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High Energy / Nuclear Theory / RIKEN seminars

[RBRC seminar] The role of the chiral anomaly in polarized deep inelastic scattering: Topological screening and transitions from emergent axion-like dynamics.

by Dr Andrey Tarasov (The Ohio State University)


I’ll discuss the role of the chiral (triangle) anomaly in polarized deep inelastic scattering (DIS) employing a worldline formalism, which is a powerful framework for the computation of perturbative multi-leg Feynman diagrams. I’ll demonstrate that the structure function $g_1(x_B,Q^2)$ measured in polarized DIS is dominated by the triangle anomaly in both Bjorken ($Q^2\rightarrow 0)$ and Regge ($x_B\rightarrow 0$) asymptotics. I’ll show that the infrared pole of the anomaly appears in both limits. In the worldline formulation of quantum field theory, the triangle anomaly arises from the imaginary part of the effective action. I’ll show explicitly how a Wess-Zumino-Witten term coupling the topological charge density to a primordial isosinglet ${\bar \eta}$ arises in the imaginary part of the effective action as well. I’ll demonstrate the fundamental role played by this contribution both in topological mass generation of the $\eta^\prime$ and in the cancellation of the infrared pole arising from the triangle anomaly in the proton's helicity $\Sigma(Q^2)$. I will introduce an axion-like effective action for $g_1$ at small $x_B$ that follows from the cancellation of the infrared pole in the matrix element of the anomaly. It describes the interplay between gluon saturation and the topology of the QCD vacuum. In this context I’ll outline the role of ``over-the-barrier" sphaleron-like transitions in spin diffusion at small $x_B$. Such topological transitions can be measured in polarized DIS at a future Electron-Ion Collider.