Dissipative spin hydrodynamics in Bjorken flow and thermal dilepton production

TL;DR

This paper develops a first-order spin hydrodynamic model for Bjorken flow, analyzing how spin transport influences temperature evolution and enhances thermal dilepton production in quark-gluon plasma.

Contribution

It introduces a coupled spin and temperature evolution framework with spin transport coefficients, linking spin dynamics to observable dilepton yields.

Findings

Spin chemical potential components evolve differently, with magnetic-like components surviving longer.

Spin dissipation causes transverse spin components to decay faster.

Spin dynamics increase thermal dilepton production compared to standard hydrodynamics.

Abstract

We investigate the boost-invariant expansion of a recently developed first-order spin hydrodynamic framework in which the spin chemical potential is treated as a leading-order hydrodynamic variable. Considering a symmetric energy-momentum tensor and a separately conserved spin tensor, we derive the coupled evolution equations for the medium temperature and the independent components of the spin chemical potential in the presence of both viscous and spin-diffusive transport coefficients. For a boost-invariant system, only the magnetic-like components of the spin chemical potential survive, and their evolution is shown to depend sensitively on the spin transport coefficients. The transverse spin components decay more rapidly due to spin dissipation, while the longitudinal component survives for a longer duration. We further demonstrate that the evolution of the spin degrees of freedom modifies the temperature profile of the expanding medium. Using the resulting temperature profiles, we calculate thermal dilepton production rates from quark-antiquark annihilation. We find that the presence of spin dynamics enhances the dilepton yield relative to standard dissipative hydrodynamics, with the magnitude of the enhancement depending on the spin transport coefficients. Our results indicate that thermal dileptons can provide an indirect probe of spin dynamics and spin transport in the quark-gluon plasma.