1. Cosmic challenges for fundamental physics Diederik Roest December 9, 2009 Symposium “The Quantum Universe”

3. Modern cosmology What are the ingredients of the universe?

4. Supernovae

5. Cosmic Microwave Background

6. Baryon acoustic oscillations

7. Putting it all together

8. Concordance Model Nearly flat Universe, 13.7 billion years old. Present ingredients: 73% dark energy 23% dark matter 4% SM baryons

9. Inflation Period of accelerated expansion in very early universe CMB anisotropies confirm inflation as source of fluctuations Inflationary properties are now being measured Planck satellite: – –Non-Gaussianities? – –Tensor modes? – –Constraints on inflation? [cf. talk by Jan Pieter van der Schaar]

10. Cosmic challenges for fundamental physics! Cosmic acceleration Two periods of accelerated expansion: inflation in very early universe present-time acceleration No microscopic understanding.

11. Cosmic acceleration Modelled by scalar field with non-trivial scalar potential V Can we get such potentials from string theory? Extreme case with extremum of scalar potential leads to De Sitter space-time.

12. Strings Quantum gravity No point particles, but small strings Unique theory Bonus: gauge forces Unification of four forces of Nature?

13. …and then some! Extra dimensions Many vacua ( ~10 500 )? Dualities Branes & fluxes Super- symmetry String theory has many implications: How can one extract 4D physics from this?

14. Compactifications

15. Stable compactifications Simple compactifications yield massless scalar fields, so-called moduli, in 4D. Would give rise to a new type of force, in addition to gravity and gauge forces. Has not been observed! Need to give mass terms to these scalar fields (moduli stabilisation). Extra ingredients of string theory, such as branes and fluxes, are crucial! energy Scalar field with fluxes and branes simple comp.

16. Building a bridge What are the scalar potentials that follow from string theory, and do these allow for cosmologically interesting solutions? Focus of my VIDI project “How stable are extra dimensions?” (2008- 2013). Keywords: flux compactifications, moduli stabilisation. Upcoming results: Relations between N=2, 4 and 8 supergravity models with (un)stable dS vacua [1]? Higher-dimensional origin in terms of gauge, geometric or non- geometric fluxes [2]? [1: D.R., Rosseel - in progress] [2: D.R. ’09, Dibitetto, Linares, D.R. – in progress]

17. Conclusions Modern cosmology requires accelerated expansion for dark energy and inflation Can we use string theory to explain this? What are the scalar potentials from string compactifications? (flux compactifications and moduli stabilisation) Many interesteresting (future) results – both theoretical and experimental

18. Thanks for your attention! Diederik Roest December 9, 2009 Symposium “The Quantum Universe”