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arXiv · 2601.14421

Thermodynamics of ideal spin fluids and pseudo-gauge ambiguity

Jay Armas·Akash Jain
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Abstract

Conserved currents of relativistic spin fluids derived from microscopic models are known to violate local thermodynamic relations. We present a systematic analysis of pseudo-gauge improvements in ideal spin hydrodynamics and identify a family of pseudo-gauges where standard thermodynamic relations are satisfied. We quantify pseudo-gauge ambiguities in the spin equation of state and derive universal thermodynamic relations that apply to conserved currents in any pseudo-gauge. As an application, we extract the thermodynamic variables and equations of state for free Dirac fermions and scalar fields.

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Jay Armas, Akash Jain. 2026-01-20. Thermodynamics of ideal spin fluids and pseudo-gauge ambiguity. https://arxiv.org/abs/2601.14421

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