[RBRC seminar] Nucleon Mass and Spin from the Instanton Vacuum

by Mr Wei-Yang Liu (Stony Brook University)

Thursday 4 Sept 2025, 12:30 → 14:00 US/Eastern

2-160 (https://bnl.zoomgov.com/j/1600983728?pwd=RAD7OLcqre7Ycsp6JfFp6HAnpyLxex.1)

We investigate the quark and gluon contributions to the nucleon’s mass and spin, together with the associated scalar, pseudoscalar, axial, and gravitational charges, within the QCD instanton vacuum framework. The nucleon mass is decomposed into the invariant mass and a Higgs-induced sigma term where three-quarters of the invariant mass can be further redistributed between quark and gluon energies at different renormalization scales. The dominant invariant mass is linked to the quantum breaking of conformal symmetry through fluctuations in the instanton number. For the spin structure, the nucleon spin is gauge-invariantly decomposed into intrinsic quark spin, quark OAM, and gluon angular momentum, where the latter two will be redistributed at different renormalization scales as well. The intrinsic quark spin tied to the quantum breaking of the chiral U(1) symmetry via fluctuations in the instanton–anti-instanton number difference. The instanton liquid model predictions for Ji’s decomposition of nucleon mass and spin are in good agreement with recent lattice QCD results, highlighting the essential role of topological fluctuations in shaping hadron structure.