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  • Open Access

Second-order spin hydrodynamics from Zubarev’s nonequilibrium statistical operator formalism

Abhishek Tiwari* and Binoy Krishna Patra†

  • *Contact author: abhi7phy@gmail.com
  • †Contact author: binoy@ph.iitr.ac.in

Phys. Rev. D 112, 036014 – Published 22 August, 2025

DOI: https://doi.org/10.1103/8jw8-9w1x

Abstract

Using the Zubarev’s nonequilibrium statistical operator formalism, we derive the second-order expression for the dissipative tensors in relativistic spin hydrodynamics, viz. rotational stress tensor (τμν), boost heat vector (qμ), shear stress tensor (πμν), and bulk viscous pressure (Π). The first two (τμν and qμ) emerge due to the inclusion of the antisymmetric part in the energy-momentum tensor, which, in turn, governs the conservation of spin angular momentum (Σαμν). As a result, new thermodynamic forces, generated due to the antisymmetric part of Tμν, contain the spin chemical potential. In this work, we have also taken the spin density (Sμν) as an independent thermodynamic variable, in addition to the energy density and particle density, thereby resulting in two novel transport coefficients given by the correlation between spin density tensor and rotational stress tensor and vice versa. Additionally, the newly found terms in πμν and Π are the artifacts of the new thermodynamic forces that arise due to the antisymmetric part of Tμν. Finally, we have derived the evolution equations for the aforesaid tensors: τμν, qμ, πμν, and Π.

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