Speaker
Description
We study the quantum field theory of zero-temperature perfect fluids. These systems can be defined by quantizing a classical field theory of scalar fields $\phi^I$, which act as Lagrange coordinates on an internal spatial manifold of fluid configurations. Invariance under volume-preserving diffeomorphisms acting on these scalars implies that the long-wavelength spectrum contains vortex (transverse) modes with an exact $\omega_T=0$ dispersion relation. As a result, physically interpreting the theory within perturbative quantization has proven challenging.
In this talk, I will show that correlators evaluated in a class of semi-classical (Gaussian) initial states prepared at $t=0$ are nevertheless well-defined and accessible via perturbation theory. The width of the initial state effectively acts as an infrared regulator, without explicitly breaking the diffeomorphism invariance of the classical action. As an application, I will present the computation of stress-tensor two-point correlators and show that vortex modes give a non-trivial contribution to the response function, which is non-local in both space and time.