2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/181739We 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.1+12 pages, 4 ps figures; v2: few references and one sentence added in the introduction; final version published in Phys. Lett. BHigh Energy Physics - Phenomenologytext