Quark spin in proton from anomalous Ward indentity

Yi Bo Yang, Ming Gong, Keh Fei Liu, Mingyang Sun

Research output: Contribution to journalConference articlepeer-review

2 Scopus citations


We report a quark spin calculation from the anomalous Ward identity with overlap fermions on 2+1 flavor dynamical fermion configurations with light sea quark masses. Such a formulation decomposes the divergence of the flavor-singlet axial-vector current into a quark pseudoscalar term and a triangle anomaly term, flavor by flavor. A large negative contribution from the anomaly term is observed and it is canceled within errors by the contribution from the pseudoscalar term in the disconnected insertion in the heavy quark region. On the other hand, net negative contributions are obtained for the light and strange quarks in the disconnected insertion, since their quark pseudoscalar terms are smaller than that of the heavy quark. Our results are obtained from the 2+1 flavor domain wall fermion configurations on the 243 ×64 lattice with a-1 = 1.78(5) GeV and the light sea quark at mπ = 330 MeV. We use the overlap fermion for the valence and the quark loop so that the renormalization constants Zm and Zp cancel in the pseudoscalar operator 2mP. In addition, the overlap Dirac operator is used to calculate the local topological charge in the anomaly so that there is no renormalization for the anomaly term either. In this study, we find the total quark spin to be small mainlyly due to the large negative anomaly term which could be the source for the 'proton spin crisis'.

Original languageEnglish
Article number138
JournalProceedings of Science
VolumePart F130500
StatePublished - 2014
Event32nd International Symposium on Lattice Field Theory, LATTICE 2014 - New York, United States
Duration: Jun 23 2014Jun 28 2014

ASJC Scopus subject areas

  • General


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