Chiral symmetry breaking in the colour dielectric model

Approximating the long-distance gluon dynamics ofSU(3)_colour by colour-dielectric block-spin variables, we obtain an effective QCD theory of a scalar colour-dielectric field and a massive colour-bleached gluon field coupled to light quarks. The massive vector field produces a strong attraction betweenq (bar q) pairs, which leads toq (bar q) condensation when the colour-dielectric field becomes small. We calculate (leftlangle {bar psi psi } rightrangle) and the pion decay constantf _n as a function of the dielectric field expectation value, by evaluating the fermion determinant in a derivative expansion, and integrating out the bosonic variables. We find that the effective quark-gluon coupling,α _s ^eff , including quark effects, is large on the surface of bags, where (leftlangle {bar psi psi } rightrangle) ±0, but decreases inside hadronic bags, where | (leftlangle {bar psi psi } rightrangle) | is decreasing.