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Cosmic challenges for
fundamental physics
Diederik Roest
December 9, 2009
Symposium “The Quantum Universe”
Modern cosmology
What are the ingredients of the universe?
Supernovae (SNe)
Baryon Acoustic
Oscillations (BAO)
Cosmic Microwave
Background (CMB)
Supernovae
Cosmic Microwave Background
Baryon acoustic oscillations
Putting it all
together
Concordance Model
Nearly flat Universe, 13.7 billion years old.
Present ingredients:
 73% dark energy
 23% dark matter
 4% SM baryons
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]
Cosmic acceleration
Two periods of accelerated expansion:

inflation in very early universe

present-time acceleration
No microscopic understanding.
Cosmic challenges
for fundamental
physics!
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.
Strings




Quantum gravity
No point particles, but small strings
Unique theory
Bonus: gauge forces
Unification of four forces of Nature?
…and then some!
String theory has many
implications:
Supersymmetry
Extra
dimensions
Many vacua
(~10500)?
Branes
& fluxes
Dualities
How can one extract 4D
physics from this?
Compactifications
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
simple
comp.
with fluxes
and branes
Scalar field
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?” (20082013). 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 nongeometric fluxes [2]?
[1: D.R., Rosseel - in progress]
[2: D.R. ’09, Dibitetto, Linares, D.R. – in progress]
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
Thanks for your attention!
Diederik Roest
December 9, 2009
Symposium “The Quantum Universe”