Holographic model of the thermal phases of QCD

Tel Aviv University
Fri, Feb. 16th 2007, 11:00
Salle Claude Itzykson, Bât. 774, Orme des Merisiers
We construct and analyze a holographic model of the thermal phases of QCD. It is based on Sakai-Sugimoto model, which is a holographic dual of a theory which spontaneously breaks a $U(N_f)_L\times U(N_f)_R$ chiral flavor symmetry at zero temperature. The theory involved is a $4+1$ dimensional supersymmetric $SU(N_c)$ gauge theory compactified on a circle of radius $R$ with anti-periodic boundary conditions for fermions, coupled to $N_f$ left-handed quarks and $N_f$ right-handed quarks which are localized at different points on the compact circle (separated by a distance $L$). In the supergravity limit which we analyze, the theory undergoes a deconfinement phase transition at a temperature $T_d = 1 / 2\pi R$. For quark separations obeying $L > L_c \simeq 0.97*R$ the chiral symmetry is restored at this temperature, but for $L < L_c \simeq 0.97*R$ there is an intermediate phase which is deconfined with broken chiral symmetry, and the chiral symmetry is restored at $T_{\chi SB} \simeq 0.154 / L$. All of these phase transitions are of first order. We further analyse the mesonic spectra at finite temperature. The temperature dependence of low-spin as well as high-spin meson masses is shown to exhibit a pattern familiar from the lattice. Furthermore, we find the dissociation temperature of mesons as a function of their spin, showing that at a fixed quark mass, mesons with larger spins dissociate at lower temperatures. The Goldstone bosons associated with chiral symmetry breaking are shown to disappear above the chiral symmetry restoration temperature. Finally, we show that holographic consideration imply that large-spin mesons do not experience drag effects when moving through the quark gluon plasma.