221 research outputs found
Generalized form factors of the nucleon in a light-cone spectator-diquark model
We investigate the generalized form factors of the nucleon in a light-cone
spectator-diquark model. Compared to the form factors, the generalized form
factors contain some more information of the structure of the nucleon. In our
calculation, both the scalar and the axial-vector spectator-diquark are taken
into account. As a relation between the spin in the instant form and that in
the light-cone form, the Melosh-Wigner rotation effect is included for both the
quark and the axial-vector diquark. We also provide numerical results from our
model calculations, and the results are comparable with those from lattice QCD.Comment: 19 latex pages, 6 figure
Quark angular momentum in a spectator model
We investigate the quark angular momentum in a model with the nucleon being a
quark and a spectator. Both scalar and axial-vector spectators are included. We
perform the calculations in the light-cone formalism where the parton concept
is well defined. We calculate the quark helicity and canonical orbital angular
momentum. Then we calculate the gravitational form factors which are often
related to the kinetic angular momentums, and find that even in a no gauge
field model we cannot identify the canonical angular momentums with half the
sum of gravitational form factors. In addition, we examine the model relation
between the orbital angular momentum and pretzelosity, and find it is violated
in the axial-vector case.Comment: 6 pages, final version to appear in PL
Quark Wigner distributions in a light-cone spectator model
We investigate the quark Wigner distributions in a light-cone spectator
model. The Wigner distribution, as a quasi-distribution function, provides the
most general one-parton information in a hadron. Combining the polarization
configurations, unpolarized, longitudinal polarized or transversal polarized,
of the quark and the proton, we can define 16 independent Wigner distributions
at leading twist. We calculate all these Wigner distributions for the quark
and the quark respectively. In our calculation, both the scalar and the
axial-vector spectators are included, and the Melosh-Wigner rotation effects
for both the quark and the axial-vector spectator are taken into account. The
results provide us a very rich picture of the quark structure in the proton.Comment: 28 pages, 11 figures, version accepted for publication in PR
Present status on experimental search for pentaquarks
It has been ten years since the first report for a positive strangeness
pentaquark-like baryon state. However the existence of the pentaquark state is
still controversial. Some contradictions between the experiments are unsolved.
In this paper we review the experimental search for the pentaquark candidates
, , , and in details. We
review the experiments with positive results and compare the experiments with
similar conditions but opposite results.Comment: 20 latex pages, 2 figures, to appear in IJMPA as a revie
Learning Unmanned Aerial Vehicle Control for Autonomous Target Following
While deep reinforcement learning (RL) methods have achieved unprecedented
successes in a range of challenging problems, their applicability has been
mainly limited to simulation or game domains due to the high sample complexity
of the trial-and-error learning process. However, real-world robotic
applications often need a data-efficient learning process with safety-critical
constraints. In this paper, we consider the challenging problem of learning
unmanned aerial vehicle (UAV) control for tracking a moving target. To acquire
a strategy that combines perception and control, we represent the policy by a
convolutional neural network. We develop a hierarchical approach that combines
a model-free policy gradient method with a conventional feedback
proportional-integral-derivative (PID) controller to enable stable learning
without catastrophic failure. The neural network is trained by a combination of
supervised learning from raw images and reinforcement learning from games of
self-play. We show that the proposed approach can learn a target following
policy in a simulator efficiently and the learned behavior can be successfully
transferred to the DJI quadrotor platform for real-world UAV control
Angular momentum decomposition from a QED example
We investigate the angular momentum decomposition with a quantum
electrodynamics example to clarify the proton spin decomposition debates. We
adopt the light-front formalism where the parton model is well defined. We
prove that the sum of fermion and boson angular momenta is equal to half the
sum of the two gravitational form factors and , as is well known.
However, the suggestion to make a separation of the above relation into the
fermion and boson pieces, as a way to measure the orbital angular momentum of
fermions or bosons, respectively, is not justified from our explicit
calculation.Comment: 5 latex page, version for publication in PR
Complete gradient expanding Ricci solitons with finite asymptotic scalar curvature ratio
Let , , be a complete gradient expanding Ricci soliton
with nonnegative Ricci curvature . In this paper, we show that if the
asymptotic scalar curvature ratio of is finite (i.e., ), then the Riemann curvature tensor must
have at least sub-quadratic decay, namely, for any .Comment: 20 pages. Lemma 3.1 statement simplified; the proof of Lemma 3.2 &
Lemma 3.3 streamlined. arXiv admin note: text overlap with arXiv:2111.0984
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