A New Mechanism for Single Spin Asymmetries in Strong Interactions

TL;DR

This paper proposes a novel nonperturbative mechanism involving instantons in QCD that explains the observed single-spin asymmetries in high-energy hadron and lepton interactions.

Contribution

It introduces a new mechanism based on instanton-induced quark spin-flip and the resulting imaginary part in scattering amplitudes, explaining single-spin asymmetries.

Findings

Instantons contribute to quark fragmentation processes.

Imaginary parts in scattering amplitudes arise from instanton effects.

The mechanism accounts for observed single-spin asymmetries.

Abstract

It is shown that the contribution of the instantons to the fragmentation of quarks leads to the appearance of a imaginary part in diagrams of quark-quark scattering at large transfer momentum. The imaginary part comes from the analytical continuation of the instanton amplitudes from Euclidean to Minkowsky space-time and reflects quasiclassical origin of instanton solution of QCD equations of motion. This phenomenon and instanton--induced quark spin-flip give a new nonperturbative mechanism for the observed anomalous single-spin asymmetries in hadron-hadron and lepton-hadron interactions.