1. University of California, Berkeley Lawrence Berkeley National Lab
A Cosmic Vision
Beyond Einstein
Eric Linder
University of California, Berkeley
Lawrence Berkeley National Lab
JDEM constraints

2. Cosmic Vision / Beyond Einstein
Dune/Space/Euclid
JDEM
How did the universe originate and what is it made of?

3. Describing Our UniverseUs
STScI
95% of the universe is unknown!

4. New Frontiers
Beyond Einstein: What happens when gravity is no longer an attractive force?
Scientific American
Discovery (SCP,HiZ 1998): 70% of the universe acts this way!
Fundamentally new physics. Cosmology is the key.

5. Cosmic Coincidence Why not just settle for a cosmological constant ?
 For 90 years we have tried to understand why  is at least times smaller than we would expect – and failed.
 We know there was an epoch of time varying vacuum once – inflation.
We cannot calculate the vacuum energy to within But it gets worse: Think of the energy in  as the level of the quantum “sea”. At most times in history, matter is either drowned or dry.
Size=1/4
Size=1/2
Matter
Dark energy
Today
Size=2
Size=4

6. Nature of Acceleration
Is dark energy static? Einstein’s cosmological constant .
Is dark energy dynamic? A new, time- and space-varying field.
How do we learn what it is, not just that it is?
How much dark energy is there? energy density 
How springy/stretchy is it? equation of state w, w

7. On Beyond !
We need to explore further frontiers in high energy physics, gravitation, and cosmology.
New quantum physics? Does nothing weigh something? Einstein’s cosmological constant, Quintessence, M/String theory
New gravitational physics? Is nowhere somewhere? Quantum gravity, supergravity, extra dimensions?
We need new, highly precise data

8. Dynamics of Quintessence
Equation of motion of scalar field
driven by steepness of potential
slowed by Hubble friction
Broad categorization -- which term dominates:
field rolls but decelerates as dominates energy
field starts frozen by Hubble drag and then rolls
Freezers vs. Thawers
 + 3H = -dV()/d ˙ 

9. Limits of Quintessence
2/2 - V()
2/2 + V() .
w =
Distinct, narrow regions of w-w
Caldwell & Linder PRL 95,
Entire “thawing” region looks like <w> = -1 ± Need w experiments with  (w) ≈ 2(1+w).

10. Calibrating Dark Energy
Models have a diversity of behavior, within thawing and freezing.
But we can calibrate w by “stretching” it: w w(a)/ a. Calibrated parameters w0, wa.
de Putter & Linder
These two parameters achieve level accuracy on observables d(z), H(z).

11. 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.

12. BREAK

13. 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. 2008, ApJ accepted [arXiv: ]

14. 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 accepted [arXiv: ]

15. Latest Results Systematics already dominate error budget
Curvature free/flat
We do not know w(z) = -1 or what dark energy was doing at z>1.

16. Beyond Lambda
Compare current data (SN+CMB+BAO) vs dark energy models.
Choose “motivated” models widely covering Beyond  physics. Includes thawing, freezing, phase transition, modGR, geometric.
Most models have limit approaching  but two don’t.
Rubin et al. 2008, ApJ accepted [arXiv: ]

17. DGP Braneworld
2 parameters - m and k or bw or rc
H2=(8G/3)m+H/rc

18. Growing Neutrino V  3 parameters - m, e, and m0
Wetterich , Amendola, Baldi, Wetterich
V()
Veff(m)  V
Cosmological selection of dark energy density
3 parameters - m, e, and m0
Break early DE degeneracy with growth prior

19. Beyond Lambda
While  is consistent with data, many varieties of physics are also.
Improvements in systematics will have large impact - e.g. Braneworld disfavored at 2=+15 if statistical errors only. Uniform data set / analysis key, as is next generation ability to see w.
Two models improve in 2 over  by (slightly) more than Npar added: Algebraic Thawing (Linder 2007) and Rlow Geometric DE (Linder 2004).
Apart from testing “exotic cosmologies”, such comparisons are useful because model variety includes sensitivity to systematics that don’t “look like” . No indication of any such systematics.

20. Why Space? Innate cosmology dependence requires survey depth z>1.
This requires NIR.
We go to space because we must.

21. Gravitational Lensing
Lensing measures the mass of clusters of galaxies.
By looking at lensing of sources at different distances (times), we measure the growth of mass.
Acceleration - stretching space - shuts off growth.
WL signal
WL noise
Subaru - best ground
HST - space
Bacon, Ellis, Refregier 2000
Kasliwal, Massey, Ellis, Miyazaki, Rhodes 2007

22. Dark Energy – The Next Generation
104  the Hubble Deep Field [SN] plus 107  HDF [WL]
w i d e
deep
Redshifts z= (10 billion years / 70% age of the universe)
colorful
Optical + IR to see thru dust, to high redshift.
SNAP: Supernova/Acceleration Probe
1% distance measurements over last e-fold of expansion (Supernovae)
2% growth measurements over last e-fold of expansion (Weak Lensing)
Weak Lensing over deg2, high resolution, stable PSF, exc photo-z, z=0-3 +SL
Cluster survey - deepest, optical+WL
2000 SN with spectra z< z= SN II
BAO over deg2, exc photo-z

23. Discovery Space Dark energy may be a decades long mystery.
Space wide-field surveys maximize the discovery space.
Fundamental physics of inflation:
Weak lensing - ns primordial perturbation spectrum
Cluster abundances - non-Gaussianity
Dark Matter maps -
40 trillion pixels on sky! 20x ground.
“the skeleton of the universe”
Imagine COSMOS x 2000!

24. The Next Physics Let’s find out!
Current data do not tell us  is the answer (or anything about dark energy at z>1).
Odds against : Einstein+us failed for 90 years to explain it.
Experiments to reveal dynamics (w-w) are essential to reveal physics. Space is the low risk option for dependable answers.
Expansion plus growth is critical combination. We can test GR and can test geometry.
Space mission(s) provide high resolution and low systematics, multi-probes, Cosmic Vision Beyond Einstein.
What is dark energy? What is dark matter?
What is the fate of the universe?
How did structure first form and evolve?
How many dimensions are there?
Let’s find out!