Holography of the spin current

Specialist level
Umut Gürsoy
U. Utrecht



Recent developments both in high and low energy physics have increased the importance of hydrodynamics of matter with correlated spin degrees of freedom. In particular, Takahashi et al managed to create stable spin currents in liquid metals sourced by vorticity, and the STAR collaboration at RHIC observed nontrivial polarization of hyperon particles in off-central heavy ion collisions. Theoretical understanding of these findings requires adding the spin current to (relativistic) hydrodynamics as a new degree of freedom. In this talk — that will be based on arXiv:2004.05148  — I will describe how this can be done by sourcing the spin current by torsion. I will classify different types of torsion in 3+1 dimensions and develop the corresponding constitutive equations for the energy-momentum tensor and the spin current. We will then analyze the problem in a toy holographic model based on the 5D Lovelock-Chern-Simons theory. As a byproduct, I will introduce a number of  previously unknown blackhole solutions to this theory and map these solutions to hydrodynamics by the fluid-gravity correspondence. The resulting energy-momentum and spin flow exhibits interesting features including a dynamical version of the Barnett effect and indicate various novel mechanisms through which spin currents may be generated in strongly correlated systems.