Polarization of the Cosmic Microwave Background: Are Those Guys Serious? Al Kogut Goddard Space Flight Center

Transcription

1 Polarization of the Cosmic Microwave Background: Are Those Guys Serious? Al Kogut Goddard Space Flight Center

2 Precision Cosmology CMB Lensing Galaxy Surveys Structure formation seeded by adiabatic scale-invariant perturbations ΛCDM 6 Parameters get you all this!

3 The End Of Cosmology? Breakfast of Theorists

4 Horizon Problem ΔT T < 10-4 Observer T 0 = 2.7 K Time 10,000 Causally disconnected regions: Why is the CMB so uniform? Last Scattering Big Bang Space 1.5º 2cΔt Δt

5 Flatness Problem Ω = 1 Is Unstable! Now: 0.98 < Ω < 1.02 Then: < Ω < Why is the universe so flat?

6 Initial Conditions Problem Observed Power Spectrum Compression Rarefaction Primordial Scale-Invariant Power Spectrum Compression What generated primordial density fluctuations?

7 Same region stretched to macroscopic size Solution: Inflation Time Solves Horizon Problem Space Small region in causal contact Inflation Ends Inflation Begins Guth 1981, Linde 1982, Albrecht & Steinhardt 1982 Solves Flatness Problem Stretch e 60 Stretch e 23 Stretch e 5 Scale-Invariant Fluctuations

8 Inflation 101 V(Φ) T» Tc T < Tc Phase transition at T=Tc drives exponential expansion R d 2 R GM = - dt 2 R 2 Φ Case 1: Matter-Dominated M = Const, d2 R < 0 dt 2 Case 2: Vacuum Energy Density d M = -V 0 R 3, 2 R = R dt 2 R(t) = R 0 exp(t) Need ~60 e-foldings before inflation ends

9 Quantum Physics on a Cosmic Scale! Stretched to Cosmic Scales Quantum Fluctuations

10 Is Inflation a Testable Theory? Prediction Inflation Ekpyrotic Flat (Ω = 1) Yes Yes No Monopoles Yes Yes Gaussian Fluations Yes Yes Scale-Invariant (ns ~ 1) Yes Yes Superhorizon Modes Yes Yes Gravity Waves Exist Don't Exist Search for Primordial Gravity Waves via CMB Polarization!

11 Towards a "Theory of Everything" M Theory Quantum Theory Strong TOE Electroweak Electromagnetic Weak Gravity ACCELERATING UNIVERSE M THEORY Intersection of Particle Physics and Cosmology

12 The Oldest Light In The Universe Fossil Relic of Early Universe GUT Physics at GeV Inflation/Phase Transitions Geometry of Space-Time Contents of Universe Gravity & Structure Formation

13 Physics of CMB Polarization Incident Photons Thomson scattering of anisotropic photon distribution by free electrons x Scattered Photons Quadropolar temperature anisotropy produces net linear polarization Expect few percent linear polarization y z Whole New Look at Early Universe

14 Source Terms for Polarization Temperature Quadrupole Scalar Source Gradient ( E mode ) Pattern Gravity Wave Tensor Source Gradient ( E mode ) Pattern Curl ( B mode ) Pattern B-Mode Polarization "Smoking Gun" For Inflation!

15 Polarization Patterns E Modes Even Parity B Modes Odd Parity Superposition E + B

16 Which Sources CMB Polarization Polarization and Inflation Model-Independent Result: Polarization ~ [ Inflaton Potential ] 1/4 Inflating Space-Time Creates Gravity-Wave Background

17 Show Me The Polarization? 2.7 K Isotropic CMB 80 μk Temperature Anisotropy -45 db B-Mode Detection: Inflation is real 3 μk Polarization -60 db Determine energy scale 3 μk E Modes 30 nk B Modes -80 db Parameterize using Tensor/Scalar ratio r Hierarchy for CMB Signals WMAP Prediction: Signal should exist at nk!

18 Angular Scale For Polarization Observer Today Time Space Ionized Neutral Reionization z ~ 15 θ ~ 30º Decoupling z ~ 1089 θ ~ 1º Ionized Big Bang

19 A Polarized Gold Mine for Cosmology

20 A Polarized Gold Mine for Cosmology Physics at Decoupling

21 A Polarized Gold Mine for Cosmology Physics at Decoupling Reionization & First Stars

22 A Polarized Gold Mine for Cosmology Physics at Decoupling Reionization & First Stars Gravity Waves GUT Physics

23 Experimental Challenges Faint Signal Photon Statistics Limit Large Arrays of Detectors Avoid Aliasing Unpolarized Light Control Stray Light Modulation/Chopping E y E x E y E x E y Polarized Galactic Foregrounds Multiple Frequency Bands

24 First Generation Measurements Each detector measures single linear polarization Difference detectors to get 2 2 Stokes Q = E x -E y Sky rotation maps Q and U Incident Light E x 2 E y 2 WMAP, BOOMERanG, QUaD, Planck,

25 WMAP Full-Sky Polarization 9 mm 7 mm λ = 13 mm 0 50 T (μk) Foregrounds brighter than CMB E-mode comparable to B-mode Page et al. 2006, ApJ in press, astro-ph/ mm 3 mm

26 WMAP and Inflation Temperature-Polarization Cross-Correlation Horizon Continuity: ρ/ t + (ρv) = 0 Observe beating between ρ and v Super-Horizon Modes v 0 on super-horizon scales requires superhorizon potential: Inflation! Peiris et al. 2003, ApJS, 148, 213

27 2nd Generation: Add Modulation T A T B Temperature Anisotropy: ΔT/T ~ 10-5 Difference 2 beam spots on single detector E x E y Polarization: ΔP/T < 10-6 Difference 2 polarizations on single detector Many Approaches In Development!

28 Rotating Quarter-Wave Plate Incident Light Rotate polarization on each detector Macroscopic moving parts Achromatic plate possible but hard MAXIPOL, EBEX, SPIDER balloon instruments β Wave Plate 2β Rotated Light EBEX schematic

29 Faraday Rotation BICEP at South Pole β = e3 λ 2 n 2ε 0 m 2 e c e (z) B(z) dz Rotate polarization in magnetic medium No moving parts Hand fabrication, high power BICEP ground-based instrument

30 Phase-Sensitive Detection Polarizer Ex, Ey Ex Chopped Phase Delay Ey λ/2 Switch Pu = (Ex + Ey) 2 Up = Ex 2 + Ey ExEy Power-Law Detector 2ExEy (Stokes U) 2 2 Ex + Ey (Stokes I) Switch Pd = (Ex -Ey) 2 Down = Ex 2 + Ey 2-2 ExEy Output Pdc = 1/2 Pu + Pd = Ex 2 + Ey 2 Pac = 1/2 Pu -Pd = 2 ExEy Demodulated Output ~ Linear Polarization

31 Polarimeter On A Chip PAPPA Phase Switch Photolithography for large arrays MEMS phase switches No macroscopic moving parts PAPPA balloon instrument Transmission Line Switch Electrode

32 State Of The Art 2007 Beginning to map E-mode Upper limits to B-mode r < 0.28 WMAP 3-year full-sky T + E-modes BOOMERanG 2003

33 Towards a B-Mode Machine

34 Kilo-Pixel Detector Arrays APEX element (A. Lee, UCB) Transition-Edge Superconducting bolometers with SQUID readout 10 2 to 10 3 element arrays now coming on line! Beat photon noise by using multiple independent detectors

35 Future Missions Open Opportunity: NASA Explorer Program (2013?) Open Opportunity: ESA "Cosmic Vision" Program (2017) Dedicated Mission: NASA "Beyond Einstein" Program (2019?) NASA "Beyond Einstein" Program

36 Experimental Probe of Inflationary Cosmology (EPIC) J. Bock et al. (JPL) Deployed Sunshield Liquid Helium Cryostat (450 l) Six 30 cm Telescopes 30/40 GHz 60 GHz 2 x 90 GHz 135 GHz 200/300 GHz Solar Panels Commercia l Spacecraft 6 Independent Telescopes Quarter-Wave Plates 2 K Refracting Optics K 40 K Absorbing Forebaffle Half-Wave Plate 100 mk Focal Plane Array 830 or 2366 detectors 295 K 3-Stage V-Groove Radiator Toroidal-Beam Antenna 8 m

37 Einstein Polarization Interferometer for Cosmology (EPIC) P. Timbie et al. (U Wisc) Interferometer measures power spectrum of Stokes U 1024 detectors

38 G. Hinshaw et al. (GSFC) CMB Polarimeter (CPMPol) Optical phase delay as first element Modulates sky signal, not instrument Fast compared to 1/f knee 1024 TES detectors

39 Plausible Achievability

40 Coming Soon From a Spacecraft Near You: Inflation, Quantum Gravity, And the Theory of Everything!