Einstein-de Haas effect and induced rotation in QCD matter

TL;DR

This paper demonstrates the Einstein-de Haas effect in QCD matter, showing magnetic fields can induce collective rotation without initial vorticity, revealing new angular momentum dynamics in relativistic nuclear collisions.

Contribution

First identification of the Einstein-de Haas effect in QCD matter, linking magnetic fields to induced rotation and self-vorticity in hot QCD systems.

Findings

Magnetic fields induce rotations comparable to fluid vorticity in heavy-ion collisions.

Rotation arises solely from magnetic field-induced spin alignment, without initial vorticity.

Establishes QCD matter as a self-vortical magnetofluid with spin-rotation coupling.

Abstract

In this study, we report the first identification of the Einstein-de Haas (EdH) effect in the QCD matter. The EdH effect is a fundamental magnetomechanical coupling wherein magnetic-field-induced spin alignment generates a compensating collective rotation to conserve the total angular momentum. Using an equilibrium hadron gas under an external magnetic field, we show that even remnant magnetic fields at the freeze-out produce induced rotations ($\omega_{\mathrm{EdH}}$) comparable to typical estimates of fluid vorticity in heavy-ion collisions as inferred from final-state hyperon polarization. This rotation emerges from the magnetic field alone, without any initial vorticity as input. The Einstein-de Haas effect thus establishes hot QCD matter as a self-vortical magnetofluid, where collective rotation can be generated purely from spin alignment, and identifies spin-rotation coupling as a potentially important, previously overlooked component of angular momentum dynamics in relativistic nuclear collisions.