Bogoliubov Laboratory of Theoretical Physics

Seminar “Theory of Hadronic Matter under Extreme Conditions

Date and Time: Tuesday, 23 December 2025, at 4:00 PM

Venue: Blokhintsev Lecture Hall, Bogoliubov Laboratory of Theoretical Physics, online on Zoom

1. Seminar topic: “Gaussian generally covariant hydrodynamics”

   Speaker: Giorgio Torrieri (Unicamp, Brazil)

Annotation:

We develop a version of fluctuating relativistic hydrodynamics in a way very different from the usual derivation: Instead of treating it as a coarse-grained deterministic theory expanded in gradients of equilibrium quantities, we treat it as a stochastic theory, characterized by partition functions in each cells, expanded in cumulants. We show that the Gaussian ansatz allows us, via the gravitational Ward identities acting as a constraint between the variance and the average, to maintain full general covariance, with hydrodynamic flow emerging as an approximate Killing vector. If the symmetry of ideal hydrodynamics, volume-preserving diffeomorphisms, is preserved, we show that linear response formulas are also generally covariant. We discuss our results and argue that in this approach, the applicability of the effective theory is parametrized around a very different quantity than the Knudsen number, offering hope of understanding the applicability of hydrodynamics to small systems.

2. Seminar topic: “Causality of polarizable dissipative fluids from Lagrangian hydrodynamics”

   Speaker: David Montenegro

   Annotation:

   We perform a causality analysis on the dispersion relation of hydrodynamics with spin as well as shear and bulk viscosity, including the relaxation times for all these quantities. We find that the interplay of the three relaxational scales, for shear and bulk viscosity as well as polarization, leads to nontrivial effects on the dispersion relation. Unexpectedly, the presence of polarization leads to lower effective viscosity and a longer relaxation time, and the presence of viscosity leads to lower limits as well as upper ones on the group velocity and constraints relating polarization to viscosity relaxation times. We conclude with a qualitative discussion on how these results impact phenomenology, specifically the low effective viscosity in strongly interacting matter as well as shear-vorticity coupling.