Enrico Pajer - Cosmological Soft Theorems
These lecture notes give an introduction to cosmological soft theorems. The goal is to provide a tool kit to extract observational predictions from symmetries in cosmological setups. The emphasis is on simple examples and basic derivations, which can work as toy models to understand the main underlying ideas. The main target for these notes are students and researchers familiar with standard introductory QFT and cosmology courses. These notes are based on the lectures I gave at the 2019 Asian-Pacific Winter School hosted by the Yukawa Institute of Theoretical Physics in Kyoto, Japan.
Contents
- Invitation to cosmological soft theorems
- Cosmological correlators
- Symmetries
- Cosmological correlators and linearly realized symmetries
- Adiabatic modes
- Background-wave method
- Ward Takahashi identities
- Conclusions