
the real and imaginary parts of the form factor. For the low energy regime, we
compare our LFQM results of the transition form factors (TFFs) for the low
timelike momentum transfer region and the slope parameters at with the
recent experimental data from the Dalitz decays of . For
the high energy regime, we incorporate the QCD factorization in our LFQM to
examine the asymptotic behavior of TFFs both for the spacelike region and the
timelike region. We compare our results with the available experimental data.Comment: 13 pages, 7 figures, changed the title and corrected typ
Variational Analysis of Mass Spectra and Decay Constants for Ground State Pseudoscalar and Vector Mesons in Light-Front Quark Model
Using the variational principle, we compute mass spectra and decay constants
of ground state pseudoscalar and vector mesons in the light-front quark model
(LFQM) with the QCD-motivated effective Hamiltonian including the hyperfine
interaction. By smearing out the Dirac delta function in the hyperfine
interaction, we avoid the issue of negative infinity in applying the
variational principle to the computation of meson mass spectra and provide
analytic expressions for the meson mass spectra. Our analysis with the smeared
hyperfine interaction indicates that the interaction for the heavy meson sector
including the bottom and charm quarks gets more point-like. We also consider
the flavor mixing effect in our analysis and determine the mixing angles from
the mass spectra of and . Our variational
analysis with the trial wave function including the two lowest order harmonic
oscillator basis functions appears to improve the agreement with the data of
meson decay constants and the heavy meson mass spectra over the previous
computation handling the hyperfine interaction as perturbation.Comment: 5 figures. Added the flavor mixing effect in our analysis and
determine the mixing angles from the mass spectra of (\omega,\phi) and
(\eta,\eta'). Improved the fitting for the hyperfine splitting in heavy
mesons. arXiv admin note: text overlap with arXiv:1206.335
Consistent Community Identification in Complex Networks
We have found that known community identification algorithms produce
inconsistent communities when the node ordering changes at input. We propose
two metrics to quantify the level of consistency across multiple runs of an
algorithm: pairwise membership probability and consistency. Based on these two
metrics, we address the consistency problem without compromising the
modularity. Our solution uses pairwise membership probabilities as link weights
and generates consistent communities within six or fewer cycles. It offers a
new tool in the study of community structures and their evolutions.Comment: 4 pages, 4 figure
General Geometric Fluctuation Modeling for Device Variability Analysis
The authors propose a new modeling approach based on the impedance field
method (IFM) to analyze the general geometric variations in device simulations.
Compared with the direct modeling of multiple variational devices, the proposed
geometric variation (GV) model shows a better efficiency thanks to its IFM
based nature. Compared with the existing random geometric fluctuation (RGF)
model where the noise sources are limited to the interfaces, the present GV
model provides better accuracy and wider application areas as it transforms the
geometric variation into global mesh deformation and computes the noise sources
induced by the geometric variation in the whole simulation domain. GV model
also provides great insights into the device by providing the effective noise
sources, equation-wise contributions, and sensitivity maps that are useful for
device characterization and optimization
Hybridized/Coupled Multiple Resonances in Nacre
We report that nacre (also known as mother-of-pearl), a wondrous
nanocomposite found in nature, is a rich photonic nanomaterial allowing the
experimental realization of collective excitation and light amplification via
coupled states. Localized modes in three-dimensional complex media are
typically isolated in frequency and space. However, multiple local resonances
can be hybridized in multilayered nanostructures of nacre so that the effective
cavity size for efficient disordered resonators is scaled up. Localized modes
in hybridized states in nacre are overlapped in frequency with similar shapes
in space, thus being collectively excited and synergistically amplified. These
hybridized states boost light amplification, leading to stable and regular
multimode lasing at low excitation energy. The simplicity of ameliorating
disordered resonators by mimicking nacre can further serve as platforms for
developing cost-effective photonic systems and provide materials for
fundamental research on complex mediaComment: 7 pages and 6 figure
Interference effect on Raman spectrum of graphene on SiO_2/Si
The intensity ratio between two major Raman bands in graphene is one of the
most important information for physics of graphene and has been believed to
represent various intrinsic properties of graphene without critical assessment
of extrinsic effects. We report a micro Raman spectroscopy study on the Raman
intensity ratio of the 2D band to the G Raman band of graphene varying the
thickness of dielectric layers (SiO_2) underneath it. The ratio is shown to
change by almost 370% when the thickness is varied by 60%. The large variation
in the ratio is well explained by theoretical calculations considering multiple
Raman scattering events at the interfaces. Our analysis shows that the
interference effect is critical in extracting the intrinsic 2D to G intensity
ratio and therefore must be taken into account in extracting various physical
properties of graphene from Raman measurements.Comment: 21 pages, 5 figures. Phys. Rev. B; in pres
Large Language Models can Share Images, Too!
This paper explores the image-sharing capability of Large Language Models
(LLMs), such as InstructGPT, ChatGPT, and GPT-4, in a zero-shot setting,
without the help of visual foundation models. Inspired by the two-stage process
of image-sharing in human dialogues, we propose a two-stage framework that
allows LLMs to predict potential image-sharing turns and generate related image
descriptions using our effective restriction-based prompt template. With
extensive experiments, we unlock the \textit{image-sharing} capability of LLMs
in zero-shot prompting, with GPT-4 achieving the best performance.
Additionally, we uncover the emergent \textit{image-sharing} ability in
zero-shot prompting, demonstrating the effectiveness of restriction-based
prompts in both stages of our framework. Based on this framework, we augment
the PhotoChat dataset with images generated by Stable Diffusion at predicted
turns, namely PhotoChat++. To our knowledge, this is the first study to assess
the image-sharing ability of LLMs in a zero-shot setting without visual
foundation models. The source code and the dataset will be released after
publication
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