Post on 05-Jan-2016
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
nct
ion
rel
. toL
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