11,021 research outputs found
Electromagnetic fields, size, and copy of a single photon
Photons are almost involved in each field of science and daily life of
everyone. However, there are still some fundamental and puzzling questions such
as what a photon is.The expressions of electromagnetic fields of a photon are
here proposed. On the basis of the present expressions, we calculate the
energy, momentum, and spin angular momentum of a photon, derive the relations
between the photon size and wavelength, and reveal the differences between a
photon and its copy. The results show that the present expressions properly
describe the particle characteristics of a photon; the length of a photon is
half of the wavelength, and the radius is proportional to square root of the
wavelength; a photon can ionize a hydrogen atom at the ground state only if its
radius is less than the Bohr radius; a photon and its copy have the phase
difference of {\pi} and constitute a phase-entangled photon pair; the
phase-entangled n-photon train results from the sequential stimulated emissions
and belongs to the Fock state. A laser beam is an ensemble of the n-photon
trains and belongs to the coherent state. The threshold power of a laser is
equal to the power of the n-photon train. These provide a bridge between the
wave theory of light and quantum optics and will further advance research and
application of the related fields.Comment: 4 pages, crrected typos, improved some descriptions and reference
Interference and wave-particle duality of single photons
The wave-particle duality has been said to contain the entire mystery of
quantum mechanics. Many delayed-choice experiments have been performed to
further understand the wave-particle duality. Here, we reveal some flaws in the
known interference theories by comparing the theoretical predictions with the
experimental facts and show that the presence of media is a necessary condition
for interference of single photons, a photon interferes with other photon via
microscopic particles in the interface of media, and the wave-like property of
a photon originates from interaction between the photon and media; the particle
property is the inherent characteristic of a photon, and the wave-like behavior
of a photon always accompanies the particle behavior; the coherent time of
single photons cannot be longer than the lifetime of the polarized states of
the microscopic particles. Interference of single photons is interpreted
properly, and the conundrum of the wave-particle duality is well solved.Comment: 4 pages, 2 figures, 19 references. Corrected typos, added references
and arguments, and some descriptions are improve
Constraints on Cardassian universe from Gamma ray bursts
Constraints on the original Cardassian model and the modified polytropic
Cardassian model are examined from the recently derived 42 gamma-ray bursts
(GRBs) data calibrated with the method avoiding the circularity problem. The
results show that GRBs can be an optional observation to constrain on the
Cardassian models. Combining the GRBs data with the newly derived size of
baryonic acoustic oscillation peak from the Sloan Digital Sky Survey (SDSS),
and the position of first acoustic peak of the Cosmic Microwave Background
radiation (CMB) from Wilkinson Microwave Anisotropy Probe (WMAP), we find
() for the
original Cardassian model, and ,
() for the
modified polytropic Cardassian model.Comment: 11 pages, 4 figures, accepted for publication in Science in China
Discovery of -ray emission from the radio-intermediate quasar III Zw 2: violent jet activity with intraday -ray variability
III Zw 2 is the prototype of radio-intermediate quasars. Although there is
the evidence of possessing strong jet, significant -ray emission has
not been reported before. In this work, we carry out a detailed analysis of the
latest {\it Fermi}-LAT {\it Pass} 8 data. No significant -ray signal
has been detected in the time-averaged 7-year {\it Fermi}-LAT data of III Zw 2,
we however have identified two distinct -ray flares with isotropic
luminosities of erg . Multiwavelength data analysis
(including also the optical photometric observations from Yunnan Observatories)
are presented and the main finding is the simultaneous optical and -ray
flares of III Zw 2 appearing in Nov. 2009. Violent -ray variability
with doubling timescale of 2.5 hours was detected in another -ray flare
in May 2010, for which the 3-hour -ray peak flux is times of
the average flux in 7 years. Rather similar behaviors are observed in blazars
and the blazar model can reasonably reproduce the spectral energy distribution
of III Zw 2 in a wide energy range, strongly suggesting that its central engine
resembles that of blazars. In view of its core which shares radio similarities
with young radio sources together with the weak extended radio lobe emission,
we suggest that III Zw 2 harbors a recurrent activity core and serves as a
valuable target for investigating the fuelling and triggering of the activity
in radio loud AGNs.Comment: ApJS in press, welcome any comment
Neutral Higgs production on LHC in the two-Higgs-doublet model with spontaneous violation
Spontaneous CP violation motivates the introduction of two Higgs doublets in
the electroweak theory, such a simple extension of the standard model has five
physical Higgs bosons and rich CP-violating sources. Exploration on more than
one Higgs boson is a direct evidence for new physics beyond the standard model.
The neutral Higgs production at LHC is investigated in such a general two Higgs
doublet model with spontaneous CP violation, it is shown that the production
cross section and decays of the neutral Higgs boson can significantly be
different from the predictions from the standard model.Comment: 15 pages, 12 figures, published version in PR
The center of monoidal 2-categories in 3+1D Dijkgraaf-Witten Theory
In this work, for a finite group and a 4-cocycle , we compute explicitly the center of the monoidal
2-category of -twisted -graded
1-categories of finite dimensional -vector spaces. This center
gives a precise mathematical description of the topological defects in the
associated 3+1D Dijkgraaf-Witten TQFT. We prove that this center is a braided
monoidal 2-category with a trivial sylleptic center.Comment: 24 page
Hidden pseudospin and spin symmetries and their origins in atomic nuclei
Symmetry plays a fundamental role in physics. The quasi-degeneracy between
single-particle orbitals and
indicates a hidden symmetry in atomic nuclei, the so-called pseudospin symmetry
(PSS). Since the introduction of the concept of PSS in atomic nuclei, there
have been comprehensive efforts to understand its origin. Both splittings of
spin doublets and pseudospin doublets play critical roles in the evolution of
magic numbers in exotic nuclei discovered by modern spectroscopic studies with
radioactive ion beam facilities. Since the PSS was recognized as a relativistic
symmetry in 1990s, many special features, including the spin symmetry (SS) for
anti-nucleon, and many new concepts have been introduced. In the present
Review, we focus on the recent progress on the PSS and SS in various systems
and potentials, including extensions of the PSS study from stable to exotic
nuclei, from non-confining to confining potentials, from local to non-local
potentials, from central to tensor potentials, from bound to resonant states,
from nucleon to anti-nucleon spectra, from nucleon to hyperon spectra, and from
spherical to deformed nuclei. Open issues in this field are also discussed in
detail, including the perturbative nature, the supersymmetric representation
with similarity renormalization group, and the puzzle of intruder states.Comment: Review Article, 242 pages, 58 figures, 10 table
Anti-Hyperon polarization in high energy pp collisions with polarized beams
We study the longitudinal polarization of the Sigma_bar and Xi_bar
anti-hyperons in polarized high energy pp collisions at large transverse
momenta, extending a recent study for the Lambda_bar anti-hyperon. We make
predictions by using different parametrizations of the polarized parton
densities and models for the polarized fragmentation functions. Similar to the
Lambda_bar polarization, the Xi_bar0 and Xi_bar+ polarizations are found to be
sensitive to the polarized anti-strange sea in the nucleon. The Sigma_bar- and
Sigma_bar+ polarizations show sensitivity to the light sea quark polarizations,
\Delta \bar u(x) and \Delta \bar d(x), and their asymmetry.Comment: 17 pages, 9 figures,version to appear in PR
TG-GAN: Continuous-time Temporal Graph Generation with Deep Generative Models
The recent deep generative models for static graphs that are now being
actively developed have achieved significant success in areas such as molecule
design. However, many real-world problems involve temporal graphs whose
topology and attribute values evolve dynamically over time, including important
applications such as protein folding, human mobility networks, and social
network growth. As yet, deep generative models for temporal graphs are not yet
well understood and existing techniques for static graphs are not adequate for
temporal graphs since they cannot 1) encode and decode continuously-varying
graph topology chronologically, 2) enforce validity via temporal constraints,
or 3) ensure efficiency for information-lossless temporal resolution. To
address these challenges, we propose a new model, called ``Temporal Graph
Generative Adversarial Network'' (TG-GAN) for continuous-time temporal graph
generation, by modeling the deep generative process for truncated temporal
random walks and their compositions. Specifically, we first propose a novel
temporal graph generator that jointly model truncated edge sequences, time
budgets, and node attributes, with novel activation functions that enforce
temporal validity constraints under recurrent architecture. In addition, a new
temporal graph discriminator is proposed, which combines time and node encoding
operations over a recurrent architecture to distinguish the generated sequences
from the real ones sampled by a newly-developed truncated temporal random walk
sampler. Extensive experiments on both synthetic and real-world datasets
demonstrate TG-GAN significantly outperforms the comparison methods in
efficiency and effectiveness
Acoustic imaging and collimating by slabs of sonic crystals made from arrays of rigid cylinders in air
We show some new properties of the acoustic propagation in two-dimensional
sonic crystals, formed by parallel rigid cylinders placed in air. The
transmission through slabs of sonic crystals and the associated band structures
are considered. It is shown that within partial bandgaps, the waves tend to be
collimated or guided into the direction in which the propagation is allowed.
Such a feature also prevails in the situations in which deaf bands appear. We
show that within the partial bandgaps, a stable imaging effect can be obtained
for flat sonic crystal slabs, in analogy to the cases with photonic crystals.Comment: 11 pages, 5 figure
- β¦