A holographic model for large N thermal QCD

TL;DR

This paper presents a holographic model for large N thermal QCD, capturing key features like running coupling, confinement, and deconfinement, and computes physical properties such as viscosity, entropy, and quark diffusion.

Contribution

It introduces a new holographic model for large N QCD with matter in the fundamental representation, analyzing its thermodynamic and transport properties.

Findings

The model exhibits a logarithmic running of the gauge coupling at low energies.

It predicts a violation of the viscosity to entropy ratio bound.

Quark confinement and deconfinement phases are successfully modeled.

Abstract

We summarize the dual gravity description for a thermal gauge theory, reviewing the key features of our holographic model of large N QCD and elaborating on some new results.The theory has matter in the fundamental representation and the gauge coupling runs logarithmically with energy scale at low energies. At the highest energies the theory becomes approximately scale invariant, much like what we would expect for large N QCD although not with asymptotic freedom. In this limit the theory has a gravity dual captured by an almost classical supergravity description with a controlled quantum behavior, such that by renormalizing the supergravity action, we can compute the stress tensor of the dual gauge theory. From the stress tensor we obtain the shear viscosity and the entropy of the medium at a temperature T, and the violation of the bound for the viscosity to the entropy ratio is then investigated. By considering dynamics of open strings in curved spacetime described by the supergravity limit, we compute the drag and diffusion coefficients for a heavy parton traversing the thermal medium. It is shown that both coefficients have a logarithmic dependence on momentum, consistent with pQCD expectations. Finally, we study the confinement/deconfinement mechanism for quarks by analyzing open strings in the presence of the flavor seven branes. We find linear confinement of quarks at low temperatures, while at high temperatures the quarkonium states melt, a behavior consistent with the existence of a deconfined phase.