Violation of the KSS Bound in Holographic Bjorken-Flow

TL;DR

This paper investigates entanglement entropy in holographic Bjorken-flow systems and finds a transient violation of the KSS bound on viscosity-to-entropy ratio, providing insights into quark-gluon plasma dynamics.

Contribution

It demonstrates a momentary violation of the KSS bound in a holographic model of Bjorken-flow, linking entanglement entropy to boundary QCD variables.

Findings

The $ ext{eta}/s$ ratio dips below $1/4 extpi$ temporarily.

The $ ext{eta}/s$ ratio asymptotes to $1/4 extpi$ at large times.

Holographic entanglement entropy reflects the transient violation.

Abstract

In a system with a Bjorken-flow (BF), considering the inside of a BF as a subsystem for the reason explained in the body text, we compute entanglement entropy appearing in our side holographically . BF consists of many concentrically scattering quark-gluon plasmas created by colliding two masses of hadrons. Our BF is defined in the boundary space in an asymptoticly five-dimensional Anti de-Sitter space with a growing Schwartzshild black hole. %, where its Hawking temperature diminishes with time. In our analysis we can get a parameter prescribing our bulk space-time in terms of the boundary QCD's variables. Using this, we find that the $\eta/s$ dips from $1/4\pi$ just for a moment before asymptoting to $1/4\pi$ at infinitely large time. Since $1/4\pi$ is the KSS bound, this result is intriguing as an example of violation of the KSS bound.