The Science Potential of Planck

1. The Science Potential of Planck Lloyd Knox (UC Davis)

2. Outline • Review of Accomplishments of CMB Science • Great Opportunities Remain and Planck is poised to exploit them • Planck capabilities compared with WMAP • Parameter Error Forecasts • Planck as an Inflation Probe • Other Science: BBN, dark energy

3. 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 important 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 (Wtot = 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 3207 citations to date! This has been the default paper to cite for ‘cosmology’. 3239

4. Great Opportunities Remain: Forecasted TT Power Spectrum Errors Model (red curves) has n_s = 1 Simulated 4-year WMAP has revealed 4% of the information content* of the CMB temperature anisotropies. Planck will reveal 64%. *(Percentage of a_{lm}’s at l < 2000 with s/n > 1) Enabled by Planck’s greater sensitivity, angular resolution and frequency coverage

5. Great Opportunities Remain: Forecasted EE Power Spectrum Errors Simulated 4-year Enabled by Planck’s greater sensitivity, angular resolution and frequency coverage

6. Planck Baryon Density Parameter Error Forecasts WMAP 4yr Dark Matter Density Qualitative Advance in Precision Optical Depth of Reionized IGM Primordial Perturbation Power Spectrum Power Law Spectral Index Running Inflation Primordial Amplitude Expansion Rate

7. Inflation • Inflation is our leading paradigm for the origin of the hot Big Bang and generator of the primordial perturbations which are the seeds of all structures in the Universe (galaxies, stars, advisory boards). • The CMB is the single best way, by far, to study inflation and the primordial perturbations no matter what their origin.

8. Current Constraints on Inflation Parameters Spergel et al. (2006) On the verge of verifying yet another prediction of inflation!

9. 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 t with low-l polarization to break the t-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 n_s. Discarding all data at l < 40 will degrade Planck’s error on n_s by less than 10%.

10. Long Lever Arm Model (red curves) has n_s = 1 Simulated 4-year Planck will provide precision probe of primordial scalar power spectrum.

11. Detecting Tensor (Gravitational Wave) Perturbations • The scalar perturbation spectrum is a great probe of inflation, but the tensor perturbation spectrum is more direct. • The scalar spectrum is determined by a combination of the expansion rate during inflation and how it’s changing with time. The tensor spectrum depends only on the expansion rate during inflation, and thus the energy scale of inflation. • Tensor perturbations produce polarization B modes, while scalar perturbations, to first-order, do not. • Detectability of tensor B modes depends sensitively on this energy scale. • + GUT-scale inflation produces detectable tensor perturbations. • + Simplest models of inflation, when tuned to have the observed scalar perturbation amplitude, have an energy scale ~ GUT-scale. • + Gauge-coupling unification hints at new physics at the GUT scale.

12. BB Power Spectrum Scalar contamination 0.1 mK2 BB power spectrum for r=0.1 and t=0.17 Influence of tensors may be detectable in the BB power spectrum. r = T/S is proportional to H_{inf}^2 Planck Bluebook Tensor signal

13. Current Constraints on Inflation Parameters Spergel et al. (2006) Simplest models have detectable values of r.

14. BB Power Spectrum 0.1 mK2 BB power spectrum for r=0.1 and t=0.17 Influence of tensors may be detectable in the BB power spectrum. r = T/S is proportional to H_{inf}^2 Planck Bluebook

15. Polarized Foreground Emission 0.1 mK2 Page et al. (2006) Foreground cleaning is terribly important for polarization! Planck’s broad frequency coverage will be highly valuable.

16. Other Signatures of Inflation • Isocurvature modes. Some inflation models produce isocurvature perturbations. Planck’s polarization measurements enable it to set much tighter upper limits on their ampitudes, or possibly detect them. • Non-Gaussianity. Planck will improve error on the primordial non-Gaussianity parameter f_{nl} from \pm 25 to \pm 2.7, providing a strong constraint on the inflationary model space. Even with currrent accuracies some string-inspired inflation models have been ruled out already.

17. Outline • Review of Accomplishments of CMB Science • Great Opportunities Remain and Planck is poised to exploit them • Planck capabilities compared with WMAP • Parameter Error Forecasts • Planck as an Inflation Probe • Other Science: BBN and dark energy

18. Planck and 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 do 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. • There are interesting discrepancies in light element abundance determinations. Only deuterium agrees with nominal WMAP constraint.

19. Dark Energy • CMB experiments are important for Dark Energy probes because they pin down the parameters of the high-redshift Universe and the distance to last scattering. • All forecasts for proposed dark energy probes assume that • Planck flies • The data are analyzed • The data are released

20. Summary • The CMB has been the technique for studying cosmology. • Most of the information content in the CMB has not yet been revealed, but will be by Planck (4% c.f. 64%). • Planck is an inflation probe that is going to happen soon.

21. Parameter errors and assumptions about initial conditions Trotta and Durrer (2004) e.g., error in zeq goes from 3.5% to 14% for WMAP4 And the error in zeq goes from 1% to 1.5% for Planck