The spin tensor in relativistic fluids in local equilibrium

• Andrea Palermo (Stony Brook University)

Room: Peter Paul Seminar Room The measurement of spin polarization in heavy-ion collisions spurred theoretical research in different directions. Among these, spin hydrodynamics advocates for including the spin tensor as an independent degree of freedom in hydrodynamics. However, the definition of the spin tensor is not unique, an ambiguity known as pseudogauge symmetry that hinders the interpretation of spin hydrodynamics. After reviewing the quantum relativistic statistical operator formalism, I show that a rotating NJL-like model with axial current interactions is equivalent to a theory of spin hydrodynamics with a specific choice of spin tensor. This duality suggests that the underlying QCD dynamics can automatically select the spin tensor for the statistical description of heavy-ion collisions. The conclusions of this study favor the use of the canonical spin tensor.