How can CMB help constraining dark energy?

1. How can CMB help constraining dark energy? Licia Verde ICREA & Institute of space Sciences (ICE CSIC-IEEC)

2. The standard cosmological model CDM model  Spatially flat Universe Power-law, primordial power spectrum Only 6 parameters: WMAP5yr analysis

3. recombination

4. Hot and cold spots  Tiny ripples in density  seeds of galaxies Detailed statistical properties of these ripples tell us a lot about the Universe

5. How’s that? The Universe back then was made of a very hot and dense “gas”, so it was emitting radiation This is the radiation we see when we look at the CMB Uniform , but with tiny (contrast x 100000) density (and temperature) ripples Ripples in a gas? SOUND WAVES! Truly a cosmic symphony… We are seeing sound! These tiny fluctuations, quantitatively, give rise galaxies We try to listen to the sound and figure out how the instrument is made Fundamental scale Fundamental mode and overtones like blowing on a pipe….

6. Even for LCDM CMB alone does NOT imply >0 How many of you really believe H0=30?

7. Dark energy WMAP5 Komatsu et al (2008)

8. Why so weak dark energy constraints from CMB? WMAP5 Dunkley et al (2008)

9. Why so weak dark energy constraints from CMB? The limitation of the CMB in constraining dark energy is that the CMB is located at z=1090. WMAP5 Dunkley et al (2008) We need to look at the expansion history (I.e. more than one snapshot of the Universe) Several options….

10. THE SYMPTOMS Or OBSERVATIONAL EFFECTS of DARK ENERGY Recession velocity vs brightness of standard candles: dL(z) CMB acoustic peaks: Da to last scattering Da to zsurvey LSS: perturbations amplitude today, to be compared with CMB Perturbation amplitude at zsurvey

11. Leading observational techniques to go after dark energy (expansion history) Supernovae (mostly growth of structure) Galaxy clusters number counts Weak Lensing (growth of structure and expansion history) Baryonic Acoustic Oscillations (BAO) (expansion history) Q: A combination of techniques will be best for at least two reasons

12. weak dark energy constraints from CMB? BUT The CMB encloses information about the growth of foreground structures: secondary CMB! A Integrated Sachs Wolfe effect Secondary effects: Sunyaev Zeldovich(SZ), Kintetic SZ, Rees-Sciama, Lensing. What if one could see the peaks pattern also at lower redshifts? B (and get other things for free) C … resort to other probes (CMB serves as anchor point)

13. USE the CMB as BACKLIGHT, illuminating the foreground universe • First galaxies • Universe is reionized • Ostriker-Vishniac • Diffuse thermal SZ • Cluster formation: Sunyaev-Zel’dovich (SZ) • Kinematic SZ • Lensing of the CMB Cosmic Microwave Background • The growth of structure is sensitive to dark energy • Rich additional science from correlations among effects • Extraction of cosmological parameters • Initial conditions for structure formation High z mid z low z

14. Sunyaev-Zel’dovich (SZ) clusters Coma Cluster Telectron = 108 K e- e- e- e- e- e- e- Cosmic Microwave Background e- e- X-ray Flux: Mass Optical: Redshift and Mass mm-Wave: SZ – Compton Scattering

15. http://www.physics.princeton.edu/act/ Barcelona, Cardiff, Columbia, Haverford, Inaoe, KwaZulu-Natal, NASA, NIST,UPenn, Princeton, U. Pittsburgh, Rutgers, Toronto, UBC, Cape Town, Universidad Catolica, York College

16. The south pole telescope http://pole.uchicago.edu/public/

17. Summary: Much ado about nothing The standard cosmological model is extremely successful, but…. Observations indicate that nothing weighs something (but much less than expected) and make the universe accelerate (other options are still Possible, inhomogeneities, gravity, but the result must “look like ”). What would it take to discriminate? discussion Heroic observational effort is on going (we’ll learn not only about dark energy from it) The“Accelerating universe challenge”

18. “In the middle of difficulty lies opportunity" ---  A. Einstein