The quark-gluon plasma: collective dynamics and hard thermal loops

By J. Blaizot, E. Iancu. 2001

353 citations recorded by the source corpus.

Abstract We present a unified description of the high temperature phase of QCD, the so-called quark–gluon plasma, in a regime where the effective gauge coupling g is sufficiently small to allow for weak coupling calculations. The main focus is the construction of the effective theory for the collective excitations which develop at a typical scale gT, well separated from the typical energy of single particle excitations which is the temperature T. We show that the short wavelength thermal fluctuations, i.e., the plasma particles, provide a source for long wavelength oscillations of average fields which carry the quantum numbers of the plasma constituents, the quarks and the gluons. To leading order in g, the plasma particles obey simple gauge-covariant kinetic equations, whose derivation from the general Dyson–Schwinger equations is outlined. By solving these equations, we effectively integrate out the hard degrees of freedom, and are left with an effective theory for the soft collective excitations. As a by-product, the “hard thermal loops” emerge naturally in a physically transparent framework. We show that the collective excitations can be described in terms of classical fields, and develop for these a Hamiltonian formalism. This can be used to estimate the effect of the soft thermal fluctuations on the correlation functions. The effect of collisions among the hard particles is also studied. In particular we discuss how the collisions affect the lifetimes of quasiparticle excitations in a regime where the mean free path is comparable with the range of the relevant interactions. Collisions play also a decisive role in the construction of the effective theory for ultrasoft excitations, with momenta ∼g2T, a topic which is briefly addressed at the end of this paper.

Subfields: Atomic and Molecular Physics, and Optics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/46d035c9337427e4d0ffa3732c9de9d772c8a0b4

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In Atomic and Molecular Physics, and Optics

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Citations in the corpus

Relativistic viscous hydrodynamics, conformal invariance, and holography (2007, background): “It may be possible to compute the coefficients of these terms for QCD in the weak-coupling regime by going beyond the lowest order gradient expansion given in [42].”
Issues on tadpoles and vacuum redefinitions in String Theory (2004, background): “The behavior of massless fields in simple models can give a taste of similar difficulties that they introduce in String Theory, and is also a familiar fact in Thermal Field Theory [87], where a proper treatment of IR divergences points clearly to the distinct roles of two power-series expansions, in”
Collective Phenomena in the Non-Equilibrium Quark-Gluon Plasma (2008, methodology): “Following [113], in this chapter we will derive the collisionless kinetic equations from the Kadanoff-Baym equations in the mean-field approximation using a gradient expansion.”
Relativistic Fluid Dynamics in and out of Equilibrium (2017, background): “At weak coupling τRT →∞, this non-hydrodynamic branch cut moves closer to the real axis and becomes the branch cut familiar from Landau-damping [192], with branch points at ω = ±k corresponding to single-particle excitations.”