Hidden Local Symmetry and Dense Half-Skyrmion Matter

Transition from baryonic matter to color-flavor-locked quark matter is described in terms of skyrmion matter changing into half-skyrmion matter. The intermediate phase between the density $n_p$ at which a skyrmion turns into two half skyrmions and the chiral transition density $n_c^{\chi SR}$ at which hadronic matter changes over to quark matter corresponds to a chiral symmetry restored phase characterized by a vanishing quark condensate and a {\em non-vanishing} pion decay constant. When hidden local fields are incorporated, the vector manifestation of Harada-Yamawaki HLS theory implies that as density approaches $n_c^{\chi SR}$, the gauge coupling $g$ goes to zero (in the chiral limit) and the symmetry "swells" to $SU(N_f)^4$ as proposed by Georgi for the "vector limit." This enhanced symmetry, not present in QCD, can be interpreted as "emergent" in medium due to collective excitations. The fractionization of skyrmions into half-skyrmions resembles closely the magnetic N\'eel--to-valence bond solid (VBS) paramagnet transition where "baby" half-skyrmions enter as relevant degrees of freedom in the intermediate phase. It is suggested that the half-skyrmion phase in dense matter corresponds to the "hadronic freedom" regime that plays a singularly important role in inducing kaon condensation that leads to the collapse of massive compact stars into black holes..