1. University of California, Berkeley Lawrence Berkeley National Lab
Course on Dark Energy
Cosmology at the Beach 2009
Eric Linder
University of California, Berkeley
Lawrence Berkeley National Lab
JDEM constraints

2. Outline Lecture 1: Dark Energy in Space The panoply of observations
Lecture 2: Dark Energy in Theory
The garden of models
Lecture 3: Dark Energy in your Computer
The array of tools – Don’t try this at home!

3. Describing Our Universe
New Stuff
Old New Stuff Us
STScI
95% of the universe is unknown!
Had I been present at the creation of the world, I should have recommended something simpler. - Alfonso X ‘The Wise’, King of Castile and Leon

4. Mapping History

5. Acceleration Acceleration has:
- Direct (kinematic) effect on spacetime through a(t)
- Dynamic effects on objects within spacetime, e.g. growth, ISW
What appears in the metric is the cosmic scale factor a(t).
The metric can be spatially flat (k=0) but the spacetime is curved if
This is exactly the Equivalence Principle: Gravity = Curvature = Acceleration

6. Windows on Dark Energy
Light signals travel on null geodesics (ds=0) and measure dt/a = dz/H. Distances are directly affected by acceleration.
Growth, ISW, abundances measure competition between acceleration and gravitational attraction. ISW (decaying potentials) is direct measure of violation of matter domination, not acceleration.
Stretching space suppresses growth. Recall Jeans instability gives exponential growth – expanding space reduces this to power law. Friction term ~ (3-q).

7. Dark Energy – the Easy Way?
Direct detection?
(Dark energy in solar system = 3 hours of sunlight).
Co-dependence? Variations of fundamental constants; lab/accelerator/universe
Direct acceleration?
Redshift drift (Sandage 1962; McVittie 1962; Linder 1991,1997)
dz=10-8 over 100 years
Redshifts are changes in scale/position (“velocities”):
z=[a(t0)-a(te)]/a(te)  H0 (t0-te)
Redshift shifts are changes in changes (“acceleration”):
dz/dt0 = [a0-ae]/ae = H0(1+z)-H(z)  -zq0H0 t .

8. Cosmic Archaeology CMB: direct probe of quantum fluctuations
3D surveys of galaxies and clusters: probes of expansion + growth
Pattern of ripples, clumping in space, growing in time.
BAO, Lensing, Matter power spectrum.
Supernovae: direct probe of cosmic expansion
Time: % of present age of universe
CMB: direct probe of quantum fluctuations
Time: 0.003% of the present age of the universe.

9. BREAK
CMB

10. What do we see in the CMB?
Planck
COBE
WMAP
“GroundPol” has 2.5x the resolution and 1/5x the noise
A view of the universe % of the way back toward the Big Bang - and much more.

11. See poster by Roland de Putter and 0901.0916
CMB and Dark Energy
CMB provides a lever to break degeneracies
CMB provides a key window on microphysics of dark energy - spatial fluctuations  and sound speed cs2
CMB Polarization (B-mode) is dominated at small angles by high redshift lensing - hence high z structure formation.
Polarization lensing “focuses” on the universe at z=1-4,
giving a window on early dark energy, and neutrinos.
See poster by Roland de Putter and

12. Mapping Our History
The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history.
STScI

13. Standard explosion from nuclear physics
Type Ia Supernovae
Exploding star, briefly as bright as an entire galaxy
Characterized by no Hydrogen, but with Silicon
Gains mass from companion until undergoes thermonuclear runaway
Standard explosion from nuclear physics
Insensitive to initial conditions: “Stellar amnesia”

14. Type Ia Supernovae Brightness tells us distance away (lookback time t)
Redshift tells us the expansion factor a
Time after explosion

15. Standardized Candles
Supernova Legacy Survey (SNLS)
Conley et al 2006

16. Supernova Properties Astrophysics
Understanding Supernovae
Supernova Properties Astrophysics
Nearby Supernova Factory
400 SN Ia with spectra, z= >3000 spectra of SN Ia
Cleanly understood astrophysics leads to cosmology (and astrophysics!)
G. Aldering (LBL)

17. Current Data: World Union SN Set
Complete reanalysis, refitting of 13 SN data sets
396 SNe Ia (58+249) - new low z SN
Fit Mi between sets and between low-high z
Study of set by set deviations (residuals, color)
Blind cosmology analysis!
Systematic errors ≈ statistical errors
Kowalski et al., ApJ 2008 [arXiv: ]

18. Tests for Systematics and Evolution
No significant deviations from mean of Hubble diagram, or (mostly) in residual slope.
Also no evolution seen in redshift or population tests.
Kowalski et al. 2008, ApJ 2008 [arXiv: ]

19. Current Data: SNLS ~310 confirmed SN Ia, 50-60 to be processed
Preliminary ~240 SN
Sullivan et al 2008
On track for ~500 total 3y data paper ~ early ’09

20. Imminent Results SDSS SN: z=0.1-0.4, 99 SN for Y1 release [498]
Essence: z= , Y6 release 156 SN
CSP: followup 21 [ ], I-band Hubble diagram
Local SN studies: KAIT, CfA, PTF, SkyMapper
Decelerating and Dustfree with HST: 15 SN z>1 (each SNell worth 9x SNext statistically)
Preliminary
Frieman, Jha, Kessler et al 2008

21. Gravitational Weak Lensing
Gravitational potentials deflect light, creating convergence (magnification) and shear (shape distortion).
This depends on the focal length (geometric kernel of dldls/ds) and potential power spectrum (density growth).
Acceleration affects both distances and growth.
Convergence  is very difficult to measure (no absolute size) and shear  needs to be measured statistically (averaging over intrinsic ellipticities).
Need surveys with millions of well-resolved galaxies. Need good source redshift information to un-blur focal lengths.

22. Weak Lensing Subaru deep field 17 deg2 Miyazaki et al. 2007
CFHT Legacy Survey - Wide + Deep Semboloni et al. 2006, Hoekstra et al. 2006, Benjamin et al. 2007, Fu et al. 2008, Dore et al. 2008
For dark energy not yet precision, “pre-Boomerang”
COSMOS (HST)
2 deg2 space WL
Full tomographic analysis
Kitching, Massey, et al. 2008
Massey et al. 2007

23. Baryon Acoustic Oscillations
In the beginning... (well, ,000 years after)
It was hot. Normal matter was p+,e- – charged – interacting fervently with photons.
This tightly coupled them, photon mfp << ct, and so they acted like a fluid.
Density perturbations in one would cause perturbations in the other, but gravity was offset by pressure, so they couldn’t grow - merely oscillated.
On the largest scales, set by the sound horizon, the perturbations were preserved.
M. White
(CMB)
Galaxy cluster size
Baryon acoustic oscillations = patterned distribution of galaxies on very large scales (~150 Mpc). “Standard ruler”

24. Baryon Acoustic Oscillations
BAO need millions of galaxy positions spread over >1 Gpc3 volume, ideally spectroscopic z. Issues of nonlinearity, bias, z-space, selection effects.
Eisenstein et al. 2005
Martinez et al
Does any model agree with the data?
A peak? Multi-peaks?
Sanchez & Cole 2008
Galaxy selection and scale-dependent bias?

25. Precision Cosmology for Dark Energy?
Reality check - what do we really know now:
Supernovae see acceleration
Weak lensing sees dark matter
acc
dec
1.5 cl
Clusters see dark matter
BAO sees baryons
Vikhlinin et al

26. Distance Complementarity
Distances relative to low and high redshift
have different degeneracies, hence complementarity

27. Redshift Range
Deep enough that is less than 10% energy density? Not next-to-dominant?
Deep enough that have accounted for >2/3 of the acceleration?

28. END Lecture 1 For more dark energy resources, see
Lecture 1: Dark Energy in Space
The panoply of observations
Lecture 2: Dark Energy in Theory
The garden of models
Lecture 3: Dark Energy in your Computer
The array of tools – Don’t try this at home!
For more dark energy resources, see
Resource Letter on Dark Energy
Mapping the Cosmological Expansion
and the references cited therein.