Impact of spin polarization on transport and thermodynamic coefficients

This work investigates the influence of parton spin polarization on effective transport and thermodynamic coefficients in noncentral light- and heavy-ion collisions. To model this influence, I consider two sources of spin polarization: thermal vorticity, induced by angular momentum, and thermal shear, arising from local velocity gradients. Using a novel kinetic theory framework, one finds that transport and thermodynamic coefficients – including the speed of sound squared $c_s^2$, specific shear viscosity $\eta \mathrm{/}s$, specific bulk viscosity $\zeta \mathrm{/}s$, and mean free path $\lambda$ – are substantially modified by spin polarization effects. Among the two sources, thermal vorticity-induced spin polarization dominates the modifications to these coefficients. Moreover, both $c_s^2$ and $\zeta \mathrm{/}s$ exhibit a nonmonotonic dependence on the collision energy, and the associated scaling behaviors potentially serve as indicators of the critical phenomena of quantum chromodynamics.