Harry Goodhew - The Cosmological CPT Theorem

Abstract: The CPT theorem states that a unitary and Lorentz-invariant theory must also be invariant under a discrete symmetry, CRT which reverses charge, time, and one spatial direction. In this talk, I will present a new derivation of this result by considering discrete symmetries built from CRT, Lorentz Invariance and Unitarity which form a Z2xZ2 group structure. The benefit of this approach is that it allows for the construction of converse statements to the standard CPT theorem, which leads to accidental unitarity in a broad class of theories. Furthermore, I will present an extension of these results to de Sitter where a similar group structure relates CRT and Scale Invariance to a non-perturbation extension of the Cosmological Optical Theorem.