The 11th International Workshop on Chiral Dynamics

Trace anomaly and gravitational form factors in the QCD instanton vacuum

27 Aug 2024, 17:40

20m

Saal 2 (Convention Centre)

Working group talk WG2: Hadron Structure and Meson-Baryon Interactions WG2 parallel session

Speaker

Christian Weiss (Jefferson Lab)

Description

The breaking of conformal and chiral symmetry determine the structure of the QCD vacuum and condition the emergent properties of light hadrons. We review recent efforts in studying these phenomena in the instanton liquid model of the QCD vacuum, a semiclassical picture abstracted from lattice QCD calculations. Chiral symmetry breaking is caused by the fermionic zero modes induced by the topological gauge fields of the instantons. Conformal symmetry breaking is encoded in the fluctuations of the number of instantons dictated by the renormalization properties of QCD [1]. An effective theory is derived in the $1/N_c$ expansion, describing massive quarks with chiral spin-flavor interactions. Gluonic operators such as the trace anomaly $F^2$ are represented by effective operators. Hadronic matrix elements of the trace anomaly are obtained in accordance with low-energy theorems. We summarize recent results for the mass decomposition and gravitational form factors of the pion [2] and the nucleon and their mechanical interpretation. We also present predictions for instanton-induced quark-gluon correlations in the twist-3 generalized parton distributions [3].

[1] D. Diakonov, M.V. Polyakov, C. Weiss, Nucl. Phys. B 461, 539 (1996)
[2] W.Y. Liu, E. Shuryak, C. Weiss, I. Zahed, arXiv:2405.14026 [hep-ph]
[3] J.Y. Kim, C. Weiss, Phys. Lett. B 848, 138387 (2024)

Presentation materials

weiss24_chiral24.pdf