Michael Doran

1
Time Evolution of Dark Energy(if any )

• Michael Doran
• Institute for Theoretical Physics
• Universität Heidelberg

2
Dark energy (a.k.a. quintessence)
3
(Semi-) Known Dark Energy Properties

• D.E. does not cluster on scales within horizon,
  because canonical
• D.E. not coupled or very weakly coupled to
  matter
• Cosmological constant fits all observations
• Descriptions in terms of modified Einstein
  action and scalar fields possible and related

4
Extracting information on
5
Effects of dark energy I -- Geometry

• Additional component changes expansion history
  and horizons.
• Geometrical tests include
• Acoustic scale of the CMB
• Baryon acoustic oscillations at low redshifts
• Luminosity distance at low redshift
  from SNe Ia
• Luminosity distance up to from ?-ray
  bursts (?)
• Angular diameter distance using shape of

6
Effects of dark energy II -- Couplings

• If D.E. coupled to baryons
• mediates additional fifth force (hence very
  restricted)
• might be linked to running coupling constants
• If D.E. coupled to cold dark matter acts like
  self-interaction for dark matter, i.e. enhances
  clustering. Caution
  exchange.

7
Effects of dark energy III -- Structure growth
CMB

• Not coupled Suppresses growth of linear matter
  perturbations because additional non-clustering
  component is present.
• Consequences?

8
Consequences!

• Gravitational potential decays during matter
  domination if D.E. present ISW effect in
  CMB
• The longer a mode is inside the horizon, the
  more it gets suppressed if D.E. present.
  However, all modes inside horizon at
  matter-radiation equality are equally
  suppressed. Up to running spectral
  index then equal suppression.
• Rough rule of thumb 10 dark energy during
  structure formation 50 less

9
Linear Power Spectrum
?-CDM
Early Dark Energy
10
Counterintuitive More structure at higher
redshifts

• Conditions for collapse roughly the same as in
  -CDM
• Yet, even after collapse of some halo starts,
  linear theory fluctuations grow less compared
  to -CDM
• So linear overdensity corresponding to
  collapsed object is lower than in -CDM
• Same non-linear structure with lower

11
.. more non-linear structure at higher redshift
10
z1
Mass Function rel. toLCDM
z0
1
1013
1014
1015
Halo Mass h-1 Msun
12
Early Dark Energy influences the CMB ...
R.R. Caldwell et. al. (2003)
13
Dark Energy influences structure growth...

• Linear fluctuations grow less with dark energy.
• CMB normalized, early dark energy predicts more
  non-linear structure at higher redshifts compared
  to standard cosmological constant. M.
  Bartelmann, M.D., C. Wetterich (2005)

Mass Function rel. to LCDM
Halo mass
14
.. more non-linear structure at higher redshift
10
z1
Mass Function rel. toLCDM
z0
1
1013
1014
1015
Halo Mass h-1 Msun