Abstract

In Minkowski space the S-matrix in an invaluable tool for analysing quantum field theories. Scattering matrices may also be constructed and exploited in eternally inflating spacetimes. In the first part of this talk I will review the perturbative construction of the S-matrix in global de Siter space. I will emphasize it’s value as a gauge and field redefinition-invariant probe for QFTs in the inflationary setting. As time allows I will also discuss features of such QFTs which, while obscure from the vantage point of local correlation functions, are transparent when viewed through the S-matrix.

In the second part of my talk I will discuss recent progress towards constructing the exact S-matrix of the Principal Chiral Model (PCM) in de Sitter space. The PCM is a 2-dimensional non-linear sigma model endowed with many of the mature attributes of QCD , including asymptotic freedom and dimensional transmutation. The PCM also contains an infinite number of hidden symmetries which make the theory integrable in Minkowski space. A sufficient number of these symmetries exist also in the de Sitter theory, and thus the de Sitter S-matrix may be determined up to a CDD -type ambiguity.