Cosmic acceleration and turns in the Swampland

Abstract

We argue that field trajectories, which lead to cosmic acceleration and feature rapid turns near the boundary of the moduli space, are in the Swampland. We obtain this result by assuming the validity of the Swampland Distance Conjecture (SDC) in the presence of a positive scalar potential and by focusing on hyperbolic spaces, as prototype geometries of infinite distance limits of Calabi-Yau compactifications. We find that, in a quasi-de Sitter space with Hubble rate H and acceleration parameter ϵ, the turning rate Ω is upper bounded such as Ω/H < 𝒪(√(ϵ)). Therefore, field trajectories consistent with the SDC can only have a negligible deviation from geodesics. This has direct implications for the realization and consistency of multi-field scenarios in string theory. Moreover, it implies a tension between asymptotic accelerating expansion, consistent with observations, and the de Sitter conjecture.

No accelerating scaling cosmologies at string tree level?

“…Inspired by the difficulties in obtained controlled dS vacua, there is a renewed interest in rolling cosmological scenarios [12][13][14][15][16][17][18][19][20][21][22][23][24][25] to describe quintessence or inflation. 1 And even more recently, the exponential form of the fall-off was the inspiration of [20][21][22] for looking for so-called scaling solutions.…”

News from the Swampland — constraining string theory with astrophysics and cosmology

“…As such, it is fundamentally important to ask how they can be constructed in a consistent unified theory. Indeed, Swampland conjectures have been extensively confronted with inflation models, showing significant tensions and providing strong restrictions on the allowed parameter space of the simplest class of models: those involving a single field 1 [12][13][14][15][16][17][18]. However, hope is not lost for inflationary scenarios remaining valid even when Swampland criteria are imposed, as a large variety of proposals has been put forth to rescue the inflationary paradigm.…”