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

Abstract: Using the Zubarev's nonequilibrium statistical operator formalism, we derive the second-order dissipative tensors in relativistic spin hydrodynamics, {\em viz.} rotational stress tensor ($\tau_{\mu\nu}$), boost heat vector ($q_\mu$), shear stress tensor ($\pi_{\mu\nu}$) and bulk viscous pressure ($\Pi$). The first two ($\tau_{\mu\nu}$ and $q_\mu$) emerge due to the inclusion of the antisymmetric part in the energy-momentum tensor, which, in turn, governs the conservation of spin angular momentum ($\Sigma^{\alpha\mu\nu}$). As a result, new thermodynamic forces, generated due to the antisymmetric part of $T_{\mu \nu}$, contains the spin chemical potential. In this work, we have also taken the spin density ($S^{\mu \nu}$) as an independent thermodynamic variable, in addition to the energy density and particle density, thereby resulting in an additional transport coefficient given by the correlation between $S^{\mu \nu}$ and $\tau^{\mu \nu}$. The newly found terms in $\pi_{\mu\nu}$ and $\Pi$ are the artifacts of the new thermodynamic forces that arise due to the antisymmetric part of $T^{\mu \nu}$. Finally we have derived the evolution equations for the aforesaid tensors - $\tau_{\mu\nu}$, $q_\mu$, $\pi_{\mu\nu}$, and $\Pi$.