Michael Doran

Institute for Theoretical Physics

Universität Heidelberg

Time Evolution of Dark Energy(if any …)

Dark energy (a.k.a. quintessence)

(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

Extracting information on

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

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.

Effects of dark energy III -- Structure growth & CMB

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

Consequences?

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

Linear Power Spectrum

CDM

Early Dark Energy

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

.. more non-linear structure at higher redshiftM

ass

Fu

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rel

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CD

M

1

10

1013 1014 1015

Halo Mass [h-1 Msun]

z=1

z=0

Early Dark Energy influences the CMB ...

R.R. Caldwell et. al. (2003)

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)

Mas

s F

unct

ion

rel.

to L

CD

M

Halo mass

.. more non-linear structure at higher redshiftM

ass

Fu

nct

ion

rel

. toL

CD

M

1

10

1013 1014 1015

Halo Mass [h-1 Msun]

z=1

z=0