Wave Speed in the Macroscopic Extended Model for Ultrarelativistic Gases

TL;DR

This paper analyzes wave speeds in a macroscopic extended model for ultrarelativistic gases, revealing that some wave speeds are rational and identical to those in the kinetic model, with the system decomposing into independent subsystems.

Contribution

It demonstrates that wave speeds in the macroscopic model can be fully characterized and are identical to kinetic model speeds, with a novel decomposition into independent subsystems.

Findings

Wave speeds can be divided into independent subsystems.

Some wave speeds are rational numbers.

Wave speeds match those in the kinetic model.

Abstract

An exact macroscopic extended model for ultrarelativistic gases, with an arbitrary number of moments, is present in the literature. Here we exploit equations determining wave speeds for that model. We find interesting results; for example, the whole system for their determination can be divided into independent subsystems and some, but not all, wave speeds are expressed by rational numbers. Moreover, the extraordinary property that these wave speeds for the macroscopic model are the same of those in the kinetic model, is proved.