Do nuclear collisions create a locally equilibrated quark-gluon plasma?

Abstract

Experimental results on azimuthal correlations in high energy nuclear collisions (nucleus-nucleus, proton-nucleus and proton-proton) seem to be well described by viscous hydrodynamics. It is often argued that this agreement implies either local thermal equilibrium or at least local isotropy. In this note, I present arguments why this is not the case. Neither local near-equilibrium nor near-isotropy are required in order for hydrodynamics to offer a successful and accurate description of experimental results. However, I predict the breakdown of hydrodynamics at momenta of order seven times the temperature, corresponding to a smallest possible QCD liquid drop size of 0.15 fm.

14 pages, 6 figures; v2: references added, major changes in section VI, qualitative conclusions unchanged; v3: minor typos fixed, matches published version

References in corpus (14)

• Relativistic viscous hydrodynamics, conformal invariance, and holography
• Horizon formation and far-from-equilibrium isotropization in supersymmetric Yang-Mills plasma
• Holography and colliding gravitational shock waves in asymptotically AdS_5 spacetime
• Gauge/gravity duality and thermalization of a boost-invariant perfect fluid
• The stickiness of sound: An absolute lower limit on viscosity and the breakdown of second order relativistic hydrodynamics
• Instabilities of an anisotropically expanding non-Abelian plasma: 1D+3V discretized hard-loop simulations
• Bottom-up isotropization in classical-statistical lattice gauge theory
• Plasma Instabilities in an Anisotropically Expanding Geometry
• Non-abelian plasma instabilities for strong anisotropy
• Holographic thermalization with radial flow
• Particle spectra and HBT radii for simulated central nuclear collisions of C+C, Al+Al, Cu+Cu, Au+Au, and Pb+Pb from Sqrt(s)=62.4-2760 GeV
• Linearized fluid/gravity correspondence: from shear viscosity to all order hydrodynamics
• Absence of a local rest frame in far from equilibrium quantum matter
• Accelerating cosmological expansion from shear and bulk viscosity

Cited by in corpus (14)

• Imprints of fluctuating proton shapes on flow in proton-lead collisions at the LHC
• Phenomenological Review on Quark-Gluon Plasma: Concepts vs. Observations
• On the hydrodynamic attractor of Yang-Mills plasma
• Relativistic Hydrodynamic Attractors with Broken Symmetries: Non-Conformal and Non-Homogeneous
• Importance of initial and final state effects for azimuthal correlations in p+Pb collisions
• QCD Equation of State at Finite Chemical Potentials for Relativistic Nuclear Collisions
• Transasymptotics and hydrodynamization of the Fokker-Planck equation for gluons
• Quarkonium dissociation in a far-from-equilibrium holographic setup
• Primordial gravitational waves amplification from causal fluids
• Medium effects for hadron-tagged jets in proton-proton collisions
• Aspects of relativistic heavy-ion collisions
• Strangeness enhancement and flow-like effects in $e^{+}{e}^{-}$ annihilation at high parton density
• Importance of initial and final state effects for azimuthal correlations in p+Pb collisions
• Effects of magnetic field on the evolution of energy density fluctuations