Physical Representations for Scattering Amplitudes and the Wavefunction of the Universe

Understand

The way we organise perturbation theory is of fundamental importance both for computing the observables of relevance and for extracting fundamental physics out of them.

• If on one hand the different ways in which the perturbative observables can be written make manifest different features (e.g.
• symmetries as well as principles such as unitarity, causality and locality), on the other hand precisely demanding that some concrete features are manifest lead to different ways of organising perturbation theory.
• In the context of flat-space scattering amplitudes, a number of them are already known and exploited, while much less is known for cosmological observables.