Rethinking the Properties of the Quark-Gluon Plasma at $T\sim T_c$

Abstract

We argue that although at asymptotically high temperatures the QGP in bulk behaves as a gas of weakly interacting quasiparticles (modulo long-range magnetism), at temperatures up to few times the critical temperature $T_c$ it displays different properties. If the running of the QCD coupling constant continues in the Coulomb phase till the screening length scale, it reaches the strong coupling treshold $α_s(m_D)\sim 1$. As a result, the Coulomb phase supports weakly bound Coulombic s-wave $\bar c c$, light quark and even $gg$ states. The existence of shallow bound states dramatically increases the quasiparticle rescattering at low energies, reducing the viscosity and thereby explaining why heavy ion collisions at RHIC exhibit robust collective phenomena. In conformal gauge theories at finite temperature the Coulomb binding persists further in the strong coupling regime, as found for ${\cal N}=4$ SUSY YM in the Maldacena regime.

Figures (2)

• Figure 1: (a)The combination $(M_c/M_D) rV(r)$, versus the distance $r M_D$. The dashed line corresponds to $4\alpha_s/3=0.471$, while the solid lines correspond to the running coupling constant, for $T=1;1.5;3;10 T_c$, from bottom up. The cusps occur when $\alpha_s$ reaches 1. (b) The (modulus of the) binding energy of two gluons, versus $T/T_c$.
• Figure 2: Schematic dependence of hadronic masses on temperature $T$ (in units of the critical one $T_c$), for 2-flavor QCD in the chiral limit. The dash-dotted line corresponds to twice the (chiral) effective mass of a quark. Black dots marked $s,p,d$ correspond to the points where the binding vanishes for states with orbital momentum $l=0,1,2...$.