Global equilibrium at order πͺ(β2): pseudo-gauge ambiguity, Maxwell relations, and thermodynamic consistency
Abstract
We study massive spin-1/2 Boltzmann particles in global thermodynamic equilibrium with rotation and acceleration, consistently including quantum corrections up to order πͺ(β2). For such a system, the fluid velocity becomes an independent thermodynamic variable and fundamental thermodynamic relations have to be extended. Employing the Wigner-function formalism, we show that the standard mass-shell condition k2 = m2 is modified at order πͺ(β2) by contributions quadratic in the thermal vorticity. Incorporating this modified mass-shell constraint, we derive the (net) particle-number current, energy-momentum tensor, spin-current tensor, and associated thermodynamic quantities in the kinetic, canonical, and de Groot--van Leeuwen--van Weert (GLW) pseudo-gauges. We explicitly demonstrate that, while global quantities, like the total particle number or total energy, are independent of the choice of pseudo-gauge, local quantities, like the particle-number density or the energy density, are pseudo-gauge dependent. We then examine the thermodynamic relations in each pseudo-gauge and demonstrate that thermodynamic consistency requires that the thermodynamic Maxwell relations are satisfied. We find that these relations hold in the kinetic-theory pseudo-gauge, whereas they are in general violated in the canonical and GLW pseudo-gauges. These findings suggest a preference for using the kinetic-theory pseudo-gauge in applications such as spin hydrodynamics.
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BibTeX
@misc{daher2026global,
title = {{Global equilibrium at order $\mathcalO(\hbar^2)$: pseudo-gauge ambiguity, Maxwell relations, and thermodynamic consistency}},
author = {Asaad Daher and David Wagner and Masoud Shokri and Dirk H. Rischke},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.31819},
eprint = {2609.31819},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.31819},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Global equilibrium at order πͺ(β^2): pseudo-gauge ambiguity, Maxwell relations, and thermodynamic consistency
AU - Asaad Daher
AU - David Wagner
AU - Masoud Shokri
AU - Dirk H. Rischke
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.31819
UR - https://arxiv.org/abs/2609.31819
AB - We study massive spin-1/2 Boltzmann particles in global thermodynamic equilibrium with rotation and acceleration, consistently including quantum corrections up to order πͺ(β^2). For such a system, the fluid velocity becomes an independent thermodynamic variable and fundamental thermodynamic relations have to be extended. Employing the Wigner-function formalism, we show that the standard mass-shell condition k^2 = m^2 is modified at order πͺ(β^2) by contributions quadratic in the thermal vorticity. Incorporating this modified mass-shell constraint, we derive the (net) particle-number current, energy-momentum tensor, spin-current tensor, and associated thermodynamic quantities in the kinetic, canonical, and de Groot--van Leeuwen--van Weert (GLW) pseudo-gauges. We explicitly demonstrate that, while global quantities, like the total particle number or total energy, are independent of the choice of pseudo-gauge, local quantities, like the particle-number density or the energy density, are pseudo-gauge dependent. We then examine the thermodynamic relations in each pseudo-gauge and demonstrate that thermodynamic consistency requires that the thermodynamic Maxwell relations are satisfied. We find that these relations hold in the kinetic-theory pseudo-gauge, whereas they are in general violated in the canonical and GLW pseudo-gauges. These findings suggest a preference for using the kinetic-theory pseudo-gauge in applications such as spin hydrodynamics.
ER -