  We perform a study of the non-perturbative dynamics of the light-quark sector
of QCD, based on some recent results of lattice simulations with chiral
fermions. We analyze some correlators that are designed to probe the Dirac
structure of the quark-quark interaction at different scales. We show that, in
the non-perturbative regime, such an interaction contains very large scalar and
pseudo-scalar components. We observe quantitative agreement between lattice QCD
results and the predictions of the Instanton Liquid Model (ILM). Moreover, we
study how the the quark-quark interaction is modified, when quark loops are
suppressed. We observe a dramatic effect related to the loss of unitarity,
which is naturally explained in the instanton picture. Such an effect cannot be
explained in a Dyson-Schwinger Equations (DSE) approach, if one assumes a
simple vector quark-gluon coupling. Therefore, from the present study it
emerges that DSE models with such an ansatz for the vertex function are not
consistent with QCD.

High Energy Physics - Phenomenology