Causal Electric Charge Diffusion and Balance Functions in Relativistic Heavy Ion Collisions

TL;DR

This paper investigates how electric charge fluctuations propagate and diffuse in high-energy heavy ion collisions, using a causal diffusion model that limits propagation speed, affecting observable charge balance functions.

Contribution

It introduces a causal diffusion approach with the Cattaneo form to study charge fluctuations, incorporating fluctuation-dissipation noise, and estimates diffusion parameters from AdS/CFT.

Findings

Limiting charge propagation speed increases balance function height.

It reduces the width of charge balance functions in rapidity.

Provides an estimate for the diffusion time constant from AdS/CFT.

Abstract

We study the propogation and diffusion of electric charge fluctuations in high energy heavy ion collisions using the Cattaneo form for the dissipative part of the electric current. As opposed to the ordinary diffusion equation this form limits the speed at which charge can propagate. Including the noise term in the current, which arises uniquely from the fluctuation-dissipation theorem, we calculate the balance functions for charged hadrons in a simple 1+1 dimensional Bjorken hydrodynamical model. Limiting the speed of propagation of charge fluctuations increases the height and reduces the width of these balance functions when plotted versus rapidity. We also estimate the numerical value of the associated diffusion time constant from AdS/CFT theory.