michael doran institute for theoretical physics universität heidelberg time evolution of dark...

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

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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

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Halo mass

.. more non-linear structure at higher redshiftM

ass

Fu

nct

ion

rel

. toL

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M

1

10

1013 1014 1015

Halo Mass [h-1 Msun]

z=1

z=0