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

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

recombination

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

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 ) density (and temperature) ripples Ripples in a gas? SOUND WAVES! We are seeing sound!Truly a cosmic symphony… How’s that? 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….

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

Dark energy WMAP5 Komatsu et al (2008)

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

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. We need to look at the expansion history (I.e. more than one snapshot of the Universe) WMAP5 Dunkley et al (2008) Several options….

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

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

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

USE the CMB as BACKLIGHT, illuminating the foreground universe High zmid z low z First galaxies Universe is reionized Ostriker-Vishniac Diffuse thermal SZ Cluster formation: Sunyaev-Zel’dovich (SZ) Kinematic SZ Lensing of the CMB 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

Sunyaev-Zel’dovich (SZ) clusters e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Coma ClusterT electron = 10 8 K Optical: Redshift and Mass mm-Wave: SZ – Compton Scattering X-ray Flux: Mass

Barcelona, Cardiff, Columbia, Haverford, Inaoe, KwaZulu-Natal, NASA, NIST, UPenn, Princeton, U. Pittsburgh, Rutgers, Toronto, UBC, Cape Town, Universidad Catolica, York College

The south pole telescope

Summary: Much ado about nothing 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  ”). Heroic observational effort is on going (we’ll learn not only about dark energy from it) What would it take to discriminate?discussion The“Accelerating universe challenge” The standard cosmological model is extremely successful, but….

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