Status on lattice calculations of the proton spin decomposition

Keh Fei Liu

doi:10.1007/s43673-022-00037-4

Status on lattice calculations of the proton spin decomposition

Keh Fei Liu

Research output: Contribution to journal › Review article › peer-review

17 Scopus citations

Abstract

Lattice calculations of the proton spin components is reviewed. The lattice results of the quark spin from the axial-vector current matrix element at ∼ 0.3−0.4 is smaller than those from the constituent quark models. This is largely due to the fact that the vacuum polarization contribution from the disconnected insertion is negative. Its connection with the anomalous Ward identity is clarified and verified numerically. This resolves the contentious issue in the “proton spin crisis.” The glue spin and angular momentum are found to be large and there is notable contribution from the quark orbital angular momentum. Renormalization, mixing, and normalization of the quark and glue angular momenta are discussed. With sufficient precision, they can be compared with more precise experimental measurements when the electron-ion collider facility is available.

Original language	English
Article number	8
Journal	AAPPS Bulletin
Volume	32
Issue number	1
DOIs	https://doi.org/10.1007/s43673-022-00037-4
State	Published - Dec 2022

Bibliographical note

Publisher Copyright:
© 2022, The Author(s).

Funding

The author is indebted to M. Engelhardt, X. Ji, C. Lorcé, Yi-Bo Yang, F. Yuan, and Y. Zhao for fruitful discussions. He also thanks Jian Liang, G. Wang, and Yi-Bo Yang for the results of the χQCD Collaboration. This work is partially support by the U.S. DOE grant DE-SC0013065 and DOE Grant No. DE-AC05-06OR23177 which is within the framework of the TMD Topical Collaboration. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. This work used Stampede and Frontera time under the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. ACI-1053575. We also thank the National Energy Research Scientific Computing Center (NERSC) for providing HPC resources that have contributed to the research results reported within this paper. We also acknowledge the facilities of the USQCD Collaboration used for this research in part, which are funded by the Office of Science of the U.S. Department of Energy.

Funders	Funder number
Office of Science Programs
National Energy Research Scientific Computing Center
U.S. Department of Energy	DE-AC05-00OR22725, DE-SC0013065, DE-AC05-06OR23177
National Science Foundation Arctic Social Science Program	1053575, ACI-1053575

Keywords

Gluon spin
Lattice QCD
Quantum chromodynamics
Quark spin

ASJC Scopus subject areas

General Physics and Astronomy

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10.1007/s43673-022-00037-4

Cite this

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title = "Status on lattice calculations of the proton spin decomposition",

abstract = "Lattice calculations of the proton spin components is reviewed. The lattice results of the quark spin from the axial-vector current matrix element at ∼ 0.3−0.4 is smaller than those from the constituent quark models. This is largely due to the fact that the vacuum polarization contribution from the disconnected insertion is negative. Its connection with the anomalous Ward identity is clarified and verified numerically. This resolves the contentious issue in the “proton spin crisis.” The glue spin and angular momentum are found to be large and there is notable contribution from the quark orbital angular momentum. Renormalization, mixing, and normalization of the quark and glue angular momenta are discussed. With sufficient precision, they can be compared with more precise experimental measurements when the electron-ion collider facility is available.",

keywords = "Gluon spin, Lattice QCD, Quantum chromodynamics, Quark spin",

author = "Liu, \{Keh Fei\}",

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year = "2022",

month = dec,

doi = "10.1007/s43673-022-00037-4",

language = "English",

volume = "32",

journal = "AAPPS Bulletin",

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T1 - Status on lattice calculations of the proton spin decomposition

AU - Liu, Keh Fei

PY - 2022/12

Y1 - 2022/12

N2 - Lattice calculations of the proton spin components is reviewed. The lattice results of the quark spin from the axial-vector current matrix element at ∼ 0.3−0.4 is smaller than those from the constituent quark models. This is largely due to the fact that the vacuum polarization contribution from the disconnected insertion is negative. Its connection with the anomalous Ward identity is clarified and verified numerically. This resolves the contentious issue in the “proton spin crisis.” The glue spin and angular momentum are found to be large and there is notable contribution from the quark orbital angular momentum. Renormalization, mixing, and normalization of the quark and glue angular momenta are discussed. With sufficient precision, they can be compared with more precise experimental measurements when the electron-ion collider facility is available.

AB - Lattice calculations of the proton spin components is reviewed. The lattice results of the quark spin from the axial-vector current matrix element at ∼ 0.3−0.4 is smaller than those from the constituent quark models. This is largely due to the fact that the vacuum polarization contribution from the disconnected insertion is negative. Its connection with the anomalous Ward identity is clarified and verified numerically. This resolves the contentious issue in the “proton spin crisis.” The glue spin and angular momentum are found to be large and there is notable contribution from the quark orbital angular momentum. Renormalization, mixing, and normalization of the quark and glue angular momenta are discussed. With sufficient precision, they can be compared with more precise experimental measurements when the electron-ion collider facility is available.

KW - Gluon spin

KW - Lattice QCD

KW - Quantum chromodynamics

KW - Quark spin

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U2 - 10.1007/s43673-022-00037-4

DO - 10.1007/s43673-022-00037-4

M3 - Review article

AN - SCOPUS:85142518699

SN - 0218-2203

VL - 32

JO - AAPPS Bulletin

JF - AAPPS Bulletin

IS - 1

M1 - 8

ER -

Status on lattice calculations of the proton spin decomposition

Abstract

Bibliographical note

Funding

Keywords

ASJC Scopus subject areas

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