  For the study of dynamical chiral-symmetry breaking (DCSB) in QCD, we
investigate the Schwinger-Dyson (SD) formalism based on lattice QCD data. From
the quenched lattice data for the quark propagator in the Landau gauge, we
extract the SD kernel function K(p^2), which is the product of the quark-gluon
vertex and the polarization factor in the gluon propagator, in an
Ansatz-independent manner. We find that the SD kernel function K(p^2) exhibits
infrared vanishing and a large enhancement at the intermediate-energy region
around p \sim 0.6GeV. We investigate the relation between the SD kernel and the
quark mass function, and find that the infrared and intermediate energy region
(0.35GeV<p<1.5GeV) would be relevant for DCSB. We apply the lattice-QCD-based
SD equation to thermal QCD, and calculate the quark mass function at the finite
temperature. Spontaneously broken chiral symmetry is found to be restored at
the high temperature above 100MeV.
