The first light in the universe

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Kerrie Randall
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1 The first light in the universe Aniello Mennella Università degli Studi di Milano Dipartimento di Fisica

Photons in the early universe Early universe is a hot and dense expanding plasma 14 May 1964, 11:15 am Photons are coupled to matter via Compton scattering At ~300000 yrs T falls below

2 Photons in the early universe Early universe is a hot and dense expanding plasma 14 May 1964, 11:15 am Photons are coupled to matter via Compton scattering At ~ yrs T falls below 3000 K and matter becomes neutral At that time photons freely travel carrying the imprinting of the baby universe We detect it today as a microwave signal, red shifted by a factor ~1000

3 Perfect black body Radiation and matter in the primordial plasma are in thermal equilibrium Expansion provides a redshift in frequency but maintains the shape unaltered This implies a black body spectrum of the CMB today at a temperature 1000 times smaller

4 Perfect black body Radiation and matter in the primordial plasma are in thermal equilibrium Expansion provides a redshift in frequency but maintains the shape unaltered This implies a black body spectrum of the CMB today at a temperature 1000 times smaller No significant deviations from black body distribution over 5 decades in frequency

5 Seeds in the universe CMB angular distribution closely tracks matter density distribution at the last scattering surface COBE T» 10 5 T DMR

6 CMB polarisation d¾t 0 2 / j^ ² ²^ j d Thompson scattered light is polarised. Only polarisation perpendicular to propagation direction is maintained To produce average polarisation in the CMB photon (and therefore matter) distribution must have a non zero quadrupole.

7 CMB polarisation Three mechanisms can produce quadrupolar anisotropy Scalar perturbations (perturbations of the energy density at last scattering) Vector perturbations (matter vortical motions) Tensor perturbation (metric perturbations, i.e. gravitational waves) Stokes Q; U! E; B modes

8 CMB polarisation Three mechanisms can produce quadrupolar anisotropy Scalar perturbations (perturbations of the energy density at last scattering) Vector perturbations (matter vortical motions) Tensor perturbation (metric perturbations, i.e. gravitational waves) Stokes Q; U! E; B modes

9 CMB polarisation Three mechanisms can produce quadrupolar anisotropy Scalar perturbations (perturbations of the energy density at last scattering) Vector perturbations (matter vortical motions) Tensor perturbation (metric perturbations, i.e. gravitational waves) Stokes Q; U! E; B modes

10 Spherical harmonics T (µ; Á) = 1 X X a`;m Y`;m (µ; Á) `=1 m= ` COBE T» 10 5 T DMR

11 Power spectrum 180±» 20±» 2±» 100» 10 4 The power spectrum provides a statistical description of `(` + 1)C` (¹K2 ) 104 the angular distribution of anisotropies in the sky 3 2 C` = hja`;m j i `

Power spectrum 180±» 20±» 2± 4 Large angular scales (> 1 ): CMB» 100» 10 1000 10000 `(` + 1)C` (¹K2 ) 104

12 Power spectrum 180±» 20±» 2± 4 Large angular scales (> 1 ): CMB» 100» `(` + 1)C` (¹K2 ) 104 anisotropies trace scalar perturbations in gravitational potential before inflation 3 T 1 ±Á = T 3 Á `

Power spectrum ± ± ± 180» 20» 2 Medium to small angular scales 4» 10 1000 10000 `(` + 1)C` (¹K2 ) 104 (1 < δθ < 5') trace

13 Power spectrum ± ± ± 180» 20» 2 Medium to small angular scales 4» `(` + 1)C` (¹K2 ) 104 (1 < δθ < 5') trace perturbations driven by acoustic oscillations in the expanding plasma before 3 decoupling» k c Ä 2 + '0 3 ±T 1 ±Á 1 = T c2 Á `

Power spectrum 180± 4» 20±» 2±» 100» 10 1000 10000 `(` + 1)C` (¹K2 ) 104 Below 5'

14 Power spectrum 180± 4» 20±» 2±» 100» `(` + 1)C` (¹K2 ) 104 Below 5' anisotropies are washed out by photon diffusion 3 happening during recombination `

15 Experimental requirements for high precision anisotropy experiments ±C` = C` s " 2 µpix ¾pix 2 1+ fsky (2` + 1) C` W` # As a first approximation power spectrum uncertainty depends on surveyed area, optical and noise performances

16 Low multipoles ±C` = C` s " 2 µpix ¾pix 2 1+ fsky (2` + 1) C` W` # Large sky surveys required for accuracy at low multipoles

17 High multipoles Low noise detectors ±C` = C` s " 2 µpix ¾pix 2 1+ fsky (2` + 1) C` W` #

18 High multipoles Sub degree angular resolution ±C` = C` s " 2 µpix ¾pix 2 1+ fsky (2` + 1) C` W` #

19 High multipoles ±C` = C` s " 2 µpix ¾pix 2 1+ fsky (2` + 1) C` W` # Optimal optical response reconstruction

20 An example from Planck ±C1500 =C1500 Expected Planck performances

21 Requirements for polarisation measurements `(` + 1) C` (¹K2 ) 106 C`TT C`EE 10 C`BB r = 0: ` 10000

22 Requirements for polarisation measurements `(` + 1) C` (¹K2 ) 106 C`TT Sensitive to reionisation C EE ` 10 C`BB r = 0: ` 10000

Requirements for polarisation measurements `(` + 1) C` (¹K2 ) 106 104 102 10 10 2 E mode polarisation

tensor scalar ratio EE C` Requires new generation of instruments and experiments C`BB Key issues: Low

23 Requirements for polarisation measurements `(` + 1) C` (¹K2 ) E mode polarisation between TT 1 2 order of C magnitudes smaller than` T anisotropies B mode even smaller, depending on tensor scalar ratio EE C` Requires new generation of instruments and experiments C`BB Key issues: Low noise detectors r= 0: Clean optics Modular, scalable instrument architecture ` 10000

24 15 years testing the universe 1992 COBE DMR First evidence of temperature anisotropies First points on the power spectrum C2 is somewhat surprisingly low

25 15 years testing the universe 2000 waiting for WMAP First evidence of temperature anisotropies First points on the power spectrum C2 is somewhat surprisingly low

26 15 years testing the universe First sub degree CMB measurements 2000 waiting for WMAP Boomerang and MAXIMA measure first peak the universe is FLAT! Several measurements all over the world all speak the same language. The power spectrum actually looks like what it should

27 15 years testing the universe 2002 DASI detects polarization First faint detection of E mode polarisation B modes still out of reach Ground measurements show their potential for the forthcoming polarisation challenges

28 2001 WMAP: the baby universe smiles again Instrument Front-end Assembly WMAP W-band feed horn

Systematic error control: the key factor 1.

Jupiter-crossing data sets Beam solid angles found 1% larger

Radiometer gain model If not corrected for, it would lead to

29 Systematic error control: the key factor 1. Window function determination WMAP 3yrs: six Jupiter-crossing data sets Beam solid angles found 1% larger than assumed in 1st year (1.5% effect on power spectrum). 2. Radiometer gain model If not corrected for, it would lead to mk effect on maps 1st yr model Gain data New model From WMAP 3 years data (Jarosik et al 2006)

30 Foregrounds: a complex issue Foreground minumum contamination at ~70 GHz; Polarisation: even at optimal frequencies, signal (on average) is dominated by polarized galactic signal

31 : 5 years of WMAP

32 : 5 years of WMAP C2 is always low...

33 : 5 years of WMAP T E correlation clearly shows a signal

34 : 5 years of WMAP E modes start outlining

35 : 5 years of WMAP B modes still out of reach...

36 Planck, the next big step ESA space mission, unprecedented combination of sensitivity, angular resolution, sky coverage and systematic error control Successful cold vacuum testing completed this summer Launch with Herschel foreseen first half month continuous observations from L2

Low Frequency Instrument 20 K radiometric array 30

37 Low Frequency Instrument 20 K radiometric array GHz All polarisation sensitive Single receiver

38 Spider web PSB High Frequency Instrument 0.1 K bolometric array GHz Polarisation sensitive between spaziale I 100 and 353

40 WMAP Angular resolution Average T/T per pixel/yr Average P/P per pixel/yr Mission lifetime Spectral coverage Detector technology Detector temperature Cooling 14'-56' yr GHz HEMT 90 K Passive PLANCK 5'-33' >14 months GHz HEMT+BOL 20K/4K/0.1K Active 27/10/2008

41 Imaging the first light ESA-SCI(2005)1 ( Blue book ) COBE resolution

42 Imaging the first light ESA-SCI(2005)1 ( Blue book ) Planck resolution

43 Imaging the first light ESA-SCI(2005)1 ( Blue book ) WMAP 2 yrs

44 Imaging the first light ESA-SCI(2005)1 ( Blue book ) WMAP 8 yrs

45 Imaging the first light ESA-SCI(2005)1 ( Blue book ) Planck 1 yr

46 T power spectrum ESA-SCI(2005)1 ( Blue book )

47 E-mode polarisation ESA-SCI(2005)1 ( Blue book )

48 B-mode polarisation ESA-SCI(2005)1 ( Blue book ) r = 0:1

49 Cosmological parameters ESA-SCI(2005)1 ( Blue book ) WMAP, 4yr observation PLANCK, 1yr observation Marginalized posterior distributions for each parameter

50 Foregrounds WMAP Planck

51 What after Planck? Many of the outstanding questions standing out from current theories will require new measurements What is dark matter? Does dark energy exist and what is its nature? Did inflation actually happened and what were the conditions? Did the primordial gravitational potential present tensor fluctuations (gravitational waves)? How did structures start forming? When and how the universe reionised on large scales? Many of these issues can be addressed by precision CMB polarisation measurements

52 The quest for polarisation: experimental challenges Sub microk sensitivity (need for thousand sized arrays of very low noise detectors) Micro packaged coherent receivers (QUIET experiment)

53 The quest for polarisation: experimental challenges Sub microk sensitivity (need for thousand sized arrays of very low noise detectors) Resistor Antenna Antenna coupled bolometers (Boch, 2002, POLARBEAR exp.) ~ 1 mm Superconducting Nb microstrip

54 The quest for polarisation: experimental challenges Clean, modular, scalable optical front ends W band 2x2 feed array developed from machined platelets (UniMi, UniMib, 2007)

55 The quest for polarisation: experimental challenges Clean, modular, scalable optical front ends W band 2x2 feed array developed from machined platelets (UniMi, UniMib, 2007)

56 The quest for polarisation: experimental challenges Polarised foregrounds, systematic error control, calibration... Strong galactic contamination at all latitudes. Need precise measurements of galactic polarisation Hinshaw et al, 2008

57 Conclusions The CMB is like the snapshot of a newborn baby from which we want to know about his past and infer his future Clearly we want the picture to be a GOOD one! In 50 years the CMB has proved a powerful means to understand the universe. Measurements and theories often wonderfully match But nature never gets short of surprises. And the future is rich with profound and interesting questions. The game is not a quest for the ultimate answer, but to establish a dialogue with the surrounding world which is, ultimately, a part of ourselves

Power spectrum exercise

Power spectrum exercise In this exercise, we will consider different power spectra and how they relate to observations. The intention is to give you some intuition so that when you look at a microwave