Unitarity for a de Sitter S-matrix

Santiago Agüí Salcedo - DAMTP
Unitarity for a de Sitter S-matrix

Abstract
For the last 20 years, there has been an increasing interplay between scattering amplitudes and the study of primordial correlators. These encode the information about the dynamics of the very early universe (before reheating) and can be inferred from the CMB anisotropies and the galaxy distribution in the night sky. One of the fundamental principles in studying scattering amplitudes has been unitarity, the conservation of information, which has given very tight constraints on scattering processes via the optical theorem. In this talk, I will briefly review the relation of primordial correlators with observations and the optical theorem in particle physics. I will present a recently developed S-matrix for cosmological spacetimes that allows for an optical theorem. I will discuss how particle production in cosmology modifies the optical theorem, focusing on 2->2 scattering processes. If time allows, I will discuss a derivation of positivity bounds using this new optical theorem and its connection to existing bounds in the literature.