Relativistic spin hydrodynamics with momentum- and spin-dependent relaxation time

Using the extended relaxation time approximation along with the theory of semiclassical spin, a framework of relativistic dissipative spin hydrodynamics is developed such that the relaxation time can depend on the momenta and spin of the constituent spin-1/2 particles. A general definition of the fluid four-velocity is considered, allowing the theory to be valid in a general frame and matching conditions. Consequently, the frame-invariant bulk, shear, particle diffusion, and spin transport coefficients are obtained, showing that the evolution of fluid remains unaffected by spin in the limit of small polarization as was the case where the relaxation time was independent of spin or momentum.