Würzburg Seminar on Quantum Field Theory and Gravity

Collective motion of spin degrees of freedom has been playing an increasingly prominent role both in high energy and condensed matter  physics, especially after the observation of global polarization of Lambda hyperons in heavy ion collisions and generation of spin currents in liquid metals. In this talk, I will introduce a first principles construction of spin hydrodynamics, that is, relativistic hydrodynamics of spin currents coupled to stress tensor. The basic idea is to borrow the notion of ‘torsion' from general relativity to remove the Belinfante-Rosenfeld ambiguity in definition of the spin current in QFT, and use 'spin-connection', again a notion from the Einstein-Cartan theory, to introduce spin chemical potentials as dynamical variables for hydrodynamics. We then apply this formulation to heavy ion collisions and find good agreement with data.