Abstract
We discuss the diffusion currents occurring in a dilute system and show that the charge currents do not only depend on gradients in the corresponding charge density, but also on the other conserved charges in the system—the diffusion currents are therefore coupled. Gradients in one charge thus generate dissipative currents in a different charge. In this approach, we model the Navier-Stokes term of the generated currents to consist of a diffusion coefficient matrix, in which the diagonal entries are the usual diffusion coefficients and the off-diagonal entries correspond to the coupling of different diffusion currents. We evaluate the complete diffusion matrix for a specific hadron gas and for a simplified quark-gluon gas, including baryon, electric and strangeness charge. Our findings are that the off-diagonal entries can range within the same magnitude as the diagonal ones.
Highlights
To study the properties of dense and hot nuclear matter, much attention was given to the ultrarelativistic collisions of heavy ions
In order to describe diffusion processes in heavy ion collisions, we suggest that the complete diffusion coefficient matrix, and the implied cross-coupling of diffusion currents, must be taken into account
We presented the first results for the coefficient matrix of two systems consisting of baryon, strangeness and electric charge: for a hot hadron gas and a simplified model for a QGP
Summary
To study the properties of dense and hot nuclear matter, much attention was given to the ultrarelativistic collisions of heavy ions. Since the net-charge density of nuclear matter produced in high energy heavy ion collisions is almost homogeneously vanishing and dissipative effects due to diffusion are hard to observe [13], diffusion processes received less attention. It is essential to study the effects of these gradients in order to better understand the evolution of heavy ion collisions at lower energies.
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