Title: [NTU-NCTS String Seminar] Kallen-Lehmann spectral decomposition in dS
Speaker: Dr. Kamran Salehi (Univ. of Amsterdam)
Time: May. 25, 2023 (Thur.) 14:30-15:30
Venue: Rm. 815, Dept. of Physics, NTU

Abstract:
The implications of unitarity in cosmology is not as well understood as those in the flat space: the absence of time reversal symmetry makes it ambiguous to define a functionally well-defined unitary evolution operator; and, the cosmological optical theorem suffers order of limit ambiguities, making it impossible to determine (and interpret) distributional pieces in it, along with their role in the flat space limit. In this talk, I'll review these problems and argue how a purely geometric approach based on what we name "the optical polytope" can resolve them.