Tachyonic de Sitter solutions of 10d type II supergravities

TL;DR

This paper investigates the instability of de Sitter solutions in 10d type II supergravities, develops methods to identify tachyons, and discovers new solutions with varied stability properties, advancing understanding of string cosmology.

Contribution

It introduces three methods to systematically identify tachyons in de Sitter solutions and reports 10 new solutions with diverse stability characteristics.

Findings

All known de Sitter solutions are unstable with ta_V < -1.

Developed methods provide sufficient conditions for tachyon presence.

Discovered 10 new solutions, including one potentially stable with non-compact extra dimensions.

Abstract

Cosmological models of the early or late universe exhibit (quasi) de Sitter space-times with different stability properties. Considering models derived from string theory, the swampland program does not provide for now a definite characterisation of this stability. In this work we focus on de Sitter solutions of 10d type II supergravities, candidates for classical de Sitter string backgrounds: surprisingly, all known examples are unstable with $\eta_V < -1$. We aim at proving the existence of such a systematic tachyon, and getting formally a bound on the value of $\eta_V$. To that end, we develop three methods, giving us various sufficient conditions for having a tachyon upon assumptions, in analogy with de Sitter no-go theorems. Our analysis eventually indicates the existence of variety of different tachyons, and related bounds on $\eta_V$. We use this knowledge to find 10 new de Sitter solutions of type IIB supergravity, that have tachyons of a different kind, higher $\eta_V$ values and new 6d geometries. One solution even appears to be stable, with however non-compact extra dimensions.