Boost-invariant and cylindrically symmetric perfect spin hydrodynamics

TL;DR

This paper numerically solves boost-invariant, cylindrically symmetric perfect spin hydrodynamics equations, revealing a coupling between spin polarization components and potential polarization effects in relativistic gases.

Contribution

It introduces a more general initial condition framework and expansion geometry for spin hydrodynamics, extending previous symmetry-based studies.

Findings

Coupling between azimuthal and longitudinal spin components identified.

Only longitudinal magnetic component can induce net polarization under the assumed geometry.

Results provide a reference for more realistic hydrodynamic models.

Abstract

Equations of a boost-invariant and cylindrically symmetric perfect hydrodynamics are solved numerically for initial conditions inspired by the wounded nucleon model. The energy-momentum and spin tensors are used in the form that describes a relativistic massive gas governed by Boltzmann statistics. In contrast to one dimensional boost-invariant expansion, we find a coupling between the azimuthal and longitudinal components of the electric and magnetic components of the spin polarization tensor. This feature is similar to that found earlier for the Gubser symmetry, however, our treatment allows for a more general form of initial conditions and expansion geometry. Defining the freeze-out hypersurface by the constant temperature condition, we evaluate the Pauli-Luba\'nski four-vector and find that for the assumed geometry the only nonzero total polarization may be induced by the longitudinal component of the magnetic part of the spin polarization tensor coupled with the azimuthal electric component. The obtained results may serve as a reference point for more realistic models of hydrodynamic expansion.