Spin alignment, tensor polarizabilities, and local equilibrium for spin-1 particles

TL;DR

This paper develops a theoretical framework for understanding spin alignment and tensor polarizabilities of spin-1 particles, connecting density matrix components with observables in heavy-ion collisions and formulating perfect spin hydrodynamics.

Contribution

It introduces a unified approach to describe spin-1 particles using different bases and the adjoint representation, extending spin hydrodynamics to spin-1 particles.

Findings

Clarifies the connection between density matrix components and observables.

Introduces the equilibrium spin density matrix and Wigner function for spin-1 particles.

Formulates perfect spin hydrodynamics for spin-1 particles.

Abstract

Different bases for the spin-1 density matrix are discussed to clarify the connection between its components and observables measured in heavy-ion collisions. The theoretical advantage of using the adjoint representation for spin matrices is emphasized. Next, the equilibrium spin density matrix and the corresponding Wigner function are introduced. With appropriate definitions of the energy-momentum and spin tensors, this framework allows for the formulation of perfect spin hydrodynamics in the same way as previously done for spin-1/2 particles. Together, these results provide a unified description of spin-1/2 and spin-1 particles.