Gauge/String Duality, Hot QCD and Heavy Ion Collisions

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Abstract:We use holographic duality to analyze the drag force on, and consequent energy loss of, a heavy quark moving through a strongly coupled conformal fluid with non-vanishing gradients in its velocity and temperature. We derive the general expression for the drag force to first order in the fluid gradients. Using this general expression, we show that a quark that is instantaneously at rest, relative to the fluid, in a fluid whose velocity is changing with time feels a nonzero force. And, we show that for a quark that is moving ultra-relativistically, the first order gradient "corrections" become larger than the zeroth order drag force, suggesting that the gradient expansion may be unreliable in this regime. We illustrate the importance of the fluid gradients for heavy quark energy loss by considering a fluid with one-dimensional boost invariant Bjorken expansion as well as the strongly coupled plasma created by colliding sheets of energy.

Section: Jhep02(2014)068mentioning

confidence: 99%

Section: Jhep02(2014)068mentioning

confidence: 99%

Effects of fluid velocity gradients on heavy quark energy loss

Lekaveckas

Rajagopal

2014

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“…Top-down theories arising from string theory have been studied extensively to give ballpark estimates of strongly coupled phases of QCD [2] and condensed matter systems [3].…”

Section: Introductionmentioning

confidence: 99%

Transport properties of spacetime-filling branes

Tarrío

2014

A model consisting of (d+1)-dimensional gravity coupled to spacetime filling charged branes is used to study the effects of backreaction. The charged black holes arising from this simple model reflect the non-linearity of the gauge field and are thermodynamically stable. By analysing fluctuations of the system we corroborate that at low values of the temperature (or large chemical potential) backreaction effects from the branes are dominant. We also provide a generalisation of the Iqbal and Liu strategy to calculate the DC conductivity, in which a mass term for the gauge field fluctuation is included. This mass term gives the value of the residue of the pole at zero frequency in the imaginary part of the AC conductivity, as well as the running of the DC conductivity with the bulk radius.

“…Several such studies have now been performed in cases in which the gauge theory is a Conformal Field Theory (CFT) [3][4][5][6]. 2 The goal of this paper is to give a first step towards extending this program to gravitational duals of confining gauge theories. For this purpose we will consider collisions in the so-called AdS-soliton [14,15].…”

Section: Introductionmentioning

confidence: 99%

Holographic collisions in confining theories

Cardoso

Matéos

Pani

et al. 2014

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Abstract:We study the gravitational dual of a high-energy collision in a confining gauge theory. We consider a linearized approach in which two point particles traveling in an AdSsoliton background suddenly collide to form an object at rest (presumably a black hole for large enough center-of-mass energies). The resulting radiation exhibits the features expected in a theory with a mass gap: late-time power law tails of the form t −3/2 , the failure of Huygens' principle and distortion of the wave pattern as it propagates. The energy spectrum is exponentially suppressed for frequencies smaller than the gauge theory mass gap. Consequently, we observe no memory effect in the gravitational waveforms. At larger frequencies the spectrum has an upward-stairway structure, which corresponds to the excitation of the tower of massive states in the confining gauge theory. We discuss the importance of phenomenological cutoffs to regularize the divergent spectrum, and the aspects of the full non-linear collision that are expected to be captured by our approach.