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Dissipative spin hydrodynamics in Bjorken flow and thermal dilepton production

Sejal Singh1,*, Sourav Dey1,2,†, Arpan Das1,‡, Hiranmaya Mishra2,3,§, and Amaresh Jaiswal2,∥

  • *Contact author: p20230472@pilani.bits-pilani.ac.in
  • †Contact author: sourav.dey@niser.ac.in
  • ‡Contact author: arpan.das@pilani.bits-pilani.ac.in
  • §Contact author: hiranmaya@niser.ac.in
  • ∥Contact author: a.jaiswal@niser.ac.in
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Phys. Rev. D 114, 054023 – Published 11 September, 2026

DOI: https://doi.org/10.1103/8qmn-6wvl

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 magneticlike 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. Within the simplified hydrodynamic evolution considered here, our results qualitatively indicate that thermal dileptons can possibly provide an indirect probe of spin dynamics and spin transport in the quark-gluon plasma.

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Phys. Rev. D 114, 054023– Published 11 September, 2026
  • Received 15 April 2026
  • Accepted 13 August 2026
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