Tachyons in Classical de Sitter Vacua

TL;DR

This paper investigates the origin of tachyons in classical de Sitter vacua within string theory, revealing their relation to sgoldstino mixing and proposing a stability criterion for such vacua.

Contribution

It identifies the source of tachyons in known unstable dS solutions and explains their behavior through a generalized no-go theorem involving moduli mixing.

Findings

Tachyons are close to, but not aligned with, the sgoldstino direction.

The behavior is explained by a generalized no-go theorem with large moduli mixing.

Provides a potential stability criterion for dS vacua in supergravity and string theory.

Abstract

We revisit the possibility of de Sitter vacua and slow-roll inflation in type II string theory at the level of the classical two-derivative supergravity approximation. Previous attempts at explicit constructions were plagued by ubiquitous tachyons with a large $\eta$ parameter whose origin has not been fully understood so far. In this paper, we determine and explain the tachyons in two setups that are known to admit unstable dS critical points: an SU(3) structure compactification of massive type IIA with O6-planes and an SU(2) structure compactification of type IIB with O5/O7-planes. We explicitly show that the tachyons are always close to, but never fully aligned with the sgoldstino direction in the considered examples and argue that this behavior is explained by a generalized version of a no-go theorem by Covi et al, which holds in the presence of large mixing in the mass matrix between the sgoldstino and the orthogonal moduli. This observation may also provide a useful stability criterion for general dS vacua in supergravity and string theory.