Nuclear Physics Seminar

Chiral Symmetry Meets Confinement:
Implications of Spin-Orbit Dynamics in QCD

ABSTRACT

Parity-conserving single-spin asymmetries provide a specific measure of coherent spin-orbit dynamics in quantum chromodynamics. The origin of these effects can be traced to the interplay of chiral dynamics and confinement in the theory. The cleanest and most elegant display of the appropriate mechanisms appears in the Collins functions and in the polarizing fragmentation functions and fracture functions for hadrons with spin. In the nucleon, the same dynamical mechanisms generate virtual quantum structures leading to the Boer-Mulders functions and orbital distributions. Two complementary formalisms for these distributions functions occur. The familiar gauge-link formalism incorporates all nonperturbative dynamics for a specific measurement into an nonlocal correlator. The constructive formalism introduced by the author describes an intrinsic property of the nucleon, namely, the currents specified in the Bakke-Leader-Trueman sum rule, and gives a recipe for how these currents are probed by soft initial-state and final-state interactions. The connection between the two approaches can be studied in the process dependence of single-spin asymmetries.