Quarkonium dissociation in a far-from-equilibrium holographic setup

Abstract

The real-time dissociation of the heavy quarkonium in a strongly coupled boost-invariant nonAbelian plasma relaxing towards equilibrium is analyzed in a holographic framework. The effects driving the plasma out of equilibrium are described by boundary quenching, impulsive variations of the boundary metric. Quarkonium is represented by a classical string with endpoints kept close to the boundary. The evolution of the string profile is computed in the time-dependent geometry, and the dissociation time is evaluated for different configurations with respect to the direction of the plasma expansion. Dissociation occurs quickly for the quarkonium placed in the transverse plane.PACS numbers: 12.38. Mb, 11.25.Tq The discovery that the QCD matter produced in ultrarelativistic heavy ion collisions behaves as a hightemperature, nearly frictionless, strongly coupled fluid raises new questions, both to experiment and theory [1]. On the one hand, through the study of new production modes and observables it is important to identify the smallest size of the QCD system characterized by this behavior, interpreting the hints of collective features observed in high energy pp and pA collisions [2]. On the other hand, the real-time dynamics of the relaxing fluid needs to be quantitatively described, starting from the far-from-equilibrium state produced immediately after the collision and relaxing towards a hydrodynamic regime: this issue is difficult to face using traditional theoretical techniques, which deal either with weakly coupled systems or, as in lattice QCD, with systems at equilibrium in the Euclidean time. The importance of theoretical analyses of processes occurring in outof-equilibrium matter has been recently emphasized [3]. Among those phenomena, the heavy quarkonium dissociation plays a role in the characterization of the plasma, since it can be interpreted as a signature of deconfinement [4].Gauge/gravity duality [5][6][7] ("holographic") methods provide tools to describe out-of-equilibrium strongly coupled systems, mapping the dynamics of a gauge system into a gravity problem. Although the existence of a gravitational dual of QCD has not been established, yet, insights can be gained by the study of theories sharing various properties with QCD. In particular, a plasma of N = 4 supersymmetric Yang-Mills theory (SYM), similarly to the QCD plasma (QGP), is nonconfined and strongly interacting. Adopting the gauge/gravity approach the gravitational dual of N = 4 SYM in the large N c limit, the ten dimensional AdS 5 × S 5 space, can be considered, with a black-hole (BH) to describe the boundary theory at finite temperature 1 .In this framework, quarks can be treated as dual to open strings in the higher dimensional space [11]. Their in-medium dynamics is described starting from the initial configuration of a classical string in the dual space, and following the string evolution dictated by the equations of motion resulting from the Nambu-Goto action.Different configurations have been considered in a static gravitational...

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Investigating thermalization of a strongly interacting non-Abelian plasma

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Anisotropic and frame dependent chaos of suspended strings from a dynamical holographic QCD model with magnetic field

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