Comments on the vacuum energy decay

TL;DR

This paper discusses the instability of vacuum energy in de Sitter space, linking it to forbidden decay processes caused by external gravitational fields, supported by calculations in conformally invariant and flat space models.

Contribution

It provides a detailed analysis of vacuum energy decay mechanisms in curved spacetime, extending previous work and highlighting the role of gravitational fields in such instabilities.

Findings

Vacuum energy in de Sitter space is generically unstable.

Forbidden decay processes are related to external gravitational fields.

Calculations support the connection between gravitational fields and vacuum decay.

Abstract

The {\em instability of vacuum energy} in de Sitter space as discussed recently by Polyakov is argued to be a generic feature when external gravitational fields are present. It is related to the existence of {\em forbidden} (by momentum conservation) decays derived in some detail by Bros, Epstein and Moschella. Some calculations are discussed in a conformally invariant setting, and a flat space model is presented.