Abstract
A new mechanism of spontaneous chiral symmetry breaking in the instanton vacuum of OCD is proposed. It is based on the delocalization of zero fermionic modes in the pseudoparticles' medium. This medium exists due to the effective repulsion of pseudoparticles discovered by us previously. We build a systematic theory of light quarks in such a medium. We find the quark propagator in the instanton vacuum and demonstrate that the quark acquires an effective momentum-dependent mass. It means that the approximate chiral symmetry of QCD breaks down spontaneously, and we find the value of the chiral condensate 〈 ψψ〉 . Further on, we calculate various current-current correlation functions in the instanton vacuum and demonstrate explicitly the appearance of a massless pion pole in the pseudoscalar and axial channels. We calculate the pion constant f π and its charge radius r π . All observables are expressed through the average size of pseudoparticles ϱ and the average distance between them R , these quantities being calculable from a variational principle using the QCD Λ parameter. The obtained numerical values of M eff , 〈 ψψ〉, f π, r π are in good accordance with the phenomenology. We also construct the effective chiral langrangian for pions; this contains all powers of derivatives of the pion field.
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