On Monday, Jan. 27, at 1 p.m., Ignacio Castelli of Temple University will present "Unraveling the Axial Anomaly: Its Role in the ‘Spin Crisis’ and the ‘UA(1) Problem’" in CEBAF Center rm. L102 and via Zoom.
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Abstract: In the Standard Model of particle physics, the axial current is not conserved, due both to fermion masses and to the axial anomaly. In the late 1980s, it was proposed that the axial anomaly could help understand the results of the European Muon Collaboration (EMC) measurements that led to the nucleon spin crisis. Recent work has taken a fresh look at the role of the axial anomaly in polarized deep-inelastic scattering and also extended the discussion to deep-virtual Compton scattering. Important aspects of those works include the apparent connection between the UA(1) problem and 'anomaly poles', as well as the dependence of pertinent perturbative results on the infrared regulator. I will discuss these and related topics, and our understanding of the current status of the field.