Science with Future CMB Observations

Lloyd Knox

UC Davis

CMB Accomplishments• CMB is a powerful cosmological probe

– Applicability of linear theory highly precise theoretical calculations

– Richness of angular power spectrum phenomenology (all those bumps and wiggles… not just a power law) lots of information

• CMB is a proven technique with many importantimportant accomplishments– Confirming our basic picture of structure formation (gravitational instability)

– Confirming dark energy (acceleration inferred from SN data not widely accepted until confirmed by CMB)

– Verifying prediction #1 of inflation (tot = 1 c.f. ~0.2)

– Ruling out defect model for structure formation in favor of inflation

– Verifying prediction #2 of inflation: correlations on super-horizon scales

– Verifying prediction #3 of inflation: nearly scale-invariant spectrum of primordial perturbations

– Best constraints on key cosmological parameters: baryon density, matter density, amplitude of primordial perturbations, temperature of the CMB

– WMAP1 cosmological interpretation paper (Spergel et al. 2003) has 3795 citations to date! This has been the default paper to cite for ‘cosmology’.

Future Goals

• Detect a departure from scale invariance

• Reduce model dependence

• Detect gravity waves and determine the energy scale of inflation

• Find evidence of the ‘Landscape’

Current Constraints on Inflation Parameters

Sp

erge

l et

al. (

2006

)

On the verge of verifying yet another prediction of inflation!

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are needed to see this picture.

Ruling Out Harrison-Zeldovich• Planck will nail it by

– using long lever arm enabled by high resolution and high sensitivity with no cross-experiment relative calibration challenges

– cleanly controlling SZ contribution due to frequency coverage to higher frequencies where spectral shapes are very different

– determining with low-l polarization to break the -ns degeneracy

The first point is the dominant one. With the measurement extended to high l there is no need to use the low l data (affected by reionization) to get ns.

Discarding all data at l < 40 will degrade Planck’s error on ns by less than 10%.

Forecasted Power Spectrum ErrorsSimulated 4-year

Model (red curves) has ns = 1

Enabled by Planck’s greater sensitivity, angular resolution and frequency coverage

WMAP -- 4 years Planck

South Pole Telescope (SPT)

First light achieved with the 10m South Pole Telescope, February 16, 2007.

•Maps of Jupiter made, showing telescope and optics working as designed.

• Plan to do 4,000 sq. degree survey at 90, 150 and 220 GHz at ~ arc minute resolution.

The SPT is a collaboration between the U of Chicago, UC Berkley, Case Western Reserve University, U of Illinois, and Smithsonian Astrophysical Observatory

Deployment at South Pole

Forecasts for SPT + WMAP6Assumes SPT maps useable from 200 < l < 2000.

Relative calibration allowed to float freely.

Discriminates among inflation models.

Again, long lever arm means low l polarization info unnecessary.

Future Goals

• Detect a departure from scale invariance

• Reduce model dependence

• Detect gravity waves and determine the energy scale of inflation

• Find evidence of the ‘Landscape’

Model Dependence• All parameter inferences from the CMB are highly

indirect and therefore model dependent.• Planck will enable us to test the models much

better than can be done with current data. • BBN example:

– Assuming no isocurvature modes the WMAP3 constraints on baryon density have errors of a few per cent.

– Dropping this assumption the uncertainty becomes 20%, assuming 4 years of WMAP and 2% assuming Planck.

Another Model Dependence Example: JDEM/SNe + CMB

WMAP4

Planck

Allowing for adiabatic + isocurvature initial

conditions

Planck ellipse area (the DETF figure-of-merit) is 3.5 times smaller.

Knox, Trotta & Song (preliminary)

CMB experiments are important for Dark

Energy probes because they pin down the matter density, baryon density and the distance to last

scattering.

Future Goals

• Detect a departure from scale invariance

• Reduce model dependence

• Detect gravity waves and determine the energy scale of inflation

• Find evidence of the ‘Landscape’

Current Constraints on Inflation Parameters

Sp

erge

l et

al. (

2006

)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Future Goals

• Detect a departure from scale invariance

• Reduce model dependence

• Detect gravity waves and determine the energy scale of inflation

• Find evidence of the ‘Landscape’

Let 10Let 101000 1000 flowers flowers blossomblossom Let 10Let 101000 1000 flowers flowers blossomblossom

< < 00< < 00

= = 00= = 00

> 0> 0> 0> 0

A. Linde

Potentially Observable Consequence of the Landscape• Our hot big bang born in a tunnelling

event from a neighboring metastable vacuum ==> open FRW Universe.

• Tunnelling event followed by slow roll inflation and then reheating.

• The fewer the e-foldings of inflation, N, the larger the residual curvature.

Freivogel et al. 2005

Potentially Observable Consequence of the Landscape• Observational bound: N > 62

(assuming tot > 0.98 and some reheat temperature).

• Anthropic bound: N > 59.5 (otherwise curvature domination sets in too early for galaxy formation)*

• These numbers are not very different!

Freivogel et al. 2005

*Weinberg (1987), Tegmark & Rees (1998)

Potentially Observable Consequence of the Landscape

• Assume – V() = V0(1-x /) in region of interest– V0, x and vary from 0 to 1 with a uniform measure.

• Result is P(N) / 1/N4.• Normalizing with anthropic bound so that s59.5

1 P(N) dN = 1, they find P(N>62) = 0.88.

• With improving bounds on curvature do we have a chance of detecting it? – P(64>N>62) ~0.1. [N=64 ==> k = 0.0004]

Freivogel et al. 2005

Determining CurvatureSN: space-based

supernova mission similar to DETF modeling

WL, BAO: LSST

Knox, Song & Zhan 2006

All these forecasts include Planck

Assumes dark energy parametrized by w0, wa.

Summary

• Future CMB observations will– Detect expected departure from scale invariance

at high precision– Greatly reduce model dependence / allow for more

rigorous tests of the adiabatic Gaussian model– Tensor signal from simplest inflationary models

are within reach– Combined with dark energy probes, potentially

provide observational evidence for the string theory landscape.