Thermodynamics of ideal spin fluids

Conserved currents of relativistic spin fluids derived from 
microscopic models appear to violate local thermodynamic relations. In 
this talk, I will present how pseudo-gauge improvements in ideal spin 
hydrodynamics, i.e. improvements of conserved currents with total 
derivative terms, restore standard thermodynamic relations. We will 
quantify ambiguities in the spin equation of state and derive universal 
thermodynamic relations that apply to conserved currents in any 
pseudo-gauge. Time permitting, we will extract the thermodynamic 
variables and equations of state for free Dirac fermions and scalar 
fields. The talk is based on arXiv:2601.14421.