Title: Towards a unitary quantum field theory in curved spacetime I: the case of de Sitter spacetime

Abstract: In this talk, I shall discuss the decade’s worries of theoretical physicists about quantum field theory in curved spacetime especially in the context of de Sitter (dS) spacetime. Several conceptual problems have raised concerns over several decades, mainly because no S-matrix formulation is yet found in QFTCS. I argue that the institutional thinking of fixing a spacetime geometry, observers, and light cones, and then quantizing the fields in that “intuitively”, or “classically”, fixed spacetime is the origin of the problem. Sticking to the so-called “quantum first approach” I shall present a new formalism of QFTCS based on the refined understanding of the role of discrete transformations (CPT). I shall explain how this new approach shall give unitarity and observer complementarity in dS space. Finally, I briefly discuss the impact of this formalism on the current and future of quantum gravity research.

The talk is based on a recent preprint https://arxiv.org/abs/2305.06046