News from the Swampland -- Constraining string theory with astrophysics and cosmology

TL;DR

This paper reviews how cosmological observations impact string theory's Swampland criteria, showing current data allows more flexibility and highlighting potential fine-tuning issues in dark energy models.

Contribution

It assesses the latest cosmological data's implications on Swampland conjectures and explores the effects of moduli interactions with electromagnetic fields.

Findings

Current data slightly relaxes Swampland constraints.

No theoretical barrier to moduli-electromagnetic interactions leads to fine-tuning.

Caution advised in model-independent Swampland reconstructions.

Abstract

Our current best guess for a unified theory of gravitation and quantum field theory (string theory) generically predicts a set of requirements for a consistently quantized theory, the Swampland criteria. Refined versions of these criteria have recently been shown to be in mild tension with cosmological observations. We summarize the status of the current impact of and constraints on the Swampland conjectures from cosmology, and subject a variety of dark energy quintessence models to recently released cosmological datasets. We find that instead of tightening the tension, the new data allows for slightly more freedom in the Swampland criteria. We further demonstrate that if there is no theoretical argument made to prevent interactions of the moduli fields with the electromagnetic sector, a novel fine-tuning argument arises from the extremely tight current constraints on such interactions. Finally, we conclude with a cautionary tale on model-independent reconstructions of the Swampland criteria from expansion rate data.