# O(D,D) completion of the Friedmann equations

- Institution: CERN
- Department: Conferences & Workshops
- Speaker: Stephen Angus
- Year: 2019
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3016784)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

String theory suggests a unique and unambiguous augmentation of General Relativity, in which the entire closed-string massless NS-NS sector is promoted to stringy graviton fields. O(D,D) T-duality then uniquely fixes the coupling of this 'Stringy Gravity' to other matter, leading to a generalization of Einstein's equations with an enhanced energy-momentum tensor. In this talk I will explore the resulting cosmological implications and show that this yields an enriched framework beyond typical string cosmology, with solutions characterized by two equation-of-state parameters (w,\lambda) rather than one (w). This includes a line in parameter space where GR-like solutions with constant dilaton are admitted for any w. However, while apparently present on the GR line, there is no de Sitter solution arising from an O(D,D)-symmetric cosmological constant or scalar field with positive energy density, suggesting that de Sitter may simply be an artefact of GR and belong to the swampland..

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## Lectures

1. [O(D,D) completion of the Friedmann equations](https://invisiblenetwork.ai/learn/cern/3016784/05d353198d6a), 17 min (CERN's player)