Physics of Strongly coupled Quark-Gluon Plasma

TL;DR

The paper surveys the physics of strongly coupled Quark-Gluon Plasma (sQGP), summarizing evidence that RHIC/LHC data are best described by near-perfect fluid dynamics with very small viscosity. It combines lattice QCD results, electric–magnetic duality arguments, and AdS/CFT holography to illuminate the properties and real-time dynamics of sQGP, including magnetic monopole dynamics near Tc and the emergence of hydrodynamics from gravity. Key contributions include a magnetic scenario for the near-Tc region, a detailed account of the AdS/CFT description of conformal plasmas and their relaxation, and a synthesis of heavy-quark diffusion, jet quenching, and charmonium survival within strong-coupling frameworks. The work highlights how dual perspectives—electric/magnetic descriptions and holographic gravity duals—complement each other, guiding understanding of transport, equilibration, and the potential gravity duals to heavy-ion collisions, while pointing to open experimental and theoretical challenges for connecting these pictures across temperature regimes.

Abstract

This review cover our current understanding of strongly coupled Quark-Gluon Plasma (sQGP), especially theoretical progress in (i) explaining the RHIC data by hydrodynamics, (ii) describing lattice data using electric-magnetic duality; (iii) understanding of gauge-string duality known as AdS/CFT and its application for "conformal" plasma. In view of interdisciplinary nature of the subject, we include brief introduction into several topics "for pedestrians". Some fundamental questions addressed are: Why is sQGP such a good liquid? What is the nature of (de)confinement and what do we know about ''magnetic'' objects creating it? Do they play any important role in sQGP physics? Can we understand the AdS/CFT predictions, from the gauge theory side? Can they be tested experimentally? Can AdS/CFT duality help us understand rapid equilibration/entropy production? Can we work out a complete dynamical "gravity dual" to heavy ion collisions?

Figures (33)

• Figure 1: (Color online) $G_{d}$ correlation function for $\Gamma=0.83,31.3,131$, respectively. Red circles correspond to $t^{*}=0$, and blue squares correspond to $t^{*}=6$.
• Figure 2: (a) False color absorption images of a strongly interacting degenerate Fermi gas of ultracold $^6$Li atoms as a function of time after release from a laser trap. From O'Hara et al.OHGGT02 (b)"Quantum viscosity" in strongly-interacting Fermi gas $\alpha=\eta/\hbar\,n$ (trap-averaged). (c) Same data for the shear viscosity as $\eta/\hbar s$ in units of the entropy density $s$ as a function of energy $E$. The lower green dotted line shows the string theory prediction $1/(4\pi)$. The light blue bar shows the estimate for a quark-gluon plasma (QGP) while the blue solid bar shows the estimate for $^4$He, near the $\lambda$- point.
• Figure 3: (a) Schematic phase diagram for QCD, in the plane baryon chemical potential - temperature. M (multifragmentation) point is the endpoint of nuclear gas-liquid transition. E is a similar endpoint separating the first order transition to the right from a crossover to the left of it. (Black) solid lines show phase boundaries, dashed lines are curves of marginal stability of indicated states. Two dash-dotted straight lines are related with bounds from atomic experiments we discuss in the text, they intersect with unbinding of diquark Cooper pairs (D) and most strongly coupled point (S), which is at the maximum of the transition line and is also a divider between BCS-like and BEC-like color superconductor. Other lines are zero binding for singlet $gg$, singlet $\bar{c} c$, octet $qg,gg$ and finally triplet $qq$ states. (right) Compilation of experimental data on the chemical freezeout from different experiments: squares (circles) are for fits at mid-rapidity (all particles), respectively. Two solid lines are the phase transition lines with the quark effective mass $M_1=0$ and $100\, MeV$, two dashed lines show pair unbinding lines for the same masses.
• Figure 4: The left and right sides show the hydrodynamic solution at the SPS and RHIC. The thin lines show contours of constant transverse fluid rapidity ($v_{T} = \tanh(y_{T})$) with values 0.1,0.2,...,0.7 . The thick lines show contours of constant energy density. $e_{120}$ denotes the energy density where $T=120\,\hbox{MeV}$. $e_{H}$ and $e_{Q}$ denote the energy density where the matter shifts from hadronic to mixed and mixed to a QGP, respectively. The shift to hadronic cascade is made at $e_{H}$. $\langle y_{T} \rangle$ denotes the mean transverse rapidity weighted with the total entropy flowing through the energy density contours. Walking along these contours, the line is broken into segments by dashed and then solid lines. 20% of the total entropy passing through the entire arc passes through each segment.
• Figure 5: Top two panels: On the left, proton $v_2(p_T)/\epsilon$ vs. $p_T$ for minimum-bias collisions at RHIC Adler:2003ktAdler:2001nb are compared with hydro calculations Teaney:2001avHirano:2002dsKolb:2003dzHuovinen:2001cy, and on the right is the same comparison for pions. Bottom two panels: $(1/2\pi)d^2N/p_{t}dp_tdy$. On the left, for protons, for 0--5% centrality bin collisions at RHIC Adler:2003cb are compared with the same hydro calculations. On the the right, the same comparison for pions.