Instanton contribution to the Sivers function
  We study the Sivers function for valence u and d quarks in the proton within the instanton model for QCD vacuum, adopting the MIT bag model wave functions for quarks. Within approaches based on perturbative one-gluon final state interactions a non-zero value of the Sivers function is related to the presence of both S and P wave components in quark wave functions. We show that the instanton-induced chromomagnetic, nonperturbative interaction leads to very specific spin-spin correlations between the struck and spectator quarks, resulting in a non-trivial flavour dependence of the Sivers function. Comparison of the obtained Sivers functions with phenomenological parameterizations is discussed. 
I.O. Cherednikov (1,2,3), U. D'Alesio (2), N.I. Kochelev (3,4), F.   Murgia (2) ((1) Ruhr-Universitat, Bochum, Germany, (2) ...