Heavy Operators and Hydrodynamic Tails

Understand

The late time physics of interacting QFTs at finite temperature is controlled by hydrodynamics.

• For CFTs this implies that heavy operators -- which are generically expected to create thermal states -- can be studied semiclassically.
• We show that hydrodynamics universally fixes the OPE coefficients $C_{HH'L}$, on average, of all neutral light operators with two non-identical heavy ones, as a function of the scaling dimension and spin of the operators.
• These methods can be straightforwardly extended to CFTs with global symmetries, and generalize recent EFT results on large charge operators away from the case of minimal dimension at fixed charge.