a coefficient $a/2$. In matter-free space, $a\approx 2$, so the form factor is vector-dominated with the direct coupling vanishing. What Harada and Yamawaki found was that the $a=2$ point sitting in free space is purely $accidental$, with $a$ lying on a RG trajectory that does not contain $a=2$. Thus if the system is slightly perturbed, $a$ quickly flows from 2 toward 1. At the VM fixed point, therefore the standard vector dominance is $strongly$ violated [^7].

“Seeing" the Dropping Mass
==========================

On-shell probes
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There is a flurry of activities, both in theory and experiment, to “see" evidence for the manifestation of chiral symmetry in the behavior of masses and coupling constants in hot and/or dense medium. One would first like to observe it at a density and/or temperature readily available in laboratories before reaching the critical point and then ultimately go to the critical point. The former is looked for in precursor phenomena to the chiral phase transition. The idea is to create a hot/dense environment in which the produced particles propagate and look for signals that take a “snap-shot" of the particle propagation in the medium that is as free as possible from subsequent interactions with the medium.

