Cosmic Microwave Background

1. Cosmic Microwave Background Presentation to P5 Scott Dodelson

2. Observations of CMB temperature anisotropies are the basis of modern cosmology Scott Dodelson

3. Temperature anisotropies have secured the notion of a dark sector … Scott Dodelson

4. … and pointed to inflation as the generator of perturbations • Position of first peak • Temporal phases set early on as evidenced by peak structure • Shape of primordial spectrum close to scale-invariant Can we obtain more direct evidence for inflation? Scott Dodelson

5. Evidence for Inflation CMB polarization sensitive to gravity waves produced during inflation. CMB Polarization experiments probe physics at the GUT-scale. Scott Dodelson

6. Unpolarized isotropic radiation Compton scattering does not produce polarization Scott Dodelson

7. Unpolarized anisotropic radiation Compton scattering does produce polarization • Require Quadrupole (small before recombination) • Require Compton scattering (rare after recombination) • Signals factor of 10 smaller than temperature anisotropies • Generated during 2 epochs: pre-recombination (z~1000) and after reionization (z~10) Scott Dodelson

8. Current Results Samtleben, Staggs, & Winstein 2008 Scott Dodelson

9. Polarization field composed of E- and B- modes E Weiss Report 2005 B Scott Dodelson

10. Quantum mechanical fluctuations during inflation are stretched to astronomical scales Inflation produces perturbations to scalar potential Φ and these grow to be majestic structure we see today… but also tensor perturbations Scalar perturbations source (T,E) but not B. Tensor perturbations source (T,E,B), so B-mode detection would be clear signal of inflation-produced gravity waves. Scott Dodelson

11. Amplitude of B-mode signal tied to physics of inflation Tensor/scalar ratio teaches us about the GUT scale physics driving inflation. Scott Dodelson

12. Expected Signal Models with single scalar field with polynomial potential predict: • Small deviation from scale invariance • r > 0.1 Confirmed by WMAP! Attempts to make more generic predictions point to r>0.01… … but this is the science risk. Will Andrei Linde abandon inflation if experiments show that r<0.01? Boyle, Steinhardt, Turok (2005) Scott Dodelson

13. Other Science: Lensing of Last Scattering Map Photons traveling from last scattering surface are deflected by fluctuating potential along the line of sight. Leaves a distinctive signature in observed temperature/polarization maps. Use this signature to extract gravitational potential maps and spectrum. Hu 2001 Scott Dodelson

14. Extract gravitational potential along the line of sight Potential depends on neutrino mass. Could detect 0.05 eV signal (which must be there!) Input potential Extracted from CMB simluation Seljak & Hirata 2003 Scott Dodelson

15. Challenges • B signal is unknown but < 0.1 microK • Characteristic double peaked (l=6 and l=100) signature • E- converted to B- via lensing; lensing signal dominates on small scales • Foregrounds need to be studied; if cleaned by a factor of 10, will have residual ~30nK amplitude • r=0.01 (Vinf~2 x1016 GeV) might be best we can do Weiss Report 2005 Dashed lines estimates of residual foreground noise Scott Dodelson

16. Need Increase in Sensitivity Reaching fundamental limits on noise/detector. Need to multiplex many detectors to reach 30nK noise level. Weiss Report 2005 Scott Dodelson

17. Experts say … • Connecting Quarks with the Cosmos (2003): “Measure the polarization of the cosmic microwave background with the goal of detecting the signature of inflation” • Physics of the Universe (2004): “The three agencies will work together to develop by 2005 a roadmap for decisive measurements of both types of CMB polarization.” • Task Force on Cosmic Microwave Background Research (2005): “Detector development is a particularly appropriate area for increased involvement by DOE in CMB research.” • Beyond Einstein Program Assessment Committee (2007): “The Beyond Einstein scientific issues are so compelling that research in this area will be pursued for many years to come. All five mission areas in NASA’s Beyond Einstein plan address key questions that take physics and astronomy beyond where the century of Einstein left them.” • Primordial Polarization Program Definition Team (PPPDT):chartered by the Astrophysics Research Program. The PPPDT reports to the Astrophysics Research Program Manager at NASA Headquarters. • CMBPol Mission Concept Study (2008): Recently funded by NASA; hosting 3 workshops this summer (one at FNAL); will produce documents in preparation for the Decadel Survey Scott Dodelson

18. Funding Weiss Report 2005 Code R eliminated from NASA Scott Dodelson

19. US-Funded CMB Experiments Scott Dodelson

20. DOE Technology SiDet (FNAL) Backend Electronics designed at LBNL TES detectors for CDMS DOE institutions have technological resources to contribute significantly to this field CMB Data Analysis at NERSC Center for Nanoscale Materials (Argonne) Scott Dodelson

21. The Next Next Big Thing? Redshifted 21 cm studies can produce 3D maps of neutral H Scott Dodelson

22. 21 cm Surveys Scott Dodelson

23. Conclusions • CMB is the cornerstone of modern cosmology • CMB polarization studies may provide evidence for inflation, non-zero neutrino mass, and the end of the Dark Ages. • DOE could play a significant role, leveraging existing facilities/talents. • The future is promising: many upcoming polarization projects; plans for satellite mission; 21 cm surveys may point to new directions Scott Dodelson

24. Foregrounds Scott Dodelson