Quark Correlations and Single Spin Asymmetries
Matthias Burkardt
TL;DR
The paper analyzes the Sivers single-spin asymmetry in light-cone gauge, showing that the phase responsible for the asymmetry arises from the transverse gauge field at $x^-= abla\to\infty$ and can be recast in terms of transverse color-density correlations by imposing finiteness conditions on the light-cone Hamiltonian. It derives an operator relation linking the infinity-field to the integrated color density, enabling a gauge-invariant expression for the average quark transverse momentum in terms of density correlations. In QED this relation is exact, while in QCD it is established to leading order, yielding a Coulomb-like interpretation of final-state interactions and a direct connection between SSA and transverse-plane parton correlations. The results provide a practical route to compute Sivers effects from light-cone wave functions and motivate further nonperturbative extensions, including exact QCD solutions and lattice formulations.
Abstract
We analyze the Sivers asymmetry in light-cone gauge. The average transverse momentum of the quark distribution is related to the correlation between the quark distribution and the transverse component of the gauge field at $x^-\pm \infty$. We then use finiteness conditions for the light-cone Hamiltonian to relate the transverse gauge field at $x^-=\pm \infty$ to the color density integrated over $x^-$. This result allows us to relate the average transverse momentum of the active quark to color charge correlations in the transverse plane.