S-Matrix and Anomaly of de Sitter

S-matrix formulation of gravity excludes de Sitter vacua. In particular, this is organic to string theory. The S-matrix constraint is enforced by an anomalous quantum break-time proportional to the inverse values of gravitational and/or string couplings. Due to this, de Sitter can satisfy the conditions for a valid vacuum only at the expense of trivializing the graviton and closed-string S-matrices. At non-zero gravitational and string couplings, de Sitter is deformed by corpuscular 1/N effects, similarly to Witten-Veneziano mechanism in QCD with N colors. In this picture, an S-matrix formulation of Einstein gravity, such as string theory, nullifies an outstanding cosmological puzzle. We discuss possible observational signatures which are especially interesting in theories with a large number of particle species. Species can enhance the primordial quantum imprints to potentially observable level even if the standard inflaton fluctuations are negligible.

Automated summary

The S-matrix formulation of gravity excludes de Sitter vacua, especially in the context of string theory, due to the anomalous quantum break-time enforced by the inverse values of gravitational and/or string couplings. De Sitter vacua can only be valid at the expense of trivializing the graviton and closed-string S-matrices. Additionally, observational signatures and the effects of particle species on quantum imprints are discussed, particularly in theories with a large number of species.