field theories. There is some help from lattice calculations but at the present stage, not much on what happens to light-quark hadrons, e.g., nucleons, vector mesons, pions etc. when they are immersed in hot and/or dens medium.

The question we are interested in answering is: If the hadron mass vanishes at the phase transition, how can one “see" it or what is the appropriate tool for it?

In what follows, we shall mostly deal with the chiral limit. Our principal theme in addressing the above question is that [*the most important ingredient in an effective field theory that enables one to probe the regime where the effective mass of the vector meson can drop to that of the pion mass is hidden local symmetry.*]{} Our theme is anchored on the argument by Harada and Yamawaki [@HY:PR] that without hidden local symmetry, there is no consistent [*as well as*]{} simple way to allow the vector mass become as light as the pion mass. We suggest that the lack of hidden gauge symmetry is the reason why phenomenological models often used in the literature fail to observe dropping masses in hot/dense matter.

HLS as emergent gauge symmetry
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At very low energy 