Diffusion of conserved charges in relativistic heavy ion collisions

TL;DR

This paper calculates the full diffusion matrix for baryon, electric, and strangeness charges in nuclear matter, revealing significant coupling effects between different charge currents in relativistic heavy ion collisions.

Contribution

It introduces the first comprehensive calculation of the complete diffusion matrix including three conserved charges, highlighting inter-charge coupling effects.

Findings

Baryon diffusion is influenced by baryon and strangeness gradients.

Electric charge diffusion is affected by electric and strangeness gradients.

Strangeness currents depend mainly on strange and baryon gradients.

Abstract

In order to characterize nuclear matter under extreme conditions, we calculate all diffusion transport coefficients related to baryon, electric and strangeness charge for both a hadron resonance gas and a simplified kinetic model of the quark-gluon plasma. We demonstrate that the diffusion currents do not depend only on gradients of their corresponding charge density. Instead, we show that there exists coupling between the different charge currents, in such a way that it is possible for density gradients of a given charge to generate dissipative currents of another charge. Within this scheme, the charge diffusion coefficient is best viewed as a matrix, in which the diagonal terms correspond to the usual charge diffusion coefficients, while the off-diagonal terms describe the coupling between the different currents. In this letter, we calculate for the first time the complete diffusion matrix including the three charges listed above. We find that the baryon diffusion current is strongly affected by baryon charge gradients, but also by its coupling to gradients in strangeness. The electric charge diffusion current is found to be strongly affected by electric and strangeness gradients, whereas strangeness currents depend mostly on strange and baryon gradients.