RelSpinHydro · Relativistic Spin Hydrodynamics: Theory and Applications

This proposal establishes connections between fluid dynamics, quantum field theory, and mathematical physics to develop new tools to better characterise out-of-equilibrium properties of relativistic quantum many-body systems. My work is instrumental to understand the emergence of novel fluid-like behaviours which are not apparent in the fundamental laws. The focus of my research is the quark-gluon plasma (QGP), an exotic phase of quantum chromodynamics (QCD) where quarks and gluons are not confined inside of nucleons. The QGP is formed in relativistic heavy-ion collisions performed at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). A huge surprise was the discovery that the QGP behaves as a relativistic liquid with very special properties, namely, it flows with the lowest specific viscosity of any known liquid, and it is by far the system with the largest vorticity ever observed. Such large vorticity triggers particle polarisation, which is a phenomenon resembling the magnetisation displayed by a ferromagnet that is spinning around an axis. This effect shows the interplay between a macroscopic quantity, the fluid rotation, and a microscopic quantity, which is inherently of quantum nature: the spin of the particles. The recent observation of polarisation phenomena of hadrons emitted from the rotating QGP in heavy-ion collisions calls for a new formulation of relativistic fluids where spin degrees of freedom are crucial to the dynamics -- this is called relativistic spin hydrodynamics. Despite fluid dynamics being an old subject, the formulation of the full causal and stable theory of relativistic spin hydrodynamics which can be used for theoretical predictions is yet to be developed.Expected outcomes from this proposal include:* the formulation of causal and stable theories of relativistic spin hydrodynamics,* their extensions to the far-from-equilibrium regime,* applications to QGP physics.