Polarization in relativistic fluids: a quantum field theoretical derivation

Understand

We review the calculation of polarization in a relativistic fluid within the framework of statistical quantum field theory.

• We derive the expressions of the spin density matrix and the mean spin vector both for a single quantum relativistic particle and for a quantum free field.
• After introducing the formalism of the covariant Wigner function for the scalar and the Dirac field, the relation between spin density matrix and the covariant Wigner function is obtained.
• The formula is applied to the fluid produced in relativistic nuclear collisions by using the local thermodynamic equilibrium density operator and recovering previously known formulae.