Five easy pieces: The dynamics of quarks in strongly coupled plasmas

Abstract

We revisit the analysis of the drag a massive quark experiences and the wake it creates at a temperature T while moving through a plasma using a gravity dual that captures the renormalisation group runnings in the dual gauge theory. Our gravity dual has a black hole and seven branes embedded via Ouyang embedding, but the geometry is a deformation of the usual conifold metric. In particular the gravity dual has squashed two spheres, and a small resolution at the IR. Using this background we show that the drag of a massive quark receives corrections that are proportional to powers of log T when compared with the drag computed using AdS/QCD correspondence. The massive quarks map to fundamental strings in the dual gravity theory. We use the perturbation produced by these strings to compute the wake and compare with the results obtained using AdS/QCD correspondence. We also study the shear viscosity in the theory with running couplings, analyze the viscosity to entropy ratio and compare the result with the bound derived from AdS backgrounds. In the presence of higher order curvature square corrections from the back-reactions of the embedded D7 branes, we argue the possibility of the entropy to viscosity bound being violated. Finally, we show that our set-up could in-principle allow us to study a family of gauge theories at the boundary by cutting off the dual geometry respectively at various points in the radial direction. All these gauge theories can have well defined UV completions, and more interestingly, we demonstrate that any thermodynamical quantities derived from these theories would be completely independent of the cut-off scale and only depend on the temperature at which we define these theories. Such a result would justify the holographic renormalisabilities of these theories which we, in turn, also demonstrate. We give physical interpretations of these results and compare them with more realistic scenarios.

Viscous photons in relativistic heavy ion collisions

“…In the case with a non-zero shear viscosity, a value of η/s (the shear viscosity divided by the entropy density) = 1/4π has been used. This value has been suggested as a lower universal bound [25], a statement which has raised some controversy and thus needed to be qualified [26][27][28]. Furthermore, η/s will also depend on the local temperature of the medium, but a constant value will suffice for the study in this work.…”

QCD on a small circle

“…If center symmetry is stabilized by a double trace deformation, then parametrically [12] 14) and m γ /m W = O(η 11/6 ). 8 …”

“…But the demonstration of chiral symmetry breaking and determination of these low energy constants requires other methods, such as large scale lattice gauge theory simulations or input of experimental data. Gauge-gravity duality [2] has provided insight into some 4D confining gauge theories [3][4][5][6][7][8], but is usefully applicable primarily in theories which are strongly coupled at all scales, not asymptotically free, and have a large number N of colors. For 4D confining, asymptotically free gauge theories, analytic methods based on controlled approximations are generally unavailable.…”

Non-extremal geometries and holographic phase transitions

“…Working with the ten dimensional geometry, we avoid the difficulty of KK reduction while extracting the exact RG flow of the gauge theory. The thermal gauge theory studied in [52]- [58] has a rich phase structure and as temperature is altered, we expect phase transitions. Our goal is to study the phase transitions at strong coupling, but to do so, we must first understand how geometries can describe different phases.…”

“…In a series of papers [52]- [58], we proposed the ten dimensional deformed resolved conifold black hole geometry as the dual to UV complete gauge theory which resembles large N thermal QCD. Working with the ten dimensional geometry, we avoid the difficulty of KK reduction while extracting the exact RG flow of the gauge theory.…”