Instanton-induced azimuthal spin asymmetry in deep inelastic scattering

We propose a new dynamical mechanism for spin asymmetries in semi-inclusive deep inelastic scattering, utilizing strong vacuum fluctuations of the gluon field described semiclassically by instantons. Those can generate large asymmetry because they can simultaneously generate (i) a chirality flip of the struck quark; (ii) large 0(1) T-odd phase due to its final state interaction. The absolute magnitude of the effect is estimated using known parameters of the instanton ensemble in the QCD vacuum and known structure and fragmentation functions, without any new free parameters. The result agrees in sign and (roughly) in magnitude with the available data on single particle inclusive DIS. Furthermore, our predictions uniquely relate effects for longitudinally and transversely polarized targets.