Spin-thermal shear coupling in a relativistic fluid

TL;DR

This paper demonstrates that thermal shear in a relativistic fluid can generate spin polarization of fermions, adding a new non-dissipative mechanism that may explain polarization phenomena in heavy ion collisions.

Contribution

It introduces the concept that thermal shear, via the symmetric derivative of the four-temperature vector, contributes to spin polarization, expanding the understanding beyond vorticity effects.

Findings

Thermal shear contributes to fermion spin polarization.

The shear-induced polarization is non-dissipative.

Implications for resolving polarization puzzles in heavy ion collisions.

Abstract

We show that spin polarization of a fermion in a relativistic fluid at local thermodynamic equilibrium can be generated by the symmetric derivative of the four-temperature vector, defined as thermal shear. As a consequence, besides vorticity, acceleration and temperature gradient, also the shear tensor contributes to the polarization of particles in a fluid. This contribution to the spin polarization vector, which is entirely non-dissipative, adds to the well known term proportional to thermal vorticity and may thus have important consequences for the solution of the local polarization puzzles observed in relativistic heavy ion collisions.