819 research outputs found
One-Loop Matching for Parton Distributions: Non-Singlet Case
We derive one-loop matching condition for non-singlet quark distributions in
transverse-momentum cut-off scheme, including unpolarized, helicity and
transversity distributions. The matching is between the quasi-distribution
defined by static correlation at finite nucleon momentum and the light-cone
distribution measurable in experiments. The result is useful for extracting the
latter from the former in a lattice QCD calculation.Comment: 10 pages, 1 figur
Spin Decomposition of Electron in QED
We perform a systematic study on the spin decomposition of an electron in QED
at one-loop order. It is found that the electron orbital angular momentum
defined in Jaffe-Manohar and Ji spin sum rules agrees with each other, and the
so-called potential angular momentum vanishes at this order. The calculations
are performed in both dimensional regularization and Pauli-Villars
regularization for the ultraviolet divergences, and they lead to consistent
results. We further investigate the calculations in terms of light-front wave
functions, and find a missing contribution from the instantaneous interaction
in light-front quantization. This clarifies the confusing issues raised
recently in the literature on the spin decomposition of an electron, and will
help to consolidate the spin physics program for nucleons in QCD.Comment: 8 page
Factorization Theorem Relating Euclidean and Light-Cone Parton Distributions
In a large-momentum nucleon state, the matrix element of a gauge-invariant
Euclidean Wilson line operator accessible from lattice QCD can be related to
the standard light-cone parton distribution function through the large-momentum
effective theory (LaMET) expansion. This relation is given by a factorization
theorem with a non-trivial matching coefficient. Using the operator product
expansion we prove the large-momentum factorization of the quasi-parton
distribution function in LaMET, and show that the more recently discussed
Ioffe-time distribution approach also obeys an equivalent factorization
theorem. Explicit results for the coefficients are obtained and compared at
one-loop. Our proof clearly demonstrates that the matching coefficients in the
scheme depend on the large partonic momentum rather than
the nucleon momentum.Comment: 19 pages, 4 figure
Proton spin after 30 years: what we know and what we don't?
More than three decades has passed since the European Muon Collaboration
published the first surprising result on the spin structure of the proton. Much
theoretical and experimental progress has been made in understanding the
origins of the proton spin. In this review, we will discuss what we have
learned so far, what are still missing, and what we shall expect to learn from
the upcoming experiments including JLab 12 GeV and Electron-Ion Collider. In
particular, we focus on first principles calculations and experimental
measurements of the total gluon helicity , and quark and gluon
orbital angular momenta.Comment: 17 pages, 4 figures, to appear in Nature Revie
Gluon Helicity Delta G from a Universality Class of Operators on a Lattice
We show that the total gluon helicity in a polarized nucleon can
be calculated on a Euclidean lattice through a universality class of QCD
operators that describe the helicity or polarization of the onshell gluon
radiation. We in particular find some operators whose matrix elements in a
nucleon of momentum are directly related to with only
power-law corrections.Comment: 11 page
Comparison and Design Optimization of a Five-Phase Flux-Switching PM Machine for In-Wheel Traction Applications
A comparative study of five-phase outer-rotor flux-switching permanent magnet (FSPM) machines with different topologies for in-wheel traction applications is presented in this paper. Those topologies include double-layer winding, single-layer winding, C-core, and E-core configurations. The electromagnetic performance in the low-speed region, the flux-weakening capability in the high-speed region, and the fault-tolerance capability are all investigated in detail. The results indicate that the E-core FSPM machine has performance advantages. Furthermore, two kinds of E-core FSPM machines with different stator and rotor pole combinations are optimized, respectively. In order to reduce the computational burden during the large-scale optimization process, a mathematical technique is developed based on the concept of computationally efficient finite-element analysis. While a differential evolution algorithm serves as a global search engine to target optimized designs. Subsequently, multiobjective tradeoffs are presented based on a Pareto-set for 20 000 candidate designs. Finally, an optimal design is prototyped, and some experimental results are given to confirm the validity of the simulation results in this paper
NATURE OF THE LATE CARBONIFEROUS TO TRIASSIC MAGMATISM ALONG THE NORTHERN MARGIN OF THE NORTH CHINA BLOCK: LINK WITH THE EVOLUTION OF THE CENTRAL ASIAN OROGEN
There are two episodes of magmatism along the northern margin of the North China block during the Late Carboniferous to Late Triassic, one at 310–250 Ma (Late Carboniferous to Permian) and the other at 235–210 Ma (Late Triassic). The former group comprises plutonic rocks (gabbro-diorite-monzodioritemonzogranite-granite), mafic to intermediate dykes (diorite to dolerite) and a few felsic volcanics (andesite to dacite).There are two episodes of magmatism along the northern margin of the North China block during the Late Carboniferous to Late Triassic, one at 310–250 Ma (Late Carboniferous to Permian) and the other at 235–210 Ma (Late Triassic). The former group comprises plutonic rocks (gabbro-diorite-monzodioritemonzogranite-granite), mafic to intermediate dykes (diorite to dolerite) and a few felsic volcanics (andesite to dacite)
- …