Cosmic challenges forCosmic challenges forfundamental physicsfundamental physics

Diederik Roest December 9, 2009

Symposium “The Quantum Universe”

Modern cosmologyModern cosmology

Supernovae (SNe)

Cosmic Microwave Background (CMB)

Baryon AcousticOscillations (BAO)

What are the ingredients of the universe?

SupernovaeSupernovae

Cosmic Microwave Cosmic Microwave BackgroundBackground

Baryon acoustic oscillationsBaryon acoustic oscillations

Putting it all Putting it all togethertogether

Concordance ModelConcordance Model

Nearly flat Universe, 13.7 billion years old.

Present ingredients: 73% dark energy 23% dark matter 4% SM baryons

InflationInflation 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]

Cosmic challenges for fundamental

physics!

Cosmic accelerationCosmic acceleration

Two periods of accelerated expansion: inflation in very early universe present-time acceleration

No microscopic understanding.

Cosmic acceleration 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.

StringsStrings

Quantum gravity No point particles, but small

strings Unique theory Bonus: gauge forces

Unification of four forces of Nature?

……and then some!and then some!

Super-symmetry

Dualities

Many vacua (~10500)?

Extradimensions

Branes& fluxes

String theory has many implications:

How can one extract 4D physics

from this?

CompactificationsCompactifications

Stable compactificationsStable 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.

Building a bridgeBuilding 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]

ConclusionsConclusions

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

Thanks for your attention!Thanks for your attention!

Diederik Roest December 9, 2009

Symposium “The Quantum Universe”