Title: Solid Adiabatic Modes and Soft Theorems
Abstract: Cosmological observations, from the cosmic microwave background to large-scale structure, indicate that the initial condition for inhomogeneities in our universe has been adiabatic, namely, in the long wavelength limit, any perturbation in our universe locally mimics a coordinate change.
I first review the concept of adiabatic modes; I demonstrate two empirical consequences of adiabaticity: conservation of the curvature perturbation and soft theorems for single field inflation.
Adiabatic modes for perfect fluids and scalar fields have been extensively studied in the literature. In this talk, I investigate a solid coupled to gravity; I study its adiabatic modes and their corresponding soft theorems. Although almost every deformation in a solid—even in the long wavelength limit—is non-adiabatic, I will show that a solid exhibits infinitely many adiabatic modes.