Speaker
Description
Relativistic hydrodynamics is the universal long-wavelength framework for many-body systems near local equilibrium. Motivated by spin hydrodynamics and by the approximate scale symmetry of high-temperature QCD matter, I will discuss a relativistic hydrodynamic theory in which spin and intrinsic dilation are treated as quasi-hydrodynamic degrees of freedom. This talk will be based on our recent work, available as arXiv:2603.17794.
The theory is constructed phenomenologically from the conservation laws associated with the Weyl-Poincaré group, together with the local second law of thermodynamics. The resulting constitutive relations contain, in addition to shear and rotational viscosities, a bulk-viscosity-like coefficient controlling the relaxation of intrinsic dilation and a dilation conductivity governing its diffusion. This bulk-like response does not represent explicit breaking of scale invariance; rather, it describes how microscopic stretching or compression of fluid elements relaxes toward the macroscopic expansion.
The linearized theory contains a gapped dilation mode and exhibits freeze-out of long-wavelength sound perturbations in an expanding or contracting background. In the nonrelativistic limit, it reduces to microstretch-fluid dynamics, where spin and intrinsic dilation correspond to microrotation and microstretch, respectively.
I will also discuss how the scale anomaly modifies this hydrodynamic structure when the fluid is coupled to electromagnetic fields. The anomaly induces a nondissipative electric current, but local thermodynamic consistency requires this current to be accompanied by additional nondissipative corrections to the energy-momentum tensor and the dilation density.