37,667 research outputs found
Explicit High-Order Gauge-Independent Symplectic Algorithms for Relativistic Charged Particle Dynamics
Symplectic schemes are powerful methods for numerically integrating
Hamiltonian systems, and their long-term accuracy and fidelity have been proved
both theoretically and numerically. However direct applications of standard
symplectic schemes to relativistic charged particle dynamics result in implicit
and electromagnetic gauge-dependent algorithms. In the present study, we
develop explicit high-order gauge-independent noncanonical symplectic
algorithms for relativistic charged particle dynamics using a Hamiltonian
splitting method in the 8D phase space. It also shown that the developed
algorithms can be derived as variational integrators by appropriately
discretizing the action of the dynamics. Numerical examples are presented to
verify the excellent long-term behavior of the algorithms.Comment: 8 figure
Structure-preserving geometric particle-in-cell algorithm suppresses finite-grid instability -- Comment on "Finite grid instability and spectral fidelity of the electrostatic Particle-In-Cell algorithm'' by Huang et al
A recent paper by Huang et al. [Computer Physics Communications 207, 123
(2016)] thoroughly analyzed the Finite Grid Instability(FGI) and spectral
fidelity of standard Particle-In-Cell (PIC) methods. Numerical experiments were
carried out to demonstrate the FGIs for two PIC methods, the energy-conserving
algorithm and the momentum-conserving algorithm. The paper also suggested that
similar numerical experiments should be performed to test the newly developed
Structure-Preserving Geometric (SPG)-PIC algorithm. In this comment, we supply
the results of the suggested numerical experiments, which show that the SPG-PIC
algorithm is able to suppress the FGI
Signature of heavy sterile neutrinos at CEPC
We study the production of heavy sterile neutrino , , at the Circular Electron Positron Collider(CEPC) and its
signal in its decay to three charged fermions. We study background events
for this process which are mainly events coming from W pair production. We
study the production of a single heavy sterile neutrino and the sensitivity of
CEPC to the mixing of sterile neutrino with active neutrinos. We study the
production of two degenerate heavy sterile neutrinos in a low energy see-saw
model by taking into account the constraints on mixings of sterile neutrinos
from the neutrino-less double decay experiment and the masses and
mixings of active neutrinos. We show that CEPC under proposal has a good
sensitivity to the mixing of sterile neutrinos with active neutrinos for a mass
of sterile neutrino around 100 GeV.Comment: 24 pages, 11 figures, 1 table, published versio
Dynamical gap generation in 2D Dirac semimetal with deformed Dirac cone
According to the extensive theoretical and experimental investigations, it is
widely accepted that the long-range Coulomb interaction is too weak to generate
a dynamical excitonic gap in graphene with a perfect Dirac cone. We study the
impact of the deformation of Dirac cone on dynamical gap generation. When a
uniaxial strain is applied to graphene, the Dirac cone is made elliptical in
the equal-energy plane and the fermion velocity becomes anisotropic. The
applied uniaxial strain has two effects: it decreases the fermion velocity; it
increases the velocity anisotropy. After solving the Dyson-Schwinger gap
equation, we show that dynamical gap generation is promoted by the former
effect, but is suppressed by the latter one. For suspended graphene, we find
that the systems undergoes an excitonic insulating transition when the strain
is roughly 7.34. We also solve the gap equation in case the Dirac cone is
tiled, which might be realized in the organic material
-(BEDT-TTF)I, and find that the tilt of Dirac cone can
suppress dynamical gap generation. It turns out that the geometry of the Dirac
cone plays an important role in the formation of excitonic pairing.Comment: 11 pages,11 figure
Charged lepton flavor violation on target at GeV scale
We study the lepton flavor violating process, , at a few
GeV. This process can be studied by experiments directing GeV scale electron or
positron beams on internal or fixed targets. We study the effects of some low
energy lepton flavor violating interactions on this process. We study the
sensitivities of this process on these low energy lepton flavor violating
interactions and compare them to the sensitivities of lepton flavor violating
decay processes. Comparing with decay processes, this process
provides another way to study the lepton flavor violating effects with
conversion and it can be searched for in facilities with GeV scale electron or
positron beams which are available in a number of laboratories in the world.Comment: 22 pages, 4 figure
Mid-to-Far Infrared Spectral Energy Distribution of Galaxies in Spitzer First Look Survey Field
We made model fitting to the mid-to-far infrared spectral energy
distributions (SEDs) for different categories of galaxies in the main
extragalactic field of the {\it Spitzer} First Look Survey with the aid of
spectroscopic information from the Sloan Digital Sky Survey. We find that the
mid-to-far infrared SEDs of HII galaxies, mixture type galaxies and LINERs can
be well fitted by the one-parameter () dust model of Dale et al. plus
the 13 Gyr dust-free elliptical galaxy model. The statistics of values
indicates that all these galaxies tend to be quiescent, although the HII
galaxies are relatively more active than the LINERs. The mid-infrared SEDs of
absorption galaxies are well fitted simply by the 13 Gyr dust-free elliptical
galaxy template, and the near-to-mid infrared SEDs of QSOs can be represented
by AGN NGC 5506.Comment: 12 pages with 8 figures, will be appeared in ChJAA, Vol.7 (2007),
No.
Canonical Form and Separability of PPT States on Multiple Quantum Spaces
By using the "subtracting projectors" method in proving the separability of
PPT states on multiple quantum spaces, we derive a canonical form of PPT states
in {\Cb}^{K_1} \otimes {\Cb}^{K_2} \otimes ... \otimes {\Cb}^{K_m} \otimes
{\Cb}^N composite quantum systems with rank , from which a sufficient
separability condition for these states is presented.Comment: 5 page
PT-symmetry entails pseudo-Hermiticity regardless of diagonalizability
We prove that in finite dimensions, a Parity-Time (PT)-symmetric Hamiltonian
is necessarily pseudo-Hermitian regardless of whether it is diagonalizable or
not. This result is different from Mostafazadeh's, which requires the
Hamiltonian to be diagonalizable. PT-symmetry breaking often occurs at
exceptional points where the Hamiltonian is not diagonalizable. Our result
implies that PT-symmetry breaking is equivalent to the onset of instabilities
of pseudo-Hermitian systems, which was systematically studied by Krein et al.
in 1950s. In particular, we show that the mechanism of PT-symmetry breaking is
the resonance between eigenmodes with different Krein signatures.Comment: 11pages, 1 figure. arXiv admin note: text overlap with
arXiv:1801.0167
Synchrotron spectrum of fast cooling electrons in GRBs
We discuss the synchrotron emission of fast cooling electrons in shocks. The
fast cooling electrons behind the shocks can generate a position-dependent
inhomogeneous electron distribution if they do not have enough time to mix
homogeneously. This would lead to a very different synchrotron spectrum in
low-frequency bands to that in the homogeneous case due to the synchrotron
absorption. In this paper, we calculate the synchrotron spectrum in the
inhomogeneous case in a gamma-ray burst (GRB). Both the forward shock and the
reverse shock are considered. We find for the reverse shock dominated case, we
would expect a "reverse shock bump" in the low-frequency spectrum. The spectral
bump is due to the combination synchrotron absorption in both the forward and
reverse shock regions. In the forward shock spectrum in the low frequencies has
two unconventional segments with spectral slopes of and . The
slope of has been found by some authors, while the slope of
is new, which is due to the approximately constant electron temperature in the
optically thick region. In the future, simultaneous observations in multiple
bands (especially in the low frequency bands) in the GRB early afterglow or
prompt emission phases will possibly reveal these spectral characteristics and
enable us to identify the reverse shock component and distinguish between the
forward and reverse shock emissions. This also may be a method with which to
diagnose the electron distribution status (homogeneous or inhomogeneous) after
fast cooling in the relativistic shock region.Comment: Published in ApJ, 839, 74 (7pp), 2017, Apri
Double Electromagnetically Induced Transparency in a Tripod-type Atom System
The electromagnetically induced transparency (EIT) phenomenon in a four level
atomic system with tripod configuration is studied. The results show that this
configuration is equivalent to the combination of two single three-level
configurations, which, under certain conditions, results in the
so-called double-EIT (DEIT) phenomenon. The properties of the double
transparency windows for DEIT are discussed in detail and the possible
experimental scheme is proposed.Comment: 5 pages, and 8 figure
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