Hybrid approach to perfect and dissipative spin hydrodynamics

TL;DR

This paper introduces a hybrid spin hydrodynamics framework combining kinetic theory and Israel-Stewart methods, capturing both perfect and dissipative spin dynamics while conserving total angular momentum.

Contribution

It develops a novel hybrid model that integrates kinetic theory with nonequilibrium dynamics to describe spin hydrodynamics, including dissipation effects.

Findings

Entropy is conserved in the perfect-fluid limit.

Dissipative terms facilitate spin-orbit angular momentum transfer.

Total angular momentum remains conserved despite dissipation.

Abstract

A hybrid framework of spin hydrodynamics is proposed that combines the results of kinetic theory for particles with spin 1/2 with the Israel-Stewart method of introducing nonequilibrium dynamics. The framework of kinetic theory is used to define the perfect-fluid description that conserves baryon number, energy, linear momentum and spin part of angular momentum. This leads to the entropy conservation although, in the presence of spin degrees of freedom, the perfect-fluid formalism includes extra terms whose structure is usually attributed to dissipation. The genuine dissipative terms appear from the condition of positive entropy production in nonequilibrium processes. They are responsible for the transfer between the spin and orbital parts of angular momentum, with the total angular momentum being conserved.