# High Energy Physics Seminar

*,*Stanford University

*,*

I will discuss the fundamentals of quantum field theory on a rigid de Sitter space. I will show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. This finding simplifies dramatically perturbative computations, as well as allows us to establish basic properties of these correlators, which comprise a Euclidean CFT. This is used to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of late-time four-point functions, to derive an OPE expansion, and to constrain the operator spectrum that appears in it. Generically, dimensions and OPE coefficients do not obey the usual CFT notion of unitarity. Instead, unitarity of the de Sitter theory manifests itself as the positivity of the spectral density. I will illustrate these properties by explicit calculations in a scalar theory by computing the exchange diagrams. An exchanged particle appears as a resonant feature in the spectral density which can be potentially useful in experimental searches.

Contact [email protected] for Zoom link.