Why in QCD chiral symmetry breaking study only the light quarks are taken into account? And why are their masses usually set to zero, Goldstone bosons are found, and then their masses are corrected by letting the quarks have non-zero mass? What happens if one study this symmetry breaking with massive quarks instead? And what exactly are quark condensates? I mean, I know they break the chiral symmetry because of their VEV, but what is their meaning? What is the relation between a particle's self-energy and its mass? (if any) Thanks in advance.