[Theory-seminars] Cake Seminar Wednesday - Christian Weiss

[Zheng-Yang Li]

Dear all,

On Wednesday, November 8th, 2023 at 1pm EST, we will have a cake seminar given by Christian Weiss of JLab in CC F224-225. Please see below for the title and abstract.


Cake Seminar: Wednesday, November 8th, 1pm EST


Speaker: Christian Weiss (JLab)


Title: Gluonic structure of hadrons from the instanton vacuum


Abstract: The dynamical breaking of chiral symmetry is fundamental to the emergence of mass in QCD and the long-range structure of light hadrons. Lattice QCD simulations show that the breaking of chiral symmetry is caused by topological vacuum fluctuations of the gauge fields, which induce chiral zero modes of the fermion fields. The same topological gauge fields generate a gluonic structure of the hadrons, as measured by the matrix elements of QCD composite operators (local or partonic).

The gluonic structure produced by topological gauge fields is studied using the instanton vacuum, an explicit realization of chiral symmetry breaking by topological gauge fields that permits systematic calculations (diluteness parameter). QCD operators involving gauge fields are converted to effective operators in the effective theory obtained after chiral symmetry breaking [1]. The method preserves operator relations resulting from the trace and axial anomalies and the QCD equations of motion. Applications include (i) twist-2 quark and gluon operators (PDFs/GPDs); (ii) twist-3 quark operators, where large instanton effects have recently been demonstrated in nonforward matrix elements (spin-orbit correlations, twist-3 GPDs) [2]; (iii) twist-3 and 4 operators in power corrections to DIS structure functions; (iv) the nucleon form factors of the operators F^2 (trace anomaly, nucleon mass) and F-Fdual (axial anomaly, nucleon spin) [1].

The seminar presents an overview of the physical picture, the instanton vacuum method, the results for various QCD operators measuring gluonic structure in hadrons, and future directions in this effort.

[1] D. Diakonov, M.V. Polyakov, C. Weiss, Nucl. Phys. B 461, 539 (1996)
[2] J.-Y. Kim and C. Weiss, arXiv:2310.16890


See you on Wednesday.


Best regards,

Caroline, Joe, and Zheng-Yang

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