Chiral Dynamics and Single-Spin Asymmetries

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 most elegant display of the relevant mechanisms occurs in the Collins functions and the polarizing fragmentation functions and fracture functions for particles with spin. In the nucleon, these same dynamical mechanisms generate virtual quantum structures leading to the Boer-Mulders functions and orbital distributions. Two complementary formalisms for these distributions appear. The familiar gauge-link formalism incorporates oll nonperturbative dynamics into nonlocal correlators. The constructive formalism introduced by the author describes distributions normalized to an intrinsic property of the nucleon, namely, the currents specified in the Bakker-Leader-Trueman sum rule. The connection between these two approaches can be explored in the process dependence of single-spin asymmetries in various hard-scattering processes. The study of the SU(2) Weyl-Dirac equation in spherical coordinates allows typical Wilson operators that determine this process dependence to be evaluated in the coordinate gauge.