A new paper by Jens Braun and Holger Gies gives a nice picture of the chiral phase transition that links the finite temperature phase transition with the chiral phase transition that appears as the number of quark flavors is varied at zero temperature. The idea is that in the chiral symmetric phase there is an infrared fixed point for the gauge coupling. As the temperature or number of flavors in lowered, the fixed point coupling moves to stronger coupling. Eventually the fixed point coupling is large enough that four quark operators become relevant (i.e have scaling dimensions less than four) and produce chiral symmetry breaking and destroy the infrared fixed point. It would be nice if lattice gauge theorists who do Monte Carlo simulations would try to verify this picture.

Now all is clear, I thank for the information.